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Hi all-<br>
1- The original Toshiba laser used by Beckman had a nominal wavelength
of 672 nm. That laser had a habit of mode skipping during at the edges
of the pulse, leading to short periods where the wavelength could be
anywhere from 670-678 nm. The mode skipping resulted in no noticeable
degradation of the data (there are plenty of other sources of noise).
Over the years, Beckman may have changed laser vendors and used lasers
with slightly different wavelengths. I believe the wavelength that
appears in the data files is "hard coded" in the program and cannot be
changed. Its value may or may not match the laser, depending on the
relative age of your laser and the program. I would trust the number
stamped on the light source.<br>
2- The kink is not significant, and you want to use the maximum. Slight
variations in the amplitude of the Fourier are a consequence of the
mismatch of the sine wave and the fringe pattern. The appearance of
kinks will also depend on the column of pixels chosen to determine the
pixels per fringe. Any blemish or problem with pixels (e.g. differences
in sensitivity) will cause wiggles in the curve (which is essentially a
power spectrum). The fewer the pixels in a column, the more sensitive
the analysis will be to flaws in individual pixels. The same is true
for determining the phase, which is used to calculate the fringe
displacement. David Yphantis and Jeff Lary showed that increasing the
number of pixels per column from 96 (Beckman's camera) to 1024 or 2048
results in a ~100-fold improvement in the precision of the fringe
displacements.<br>
3- The magnetic field is negligible at the position of the cells. I
recall that David Yphantis and, I believe Walter Stafford, have
sedimented magnetic particles in the XLI without any problems.<br>
Best wishes,<br>
Tom <br>
<br>
<br>
Karel Planken wrote:
<blockquote
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<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Dear RASMB’er,<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Here are a few questions
regarding our XL-I.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Question 1:<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">On the laser tube it
reads for the wavelength of the laser
675 nm. Since we have a new computer the reported wavelength for the
recorded
scans is 655 nm (before it was 660 nm!?). Why are these different and
how can
we change or set this back to 675 nm?<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Question 2:<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">If I set up the laser
(delay and duration) and check the
magnitude versus pixels per fringe (see attachment) I often get a
pretty smooth
curve but with a kink half way, just before the maximum. Is it very
important
to obtain a completely smooth curve? Adjusting the laser delay, the
kink can be
minimized but usually doesn’t disappear completely.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Question 3:<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">The rotor is driven by
three coils underneath the rotor
chamber that produce a (alternating?) magnetic field(s). Since I
measured the
sedimentation velocity of magnetic particles I would like to raise the
following
question: can somebody provide me information on how strong this
magnetic field
is (or better: how strong is the magnetic field that the sample sector
of a
standard d.s. centerpiece experiences?) and how the magnetic field
lines in the
rotor chamber and in the sample sector of a standard d.s. centerpiece
look like?<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Thank you in advance for
your answer(s) (and time),<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Kind regards, Karel
Planken.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">K. L. Planken</span></font><o:p></o:p></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Van 't Hoff Laboratory
for Physical and Colloid Chemistry</span></font><o:p></o:p></p>
<p class="MsoNormal"><st1:place w:st="on"><st1:PlaceName w:st="on"><font
face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Utrecht</span></font></st1:PlaceName><font
face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"> <st1:PlaceType w:st="on">University</st1:PlaceType></span></font></st1:place><o:p></o:p></p>
<p class="MsoNormal"><st1:PlaceType w:st="on"></st1:PlaceType><st1:place
w:st="on"></st1:place><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">H.R.
Kruytgebouw</span></font><o:p></o:p></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Padualaan 8</span></font><font
face="Verdana" size="2"><span
style="font-size: 10pt; font-family: Verdana;"><o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">3584 CH <st1:City
w:st="on">Utrecht</st1:City>, The <st1:place w:st="on"><st1:country-region
w:st="on">Netherlands</st1:country-region></st1:place></span></font><o:p></o:p></p>
<p class="MsoNormal"><font face="Times New Roman" size="3"><span
style="font-size: 12pt;"> <o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Phone: +31-30-253 2888</span></font><o:p></o:p></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Fax: +31-30-253 3870</span></font><o:p></o:p></p>
<p class="MsoNormal"><font face="Times New Roman" size="3"><span
style="font-size: 12pt;"> <o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><a
href="http://www.chem.uu.nl/fcc/www/peopleindex/karel/karel.htm">Please
visit
my webpage!</a></span></font><o:p></o:p></p>
<p class="MsoNormal"><font face="Times New Roman" size="3"><span
style="font-size: 12pt;"><o:p> </o:p></span></font></p>
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