简介:本文研究kolmogorov捕食系统{(dx/dt)=x(ψ(x)-φ(y)(dx/dt)=y(bx^m-d)得到了极限环存在唯一的条件,从而推广了前人相关的结果.其中:ψ(x)=a0+a1x+a2x^2+…+a(a-1)x^(n-1)-anx^n;n≥m≥1(n,m∈N),φ(0)=0,φ(y)〉ε〉0(y〉0).
简介:Inthispaperwestudytheexistenceoflimitcycleforcubicsystem(E)3,ofKolmogorovtypewithaconicalgebraictrajectoryF2(x,y)=ax2+2bxy+cy2+dx+ey+f=0Ithasbeenprovedinmyformerpapersthat(E)3doesn’thaveanylimitcycleonthewholeplaneIfb2-ac≠0,Nowweareinvestigatingthecasewhereb2-ac=0.Weprovethesufficientandnecessaryformula(2)or(13)witbwhich(E)3musthaveaparabolictrajectoryF2(x,y)=0.Thentherewillnotbeanylimitcycleonthefullplane.Onthebasisofthis,weconclude:ThecubicsystemofKolmogorovtypewithanon-degeneratedquadraticalgebraictrajectoryonthewholeplanehasnolimitcycle.
简介:WemodeltheeffectsofweakfluctuationsontheprobabilitydensitiesandnormalizedpowersofvortexmodelsfortheBessel–Gaussphotonbeamwithfractionaltopologicalchargeintheparaxialnon-Kolmogorovturbulencechannel.Wefindthatprobabilitydensityofsignalvortexmodelsisafunctionofdeviationfromthecenterofthephotonbeam,andthefartherawayfromthebeamcenteritis,thesmallertheprobabilitydensityis.Forfractionaltopologicalcharge,theaverageprobabilitydensitiesofsignal/crosstalkvortexmodesoscillatealongthebeamradiusexceptthehalf-integerorder.Asthebeamwaistofthephotonsourcegrows,theaverageprobabilitydensityofsignalandcrosstalkvortexmodesgrowtogether.Moreover,thepeakoftheaverageprobabilitydensityofcrosstalkvortexmodesshiftsoutwardfromthebeamcenterasthebeamwaistgetslarger.Theresultsalsoshowthatthesmallerindexofnon-Kolmogorovturbulenceandthesmallergeneralizedrefractive-indexstructureparametermayleadtothehigheraverageprobabilitydensitiesofsignalvortexmodesandloweraverageprobabilitydensitiesofcrosstalkvortexmodes.Lower-coherenceradiusorbeamwaistcangiverisetolessreductionofthenormalizedpowersofthesignalvortexmodes,whichisoppositetothenormalizedpowersofcrosstalkvortexmodes.