261,266 research outputs found
Collective excitations in the inner crust of neutron stars : supergiant resonances
We investigate the nuclear collective excitations of Wigner-Seitz cells
containing nuclear clusters immersed in a gas of neutrons. This baryonic
non-uniform system is specific to the structure of inner crust matter of
neutron stars. The collective excitations are studied in the framework of a
spherical Hartree-Fock-Bogoliubov + Quasiparticle Random Phase Approximation,
formulated in coordinate representation. The calculations are done for two
representative Wigner-Seitz cells with baryonic density equal to 0.02 fm
and 0.08 fm. It is shown that the excitations with low multipolarities
are concentrated almost entirely in one strongly collective mode which exhausts
a very large fraction of the energy-weighted sum rule. Since these collective
modes are located at very low energies compared to the giant resonances in
standard nuclei, they may affect significantly the specific heat of baryonic
inner crust matter of neutron stars.Comment: 6 pages, 4 figure
A geometric constraint over k-dimensional objects and shapes subject to business rules
This report presents a global constraint that enforces rules written
in a language based on arithmetic and first-order logic to hold among a set of objects. In a first step, the rules are rewritten to Quantifier-Free Presburger Arithmetic (QFPA) formulas. Secondly, such
formulas are compiled to generators of k-dimensional forbidden sets. Such generators are a generalization of the indexicals of cc(FD). Finally, the forbidden sets generated by such indexicals are
aggregated by a sweep-based algorithm and used for filtering. The business rules allow to express a great variety of packing and placement constraints, while admitting efficient and effective filtering of the domain variables of the k-dimensional object, without the need to use spatial data structures. The constraint was used to directly encode the packing knowledge of a major car manufacturer and tested on a set of real packing problems under these rules, as well as on a packing-unpacking problem
Yang-Yang thermodynamics on an atom chip
We investigate the behavior of a weakly interacting nearly one-dimensional
(1D) trapped Bose gas at finite temperature. We perform in situ measurements of
spatial density profiles and show that they are very well described by a model
based on exact solutions obtained using the Yang-Yang thermodynamic formalism,
in a regime where other, approximate theoretical approaches fail. We use
Bose-gas focusing [Shvarchuck etal., Phys. Rev. Lett. 89, 270404 (2002)] to
probe the axial momentum distribution of the gas, and find good agreement with
the in situ results.Comment: extended introduction and conclusions, and minor changes throughout;
accepted for publication in Phys. Rev. Let
Towards Low Cost Coupling Structures for Short-Distance Optical Interconnections
The performance of short distance optical interconnections in general relies
very strongly on coupling structures, since they will determine the overall
efficiency of the system to a large extent. Different configurations can be
considered and a variety of manufacturing technologies can be used. We present
two different discrete and two different integrated coupling components which
can be used to deflect the light beam over 90 degrees and can play a crucial
role when integrating optical interconnections in printed circuit boards. The
fabrication process of the different coupling structures is discussed and
experimental results are shown. The main characteristics of the coupling
structures are given. The main advantages and disadvantages of the different
components are discussed
Potential environmental impact of tidal energy extraction in the Pentland Firth at large spatial scales : results of a biogeochemical model
A model study was carried out of the potential large-scale (> 100 km) effects of marine renewable tidal energy generation in the Pentland Firth, using the 3-D hydrodynamics–biogeochemistry model GETM-ERSEM-BFM. A realistic 800 MW scenario and a high-impact scenario with massive expansion of tidal energy extraction to 8 GW scenario were considered. The realistic 800 MW scenario suggested minor effects on the tides, and undetectable effects on the biogeochemistry. The massive-expansion 8 GW scenario suggested effects would be observed over hundreds of kilometres away with changes of up to 10 % in tidal and ecosystem variables, in particular in a broad area in the vicinity of the Wash. There, waters became less turbid, and primary production increased with associated increases in faunal ecosystem variables. Moreover, a one-off increase in carbon storage in the sea bed was detected. Although these first results suggest positive environmental effects, further investigation is recommended of (i) the residual circulation in the vicinity of the Pentland Firth and effects on larval dispersal using a higher-resolution model and (ii) ecosystem effects with (future) state-of-the-art models if energy extraction substantially beyond 1 GW is planned
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