2,468 research outputs found
First Kepler results on compact pulsators VIII: Mode identifications via period spacings in mode pulsating Subdwarf B stars
We investigate the possibility of nearly-equally spaced periods in 13 hot
subdwarf B (sdB) stars observed with the Kepler spacecraft and one observed
with CoRoT. Asymptotic limits for gravity (g-)mode pulsations provide
relationships between equal period spacings of modes with differing degrees and
relationships between periods of the same radial order but differing degrees.
Period transforms, Kolmogorov-Smirnov tests, and linear least-squares fits have
been used to detect and determine the significance of equal period spacings. We
have also used Monte Carlo simulations to estimate the likelihood that the
detected spacings could be produced randomly.
Period transforms for nine of the Kepler stars indicate ell=1 period
spacings, with five also showing peaks for ell=2 modes. 12 stars indicate ell=1
modes using the Kolmogorov-Smirnov test while another shows solely ell=2 modes.
Monte Carlo results indicate that equal period spacings are significant in 10
stars above 99% confidence and 13 of the 14 are above 94% confidence. For 12
stars, the various methods find consistent regular period spacing values to
within the errors, two others show some inconsistencies, likely caused by
binarity, and the last has significant detections but the mode assignment
disagrees between methods.
We find a common ell=1 period spacing spanning a range from 231 to 272 s
allowing us to correlate pulsation modes with 222 periodicities and that the
ell=2 period spacings are related to the ell=1 spacings by the asymptotic
relationship . We briefly discuss the impact of equal period
spacings which indicate low-degree modes with a lack of significant mode
trappings.Comment: 27 pages, 4 figures, 17 tables. Accepted for publication in Monthly
Notices of the Royal Astronomical Societ
The ground state of a general electron-phonon Hamiltonian is a spin singlet
The many-body ground state of a very general class of electron-phonon
Hamiltonians is proven to contain a spin singlet (for an even number of
electrons on a finite lattice). The phonons interact with the electronic system
in two different ways---there is an interaction with the local electronic
charge and there is a functional dependence of the electronic hopping
Hamiltonian on the phonon coordinates. The phonon potential energy may include
anharmonic terms, and the electron-phonon couplings and the hopping matrix
elements may be nonlinear functions of the phonon coordinates. If the hopping
Hamiltonian is assumed to have no phonon coordinate dependence, then the ground
state is also shown to be unique, implying that there are no ground-state level
crossings, and that the ground-state energy is an analytic function of the
parameters in the Hamiltonian. In particular, in a finite system any
self-trapping transition is a smooth crossover not accompanied by a
nonanalytical change in the ground state. The spin-singlet theorem applies to
the Su-Schrieffer-Heeger model and both the spin-singlet and uniqueness
theorems apply to the Holstein and attractive Hubbard models as special cases.
These results hold in all dimensions --- even on a general graph without
periodic lattice structure.Comment: 25 pages, no figures, plainte
Functional evolution of quantum cylindrical waves
Kucha{\v{r}} showed that the quantum dynamics of (1 polarization) cylindrical
wave solutions to vacuum general relativity is determined by that of a free
axially-symmetric scalar field along arbitrary axially-symmetric foliations of
a fixed flat 2+1 dimensional spacetime. We investigate if such a dynamics can
be defined {\em unitarily} within the standard Fock space quantization of the
scalar field.
Evolution between two arbitrary slices of an arbitrary foliation of the flat
spacetime can be built out of a restricted class of evolutions (and their
inverses). The restricted evolution is from an initial flat slice to an
arbitrary (in general, curved) slice of the flat spacetime and can be
decomposed into (i) `time' evolution in which the spatial Minkowskian
coordinates serve as spatial coordinates on the initial and the final slice,
followed by (ii) the action of a spatial diffeomorphism of the final slice on
the data obtained from (i). We show that although the functional evolution of
(i) is unitarily implemented in the quantum theory, generic spatial
diffeomorphisms of (ii) are not. Our results imply that a Tomanaga-Schwinger
type functional evolution of quantum cylindrical waves is not a viable concept
even though, remarkably, the more limited notion of functional evolution in
Kucha{\v{r}}'s `half parametrized formalism' is well-defined.Comment: Replaced with published versio
Plane waves in quantum gravity: breakdown of the classical spacetime
Starting with the Hamiltonian formulation for spacetimes with two commuting
spacelike Killing vectors, we construct a midisuperspace model for linearly
polarized plane waves in vacuum gravity. This model has no constraints and its
degrees of freedom can be interpreted as an infinite and continuous set of
annihilation and creation like variables. We also consider a simplified version
of the model, in which the number of modes is restricted to a discrete set. In
both cases, the quantization is achieved by introducing a Fock representation.
We find regularized operators to represent the metric and discuss whether the
coherent states of the quantum theory are peaked around classical spacetimes.
It is shown that, although the expectation value of the metric on Killing
orbits coincides with a classical solution, its relative fluctuations become
significant when one approaches a region where null geodesics are focused. In
that region, the spacetimes described by coherent states fail to admit an
approximate classical description. This result applies as well to the vacuum of
the theory.Comment: 11 pages, no figures, version accepted for publication in Phys. Rev.
