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881.
The application of parallel processing techniques to molecular mechanics calculations is evaluated. Using the standard molecular mechanics package, MM2, four different parallel versions of the program are implemented in a four-processor computing environment. A set of 529 test structures is used to compare the efficiency of the parallel versions of MM2 to a standard serial version of the program. Statistics describing execution times and program execution cycles are gathered and analyzed. The effects of parallel processing overhead and computer system load are explored, and the practical utility of parallel processing in molecular mechanics is estimated. The results of these parallelization experiments indicate that for geometry optimizations requiring significant amounts of computing time an improvement in program execution speed approaching 50% is realizable. © 1993 John Wiley & Sons, Inc. 相似文献
882.
Rare earth element concentrations in the minerals biotite and muscovite from the mica schist country rocks of the Etta pegmatite and tourmalines from the Bob Ingersoll pegmatite have been measured by INAA and CNAA. The concentrations range from 10–4 g/g to 10–10 g/g. The REE patterns of biotite, muscovite and tourmaline reported herein are highly fractionated from light to heavy REE. The REE concentrations in biotite and muscovite are high and indigenous. The pegmatite tourmalines contain low concentrations of REE. Variations in tourmaline REE patterns reflect the geochemical evolution of pegmatite melt/fluid system during crystallization.Work supported by the U. S. Department of Energy under Contract DE-AC06-76RLO 1830. 相似文献
883.
C. Cativiela M. D. Diaz De Villegas E. Melndez 《Journal of heterocyclic chemistry》1985,22(6):1655-1657
Several Z-2-methyl(or phenyl)-4-[α-arylethylidene]-5(4H)-oxazolones 3Z, 4Z were prepared. The results obtained were compared by diazomethane insertion and condensation procedure. In order to synthesize E-2-phenyl-4-[α-arylethylidene]-5(4H)-oxazolones 4E hydrogen bromide isomerization in dry benzene was used. 相似文献
884.
C.N.R. Rao Om Parkash D. Bahadur P. Ganguly S. Nagabhushana 《Journal of solid state chemistry》1977,22(3):353-360
Electronic and magnetic properties of Ln1?xSrxCoO3 (Ln = Pr, Nd, Sm, Eu, and Gd) systems show that above a critical value of x, the d electrons become itinerant while the materials become ferromagnetic at low temperatures. The ferromagnetic component increases with increase in x and decrease in temperature. The Curie temperature increases with x and decreases with decrease in the size of the rare-earth ion. Incorporation of Ba2+ in LaCoO3 favors itinerant electron ferromagnetism relative to Sr2+ while Ca2+ is less favorable than Sr2+. 相似文献
885.
Manvendra B. Shambhu Michael C. Theodorakis George A. Digenis 《Journal of polymer science. Part A, Polymer chemistry》1977,15(3):525-531
Three polyamine ligands, ethylenediamine (EDA), diethylenetriamine (DTA), and triethylenetetramine (TETA), were bound to three chloromethylated “popcorn” polystyrene resins (16, 50, and 100% phenyl ring substitution) with the use of pyridine as the reaction medium. The rate of chloride displacement decreased with increasing molecular weight of the amine and higher degree of resin chloromethylation, while the extent of multiple attachments to the polymer matrix increased. The additional crosslinking, a result of multiple attachments, caused the polyamine resins to swell to a lesser extent in pyridine and water. The ability of the insoluble polyamine–polystyrene resins to chelate Cu2+ ions from dilute solutions (200 ppm) was determined at pH 5. With EDA resins the capacity for Cu2+ increased with increasing amount of the bound polyamine, with DTA it remained unchanged, while with TETA it was found to decrease. 相似文献
886.
P. Maillard P. Krausz C. Giannotti S. Gaspard 《Journal of organometallic chemistry》1980,197(3):285-290
Aerobic irradiation of tetraphenylporphyrins, phthalocyanines, tetra-t-butylphthalocyanines, tetracarboxylphthalocyanines, tetrapyridinoporphyrazins and some of their metal derivatives with visible light (λ > 420 nm) give singlet oxygen by energy transfer and oxygen superoxide by electron transfer, but some of their Cu, Zn of Pt derivatives are efficient quenchers for superoxide formation. 相似文献
887.
HOST CELL REACTIVATION BY FIBROBLASTS FROM PATIENTS WITH PIGMENTARY DEGENERATION OF THE RETINA 总被引:1,自引:0,他引:1
C. DavidLytle RobertE. Tarone†SusannaF. Barrett‡JonathanD. Wirtschafter§Jean-Marie Dupuy¶JayH. Robbins‡ 《Photochemistry and photobiology》1983,37(5):503-508
–Cockayne syndrome (CS) is an autosomal recessive disease characterized by numerous clinical abnormalities including acute sun sensitivity and primary pigmentary degeneration of the retina. Cultured fibroblasts from CS patients are hypersensitive to ultraviolet (UV) radiation. Since host cell reactivation of irradiated virus is a useful probe to evaluate repair in different host cells, we studied such host cell reactivation in CS and in other diseases with retinal degeneration. The survival of UV-irradiated Herpes simplex virus type 1 was determined in fibroblast lines from four normal donors. two patients with CS, one with both xeroderma pigmentosum (XP) and CS, and from several other patients with (Usher syndrome, olivopontocerebellar atrophy, retinitis pigmentosa) and without (XP, ataxia telangiectasia) primary pigmentary degeneration of the retina. The viral survival curves (log survival vs linear fluence) in all cell lines showed two components: a very sensitive initial component (not quantitated in this study) followed by an exponential, less sensitive component. The exponential component had greater sensitivity than normal in the case of the CS patients, the patient with both XP and CS. and the XP patient. We propose that patients with CS have defective repair of DNA which may be the cause of their retinal degeneration. 相似文献
888.
Preparation, Thermal Stability, and Crystal Structure of the Calcium Arsenide Chloride Ca3AsCl3 CaAsCa3AsCl3 was prepared as a grayish white, microcrystalline powder by the reaction of Ca, As, and CaCl2 in the molar ratio 3:2:3 and by the reaction of “Ca3As2” and CaCl2 in the molar ratio 1:3. Colourless single crystals of the compound were obtained. Ca3AsCl3 begins to decompose reversibly at 1 025°C by forming the phase Ca2? xAs1? xCl1+x with x = 0.13 and CaCl2. Single crystal investigations show that Ca3AsCl3 is isotypic with Mg3NF3; see: “Inhaltsübersicht”. 相似文献
889.
890.
The influence of catalysis on chemical modification of 1,2-polybutadienes (Mn < 10,000) by CX3Z reagents (X = halogen; Z = functional group or halogen), in order to obtain polymers soluble in common solvents, has been studied. The work has been carried out with carbon tetrachloride, trichloromethylphosphonyldichloride (CCl3POCl2) and ethyl trichloroacetate (CCl3CO2Et) in the presence of solvents such as C6H6, CH2Cl2. Among the compounds tested as catalysts for the addition of CX3Z to 1,2-polybutadiene (transition metal salts and complexes; radical initiators) only the systems formed with metal salts such as CuCl2, FeCl3, RuCl3 3H2O, Fe2(CO)9 and Cl2Ru(PPh3)3 were found to show high catalytic activity. The most active is Cl2Ru(PPh3)3: used without or with cocatalysts (Et3NHCl/benzôin, alcohols), it leads always, to the best yields whatever the nature of CX3Z. The activity of the other catalysts is generally dependent on CX3Z structure. Some secondary reactions (cross-linking, cyclization, transesterification) have been found. 相似文献