基于功能近红外光谱技术(fNIRs)的帕金森病大鼠模型脑组织特性研究

利用功能近红外光谱技术(functionality near infrared spectroscopy,fNIRs)探索帕金森病(parkin-son's disease,PD)大鼠模型的脑组织功能特性.通过小动物磁共振(magnetic resonance imaging,MRI)和电子计算机断层扫描(computed tomography,CT)对PD大鼠模型进行影像学研究,用fNIRs系统测试大鼠模型脑组织纹状体特征参数.实验结果表明,PD大鼠脑部没有明显的形态结构变化;优化散射系数(reduced scattering coefficient:μ's)、脑血容量(cerobral bloodvolume:CBV)在PD大鼠的纹状体部与对照组间存在显著的差别;fNIRs测量参数(μ's、CBV)与CT灌注(CTP)测定参数[CBF(cerebral blood flow),CBV]之间存在相关性.这些结果表明fNIRs可以作为PD研究的重要参考手段.     

Levy噪声激励下的幂函数型单稳随机共振特性分析

将Levy噪声与幂函数型单稳随机共振系统相结合, 为确保实验数据的可靠性, 以平均信噪比增益为衡量指标, 针对Levy噪声激励下的随机共振现象进行了研究. 详细介绍了单稳系统势函数形式及Levy噪声的产生原理, 深入探究了不同特征指数α 和不同对称参数β 取值条件下, 单稳系统参数a和b、Levy噪声强度放大系数D对幂函数型单稳系统共振输出的作用规律. 研究结果表明, 在任意Levy噪声分布条件下, 通过对系统参数a和b的适当调整均能诱导随机共振, 完成微弱信号检测, 且有多个随机共振区间与之对应, 同时这些区间不随α 或β 的改变而改变; 此外, 在研究噪声诱导的随机共振时也发现了同样的规律, 通过调节噪声强度放大系数D也能产生随机共振, 且随机共振区间也不随α 或β 的改变而改变; 最后, 在研究系统参数a和b之间的相互作用关系时发现, 一个系统参数的随机共振取值区间会随着另一个系统参数的改变而改变. 所获得的研究结果有效解决了Levy噪声激励下幂函数型单稳随机共振系统的系统参数、噪声强度放大系数的选择问题, 为其应用于工程实践提供了可靠的理论依据.     

振幅相位调制驻波光场中冷却原子的动力学局域

分析了二能级原子在振幅相位调制驻波场作用下动量扩散模型,这是一个双频参数激励的非线性量子单摆模型。这个系统在经典极限下表现混沌行为,在相同参数条件下,这个系统具有动力学局域特征,具有两个不可约频率扰动的系统的局域长度要比单个频率扰动时大得多。     

Effect of charge-spin separation on the conductance through interacting low-dimensional rings

We calculate the conductance through Aharonov-Bohm chain and ladder rings pierced by a magnetic flux which couples with the charge degrees of freedom. The system is weakly coupled to two leads and contains strongly interacting electrons modeled by the prototypical t-J and Hubbard models. For a wide range of parameters we observe characteristic dips in the conductance as a function of magnetic flux which are a signature of spin and charge separation. We also show how the dips evolve when the parameters of the models depart from the ideal case of total spin-charge separation. The ladder ring can be mapped onto an effective model for large anisotropy which can be easily analyzed. These results open the possibility of observing this peculiar many-body phenomenon in anisotropic ladder systems and in real nanoscopic devices.     

On the problem of homogenizing one-dimensional systems

The possibility of introducing effective one-dimensional medium parameters in the long-wave approximation is considered. A layered system was used as a model of one-dimensional medium. The effective parameters were shown to be functions of sample thickness. Both periodic and random media were studied; the thicknesses of random samples were assumed to be much smaller than the localization length, which allowed us to ignore the localization effect. The results are compared with the Rytov solution. The wave vector was found to tend to the Rytov value as the thickness of the sample increased, whereas the characteristic impedance had no limit in the long-wave approximation. What is more, the characteristic impedance could differ from the Rytov value by 100%. The results were obtained by computer simulation of the propagation of electromagnetic waves in a layered system.     

Millimeter Wave Passive Detection Simulation System

In this paper, millimeter wave Radiometer Dynamic Simulation system (RDS) is presented as a typical pre-verification system. Before designing hardware circuit, we can utilize RDS system to simulate radiometric working orders by presetting its technical parameters and simulation environment. Thus it can improve radiometric validity and accuracy on target detection and pattern recognition. On the basis of discussing radiation characteristic and mathematical model, a system framework was proposed.     

偏振模色散影响色散控制孤子传输的理论研究

采用变分法分析高速色散控制孤子在双折射光纤中的传输规律。首先建立了色散控制孤子在双折射光纤中的扰动传输模型 ,然后解析了偏振模色散影响下色散控制孤子各参量的传输演化规律 ,最后对解析结果进行了计算。研究结果表明 ,偏振模色散参量对色散控制孤子能量、脉宽的演化影响很大 ,当偏振模色散很大时 ,如Dp>0 .3ps/km1/ 2 时 ,必须考虑采用某些在线控制手段来有效抑制偏振模色散对传输系统的影响 ,然而 ,当Dp≤ 0 .1ps/km1/ 2 时 ,系统几乎不受影响 ,同时本文还证明了色散控制孤子抗偏振模色散扰动的能力强的这一特点。为研究偏振模色散对高速非线性传输系统、特别是色散控制孤子传输系统的影响提供了理论依据和研究方法。     

磁致伸缩-压电混合激励Janus换能器结构特征参量与纵振频率之间的关系

为了拓宽Janus换能器的工作频带,使用超磁致伸缩材料Terfenol-D与PZT压电陶瓷作为混合激励元件驱动Janus换能器,研究了其结构特征参量与纵振频率之间的关系.首先归纳了磁致伸缩-压电混合激励Janus换能器的12个结构特征参量.随后通过模态分析,证明换能器具有两种纵振动模态.最终经过有限元仿真计算,总结分析...     

