3,812 research outputs found
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The Floor of the Mediterranean Sea
The bathymetry, magnetic anomalies, gravity anomalies and sediment layer is presented to support a young Western Mediterranean no older than 25 million years and an Eastern Mediterranean as old as 200 million years. A buried salt layer is detected in seismic reflection profiles lying below a sediment cover whose base is 4 to 5 million years in age. The seafloor in the eastern Mediterranean is being actively deformed by compressional folding and thrusting beneath the Mediterranean Ridge. The Western Mediterranean opened by rifting and is floored by oceanic crust
Quadrupole moments of rotating neutron stars
Numerical models of rotating neutron stars are constructed for four equations
of state using the computer code RNS written by Stergioulas. For five selected
values of the star's gravitational mass (in the interval between 1.0 and 1.8
solar masses) and for each equation of state, the star's angular momentum is
varied from J=0 to the Keplerian limit J=J_{max}. For each neutron-star
configuration we compute Q, the quadrupole moment of the mass distribution. We
show that for given values of M and J, |Q| increases with the stiffness of the
equation of state. For fixed mass and equation of state, the dependence on J is
well reproduced with a simple quadratic fit, Q \simeq - aJ^2/M c^2, where c is
the speed of light, and a is a parameter of order unity depending on the mass
and the equation of state.Comment: ReVTeX, 7 pages, 5 figures, additional material, and references adde
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Spatial Variations in a Condensed Interval between Estuarine and Open-Marine Settings: Holocene Hudson River Estuary and Adjacent Continental Shelf
An interval of stratigraphic condensation extending for 300 km from the fluvially dominated Hudson River estuary to the adjacent continental shelf reveals stratal relationships within an unconformity-related depositional sequence that are commonly difficult to resolve in seismic reflection profiles and outcrop. High-resolution side-scan sonar and bathymetry, more than 100 sediment cores ∼2 m long, and radioisotope (14C, 137Cs) age control show that much of the valley was filled by ca. 3 to 1 ka. The present rate of sediment accumulation averages 1 mm/yr, corresponding with a sea-level rise of ∼1.2 mm/yr relative to local bedrock. Condensation is manifested today by sedimentary bypass in most parts of the estuary and by the trapping of available sediment (1.2–5.6 × 105 t/yr [metric tons]) along narrow reaches and primarily in the vicinity of the estuarine turbidity maximum, a part of the estuary located upstream of the salinity intrusion ∼25 km from the mouth (3.0 × 105 t/yr). Shelf condensation is due to sediment starvation. The condensed interval merges updip with a nascent sequence boundary as the estuary reaches its final filling phase and downdip with the sequence boundary that developed at the Last Glacial Maximum. Delta progradation may take place as available shelf accommodation is filled, but such sediments are expected to be removed once sea level begins to fall. This sedimentation pattern, in which a condensed interval merges with different sequence boundaries, is consistent with the stratigraphic record of the Atlantic margin back to the Paleogene and may be typical of sediment-starved margins
Inferring Tunicate Relationships And The Evolution Of The Tunicate Hox Cluster With The Genome Of Corella Inflata
Tunicates, the closest living relatives of vertebrates, have served as a foundational model of early embryonic development for decades. Comparative studies of tunicate phylogeny and genome evolution provide a critical framework for analyzing chordate diversification and the emergence of vertebrates. Towards this goal, we sequenced the genome of Corella inflata (Ascidiacea, Phlebobranchia), so named for the capacity to brood self-fertilized embryos in a modified, “inflated” atrial chamber. Combining the new genome sequence for Co. inflata with publicly available tunicate data, we estimated a tunicate species phylogeny, reconstructed the ancestral Hox gene cluster at important nodes in the tunicate tree, and compared patterns of gene loss between Co. inflata and Ciona robusta, the prevailing tunicate model species. Our maximum-likelihood and Bayesian trees estimated from a concatenated 210-gene matrix were largely concordant and showed that Aplousobranchia was nested within a paraphyletic Phlebobranchia. We demonstrated that this relationship is not an artifact due to compositional heterogeneity, as had been suggested by previous studies. In addition, within Thaliacea, we recovered Doliolida as sister to the clade containing Salpida and Pyrosomatida. The Co. inflata genome provides increased resolution of the ancestral Hox clusters of key tunicate nodes, therefore expanding our understanding of the evolution of this cluster and its potential impact on tunicate morphological diversity. Our analyses of other gene families revealed that several cardiovascular associated genes (e.g., BMP10, SCL2A12, and PDE2a) absent from Ci. robusta are present in Co. inflata. Taken together, our results help clarify tunicate relationships and the genomic content of key ancestral nodes within this phylogeny, providing critical insights into tunicate evolution
Magmatic Subsidence of the East Pacific Rise (EPR) at 18˚14\u27S Revealed Through Fault Restoration of Ridge Crest Bathymetry
