美赛—21组
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TransmissionmodelofinfectiousdiseasesSummaryTask1,Weassumethatthenumberofpersonswhichareinfectedbyainfectedpersonatonetimeisaconstant,andthepersonwhoisinfectedwillnotdieintheinfectiousperiod.Accordingtotheassumptions,weestablishasimplemodel.Wecanconcludethatthespreadoffluisexponential,thisisconsistentwiththeearlystagesofthespreadofflu.Becauseoftheinfiniteincreaseofthenumberofpeopleinthelaterstageofthesimplemodel,itdoesnotaccordwiththeactualsituation,wemodifythemodelontheoriginalmodel.Wedividethepopulationintotwogroups:Onegroupisthepeoplewhohasbeeninfected,theothergroupisthepeoplewhoissusceptibletoinfection.Throughtheanalysisofthemodel,wefoundthatthepeakofthespreadoffluisconsistentwiththeactualsituation.Task2,theconclusionthateveryonewillgetsickisn'tconformtotheactualsituation.Wefurthersubdividetheresearchobjecttoimprovethemodel.Wedividethepopulationintothreegroups:Thefirstgroupisthepeoplewhohavebeeninfected,Thesecondgroupisthepeoplewhoareeasytobeinfected,Thethirdgroupisthepeoplewhohavebeenremoved,includingthemanwhodiedafterbeingsick,Peoplewithlong-termimmunityafterillness,andthosewhohavebeenquarantinedaftertheillness.Throughtheanalysisofthemodel,Themodeldescribesrightlythelawofflu.Basedonthemodel,Wedofurtherresearchonthecontrolofflu.Wefoundthatthecontroloffluiscloselyrelatedtotheparametersofthemodel,suchasthethreshold,theinfectionrateandtheexclusionrate.Wecanadjusttheseparameters,soastoachievethepurposeofcontrollingflu.IntroductionAsisknowntoall,theoutbreakofinfluenzaisaseriousthreattohumanhealth.Inordertoexplorethelawofthespreadoffluandcontrolthespreadofflu,Weestablishamathematicalmodeltostudythespreadofflu.Thespecificprocessisasfollows:
Firstofall,westartfromthegeneraldiseases,makeassumptionsandestablisha
simplemodelofthespreadofflu.Then,wefurtherdividedtheresearchobjects.Combiningwiththeactualsituation,wemodifythesimplemodel.Throughanalyzingandimprovingthemodel,wegetthemodelofthespreadofflu.onthebasisofthemodel,wegetthetheoreticalsupportofthevaccinethatcaneffectivelysuppressthespreadofflu.TheStrengthsandweaknessesofthemodelwhichweestablishedWecometotheconclusion.
SymbolsSymbolQuantitykThenumberofpersonswhichareinfectedbyainfectedpersonatonetimeisaconstant
0kThenumberofpersonswhichareinfectedbyainfectedpersonatonetime
tTime
I(t)&i(t)Thenumberofpatientsatthetimeofti0Thenumberofpatientsinitiallyinfected
S(t)&s(t)ThenumberofpeoplenotinfectedatthetimeoftsThenumberofpersonwhoarenotinfectedR(t)Thenumberofpeoplewhohavebeenremovedatthetimeoft
nTotalnumberofpopulationrInfectionrateλExclusionrateThreshold
Tab1:Symbolsusedinthispaper
Model
Task1BasicmodelHypothesis:ThenumberofpersonswhichareinfectedbyainfectedpersonatonetimeisaconstantK.Thepersonwhoisinfectedwillnotdieintheinfectiousperiod.
Weuse)(titostandforthenumberofinfectedpersonsatthetimeoft.Anduse0k
tostandforthenumberoftheinfectedinfectedbypatientsattheunittime.”0)0(ii”standfortheInitialnumberofthepatient.While,theincreasingnumberofthetimeslotoftisttiktitti
0
bothsidesDividebytatthesametimeandletting0Δtcangetthedifferentialequation.
0
00ditkitdtii
Itssolutionistkeiti00
.0246810121416182000.511.522.533.544.55x 108ti(t)i(t)=e
t曲线图
Figure1i-trelationgraphThisindicatesthatthespreadoffluisexponentialgrowth.Theresultsareinagreementwiththeinitialstageofthespreadofflu.Intheearlystageofthespreadofflu,thepropagationspeedisveryfastandthenumberofinfectedpeopleisafunctionofgrowth.Butitcanbeknownfromtheformula,Whentapproachesinfinity,tiapproachesinfinity.Itisclearlynotinlinewiththeactualsituation.Theproblemisthatthehypothesisdoesnotapplytoalongerperiodoftime.Inparticular,thehypothesis(1)thatthenumberofinfectedpersonsatonetimeisconstant,whichisnotconsistentwiththeactualsituation.Becausewiththepassageoftime,moreandmorepeopleinfected,andthenumberofvulnerablepeoplearelessandless,sothesituationsofthespreadoffluindifferentperiodsaredifferent.Inordertocoincidewiththeactualsituation,wemodifythebasicmodel.
ModificationofmodelThepopulationisdividedintotwocategories:onefortheinfected,andtheotherforthevulnerable.Weuse)(tiand)(tstostandforthenumberofthetwocategoriesatthetimeoft.0iti.Hypothesis: