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

Reduced chi square values versus F-tests for second shell fits
by Matt Siebecker 22 Mar '13

22 Mar '13

Dear All, Would it be recommended to compare reduced chi square (RCS) values from the fit of the second shell only? While fitting the second shell only, the differences between RCS values of different models can be greater than when including both the first and second shells in the fit. For example, the RCS values of model 1 and model 2 for fits of the first and second shells versus just the second shell are 45 and 18, and then 60 and 17, respectively. This to me indicates that fitting the second shell separately from the first gave me a slightly better description of the misfit in that R-range. Regardless of the fitting range the RCS values say model 2 improves the fit significantly. However, if I use an F-test to compare models while fitting the second shell only, I’ve found that the difference between the models is actually less important than when including both the first and second shells in the fit. For examples, the F-test values of model 1 versus model 2 for fits of the first and second shell versus just the second shell are P=0.047 and then P=0.113, respectively. This is perhaps caused by the small R-range and hence decreased Nind when fitting the second shell only. However, it also indicates to me that the F-test says perhaps one fitting model is not such an improvement on the fit as I thought it was based purely on the decrease in RCS value. I assume significant decreases in RCS values to be about >2x, and P <0.05 for the F-test. Should RCS values and F-tests for comparing fitting models only be used when fitting two shells together or can they be used when just fitting the second shell? Kind regards, Matt Siebecker

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Core-Shell Spectroscopy session at Denver X-Ray Conference
by Carlo Segre 21 Mar '13

21 Mar '13

Hello All: This year we will once again have a core-shell spectroscopy session at the Denver X-ray Conference. The conference web site is http://www.dxcicdd.com/13/index.htm The conference organizers are accepting abstracts for talks and posters until April 5, 2013 (the web page says that submission is closed but it is really open for this specific session). Bruce Ravel and I are organizing the session and we would like to encourage you to submit your abstracts for talks and posters as soon as possible so that we can keep a yearly meeting where our community can present talks in North America. Denver is a nice centrally located venue where students can easily drive in from many places in North America (certainly from Chicago!) and save some travel costs. There are special student registration rates and there are also funds which students may apply for to defray expenses. I hope that you will participate and encourage your collegues in the field to do so as well. Carlo -- Carlo U. Segre -- Duchossois Leadership Professor of Physics Director, Center for Synchrotron Radiation Research and Instrumentation Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre(a)iit.edu http://phys.iit.edu/~segre segre(a)debian.org

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(no subject)
by davood dar 13 Mar '13

13 Mar '13

Respected Sir, I am new in the field of EXAFS. I have few questions regarding to IFEFFIT i.e., fitting of theoretical models to the experimental EXAFS data. 1. * 1*. What is the ideal value of R- factor for any fit. 2. * 2. * Can we use (fit) the theoretical model generated from square pyramidal structure to EXAFS data of octahedral structure by assigning degeneracy of 2 for the apical atom. OR using octalhedral for square planar by not using apical path Yours faithfully Davood Ah. Dar EXAFS research scholar India

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questions related to ifeffit fitting
by davood dar 13 Mar '13

13 Mar '13

Respected Sir, I am new in the field of EXAFS. I have few questions regarding to IFEFFIT i.e., fitting of theoretical models to the experimental EXAFS data. 1. What is the ideal value of R- factor for any fit. 2. * * Can we use (fit) the theoretical model generated from square pyramidal structure to EXAFS data of octahedral structure by assigning degeneracy of 2 for the apical atom. OR using octalhedral for square planar by not using apical path Yours faithfully Davood Ah. Dar EXAFS research scholar India

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questions regarding to ifeffit fitting
by davood dar 13 Mar '13

13 Mar '13

Respected Sir, I am new in the field of EXAFS. I have few questions regarding to IFEFFIT i.e., fitting of theoretical models to the experimental EXAFS data. 1. What is the ideal value of R- factor for any fit. 2. * * Can we use (fit) the theoretical model generated from square pyramidal structure to EXAFS data of octahedral structure by assigning degeneracy of 2 for the apical atom. OR using octalhedral for square planar by not using apical path Yours faithfully Davood Ah. Dar EXAFS research scholar India

