function check_empty(yield,alertstring){
  if(yield==null) return true;
  if(yield.value==""||yield.value==null)  {
    alert(alertstring);
    yield.focus();
    return false;
  }
  return true;
}
function check_email(yield,alertstring) { 
	var email = /^\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$/; 
	//return email.test(val); 
	if (!email.test(yield.value)&&yield.value!="") { 
		alert(alertstring); 
		yield.select();
		yield.focus();
        return false;
	} 
  return true;
}