1,825 research outputs found
Are Proxima and Alpha Centauri Gravitationally Bound?
Using the most recent kinematic and radial velocity data in the literature,
we calculate the binding energy of Proxima Centauri relative to the center of
mass of the Alpha Centauri system. When we adopt the centroids of the observed
data, we find that the three stars constitute a bound system, albeit with a
semi-major axis that is on order the same size as Alpha Centauri AB's Hill
radius in the galactic potential. We carry out a Monte Carlo simulation under
the assumption that the errors in the observed quantities are uncorrelated. In
this simulation, 44% of the trial systems are bound, and systems on the 1-3
sigma tail of the radial velocity distribution can have Proxima currently
located near the apastron position of its orbit. Our analysis shows that a
further, very significant improvement in the characterization of the system can
be gained by obtaining a more accurate measurement of the radial velocity of
Proxima Centauri.Comment: 10 pages total, 4 pages of text, 1 page of references, 3 figures, and
2 tables This article will be published in The Astronomical Journa
Neural superposition and oscillations in the eye of the blowfly
Neural superposition in the eye of the blowfly Calliphora erythrocephala was investigated by stimulating single photoreceptors using corneal neutralization through water immersion. Responses in Large Monopolar Cells (LMCs) in the lamina were measured, while stimulating one or more of the six photoreceptors connected to the LMC. Responses to flashes of low light intensity on individual photoreceptors add approximately linearly at the LMC. Higher intensity light flashes produce a maximum LMC response to illumination of single photoreceptors which is about half the maximum response to simultaneous illumination of the six connecting photoreceptors. This observation indicates that a saturation can occur at a stage of synaptic transmission which precedes the change in the post-synaptic membrane potential.
Stimulation of single photoreceptors yields high frequency oscillations (about 200 Hz) in the LMC potential, much larger in amplitude than produced by simultaneous stimulation of the six photoreceptors connected to the LMC. It is discussed that these oscillations also arise from a mechanism that precedes the change in the postsynaptic membrane potential.
Multiple Bosonic Mode Coupling in Electron Self-Energy of (La_2-xSr_x)CuO_4
High resolution angle-resolved photoemission spectroscopy data along the
(0,0)-(,) nodal direction with significantly improved statistics
reveal fine structure in the electron self-energy of the underdoped
(LaSr)CuO samples in the normal state. Fine structure at
energies of (4046) meV and (5863)meV, and possible fine structure
at energies of (2329)meV and (7585)meV, have been identified. These
observations indicate that, in LSCO, more than one bosonic modes are involved
in the coupling with electrons.Comment: 4 pages, 3 figures, Fig. 2 update
Cumulative and Differential Effects of Early Child Care and Middle Childhood Out-of-School Time on Adolescent Functioning.
