High intakes of Cr, Ni, and Zn in clinker_Part I. Influence on burning process and formation of

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《高级英语》第一册课文7-15翻译、词汇_张汉熙

Learn General Secretary on "two to learn a" strengthening "four Consciousnesses" important speech caused a strong reaction in the country. Time, watching "red treasure", the origin of building the party back to power, how to strengthen services for the masses, improve party cohesion, fighting to become the grass-roots party members and masses hot topic. Grass-roots party organizations "two" is to strengthen the service of party members and cadres, the pioneer spirit. Distribution of grass-roots party organizations in all walks of people, clothing, shelter, which belongs to the nerve endings of the party organization and comments reputation has a direct perception of the masses. Strengthen the party ahead of the "pedal" spirit; strengthen the party members and cadres "success does not have to be me" and "the first to bear hardships, the last to" service spirit to set the party's positive image among the people is important. Grass-roots party organizations "two" is to cleanse all people not happy not to see "stereotypes", establish the honest faithful, diligent faith for the people. No need to avoid mentioning that, some members of our party can not stand the "money," corrosion of temptation, thin, Xu Zhou, such abuse and corrupt bribery, malfeasance borers, and rats. Two, is to clean up, thin, Xu, Zhou's solution to restore the party's fresh and natural, solid and honest work style. Cleansing "take, eat, card," undesirable and behaviour, "cross, hard and cold, push" attitude. Grass-roots party organizations "two" is to strengthen the sense of ordinary party members, participating in consciousness, unity consciousness. For reasons known, members of grass-roots party branches less mobile, less resources, and the construction of party organizations have some lag. Two studies, is to focus on the grass-roots party branches "loose, soft, loose" problem, advance the party members and cadres, "a gang working", "Hong Kong report." Strong cleanup actions, style and rambling, presumptuous "unqualified" party members, pays special attention to party members and cadres "joining party of thought" problem. "Party building" is obtained in the long-term development of our party's historical experience accumulated. Two is our party under the new historical conditions, strengthen the party's construction of a new "rectification movement." Grass-roots party organizations should always catch the hard work, results-oriented. Two educational outcomes are long-term oriented and become an important impetus for the work. "Two" should have three kinds of consciousness "two" study and education, basic learning lies in the doing. Only the Constitution address the series of party rules, and do solid work, be qualified party members had a solid ideological basis. Only the "learning" and "do" real unity, to form a "learn-learn-do-do" the virtuous cycle, and ultimately achieve the fundamental objective of education. This requires that the Organization《高级英语》第一册课文翻译及词汇章美芳第七课神奇的集成电路片时代 (1)第八课互相作用的生活 (1)第九课马克•吐温——美国的一面镜子 (6)第十课震撼世界的审判 (13)第十一课词典的用途究竟何在? (21)第十二课潜水鸟 (29)第十三课大不列颠望洋兴叹 (40)第十四课阿真舍湾 (46)第十五课海上无路标 (62)learning education, need three kinds of consciousness: one is to establish an integrated awareness. "Learning" and "do" what car isTwo-wheel, bird wings, need to go hand in hand, one end can be neglected. Communist theoretician and man. Only by closely combining theory and practice together in order to truly realize their value. "Learning" is the Foundation, the Foundation is not strong, shaking; " "Is the key to net to net thousands of accounts. "Two" education, "" lay the basis, going to "do" the key grip, so that the "learning" and "doing" back to standard, so that the majority of party members "learn" learning theory of nutrients, in the "doing" practice party's purposes. Second, to establish a sense of depth. "Learning" and "do" not Chu drawn, entirely different, but the organic unity of the whole. "Two" learning education, we need to explore integrating "learning" in "do", exhibit "do" in "Science". To avoid the "learning" into simple room instruction, "do" into a monotone for doing. Should exploration "learn" in the has "do", "do" in the has "learn" of education and practice of carrier, makes general grass-roots members can in "learn" in the has "do" of achievements sense, in "do" in the has "learn" of get sense, real makes party of theory brain into heart, put for people service concept outside of Yu shaped. Third, to adhere to long-term the awareness. Style construction on the road forever, "two" had to catch the long-term. "Two" study and education, by no means, assault-style wind-sport, but the recurrent education within the party. In recent years, the party's mass line education practice and "three-three" special education in grass-roots borne rich fruits, vast numbers of party members and cadres withstood the baptism of the spirit. "Two" greater need to focus on longer hold long-term, to establish and perfect the effective mechanism of the education, focusing on the creation of long-term education, strive to make the vast number of party members to maintain their vanguard Color, maintain the party's advanced nature and purity. Awareness-raising, antennas and atmosphere – a discussion on how leading cadres of party members "two" current, "two" activity is in full swing up and down the country, party cadres as a "key minority" is both a barometer and impetus. The "two" meaning enough deep, is to determine the party cadres can resolve to study hard first. In the "two" in the process, some cadres of himself, standing long, high awareness, that Constitution Party rules is simple, its not worth bothering some party cadres think speak series has nothing to do with the grass-roots work, water business learning series of speeches seen as window dressing. These "lazy, casual, and decadent" ideas learning lacks motivation, a serious impediment to "two" effect. John Stuart Mill once said, only a basic element of human thought patterns change dramatically, human destiny can make great improvement. The same, only party members and第七课神奇的集成电路片时代(节选)新生的微型技术将使社会发生巨变1这是一个极小的薄片，只有大约四分之一英寸见方。

Facing the challenges of Cu_ Fe and Zn homeostasis in plants

such as its use in the Zn finger family of transcription factors for formation of the DNA binding domain that interacts with the major groove of DNA4,5. Mechanisms of metal mobilization and uptake The primary source of metals for the plant is the soil (Table 1); thus, efficient uptake is essential for life. Even when abundant, metals can be inaccessible in the soil owing to their tendency to be present predominantly in an insoluble form. Zn and Cu are primarily insoluble in soils because of adsorption to clay, CaCO 3 or organic matter, whereas Fe is predominantly found as Fe hydroxides1. Insolubility is particularly pronounced at the higher pH of alkaline soils, which represent approximately 30% of the world’s soils. To deal with the inaccessibility of some metals, nongraminaceous plants rely primarily on a reduction-based strategy of uptake (Fig. 1), whereas graminaceous plants (grasses) more commonly use a chelation-based method (Fig. 2). Acidification of the soil. To overcome the challenge of insolubility in alkaline soils, plants can use ATPase activity to extrude protons into the rhizosphere to decrease the pH of the soil under metal-limiting conditions6. As the pH of the soil decreases, the increased concentration of protons helps to generate free metal. For example, Fe3+ is released from insoluble oxides with the concomitant formation of water:

