712 research outputs found
Measurement of Tritium Partial Pressure by BIXS (I) : Total Pressure Dependence of Hydrogen Isotopes
The correlation between the intensity of X-rays induced by ÎČ-rays of tritium and the total pressure of hydrogen isotope mixtures was examined in a pressure range from 10-1 to 105 Pa by using three different tritium gases, i.e., pure T2, D2-1%T2 and H2-1%T2 mixtures. It was found that linear pressure dependence was obtained up to a few kPa for all of the measured gases by taking dead time of the X-ray detector into account. Above this pressure, however, downward deviation from the linear relation appeared. It was revealed that the effect of self-absorption of ÎČ-rays on the pressure dependence was not negligibly small, because the ratios of the counting rates corrected by dead time to total pressure, i.e., specific counting rates, could not be reproduced by a simple exponential function using the absorption coefficients of hydrogen isotopes as variables. The results suggested that an additional factor such as contribution of an X-ray formation on the surfaces of a measuring cell must be taken into consideration in changing in the specific counting rates
Towards Contextual Action Recognition and Target Localization with Active Allocation of Attention
Exploratory gaze movements are fundamental for gathering the most relevant information regarding the partner during social interactions. We have designed and implemented a system for dynamic attention allocation which is able to actively control gaze movements during a visual action recognition task. During the observation of a partners reaching movement, the robot is able to contextually estimate the goal position of the partner hand and the location in space of the candidate targets, while moving its gaze around with the purpose of optimizing the gathering of information relevant for the task. Experimental results on a simulated environment show that active gaze control provides a relevant advantage with respect to typical passive observation, both in term of estimation precision and of time required for action recognition. © 2012 Springer-Verlag
Dynamic scaling and aging phenomena in short-range Ising spin glass: CuCoCl-FeCl graphite bi-intercalation compound
Static and dynamic behavior of short-range Ising-spin glass
CuCoCl-FeCl graphite bi-intercalation compounds
(GBIC) has been studied with SQUID DC and AC magnetic susceptibility. The
dependence of the zero-field relaxation time above a spin-freezing
temperature (= 3.92 0.11 K) is well described by critical slowing
down. The absorption below decreases with
increasing angular frequency , which is in contrast to the case of 3D
Ising spin glass. The dynamic freezing temperature at which
dd, is determined as a function of
frequency (0.01 Hz 1 kHz) and magnetic field (0 5 kOe). The dynamic scaling analysis of the relaxation time
defined as at suggests the absence of
SG phase in the presence of (at least above 100 Oe). Dynamic scaling
analysis of and near
leads to the critical exponents ( = 0.36 0.03, = 3.5
0.4, = 1.4 0.2, = 6.6 1.2, = 0.24
0.02, and = 0.13 0.02). The aging phenomenon is studied through
the absorption below . It obeys a
power-law decay with an exponent . The rejuvenation effect is also observed under
sufficiently large (temperature and magnetic-field) perturbations.Comment: 14 pages, 19 figures; to be published in Phys. Rev. B (September 1,
2003
Stability of circular orbits of spinning particles in Schwarzschild-like space-times
Circular orbits of spinning test particles and their stability in
Schwarzschild-like backgrounds are investigated. For these space-times the
equations of motion admit solutions representing circular orbits with particles
spins being constant and normal to the plane of orbits. For the de Sitter
background the orbits are always stable with particle velocity and momentum
being co-linear along them. The world-line deviation equations for particles of
the same spin-to-mass ratios are solved and the resulting deviation vectors are
used to study the stability of orbits. It is shown that the orbits are stable
against radial perturbations. The general criterion for stability against
normal perturbations is obtained. Explicit calculations are performed in the
case of the Schwarzschild space-time leading to the conclusion that the orbits
are stable.Comment: eps figures, submitted to General Relativity and Gravitatio
Interplay of quantum and thermal fluctuations in a frustrated magnet
We demonstrate the presence of an extended critical phase in the transverse
field Ising magnet on the triangular lattice, in a regime where both thermal
and quantum fluctuations are important. We map out a complete phase diagram by
means of quantum Monte Carlo simulations, and find that the critical phase is
the result of thermal fluctuations destabilising an order established by the
quantum fluctuations. It is separated by two Kosterlitz-Thouless transitions
from the paramagnet on one hand and the quantum-fluctuation driven
three-sublattice ordered phase on the other. Our work provides further evidence
that the zero temperature quantum phase transition is in the 3d XY universality
class.Comment: 9 pages, revtex
Gauged Inflation
We propose a model for cosmic inflation which is based on an effective
description of strongly interacting, nonsupersymmetric matter within the
framework of dynamical Abelian projection and centerization. The underlying
gauge symmetry is assumed to be with . Appealing to a
