302 research outputs found
The silicon stable isotope distribution along the GEOVIDE section (GEOTRACES GA-01) of the North Atlantic Ocean
The stable isotope composition of dissolved silicon in seawater (ÎŽ30SiDSi) was examined at 10 stations along the GEOVIDE section (GEOTRACES GA-01), spanning the North Atlantic Ocean (40â60ââN) and Labrador Sea. Variations in ÎŽ30SiDSi below 500âm were closely tied to the distribution of water masses. Higher ÎŽ30SiDSi values are associated with intermediate and deep water masses of northern Atlantic or Arctic Ocean origin, whilst lower ÎŽ30SiDSi values are associated with DSi-rich waters sourced ultimately from the Southern Ocean. Correspondingly, the lowest ÎŽ30SiDSi values were observed in the deep and abyssal eastern North Atlantic, where dense southern-sourced waters dominate. The extent to which the spreading of water masses influences the ÎŽ30SiDSi distribution is marked clearly by Labrador Sea Water (LSW), whose high ÎŽ30SiDSi signature is visible not only within its region of formation within the Labrador and Irminger seas, but also throughout the mid-depth western and eastern North Atlantic Ocean. Both ÎŽ30SiDSi and hydrographic parameters document the circulation of LSW into the eastern North Atlantic, where it overlies southern-sourced Lower Deep Water. The GEOVIDE ÎŽ30SiDSi distribution thus provides a clear view of the direct interaction between subpolar/polar water masses of northern and southern origin, and allow examination of the extent to which these far-field signals influence the local ÎŽ30SiDSi distribution
Tectono-thermal evolution in a region with thin-skinned tectonics: the western nappes in the Cantabrian Zone (Variscan belt of NW Spain)
The palaeotemperature distribution in the transition from diagenesis to metamorphism in the western nappes of the Cantabrian Zone (Somiedo, La Sobia and Aramo Units) are analysed by conodont colour alteration index (CAI) and illite crystallinity (IC). Structural and stratigraphic control in distribution of CAI and IC values is observed. Both CAI and IC value distributions show that anchizonal conditions are reached in the lower part of the Somiedo Unit. A disruption of the thermal trend by basal thrusts is evidenced by CAI and IC values. There is an apparent discrepancy between the IC and CAI values in carboniferous rocks of the Aramo Unit; the IC has mainly anchizonal values, whereas the CAI has diagenetic values. Discrepant IC values are explained as a feature inherited from the source area. In the Carboniferous rocks of the La Sobia Unit, both IC and CAI indicate diagenetic conditions. The anchimetamorphism predated completion of emplacement of the major nappes; it probably developed previously and/or during the early stages of motion of the units. Temperature probably decreased when the metamorphosed zones of the sheets rose along ramps and were intensely eroded. In the context of the Iberian Variscan belt, influence of tectonic factors on the metamorphism is greater in the internal parts, where the strain and cleavage are always present, than in the external parts (Cantabrian Zone), where brittle deformation and rock translation are dominant, with an increasing role of the burial on the metamorphism
Particulate barium tracing of significant mesopelagic carbon remineralisation in the North Atlantic
The remineralisation of sinking particles by prokaryotic heterotrophic activity is important for controlling oceanic carbon sequestration. Here, we report mesopelagic particulate organic carbon (POC) remineralisation fluxes in the North Atlantic along the GEOTRACES-GA01 section (GEOVIDE cruise; May-June 2014) using the particulate biogenic barium (excess barium; Baxs/ proxy. Important mesopelagic (100-1000 m) Baxs differences were observed along the transect depending on the intensity of past blooms, the phytoplankton community structure, and the physical forcing, including downwelling. The subpolar province was characterized by the highest mesopelagic Baxs content (up to 727 pmol L-1/, which was attributed to an intense bloom averaging 6 mg chl a m-3 between January and June 2014 and by an intense 1500m deep convection in the central Labrador Sea during the winter preceding the sampling. This downwelling could have promoted a deepening of the prokaryotic heterotrophic activity, increasing the Baxs content. In comparison, the temperate province, characterized by the lowest Baxs content (391 pmol L-1/, was sampled during the bloom period and phytoplankton appear to be dominated by small and calcifying species, such as coccolithophorids. The Baxs content, related to oxygen consumption, was converted into a remineralisation flux using an updated relationship, proposed for the first time in the North Atlantic. The estimated fluxes were of the same order of magnitude as other fluxes obtained using independent methods (moored sediment traps, incubations) in the North Atlantic. Interestingly, in the subpolar and subtropical provinces, mesopelagic POC remineralisation fluxes (up to 13 and 4.6 mmol Cm-2 d-1, respectively) were equalling and occasionally even exceeding upper-ocean POC export fluxes, deduced using the 234Th method. These results highlight the important impact of the mesopelagic remineralisation on the biological carbon pump of the studied area with a near-zero, deep (> 1000 m) carbon sequestration efficiency in spring 2014
Determinação de selenometionina por quimiolumiescĂȘncia em castanha do Brasil.
