Tight lower bounds for certain parameterized NP-hard problems

Based on the framework of parameterized complexity theory, we derive tight lower bounds on the computational complexity for a number of well-known NP-hard problems. We start by proving a general result, namely that the parameterized weighted satisfiability problem on depth-t circuits cannot be solved in time n^o(k)m^O(1), where n is the circuit input length, m is the circuit size, and k is the parameter, unless the (t − 1)-st level W[t − 1] of the W-hierarchy collapses to FPT. By refining this technique, we prove that a group of parameterized NP-hard problems, including weighted sat, hitting set, set cover, and feature set, cannot be solved in time n^o(k)m^O(1), where n is the size of the universal set from which the k elements are to be selected and m is the instance size, unless the first level W[1] of the W-hierarchy collapses to FPT. We also prove that another group of parameterized problems which includes weighted q-sat (for any fixed q 2), clique, independent set, and dominating set, cannot be solved in time n^o(k) unless all search problems in the syntactic class SNP, introduced by Papadimitriou and Yannakakis, are solvable in subexponential time. Note that all these parameterized problems have trivial algorithms of running time either n^km^O(1) or O(n^k).     

PEMFC电催化剂研究进展

介绍了质子交换膜燃料电池用电催化剂的研究进展.论述了Pt-Ru、Pt-Sn、Pt-W、Pt-Mo等阳极催化剂以及Pt-Fe、Pt-Co、Pt-Cr等阴极催化剂的制备方法、催化机理和性能;介绍了无铂大环螯合物和过渡金属复合氧化物等非铂系催化剂和碳纳米管等新型载体催化剂的研究进展,提出了PEMFC用催化剂的研究方向.     

RF等离子体聚合类聚氧化乙烯(PEO-like)功能薄膜研究

采用射频等离子体，以乙二醇二甲基醚（Ethylene Glycol Dimethyl Ether）为聚合单体，用氩气作为工作气体，合成类聚氧化乙烯（PEO-like）官能聚合物。实验采用连续和脉冲射频等离子体两种放电模式聚合PEO功能薄膜，研究了等离子体放电参数：等离子体放电功率、工作气压、放电模式（连续或脉冲）和聚合时对聚合物表面结构、官能团含量以及表面特性等影响。利用接触角测试仪、表面张力仪、傅里叶变换红外光谱（FTIR）、膜厚仪和X-射线光电子能谱（XPS）等多种手段对聚合薄膜的组成、结构和性能进行了表征。结果表明，较小的功率以及较长的脉冲条件下有利于EO基团的形成。     

射频等离子体聚合SiOx薄膜的研究

在射频等离子体放电条件下，以六甲基二硅氧烷（Hexamethyldisilone，HMDSO）为单体，氧气为反应气体，在PET薄膜及载玻片上聚合SiOx薄膜。通过红外光谱（FTIR）分析了工作压强、功率、单体氧气比、聚合时间等对聚合薄膜的结构和沉积速度的影响；通过扫描电子显微镜（SEM）观察了薄膜的表面形貌；通过表面轮廓仪测试了薄膜厚度，计算了沉积速率并对薄膜的均匀性做了研究。在38％恒温水浴箱中进行的水蒸汽阻隔实验表明，PET薄膜的阻隔性能得到有效的提高。     

