3,432 research outputs found
Constraint Satisfaction with Counting Quantifiers
We initiate the study of constraint satisfaction problems (CSPs) in the
presence of counting quantifiers, which may be seen as variants of CSPs in the
mould of quantified CSPs (QCSPs). We show that a single counting quantifier
strictly between exists^1:=exists and exists^n:=forall (the domain being of
size n) already affords the maximal possible complexity of QCSPs (which have
both exists and forall), being Pspace-complete for a suitably chosen template.
Next, we focus on the complexity of subsets of counting quantifiers on clique
and cycle templates. For cycles we give a full trichotomy -- all such problems
are in L, NP-complete or Pspace-complete. For cliques we come close to a
similar trichotomy, but one case remains outstanding. Afterwards, we consider
the generalisation of CSPs in which we augment the extant quantifier
exists^1:=exists with the quantifier exists^j (j not 1). Such a CSP is already
NP-hard on non-bipartite graph templates. We explore the situation of this
generalised CSP on bipartite templates, giving various conditions for both
tractability and hardness -- culminating in a classification theorem for
general graphs. Finally, we use counting quantifiers to solve the complexity of
a concrete QCSP whose complexity was previously open
Bundling Payment for Episodes of Hospital Care: Issues and Recommendations for the New Pilot Program in Medicare
Outlines the 2010 healthcare reform's provision to launch a pilot project for bundling Medicare payments around hospitalization episodes of care, the rationale for hospital episode bundling, and guidance on designing an effective pilot program
Optical guiding in meter-scale plasma waveguides
We demonstrate a new highly tunable technique for generating meter-scale low
density plasma waveguides. Such guides can enable electron acceleration to tens
of GeV in a single stage. Plasma waveguides are imprinted in hydrogen gas by
optical field ionization induced by two time-separated Bessel beam pulses: The
first pulse, a J_0 beam, generates the core of the waveguide, while the delayed
second pulse, here a J_8 or J_16 beam, generates the waveguide cladding. We
demonstrate guiding of intense laser pulses over hundreds of Rayleigh lengths
with on axis plasma densities as low as N_e0=5x10^16 cm^-3
Roughening of Fracture Surfaces: the Role of Plastic Deformations
Post mortem analysis of fracture surfaces of ductile and brittle materials on
the m-mm and the nm scales respectively, reveal self affine graphs with an
anomalous scaling exponent . Attempts to use elasticity
theory to explain this result failed, yielding exponent up
to logarithms. We show that when the cracks propagate via plastic void
formations in front of the tip, followed by void coalescence, the voids
positions are positively correlated to yield exponents higher than 0.5.Comment: 4 pages, 6 figure
Molecular dynamics study of solvation effects on acid dissociation in aprotic media
Acid ionization in aprotic media is studied using Molecular Dynamics
techniques. In particular, models for HCl ionization in acetonitrile and
dimethylsulfoxide are investigated. The proton is treated quantum mechanically
using Feynman path integral methods and the remaining molecules are treated
classically. Quantum effects are shown to be essential for the proper treatment
of the ionization. The potential of mean force is computed as a function of the
ion pair separation and the local solvent structure is examined. The computed
dissociation constants in both solvents differ by several orders of magnitude
which are in reasonable agreement with experimental results. Solvent separated
ion pairs are found to exist in dimethylsulfoxide but not in acetonitrile.
Dissociation mechanisms in small clusters are also investigated. Solvent
separated ion pairs persist even in aggregates composed of rather few
molecules, for instance, as few as thirty molecules. For smaller clusters or
for large ion pair separations cluster finite-size effects come into play in a
significant fashion.Comment: Plain LaTeX. To appear in JCP(March 15). Mpeg simulations available
at http://www.chem.utoronto.ca/staff/REK/Videos/clusters/clusters.htm
Low-lying excitations of a trapped rotating Bose-Einstein condensate
We investigate the low-lying excitations of a weakly-interacting,
harmonically-trapped Bose-Einstein condensed gas under rotation, in the limit
where the angular mometum of the system is much less than the number of the
atoms in the trap. We show that in the asymptotic limit the
excitation energy, measured from the energy of the lowest state, is given by
, where is the number of octupole
excitations and is the unit of the interaction energy.Comment: 3 pages, RevTex, 2 ps figures, submitted to PR
Assessment of the effectiveness of head only and back-of-the-head electrical stunning of chickens
The study assesses the effectiveness of reversible head-only and back-of-the-head electrical stunning of chickens using 130–950 mA per bird at 50 Hz AC
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