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controls and data acquisition workshop ot SRI 2013
by Bruce Ravel 13 Mar '13

13 Mar '13

Hi! This year's Pan-American Synchrotron Radiation Instrumentation Conference will be held June 19-21 in Gaithersburg, MD, USA, with satellite workshops on June 17 and 18. Here's the URL: http://pml.nist.gov/Meetings/SRI2013/index.html I am organizing Workshop #8 on June 18th. It will be on the topic of software for beamline controls and data acquisition. If you work in this area, please consider submitting an abstract. Please pass word about this workshop to your favorite beamline scientist or to the controls and acquisition people at your synchrotron. Thanks! Bruce -- Bruce Ravel ------------------------------------ bravel(a)bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://xafs.org/BruceRavel Software: https://github.com/bruceravel

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MBACK and Athena
by Bajamundi Cyril 12 Mar '13

12 Mar '13

Hello, I have 3 spectra taken from a single sample, I align, merge and save the merged data as merge.xmu file. I then normalize this merged data using the MBACK algorithm in Matlab, the results of which is stored as merged.xmu.mnor file. This file, I then import to ATHENA using the instructions in http://www.mail-archive.com/ifeffit@millenia.cars.aps.anl.gov/msg03523.html. I do this for all my samples and standards in order for me to perform LCF. My questions are 1. Is this procedure valid? In the sense that no information or features of the spectrum are lost from merge.xmu to merged.xmu.mnor file. 2. How will the procedure <Calibrate data> affect this procedure? Thank you for your time in answering my questions. Regards, Cyril PS: This query is in relation to my previous question [Ifeffit] Basic question in normalization and background removal

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Theoretical calculation of Chi(k)
by John Farell 04 Mar '13

04 Mar '13

Dear Sir, I am trying to calculate the value of Chi(k) theoretically. I have taken Fe data. I need the values of scattering amplitude, phase shift at different energies. Where I could get those values ?.. Help me in this regard... Thanking you John

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Calibration for Sb K edge
by Darren Dale 28 Feb '13

28 Feb '13

Hello All, I have the CHESS F3 beamline set up with a dispersive monochromator for XANES at the Sb K edge with ~1 eV resolution. I didn't find a reference spectrum for Sb in Hephaestus, and would like to contribute one. But first I would like to have a little more confidence in the energy calibration. Does anyone know if 30.491 keV corresponds to the inflection point of mu for Sb(0) (or if not, what energy does)? Alternatively, does anyone know the energy of the Sb(0) white line (ideally with a reference)? Thanks, Darren

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Demeter 0.9.15
by Bruce Ravel 28 Feb '13

28 Feb '13

Hi! Today I released an update to Demeter and tagged version 0.9.15 it at GitHub. Windows users can download the updater package from http://bruceravel.github.com/demeter/ Source code installation instructions are near the end of that page. Windows users will notice a new download link for a documentation package. Simply download that package and double-click on it to install the Users' Guides for Athena and Artemis on your computer. If installing from source, the documents will be built and installed as part of the installation. There are a lot of swell new features and important bug fixes in this version. Some of the highlights are: * A fix for last week's report of problems with reference channels * Much improved performance by Athena once data is loaded * Direct links to document pages scattered throughout Athena and Artemis. If you have installed the documentation package, the local version will be displayed in a web browser. If the documentation package is absent, the programs will attempt to fetch the relevant document page from my github site. * Plucking points from the plotting window now works much more reliably For the full list, see https://github.com/bruceravel/demeter/blob/master/Changes.org For those following the development of Matt's Larch project, I have begun work on making Demeter use Larch rather than Ifeffit as its data processing backend. This is going well -- thus far, Athena can import data and do basic data processing using only Larch. Interaction with Larch is normally disabled. If anyone is interested in following along with that development more closely, let me know and I will write a wiki page about how to enable Larch support in Demeter. Regards, B -- Bruce Ravel ------------------------------------ bravel(a)bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://xafs.org/BruceRavel Software: https://github.com/bruceravel

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