558 research outputs found
Preface: Impacts of extreme climate events and disturbances on carbon dynamics
The impacts of extreme climate events and disturbances (ECE&D) on the carbon cycle have received growing attention in recent
years. This special issue showcases a collection of recent advances in
understanding the impacts of ECE&D on carbon cycling. Notable advances
include quantifying how harvesting activities impact forest structure,
carbon pool dynamics, and recovery processes; observed drastic increases of
the concentrations of dissolved organic carbon and dissolved methane in
thermokarst lakes in western Siberia during a summer warming event;
disentangling the roles of herbivores and fire on forest carbon dioxide
flux; direct and indirect impacts of fire on the global carbon balance; and
improved atmospheric inversion of regional carbon sources and sinks by
incorporating disturbances. Combined, studies herein indicate several major
research needs. First, disturbances and extreme events can interact with one
another, and it is important to understand their overall impacts and also
disentangle their effects on the carbon cycle. Second, current ecosystem
models are not skillful enough to correctly simulate the underlying
processes and impacts of ECE&D (e.g., tree mortality and carbon
consequences). Third, benchmark data characterizing the timing, location,
type, and magnitude of disturbances must be systematically created to
improve our ability to quantify carbon dynamics over large areas. Finally,
improving the representation of ECE&D in regional climate/earth system
models and accounting for the resulting feedbacks to climate are essential
for understanding the interactions between climate and ecosystem dynamics
Tooth Discoloration in Patients With Neonatal Diabetes After Transfer Onto Glibenclamide: A previously unreported side effect
PublishedJournal ArticleMulticenter StudyResearch Support, N.I.H., ExtramuralResearch Support, Non-U.S. Gov'tOBJECTIVE To assess if tooth discoloration is a novel side effect of sulfonylurea therapy in patients with permanent neonatal diabetes due to mutations in KCNJ11. RESEARCH DESIGN AND METHODS A total of 67 patients with a known KCNJ11 mutation who had been successfully transferred from insulin injections onto oral sulfonylureas were contacted and asked about the development of tooth discoloration after transfer. RESULTS Altered tooth appearance was identified in 5 of the 67 patients. This was variable in severity, ranging from mild discoloration/staining (n = 4) to loss of enamel (n = 1) and was only seen in patients taking glibenclamide (glyburide). CONCLUSIONS These previously unreported side effects may relate to the developing tooth and/or to the high local concentrations in the children who frequently chewed glibenclamide tablets or took it as a concentrated solution. Given the multiple benefits of sulfonylurea treatment for patients with activating KCNJ11 mutations, this association warrants further investigation but should not preclude such treatment.This work was funded by the Welcome Trust (grant 067463/Z/2/Z), National Institutes of Health Grants DK-44752 and DK-20595, and a gift from the Kovler Family Foundation. S.E.F. is the Sir
Graham Wilkins, Peninsula Medical School Research Fellow. A.T.H. is a Welcome Trust
Research Leave Fellow. O.R.-C. was supported by an “Ayuda para contratos post-Formacio´n
Sanitaria Especializada” from the “Instituto de Salud Carlos III” (FIS CM06/00013
The Primordial Helium Abundance: Towards Understanding and Removing the Cosmic Scatter in the dY/dZ Relation
We present results from photoionization models of low-metallicity HII
regions. These nebulae form the basis for measuring the primordial helium
abundance. Our models show that the helium ionization correction factor (ICF)
can be non-negligible for nebulae excited by stars with effective temperatures
larger than 40,000 K. Furthermore, we find that when the effective temperature
rises to above 45,000 K, the ICF can be significantly negative. This result is
independent of the choice of stellar atmosphere. However, if an HII region has
an [O III] 5007/[O I] 6300 ratio greater than 300, then our models show that,
regardless of its metallicity, it will have a negligibly small ICF. A similar,
but metallicity dependent, result was found using the [O III] 5007/H
ratio. These two results can be used as selection criteria to remove nebulae
with potentially non-negligible ICFs. Using our metallicity independent
criterion on the data of Izotov & Thuan (1998) results in a 20% reduction of
the rms scatter about the best fit line. A fit to the selected data
results in a slight increase of the value of the primordial helium abundance.Comment: 10 pages, 5 figures, accepted by the Ap
The Low- and Intermediate-Mass Stellar Population in the Small Magellanic Cloud: The Central Stars of Planetary Nebulae
We present a study on the central stars (CSs) of Planetary Nebulae (PNe)
observed in the Small Magellanic Cloud (SMC) with the Space Telescope Imaging
Spectrograph instrument on-board the HST. The stellar magnitudes have been
measured using broad-band photometry, and Zanstra analysis of the nebulae
provided the stellar temperatures. From the location of the CSs on the HR
diagram, and by comparing the observed CSs with current models of stellar
evolution, we infer the CSs masses. We examine closely the possibility of light
contamination in the bandpass from an unrecognized stellar companion, and we
establish strong constraints on the existence and nature of any binary
companion. We find an average mass of 0.63 Msun, which is similar to the mass
obtained for a sample of CSs in the LMC (0.65 Msun). However, the SMC and LMC
CS mass distributions differ slightly, the SMC sample lacking an
intermediate-mass stellar population (0.65 to 0.75 Msun). We discuss the
significance and possible reasons for the difference between the two mass
distributions. In particular, we consider the differences in the star formation
history between the clouds and the mass-loss rate dependence on metallicity.Comment: 30 pages, 6 figures, 5 tables. To be published in ApJ (October 20
An Approach to the Bio-Inspired Control of Self-reconfigurable Robots
Self-reconfigurable robots are robots built by modules which
can move in relationship to each other. This ability of changing its physical
form provides the robots a high level of adaptability and robustness.
