[Ifeffit] RE: XAFS 12

4 Mar 2004

      Hi Bruce,

I wondered about the same thing but it seems like editors of Physica
Scripta are very reluctant to say anything. I tried repeatedly to send
e-mails to them asking about any approximation when the topical issue on
XAFS 12 will come out but I got no response. So it seems like we have to
patiently wait and check their web site from time to time.
I know it doesn't sound great...
Greetings,

Wojciech Gawelda

*********************************************************************
Wojciech Gawelda

Laboratoire de Spectroscopie Ultrarapide (LSU)

Institut des Sciences et Ingénierie Chimiques (ISIC),

Faculté des Sciences de Base (SB-BSP)

Ecole Polytechnique Fédérale de Lausanne (EPFL)

CH-1015 Lausanne-Dorigny, Switzerland

Tel.:  +41 (21) 693 0452

Fax.: +41 (21) 693 0422

E-mail: wojciech.gawelda@epfl.ch

WWW: http://lsu.epfl.ch

*********************************************************************

-----Original Message-----
From: ifeffit-bounces@millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of
ifeffit-request@millenia.cars.aps.anl.gov
Sent: mercredi, 3. mars 2004 19:00
To: ifeffit@millenia.cars.aps.anl.gov
Subject: Ifeffit Digest, Vol 13, Issue 3

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Today's Topics:

   1. references for fluorescence corrections (Grant Bunker)
   2. XAFS12 (Bruce Ravel)
   3. Chi^2-Map question (Norbert Weiher)

----------------------------------------------------------------------

Message: 1
Date: Tue, 2 Mar 2004 22:21:17 -0600 (CST)
From: Grant Bunker 
Subject: [Ifeffit] references for fluorescence corrections
To: ifeffit@millenia.cars.aps.anl.gov
Message-ID:

Content-Type: TEXT/PLAIN; charset=US-ASCII

Greetings, All - I'll make another effort to get this by the ANL Spam
filters.

A references for fluorescence corrections can be found in Booth and
Bridge's paper
http://xxx.lanl.gov/abs/cond-mat/0306252

they have refs to earlier work also.

thanks - grant

On Tue, 2 Mar 2004 ifeffit-request@millenia.cars.aps.anl.gov wrote:
...
Send Ifeffit mailing list submissions to
  ifeffit@millenia.cars.aps.anl.gov
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When replying, please edit your Subject line so it is more specific
than "Re: Contents of Ifeffit digest..."
Today's Topics:
1. Re: question about S02 (passive electron reduction  factor)
      (Matt Newville)
   2. *****SPAM***** references for self-absorption correction
      (Grant Bunker)
   3. Correlations (Scott Calvin)
----------------------------------------------------------------------
Message: 1
Date: Mon, 1 Mar 2004 12:16:38 -0600 (CST)
From: Matt Newville 
Subject: Re: [Ifeffit] question about S02 (passive electron reduction
  factor)
To: XAFS Analysis using Ifeffit 
Message-ID:
...
Content-Type: TEXT/PLAIN; charset=US-ASCII
Hi Scott,
First, I'm not sure how your message got tagged as Spam by Argonne's
SpamAssassin (words or phrases selling drugs??? huh???), but that
happens well before I can do anything about it.  I've forwarded this
message on as a false positive for spam.  For better archiving, I
also included the full message you sent below.
...
Good point. It is much more straightforward to check the uncertainty
...
...
the correlation to determine if that could be responsible for the
anomalous S02...so I should have said that Yu-Chuan should check the
uncertainty of the S02 parameter. If it is very large (say 0.8),
...
...
Ifeffit is in effect reporting that it cannot determine S02 well for
some
reason. At that point, I think it is helpful to see if there is a
high
correlation, since that may give a clue as to the reason for the
large
uncertainty.
Knowing the correlations always helps.  And stating a best-fit value
without an uncertainty is dangerous (one might take an implicit
uncertainty, which may not be what you mean).
This is probably a bit off-topic from the original question (where
I'd guess self-absorption to be the main issue,....), but let's
consider typical fit results: S02= 0.9 +/- 0.1, sigma2= 0.015 +/-
0.005, and a correlation between S02 and sigma2 C_S02_sigma2= +0.90.
One could conclude from these that a true value of S02= 1.0 was
reasonable.  But in order to get to S02= 1.0, sigma2 has to go up to
~= 0.019 (~= sigma2_best + C_S02_sigma2 * delta_sigma2).  S02= 0.80
is also reasonable, but this implies sigma2 would drop to around
0.011.  The correlation means that, although having either S02= 0.80
OR sigma2= 0.020 would be reasonable,t having both S02= 0.80 AND
sigma2= 0.020 is much less likely.
The correlation by itself says nothing about the likelihood of
having a true value for S02 of, say, 0.5.  There is a chance this
can happen, but it's small because the uncertainty in S02 is 0.1.
The correlation simply tells you how sigma2 would respond if S02
were 0.5, but nothing more.
...
So this brings up a (possibly contentious) point. In their reporting
recommendations, the IXS suggests reporting high correlations,
particularly when they are between parameters that do not routinely
show
high correlations. What is the reason for this suggestion? I'm not
criticizing it...just looking for the rationale.
It's hard to speak for the IXS, but I'd say that correlations are
recommended to be reported because they're important statistics. The
correlations, along with the best-fit values and uncertainties, help
more fully describe the range of plausible results.
It's generally well-known that the parameters (S02,sigma2) and
(E0,R) are highly correlated for a single shell of a single data
set, and the implications of these are generally understood, I
think.  Sometimes other variables are correlated, and some people
even do complex fits with multiple data sets or generalized
variables that are not the simple XAFS parameters ;). In these
cases, it may not be obvious how the variables are correlated.  I
think the IXS committee was concerned about this, and so recommended
reporting correlations in such cases.  That seems sensible to me.
--Matt
...
On Sat, 28 Feb 2004, Scott Calvin wrote:
Matt,
Good point. It is much more straightforward to check the uncertainty
...
...
the correlation to determine if that could be responsible for the
anomalous
S02...so I should have said that Yu-Chuan should check the
uncertainty of
the S02 parameter. If it is very large (say 0.8), then Ifeffit is in
effect
reporting that it cannot determine S02 well for some reason. At that
...
...
I think it is helpful to see if there is a high correlation, since
...
...
give a clue as to the reason for the large uncertainty.
So this brings up a (possibly contentious) point. In their reporting
recommendations, the IXS suggests reporting high correlations,
...
...
when they are between parameters that do not routinely show high
correlations. What is the reason for this suggestion? I'm not
criticizing
it...just looking for th erationale.
--Scott Calvin
Sarah Lawrence College
------------------------------
Message: 2
Date: Mon, 1 Mar 2004 13:53:53 -0600 (CST)
From: Grant Bunker 
Subject: [Ifeffit] *****SPAM***** references for self-absorption
  correction
To: ifeffit@millenia.cars.aps.anl.gov
Message-ID:

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