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991.
This paper describes the evaluation of synchronous fluorescence spectroscopy (SFS) and excitation emission matrix fluorescence (EEMF) spectroscopy as means of monitoring transformer oil degradation. When accelerated thermal ageing method is used, the onset of degradation of transformer oil on 17th day and transformer oil with polypropylene and cellulosic paper on 23rd and 27th days is sensitively reflected in the SFS and EEMF fluorescence spectral characteristics. 相似文献
992.
The regioselective aminoethylation of 1,4-benzodiazepin-2-one 1 can be carried out using classical heating or microwave irradiation as the source of energy to furnish either N-1 or N-4 aminoethylated products 2a-d and 3a-d, respectively. The regioselectivity observed has been rationalized using computational studies and has been traced to the disparity of the rate-determining steps along the N-1 product (N-1 PR) and N-4 product (N-4 PR) formation pathways. 相似文献
993.
The oxidation kinetics of various aliphatic primary and secondary alcohols having varied hydrocarbon chain length were studied using cetyltrimethylammonium dichromate (CTADC) in dichloromethane (DCM) in the presence of acetic acid and in the presence of a cationic surfactant. The rate of the reaction is highly sensitive to the change in [CTADC], [alcohol], [acid], [surfactant], polarity of the solvents, and reaction temperature. A Michaelis-Menten type kinetics was observed with respect to substrate. The chemical nature of the intermediate and the reaction mechanism were proposed on the basis of (i) observed rate constant dependencies on the reactants, that is, fractional order with respect to alcohol and acid and a negative order with respect to oxidant, (ii) high negative entropy change, (iii) inverse solvent kinetic isotope effect, k(H2O)/k(D2O) = 0.76, (iv) low primary kinetic isotope effect, kH/kD = 2.81, and (v) the k(obs) dependencies on solvent polarity parameters. The observed experimental data suggested the self-aggregation of CTADC giving rise to a reverse micellar system akin to an enzymatic environment, and the proposed mechanism involves the following: (i) formation of a complex between alcohol and the protonated dichromate in a rapid equilibrium, equilibrium constant K = 5.13 (+/-0.07) dm(3) mol(-1), and (ii) rate determining decomposition (k(2) = (7.6 +/- 0.7) x 10(-3) s(-1)) of the ester intermediate to the corresponding carbonyl compound. The effect of [surfactant] on the rate constant and the correlation of solvent parameters with the rate constants support the contribution of hydrophobic environment to the reaction mechanism. 相似文献
994.
The oxidation of cholesterol by cetyltrimethylammonium dichromate (CTADC) in dichloromethane (DCM) yielded 7-dehydrocholesterol, while with addition of acetic acid in DCM the product was found to be 5-cholesten-3-one. The kinetics of oxidation of cholesterol by CTADC in DCM, in the presence of acid, was investigated with change in [acid], [cholesterol], [CTADC], [surfactant], temperature, and solvents. The reaction was found to be first order with acetic acid and fractional order with CTADC and cholesterol. Michaelis-Menten-type kinetics was observed with respect to cholesterol. The solvent isotope effect was found to be k(D2O)/k(H2O) = 0.72. The observed experimental data suggest that the reaction occurs in reversed micellar system, akin to an enzymatic environment, and the reaction path involves the intermediate formation of an ester complex, which undergoes decomposition to give the product. 相似文献
995.
Helmut Ehrenberg P.C. Schmidt R. McSweeney K.C. Mishra 《Journal of solid state chemistry》2006,179(4):968-973
Strontium borophosphate phosphate (Sr6BP5O20, SrBP), activated by divalent europium ions is a bluish-green phosphor emitting in a broad band with the emission peak near 480 nm. In this paper, we report the crystal structure of SrBP determined from an analysis of the X-ray diffraction pattern of a prismatic single crystal (size 60 μm×50 μm×40 μm). This crystal was chosen from undoped phosphor powder samples prepared for this purpose by solid-state reaction. SrBP is observed to crystallize in a body-centered tetragonal lattice with the lattice parameters and , the associated space group being (space group 120). Using the structural data from this study, we have also calculated its electronic structure using the augmented spherical wave method and the local density approximation (LDA). We show the ordering of the electronic states by the density of states (DOS) and the partial DOS plots. The LDA gives a direct optical band gap at the Γ point of about 5 eV. The significance of the crystal structure and associated electronic structure is discussed with respect to maintenance of this phosphor in Hg-discharge lamps. 相似文献
996.
