A fast 600-V Tandem PiN Schottky (TPS) rectifier with ultra-low on-state voltage

The Tandem PiN Schottky (TPS) rectifier features lowly-doped p-layers in both active and termination regions, and is applied in 600-V rating for the first time. In the active region, the Schottky contact is in series connection with a transparent p-layer, leading to a superior forward performance than the conventional diodes. In addition, due to the benefit of moderate hole injection from the p-layer, the TPS offers a better trade-off between the on-state voltage and the switching speed. The active p-layer also helps to stabilise the Schottky contact, and hence the electrical data distributions are more concentrated. Regarding the floating p-layer in the termination region, its purpose is to reduce the peak electric fields, and the TPS demonstrates a high breakdown voltage with a compact termination width, less than 70% of the state-of-the-art devices on the market. Experimental results have shown that the 600-V TPS rectifier has an ultra-low on-state voltage of 0.98 V at 250 A/cm 2, a fast turn-off time of 75 ns by the standard RG1 test (I F=0.5A, I R=1A, and I RR=0.25A) and a breakdown voltage over 720 V. It is noteworthy that the p-layers in the active and termination regions can be formed at no extra cost for the use of self-alignment process. © 2012 IEEE.

两个冠醚分子在简正坐标分析及NRCC程序在微机上的移植

本文用加拿大国立研究院(National Research Council of Canada) Fuhrer等人编制的FORTRAN语言程序（以下简称NRCC程序），对两个冠醚类化合物进行了简正坐标分析，这两个化合物分子是二氧六环(C_4H_8O_2)和12－冠－4(C_8H_(16)O_4)。作者用Synder和Zerbi提出的一般价力场，计算了二氧六环的36个简正振动频率，精化四次后的结果误差为14.04 cm~(-1)，得到了二氧六环的精化力场和势能分析矩阵；做了12－冠－4－的中红外光谱(3200-5000cm~(-1))。远红外光谱(500-70cm~(-1))和拉曼光谱(3200-50 cm~(-1)，从而归属出12－冠－4的78个简正振动频率实验值；利用二氧六环的精化力场作为初始力场，计算了12－冠－4的简正振动频率，对78个简正振动频率进行了精化计算，精化三次后的结果误差为13.99 cm~(-1)，精化后得到12－冠－4的精化力场和势能分布矩阵；将NRCC程序以BASIC语言移至TRS-80微型机上，对二氧六环进行了计算，结果良好，首次给出二氧六环一般价力场的势能分布。一、对二氧六环的处理 二氧六环分子式C_4H_8O_2，合14个原子，有3N－6＝36个简正振动频率。分子结构系由二个乙氧基(-CH_2-CH_2-O-)单元组成的含有四个碳，两个氧的六元环，平衡态分子为椅式构象，属于C_(2h)点群，36个简正振动频率分为四个对称类Ag、Au、Bg和Bu，分布是：Ag 10个，Bg 8个，Au 9个，Bu9个。二氧六环的分子结构及坐标示意图见28而图5，定义了14个伸缩内坐标，26个弯曲内坐标，6个扭曲内坐标，共46个，C－C键长1.54A，C-O键长1.41 A，C－H键长1.096A，键角都用109°28'。用CART程序（NRCC程序之一）计算二氧六环14个原子的笛卡尔坐标，用GMAT程序（NRCC程序之二）计算其B矩阵和G矩阵，用FPERT程序（NRCC程序之三）计算其简正振动频率、精化力场，计算用一般价力场，引入V矩阵对称化，将46个坐标化为46个（内）对称坐标，10个多余坐标在FPERT程序计算中除去。