Query regarding measurement uncertainity
Dear all, I have one doubt regarding the measurement uncertainty in R- space (εR). In the manual it is written that εR is evaluated from the rms value of FT in the range 15-20 Å. My doubt is..... In case the FT in R-space does not extend up to the range mentioned above, then how does the fitting program choose the value of εR? Please clarify me this. With best regardsBIndu Dr.Bindu R. Visiting Fellow BG-37 DCMP&MS Tata Institute of Fundamental Research Homi Bhabha Road Colaba Mumbai-400 005 India Contact Number Lab- 022-2278 2256, 022-2278 2671 Mobile-919892536830 Add more friends to your messenger and enjoy! Go to http://messenger.yahoo.com/invite/
On Monday 26 January 2009 09:28:08 am Bindu R. wrote:
I have one doubt regarding the measurement uncertainty in R- space (εR). In the manual it is written that εR is evaluated from the rms value of FT in the range 15-20 Å. My doubt is.....
In case the FT in R-space does not extend up to the range mentioned above, then how does the fitting program choose the value of εR?
The case where there is no signal in the very-high-R range is the case in which this approximation is most valid. If there is no EXAFS above 15 A, then the only source of non-zero spectral weight is noise. B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
Hi Bindu,
On Mon, Jan 26, 2009 at 8:28 AM, Bindu R.
I have one doubt regarding the measurement uncertainty in R- space (εR). In the manual it is written that εR is evaluated from the rms value of FT in the range 15-20 Å. My doubt is.....
In case the FT in R-space does not extend up to the range mentioned above, then how does the fitting program choose the value of εR?
The FT transform from k to R space that ifeffit does always extends to R = 10*pi Ang. The R-range saved into a data array is usually much shorter (it's usually out to 10Ang), though you can change this if you'd like. There are always high-frequency components of a real XAFS spectra. Anyway, when doing a fit, the data is FT to R-space internally, and the range between 15 and 20 Ang is used to estimate epsilon_R. Knowing the FT parameters (especially the k-weight), that can be converted into epsilon_k. --Matt
participants (3)
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Bindu R. -
Bruce Ravel -
Matt Newville