1,899 research outputs found
A Pinned Polymer Model of Posture Control
A phenomenological model of human posture control is posited. The dynamics
are modelled as an elastically pinned polymer under the influence of noise. The
model accurately reproduces the two-point correlation functions of experimental
posture data and makes predictions for the response function of the postural
control system. The physiological and clinical significance of the model is
discussed.Comment: uuencoded post script file, 17 pages with 3 figure
Nonstationary Stochastic Resonance in a Single Neuron-Like System
Stochastic resonance holds much promise for the detection of weak signals in
the presence of relatively loud noise. Following the discovery of nondynamical
and of aperiodic stochastic resonance, it was recently shown that the
phenomenon can manifest itself even in the presence of nonstationary signals.
This was found in a composite system of differentiated trigger mechanisms
mounted in parallel, which suggests that it could be realized in some
elementary neural networks or nonlinear electronic circuits. Here, we find that
even an individual trigger system may be able to detect weak nonstationary
signals using stochastic resonance. The very simple modification to the trigger
mechanism that makes this possible is reminiscent of some aspects of actual
neuron physics. Stochastic resonance may thus become relevant to more types of
biological or electronic systems injected with an ever broader class of
realistic signals.Comment: Plain Latex, 7 figure
Stochastic Resonance in Ion Channels Characterized by Information Theory
We identify a unifying measure for stochastic resonance (SR) in voltage
dependent ion channels which comprises periodic (conventional), aperiodic and
nonstationary SR. Within a simplest setting, the gating dynamics is governed by
two-state conductance fluctuations, which switch at random time points between
two values. The corresponding continuous time point process is analyzed by
virtue of information theory. In pursuing this goal we evaluate for our
dynamics the tau-information, the mutual information and the rate of
information gain. As a main result we find an analytical formula for the rate
of information gain that solely involves the probability of the two channel
states and their noise averaged rates. For small voltage signals it simplifies
to a handy expression. Our findings are applied to study SR in a potassium
channel. We find that SR occurs only when the closed state is predominantly
dwelled. Upon increasing the probability for the open channel state the
application of an extra dose of noise monotonically deteriorates the rate of
information gain, i.e., no SR behavior occurs.Comment: 10 pages, 2 figures, to appear in Phys. Rev.
Scaling-violation phenomena and fractality in the human posture control systems
By analyzing the movements of quiet standing persons by means of wavelet
statistics, we observe multiple scaling regions in the underlying body
dynamics. The use of the wavelet-variance function opens the possibility to
relate scaling violations to different modes of posture control. We show that
scaling behavior becomes close to perfect, when correctional movements are
dominated by the vestibular system.Comment: 12 pages, 4 figures, to appear in Phys. Rev.
Access to public information through localisation
The paper analyses language policy in Ireland and the extent to which multilingual
information is provided on public service websites
Nonstationary Stochastic Resonance
It is by now established that, remarkably, the addition of noise to a
nonlinear system may sometimes facilitate, rather than hamper the detection of
weak signals. This phenomenon, usually referred to as stochastic resonance, was
originally associated with strictly periodic signals, but it was eventually
shown to occur for stationary aperiodic signals as well. However, in several
situations of practical interest, the signal can be markedly nonstationary. We
demonstrate that the phenomenon of stochastic resonance extends to
nonstationary signals as well, and thus could be relevant to a wider class of
biological and electronic applications. Building on both nondynamic and
aperiodic stochastic resonance, our scheme is based on a multilevel trigger
mechanism, which could be realized as a parallel network of differentiated
threshold sensors. We find that optimal detection is reached for a number of
thresholds of order ten, and that little is gained by going much beyond that
number. We raise the question of whether this is related to the fact that
evolution has favored some fixed numbers of precisely this order of magnitude
in certain aspects of sensory perception.Comment: Plain Latex, 6 figure
Exponential-Potential Scalar Field Universes I: The Bianchi I Models
We obtain a general exact solution of the Einstein field equations for the
anisotropic Bianchi type I universes filled with an exponential-potential
scalar field and study their dynamics. It is shown, in agreement with previous
studies, that for a wide range of initial conditions the late-time behaviour of
the models is that of a power-law inflating FRW universe. This property, does
not hold, in contrast, when some degree of inhomogeneity is introduced, as
discussed in our following paper II.Comment: 16 pages, Plain LaTeX, 1 Figure to be sent on request, to appear in
Phys. Rev.
Consistent histories of systems and measurements in spacetime
Traditional interpretations of quantum theory in terms of wave function
collapse are particularly unappealing when considering the universe as a whole,
where there is no clean separation between classical observer and quantum
system and where the description is inherently relativistic. As an alternative,
the consistent histories approach provides an attractive "no collapse"
interpretation of quantum physics. Consistent histories can also be linked to
path-integral formulations that may be readily generalized to the relativistic
case. A previous paper described how, in such a relativistic spacetime path
formalism, the quantum history of the universe could be considered to be an
eignestate of the measurements made within it. However, two important topics
were not addressed in detail there: a model of measurement processes in the
context of quantum histories in spacetime and a justification for why the
probabilities for each possible cosmological eigenstate should follow Born's
rule. The present paper addresses these topics by showing how Zurek's concepts
of einselection and envariance can be applied in the context of relativistic
spacetime and quantum histories. The result is a model of systems and
subsystems within the universe and their interaction with each other and their
environment.Comment: RevTeX 4; 37 pages; v2 is a revision in response to reviewer
comments, connecting the discussion in the paper more closely to consistent
history concepts; v3 has minor editorial corrections; accepted for
publication in Foundations of Physics; v4 has a couple minor typographical
correction
Hydrogen-Helium Mixtures at High Pressure
The properties of hydrogen-helium mixtures at high pressure are crucial to
address important questions about the interior of Giant planets e.g. whether
Jupiter has a rocky core and did it emerge via core accretion? Using path
integral Monte Carlo simulations, we study the properties of these mixtures as
a function of temperature, density and composition. The equation of state is
calculated and compared to chemical models. We probe the accuracy of the ideal
mixing approximation commonly used in such models. Finally, we discuss the
structure of the liquid in terms of pair correlation functions.Comment: Proceedings article of the 5th Conference on Cryocrystals and Quantum
Crystals in Wroclaw, Poland, submitted to J. Low. Temp. Phys. (2004
Examining the ecological validity of the Talent Development Environment Questionnaire
It is clear that high class expertise and effective practice exists within many talent development environments across the world. However, there is also a general consensus that widespread evidence-based policy and practice is lacking. As such, it is crucial to develop solutions which can facilitate effective dissemination of knowledge and promotion of evidence-based talent development systems. While the Talent Development Environment Questionnaire (Martindale et al., 2010 ) provides a method through which this could be facilitated, its ecological validity has remained untested. As such, this study aimed to investigate the real world applicability of the questionnaire through discriminant function analysis. Athletes across ten distinct regional squads and academies were identified and separated into two broad levels, 'higher quality' (n = 48) and 'lower quality' (n = 51) environments, based on their process quality and productivity. Results revealed that the Talent Development Environment Questionnaire was able to discriminate with 77.8% accuracy. Furthermore, in addition to the questionnaire as a whole, two individual features, 'quality preparation' (P < 0.01) and 'understanding the athlete' (P < 0.01), were found to be significant discriminators. In conclusion, the results indicate robust structural properties and sound ecological validity, allowing the questionnaire to be used with more confidence in applied and research settings
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