'Working outâ identity: distance runners and the management of disrupted identity
This article contributes fresh perspectives to the empirical literature on the sociology of the body, and of leisure and identity, by analysing the impact of long-term injury on the identities of two amateur but serious middle/long-distance runners. Employing a symbolic interactionist framework,and utilising data derived from a collaborative autoethnographic project, it explores the role
of âidentity workâ in providing continuity of identity during the liminality of long-term injury and
rehabilitation, which poses a fundamental challenge to athletic identity. Specifically, the analysis
applies Snow and Andersonâs (1995) and Perinbanayagamâs (2000) theoretical conceptualisations
in order to examine the various forms of identity work undertaken by the injured participants, along
the dimensions of materialistic, associative and vocabularic identifications. Such identity work was
found to be crucial in sustaining a credible sporting identity in the face of disruption to the running
self, and in generating momentum towards the goal of restitution to full running fitness and reengagement
with a cherished form of leisure.
KEYWORDS: identity work, symbolic interactionism, distance running, disrupted identit
Seeing the way: visual sociology and the distance runner's perspective
Employing visual and autoethnographic data from a twoâyear research project on distance runners, this article seeks to examine the activity of seeing in relation to the activity of distance running. One of its methodological aims is to develop the linkage between visual and autoethnographic data in combining an observationâbased narrative and sociological analysis with photographs. This combination aims to convey to the reader not only some of the specific subcultural knowledge and particular ways of seeing, but also something of the runner's embodied feelings and experience of momentum en route. Via the combination of narrative and photographs we seek a more effective way of communicating just how distance runners see and experience their training terrain. The importance of subjecting mundane everyday practices to detailed sociological analysis has been highlighted by many sociologists, including those of an ethnomethodological perspective. Indeed, without the competence of social actors in accomplishing these mundane, routine understandings and practices, it is argued, there would in fact be no social order
The Observed Growth of Massive Galaxy Clusters I: Statistical Methods and Cosmological Constraints
(Abridged) This is the first of a series of papers in which we derive
simultaneous constraints on cosmological parameters and X-ray scaling relations
using observations of the growth of massive, X-ray flux-selected galaxy
clusters. Our data set consists of 238 clusters drawn from the ROSAT All-Sky
Survey, and incorporates extensive follow-up observations using the Chandra
X-ray Observatory. Here we describe and implement a new statistical framework
required to self-consistently produce simultaneous constraints on cosmology and
scaling relations from such data, and present results on models of dark energy.
In spatially flat models with a constant dark energy equation of state, w, the
cluster data yield Omega_m=0.23 +- 0.04, sigma_8=0.82 +- 0.05, and w=-1.01 +-
0.20, marginalizing over conservative allowances for systematic uncertainties.
These constraints agree well and are competitive with independent data in the
form of cosmic microwave background (CMB) anisotropies, type Ia supernovae
(SNIa), cluster gas mass fractions (fgas), baryon acoustic oscillations (BAO),
galaxy redshift surveys, and cosmic shear. The combination of our data with
current CMB, SNIa, fgas, and BAO data yields Omega_m=0.27 +- 0.02, sigma_8=0.79
+- 0.03, and w=-0.96 +- 0.06 for flat, constant w models. For evolving w
models, marginalizing over transition redshifts in the range 0.05-1, we
constrain the equation of state at late and early times to be respectively
w_0=-0.88 +- 0.21 and w_et=-1.05 +0.20 -0.36. The combined data provide
constraints equivalent to a DETF FoM of 15.5. Our results highlight the power
of X-ray studies to constrain cosmology. However, the new statistical framework
we apply to this task is equally applicable to cluster studies at other
wavelengths.Comment: 16 pages, 7 figures. v4: final version (typographic corrections).
Results can be downloaded at
https://www.stanford.edu/group/xoc/papers/xlf2009.htm
Phase Space Reduction and Vortex Statistics: An Anyon Quantization Ambiguity
We examine the quantization of the motion of two charged vortices in a
Ginzburg--Landau theory for the fractional quantum Hall effect recently
proposed by the first two authors. The system has two second-class constraints
which can be implemented either in the reduced phase space or
Dirac-Gupta-Bleuler formalism. Using the intrinsic formulation of statistics,
we show that these two ways of implementing the constraints are inequivalent
unless the vortices are quantized with conventional statistics; either
fermionic or bosonic.Comment: 14 pages, PHYZZ
âGet yourself some nice, neat, matching box filesâ: research administrators and occupational identity work
To date, qualitative research into occupational groups and cultures within academia has been relatively scarce, with an almost exclusive concentration upon teaching staff within universities and colleges. This article seeks to address this lacuna and applies the interactionist concept of âidentity workâ in order to examine one specific group to date under-researched: graduate research administrators.
This occupational group is of sociological interest as many of its members appear to span the putative divide between âacademicâ and âadministrativeâ occupational worlds within higher education. An exploratory, qualitative research project was undertaken, based upon interviews with
27 research administrators. The study analyses how research administrators utilise various forms of identity work to sustain credible occupational identities, often in the face of considerable challenge from their academic colleagues
Evidence for TeV gamma ray emission from Cassiopeia A
232 hours of data were accumulated from 1997 to 1999, using the HEGRA
Stereoscopic Cherenkov Telescope System to observe the supernova remnant
Cassiopeia A. TeV gamma ray emission was detected at the 5 sigma level, and a
flux of (5.8 +- 1.2(stat) +- 1.2(syst)) 10^(-9) ph m^(-2) s^(-1) above 1 TeV
was derived. The spectral distribution is consistent with a power law with a
differential spectral index of -2.5 +- 0.4(stat) +- 0.1(syst) between 1 and 10
TeV. As this is the first report of the detection of a TeV gamma ray source on
the "centi-Crab" scale, we present the analysis in some detail. Implications
for the acceleration of cosmic rays depend on the details of the source
modeling. We discuss some important aspects in this paper.Comment: 9 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
- âŠ