function popup(w,h,url)
{
        x = screen.availWidth/2-w/2;
        y = screen.availHeight/2-h/2;
        var popupWindow = window.open(
            url,'','width='+w+',height='+h+',left='+x+',top='+y+',screenX='+x+',screenY='+y+',scrollbars=no');
}