296 research outputs found
Physical Nucleon Properties from Lattice QCD
We demonstrate that the extremely accurate lattice QCD data for the mass of
the nucleon recently obtained by CP-PACS, combined with modern chiral
extrapolation techniques, leads to a value for the mass of the physical nucleon
which has a systematic error of less than one percent.Comment: 4 pages, 2 figure
Sigma-term physics in the perturbative chiral quark model
We apply the perturbative chiral quark model (PCQM) at one loop to analyse
meson-baryon sigma-terms. Analytic expressions for these quantities are
obtained in terms of fundamental parameters of low-energy pion-nucleon physics
(weak pion decay constant, axial nucleon coupling, strong pion-nucleon form
factor) and of only one model parameter (radius of the nucleonic three-quark
core). Our result for the piN sigma term of about 45 MeV is in good agreement
with the value deduced by Gasser, Leutwyler and Sainio using
dispersion-relation techniques and exploiting the chiral symmetry constraints.Comment: 19 pages, LaTeX-file, 2 Figure
Chiral extrapolation of lattice moments of proton quark distributions
We present the resolution of a long-standing discrepancy between the moments
of parton distributions calculated from lattice QCD and their experimental
values. We propose a simple extrapolation formula for the moments of the
nonsinglet quark distribution u-d, as a function of quark mass, which embodies
the general constraints imposed by the chiral symmetry of QCD. The inclusion of
the leading nonanalytic behavior leads to an excellent description of both the
lattice data and the experimental values of the moments.Comment: 9 pages, 1 figure, to appear in Physical Review Letter
Partial pulpotomy without age restriction: a retrospective assessment of permanent teeth with carious pulp exposure
OBJECTIVES
This study aimed to retrospectively evaluate clinical and radiographic outcomes of partial pulpotomy performed in permanent teeth with carious pulp exposure.
MATERIALS AND METHODS
Records of patients undergoing treatment at an undergraduate dental clinic between 2010 and 2019 were screened for partial pulpotomies in teeth with a presumptive diagnosis of normal pulp or reversible pulpitis. The follow-up had to be ≥ 1 year. Patient data were retrieved and analyzed using Mantel-Cox chi square tests and Kaplan-Meier statistics. The level of significance was set at α = 0.05.
RESULTS
Partial pulpotomy was performed in 111 cases, of which 64 (58%) fulfilled the eligibility criteria. At the time of partial pulpotomy, the mean age was 37.3 (± 13.5) years (age range 18-85). The mean observation period was 3.1 (± 2.0) years. Two early failures (3.1%) and five late failures (7.7%) were recorded. The overall success rate of maintaining pulp vitality was 89.1%, with 98.4% tooth survival. The cumulative pulp survival rates of partial pulpotomy in patients aged  40 years were 100%, 75.5%, and 90.5%, respectively, with no significant difference between the age groups (p = 0.225). At follow-up, narrowing of the pulp canal space and tooth discoloration were observed in 10.9% and 3.1% of cases, respectively.
CONCLUSIONS
Across age groups, partial pulpotomy achieved favorable short and medium-term outcomes in teeth with carious pulp exposure.
CLINICAL RELEVANCE
Adequate case selection provided, partial pulpotomy is a viable operative approach to treat permanent teeth with deep carious lesions irrespective of patients' age
Nucleon Magnetic Moments Beyond the Perturbative Chiral Regime
The quark mass dependence of nucleon magnetic moments is explored over a wide
range. Quark masses currently accessible to lattice QCD, which lie beyond the
regime of chiral perturbation theory (chiPT), are accessed via the cloudy bag
model (CBM). The latter reproduces the leading nonanalytic behavior of chiPT,
while modeling the internal structure of the hadron under investigation. We
find that the predictions of the CBM are succinctly described by the simple
formula, \mu_N(m_\pi) = \mu^{(0)}_N / (1 + \alpha m_\pi + \beta m_\pi^2), which
reproduces the lattice data, as well as the leading nonanalytic behavior of
chiPT. As this form also incorporates the anticipated Dirac moment behavior in
the limit m_\pi \to \infty, it constitutes a powerful method for extrapolating
lattice results to the physical mass regime.Comment: Revised version accepted for publication includes a new section
demonstrating extrapolations of lattice QCD result
Soft tissue augmentation with a volume-stable collagen matrix or an autogenous connective tissue graft at implant sites: Five-year results of a randomized controlled trial post implant loading
BACKGROUND
Interventions to augment the mucosal thickness around dental implants are indicated to optimize esthetics and maintain peri-implant health. However, there is a lack of clinical data on the long-term performance of soft tissue substitutes, such as volume-stable collagen matrix (VCMX), compared to autogenous grafts, such as subepithelial connective tissue grafts (SCTGs). This randomized controlled trial aimed to assess 5-year data on clinical and radiographic outcomes at implant sites previously augmented with VCMX or SCTG.
