Percolation on a non-homogeneous Poisson blob process

tpo32三篇托福阅读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 (7)答案 (16)背景知识 (16)阅读-2 (25)原文 (25)译文 (28)题目 (31)答案 (40)背景知识 (41)阅读-3 (49)原文 (49)译文 (53)题目 (55)答案 (63)背景知识 (64)阅读-1原文Plant Colonization①Colonization is one way in which plants can change the ecology of a site. Colonization is a process with two components: invasion and survival. The rate at which a site is colonized by plants depends on both the rate at which individual organisms (seeds, spores, immature or mature individuals) arrive at the site and their success at becoming established and surviving. Success in colonization depends to a great extent on there being a site available for colonization – a safe site where disturbance by fire or by cutting down of trees has either removed competing species or reduced levels of competition and other negative interactions to a level at which the invading species can become established. For a given rate of invasion, colonization of a moist, fertile site is likely to be much more rapid than that of a dry, infertile site because of poor survival on the latter. A fertile, plowed field is rapidly invaded by a large variety of weeds, whereas a neighboring construction site from which the soil has been compacted or removed to expose a coarse, infertile parent material may remain virtually free of vegetation for many months or even years despite receiving the same input of seeds as the plowed field.②Both the rate of invasion and the rate of extinction vary greatly among different plant species. Pioneer species - those that occur only in the earliest stages of colonization -tend to have high rates of invasion because they produce very large numbers of reproductive propagules (seeds, spores, and so on) and because they have an efficient means of dispersal (normally, wind).③If colonizers produce short-lived reproductive propagules, they must produce very large numbers unless they have an efficient means of dispersal to suitable new habitats. Many plants depend on wind for dispersal and produce abundant quantities of small, relatively short-lived seeds to compensate for the fact that wind is not always a reliable means If reaching the appropriate type of habitat. Alternative strategies have evolved in some plants, such as those that produce fewer but larger seeds that are dispersed to suitable sites by birds or small mammals or those that produce long-lived seeds. Many forest plants seem to exhibit the latter adaptation, and viable seeds of pioneer species can be found in large numbers on some forest floors. For example, as many as 1,125 viable seeds per square meter were found in a 100-year-old Douglas fir/western hemlock forest in coastal British Columbia. Nearly all the seeds that had germinated from this seed bank were from pioneer species. The rapid colonization of such sites after disturbance is undoubtedly in part a reflection of the largeseed band on the forest floor.④An adaptation that is well developed in colonizing species is a high degree of variation in germination (the beginning of a seed’s growth). Seeds of a given species exhibit a wide range of germination dates, increasing the probability that at least some of the seeds will germinate during a period of favorable environmental conditions. This is particularly important for species that colonize an environment where there is no existing vegetation to ameliorate climatic extremes and in which there may be great climatic diversity.⑤Species succession in plant communities, i.e., the temporal sequence of appearance and disappearance of species is dependent on events occurring at different stages in the life history of a species. Variation in rates of invasion and growth plays an important role in determining patterns of succession, especially secondary succession. The species that are first to colonize a site are those that produce abundant seed that is distributed successfully to new sites. Such species generally grow rapidly and quickly dominate new sites, excluding other species with lower invasion and growth rates. The first community that occupies a disturbed area therefore may be composed of specie with the highest rate of invasion, whereas the community of the subsequent stage may consist of plants with similar survival ratesbut lower invasion rates.译文植物定居①定居是植物改变一个地点生态环境的一种方式。

2019年12月英语六级试卷及解答（第一套）Part Ⅰ Writing (30 minutes) Directions: For this part, you are allowed 30 minutes to write an essay on the importance of having a sense of community responsibility. You should write at least 150 words but no more than 200 words.【参照范文】There is no doubt that community responsibility plays an indispensable role in personal development, for instance, in the workplace.There are several factors accounting for this perspective and the following are the most typical ones. First and foremost, a strong sense of community responsibility is helpful to develop harmonious interpersonal relationships. As we all know, we are very likely to spend more time with our colleagues than our families after entering the workplace. Therefore, the sound wor atmosphere and interpersonal relationships among employees are crucial to both physical and mental pleasure. In addition, community responsibility can improve efficiency. In the fast-paced modern society, time is money and efficiency holds the key to saving time. As the saying goes, two heads are better than one. So great importance should be attached to the cultivation of the sense of community responsibility and we will eventually benefit from it.From what has been mentioned above, we can come to the conclusion that the sense of community responsibility is a kind of good personal quality, which deserves our attention.【参照译文】毫无疑问，集体责任在个人发展中起着不可或缺的作用，例如在工作场所。

This article appeared in a journal published by Elsevier.The attached copy is furnished to the author for internal non-commercial research and education use,including for instruction at the authors institutionand sharing with colleagues.Other uses,including reproduction and distribution,or selling or licensing copies,or posting to personal,institutional or third partywebsites are prohibited.In most cases authors are permitted to post their version of thearticle(e.g.in Word or Tex form)to their personal website orinstitutional repository.Authors requiring further informationregarding Elsevier’s archiving and manuscript policies areencouraged to visit:/copyrightThe occurrence of per fluorinated alkyl compounds in human milk from different regions of ChinaJiaying Liu a ,b ,Jingguang Li a ,⁎,Yunfeng Zhao a ,Yuxin Wang a ,Lei Zhang a ,Yongning Wu a ,⁎a National Institute for Nutrition and Food Safety,Chinese Center for Disease Control and Prevention,No.29,Nanwei Road,Beijing,100050,China bChaoyang District Center for Disease Control and Prevention,No.25,Huaweili,Beijing,100021,Chinaa b s t r a c ta r t i c l e i n f o Article history:Received 22December 2009Accepted 12March 2010Available online 18April 2010Keywords:Per fluorinated compounds Human milkBreastfeeding infant Dietary intakePer fluorinated compounds (PFCs),especially per fluorooctanesulfonate (PFOS)and per fluorooctanoate (PFOA),are known to occur throughout the environment and in the human population (Houde et al.,2006).The occurrence of PFCs in human umbilical cord blood and human milk,coupled with the potential developmental toxicity of PFCs,suggests the need for determining the exposure sources and magnitudes of PFCs in infants.In this study,10PFCs were measured in 24pooled samples consisting of 1237individual human milk samples.The samples were collected from 12provinces of China in 2007.PFOS and PFOA were the predominant PFCs found in all the samples tested.The geometric mean (GM)and median of the concentrations were 46pg/mL and 49pg/mL for PFOS,46pg/mL and 34.5pg/mL for PFOA respectively.A large variation in geographical distribution was observed for PFCs in human milk.High concentrations of PFOA (814pg/ml for the rural samples and 616pg/ml for the urban samples)were found in human milk from Shanghai.Estimated dietary intakes (EDI)were established and the median,GM and the highest EDI of the total PFCs were 17.2ng/kg/d,17.8ng/kg/d and 129.1ng/kg/d respectively.The EDI for PFOA (88.4ng/kg/d)for Shanghai was close to the tolerable daily intake (100ng/kg/d)proposed by the German Federal Institute for Risk Assessment and the Drinking Water Commission.The results suggest both mothers and infants have a high exposure to PFCs in the Shanghai region.The potential health impact of postnatal exposure through breastfeeding to infants should therefore be comprehensively evaluated.