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1.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
2.
L.A. Leites A.V. Zabula S.S. Bukalov A.A. Korlyukov P.S. Koroteev O.S. Maslennikova M.P. Egorov O.M. Nefedov 《Journal of Molecular Structure》2005,750(1-3):116-122
Vibrational (Raman and IR) spectra of the 1:1 complexes of dihalogermylene and dihalostannylene with 1,4-dioxane and PPh3 have been reported, the structures of the complexes Cl2Ge·C4H8O2 and Cl2Ge·PPh3 updated using high-resolution X-ray method. Quantum-chemistry calculations of the geometry and normal mode frequencies and eigenvectors were carried out for some of the complexes. The results show that in the structure of the polymeric solid complexes of X2M with 1,4-dioxane, intermolecular coordination XM plays a prominent role, whereas the corresponding complexes with PPh3 are monomeric. In the vibrational spectra of all the complexes, an inversion of symmetric and antisymmetric stretching νXM (X=Cl, Br; M=Ge, Sn) frequencies, found for ‘free’ X2MII particles, still persists, suggesting that the X2M moieties preserve their specifity as carbene analogues also in the complexes. 相似文献
3.
L. A. Leites A. V. Zabula S. S. Bukalov P. S. Koroteev O. S. Maslennikova M. P. Egorov O. M. Nefedov 《Russian Chemical Bulletin》2005,54(5):1117-1120
The vibrational spectra of tetravalent metal halides (M = Si, Ge, Sn) and the corresponding dihalocarbene analogs MIIHal2, obtained by the authors, and the relevant published data are compared. The spectra of the MIIHal2 species exhibit inversion of the M-Hal stretching frequencies (νs(MIIHal) > ν as(MIIHal)). This can be used for analytical purposes and allows one to distinguish between the spectra of the MIV and MII halides. The IR and Raman spectra of the complexes of dihalogermylenes and -stannylenes with triphenylphosphine and 1,4-dioxane
also exhibit inversion of the ν(MHal) stretching frequencies. This confirms the conclusion drawn earlier based on the analysis
of the geometric parameters and reactivities of the complexes in question that the divalent state of the M atom in these species
is retained.
Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1089–1092, May, 2005. 相似文献
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5.
R. R. Aysin L. A. Leites S. S. Bukalov V. N. Khrustalev I. V. Borisova N. N. Zemlyanskii A. Yu. Smirnov M. S. Nechaev 《Russian Chemical Bulletin》2011,60(1):69-80
Vibrational spectra of compounds of divalent Group 14 elements ElII(OCH2CH2NMe2)2 with ElII = Ge (1), Sn (2), Pb (3) and ClElIIOCH2CH2NMe2 with ElII = Ge (4) and Sn (5) were measured for the first time and analyzed within the framework of DFT calclations. Monomeric compounds 1 and 2 whose molecules are stabilized only through intramolecular coordination were confirmed to be isostructural. Unlike 1 and 2, plumbylene 3 is a polymer in both solution and the crystalline state; the latter was confirmed by X-ray diffraction analysis. The νs
C-N stretching frequency in the CH2NMe2 fragment was shown to decrease by 80–100 cm−1 owing to the formation of the coordination bond El←N. To elucidate the mechanism of a dynamic flip-flop process suggested earlier based on the broadening of some signals in the NMR spectra of compounds 1 and 4, the Raman spectra of solutions of compounds 1 and 2 in THF and Py were obtained. These experiments revealed no equilibrium with participation of a stable form with one coordination
bond El←N cleaved along with the starting molecule. This is consistent with the results of the corresponding quantum chemical
calculations of thermo-dynamic parameters. A somewhat different, more probable mechanism of the dynamic process was proposed,
which involves an overturn of the CH2NMe2 fragment with cleavage of the El←N bond in the transition state only. 相似文献
6.
In subnormal glow discharge under d.c. excitation at different pressure in a varying transverse magnetic field (0 to 30 G)
some measurements have been carried out for various initial average tube currents. The voltage across the discharge increases
and average tube current and residual current decreases in the magnetic field. With the help of Beckman’s expression [4] for
the axial field and the electron density distribution in a transverse magnetic field the observed variation of current and
voltage can be satisfactorily explained. The variation of axial electric field with transverse magnetic field can be represented
to a fair degree of accuracy by the derived equation. The behaviour of residual current with magnetic field has been observed
in these oscillations. 相似文献
7.
An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations. 相似文献
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