209 research outputs found
Contiguous redshift parameterizations of the growth index
The growth rate of matter perturbations can be used to distinguish between
different gravity theories and to distinguish between dark energy and modified
gravity at cosmological scales as an explanation to the observed cosmic
acceleration. We suggest here parameterizations of the growth index as
functions of the redshift. The first one is given by that
interpolates between a low/intermediate redshift parameterization
and a high
redshift constant value. For example, our interpolated form
can be used when including the CMB to the rest of the data while
the form can be used otherwise. It is found that the
parameterizations proposed achieve a fit that is better than 0.004% for the
growth rate in a CDM model, better than 0.014% for
Quintessence-Cold-Dark-Matter (QCDM) models, and better than 0.04% for the flat
Dvali-Gabadadze-Porrati (DGP) model (with ) for the entire
redshift range up to . We find that the growth index parameters
take distinctive values for dark energy models and
modified gravity models, e.g. for the CDM model
and for the flat DGP model. This provides a means for future
observational data to distinguish between the models.Comment: 7 pages, 6 figures, matches PRD accepted versio
The 2dF QSO Redshift Survey - XIV. Structure and evolution from the two-point correlation function
In this paper we present a clustering analysis of quasi-stellar objects (QSOs) using over 20000 objects from the final catalogue of the 2dF QSO Redshift Survey (2QZ), measuring the redshift-space two-point correlation function, ξ(s). When averaged over the redshift range 0.3 < z < 2.2 we find that ξ(s) is flat on small scales, steepening on scales above ~25h-1 Mpc. In a WMAP/2dF cosmology (Ωm= 0.27, ΩΛ= 0.73) we find a best-fitting power law with s0= 5.48+0.42-0.48h-1 Mpc and γ= 1.20 +/- 0.10 on scales s= 1 to 25h-1 Mpc. We demonstrate that non-linear redshift-space distortions have a significant effect on the QSO ξ(s) at scales less than ~10h-1 Mpc. A cold dark matter model assuming WMAP/2dF cosmological parameters is a good description of the QSO ξ(s) after accounting for non-linear clustering and redshift-space distortions, and allowing for a linear bias at the mean redshift of bQ(z= 1.35) = 2.02 +/- 0.07. We subdivide the 2QZ into 10 redshift intervals with effective redshifts from z= 0.53 to 2.48. We find a significant increase in clustering amplitude at high redshift in the WMAP/2dF cosmology. The QSO clustering amplitude increases with redshift such that the integrated correlation function, , within 20h-1 Mpc is and . We derive the QSO bias and find it to be a strong function of redshift with bQ(z= 0.53) = 1.13 +/- 0.18 and bQ(z= 2.48) = 4.24 +/- 0.53. We use these bias values to derive the mean dark matter halo (DMH) mass occupied by the QSOs. At all redshifts 2QZ QSOs inhabit approximately the same mass DMHs with MDH= (3.0 +/- 1.6) × 1012h-1 Msolar, which is close to the characteristic mass in the Press-Schechter mass function, M*, at z= 0. These results imply that L*Q QSOs at z~ 0 should be largely unbiased. If the relation between black hole (BH) mass and MDH or host velocity dispersion does not evolve, then we find that the accretion efficiency (L/LEdd) for L*Q QSOs is approximately constant with redshift. Thus the fading of the QSO population from z~ 2 to ~0 appears to be due to less massive BHs being active at low redshift. We apply different methods to estimate, tQ, the active lifetime of QSOs and constrain tQ to be in the range 4 × 106-6 × 108 yr at z~ 2. We test for any luminosity dependence of QSO clustering by measuring ξ(s) as a function of apparent magnitude (equivalent to luminosity relative to L*Q). However, we find no significant evidence of luminosity-dependent clustering from this data set
Multiple Sclerosis Patient Management During the COVID-19 Pandemic: Practical Recommendations From the Portuguese Multiple Sclerosis Study Group (GEEM)
