Photovoltaic Oscillations Due to Edge-Magnetoplasmon Modes in a Very-High Mobility 2D Electron Gas

Using very-high mobility GaAs/AlGaAs 2D electron Hall bar samples, we have experimentally studied the photoresistance/photovoltaic oscillations induced by microwave irradiation in the regime where both 1/B and B-periodic oscillations can be observed. In the frequency range between 27 and 130 GHz we found that these two types of oscillations are decoupled from each other, consistent with the respective models that 1/B oscillations occur in bulk while the B-oscillations occur along the edges of the Hall bars. In contrast to the original report of this phenomenon (Ref. 1) the periodicity of the B-oscillations in our samples are found to be independent of L, the length of the Hall bar section between voltage measuring leads.Comment: 4 pages, 4 figure

Superior vena cava thrombectomy with the X-SIZER® catheter system in a child with Fontan palliation

A 4-year-old female with hypoplastic left heart syndrome and Fontan palliation presented with severe neurologic impairment from thrombosis of the superior vena cava (SVC). She underwent successful SVC thrombectomy with the X-SIZER® Thrombectomy Catheter System, followed by balloon angioplasty. She demonstrated rapid improvement in her neurologic deficits after the procedure. This represents the first published use of the X-SIZER in a child and its first published use for SVC thrombectomy. © 2006 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/55911/1/20927_ftp.pd

Millimeter wave transmission spectroscopy of gated two-dimensional hole systems

We developed a differential transmission to study cyclotron resonance of GaAs/AlxGa1 xAs two-dimensional hole samples. The technique utilizes a modulated AuPd gate isolated by a Si3N4 dielectric from the sample, which is irradiated opposite the gate by millimeter waves ranging from 2 to 40GHz. This technique effectively removes the background signal and yields a hole effective mass of 0:41me with a cyclotron scattering time of 20 ps, consistent with the previous results using different techniques

Quantum Chaos in Quantum Wells

We develop a quantitative semiclassical theory for the resosnant tunneling through a quantum well in a tilted magnetic field. It is shown, that in the leading semiclassical approximation the tunneling current depends only on periodic orbits within the quantum well. Further corrections (due to e.g. "ghost" effect) can be expressed in terms of closed, but non-periodic orbits, started at the "injection point". The results of the semiclassical theory are shown to be in good agreement with both the experimental data and numerical calculations.Comment: 25 pages, 15 figures, accepted for publication in Physica

Cold Fermi-gas with long range interaction in a harmonic trap

We study equilibrium density and spin density profiles for a model of cold one-dimensional spin 1/2 fermions interacting via inverse square interaction and exchange in an external harmonic trap. This model is the well-known spin-Calogero model (sCM) and its fully nonlinear collective field theory description is known. We extend the field theory description to the presence of an external harmonic trap and obtain analytic results for statics and dynamics of the system. For instance, we find how the equilibrium density profile changes upon tuning the interaction strength. The results we obtain for equilibrium configurations are very similar to the ones obtained recently by Ma and Yang [1] for a model of fermions with short ranged interactions. Our main approximation is the neglect of the terms of higher order in spatial derivatives in equations of motion - gradientless approximation [2]. Within this approximation the hydrodynamic equations of motion can be written as a set of decoupled forced Riemann-Hopf equations for the dressed Fermi momenta of the model. This enables us to write analytical solutions for the dynamics of spin and charge. We describe the time evolution of the charge density when an initial non-equilibrium profile is created by cooling the gas with an additional potential in place and then suddenly removing the potential. We present our results as a simple "single-particle" evolution in the phase-space reminiscing a similar description of the dynamics of non-interacting one-dimensional fermions.Comment: 11 pages, 5 figures (figure typo corrected and references added

A Simplified Approach to Determine α\alpha and the Penguin Amplitude in Bd→ππB_{d}\to \pi\pi

The effect of inelastic final-state interactions (IFSI's) on the determination of the weak phase $\alpha$ from the isospin triangles of $B\rightarrow \pi\pi$ is qualitatively illustrated. Neglecting the electroweak penguins and IFSI's and assuming the dominance of the top-quark loop in strong penguin diagrams, we propose an experimentally accessible way to approximately determine $\alpha$ and the penguin amplitude in $B_{d}\rightarrow \pi\pi$. This approach relies on a simplified isospin consideration and the factorization approximation, and its feasibility is irrelevant to the time-dependent measurements of $B_d\rightarrow \pi\pi$.Comment: This work has been accepted for publication in Phys. Lett. B. In the revised version, we add a new section to give a qualitative illustration of the effect of inelastic final-state interactions on the determination of the weak phase $\alpha$ from the isospin triangles of $B\to \pi\pi$ . 10 Latex pages (with 1 figure

