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931.
Magnetic powders for sintered NdFeB magnets have been prepared by using an advanced processing method including strip casting, hydrogen decrepitation, jet milling and rubber isotropic press. The effects of Dy, Ga and Co addition on the microstructure and magnetic properties of sintered magnets have been investigated. By adopting a suitable component ratio and adjusting proper technological parameters, we have prepared high-coercivity sintered NdFeB magnets with hard magnetic properties of jHc=25.6 kOe, Br=13.2 kG and (BH)max=39.9 MGOe. The temperature coefficient of coercivity of the magnets (between 20 and 150 °C) is –0.53%/°C. The magnetic properties at high temperature satisfy the needs of permanent magnet motors. 相似文献
932.
Effects of the passivation of SiNx on the high temperature transport characteristics of the two-dimensional electron gas (2DEG) in unintentionally doped AlxGa1−xN/GaN heterostructures have been investigated by means of high temperature Hall measurements. The 2DEG density increases much after SiNx passivation, and the increment is proportional to the Si content in SiNx layer, indicating that the increment is mainly caused by ionized Si atoms at the SiN/AlxGa1−xN interface with dangling bonds or by Si atoms incorporated into the AlxGa1−xN layer during the SiNx growth, which is approved by strain analysis and X-ray photoemission spectroscopy (XPS). There is lower 2DEG mobility at room temperature in a passivated sample than in an unpassivated one. However, the 2DEG mobility becomes to be higher in a passivated sample than in an unpassivated one when the temperature is above 250 °C, which is suggested to be caused by different subband occupation ratios in the triangular quantum well at the heterointerface before and after passivation. 相似文献
933.
The dielectric and ferroelectric properties of Ba1−xSrxTiO3 (BST) (x=0.10,0.20,0.30,0.40 and 0.60) ceramics and Ba1−2xSrxCaxTiO3 (BSCT) (x=0.10,0.20,0.30) ceramics have been investigated. The low temperature phase transitions of BST ceramics vanish after Ca2+ substitution while the high temperature transition is diffused and relaxed, which becomes more obvious with increasing x. Ca2+ substitution obviously decreases the dielectric constant maximum, Km, of BST ceramics and changes the temperature of dielectric constant maximum, Tm, of BST ceramics. The shift of Tm in BST is attributed mainly to the Sr2+ and Ba2+ concentration. BST ceramics exhibit almost normal ferroelectric characteristics, while a typical relaxor behavior was observed in BSCT ceramics. The relaxor behavior observations may be understood by a random electric field induced domain state. 相似文献
934.
Surface morphology in 3.5 × 3.5 μm2 area of spinel LiMn2O4, which is a typical cathode material for Li ion secondary batteries, is studied using an atomic force microscopy (AFM) with a conductive probe. Negative bias voltage is applied to the probe to attract Li+ ions toward LiMn2O4 surface during the AFM observation. Before applying the voltage (0 V), the whole LiMn2O4 surface is covered with scale-shaped grains. Under the negative voltage of 5.5 V, electric current abruptly increases, indicating Li+ ionic conduction. Simultaneously, part of the scale-shaped grains expand and flatten. Jahn-Teller phase transition, which is induced by the repulsive interaction between the Mn-eg and O-2p electrons in Li accumulated layer, is proposed as a possible origin of these results. 相似文献
935.
The present paper focusses on the application of the transmission line matrix method (TLM) for outdoor sound propagation simulations. It is shown how the reflection at the ground and vertical sound speed gradients can be taken into account. The comparison with calculations using finite differences in the time domain (FDTD), with calculations using parabolic equation and with analytical solutions showed all very good agreement. Thereby the computational effort of TLM is significantly lower compared to common FDTD calculation schemes. 相似文献
936.
《Quaestiones Mathematicae》2013,36(4):425-438
Abstract We construct the Riesz tensor product of Archimedean Riesz spaces and derive its properties using functional calculus and f-algebras. We improve results on the approximation of elements in the Riesz tensor product by means of elements in the vector space tensor product in such a way that the order density property is a consequence of the improved approximation result. 相似文献
937.
We study Brauer–Manin obstructions to the Hasse principle and to weak approximation on algebraic surfaces over number fields. A technique for constructing Azumaya algebra representatives of Brauer group elements is given, and this is applied to the computation of obstructions. 相似文献
938.
Digital image correlation (DIC) has received a widespread research and application in experimental mechanics. In DIC, the performance of subpixel registration algorithm (e.g., Newton-Raphson method, quasi-Newton method) relies heavily on the initial guess of deformation. In the case of small inter-frame deformation, the initial guess could be found by simple search scheme, the coarse-fine search for instance. While for large inter-frame deformation, it is difficult for simple search scheme to robustly estimate displacement parameters and deformation parameters simultaneously with low computational cost. In this paper, we proposed three improving strategies, i.e. Q-stage evolutionary strategy (T), parameter control strategy (C) and space expanding strategy (E), and then combined them into three population-based intelligent algorithms (PIAs), i.e. genetic algorithm (GA), differential evolution (DE) and particle swarm optimization (PSO), and finally derived eighteen different algorithms to calculate the initial guess for qN. The eighteen algorithms were compared in three sets of experiments including large rigid body translation, finite uniaxial strain and large rigid body rotation, and the results showed the effectiveness of proposed improving strategies. Among all compared algorithms, DE-TCE is the best which is robust, convenient and efficient for large inter-frame deformation measurement. 相似文献
939.
Yoav Yaffe 《Topology and its Applications》2011,158(11):1307-1313
We show that a Polish metric space X which has ‘compact configuration spaces’ is free of almost isometric embeddings, i.e. given such an embedding into X one gets an isometric embedding. By assuming a continuous version of ℵ0-homogeneity we get the converse statement, and also prove almost isometry uniqueness. 相似文献
940.
Scanning deflectometric profilers based on an f–gθ system are typical optical tools used to measure mirror profiles at many synchrotron facilities. Unlike these profilers, which are based on a pencil beam, here a secondary light source and a pinhole are used to construct a system that automatically selects a beam that will always pass through the pinhole and propagate along the normal direction of the measured area on the surface under test. By measuring the angle variation of the selected beam, slope variations of the surface under test can be measured. Systematic errors introduced by manufacturing defects or aberrations of an optical element, which greatly degrade the performance of traditional profilers, could be minimized by using the developed method. Simulation values of the proposed method and a conventional method are compared. 相似文献