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41.
The influence of the non-zero value of exchange integrals between Wannier functions, localized in non-neighbouring elementary cells (higher approximation than tight-binding), on the conditions of existence of Tamm surface states and the position of the energy level corresponding to the surface state is shown.
This paper is part of M. Tomáek's candidate's thesis. 相似文献
, ( ) , .
This paper is part of M. Tomáek's candidate's thesis. 相似文献
42.
Ana-Maria Matache Tomáš Roubíček Christoph Schwab 《Advances in Computational Mathematics》2003,19(1-3):73-97
The general theory of approximation of (possibly generalized) Young measures is presented, and concrete cases are investigated. An adjoint-operator approach, combined with quasi-interpolation of test integrands, is systematically used. Applicability is demonstrated on an optimal control problem for an elliptic system, together with one-dimensional illustrative calculations of various options. 相似文献
43.
We derive the incompressible and compressible k–ε model for locally homogeneous turbulence. The model is rigorously derived on formal mathematical grounds using the MPP modelling technique. This lets us calculate by either analytical or numerical means the closure constants of the model. To cite this article: T. Chacón Rebollo, D. Franco Coronil, C. R. Acad. Sci. Paris, Ser. I 337 (2003). 相似文献
44.
Valence bond ground states in isotropic quantum antiferromagnets 总被引:5,自引:0,他引:5
Ian Affleck Tom Kennedy Elliott H. Lieb Hal Tasaki 《Communications in Mathematical Physics》1988,115(3):477-528
Haldane predicted that the isotropic quantum Heisenberg spin chain is in a massive phase if the spin is integral. The first rigorous example of an isotropic model in such a phase is presented. The Hamiltonian has an exactSO(3) symmetry and is translationally invariant, but we prove the model has a unique ground state, a gap in the spectrum of the Hamiltonian immediately above the ground state and exponential decay of the correlation functions in the ground state. Models in two and higher dimension which are expected to have the same properties are also presented. For these models we construct an exact ground state, and for some of them we prove that the two-point function decays exponentially in this ground state. In all these models exact ground states are constructed by using valence bonds.Supported in part by N.S.F. Grant PHY-80-19754. Fellow of the A.P. Sloan Foundation and the Canadian Institute for Advanced ResearchN.S.F. Post-doctoral FellowSupported in part by N.S.F. Grant PHY-85-15288-A01 相似文献
45.
In non-destructive assay there exist techniques founded on physics principles and experimental design for which the quantity of interest yTrue to be estimated is expected to vary in direct proportion to the true value xTrue of the experimentally observed predictor quantity x. In other words, the calibration is a straight line passing through the origin, so that the assay method is fully described by a single parameter, the slope. In principle a single reference item is sufficient to estimate the slope. However, there are good reasons for including more than a single item in the calibration procedure. When multiple items are used questions arise regarding how to make best use of all the available calibration data in estimating the slope. This paper shows that the usual weighted least squares curve fitting approach can be circumvented by using only the familiar notion of a weighted arithmetic mean. In particular we draw attention to the ease with which uncertainties in both x and y can be incorporated using this simple and direct approach. Moreover the uncertainty in the calibration parameter is estimated using familiar techniques and with an appropriate magnitude for subsequent use, for instance, in setting reasonable uncertainties on assay results performed using the calibration. For completeness, weighted least squares accounting for nonzero covariances among the measurements y of yTrue together with an errors in predictors approach accounting for errors in x is also presented. 相似文献
46.
Tom G. Ryan 《Optics Communications》2007,273(1):159-161
The cooperative luminescence and absorption properties of Yb3+ doped aluminosilicate glass optical fibres and preforms are investigated in detail. In accordance with previous investigations, both the visible cooperative luminescence and the infrared luminescence decay measurements have been resolved into a single exponential decay component. We show that for a glass with similar Yb3+ dopant concentration but more Al3+, the glass emits less visible luminescence. Absorption loss measurements completed on fibre samples revealed a broad absorption in the 350-500 nm range, which we propose is due to a combination of Yb2+ absorption and cooperative absorption from Yb3+ ion pairs. 相似文献
47.
Shivaji S. Kadam Lukáš Maier Tomáš Šolomek Marek Nečas Karel Šmejkal Jiří Dostál Vladimír Sklenář Radek Marek 《Journal of Physical Organic Chemistry》2013,26(10):814-821
We report a preparation of new 6‐substituted‐5,6‐dihydrobenzo[c]phenanthridines by the reaction of azoles with quaternary benzo[c]phenanthridine alkaloids sanguinarine and chelerythrine. The prepared compounds have been characterized by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. Conformational behaviors of carbazole derivatives in solution have been investigated by low‐temperature NMR experiments. Barriers to rotation around newly formed C6–N bonds were determined to be 12–13 kcal/mol. Quantum chemical calculations have been used to reproduce the experimental observations. Large structural effects on several 1H NMR resonances were observed experimentally, analyzed by Density Functional Theory (DFT) calculations at B3LYP/6‐311+G(d,p)/PCM level, and interpreted by ring‐current effects of the benzo[c]phenanthridine and carbazole units. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
48.
49.
Zeeman mixing of singlet and triplet 2P states of positronium (Ps) atoms, followed by decay back to the ground state, can effectively turn a long-lived triplet atom into a short-lived singlet state, which would seem to preclude laser cooling of Ps in a magnetic field. Here we report experiments which show that, in fact, because of the large splitting of the n=2 states in a high magnetic field (the Paschen-Back regime), the amount of such mixing diminishes approximately exponentially with an increasing magnetic field >0.01 T and is essentially eliminated above ~2 T. Thus, laser cooling of Ps should be feasible at high fields, which will facilitate the production of a Ps Bose-Einstein condensate. 相似文献
50.