372 research outputs found
Flavor-Symmetry Restoration and Symanzik Improvement for Staggered Quarks
We resolve contradictions in the literature concerning the origins and size
of unphysical flavor-changing strong interactions generated by the
staggered-quark discretization of QCD. We show that the leading contributions
are tree-level in \order(a^2) and that they can be removed by adding three
correction terms to the link operator in the standard action. These corrections
are part of the systematic Symanzik improvement of the staggered-quark action.
We present a new improved action for staggered quarks that is accurate up to
errors of \order(a^4,a^2\alpha_s) --- more accurate than most, if not all,
other discretizations of light-quark dynamics.Comment: 7 page
Local topological and chiral properties of QCD
To elucidate the role played by instantons in chiral symmetry breaking, we
explore their properties in full QCD, around the critical temperature. We study
in particular spatial correlations between low-lying Dirac eigenmodes and
instantons. Our measurements are compared with the predictions of
instanton-based models.Comment: LATTICE98(confine), 3 pgs, 4 figures (3 color
Magneto-optic contact for application in an amplifying waveguide optical isolator
We present the development of a metal-semiconductor contact for a TM-mode amplijying waveguide optical isolator and show that it is a compromise between good (magneto-)optical performance and good electrical behavior
Reduced glutamate decarboxylase activity in rat islet β cells which survived streptozotocin-induced cytotoxicity
AbstractRat pancreatic β cells exhibit a 16-fold higher glutamate decarboxylase (GAD) activity than islet non-β cells, but a similar glutamate dehydrogenase (GDH) activity, β Cells which survive exposure to 2 mM streptozotocin only contain 10 percent of the GAD activity of control cells, but their GDH activity remains unaltered. Culture of streptozotocin-treated β cell preparations with 2 mM nicotinamide reduces the number of dead cells and prevents in part the decline in GAD activity of surviving β cells. These data indicate that loss in activity of the β cell specific enzyme GAD can serve as marker for β cells which survived a destructive process. It is furthermore demonstrated that nicotinamide increases the percent surviving cells and decreases their loss in GAD activity
Direct current control of three magnon scattering processes in spin-valve nanocontacts
We have investigated the generation of spin waves in the free layer of an
extended spin-valve structure with a nano-scaled point contact driven by both
microwave and direct electric current using Brillouin light scattering
microscopy. Simultaneously with the directly excited spin waves, strong
nonlinear effects are observed, namely the generation of eigenmodes with
integer multiple frequencies (2 \emph{f}, 3 \emph{f}, 4 \emph{f}) and modes
with non-integer factors (0.5 \emph{f}, 1.5 \emph{f}) with respect to the
excitation frequency \emph{f}. The origin of these nonlinear modes is traced
back to three magnon scattering processes. The direct current influence on the
generation of the fundamental mode at frequency \emph{f} can be related to the
spin-transfer torque, while the efficiency of three-magnon-scattering processes
is controlled by the Oersted field as an additional effect of the direct
current
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