1,524 research outputs found
Magmatic focusing to mid-ocean ridges: the role of grain size variability and non-Newtonian viscosity
Melting beneath mid-ocean ridges occurs over a region that is much broader
than the zone of magmatic emplacement to form the oceanic crust. Magma is
focused into this zone by lateral transport. This focusing has typically been
explained by dynamic pressure gradients associated with corner flow, or by a
sub-lithospheric channel sloping upward toward the ridge axis. Here we discuss
a novel mechanism for magmatic focusing: lateral transport driven by gradients
in compaction pressure within the asthenosphere. These gradients arise from the
co-variation of melting rate and compaction viscosity. The compaction
viscosity, in previous models, was given as a function of melt fraction and
temperature. In contrast, we show that the viscosity variations relevant to
melt focusing arise from grain-size variability and non-Newtonian creep. The
asthenospheric distribution of melt fraction predicted by our models provides
an improved ex- planation of the electrical resistivity structure beneath one
location on the East Pacific Rise. More generally, although grain size and
non-Newtonian viscosity are properties of the solid phase, we find that in the
context of mid-ocean ridges, their effect on melt transport is more profound
than their effect on the mantle corner-flow.Comment: 20 pages, 4 figures, 1 tabl
DIOS: the Diffuse Intergalactic Oxygen Surveyor
We present our proposal for a small X-ray mission DIOS (Diffuse Intergalactic
Oxygen Surveyor), consisting of a 4-stage X-ray telescope and an array of TES
microcalorimeters, cooled with mechanical coolers, with a total weight of about
400 kg. The mission will perform survey observations of warm-hot intergalactic
medium using OVII and OVIII emission lines, with the energy coverage up to 1.5
keV. The wide field of view of about 50' diameter, superior energy resolution
close to 2 eV FWHM, and very low background will together enable us a wide
range of science for diffuse X-ray sources. We briefly describe the design of
the satellite, performance of the subsystems and the expected results.Comment: 9 pages, 11 figures, a proceedings of SPIE "Astronomical Telescopes
and Instrumentation" 200
Azimuthally Resolved X-Ray Spectroscopy to the Edge of the Perseus Cluster
We present the results from extensive, new observations of the Perseus
Cluster of galaxies, obtained as a Suzaku Key Project. The 85 pointings
analyzed span eight azimuthal directions out to 2 degrees = 2.6 Mpc, to and
beyond the virial radius r_200 ~ 1.8 Mpc, offering the most detailed X-ray
observation of the intracluster medium (ICM) at large radii in any cluster to
date. The azimuthally averaged density profile for r>0.4r_200 is relatively
flat, with a best-fit power-law index of 1.69+/-0.13 significantly smaller than
expected from numerical simulations. The entropy profile in the outskirts lies
systematically below the power-law behavior expected from large-scale structure
formation models which include only the heating associated with gravitational
collapse. The pressure profile beyond ~0.6r_200 shows an excess with respect to
the best-fit model describing the SZ measurements for a sample of clusters
observed with Planck. The inconsistency between the expected and measured
density, entropy, and pressure profiles can be explained primarily by an
overestimation of the density due to inhomogeneous gas distribution in the
outskirts; there is no evidence for a bias in the temperature measurements
within the virial radius. We find significant differences in thermodynamic
properties of the ICM at large radii along the different arms. Along the
cluster minor axis, we find a flattening of the entropy profiles outside
~0.6r_200, while along the major axis, the entropy rises all the way to the
outskirts. Correspondingly, the inferred gas clumping factor is typically
larger along the minor than along the major axis.Comment: submitted to MNRA
Warm-Hot Intergalactic Medium Associated with the Coma Cluster
We present our XMM-Newton RGS observations of X Comae, an AGN behind the Coma cluster. We detect absorption by NeIX and OVIII at the redshift of Coma with an equivalent width of 3.3+/-1.8 eV and 1.7+/-1.3 eV, respectively (90% confidence errors or 2.3 sigma and 1.9 sigma confidence detections determined from Monte Carlo simulations). The combined significance of both lines is 3.0 sigma, again determined from Monte Carlo simulations. The same observation yields a high statistics EPIC spectrum of the Coma cluster gas at the position of X Comae. We detect emission by NeIX with a flux of 2.5+/-1.2 x 10^-8 photons cm^-2 s^-1 arcmin^-2 (90% confidence errors or 3.4 sigma confidence detection). These data permit a number of diagnostics to determine the properties of the material causing the absorption and producing the emission. Although a wide range of properties is permitted, values near the midpoint of the range are T = 4 x 10^6 K, n_H = 6 x 10^-6 cm^-3 corresponding to an overdensity with respect to the mean of 32, line of sight path length through it 41 Z/Zsolar^-1 Mpc where Z/Zsolar is the neon metallicity relative to solar. All of these properties are what has been predicted of the warm-hot intergalactic medium (WHIM), so we conclude that we have detected the WHIM associated with the Coma cluster
