Synthesis,characterisation and dosimetric evaluation of MgB4O7 glass as thermoluminescent dosimeter

This study presumably reports the dosimetric properties of MgB₄O₇ glass system. A series of MgB₄O₇ glass samples with nominal compositions XMgO-(100-X) B₂O₃, with X?=?35, 40 and 45?mol% was successfully synthesied using conventional melt quenching method. The presence of broad humps and absence of any sharp peak in typical X-ray diffraction patterns confirm the amorphous nature of the synthesised glass samples. Good glass forming ability, 0.55, of the mixture resulting in a glass with excellent glass stability, 1.4, was observed. Thermoluminescence glow curve was observed to be simple with a single well defined dosimetric peak around 200°C. The dose response was found to be linear from 6?µGy to 0.5?kGy when irradiated to Cs-137 gamma rays. Considerably satisfying thermoluminescent (TL) characteristics suggests that the MgB₄O₇ glass could be recommended as a TL dosimeter.     

带有非线性边界条件的弱衰退记忆型非自治经典反应扩散方程解的渐近性

考虑当内部非线性项和边界非线性项均以超临界指数增长并满足一定的平衡条件, 且外力项仅为平移有界而非平移紧时, 弱衰退记忆型非自治经典反应扩散方程解的渐近性态. 应用收缩函数方法和新的先验估计技术, 证明在拓扑空间L²(Ω)×L²_μ(R⁺;L²(Ω))上一致吸引子的存在性, 并给出其拓扑结构.     

基于双选衰落信道的差分空时协作技术

协作分集技术解决了MIMO技术在移动终端受天线制约的问题.由于无线通信环境的特殊性和复杂性,对信道估计十分困难,因此引入了不需要信道估计的差分空时编码,并在时间选择性衰落信道和频率选择性衰落信道的基础上研究了时间-频率双选择性衰落信道模型,在更接近实际信道环境的基础上将差分空时编码和协作分集技术相融合.理论研究和仿真结果均表明系统性能在信道容量、误比特率等方面均得到了提高.     

一种新的Rayleigh-Normal仿真模型

信道特性的仿真和研究对设计无线通信系统具有重要的意义;在研究现有的信道仿真模型的基础上,提出了Rayleigh-Normal仿真模型;用Rayleigh随机信号和Normal随机信号的线性组合来仿真接收信号,并用该仿真模型仿真了Rayleigh、Ricean、Nakagami和Lognormal等常见信道模型的一阶统计特性,仿真结果证明了Rayleigh-Normal仿真模型是一种准确而有效的衰落信道仿真模型.     

On signal space diversity: An adaptive interleaver for enhancing physical layer security in frequency selective fading channels

Signal space diversity is a powerful technique that increases reliability of detection over fading channels. In this paper, we explore the ability of this technique to provide secure communication. We enhance the security of OFDM systems in frequency selective fading channels by providing more diversity gain to the legitimate user compared to an eavesdropper. This is done by adapting the interleaving pattern to the channel of the legitimate user in rich multipath environments, where spatially separated channels are typically independent to each other. This ensures secrecy in a time division duplex system, where the eavesdropper has no information regarding the channel of the legitimate user. The scheme can also be used in the conventional frequency division duplex system, which is more challenging in terms of security aspects because of the channel state information leakage. A theoretical analysis is presented on the bit-error probability in Rayleigh fading environment. The numerical results support the conclusion that adapting the interleaving pattern to the CSI of the legitimate user provides a gain in the bit-error rate performance over the eavesdropper.     

甲基绿褪色分光光度法测定红霉素

建立了褪色分光光度法测定红霉素肠溶片中红霉素含量的方法。用二次石英蒸馏水为溶剂,甲基绿和红霉素在40℃下可以反应形成稳定的离子缔合物,以试剂空白做参比测定离子缔合物溶液的吸光度,离子缔合物的生成导致吸收光谱发生变化,且在一定范围内吸光度变化值ΔA与红霉素的浓度成正比,红霉素的浓度在0.000 6~0.105 0mg/mL范围内服从Beer定律,在635nm处测得ε=4.23×104 L/(mol·cm)-1,方法检出限达到0.26μg/mL。方法简便快捷,重现性和选择性好,可用于红霉素肠溶片中红霉素含量的测定。     

一种在宽带无线网络环境下的协作分集方法

协作通信可以使单天线的移动终端共享它们的天线而产生虚拟多发射天线阵列以获得发射分集.提出了一种在频率选择性衰落信道条件下的协作分集方法,信宿不仅利用转接节点转发的信号而且还利用了信源直接传来的信号来进行解码.通过计算机仿真,比较了考虑信源到信宿的直接传榆的协作方法和未考虑信源到信宿的直接传输的协作方法的误比特率性能.结果表明,考虑信源到信宿的直接传输可提高系统的协作分集增益.     

Turbo网格编码调制结合两典型映射在慢衰落信道下的性能分析

基于Turbo码和网格编码调制的特点，分析了TYCM(Turbo Trellis Coded Modulation)的具体编译码方法，比较了移动通信中TTCM在8PSK调制下结合两种典型映射方案UP(Ungerboeck Partitioning)、BP(Block Panitioning)在平坦Rayleigh衰娩信道下的性能差异，给出了计算机仿真结果．     

多径Rayleigh衰落信道中二元正交码扩频多址通信系统的性能分析

研究了随机二元正交码直接序列扩频多址信号在多径Rayleigh衰落信道传输中,在非相干RAKE接收机中采用两种不同最大选择接收方案(最大输出信噪比选择及最大输出功率选择分集接收)时,系统的差错特性和差错概率表达式.数值计算结果示出了在多径衰落信道中,分集接收对扩频多址系统性能的影响,同时表明在多径Rayleigh衰落信道中,最大输出功率选择分集接收时扩频系统的差错性能优于最大输出信噪比选择时扩频系统的差错特性.