Are these "flavored" comments appropriate for scientific discussion?
Peter Zavalij -----Original Message----- From: Smirnova Olga [mailto:olga.smirn...@hw7.ecs.kyoto-u.ac.jp] Sent: Sunday, March 08, 2009 5:58 AM To: Brian H. Toby; rietveld_l@ill.fr Subject: Re: background subtraction R values >> The unweighted r-factor is pretty much meaningless, so again who cares? A mean deviance (just the sum of deviances divided per the number of points) divided per mean peak intensity (or highest peak) might be an alternative to R factor, perhaps. I do not have practical experience with xye input, and I was confused (because the bad russian word is not to be pronounced in the presence of a lady, in particular a little one). I forgot an attachment because it is in electrochemistry field, but I attach it now; it is weighted enough to become not only a Chair of Electrochemistry Dep, but a head of an Institute. Sorry it went wrongly. ----- Original Message ----- >> From: "Brian H. Toby" <brian.t...@anl.gov> >> To: rietveld_l@ill.fr >> Date: 2009-03-07 04:55:56 >> Subject: background subtraction R values >> >> I am not sure what all the fuss on background subtraction is all >> about, as long as the uncertainties in the data are unchanged. We >> have to model background in all powder methods and add it to the >> computed pattern. If you subtract something from the obs pattern >> before you fit, the only things that changes is the normalization >> term in the R factors. Since the purpose of the weighted R-factor is >> to measure the quality of different models to the same data, this >> really makes no difference. The unweighted r-factor is pretty much >> meaningless, so again who cares? >> >> I don't love the idea of modifying data, rather than applying a >> correction to a calculated value -- observations should be >> sacrosanct, IMHO, but having said that, more than once have I applied >> an absorption correction directly to measured intensities. >> >> The important point is that if you measure 100 counts at a point, the >> uncertainty in that is 10. If you decide that 95 of those counts are >> background, go ahead and subtract them if you must, but the >> uncertainty on the observation remains 10, and does not drop to sqrt >> (5) -- this means you must compute uncertainties before subtracting >> and use a Rietveld code that will accept "xye" input, as Pam pointed >> out. >> >> Brian >> >> ******************************************************************** >> Brian H. Toby, Ph.D. office: 630-252-5488 >> Senior Physicist/Materials Characterization Group Leader Advanced >> Photon Source >> 9700 S. Cass Ave, Bldg. 433/D003 work cell: 630-327-8426 >> Argonne National Laboratory secretary (Marija): 630-252-5453 >> Argonne, IL 60439-4856 e-mail: brian dot toby at anl dot gov >> ******************************************************************** >> "We will restore science to its rightful place, and wield >> technology's wonders... We will harness the sun and the winds and the >> soil to fuel our cars and run our factories... All this we can do. >> All this we will do." >> >> >>
