Out-of-equilibrium kondo effect in double quantum dots

We present results of high resolution experiments on kinetic roughening of slow combustion fronts in paper, focusing on short length and time scales. Using three different grades of paper, we find that the combustion fronts show apparent spatial and temporal multiscaling at short scales. The scaling exponents decrease as a function of the order of the corresponding correlation functions. The noise affecting the fronts reveals short range temporal and spatial correlations, and non-Gaussian noise amplitudes. Our results imply that the overall behavior of slow combustion fronts cannot be explained by standard theories of kinetic roughening.     

Wave fronts in inhomogeneous neural field models

In this work we investigate the influence of inhomogeneities on wave front propagation in an excitatory neural field model describing synaptic activity in the absence of delays. This allows the derivation of the spatial (and hence temporal) behaviour of the front velocity under the assumption that the front is approximatively homogeneous in a very small time window. With this assumption we can also derive the spatiotemporal behaviour of the membrane potential analytically in the vicinity of the wave front. In addition to this we investigate stationary solutions such as standing wave fronts and localised activity (so-called bumps) to determine the existence condition of travelling and standing fronts. Numerical results are included to point out the accordance of theory and simulation.     

Partial entrainment in the finite Kuramoto-Sakaguchi model

Although modifications of the Kuramoto model have been the subject of extensive research, the model itself is not yet fully understood. We offer several results and observations, some analytic, others through simulations. We derive a sufficient condition for the existence of a solution exhibiting partial entrainment with respect to a given subset of oscillators; the result also implies persistence of the entrainment behavior under perturbations.The critical values of the coupling strength, defining the transitions between different forms of partial entrainment, are predicted by an analytical approximation, based on the fact that oscillators with large differences in their natural frequencies have little influence on each other’s entrainment behavior; the predictions agree with the actual values, obtained by simulations.We indicate (by simulations) that entrainment can disappear with increasing coupling strength, and that, in arrays of Josephson junctions, a similar phenomenon can be observed, where it is also possible that a junction leaving one entrained subset joins another entrained subset.     

Stationary and oscillatory fronts in a two-component genetic regulatory network model

We investigate a two-component gene network model, originally used to describe the spatiotemporal patterning of the gene products in early Drosophila development. By considering a particular mode of interaction between the two gene products, denoted proteins A and B, we find both stable stationary and time-oscillatory fronts can occur in the reaction-diffusion system. We reduce the system by replacing B with its spatial average (shadow system) and assume an abrupt “on-and-off” switch for the genes. In doing so, explicit formula are obtained for all steady-state solutions and their linear eigenvalues. Using the diffusion of A,D_a, and the basal production rate, r, as bifurcation parameters, we explore ranges in which a monotone, stationary front is stable, and show it can lose stability through a Hopf bifurcation, giving rise to oscillatory fronts. We also discuss the existence and stability of steady-state and time-oscillatory solutions with multiple extrema. An intuitive explanation for the occurrence of stable stationary and oscillatory front solutions is provided based on the behavior of A in the absence of B and the opposite regulation between A and B. Such behavior is also interpreted in terms of the biological parameters in the model, including those governing the connection of the gene network.     

Persistence in Extended Dynamical Systems

Persistence in spatially extended dynamical systems (e.g., coarsening and other nonequilibrium systems) is reviewed. We discuss, in particular, the spatial correlations in the persistent regions and their evolution in time. We also discuss the dependence of the persistence behavior on the dynamics of the system, and consider the specific example of different updating rules in the temporal evolution of the system. Finally, we discuss the universal behavior shown by persistence in various stochastic models belonging to the directed percolation universality class.     

H-theorem for a mean field model describing coupled oscillator systems under external forces

This article studies the asymptotic behavior of solutions of Fokker–Planck equations describing mean field approximations of weakly coupled oscillator systems subjected to external forces. Using an H-theorem we show that transient probability densities converge to stationary ones. Furthermore, stability criteria are derived for the stationary solutions of these Fokker–Planck equations. The obtained results are applied to a model that combines the Haken–Kelso–Bunz model and the models of weakly coupled oscillators proposed by Winfree and Kuramoto. The stability criteria based on the H-theorem agree with those derived in our earlier analyses.     

Harnessing caustics for wave-front sensing

Scintillation in measured wave fronts adds spurious dislocations and deformations to their reconstruction. The source of the problem is caustics formed by aberrations in intermediate planes. I propose to use intentional caustics to measure wave fronts under severe conditions such as low light level, fast scale variations, large aberrations, and discontinuities in the wave front. A simple realization is based on the Hartmann-Shack sensor, which samples the wave front with a lenslet array. Movement of the lenslets' foci is linear with slope changes. Here the lenslets are effectively formed in an acousto-optic device: Two standing waves are launched perpendicularly to the light beam and to each other. At some distance down the beam, each wave creates a comb of caustics, and the two orthogonal combs add up to an array of caustic spots. The spatial frequency of the array is linear with the temporal frequency of the standing sound waves. A simple Fourier demodulation scheme supplies the two wave-front gradients.     

