protected void Session_End(Object sender, EventArgs e)
{
string userName = Membership.GetUserNameByEmail(User.Identity.Name);
Guid userId = Guid.Parse(Membership.GetUser(userName).ProviderUserKey.ToString());
ParticipantRepository participantRepository = new ParticipantRepository();
participantRepository.RemoveUserFromAllTubes(userId);
HttpContext.Current.Cache[userId.ToString() + "online"] = false;
}