7,447 research outputs found
Cavity-enhanced optical detection of carbon nanotube Brownian motion
Optical cavities with small mode volume are well-suited to detect the
vibration of sub-wavelength sized objects. Here we employ a fiber-based,
high-finesse optical microcavity to detect the Brownian motion of a freely
suspended carbon nanotube at room temperature under vacuum. The optical
detection resolves deflections of the oscillating tube down to 50pm/Hz^1/2. A
full vibrational spectrum of the carbon nanotube is obtained and confirmed by
characterization of the same device in a scanning electron microscope. Our work
successfully extends the principles of high-sensitivity optomechanical
detection to molecular scale nanomechanical systems.Comment: 14 pages, 11 figure
Detecting Compton Reflection and a Broad Iron Line in MCG-5-23-16 with the Rossi X-ray Timing Explorer
We report the detection with the Rossi X-ray Timing Explorer of a Compton
reflection signature in the Seyfert galaxy MCG-5-23-16. RXTE also resolves the
Fe K-alpha fluorescence line with FWHM ~48,000 km s^{-1}. This measurement
provides the first independent confirmation of ASCA detections in Seyfert
galaxies of broad Fe K-alpha lines that are thought to be the signature of
emission from the inner regions of an accretion disk orbiting a black hole.
Under the assumption that reflection arises from an isotropic source located
above a neutral accretion disk, and using a theoretical model that accounts for
the dependence of the reflected spectrum on inclination angle, we derive a 90%
confidence range for the disk inclination of i = 50 to 81 degrees. The large
inclination is consistent with that expected from the unified model for
MCG-5-23-16 based on its Seyfert 1.9 classification. If we assume that the
high-energy cutoff in the incident spectrum lies at energies larger than a few
hundred keV, then the equivalent width of the Fe K-alpha line is much larger
than predicted for the amount of reflection. This implies either an enhanced
iron abundance, a covering factor of reflecting material > 0.5, or a cutoff in
the incident spectrum at energies between ~60 and ~200 keV.Comment: Accepted for publication in ApJ, LaTeX. 14 pages including 3 figures,
with 1 table as a separate postscript file. Typo corrected in abstrac
Sound modes broadening for Fibonacci one dimensional quasicrystals
We investigate vibrational excitation broadening in one dimensional Fibonacci
model of quasicrystals (QCs). The chain is constructed from particles with two
masses following the Fibonacci inflation rule. The eigenmode spectrum depends
crucially on the mass ratio. We calculate the eigenstates and eigenfunctions.
All calculations performed self-consistently within the regular expansion over
the three wave coupling constant. The approach can be extended to three
dimensional systems. We find that in the intermediate range of mode coupling
constants, three-wave broadening for the both types of systems (1D Fibonacci
and 3D QCs) depends universally on frequency. Our general qualitative
conclusion is that for a system with a non-simple elementary cell phonon
spectrum broadening is always larger than for a system with a primitive cell
(provided all other characteristics are the same).Comment: 2o pages, 15 figure
Spitzer observations of the asteroid-comet transition object and potential spacecraft target 107P (4015) Wilson-Harrington
Context. Near-Earth asteroid-comet transition object 107P/ (4015)
Wilson-Harrington is a possible target of the joint European Space Agency (ESA)
and Japanese Aerospace Exploration Agency (JAXA) Marco Polo sample return
mission. Physical studies of this object are relevant to this mission, and also
to understanding its asteroidal or cometary nature. Aims. Our aim is to obtain
significant new constraints on the surface thermal properties of this object.
Methods. We present mid-infrared photometry in two filters (16 and 22 microns)
obtained with NASA's Spitzer Space Telescope on February 12, 2007, and results
from the application of the Near Earth Asteroid Thermal Model (NEATM).We
obtained high S/N in two mid-IR bands allowing accurate measurements of its
thermal emission. Results. We obtain a well constrained beaming parameter (eta
= 1.39 +/- 0.26) and obtain a diameter and geometric albedo of D = 3.46 +/-
0.32 km, and pV = 0.059 +/- 0.011. We also obtain similar results when we apply
this best-fitting thermal model to single-band mid-IR photometry reported by
Campins et al. (1995), Kraemer et al. (2005) and Reach et al. (2007).
