47,564 research outputs found
Test stand system for vacuum chambers
A test stand system for supporting test items in a vacuum chamber is described. The system consists of a frame adapted to conform to the inside of the vacuum chamber and supporting a central vertical shaft. The shaft rotates on bearings located at each end of the shaft. Several vertically spaced plates which fixed to the vertical shaft may be adjusted for height to support the test equipment as required. The test equipment may be rotated during tests without disturbing the vacuum by a manually actuated drive external to the vacuum chamber
Uniqueness of Ground States for Short-Range Spin Glasses in the Half-Plane
We consider the Edwards-Anderson Ising spin glass model on the half-plane with zero external field and a wide range of choices, including
mean zero Gaussian, for the common distribution of the collection J of i.i.d.
nearest neighbor couplings. The infinite-volume joint distribution
of couplings J and ground state pairs with periodic
(respectively, free) boundary conditions in the horizontal (respectively,
vertical) coordinate is shown to exist without need for subsequence limits. Our
main result is that for almost every J, the conditional distribution
is supported on a single ground state pair.Comment: 20 pages, 3 figure
INTRODUCTION: SOUTHERN AGRICULTURE AND THE WORLD ECONOMY: THE MULTILATERAL TRADE NEGOTIATIONS
International Relations/Trade,
Efficient configurational-bias Monte-Carlo simulations of chain molecules with `swarms' of trial configurations
Proposed here is a dynamic Monte-Carlo algorithm that is efficient in
simulating dense systems of long flexible chain molecules. It expands on the
configurational-bias Monte-Carlo method through the simultaneous generation of
a large set of trial configurations. This process is directed by attempting to
terminate unfinished chains with a low statistical weight, and replacing these
chains with clones (enrichments) of stronger chains. The efficiency of the
resulting method is explored by simulating dense polymer brushes. A gain in
efficiency of at least three orders of magnitude is observed with respect to
the configurational-bias approach, and almost one order of magnitude with
respect to recoil-growth Monte-Carlo. Furthermore, the inclusion of `waste
recycling' is observed to be a powerful method for extracting meaningful
statistics from the discarded configurations
Are There Incongruent Ground States in 2D Edwards-Anderson Spin Glasses?
We present a detailed proof of a previously announced result (C.M. Newman and
D.L. Stein, Phys. Rev. Lett. v. 84, pp. 3966--3969 (2000)) supporting the
absence of multiple (incongruent) ground state pairs for 2D Edwards-Anderson
spin glasses (with zero external field and, e.g., Gaussian couplings): if two
ground state pairs (chosen from metastates with, e.g., periodic boundary
conditions) on the infinite square lattice are distinct, then the dual bonds
where they differ form a single doubly-infinite, positive-density domain wall.
It is an open problem to prove that such a situation cannot occur (or else to
show --- much less likely in our opinion --- that it indeed does happen) in
these models. Our proof involves an analysis of how (infinite-volume) ground
states change as (finitely many) couplings vary, which leads us to a notion of
zero-temperature excitation metastates, that may be of independent interest.Comment: 18 pages (LaTeX); 1 figure; minor revisions; to appear in Commun.
Math. Phy
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