首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
A metal with a built in memory is one of the very useful discoveries made during America’s space program. Nitinol was discovered
A metal with a built in memory is one of the very useful discoveries made during America’s space program. Nitinol was discovered
admin
2010-04-30
24
问题
A metal with a built in memory is one of the very useful discoveries made during America’s space program. Nitinol was discovered by scientists working at the Naval Surface Weapons Center. They were looking for heat shield metals for missiles and satellites, but what they found was nitinol. This alloy can be formed into shapes just like any other metal, but it returns to its original form at a certain temperature.
When this alloy of nickel and titanium is first formed, it is shaped into ingots, brick shaped masses of the metal. Then it is drawn out into a wire of varying thickness, depending on the job it is destined to do. It is set into its desired curve or shape and heated briefly. It is then cooled off by dipping the wire in cold water. This "sets" its memory. The metal can then be formed into any desired shape, but whenever its temperature exceeds its room temperature, ’ it returns to the shape it has memorized.
This makes nitinol perfect, of course, for, spacecraft, for antennas, probes, shields, and folding "arms" made of nitinol can be stored safely inside a spacecraft, protecting them from damage during launching. Then, once safe in orbit, the spacecraft would suddenly "grow" antennas and other structures. The sun’s rays would have warmed up the folded and coiled nitinol, and it would have returned to its original shape.
But scientists have found a more down to earth use for this wire: they now use it to strengthen teeth. Before nitinol, teeth that needed straightening have brackets attached to them; wires were attached to these to exert a pull in the right direction. But this pull must be constant, and the stainless steel arch wire cannot exert the correct force if it has been bent several times or if the tooth has actually moved toward it as planned. As a result, many people with dental braces must have the wire replaced monthly, tightened every few weeks, or adjusted painfully tight at the beginning of the treatment.
But nitinol wires can be formed to exert force in a certain direction, cooled of and then reformed to fit the patient’s mouth. As the mouth warms the nitinol, it begins to try to assume its preset shape. This exerts a steadier, more constant pull on the tooth than could ever be achieved with stainless steel wire. Nitinol can be bent into such intricate shapes — while maintaining its pull — that very difficult treatments, such as moving one tooth from behind another, can be done now without the expense or pain of constant adjustment. Nitinol has cut tile time needed for these treatments by almost half, a real benefit for both patient and dentist.
The main idea of this passage is that ______.
选项
A、nitinol is a highly versatile metal
B、nitinol helped make the space program a success
C、nitinol has revolutionized dental care
D、most alloys have "memories"
答案
A
解析
主旨大意题。A项:镍钛诺是一种用途很广的金属;B项:镍钛诺有利于太空计划的成功实现;C项:镍钛诺带来牙科护理领域的革命,D项:大部分金属都具有“记忆力”。还是按照处理主旨大意题的一贯做法,我们先来回顾一下全文;文中先讲到意外地获得镍钛诺合金,而后谈到其奇异的特i生,因为此种特性,它被广泛地应用于宇宙飞船、天线,探测器、防护材料等领域,文末又盲及,科学家而今又发现诙种合金可以有效地用于固牙齿,正在一步步得到推广,所以,本文重在介绍镍钛诺合金的特性及其广泛用途,A项正确。
转载请注明原文地址:https://kaotiyun.com/show/DgOK777K
0
大学英语六级
相关试题推荐
A、TuitionGPA.B、Fearofatoohighlistprice.C、Debt.D、Highacademicvalue.BWhatisthebiggestwrongideawhenpeoplearel
Technologyisanothergreatforceforchange.Inpart,technologyhascausedthepopulationexplosion;manyofuswon’tnowbea
A、Whichdayspeopleshouldwork.B、Howtheweekisdividedintodays.C、Whichdaybeginstheweek.D、Howmanyweekstherearein
Accordingtothispassage,adiethighinplant-basedfoodsplaysanimportantroleinfightingallkindsofdiseases.Ifyouw
A、Theyusuallyacceptresponsibility.B、Theyblamefactorsbeyondtheircontrol.C、Theycomplainabouttheirpersonalproblems.
Thispassageisabouta______.AccordingtoDr.Scorer,lightningiscausedby______.
Forthispart,youareallowed30minutestowriteashortessayentitledPreservingCultureintheFaceofGlobalization.Yous
InMedievalEnglandthetallesthorseswereriddenbypeopleofthehighestrankwho,fromtheirlofty(36)______,lookeddowno
A、Theywereexpensive.B、Noonebelievesthem.C、Theywereunsuccessful.D、Theywereoftendeceptive.DWhatwastheproblemwith
A、aninterestingtopicB、specificfactsC、thewriter’suniqueperspectiveD、ageneralimpressionC由题干agoodwritingmustpresent
随机试题
由于电子从基态到第一激发态的跃迁最容易发生,对大多数元素来说,共振吸收线就是最灵敏线。因此,元素的共振线又叫分析线。()
Musiccomesinmanyforms,mostcountrieshaveastyleoftheirown.【C1】______theturnofthecenturywhenjazzwasborn,Americ
绞窄性疝的处理原则是()。
粗装修消防验收是对消防工程的()安装调试完毕的消防验收。
资产负债表中“存货”项目的金额,应根据()账户的余额分析填列。
一天,香烟对蜡烛说道:“蜡烛哥哥,人们都说您的精神伟大______‘烧毁了自己,照亮了别人。’其实,我跟你差不多______烧毁了自己,提醒了别人。”蜡烛听了,哈哈笑道:“你是用甜言蜜语使一些意志薄弱的人上当,损害他们的健康。你是‘烧毁了自已,毒害了别人。
材料12019年6月28日,伊朗核问题全面协议联合委员会会议在奥地利维也纳举行。各方表示将继续推动完整、有效执行全面协议,支持国际原子能机构客观公正履行职责。各方强调将继续落实去年两次外长会声明,采取措施减少美单边制裁的影响,保障伊朗从全面协议获
目前美国的所谓“人文教育”(1iberalartseducation)的理念,在中国颇有些鼓吹者。但“人文教育”后面还有体育这—层。体育是学习人生的最好手段。体育和人生的关系,如同数学和科学的关系一样,因为体育能够把人生中千变万化的现象,抽象为几个最简
WhyAreAsianAmericansMissingfromOurTextbooks?A)Istillremembermyfourth-gradesocialstudiesproject.Ourclasswas
A、Theyoungertheyare,thelesstheyusebothoftheirhands.B、Theybecomeone-handedandstartusingbothhandsalternately.
最新回复
(
0
)