Filamentary fragmentation in a turbulent medium

We present the results of smoothed particle hydrodynamic simulations investigating the evolution and fragmentation of filaments that are accreting from a turbulent medium. We show that the presence of turbulence, and the resulting inhomogeneities in the accretion flow, play a significant role in the fragmentation process. Filaments which experience a weakly turbulent accretion flow fragment in a two-tier hierarchical fashion, similar to the fragmentation pattern seen in the Orion Integral Shaped Filament. Increasing the energy in the turbulent velocity field results in more sub-structure within the filaments, and one sees a shift from gravity-dominated fragmentation to turbulence-dominated fragmentation. The sub-structure formed in the filaments is elongated and roughly parallel to the longitudinal axis of the filament, similar to the fibres seen in observations of Taurus, and suggests that the fray and fragment scenario is a possible mechanism for the production of fibres. We show that the formation of these fibre-like structures is linked to the vorticity of the velocity field inside the filament and the filament's accretion from an inhomogeneous medium. Moreover, we find that accretion is able to drive and sustain roughly sonic levels of turbulence inside the filaments, but is not able to prevent radial collapse once the filaments become supercritical. However, the supercritical filaments which contain fibre-like structures do not collapse radially, suggesting that fibrous filaments may not necessarily become radially unstable once they reach the critical line-density.Comment: (Accepted for publication in MNRAS

Quantitative constraints on modified gravity paradigms

We use low-redshift background cosmology data to place quantitative constraints on three separate modified gravity models, each of which aims to explain the low-redshift acceleration through a different physical mechanism. The Lifshitz cosmology is effectively a parametric extension of the canonical $\Lambda$CDM model, where a time-dependent cosmological constant originates from vacuum energy. The Infinite Statistics model is also a parametric extension of $\Lambda$CDM, where the dark energy is dynamic and originates from the curvature of a dual space-time. We show that the data restricts the additional parameters in these models to be consistent with their $\Lambda$CDM values, and in particular that it implies that the theoretically predicted value for a dimensionless coupling parameter in the Lifshitz model is ruled out at more than six standard deviations. In the Regge-Teitelboim model, gravity is described by embedding the usual space-time manifold in a fixed higher-dimensional background, and there is no parametric $\Lambda$CDM limit. We study several separate realizations of the model, respectively introduced by Davidson, by Fabi \textit{et al.}, and by Stern \& Xu, and show that the first two are ruled out by the low-redshift data we use, while the latter is consistent with this data but requires a non-standard value of the matter density. Overall, our analysis highlights the tight constraints imposed by current data on the allowed low-redshift deviations from the standard $\Lambda$CDM background evolution.Comment: 11 pages, 8 figures, Phys. Rev. D (in press

HLA-DR expression in cytotoxic and regulatory T cells

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Nonketotic Hyperglycinemia: A Report of Two Infants Treated with Dextromethorphan and Sodium Benzoate

A hiperglicinémia não cetótica é um erro inato da degradação da glicina, resultando na sua excessiva acumulação nos tecidos corporais, designadamente no sistema nervoso central. Trata-se de uma doença muito grave e uma das terapêuticas recentemente propostas consiste na associação do dextrometorfano com o benzoato de sódio em altas doses. Admite-se a possibilidade de o dextrometorfano bloquear o complexo-canal receptor de N-metil-D-aspartato, implicado na toxicidade da hiperglicinémia ao nível do cérebro e de o benzoato reduzir os níveis de glicina, pela sua conjugação e eliminação como hipurato. Relatamos dois casos clínicos de crianças com hiperglicinémia não cetótita, actualmente com mais de 15 meses de idade, as quais foram medicadas com dextrometorfano e benzoato de sódio desde as primeiras semanas após o parto. Não obstante se ter verificado sobrevivência para além do período neonatal e aquisição de autonomia respiratória, a evolução neurológica, até à data, não tem sido satisfatória, porventura devido ao atraso no início da terapêutica