松质骨超声背散射信号的谱信息熵判断方法

在松质骨超声背散射评价的实际应用中,如何快速准确地判断接收到的信号中是否包含有效背散射信号是一个重要问题。提出一种基于谱信息熵的背散射信号判断方法。对在体采集的984例成人跟骨处临床数据,采用该方法判断背散射信号的有效性,将判断结果与经验判断结果进行对照分析,并分析该方法中的信号区间长度和谱信息熵分段数对判断结果的影响。结果表明,当信号区间长度为13μs,谱信息熵分段数为15~20时,该方法可以获得最佳的判断结果(准确度〉95%,灵敏度〉99%,特异度〉87%),并且计算时间极短(1.5 ms)。因此采用谱信息熵方法判断背散射信号的有效性,可以满足超声骨质评价中对准确性和实时性的要求。     

Computational aerodynamics of low Reynolds number plunging,pitching and flexible wings for MAV applications

Micro air vehicles （MAV＇s） have the potential to revolutionize our sensing and information gathering capabilities in environmental monitoring and homeland security areas. Due to the MAV＇s＇ small size, flight regime, and modes of operation, significant scientific advancement will be needed to create this revolutionary capability. Aerodynamics, structural dynamics, and flight dynamics of natural flyers intersects with some of the richest problems in MAV＇s, inclu- ding massively unsteady three-dimensional separation, transition in boundary layers and shear layers, vortical flows and bluff body flows, unsteady flight environment, aeroelasticity, and nonlinear and adaptive control are just a few examples. A challenge is that the scaling of both fluid dynamics and structural dynamics between smaller natural flyer and practical flying hardware/lab experiment （larger dimension） is fundamentally difficult. In this paper, we offer an overview of the challenges and issues, along with sample results illustrating some of the efforts made from a computational modeling angle.     

充粘液管材中超声纵向轴对称导波的频散特性分析

模拟分析充粘液管内径-壁厚比和超声纵向轴对称导波波包宽度的关系。考虑了衰减的情况下,在各传播距离、频厚积和激发脉冲周数上,采用脉冲回波法,分析了导波的频散特性。结果表明:对于特定的材料,当频厚积一定时,充粘液管材中传播的导波特性只与内径-壁厚比有关;各高阶模式的截止频厚积随内径-壁厚比的增大而减小。用L(0,1)模式检测内径-壁厚比在4附近的充粘液管时灵敏度较低;而用L(0,2)模式检测内径-壁厚比在9.2附近的管时灵敏度较低。对于不同内径-壁厚比的充粘液管,检测中应当用不同的纵向轴对称导波模式,所用的激发脉冲周数和频厚积也应当不同。     

超声诊断骨质疏松症中松质骨的模型

骨质疏松症(OP)是老龄化社会中影响健康的一个重要问题，超声技术已成为诊断骨质疏松症的一种常用方法。文中综述了近年来用超声诊断骨质疏松症中松质骨模型研究的进展，对棒状模型、流体多孔介质模型(Biot理论)和层状模型(schoenberg理论)进行了分析和讨论，指出了各理论模型存在的缺陷，对下一步的研究工作提出了建议。     

基于催化应用调控氧化铈纳米材料的形貌

催化剂的设计、合成和结构调控是获得优异性能的关键.传统的策略主要是尽量减小催化剂颗粒尺寸以增加活性中心的数目,即尺寸效应.近年来,材料科学的快速发展使得在纳米尺度上调变催化剂的尺寸和形貌成为可能,特别是通过形貌调控可暴露更多的高活性晶面,大幅度提高催化性能,即纳米催化中的形貌效应.因此,调节催化剂的尺寸与形貌可以单独或协同优化材料的性能.氧化铈作为催化剂的重要组分与结构、电子促进剂被广泛应用于多相催化剂体系.本文总结了近期氧化铈材料形貌可控合成的进展,包括主要的合成策略和表征方法; 进而分析了氧化铈和金-氧化铈催化材料的形貌效应,指出金-氧化铈之间独特的相互作用与载体形貌密切相关; 阐述了氧化铈纳米材料因暴露晶面的差异而获得不同催化性能的化学机制.     

Comment: Comment on saturation effects in high-resolution coherent anti-stokes Raman spectroscopy of a pulsed molecular beam

Saturation broadening in coherent anti-stokes Raman spectroscopy (CARS) is analyzed under conditions where relaxation effects are negligible by solving the appropriate Bloch equations exactly. The present analysis extends that previously given by Duncan, Oesterlin, König and Byer, who experimentally observed saturation broadening in high-resolution CARS.     

Über die Aufnahme von Äthylendiamintetraessigsäure durch Kationenaustauscher

Ohne ZusammenfassungMit 1 Abbildung     

A superpolynomial lower bound for strategy iteration based on snare memorization

This paper presents a superpolynomial lower bound for the recently proposed snare memorization non-oblivious strategy iteration algorithm due to Fearnley. Snare memorization is a method to train strategy iteration techniques to remember certain profitable substrategies and reapply them again. We show that there is not much hope to find a polynomial-time algorithm for solving parity games by applying such non-oblivious techniques.