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71.
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Optimum detectors for pilot symbol assisted modulation (PSAM) signals in Rayleigh and Rician fading channels are derived. Conventional PSAM as used on Rayleigh fading channels is also employed on Rician fading channels. It is shown that the conventional PSAM receiver is optimal for binary phase shift keying in Rayleigh fading but suboptimal for Rician fading and suboptimal for 16-ary quadrature amplitude modulation in Rayleigh fading. The optimum PSAM signal detector uses knowledge of the specular component and also jointly processes the pilot symbols and the data symbol. The performance of the optimum detector is analyzed and compared with that of the conventional detector. It is concluded that substantial gains can be achieved by exploiting knowledge of the specular component while joint processing of the data symbol with the pilot symbols may offer small benefits. 相似文献
73.
二层信用策略下部分延期付款的库存模型 总被引:1,自引:0,他引:1
当前二层信用期相关文献考虑的都是零售商提供给其顾客相同的信用期,但现实中零售商往往会根据物品的种类不同提供给顾客不同的信用期.为研究此问题,建立了优化供货周期使零售商平均相关成本最小的库存模型,证明了最优供货周期的存在性,并给出实例加以说明. 相似文献
74.
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76.
A maximum likelihood estimator for the local average signal-to-noise ratio in a slowly fading Rician channel is proposed. The probability density function of the estimator is derived and the mean, the variance and the mean square error of the estimator are obtained. The performance of the estimator is examined. Numerical results show the asymptotic optimality of the estimator. 相似文献
77.
Electrochemical properties of nicotine at the glassy carbon electrode modified with multi-walled carbon nanotubes were explored. Nicotine underwent irreversible reduction at the modified electrode, which was an adsorption-controlled process with two protons and two electrons. The reductive peak current of nicotine significantly increased at the modified electrode compared with the bare glassy carbon electrode, suggesting that the multi-walled carbon nanotubes can enhance the electron transfer rate. The current was proportional to the concentration of nicotine over two line ranges, and the detection limit was 9.3 µM (at S/N?=?3). For ten parallel detections of 0.62 mM nicotine, the relative standard deviation was 2.67%, suggesting that the film modified electrode had excellent reproducibility. The modified electrode was applied to the direct determination of nicotine in tobacco samples with good sensitivity, selectivity and stability. 相似文献
78.
79.
Yunfei Sha Jiaoran Meng Huaqing Lin Chunhui Deng Baizhan Liu 《Journal of separation science》2010,33(9):1283-1287
In this work, for the first time, headspace (HS) single‐drop microextraction and simultaneous derivatization followed by GC‐MS was developed to determine the aliphatic amines in tobacco samples. In the HS extraction procedure, the mixture of derivatization reagent and organic solvent was employed as the extraction solvent for HS single‐drop microextraction and in situ derivatization of aliphatic amine in the samples. Fast extraction and simultaneous derivatization of the analytes were performed in a single step, and the obtained derivatives in the microdrop extraction solvent were analyzed by GC‐MS. The optimized experiment conditions were: sample preparation temperature of 80°C and time of 30 min, HS extraction solvent (the mixture of benzyl alcohol and 2,3,4,5,6‐pentafluorobenzaldehyde) volume of 2.0 μL, extraction time of 90 s. With the optimal conditions, the method validations were also studied. The method has good linearity (R2 more than 0.99), accepted precision (RSD less than 13%), good recovery (98–104%) and low limit of detection (0.11–0.97 μg/g). Finally, the proposed technique was successfully applied to the analyses of aliphatic amines in tobacco samples of seven different brands. It was further demonstrated that the proposed method offered a simple, low‐cost and reliable approach to determine aliphatic amines in tobacco samples. 相似文献
80.
大功率LED照明灯有限元热设计与高效系统开发 总被引:1,自引:0,他引:1
随着LED亮度要求的不断提高,LED的温度分布和采用的散热手段对LED的可靠性有很大影响。利用ANSYS软件对LED照明的散热问题进行了详细的模拟计算。基于100 WLED实验和模拟结果的一致性,分析比较了不同结构和加载方式对200 WLED温度分布的影响。采用增加散热片个数及其长度、Al锭厚度、灯头的直径等因素,对LED的散热进行了优化设计,结合基于VC++的二次开发系统,较好实现了LED热模拟分析。研究发现LED照明灯的传热方向主要是轴向,轴向散热设计可提高LED开发效率;点阵排列LED灯的温度分布呈现一定的温度梯度;在基于实验验证的模拟可以较好实现不同功率的LED灯散热设计。模拟分析为LED的散热方案优化设计提供了有效的参考依据和手段。 相似文献