©2010Elsevier Ltd.All rights reserved.1.IntroductionPer fluorinated compounds (PFCs)have been produced industrially for several decades.Their unique characteristics (hydrophobicity and lipophobicity)make them useful in a wide range of industrial and commercial products such as surfactants,lubricants,paints,polishes,fire retardants and food packaging (Hekster et al.,2003;Lehmler,2005).Due to their widespread distribution and persistence in the environment,the health concerns arising from these compounds,especially per fluorooctanesulfonate (PFOS)and per fluorooctanoate (PFOA),have increased (Giesy and Kannan,2001;Houde et al.,2006).Mean serum elimination half-lives were 5.4years for PFOS;3.8years for PFOA;8.5years for per fluorohexanesulfonate (PFHxS).These figures were obtained from retired fluorochemical production work-ers (Olsen et al.,2007).In May 2009,PFOS and per fluorooctane sulfonyl fluoride were listed as “restricted use ”compounds in Annex B under the Stockholm Convention on persistent organic pollutants (Stockholm Convention on POPs,2009).As infants and foetus are generally regarded as more vulnerable than adults are to the potential harmful effects of chemicals,the develop-mental effects in relation to PFOA and PFOS have increasingly raised concerns.So far,most toxicological studies on developmental effects associated with PFCs have been conducted on rodents.Developmental toxicity is thought to be one of the most sensitive adverse effects associated with PFOA exposures in rodents (Rodriguez et al.,2009).PFHxS did not show the reproductive or developmental toxicity with doses up to 10mg/kg/d (Butenhoff et al.,2009).The developmental toxicity in laboratory animals was shown at much higher doses than those seen in human sera and blood.However,in some recent epidemiological studies,PFOS and PFOA concentrations in umbilical cord blood or maternal pregnancy serum were associated with human birth weight and other anthropometric measurements (Apelberg et al.,2007;Fei et al.,2007;Washino et al.,2009).Moreover,according to the initial findings of a study of 69,000people who live near a PFCs manufacturing plant in Washington,West Virginia,elevated PFOA levels in children were associated with high cholesterol levels,predisposing children to future weight problems and higher risk of heart disease (Steenland et al.,2009).Transplacental exposure to the foetus and postnatal exposure to PFCs through breastfeeding have been con firmed in humans (Apelberg et al.,2007;Inoue et al.,2004;Karrman et al.,2007;Monroy et al.,2008;Environment International 36(2010)433–438⁎Corresponding authors.Li is to be contacted at Tel./fax:+861083132933.Wu,Tel./fax:+861067776790.E-mail addresses:lichrom@ (J.Li),wuyncdc@ (Y.Wu).0160-4120/$–see front matter ©2010Elsevier Ltd.All rights reserved.doi:10.1016/j.envint.2010.03.004Contents lists available at ScienceDirectEnvironment Internationalj o u r n a l h o me p a g e :w w w.e l s ev i e r.c om /l o c a t e /e n v i n tSo et al.,2006;Tao et al.,2008a,b).Although PFCs are strongly bound to the proteins in maternal blood which limits the possibility of PFCs occurring in breast milk,several PFCs were found in human milk from some countries at lower concentration than those in maternal blood.In a Swedish study,PFOS concentration in human milk samples was on average two orders of magnitude lower than its concentration in the serum of the same donors(Karrman et al.,2007).Due to a lack of data, it is impossible to perform a reliable estimation of the ratio of PFOA concentration in human milk and serum samples from the same donors. However,it appears that the levels of PFOA in human milk could be at least an order of magnitude lower than those in serum(EFSA,2008).On a body mass basis,infants may be subjected to proportionately higher levels of certain chemicals than adults are.The exposure occur-ring earlier in life may predispose infants to a greater risk of chronic toxic effects than exposure occurring at a later stage in life(Landrigan et al., 2002).Traditional approaches to health risk assessment need to be expanded to encompass those factors and adequately protect infants. However,there is only limited data on the residual levels of PFCs in human milk that is required for a comprehensive risk assessment.To characterise the occurrence and geographical variations of PFCs in human milk in China,24pools of human milk samples were obtained from1237individuals from12provinces of China.Concentrations of10 PFCs were determined from the sample pools.The daily intake of PFCs by breastfeeding infants were estimated as basis for the purpose of risk assessment.2.Materials and methods2.1.Human milk samples collectionIn2007,1237individual human milk samples were collected from 12provinces of China including Heilongjiang,Liaoning,Hebei,Henan, Shanxi,Ningxia,Jiangxi,Fujian,Shanghai,Hubei,Sichuan and Guangxi as shown in Fig.1.Population of the provinces involved in this study accounts for approximately50%of the population of China.The criteria and approach for donor selection and sampling human milk were based on the“Guidelines for Developing a National Protocol”of the Fourth WHO-Coordinated Survey of Human milk for Persistent Organic Pollutants in Cooperation with UNEP(WHO,2007).In each province,50donors from one urban site and50–60donors from two rural sites were selected.All the mothers were primiparous.A questionnaire was completed in a face-to-face interview with each mother.The mother's information included date of birth,place of birth, residence record,dietary habits and occupation before pregnancy. Mothers who donated breast milk were fully informed of the nature and purpose of the study and then signed consent forms.The sampling was conducted from August to November in2007. For each mother,approximately50mL breast milk was collected under supervised conditions at local contact centres.The samples were collected in polypropylene jars,pre-cleaned with methanol and Milli-Q water.The individual samples were then stored at−20°C until the analysis.Before analysis,the individual samples were thawed at ambient temperature and pooled according to their collection regions. For each province,the individual samples from the urban areas and the rural areas were pooled separately resulting in24pooled human milk samples.2.2.ChemicalsThe standard solution containing perfluoropentanoic acid(PFPeA), perfluorohexanoic acid(PFHxA),perfluoroheptanoic acid(PFHpA), perfluorooctanoic acid(PFOA),perfluorononanoic acid(PFNA),per-fluorodecanoic acid(PFDA),perfluoroundecanoic acid(PFUdA)and the standard solution containing perfluorohexanesulfonate(PFHxS),per-fluoroheptanesulfonate(PFHpS)and perfluorooctanesulfonate(PFOS) were supplied by Wellington Laboratories(Guelph,Canada).The internal standard solution containing perfluoro-n-(1,2,3,4-13C4)octa-noic acid(13C4-PFOA)and perfluoro-1-(1,2,3,4-13C4)octanesulfonate (13C4-PFOS)were also supplied by Wellington Laboratories.High performance liquid chromatography(HPLC)grade methanolwasFig.1.Sampling provinces in China.434J.Liu et al./Environment International36(2010)433–438supplied by J.T.Baker(Phillipsburg,USA).Milli-Q water was used throughout the study.HPLC grade ammonium acetate and formic acid were purchased from Dikma Pure(Richmond Hill,USA).Analytical grade ammonium hydroxide(25%)was supplied by Xin Guang(Beijing, China).2.3.Extraction and instrumental analysisThe human milk samples were extracted using the method described elsewhere(Liu et al.,2008).Briefly,100pg of13C4-PFOA and100pg of13C4-PFOS as internal standards and8mL2%formic acid in water were added into2mL human milk.After sonication and centrifugation,the supernatant was transferred to the60mg/3mL Oasis WAX cartridges(Waters,Milford,USA)preconditioned with 2mL methanol and2mL water.The cartridges were then washed with1mL2%formic acid in water and1mL2%aqueous formic acid solution/methanol(50:50).The target analytes were eluted by2mL 9%ammonium hydroxide in methanol which was evaporated to dryness,then methanol/water(50:50)was added to afinal volume of 200μL.The particles in thefinal solution were removed byfiltration using nylon syringefilter(Sartorius,Goettingen,Germany).Analytes were separated and quantified using an ultra-perfor-mance liquid chromatography system coupled to a triple quadrupole MS system(Quattro Premier,Waters,Milford,USA).A20μL aliquot of the sample extract was injected with a full loop injection into a 2.1×50mm BEH C18column(1.7µm;Waters,USA).A gradient of 2mM aqueous ammonium acetate solution and methanol were used as mobile phases at aflow rate of0.4mL/min.The triple-quadrupole mass spectrometer was operated in the negative electrospray mode with multiple-reaction-monitoring(MRM).The mass transition for each analyte is list in Table1.2.4.Quantification and quality assuranceAll the solutions and reagents used in the study were tested for contamination before use,those with the lowest contamination levels then used in the study.Before extraction,the tubes and containers were washed