5,670 research outputs found
SLT-Resolution for the Well-Founded Semantics
Global SLS-resolution and SLG-resolution are two representative mechanisms
for top-down evaluation of the well-founded semantics of general logic
programs. Global SLS-resolution is linear for query evaluation but suffers from
infinite loops and redundant computations. In contrast, SLG-resolution resolves
infinite loops and redundant computations by means of tabling, but it is not
linear. The principal disadvantage of a non-linear approach is that it cannot
be implemented using a simple, efficient stack-based memory structure nor can
it be easily extended to handle some strictly sequential operators such as cuts
in Prolog.
In this paper, we present a linear tabling method, called SLT-resolution, for
top-down evaluation of the well-founded semantics. SLT-resolution is a
substantial extension of SLDNF-resolution with tabling. Its main features
include: (1) It resolves infinite loops and redundant computations while
preserving the linearity. (2) It is terminating, and sound and complete w.r.t.
the well-founded semantics for programs with the bounded-term-size property
with non-floundering queries. Its time complexity is comparable with
SLG-resolution and polynomial for function-free logic programs. (3) Because of
its linearity for query evaluation, SLT-resolution bridges the gap between the
well-founded semantics and standard Prolog implementation techniques. It can be
implemented by an extension to any existing Prolog abstract machines such as
WAM or ATOAM.Comment: Slight modificatio
Central engine afterglow of Gamma-ray Bursts
Before 2004, nearly all GRB afterglow data could be understood in the context
of the external shocks model. This situation has changed in the past two years,
when it became clear that some afterglow components should be attributed to the
activity of the central engine; i.e., the {\it central engine afterglow}. We
review here the afterglow emission that is directly related to the GRB central
engine. Such an interpretation proposed by Katz, Piran & Sari, peculiar in
pre-{\it Swift} era, has become generally accepted now.Comment: 4 pages including 1 figure. Presented at the conference "Astrophysics
of Compact Objects" (July 1-7, 2007; Huangshan, China
Linear Tabulated Resolution Based on Prolog Control Strategy
Infinite loops and redundant computations are long recognized open problems
in Prolog. Two ways have been explored to resolve these problems: loop checking
and tabling. Loop checking can cut infinite loops, but it cannot be both sound
and complete even for function-free logic programs. Tabling seems to be an
effective way to resolve infinite loops and redundant computations. However,
existing tabulated resolutions, such as OLDT-resolution, SLG- resolution, and
Tabulated SLS-resolution, are non-linear because they rely on the
solution-lookup mode in formulating tabling. The principal disadvantage of
non-linear resolutions is that they cannot be implemented using a simple
stack-based memory structure like that in Prolog. Moreover, some strictly
sequential operators such as cuts may not be handled as easily as in Prolog.
In this paper, we propose a hybrid method to resolve infinite loops and
redundant computations. We combine the ideas of loop checking and tabling to
establish a linear tabulated resolution called TP-resolution. TP-resolution has
two distinctive features: (1) It makes linear tabulated derivations in the same
way as Prolog except that infinite loops are broken and redundant computations
are reduced. It handles cuts as effectively as Prolog. (2) It is sound and
complete for positive logic programs with the bounded-term-size property. The
underlying algorithm can be implemented by an extension to any existing Prolog
abstract machines such as WAM or ATOAM.Comment: To appear as the first accepted paper in Theory and Practice of Logic
Programming (http://www.cwi.nl/projects/alp/TPLP
Revisiting B_s\to\mu^+\mu^- and B\to K^{(*)}\mu^+\mu^- decays in the MSSM with and without R-parity
The rare decays B_s -> \mu^+\mu^- and B -> K^{(*)}\mu^+\mu^- are sensitive to
new particles and couplings via their interferences with the standard model
contributions. Recently, the upper bound on B(B_s -> \mu^+\mu^-) has been
improved significantly by the CMS, LHCb, CDF, and D{\O} experiments. Combining
with the measurements of B(B-> K^{(*)}\mu^+\mu^-), we derive constraints on the
relevant parameters of minimal supersymmetic standard model with and without
R-parity, and examine their contributions to the dimuon forward-backward
asymmetry in B-> K^{*}\mu^+\mu^- decay. We find that (i) the contribution of
R-parity violating coupling products
\lambda^{\prime}_{2i2}\lambda^{\prime*}_{2i3} due to squark exchange is
comparable with the theoretical uncertainties in B-> K \mu^+\mu^- decay, but
still could be significant in B-> K^{*}\mu^+\mu^- decay and could account for
the forward-backward asymmetry in all dimuon invariant mass regions; (ii) the
constrained mass insertion (\delta^{u}_{LL})_{23} could have significant
contribution to dA_{FB}(B-> K^{*}\mu^+\mu^-)/ds, and such effects are favored
by thr recent results of the Belle, CDF, and LHCb experiments.Comment: 20 pages, 9 figures, published versio
Half Metallic Bilayer Graphene
Charge neutral bilayer graphene has a gapped ground state as transport
experiments demonstrate. One of the plausible such ground states is layered
antiferromagnetic spin density wave (LAF) state, where the spins in top and
bottom layers have same magnitude with opposite directions. We propose that
lightly charged bilayer graphene in an electric field perpendicular to the
graphene plane may be a half metal as a consequence of the inversion and
particle-hole symmetry broken in the LAF state. We show this explicitly by
using a mean field theory on a 2-layer Hubbard model for the bilayer graphene.Comment: 4+ pages, 4 figure
An improved kinetic model for the acetone-butanol-ethanol pathway of Clostridium acetobutylicum and model-based perturbation analysis
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