jdtounix(JD_day);
Here is an example.
$day = cal_to_jd(CAL_GREGORIAN,2,2,2010); // Julian Day count
$day_unix=jdtounix($day); // Unix time stamp
echo date('m/d/y',$day_unix);// In date format
The output is here 02/02/10
Note: jdtounix() returns the local time, where Unix Timestamp generator uses GMT