The spread of the COVID-19 pandemic has imposed significant challenges on healthcare provision, requiring changes in the conventional patient management, particularly in chronic diseases like multiple sclerosis (MS). To increase patient safety and reduce the risk of infection, while ensuring an appropriate and regular follow-up, tele-medicine gained prominence as a valid alternative to face-to-face appointments. However, the urgency of the implementation and the lack of experience in most MS centers led to "ad hoc" and extremely diverse approaches, which now merit to be standardized and refined. Indeed, while tele-consultation cannot fully replace face-to-face visits, it certainly can, and will, be incorporated as part of the routine care of MS patients in the near future. Bearing this in mind, the Portuguese Multiple Sclerosis Study Group (GEEM) has developed a set of recommendations for the usage of tele-medicine in the management of MS patients, both during the pandemic and in the future. The consensus was obtained through a two-step modified Delphi methodology, resulting in 15 recommendations, which are detailed in the manuscript.The consensus and the publication of this manuscript were supported by an educational grant from Novartis Portugal to the Grupo de Estudos de Esclerose Múltipla. These funds were used to pay the work of the consultancy MOAI, which set up the online questionnaire and helped with writing the summary of the meeting and the first draft of the consensus, and the publishing fee (article processing charge). The funding source had no role in the process and did not influence, by any means, the content of the consensus or the present manuscriptinfo:eu-repo/semantics/publishedVersio
Obesity and treatment meanings in bariatric surgery candidates: a qualitative study
Background
This study used a qualitative approach to comprehend how the morbid obese conceptualize and deal with obesity and obesity treatment, with the particular aim of exploring the expectations and beliefs about the exigencies and the impact of bariatric surgery.
Methods
The study population included 30 morbid obese patients (20 women and 10 men) with a mean age of 39.17 years (SD = 8.81) and a mean body mass index of 47.5 (SD = 8.2) interviewed individually before surgery using open-ended questions. The interviews were audiotaped, transcribed, and then coded according to grounded analysis methodology.
Results
Three main thematic areas emerged from the data: obesity, eating behavior, and treatment. Obesity is described as a stable and hereditary trait. Although participants recognize that personal eating behavior exacerbates this condition, patients see their eating behavior as difficult to change and control. Food seems to be an ever-present dimension and a coping strategy, and to follow an adequate diet plan is described as a huge sacrifice. Bariatric surgery emerges as the only treatment for obesity, and participants highlight this moment as the beginning of a new life where health professionals have the main role. Bariatric surgery candidates see their eating behavior as out of their control, and to commit to its demands is seen as a big sacrifice. For these patients, surgery is understood as a miracle moment that will change their lives without requiring an active role or their participation.
Conclusion
According to these results, it is necessary to validate them with qualitative and quantitative studies; it is necessary to promote a new awareness of the weight loss process and to empower patients before and after bariatric surgery.Bolsa de doutoramento SFRH/BD/37069/2007 da Fundação para a Ciência e a Tecnologia (FCT
On merger bias and the clustering of quasars
We use the large catalogues of haloes available for the Millennium Simulation
to test whether recently merged haloes exhibit stronger large-scale clustering
than other haloes of the same mass. This effect could help to understand the
very strong clustering of quasars at high redshift. However, we find no
statistically significant excess bias for recently merged haloes over the
redshift range 2 < z < 5, with the most massive haloes showing an excess of at
most ~5%. We also consider galaxies extracted from a semianalytic model built
on the Millennium Simulation. At fixed stellar mass, we find an excess bias of
~ 20-30% for recently merged objects, decreasing with increasing stellar mass.
