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Ngày tải lên: 29/03/2014, 14:20

... be sure to: • Wash your hands often with soap and water. Use alcohol-based hand sanitizer when soap and water are not available. • Avoid touching your eyes, nose, and mouth. The flu often ... telephones and light switches with a disinfectant cleaner or a cleaner with bleach. You can also mix your own water and bleach solution. Mix ten parts water with one part bleach. • Limit your ... ăn cho thú nuôi trong nhà 1 Pandemic Flu: What it is and How to Prepare When many people get a disease at the same time, it is called a pandemic. Pandemic flu is caused when people...

Ngày tải lên: 20/12/2013, 23:15

... knowledge, understanding and skills in a variety of contexts and in designing and making products. AO3 Analyse and evaluate products, including their design and production. Quality of Written Communication ... weaknesses which limit its suitability for the • target market Criterion 4 Mark Band Testing and Evaluation 9 –12 Detailed testing and evaluation as appropriate throughout the designing and • making ... little evidence of research and analysis of context • Design criteria is very general and is lacking in any detail• Limited understanding of the target market/user evident• 16 GCSE Design and...

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... Software Design & Development Software Design & Development Day 1 - Definitions and Overview Day 2 - Software Design Software Development Day 2 - Software Design Reviewing the design ... testing Software Design Software Design Day 2 - Software Design Analyze requirements Create design Analyze and review Correct and improve Utilize prototype to investigate and resolve key ... Day 2 - Software Design Reviewing the design - finally  Scrutinize the list of planned activities and test activities to ascertain whether any changes or additions are needed  The design...

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Ngày tải lên: 28/06/2014, 07:20

... I2C subsystem, and USB gadgets. vi Embedded Linux System Design and Development Ⅲ Borland is a registered trademark of Borland Software Corporation in the United States and other countries. ... Sriram Neelakandan xx Embedded Linux System Design and Development Linux-based embedded system does not stop with the OS but has to do a lot with writing and building applications. And applications ... leaks and memory corruption in applica- tions and drivers. Ⅲ Learn methods to profile applications and the kernel. Ⅲ Understand uCLinux architecture and its programming model. Ⅲ Understand the...

Ngày tải lên: 04/08/2012, 14:23

... logo, and the Sybex logo are trademarks or registered trademarks of John Wiley & Sons, Inc. and/ or its affiliates, in the United States and other countries, and may not be used without written ... years, and has created lay- outs and designs for many successful software training books, videos, and magazines. Ted is the author of InDesign CS2 at Your Fingertips, The InDesign Effects Book, and ... Creative Suite 2 Integration: Print Project Workflow, Getting Started with Quark Interactive Designer, and Bridge and Version Cue CS3 Essential Training—all available at Lynda.com. And he teaches a digital...

Ngày tải lên: 13/12/2013, 02:16

... overcome the complexity that exists in large applications. The following is a brief summary of the benefits of design patterns and reusable components: ● Design patterns – Design patterns provide ... methodologies for solving general problems and the ability to use the collective knowledge and experience of the IT community to improve the quality of your own applications. You can use ... well-documented and wellunderstood design patterns. The purpose of design patterns is to: ● Document simple mechanisms that work ● Provide a common vocabulary and taxonomy for developers and architects...

Ngày tải lên: 14/12/2013, 13:15

... world-ready Web applications and also simplifies maintenance and extensibility after the application has been deployed. Chapter 7: Globalization and Localization 135 Additional Information For ... to fit on the screen, and regenerating images for specific cultures. To simplify localization efforts and minimize costs, deal with globalization and localization issues during the design ... Design and Implementation Guidelines for Web Clients With such a rich selection of synchronization mechanisms available to you, you must plan your thread synchronization design carefully and...

