772 research outputs found
Limit Theorems and Governing Equations for Levy Walks
The Levy Walk is the process with continuous sample paths which arises from
consecutive linear motions of i.i.d. lengths with i.i.d. directions. Assuming
speed 1 and motions in the domain of beta-stable attraction, we prove
functional limit theorems and derive governing pseudo-differential equations
for the law of the walker's position. Both Levy Walk and its limit process are
continuous and ballistic in the case beta in (0,1). In the case beta in (1,2),
the scaling limit of the process is beta-stable and hence discontinuous. This
case exhibits an interesting situation in which scaling exponent 1/beta on the
process level is seemingly unrelated to the scaling exponent 3-beta of the
second moment. For beta = 2, the scaling limit is Brownian motion
Spinal corollary discharge modulates motion sensing during vertebrate locomotion
During active movements, neural replicas of the underlying motor commands may assist in adapting motion-detecting sensory systems to an animal's own behaviour. The transmission of such motor efference copies to the mechanosensory periphery offers a potential predictive substrate for diminishing sensory responsiveness to self-motion during vertebrate locomotion. Here, using semi-isolated in vitro preparations of larval Xenopus, we demonstrate that shared efferent neural pathways to hair cells of vestibular endorgans and lateral line neuromasts express cyclic impulse bursts during swimming that are directly driven by spinal locomotor circuitry. Despite common efferent innervation and discharge patterns, afferent signal encoding at the two mechanosensory peripheries is influenced differentially by efference copy signals, reflecting the different organization of body/water motion-detecting processes in the vestibular and lateral line systems. The resultant overall gain reduction in sensory signal encoding in both cases, which likely prevents overstimulation, constitutes an adjustment to increased stimulus magnitudes during locomotion
Magellan LDSS3 emission confirmation of galaxies hosting metal-rich Lyman-alpha absorption systems
Using the Low Dispersion Survey Spectrograph 3 at the Magellan II Clay
Telescope, we target {candidate absorption host galaxies} detected in deep
optical imaging {(reaching limiting apparent magnitudes of 23.0-26.5 in and filters) in the fields of three QSOs, each of which shows the
presence of high metallicity, high absorption systems in their
spectra (Q0826-2230: =0.9110, Q1323-0021: ,
Q1436-0051: ). We confirm three host galaxies {at
redshifts 0.7387, 0.7401, and 0.9286} for two of the Lyman- absorption
systems (one with two galaxies interacting). For these systems, we are able to
determine the star formation rates (SFRs); impact parameters (from previous
imaging detections); the velocity shift between the absorption and emission
redshifts; and, for one system, also the emission metallicity.} Based on
previous photometry, we find these galaxies have LL. The [O II]
SFRs for these galaxies are in the range M yr
{(uncorrected for dust)}, while the impact parameters lie in the range
kpc. {Despite the fact that we have confirmed galaxies at 50 kpc from the QSO,
no gradient in metallicity is indicated between the absorption metallicity
along the QSO line of sight and the emission line metallicity in the galaxies.}
We confirm the anti-correlation between impact parameter and from
the literature. We also report the emission redshift of five other galaxies:
three at , and two (LL) at not
corresponding to any known absorption systems.Comment: 14 pages, 7 figures, 4 tables, accepted to MNRA
Fractional Fokker-Planck Equations for Subdiffusion with Space-and-Time-Dependent Forces
We have derived a fractional Fokker-Planck equation for subdiffusion in a
general space-and- time-dependent force field from power law waiting time
continuous time random walks biased by Boltzmann weights. The governing
equation is derived from a generalized master equation and is shown to be
equivalent to a subordinated stochastic Langevin equation.Comment: 5 page
A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to Damped Lyman-alpha Systems - VI. Metallicity and Geometry as Gas Flow Probes
The use of background quasars provides a powerful tool to probe the cool gas
in the circum-galactic medium of foreground galaxies. Here, we present new
observations with SINFONI and X-Shooter of absorbing-galaxy candidates at
z=0.7-1. We report the detection with both instruments of the H-alpha emission
line of one sub-DLA at z_abs=0.94187 with log N(HI)=19.38^+0.10_-0.15 towards
SDSS J002133.27+004300.9. We estimate the star formation rate: SFR=3.6+/-2.2
solar masses per year in that system. A detailed kinematic study indicates a
dynamical mass M_dyn=10^9.9+/-0.4 solar masses and a halo mass
M_halo=10^11.9+/-0.5 solar masses. In addition, we report the OII detection
with X-Shooter of another DLA at z_abs=0.7402 with log N(HI)=20.4+/-0.1 toward
Q0052+0041 and an estimated SFR of 5.3+/-0.7 solar masses per year. Three other
objects are detected in the continuum with X-Shooter but the nature and
redshift of two of these objects are unconstrained due to the absence of
emission lines, while the third object might be at the redshift of the quasar.
