395 research outputs found
Spin-orbit interaction and weak localization in heterostructures
Theory of weak localization in two-dimensional high-mobility semiconductor
systems is developed with allowance for the spin-orbit interaction. The
obtained expressions for anomalous magnetoresistance are valid in the whole
range of classically weak magnetic fields and for arbitrary strengths of bulk
and structural inversion asymmetry contributions to the spin splitting. The
theory serves for both diffusive and ballistic regimes of electron propagation
taking into account coherent backscattering and nonbackscattering processes.
The transition between weak localization and antilocalization regimes is
analyzed. The manifestation of the mutual compensation of Rashba and
Dresselhaus spin splittings in magnetoresistance is discussed. Perfect
description of experimental data on anomalous magnetoresistance in
high-mobility heterostructures is demonstrated. The in-plane magnetic field
dependence of the conductivity caused by an interplay of the spin-orbit
splittings and Zeeman effect is described theoretically.Comment: Review for the special issue of Semicond. Sci. Technol. "The effects
of spin-orbit interaction on charge transport". 8 pages, 5 figure
Gate-Controlled Spin-Orbit Quantum Interference Effects in Lateral Transport
In situ control of spin-orbit coupling in coherent transport using a clean
GaAs/AlGaAs 2DEG is realized, leading to a gate-tunable crossover from weak
localization to antilocalization. The necessary theory of 2D magnetotransport
in the presence of spin-orbit coupling beyond the diffusive approximation is
developed and used to analyze experimental data. With this theory the Rashba
contribution and linear and cubic Dresselhaus contributions to spin-orbit
coupling are separately estimated, allowing the angular dependence of
spin-orbit precession to be extracted at various gate voltages.Comment: related papers at http://marcuslab.harvard.ed
Fermi-liquid behaviour of the low-density 2D hole gas in GaAs/AlGaAs heterostructure at large values of r_s
We examine the validity of the Fermi-liquid description of the dilute 2D hole
gas in the crossover from 'metallic'-to-'insulating' behaviour of R(T).It has
been established that, at r_s as large as 29, negative magnetoresistance does
exist and is well described by weak localisation. The dephasing time extracted
from the magnetoresistance is dominated by the T^2 -term due to Landau
scattering in the clean limit. The effect of hole-hole interactions, however,
is suppressed when compared with the theory for small r_s.Comment: 4 pages ReVTeX, 4 ps figure
Power counting and renormalization group invariance in the subtracted kernel method for the two-nucleon system
We apply the subtracted kernel method (SKM), a renormalization approach based
on recursive multiple subtractions performed in the kernel of the scattering
equation, to the chiral nucleon-nucleon (NN) interactions up to
next-to-next-to-leading-order (NNLO). We evaluate the phase-shifts in the 1S0
channel at each order in Weinberg's power counting scheme and in a modified
power counting scheme which yields a systematic power-law improvement. We also
explicitly demonstrate that the SKM procedure is renormalization group
invariant under the change of the subtraction scale through a non-relativistic
Callan-Symanzik flow equation for the evolution of the renormalized NN
interactions.Comment: Accepted for publication in Journal of Physics G: Nuclear and
Particle Physic
Development and Validation of a New Hierarchical Composite End Point for Clinical Trials of Kidney Disease Progression
BACKGROUND: The established composite kidney end point in clinical trials combines clinical events with sustained large changes in GFR. However, the statistical method does not weigh the relative clinical importance of the end point components. A HCE accounts for the clinical importance of the end point components and enables combining dichotomous outcomes with continuous measures. METHODS: We developed and validated a new HCE for kidney disease progression, performing post hoc analyses of seven major Phase 3 placebo-controlled trials that assessed the effects of canagliflozin, dapagliflozin, finerenone, atrasentan, losartan, irbesartan, and aliskiren in patients with CKD. We calculated the win odds (WOs) for treatment effects on a kidney HCE, defined as a hierarchical composite of all-cause mortality; kidney failure; sustained 57%, 50%, and 40% GFR declines from baseline; and GFR slope. The WO describes the odds of a more favorable outcome for receiving the active compared with the control. We compared the WO with the hazard ratio (HR) of the primary kidney outcome of the original trials. RESULTS: In all trials, treatment effects calculated with the WO reflected a similar direction and magnitude of the treatment effect compared with the HR. Clinical trials incorporating the HCE would achieve increased statistical power compared with the established composite end point at equivalent sample sizes. CONCLUSIONS: In seven major kidney clinical trials, the WO and HR provided similar direction of treatment effect estimates with smaller HRs associated with larger WOs. The prioritization of clinical outcomes and inclusion of broader composite end points makes the HCE an attractive alternative to the established kidney end point
Model dependence of single-energy fits to pion photoproduction data
Model dependence of multipole analysis has been explored through
energy-dependent and single-energy fits to pion photoproduction data. The MAID
energy-dependent solution has been used as input for an event generator
producing realistic pseudo data. These were fitted using the SAID
parametrization approach to determine single-energy and energy-dependent
solutions over a range of lab photon energies from 200 to 1200 MeV. The
resulting solutions were found to be consistent with the input amplitudes from
MAID. Fits with a -squared per datum of unity or less were generally
achieved. We discuss energy regions where consistent results are expected, and
explore the sensitivity of fits to the number of included single- and
double-polarization observables. The influence of Watson's theorem is examined
in detail.Comment: 12 pages, 8 figure
Strangeness Production in Proton-Proton Collisions Close to Threshold
Exclusive data on the reactions pp -> ppK+K- and pp -> pK+ Lambda/Sigma0 have
been taken at the cooler synchrotron COSY close to threshold. At equal excess
energies, an enhancement of the Lambda/Sigma0 ratio by one order of magnitude
has been observed compared to data at higher excess energies. New results
obtained at the COSY-11 facility explore the transition region between this
low-energy Sigma0 suppression and excess energies of 60 MeV. A first total
cross section for elementary antikaon production below the phi threshold has
been determined, two orders of magnitude smaller compared to kaon production at
the same excess energy.Comment: 4 pages, 2 figures, Talk given by P. Moskal at 16th International
Conference on Particles and Nuclei (PANIC 02), Osaka, Japan, 30 Sep - 4 Oct
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