Ngày tải lên: 14/12/2013, 13:15

... Inc. 4 LinearlyActingExternalandInternal DrumBrakes Linearlyactingdrumbrakesarethosefittedwithshoeswhich,whenacti- vated,approachthedrumbymovingparalleltoaradiusthroughthecen- teroftheshoe.TypicallinearlyactingdrumbrakesareillustratedinFigures 1–3. Analysisoflinearlyactingbrakesincludesthoseinwhichthecentrally pivotedshoesareattachedtopivotedlevers,asinFigure1.Includingbrakes ofthisdesignwithinthecategoryoflinearlyactingbrakesisjustifiedifthey aredesignedsothattheappliedforcesontheshoesandliningsactalongthe radiioftheshaftsthattheygripwhenthebrakesareapplied.Brakesofthis typemayacteitheruponbrakedrumsordirectlyuponrotatingshaftsandare suitableforuseinheavy-dutyapplications,suchasfoundinminingand constructionequipmentandinmaterials-handlingmachinery. Internallinearlyactingdrumbrakes,suchasusedontrucksinEurope, maybedesignedasinFigure2.Eitherpneumaticorhydrauliccylindersor cams ... signreversalfoundintheexpression(RcosuÀr)whenequation(1-5a)is appliedtoaninternalshoe.Thesignreversalsimplychangesthedirectionof rotationimpliedbyapositivevalueofM f ,aswasdiscussedinanearlier section. Thenearlyhorizontalportionfrom0jtoabout30jimpliesthatfor externalshoeswhichsubtendananglelessthan30j,anychangesinthelength oftheshoethatdonotincreasethesubtendedanglebeyond30jwillhavea negligibleeffectontheR/rratio.Thiscorrelateswiththeshort-shoesegments usedinthebrakesshowninFigure3.Moreover,thevalueofM f causedbya deviationfromtheR/rratiothatyieldsazerovalueofM f willbesmalliff 0 remainssmall.Inparticular,iftheRvaluethatyieldsM f =0isreplacedby R+yRinequation(1-5a),themomentduetofrictionwillincreasetoonly Ap max rw yR 2 ðf 0 þsinf 0 Þ whichissmallenoughtobeeasilyresistedbytheshouldersshownontheshoes inFigure3. ActivationforceF s andtangentialforceF t onasymmetricallyplaced pivotaregivenbytherelations F s ¼2p max rw Z f 0 =2 0 cos 2 udu¼ 1 2 p max rwðf 0 þsinf 0 Þð1-8Þ and F t ¼2Ap max rw Z f 0 =2 0 cos 2 udu¼AF s ð1-9Þ F IGURE 5VariationofR/rwithanglef 0 . Linearly Acting External and Internal Drum Brakes 73 Copyright © 2004 Marcel Dekker, Inc. Substitution for M p and M f from equations (2-7) and (2-11) into equation (2-12) ... Acting External and Internal Drum Brakes 79 Copyright © 2004 Marcel Dekker, Inc. Let the shoe be restrained at A to prevent it from rotating with the drum, with the restraint moving with the shoe....

Ngày tải lên: 17/12/2013, 11:15

... Inc. SimplatrolDanaproducesasmall-capacity(under8oz-in.)unitde- signedtohaveanadjustabletorquerangeandtousetheconstructionsim- ilaritiesbetweeneddy-currentandhysteresisbrakes/clutches.InittheIMand OMarereplacedbyapermanent-magnetdiskandeitheraneddy-currentor hysteresisdisk.Torquecapacitymaybeadjustedbymeansofthefluxgate placedbetweenthem,asshowninthebrakeversioninFigure18.Manual rotationofthefluxgaterelativetothemagneticdiskdeterminesthestrength ofthemagneticfieldthatactsoneitherthehysteresisoreddy-currentdisk attachedtothefront,unthreaded,shaftontheassemblyshown.Thereardisk, themagneticplate,andthefluxgaterotatetogetherinthecaseofaclutch,or remainstationaryinthecaseofabrake.Clutchandbrakeunitsdifferonlyin thattherearshaftofthebrakeisthreaded,asshowninthefigure. Thetorqueversusspeedcurvesforaneddy-currentbrakeinFigure16 mayalsobeusedtodeducethecharacteristicsofaneddy-currentclutch; namely,thataneddy-currentclutchcanprovideacontrolledsoftstartbe- tweenadriverandadrivenunitbycontrollingtheexcitationcurrentasa functionofthespeeddifference.Likewise,aneddy-currentclutchmayalsobe consideredwhenadrivenmachinemayexperiencespeedchangesofseveral hundredrpmthatshouldnotimposealargetorquechangeondrivingma- chine.Sincethetorqueavailabletoaccelerateadrivenmachinebackupto speedwillbesmall,aneddy-currentclutchwillbesuitableonlyifprolonged F IGURE 16Combinedtorquerotationalspeedcurveandtorqueexcitationcurves for ... Inc. OMandtheIM.Thebrakeconfigurationdiffersfromtheclutchonlyinthat theIMisrigidlyattachedtothebrakeframe. AnelectromagneticcoiloutsidetheOMandconcentricwithitisusedto activatethebrakeorclutch.Whenthecoilinenergizedbypassingcurrent throughitamagneticfieldisestablishedwhichcausestheparticlestobridge thegapbetweentheIMandtheOMandformlinksbetweenthetwo,as representedinFigure6(b).Theselinksarealongthemagneticlinesofforce, whicharemadenearlyperpendiculartotheOMbytheconfigurationofthe OMandthecoilhousing,asshowninFigures 6and7 . Boththeshearandtensilestressesintheselinksresistrelativemotion betweentheIMandtheOMandsotransmittorqueforthebrake/clutch. Theseshearandtensilestressesdevelopedaredependentonthecoilcurrent F IGURE 4Hysteresisbrakewitha8-lb-ftcapacity.(CourtesyofMagneticPower Systems, ... and j Á D ¼ U D ¼ q o E and H ¼ B A o ð1-2Þ where U denotes the charge density (coulombs/meter 3 ) and constants q o and A o denote the electric and magnetic permeabilities of free space, respectively....

