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Showing papers in "Computers in Physics in 1990"


Journal ArticleDOI

17,845 citations



Journal ArticleDOI
TL;DR: A method for titling negative or positive photographic film with a minimum of film base embossing comprising the steps of:
Abstract: A method for titling negative or positive photographic film with a minimum of film base embossing comprising the steps of:

122 citations


Journal ArticleDOI
TL;DR: A steering column for absorbing impact energy comprising a steering shaft mounted for rotation in a vehicle by an upper bearing which collapses under a predetermined load if the vehicle is impacted so that the steering wheel remains in position and so that impact energy is absorbed.
Abstract: A steering column for absorbing impact energy comprising a steering shaft mounted for rotation in a vehicle by an upper bearing. The steering shaft can be turned by a steering wheel operatively connected to the upper end of the shaft by first energy absorbing device which deforms in a controlled manner when impacted. The steering shaft also has an integral helical portion between the upper and lower ends which collapses under a predetermined load if the vehicle is impacted so that the steering wheel remains in position and so that impact energy is absorbed.

87 citations







Journal ArticleDOI
TL;DR: In this article, large two-dimensional lattices of interacting magnetic dipoles representing thin films of amorphous rare earth transition metal alloys were studied on the Connection Machine, and the accuracy of the results was established by comparing the simulated dynamics of isolated Bloch walls with theoretical predictions.
Abstract: Large two‐dimensional lattices of interacting magnetic dipoles representing thin films of amorphous rare‐earth–transition‐metal alloys are studied on the Connection Machine. The accuracy of the results is established by comparing the simulated dynamics of isolated Bloch walls with theoretical predictions. The effects of random axis anisotropy on the process of magnetization reversal are then investigated, and the nucleation and growth of reverse‐magnetized domains are found to be the mechanism of reversal. The obtained hysteresis loops have very high squareness, and sample coercivities are well within the range of experimental values.

27 citations



Journal ArticleDOI
TL;DR: It is shown that a single past analog can predict a dripping faucet with reasonable accuracy 7-10 drops ahead, which aids in understanding how fluid flow may be predicted even under conditions of unstable flows caused by increase in velocity.
Abstract: An experiment was conducted which showed that a leaky faucet can offer valuable insights on predicting fluid flow. In this experiment, a flow control and drop detector were connected to the printer port of an IBM PC, which computed and saved the time intervals using a program for droptime compiled with Turbo C. It is noted that the time intervals change from periodic to doubly periodic as the flow rate is increased and then to various forms of chaos, interrupted by windows of periodicity. A number of two- and three-dimensional plots are displayed and discussed. Attention is focused on one of the simpler plots which is approximately parabolic, where each successive time interval is a quadratic function of the preceding interval, with a steepness which depends upon the flow rate. It is shown that a single past analog can predict a dripping faucet with reasonable accuracy 7-10 drops ahead. While such methods are more difficult to apply in higher-dimensional systems, this experiment aids in understanding how fluid flow may be predicted even under conditions of unstable flows caused by increase in velocity.

Journal ArticleDOI
TL;DR: A new, nonparametric integer‐arithmetic noninterpolating algorithm (NI0) and an extension using first‐order interpolation (NI1) are presented here and are compared for accuracy and speed with both Siddon's parametric floating point algorithm and the authors' extension.
Abstract: Integrals along lines passing through arrays of integer data are used in many applications. Existing algorithms employ parametric methods and floating point calculations to determine the data values that contribute to the line integrals, along with some form of interpolation to weight these data values. A new, nonparametric integer‐arithmetic noninterpolating algorithm (NI0) and an extension using first‐order interpolation (NI1) are presented here. These algorithms are compared for accuracy and speed with both Siddon’s [Med. Phys. 1 2, 252 (1985)] parametric floating point algorithm using no interpolation (PF0) and our extension using first‐order interpolation (PF1). NI1 gives line integral values significantly closer to those of PF1 than does PF0 and runs nine times faster on a VAXstation 2000. NI0 gives less accurate line integral values than does PF0 but runs 19 times faster.



