On the Influence of Magnetic Fields on the Structure of Protostellar Jets

We here present the first results of fully three-dimensional (3-D) MHD simulations of radiative cooling pulsed (time-variable) jets for a set of parameters which are suitable for protostellar outflows. Considering different initial magnetic field topologies in approximate $equipartition$ with the thermal gas, i.e., (i) a longitudinal, and (ii) a helical field, both of which permeating the jet and the ambient medium; and (iii) a purely toroidal field permeating only the jet, we find that the overall morphology of the pulsed jet is not very much affected by the presence of the different magnetic field geometries in comparison to a nonmagnetic calculation. Instead, the magnetic fields tend to affect essentially the detailed structure and emission properties behind the shocks at the head and at the pulse-induced internal knots, particularly for the helical and toroidal geometries. In these cases, we find, for example, that the $H_\alpha$ emissivity behind the internal knots can be about three to four times larger than that of the purely hydrodynamical jet. We also find that some features, like the nose cones that often develop at the jet head in 2-D calculations involving toroidal magnetic fields, are smoothed out or absent in the 3-D calculations.Comment: 13 pages, 3 figures, Accepted by ApJ Letters after minor corrections (for high resolution figures, see http://www.iagusp.usp.br/~adriano/h.tar

Severe Invasive Streptococcal Disease - Emerging Disease?

Introdução: A incidência da doença estreptocócica invasiva (DSI) tem vindo a aumentar na Europa e América do Norte desde o final dos anos 1980, provavelmente relacionada com a emergência de estirpes mais virulentas. Em oito meses foram internados no nosso hospital seis casos desta entidade rara. Objectivos: Descrever as características da doença estreptocócica invasiva grave. Métodos: Estudo descritivo, de Dezembro de 2007 a Julho de 2008. Analisaram-se parâmetros demográficos, factores de risco, clínica, terapêutica, complicações e evolução. Resultados: Identificaram-se seis casos com mediana de idade de 2,5 anos: síndrome de choque tóxico estreptocócico (STSS) (2), fasceíte necrotizante (2), bacteriémia (1) e infecção estreptocócica grave (1). Cinco casos ocorreram entre Dezembro e Fevereiro. Em quatro doentes registaram-se eventuais factores de risco (infecções virais e anti-inflamatórios não esteroides). Duas crianças necessitaram de cirurgia e três de tratamento em cuidados intensivos. Todas as estirpes eram susceptíveis à penicilina e clindamicina. Ocorreram complicações em 5/6 doentes: choque séptico (3), coagulação intravascular disseminada (2), insuficiência renal (2), abcesso de tecidos moles (2), sobreinfecção bacteriana (2), síndrome de dificuldade respiratória do adulto (1), osteomielite /artrite séptica (1) e pneumonia/derrame pleural (1). Não se registaram óbitos. Comentários: Seis casos de DSI num curto espaço de tempo podem indiciar a emergência de estirpes de Streptococcus grupo A (GAS) de maior virulência no nosso país, pelo que a realização de estudos moleculares será fundamental na identificação de clones invasivos. Apesar da susceptibilidade à penicilina, a DSI cursa com morbilidade elevada, pelo que, o importante parece ser procurar novas formas de tratar o doente e não o agente

The precession of the giant HH34 outflow: a possible jet deceleration mechanism

The giant jets represent a fundamental trace of the historical evolution of the outflow activity over timescales which are comparable to the accretion time of the outflow sources in their main protostellar phase. The study of such huge jets provides the possibility of retrieving important elements related to the life of the outflow sources. In this paper, we study the role of precession (combined with jet velocity-variability and the resulting enhanced interaction with the surrounding environment) as a deceleration mechanism for giant jets using a numerical approach. We obtain predictions of H alpha intensity maps and position-velocity diagrams from 3D simulations of the giant HH 34 jet (including an appropriate ejection velocity time-variability and a precession of the outflow axis), and we compare them with previously published observations of this object. Our simulations represent a step forward from previous numerical studies of HH objects, in that the use of a 7-level, binary adaptive grid has allowed us to compute models which appropiately cover all relevant scales of a giant jet, from the ~ 100 AU jet radius close to the source to the ~ 1 pc length of the outflow. A good qualitative and quantitative agreement is found between the model predictions and the observations. Moreover, we show that a critical parameter for obtaining a better or worse agreement with the observations is the ratio rho_j/rho_a between the jet and the environmental densities. The implications of this result in the context of the current star formation models are discussed (ABRIDGED).Comment: 19 pages, 8 eps figs.,uses aaspp4; accepted by the Ap

