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Hierarchical Chain Model of Spider Capture Silk Elasticity

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a r X i v :c o n d -m a t /0412538v 2 [c o n d -m a t .s o f t ] 24 J a n 2005Hierarchical Chain Model of Spider Capture Silk ElasticityHaijun Zhou 1and Yang Zhang 21Max-Planck-Institute of Colloids and Interfaces,14424Potsdam,Germany2Center of Excellence in Bioinformatics,University at Buffalo,901Washington St.,Buffalo,NY 14203(Dated:21January,2005)Spider capture silk is a biomaterial with both high strength and high elasticity,but the structural design principle underlying these remarkable properties is still unknown.It was revealed recently by atomic force microscopy that an exponential force-extension relationship holds both for capture silk mesostructures and for intact capture silk fibers [N.Becker et al.,Nat.Mater.2,278(2003)].In this Letter a simple hierarchical chain model was proposed to understand and reproduce this striking observation.In the hierarchical chain model,a polymer is composed of many structural motifs which organize into structural modules and supramodules in a hierarchical manner.Each module in this hierarchy has its own characteristic force.The repetitive patterns in the amino acid sequence of the major flagelliform protein of spider capture silk is in support of this model.[Phys.Rev.Lett.94,028104(2005)]PACS numbers:87.15.-v,78.40.Me,81.05.Lg,87.10.+eThe capture silk is a natural material produced by orb-web weaving spiders.Spiders rely on it to entrap flying preys [1].Like the spider dragline silk and many other naturally occurring silks,the capture silk has a tensile strength that is comparable to steel;but,unlike steel,it is also extremely elastic,with the ability to be stretched to almost 10times its relaxed contour length without breaking [2,3].This perfect combination of strength and extensibility conveys a high degree of toughness to the capture silk:its breakage energy per unit weight is more than 20times that of a high-tensile steel [2].With the aim to produce synthetic silks with similar mechanical properties,materials scientists have devoted many exper-imental and computational efforts to the understanding of spider silk’s structural organization [4].Despite these painstaking efforts,the mechanism behind spider silk’s remarkable strength and elasticity is still largely miss-ing,partly because of the difficulty to obtain high-quality crystallized structures of silk proteins.Single-molecule manipulation methods have been re-cently applied on spider silks to obtain very detailed in-formation on their force-extension response [3,5].In a recent experiment,Hansma and co-workers [3]attached capture silk mesostructures (probably composed of a sin-gle protein molecule)or intact capture silk fibers to an atomic force microscopy tip and recorded the response of the samples to external stretching force.They found a re-markable exponential relationship between the extension x and the external force f ,f ∝exp(x/ℓ),(1)where ℓ,the length constant referred to in [3],is a fitting parameter whose physical meaning needs to be decided (see below).ℓ=110±30nm for a capture silk molecule and ℓ=11±3mm for an intact capture silk fiber [3].The length constant of a silk fiber is about 105times that of a silk molecule;its relaxed contour length is alsoabout 105times that of a molecule [3].It appears that ℓholds an approximately linear relationship with the con-tour length.The exponential force-extension curve is significantly different from the data observed during stretching single double-stranded (ds)DNA molecules [6]or single titin proteins [7,8].The behavior of dsDNA can be under-stood by the wormlike chain model of entropic elasticity [9,10],and that of titin by a two-level system coupled with entropic elasticity [11].Similar exponential force-extension data were also observed by Dessinges et al.when they stretched a single-stranded (ss)DNA molecule at low salt conditions [12].The data was explained as a result of the interplay of electrostatic repulsion and en-tropic elasticity [12,13].However,the success of this model depends on the specific ionic concentration (i.e.,low salt and high electrostatic interaction);and it could not naturally reproduce the exponential stretching data at extremely high force (i.e.,when the extension is larger than 1.1times the ssDNA backbone length)if higher or-der deformation energy terms are not included [12].In the spider capture silk experiment,the exponential be-havior was observed at both fluid and air within a force range from about 100piconewton (pN)to about 106pN [3].Equation (1)indicates the following:(i )Because the capture silk is highly extensible,a great amount of ex-tra length must have been stored in its relaxed form.