function abreJanela(a,w,h,b) {
		b = b + ",width=" + w + ",height=" + h + ",top=" + ((screen.height / 2) - (h / 2)) + ",left=" + ((screen.width / 2) - (w / 2));
		var win = window.open(a,"_blank",b);
		if(!win){
			alert("Desative o bloqueador de popup's para ativar este recurso!");
		};
	}