SQL Server Express空闲超时期限？

I am using SQL Server Express 2012 for an ASP.NET application, and I noticed that if no one had used the site for more than 20 minutes or so then the first time a page hit the DB it would take more than 10 seconds to load, with subsequent hits to the DB being fast. I looked at the event log and discovered that SQL Server was being woken up by the page hit. I created a command line application that does a simple query to the DB and set it to run in the task manager every 20 minutes. Then I still noticed the "wakeup" entry like this every 20 minutes:I am using SQL Server Express 2012 for an ASP.N