Large deviations for Langevin spin glass dynamics

到9月9日，社保基金正式进入股市整整3个月，按照有关规定，社保基金必须通过基金管理公司在三个月内完成建仓，并且其持仓市值要达到投资组合总市值80%的水平。

与此前大受追捧的QFII概念相比，社保基金及其所持有的股票显然低调得多，但是在西南证券分析师田磊看来，至少就目前来看，社保基金无论是在资金规模，还是在持股数量上明显都强于境外投资者，其投资理念和行为更可能给市场带来影响。

基金操作的社保基金的选股思路并不侧重某个行业，而更看重企业本身的发展和成长性，并且现阶段的企业经营业绩和走势也不是基金重点考虑的方面。

目前入市的社保基金都是委托南方、博时、华夏、鹏华、长盛、嘉实6家基金管理公司管理。

社保基金大致是被分为14个组合由以上6家管理公司分别管理，每个组合都有一个三位数的代码，第一位代表投资方向，其中“1”指股票投资、“2”指债券投资；第三位数字则代表基金公司名称，其中“1”为南方、“2”为博时、“3”为华夏、“4”为鹏华、“5”为长盛、“6”为嘉实；另有107、108组合主要运作社保基金此前一直持有的中石化股票，分别由博时与华夏基金公司管理。

在许多社保基金介入的股票中经常可以看到开放式基金的身影，例如在被社保基金大量持有的安阳钢铁(600569)的前10大股东中，其第2、6、7、8、9大股东均为开放式基金，而社保基金则以持股500多万股位列第3大股东。

类似的情况也出现在社保基金103组合所持有的华菱管线(000932)上，其第二大股东即为鹏华行业成长证券投资基金，社保基金则以200多万股的持仓量位列第7大股东，此外，在其前10大股东中还有5家是封闭式基金。

对此，某基金公司人士解释说，在获得社保基金管理人资格后，6家基金公司成立了专门的机构理财部门负责社保基金的投资管理，但是其研究、交易系统等则与公募基金共用一个平台，因此社保基金和开放式基金在选股时才会如此一致。

针对“社保概念股”的走势，国盛证券的分析师王剑认为，虽然社保基金此次委托入市资金超过百亿元，但大部分投向是债券，而且由于社保基金的特殊地位，因此基金管理公司对社保基金的操纵策略应该是以“集中持股，稳定股价”为主，不大可能博取太高的收益。

REVIEW ARTICLERole of oxidative stress in alcohol-induced liver injuryArthur I.Cederbaum ÆYongke Lu ÆDefeng WuReceived:9March 2009/Accepted:28April 2009/Published online:16May 2009ÓSpringer-Verlag 2009Abstract Reactive oxygen species (ROS)are highly reactive molecules that are naturally generated in small amounts during the body’s metabolic reactions and can react with and damage complex cellular molecules such as lipids,proteins,or DNA.Acute and chronic ethanol treat-ments increase the production of ROS,lower cellular antioxidant levels,and enhance oxidative stress in many tissues,especially the liver.Ethanol-induced oxidative stress plays a major role in the mechanisms by which ethanol produces liver injury.Many pathways play a key role in how ethanol induces oxidative stress.This review summarizes some of the leading pathways and discusses the evidence for their contribution to alcohol-induced liver injury.Special emphasis is placed on CYP2E1,which is induced by alcohol and is reactive in metabolizing and activating many hepatotoxins,including ethanol,to reac-tive products,and in generating ROS.Keywords Oxidative stress ÁAlcoholic liver injury ÁReactive oxygen species ÁAntioxidants ÁCYP2E1ÁTNF aIntroductionUnder certain conditions,such as acute or chronic alcohol exposure,production of reactive oxygen species (ROS)is enhanced and/or the level or activity of antioxidants is reduced.The resulting state,which is characterized by a disturbance in the balance between ROS production,on one hand and ROS removal and repair of damaged com-plex molecules,on the other is called oxidative stress.ROS have been implicated in many of the major dis-eases that plague mankind,including the toxicity of O 2itself;hyperbaric O 2;ischemia–reperfusion injury;cardio-vascular diseases;atherosclerosis;carcinogenesis;diabetes;neurodegenerative diseases,including Parkinson’s disease and Alzheimer’s disease;toxicity of heavy metals,e.g.,iron;asbestos injury;radiation injury;vitamin deficiency;drug (e.g.,redox cycling agents)toxicity;aging;inflam-mation;smoke toxicity;emphysema;and toxicity of acute and chronic ethanol treatment (Knight 1998;Kehrer 1993;Bondy 1992;Nordman et al.1992;Cederbaum 2001).ROS can be produced from many systems in cells including the mitochondrial respiratory chain (Chance et al.1979);the cytochrome P450s (White 1991;Blanck et al.1991);oxi-dative enzymes such as xanthine oxidase,aldehyde oxi-dase,cyclooxygenase,monoamine oxidase,the NADPH oxidase complex (Toykuni 1999;De Groot 1994);auto-oxidation of heme proteins such as ferrohemoglobin or myoglobin or biochemicals such as catecholamines,qui-nones or tetrahydrobiopterins.In addition to these cellular sources of ROS,environmental sources of ROS include radiation,UV light,smoke and certain drugs which are metabolized to radical intermediates or which can redox cycle.ROS are toxic to cells because they can react with most cellular macromolecules inactivating enzymes or denaturing proteins,causing DNA damage such as strandA.I.Cederbaum (&)ÁY.Lu ÁD.WuDepartment of Pharmacology and Systems Therapeutics,Mount Sinai School of Medicine,Box 1603,One Gustave L Levy Place,New York,NY 10029,USA e-mail:Arthur.cederbaum@ Y.Lue-mail:Yongke.lu@ D.Wue-mail:Defeng.wu@Arch Toxicol (2009)83:519–548DOI 10.1007/s00204-009-0432-0breaks,base removal or base modifications which can result in mutation,peroxidation of lipids which can result in destruction of biological membranes and produce reac-tive aldehydic products such as malondialdehyde or4-hy-droxynonenal(Nakazawa et al.1996;McCord1998).A variety of enzymatic and non-enzymatic mechanisms have evolved to protect cells against ROS,including the super-oxide dismutases(SODs),which remove O2-Á;catalase and the glutathione(GSH)peroxidase system which remove H2O2;glutathione transferases which can remove reactive intermediates and lipid aldehydes,metallothioneins,heme oxygenase,thioredoxin which remove various ROS;ceru-loplasmin and ferritin which help remove metals such as iron which promote oxidative reactions;non-enzymatic, low molecular weight antioxidants such as GSH itself, vitamin E,ascorbate(vitamin C),vitamin A,ubiquinone, uric acid,bilirubin(Halliwell1999;Yu1994).Oxidative stress or toxicity by ROS reflects a balance between the rates of production of ROS compared to the rates of removal of ROS plus repair of damaged cellular macro-molecules.While excess ROS can cause toxicity,macro-phages and neutrophils contain an NADPH oxidase which produces ROS to destroy foreign organisms(Rosen et al. 1995),and the enzyme myeloperoxidase catalyzes a reac-tion between H2O2and chloride to produce the powerful oxidant hypochlorite(bleach)to help destroy foreign invaders.In addition,ROS at low concentrations,espe-cially H2O2,may be important in signal transduction mechanisms in cells,and thus be involved in cellular physiology and metabolism(Lander1997).Alcohol,oxidative stress and cell injuryThe ability of acute and chronic ethanol treatment to increase production of ROS and enhance peroxidation of lipids,protein,and DNA has been demonstrated in a variety of systems,cells,and species,including humans. Much has been learned about alcohol metabolism,the various enzymes and pathways involved,and how alcohol, directly via its metabolism,or indirectly via its solvent-like action affecting cellular membranes impacts on cell func-tion.Yet,despite this tremendous growth in understanding alcohol metabolism and actions,the mechanism(s)by which alcohol causes cell injury are still not clear.A variety of leading mechanisms have been briefly summa-rized(Cederbaum2001;Bondy1992;Nordman et al. 1992),and it is likely that many of them ultimately con-verge as they reflect a spectrum of the organism’s response to the myriad of direct and indirect actions of alcohol.A major mechanism that is a focus of considerable research is the role of lipid peroxidation and oxidative stress in alcohol toxicity.Many pathways have been suggested to play a key role in how ethanol induces‘‘oxidative stress’’.Some of these include redox state changes(decrease in the NAD?/ NADH redox ratio)produced as a result of ethanol oxi-dation by alcohol and aldehyde dehydrogenases;produc-tion of the reactive product acetaldehyde as a consequence of ethanol oxidation by all major oxidative pathways; damage to mitochondria which results in decreased ATP production;direct or membrane effects caused by hydro-phobic ethanol interaction with either phospholipids or protein components or enzymes;ethanol-induced hypoxia, especially in the pericentral zone of the liver acinus as oxygen is consumed in order for the liver to detoxify eth-anol via oxidation;ethanol effects on the immune system, and altered cytokine production;ethanol-induced increase in bacterial-derived endotoxin with subsequent activation of Kupffer cells;ethanol induction of CYP2E1;ethanol mobilization of iron which results in enhanced levels of low molecular weight non-heme iron;effects on antioxi-dant enzymes and chemicals,particularly mitochondrial and cytosolic glutathione;one electron oxidation of ethanol to the1-hydroxyethyl radical;conversion of xanthine dehydrogenase to the xanthine oxidase form.Again,many of these pathways are not exclusive of one another and it is likely that several,indeed many,systems contribute to the ability of ethanol to induce a state of oxidative stress.What is the evidence that ethanol-induced oxidative stress plays a role in cell injury?While many studies have shown increases in lipid peroxidation or protein carbonyl formation by alcohol,it is not always clear if these are causes of or consequences of the alcohol-induced tissue injury.Nevertheless,there are many studies which show that administration of antioxidants or iron chelators or GSH-replenishing agents can prevent or ameliorate the toxic actions of alcohol.The most convincing data that oxidative stress contributes to alcohol-induced liver injury comes from the studies using the intragastric infusion model of alcohol administration.In these studies,alcohol-induced liver injury was associated with enhanced lipid peroxidation,protein carbonyl formation,formation of the 1-hydroxyethyl radical,formation of lipid radicals, decreases in hepatic antioxidant defense especially GSH (Knecht et al.1995;Tsukamoto and Lu2001;Iimuro et al. 2000;Nanji et al.1994a,b;Morimoto et al.1994). Replacement of polyunsaturated fat(required for lipid peroxidation to occur)with saturated fat or medium chain triglycerides in the diets fed to rats intragastrically,lowered or prevented the lipid peroxidation,and the alcohol-induced liver injury.Thus,alcohol plus polyunsaturated fat was required for the injury to occur.Addition of iron, known to generate OH•and promote oxidative stress,to these diets exacerbated the liver injury(Tsukamoto et al. 1995).Importantly,addition of antioxidants such as vita-min E,ebselen,superoxide dismutase,GSH precursors,prevented the alcohol-induced liver injury.Because alco-hol-induced liver injury has been linked to oxidative stress, we investigated the effect of a compromised antioxidant defense system,copper–zinc superoxide dismutase(SOD1) deficiency on alcohol-induced liver injury(Kessova et al. 2003).C57BL/SV129wild type and SOD1knockout mice were fed dextrose or ethanol(10%total calories)liquid diets for3weeks.Absence of SOD1in the knockouts was confirmed by immunoblot.Histological evaluation of the liver showed the development of liver injury ranging from mild to extensive centrilobular necrosis and inflammation (Fig.1a,b).Alanine aminotransferase levels were elevated only in the SOD1knockouts fed ethanol and not in the other three groups(Fig.1).Hepatic ATP levels were lowered only in the SOD1knockout mice fed ethanol (Fig.1),and oxidative and nitrosative stress was found in their livers.Wild type mice fed ethanol showed mild ste-atosis(Fig.1d)while wild type or knockout mice fed the dextrose diet showed normal histology(Fig.1c,e).Thus,a rather moderate ethanol consumption promoted oxidative stress and liver injury in Sod1knockout mice indicating that compromised antioxidant defense promotes alcohol liver injury.In addition to these in vivo studies,in vitro studies with hepatocytes also showed that ethanol can produce oxida-tive stress and hepatocyte toxicity.Studies with isolated hepatocytes from control rats or chronic ethanol-fed rats indicated that ethanol metabolism via alcohol dehydroge-nase results in an increase in ROS production,hepatocyte injury,and apoptosis,reactions blocked by antioxidants (Adachi and Ishii2002;Bailey and Cunningham2002). Studies in our laboratory with HepG2cell lines expressing CYP2E1showed that addition of ethanol or polyunsatu-rated fatty acids(PUFA)or iron,or depletion of GSH, resulted in cell toxicity,increased oxidative stress and mitochondrial damage,reactions prevented by antioxidants (Wu and Cederbaum1999).HepG2cells expressing both CYP2E1and alcohol dehydrogenase have been very valuable in studies on ethanol-induced oxidative stress and cell injury(Osna et al.2003;Donohue et al.2006).The sections below explore in more detail some of the major mechanisms which are believed to play an important role in pathways contributing to alcohol-induced oxidative stress.Kupffer cells and alcoholic liver diseaseKupffer cells are stimulated by chronic ethanol treatment to produce free radicals and cytokines,including tumor necrosis factor alpha(TNF a),which plays a role in ALD (Adachi et al.1994;Iimuro et al.1997).This stimulation is mediated by bacterial-derived endotoxin,and ALD is decreased when gram-negative bacteria are depleted from the gut by treatment with lactobacillus or antibiotics(Nanji et al.1994a,b).Destruction of Kupffer cells with gado-linium chloride attenuated ALD(Adachi et al.1994).A major advance was thefinding that anti-TNF a antibodies protect against ALD(Iimuro et al.1997).NADPH oxidase was identified as a key enzyme for generating ROS in Kupffer cells after ethanol treatment(Kono et al.2001). Moreover,in mice deficient in a subunit of NADPH oxi-dase,p47phox,the ethanol-induced increase in ROS and TNF a and liver injury was decreased(Kono et al.2000). The role of TNF a in ALD was further validated by the findings that the ethanol-induced pathology was nearly completely blocked in TNF a receptor1knockout mice(Yin et al.1999).The transcription factor nuclear factor-kappaB(NF-kB) regulates activation of many inflammatory genes,including TNF a.Endotoxin activates NF-kB,leading to the hypoth-esis that inhibition of NF-kB would prevent ALD(Uesugi et al.2001).Administration of an adenovirus encoding for the IkB superrepressor to rats chronically infused with ethanol blunted the ethanol-induced activation of NF-kB, TNF a production and pathological changes.A general scheme to explain these results is that chronic ethanol treatment elevates endotoxin levels,endotoxin activates Kupffer cells to produce free radicals via NADPH oxidase, the free radicals activate NF-kB,leading to an increase in production of TNF a,followed eventually by tissue damage (Thurman1998;Wheeler and Thurman2001;Takei et al. 2005).Iron-and alcohol-induced oxidative stressMost of the systems for the production of ROS described above produce superoxide radicals or hydrogen peroxide. In the presence of certain metals,particularly free iron or copper ions,hydroxyl radical,the most powerful ROS,can be produced via the Fenton or the metal-catalyzed Haber–Weiss reaction(McCord1998).These two chemical reac-tions appear to account for most of the hydroxyl radical production in biological systems and explain,at least in part,why metals such as iron and copper produce oxidative stress and ROS-induced injury in cells.As discussed above,iron promotes oxidative stress by catalyzing the conversion of less reactive oxidants such as superoxide or H2O2to more powerful oxidants such as hydroxyl radical or perferryl-type oxidants.An increase in hepatic iron concentrations occurs in alcohol-dependent individuals and elevated hepatic iron uptake is seen in patients with alcohol-induced cirrhosis(Chapman et al. 1983).An increase in the cellular pool of low-molecular weight iron occurs during ethanol metabolism in rathepatocyte cultures (Sergent et al.1995).In rats,chronic ethanol feeding for 8weeks elevated iron content in the hepatocytes and Kupffer cells (Valerio et al.1996).Treatment of rats with ethanol plus carbonyl iron strikingly elevated liver iron levels and produced significant liver injury (Valerio et al.1996;Stal et al.1996).In the intra-gastric infusion model,addition of a small amount of iron,which only elevated hepatic iron levels twofold to three-fold,enhanced lipid peroxidation,serum transaminase levels,and induced fibrosis (Tsukamoto et al.1995).Ethanol administration elevated the iron content of Kupffer cells,and this was suggested to prime Kupffer cells for NF-kB activation and ultimately for TNF a production and ALD (Tsukamoto et al.1999).Addition of Fe 2?butnotFig.1Chronic ethanolconsumption causes liver injury and a decrease in hepatic ATP levels in SOD 1knockout mice as compared to wild type mice.Arrows in a and b indicate necrosisFe3?increased TNF a release by rat Kupffer cells in an NF-kB—dependent manner(She et al.2002).Oral iron chelators attenuated these effects,reducing the elevations in non-heme iron,lipid peroxidation,and liver fat accu-mulation and injury(Tsukamoto et al.1999;Sadrzadeh et al.1994).ROS production,lipid peroxidation,and interaction with iron chelates were enhanced with microsomes from etha-nol-treated rats(Cederbaum2003).This was associated with elevated levels of CYP2E1and blocked by inhibitors of CYP2E1or by anti-CYP2E1immunoglobulin.In HepG2cells expressing CYP2E1,an iron chelator,ferric-nitrilotriacetate,produced greater toxicity than that found with control HepG2cells(Cederbaum2003).Damage to the mitochondria played a critical role in the CYP2E1plus iron-dependent toxicity.In the CYP2E1-expressing HepG2 cells,synergistic interactions between iron and PUFA were observed.1-Hydroxyethyl radical(HER)Ethanol is a hydroxyl radical scavenger;the product of the interaction of ethanol with hydroxyl radical is HER.Liver microsomes can oxidize ethanol to HER in an NADPH dependent manner(Albano et al.1987).The mechanism involves production of superoxide and H2O2by cyto-chrome P450,followed by an iron-catalyzed generation of hydroxyl radical like—oxidants,which interact with etha-nol to yield HER(Knecht et al.1993;Rashba-Step and Cederbaum1994).Microsomes isolated from rats treated chronically with ethanol were more reactive in producing HER from ethanol than control microsomes(Albano et al. 1991).This was due to induction of CYP2E1.HER pro-duction from ethanol has been demonstrated in vivo,as a spin-trapped HER adduct was detected in bile from mice or rats treated with ethanol(Knecht et al.1990).The role of HER adducts in ALD is not known.HER binds readily to proteins to produce ethanol-derived protein adducts,which are immunogenic,and production of antibodies that spe-cifically recognize HER protein adducts was found after chronic ethanol consumption(Moncada et al.1994),as well as in patients with alcohol-induced cirrhosis(Clot et al.1995).Interaction of HER with cellular antioxidants could contribute to mechanisms by which ethanol produces a state of oxidative stress(Reinke2002).Protection against ROS toxicity/GSHBecause ROS production is a naturally occurring process,a variety of enzymatic and nonenzymatic mechanisms have evolved to protect cells against ROS(Halliwell1999;Yu 1994).At least some of these mechanisms are impaired after long-term alcohol consumption.Antioxidant enzymes involved in the elimination of ROS include SODs,catalase,and glutathione peroxidase. SODs catalyze removal of superoxide radicals.A copper–zinc SOD is present in the cytosol and in the space between the two membranes surrounding the mitochondria,while a manganese-containing SOD is present in the mitochondrial matrix.Both of these enzymes are critical for prevention of ROS-induced toxicity(Fridovich1997).The effects of chronic alcohol exposure on the cellular content or activity of SODs are controversial,with reports of increases,no changes,or decreases,depending on the model,diet, amount,and time of alcohol feeding.Studies employing the intragastric infusion model,found decreases in SOD activity in the liver(Polavarapu et al.1998).Catalase and the glutathione peroxidase system both help to remove hydrogen peroxide.Catalase is found pri-marily in peroxisomes;it catalyzes a reaction between two hydrogen peroxide molecules,resulting in the formation of water and O2.In addition,catalase can promote the inter-action of hydrogen peroxide with hydrogen donors so that the hydrogen peroxide can be converted to one molecule of water,and the reduced donor becomes oxidized(peroxid-atic activity of catalase).Compounds that can provide these hydrogen atoms include ethanol and methanol,which are oxidized to acetaldehyde and formaldehyde,respectively. The glutathione peroxidase system consists of several components,including the enzymes glutathione peroxidase and glutathione reductase and the cofactors GSH and NADPH.Together,these molecules effectively remove hydrogen peroxide.GSH is an essential component of this system and serves as a cofactor for glutathione transferase, which helps remove certain drugs and chemicals as well as other reactive molecules from the cells.Because of all its functions,GSH is probably the most important nonenzymatic antioxidant present in cells. Therefore,enzymes that help generate GSH are critical to the body’s ability to protect itself against oxidative stress. Alcohol has been shown to deplete GSH levels,particularly in the mitochondria,which normally are characterized by high levels of GSH needed to eliminate the ROS generated during activity of the respiratory chain(Fernandez-Checa et al.1997).Numerous other nonenzymatic antioxidants are present in the cells,most prominently vitamin E (a-tocopherol)and vitamin C(ascorbate).Vitamin E is a major antioxidant found in the lipid phase of membranes and,acts as a powerful terminator of lipid peroxidation. During the reaction between vitamin E and a lipid radical, the vitamin E radical is formed,from which vitamin E can be regenerated in a reaction involving GSH and ascorbate. Alcohol also appears to interfere with the body’s normal vitamin E content because patients with ALD commonlyexhibit reduced vitamin E levels(Nanji and Hiller-Sturmho¨fel1997).The effects of ethanol on total hepatic GSH levels are variable,with reports of decreases,no effects,or even an increase(Fernandez-Checa et al.1989;Iimuro et al.2000; Oh et al.1998).Lowering of mitochondrial GSH by chronic ethanol treatment has been a more consistent observation and appears to be a key lesion contributing to ALD.Because liver mitochondria lack catalase,mito-chondrial GSH in association with glutathione peroxidase is the major mechanism by which H2O2is detoxified by mitochondria.Chronic ethanol intake either in the Lieber–DeCarli model or the intragastric infusion model selec-tively lowers levels of mitochondrial GSH in hepatocytes (Fernandez-Checa et al.1989,1997).Depletion of mito-chondrial GSH by chronic ethanol feeding occurs prefer-entially in pericentral hepatocytes,where most of the liver injury originates(Garcia-Ruiz et al.1995).This depletion by ethanol is attributable to defective transport of GSH from the cytosol into the mitochondria and can be pre-vented byfluidization of the mitochondrial membrane by S-adenosylmethionine(Colell et al.1998).Lowering of mitochondrial GSH by ethanol has been suggested to sensitize hepatocytes to TNF a-induced cell death,and replenishment of mitochondrial GSH with S-adenosylme-thionine protects hepatocytes from alcohol-treated rats to TNF toxicity(Colell et al.1998).Bailey et al.(2001), however,found that mitochondrial GSH levels were increased after chronic ethanol feeding in the Lieber–DeCarli model by approximately25%.Thisfinding was suggested to reflect an adaptive response to counteract ethanol-related increases in mitochondrial production of ROS.Deaciuc et al.(1999)reported no change in mito-chondrial GSH levels after7weeks of ethanol intake. Thus,the effects of ethanol on mitochondrial GSH,as with total GSH,remain controversial.S-Adenosyl-L-methionineS-Adenosyl-L-methionine(SAM)is the principal biological methyl donor,the precursor of aminopropyl groups utilized in polyamine biosynthesis and,in the liver,SAM is also a precursor of glutathione(GSH)through its conversion to cysteine via the transsulfuration pathway(Avila et al.2002; Lieber2002).SAM is particularly important in opposing the toxicity of free radicals generated by various toxins, including alcohol.Abnormalities in SAM metabolism have been well recognized in liver diseases and in various neurological disorders.Methionine adenosyltransferase (MAT)is the enzyme responsible for the synthesis of SAM using methionine and ATP.Liver injury causes a decrease in SAM concentration largely because of decreased MAT1A activity(Cabrero et al.1988;Avila et al.2000). Impairment of SAM synthesis is believed to play an important role in hepatic injury induced by various agents, and indeed there is a considerable literature,which shows that exogenous administration of SAM can protect against injury induced by CCl4,acetaminophen,galactosamine, cytokines,thioacetamide,ischemia–reperfusion(Chawla et al.1998;Bray et al.1992;Wu et al.1996;Song et al. 2004).The effects of ethanol on SAM concentrations are somewhat variable.Baboons fed ethanol chronically had decreased hepatic levels of SAM and GSH,and adminis-tration of SAM elevated these and protected against liver injury(Lieber et al.1990).Rats fed the Lieber–DeCarli diet showed no or a small decrease in SAM after4weeks but a more substantial decrease in8weeks on the diet(Barak et al.1987;Trimble et al.1993).Mini pigs fed ethanol for 1year had no change in SAM levels(Halsted et al.1996). Rats fed ethanol in the intragastric infusion model for 9weeks had an increase in MAT1A and MAT2A mRNA but only MAT2A protein was elevated(Lu et al.2000); these changes were associated with a40%fall in SAM levels.Depletion of mitochondrial GSH appears to be an important sensitizing factor for susceptibility to TNF a toxicity after chronic ethanol feeding(Fernandez-Checa et al.1997).This depletion is due to a decrease in transport of GSH into the mitochondria and can be corrected by administration of SAM(Garcia-Ruiz et al.1995).In iso-lated hepatocytes,SAM prevented the decrease in GSH caused by ethanol(Gigliozzi et al.1998)and in perfused rat liver studies,SAM prevented the decline in GSH and oxygen consumption and liver damage produced by etha-nol(Bosch-Morell et al.1998).Kharbanda et al.(2005) compared the effects of betaine and SAM,on ethanol-induced changes of methionine metabolism and hepatic steatosis.Wistar rats were fed ethanol or control Lieber–Decarli liquid diet for4weeks and metabolites of the methionine cycle were measured in isolated hepatocytes. Hepatocytes from ethanol-fed rats had a50%lower intra-cellular SAM/SAH ratio and almost twofold greater homocysteine release into the media compared with con-trols.Supplementation of betaine or SAM in the incubation media increased the SAM/SAH ratio in hepatocytes from both control and ethanol-fed rats and attenuated the etha-nol-induced increased hepatocellular triglyceride levels by approximately20%.SAM protects against alcohol-dependent toxicity in vivo Chronic ethanol consumption by baboons(50%of energy from a liquid diet)for18–36months resulted in significant depletion of hepatic SAM concentration and levels of GSH (Lieber et al.1990).These depletions were corrected withSAM administration.There was a significant correlation between hepatic SAM and GSH level.Esfandiari et al. (2007)reported that feeding micropigs with ethanol at40% of total calories with folate-deficient diets for14weeks increased and supplemental SAM maintained control levels of liver and plasma triglyceride.Serum adiponectin,liver transcripts of adiponectin receptor-1,and phosphorylated adenosine monophosphate kinase-beta were each reduced by ethanol feeding and were sustained at normal levels by SAM supplementation of the ethanol diets.Ethanol feeding activated and SAM supplementation maintained control levels of ER stress-induced transcription factor sterol regulatory element-binding protein-1c and its targeted transcripts of lipid synthesizing enzymes acetyl-CoA car-boxylase,fatty acid synthase,and glycerol-3-phosphate acyltransferase(Esfandiari et al.2007).The protective effect of SAM against rat liver steatosis induced by chronic ethanol ingestion was investigated by Feo et al.(1986).SAM given during ethanol treatment prevented steatosis and accelerated recovery from steatosis when given after ethanol withdrawal.Bailey et al.(2006) found that alcohol feeding to rats caused a significant decrease in mitochondrial state three respiration and the respiratory control ratio in5weeks,whereas SAM administration prevented these alcohol-mediated defects and preserved hepatic SAM levels.SAM treatment pre-vented alcohol-associated increases in mitochondrial superoxide production,mitochondrial DNA damage,and inducible nitric oxide synthase induction,without a sig-nificant lessening of steatosis.Although SAM supplemen-tation did not alleviate steatosis by itself,SAM prevented several key alcohol-mediated defects to the mitochondrial genome and proteome that contribute to the bioenergetic defect in the liver after alcohol consumption(Bailey et al. 2006).Acute ethanol administration caused prominent micro-vesicular steatosis with mild necrosis and an elevation of serum L-alanine:2-oxoglutarate aminotransferase activity. SAM treatment significantly attenuated the liver injury. SAM treatment attenuated hepatic SAM and mitochondrial GSH depletion and lipid peroxidation following acute alcohol exposure(Song et al.2003).SAM protects against CYP2E1-dependent toxicityin vivoWe recently reported that induction of CYP2E1in mice by treatment with pyrazole increased the hepatotoxicity caused by Fas agonistic Jo2antibody(Wang et al.2005). Increased hepatotoxicity in the pyrazole/Jo2-treated mice was associated with increased oxidative and nitrosative stress in association with decreased GSH and other antioxidant levels.Exogenous administration of SAM (50mg/kg body weight i.p.every12h for3days)signif-icantly decreased serum transaminases and ameliorated morphological changes of the liver(Wang and Cederbaum 2006).Addition of SAM elevated hepatic SAM and total reduced glutathione levels and inhibited CYP2E1activity. SAM also lowered the elevated oxidative stress(lipid peroxidation,protein carbonyls,and superoxide produc-tion)and nitrosative stress(induction of inducible nitric oxide synthase and3-nitrotyrosine adducts)and increases in caspase-8and-3activation produced by the pyrazole plus Jo2treatment.These results indicate that SAM can have an important hepatoprotective role as an effective reagent against Fas plus CYP2E1-induced hepatotoxicity by lowering oxidative and nitrosative stress.Obese mice have been used extensively as animal models to study human obesity.We have recently observed that pyrazole-induced CYP2E1promotes liver injury in ob/ ob mice,compared with saline-treated ob/ob mice or with lean controls treated with pyrazole(Dey and Cederbaum 2007).Administration of SAM(50mg/kg body weight i.p. every12h for3days)prevented the observed pathological changes as well as the increase of apoptotic hepatocytes, caspase3activity,and serum TNF a levels.SAM admin-istration inhibited CYP2E1activity but not CYP2E1con-tent.The pyrazole treatment increased lipid peroxidation, 4-hydroxynonenal and3-nitrotyrosine protein adducts,and protein carbonyls.These increases in oxidative and nitro-sative stress were prevented by SAM(Dey et al.2007). SAM is effective in protecting against pyrazole-induced oxidative and nitrosative stress and liver injury in obese mice by lowering CYP2E1-generated oxidative/nitrosative stress in the liver and in the mitochondrial compartment.As mentioned above,a model of chronic alcohol-induced liver injury using Cu,Zn-superoxide dismutase deficient mice(SOD-/-)was developed(Kessova et al. 2003).Feeding the homozygous SOD-/-mice ethanol resulted in liver injury characterized by extensive centri-lobular necrosis and inflammation,and increased trans-aminase levels(but not the wild type SOD?/?mice).Liver injury in the SOD-/-mice was associated with induction of CYP2E1,and increased protein carbonyls,lipid perox-idation aldehydic products and3-nitrotyrosine protein adducts,indicative of enhanced oxidative and nitrosative stress.SAM protected SOD-/-mice from alcohol-induced liver injury.SAM lowered the serum L-alanine:2-oxoglu-tarate aminotransferase and aspartate aminotransferase levels,decreased steatosis,necrosis and inflammation upon histological evaluation as compared to alcohol treated alone mice(Fig.2).The ability of SAM in vitro to protect against CYP2E1-dependent toxicity was studied in pyrazole-treated rat hepatocytes,with high levels of CYP2E1(Wu and。

