Massively parallel computers

These codes have stressed the current supercomputer, whether it was the CDC 6600 in the 1970s, the Grays in the 1980s, or the massively parallel computers of the 1990s. Multimillion cell calculations are routinely performed at Sandia National Laboratories with the CTH [1], [2] code, yet... 

C.T. Vaughan, Structural Analysis on Massively Parallel Computers, SAND90-1706C, Sandia National Laboratories Report, Albuquerque, NM 87185, 1991. 

The numerical solution of these equations is not trivial, since for reasonably low viscosities the flow becomes turbulent. A popular method of treating these equations (together with the equations of energy and mass conservation) is the MAC method [156,157]. For the case of immiscible fluids or moving internal interface a phase-field-type approach seems to be successful [78,158,159]. Because of the enormous requirements of computing ressources the development in this field is still relatively slow. We expect, however, an impact from the more widespread availability of massively parallel computers in the near future. 

Over the past 15-20 years, the advances in numerical simulation of turbulent combustion have been more or less driven by the increase in computational power and the development of massively parallel computing, which have very good chances to continue. 

Brommer et al. Large solid circles denote adatoms. The size of the circle indicates the distance of the atoms from the top of the surface. The (7 x 7) unit cell is outlined, (b) STM image of the reconstruction. [Reprinted with permission from K. D. Brommer, M. Needels, B. E. Larson, and J. D. Joannopoulos, Ab Initio Theory of the Si(lll) (7 x7) Surface Reconstruction A Challenge for Massively Parallel Computation, Phys. Rev. Lett. 68 (1992), 1355 (Copyright 1992 by the American Physical Society).]... 

Dabdub, D and J. H. Seinfeld, Air Quality Modeling on Massively Parallel Computers, Atmos. Environ., 28, 1679-1687 (1994a). 

However, since one electron or proton has two possible spin states, N electrons or protons have 2N possible states (just like the coin toss case). Molecules can be configured to be simultaneously in many different quantum states, just as the electron in the two-slit experiment seems to pass through both slits simultaneously. In principle, this property can be used someday to make massively parallel computers, and such computers with five or six bits have been made in the laboratory (using NMR). As of this writing, nobody knows whether or not it will ever be possible to build a quantum computer which is big enough to do a computation faster than a conventional machine, although it is clear that NMR will not work for this application. 

It must also be emphasized that the a-p VEGAS is designed to deal with the d-d problem found in the real 8 calculation. If the d-d problem occurs in real 16, it is necessary to go to even higher precision arithmetic. Unfortunately, such a device is not available at present on massively parallel computers. Thus we may be forced to deal with the d-d problem in combination with other techniques described in the following. 

Order No. DE87012058. Available from National Technical Information Center Energy Research Abstracts 1987, 12(18), Abstr. No. 38308, 1986. Quantum Chemical Methods for Massively Parallel Computers. 

L. L. Boyer and G. S. Pawley, J. Comput. Phys., 78, 405 (1988). Molecular Dynamics of Clusters of Particles Interacting with Pairwise Forces Using a Massively Parallel Computer. 

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