6,363 research outputs found
Electrical neurostimulation for chronic pain: on selective relay of sensory neural activities in myelinated nerve fibers
Chronic pain affects about 100 million adults in the US. Despite their great
need, neuropharmacology and neurostimulation therapies for chronic pain have
been associated with suboptimal efficacy and limited long-term success, as
their mechanisms of action are unclear. Yet current computational models of
pain transmission suffer from several limitations. In particular, dorsal column
models do not include the fundamental underlying sensory activity traveling in
these nerve fibers. We developed a (simple) simulation test bed of electrical
neurostimulation of myelinated nerve fibers with underlying sensory activity.
This paper reports our findings so far. Interactions between stimulation-evoked
and underlying activities are mainly due to collisions of action potentials and
losses of excitability due to the refractory period following an action
potential. In addition, intuitively, the reliability of sensory activity
decreases as the stimulation frequency increases. This first step opens the
door to a better understanding of pain transmission and its modulation by
neurostimulation therapies
An Alignment Scheme for Atomic Force Tomograms of Conductive Filaments in Resistance Switching Devices
The search for a memristive device for use in neuromorphic circuits has brought great interest to research regarding resistance switching devices (also known RRAM devices). These devices, which grow metallic filaments through an insulating material, presently have one major drawback: the electrical characteristics (namely on-state resistance) have a high level of variability from device to device which renders them unusable. Much of this variability can conceivably be attributed to the structure of the metallic filaments. This research presents the development of a reliable means of spatially characterizing the filaments using a tomographic technique based on atomic force microscopy, especially focusing on a post-processing software to analyze the microscopy data
Regular realizability problems and context-free languages
We investigate regular realizability (RR) problems, which are the problems of
verifying whether intersection of a regular language -- the input of the
problem -- and fixed language called filter is non-empty. In this paper we
focus on the case of context-free filters. Algorithmic complexity of the RR
problem is a very coarse measure of context-free languages complexity. This
characteristic is compatible with rational dominance. We present examples of
P-complete RR problems as well as examples of RR problems in the class NL. Also
we discuss RR problems with context-free filters that might have intermediate
complexity. Possible candidates are the languages with polynomially bounded
rational indices.Comment: conference DCFS 201
Therapeutic Challenges Of Multi-Being
This paper emerges from an attempt to shift the locus of understanding human action from the individual to relationship. In doing so we come to see persons as multi-beings, that is, as constituted within multiple relationships from which they emerge with multiple, incoherent, and often conflicting potentials. Therapy, in this context, becomes a collaborative relationship with the aim of transforming the client\u27s broader relational network. In this view, schooling in a singular practice of therapy artificially limits the therapist\u27s potential, and thus the possible outcomes of the client–therapist relationship. Invited, then, is a reflective eclecticism, in which the myriad potentials of both the therapist and client are considered in tandem. This view is illustrated by contrasting three relational conditions in which clients find themselves, each of which invites a different form of self-expression from the therapist
Observational calibration of the projection factor of Cepheids. II. Application to nine Cepheids with HST/FGS parallax measurements
The distance to pulsating stars is classically estimated using the
parallax-of-pulsation (PoP) method, which combines spectroscopic radial
velocity measurements and angular diameter estimates to derive the distance of
the star. An important application of this method is the determination of
Cepheid distances, in view of the calibration of their distance scale. However,
the conversion of radial to pulsational velocities in the PoP method relies on
a poorly calibrated parameter, the projection factor (p-factor). We aim to
measure empirically the value of the p-factors of a homogeneous sample of nine
Galactic Cepheids for which trigonometric parallaxes were measured with the
Hubble Space Telescope Fine Guidance Sensor. We use the SPIPS algorithm, a
robust implementation of the PoP method that combines photometry,
interferometry, and radial velocity measurements in a global modeling of the
pulsation. We obtained new interferometric angular diameters using the PIONIER
instrument at the Very Large Telescope Interferometer, completed by data from
the literature. Using the known distance as an input, we derive the value of
the p-factor and study its dependence with the pulsation period. We find the
following p-factors: 1.20 0.12 for RT Aur, 1.48 0.18 for T Vul,
1.14 0.10 for FF Aql, 1.31 0.19 for Y Sgr, 1.39 0.09 for X
Sgr, 1.35 0.13 for W Sgr, 1.36 0.08 for Dor, 1.41
0.10 for Gem, and 1.23 0.12 for Car. These values are
consistently close to p = 1.324 0.024. We observe some dispersion around
this average value, but the observed distribution is statistically consistent
with a constant value of the p-factor as a function of the pulsation period.