Some global dynamical properties of the Kuramoto-Sivashinsky equations: Nonlinear stability and attractors

The Kuramoto-Sivashinsky equations model pattern formations on unstable flame fronts and thin hydrodynamic films. They are characterized by the coexistence of coherent spatial structures with temporal chaos. We investigate some global dynamical properties, including nonlinear stability. We demonstrate their low modal behavior, in terms of determining modes; and that the fractal dimension of all attractors is bounded by a universal constant times $\text{≈L}{}^{\mathrm{<mtext>13</mtext><mtext>8</mtext>}}$, where ≈L is a dimensionless pattern cell size (in the one-dimensional case). Such equations are indeed a paradigm of low-dimensional behavior for infinite-dimensional systems.     

Single-shot measurement of temporal phase shifts by frequency-domain holography

Frequency-domain holography is used to measure ultrafast phase shifts induced either by the nonlinear susceptibility ?(3) of fused silica or by ionization fronts in air over a temporal region of 1 ps with 70-fs resolution in a single shot. The use of an imaging spectrometer adds one-dimensional spatial resolution to the single-shot temporal measurements.     

多块对接网格技术在电磁场散射问题中的应用

采用多块对接网格技术和时域有限体积法(FVTD)研究了典型目标和多体的电磁场散射问题.控制方程采用三维一般曲线坐标系下的时变麦克斯韦方程组.时间方向采用四步Runge-Kutta方法,空间离散采用基于通量雅可比矩阵特征结构的通矢量差分分裂,依赖变量采用MUSCL插值.时间方向的计算精度为2阶,空间方向的计算精度可达3阶.典型算例的雷达散射截面(RCS)的计算结果与理论解吻合很好.对于多体问题计算与文献结果相当一致,说明该算法具有对复杂拓扑结构外形(包括多体问题)进行数值模拟的能力.     

Ultrafast x-ray phase-contrast imaging of the initial coalescence phase of two water droplets

We report an ultrafast x-ray phase-contrast imaging study of the early merging dynamics of two water drops in air. Owing to the edge-enhancement capability, the high penetrability, and the unprecedented temporal and spatial resolutions offered by this new x-ray technique, the coalescence singularity of two water drops was revisited. A finite initial contact radius was identified and the evolvement of the trapped toroidal air bubble was studied for the first time. Despite the existence of this finite initial contact radius, the subsequent meniscus radius followed power laws which agree with theoretical predictions for the inviscid regime.     

Spatiotemporal self-organization in the oscillatory HCOOH oxidation on a Pt ribbon electrode – Theory and experiments

Since the current density near the edges of ribbon and disk electrodes is enhanced, the resulting stationary and non-stationary double layer potential is generally inhomogeneous in all electrochemical reactions. We investigate the impact of this edge effect induced spatial inhomogeneity on the pattern formation of the oscillatory formic acid oxidation on thin Pt ribbon electrodes. In order to be able to theoretically describe the spatiotemporal behavior of the double layer potential distribution, we derive and discuss the properties of the electrochemical ribbon coupling function for various distances of the reference electrode. The resulting reaction–migration equation is analyzed in connection with a chemical model accounting for the specific reaction mechanism of the formic acid oxidation. The interaction of structural inhomogeneity, chemically induced temporal instability and nonlocal spatial coupling due to ion migration gives rise to novel types of spatiotemporal behavior. The results compare favorably with experiments conducted so far, which are presented as well and can be explained within the framework of reaction–migration equations.     

Stroboscopic wave packet description of time-dependent currents through ring-shaped nanostructures

We present an implementation of a new method for explicit simulations of time-dependent electric currents through nanojunctions. The method is based on unitary propagation of stroboscopic wave packet states and is designed to treat open systems with fluctuating number of electrons while preserving full quantum coherence throughout the whole infinite system. We demonstrate the performance of the method on a model system consisting of a ring-shaped nanojunction with two semi-infinite tight-binding leads. Time-dependent electron current responses to abrupt bias turn-on or gate potential switching are computed for several ring configurations and ring-leads coupling parameters. The found current-carrying stationary states agree well with the predictions of the Landauer formula. As examples of genuinely time-dependent process we explore the presence of circulating currents in the rings in transient regimes and the effect of a time-dependent gate potential.     

