Oracle Scheduled job not running as per schedule.

Hi,
Though this is a unix forum mainly, am posting this oracle query here hoping to get a resolution.

I have set up two scheduled jobs in oracle 11g for executiong a procedure in specific time intervals. One as Hourly and other as minutely.
But the scheduled jobs are not running as per schedule. i.e the minutely job is not running every minute. But If i see the run logs for some period it would have run every minute, and suddenly it will not execute and give a gap of 30 mins or 1 hour and then run again.

Have attached the script for the scheduler and the run logs for the minutely job. Please advice what can be done.

P.s. The job priority is set as 3. and except for these two jobs there are no other jobs set. But this is an important job which needs to be run every minute.

What is the setting of JOB_QUEUE_PROCESSES and what's the maximum number of concurrently running jobs?

JOB_QUEUE_PROCESSES is set to 1000, which is max. And there are only 3 scheduled jobs in the whole DB.