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S.F. Lienin R. Brüschweiler R.R. Ernst 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,131(2):184-190
The viscosity-dependent retarding effect of a polymeric solvent on the rotation of small solute molecules is investigated by13C NMR relaxation measurements. It is found that the relaxation data of 1,3-dibromoadamantane in highly viscous polymeric chlorotrifluoroethene can be explained neither by isotropic nor by realistic anisotropic tumbling in a single environment. The experimental data are rationalized in terms of fast exchange between at least two environments with correlation times differing by up to two orders of magnitude. The study shows that a uniform retardation of molecular tumbling by a polymeric solvent, desirable for shifting the NMR observation window in studies of intramolecular mobility, is not always feasible. 相似文献
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SF. Chichibu T. Onuma T. Kitamura T. Sota S.P. DenBaars S. Nakamura H. Okumura 《physica status solidi b》2002,234(3):746-749
Recombination dynamics of localized excitons in strained cubic (c‐)InxGa1—xN/c‐GaN multiple quantum wells (MQWs) were studied. In contrast to hexagonal (h‐)InGaN quantum wells (QWs), low‐excitation photoluminescence (PL) peak energy increased moderately with decreasing well thickness L and the PL decay time did not depend on L. The results indicated that piezoelectric field had negligible influence on the transition processes. The time‐resolved photoluminescence (TRPL) signal showed a stretched exponential decay up to 300 K, showing that the spontaneous emission is due to the radiative recombination of excitons localized in disordered quantum nanostructures even at 300 K. Decrease in internal quantum efficiency (η), which is related to the increase in quasi‐radiative lifetime, with the increase in temperature was explained to be due to reduced localization rate. 相似文献
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I motivate and discuss non-minimal and non-universal models of supersymmetry and supergravity consistent with string unification
at 1010 GeV. 相似文献
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T. Suski H. Teisseyre S.P. &#x;epkowski P. Perlin T. Kitamura Y. Ishida H. Okumura SF. Chichibu 《physica status solidi b》2002,234(3):759-763
We have studied influence of hydrostatic pressure on the light emission from cubic InGaN/GaN quantum wells (QWs) and cubic InGaN thick epilayers. A qualitative difference between pressure dependence of photoluminescence peak energies for cubic and wurtzite symmetry InGaN/GaN QWs was found. Cubic samples revealed magnitude of dEE/dP of 26–30 meV/GPa, practically independent of the QW width. Previous studies of the hexagonal InGaN/GaN structures showed a drastic drop of dEE/dP with increasing QW width. This different behavior of two types of QWs is explained by the lack of built‐in electric field (along growth direction) in case of cubic structures. To describe pressure evolution of the optical transitions in cubic InGaN/GaN QWs, we use a simple k · p model based on the linear theory of elasticity. To reproduce the experimental data it is necessary to invoke presence of In‐rich fluctuations in the studied samples. In contrast to QWs, thick epilayers of cubic InGaN exhibit the anomalously small dEE/dP. We suggest mechanisms causing likely this effect. 相似文献
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