with methanol.The vessels of liquid chromatography system were rinsed with methanol for half an hour before sample runs.Procedural blank analysis was conducted using Milli-Q water for each batch of samples.The quantification of analytes was performed using13C labeled internal standards.13C4-PFOA was used for perfluoroalkylcarboxylic acids and13C4-PFOS was used for perfluoroalkylsulfonates.System linearity was evaluated using six different concentrations covering the range from50pg/mL–5000pg/mL.The LODs shown in Table1 were higher value of either the signal-to-noise ratio of three(S/N=3) or the average blank signal plus three times the standard deviation in chromatograms of sample extracts from blank bovine milk.The recovery test was conducted by analysing blank bovine milk samples spiked with each analyte at a concentration of100pg/mL.Analyte recovery is detailed in Table1.The intra-day relative standard deviation (RSD)offive spiked human milk samples was between5%and13%and inter-days RSD(n=4)over a period of3weeks was between5%and 33%.2.5.Estimated dietary intake of PFCs for infantsThe estimated dietary intakes(EDI)of PFCs for breastfeeding infants in China were calculated on the basis of PFC levels in human milk and the average infant daily consumption data(742mL/day) given in the U.S.EPA(EPA,2002)and a body mass of6kg(Tao et al., 2008b).Concentration below the LOD was assigned a value equal to the LOD divided by the square root of2(Calafat et al.,2007;Hornung and Reed,1990).3.ResultsOf the10PFCs analysed,6PFCs were found above the detection limit with varying frequency of detection in the samples.The highest frequencies of detection were obtained from PFOS(100%)and PFNA(100%)followed by PFOA(87.5%),PFDA(87.5%), PFHxS(83%)and PFUdA(83%).The concentrations of the6PFCs detected in the24 pooled samples are detailed in Table2.Generally,PFOS and PFOA were the pre-dominant PFCs found in all the samples.The geometric mean(GM)and median concentration of PFOA were46pg/mL and34.5pg/mL respectively with a range from b LOD to814pg/mL.The GM and median concentration of PFOS were46pg/mL and 49pg/mL respectively with a range from6pg/mL to137pg/mL.PFUdA was another PFC with a high concentration in the samples,especially in samples from Shanghai in which the concentrations of PFUdA(196pg/mL for rural areas and78pg/mL for urban areas)were even higher than those of PFOS(100pg/mL for rural areas and74pg/mL for urban areas).PFHxS,PFDA and PFNA were found at low concentrations with little variation in all the samples except for the samples from Shanghai.The total con-centrations of6PFCs ranged from26pg/mL to1252pg/mL with a GM concentration of 140pg/mL and a median of133pg/mL.The Spearman's correlation test showed that concentrations of all PFCs were significantly correlated(p b0.01)with each other in all the pooled samples except for the correlation between concentration of PFHxS,PFOA and PFDA(p b0.05).There was no significant difference in concentrations for any of the PFCs between rural and urban sample pairs(t test,p N0.05).4.DiscussionAs shown in Table2,both concentration levels and composition profiles of PFCs in human milk suggested the large variation in the geographical distribution of human exposure to PFCs,specifically PFOS, PFOA and PFUdA,within China.For PFOS,the highest concentration was found in human milk from Liaoning,this was more than10times higher than that from Ningxia,which had the lowest concentrations of all the PFCs.While,for perfluoroalkylcarboxylic acids(PFCAs)such as PFOA and PFUdA,the highest concentrations were found in human milk samples from Shanghai region.Generally,the highest PFC concentra-tions were found in human milk from the provinces with a relatively high level of economic development and industrialisation such as Shanghai and Liaoning.The lowest concentrations of PFCs were obtained from Ningxia which is one of the least developed provinces within China.A similar relationship between PFCs levels in human milk and industrial development was previously described by Tao et al.who found that the concentrations of PFOS in human milk from countries with high gross domestic product(GDP)were higher than those in countries with a low GDP(Tao et al.,2008b).The significantly high concentration and proportion of PFOA in human milk from Shanghai were found in this study.In samples from Shanghai,the concentrations of PFOA highlighted in Table2were about 8times higher than that of PFOS,while in other provinces,these two PFCs had considerable concentrations.Currently there is only a limited amount of data comparing the concentration of PFCs in human milk (Bernsmann and Furst,2008;Karrman et al.,2007;So et al.,2006;Tao et al.,2008a,b;Volkel et al.,2008).From comparison of these studies,the high levels of PFOA in human milk found in Shanghai have never been observed elsewhere,with the exception of a previous investigation fromTable1Mass transition,limit of detection(LOD)for selected PFCs and the results of recovery test for spiked cow's milk.Compound Masstransition LOD(pg/mL)Mean recovery(n=5)100pg/mL RSD(%)PFHxS399→800.69114%7 PFHpS449→80 3.77110%7 PFOS499→80 1.5496%6 PFPeA263→219 5.50136%5 PFHxA313→269 2.9199%10 PFHpA363→319 2.9895%13 PFOA413→36914.15110%5 PFNA463→419 5.4698%6 PFDA513→469 1.44102%11 PFUdA563→519 1.3057%6435J.Liu et al./Environment International36(2010)433–43812German pooled human milk samples that was thought to be an extremely high level and an unusual distribution of PFCs (EFSA,2008;Suchenwirth et al.,2006).The PFOA level in human milk from Shanghai was even higher than that from the North Rhine –Westphalian (NRW)Sauerland area in Germany where,highly PFOA contaminated industrial waste was mixed into a soil improver and spread on agricultural land resulting in highly contaminated drinking water (Bernsmann and Furst,2008).The mean PFOA levels in human milk from some recent studies are compared in Fig.2.Additionally,the concentrations of other PFCAs in human milk from Shanghai were higher than those found in other studies (Karrman et al.,2007;So et al.,2006;Tao et al.,2008a,b ).This is especially true for PFUdA,which has the second highest concentration among PFCs.The higher concentration of PFOS in human milk fromLiaoning is in agreement with the results for PFOS in human blood from nine cities within China (Yeung et al.,2006).In that study,the highest concentration of PFOS was obtained from Shenyang,the capital of Liaoning.In general,the concentration of PFOS in human milk from Liaoning was at a lower concentration than that from Japan (Tao et al.,2008b ),Sweden (Karrman et al.,2007)and Hungary (Volkel et al.,2008)and comparable to studies from Germany (Volkel et al.,2008),USA (Tao et al.,2008a ),Zhoushan in China (So et al.,2006)and some other Asian countries (Tao et al.,2008b ).The concentrations of PFOS in human milk from other provinces of China were at lower levels with moderate variation.The signi ficantly higher concentration of PFOA in human milk from Shanghai suggests that human exposure to PFOA is high in that area.In a very recent study,strikingly high levels and proportions of PFOA were found in tap water in the Shanghai region (Mak et al.,2009).High concentrations of PFOA were also reported in water samples from the Yangtze River which is the major source of water for agriculture,industry and drinking water for the population of the Shanghai region (So et al.,2007).Shanghai is one of the most industrially developed areas in China.A large number of factories exist in that area including fluoropolymer manufacturing facilities.Recently,high levels of PFOA were found in the serum of workers in a facility in Changshu which is near to Shanghai (EPA,2009).Results from our previous study indicate that the high proportion of PFOA found in human blood may be associated with the industrial discharge of PFOA from fluorochemical manufacturing plants (Liu et al.,2009).The high concentration of PFCs,especially PFOA,in human milk from Shanghai may be attributed to the local production and usage of a number of products containing PFCs.Dietary intake is an important pathway for human exposure to PFCs in adults (Fromme et al.,2009).A comprehensive review on PFC exposure for the general population in Western countries estimated the overall daily intake of PFOS and PFOA from indoor air,outdoor air,house dust,diet and drinking water.The dietary intake accounted for 91%(PFOS)and 99%(PFOA)respectively (Fromme et al.,2009).Since human milk is a primary source of food and water for 0–6month old breastfeeding infant,breastfeeding could be an important postnatal exposure pathway for infants.Table 2The numbers of mothers,average ages (years)and concentrations (pg/mL)of PFCs in each pooled samples.Regions NumberAverage age (range)PFHxS PFOS PFOA PFNA PFDA PFUdA ∑PFCs HLJ a R 5226(21–30)5403713419115bU 