var mywin = null;

function open_window(url) {
mywin = window.open(url,"v_articles",'toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=1,resizable=0,width=500,height=300,left=20,top=100');
  focusWindow();
}
function open_window_pdf(url) {
mywin = window.open(url,"v_pdf",'toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=1,resizable=1,width=440,height=580,left=20,top=100');
  focusWindow();
}
function open_window_ppt(url) {
mywin = window.open(url,"v_ppt",'toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=1,resizable=1,width=720,height=580,left=20,top=100');
  focusWindow();
}
function open_window_swf(url) {
mywin = window.open(url,"v_swf",'toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=0,resizable=0,width=600,height=450,left=0,top=0');
  focusWindow();
}
function open_window_tbl(url) {
mywin = window.open(url,"v_pdf",'toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=1,resizable=0,width=600,height=250,left=20,top=100');
  focusWindow();
}
function focusWindow(){
  if(!mywin.closed) mywin.focus(); // focus it, if it isn't already closed
  else return // or do whatever you want if it is closed
}
function closewin(){
  if(mywin && !mywin.closed) mywin.close();
}