976 research outputs found
Interpreting Spectral Energy Distributions from Young Stellar Objects. I. A grid of 200,000 YSO model SEDs
We present a grid of radiation transfer models of axisymmetric young stellar
objects (YSOs), covering a wide range of stellar masses (from 0.1Msun to
50Msun) and evolutionary stages (from the early envelope infall stage to the
late disk-only stage). The grid consists of 20,000 YSO models, with spectral
energy distributions (SEDs) and polarization spectra computed at ten viewing
angles for each model, resulting in a total of 200,000 SEDs. [...]. These
models are publicly available on a dedicated WWW server:
http://www.astro.wisc.edu/protostars/ . In this paper we summarize the main
features of our models, as well as the range of parameters explored. [...]. We
examine the dependence of the spectral indices of the model SEDs on envelope
accretion rate and disk mass. In addition, we show variations of spectral
indices with stellar temperature, disk inner radius, and disk flaring power for
a subset of disk-only models. We also examine how changing the wavelength range
of data used to calculate spectral indices affects their values. We show sample
color-color plots of the entire grid as well as simulated clusters at various
distances with typical {\it Spitzer Space Telescope} sensitivities. We find
that young embedded sources generally occupy a large region of color-color
space due to inclination and stellar temperature effects. Disk sources occupy a
smaller region of color-color space, but overlap substantially with the region
occupied by embedded sources, especially in the near- and mid-IR. We identify
regions in color-color space where our models indicate that only sources at a
given evolutionary stage should lie. [...].Comment: 69 pages, 28 figures, Accepted for publication in ApJS. Preprint with
full resolution figures available at http://www.astro.wisc.edu/protostars
Active elastohydrodynamics of vesicles in narrow, blind constrictions
Fluid-resistance limited transport of vesicles through narrow constrictions
is a recurring theme in many biological and engineering applications. Inspired
by the motor-driven movement of soft membrane-bound vesicles into closed
neuronal dendritic spines, here we study this problem using a combination of
passive three-dimensional simulations and a simplified semi-analytical theory
for active transport of vesicles that are forced through such constrictions by
molecular motors. We show that the motion of these objects is characterized by
two dimensionless quantities related to the geometry and the strength of
forcing relative to the vesicle elasticity. We use numerical simulations to
characterize the transit time for a vesicle forced by fluid pressure through a
constriction in a channel, and find that relative to an open channel, transport
into a blind end leads to the formation of an effective lubrication layer that
strongly impedes motion. When the fluid pressure forcing is complemented by
forces due to molecular motors that are responsible for vesicle trafficking
into dendritic spines, we find that the competition between motor forcing and
fluid drag results in multistable dynamics reminiscent of the real system. Our
study highlights the role of non-local hydrodynamic effects in determining the
kinetics of vesicular transport in constricted geometries
Boolean networks synchronism sensitivity and XOR circulant networks convergence time
In this paper are presented first results of a theoretical study on the role
of non-monotone interactions in Boolean automata networks. We propose to
analyse the contribution of non-monotony to the diversity and complexity in
their dynamical behaviours according to two axes. The first one consists in
supporting the idea that non-monotony has a peculiar influence on the
sensitivity to synchronism of such networks. It leads us to the second axis
that presents preliminary results and builds an understanding of the dynamical
behaviours, in particular concerning convergence times, of specific
non-monotone Boolean automata networks called XOR circulant networks.Comment: In Proceedings AUTOMATA&JAC 2012, arXiv:1208.249
Devonian Fungi: Interactions with the Green Alga Palaeonitella
This paper describes three new taxa of fossil aquatic fungi preserved in 400-million-year-old Lower Devonian Rhynie Chert. All of the fungal morphotypes are attached to cells of the green alga Palaeonitella cranii. Milleromyces rhyniensis is characterized by a holocarpic, epibiotic ^oosporangium with an elongate discharge tube that penetrates the host cell wall; arising from the base of the sporangium is an extensive rhizoidal system. Stages in infection by presumed zoospores are documented. In Lyonomyces pyriformis the globose-pyriform thallus is embedded in the surface coating of the cell wall. At
the base of each thallus is a single rhizoid. Krispiromyces is extramatrical, holocarpic, and characterized by a short beak-like discharge papilla. The rhizoidal system appears to be apophysate. Some of these fungi were probably saprobes, while others were deemed parasitic because of the extensive hypertrophy of some of the algal cells. Although not all life history stages are represented, the discovery of these Lower Devonian forms greatly expands our knowledge of the biology and diversity of aquatic fungi in an ancient freshwater ecosystem
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