5025(20–34)4402514726111LN R 6026(20–31)151378719625287U 5027(20–35)1411918520934381HeB R 6028(21–35)645b LOD 85872U 4025(19–35)7679419836230HN R 6028(21–35)b LOD 27351251391U 5024(20–30)63229951690SHX R 4027(21–35)428266b LOD b LOD 66U 5026(19–34)327187 3.4b LOD 51NX R 6025(20–35)b LOD 6b LOD 6b LOD b LOD 26U 5022(18–29)b LOD 16b LOD 6b LOD b LOD 36HuB R 6026(19–30)6822119941175U 5025(20–30)6447416929174JX R 4024(18–33)6533413622129U 5024(18–30)45558171347193SHH R 6027(23–35)610081476631961252U 5027(21–35)474616402578836SCH R 5524(20–29)b LOD 2022831567U 5025(20–30)543667415137FJ R 4026(21–29)7947815634232U 5024(18–29)6607617945213GXR 6028(23–34)455189323100U5025(18–35)8792212530155Bold data signi fies the high concentrations of PFOA in human milk from Shanghai.aRural area.bUrbanarea.Fig.2.The comparison of mean PFOA levels in human milk from different studies.436J.Liu et al./Environment International 36(2010)433–438The EDI range of PFOS was from1.4ng/kg/d(Ningxia)to15.9ng/kg/d (Liaoning).The EDI of PFOA by breastfeeding infants in Shanghai was 88.4ng/kg/d that was approximately16times higher than the median value(5.5ng/kg/d)and GM value(5.8ng/kg/d)in China.The median, GM and the highest EDI of total PFCs were17.2ng/kg/d,17.8ng/kg/d and 129.1ng/kg/d(Shanghai)respectively in China.For the breastfeeding infants from Massachusetts(USA),the average and the highest daily intake were14.7ng/kg/d and65.4ng/kg/d for PFOS,1.7ng/kg/d and 8.0ng/kg/d for PFOA and23.5ng/kg/d and87.1ng/kg/d for total PFCs respectively(Tao et al.,2008a).In another study on PFCs in human milk from several Asian countries,the average daily intake of PFOS via human milk by infants was11.8ng/kg/d with a range from5.7ng/kg/d(Indian infants)to28.7ng/kg/d(Japanese infants).The daily intake of PFOA via human milk by Japanese infants was9.6ng/kg/d.Overall,of the seven Asian countries studied,the highest average daily intake of PFOS,PFOA and total PFCs were estimated to be64.6ng/kg/d,41.3ng/kg/d and 88.4ng/kg/d,respectively(Tao et al.,2008b).The EDIs of PFCs by breastfeeding infants in China(except for PFOA in Shanghai)were lower or comparable to those from other countries.The EDI of PFOA via human milk by infants from Shanghai was higher than the highest value of those of other countries studied.It is assumed that exposure to contaminants in early life may impose greater health impacts than exposure later in life(Landrigan et al.,2002).From our previous studies,the EDI(divided by body mass)of PCDD/Fs,HBCD and TBBPA by breastfeeding infants were higher than that of adults in China(Li et al.,2009;Shi et al.,2009).To our knowledge,there is currently no data available on the dietary intake of PFCs for adults in China.The average dietary intake of PFOS and PFOA for adults were1.6ng/kg/d and1.0ng/kg/d for Canadians (Tittlemier et al.,2007),1.4ng/kg/d and2.9ng/kg/d for Germans (Fromme et al.,2007).For British adults,the estimated average dietary intakes in2007were10ng/kg/d for PFOS and10ng/kg/d for PFOA(upper bound)(UK-FSA,2009).Most of the EDIs of PFOS and PFOA for breastfeeding infants through human milk in China were higher than the EDIs for adults in Germany and Canada.Both EDIs of PFOS and PFOA for infants in Shanghai and Liaoning were higher than the upper bound value of British adults.Currently,there is no consensus on the tolerable daily intake(TDI) established for the intake of PFCs.The reference doses(RfD)of25ng/kg/d for PFOS and333ng/kg/d for PFOA were established based on rat chronic carcinogenicity studies and rat multigenerational studies by the envi-ronmental working group(EWG)of U.S.(So et al.,2006).The German Federal Institute for Risk Assessment and the Drinking Water Commis-sion(DWC)of the German Ministry of Health derived a provisional TDI of100ng/kg/d for both PFOA and PFOS after the pollution incident in Germany(Roos et al.,2008).The U.K.Food Standards Agency recom-mended TDIs of300ng/kg/d and3000ng/kg/d for PFOS and PFOA respectively(Fromme et al.,2009).Most recent TDIs of150ng/kg/d for PFOS and1500ng/kg/d for PFOA were established by the scientific panel on Contaminants in the Food Chain requested by the European Food Safety Authority in2008(EFSA,2008).The EDIs of PFOS and PFOA by breastfeeding infants from China were all lower than these TDIs or RfDs. However,the EDI of PFOA(88.4ng/kg/d)from Shanghai was very close to the German recommended TDI(100ng/kg/d).Although the TDI refers to the lifetime tolerable daily intake and the breastfeeding period is relatively short,infants are at an increased risk due to their susceptibility to chemical contaminants,such as PFOA.It was estimated that the levels of PFOA in human milk could be at least one order of magnitude below those in serum(EFSA,2008).The high concentration of PFOA in human milk suggests a high PFOA level in the blood of mothers from the Shanghai pared to PFOS, PFOA has the ability to cross the placenta readily(EFSA,2008; Midasch et al.,2007).Therefore,the prenatal exposure of PFOA has the potentiality to be more severe in Shanghai than other provinces in China.Further studies are needed to identify human exposure sources for risk management in Shanghai.AcknowledgmentsWe would like to thank all the mothers who collaborated with this study and donated breast milk samples.We also thank our colleagues from local CDCs of the12provinces for their hard work with the sample collection and handling.We would also like to thank Andrew Baldwin for his kind assistance with the English language of this article.This research was funded by the National Nature Science of Foundation of China(20607021and20837003)and the National Support Program for Science and Technology(2007BAC27B02). 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Evolution through either natural selection or genetic drift is dependent on variation at the genetic and mor-phological levels. Processes that influence the genetic structure of populations include mating systems, effective population size, mutation rates and gene flow among populations. We investigated the patterns of population genetic structure of orchids and evaluated if evolutionary processes are more likely at the indi-vidual population level than at the multipopulation/species level. We hypothesized that because orchid populations are frequently small and reproductive success is often skewed, we should observe many orchids with high population genetic substructure suggesting limited gene flow among pop-ulations. If limited gene flow among populations is a common pattern in orchids, then it may well be an important component that affects the likelihood of genetic drift and selection at the local population level. Such changes may lead to differentiation and evolu-tionary diversification.A main component in evolutionary processes is the necessary condition of isolation. The amount of gene flow among local populations will determine whether or not individual populations (demes) can evolve inde-pendently which may lead to cladogenesis. Usually one migrant per generation is sufficient to prevent populations from evolving independently from other populations when effective population sizes are large. Theoretically, if the gene flow rate, Nm (the effective number of migrants per generation; N = effective pop-ulation size, m = migration rate), is larger than two individuals per generation, then it is sufficient to pre-vent local adaptation while gene flow less than one per generation will likely result in population differen-tiation by selection or genetic drift (Merrell 1981, Roughgarden 1996). If Nm lies between one and two, there will be considerable variation in gene frequen-cies among populations (Merrell 1981). Consequently,populations will have similar genetic structure as if mating were panmictic (Nm >2). Alternatively, if gene flow is low (Nm < 1), populations will have different genetic structures that may result in evolutionary change through either adaptation to the local environ-ments via natural selection or through random effects such as genetic drift.Direct observation of gene flow can be viewed by the use of mark and recapture studies (for mobile organisms, or stained pollen) or tracking marker alle-les (paternity analysis) over a short number of genera-tions. Few orchid studies have attempted to directly observe gene flow and thus far only staining or micro-tagging pollinaria have been used (Peakall 1989, Nilsson et al.1992, Folsom 1994, Tremblay 1994, Salguero-Faría & Ackerman 1999). All these studies examined gene flow only within populations. Indirect methods for detecting gene flow are obtained from allele frequencies and are an estimate of the average long-term effect of genetic differentiation by genetic drift. The alleles are assumed to be neutral so that genetic differentiation based on these markers would be a consequence of drift rather than natural selection. Bohomak (1999) concluded that simple population genetic statistics are robust for inferring gene flow among groups of individuals.The most common approach is the degree of popula-tion differentiation at the genetic level using Wright’s F estimates on data obtained through protein elec-trophoresis or various PCR type approaches. The F statistics separate the amount of genetic variation which can be attributed to inbreeding among closely related individuals in a population: FIS is the inbreed-ing coefficient within individuals; FIT is the result of non random mating within a population and the effect of population subdivision; and a third statistic, FST, is the fixation index due to random genetic drift and the lack of panmixia among populations (Wright 1978).THE GENETIC STRUCTURE OF ORCHID POPULATIONSAND ITS EVO L U T I O N A R Y IMPORTA N C ER AYMOND L. T REMBLAY1,3&J AMES D. A CKERMAN21University of Puerto Rico – Humacao, Department of Biology, Humacao, Puerto Rico, 00791, U.S.A.2University of Puerto Rico – Río Piedras, Department of BiologyP.O. Box 23360, San Juan, Puerto Rico, 00931-3360, U.S.A.3Author for correspondence: raymond@LANKESTERIANA 7: 87-92. 