孔径扩展中相位修正因子估计的改进算法

传统的扩展拖曳阵列尺寸算法(Extended Towed Array Measurement,ETAM)在信噪比不够高、相位修正因子的相位角处于以间断点为中心的\     

Spiral waves in systems with fractal heterogeneity

The influence of fractal heterogeneity on a spiral wave in an excitable system is numerically studied based on the Barkley model. The heterogeneity is implemented by letting the diffusive coefficient in the heterogeneous area be different from the other area. The results show that fruitful transitions of the spiral tip trajectories are induced by the fractal heterogeneity. In particular, when the heterogeneity increases to a sufficiently high level the spiral tip trajectory always changes to a stable rotating trajectory (closed-circle tip trajectory), whatever transitions have been induced by a lower level of heterogeneity. We qualitatively ascribe the transitions to the attraction on the spiral tip exerted by the heterogeneous area.     

Spatial heterogeneity in liquid–liquid phase transition

Molecular dynamics simulations are performed to investigate the liquid–liquid phase transition(LLPT) and the spatial heterogeneity in Al–Pb monotectic alloys. The results reveal that homogeneous liquid Al–Pb alloy undergoes an LLPT,separating into Al-rich and Pb-rich domains, which is quite different from the isocompositional liquid water with a transition between low-density liquid(LDL) and high-density liquid(HDL). With spatial heterogeneity becoming large, LLPT takes place correspondingly. The relationship between the cooling rate, relaxation temperature and percentage of Al and the spatial heterogeneity is also reported. This study may throw light on the relationship between the structure heterogeneity and LLPT, which provides novel strategies to control the microstructures in the fabrication of the material with high performance.     

Prosocial norms and degree heterogeneity in social networks

We provide empirical evidence to support the claims that social diversity promotes prosocial behavior. We elicit a real-life social network and its members’ adherence to a social norm, namely inequity aversion. The data reveal a positive relationship between subjects’ prosociality and several measures of centrality. This result is in line with the theoretical literature that relates the evolution of social norms to the structure of social interactions and argues that central individuals are crucial for the emergence of prosocial behavior.     

On the accuracy of various statistical methods for describing ordering phase transitions in BCC alloys

The accuracy of various statistical methods for describing B2-or D0₃-type (CuZn or Fe₃Al) ordering phase transitions characteristic of BCC alloys is examined. The temperature-concentration phase diagrams were calculated for several models of alloys discussed in the literature with the use of three methods, namely, the mean-field and pair cluster approximations and the tetrahedron cluster field method developed in this work. The calculation results were compared with each other and with Monte Carlo calculations. The accuracy of various methods was found to sharply depend on the type of interactions in the system, primarily, on the presence of strong competing interactions and short-range correlations that hinder ordering. In the absence of such correlations, in particular, in Fe-Al type alloys with extended interactions, the use of the pair cluster approximation allows the results obtained in the mean-field approximation to be substantially refined without any noticeable complication of calculations. At the same time, for systems with short-range and competing interactions, the use of this approximation could drastically distort the form of phase diagrams, whereas the tetrahedron cluster field method allows the phase diagrams of these systems to be calculated fairly accurately for temperatures and concentrations of interest to physics.     

Controlling chaos by developing spiral wave from heterogeneity in excitable medium

We study pattern formation induced by a spiral wave developing from heterogeneities in an excitable medium. Turbulence can be suppressed by a spiral wave from the heterogeneity, forming multiple coexistent systems of regular geometrical patterns. We find that the types of these patterns depend critically on the degree of heterogeneity. The underlying mechanism is due to dispersion relation which is characterized by excitability.      

无源测向跟踪的数值预测方法

本文提出了一类基于最小二乘估计的数值算法，用于解决无源被动测向系统预置跟踪的实际问题，通过建立观测器及目标运动模型，分析了算法理论上的合理性，计算机模拟实验结果示出了预测方法的良好性能，并就其对机动目标的适应能力进行了比较。     

An effective mean-field method for describing surface effects in polymer layers

The peeling off of an adsorbed flexible macromolecule from a surface under the action of an effective mean field formed due to intermolecular interactions with the ends of other extended chains is considered. It is shown that there is a first order phase transition in the system that is accompanied by a rise of fluctuations, the existence of metastable states, and jumps of the extension and heat capacity of chains.     