Ngày tải lên: 17/12/2013, 11:15

... Inc. maximuminFigure16,setg=13.52j,asreadusingtheMathcadTrace feature.Evaluationofequation(1-13)forn=0.2,g=180,U=0.3,a=14j, andh=20foru=13.52jandforu=20jgivesadetentforceof4.544lb, whichiswithintheacceptablerange.Substitutionofg=180andq=1/32in. intoa=gq=180/32=5.625in.enablesdeterminationofrfromr=Ua= 0.(5.625)=1.688in.Withlengthlgivenbyl=r/n=1.688/0.2=8.44in. ,it followsthattheclearancegivenbylÀr=8.440À1.688=6.752in.exceeds thatspecified. Thisclearancerequirementmaybesatisfiedbyincreasingthemagni- tudeofnandreducingthemagnitudeofg.Thus,ifn=0.28andg=150,the detentforcebecomes4.702lb,aisreducedto4.688in.,andrbecomes1.406in. Thesevaluesgivel=5.021in.,sotheclearanceis5.021À1.406=3.615in., whichiswithinthedesiredrange. VI.EXAMPLE3:CONEDRIVE Selectaconedriveforacombinationgolfcardandaproposedcongestedarea commutercartforuseincommunitiesthatacceptthem.Analysisoftorque transmissiononthebasisofthedynamiccoefficientsoffrictionforacceptable liningsindicatesthata2.00-in.overlapwouldbesufficient. Forcomparison,consideronedesignwiththedriverconehavingan apexhalf-angleof40janddrivenconeshavingapexhalf-anglesof50janda seconddesigninwhichboththedriveranddrivenconeshaveapexhalf-angles of45j.Inbothcasesinitiallyselectaconegeneratorlengthof6.00in.toallow theoverlaptobegreaterthan2.00in.intheeventthattheprototypeshould requiremodification. Beginwiththe40j,50jcombinationandturntoFigure11toselectthe dimensionsoftheconesbyenteringthecurveatz=6andreadinguptothe 40jline.Theprincipalradiusofcurvatureatthatpointis5.0346.Sincezis measuredininches,theprincipalradiusofcurvatureis5.0346in.Readingto theleftatthisvalueofUyieldsthatatz=4.25in.,theprincipalradiusof curvatureofthe50jhalf-angleconeis5.0650in.Aplotofthex-dimensionfor eachcone,showninFigure17(a),confirmsthatthetwoconesshouldroll without ... between the driver and driven cones coincide with the z-axis so that u = f in (3-4), (3-6), and (3-7). Since the driver cone must roll freely within a driven cones, it is essential that its radius of ... Inc. setofunitstobeusedforeachratio,andtheresultingratiosareindependent oftheunitsused. Relativelybroadcurvesareshowninthefollowingcomputer-generated graphsforeasyreadingtoshowcharacteristicbehaviorandtoprovide contrastagainstthegridlines.Associatedroutines,suchasMathcadTrace, appeartoreadthemfromtheoriginatingdata,therebyeliminatingtheread- ingerrorsassociatedwithtracewidths. I.BELTDRIVES Equipmentusingnonmetallicbeltdrivesmayincludetheclutchcapabilityby mountingthemotor(becauseitisusuallysmallerthanthedrivenmachine) eitheruponahingedbaseoruponaslidingbasefittedwithaleveroralinkage thatpermitsthemotortobemovedtoandfromthedrivenmachineinorder toapplyandrelievethebelttensionandtherebygiveclutching(applyingbelt tension)anddeclutching(relievingbelttension)capability. Thesedesignseliminatetheneedforamechanicalclutch.Theirsim- plicityisachieved,however,attheriskofintroducingthepossibilitythat frictionalheatingofthebeltduringidling,whenthebelt(orbelts)mayreston themotor’srotatingsheave(pulley).Thatmaygenerateenoughheattocause beltingmaterialstoslowlyshrink.Thisreductioninthecenterdistance betweenthedrivinganddrivenpulleys,orsheaves,maybegreatenoughto causeanunintendedre-engagementofthemotorandthedrivenmachine .It mayalsoinhibittheirdisengagement.Consequently,somebeltmanufacturers producebeltsthatresistshrinkageduetoheatingforuseintheseclutching anddeclutchingapplications. Torquecapabilityforthesedrivesisaseparatecalculationtobe performedaccordingtotheproceduresgivenbythebeltmanufacturers. Therefore,itwillnotbeconsideredinthefollowingdiscussion. A.HingedBase Atfirstglanceitmayappearthatmovingamotorbymountingiteitherona hingedbaseoronaslidingbaseissosimplethatnoanalysisisnecessary.An analysis,however,doesbringforthseveralconsiderationsthatmaybemissed inselectingthedimensionsofthebaseplate,inlocatingthepositionofthe baseplatehinge,orindesigningthelinkagefortheslidingbaseplate. Twosimilar,butdistinct,mountingdesignsforhingedbaseswillbe considered.Intheseconfigurationsitistheweightofthemotoralonethat providesthebelttension.ThetensionvectorshowninFigure1(a )and( b) acting...