2003.LANKESTERIANA SpeciesReferencesNm(W)Gst Calypso bulbosa (L.) Oakes Alexandersson & Ågren 2000 3.200.072Caladenia tentaculata TatePeakall & Beattie 19967.1010.0346Cephalanthera damasonium (Mill.) Druce Scacchi, De Angelis & Corbo 1991--5--5C ephalanthera longifolia (L.) Fritsch Scacchi, De Angelis & Corbo 1991 2.1510.104Cephalanthera rubra (L.) Rich.Scacchi, De Angelis & Corbo 19910.7610.247Cymbidium goeringii Rchb. f.Chung & Chung 1999 2.300.098Cypripedium acaule Ait.Case 19941.2710.164Cypripedium calceolus L.Case 1993, 1994 1.6310.196Cypripedium candidum Muhl. ex Willd.Case 19943.3710.069Cypripedium fasciculatum Kellogg ex S. Watson Aagaard, Harrod & Shea 1999 6.000.04Cypripedium kentuckiense C. F. Reed Case et al.1998 1.1210.182Cypripedium parviflorum Salisb.var. pubescens (Willd.) O. W. Knight Case et al.19981.2810.163Southern populations Wallace & Case 20000.940.209Northern populations1.570.137var. makasin (Farw.) Sheviak 1.000.199var parviflorum 1.430.149species level0.830.232Cypripedium reginae WalterCase 19940.4710.349Dactylorhiza romana (Sebastiani) SoóBullini et al.2001 3.3210.07Dactylorhiza sambucina (L.) SoóBullini et al.20011.3110.16Epidendrum conopseum R. Br.Bush, Kutz & Anderton 19991.4330.149Epipactis helleborine (L.) Crantz Scacchi, Lanzara & De Angelis 19877.310.033European populations Squirrell et al., 20011.0010.2000.241,40.5064North AmericanHollingsworth & Dickson 19970.09042.5310.2400.791Epipactis youngiana Richards & Porter Harris & Abbott 1997 2.4310.093Eulophia sinensis Miq.Sun & Wong 2001---0.00.1331,30.6533Gooyera procera Ker-Gawl.Wong & Sun 19990.22110.5230.3971,30.3863Gymnadenia conopsea (L.) R. Br.Scacchi & De Angelis 19900.28010.471Gymnadenia conopsea (L.) R. Br. conopsea Soliva & Widmer 19992.960.078Gymnadenia conopsea (L.) R. Br.subsp densiflora (Wahl) E.G. Camus & A. Camus Soliva & Widmer 19990.390.391Lepanthes caritensis Tremblay & Ackerman Carromero, Tremblay & Ackerman 1.300.167(unpublished)Lepanthes rupestris Stimson Tremblay & Ackerman 2001 1.840.170Lepanthes rubripetala Stimson Tremblay & Ackerman 20010.620.270Lepanthes eltoroensis Stimson Tremblay & Ackerman 20010.890.220Lepanthes sanguinea Hook.Carromero, Tremblay & Ackerman 1.450.144(unpublished)Table 1. Estimates of gene flow in orchids. Nm(W) = gene flow estimates based on Wright’s statistics; Gst coeff-cient of genic differentiation among populations. 1Nm calculated by the present authors from Gst or Fst using formula on p. 320 of Hartl & Clark (1989). 2Recalculated using previous formula, original Nm value 3.70. 3Calculated from RAPD markers. 4Calculated from cpDNA. 5No genetic differentiation found among populations. 6Calculated according to Weir and Cockerham’s statistics. 7. Estimated using RAPD’s and AMOVA.88Nº 7T REMBLAY&A CKERMAN- Genetic structure of orchid populationsConsequently, if we make the assumption that the genetic markers sampled are neutral or nearly neutral and that the observed level of FST is a measure of the current gene flow among populations (rather than a historical remnant), then we can evaluate the likelihood that populations are effectively isolated. The scale of FST is from 0 (no population subdivision) to 1.0 (com-plete genetic differentiation among populations).We gathered population genetic data for 58 species of terrestrial and epiphytic orchids from temperate and tropical species. The data are biased toward ter-restrial/temperate species (N = 44). We found only three studies of terrestrial/tropical species and ten epi-phytic/tropical. There is also a bias toward certain taxa: Orchis, Cypripedium, Pterostylis and Lepanthes account for nearly half (30) of the 61 records (Table 1), 10 species of O r c h i s, 7 species each of Cypripedium and Pterostylis, 6 species of Lepanthes,3 species of S p i r a n t h e s, Epipactis, Cephalantheraa n d G y m n a d e n i a, 2 species of D a c t y l o r h i z a, Epipactis, Vanilla and Zeuxine, and one species each of Caladenia, Calypso, Cymbidium, Epidendrum, Eulophia, Goodyera, Nigritella, Paphiopedilum, Platanthera, Tipularia, and Tolumnia.89Mayo 2003Gene flow among populations varies among species ranging from a high of 12 effective migrants per gen-eration in Orchis longicornu(Corrias et al. 1991) to lows of less then 0.2 in Zeuxine strateumatica(Sun & Wong 2001). Assembling the species in groups based on their estimates of gene flow, we note that 18 species have less then one migrant per generation, while 19 species have more than two migrants per generation, and 17 of the species have a migration rates between one and two. No genetic differentiation was found among populations for C e p h a l a n t h e r a d a m a s o n i u m(Scacchi, De Angelis & Corbo 1991) and Spiranthes hongkongensis(Sun 1996). Consequently these two species are excluded from further analysis.O r c h i s species typically have high estimates of gene flow among populations (Scacchi, De Angelis & Lanzara 1990, Corrias et al. 1991, Rossi et al. 1992) whereas Lepanthes and Pterostylis species have much lower gene flow estimates (Tremblay & Ackerman 2001, Sharma, Clements & Jones 2000; Sharma et al.2001). However even within a genus variation in gene flow can be extensive (Table 1).Are there phylogenetic associations with gene flow? The data for O r c h i s(mean Nm = 5.7), L e p a n t h e s(mean Nm = 2.1) and P t e r o s t y l i s( m e a n Nm = 1.0) are suggestive, but much more extensive sampling is needed for both temperate and tropical species. Curiously, L e p a n t h e s and O r c h i s have very different population genetic parameters yet both are species-rich genera and are likely in a state of evolu-tionary flux. It seems to us that orchids have taken more than one expressway to diversification. For the group of species which has more than 2 migrants per generation local populations will not evolve indepen-dently, but as a group, consequently local morpholog-ical and genetic differences among groups will be wiped out, and populations will become homoge-neous if gene flow continues at the level. When gene flow is high, selection studies from different popula-tions should be evaluated together (Fig. 1).For populations that have less than one migrant perLANKESTERIANAFigure 1: Distribution of mean (s.e.) gene flow (Nm) among genera of Orchids. Bars without error bars of single datap o i n t s.90Nº 7T REMBLAY&A CKERMAN- Genetic structure of orchid populationsgeneration, local populations can evolve independent-ly, and evolutionary studies should be done at the local level. In small populations, we may expect genetic drift to be present and selection coefficients should be high to counteract the effects of drift.For species with intermediate gene flow it is proba-bly wise to evaluate evolutionary processes at the local and multi-population/species level. We expect variance in migration rates to be large because of the skewed reproductive success among individuals, time periods and populations. Consequently, the outcome of the evolutionary process will likely depend on the amount and variation of the migration events and consistency in migration rates in time. If variance in gene flow through space and time is small, then the genetic dif-ferentiation will be more or less stable. But, for exam-ple, if variance in gene flow is high, with some periods having high gene flow followed by little or no gene flow for an extended period of time, it is possible that through natural selection and genetic drift local popula-tions might differentiate sufficiently for cladogenesis during the period of reduced immigration.Species with less than one migrant per population are basically unique evolutionary units evolving inde-pendently from other local populations. In popula-tions with large Ne (> 50), it is likely that natural selection will dominate evolutionary processes while if Ne is small (< 50) genetic drift and selection can both be responsible for evolution. Consequently for these species, local adaptation to specific environ-mental conditions is possible.This survey of population genetics studies of orchids shows that multiple evolutionary processes have likely been responsible for the remarkable diver-sification in orchids.L ITERATURE C ITEDAagaard J.E., R.J. Harrod & K.L. Shea. 1999. Genetic vari-ation among populations of the rare clustered lady-slip-per orchid (Cypripedium fasciculatum) from Washington State, USA. Nat. Areas J. 19: 234-238Ackerman J.D. & S. Ward. 1999. Genetic variation in a widespread epiphytic orchid: where is the evolutionary potential? Syst. Bot. 24: 282-291.Alexandersson, R. & J. Ågren. 