1,153 research outputs found
Spin-wave coupling to electromagnetic cavity fields in dysposium ferrite
Coupling of spin-waves with electromagnetic cavity field is demonstrated in
an antiferromagnet, dysprosium ferrite (DyFeO3). By measuring transmission at
0.2-0.35 THz and sweeping sample temperature, magnon-photon coupling signatures
were found at crossings of spin-wave resonances with Fabry-Perot cavity modes
formed in samples. The obtained spectra are explained in terms of classical
electrodynamics and a microscopic model.Comment: 3 pages, 2 figure
Hydrodynamic simulations of correlation and scatter in galaxy cluster maps
The two dimensional structure of hot gas in galaxy clusters contains
information about the hydrodynamical state of the cluster, which can be used to
understand the origin of scatter in the thermodynamical properties of the gas,
and to improve the use of clusters to probe cosmology. Using a set of
hydrodynamical simulations, we provide a comparison between various maps
currently employed in the X-ray analysis of merging clusters and those cluster
maps anticipated from forthcoming observations of the thermal
Sunyaev-Zel'dovich effect. We show the following: 1) an X-ray pseudo-pressure,
defined as square root of the soft band X-ray image times the temperature map
is a good proxy for the SZ map; 2) we find that clumpiness is the main reason
for deviation between X-ray pseudo-pressure and SZ maps; 3) the level of
clumpiness can be well characterized by X-ray pseudo-entropy maps. 4) We
describe the frequency of deviation in various maps of clusters as a function
of the amplitude of the deviation. This enables both a comparison to
observations and a comparison to effects of introduction of complex physical
processes into simulation.Comment: 7 pages, A&A in pres
Predicting rare events in chemical reactions: application to skin cell proliferation
In a well-stirred system undergoing chemical reactions, fluctuations in the
reaction propensities are approximately captured by the corresponding chemical
Langevin equation. Within this context, we discuss in this work how the Kramers
escape theory can be used to predict rare events in chemical reactions. As an
example, we apply our approach to a recently proposed model on cell
proliferation with relevance to skin cancer [P.B. Warren, Phys. Rev. E {\bf
80}, 030903 (2009)]. In particular, we provide an analytical explanation for
the form of the exponential exponent observed in the onset rate of uncontrolled
cell proliferation.Comment: New materials and references added. To appear in Physical Review
Information Optimization in Coupled Audio-Visual Cortical Maps
Barn owls hunt in the dark by using cues from both sight and sound to locate
their prey. This task is facilitated by topographic maps of the external space
formed by neurons (e.g., in the optic tectum) that respond to visual or aural
signals from a specific direction. Plasticity of these maps has been studied in
owls forced to wear prismatic spectacles that shift their visual field.
Adaptive behavior in young owls is accompanied by a compensating shift in the
response of (mapped) neurons to auditory signals. We model the receptive fields
of such neurons by linear filters that sample correlated audio-visual signals,
and search for filters that maximize the gathered information, while subject to
the costs of rewiring neurons. Assuming a higher fidelity of visual
information, we find that the corresponding receptive fields are robust and
unchanged by artificial shifts. The shape of the aural receptive field,
however, is controlled by correlations between sight and sound. In response to
prismatic glasses, the aural receptive fields shift in the compensating
direction, although their shape is modified due to the costs of rewiring.Comment: 7 pages, 1 figur
The thermodynamics of prediction
A system responding to a stochastic driving signal can be interpreted as
computing, by means of its dynamics, an implicit model of the environmental
variables. The system's state retains information about past environmental
fluctuations, and a fraction of this information is predictive of future ones.
The remaining nonpredictive information reflects model complexity that does not
improve predictive power, and thus represents the ineffectiveness of the model.
We expose the fundamental equivalence between this model inefficiency and
thermodynamic inefficiency, measured by dissipation. Our results hold
arbitrarily far from thermodynamic equilibrium and are applicable to a wide
range of systems, including biomolecular machines. They highlight a profound
connection between the effective use of information and efficient thermodynamic
operation: any system constructed to keep memory about its environment and to
operate with maximal energetic efficiency has to be predictive.Comment: 5 pages, 1 figur
Enhancement of the stability of genetic switches by overlapping upstream regulatory domains
We study genetic switches formed from pairs of mutually repressing operons.
The switch stability is characterised by a well defined lifetime which grows
sub-exponentially with the number of copies of the most-expressed transcription
factor, in the regime accessible by our numerical simulations. The stability
can be markedly enhanced by a suitable choice of overlap between the upstream
regulatory domains. Our results suggest that robustness against biochemical
noise can provide a selection pressure that drives operons, that regulate each
other, together in the course of evolution.Comment: 4 pages, 5 figures, RevTeX
Measuring Physical and visual material properties to determine their perceives degree of naturalness
On the criticality of inferred models
Advanced inference techniques allow one to reconstruct the pattern of
interaction from high dimensional data sets. We focus here on the statistical
properties of inferred models and argue that inference procedures are likely to
yield models which are close to a phase transition. On one side, we show that
the reparameterization invariant metrics in the space of probability
distributions of these models (the Fisher Information) is directly related to
the model's susceptibility. As a result, distinguishable models tend to
accumulate close to critical points, where the susceptibility diverges in
infinite systems. On the other, this region is the one where the estimate of
inferred parameters is most stable. In order to illustrate these points, we
discuss inference of interacting point processes with application to financial
data and show that sensible choices of observation time-scales naturally yield
models which are close to criticality.Comment: 6 pages, 2 figures, version to appear in JSTA
Chemical Gradients in Galaxy Clusters and the Multiple Ways of Making a Cold Front
Cold fronts were originally interpreted as being the result of
subsonic/transonic motions of head-on merging substructures. This merger core
remnant model is theoretically justified and hold relatively well for clusters
that have clear signs of merging, such as 1E0657-56, but they do not work well
for the increasing number of cold fronts found in clusters that do not show
clear merging signs, such as A496. Here we report the results of a deeper
observation of that cluster that allowed us to produce high quality maps of the
gas parameters and to compare more closely the observations with the
predictions given by different models for cold front formation. We found for
the first time a ``cold arm'' characteristic of a flyby of a massive DM halo
near the core of the cluster. The cold arm is accompanied by an enhanced SN II
Fe mass fraction, inconsistent with the merger core remnant scenario.Comment: 3 pages, 1 figures, to appear in the Proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching
(Germany
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