二、对12－冠－4的处理 12－冠－4分子式C_8H_(16)O_4，含28个原子，共3N－6＝78个简正振动频率，分子结构为四个乙氧基(-CH_2-CH_2-O-)单元组成的含八个碳、四个氧的12元环，自由分子的12－冠－4属于C点群。结构数据引自Groth的X光衍射分数和坐标，自己编制了BASIC语言程度将分数坐标化为笛卡尔坐标，用GMAT程序计算B矩阵和G矩阵，FPERT程序计算78个简正振动频率、精化力场、计算势能分布矩阵，引入U矩阵将92个内坐标化为92个对称坐标，14个多余坐标在FPERT程序中自动除去。三、结果 势能分布矩阵给出分子的振动归属，对这两个冠醚类分子的3N－6个简正振动频率，可以划分为五个振动区域。1．C－H伸缩振动区（3000－2800 cm~(-1)） 在该区中，二氧六环有八个值：2974、2966、2854和2867 cm~(-1)各两个，12－冠－4有16个值：2935、2923、2915和2907 cm~(-1)各两个，2860 cm~(-1)8个，高于2900 cm~(-1)者为反对称伸缩振动，低于2900 cm~(-1)者为对称伸缩振动。2．亚甲基弯曲振动之一(1500-1400 cm~(-1)) 该区的主要振动是亚甲基剪式振动(Scissor)，其它振动小于10％二氧六环在该区有四个频率：1443、1461、1451和1457 cm~(-1)，12－冠－4有八个频率：1466、1450、1450和1405 cm~(-1)各两个。3．亚甲基弯曲振动区二(1400-1200 cm~(-1))该区的主要振动模式为亚甲基的颤动(wag)、卷曲(twist)和摆动(rock)振动，其它振动小于13％。二氧六环在该区有八个频率：1334、1303、1396、1216、1367、1264、1377和1296 cm~(-1)，12－冠－4有十六个频率：1388、1363、……1229 cm~(-1)（其中1288、1307cm~(-1)非简并，其余皆两重简并）。4．环的骨架伸缩振动区(1200-600 cm~(-1))该区振动模式复杂，除环的骨架伸缩振动外，还有亚甲基的wag、twist、rock以及环的骨架弯曲振动，而且这些振动的势能分布值都不小。二氧六环在该区有十一个频率，从1127至610 cm~(-1)，12－冠－4有二十个频率，从1135至184 cm~(-1)且大都是二重简并的。5．低频区(600-50cm~(-1))这两个分子在低频区的势能分布略有差别。二氧六环在该区有五个频率：503、486、427、276和224 cm~(-1)，主要振动模式为骨架弯曲振动和扭曲振动，C－O、C－C的扭曲振动在三个最低频率中分布占10－30％。12－冠－4在该区有18个频率，除570和547cm~(-1)处，都是二重简并的，六个最低频率的振动模式完全属于C－O、C－C键的扭曲振动，其它振动小于10％，所以200 cm~(-1)以下可称为12－冠－4的扭曲振动区，在600－200cm~(-1)之间的12个频率主要是骨架的弯曲振动，也有一定量的亚甲基wag、twist、rock振动。12－冠－4的简正坐标分析尚未有人做过。二氧六环的计算结果与Snyder和Zerbi的分析相吻合，12－冠－4和二氧六环两分子势能分布的相对一致性证明了对12－冠－4的简正坐标分析基本是正确的。本文比较了二分子的力常数和振动频率，探讨了环的大小对振动光谱的影响。四、NRCC程序简介 NRCC程序由CART、GMAT和FPERT三个程序组成，即可联一起运用，亦可分开独立进行运算。该程序功能强，所占内存大，适于大、中型计算机使用。CART程序之名字取自Cartisian Co-or-dinates的前四个字母，功能系由分子结构参数（键长、键角）计算分子内各原子的笛卡尔坐标。GMAT程序之名字取自G matrix的前四个字母，功能系由分子内各原子的笛卡尔坐标，原子质量和内坐标定义计算分子内各原子的坐标交换矩阵B和Wilson振动动能矩阵G。FPERT程序之名字取自F Perturbation的前五个字母，功能系由分子振动功能矩阵G、势能常数即力常数矩阵F计算分子的简正振动频率和势能分布矩阵，再通过实验频率精化势能矩阵F。NRCC程序可对含30个原子、60个内坐标的分子进行简正坐标分析，扩充后容量增大一倍。该程序可选用一般价力场(General Valence Force Field, 简称GVFF)和UBS力场(Urey-Bradley-Shimanouchi Force Field)，简称UBSFF或UBFF)。可选用对称化U矩阵，可自行决定力场精化次数和阻尼常数以限制精化结果的收敛性。五、NRCC程序在TRS－80微型机上移植试尝（该部分曾在第三届长春夏季化学讨论会上宣读）针对NRCC程序占内存空间大、难以在微型机上实现的情况，作者将NRCC程序改编为BASIC语言，改变程序的原来结构，形成一组BASIC语言程序：CART／BAS、GMAT／BAS和VIFR／BAS，改编后的BASIC程序在TRS－80微型机调试通过，TRS－80机字长8位，New Dos系统内存32K。改写后的程序只保持了原程序的基本原理，在内存，语句上改动很大，以适于微型机使用。数据在程序中直接嵌入，利于修改替换，且BASIC语言简单易学，便于操作。CART／BAS程序可计算含30个原子以内的分子的笛卡尔坐标，GMAT／BAS程序可计算含20个原子、45个内坐标的分子的G矩阵，VIFR／BAS程序可计算含15个原子的分子的简正振动频率。利用这组程序，作者以二氧六环分子为例做了一些试尝运算，误差14.4 cm~(-1)，相对误差1.8%，结果较理想。

