1,762 research outputs found
Tectonic significance of Late Paleozoic deformation in the Cape George Peninsula, Antigonish Highlands, Nova Scotia
Late Paleozoic deformation of the Cape George Peninsula, Antigonish Highlands, Nova Scotia, provides information on post-accretionary fault movements associated with waning stages of Appalachian orogenic activity. Anomalously intense brittle to ductile deformation of the low-grade Late Paleozoic rocks of the peninsula occurred along east-west shear zones in a ca. 4 km-wide belt bounded by the NE-trending Hollow and Greendale faults. Deformation adjacent to, and between, these two faults resulted in brecciation, folding and thrusting, the development of slickensides on major dislocation surfaces, the local development of S-C fabrics and stretching lineations defined by elongate pebbles, and/or the production of extensional fractures and veins. The data suggest dextral and subordinate thrust components of movement along the east-west shear zones. Deformation is attributed to dextrally oblique compression between the bounding Hollow and Greendale faults along which significant reverse displacements are proposed on the basis of fault geometry and kinematics. The Cape George Peninsula is interpreted as a "popup" structure between these back-to-back oblique-slip reverse faults and is considered to occupy a strongly transpressive step-over zone between them. The east-west shear zones, which record dextral transpressive motion and steepen towards the north in a positive half-flower structure configuration, are parallel to Reidel R-shears of the shear fracture array and are interpreted to be transfer faults within the step-over zone along which oblique slip with dextral and reverse components of motion was transferred from the Hollow Fault to the Greendale Fault. Development of the regional stress regime required by these fault kinematics is consistent with coeval post-accretionary dextral motion between the Meguma and Avalon composite terranes along the east-west Cobcquid-Chedabucto fault system.
RÉSUMÉ
La déformation du Paléozoique tandif de la péninsule dc Cap George, dans les hautes terres d'Antigonish en Nouvelle-Écosse, fournit des informations sur les mouvements de failles post-accrétionaires associés aux stades terminaux de l'activité orogénique appalachienne. Une déformation fragile à ductile anormalement intense des roches du Paléozoique supérieur de faible grade s'est produite le long de zones de cisaillement est-ouest dans une ceinture d'environ 4 km de largeur limited par les failles de Hollow et de Greendale d'orientation nord-est. La déformation adjacente et entre ces failles a résulté en de la bélchification, du plissement et du chevauchement, le développement de slickensides sur des surfaces de dislocation majeures, le développement local de fabriques C-S et de linéations d'étirement définies par des cailloux allongés, et/ou la production de fractures et de veines d'extension. Les données suggèrent des composantes de mouvement dextres et, dans une moindre mesure, de chevauchement le long des zones de cisaillement est-ouest. La déformation est attributée à une compression dextre oblique entre les failles limitrophes de Hollow et de Greendale le long desquelles des deplacements inverses importants sont proposés sur la base de la géométrie et de la cinémalique des failles. La péninsule de Cap George est interprét6e comme une structure d'extrusion verticale entre ces deux failles obliques a mouvement inverse, dos à dos, et est considérée comme occupant une zone de recouvrement fortement transpressive entre elles. Les zones de cisaillement est-ouest, qui montrent un mouvement de transpression dextre et deviennent plus abruples vers le nord en une configuration de demie "flower structure" positive, sont parallèles aux riedels synlhétiques du réseau de fractures de cisaillement et sont interprétées comme étant des failles de transfert à l'intérieur de la zone de transfert suivant lesquelles un mouvement oblique avec des composantes de mouvement dextre et inverse furent transferées de la faille de Hollow à la faille de Greendale. Le développement du régime de contrainte régional requis par ces cindmatiques de failles est en accord avec un mouvement post-accrétionaire dextre entre les terrains de Meguma et d'Avalon composite le long du systeme de faille est-ouest de Cobcquid-Chedabucto.
