November 2022 - Ifeffit - millenia.cars.aps.anl.gov

Parameters for parent function in wavelet transform analysis
by Scott Calvin 09 Feb '23

09 Feb '23

Hi all, I’ve never actually tried wavelet transform analysis before, so I’m trying to understand it better, but there’s one aspect that’s puzzling me: The Morlet wavelet has two parameters, eta and sigma. Eta controls how fast it wiggles, and sigma how quickly the function dies out. (Essentially, it’s like the basis function for a Fourier transform multiplied by a Gaussian envelope.) In wavelet analysis we pick a parent function, which is often a Morlet wavelet with particular values of eta and sigma that we have chosen. We then create a set of child functions from the parent function by shifting and dilating the function in k-space. Each child function is then used as a basis function for a transform of chi(k) calculated by integrating over a range of k-values, much like what is done to calculate a Fourier transform. Since the Morlet wavelet is localized in k-space, and the child functions are shifted to focus on different regions of k-space, our wavelet transform produces plots which are a function of k. But since dilating the parent function by different amounts yields child functions with different frequencies, the plots are also a function of R. Therefore the result is a two-dimensional (k and R) contour plot. So far, so good. But what I’m wondering about is the effect of the initial choice of eta and sigma for the parent function. The dimensionless product of eta and sigma has a clear effect. If (eta)(sigma) is small, the parent function will not have very many oscillations of significant size; it it’s large, it will have a lot of oscillations. So if we want good resolution in R (and thus relatively poor resolution in k), we want a big value of (eta)(sigma). In the limit as (eta)(sigma) becomes arbitrarily large, we recover the Fourier transform. If we want good resolution in k, we use a small value for (eta)(sigma). In the limit as (eta)(sigma) becomes arbitrarily small we recover chi(k). That still makes sense to me! But what difference do sigma and eta make individually? In other words, how is sigma = 0.5 and eta = 10.0 different from sigma = 1.0 and eta = 5.0? Since we end up creating child functions that dilate the parent function anyway, I can’t see that it should have any effect at all. And if those two parameters don’t make an independent effect, why do we pretend there are two independent-looking parameters? I’ve seen at least one early paper that suggests choosing eta so that it’s close to the path length you’re most interested in probing, but I can’t see how that actually makes any difference, given the dilation. I expect there’s a good chance I’m missing something obvious, or have a fundamental misunderstanding of part of the process, and look forward to learning more! Best, Scott Calvin Lehman College of the City University of New York

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Installing Larch without installing Anaconda
by TRANCHANT Laurent 13 Dec '22

13 Dec '22

Dear Mr or Mrs, I am Laurent Tranchant, post-doctoral researcher working at the IPANEMA laboratory at the SOLEIL synchrotron in France. I would like to install Larch (especially to use XAS Viewer to treat my XAS data) without installing Anaconda on MacOS. Do you know if it is possible or not ? For example by using MacPorts instead of Anaconda... It seems that all the solutions proposed online to install Larch on MacOS require the installation of Anaconda Python environment. I thank you in advance for your help. Best regards, Laurent Tranchant

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PosDoc position at KIT
by Zimina, Anna (IKFT) 30 Nov '22

30 Nov '22

Dear all, Postdoc position for operando X-ray absorption studies on Fischer-Tropsch catalysts for the CARE-O-SENE Project is open now in our group at IKFT/KIT: https://www.pse.kit.edu/karriere/joboffer.php?id=91688 <https://www.pse.kit.edu/karriere/joboffer.php?id=91688&new=true> &new=true https://care-o-sene.com/en/ Feel free to apply and distribute the information further. Best regards, Anna Zimina ____________________________________________________________________________ __________ Karlsruhe Institute of Technology (KIT) Institute of Catalysis Research and Technology (IKFT) Dr. Anna Zimina Senior scientist Hermann-von-Helmholtz-Platz 1 Building 345 Office 304 76344 Eggenstein-Leopoldshafen Phone: +49 721 608 28673 Fax: +49 721 608 26789 E-Mail <mailto:anna.zimina@kit.edu> anna.zimina(a)kit.edu

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Re: [Ifeffit] XANES temperature estimation (Robert Gordon)
by Gabriele Garofalo 21 Nov '22