A method for improving the performance of MVDR beamforming

I.IntroductionInbeamformingforsonaritisthemostinterestingfunctionthatonecanobtainthctimcwaveformoutputsofthedesiredsignaltobedetectcdwithanimprovcdSignal-to-NoiseplusInterferenceRatio(SNIR).ItiswellknownthatMVDRbeamforminghasoptimumcapabi1i-hesofsignalprotection,interferenccremovalandnoisercduction.NootherbeamformingtochniquecanyicldalargerincreascinSNIR.Itspoweroutputcanbeusedasawavenumberspectrum(bearing)estimation,whoseprecisionorreso1utionisdeterminedprimarilybySignal-to-NoiseRatio…     

A Fourier method for the fractional diffusion equation describing sub-diffusion

In this paper, a fractional partial differential equation (FPDE) describing sub-diffusion is considered. An implicit difference approximation scheme (IDAS) for solving a FPDE is presented. We propose a Fourier method for analyzing the stability and convergence of the IDAS, derive the global accuracy of the IDAS, and discuss the solvability. Finally, numerical examples are given to compare with the exact solution for the order of convergence, and simulate the fractional dynamical systems.     

关于单元体系Cu的玻璃转变过程中动力学不均匀性的研究

基于分子动力学模拟技术,采用非高斯参数α_2(t)来描述单元体系Cu的玻璃转变过程中动力学不均匀性的变化.研究表明在β弛豫阶段,非高斯参数α_2(t)随时间的变化满足幂律函数,而非高斯参数峰值α_(max)和β弛豫时间τ_β与温度的关系均符合Arrhenius函数,且温度越接近玻璃转变温度T_g,体系的动力学不均匀性越明显.     

Numerical method for hydrodynamic modulation equations describing Bloch oscillations in semiconductor superlattices

We present a finite difference method to solve a new type of nonlocal hydrodynamic equations that arise in the theory of spatially inhomogeneous Bloch oscillations in semiconductor superlattices. The hydrodynamic equations describe the evolution of the electron density, electric field and the complex amplitude of the Bloch oscillations for the electron current density and the mean energy density. These equations contain averages over the Bloch phase which are integrals of the unknown electric field and are derived by singular perturbation methods. Among the solutions of the hydrodynamic equations, at a 70 K lattice temperature, there are spatially inhomogeneous Bloch oscillations coexisting with moving electric field domains and Gunn-type oscillations of the current. At higher temperature (300 K) only Bloch oscillations remain. These novel solutions are found for restitution coefficients in a narrow interval below their critical values and disappear for larger values. We use an efficient numerical method based on an implicit second-order finite difference scheme for both the electric field equation (of drift-diffusion type) and the parabolic equation for the complex amplitude. Double integrals appearing in the nonlocal hydrodynamic equations are calculated by means of expansions in modified Bessel functions. We use numerical simulations to ascertain the convergence of the method. If the complex amplitude equation is solved using a first order scheme for restitution coefficients near their critical values, a spurious convection arises that annihilates the complex amplitude in the part of the superlattice that is closer to the cathode. This numerical artifact disappears if the space step is appropriately reduced or we use the second-order numerical scheme.     

异质双层磁性薄膜中自旋波的波形演化

在一维海森堡模型的基础上,采用界面参数化方法,将双层异质磁薄膜中自旋波本征值问题归结为联立求解能量约束方程和界面参数化方程．重点讨论体系中体模和完全禁闭模的波形演化过程,发现体系中体模波形随自旋波矢呈余弦变化,会出现局域共振现象．激发能对两子层中体模有较大的影响,不仅影响体模的振幅,而且还影响体模的波长．另外,激发能对体系中的完全禁闭模也有较大影响,随着激发能增大,铁磁层中完全禁闭模波长变短,波速变小,但振幅不变．     

Microcirculatory fraction (MCF(I)) as a potential imaging marker for tumor heterogeneity in breast cancer

Cancer is a heterogeneous disease by nature. Current imaging studies usually ignore intratumor variability in imaging biomarkers. We postulate that quantifying tumor heterogeneity with imaging techniques can provide useful information about cancer biology and potentially serve as novel imaging biomarkers. In this retrospective study, we identify a potential imaging marker, the microcirculatory fraction (MCF(I)), that quantifies tumor heterogeneity in normoxic/hypoxic cellular composition. We demonstrate its application on a test population of 22 women with stage II/III HER-2 negative breast cancer receiving antiangiogenic-cytotoxic combination neoadjuvant chemotherapy. Early change in MCF(I) (ΔMCF(I)) is assessed with dynamic contrast enhanced magnetic resonance imaging at the end of Cycle 2 and associated with pathologic response. Its performance is compared with other established volumetric imaging biomarkers (initial tumor volume and volume change) by statistical and graphic methods. We demonstrate that a significant (P<.01) difference in ΔMCF(I) can be detected between good (median ΔMCF(I) 0.27) and poor (median ΔMCF(I) -0.12) responders, despite the limited population size. Differences in the volumetric biomarkers are not statistically significant. Receiver operating characteristic analysis also shows that ΔMCF(I) is a good predictor for pathologic response (AUC=0.86, 95% CI 0.69-1.00, P<.01), while predictions made with the established volumetric biomarkers are not significantly better than random guesses. We conclude that ΔMCF(I) has the potential of being a better predictive biomarker for therapeutic response assessment. Our findings support our postulation that quantifying tumor heterogeneity with imaging techniques can provide additional information that can serve as novel biomarkers.     

