function popup(url,w,h) {
	var posw = (screen.width - w) / 2;
	var posh = (screen.height - h) / 2;
	pop_up = window.open(url,"Popup","status=no,scrollbars=no,resizable=no,height="+h+",width="+w+",top="+posh+",left="+posw);
}