//centered popup window
function popup(url, name, _width, _height) {
    var width  = _width;
     var height = _height;
     var left   = (screen.width  - width)/2;
     var top    = (screen.height - height)/2;
     var params = 'width='+width+', height='+height;
     params += ', top='+top+', left='+left;
     params += ', directories=no';
     params += ', location=no';
     params += ', menubar=no';
     params += ', resizable=no';
     params += ', scrollbars=no';
     params += ', status=no';
     params += ', toolbar=no';
     newwin=window.open(url, name, params);
     if (window.focus) {newwin.focus()}
        return false;
}