3,526 research outputs found
Robust Hydraulic Fracture Monitoring (HFM) of Multiple Time Overlapping Events Using a Generalized Discrete Radon Transform
In this work we propose a novel algorithm for multiple-event localization for
Hydraulic Fracture Monitoring (HFM) through the exploitation of the sparsity of
the observed seismic signal when represented in a basis consisting of space
time propagators. We provide explicit construction of these propagators using a
forward model for wave propagation which depends non-linearly on the problem
parameters - the unknown source location and mechanism of fracture, time and
extent of event, and the locations of the receivers. Under fairly general
assumptions and an appropriate discretization of these parameters we first
build an over-complete dictionary of generalized Radon propagators and assume
that the data is well represented as a linear superposition of these
propagators. Exploiting this structure we propose sparsity penalized algorithms
and workflow for super-resolution extraction of time overlapping multiple
seismic events from single well data
On the Potential of Large Ring Lasers
We describe a new ring laser with area A = 833 m^2 and update performance
statistics for several such machines. Anandan & Chaio 1982 judged ring lasers
inferior to matter interferometers as possible detectors of gravitational
waves. However, we note that geophysically interesting results have been
obtained from large ring lasers and that there is still a lot of room for
improvements.Comment: accepted optics communication
Stochastic excitation of acoustic modes in stars
For more than ten years, solar-like oscillations have been detected and
frequencies measured for a growing number of stars with various characteristics
(e.g. different evolutionary stages, effective temperatures, gravities, metal
abundances ...).
Excitation of such oscillations is attributed to turbulent convection and
takes place in the uppermost part of the convective envelope. Since the
pioneering work of Goldreich & Keely (1977), more sophisticated theoretical
models of stochastic excitation were developed, which differ from each other
both by the way turbulent convection is modeled and by the assumed sources of
excitation. We review here these different models and their underlying
approximations and assumptions.
We emphasize how the computed mode excitation rates crucially depend on the
way turbulent convection is described but also on the stratification and the
metal abundance of the upper layers of the star. In turn we will show how the
seismic measurements collected so far allow us to infer properties of turbulent
convection in stars.Comment: Notes associated with a lecture given during the fall school
organized by the CNRS and held in St-Flour (France) 20-24 October 2008 ; 39
pages ; 11 figure
Towards the Chalonge 16th Paris Cosmology Colloquium 2012: Highlights and Conclusions of the Chalonge 15th Paris Cosmology Colloquium 2011
The Chalonge 15th Paris Cosmology Colloquium 2011 was held on 20-22 July in
the historic Paris Observatory's Perrault building, in the Chalonge School
spirit combining real cosmological/astrophysical data and hard theory
predictive approach connected to them in the Warm Dark Matter Standard Model of
the Universe: News and reviews from Herschel, QUIET, Atacama Cosmology
Telescope (ACT), South Pole Telescole (SPT), Planck, PIXIE, the JWST, UFFO,
KATRIN and MARE experiments; astrophysics, particle and nuclear physics warm
dark matter (DM) searches and galactic observations, related theory and
simulations, with the aim of synthesis, progress and clarification. Philippe
Andre, Peter Biermann, Pasquale Blasi, Daniel Boyanovsky, Carlo Burigana,
Hector de Vega, Joanna Dunkley, Gerry Gilmore, Alexander Kashlinsky, Alan
Kogut, Anthony Lasenby, John Mather, Norma Sanchez, Alexei Smirnov, Sylvaine
Turck-Chieze present here their highlights of the Colloquium. Ayuki Kamada and
Sinziana Paduroiu present here their poster highlights. LambdaWDM (Warm Dark
Matter) is progressing impressively over LambdaCDM whose galactic scale crisis
and decline are staggering. The International School Daniel Chalonge issued an
statement of strong support to the James Webb Space Telescope (JSWT). The
Daniel Chalonge Medal 2011 was awarded to John C. Mather, Science PI of the
JWST. Summary and conclusions are presented by H. J. de Vega, M. C. Falvella
and N. G. Sanchez. Overall, LambdaWDM and keV scale DM particles deserve
dedicated astronomical and laboratory experimental searches, theoretical work
and simulations. KATRIN experiment in the future could perhaps adapt its set-up
to look to keV scale sterile neutrinos. It will be a a fantastic discovery to
detect dark matter in a beta decay. Photos of the Colloquium are included.
(Abridged)Comment: 65 pages, 21 figure
Excitation of the Slichter mode by collision with a meteoroid or pressure variations at the surface and core boundaries
We use a normal-mode formalism to compute the response of a spherical,
self-gravitating anelastic PREM-like Earth model to various excitation sources
at the Slichter mode period. The formalism makes use of the theory of the
Earth's free oscillations based upon an eigenfunction expansion methodology. We
determine the complete response in the form of Green's function obtained from a
generalization of Betti's reciprocity theorem. Surficial (surface load, fluid
core pressure), internal (earthquakes, explosions) and external (object impact)
sources of excitation are investigated to show that the translational motion of
the inner-core would be best excited by a pressure acting at the core
boundaries at time-scales shorter than the Slichter eigenperiods
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