21 Nov '22

Hi Gordon, I have just one spectrum per sample, all taken at different T (unknown, due to technical problems) and P (known). I'd like to find T and using an EoS is not a viable option. I was thinking that maybe, assuming that the Debye-Waller term is explained only by thermal disorder, the Debye temperature is P independent, and there are no structural or electronic transformations, I could retrieve T by fitting the Debye-Waller term and using the reference spectra. Is this possible? Best regards Gabriele > ---------------------------------------------------------------------- > > Message: 1 > Date: Mon, 21 Nov 2022 16:16:50 +0100 > From: Gabriele GAROFALO <gabriele.garofalo(a)esrf.fr> > To: ifeffit(a)millenia.cars.aps.anl.gov > Subject: [Ifeffit] XANES temperature estimation > Message-ID: <0ce690cc-ca47-5507-76b3-848bba8d7db8(a)esrf.fr> > Content-Type: text/plain; charset=UTF-8; format=flowed > > Hi everyone, > > I'd like to estimate the temperature of some samples from some XANES > spectra, is there a way to do that? I couldn't find an answer in the > mailing list archive. > > Thanks! > > > > ------------------------------ > > Message: 2 > Date: Mon, 21 Nov 2022 10:23:10 -0500 > From: Anatoly Frenkel <anatoly.frenkel(a)stonybrook.edu> > To: XAFS Analysis using Ifeffit <ifeffit(a)millenia.cars.aps.anl.gov> > Subject: Re: [Ifeffit] XANES temperature estimation > Message-ID: <B288F5DB-33C3-4F6C-A4A3-D41D713157B1(a)stonybrook.edu> > Content-Type: text/plain; charset=utf-8 > > Only evaporation temperature, when XANES spectrum disappears?:) > > Anatoly > >> On Nov 21, 2022, at 10:20 AM, Gabriele GAROFALO >> <gabriele.garofalo(a)esrf.fr> wrote: >> >> ?Hi everyone, >> >> I'd like to estimate the temperature of some samples from some XANES >> spectra, is there a way to do that? I couldn't find an answer in the >> mailing list archive. >> >> Thanks! >> >> _______________________________________________ >> Ifeffit mailing list >> Ifeffit(a)millenia.cars.aps.anl.gov >> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >> Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit > > > > ------------------------------ > > Message: 3 > Date: Mon, 21 Nov 2022 09:13:19 -0800 > From: Robert Gordon <ragordon(a)alumni.sfu.ca> > To: XAFS Analysis using Ifeffit <ifeffit(a)millenia.cars.aps.anl.gov> > Subject: Re: [Ifeffit] XANES temperature estimation > Message-ID: > <CA+FiM0EvUpbWH2=WzqjKTRMwZsw2w-DSgJ-2J9XgAVAScbiSTg(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > Hi Gabriele, > > To qualify Anatoly's cheerful, pre-morning coffee response, if your > samples > are part of a sequence of measurements > of a material whose XANES has been measured at different temperatures, > and > said XANES does have some changes > owing to changes in physical or electronic behavior with temperature > (i.e. > a phase transition), then you could estimate > where your samples fit within that determined behavior. > > Are you familiar with how temperature dependence manifests in a typical > XAFS measurement? > ...through the Debye-Waller term..the effects of which become less > pronounced at lower k... > > Temperature is more typically a controlled parameter during > measurements. > > So no, not really...unless there is a known behavior for comparison. > > -R.

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XANES temperature estimation
by Gabriele GAROFALO 21 Nov '22

21 Nov '22

Hi everyone, I'd like to estimate the temperature of some samples from some XANES spectra, is there a way to do that? I couldn't find an answer in the mailing list archive. Thanks!

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How to normalize tens of thousands of XAS data?
by 张驰 15 Nov '22

15 Nov '22

How to normalize tens of thousands of XAS data? I measured a series of the spectra of sample over time by in situ XAS, the results contained tens of thousands of sets of XAS data, and it was impossible to normalize each set of data individually.I would like to ask where to find the normalized source code of Athena, I can modify the code so I can use my computer to achieve a large number of processing.Thanks!

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