3,551 research outputs found
Influence of Fatigue on Planned Agility Performance in Soccer Players.
International Journal of Exercise Science 13(1): 656-666, 2020. We investigated the acute fatiguing effects of sprint interval training (SIT) on change of direction performance in male and female soccer players. A T-test was performed once before (PRE) and twice following (POST 1 and POST 2) the completion of four sets of 4 s cycle ergometer sprints protocol. The sprint intervals were separated by 25 s active recovery. POST 1 was performed approximately 25 s following the final cycle sprint and POST 2 began two minutes after completing POST 1. Repeated measures ANOVA and Bonferroni post hoc tests were used to determine any significant differences in the time to complete the T-tests. The average power output drop measured during cycle SIT was 30.7 ± 9%. Time to complete the T-test significantly differed among the three tests (PRE: 10.46 ± .17 s; POST 1: 11.67 ± .33 s; POST 2: 10.96 ± .19 s; F (2, 54) = 6.174, p = .003). Post hoc test revealed an increase in time from PRE to POST 1 (p = .002) but no difference between PRE and POST 2 (p = .473). Nine participants (48%) were unable to complete POST 1 without errors; however, ten (52%) participants recovered enough to perform POST 1 without error. These results show that acute fatigue from SIT impairs change of direction performance, but performance can be recovered within a few minutes of rest. Coaches can combine fatigue inducing drills and change of direction training into same sessions with the right rest interval between the training modes
Electron-vibration interaction in single-molecule junctions: from contact to tunneling regime
Point contact spectroscopy on a H2O molecule bridging Pt electrodes reveals a
clear crossover between enhancement and reduction of the conductance due to
electron-vibration interaction. As single channel models predict such a
crossover at transmission probability of t=0.5, we used shot noise measurements
to analyze the transmission and observed at least two channels across the
junction where the dominant channel has t=0.51+/-0.01 transmission probability
at the crossover conductance, which is consistent with the predictions for
single-channel models.Comment: 4 pages, 1 table, 4 figure
Quantum Detection with Unknown States
We address the problem of distinguishing among a finite collection of quantum
states, when the states are not entirely known. For completely specified
states, necessary and sufficient conditions on a quantum measurement minimizing
the probability of a detection error have been derived. In this work, we assume
that each of the states in our collection is a mixture of a known state and an
unknown state. We investigate two criteria for optimality. The first is
minimization of the worst-case probability of a detection error. For the second
we assume a probability distribution on the unknown states, and minimize of the
expected probability of a detection error.
We find that under both criteria, the optimal detectors are equivalent to the
optimal detectors of an ``effective ensemble''. In the worst-case, the
effective ensemble is comprised of the known states with altered prior
probabilities, and in the average case it is made up of altered states with the
original prior probabilities.Comment: Refereed version. Improved numerical examples and figures. A few
typos fixe
The Galactic Center as a laboratory for extreme mass ratio gravitational wave source dynamics
The massive Galactic black hole and the stars around it are a unique
laboratory for studying how relaxation processes lead to close interactions of
stars and compact remnants with the central massive black hole, in particular
those leading to the emission of gravitational waves. I review new results on
the processes of strong mass segregation and loss-cone refilling by massive
perturbers and resonant relaxation; describe observational evidence that these
processes play a role in the Galactic Center and can be studied there; and
discuss some of the implications for Extreme Mass Ration Inspiral event rates
and their properties.Comment: 8 pp, 6 figs. Invited talk. To appear in the proceedings of the 2nd
Kolkata conference on Observational Evidence for Black Holes in the Universe
(2/2008), Ed. S. Chakrabarti (AIP) [typo in equation and notation corrected
Qubit State Discrimination
We show how one can solve the problem of discriminating between qubit states.