cryocooling晶体防冻液

Acta Crystallographica Section D Biological CrystallographyISSN0907-4449Cryocooling and radiation damage in macromolecular crystallographyElspeth F.Garman*andRobin Leslie OwenLaboratory of Molecular Biophysics,Department of Biochemistry,University of Oxford,Oxford OX13QU,EnglandCorrespondence e-mail:elspeth@#2006International Union of Crystallography Printed in Denmark–all rights reserved Advances in cryocrystallographic techniques for macromole-cular crystallography have been intimately intertwined withefforts to reduce the deleterious effects of X-ray damageinﬂicted during the collection of diffraction data.A briefoverview of cryomethods and their rationale is given.This isfollowed by a summary of our current limited understandingof radiation damage in cryocooled crystals,investigationsaimed at minimizing its effects andﬁnally some developmentswhich actually utilize it both for phasing and to extendstructural knowledge.Received14June2005Accepted21October20051.IntroductionThe macromolecular cryocrystallographic techniques devel-oped over the last20years have had a huge impact on proteincrystallography and have also allowed our brightest synchro-tron sources to be utilized efﬁciently.Most macromolecularcrystals held at room temperature during data collection losetheir order after only a few seconds in an unattenuated third-generation synchrotron source X-ray beam.For a crystal heldat100K,a much longer total X-ray exposure can be toleratedwithout severely affecting the diffraction quality,so usuallyone or more complete data sets can be collected from a singlecrystal.Methods for cryocooling have thus become wellestablished and widely disseminated,with over90%ofbiological crystallographers currently collecting their data ataround100K.Research in this area is now largely directed atunderstanding the reasons why certain protocols for coolingare on average more successful than others.Although the problem of radiation damage is much reducedif the sample is held at100K during data collection,at third-generation synchrotron sources there is commonplaceobservation of decreasing diffraction quality as the cumulativeX-ray exposure increases.Damage occurring to cryocooled(100K)crystals was in factﬁrst noted at a second-generationsource(Gonzales et al.,1992).These observations haveresulted in a recent research effort to gain some understandingof the characteristics of radiation damage at100K so thatstrategies to minimize it might be devised,data might becorrected for it,and it might be established if its effects couldbe used positively to gain structural information.This researchis still in its infancy;the experiments are painstaking and timeconsuming,but the investigations have made some progressover the lastﬁve years.Theﬁrst systematic study of the effect of X-rays on proteincrystals was carried out at room temperature in1962by Blakeand Phillips on crystals of myoglobin.They observed thatdamage was proportional to dose and that each8keV X-rayphoton absorbed by the crystal appeared to disrupt~7032doi:10.1107/S0907444905034207Acta Cryst.(2006).D62,32–47molecules and somewhat disorder another90.They proposed an empirical model for diffraction decay which could not account for all the changes in diffraction intensities that they observed:‘there are,however,some small but signiﬁcant changes in the diffracted intensities which may indicate structural effects of the irradiation’(Blake&Phillips,1962). This postulate was subsequently conﬁrmed for cryocooled crystals held at100K(Burmeister,2000;Ravelli& McSweeney,2000;Weik et al.,2000).For room-temperature data collection,broken disulﬁdes were observed in electron-density maps for crystals of ribonuclease by Burley,Petsko and Ringe,this was noted in Helliwell(1988)who observed similar effects in crystals of insulin.The beneﬁt of cooling protein crystals during data collec-tion was quantiﬁed in1970by Haas and Rossmann,who reported a tenfold reduction in the rate of intensity loss of two reﬂections in lactate dehydrogenase crystals soaked in3M sucrose when they compared198K with room-temperature measurements(Haas&Rossmann,1970).A general method of exchanging mother liquor with an aqueous/organic mixture of high organic solvent concentration prior to crystal cooling was presented by Petsko(Petsko,1975),and in the1980s Hope encouraged macromolecular crystallographers to adopt the oil and glass spatula techniques of crystal mounting used for small-molecule crystallography(Hope,1988).The suggestion of using a small thin loop and surface-tension forces to hold the crystal(Teng,1990)and the commercial availability of a reliable and easy-to-use cryostat(Cosier& Glazer,1986)were both pivotal advances in the development of macromolecular cryocrystallography,and led to its wide-spread application and use.This is mainly because of the much reduced rate of radiation damage but also because of several other advantages:usually a whole data set can be collected from one crystal resulting in higher quality data,the loop mounting technique is much easier,as well as being less harmful to fragile crystals than the traditional room temperature capillary methods,crystals can beﬂash-cooled and stored under liquid nitrogen when they are in peak condition,and new types of experiments are now possible such as cryotrapping of reaction intermediates.Cryocooling protocols are now an essential step in data collection from most crystals and have had a major impact on the quality and number of biological structures being obtained. However,the increasingly highﬂuxes offered by third-generation synchrotron sources have resulted in radiation damage being observed even when the crystals are held at around100K.This damage manifests itself in a number of different ways including;decreasing diffraction power, increases in unit-cell volume,and speciﬁc structural damage to covalent bonds.The latter two phenomena result in creeping non-isomorphism as the experiment proceeds,which can cause the MAD method of structure solution to fail.While damage to speciﬁc sites can be used to obtain phase information (Ravelli et al.,2003),the observation that active sites in protein molecules seem particularly sensitive to change means that radiation damage has once again become a relevant concern for all structural biologists.In this paper we summarize the widely used cryocooling techniques and the current state of our understanding of radiation damage in macromolecular cryocrystallography.For fuller accounts of cryocrystallographic methods and hardware, the reader is referred to the comprehensive accounts that are already in the literature and which will not be repeated here (Garman&Schneider,1997;Rodgers,1997;Parkin&Hope, 1998;Garman,1999b;Hope,2001;Rodgers,2001;Garman& Doublie´,2003;Pﬂugrath,2004).Brief comments on the current status of radiation-damage studies can also be found in Garman&Nave(2002)and Nave&Garman(2005),which are the introductions to two issues of the Journal of Synchrotron Radiation containing papers from the Second (2001)and Third(2003)International Workshops on X-ray Damage to Biological Crystalline Samples,respectively.2.How do we cool?The various practical aspects of cryotechniques have become routine in macromolecular crystallography,but they often become modiﬁed and non-optimal with time as they are handed down,largely anecdotally,to new researchers.In most cases this gives reasonable results,but occasionally it fails completely,and then the basic techniques have to be revisited in order toﬁnd a suitable way forward.The various proce-dures recommended in the papers listed above have a rationale based onﬁnding the cryoprotocol which will ultimately give the optimum diffraction data quality(Garman, 1999b).Their application ensures the best chemical conditions for the crystal(e.g.cryoprotectant composition and concen-tration,minimum osmotic shock)and the least damaging manipulation andﬂash-cooling procedure,in order to retain the physical state of the crystal.Careful attention to these two factors can signiﬁcantly improve the quality of a data set and thus make subsequent structure solution and reﬁnement more straightforward.Once cooled,the crystal must be kept below the glass transition temperature of the cryobuffer at or below155K (Weik,Kryger et al.,2001)(increased from the136K of pure water by the mother liquor constituents)at all times(except if annealing–see below).2.1.CryoprotectionThe basic tenet of cryocrystallographic protocols is that on cooling,the formation of crystalline ice within the sample must be avoided since it both disrupts internal order(owing to expansion on formation)and also interferes with the diffrac-tion pattern from the protein.Thus,the crystal must be cooled so fast that the water in the solvent channels is in the vitreous rather than the crystalline state at the end of the procedure (Fig.1).For pure water,vitriﬁcation of micrometre sized drops can be achieved with cooling times of the order of10À5s (Johari et al.,1987):clearly an impossible requirement for solvent in interstitial sites in crystals.This problem can be overcome by replacing some of the water in the mother liquor with a cryoprotectant agent(‘antifreeze’)which effectivelyActa Cryst.(2006).D62,32–47Garman and Owen Cryocooling and radiation damage33extends to 1–2s the time avail-able for the cooling process toresult in vitriﬁcation as opposedto crystallization.There are twotypes of cryoprotectant agent commonly used:(a )those suchas glycerol which penetrate into solvent channels and (b )oils with which the crystal is coated(Riboldi-Tunnicliffe &Hilgen-feld,1999).A survey of cryo-protectant useage (Garman &Doublie ´,2003)showed that around 50%of researchers use glycerol,the majority adding between 20and 30%(v /v ).Thisby no means implies that glycerol is always best;it is often just the most convenient,and nosubsequent optimization takes place because it gives adequate results.Oils do not penetrate into the crystal but provide a barrier between the surface of the crystal and the air,and best results are obtained if as much mother liquor is removed as possible.The crystal can then be covered with a protective layer of oil to avoid dehydration during its transfer to cryogen,although this procedure is not always successful in avoiding ice.However,a second requirement for success in cryocooling is imposed during soaking;the chosen cryobuffer should notdegrade the crystal by either surface attack or osmotic shock.Thus,when deciding which cryoprotectant agent to try,the components of the mother liquor should ﬁrst be considered.If a cryoprotectant agent is already present at low concentration,the concentration can often be increased without deleterious effects.Table 1gives a general idea of where to start in selecting a cryoprotectant agent.A benign agent will neither attack the crystal surface (this ultimately results in the crystal dissolving),nor cause its surface to increasingly resemble crazy paving because of osmotic shock.The putative cryobuffer is ﬁrst mounted alone in the loop (i.e.no crystal)and ﬂash-frozen for a diffraction test.A glassy looking result is a necessary but not sufﬁcient condition for adequate cryoprotectant agent concentration:for instance a water:glycerol mixture of 60%:40%looks glassy but gives anice diffraction ring at 3.67A˚(see Fig.2),with a signal/noise (S/N)ratio of 2,and it is necessary to go to a 55%:45%mixture to reduce this to 1.5.Thus,a diffraction test allows the optimum concentration to be found.Since the cryobuffer concentration is often slightly diluted by the addition of thecrystal and its surrounding mother liquor;a safe strategy is to increase the initial concentration by 2–5%.Once a suitable cryobuffer has been identiﬁed,the overall cryoprotocol can be optimized along the lines shown in Fig.3,which gives a possible strategy.In the experience of the authors,the single most common reason for failure (i.e.diffraction not adequate for the planned experiment)in cryocooling is that the cryobuffer has been made by diluting 34Garman and OwenCryocooling and radiation damage Acta Cryst.(2006).D 62,32–47Table 1Possible strategy for ﬁnding an appropriate cryoprotectant buffer.Major component of mother liquor Suggested cryoprotectant agents/strategy All components Add 15–25%glycerol (works in around two thirds of cases).Drag through oil (e.g.parafﬁn,paratone-N or NVH)(Riboldi-Tunnicliffe &Hilgenfeld,1999)PEG <4K Increase PEG,add small molecular weight PEGs PEG >4K Add small molecular weight PEGs (NB large MW PEGs arepoor cryoprotectants and are very viscous)Crystal screens solutions I (14)Glycerol concentrations required given in Garman &Mitchell (1996)Crystal screen solutions I and II (14)PEG400,ethylene glycol,glycerol and 1,2propanediolconcentrations required given in McFerrin &Snell (2002)MPD Increase MPD concentration Salt (NB low-salt concentration requires a greater concentration of cryoprotectantthan high salt)(a )Add MPD and/or ethylene glycol or glycerol or a mixture of sugars such as 15%trehalose +15%sucrose (b )Increase concentration /add salt (e.g.8M Na formate or malonate)(Rubinson et al.,2000)(c )Exchange salt for organic solvent (Wierenga et al.,1992)When all else fails ...Try 20%l -(+)-2,3-butanediol (Wynne et al.,1999;Tucker,2005)Figure 2Optimization of cryobuffer.Diffraction patterns illustrating the effect of adding increasing concentrations of glycerol to water.For 100%water,discrete reﬂections from individual ice crystals are observed.As theconcentration of glycerol is raised,the diffraction shows typical sharppowder pattern rings from the ice crystallites,becoming a single sharp ring and then a diffuse ring with gentle gradients on both the high-andlow-resolution sides.Adequate cryoprotection has been achieved with45%:55%(v /v )glycerol:water.The resolutions at which ice reﬂectionsappear are alsotabulated.Figure 1An apoferritin crystal cryocooled in a ﬁbre loop.The glassy appearance isa necessary but not sufﬁcient condition for adequate cryoprotection:adiffraction test of the cryobuffer alone is the best initial strategy.the mother liquor with cryoprotectant agent,rather than byreplacing the water in it.The dilution method,although moreconvenient,lowers the concentration of the components of themother liquor,and it is thus not surprising that the crystalsoften do not survive the experience.In cases where difﬁculty is experienced in ﬁnding suitablecryoconditions,the effects of temperature and osmotic shockshould be investigated.For instance,a 277K soak and/or insitu serial transfer could be tried,or more exotic cryoprotec-tants such as mixtures of light and heavier sugars could beused,e.g.15%trehalose +15%sucrose is particularly good forsalt-based crystal buffers.Also mixtures of different cryo-protectant agents have been used,or a cryobuffer followed byimmersion in oil (Kwong &Lui,1999).The best scenario is when the crystal mother liquor already contains a high enough concentration of cryoprotectant agent for ﬂash-cooling so that no more need be added.The crystal can then be ﬁshed directly from the mother liquor for cooling.There are now several commercial crystallization screens available in which the solutions are already fully cryoprotected,and this is an increasing trend.It is believed that the optimum cryobuffer for a particular crystal species is the one which contracts on cooling by the same or similar propor-tion to the crystal lattice,so that the minimum of disruption to the crystal order will be inﬂicted (Kriminski et al.,2002).2.2.EquipmentSome equipment and instruction in its use is necessary before starting to ﬂash-cool crystals:a reliable cryostat deli-vering a stream of gaseous nitrogen at around 100Æ1.0K with an outer sheath of room-temperature dry air or nitrogen,a magnet which ﬁts into the 3mm diameter hole in the top of a goniometer head,some top-hats (cryocaps),pins and rayon/nylon loops,cryovials,cryo-canes,cryosleeves to secure the vials on the canes for transport,and lastly but not least,handling tools.This equipment is well described in the literature,and available from several vendors.However,it is still far fromstandard,and this is well illustrated in Fig.4,where four different cryopin/cryocap arrangements are shown.Efforts by the SPINE collaboration to arrive at a concensus common design of cryopins for Europe have resulted in the develop-ment of the pin in Fig.4(d ).Recent developments have provided experimenters with two more robust alternatives to the commercially available rayon loops.These are the so-called ‘litho-loops’1which are etched from mylar ﬁlm and come in a range of circular and elliptical sizes,and the ‘micro-mounts’2(Thorne et al.,2003)which are fabricated from patterned and shaped thin poly-imide ﬁlm.Both of these represent signiﬁcant improvements,since they do not unwind with time,they are precisely the size they claim to be and they are more rigid than ﬁbre loops.Acta Cryst.(2006).D 62,32–47Garman and OwenCryocooling and radiation damage35Figure 3Flow diagram showing a possible strategy for optimizing the cryoprotocol.1Molecular Dimensions,.2MiTeGen,.As with the cryoprotection,there is a single common and easily rectiﬁed problem which often results in a failed experiment:the pins should all be a standard known length that will keep crystals in the centre of the cryostat nitrogen stream at all times,even when rotated on a removable arc (see below).Ideally all of the pins and cryocaps in the laboratory should conform to the standard length.This will save a great deal of aggravation in the long run.Before stream-cooling,a standard length pin should be pre-aligned on the goniometer before the crystals are opened and manipulated.2.3.Transfer of crystal to cryobufferIf the crystals require gentle surgery to remove ‘skin’or separate clusters before being mounted in a loop,acupuncture needles are very useful for this purpose since they are thin,slightly ﬂexible,and better than syringe needles as there is no capillary action to remove liquid and beach the crystals.The needles can be reused many times.For a crystal grown in the presence of an adequate concentration of cryo-agent,the transfer step is unnecessary and it can be ﬁshed straight out of the drop into the cryogen,thereby minimizing handling.As a general rule,the less a crystal is manipulated the better.Handling can cause damage to the crystal surface as well as dehydration,especially if the crystal is transferred in the loop through air several times.These traumas invariably result in an increase in the mosaicity of the crystal.There are broadly three ways to transfer a crystal from its growth drop into the cryobuffer:soaking,vapour-pressure equilibration and dialysis.For the soaking method used in the vast majority of cases,the crystal is transferred from its growth drop with a loop (or for fragile crystals,a suction device made from a pulled Pasteur pipette,a piece of ﬂexible tube and a small syringe)straight into the ﬁnal concentration of cryo-buffer.It is left there for anything from 1s (‘quick dip’)to minutes or days,depending on whether or not it is stable.A soak time of between 1and 3min is the general norm.Akinder strategy for the crystal is to transfer it ﬁrst into a small volume of mother liquor,and then to pipette a volume of the cryobuffer onto it,mix with the pipette tip,remove an equal volume and repeat.This method can also be used for serial increase of the cryobuffer concentration,starting with say 10%(v /v )added,mixed and removed twice,moving on to 20%and so on until the required concentration is reached.40%can be reached in about 3min in this way,and in a signiﬁcant number of cases this strategy has been found to produce better results (higher resolution diffraction and lower mosaicity)than quick dips or serial transfers where the crystal is moved between drops of increasing concentration.It involves a lot less crystal manipulation and a gentler gradient to the cryo-agent concentration increase (Garman,1999b ).For vapour-pressure equilibration,the cover slip with the hanging drop containing the crystals is sealed over a volume of cryobuffer in the bottom of a tray overnight,to allow equili-bration of the vapour components.The crystal is then given a quick soak as before.This method has been found to be less invasive by some researchers,who always use it (Gamblin,2005).In difﬁcult cases,the cryobuffer can be dialysed slowly into the crystal.This method is not often used,but can be some-thing to try for cases where a benign cryobuffer cannot be found,and the use of oil fails.The crystal is now ready to be ﬁshed out of the cryobuffer and ﬂash-cooled straight into liquid cryogen (which should be positioned next to the microscope)or in a gas stream (move the microscope as near to the stream as possible).It is a good idea to practice ﬁshing some non-essential crystals before trying the precious ones.In most cases,a size of loop matched to the crystal size should be chosen,as this will minimize the liquid volume (i.e.reduce X-ray scatter and thus maximize signal/noise)and small crystals are very hard to ‘catch’in a large loop as they just go through it.To ﬁsh,the liquid is ﬁrst agitated in order to lift the crystal from the bottom of the drop.If it is stuck,an acupuncture needle can be gently used to free it.The loop is brought up to the crystal from the side with its plane vertical,so that it encloses the crystal.The loop is then pulled upwards so that its edge breaks the surface tension of the drop.Leaving the plane of the loop perpendicular to the surface of the liquid minimizes the forces on the crystal and also minimizes the thickness of the liquid ﬁlm.The two pivotal times in this procedure are the time it takes to transfer the crystal from the cryobuffer to the cryogen,and the time the crystal takes to be cooled below the glass tran-sition at around 155K.For optimum results,both these times should be as short as is practicable.2.4.CryogenOut of all diffraction experiments reported in Acta Crys-tallographica Section D in 2002,60%of crystals were ﬂash-cooled in a nitrogen gas stream (~100K),37%in liquid nitrogen (77K),and 3%in liquid ethane or propane:experimentally there is no compelling evidence to favour the36Garman and OwenCryocooling and radiation damageActa Cryst.(2006).D 62,32–47Figure 4A gallery of some cryopins currently available.(a )Pins used at SPring-8,Japan (Ueno et al.,2004),(b )Oxford Cryosystems nickel pin,(c )Hampton Research brass pin on stainless base,and (d )SPINE (Structural Proteomics in Europe)pin machined for use with robotic sample changers and having a data matrix barcode on its base to allow tracking of a sample through the experimental structure-determination process.latter choice.Recently there has been a demise in propane use because of the extra handling precautions necessary and the safety difﬁculties of shipping it in Dewars.Nitrogen is the cryogen of choice since it is cheap,abundant and safe,and in its liquid form always takes the crystal solvent below the critical phase transition at around 155K (Weik,Kryger et al.,2001).Although other cryogens have been andare still being utilized,safety considerations and the problems of shipping ﬂammable gases mean that in practice nitrogen is the preferred option.With nitrogen,there are two possibi-lities:plunge cooling into a small Dewar of liquid,or stream freezing using a goniometer and cryostat.Although for particular crystal species there is anecdotal evidence that one method is preferred over the other,there has so far been no systematic study that allows a rational decision to be taken,so it is usually a question of which is more convenient.For stream-cooling there are some compelling reasons for blocking the gas stream with a piece of card or so called ‘cryo-shutter’while positioning the crystal on the goniometer,and then swiftly removing the card.This will:(i)avoid the crystal being dehydrated by dry nitrogen/air stream which surrounds the cryogen,(ii)avoid the crystal being waved in and out of stream while positioning it resulting in slow cooling which will give ice,and (iii)ensure that the crystal is cooled as fast as possible,so that vitriﬁcation is more likely.A recent theoretical study modelling cooling rates for the ﬂash-cooling of protein crystals in loops (Kriminski et al.,2003)concluded that the choice of cryogen was of relatively low importance to successful cryocooling.The crystal solvent content and solvent composition came top of the list,followed by the crystal size and shape (crystals with large surface to volume values cool faster and more uniformly than those with small S /V ),amount of residual liquid around the crystal (which should be minimized),the cooling method (liquid or stream cooling),choice of gas/liquid cryogen and lastly the relative speed between the cooling agent and the crystal.This theor-etical study has given some rationale to procedures which have been empirically determined over the last ten years.Note that proper safety precautions such as the wearing of goggles and gloves (but preferably not sandals)should always be followed when using cryogens.2.5.IceThe formation of ice in,on and around the crystal is an irritation which can negatively affect the experimental outcome (see Fig.5for some examples).There is absolutely no need for ice to be a problem.For a full trouble-shooting guide see Garman &Schneider (1997).Common causes of ice on and around the crystal are:poor experimental geometry,misaligned cryostat nozzle (Fig.5a ),nozzle too far from the experiment,the outer sheath of dry air/nitrogen ﬂow rate not being matched to the cryogen ﬂow rate (Fig.5b ),and a draughty environment.The stream of nitrogen must hit the crystal not the pin ﬁrst,and prior to the experi-ment,a cryostat alignment nozzle (Mitchell &Garman,1994)can be used to ensure that the cryostat is properly centred.The end of the nozzle should ideally be 5–8mm from the crystal.Shielding the crystal position from draughts helps ensure the crystal is kept at cryotemperatures the whole time.Ice which accumulates on the crystal during data collection (Fig.5c )can be removed using an acupuncture needle or an artist’s brush.Alternatively a small volume of liquid nitrogenActa Cryst.(2006).D 62,32–47Garman and OwenCryocooling and radiation damage37Figure 5Examples of different icing problems.(a )Ice on,within and around sample.Loop too far from end of cryostat nozzle (5–8mm recommended)and not correctly aligned in the cold nitrogen stream.After correction of alignment and distance,annealing could be tried and might rescue this sample.(b )Flow-rate of outside dry air/nitrogen stream not matched to inner cold nitrogen stream,so that turbulence on the gas interface draws in wet warm air from the room.Moisture from the air drops out giving a cylindrical wall of frost round the sample.Adjustment of the dry air/nitrogen ﬂow will clear this and for this sample,a data set was subsequently successfully collected.(c )An ice blob deposited on a crystal during storage or transport.This can be cleared by brushing the sample with a small artist’s brush or pouring a small volume of liquid nitrogen over the loop (taking care not to crack the beamline camera lens if it is directly below the sample).。

