科技文章.docx
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科技文章.docx
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科技文章
触摸屏
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匿名2009-12-1012:
51:
41
Weusetouchscreenseverywhere:
touristkiosks,automatictellermachines,point-of-saleterminals,industrialcontrols.Halfadozenvendors,plusin-housedepartmentsatmajormanufacturers,produced$800millionworthin2000.Themarketisgrowingbecausetheinterfacesareeasy-to-use,durableandinexpensive.
Touchscreensemployoneofthreephysicsprinciplesfordetectingthepointoftouch.Pressinga“resistive”designwithafingerorotherstylusraisesavoltage.In“capacitive”models,afingerdrawsaminutecurrent(thismethodisoftenusedforcursorpadsonnotebookcomputers).Inotherdesigns,afingerorstylusinterruptsastandingpatternofacousticwavesorinfraredlightsthatblanketthesurface.
Resistivescreensaretheoldest,mostwidelyusedandleastexpensive,andtheyworkwithanystylus(finger,pen).Capacitivescreensmustbetouchedbyafingeroranelectricallygroundedstylustoconductcurrent.Wavescreensarethenewestandmostexpensive.Surfaceacousticwavescreensmustbetouchedbyafingerorasoftstylussuchasapencilerasertoabsorbenergy;infraredscreensworkwithanystylus.Thedifferenttechnologiesmaybeusedinthesameapplications,althoughprosandconsleadtoprevalentcombinations:
resistivescreensforindustrialcontrolsandPalmPilots;capacitivescreensforslotmachines;wavescreensforATMsandindoorkiosks.
Mostpeopleareunawareofthetypeofscreentheyareusing.Buttrickscanhelpyoutell,accordingtoFrankShenofEloTouchSystemsinFremont,Calif.,thelargestU.S.maker.Pushthescreenlightlywithyourfingernail(notyourskin).Ifitresponds,itcouldberesistiveorinfrared.Inthiscase,placetwoseparatedfingersagainstthescreenatthesametime.Ifthecursormovesbeneathonefinger,theunitisinfrared(softwareregistersthefirsttouch);ifthecursormovesbetweenthefingers,itisresistive(thepointsareaveraged).Iftheunitdoesnotrespondtoyourfingernail,againplacetwoseparatedfingersagainstit.Ifthecursormovesbeneathonefinger,theunitisacousticwave;ifthecursormovesbetweenthefingers,itiscapacitive.
凉爽的空调历史
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匿名2009-12-1012:
50:
50
[标签:
历史]
Temperaturesinsomepartsofthecountryhaveeasedabitovertheweekend.Butthereisnoriskthatthrongsofpeoplearesuddenlygoingtoturntheirbacksonair-conditioning.Theair-conditionerhasestablisheditselfwellintheheartsofAmericans.Thefirstwidespreaduseofair-conditionerscameduringthe1920whenmovietheatersusedwhattheycalledman-madeweathertolurecustomerstothesilverscream.AfterWorldWar2,thecostforair-conditionersstartedtocomedownandmanufacturesadvertisedthemasforthemillionsnotjustformillionaires.DeborahHawkins,knowshowtokeepcool.SheischairmanoftheAir-conditionerandRefrigerationInstitute.WecalledherinherofficeinFortWorth.Texaswherethetemperaturethisisabalmy,low-100s.Welcometotheprogram.
WellThankyou.
Iassumeyou'vegotyourair-conditionergoinggreatguns.
Yes,wedo,Fullblastinfact.
Allright,takeusback,wherewasthefirstair-conditionedmovietheaterintheUnitedStates.
Well,it'sprobablyintheCentralParktheaterinChicago,Illinois.WillisCarrierconsideredthekingofcoolandthefounderofair-conditioningactuallysoldhisinventionstomovietheateroperatorsduringthelate19thandearly20th.Andthiswasoneofthefirstonetohavereceivedit.Andtheyactuallyhadsomeofthelargestaudiencesthananywhereelseinthecountryasyoucanimagine.
Sodoestheair-conditionergetcreditormaybetheblamefortheadditamentofsummerblockbusters.
Err,both,Thankyougiveboth.Definitelythetermwascoinbecausepeopleweretryingtogetawayfromtheheatduringthesummermonthsandtheycameinanddrovetogetoutofthatintothecoolairandwatchedmovies,causethatwasprobablytheonlyeventthatallowedthemtodothatatthattime.
AndalsoIassumethatthetheaterjuststayedopenduringthesummer.
Well,yearlong,yearlong,WellbeforetheywereprimarilyjustopenfromNovembertoMay.
Well,whataresomeoftheotherearlyplacestobecooleddownbyair-conditioning.
Well,rightafterthemovietheaters,thegovernmentbuildingsinWashingtonD.Cwereair-conditioned,startedwiththeUSHouseofRepresentativesbuilding,theSenatebuilding,eventheWhiteHouseandit'sfunnytoobecauepriortothat,thelawmakersonlyworkedfromNovembertoMay,andthentheydispersed,youknow,wenthome.Andit'sfunnybecausemostpeoplesaythismayormaynothavebeenagoodideatoallowthemtowork12monthsallovertheyear.
Whendidair-conditioningbecomeastableoftheMiddleClass.
