Identifying time-dependent damping and stiffness functions by a simple and yet accurate method

The inverse vibration problem is a mathematical process to determine unknown mechanical parameters from measured vibration data. In this study the data of displacement are chosen in order to identify a time-dependent function of damping or stiffness. However, when both functions are to be identified we require both the data of displacement and velocity. This is the first time that a closed-form estimation method for the inverse vibration problems of estimating time-dependent parameters has been constructed. We are able to transform the inverse vibration problem into an identification problem governed by a parabolic-type partial differential equation (PDE). Then, a one-step group-preserving scheme (GPS) for the semi-discretization of PDE is established, which can be used to derive a closed-form solution for estimating parameters. The new Lie-group estimation method has three further advantages: it does not require any prior information on the functional forms of unknown functions; no initial guesses are required; and no iterations are required. Numerical examples were examined to show that the present approach is highly accurate and efficient even for identifying discontinuous and oscillatory parameters. Against the noise is good when only one function is estimated; however, the present approach is slightly weak against the noise when both functions are identified.     

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。     

The generating functional for the probability density functions of Navier-Stokes turbulence

A generating functional for the equal-time spatial probability density functions which represent the ensemble of turbulent incompressible Navier-Stokes fluids is introduced. By formally solving the linear evolution equation satisfied by this functional, the probability densities are represented as functional integrals. It is shown that the generating functional can be regarded as the space characteristic functional of a generalized random field defined on the phase space spanned by the material position and velocity fields of a fluid particle. The interpretation of this random field, which satisfies a dynamical equation similar to Vlasov's, is clarified through the formal analogies between the statistics of molecules and fluid particles at the functional level. A class of statistically realizable and solvable models is also considered within the context of the present formalism.     

不同维度ZnO能带结构和电子态密度的研究

本文采用基于密度泛函理论的第一性原理计算方法来研究不同维度ZnO的能带结构和电子态密度.参考实验上的ZnO晶格参数构建不同维度的ZnO模型并进行结构优化后再计算能带结构和电子态密度.研究结果表明二维和三维ZnO都属于直接带隙半导体且二维ZnO的禁带宽度大于三维ZnO;从三维变到二维,ZnO的电子局域化程度变高且Zn 3d轨道电子从能量较低的能级向能量较高的能级跃迁.本文的研究展示了二维和三维ZnO能带结构和电子态密度的异同,为二维ZnO基的器件研究提供了一定的理论参考价值.     

Maximum cross-correlated kurtosis-based unsaturated stochastic resonance and its application to bearing fault diagnosis

Considering the random impulses of mechanical noise and the limitations involved while identifying mechanical fault impulse signals via traditional measurement indices of signal-to-noise ratio, which require the characteristic frequency to be known in advance, this study proposes an adaptive unsaturated stochastic resonance method employing maximum cross-correlated kurtosis as the signal detection index. The proposed method combines the features of a cross-correlated coefficient to indicate periodic fault transients and those of spectrum kurtosis to locate these transients in the frequency domain. Actual vibration signals collected from motor and gear bearings subjected to heavy noise are used to demonstrate the effectiveness of the proposed method. Through a coarse tree-based machine learning method, the proposed method is verified to be more suitable for explaining the periodic impulse components of bearing signals, as compared to the ensemble empirical mode decomposition denoising method and unsaturated stochastic resonance using the kurtosis-intercorrelation index.     

Nonuniqueness of the potentials of spin-density-functional theory.

It is shown that, contrary to widely held beliefs, the potentials of spin-density-functional theory (SDFT) are not unique functionals of the spin densities. Explicit examples of distinct sets of potentials with the same ground-state densities are constructed. These findings imply that the zero-temperature exchange-correlation energy is not always a differentiable functional of the spin density. As a consequence, various types of applications of SDFT must be critically reexamined.     

Time-dependent transport: Time domain recursively solving NEGF technique

We present a numerical method in this paper to calculate time-dependent transport properties in mesoscopic systems. This method recursively computes the non-equilibrium Green's functions (NEGF) in the time domain. In the simulations, we utilize a dynamically allocated data structure to compute current densities in response to input signals of any time duration and arbitrary shape. To demonstrate the performance, we apply the proposed method to solve NEGF for time-dependent transport in resonant-tunneling devices (RTD) with a single resonant level. We also investigate how the electrodes’ energy band structure affects the transport properties.     

一种强噪声背景下微弱超声信号提取方法研究

为解决在强噪声背景下获取超声信号的难题,基于粒子群优化算法和稀疏分解理论提出一种强噪声背景下微弱超声信号提取方法.该方法将降噪问题转换为在无穷大参数集上对函数进行优化的问题,首先以稀疏分解理论和超声信号的结构特点为依据构建了粒子群优化算法运行所需要的目标函数及去噪后信号的重构函数,从而将粒子群优化算法和超声信号降噪联系在一起;然后根据粒子群优化算法可以在连续参数空间寻优的特点建立了用于匹配超声信号的连续超完备字典,并采用改进的自适应粒子群优化算法在该字典中对目标函数进行优化;最后根据对目标函数在字典上的优化结果确定最优原子,并利用最优原子按照重构函数重构出降噪后的超声信号.通过对仿真超声信号和实测超声信号的处理,结果表明本文提出的方法可以有效提取信噪比低至-4 dB的强噪声背景下的微弱超声信号,且和基于自适应阈值的小波方法相比本文方法表现出更好的降噪性能.     

