public function setDateByTimezone($timezone) {
    if (is_string($timezone)) {
      $timezone = new DateTimeZone($timezone);
    }
    $this->convertedTimezone = $timezone;
    $new_date_utc = $this->date->getTimeStamp() - $timezone->getOffset($this->date);
    $new_date = new DateTime();
    $new_date->setTimestamp($new_date_utc);
    $this->date = $new_date;
  }