2000. Genetic structure of the nonrewarding bumblebee pollinated Calypso bul-bosa. Heredity 85: 401-409Arduino, P., F. Verra, R. Cianchi, W. Rossi, B. Corrias, & L. Bullini. 1996. Genetic variation and natural hybridization between Orchis laxiflora and O r c h i s palustris(Orchidaceae). Pl. Syst. Evol. 202: 87-109. Arft, A.M. & T.A. Ranker. 1998. Allopolyploid origin and population genetics of the rare orchid Spiranthes diluvi-alis. Am. J. Bot. 85: 110-122.Bohomak, A.J. 1999. Dispersal, gene flow, and population structure. Quart. Rev. Biol. 74: 21-45.Bullini, L., R. Cianchi, P. Arduino, L. De Bonis, M. C. Mosco, A. Verdi, D. Porretta, B. Corrias & W. Rossi. 2001. Molecular evidence for allopolyploid speciation and a single origin of the western Mediterranean orchid Dactylorhiza insularis(Orchidaceae). Biol. J. Lin. Soc. 72: 193-201.Bush, S.T., W.E. Kutz & J.M. Anderton. 1999. RAPD variation in temperate populations of epiphytic orchid Epidendrum conopseum and the epiphytic fern Pleopeltis polypodioides. Selbyana 20: 120-124. Case, M.A. 1993. High levels of allozyme variation within Cypripedium calceolus(Orchidaceae) and low levels of divergence among its varieties. Syst. Bot. 18: 663-677. Case, M.A. 1994. Extensive variation in the levels of genetic diversity and degree of relatedness among five species of Cypripedium(Orchidaceae). Amer. J. Bot. 81: 175-184.Case, M.A., H.T. Mlodozeniec, L.E. Wallace & T.W. Weldy. 1998. Conservation genetics and taxonomic sta-tus of the rare Kentucky Lady’s slipper: C y p r i p e d i u m k e n t u c k i e n s e(Orchidaceae). Amer. J. Bot. 85: 1779-1779.Chung, M.Y. & M.G. Chung. 1999. Allozyme diversity and population structure in Korean populations of Cymbidium goeringii(Orchidaceae). J. Pl. Res. 112: 139-144.Corrias, B., W. Rossi, P. Arduino, R. Cianchi & L. Bullini. 1991. Orchis longicornu Poiret in Sardinia: genetic, morphological and chronological data. Webbia 45: 71-101.Folsom, J.P. 1994. Pollination of a fragrant orchid. Orch. Dig. 58: 83-99.Harris, S.A. & R. J. Abbott. 1997. Isozyme analysis of the reported origin of a new hybrid orchid species, Epipactis y o u n g i a n a(Young’s helleborine), in the British Isles. 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A new technique for monitoring pollen flow in orchids. Oecologia 79: 361-365.Peakall, R. & A. J. Beattie. 1996. Ecological and genetic consequences of pollination by sexual deception in the orchid Caladenia tentaculata. Ecology 50: 2207-2220. Rossi, W., B. Corrias, P. Arduino, R. Cianchi & L. Bullini L. 1992. Gene variation and gene flow in Orchis morio (Orchidaceae) from Italy. Pl. Syst. Evol. 179: 43-58. Roughgarden, J. 1996. Theory of population genetics and evolutionary ecology: An Introduction. Prentice Hall, Upper Saddle River, NJ, USA.Salguero-Faría, J.A. & J.D. Ackerman. 1999. A nectar reward: is more better? Biotropica 31: 303-311. Scacchi, R., G. De Angelis & R.M. Corbo. 1991. Effect of the breeding system ion the genetic structure in C e p h a l a n t h e r a spp. (Orchidaceae). Pl. Syst. Evol. 176: 53-61.Scacchi, R., G. De Angelis & P. Lanzara. 1990. Allozyme variation among and within eleven Orchis species (fam. Orchidaceae), with special reference to hybridizing apti-tude. Genetica 81: 143-150.Scacchi, R. and G. De Angelis. 1990. Isoenzyme polymor-phisms in G y m n a e d e n i a[sic] c o n o p s e a and its infer-ences for systematics within this species. Bioch. Syst. Ecol. 17: 25-33.Scacchi, R., P. Lanzara & G. De Angelis. 1987. Study of electrophoretic variability in Epipactis heleborine ( L.) Crantz, E. palustris(L.) Crantz and E. microphylla (Ehrh.) Swartz (fam. Orchidaceae). Genetica 72: 217-224.Sharma, I.K., M.A. Clements & D.L. Jones. 2000. Observations of high genetic variability in the endan-gered Australian terrestrial orchid Pterostylis gibbosa R. Br. (Orchidaceae). Bioch. Syst. Ecol. 28: 651-663. Sharma, I.K., D.L. Jones, A.G. Young & C.J. French. 2001. Genetic diversity and phylogenetic relatedness among six endemic P t e r o s t y l i s species (Orchidaceae; series Grandiflorae) of Western Australia, as revealed by allozyme polymorphisms. Bioch. Syst. 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Variability within and among natural pop-ulations. Chicago, The University of Chicago Press.Raymond L. Tremblay is an associate professor at the University of Puerto Rico in Humacao and the graduate faculty at UPR- Río Piedras. He obtained his B.Sc. with Honours at Carleton University, Ottawa, Canada in 1990 and his PhD at the University of Puerto Rico in Rio Piedras in 1996. He is presently the chairman of the In situ Orchid Conservation Committee of the Orchid Specialist Group. He is interested in evolutionary and con-servation biology of small populations. Presently his interest revolves in determining the life history characters that limit population growth rate in orchids and evaluating probability of extinction of small orchid populations. James D. Ackerman, Ph.D., is Senior Professor of Biology at the Univesrity of Puerto Rico, Río Piedras. He is an orchidologist, studying pollination an systematics.92Nº 7。

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托福阅读原文【1】Evolutionary biologists believe that speciation, the formation of a new species, often begins when some kind of physical barrier arises and divides a population of a single species into separate subpopulations. Physical separation between subpopulations promotes the formation of new species because once the members of one subpopulation can no longer mate with members of another subpopulation, they cannot exchange variant genes that arise in one of the subpopulations. In the absences of gene flow between the subpopulations, genetic differences between the groups begin to accumulate. Eventually the subpopulations become so genetically distinct that they cannot interbreed even if the physical barriers between them were removed. At this point the subpopulations have evolved into distinct species. This route to speciation is known as allopatry (“alio-” means “different”，and “patria” means “homeland”).【2】Allopatric speciation may be the main speciation route. This should not be surprising, since allopatry is pretty common. In general, the subpopulations of most species are separated from each other by some measurable distance. So even under normal situations the gene flow among the subpopulations is more of an intermittent trickle than a steady stream. In addition, barriers can rapidly arise and shut off the trickle. For example, inthe 1800s a monstrous earthquake changed the course of the Mississippi River, a large river flowing in the central part of the United States of America. The change separated populations of insects now living along opposite shore, completely cutting off gene flow between them.【3】Geographic isolation also can proceed slowly, over great spans of time. We find evidence of such extended events in the fossil record, which affords glimpses into the breakup of formerly continuous environments. For example, during past ice ages, glaciers advanced down through North America and Europe and gradually cut off parts of populations from one another. When the glacier retreated, the separated populations of plants and animals came into contact again. Some groups that had descended from the same parent population were no longer reproductively compatible—they had evolved into separate species. In other groups, however, genetic divergences had not proceeded so far, and the descendants could still interbreed—for them, reproductive isolation was not completed, and so speciation had not occurred.