等离激元共振峰英文全文共四篇示例，供读者参考第一篇示例：Plasmon Resonance PeakIntroductionPlasmon resonance is a collective oscillation of free electrons in a material that occurs when the frequency of incident light matches the natural frequency of the electrons in the material. This phenomenon is often observed in metallic nanoparticles, where the conduction electrons can be excited by incident electromagnetic radiation. One of the most prominent features of plasmon resonance is the appearance of a distinct peak in the absorption or scattering spectra of the material, known as the plasmon resonance peak or plasmon resonance band.第二篇示例：Plasmon resonance refers to the collective oscillation of free electrons in a metal when it is subjected to electromagnetic radiation. This phenomenon, also known as surface plasmon resonance (SPR), has been extensively studied and applied invarious fields such as sensing, imaging, and light manipulation. One of the key features of plasmon resonance is the emergence of a characteristic peak in the absorption or scattering spectrum, known as the plasmon resonance peak or plasmon resonance band. In this article, we will focus on a specific type of plasmon resonance peak – the localized surface plasmon resonance peak, which is commonly referred to as the plasmon resonance peak.第三篇示例：Plasmonic resonance peak, also known as localized surface plasmon resonance (LSPR) peak, is a phenomenon in which free electrons in a metal nanoparticle oscillate collectively in response to incident light. This oscillation creates a strong electromagnetic field enhancement around the nanoparticle, leading to enhanced light-matter interactions. The spectral position of the plasmonic resonance peak, known as the plasmon resonance wavelength, depends on the size, shape, composition, and surrounding environment of the nanoparticle.第四篇示例：One specific type of surface plasmon resonance that has attracted attention is the localized surface plasmon resonance (LSPR) peak. LSPR peaks manifest as sharp extinction peaks inthe absorption or scattering spectra of metal nanoparticles due to the resonance between incident light and the localized surface plasmons on the nanoparticle surface. These peaks are highly sensitive to the size, shape, and composition of the nanoparticle, making them an excellent candidate for various applications such as chemical sensing, biological detection, and single molecule analysis.。

Optimization of ultrasonic extraction of Flammulina velutipes polysaccharides and evaluation of its acetylcholinesterase inhibitory activityWenjian Yang a ,Yong Fang b ,Jin Liang a ,Qiuhui Hu a ,b ,⁎a College of Food Science and Technology,Nanjing Agricultural University,Weigang,Nanjing 210095,ChinabCollege of Food Science and Engineering,Nanjing University of Finance and Economics,Nanjing,210046,People's Republic of Chinaa b s t r a c ta r t i c l e i n f o Article history:Received 19September 2010Accepted 15November 2010Available online xxxxKeywords:Flammulina velutipes Polysaccharides OptimizationResponse surface methodology Ultrasonic extraction AcetylcholinesterasePolysaccharide was testi fied to be the main component of Flammulina velutipes for inhibiting AChE activity in our preliminary study.Therefore,response surface methodology,based on Box –Behnken design,was used to optimize the ultrasonic extraction conditions of F.velutipes polysaccharides (FVP).Four independent variables (ratio of water to raw material,ultrasonic power,ultrasonic time,and ultrasonic temperature)were taken into consideration.A quadratic model,adequate for reasonably predicting the yield of FVP,was constructed between ultrasonic conditions and yield of FVP.A yield of FVP of 8.33%was obtained under a modi fied condition (ratio of water to material of 25ml/g,ultrasonic power of 620W,ultrasonic time of 20min,and ultrasonic temperature of 45°C).Subsequently,acetylcholinesterase (AChE)inhibitory activity and 1,1-diphenyl-2-picryl hydrazine (DPPH)scavenging activity of FVP were determined.AChE inhibitory rate of 18.51%and DPPH scavenging rate of 61.24%were obtained at 0.6mg/ml of FVP,indicating a good potential of FVP to enhance learning and cognitive ability.©2010Elsevier Ltd.All rights reserved.1.IntroductionNowadays,edible mushrooms are distinguished as important natural resources of immunomodulating and anticancer agents and have been cultured on a large scale in Asia (Wasser,2002).Flammulina velutipes ,one of the most popular edible mushrooms,has attracted considerable attention in the fields of biochemistry and pharmacology due to its biological activities.Polysaccharides,as one of the important active components of F.velutipes ,have been proved to be bene ficial in immunomodulating antitumor and anti-in flammatory activities (Leung,Fung &Choy,1997).Therefore,much attention has been paid to the studies of F.velutipes polysaccharides (FVP).Although polysaccharides have been well known for their various pharmacological functions,their extraction is still mainly performed with conventional techniques,which are based on proper solvents,prolonging extraction time,heating process,and agitation to increase extraction yield (Wang,Cheng,Mao,Fan &Wu,2009).In these methods,the extraction process usually consumes a long time and a lot of energy,but the extraction ef ficiency is very low.Therefore,it is essential and desirable to find out an economical and highly ef ficient extraction method.Ultrasonic has been used to increase extraction yield of bioactive substances from natural products,which is mainly attributed to disruption of cell walls,particle-size reduction,and enhanced mass transfer to the cell contents as a result of cavitationbubble collapse (Li,Pordesimo,&Weiss,2004;Vinatoru et al.,1997;Wang et al.,2009).However,there is hardly any report that ultrasonic is applied to separate FVP.Therefore,ultrasonic was employed for the extraction of FVP in our study.Especially,temperature was controlled during the extraction process to prevent overheating-induced oxidation and degradation of polysaccharides.The worldwide population ageing has increased the incidence of cognitive de ficits,such as the age-associated memory impairment and senile dementias and Alzheimer's disease (Hornick et al.,2008).Extensive evidence supports the view that cholinergic mechanisms modulate learning and memory formation.Neuropathological occur-rences of cognitive de ficits are associated with the cholinergic de ficiency (Gold,2003;Roberson &Harrell,1997).Inhibitors of acetylcholinesterase (AChE)have been extensively used to increase the effectiveness of cholinergic transmissions and endogenous acetylcholine levels and thus overcome cognitive de ficits (Hornick et al.,2008;Silman &Sussman,2005).F.velutipes is bene ficial to human memory.FVP has been proven to improve learning and memory ability of scopolamine hydrobromid-induced model mice and rats using step-through test and Morris water test (Zou,Liao,Wu &Liu,2010).However,the effect of FVP on AChE activity has not been studied.In our preliminary study,crude polysaccharide solution was testi fied to be the main fraction in F.velutipes for inhibiting AChE activity.In view of the above,it is necessary to research the AChE inhibitory activity of FVP.In addition,it is suggested that polysaccharides induced cognitive improvement owing to their antioxidant activity (Fan et al.,2005;Zhang,Zhang,Wang &Mao,2008),so antioxidant activity of FVP was also investigated.Food Research International xxx (2010)xxx –xxx⁎Corresponding author.Tel./fax:+862584399086.E-mail address:qiuhuihu@ (Q.Hu).FRIN-03416;No of Pages 70963-9969/$–see front matter ©2010Elsevier Ltd.All rights reserved.doi:10.1016/j.foodres.2010.11.027Contents lists available at ScienceDirectFood Research Internationalj o u r n a l h o me p a g e :w w w.e l s e v i e r.c om /l oc a te /fo o d r e sThe objective of this study was to optimize the ultrasonic-assisted extraction conditions of FVP using response surface methodology. Effects of ratio of water to raw material,ultrasonic power,ultrasonic time,and ultrasonic temperature on the extraction yield of FVP were fully examined.Moreover,AChE inhibitory activity of FVP was investigated to study its potential to improve memory impairment and cognitive deficit.On account of the relationship between oxidative stress and cognitive deficit,1,1-diphenyl-2-picryl hydrazine (DPPH)radicals scavenging assay was also conducted to evaluate the antioxidant ability of FVP.2.Materials and methods2.1.Materials and chemicalsF.velutipes was purchased from local market(Nanjing,China)and then dried at60°C and ground to pass through80mesh screen,the powder was stored at4°C until used.Glucose,phenol,and sulfuric acid were obtained from Shanghai Chemical Co.(Shanghai,China).1,1-Diphenyl-2-picryl hydrazine(DPPH),5,5′-dithio-bis-(2-nitrobenzoic) acid,acetylthiocholine iodide,ascorbic acid,acetylcholinesterase (AChE,type VI-S,EC3.1.1.7),and galanthamine were obtained from Sigma-Aldrich Chemical Co.(St.Louis,MO,USA).All other chemicals used in experiments were of analytical grade.2.2.AChE inhibitory activity of Flammulina velutipes extracts10g F.velutipes powder was extracted with200ml of different solvents(deionized water,ethanol,petroleum ether,and ethyl acetate),respectively,and AChE inhibitory activities of the extracts were compared.Subsequently,the water extract was mixed with quadruplicate anhydrous ethanol and then centrifuged.The precip-itate,crude polysaccharides,was lyophilized and redissolved in water as crude polysaccharide solution(CPS).The supernatant was concentrated under reduced pressure,lyophilized,and redissolved in water as water–ethanol solution(WES).The AChE inhibitory activities of CPS and WES were further investigated.2.3.Ultrasonic extraction and determination of polysaccharidesF.velutipes powder was weighed accurately(10.0g)and extracted with distilled water in ultrasonic cell disintegrator((DCTZ-2000, Beijing Hongxianglong Biotechnology Development Co.Ltd).Subse-quently,the treated mixture was air cooled to room temperature and centrifuged(10,000rpm/min,15min).The supernatant was concen-trated under reduced pressure at65°C.The polysaccharides extracts obtained above were then mixed with4-fold volume anhydrous ethanol(ethanolfinal concentration,80%)and kept at4°C for24h. After centrifugation at5000rpm/min for15min,the precipitate was washed three times with anhydrous ethanol and then dialyzed and lyophilized to yield FVP sample.The percentage polysaccharides yield(%)is calculated as follows:Yield of polysaccharideð%Þ¼weight of dried crude FVPðgÞ×1002.4.Experimental designA three-level-four-factor,Box–Behnken factorial design(BBD)was employed in this optimization study.Ratio of water to raw material (X1),ultrasonic power(X2),ultrasonic time(X3),and ultrasonic temperature(X4)were chosen for independent variables to be optimized for the extraction of FVP.Yield of polysaccharides(Y)was taken as the response of the design experiments.Twenty-nine experiments were carried out in BBD(Table1).Five replicates at the center point were used for estimation of a pure error sum of squares.Triplicate determinations were performed at all design points in randomized order.A quadratic polynomial model wasfitted to correlate the response variable(yield of polysaccharide)to the independent variables.The general form of quadratic polynomial equation is as follows:Y¼β0þ∑4i¼1βi X iþ∑4i¼1βii X i2þ∑i¼1∑4j¼iþ1βijXiXjwhere Y is the response variable,andβ0,βi,βii,andβij are the regression coefficients for intercept,linearity,square,and interaction, respectively,while X i and X j are the independent variables.2.5.AChE inhibitory activityThe AChE inhibitory activity assay was performed according to the protocol described by Langjae,Bussarawit,Yuenyongsawad, Ingkaninan and Plubrukarn(2007)with slight modifications.Briefly, 125μl of3mM5,5′-dithio-bis-(2-nitrobenzoic)acid,25μl of1.5mM acetylthiocholine iodide,50μl of50μM Tris–HCl buffer(pH8.0),25μl of sample,and25μl of0.25U/ml AChE were added consecutively into 96-well plate.Then the absorbance was measured immediately at 412nm using an ELISA plate reader(TECAN Infinite F200, Switzerland).The potency of AChE inhibitory activity of FVP was expressed as the inhibition rate.Galanthamine was used as a positive control.Table1Experiment of ultrasonic extraction of polysaccharides from Flammulina velutipes.(Data presented are the mean of triplicate determinations.)Run X1-ratio(ml/g)X2-ultrasonicpower(W)X3-ultrasonictime(min)X4-ultrasonictemperature(°C)Yield of FVP(%)ActualvaluePredictedvalue 12060015508.218.08 2304001550 6.887.05 32060015507.998.08 4204001565 6.63 6.76 5208001565 6.46 6.38 6208002550 6.64 6.82 7206005357.577.30 820400550 6.45 6.25 9108001550 6.21 6.16 1010600550 6.33 6.57 11104001550 6.18 6.14 1220600565 6.897.09 132040025507.597.56 143060015657.797.48 152060015508.178.08 163080015507.467.61 173********.557.55 182******** 6.58 6.96 193060025508.398.03 202060015508.298.08 21106001565 6.28 5.94 222080015357.917.66 23204001535 6.75 6.70 242060025358.067.98 25106001535 6.63 6.92 26106002550 6.77 6.64 272060015507.788.08 283060015357.427.74 29208005507.577.58 Optimumconditions24.81618.9818.6444.73–8.32Modifiedconditions2562020458.338.302W.Yang et al./Food Research International xxx(2010)xxx–xxx2.6.DPPH radicals scavenging assayThe DPPH radicals scavenging assay was carried out as previously described by Yang et al (2009).Brie fly,0.1ml of FVP in water was added directly to 3.9ml of a DPPH solution in ethanol (0.1mM).The mixture was immediately shaken for 10s using a vortex mixer,kept at 37°C for 30min,and then centrifuged at 5000rpm/min for 10min.Absorbance of the supernatant was measured at 517nm.Antioxidant capability (AA)was expressed as the percentage of DPPH radicals reduced,which was calculated with the following formula:AA DPPH =A B −A S ðÞ=A B ðÞ×100;where A S is the absorbance of the DPPH solution after reacting with FVP sample at a given concentration and A B is the absorbance of the DPPH solution after reacting with distilled water instead of sample.Ascorbic acid was measured as a positive control.2.7.Statistical analysesData were expressed as means of three replicated determinations.Design Expert (Trial Version 7.0.3)was employed for experimental design,analysis of variance (ANOVA),and model building.SPSS 12.0software was used for statistical calculations and correlation analysis.Values of p b 0.05were considered to be statistically signi ficant.3.Result and discussion3.1.AChE inhibitory activities of Flammulina velutipes extracts In order to study the AChE inhibitory activity of F.velutipes ,four solvent extracts of F.velutipes were prepared for AChE inhibitory activities assay.Results showed that the AChE inhibitory activity of water extract was signi ficantly better than the other solvents extracts (ethanol,petroleum ether,and ethyl acetate).Subsequently,water extract of F.velutipes was separated into two parts (CPS and WES).The results of CPS and WES inhibiting AChE activities suggested that polysaccharides were the principal effective fraction of water extract (Fig.1).Therefore,FVP was selected for further study.3.2.Fitting the model and evaluation of the model predictability In order to obtain more polysaccharides,ratio of water to raw material (10–30ml/g),ultrasonic power (400–800W),ultrasonictime (5–25min),and ultrasonic temperature (35–65°C)was adopted to research their effects on the yield of FVP.The experiments were designed to evaluate the effects of four factors on the yield of FVP using ultrasonic extraction method (Table 1).The mathematical model representing the yield of polysaccharides as a function of the independent variables within the region under investigation was expressed as follows:Y =−11:94+0:18d X 1+0:03d X 2+0:30d X 3+0:25d X 4+6:88×10−5d X 1X 2+1:0×10−3d X 1X 3+1:2×10−3d X 1X 4−2:59×10−4d X 2X 3−1:11×10−4d X 2X 4−1:33×10−3d X 3X 4−5:99×10−3d X 21−1:86×10−5d X 22−2:87×10−3d X 23−2:06×10−3d X 24where Y is the yield of polysaccharides,and X 1,X 2,X 3,and X 4represent ratio of water to raw material,ultrasonic power,ultrasonic time,and ultrasonic temperature,respectively.Predicted response values for the yield of polysaccharides could be obtained using this quadratic polynomial equation in terms of independent variables values.ANOVA for the fitted quadratic polynomial model was given to check the model adequacy (Table 2).F -test suggested that model had a high F -value (F =10.627)and a very low p -value (p b 0.0001),indicating that the fitness of this model was highly signi fick of fit is the variation of the data around the fitted model.The F -value and p -value of the lack of fit were 2.576and 0.188,respectively,which implied an insigni ficant difference relative to the pure error and a good fitness of the model.Coef ficient of determination (R 2)is de fined as the ratio of the explained variation to the total variation,and R 2=0.914approaching unity suggested a good relevance of the dependent variables in the model (Yang,Zhao,Shi,Yang &Jiang,2008).The adjusted determination coef ficient of the model (R 2adj =0.828)con firmed that the model was signi ficant,indicating a good degree of correlation between the actual values and the predicted values of FVP yield.Adeq precision measures the signal to noise ratio,and a ratio greater than 4is desirable (Zhu,Heo,&Row,2010).An adequate ratio (Adeq precision =10.00)of this fitted model indicated that it can be used to navigate the design space.Coef ficient of variation (CV)is a standard deviation expressed as a percentage of the mean.The lower the CV,the smaller the residuals relative to the predicted value (Zhong &Wang,2010).A low CV of the model (CV=4.12)suggested a good precision and higher reliability oftheFig. 1.AChE inhibitory activity of Flammulina velutipes extracts.CPS:crude polysaccharide solution,WES:water –ethanol solution.Values are means ±SD.Values with same superscript letters are statistically not signi ficantly different at p b 0.05(analysis of variance).Table 2Analysis of variance for the fitted quadratic polynomial model of extraction of polysaccharides.Source Sum of squares dfMean Square F Value p -value Prob N F X 1 4.1891 4.18947.237b 0.0001X 20.26110.261 2.9440.1082X 30.23210.232 2.6210.1278X 41.1471 1.14712.9340.0029X 1X 20.07610.0760.8530.3714X 1X 30.0410.040.4510.5128X 1X 40.13010.130 1.4610.2467X 2X 3 1.0711 1.07112.0800.0037X 2X 40.44210.442 4.9870.0424X 3X 40.16010.16 1.8040.2006X 12 2.3271 2.32726.2440.0002X 223.5911 3.59140.488b 0.0001X 320.53210.532 6.0040.0280X 42 1.3971 1.39715.7480.0014Model 13.194140.94210.627b 0.0001Residual 1.242140.0887Lack of fit 1.07100.107 2.5760.188Pure error 0.1740.042Cor total14.4428R 2=0.914R 2Adj =0.828CV =4.12Adeq precision =10.003W.Yang et al./Food Research International xxx (2010)xxx –xxxexperiments carried out(Gangadharan,Nampoothir,Sivaramakrishnan, &Pandey,2009).These results suggested that the model equation was adequate for reasonably predicting the yield of polysaccharides under any combination of values of the variables.The correlation between the predicted values and the actual values of FVP yield was analyzed according previous reports(Gan,Abdul Manaf&Latiff,2010).The closer the value of correlation coefficient to 1,the better the correlation between the observed and predicted values(Banik&Pandey,2009).As shown in Fig.2,the Pearson's correlation coefficient R=0.962approaching unity indicated a good agreement between the predicted values and the actual values and a good suitability of thefitted model equation for reflecting the expected optimization.3.3.Effects of extraction conditions on the yield of FVPThe effects of ratio of water to raw material,ultrasonic power, ultrasonic time,and ultrasonic temperature on the yield of poly-saccharides as well as their interactions were analyzed.Three-dimensional response surface plots for the response(the yield of polysaccharides)were plotted in Fig.3.Fig.3a shows the effects of ratio of water to raw material(X1)and ultrasonic power(X2)on the yield of FVP.With the increase of ultrasonic power,the yield of polysaccharides increased to a value and then declined when ratio of water to raw material was low but constantly increased when ratio of water to raw material was high.The yield of polysaccharides increased with increasing of ratio of water to raw material when ultrasonic power,as well as ultrasonic time(Fig.3b)and ultrasonic temperature(Fig.3c)was kept at a constant value.Fig.3b shows the effects of ratio of water to raw material(X1)and ultrasonic time(X3) on the yield of FVP.The yield of polysaccharides increased with the extension of ultrasonic time.Fig.3c shows the effects of ratio of water to raw material(X1)and ultrasonic temperature(X4)on the yield of FVP.The yield of polysaccharides decreased with the elevation of ultrasonic temperature.Fig.3d shows the effects of ultrasonic power (X2)and ultrasonic time(X3)on the yield of FVP.The yield of polysaccharides increased with the increasing of ultrasonic power when extraction bearing a short ultrasonic time,while a contrary result was obtained when extraction bearing a long ultrasonic time. Similarly,the yield of polysaccharides increased with the extension of ultrasonic time when ultrasonic power was low but decreased when ultrasonic power was high.Fig.3e shows the effects of ultrasonic power(X2)and ultrasonic temperature(X4)on the yield of FVP.The extraction yield of polysaccharides decreased with the elevation of ultrasonic temperature when ultrasonic power was high,butfirstly increased to a value and then declined when ultrasonic power was low.The possible mechanism was due to the degradation effect of ultrasonic wave and too high temperature(Yang,Zhao&Jiang,2008). The extraction yield of polysaccharides increased with the increase of ultrasonic power at low ultrasonic temperature,butfirst increased to a value and then declined at high ultrasonic temperature.Fig.3f shows the effects of ultrasonic time(X3)and ultrasonic temperature (X4)on the yield of FVP.The longer ultrasonic time and lower ultrasonic temperature,the higher polysaccharides yield.Taken altogether,the augment of all the four factors in a certain extent could increase the yield of polysaccharides,but higher ultrasonic power,if accompanied with higher ultrasonic temperature or longer ultrasonic time,would lower the yield of the yield of polysaccharides.The significance of each coefficient was checked by F-test and p-value(Table2).Values of“prob N F”less than0.05indicate model terms are significant.It can be seen that the variables with the largest effect on the yield of FVP were X1,X4,X2X3,X2X4,X12,X22,X32,and X42,which suggested that ratio of water to raw material and ultrasonic temperature significantly influenced the yield of FVP.Meanwhile,significant interactions between ultrasonic power and ultrasonic time,and ultrasonic power and ultrasonic temperature were observed.This indicated that high ultrasonic power could reduce extraction time and temperature to avoid oxidation induced by high temperature.3.4.The optimal conditions and validation of the modelBy prediction of computing program,the optimal conditions for the highest yield of polysaccharides were as follows:ratio of water to material of24.81ml/g,ultrasonic power of618.98W,ultrasonic time of18.64min,and ultrasonic temperature of44.73°C.A predicted value of8.32%was obtained for yield of polysaccharides under the optimal conditions.In order to facilitate the practical extraction process of FVP,the optimal conditions were modified as follows:ratio of water to material of25ml/g,ultrasonic power of620W,ultrasonic time of20min,and ultrasonic temperature of45°C.A predicted value of8.30%was obtained under the modified conditions.The modified conditions were used to validate the suitability of thefitted model equation for accurately predicting the responses values.The results showed that the actual values of polysaccharides yield were8.29% under the modified conditions(Table1),which were in agreement with the predict values significantly(p N0.05).Furthermore,FVP was extracted with a conventional method (ratio of water to material of25ml/g,extraction in80°C water bath for4h),and a yield of5.12%was obtained,which is significantly less than that obtained with the ultrasonic extraction method.The results suggested that ultrasonic assistant extraction of FVP was a time and energy saving and high yielding method.3.5.AChE inhibitory activity of FVPAlzheimer's disease,a disorder associated with progressive degeneration of memory and cognitive function,results from a deficit of cholinergic function in brain.The most important changes observed in brain are a decrease in hippocampal and cortical levels of the neurotransmitter acetylcholine and associated choline transferase (López,Bastida,Viladomat&Codina,2002;Perry,1986).Inhibiting AChE activity is considered as one of the most important methods to improve cognitive deficit and learning and memory impairment by restoring the level of acetylcholine.In this study,concentration-dependent inhibition of AChE was observed for galanthamine.FVP exhibited moderate AChE inhibitory activity(up to20%)that was not dose-dependent(Fig.4).It is reported that polyphenol-rich extract of Vaccinium angustifolium exhibited moderate AChE inhibitory activity in vitro(up to30%),but the polyphenol treated mice exhibited a significant improvement in learning and memory(Papandreou et al.,2009).Thesefindings indicated that FVP may be having a potential application value in improving cognitive deficit and memory impairment.It has been reported that FVP improved the learning and memory ability of dysmnesia model animals effectively evaluated bystep-Fig.2.Correlation between the predicted values and actual values of FVP yield.4W.Yang et al./Food Research International xxx(2010)xxx–xxxthrough test and Morris water test (Zou et al.,2010).In the present study,the results of AChE inhibitory activity in vitro suggest a potential application of FVP to improve cognitive de ficit.This may be one of the most important pharmacological mechanisms of enhancing the learning and memory capability of dysmnesia mice,which need our furtherinvestigation.Fig.3.(a)Response surface plots showing the effects of ratio of water to raw material (X 1)and ultrasonic power (X 2)on the yield of FVP (Y ).(b)Response surface plots showing the effects of ratio of water to raw material (X 1)and ultrasonic time (X 3)on the yield of FVP (Y ).(c)Response surface plots showing the effects of ratio of water to raw material (X 1)and ultrasonic temperature (X 4)on the yield of FVP (Y ).(d)Response surface plots showing the effects of ultrasonic power (X 2)and ultrasonic time (X 3)on the yield of FVP (Y ).(e)Response surface plots showing the effects of ultrasonic power (X 2)and ultrasonic temperature (X 4)on the yield of FVP (Y ).(f)Response surface plots showing the effects of ultrasonic time (X 3)and ultrasonic temperature (X 4)on the yield of FVP (Y ).5W.Yang et al./Food Research International xxx (2010)xxx –xxx3.6.DPPH radicals scavenging activity of FVPFree radical species have been reported to contribute to cellular ageing and neuronal damage (Sastre,Pallardo &Vina,2000).Excess amount of reactive oxygen species,which causes oxidative stress,is associated with pathology of memory de ficits and associated diseases including Alzheimer's disease (Silva et al.,2004;Soholm,1998).DPPH radicals have been widely used as model systems to investigate the antioxidant ability of compounds.In this study,the DPPH scavengingactivity of FVP was concentration-dependent and the scavenging rate was up to 61.24%at concentration of 0.6mg/ml (Fig.5).Good antioxidant ability of FVP implies a potential of FVP to protect cognitive impairment.Moreover,polysaccharides have been proved to exhibit indirect antioxidant ability in vivo by increasing glutathione peroxidase and superoxide dismutase activities (Zhang et al.,2003).Therefore,in order to have a thorough knowledge of pharmacological mechanisms of improving cognitive de ficit,the effect of FVP on antioxidant enzymes in vivo needs to be further studied.4.ConclusionExtraction conditions of FVP were optimized using BBD in response surface methodology,and a quadratic model was fitted for the extraction conditions of FVP.Results of ANOVA and validation experiments suggested that the fitted model was adequate for reasonably predicting the yield of FVP.A FVP yield of 8.33%was obtained under the modi fied conditions (ratio of water to material of 25ml/g,ultrasonic power of 620W,ultrasonic time of 20min,and ultrasonic temperature of 45°C).A good potential of FVP to enhance cognitive ability was testi fied by DPPH scavenging activity assay and AChE inhibitory activity test,which indicate that consummation of F.velutipes is bene ficial to improve learning and memory de ficit.AcknowledgmentThis work is financially supported by the earmarked fund for Modern Agro-industry Technology Research System of China.ReferencesBanik,R.M.,&Pandey,S.K.(2009).Selection of metal salts for alkaline phosphataseproduction using response surface methodology.Food Research International ,42,470−475.Fan,Y.,Hu,J.,Li,J.,Yang,Z.,Xin,X.,Wang,J.,Ding,J.,&Geng,M.(2005).Effect of acidicoligosaccharide sugar chain on scopolamine-induced memory impairment in rats and its related mechanisms.Neuroscience Letters ,374,222−226.Gan,C.-Y.,Abdul Manaf,N.H.,&Latiff,A.A.(2010).Optimization of alcohol insolublepolysaccharides (AIPS)extraction from the Parkia speciosa pod using response surface methodology (RSM).Carbohydrate Polymers ,79,825−831.Gangadharan, D.,Nampoothiri,K.M.,Sivaramakrishnan,S.,&Pandey, A.(2009).Immobilized bacterial α-amylase for effective hydrolysis of raw and soluble starch.Food Research International ,42,436−442.Gold,P.E.(2003).Acetylcholine modulation of neural systems involved in learning andmemory.Neurobiology of Learning and Memory ,80,194−210.Hornick,A.,Schwaiger,S.,Rollinger,J.M.,Vo,N.P.,Prast,H.,&Stuppner,H.(2008).Extracts and constituents of Leontopodium alpinum enhance cholinergic transmis-sion:Brain ACh increasing and memory improving properties.Biochemical Pharmacology ,76,236−248.Langjae,R.,Bussarawit,S.,Yuenyongsawad,S.,Ingkaninan,K.,&Plubrukarn,A.(2007).Acetylcholinesterase-inhibiting steroidal alkaloid from the sponge Corticium sp.Steroids ,72,682−685.Leung,M.Y.K.,Fung,K.P.,&Choy,Y.M.(1997).The isolation and characterization of animmunomodulatory and anti-tumor polysaccharide preparation from Flammulina velutipes .Immunopharmacology ,35,255−263.Li,H.,Pordesimo,L.,&Weiss,J.(2004).High intensity ultrasound-assisted extraction ofoil from soybeans.Food Research International ,37(7),731−738.López,S.,Bastida,J.,Viladomat,F.,&Codina,C.(2002).Acetylcholinesterase inhibitoryactivity of some Amaryllidaceae alkaloids and Narcissus extracts.Life Sciences ,71,2521−2529.Papandreou,M.A.,Dimakopoulou,A.,Linardaki,Z.I.,Cordopatis,P.,Klimis-Zacas,D.,Margarity,M.,&Lamari,F.N.(2009).Effect of a polyphenol-rich wild blueberry extract on cognitive performance of mice,brain antioxidant markers and acetylcholinesterase activity.Behavioural Brain Research ,198,352−358.Perry,E.K.(1986).The cholinergic hypothesis —ten years on.British Medical Bulletin ,42,63−69.Roberson,M.R.,&Harrell,L.E.(1997).Cholinergic activity and amyloid precursorprotein metabolism.Brain Research.Brain Research Reviews ,25,50−69.Sastre,J.,Pallardo,F.V.,&Vina,J.(2000).Mitochondrial oxidative stress plays a key rolein aging and apoptosis.IUBMB Life ,49,427−435.Silman,I.,&Sussman,J.L.(2005).Acetylcholinesterase:‘Classical ’and 'non-classical'functions and pharmacology.Current Opinion in Pharmacology ,5,293−302.Silva,R.H.,Abilio,V.C.,Takatsu,A.L.,Kameda,S.R.,Grassl,C.,Chehin,A.B.,Medrano,W.A.,Calzavara,M.B.,Registro,S.,Andersen,M.L.,Machado,R.B.,Carvalho,R.C.,Ribeiro,R.d.A.,Tu fik,S.,&Frussa-Filho,R.(2004).Role of hippocampal oxidative stress in memory de ficits induced by sleep deprivation in mice.Neuropharmacology ,46,895−903.Fig.4.AChE inhibitory activity of galanthamine and FVP with various concentrations (data are in mean ±SD,n =3).Fig. 5.DPPH radicals scavenging activity of FVP and ascorbic acid with various concentrations (data are in mean±SD,n =3).6W.Yang et al./Food Research International xxx (2010)xxx –xxx。