沈阳城市森林生态系统健康与管理研究

本文系统研究了沈阳城市森林的布局与结构、城市森林功能、城市森林病虫害发生与树木健康状况和城市自然资源与社会经济状况等指标对沈阳城市森林生态系统健康与管理的影响。同时一，采用2种生态系统健康评价方法对沈阳城市森林生态系统健康状况进行了评价，并提出了沈阳城市森林生态系统健康管理的对策。研究结果如下：1、截至2004年末，沈阳城市森林植被覆盖率已经达到35％，城市森林林地分布基本合理，但需要进一步加强道路林地、居住区林地和城郊大面积生态林建设。2、沈阳城市森林以乔木为主，乔灌株数比为1.7：1，乔灌的覆盖度比约为7:1。3、沈阳城市森林不同类型林地中植物组成不同。公园林地中有74个属，137个种（变种）；庭院林地中有53个属，104个种（变种）；居住区林地中有45个属，81个种（变种）；道路林地中有43个属，94个种（变种）；运河风景林地中有75个属，142个种（变种）；棋盘山风景林地中有48个属，118个种（变种）。4、公园林地、庭院林地、居住区林地、道路林地和运河风景林地的Shannon一Wiener多样性指数分别为2.78、3.05、3.15、3.18和3.18，均匀度指数分别为0.56、0.66、0.72、0.70和0.64。除了棋盘山风景林地外，沈阳城市森林中栽植总量超过乔木总量5％的乔木树种有7个属，分别为李、柳树、杨树、桧柏、榆树、槐树和银杏，7种树木总量达到了全部乔木总量的82.09％；栽植总量超过灌木总量5％的灌木树种也有7个属，分别为水腊、丁香、李属，小聚、玫瑰、忍冬和连翘，7个属灌木总量达到了全部灌木总量的87.92％。5、公园林地、庭院林地、道路林地和防护林地中OBH＜20cm、20cm＜DBH＜60cm和DBH＞60cm树木的比例分别为：57.9％、40.0％、2.1％，49.2％、47.8％、3.0％，65.3％、33.1％、1.6％和64.6％、34.9％、0.5％，表明沈阳城市森林树木的规格总体上偏小。6、经样方调查和CITYgreen模型计算，沈阳城市森林的生态效益约2.0亿USD／yr.。公园林地、庭院林地和风景林地的景观指标相对较高；道路林地和居住区林地的景观效果一般；防护林地的景观效果较差。7、目前已经发现的沈阳城市森林病害约600余种，虫害约700余种，其中杨树主要病虫害39种，柳树的主要病虫害有33种，榆树和槐树的主要病虫害均为，1种。杨柳树腐烂病、光肩星天牛、天幕毛虫、桃红颈天牛和美国白蛾等是近10年来沈阳城市森林中普遍发生和造成严重危害的主要病虫害。沈阳城市森林主要树木的平均健康指数为2.68，处于一般健康状态。8、沈阳城市森林的土壤和水资源状况均不利于树木的健康生长，沈阳的社会经济发展也有待于进一步提高。9、经过生物指示物法（光肩星天牛为生物指示物）、专家权重法、公众问卷调查和对比研究，沈阳城市森林生态系统总体上处于亚健康状态。10、通过对沈阳城市森林资源、管理状况的调查研究和健康状况的评价，本文提出了沈阳城市森林生态系统健康管理的对策，包括合理规划沈阳城市森林林地布局，增加道路林地、居住区林地和城郊林地的面积和植被覆盖率；调整树木种类组成，避免单一或少数树种的大量栽植，提高生物多样性水平；保护大树和古树；增加城市森林管理资金的投入；应用先进技术，采取科学的病虫害防治和植物养护方法，促进树木的健康生长等。This project systematically studied the urban forest ecosystem health and management in Shenyang. The study explored factors, such as urban forest structure, distribution, pests, aesthetic value, ecological benefit, natural resources and socieo-economic status, that affecting the urban forest ecosystem health and management. Two methods were used to evaluate the ecosystem health. This project also proposed Shenyang's urban forest ecosystem health management strategies. The research results can be summarized as follows: 1. As of the end of 2004, urban forest coverage in Shenyang is about 35%, and is in relatively even patch distribution pattern. However, the street trees and roadside forest patches, residential block forest patches should be enhanced. 2. Trees are the major component of the Shenyang s urban forest, followed by shrubs. The quantity ratio of tree to shrub is about 1.7:1, and the coverage ratio of trees to shrub is about 7:1. 3. Species composition varies by location. There are 74 genera, 137 species (including varieties) in the public parks; 53 genera, 104 species (and var.) in the green spaces of the institution (including school), factory, and company; 45 genera, 81 species (var.) in residential blocks; 43 genera, 94 species (var.) in streets and roadside forest patches; 75 genera, 142 species (var.) in the Canal landscape forest patches; 48 genera, 118 species (var.) in the Qipan Mountain recreation forest. 4. The Shannon-Woener indices varies in parks, in institution, factory, and company yards, in streets and roadside forest patches, in residential blocks.there are 2.78, 3.05, 3.18, 3.15, 3.18, respectively; and the evenness indices are 0.56, 0.66, 0.70, 0.72, 0.64, respectively. Besides the Qipan Mountain forest patches, trees of 7 genera, Prunus spp., Salix spp., Populus spp., Sabina spp., Ulmus spp., Robinia spp. and Ginkgo biloba are of more than 5% the total urban trees, respectively. In fact, trees from these 7 genera are about 82% of all trees in Shenyang's urban forests. In terms of shrubs, species of 7 genera, Ligustrum spp., Syringa spp., Prunus spp., Berberis spp., Rosa spp., Lonicera spp., and Forsythia spp. are more than 5% the total urban shrubs, respectively. 88% of all the shrubs in Shenyang s urban forest are from these 7 genera. 5. The diameter class of DBH<20cm, 20cm60cm of trees in parks, in institution, factory, and company yards, in in streets and roadside forests, and in protective forests are 57.9%, 40.0%, 2.1%; 49.2%, 47.8%, 3.0%; 65.3%, 33.1%, 1.6%; and 64.6%, 34.9%, 0.5%, respectively. The result indicated that the DBH is relatively small in Shenyang s urban forests. 6. Using random plots sampling and CITYgreen model calculation, the ecological benefit of Shenyang's urban is about 0.2 billion US dollars per year. The aesthetic value of parks, institution and company yards, and scenary forest patches is relative high; however, the aesthetic value of protective forest patches is low. 7. There are more than 600 types of diseases and more than 700 kinds of insects in Shenyang's urban forest. Among them, Populus spp., Salix spp., Ulmus spp. and Robinia spp., are attached mainly by 39, 33, 11, and 11, difference types of pests respectively. The rot disease of the Populus spp. and Salix spp., and the insects such as, Anoplophora glabripennis, Malacosoma neustria, Aromia bungii, and Hyphantria cunea are major pests in Shenyang s urban forest for the past 10 years. The trees health condition is relatively poor by having the average health index of 2.68 for major species. 8. The urban soil and water resource are not favorable to tree's growth in Shenyang, and so is the socieo-economic status. 9. Through using bio-indicator, professional and public evaluation, and comparision with other urban forests, it can be concluded that the status of Shenyang s urban forest is not very healthy in general. 10. To improve the urban forest ecosystem health in Shenyang, a better urban forest design need to be implemented to enhance the area and vegetation coverage of the street and roadside forests, the residential block forests, and the surburb forest Species biodiversity need to be enhanced by adjust the species composition of urban forest trees to reduce the single or several tree species populations and to plant more varieties. A better fundings for urban forest health management need to be budgeted. Advanced technologies in tree care and scientific measures to control pests need to be adopted to prove better care for plants and to keep trees grow healthfully.