Recent development of in silico molecular modeling for gas and

Available online at Recent development of in silico molecular modeling for gas and liquid separations in metal–organic frameworksJianwen JiangAs a new family of nanoporous materials,metal–organic frameworks(MOFs)are considered versatile materials for widespread applications.Majority of current studies in MOFs have been experimentally based,thus little fundamental guidance exists for the judicious screening and design of task-speciﬁc MOFs.With synergistic advances in mathematical methods,computational hardware and software,in silico molecular modeling has become an indispensable tool to unravel microscopic properties in MOFs that are otherwise experimentally inaccessible or difﬁcult to obtain.In this article,the recent development of molecular modeling is critically highlighted for gas and liquid separations in MOFs.Bottom-up strategies have been proposed for gas separation in MOFs,particularly CO2capture.Meanwhile, interest for liquid separation in MOFs is growing and modeling is expected to provide in-depth mechanistic understanding. Despite considerable achievements,substantial challenges and new opportunities are foreseeable in more practical modeling endeavors for economically viable separationsin MOFs.AddressDepartment of Chemical and Biomolecular Engineering,National University of Singapore,117576,SingaporeCorresponding author:Jiang,Jianwen(chejj@.sg)Current Opinion in Chemical Engineering2012,1:138–144This review comes from a themed issue onNanotechnologyEdited by Hua Chun ZengAvailable online23rd December20112211-3398/$–see front matter#2011Elsevier Ltd.All rights reserved.DOI10.1016/j.coche.2011.11.002IntroductionDuring the past decade,metal–organic frameworks (MOFs)have emerged as a new family of nanoporous materials[1,2].In remarkable contrast to traditional inor-ganic zeolites,MOFs can be synthesized from various inorganic clusters and organic linkers,thus possess a wide range of surface area and pore size.More fascinatingly, the judicious selection of building blocks allows the pore volume and functionality to be tailored in a rational manner.With such salient features,MOFs are considered versatile materials for widespread potential applications [3,4]as illustrated in Figure1.Indeed,MOFs have been identiﬁed as a topical area in materials science and technology because of their implications for global and national economies[5].To date,thousands of MOFs have been synthesized in this vibrantﬁeld and several(Cu-BTC,ZIF-8,MIL-53,etc.) are commercially available under the trade name Basoli-te TM[6].However,massive research efforts on MOFs have been primarily based on experiments.It is impractical to search for task-speciﬁc MOFs by trial-and-error from inﬁnitely large number of possible candidates.Therefore, quantitative guidelines are desired for the high-throughput screening of enormous MOFs and the rational design of new MOFs towards practical applications.In this context, clear and deep microscopic understanding from a molecu-lar level is indispensable.With synergistic advances in mathematical methods,computational hardware and soft-ware,in silico molecular modeling has played an increas-ingly important role in unraveling microscopic properties in MOFs[7 ,8 ,9 ].Sophisticated modeling and simu-lation provide molecular insights that are experimentally intractable,if not impossible,thus elucidate underlying physics from bottom-up.Among many potential appli-cations of MOFs,separations are of central importance in chemical industry and have been actively investigated [10].In this article,the recent development of molecular modeling is critically highlighted for both gas and liquid separations in MOFs,and the foreseeable challenges and opportunities are discussed.Gas separationThe overwhelming majority of studies for gas separation in MOFs have been focused on CO2capture.This is because the combustion of fossil fuels produces a huge quantity of CO2emissions into the atmosphere.Carbon capture and sequestration is crucial to environmental protection and sustainable economy.As an essential pre-requisite,CO2has to be captured fromﬂue gas/ shifted syngas in post-/pre-combustion processes. Another important gas separation involving CO2is puri-ﬁcation of natural gas,in which impurities such as CO2 need to be separated to enhance calorie content.MOF adsorbentsMost synthesized MOFs are crystallites and tested as adsorbents for gas separation.Several reviews have sum-marized numerous experimental studies for CO2capture in MOF adsorbents[11–13].Nevertheless,nearly all these experiments examined the adsorption of pure gases (e.g.CO2,N2,CH4,and H2)due to the formidable difﬁculty associated with mixtures.By contrast,simu-lation can be readily used for single or multi-componentsystems.Thus,quantitative understanding of mixture adsorption in MOFs has been obtained,to a large extent,from simulation studies.Several bottom-up strategies as illustrated in Figure 2have been proposed to tune CO 2capture performance,for example,using speciﬁc MOFs with small pores,catenation,functionalization,ionic fra-meworks,exposed metals or metal doping.Yang and Zhong [14]simulated the adsorption of CO 2/CH 4/H 2mixture in two MOFs (IRMOF-1and Cu-BTC)and found pore size strongly affects separation efﬁciency.However,IRMOF-1and Cu-BTC do not possess iden-tical topology,leading to ambiguous interplay with the effect of pore size.In this regard,Babarao et al.[15]examined the separation of CO 2/CH 4mixture in isostruc-tural MOFs (Cu-BTC and PCN-60)and observed that the selectivity in Cu-BTC with small pores is nearly twice of that in PCN-60.This strategy of small pores is also reﬂected in framework catenation that can induce con-stricted pores and greater potential overlaps.For example,catenated IRMOF-13and PCN-6exhibit a larger selectivity for CO 2/CH 4mixture than non-cate-nated counterparts [15].An appealing strategy is to use ionic MOFs as demonstrated by Jiang and co-workers [16,17 ,18]for the separation of CO 2-containing mixtures.Simulation reveals that CO 2molecules are strongly adsorbed onto the ionic frameworks and nonframeworkions,and the predicted selectivity is signiﬁcantly higher than in neutral MOFs and many other nanoporous materials.On the other hand,Yazaydin et al.[19]screened a diverse set of 14MOFs for low-pressure CO 2capture from ﬂue gas combining simulation and experiment.The results show that M/DOBDC (M =Zn,Mg,Co or Ni)with high density of exposed metals strongly interact with CO 2.By physical and chemical doping,Xu et al.[20 ]estimated the separation of CO 2/CH 4mixtures in Li-modiﬁed MOF-5.Owing to the enhancement of electro-static potentials,adsorption selectivity was predicted to be much higher than in MOF-5.In a separate study,Lan et al.[21 ]simulated CO 2capture in covalent-organic frameworks doped by alkali,alkaline-earth and transition metals,and concluded that Li is the best surface modiﬁer for CO 2capture.The strategies outlined in Figure 2have been compre-hensively discussed [24 ,25 ].Two of them (ionic fra-meworks and metal doping)appear to be more efﬁcient to enhance CO 2capture.It should be noted that these strategies also can tune the separation of other mixtures,for example,the selectivity of alkane isomers was found to be enhanced by framework catenation [26].In a recent perspective,Krishna and van Baten [27 ]highlighted the potency of simulation in screening of best MOFs for CO 2capture and hydrocarbon separation,and they furtherRecent development of in silico molecular modeling Jiang 139Figure 1Purification Toxics RemovalDrug DeliveryFuel Cell SystemsStorageStorage and SeparationCarbon SequestrationSensingMOPWidespread potential applications of MOFs (/ees6/clathrates/index.shtml ).compared MOFs against traditional zeolites with regard to separation characteristics.As an alternative to simulation,analytical theories have been developed for gas separation in MOFs.Liu et al.[28,29]proposed a density functional theory (DFT)in 3D-nanoconﬁned space.The theory was applied to adsorption and separation in 3D-MOFs with complex pore networks,whereas most DFT studies are limited in simple conﬁned geometries (e.g.slit and cylindrical pores).Good agree-ment was obtained between theoretical predictions,simu-lation and experimental data.Coudert et al.[30]developed the osmotic framework adsorbed solution theory (OFAST)in terms of a competition between host’s free energy and adsorption energy.This theory is based exclusively on pure-component adsorption and has the superior capability to describe ﬂexible MOFs.For illustration,the authors used the OFAST to examine the effect of breathing on separation of CO 2/CH 4mixtures in MIL-53.The modeling studies discussed above for gas separation in MOF adsorbents are primarily focused on adsorption selectivity.However,several other factors (e.g.working capacity,regenerability,etc.)should be included in prac-tice as discussed by Bae and Snurr [31 ].Another crucial issue is how moisture in gas mixtures would affect sep-aration performance?From systematical simulation stu-dies in various neutral and ionic MOFs,Jiang and coworkers observed four different intriguing effects ofH 2O on CO 2capture [25 ].It is also instructive to examine structural change in ﬂexible MOFs that might occur upon adsorption [32].The incorporation of ﬂexi-bility to simulate structural change would need a robust force ﬁeld.However,a general force ﬁeld is currently unavailable for MOFs and ﬁrst-principles modeling is expected to play a pivotal role [33 ].In addition,the chemical and thermal stability of MOFs are important for separation [34].A large number of MOFs are unstable in atmosphere or under moisture,which impedes their util-ization.Therefore,it is indispensable to develop molecu-lar guidelines for the design of stable MOFs.Nevertheless,unraveling what govern the stability of MOFs at a microscopic level is a challenge.MOF membranesCompared with adsorptive separation,membrane-based separation is considered to be energetically more efﬁ-cient,lower capital cost and larger separation capability.However,the fabrication of MOF membranes is a for-midable task [35].Only in recent years,have there been active experimental endeavors to explore MOF mem-branes for gas separation [36 ].Since both equilibrium and dynamic properties are required,simulation for gas separation in MOF mem-branes is more time-consuming than in MOF adsorbents.Nevertheless,a handful of simulation studies have been reported.Keskin and Sholl [37 ]examined the separation140NanotechnologyFigure 2functionalizationmetal dopingionic frameworksexposed metalssmall porescatenationBottom-up strategies to tune CO 2capture performance.The representative MOFs are from [15,17 ,20 ,22,23].performance of diverse MOFs for CO2/CH4and CO2/H2 mixtures.They found that all the MOFs examined exhi-bit unfavorably low CO2selectivities and mixture effects play a crucial role in determining the performance.By combining simulation and IR microscopy,Bux et al.[38] simulated ethene/ethane separation in ZIF-8membrane. They found that ethane adsorbs more strongly than ethene,but ethene diffuses faster;and the interplay results in a membrane permeation selectivity for ethene. Krishna and van Baten[27 ]underlined the advantages of using simulation tools in the screening of MOF mem-branes for CO2capture.Along with considerable interest in MOF membranes, MOF-based composite membranes have received increasing attention for gas separation.In this emerging area,a handful of experiments have been conducted[39], but modeling studies are ing atomistic simulation and continuum model,Keskin and Sholl[40]attempted to select MOF/polymer membranes for high-perform-ance gas separation.A highly selective MOF was ident-iﬁed and predicted to enhance the performance of Matrimid and other polymers for CO2/CH4separation. Chen et al.[41]proposed a composite with ionic liquid (IL)supported on IRMOF-1.The simulation reveals that ions in the composite act as favorable sites for CO2adsorption,and the selectivity for CO2/N2mixture is higher than in neat IL,IRMOF-1and many other supported IL membranes.It is worthwhile to note that defects and inter-crystalline interstices usually exist in synthesized MOF membranes. Nevertheless,most simulation studies use perfect and rigid models for MOF membranes.How to incorporate defects and interstices into practical modeling is challenging.On the other hand,theﬂexibility of MOF structures may have a larger inﬂuence in membrane separation than adsorbent separation[36 ],and should be implemented as well into modeling.Another essential issue is the mech-anical properties of MOFs[42].The high pressure exerted for membrane separation may distort MOF structures and deteriorate performance.It is thus crucial to quantitatively understand how pressure affects pore geometries and framework dimensionalities.For MOF-based composite membranes,microscopic insights into the interactions between MOF and other species(e.g.polymer or ionic liquid)are strikingly important and fundamental studies at a molecular level are desired.Liquid separationWhile gas separation in MOFs has been extensively investigated,endeavors for liquid separation are lagged behind[43 ].A recent trend has been to explore the use of MOF adsorbents and membranes for liquid separation. By combining chromatographic and breakthrough exper-iments,Alaerts et al.determined the adsorption and separation of ortho-substituted alkylaromatics(xylenes, ethylbenzene,ethyltoluenes and cymenes)in a column packed with MIL-53crystallites[44].Jin and coworkers tested the separation of water/organics mixtures in MIL-53membrane and observed a high selectivity for water removal from ethyl acetate solution[45].Simulation for liquid separation in MOFs is scarce owing to the signiﬁcant amount of computational time required to sample liquid phase.Consequently,the microscopic understanding of liquid separation in MOFs is far from complete.To the best of our knowledge,only two simu-lation studies have been reported in this area,one for water desalination and the other for biofuel puriﬁcation. Recent development of in silico molecular modeling Jiang141Figure3Selectivities of biofuel in Na-rho-ZMOF and Zn4O(bdc)(bpz)2by pervaporation[47 ].Speciﬁcally,Hu et al.