嵌入原子法计算金属钚中点缺陷的能量

钚因放射性衰变而出现老化效应.钚中点缺陷的性质和行为是理解钚老化效应的一个基础和前提.运用分子动力学模拟技术,计算了金属钚中点缺陷和点缺陷团簇的形成能和结合能.其中钚-钚、钚-氦和氦-氦相互作用势分别采用嵌入原子多体势、Morse对势和Lennard-Jones对势.计算结果表明,单个自间隙原子易以〈100〉哑铃状形态存在;间隙氦原子在理想晶格的八面体间隙位置相对较为稳定;氦原子与空位的结合能较大,在钚的自辐照过程中两者易于结合并形成氦-空位团簇;氦-空位团簇的形成能随氦原子数的增加而增大,当氦与空位的数     

球壳型钚部件中子多重性测量点模型修正算法

针对中子多重性测量技术中点模型假设在军控核查情况下存在的局限性,为提高核查可靠度,研究点模型算法在武器级球壳型钚部件测量中的逻辑悖论,提出了点模型修正算法。在点模型算法中引入自发裂变中子和氧化物次生中子的二阶矩及三阶矩修正因子,获取了修正后的点模型公式。利用探测效率和门份额均为1的理想中子多重性探测器,结合蒙特卡罗模拟平台,研究了修正因子与球壳型钚部件质量、泄漏增殖因子的关系,并定量了该关系,提出利用迭代法求解修正后的点模型公式。结合蒙特卡罗方法对修正算法进行了数值验证,与点模型算法结果比较：修正算法能将质量偏差平均值从-4.70%降低至-0.70%,氧化物含量份额偏差平均值从11.45%降低至2.31%。     

球壳型钚部件中子多重性测量点模型修正算法

针对中子多重性测量技术中点模型假设在军控核查情况下存在的局限性,为提高核查可靠度,研究点模型算法在武器级球壳型钚部件测量中的逻辑悖论,提出了点模型修正算法。在点模型算法中引入自发裂变中子和氧化物次生中子的二阶矩及三阶矩修正因子,获取了修正后的点模型公式。利用探测效率和门份额均为1的理想中子多重性探测器,结合蒙特卡罗模拟平台,研究了修正因子与球壳型钚部件质量、泄漏增殖因子的关系,并定量了该关系,提出利用迭代法求解修正后的点模型公式。结合蒙特卡罗方法对修正算法进行了数值验证,与点模型算法结果比较:修正算法能将质量偏差平均值从-4.70%降低至-0.70%,氧化物含量份额偏差平均值从11.45%降低至2.31%。     

A novel algorithm to solve the differential equation describing the non-interactive multiple-trap system model in thermoluminescence

The analysis of glow curves in thermoluminescence requires finding a closed expression for the light emitted as a function of the temperature and the parameters characterizing trap and recombination centers. Since it is not possible to derive a closed expression from the set of coupled differential equations describing the thermoluminescence phenomenon, approximations are made even for the simplest models. All of them resort to an approximation known as the quasi-equilibrium approximation (QE), and to further approximations. In this article, an algorithm is reported that permit the derivation of a closed expression for the emitted light for the model known as the non-interactive multi-trap system (NMTS) model by resorting only to the QE approximation. It is shown that the integration of the first order differential equation related to the NMTS model can be replaced by finding the roots of an analytical expression.     

Secondary relaxation and dynamic heterogeneity in metallic glasses:A brief review

Understanding mechanical relaxation, such as primary(α) and secondary(β) relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses. At a fundamental level, relaxation, plastic deformation, glass transition, and crystallization of metallic glasses are intimately linked to each other, which can be related to atomic packing, inter-atomic diffusion, and cooperative atom movement. Conceptually, βrelaxation is usually associated with structural heterogeneities intrinsic to metallic glasses. However, the details of such structural heterogeneities, being masked by the meta-stable disordered long-range structure, are yet to be understood. In this paper, we briefly review the recent experimental and simulation results that were attempted to elucidate structural heterogeneities in metallic glasses within the framework of β relaxation. In particular, we will discuss the correlation amongβ relaxation, structural heterogeneity, and mechanical properties of metallic glasses.     

原子尺寸对Lennard-Jones液体玻璃转变过程中动力学不均匀性的影响

采用分子动力学模拟技术,通过对非高斯参数α_2(t)、粘度η等动力学参数的计算探究了原子尺寸对Lennard-Jones(LJ)液体在玻璃转变过程中动力学不均匀性的影响.结果表明在玻璃转变温度T_g附近,原子尺寸越小,粘度值增加越显著,且粘度随温度的变化满足Vogel–Fulcher–Tammann (VFT)方程;β弛豫阶段的非高斯参数α_2(t)与时间的关系满足幂律函数,且随着原子尺寸的减小动力学不均匀性越来越明显.