29,746 research outputs found
Report of IAU Commission 30 on Radial Velocities (2006-2009)
Brief summaries are given on the following subjects: Radial velocities and
exoplanets (Toward Earth-mass planets; Retired A stars and their planets;
Current status and prospects); Toward higher radial velocity precision; Radial
velocities and asteroseismology; Radial velocities in Galactic and
extragalactic clusters; Radial velocities for field giants; Galactic structure
-- Large surveys (The Geneva-Copenhagen Survey; Sloan Digital Sky Survey;
RAVE); Working groups (WG on radial velocity standards; WG on stellar radial
velocity bibliography; WG on the catalogue of orbital elements of spectroscopic
binaries [SB9]).Comment: 11 pages, to appear in the IAU Transactions Vol. XXVIIA, Reports on
Astronomy 2006-2009, ed. Karel van der Hucht. Editor: G. Torre
Two interacting atoms in a cavity: exact solutions, entanglement and decoherence
We address the problem of two interacting atoms of different species inside a
cavity and find the explicit solutions of the corresponding eigenvalues and
eigenfunctions using a new invariant. This model encompasses various commonly
used models. By way of example we obtain closed expressions for concurrence and
purity as a function of time for the case where the cavity is prepared in a
number state. We discuss the behaviour of these quantities and and their
relative behaviour in the concurrence-purity plane.Comment: 10 pages, 3 figure
Casimir torque
We develop a formalism for the calculation of the flow of angular momentum
carried by the fluctuating electromagnetic field within a cavity bounded by two
flat anisotropic materials. By generalizing a procedure employed recently for
the calculation of the Casimir force between arbitrary materials, we obtain an
expression for the torque between anisotropic plates in terms of their
reflection amplitude matrices. We evaluate the torque in 1D for ideal and
realistic model materials.Comment: 8 pages, 4 figs, Submitted to Proc. of QFEXT'05, to appear in J.
Phys.
Production of optical phase space vortices with non-locally distributed mode converters
Optical vortices have been observed in a wide variety of optical systems.
They can be observed directly in the wavefront of optical beams, or in the
correlations between pairs of entangled photons. We present a novel optical
vortex which appears in a non-local plane of the two-photon phase space,
composed of a single degree of freedom of each photon of an entangled pair. The
preparation of this vortex can be viewed as a "non-local" or distributed mode
converter. We show how these novel optical vortices of arbitrary order can be
prepared in the spatial degrees of freedom of entangled photons.Comment: To appear in upcoming special issue "Orbital Angular Momentum" of the
Journal of Optic
Possible surface plasmon polariton excitation under femtosecond laser irradiation of silicon
The mechanisms of ripple formation on silicon surface by femtosecond laser
pulses are investigated. We demonstrate the transient evolution of the density
of the excited free-carriers. As a result, the experimental conditions required
for the excitation of surface plasmon polaritons are revealed. The periods of
the resulting structures are then investigated as a function of laser
parameters, such as the angle of incidence, laser fluence, and polarization.
The obtained dependencies provide a way of better control over the properties
of the periodic structures induced by femtosecond laser on the surface of a
semiconductor material.Comment: 11 pages, 8 figures, accepted for publication in Journal of Applied
Physic
Tuning the Kondo effect with a mechanically controllable break junction
We study electron transport through C60 molecules in the Kondo regime using a
mechanically controllable break junction. By varying the electrode spacing, we
are able to change both the width and height of the Kondo resonance, indicating
modification of the Kondo temperature and the relative strength of coupling to
the two electrodes. The linear conductance as a function of T/T_K agrees with
the scaling function expected for the spin-1/2 Kondo problem. We are also able
to tune finite-bias Kondo features which appear at the energy of the first C60
intracage vibrational mode.Comment: 4 pages with 4 figure
Conservation laws for invariant functionals containing compositions
The study of problems of the calculus of variations with compositions is a
quite recent subject with origin in dynamical systems governed by chaotic maps.
Available results are reduced to a generalized Euler-Lagrange equation that
contains a new term involving inverse images of the minimizing trajectories. In
this work we prove a generalization of the necessary optimality condition of
DuBois-Reymond for variational problems with compositions. With the help of the
new obtained condition, a Noether-type theorem is proved. An application of our
main result is given to a problem appearing in the chaotic setting when one
consider maps that are ergodic.Comment: Accepted for an oral presentation at the 7th IFAC Symposium on
Nonlinear Control Systems (NOLCOS 2007), to be held in Pretoria, South
Africa, 22-24 August, 200
Schmidt number of pure bi-partite entangled states and methods of its calculation
An entanglement measure for pure-state continuous-variable bi-partite
problem, the Schmidt number, is analytically calculated for one simple model of
atom-field scattering.Comment: 3 pages, 1 figure; based on the poster presentation reported on the
11th International Conference on Quantum Optics (ICQO'2006, Minsk, May 26 --
31, 2006), to be published in special issue of Optics and Spectroscop
Astrometric-spectroscopic determination of the absolute masses of the HgMn binary star Phi Herculis
The Mercury-Manganese star Phi Her is a well known spectroscopic binary that
has been the subject of a recent study by Zavala et al. (2006), in which they
resolved the companion using long-baseline interferometry. The total mass of
the binary is now fairly well established, but the combination of the
spectroscopy with the astrometry has not resulted in individual masses
consistent with the spectral types of the components. The motion of the center
of light of Phi Her was clearly detected by the Hipparcos satellite. Here we
make use of the Hipparcos intermediate data (`abscissa residuals') and show
that by combining them in an optimal fashion with the interferometry the
individual masses can be obtained reliably using only astrometry. We re-examine
and then incorporate existing radial-velocity measurements into the orbital
solution, obtaining improved masses of 3.05 +/- 0.24 M_Sun and 1.614 +/- 0.066
M_Sun that are consistent with the theoretical mass-luminosity relation from
recent stellar evolution models. These mass determinations provide important
information for the understanding of the nature of this peculiar class of
stars.Comment: Total of 18 pages including figures and tables, in emulateapj format.
To appear in The Astronomical Journal, June 2007 issu
- …