2,792 research outputs found
BTZ black hole from Poisson-Lie T-dualizable sigma models with spectators
The non-Abelian T-dualization of the BTZ black hole is discussed in detail by
using the Poisson-Lie T-duality in the presence of spectators. We explicitly
construct a dual pair of sigma models related by Poisson-Lie symmetry. The
original model is built on a -dimensional manifold , where as a two-dimensional real non-Abelian Lie group
acts freely on , while is the orbit of in . The
findings of our study show that the original model indeed is canonically
equivalent to the Wess-Zumino-Witten (WZW) model for a given
value of the background parameters. Moreover, by a convenient coordinate
transformation we show that this model describes a string propagating in a
spacetime with the BTZ black hole metric in such a way that a new family of the
solutions to low energy string theory with the BTZ black hole vacuum metric,
constant dilaton field and a new torsion potential is found. The dual model is
built on a -dimensional target manifold with
two-dimensional real Abelian Lie group acting freely on it.
We further show that the dual model yields a three-dimensional charged black
string for which the mass and axion charge per unit length are
calculated. After that, the structure and asymptotic nature of the dual
space-time including the horizon and singularity are determined.Comment: 20 page
The effect of gag reflex on cardiac sympatovagal tone
Objectives: Heart velocity may be influenced by gagging. The medulla oblongata receives the afferents of gag reflex. Neuronal pools of vomiting, salivation and cardiac parasympathetic fibers are very close in this area. So, their activities may be changed by spillover from each other. Using the heart rate variability (HRV) analysis, the effect of gagging on cardiac sympatovagal balance was studied. Methods: ECG was recorded from 9 healthy nonsmoker volunteer students for 10 minutes in the sitting position between 10 and 11 AM. Gagging was elicited by tactile stimulation of the posterior pharyngeal wall. At 1 kHz sampling rate, HRV was calculated. The mean of heart rate at low and high frequencies (LF: 0.04-0.15; HF: 0.15-0.4 Hz) were compared before and after the stimulus. Results: The mean of average heart rate, LF and HF in normalized units (nu) and the ratio of them (LF/HF) before and after the gagging were 89.9 ± 3 and 95.2 ± 3 bpm; 44.2 ± 5.8 and 21.2 ± 4; 31.1 ± 5.3 and 39.4 ± 3.8; and 1.7 ± 0.3 and 0.6 ± 0.2 respectively. Conclusion: Gagging increased heart velocity and had differential effect on two branches of cardiac autonomic nerves. The paradoxical relation between average heart rate and HRV indexes of sympatovagal tone may be due to unequal rate of change in autonomic fiber activities which is masked by 5 minutes interval averaging. © OMSB, 2012
The long reach of DNA sequence heterogeneity in diffusive processes
Many biological processes involve one dimensional diffusion over a correlated
inhomogeneous energy landscape with a correlation length . Typical
examples are specific protein target location on DNA, nucleosome repositioning,
or DNA translocation through a nanopore, in all cases with 10
nm. We investigate such transport processes by the mean first passage time
(MFPT) formalism, and find diffusion times which exhibit strong sample to
sample fluctuations. For a a displacement , the average MFPT is diffusive,
while its standard deviation over the ensemble of energy profiles scales as
with a large prefactor. Fluctuations are thus dominant for
displacements smaller than a characteristic : typical values are
much less than the mean, and governed by an anomalous diffusion rule. Potential
biological consequences of such random walks, composed of rapid scans in the
vicinity of favorable energy valleys and occasional jumps to further valleys,
is discussed
Linear response relations in fluctuational electrodynamics
Near field radiative heat transfer and dynamic Casimir forces are just two
instances of topics of technological and fundamental interest studied via the
formalism of fluctuational electrodynamics. From the perspective of experiment
and simulations, it is hard to precisely control and probe such non-equilibrium
situations. Fluctuations in equilibrium are easier to measure, and can
typically be related to non-equilibrium response functions by Green-Kubo
relations. We consider a collection of arbitrary objects in vacuum, perturbed
by changing the temperature or velocity of one object. Developing a method for
computation of higher order correlation functions in fluctuational
electrodynamics, we explicitly compare linear response and equilibrium
fluctuations. We obtain a Green-Kubo relation for the radiative heat transfer,
as well as a closed formula for the vacuum friction in arbitrary geometries in
the framework of scattering theory. We comment on the signature of the