[46]performed simulation on the desalination of NaCl aqueous solution through a ZIF-8 membrane by reverse osmosis.Because of the sieving effect of small apertures in ZIF-8,Na+and ClÀions could not transport through ZIF-8membrane and water desa-lination was observed.Theﬂux of water permeating the membrane was found to scale linearly with external pressure.In a separate study,Nalaparaju et al.[47 ] examined hydrophilic Na-rho-ZMOF and hydrophobic Zn4O(bdc)(bpz)2for biofuel puriﬁcation.The selectiv-ities between water and ethanol in the two MOFs are largely determined by adsorption behavior.As indicated in Figure3,Na-rho-ZMOF is preferable to remove water, whereas Zn4O(bdc)(bpz)2is promising to enrich ethanol. The simulation provides molecular guidelines for the selection of appropriate MOFs towards efﬁcient biofuel puriﬁcation.Currently,modeling for liquid separation in MOFs is very limited.With increasing demands for clean water,liquid fuels and other liquid-based applications,more efforts are expected in order to provide deep molecular insights.A pre-requisite for liquid separation is that the MOFs used should be stable in water or other liquids[48],it is crucial to understand what factors govern the stability of MOFs, which would allow to produce stable MOFs for liquid separation.ConclusionAs a burgeoningﬁeld,research activities in MOFs are rather hectic.In addition to enormous experimental stu-dies,we have witnessed the recent development of in silico molecular modeling for MOFs.Microscopic under-standing has been achieved for gas separation particularly CO2capture in MOFs,and bottom-up strategies have been proposed to enhance separation efﬁciency.How-ever,liquid separation in MOFs remains largely unex-plored at a molecular level and more endeavors are desired towards this end.It is obvious that current molecular modeling for separ-ations using MOFs is still in an infant stage.As discussed above,substantial challenges are foreseen for more prac-tical modeling and precise description.A number of issues should be considered in future modeling,such as the stability and mechanical properties of MOFs, structuralﬂexibility,material regenerability,and effect of moisture(in gas separation).These challenges provide new opportunities for modeling studies to unravel in-depth microscopic insights and thus provide quantitative guidelines on the rational screening and design of novel MOFs.Furthermore,for energy-efﬁcient and cost-effec-tive separations,process requirements are essential to be integrated with material properties at a system level.In this context,molecular modeling,process optimization, as well as material synthesis,should be synergized holi-stically towards the development of best MOFs for economically viable separations and other practical appli-cations.AcknowledgementsThe author gratefully acknowledges the National University of Singapore, the Singapore National Research Foundation,and the Ministry of Education of Singapore for support.References and recommended readingPapers of particular interest,published within the period of review, have been highlighted as:of special interestof outstanding interest1.Yaghi OM,O’Keefe M,Ockwig NW,Chae HK,Eddaoudi M,Kim J:Reticular synthesis and design of new materials.Nature2003, 423:705-714.2.Long JR,Yaghi OM:The pervasive chemistry of metal–organicframeworks.Chem Soc Rev2009,38:1213-1214.3.MacGillivray LR(Ed):Metal–Organic Frameworks:Design andApplication.Hoboken,New Jersey:John Wiley&Sons,Inc.;2010.4.Farrusseng D(Ed):Metal–Organic Frameworks:Applications fromCatalysis to Gas Storage.Weinheim,Germany:Wiley-VCH;2011.5.Adams J,Pendlebury D:Global Research Report:MaterialsScience and Technology.Leeds,UK:Thomson Reuters;2011. 6.Czaja AU,Trukhan N,Muller U:Industrial applications of metal–organic frameworks.Chem Soc Rev2009,38:1284-1293.7.Keskin S,Liu J,Rankin RB,Johnson JK,Sholl DS:Progress,opportunities,and challenges for applying atomically detailed modeling to molecular adsorption and transport in metal–organic framework materials.Ind Eng Chem Res2009,48:2355-2371.This article reviews the applications of atomically detailed modeling for MOFs.Quantum mechanical calculations are used to examine structural and electronic properties,while molecular modeling calculations are used to study adsorption and diffusion in MOFs.8.DU¨ren T,Bae YS,Snurr RQ:Using molecular simulation tocharacterise metal–organic frameworks for adsorptionapplications.Chem Soc Rev2009,38:1203-1212.This review gives an overview of how molecular simulation can be used to characterize MOFs for gas adsorption,and how molecular insights can be combined to develop design principles for speciﬁc applications.9.Jiang JW,Babarao R,Hu ZQ:Molecular simulations for energy, environmental and pharmaceutical applications of nanoporous materials:from zeolites,metal–organic frameworks to protein crystals.Chem Soc Rev2011,40:3599-3612.This review summarizes the recent simulation studies for energy,envir-onmental and pharmaceutical applications of nanoporous materials ran-ging from zeolites,MOFs to protein crystals with increasing degree of complexity in building blocks.Major challenges in future simulation exploration are discussed.10.Li JR,Sculley J,Zhou HC:Metal–organic frameworks forseparations.Chem Rev2012,112,doi:10.1021/cr200190s,inpress.11.Keskin S,van Heest TM,Sholl DS:Can metal–organicframework materials play a useful role in large-scale carbon dioxide separations?ChemSusChem2010,3:879-891.12.Fe´rey G,Serre C,Devic T,Maurin G,Jobic H,Llewellyn PL,Weireld GD,Vimont A,Daturi M,Chang JS:Why hybrid porous solids capture greenhouse gases?Chem Soc Rev2011,40:550-562.13.Li JR,Ma YG,McCarthy MC,Sculley J,Yu JM,Jeong HK,Balbuena PB,Zhou HC:Carbon dioxide capture-related gasadsorption and separation in metal–organic frameworks.Coord Chem Rev2011,255:1791-1823.14.Yang QY,Zhong CL:Molecular simulation of CO2/CH4/H2mixture adsorption in metal–organic frameworks.J Phys Chem B2006,110:17776-17783.142Nanotechnology15.Babarao R,Jiang JW,Sandler SI:Adsorptive separation of CO2/CH4mixture in metal–exposed,catenated and charged metal–organic frameworks:insight from molecular simulation.Langmuir2009,25:5239-5247.16.Jiang JW:Charged soc metal–organic framework for high-efﬁcacy H2adsorption and syngas puriﬁcation:atomisticsimulation study.AIChE J2009,55:2422-2432.17. Babarao R,Jiang JW:Unprecedentedly high selective adsorption of gas mixtures in rho zeolite-like metal–organic framework:a molecular simulation study.J Am Chem Soc 2009,131:11417-11425.A simulation study is reported for the separation of CO2-containingmixtures in rho zeolite-like MOF(ZMOF)with anionic framework.Fortheﬁrst time,this study characterizes nonframework Na+ions,examines gas separation in ionic ZMOF,and reveals that rho-ZMOF is a promisingcandidate for CO2capture.18.Babarao R,Eddaoudi M,Jiang JW:Highly porous ionic rhtmetal–organic framework for H2and CO2storage andngmuir2010,26:11196-11203.19.Yazaydin AO,Snurr RQ,Park TH,Koh K,Liu J,LeVan MD,Benin AI,Jakubczak P,Lanuza M,Galloway DB et al.:Screeningof MOFs for CO2capture fromﬂue gas using a combinedexperimental and modeling approach.J Am Chem Soc2009,131:18198-18199.20. Xu Q,Liu DH,Yang QY,Zhong CL,Mi JG:Li-modiﬁed metal–organic frameworks for CO2/CH4separation.J Mater Chem 2010,20:706-714.The separation of CO2/CH4mixtures is simulated in Li-modiﬁed MOF-5. The selectivity is found to be greatly improved owing to the enhancement of electrostatic potential by Li doping.21. Lan JH,Cao DP,Wang WC,Smit B:Doping of alkali,alkaline-earth,and transition metals in covalent-organic frameworks for enhancing CO2capture byﬁrst-principles calculations and molecular simulations.ACS Nano2010,4:4225-4237.This study examines the doping of a series of alkali(Li,Na,and K), alkaline-earth(Be,Mg,and Ca),and transition(Sc and Ti)metals in covalent-organic frameworks,and the effects of the doped metals on CO2capture.22.Dietzel PDC,Johnsen RE,Fjellvag H,Bordiga S,Groppo E,Chavan S,Blom R:Adsorption properties and structure of CO2 adsorbed on open coordination sites of metal–organicframework Ni2(dhtp)from gas adsorption.IR spectroscopyand X-ray diffraction.Chem Commun2008,44:5125-5127.23.Babarao R,Dai S,Jiang DE:Functionalizing porous aromaticframeworks with polar organic groups for high-capacity and selective CO2separation:a molecular simulation study.Langmuir2011,27:3451-3460.24. Liu DH,Zhong CL:Understanding gas separation in metal–organic frameworks.J Mater Chem2010,20:10308-10318.This feature article summarizes the recent advances of computer model-ing on gas separation in MOFs and demonstrates how computer model-ing can help to understand the separation characteristics of MOFs.Several strategies are proposed to improve the separation efﬁciency of MOFs.25. Jiang JW:Metal–organic frameworks for CO2capture:what are learned from molecular simulations.In Coordination Polymers and Metal Organic Frameworks.Edited by OO L,Ramı´rez LD.Nova Science Publishers;2011.In this book chapter,recent simulation studies are summarized for CO2 capture in MOFs.A number of strategies are discussed towards improv-ing capture performance.In addition,the effects of moisture in various MOFs on CO2adsorption and separation are presented.26.Babarao R,Tong YH,Jiang JW:Molecular insight intoadsorption and diffusion of alkane isomer mixtures in metal–organic frameworks.J Phys Chem B2009,113:9129-9136.27. Krishna R,van Baten JM:In silico screening of metal–organic frameworks in separation applications.Phys Chem Chem Phys 2011,13:10510-10593.This perspective highlights the potency of molecular simulation in deter-mining the best MOF for a given separation task.A variety of metrics that quantify separation performance such as adsorption selectivity,working capacity,diffusion selectivity and membrane permeability are determined by simulation.28.Liu Y,Liu HL,Hu Y,Jiang JW:Development of a densityfunctional theory in three-dimensional nanoconﬁned space:H2storage in metal–organic frameworks.J Phys Chem B2009, 113:12326-12331.29.Liu Y,Liu HL,Hu Y,Jiang JW:Density functional theory foradsorption of gas mixtures in metal–organic frameworks.J Phys Chem B2010,114:2820-2827.30.Coudert FX,Mellot-Draznieks C,Fuchs AH,Boutin A:Predictionof breathing and gate-opening transitions upon binary mixture adsorption in metal–organic frameworks.J Am Chem Soc2009,131:11329-11331.31.Bae YS,Snurr RQ:Development and evaluation of porousmaterials for carbon dioxide separation and capture.AngewChem Int Ed2011,50:11586-11596.The question of how a large number of MOFs can be quickly evaluated for CO2separation is addressed.Five adsorbent evaluation criteria are described and used to assess over40MOFs for their potential in CO2 separation processes for natural gas puriﬁcation,landﬁll gas separation, and CO2capture from power-plantﬂue gas.32.Horike S,Shimomura S,Kitagawa S:Soft porous crystals.NatChem2009,1:695-704.33.Taﬁpolsky M,Amirjalayer S,Schmid R:Atomistic theoreticalmodels for nanoporous hybrid materials.MicroporousMesoporous Mater2010,129:304-318.Available atomistic theoretical models are overviewed for the new class of functional porous hybrid materials such as MOFs and COFs.The current status of both periodic and non-periodic quantum mechanic,as well as molecular mechanic models are discussed.34.Kang IJ,Khan NA,Haque E,Jhung SH:Chemical and thermalstability of isotypic metal–organic frameworks.Chem Eur J2011,17:6437-6442.35.Shekhah O,Liu J,Fischer RA,Woll C:MOF thinﬁlms:existingand future applications.Chem Soc Rev2011,40:1081-1106. 36.Caro J:Are MOF membranes better in gas separation thanthose made of zeolites.Curr Opin Chem Eng2011,1:77-83. MOF membranes developed and tested for gas separation during the past5years have been reviewed.The structuralﬂexibility of MOFs prevents a sharp molecular sieving effect.Mixed-matrix membranes containing MOFs are predicted for the near future.37.Keskin S,Sholl DS:Efﬁcient methods for screening of metalorganic framework membranes for gas separations usingatomically detailed ngmuir2009,25:11786-11795. An efﬁcient approximate method is introduced to screen MOF mem-branes for gas separation with a connection between mixture adsorption and mixture self-diffusion properties.The method is applied to MOF membranes with chemical diversity for light gas separation.38.Bux H,Chmelik C,Krishna R,Caro J:Ethene/ethane separationby ZIF-8membrane:molecular correlation of permeation,adsorption,diffusion.J Membr Sci2011,369:284-289.39.Vinh-Thang H,Kaliaguine S:MOF-based mixed-matrix-membranes for industrial applications.In CoordinationPolymers and Metal Organic Frameworks.Edited by Ortiz OL,Ramı´rez LD.Nova Science Publishers;2011.40.Keskin S,Sholl DS:Selecting metal organic frameworks asenabling materials in mixed matrix membranes for highefﬁciency natural gas puriﬁcation.Energy Environ Sci2010,3:343-351.41.Chen YF,Hu ZQ,Gupta KM,Jiang JW:Ionic liquid/metal–organicframework composite for CO2capture:a computationalinvestigation.J Phys Chem C2011,115:21736-21742.42.Tan JC,Cheetham AK:Mechanical properties of hybridinorganic-organic framework materials:establishingfundamental structure–property relationships.Chem Soc Rev 2011,40:1059-1080.43.Cychosz KA,Ahmad R,Matzger AJ:Liquid phase separation by crystalline microporous coordination polymers.Chem Sci2010,1:293-302.This perspective details the experimental studies reported on liquid-phase separation using microporous coordination polymers(MCPs).Guest mole-cules examined include those as small as water to large organic dyes.In many cases,MCPs outperform zeolites and activated carbons in both kinetics and efﬁciency.Recent development of in silico molecular modeling Jiang143。

英文化学资料 Aluminium and Titanium powerpoint

Extraction
Unlike iron, aluminium and titanium cannot be extracted from their oxides by reduction with carbon because:
Aluminium is more reactive than carbon, so the reaction does not work. Titanium forms titanium carbide with carbon, which makes the metal brittle.
Aluminium and Titanium
These are two metals with a low density which means they are lightweight for their size.
Aluminium is used for aircraft, trains, overhead power cables, saucepans and cooking foil.
Aluminium is mined in huge scales as bauxite.
• In order to isolate pure aluminium, impurities must be removed from the bauxite.
• This is done by the Bayer process, which involves treatment with sodium hydroxide solution, followed by purification using electrolysis.
Summary
• Aluminium and Titanium both have a low density which means they are lightweight for their size. • They resist corrosion. • They cannot be extracted by reduction. • Extraction is expensive because there are several stages involved and the processes require a lot of eneated using the Kroll method.

南美洲英语作文

South America is a continent of immense diversity,rich in natural beauty,vibrant cultures,and a fascinating history.When writing an essay about South America,one can explore various aspects such as geography,history,culture,and the environment.Geography and Natural WondersSouth America is home to some of the worlds most breathtaking landscapes.The Andes mountain range stretches the length of the continent,offering a dramatic backdrop to many countries.The Amazon Rainforest,often referred to as the lungs of the Earth,is the largest tropical rainforest in the world,teeming with biodiversity.The essay could describe the unique ecosystems found in places like the Galápagos Islands,known for their unique wildlife and role in the development of Charles Darwins theory of evolution.Historical SignificanceThe history of South America is marked by the rise and fall of great civilizations,such as the Inca Empire,which was the largest empire in preColumbian America.The essay could delve into the Incas advanced architectural feats,like the city of Machu Picchu, which is perched high in the Andes and offers a glimpse into the past.Additionally,the continents history with European colonization and the subsequent impact on indigenous populations could be discussed.Cultural DiversitySouth America is a melting pot of cultures,with each country having its own unique traditions,music,and cuisine.The essay could explore the rich tapestry of indigenous, European,African,and Asian influences that have shaped the continents cultural identity. From the passionate rhythms of the tango in Argentina to the vibrant festivals of Carnival in Brazil,the continent offers a wealth of cultural experiences.Economic and Social ChallengesDespite its natural wealth,South America faces significant economic and social challenges.The essay could address issues such as income inequality,political instability, and the struggle for sustainable development.It could also discuss how these challenges are being addressed through international cooperation and local initiatives. Environmental ConcernsThe environment is a critical topic in South America,given the continents vast naturalresources and the threats they face from deforestation,mining,and climate change.The essay could highlight the efforts being made to protect the Amazon Rainforest and other ecosystems,as well as the role of indigenous communities in conservation.ConclusionIn conclusion,an essay on South America would ideally capture the essence of this vibrant continent,exploring its natural wonders,historical depth,cultural richness,and the challenges it faces.By providing a comprehensive view,the essay can offer readers a deeper understanding of the complexities and beauty of South America.。

托特的翡翠石板(非翠玉录)

亚特兰蒂斯岛- 序文The history of the tablets translated in the following pages is strange and beyond the belief of modern scientists. Their antiquity is stupendous, dating back some 36,000 years B.C. The writer is Thoth, an Atlantean Priest-King, who founded a colony in ancient Egypt after the sinking of the mother country.在接下来被翻译的石板历史很令人奇怪及超出现代科学家信念。

它们的古老是惊人的,追溯到西元前36,000年。

作者是托特,一个亚特兰蒂斯岛祭司, 在祖国沉没之后在古埃及建立了殖民地。

He was the builder of the Great Pyramid of Giza, erroneously attributed to Cheops. In it he incorporated his knowledge of the ancient wisdom and also securely secreted records and instruments of ancient Atlantis.他是吉萨大金字塔的建造者, 错误的归到基奥普斯身上。

在它里面他形成了他的古代智慧知识以及安全地隐藏了古代亚特兰蒂斯岛记录和工具。

For some 16,000 years, he ruled the ancient race of Egypt, from approximately 52,000 B.C. to 36,000 B.C. At that time, the ancient barbarous race among which he and his followers had settled had been raised to a high degree of civilization.大约为16,000年，他那时从大约西元前52,000 年到大约西元前36,000年管理古埃及人，在古代野蛮民族中他和他的信徒已经定居下来已经发展了一个很高的文明。

F__high-english_高级职称英语高级英语

page 30（一）1.There is an increase增长in demand需求for all kinds of consumer goods消费品in every part of our country.2.We also realized认识到the growing need and necessity to industrialize使……工业化certain sectors of the economy 经济的部门.3.They are deeply convinced确信of the correctness of this policy政策的正确性and firmly determined坚决to pursue从事,继续it.4.We seek a deep-rooted understanding理解through the multiplication 增长of our economic, cultural, scientific, technical and human ties 人类关系.5.Rockets have found applications应用for the exploration探险of the universe宇宙.6. If we were ignorant of the atom对原子无知, it would be impossible 不可能for us to study nuclear physics核子物理.7.Electronic control techniques电控制技术can be designed to take full advantage of最大限度利用quick response反应inherent内在的in a gas turbine propulsion system气轮推进系统.8.His treatise论文aims at对准discussing the properties of the newly discovered elements新发现元素的特征.9.These pumps are featured具有……的特征by their simple operation 简单操作, easy maintenance维护, low power consumption能量消耗and durable service持久的服务.10.No one has ever seen a single atom or molecule单个原子或分子even with the most powerful microscope显微镜.(二)1.Cargo insurance货物保险is to protect保护the trade from losses损失that many dangers may cause引起.2.English is the language of commerce商业and second language ofmany countries which formerly以前had French or German in that position.3.Reading makes a full man; conference讨论 a ready man; andwriting an exact man.读书使人充实….4.The problem of acquiring获得, tracking跟踪and discriminating识别all the targets目标needs the full capability能力of the phased array radar定向的布置雷达.5.The principal function主要功能that may be performed by vacuumtubes真空管are rectification, amplification, oscillation, modulation and detection.整流、放大、震荡、调制、检波6.A key键is a piece inserted插入between a shaft and a hub轴和木片to prevent relative rotation防止相关的旋转.7.My work, my family, my friends were more than enough to fill mytime足以占用我全部的时间.8.The former前者is more common in adult成人普遍, the latter后者in children.9.Tighter tolerances公差are possible, but with lower yield生产andgreat cost成本.10.T his experience经验has been obtained获得in the realm领域offar less远不stringent operation requirements严格的操作要求and conditions, particularly特别in regard to power dissipation消耗.(三)1.The experience经验has told us that this kind of material is ofgood quality质量.2.The products should be sampled抽样to check检查theirquality before they leave the factory.3.They have fitted适应themselves to the land and the rhythm节奏of its seasons.水土和季节4.Physics is the study of heat, sound, magnetism磁, electricity,light, the properties of matter物质的特性and what it is composed组成of.5.We have solved解决the problem and have arrived at the sameconclusion结论as they arrived at.6.Edison and his men were very much excited激动as the firstelectric light电灯sent out its glow光.7.It is to increase the friction增加摩擦that the surfaces ofautomobile tyres汽车轮胎are made with projections突起的点点块块.8.When we want to move a body of great mass, we must apply agreat force用大力.9.The high temperature高温and high rotational speeds转速atwhich the gas turbine气轮operates present difficulties in manufacture加工制造.10.P ractically all substances expand when heated and contract whencooled.page 37?1. What I was learning我所学到的was what Dick Darman later saidat Ben’s goodbye party two years later.2. That the British and American governments政府remainedunperturbed泰然自若was due in great part to a unique service独特的服务provided by the British Broadcasting Corporation被英国广播公司提供的.3. Our position立场has always been that such intervention干涉istotally unjustified完全不公平的.4. I don’t think that he has at all weighed权衡the advantages ofchanging his job against the disadvantages改变工作的利弊.5. She told me that she would often spend a whole morning workingupon a single page在一页书上花一整上午.6. We knew that we never could find peace as long as we were filledwith hatred仇恨.7. I had heard you were coming, but we had no idea it would be thissoon.8. There is no question that the Soviet Union苏联will seek to gain寻求获利（捞得好处）from the instability不稳定.9. The 25-year teaching veteran老手says he was denied拒绝 apromotion and pay raise提职和提薪last year because he hadn’t published a sufficient number of research papers出版足够的研究论文.10. W hat America has lost美国人丧失的is the cocky骄傲自大, do-anything assurance确信of the 1950s.11. A nd it is not whether universities大学have produced valuable有价值的research and scholarship.12. W e should remember that the scientific developments科学发展inone field are closely related与—密切相关to the developments of the same time in other fields.13. I t has been said that in American, people think in terms of decades十年; in Europe, they think in terms of generations一代; in China, they think in terms of centuries.14. D on’t take for granted以为that it will be all plain sailing（固定：一帆风顺）.15.L egend传说has it that Da Yu was made emperor皇帝because ofhis success in controlling floods控制洪水.(二)1.There has never been a man around me我周围who wrote so manymemos回忆录.2.He whishes to write an article that will attract public attention吸引公众的主义to the matter.3.The sun emit发出a large amount of invisible rays看得见的光of anature similar to radio waves and light, which are electromagnetic waves电磁波.4.The melting point熔点of cast-iron of which the carbon content ishigher, is slower.含碳越高，熔点越低5.This factory produced machine tools机床to which precisioninstruments精密仪器were attached附加.6.Such people as they are will never do that sort of thing.7.China’s isolation孤立from the West was finally broken in the 19thcentury, when it was invaded from the sea来自海上的入侵.8.The whole staff人员consisted of包含about 250 doctors andnurses, nearly half of whom were women.9.The reason why John failed was his laziness懒惰.10.I would like to live in a place where trees are green all the year round.(三)1.When a giant radio-telescope巨型射电望远镜turns in on themessages sent from a rocket in place, a computer guides the turning of the telescope in the right direction.2.The drill may just miss错过the oil although it is near: on the otherhand, it may strike oil at a fairy high level很浅的地方.3.The oil used for this purpose用途must be of the correct thickness浓度: if it is too thin it will not give sufficient lubrication充分的润滑, and if it is too thick it will not reach all parts that must be lubricated.4.We do not read history simply of pleasure, but in order that we maydiscover the laws of politic growth and change发现政治---规律. 5.The more corporate staff abroad who can communicate交流well inEnglish the greater your trading opportunity（做）生意机会.6.As divorce rates离婚率in Asia are on the rise, moral education道德教育is getting more and more important.7.He knew nothing about the blue print蓝图until I told him.8.This material is no more elastic有弹性的than that one.9.Many centuries had passed before man learned to make fire.10.H e speaks quickly, the tone语调of his voice so arresting吸引人的that it sobers镇定（住了）everyone.Page 45(一)1.Current电流will not flow continually继续, since the circuit电路is broken by the insulating material绝缘材料.2.The working plan will be examined检查by a special committee特别委员会first.3.If the pressure压力in the closed vessel关着的（密闭的）容器isallowed to rise too high, the vessel will burst爆炸.4.Most of the questions have been settled解决satisfactorily满意地;only a few questions of second importance次要的remain to be discussed.5.Now so much has been published on all kinds of subjects that even aspecialist专家who devoted投入all his time to reading could not keep up with it.6.Therefore, when we are received with so much honor and so muchkindness in this great country, I believe that the People’s Republic of China is doing a very significant有意义的thing.7.Now fresh water淡水is becoming scarce奇缺, but more and moreis needed because of the increasing增长的number of people in the world.8.It is required必需that the machine should be maintained维护atregular intervals定期.9.It should be pointed out that this process过程is oxidation氧化.10.I t is generally recognized that the insulation resistance绝缘电阻ofa cable is inversely proportional反比例的to its length.(二)1.Such a poor state could not possibly have waged against发动战争its neighbor without backing后盾from other countries.2.Nothing in the world moves faster than light.3.All these metals are not good conductors.4.Not every minute difference微小的差异is noted注意.5.There is no material but will deform使变形more or less underthe action of force.6.They worked neither for fame名声nor for personal gains个人利益.7.The speed of light is too great to be measured测量with a simpleunit单位.8.Although he explained解释it to her, she was still completely atsea迷惑不解.9.We were kept in the dark蒙在鼓里（不知）as to future plans未来计划.10.J apan is the last country to invent radar发明雷达, but England.(三)1.Much more important than the element元素itself are some ofits compounds化合物.2.Of considerable interest is that many planets revolve旋转roundthe sun besides the earth.3.With the development of electrical engineering电机（气）工程,power can be transmitted over a long distance.4.Surrounding包围the earth is a layer层of air of great thickness.5.Between atoms there is enough space for them to move, andmove they do.6.Different metals do differ in their conductivity传导性.7.It is the power station电厂that supplies供应the motive power动力to the whole city.8.It was Newton who proved mathematically用数学证明that thepath of a planet must be an ellipse椭圆.9.It is only through a great deal of practice that we shall be able tooperate this machine tool.10.T he notion of energy能的概念thermodynamics热力学emphasizes强调.(四)1.If these stamps were genuine真实的, they would be worth a lotof money.2.If this bridge had been built of armoured concrete钢筋混凝土,its strength would have been much greater.3.If any country were in the same position that we are, they wouldbe making the same case with the same force and conviction确信.4.The nation was on its knees跪着and, were nothing done, wouldsoon be prostrate降伏的.5.Without her advice建议, I would have failed.6.I suppose poor Marry is all broken up伤心透了. I would be inher case.7.If computers were not be used, our research work would bedifficult.8.How could he have operated the machine-tool操作机床if hehadn’t learned the technique技术some weeks ago?9.She wished she had stayed at home.10.I suppose想when I was a young man I should have done thesame fool thing.(五)ser激光, its creation being thought to be one of today’swonders, is nothing more than a light that differs from ordinary lights only in that it is many times more powerful and so can be applied in fields that no ordinary light or other substance has ever been able to get in.2.A good way of learning to make the sound of a new language isto use recordings which have pauses after each sentence giving you time to say what you have learnt before the next sentence comes.3.Automatic control which is known as automation is not limited tosuch operations as have some connection with the controlling or adjustment of individual machines or instruments, the system set up with automatic control being, in a wider sense, a long producing line which enables material to be fed from one end and the products to be turned out at the other with the whole process being controlled automatically.4.Those who have scrupulously studied the national statistics haveconcluded that there is nothing in them that would support the general belief that there has been some lessening of economic inequality in the United States in recent decades.5.China has always been a disciplined and cultured nation, and if itseemed to old China hands that it was not, it is likely that it was the disturbing influence of western materialism and amorality that corrupted the personality of the Chinese who were in contact with it, and who thus became, in essence, its victims.6.Galileo was the first to explain by this method that any fallingobject, whether it weighs little or much, gains speed at the same rate while it falls, and any ball thrown, whatever its size and speed, has the same pull from the earth bringing it down.7.Owing to the fact that electricity can be transmitted from where itis generated to where it is needed by means of power lines and transformers, large power stations can be built in remote placesfar from industrial centers or large cities, as is often the case with hydroelectric generating stations that are inseparable from water sources.8.There are several reasons why he no longer appears to be themagician the world press had made him out to be, an illusion which he failed to discourage because, as he would admit himself, he has a tendency toward megalomania.9.While the higher IMF (International Monetary Fund) estimatesmay be better yardsticks of economic progress, they have also aroused Third World concern that some hard-pressed developing nations may suddenly be seen as too well-off to receive needed World Bank loans.10.T here is just the same kind of difference between the mentaloperation of a man of science and those of an ordinary person, as there is between the operations and the methods of a baker or a butcher weighing out his goods in common scales, and the operations of a chemist in performing a difficult and complex analysis by means of his balance and finely graduated weights. Page 521.Doctors also say eating less fat will reduce the amount ofdangerous cholesterol in the blood. This cholesterol can stickto the wall of blood passages, blocking the flow of blood. Inthe arteries that carry blood to the heart muscle, suchblockages cause a heart attack. Instead, eat more foods low infat. This includes low-fat milk and dairy products, lean meats,poultry without the skin, and fish and shellfish. Experts alsosay cooking foods in olive oil and fish oil will help lowcholesterol. And they say it is best to steam, bake, roast orbroil foods, not to fry. They also say eating dried peas andbeans helps lower the amount of fat in the blood.Health experts also say we should eat more fruit and vegetables, and foods high in fibers such as whole grain breads and cereals and brown rice. Some fibers help lower levels of dangerous cholesterol. This would help reduce the danger of heart disease. Most experts agree that fiber also can protect against cancer. They are not sure how fiber does this. Some believe it helps the body to quickly remove fat that may cause cancer to develop.(2) Doctors say that emotions problem also can cause growthdisorders. A child may suddenly stop growing because ofstress, from being sick or perhaps from reaction to a familyproblem. Such a growth disorder is temporary. The child willstar growing again as suddenly as he stopped, just as soon asthe cause of stress is removed.Doctors also note that most growth hormone is produced during sleep. This means that a child with serious sleeping problems may not grow normally. However, normal growth would return once the sleeping problem is solved.Doctors say that some growth disorders are apparent at birth. Othersare not be noticed for years until the child falls behind normal growth rates. So growth experts urge parents to measure a child at least once every year. Children grow at different rates, of course. Most girls grow faster than boys, and they stop growing sooner. But generally a child grows five centimeters or more each year. They say parents should talk to a doctor if a child’s yearly growth falls below five centimeters.(3) The most important psychological discovery of this centuryis the discovery of the “self-image”. Whether we realize it ornot, each of us carries about with us a mental blueprint orpicture of ourselves. It may be vague and ill-defined to ourconscious gaze. In fact, it may not be consciouslyrecognizable at all. But it is there, complete down to the lastdetail. This self-image is our own conception of the “sort ofperson I am”. It has been built up from our own beliefs aboutourselves. But most of these beliefs about ourselves haveunconsciously been formed from our past experiences, oursuccesses and failures, our humiliations, our triumphs, andthe way other people have reacted to us, especially in earlychildhood. From all these we mentally construct a “self”, (ora picture of a self). Once an idea or a belief about ourselvesgoes into thi s picture it becomes “true”, as far as wepersonally are concerned. We do not question its validity,but proceed to act upon it just as if it were true.(4) Advertising has become a very specialized activity inmodern times. In the business world of today, supply isgreater than demand. There is great competition betweendifferent manufacturers of the same kind of product topersuade customers to buy their own particular brand. Theyalways have to remind the consumer of the name andqualities of their product. They do this by advertising. Themanufacturer advertises in the newspapers and on posters.He sometimes pays for songs about his product incommercial radio programs. He organizes competitions, withprizes for winners. He often advertises on local cinemas.Manufacturers often spend large sums of money onadvertisement. We buy a particular product because we thinkthat it is the best. We usually think so because of theadvertisements that say so. Some people never pause to askthemselves if the advertisements are telling the truth.(5) By and large, business can make profits only by producinggoods and services that people want to buy autos, houses,dry cleaning, dogfood. If there is no consumer who is willingand able to buy, the businessman is out of luck. Maybe thegovernment will temporarily come to his rescue with asubsidy, or maybe he can keep going by using up hisinvested capital. But over the long pull, it is the customerswho are willing and able to buy who direct production in aprivate-enterprise economy. Since consumer demand largelydirects production in a private-enterprise system, it isimportant to define “demand” accurately at the outset.“Demand” is the schedule of amounts of any product that buyers will purchase at different prices during the stated time period. This definition takes some explaining, since it obviously isn’t what the word means in every conversation.(6) In future trade the key development to watch is therelationship between the industrialized and the developing nations. Third World countries export their mineral deposits and tropical agricultural products, which bring them desired foreign exchange. Tourism has also been greatly responsible for the rapid development of some developing nations. Many Third World nations with high unemployment and low wages have seen an emigration of workers to the developed nations. Western Europe has received millions of such workers from Mediterranean countries. The developing nations profit when these workers bring their saving and their acquired technical skills back home. Many developing nations benefit when Western nations establish manufacturing in their countries to take advantage of cheap labor.International monetary cooperation will have a significant impact on future trade. If the IMF countries are not able to agree upon a new international monetary order in the years to come, international trade may become too risky for some companies to get involved in. If the IMF is unable to create sufficient international liquidity reserves in the future, there may not be enough liquidity to sustain growth in trade.(7) Just as Darwin discovered the law of development of organicnature, so Marx discovered the law of development of human history: the simple fact, hitherto concealed by an overgrowth of ideology, that mankind must first of all eat, drink, have shelter and clothing, before it can pursue politics, science, art, religion, etc., that therefore the production of the immediate material means of subsistence and consequently the degree of economic development attained by a given people or during a given epoch form the foundation upon which the state institutions, the legal conceptions, art, and even the ideas on religion, of the people concerned have been evolved, and in the light of which they must, therefore, be explained, instead of vice versa, as had hitherto been the case.But that is not all. Marx also discovered the special law of motion governing the present-day capitalist mode of production and the bourgeois society that this mode of production has created. The discovery of surplus value suddenly threw light on the problem, in trying to solve which all previous investigations, of both bourgeois economists and socialist critics, had been groping in the dark.(8) Science is the body of knowledge about nature thatrepresents the collective efforts, insights, findings, and wisdom of the human race. Science is not something new but had its beginning before recorded history when humans first discovered reoccurring relationships around them. Through careful observations of these relationships, they began to know nature and, because of nature’s dependability, found they could make predictions to enable some control over their surroundings.Science made its greatest headway in the sixteenth century when people began asking answerable questions about nature---when they began replacing superstition by a systematic search for order---when experiment in addition to logic was used to test ideas. Where people once tried to influence natural events with magic and supernatural forces, they now had science to guide them. Advance was slow, however, because of the powerful opposition to scientific methods and ideas.(9) The greatest of all the accomplishments of twentieth-centuryscience has been the discovery of human ignorance. We live, as never before, in puzzlement about nature, the universe, and ourselves most of all. It is a new experience for the species. A century ago, after the turbulence caused by Darwin and Wallace had subsided and the central idea of natural selection had been grasped and accepted, we thought we knew everything essential about evolution. In the eighteenth century there were no huge puzzles; human reason was all you needed in order to figure out the universe.And for most of the earlier centuries, the Church provided both the questions and answers, neatly packaged. Now, for the first time in human history, we are catching glimpses of our incomprehension. We can still make up stories to explain the world, as we always have, but now the stories have to be confirmed and reconfirmed by experiment. This is the scientific method, and once started on this line we can not turn back. We are obliged to grow up in skepticism, requiring proofs for every assertion about nature, and there is no way out except to move ahead and plug away, hoping for comprehension in the future but living in a condition of intellectual instability for the long time.(10) Transistors can be made with other materials. They areless costly, and produce less heat. But they also permit less electricity to pass through. These other transistors are made with what is called amorphous silicon. This material is not as pure as silicon crystals. It has tiny spaces between the atoms that limit the flow of electrical current.The American company---Energy Conversion Devices of Detroit-said it found ways to treat amorphous materials physically and chemically. These treatments sharply reduce the number of defects that block the flow of current. The company said it then was able to produce amorphous transistors. But theycost much less to make. They produce much less heat. And thinlayers, or films of amorphous silicon can be made in any size.This means it can be used to make electrical circuits or system aslarge as needed.(11) Experts say they now know that efforts to save specieswill be useless unless efforts are made to solve some humanproblems that help cause the destruction of wildlife and wildplaces. They saw wildlife is disappearing partly becauseexpanding human populations need more land, food andmaterials to live.This is why some new plans to save endangered species and their natural areas include economic development plans as well as ideas of protecting the environment. Scientists and other experts feel human needs must be met if wildlife and wild places are to be saved.One of these new plans is the “World Conservation Strategy”. Another is the American “Strategy for the Conservation of Biological Diversity in Developing Countries.” Both cal for programs that prov ide direct economic gains. The plans urge more studies of the ways many plants and animals can be used to provide food, clothing and housing. And they call for educating governments and citizens about policies that provide for development, while protecting the environment for present and future populations.International efforts to protect wildlife and wild places gain strength when they link such protection to economic progress.12Some scientists working on the question of extraterrestrial intelligence, myself among them, have attempted to estimate the number of advanced technical civilizations----defined operationally as societies capable of radio astronomy--- in the Milky Way Galaxy. Such estimates are little better than guesses. They require assigning numerical values to quantities such as the number and ages of stars; the abundance of planetary systems and the likelihood of the origin of life, which we know less well, and the probability of the evolution of intelligent life and the lifetime of technical civilizations, about which we know very little indeed.When we do the arithmetic, the sorts of numbers we come up with are, characteristically, around a million technical civilizations.A million civilizations is a breathtaking large number, and it is exhilarating to imagine the diversity, lifestyles and commerce of those million worlds. But the Milky Way Galaxy contains some 250 billion stars, and even with a million civilizations, less than one star in 200,000 would have a planet inhabited by an advanced civilization. Since we have little idea which stars are likely candidates, we will have to examine a very large number of them. Such considerations suggest that the quest forextraterrestrial intelligence may require a significant effort.13Reading is a pleasure of the mind, which means that it is a little like a sport: your eagerness and knowledge and quickness make you a good reader. Reading is fun, not because the writer is telling you something, but because it makes your mind work. Your own imagination works along with the author's or even goes beyond his. Your experience, compared with his, brings you to the same or different conclusions and your ideas develop as you understand his.Every book stands by itself, like a one-family house, but books in a library are like houses in a city. Although they are separate, together they all add up to something; they are connected with each other and with other cities. The same ideas, or related ones, turn up in different places; the human problems that repeat themselves in life repeat themselves in literature, but with different solutions according to different writings at different times.Reading can only be fun if you expect it to be. If you concentrate on books somebody tells you you "ought" to read, you probably won't have fun. But if you put down a book you don't like and try another till you find one that means something to you, and then relax with it, you will almost certainly have a good time.14We have entered the age of "thinking" machine. Fifteen to twenty years ago it was known in what direction certain formulas were to be found, but their calculation seemed impossible, as the exact solution of the problems would have required the total working lives of several hundred mathematicians. The scientists stood before an ocean of formulas, calculations and partial solutions, unable "to reach the shore on the other side". Here the electronic brains came to their help: if a mathematician could not solve equations with more than 12 unknowns, the electronic brain could easily solve equations with 50, 100 or 200 unknowns.Different branches of science and technology today are unable to function without "artificial brains": we have to solve problems for which the reactions of the human brain prove too slow. The electronic brain calculates a thousand times quicker, and more accurately than is possible for the human being. The solution of only a partial problem which would keep a mathematician busy for six months is completed by the electronic brain in seven minutes.15Petroleum is the largest source of liquid fuel, and, in spite of attempts to develop synthetic fuels, and the continued use of solid fuels, world consumption of petroleum products is about four times greater now than in 1940.。

