如何将当地时间转换为UTC格式？

$timeZome = timezone_open(\'Europe/Kiev\');
$date = new DateTime();
$date->setTimezone($timeZome);
$date->setDate(2011, 06,25);
$date->setTime(11,35,00);

20110625T040000Z

$date = new DateTime();
$date->setTimezone(new DateTimeZone(\'Europe/Kiev\'));
$date->setDate(2011, 06,25);
$date->setTime(11,35,00);
$date->setTimezone(new DateTimeZone(\'UTC\'));

echo $date->format(\'Ymd\\THis\\Z\'); // format string to match question

echo $date->format(\'Ymd\'); // 20110625