from SHELXE. These all
looked quite convincing, so hopefully my referees will be happy.]
--
Marc SCHILTZ http://lcr.epfl.ch
Quoting Dale Tronrud :
P.S. to respond out-of-band to Dr. Schiltz: On the US flag I see 7
"red stripes",
6 "white stripes", and 50 "stars". If I state "I see 7" I have conveyed no
useful information.
Yes, but cast in a mathematical equations one would write :
Number of red stripes = 7
N
Quoting Dale Tronrud :
I've held off on getting involved in this as long as I could,
but you are so definitive in your comment. I could make the
same argument that the unit of electron density is "1" because,
after all, the volume is just the count of the number of Å^3 and
a count is not a
I fully agree with Ian and would again point to the authoritative
documentation :
http://www.bipm.org/en/si/derived_units/2-2-3.html
The quantities f^0, f' and f" are unitless, i.e. simply numbers (or
rather: their unit is the number one, which is usually omitted).
The unit of the electron
what again ?
--
Marc SCHILTZ http://lcr.epfl.ch
Quoting James Holton :
Now the coefficients of a Taylor polynomial are themselves values of the
derivatives of the function being approximated. Each time you take a
derivative of "f(x)", you divide by the units (and therefore dimensions)
of "x". So, Pete's coefficients below: 1, -1/6, and 1/12
I would believe that the official SI documentation has precedence over
Wikipedia. In the SI brochure it is made quite clear that Radian is
just another symbol for the number one and that it may or may no be
used, as is convenient.
Therefore, stating alpha = 15 (without anything else) is per
Not at all !
If I want to compute the sinus of 15 degrees, using the series
expansion, I write
X = 15 degrees = 15 * pi/180 = 0.2618
because, 1 degree is just a symbol for the unitless, dimensionless
number pi/180.
I plug this X into the series expansion and get the right result.
Marc
e and
refine U's) rarely see values as low as U = 0.00438 Å^2.
Cheers
Marc
Quoting James Holton :
Marc SCHILTZ wrote:
Hi James
I must confess that I do not understand your point. If you read a
value from the last column of a PDB file, say 27.34, then this really
means :
B = 27.3
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cles per second or radians per second?
The dimension of an angular frequency can not be "cycles per second",
because that contradicts the definition of this quantity, which is
defined to be an angle per time. Again, there is no need to specifically
pack this information into the unit (althoug
This is absolutely correct. Radian is in fact just another symbol for 1.
Thus : 1 rad = 1
From the official SI documentation
(http://www.bipm.org/en/si/si_brochure)(section 2.2 - table 3) :
"The radian and steradian are special names for the number one that
may be used to convey information abo
Yes, but Å is really only just tolerated.
It has evaded the Guillotine - for the time being ;-)
Frank von Delft wrote:
Eh? m and Å are related by the dimensionless quantity 10,000,000,000.
Vive la révolution!
Marc SCHILTZ wrote:
Frank von Delft wrote:
Hi Marc
Not at all, one uses
urpose. However, within a system of units (whichever is adopted),
the number of different units should be kept reasonably small.
Cheers
Marc
Sounds familiar...
phx
Marc SCHILTZ wrote:
Hi James,
James Holton wrote:
Many textbooks describe the B factor as having units of square
Angst
uot;B", which will make it easy to say that the B
factor was "80 B". This might be very handy indeed if, say, you had an
editor who insists that all reported values have units?
Anyone disagree or have a better name?
Good luck in submitting your proposal to the General Conference on
Weights and Measures.
--
Marc SCHILTZ http://lcr.epfl.ch
background). So
if the fall-off due to overall thermal motion etc as described by Kevin
causes the S/N ratio to dip much below 1 then the anomalous signal won't
help you.
Cheers
-- Ian
-Original Message-
From: owner-ccp...@jiscmail.ac.uk [mailto:owner-ccp...@jiscmail.ac.uk]
Kevin Cowtan wrote:
Marc SCHILTZ wrote:
I agree with everything but would like to add the following: if we
assume an overall atomic displacement parameter, the drop-off in both
the anomalous and non-anomalous scattering is the same. Therefore, the
ratio of anomalous differences over mean
effectively small atomic
radii (only inner shell being effective). FOR HIGH
ANGLE REFLECTIONS ANOMALOUS DATA
BECOMES IMPORTANT.