Biswas N Thomas S Kapoor S Mishra A Wategaonkar S Venkateswaran S Mukherjee T 《The journal of physical chemistry. A》2006,110(5):1805-1811
Resonance Raman (RR) and surface-enhanced resonance Raman scattering (SERRS) of 4'-(N,N'-dimethylaminostyryl)-4-propylpyridinium bromide (hemicyanine, HC dye) in acetonitrile solution and on a colloidal silver surface have been investigated. The structure of the dye in the ground (S0) and excited (S1) electronic states was optimized using density functional calculations along with the B3LYP and the configuration interaction with the singlet excitation (CIS) methods, respectively, using the 6-31G basis set. The vibrational frequencies of the molecule were computed at the optimized geometry and compared with the observed Raman bands. A complete normal-mode analysis has been carried out because it is essential for the accurate assignment of the vibrational spectra. From the observed enhancement along various in-plane and out-of-plane vibrations in the SERRS spectrum and from theoretical calculations, it has been inferred that the interaction with the silver surface occurs via the nitrogen lone pair of the pyridyl or the dimethylamino group of the molecule with a tilted orientation. The observed red-shifts in the SERRS spectrum along various vibrations indicate strong interaction (chemisorption) of the HC dye with the silver surface. This is also supported by the presence of a Ag-N stretching vibration at 241 cm(-1). The effect of the dye concentration on the orientation of the molecule is also discussed. 相似文献
997.
R. Biswal P. K. Agrawal G. K. Mishra S. V. Nakhe S. K. Dixit J. K. Mittal 《Pramana》2010,75(5):953-959
This paper presents the design and performance analysis of an indigenously developed 110 W average output power copper HyBrID
laser operating at 16 kHz pulse repetition rate. The laser active medium was confined within a fused silica tube of ∼6 cm
diameter and ∼200 cm active length. An in-house developed high-power (∼10 kW) solidstate pulser was used as the electrical
excitation source. A simple estimation of deposited electrical power, at the laser head, was carried out and based on it,
the laser tube efficiency was found to be 2.9% at 70 W and 2.2% at 110 W laser power levels. 相似文献
998.
The Schrödinger equation was solved for a generalized PT-symmetric quartic potential in two dimensions. It was found that, under a suitable ansatz for the wave function, the system possessed real and discrete energy eigenvalues. Analytic expressions for the energy eigenvalues and the eigenfunctions for the first four states were obtained. Some constraining relations among the wave function parameters rendered the problem quasi-solvable. 相似文献
999.
A. Mishra A. Kumar S. Sanyal V. Dexheimer S. Schramm 《The European Physical Journal A - Hadrons and Nuclei》2010,45(2):169-177
The modification of kaon and antikaon properties in the interior of (proto-)neutron stars is investigated using a chiral SU(3) model. The parameters of the model are fitted to nuclear-matter saturation properties, baryon octet vacuum masses, hyperon
optical potentials and low-energy kaon-nucleon scattering lengths. We study the kaon/antikaon medium modification and explore
the possibility of antikaon condensation in (proto-)neutron star matter at zero as well as finite temperature/entropy and
neutrino content. The effect of hyperons on kaon and antikaon optical potentials is also investigated at different stages
of the neutron star evolution. 相似文献
1000.
F.G. Fuchs A.D. McMurry S. Mishra N.H. Risebro K. Waagan 《Journal of computational physics》2010,229(11):4033-4058
Wave propagation in idealized stellar atmospheres is modeled by the equations of ideal MHD, together with the gravity source term. The waves are modeled as small perturbations of isothermal steady states of the system. We consider a formulation of ideal MHD based on the Godunov–Powell form, with an embedded potential magnetic field appearing as a parameter. The equations are discretized by finite volume schemes based on approximate Riemann solvers of the HLL type and upwind discretizations of the Godunov–Powell source terms. Local hydrostatic reconstructions and suitable discretization of the gravity source term lead to a well-balanced scheme, i.e., a scheme which exactly preserves a discrete version of the relevant steady states. Higher order of accuracy is obtained by employing suitable minmod, ENO and WENO reconstructions, based on the equilibrium variables, to construct a well-balanced scheme. The resulting high order well-balanced schemes are validated on a suite of numerical experiments involving complex magnetic fields. The schemes are observed to be robust and resolve the complex physics well. 相似文献