Three-dimensional electromagnetic particle-in-cell with Monte Carlo collision simulations on three MIMD parallel computers

A three-dimensional electromagnetic particle-in-cell code with Monte Carlo collision (PIC-MCC) is developed for MIMD parallel supercomputers. This code uses a standard relativistic leapfrog scheme incorporating Monte Carlo calculations to push plasma particles and to include collisional effects on particle orbits. A local finite-difference time-domain method is used to update the self-consistent electromagnetic fields. The code is implemented using the General Concurrent PIC (GCPIC) algorithm, which uses domain decomposition to divide the computation among the processors. Particles must be exchanged between processors as they move among subdomains. Message passing is implemented using the Express Cubix library and the PVM. We evaluate the performance of this code using a 512-processor Intel Touchstone Delta, a 512-processor Intel Paragon, and a 256-processor CRAY T3D. It is shown that a high parallel efficiency exceeding 95% has been achieved on all three machines for large problems. We have run PIC-MCC simulations using several hundred million particles with several million collisions per time step. For these large-scale simulations the particle push time achieved is in the range of 90–115 ns/particle/time step, and the collision calculation time in the range of a few hundred nanoseconds per collision.     

A one-point quadrature eight-node brick element with hourglass control

An efficient and accurate eight-node brick element is developed for linear static and dynamic structural analyses. In the element formulation, one-point quadrature is used so that computational time is substantially reduced without adversely effecting the accuracy. Hourglass control is provided to suppress spurious modes, and the stabilization parameters which must be specified by users in many other one-point quadrature elements are not required. An effective procedure to eliminate volumetric and shear locking is also developed. Several examples are presented to demonstrate the performance of this element.     

A one-point integration quadrilateral with hourglass control in axisymmetric geometry

A one-point integration scheme which analytically integrates element volume and uniform strain modes for general isoparametric quadrilateral in axisymmetric geometry is described. A method for isolating proper hourglass modes is presented. It is shown that these modes rather differ from hourglass modes in plane Cartesian geometry, especially near the axis of symmetry. A simple elastic and viscous hourglass control scheme is presented and discussed. Bounds on the quadrilateral eigenvalues that provide stable time steps for explicit time integration algorithms are obtained considering isotropic hypoelastic material. Numerical examples demonstrate the effectiveness of the developed technique for finite element code.     

Least squares stabilization for one-point integration

A simple one-point stabilization method is presented. It relies on the addition of a small least squares contribution to the element energy norm.     

CSMA with collision avoidance

Advances in local area networking have allowed users to run many different applications on one system. Users are now asking for greater access, more functions, more power and greater reliability. This requires that the system tasks should be distributed, and means that the interconnection system used should be highly reliable; ‘passive’, so that no failed component can bring the entire system down; support high through-put; and operate on low-cost cable. This paper describes a broadband transmission system based on a single, passive coaxial cable which detects possible collisions before the data is sent. Examples of two remote stations and two adjacent stations competing for transmission are given, along with performance comparisons of CSMA/CD and CSMA/CA.     

Schema theory for genetic programming with one-point crossover and point mutation

We review the main results obtained in the theory of schemata in genetic programming (GP), emphasizing their strengths and weaknesses. Then we propose a new, simpler definition of the concept of schema for GP, which is closer to the original concept of schema in genetic algorithms (GAs). Along with a new form of crossover, one-point crossover, and point mutation, this concept of schema has been used to derive an improved schema theorem for GP that describes the propagation of schemata from one generation to the next. We discuss this result and show that our schema theorem is the natural counterpart for GP of the schema theorem for GAs, to which it asymptotically converges.     

Isoparametric linear bending element and one-point integration

An isoparametric linear plate bending element is introduced and its use for the analysis of beams, square and rhombic plates is examined. One-point integration for the generation of an element stiffness matrix has been carried out. When compared with available solutions, the agreement of the results have been excellent. Isoparamctric linear elements have been found to be more economical than isoparametric quadratic elements at least for beams and plates with straight edges.     

Brachistochrone with friction

The brachistochrone problem is solved under the action of dry and viscous friction. For this purpose, this problem is represented as a problem of choosing a time optimal normal component (control) of the reaction of the support curve, whose shape is to be found. The Okhotsimsky-Pontryagin method of investigation of the functional differential is applied. Necessary optimality conditions that give the solution of the classical brachistochrone problem without friction and provide the corresponding optimal curves with friction are found. Parametric formulas for brachistochrones under the action of dry and viscous frictions are found analytically. Their properties are investigated. Attainability domains are determined. For certain values of the friction coefficients, the results of calculations are presented, which show the shape of the found brachistochrones and the optimal motion time.     

