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<DIV><FONT face=Arial size=2>Dear Nobert , dear Colleauges,</FONT></DIV>
<DIV><FONT face=Arial size=2>I just like to add (as I worked
with the model E /schlieren +abs. simultaneous, many
years) and to emphasize what J.Correia wrote, that this phenomena appears
at high MW's, and to the others who wrote ...at high
concentration as Nobert discribed.</FONT></DIV>
<DIV><FONT face=Arial size=2> Sure that it is a phenomea that pappens when
the light is deviated too strong out of the optical system so
with schlieren we get a black line=no light. Reducing
the cell thickness as J Philo suggested is good
advise.Theoretically</FONT></DIV>
<DIV><FONT face=Arial size=2>it would not happen if you enlarge the
diameter of the lenses (practically impossible).</FONT></DIV>
<DIV><FONT face=Arial size=2>This phenomena may occure also at not so
high concentration about 1/4 mgmL of DNA or
similar nerrow </FONT></DIV>
<DIV><FONT face=Arial size=2>boundaries where the diffusion
constant is very small and the boundary spreads slowly . In
many cases it happens </FONT></DIV>
<DIV><FONT face=Arial size=2>with high molecular species where
normaly diffusion is low but I would say that it is
a<STRONG> Diffusion dependent phenomena!</STRONG> </FONT></DIV>
<DIV><FONT face=Arial size=2>Also at the <STRONG>beginning </STRONG>of a
SE run it may happen, but it don't bother us as we do not suffer from
diffusion spreading time, but I believe that some newcommers
may stop such a run thinking that it was acell-filling
error....yours ariel </FONT></DIV></BODY></HTML>