Wideband spectrum sensing has drawn much attention in recent years since it provides more opportunities to the secondary users. However, wideband spectrum sensing requires a long time and a complex mechanism at the se...Wideband spectrum sensing has drawn much attention in recent years since it provides more opportunities to the secondary users. However, wideband spectrum sensing requires a long time and a complex mechanism at the sensing terminal. A two-stage wideband spectrum sensing scheme is considered to proceed spectrum sensing with low time consumption and high performance to tackle this predicament. In this scheme, a novel multitaper spectrum sensing （MSS） method is proposed to mitigate the poor performance of energy detection （ED） in the low signal-to-noise ratio （SNR） region. The closed-form expression of the decision threshold is derived based on the Neyman-Pearson criterion and the probability of detection in the Rayleigh fading channel is analyzed. An optimization problem is formulated to maximize the probability of detection of the proposed two-stage scheme and the average sensing time of the two-stage scheme is analyzed. Numerical results validate the efficiency of MSS and show that the two-stage spectrum sensing scheme enjoys higher performance in the low SNR region and lower time cost in the high SNR region than the single-stage scheme.展开更多
针对阶梯块谱下的材料疲劳寿命预测问题,尤其是已有相关非线性模型的计算参数依赖大量试验数据或较难选取合适的基准值,导致在实际工程中应用有一定局限性。提出了一种新的基于相邻载荷的作用系数α_(i)=(S_(i+1)/S_(i))1/b lg K,该系...针对阶梯块谱下的材料疲劳寿命预测问题,尤其是已有相关非线性模型的计算参数依赖大量试验数据或较难选取合适的基准值,导致在实际工程中应用有一定局限性。提出了一种新的基于相邻载荷的作用系数α_(i)=(S_(i+1)/S_(i))1/b lg K,该系数中两个参数b、K来自材料疲劳寿命关系式S=KN^(-b)。结合前人的二级、三级、四级应力加载试验结果,分别计算并对比了与多种疲劳损伤模型的结果。结果表明,新模型在疲劳寿命/损伤的预测结果优于Miner模型、Manson模型、Subramanyan模型及Hashin模型,可更为准确地预测阶梯块谱下的疲劳寿命/损伤。展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.61301179)the China Postdoctoral Science Foundation(Grant No.2014M550479)the Doctorial Programs Foundation of the Ministry of Education,China(Grant No.20110203110011)
文摘Wideband spectrum sensing has drawn much attention in recent years since it provides more opportunities to the secondary users. However, wideband spectrum sensing requires a long time and a complex mechanism at the sensing terminal. A two-stage wideband spectrum sensing scheme is considered to proceed spectrum sensing with low time consumption and high performance to tackle this predicament. In this scheme, a novel multitaper spectrum sensing （MSS） method is proposed to mitigate the poor performance of energy detection （ED） in the low signal-to-noise ratio （SNR） region. The closed-form expression of the decision threshold is derived based on the Neyman-Pearson criterion and the probability of detection in the Rayleigh fading channel is analyzed. An optimization problem is formulated to maximize the probability of detection of the proposed two-stage scheme and the average sensing time of the two-stage scheme is analyzed. Numerical results validate the efficiency of MSS and show that the two-stage spectrum sensing scheme enjoys higher performance in the low SNR region and lower time cost in the high SNR region than the single-stage scheme.
文摘针对阶梯块谱下的材料疲劳寿命预测问题,尤其是已有相关非线性模型的计算参数依赖大量试验数据或较难选取合适的基准值,导致在实际工程中应用有一定局限性。提出了一种新的基于相邻载荷的作用系数α_(i)=(S_(i+1)/S_(i))1/b lg K,该系数中两个参数b、K来自材料疲劳寿命关系式S=KN^(-b)。结合前人的二级、三级、四级应力加载试验结果,分别计算并对比了与多种疲劳损伤模型的结果。结果表明,新模型在疲劳寿命/损伤的预测结果优于Miner模型、Manson模型、Subramanyan模型及Hashin模型,可更为准确地预测阶梯块谱下的疲劳寿命/损伤。
文摘由规范反应谱合成的地震动功率谱实用模型具有较高的工程应用价值.提出从功率谱零频含量特征和地面最大位移2个方面判断地震动功率谱实用模型低频段的合理性.以多国规范反应谱为目标谱合成地震动功率谱,对比分析各功率谱低频段的合理性.分析结果表明,由加速度反应谱合成的功率谱的合理性取决于反应谱的合理性,而合理的加速度反应谱在长周期(低频)段应随周期(T)的增长以T-2的速度下降.据此修正GB50011—2010反应谱,引入T-2下降段,并将起始下降周期初步定为2 s.