radiative heat conductivity in equilibrium fluctuations.Comment: Main article: 5 pages, 2 figures; Supplemental Material: 2 page
Interplay of roughness/modulation and curvature at proximity
We show that roughness or surface modulations change the distance dependence
of (power-law) interactions between curved objects at proximity. The modified
scaling law is then simply related to the order of the first non-vanishing
coefficient of the Taylor expansion of the distribution of separations between
the surfaces. The latter can in principle be estimated by scanning
measurements, or computed for well characterized modulations, and then used to
predict short-distance scaling behavior in disparate experiments. For example,
we predict that the radiative heat transfer between a rough sphere and a plate
approaches a constant with decreasing separation. Similar saturation is
expected for the Casimir force between dielectric or metallic surfaces with
appropriate modulations over distinct length scales.Comment: 5 pages, 2 figure
Small distance expansion for radiative heat transfer between curved objects
We develop a small distance expansion for the radiative heat transfer between
gently curved objects, in terms of the ratio of distance to radius of
curvature. A gradient expansion allows us to go beyond the lowest order
proximity transfer approximation. The range of validity of such expansion
depends on temperature as well as material properties. Generally, the expansion
converges faster for the derivative of the transfer than for the transfer
itself, which we use by introducing a near-field adjusted plot. For the case of
a sphere and a plate, the logarithmic correction to the leading term has a very
small prefactor for all materials investigated.Comment: 5 pages, 3 figure
Evolution in range expansions with competition at rough boundaries.
When a biological population expands into new territory, genetic drift develops an enormous influence on evolution at the propagating front. In such range expansion processes, fluctuations in allele frequencies occur through stochastic spatial wandering of both genetic lineages and the boundaries between genetically segregated sectors. Laboratory experiments on microbial range expansions have shown that this stochastic wandering, transverse to the front, is superdiffusive due to the front's growing roughness, implying much faster loss of genetic diversity than predicted by simple flat front diffusive models. We study the evolutionary consequences of this superdiffusive wandering using two complementary numerical models of range expansions: the stepping stone model, and a new interpretation of the model of directed paths in random media, in the context of a roughening population front. Through these approaches we compute statistics for the times since common ancestry for pairs of individuals with a given spatial separation at the front, and we explore how environmental heterogeneities can locally suppress these superdiffusive fluctuations
A Performance Study of Dynamic Zone Topology Routing Protocol
In this paper we present a simulation study of a hybrid routing protocol we proposed in our previous work. Our hybrid routing strategy is called Dynamic Zone Topology Routing protocol (DZTR). This protocol has been designed to provide scalable routing in a Mobile Ad hoc Networking (MANET) environment. DZTR breaks the network into a number of zones by using a GPS. The topology of each zone is maintained proactively and the route to the nodes in other zones are determined reactively. DZTR proposes a number of different strategies to reduce routing overhead in large networks and reduce the single point of failure during data forwarding. In this paper, we propose a number of improvements for DZTR and investigate its performance using simulations. We compare the performance of DZTR against AODV, LAR1 and LPAR. Our results show that DZTR has fewer routing overheads than the other simulated routing protocols and achieves higher levels of scalability as the size and the density of the network is increased
Formation and Stability of Synaptic Receptor Domains
Neurotransmitter receptor molecules, concentrated in postsynaptic domains
along with scaffold and a number of other molecules, are key regulators of
signal transmission across synapses. Employing experiment and theory, we
develop a quantitative description of synaptic receptor domains in terms of a
reaction-diffusion model. We show that interactions between only receptor and
scaffold molecules, together with the rapid diffusion of receptors on the cell
membrane, are sufficient for the formation and stable characteristic size of
synaptic receptor domains. Our work reconciles long-term stability of synaptic
receptor domains with rapid turnover and diffusion of individual receptors.Comment: 5 pages, 3 figures, Supplementary Materia
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