3,962 research outputs found
Hypersurfaces and the Weil conjectures
We give a proof that the Riemann hypothesis for hypersurfaces over finite
fields implies the result for all smooth proper varieties, by a deformation
argument which does not use the theory of Lefschetz pencils or the l-adic
Fourier transform.Comment: 12 pages; a few trivial correction
Fabrication and test of lightweight honeycomb sandwich structures Final report
Fabrication and testing of lightweight honeycomb sandwich structure
Subclustering and Luminous-Dark Matter Segregation in Galaxy Clusters
We have performed a series of N-body experiments on Connection Machine-5 in
order to simulate the formation of galaxy clusters gravitationally dominated by
a massive dark background. In accordance with previous authors we find an
extremely inhomogeneous evolution where subcondensations are continually formed
and merged. The final distribution of galaxies is more centrally condensed than
that of dark matter particles. We have analyzed the origin of this galaxy-dark
matter segregation and also the origin of subclustering leading to this effect.
We have then analysed, analytically and numerically, the dependence of final
segregation on the physical parameters characterizing the model of
protocluster. We also find that such a segregation persists even when inelastic
encounters of dark halos around galaxies are taken into account. We conclude
that this effect cannot be in general avoided in any hierarchical clustering
scenario.Comment: 26 pages plus 13 figures (4 of which, not included, available upon
request to [email protected]), postscript, Preprint OP-9303
A storage and access architecture for efficient query processing in spatial database systems
Due to the high complexity of objects and queries and also due to extremely
large data volumes, geographic database systems impose stringent requirements on their
storage and access architecture with respect to efficient query processing. Performance
improving concepts such as spatial storage and access structures, approximations, object
decompositions and multi-phase query processing have been suggested and analyzed as
single building blocks. In this paper, we describe a storage and access architecture which
is composed from the above building blocks in a modular fashion. Additionally, we incorporate
into our architecture a new ingredient, the scene organization, for efficiently
supporting set-oriented access of large-area region queries. An experimental performance
comparison demonstrates that the concept of scene organization leads to considerable
performance improvements for large-area region queries by a factor of up to 150
Non-linear Relaxation of Interacting Bosons Coherently Driven on a Narrow Optical Transition
We study the dynamics of a two-component Bose-Einstein condensate (BEC) of
Yb atoms coherently driven on a narrow optical transition. The
excitation transfers the BEC to a superposition of states with different
internal and momentum quantum numbers. We observe a crossover with decreasing
driving strength between a regime of damped oscillations, where coherent
driving prevails, and an incoherent regime, where relaxation takes over.
Several relaxation mechanisms are involved: inelastic losses involving two
excited atoms, leading to a non-exponential decay of populations; Doppler
broadening due to the finite momentum width of the BEC and inhomogeneous
elastic interactions, both leading to dephasing and to damping of the
oscillations. We compare our observations to a two-component Gross-Pitaevskii
(GP) model that fully includes these effects. For small or moderate densities,
the damping of the oscillations is mostly due to Doppler broadening. In this
regime, we find excellent agreement between the model and the experimental
results. For higher densities, the role of interactions increases and so does
the damping rate of the oscillations. The damping in the GP model is less
pronounced than in the experiment, possibly a hint for many-body effects not
captured by the mean-field description.Comment: 7 pages, 4 figures; supplementary material available as ancillary
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