CHAPTER8MOLECULAR COLLISIONS8.1INTRODUCTIONBasic concepts of gas-phase collisions were introduced in Chapter3,where we described only those processes needed to model the simplest noble gas discharges: electron–atom ionization,excitation,and elastic scattering;and ion–atom elastic scattering and resonant charge transfer.In this chapter we introduce other collisional processes that are central to the description of chemically reactive discharges.These include the dissociation of molecules,the generation and destruction of negative ions,and gas-phase chemical reactions.Whereas the cross sections have been measured reasonably well for the noble gases,with measurements in reasonable agreement with theory,this is not the case for collisions in molecular gases.Hundreds of potentially significant collisional reactions must be examined in simple diatomic gas discharges such as oxygen.For feedstocks such as CF4/O2,SiH4/O2,etc.,the complexity can be overwhelming.Furthermore,even when the significant processes have been identified,most of the cross sections have been neither measured nor calculated. Hence,one must often rely on estimates based on semiempirical or semiclassical methods,or on measurements made on molecules analogous to those of interest. As might be expected,data are most readily available for simple diatomic and polyatomic gases.Principles of Plasma Discharges and Materials Processing,by M.A.Lieberman and A.J.Lichtenberg. ISBN0-471-72001-1Copyright#2005John Wiley&Sons,Inc.235236MOLECULAR COLLISIONS8.2MOLECULAR STRUCTUREThe energy levels for the electronic states of a single atom were described in Chapter3.The energy levels of molecules are more complicated for two reasons. First,molecules have additional vibrational and rotational degrees of freedom due to the motions of their nuclei,with corresponding quantized energies E v and E J. Second,the energy E e of each electronic state depends on the instantaneous con-figuration of the nuclei.For a diatomic molecule,E e depends on a single coordinate R,the spacing between the two nuclei.Since the nuclear motions are slow compared to the electronic motions,the electronic state can be determined for anyfixed spacing.We can therefore represent each quantized electronic level for a frozen set of nuclear positions as a graph of E e versus R,as shown in Figure8.1.For a mole-cule to be stable,the ground(minimum energy)electronic state must have a minimum at some value R1corresponding to the mean intermolecular separation (curve1).In this case,energy must be supplied in order to separate the atoms (R!1).An excited electronic state can either have a minimum( R2for curve2) or not(curve3).Note that R2and R1do not generally coincide.As for atoms, excited states may be short lived(unstable to electric dipole radiation)or may be metastable.Various electronic levels may tend to the same energy in the unbound (R!1)limit. Array FIGURE8.1.Potential energy curves for the electronic states of a diatomic molecule.For diatomic molecules,the electronic states are specifiedfirst by the component (in units of hÀ)L of the total orbital angular momentum along the internuclear axis, with the symbols S,P,D,and F corresponding to L¼0,+1,+2,and+3,in analogy with atomic nomenclature.All but the S states are doubly degenerate in L.For S states,þandÀsuperscripts are often used to denote whether the wave function is symmetric or antisymmetric with respect to reflection at any plane through the internuclear axis.The total electron spin angular momentum S (in units of hÀ)is also specified,with the multiplicity2Sþ1written as a prefixed superscript,as for atomic states.Finally,for homonuclear molecules(H2,N2,O2, etc.)the subscripts g or u are written to denote whether the wave function is sym-metric or antisymmetric with respect to interchange of the nuclei.In this notation, the ground states of H2and N2are both singlets,1Sþg,and that of O2is a triplet,3SÀg .For polyatomic molecules,the electronic energy levels depend on more thanone nuclear coordinate,so Figure8.1must be generalized.Furthermore,since there is generally no axis of symmetry,the states cannot be characterized by the quantum number L,and other naming conventions are used.Such states are often specified empirically through characterization of measured optical emission spectra.Typical spacings of low-lying electronic energy levels range from a few to tens of volts,as for atoms.Vibrational and Rotational MotionsUnfreezing the nuclear vibrational and rotational motions leads to additional quan-tized structure on smaller energy scales,as illustrated in Figure8.2.The simplest (harmonic oscillator)model for the vibration of diatomic molecules leads to equally spaced quantized,nondegenerate energy levelse E v¼hÀv vib vþ1 2(8:2:1)where v¼0,1,2,...is the vibrational quantum number and v vib is the linearized vibration frequency.Fitting a quadratic functione E v¼12k vib(RÀ R)2(8:2:2)near the minimum of a stable energy level curve such as those shown in Figure8.1, we can estimatev vib%k vibm Rmol1=2(8:2:3)where k vib is the“spring constant”and m Rmol is the reduced mass of the AB molecule.The spacing hÀv vib between vibrational energy levels for a low-lying8.2MOLECULAR STRUCTURE237stable electronic state is typically a few tenths of a volt.Hence for molecules in equi-librium at room temperature (0.026V),only the v ¼0level is significantly popula-ted.However,collisional processes can excite strongly nonequilibrium vibrational energy levels.We indicate by the short horizontal line segments in Figure 8.1a few of the vibrational energy levels for the stable electronic states.The length of each segment gives the range of classically allowed vibrational motions.Note that even the ground state (v ¼0)has a finite width D R 1as shown,because from(8.2.1),the v ¼0state has a nonzero vibrational energy 1h Àv vib .The actual separ-ation D R about Rfor the ground state has a Gaussian distribution,and tends toward a distribution peaked at the classical turning points for the vibrational motion as v !1.The vibrational motion becomes anharmonic and the level spa-cings tend to zero as the unbound vibrational energy is approached (E v !D E 1).FIGURE 8.2.Vibrational and rotational levels of two electronic states A and B of a molecule;the three double arrows indicate examples of transitions in the pure rotation spectrum,the rotation–vibration spectrum,and the electronic spectrum (after Herzberg,1971).238MOLECULAR COLLISIONSFor E v.D E1,the vibrational states form a continuum,corresponding to unbound classical motion of the nuclei(breakup of the molecule).For a polyatomic molecule there are many degrees of freedom for vibrational motion,leading to a very compli-cated structure for the vibrational levels.The simplest(dumbbell)model for the rotation of diatomic molecules leads to the nonuniform quantized energy levelse E J¼hÀ22I molJ(Jþ1)(8:2:4)where I mol¼m Rmol R2is the moment of inertia and J¼0,1,2,...is the rotational quantum number.The levels are degenerate,with2Jþ1states for the J th level. The spacing between rotational levels increases with J(see Figure8.2).The spacing between the lowest(J¼0to J¼1)levels typically corresponds to an energy of0.001–0.01V;hence,many low-lying levels are populated in thermal equilibrium at room temperature.Optical EmissionAn excited molecular state can decay to a lower energy state by emission of a photon or by breakup of the molecule.As shown in Figure8.2,the radiation can be emitted by a transition between electronic levels,between vibrational levels of the same electronic state,or between rotational levels of the same electronic and vibrational state;the radiation typically lies within the optical,infrared,or microwave frequency range,respectively.Electric dipole radiation is the strongest mechanism for photon emission,having typical transition times of t rad 10À9s,as obtained in (3.4.13).The selection rules for electric dipole radiation areDL¼0,+1(8:2:5a)D S¼0(8:2:5b) In addition,for transitions between S states the only allowed transitions areSþÀ!Sþand SÀÀ!SÀ(8:2:6) and for homonuclear molecules,the only allowed transitions aregÀ!u and uÀ!g(8:2:7) Hence homonuclear diatomic molecules do not have a pure vibrational or rotational spectrum.Radiative transitions between electronic levels having many different vibrational and rotational initial andfinal states give rise to a structure of emission and absorption bands within which a set of closely spaced frequencies appear.These give rise to characteristic molecular emission and absorption bands when observed8.2MOLECULAR STRUCTURE239using low-resolution optical spectrometers.As for atoms,metastable molecular states having no electric dipole transitions to lower levels also exist.These have life-times much exceeding10À6s;they can give rise to weak optical band structures due to magnetic dipole or electric quadrupole radiation.Electric dipole radiation between vibrational levels of the same electronic state is permitted for molecules having permanent dipole moments.In the harmonic oscillator approximation,the selection rule is D v¼+1;weaker transitions D v¼+2,+3,...are permitted for anharmonic vibrational motion.The preceding description of molecular structure applies to molecules having arbi-trary electronic charge.This includes neutral molecules AB,positive molecular ions ABþ,AB2þ,etc.and negative molecular ions ABÀ.The potential energy curves for the various electronic states,regardless of molecular charge,are commonly plotted on the same diagram.Figures8.3and8.4give these for some important electronic statesof HÀ2,H2,and Hþ2,and of OÀ2,O2,and Oþ2,respectively.Examples of both attractive(having a potential energy minimum)and repulsive(having no minimum)states can be seen.The vibrational levels are labeled with the quantum number v for the attrac-tive levels.The ground states of both Hþ2and Oþ2are attractive;hence these molecular ions are stable against autodissociation(ABþ!AþBþor AþþB).Similarly,the ground states of H2and O2are attractive and lie below those of Hþ2and Oþ2;hence they are stable against autodissociation and autoionization(AB!ABþþe).For some molecules,for example,diatomic argon,the ABþion is stable but the AB neutral is not stable.For all molecules,the AB ground state lies below the ABþground state and is stable against autoionization.Excited states can be attractive or repulsive.A few of the attractive states may be metastable;some examples are the 3P u state of H2and the1D g,1Sþgand3D u states of O2.Negative IonsRecall from Section7.2that many neutral atoms have a positive electron affinity E aff;that is,the reactionAþeÀ!AÀis exothermic with energy E aff(in volts).If E aff is negative,then AÀis unstable to autodetachment,AÀ!Aþe.A similar phenomenon is found for negative molecular ions.A stable ABÀion exists if its ground(lowest energy)state has a potential minimum that lies below the ground state of AB.This is generally true only for strongly electronegative gases having large electron affinities,such as O2 (E aff%1:463V for O atoms)and the halogens(E aff.3V for the atoms).For example,Figure8.4shows that the2P g ground state of OÀ2is stable,with E aff% 0:43V for O2.For weakly electronegative or for electropositive gases,the minimum of the ground state of ABÀgenerally lies above the ground state of AB,and ABÀis unstable to autodetachment.An example is hydrogen,which is weakly electronegative(E aff%0:754V for H atoms).Figure8.3shows that the2Sþu ground state of HÀ2is unstable,although the HÀion itself is stable.In an elec-tropositive gas such as N2(E aff.0),both NÀ2and NÀare unstable. 240MOLECULAR COLLISIONS8.3ELECTRON COLLISIONS WITH MOLECULESThe interaction time for the collision of a typical (1–10V)electron with a molecule is short,t c 2a 0=v e 10À16–10À15s,compared to the typical time for a molecule to vibrate,t vib 10À14–10À13s.Hence for electron collisional excitation of a mole-cule to an excited electronic state,the new vibrational (and rotational)state canbeFIGURE 8.3.Potential energy curves for H À2,H 2,and H þ2.(From Jeffery I.Steinfeld,Molecules and Radiation:An Introduction to Modern Molecular Spectroscopy ,2d ed.#MIT Press,1985.)8.3ELECTRON COLLISIONS WITH MOLECULES 241FIGURE 8.4.Potential energy curves for O À2,O 2,and O þ2.(From Jeffery I.Steinfeld,Molecules and Radiation:An Introduction to Modern Molecular Spectroscopy ,2d ed.#MIT Press,1985.)242MOLECULAR COLLISIONS8.3ELECTRON COLLISIONS WITH MOLECULES243 determined by freezing the nuclear motions during the collision.This is known as the Franck–Condon principle and is illustrated in Figure8.1by the vertical line a,showing the collisional excitation atfixed R to a high quantum number bound vibrational state and by the vertical line b,showing excitation atfixed R to a vibra-tionally unbound state,in which breakup of the molecule is energetically permitted. Since the typical transition time for electric dipole radiation(t rad 10À9–10À8s)is long compared to the dissociation( vibrational)time t diss,excitation to an excited state will generally lead to dissociation when it is energetically permitted.Finally, we note that the time between collisions t c)t rad in typical low-pressure processing discharges.Summarizing the ordering of timescales for electron–molecule collisions,we havet at t c(t vib t diss(t rad(t cDissociationElectron impact dissociation,eþABÀ!AþBþeof feedstock gases plays a central role in the chemistry of low-pressure reactive discharges.The variety of possible dissociation processes is illustrated in Figure8.5.In collisions a or a0,the v¼0ground state of AB is excited to a repulsive state of AB.The required threshold energy E thr is E a for collision a and E a0for Array FIGURE8.5.Illustrating the variety of dissociation processes for electron collisions with molecules.collision a0,and it leads to an energy after dissociation lying between E aÀE diss and E a0ÀE diss that is shared among the dissociation products(here,A and B). Typically,E aÀE diss few volts;consequently,hot neutral fragments are typically generated by dissociation processes.If these hot fragments hit the substrate surface, they can profoundly affect the process chemistry.In collision b,the ground state AB is excited to an attractive state of AB at an energy E b that exceeds the binding energy E diss of the AB molecule,resulting in dissociation of AB with frag-ment energy E bÀE diss.In collision b0,the excitation energy E b0¼E diss,and the fragments have low energies;hence this process creates fragments having energies ranging from essentially thermal energies up to E bÀE diss few volts.In collision c,the AB atom is excited to the bound excited state ABÃ(labeled5),which sub-sequently radiates to the unbound AB state(labeled3),which then dissociates.The threshold energy required is large,and the fragments are hot.Collision c can also lead to dissociation of an excited state by a radiationless transfer from state5to state4near the point where the two states cross:ABÃðboundÞÀ!ABÃðunboundÞÀ!AþBÃThe fragments can be both hot and in excited states.We discuss such radiationless electronic transitions in the next section.This phenomenon is known as predisso-ciation.Finally,a collision(not labeled in thefigure)to state4can lead to dis-sociation of ABÃ,again resulting in hot excited fragments.The process of electron impact excitation of a molecule is similar to that of an atom,and,consequently,the cross sections have a similar form.A simple classical estimate of the dissociation cross section for a level having excitation energy U1can be found by requiring that an incident electron having energy W transfer an energy W L lying between U1and U2to a valence electron.Here,U2is the energy of the next higher level.Then integrating the differential cross section d s[given in(3.4.20)and repeated here],d s¼pe24021Wd W LW2L(3:4:20)over W L,we obtains diss¼0W,U1pe24pe021W1U1À1WU1,W,U2pe24021W1U1À1U2W.U28>>>>>><>>>>>>:(8:3:1)244MOLECULAR COLLISIONSLetting U2ÀU1(U1and introducing voltage units W¼e E,U1¼e E1and U2¼e E2,we haves diss¼0E,E1s0EÀE11E1,E,E2s0E2ÀE1EE.E28>>>><>>>>:(8:3:2)wheres0¼pe4pe0E12(8:3:3)We see that the dissociation cross section rises linearly from the threshold energy E thr%E1to a maximum value s0(E2ÀE1)=E thr at E2and then falls off as1=E. Actually,E1and E2can depend on the nuclear separation R.In this case,(8.3.2) should be averaged over the range of R s corresponding to the ground-state vibrational energy,leading to a broadened dependence of the average cross section on energy E.The maximum cross section is typically of order10À15cm2. Typical rate constants for a single dissociation process with E thr&T e have an Arrhenius formK diss/K diss0expÀE thr T e(8:3:4)where K diss0 10À7cm3=s.However,in some cases E thr.T e.For excitation to an attractive state,an appropriate average over the fraction of the ground-state vibration that leads to dissociation must be taken.Dissociative IonizationIn addition to normal ionization,eþABÀ!ABþþ2eelectron–molecule collisions can lead to dissociative ionizationeþABÀ!AþBþþ2eThese processes,common for polyatomic molecules,are illustrated in Figure8.6.In collision a having threshold energy E iz,the molecular ion ABþis formed.Collisionsb andc occur at higher threshold energies E diz and result in dissociative ionization,8.3ELECTRON COLLISIONS WITH MOLECULES245leading to the formation of fast,positively charged ions and neutrals.These cross sections have a similar form to the Thompson ionization cross section for atoms.Dissociative RecombinationThe electron collision,e þAB þÀ!A þB Ãillustrated as d and d 0in Figure 8.6,destroys an electron–ion pair and leads to the production of fast excited neutral fragments.Since the electron is captured,it is not available to carry away a part of the reaction energy.Consequently,the collision cross section has a resonant character,falling to very low values for E ,E d and E .E d 0.However,a large number of excited states A Ãand B Ãhaving increasing principal quantum numbers n and energies can be among the reaction products.Consequently,the rate constants can be large,of order 10À7–10À6cm 3=s.Dissocia-tive recombination to the ground states of A and B cannot occur because the potential energy curve for AB þis always greater than the potential energycurveFIGURE 8.6.Illustration of dissociative ionization and dissociative recombination for electron collisions with molecules.246MOLECULAR COLLISIONSfor the repulsive state of AB.Two-body recombination for atomic ions or for mol-ecular ions that do not subsequently dissociate can only occur with emission of a photon:eþAþÀ!Aþh n:As shown in Section9.2,the rate constants are typically three tofive orders of magnitude lower than for dissociative recombination.Example of HydrogenThe example of H2illustrates some of the inelastic electron collision phenomena we have discussed.In order of increasing electron impact energy,at a threshold energy of 8:8V,there is excitation to the repulsive3Sþu state followed by dissociation into two fast H fragments carrying 2:2V/atom.At11.5V,the1Sþu bound state is excited,with subsequent electric dipole radiation in the ultraviolet region to the1Sþg ground state.At11.8V,there is excitation to the3Sþg bound state,followedby electric dipole radiation to the3Sþu repulsive state,followed by dissociation with 2:2V/atom.At12.6V,the1P u bound state is excited,with UV emission tothe ground state.At15.4V,the2Sþg ground state of Hþ2is excited,leading to the pro-duction of Hþ2ions.At28V,excitation of the repulsive2Sþu state of Hþ2leads to thedissociative ionization of H2,with 5V each for the H and Hþfragments.Dissociative Electron AttachmentThe processes,eþABÀ!AþBÀproduce negative ion fragments as well as neutrals.They are important in discharges containing atoms having positive electron affinities,not only because of the pro-duction of negative ions,but because the threshold energy for production of negative ion fragments is usually lower than for pure dissociation processes.A variety of pro-cesses are possible,as shown in Figure8.7.Since the impacting electron is captured and is not available to carry excess collision energy away,dissociative attachment is a resonant process that is important only within a narrow energy range.The maximum cross sections are generally much smaller than the hard-sphere cross section of the molecule.Attachment generally proceeds by collisional excitation from the ground AB state to a repulsive ABÀstate,which subsequently either auto-detaches or dissociates.The attachment cross section is determined by the balance between these processes.For most molecules,the dissociation energy E diss of AB is greater than the electron affinity E affB of B,leading to the potential energy curves shown in Figure8.7a.In this case,the cross section is large only for impact energies lying between a minimum value E thr,for collision a,and a maximum value E0thr for8.3ELECTRON COLLISIONS WITH MOLECULES247FIGURE 8.7.Illustration of a variety of electron attachment processes for electron collisions with molecules:(a )capture into a repulsive state;(b )capture into an attractive state;(c )capture of slow electrons into a repulsive state;(d )polar dissociation.248MOLECULAR COLLISIONScollision a 0.The fragments are hot,having energies lying between minimum and maximum values E min ¼E thr þE affB ÀE diss and E max ¼E 0thr þE af fB ÀE diss .Since the AB Àstate lies above the AB state for R ,R x ,autodetachment can occur as the mol-ecules begin to separate:AB À!AB þe.Hence the cross section for production of negative ions can be much smaller than that for excitation of the AB Àrepulsive state.As a crude estimate,for the same energy,the autodetachment rate is ffiffiffiffiffiffiffiffiffiffiffiffiffiM R =m p 100times the dissociation rate of the repulsive AB Àmolecule,where M R is the reduced mass.Hence only one out of 100excitations lead to dissociative attachment.Excitation to the AB Àbound state can also lead to dissociative attachment,as shown in Figure 8.7b .Here the cross section is significant only for E thr ,E ,E 0thr ,but the fragments can have low energies,with a minimum energy of zero and a maximum energy of E 0thr þE affB ÀE diss .Collision b,e þAB À!AB ÀÃdoes not lead to production of AB Àions because energy and momentum are not gen-erally conserved when two bodies collide elastically to form one body (see Problem3.12).Hence the excited AB ÀÃion separates,AB ÀÃÀ!e þABunless vibrational radiation or collision with a third body carries off the excess energy.These processes are both slow in low-pressure discharges (see Section 9.2).At high pressures (say,atmospheric),three-body attachment to form AB Àcan be very important.For a few molecules,such as some halogens,the electron affinity of the atom exceeds the dissociation energy of the neutral molecule,leading to the potential energy curves shown in Figure 8.7c .In this case the range of electron impact ener-gies E for excitation of the AB Àrepulsive state includes E ¼0.Consequently,there is no threshold energy,and very slow electrons can produce dissociative attachment,resulting in hot neutral and negative ion fragments.The range of R s over which auto-detachment can occur is small;hence the maximum cross sections for dissociative attachment can be as high as 10À16cm 2.A simple classical estimate of electron capture can be made using the differential scattering cross section for energy loss (3.4.20),in a manner similar to that done for dissociation.For electron capture to an energy level E 1that is unstable to autode-tachment,and with the additional constraint for capture that the incident electron energy lie within E 1and E 2¼E 1þD E ,where D E is a small energy difference characteristic of the dissociative attachment timescale,we obtain,in place of (8.3.2),s att¼0E ,E 1s 0E ÀE 1E 1E 1,E ,E 20E .E 28>><>>:(8:3:5)8.3ELECTRON COLLISIONS WITH MOLECULES 249wheres 0%p m M R 1=2e 4pe 0E 1 2(8:3:6)The factor of (m =M R )1=2roughly gives the fraction of excited states that do not auto-detach.We see that the dissociative attachment cross section rises linearly at E 1to a maximum value s 0D E =E 1and then falls abruptly to zero.As for dissociation,E 1can depend strongly on the nuclear separation R ,and (8.3.5)must be averaged over the range of E 1s corresponding to the ground state vibrational motion;e.g.,from E thr to E 0thr in Figure 8.7a .Because generally D E (E 0thr ÀE thr ,we can write (8.3.5)in the forms att %p m M R 1=2e 4pe 0 2(D E )22E 1d (E ÀE 1)(8:3:7)where d is the Dirac delta ing (8.3.7),the average over the vibrational motion can be performed,leading to a cross section that is strongly peaked lying between E thr and E 0thr .We leave the details of the calculation to a problem.Polar DissociationThe process,e þAB À!A þþB Àþeproduces negative ions without electron capture.As shown in Figure 8.7d ,the process proceeds by excitation of a polar state A þand B Àof AB Ãthat has a separ-ated atom limit of A þand B À.Hence at large R ,this state lies above the A þB ground state by the difference between the ionization potential of A and the electron affinity of B.The polar state is weakly bound at large R by the Coulomb attraction force,but is repulsive at small R .The maximum cross section and the dependence of the cross section on electron impact energy are similar to that of pure dissociation.The threshold energy E thr for polar dissociation is generally large.The measured cross section for negative ion production by electron impact in O 2is shown in Figure 8.8.The sharp peak at 6.5V is due to dissociative attachment.The variation of the cross section with energy is typical of a resonant capture process.The maximum cross section of 10À18cm 2is quite low because autode-tachment from the repulsive O À2state is strong,inhibiting dissociative attachment.The second gradual maximum near 35V is due to polar dissociation;the variation of the cross section with energy is typical of a nonresonant process.250MOLECULAR COLLISIONS。