(ii )Since extension increases with force logarithmically,some fraction of the stored length must be easy to be pulled out,some fraction be harder to be pulled out,and till some other fraction be even harder to be pulled out.To model this kind of heuristic cascading responses,here we propose a hierarchical chain model for spider capture silk.In the hierarchical chain model,the polymer is composed of many basic structural motifs;these motifs are then or-ganized into a hierarchy,forming structural modules on2more and more longer length scales.At the deepest hier-archy level h m,the structural motifs could beβ-sheets,β-spirals,helices[4]or microcrystal structures[14].The interactions among some of these motifs are much more stronger than their interactions with other motifs,there-fore they form a structural module at the hierarchy level (h m−1).These level-(h m−1)modules are then merged into level-(h m−2)modules through their mutual interac-tions.This merging process is continued;andfinally at the global scale,the whole spider silk string is regarded as a single module of the hierarchy level h=0.In nature,the structures of many biomaterials are in-deed hierarchically organized.As a composite material, chromosome is a mixture of DNA,histone,and other non-histone structural proteins[15].The DNA moleculefirstwraps onto histone proteins to form nucleosome particles, the basic units of chromosome.With the help of H1his-tone,this linear sequence of nucleosomes are then coiled and folded to form the30-nm chromatinfiber.With the help of other scaffold proteins,the chromatinfiber is then further coiled and folded at several levels to form the compact chromosome structure.As another example,the amino acid sequence of a proteinfirst forms basic struc-tural modules ofα-helix andβ-sheet,called secondary structures.By different ways of connections of these sec-ondary modules,the protein constructs various tertiary topologies that are critical for its specific biological func-tions.In a higher level,these tertiary domains then form quaternary structures of protein complexes consisting of multiple chains[16].Recent experimental and theoreti-cal studies have shown that the force–induced unfolding of protein molecules is indeed processed in a hierarchical way,i.e.the tertiary structure precedes the secondary structures to be pulled over at increasing external forces [7,17].Our hierarchical chain model may also serve as a framework to understand the mechanical property of these biomaterial systems.Consider a polymer of contour length L0.It is regarded as the module of hierarchy level h=0(the module M0). M0is composed of a tandem sequence of m0subunits M1of contour length L1=L0/m0(Fig.1).Under the action of an external forcefield f,the extension of M0 is denoted as x0(f).It was observed that water-induced protein mobility is a significant contribution to capture silk elasticity[18].Therefore,we decompose x0into two parts:(i)the extension∆x0caused by the displacement and position-rearrangement of these m0subunits and, (ii)the total extension m0x1caused by the inherent de-formations of these m0subunits:x0(f)=∆x0(f)+m0x1(f).(2) Similarly,at the hierarchy level h=1,each unit is itself composed of m1level-2subunits M2of length L2=L0/(m0m1).Therefore,x1(f)can be written as x1(f)=∆x1(f)+m1x2(f),where∆x1(f)is the contri-bution to the extension of a level-1module due to the FIG.1:The hierarchical chain model.At each hierarchy level h a structural module M h is composed of a tandem sequence of m h submodules M h+1of hierarchy level h+1.Under exter-nal stretching,M h responds by(i)adjusting the arrangements of its m h subunits and making them more aligned along the force direction,and(ii)extending these m h subunits.The thick broken lines between submodules of each hierarchy level indicate the existence of sacrificial bonds.displacement and position-rearrangement of its m1sub-units;and x2(f)denotes the extension because of the inherent deformation of a level-2subunit M2.As this structural hierarchy is continued,we arrive at the follow-ing expression concerning the total extension x(f):x(f)=∆x0(f)+ h=0m0m1...m h∆x h+1(f).