32,830 research outputs found
Studying the infrared region in Landau gauge QCD
We report on the progress we made in studying the infrared behavior of the
ghost and gluon dressing functions in Landau gauge. Related to this we also
investigate a running coupling given in terms of those functions and compare
our results to those coming from the Dyson-Schwinger approach. We present first
numerical results for the SU(3) ghost-ghost-gluon vertex renormalization
constant. In addition the spectrum of low-lying eigenvalues and eigenfunctions
of the Faddeev-Popov operator is determined. The saturation of the ghost
propagator in terms of those eigenvalues and eigenmodes is discussed at lower
momenta.Comment: 6 pages, 4 figures, talk presented at Lattice 2005 (Topology and
Confinement
The influence of Gribov copies on the gluon and ghost propagator
The dependence of the gluon and ghost propagator in pure SU(3) gauge theory
on the choice of Gribov copies in Landau gauge is studied. Simulations were
performed on several lattice sizes at =5.8, 6.0 and 6.2. In the infrared
region the ghost propagator turns out to depend on the choice, while the impact
on the gluon propagator is not resolvable. Also the eigenvalue distribution of
the Faddeev-Popov operator is sensitive to Gribov copies.Comment: Talk presented at Quark Confinement and the Hadron Spectrum VI,
Villasimius, Sardinia, Italy, September 21-25, 2004, 3 pages, 2 figure
The core helium flash revisited: II. Two and three-dimensional hydrodynamic simulations
We study turbulent convection during the core helium flash close to its peak
by comparing the results of two and three-dimensional hydrodynamic simulations.
We use a multidimensional Eulerian hydrodynamics code based on
state-of-the-art numerical techniques to simulate the evolution of the helium
core of a Pop I star.
Our three-dimensional hydrodynamic simulations of the evolution of a star
during the peak of the core helium flash do not show any explosive behavior.
The convective flow patterns developing in the three-dimensional models are
structurally different from those of the corresponding two-dimensional models,
and the typical convective velocities are smaller than those found in their
two-dimensional counterparts. Three-dimensional models also tend to agree
better with the predictions of mixing length theory. Our hydrodynamic
simulations show the presence of turbulent entrainment that results in a growth
of the convection zone on a dynamic time scale. Contrary to mixing length
theory, the outer part of the convection zone is characterized by a
sub-adiabatic temperature gradient.Comment: 19 pages, 18 figure
The Aoki phase for N_f=2 Wilson fermions revisited
We report on a numerical reinvestigation of the Aoki phase in full lattice
QCD with two flavors of unimproved Wilson fermions. For zero temperature the
Aoki phase can be confirmed at inverse coupling and ,
but not at and . At non-zero temperature the Aoki phase
was found to exist also at .Comment: 3 pages LaTex, 5 figures. Parallel talk at Lattice2003(Theory
Rotational States of Magnetic Molecules
We study a magnetic molecule that exhibits spin tunneling and is free to
rotate about its anisotropy axis. Exact low-energy eigenstates of the molecule
that are superpositions of spin and rotational states are obtained. We show
that parameter determines the ground state of
the molecule. Here is the spin, is the moment of inertia, and
is the tunnel splitting. The magnetic moment of the molecule is zero
at . At the spin of the molecule localizes in one of
the directions along the anisotropy axis.Comment: 4 pages, 3 figure
N/P GaAs concentrator solar cells with an improved grid and bushbar contact design
The major requirements for a solar cell used in space applications are high efficiency at AMO irradiance and resistance to high energy radiation. Gallium arsenide, with a band gap of 1.43 eV, is one of the most efficient sunlight to electricity converters (25%) when the the simple diode model is used to calculate efficiencies at AMO irradiance, GaAs solar cells are more radiation resistant than silicon solar cells and the N/P GaAs device has been reported to be more radiation resistant than similar P/N solar cells. This higher resistance is probably due to the fact that only 37% of the current is generated in the top N layer of the N/P cell compared to 69% in the top layer of a P/N solar cell. This top layer of the cell is most affected by radiation. It has also been theoretically calculated that the optimized N/P device will prove to have a higher efficiency than a similar P/N device. The use of a GaP window layer on a GaAs solar cell will avoid many of the inherent problems normally associated with a GaAlAs window while still proving good passivation of the GaAs surface. An optimized circular grid design for solar cell concentrators has been shown which incorporates a multi-layer metallization scheme. This multi-layer design allows for a greater current carrying capacity for a unit area of shading, which results in a better output efficiency
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