What can cause an ASP.NET worker process to be recycled?

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<system.web>
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    <healthMonitoring>
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        <add name="Application Events"
            eventName="Application Lifetime Events"
            provider="EventLogProvider"
            profile="Default"
            minInterval="00:01:00" />
      </rules>
    </healthMonitoring>
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<compilation debug="true" tempDirectory="c:AnkerExTemporary ASP.NET files">
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