(3)It is reasonable that the average extension∆x h(f)of a M h contributed by the reorientation or rearrangement of its level-(h+1)subunits is proportional to the relaxed contour length L h of this module.To facilitate the fol-lowing analytical calculation,let us assume∆x h(f)has the following non-linear form(we will show that thefinal force-extension relationship is not sensitive to the specific assumption made here):∆x h(f)= αL h f/f h,f<f hαL h,f≥f h(4)whereαis a dimensionless proportional constant;f h is the characteristic force needed to displace and rearrange the positions of the m h submodules contained in a M h (during this process some sacrificial bonds are broken). Equation(4)is in agreement with the experimental ob-servation[3]that,between adjacent rapture events,a capture silk responds to external stretching in a linear way.Denote∆E h as the energy cost of breaking all the sacrificial bonds between a level-h module’s m h subunits. From Eq.(4)we know that f h+1/f h=m h∆E h+1/∆E h. Consider a level-(h+2)module M a h+2,it is in M a h+1which in turn is in M a h.M a h+2feels an internal energyǫdue to3 its interaction with other subunits in M a h+1,and it feelsan external energyǫ′due to its interactionwith other sub-unitsin M a h but not in M a h+1.Based on Fig.1,we knowthat∆E h+1=m h+1ǫ/2and∆E h=m h m h+1ǫ′/2.Thehierarchical organization of the polymer requires thatǫ>ǫ′,so as to ensure that structural modules of shorterlength scales will be formed earlier.Based on these con-siderations,we arrive at the following self-similar scalingform:f h+1=(ǫ/ǫ′)f h=βf h(β≡ǫ/ǫ′>1).(5)The parameterβcharacterizes the degree of coherencein the modular organization of the polymer:a largeβvalue means that a submodule has much stronger internalinteractions compared with its external interactions.From Eqs.(3)and(4)wefind that when f h−1<f≤f hd x(f)f h′=αβL0β−1L0.(7)The length constantℓis proportional to the relaxed con-tour length L0of the whole polymer,in consistence withRef.[3].Figure2demonstrates the numerically calculatedforce-extension curve based on Eqs.(3),(4),and(5).Asa comparison,the experimental data[3]on intact spidercapture silk is also shown.Asβ≃2and the exprimen-tal exponential force range is roughly from6×10−5NFIG.2:Exponential force-extension relationship for the hi-erarchical chain model.Equation(4)is used in the numericalcalculation.The parameters are f0=10−4N,α=0.3,andβ=2(the upper curve)orβ=1.75(the lower curve).Ex-tension is in units of L0.Symbols are experimental data fromFig.4of[3].to10−3N,it appears that4–5levels of hierarchy wereprobed.The exponential relationship shown in thefigure is in-sensitive to our particular assumption Eq.(4),as longas the elastic response at each hierarchy level is non-linear and bounded.As an example,the solid curvesin Fig.3show the resulting force-extension relationshipwhen Eq.(4)is replaced by∆x h(f)=αL h 1−exp(−f/f h) .(8)The same exponential behavior as in Fig.2is obtained.However,the hierarchical scaling form Eq.(5)is neededfor the exponential force-extension correlations.For ex-ample,when Eq.(5)is replaced by a power-law,f h∝f0hγ,the response is not exponential(the dotted line inFig.3).We also noticed that,when in Eq.(5)the param-eterβis not a constant butfluctuates over somefiniterange ofβ>1,the resulting force-extension curve is stillexponential(Fig.3,dashed lines).In summary,we have developed a hierarchical chainmodel to understand the strength and elasticity of spidersilks.Remarkably,this simple model was able to repro-duce the peculiar exponential force-extension response ofspider capture silk reported by Becker et al.[3].Themodel can also be used as a framework to understandthe elasticity of other spider silks and other biopolymerswith hierarchically organized structures.FIG.3:The force-extension relationship of a hierarchicalchain is insensitive to the assumption made to the response∆x h(f)of Eq.(4),but is sensitive to the hierarchical scal-ing form of the characteristic force f h.The solid lines areobtained by assuming∆x h(f)has the form of Eq.(8),whileother parameters are the same as those in Fig.2.The dot-ted line shows the change in the force-extension curve whenadditionally a power-law form of f h=f0hγwithγ=3.0isassumed for f h.The dashed lines are obtained by assum-ing Eq.(8)and Eq.(5),withβfluctuating uniformly within[1.25,2.25](the lower curve)and within[1.5,2.5](the uppercurve).4Becker et al.[3]have proposed an alternate and inter-esting idea to model the spider silk as a branched network of interconnected springs.In their model,the system re-sponds to external stretching byfirst unfolding the sin-gle spring at the root level,then the m springs at the first branching level,then the m2springs at the second branching level,and so on.The hierarchical chain model developed here is different from Becker et al.’s model. First,the molecule in the hierarchical chain model con-sists of a tandem sequence of structural modules of differ-ent length scales.Therefore,no assumption of branching structure is made in our model.Second,the response of the chain to external perturbations is in a hierarchi-cal manner.If the external force is small,only those structural units of length scale comparable to the whole polymer length will be displaced and rearranged;struc-tural units at short and moderate length scales will re-main intact.As the external perturbation is elevated, additional structural units at more shorter length scales are also deformed.Through such a hierarchical orga-nization,a single polymer chain can respond to a great variety of external conditions;at the same time,it is able to keep its degree of structural integrity as high as possi-ble.This hierarchical modular structure also indicates a broad spectrum of relaxation times.The modules at the shorter length scales will have much shorter relaxation times and will be refoldedfirst when the external force decreases.This gap in relaxation times ensures that,af-ter extension,the spider capture silk will return to its relaxed state gradually and slowly.This is a desirable feature for spider capture silk,because a too rapid con-tract following the insect’s impact would propel the vic-tim away from the web.The simple hierarchical chain model,while appealing, needs further experimental validation.This model seems to be supported by recent genetic sequencing efforts.By analyzing the cDNA sequence of the major protein of spi-der capture silk,theflagelliform protein,it was revealed that the amino-acid sequence offlagelliform has a hier-archy of modularity[19,20,21].At the basic level,the flagelliform sequence is consisted of three repetitive mod-ules(motifs):(i)the GPGGX motif(Gly-Pro-Gly-Gly-X,X∈{Ala,Ser,Tyr,Val});(ii)the GGX(Gly-Gly-X,X ∈{Ala,Ser,The});(iii)the highly conserved spacer motif of length28amino-acids.At the next level,an ensem-ble motif is formed,which is a tandem array of43−63 GPGGX followed by6−12GGX,the spacer and another GGX[19].At the even higher level,the ensemble motif then repeats itself about14times to form theflagelliform monomer.The variable residues X are not randomly dis-tributed along the protein sequence[19],which may en-code important structural information.The structures of spider capture silks(and other spider silks)therefore have the potential to be hierarchically organized.For spider capture silk,one important experiment will be to check the validity of Eq.(5)by single-molecule force spectroscopy.The characteristic forces f h may cor-respond to the forces at the saw-tooth rapture events ob-served by Hansma and co-workers[3].Although the ex-perimental curves of Ref.[3]is in agreement with Eq.(5), more systematic investigations are necessary to draw a solid conclusion.We are grateful to H.Hansma for communicating her experimental results with us prior to publication and for the experimental data used in Fig.2,and to D.E.Makarov for comments on the manuscript.Thanks are also due to R.Lipowsky,Z.C.Ou-Yang,and J.Skol-nick for their support.[1]F.Vollrath,Sci.Am.266,70(1992).[2]J.M.Gosline,P.A.Guerette,C.S.Ortlepp,and K.N.Savage,J.Exp.Biol.202,3295(1999).[3]N.Becker,E.Oroudjev,S.Mutz,J.P.Cleveland,P.K.Hansma, C.Y.Hayashi, D. E.Makarov,and H.G.Hansma,Nature Materials2,278(2003).[4]D.Kaplan,ed.,Silk Polymers:Materials Science andBiotechnology,ACS Symposium Series(Am.Chem.Soc., Washington DC,1994).[5]E.Oroudjev,J.Soares,S.Arcidiacono,J.B.Thompson,S.A.Fossey,and H.G.Hansma,Proc.Natl.Acad.Sci.USA99,6460(2002).[6]S.B.Smith,L.Finzi,and C.Bustamante,Science258,1122(1992).[7]M.Rief,M.Gautel,F.Oesterhelt,J.M.Fernandez,andH.E.Gaub,Science276,1109(1997).[8]K.S.Z.Kellermayer,S.B.Smith,H.L.Granzier,andC.Bustamante,Science276,1112(1997).[9]J.F.Marko and E.D.Siggia,Macromolecules28,8759(1995).[10]H.Zhou,Y.Zhang,and Z.-C.Ou-Yang,Phys.Rev.Lett.82,4560(1999).[11]M.Rief,J.M.Fernandez,and H.E.Gaub,Phys.Rev.Lett.81,4764(1998).[12]M.N.Dessinges,B.Maier,Y.Zhang,M.Peliti,D.Ben-simon,and V.Croquette,Phys.Rev.Lett.89,248102 (2002).[13]Y.Zhang,H.Zhou,and Z.-C.Ou-Yang,Biophys.J.81,1133(2001).[14]F.Vollrath and D.P.Knight,Nature410,541(2001).[15]K.E.van Holde,Chromatin(Springer-Verlag,New York,1989).[16]C.Branden and J.Tooze,Introduction to Protein Struc-ture(Garland Pub.,New York,1999),2nd ed.[17]H.Lu, B.Isralewitz, A.Krammer,V.Vogel,andK.Schulten,Biophys.J.75,662(1998).[18]K.M.Bonthrone,F.Vollrath,B.K.Hunter,and J.K.M.Sanders,Proc.R.Soc.Lond.B248,141(1992). [19]C.Y.Hayashi and R.V.Lewis,J.Mol.Biol.275,773(1998).[20]P.A.Guerette,D.G.Ginzinger,B.H.F.Weber,andJ.M.Gosline,Science272,112(1996).[21]C.Y.Hayashi and R.V.Lewis,Science287,1477(2000).。

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上海市实验学校2021届高三上学期摸底考试英语试题

上海市实验学校2021届高三上学期摸底考试英语试题

上海市实验学校2021届高三上学期摸底考试英语试题一、句子翻译1．他从来没有意识到题目越容易就应该越仔细。

(occur)（汉译英）____________________________________________________________________________________________ ____________________________________________________________________________________________【解析】考查固定搭配、主语从句。

表述过去发生的事情使用一般过去时。

occur to是固定搭配意为“想起、意识到”。

当主语从句作主语时，一般习惯于将主语从句后置，使用形式主语指代主语从句。

主语为it，谓语为occurred，主语从句为that the easier the questions were, the more careful he should be。

再结合其他汉语提示故翻译为It never occurred to him that the easier the questions were, the more careful he should be。

二、完形填空Lawmakers in New Jersey recently advanced a bill that would ban businesses from going cashless—a move that would put the state at odds with the global trend toward electronic payments but would 5．_____resistance from local officials who see no-cash policies as unfair.Almost 1 of 3 Americans in 2018 say they don't use cash during a typical week of purchases, according to the Pew study released this week. The findings reveal life that Americans are becoming less reliant on paper currency, mirroring 6．_____ in Sweden, India and China. But state and local officials say that restaurants and shops do that adopt cashless policies have left some members of the community behind— individuals without the 7．_____ to open a bank account or who lack access to lines of credit or the mobile apps that power digital payments.The New Jersey measure, which would apply only to face-to-face sales and would 8．_____ internet and phone purchases, comes as officials push 9．_____ efforts to bar no-cash rules in New York and Philadelphia. 10．_____ cashless policies offer consumers the promise of convenience and provide businesses greater protection against theft, they also can exclude low-income consumers or undocumented immigrants, critics say. "Cash-free businesses are discriminatory by design and pose 11．_____ to low-income communities that may not have access to credit or debit," New York Council member Torres said on Twitter when he introduced a bill that would ban the practice.According to the Pew study, the decline in the use of 12．_____ currency is uneven among the populationwhen race, age and income are accounted for. Pew found a significant 13．_____ in cashless adoption tied to annual household income, with adults making at least $75,000 more than twice as likely to make all their purchases without using cash in a typical week, 14．_____ with people who make less than $30,000. The Pew findings suggest that the 15．_____of going cashless may come with a cost that only some groups of people will bear. Americans with lower incomes are roughly four times as likely than higher earners to make almost all of their purchases with cash, according to the study.As has been noted, business leaders have 16．_____cashless policies by pointing to higher security and 17．_____ customer service and efficiency. Some advocates have focused on providing people who are underserved by the 18．_____ banking system with more affordable options, attacking the root cause behind the 19．_____ of cashless payments.5．A．set up B．put up C．back up D．step up6．A．deposits B．exchanges C．shifts D．currencies7．A．ideas B．means C．directions D．outlets8．A．attract B．exclude C．advance D．include9．A．opposite B．associated C．similar D．collective10．A．While B．Provided C．Because D．As11．A．discounts B．traps C．challenges D．risks12．A．electronic B．physical C．virtual D．circulating13．A．similarity B．expense C．gap D．consumption14．A．linked B．associated C．combined D．compared15．A．outcomes B．effects C．benefits D．disadvantages16．A．adopted B．defended C．developed D．criticized17．A．hindered B．accomplished C．improved D．desired18．A．traditional B．fading C．aggressive D．unqualified 19．A．transformations B．developments C．criticisms D．creations三、阅读理解“Deep reading” —as opposed to the often superficial reading we do on the Web —is an endangered practice, one we ought to take steps to preserve as we would a historic building or a significant work of art. Its disappearance would jeopardize(危及) the intellectual and emotional development of generations growing up online, as well asthe preservation of a critical part of our culture: the novels, poems and other kinds of literature that can be appreciated only by readers whose brains, quite literally, have been trained to understand them.Recent research in cognitive science and psychology has demonstrated that deep reading —slow, immersive, rich in sensory detail and emotional and moral complexity—is a distinctive experience, different in kind from the mere decoding of words. Although deep reading does not, strictly speaking, require a conventional book, thebuilt-in limits of the printed page are uniquely helpful to the deep reading experience. A book’s lack of hyperlinks(超链接), for example, frees the reader from making decisions —Should I click on this link or not? —allowing her to remain fully immersed in the narrative.That immersion is supported by the way the brain handles language rich in detail, indirect reference and figures of speech: by creating a mental representation that draws on the same brain regions that would be active if the scene were unfolding in real life. The emotional situations and moral dilemmas that are the stuff of literature are also vigorous exercise for the brain, propelling