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121.
A circulation in a digraph is a spanning subgraph with indegree equal to outdegree at each vertex. Alon and Tarsi proved that a graph is d-choosable when it has an orientation that has no vertex of outdegree at least d and has the property that the numbers of circulations with even-sized and odd-sized edge sets differ. We generalize this to k-uniform hypergraphs for prime k. We use a hypergraph polynomial and a notion of hypergraph orientation defined by choosing a source vertex from each edge.* Project sponsored by the National Security Agency under Grant Number MDA904-03-1-0037. The United States Government is authorized to reproduce and distribute reprints notwithstanding any copyright notation herein. 相似文献
122.
Chemical investigations on the methanolic extract of Cladiella species, collected from Andaman Island, India, yielded a novel sesquiterpene, cladioxazole (1). Its structure was established with the aid of extensive spectral studies. 相似文献
123.
Radhika Sanduja Gary S. Linz Maktoob Alam Alfred J. Weinheimer Gary E. Martin Edward L. Ezell 《Journal of heterocyclic chemistry》1986,23(2):529-535
Numerous cembranoic diterpenes have been isolated from marine gorgonians and terrestrial plants. There have, however, been only a few reports of the isolation and identification of these interesting compounds from higher animal sources. The isolation of the oxo-bridged cembranoid diterpene jeunicin from the mollusc Planaxis sulcatus is reported. A comparative discussion of the utility of COSY, homonuclear RELAY (relayed COSY) and proton double quantum coherence techniques is presented, the latter successfully establishing the identities of all of the proton resonances. Acquisition of a two-dimensional proton-carbon chemical shift correlation spectrum provided the means of unequivocally establishing 13C resonance assignments. 相似文献
124.
Tatineni R Doddapaneni KK Potumarthi RC Mangamoori LN 《Applied biochemistry and biotechnology》2007,141(2-3):187-201
A two-step response surface methodology (RSM) study was conducted for the optimization of keratinase production and enzyme
activity from poultry feather byStreptomyces sp7. Initially different combinations of salts were screened for maximal production of keratinase at a constant pH of 6.5
and feather meal concentration of 5 g/L. A combination of K2HPO4, KH2PO4, and NaCl gave a maximum yield of keratinase (70.9 U/mL) production. In the first step of the RSM study, the selected five
variables (feather meal, K2HPO4, KH2PO4, NaCl, and pH) were optimized by a 25 full-factorial rotatable central composite design (CCD) that resulted in 95 U/mL of keratinase production. The results of
analysis of variance and regression of a second-order model showed that the linear effects of feather meal concentration (p<0.005) and NaCl (p<0.029) and the interactive effects of all variables were more significant and that values of the quadratic effects of feather
meal (p<1.72e-5), K2HPO4 (p<4.731e-6), KH2PO4 (p<1.01e-10), and pH (p 7.63e-7) were more significant than the linear and interactive effects of the process variables. In the second step, a 23 rotatable full-factorial CCD and response surface analysis were used for the selection of optimal process parameters (pH,
temperature, and rpm) for keratinase enzyme activity. These optima were pH 11.0, 45°C, and 300 rpm. 相似文献
125.
Shrikar M. Bhosale Rupesh L. Gawade Vedavati G. Puranik Radhika S. Kusurkar 《Tetrahedron letters》2012,53(23):2894-2896
An efficient synthesis of calothrixin B (2) is demonstrated starting from 9H-carbazol-4-ol, having two one-pot reaction sequences as key steps. As a novel observation, DMF–methanol was shown to be a hydride donor for reduction of aldehyde to alcohol. Unexpectedly, nucleophilic substitution of benzyloxy by methoxy group was observed. 相似文献
126.
Radhika M. Rao Ankush R. Parab K. Sasi Bhushan Suresh K. Aggarwal 《Mikrochimica acta》2010,169(3-4):227-231
Boron was determined at sub-ppm levels in uranium oxide by ID-TIMS. Following nitric acid dissolution, a solvent extraction method was adapted for extraction of boron by 5% 2-ethylhexane-1,3-diol in chloroform followed by evaporation of the extractant in presence of sodium carbonate and mannitol. This procedure allowed TIMS analysis of boron by monitoring the Na2BO 2 + ions formed from the sodium borate salt in the ion source. Reproducibility of about 1% was obtained for boron determination in the three different uranium oxide samples containing sub-ppm amounts of boron. 相似文献
127.
The synthesis of nanostructured polyaniline (PANI) with different morphologies by simple alkali‐guided template‐free method followed by doping them with vanadium has been described. The synthesized polyaniline nanoparticles have been well characterized by various techniques. Further, the catalytic activity of the undoped and doped PANI nanostructures for selective oxidation of sulfides to sulfoxides in water has been studied. It was observed that the special morphology of nanostructures plays an important role in enhancement of catalytic activity. Vanadium‐doped PANI nanotubes and nanorods showed higher activity and selectivity than nanospheres. The catalyst has been reused for five consecutive cycles with consistent activity. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
128.