737 research outputs found
Environment-induced dynamical chaos
We examine the interplay of nonlinearity of a dynamical system and thermal
fluctuation of its environment in the ``physical limit'' of small damping and
slow diffusion in a semiclassical context and show that the trajectories of
c-number variables exhibit dynamical chaos due to the thermal fluctuations of
the bath.Comment: Revtex, 4 pages and 4 figure
Weak force detection with superposed coherent states
We investigate the utility of non classical states of simple harmonic
oscillators, particularly a superposition of coherent states, for sensitive
force detection. We find that like squeezed states a superposition of coherent
states allows displacement measurements at the Heisenberg limit. Entangling
many superpositions of coherent states offers a significant advantage over a
single mode superposition states with the same mean photon number.Comment: 6 pages, no figures: New section added on entangled resources.
Changes to discussions and conclusio
Cosmological parameters from large scale structure - geometric versus shape information
The matter power spectrum as derived from large scale structure (LSS) surveys
contains two important and distinct pieces of information: an overall smooth
shape and the imprint of baryon acoustic oscillations (BAO). We investigate the
separate impact of these two types of information on cosmological parameter
estimation, and show that for the simplest cosmological models, the broad-band
shape information currently contained in the SDSS DR7 halo power spectrum (HPS)
is by far superseded by geometric information derived from the baryonic
features. An immediate corollary is that contrary to popular beliefs, the upper
limit on the neutrino mass m_\nu presently derived from LSS combined with
cosmic microwave background (CMB) data does not in fact arise from the possible
small-scale power suppression due to neutrino free-streaming, if we limit the
model framework to minimal LambdaCDM+m_\nu. However, in more complicated
models, such as those extended with extra light degrees of freedom and a dark
energy equation of state parameter w differing from -1, shape information
becomes crucial for the resolution of parameter degeneracies. This conclusion
will remain true even when data from the Planck surveyor become available. In
the course of our analysis, we introduce a new dewiggling procedure that allows
us to extend consistently the use of the SDSS HPS to models with an arbitrary
sound horizon at decoupling. All the cases considered here are compatible with
the conservative 95%-bounds \sum m_\nu < 1.16 eV, N_eff = 4.8 \pm 2.0.Comment: 18 pages, 4 figures; v2: references added, matches published versio
The Empirical Mass-Luminosity Relation for Low Mass Stars
This work is devoted to improving empirical mass-luminosity relations and
mass-metallicity-luminosity relation for low mass stars. For these stars,
observational data in the mass-luminosity plane or the
mass-metallicity-luminosity space subject to non-negligible errors in all
coordinates with different dimensions. Thus a reasonable weight assigning
scheme is needed for obtaining more reliable results. Such a scheme is
developed, with which each data point can have its own due contribution.
Previous studies have shown that there exists a plateau feature in the
mass-luminosity relation. Taking into account the constraints from the
observational luminosity function, we find by fitting the observational data
using our weight assigning scheme that the plateau spans from 0.28 to 0.50
solar mass. Three-piecewise continuous improved mass-luminosity relations in K,
J, H and V bands, respectively, are obtained. The visual
mass-metallicity-luminosity relation is also improved based on our K band
mass-luminosity relation and the available observational metallicity data.Comment: 8 pages, 2 figures. Accepted for publication in Astrophysics & Space
Scienc
Partial discharge testing of defects in dielectric insulation under DC and voltage ripple conditions
This paper details testing conducted on selected void defects in dielectric insulation samples under various HVDC voltage conditions. The aim of this work is to illustrate the type of PD activity that could be observed in HVDC insulation systems. Initially the samples were subject to HVAC excitation to confirm the defect type and establish the PD inception voltage. HVDC testing was then conducted using a âramp and holdâ test technique with different hold voltages in the ramp determined from the measured HVAC inception voltage. The effect of harmonic ripple superimposed on the HVDC voltage waveform, which is typically a result of the converter switching operation, was also investigated. The findings from this study should provide network operators and insulation manufacturers a greater insight into the behavior of PD phenomena in solid insulation under HVDC conditions, enabling greater confidence in the diagnosis of defect type and severity in such systems
Momentum Distribution in Nuclear Matter and Finite Nuclei
A simple method is presented to evaluate the effects of short-range
correlations on the momentum distribution of nucleons in nuclear matter within
the framework of the Green's function approach. The method provides a very
efficient representation of the single-particle Green's function for a
correlated system. The reliability of this method is established by comparing
its results to those obtained in more elaborate calculations. The sensitivity
of the momentum distribution on the nucleon-nucleon interaction and the nuclear
density is studied. The momentum distributions of nucleons in finite nuclei are
derived from those in nuclear matter using a local-density approximation. These
results are compared to those obtained directly for light nuclei like .Comment: 17 pages REVTeX, 10 figures ps files adde
The Two-Nucleon Potential from Chiral Lagrangians
Chiral symmetry is consistently implemented in the two-nucleon problem at
low-energy through the general effective chiral lagrangian. The potential is
obtained up to a certain order in chiral perturbation theory both in momentum
and coordinate space. Results of a fit to scattering phase shifts and bound
state data are presented, where satisfactory agreement is found for laboratory
energies up to about 100 Mev.Comment: Postscript file; figures available by reques
The DA+dMe eclipsing binary EC13471-1258: its cup runneth over...just
EC13471-1258 is a detached eclipsing binary with Porb = 3h37m, comprising a
DA white dwarf and a dMe dwarf. Total eclipses of the white dwarf lasting 14
min, and a large amplitude ellipsoidal variation are seen in the light curve.
