48,782 research outputs found
Ventricular Action Potential Adaptation to Regular Exercise: Role of β-adrenergic and K\u3csub\u3eATP\u3c/sub\u3e Channel Function
Regular exercise training is known to affect the action potential duration (APD) and improve heart function, but involvement of β-adrenergic receptor (β-AR) subtypes and/or the ATP-sensitive K+ (KATP) channel is unknown. To address this, female and male Sprague-Dawley rats were randomly assigned to voluntary wheel-running or control groups; they were anesthetized after 6–8 wk of training, and myocytes were isolated. Exercise training significantly increased APD of apex and base myocytes at 1 Hz and decreased APD at 10 Hz. Ca2+ transient durations reflected the changes in APD, while Ca2+ transient amplitudes were unaffected by wheel running. The nonselective β-AR agonist isoproterenol shortened the myocyte APD, an effect reduced by wheel running. The isoproterenol-induced shortening of APD was largely reversed by the selective β1-AR blocker atenolol, but not the β2-AR blocker ICI 118,551, providing evidence that wheel running reduced the sensitivity of the β1-AR. At 10 Hz, the KATP channel inhibitor glibenclamide prolonged the myocyte APD more in exercise-trained than control rats, implicating a role for this channel in the exercise-induced APD shortening at 10 Hz. A novel finding of this work was the dual importance of altered β1-AR responsiveness and KATP channel function in the training-induced regulation of APD. Of physiological importance to the beating heart, the reduced response to adrenergic agonists would enhance cardiac contractility at resting rates, where sympathetic drive is low, by prolonging APD and Ca2+ influx; during exercise, an increase in KATP channel activity would shorten APD and, thus, protect the heart against Ca2+ overload or inadequate filling
Ventricular Action Potential Adaptation to Regular Exercise: Role of β-adrenergic and K\u3csub\u3eATP\u3c/sub\u3e Channel Function
Regular exercise training is known to affect the action potential duration (APD) and improve heart function, but involvement of β-adrenergic receptor (β-AR) subtypes and/or the ATP-sensitive K+ (KATP) channel is unknown. To address this, female and male Sprague-Dawley rats were randomly assigned to voluntary wheel-running or control groups; they were anesthetized after 6–8 wk of training, and myocytes were isolated. Exercise training significantly increased APD of apex and base myocytes at 1 Hz and decreased APD at 10 Hz. Ca2+ transient durations reflected the changes in APD, while Ca2+ transient amplitudes were unaffected by wheel running. The nonselective β-AR agonist isoproterenol shortened the myocyte APD, an effect reduced by wheel running. The isoproterenol-induced shortening of APD was largely reversed by the selective β1-AR blocker atenolol, but not the β2-AR blocker ICI 118,551, providing evidence that wheel running reduced the sensitivity of the β1-AR. At 10 Hz, the KATP channel inhibitor glibenclamide prolonged the myocyte APD more in exercise-trained than control rats, implicating a role for this channel in the exercise-induced APD shortening at 10 Hz. A novel finding of this work was the dual importance of altered β1-AR responsiveness and KATP channel function in the training-induced regulation of APD. Of physiological importance to the beating heart, the reduced response to adrenergic agonists would enhance cardiac contractility at resting rates, where sympathetic drive is low, by prolonging APD and Ca2+ influx; during exercise, an increase in KATP channel activity would shorten APD and, thus, protect the heart against Ca2+ overload or inadequate filling
Inter-satellite Quantum Key Distribution at Terahertz Frequencies
Terahertz (THz) communication is a topic of much research in the context of
high-capacity next-generation wireless networks. Quantum communication is also
a topic of intensive research, most recently in the context of space-based
deployments. In this work we explore the use of THz frequencies as a means to
achieve quantum communication within a constellation of micro-satellites in
Low-Earth-Orbit (LEO). Quantum communication between the micro-satellite
constellation and high-altitude terrestrial stations is also investigated. Our
work demonstrates that THz quantum entanglement distribution and THz quantum
key distribution are viable deployment options in the micro-satellite context.
We discuss how such deployment opens up the possibility for simpler integration
of global quantum and wireless networks. The possibility of using THz
frequencies for quantum-radar applications in the context of LEO deployments is
briefly discussed.Comment: 7 pages, 6 figure
Detecting Orbital Angular Momentum of Light in Satellite-to-Ground Quantum Communications
Satellite-based quantum communications enable a bright future for
global-scale information security. However, the spin orbital momentum of light,
currently used in many mainstream quantum communication systems, only allows
for quantum encoding in a two-dimensional Hilbert space. The orbital angular
momentum (OAM) of light, on the other hand, enables quantum encoding in
higher-dimensional Hilbert spaces, opening up new opportunities for
high-capacity quantum communications. Due to its turbulence-induced decoherence
effects, however, the atmospheric channel may limit the practical usage of OAM.
In order to determine whether OAM is useful for satellite-based quantum
communications, we numerically investigate the detection likelihoods for OAM
states that traverse satellite-to-ground channels. We show that the use of OAM
through such channels is in fact feasible. We use our new results to then
investigate design specifications that could improve OAM detection -
particularly the use of advanced adaptive optics techniques. Finally, we
discuss how our work provides new insights into future implementations of
space-based OAM systems within the context of quantum communications.Comment: 7 pages, 7 figure
Combinatorial cobordism maps in hat Heegaard Floer theory
In a previous paper, Sarkar and the third author gave a combinatorial
description of the hat version of Heegaard Floer homology for three-manifolds.
Given a cobordism between two connected three-manifolds, there is an induced
map between their Heegaard Floer homologies. Assume that the first homology
group of each boundary component surjects onto the first homology group of the
cobordism (modulo torsion). Under this assumption, we present a procedure for
finding the rank of the induced Heegaard Floer map combinatorially, in the hat
version.Comment: 34 pages, 31 figures; discussion now limited to cobordisms satisfying
a homological assumption; Section 4 completely rewritten; various other
revisions; this version to appear in Duke Math.
Replica Monte Carlo Simulation (Revisited)
In 1986, Swendsen and Wang proposed a replica Monte Carlo algorithm for spin
glasses [Phys. Rev. Lett. 57 (1986) 2607]. Two important ingredients are
present, (1) the use of a collection of systems (replicas) at different of
temperatures, but with the same random couplings, (2) defining and flipping
clusters. Exchange of information between the systems is facilitated by fixing
the tau spin (tau=sigma^1\sigma^2) and flipping the two neighboring systems
simultaneously. In this talk, we discuss this algorithm and its relationship to
replica exchange (also known as parallel tempering) and Houdayer's cluster
algorithm for spin glasses. We review some of the early results obtained using
this algorithm. We also present new results for the correlation times of
replica Monte Carlo dynamics in two and three dimensions and compare them with
replica exchange.Comment: For "Statistical Physics of Disordered Systems and Its Applications",
12-15 July 2004, Shonan Village Center, Hayama, Japan, 7 page
Multi-Stream Inflation in a Landscape
There are hidden observables for inflation, such as features localized in
position space, which do not manifest themselves when only one inflation
trajectory is considered. To address this issue, we investigate inflation
dynamics in a landscape mimicked by a random potential. We calculate the
probability for bifurcation of the inflation trajectory in multi-stream
inflation. Depending on the shape of the random bumps and the distance between
bumps in the potential, there is a phase transition: on one side of the
critical curve in parameter space isocurvature fluctuation are exponentially
amplified and bifurcation becomes very probable. On the other side bifurcation
is dominated by a random walk where bifurcations are less likely to happen.Comment: Reference added to match published version in JCA
- …