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51.
We show that an electron confined to a single finite parabolic quantum well in crossed electric and magnetic fields can behave as a double quantum well system. The magnetic field is parallel to the heterostructure layers and the electric field is perpendicular to those. For a suitable choice of both fields and quantum well width, the electron can be confined to a double quantum well effective potential that is very similar to the electronic potential model for diatomic molecules. The double quantum well spectrum is calculated using a numerical algorithm based on semiclassical methods. A physical interpretation of this quantum system is given based on the analogy to the electrons bound to diatomic molecules. 相似文献
52.
The gauge compensation fields induced by the differential operators of the Stueckelberg-Schrödinger equation are discussed, as well as the relation between these fields and the standard Maxwell fields; An action is constructed and the second quantization of the fields carried out using a constraint procedure. The properties of the second quantized matter fields are discussed. 相似文献
53.
Double-diffusive convection due to a cylindrical source submerged in a salt-stratified solution is numerically investigated
in this study. For proper simulation of the vortex generated around the cylinder, a computational domain with irregular shape
is employed. Flow conditions depend strongly on the thermal Rayleigh number, Ra
T
, and the buoyancy ratio, R
ρ. There are two types of onset of instability existing in the flow field. Both types are due to either the interaction of
the upward temperature gradient and downward salinity gradient or the interaction of the lateral temperature gradient and
downward salinity gradient. The onset of layer instability due to plume convection is due to the former, whereas, the onset
of layer instability of layers around the cylinder is due to the latter. Both types can be found in the flow field. The transport
mechanism of layers at the top of the basic plume belongs to former while that due to basic plume and layer around the cylinder
are the latter. The increase in Ra
T
reinforces the plume convection and reduces the layer numbers generated around the cylinder for the same buoyancy ratio.
For the same Ra
T
, the increase of R
ρ suppresses the plume convection but reinforces the layers generated around the cylinder. The profiles of local Nusselt number
reflects the heat transfer characteristics of plume convection and layered structure. The profiles of averaged Nusselt number
are between the pure conduction and natural convection modes and the variation is due to the evolution of layers.
Received on 13 September 1996 相似文献
54.
The micro element content of food is an important quality index due to the action of these elements on human health. In this
article, we discuss how to ensure the reliability of analytical data on micro elements in order to truly represent the condition
of food. Sampling, treatment of the analytical sample, selection of the analytical method, standard solution, and certified
reference material, blank test, calibration of the instrument and equipment, application of the quality control chart, assessment
of the final analytical result, and quality assurance system are briefly described.
Received: 5 July 2001 Accepted: 19 November 2001 相似文献
55.
56.
Although the most important use of nuclear magnetic resonance imaging (MRI) continues to be for diagnostic medicine, recognition is being gained for many nonmedical applications. Examples include the following areas: petrogeology, food, agriculture, polymers and polymer-composites, and pharmaceuticals. These areas all involve studies of species that have short spin-spin relaxation times, and consequently need far fast gradient switching. These technical details are discussed and typical applications given. 相似文献
57.
In this paper we construct a primitive, non-symmetric 3-class association scheme with parameters v = 36, v1 = 7, p111 = 0 and p211 = 4 and show that such a scheme is determined by its parameters. 相似文献
58.
Semi-empirical molecular orbital calculations were carried out for the compounds (C2H5)3As, (C2H5)3Ga and RAsH2 (R = C2H5, i-C3H7, i-C4H9, and t-C4H9) by using the CNDO/2-U program, and their capability of β-elimination reaction is compared on the basis of the torsion energy to the transition state, electrostatic interactions and orbital overlapping between the central atom and the β-hydrogen, and bond order of the metal-carbon, and carbon-hydrogen bond. In the comparison of (C2H5)3As with (C2H5)3Ga, we found that the β-elimination of (C2H5)3As could hardly be expected to take place in the thermal decomposition. The capability of β-elimination would be smaller in C2H5AsH2 than that in (C2H5)3As. Moreover when the ethyl group is replaced by a t-butyl group in RAsH2, the β-elimination reaction appears to become more difficult and a large possibility for a radical process is suggested. 相似文献
59.
M. L. Ellzey Jr. 《Journal of mathematical chemistry》1991,8(1):333-344
TheSU(2) rotation matricesD
(j), specified in terms of axis and angle of rotation, are expressed as linear combination of normalized irreducible tensorial matricces (NITM) of rankl = 0 to 2j rotated to the polar angles of the axis. The rotated NITM are constructed from spherical harmonics of the same rank. Since this formulation requires no matrix products, it may be computationally more efficient than Euler angle formulas, particularly for largej. Rotated NITM and formulas for theD
(j) withj = 1/2 andj = 1 are written out explicitly. A formula for the structure constants of the products of conformable NITM is also given in terms of 3-j and 6-j symbols. 相似文献
60.
Silver nitrate-acetonitrile and π iodine-benzene complexes in thermotropic liquid crystals have been studied by 1H, 2H, and 13C NMR spectroscopy and by optical microscopy. Evidence for at least two silver complexes in each liquid crystal is presented. 相似文献