var winHandle=null;
 function openWindow(url) {
 if(winHandle==null){
     winHandle=window.open(url,'tavant_login_window');
	}
	else if(winHandle.closed==true){
	   winHandle=window.open(url,'tavant_login_window');
	}
	else{
	alert("A window is already open");
	}
	}