METHODS
Twenty patients were randomly assigned for soft tissue augmentation with VCMX or SCTG at single implant sites. Following abutment connection, final restorations were inserted (baseline; BL) and patients were reexamined up to 5 years (FU-5). Measurements included clinical data, marginal bone levels, mucosal thickness, and ridge contour changes. Nonparametric tests and estimates were applied for the statistical analysis.
RESULTS
The median buccal mucosal thickness increased by 0.3Â mm (Q1: -0.8; Q3: 1.0) in the VCMX group (PÂ =Â 0.656) and 0.3Â mm (Q1: 0.0; Q3: 1.0) in the SCTG group (PÂ =Â 0.188) between BL and FU-5 (intergroup PÂ =Â 0.752), while the ridge contour decreased by a median of -0.3Â mm (-0.9; -0.1) (PÂ =Â 0.078) for VCMX and -0.3Â mm (-0.4; -0.2) (PÂ =Â 0.039) for SCTG (intergroup PÂ =Â 0.817). Peri-implant health was maintained in both groups with stable clinical and radiographic outcomes and without significant differences between the treatments.
CONCLUSION
Despite the limited power and considerable dropout rate in the present study, soft tissue augmentation at implant sites with either VCMX or SCTG resulted in similar stable peri-implant tissues, favorable esthetics, and clinically negligible contour changes at 5 years post loading
Variations of Hadron Masses and Matter Properties in Dense Nuclear Matter
Using a self-consistent quark model for nuclear matter we investigate
variations of the masses of the non-strange vector mesons, the hyperons and the
nucleon in dense nuclear matter (up to four times the normal nuclear density).
We find that the changes in the hadron masses can be described in terms of the
value of the scalar mean-field in matter. The model is then used to calculate
the density dependence of the quark condensate in-medium, which turns out to be
well approximated by a linear function of the nuclear density. Some relations
among the hadron properties and the in-medium quark condensate are discussed.Comment: 22 pages, University of Adelaide preperint ADP-94-20/T160, submitted
to Physical Review
Chiral Analysis of Quenched Baryon Masses
We extend to quenched QCD an earlier investigation of the chiral structure of
the masses of the nucleon and the delta in lattice simulations of full QCD.
Even after including the meson-loop self-energies which give rise to the
leading and next-to-leading non-analytic behaviour (and hence the most rapid
variation in the region of light quark mass), we find surprisingly little
curvature in the quenched case. Replacing these meson-loop self-energies by the
corresponding terms in full QCD yields a remarkable level of agreement with the
results of the full QCD simulations. This comparison leads to a very good
understanding of the origins of the mass splitting between these baryons.Comment: 23 pages, 6 figure
Baryon masses and nucleon sigma terms in manifestly Lorentz-invariant baryon chiral perturbation theory
We discuss the masses of the ground state baryon octet and the nucleon sigma
terms in the framework of manifestly Lorentz-invariant baryon chiral
perturbation theory. In order to obtain a consistent power counting for
renormalized diagrams the extended on-mass-shell renormalization scheme is
applied.Comment: 18 pages, 3 figures, accepted for publication in J. Phys.
Quark mass dependence of the nucleon axial-vector coupling constant
We study the quark mass expansion of the axial-vector coupling constant g_A
of the nucleon. The aim is to explore the feasibility of chiral effective field
theory methods for extrapolation of lattice QCD results - so far determined at
relatively large quark masses corresponding to pion masses larger than 0.6 GeV
- down to the physical value of the pion mass. We compare two versions of
non-relativistic chiral effective field theory: One scheme restricted to pion
and nucleon degrees of freedom only, and an alternative approach which
incorporates explicit Delta(1230) resonance degrees of freedom. It turns out
that, in order to approach the physical value of g_A in a leading-one-loop
calculation, the inclusion of the explicit Delta(1230) degrees of freedom is
crucial. With information on important higher order couplings constrained from
analyses of inelastic pion production processes, a chiral extrapolation
function for g_A is obtained, which works well from the chiral limit across the
physical point into the region of present lattice data. The resulting
enhancement of our extrapolation function near the physical pion mass is found
to arise from an interplay between long- and short- distance physics.Comment: 21 pages, LaTeX, 7 figure
- …