Dear Zbyszek
Wouldn't ripples be the results of calculating maps with truncated
Fourier summations (unavoidably), and, consequently, be more obvious
around a sharp feature such as an heavy atom metal center?
The mathematic basis can be found here:
http://en.wikipedia.org/wiki/Gibbs_phenomenon
With best regards,
Thierry
Note: sent a 2nd time as it seems that it did not reach the BB the first
time. Apologies if the message reaches you twice.
-----Original Message-----
From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of
Zbyszek Otwinowski
Sent: Wednesday, July 06, 2011 1:19 PM
To: [log in to unmask]
Subject: Re: [ccp4bb] How to evaluate Fourier transform ripples
The question about Fourier transformation ripples has a straightforward
answer in a fairly typical situation:
A) data are collected to the resolution limit of diffraction,
B) phases are uniform in quality across the resolution range, which is
equivalent to R-free being uniform with respect to resolution within a
factor of 2 or so,
C) maps are not sharpened.
The ripples originate from not including unobserved structure factors.
The
intensity of diffraction decreases rapidly past the measurability limit,
so, in the above situation, the unobserved diffraction contributes very
little. Consequently, the answer is that typically one should not see
ripples.
Ripples should not be confused with the effect of electron density maps
being smoothed by vibrations and other forms of disorder.
Zbyszek Otwinowski
>
> Dear All, Hi. I was asked in a manuscript revision to discuss
> about the possible effects of Fourier transformation ripples on the
> crystallographic results. Specifically, the reviewers question whether
> ripples may affect on the electron density around heavy metal center
which
> has a Mo-S-As connection. From which angle or in which way this
problem
> should be addressed most convincingly ? Thank you for any
> suggestion.Best,Conan
Zbyszek Otwinowski
UT Southwestern Medical Center at Dallas
5323 Harry Hines Blvd.
Dallas, TX 75390-8816
Tel. 214-645-6385
Fax. 214-645-6353
Notice: This e-mail message, together with any attachments, contains
information of Merck & Co., Inc. (One Merck Drive, Whitehouse Station,
New Jersey, USA 08889), and/or its affiliates Direct contact information
for affiliates is available at
http://www.merck.com/contact/contacts.html) that may be confidential,
proprietary copyrighted and/or legally privileged. It is intended solely
for the use of the individual or entity named on this message. If you are
not the intended recipient, and have received this message in error,
please notify us immediately by reply e-mail and then delete it from
your system.
|