Modeling the spectrum of gravitational waves in the primordial Universe

Recent observations from type Ia Supernovae and from cosmic microwave background (CMB) anisotropies have revealed that most of the matter of the Universe interacts in a repulsive manner, composing the so-called dark energy constituent of the Universe. The analysis of cosmic gravitational waves (GW) represents, besides the CMB temperature and polarization anisotropies, an additional approach in the determination of parameters that may constrain the dark energy models and their consistence. In recent work, a generalized Chaplygin gas model was considered in a flat universe and the corresponding spectrum of gravitational waves was obtained. The present work adds a massless gas component to that model and the new spectrum is compared to the previous one. The Chaplygin gas is also used to simulate a $\Lambda$-CDM model by means of a particular combination of parameters so that the Chaplygin gas and the $\Lambda$-CDM models can be easily distinguished in the theoretical scenarios here established. The lack of direct observational data is partialy solved when the signature of the GW on the CMB spectra is determined.Comment: Proc. of the Conference on Magnetic Fields in the Universe: from laboratories and stars to primordial structures, AIP(NY), eds. E. M. de Gouveia Dal Pino, G. Lugones & A. Lazarian (2005), in press. (8 pages, 11 figures

Percolation in binary mixtures of linkers and particles: chaining {\it {vs}} branching

Equilibrium gels of colloidal particles can be realized through the introduction of a second species, a linker that mediates the bonds between the colloids. A gel forming binary mixture whose linkers can self-assemble into linear chains while still promoting the aggregation of particles is considered in this work. The particles are patchy particles with $f_C$ patches of type $C$ and the linkers are patchy particles with $2$ patches of type $A$ and $f_B$ patches of type B. The bonds between patches of type $A$ ($AA$ bonds) promote the formation of linear chains of linkers. Two different ways (model A and model B) of bonding the linkers to the particles - or inducing branching - are studied. In model A, there is a competition between chaining and branching, since the bonding between linkers and particles is done through $AC$ bonds only. In model B linkers aggregate to particles through bonds $BC$ only, making chaining and branching independent. The percolation behaviour of these two models is studied in detail, employing a generalized Flory-Stockmayer theory and Monte Carlo simulations. The self-assembly of linkers into chains reduces the fraction of particles needed for percolation to occur (models A and B) and induces percolation when the fraction of particles is high (model B). Percolation by heating and percolation loops in temperature composition diagrams are obtained when the formation of chains is energetically favourable, by increasing the entropic gain of branching (model A). Chaining and branching are found to follow a model dependent relation at percolation, which shows that, for the same composition, longer chains require less branching for percolation to occur

BEfree : Contextualização e desenvolvimento de um programa de intervenção em grupo para a Ingestão Alimentar Compulsiva e Obesidade

Pinto-Gouveia, J., Ferreira, C., Matos, M., & Carvalho, S. (2014). BEfree: contextualização e desenvolvimento de um programa de intervenção em grupo para a Ingestão Alimentar Compulsiva e Obesidade. Revista Factores de Risco, 34(9), 94-100. http://www.spc.pt/spc/default.aspx?redir=http://www.spc.pt/SPC/AreaCientifica/publicacoes/rfr/rfr.asp

Magnetic Field Effects on the Structure and Evolution of Overdense Radiatively Cooling Jets

We investigate the effect of magnetic fields on the propagation dynamics and morphology of overdense, radiatively cooling, supermagnetosonic jets, with the help of fully three-dimensional SPMHD simulations. Evaluated for a set of parameters which are mainly suitable for protostellar jets (with density ratios between the jet and the ambient medium 3-10, and ambient Mach number ~ 24), these simulations are also compared with baseline non-magnetic and adiabatic calculations. We find that, after amplification by compression and re-orientation in nonparallel shocks at the working surface, the magnetic field that is carried backward with the shocked gas into the cocoon improves the jet collimation relative to the purely hydrodynamic (HD) systems. Low-amplitude, approximately equally spaced internal shocks (which are absent in the HD systems) are produced by MHD K-H reflection pinch modes. The longitudinal field geometry also excites non-axisymmetric helical modes which cause some beam wiggling. The strength and amount of these modes are, however, reduced (by ~ twice) in the presence of radiative cooling relative to the adiabatic cases. Besides, a large density ratio between the jet and the ambient medium also reduces, in general, the number of the internal shocks. As a consequence, the weakness of the induced internal shocks makes it doubtful that the magnetic pinches could produce by themselves the bright knots observed in the overdense, radiatively cooling protostellar jets.Comment: To appear in ApJ; 36 pages + 16 (gif) figures. PostScript files of figures are available at http://www.iagusp.usp.br/preprints/preprint.htm

Uncommon Kingella Kingae Lytic Bone Lesions in Children

info:eu-repo/semantics/publishedVersio