K-600中子发生器辐射防护的改进

目的　对K -60 0中子发生器原有的辐射防护做出评价 ,提出改进措施。方法　使用高灵敏度中子探测器和γ监测器 ,对中子发生器运行时n、γ辐射进行了全面的测量并对辐射场围周的防护设施进行改造。结果　改造前在中子厅西、南屏蔽墙外表面有贯穿辐射 ,特别是中子发生器建筑物项部表面有明显的贯穿辐射 ,并且在距离辐射源 3 0～ 40m处呈现峰值 ,显示出天空反射的效果。改造后辐射场外部周围贯穿辐射大为减弱。结论　通过改进措施达到了降低贯穿辐射的目的

Structural and optical properties of 6H-SiC helium-implanted at 600 K

Single crystals of 6H-SiC were implanted at 600 K with 100 key He ions to three successively fluences and subsequently annealed at different temperatures ranging from 873 to 1473 K in vacuum. The recovery of lattice damage was investigated by different techniques including Rutherford backscattering spectrometry in channeling geometry, Raman spectroscopy and Fourier transform infrared spectroscopy. All three techniques showed that the damage induced by helium ion implantation in the lattice is closely related to the fluence. Rutherford backscattering spectrometry/channeling data on high temperature implantations suggest that for a fluence of 3 x 10(16) He+/cm(2), extended defects are created by thermal annealing to 1473 K. Apart from a well-known intensity decrease of scattering peaks in Raman spectroscopy it was found that the absorbance peak in Fourier transform infrared spectroscopy due to the stretching vibration of Si-C bond shifted to smaller wave numbers with increasing fluence, shifting back to larger wave numbers with increasing annealing temperature. These phenomena are attributed to different lattice damage behavior induced by the hot implantation process, in which simultaneous recovery was prevailing. (C) 2010 Elsevier B.V. All rights reserved.

