9,122 research outputs found
Identification of Naegleria fowleri proteins linked to primary amoebic meningoencephalitis
Naegleria fowleri (N. fowleri) causes primary amoebic meningoencephalitis, a rapidly fatal disease of the central nervous system. N. fowleri can exist in cyst, flagellate or amoebic forms, depending on environmental conditions. The amoebic form can invade the brain following introduction into the nasal passages. When applied intranasally to a mouse model, cultured N. fowleri amoebae exhibit low virulence. However, upon serial passage in mouse brain, the amoebae acquire a highly virulent state. In the present study, a proteomics approach was applied to the identification of N. fowleri amoeba proteins whose expression was associated with the highly virulent state in mice. Mice were inoculated intranasally with axenically cultured amoebae or with mouse-passaged amoebae. Examination by light and electron microscopy revealed no morphological differences. However, mouse-passaged amoebae were more virulent in mice as indicated by exhibiting a two log10 titre decrease in median infective dose 50 (ID50). Scatter plot analysis of amoebic lysates revealed a subset of proteins, the expression of which was associated with highly virulent amoebae. MS-MS indicated that this subset contained proteins that shared homology with those linked to cytoskeletal rearrangement and the invasion process. Invasion assays were performed in the presence of a select inhibitor to expand on the findings. The collective results suggest that N. fowleri gene products linked to cytoskeletal rearrangement and invasion may be candidate targets in the management of primary amoebic meningoencephalitis
The evolution of Giant Molecular Filaments
In recent years there has been a growing interest in studying giant molecular
filaments (GMFs), which are extremely elongated (> 100pc in length) giant
molecular clouds (GMCs). They are often seen as inter-arm features in external
spiral galaxies, but have been tentatively associated with spiral arms when
viewed in the Milky Way. In this paper, we study the time evolution of GMFs in
a high-resolution section of a spiral galaxy simulation, and their link with
spiral arm GMCs and star formation, over a period of 11Myrs. The GMFs generally
survive the inter-arm passage, although they are subject to a number of
processes (e.g. star formation, stellar feedback and differential rotation)
which can break the giant filamentary structure into smaller sections. The GMFs
are not gravitationally bound clouds as a whole, but are, to some extent,
confined by external pressure. Once they reach the spiral arms, the GMFs tend
to evolve into more substructured spiral arm GMCs, suggesting that GMFs may be
precursors to arm GMCs. Here, they become incorporated into the more complex
and almost continuum molecular medium that makes up the gaseous spiral arm.
Instead of retaining a clear filamentary shape, their shapes are distorted both
by their climb up the spiral potential and their interaction with the gas
within the spiral arm. The GMFs do tend to become aligned with the spiral arms
just before they enter them (when they reach the minimum of the spiral
potential), which could account for the observations of GMFs in the Milky Way.Comment: 15 pages, 11 figures, MNRAS accepte
Extrapolation for classes of weights related to a family of operators and applications
In this work we give extrapolation results on weighted Lebesgue spaces for weights associated to a family of operators. The starting point for the extrapolation can be the knowledge of boundedness on a particular Lebesgue space as well as the boundedness on the extremal case L∞. This analysis can be applied to a variety of operators appearing in the context of a Schrödinger operator ( −Δ + V) where V satisfies a reverse Hölder inequality. In that case the weights involved are a localized version of Muckenhoupt weights.Fil: Bongioanni, Bruno. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Santa Fe. Instituto de Matemática Aplicada del Litoral. Universidad Nacional del Litoral. Instituto de Matemática Aplicada del Litoral; ArgentinaFil: Cabral, A.. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Santa Fe. Instituto de Matemática Aplicada del Litoral. Universidad Nacional del Litoral. Instituto de Matemática Aplicada del Litoral; ArgentinaFil: Harboure, Eleonor Ofelia. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Santa Fe. Instituto de Matemática Aplicada del Litoral. Universidad Nacional del Litoral. Instituto de Matemática Aplicada del Litoral; Argentin
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
Tightening the belt: Constraining the mass and evolution in SDC335
Recent ALMA observations identified one of the most massive star-forming
cores yet observed in the Milky Way; SDC335-MM1, within the infrared dark cloud
SDC335.579-0.292. Along with an accompanying core MM2, SDC335 appears to be in
the early stages of its star formation process. In this paper we aim to
constrain the properties of the stars forming within these two massive
millimetre sources. Observations of SDC335 at 6, 8, 23 and 25GHz were made with
the ATCA. We report the results of these continuum measurements, which combined
with archival data, allow us to build and analyse the spectral energy
distributions (SEDs) of the compact sources in SDC335. Three HCHII regions
within SDC335 are identified, two within the MM1 core. For each HCHII region, a
free-free emission curve is fit to the data allowing the derivation of the
sources' emission measure, ionising photon flux and electron density. Using
these physical properties we assign each HCHII region a ZAMS spectral type,
finding two protostars with characteristics of spectral type B1.5 and one with
a lower limit of B1-B1.5. Ancillary data from infrared to mm wavelength are
used to construct free-free component subtracted SEDs for the mm-cores,
allowing calculation of the bolometric luminosities and revision of the
previous gas mass estimates. The measured luminosities for the two mm-cores are
lower than expected from accreting sources displaying characteristics of the
ZAMS spectral type assigned to them. The protostars are still actively
accreting, suggesting that a mechanism is limiting the accretion luminosity, we
present the case for two different mechanisms capable of causing this. Finally,
using the ZAMS mass values as lower limit constraints, a final stellar
population for SDC335 was synthesised finding SDC335 is likely to be in the
process of forming a stellar cluster comparable to the Trapezium Cluster and
NGC6334 I(N).Comment: 10 pages, 5 figures. Accepted for publication in A&
Some Problems on the Classical N-Body Problem
Our idea is to imitate Smale's list of problems, in a restricted domain of
mathematical aspects of Celestial Mechanics. All the problems are on the n-body
problem, some with different homogeneity of the potential, addressing many
aspects such as central configurations, stability of relative equilibrium,
singularities, integral manifolds, etc. Following Steve Smale in his list, the
criteria for our selection are: (1) Simple statement. Also preferably
mathematically precise, and best even with a yes or no answer. (2) Personal
acquaintance with the problem, having found it not easy. (3) A belief that the
question, its solution, partial results or even attempts at its solution are
likely to have great importance for the development of the mathematical aspects
of Celestial Mechanics.Comment: 10 pages, list of mathematical problem
Role of heat generation and thermal diffusion during frontal photopolymerization
Frontal photopolymerization (FPP) is a rapid and versatile solidification process that can be used to fabricate complex three-dimensional structures by selectively exposing a photosensitive monomer-rich bath to light. A characteristic feature of FPP is the appearance of a sharp polymerization front that propagates into the bath as a planar traveling wave. In this paper, we introduce a theoretical model to determine how heat generation during photopolymerization influences the kinetics of wave propagation as well as the monomer-to-polymer conversion profile, both of which are relevant for FPP applications and experimentally measurable. When thermal diffusion is sufficiently fast relative to the rate of polymerization, the system evolves as if it were isothermal. However, when thermal diffusion is slow, a thermal wavefront develops and propagates at the same rate as the polymerization front. This leads to an accumulation of heat behind the polymerization front which can result in a significant sharpening of the conversion profile and acceleration of the growth of the solid. Our results also suggest that a novel way to tailor the dynamics of FPP is by imposing a temperature gradient along the growth directio
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