[Ifeffit] references for fluorescence corrections

Grant Bunker bunker at biocat1.phys.iit.edu
Tue Mar 2 22:21:17 CST 2004


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 at millenia.cars.aps.anl.gov wrote:

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> Today's Topics:
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>    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 <newville at cars.uchicago.edu>
> Subject: Re: [Ifeffit] question about S02 (passive electron reduction
> 	factor)
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Message-ID:
> 	<Pine.LNX.4.44.0403011211200.10753-100000 at millenia.cars.aps.anl.gov>
> 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 than
> > 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 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 than
> > 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 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.
> >
> > 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 th erationale.
> >
> > --Scott Calvin
> > Sarah Lawrence College
> >
>
>
> ------------------------------
>
> Message: 2
> Date: Mon, 1 Mar 2004 13:53:53 -0600 (CST)
> From: Grant Bunker <bunker at biocat1.phys.iit.edu>
> Subject: [Ifeffit] *****SPAM***** references for self-absorption
> 	correction
> To: ifeffit at millenia.cars.aps.anl.gov
> Message-ID:
> 	<Pine.LNX.4.44.0403011343220.6220-100000 at biocat1.phys.iit.edu>
> Content-Type: text/plain; charset="us-ascii"
>
> -------------------- Start SpamAssassin results ----------------------
> Content analysis details:   (7.1 hits, 5.6 required)
> -4.9 BAYES_00               BODY: Bayesian spam probability is 0 to 1%
>                             [score: 0.0000]
>  6.0 PORN_4                 URI: URL uses words/phrases which indicate porn
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> Subject: references for self-absorption correction
> Date: Mon, 1 Mar 2004 13:53:53 -0600 (CST)
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> ------------------------------
>
> Message: 3
> Date: Mon, 01 Mar 2004 16:00:16 -0500
> From: Scott Calvin <scalvin at slc.edu>
> Subject: [Ifeffit] Correlations
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Message-ID: <3.0.1.32.20040301160016.00b22028 at mail.slc.edu>
> Content-Type: text/plain; charset="us-ascii"
>
> Thanks, Matt. That clarifies a few things...in particular, I found the
> example you gave (quoted below) to be quite helpful.
>
> --Scott Calvin
> Sarah Lawrence College
>
> At 12:16 PM 3/1/2004 -0600, you wrote:
> >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.
> >>
> >--Matt
> >
> >
>
>
> ------------------------------
>
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