Conclusions. The albedo of 4015 Wilson-Harrington is low, consistent with those
of comet nuclei and primitive C-, P-, D-type asteorids. We establish a rough
lower limit for the thermal inertia of W-H of 60 Jm^-2s^(-0.5)K^-1 when it is
at r=1AU, which is slightly over the limit of 30 Jm^-2s^(-0.5)K-1 derived by
Groussin et al. (2009) for the thermal inertia of the nucleus of comet
22P/Kopff.Comment: 4 pages, 1 figure and 3 tables. Paper accepted for publicatio
Effects of the and of other processes on the mixing hierarchies in the four-generation model
We analyze in the four-generation model the first measurement of the
branching ratio of rare kaon decay , along with the
other processes of mass difference , CP-violating
parameter mixing, mixing,
, and the upper bound values of mixing
and , and try to search for mixing of the fourth
generation in the hierarchical mixing scheme of the Wolfenstein
parametrization. Using the results for the mixing of the fourth generation, we
discuss predictions of the mixing () and the
branching ratio of directly CP-violating decay process
, and the effects on the CP asymmetry in neutral B
meson decays and the unitarity triangle.Comment: 29 pages written in LaTex. 6 figures(drawn on LaTeX). Revised from
" in the four-generation model" of the same
Authors(TOKUSHIMA 99-1, January 1999). A minor chang
Cavity cooling of a nanomechanical resonator by light scattering
We present a novel method for opto-mechanical cooling of sub-wavelength sized
nanomechanical resonators. Our scheme uses a high finesse Fabry-Perot cavity of
small mode volume, within which the nanoresonator is acting as a
position-dependant perturbation by scattering. In return, the back-action
induced by the cavity affects the nanoresonator dynamics and can cool its
fluctuations. We investigate such cavity cooling by scattering for a nanorod
structure and predict that ground-state cooling is within reach.Comment: 4 pages, 3 figure
Intensity Fluctuations in Closed and Open Systems
We consider the intensity pattern, generated by a monochromatic source, in a
disordered cavity coupled to the environment. For weak coupling, and when the
source frequency is tuned to a resonance, the intensity distribution is close
to Porter-Thomas distribution. When the coupling increases, gradually crosses
over to the Rayleigh distribution. The joint probability distribution for
intensities at two different points is also discussed.Comment: 11 pages, LATEX, no figure
A New Algorithm for Supernova Neutrino Transport and Some Applications
We have developed an implicit, multi-group, time-dependent, spherical
neutrino transport code based on the Feautrier variables, the tangent-ray
method, and accelerated iteration. The code achieves high
angular resolution, is good to O(), is equivalent to a Boltzmann solver
(without gravitational redshifts), and solves the transport equation at all
optical depths with precision. In this paper, we present our formulation of the
relevant numerics and microphysics and explore protoneutron star atmospheres
for snapshot post-bounce models. Our major focus is on spectra, neutrino-matter
heating rates, Eddington factors, angular distributions, and phase-space
occupancies. In addition, we investigate the influence on neutrino spectra and
heating of final-state electron blocking, stimulated absorption, velocity terms
in the transport equation, neutrino-nucleon scattering asymmetry, and weak
magnetism and recoil effects. Furthermore, we compare the emergent spectra and
heating rates obtained using full transport with those obtained using
representative flux-limited transport formulations to gauge their accuracy and
viability. Finally, we derive useful formulae for the neutrino source strength
due to nucleon-nucleon bremsstrahlung and determine bremsstrahlung's influence
on the emergent and neutrino spectra.Comment: 58 pages, single-spaced LaTeX, 23 figures, revised title, also
available at http://jupiter.as.arizona.edu/~burrows/papers, accepted for
publication in the Ap.
Magnetic Flux Expulsion in the Powerful Superbubble Explosions and the Alpha-Omega Dynamo
The possibility of the magnetic flux expulsion from the Galaxy in the
superbubble (SB) explosions, important for the Alpha-Omega dynamo, is
considered. Special emphasis is put on the investigation of the downsliding of
the matter from the top of the shell formed by the SB explosion which is able
to influence the kinematics of the shell. It is shown that either Galactic
gravity or the development of the Rayleigh-Taylor instabilities in the shell
limit the SB expansion, thus, making impossible magnetic flux expulsion. The
effect of the cosmic rays in the shell on the sliding is considered and it is
shown that it is negligible compared to Galactic gravity. Thus, the question of
possible mechanism of flux expulsion in the Alpha-Omega dynamo remains open.Comment: MNRAS, in press, 11 pages, 9 figure
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