function changeSector(f, sectorID) 
{
  for (i = 0; i < f.length; i++)
  {
    e = f.elements[i];
    if (e.id.indexOf('discipline_') == 0) 
    { 
      e.style.display = 'none';
      for (j = 0; j < e.options.length; j++)
      {
        e.options[j].selected = false;
      }
    }
  }
  selectedDiscipline = f['discipline_' + sectorID];
  selectedDiscipline.style.display = 'block';
  selectedDiscipline.options[0].selected = true;
}