281 research outputs found
Event-Driven Molecular Dynamics in Parallel
Although event-driven algorithms have been shown to be far more efficient
than time-driven methods such as conventional molecular dynamics, they have not
become as popular. The main obstacle seems to be the difficulty of
parallelizing event-driven molecular dynamics. Several basic ideas have been
discussed in recent years, but to our knowledge no complete implementation has
been published yet. In this paper we present a parallel event-driven algorithm
including dynamic load-balancing, which can be easily implemented on any
computer architecture. To simplify matters our explanations refer to a basic
multi-particle system of hard spheres, but can be extended easily to a wide
variety of possible models.Comment: 10 pages, 9 figure
Minimum Perimeter Rectangles That Enclose Congruent Non-Overlapping Circles
We use computational experiments to find the rectangles of minimum perimeter
into which a given number n of non-overlapping congruent circles can be packed.
No assumption is made on the shape of the rectangles. In many of the packings
found, the circles form the usual regular square-grid or hexagonal patterns or
their hybrids. However, for most values of n in the tested range n =< 5000,
e.g., for n = 7, 13, 17, 21, 22, 26, 31, 37, 38, 41, 43...,4997, 4998, 4999,
5000, we prove that the optimum cannot possibly be achieved by such regular
arrangements. Usually, the irregularities in the best packings found for such n
are small, localized modifications to regular patterns; those irregularities
are usually easy to predict. Yet for some such irregular n, the best packings
found show substantial, extended irregularities which we did not anticipate. In
the range we explored carefully, the optimal packings were substantially
irregular only for n of the form n = k(k+1)+1, k = 3, 4, 5, 6, 7, i.e., for n =
13, 21, 31, 43, and 57. Also, we prove that the height-to-width ratio of
rectangles of minimum perimeter containing packings of n congruent circles
tends to 1 as n tends to infinity.Comment: existence of irregular minimum perimeter packings for n not of the
form (10) is conjectured; smallest such n is n=66; existence of irregular
minimum area packings is conjectured, e.g. for n=453; locally optimal
packings for the two minimization criteria are conjecturally the same (p.22,
line 5); 27 pages, 12 figure
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