【4】Allopatric speciation can also be brought by the imperceptibly slow but colossal movements of the tectonic plates that make up Earth’s surface. About 5 million years ago such geologic movements created the land bridge between North America and South America that we call the Isthmus of Panama. The formation of the isthmus had important consequences for global patterns of ocean water flow. While previously the gap between the continents had allowed a free flow of water, now the isthmus presented a barrier that divided the Atlantic Ocean from the Pacific Ocean. This division set the stage for allopatric speciation among populations of fishes and other marine species.【5】In the 1980s, John Graves studied two populations of closely related fishes, one population from the Atlantic side of isthmus, the other from the Pacific side. He compared four enzymes found in the muscles of each population. Graves found that all four Pacific enzymes function better at lower temperatures than the four Atlantic versions of the same enzymes. This is significant because Pacific seawater is typically 2 to 3 degrees cooler than seawater on the Atlantic side of isthmus. Analysis by gel electrophoresis revealed slight differences in amino acid sequence of the enzymes of two of the four pairs. This is significant because the amino acid sequence of an enzyme is determined by genes.【6】Graves drew two conclusions from these observations. First, at least some of the observed differences between the enzymes of the Atlantic and Pacific fish populations were not random but were the result of evolutionary adaption. Second, it appears that closely related populations of fishes on both sides of the isthmus are starting to genetically diverge from each other. Because Graves’s study of geographically isolated populations of isthmus fishes offers a glimpse of the beginning of a process of gradual accumulation of mutations that are neutral or adaptive, divergences here might be evidence of allopatric speciation in process.托福阅读试题1.The word "promotes" in the passage is closest in meaning toA.describes.B.encourages.C.delays.D.requires.2.According to paragraph 1, allopatric speciation involves which of the following?A.The division of a population into subspecies.B.The reuniting of separated populations after they have become distinct species.C.The movement of a population to a new homeland.D.The absence of gene flow between subpopulations.3.Why does the author provide the information that "the subpopulations of most species are separated from each other by some measurable distance"?A.To indicate how scientists are able to determine whether subpopulations of a species are allopatric.B.To define what it means for a group of animals or plants to be a subpopulation.C.To suggest that allopatric speciation is not the only route to subpopulation.D.To help explain why allopatric speciation is a common way for new species to come about.4.The word "accumulate" in the passage is closest in meaning toA.Become more significant.B.Occur randomly.C.Gradually increase in number.D.Cause changes.5.In paragraph 2,why does the author mention that some insect populations were separated from each other by a change in the course of Mississippi River caused by an earthquake?A.To make the point that some kind of physical barrier separates the subpopulations of most species.B.To support the claim that the condition of allopatry cansometimes arise in a short time.C.To provide an example of a situation in which gene flow among the subpopulations of a species happens at a slow rate.D.To explain why insects living along opposite shores of the Mississippi River are very different from each other.6.According to paragraph 3，separation of subpopulations by glaciers resulted in speciation in those groups of plants and animals thatA.were reproductively isolated even after the glaciers disappeared.B.had adjusted to the old conditions caused by the glaciers.C.were able to survive being separated from their parent population.D.had experienced some genetic divergences from their parent population.7.The word "colossal" in the passage is closet in meaning toA.consistent.B.gradual.C.enormous.D.effective.8.According to paragraph 4, which of the following is true of the geologic movements that brought about the Isthmus of Panama?A.The movements brought populations of certain fishes and marine organisms into contact with one another for the first time.B.The movements transferred populations of fishes and other marine animals between the Pacific and Atlantic Oceans.C.The movements created conditions that allowed water to flow more freely between the Pacific and Atlantic Oceans.D.The movements created conditions for the formation ofnew species of fishes and other marine animals.9.The word "sequence" in the passage is closet in meaning toA.quality.B.order.C.function.D.number.10.According to paragraph 5, by comparing the enzymes from two related groups of fishes on opposite sides of the isthmus, Graves found evidence thatA.there were slight genetic divergences between the two groups.B.the Atlantic group of fishes were descended from the Pacific group of fishes.C.the temperature of water on either side of the isthmus had changed.D.genetic changes in the Atlantic group of fishes were more rapid and frequent than in the Pacific group of fishes.11.It can be inferred from paragraph 5 and 6 that the reason Graves concluded that some of the differences between the Pacific and Atlantic enzymes were not random was thatA.each of the Pacific enzymes works better in cooler waters.B.the Enzymes of the Atlantic fish populations had not changed since the formation of the Isthmus of Panama.C.gel electrophoresis showed that the changes benefited both the Atlantic and the Pacific fish populations.D.the differences between the enzymes disappeared when the two fish populations were experimentally switched to other side of the isthmus.12.Which of the sentence below best expresses the essential information in the highlighted sentence in the passage? Incorrectchoices change the meaning in important ways or leave out essential information.A.Graves's study provides evidence that isthmus fishes are in the process of becoming geographically isolated.B.Graves's study of mutating isthmus fishes yields results that differ from results of other studies involving allopatric speciation.C.Graves's study of isolated populations of isthmus fishes provides some evidence that allopatric speciation might be beginningD.Grave's study indicates that when isolated, populations of isthmus fished register neutral or adaptive mutations.13. Look at the four squares [■] that indicate where the following sentence can be added to the passage.Where would the sentence best fit? The formation of the isthmus had important consequences for global patterns of ocean water flow.Allopatric speciation can also be brought by the imperceptibly slow but colossal movements of the tectonic plates that make up Earth's surface. ■【A】 About 5 million years ago such geologic movements created the land bridge between North America and South America that we call the Isthmus of Panama. The formation of the isthmus had important consequences for global patterns of ocean water flow. ■【B】While previously the gap between the continents had allowed a free flow of water, now the isthmus presented a barrier that divided the Atlantic Ocean from the Pacific Ocean. ■【C】This division set the stage for allopatric speciation among populations of fishes and other marine species. ■【D】14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the mostimportant ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passages or are minor ideas in the passage. This question is worth 2 points.Allopatric speciation takes place when physically separated populations of a single species gradually diverge genetically to the point of becoming unable to interbreedA.Allopatric speciation is common because the gene flow between subpopulations is generally limited and the barriers that completely separate subpopulations can arise in a variety of ways.B.During past ice ages, some, but not all, subpopulations separated by glaciers evolved into distinct species.C.Speciation does not need to take place through allopatry because subpopulations will form distinct species whenever there are adaptive advantages or notD.Physical barriers from glaciers and the movement of tectonic plates form so slowly that the subpopulations on either side of the barriers usually do not form distinct species.E.Graves's study of fish populations separated by the Isthmus of Panama may well provide a picture of the beginning stages of speciation.F.Graves's study of physically separated fish populations show that there must be large differences between the environments of the isolated populations if allopatric speciation is to take place.托福阅读答案1.promote本身是促进的意思。

· 综述·国内外异种器官移植的现状及进展张小燕　王国辉　韩士超　戚若晨　刘克普　魏迪　杨晓剑　马帅军　窦科峰　秦卫军【摘要】　器官短缺已成为阻碍器官移植发展的主要难题，异种移植是解决全球器官匮乏最有价值的方法之一。

近年来，基因工程技术的发展和新型免疫抑制药的研发为异种移植提供了新的理论基础。

国外陆续开展基因修饰猪-非人灵长类动物或脑死亡受者的相关异种移植研究，并取得一些实质性的进展，但大部分的研究仍处于临床前阶段，距离投入临床跨越巨大。

因此，本文结合目前国内外最新的临床前实验研究进展，对异种移植的历史、基因修饰技术发展、异种移植排斥反应及免疫抑制方案等问题进行综述，以期为异种移植的进一步研究提供参考，促进异种移植临床应用，造福更多终末期疾病患者。