国外放牧方法研究概述赵瑞雪，程钰宏，董宽虎山西农业大学动物科技学院，山西太谷（030801）mail zhaoruixue1234@E-：摘要：放牧方法是在长期的放牧实践和研究中得出的，其能够平衡饲草供给、满足家畜需要、增加畜产品以满足人们需求。

本文对国外放牧方法：连续放牧、季节适宜性放牧、延迟放牧/休牧、高密度放牧方法进行详细的介绍。

关键词：连续放牧，季节适宜性放牧，延迟放牧/休牧，高密度放牧人们在长期的放牧实践和研究中，为了平衡饲草供给，满足人们需求，得出了许多优良的、适应时代发展要求的放牧方法。

放牧是草地利用的基本方式，它既关系到草地放牧业的稳定和发展，也关系到草地保护和生产效率的提高。

目前世界各国草地畜牧业中，放牧仍然是主要的饲养方式。

当今社会，在同一放牧地上用运两种或两种以上的放牧方法已成为一种趋势，不同放牧方法有机结合更有利于提高家畜产量，为长久利用草地提供了合理的理论依据。

这些不同放牧方法的有机结合，形成了不同的放牧制度，从历史发展来看，放牧制度大体经历了原始游牧制、季节性游牧制、半定居放牧制和定居放牧制四个阶段。

各个历史阶段则是生产与生产能力的适应。

放牧制度是草地用于放牧时的基本利用体系，其规定了家畜对牧草地利用的时间和空间上的通盘安排。

为了选择合理的放牧制度，本文就以下放牧制度及其包含的放牧方法进行详细地介绍，以利于人们合理利用草地资源，为在我国草原地区的推广利用，提供基础资料。

1.放牧方法的作用优良的放牧方法或放牧制度是非常实际有效的，可以根据当地气候条件机动调节并应用于生产，实现最优饲草转化。

放牧方法和放牧管理的结合用运已成为一种趋势，根据实际情况进行科学管理是牧场获利的最佳途径。

由于饲草供给、气候变化、目标转换，经济波动等原因，复杂的放牧方法在实践中经常被相应的调整，达到最优的放牧强度以适应生产发展需要。

Heady认为实现饲草最优化转化的处理方法是不同的，但它们遵循以下法则[1]：第一、必须遵循主要饲草植物的生理生态学需要；第二、改善植物生长条件，维持较高的生长活力；第三、提供良好的牧草生长环境，防止过度放牧；第四、提高植物的适口性和饲草产量；第五、在草地上维持草畜平衡；第六、在实际操作过程中执行理论和实际相结合的原理；为了使草地生态系统有高的第二性生产，必须保证有足够的第一性生产，科学合理地选择放牧方法是关键，管理者在选择放牧方法时，必须优先考虑如下目标：表1 选择放牧方法需考虑达到的目标植物/生存条件要达到的目标动物/市场经济需要达到的目标1、改善植物生长条件，提高植物生长活力1、在市场低峰期购买家畜2、维持植物高的生长条件2、维持高的饲草营养水平3、合理分配利用牧草3、保证高的营养水平在动物生长敏感期4、减少动物对植物的选择性4、合理的放牧管理计划5、合理的载畜量6、保证饲草供应充足7、在干旱或其它紧急情况下采取延迟放牧或休牧2.放牧方法的适应性放牧方法得到人们的认可，是因为其不是单纯的实验研究，而是在实践中产生，在实践中有强的适应性和高的经济回报。

