Two-dimensional IrO2/MnO2 enabling conformal growth of amorphous Li2O2 for high-performance Li–O2 batteries
Cong TangPengcheng SunJian XieZhichu TangZixu YangZexi DongGaoshao CaoShichao ZhangPaul V. BraunXinbing Zhao
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A semitransparent cathode is proposed for an efficient operation of the relativistic magnetron (RM) with axial extraction. The semitransparent cathode is a kind of shaped cathode. It is achieved using a cylindrical cathode with longitudinal strips removed. The cross section of each removed strip is fan-shaped and all the emit strips are connected in the central area of the cathode. Results of the 3-D particle-in-cell simulations show that the using a semitransparent cathode yields similar performance benefits compared with that using the transparent cathode proposed by the University of New Mexico. Simulation results also show that output characteristics of the RM using the semitransparent cathode are insensitive to the depth and width of each cathode slot. Thus, the semitransparent cathode might be more robust for practical applications.
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We have designed a high-impedance (5000 omega-cm), tapered, gelled-pad, external cardiac pacing electrode that limits the migration of charges to the perimeter of a circular electrode and produces a more uniform current-density distribution than external cardiac pacing electrodes in clinical use. A computer simulation was developed that uses cylindrical coordinates to analyze the current-density distribution at the interface between the electrode and human tissue. Our computer simulation analyzed 32 different electrodes, and the results showed that the gelled-pad thickness, the gelled-pad taper, and the radius of the conducting disk were not significant parameters in determining the current-density distributions for low-resistivity electrodes. Those parameters were, however, significant for high-resistivity electrodes. We defined the optimum resistivity as that at which the tapered, gelled-pad electrode produces the most uniform current-density distribution and delivers the most current to human tissue. When evaluating electrodes at the optimum resistivity, we determined that the peak current density of the tapered, gelled-pad electrode was 50% lower than that of the clinically available electrodes, while delivering 58% more current to the human tissue.
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An electrode that produces an injected charge density that is uniform over the surface of the electrode and thus permits maximum utilization of the surface is described. Charge density is the time integral of current density, and the alteration of the current density is obtained by adding curvature to the electrode and recessing it within a cylindrical insulating well. A novel numerical method is used to determine the recession and curvature. The benefit of this technique is that it permits a reduction in the electrode size while maintaining the maximum safe injected charge level of a disk-type electrode. A minimum profile uniform current density electrode and the algorithms used in its design are presented. Finally, a flat electrode that is recessed by as little as 1/10 of its diameter is shown to have an injected current density on the electrode surface that is superior to that of a flat surface mounted electrode.< >
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The current-density distribution of resistive disk surface electrodes is analyzed using a model in which the body is locally represented by a planar two-layer resistive medium and the electrode by a resistive disk with a concentric perfectly conducting feed contact. The exact current-density distribution on and in the electrode is obtained by solving a three-dimensional Laplace's equation numerically by means of the moment method. The following physical factors that affect the current-density distribution are analyzed: electrode size, feed region size, electrode thickness, electrode resistivity, skin conductivity, and skin thickness. The results demonstrate both an edge peak, which occurs with a highly conducting electrode on a uniform medium, and a peak in the current density near the feed region, which occurs if the electrode properties are not well matched to the properties of the tissues.< >
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Based on a 2-D magnetohydrodynamic model, high-current vacuum arcs (HCVAs) under axial magnetic fields (AMFs) with consideration of current density distribution at the cathode are simulated and analyzed. The current density distribution at the cathode used in the simulation is obtained by processing the image of cathode spots from experiments. In order to study the influence of current density distribution at the cathode on vacuum arc characteristics, HCVA is simulated under two kinds of current density distribution at the cathode. Then, for HCVA simulation in a half-sinusoidal period, the current density distribution at the cathode and the AMF delay are both taken into account. The simulation results show that the nonuniform current density at the cathode makes the values of the arc plasma parameters in the interelectrode region larger and their radial distribution more nonuniform than the uniform current density at the cathode. The more uniform current density at the cathode and the stronger AMF at the moments in the second 1/4 cycle make the values of the arc plasma parameters in the central region smaller and their radial distribution broader than those in the first 1/4 cycle. In addition, the simulation results will also be compared with the experimental results.
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With the development of high power magnetron, cathode is researched a lot to endure higher temperature and intense electron bombardment. In order to decrease the central part temperature of cathode in magnetron and extend magnetron's lifetime, a kind of variable pitch helical cathode is proposed in this paper. Computer simulations are adopted to verify whether cathode surface electric field distribution is consistent with its structural uniformity. So electrostatic field uniformity of variable pitch helical cathode is simulated by CST-EM and compared with cylindrical cathode and even pitch helical cathode. The results show that thought variable pitch cathode has the worst structural uniformity, it has similar field uniformity to even pitch cathode, and the uniformity of electric field near the cathode surface of variable pitch cathode is relatively close to that of the cylindrical cathode. So it may be adopted in magnetrons to improve magnetrons' performance and extend their lifetime.
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Mixed metal matrix cathodes (MM-cathodes) were optimized and their life behavior was tested in different test vehicles. In two separate life test programs, 57 MM-cathodes with a W/Os matrix were investigated in test vehicle (tetrodes) where the cathode environment was similar to that of a tube. In parallel, a further 100 MM-cathodes in other types of test vehicles were operated for supplementary investigations and cathode design optimization. The operational temperatures were between 880 degrees C/sub B/ and 1200 degrees C/sub B/ (brightness). One group of cathodes was operated at constant anode voltage with an initial current density of 0.75 A/cm/sup 2/, and the other group was operated with a loading of 2 A/cm/sup 2/ for as long as the anode voltage could be adjusted. The cathodes at lower temperatures (>
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In a dispenser cathode the surface is composed of many small regions having different and individual values of work functions called "patches". The non-uniform emission results in a gradual transition from space-charge (SC) region to temperature limited (TL) region. The emission of a planar cathode is modeled using a 'top-hat' model. In practice, the convergent guns are incorporated with a spherical cathode. The above model is applied to a spherical cathode-anode system. This model can also be extended to a gun geometry provided that the field distribution across the cathode cross section is uniform. In this paper the performance of three types of cathode, viz. B-Type, Alloy-coated, and Scandate cathodes are studied. In the present model the real cathode is replaced by a fictitious cathode, having a maximum current density at θ = 0° and a minimum at the rim. The analysis shows that there exists an analogy between a planar cathode and a spherical cathode, enabling the emission current to be modeled in a manner similar to a planar cathode.
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