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Hello Ranjani-- > I am using XPLOR-NIH to simulate some SANS data (using bin/calcSAXS in > version 2.26) and had a question re how the data is simulated -- > > -- the script calcSAXS describes that solvent background is added to the > simulated data for easier comparison with experimental data, and I noticed > that the term 'scat.bg' is added to the calc(i) and expt(i) terms. > > 1. Does this addition of the bkgd occur only if the background is > specified using the -background option? In other words, if no -background > value is specified, can one directly compare the simulated and background > subtracted experimental data? for SANS data, an optimal background value is computed automatically if you specify the -fit flag (and this requires an experimental SANS curve). An isotropic background is not normally computed for SAXS data. > > 2. In what cases does the 'background' value have to be specified? How is > it different from specifying the 'fractionD2O'? The fraction of D2O should always be specified (if it is not the default value of 1). The background is a fit parameter which takes into account inaccuracies in the subtraction of isotropic background from the experimental curve. best regards-- Charles -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Processed by Mailcrypt 3.5.9 <http://mailcrypt.sourceforge.net/> iEYEARECAAYFAkza+1wACgkQPK2zrJwS/lb1KgCfRsi5rAVNOIRb02nprpzkFOOy F0YAmwUWVcXyRpM68dV5qRYV19JSOP9t =qFcq -----END PGP SIGNATURE-----
