Search results for " 65Z05"
showing 3 items of 3 documents
Inexpensive discrete atomistic model technique for studying excitations on infinite disordered media: the case of orientational glass ArN$_2$
2014
Excitations of disordered systems such as glasses are of fundamental and practical interest but computationally very expensive to solve. Here we introduce a technique for modeling these excitations in an infinite disordered medium with a reasonable computational cost. The technique relies on a discrete atomic model to simulate the low-energy behavior of an atomic lattice with molecular impurities. The interaction between different atoms is approximated using a spring like interaction based on the Lennard Jones potential but can be easily adapted to other potentials. The technique allows to solve a statistically representative number of samples with a minimum of computational expense, and us…
An algorithm for computing geometric relative velocities through Fermi and observational coordinates
2013
We present a numerical method for computing the \textit{Fermi} and \textit{observational coordinates} of a distant test particle with respect to an observer. We apply this method for computing some previously introduced concepts of relative velocity: \textit{kinematic}, \textit{Fermi}, \textit{spectroscopic} and \textit{astrometric} relative velocities. We also extend these concepts to non-convex normal neighborhoods and we make some convergence tests, studying some fundamental examples in Schwarzschild and Kerr spacetimes. Finally, we show an alternative method for computing the Fermi and astrometric relative velocities.
Optimal recovery of a radiating source with multiple frequencies along one line
2020
We study an inverse problem where an unknown radiating source is observed with collimated detectors along a single line and the medium has a known attenuation. The research is motivated by applications in SPECT and beam hardening. If measurements are carried out with frequencies ranging in an open set, we show that the source density is uniquely determined by these measurements up to averaging over levelsets of the integrated attenuation. This leads to a generalized Laplace transform. We also discuss some numerical approaches and demonstrate the results with several examples.