Simulation of unsteady combustion in a solid-propellant rocket motor

Various regimes of combustion in end-burning-grain solid-propellant rocket motors were examined within the framework of the phenomenological theory of unsteady combustion. A system of equations capable of describing the interaction between the process of burning and acoustic waves was derived. A specific feature of the problem is that its formulation involves two characteristic times: the acoustic time and oscillation amplitude variation time. These characteristic times differ by about three orders of magnitude, a circumstance that requires a high accuracy of calculations. Based on the quadratic approximation in oscillation amplitude, a simpler method for solving the problem was proposed, according to which only the effects associated with the oscillation amplitude variation time are taken into account. Numerical results were obtained for the simplest model of propellant burning, which contains the minimum number of parameters and disregards entropy waves in the combustion products. The steady and unsteady regimes of burning were identified. In the latter case, nonlinear effects may generate shock waves in the combustion chamber.     

量子参数激励单摆的局域效应研究

分析了二能级原子在振幅调制主波场中动量扩散模型。这是一个量子参数激励单摆系统。这个量子系统在经典极限下表现混沌行为。在相同参数条件下,这个系统具有动力学特征。     

The effects of surface dilution on magnetic properties in a transverse Ising nanowire

The phase diagrams (transition temperature and compensation temperature) and magnetizations of a cylindrical nanowire with a (positive or negative) core–shell interaction and a surface dilution, described by the transverse Ising model (TIM), are investigated by the use of the effective-field theory with correlations. The magnetic properties of the system are strongly affected by the surface dilution. In particular, the temperature dependences of magnetizations in the system have shown many characteristic phenomena, depending on the selected physical parameters.     

调制驻波光场中二能级原子动量扩散的动力学研究

分析了二能级原子在振幅调制驻波光场作用下动量扩散模型.这个量子系统在经典极限下表现混沌行为.在相同参数条件下,这个系统具有动力学局域特征. 关键词：     

Phase diagrams of a transverse Ising nanowire

Phase diagrams of a cylindrical nanowire described by the transverse Ising model are investigated by the use of two theoretical frameworks, namely the mean field theory and the effective field theory with correlations. The phase diagram of the system is strongly affected by the surface situations. Some characteristic phenomena are found in the phase diagram, depending on the ratio of the physical parameters in the surface shell and the core.     

概率神经网络在高功率微波探测数据处理中的应用

为了更好地处理高功率微波探测过程中产生的样本数据,在深入分析高功率微波特性参数的基础上,建立一个高功率微波器件特征参数库,并结合概率神经网络系统建立了一个高功率微波探测预测模型。通过部分学习样本和非学习样本进行预测,预测结果证明该模型能够基本再现原始数据,同时,对非样本数据有着较好的预测能力。这一数据处理方法在处理复杂样本、模式分类和判别过程中具有较高的实用性和实时性,能够在高功率微波探测数据的数据分类、结果预测等方面得到较好的应用。     

多无人机协同的稳定控制机理研究

多无人机协同系统的过度扩散会引起协同失效, 对系统进行规模控制是解决该问题的一种潜在方法. 首先抽象出多无人机协同搜索系统的宏观运动特征, 进而建立平台的运动方程, 然后通过构造合适的李雅普诺夫函数, 获得该系统的稳定控制规律及其控制参数. 仿真结果表明: 1)本文所提的稳定控制机制不仅能够使多无人机系统实现有效的协同, 还能确保系统的稳定性; 2)在系统稳定时, 通过调整相关控制参数可以有效地控制系统规模. 关键词： 无人机 协同系统 稳定控制     

一种光谱识别的新方法

提出了一种对光谱信号识别的新方法。针对光谱信号的特征 ,我们设计了基于径向基函数神经网络组成的统计混合模型 ,并构造了识别系统的代价函数。通过优化系统的代价函数 ,导出了类EM算法去估计混合模型的参数 ,从而构建对光谱特征识别的识别器。利用实际的拉曼光谱 ,对本文所提出的估计模型参数的算法与建立的光谱识别器进行了检验。我们还讨论了利用特征波长与相应的光谱强度 ,以及利用主分量分析组成输入特征矢量 ,及其这些输入特征矢量对光谱识别器应用的效果。实验结果表明 ,所提出的算法可以有效地估计模型参数 ,其建立的光谱识别模型具有较高的识别准确率。所提出的对光谱信号识别的方法通用性强 ,因此具有较为广阔的应用前景。     

Identification of a parametric loudspeaker system using an adaptive Volterra filter

Due to the parametric acoustic array effect in air, the input audible signal of a parametric loudspeaker system can be reproduced with high directivity at the target region. However, the reproduced audible signal suffers from harmonic distortion, which is the by-product of nonlinear interaction between the primary waves. In order to investigate this inherent nonlinear phenomenon, a nonlinear system identification model is developed based on an adaptive Volterra filter. Unlike the conventional loudspeaker, the nonlinear characteristic of a parametric loudspeaker system is dependent on several primary parameters in nonlinear acoustics, which include the initial pressure of the primary waves, the observing distance and angle, as well as ambient temperature and relative humidity. By using a truncated Volterra series up to the 2nd-order kernel, numerical simulations are conducted to develop a system model with one group of parameters and examine the quadratic nonlinear intensity for different parameters’ settings. Experimental measurements, which take into account of emitter’s response, are carried out to verify the modeling result and evaluate the model performance. Based on the Volterra system model, the sound pressure level and the harmonic distortion can be accurately predicted.