Guaranteed collision detection with toleranced motions

We present a method for guaranteed collision detection with toleranced motions. The basic idea is to consider the motion as a curve in the 12-dimensional space of affine displacements, endowed with an object-oriented Euclidean metric, and cover it with balls. The associated orbits of points, lines, planes and polygons have particularly simple shapes that lend themselves well to exact and fast collision queries. We present formulas for elementary collision tests with these orbit shapes and we suggest an algorithm, based on motion subdivision and computation of bounding balls, that can give a no-collision guarantee. It allows a robust and efficient implementation and parallelization. At hand of several examples we explore the asymptotic behavior of the algorithm and compare different implementation strategies.     

Spacecraft formation reconfiguration with collision avoidance

In this paper we present a behavioral control solution for reconfiguration of a spacecraft formation using the Null-Space Based (NSB) concept. The solution is task based, and aims to reconfigure and maintain a rigid formation while avoiding collisions between spacecraft. A model of relative translation is derived, together with a passivity-based sliding surface controller which globally stabilizes the equilibrium point of the closed-loop system. The NSB control method is implemented by giving each task different priorities and then calculating desired velocity and a Jacobian matrix for each spacecraft and each task. The velocity vector for each task is then projected into the null-space for higher prioritized tasks to remove conflicting velocity components. Simulation results are presented, showing that each spacecraft moves into the predefined formation without breaking any rules for the higher priority tasks, and all collisions are avoided.     

A construction of one-point bases in extended lambda calculi

We present a general schema for constructing infinitely-many one-point bases for -calculi extended by finitely-many constants. The constants are usually present in programming languages, and may involve reduction rules other than β-reduction. The construction can be implemented in a functional subset of LISP/Scheme, giving one-point bases for applicative-order calculi extended by constants from the underlying programming language.     

Efficient emulation of single-hop radio network with collision detection on multi-hop radio network with no collision detection

Summary This paper presents an efficient randomized emulation ofsingle-hop radio networkwith collision detection onmulti-hop radio networkwithout collision detection. Each step of the single-hop network is emulated by rounds of the multi-hop network and succeeds with probability 1–. (n is the number of processors,D the diameter and the maximum degree). It is shown how to emulate any polynomial algorithm such that the probability of failure remains . A consequence of the emulation is an efficient randomized algorithm for choosing a leader in a multi-hop network. Reuven Bar-Yehuda was born in Iran, on July 17th 1951. Received B.A., M.Sc., and D.Sc. in Computer Science from the Technion — Israel Institute of Technology, Haifa, Israel, in 1978, 1980, and 1983, respectively. He is currently a Senior Lecturer of Computer Science at the Technion. From 1984 to 1986, he was a visiting assistant professor in the Computer Science Dept. at the Duke Univesity His research interests include computational geometry, VLSI, graph algorithms and distributed algorithms. Oded Goldreich was born in Tel-Aviv, Israel, on February 4th 1957. Received B.A., M.Sc., and D.Sc. in Computer Science from the Technion — Israel Institute of Technology, Haifa, Israel, in 1980, 1982, and 1983, respectively. He is currently an Associate Professor of Computer Science at the Technion. From 1983 to 1986, he was a postdoctoral fellow at MIT's Laboratory for Computer Science. His research interests include cryptography and related areas, relation between randomness and algorithms, and distributed computation. Alon Itai was born in Scotland, on December 12th 1946. Received B.Sc. in Mathematics from the Hebrew University in Jerusalem in 1969. M.Sc., and Ph.D. in Computer Science from the Weizmann Institute of Science, Rehovot, Israel in 1971 and 1976. He is currently an Associate Professor of Computer Science at the Technion. His research interests include randomized and distributed algorithms, computational learning theory and performance evaluation.The second author was partially supported by grant No. 86-00301 from the United States—Israel Bi-national Science Foundation BSF), Jerusalem, Israel.     

Elastic bar transfer functions determination using one-point strain measurements

Measurements of impulsive forces and pressures by means of the elastic bar require that the effect of waves’ dispersion in the bar on the sensor's output signal be corrected. The correction problem can be solved using deconvolution techniques. For this purpose it is necessary to determine the elastic bar's transfer functions. In this paper, an experimental method of determining the elastic bar's transfer functions in form of formulas is described, which can be used to reconstruct the input waveform. The method is based on: one-point measurement of the elastic strain waves propagating inside the bar, the spectral analysis of these waves and making use of the general solution of the equation of movement of the bar in the frequency domain. The determined transfer functions of the bar are used for impulsive strain waveform reconstruction by means of deconvolution in the frequency domain, and for the validity check of the reconstruction. The application of this method to the reconstruction of impulsive force waveforms generated by the mechanical impact of bodies is presented.     

Tight bounds on the complexity index of one-point iterations

We study the minimal complexity index of one-point iterations without memory for the solution of a system of N nonlinear equations F(x)=0. We present an iteration ^* with maximal order of convergence and with linear combinatory complexity. We show the complexity index of ^* is close to the lower bound on the minimal complexity index.     

