public function check_username_availability()
 {
     if (isset($_POST['txt_username'])) {
         $applicantModel = new applicantModel();
         $applicant = $applicantModel->get_by_username($_POST['txt_username']);
         if ($applicant) {
             echo '<font color="red">The <STRONG>' . $applicant[1] . '</STRONG> not available.</font>';
         } else {
             echo 'OK';
         }
     }
 }