17,315 research outputs found
Effective order strong stability preserving RungeâKutta methods
We apply the concept of effective order to strong stability preserving (SSP) explicit RungeâKutta methods. Relative to classical RungeâKutta methods, effective order methods are designed to satisfy a relaxed set of order conditions, but yield higher order accuracy when composed with special starting and stopping methods. The relaxed order conditions allow for greater freedom in the design of effective order methods. We show that this allows the construction of four-stage SSP methods with effective order four (such methods cannot have classical order four). However, we also prove that effective order five methodsâlike classical order five methodsârequire the use of non-positive weights and so cannot be SSP. By numerical optimization, we construct explicit SSP RungeâKutta methods up to effective order four and establish the optimality of many of them. Numerical experiments demonstrate the validity of these methods in practice
Temperature dependent carrier lifetime studies of Mo in crystalline silicon
The capture cross sections of both electronsÏn and holes Ïp were determined for interstitialmolybdenum in crystalline silicon over the temperature range of â110 to 150â°C. Carrier lifetimemeasurements were performed on molybdenum-contaminated silicon using a temperature controlled photoconductance instrument. Injection dependent lifetime spectroscopy was applied at each temperature to calculate Ïp and Ïn. This analysis involved a novel approach that independently determined the capture cross sections at each temperature assuming a known defect density and thermal velocity. Since the energy state is in the lower half of the bandgap, the determination of Ïp is unaffected by the defect energy at all temperatures, and Ïp is found to decrease with temperature in a fashion consistent with excitonic Auger capture. At temperatures below 0â°C, the determination of Ïn is also unaffected by the defect energy due to the suppression of thermal emission, and Ïn decreases with temperature as well. It is shown that a projection of Ïn to higher temperature suggests the defect has an energy of 0.375 eV above the valance band edge of silicon.D.M. likes to thank the Australian Research Council for
fellowship and G.C. likes to thank âCrystalClear Integrated
Projectâ Contract No. SES6-CT_2003-502583 funded by
the European Commission
The Pathological Changes affecting the Endometrium: A Contribution towards their Classification.*
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On the Conductance Sum Rule for the Hierarchical Edge States of the Fractional Quantum Hall Effect
The conductance sum rule for the hierarchical edge channel currents of a
Fractional Quantum Hall Effect state is derived analytically within the
Haldane-Halperin hierarchy scheme. We provide also an intuitive interpretation
for the hierarchical drift velocities of the edge excitations.Comment: 11 pages, no figure, Revtex 3.0, IC/93/329, ASITP-93-5
Charged Defects and Phonon Hall Effects in Ionic Crystals
It has been known for decades that a magnetic field can deflect phonons as
they flow in response to a thermal gradient, producing a thermal Hall effect.
Several recent experiments have revealed ratios of the phonon Hall conductivity
to the phonon longitudinal conductivity in oxide dielectrics that are larger
than when phonon mean-free-paths exceed phonon wavelengths. At the
same time is not strongly temperature dependent. We
argue that these two properties together imply a mechanism related to phonon
scattering from defects that break time-reversal symmetry, and we show that
Lorentz forces acting on charged defects produce substantial skew-scattering
amplitudes, and related thermal Hall effects that are consistent with recent
observations
Observability of counterpropagating modes at fractional-quantum-Hall edges
When the bulk filling factor is equal to 1 - 1/m with m odd, at least one
counterpropagating chiral collective mode occurs simultaneously with
magnetoplasmons at the edge of fractional-quantum-Hall samples. Initial
experimental searches for an additional mode were unsuccessful. In this paper,
we address conditions under which its observation should be expected in
experiments where the electronic system is excited and probed by capacitive
coupling. We derive realistic expressions for the velocity of the slow
counterpropagating mode, starting from a microscopic calculation which is
simplified by a Landau-Silin-like separation between long-range Hartree and
residual interactions. The microscopic calculation determines the stiffness of
the edge to long-wavelength neutral excitations, which fixes the slow-mode
velocity, and the effective width of the edge region, which influences the
magnetoplasmon dispersion.Comment: 18 pages, RevTex, 6 figures, final version to be published in
Physical Review
Streda-like formula in spin Hall effect
A generalized Streda formula is derived for the spin transport in spin-orbit
coupled systems. As compared with the original Streda formula for charge
transport, there is an extra contribution of the spin Hall conductance whenever
the spin is not conserved. For recently studied systems with quantum spin Hall
effect in which the z-component spin is conserved, this extra contribution
vanishes and the quantized value of spin Hall conductivity can be reproduced in
the present approach. However, as spin is not conserved in general, this extra
contribution can not be neglected, and the quantization is not exact.Comment: 4 pages, no figur
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