5,425 research outputs found
Isolating the Roper Resonance in Lattice QCD
We present results for the first positive parity excited state of the
nucleon, namely, the Roper resonance (=1440 MeV) from a
variational analysis technique. The analysis is performed for pion masses as
low as 224 MeV in quenched QCD with the FLIC fermion action. A wide variety of
smeared-smeared correlation functions are used to construct correlation
matrices. This is done in order to find a suitable basis of operators for the
variational analysis such that eigenstates of the QCD Hamiltonian may be
isolated. A lower lying Roper state is observed that approaches the physical
Roper state.
To the best of our knowledge, the first time this state has been identified
at light quark masses using a variational approach.Comment: 7pp, 4 figures; minor typos corrected and one Ref. adde
Bounded LTL Model Checking with Stable Models
In this paper bounded model checking of asynchronous concurrent systems is
introduced as a promising application area for answer set programming. As the
model of asynchronous systems a generalisation of communicating automata,
1-safe Petri nets, are used. It is shown how a 1-safe Petri net and a
requirement on the behaviour of the net can be translated into a logic program
such that the bounded model checking problem for the net can be solved by
computing stable models of the corresponding program. The use of the stable
model semantics leads to compact encodings of bounded reachability and deadlock
detection tasks as well as the more general problem of bounded model checking
of linear temporal logic. Correctness proofs of the devised translations are
given, and some experimental results using the translation and the Smodels
system are presented.Comment: 32 pages, to appear in Theory and Practice of Logic Programmin
Decays of mesons with charm quarks on the lattice
We investigate mesons containing charm quarks on fine lattices with a^{-1}
\sim 5 GeV. The quenched approximation is employed using the Wilson gauge
action at \beta = 6.6 and nonperturbatively O(a) improved Wilson quarks. We
present results for decay constants using various interpolating fields and give
preliminary results for form factors of semileptonic decays of D_s mesons to
light pseudoscalar mesons.Comment: 7 pages, 3 figures, talk presented at the XXV International Symposium
on Lattice Field Theory, 30 July - 4 August 2007, Regensburg, German
Excited hadrons on the lattice: Mesons
We present results for masses of excited mesons from quenched calculations
using chirally improved quarks at pion masses down to 350 MeV. The key features
of our analysis are the use of a matrix of correlators from various source and
sink operators and a basis which includes quark sources with different spatial
widths, thereby improving overlap with states exhibiting radial excitations.Comment: 8 pages, 8 figures; version accepted to PR
Lateral cephalometric analysis of asymptomatic volunteers and symptomatic patients with and without bilateral temporomandibular joint disk displacement
Few studies of dentofacial and orthodontic structural relationships relative to temporomandibular joint (TMJ) dysfunction have been reported. We undertook this investigation to determine any correlation of orthodontic and dentofacial characteristics with TMJ bilateral disc displacement. The population of patients was selected from a TMJ clinic where a control group of asymptomatic volunteers had been previously established and standardized. Differences in skeletal structural features were determined among three study groups: (1) asymptomatic volunteers with no TMJ disk displacement, (2) symptomatic patients with no TMJ disc displacement, and (3) symptomatic patients with bilateral TMJ disk displacement. Thirty-two asymptomatic volunteers without disk displacement (25 female, 7 male) were compared with the same number each of symptomatic patients without TMJ disk displacement and symptomatic patients with bilateral TMJ disk displacement. All subjects had undergone a standardized clinical examination, bilateral TMJ magnetic resonance imaging, and lateral cephalometric radiographic analysis. The groups were matched according to sex, TMJ status, age, and Angle classification of malocclusion. Seventeen lateral cephalometric radiographic cranial base, maxillomandibular, and vertical dimension variables were evaluated and compared among the study groups. The mean angle of SNB, or the intersection of the sella-nasion plane and the nasion–point B line (indicating mandibular retrognathism relative to cranial base), of the symptomatic patients-with-displacement group was significantly smaller than that in the asymptomatic volunteers and symptomatic patients without bilateral disk displacement (p \u3c 0.05). Female subjects showed smaller linear measurements of mandibular length, lower facial height, and total anterior facial height than male subjects in all three groups (p \u3c 0.05). The mean angle of ANB, or the intersection of the nasion–point A and nasion–point B planes (indicating retrognathism of mandible relative to maxilla), was significantly greater in female than in male subjects, in all groups (p \u3c 0.05). Symptomatic patients with bilateral disk displacement had a retropositioned mandible, indicated by a smaller mean SNB angle compared with that in asymptomatic volunteers and symptomatic patients with no disk displacement on either side. Lateral cephalometric radiographic assessment may improve predictability of TMJ disk displacement in orthodontic patients but is not diagnostic; nor does the assessment explain any cause-and-effect relationship. (Am J Orthod Dentofacial Orthop 1998;114:248-55.
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