public function getSemTreeLevel($parentId)
 {
     $level = array();
     $children = StudipStudyArea::findByParent($parentId);
     foreach ($children as $c) {
         $level[] = array('id' => $c->sem_tree_id, 'name' => studip_utf8encode($c->getName()), 'has_children' => $c->hasChildren(), 'parent' => $parentId, 'assignable' => $c->isAssignable());
     }
     if (Request::isXhr()) {
         return json_encode($level);
     } else {
         return $level;
     }
 }