3,439 research outputs found
Fabrication and test of lightweight honeycomb sandwich structures Final report
Fabrication and testing of lightweight honeycomb sandwich structure
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
fil
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
Simple heuristics for the assembly line worker assignment and balancing problem
We propose simple heuristics for the assembly line worker assignment and
balancing problem. This problem typically occurs in assembly lines in sheltered
work centers for the disabled. Different from the classical simple assembly
line balancing problem, the task execution times vary according to the assigned
worker. We develop a constructive heuristic framework based on task and worker
priority rules defining the order in which the tasks and workers should be
assigned to the workstations. We present a number of such rules and compare
their performance across three possible uses: as a stand-alone method, as an
initial solution generator for meta-heuristics, and as a decoder for a hybrid
genetic algorithm. Our results show that the heuristics are fast, they obtain
good results as a stand-alone method and are efficient when used as a initial
solution generator or as a solution decoder within more elaborate approaches.Comment: 18 pages, 1 figur
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
Reduction of Birth Weight Among Infants Born to Adolescents: MaternalâFetal Growth Competition
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72838/1/j.1749-6632.1997.tb48213.x.pd
Using an interactive water bottle to target fluid adherence in pediatric kidney transplant recipients: A pilot study
Hydration is important postârenal transplant to maintain adequate renal perfusion and graft function. Adherence to fluid recommendations is challenging given barriers to staying hydrated. There are no studies of adherence to fluid intake recommendations following pediatric renal transplant. Through this pilot study, we sought to determine whether the use of a commercially available interactive water bottle would lead to better adherence to recommended fluid intake and improved kidney functioning postâtransplant relative to standard of care. Participants included 32 youth ages 7â19 â„1Â month postâkidney transplant randomized to the intervention (HydraCoach Âź water bottle) or standard education control group. Laboratory records were reviewed for serum chemistries (Na, BUN , creatinine) at baseline and oneâmonth followâup, and participants recorded daily fluid intake for 28Â days. Those in the intervention group were significantly more likely to meet or exceed their fluid target, but this did not translate into better kidney functioning. Participants in the intervention group largely reported satisfaction with the water bottle and were likely to continue its use. While an interactive water bottle providing realâtime feedback may be a promising intervention to help pediatric kidney transplant patients meet fluid goals, it did not appear to impact kidney function.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109912/1/petr12385.pd
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