重要-Ballistic phonons and the shape of the ray surface in cubic crystals 外文学习材料

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1、PHYSICALREVIEWBVOLUME24,NUMBER615SEPTEMBER1981BallisticphononsandtheshapeoftheraysurfaceincubiccrystalsA.G.EveryDepartmentofPhysics,UniversityoftheWituatersrand,Johannesburg200l,SouthAfrica(Received1.1March1981)Theshapeoftheacousticraysurfaceofcubiccry

2、stalsisinvestigatedwiththeobjectofprovidingaframeworkwithinwhichtheresultsofphononimagingandotherballisticphononexperimentscanbeinterpreted.Thissurfaceisshowntodisplayconsiderablevariabilityinshape,particularlywithregardtothewayinwhichitisfolded.Thecor

3、respondencebetweenthesefoldsandcontoursofzeroGaussiancurvatureontheslownesssurfaceisexplored,andthebearingthishasonthepresenceofcausticsintheanistropicfluxofphononsemanatingfromalocalizedhearsourceisdiscussed.Severaloftheelementarycatastrophesaswellass

4、omeremarkabletypesofstructuralinstabilityar'eshowntooccurinthesecaustics.Conditionsontheelasticconstantsareestablishedfortheexistenceofvarioussystemsoffoldsintheraysurface.I.INTRODUCTIONofflighttechniquesthatare"nowavailablefortheonestudyofballisticpho

5、nons,cananticipateaThevel.ocity,slowness,andraysurfacesarerapidincreaseinthegenerationofdetailedexperi-invaluableaidstotheunderstandingofthenaturementaldataontheraysurfaceandrelatedmatters.ofacoustic-wavepropagationinelasticallyaniso-Theaboveconsiderat

6、ionshavemotivatedthetropicsolids.Indeed,itisdifficulttoimaginetheoreticalinvestigationwhichwereportinthishowthesubjectofcrystalacousticscouldbede-paper.Asystematicsurveyhasbeencarriedoutvelopedwithouttheseconstructs.Theraysurfacetodetermineallthetopolo

7、gicallydistinctshapesisphysicallythemostmeaningfulofthethreeinthattheraysurfaceofcubiccrystalscantakeonthatitrepresentsthewavefrontorsurfaceofundertheconditionsthattheelasticconstantssat-equalphaseforanoscillatorydisturbanceaunitisfythethermodynamiccon

8、straintsandthelong-timeintervalafterithasbeencreatedattheitudinalphasevelocityisgreaterthanthetwoorigin.Italsohappenstobethemostcomplica-transversevelocitiesinalldirections.Itishopedtedofthethree.Inspiteofitsimportance,ourthatthisstudyw