Computers in Physics
Index of content:
Volume 5, Issue 5, September 1991
- PEER-REVIEWED PAPERS
5(1991); http://dx.doi.org/10.1063/1.168399View Description Hide Description
A two‐dimensional model for molecular condensed matter phases is proposed, based on triatomic triangular molecules. The governing potential function is carefully chosen to give many different structures with the same crystal potential. Part of a molecular dynamics teaching project is presented, showing that a number of these structures occur naturally in a simulation. This form of computational project well suits parallel computation, and the present results were obtained on an AMT DAP computer. Further possibilities for this model are presented, some of which involve the ideas of quasicrystals.
5(1991); http://dx.doi.org/10.1063/1.168400View Description Hide Description
Algorithms are described for the accurate evaluation of a class of integrals, including Fourier transforms, in which the integral is well represented as the product of an exponential and a polynomial. The algorithms treat all or a part of the exponential dependence exactly and represent the polynomial by conventional finite difference. Numerical examples of Fourier transforms are given that illustrate the accuracy and stability of the algorithms and include a case in which the evaluation of Fourier transforms does n o t require the evaluation of any sine, cosine, or complex exponential functions.
5(1991); http://dx.doi.org/10.1063/1.168401View Description Hide Description
Eight‐bit parallel input/output (I/O) ports for the IBM microchannel are described. First, the microchannel signals needed for the ports are identified and defined. Next, the states of the data and address lines and the controls during input and output sequences are described. Finally, ports circuitry which responds to the sequences is presented and explained.
5(1991); http://dx.doi.org/10.1063/1.168402View Description Hide Description
Given an integrable dynamical system with one degree of freedom, ‘‘painting’’ the integral over phase space proves to be a powerful technique for uncovering both global and local behavior.This graphical technique avoids numerical integration, employing instead a nonlinear method of assigning contrasting colors to the energy values to distinguish subtle details of the flow.
5(1991); http://dx.doi.org/10.1063/1.168403View Description Hide Description
Classical scattering from a cluster of N hard spheres, in particular for N=3 and 4, is discussed. In addition, the case of planar scattering from three disks is considered. The scattering is chaotic and shows a fractal structure, whose fractal dimension increases with the number of spheres as well as with the ratio radius/distance. The scattering system can be reinterpreted as a system of polished balls reflecting each other, which generates a fascinating nested structure of fractal mirror images.
5(1991); http://dx.doi.org/10.1063/1.168404View Description Hide Description
A new method for visualizing data on a globe or unit sphere is described. Information that is distributed over a sphere—global oceanographic or geographic measurements, all‐sky astronomy observations, or any quantities that are best represented in spherical coordinates—can benefit from this technique. Retaining a better sense of the geometry and information content of the data, 3‐D graphics can provide an unobstructed view of the entire sphere, without undo deformation of its surface area. A ‘‘parametrized ray trace’’ produces look‐up tables (LUTs) that can be used for all visualizations. The ray trace result shows one or more spheres with the data as a texture map and three reflecting rectangles that ‘‘mirror’’ the far sides of the sphere(s) into view. The LUTs need only be created once, and a general purpose computer will do. No special purpose hardware is required beyond a PC or workstation that supports color. Examples from astronomical and geophysical datasets, which are commonly displayed with an area deforming (2‐D) projection, are presented.