We use the quantum state discrimination duality theorem and the Bloch sphere
representation of qubits which allows for an easy geometric and analytical
representation of the optimal guessing strategies.Comment: 6 pages, 4 figures. v2 has small corrections and changes in
reference
Stellar Dynamics of Extreme-Mass-Ratio Inspirals
Inspiral of compact stellar remnants into massive black holes (MBHs) is
accompanied by the emission of gravitational waves at frequencies that are
potentially detectable by space-based interferometers. Event rates computed
from statistical (Fokker-Planck, Monte-Carlo) approaches span a wide range due
to uncertaintities about the rate coefficients. Here we present results from
direct integration of the post-Newtonian N-body equations of motion descrbing
dense clusters of compact stars around Schwarzschild MBHs. These simulations
embody an essentially exact (at the post-Newtonian level) treatment of the
interplay between stellar dynamical relaxation, relativistic precession, and
gravitational-wave energy loss. The rate of capture of stars by the MBH is
found to be greatly reduced by relativistic precession, which limits the
ability of torques from the stellar potential to change orbital angular
momenta. Penetration of this "Schwarzschild barrier" does occasionally occur,
resulting in capture of stars onto orbits that gradually inspiral due to
gravitational wave emission; we discuss two mechanisms for barrier penetration
and find evidence for both in the simulations. We derive an approximate formula
for the capture rate, which predicts that captures would be strongly disfavored
from orbits with semi-major axes below a certain value; this prediction, as
well as the predicted rate, are verified in the N-body integrations. We discuss
the implications of our results for the detection of extreme-mass-ratio
inspirals from galactic nuclei with a range of physical properties.Comment: 28 pages, 16 figures. Version 2 is significantly revised to reflect
new insights into J and Q effects, to be published late
Measurement of transparency ratios for protons from short-range correlated pairs
Nuclear transparency, Tp(A), is a measure of the average probability for a
struck proton to escape the nucleus without significant re-interaction.
Previously, nuclear transparencies were extructed for quasi-elastic A(e,e'p)
knockout of protons with momentum below the Fermi momentum, where the spectral
functions are well known. In this paper we extract a novel observable, the
transparency ratio, Tp(A)/T_p(12C), for knockout of high-missing-momentum
protons from the breakup of short range correlated pairs (2N-SRC) in Al, Fe and
Pb nuclei relative to C. The ratios were measured at momentum transfer Q^2 >
1.5 (GeV/c)^2 and x_B > 1.2 where the reaction is expected to be dominated by
electron scattering from 2N-SRC. The transparency ratios of the knocked-out
protons coming from 2N-SRC breakup are 20 - 30% lower than those of previous
results for low missing momentum. They agree with Glauber calculations and
agree with renormalization of the previously published transparencies as
proposed by recent theoretical investigations. The new transparencies scale as
A^-1/3, which is consistent with dominance of scattering from nucleons at the
nuclear surface.Comment: 6 pages, 4 figure
An efficient scheme for numerical simulations of the spin-bath decoherence
We demonstrate that the Chebyshev expansion method is a very efficient
numerical tool for studying spin-bath decoherence of quantum systems. We
consider two typical problems arising in studying decoherence of quantum
systems consisting of few coupled spins: (i) determining the pointer states of
the system, and (ii) determining the temporal decay of quantum oscillations. As
our results demonstrate, for determining the pointer states, the
Chebyshev-based scheme is at least a factor of 8 faster than existing
algorithms based on the Suzuki-Trotter decomposition. For the problems of
second type, the Chebyshev-based approach has been 3--4 times faster than the
Suzuki-Trotter-based schemes. This conclusion holds qualitatively for a wide
spectrum of systems, with different spin baths and different Hamiltonians.Comment: 8 pages (RevTeX), 3 EPS figure
A decomposition algorithm for robust lot sizing problem with remanufacturing option
In this paper, we propose a decomposition procedure for constructing robust optimal production plans for reverse inventory systems. Our method is motivated by the need of overcoming the excessive computational time requirements, as well as the inaccuracies caused by imprecise representations of problem parameters. The method is based on a min-max formulation that avoids the excessive conservatism of the dualization technique employed by Wei et al. (2011). We perform a computational study using our decomposition framework on several classes of computer generated test instances and we report our experience. Bienstock and Ă–zbay (2008) computed optimal base stock levels for the traditional lot sizing problem when the production cost is linear and we extend this work here by considering return inventories and setup costs for production. We use the approach of Bertsimas and Sim (2004) to model the uncertainties in the input
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