15,306 research outputs found
Determination of the chemical potential using energy-biased sampling
An energy-biased method to evaluate ensemble averages requiring test-particle
insertion is presented. The method is based on biasing the sampling within the
subdomains of the test-particle configurational space with energies smaller
than a given value freely assigned. These energy-wells are located via unbiased
random insertion over the whole configurational space and are sampled using the
so called Hit&Run algorithm, which uniformly samples compact regions of any
shape immersed in a space of arbitrary dimensions. Because the bias is defined
in terms of the energy landscape it can be exactly corrected to obtain the
unbiased distribution. The test-particle energy distribution is then combined
with the Bennett relation for the evaluation of the chemical potential. We
apply this protocol to a system with relatively small probability of low-energy
test-particle insertion, liquid argon at high density and low temperature, and
show that the energy-biased Bennett method is around five times more efficient
than the standard Bennett method. A similar performance gain is observed in the
reconstruction of the energy distribution.Comment: 10 pages, 4 figure
Searching for galaxy clusters in the VST-KiDS Survey
We present the methods and first results of the search for galaxy clusters in
the Kilo Degree Survey (KiDS). The adopted algorithm and the criterium for
selecting the member galaxies are illustrated. Here we report the preliminary
results obtained over a small area (7 sq. degrees), and the comparison of our
cluster candidates with those found in the RedMapper and SZ Planck catalogues;
the analysis to a larger area (148 sq. degrees) is currently in progress. By
the KiDS cluster search, we expect to increase the completeness of the clusters
catalogue to z = 0.6-0.7 compared to RedMapper.Comment: 5 pages, 4 figures, to be published in the Proceedings of the
Conference "The Universe of Digital Sky Surveys", Naples, November 25-28 201
Current Star Formation in the Ophiuchus and Perseus Molecular Clouds: Constraints and Comparisons from Unbiased Submillimeter and Mid-Infrared Surveys. II
We present a census of the population of deeply embedded young stellar
objects (YSOs) in the Ophiuchus molecular cloud complex based on a combination
of Spitzer Space Telescope mid-infrared data from the "Cores to Disks" (c2d)
legacy team and JCMT/SCUBA submillimeter maps from the COMPLETE team. We have
applied a method developed for identifying embedded protostars in Perseus to
these datasets and in this way construct a relatively unbiased sample of 27
candidate embedded protostars with envelopes more massive than our sensitivity
limit (about 0.1 M_sun). Embedded YSOs are found in 35% of the SCUBA cores -
less than in Perseus (58%). On the other hand the mid-infrared sources in
Ophiuchus have less red mid-infrared colors, possibly indicating that they are
less embedded. We apply a nearest neighbor surface density algorithm to define
the substructure in each of the clouds and calculate characteristic numbers for
each subregion - including masses, star formation efficiencies, fraction of
embedded sources etc. Generally the main clusters in Ophiuchus and Perseus
(L1688, NGC1333 and IC348) are found to have higher star formation efficiencies
than small groups such as B1, L1455 and L1448, which on the other hand are
completely dominated by deeply embedded protostars. We discuss possible
explanations for the differences between the regions in Perseus and Ophiuchus,
such as different evolutionary timescales for the YSOs or differences, e.g., in
the accretion in the two clouds.Comment: Accepted for publication in ApJ (56 pages, 13 figures; abstract
abridged). Version with full-resolution figures available at
http://www.astro.uni-bonn.de/~jes/paper120.pd
Dirac fermions on a disclinated flexible surface
A self-consisting gauge-theory approach to describe Dirac fermions on
flexible surfaces with a disclination is formulated. The elastic surfaces are
considered as embeddings into R^3 and a disclination is incorporated through a
topologically nontrivial gauge field of the local SO(3) group which generates
the metric with conical singularity. A smoothing of the conical singularity on
flexible surfaces is naturally accounted for by regarding the upper half of
two-sheet hyperboloid as an elasticity-induced embedding. The availability of
the zero-mode solution to the Dirac equation is analyzed.Comment: 6 page
Young people's uses of celebrity: Class, gender and 'improper' celebrity
This is an Author's Accepted Manuscript of an article published in Discourse: Studies in the Cultural
Politics of Education, 34(1), 2013, copyright Taylor & Francis, available online at:
http://www.tandfonline.com/10.1080/01596306.2012.698865.In this article, we explore the question of how celebrity operates in young people's everyday lives, thus contributing to the urgent need to address celebrity's social function. Drawing on data from three studies in England on young people's perspectives on their educational and work futures, we show how celebrity operates as a classed and gendered discursive device within young people's identity work. We illustrate how young people draw upon class and gender distinctions that circulate within celebrity discourses (proper/improper, deserving/undeserving, talented/talentless and respectable/tacky) as they construct their own identities in relation to notions of work, aspiration and achievement. We argue that these distinctions operate as part of neoliberal demands to produce oneself as a ‘subject of value’. However, some participants produced readings that show ambivalence and even resistance to these dominant discourses. Young people's responses to celebrity are shown to relate to their own class and gender position.The Arts and Humanities Research Council, the British Academy, the
Economic and Social Research Council, and the UK Resource Centre for
Women in Science Engineering and Technology
Finite Temperature Effective Potential for Gauge Models in de Sitter Space
The one-loop effective potential for gauge models in static de Sitter space
at finite temperatures is computed by means of the --function method. We
found a simple relation which links the effective potentials of gauge and
scalar fields at all temperatures.