Well,actuallyitstartedinthe50swhensalesexceededoveronemillionunits.Andthenateachdecade,itincreasedenormously.Towherenowtoday,probably82%ofallhomeseitherhaveroomair-conditioningunitsorcentralair-conditioningunitsinAmerica.
DeborahHawkins,ischairmanoftheAir-conditionerandRefrigerationInstitutions.Thanksalot,keepcool.
清洁能源
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匿名2009-12-1012:
50:
07
[标签:
能源]
Cleanenergiesareformsofenergywhichdonotpollutetheair,theground,orthesea.
Cleanenergiesinclude:
Solarpower
SolarpowerdescribesanumberofmethodsofharnessingenergyfromthelightoftheSun.Ithasbeenpresentinmanytraditionalbuildingmethodsforcenturies,buthasbecomeofincreasinginterestindevelopedcountriesastheenvironmentalcostsandlimitedsupplyofotherpowersourcessuchasfossilfuelsarerealized.Itisalreadyinwidespreadusewhereothersuppliesofpowerareabsentsuchasinremotelocationsandinspace.
AstheEarthorbitstheSun,itreceivesapproximately1,400W/m2ofenergy,asmeasureduponasurfacekeptnormal(atarightangle)totheSun(thisnumberisreferredtoasthesolarconstant).Oftheenergyreceived,roughly19%isabsorbedbytheatmosphere,whilecloudsonaveragereflectafurther35%ofthetotalenergy.Thegenerallyacceptedstandardis1020wattspersquaremeteratsealevel.
AfterpassingthroughtheEarth'satmosphere,mostofthesun'senergyisintheformofvisibleandultravioletlight.Plantsusesolarenergytocreatechemicalenergythroughphotosynthesis.Weusethisenergywhenweburnwoodorfossilfuelsorwhenweconsumetheplantsasasourceoffood.
Windpower
Windpoweristhekineticenergyofwind,ortheextractionofthisenergybywindturbines.Thisarticledealsmainlywiththeintricaciesoflarge-scaledeploymentofwindturbinestogenerateelectricity.
Wavepower
Wavepowerreferstothecaptureofoceansurfacewaveenergytodousefulworkincludingelectricitygeneration,desalination,andfillingareservoirwithwater.Wavepowerisaformofrenewableenergy.Thoughoftenco-mingled,wavepowerisphysiologicallydistinctfromthediurnalfluxoftidalpowerandthesteadygyreofoceancurrentswhicharepoweredbytheearth'srotation.Wavepowergenerationisnotawidelyemployedtechnologywithonlyafewexperimentalsitesinexistence.
Salinitygradientpower
SalinityGradientisatechnologythattakesadvantageoftheosmoticpressuredifferencesbetweensaltandfreshwater.
Ifweplaceasemipermeablemembrane(likethatinareverseosmosisfilter)betweensealedbodiesofsaltwaterandfreshwater,thefreshwaterwillgraduallytravelthroughthefilterbyosmosis.Byexploitingthepressuredifferencebetweenthesetwobodiesofwaterwecanextractenergycommensuratetothedifferenceinpressure.
Tidalpower
Tidalpowerisameansofelectricitygenerationachievedbycapturingtheenergycontainedinmovingwatermassduetotides.Twotypesoftidalenergycanbeextracted:
kineticenergyofcurrentsduethetidesandpotentialenergyfromthedifferenceinheight(orhead)betweenhighandlowtides.
Geothermalpower
Geothermalpoweriselectricitygeneratedbyutilizingnaturallyoccurringgeologicalheatsources.Itisaformofrenewableenergy.
Somerenewableenergiesarenotcleanenergies-forexample:
BiofuelsbecausetheyreleaseNOXandparticulatesintotheenvironment.
Hydroelectricpowerbecauseitdestroystheriverbasinandhasanegativeeffectonfishmigration.
高里程黑洞
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匿名2009-12-1012:
48:
21
Wastenot.
Surroundingmatterissuckedtowardasupermassiveblackhole,whereitisexpelledbackoutatenormousspeedinanincrediblyefficientprocess.
Credit:
Harvard-SmithsonianCenterforAstrophysics
High-MileageBlackHoles
ByPhilBerardelli
ScienceNOWDailyNews
24April2006
Astronomershavediscoveredthat,deepinsidethebiggestandbrightestgalaxiesintheuniverse,jetsarespewingparticlesfromaroundblackholesinanincrediblyenergy-efficientmanner.Ifanautomobileengineworkedaswellasoneofthesemonsters,itcouldgomorethanabillionmilesonagallonofgas.
Thesurpriseisthesehigh-mileageblackholesaren'tquasars,whichareconsideredthemostenergeticandefficientbodiesintheuniverseatconvertingmattertoenergy.Instead,astronomershavediscovered,theyarerelativelyoldandquietsupermassiveblackholesthatsomehowcanmaintainsimilarefficiencieswhileexpellingmuchlessenergy.
TheastronomersuseddatafromtheChandraX-rayObservatorytostudyninesupermassiveblackholespopulatingverylargeellipticalgalaxies.Inallcases,theyfoundtheareasaroundtheblackholestobediminvisiblelightbutquitebrightinx-raywavelengths.Forthenineobjectsstudied,theycalculatedthattheblackholescouldconvertupto2.5%ofthe
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