223 research outputs found
Carbon to oxygen ratios in extrasolar planetesimals
Observations of small extrasolar planets with a wide range of densities imply a variety of planetary compositions and structures. Currently, the only technique to measure the bulk composition of extrasolar planetary systems is the analysis of planetary debris accreting onto white dwarfs, analogous to abundance studies of meteorites. We present measurements of the carbon and oxygen abundances in the debris of planetesimals at ten white dwarfs observed with the Hubble Space Telescope, along with C/O ratios of debris in six systems with previously reported abundances. We find no evidence for carbon-rich planetesimals, with C/O ) = â0.92, and oxygen-rich objects with C/O less than or equal to that of the bulk Earth. The latter group may have a higher mass fraction of water than the Earth, increasing their relative oxygen abundance
Geophysical and geochemical constraints on geoneutrino fluxes from Earth's mantle
Knowledge of the amount and distribution of radiogenic heating in the mantle
is crucial for understanding the dynamics of the Earth, including its thermal
evolution, the style and planform of mantle convection, and the energetics of
the core. Although the flux of heat from the surface of the planet is robustly
estimated, the contributions of radiogenic heating and secular cooling remain
poorly defined. Constraining the amount of heat-producing elements in the Earth
will provide clues to understanding nebula condensation and planetary formation
processes in early Solar System. Mantle radioactivity supplies power for mantle
convection and plate tectonics, but estimates of mantle radiogenic heat
production vary by a factor of more than 20. Recent experimental results
demonstrate the potential for direct assessment of mantle radioactivity through
observations of geoneutrinos, which are emitted by naturally occurring
radionuclides. Predictions of the geoneutrino signal from the mantle exist for
several established estimates of mantle composition. Here we present novel
analyses, illustrating surface variations of the mantle geoneutrino signal for
models of the deep mantle structure, including those based on seismic
tomography. These variations have measurable differences for some models,
allowing new and meaningful constraints on the dynamics of the planet. An ocean
based geoneutrino detector deployed at several strategic locations will be able
to discriminate between competing compositional models of the bulk silicate
Earth.Comment: 34 pages, 6 tables, 5 figures, 2 supplementary figures; revised
version submitted to Earth Planet. Sci. Let
A Study of the Day - Night Effect for the Super - Kamiokande Detector: I. Time Averaged Solar Neutrino Survival Probability
This is the first of two articles aimed at providing comprehensive
predictions for the day-night (D-N) effect for the Super-Kamiokande detector in
the case of the MSW \nu_e \to \numt transition solution of the solar neutrino
problem. The one-year averaged probability of survival of the solar \nue
crossing the Earth mantle, the core, the inner 2/3 of the core, and the (core +
mantle) is calculated with high precision (better than 1%) using the elliptical
orbit approximation (EOA) to describe the Earth motion around the Sun. Results
for the survival probability in the indicated cases are obtained for a large
set of values of the MSW transition parameters and
from the ``conservative'' regions of the MSW solution,
derived by taking into account possible relatively large uncertainties in the
values of the B and Be neutrino fluxes. Our results show that the
one-year averaged D-N asymmetry in the survival probability for
neutrinos crossing the Earth core can be, in the case of , larger than the asymmetry in the probability for (only mantle
crossing + core crossing) neutrinos by a factor of up to six. The enhancement
is larger in the case of neutrinos crossing the inner 2/3 of the core. This
indicates that the Super-Kamiokande experiment might be able to test the
region of the MSW solution of the solar neutrino
problem by performing selective D-N asymmetry measurements.Comment: LaTeX2e - 18 Text Pages + 21 figures = 39 Pages. - Figures in PS +
text file sk1b14.tex requires two auxiliary files (included
Tri-critical behavior in rupture induced by disorder
We discover a qualitatively new behavior for systems where the load transfer
has limiting stress amplification as in real fiber composites. We find that the
disorder is a relevant field leading to tri--criticality, separating a
first-order regime where rupture occurs without significant precursors from a
second-order regime where the macroscopic elastic coefficient exhibit power law
behavior. Our results are based on analytical analysis of fiber bundle models
and numerical simulations of a two-dimensional tensorial spring-block system in
which stick-slip motion and fracture compete.Comment: Revtex, 10 pages, 4 figures available upon reques
A Study of the Day - Night Effect for the Super-Kamiokande Detector: II. Electron Spectrum Deformations and Day - Night Asymmetries
