2,876 research outputs found
Glacial cycles drive variations in the production of oceanic crust
Glacial cycles redistribute water between oceans and continents causing
pressure changes in the upper mantle, with consequences for melting of Earth's
interior. Using Plio-Pleistocene sea-level variations as a forcing function,
theoretical models of mid-ocean ridge dynamics that include melt transport
predict temporal variations in crustal thickness of hundreds of meters. New
bathymetry from the Australian-Antarctic ridge shows significant spectral
energy near the Milankovitch periods of 23, 41, and 100 ky, consistent with
model predictions. These results suggest that abyssal hills, one of the most
common bathymetric features on Earth, record the magmatic response to changes
in sea level. The models and data support a link between glacial cycles at the
surface and mantle melting at depth, recorded in the bathymetric fabric of the
sea floor.Comment: 30 pages, 6 figures (including supplementary information).
Resubmitted to Science on 12 December 201
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Glacial cycles drive variations in the production of oceanic crust
Glacial cycles redistribute water between oceans and continents, causing pressure changes in the upper mantle, with consequences for the melting of Earth’s interior. Using Plio-Pleistocene sea-level variations as a forcing function, theoretical models of mid-ocean ridge dynamics that include melt transport predict temporal variations in crustal thickness of hundreds of meters. New bathymetry from the Australian-Antarctic ridge shows statistically significant spectral energy near the Milankovitch periods of 23, 41, and 100 thousand years, which is consistent with model predictions. These results suggest that abyssal hills, one of the most common bathymetric features on Earth, record the magmatic response to changes in sea level. The models and data support a link between glacial cycles at the surface and mantle melting at depth, recorded in the bathymetric fabric of the sea floor.Earth and Planetary Science
Exotic torus manifolds and equivariant smooth structures on quasitoric manifolds
In 2006 Masuda and Suh asked if two compact non-singular toric varieties
having isomorphic cohomology rings are homeomorphic. In the first part of this
paper we discuss this question for topological generalizations of toric
varieties, so-called torus manifolds. For example we show that there are
homotopy equivalent torus manifolds which are not homeomorphic. Moreover, we
characterize those groups which appear as the fundamental groups of locally
standard torus manifolds.
In the second part we give a classification of quasitoric manifolds and
certain six-dimensional torus manifolds up to equivariant diffeomorphism.
In the third part we enumerate the number of conjugacy classes of tori in the
diffeomorphism group of torus manifolds. For torus manifolds of dimension
greater than six there are always infinitely many conjugacy classes. We give
examples which show that this does not hold for six-dimensional torus
manifolds.Comment: 21 pages, 2 figures, results about quasitoric manifolds adde
Characterizing Atacama B-mode Search Detectors with a Half-Wave Plate
The Atacama B-Mode Search (ABS) instrument is a cryogenic (10 K)
crossed-Dragone telescope located at an elevation of 5190 m in the Atacama
Desert in Chile that observed for three seasons between February 2012 and
October 2014. ABS observed the Cosmic Microwave Background (CMB) at large
angular scales () to limit the B-mode polarization spectrum around
the primordial B-mode peak from inflationary gravity waves at .
The ABS focal plane consists of 480 transition-edge sensor (TES) bolometers.
They are coupled to orthogonal polarizations from a planar ortho-mode
transducer (OMT) and observe at 145 GHz. ABS employs an ambient-temperature,
rapidly rotating half-wave plate (HWP) to mitigate systematic effects and move
the signal band away from atmospheric noise, allowing for the recovery of
large angular scales. We discuss how the signal at the second harmonic of the
HWP rotation frequency can be used for data selection and for monitoring the
detector responsivities.Comment: 7 pages, 3 figures, conference proceedings submitted to the Journal
of Low Temperature Detector
Signaling Role of Prokineticin 2 on the Estrous Cycle of Female Mice
The possible signaling role of prokineticin 2 (PK2) and its receptor, prokineticin receptor 2 (PKR2), on female reproduction was investigated. First, the expression of PKR2 and its co-localization with estrogen receptor (ERα) in the hypothalamus was examined. Sexually dimorphic expression of PKR2 in the preoptic area of the hypothalamus was observed. Compared to the male mice, there was more widespread PKR2 expression in the preoptic area of the hypothalamus in the female mice. The likely co-expression of PKR2 and ERα in the preoptic area of the hypothalamus was observed. The estrous cycles in female PK2-null, and PKR2-null heterozygous mice, as well as in PK2-null and PKR2-null compound heterozygous mice were examined. Loss of one copy of PK2 or PKR2 gene caused elongated and irregular estrous cycle in the female mice. The alterations in the estrous cycle were more pronounced in PK2-null and PKR2-null compound heterozygous mice. Consistent with these observations, administration of a small molecule PK2 receptor antagonist led to temporary blocking of estrous cycle at the proestrous phase in female mice. The administration of PKR2 antagonist was found to blunt the circulating LH levels. Taken together, these studies indicate PK2 signaling is required for the maintenance of normal female estrous cycles
An initial intercomparison of atmospheric and oceanic climatology for the ICE-5G and ICE-4G models of LGM paleotopography
This paper investigates the impact of the new ICE-5G paleotopography dataset for Last Glacial Maximum (LGM) conditions on a coupled model simulation of the thermal and dynamical state of the glacial atmosphere and on both land surface and sea surface conditions. The study is based upon coupled climate simulations performed with the ocean–atmosphere–sea ice model of intermediate-complexity Climate de Bilt-coupled large-scale ice–ocean (ECBilt-Clio) model. Four simulations focusing on the Last Glacial Maximum [21 000 calendar years before present (BP)] have been analyzed: a first simulation (LGM-4G) that employed the original ICE-4G ice sheet topography and albedo, and a second simulation (LGM-5G) that employed the newly constructed ice sheet topography, denoted ICE-5G, and its respective albedo. Intercomparison of the results obtained in these experiments demonstrates that the LGM-5G simulation delivers significantly enhanced cooling over Canada compared to the LGM-4G simulation whereas positive temperature anomalies are simulated over southern North America and the northern Atlantic. Moreover, introduction of the ICE-5G topography is shown to lead to a deceleration of the subtropical westerlies and to the development of an intensified ridge over North America, which has a profound effect upon the hydrological cycle. Additionally, two flat ice sheet experiments were carried out to investigate the impact of the ice sheet albedo on global climate. By comparing these experiments with the full LGM simulations, it becomes evident that the climate anomalies between LGM-5G and LGM-4G are mainly driven by changes of the earth’s topography
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