SelĂȘnio Ă© reconhecido como um micronutriente essencial. PorĂ©m, a bioutilidade deste elemento estĂĄ intrĂsecamente dependente da sua forma quĂmica. EspĂ©cies orgĂąnicas de selĂȘnio sĂŁo mais facilmente absorvidas por organismos humanos quando comparado a suas espĂ©cies inorgĂąnicas. Castanhas do Brasil podem ser consideradas uma boa fonte de selĂȘnio, pois apresenta concentraçÔes significativas deste elemento, principalmente na forma de selenometionina.1 Neste trabalho, sistema para anĂĄlise em fluxo para a determinação de selenometionina em amostras de castanha do Brasil empregando quimioluminescĂȘncia foi desenvolvido, utilizando uma cĂ©lula de reação com estrutura em vĂłrtex construĂda com tecnologia LTCC2
Multifield Dynamics in Higgs-otic Inflation
In Higgs-otic inflation a complex neutral scalar combination of the and
MSSM Higgs fields plays the role of inflaton in a chaotic fashion. The
potential is protected from large trans-Planckian corrections at large inflaton
if the system is embedded in string theory so that the Higgs fields parametrize
a D-brane position. The inflaton potential is then given by a DBI+CS D-brane
action yielding an approximate linear behaviour at large field. The inflaton
scalar potential is a 2-field model with specific non-canonical kinetic terms.
Previous computations of the cosmological parameters (i.e. scalar and tensor
perturbations) did not take into account the full 2-field character of the
model, ignoring in particular the presence of isocurvature perturbations and
their coupling to the adiabatic modes. It is well known that for generic
2-field potentials such effects may significantly alter the observational
signatures of a given model. We perform a full analysis of adiabatic and
isocurvature perturbations in the Higgs-otic 2-field model. We show that the
predictivity of the model is increased compared to the adiabatic approximation.
Isocurvature perturbations moderately feed back into adiabatic fluctuations.
However, the isocurvature component is exponentially damped by the end of
inflation. The tensor to scalar ratio varies in a region ,
consistent with combined Planck/BICEP results.Comment: 35 pages, 11 figure
Inflationary Scenarios from Branes at Angles
We describe a simple mechanism that can lead to inflation within string-based
brane-world scenarios. The idea is to start from a supersymmetric configuration
with two parallel static Dp-branes, and slightly break the supersymmetry
conditions to produce a very flat potential for the field that parametrises the
distance between the branes, i.e. the inflaton field. This breaking can be
achieved in various ways: by slight relative rotations of the branes with small
angles, by considering small relative velocities between the branes, etc. If
the breaking parameter is sufficiently small, a large number of e-folds can be
produced within the D-brane, for small changes of the configuration in the
compactified directions. Such a process is local, i.e. it does not depend very
strongly on the compactification space nor on the initial conditions. Moreover,
the breaking induces a very small velocity and acceleration, which ensures very
small slow-roll parameters and thus an almost scale invariant spectrum of
metric fluctuations, responsible for the observed temperature anisotropies in
the microwave background. Inflation ends as in hybrid inflation, triggered by
the negative curvature of the string tachyon potential. In this paper we
elaborate on one of the simplest examples: two almost parallel D4-branes in a
flat compactified space.Comment: 29 pages, 9 eps figures, using JHEP3.cls, published in JHE
Transplanckian axions !?