thermodynamical treatment, the ground-state structure of the model is
classically determined by a potential for the inflaton field (dynamical
monopole condensate) which allows for nontrivially BPS saturated and thereby
stable solutions. For this leads to decoupling of gravity from the
inflaton dynamics. The ground state dynamics implies a heat capacity for the
vacuum leading to inflation for temperatures comparable to the mass scale
of the potential. The dynamics has an attractor property. In contrast to the
usual slow-roll paradigm we have during inflation. As a consequence,
density perturbations generated from the inflaton are irrelevant for the
formation of large-scale structure, and the model has to be supplemented with
an inflaton independent mechanism for the generation of spatial curvature
perturbations. Within a small fraction of the Hubble time inflation is
terminated by a transition of the theory to its center symmetric phase. The
spontaneously broken symmetry stabilizes relic vector bosons in the
epochs following inflation. These heavy relics contribute to the cold dark
matter of the universe and potentially originate the UHECRs beyond the GZK
bound.Comment: 23 pages, 4 figures, subsection added, revision of text, to app. in
PR
Modeling oscillatory Microtubule--Polymerization
Polymerization of microtubules is ubiquitous in biological cells and under
certain conditions it becomes oscillatory in time. Here simple reaction models
are analyzed that capture such oscillations as well as the length distribution
of microtubules. We assume reaction conditions that are stationary over many
oscillation periods, and it is a Hopf bifurcation that leads to a persistent
oscillatory microtubule polymerization in these models. Analytical expressions
are derived for the threshold of the bifurcation and the oscillation frequency
in terms of reaction rates as well as typical trends of their parameter
dependence are presented. Both, a catastrophe rate that depends on the density
of {\it guanosine triphosphate} (GTP) liganded tubulin dimers and a delay
reaction, such as the depolymerization of shrinking microtubules or the decay
of oligomers, support oscillations. For a tubulin dimer concentration below the
threshold oscillatory microtubule polymerization occurs transiently on the
route to a stationary state, as shown by numerical solutions of the model
equations. Close to threshold a so--called amplitude equation is derived and it
is shown that the bifurcation to microtubule oscillations is supercritical.Comment: 21 pages and 12 figure
Partial Dynamical Symmetry in the Symplectic Shell Model
We present an example of a partial dynamical symmetry (PDS) in an interacting
fermion system and demonstrate the close relationship of the associated
Hamiltonians with a realistic quadrupole-quadrupole interaction, thus shedding
new light on this important interaction. Specifically, in the framework of the
symplectic shell model of nuclei, we prove the existence of a family of
fermionic Hamiltonians with partial SU(3) symmetry. We outline the construction
process for the PDS eigenstates with good symmetry and give analytic
expressions for the energies of these states and E2 transition strengths
between them. Characteristics of both pure and mixed-symmetry PDS eigenstates
are discussed and the resulting spectra and transition strengths are compared
to those of real nuclei. The PDS concept is shown to be relevant to the
description of prolate, oblate, as well as triaxially deformed nuclei.
Similarities and differences between the fermion case and the previously
established partial SU(3) symmetry in the Interacting Boson Model are
considered.Comment: 9 figure
Domain wall fermion and chiral gauge theories on the lattice with exact gauge invariance
We discuss how to construct anomaly-free chiral gauge theories on the lattice
with exact gauge invariance in the framework of domain wall fermion. Chiral
gauge coupling is realized by introducing a five-dimensional gauge field which
interpolates between two different four-dimensional gauge fields at boundaries.
The five-dimensional dependence is compensated by a local and gauge-invariant
counter term. The cohomology problem to obtain the counter term is formulated
in 5+1 dimensional space, using the Chern-Simons current induced from the
five-dimensional Wilson fermion. We clarify the connection to the invariant
construction based on the Ginsparg-Wilson relation using overlap Dirac
operator. Formula for the measure and the effective action of Weyl fermions are
obtained in terms of five-dimensional lattice quantities.Comment: 46 pages, LaTeX, references added and updated, minor text correction
From thermal rectifiers to thermoelectric devices
We discuss thermal rectification and thermoelectric energy conversion from
the perspective of nonequilibrium statistical mechanics and dynamical systems
theory. After preliminary considerations on the dynamical foundations of the
phenomenological Fourier law in classical and quantum mechanics, we illustrate
ways to control the phononic heat flow and design thermal diodes. Finally, we
consider the coupled transport of heat and charge and discuss several general
mechanisms for optimizing the figure of merit of thermoelectric efficiency.Comment: 42 pages, 22 figures, review paper, to appear in the Springer Lecture
Notes in Physics volume "Thermal transport in low dimensions: from
statistical physics to nanoscale heat transfer" (S. Lepri ed.
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