[Traduit par la rédaction
He II 4686 emission from the massive binary system in Car: constraints to the orbital elements and the nature of the periodic minima
{\eta} Carinae is an extremely massive binary system in which rapid spectrum
variations occur near periastron. Most notably, near periastron the He II
line increases rapidly in strength, drops to a minimum value,
then increases briefly before fading away. To understand this behavior, we
conducted an intense spectroscopic monitoring of the He II
emission line across the 2014.6 periastron passage using ground- and
space-based telescopes. Comparison with previous data confirmed the overall
repeatability of EW(He II ), the line radial velocities, and the
timing of the minimum, though the strongest peak was systematically larger in
2014 than in 2009 by 26%. The EW(He II ) variations, combined
with other measurements, yield an orbital period d. The observed
variability of the EW(He II ) was reproduced by a model in which
the line flux primarily arises at the apex of the wind-wind collision and
scales inversely with the square of the stellar separation, if we account for
the excess emission as the companion star plunges into the hot inner layers of
the primary's atmosphere, and including absorption from the disturbed primary
wind between the source and the observer. This model constrains the orbital
inclination to -, and the longitude of periastron to
-. It also suggests that periastron passage occurred on
d. Our model also reproduced EW(He II )
variations from a polar view of the primary star as determined from the
observed He II emission scattered off the Homunculus nebula.Comment: The article contains 23 pages and 17 figures. It has been accepted
for publication in Ap
Topological gap solitons in a 1D non-Hermitian lattice
Nonlinear topological photonics is an emerging field aiming at extending the
fascinating properties of topological states to the realm where interactions
between the system constituents cannot be neglected. Interactions can indeed
trigger topological phase transitions, induce symmetry protection and
robustness properties for the many-body system. Moreover when coupling to the
environment via drive and dissipation is also considered, novel collective
phenomena are expected to emerge. Here, we report the nonlinear response of a
polariton lattice implementing a non-Hermitian version of the
Su-Schrieffer-Heeger model. We trigger the formation of solitons in the
topological gap of the band structure, and show that these solitons demonstrate
robust nonlinear properties with respect to defects, because of the underlying
sub-lattice symmetry. Leveraging on the system non-Hermiticity, we engineer the
drive phase pattern and unveil bulk solitons that have no counterpart in
conservative systems. They are localized on a single sub-lattice with a spatial
profile alike a topological edge state. Our results demonstrate a tool to
stabilize the nonlinear response of driven dissipative topological systems,
which may constitute a powerful resource for nonlinear topological photonics
Functional characterization of a melon alcohol acyl-transferase gene family involved in the biosynthesis of ester volatiles. Identification of the crucial role of a threonine residue for enzyme activity
Volatile esters, a major class of compounds contributing to the aroma of many fruit, are synthesized by
alcohol acyl-transferases (AAT). We demonstrate here that, in Charentais melon (Cucumis melo var.
cantalupensis), AAT are encoded by a gene family of at least four members with amino acid identity ranging
from 84% (Cm-AAT1/Cm-AAT2) and 58% (Cm-AAT1/Cm-AAT3) to only 22% (Cm-AAT1/Cm-AAT4).
All encoded proteins, except Cm-AAT2, were enzymatically active upon expression in yeast and show
differential substrate preferences. Cm-AAT1 protein produces a wide range of short and long-chain acyl
esters but has strong preference for the formation of E-2-hexenyl acetate and hexyl hexanoate. Cm-AAT3
also accepts a wide range of substrates but with very strong preference for producing benzyl acetate.
Cm-AAT4 is almost exclusively devoted to the formation of acetates, with strong preference for cinnamoyl
acetate. Site directed mutagenesis demonstrated that the failure of Cm-AAT2 to produce volatile esters is
related to the presence of a 268-alanine residue instead of threonine as in all active AAT proteins. Mutating
268-A into 268-T of Cm-AAT2 restored enzyme activity, while mutating 268-T into 268-A abolished
activity of Cm-AAT1. Activities of all three proteins measured with the prefered substrates sharply increase
during fruit ripening. The expression of all Cm-AAT genes is up-regulated during ripening and inhibited in
antisense ACC oxidase melons and in fruit treated with the ethylene antagonist 1-methylcyclopropene
(1-MCP), indicating a positive regulation by ethylene. The data presented in this work suggest that the
multiplicity of AAT genes accounts for the great diversity of esters formed in melon
Impact of ultraviolet radiation on marine crustacean zooplankton and ichthyoplankton: a synthesis of results from the estuary and Gulf of St. Lawrence, Canada
The objectives of the research program reported upon here were (1) to measure ambient levels of UV radiation and
determine whichvariables most strongly affected its attenuation in the waters of the estuary and Gulf of St. Lawrence, Canada; and
(2) to investigate the potential direct impacts of W radiation on species of crustacean zooplankton and fish whose early life stages
are planktonic. In this geographic region, productivity-determining biophysical interactions occur in the upper 0 to 30 m of the
water column. Measurements of the diffuse attenuation coefficients for ultraviolet-B radiation (W-B, 280 to 320 nm) at various
locations in this region indicated maximum 10% depths (the depth to which 10% of the surface energy penetrates at a given wavelength)
of 3 to 4 m at a wavelength of 310 nm. Organisms residing in this layer-including the eggs and larvae of Calanus finmarchicus
and Atlantic cod Gadus morhua-are exposed to biologically damaging levels of W radiation. As a result of these physical
and biological characteristics, this system offered a relevant opportunity to assess the impacts of UV on subarctic marine
ecosystems. Eggs of C. finmarchicus were incubated under the sun, with and without the W-B and/or UV-A (320 to 400 nm) wavebands.
