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
考研
At the moment, there are two reliable ways to make electricity from sunlight.【F1】You can use a panel of solar cells to create th
At the moment, there are two reliable ways to make electricity from sunlight.【F1】You can use a panel of solar cells to create th
admin
2016-03-22
23
问题
At the moment, there are two reliable ways to make electricity from sunlight.【F1】
You can use a panel of solar cells to create the current directly, by liberating electrons from a semiconducting material such as silicon. Or you can concentrate the sun’s rays using mirrors, boil water with them, and employ the steam to drive a generator.
Both work. But both are expensive. Gang Chen of the Massachusetts Institute of Technology and Zhifeng Ren of Boston College therefore propose, in a paper in Nature Materials, an alternative. They suggest that a phenomenon called the thermoelectric effect might be used instead—and they have built a prototype to show that the idea is practical.
In their view, three things are needed to create a workable solar-thermoelectric device. The first is to make sure that most of the sunlight which falls on it is absorbed, rather than being reflected. The second is to choose a thermoelectric material which conducts heat badly(so that different parts remain at different temperatures)but electricity well.【F2】
The third is to be certain that the temperature gradient which that badly conducting material creates is not frittered away by poor design.
The two researchers overcame these challenges through clever engineering. The first they dealt with by coating the top of the device with oxides of hafnium, molybdenum and titanium, in layers about 100 nanometres thick.【F3】
These layers acted like the anti-reflective coatings on spectacle lenses and caused almost all the sunlight falling on the device to be absorbed.
The second desideratum, of low thermal and high electrical conductivity, was achieved by dividing the bismuth telluride into pellets a few nanometres across.【F4】
That does not affect their electrical conductivity, but nanoscale particles like this are known to scatter and obstruct the passage of heat through imperfectly understood quantum-mechanical processes.
The third objective, efficient design, involved sandwiching the nanostructured bismuth telluride between two copper plates and then enclosing the upper plate(the one coated with the light-absorbing oxides)and the bismuth telluride in a vacuum. The copper plates conducted heat rapidly to and from the bismuth telluride, thus maintaining the temperature difference. The vacuum stopped the apparatus losing heat by convection. The upshot was a device that converts 4.6% of incident sunlight into electricity.【F5】
That is not great compared with the 20% and more achieved by a silicon-based solar cell, the 40% managed by a solar-thermal turbine, or even the 18-20% of one of the new generation of cheap and cheerful thin-film solar cells.
But it is enough, Dr Chen reckons, for the process to be worth considering for mass production.
【F2】
选项
答案
第三是确保那种导热性差的材料产生的温度变化不会因为设计缺陷而白白浪费。
解析
转载请注明原文地址:https://jikaoti.com/ti/YYZ7FFFM
0
考研英语一
相关试题推荐
Americansbelievenoonestandsstill.Ifyouarenotmovingahead,youarefallingbehind.Thisattituderesultsinanationof
Americansbelievenoonestandsstill.Ifyouarenotmovingahead,youarefallingbehind.Thisattituderesultsinanationof
[A]TheLaborDepartmentexpectstwomillionnewjobsthisyearontopofthe1.7millioncreatedlastyear.Helpingtofuelwha
Whatmakesagreathighschool?Americansthinkalotofthingsdo,fromoutstandingacademicsorasupportiveenvironmentfors
Whatmakesagreathighschool?Americansthinkalotofthingsdo,fromoutstandingacademicsorasupportiveenvironmentfors
WhenGeorgeBushleftthepresidencyonJanuary20th,manyAmericanswerekeentoturnthepage.Theyhavewarmlywelcomedanew
Intheiridlemoments,historiansoccasionallyspeculateonhowtheworldwouldbedifferentifAdolfHitlerhadpassedtheentr
Athleteswhocheatbyinjectingthemselveswithstoredsuppliesoftheirownbloodmightsoonbecaughtout.Arevealingtrailo
Iamaddictedtoelectricity.Soareyou.Andsoisyourbusiness.Weliveinan"alwayson"world—airconditioners,streetlight
随机试题
某鸡场幼龄鸡表现为浆液或黏液性鼻液,鼻孔堵塞、频频摇头、喷嚏。部分鸡有呼吸道哕音。病鸡食欲不振,生长停滞。后期鼻腔和眶下窦中蓄积渗出物而引起眼睑肿胀,症状消失后,发育受到不同程度的抑制。产蛋鸡表现产蛋量下降和孵化率低,孵出的雏鸡活力降低。最可能的疫病是
认知过程不包括
患儿2.5个月,面色略苍白,精神反应尚可,因咳嗽,流涕2天来院就诊。查体:精神面色可,睑结膜略苍白,心肺(-),肝肋下1cm,脾未及。末梢血:血红蛋白110g/L(11g/dl),红细胞3.1×1012/L(310万/mm3),网织红细胞0.5%,白细胞及
基础体温随月经周期变化,与孕激素有关。()
对城市地下工程管线避让原则的表述,错误的是()
甲公司向乙公司购买水泵一台,为支付货款,签发了一张以自己为出票人、以乙公司为收款人、以丙银行为承兑人、票面金额为30万元、到期日为2011年8月3日的银行承兑汇票,并交付给乙公司。甲公司和丙银行均在该汇票上进行了签章。乙公司的财务人员A利用工作之便,将上述
已知总体X的概率密度f(x)=(λ>0),X1,…,Xn为来自总体X的简单随机样本,Y=X2.(I)求Y的期望EY(记EY为b);(Ⅱ)求λ的矩估计量和最大似然估计量(Ⅲ)利用上述结果求b的最大似然估计量.
Ifyouhavehighbloodpressure,you’reingood【C1】______.Hypertensionaffects67millionAmericans,includingnearlytwo-third
A、Heusesdifferentcameras.B、Heoftenmakesthemposeforpictures.C、Heusuallycatchesthemunawares.D、Healwaysasksthem
Agoodmany(build)havebeenburntduringthefire.
最新回复
(
0
)