Obstacle Effects on One-Dimensional Translocation of ATPase

We apply a general random walk model to the study of the ATPase‘s one-dimensional translocation along obstacle biological environment, and show the effects of random obstacles on the ATPase translocation along single stranded DNA. We find that the obstacle environment can reduce the lifetime of ATPase lattice-bound state which results in the inhibition of ATPase activity. We also carry out the ranges of rate constant of ATPase unidirectonal translocation and bidirectional translocation. Our results are consistent with the experiments and relevant theoretical consideration, and can be used to explain some physiological phenomena.     

Translocation of knotted proteins through a pore

We report the results of molecular dynamics simulations of translocation of knotted proteins through pores. The protein is pulled into the pore with a constant force, which in many cases leads to the tightening of the knot. Since the radius of tightened knot is larger than that of the pore opening, the tight knot can block the pore thus preventing further translocation of the chain. Analyzing six different proteins, we show that the stuck probability increases with the applied force and that final positions of the tightened knot along the protein backbone are not random but are usually associated with sharp turns in the polypeptide chain. The combined effect of the confining geometry of the pore and the inhomogeneous character of the protein chain leads thus to the appearance of topological traps, which can immobilize the knot and lead to the jamming of the pore.     

一种复杂环境下移动机器人避障新方法

基于传统人工势场法的机器人避障算法虽然计算量小、实时性好,但在陷阱区域或在障碍物前可能产生震荡,导致机器人不能到达目标点,为解决上述缺陷,提出一种带记忆功能的沿边法。通过记录和分析障碍物边缘人工势场法的局部最小点来判断目标点是否被障碍物包围,从而避免机器人来回震荡和围着目标点旋转的发生。该方法步骤分为沿边行为激活和退出条件、局部最小点记录条件以及目标点被障碍物包围的判断准则。通过实验,结果表明该方法解决了复杂环境下机器人的避障问题。该方法用于复杂环境下的机器人避障是可行的、有效的。     

基于激光雷达的多旋翼飞行器实时避障系统

针对多旋翼飞行器的障碍物规避问题,提出一种基于激光雷达的自主飞行多旋翼飞行器避障系统,实现多旋翼飞行器自主飞行的实时避障;该避障系统针对静态、低速运动障碍物,综合飞行器本体姿态、速度、加速度等状态信息,建立基于改进势场法的避障模型和算法;在机器人操作系统(ROS,Robot Operating System)平台进行该避障系统的软件实现,其通过串口与飞控进行通信,完成多旋翼飞行器的自主避障飞行;同时,为了使该系统能在强光环境正常工作,在不影响系统实时性的前提下,对激光雷达的干扰问题进行优化设计;大量实验表明:该避障算法计算量小,能够保证避障系统的实时性,在机体慢速以及低速运动(机体与障碍物之间的相对运动速度小于等于3 m/s)的场景中能够正确检测范围6 m内,并迅速规避障碍物。     

Continuity and Anomalous Fluctuations in Random Walks in Dynamic Random Environments: Numerics,Phase Diagrams and Conjectures

We perform simulations for one dimensional continuous-time random walks in two dynamic random environments with fast (independent spin-flips) and slow (simple symmetric exclusion) decay of space-time correlations, respectively. We focus on the asymptotic speeds and the scaling limits of such random walks. We observe different behaviors depending on the dynamics of the underlying random environment and the ratio between the jump rate of the random walk and the one of the environment. We compare our data with well known results for static random environment. We observe that the non-diffusive regime known so far only for the static case can occur in the dynamical setup too. Such anomalous fluctuations give rise to a new phase diagram. Further we discuss possible consequences for more general static and dynamic random environments.     

Geodesics of Random Riemannian Metrics

We analyze the disordered Riemannian geometry resulting from random perturbations of the Euclidean metric. We focus on geodesics, the paths traced out by a particle traveling in this quenched random environment. By taking the point of the view of the particle, we show that the law of its observed environment is absolutely continuous with respect to the law of the random metric, and we provide an explicit form for its Radon–Nikodym derivative. We use this result to prove a “local Markov property” along an unbounded geodesic, demonstrating that it eventually encounters any type of geometric phenomenon. We also develop in this paper some general results on conditional Gaussian measures. Our Main Theorem states that a geodesic chosen with random initial conditions (chosen independently of the metric) is almost surely not minimizing. To demonstrate this, we show that a minimizing geodesic is guaranteed to eventually pass over a certain “bump surface,” which locally has constant positive curvature. By using Jacobi fields, we show that this is sufficient to destabilize the minimizing property.     

Variational Formulas and Cocycle solutions for Directed Polymer and Percolation Models

We discuss variational formulas for the law of large numbers limits of certain models of motion in a random medium: namely, the limiting time constant for last-passage percolation and the limiting free energy for directed polymers. The results are valid for models in arbitrary dimension, steps of the admissible paths can be general, the environment process is ergodic under spatial translations, and the potential accumulated along a path can depend on the environment and the next step of the path. The variational formulas come in two types: one minimizes over gradient-like cocycles, and another one maximizes over invariant measures on the space of environments and paths. Minimizing cocycles can be obtained from Busemann functions when these can be proved to exist. The results are illustrated through 1+1 dimensional exactly solvable examples, periodic examples, and polymers in weak disorder.     