Using the results of a high precision calculation of the solar neutrino
survival probability for Earth crossing neutrinos in the case of MSW transition solution of the solar neutrino problem, performed
in an earlier study, we derive predictions for the one-year averaged day-night
(D-N) asymmetry in the deformations of the - spectrum to be measured with
the Super - Kamiokande detector, and for the D-N asymmetry in the energy-
integrated one year signal in this detector. The asymmetries are calculated for
solar crossing the Earth mantle only, the core and the (mantle + core)
for a large representative set of values of the MSW transition parameters
and from the ``conservative'' MSW solution
region obtained by taking into account possible uncertainties in the values of
the B and Be neutrino fluxes. The effect of the uncertainties in the
value of the bulk matter density and in the chemical composition of the core,
on the D-N asymmetry predictions is discussed. It is shown, in particular, that
for the one year average D-N asymmetry for
neutrinos crossing the Earth core can be larger than the asymmetry for (only
mantle crossing + core crossing) neutrinos by a factor of up to six. Iso -
(D-N) asymmetry contours in the plane for the
Super - Kamiokande detector are derived in the region \sin^2 2\theta_v \gsim
10^{-4} for only mantle crossing, core crossing and (only mantle crossing +
core crossing) neutrinos. Our results indicate that the Super - Kamiokande
experiment might be able to test the region of the
MSW solution of the solar neutrino problem by performing selective D-N
asymmetry measurements.Comment: LaTeX, 18 pages, 3 Tables, 16 Figures in 7 postscript file
Geo-neutrinos and the Radioactive Power of the Earth
Chemical and physical Earth models agree little as to the radioactive power
of the planet. Each predicts a range of radioactive powers, overlapping
slightly with the other at about 24 TW, and together spanning 14-46 TW.
Approximately 20 % of this radioactive power (3-8 TW) escapes to space in the
form of geo-neutrinos. The remaining 11-38 TW heats the planet with significant
geo-dynamical consequences, appearing as the radiogenic component of the 43-49
TW surface heat flow. The non-radiogenic component of the surface heat flow
(5-38 TW) is presumably primordial, a legacy of the formation and early
evolution of the planet. A constraining measurement of radiogenic heating
provides insights to the thermal history of the Earth and potentially
discriminates chemical and physical Earth models. Radiogenic heating in the
planet primarily springs from unstable nuclides of uranium, thorium, and
potassium. The paths to their stable daughter nuclides include nuclear beta
decays, producing geo-neutrinos. Large sub-surface detectors efficiently record
the energy but not the direction of the infrequent interactions of the highest
energy geo-neutrinos, originating only from uranium and thorium. The measured
energy spectrum of the interactions estimates the relative amounts of these
heat-producing elements, while the intensity estimates planetary radiogenic
power. Recent geo-neutrino observations in Japan and Italy find consistent
values of radiogenic heating. The combined result mildly excludes the lowest
model values of radiogenic heating and, assuming whole mantle convection,
identifies primordial heat loss. Future observations have the potential to
measure radiogenic heating with better precision, further constraining
geological models and the thermal evolution of the Earth.Comment: 48 pages, 11 figures, 8 table
Mutations in BHD and TP53 genes, but not in HNF1β gene, in a large series of sporadic chromophobe renal cell carcinoma
BHD, TP53, and HNF1β on chromosome 17 were studied in 92 cases of renal cell carcinoma (46 chromophobe, 19 clear cell, 18 oncocytoma, and nine papillary). Six, thirteen, and zero cases had, respectively BHD, TP53, and HNF1β mutations, (84% mutations involved chromophobe), suggesting a role for BHD and TP53 in chromophobe subtype
Dragon-kings: mechanisms, statistical methods and empirical evidence
This introductory article presents the special Discussion and Debate volume
"From black swans to dragon-kings, is there life beyond power laws?" published
in Eur. Phys. J. Special Topics in May 2012. We summarize and put in
perspective the contributions into three main themes: (i) mechanisms for
dragon-kings, (ii) detection of dragon-kings and statistical tests and (iii)
empirical evidence in a large variety of natural and social systems. Overall,
we are pleased to witness significant advances both in the introduction and
clarification of underlying mechanisms and in the development of novel
efficient tests that demonstrate clear evidence for the presence of
dragon-kings in many systems. However, this positive view should be balanced by
the fact that this remains a very delicate and difficult field, if only due to
the scarcity of data as well as the extraordinary important implications with
respect to hazard assessment, risk control and predictability.Comment: 20 page
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