112 research outputs found
A new approach for diagnosability analysis of Petri nets using Verifier Nets
In this paper, we analyze the diagnosability properties of labeled Petri nets. We consider the standard notion of diagnosability of languages, requiring that every occurrence of an unobservable fault event be eventually detected, as well as the stronger notion of diagnosability in K steps, where the detection must occur within a fixed bound of K event occurrences after the fault. We give necessary and sufficient conditions for these two notions of diagnosability for both bounded and unbounded Petri nets and then present an algorithmic technique for testing the conditions based on linear programming. Our approach is novel and based on the analysis of the reachability/coverability graph of a special Petri net, called Verifier Net, that is built from the Petri net model of the given system. In the case of systems that are diagnosable in K steps, we give a procedure to compute the bound K. To the best of our knowledge, this is the first time that necessary and sufficient conditions for diagnosability and diagnosability in K steps of labeled unbounded Petri nets are presented
High statistics calculations of quenched QCD spectrum using various quark sources
We present the results for the hadron spectrum calculated on 400
configurations using point source, wall source and 8-cubic sources, in quenched
QCD with Wilson fermions at and on a
lattice. The results for the ground state masses obtained with three types of
quark sources agree well with each other. Masses of the first excited states
appear consistent with experimental values within large errors.Comment: 3 pages, 2 postscript figures, to appear in the Proceedings of
LATTICE 93, Dallas, USA; preprint UTHEP-26
Extremal Optimization for Sherrington-Kirkpatrick Spin Glasses
Extremal Optimization (EO), a new local search heuristic, is used to
approximate ground states of the mean-field spin glass model introduced by
Sherrington and Kirkpatrick. The implementation extends the applicability of EO
to systems with highly connected variables. Approximate ground states of
sufficient accuracy and with statistical significance are obtained for systems
with more than N=1000 variables using bonds. The data reproduces the
well-known Parisi solution for the average ground state energy of the model to
about 0.01%, providing a high degree of confidence in the heuristic. The
results support to less than 1% accuracy rational values of for
the finite-size correction exponent, and of for the fluctuation
exponent of the ground state energies, neither one of which has been obtained
analytically yet. The probability density function for ground state energies is
highly skewed and identical within numerical error to the one found for
Gaussian bonds. But comparison with infinite-range models of finite
connectivity shows that the skewness is connectivity-dependent.Comment: Substantially revised, several new results, 5 pages, 6 eps figures
included, (see http://www.physics.emory.edu/faculty/boettcher/ for related
information
Finite-Size Effect of Hadron Masses with Kogut-Susskind Quarks
We present numerical results and their analyses of finite-size effects of
hadron masses for both quenched and full QCD calculations. We show that they
are much larger for full QCD due to dynamical sea quarks and the associated
breaking of symmetry. We also argue that finite-size effects are
non-negligible even for the largest lattice size simulation currently being
made for a very small quark mass. (talk at lattice93)Comment: 4 pages, compressed, uuencoded PostScript file(name:lat93.ps.Z
Phenomenology with Wilson fermions using smeared sources
We investigate the use of two types of non-local (``smeared'') sources for
quark propagators in quenched lattice QCD at using Wilson fermions
at and . We present results for the hadron mass spectrum,
meson decay constants, quark masses, the chiral condensate and the quark
distribution amplitude of the pion. The use of smeared sources leads to a
considerable improvement over previous results. We find a disturbing
discrepancy between the baryon spectra obtained using Wuppertal and wall
sources. We find good signals in the ratio of correlators used to calculate the
quark mass and the chiral condensate and show that the extrapolation to the
chiral limit is smooth.Comment: (revised), 57 pages (29 pages of PostScript in landscape mode, 765924
bytes
APE Results of Hadron Masses in Full QCD Simulations
We present numerical results obtained in full QCD with 2 flavors of Wilson
fermions. We discuss the relation between the phase of Polyakov loops and the
{\bf sea} quarks boundary conditions. We report preliminary results about the
HMC autocorrelation of the hadronic masses, on a lattice
volume, at with .Comment: 3 pages, compressed ps-file (uufiles), Contribution to Lattice 9
Pion-Nucleon Sigma Term in Lattice QCD
We calculate both connected and disconnected contribution to the -
-term in quenched lattice QCD with Wilson quark action on a lattice at . The latter is evaluated with the aid of the variant
wall source method, which was previously applied successfully for extraction of
- scattering lengths and meson mass. We found that the
disconnected contribution is about twice larger than the connected one. The
value for the full - term MeV is consistent
with the experimental estimates. The nucleon matrix element of the strange
quark density is fairly large in our result.Comment: 11 pages. Latex file. Figures are also included as ps file
Progress and status of APEmille
We report on the progress and status of the APEmille project: a SIMD parallel
computer with a peak performance in the TeraFlops range which is now in an
advanced development phase. We discuss the hardware and software architecture,
and present some performance estimates for Lattice Gauge Theory (LGT)
applications.Comment: Talk presented at LATTICE97, 3 pages, Late
Light Quark Masses from Lattice QCD
We present estimates of the masses of light quarks using lattice data. Our
main results are based on a global analysis of all the published data for
Wilson, Sheikholeslami-Wohlert (clover), and staggered fermions, both in the
quenched approximation and with dynamical flavors. We find that the
values of masses with the various formulations agree after extrapolation to the
continuum limit for the theory. Our best estimates, in the MSbar scheme
at , are \mbar=3.4 +- 0.4 +- 0.3 MeV and in the quenched approximation. The results, \mbar = 2.7 +- 0.3 +-
0.3 MeV and , are preliminary. (A linear
extrapolation in would further reduce these estimates for the physical
case of three dynamical flavors.) These estimates are smaller than
phenomenological estimates based on sum rules, but maintain the ratios
predicted by chiral perturbation theory. The new results have a significant
impact on the extraction of from the Standard Model. Using
the same lattice data we estimate the quark condensate using the
Gell-Mann-Oakes-Renner relation. Again the three formulations give consistent
results after extrapolation to , and the value turns out to be
correspondingly larger, roughly preserving m_s \vev{\bar \psi \psi}.Comment: 32 pages. Package submitted in uufiles format: unpack and tex
paper.tex. Modified "axis" source for figures also included. Latex2e
document. Uncomment hyperref if available. This is the final published
versio
Decay Constants of Heavy-Light Mesons
The decay constants of the heavy-light pseudoscalar mesons are studied in a
high statistics run using the Wilson action at and , and
the clover action at . The systematics of discretisation
errors are discussed. Our best estimates of the decay constants are: =
218(9) MeV, = 1.11(1) and we obtain preliminary values for .Comment: at the Dallas Lattice Conference, October 1993. 3 pages in a single
postscript file, uuencoded form. Rome Preprint 93/98
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