var wnd;
function open_doc(url, height, width)
{
    l = Math.floor(screen.width/2 -width/2);
    t = Math.floor(screen.height/2 -height/2);
    if (wnd){
        wnd.close();
    }
    if (!height){
        wnd = window.open(url, "_blank",  "top="+t+",left="+l+" ,toolbar=0,status=0,location=0,menubar=1,directories=0,resizeable=1,scrollbars=1,width="+width); 
    }else{
        wnd = window.open(url, "_blank", "top="+t+",left="+l+",toolbar=0,status=0,location=0,menubar=1,directories=0,resizeable=1,scrollbars=1,width="+width+",height="+height);
    }
}