Journal ArticleDOI
TL;DR: In this article, a transfer matrix approach to deal with the problems of electrons in a periodic potential in one dimension is presented, and a nonlinear recursive formula for the transmission coefficient is derived and used to study the band structure of crystals.
Abstract: A transfer matrix approach to deal with the problems of electrons in a periodic potential in one dimension is presented. A nonlinear recursive formula for the transmission coefficient is derived and used to study the band structure of crystals. The present method is shown to be more powerful than the well‐known Kronig–Penney model.

Journal ArticleDOI
TL;DR: It is demonstrated that especially for short data sequences the ME method is capable of delivering superior spectral estimates, and how it works and why the ME estimation produces such unexpectedly good results is discussed.
Abstract: For spectrum estimation of stationary time series the method of maximum entropy (ME) is compared to the method using fast Fourier transforms (FFT). As the maximum entropy method is highly nonlinear such a comparison is done on the basis of a simulation. The ME method is introduced and it is demonstrated that especially for short data sequences the ME method is capable of delivering superior spectral estimates. How the ME method works and why the ME estimation produces such unexpectedly good results is discussed. Further, the influence of a digitizing signal acquisition apparatus, of additive white noise, and of the initial phase on the variability of the estimated spectra are investigated. Fitting an autoregressive process to the time signal is equivalent to the ME procedure. An autoregressive fit code is presented.

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional numerical model with a twisted topology, sometimes a Klein bottle, is shown as well as the fact that local properties of the model are not dependent on topology.
Abstract: Numerical simulations with periodic boundary conditions are widely used in cosmology. These have a multiply connected topology known as a three-torus. Such nontrivial topologies for the actual universe may have arisen in the Big Bang. A two-dimensional numerical model with a twisted topology, sometimes a Klein bottle, is shown as well as the fact that local properties of the model are not dependent on topology.

Journal ArticleDOI
TL;DR: This paper shows how to use the symbol manipulator MACSYMA to do arbitrarily long calculations and how to translate the typically lengthy results into FORTRAN so that they can be tested, appreciated, and used.
Abstract: This paper shows how to use the symbol manipulator MACSYMA to do arbitrarily long calculations and how to translate the typically lengthy results into FORTRAN so that they can be tested, appreciated, and used. This procedure is illustrated by its application to the task of writing the code for a noncompact lattice simulation of a nonabelian gauge theory.


Journal ArticleDOI
TL;DR: In this paper, an efficient method of calculating spherical Bessel functions of complex argument based on continued fractions was developed, which does not depend on recurrence relations and allows accurate calculations on computers with differing word lengths.
Abstract: An efficient new method of calculating spherical Bessel functions of complex argument based on continued fractions is developed. The method does not depend on recurrence relations, and it allows accurate calculations on computers with differing word lengths. The method may be easily extended to other types of Bessel functions and to complex orders.

Journal ArticleDOI
TL;DR: A simple, fast, noniterative and real‐time data smoothing algorithm is described based on the sensors’ system function that features near optimum noise suppression consistent with preservation of the intrinsic sequential detail in the data.
Abstract: A simple, fast, noniterative and real‐time data smoothing algorithm is described based on the sensors’ system function. The technique features near optimum noise suppression consistent with preservation of the intrinsic sequential detail in the data. For sensors with Gaussianlike impulse response functions, a simple technique for computing the sequential domain filter coefficients is illustrated.

Journal ArticleDOI
TL;DR: An efficient algorithm is presented that allows walkers to move very large distances in one step and uses a first‐passage time distribution for d‐dimensional spherical surfaces.
Abstract: Random walks can be used to obtain the diffusion constant and thus the conductivity for continuum percolation problems. This paper presents an efficient algorithm that allows walkers to move very large distances in one step. The algorithm uses a first‐passage time distribution for d‐dimensional spherical surfaces. Results are given for overlapping nonconducting disks in two dimensions. Depending on the density of disks, it is found that the present algorithm is about 5 to 50 times faster than an equivalent algorithm using fixed step lengths.

Journal ArticleDOI
TL;DR: In this paper, a spreadsheet program is used to solve the Laplace equation and calculate charged particle trajectories in geometrically complex electrostatic fields, which is applied to the development of a new electron scattering apparatus.
Abstract: Use of a spreadsheet program to solve the Laplace equation and calculate charged‐particle trajectories in geometrically complex electrostatic fields is described. The technique is applied to the development of a new electron‐scattering apparatus.

