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101.
J. S. Saini A. K. Singh V. K. Garg S. K. Jaireth K. Chandra 《Hyperfine Interactions》1987,35(1-4):907-911
Powdered samples of Indian Natural Wolframites, (FexMn1?x) WO4 with x=0.95 to 0.41, obtained from seven different locations of two quartz-wolframite deposits of Degana and Sirohi in Rajasthan, have been investigated by Mössbauer spectroscopy down to 20K and magnetic susceptibility down to 77K. The Mössbauer spectra from 300K to 30K clearly indicate multiple sites which is at variance with the reported work. Below 50K a weak magnetic interaction with Hint~45Koe is observed. The spectra above transition temperature are resolved in three doublets and explained on the basis of reported crystal structure. The values of isomer shift, quadrupole splitting and magnetic hyperfine field have been attributed to high spin ferrous ions with octahedral symmetry. Relatively small value of Q.S. (~1.5 mm/sec. at 300K) indicate a strong contribution of the lattice term to the electric field gradient. 相似文献
102.
Garg BS Sharma RK Kumar V Reddy MJ Mittal S 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(12):2789-2794
Novel complexes of Co(II), Ni(II), Cu(II) and Pd(II) with the new ligand [N,N'-bis(2-carboxy-1-oxo-phenelenyl)ethylenediamine] (H2L) have been synthesized and characterized on the basis of elemental analyses, magnetic susceptibility, thermal, infrared, electronic, 1H NMR and EPR spectral studies. Infrared and 1H NMR spectra show that H2L acts as a binegative tetradentate ligand. Coordination occurs through deprotonated carboxylate oxygens and nondeprotonated amido nitrogens in all the complexes. Electronic spectral studies and magnetic moment values suggest N2O2 coordination around each metal centre with strong field square planar chromophores. The probable structures of the complexes have been assigned on the basis of spectral studies. The complex formation between M(II) [M(II) = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)] and (L2-) has also been studied potentiometrically in 75% aqueous DMF at 25 degrees C in 0.1 M NaClO4. The stability constants were found to follow the order: Mn(II) < Co(II) < Ni(II) < Cu(II) > Zn(II). 相似文献
103.
An efficient and controlled means to achieve a rare cine substitution of arenes is reported. The methodology relies on the strategic use of aryl O-carbamates as readily removable directing groups for arene functionalization. The removal of aryl carbamates is achieved by employing an air-stable Ni(II) precatalyst, along with an inexpensive reducing agent, to give synthetically useful yields across a range of substrates. The net cine substitution process offers a new strategy for analogue synthesis, which complements the well-established logic for achieving arene functionalization by ipso substitution. 相似文献
104.
Kavita Garg Deepshikha Chatterjee Prakash P. Wadgaonkar 《Journal of polymer science. Part A, Polymer chemistry》2017,55(6):1008-1020
A new s‐triazine ring containing aromatic diisocyanate bearing a pendent alkyne group, namely, 2,4‐bis(4‐isocyanatophenoxy)?6‐(prop‐2‐yn‐1‐yloxy)?1,3,5‐triazine was synthesized and reacted with various diols viz., 1,10‐decanediol, tetraethylene glycol and polyethylene glycols in the presence of dibutyltin dilaurate as the catalyst to obtain a series of linear polyurethanes. The selected polyurethanes possessing pendent alkyne groups were postmodified with chemically diverse azides viz., 1‐(azidomethyl)benzene, 1‐(azidomethyl)pyrene, and methoxy end‐caped poly(ethylene glycol) azide via copper‐catalysed azide‐alkyne Huisgen 1,3‐dipolar cycloaddition. FTIR and 1H NMR spectra indicated quantitative click reaction. UV–vis and fluorescence spectroscopic analysis confirmed complete incorporation of pyrenyl groups indicating the formation of fluorescence active polyurethane by postmodification with 1‐(azidomethyl)pyrene. TG analysis of polyurethanes indicated two stage weight loss and their thermal stability, as judged by T 10 values, was governed by weight percent of urethane linkages. The water contact angle measurements revealed improved wettability with increased content of PEG either in the backbone of polyurethanes or as grafted chains. DLS and TEM studies confirmed that certain polyurethanes possessing PEG segments displayed self‐assembly in aqueous solution, which was further supported by pyrene encapsulation studies using UV–vis spectroscopy. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1008–1020 相似文献
105.
