From: pascal <pascal@bcserv.wustl.edu>
  To  : Jack Correia <jcorreia@fiona.umsmed.edu>
  Date: Mon, 26 Aug 1996 16:03:10 -0600

Re: Optics & Biophysics Ultracentrifuge Workshop on XLA Applications

Jack Correia wrote:
> 
> Rasmbers,
> 
>         I'm passing on an observation that may be unique to our situation,
> but may also be helpful in the future for others.  Just before XMAS we had a
> PM done where bellows seals were replaced along with oil changes and routine
> stuff.  For the next 6 weeks we had to clean the optics every 2 weeks or so;
> the intensity at 230 nm would decay from 20,000 to < 5000, and a large dark
> spot was very obvious on the lamp face.  We started to keep track of plateau
> noise in every vel run to try to monitor the process as if it occurred
> gardually, but it appears to be catastrophic, OK one run and terrible the
> next.  I assumed either a small air leak was the problem (it did seem to
> hold a vacumn) or a contaminant in the fresh oil.  Thus we got into the
> habit of checking radial and wavelength intensities often.  But then after
> those 6 weeks, the intensities were stable at ~20,000 at 230 nm????? and
> have continued to be so up to the present??????  I am now knocking on the
> hardest wood I can find (yes its my head) because I know this telling will
> cause us trouble!
> 
>         During this time period, Feb, 1996 - present, we have done a lot of
> low (4C) and high (37C) temperature work which requires preequilibration of
> the rotor and the monochromator overnight at the desired temperature
> (actually 2 degrees colder or warmer).  My hypothesis is long term pumping
> cleans the system or keeps the seals firm, thus preventing optical problems.
> 
>         I just had another PM and, even though we are currently doing 25C
> runs, we pumped overnight for a week on the assumption my hypothesis was
> partially correct.  Its 8 days, 16 velocity runs and counting and the noise
> is still OK.
> 
>         So let me know if this helps anyone or if we're just being compulsive!
> 


Hi Jack and others!

in my experience with the XLA, lamp performace simply deteriorates 
quickly, and our only recourse is to clean the lamp after ever 2-3 days 
of use. it isn't an ideal situation, but it gives quality data... 
Just my $0.02
Razmic