372 research outputs found
Influence of a Brane Tension on Phantom and Massive Scalar Field Emission
We elaborate the signature of the extra dimensions and brane tension in the
process of phantom and massive scalar emission in the spacetime of
(4+n)-dimensional tense brane black hole. Absorption cross section, luminosity
of Hawking radiation and cross section in the low-energy approximation were
found. We envisage that parameter connected with the existence of a brane
imprints its role in the Hawking radiation of the considered fields.Comment: 7 pages, * figures, RevTex, to be published in General Relativity and
Gravitatio
Greybody factors in a rotating black-hole background-II : fermions and gauge bosons
We study the emission of fermion and gauge boson degrees of freedom on the
brane by a rotating higher-dimensional black hole. Using matching techniques,
for the near-horizon and far-field regime solutions, we solve analytically the
corresponding field equations of motion. From this, we derive analytical
results for the absorption probabilities and Hawking radiation emission rates,
in the low-energy and low-rotation case, for both species of fields. We produce
plots of these, comparing them to existing exact numerical results with very
good agreement. We also study the total absorption cross-section and
demonstrate that, as in the non-rotating case, it has a different behaviour for
fermions and gauge bosons in the low-energy limit, while it follows a universal
behaviour -- reaching a constant, spin-independent, asymptotic value -- in the
high-energy regime.Comment: 22 pages, 8 figures, added reference
Emergent Universe in Brane World Scenario with Schwarzschild-de Sitter Bulk
A model of an emergent universe is obtained in brane world. Here the bulk
energy is in the form of cosmological constant, while the brane consists of a
fluid satisfying an equation of state of the form , which
is effectively a radiation equation of state at high energies. It is shown that
with the positive bulk cosmological constant, one of our models represents an
emergent universe.Comment: 4 pages, no figure, accepted for publication in Gen.Relt.Gra
Untargeted metabolomics analysis reveals key pathways responsible for the synergistic killing of colistin and doripenem combination against Acinetobacter baumannii
Combination therapy is deployed for the treatment of multidrug-resistant Acinetobacter baumannii, as it can rapidly develop resistance to current antibiotics. This is the first study to investigate the synergistic effect of colistin/doripenem combination on the metabolome of A. baumannii. The metabolite levels were measured using LC-MS following treatment with colistin (2 mg/L) or doripenem (25 mg/L) alone, and their combination at 15 min, 1 hr and 4 hr (n = 4). Colistin caused early (15 min and 1 hr) disruption of the bacterial outer membrane and cell wall, as demonstrated by perturbation of glycerophospholipids and fatty acids. Concentrations of peptidoglycan biosynthesis metabolites decreased at 4 hr by doripenem alone, reflecting its mechanism of action. The combination induced significant changes to more key metabolic pathways relative to either monotherapy. Down-regulation of cell wall biosynthesis (via D-sedoheptulose 7-phosphate) and nucleotide metabolism (via D-ribose 5-phosphate) was associated with perturbations in the pentose phosphate pathway induced initially by colistin (15 min and 1 hr) and later by doripenem (4 hr). We discovered that the combination synergistically killed A. baumannii via time-dependent inhibition of different key metabolic pathways. Our study highlights the significant potential of systems pharmacology in elucidating the mechanism of synergy and optimizing antibiotic pharmacokinetics/pharmacodynamics
Benznidazole biotransformation and multiple targets in <i>Trypanosoma</i> cruzi revealed by metabolomics
<b>Background</b><p></p>
The first line treatment for Chagas disease, a neglected tropical disease caused by the protozoan parasite Trypanosoma cruzi, involves administration of benznidazole (Bzn). Bzn is a 2-nitroimidazole pro-drug which requires nitroreduction to become active, although its mode of action is not fully understood. In the present work we used a non-targeted MS-based metabolomics approach to study the metabolic response of T. cruzi to Bzn.<p></p>
<b>Methodology/Principal findings</b><p></p>
Parasites treated with Bzn were minimally altered compared to untreated trypanosomes, although the redox active thiols trypanothione, homotrypanothione and cysteine were significantly diminished in abundance post-treatment. In addition, multiple Bzn-derived metabolites were detected after treatment. These metabolites included reduction products, fragments and covalent adducts of reduced Bzn linked to each of the major low molecular weight thiols: trypanothione, glutathione, Îł-glutamylcysteine, glutathionylspermidine, cysteine and ovothiol A. Bzn products known to be generated in vitro by the unusual trypanosomal nitroreductase, TcNTRI, were found within the parasites, but low molecular weight adducts of glyoxal, a proposed toxic end-product of NTRI Bzn metabolism, were not detected.<p></p>
<b>Conclusions/significance</b><p></p>
Our data is indicative of a major role of the thiol binding capacity of Bzn reduction products in the mechanism of Bzn toxicity against T. cruzi
Braneworld stars and black holes
We look for spherically symmetric star or black hole solutions on a
Randall-Sundrum brane from the perspective of the bulk. We take a known bulk
solution, and analyse possible braneworld trajectories within it that
correspond, from the braneworld point of view, to solutions of the brane
Tolman-Oppenheimer-Volkoff equations. Our solutions are therefore embedded
consistently into a full bulk solution. We find the full set of static