Appl.Phys.A74,19–25(2002)/Digital Object Identifier(DOI)10.1007/s003390100893Applied Physics AMaterialsScience&ProcessingFemtosecond laser ablation of silicon–modification thresholds and morphologyJ.Bonse∗,S.Baudach,J.Krüger,W.Kautek,M.LenznerLaboratory for Thin Film Technology,Federal Institute for Materials Research and Testing(BAM),Unter den Eichen87,12205Berlin,Germany Received:4December2000/Revised version:29March2001/Published online:20June2001– Springer-Verlag2001Abstract.We investigated the initial modification and abla-tion of crystalline silicon with single and multiple Ti:sapphire laser pulses of5to400fs duration.In accordance with earlier established models,we found the phenomena amorphization, melting,re-crystallization,nucleated vaporization,and abla-tion to occur with increasing laserfluence down to the short-est pulse durations.We noticed new morphological features (bubbles)as well as familiar ones(ripples,columns).A nearly constant ablation thresholdfluence on the order of0.2J/cm2 for all pulse durations and multiple-pulse irradiation was ob-served.For a duration of≈100fs,significant incubation can be observed,whereas for5fs pulses,the ablation threshold does not depend on the pulse number within the experimental error.For micromachining of silicon,a pulse duration of less than500fs is not advantageous.PACS:79.20D;42.70.QMicromachining with ultrashort laser pulses has attracted growing interest even in industry and medicine since the ap-propriate lasers were made readily available for a wide set of parameters[1,2].It has been demonstrated that ultrashort pulses bear the potential for precise micromachining(later-ally and vertically)in transparent dielectrics[3].In the course of investigations with femtosecond pulses,it became obvious that the detailed mechanisms of damage to solids caused by laser light are far from fully understood.A number of phenomena concerning photo-induced mod-ification of silicon surfaces have been explored in different ranges of wavelength,intensity and duration of the applied laser pulses.In this paper,we want to extend the existing investigations on laser-induced surface damage in silicon to pulse durations as short as5fs.We also observed several different phenomena;we try to methodically“file”these ob-servations into a physical overview.We will demonstrate that the so-far-assumed sequence of physical processes,namely amorphization[4],melting[5, 6],re-crystallization[4,7],nucleated vaporization[8],andfi-nally ablation[9],can also account for these experimental re-∗Corresponding author.(Fax:+49-30/8104-1827,E-mail:joern.bonse@bam.de)sults.Various well-known features,for example,ripples[10] and columns[11],could be realized and appropriately ex-plained as well.In Sect.1,the current knowledge about the interaction between laser pulses and silicon is reviewed. Our experimental results are shown and compared to this in Sect.2.1Physical considerationsThe deposition of the laser energy into a solid is usually viewed in the quantum-mechanical formalism of particle in-teraction.The incident pulse energy is absorbed by the elec-trons,dependent on the peak intensity,by one-,two-or more-photon absorption.Absorption by free carriers(sometimes called inverse bremsstrahlung)depends on the number of al-ready existing carriers and is therefore a subsequent process. The same applies to collisional ionization,which utilizes part of the energy of highly excited carriers to generate new free electrons.These carriers then thermalize to a Fermi–Dirac distribution while transferring their excess energy to phonons, typically on a time scale of100fs.These phonons afterwards recombine to a Bose–Einstein distribution in a few picosec-onds[12].During the detailed exploitation of pulsed-laser annealing(PLA,typically done with nanosecond pulses),a “plasma-annealing”model was established,which stated that a non-thermal“bond softening”was responsible for the loss of the crystal structure[13,14].Recently,this non-thermal model was shown to be applicable for several semiconductors irradiated with femtosecond pulses[15–18].So far,no spatial transport of energy out of the excitation region has been considered.In order to treat the subsequent processes,including melting,boiling,and ablation of mate-rial,one usually uses either a two-temperature model[19,20], which distinguishes between electron and lattice(ion)tem-peratures,or a completely classical model of thermal trans-port in a continuum[8,21].The latter one describes phase changes from the molten phase to a gas,considering the ex-istence of transient thermodynamical states(such as super-heated liquids)due to the rapid action of the ultrashort laser pulses.The physical mechanisms that are involved in photo-excitation of the solid are manifested also in irreversible20changes of the irradiated surface.These changes can be used for identification of some of the processes and also for deter-mination of their thresholdfluences.After irradiation with short laser pulses,re-solidification of molten material was observed to happen in two stages: amorphization and re-crystallization[4].The difference was simply attributed to the amount of energy deposited in the ma-terial(the temperature)and the consequent cooling velocity. At lower temperatures,the material has not enough time to re-crystallize from the melt,thus leaving the semiconductor in an amorphous state.In regions with higher temperatures, cooling is sufficiently slow to allow re-crystallization.Already in previous experiments,a rather mysterious phe-nomenon has been discovered after the solids have been ir-radiated with multiple subsequent pulses[22].Finally termed “ripples”,these periodic surface structures appear as lines orthogonal to the direction of the electricfield vector of the incident light and show a period on the order of the wave-length of the generating light[10,23].The generally accepted explanation of these ripples is an interference between the in-cident light and a surface wave(generated by scattering).This interference leads to periodic modulation of the absorbed in-tensity and consequently to modulated ablation.Column formation in crystalline silicon as a result of multi-pulse laser irradiation has been observed in the past at different laser wavelengths(UV–NIR),for different pulse durations(fs–ns),and in different environments(vacuum, air,different gases).A certain number of laser pulses is re-quired to initiate the self-organized growth process of Si microcolumns in the irradiated region.This phenomenon is of major importance because it can limit the precision of laser ablation.For the treatment with ultrashort(fs) laser pulses,the Si-column formation was observed by sev-eral groups under different experimental conditions(λ= 248nm,τ=105fs,vacuum[24];λ=390nm,τ=250fs, vacuum[9];λ=620nm,τ=300fs,air[25];λ=780nm,τ=100fs,SF6,Cl2,N2,He,vacuum[11]).The phenomenon was also found for short-pulse(ns)excimer-laser irradiation (λ=193nm,τ=23ns,air[26];λ=248nm,τ=25ns, SF6,N2,O2,Ar[27];λ=248nm,τ=12ns,vacuum[28];λ=308nm,τ=28ns,vacuum[29]).The process strongly depends on the number of pulses ap-plied to the same spot and the laserfluence.A further key parameter for the formation process and the shape of the microstructures seems to be the ambient environment.Ox-idizing or halogen-containing atmospheres such as air,O2 or SF6support the generation of high-aspect-ratio pillars, whereas the formation of sharp spikes can be reduced in vac-uum,N2or He[11].On the other hand,column formation is rather insensitive to the laser wavelength[9,11,24,25]and the pulse duration[30,31].Influences of the doping concen-tration have not been observed[11,27].For these reasons, a chemical control of the dimensions of microcolumns seems to be possible[31].2Experimental results and analysisExperiments were carried out with two different Ti:sap-phire laser systems,a commercial CPA system(SPECTRA PHYSICS,Spitfire)at the BAM Berlin and the Vienna sys-tem,comprised of an amplifier and hollowfiber compressor,which is capable of producing5-fs pulses with a maximum energy of500µJ[32].The pulse duration of the latter one was changed between5fs and400fs by inserting dispersive material(glass blocks)in the beam path.The experimen-tal conditions were kept similar.The center wavelengths of the linearly polarized laser pulses differed by only20nm (BAM:800nm,Vienna:780nm).The different repetition rates(BAM:10Hz,Vienna:1kHz)should have no influence on the experimental results because every physical process known to be important here is terminated after1ms.An im-portant measurement–actually the one that dominates the overall error–is the energy detection.Here we used a py-roelectric detector BESTEC PM200(BAM)and the OPHIR pulse energy detector NOV A(Vienna),respectively.Different pulse numbers with varying energy were fo-cused to a diameter on the order of several10µm(BAM: f=60mm plano-convex lens,Vienna:R=100mm spher-ical silver mirror)onto the polished(111)surface of n-doped silicon samples.On these samples,a native oxide layer of about2.7nm thickness has been found from ellip-sometric measurements.For higher appliedfluences(in the single-pulse case for5-fs pulses),the sample was placed in a slightly evacuated chamber(p≈10−4mbar)in order to pre-vent ionization or non-linear effects in air and resulting pulse distortions.Inspection of the irradiated surface regions was performed using an optical microscope(Reichert–Jung,Polyvar)in No-marski mode.A more detailed characterization of morpho-logical changes of the laser-modified areas was done by means of a scanning electron microscope(SEM)equipped with a cold-field electron emission cathode(Hitachi,S-4100, accelerating voltage10kV)and an atomic force microscope (AFM,Digital Instruments,Dimension3000SPM)operated in tapping mode.Anticipating the results of our investigations,we outline the principal physical processes occurring on the Si surface after a Gaussian laser pulse was incident in Fig.1.For com-parison,a damage spot on the silicon surface generated by a single laser pulse is shown in Fig.2exhibiting different cir-cular regions of modification,annealing,and ablation.The formation of ripples cannot be seen in this picture because it only occurs after irradiation with multiple pulses onto the same sample spot.In the following section,these thresholds will be further investigated and classified quantitatively.2.1Modification thresholdsSome of the early experiments on laser-induced modification of silicon surfaces distinguish regions of amorphization and crystallization[4].We observed the same phenomena in our experiments,but the zone of amorphization showed a fur-ther substructure which we believe is related to oxidation of the surface layers of silicon.The thresholds of oxidation and amorphization are so close together that unambiguous iden-tification is hardly possible.However,in order to take this fact into account,we call the physical process in this region modification rather than amorphization.The thresholdfluences for these phenomena can be de-termined similar to the ablation thresholdfluence,namely measuring the diameter of the modified areas versus the pulse fluence and extrapolating to zero[33].In Fig.3,the square of21/xFig.1.Physical processes during the modification of silicon with femtosec-ond laser pulses and their threshold fluencesFig.2.Nomarski optical micrograph of the silicon sample surface treated with a single laser pulse in air (λ=800nm,τ=130fs,Φ0=1.5J /cm 2).The outermost ring has a diameter of 45µmthe diameter (corresponding to a modified area)is depicted versus increasing peak fluence of the laser pulses.Extending the regression of this line to zero yields the threshold values to Φmod =0.26J /cm 2and Φann =0.55J /cm 2,respectively.Forthe applied pulse duration,this is identical to the single-pulse threshold measured by Pronko et al.[20].The ablation thresholds of multi-shot experiments in air for different pulse durations are shown in Fig.4.For pulse durations below 100fs,the threshold becomes constant,a be-havior that is well known for metals [34].For higher pulse numbers,one can find no more evidence for crystallization or oxidation/amorphization.A clean edge of ablation as in Fig.9a can be recognized.From the dimen-sions of these craters,an ablation threshold is determined which cannot be distinguished from other thresholds due to morphological changes in the irradiated surface region.The values in Fig.4are significantly lower than the single-pulse thresholds evaluated from Fig.3,because the thresholds of modification and ablation depend on the number of applied laser pulses.This incubation effect rests on a non-ablating modification of the sample material by the laser pulses in such a manner that the threshold for damage decreases.This effect has been extensively studied at the surface of single-crystal metals [35].A dependence in the form of a power law was found:Φmod (N )=Φmod (1)·N ξ−1.(1)Φmod (N )denotes the modification threshold fluence for N laser pulses,and ξis a material-dependent coefficient.In-cubation is related to an accumulation of energy (i.e.non-complete dissipation of the deposited energy)into plastic stress–strain of the metal.However,this formula has also suc-cessfully been employed in the case of indium phosphide (InP)[36],where it is unclear whether intermediate storage of laser energy is mechanical or,for example,chemical (as in several glasses by F-center formation [37]).In Fig.5,the dependence of N ·Φmod (N )on the number of pulses is plot-ted for our data.The fit according to (1)(solid line)yields a coefficient ξof 0.84.From Fig.5,one can conclude that there is significant in-cubation in silicon for pulses with a duration of ≈100fs.Laser fluence Φ0[ J/cm 2]1S q u a r e d d i a m e t e r D 2[µm 2]1000200030000.50.35Fig.3.Diameter (squared)of modification and re-crystallization of the sili-con surface versus the incident peak fluence of the laser pulse (λ=800nm,τ=130fs,N =1,in air).Squares belong to the areas of modification,whereas circles belong to the re-crystallization regions.Solid lines are lin-ear regressions within the semi-logarithmic plot.The deviation of the data from the regression for high fluences is attributed to a slightly non-Gaussian beam profile (caused by apertures)22T h r e s h o l d f l u e n c e [J /c m 2]Fig.4.Ablation threshold fluence of n-Si(111)for several pulse durations,100pulses per spot,in air.Values measured at λ=780nm,except the solid circle (λ=800nm)Number of pulses N110100N ∗Φm o d (N ) [ J /c m 2]110Fig.5.Threshold fluence of laser-induced damage of silicon versus num-ber of laser pulses with a duration of τ=130fs and λ=800nm in an air environment.The solid line represents a least-squares-fit with (1),where ξ=0.84Fig.6.AFM picture of damage in silicon generated with a single Ti:sapphire laser pulse (λ=780nm,τ=5fs,Φ0=7.7J /cm 2).Dark areas indicate more ablated material.The inset at the bottom of the picture is a line-scan along the dotted white line ,the depth scale is indicated in blackThe precise nature of this effect,whether energy is stored in the form of chemical modification or by mechanical stress (as in the case of metals),cannot be deduced from these results.Interestingly,single-shot measurements with 5-fs pulses yield a damage threshold of 0.20±0.05J /cm 2,which agrees with the threshold achieved with multiple pulses within the experimental error (compare Fig.4).Obviously –for these short pulses –there is no such intermediate storage of energy below the damage threshold as it was found,for example,in fused silica [38].2.2Single-pulse experimentsSurface images taken with an atomic force microscope (AFM)and a scanning electron microscope (SEM)reveal in-teresting morphological features of the damaged areas.TheFig.7a,b.SEM picture (0◦)of damage in silicon generated with Ti:sap-phire laser pulses in air (λ=780nm,τ=5fs,Φ0=2.5J /cm 2,N =5).Three different regions of modification (ablation including ripples,re-crystallization,and amorphization)can be recognized.a Full view,b detail23formation of circular substructures (holes)within the cavities can be observed (see Fig.6).These holes vanish or are ob-scured by other morphological features when the same spot is illuminated with subsequent pulses.With increasing laser fluence,the size of these holes increases.Phenomena such as these are frequently attributed to a locally enhanced car-rier density generated either by an inhomogeneous laser beam profile or by locally enhanced absorption (scratches,crystal defects,dust).An initialization of inhomogeneous surface structures due to “hot spots”in the beam profile can be ruled out because –due to the efficient spatial filtering by guiding in a hollow fiber –the Vienna system exhibits an extremely smooth beam profile [32].External surface impurities (dust,scratches due to pol-ishing)cannot be significant,as we will see in the follow-ing argument.We consider indirect two-photon absorption with a coefficient of only 1cm /GW [39]as the domin-ant carrier-generating mechanism.Calculating the penetra-tion depth induced by this mechanism,one finds that the number of absorbing atoms in the excited volume is far smaller than the number of photons supposedly absorbed in this volume.Thus,even the indirect two-photon absorp-tion is already strongly saturated.Virtually all available electrons are excited and it is hardly conceivable that the carrier density exhibits local spikes (e.g.by absorption of defects)so distinct that locally enhanced ablation could occur.Although an enhancement of surface absorption is no appropriate explanation for the observed substructures,en-hancement of absorption at depth in the semiconductor (where the light intensity already dropped one or moreordersFig.9a–f.SEM pictures (60◦)of damage in silicon generated with Ti:sapphire laser pulses in air.a Φ0=1.0J /cm 2,b 1.3J /cm 2,c 1.8J /cm 2(λ=780nm,τ=100fs,N =100).d Φ0=2.0J /cm 2,e 2.8J /cm 2,f 4.1J /cm 2(λ=800nm,τ=130fs,N =100)of magnitude)could account for an evolving inhomogeneous energy deposition.Consequently,after the strongly saturated and overheated surface layer was removed by phase explosion,normal boil-ing including inhomogeneous nucleation of bubbles occurs in the remaining liquid layer [21].This scenario is sup-ported by the fact that larger bubbles are formed in regions of higher fluences,i.e.regions of higher temperature (and therefore slower cooling)where bubbles have more time togrow.Fig.8.SEM picture (0◦)of damage in silicon generated with Ti:sapphire laser pulses in air (λ=800nm,τ=130fs,Φ0=0.42J /cm 2,N =5)242.3Ablation with multiple pulsesThe application of a moderate number(N≈5)of laser pulses leads to characteristic laser-induced periodic surface struc-tures(ripples).In single-pulse experiments,these highly ori-ented structures were not observed,indicating that a feed-back mechanism is involved during the formation of the sur-face patterns.Fig.7shows typical surface damage in silicon(λ=800nm,τ=5fs)at afluence of2.5J/cm2.Three dif-ferent modified zones are clearly visible(compare Fig.1): ablation and ripple-formation in the central region,anneal-ing in thefirst annular structure,and modification in the outer annular border.It is interesting to note,that all these surface modifications known from longer pulses also occur at this ul-trashort pulse duration of5fs.A magnified view(Fig.7b) reveals average lateral ripple periods between650nm and 750nm which is comparable to the laser wavelength.The rip-ples were always oriented perpendicular to the electric-field vector of the incident radiation.Thus,we attribute this phe-nomenon to the well-known mechanism of interference andsubsequent localfield enhancement[10].Small globules of re-deposited material were observed on the top of the surface corrugations.The same characteristic ripple morphology was detected in the central crater region at an≈25times longer pulse duration(λ=800nm,τ=130fs,Φ0=0.42J/cm2,N=5, see Fig.8).Additionally,some outspread periodic patterned(triangular)regions are seen in the direction of the electric field.A further increased number of laser pulses(N≈100) leads to another characteristic surface morphology:the columns or pillars,already introduced in Sect.1.A certain pulse number is required to nucleate the column growth pro-cess.The evolution of silicon microcones and mirocolumns in a series of laser-generated craters,obtained with a con-stant number of100Ti:sapphire laser pulses(τ=100fs at λ=780nm,andτ=130fs atλ=800nm)at varying peak fluences in air is shown in Fig.9.At a comparatively lowfluence of1.0J/cm2(which is ≈5−6times above the ablation threshold),a uniformly ablated crater with a rough,but featureless bottom can be seen as well as highly directed nearly wavelength-sized rip-ple structures in the border region(Fig.9a).With increas-ing laserfluence,small conical structures arise from the bottom of the craters to form the initial stages of micro-columns(Fig.9b,c).The lateral and vertical extent of the columns and the spacing between them strongly depends on the localfluence.In the center of the irradiated area, the columns are wider,taller and more sparse.In the bor-der region they are packed closer together.Up to afluence of≈2J/cm2,the columns are formed in the middle of the crater(Fig.9d),while at higherfluences(Φ0=2.8J/cm2) the morphology appears crown-like.At this stage of devel-opment,the columns can protrude above the original surface plane(Fig.9e),which provides conclusive evidence for the redeposition/re-crystallization origin of these columns.At further increased laserfluences ofΦ0≈4.1J/cm2,a volcano-like structure is observed within the ablated region(Fig.9f). It is probably formed by not completely ejected mate-rial,which is redeposited at the crater walls when the crater depth exceeds a certain value.The height of the columns grows with an increasing number of laser pulses.If a critical size is reached,a destruction of the Si pillars occurs[24].Concerning the formation mechanism of the silicon columns,we suggest a similar explanation as Lowndes et al.[31].Initial surface corrugation inhomogeneously nucle-ates from local vaporization(bubble ejection from the melt layer)and/or ripple formation and subsequently re-deposited material.On the edges of these corrugations,the absorbed local laserfluence is reduced due to an altered angle of inci-dence of the laser radiation.Therefore,ablation takes place preferably at the minima and maxima of the surface topog-raphy.The silicon-rich vapor which is formed at the grooves cools during the material transport(expansion of the vapor plume)and can be re-deposited at the protruding features of the surface.During a large number of these transport cycles,a highly protruding column can be formed.Addi-tionally,the effect can be enhanced by multiple reflections of the incident laser radiation on the bodies of thecolumns, Fig.10a,b.Cross-sectional SEM picture of damage in silicon gener-ated with Ti:sapphire laser pulses in air(λ=800nm,τ=130fs,Φ0= 0.65J/cm2,N=500).a Full view,b detail25Fig.11.Scheme of the different morphological phenomena after irradiation of the silicon surface with linearly polarized femtosecond laser pulses of typically 100fs durationwhich “guides”the light into the grooves.Therefore,the re-gions between the columns again act as emitters of ablated material.A cross-section through a crater (depth ≈9µm)in silicon obtained after the application of 500subsequent laser pulses in air (λ=800nm,τ=130fs,Φ0=0.65J /cm 2)is shown in Fig.10a.A detail of the crater wall can be seen in Fig.10b.Besides an irregular surface morphology and remaining parts of small columns,only a thin thermally or chemically modi-fied layer (depth <500nm)is visible.Figure 11summarizes the different morphological fea-tures (bubbles,ripples,microcolumns)formed after irradi-ation of silicon surfaces with linearly polarized laser pulses for pulse durations of approximately 100fs.3ConclusionWe investigated laser-induced modification and ablation of silicon surfaces with laser pulse durations in the range be-tween 5fs and 400fs.The multi-pulse ablation threshold flu-ence is almost constant around 0.2J /cm 2.We found several physical processes resulting in clearly distinguishable mor-phological features.These are (from lower to higher fluences)oxidation,amorphization,re-crystallization,the formation of bubbles due to boiling below the surface,and finally ablation.Other features occur while treating the sample with multiple subsequent pulses,namely ripple formation,column growth,and crater formation due to material removal.Although these phenomena can limit the precision of micromachining,there are potential applications of controlled manufactured sili-con microcolumns and needles,for example,field-emission sources in the display technology [40].With respect to the feasibility of using femtosecond pulses for microstructuring of semiconductors one can state that –in contrast to transpar-ent materials –a reduction of the pulse duration below 500fs does not offer significant advantage,because of the nearly constant ablation threshold fluence and the similarity of the observed surface morphologies.Acknowledgements.We thank Birgid Strauss,Sigrid Benemann,and Marion Männ (all at BAM)for their technical assistance.M.L.acknowledges sup-port by the Austrian Science Foundation (FWF)under grant No.P-12762.We are grateful to Harald Bergner and Gabriele Pfeiffer from the Fach-hochschule Jena for help with the AFM.References1.R.Haigh,D.Hayden,P.Longo,T.Neary,A.Wagner:Proc.SPIE 3546,477(1998)2.M.H.Niemz:Laser–Tissue Interactions (Springer,Berlin,Heidelberg 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非等位基因概述非等位基因是指同一基因座上的不同等位基因。

等位基因是指在某个给定的基因座上，可以存在多种不同的变体。

每个个体继承了一对等位基因，一对等位基因可能会导致不同的表型表达。

非等位基因的存在使得遗传学研究更加复杂，因为不同的等位基因会对个体的表型产生不同的影响。

背景在生物学中，基因座是指染色体上一个特定的位置，该位置上的基因决定了某个特征的表达方式。

每个基因座上可以有多种不同的等位基因。

等位基因是指在某个特定基因座上的不同基因变体。

每个个体都会继承一对等位基因，通过这对等位基因的不同组合，决定了个体的表型。

然而，并非所有基因座上的等位基因都具有相同的表现型。

非等位基因的影响非等位基因的存在导致不同等位基因会对个体表型产生不同的影响。

有些非等位基因会表现出显性效应，也就是说，当个体继承了一个突变的等位基因时，即使同时继承了一个正常的等位基因，但显性效应会使得突变的等位基因的表型表达得到体现。

相反，有些非等位基因会表现出隐性效应，当个体继承了两个突变的等位基因时，才会表现出突变的表型。

除了显性和隐性效应之外，非等位基因还可能发生两种其他类型的表型效应。

一种是共显效应，当个体继承了两个不同的突变等位基因时，在表型表达上会表现出一种新的特征，这个特征并不是单个突变等位基因所能导致的。

另一种是部分显性效应，当个体继承了两个不同的突变等位基因时，表型表达将介于两个单独突变等位基因的表型之间。

重组和非等位基因重组是指两个不同的染色体交换部分基因序列的过程。

在重组的过程中，非等位基因可能会发生改变，导致新的等位基因组合形成。

这一过程使得非等位基因的表型效应更加复杂，因为新的等位基因可能将不同基因座的效应组合起来。

非等位基因的重要性非等位基因对生物的适应性和多样性起着重要作用。

通过对等位基因的各种组合的研究，人们可以更好地理解基因与表型之间的关系，并揭示遗传变异对物种适应环境的重要性。

总结非等位基因是指同一基因座上的不同等位基因。

大角度晶界的英语Abstract:Macroscopic grain boundaries (MGBs) are a critical feature in polycrystalline materials, significantly influencing mechanical properties, thermal conductivity, and electrical conductivity. This paper delves into the characteristics, formation mechanisms, and the impact of MGBs on the performance of materials, with a focus on their rolein various applications.1. IntroductionGrain boundaries are interfaces between two crystalline grains in a polycrystalline solid. When the misorientation between grains is significant, these boundaries can be considered macroscopic, exhibiting distinct properties that differ from those of the bulk material. The study of MGBs is essential for understanding material behavior and optimizing performance in engineering applications.2. Characteristics of Macroscopic Grain BoundariesMacroscopic grain boundaries are characterized by their misorientation angles, which are typically greater than 15 degrees. They can be classified into several types based on the crystallographic relationship between the grains they separate:- Twin boundaries: Where the misorientation is a mirror reflection across the boundary plane.- Coincidence site lattice (CSL) boundaries: Where a high density of lattice points from both grains coincide at the boundary.- General boundaries: With no specific crystallographic relationship, these are the most common type.3. Formation MechanismsMGBs can form during various material processing techniques:- Recrystallization: After severe deformation, grains can grow, leading to the formation of MGBs.- Grain growth: During annealing, larger grains can consume smaller ones, resulting in increased misorientations at the boundaries.- Phase transformations: Changes in crystal structure during phase transitions can create MGBs.4. Impact on Material PropertiesThe presence of MGBs has a profound effect on the properties of polycrystalline materials:- Strength: MGBs can impede dislocation motion, increasing the material's strength.- Ductility: They can act as sites for crack initiation, affecting ductility.- Conductivity: MGBs can scatter electrons and phonons, reducing thermal and electrical conductivity.5. ApplicationsUnderstanding MGBs is crucial for optimizing materials in various applications:- Metalworking: Controlling grain size and boundary characteristics can enhance the mechanical properties of metals.- Electronics: In semiconductor devices, MGBs can influence carrier mobility and device performance.- Ceramics: MGBs in ceramics can affect fracture toughness and thermal shock resistance.6. Experimental Techniques for Studying MGBsSeveral experimental methods are used to study MGBs:- Scanning electron microscopy (SEM): Can reveal the morphology of MGBs.- Transmission electron microscopy (TEM): Provides detailed information on the atomic structure of boundaries.- Electron backscatter diffraction (EBSD): Allows for the determination of grain orientation and the identification of MGBs.7. Computational ModelingComputational techniques, such as molecular dynamics and phase-field modeling, are used to simulate MGB formation and behavior:- Molecular Dynamics (MD): Offers insights into atomic-scale processes at MGBs.- Phase-Field Modeling: Can predict the evolution of grain structures and boundary characteristics during processing.8. ConclusionMacroscopic grain boundaries play a critical role in determining the properties of polycrystalline materials. Understanding their characteristics, formation, and impact is essential for the development of advanced materials with tailored properties for specific applications. Future research should focus on developing new techniques to control MGBs and on multiscale modeling to predict their effects on material behavior.References1. Hull, D., & Bacon, D. J. (2011). Introduction to Dislocations (5th ed.). Butterworth-Heinemann.2. Humphreys, F. J., & Hatherly, M. (2004). Recrystallization and Related Annealing Phenomena (2nd ed.). Elsevier.3. Gottstein, G. (2002). Physical Foundations ofMaterials Science. Springer.4. Randle, V. (2017). Grain Boundary CharacterDistribution and its Applications. CRC Press.This document provides a comprehensive overview of macroscopic grain boundaries, discussing theircharacteristics, formation, and impact on material properties, as well as the experimental and computational techniques used to study them. It concludes with the significance of MGBs in material applications and the importance of future researchin this area.。