The fact that recently-merged galaxies are found in systematically more massive
haloes than other galaxies of the same stellar mass accounts for about half of
this signal, and perhaps more for high-mass galaxies. The weak merger bias of
massive systems suggests that objects of merger-driven nature, such as quasars,
do not cluster significantly differently than other objects of the same
characteristic mass. We discuss the implications of these results for the
interpretation of clustering data with respect to quasar duty cycles,
visibility times, and evolution in the black hole-host mass relation.Comment: 10 pages, 9 figures. Submitted to MNRAS. Comments welcom
X-ray selected AGN in groups at redshifts z~1
We explore the role of the group environment in the evolution of AGN at the
redshift interval 0.7<z<1.4, by combining deep Chandra observations with
extensive optical spectroscopy from the All-wavelength Extended Groth strip
International Survey (AEGIS). The sample consists of 3902 optical sources and
71 X-ray AGN. Compared to the overall optically selected galaxy population,
X-ray AGN are more frequently found in groups at the 99% confidence level. This
is partly because AGN are hosted by red luminous galaxies, which are known to
reside, on average, in dense environments. Relative to these sources, the
excess of X-ray AGN in groups is significant at the 91% level only. Restricting
the sample to 0.7<z<0.9 and M_B<-20mag in order to control systematics we find
that X-ray AGN represent (4.7\pm1.6) and (4.5\pm1.0)% of the optical galaxy
population in groups and in the field respectively. These numbers are
consistent with the AGN fraction in low redshift clusters, groups and the
field. The results above, although affected by small number statistics, suggest
that X-ray AGN are spread over a range of environments, from groups to the
field, once the properties of their hosts (e.g. colour, luminosity) are
accounted for. There is also tentative evidence, significant at the 98% level,
that the field produces more X-ray luminous AGN compared to groups, extending
similar results at low redshift to z~1. This trend may be because of either
cold gas availability or the nature of the interactions occurring in the denser
group environment (i.e. prolonged tidal encounters).Comment: To appear in MNRA
Conservation genomics of the endangered Seychelles Magpie‐Robin (Copsychus sechellarum):a unique insight into the history of a precious endemic bird
The Seychelles Magpie-Robin Copsychus sechellarum is an IUCN Red-List Endangered species endemic to the Seychelles, whose population was reduced to eight individuals on a single island in the 1960s. Translocations from the remaining population to four additional islands have been an integral factor in their recovery, but the potential genetic consequences of their translocation history have not previously been explored. We resequenced the genomes of 141 individuals sampled across the five current island populations and analysed the data to characterize their population structure, as well as to explore suspected inbreeding. Overall, very low levels of heterozygosity were observed, all coupled with long homozygous segments that suggest recent inbreeding, probably the consequence of a population bottleneck in the 1960s. Three of the four translocated populations displayed less genetic diversity than the founder population from which they were taken, a familiar pattern observed as a result of the evolutionary force of genetic drift following founder events. Furthermore, and perhaps surprising given the recent time since the new populations were established, population structure was observed within these same three populations. New awareness of inbreeding in the Seychelles Magpie-Robin populations, and continued genetic monitoring, will allow for genetically informed management decisions. This is particularly prudent in maximizing the success of the future conservation translocation planned for this species
Counting quasar–radio source pairs to derive the millijansky radio luminosity function and clustering strength to z
Assessing the reliability of retrospective reports of adverse childhood experiences among adolescents with documented childhood maltreatment
The literature suggests that childhood maltreatment
is related to a higher probability of developing psychopathology
and disease in adulthood. However, some authors have
questioned the reliability of self-reports of maltreatment, suggesting
that psychopathology at the time of evaluation affects
self-reports. We evaluated the reliability of the self-reports of
79 young adults who were identified in childhood by Child
Protective Services by comparing two moments of evaluation.
Psychological and physical symptoms were tested to evaluate
their interference with the reports. We found good to excellent
agreement, with no significant correlation between the changes
in self-reported experiences and the changes in physical and
psychological symptoms, suggesting that the reliability of
reports is not related to the health state at the time of the report
Evidence for Merger-Driven Activity in the Clustering of High Redshift Quasars
Recently, a very large clustering length has been measured for quasars at a
redshift of z~4. In combination with the observed quasar luminosity function we
assess the implications of this clustering for the relationship between quasar
luminosity and dark matter halo mass. Our analysis allows for non-linearity and
finite scatter in the relation between quasar luminosity and halo mass, as well
as a luminosity dependent quasar lifetime. The additional novel ingredient in
our modelling is the allowance for an excess in the observed bias over the
underlying halo bias owing to the merger driven nature of quasar activity. We
find that the observations of clustering and luminosity function can be
explained only if both of the following conditions hold: (i) The luminosity to
halo mass ratio increases with halo mass; (ii) The observed clustering
amplitude is in excess of that expected solely from halo bias. The latter
result is statistically significant at the 99% level. Taken together, the
observations provide compelling evidence for merger driven quasar activity,
with a black-hole growth that is limited by feedback. In difference from
previous analyses, we show that there could be scatter in the luminosity halo
mass relation of up to 1 dex, and that quasar clustering can not be used to
estimate the quasar lifetime.Comment: 11 pages, 8 figures. Submitted to MNRA
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