Topology and Fractional Quantum Hall Effect

Starting from Laughlin type wave functions with generalized periodic boundary conditions describing the degenerate groundstate of a quantum Hall system we explictly construct $r$ dimensional vector bundles. It turns out that the filling factor $\nu$ is given by the topological quantity $c_1 \over r$ where $c_1$ is the first chern number of these vector bundles. In addition, we managed to proof that under physical natural assumptions the stable vector bundles correspond to the experimentally dominating series of measured fractional filling factors $\nu = {n \over 2pn\pm 1}$. Most remarkably, due to the very special form of the Laughlin wave functions the fluctuations of the curvature of these vector bundles converge to zero in the limit of infinitely many particles which shows a new mathematical property. Physically, this means that in this limit the Hall conductivity is independent of the boundary conditions which is very important for the observabilty of the effect. Finally we discuss the relation of this result to a theorem of Donaldson.Comment: 15 pages, latex, no figure

On Measuring CPCP Violation in Neutral BB-meson Decays at the Υ(4S)\Upsilon (4S) Resonance

Within the standard model we carry out an analysis of $CP$-violating observables in neutral $B$-meson decays at the $\Upsilon (4S)$ resonance. Both time-dependent and time-integrated $CP$ asymmetries are calculated, without special approximations, to meet various possible measurements at symmetric and asymmetric $e^{+}e^{-}$ $B$ factories. We show two ways to distinguish between direct and indirect $CP$-violating effects in the $CP$-eigenstate channels such as $B^{0}_{d}/\bar{B}^{0}_{d}\rightarrow \pi^{+}\pi^{-}$ and $\pi^{0} K_{S}$. Reliable knowledge of the Cabibbo-Kobayashi-Maskawa phase and angles can in principle be extracted from measurements of some non-$CP$-eigenstate channels, e.g. $B^{0}_{d}/\bar{B}^{0}_{d}\rightarrow D^{\pm}\pi^{\mp}$ and $\stackrel{(-)}{D}$$^{(*)0}K_{S}$, even in the presence of significant final-state interactions.Comment: Latex file 13 pages, CERN-TH.7194/94 and PVAMU-HEP-94-2 (Phys. Lett. B328 (1994) 477). (A few minor typing errors have been corrected.

Changes in synaptic transmission and protein expression in the brains of adult offspring after prenatal inhibition of the kynurenine pathway

During early brain development, N-methyl-d-aspartate (NMDA) receptors are involved in cell migration, neuritogenesis, axon guidance and synapse formation, but the mechanisms which regulate NMDA receptor density and function remain unclear. The kynurenine pathway of tryptophan metabolism includes an agonist (quinolinic acid) and an antagonist (kynurenic acid) at NMDA receptors and we have previously shown that inhibition of the pathway using the kynurenine-3-monoxygenase inhibitor Ro61-8048 in late gestation produces rapid changes in protein expression in the embryos and effects on synaptic transmission lasting until postnatal day 21 (P21). The present study sought to determine whether any of these effects are maintained into adulthood. After prenatal injections of Ro61-8048 the litter was allowed to develop to P60 when some offspring were euthanized and the brains removed for examination. Analysis of protein expression by Western blotting revealed significantly reduced expression of the GluN2A subunit (32%) and the morphogenetic protein sonic hedgehog (31%), with a 29% increase in the expression of doublecortin, a protein associated with neurogenesis. No changes were seen in mRNA abundance using quantitative real-time polymerase chain reaction. Neuronal excitability was normal in the CA1 region of hippocampal slices but paired-pulse stimulation revealed less inhibition at short interpulse intervals. The amount of long-term potentiation was decreased by 49% in treated pups and recovery after low-frequency stimulation was delayed. The results not only strengthen the view that basal, constitutive kynurenine metabolism is involved in normal brain development, but also show that changes induced prenatally can affect the brains of adult offspring and those changes are quite different from those seen previously at weaning (P21). Those changes may be mediated by altered expression of NMDAR subunits and sonic hedgehog