Am 20:59, schrieb James Holton:
...
The loss of the 1/r^2 term arises because diffraction from a crystal is
"compressed" into very sharp peaks. That is, as the crystal gets larger,
the interference fringes (spots) get smaller, but the total number of
scattered photons must remain constant. The p
Actually, people forget the 1/r term because it is gone by the end of
Chapter 6 of Woolfson.
Yes, it is true that, for the single "reference electron" the scattered
intensity falls off with the inverse square law of distance (r) and,
hence, the amplitude falls off with 1/r. However, the units
On Oct 14, 2010, at 2:28 PM, Jacob Keller wrote:
> I have always found this angle independence difficult. Why, if the anomalous
> scattering is truly angle-independent, don't we just put the detector at 90
> or 180deg and solve the HA substructure by Patterson or direct methods using
> the pure
On Oct 14, 2010, at 2:31 PM, Tim Gruene wrote:
> I would like to understand how the notion of a photon being scattered from all
> electrons in the crystal lattice explains the observation that radiation
> damage
> is localised to the size of the beam so that we can move the crystal along and
> sh
It is mostly because in the higher angles intensity of the reflection is lower,
precision is lower and anomalous signal is washed out by counting statistics.
For very well diffracting test crystals anomalous signal is MEASURABLE to very
high resolution providing good enough I/sigma(I) is generate
On Thursday, October 14, 2010 02:28:26 pm Jacob Keller wrote:
> I have always found this angle independence difficult. Why, if the anomalous
> scattering is truly angle-independent, don't we just put the detector at 90
> or 180deg and solve the HA substructure by Patterson or direct methods using
On Thu, 2010-10-14 at 23:31 +0200, Tim Gruene wrote:
> you observe that each photon decides on exactly one slit
> that it goes through.
That is if you observe which slit it goes through.
--
"I'd jump in myself, if I weren't so good at whistling."
Julian, King of L
On Thu, 2010-10-14 at 23:31 +0200, Tim Gruene wrote:
> I would like to understand how the notion of a photon being scattered
> from all
> electrons in the crystal lattice explains the observation that
> radiation damage
> is localised to the size of the beam so that we can move the crystal
> along
On Thu, Oct 14, 2010 at 04:28:26PM -0500, Jacob Keller wrote:
> I have always found this angle independence difficult. Why, if the anomalous
> scattering is truly angle-independent, don't we just put the detector at 90
> or 180deg and solve the HA substructure by Patterson or direct methods using
Good evening citizens and non-citizens,
On Thu, Oct 14, 2010 at 08:21:19AM -0700, William G. Scott wrote:
> On Oct 14, 2010, at 7:40 AM, Ed Pozharski wrote:
>
> > On Thu, 2010-10-14 at 08:41 +0200, Tim Gruene wrote:
> >> This sounds as though you are saying that a single photon interacts
> >> wit
I have always found this angle independence difficult. Why, if the anomalous
scattering is truly angle-independent, don't we just put the detector at 90 or
180deg and solve the HA substructure by Patterson or direct methods using the
pure anomalous scattering intensities? Or why don't we see pur
On Thursday, October 14, 2010 01:18:04 pm Bart Hazes wrote:
>
> On 10-10-14 01:34 PM, Ethan Merritt wrote:
>
>
> ...
>
> The contribution from normal scattering, f0, is strong at low resolution
> but becomes weaker as the scattering angle increases.
> The contribution from anomalous scatte
On 10-10-14 01:34 PM, Ethan Merritt wrote:
...
The contribution from normal scattering, f0, is strong at low resolution
but becomes weaker as the scattering angle increases.
The contribution from anomalous scattering, f' + f", is constant at
all scattering angles.
...
My simple
movie,
> >>>> which I have placed here:
> >>>>
> >>>> http://bl831.als.lbl.gov/~jamesh/nearBragg/near2far.html
> >>>>
> >>>> -James Holton
> >>>> MAD Scientist
> >>>>
> >>>&g
>>> or whatever else? Since I have no access to f000 experimentally,
> >>> isn't
> >>> it strange to define its phase as 0 rather than some other
> >>> reflection?