Confocal Fluorescence Endomicroscopyof the Human AirwaysLuc Thiberville1,2,Mathieu Salau¨n1,2,Samy Lachkar1,Stephane Dominique1,Sophie Moreno-Swirc1,Christine Vever-Bizet3,4,and Genevieve Bourg-Heckly3,41Rouen University Hospital,Rouen,France;2Faculte´de Me´decine-Pharmacie,Rouen,France;LITIS EA4108(groupe Quant-IF),Rouen,France; 3Universite´Pierre et Marie Curie,Paris,France;and4UMR CNRS7033,BioMoCeTi,Paris,FranceConfocal endomicroscopes aim at providing to the clinician microscopic imaging of a living tissue.The currently available micro-endoscopic devices use the principle of confocalfluorescent micros-copy,in which the objective is replaced by an opticalfiber and a miniaturized scanhead at the distal end of the endoscope or by a retractable bundle of opticalfibers.Such systems have recently been applied to the explorations of several organs,including the gastrointestinal tract,and more recently to the proximal and distal airways in vivo.Respiratoryfluorescence microendoscopes use488nm or660nm excitation laser light and thinflexible miniprobes that are introduced into the working channel of the bronchoscope.The devices have a lateral resolution of3m m,afield of view of600m m,and produce real-time imaging at9frames per second.For in vivo imaging,the miniprobe is applied onto the bronchial wall surface or advanced into a distal bronchiole down to the acinus.In nonsmokers,the488-nm excitation device images the autofluorescence of the elastin that is contained in the basement membrane of the proximal airways and that participates to the axial backbone of the peripheral interstitial respiratory system.In smok-ers,a specific tobacco tar–inducedfluorescence allows in vivo mac-rophage and alveolar wall ing660nm excitation and topical methylene blue,the technique enables cellular imaging of both bronchial epithelial layer and peripheral lung nodules.This article reviews the capabilities and possible limitations of confocal microendoscopy for in vivo proximal and distal lung explorations. Keywords:bronchoscopy;diagnostic imaging;laser scanning;confo-cal microscopy;pulmonary alveoliOver the last decade,in vivo intravital microscopy has proven to be an important tool in physiology and pathophysiology re-search.Within thisfield,confocal microscopy offers unique capabilities,allowing in vivo optical sectioning of cells and tissue,with enhanced lateral and axial resolutions(1,2).The principle by which confocal microscopy images a thin slide of a sample relies on both the use of a narrow point source on the illumination path and of a small aperture or pinhole on the light detection path.According to this principle,a laser source(the point source)focuses on a single spot in the sample,and the light emitted from this focal point is imaged through the pinhole onto a detector.This results in the rejection of the light coming from depths adjacent to the focal plane region,and therefore of out-of-focus information from the material above and below a very thin plane of focus.The illumination and detection systems being conjugated on the same focal plane are termed ‘‘confocal.’’To obtain a two-dimensional image within the tissue,confocal microscopes use various systems that scan the sample in both lateral dimensions.Translating the confocal microscopy principles into the clinic for endomicroscopic explorations is currently the subject of significant scientific efforts(1,2),which recently ended in the availability of two commercial systems for both animal(3–5) and human in vivo explorations(6–8).CONFOCAL ENDOMICROSCOPES FORHUMAN EXPLORATIONConfocal endomicroscopes aim at providing to the clinician ‘‘optical biopsies,’’—that is,in vivo microscopic imaging—of a living tissue(9,10).Such systems have been successfully applied to the in vivo explorations of the human skin(11,12), cervix(13),and oral cavity(14,15),as well as to the endomicro-scopic exploration of the gastric and colonic mucosae,biliary tract(16–19),and more recently to the microscopic imaging of the proximal(7)and distal respiratory systems(8).Both commercially available confocal endomicroscopes use fluorescence imaging instead of reflectance imaging.The con-sequences of this choice will be discussed later in this article. These two systems can be distinguished by the technical approach used to conduct the light to the tissue.The distal scanning principle is used in the Optisan/Pentax endomicro-scopic system(20).In distal scanning,the light is conducted by a singlefiber back and forth from the distal tip of the system, and the scanning function is accomplished by a very small scanhead(4.5cm long33.5mm diameter)that is included in the distal end of the endoscope.Optiscan endomicroscopic images from the gastro intestinal tract appear very close to conventional histology,with a lateral resolution below1m m and optical slices of7m m for afield of view of4753475m m.The system offers the possibility to adjust the Z-depth range from0to250m m below the contact surface,so that three-dimensional structures in the specimen and successive layers of the mucosae can be imaged.Two potential drawbacks explain why this system is not yet available for the respiratory tract imaging.First,because of the added sizes of the distal scanhead, working channel,conventionnal light guide,and CCD camera,the diameter of the distal tip of the endoscope is currently larger than 12mm,a size barely compatible with the exploration of the human trachea and large main bronchi.Second,the miniaturization of the distal scanhead results in scanning rates of1frame/second, which needs a very efficient stabilization system of the distal tip of the endoscope onto the mucosae,to produce crisp microscopic images of the epithelium.The second commercially available confocal endomicro-scopy system(Cellvizio;Mauna Kea Technologies,Paris, France)uses the principle of proximal scanning,in which the illumination light scans the proximal part of a coherentfiber bundle or miniprobe.This bundle conducts the light back and forth from the imaged area at the tip of the miniprobe(21).The light delivery,scanning,spectralfiltering,and imaging systems(Received in original form February23,2009;accepted infinal form April28,2009) Funded by Program Hospitalier de Recherche Clinique2007,French ministry of Health;Canceropole Nord Ouest,Lille,France;Institut National du Cancer(Grant INCa-Lilly#0612-3D1317-31),Boulogne Billancourt,France;and Association pour le traitement a`Domicile de l’Insuffisance Respiratoire(ADIR),Rouen,France. Correspondence and requests for reprints should be addressed to Luc Thiberville, M.D.,Clinique Pneumologique,Hoˆpital Charles Nicolle,CHU de Rouen,1rue de Germont,76031Rouen Cedex,France.E-mail:Luc.Thiberville@univ-rouen.fr Proc Am Thorac Soc Vol6.pp444–449,2009DOI:10.1513/pats.200902-009AWInternet address:are located at the proximal part of the device,the distal part being a separate miniprobe,including both thefiber bundle and its connector to the Laser Scanning Unit(Figure1).Thisfiber bundle–based system,also described as‘‘fibered confocalfluorescent microscopy(FCFM),’’uses very thin and flexible miniprobes(300m m to2mm in diameter)that can contain up to30,000compacted microfibers.Similar to conven-tional confocal microscopes,FCFM uses two rapidly moving mirrors to scan the microfibers across the coherentfiber bundle in a raster fashion.Each microfiber,which is scanned one at a time by the laser light,acts as a light delivery and collection system and is,in essence,its own pinhole.The main advantages of this design are the very small size and theflexibility of the probe that can reach the more distal part of the lungs(8),as well as the fast image collection speed that helps to avoid artifacts due to tissue movement.Specific miniprobes for bronchial and alveolar imaging have a diameter of1mm that can enter the working channel of any adult bronchoscope.These miniprobes are devoid of distal optics and have a depth of focus of0to50m m and a lateral resolution of 3m m,for afield of view of6003600m m.The system produces endomicroscopic imaging in real time at9to12frames/second.Two different wavelengths are available.The Cellvizio 488nm is used for autofluorescence imaging of the respiratory tract as well as forfluorescein-induced imaging of the GI tract (7,8,22).Another device at660nm excitation can be used for epithelial cell imaging after topical application of exogenous fluorophores such as methylene blue(23–25).The main limitations of the system are related to its maximal imaging capabilities(30,000pixels),which restrict the lateral resolution to thefiber intercore distance(3m m),and the fact that the focus point of the system cannot be adjusted.As discussed later,interpretation of the data also relies on the fluorescence properties of the imaged tissue.HUMAN IN VIVO CONFOCAL MICROIMAGING OF THE NORMAL LUNG USING FCFMFCFM Imaging of the Proximal BronchiFCFM can easily be performed during afiberoptic bronchos-copy under local anesthesia(7,8).The technique of in vivo bronchial FCFM imaging is simple:the miniprobe is introduced into the2-mm working channel of the bronchoscope,and the probe tip applied onto the bronchial mucosae under sight control.The depth of focus being50m m below the contact surface,the system can image thefirst layers of the bronchial subepithelial connective tissue,presumably the lamina densa and the lamina reticularis(7).At488nm excitation,FCFM produces very precise micro-scopicfluorescent images of the bronchial basement membrane zone.As seen in Figure2,FCFM bronchial microimaging reveals a mat of largefibers mainly oriented along the longitu-dinal axis of the airways with crosslinked smallerfibers,as well as larger openings—100m m to200m m—corresponding to the bronchial glands origins.In vivo,the technique also makes it possible to record high-resolution images of small airways such as terminal bronchioles,which are recognizable by the presence of the helicoidal imprint of the smooth muscle on the inner part of the bronchiole(7).Nature of Bronchial and Alveolar FCFM Signals Fluorescence properties of the bronchial mucosae at488nm excitation are determined by the concentration of various cellular and extracellularfluorophores,including the intracellu-larflavins,that could originate from the epithelial cells,and specific crosslinks of collagens and elastin present in the subepithelial areas(1,26,27).Microspectrometer experiments, coupled with FCFM imaging,have clearly demonstrated that the mainfluorescence signal emitted after488nm excitation from both bronchial and alveolar human system originates from the elastin component of the tissue(7,8,28).Indead,flavin cellular autofluorescence appears too weak to allow imaging of the epithelial layer using488nm FCFM without exogenous fluorophore(29).Similarly,the collagenfluorescence does not significantly affect the FCFM image produced at488nm,the fluorescence yield of collagen at this wavelength being at least one order of magnitude smaller than that of elastin.As a result,488nm excitation FCFM specifically images the elastin respiratory network that is contained in the basement membrane of the proximal airways and participates to the axial backbone of the peripheral interstitial respiratory system.In the future,it is possible that a modified FCFM device usingseveralFigure1.Schematic diagram of afiberedconfocalfluorescence microscope(Cell-vizio;Mauna Kea Technologies,Paris,France).Modified by permission FromReference8.Thiberville,Salau¨n,Lachkar,et al.:Microconfocal Imaging during Bronchoscopy445wavelengths (30),or devices based on a multiphoton approach (2),may enable imaging of collagen,elastin,and flavins simultaneously.Distal Lung FCFM Imaging In Vivo :From the Distal Bronchioles Down to the Lung AciniEarlier work has demonstrated that elastin represents up to 50%of the peripheral lung connective tissue fibers (31).In the acinus,elastin is present in the axial backbone of the alveolar ducts and alveolar entrances,as well as in the external sheath of the extra-alveolar microvessels (32,33).After our previous observation in the proximal bronchi,we demonstrated that FCFM could also image the elastic framework of the distal lung (8,28).For distal lung microimaging,we use a 4.4-mm bronchoscope (MP60model;Olympus,Tokyo,Japan)that is inserted into the airways down to the smallest reachable bronchi.The FCFM miniprobe is then gently advanced into the distal bronchiole until the alveolar system is observed.During the procedure,several acinar areas can be successively explored by selecting different bronchioles,with real-time imaging.Once the alveoli are reached,the probe is slightly pulled back until the contact is lost,to ensure that the probe compression effect onto the alveolar system is minimal.Experience of FCFM alveolar imaging in more than 150healthy volunteers and patients has demonstrated that the technique is very well tolerated under topical anesthesia,in spontaneously breathing awake subjects.Due to the lack of pain receptors in the bronchial tree down to the subpleural level,the penetration of the miniprobe into the pulmonary lobule through the distal bronchiolar wall is painless (8).In addition,acinar imaging is not associated with significant bleeding in the proximal airways,in contrast to what is usually observed with transbronchial biopsy sampling.This can be explained by the low pressure in the alveolar capillaries that could be alteredduring the progression of the probe,as well as by the smooth design of the probe tip that can displace the extra-alveolar microvessels without damage.Finally,no pleural complication occurred in our experience when the system is used in awake,spontaneously breathing subjects,despite multiple lung segment imaging during the endoscopy.Acinar FCFM Imaging in Nonsmoking SubjectsAcinar imaging is easily obtained by pushing forward the probe a few centimeters after the endoscope is distally blocked into a subsegmental bronchi.Due to the respective sizes of the probes and of the distal bronchiolar structures,the presence of alveolar buds in the respiratory bronchioles is rarely identified during the bronchoalveoscopy procedure (Figure 2D).When progressing toward the more distal parts of the lungs,the entry into the alveolar space is therefore obtained by penetration through the bronchiolar wall.In nonsmokers,FCFM mainly produces images of the elastic fibers that encircle the alveolar openings,reinforce the virtual wall of the alveolar ducts,and surround the extra-alveolar microvessels (Figure 3).The in vivo aspects of the distal elastic framework may vary depending on the angle of penetration of the probe into the alveolar unit.A direct view down the axis of the duct or an oblique view could be commonly obtained,from which the ‘‘helical’’or ‘‘looped’’shape of the duct’s elastic structure could be easily recognized (Figure 3A).The reproducibility of the technique has been demonstrated in a series of healthy volunteers,where alveolar opening sizes measured from in vivo imaging were found normally distributed with mean values (around 275m m)close to what is observed using complex stereological methods in vitro (32,33),with thickness of the elastic fibers 1062.7m m.In the published series,smaller alveolar mouths were observed in the right upper lobe and paracardiac segments,presumably in relation totheFigure 2.Bronchial fibered confocal fluores-cent microscopy (FCFM)microimaging showing the elastin network of the base-ment membrane zone.(A )Opening of a bronchial gland (star ).(B )Elastic fibered network oriented along the longitudinal axis of the airways.(C )Distal bronchiole showing helicoidal imprints of smooth muscles (arrow ).(D )Transitional bronchiole showing an alveolar bud (arrowhead ).446PROCEEDINGS OF THE AMERICAN THORACIC SOCIETY VOL 62009lower ventilation of these segments in supine position (8).The technique also enables precise measurements of the extra alveolar lobular microvessels.A significant variation in the intensity of the autofluorescence signal could be observed between the subjects in relation with their age,the oldest individuals presenting the strongest signal.Acinar and Alveolar Imaging in Active Smokers Alveolar fluorescence imaging in active smokers dramatically differs from imaging in nonsmokers (Figures 3C and 3D).The alveolar areas of smokers are usually filled with highly fluores-cent cells corresponding to alveolar fluorescent macrophages,the presence of which appears very specific of active ing FCFM,morphologic markers of alveolar macrophage activation such as size,number,and mobility can be assessed that appear highly correlated with the amount of cigarettes smoked per day (8).The alveolar autofluorescence intensity appears signifi-cantly higher in active smokers compared with non-smokers,in relation to the intensity of the macrophage alveolitis.In situ alveolar microspectrometric measurements have been per-formed in active smokers,which evidenced that the main fluorophore contributing to the FCFM alveolar signal corre-sponds to the tobacco tar by itself,explaining this difference (8,28).Due to this specific contrast imaging in smokers,details of the alveolar and ductal surface could often be obtained.(Figure 3C).POTENTIAL CLINICAL APPLICATIONS OF BRONCHOALVEOLAR CONFOCAL IMAGINGProximal Bronchial ExplorationPreliminary studies have shown that per endoscopic FCFM could be used to study specific basement membrane remodel-ing alterations in benign or malignant/premalignant bronchial alterations (7).The FCFM microstructure of the bronchial walls underlying premalignant epithelia is significantly altered.In these precancerous conditions,the elastic fibered pattern oftheFigure 3.FCFM acinar imaging (488nm).(A and B )Nonsmoking subject.Elastin framework of an alveolar duct (A,arrow-head ),and of an extra-alveolar microvessel (B,arrow ).(C and D )FCFM imaging of smoker alveoli,showing alveolar walls (arrowhead )and alveolar macrophages (asterisk).Figure 4.FCFM (660nm ex-citation)after topical applica-tion of methylene blue (0.1%).(A )regular normal bronchial epithelium.(B )Pe-ripheral lung nodule (adeno-carcinoma).Thiberville,Salau ¨n,Lachkar,et al.:Microconfocal Imaging during Bronchoscopy 447lamina reticularis is absent or disorganized in almost every preinvasive lesion,supporting the hypothesis of an early degra-dation of the basement membrane components in preinvasive bronchial lesions.However,although this observation shed some light on the origin of the autofluorescence defect in precancerous bronchial lesions,the absence of epithelial cell visualization does not allow the technique to differentiate between the different grades of progression of the precancerous bronchial lesions such as metaplasia/dysplasia/carcinoma in situ.To be successfully applied to the exploration of precancer-ous/cancerous bronchial epithelial layer,the FCFM technique would need to be coupled with the use of an exogenous non-toxicfluorophore.Ex vivo studies have shown that the resolu-tion of the system is not a limitation for nuclear or cellular imaging(7,8).Exogenousfluorophores that could be activated at488nm(such as Acriflavin—a putative mutagen agent—or fluorescein solution,which does not stain the nuclei)(34)are not approved for intrabronchial use.Recently,Lane and coworkers have used a confocal microendoscope prototype at 488nm excitation and topical physiologic PH cresyl violet to provide cellular contrast in the bronchial epithelium both in vitro and in vivo(35).Methylene blue is a nontoxic agent that is commonly used during bronchoscopy for the diagnosis of bronchopleuralfistu-lae.MB is also used in gastroenterology for chromo-endoscopic detection of precancerous lesions(36–38),as well as for in vivo microscopic examination of the GI tract and bronchus using a novel endocytoscopic system(39,40).MB is a potentfluo-rophore that enters the nuclei and reversibly binds to the DNA, before being reabsorbed by the lymphatics.To give afluorescent signal,MB needs to be excited around660nm,and is therefore accessible to FCFM intravital imaging using this excitation wavelength.Preliminary study has demonstrated that Cellvizio660/ topical methylene blue makes it possible to reproducibly image the epithelial layer of the main bronchi as well as cellular patterns of peripheral solide lung nodules(24,25)(Figure4). Future studies using this technique could make it possible to differentiate normal,premalignant,and malignant alterations at the microscopic level.If this strategy is successful,FCFM may become a very powerful technique for in vivo diagnosis of early malignant and premalignant conditions of the bronchial tree, allowing the analysis of both the epithelial and subepithelial layers during the same procedure.Potential Applications for Distal Lung ImagingThe broncho-alveoscopy procedure described in this article is thefirst technique that makes it possible to obtain real-time, high-resolution,microstructural images of lobular and alveolar lung structures in living humans.Whereas the technique appears to have a great potential for in vivo distal lung explorations,both experimentally and clinically,some technical aspects and potential limitations for its clinical use should be discussed.First,because of the orthogonal branching and the small caliber of the terminal and respiratory bronchioles in humans compared with the probe size,alveolar imaging regularly bypasses the transitional respiratory bronchioles.This could represent a limitation for the study of the distal membranous and respiratory bronchioles,unless thinner probes,currently devoted to experimental animal imaging,become clinically available in the future(5).Second,the probe progression into the lobule supposes the disruption of alveolar walls,followed by a compression effect on the more resistant ductal structures.Minimal imaging distortion is observed when the probe is applied on the axis of the duct,resulting in the visualization of more details in the background planes than theoritically allowed by the50-m m depth of focus of the system(5).This compression effect may be difficult to control in vivo.In our hands,the more reproducible results were obtained in gently pulling back the probe once the alveolar imaging is obtained and analyzing the last images before the contact is lost.Therefore,future studies should include a stan-dardization of the endoscopic technique.Third,fluorescence microimaging by itself has some advan-tages and limitations.In contrast to reflectance imaging,fluo-rescence microimaging is devoid of interference with the reflected and refracted light at the air–liquid interface,because the backscattered excitation light isfiltered out by the detection system.This merely produces a small decrease in the signal intensity at the air–liquid interface,without any other optical artifact.This property allows the visualization of bubble-like structures as well as the presence offluorescent cells within this liquid phase.These observations indicate that a small quantity of liquid interposes at the probe tip that may contribute to the imaging signal.The nature of this liquid interface as well as its consequences on alveolar imaging should be further analyzed.On the other hand,FCFM exclusively records the signal coming fromfluorescent structures in response to appropriate excitation wavelengths.In this regards,in vivo FCFM in non-smokers only images the elastin of the peripheral and axial connective tissues.Data from the literature indicate that such information might be helpful for the exploration of several peripheral lung diseases(41,42).However,as the confocal fluorescence imaging of the distal lung is likely to appear very different from the corresponding histopathology,the semeiol-ogy of the FCFM elastin lung network imaging will have to be characterized in pathological conditions.In this regard,in vivo comparative studies on confocal alveolar imaging in patients with peripheral lung diseases and healthy volunteers appear mandatory,before the place of FCFM in the routine explora-tion of the peripheral lung could be appreciated.Until now,confocal microendoscopy of the airways has only used endogenous autofluorescence or simplefluorescent contrast agents to visualize the in vivo cellular and interstitial organization of the airways and distal lung parenchyma.In the future,using molecular contrast coumponds,it will be possible to extend the range of biomarkers that may be imaged.Pilot studies exploring this strategy have recently been published,that provided specific confocal imaging of molecular probes in precancerous conditions of the oral cavity ex vivo(43)and of colonic dysplasia in vivo(44). Coupled to FCFM,molecular imaging may help in the future to enable early diagnosis,rapid typing of molecular markers,and assessment of therapeutic outcome in many lung diseases.Conflict of Interest Statement:L.T.received grant support from the French National Institute of Cancer,Lilly Institute,and is listed as a coinventor in a patent concerning the use of a system for imaging confocalfluorescence in vivo in situ.M.S.does not have afinancial relationship with a commercial entity that has an interest in the subject of this manuscript.S.L.does not have afinancial relationship with a commercial entity that has an interest in the subject of this manuscript.S.D.received lecture fees from Actelion up to$1,000 for nonpromotional CME activity.S.M.-S.does not have afinancial relationship with a commercial entity that has an interest in the subject of this manuscript.C.V.-B.does not have afinancial relationship with a commercial entity that has an interest in the subject of this 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CHAPTER 2BASIC PLASMA EQUATIONS AND EQUILIBRIUM2.1INTRODUCTIONThe plasma medium is complicated in that the charged particles are both affected by external electric and magnetic fields and contribute to them.The resulting self-consistent system is nonlinear and very difficult to analyze.Furthermore,the inter-particle collisions,although also electromagnetic in character,occur on space and time scales that are usually much shorter than those of the applied fields or the fields due to the average motion of the particles.To make progress with such a complicated system,various simplifying approxi-mations are needed.The interparticle collisions are considered independently of the larger scale fields to determine an equilibrium distribution of the charged-particle velocities.The velocity distribution is averaged over velocities to obtain the macro-scopic motion.The macroscopic motion takes place in external applied fields and in the macroscopic fields generated by the average particle motion.These self-consistent fields are nonlinear,but may be linearized in some situations,particularly when dealing with waves in plasmas.The effect of spatial variation of the distri-bution function leads to pressure forces in the macroscopic equations.The collisions manifest themselves in particle generation and loss processes,as an average friction force between different particle species,and in energy exchanges among species.In this chapter,we consider the basic equations that govern the plasma medium,con-centrating attention on the macroscopic system.The complete derivation of these 23Principles of Plasma Discharges and Materials Processing ,by M.A.Lieberman and A.J.Lichtenberg.ISBN 0-471-72001-1Copyright #2005John Wiley &Sons,Inc.equations,from fundamental principles,is beyond the scope of the text.We shall make the equations plausible and,in the easier instances,supply some derivations in appendices.For the reader interested in more rigorous treatment,references to the literature will be given.In Section2.2,we introduce the macroscopicfield equations and the current and voltage.In Section2.3,we introduce the fundamental equation of plasma physics, for the evolution of the particle distribution function,in a form most applicable for weakly ionized plasmas.We then define the macroscopic quantities and indicate how the macroscopic equations are obtained by taking moments of the fundamental equation.References given in the text can be consulted for more details of the aver-aging procedure.Although the macroscopic equations depend on the equilibrium distribution,their form is independent of the equilibrium.To solve the equations for particular problems the equilibrium must be known.In Section2.4,we introduce the equilibrium distribution and obtain some consequences arising from it and from thefield equations.The form of the equilibrium distribution will be shown to be a consequence of the interparticle collisions,in Appendix B.2.2FIELD EQUATIONS,CURRENT,AND VOLTAGEMaxwell’s EquationsThe usual macroscopic form of Maxwell’s equations arerÂE¼Àm0@H@t(2:2:1)rÂH¼e0@E@tþJ(2:2:2)e0rÁE¼r(2:2:3) andmrÁH¼0(2:2:4) where E(r,t)and H(r,t)are the electric and magneticfield vectors and wherem 0¼4pÂ10À7H/m and e0%8:854Â10À12F/m are the permeability and per-mittivity of free space.The sources of thefields,the charge density r(r,t)and the current density J(r,t),are related by the charge continuity equation(Problem2.1):@rþrÁJ¼0(2:2:5) In general,J¼J condþJ polþJ mag24BASIC PLASMA EQUATIONS AND EQUILIBRIUMwhere the conduction current density J cond is due to the motion of the free charges, the polarization current density J pol is due to the motion of bound charges in a dielectric material,and the magnetization current density J mag is due to the magnetic moments in a magnetic material.In a plasma in vacuum,J pol and J mag are zero and J¼J cond.If(2.2.3)is integrated over a volume V,enclosed by a surface S,then we obtain its integral form,Gauss’law:e0þSEÁd A¼q(2:2:6)where q is the total charge inside the volume.Similarly,integrating(2.2.5),we obtaind q d t þþSJÁd A¼0which states that the rate of increase of charge inside V is supplied by the total currentflowing across S into V,that is,that charge is conserved.In(2.2.2),thefirst term on the RHS is the displacement current densityflowing in the vacuum,and the second term is the conduction current density due to the free charges.We can introduce the total current densityJ T¼e0@E@tþJ(2:2:7)and taking the divergence of(2.2.2),we see thatrÁJ T¼0(2:2:8)In one dimension,this reduces to d J T x=d x¼0,such that J T x¼J T x(t),independent of x.Hence,for example,the total currentflowing across a spatially nonuniform one-dimensional discharge is independent of x,as illustrated in Figure2.1.A generalization of this result is Kirchhoff’s current law,which states that the sum of the currents entering a node,where many current-carrying conductors meet,is zero.This is also shown in Figure2.1,where I rf¼I TþI1.If the time variation of the magneticfield is negligible,as is often the case in plasmas,then from Maxwell’s equations rÂE%0.Since the curl of a gradient is zero,this implies that the electricfield can be derived from the gradient of a scalar potential,E¼Àr F(2:2:9)2.2FIELD EQUATIONS,CURRENT,AND VOLTAGE25Integrating (2.2.9)around any closed loop C givesþC E Ád ‘¼ÀþC r F Ád ‘¼ÀþC d F ¼0(2:2:10)Hence,we obtain Kirchhoff’s voltage law ,which states that the sum of the voltages around any loop is zero.This is illustrated in Figure 2.1,for which we obtainV rf ¼V 1þV 2þV 3that is,the source voltage V rf is equal to the sum of the voltages V 1and V 3across the two sheaths and the voltage V 2across the bulk plasma.Note that currents and vol-tages can have positive or negative values;the directions for which their values are designated as positive must be specified,as shown in the figure.If (2.2.9)is substituted in (2.2.3),we obtainr 2F ¼Àre 0(2:2:11)Equation (2.2.11),Poisson’s equation ,is one of the fundamental equations that we shall use.As an example of its application,consider the potential in the center (x ¼0)of two grounded (F ¼0)plates separated by a distance l ¼10cm and con-taining a uniform ion density n i ¼1010cm 23,without the presence of neutralizing electrons.Integrating Poisson’s equationd 2F d x 2¼Àen i eFIGURE 2.1.Kirchhoff’s circuit laws:The total current J T flowing across a nonuniform one-dimensional discharge is independent of x ;the sum of the currents entering a node is zero (I rf ¼I T þI 1);the sum of voltages around a loop is zero (V rf ¼V 1þV 2þV 3).26BASIC PLASMA EQUATIONS AND EQUILIBRIUMusing the boundary conditions that F ¼0at x ¼+l =2and that d F =d x ¼0at x ¼0(by symmetry),we obtainF ¼12en i e 0l 22Àx 2"#The maximum potential in the center is 2.3Â105V,which is impossibly large for a real discharge.Hence,the ions must be mostly neutralized by electrons,leading to a quasi-neutral plasma.Figure 2.2shows a PIC simulation time history over 10210s of (a )the v x –x phase space,(b )the number N of sheets versus time,and (c )the potential F versus x for 100unneutralized ion sheets (with e /M for argon ions).We see the ion acceleration in (a ),the loss of ions in (b ),and the parabolic potential profile in (c );the maximum potential decreases as ions are lost from the system.We consider quasi-neutrality further in Section 2.4.Electric and magnetic fields exert forces on charged particles given by the Lorentz force law :F ¼q (E þv ÂB )(2:2:12)FIGURE 2.2.PIC simulation of ion loss in a plasma containing ions only:(a )v x –x ion phase space,showing the ion acceleration trajectories;(b )number N of ion sheets versus t ,with the steps indicating the loss of a single sheet;(c )the potential F versus x during the first 10210s of ion loss.2.2FIELD EQUATIONS,CURRENT,AND VOLTAGE 2728BASIC PLASMA EQUATIONS AND EQUILIBRIUMwhere v is the particle velocity and B¼m0H is the magnetic induction vector.The charged particles move under the action of the Lorentz force.The moving charges in turn contribute to both r and J in the plasma.If r and J are linearly related to E and B,then thefield equations are linear.As we shall see,this is not generally the case for a plasma.Nevertheless,linearization may be possible in some cases for which the plasma may be considered to have an effective dielectric constant;that is,the “free charges”play the same role as“bound charges”in a dielectric.We consider this further in Chapter4.2.3THE CONSERVATION EQUATIONSBoltzmann’s EquationFor a given species,we introduce a distribution function f(r,v,t)in the six-dimensional phase space(r,v)of particle positions and velocities,with the interpret-ation thatf(r,v,t)d3r d3v¼number of particles inside a six-dimensional phasespace volume d3r d3v at(r,v)at time tThe six coordinates(r,v)are considered to be independent variables.We illus-trate the definition of f and its phase space in one dimension in Figure2.3.As particles drift in phase space or move under the action of macroscopic forces, theyflow into or out of thefixed volume d x d v x.Hence the distribution functionaf should obey a continuity equation which can be derived as follows.InFIGURE2.3.One-dimensional v x–x phase space,illustrating the derivation of the Boltzmann equation and the change in f due to collisions.time d t,f(x,v x,t)d x a x(x,v x,t)d t particlesflow into d x d v x across face1f(x,v xþd v x,t)d x a x(x,v xþd v x,t)d t particlesflow out of d x d v x across face2 f(x,v x,t)d v x v x d t particlesflow into d x d v x across face3f(xþd x,v x,t)d v x v x d t particlesflow out of d x d v x across face4where a x v d v x=d t and v x;d x=d t are theflow velocities in the v x and x directions, respectively.Hencef(x,v x,tþd t)d x d v xÀf(x,v x,t)d x d v x¼½f(x,v x,t)a x(x,v x,t)Àf(x,v xþd v x,t)a x(x,v xþd v x,t) d x d tþ½f(x,v x,t)v xÀf(xþd x,v x,t)v x d v x d tDividing by d x d v x d t,we obtain@f @t ¼À@@x(f v x)À@@v x(fa x)(2:3:1)Noting that v x is independent of x and assuming that the acceleration a x¼F x=m of the particles does not depend on v x,then(2.3.1)can be rewritten as@f @t þv x@f@xþa x@f@v x¼0The three-dimensional generalization,@f@tþvÁr r fþaÁr v f¼0(2:3:2)with r r¼(^x@=@xþ^y@=@yþ^z@=@z)and r v¼(^x@=@v xþ^y@=@v yþ^z@=@v z)is called the collisionless Boltzmann equation or Vlasov equation.In addition toflows into or out of the volume across the faces,particles can “suddenly”appear in or disappear from the volume due to very short time scale interparticle collisions,which are assumed to occur on a timescale shorter than the evolution time of f in(2.3.2).Such collisions can practically instantaneously change the velocity(but not the position)of a particle.Examples of particles sud-denly appearing or disappearing are shown in Figure2.3.We account for this effect,which changes f,by adding a“collision term”to the right-hand side of (2.3.2),thus obtaining the Boltzmann equation:@f @t þvÁr r fþFmÁr v f¼@f@tc(2:3:3)2.3THE CONSERVATION EQUATIONS29The collision term in integral form will be derived in Appendix B.The preceding heuristic derivation of the Boltzmann equation can be made rigorous from various points of view,and the interested reader is referred to texts on plasma theory, such as Holt and Haskel(1965).A kinetic theory of discharges,accounting for non-Maxwellian particle distributions,must be based on solutions of the Boltzmann equation.We give an introduction to this analysis in Chapter18. Macroscopic QuantitiesThe complexity of the dynamical equations is greatly reduced by averaging over the velocity coordinates of the distribution function to obtain equations depending on the spatial coordinates and the time only.The averaged quantities,such as species density,mean velocity,and energy density are called macroscopic quantities,and the equations describing them are the macroscopic conservation equations.To obtain these averaged quantities we take velocity moments of the distribution func-tion,and the equations are obtained from the moments of the Boltzmann equation.The average quantities that we are concerned with are the particle density,n(r,t)¼ðf d3v(2:3:4)the particlefluxG(r,t)¼n u¼ðv f d3v(2:3:5)where u(r,t)is the mean velocity,and the particle kinetic energy per unit volumew¼32pþ12mu2n¼12mðv2f d3v(2:3:6)where p(r,t)is the isotropic pressure,which we define below.In this form,w is sumof the internal energy density32p and theflow energy density12mu2n.Particle ConservationThe lowest moment of the Boltzmann equation is obtained by integrating all terms of(2.3.3)over velocity space.The integration yields the macroscopic continuity equation:@n@tþrÁ(n u)¼GÀL(2:3:7)The collision term in(2.3.3),which yields the right-hand side of(2.3.7),is equal to zero when integrated over velocities,except for collisions that create or destroy 30BASIC PLASMA EQUATIONS AND EQUILIBRIUMparticles,designated as G and L ,respectively (e.g.,ionization,recombination).In fact,(2.3.7)is transparent since it physically describes the conservation of particles.If (2.3.7)is integrated over a volume V bounded by a closed surface S ,then (2.3.7)states that the net number of particles generated per second within V ,either flows across the surface S or increases the number of particles within V .For common low-pressure discharges in the steady state,G is usually due to ioniz-ation by electron–neutral collisions:G ¼n iz n ewhere n iz is the ionization frequency.The volume loss rate L ,usually due to recom-bination,is often negligible.Hencer Á(n u )¼n iz n e (2:3:8)in a typical discharge.However,note that the continuity equation is clearly not sufficient to give the evolution of the density n ,since it involves another quantity,the mean particle velocity u .Momentum ConservationTo obtain an equation for u ,a first moment is formed by multiplying the Boltzmann equation by v and integrating over velocity.The details are complicated and involve evaluation of tensor elements.The calculation can be found in most plasma theory texts,for example,Krall and Trivelpiece (1973).The result is mn @u @t þu Ár ðÞu !¼qn E þu ÂB ðÞÀr ÁP þf c (2:3:9)The left-hand side is the species mass density times the convective derivative of the mean velocity,representing the mass density times the acceleration.The convective derivative has two terms:the first term @u =@t represents an acceleration due to an explicitly time-varying u ;the second “inertial”term (u Ár )u represents an acceleration even for a steady fluid flow (@=@t ;0)having a spatially varying u .For example,if u ¼^xu x (x )increases along x ,then the fluid is accelerating along x (Problem 2.4).This second term is nonlinear in u and can often be neglected in discharge analysis.The mass times acceleration is acted upon,on the right-hand side,by the body forces,with the first term being the electric and magnetic force densities.The second term is the force density due to the divergence of the pressure tensor,which arises due to the integration over velocitiesP ij ¼mn k v i Àu ðÞv j Àu ÀÁl v (2:3:10)2.3THE CONSERVATION EQUATIONS 31where the subscripts i,j give the component directions and kÁl v denotes the velocity average of the bracketed quantity over f.ÃFor weakly ionized plasmas it is almost never used in this form,but rather an isotropic version is employed:P¼p000p000p@1A(2:3:11)such thatrÁP¼r p(2:3:12) a pressure gradient,withp¼13mn k(vÀu)2l v(2:3:13)being the scalar pressure.Physically,the pressure gradient force density arises as illustrated in Figure2.4,which shows a small volume acted upon by a pressure that is an increasing function of x.The net force on this volume is p(x)d AÀp(xþd x)d A and the volume is d A d x.Hence the force per unit volume isÀ@p=@x.The third term on the right in(2.3.9)represents the time rate of momentum trans-fer per unit volume due to collisions with other species.For electrons or positive ions the most important transfer is often due to collisions with neutrals.The transfer is usually approximated by a Krook collision operatorf j c¼ÀXbmn n m b(uÀu b):Àm(uÀu G)Gþm(uÀu L)L(2:3:14)where the summation is over all other species,u b is the mean velocity of species b, n m b is the momentum transfer frequency for collisions with species b,and u G and u L are the mean velocities of newly created and lost particles.Generally j u G j(j u j for pair creation by ionization,and u L%u for recombination or charge transfer lossprocesses.We discuss the Krook form of the collision operator further in Chapter 18.The last two terms in(2.3.14)are generally small and give the momentum trans-fer due to the creation or destruction of particles.For example,if ions are created at rest,then they exert a drag force on the moving ionfluid because they act to lower the averagefluid velocity.A common form of the average force(momentum conservation)equation is obtained from(2.3.9)neglecting the magnetic forces and taking u b¼0in theÃWe assume f is normalized so that k f lv ¼1.32BASIC PLASMA EQUATIONS AND EQUILIBRIUMKrook collision term for collisions with one neutral species.The result is mn @u @t þu Ár u !¼qn E Àr p Àmn n m u (2:3:15)where only the acceleration (@u =@t ),inertial (u Ár u ),electric field,pressure gradi-ent,and collision terms appear.For slow time variation,the acceleration term can be neglected.For high pressures,the inertial term is small compared to the collision term and can also be dropped.Equations (2.3.7)and (2.3.9)together still do not form a closed set,since the pressure tensor P (or scalar pressure p )is not determined.The usual procedure to close the equations is to use a thermodynamic equation of state to relate p to n .The isothermal relation for an equilibrium Maxwellian distribution isp ¼nkT(2:3:16)so thatr p ¼kT r n (2:3:17)where T is the temperature in kelvin and k is Boltzmann’s constant (k ¼1.381Â10223J /K).This holds for slow time variations,where temperatures are allowed to equilibrate.In this case,the fluid can exchange energy with its sur-roundings,and we also require an energy conservation equation (see below)to deter-mine p and T .For a room temperature (297K)neutral gas having density n g and pressure p ,(2.3.16)yieldsn g (cm À3)%3:250Â1016p (Torr)(2:3:18)p FIGURE 2.4.The force density due to the pressure gradient.2.3THE CONSERVATION EQUATIONS 33Alternatively,the adiabatic equation of state isp¼Cn g(2:3:19) such thatr p p ¼gr nn(2:3:20)where g is the ratio of specific heat at constant pressure to that at constant volume.The specific heats are defined in Section7.2;g¼5/3for a perfect gas; for one-dimensional adiabatic motion,g¼3.The adiabatic relation holds for fast time variations,such as in waves,when thefluid does not exchange energy with its surroundings;hence an energy conservation equation is not required. For almost all applications to discharge analysis,we use the isothermal equation of state.Energy ConservationThe energy conservation equation is obtained by multiplying the Boltzmannequation by12m v2and integrating over velocity.The integration and some othermanipulation yield@ @t32pþrÁ32p uðÞþp rÁuþrÁq¼@@t32pc(2:3:21)Here32p is the thermal energy density(J/m3),32p u is the macroscopic thermal energyflux(W/m2),representing theflow of the thermal energy density at thefluid velocityu,p rÁu(W/m3)gives the heating or cooling of thefluid due to compression orexpansion of its volume(Problem2.5),q is the heatflow vector(W/m2),whichgives the microscopic thermal energyflux,and the collisional term includes all col-lisional processes that change the thermal energy density.These include ionization,excitation,elastic scattering,and frictional(ohmic)heating.The equation is usuallyclosed by setting q¼0or by letting q¼Àk T r T,where k T is the thermal conduc-tivity.For most steady-state discharges the macroscopic thermal energyflux isbalanced against the collisional processes,giving the simpler equationrÁ32p u¼@32pc(2:3:22)Equation(2.3.22),together with the continuity equation(2.3.8),will often prove suf-ficient for our analysis.34BASIC PLASMA EQUATIONS AND EQUILIBRIUMSummarySummarizing our results for the macroscopic equations describing the electron and ionfluids,we have in their most usually used forms the continuity equationrÁ(n u)¼n iz n e(2:3:8) the force equation,mn @u@tþuÁr u!¼qn EÀr pÀmn n m u(2:3:15)the isothermal equation of statep¼nkT(2:3:16) and the energy-conservation equationrÁ32p u¼@@t32pc(2:3:22)These equations hold for each charged species,with the total charges and currents summed in Maxwell’s equations.For example,with electrons and one positive ion species with charge Ze,we haver¼e Zn iÀn eðÞ(2:3:23)J¼e Zn i u iÀn e u eðÞ(2:3:24)These equations are still very difficult to solve without simplifications.They consist of18unknown quantities n i,n e,p i,p e,T i,T e,u i,u e,E,and B,with the vectors each counting for three.Various simplifications used to make the solutions to the equations tractable will be employed as the individual problems allow.2.4EQUILIBRIUM PROPERTIESElectrons are generally in near-thermal equilibrium at temperature T e in discharges, whereas positive ions are almost never in thermal equilibrium.Neutral gas mol-ecules may or may not be in thermal equilibrium,depending on the generation and loss processes.For a single species in thermal equilibrium with itself(e.g.,elec-trons),in the absence of time variation,spatial gradients,and accelerations,the2.4EQUILIBRIUM PROPERTIES35Boltzmann equation(2.3.3)reduces to@f @tc¼0(2:4:1)where the subscript c here represents the collisions of a particle species with itself. We show in Appendix B that the solution of(2.4.1)has a Gaussian speed distribution of the formf(v)¼C eÀj2m v2(2:4:2) The two constants C and j can be obtained by using the thermodynamic relationw¼12mn k v2l v¼32nkT(2:4:3)that is,that the average energy of a particle is12kT per translational degree offreedom,and by using a suitable normalization of the distribution.Normalizing f(v)to n,we obtainCð2p0d fðpsin u d uð1expÀj2m v2ÀÁv2d v¼n(2:4:4)and using(2.4.3),we obtain1 2mCð2pd fðpsin u d uð1expÀj2m v2ÀÁv4d v¼32nkT(2:4:5)where we have written the integrals over velocity space in spherical coordinates.The angle integrals yield the factor4p.The v integrals are evaluated using the relationÃð10eÀu2u2i d u¼(2iÀ1)!!2ffiffiffiffipp,where i is an integer!1:(2:4:6)Solving for C and j we havef(v)¼nm2p kT3=2expÀm v22kT(2:4:7)which is the Maxwellian distribution.Ã!!denotes the double factorial function;for example,7!!¼7Â5Â3Â1. 36BASIC PLASMA EQUATIONS AND EQUILIBRIUMSimilarly,other averages can be performed.The average speed vis given by v ¼m =2p kT ðÞ3=2ð10v exp Àv 22v 2th !4p v 2d v (2:4:8)where v th ¼(kT =m )1=2is the thermal velocity.We obtainv ¼8kT p m 1=2(2:4:9)The directed flux G z in (say)the þz direction is given by n k v z l v ,where the average is taken over v z .0only.Writing v z ¼v cos u we have in spherical coordinatesG z ¼n m 2p kT 3=2ð2p 0d f ðp =20sin u d u ð10v cos u exp Àv 22v 2th v 2d v Evaluating the integrals,we findG z ¼14n v (2:4:10)G z is the number of particles per square meter per second crossing the z ¼0surfacein the positive direction.Similarly,the average energy flux S z ¼n k 1m v 2v z l v in theþz direction can be found:S z ¼2kT G z .We see that the average kinetic energy W per particle crossing z ¼0in the positive direction isW ¼2kT (2:4:11)It is sometimes convenient to define the distribution in terms of other variables.For example,we can define a distribution of energies W ¼12m v 2by4p g W ðÞd W ¼4p f v ðÞv 2d vEvaluating d v =d W ,we see that g and f are related byg W ðÞ¼v (W )f ½v (W ) m (2:4:12)where v (W )¼(2W =m )1=2.Boltzmann’s RelationA very important relation can be obtained for the density of electrons in thermal equilibrium at varying positions in a plasma under the action of a spatially varying 2.4EQUILIBRIUM PROPERTIES 3738BASIC PLASMA EQUATIONS AND EQUILIBRIUMpotential.In the absence of electron drifts(u e;0),the inertial,magnetic,and fric-tional forces are zero,and the electron force balance is,from(2.3.15)with@=@t;0,en e Eþr p e¼0(2:4:13) Setting E¼Àr F and assuming p e¼n e kT e,(2.4.13)becomesÀen e r FþkT e r n e¼0or,rearranging,r(e FÀkT e ln n e)¼0(2:4:14) Integrating,we havee FÀkT e ln n e¼constorn e(r)¼n0e e F(r)=kT e(2:4:15)which is Boltzmann’s relation for electrons.We see that electrons are“attracted”to regions of positive potential.We shall generally write Boltzmann’s relation in more convenient unitsn e¼n0e F=T e(2:4:16)where T e is now expressed in volts,as is F.For positive ions in thermal equilibrium at temperature T i,a similar analysis shows thatn i¼n0eÀF=T i(2:4:17) Hence positive ions in thermal equilibrium are“repelled”from regions of positive potential.However,positive ions are almost never in thermal equilibrium in low-pressure discharges because the ion drift velocity u i is large,leading to inertial or frictional forces in(2.3.15)that are comparable to the electricfield or pressure gra-dient forces.Debye LengthThe characteristic length scale in a plasma is the electron Debye length l De.As we will show,the Debye length is the distance scale over which significant charge densities can spontaneously exist.For example,low-voltage(undriven)sheaths are typically a few Debye lengths wide.To determine the Debye length,let us intro-duce a sheet of negative charge having surface charge density r S,0C/m2into an。

