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891.
A new superfluid specific additive integral of motion is found. This facilitates investigation of the general thermodynamic equilibrium conditions of a superfluid. The analysis is performed in an extended space of thermodynamic variables containing (along with the usual thermodynamic coordinates such as pressure and temperature) superfluid velocity and momentum density. The equilibrium stability conditions lead to thermodynamic inequalities which replace the Landau superfluidity criterion at finite temperatures. 相似文献
892.
S. Klages M. Schöck C. Sürgers H. v. Löhneysen 《Journal of Low Temperature Physics》2004,137(3-4):509-522
The morphology and electronic transport of ultrathin Au films with thicknesses d = 1 ? 5 monolayers (ML) deposited on Si(111)7 × 7 surfaces is investigated by in situ scanning tunneling microscopy and electrical resistance measurements for temperatures T = 2 ? 300 K. With decreasing film thickness, i.e. decreasing sheet conductance Gs, a transition from a weakly conducting regime described by a logarithmic temperature dependence to an insulating regime occurs. In the insulating regime, the temperature dependence is described by Gs ∝ exp[?(T 0 /T) n] with an exponent n which gradually changes from 0.69 to 1 with decreasing film thickness. In contrast, for the Si(111)6 × 6-Au reconstruction obtained after annealing, an exponent n = 1/2 is found suggesting the formation of a soft Coulomb gap due to electron-electron interaction. PACS numbers: 68.37.-d, 68.55.-a, 73.50.-h, 73.25.+i, 81.15.-z 相似文献
893.
894.
L. K. Isaev 《Measurement Techniques》2007,50(11):1214-1217
The main prerequisites are considered in a historical aspect and steps ate taken in creating a world-wide metrology system
with the aim of providing conditions for the mutual recognition of measurement results.
__________
Translated from Izmeritel’naya Tekhnika, No. 11. pp. 59–62, November, 2007. 相似文献
895.
The methods of X-ray photoelectron spectroscopy and Auger spectroscopy are used to study surface films formed on zinc and zinc-plated steel in the process of holding in aqueous extracts of mixtures of phosphate and calcium-containing pigments. It is shown that protective films formed mainly of zinc and calcium phosphates of different chemical structure are deposited in inhibited solutions on specimens of pure zinc and zinc-plated steel. The protective properties of these films are much better than the protective properties of the surface layers formed on the metal in the extracts of a single phosphate (or calcium-containing) pigment. The mixture of these pigments may serve as a promising substitution of chromate inhibitors in anticorrosive organic coatings. 相似文献
896.
897.
A weighting algorithm to determine the coordinates of the center of a Gaussian laser beam projected onto a matrix photodetector is considered. The influence of the internal noise of the photodetector, the maximum brightness of the signal at the beam maximum, and the beam radius on the precision of the algorithm is investigated. Recommendations on image processing are presented. 相似文献
898.
A. Pizzinat B.S. Marks L. Palmieri C.R. Menyuk A. Galtarossa 《Photonics Technology Letters, IEEE》2003,15(6):819-821
We consider the two Wai-Menyuk models of birefringence in periodically spun fibers, and we show that the differential group delay differs significantly for the two models when the spin period approaches or exceeds the fiber beat length. When the fiber correlation length is large, we explain this difference quantitatively, and we explain it qualitatively for any fiber correlation length. 相似文献
899.
Sensitivity analysis of simulations for magnetic particle inspection using the finite-element method 总被引:2,自引:0,他引:2
Lee J.Y. Lee S.J. Jiles D.C. Garton M. Lopez R. Brasche L. 《IEEE transactions on magnetics》2003,39(6):3604-3606
Magnetic particle inspection (MPI) is widely used for nondestructive evaluation in aerospace applications in which interpretation of inspection results is currently limited to empirical knowledge and experience-based approaches. Advances in computational magnetics, particularly the use of finite-element calculations, have enabled realistic numerical simulations of magnetic particle inspection to be undertaken with complicated geometries. In this paper, we report a sensitivity analysis using finite-element-method simulations of magnetic particle inspection for defects with various sizes and geometries. As a result, improved quantitative understanding of the MPI technique and factors that affects its sensitivity and reliability has been achieved. These results can be used to optimize conditions for conducting these inspections and should lead to improvement in analysis and interpretation of experimental results. 相似文献
900.
Calvente J. Martinez-Salamero L. Valderrama H. Vidal-Idiarte E. 《Power Electronics Letters, IEEE》2004,2(2):58-62
A dynamic analysis of the boost converter with an output filter reveals that magnetic coupling between inductors allows transfer of the zeros to the left half-plane of the control-to-output transfer function. Similar results requiring smaller magnetic components are obtained by combining magnetic coupling with damping of the output filter. The analysis is based on the application of the Routh-Hurtwitz's criterion to the numerator of the transfer function in order to derive the design conditions for the converter parameters. A design example illustrates the procedure, and experimental results verify the theoretical predictions. The application of these techniques will allow the design of high efficiency voltage boost-based regulators with dynamic behavior similar to buck-derived structures. 相似文献