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

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

Kelvin-Helmholtz instability of the Dirac fluid of charge carriers on graphene

FUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIRO - FAPERJWe provide numerical evidence that a Kelvin-Helmholtz instability occurs in the Dirac fluid of electrons in graphene and can be detected in current experiments. This instability appears for electrons in the viscous regime passing though a micrometer-scale obstacle and affects measurements on the time scale of nanoseconds. A possible realization with a needle-shaped obstacle is proposed to produce and detect this instability by measuring the electric potential difference between contact points located before and after the obstacle. We also show that, for our setup, the Kelvin-Helmholtz instability leads to the formation of whirlpools similar to the ones reported in Bandurin et al. [Science 351, 1055 (2016)]. To perform the simulations, we develop a lattice Boltzmann method able to recover the full dissipation in a fluid of massless particles.9618111FUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIRO - FAPERJFUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIRO - FAPERJSem informaçãoR.C.V.C., M.M., and H.J.H. thank the European Research Council (ERC) Advanced Grant No. 319968-FlowCCS and R.C.V.C. thanks FAPERJ for the financial support. The authors are grateful to Prof. K. Ensslin and his team for fruitful discussions about experimental realizations

Magnetic reconfiguration of MnAs/GaAs(001) observed by Magnetic Force Microscopy and Resonant Soft X-ray Scattering

We investigated the thermal evolution of the magnetic properties of MnAs epitaxial films grown on GaAs(001) during the coexistence of hexagonal/orthorhombic phases using polarized resonant (magnetic) soft X-ray scattering and magnetic force microscopy. The results of the diffuse satellite X-ray peaks were compared to those obtained by magnetic force microscopy and suggest a reorientation of ferromagnetic terraces as temperature rises. By measuring hysteresis loops at these peaks we show that this reorientation is common to all ferromagnetic terraces. The reorientation is explained by a simple model based on the shape anisotropy energy. Demagnetizing factors were calculated for different configurations suggested by the magnetic images. We noted that the magnetic moments flip from an in-plane mono-domain orientation at lower temperatures to a three-domain out-of-plane configuration at higher temperatures. The transition was observed when the ferromagnetic stripe width L is equal to 2.9 times the film thickness d. This is in good agreement with the expected theoretical value of L = 2.6d.Comment: 16 pages in PD

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

Soil organic carbon stocks under pasture atlantic forest in Rio de Janeiro state, Brazil.

The objective of this study is to perform a comparative analysis of the soil carbon stock under pasture (Brachiaria spp) and semideciduous broadleaf Atlantic Forest fragments

Avaliação da qualidade do solo e sanidade das plantas utilizando método participativo.

No Brasil, há cerca de 20 milhões de pessoas que têm a agricultura como fonte de renda para sustento de suas famílias. A ela se dedicam, como profissão, envolvem a família, residem na propriedade ou moram perto. Uns vivem bem, outros mal; podem ser estratificados, de acordo com os critérios utilizados, em diversas categorias, cultivam desde uma especiaria ou "commodity" para exportação, até dezenas de produtos, para consumo próprio em mercado local; e, outros, nem produzem o suficiente para sobreviver. É a agricultura familiar. A maior parte dessas famílias encontra-se no Nordeste e é pobre (Souza & Cabral, 2009). Na pesquisa participativa, o olhar do agricultor e sua visão de negócio é fundamental para adoção de uma prática ou adaptação de tecnologia. A utilização dessa metodologia avalia o agroecossistema de forma participativa e relativamente rápida, contribuindo para elevar a autoestima do agricultor. Ademais, os indicadores utilizados podem ser quantificados e ser inclusive objetos de estudo para relação custo beneficio de tecnologias ou processos adotados, bastando-se para isso, manter as referencias de construção da teia ou mandala. Segundo Zoby et al. (2003) a utilização de referências permite refletir melhor sobre o sistema e validade de práticas adotadas pelo agricultor. O grande desafio continua operacionalizar o seu uso (Zoby et al., 2003). Assim, para a instituição de pesquisa, é importante conhecer as estratégias do agricultor frente à pressão da natureza para adaptar os seus dispositivos de ação a melhoria de sistema (Bonal et al., 1994). Esse trabalho apresenta as experiências adquiridas por pesquisadores envolvidos na execução de atividades no projeto "Alternativas orgânicas no manejo de pragas em fruteiras tropicais para agricultura familiar". Objetivou-se aplicar a técnica da teia para estimar a qualidade do solo e a sanidade das plantas, visando identificar, de forma participativa, limitações de ordem fitossanitária e selecionar manejos eficientes e sustentáveis.pdf 236