3,740 research outputs found
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
CDM model, where a time-dependent cosmological constant originates
from vacuum energy. The Infinite Statistics model is also a parametric
extension of 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 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 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
CDM background evolution.Comment: 11 pages, 8 figures, Phys. Rev. D (in press
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
Identification and recovery of volatiles organic compounds (VOCs) in the coffee-producing wastewater.
Volatile composition of concentrated aroma extracts of soluble coffee beverage obtained by pervaporation.
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