19,738 research outputs found
Answer Sets for Logic Programs with Arbitrary Abstract Constraint Atoms
In this paper, we present two alternative approaches to defining answer sets
for logic programs with arbitrary types of abstract constraint atoms (c-atoms).
These approaches generalize the fixpoint-based and the level mapping based
answer set semantics of normal logic programs to the case of logic programs
with arbitrary types of c-atoms. The results are four different answer set
definitions which are equivalent when applied to normal logic programs. The
standard fixpoint-based semantics of logic programs is generalized in two
directions, called answer set by reduct and answer set by complement. These
definitions, which differ from each other in the treatment of
negation-as-failure (naf) atoms, make use of an immediate consequence operator
to perform answer set checking, whose definition relies on the notion of
conditional satisfaction of c-atoms w.r.t. a pair of interpretations. The other
two definitions, called strongly and weakly well-supported models, are
generalizations of the notion of well-supported models of normal logic programs
to the case of programs with c-atoms. As for the case of fixpoint-based
semantics, the difference between these two definitions is rooted in the
treatment of naf atoms. We prove that answer sets by reduct (resp. by
complement) are equivalent to weakly (resp. strongly) well-supported models of
a program, thus generalizing the theorem on the correspondence between stable
models and well-supported models of a normal logic program to the class of
programs with c-atoms. We show that the newly defined semantics coincide with
previously introduced semantics for logic programs with monotone c-atoms, and
they extend the original answer set semantics of normal logic programs. We also
study some properties of answer sets of programs with c-atoms, and relate our
definitions to several semantics for logic programs with aggregates presented
in the literature
Surface morphological evolutions on single crystal films by strong anisotropic drift-diffusion under the capillary and electromigration forces
The morphological evolution of voids at the unpassivated surfaces and the
sidewalls of the single crystal metallic films are investigated via computer
simulations by using the novel mathematical model developed by Ogurtani relying
on the fundamental postulates of irreversible thermodynamics. The effects of
the drift-diffusion anisotropy on the development of the surface morphological
scenarios are fully explored under the action of the electromigration (EM) and
capillary forces (CF), utilizing numerous combination of the surface textures
and the directions of the applied electric field. The interconnect failure time
due to the EM induced wedge shape internal voids and the incubation time of the
oscillatory surface waves, under the severe instability regimes, are deduced by
the novel renormalization procedures applied on the outputs of the computer
simulation experiments.Comment: 41 pages, 18 figures. related simulation movies utilizing numerous
combination of the surface texture, see
http://www.csl.mete.metu.edu.tr/aytac/thesis/movies/index.ht
Key Findings From HSC's 2010 Site Visits: Health Care Markets Weather Economic Downturn, Brace for Health Reform
Presents findings about hospital payment rate increases, hospital-physician alignment, and insurance premiums, funding for safety-net providers, and their implications from HSC's site visits to twelve nationally representative metropolitan communities
Differential-geometric approach to the integrability of hydrodynamic chains: the Haantjes tensor
The integrability of an m-component system of hydrodynamic type, u_t=V(u)u_x,
by the generalized hodograph method requires the diagonalizability of the mxm
matrix V(u). This condition is known to be equivalent to the vanishing of the
corresponding Haantjes tensor. We generalize this approach to hydrodynamic
chains -- infinite-component systems of hydrodynamic type for which the
infinite matrix V(u) is `sufficiently sparse'. For such systems the Haantjes
tensor is well-defined, and the calculation of its components involves finite
summations only. We illustrate our approach by classifying broad classes of
conservative and Hamiltonian hydrodynamic chains with the zero Haantjes tensor.
We prove that the vanishing of the Haantjes tensor is a necessary condition for
a hydrodynamic chain to possess an infinity of semi-Hamiltonian hydrodynamic
reductions, thus providing an easy-to-verify necessary condition for the
integrability.Comment: 36 pages, the classification results and proofs are refined. A
section on generating functions is adde
Quantum spin models for the SU(n)_1 Wess-Zumino-Witten model
We propose 1D and 2D lattice wave functions constructed from the SU(n)_1
Wess-Zumino-Witten (WZW) model and derive their parent Hamiltonians. When all
spins in the lattice transform under SU(n) fundamental representations, we
obtain a two-body Hamiltonian in 1D, including the SU(n) Haldane-Shastry model
as a special case. In 2D, we show that the wave function converges to a class
of Halperin's multilayer fractional quantum Hall states and belongs to chiral
spin liquids. Our result reveals a hidden SU(n) symmetry for this class of
Halperin states. When the spins sit on bipartite lattices with alternating
fundamental and conjugate representations, we provide numerical evidence that
the state in 1D exhibits quantum criticality deviating from the expected
behaviors of the SU(n)_1 WZW model, while in 2D they are chiral spin liquids
being consistent with the prediction of the SU(n)_1 WZW model.Comment: 28 pages, 9 figures, published versio
Forecasting the equity risk premium: The role of technical indicators
Ministry of Education, Singapore under its Academic Research Funding Tier
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