角向偏振无衍射光束的传输特性及其偏振态研究

从理论和实验两个方面研究角向偏振无衍射光束在自由空间和障碍物空间中的传输特性. 理论上模拟了角向偏振无衍射光束在自由空间以及障碍物空间传播过程中的光强分布与偏振态变化情况. 实验中利用高斯光束先通过偏振转换仪, 再入射到轴棱锥上产生角向偏振无衍射光束. 进而研究其在空间中的传输情况, 并通过分析其经过扇形障碍物后光强分布变化情况讨论障碍物对偏振态的影响和光束的自重建特性. 结果表明: 障碍物遮挡区域光强沿z轴方向逐渐恢复, 且阴影区域沿障碍物所在位置的相反方向移动; 光束的偏振态局部发生变化, 该变化与障碍物所在位置有关. 理论仿真和实验结果一致.     

Scattering by an E plane dielectric sheet in rectangular waveguide

A method for the computation of S-parameters associated with a rectangular waveguide with a rectangular dielectric obstacle is presented. The method uses the Method of Lines and discretization of the dielectric permittivity to treat the dielectric discontinuity along the discretization direction. In this way, the Method of Lines can be applied to analyze waveguide discontinuity with dielectric inhomogenousity along the discretization direction. The numerical results have been verified by both theoretical and experimental results.     

存在障碍物时电波传播抛物线方程分析及其验证

双向抛物线方法主要用于起伏地形下电波传播问题的计算,该算法本身无法处理地面存在障碍物,尤其是真实环境下障碍物与地面为不同媒质的情况.因此本文提出一种用于存在障碍物时电波传播计算的抛物线方程新算法.该方法采用区域分解,对不同障碍物区域的场值进行分区计算,并对计算结果进行相位修正,从而实现该情况下空间中场值的计算.在此基础上,使用矩量法来精确验证抛物线方法的计算精度.通过实例分析,证明了存在障碍物时新算法的精确性,为之后求解真实环境下的电波传播问题提供了参考.     

General Random Walk in One Dimension and Its Application to DNA Transcription Process

We have derived a two-order difference equation about the general random walk in one dimension. Using this model in some physiological processes, we have calculated the average time in which enzyme released at random anywhere moves along a one-dimensional macromolecular strand to the end in quest of its binding site. From the results we can see that the average time can be affected greatly owing to the presence of "obstacles" on the macromolecular strand.     

Reptational dynamics of a polymer chain is stable against kinematic disorder

We study the diffusive motion of a (non-selfinteracting) chain through a quenched random environment, constructed such that it influences only the local dynamics but not the equilibrium configuration of the chain. Our Monte Carlo results show that this type of disorder, which we call kinematic, does not ruin reptation. This is in sharp contrast to disorder including also entropic traps and it supports the view that reptation prevails in melts, where in contrast to a gel entropic trapping is absent. Our data show the characteristic features of reptation, irrespective of the dilution or randomness of the kinematic obstacles. Our Monte Carlo results are in quantitative agreement with our recent detailed analytical evaluation of the reptation model (J. Stat. Phys. 90, 1325 (1998)). The analysis suggests that we effectively see reptation of a “blob”-chain, where the size of the blob rapidly increases with decreasing obstacle concentration. Received 30 November 1998 and Received in final form 18 December 1998     

基于人工免疫改进的搬运机器人蚁群路径规划

针对搬运机器人在障碍环境下的路径寻优问题,提出一种基于人工免疫改进的蚁群路径规划算法(AI-ACA)。蚁群算法(ACA)的规划依赖于信息素挥发系数、期望启发因子和信息启发因子等参数的选取,传统ACA通过经验来设定这三个参数,但路径寻优中的最优参数因障碍环境而异,为解决经验参数对不同环境路径寻优结果的影响,引入人工免疫算法(AIA),对ACA的相关参数进行迭代优化,以此改善路径寻优结果。仿真结果及在自制机器人平台上测试表明,AI-ACA对于不同障碍环境可以准确地进行路径规划,在同样环境下较所参考的定参数蚁群路径规划效果有明显提升,提高了整个系统的运输效率。     

基于超声干涉测量的光声断层成像方法性能优化*

生物组织声学参数的不均匀性是光声断层成像技术面临的棘手问题,基于超声干涉测量的光声断层成像方法已被初步证明可以适用于声参数不均匀情形,但对如何取得最佳成像效果缺少深入研究。针对这一问题,该文将基于超声干涉测量的光声断层成像方法应用于同时含有声速不均匀和随机声散射现象的复杂成像媒质模型,并对如何优化成像效果开展相关研究。该文首先验证了该方法在数值模型中的有效性,随后针对相关测量参数与成像质量之间的关系开展定量研究,提出了优化成像效果的方法。结果表明,设计适合的波形滤波器、合理选择干涉测量过程中超声信号的中心频率均可优化成像效果,该文的相关研究结果可为进一步拓展基于超声干涉测量的光声断层成像的应用范围提供参考。     

