359 research outputs found
Solving parity games: Explicit vs symbolic
In this paper we provide a broad investigation of the symbolic approach for solving Parity Games. Specifically, we implement in a fresh tool, called, four symbolic algorithms to solve Parity Games and compare their performances to the corresponding explicit versions for different classes of games. By means of benchmarks, we show that for random games, even for constrained random games, explicit algorithms actually perform better than symbolic algorithms. The situation changes, however, for structured games, where symbolic algorithms seem to have the advantage. This suggests that when evaluating algorithms for parity-game solving, it would be useful to have real benchmarks and not only random benchmarks, as the common practice has been
Reasoning About Strategies: On the Model-Checking Problem
In open systems verification, to formally check for reliability, one needs an
appropriate formalism to model the interaction between agents and express the
correctness of the system no matter how the environment behaves. An important
contribution in this context is given by modal logics for strategic ability, in
the setting of multi-agent games, such as ATL, ATL\star, and the like.
Recently, Chatterjee, Henzinger, and Piterman introduced Strategy Logic, which
we denote here by CHP-SL, with the aim of getting a powerful framework for
reasoning explicitly about strategies. CHP-SL is obtained by using first-order
quantifications over strategies and has been investigated in the very specific
setting of two-agents turned-based games, where a non-elementary model-checking
algorithm has been provided. While CHP-SL is a very expressive logic, we claim
that it does not fully capture the strategic aspects of multi-agent systems. In
this paper, we introduce and study a more general strategy logic, denoted SL,
for reasoning about strategies in multi-agent concurrent games. We prove that
SL includes CHP-SL, while maintaining a decidable model-checking problem. In
particular, the algorithm we propose is computationally not harder than the
best one known for CHP-SL. Moreover, we prove that such a problem for SL is
NonElementarySpace-hard. This negative result has spurred us to investigate
here syntactic fragments of SL, strictly subsuming ATL\star, with the hope of
obtaining an elementary model-checking problem. Among the others, we study the
sublogics SL[NG], SL[BG], and SL[1G]. They encompass formulas in a special
prenex normal form having, respectively, nested temporal goals, Boolean
combinations of goals and, a single goal at a time. About these logics, we
prove that the model-checking problem for SL[1G] is 2ExpTime-complete, thus not
harder than the one for ATL\star
Colossal electroresistance and colossal magnetoresistive step in paramagnetic insulating phase of single crystalline bilayered manganite(LaPr)SrMnO
We report a significant decrease in the low-temperature resistance induced by
the application of an electric current on the -plane in the paramagnetic
insulating (PMI) state of
(LaPr)SrMnO. A colossal
electroresistance effect attaining -95% is observed at lower temperatures. A
colossal magnetoresistive step appears near 5T at low temperatures below 10K,
accompanied by an ultrasharp width of the insulator-metal transition. Injection
of higher currents to the crystal causes a disappearance of the steplike
transition. These findings have a close relationship with the presence of the
short-range charge-ordered clusters pinned within the PMI matrix of the crystal
studied.Comment: 4 pages 3 figure
Spin-Orbit Force from Lattice QCD
We present a first attempt to determine nucleon-nucleon potentials in the
parity-odd sector, which appear in 1P1, 3P0, 3P1, 3P2-3F2 channels, in Nf=2
lattice QCD simulations. These potentials are constructed from the
Nambu-Bethe-Salpeter wave functions for J^P=0^-, 1^- and 2^-, which correspond
to A1^-, T1^- and T2^- + E^- representation of the cubic group, respectively.
We have found a large and attractive spin-orbit potential VLS(r) in the
isospin-triplet channel, which is qualitatively consistent with the
phenomenological determination from the experimental scattering phase shifts.
The potentials obtained from lattice QCD are used to calculate the scattering
phase shifts in 1P1, 3P0, 3P1 and 3P2-3F2 channels. The strong attractive
spin-orbit force and a weak repulsive central force in spin-triplet P-wave
channels lead to an attraction in the 3P2 channel, which is related to the
P-wave neutron paring in neutron stars.Comment: 14 pages, 5 figures, Physics Letters B published versio
Coupled channel approach to strangeness S = -2 baryon-bayron interactions in Lattice QCD
The baryon-baryon interactions with strangeness S = -2 with the flavor SU(3)
breaking are calculated for the first time by using the HAL QCD method extended
to coupled channel system in lattice QCD. The potential matrices are extracted
from the Nambu-Bethe-Salpeter wave functions obtained by the 2+1 flavor gauge
configurations of CP-PACS/JLQCD Collaborations with a physical volume of 1.93
fm cubed and with m_pi/m_K = 0.96, 0.90, 0.86. The spatial structure and the
quark mass dependence of the potential matrix in the baryon basis and in the
SU(3) basis are investigated.Comment: 17 pages, 15 figure
Kaon-Nucleon potential from lattice QCD
We study the KN interactions in the I(J^{\pi})=0(1/2^-) and 1(1/2^-) channels
and associated exotic state \Theta^+ from 2+1 flavor full lattice QCD
simulation for relatively heavy quark mass corresponding to m_{\pi}=871 MeV.
The s-wave KN potentials are obtained from the Bethe-Salpeter wave function by
using the method recently developed by HAL QCD (Hadrons to Atomic nuclei from
Lattice QCD) Collaboration. Potentials in both channels reveal short range
repulsions: Strength of the repulsion is stronger in the I=1 potential, which
is consistent with the prediction of the Tomozawa-Weinberg term. The I=0
potential is found to have attractive well at mid range. From these potentials,
the scattering phase shifts are calculated and compared with the
experimental data.Comment: Talk given at 19th International IUPAP Conference on Few-Body
Problems in Physics (fb19), Bonn, Germany, 30 Aug - 5 Sep 200
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