多元时间序列复杂网络流型动力学分析

针对气液两相流流动特性,利用有限元分析方法设计变曲率对壁式电导传感器.采用设计加工的传感器在多相流装置上进行气液两相流动态实验,并测得多组对应于不同流型的电导波动信号. 基于测量数据,采用多元时间序列复杂网络构建算法构建对应于不同流型的复杂网络.在此基础上, 对网络的社团特性进行了分析, 研究发现,不同的社团结构对应于不同的流型,而社团内部网络特征可有效刻画不同流型内在动力学特性.多元时间序列复杂网络分析可为两相流流型演化动力学特性研究及流型识别提供新理论、开拓新途经.     

一种抗血氧波动干扰的肝储备功能测量方法

肝储备功能参数是评估肝脏代谢作用是否正常的关键指标,也是判断切除肝叶手术能否进行的重要依据。当前临床上获取肝储备功能参数是通过脉搏色素分光光度法测量吲哚菁绿色素浓度实现的,但是该方法需要假设血氧值为100%,这将导致肝储备功能参数的计算值存在一定误差。针对这一问题,提出了一种抗血氧波动干扰的肝储备功能参数测量方法,以修正的朗伯-比尔定律为理论基础,实现了对脉搏色素分光光度法测量的吲哚菁绿色素浓度的修正。在人体注入吲哚菁绿后,利用自制的数据采集单元在指端皮肤处同步采集805和940 nm的双波长透射信号,以及730,805和890 nm的三波长反射信号,将收集到的五组数据依次上传至计算机,利用接收到的数据和人体注射色素前的血氧值绘制出吲哚菁绿色素的浓度曲线,并计算其特征参数,根据浓度曲线的特征参数计算出肝储备功能参数。以有效肝脏血流量为例,将所提出的方法和脉搏色素分光光度法的测量结果分别跟目前测量有效肝脏血流量最准确的电磁流量计法的测量结果相比较,测量误差得到了明显的改善。实验结果表明,该方法提高了肝储备功能参数测量的精确度,为临床提供了一种更加准确的肝储备功能参数检测方法。     

Construction of Coarse-Grained Models by Reproducing Equilibrium Probability Density Function

The present work proposes a novel methodology for constructing coarse-grained(CG) models, which aims at minimizing the difference between CG model and the corresponding original system. The difference is defined as a functional of their equilibrium conformational probability densities, then is estimated from equilibrium averages of many independent physical quantities denoted as basis functions. An orthonormalization strategy is adopted to get the independent basis functions from sufficiently preselected interesting physical quantities of the system. Thus the current method is named as probability density matching coarse-graining(PMCG) scheme, which effectively takes into account the overall characteristics of the original systems to construct CG model, and it is a natural improvement of the usual CG scheme wherein some physical quantities are intuitively chosen without considering their correlations. We verify the general PMCG framework in constructing a one-site CG water model from TIP3 P model. Both structure of liquids and pressure of the TIP3 P water system are found to be well reproduced at the same time in the constructed CG model.     

Identifying well-bleached quartz using the different bleaching rates of quartz and feldspar luminescence signals

When dating older sedimentary deposits using quartz, there are no unambiguous methods for identifying the presence of incomplete bleaching. Current statistical analysis of dose distributions depends entirely on the assumption that incomplete bleaching and mixing are the main causes of any excess dispersion in the distribution; the only existing way to test this assumption is using independent age control. Here we suggest a new approach to this question, based on the differential bleaching rates of quartz and feldspar luminescence signals. We first present data that confirm the differences in relative bleaching rates of quartz optically stimulated luminescence (OSL) and feldspar luminescence stimulated at 50 °C by infrared light (IR₅₀) and feldspar luminescence stimulated at 290 °C by infrared light after a stimulation at 50 °C (pIRIR₂₉₀), and use recently deposited samples to determine the likely significance of the difficult-to-bleach residual feldspar signals in non-aeolian samples. For a set of mainly Late Pleistocene non-aeolian sediments, large aliquot quartz doses are then used to predict feldspar doses (based on a knowledge of the sample dose rates). The differences between observed and predicted feldspar doses as a function of the quartz dose, combined with a conservative assumption concerning the relative feldspar and quartz residual signals after natural bleaching prior to deposition, are used to identify those samples for which the quartz is very likely to be well bleached (20 out of 24). Two of these apparently well-bleached samples are then examined using single-grain quartz dose distributions; one of these is consistent with the well-bleached hypothesis, and one indicates poor bleaching or a multi-component mixture. However, independent age control makes it clear that the large aliquot data are more likely to be correct. We conclude that a comparison of quartz and feldspar doses provides a useful independent method for identifying well-bleached quartz samples, and that it is unwise to apply statistical models to dose distributions without clear evidence for the physical origins of the distributions.     

