131 research outputs found
Probing Star Formation at Low Metallicity: The Radio Emission of Super Star Clusters in SBS0335-052
We present high-resolution radio continuum observations of the nascent
starburst in the metal-poor galaxy SBS 0335-052. These radio data were taken
with the Very Large Array and include observations at 0.7cm, 1.3cm, 2cm, 3.6cm,
and 6cm. These observations enable us to probe the thermal radio nebulae
associated with the extremely young star-forming regions in this galaxy. Two
discrete and luminous star-forming regions are detected in the south of the
galaxy that appear to be associated with massive star clusters previously
identified at optical wavelengths. However, the remaining optically-identified
massive star clusters are not clearly associated with radio emission (either
thermal or non-thermal) down to the sensitivity limits of these radio data. The
spectral energy distributions of the two radio-detected clusters are consistent
with being purely thermal, and the entire region has an inferred ionizing flux
of ~1.2 x 10^ 53 s^-1, which is equivalent to ~12,000 "typical" O-type stars
(type O7.5 V). The observations presented here have resolved out a significant
contribution from diffuse non-thermal emission detected previously, implying a
previous episode of significant star formation. The current star formation rate
(SFR) for this southern region alone is ~1.3 M_sun yr^-1, or ~ 23M_sun yr^-1
kpc^-2. This SFR derived from thermal radio emission also suggests that
previous optical recombination line studies are not detecting a significant
fraction of the current star formation in SBS 0335-052. From model fits to the
radio spectral energy distribution, we infer a global mean density in the two
youngest clusters of n_e > 10^3-10^4 cm^-3. In addition, a comparison between
the compact and diffuse radio emission indicates that up to ~50% of the
ionizing flux could be leaking out of the compact HII regions.Comment: accepted AJ, 14 pages, 5 figure
The Adsorption of H2O on TiO2 and SnO2(110) Studied by First-Principles Calculations
First-principles calculations based on density functional theory and the
pseudopotential method have been used to investigate the energetics of HO
adsorption on the (110) surface of TiO and SnO. Full relaxation of all
atomic positions is performed on slab systems with periodic boundary
conditions, and the cases of full and half coverage are studied. Both molecular
and dissociative (HO OH + H) adsorption are treated,
and allowance is made for relaxation of the adsorbed species to unsymmetrical
configurations. It is found that for both TiO and SnO an unsymmetrical
dissociated configuration is the most stable. The symmetrical molecularly
adsorbed configuration is unstable with respect to lowering of symmetry, and is
separated from the fully dissociated configuration by at most a very small
energy barrier. The calculated dissociative adsorption energies for TiO and
SnO are in reasonable agreement with the results of thermal desorption
experiments. Calculated total and local electronic densities of states for
dissociatively and molecularly adsorbed configurations are presented and their
relation with experimental UPS spectra is discussed
Red wine polyphenols prevent metabolic and cardiovascular alterations associated with obesity in Zucker fatty rats (Fa/Fa)
Peer reviewedPublisher PD
The Value of Information for Populations in Varying Environments
The notion of information pervades informal descriptions of biological
systems, but formal treatments face the problem of defining a quantitative
measure of information rooted in a concept of fitness, which is itself an
elusive notion. Here, we present a model of population dynamics where this
problem is amenable to a mathematical analysis. In the limit where any
information about future environmental variations is common to the members of
the population, our model is equivalent to known models of financial
investment. In this case, the population can be interpreted as a portfolio of
financial assets and previous analyses have shown that a key quantity of
Shannon's communication theory, the mutual information, sets a fundamental
limit on the value of information. We show that this bound can be violated when
accounting for features that are irrelevant in finance but inherent to
biological systems, such as the stochasticity present at the individual level.
This leads us to generalize the measures of uncertainty and information usually
encountered in information theory
Contact mechanics of modular metal-on-polyethylene total hip replacement under adverse edge loading conditions
Edge loading can negatively impact the biomechanics and long-term performance of hip replacements. Although edge loading has been widely investigated for hard-on-hard articulations, limited work has been conducted for hard-on-soft combinations. The aim of the present study was to investigate edge loading and its effect on the contact mechanics of a modular metal-on-polyethylene (MoP) total hip replacement (THR). A three-dimensional finite element model was developed based on a modular MoP bearing. Different cup inclination angles and head lateral microseparation were modelled and their effect on the contact mechanics of the modular MoP hip replacement were examined. The results showed that lateral microseparation caused loading of the head on the rim of the cup, which produced substantial increases in the maximum von Mises stress in the polyethylene liner and the maximum contact pressure on both the articulating surface and backside surface of the liner. Plastic deformation of the liner was observed under both standard conditions and microseparation conditions, however, the maximum equivalent plastic strain in the liner under microseparation conditions of 2000 µm was predicted to be approximately six times that under standard conditions. The study has indicated that correct positioning the components to avoid edge loading is likely to be important clinically even for hard-on-soft bearings for THR
Selecting Indicator Portfolios for Marine Species and Food Webs: A Puget Sound Case Study
Ecosystem-based management (EBM) has emerged as a promising approach for maintaining the benefits humans want and need from the ocean, yet concrete approaches for implementing EBM remain scarce. A key challenge lies in the development of indicators that can provide useful information on ecosystem status and trends, and assess progress towards management goals. In this paper, we describe a generalized framework for the methodical and transparent selection of ecosystem indicators. We apply the framework to the second largest estuary in the United States – Puget Sound, Washington – where one of the most advanced EBM processes is currently underway. Rather than introduce a new method, this paper integrates a variety of familiar approaches into one step-by-step approach that will lead to more consistent and reliable reporting on ecosystem condition. Importantly, we demonstrate how a framework linking indicators to policy goals, as well as a clearly defined indicator evaluation and scoring process, can result in a portfolio of useful and complementary indicators based on the needs of different users (e.g., policy makers and scientists). Although the set of indicators described in this paper is specific to marine species and food webs, we provide a general approach that could be applied to any set of management objectives or ecological system
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