us inside the heads of fictional characters and even, studies suggest, increasing our real-life capacity for empathy (认同).None of this is likely to happen when we’re browsing through a website. Although we call the activity by the same name, the deep reading of books and the information-driven reading we do on the Web are very different, both in the experience they produce and in the capacities they develop. A growing body of evidence suggests that online reading may be less engaging and less satisfying, even for the “digital natives” to whom it is so familiar. Last month, for example, Britain’s National Literacy Trust released the results of a study of 34,910 young people aged 8 to 16. Researchers reported that 39% of children and teens read daily using electronic devices, but only 28% read printed materials every day. Those who read only onscreen were three times less likely to say they enjoy reading very much and a third less likely to have a favorite book. The study also found that young people who read daily only onscreen were nearly two times less likely to be above-average readers than those who read daily in print or both in print and onscreen.20．What does the author say about “deep reading”?A．It serves as a complement to online reading.B．It should be preserved before it is too late.C．It is mainly suitable for reading literature.D．It is an indispensable part of education.21．Why does the author advocate the reading of literature?A．It helps promote readers’ intellectual and emotional growth.B．It enables readers to appreciate the complexity of language.C．It helps readers build up immersive reading habits.D．It is quickly becoming an endangered practice.22．In what way does printed-page reading differ from online reading?A．It ensures the reader’s cognitive growth.B．It enables the reader to be fully engaged.C．It activates a different region of the brain.D．It helps the reader learn rhetorical devices.23．What do we learn from the study released by Britain’s National Literacy Trust?A．Onscreen readers may be less competent readers.B．Those who do reading in print are less informed.C．Young people find reading onscreen more enjoyable.D．It is now easier to find a favorite book online to read.Earthquake survivors trapped in rubble could one day be saved by an unlikely rescuer: a robotic caterpillar that digs its way through debris. Just a few centimeters wide, the robot relies on magnetic fields to propel it through the kind of tiny cracks that would defeat the wheeled or tracked search robots currently used to locate people trapped in collapsed buildings.The caterpillar's inventor, Norihiko Saga of Akita Prefectural University in Japan, will demonstrate his new method of motion at a conference on magnetic materials in Seattle. In addition to lights and cameras, a search caterpillar could be equipped with an array of sensors to measure other factors --such as radioactivity or oxygen levels --that could tell human rescuers if an area is safe to enter.The magnetic caterpillar is amazingly simple. It moves by a process similar to peristalsis(蠕动), the rhythmic contraction that moves food down your intestine. Saga made the caterpillar from a series of rubber capsules filled with a magnetic fluid consisting of iron particles, water, and a detergent-like surfactant, which reduces the surface tension of the fluid. Each capsule is linked to the next by a pair of rubber rods. The caterpillar's guts are wrapped in a clear, flexible polymer tube that protects it from the environment.To make the caterpillar move forwards, Saga moves a magnetic field backwards along the caterpillar. Inside the caterpillar's “head” capsule, magnetic fluid surges towards the attractive magnetic field, causing the capsule to bulge out(鼓起) to the sides and draw its front and rear portions up. As the magnetic field passes to the next capsule,the first breaks free and springs forward and the next capsule bunches up(聚成一团). In this way, the caterpillar can reach speeds of 4 centimeters per second as it crawls along.Moving the magnetic field faster can make it traverse(穿过) the caterpillar before all the capsules have sprung back to their original shapes. The segments then all spring back, almost but not quite simultaneously.Saga plans to automate the movement of the caterpillar by placing electromagnets at regular intervals along the inside of its polymer tube. By adjusting the current flow to the electromagnets, he'll be able to control it wirelessly via remote control. He also needs to find a new type of rubber for the magnetic capsules, because the one he's using at the minute eventually begins to leak.But crawling is not the most efficient form of motion for robots, says Robert Full of the University of California at Berkeley, an expert in animal motion who occasionally advises robotics designers. "If you look at the energetic cost of crawling, compare d to walking, swimming or flying, crawling is very expensive,” he says. In walking, energy is conserved in the foot and then released to help the foot spring up.Saga acknowledges this inefficiency but says his caterpillar is far more stable than one that walks, rolls on wheels or flies. It has no moving parts save for a few fluid-filled rubber capsules. Biped robots and wheeled robots require a smooth surface and are difficult to miniaturize, and flying robots have too many moving parts. “My peristaltic crawling robot is simple--and it works,” he says.24．