3,738 research outputs found
On the probability of occurrence of rogue waves
A number of extreme and rogue wave studies have been conducted theoretically, numerically, experimentally and based on field data in the last years, which have significantly advanced our knowledge of ocean waves. So far, however, consensus on the probability of occurrence of rogue waves has not been achieved. The present investigation is addressing this topic from the perspective of design needs. Probability of occurrence of extreme and rogue wave crests in deep water is here discussed based on higher order time simulations, experiments and hindcast data. Focus is given to occurrence of rogue waves in high sea states
Bright single-photon sources in bottom-up tailored nanowires
The ability to achieve near-unity light extraction efficiency is necessary
for a truly deterministic single photon source. The most promising method to
reach such high efficiencies is based on embedding single photon emitters in
tapered photonic waveguides defined by top-down etching techniques. However,
light extraction efficiencies in current top-down approaches are limited by
fabrication imperfections and etching induced defects. The efficiency is
further tempered by randomly positioned off-axis quantum emitters. Here, we
present perfectly positioned single quantum dots on the axis of a tailored
nanowire waveguide using bottom-up growth. In comparison to quantum dots in
nanowires without waveguide, we demonstrate a 24-fold enhancement in the single
photon flux, corresponding to a light extraction efficiency of 42 %. Such high
efficiencies in one-dimensional nanowires are promising to transfer quantum
information over large distances between remote stationary qubits using flying
qubits within the same nanowire p-n junction.Comment: 19 pages, 6 figure
Large-Area Mapping at 850 Microns. I. Optimum Image Reconstruction from Chop Measurements
We present results on the optimum reconstruction of chop data taken using the Submillimeter Common-User Bolometer Array on the James Clerk Maxwell Telescope. Using an artificial data set with known noise properties, we analyze three techniques for constructing images of the sky from the chop data: Emerson Fourier deconvolution, matrix inversion, and maximum entropy reconstruction. We conclude that a matrix inversion formulation via an iterative procedure produces the best image reconstructions. We apply the three reconstruction techniques to produce maps of the calibration point source CRL 618 and the ? Ophiuchi A core at 850 ?m and use Wiener filtering to remove the high-frequency noise component from the matrix inversion method
Molecular Inventories and Chemical Evolution of Low-mass Protostellar Envelopes
This paper presents the first substantial study of the chemistry of the
envelopes around a sample of 18 low-mass pre- and protostellar objects for
which physical properties have previously been derived from radiative transfer
modeling of their dust continuum emission. Single-dish line observations of 24
transitions of 9 molecular species (not counting isotopes) including HCO+,
N2H+, CS, SO, SO2, HCN, HNC, HC3N and CN are reported. The line intensities are
used to constrain the molecular abundances by comparison to Monte Carlo
radiative transfer modeling of the line strengths. An empirical chemical
network is constructed on the basis of correlations between the abundances of
various species. For example, it is seen that the HCO+ and CO abundances are
linearly correlated, both increasing with decreasing envelope mass. Species
such as CS, SO and HCN show no trend with envelope mass. In particular no trend
is seen between ``evolutionary stage'' of the objects and the abundances of the
main sulfur- or nitrogen-containing species. Among the nitrogen-bearing species
abundances of CN, HNC and HC3N are found to be closely correlated, which can be
understood from considerations of the chemical network. The CS/SO abundance
ratio is found to correlate with the abundances of CN and HC3N, which may
reflect a dependence on the atomic carbon abundance. An anti-correlation is
found between the deuteration of HCO+ and HCN, reflecting different temperature
dependences for gas-phase deuteration mechanisms. The abundances are compared
to other protostellar environments. In particular it is found that the
abundances in the cold outer envelope of the previously studied class 0
protostar IRAS16293-2422 are in good agreement with the average abundances for
the presented sample of class 0 objects.Comment: Accepted for publication in A&A. 29 pages, 23 figures. Abstract
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Model for Electrical Field Distribution in the Human Esophagus during Stimulation with Patch and Ring Electrodes
Introduction. Electrical stimulation is used in experimental human pain models. The aim was to develop a model that visualizes the distribution of electrical field in the esophagus close to ring and patch electrodes mounted on an esophageal catheter and to explain the obtained sensory responses.
Methods. Electrical field distribution in esophageal layers (mucosa, muscle layers, and surrounding tissue) was computed using a finite element model based on a 3D model. Each layer was assigned different electrical properties. An electrical field exceeding 20 V/m was considered to activate the esophageal afferents. Results. The model output showed homogeneous and symmetrical field surrounding ring electrodes compared to a saddle-shaped field around patch electrodes. Increasing interelectrode distance enlarged the electrical field in muscle layer.
Conclusion. Ring electrodes with 10 mm interelectrode distance seem optimal for future catheter designs. Though the model needs further validation, the results seem useful for electrode designs and understanding of electrical stimulation patterns
Novel ETHE1 mutation in a carrier couple having prior offspring affected with ethylmalonic encephalopathy: Genetic analysis, clinical management and reproductive outcome.
Ethylmalonic encephalopathy (EE) is an autosomally recessive inherited disorder with a relentlessly progressive decline in neurological function, usually fatal by the age of ten. It is characterised by generalised hypotonia, psychomotor regression, spastic tetraparesis, dystonia, seizures and, eventually, global neurological failure. Approximately 50 reports have been published worldwide describing this devastating disease, most involving patients of Mediterranean or Arab origin. The fundamental defect in EE likely involves the impairment of a mitochondrial sulphur dioxygenase coded by the ETHE1 gene responsible for the catabolism of sulphide, which subsequently accumulates to toxic levels. A diagnosis of EE should initiate careful genetic evaluation and counselling, particularly if the parents intend to have additional offspring. The present report describes the diagnosis of EE in a reproductive endocrinology context, where both members of a non-consanguineous couple were confirmed to be carriers of an identical A↷G mutation. This previously unknown mutation at nucleotide position c.494 resulted in an amino acid substitution, p.Asp165Gly. Although consideration was given to in vitro fertilisation, embryo biopsy and single gene pre-implantation genetic diagnosis, the couple decided to first utilise a less aggressive therapeutic approach with donor sperm insemination. Pregnancy with a low risk of EE was indeed achieved; however, the infant was affected with a different anomaly (hypoplastic left heart). As this case demonstrates, prior to the initiation of fertility therapy, genetic analysis may be used to provide a confirmatory diagnosis when EE is suspected
Rotation of the pre-stellar core L1689B
The search for the onset of star formation in pre-stellar cores has focussed
on the identification of an infall signature in the molecular line profiles of
tracer species. The classic infall signature is a double peaked line profile
with an asymmetry in the strength of the peaks such that the blue peak is
stronger. L1689B is a pre-stellar core and infall candidate but new JCMT HCO+
line profile data, presented here, confirms that both blue and red asymmetric
line profiles are present in this source. Moreover, a dividing line can be
drawn between the locations where each type of profile is found. It is argued
that it is unlikely that the line profiles can be interpreted with simple
models of infall or outflow and that rotation of the inner regions is the most
likely explanation. A rotational model is developed in detail with a new 3D
molecular line transport code and it is found that the best type of model is
one in which the rotational velocity profile is in between solid body and
Keplerian. It is firstly shown that red and blue asymmetric line profiles can
be generated with a rotation model entirely in the absence of any infall
motion. The model is then quantitively compared with the JCMT data and an
iteration over a range of parameters is performed to minmize the difference
between the data and model. The results indicate that rotation can dominate the
line profile shape even before the onset of infall.Comment: Accepted by MNRAS, 7 pages, 4 figure
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