tpo40三篇托福阅读TOEFL原文译文题目答案译文背景知识阅读-1 (2)原文 (2)译文 (5)题目 (8)答案 (17)背景知识 (17)阅读-2 (20)原文 (20)译文 (23)题目 (25)答案 (35)背景知识 (35)阅读-3 (38)原文 (38)译文 (41)题目 (44)答案 (53)背景知识 (54)阅读-1原文Ancient Athens①One of the most important changes in Greece during the period from 800 B.C. to 500 B.C. was the rise of the polis, or city-state, and each polis developed a system of government that was appropriate to its circumstances. The problems that were faced and solved in Athens were the sharing of political power between the established aristocracy and the emerging other classes, and the adjustment of aristocratic ways of life to the ways of life of the new polis. It was the harmonious blending of all of these elements that was to produce the classical culture of Athens.②Entering the polis age, Athens had the traditional institutions of other Greek protodemocratic states: an assembly of adult males, an aristocratic council, and annually elected officials. Within this traditional framework the Athenians, between 600 B.C. and 450 B.C., evolved what Greeks regarded as a fully fledged democratic constitution, though the right to vote was given to fewer groups of people than is seen in modern times.③The first steps toward change were taken by Solon in 594 B.C., when he broke the aristocracy's stranglehold on elected offices by establishing wealth rather than birth as the basis of office holding, abolishing the economic obligations of ordinary Athenians to the aristocracy, and allowing the assembly (of which all citizens were equal members) to overrule the decisions of local courts in certain cases. The strength of the Athenian aristocracy was further weakened during the rest of the century by the rise of a type of government known as a tyranny, which is a form of interim rule by a popular strongman (not rule by a ruthless dictator as the modern use of the term suggests to us). The Peisistratids, as the succession of tyrants were called (after the founder of the dynasty, Peisistratos), strengthened Athenian central administration at the expense of the aristocracy by appointing judges throughout the region, producing Athens’ first national coinage, and adding and embellishing festivals that tended to focus attention on Athens rather than on local villages of the surrounding region. By the end of the century, the time was ripe for more change: the tyrants were driven out, and in 508 B.C. a new reformer, Cleisthenes, gave final form to the developments reducing aristocratic control already under way.④Cleisthenes' principal contribution to the creation of democracy at Athens was to complete the long process of weakening family and clanstructures, especially among the aristocrats, and to set in their place locality-based corporations called demes, which became the point of entry for all civic and most religious life in Athens. Out of the demes were created 10 artificial tribes of roughly equal population. From the demes, by either election or selection, came 500 members of a new council, 6,000 jurors for the courts, 10 generals, and hundreds of commissioners. The assembly was sovereign in all matters but in practice delegated its power to subordinate bodies such as the council, which prepared the agenda for the meetings of the assembly, and courts, which took care of most judicial matters. Various committees acted as an executive branch, implementing policies of the assembly and supervising, for instance, the food and water supplies and public buildings. This wide-scale participation by the citizenry in the government distinguished the democratic form of the Athenian polis from other less liberal forms.⑤The effect of Cleisthenes’ reforms was to establish the superiority of the Athenian community as a whole over local institutions without destroying them. National politics rather than local or deme politics became the focal point. At the same time, entry into national politics began at the deme level and gave local loyalty a new focus: Athens itself. Over the next two centuries the implications of Cleisthenes’ reforms were fully exploited.⑥During the fifth century B.C. the council of 500 was extremely influential in shaping policy. In the next century, however, it was the mature assembly that took on decision-making responsibility. By any measure other than that of the aristocrats, who had been upstaged by the supposedly inferior "people", the Athenian democracy was a stunning success. Never before, or since, have so many people been involved in the serious business of self-governance. It was precisely this opportunity to participate in public life that provided a stimulus for the brilliant unfolding of classical Greek culture.译文古雅典①在公元前800年到公元前500年期间，希腊最重要的变化之一是城邦的崛起，并且每个城邦都发展了适合其情况的政府体系。

