1,594 research outputs found
Improved Smoothing Algorithms for Lattice Gauge Theory
The relative smoothing rates of various gauge field smoothing algorithms are
investigated on -improved \suthree Yang--Mills gauge field
configurations. In particular, an -improved version of APE
smearing is motivated by considerations of smeared link projection and cooling.
The extent to which the established benefits of improved cooling carry over to
improved smearing is critically examined. We consider representative gauge
field configurations generated with an -improved gauge field
action on \1 lattices at and \2 lattices at
having lattice spacings of 0.165(2) fm and 0.077(1) fm respectively. While the
merits of improved algorithms are clearly displayed for the coarse lattice
spacing, the fine lattice results put the various algorithms on a more equal
footing and allow a quantitative calibration of the smoothing rates for the
various algorithms. We find the relative rate of variation in the action may be
succinctly described in terms of simple calibration formulae which accurately
describe the relative smoothness of the gauge field configurations at a
microscopic level
Quark propagator in a covariant gauge
Using mean--field improved gauge field configurations, we compare the results
obtained for the quark propagator from Wilson fermions and Overlap fermions on
a \3 lattice at a spacing of fm.Comment: 5 pages, 8 figures, talk given by F.D.R. Bonnet at LHP 2001 workshop,
Cairns, Australi
Light quark electromagnetic structure of baryons
Fascinating aspects of the light quark-mass behavior of baryon
electromagnetic form factors are highlighted. Using FLIC fermions on quenched -improved gauge fields, we explore charge
radii and magnetic moments at pion masses as light as 300 MeV. Of particular
interest is chiral curvature of proton charge radii and magnetic moments, the
environmental dependence of strange quark properties in hyperons, and the
remarkable signature of quenched chiral-nonanalytic behavior in the magnetic
moment of baryon resonances.Comment: 7 pages, 6 figures, Presented at the 24th International Symposium on
Lattice Field Theory (Lattice 2006), Tucson, Arizona, 23-28 Jul 200
General relativistic radiation hydrodynamics of accretion flows: II. Treating stiff source terms and exploring physical limitations
We present the implementation of an implicit-explicit (IMEX) Runge-Kutta numerical scheme for general relativistic hydrodynamics coupled to an optically thick radiation field in two existing GR-hydrodynamics codes. We argue that the necessity of such an improvement arises naturally in astrophysically relevant regimes where the optical thickness is high as the equations become stiff. By performing several 1D tests we verify the codes' new ability to deal with this stiffness and show consistency. Then, still in 1D, we compute a luminosity versus accretion rate diagram for the setup of spherical accretion onto a Schwarzschild black hole and find good agreement with previous work. Lastly, we revisit the supersonic Bondi Hoyle Lyttleton (BHL) accretion in 2D where we can now present simulations of realistic temperatures, down to T~10^6 K. Here we find that radiation pressure plays an important role, but also that these highly dynamical set-ups push our approximate treatment towards the limit of physical applicability. The main features of radiation hydrodynamics BHL flows manifest as (i) an effective adiabatic index approaching gamma_effective ~ 4/3; (ii) accretion rates two orders of magnitude lower than without radiation pressure; (iii) luminosity estimates around the Eddington limit, hence with an overall radiative efficiency as small as eta ~ 10^{-2}; (iv) strong departures from thermal equilibrium in shocked regions; (v) no appearance of the flip-flop instability. We conclude that the current optically thick approximation to the radiation transfer does give physically substantial improvements over the pure hydro also in set-ups departing from equilibrium, and, once accompanied by an optically thin treatment, is likely to provide a fundamental tool for investigating accretion flows in a large variety of astrophysical systems
wake measurements behind an oscillating airfoil in dynamic stall conditions
The unsteady flow field in the wake of an NACA 23012 pitching airfoil was investigated by means of triple hot-wire probe measurements. Wind tunnel tests were carried out both in the light and deep dynamic stall regimes. The analysis of the wake velocity fields was supported by the measurements of unsteady flow fields and airloads. In particular, particle image velocimetry surveys were carried out on the airfoil upper surface, while the lift and pitching moments were evaluated integrating surface pressure measurements. In the light dynamic stall condition, the wake velocity profiles show a similar behaviour in upstroke and in downstroke motions as, in this condition, the flow on the airfoil upper surface is attached for almost the whole pitching cycle and the airloads show a small amount of hysteresis. The deep dynamic stall measurements in downstroke show a large extent of the wake and a high value of the turbulent kinetic energy due to the passage of strong vortical structures, typical of this dynamic stall regime. The comprehensive experimental database can be considered a reference for the development and validation of numerical tools for such peculiar flow conditions
Light-Quark FLIC Fermion Simulations of the Exotic Meson
We investigate the mass of the exotic meson, created with hybrid
interpolating fields. Access to light quark masses approaching 25 MeV is
facilitated by the use of the Fat-Link Irrelevant Clover (FLIC) fermion action,
and large () lattices. Our results indicate that the
exotic exhibits significant curvature close to the chiral limit, and yield a
mass in agreement with the candidate and exclusive of
the .Comment: 6 pages, 1 table, 2 figures, talk given at Lattice '05. Removed
unccessary figure
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