Improved LUT Technique for HPA Nonlinear Pre-Distortion in OFDM Systems

In this paper, we focus on the Look-up Table (LUT) technique for the compensation of HPA nonlinear distortion. An improved LUT method is proposed with better performance compared with conventional LUT technique in terms of convergence speeds, BER and total degradation (TD). It can get over 8 dB gain in out-of-band spectrum re-growth suppression and about 0.3 dB BER performance gain than conventional LUT technique with the same iteration times. Also, we propose an actual application of HPA with pre-distorter in OFDM transmitter. Ai Bo was born in Shannxi Province in China on February 7, 1974. He received a BSc. Degree from Engineering Institute of Armed Police Force in 1997, a Master and Dr. degree from Xidian University in 2002 and 2004 in China respectively, and now working as a post dr. in Dept. of E&E, state of key lab. on microwave and digital communications in Tsinghua University in China. He has once participated in the key research project on HDTV in TEEG (Team of Engineering Expert Group) of China. He is an editorial committee member of journal of “Computer Simulations”, “Information and Electronic Engineering”, an IEEE member and a senior member of Electronics Institute of China (CIE). He has published over 60 scientific papers in his research area till now. His current interests are the research and applications of OFDM techniques with emphasis on synchronization and HPA linearization techniques. Yang Zhi-Xing graduated from Tsinghua University, P.R. China in 1970. He is now a Professor and Deputy Director of State Key Lab. on Microwave and Digital Communication at the Department of Electronic Engineering and the Director of the DTV R&D Center in Tsinghua University. As a DTV technical expert for the Chinese government, Professor Yang has also been a member of the DTV standardization Committee of China and a leader of the DTV Standardization Harmonizing Group in Ministry of Information Industry of China. His major research interests include broadband information transmission technologies and DTV broadcasting systems. Pan Chang-Yong received the B.S. and M.S. degrees from the Department of Electronic Engineering in Tsinghua University, P.R. China, in 1996 and 1999, respectively. He is now an associate professor in the Department of Electronic Engineering and a member of the DTV R&D Center in Tsinghua University. His research interests are in the areas of broadband wireless transmission systems and satellite communications. Zhang Tao-Tao was born in Shandong Province in China in 1982, he received BSc. degree from Tsinghua University in 2004 and now pursing his Master degree in Dept. of E&E, state of key lab. on microwave and digital communications in Tsinghua University in China. His research interests is the power amplifier linearization techniques. Wang Yong was born in Shannxi Province in China in 1976. He received a BSc., a Master and a Dr. Degree from Xidian University in China in 1997, 2002 and 2005, respectively, and now is an associate professor in Xidian University. He has once participated in the key research project on HDTV in TEEG (Team of Engineering Expert Group) in China and is an IEEE Member. His interests are broadband multimedia communications. Ge Jian-Hua was born in September, 1961 in JiangSu Province in China. He received the B.Sc., Master and Ph.D. degree from Xidian University in 1982, 1985 and 1989, respectively. He is now the professor in both Xidian University in Xi’an and Shanghai Jiaotong University in Shanghai. He is the senior member of Chinese Electronics Institute. He has won lots of scientific and technical prizes in China and published many papers. His interests are transmission communications and web security.     

互通式立交桥桥梁桥面板变宽的几何设计

为了解决互通式立交中位于加减速车道上桥梁外边线与路线线形的吻合问题,提出了采用不同板宽调整桥面宽度的设计方法.针对该桥梁位于加速车道的渐变段内的特点,在满足规范的条件下,通过调整渐变段内每块板的宽度,解决各孔内桥面宽度不等的问题,达到渐变段内的桥面板受力合理、科学精确的几何设计.     

关于可信计算平台模块的研究

随着信息技术的飞速发展,可信计算机在安全方面的优越性越来越受到国内外计算机领域工作者的重视。可信计算机的核心部件是可信计算平台模块(TPM),文章介绍了关于TPM的体系结构、使用、平台证实等内容,并对可信计算平台的信任链及其安全引导进行了分析。     

A Parallel Implementation of the Katsevich Algorithm for 3-D CT Image Reconstruction

Yu and Wang [1, 2] implemented the first theoretically exact spiral cone-beam reconstruction algorithm developed by Katsevich [3, 4]. This algorithm requires a high computational cost when the data amount becomes large. Here we study a parallel computing scheme for the Katsevich algorithm to facilitate the image reconstruction. Based on the proposed parallel algorithm, several numerical tests are conducted on a high performance computing (HPC) cluster with thirty two 64-bit AMD-based Opteron processors. The standard phantom data [5] is used to establish the performance benchmarks. The results show that our parallel algorithm significantly reduces the reconstruction time, achieving high speedup and efficiency.     

Fretting wear of steel wires in hoisting ropes

To investigate the fretting wear of steel wires in hoisting ropes, specimens were made of 6 × 19 point contact ropes. A model for the fretting wear was developed and a fretting wear test rig was designed in laboratory. A series of experiments were performed on this test rig. The wear volume was taken as a characteristic parameter to describe the fretting wear in relation to the contact load, reciprocating cycles and amplitude. Moreover, the wear mechanisms were discussed in the fretting process.     

Thermoelectric properties of p-type Bi-Sb-Te compositionally graded thermoelectric materials with different barriers

In order to find more suitable materials as barriers and to improve the thermoelectric properties, p-type (Bi_(l-x)Sb_x)_2 Te_3 (x = 0.85, 0.9) two segments compositionally graded thermoelectric materials (CGTM) with different barriers were fabricated by conventional hot pressure method. Metals Fe, Co, Cu and Al were used as barriers between two segments. The effects of different barriers on thermoelectric properties of CGTM were investigated. The results show that metal Fe is more stable and suitable as the barrier.