1,422 research outputs found
Evaluando los niveles tróficos de dos tiburones oceánicos del Océano PacÃfico suroriental
Indexación: Web of ScienceStable isotope analyses for shortfin mako (Isurus oxyrinchus) and blue sharks (Prionace glauca) were conducted to assess their trophic position in two periods of time (before 1980 and after 2000) in the Southeastern Pacific waters (SEP). Both sharks showed that their trophic position decreased over time (P < 0.05). Many factors could be involved in this change such as dietary shifts, prey availability, or indirect fishing effects in SEP waters.RESUMEN. Para evaluar los niveles tróficos de los tiburones marrajo (Isurus oxyrinchus) y azulejo (Prionace glauca) en dos perÃodos de tiempo (previo a 1980 y posterior al 2000) en aguas del PacÃfico suroriental (SEP), se realizaron análisis de isótopos estables. Ambos tiburones mostraron un descenso del nivel trófico en el tiempo (P < 0,05). Varios son los factores que pueden estar involucrados en este evento, como los cambios dietarios, la disponibilidad de las presas o los efectos indirectos de la pesquerÃa en aguas del PacÃfico suroriental.http://www.lajar.cl/pdf/imar/v44n2/Art%C3%ADculo_44_2_25.pd
A possible signature of terrestrial planet formation in the chemical composition of solar analogs
Recent studies have shown that the elemental abundances in the Sun are
anomalous when compared to most (about 85%) nearby solar twin stars. Compared
to its twins, the Sun exhibits a deficiency of refractory elements (those with
condensation temperatures Tc>900K) relative to volatiles (Tc<900K). This
finding is speculated to be a signature of the planet formation that occurred
more efficiently around the Sun compared with the majority of solar twins.
Furthermore, within this scenario, it seems more likely that the abundance
patterns found are specifically related to the formation of terrestrial
planets. In this work we analyze abundance results from six large independent
stellar abundance surveys to determine whether they confirm or reject this
observational finding. We show that the elemental abundances derived for solar
analogs in these six studies are consistent with the Tc trend suggested as a
planet formation signature. The same conclusion is reached when those results
are averaged heterogeneously. We also investigate the dependency of the
abundances with first ionization potential (FIP), which correlates well with
Tc. A trend with FIP would suggest a different origin for the abundance
patterns found, but we show that the correlation with Tc is statistically more
significant. We encourage similar investigations of metal-rich solar analogs
and late F-type dwarf stars, for which the hypothesis of a planet formation
signature in the elemental abundances makes very specific predictions. Finally,
we examine a recent paper that claims that the abundance patterns of two stars
hosting super-Earth like planets contradict the planet formation signature
hypothesis. Instead, we find that the chemical compositions of these two stars
are fully compatible with our hypothesis.Comment: To appear in Astronomy and Astrophysic
Stellar Chemical Abundances: In Pursuit of the Highest Achievable Precision
The achievable level of precision on photospheric abundances of stars is a
major limiting factor on investigations of exoplanet host star characteristics,
the chemical histories of star clusters, and the evolution of the Milky Way and
other galaxies. While model-induced errors can be minimized through the
differential analysis of spectrally similar stars, the maximum achievable
precision of this technique has been debated. As a test, we derive differential
abundances of 19 elements from high-quality asteroid-reflected solar spectra
taken using a variety of instruments and conditions. We treat the solar spectra
as being from unknown stars and use the resulting differential abundances,
which are expected to be zero, as a diagnostic of the error in our
measurements. Our results indicate that the relative resolution of the target
and reference spectra is a major consideration, with use of different
instruments to obtain the two spectra leading to errors up to 0.04 dex. Use of
the same instrument at different epochs for the two spectra has a much smaller
effect (~0.007 dex). The asteroid used to obtain the solar standard also has a
negligible effect (~0.006 dex). Assuming that systematic errors from the
stellar model atmospheres have been minimized, as in the case of solar twins,
we confirm that differential chemical abundances can be obtained at sub-0.01
dex precision with due care in the observations, data reduction and abundance
analysis.Comment: Accepted for publication in ApJ; 13 pages, 6 figures, 7 table
siRNA knockdown of SPHK1 in vivo protects mice from systemic, type-I Allergy.
Systemic anaphylaxis is considered to be a typical immediate hypersensitivity response, determined by the activation of immune cells,
via antigen-induced aggregation of IgE-sensitized FcεRI cells. Perhaps most the important cells, in the immediate hypersensitivity responses, are mast cells. We have previously shown that SPHK1 plays a key role in the intracellular signaling pathways triggered by FceRI aggregation on human
mast cells. More recently, we performed a genome-wide gene expression profiling of human mast cells, sensitized with IgE alone, or stimulated by FcεRI aggregation. We found that sphingosine kinase 1 (SPHK1) was one
of genes activated at the earlier stages of mast cell activation, including during sensitization. Moreover, SPHK1 has been shown, by us and others, to be a key player in the intracellular signaling pathways triggered by
several immune-receptors, including fMLP, C5a, and Fcg- and Fcereceptors. Here we have investigated the in vivo role of SPHK1 in allergy, using a specific siRNA to knockdown SPHK1 in vivo. Our results support a role for
SPHK1 in the inflammatory responses that share clinical, immunological, and histological features of type I hypersensitivity. Thus, mice pretreated with the siRNA for SPHK1 were protected from the IgE mediated allergic
reactions including: temperature changes, histamine release, cytokine production, cell-adhesion molecule expression, and immune cell infiltration into the lungs
On the Change in Surpluses Equivalence: Measuring Benefits from Transport Infrastructure Investments
Reductions in transport costs resulting from infrastructure improvements generate benefits that can be
measured as surplus changes either at an economy-wide scale (social welfare changes) or, as is common
practice in cost-benefit analysis (CBA), at a transport market level as transport users’ surplus changes. In
this paper we look at an economy with spatially separated markets embedded in a transport network (a
spatial price equilibrium model) to study the equivalence between these two benefit measures. Three
different product market competition arrangements are considered. A similar question and strategy is
presented in Jara-DÃaz (1986) employing a two-node network and extreme competition assumptions on
the production side: perfect competition and monopolistic production with arbitrage. We extend his work
by additionally considering perfect collusion (monopoly without resale) and Cournot-Nash oligopoly
under flow-dependent transport costs (i.e. congestion in transport). Numerical simulations in a three-node
network with and without transshipment nodes, illustrate our main results
Combination methods for HIV prevention in men who have sex with men (MSM)
This is the protocol for a review and there is no abstract. The objectives are as follows: This review seeks to examine the effectiveness of prevention interventions for MSM that combine at least two of the three categories of intervention modality (biomedical, behavioural and structural) compared either to other HIV prevention interventions or to minimal/no HIV prevention. Below, descriptions of the criteria that will be used to categorise intervention components are provided under the heading Types of interventions' and the full list of outcomes of interest are provided in the section Types of outcome measures'. All planned comparisons are detailed in the section Data synthesis', followed by the planned variables of interest for subgroup and meta-regression analyses
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