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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.TheStrengthsandweaknessesofthemodelwhichweestablishedWecometotheconclusion.

SymbolsSymbolQuantitykThenumberofpersonswhichareinfectedbyainfectedpersonatonetimeisaconstant

0kThenumberofpersonswhichareinfectedbyainfectedpersonatonetime

tTime

I(t)&i(t)Thenumberofpatientsatthetimeofti0Thenumberofpatientsinitiallyinfected

S(t)&s(t)ThenumberofpeoplenotinfectedatthetimeoftsThenumberofpersonwhoarenotinfectedR(t)Thenumberofpeoplewhohavebeenremovedatthetimeoft

nTotalnumberofpopulationrInfectionrateλExclusionrateThreshold

Tab1:Symbolsusedinthispaper

Model

Task1BasicmodelHypothesis:ThenumberofpersonswhichareinfectedbyainfectedpersonatonetimeisaconstantK.Thepersonwhoisinfectedwillnotdieintheinfectiousperiod.

Weuse)(titostandforthenumberofinfectedpersonsatthetimeoft.Anduse0k

tostandforthenumberoftheinfectedinfectedbypatientsattheunittime.”0)0(ii”standfortheInitialnumberofthepatient.While,theincreasingnumberofthetimeslotoftisttiktitti

0

bothsidesDividebytatthesametimeandletting0Δtcangetthedifferentialequation.

0

00ditkitdtii





Itssolutionistkeiti00

.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: