Richards comparator

It has been common practice to fit a skeletal model to the electron density map, usually by means of a Richards comparator, a device with a half-silvered mirror that enables an observer to see a reflected image of a wire model projected within the three-dimensional map.14 The model is adjusted by varying the torsional angles and in some cases distorting the interbond angles to allow for departures from ideal values, until the atoms are in positions that appear best to satisfy the electron density. It must be emphasized that the fit is a subjective one and that it is impossible to make an objective assessment. Errors in coordinates from models fit to maps at resolutions of 2-2.5 A are usually estimated to be in the 0.2- to 0.5-A range,s although errors much in excess of this may be made. 

The Emulsion Polymerization Model (EPM) described in this paper will be presented without a detailed discussion of the model equations due to space limitations. The complete set of equations has been presented in a formal publication (Richards, J. R. et al. J. AppI. Poly. Sci . in press). Model results will then be compared to experimental data for styrene and styrene-methyl methacrylate (MMA) copolymers published by various workers. 

Table 25.3 compares the characteristics of these four models.14 UNSAT-H and HYDRUS are the most widely known Richards equation models that use modem soil physics principles to estimate water movement within the soil profile. HELP and EPIC are widely known engineering models. 

Hunter ES III, Rogers EH, Schmid JE, Richard A (1996) Comparative effects of haloacetic acids in whole embryo culture. Teratology 54 57-64... 

Kundu B, Richardson SD, Granville CA, Shaughnessy DT, Hanley NM, Swartz PD, Richard AM, DeMarini DM (2004) Comparative mutagenicity of halomethanes and halonitromethanes in Salmonella TAIOO structure-activity analysis and mutation spectra. Mutat Res 554(l-2) 335-350... 

RSRP [Richards sulphur recoveiy process] A proposed modification of the Claus process in which liquid sulfur is used to cool the catalyst bed. Developed jointly by the Alberta Energy Comparer and the Hudson s Bay Oil Gas Company, but not reported to have been commercialized. 

It is more problematical to define the third law of thermodynamics compared to the first and second laws. Experimental work by Richards (1902) and Nemst (1906) led Nemst to postulate that, as the temperature approached absolute zero, the entropy of the system would also approach zero. This led to a definition for the third law of thermodynamics that at a temperature of absolute zero the entropy of a condensed system would also be zero. This was further refined by Planck (1911) who suggested this be reworded as the entropy of a pure element or substance in a perfect crystalline form is zero at absolute zero. 

Richard H. M., Eertman, Wouter Zurburg, Cor A. Schipper, Ben Sandee and Aad C. Smaal, (1996). Effects of PCB 126 and cadmium on the anaerobic metabolism of the mussel Mytilus edulis L. Comparative Biochemistry and Physiology Part C Pharmacology, Toxicology and Endocrinology Volume 113, Issue 2,261-212. 

Mitchell CD, Richards SM, Kinsey SE. Medical Research Council Childhood Leukaemia Working Party. Benefit of dexamethasone compared with prednisolone for childhood acute lymphoblastic leukaemia results of the UK Medical Research Council ALL97 randomized trial. Br J Haematol 2005 129 734-745. 

Grimwood, S., Richards, P., Murray, F., Harrison, N., Wingrove, P. B., Hutson, P. H. Characterisation of N-methyl-D-aspartate receptor-specific fHjifenprodil binding to recombinant human NR1a/NR2B receptors compared with native receptors in rodent brain membranes, J. Neurosci. 2000, 75, 2455-2463. 

Richards, Aute. Outline of Comparative Embryology. John Wiley and Sons, New York. 1931. 

ERNST. RICHARD R. (I933-). A native of Switzerland who won the Nobel prize in chemistry in 1991 for important methodological developments in NMR spectroscopy. He invented Fourier-transform NMR lET-NMR). which multiplied sensitivity It) to 100 times compared to dispersive instruments. He also devised two-dimensional NMR techniques, increasing resolution and enabling structure determinations of biologically important macromolecules. Ernst received his Pli.D from the Federal Technical Institute (ETH) in Zurich. Switzerland... 

Quantitative differences between susceptibility of compounds containing different sugars exist. Richards et al. (35) made a systematic study of a number of dinucleosidemonophosphates (N°pNP) in which either the a- or /3-nucleoside contained arabinose, while the other nucleoside contained ribose or deoxyribose. All compounds were found susceptible to venom exonuclease. The surprising finding was that the extremes of differences in the values of Vm and Km lay in a comparatively narrow range of 20-fold. 

Rate and equilibrium constants have been measured for representative intramolecular aldol condensations of dicarbonyls.60a For the four substrates studied (32 n = 2, R = Me n = 3, R = H/Me/Ph), results have been obtained for both the aldol addition to give ketol (33), and the elimination to the enone (34). A rate-equilibrium mismatch for the overall process is examined in the context of Baldwin s rales. The data are also compared with Richard and co-workers study of 2-(2-oxopropyl)benzaldehyde (35), for which the enone condensation product tautomerizes to the dienol60b (i.e. /(-naphthol). In all cases, Marcus theory can be applied to these intramolecular aldol reactions, and it predicts essentially the same intrinsic barrier as for their intermolecular counterparts. 

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