138 research outputs found
Phantom Accretion by Black Holes and the Generalized Second Law of Thermodynamics
The accretion of a phantom fluid with non-zero chemical potential by black
holes is discussed with basis on the Generalized Second Law of thermodynamics.
For phantom fluids with positive temperature and negative chemical potential we
demonstrate that the accretion process is possible, and that the condition
guaranteeing the positiveness of the phantom fluid entropy coincides with the
one required by Generalized Second Law. In particular, this result provides a
complementary confirmation that cosmological phantom fluids do not need to have
negative temperatures
Realistic fluids as source for dynamically accreting black holes in a cosmological background
We show that a single imperfect fluid can be used as a source to obtain the
generalized McVittie metric as an exact solution to Einstein's equations. The
mass parameter in this metric varies with time thanks to a mechanism based on
the presence of a temperature gradient. This fully dynamical solution is
interpreted as an accreting black hole in an expanding universe if the metric
asymptotes to Schwarzschild-de Sitter at temporal infinity. We present a simple
but instructive example for the mass function and briefly discuss the structure
of the apparent horizons and the past singularity.Comment: 5 pages, 2 figures. Updated references and minor changes to match the
version accepted for publishing in PR
Analytical solutions of accreting black holes immersed in a Lambda-CDM model
The evolution of the mass of a black hole embedded in a universe filled with
dark energy and cold dark matter is calculated in a closed form within a test
fluid model in a Schwarzschild metric, taking into account the cosmological
evolution of both fluids. The result describes exactly how accretion
asymptotically switches from the matter-dominated to the Lambda-dominated
regime. For early epochs, the black hole mass increases due to dark matter
accretion, and on later epochs the increase in mass stops as dark energy
accretion takes over. Thus, the unphysical behaviour of previous analyses is
improved in this simple exact model.Comment: 8 pages, 1 figure, accepted for publication in Physics Letters
Exhaustive CoMFA and CoMSIA analyses around different chemical entities: a ligand-based study exploring the affinity and selectivity profiles of 5-HT1A ligands
The 5-hydroxytryptamine (5-HT1A) receptors represent an attractive target in drug discovery. In particular, 5-HT1A agonists and partial agonists are deeply investigated for their potential role in the treatment of anxiety, depression, ischaemic brain disorder and more recently, of pain. On the other hand, 5-HT1A antagonists have been revealed promising compounds in cognition disorders and, lately, in cancer. Thus, the discovery of 5HT1A ligands is nowadays an appealing research activity in medicinal chemistry. In this work, Comparative Molecular Fields Analysis (CoMFA) and Comparative Molecular Similarity Index Analysis (CoMSIA) were applied on an in-house library of 5-HT1A ligands bearing different chemical scaffolds in order to elucidate their affinity and selectivity for the target. Following this procedure, a number of structural modifications have been drawn for the development of much more effective 5-HT1AR ligands
Unified dark energy thermodynamics: varying w and the -1-crossing
We investigate, in a unified and general way, the thermodynamic properties of
dark energy with an arbitrary, varying equation-of-state parameter w(a). We
find that all quantities are well defined and regular for every w(a), including
at the -1-crossing, with the temperature being negative in the phantom regime
(w(a)-1). The density and
entropy are always positive while the chemical potential can be arbitrary. At
the -1-crossing, both temperature and chemical potential are zero. The
temperature negativity can only be interpreted in the quantum framework. The
regular behavior of all quantities at the -1-crossing, leads to the conclusion
that such a crossing does not correspond to a phase transition, but rather to a
smooth cross-over.Comment: 5 pages, version published in Class. Quant. Gra
Citocinas séricas na forma crônica da doenca de Chagas
We studied the serum levels of IL-2, IFN-g and TNF in different clinical forms of Chagas' disease and in patients clinically compensated and decompensated. Cytokines measured in 91 patients with the chronic form of the disease did not differ from those of 13 normal individuals, suggesting the absence of activation of the TH1 pattern of lymphocyte response. There were no statistical differences among the 17 patients in the indeterminate form of the disease, the patients presenting either early (n = 4) or well-developed signs of cardiomyopathy (n = 62), the digestive (n = 4) or the mixed (n = 4) forms of the disease. Serum TNF was undetectable and IFN-g levels did not differ between clinical forms and severities of Chagas' disease. However, we found IL-2 higher levels in the 25 non-controlled patients than in the 66 controlled individuals (p < 0,001). We suggest that IL-2 dosage may be useful as an indicator of the need for more aggressive procedures.Estudamos os nÃveis séricos da IL-2, IFN-g e do TNF-a de portadores da doença de Chagas em suas diferentes formas clÃnicas, compensados e descompensados. As citocinas medidas nos 91 pacientes com a forma crônica da doença não diferiram dos nÃveis de 13 indivÃduos controle. Não houve diferença estatÃstica entre os 17 portadores da forma indeterminada da doença e os portadores de cardiopatia insipiente (n = 4), de cardiopatia bem estabelecida (n = 62), da forma digestiva (n = 4) ou da forma mista (n = 4) da doença. Os nÃveis séricos de TNF foram indetectáveis e IFN-g não diferiu nas diferentes formas clÃnicas ou com a severidade da doença. No entanto, encontramos nÃveis mais elevados de IL-2 nos 25 pacientes não-contrololados do que nos 66 pacientes bem compensados (p < 0,001). Sugerimos que a dosagem de IL-2 possa servir como indicadora da necessidade de terapêuticas mais agressivas nestes pacientes.28528