Ngày tải lên: 17/12/2013, 11:15

... Inc. Typicalmodesofbackplatevibrationinthefirstmodeareshownin Figure7anditsnodallines,indicatedbydashedcurvesinFigure7,are shownaloneinFigure8.Figures 9and1 0showabackplatebeforeandafter araisedportion(Figure11)wasaddedtoreducethefrequencyofthenoise generated. III.FINITEELEMENTANALYSIS Murakami,Tsudada,andKitamura[13]reportedonafiniteelementanalysis ofautomotivediskbrakestocomparethecalculatedresonancefrequencies withpreviousmeasurementsofbrakesquealonachassisdynamometerand toassociatethemwithcalculateddeformationofthebrakecomponents. Secondarylow-frequencysquealfrom2to3kHzandprimaryhigh-frequency squealfromabout5.5to10.5kHz,asshowninthehistograminFigure12, correlatedwellwiththeclusteringoffrequenciesfoundforthebrakedisk, cylinder,pad,andtorquemember,showninFigure13.Calculateddiskand caliperfrequencymodeswhereverifiedbyholographicinterferometryandby accelerometermeasurementsinthecaseofthecaliper,orcylinder. Althoughtheclusteroffrequenciescorrelatedwiththeprimaryand secondarysquealregions,severalcomponentresonantfrequenciesbetween3 and5 .5kHzdidnotresultinbrakesquealinthisfrequencyrange.This impliedthatthedrivingforce,thestick-slipphenomenon,didnotexcitethese frequenciesandthattheywerenotexcitedbystructuralcoupling.Linearized, seven-degree-of-freedomanalysisofthesystemusingthelumped-parameter model,asshowninFigure14,gavesolutionsoftheform u¼Ae at sinðNtþfÞð3-1Þ foreachofthesevenvariablesinwhichexponenta,whichdeterminedthe regionsofinstabilityintheJarvisandMillsanalysis,wastermedthesqueal index.Thisanalysisindicatedthatthesquealindexwasrelatedtothenegative gradientofthefrictioncoefficient,asillustratedinFigure15,whichalso showstestresultsfortwotestbrakeliningpads.Theseresultsalsocorrelate withSpurr’sfindingthatthesquealprobabilityincreasedasthefrictionco- efficientincreased.Thelowsquealindexbetween3. 0and5 .5kHzanditsslope alsocorrelatewiththehistogramshowninFigure12,whichimpliesthat negativeslopeofthefrictioncoefficientversusvelocitycurveisoneof severalsignificantparametersinthegenerationofbrakesqueal.Analysis oftheinfluenceofthetorquemember,showninFigure16,indicatedthat itsinfluencewasalsominimuminthevicinityof3kHz,asshowninFigure 17,whichalsoaccountsforthelowsquealamplitudebetween3. 0and 5.5. ... Inc. ingsurfacessufficientlyforthecomponentstonearlyreassumetheiroriginal configurationandtheprocesstorepeat.Intheyearsthatfollowed,many investigationswereconductedtobetterunderstandtheroleofthefactorsthat affectedbrakeandclutchvibration.Onlyafewofthemanycontributorsto theliteratureofbrakevibrationwillbediscussedexplicitlyinthissection.This partiallistingissufficient,however,toportraythegeneraltrendsintheyears after1935. AnexperimentalinvestigationbyHollmann[2],reportedin1954, indicatedthatthetendencyforfrictionalvibrationincreasedwiththecontact pressureandthatitalsoincreasedwiththetemperatureofthefrictionma- terialsupto100jCbutthendecreasedrapidlyasthetemperatureroseabove 100jC.Afterstudiesofbrakesquealonrailwayvehicles,Broadbent[3]also concludedthatbrakevibrationwasdependentonthemechanicallinkageused andwasassociatedwithafrictioncoefficientthatdecreasedwithincreasing velocitybetweenshoeandbrake.Healsoobservedthatnochatterwasfound whenwoodenbrakeswhosefrictioncoefficientincreasedwithincreasedslip