Performance of orthogonal STBC-MIMO with variable-power adaptive modulation and delayed feedback in Nakagami fading channels

A variable-power （VP） adaptive modulation （AM） scheme with space-time block code （STBC） is developed in MIMO systems, and the corresponding performance is investigated in Nakagami fading channels. The optimum switching thresholds are derived so that the spectrum efficiency （SE） under an average power and a target bit error rate （BER） constraint is maximized. By the switching thresholds, average BER and SE are further derived. As a result, closed-form expressions are obtained. Besides, the exact and approximate BER expressions of VP AM and constant-power （CP） AM systems with delayed feedback are respectively derived. Simulation results show that the theoretical SE and BER can match the corresponding simulation well. The results indicate that VP-AM with STBC provide higher spectrum efficiency than the CP counterparts, and has slighter bite error rate performance degradation when the normalized delay is less than 0.01.     

通过调节种群适应度改善遗传编程的收敛特性

根据遗传算法理论分析了遗传编程中种群适应度对算法收敛特性的影响,为改善遗传编程的算法收敛特性,提出了通过调节种群适应度进行改善的具体方法。以求证旅行商问题为例,通过统计性实验数据验证了改进后的算法较采用同样局部优化的常规遗传算法具有更好的收敛速度和优化解,并对改进后算法的相关控制参数选择进行了实验分析。结论为改进算法使遗传编程运行期能获得更好的收剑性能,该方法与具体求解问题无关,适用于常规遗传编程。     

基于Flash AT45DB081B的机车火灾数据的存储系统

本文介绍了机车火灾探测数据存储系统的工作原理和可靠性设计,以及系统主要核心器件单片机C8051F236和Flash存储器AT45DB081B优选的特点.介绍了SPI总线结构,以及系统主程序流程和模块化、结构化设计的相关函数指令集.试验表明该系统能够安全可靠存储和分析数据.     

Corrosion and irradiation behavior of Fe-based amorphous coating in lead-bismuth eutectic liquids

Lead-bismuth eutectics (LBE) have considerable potential as a candidate material for accelerator-driven sub-critical systems (ADS). However, LBE corrosion and irradiation damage are two urgent challenges remaining to be solved for impellers of primary pumps. In this study, we have explored the possibility of using Fe-based amorphous coatings to overcome LBE corrosion and concurrently to sustain irradiation damage. Specifically, the Fe₅₄Cr₁₈Mo₂Zr₈B₁₈ amorphous coating was prepared by high-velocity oxygen-fuel (HVOF) spraying on 316L steel and exposed to saturated oxygen static LBE for 500 h at 400°C. The coating with high thermal stability (T_g=615°C and T_x=660°C) effectively prevented the substrate steel from being corroded by LBE owing to its unique long-range disordered atomic packing. The coating also exhibited strong irradiation resistance when being subjected to 45 dpa (displacement per atom) Au ion irradiation at room temperature, with no sign of crystallization even at the maximum implantation depth of 300 nm. Consequently, the hardness of the coatings before and after irradiation increased slightly. The current findings shed new insights into understanding corrosion mechanism and irradiation behavior of amorphous solids in LBE and expand the application range of amorphous materials.

     

Low-complexity distributed differential spacetime coding scheme for amplify-and-forward cooperative networks

By introducing a space-time coding scheme based on amicable orthogonality, we develop a distributed differential space-time coding scheme with the amplify-and-forward (AF) method for wireless cooperative networks. The scheme requires no knowledge of the channel state information at both transmitters and receivers, and effectively decreases the realization complexity due to no channel estimation. Moreover, it has lower decoding complexity and higher coding advantage than the existing scheme, thus avoiding the shortcoming of exponential decoding complexity of some existing schemes. According tothe pairwise error probability (PEP) analysis of the system, the power allocations of source and relay terminals are jointly optimized, and as a result, the PEP is minimized, which will provide a helpful guideline for system design. Numerical calculation and simulation results show that the developed scheme is superior to the existing scheme. Moreover, the scheme with optimal power allocation yields obvious performance improvement over that with equal power allocation. Supported partially by the China Postdoctoral Science Foundation (Grant No. 2005038242) and the startup fund of Nanjing University of Aeronautics and Astronautics (Grant No. S0855-041)     

船用阀门填料的选用

介绍了船用阀门密封填料结构型式的主要类型和适用范围。讨论了填料函结构尺寸和密封填料规格的相互关系。给出了密封填料的选型实例。     

Preparation and electrochemical performance of LiFePO4/C composite with network connections of nano-carbon wires

LiFePO₄/C composite with network connections of nano-carbon wires was successfully prepared by using polyvinyl alcohol as carbon source. The composite was characterized by X-ray diffraction and transmission electron microscopic, and its electrochemical performance was investigated by galvanostatic charge and discharge tests. The experimental results show that LiFePO₄ grains are tightly connected by the network of nano-carbon wires. Moreover LiFePO₄/C composite exhibits high capacity of 168 mAh g⁻¹ applied 15 mA g⁻¹ current density (C/10), excellent cyclic ability and rate capability. When 1500 mA g⁻¹ current density (10C) was applied, the high discharge capacity of 129 mAh g⁻¹ has been obtained at room temperature.     

Performance of multiuser CDMA system with space-time block coding in MIMO Rayleigh fading channels

In this paper, by introducing orthogonal space-time coding scheme, the multiuser CDMA systems with different space time codes are given, and corresponding system performance is investigated over Rayleigh fading channel. A low-complexity multiuser receiver scheme is developed for space-time coded CDMA systems. The scheme can make full use of the complex orthogonality of space-time coding to simplify the high decoding complexity of the existing scheme. Compared to the existing scheme with exponential decoding complexity, it has linear decoding complexity. Based on the performance analysis and mathematical calculation, average bit error rate (BER) of the system is derived in detail, and tight closed-form approximation expressions of BER are attained. Simulation results on average BER are in agreement with the theory analysis. The results show that the proposed scheme can achieve almost the same performance as the existing scheme. Moreover, on the condition of same system throughput and concatenation of channel code, the given full-rate space-time coded CDMA system has lower BER than the full-diversity space-time coded CDMA systems.     

一种基于IEEE1451的网络化智能传感器设计

文章在介绍IEEE1451标准的基本思想的基础上,提出了一种网络化智能传感器的设计方案,详细介绍了其设计思想、系统结构,介绍了STIM模块的硬件设计和软件设计,介绍了基于"32位微处理器 RTOS"的NCAP模块的硬件设计和软件结构设计,并用Java语言建立了基于IEEE1451.1标准的类.最后,文章对该方案提出了应用前景和展望.