Privacy-preserving distributed projected one-point bandit online optimization over directed graphs

The distributed online optimization (DOO) problem with privacy-preserving properties over multiple agents is considered in this paper, where the network model is built by a strongly connected directed graph. To solve this problem, a stochastic bandit DOO algorithm based on differential privacy is proposed. This algorithm uses row- and column-stochastic matrix as the weighting matrices, the requirement of the double random weighting matrix is released. To handle the unknown objective function, the one-point bandit is used to estimate the true gradient information, and the estimated gradient information is used to update of decision variables. Different from the existing DOO algorithms that ignore privacy issues, this algorithm successfully protects the privacy of nodes through a differential privacy policy. Theoretical results show that the algorithm can not only achieve sublinear regret bounds but also protect the privacy of nodes. Finally, simulation results verify the effectiveness of the algorithm.     

Genetic programming with one-point crossover and subtree mutation for effective problem solving and bloat control

Genetic programming (GP) is one of the most widely used paradigms of evolutionary computation due to its ability to automatically synthesize computer programs and mathematical expressions. However, because GP uses a variable length representation, the individuals within the evolving population tend to grow rapidly without a corresponding return in fitness improvement, a phenomenon known as bloat. In this paper, we present a simple bloat control strategy for standard tree-based GP that achieves a one order of magnitude reduction in bloat when compared with standard GP on benchmark tests, and practically eliminates bloat on two real-world problems. Our proposal is to substitute standard subtree crossover with the one-point crossover (OPX) developed by Poli and Langdon (Second online world conference on soft computing in engineering design and manufacturing, Springer, Berlin (1997)), while maintaining all other GP aspects standard, particularly subtree mutation. OPX was proposed for theoretical purposes related to GP schema theorems, however since it curtails exploration during the search it has never achieved widespread use. In our results, on the other hand, we are able to show that OPX can indeed perform an effective search if it is coupled with subtree mutation, thus combining the bloat control capabilities of OPX with the exploration provided by standard mutation.     

降低相似度碰撞的证据融合方法

针对相似度碰撞引发证据融合结果错误的问题,提出一种新的证据融合方法。首先,提取证据的焦元序列特征并将其转化为排序矩阵以弥补证据相似度易碰撞的不足;其次,联合证据的排序矩阵和信息熵完成对证据权重的确定;最后,生成归一化证据（MAE）并使用Dempster融合公式将MAE融合n-1次获得最终的结果。基于在线的鸢尾花数据集对证据平均融合方法、余弦相似度证据融合方法、证据距离融合方法和证据信誉度融合方法进行了花类型识别准确性的F-Score对比,上述四种方法的F-Score分别为0.84、0.88、0.88和0.88,而所提方法的F-Score为0.91。实验结果表明,所提方法的决策准确率更高,融合结果更加可靠,能为证据决策提供了有效的解决方案。     

An integrated friction model structure with improved preslidingbehavior for accurate friction compensation

Presents a dynamical friction model structure which allows accurate modeling both in the sliding and the presliding regimes. Transition between these two regimes is accomplished without a switching function. The model incorporates a hysteresis function with nonlocal memory and arbitrary transition curves. These last aspects prove essential for modeling presliding friction that is encountered in real physical situations. The model as a whole can also handle the Stribeck effect and stick-slip behavior as has been demonstrated by validation on a KUKA IR 361 robot. In this sense, this model can be considered as more complete in comparison with others found in the literature. The general friction model allows modeling of individual friction systems through the identification of a set of parameters that determine the complete behavior of the system. In this way, the model structure has been used to identify the friction behavior of a linear slide as well as that of the above mentioned KUKA robot. The results of the latter identification have been consequently used for feedforward friction compensation to obtain the most accurate tracking     

Design,tuning, and evaluation of a full-range adaptive cruise control system with collision avoidance

This paper describes the design, tuning, and evaluation of a full-range adaptive cruise control (ACC) system with collision avoidance (CA). The control scheme is designed to improve drivers’ comfort during normal, safe-driving situations and to completely avoid rear-end collision in vehicle-following situations. Driving situations are divided into safe, warning, and dangerous modes. Three different control strategies have been proposed, depending on the driving situation. The driving situations are determined using a non-dimensional warning index and the time-to-collision (TTC). The control parameters of the proposed ACC/CA system are tuned by a confusion-matrix method using manual-driving data in no-crashing driving situations. The vehicle-following characteristics of the subject vehicle were compared to real-world, manual-driving data. Finally, the ACC/CA system was also implemented in a real vehicle and tested in both safe-traffic and severe-braking situations. It is shown that the proposed control strategy can provide natural following performance that is similar to human manual-driving in both high-speed driving and low-speed stop-and-go situations. Furthermore, it can prevent the vehicle-to-vehicle distance from dropping to an unsafe level in a variety of driving conditions.