gravitating matter sources on a brane in a range of bulk spacetimes, analyzing
which can correspond to physically sensible sources. Finally, we look at
time-dependent trajectories in a Schwarzschild--anti de Sitter spacetime as
possible descriptions of time-dependent braneworld black holes, highlighting
some of the general features one might expect, as well as some of the
difficulties involved in getting a full solution to the question.Comment: 39 pages, 15 figure
Time-symmetric initial data of large brane-localized black hole in RS-II model
In the aim of shedding a new light on the classical black hole evaporation
conjecture stating that a static brane-localized black hole (BH) larger than
the bulk curvature scale does not exist in Randall-Sundrum II (RS-II) model, we
investigate time-symmetric initial data with a brane-localized apparent horizon
(AH) and analyzed its properties. We find that a three-parameter family of such
initial data can be constructed by simply placing a brane on a constant time
surface of Schwarzschild anti-de Sitter space. By this method, we unambiguously
confirm that initial data with an arbitrarily large AH area do exist. We
compare the ADM mass and the horizon area of our initial data with that of the
black string (BS) solution, and find that any initial data constructed by this
method do not have a smaller mass than the BS solution when the horizon area is
larger than the size determined by the bulk curvature scale. We further
investigate what kind of configuration realizes the minimum mass for the same
AH area. The configuration that realizes the smallest mass turns out to be the
one close to the BS truncated by a cap. We also demonstrate that the same
method applies to construct initial data in (3+1)-dimensional RS-II brane
world. In this case an exact solution of a brane-localized BH exists but BS
solution does not. Nevertheless, the behavior of the initial data is quite
similar in both cases. We find that the known exact solution always has a
smaller mass than our initial data with the same horizon area. This result
enforces the standard belief that the exact BH solution is the most stable
black object in the four-dimensional RS-II model. These results are all
consistent with the classical BH evaporation conjecture, but unfortunately it
turns out that they do not provide a strong support of it.Comment: 14 pages, 9 figures. Typo correcte
Co-constructing desired activities : Small-scale activity decisions in occupational therapy
Social inclusion and exclusion are buzzwords in todayâs political discourse. While there are many causes of social exclusion, one of the factors repeatedly shown to lead to social exclusion is mental illness, which may hinder people in developing themselves in accordance with their wishes and abilities. Participation is a key dimension of social inclusionâand one that we particularly seek to increase understanding of in this volume. We focus on participation taking place in face-to-face social encounters, seeking to get to the root of the preconditions and consequences of participation by unraveling the interactional processes that underlie what makes it possible. We presuppose that participation in any social or societal sphere presupposes social interaction, which in turn requires the capacity to coordinate with and make sense of othersâ actions. Thus, drawing on joint decision-making as a specific arena of social interaction, where the participantsâ collaborative management of the turn-by-turn sequential unfolding of interaction can have tangible consequences for the participantsâ social and economic circumstances, we seek to increase understanding of the specific vulnerabilities that individuals with mental illness have in this context.In occupational therapy, a therapist and client engage in shared activities that they perform collaboratively during therapeutic sessions. An important part of this joint performance involves providing the client with the opportunity to make short-term decisions on the activities they wish to perform. Analyzing 15 occupational therapy encounters at psychiatric outpatient clinics, in the chapter I explore the functions of these small-scale decisions. The analysis demonstrates that therapists (1) make room for the clientâs proposals by shaping the activity context and (2) make proposals themselves on the ways the performance should be accomplished. To summarize, clients are given decision-making power over the content of the activity, whereas therapists use their decision-making power to assist the clientâs performance. The analysis shows how small-scale decisions can be employed to construct the occupational performance as shared endeavors and to position the clients as active subjects rather than objects of the professionalsâ performance.Peer reviewe
Consequences of HIV for children: avoidable or inevitable?
The HIV/AIDS epidemic has many serious consequences for children. These consequences are, however, rarely inevitable. Families can provide a protective barrier that deflects blows, or minimises their impact and a supportive nurturing environment that can help children recover from harm. If strong enough, and with sufficient access to quality services and support from communities, families can reduce the impacts of HIV/AIDS on children to negligible levels in most areas of impact. It is apparent that the impacts felt by children are not simply unfortunate, inevitable consequences of this epidemic. A strong and supported family with good access to quality services can deflect almost all of the impact. It is as a result of an interaction of the context of poverty, which weakens families, and a failure to adequately respond, that impacts are felt by children
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