en>Addbot: Bot: Migrating 1 interwiki links, now provided by Wikidata on d:q4377358

2013-03-15T21:14:23Z

Bot: Migrating 1 interwiki links, now provided by Wikidata on d:q4377358

← Older revision		Revision as of 23:14, 15 March 2013
Line 1:		Line 1:
	~~Hello~~ and ~~welcome~~. My title ~~is Ling~~. ~~Her family lives in Idaho~~. The ~~preferred hobby for my children~~ and me is ~~playing crochet~~ and ~~now I'm trying~~ to ~~make money~~ with it. ~~Bookkeeping is how he supports his family members~~ and ~~his wage has been truly fulfilling~~.<br><br>~~Feel free to visit my site~~: ~~extended auto warranty ([~~http://~~Chorokdeul~~.co.kr/~~index~~.~~php?document_srl~~=~~322566&mid~~=~~customer21 you can find out more~~])		In [[crystallography]], the '''R-factor''' (sometimes called residual factor or reliability factor or the R-value or R<sub>Work</sub>) is a measure of the agreement between the crystallographic model and the experimental [[X-ray diffraction]] data. In other words, it is a measure of how well the refined structure predicts the observed data.<ref name="Morris1992">{{cite journal \|author=Morris AL, MacArthur MW, Hutchinson EG, Thornton JM \|title=Stereochemical quality of protein structure coordinates \|journal=Proteins \|volume=12 \|issue=4 \|pages=345–64 \|date=April 1992 \|pmid=1579569 \|doi=10.1002/prot.340120407 \|url=}}</ref> The value is also sometimes called the '''discrepancy index''', as it mathematically describes the difference between the experimental observations and the ideal calcluated values.<ref>{{cite web \|url= http://reference.iucr.org/dictionary/R_factor \|title= R factor \|publisher= International Union of Crystallography \|accessdate= 2013-12-13 }}</ref> It is defined by the following equation:

			:<math>R = \frac{ \sum{\|\|F_\text{obs}\| - \|F_\text{calc}\|\| } }{ \sum{ \|F_\text{obs}\|}}</math>

			where ''F'' is the so-called [[structure factor]] and the sum extends over all the reflections measured and their calculated counterparts respectively. The structure factor is closely related to the intensity of the reflection it describes:

			:<math>I_{hkl} \propto \|F(hkl)\|^2</math>

			The absolute range of values is zero to one, with a large R-factor indicating a poorly refined, low-resolution model or a disordered crystal. For large molecules, R-factor usually ranges between 0.6 (when comparing a random set of reflections with a given model) and 0.2 (for example for a well refined macro-molecular model at a resolution of 2.5 Ångström). Small molecules (up to 300 atoms) usually form more ordered crystals than large molecules, it is possible to attain lower R-factors. In the [[Cambridge Structural Database]] more than 95% of the 500,000+ crystals have an R-factor lower than 0.15 and 9.5% have an R-factor lower than 0.03.

			Crystallographers also use the Free R-Factor (<math>R_{Free}</math>) <ref name="Brunger1992">{{cite journal \|author=Brunger AT \|title=Free R value: a novel statistical quantity for assessing the accuracy of crystal structures \|journal=Nature \|volume=355 \|pages=472–475 \|date=January 1992 \|pmid=18481394 \|doi=10.1038/355472a0 \|url=http://www.nature.com/nature/journal/v355/n6359/abs/355472a0.html \|issue=6359\|bibcode = 1992Natur.355..472B }}</ref> to describe the quality of a model.

			The quantities <math>R_\text{sym}</math> and <math>R_\text{merge}</math> are similarly used to describe the internal agreement of measurements in a crystallographic data set.

			==References==
			{{reflist}}

			==See also==
			* [[Patterson function]]

			[[Category:Crystallography]]

en>Suslindisambiguator: /* References */

2012-07-25T21:08:34Z

References

New page

Hello and welcome. My title is Ling. Her family lives in Idaho. The preferred hobby for my children and me is playing crochet and now I'm trying to make money with it. Bookkeeping is how he supports his family members and his wage has been truly fulfilling.<br><br>Feel free to visit my site: extended auto warranty ([http://Chorokdeul.co.kr/index.php?document_srl=322566&mid=customer21 you can find out more])

Kelvin transform - Revision history

en>Addbot: Bot: Migrating 1 interwiki links, now provided by Wikidata on d:q4377358

en>Suslindisambiguator: /* References */