The fault restoration technique of De Chabalier and Avouac [1994] is applied to an ultra-highresolution bathymetry data set from the East Pacific Rise (EPR) at 18140S. Fault offsets are calculated and subtracted from the original seafloor bathymetry to examine the morphology of the unfaulted seafloor surface within an area encompassing the ridge axis 400 [1] 1600 m in dimension. The restored topography reveals a gently sloping seafloor 200 m wide, which slopes 5 inward toward the spreading axis. We attribute this inward sloping seafloor to subsidence within the axial trough due to subsurface magmatic deflation. The vertical deformation field extracted from the bathymetry is used to characterize the ridge axis fault population present in the area. Median fault throws (9 m for inward-facing and 8 m for outwardfacing faults) are comparable to values measured for nearby mature abyssal hill fault populations, suggesting a genetic link. However, median fault spacings (70 and 46 m) are an order of magnitude smaller, and estimated total extensional strain is 3[1]–4[1] greater than values measured for ridge flank faults. These differences indicate the axial fault population at 18140S cannot be rafted onto the ridge flanks to form abyssal hill faults without significant modification, presumably via volcanic burial. We attribute the dense faulting observed in this area to slip on axial fissures during subsidence of the crestal region. The surface subsidence of a volcanic edifice can be modeled in terms of volume change in the magma source reservoir and volume of magma withdrawn from the reservoir. Using the relationship derived for a sill-like magma body, we estimate that the axial depression at 18140S could represent magma withdrawal associated with a small number (4–22) of the frequent dike injection and eruption events required to build the upper crust during the evolution of the trough. The subsidence volumes represented by the axial topography at 18140S are a small percentage of the underlying upper crustal sections (3–4%), suggesting that only a minor mismatch between magma recharge and withdrawal from the axial melt lens during ongoing plate separation could account for this pronounced axial depression
Persistent starspot signals on M dwarfs: multi-wavelength Doppler observations with the Habitable-zone Planet Finder and Keck/HIRES
Young, rapidly-rotating M dwarfs exhibit prominent starspots, which create
quasiperiodic signals in their photometric and Doppler spectroscopic
measurements. The periodic Doppler signals can mimic radial velocity (RV)
changes expected from orbiting exoplanets. Exoplanets can be distinguished from
activity-induced false positives by the chromaticity and long-term incoherence
of starspot signals, but these qualities are poorly constrained for
fully-convective M stars. Coherent photometric starspot signals on M dwarfs may
persist for hundreds of rotations, and the wavelength dependence of starspot RV
signals may not be consistent between stars due to differences in their
magnetic fields and active regions. We obtained precise multi-wavelength RVs of
four rapidly-rotating M dwarfs (AD Leo, G 227-22, GJ 1245B, GJ 3959) using the
near-infrared (NIR) Habitable-zone Planet Finder, and the optical Keck/HIRES
spectrometer. Our RVs are complemented by photometry from Kepler, TESS, and the
Las Cumbres Observatory (LCO) network of telescopes. We found that all four
stars exhibit large spot-induced Doppler signals at their rotation periods, and
investigated the longevity and optical-to-NIR chromaticity for these signals.
The phase curves remain coherent much longer than is typical for Sunlike stars.
Their chromaticity varies, and one star (GJ 3959) exhibits optical and NIR RV
modulation consistent in both phase and amplitude. In general, though, we find
that the NIR amplitudes are lower than their optical counterparts. We conclude
that starspot modulation for rapidly-rotating M stars frequently remains
coherent for hundreds of stellar rotations, and gives rise to Doppler signals
that, due to this coherence, may be mistaken for exoplanets.Comment: Accepted for publication in the Astrophysical Journa
Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b
The nearby extrasolar planet GJ 436b--which has been labelled as a 'hot
Neptune'--reveals itself by the dimming of light as it crosses in front of and
behind its parent star as seen from Earth. Respectively known as the primary
transit and secondary eclipse, the former constrains the planet's radius and
mass, and the latter constrains the planet's temperature and, with measurements
at multiple wavelengths, its atmospheric composition. Previous work using
transmission spectroscopy failed to detect the 1.4-\mu m water vapour band,
leaving the planet's atmospheric composition poorly constrained. Here we report
the detection of planetary thermal emission from the dayside of GJ 436b at
multiple infrared wavelengths during the secondary eclipse. The best-fit
compositional models contain a high CO abundance and a substantial methane
(CH4) deficiency relative to thermochemical equilibrium models for the
predicted hydrogen-dominated atmosphere. Moreover, we report the presence of
some H2O and traces of CO2. Because CH4 is expected to be the dominant
carbon-bearing species, disequilibrium processes such as vertical mixing and
polymerization of methane into substances such as ethylene may be required to
explain the hot Neptune's small CH4-to-CO ratio, which is at least 10^5 times
smaller than predicted
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An Abrupt Drowning of the Black Sea Shelf at 7.5 KYR BP
During latest Quaternary glaciation, the Black Sea became a giant freshwater lake. The surface of this lake drew down to levels more than 100m below its outlet. When the Mediterranean rose to the Bosporus sill at 7.5 kyr BP, saltwater poured through this spillway to refill the and submerge in less than a year, more than 100,000km2 of its exposed continental shelf
The sweet spot in sustainability: a framework for corporate assessment in sugar manufacturing
The assessment of corporate sustainability has become an increasingly important topic, both within academia and in industry. For manufacturing companies to conform to their commitments to sustainable development, a standard and reliable measurement framework is required. There is, however, a lack of sector-specific and empirical research in many areas, including the sugar industry. This paper presents an empirically developed framework for the assessment of corporate sustainability within the Thai sugar industry. Multiple case studies were conducted, and a survey using questionnaires was also employed to enhance the power of generalisation. The developed framework is an accurate and reliable measurement instrument of corporate sustainability, and guidelines to assess qualitative criteria are put forward. The proposed framework can be used for a company’s self-assessment and for guiding practitioners in performance improvement and policy decision-maki
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