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161.
M. Andreis J. L. Koenig M. Gupta S. Ramesh 《Journal of Polymer Science.Polymer Physics》1995,33(10):1449-1460
Molecular dynamics and structure of uncured and cured melamine-formaldehyde resins isotopically 15N enriched at amine sites were studied by solid-state 15N nuclear magnetic resonance (NMR). Spectra recorded with direct (DP) and cross-polarization (CP) pulse sequences reflect two motionally different regions arising from similar chemical structures. DP spectra of uncured resins at higher temperatures have narrow lines and the detection of slightly different structural units is possible. With increasing crosslinking resonances broaden and overlap and the direct detection of individual signals in cured resins is not possible. On the basis of variable contact time, variable spinning speed, and interrupted decoupling experiments three protonated and one nonprotonated group of signals are identified in the CP spectra for all samples. Short polarization-transfer rates, TNH, for nonprotonated nitrogen in uncured and lightly cured samples reveal more effective hydrogen bonding in viscous and rubber-like resins compared to the highly cured rigid resins. The rigid portions of the resins exhibit longer T1 and short T1ρ relaxation times, while the shorter T1 times and longer T1ρ times are associated with the more mobile portion of samples. ©1995 John Wiley & Sons, Inc. 相似文献
162.
Anudeep K. Narula Beer Singh Sandhya Gupta Ramesh N. Kapoor 《Transition Metal Chemistry》1984,9(10):379-382
Summary Niobium(V) and tantalum(V) pentaethoxides react with monofunctional benzoyl hydrazones (BHy) in refluxing benzene to give products of the type, M(OEt)5–n(BHy)n (where M=Nb or Ta and n=1, 2 or 3). The complexes have been characterised on the basis of elemental analysis, spectral (i.r. and n.m.r.) and molecular weight data. 相似文献
163.
Ramesh Tikekar 《General Relativity and Gravitation》1984,16(5):445-451
Using static spherically symmetric space-times with associated 3-spaces obtained as hypersurfacest= const as 3-spheroidal, a class of physically viable relativistic models for spherical distributions of uniformly charged dust in equilibrium is obtained. The charged analog of Schwarzschild interior solution given by Cooperstock and de la Cruz follows as a particular case of this class. 相似文献
164.
The possibility of writing the repulsive energy in the Born model of binary ionic crystals as a sum of two separate contributions
from the two ions has been investigated. Such an approach leads to two identities, one connecting the lattice spacings of
a family of ionic crystals and the other connecting their compressibilities. These identities have been tested on the alkali
halide crystals over a range of pressures. The agreement is found to be quite satisfactory. Some further predictions with
respect to crystals which exist as two polymorphs have also been tested. In all cases, the deviations of the experimental
values from the exact identities can be traced to the fact that second neighbour repulsions in the crystals have been neglected.
It is hence concluded that individual compressive energies for ions in ionic crystals is a very attractive possibility. 相似文献
165.
Comparative selectivities toward alkenes of CH3CCl, CCl2, and CH3OCCl establish the former two carbenes as electrophiles; the latter is an ambiphile. 相似文献
166.
167.
Grant R. Krow Yoon B. Lee Steven W. Szczepanski Ramesh Raghavachari A. David Baker 《Tetrahedron letters》1985,26(22):2617-2618
Steric effects have been found to predominate over Frontier Molecular Orbital (FMO) effects in controlling the relative rates of intramolecular cycloadditions of 3-R-substituted- 2-(3-butenyl)1,2-dihydropyridines (DHP) in the series (R = H, Me, Et). 相似文献
168.
Ramesh Narayan 《Journal of Physics and Chemistry of Solids》1977,38(9):1097-1100
A formula has been derived based on a variational approach for the van der Waals dipole-quadrupole interaction coefficient between two atoms or ions. The coefficients for the various ion pairs in the alkali halides have been estimated on the basis of this formula. The results agree quite well with those estimated by Mayer (J. Chem. Phys.1, 270 (1933)) using a perturbation approach. The present formula is shown to have a practical advantage over the perturbation formula. 相似文献
169.
Ramesh Chander Kapoor 《Pramana》1976,7(5):334-343
Gravitational recoil of a gigantic black hole (M∼108–9 M⊙) formed in the nonspherical collapse of the nuclear part of a typical galaxy can take place with an appreciable speed as
a consequence of the anisotropic emission of gravitational radiation. Accretion of gaseous matter during its flight through
the galaxy results in the formation of a glowing shock front. The accompanying stellar captures can lead to the formation
of an accretion disk-star system about the hole. Consequently, the hole can become “luminous” enough to be observable after
it emerges out of the galaxy. The phenomenon seems to have an importance in relation to the observations of quasar-galaxy
association in a number of cases. 相似文献
170.
Shukla R Bansal V Chaudhary M Basu A Bhonde RR Sastry M 《Langmuir : the ACS journal of surfaces and colloids》2005,21(23):10644-10654
Macrophages are one of the principal immune effector cells that play essential roles as secretory, phagocytic, and antigen-presenting cells in the immune system. In this study, we address the issue of cytotoxicity and immunogenic effects of gold nanoparticles on RAW264.7 macrophage cells. The cytotoxicity of gold nanoparticles has been correlated with a detailed study of their endocytotic uptake using various microscopy tools such as atomic force microscopy (AFM), confocal-laser-scanning microscopy (CFLSM), and transmission electron microscopy (TEM). Our findings suggest that Au(0) nanoparticles are not cytotoxic, reduce the production of reactive oxygen and nitrite species, and do not elicit secretion of proinflammatory cytokines TNF-alpha and IL1-beta, making them suitable candidates for nanomedicine. AFM measurements suggest that gold nanoparticles are internalized inside the cell via a mechanism involving pinocytosis, while CFLSM and TEM studies indicate their internalization in lysosomal bodies arranged in perinuclear fashion. Our studies thus underline the noncytotoxic, nonimmunogenic, and biocompatible properties of gold nanoparticles with the potential for application in nanoimmunology, nanomedicine, and nanobiotechnology. 相似文献