Why doesn't Oracle kill dead connections?

[Sona]

Hi I have a Reporting appliaction. The reports are run from the browser . The reports are basically Pl/SQL packages .the request is made from the browser and then communicated to the database thru  OAS .(oracle application server) which acts as web server. The problem is when a user executes a report (i.e. hits the RUN button) and then closes the broser before the execution of the report is completed.Oracle still contimues running the query in the database. The session still remains ACTIVE in the database even though the client has closed the connection (i.e. the user has closed the browser). Is there any way to force Oracle to kill the session when the user closes the browser?   TIA