From this passage, we can learn that ________.A．a robotic caterpillar can crawl by a pair of rubber rodsB．when a caterpillar moves, the magnetic field moves backwards along itC．the environment couldn't influence a robotic caterpillar's guts, which are wrapped in a capsuleD．crawling is very stable and efficient, and when it moves, only a few elements are needed25．According to this passage, which is NOT TRUE about the construction of the robotic caterpillar?A．A robotic caterpillar is made from a series of rubber capsules filled with a magnetic fluid.B．Iron particles, water, and a detergent-like surfactant form a magnetic fluid.C．Each capsule filled with a magnetic fluid is linked to a pair of rubber rods.D．In order to keep stable condition, the caterpillar's guts are wrapped in a clear, flexible polymer tube. 26．Comparing the robotic caterpillar and the other robots, which of the following is NOT TRUE?A．A smooth surface is indispensable to biped robots and wheeled robots.B．Flying robots are very inconvenient when moving, because they have too many moving parts.C．The robotic caterpillar only has rubber capsules filled with a magnetic fluid.D．Wheeled robots are unable to locate trapped people because they cannot miniaturize.Criticism of Big Tech is intensifying. At Congressional hearings last week, politicians from across the aisle gave a rough ride to executives of some of the world's most valuable companies. Amid the hubbub(喧哗), the resignation of Google's Meredith Whittaker was less noticed, but significant. Ms Whittaker, a Google artificial intelligence researcher, was a leader of protests insider the company last year. In an internal note to fellow employees, she warned that developers have a “sh ort window in which to act" to stop increasingly dangerous uses of artificial intelligence.Ms Whittaker' s resignation reflects a growing tendency for tech companies' own staff to try to serve as the moral compass and conscience of their businesses. In companies whose value relies so much on human and intellectual capital ---and in being able to attract the sharpest minds ---employees have considerable potential impact, especially collectively.The Google Walkouts of which Ms Whittaker was a leader began in response to the search group's treatment of sexual harassment complaints. They snowballed to include broader issues around the company’s technologies. Ms Whittaker’s decision now to resign suggests many Big Tech companies are still not doing enough to at tend to employees' concerns over corporate culture. Yet responding to internal calls to action should be an obvious choice. Threats of strikes or resignations by the talented staff who build systems risk undermining technology companies' competitiveness. Employee action can act to strengthen measures by regulators who are increasingly proactive in dealing with the excesses of Big Tech.The rise of collective action for social good is encouraging. Traditional labour focuses ----such as workers' rights around pay and hours ----- remain important in a sector which still also makes heavy uses of cheap and poorly-skilled workers. Attempts to pressure companies into behaving ethically have more often been driven by single employees. Avenues are needed to ensure that workers can discuss potentially unethical practices without risking revenge.Ms Whittaker’s proposal for unionisation is part of a broader chorus demanding greater employee oversight. Alphabet, Google’s parent, has already faced calls from union-sponsored pension funds to add a non-executive employee representative to its board. While not successful this year, the move showed that stakeholders such as investors are pressing for culture change within Big Tech companies.Workers outside the tech sector, too, are forcing companies to try to solve international problems. A global climate strike is planned for September，encouraging workers to join the thousands of school students who haveprotested over the past year. In the advertising industry, workers at over 20 agencies refused to work on fossil fuel briefs in solidarity, inspired by the Extinction Rebellion protests. Big Tech, facing ever more open criticism should see the message is clear. To regain trust, it will have to engage not just with regulators, but with its own employees and stakeholders.27．We can learn from the first paragraph that Ms Whittaker _________A．drew much criticism from politicians.B．opposed Google's risky uses of AL.C．disagreed with her colleagues on the future of AI.D．resigned because her talent in AI was not recognized.28．The author argues in Paragraph 2 that tech companies' staff _________A．can serve as the moral models for traditional labour.B．should keep sharpening their minds.C．can pressure companies into behaving ethically.D．should improve internal collaboration.29．According to Paragraph3, internal calls to action may _________.A．damage a company's reputation.B．threaten a company's competitiveness.C．impair a company' s corporate culture.D．strengthen a company 's management system.30．Which of the following would be the best title for the text?A．Employees Can Help to Make Big Tech MoralB．Big Tech Staff Are Different from Traditional LabourC．The Tech Sector Is Facing Ever More CriticismD．The Tech Sector Is in a Wave of Resignations四、书面表达31.现在很多公园向民众免费开放。

