55 research outputs found
Newtonian vs. relativistic chaotic scattering
It is shown that Newtonian mechanics is not appropriate to compute
approximate individual trajectories with small velocities in chaotic
scattering. However, some global properties of the dynamical system, such as
the dimension of the non-attracting chaotic invariant set, are more robust and
the Newtonian approximation provides reasonably accurate results for them in
slow chaotic scattering.Comment: 2 pages, 2 figures
Symmetries leading to inflation
We present here the general transformation that leaves unchanged the form of
the field equations for perfect fluid Friedmann--Robertson--Walker and Bianchi
V cosmologies. The symmetries found can be used as algorithms for generating
new cosmological models from existing ones. A particular case of the general
transformation is used to illustrate the crucial role played by the number of
scalar fields in the occurrence of inflation. Related to this, we also study
the existence and stability of Bianchi V power law solutions.Comment: 16 pages, uses RevTeX 4, to appear in Phys. Rev.
Stability of the intrinsic energy vanishing in the Schwarzschild metric under slow rotation
The linearized Kerr metric is considered and put in some Gauss coordinates which are further intrinsic ones. The linear and angular 4-momenta of this metric are calculated in these coordinates and the resulting value is just zero. Thus, the global vanishing previously found for the Schwarzschild metric remains linearly stable under slow rotational perturbations of this metric
Chaotic scattering around black holes
It is shown that the scattering of a charged test particle by a system of
four extreme Reissner-Nordtr\"om black holes is chaotic in some cases. The
fractal structure of the scattering angle and time delay functions is another
manifestation of the existence of a nonattracting chaotic set: fractal basin
boundaries were previously known.Comment: REVTeX, 11 pages, 7 Postscript figures. References to recent
(published and unpublished) works by other authors have been added. Results
and figures remain unchange
Anisotropy and inflation in Bianchi I brane worlds
After a more general assumption on the influence of the bulk on the brane, we
extend some conclusions by Maartens et al. and Santos et al. on the asymptotic
behavior of Bianchi I brane worlds. As a consequence of the nonlocal
anisotropic stresses induced by the bulk, in most of our models, the brane does
not isotropize and the nonlocal energy does not vanish in the limit in which
the mean radius goes to infinity. We have also found the intriguing possibility
that the inflation due to the cosmological constant might be prevented by the
interaction with the bulk. We show that the problem for the mean radius can be
completely solved in our models, which include as particular cases those in the
references above.Comment: 10 pages, improved discussion on the likeliness of
non-isotropization, completed list of references, matches version to appear
in Class. Quantum Gra
Quintessence as k-essence
Quintessence and k-essence have been proposed as candidates for the dark
energy component of the universe that would be responsible of the currently
observed accelerated expansion. In this paper we investigate the degree of
resemblance between those two theoretical setups, and find that every
quintessence model can be viewed as a k-essence model generated by a kinetic
linear function. In addition, we show the true effects of k-essence begin at
second order in the expansion of the kinetic function in powers of the kinetic
energy.Comment: 14 pages, improved discussion, matches published versio
Multicentre, randomised, open-label, phase IV-III study to evaluate the efficacy of cloxacillin plus fosfomycin versus cloxacillin alone in adult patients with methicillin-susceptible Staphylococcus aureus bacteraemia: Study protocol for the SAFO trial
Introduction Methicillin-susceptible Staphylococcus aureus (MSSA) bacteraemia is a frequent condition, with high mortality rates. There is a growing interest in identifying new therapeutic regimens able to reduce therapeutic failure and mortality observed with the standard of care of beta-lactam monotherapy. In vitro and small-scale studies have found synergy between cloxacillin and fosfomycin against S. aureus. Our aim is to test the hypothesis that cloxacillin plus fosfomycin achieves higher treatment success than cloxacillin alone in patients with MSSA bacteraemia. Methods We will perform a superiority, randomised, open-label, phase IV-III, two-armed parallel group (1:1) clinical trial at 20 Spanish tertiary hospitals. Adults (=18 years) with isolation of MSSA from at least one blood culture =72 hours before inclusion with evidence of infection, will be randomly allocated to receive either cloxacillin 2 g/4-hour intravenous plus fosfomycin 3 g/6-hour intravenous or cloxacillin 2 g/4-hour intravenous alone for 7 days. After the first week, sequential treatment and total duration of antibiotic therapy will be determined according to clinical criteria by the attending physician. Primary endpoints: (1) Treatment success at day 7, a composite endpoint comprising all the following criteria: patient alive, stable or with improved quick-Sequential Organ Failure Assessment score, afebrile and with negative blood cultures for MSSA at day 7. (2) Treatment success at test of cure (TOC) visit: patient alive and no isolation of MSSA in blood culture or at another sterile site from day 8 until TOC (12 weeks after randomisation). We assume a rate of treatment success of 74% in the cloxacillin group. Accepting alpha risk of 0.05 and beta risk of 0.2 in a two-sided test, 183 subjects will be required in each of the control and experimental groups to obtain statistically significant difference of 12% (considered clinically significant). Ethics and dissemination Ethical approval has been obtained from the Ethics Committee of Bellvitge University Hospital (AC069/18) and from the Spanish Medicines and Healthcare Product Regulatory Agency (AEMPS, AC069/18), and is valid for all participating centres under existing Spanish legislation. The results will be presented at international meetings and will be made available to patients and funders. © Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ
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Educação Superior::Ciências Exatas e da Terra::FísicaSimulação da dinâmica de uma conta que pode mover-se sem atrito ao longo de uma haste vertical, presa a duas molas simétricas. O usuário pode arrastar a conta para ajustar sua posição inicial ao longo da haste. É mostrado um gráfico do espaço de fase do sistema.Mecânica Gera
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