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1.
Cui Shisheng Shanbhag Uday Staudigl Mathias Vuong Phan 《Computational Optimization and Applications》2022,82(2):465-498
Computational Optimization and Applications - We develop a globalized Proximal Newton method for composite and possibly non-convex minimization problems in Hilbert spaces. Additionally, we impose... 相似文献
2.
We study the effect of numerical integration when the p-version of the finite element method is used to approximate the eigenpairs of elliptic partial differential operators. We obtain optimal orders of convergence for approximate eigenvalues and eigenvectors under a certain set of requirements on the quadrature rules employed. This is the same set of conditions that has been shown (in an earlier work) to be sufficient for the optimal approximation of the solutions of the corresponding source problems. 相似文献
3.
Devendra Kumar Uday Razdan Alka D. Gupta 《Journal of polymer science. Part A, Polymer chemistry》1992,30(7):1477-1487
Various melt-polymerizable bisimido-bisphthalonitrile polymer precursors were synthesized by the reaction of 4-aminophthalonitrile (4-APN) with bis(3,4-dicarboxyphenyl) dimethylsilane dianhydride (SIDA), 4,4′-hexafluoroisopropylidene diphthalic anhydride (6FDA), bis(3,4-dicarboxyphenyl)ether dianhydride (ODPA), and 3,3′, 4,4′-tetracarboxylichenzophen+ne dianhydride (BTDA) in an aprotic solvent. The synthesized monomers showed crystalline melting at 269 and 271°C. Elemental analysis, differential thermal analysis (DTA), infrared (IR), nuclear magnetic resonance (1H-NMR) and mass spectral studies were carried out to characterize the synthesized monomers. Thermogravimetric analysis (TGA) of the synthesized monomers showed their thermal stability at 410–400°C. A detailed study and NMR investigation of the first step of condensation reaction was carried out and indicated the formation of a transient charge transfer complex. Thermal cyclization of the formed intermediate, however, gave the required monomers. A preliminary study demonstrated that melt-polymerization of the synthesized monomers gave thermallystable, tough polymers. 相似文献
4.
The molybdenum complexes of Schiff base ligands viz. [MoO2LH2O] where L1 = tris(hydroxymethyl)(salicylide-neamino)methane, L2 = tris(hydroxymethyl)(2,3-dihydroxybenzylideneamino)methane and L3 = tris(hydroxymethyl)(2,3,4-trihydroxybenzylideneamino)methane have been synthesized and characterized by spectroscopic and electrochemical techniques. The X-ray crystal structure of the complex [MoO2L1H2O] reveals a distorted octahedral geometry with one ligand and a water molecule coordinated to the MoO2 center. No previous complex of this type contains a coordinated water molecule. The complex undergoes an oxotransfer in the presence of Bu3P to form a -oxobridged molybdenum(V,V) dimer. This rules out Mo—S coordination as a prerequisite for oxotransfer in such molybdenum(VI) complexes. 相似文献
5.
Devendra Kumar Uday Razdan Alka D. Gupta 《Journal of polymer science. Part A, Polymer chemistry》1993,31(3):797-804
Heat-resistant polymers which are processable into void-free components and suitable for composite applications have been synthesized by thermal/chemical polymerization of four newly developed bisimido-bisphthalonitriles containing silicon, ether, carbonyl, and hexafluoroisopropylidene groups. Thermal polymerization involving addition reactions was performed at 200–275°C for 2–10 h and then post-curing at 310°C for 10 h. Polymers VI, VII, VIII , and IX were obtained. The thermal polymerization was monitored using infrared spectroscopy. Thermal polymerization was also carried out in the presence of an aromatic diamine. A polyhexasocyclane ( V ) was synthesized by condensation polymerization of ether containing bisimido-bisphthalonitrile with 4,4′-diaminodiphenyl ether in solvent phenol. The synthesized polymers were evaluated for thermal stability using dynamic thermogravimetric analysis (TGA). Polymers VII, VIII, IX , and X showed thermal decomposition temperature in the range of 475–500°C in nitrogen and air atmosphere. The char yield of the polymers was in the range of 60–69% in nitrogen at 800°C. This study indicated that synthesized thermosetting polymers from ether and keto containing bisimido-bisphthalo-nitrile are potential candidates for development of graphite composites. © 1993 John Wiley & Sons, Inc. 相似文献
6.
The Ramanujan Journal - In 1857, Sylvester established an elegant theory that certain counting functions (which he termed denumerants) are quasi-polynomials by decomposing them into periodic and... 相似文献
7.