> >>>
> >>> JPK
> >>>
> >>> On Wed, Oct
On Oct 14, 2010, at 7:40 AM, Ed Pozharski wrote:
> On Thu, 2010-10-14 at 08:41 +0200, Tim Gruene wrote:
>> This sounds as though you are saying that a single photon interacts
>> with several
>> electrons to give rise to a reflection.
>
> Not only with several - it shouldn't be much of an exagger
the origin?
=
No, it is a real one, detectable but not measurable.
Lijun
Jacob Keller
- Original Message -
From: "William Scott"
To:
Sent: Wednesday, October 13, 2010 3:58 PM
Subject: [ccp4bb] Summary : [ccp4bb] embarrassingly simple MAD
phasing
question
Thanks for the o
reflection?
-Is it used in the Fourier synthesis of the electron density map, and
if so, do we just guess its amplitude?
JPK
- Original Message - From: "Dale Tronrud"
To:
Sent: Thursday, October 14, 2010 11:28 AM
Subject: Re: [ccp4bb] embarrassingly simple MAD phasin
To:
Sent: Thursday, October 14, 2010 11:28 AM
Subject: Re: [ccp4bb] embarrassingly simple MAD phasing question (another)
Just to throw a monkey wrench in here (and not really relevant to
the original question)...
I've understood that, just as the real part of F(000) is the sum
of
t; a long
>>> time what is the reference phase for reflections? I.e. a given phase
>>> of say
>>> 45deg is 45deg relative to what?
>>>
>>> =
>>> Relative to a defined 0.
>>>
>>> Is it the centrosymmetric phases?
>>
On Thu, 2010-10-14 at 08:41 +0200, Tim Gruene wrote:
> This sounds as though you are saying that a single photon interacts
> with several
> electrons to give rise to a reflection.
Not only with several - it shouldn't be much of an exaggeration to say
that the photon senses all the electrons in th
is already vertical, relative to the real part of Fa (in red), i.e. the
>> > blue vector is always vertical to the red vector in this picture (and
>> > counter-clockwise).
>> >
>> > Yong
>> >
>> >
>> >
>> >
>> > William Scott
>
e).
> >
> > Yong
> >
> >
> >
> >
> > William Scott
> > Sent by: CCP4 bulletin board
> > 10/13/2010 01:48 PM
> > Please respond to
> > William Scott
> >
> >
> > To
> > CCP4BB@JISCMAIL.AC.UK
> > cc
ent by: CCP4 bulletin board
> 10/13/2010 01:48 PM
> Please respond to
> William Scott
>
>
> To
> CCP4BB@JISCMAIL.AC.UK
> cc
>
> Subject
> [ccp4bb] embarrassingly simple MAD phasing question
>
>
>
>
>
>
> Hi Citizens:
>
> Try not
Hi Bernhard,
On Wed, Oct 13, 2010 at 08:07:04PM -0700, Bernhard Rupp wrote:
[...]
> BR
>
> PS: Just in case it might come up - there is NO destructive interference
> between F000 and direct beam - the required coherence that leads to
> extinction/summation of 'partial waves' is limited to a sing
=
No, it is a real one, detectable but not measurable.
Lijun
Jacob Keller
- Original Message -----
From: "William Scott"
To:
Sent: Wednesday, October 13, 2010 3:58 PM
Subject: [ccp4bb] Summary : [ccp4bb] embarrassingly simple MAD phasing
question
Thanks for the overwhelm
hat of F(000).
Or a theoretical wave from the origin?
=
No, it is a real one, detectable but not measurable.
Lijun
Jacob Keller
- Original Message -
From: "William Scott"
To:
Sent: Wednesday, October 13, 2010 3:58 PM
Subject: [ccp4bb] Summary : [ccp4bb] embarrassingly
> Does f000 mean the direct beam? Having a hard time imagining such a miller
index or the corresponding planes...
No, F000 is NOT the direct beam. I may not have made that clear enough in
some of my drawings and captions, and it will be emphasized in the second
printing/ebook. There is in fact sc
wave from the origin?
>
> =
> No, it is a real one, detectable but not measurable.
> Lijun
>
>
> Jacob Keller
>
> - Original Message -
> From: "William Scott"
> To:
> Sent: Wednesday, October 13, 2010 3:58 PM
> Subject: [ccp4bb] Summar
On Oct 13, 2010, at 3:09 PM, Tim Gruene wrote:
> Dear Bill,
>
> The discussion is becoming complicated because of the mixing of notations.