The error budget of our determination of the p-factor values is presently
dominated by the uncertainty on the parallax, a limitation that will soon be
waived by Gaia.Comment: 18 pages, 13 figure
Letters
A Footnote to Tales Before Narnia by Douglas A. Anderson: Suggests an addition to the list of recommended reading in the author’s Tales Before Narnia: M.P. Shiel. C.S. Lewis was known to have owned several books by this author.
The Origins of Dwarves by Pierre H. Berube: Following on Helios de Rosario Martinez’s article in Mythlore 109/110, suggests several avenues of exploration for the popular folkloric concept of dwarves as miners
Observational calibration of the projection factor of Cepheids I. The Type II Cepheid kappa Pavonis
The distances of pulsating stars, in particular Cepheids, are commonly
measured using the parallax of pulsation technique. The different versions of
this technique combine measurements of the linear diameter variation (from
spectroscopy) and the angular diameter variation (from photometry or
interferometry) amplitudes, to retrieve the distance in a quasi-geometrical
way. However, the linear diameter amplitude is directly proportional to the
projection factor (hereafter p-factor), which is used to convert spectroscopic
radial velocities (i.e., disk integrated) into pulsating (i.e., photospheric)
velocities. The value of the p-factor and its possible dependence on the
pulsation period are still widely debated. Our goal is to measure an
observational value of the p-factor of the type-II Cepheid kappa Pavonis, whose
parallax was measured with an accuracy of 5% using HST/FGS. We used this
parallax as a starting point to derive the p-factor of kappa Pav, using the
SPIPS technique, which is a robust version of the parallax-of-pulsation method
that employs radial velocity, interferometric and photometric data. We applied
this technique to a combination of new VLTI/PIONIER optical interferometric
angular diameters, new CORALIE and HARPS radial velocities, as well as
multi-colour photometry and radial velocities from the literature. We obtain a
value of p = 1.26 +/- 0.07 for the p-factor of kappa Pav. This result agrees
with several of the recently derived Period-p-factor relationships from the
literature, as well as previous observational determinations for Cepheids.
Individual estimates of the p-factor are fundamental to calibrating the
parallax of pulsation distances of Cepheids. Together with previous
observational estimates, the projection factor we obtain points to a weak
dependence of the p-factor on period.Comment: 8 pages, 6 figures, accepted in A&
Temporally resolved second-order photon correlations of exciton-polariton Bose-Einstein condensate formation
Second-order time correlation measurements with a temporal resolution better
than 3 ps were performed on a CdTe microcavity where spontaneous Bose-Einstein
condensation is observed. After the laser pulse, the nonresonantly excited
thermal polariton population relaxes into a coherent polariton condensate.
Photon statistics of the light emitted by the microcavity evidences a clear
phase transition from the thermal state to a coherent state, which occurs
within 3.2 ps after the onset of stimulated scattering. Following this very
fast transition, we show that the emission possesses a very high coherence that
persists for more than 100 ps after the build-up of the condensate.Comment: 4 pages, 3 figure
Propagation dynamics on networks featuring complex topologies
Analytical description of propagation phenomena on random networks has
flourished in recent years, yet more complex systems have mainly been studied
through numerical means. In this paper, a mean-field description is used to
coherently couple the dynamics of the network elements (nodes, vertices,
individuals...) on the one hand and their recurrent topological patterns
(subgraphs, groups...) on the other hand. In a SIS model of epidemic spread on
social networks with community structure, this approach yields a set of ODEs
for the time evolution of the system, as well as analytical solutions for the
epidemic threshold and equilibria. The results obtained are in good agreement
with numerical simulations and reproduce random networks behavior in the
appropriate limits which highlights the influence of topology on the processes.
Finally, it is demonstrated that our model predicts higher epidemic thresholds
for clustered structures than for equivalent random topologies in the case of
networks with zero degree correlation.Comment: 10 pages, 5 figures, 1 Appendix. Published in Phys. Rev. E (mistakes
in the PRE version are corrected here
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