11,704 research outputs found

    Comment on ``Relativistic kinetic equations for electromagnetic, scalar and pseudoscalar interactions''

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    It is found that the extra quantum constraints to the spinor components of the equal-time Wigner function given in a recent paper by Zhuang and Heinz should vanish identically. We point out here the origin of the error and give an interpretation of the result. However, the principal idea of obtaining a complete equal-time transport theory by energy averaging the covariant theory remains valid. The classical transport equation for the spin density is also found to be incorrect. We give here the correct form of that equation and discuss briefly its structure.Comment: 5 pages LaTe

    Hysteretic current-voltage characteristics and resistance switching at an epitaxial oxide Schottky junction SrRuO3_{3}/SrTi0.99_{0.99}Nb0.01_{0.01}O3_{3}

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    Transport properties have been studied for a perovskite heterojunction consisting of SrRuO3_{3} (SRO) film epitaxially grown on SrTi0.99_{0.99}Nb0.01_{0.01}O3_{3} (Nb:STO) substrate. The SRO/Nb:STO interface exhibits rectifying current-voltage (II-VV) characteristics agreeing with those of a Schottky junction composed of a deep work-function metal (SRO) and an nn-type semiconductor (Nb:STO). A hysteresis appears in the II-VV characteristics, where high resistance and low resistance states are induced by reverse and forward bias stresses, respectively. The resistance switching is also triggered by applying short voltage pulses of 1 μ\mus - 10 ms duration.Comment: 3 pages, 3 figures, Appl. Phys. Lett., in pres

    Numerical Modelling of Needle-Grid Electrodes Negative Surface Corona Charge System

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    Surface potential decay measurement is a simple and low cost tool to examine electrical properties of insulation materials. During corona charging stage, needle-grid electrodes system is often used to achieve uniform charge distribution on the surface of the sample. However, there is little report on the effects of geometrical parameters and voltage values of the charging system on the surface potential and its characteristics. In the present report simulations based on gas discharging physics similar to [1] have been carried out to investigate dynamic surface charge formation. The geometry of in the model includes a 174?m radius of curvature needle setting perpendicular to a 0.5mm thickness grid electrode and a 27.5mm diameter with 50?m thickness polyethylene. The bottom surface of the polyethylene is grounded and it is 3cm and 1.5cm away from the needle electrode and grid electrode respectively. The simulations were initially performed under the following conditions: the needle electrode was set as -8000V and the grid electrode -2000V. It has been found that an impulse current appeared after 0.3?s charging which represented the corona effect. The effect of adding a grid electrode can be clearly seen from the logarithmic plot of electrons. Finally, surface charge density on the sample has been obtained

    Exclusive B→PVB \to PV Decays and CP Violation in the General two-Higgs-doublet Model

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    We calculate all the branching ratios and direct CP violations of B→PVB \to PV decays in a most general two-Higgs-doublet model with spontaneous CP violation. As the model has rich CP-violating sources, it is shown that the new physics effects to direct CP violations and branching ratios in some channels can be significant when adopting the generalized factorization approach to evaluate the hadronic matrix elements, which provides good signals for probing new physics beyond the SM in the future B experiments.Comment: 21 page

    Active optical clock based on four-level quantum system

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    Active optical clock, a new conception of atomic clock, has been proposed recently. In this report, we propose a scheme of active optical clock based on four-level quantum system. The final accuracy and stability of two-level quantum system are limited by second-order Doppler shift of thermal atomic beam. To three-level quantum system, they are mainly limited by light shift of pumping laser field. These limitations can be avoided effectively by applying the scheme proposed here. Rubidium atom four-level quantum system, as a typical example, is discussed in this paper. The population inversion between 6S1/26S_{1/2} and 5P3/25P_{3/2} states can be built up at a time scale of 10−610^{-6}s. With the mechanism of active optical clock, in which the cavity mode linewidth is much wider than that of the laser gain profile, it can output a laser with quantum-limited linewidth narrower than 1 Hz in theory. An experimental configuration is designed to realize this active optical clock.Comment: 5 page

    Spectral and dynamic characteristics of buried-heterostructure single quantum well (Al,Ga)As lasers

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    We demonstrate that, as predicted, (Al,Ga)As single quantum well (SQW) lasers have substantially narrower spectral linewidths than bulk double-heterostructure lasers. We have observed a further major reduction (>3×) in the linewidth of these SQW lasers when the facet reflectivities are enhanced. This observation is explained theoretically on the basis of the very low losses in coated SQW lasers and the value of the spontaneous emission factor at low threshold currents. We also report on the modulation frequency response parameter of these SQW lasers

    Exploring semantic inter-class relationships (SIR) for zero-shot action recognition

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    © Copyright 2015, Association for the Advancement of Artificial Intelligence (www.aaai.org). All rights reserved. Automatically recognizing a large number of action categories from videos is of significant importance for video understanding. Most existing works focused on the design of more discriminative feature representation, and have achieved promising results when the positive samples are enough. However, very limited efforts were spent on recognizing a novel action without any positive exemplars, which is often the case in the real settings due to the large amount of action classes and the users' queries dramatic variations. To address this issue, we propose to perform action recognition when no positive exemplars of that class are provided, which is often known as the zero-shot learning. Different from other zero-shot learning approaches, which exploit attributes as the intermediate layer for the knowledge transfer, our main contribution is SIR, which directly leverages the semantic inter-class relationships between the known and unknown actions followed by label transfer learning. The inter-class semantic relationships are automatically measured by continuous word vectors, which learned by the skip-gram model using the large-scale text corpus. Extensive experiments on the UCF101 dataset validate the superiority of our method over fully-supervised approaches using few positive exemplars

    Integrated Tunable Magnetic RF Inductor

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