3,150 research outputs found
Viable inflationary models ending with a first-order phase transition
We investigate the parameter space of hybrid inflation models where inflation
terminates via a first-order phase transition causing nucleation of bubbles.
Such models experience a tension from the need to ensure nearly scale invariant
density perturbations, while avoiding a near scale-invariant bubble size
distribution which would conflict observations. We perform an exact analysis of
the different regimes of the models, where the energy density of the inflaton
field ranges from being negligible as compared to the vacuum energy to
providing most of the energy for inflation. Despite recent microwave anisotropy
results favouring a spectral index less than one, we find that there are still
viable models that end with bubble production and can match all available
observations. As a by-product of our analysis, we also provide an up-to-date
assessment of the viable parameter space of Linde's original second-order
hybrid model across its full parameter range.Comment: 9 pages, 7 figures. Revised version: corrections to description of
the historical development of the models. v3: Minor corrections to match
version accepted by PR
Fluorine gas as a cleaning agent for Apollo bulk-sample containers
A technique has been developed for cleaning Apollo bulk sample containers using fluorine gas as the cleaning agent
Dark spinor inflation -- theory primer and dynamics
Inflation driven by a single dark spinor field is discussed. We define the
notion of a dark spinor field and derive the cosmological field equations for
such a matter source. The conditions for inflation are determined and an
exactly solvable model is presented. We find the power spectrum of the quantum
fluctuation of this field and compare the results with scalar field inflation.Comment: 13 pages; typo in Eq. (12) corrected, minor improvement
Can Inflation be Falsified?
Despite its central role in modern cosmology, doubts are often expressed as
to whether cosmological inflation is really a falsifiable theory. We
distinguish two facets of inflation, one as a theory of initial conditions for
the hot big bang and the other as a model for the origin of structure in the
Universe. We argue that the latter can readily be excluded by observations, and
that there are also a number of ways in which the former can find itself in
conflict with observational data. Both aspects of the theory are indeed
falsifiable.Comment: 7 pages LaTeX file with two figures incorporated by epsf. Fifth Prize
in Gravity Research Foundation Essay Competition. To appear, General
Relativity and Gravitatio
Investigations of the Non-Linear LMC Cepheid Period-Luminosity Relation with Testimator and Schwarz Information Criterion Methods
In this paper, we investigate the linearity versus non-linearity of the Large
Magellanic Cloud (LMC) Cepheid period-luminosity (P-L) relation using two
statistical approaches not previously applied to this problem: the testimator
method and the Schwarz Information Criterion (SIC). The testimator method is
extended to multiple stages for the first time, shown to be unbiased and the
variance of the estimated slope can be proved to be smaller than the standard
slope estimated from linear regression theory. The Schwarz Information
Criterion (also known as the Bayesian Information Criterion) is more
conservative than the Akaike Information Criterion and tends to choose lower
order models. By using simulated data sets, we verify that these statistical
techniques can be used to detect intrinsically linear and/or non-linear P-L
relations. These methods are then applied to independent LMC Cepheid data sets
from the OGLE project and the MACHO project, respectively. Our results imply
that there is a change of slope in longer period ranges for all of the data
sets. This strongly supports previous results, obtained from independent
statistical tests, that the observed LMC P-L relation is non-linear with a
break period at/around 10 days.Comment: 9 pages, 5 figures and 3 tables, PASP accepte
Hybrid vehicle assessment. Phase 1: Petroleum savings analysis
The results of a comprehensive analysis of near term electric hybrid vehicles are presented, with emphasis on their potential to save significant amounts of petroleum on a national scale in the 1990s. Performance requirements and expected annual usage patterns of these vehicles are first modeled. The projected U.S. fleet composition is estimated, and conceptual hybrid vehicle designs are conceived and analyzed for petroleum use when driven in the expected annual patterns. These petroleum consumption estimates are then compared to similar estimates for projected 1990 conventional vehicles having the same performance and driven in the same patterns. Results are presented in the form of three utility functions and comparisons of sevral conceptual designs are made. The Hybrid Vehicle (HV) design and assessment techniques are discussed and a general method is explained for selecting the optimum energy management strategy for any vehicle mission battery combination. Conclusions and recommendations are presented, and development recommendations are identified
Layzer-Irvine equation: new perspectives and the role of interacting dark energy
We derive the Layzer-Irvine equation in the presence of a homogeneous (or
quasi-homogeneous) dark energy component with an arbitrary equation of state.
