4,050 research outputs found
Random Measurable Sets and Covariogram Realisability Problems
We provide a characterization of the realisable set covariograms, bringing a
rigorous yet abstract solution to the problem in materials science. Our
method is based on the covariogram functional for random mesurable sets (RAMS)
and on a result about the representation of positive operators in a locally
compact space. RAMS are an alternative to the classical random closed sets in
stochastic geometry and geostatistics, they provide a weaker framework allowing
to manipulate more irregular functionals, such as the perimeter. We therefore
use the illustration provided by the problem to advocate the use of
RAMS for solving theoretical problems of geometric nature. Along the way, we
extend the theory of random measurable sets, and in particular the local
approximation of the perimeter by local covariograms.Comment: 35p
O palanque da grande imprensa escrita brasileira: os editoriais e os posicionamentos politico-ideológicos
Este trabalho observa como e com que intensidade se manifestam os
posicionamentos político-ideológicos da grande imprensa escrita brasileira
através de uma análise do discurso de seus editoriais. A partir dos resultados
obtidos, que revelam o comprometimento do sujeito imprensa com determinada
percepção de mundo social vinculada ao modelo capitalista de sociedade,
discute alguns dos impactos sobre a prática jornalística derivados dessa
constatação
Provably Secure and Practical Quantum Key Distribution over 307 km of Optical Fibre
Proposed in 1984, quantum key distribution (QKD) allows two users to exchange
provably secure keys via a potentially insecure quantum channel. Since then,
QKD has attracted much attention and significant progress has been made in both
theory and practice. On the application front, however, the operating distance
of practical fibre-based QKD systems is limited to about 150 km, which is
mainly due to the high background noise produced by commonly used semiconductor
single-photon detectors (SPDs) and the stringent demand on the minimum
classical- post-processing (CPP) block size. Here, we present a compact and
autonomous QKD system that is capable of distributing provably-secure
cryptographic key over 307 km of ultra-low-loss optical fibre (51.9 dB loss).
The system is based on a recently developed standard semiconductor (inGaAs)
SPDs with record low background noise and a novel efficient finite-key security
analysis for QKD. This demonstrates the feasibility of practical long-distance
QKD based on standard fibre optic telecom components.Comment: 6+7 pages, 3 figure
New model Hamiltonians for improved orbital basis set convergence
The standard approach in quantum chemistry is to expand the eigenfunctions of the non relativistic Born Oppenheimer Hamiltonian in terms of Slater determinants. The quality improvements of such wavefunctions in terms of the underlying one electron basis is frustratingly slow. The error in the correlation energy decreases only with L 3 where L is the maximum angular momentum present in the basis. The integral evaluation effort that grows with 0(N4) prevents the use of ever larger bases for obtaining more accurate results. Most of the developments are therefore focused on wavefunction models with explicit correlation to get faster convergence. Although highly successful these approaches are computationally very demanding. A different solution might be provided by constructing new operators which take care of the information loss introduced by truncating the basis. In this thesis different routes towards such new operators are investigated.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Active Testing for Face Detection and Localization
We provide a novel search technique which uses a hierarchical model and a mutual information gain heuristic to efficiently prune the search space when localizing faces in images. We show exponential gains in computation over traditional sliding window approaches, while keeping similar performance levels
Modelling of fatigue damage in aluminum cylinder heads
International audienceCar manufacturers are very much concerned with thermal fatigue ....
New model Hamiltonians for improved orbital basis set convergence
The standard approach in quantum chemistry is to expand the eigenfunctions of the non relativistic Born Oppenheimer Hamiltonian in terms of Slater determinants. The quality improvements of such wavefunctions in terms of the underlying one electron basis is frustratingly slow. The error in the correlation energy decreases only with L 3 where L is the maximum angular momentum present in the basis. The integral evaluation effort that grows with 0(N4) prevents the use of ever larger bases for obtaining more accurate results. Most of the developments are therefore focused on wavefunction models with explicit correlation to get faster convergence. Although highly successful these approaches are computationally very demanding. A different solution might be provided by constructing new operators which take care of the information loss introduced by truncating the basis. In this thesis different routes towards such new operators are investigated
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