We use the objects detected in our whole N(HI)-selected SINFONI survey to
compute the metallicity difference between the galaxy and the absorbing gas,
delta_HI(X), where a positive (negative) value indicates infall (outflow). We
compare this quantity with the quasar line of sight alignment with the galaxy's
major (minor) axis, another tracer of infall (outflow). We find that these
quantities do not correlate as expected from simple assumptions. Additional
observations are necessary to relate these two independent probes of gas flows
around galaxies.Comment: 16 pages, 8 figures, accepted for publication in MNRA
Somatosensory Influence on Platform-Induced Translational Vestibulo-Ocular Reflex in Vertical Direction in Humans
The vestibulo-ocular reflex (VOR) consists of two components, the rotational VOR (rVOR) elicited by semicircular canal signals and the translational VOR (tVOR) elicited by otolith signals. Given the relevant role of the vertical tVOR in human walking, this study aimed at measuring the time delay of eye movements in relation to whole-body vertical translations in natural standing position. Twenty (13 females and 7 males) healthy, young subjects (mean 25 years) stood upright on a motor-driven platform and were exposed to sinusoidal movements while fixating a LED, positioned at a distance of 50 cm in front of the eyes. The platform motion induced a vertical translation of 2.6 cm that provoked counteracting eye movements similar to self-paced walking. The time differences between platform and eye movements indicated that the subject's timing of the extraocular motor reaction depended on stimulus frequency and number of repetitions. At low stimulus frequencies (<0.8 Hz) and small numbers of repetitions (<3), eye movements were phase advanced or in synchrony with platform movements. At higher stimulus frequencies or continuous stimulation, eye movements were phase lagged by ~40 ms. Interestingly, the timing of eye movements depended on the initial platform inclination. Starting with both feet in dorsiflexion, eye movements preceded platform movements by 137 ms, whereas starting with both feet in plantar flexion eye movement precession was only 19 ms. This suggests a remarkable influence of foot proprioceptive signals on the timing of eye movements, indicating that the dynamics of the vertical tVOR is controlled by somatosensory signals
Space and Ground Based Pulsation Data of Eta Bootis Explained with Stellar Models Including Turbulence
The space telescope MOST is now providing us with extremely accurate low
frequency p-mode oscillation data for the star Eta Boo. We demonstrate in this
paper that these data, when combined with ground based measurements of the high
frequency p-mode spectrum, can be reproduced with stellar models that include
the effects of turbulence in their outer layers. Without turbulence, the l=0
modes of our models deviate from either the ground based or the space data by
about 1.5-4.0 micro Hz. This discrepancy can be completely removed by including
turbulence in the models and we can exactly match 12 out of 13 MOST frequencies
that we identified as l=0 modes in addition to 13 out of 21 ground based
frequencies within their observational 2 sigma tolerances. The better agreement
between model frequencies and observed ones depends for the most part on the
turbulent kinetic energy which was taken from a 3D convection simulation for
the Sun.Comment: 13 pages, 7 figures, ApJ in pres
YREC: The Yale Rotating Stellar Evolution Code
The stellar evolution code YREC is outlined with emphasis on its applications
to helio- and asteroseismology. The procedure for calculating calibrated solar
and stellar models is described. Other features of the code such as a non-local
treatment of convective core overshoot, and the implementation of a
parametrized description of turbulence in stellar models, are considered in
some detail. The code has been extensively used for other astrophysical
applications, some of which are briefly mentioned at the end of the paper.Comment: 10 pages, 2 figures, ApSS accepte
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