229 research outputs found
New complexity results for parallel identical machine scheduling problems with preemption, release dates and regular criteria
In this paper, we are interested in parallel identical machine scheduling
problems with preemption and release dates in case of a regular criterion to be
minimized. We show that solutions having a permutation flow shop structure are
dominant if there exists an optimal solution with completion times scheduled in
the same order as the release dates, or if there is no release date. We also
prove that, for a subclass of these problems, the completion times of all jobs
can be ordered in an optimal solution. Using these two results, we provide new
results on polynomially solvable problems and hence refine the boundary between
P and NP for these problems
Methyl group dynamics in a confined glass
We present a neutron scattering investigation on methyl group dynamics in
glassy toluene confined in mesoporous silicates of different pore sizes. The
experimental results have been analysed in terms of a barrier distribution
model, such a distribution following from the structural disorder in the glassy
state. Confinement results in a strong decreasing of the average rotational
barrier in comparison to the bulk state. We have roughly separated the
distribution for the confined state in a bulk-like and a surface-like
contribution, corresponding to rotors at a distance from the pore wall
respectively larger and smaller than the spatial range of the interactions
which contribute to the rotational potential for the methyl groups. We have
estimated a distance of 7 Amstrong as a lower limit of the interaction range,
beyond the typical nearest-neighbour distance between centers-of-mass (4.7
Amstrong).Comment: 5 pages, 3 figures. To be published in European Physical Journal E
Direct. Proceedings of the 2nd International Workshop on Dynamics in
Confinemen
Recovering Beam Search Approach for the Multi-Skill Project Scheduling Problem
International audienc
Influence of Elastic Strains on the Adsorption Process in Porous Materials. An Experimental Approach
The experimental results presented in this paper show the influence of the
elastic deformation of porous solids on the adsorption process. With p+-type
porous silicon formed on highly boron doped (100) Si single crystal, we can
make identical porous layers, either supported by or detached from the
substrate. The pores are perpendicular to the substrate. The adsorption
isotherms corresponding to these two layers are distinct. In the region
preceding capillary condensation, the adsorbed amount is lower for the membrane
than for the supported layer and the hysteresis loop is observed at higher
pressure. We attribute this phenomenon to different elastic strains undergone
by the two layers during the adsorption process. For the supported layer, the
planes perpendicular to the substrate are constrained to have the same
interatomic spacing as that of the substrate so that the elastic deformation is
unilateral, at an atomic scale, and along the pore axis. When the substrate is
removed, tridimensional deformations occur and the porous system can find a new
configuration for the solid atoms which decreases the free energy of the system
adsorbate-solid. This results in a decrease of the adsorbed amount and in an
increase of the condensation pressure. The isotherms for the supported porous
layers shift toward that of the membrane when the layer thickness is increased
from 30 to 100 microns. This is due to the relaxation of the stress exerted by
the substrate as a result of the breaking of Si-Si bonds at the interface
between the substrate and the porous layer. The membrane is the relaxed state
of the supported layer.Comment: Accepted in Langmui
On the correlation between fragility and stretching in glassforming liquids
We study the pressure and temperature dependences of the dielectric
relaxation of two molecular glassforming liquids, dibutyl phtalate and
m-toluidine. We focus on two characteristics of the slowing down of relaxation,
the fragility associated with the temperature dependence and the stretching
characterizing the relaxation function. We combine our data with data from the
literature to revisit the proposed correlation between these two quantities. We
do this in light of constraints that we suggest to put on the search for
empirical correlations among properties of glassformers. In particular, argue
that a meaningful correlation is to be looked for between stretching and
isochoric fragility, as both seem to be constant under isochronic conditions
and thereby reflect the intrinsic effect of temperature
Cut generation for obtaining strong makespan lower bounds for the multi-skill project scheduling problem
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