Gerard,

You are absolutely right. My apology for the confusion. Keep on reading, looks like that James called |F| "geometrical structure factor", which probably is not commonly used anymore.

-- Jianghai






On Jan 12, 2009, at 1:45 PM, Gerard Bricogne wrote:

Dear Jacob and Jianghai,

The trouble with this "King James version" is that what he calls the "structure amplitude" A is the amplitude of the scattered electromagnetic wave! If you look at equation (2.3) on p.27, the expression for A is first of all complex (!), and refers for each atom to its "scattering power", denoted phi[j]. This phi[j] is subsequently expressed in equation (2.11) in terms of some physical constants, of the squared atomic form factor, and of the polarisation factor, allowing A to be written in terms of the "structure
factor" F defined in the familiar manner and of these other factors.

Therefore, what Ewald and James call the "structure amplitude" is NOT AT ALL the amplitude (or modulus) of the structure factor, and therefore
these venerable authors cannot be brought into the debate in this way!


    With best wishes,

         Gerard.

--
On Mon, Jan 12, 2009 at 12:58:27PM -0500, Jianghai Zhu wrote:
JPK beats me on this one. Here is the quote from R. W. James, "The Optical
Principles of the Diffraction of X-rays".

"We shall call A the 'structure amplitude', a name introduced by Ewald, to denote the fact that its value depends essentially on the structure of the group associated with each lattice-point. It is the amplitude, at unit
distance, of the wave scattered by the unit group of s points."

-- Jianghai

++++++++++++++++++++
Jianghai Zhu, PhD
Immune Disease Institute
Dept. of Pathology
Harvard Medical School
3 Blackfan Circle, CLSB
Boston, MA 02115
Tel: 617-713-8224
Fax: 617-713-8232
++++++++++++++++++++







On Jan 12, 2009, at 12:43 PM, Jacob Keller wrote:

[King?] James says "structure amplitude."

(1950 ed., Ch II, 1a (p27))

JPK

*******************************************
Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
Dallos Laboratory
F. Searle 1-240
2240 Campus Drive
Evanston IL 60208
lab: 847.491.2438
cel: 773.608.9185
email: j-kell...@northwestern.edu
*******************************************

----- Original Message ----- From: "Ethan Merritt"
<merr...@u.washington.edu>
To: <CCP4BB@JISCMAIL.AC.UK>
Sent: Monday, January 12, 2009 10:59 AM
Subject: Re: [ccp4bb] structure (factor) amplitude


On Monday 12 January 2009 02:42:43 Ian Tickle wrote:

Also I did a 'Google vote' for the two terms. 'Structure amplitude' has 11300 hits. 'Structure factor amplitude' has only 4750. So all round I would say that 'structure amplitude' wins by a considerable margin.

The field of crystagooglography is relatively young,
and standard procedures have not yet been established :-)
Here's what I get:

+"structure factor amplitude"  18,000 hits
+"structure amplitude"         17,100 hits

Ethan



Cheers

-- Ian

-----Original Message-----
From: owner-ccp...@jiscmail.ac.uk
[mailto:owner-ccp...@jiscmail.ac.uk] On Behalf Of Pavel Afonine
Sent: 11 January 2009 03:01
To: Ethan A Merritt
Cc: CCP4BB@jiscmail.ac.uk
Subject: Re: [ccp4bb] structure (factor) amplitude



On 1/10/2009 5:14 PM, Ethan A Merritt wrote:

On Saturday 10 January 2009, Bernhard Rupp wrote:


Dear All,

I am getting conflicting comments on the use of
'structure factor amplitude'
vs. just
'structure amplitude'
for |F|.



???
That's just... odd.

|F| is the amplitude of F.
But no way F is a "structure".



I agree. If F is a structure factor then |F| is a structure
factor amplitude. "structure amplitude" doesn't make much sense...
Pavel.


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Biomolecular Structure Center
University of Washington, Seattle 98195-7742



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