function abre(url,window_width,window_height){
		var window_top = (screen.height-window_height)/2;
		var window_left = (screen.width-window_width)/2;
		window.open(url,"net","top="+window_top+",left="+window_left+",width="+window_width+",height="+window_height+", maximized=no, toolbar=no, location=no, status=no, menubar=no, scrollbars=no, scrolling=no, resizebled=no");	
}