29,636 research outputs found
Status of the ANTARES Project
The ANTARES collaboration is constructing a neutrino telescope in the
Mediterranean Sea at a depth of 2400 metres, about 40 kilometres off the French
coast near Toulon. The detector will consist of 12 vertical strings anchored at
the sea bottom, each supporting 25 triplets of optical modules equipped with
photomultipliers, yielding sensitivity to neutrinos with energies above some 10
GeV. The effective detector area is roughly 0.1 square kilometres for neutrino
energies exceeding 10 TeV. The measurement of the Cherenkov light emitted by
muons produced in muon-neutrino charged-current interactions in water and
under-sea rock will permit the reconstruction of the neutrino direction with an
accuracy of better than 0.3 degrees at high energies. ANTARES will complement
the field of view of neutrino telescopes at the South Pole in the
low-background searches for point-sources of high-energy cosmic neutrinos and
will also be sensitive to neutrinos produced by WIMP annihilation in the Sun or
the Galactic centre.Comment: 3 pages, 3 figures, to appear in Proc. HEP2003 Europhysics Conf.,
Aachen, Germany, 17-23 July 200
Layoffs, Recall and the Duration of Unemployment
This paper shows that the prospect of recall to previous employer is important for a significant number of the unemployed in the United States and that taking into account the possibility of recalls has important implications for the study of unemployment spell durations. A job search model that allows for recalls is shown to lead naturally to a competing risks specification of the distribution of layoff unemployment spell durations in which recall and the taking of a new job are alternate routes for leaving unemployment. A large sample of individual layoff unemployment spell observations derived from the Panel Study of Income Dynamics is analyzed. The common finding for samples containing individuals with nonnegligible recall prospects of an escape rate from unemployment that declines with spell duration is shown to almost entirely result from a declining recall rate. The apparent declining recall rate may be indicative of important uncontrolled heterogeneity rather than true negative duration dependence. Strong positive duration dependence in the new job finding rate is uncovered for UI recipients. Factors raising the likelihood and value of recall appear to depress the new job finding rate. Substantial differences in the distribution of unemployment spell durations are found for UI recipients and nonrecipients. Large positive jumps in both the recall rate and new job finding rate are apparent around the point of UI benefits exhaustion for UI recipients. The results indicate that the potential duration of UI benefits plays an important role in the timing of recalls and of new job acceptances.
Pipe Poiseuille flow of viscously anisotropic, partially molten rock
Laboratory experiments in which synthetic, partially molten rock is subjected
to forced deformation provide a context for testing hypotheses about the
dynamics and rheology of the mantle. Here our hypothesis is that the aggregate
viscosity of partially molten mantle is anisotropic, and that this anisotropy
arises from deviatoric stresses in the rock matrix. We formulate a model of
pipe Poiseuille flow based on theory by Takei and Holtzman [2009a] and Takei
and Katz [2013]. Pipe Poiseuille is a configuration that is accessible to
laboratory experimentation but for which there are no published results. We
analyse the model system through linearised analysis and numerical simulations.
This analysis predicts two modes of melt segregation: migration of melt from
the centre of the pipe toward the wall and localisation of melt into
high-porosity bands that emerge near the wall, at a low angle to the shear
plane. We compare our results to those of Takei and Katz [2013] for plane
Poiseuille flow; we also describe a new approximation of radially varying
anisotropy that improves the self-consistency of models over those of Takei and
Katz [2013]. This study provides a set of baseline, quantitative predictions to
compare with future laboratory experiments on forced pipe Poiseuille flow of
partially molten mantle.Comment: 23 pages, 7 figures. Submitted to Geophysical Journal International
on 25 April 2014. Revised after reviewer comments and resubmitted on 20
August 201
Consequences of viscous anisotropy in a deforming, two-phase aggregate. Why is porosity-band angle lowered by viscous anisotropy?
In laboratory experiments that impose shear deformation on partially molten
aggregates of initially uniform porosity, melt segregates into high-porosity
sheets (bands in cross-section). The bands emerge at 15-20 degrees to the shear
plane. A model of viscous anisotropy can explain these low angles whereas
previous, simpler models have failed to do so. The anisotropic model is
complex, however, and the reason that it produces low-angle bands has not been
understood. Here we show that there are two mechanisms: (i) suppression of the
well-known tensile instability, and (ii) creation of a new, shear-driven
instability. We elucidate these mechanisms using linearised stability analysis
in a coordinate system that is aligned with the perturbations. We consider the
general case of anisotropy that varies dynamically with deviatoric stress, but
approach it by first considering uniform anisotropy that is imposed a priori
and showing the difference between static and dynamic cases. We extend the
model of viscous anisotropy to include a strengthening in the direction of
maximum compressive stress. Our results support the hypothesis that viscous
anisotropy is the cause of low band-angles in experiments.Comment: 32 pages, 8 figures. Accepted for publication in the Journal of Fluid
Mechanics on 4 October 201
The energetics of melting fertile heterogeneities within the depleted mantle
To explore the consequences of mantle heterogeneity for primary melt production, we develop a
mathematical model of energy conservation for an upwelling, melting body of recycled oceanic crust
embedded in the depleted upper mantle. We consider the endâmember geometric cases of spherical blobs
and tabular veins. The model predicts that thermal diffusion into the heterogeneity can cause a factorâofâ
two increase in the degree of melting for bodies with minimum dimension smaller than âŒ1 km, yielding
melt fractions between 50 and 80%. The role of diffusion is quantified by an appropriately defined Peclet
number, which represents the balance of diffusionâdriven and adiabatic melting. At intermediate Peclet
number, we show that melting a heterogeneity can cool the ambient mantle by up to âŒ20 K (spherical)
or âŒ60 K (tabular) within a distance of two times the characteristic size of the body. At small Peclet
number, where heterogeneities are expected to be in thermal equilibrium with the ambient mantle, we
calculate the energetic effect of pyroxenite melting on the surrounding peridotite; we find that each 5%
of recycled oceanic crust diminishes the peridotite degree of melting by 1â2%. Injection of the magma from
highly molten bodies of recycled oceanic crust into a melting region of depleted upper mantle may nucleate
reactiveâdissolution channels that remain chemically isolated from the surrounding peridotite
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