R. Garg C. Narayanan D. Lakehal S. Subramaniam 《International Journal of Multiphase Flow》2007,33(12):1337-1364
The Lagrangian–Eulerian (LE) approach is used in many computational methods to simulate two-way coupled dispersed two-phase flows. These include averaged equation solvers, as well as direct numerical simulations (DNS) and large-eddy simulations (LES) that approximate the dispersed-phase particles (or droplets or bubbles) as point sources. Accurate calculation of the interphase momentum transfer term in LE simulations is crucial for predicting qualitatively correct physical behavior, as well as for quantitative comparison with experiments. Numerical error in the interphase momentum transfer calculation arises from both forward interpolation/approximation of fluid velocity at grid nodes to particle locations, and from backward estimation of the interphase momentum transfer term at particle locations to grid nodes. A novel test that admits an analytical form for the interphase momentum transfer term is devised to test the accuracy of the following numerical schemes: (1) fourth-order Lagrange Polynomial Interpolation (LPI-4), (3) Piecewise Cubic Approximation (PCA), (3) second-order Lagrange Polynomial Interpolation (LPI-2) which is basically linear interpolation, and (4) a Two-Stage Estimation algorithm (TSE). A number of tests are performed to systematically characterize the effects of varying the particle velocity variance, the distribution of particle positions, and fluid velocity field spectrum on estimation of the mean interphase momentum transfer term. Numerical error resulting from backward estimation is decomposed into statistical and deterministic (bias and discretization) components, and their convergence with number of particles and grid resolution is characterized. It is found that when the interphase momentum transfer is computed using values for these numerical parameters typically encountered in the literature, it can incur errors as high as 80% for the LPI-4 scheme, whereas TSE incurs a maximum error of 20%. The tests reveal that using multiple independent simulations and higher number of particles per cell are required for accurate estimation using current algorithms. The study motivates further testing of LE numerical methods, and the development of better algorithms for computing interphase transfer terms. 相似文献
106.
107.
Small-angle light-scattering (SALS) studies were carried out on block copolymers of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), the synthesis and characterization of which have been reported in an earlier paper. Samples were crystallized isothermally from the melt at 95°C for predetermined crystallization times in order to follow the formation and growth of crystalline superstructure. During the early stages of crystallization, the block copolymers showed unusual Hv patterns with the four lobes along the polarizer directions, while at later stages they showed the usual Hv patterns with the four lobes at 45° to the polarizer directions. The unusual patterns are characteristic of PBT superstructure, while the usual patterns are characteristic of PET superstructure. These results show that PBT, which is the faster-crystallizing component, crystallizes first and provides nucleation sites for the crystallization of PET, which crystallizes later. Similar behavior was not observed in PET homopolymer and random copolymers of equivalent compositions. In each case the spherulite size increased with the time of crystallization. The ultimate spherulite size decreased with increasing PBT content in the block copolymer, thus showing an increase in nucleation density. It was demonstrated that light scattering is a useful tool to characterize block copolymers of two crystalline components which have different types of superstructure. 相似文献
108.
Consider the polyhedron represented by the dual of the LP formulation of the maximums–t flow problem. It is well known that the vertices of this polyhedron are integral, and can be viewed ass–t cuts in the given graph. In this paper we show that not alls–t cuts appear as vertices, and we give a characterization. We also characterize pairs of cuts that form edges of this polyhedron. Finally, we show a set of inequalities such that the corresponding polyhedron has as its vertices alls–t cuts.Work done at the Department of Computer Science and Engineering, Indian Institute of Technology, Delhi, India. 相似文献
109.
Complexation reactions of bivalent metal ions and ethyl-2,3-dioxobutyrate-2p-bromophenylhydrazone (EDOB-2p-BPH) have been studied potentiometrically in 50% (v/v) ethanol/water medium at different ionic strengths with respect to
NaClO4 and at different temperatures and their stability constants determined. The method of Bjerrum and Calvin as modified by Irving
and Rossotti has been used to determine then andpL values. Smin values which have the same significance as ‘T2’ have also been calculated. The thermodynamic stability constants and standard free energy change (ΔG) have also been calculated.
ΔG values are negative in all cases indicating that the reactions are spontaneous. The ligand field stabilization energy (δH)
has also been calculated for the 3d transition metals. 相似文献
110.
Komal Garg Yasuo Matsubara Mehmed Z. Ertem Anna Lewandowska‐Andralojc Shunsuke Sato David J. Szalda James T. Muckerman Etsuko Fujita 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(47):14334-14338
We prepared two geometric isomers of [Ir(tpy)(ppy)H]+, previously proposed as a key intermediate in the photochemical reduction of CO2 to CO, and characterized their notably different ground‐ and excited‐state interactions with CO2 and their hydricities using experimental and computational methods. Only one isomer, C‐trans‐[Ir(tpy)(ppy)H]+, reacts with CO2 to generate the formato complex in the ground state, consistent with its calculated hydricity. Under photocatalytic conditions in CH3CN/TEOA, a common reactive C‐trans‐[Ir(tpy)(ppy)]0 species, irrespective of the starting isomer or monodentate ligand (such as hydride or Cl), reacts with CO2 and produces CO with the same catalytic efficiency. 相似文献