7,604 research outputs found
Clarifying spherical collapse in coupled dark energy cosmologies
The spherical collapse model is often used to follow the evolution of
overdensities into the nonlinear regime. We describe the correct approach to be
used in coupled dark energy cosmologies, where a fifth force, different from
gravity and mediated by the dark energy scalar field, influences the collapse.
We reformulate the spherical collapse description by deriving it directly from
the set of nonlinear hydrodynamical Navier Stokes equations. By comparing with
the corresponding relativistic equations, we show how the fifth force should be
taken into account within the spherical collapse picture and clarify the
problems arising when an inhomogeneous scalar field is considered within a
spherical collapse picture. We then apply our method to the case of coupled
quintessence, where the fifth force acts among cold dark matter particles, and
to growing neutrino quintessence, where the fifth force acts between neutrinos.
Furthermore, we review this method when applied to standard cosmologies and
apply our analysis to minimally coupled quintessence and check past results for
early dark energy parametrizations.Comment: 16 pages, 13 figures, published in Physical Review D, minor changes
and correction
Dark Matter, Modified Gravity and the Mass of the Neutrino
It has been suggested that Einstein's theory of General Relativity can be
modified to accomodate mismatches between the gravitational field and luminous
matter on a wide range of scales. Covariant theories of modified gravity
generically predict the existence of extra degrees of freedom which may be
interpreted as dark matter. We study a subclass of these theories where the
overall energy density in these extra degrees of freedom is subdominant
relative to the baryon density and show that they favour the presence of
massive neutrinos. For some specific cases (such as a flat Universes with a
cosmological constant) one finds a conservative lower bound on the neutrinos
mass of eV.Comment: 5 pages, 2 figures, 2 tables, submitted to Phys. Rev.
Measuring the galaxy power spectrum with multiresolution decomposition -- II. diagonal and off-diagonal power spectra of the LCRS galaxies
The power spectrum estimator based on the discrete wavelet transform (DWT)
for 3-dimensional samples has been studied. The DWT estimator for
multi-dimensional samples provides two types of spectra with respect to
diagonal and off-diagonal modes, which are very flexible to deal with
configuration-related problems in the power spectrum detection. With simulation
samples and mock catalogues of the Las Campanas redshift survey (LCRS), we show
(1) the slice-like geometry of the LCRS doesn't affect the off-diagonal power
spectrum with ``slice-like'' mode; (2) the Poisson sampling with the LCRS
selection function doesn't cause more than 1- error in the DWT power
spectrum; and (3) the powers of peculiar velocity fluctuations, which cause the
redshift distortion, are approximately scale-independent. These results insure
that the uncertainties of the power spectrum measurement are under control. The
scatter of the DWT power spectra of the six strips of the LCRS survey is found
to be rather small. It is less than 1- of the cosmic variance of mock
samples in the wavenumber range h Mpc. To fit the detected
LCRS diagonal DWT power spectrum with CDM models, we find that the best-fitting
redshift distortion parameter is about the same as that obtained from
the Fourier power spectrum. The velocity dispersions for SCDM and
CDM models are also consistent with other detections with
the LCRS. A systematic difference between the best-fitting parameters of
diagonal and off-diagonal power spectra has been significantly measured. This
indicates that the off-diagonal power spectra are capable of providing
information about the power spectrum of galaxy velocity field.Comment: AAS LaTeX file, 41 pages, 10 figures included, accepted for
publication in Ap
An imaging K-band survey - I: The catalogue, star and galaxy counts
We present results from a large area (552\,\sqamin) imaging -band survey
to a 5 limit of . We have optical-infrared colours of
almost all the objects in the sample. Star-galaxy discrimination is performed
and the results used to derive the infrared star and galaxy counts. -band
``no-evolution'' galaxy-count models are constructed and compared with the
observed data. In the infrared, there is no counterpart for the large excess of
faint galaxies over the no-evolution model seen in optical counts. However, we
show that the counts can be remarkably insensitive to evolution under
certain reasonable assumptions. Finally, model predictions for -selected
redshift surveys are derived.Comment: MNRAS in press. 21 pages plain TeX; figs plus table 4 available via
anonymous ftp from /pub/kgb/paper1/sissa.uu at ftp.ast.cam.ac.u
The Angular Power Spectrum of EDSGC Galaxies
We determine the angular power spectrum, C_l, of the Edinburgh/Durham
Southern Galaxy Catalog (EDSGC) and use this statistic to constrain
cosmological parameters. Our methods for determining C_l, and the parameters
that affect it are based on those developed for the analysis of cosmic
microwave background maps. We expect them to be useful for future surveys.