钙生物利用率及其影响因素_王晓燕

综述作者简介王晓燕(1977~ ),女,新疆人,在读硕士研究生,主要研究方向为学生营养。

作者单位中国疾病预防控制中心营养与食品安全所,北京100050。

钙生物利用率及其影响因素王晓燕综述,马冠生审校文献标识码 B中图分类号 Q 582 Q 591.7 R 151.4 文章编号 1000 9817(2005)09 0793 03 关键词钙;生物利用度;因素分析,统计学钙是人体的重要组成成分,并在机体各种生理变化过程中起着重要的调节作用。

但是钙在人体内的生物利用是个复杂的过程,包括钙的摄入、吸收和排泄,以及吸收的钙被用以维持生理功能的程度。

本文就钙的生物利用率及其影响因素综述如下。

1 钙生物利用率的定义钙的生物利用率是反映在肠道内吸收后的钙,被机体用以维持正常生理功能和储备的程度[1]。

潜在的钙能被吸收的能力依赖食物以及肠道的吸收能力,而肠道对钙的吸收能力又受生理因素的影响,如钙的储留、激素的调节或者以前膳食钙的供应。

因此,潜在钙吸收就是在最有利的生理环境下钙的吸收值[2]。

被吸收的钙用于骨骼的结合,肾脏的排泄以及粪内源性钙损失。

肠道的吸收、生理因素尤其是激素,对于钙结合到骨骼起重要作用,而食物中钙的存在形式也可以影响吸收后的钙结合至骨骼的可能性。

钙的其他代谢产物主要通过肾脏排泄。

研究发现一些阴离子,如硫酸盐、氯、螯合剂、过量的蛋白质和钠使钙在肾脏的损失增加,并阻碍钙在骨骼的结合。

所以,钙的生物利用率可以定义为:膳食中的钙,能被肠道潜在吸收并用于维持生理功能,尤其是用于骨矿化或限制骨吸收的比率。

钙的生物利用包括钙的摄入、吸收、排泄这3个过程[2]。

目前广为学者接受的计算钙生物利用率的公式是[3]:生物利用率=[摄入-(粪钙-粪内源性钙)-(尿钙-尿内源性钙)]*B/摄入B=储留中的钙能用以机体构造和功能的程度吸收率=摄入-粪钙/摄入2 影响钙生物利用率的因素钙的生物利用包括钙的摄入、吸收、排泄这3个过程。