Herbert C. Brown Uday S. Racherla Shankar M. Singh Richard B. Wetherill 《Tetrahedron letters》1984,25(23):2411-2414
A wide variety of α,β-acetylenic ketones were synthesized in very high yields via an exceptionally facile intermolecular reaction of lithium alkynyltrifluoroborates and carboxylic acid anhydrides. 相似文献
8.
Krishna C. Majumdar Uday K. Kundu Swapan K. Samanta Nirmal K. Jana 《Monatshefte für Chemie / Chemical Monthly》2003,134(8):1137-1143
Summary. Two hitherto unreported pyrimidine annelated heterocycles were synthesized from 6-cyclopent-2-enyl-5-hydroxy-1,3-dimethylpyrimidine-2,4(1H,3H)-dione and 5-cyclopent-2-enyl-6-hydroxy-1,3-dimethylpyrimidine-2,4(1H,3H)-dione by reaction with pyridine hydrotribromide or hexamethylenetetramine hydrotribromide. The first one was also obtained by reaction with concentrated sulfuric acid.Received October 28, 2002; accepted October 30, 2002
Published online June 2, 2003 相似文献
9.
Tushar K. Chakraborty V. Ramakrishna Reddy S. Uday Kumar S. Kiran Kumar Archna Mathur Neena Gupta 《Tetrahedron》2004,60(38):8329-8339
Conformational analysis of vasoactive intestinal peptide (VIP) receptor binding inhibitor Leu1-Met2-Tyr3-Pro4-Thr5-Tyr6-Leu7-Lys81 by various NMR techniques and constrained molecular dynamics (MD) simulation studies revealed that the molecule had a turn structure involving its Tyr3-Pro4-Thr5-Tyr6 moiety with intramolecular hydrogen bond between Tyr6NH→Tyr3CO. In order to mimic the structure of 1, peptidomimetic analogs 2-4 were synthesized using conformationally constrained scaffolds of 3,4-dideoxy furanoid sugar amino acids (2S,5R)-ddSaa1 5 and its enantiomer (2R,5S)-ddSaa2 6. All these analogs displayed well defined three-dimensional structures akin to that found in 1. Peptides 2 and 3, which differed only in the sugar amino acid stereochemistry, show propensity of structures with identical intramolecular hydrogen bonds between ThrNH→MetCO. A similar structure with a hydrogen bond between TyrNH→MetCO was observed in 4. 相似文献
10.
Cleavage of the peptide bond occurs when beta]-alanyl-L-histidine (carnosine) reacts with [Co(tren)Cl2]+ (tren = tris(2-aminoethyl)amine) to give [Co(tren)(histidine)](2+) 1 and [Co(tren)(beta-alanine)](2+) 2. [Co(tren)(histidine)](2+) 1 crystallizes in the enantiomorphic space group P2(1)2(1)2(1) and 2 crystallizes in the P2(1)/c space group. The mechanism of the cleavage reactions were studied in detail for the precursor [Co(tren)Cl2]+ and [Co(trien)Cl2]+, which convert into [Co(tren)(OH)2]+/[Co(tren)(OH)(OH2)]2+ and [Co(trien)(OH)2]+/[Co(trien)(OH)(OH2)]2+ in water at basic pH (trien = 1,4,7,10-tetraazadecane). At a slightly basic pH, the initial coordination of the substrate (beta-alanyl-L-histidine) is by the carboxylate group for the reaction with [Co(tren)Cl2]+. This is followed by a rate-limiting nucleophilic attack of the hydroxide group at the beta-alanyl-L-histidine carbonyl group. In a strongly basic reaction medium substrate, binding of the metal was through carboxylate and amine terminals. On the other hand, for the reaction between [cis-beta-Co(trien)Cl2]+ and beta-alanyl-L-histidine, the initial coordination of the substrate takes place via an imidazole ring nitrogen, independently, and followed by a nucleophilic attack of the hydroxide group at the beta-alanyl-L-histidine carbonyl group. The circular dichroism spectrum for 1 suggests that a very small extent of racemization of the amino acid (L-histidine) takes place during the cleavage reaction between [Co(tren)Cl2]+ and beta-alanyl-L-histidine. Reaction between [cis-beta-Co(trien)Cl2]+ and beta-alanyl-L-histidine also causes cleavage of the peptide bond, producing a free beta-alanyl molecule and a cationic fragment [cis-alpha-Co(trien)(histidine)](2+) 3 that crystallizes in the optically active space group P2(1)2(1)2(1). Unlike the previous case an appreciable degree of racemization of the L-histidine takes place during the reaction between [cis-beta-Co(trien)Cl2]+ and beta-alanyl-L-histidine. Crystals containing L-histidine and D-histidine fragments in the [cis-alpha-Co(trien)(histidine)]2+ moiety were crystallographically documented by mounting a number of randomly selected crystals. 相似文献