Journal ArticleDOI
TL;DR: The architecture of the Heidelberg Polyp multiprocessor is described, which is used for real‐time preprocessing and filtering of events that are read in from Fastbus front‐end electronics at a rate of ≤108 parameters/s.
Abstract: This article describes the architecture of the Heidelberg Polyp multiprocessor and its application in nuclear physics. The system is used for real‐time preprocessing and filtering of events that are read in from Fastbus front‐end electronics at a rate of ≤108 parameters/s. The computing power is provided by a concurrent operation of many microprocessors (currently 30 Motorola 68000 CPUs with 16 kbytes of cache memory and 1 Mbyte of main memory each). They are interconnected by a multiple bus system, which allows adjustment of the bus bandwidth from 10 to 200 Mbytes/s. The processors and buses constitute pools that are managed by a decentralized hardware that permits making changes to the computing power and bus bandwidth without any software modifications. Another special feature is provided by the Syncbus that supports distributed scheduling by hardware. In addition, fault tolerance is achieved by forward and backward hardware error correction. Several systems have been runnning for more than 2 years, with one of them being currently upgraded to 48 processors (68020/68882 Motorola VME boards with 4 Mbytes each).


Journal ArticleDOI
TL;DR: In fact, the typical physics student gets almost no training in integral equations, in contrast to differential equations, for example as discussed by the authors, since numerical solution of integral equations must be an extremely arcane topic, since it is almost never dealt with in numerical analysis textbooks.
Abstract: Integral equations are often the best way to formulate physics problems. However, the typical physics student gets almost no training in integral equations, in contrast to differential equations, for example. Many physicists thus believe that numerical solution of integral equations must be an extremely arcane topic, since it is almost never dealt with in numerical analysis textbooks!

Journal ArticleDOI
TL;DR: In this article, the authors present papers on the largest, fastest, and most powerful computers presently available, including the programs of the National Science Foundation, programming environments, Lisptran, a magentohydrodynamic particle code, numerical cosmology, knowledge-based simulation, the performance of the Caltech hypercube, Monte Carlo methods, point defects, computer vision, a new generation data flow supercomputer, vectorization of a reservoir simulator, the simulation of plasma microinstabilities, parallel iteration schemes, and mathematics with computers.
Abstract: This book presents papers on the largest, fastest, and most powerful computers presently available. Topics considered include the programs of the National Science Foundation, programming environments, Lisptran, a magentohydrodynamic particle code, numerical cosmology, knowledge-based simulation, the performance of the Caltech hypercube, Monte Carlo methods, point defects, computer vision, a new generation data flow supercomputer, vectorization of a reservoir simulator, the simulation of plasma microinstabilities, parallel iteration schemes, and mathematics with computers.

Journal ArticleDOI
TL;DR: This paper describes techniques for reducing CPU time, memory, and I/O time required to perform a three‐dimensional convolution on real data, and the use of an array processor that takes advantage of convolution kernels having mirror symmetry in three dimensions.
Abstract: This paper describes techniques for reducing CPU time, memory, and I/O time required to perform a three‐dimensional convolution on real data, and the use of an array processor These techniques capitalize on the Hermitian nature of the Fourier transform of mathematically real input data, take advantage of convolution kernels having mirror symmetry in three dimensions, and eliminate trivial transformations The result is convolution over a three‐dimensional 64×64×64 array containing 250 K real elements that requires only 28 s to execute Memory space of a medium‐sized array processor is sufficiently large for the procedures to be carried out on entire real, single‐precision arrays at one time without transferring data between the array processor and disk storage

Journal ArticleDOI
TL;DR: A realistic model is presented that allows rapid calculation and display of both exact, three‐dimensional, magnetic flux density lines and the associated trajectories of spherical and ellipsoidal magnetic particles suspended within a viscous liquid.
Abstract: A realistic model is presented that allows rapid calculation and display of both exact, three‐dimensional, magnetic flux density lines and the associated trajectories of spherical and ellipsoidal magnetic particles suspended within a viscous liquid. The particles may be saturable and subject to the spatially nonuniform, magnetic flux densities produced by an array of arbitrarily positioned, rectangular, rare‐earth, permanent magnets. An iterative technique based on the model is applied to the design of a miniature magnetic separator used in a commercial diagnostic blood assay for HIV (AIDS) infection.