In the de Sitter invariant and zero-temperature states the potential for the
scalar electrodynamics is explicitly obtained, and its properties in these two
vacua are compared. In this theory the two states are shown to behave similarly
in the regimes of very large and very small radii a of the background space.
For the gauge symmetry broken in the flat limit () there is a
critical value of a for which the symmetry is restored in both quantum states.
Moreover, the phase transitions which occur at large or at small a are of the
first or of the second order, respectively, regardless the vacuum considered.
The analytical and numerical analysis of the critical parameters of the above
theory is performed. We also established a class of models for which the kind
of phase transition occurring depends on the choice of the vacuum.Comment: 23 pages, LaTeX, 5 figure.ep
Self-trapped Exciton and Franck-Condon Spectra Predicted in LaMnO
Because the ground state has cooperative Jahn-Teller order, electronic
excitations in LaMnO are predicted to self-trap by local rearrangement of
the lattice. The optical spectrum should show a Franck-Condon series, that is,
a Gaussian envelope of vibrational sidebands. Existing data are reinterpreted
in this way. The Raman spectrum is predicted to have strong multiphonon
features.Comment: 5 pages with two embedded postscript figure
Does the nuclear spin relaxation rate in superconductors depend on disorder?
We calculate the relaxation rate of a nuclear spin in s-wave superconductor
with nonmagnetic impurities, including the strong-coupling effects. We show
that in a weakly disordered three-dimensional system the corrections due to
disorder are negligibly small.Comment: 9 page
Position and frequency shifts induced by massive modes of the gravitational wave background in alternative gravity
Alternative theories of gravity predict the presence of massive scalar,
vector, and tensor gravitational wave modes in addition to the standard
massless spin~2 graviton of general relativity. The deflection and frequency
shift effects on light from distant sources propagating through a stochastic
background of gravitational waves, containing such modes, differ from their
counterparts in general relativity. Such effects are considered as a possible
signature for alternative gravity in attempts to detect deviations from
Einstein's gravity by astrophysical means.Comment: 9 pages, 1 figur
A Search for OH Megamasers at z > 0.1. I. Preliminary Results
We present the preliminary results of a survey for OH megamasers underway at
the Arecibo Observatory. The goals of the survey are to calibrate the
luminosity function of OH megamasers to the low-redshift galaxy merger rate
(0.1 < z < 0.2), and to use the enhanced sample of OH megamasers provided by
the survey to study OH megamaser environments, engines, lifetimes, and
structure. The survey should double the known OH megamaser sample to roughly
100 objects. Survey results will be presented in installments to facilitate
community access to the data. Here we report the discovery of 11 OH megamasers
and one OH absorber, and include upper limits on the isotropic 1667 MHz OH line
luminosity of 53 other luminous infrared galaxies at z > 0.1. The new
megamasers show a wide range of spectral properties, but are consistent with
the extant set of 55 previously reported objects, only 8 of which have z > 0.1.Comment: 18 pages, 3 figures, accepted for publication in the Astronomical
Journa
- …