2,746 research outputs found
Edge Magnetoplasmons in Quantum Hall Line Junction Systems
A quantum Hall line junction system consists of a one-dimensional Luttinger
liquid (LL) and two chiral channels that allow density waves incident upon and
reflected by the LL to be measured separately. We demonstrate that interactions
in a quantum Hall line junction system can be probed by studying edge
magnetoplasmon absorption spectra and their polarization dependences. Strong
interactions in the junction lead to collective modes that are isolated in
either Luttinger liquid or contact subsystems.Comment: 4 pages, 3 figures, submitted to Phys. Rev. B Rapid Communicatio
Smoothing a Rock by Chipping
We investigate an idealized model for the size reduction and smoothing of a
polygonal rock due to repeated chipping at corners. Each chip is sufficiently
small so that only a single corner and a fraction of its two adjacent sides are
cut from the object in a single chipping event. After many chips have been cut
away, the resulting shape of the rock is generally anisotropic, with facet
lengths and corner angles distributed over a broad range. Although a
well-defined shape is quickly reached for each realization, there are large
fluctuations between realizations.Comment: 7 pages, 10 figures, 2-column revtex4 format; version 2: final
published form in PRE; contains minor changes in response to referee comment
Longitudinal analysis of the developing rhesus monkey brain using magnetic resonance imaging: birth to adulthood.
We have longitudinally assessed normative brain growth patterns in naturalistically reared Macaca mulatta monkeys. Postnatal to early adulthood brain development in two cohorts of rhesus monkeys was analyzed using magnetic resonance imaging. Cohort A consisted of 24 rhesus monkeys (12 male, 12 female) and cohort B of 21 monkeys (11 male, 10 female). All subjects were scanned at 1, 4, 8, 13, 26, 39, and 52Â weeks; cohort A had additional scans at 156Â weeks (3Â years) and 260Â weeks (5Â years). Age-specific segmentation templates were developed for automated volumetric analyses of the T1-weighted magnetic resonance imaging scans. Trajectories of total brain size as well as cerebral and subcortical subdivisions were evaluated over this period. Total brain volume was about 64Â % of adult estimates in the 1-week-old monkey. Brain volume of the male subjects was always, on average, larger than the female subjects. While brain volume generally increased between any two imaging time points, there was a transient plateau of brain growth between 26 and 39Â weeks in both cohorts of monkeys. The trajectory of enlargement differed across cortical regions with the occipital cortex demonstrating the most idiosyncratic pattern of maturation and the frontal and temporal lobes showing the greatest and most protracted growth. A variety of allometric measurements were also acquired and body weight gain was most closely associated with the rate of brain growth. These findings provide a valuable baseline for the effects of fetal and early postnatal manipulations on the pattern of abnormal brain growth related to neurodevelopmental disorders
Nanometer-scale sharpness in corner-overgrown heterostructures
A corner-overgrown GaAs/AlGaAs heterostructure is investigated with
transmission and scanning transmission electron microscopy, demonstrating
self-limiting growth of an extremely sharp corner profile of 3.5 nm width. In
the AlGaAs layers we observe self-ordered diagonal stripes, precipitating
exactly at the corner, which are regions of increased Al content measured by an
XEDS analysis. A quantitative model for self-limited growth is adapted to the
present case of faceted MBE growth, and the corner sharpness is discussed in
relation to quantum confined structures. We note that MBE corner overgrowth
maintains nm-sharpness even after microns of growth, allowing the realization
of corner-shaped nanostructures.Comment: 4 pages, 3 figure
Tunnelling Spectroscopy of Localized States near the Quantum Hall Edge
In the paper we dscuss experimental results of M. Grayson et al. on tunneling
- characteristics of the quantum Hall edge. We suggest a two step
tunneling mechanism involving localized electron states near the edge, which
might account for discrepancy between the experimental data and the predictions
of the chiral Luttinger liquid theory of the quantum Hall edge.Comment: 4 pages, revte
Fermi liquid to Luttinger liquid transition at the edge of a two-dimensional electron gas
We present experimental results on the tunneling into the edge of a two
dimensional electron gas (2DEG) obtained with a GaAs/AlGaAs cleaved edge
overgrown structure in a strong perpendicular magnetic field. While the 2DEG
exhibits typical fractional quantum Hall features of a very high mobility
sample, we observe the onset of a non-linear current-voltage characteristic in
the vicinity of nu=1. For filling factor nu<1 the system is consistent with a
non-Fermi liquid behavior, such as a Luttinger liquid, whereas for nu>1 we
observe an Ohmic tunneling resistance between the edge and a three dimensional
contact, typical for a Fermi liquid. Hence, at the edge, there is a transition
from a Luttinger liquid to a Fermi liquid. Finally, we show that the Luttinger
liquid exponent at a given filling factor is not universal but depends on
sample parameters.Comment: 4 pages, 4 figure
Multicystic adenomatoid hamartoma of the pancreas
Multicystic adenomatoid hamartoma is an extremely rare tumor of the pancreas, with only 4 other cases reported in the literature. We report a case of a 4-year old boy who presented with an 8 month history of abdominal pain, steatorrhea, and failure to thrive. Work-up showed severe pancreatic insufficiency and a large, multiseptated, cystic mass originating from the head of the pancreas and compressing the duodenum. The child underwent a classic pancreaticoduodenectomy with portal vein reconstruction. He tolerated the procedure well and has been seen in follow-up
Improving the Sensitivity of LISA
It has been shown in the past, that the six Doppler data streams obtained
LISA configuration can be combined by appropriately delaying the data streams
for cancelling the laser frequency noise. Raw laser noise is several orders of
magnitude above the other noises and thus it is essential to bring it down to
the level of shot, acceleration noises. A rigorous and systematic formalism
using the techniques of computational commutative algebra was developed which
generates all the data combinations cancelling the laser frequency noise. The
relevant data combinations form a first module of syzygies. In this paper we
use this formalism for optimisation of the LISA sensitivity by analysing the
noise and signal covariance matrices. The signal covariance matrix, averaged
over polarisations and directions, is calculated for binaries whose frequency
changes at most adiabatically. We then present the extremal SNR curves for all
the data combinations in the module. They correspond to the eigenvectors of the
noise and signal covariance matrices. We construct LISA `network' SNR by
combining the outputs of the eigenvectors which improves the LISA sensitivity
substantially. The maximum SNR curve can yield an improvement upto 70 % over
the Michelson, mainly at high frequencies, while the improvement using the
network SNR ranges from 40 % to over 100 %. Finally, we describe a simple toy
model, in which LISA rotates in a plane. In this analysis, we estimate the
improvement in the LISA sensitivity, if one switches from one data combination
to another as it rotates. Here the improvement in sensitivity, if one switches
optimally over three cyclic data combinations of the eigenvector is about 55 %
on an average over the LISA band-width. The corresponding SNR improvement is 60
%, if one maximises over the module.Comment: 16 pages, 10 figures, Submitted to Class. Quant. Gravit
Experiments on the Fermi to Tomonaga-Luttinger liquid transition in quasi-1D systems
We present experimental results on the tunneling into the edge of a two
dimensional electron gas (2DEG) obtained with GaAs/AlGaAs cleaved edge
overgrown structures. The electronic properties of the edge of these systems
can be described by a one-dimensional chiral Tomonaga-Luttinger liquid when the
filling factor of the 2DEG is very small. Here we focus on the region where the
Tomonaga-Luttinger liquid breaks down to form a standard Fermi liquid close to
and show that we recover a universal curve, which describes all
existing data.Comment: 5 pages, localisation 2002, conference proceeding
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