397 research outputs found
A review of astrophysics experiments on intense lasers
Astrophysics has traditionally been pursued at astronomical observatories and on theorists’ computers. Observations record images from space, and theoretical models are developed to explain the observations. A component often missing has been the ability to test theories and models in an experimental setting where the initial and final states are well characterized. Intense lasers are now being used to recreate aspects of astrophysical phenomena in the laboratory, allowing the creation of experimental testbeds where theory and modeling can be quantitatively tested against data. We describe here several areas of astrophysics—supernovae, supernova remnants, gamma-ray bursts, and giant planets—where laser experiments are under development to test our understanding of these phenomena. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71013/2/PHPAEN-7-5-1641-1.pd
A game-theoretic approach to the enforcement of global consistency in multi-view feature matching
In this paper we introduce a robust matching technique that allows to operate a very accurate selection of corresponding feature points from multiple views. Robustness is achieved by enforcing global geometric consistency at an early stage of the matching process, without the need of ex-post verification through reprojection. Two forms of global consistency are proposed, but in both cases they are reduced to pairwise compatibilities making use of the size and orientation information provided by common feature descriptors. Then a game-theoretic approach is used to select a maximally consistent set of candidate matches, where highly compatible matches are enforced while incompatible correspondences are driven to extinction. The effectiveness of the approach in estimating camera parameters for bundle adjustment is assessed and compared with state-of-the-art techniques. © 2010 Springer-Verlag Berlin Heidelberg
Progressive Structure from Motion
Structure from Motion or the sparse 3D reconstruction out of individual
photos is a long studied topic in computer vision. Yet none of the existing
reconstruction pipelines fully addresses a progressive scenario where images
are only getting available during the reconstruction process and intermediate
results are delivered to the user. Incremental pipelines are capable of growing
a 3D model but often get stuck in local minima due to wrong (binding) decisions
taken based on incomplete information. Global pipelines on the other hand need
the access to the complete viewgraph and are not capable of delivering
intermediate results. In this paper we propose a new reconstruction pipeline
working in a progressive manner rather than in a batch processing scheme. The
pipeline is able to recover from failed reconstructions in early stages, avoids
to take binding decisions, delivers a progressive output and yet maintains the
capabilities of existing pipelines. We demonstrate and evaluate our method on
diverse challenging public and dedicated datasets including those with highly
symmetric structures and compare to the state of the art.Comment: Accepted to ECCV 201
The MAJORANA DEMONSTRATOR: A Search for Neutrinoless Double-beta Decay of Germanium-76
The {\sc Majorana} collaboration is searching for neutrinoless double beta
decay using Ge, which has been shown to have a number of advantages in
terms of sensitivities and backgrounds. The observation of neutrinoless
double-beta decay would show that lepton number is violated and that neutrinos
are Majorana particles and would simultaneously provide information on neutrino
mass. Attaining sensitivities for neutrino masses in the inverted hierarchy
region, meV, will require large, tonne-scale detectors with extremely
low backgrounds, at the level of 1 count/t-y or lower in the region of
the signal. The {\sc Majorana} collaboration, with funding support from DOE
Office of Nuclear Physics and NSF Particle Astrophysics, is constructing the
{\sc Demonstrator}, an array consisting of 40 kg of p-type point-contact
high-purity germanium (HPGe) detectors, of which 30 kg will be enriched
to 87% in Ge. The {\sc Demonstrator} is being constructed in a clean
room laboratory facility at the 4850' level (4300 m.w.e.) of the Sanford
Underground Research Facility (SURF) in Lead, SD. It utilizes a compact graded
shield approach with the inner portion consisting of ultra-clean Cu that is
being electroformed and machined underground. The primary aim of the {\sc
Demonstrator} is to show the feasibility of a future tonne-scale measurement in
terms of backgrounds and scalability.Comment: Proceedings for the MEDEX 2013 Conferenc
Relativistic laser channeling in plasmas for fast ignition
We report an experimental observation suggesting plasma channel formation by focusing a relativistic laser pulse into a long-scale-length preformed plasma. The channel direction coincides with the laser axis. Laser light transmittance measurement indicates laser channeling into the high-density plasma with relativistic self-focusing. A three-dimensional particle-in-cell simulation reproduces the plasma channel and reveals that the collimated hot-electron beam is generated along the laser axis in the laser channeling. These findings hold the promising possibility of fast heating a dense fuel plasma with a relativistic laser pulse
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