Hawking radiation and thermodynamics of dynamical black holes in phantom dominated universe
The thermodynamic properties of dark energy-dominated universe in the
presence of a black hole are investigated in the general case of a varying
equation-of-state-parameter . We show that all the thermodynamics
quantities are regular at the phantom divide crossing, and particularly the
temperature and the entropy of the dark fluid are always positive definite. We
also study the accretion process of a phantom fluid by black holes and the
conditions required for the validity of the generalized second law of
thermodynamics. As a results we obtain a strictly negative chemical potential
and an equation-of-state parameter Comment: 22 pages,3 figure
Brans-Dicke Theory and primordial black holes in Early Matter-Dominated Era
We show that primordial black holes can be formed in the matter-dominated era
with gravity described by the Brans-Dicke theory. Considering an early
matter-dominated era between inflation and reheating, we found that the
primordial black holes formed during that era evaporate at a quicker than those
of early radiation-dominated era. Thus, in comparison with latter case, less
number of primordial black holes could exist today. Again the constraints on
primordial black hole formation tend towards the larger value than their
radiation-dominated era counterparts indicating a significant enhancement in
the formation of primordial black holes during the matter-dominaed era.Comment: 9 page
Reporting of rehabilitation intervention for low back pain in randomized controlled trials : Is the treatment fully replicable?
Study Design. Methodological review of randomized controlled trials (RCTs). Objective. To assess the quality of reporting of rehabilitation interventions for mechanical low back pain (LBP) in published RCTs. Summary of Background Data. Reporting of interventions in RCTs often focused on the outcome value and failed to describe interventions adequately. Methods. We systematically searched for all RCTs in Cochrane systematic reviews on LBP published in the Cochrane Database of Systematic Reviews until December 2013. The description of rehabilitation interventions of each RCT was evaluated independently by 2 of the investigators, using an ad hoc checklist of 7 items. The primary outcome was the number of items reported in sufficient details to be replicable in a new RCT or in everyday practice. Results. We found 11 systematic reviews, including 220 eligible RCTs, on LBP. Of those, 185 RCTs were included. The median publication year was 1998 (I-III quartiles, 1990 to 2004). The most reported items were the characteristics of participants (91.3%; 95% confidence interval [CI], 87.3-95.4), the intervention providers (81.1%; 95% CI, 75.4-86.7), and the intervention schedule (69.7%; 95% CI, 63-76). Based on the description of the intervention, less than one fifth would be replicable clinically. The proportion of trials providing all essential information about the participants and interventions increased from 14% (n=7) in 1971 to 1980 to 20% (n=75) in 2001 to 2010. Conclusion. Despite the remarkable amount of energy spent producing RCTs in LBP rehabilitation, the majority of RCTs failed to report sufficient information that would allow the intervention to be replicated in clinical practice. Improving the quality of intervention description is urgently needed to better transfer research into rehabilitation practices
Simulating Food Web Dynamics along a Gradient: Quantifying Human Influence
Realistically parameterized and dynamically simulated food-webs are useful tool to explore the importance of the functional diversity of ecosystems, and in particular relations between the dynamics of species and the whole community. We present a stochastic dynamical food web simulation for the Kelian River (Borneo). The food web was constructed for six different locations, arrayed along a gradient of increasing human perturbation (mostly resulting from gold mining activities) along the river. Along the river, the relative importance of grazers, filterers and shredders decreases with increasing disturbance downstream, while predators become more dominant in governing eco-dynamics. Human activity led to increased turbidity and sedimentation which adversely impacts primary productivity. Since the main difference between the study sites was not the composition of the food webs (structure is quite similar) but the strengths of interactions and the abundance of the trophic groups, a dynamical simulation approach seemed to be useful to better explain human influence. In the pristine river (study site 1), when comparing a structural version of our model with the dynamical model we found that structurally central groups such as omnivores and carnivores were not the most important ones dynamically. Instead, primary consumers such as invertebrate grazers and shredders generated a greater dynamical response. Based on the dynamically most important groups, bottom-up control is replaced by the predominant top-down control regime as distance downstream and human disturbance increased. An important finding, potentially explaining the poor structure to dynamics relationship, is that indirect effects are at least as important as direct ones during the simulations. We suggest that our approach and this simulation framework could serve systems-based conservation efforts. Quantitative indicators on the relative importance of trophic groups and the mechanistic modeling of eco-dynamics could greatly contribute to understanding various aspects of functional diversity
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