与植物保护专业相关的太赫兹方面的资料

与植物保护专业相关的太赫兹方面的资料

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蜘蛛侠机器人英语作文

蜘蛛侠机器人英语作文

In the realm of science fiction,the concept of a SpiderMan robot is a fascinating one. Imagine a machine that embodies the agility,strength,and heroism of the iconic webslinger.Heres a detailed English composition on such a concept:Title:The SpiderMan Robot:A Leap into the Future of TechnologyIn the heart of New York City,where skyscrapers touch the sky and the streets buzz with life,a new protector has emerged.Its not a human,but a technological marvel:the SpiderMan Robot.This advanced piece of machinery is designed to patrol the city, ensuring the safety of its inhabitants with the grace and power of SpiderMan himself.Design and CapabilitiesThe SpiderMan Robot is an engineering feat,standing tall at six feet with a sleek, aerodynamic design.Its exterior is made of a composite material that is both lightweight and incredibly strong,capable of withstanding the rigors of urban patrolling.The robot is equipped with a sophisticated AI system that allows it to make quick decisions,analyze situations,and respond to emergencies with the efficiency of a seasoned superhero.One of its most notable features is the ability to mimic SpiderMans signature webslinging. The robot can shoot artificial webs from its mechanical wrists,enabling it to swing from building to building with remarkable agility.These webs are strong enough to support the robots weight and can adhere to various surfaces,including glass and metal.Artificial Intelligence and EthicsThe AI within the SpiderMan Robot is programmed with a strong ethical code,ensuring that it respects human rights and operates within the boundaries of the law.It is designed to assist,not replace,human law enforcement,providing support during highrisk situations such as hostage rescues or the pursuit of dangerous criminals.The robots AI is also capable of learning and adapting.It can analyze data from past incidents to improve its response strategies,making it an everevolving guardian of the city.Integration with SocietyFor the SpiderMan Robot to be truly effective,it must be accepted and integrated intosociety.It is designed to interact with the public in a friendly and approachable manner, using a voice synthesizer to communicate and reassure those it encounters.The robots creators have also ensured that it is recognizable,with a design that pays homage to the classic SpiderMan suit,complete with the iconic web pattern and mask.Challenges and ControversiesDespite its many benefits,the SpiderMan Robot also faces challenges and controversies. Some argue that the presence of such a powerful machine could infringe on personal freedoms or lead to an overreliance on technology for security.Others worry about the potential for misuse or malfunction,which could have disastrous consequences.To address these concerns,the robots creators have implemented strict protocols for its operation and maintenance.It is regularly monitored and updated to ensure that it remains a force for good.ConclusionThe SpiderMan Robot represents a bold step into the future of technology and law enforcement.It stands as a testament to human ingenuity and our neverending quest to create a safer,more secure world.As we continue to push the boundaries of what is possible,the SpiderMan Robot serves as a symbol of our potential to harness technology for the greater good.In the end,the SpiderMan Robot is more than just a machine it is a symbol of hope,a guardian that watches over the city with the same unwavering dedication as its human counterpart.As we look to the future,it is inspiring to imagine a world where such advanced technology works hand in hand with humanity to protect and serve.This composition explores the potential of a SpiderManinspired robot,its integration into society,and the ethical considerations that come with such advanced technology.。

(2021年)甘肃省兰州市大学英语6级大学英语六级真题(含答案)

(2021年)甘肃省兰州市大学英语6级大学英语六级真题(含答案)

（2021年）甘肃省兰州市大学英语6级大学英语六级真题(含答案)学校:________ 班级:________ 姓名:________ 考号:________一、1.Writing(10题)1. Directions: For this part, you are allowed 30 minutes to write a composition on the topic Harmfulness of Fake Commodities. You should write at least 150 words and you should base your composition on the outline ( given in Chinese) below:1. 目前社会上有不少假冒伪劣商品，为什么会有这种现象？2.举例说明假冒伪劣商品对消费者个人，社会等的危害。

2. Directions: For this part, you are allowed 30 minutes to write a composition on the title: Is Long Holiday Necessary? You should write at least 150 words following the outline given below in Chinese.Is Long Holiday Necessary1．对于长假是否必要，不同的人有不同的看法2．我认为长假是必要的，因为……3．如何度长假3. 1. 调查显示，某大学61%的学生需要人际关系方面的心理帮助2. 出现这种情况的主要原因3. 我的建议4. Directions: For this part, you are allowed 30 minutes to write a short essay entitled Say No to Drunk Driving. You should write at least 150 words following the outline given below.1. 众所周知，酒后驾车十分危险2．但近年来越来越多的人酒后驾车．原因是……3．我认为……Say No to Drunk Driving5. Directions: For this part, you are allowed 30 minutes to write a composition on the topic Changes in People's Ways of Communication. You should write at least 150 words following the outline given below in Chinese:1. 以下图为依据描述1975年和1995年人们交流通讯方式的变化情况2. 说明引起变化的各种原因3. 预测未来的情况6. Directions: For this part, you are allowed 30 minutes to write a short essay entitled Studying Abroad. You should write at least 150 words following the outline given below:1. 有些人认为学生应该呆在自己的国家学习。