We discuss quantum gravitational effects in Einstein theory coupled to
periodic axion scalars to analyze the viability of several proposals to achieve
superplanckian axion periods (aka decay constants) and their possible
application to large field inflation models. The effects we study correspond to
the nucleation of euclidean gravitational instantons charged under the axion,
and our results are essentially compatible with (but independent of) the Weak
Gravity Conjecture, as follows: Single axion theories with superplanckian
periods contain gravitational instantons inducing sizable higher harmonics in
the axion potential, which spoil superplanckian inflaton field range. A similar
result holds for multi-axion models with lattice alignment (like the
Kim-Nilles-Peloso model). Finally, theories with axions can still achieve a
moderately superplanckian periodicity (by a factor) with no higher
harmonics in the axion potential. The Weak Gravity Conjecture fails to hold in
this case due to the absence of some instantons, which are forbidden by a
discrete gauge symmetry. Finally we discuss the realization of
these instantons as euclidean D-branes in string compactifications.Comment: 46 pages, 6 figures. Added references, clarifications, and missing
factor of 1/2 to instanton action. Conclusions unchange
Complex structure moduli stability in toroidal compactifications
In this paper we present a classification of possible dynamics of closed
string moduli within specific toroidal compactifications of Type II string
theories due to the NS-NS tadpole terms in the reduced action. They appear as
potential terms for the moduli when supersymmetry is broken due to the presence
of D-branes. We particularise to specific constructions with two, four and
six-dimensional tori, and study the stabilisation of the complex structure
moduli at the disk level. We find that, depending on the cycle on the compact
space where the brane is wrapped, there are three possible cases: i) there is a
solution inside the complex structure moduli space, and the configuration is
stable at the critical point, ii) the moduli fields are driven towards the
boundary of the moduli space, iii) there is no stable solution at the minimum
of the potential and the system decays into a set of branes.Comment: 24 pages, JHEP3.cls, 19 figures. A few references adde
Selection for environmental variance of litter size in rabbits
[EN] Background: In recent years, there has been an increasing interest in the genetic determination of environmental variance. In the case of litter size, environmental variance can be related to the capacity of animals to adapt to new environmental conditions, which can improve animal welfare.
Results: We developed a ten-generation divergent selection experiment on environmental variance. We selected one line of rabbits for litter size homogeneity and one line for litter size heterogeneity by measuring intra-doe phenotypic variance. We proved that environmental variance of litter size is genetically determined and can be modified by selection. Response to selection was 4.5% of the original environmental variance per generation. Litter size was consistently higher in the Low line than in the High line during the entire experiment.
Conclusions: We conclude that environmental variance of litter size is genetically determined based on the results of our divergent selection experiment. This has implications for animal welfare, since animals that cope better with their environment have better welfare than more sensitive animals. We also conclude that selection for reduced environmental variance of litter size does not depress litter size.This research was funded by the Ministerio de EconomĂa y Competitividad (Spain), Projects AGL2014-55921, C2-1-P and C2-2-P. Marina MartĂnez-Alvaro has a Grant from the same funding source, BES-2012-052655.Blasco Mateu, A.; MartĂnez Ălvaro, M.; GarcĂa Pardo, MDLL.; Ibåñez Escriche, N.; Argente, MJ. (2017). Selection for environmental variance of litter size in rabbits. Genetics Selection Evolution. 49(48):1-8. https://doi.org/10.1186/s12711-017-0323-4S184948Morgante F, SĂžrensen P, Sorensen DA, Maltecca C, Mackay TFC. 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