(function(jQuery) {
	jQuery.fn.ptop = function () {
		var plink = jQuery(this);
		var poffsettop = jQuery(plink).offset().top;
		var h = jQuery(window).height();
		if (h > poffsettop) {
			plink.css('visibility','hidden');
		} else {
			plink.css('visibility','visible');
		}
	};
})(jQuery);