Molybdenum L-shell X-ray production by 350-600 keV Xeq+ (q=25-30) ions

Molybdenum L-shell X-rays were produced by Xeq+ (q = 25-30) bombardment at low energies from 2.65 to 4.55 keV/amu (350-600 keV). We observed a kinetic energy threshold of Mo L-shell ionization down to 2.65-3.03 keV/amu (350-400 keV). The charge state effect of the incident ions was not observed which shows that the ions were neutralized, reaching an equilibrium charge state and losing their initial charge state memory before production of L-shell vacancies resulted in X-ray production. The experimental ionization cross sections were compared with those from Binary Encounter Approximation theory. Taking into account projectile deflection in the target nuclear Coulomb field, the ionization cross section of Mo L-shell near the kinetic energy threshold was well described. (C) 2010 Published by Elsevier B.V.

A mixing scheme for the structure of f(0)(600) and f(0)(1370)

Within the framework of a nonlinear chiral Lagrangian we explore the nontrivial nature of f(0)(600) and f(0)(1370) in terms of quarkonium, tetraquark and gluonium components. The mass constraints are obtained and the strong and radiative partial widths are calculated to demonstrate and discriminate these components. The static properties of f(0)(1500) and glueball are also studied. Our results are confronted with the experimental and theoretical data available as well as the upcoming measurements. (C) 2010 Elsevier B.V. All rights reserved.

Two-electron-one-photon M1 and E2 transitions between the states of the 2p(3) and 2s(2)2p odd configurations for B-like ions with 18 <= Z <= 92

Two-electron-one-photon (TEOP) M1 and E2 transition energies, line strengths and transition probabilities between the states of the 2p(3) and 2s(2)2p odd configurations for B-like ions with 18 <= Z <= 92 have been calculated using the GRASP2K package based on the multiconfiguration Dirac-Hartree-Fock (MCDHF) method. Employing active-space techniques to expand the configuration list, we have systematically considered the valence, core-valence and core-core electron correlation effects. Breit interaction and quantum electrodynamical (QED) effects were also included to correct atomic state wavefunctions and the corresponding energies. Influences of electron correlation, Breit interaction and QED effects on transition energies and line strengths of the TEOP M1 and E2 transitions were analysed in detail. The present results were also compared with other theoretical and experimental values.

Cys-92, Cys-95, and the C-terminal 12 residues of the Vibrio harveyi ferric uptake regulator (Fur) are functionally inessential

Ferric uptake regulator (Fur) is a global regulator involved in multiple aspects of bacterial life. The gene encoding the Vibrio harveyi Fur (Fur(vh)) was cloned from a pathogenic V. harveyi strain isolated from diseased fish. Furvh shares 77% overall sequence identity with the Escherichia coli Fur (Fur(Ec)) and could complement a mutant of Fur(Ec). Like Fur(Ec), Fur(Vh), possesses two cysteine residues at positions 92 and 95, yet unlike Fur(Ec), in which these cysteine residues constitute part of the metal ion coordination site and hence are vital to the repressor activity, C92 and C95 of Fur(Vh) proved to be functionally inessential. Further study identified a Vibrio Fur signature sequence, which is preserved in all the ten Vibrio Fur proteins that have been discovered to date but in none of the non-vibrio Fur proteins. Site-directed and random mutation analyses of the signature residues, the cysteine residues, and seven highly charged amino acid residues indicated that D9, H32, C137, and K138 of Fur(vh) are functionally important but D9, C137, and K138 can be replaced by more than one functional substitutes. Systematic deletion analysis demonstrated that the C-terminal 12 residues of Fur(Vh) are functionally inessential. These results (i) indicated that the activation mechanism, or certain aspects of which, of Fur(Vh) is possibly different from that of Fur(Ec); and (ii) suggested that it is not very likely that the C-terminal 12 residues play any significant role in the activation or stability of Fur(Vh); and (iii) provided insights into the potential function of the local structure involving C137 and K138.