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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>>>
>>>
>>> --
>>> Ethan A Merritt
>>> Biomolecular Structure Center
>>> University of Washington, Seattle 98195-7742
>>
>
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