氡子体平衡当量浓度英文回答：Radon progeny equilibrium equivalent concentration (EEC) is a measure of the potential alpha energy exposure fromthe inhalation of radon and its progeny. It is calculatedby multiplying the radon concentration in air by a factor that accounts for the equilibrium between radon and its progeny. The EEC is expressed in units of working level months (WLM).The EEC is used to estimate the potential lung cancer risk from exposure to radon. The risk of lung cancer increases with increasing EEC. The Environmental Protection Agency (EPA) has set a recommended maximum indoor radonlevel of 4 pCi/L. This level corresponds to an EEC of 0.02 WLM.There are a number of factors that can affect the EEC, including the ventilation rate of the building, thepresence of radon sources, and the type of building materials used. Homes with low ventilation rates and high radon levels are more likely to have elevated EECs.The EEC can be reduced by increasing the ventilation rate of the building, sealing radon entry points, and using radon-resistant building materials.中文回答：氡子体平衡当量浓度（EEC）是衡量吸入氡及其子体所产生的潜在α能量暴露量的指标。

a rXiv:as tr o-ph/48383v21J ul28The Fueling and Evolution of AGN:Internal and External Triggers Shardha Jogee 1Space Telescope Science Institute,3700San Martin Drive,Baltimore MD 21218,U.S.A jogee@ 1Introduction The quest for a coherent picture of nuclear activity has witnessed giant leaps in the last decades.Four decades ago,the idea was put forward that accre-tion of matter onto a massive compact object or a supermassive black hole (SMBH)of mass >106M ⊙could power very luminous active galactic nu-clei (AGN),in particular,quasi-stellar objects (QSOs)(Lynden-Bell 1969;Soltan 1982;Rees 1984).In the last decade,dynamical evidence increasingly suggests that SMBH pervade the centers of most massive galaxies (§2and references therein).The challenge has now shifted towards probing the fu-eling and evolution of AGN over a wide range of cosmic lookback times,and elucidating how they relate to their host galaxies in both the local and cosmological context.In this review,I will focus on the fueling and evolution of AGN under the influence of internal and external triggers.In the nature versus nur-ture paradigm,I use the term internal triggers to refer to intrinsic prop-erties of host galaxies (e.g.,morphological or Hubble type,color,and non-axisymmetric features such as large-scale bars and nuclear bars)while ex-ternal triggers refer to factors such as environment and interactions.The distinction is an over-simplification as many of the so called intrinsic prop-erties of galaxies can be induced or dissolved under the influence of external triggers.Connections will be explored between the nuclear and larger-scale properties of AGN,both locally and at intermediate redshifts.One of the driving objectives is to understand why not all relatively massive galaxies show signs of AGN activity (via high-excitation optical lines or X-ray emis-sion)despite mounting dynamical evidence that they harbor SMBHs.Themost daunting challenge in fueling AGN is arguably the angular momentum problem (§3.2).Even matter located at a radius of a few hundred pc must lose more than 99.99%of its specific angular momentum before it is fit for consumption by a BH.The sequence of this review is as follows.§2briefly addresses BH de-mographics and the BH-bulge-halo correlations.§3sets the stage for the rest of this paper by providing an overview of central issues in the fueling of AGN and circumnuclear starbursts.In particular,I review mass accretion rates,angular momentum requirements,the effectiveness of different fueling2Shardha Jogeemechanisms,and the growth and mass density of BHs at different epochs. These central issues in§3are attacked in more detail in§4–9which de-scribe different fueling mechanisms including mergers and interactions(§5), large-scale bars(§6),nuclear bars(§7),nuclear spirals(§8),and processes relevant on hundred pc to sub-pc scales(§9).I conclude with a summary and future perspectives in§plementary reviews on mass transfer and central activity in galaxies include those by Shlosman(2003),Combes (2003),Knapen(2004),and Martini(2004).2BH Demographics and BH-Bulge-Halo Correlations 2.1Measurement of BH MassesThe term SMBHs refers to BHs having masses M bh>106M⊙,in contrast to intermediate mass BHs(IMBHs)with M bh∼102–106M⊙,and stellar mass BHs.Properties of SMBHs are generally studied through accretion signatures of BHs or their gravitational influence.The strongest dynamical evidence for SMBHs are in our Galaxy and in NGC4258.In these systems,the large central densities inferred within a small resolved radius can be accounted for by a SMBH,but not by other possibilities such as collections of compact objects,star clusters,or exotic particles.In our Galaxy,proper motion mea-surements set stringent constraints on the central potential(Sch¨o del et al. 2003;Ghez et al.2003;Genzel et al.2000),yielding M bh∼3–4×106M⊙. In NGC5248,VLBA maser observations reveal Keplerian motions implying M bh∼3.9×107M⊙(Miyoshi et al.95).In the last decade,high resolution gas and stellar dynamical measure-ments from ground-based(e.g.,Kormendy&Richstone1995)and HST ob-servations(e.g.,Harms et al.1994;Ferrarese et al.1996;van de Marel&van den Bosch1998;Ferrarese&Ford99;Gebhardt et al.2000)have provided compelling evidence that several tens of galaxies host massive central dark objects(CDOs)which are likely to be SMBHs.The more reliable dynamical measurements tend to be from observations which resolve the radius of influ-ence(R g−bh)within which the gravitational force of the BH exceeds that of nearby stars with velocity dispersionσ,namely,R g−bh=GM bh108M⊙σc2=5×10−4pc M bhFueling AGN and Starbursts3 probe BH masses in the range107–109M⊙.Conversely,measuring BH masses in late-type spirals and dwarf galaxies poses many challenges,and there are nofirm measurements of BH masses below106M⊙.However,theoretical models and a mounting body of observational evidence put the existence of IMBHs on a relativelyfirm footing(see review by van der Marel2003). Thefirst challenge in measuring the masses of IMBHs is that the gravita-tional radii of such BHs are typically too small to be easily resolved even with HST.A second complication is that late-type spirals and dwarf galax-ies which might harbor such BHs also tend to host a bright106–107M⊙stellar cluster(Boker et al.1999)whose dynamical effect can mask that of the BH.A104–105M⊙BH(Filipenko&Ho2003)has been invoked in the Sm dwarf NGC4395which hosts the nearest and lowest luminosity Seyfert 1nucleus.Upper limits on BH masses are reported in several systems,e.g., 106–107M⊙for six dwarf ellipticals in Virgo(Geha,Guhathakurta,&van der Marel2002),5×105M⊙for the Scd spiral IC342(Boker et al.1999). Gebhardt,Rich,&Ho(2002)infer the presence of an IMBH with a mass of a few×104M⊙in one of the most massive stellar clusters(G1)in M31,but an alternative interpretation of the dataset has been presented by Baumgardt et al.(2003).A tantalizing dark central mass concentration of a few×103 M⊙(Gerssen et al.2003)is reported in the globular cluster M15from HST data,but it remains unclear whether it is an IMBH.Chandra observations of ultraluminous X-ray sources also suggest the presence of IMBHs(Clobert &Miller2004and references therein).At many levels,measuring BH masses in local AGN such as Seyferts and LINERS is more challenging than corresponding measurements in massive quiescent galaxies.The bright non-thermal active nucleus in Seyfert galaxies can drown the spectroscopic features from which dynamical measurements are made.Consequently,BH masses in local AGN are commonly mapped with alternative techniques such as reverberation mapping(Blandford&Mc Kee1982;Peterson1993;see Peterson these proceedings)where one estimates the virial mass inside the broad-line region(BLR)by combining the velocity of the BLR with an estimate of the size of the BLR based on time delay mea-surements.Reverberation mapping can typically probe scales∼600R s−bh and has yielded BH masses for several tens of AGN(Peterson1993;Wan-del,Peterson,&Malkan1999;Kaspi2000).Earlier controversies existed on the reliability of the method due to purported systematic differences in the BH-to-bulge mass ratio between AGN with reverberation mapping data and quiescent galaxies or QSOs.However,recent work(e.g.,Ferrarese et al.2001) claims that for AGN with accurate measurements of stellar velocity disper-sions,the reverberation masses agree with the BH mass determined from the tight M bh–σrelation(§2.2)which is derived from quiescent galaxies.4Shardha JogeeFig.1.Correlation between central BH mass and circumnuclear velocity dispersion–Black hole mass versus bulge luminosity(left)and the luminosity-weighted aperture dispersion within the effective radius(right).Green squares de-note galaxies with maser detections,red triangles are from gas kinematics,and blue circles are from stellar kinematics.Solid and dotted lines are the best-fit correlations and their68%confidence bands.(From Gebhardt et al.2000)2.2Relationship of the Central BH to the Bulge and Dark HaloA tight correlation has been reported between the mass of a central BH and the stellar velocity dispersion(σ)of the host galaxy’s bulge(Ferrarese& Merritt2000;Gebhardt et al.2000):M h=α σFueling AGN and Starbursts5 work(H¨a ring&Rix2004)based on improved BH and bulge masses yield a very tight M bh–M bulge relation.Graham et al.(2001)find a correlation between the light concentration of galaxies and the mass of their SMBHs, and claim this relation is as tight as the M bh–σrelation.Grogin et al.(2004) have searched for signs of this correlation at z∼0.4–1.3in a comparative study of structural parameters among34000galaxies in the GOODSfields, including350X-ray selected AGN hosts in the overlapping Chandra Deep pared to the inactive galaxies,the AGN hosts have significantly enhanced concentration indices throughout the entire redshift range,as mea-sured in rest frame B-band for a volume-limited sample to M B<-19.5(and to L(2–8keV)>1042for the AGN).Finally,Ferrarese(2002)shows that the M bh–σrelation translates to a relation between the mass of the BH and that of the dark matter(DM)halo(M dm)M h=107M⊙ M dm6Shardha Jogee3.1Mass Accretion RatesFor a standard BH accretion disk with an efficiencyǫof conversion between matter and energy,the radiated bolometric luminosity L bol is related to the mass accretion rate(˙M bh)at the last stable orbit of a BH by˙M=0.15M⊙yr−1 0.11045ergs s−1 (5) bhTable1shows typical observed bolometric luminosities and inferred mass accretion rates for QSOs and local AGN(Seyfert,LINERS)assuming a stan-dard radiative efficiencyǫ∼0.1.The standard value ofǫ∼0.1applies if the gravitational binding energy liberated by the accreting gas at the last stable orbit of the BH is radiated with an efficiency of∼0.1c2.In prac-tice,the radiative efficiency depends on the nature of the accretion disk and gas accretionflows.For instance,thin-disk accretion onto a Kerr BH can lead to a radiative efficiencyǫ∼0.2.It has been suggested that the most luminous quasars at high redshift may have grown withǫ∼0.2,or alterna-tively that they have a super-Eddington luminosity(Yu&Tremaine2002). Conversely,in certain popular models of gas accretionflows such as adi-abatic inflow-outflow solutions(ADIOS;Blandford&Begelman1999)and convection-dominated accretionflows(CDAF:Narayan et al.2000)only a small fraction of the matter which accretes at the outer boundary of theflow contributes to the mass accretion rate at the BH due to turbulence and strong mass loss.This leads to an effective radiation efficiency≪0.1when applied to the mass accretion rate at the outer boundary of the accretionflow.Thus, within the CDAF and ADIOS paradigms,the gas inflow rates that must be supplied on scales of tens of pc may be much larger than those quoted in Table1,even for low luminosity Seyferts.M bh for QSOs and local AGNTable1.Typical L bol and˙QSOs1046–10481047–104810–100Seyferts1040–10451043-104410−3–10−2LINERs1039–1043.51041–104210−5–10−4Fueling AGN and Starbursts7 3.2The Angular Momentum ProblemThe most important challenge in fueling AGN is the angular momentum prob-lem rather than the amount of fuel per se.The angular momentum per unit mass or specific angular momentum L=r×v of fuel at the last stable radius of a BH of mass(M8×108M⊙)is several times1024M8cm2s−1.In contrast, matter(star or gas)rotating in a spiral or elliptical galaxy at a radius of10 kpc has a specific angular momentum of several times1029M8cm2s−1.This is illustrated in Fig.2assuming typical galactic rotation velocities.Thus,the specific angular momentum of matter located at a radius of a few kpc must be reduced by more than104before it isfit for consumption by a BH.Searching for mechanisms which can achieve this miraculous reduction of angular mo-mentum is one of the driving objectives of AGN research.Even at a radius of200pc,L is still a factor of1000too large,and the angular momentum barrier is a more daunting challenge than the amount of gas.For instance,in the case of a Seyfert with an accretion rate of∼10−2M⊙yr−1and a duty cycle of108years,a gas cloud of106M⊙may provide adequate fuel.Such clouds are certainly common within the inner200pc radius of spiral galaxies, but we yet have to understand what physical processes are able to squeeze their angular momentum out by more than99.99%.The BH is analogous to an exigent dieter who has a plentiful supply of rich food,but can only consume99.9%fat-free items!3.3Dominant Fueling Mechanisms on Different Scales Gravitational torques,dynamical friction,viscous torques,and hydrody-namical torques(shocks)are some of the mechanisms which remove angular momentum from the dissipative gas component and channel it to small scales, thereby helping to fuel central starbursts and massive BHs.These different fueling mechanisms assume a different relative importance at different radii in a galaxy,and also,when dealing with a strongly interacting galaxy versus an isolated one.I will review these different mechanisms in detail from an observational and theoretical perspective in§4–9,but here I discuss a few key concepts and provide a schematic overview in Fig.2.Table2.Gravitational Torques,Dynamical Friction,and Viscous Torques10001e720102010002001e7460-8Shardha JogeeFig.2.The angular momentum problem in the fueling of AGN and starbursts:The specific angular momentum(L)of gas located at a radius(R)of several kpc must be reduced by more than104before it isfit for consumption at the last stable orbit(R last)of a BH.In contrast,powerful starbursts can be more easily triggered via gravitational torques which build large gas densities on circumnuclear (R=500pc)scales.Thisfigure schematically illustrates some mechanisms that can reduce L and drive gas inflow on various spatial scales in a relatively quiescent galaxy(left)and in a major merger(right).R is in pc,L is in units of cm2s−1, and a(M8×108M⊙)BH is assumed.See text for details.Fueling AGN and Starbursts9 Gravitational torques operate on a timescale(t gra)comparable to the orbital timescale and provide,therefore,the most efficient way of reducing angular momentum on large to intermediate scales(tens of kpc–a few100 pc).This can be seen by comparing t gra with the typical timescales on which dynamical friction(t df)and viscous torques(t vis)operate for a cloud of mass M(Table2).Dynamical friction on a clump of mass M and speed v at a radius R operates on a timescale which is∝(R2v/M lnΛ),where lnΛis the Coulomb logarithm(Binney&Tremaine1987).For a107M⊙gas cloud at a kpc radius in a disk galaxy,t df is an order of magnitude larger than t gra (Table2).However,for massive gas clumps at low radii,dynamical friction becomes increasingly important:it can drive a108M⊙cloud from R∼200 pc down to R∼10pc within a few times107yrs(§9).In an isolated galaxy(Fig.2),gravitational torques are exerted by non-axisymmetric features such as large-scale(§6)and nuclear(§7)bars.While a large-scale bar efficiently drives gas from the outer disk into the inner kpc, the bar-driven gasflow slows or even stalls as it crosses the inner Lindblad resonance(ILR)for reasons described in§6.At this stage,the gas piles up typically at a radius of several100pc where powerful starbursts are commonly observed(§6;Fig6).However,gas on these scales has a specific angular momentum that is still more than1000times too high for it to be digestible by a BH.If a nuclear bar(§7)is present,it can break the status quo and torque gas from the ILR region of the large-scale bar down to tens of pc. In addition,if massive gas clumps exist in the inner few100pc,dynamical friction can drive them down to tens of pc(§9).Finally,feedback from SF (e.g.,shocks from supernovae)can remove energy and angular momentum (§9)from a small fraction of the circumnuclear gas.On scales of tens of pc,the tidal torque from the BH itself can disrupt gas clumps and stellar clusters,possibly into an accretion disk(§9).Subsequently,on pc and sub-pc scales,viscous torques and hydromagnetic outflows in AGN(§9)may become important.Simulations suggest that induced large-scale stellar bars remain the main driver of gas inflows down to scales of a few100pc,even in the case of inter-acting galaxies(Fig.2),namely in many minor mergers(§5.2)and during the early stages of major(1:1)and intermediate mass ratio(1:3)interactions(§5.1).Just like in the case of an isolated barred galaxy,gas inflows driven by an induced bar also slow down near the ILR.However,thefinal stages of a major or intermediate mass ratio merger bring in very different elements.As violent relaxation starts,gas experiences strongly-varying gravitational torques,and if it is on interacting and crossing orbits,it also suffers strong shocks(§5.1; Fig.2).Thus,in thefinal merger stages,gas loses angular momentum and large gas inflows(≫1M⊙yr−1)down to small scales can result,provided the earlier episodes of SF have not depleted most of the circumnuclear gas already(§5.1).10Shardha Jogee3.4Census and Growth Epoch of BHsTable3compares the BH mass density(ρbh−qso)accreted during the opti-cally bright QSO phases(z=0.2–5)to the BH mass density in present-day galaxies(both active and inactive).Yu&Tremaine(2002)findρbh−qso∼(2.5±0.4)×105(h0/65)2M⊙Mpc−3using the extrapolated QSO luminosity function from the2dF redshift survey and a radiative efficiency of0.1.Sim-ilar values have been reported by others including Wyithe&Loeb(2003), Ferrarese(2002b),and Chokshi&Turner(1992).This value ofρbh−qso is a lower limit to the total BH mass density we expect to be in place by z=0.2 since it does not incorporate optically obscured QSOs and any build-up of the BH mass occurring outside the QSO phase.However,it is probably not far off,since the BH mass density from X-ray AGN counts at z>0.2(ρbh−xray) is estimated to be2–5×105M⊙Mpc−3(Cowie&Barger2004;Fabian& Iwasawa1999;Table3).Table3.Census of BH Mass densityρbh−QSO accreted during optical QSO phase(z=0.2–5)2–4a,b,c,dρbh−Xray from X-ray background(z>0.2)2–5e,fρbh−local in local early-type galaxies(z<0.1)2–6a,b,gρbh−Sy in local Seyferts<0.5cthe host galaxy.For instance,tidal interactions and minor or major mergers may have been much more important in the quasar era and early epochs of galaxy growth than they are in activating present-day Seyfert galaxies.3.5The Starburst–AGN ConnectionWhile I discuss the fueling of both AGN and starbursts in this review,I will not explicitly address the starburst–AGN connection.I only mention here that this connection can be circumstantial,influential,or causal.A circum-stantial connection refers to the fact that starburst and AGN activity can both manifest in the same system simply because they are affected by a common element such as a rich supply of gas,or an external trigger(e.g., an interaction).Examples include the ULIRG–QSO connection(Sanders et al.1988),evolutionary scenarios for Seyfert2(e.g.,Storchi-Bergmann et al. 2001),and perhaps the blue color of AGN hosts described in§4.An influen-tial connection is one where the AGN and starbursts may contaminate each other’s observed properties.Examples include the starburst affecting the fea-tureless continuum and line ratios of Seyferts(Cid-Fernandes et al.2001),or washing out the hard accretion disk spectrum.A causal connection is a more fundamental connection where the starburst causes the AGN or vice versa. One example is the evolution of a dense stellar cluster into a BH(Norman& Scoville1988).3.6A Note of Caution on Empirical CorrelationsThere exists many contradictory reports in the literature of correlations or lack thereof between starburst/AGN activity and host galaxy properties(e.g., Hubble types,bar fraction,nuclear bar fraction),or external triggers(e.g., presence of companions,morphological signs of interactions/mergers).Many caveats conspire towards this dismal state of affairs and should be avoided: (1)Many early studies fail to adopt the key practice of having a large control sample which is matched to the active sample or to the starburst sample in terms of relevant parameters such as distance,morphological types,luminosi-ties,inclinations,and environments.(2)The classification of morphological features such as bars and Hubble types is still often made from optical cata-logs(e.g.,the Third Reference Catalogue(RC3);de Vaucouleurs et al.1991) and suffer from subjectivity,low spatial resolution,and contamination by dust.It is better to use a quantitative method(e.g.,ellipsefits)for charac-terizing bars and apply it to near-infrared(NIR)rather than optical images. The former are less affected by extinction and typically yield a bar fraction which is higher by20–30%(e.g.,Knapen et al.2000;Eskridge et al.2002).(3)Cross comparisons of discrepant results are often difficult because they are based on inhomogeneous samples drawn from different local AGN cat-alogs that have limited overlap and different biases.For instance,opticallyselected magnitude-limited samples may be biased against faint nuclei em-bedded in bright galaxies.UV-based catalogs may favor blue Seyfert1and monly used catalogs include the Veron-Cetty&Veron Catalog of Seyferts and LINERS,the optically selected CfA sample of48Seyferts (Huchra&Burg1992),the Palomar Optical Spectroscopic Survey(POSS; Ho et al.1997a)of486emission line nuclei geared towards low luminosity H ii and AGN nuclei,and the extended12µm Galaxy Sample(E12GS)of891 galaxies(Hunt&Malkan1999).(4)Nuclear types(H ii,LINER,Seyferts) listed in literature databases such as NED often show significant discrepan-cies from recent careful spectroscopic classifications(e.g.,Ho et al.1997a).In §4–9,I will focus on studies which tend to avoid these caveats or alternatively qualify the caveats as they arise.4Hubble Type and Colors of AGN HostsDo local Seyferts and central starbursts reside preferentially in certain type of galaxies?Using the12µm sample(E12GS)and the CfA sample of Seyferts, Hunt&Malkan(1999;Fig.3)report that Sy1and Sy2nuclei tend to reside primarily in early-type(E–Sbc)galaxies.The Hubble type quoted here is the RC3Hubble index based on visual classifications of optical images.A similar result on Seyferts is reported by Ho et al.(1997a)from the POSS optical spectroscopic survey which tends to include lower luminosity galaxies and has a median extinction-corrected Hαluminosity of only2×1039erg s−1.Thesefindings on Seyferts are consistent with earlier less comprehensive studies(e.g.,Hummel et al.1990;Terlevich,Melnick,&Moles1987;Balick &Heckman1982).H ii host galaxies tend to have later Hubble types than Seyferts according to both E12GS(Hunt&Malkan1999)and POSS(Ho et al.1997a),but the mean value of the Hubble type varies in the surveys, possibly due to luminosity differences.Properties of AGN hosts in the redshift range0.5–2.5are particularly interesting as the optical QSO activity peaks at z∼2.5.Keen insights are stemming from two large panchromatic HST surveys,the Galaxy Evolution from Morphology and SEDs(GEMS;Rix et al.2004)and the Great Observa-tories Origins Deep Surveys(GOODS;Giavalisco et al.2004).A GEMS study of15AGN which have M B≃-23and are in the redshift range0.5<z<1.1 where comparable data for control inactive galaxies exist,report that80% of the AGN hosts are early-type(bulge-dominated)compared to only20% that are disk-dominated(Sanchez et al.2004).The high rest-frame B-band concentration indices of the GOODS AGN at z∼0.4–1.3(Grogin et al.2004;§2.2)also support the interpretation that these systems are predominantly bulge-dominated.Furthermore,Sanchez et al.(2004)report that a much larger fraction (70%)of the early-type AGN hosts at0.5<z<1.1show blue global rest-frame U-V colors,compared to inactive early-type galaxies in this redshift andFig.3.Distributions of the Hubble types in AGN(Seyferts,LINERS), H ii and normal nuclei:The solid line in all four panels represents data from the 12µm sample(E12GS;Hunt&Malkan1999).The dotted line represents data taken from E12GS or other AGN catalogs.The panels represent(from top to bottom)(1) The Sy1sample from E12GS(solid line)and the CfA(dotted line)sample;(2)The Sy1sample from E12GS(solid)and the CfA(dotted)sample;(3)The H ii(solid) and LINER(dotted)samples from E12GS;(4)The normal galaxies from E12GS (solid)and the Uppsala General Catalog(dotted)as tabulated by Roberts&Haynes (1994).The numbers in each panel refer to the number of objects represented by the solid and dotted histograms.The data have been binned in terms of RC3Hubble types as follows:S0a and earlier(T>0);Sa,Sab(0<T<2);Sb,Sbc(2<T<4);Sc, Scd(4<T<6);Sd and later(T>6).The vertical arrows mark subsample medians, calculated with a type index resolution of unity.(Figure is from Hunt&Malkan 1999)luminosity range.These global blue colors are consistent with the presence of young stellar populations over large regions of the AGN host galaxies. The trend of enhanced blue colors in AGN hosts at0.5<z<1.1seems to hold both at higher and lower redshifts.SDSS spectra of local z<0.2Sy2 galaxies show a significant contribution from young stellar populations,and this trend is strongly correlated with nuclear luminosity(Kauffman et al. 2003).At higher redshifts(1.8<z<2.75),Jahnke et al.(2004)find that thehost galaxies of9moderately bright(M B≃-23)AGN in the GEMS surveyhave rest-frame UV colors that are considerably bluer than expected from an old population of stars.Unfortunately,for these9distant AGN the detection images are not deep enough to constrain the morphology.Earlier studies of a handful of luminous QSO at z>2also reported very UV-luminous hosts (e.g.,Lehnert et al.1992;Hutchings et al.2002).One possible interpretation of the enhanced global blue colors exhibited by AGN hosts is that the mechanism which ignites the central BH in these galaxies also triggers global SF.The fact that SF is triggered not only in the nuclear region,but over an extended(several kpc)region,would tend to exclude major(1:1)mergers and favor weaker(e.g.,minor(1:10)or interme-diate mass-ratio(3:1))mergers/interactions where the gas has a larger L,and typically settles in extended inner disks during simulations(see§5).In fact, only3/15of the AGN hosts in the Sanchez et al.(2004)study show signs of strong disturbances.In the same vein,the GOODS AGN study(Grogin et al.2004;§2.2)reports no significant difference between the rest-frame B asymmetry index of active and inactive galaxies over z∼0.4–1.3.This suggests that AGN do not preferentially occur in major mergers over this redshift range.5Interactions and AGN/Starburst Activity5.1Basic Physics of Major MergersThe term’major merger’usually refers to the merger of two disk galaxies with a mass ratio of order1:1.Simulations of major mergers(e.g.,Negroponte& White1983;Noguchi1988;Barnes&Hernquist1991;Heller&Shlosman 1994;Mihos&Hernquist96;Struck1997)show that they generate large gas inflows into the inner kpc and could plausibly trigger intense starbursts and AGN activity.The full parameter space controlling the outcome of major mergers has not yet been fully explored,but I summarize here(see also Fig.2)some salient generalfindings:1.Not all speeds,energies,angular momenta,and orientations are equallyeffective in inducing large gas inflows,rapid mergers,and disruptions during a major merger.For instance,while all bound orbits will eventually lead to mergers,low angular momentum and low energy orbits will lead to more rapid mergers.Prograde mergers,where the spin and orbital angular momenta are aligned,occur faster than retrograde mergers,lead to more violent disruption,and excite larger non-circular motions(e.g., Binney&Tremaine1987).2.Hydrodynamical torques(shocks)tend to be important in the initial col-lision when they add spin angular momentum to the gas in both disks (Mihos&Hernquist1996;Barnes&Hernquist1996),but gravitational torques dominate thereafter.。