Transmission problems in contrasting chiral media

Time harmonic electromagnetic waves are scattered by a homogeneous chiral obstacle embedded in a homogeneous chiral environment. The corresponding transmission problem is reduced, with the use of Beltrami fields, to an integral equation over the interface between the obstacle and the surrounding medium. This integral equation is known to be weakly uniquely solvable except for a discrete set of electromagnetic parameters of the obstacle. We establish classical solvability, and in some interesting cases (mirror conjugated and isoimpedant chiral media) it is shown that unique solvability is established without the exception of any set of electromagnetic parameters.     

Optimal transport in a ratchet coupled to a modulated environment: The role of Levy walks

We consider a Brownian particle in a ratchet potential coupled to a modulated environment and subjected to an external oscillating force. The modulated environment is modelled by a finite number N of uncoupled harmonic oscillators. Superdiffusive motion and Levy walks (anomalous random walks) are observed for any N and for low values of the external amplitude F. The coexistence of left and right running states enhances the power α from the time dependence of the mean square displacement (MSD). It is shown that α is twice the average of the power of the separated left and right MSDs. Normal random walks are obtained by increasing F. We show that the maximal mobility of particles along the periodic structure occurs just before superdiffusive motion disappears and Levy walks are transformed into normal random walks.     

基于T-S模糊神经网络的智能轮椅避障控制策略

在复杂的环境中,智能轮椅的自主避障是安全的保证。本文提出基于超声波和激光传感器的环境深度分区算法,和T-S模糊神经网路的信息融合方法,实现避障策略。提高了智能轮椅控制系统的实时性和安全性,实现避障控制的高效性。     

适用于实时避障的新型智能化机器人敏感皮肤的研究

在未知环境中,实时避障是实现智能化机器人自主工作的关键技术。敏感的皮肤可以使智能机器人具有环境感知和实时决策的能力。研制的敏感皮肤南模块化和带有强数据处理能力的微型红外传感器阵列构成,可以粘贴在机器人表面,依赖于皮肤上的红外传感器来感知外部环境。系统采用了几何光学模型法来测量敏感皮肤与障碍物间的距离。实验结果表明,在感知区域内,敏感皮肤能够实时准确地给出多关节机器人周围的障碍物存在和距离信息,为解决机器人避障问题提供新的范例。同时敏感皮肤的研制也是机器人在传感和控制领域中应用的一次尝试,对促进机器人和各相关科学的发展及提高机器人智能化的水平具有深远的意义,并将有着广阔的应用前景。     

Modeling of high-frequency propagation in inhomogeneous background random media

When a high-frequency electromagnetic wave propagates in a complicated scattering environment, the contribution at the observer is usually composed of a number of field species arriving along different ray trajectories. In order to describe each contribution separately the parabolic extension along an isolated ray trajectory in an inhomogeneous background medium was performed. This leads to the parabolic wave equation along a deterministic ray trajectory in a randomly perturbed medium with the possibility of presenting the solution of the high-frequency field and the higher-order coherence functions in the functional path-integral form. It is shown that uncertainty considerations play an important role in relating the path-integral solutions to the approximate asymptotic solutions. The solutions for the high-frequency propagators derived in this work preserve the random information accumulated along the propagation path and therefore can be applied to the analysis of double-passage effects where the correlation between the forward-backward propagating fields has to be accounted for. This results in double-passage algorithms, which have been applied to analyze the resolution of two point scatterers. Under strong scattering conditions, the backscattering effects cannot be neglected and the ray trajectories cannot be treated separately. The final part is devoted to the generalized parabolic extension method applied to the scalar Helmholtz's equation, and possible approximations for obtaining numerically manageable solutions in the presence of random media.     

Random walks on sparsely periodic and random lattices: I. Random walk properties from lattice bond enumeration

We have developed a new technique for calculating certain asymptotic random walk properties on sparsely periodic and related random lattices in two and three dimensions. This technique is based on an ansatz which relates the number of lattice bonds in “irreducible lattice fragments” to the number of steps along these bonds. We show that certain random walk properties can be calculated very simply on the basis of this ansatz and that they depend only on the density of bonds and not on the arrangement of the bonds within the lattice. The random walk properties calculated here (mean square displacements, number of distinct sites visited, probability of return to the origin) are in complete agreement with results obtained earlier via generating function techniques. A subsequent paper contains generating function calculations which verify a number of new results presented here, such as mean occupation frequency of lattice sites, and a proof of our basic assumption on the relation between the number of lattice bonds and random walk steps.