Effects associated with early child care and out-of-school time (OST) during middle childhood were examined in a large sample of U.S. adolescents (N = 958). Both higher quality early child care AND more epochs of organized activities (afterschool programs and extracurricular activities) during middle childhood were linked to higher academic achievement at age 15. Differential associations were found in the behavioral domain. Higher quality early child care was associated with fewer externalizing problems, whereas more hours of early child care was linked to greater impulsivity. More epochs of organized activities was associated with greater social confidence. Relations between early child care and adolescent outcomes were not mediated or moderated by OST arrangements in middle childhood, consistent with independent, additive relations of these nonfamilial settings
Charge distribution in two-dimensional electrostatics
We examine the stability of ringlike configurations of N charges on a plane
interacting through the potential . We interpret the equilibrium distributions in terms of a shell
model and compare predictions of the model with the results of numerical
simulations for systems with up to 100 particles.Comment: LaTe
Quantum Hall Ferromagnets
It is pointed out recently that the quantum Hall states in bilayer
systems behave like easy plane quantum ferromagnets. We study the
magnetotransport of these systems using their ``ferromagnetic" properties and a
novel spin-charge relation of their excitations. The general transport is a
combination of the ususal Hall transport and a time dependent transport with
time average. The latter is due to a phase slippage process in
and is characterized by two topological constants. (Figures will be
provided upon requests).Comment: 4 pages, Revtex, Ohio State Universit
Improved Orbital Parameters And Transit Monitoring For HD 156846b
HD 156846b is a Jovian planet in a highly eccentric orbit (e = 0.85) with a period of 359.55 days. The pericenter passage at a distance of 0.16 AU is nearly aligned to our line of sight, offering an enhanced transit probability of 5.4% and a potentially rich probe of the dynamics of a cool planetary atmosphere impulsively heated during close approach to a bright star (V = 6.5). We present new radial velocity (RV) and photometric measurements of this star as part of the Transit Ephemeris Refinement and Monitoring Survey. The RV measurements from the Keck-High Resolution Echelle Spectrometer reduce the predicted transit time uncertainty to 20 minutes, an order of magnitude improvement over the ephemeris from the discovery paper. We photometrically monitored a predicted transit window under relatively poor photometric conditions, from which our non-detection does not rule out a transiting geometry. We also present photometry that demonstrates stability at the millimagnitude level over its rotational timescale
Anomalous relaxation and self-organization in non-equilibrium processes
We study thermal relaxation in ordered arrays of coupled nonlinear elements
with external driving. We find, that our model exhibits dynamic
self-organization manifested in a universal stretched-exponential form of
relaxation. We identify two types of self-organization, cooperative and
anti-cooperative, which lead to fast and slow relaxation, respectively. We give
a qualitative explanation for the behavior of the stretched exponent in
different parameter ranges. We emphasize that this is a system exhibiting
stretched-exponential relaxation without explicit disorder or frustration.Comment: submitted to PR
Five Planets Orbiting 55 Cancri
We report 18 years of Doppler shift measurements of a nearby star, 55 Cancri,
that exhibit strong evidence for five orbiting planets. The four previously
reported planets are strongly confirmed here. A fifth planet is presented, with
an apparent orbital period of 260 days, placing it 0.78 AU from the star in the
large empty zone between two other planets. The velocity wobble amplitude of
4.9 \ms implies a minimum planet mass \msini = 45.7 \mearthe. The orbital
eccentricity is consistent with a circular orbit, but modest eccentricity
solutions give similar \chisq fits. All five planets reside in low eccentricity
orbits, four having eccentricities under 0.1. The outermost planet orbits 5.8
AU from the star and has a minimum mass, \msini = 3.8 \mjupe, making it more
massive than the inner four planets combined. Its orbital distance is the
largest for an exoplanet with a well defined orbit. The innermost planet has a
semi-major axis of only 0.038 AU and has a minimum mass, \msinie, of only 10.8
\mearthe, one of the lowest mass exoplanets known. The five known planets
within 6 AU define a {\em minimum mass protoplanetary nebula} to compare with
the classical minimum mass solar nebula. Numerical N-body simulations show this
system of five planets to be dynamically stable and show that the planets with
periods of 14.65 and 44.3 d are not in a mean-motion resonance. Millimagnitude
photometry during 11 years reveals no brightness variations at any of the
radial velocity periods, providing support for their interpretation as
planetary.Comment: accepted to Ap
Thermal properties of gauge-fields common to anyon superconductors and spin-liquids
The thermally driven confinement-deconfinement transition exhibited by
lattice quantum electrodynamics in two space dimensions is re-examined in the
context of the statistical gauge-fields common to anyon superconductors and to
spin-liquids. Particle-hole excitations in both systems are bound by a
confining string at temperatures below the transition temperature . We
argue that coincides with the actual critical temperature for anyon
superconductivity. The corresponding specific-heat contribution, however, shows
a {\it smooth} peak just below characteristic of certain high-temperature
superconductors.Comment: 13 pgs, TeX, to appear in Physical Review B (minor revisions
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