ZnSe/GaAs(100)界面电子结构的计算

利用形式散射理论的格林函数方法，采用紧束缚最近邻近似下的sp³s模型，计算了ZnSe/GaAs(100)两类界面(Se/Ga和As/Zn界面)的电子结构.分别给出了两类界面的界面带结构和波矢分辨的层态密度及其分波态密度.计算结构表明，在ZnSe/GaAs(100)两类界面的禁带隙中均无界面态，而在其价带区均存在三条束缚的界面带和四条半共振带；通过比较，分析了两类界面的界面态特征及其来源. 关键词：     

钠在空位石墨烯上吸附性能的研究

采用基于密度泛函理论的第一性原理方法,研究了本征石墨烯和空位石墨烯吸附钠原子的电荷密度、吸附能、态密度和储存量.结果表明,在两种石墨烯中,钠原子的最佳吸附位置都为H位.空位石墨烯对钠原子的吸附能是-2. 46 eV,约为本征石墨烯对钠原子吸附能的3. 4倍;钠原子与空位石墨烯中的碳原子发生轨道杂化,而与本征石墨烯没发生轨道杂化现象.存在一个空位的石墨烯能够吸附5个钠原子,与本征石墨烯相比显著提高.因此,空位石墨烯有望成为一种潜在的储钠材料.     

Characteristic correlation between propellers cavitating wake and cavitation noise

The characteristic correlation between the propellers cavitating wake and their cavitation noise has been studied. Based on the viscous multiphase flow theory, the Navier–Stokes equations, a turbulence model and a cavitation model were applied to predict numerically the vapor volume fraction and the pressure in the wake. Compared with experimental results, the numerical predictions of the sheet cavitation and the tip vortex cavitation are in agreement with the corresponding experimental data, which indicates the numerical method in present paper is feasible. The characteristic of the low line spectra of the numerical pressure fluctuation signals and the measured noise signals for uniform inflow and wake flow is analyzed, and the characteristic correlation of the two line spectra is also validated. Therefore, it can be concluded that due to the wake and the radiated noise both modulated by the revolving propeller blades, the features of the low line spectra for noise signals and the pressure signals in the wake are close to each other.     

Direct measurement of entropic forces induced by rigid rods

We present the first direct depletion potential measurements for a single colloidal sphere close to a wall in a suspension of rigid colloidal rods. Since all particle interactions are as good as hard-core-like, the depletion potentials are of entirely entropic origin. We developed a density functional theory approach that accurately accounts for this experimental situation. The depletion potentials calculated for different rod number densities are in very good quantitative agreement with the experimental results.     

基于AR模型的人体脉象信号模糊聚类研究

根据一种新的模糊聚类方法－F－PFSR（Fuzzy Pseudo F-Statistic Ratio)聚类法,对人体脉搏声信号（脉象信号）进行了聚类识别研究。首先对脉搏声信号作8阶AR模型拟合,模型系数构成信号的特征集,其次采用K－L变换对特征集进行了压缩,最后对临床实测脉象信号进行了聚类分析。实验结果表明,本文的聚类方法是可行和有效的。     

基于复杂度的针刺脑电信号特征提取

为探究针灸刺激对大脑活动产生的影响,文章设计了4种针刺频率针刺右腿足三里穴获取脑电的实验.首次采用排序递归图和关联维数方法提取针刺脑电信号的复杂度参数来反映针刺大脑的功能状态,并基于这些方法研究了针刺作用对大脑功能区域的影响以及不同针刺频率与脑电复杂度的相关性.发现针刺时脑电的复杂度高于针刺前,尤以频率为100次/min的针刺影响最为明显;从FP2, F7, T3导联脑电中提取的确定性指标(DET)可作为区分针刺状态与针刺前状态的一种特征参数. 关键词： 针灸 脑电 排序递归图 关联维数     

基于变分模态分解-传递熵的脑肌电信号耦合分析

皮层肌肉功能耦合是大脑皮层和肌肉组织间的相互作用, 脑肌电信号的多尺度耦合特征可以体现皮层-肌肉间多时空的功能联系. 本文引入变分模态分解并与传递熵结合, 构建变分模态分解-传递熵模型应用于脑肌间耦合研究. 首先基于变分模态分解将同步采集的脑电(EEG) 和肌电(EMG) 信号分别进行时频尺度化, 然后计算不同时频尺度间的传递熵值, 获取不同耦合方向(EEG→EMG 及EMG→EEG) 上不同尺度间的非线性耦合特征. 结果表明, 在静态握力输出条件下, 皮层与肌肉beta (15—35 Hz) 频段间的耦合强度最为显著; EEG→EMG 方向上脑电与肌电高gamma (50—72 Hz) 频段的耦合强度总体上高于EMG→EEG 方向.研究结果揭示皮层-肌肉功能耦合具有双向性, 且脑肌间不同耦合方向上、不同频段间的耦合强度有所差异.因此可利用变分模态分解-传递熵方法定量刻画大脑皮层与肌肉各时频段之间的非线性同步特征及功能联系.