37,974 research outputs found
The Spirituals and the Blues
Cone, James H. The Spirituals and Blues. New York: Seabury Press, 197
Encountering Marx: bonds and barriers between Christians and Marxists
Lochman, Jan Milic. Translated by Edwin Robertson. Philadelphia: Fortress Press, 197
Multiple port pressure scanner valve features greater accuracy, quicker data
Fast, accurate, multipressure measuring system, which employs a multiple port pressure scanning valve that connects a pressure transducer to many pressures, is described
A microscopic mechanism for rejuvenation and memory effects in spin glasses
Aging in spin glasses (and in some other systems) reveals astonishing effects
of `rejuvenation and memory' upon temperature changes. In this paper, we
propose microscopic mechanisms (at the scale of spin-spin interactions) which
can be at the origin of such phenomena. Firstly, we recall that, in a
frustrated system, the effective average interaction between two spins may take
different values (possibly with opposite signs) at different temperatures. We
give simple examples of such situations, which we compute exactly. Such
mechanisms can explain why new ordering processes (rejuvenation) seem to take
place in spin glasses when the temperature is lowered. Secondly, we emphasize
the fact that inhomogeneous interactions do naturally lead to a wide
distribution of relaxation times for thermally activated flips. `Memory spots'
spontaneously appear, in the sense that the flipping time of some spin clusters
becomes extremely long when the temperature is decreased. Such memory spots are
capable of keeping the memory of previous ordering at a higher temperature
while new ordering processes occur at a lower temperature. After a qualitative
discussion of these mechanisms, we show in the numerical simulation of a
simplified example that this may indeed work. Our conclusion is that certain
chaos-like phenomena may show up spontaneously in any frustrated and
inhomogeneous magnetic system, without impeding the occurrence of memory
effects.Comment: 9 pages (11 figures) - revised version, to appear in Eur. Phys. J. B
(2001
Efficient Bayesian inference for harmonic models via adaptive posterior factorization
NOTICE: this is the author’s version of a work that was accepted for publication in Neurocomputing. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in NEUROCOMPUTING, [VOL72, ISSUE 1-3, (2008)] DOI10.1016/j.neucom.2007.12.05
Symmetry breaking in general relativity
Bifurcation theory is used to analyze the space of solutions of Einstein's equations near a spacetime with symmetries. The methods developed here allow one to describe precisely how the symmetry is broken as one branches from a highly symmetric spacetime to nearby spacetimes with fewer symmetries, and finally to a generic solution with no symmetries. This phenomenon of symmetry breaking is associated with the fact that near symmetric solutions the space of solutions of Einstein's equations does not form a smooth manifold but rather has a conical structure. The geometric picture associated with this conical structure enables one to understand the breaking of symmetries. Although the results are described for pure gravity, they may be extended to classes of fields coupled to gravity, such as gauge theories. Since most of the known solutions of Einstein's equations have Killing symmetries, the study of how these symmetries are broken by small perturbations takes on considerable theoretical significance
- …