function popup(url, w, h) {
   var winl = (screen.width-w)/2;
   var wint = (screen.height-h)/2;
   var settings  ='height='+h+',';
       settings +='width='+w+',';
       settings +='top='+wint+',';
       settings +='left='+winl+',';
       settings +='scrollbars=yes,directories=no,location=no,menubar=no,status=no,toolbar=no,resizable=yes';
 window.open(url,'',settings);
 }