18,345 research outputs found
The geometrically-averaged density of states as a measure of localization
Motivated by current interest in disordered systems of interacting electrons,
the effectiveness of the geometrically averaged density of states,
, as an order parameter for the Anderson transition is
examined. In the context of finite-size systems we examine complications which
arise from finite energy resolution. Furthermore we demonstrate that even in
infinite systems a decline in with increasing disorder
strength is not uniquely associated with localization.Comment: 8 pages, 8 figures; revised text and figure
Multiplicative renormalizability and quark propagator
The renormalized Dyson-Schwinger equation for the quark propagator is
studied, in Landau gauge, in a novel truncation which preserves multiplicative
renormalizability. The renormalization constants are formally eliminated from
the integral equations, and the running coupling explicitly enters the kernels
of the new equations. To construct a truncation which preserves multiplicative
renormalizability, and reproduces the correct leading order perturbative
behavior, non-trivial cancellations involving the full quark-gluon vertex are
assumed in the quark self-energy loop. A model for the running coupling is
introduced, with infrared fixed point in agreement with previous
Dyson-Schwinger studies of the gauge sector, and with correct logarithmic tail.
Dynamical chiral symmetry breaking is investigated, and the generated quark
mass is of the order of the extension of the infrared plateau of the coupling,
and about three times larger than in the Abelian approximation, which violates
multiplicative renormalizability. The generated scale is of the right size for
hadronic phenomenology, without requiring an infrared enhancement of the
running coupling.Comment: 17 pages; minor corrections, comparison to lattice results added;
accepted for publication in Phys. Rev.
Digital computer processing of LANDSAT data for North Alabama
Computer processing procedures and programs applied to Multispectral Scanner data from LANDSAT are described. The output product produced is a level 1 land use map in conformance with a Universal Transverse Mercator projection. The region studied was a five-county area in north Alabama
Electrometry using the quantum Hall effect in a bilayer 2D electron system
We discuss the development of a sensitive electrometer that utilizes a
two-dimensional electron gas (2DEG) in the quantum Hall regime. As a
demonstration, we measure the evolution of the Landau levels in a second,
nearby 2DEG as the applied perpendicular magnetic field is changed, and extract
an effective mass for electrons in GaAs that agrees within experimental error
with previous measurements.Comment: 3.5 pages, 3 figures, submitted to APL
Origin of the hysteresis in bilayer 2D systems in the quantum Hall regime
The hysteresis observed in the magnetoresistance of bilayer 2D systems in the
quantum Hall regime is generally attributed to the long time constant for
charge transfer between the 2D systems due to the very low conductivity of the
quantum Hall bulk states. We report electrometry measurements of a bilayer 2D
system that demonstrate that the hysteresis is instead due to non-equilibrium
induced current. This finding is consistent with magnetometry and electrometry
measurements of single 2D systems, and has important ramifications for
understanding hysteresis in bilayer 2D systems.Comment: 4 pages, 3 figs. Accepted for publication in PR
Iron oxidation at low temperature (260–500 C) in air and the effect of water vapor
The oxidation of iron has been studied at low temperatures (between 260 and 500 C) in dry air or air with 2 vol% H2O, in the framework of research on dry corrosion of nuclear waste containers during long-term interim storage. Pure iron is regarded as a model material for low-alloyed steel. Oxidation tests were performed in a thermobalance (up to 250 h) or in a laboratory furnace (up to 1000 h). The oxide scales formed were characterized using SEM-EDX, TEM, XRD, SIMS and EBSD techniques. The parabolic rate constants deduced from microbalance experiments were found to be in good agreement with the few existing values of the literature. The presence of water vapor in air was found to strongly influence the transitory stages of the kinetics. The entire structure of the oxide scale was composed of an internal duplex magnetite scale made of columnar grains and an external hematite scale made of equiaxed grains. 18O tracer experiments performed at 400 C allowed to propose a growth mechanism of the scale
Disorder and chain superconductivity in YBa_2Cu_3O_{7-\delta}
The effects of chain disorder on superconductivity in YBa_2Cu_3O_{7-\delta}
are discussed within the context of a proximity model. Chain disorder causes
both pair-breaking and localization. The hybridization of chain and plane
wavefunctions reduces the importance of localization, so that the transport
anisotropy remains large in the presence of a finite fraction of
oxygen vacancies. Penetration depth and specific heat measurements probe the
pair-breaking effects of chain disorder, and are discussed in detail at the
level of the self-consistent T-matrix approximation. Quantitative agreement
with these experiments is found when chain disorder is present.Comment: 4 pages, 2 figures, submitted to PRB rapid communication
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