function Popup(url) {
    var w = 600;
    var h = 500;
    var l = Math.floor((screen.width - w) / 2);
    var t = Math.floor((screen.height - h) / 2);
    window.open(url, "", "scrollbars=yes,width=" + w + ",height=" + h + ",top=" + t + ",left=" + l);
}

function checkEmail(email) {
    var filter = /^([a-zA-Z0-9_.-])+@(([a-zA-Z0-9-])+.)+([a-zA-Z0-9]{2,4})+$/;
    if (!filter.test(email)) return false;
    else return true;
}