Diffraction of high-intensity field in focal region as dynamics of nonlinear system with low-frequency dispersion

The stationary profile in the focal region of a focused nonlinear acoustic wave is described. Three models following from the Khokhlov-Zabolotskaya (KZ) equation with three independent variables are used: (i) the simplified one-dimensional Ostrovsky-Vakhnenko equation, (ii) the system of equations for paraxial series expansion of the acoustic field in powers of transverse coordinates, and (iii) the KZ equation reduced to two independent variables. The structure of the last equation is analogous to the Westervelt equation. Linearization through the Legendre transformation and reduction to the well-studied Euler-Tricomi equation is shown. At high intensities the stationary profiles are periodic sequences of arc sections having singularities of derivative in their matching points. The occurrence of arc profiles was pointed out by Makov. These appear in different nonlinear systems with low-frequency dispersion. Profiles containing discontinuities (shock fronts) change their form while passing through the focal region and are non-stationary waves. The numerical estimations of maximum pressure and intensity in the focus agree with computer calculations and experimental measurements.

     

Temporal behavior of evolutionary dynamics in finite dimensional population

We systematically study the temporal behavior of evolutionary dynamics in finite dimensional population based on evolutionary graph theory. Besides the spread of mutants, we also consider the spread of the impact of the initial mutant seed. The time-dependent behavior of these two spreading processes and their relationship are theoretically and computationally investigated. The ingredients and scaling behaviors of the interface between mutants and wild-type individuals are analyzed in detail, which have significant impact on temporal behavior of evolutionary dynamics. Since the evolutionary systems in nature are generally local and spatial, this research provides further understanding of temporal behavior in evolutionary dynamics at the theoretical level.     

Two-dimensional front dynamics and spatial solitons in a nonlinear optical system

Two-dimensional fronts and coarsening dynamics with a t{1/2} power law are analyzed experimentally and theoretically in a nonlinear optical system of a sodium vapor cell with single-mirror feedback. Modifications of the t{1/2} power law are observed in the vicinity of a modulational instability leading to the formation of spatial solitons of different sizes. The experimental and numerical observations give direct evidence for the locking of fronts as the mechanism of soliton formation. A phenomenological equation for the dynamics of the domain radius explains the observed behavior.     

Quantum theory of the laser cooling of two-level atoms in the field of a standing light wave: A statistical description of dynamics

The time required for establishing a stationary distribution of two-level atoms in the field of a onedimensional standing light wave is studied with full allowance for recoil effects and spatial trapping. The dependences of the cooling time on the problem parameters are obtained, and their considerable deviance from semiclassical predictions is demonstrated.     

Structures of Strong Shock Waves in Dense Plasmas

Structures of strong shock waves in dense plasmas are investigated via the steady-state Navier-Stokes equations and Poisson equation. The structures from nuid simulation agree with the ones from kinetic simulation. The effects of the transport coeffcients on the structures are analysed. The enhancements of the electronic heat conduction and ionic viscosity both will broaden the width of the shock fronts, and decrease the electric fields in the fronts.     

中心对称双光子光折变低振幅灰孤子时间特性

为了得到中心对称双光子光折变晶体中低振幅灰空间孤子时间特性的结果,基于中心对称光折变晶体中双光子光折变效应的理论模型,推导出了含时间参量的空间电荷场和光波动态演化方程.采用数值方法,得到了低振幅灰孤子强度包络和强度半峰全宽的时间演化特性.结果表明:初始阶段形成宽度较宽的孤子,其宽度随时间单调递减到一个最小值直至稳态孤子的形成;在相同的演化时间内,孤子半峰全宽随着孤子峰值强度与暗辐射比值的增大而变小.研究了不同时间下低振幅灰孤子动态演化特性.     

基于时空双流卷积神经网络的红外行为识别

针对红外视频人体行为识别问题,提出了一种基于时空双流卷积神经网络的红外人体行为识别方法。通过将整个红外视频进行平均分段,然后将每一段视频中随机抽取的红外图像和对应的光流图像输入空间卷积神经网络,空间卷积神经网络通过融合光流信息可以有效地学习到红外图像中真正发生运动的空间信息,再将每一小段的识别结果进行融合得到空间网络结果。同时将每一段视频中随机抽取的光流图像序列输入时间卷积神经网络,融合每一小段的结果后得到时间网络结果。最后再将空间网络结果和时间网络结果进行加权求和,从而得到最终的视频分类结果。实验中,采用此方法对包含23种红外行为动作类别的红外视频数据集上的动作进行识别,正确识别率为92.0%。结果表明,该算法可以有效地对红外视频行为进行准确识别。