W-exposed eggs exhibited low percent hatchmg compared to those protected from W : W radiation had a strong negative
impact on C. finmarchicus eggs. Further, percent hatching in W-B-exposed eggs was not significantly lower than that in eggs
exposed to UV-A only: under natural sunlight, UV-A radiation appeared to be more detrimental to C. finmarchicus embryos than
was UV-B. In analogous experiments with Atlantic cod eggs, exposure to UV-B produced a significant negative effect. However,
UV-A had no negative effect on cod eggs. Additional experiments using a solar simulator (SS) revealed high wavelength-dependent
mortality in both C. finmarchicus and cod embryos exposed to UV. The strongest effects occurred under exposures to wavelengths
below 312 nm. At the shorter wavelengths (<305 nm) UV-B-induced mortality was strongly dose-dependent, but (for both
C. finmarchicus and cod) not significantly influenced by dose-rate. Thus, at least within the limits of the exposures under which the
biological weighting functions (BWFs) were generated, reciprocity held. The BWFs derived for UV-B-induced mortality in C. finmarchicus
and cod eggs were similar in shape to the action spectrum for UV-B effects on naked DNA. Further, the wavelengthdependence
of DNA damage was similar to that for the mortality effect. These observations suggest that W-induced mortality in
C. finmarchicus and cod eggs is a direct result of DNA damage. There was no evidence of a detrimental effect of UV-A radiation in
these SS-derived results. A mathematical model that includes the BWFs, vertical mixing of eggs, meteorological and hydrographic
conditions, and ozone depletion, indicates that W-induced mortality in the C. finmarchicus egg population could be as high as
32.5 %, while the impact on the cod egg population was no more than 1.2%. Variability in cloud cover, water transparency (and the
variables that affect it), and vertical distribution and displacement of planktonic organisms within the mixed layer can all have a
greater effect on the flux of UV-B radiation to which they are exposed than will ozone layer depletion at these latitudes. Our observations
indicate that C, finmarchicus and cod eggs present in the first meter of the water column (likely only a small percentage of
the total egg populations) are susceptible to W radiation. However, although exposure to UV can negatively impact crustacean
zooplankton and ichthyoplankton populations, these direct effects are likely minimal within the context of all the other environmental
factors that produce the very high levels of mortality typically observed in their planktonic early life stages. The impact of
indnect effects-which may well be of much greater import-has yet to be evaluated
Two Earth-sized planets orbiting Kepler-20
Since the discovery of the first extrasolar giant planets around Sun-like
stars, evolving observational capabilities have brought us closer to the
detection of true Earth analogues. The size of an exoplanet can be determined
when it periodically passes in front of (transits) its parent star, causing a
decrease in starlight proportional to its radius. The smallest exoplanet
hitherto discovered has a radius 1.42 times that of the Earth's radius (R
Earth), and hence has 2.9 times its volume. Here we report the discovery of two
planets, one Earth-sized (1.03R Earth) and the other smaller than the Earth
(0.87R Earth), orbiting the star Kepler-20, which is already known to host
three other, larger, transiting planets. The gravitational pull of the new
planets on the parent star is too small to measure with current
instrumentation. We apply a statistical method to show that the likelihood of
the planetary interpretation of the transit signals is more than three orders
of magnitude larger than that of the alternative hypothesis that the signals
result from an eclipsing binary star. Theoretical considerations imply that
these planets are rocky, with a composition of iron and silicate. The outer
planet could have developed a thick water vapour atmosphere.Comment: Letter to Nature; Received 8 November; accepted 13 December 2011;
Published online 20 December 201
A Genome-Wide Investigation of SNPs and CNVs in Schizophrenia
We report a genome-wide assessment of single nucleotide polymorphisms (SNPs) and copy number variants (CNVs) in schizophrenia. We investigated SNPs using 871 patients and 863 controls, following up the top hits in four independent cohorts comprising 1,460 patients and 12,995 controls, all of European origin. We found no genome-wide significant associations, nor could we provide support for any previously reported candidate gene or genome-wide associations. We went on to examine CNVs using a subset of 1,013 cases and 1,084 controls of European ancestry, and a further set of 60 cases and 64 controls of African ancestry. We found that eight cases and zero controls carried deletions greater than 2 Mb, of which two, at 8p22 and 16p13.11-p12.4, are newly reported here. A further evaluation of 1,378 controls identified no deletions greater than 2 Mb, suggesting a high prior probability of disease involvement when such deletions are observed in cases. We also provide further evidence for some smaller, previously reported, schizophrenia-associated CNVs, such as those in NRXN1 and APBA2. We could not provide strong support for the hypothesis that schizophrenia patients have a significantly greater “load” of large (>100 kb), rare CNVs, nor could we find common CNVs that associate with schizophrenia. Finally, we did not provide support for the suggestion that schizophrenia-associated CNVs may preferentially disrupt genes in neurodevelopmental pathways. Collectively, these analyses provide the first integrated study of SNPs and CNVs in schizophrenia and support the emerging view that rare deleterious variants may be more important in schizophrenia predisposition than common polymorphisms. While our analyses do not suggest that implicated CNVs impinge on particular key pathways, we do support the contribution of specific genomic regions in schizophrenia, presumably due to recurrent mutation. On balance, these data suggest that very few schizophrenia patients share identical genomic causation, potentially complicating efforts to personalize treatment regimens
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