外文资料

Total concentrations and fractions of Cd, Cr, Pb, Cu, Ni and Zn in sewage sludge from municipal and industrial wastewater treatment plantsAbstractHeavy metals are one of the important factors that affect the final disposal of sewage sludge. In this paper, the metal mobility and bioavailability of heavy metals in sewage sludge were studied by using Community Bureau of Reference (BCR) sequential extraction procedure to get more information for the reasonable disposal of sludge. Sewage sludge was collected from five municipal wastewater treatment plants and three industrial wastewater treatment plants. The sludge was examined for and the total concentrations and different chemical fractions of Cd, Cr, Pb, Cu, Ni and Zn. The total metal concentrations of heavy metals in sludge varied greatly. The contents of Zn and Cu were the highest, followed by then Cr, Ni and Pb and the content of Cd was the least. There was no significant difference in total metal concentration between municipal and industrial wastewater treatment plants. Fractions extracted by the BCR sequential procedure were acid soluble/exchangeable, reducible and oxidizable fraction. Sludge pH was found to have profound effect on the chemical fractions of heavy metals. Acidic sludges had higher proportion of the acid soluble/exchangeable fractions than in neutral sludge. In neutral sludges, Pb and Cr were principally distributed in between the oxidizable fraction and the residual fraction; Cu was in the oxidizable fraction; Cd mainly in the residual fraction in municipal wastewater treatment plants and had high percentage of acid soluble/exchangeable and reducible fractions in industrial wastewater treatment plants; Ni and Zn had higher percentage in the acid soluble/exchangeable and the oxidizable fraction.Keywords: Sewage sludge; Sequential extraction; Fraction; Heavy metals; Wastewater treatment plan1. IntroductionSewage sludge contains many organic contaminants (such as PCBs and PAHs), heavy metals and pathogens. Non-hazardous treatments of sewage sludges can degrade parts of the organic pollutants, effectively kill some pathogens, but heavy metals present in sludge cannot be removed by com-mon treatment technologies such as composting, aerobic or anaerobic digestion . So the sludge disposal may result in secondary environmental pollution if treated improperly. Among the different ways of sewage sludge disposal, land application is low cost and high effective and has been used widely . However, application of sewage sludge may result in heavy metal accumulation in cultivated soils. This fact has received more and more concern in recent years. Detailed information on heavy metals present in sewage is necessary before their land application. The threshold values of toxic limits heavy metals in sludge have been set in many countries for their safe disposal to agricultural fields and to reduce their potential risk hazard on agricultural ecological system. Some studies have shown that the available fraction of heavy metals mainly decided the mobility, bioavailability or phytotoxicity of heavy metals in soils . Therefore, the quantification of different chemical fractions of heavy metals in sewage is necessary for information on metal mobility, as well as on their bioavailability or phyto-toxicity. On the other hand, the source of heavy metals in wastewa-ter, whether domestic or industrial, also has profound effects on the total content as well as chemical fractions of heavy metals in sludge. For example, industrial effluents are the predominant source of Cd, Hg, Cr and Ni, while Cu and Zn are mainly of domestic origin, and the major source of Pb may be both surface runoff and domestic wastewater.In China, mainly the domestic wastewater and partly industrial wastewater and surface runoff are used in municipal wastew-ater treatment plants. Wastewater treatment plants are run by the large scale corporations to treat their effluents before their ultimate discharge into environment. So there might be some differences in total content and chemical fractions of heavy metals in selective sewage sludge samples. In the present paper, sewage sludge collected from five municipal wastewater treatment plants and three industrialwastewater treatment plants of petrochemical, brew and paper industry was examined for the total concentrations of Cd, Cr, Pb, Cu, Ni and Zn and chemical fractions of heavy metals to get a preliminary assessment for the land application of sewage sludge.2. Materials and methods2.1. Collection of sewage sludge samplesWet anaerobic sludge samples were obtained from selec-tive wastewater treatment plants listed in Table 1 . The sam-ples were air-dried, passed through a sieve having openings of 2 mm diameter and stored in dry glass bottles at room tem-perature. Sludge pH was measured in 1:2.5 sludge and water suspensions. Organic carbon of the sludge samples was deter-mined by ashing at 360℃for 2 h. Cation exchange capacity (CEC) values were determined following the procedure out-lined by Grauer . Total contents of phosphorus (P) and potassium (K) were determined by ICP-MS . Some properties of sludges from the selective wastew-ater plants are presented in Table 2 .2.2. The sequential extraction test and determination of heavy metalsSequential extraction was performed using the three-step procedure recommended by Community Bureau of Refer-ence , in which metals are divided into acid soluble/exchangeable, reducible-fraction and oxidizable-fraction .Step one : A half-gram aliquot of sludge was taken in a 50 mL polypropylene centrifuge tube and 20 mL volume of acetic acid (0.11 mol/L) was added to it. The contents were shaken for 16 h (overnight) at ambient temperature (20℃) on an end-over-end mechanical shaker operating at 40 rpm. The extract was separated from the solid residue by centrifugation(4000 rpm), decanted into a polyethylene containerand stored at 4℃untill analysis.Step two : The residue from Step one was slurried with a portion of a 20 mL volume of 0.1 mol/L hydroxylam-monium chloride . The extraction procedure described above was followed.Step three: The residue from Step one was dispersed in 5 mL volume of hydrogen peroxide (8.8 mol/L) and digested at room temperature for 1 h with occasional shaking. A second 5-mL aliquot of hydrogen peroxide was continued by heating the tube to 85℃in a water bath for 1 h. The contents were evaporated to a small volume (1–2 mL). Twenty-five milliliter of ammonium acetate was adde to the cool and moist residue,shaken, centrifuged and the extract separated as described for Step one.Step four: One milliliter each of HNO3 , HClO4 and HF were added to 0.1 g dry sludge samples taken in poly beakers. The contents were heated on a hot plate and evaporated to near dryness. After cooling, the residues were dissolved in 1% HNO3. The resultant solu-tions were subsequently used to determine the heavy metals.A blank was also run at the same time and no detectable contamination was found when aliquots of the sequential ex-traction reagents were processed and analyzed with the sam-ples. The concentrations of Cd, Cr, Pb, Cu, Ni and Zn in different fractions and the resultant solutions of Step four were determined by ICP-MS .2.3. Calculation and statistical analysisThe summation of three fractions was subtracted from the total content to get the content of the residual fraction. All statistical analyses were carried out on the Statistical Package for Social Science .3. Results and discussion3.1. Physicochemical properties of sludge from selective wastewater plantsThe data contained in Table 2 show that the properties of sludge from selectivewastewater plants varied widely. The ranges were from 250 to 560 kg−1 for organic carbon, 4 to 26 kg−1 for total N, 0.8 to 19.3 g kg−1 for total P and 2.0 to 12.6 g kg−1 for total K. Their contents are similar to or above them in farmyard manure. In China, the mean contents of soil were 10–40 g kg−1 for organic matter, 1.0–2.0 g kg−1 for to-tal N, 0.44 to 0.85 g kg−1 for total P and about 16 g/kg for total K, respectively . Comparing the contents of sludge with those of soils, the former had higher contents of organic carbon, total N and total P, but lower content of the total K. A survey in 2000 showed that 70–80% of the total cultivated land was lack of enough nutrients and insufficient application of organic fertilizer and excessive utilization of chemical fertilizers had caused the deterioration of farmland quality, the cultivated horizon became thinner and water retention ability decreased . The pH value of sewage sludge varies from 4.4 to 7.7. The CEC values varied from 17.6 to 89.6 cmol kg−1. This sewage sludge has a good manure value.3.2. Total content of Cd, Cr, Pb, Cu, Ni and Zn in sewage sludgeThe total contents of Cd, Cr, Pb, Cu, Ni and Zn in sludge presented in Table 3 showed a wide variation of the concen-tration of heavy metals. In general, these sludge samples had higher contents of Cu and Zn but relatively lower contents of Cr, Ni, Pb and Cd. Similar wide variation in the concentra-tion ranges of heavy metals have been reported by Alvarez et al. and S ˇcanˇcar et al . However, the total con-centration of Cr, Ni and Pb in sludges reported by S ˇcanˇcar et al. and for Cr and Pb observed by Alvarez et al. were much higher than the results of present investigation. On the other hand, the concentrations of Zn and Cu noted in this investi-gation were higher than the results of these workers. Statis-tical analysis showed that there was no significant difference in total concentration of metals between municipal and in-dustrial wastewater treatment plants. It appears that if the discharged standard of industrial wastewater of China were enforced strictly, the metal content in sludge could be effec-tively reduced. The source of municipal wastewater treatment plants includes industrial effluents, domestic wastewater andsurface runoff, so the control of heavy metals in wastewater source of municipal wastewater treatment plants was harder than that of industrial wastewater treat ment plants.“Discharge standards of pollutants for municipal wastew-ater treatment pla nt ” was issued in 2002 and enforced in 2003 in China . A comparison of metal concentrations in sludge with their permissible values, the concentrations of Cr, Ni and Cu in S3 and Cd and Zn in S5 were beyond the permitted values restricting their use in agriculture. Metal concentrations in other six sludge samples were below the permitted values so these could be safely used in agriculture. Soil contamination due to heavy metals was a serious problem in China, for example, concentrations of heavy metals in 36,000 ha sampled from 300,000 ha basic agricultural protecting cropland in 2000 were found to be beyond the permissible limit values of state standards for cropland . A strict enforcement of state standards should be observed to limit the indiscriminate application of sludge in cropland.3.3. Extractable contents of Cd, Cr, Pb, Cu, Ni and Zn in sewage sludgeDifferent chemical fractions of heavy metals represented as percent of their total concentrations in sludge shown in Fig. 1 revealed that the distribution of the metal fractions varied widely for different metals. The percentage of F1 frac-tion of almost all metals in S5 and S6 was higher than other sludge samples owing to the acidic nature of these two sludge samples. Merrington et al. stressed the importance of pH onthe availability of metals in sludge . The content of F1 fraction of Cr in S1, S2, S4 and S7 and of Pb in S1, S2, S4, S7 and S8 were below the detection limit of ICP-MS, therefore, these were not taken into consideration during sta-tistical analysis and not shown in Fig. 1. Chromium, Cu and Pb were found to be principally distributed in the F3 and residual fractions in all sludge samples. Nickel had higher percentage of F1 (5.6–46.7%) but lower percentage of F2 fraction (1.6–11.4%). The percentage of F1, F2 and F3 for Zn was all above 10%. Cadmium was principally distributed in the F3 and residual fractions in S1 and S4, and in F1 andF2 fraction in S5, S6, S7 and S8.Among different chemical frac-tions of heavy metals in sludge, F1 fraction represented a form of high mobility and potential bioavailiability. The per-centage of F1 for Cd in S6, S7 and S8 was much higher in S1, S2, S3 and S4. This showed that the mobility and bioavailability of Cd in sludge from in-dustrial wastewater treatment plants were much higher than from municipal wastewater treatment plants. Because the per-mitted value of Cd in the discharge standard was very below , the higher percentage of F1 fraction of Cd in acidic sludge from municipal wastewater treatment plant and sludge from industrial wastewater treatment plants may cause poten-tial phyto-toxicity after agricultural application. There is no significant difference in the percentage ofF1 for other metals. The percentage ofF1 for Ni and Zn ranged from 9.6 to 51.1 and 10.0 to 51.1, respectively. So the mobility and bioavail-ability of Ni and Zn in sludge was higher as compared to other heavy metals. These results are in corroboration to the findings of S `ean`ear et al. Attention should be, therefore, paid to the mobility of Ni and Zn in sludges from municipal treatment plants and Cd in sludges from industrial wastewater treatment plants after their application.4. ConclusionsSewage sludge collected from eight sewage treatment plants has high organic carbon, and is rich in nutrient like N and P, so they can be used as good organic fertilizers. But the impact caused by heavy metals after their agricultural application of sludge should be assessed. Total concentration of Cr, Ni and Cu in S3 and Cd and Zn in S5 exceeded the permitted values of GB 18918-2002, so S3 and S5 can not be used in agriculture due to high metal concentration. Total metal concentrations in sludge from three industrial wastew-ater treatment plants failed to show any significant difference against those from municipal wastewater treatment plants. Extractable fractions of different heavy metals varied greatly. In acidic sludge , the percentage of F1 fraction of most heavy metals was higher than that in neutral sludge. In neutral sludge, Pb and Cr were principally distributed in the oxidizable and residual fractions. Cu was mainly in the oxidizable fraction. Cadmium was principally in theresidual fraction in municipal wastewater treatment plant sludge while in industrial wastewater treatment plant sludge high percent-age of acid soluble/exchangeable and reducible fractions was noted. Nickel and Zn had higher percentage in the acid soluble/exchangeable and the oxidizable fractions. In China, a statewide survey for compilation of data on the production of sludge, their heavy metal composition and speciation should be carried out for their environmentally safe disposal.。

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