13,089 research outputs found
Investigation of the existence of hybrid stars using Nambu-Jona-Lasinio models
We investigate the hadron-quark phase transition inside neutron stars and
obtain mass-radius relations for hybrid stars. The equation of state for the
quark phase using the standard NJL model is too soft leading to an unstable
star and suggesting a modification of the NJL model by introducing a momentum
cutoff dependent on the chemical potential. However, even in this approach, the
instability remains. In order to remedy the instability we suggest the
introduction of a vector coupling in the NJL model, which makes the EoS
stiffer, reducing the instability. We conclude that the possible existence of
quark matter inside the stars require high densities, leading to very compact
stars.Comment: 4 pages, 2 figures; prepared for IV International Workshop on
Astronomy and Relativistic Astrophysics (IWARA 2009), Maresias, 4-8 Oct 200
Network influence effects in agent-based modelling of civil violence
In this paper we describe an agent-based model of civil violence with network influence effects. We considered two different networks, ‘family’ and ‘news’, as a simplified representation of multiple-context influences, to study their individual and joint impact on the size and timing of violence bursts, the perceived legitimacy, and the system’s long term behaviour. It was found that network influences do not change either the system’s long term behaviour or the periodicity of the rebellion peaks, but increase the size of violence bursts, particularly for the case of strong ‘news impact’. For certain combinations of network influences, initial legitimacy, and legitimacy feedback formulation, the solutions showed a very complicated behaviour with unpredictable alternations between long periods of calm and turmoil.info:eu-repo/semantics/acceptedVersio
Avaliação da segurança sísmica de pontes e reforço com FRP´s
A avaliação da segurança e a conservação das pontes têm vindo a suscitar
interesse crescente nos últimos anos. O reforço destas estruturas para a acção
sísmica é importante, uma vez que são infra-estruturas fundamentais para a
intervenção das equipas de socorro em acções pós-sismo, mas também pelas
consequências económicas e sociais associadas a eventuais danos severos ou
colapso destas obras. O reforço sísmico passa pela aplicação de sistemas que
permitam atenuar e controlar os efeitos produzidos pelas acções dos sismos.
Actualmente, com o aparecimento de nova regulamentação, como os Eurocódigos e
outras guidelines, e de novos materiais como os polímeros reforçados com fibras (FRP
– Fiber Reinforced Polymer), o reforço de pontes existentes é mais viável,
tecnicamente e economicamente. As vantagens da utilização de sistemas de FRP’s na
reabilitação e reforço de pontes resultam das suas propriedades mecânicas, dado que
possuem elevada resistência mecânica, reduzido peso dos materiais e elevada
resistência à corrosão, aliada à facilidade de aplicação e à disponibilidade de uma
grande diversidade de sistemas de FRP’s no mercado.
Neste trabalho procedeu-se à análise de um viaduto corrente existente, simulandose,
com recurso a um modelo numérico, o seu comportamento estrutural, identificando
e localizando as zonas críticas. Com base nos resultados da avaliação, estudou-se e
propôs-se uma solução de reforço sísmico com base nas indicações do Boletim FIB
14, e de acordo com a filosofia adoptada pelos Eurocódigos. Desse modo, procedeuse
à recolha de informação relativa à obra de arte em estudo e à simulação numérica
da estrutura. Inicialmente procedeu-se à calibração do modelo numérico com recurso
a medições das suas frequências fundamentais. De seguida, desenvolveu-se a
verificação da segurança estrutural ao nível dos elementos. E, por fim desenvolveu-se
uma proposta de reforço sísmico com recurso a sistemas de FRP’s de modo a garantir
a capacidade exigida aos elementos onde a segurança não foi verificada para a acção
sísmica
Seismic strengthening of beam-column joints with multidirectional CFRP laminates
An experimental program was carried out to analyse the potentialities of a technique based on the use of multidirectional CFRP laminates (MDL-CFRP) for the seismic repair and strengthening of reinforced concrete (RC) beam-column joints. This experimental program comprises cyclic tests on three full-scale RC joints, representative of interior beam-column connections in buildings. The joints were initially submitted to a cyclic test inducing a
damage pattern representative of a seismic event. Subsequently, they were repaired and
strengthened with MDL-CFRP. The strengthened joints were then tested for the same loading
history of the original ones up to their failure. The adopted strengthening technique uses the MDL-CFRP that are simultaneously glued and anchored to the concrete surfaces. This technique is called Mechanically Fastened and Externally Bonded Reinforcement (MF-EBR).
In the present study, the effectiveness of two different strengthening configurations was investigated. The tests are described and the main results are presented and analyzed
Ensuring successful introduction of Wolbachia in natural populations of Aedes aegypti by means of feedback control
The control of the spread of dengue fever by introduction of the
intracellular parasitic bacterium Wolbachia in populations of the vector Aedes
aegypti, is presently one of the most promising tools for eliminating dengue,
in the absence of an efficient vaccine. The success of this operation requires
locally careful planning to determine the adequate number of individuals
carrying the Wolbachia parasite that need to be introduced into the natural
population. The introduced mosquitoes are expected to eventually replace the
Wolbachia-free population and guarantee permanent protection against the
transmission of dengue to human.
In this study, we propose and analyze a model describing the fundamental
aspects of the competition between mosquitoes carrying Wolbachia and mosquitoes
free of the parasite. We then use feedback control techniques to devise an
introduction protocol which is proved to guarantee that the population
converges to a stable equilibrium where the totality of mosquitoes carry
Wolbachia.Comment: 24 pages, 5 figure
Cell-based therapies for stroke : promising solution or dead end?
The introduction of recanalization procedures has revolutionized acute stroke management, although the narrow time window, strict eligibility criteria and logistical limitations still exclude the majority of patients from treatment. In addition, residual deficits are present in many patients who undergo therapy, preventing their return to premorbid status. Hence, there is a strong need for novel, and ideally complementary, approaches to stroke management.
In preclinical experiments, cell-based treatments have demonstrated beneficial effects in the subacute and chronic stages following stroke [1; 2; 3] and therefore are considered a promising option to supplement current clinical practice. At the same time, great progress has been made in developing clinically feasible delivery and monitoring protocols [4]. However, efficacy results initially reported in clinical studies fell short of expectations [5] raising concerns that cell treatment might eventually share the ‘dead end fate’ of many previous experimental stroke therapies. This Research Topic reviews some of the latest and most innovative studies to summarize the state of the art in translational cell treatments for stroke
X-ray method to study temperature-dependent stripe domains in MnAs/GaAs(001)
MnAs films grown on GaAs (001) exhibit a progressive transition between
hexagonal (ferromagnetic) and orthorhombic (paramagnetic) phases at wide
temperature range instead of abrupt transition during the first-order phase
transition. The coexistence of two phases is favored by the anisotropic strain
arising from the constraint on the MnAs films imposed by the substrate. This
phase coexistence occurs in ordered arrangement alternating periodic terrace
steps. We present here a method to study the surface morphology throughout this
transition by means of specular and diffuse scattering of soft x-rays, tuning
the photon energy at the Mn 2p resonance. The results show the long-range
arrangement of the periodic stripe-like structure during the phase coexistence
and its period remains constant, in agreement with previous results using other
techniques.Comment: 4 pages, 4 figures, submitted to Applied Physics Letter
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