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