Flares from the dMe star occur regularly. Each star contributes roughly equal
amounts of light at 5500 Ang.
HST STIS spectra show strong Ly alpha with weak metal lines, and yield Teff =
14220 K, log g = 8.34, Z = 1/30th solar, K = 138 km/s and V sin i = 400 km/s
for the white dwarf. Optical spectra yield the spectral type (M3.5-4.0), Teff =
3100 K, Z = solar, K = 266 km/s and V sin i = 140 km/s for the dMe star. The H
alpha emission line comprises 2 or more components and implies that very weak
mass transfer is occurring. The dynamical solution also implies that the dMe
star just fills its Roche lobe. Accurate masses and radii for each star were
derived: the dMe values favour the Clemens et al. (1998) mass-radius relation.
The large rotational velocity of the white dwarf (400 km/s) suggests that the
system has transferred mass in the past so that it is presently a hibernating
cataclysmic variable. The metallicity contrast between the component stars
provides an opportunity for tests of diffusion theory.Comment: 25 pages, 18 figures, accepted for publication in MNRA
The Planetary Nebula Luminosity Function at the Dawn of Gaia
The [O III] 5007 Planetary Nebula Luminosity Function (PNLF) is an excellent
extragalactic standard candle. In theory, the PNLF method should not work at
all, since the luminosities of the brightest planetary nebulae (PNe) should be
highly sensitive to the age of their host stellar population. Yet the method
appears robust, as it consistently produces < 10% distances to galaxies of all
Hubble types, from the earliest ellipticals to the latest-type spirals and
irregulars. It is therefore uniquely suited for cross-checking the results of
other techniques and finding small offsets between the Population I and
Population II distance ladders. We review the calibration of the method and
show that the zero points provided by Cepheids and the Tip of the Red Giant
Branch are in excellent agreement. We then compare the results of the PNLF with
those from Surface Brightness Fluctuation measurements, and show that, although
both techniques agree in a relative sense, the latter method yields distances
that are ~15% larger than those from the PNLF. We trace this discrepancy back
to the calibration galaxies and argue that, due to a small systematic error
associated with internal reddening, the true distance scale likely falls
between the extremes of the two methods. We also demonstrate how PNLF
measurements in the early-type galaxies that have hosted Type Ia supernovae can
help calibrate the SN Ia maximum magnitude-rate of decline relation. Finally,
we discuss how the results from space missions such as Kepler and Gaia can help
our understanding of the PNLF phenomenon and improve our knowledge of the
physics of local planetary nebulae.Comment: 12 pages, invited review at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and Gaia Perspective", to appear in
Astrophysics and Space Scienc
Realistic Model of the Nucleon Spectral Function in Few- and Many- Nucleon Systems
By analysing the high momentum features of the nucleon momentum distribution
in light and complex nuclei, it is argued that the basic two-nucleon
configurations generating the structure of the nucleon Spectral Function at
high values of the nucleon momentum and removal energy, can be properly
described by a factorised ansatz for the nuclear wave function, which leads to
a nucleon Spectral Function in the form of a convolution integral involving the
momentum distributions describing the relative and center-of-mass motion of a
correlated nucleon-nucleon pair embedded in the medium. The Spectral Functions
of and infinite nuclear matter resulting from the convolution formula
and from many-body calculations are compared, and a very good agreement in a
wide range of values of nucleon momentum and removal energy is found.
Applications of the model to the analysis of inclusive and exclusive processes
are presented, illustrating those features of the cross section which are
sensitive to that part of the Spectral Function which is governed by
short-range and tensor nucleon-nucleon correlations.Comment: 40 pages Latex , 16 ps figures available from the above e-mail
address or from [email protected]
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