2,844 research outputs found
Metastable states and information propagation in a 1D array of locally-coupled bistable cells
We study the effect of metastable states on the relaxation process (and hence
information propagation) in locally coupled and boundary-driven structures. We
first give a general argument to show that metastable states are inevitable
even in the simplest of structures, a wire. At finite temperatures, the
relaxation mechanism is a thermally assisted random walk. The time required to
reach the ground state and its life time are determined by the coupling
parameters. These time scales are studied in a model based on an array of
quantum dots.Comment: Accepted for publication in Journal of Applied Physic
Measurements of quasi-particle tunneling in the nu = 5/2 fractional quantum Hall state
Some models of the 5/2 fractional quantum Hall state predict that the
quasi-particles, which carry the charge, have non-Abelian statistics: exchange
of two quasi-particles changes the wave function more dramatically than just
the usual change of phase factor. Such non-Abelian statistics would make the
system less sensitive to decoherence, making it a candidate for implementation
of topological quantum computation. We measure quasi-particle tunneling as a
function of temperature and DC bias between counter-propagating edge states.
Fits to theory give e*, the quasi-particle effective charge, close to the
expected value of e/4 and g, the strength of the interaction between
quasi-particles, close to 3/8. Fits corresponding to the various proposed wave
functions, along with qualitative features of the data, strongly favor the
Abelian 331 state
X-raying the Beating Heart of a Newborn Star: Rotational Modulation of High-energy Radiation from V1647 Ori
We report a periodicity of ~1 day in the highly elevated X-ray emission from
the protostar V1647 Ori during its two recent multiple-year outbursts of mass
accretion. This periodicity is indicative of protostellar rotation at
near-breakup speed. Modeling of the phased X-ray light curve indicates the
high-temperature (~50 MK), X-ray-emitting plasma, which is most likely heated
by accretion-induced magnetic reconnection, resides in dense (>~5e10 cm-3),
pancake-shaped magnetic footprints where the accretion stream feeds the newborn
star. The sustained X-ray periodicity of V1647 Ori demonstrates that such
protostellar magnetospheric accretion configurations can be stable over
timescales of years.Comment: 26 pages, 10 figure
Effective Sample Size: Quick Estimation of the Effect of Related Samples in Genetic Case-Control Association Analyses
Correlated samples have been frequently avoided in case-control
genetic association
 studies in part because the methods for handling them are either not
easily implemented or not widely known. We
advocate one method for case-control association analysis of correlated
samples -- the effective sample size method -- as a simple and
accessible approach that does not require specialized computer programs.
The effective sample size method captures the variance inflation
of allele frequency estimation exactly, and can be used to modify the
chi-square test statistic, p-value, and 95% confidence interval of
odds-ratio simply by replacing the apparent number of allele counts with the
effective ones. For genotype frequency estimation, although a single
effective sample size is unable to completely characterize the variance inflation,
an averaged one can satisfactorily approximate the simulated result.
The effective sample size method is applied to the rheumatoid arthritis
siblings data collected from the North American Rheumatoid Arthritis Consortium (NARAC)
to establish a significant association with the interferon-induced
helicasel gene (IFIH1) previously being identified as a type 1 diabetes
susceptibility locus. Connections between the effective sample size
method and other methods, such as generalized estimation equation,
variance of eigenvalues for correlation matrices, and genomic controls,
are also discussed.

Topological conditions for discrete symmetry breaking and phase transitions
In the framework of a recently proposed topological approach to phase
transitions, some sufficient conditions ensuring the presence of the
spontaneous breaking of a Z_2 symmetry and of a symmetry-breaking phase
transition are introduced and discussed. A very simple model, which we refer to
as the hypercubic model, is introduced and solved. The main purpose of this
model is that of illustrating the content of the sufficient conditions, but it
is interesting also in itself due to its simplicity. Then some mean-field
models already known in the literature are discussed in the light of the
sufficient conditions introduced here
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