Assuming flat cold dark matter models with a cosmological constant (constrained
by COBE/DMR and local cluster abundances), and a scale--independent bias, b, we
find good fits to the EDSGC angular power spectrum with 1.11 < b < 2.35 and 0.2
< Omega_m < 0.55 at 95% confidence. These results are not significantly
affected by the ``integral constraint'' or extinction by interstellar dust, but
may be by our assumption of Gaussianity.Comment: 11 pages, 9 figures, version to appear in Ap
A Survey of Bariatric Surgical Patients\u27 Experiences with Behavioral and Psychological Services
The following study assessed behavioral and psychological services currently being used by bariatric patients before and after surgery. A convenience sample of N = 380 was generated through solicitation on an online support website; inclusion criteria included having had surgery in the United States after implementation of accreditation standards in 2005. Participants completed an Internet-based survey that assessed services completed, satisfaction with services, perceived impact of surgery on mental and physical health as well as diet and physical activity behaviors, and current reported diet and physical activity behaviors. Overall, participants reported completing more services before surgery, and afterwards the most commonly reported completed services were support groups and dietary consultation; more than half of participants did not meet with either a mental health professional or exercise professional following surgery. Participants expressed high satisfaction with surgery, and perceived that surgery had a positive impact on health and health behaviors. Linear regression analysis showed that satisfaction with surgery was largely predicted by percent weight loss, though it is also possible that perceived benefits to mental and physical health also contributed to satisfaction levels. Self-reported physical activity levels were increased dramatically following surgery; however, these results must be interpreted carefully due to potential sample bias and over-reporting. Because participants in the current sample reported completing few behavioral and psychological services after surgery, it is recommended that bariatric facilities and insurance providers consider requiring patients to complete post-surgical behavioral modification programs that target improvement of diet and physical activity behaviors and overall lifestyle change
A Systematic Review of Interventions for Unpaid Caregivers of Persons With Dementia
The prevalence of dementia is increasing as seniors are living longer than ever before. Due to cuts in funding for formal support such as home care and the decreased number of long-term care beds many families are having to provide care for a loved one with dementia in the community. The results of caregiving lead to both positive and negative consequences. There is an abundance of literature regarding interventions to support and maintain caregivers in the community, many with conflicting results. This study utilized a systematic review to gather and synthesize information about interventions that have an effect on the well-being of caregivers of people with dementia. The steps in a systematic review include: (a) developing a research question, (b) developing relevance and validity tools, (c) conducting a thorough literature search of published and unpublished studies,
(d) using relevance and validity tools to assess the studies, (e) completing data extraction for each study, (l) synthesizing the findings and, (g) writing the report. A search of published and some unpublished articles resulted in the retrieval of 92 studies, with 36 meeting the relevance criteria. Utilizing the validity criteria, 11 studies were rated as strong, 11 moderate, 13 weak, and 1 poor. The strong and moderate studies are the focus of the review. No one intervention demonstrated an overall significant impact on the well-being of caregivers. Several interventions have been shown to be of benefit to caregivers, however, further investigation is greatly needed. Institutionalization was delayed by the psychotherapy intervention for caregivers and in one of the case management models. Caregiver depression and strain were reduced during in-hospital respite. Two educational interventions demonstrated an increase in knowledge about dementia for caregivers. Interventions individualized to the caregiver or care receiver were successful in some outcome areas. Non-significant findings were more common. The results of this study will be disseminated to interested researchers, consumers, practitioners and policy makers in a variety of formats. Systematic reviews are an important means to guide consumers and practitioners as they make evidence-based decisions
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