Quasi-linear Stokes phenomenon for the second Painlev\'e transcendent
Using the Riemann-Hilbert approach, we study the quasi-linear Stokes
phenomenon for the second Painlev\'e equation . The
precise description of the exponentially small jump in the dominant solution
approaching as is given. For the asymptotic power
expansion of the dominant solution, the coefficient asymptotics is found.Comment: 19 pages, LaTe
Operation of an ADR Using Helium Exchange Gas as a Substitute for a Failed Heat Switch
The Soft X-ray Spectrometer (SXS) is one of four instruments on the Japanese Astro-H mission, which is currently planned for launch in late 2015. The SXS will perform imaging spectroscopy in the soft X-ray band (0.3-12 keV) using a 6 6 pixel array of microcalorimeters cooled to 50 mK. The detectors are cooled by a 3-stage adiabatic demagnetization refrigerator (ADR) that rejects heat to either a superfluid helium tank (at 1.2 K) or to a 4.5 K Joule-Thomson (JT) cryocooler. Four gas-gap heat switches are used in the assembly to manage heat flow between the ADR stages and the heat sinks. The engineering model (EM) ADR was assembled and performance tested at NASA/GSFC in November 2011, and subsequently installed in the EM dewar at Sumitomo Heavy Industries, Japan. During the first cooldown in July 2012, a failure of the heat switch that linked the two colder stages of the ADR to the helium tank was observed. Operation of the ADR requires some mechanism for thermally linking the salt pills to the heat sink, and then thermally isolating them. With the failed heat switch unable to perform this function, an alternate plan was devised which used carefully controlled amounts of exchange gas in the dewar's guard vacuum to facilitate heat exchange. The process was successfully demonstrated in November 2012, allowing the ADR to cool the detectors to 50 mK for hold times in excess of 10 h. This paper describes the exchange-gas-assisted recycling process, and the strategies used to avoid helium contamination of the detectors at low temperature
Measurement of inclusive charged current interactions on carbon in a few-GeV neutrino beam
The SciBooNE Collaboration reports a measurement of inclusive charged current
interactions of muon neutrinos on carbon with an average energy of 0.8 GeV
using the Fermilab Booster Neutrino Beam. We compare our measurement with two
neutrino interaction simulations: NEUT and NUANCE. The charged current
interaction rates (product of flux and cross section) are extracted by fitting
the muon kinematics, with a precision of 6-15% for the energy dependent and 3%
for the energy integrated analyses. We also extract CC inclusive interaction
cross sections from the observed rates, with a precision of 10-30% for the
energy dependent and 8% for the energy integrated analyses. This is the first
measurement of the CC inclusive cross section on carbon around 1 GeV. These
results can be used to convert previous SciBooNE cross section ratio
measurements to absolute cross section values.Comment: 21 pages, 16 figures. Accepted by Phys. Rev. D. Minor revisions to
match the accepted versio
How does cultural capital affect educational performance: Signals or skills?
In this paper, we test two mechanisms through which cultural capital might affect educational performance: (a) teachers misinterpreting cultural capital as signals of academic brilliance and (b) cultural capital fostering skills in children that enhance educational performance. We analyse data from the ECLSâK and ECLSâK:2011 from the United States and focus on three aspects of childrenâs cultural capital: participation in performing arts, reading interest and participation in athletics and clubs. We find that (1) none of the three aspects of cultural capital that we consider affects teachersâ evaluations of childrenâs academic skills; (2) reading interest has a direct positive effect on educational performance; and (3) the direct effect of reading interest on educational performance does not depend on schooling context. Our results provide little support for the hypothesis that cultural capital operates via signals about academic brilliance. Instead, they suggest that cultural capital fosters skills in children that enhance educational performance. We discuss the theoretical implications of our findings.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152694/1/bjos12711.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152694/2/bjos12711_am.pd
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