8,559 research outputs found
Aperiodic tilings and entropy
In this paper we present a construction of Kari-Culik aperiodic tile set -
the smallest known until now. With the help of this construction, we prove that
this tileset has positive entropy. We also explain why this result was not
expected
Localizing the Latent Structure Canonical Uncertainty: Entropy Profiles for Hidden Markov Models
This report addresses state inference for hidden Markov models. These models
rely on unobserved states, which often have a meaningful interpretation. This
makes it necessary to develop diagnostic tools for quantification of state
uncertainty. The entropy of the state sequence that explains an observed
sequence for a given hidden Markov chain model can be considered as the
canonical measure of state sequence uncertainty. This canonical measure of
state sequence uncertainty is not reflected by the classic multivariate state
profiles computed by the smoothing algorithm, which summarizes the possible
state sequences. Here, we introduce a new type of profiles which have the
following properties: (i) these profiles of conditional entropies are a
decomposition of the canonical measure of state sequence uncertainty along the
sequence and makes it possible to localize this uncertainty, (ii) these
profiles are univariate and thus remain easily interpretable on tree
structures. We show how to extend the smoothing algorithms for hidden Markov
chain and tree models to compute these entropy profiles efficiently.Comment: Submitted to Journal of Machine Learning Research; No RR-7896 (2012
Quasiperiodicity and non-computability in tilings
We study tilings of the plane that combine strong properties of different
nature: combinatorial and algorithmic. We prove existence of a tile set that
accepts only quasiperiodic and non-recursive tilings. Our construction is based
on the fixed point construction; we improve this general technique and make it
enforce the property of local regularity of tilings needed for
quasiperiodicity. We prove also a stronger result: any effectively closed set
can be recursively transformed into a tile set so that the Turing degrees of
the resulted tilings consists exactly of the upper cone based on the Turing
degrees of the later.Comment: v3: the version accepted to MFCS 201
Fixed Point and Aperiodic Tilings
An aperiodic tile set was first constructed by R.Berger while proving the
undecidability of the domino problem. It turned out that aperiodic tile sets
appear in many topics ranging from logic (the Entscheidungsproblem) to physics
(quasicrystals) We present a new construction of an aperiodic tile set that is
based on Kleene's fixed-point construction instead of geometric arguments. This
construction is similar to J. von Neumann self-reproducing automata; similar
ideas were also used by P. Gacs in the context of error-correcting
computations. The flexibility of this construction allows us to construct a
"robust" aperiodic tile set that does not have periodic (or close to periodic)
tilings even if we allow some (sparse enough) tiling errors. This property was
not known for any of the existing aperiodic tile sets.Comment: v5: technical revision (positions of figures are shifted
the role of shock waves in modulation of galactic cosmic rays
The understanding of modulation of the galactic cosmic rays has considerably progressed by the exploration by space probes of major heliospheric structures, such as the Corotating Interaction Regions, the neutral sheet, and the compression regions of intense heliospheric magnetic fields. Also relevant in this context were the detections in the outer heliosphere of long lasting Forbush type decreases of cosmic ray intensity. The results of recent theoretical studies on the changes in intensity and energy, at different location from the Sun, induced by the passage of shocks across the heliosphere are presented. In this version of the research, the simplest cases of modulation of uGV and 2GV particles by single or several shocks during periods of positive and negative solar field polarity are reviewed. The results of the theoretical aspects of the search is reported. The comparison of the theoretical predictions with space probe data allows conclusions to be drawn on the role of shocks on the modulation on both the 11 and 22 year galactic cosmic ray cycles in the outer heliosphere and on the plausibility of the models and parameters used
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Cocaine Addiction as a Homeostatic Reinforcement Learning Disorder
Drug addiction implicates both reward learning and homeostatic regulation mechanisms of the brain. This has stimulated 2 partially successful theoretical perspectives on addiction. Many important aspects of addiction, however, remain to be explained within a single, unified framework that integrates the 2 mechanisms. Building upon a recently developed homeostatic reinforcement learning theory, the authors focus on a key transition stage of addiction that is well modeled in animals, escalation of drug use, and propose a computational theory of cocaine addiction where cocaine reinforces behavior due to its rapid homeostatic corrective effect, whereas its chronic use induces slow and long-lasting changes in homeostatic setpoint. Simulations show that our new theory accounts for key behavioral and neurobiological features of addiction, most notably, escalation of cocaine use, drug-primed craving and relapse, individual differences underlying dose-response curves, and dopamine D2-receptor downregulation in addicts. The theory also generates unique predictions about cocaine self-administration behavior in rats that are confirmed by new experimental results. Viewing addiction as a homeostatic reinforcement learning disorder coherently explains many behavioral and neurobiological aspects of the transition to cocaine addiction, and suggests a new perspective toward understanding addiction
Relaxation time of the topological T1 process in a two-dimensional foam
The elementary topological T1 process in a two-dimensional foam corresponds
to the "flip" of one soap film with respect to the geometrical constraints.
From a mechanical point of view, this T1 process is an elementary relaxation
process through which the entire structure of an out-of-equilibrium foam
evolves. The dynamics of this elementary relaxation process has been poorly
investigated and is generally neglected during simulations of foams. We study
both experimentally and theoretically the T1 dynamics in a dry two-dimensional
foam. We show that the dynamics is controlled by the surface viscoelastic
properties of the soap films (surface shear plus dilatational viscosity, ms+k,
and Gibbs elasticity e), and is independent of the shear viscosity of the bulk
liquid. Moreover, our approach illustrates that the dynamics of T1 relaxation
process provides a convenient tool for measuring the surface rheological
properties: we obtained e = 32+/-8 mN/m and ms+k = 1.3+/-0.7 mPa.m.s for SDS,
and e = 65+/-12 mN/m and ms+k = 31+/-12 mPa.m.s for BSA, in good agreement with
values reported in the literature
Families Facing the Demands of Military Life: New Research Directions
Military families, whether Active-duty, Reserve, or National Guard, face a multitude of demands in times of both peace and war, and these demands will shift throughout a Servicemember’s career. Our research at the Walter Reed Army Institute of Research (WRAIR), as well as research done at other institutions, has shown that the demands experienced by military families have both negative and positive effects in terms of health, marital satisfaction, and satisfaction with the Army. Appraisal of these demands and the ability to obtain the necessary resources to deal with them are important determinants of a variety of well-being–, family-, and Army-related outcomes. This chapter will focus on the findings of family studies conducted by researchers at WRAIR and examine the road ahead with studying military families based on the outcomes discussed
West Nile outbreak in horses in southern France, 2000: the return after 35 years.
On September 6, 2000, two cases of equine encephalitis caused by West Nile (WN) virus were reported in southern France (HĂ©rault Province), near Camargue National Park, where a WN outbreak occurred in 1962. Through November 30, 76 cases were laboratory confirmed among 131 equines with neurologic disorders. The last confirmed case was on November 3, 2000. All but three cases were located in a region nicknamed "la petite Camargue," which has several large marshes, numerous colonies of migratory and resident birds, and large mosquito populations. No human case has been confirmed among clinically suspected patients, nor have abnormal deaths of birds been reported. A serosurvey has been undertaken in horses in the infected area, and other studies are in progress
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