First-principles LDA plus U and GGA plus U study of neptunium dioxide

We have performed a systematic first-principles investigation to calculate the electronic structures, mechanical properties, and phonon-dispersion curves of NpO2. The local-density approximation+U and the generalized gradient approximation+U formalisms have been used to account for the strong on-site Coulomb repulsion among the localized Np 5f electrons. By choosing the Hubbard U parameter around 4 eV, the orbital occupancy characters of Np 5f and O 2p are in good agreement with recent experiments [A. Seibert, T. Gouder, and F. Huber, J. Nucl. Mater. 389, 470 (2009)]. Comparing to our previous study of ThO2, we note that stronger covalency exists in NpO2 due to the more localization behavior of 5f electrons of Np in line with the localization-delocalization trend exhibited by the actinides series.

Analysis of leakage current in GaAs micro-solar cell arrays

The output characteristics of micro-solar cell arrays are analyzed on the basis of a modified model in which the shunt resistance between cell lines results in current leakage. The modification mainly consists of adding a shunt resistor network to the traditional model. The obtained results agree well with the reported experimental results. The calculation results demonstrate that leakage current in substrate affects seriously the performance of GaAs micro- solar cell arrays. The performance of arrays can be improved by reducing the number of cells per line. In addition, at a certain level of integration, an appropriate space occupancy rate of the single cell is recommended for ensuring high open circuit voltages, and it is more appropriate to set the rates at 80%-90% through the calculation.

Analysis of leakage current in GaAs micro-solar cell arrays

The output characteristics of micro-solar cell arrays are analyzed on the basis of a modified model in which the shunt resistance between cell lines results in current leakage. The modification mainly consists of adding a shunt resistor network to the traditional model. The obtained results agree well with the reported experimental results. The calculation results demonstrate that leakage current in substrate affects seriously the performance of GaAs micro- solar cell arrays. The performance of arrays can be improved by reducing the number of cells per line. In addition, at a certain level of integration, an appropriate space occupancy rate of the single cell is recommended for ensuring high open circuit voltages, and it is more appropriate to set the rates at 80%-90% through the calculation.

Theoretical study of p-d hybridization in Co perovskite

The real-space recursion method and unrestricted Hartree-Fock approximation have been applied to calculate the density of states of various Co perovskite, CeCoO3, SrCoO3 and Sr1-xCexCoO3. We have studied the magnetically ordered states of these Co perovskites in an enlarged double cell, and find its various magnetic structures due to the occupancy of 3d band and its interaction with neighboring Co ions. In this study, we have studied the p-d hybridization of the three Co perovskites, we find t(2g) electrons are localized and the flat e(g) band is responsible for the itinerant behavior, and although the rare earth elements itself contribute little to the DOS at the Fermi energy, the DOS at Fermi energy and the magnetic moment changed consequently because of different valence of Co ions in these compounds and p-d hybridization effect is very important. (C) 2009 Elsevier B.V. All rights reserved.

基于栅格地图的多化学羽流源定位

本文研究了移动机器人在湍流环境中定位多个化学羽流源的问题。利用粒子随机行走方法建立动态羽流模型。在此环境中机器人进行梳状搜索并采集羽流数据,使用一种基于后验概率独立假设的改进贝叶斯算法融合这些传感器数据建立一张羽流源位置的概率地图,地图中具有高概率值的栅格指出了羽流源可能的位置。仿真结果说明了该方法的有效性,通过与标准贝叶斯算法的比较说明了该方法优点。

AUV海底热液喷口探测方法研究

自1979年海底热液喷口被首次发现以来，因其巨大的经济和科研价值引起了科学界的巨大关注。海底热液喷口释放的热液与周围海水混合，形成热液羽流，其范围可以达到数千米。热液羽流的存在使在几千米深的海底定位范围只有几米的热液喷口成为可能。湍流的作用使热液羽流与喷口位置存在不确定性，而在搜索区域中包含多个热液源会增加这种不确定性，这是海底热液喷口探测需要克服的难题之一。 本文主要研究了使用AUV探测海底热液喷口的方法。这个问题从更大范畴来说属于机器人化学羽流源定位问题（也称为移动机器人气源/味源定位），其潜在应用包括污染与环境监测，化学工厂安全，搜索与救援，反恐，麻醉品控制，爆炸物清除，以及热液喷口探测等。 首先，从AUV探测的角度研究了海底热液羽流的特性，分析了海底热液羽流的模型并根据模型对羽流进行了动态仿真。 从化学羽流源定位的角度研究了两种海底热液喷口探测策略──梯度搜索策略和构建占据栅格地图(Occupancy Grid Mapping，OGM)的策略。并利用仿真羽流环境验证了上述两种定位策略的可行性。 梯度搜索策略通过基于行为的方法实现，将梯度搜索任务分解为五个行为，并设计了行为间的转换规则，AUV按此规则在不同的行为间转化，跟踪羽流浓度梯度的方向，最终到达浓度极值点。 通过将每个栅格的二值状态重新定义为是否存在一个活跃的热液源，可以将OGM应用于热液源定位。融合传感器数据得到的后验概率地图可以反映每个栅格中存在热液源的可能性。本文采用基于贝叶斯规则的算法融合传感器数据。由于热液源的数量稀少，使用标准贝叶斯方法往往对栅格的占据概率做出过高估计，无法清晰的定位热液源。为此，又研究了一种精确算法和一种基于后验独立假设（Independence of Posteriors，IP）的近似算法，并分析了三种算法的优缺点。 最后，将占据栅格地图应用于分阶段海底热液喷口探测，利用栅格地图帮助实现探测的自主嵌套。