2,684 research outputs found
Geo-neutrinos and Earth Models
We present the current status of geo-neutrino measurements and their
implications for radiogenic heating in the mantle. Earth models predict
different levels of radiogenic heating and, therefore, different geo-neutrino
fluxes from the mantle. Seismic tomography reveals features in the deep mantle
possibly correlated with radiogenic heating and causing spatial variations in
the mantle geo-neutrino flux at the Earth surface. An ocean-based observatory
offers the greatest sensitivity to the mantle flux and potential for resolving
Earth models and mantle features. Refinements to estimates of the geo-neutrino
flux from continental crust reduce uncertainty in measurements of the mantle
flux, especially measurements from land-based observatories. These refinements
enable the resolution of Earth models using the combined measurements from
multiple continental observatories.Comment: 9 pages, 4 figures; Contributed paper TAUP 201
Dislocation interactions and crack nucleation in a fatigued near-alpha titanium alloy
Dislocation interactions at the crack nucleation site were investigated in near-alpha titanium alloy Ti-6242Si subjected to low cycle fatigue. Cyclic plastic strain in the alloy resulted in dislocation pile-ups in the primary alpha grains, nucleated at the boundaries between the primary alpha and the two-phase regions. These two phase regions provided a barrier to slip transfer between primary alpha grains. We suggest that crack nucleation occurred near the basal plane of primary alpha grains by the subsurface double-ended pile-up mechanism first conceived by Tanaka and Mura. Superjogs on the basal dislocations were observed near the crack nucleation location. The two phase regions showed direct transmission of dislocations between secondary alpha plates, transmitted through the beta ligaments as , which then decompose into dislocation networks in the beta. The beta ligaments themselves do not appear to form an especially impenetrable barrier to slip, in agreement with the micropillar and crystal plasticity investigations of Zhang et al
Estimating terrestrial uranium and thorium by antineutrino flux measurements
Uranium and thorium within the Earth produce a major portion of terrestrial
heat along with a measurable flux of electron antineutrinos. These elements are
key components in geophysical and geochemical models. Their quantity and
distribution drive the dynamics, define the thermal history, and are a
consequence of the differentiation of the Earth. Knowledge of uranium and
thorium concentrations in geological reservoirs relies largely on geochemical
model calculations. This research report describes the methods and criteria to
experimentally determine average concentrations of uranium and thorium in the
continental crust and in the mantle using site-specific measurements of the
terrestrial antineutrino flux. Optimal, model-independent determinations
involve significant exposures of antineutrino detectors remote from nuclear
reactors at both a mid-continental and a mid-oceanic site. This would require
major, new antineutrino detection projects. The results of such projects could
yield a greatly improved understanding of the deep interior of the Earth.Comment: 15 pages, 2 figure
Lens magnification by CL0024+1654 in the U and R band
[ABRIDGED] We estimate the total mass distribution of the galaxy cluster
CL0024+1654 from the measured source depletion due to lens magnification in the
R band. Within a radius of 0.54Mpc/h, a total projected mass of
(8.1+/-3.2)*10^14 M_sol/h (EdS) is measured, which corresponds to a mass-
to-light ratio of M/L(B)=470+/-180. We compute the luminosity function of
CL0024+1654 in order to estimate contamination of the background source counts
from cluster galaxies. Three different magnification-based reconstruction
methods are employed using both local and non-local techniques. We have
modified the standard single power-law slope number count theory to incorporate
a break and applied this to our observations. Fitting analytical magnification
profiles of different cluster models to the observed number counts, we find
that the cluster is best described either by a NFW model with scale radius
r_s=334+/-191 kpc/h and normalisation kappa_s=0.23+/-0.08 or a power-law
profile with slope xi=0.61+/-0.11, central surface mass density
kappa_0=1.52+/-0.20 and assuming a core radius of r_core=35 kpc/h. The NFW
model predicts that the cumulative projected mass contained within a radius R
scales as M(<R)=2.9*10^14*(R/1')^[1.3-0.5lg (R/1')] M_sol/h. Finally, we have
exploited the fact that flux magnification effectively enables us to probe
deeper than the physical limiting magnitude of our observations in searching
for a change of slope in the U band number counts. We rule out both a total
flattening of the counts with a break up to U_AB<=26.6 and a change of slope,
reported by some studies, from dlog N/dm=0.4->0.15 up to U_AB<=26.4 with 95%
confidence.Comment: 19 pages, 12 figures, submitted to A&A. New version includes more
robust U band break analysis and contamination estimates, plus new plot
Cassiopeia A: dust factory revealed via submillimetre polarimetry
If Type-II supernovae - the evolutionary end points of short-lived, massive
stars - produce a significant quantity of dust (>0.1 M_sun) then they can
explain the rest-frame far-infrared emission seen in galaxies and quasars in
the first Gyr of the Universe. Submillimetre observations of the Galactic
supernova remnant, Cas A, provided the first observational evidence for the
formation of significant quantities of dust in Type-II supernovae. In this
paper we present new data which show that the submm emission from Cas A is
polarised at a level significantly higher than that of its synchrotron
emission. The orientation is consistent with that of the magnetic field in Cas
A, implying that the polarised submm emission is associated with the remnant.
No known mechanism would vary the synchrotron polarisation in this way and so
we attribute the excess polarised submm flux to cold dust within the remnant,
providing fresh evidence that cosmic dust can form rapidly. This is supported
by the presence of both polarised and unpolarised dust emission in the north of
the remnant, where there is no contamination from foreground molecular clouds.
The inferred dust polarisation fraction is unprecedented (f_pol ~ 30%) which,
coupled with the brief timescale available for grain alignment (<300 yr),
suggests that supernova dust differs from that seen in other Galactic sources
(where f_pol=2-7%), or that a highly efficient grain alignment process must
operate in the environment of a supernova remnant.Comment: In press at MNRAS, 10 pages, print in colou
Hanohano:A Deep Ocean Antineutrino Observatory
This paper presents the science potential of a deep ocean antineutrino
observatory being developed at Hawaii and elsewhere. The observatory design
allows for relocation from one site to another. Positioning the observaory some
60 km distant from a nuclear reactor complex enables preecision measurement of
neutrino mixing parameters, leading to a determination of neutrino mass
hierarchy and theta_13. At a mid-Pacific location, the observatory measures the
flux of uranium and thorium decay series antineutrinos from earth's mantle and
performs a sensitive search for a hypothetical natural fission reactor in
earth's core. A subequent deployment at another mid-ocean location would test
lateral homogeneity of uranium and thorium in earth's mantle. These
measurements have significance for earth energy studies.Comment: Poster presented at ICHEP08, Philadelphia, USA, July 2008. 3 pages.
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