3,477 research outputs found
A brief review of Regge calculus in classical numerical relativity
We briefly review past applications of Regge calculus in classical numerical
relativity, and then outline a programme for the future development of the
field. We briefly describe the success of lattice gravity in constructing
initial data for the head-on collision of equal mass black holes, and discuss
recent results on the efficacy of Regge calculus in the continuum limit.Comment: 2 pages, submitted to the Proceedings of the IX Marcel Grossmann
Meeting, Rome, July 2-8, 200
An investigation of the barriers to infectious disease interventions in Indigenous Australian communities
This research focused on two infectious diseases and used them as exemplars to provide a better understanding of barriers to effective interventions for Indigenous Australians. Key messages and five common principles were drawn from publications to inform communities, health staff and government. It was a national investigation using qualitative research methods
Quasi-periodic spatiotemporal models of brain activation in single-trial MEG experiments
Magneto-encephalography (MEG) is an imaging technique which measures neuronal activity in the brain. Even when a subject is in a resting state, MEG data show characteristic spatial and temporal patterns, resulting from electrical current at specific locations in the brain. The key pattern of interest is a ‘dipole’, consisting of two adjacent regions of high and low activation which oscillate over time in an out-of-phase manner. Standard approaches are based on averages over large numbers of trials in order to reduce noise. In contrast, this article addresses the issue of dipole modelling for single trial data, as this is of interest in application areas. There is also clear evidence that the frequency of this oscillation in single trials generally changes over time and so exhibits quasi-periodic rather than periodic behaviour. A framework for the modelling of dipoles is proposed through estimation of a spatiotemporal smooth function constructed as a parametric function of space and a smooth function of time. Quasi-periodic behaviour is expressed in phase functions which are allowed to evolve smoothly over time. The model is fitted in two stages. First, the spatial location of the dipole is identified and the smooth signals characterizing the amplitude functions for each separate pole are estimated. Second, the phase and frequency of the amplitude signals are estimated as smooth functions. The model is applied to data from a real MEG experiment focusing on motor and visual brain processes. In contrast to existing standard approaches, the model allows the variability across trials and subjects to be identified. The nature of this variability is informative about the resting state of the brain
Improved Parallel Algorithms for Spanners and Hopsets
We use exponential start time clustering to design faster and more
work-efficient parallel graph algorithms involving distances. Previous
algorithms usually rely on graph decomposition routines with strict
restrictions on the diameters of the decomposed pieces. We weaken these bounds
in favor of stronger local probabilistic guarantees. This allows more direct
analyses of the overall process, giving: * Linear work parallel algorithms that
construct spanners with stretch and size in unweighted
graphs, and size in weighted graphs. * Hopsets that lead
to the first parallel algorithm for approximating shortest paths in undirected
graphs with work
Three-body problem in 3D space: ground state, (quasi)-exact-solvability
We study aspects of the quantum and classical dynamics of a -body system
in 3D space with interaction depending only on mutual distances. The study is
restricted to solutions in the space of relative motion which are functions of
mutual distances only. It is shown that the ground state (and some other
states) in the quantum case and the planar trajectories in the classical case
are of this type. The quantum (and classical) system for which these states are
eigenstates is found and its Hamiltonian is constructed. It corresponds to a
three-dimensional quantum particle moving in a curved space with special
metric. The kinetic energy of the system has a hidden Lie (Poisson)
algebra structure, alternatively, the hidden algebra typical for the
Calogero model. We find an exactly solvable three-body generalized
harmonic oscillator-type potential as well as a quasi-exactly-solvable
three-body sextic polynomial type potential; both models have an extra
integral.Comment: 24 pages, Appendix about non-equal masses adde
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