> There is a theory or model which describes the atomic scattering factor as
>f = f0 + f' +if"
> from which the structure factor is calculated. That right
b] Summary : [ccp4bb] embarrassingly simple MAD phasing
question
Thanks for the overwhelming response. I think I probably didn't
phrase the
question quite right, but I pieced together an answer to the
question I
wanted to ask, which hopefully is right.
On Oct 13, 2010, at 1:14 PM, SHEPAR
gt; To:
> Sent: Wednesday, October 13, 2010 3:58 PM
> Subject: [ccp4bb] Summary : [ccp4bb] embarrassingly simple MAD phasing
> question
>
>
> Thanks for the overwhelming response. I think I probably didn't phrase the
> question quite right, but I pieced together an answe
On Oct 13, 2010, at 4:21 PM, Jacob Keller wrote:
> While we are on embarrassingly simple questions, I have wondered for a long
> time what is the reference phase for reflections? I.e. a given phase of say
> 45deg is 45deg relative to what? Is it the centrosymmetric phases? Or a
> theoretical wav
Message -
From: "William Scott"
To:
Sent: Wednesday, October 13, 2010 3:58 PM
Subject: [ccp4bb] Summary : [ccp4bb] embarrassingly simple MAD phasing
question
Thanks for the overwhelming response. I think I probably didn't phrase the
question quite right, but I pieced togeth
Bill,
If I understand you correctly, the problem turns to be understanding
coordinate system.
The coordinate system in the plot in your original email is not a
complex one but a polar coordinate system [|F| and phase (polar
angle)]. In order to add the contribution of an atom with anomal
Dear Bill,
The discussion is becoming complicated because of the mixing of notations.
There is a theory or model which describes the atomic scattering factor as
f = f0 + f' +if"
from which the structure factor is calculated. That right angle that you see in
the picture you sent us with that li
Thanks for the overwhelming response. I think I probably didn't phrase the
question quite right, but I pieced together an answer to the question I wanted
to ask, which hopefully is right.
On Oct 13, 2010, at 1:14 PM, SHEPARD William wrote:
> It is very simple, the structure factor for the ano
@JISCMAIL.AC.UK
cc
Subject
[ccp4bb] embarrassingly simple MAD phasing question
Hi Citizens:
Try not to laugh.
I have an embarrassingly simple MAD phasing question:
Why is it that F" in this picture isn't required to be vertical (purely
imaginary)?
http://www.doe-mbi.ucla.edu/~sawaya
an one, I guess!)?
Jacob
- Original Message -
From: "William Scott"
To:
Sent: Wednesday, October 13, 2010 12:48 PM
Subject: [ccp4bb] embarrassingly simple MAD phasing question
Hi Citizens:
Try not to laugh.
I have an embarrassingly simple MAD phasing question:
Why is i
The Fa" vector is always a 90 degree left turn from the Fa vector. For a
centrosymmetric heavy atom substructure such as 1 mercury site in P21,
the Fa" vector would point straight up or down.
hope that helps,
Citizen Dan
William Scott wrote:
Hi Citizens:
Try not to laugh.
I have an embar
Hi Bill,
the picture does not show Fa" (as a vector), but the vector addition Fp+Fa+iFa"
(it might be a naming convention of the picture to write Fa" instead of iFa",
but that's a matter of taste really).
Furthermore Fa" has the same phase as Fa plus the contribution of i, which
corresponds
to th
CP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of
William Scott
Sent: Wednesday, October 13, 2010 10:48 AM
To: CCP4BB@JISCMAIL.AC.UK
Subject: [ccp4bb] embarrassingly simple MAD phasing question
Hi Citizens:
Try not to laugh.
I have an embarrassingly simple MAD phasing question:
Why
Hi Citizens:
Try not to laugh.
I have an embarrassingly simple MAD phasing question:
Why is it that F" in this picture isn't required to be vertical (purely
imaginary)?
http://www.doe-mbi.ucla.edu/~sawaya/tutorials/Phasing/phase.gif
(Similarly in the Harker diagram of the intersection of phas
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