22,429 research outputs found
Effects of External Loads on Human Head Movement Control Systems
The central and reflexive control strategies underlying movements were elucidated by studying the effects of external loads on human head movement control systems. Some experimental results are presented on dynamic changes weigh the addition of aviation helmet (SPH4) and lead weights (6 kg). Intended time-optimal movements, their dynamics and electromyographic activity of neck muscles in normal movements, and also in movements made with external weights applied to the head were measured. It was observed that, when the external loads were added, the subject went through complex adapting processes and the head movement trajectory and its derivatives reached steady conditions only after transient adapting period. The steady adapted state was reached after 15 to 20 seconds (i.e., 5 to 6 movements)
Unpolarized fragmentation function for the pion and kaon via the nonlocal chiral-quark model
In this talk we present our recent studies for the unpolarized fragmentation
functions for the pion and kaon, employing the nonlocal chiral quark model,
which manifests the nonlocal interaction between the quarks and pseudoscalar
mesons, in the light-cone frame. It turns out that the nonlocal interaction
produces considerable differences in comparison to typical local-interaction
models.Comment: 4 pages, 2 figures, Talk given at the international conference The
Fifth Asia-Pacific Conference on Few-Body Systems in Physics 2011 (APFB2011),
Seoul, Republic of Korea, 22-26 August 201
Model simulation studies to clarify the effect on saccadic eye movements of initial condition velocities set by the Vestibular Ocular Reflex (VOR)
Voluntary active head rotations produced vestibulo-ocular reflex eye movements (VOR) with the subject viewing a fixation target. When this target jumped, the size of the refixation saccades were a function of the ongoing initial velocity of the eye. Saccades made against the VOR were larger in magnitude. Simulation of a reciprocally innervated model eye movement provided results comparable to the experimental data. Most of the experimental effect appeared to be due to linear summation for saccades of 5 and 10 degree magnitude. For small saccades of 2.5 degrees, peripheral nonlinear interaction of state variables in the neuromuscular plant also played a role as proven by comparable behavior in the simulated model with known controller signals
Twist-3 pion and kaon distribution amplitudes from the instanton vacuum with flavor SU(3) symmetry breaking
We investigate the twist-3 pion and kaon distribution amplitudes of the
pseudoscalar (phi^p_{pi,K}) and pseudotensor (phi^{sigma}_{pi,K}) types, based
on the effective chiral action from the instanton vacuum. Effects of flavor
SU(3) symmetry breaking are explicitly taken into account. The Gegenbauer
moments and the moments of the distribution amplitudes () are also
computed. Our results are summarized as follows: a^p_{2,pi} ~ 0.4, a^p_{1,K} ~
0.02 and a^p_{2,K} ~ 0.14, and a^{sigma}_{2,pi} ~ 0.02 and a^{sigma}_{1,K} ~
a^{sigma}_{2,K} ~ 0; ^p_{\pi} ~ ^p_K ~ 0.37 and ^p_K ~ 0, and
^{sigma}_{pi} ~ ^{sigma}_K ~ 0.20 and ^{sigma}_K ~ 0. We
compare our results with those from the QCD sum rules. We also discuss the
relevant Wilson coefficients which were analyzed recently in chiral
perturbation theory.Comment: 12 pages, 4 figures, accepted for publication in PR
Fragmentation and quark distribution functions for the pion and kaon with explicit flavor-SU(3)-symmetry breaking
We investigate the unpolarized pion and kaon fragmentation functions,
employing the nonlocal chiral-quark model, which manifests the nonlocal
interactions between the quarks and pseudoscalar mesons, considering the
explicit flavor-SU(3)-symmetry breaking in terms of the current-quark masses.
Moreover, we study the quark-distribution functions, derived from the
fragmentation ones with the Drell-Yan-Levi relation. Numerical results are
evaluated to higher Q^2 by the DGLAP evolution and compared with the empirical
data. The ratios between the relevant valance quark-distribution functions are
also discussed. It turns out that the present results are in relatively good
agreement with available data and other theoretical estimations.Comment: 13 pages, 16 figure
Random Walk Smooth Transition Autoregressive Models
This paper extends the family of smooth transition autoregressive (STAR) models by proposing a specification in which the autoregressive parameters follow random walks. The random walks in the parameters can capture structural change within a regime switching framework, but in contrast to the time varying STAR (TV-STAR) speciifcation recently introduced by Lundbergh et al (2003), structural change in our random walk STAR (RW-STAR) setting follows a stochastic process rather than a deterministic function of time. We suggest tests for RW-STAR behaviour and study the performance of RW-STARmodels in an empirical setting. The out-of sample forecasting performance of our RW-STAR models is encouraging - better than AR, LSTAR and TV-STAR specifications with respect to point forecasts and on a par with TV-STAR speciÞcations with respect to forecast density evaluations.Forecast density evaluation, Non-constant parameters, Random walk
Extended nonlocal chiral-quark model for the heavy-light quark systems
In this talk, we report the recent progress on constructing a
phenomenological effective model for the heavy-light quark systems, which
consist of (u,d,s,c,b) quarks, i.e. extended nonlocal chiral-quark model
(ExNLChQM). We compute the heavy-meson weak-decay constants to verify the
validity of the model. From the numerical results, it turns out that (f_D, f_B,
f_{D_s}, f_{B_s})=(207.54,208.13,262.56,262.39) MeV. These values are in
relatively good agreement with experimental data and various theoretical
estimations.Comment: 3 pages, 4 figures, Talk given at the 20th International IUPAP
Conference on Few-Body Problems in Physics (FB20), 20~25 August 2012,
Fukuoka, Japa
Intermittency in two-dimensional Ekman-Navier-Stokes turbulence
We study the statistics of the vorticity field in two-dimensional
Navier-Stokes turbulence with a linear Ekman friction. We show that the
small-scale vorticity fluctuations are intermittent, as conjectured by Nam et
al. [Phys. Rev. Lett. vol.84 (2000) 5134]. The small-scale statistics of
vorticity fluctuations coincides with the one of a passive scalar with finite
lifetime transported by the velocity field itself.Comment: 4 pages, 7 figure
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