【关键词】　异种移植；基因修饰猪；免疫抑制药；非人灵长类动物；排斥反应；炎症反应；凝血功能障碍；感染【中图分类号】　R617,Q78　【文献标志码】 A 【文章编号】 1674-7445（2024）02-0017-06Present situation and progress of xenotransplantation at home and abroad Zhang Xiaoyan, Wang Guohui, Han Shichao,Qi Ruochen, Liu Kepu, Wei Di, Yang Xiaojian, Ma Shuaijun, Dou Kefeng, Qin Weijun. Department of Urology , Xijing Hospital of Air Force Medical University , Xi’an 710032, ChinaCorrespondingauthors:DouKefeng,Email:***************.cnQinWeijun,Email:**************.cn【Abstract 】 Organ shortage has become one of the major challenges hindering the development of organ transplantation. Xenotransplantation is one of the most valuable methods to resolve global organ shortage. In recent years,the development of genetic engineering technique and research and development of new immunosuppressant have provided novel theoretical basis for xenotransplantation. International scholars have successively carried out researches on xenotransplantation in genetically modified pigs to non-human primates or brain death recipients, making certain substantial progresses. However, most of the researches are still in the preclinical stage, far from clinical application.Therefore, according to the latest preclinical experimental research progress at home and abroad, the history of xenotransplantation, the development of gene modification technology, xenotransplantation rejection and immunosuppression regimens were reviewed, aiming to provide reference for subsequent research of xenotransplantation,promote clinical application of xenotransplantation and bring benefits to more patients with end-stage diseases.【Key words 】 Xenotransplantation; Genetically modified pig; Immunosuppressant; Non-human primate; Rejection;Inflammation; Coagulation disorder; InfectionDOI: 10.3969/j.issn.1674-7445.2023193基金项目：国家自然科学基金（82101322、82200845）作者单位： 710032　西安，空军军医大学西京医院泌尿外科作者简介：张小燕（ORCID 0000-0002-1199-988X ），硕士，住院医师，研究方向为肾移植与肾纤维化，Email ：156****6095@通信作者：窦科峰（ORCID 0000-0003-1708-8048），主任医师，中国科学院院士，研究方向为异种移植与肝胆疾病，Email:***************.cn ；秦卫军（ORCID 0000-0001-5202-642X ），博士，主任医师，研究方向为肾移植与泌尿系肿瘤，Email:**************.cn第 15 卷　第 2 期器官移植Vol. 15　No.2　2024 年 3 月Organ Transplantation Mar. 2024　我国慢性肾病的发病率高达10.8%[1]。

非均匀塞曼展宽英语Inhomogeneous Zeeman Broadening in Spectral AnalysisSpectral analysis plays a crucial role in variousscientific fields, including astrophysics, chemistry, and material science. One of the phenomena that can significantly affect the interpretation of spectral lines is Zeeman broadening, which arises due to the interaction between the magnetic field and the magnetic moment of the particles emitting the light. Inhomogeneous Zeeman broadening is a specific case where the broadening effect is not uniform across the entire spectral line.The inhomogeneous broadening occurs when there is aspatial variation in the magnetic field strength across the region of the emitting source. This can lead to a spread inthe energy levels of the emitting particles, which in turn causes a broadening of the spectral lines that is not uniform. The effect is particularly noticeable in stars, where the magnetic field can vary significantly from the surface to the core.To analyze the inhomogeneous Zeeman broadening, one must consider the distribution of the magnetic field within the emitting region. This can be complex, as it may involve turbulent fields, localized magnetic spots, or other non-uniformities. The spectral lines will be broadened todifferent extents depending on the local magnetic fieldstrength, leading to a complex profile that can be challenging to interpret.In the context of stellar atmospheres, the inhomogeneous broadening can be modeled using various techniques. One common approach is to use a magneto-optical model that takes into account the Hanle and Zeeman effects. These models can help in disentangling the effects of the magnetic field from other broadening mechanisms, such as thermal broadening or pressure broadening.The study of inhomogeneous Zeeman broadening is not only important for understanding the magnetic properties of celestial objects but also for diagnosing physical conditions such as temperature, density, and velocity fields within the emitting medium. Accurate measurements and analysis of this broadening can provide insights into the dynamics of stellar interiors and the behavior of plasmas in various astrophysical environments.In conclusion, inhomogeneous Zeeman broadening is a complex but important aspect of spectral analysis that can reveal valuable information about the magnetic fields and physical conditions of the sources under study. Advanced modeling and careful interpretation of the spectral data are essential for extracting meaningful physical parameters from the observed spectra.。

生物英语测试题及答案一、选择题（每题2分，共20分）1. Which of the following is not a characteristic of living organisms?A. Requires nutrientsB. Responds to stimuliC. Can grow and reproduceD. Is always composed of cells2. What is the basic unit of life?A. OrganB. TissueC. CellD. Organ system3. What is the process by which plants convert light energy into chemical energy?A. RespirationB. PhotosynthesisC. FermentationD. Digestion4. In the context of genetics, what does the term "gene" refer to?A. A physical traitB. A unit of heredityC. A type of cellD. A biological process5. What is the term for the study of the relationships and interactions between organisms and their environment?A. AnatomyB. EcologyC. PhysiologyD. Taxonomy6. Which of the following is a type of protein?A. HemoglobinB. GlucoseC. LipidsD. Vitamins7. What is the primary function of the cell membrane?A. To provide energyB. To protect the cellC. To store genetic materialD. To facilitate cell division8. What is the process by which organisms pass on traits to their offspring?A. InheritanceB. EvolutionC. AdaptationD. Natural selection9. What is the role of chlorophyll in plants?A. To provide structural supportB. To store waterC. To absorb light for photosynthesisD. To transport nutrients10. Which of the following is not a type of tissue in animals?A. Connective tissueB. Muscle tissueC. Nervous tissueD. Plant tissue二、填空题（每题1分，共10分）1. The process by which organisms break down food intosimpler substances is called ______.2. The largest organ in the human body is the ______.3. The genetic material in cells is known as ______.4. The study of the structure of organisms is called ______.5. The cell organelle responsible for energy production isthe ______.6. The basic structural and functional unit of all living organisms is the ______.7. The process in which organisms produce more of their own kind is known as ______.8. The study of the classification of organisms is known as______.9. The process by which organisms obtain nutrients from their environment is called ______.10. The ability of an organism to change its traits in response to the environment is known as ______.三、简答题（每题5分，共20分）1. Explain the difference between mitosis and meiosis.2. Describe the role of enzymes in biological processes.3. What is the significance of biodiversity for ecosystems?4. Explain the concept of natural selection and how it contributes to evolution.四、论述题（每题15分，共30分）1. Discuss the impact of human activities on ecosystems and the importance of conservation efforts.2. Elaborate on the role of DNA in heredity and the potential ethical implications of genetic engineering.五、答案一、选择题答案1. D2. C3. B4. B5. B6. A7. B8. A9. C10. D二、填空题答案1. Digestion2. Skin3. DNA4. Anatomy5. Mitochondria6. Cell7. Reproduction8. Taxonomy9. Nutrition10. Adaptation三、简答题答案1. Mitosis is the process of cell division that results in two genetically identical daughter cells, typical of growth and repair in organisms. Meiosis, on the other hand, is a type of cell division that results in four non-identical haploid cells, which are important for sexual reproduction.2. Enzymes are biological catalysts that speed up chemical reactions in biological systems without being consumed in the process. They play a crucial role in metabolism, digestion, and many other processes.3. Biodiversity is important for ecosystems as it contributes to their resilience, stability, and the ability to provide a range of services, including nutrient cycling, pollination, and pest control.4. Natural selection is the process by which organisms with traits that are better suited to their environment are more likely to survive and reproduce. Over time, this leads to the evolution of species as advantageous traits become more common in the population.四、论述题答案1. Human activities such as deforestation, pollution, and climate change have significant impacts on ecosystems, leading to habitat loss, species extinction, and disruptions in ecological balance. Conservation efforts are vital to preserve biodiversity and maintain the health of ecosystems。