1,940 research outputs found
Critical behavior in a cross-situational lexicon learning scenario
The associationist account for early word-learning is based on the
co-occurrence between objects and words. Here we examine the performance of a
simple associative learning algorithm for acquiring the referents of words in a
cross-situational scenario affected by noise produced by out-of-context words.
We find a critical value of the noise parameter above which learning
is impossible. We use finite-size scaling to show that the sharpness of the
transition persists across a region of order about ,
where is the number of learning trials, as well as to obtain the
learning error (scaling function) in the critical region. In addition, we show
that the distribution of durations of periods when the learning error is zero
is a power law with exponent -3/2 at the critical point
First order transition and phase separation in pyrochlores with colossal-magnetoresistance
TlMnO pyrochlores present colossal magnetoresistance (CMR)
around the long range ferromagnetic ordering temperature (T). The
character of this magnetic phase transition has been determined to be first
order, by purely magnetic methods, in contrast to the second order character
previously reported by Zhao et al. (Phys. Rev. Lett. 83, 219 (1999)). The
highest CMR effect, as in TlCdMnO, corresponds to a
stronger first order character. This character implies a second type of
magnetic interaction, besides the direct superexchange between the Mn
ions, as well as a phase coexistence. A model is proposed, with a complete
Hamiltonian (including superexchange and an indirect interaction), which
reproduce the observed phenomenology.Comment: 6 pages. Figures include
Bayesian coherent analysis of in-spiral gravitational wave signals with a detector network
The present operation of the ground-based network of gravitational-wave laser
interferometers in "enhanced" configuration brings the search for gravitational
waves into a regime where detection is highly plausible. The development of
techniques that allow us to discriminate a signal of astrophysical origin from
instrumental artefacts in the interferometer data and to extract the full range
of information are some of the primary goals of the current work. Here we
report the details of a Bayesian approach to the problem of inference for
gravitational wave observations using a network of instruments, for the
computation of the Bayes factor between two hypotheses and the evaluation of
the marginalised posterior density functions of the unknown model parameters.
The numerical algorithm to tackle the notoriously difficult problem of the
evaluation of large multi-dimensional integrals is based on a technique known
as Nested Sampling, which provides an attractive alternative to more
traditional Markov-chain Monte Carlo (MCMC) methods. We discuss the details of
the implementation of this algorithm and its performance against a Gaussian
model of the background noise, considering the specific case of the signal
produced by the in-spiral of binary systems of black holes and/or neutron
stars, although the method is completely general and can be applied to other
classes of sources. We also demonstrate the utility of this approach by
introducing a new coherence test to distinguish between the presence of a
coherent signal of astrophysical origin in the data of multiple instruments and
the presence of incoherent accidental artefacts, and the effects on the
estimation of the source parameters as a function of the number of instruments
in the network.Comment: 22 page
Three-Dimensional Liquid-Vapor Interface Reconstruction from High-Speed Stereo Images during Pool Boiling
A technique for reconstruction of liquid-gas interfaces based on high-speed stereo-imaging is applied to the liquid-vapor interfaces formed above a heated surface during pool boiling. Template matching is used for determining the correspondence of local features of the liquid-vapor interfaces between the two camera views. A sampling grid is overlaid on the reference image, and windows centered at each sampled pixel are compared with windows centered along the epipolar line in the target image to obtain a correlation signal. The three-dimensional coordinates of each matched pixel are determined via triangulation, which yields the physical world representation of the liquid-vapor interface. Liquid-vapor interface reconstruction is demonstrated during pool boiling for a range of heat fluxes. Textured mushroom-like vapor bubbles that are fed by multiple nucleation sites are formed close to the heated surface. Analysis of the temporal attributes of the interface distinguishes the transition with increasing heat flux from a mode in which vapor is released from the surface as a continuous plume to one dominated by the occurrence of intermittent vapor bursts. A characteristic morphology of the vapor mushroom formed during vapor burst events is identified. This liquid-vapor interface reconstruction technique is a time-resolved, flexible and non-invasive alternative to existing methods for phase-distribution mapping, and can be combined with other opticalbased diagnostic tools, such as tomographic particle image velocimetry. Vapor flow morphology characterization during pool boiling at high heat fluxes can be used to inform vapor removal strategies that delay the occurrence of critical heat flux during pool boiling
Evidence for magnetic clusters in BaCoO
Magnetic properties of the transition metal oxide BaCoO are analyzed on
the basis of the experimental and theoretical literature available via ab inito
calculations. These can be explained by assuming the material to be formed by
noninteracting ferromagnetic clusters of about 1.2 nm in diameter separated by
about 3 diameters. Above about 50 K, the so-called blocking temperature,
superparamagnetic behavior of the magnetic clusters occurs and, above 250 K,
paramagnetism sets in.Comment: 4 pages, 1 figur
Studying stellar binary systems with the Laser Interferometer Space Antenna using Delayed Rejection Markov chain Monte Carlo methods
Bayesian analysis of LISA data sets based on Markov chain Monte Carlo methods
has been shown to be a challenging problem, in part due to the complicated
structure of the likelihood function consisting of several isolated local
maxima that dramatically reduces the efficiency of the sampling techniques.
Here we introduce a new fully Markovian algorithm, a Delayed Rejection
Metropolis-Hastings Markov chain Monte Carlo method, to efficiently explore
these kind of structures and we demonstrate its performance on selected LISA
data sets containing a known number of stellar-mass binary signals embedded in
Gaussian stationary noise.Comment: 12 pages, 4 figures, accepted in CQG (GWDAW-13 proceedings
Universal bifurcation property of two- or higher-dimensional dissipative systems in parameter space: Why does 1D symbolic dynamics work so well?
The universal bifurcation property of the H\'enon map in parameter space is
studied with symbolic dynamics. The universal- region is defined to
characterize the bifurcation universality. It is found that the universal-
region for relative small is not restricted to very small values. These
results show that it is also a universal phenomenon that universal sequences
with short period can be found in many nonlinear dissipative systems.Comment: 10 pages, figures can be obtained from the author, will appeared in
J. Phys.
Short range ferromagnetism and spin glass state in
Dynamic magnetic properties of are
reported. The system appears to attain local ferromagnetic order at
K. Below this temperature the low field
magnetization becomes history dependent, i.e. the zero field cooled (ZFC) and
field cooled (FC) magnetization deviate from each other and closely logarithmic
relaxation appears at our experimental time scales (0.3- sec). The zero
field cooled magnetization has a maximum at K,
whereas the field cooled magnetization continues to increase, although less
sharply, also below this temperature. Surprisingly, the dynamics of the system
shows non-equilibrium spin glass (SG) features not only below the maximum in
the ZFC magnetization, but also in the temperature region between this maximum
and . The aging and temperature cycling experiments show only
quantitative differences in the dynamic behavior above and below the maximum in
the ZFC-magnetization; similarly, memory effects are observed in both
temperature regions. We attribute the high temperature behavior to the
existence of clusters of short range ferromagnetic order below
; the configuration evolves into a conventional spin glass
state at temperatures below .Comment: REVTeX style; 8 pages, 8 figure
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