Given an initial configuration and a goal configuration of the robot, the
problem of self-regulation consists on finding a sequence of module moves
that will reconfigure the robot from the initial configuration to the goal
configuration. In this paper, we use a bio-inspired method for studying
this problem which combines a cluster-flow locomotion based on cellular
automata together with a decentralized local representation of the
spatial geometry based on membrane computing ideas. A promising 3D
software simulation and a 2D hardware experiment are also presented.National Natural Science Foundation of China No. 6167313
Modelling the Pan-Spectral Energy Distribution of Starburst Galaxies: III. Emission Line Diagnostics of Ensembles of Evolving HII Regions
We build, as far as theory will permit, self consistent model HII regions
around central clusters of aging stars. These produce strong emission line
diagnostics applicable to either individual HII regions in galaxies, or to the
integrated emission line spectra of disk or starburst galaxies. The models
assume that the expansion and internal pressure of individual HII regions is
driven by the net input of mechanical energy from the central cluster, be it
through winds or supernova events. This eliminates the ionization parameter as
a free variable, replacing it with a parameter which depends on the ratio of
the cluster mass to the pressure in the surrounding interstellar medium. These
models explain why HII regions with low abundances have high excitation, and
demonstrate that at least part of the warm ionized medium is the result of
overlapping faint, old, large, and low pressure HII regions. We present line
ratios (at both optical and IR wavelengths) which provide reliable abundance
diagnostics for both single HII regions or for integrated galaxy spectra, and
we find a number that can be used to estimate the mean age of the cluster stars
exciting individual HII regions.Comment: 22 pages. 18 figures. Accepted for publication in Astrophysical
journal Supplements. Electronic tabular material is available on request to
[email protected]
Farms, pipes, streams and reforestation : reasoning about structured parallel processes using types and hylomorphisms
The increasing importance of parallelism has motivated the creation of better abstractions for writing parallel software, including structured parallelism using nested algorithmic skeletons. Such approaches provide high-level abstractions that avoid common problems, such as race conditions, and often allow strong cost models to be defined. However, choosing a combination of algorithmic skeletons that yields good parallel speedups for a program on some specific parallel architecture remains a difficult task. In order to achieve this, it is necessary to simultaneously reason both about the costs of different parallel structures and about the semantic equivalences between them. This paper presents a new type-based mechanism that enables strong static reasoning about these properties. We exploit well-known properties of a very general recursion pattern, hylomorphisms, and give a denotational semantics for structured parallel processes in terms of these hylomorphisms. Using our approach, it is possible to determine formally whether it is possible to introduce a desired parallel structure into a program without altering its functional behaviour, and also to choose a version of that parallel structure that minimises some given cost model.Postprin
On the Biological Importance of the 3-hydroxyanthranilic Acid: Anthranilic Acid Ratio
Of the major components of the kynurenine pathway for the oxidative metabolism of tryptophan, most attention has focussed on the N-methyl-D-aspartate (NMDA) receptor agonist quinolinic acid, and the glutamate receptor blocker kynurenic acid. However, there is increasing evidence that the redox-active compound 3-hydroxyanthranilic acid may also have potent actions on cell function in the nervous and immune systems, and recent clinical data show marked changes in the levels of this compound, associated with changes in anthranilic acid levels, in patients with a range of neurological and other disorders including osteoporosis, chronic brain injury, Huntington’s disease, coronary heart disease, thoracic disease, stroke and depression. In most cases, there is a decrease in 3-hydroxyanthranilic acid levels and an increase in anthranilic acid levels. In this paper, we summarise the range of data obtained to date, and hypothesise that the levels of 3-hydroxyanthranilic acid or the ratio of 3-hydroxyanthranilic acid to anthranilic acid levels, may contribute to disorders with an inflammatory component, and may represent a novel marker for the assessment of inflammation and its progression. Data are presented which suggest that the ratio between these two compounds is not a simple determinant of neuronal viability. Finally, a hypothesis is presented to account for the development of the observed changes in 3-hydroxyanthranilic acid and anthranilate levels in inflammation and it is suggested that the change of the 3HAA:AA ratio, particularly in the brain, could possibly be a protective response to limit primary and secondary damage
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