function center_popup_top(url, window_name, width, height) {
	properties = "menubar=0,resizable=no,toolbar=0,location=0,scrollbars=0,height=" + height + ",width=" + width + ",left=" + (screen.width/2-width/2) + ",top=" + (screen.height/2-height/2);
	popupHandle = open(url, window_name, properties);
	popupHandle.focus();
	}