We extend the Layzer-Irvine equation to homogeneous and isotropic universes
with an arbitrary number of dimensions and obtain the corresponding virial
relation for sufficiently relaxed objects. We find analogous equations
describing the dynamics of cosmic string loops and other p-branes of arbitrary
dimensionality, discussing the corresponding relativistic and non-relativistic
limits. Finally, we generalize the Layzer-Irvine equation to account for a
non-minimal interaction between dark matter and dark energy, discussing its
practical use as a signature of such an interaction.Comment: 4 page
Phenomenological implications of an alternative Hamiltonian constraint for quantum cosmology
In this paper we review a model based on loop quantum cosmology that arises
from a symmetry reduction of the self dual Plebanski action. In this
formulation the symmetry reduction leads to a very simple Hamiltonian
constraint that can be quantized explicitly in the framework of loop quantum
cosmology. We investigate the phenomenological implications of this model in
the semi-classical regime and compare those with the known results of the
standard Loop Quantum Cosmology.Comment: 10 pages, 7 figure
The Small Scale Velocity Dispersion of Galaxies: A Comparison of Cosmological Simulations
The velocity dispersion of galaxies on small scales ( Mpc),
, can be estimated from the anisotropy of the galaxy-galaxy
correlation function in redshift space. We apply this technique to
``mock-catalogs'' extracted from N-body simulations of several different
variants of Cold Dark Matter dominated cosmological models to obtain results
which may be consistently compared to similar results from observations. We
find a large variation in the value of in different
regions of the same simulation. We conclude that this statistic should not be
considered to conclusively rule out any of the cosmological models we have
studied. We attempt to make the statistic more robust by removing clusters from
the simulations using an automated cluster-removing routine, but this appears
to reduce the discriminatory power of the statistic. However, studying
as clusters with different internal velocity dispersions are
removed leads to interesting information about the amount of power on cluster
and subcluster scales. We also compute the pairwise velocity dispersion
directly and compare this to the values obtained using the Davis-Peebles
method, and find that the agreement is fairly good. We evaluate the models used
for the mean streaming velocity and the pairwise peculiar velocity distribution
in the original Davis-Peebles method by comparing the models with the results
from the simulations.Comment: 20 pages, uuencoded (Latex file + 8 Postscript figures), uses AAS
macro
JuSt – a multimodal program for treatment of insomnia in adolescents: a pilot study
Schlarb A, Liddle CC, Hautzinger M. JuSt – a multimodal program for treatment of insomnia in adolescents: a pilot study. Nature and Science of Sleep. 2011;3:13-20.Insomnia is the most prevalent sleep disorder in adolescents. A number of studies have evaluated the efficacy of the management of chronic insomnia in adults. Behavioral therapy for insomnia is the treatment of first choice, encompassing education about sleep and sleep hygiene, stimulus control, relaxation techniques, and cognitive strategies to combat nocturnal ruminations. Special programs for adolescents are lacking. In this study an age-oriented treatment program for adolescents (JuSt) was developed and evaluated. Eighteen adolescents and their parents participated in a psychological short-term treatment comprising six sessions. First results show that the treatment was well accepted by the adolescents and their parents and led to a significant reduction in sleep problems, such as sleep onset, sleep efficacy, sleep duration, and feeling rested as well as in cognitive parameters, such as ruminations and mental health. Randomized controlled studies are needed to evaluate the efficacy of this new approach to treat insomnia in adolescents
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