speedwereused.SimilarresultswerefoundbySinclair[4],whoalsoreported thatthefrequencyofoscillationwasstronglydependentontheequivalent massandspringconstantofthemechanicalsystemthatheldthebrakelining inplaceinthesliderblockconfigurationusedinthelaboratorymodel. Spurr[5]rejectedthenotionthatitwasnecessaryforthefriction coefficienttodecreasewithincreasingslipspeedinordertohavefrictional vibration.Hisexperimentswithrailwayblockbrakesonarailwaywheelin- dicatedthatvibrationwasindependentofthechangeinthefrictioncoefficient withslipspeedbutthatitwasmorelikelyifthefrictioncoefficientwaslarge. Thestick-sliptheoryoffrictionappearedtoholdasthedrivingmeans, however,andSpurralsoobservedthatthefrequencyofoscillationdepended ontheassociatedmechanicalsystemusedtoforcethebrakeblockagainstthe wheel. InthediscussionofSpurr’spaper,F.R.Murrayintroducedwhathas beencalledthespragtheoryinBritishliterature,involvingasprag(acan- tileveredbeampressedagainstamovingsurface),asshowninFigure1.A somewhat ... Inc. Typicalmodesofbackplatevibrationinthefirstmodeareshownin Figure7anditsnodallines,indicatedbydashedcurvesinFigure7,are shownaloneinFigure8.Figures 9and1 0showabackplatebeforeandafter araisedportion(Figure11)wasaddedtoreducethefrequencyofthenoise generated. III.FINITEELEMENTANALYSIS Murakami,Tsudada,andKitamura[13]reportedonafiniteelementanalysis ofautomotivediskbrakestocomparethecalculatedresonancefrequencies withpreviousmeasurementsofbrakesquealonachassisdynamometerand toassociatethemwithcalculateddeformationofthebrakecomponents. Secondarylow-frequencysquealfrom2to3kHzandprimaryhigh-frequency squealfromabout5.5to10.5kHz,asshowninthehistograminFigure12, correlatedwellwiththeclusteringoffrequenciesfoundforthebrakedisk, cylinder,pad,andtorquemember,showninFigure13.Calculateddiskand caliperfrequencymodeswhereverifiedbyholographicinterferometryandby accelerometermeasurementsinthecaseofthecaliper,orcylinder. Althoughtheclusteroffrequenciescorrelatedwiththeprimaryand secondarysquealregions,severalcomponentresonantfrequenciesbetween3 and5 .5kHzdidnotresultinbrakesquealinthisfrequencyrange.This impliedthatthedrivingforce,thestick-slipphenomenon,didnotexcitethese frequenciesandthattheywerenotexcitedbystructuralcoupling.Linearized, seven-degree-of-freedomanalysisofthesystemusingthelumped-parameter model,asshowninFigure14,gavesolutionsoftheform u¼Ae at sinðNtþfÞð3-1Þ foreachofthesevenvariablesinwhichexponenta,whichdeterminedthe regionsofinstabilityintheJarvisandMillsanalysis,wastermedthesqueal index.Thisanalysisindicatedthatthesquealindexwasrelatedtothenegative gradientofthefrictioncoefficient,asillustratedinFigure15,whichalso showstestresultsfortwotestbrakeliningpads.Theseresultsalsocorrelate withSpurr’sfindingthatthesquealprobabilityincreasedasthefrictionco- efficientincreased.Thelowsquealindexbetween3. 0and5 .5kHzanditsslope alsocorrelatewiththehistogramshowninFigure12,whichimpliesthat negativeslopeofthefrictioncoefficientversusvelocitycurveisoneof severalsignificantparametersinthegenerationofbrakesqueal.Analysis oftheinfluenceofthetorquemember,showninFigure16,indicatedthat itsinfluencewasalsominimuminthevicinityof3kHz,asshowninFigure 17,whichalsoaccountsforthelowsquealamplitudebetween3. 0and 5.5....

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