Raja
--
Marc SCHILTZ http://lcr.epfl.ch
Quoting Jacob Keller :
Also, in your selenium crystal example, I think there would still be an
anomalous signal, because there would always be regular scattering as well
as the anomalous effect. Isn't that true?
It is certainly not correct to state that there is no anomalous
scattering in
Quoting Jacob Keller :
Aha, so I have re-invented the wheel! But I never made sense of why f' is
negative--this is beautiful! Just to make sure: you are saying that the real
part of the anomalous scattering goes negative because those photons are
sneaking out of the diffraction pattern through a
Compton wrote in the quoted
paper [read the sentence just after his equation (9)].
--
Marc SCHILTZ http://lcr.epfl.ch
astic scattering.
which probably contributed to his Nobel four years later. This is a
classic example of the confusion that can arise from the particle-wave
duality.
It seems to me that the confusion here is between energy and momentum.
--
Marc SCHILTZ http://lcr.epfl.ch
Quoting Ethan Merritt :
On Wednesday 22 April 2009 09:23:19 Jacob Keller wrote:
Hello All,
What is the reason that x-ray fluorescence is neglected in our experiments?
Obviously it is measureable, as in EXAFS experiments to determine
anomalous edges,
but should it not play a role in the int
omalous signal, based on slightly different assumptions.
And the generalization of their formulae is given in :
Flack, H. D. & Shmueli, U. (2007). Acta Cryst. A63, 257-265.
In a follow-up paper, their derivations were extended to all
spacegroups, also taking account of special reflections.
; the quantity which von Laue would
have called "lattice factor" (and they call "formfactor" the quantity
which von Laue called "structure factor") .
Seems that there will be little agreement
--
Marc SCHILTZ http://lcr.epfl.ch
Ian Tickle wrote:
OK, limi
a "rotation trace".
Mal nommer les choses, c'est ajouter au malheur des hommes. A.Camus.
--
Marc SCHILTZ http://lcr.epfl.ch
hod for
estimating S, and therefore consider it beneficial if the RMS error on
the "parameter" S is reduced. Is this really what you think ?
Best regards
Marc
--
Marc SCHILTZ http://lcr.epfl.ch
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Well, I was pointing to the Sivia & David (1994) paper because I thought
it might be helpful in the discussion about how to convert intensities
to amplitudes. The paper is probably not so well known in the PX
community, so I decided that I would advertise it on this BB. However,
since I am not one
scussed on page 710
(final part of section 5). The authors seem to be more in favor of
using F's.
Marc Schiltz
Quoting Jacob Keller <[EMAIL PROTECTED]>:
Does somebody have a .pdf of that French and Wilson paper?
Thanks in advance,
Jacob
*
quot; and "anomalous scattering" are synonyms
and it is almost a matter of taste which term one prefers. Both are
perfectly acceptable. The x-ray physics and crystallography
communities (except protein crystallography) have shifted from the
usage of "anomalous scattering" to "resonant scattering".
But then, as you write, if we want to keep the MAD SAD SIRAS etc
acronyms we are tied to "anomalous".
Marc Schiltz
adequate term since the X-ray phenomena under discussion
involve resonant interactions of photons with matter and are actually
not at all 'anomalous'.
--
Marc SCHILTZ http://lcr.epfl.ch
.
You need to have Java running on you computer.
There are other interesting applets on that page, e.g. "diffractOgram",
which illustrates the Ewald construction. I use many of these applets
for teaching purposes.
best regards
Marc Schiltz
Bernhard Rupp wrote:
Dear All:
I am
presence
of so-called diffraction fringes (Born & Wolf, section 8.1), i.e. a
variation of the intensity as a function of scattering angle. This can
only occur if the wavelength is of the same order or shorter than the
size of the aperture.
Wikipedia is great, but use it with care..
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