262 research outputs found
Normal fault earthquakes or graviquakes
Earthquakes are dissipation of energy throughout elastic waves. Canonically is the elastic energy
accumulated during the interseismic period. However, in crustal extensional settings, gravity is
the main energy source for hangingwall fault collapsing. Gravitational potential is about 100 times
larger than the observed magnitude, far more than enough to explain the earthquake. Therefore,
normal faults have a different mechanism of energy accumulation and dissipation (graviquakes) with
respect to other tectonic settings (strike-slip and contractional), where elastic energy allows motion
even against gravity. The bigger the involved volume, the larger is their magnitude. The steeper the
normal fault, the larger is the vertical displacement and the larger is the seismic energy released.
Normal faults activate preferentially at about 60° but they can be shallower in low friction rocks. In
low static friction rocks, the fault may partly creep dissipating gravitational energy without releasing
great amount of seismic energy. The maximum volume involved by graviquakes is smaller than the
other tectonic settings, being the activated fault at most about three times the hypocentre depth,
explaining their higher b-value and the lower magnitude of the largest recorded events. Having
different phenomenology, graviquakes show peculiar precursor
Precise pose estimation of the NASA Mars 2020 Perseverance rover through a stereo-vision-based approach
Visual Odometry (VO) is a fundamental technique to enhance the navigation capabilities of planetary exploration rovers. By processing the images acquired during the motion, VO methods provide estimates of the relative position and attitude between navigation steps with the detection and tracking of two-dimensional (2D) image keypoints. This method allows one to mitigate trajectory inconsistencies associated with slippage conditions resulting from dead-reckoning techniques. We present here an independent analysis of the high-resolution stereo images of the NASA Mars 2020 Perseverance rover to retrieve its accurate localization on sols 65, 66, 72, and 120. The stereo pairs are processed by using a 3D-to-3D stereo-VO approach that is based on consolidated techniques and accounts for the main nonlinear optical effects characterizing real cameras. The algorithm is first validated through the analysis of rectified stereo images acquired by the NASA Mars Exploration Rover Opportunity, and then applied to the determination of Perseverance's path. The results suggest that our reconstructed path is consistent with the telemetered trajectory, which was directly retrieved onboard the rover's system. The estimated pose is in full agreement with the archived rover's position and attitude after short navigation steps. Significant differences (~10–30 cm) between our reconstructed and telemetered trajectories are observed when Perseverance traveled distances larger than 1 m between the acquisition of stereo pairs
The -cleus experiment: A gram-scale fiducial-volume cryogenic detector for the first detection of coherent neutrino-nucleus scattering
We discuss a small-scale experiment, called -cleus, for the first
detection of coherent neutrino-nucleus scattering by probing nuclear-recoil
energies down to the 10 eV-regime. The detector consists of low-threshold
CaWO and AlO calorimeter arrays with a total mass of about 10 g and
several cryogenic veto detectors operated at millikelvin temperatures.
Realizing a fiducial volume and a multi-element target, the detector enables
active discrimination of , neutron and surface backgrounds. A first
prototype AlO device, operated above ground in a setup without
shielding, has achieved an energy threshold of eV and further
improvements are in reach. A sensitivity study for the detection of coherent
neutrino scattering at nuclear power plants shows a unique discovery potential
(5) within a measuring time of weeks. Furthermore, a site
at a thermal research reactor and the use of a radioactive neutrino source are
investigated. With this technology, real-time monitoring of nuclear power
plants is feasible.Comment: 14 pages, 19 figure
The SciCryo Project and Cryogenic Scintillation of for Dark Matter
International audienceWe discuss cryogenic scintillation of Al2O3. Room-temperature measurements with α particles are first carried out to study effect of Ti concentration on response. Measurements under X-rays between room temperature and 10 K confirm a doubling of light output. The integration of a scintillation-phonon detector into an ionization-phonon dark matter search is underway, and the quenching factor for neutrons has been verified
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