National University of Defense Technology

About: National University of Defense Technology is a education organization based out in Changsha, China. It is known for research contribution in the topics: Computer science & Radar. The organization has 39430 authors who have published 40181 publications receiving 358979 citations. The organization is also known as: Guófáng Kēxuéjìshù Dàxué & NUDT.

Analysis of Polysulfide Dissolved in Electrolyte in Discharge-Charge Process of Li-S Battery

Abstract: In this paper, the qualitative and semi-quantitative analysis of polysulfide species dissolved in electrolyte during the dischargecharge process and cycling of Li-S batteries was reported. ICP-OES (Inductively coupled plasmaOptical emission spectrometer) measurement was used to estimate the total sulfur content dissolved in electrolyte. Lithium polysulfide with different order were separated and confirmed by LC-MS (Liquid chromatography coupled with mass spectrometry). Li2S4 and Li2S6 were proved to be the most stable form of lithium polysulfide species. At the end of discharge process, total sulfur content in the form of Li2S4 and Li2S6 remained in electrolyte was about 20% of the active material in initial cathode. At the end of charge process, 45% total sulfur content was preserved in electrolyte mainly in the form of Li2S6. The partial transformation of active material from liquid phase to solid phase resulted in relatively low practical specific capacity than the theoretical. In cycles, active material transferred between liquid and solid phase kept a balance, and the content of total sulfur, Li2S4 and Li2S6 were changed slightly at the end. Consequently, polysulfide dissolved in electrolyte just took limited responsibility for the capacity fading with cycles of Li-S batteries. © 2012 The Electrochemical Society. [DOI: 10.1149/2.060204jes] All rights reserved.

Adaptive NN Control of a Class of Nonlinear Systems With Asymmetric Saturation Actuators

Abstract: In this note, adaptive neural network (NN) control is investigated for a class of uncertain nonlinear systems with asymmetric saturation actuators and external disturbances. To handle the effect of nonsmooth asymmetric saturation nonlinearity, a Gaussian error function-based continuous differentiable asymmetric saturation model is employed such that the backstepping technique can be used in the control design. The explosion of complexity in traditional backstepping design is avoided using dynamic surface control. Using radial basis function NN, adaptive control is developed to guarantee that all the signals in the closed-loop system are semiglobally uniformly ultimately bounded, and the tracking error converges to a small neighborhood of origin by appropriately choosing design constants. The effectiveness of the proposed control is demonstrated in the simulation study.

Region-Based Classification of Polarimetric SAR Images Using Wishart MRF

Abstract: The scattering measurements of individual pixels in polarimetric SAR images are affected by speckle; hence, the performance of classification approaches, taking individual pixels as elements, would be damaged. By introducing the spatial relation between adjacent pixels, a novel classification method, taking regions as elements, is proposed using a Markov random field (MRF). In this method, an image is oversegmented into a large amount of rectangular regions first. Then, to use fully the statistical a priori knowledge of the data and the spatial relation of neighboring pixels, a Wishart MRF model, combining the Wishart distribution with the MRF, is proposed, and an iterative conditional mode algorithm is adopted to adjust oversegmentation results so that the shapes of all regions match the ground truth better. Finally, a Wishart-based maximum likelihood, based on regions, is used to obtain a classification map. Real polarimetric images are used in experiments. Compared with the other three frequently used methods, higher accuracy is observed, and classification maps are in better agreement with the initial ground maps, using the proposed method.