科研成果 by Year: 2010>;

Modulations of energy band and polarization field by fluorine ions in fluorine plasma treated AlGaN/GaN heterostructures were revealed by positron annihilation spectroscopy (PAS). It is found that the annihilation probability is mainly governed by the electric field in the AlGaN/GaN heterostructure, which could be modulated by charged ions, opposite to what was first expected from the large number of plasma-induced defects such as Ga-vacancies. The modulation of electric field is successfully observed through the opposite changes in the S parameters on the two sides of the hetero-interface after fluorine plasma treatment due to the opposite E-field directions. Fluorine is experimentally proved to be negatively charged in GaN related materials, which is consistent with the operation principle of enhancement-mode AlGaN/GaN HEMT fabricated by fluorine plasma treatment. It is also suggested that PAS is a useful tool to probe the intrinsic electric field in AlGaN/GaN system. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Investigations on residues of organochlorine pesticides(OCPs) in soils in Huizhou,China were conducted.A total of 42 soil samples were collected from sites representative of the region for analysis of contents of OCPs.And with the aid of multi-variate geostatistics and GIS,residue and spatial distribution of 17 types of OCPs were analyzed.Results show that the 17 OCPs were detected,various in content in all the soil samples.HCHs and DDTs residues were detected,but below the criteria of the national standards for soil environment quality.Residue content of beta-HCH was the highest among HCHs,which implied some recent input of HCH to soils,while for DDT,no sign of new input was found.Compared with other regions in the country,Huizhou city was lower in soil HCH and DDT content.Principal component analysis demonstrated that the above-said 17 OCPs in the soil may have 5 major contributors,corresponding respectively to industrial use of HCH,natural factors,use of lindane,use of heptamul and use of Drinox.By means of ordinary Kriging interpolation,spatial distribution of OCPs was studied with results indicating that the 17 OCPs variaed greatly in spatial distribution between types选取位于珠江三角洲的惠州市为研究区域,对该市土壤进行了系统采样分析,测定了42个表层土壤样品中的17种有机氯农药的含量.利用多元地统计和GIS相 结合的方法,研究了17种有机氯农药的残留状况及空间分布情况.结果表明,17种有机氯农药在42个土壤样品中均有不同程度的检出,其中p,p′-DDE 检出率为100%,3种有机氯农药检出率在90%以上,6种有机氯农药的检出率在80%以上.其中六六六和滴滴涕残留较普遍,但并未达到污染水平.分析显 示,近期可能仍有新的六六六输入土壤环境,而滴滴涕则主要来自过去施用农药的残留.与国内其他地区比较,惠州市土壤HCH和DDT含量处于较低水平.主成 分分析显示上述17种有机氯农药可以由5个主成分反映,分别对应于工业HCH的使用,自然因素,林丹的使用以及七氯和艾氏剂等农药的使用.采用克里格插值 法对有机氯农药在研究区的空间分布进行了研究,结果表明不同有机氯农药在研究区分布存在很大差异

In this paper, we revisit the point-in-polyhedron problem. After reviewing previous work, we develop further insight into the problem. We then claim that, for a given testing point and a three-dimensional polyhedron, a single determining triangle can be found which suffices to determine whether the point is inside or outside the polyhedron.This work can be considered to be an extension and implementation of Horn's work, which inspired us to propose a theorem for obtaining determining triangles. Building upon this theorem, algorithms are then presented, implemented, and tested. The results show that although our code has the same asymptotic time efficiency as commonly used octree-based ray crossing methods, in practice it is usually several times and sometimes more than ten times faster, while other costs such as preprocessing time and memory requirements remain the same.The ideas proposed in this paper are simple and general. They thus extend naturally to multi-material models, i.e., polyhedrons subdivided into smaller regions by internal boundaries. (C) 2010 Elsevier Ltd. All rights reserved.

In this paper, we revisit the point-in-polyhedron problem. After reviewing previous work, we develop further insight into the problem. We then claim that, for a given testing point and a three-dimensional polyhedron, a single determining triangle can be found which suffices to determine whether the point is inside or outside the polyhedron.This work can be considered to be an extension and implementation of Horn's work, which inspired us to propose a theorem for obtaining determining triangles. Building upon this theorem, algorithms are then presented, implemented, and tested. The results show that although our code has the same asymptotic time efficiency as commonly used octree-based ray crossing methods, in practice it is usually several times and sometimes more than ten times faster, while other costs such as preprocessing time and memory requirements remain the same.The ideas proposed in this paper are simple and general. They thus extend naturally to multi-material models, i.e., polyhedrons subdivided into smaller regions by internal boundaries. (C) 2010 Elsevier Ltd. All rights reserved.