3,569 research outputs found
Development of a wind shear performance envelope
It is quite important that the airplane performance during a continuing headwind loss be understood. Lack of consideration of this characteristic can result in assuming almost twice the performance than that which the airplane actually has during severe wind shear at high descent rates. The example data relates to the Boeing 727-200, but the characteristics are applicable to any airplane
Generation of an intense cold-atom beam from a pyramidal magneto-optical trap: experiment and simulation
An intense cold-atom beam source based on a modified pyramidal magneto-optical trap has been developed and characterized. We have produced a slow beam of cold cesium atoms with a continuous flux of 2.2× 10^9 atoms/s at a mean velocity of 15 m/s and with a divergence of 15 mrad. The corresponding radiant intensity is 1.2×10^13 atom s^−1 sr^−1. We have characterized the performance of our beam source over a range of operating conditions, and the measured values for atom flux, mean velocity, and divergence are in good agreement with results from detailed Monte Carlo numerical simulations
Diagnosis of Helicobacter pylori by carbon-13 urea breath test using a portable mass spectrometer
CONTEXT: In the non-invasive detection of markers of disease, mass spectrometry is able to detect small quantities of volatile markers in exhaled air. However, the problem of size, expense and immobility of conventional mass spectrometry equipment has restricted its use. Now, a smaller, less expensive, portable quadrupole mass spectrometer system has been developed. Helicobacter pylori has been implicated in the development of chronic gastritis, gastric and duodenal ulcers and gastric cancer. OBJECTIVES: To compare the results obtained from the presence of H. pylori by a carbon-13 urea test using a portable quadrupole mass spectrometer system with those from a fixed mass spectrometer in a hospital-based clinical trial. METHODS: Following ethical approval, 45 patients attending a gastroenterology clinic at the Royal Liverpool University Hospital exhaled a breath sample into a Tedlar gas sampling bag. They then drank an orange juice containing urea radiolabelled with carbon and 30 min later gave a second breath sample. The carbon-13 content of both samples was measured using both quadrupole mass spectrometer systems. If the post-drink level exceeded the pre-drink level by 3% or more, a positive diagnosis for the presence of H. pylori was made. RESULTS: The findings were compared to the results using conventional isotope ratio mass spectrometry using a laboratory-based magnetic sector instrument off-site. The results showed agreement in 39 of the 45 patients. CONCLUSIONS: This study suggests that a portable quadrupole mass spectrometer is a potential alternative to the conventional centralised testing equipment. Future development of the portable quadrupole mass spectrometer to reduce further its size and cost is indicated, together with further work to validate this new equipment and to enhance its use in mass spectrometry diagnosis of other medical conditions
Reduced order models for nonlinear aerodynamics
Reduced order models are needed for reliable, efficient and accurate prediction of aerodynamic forces to analyze fluid structure interaction problems in turbomachinery, including propfans. Here, a finite difference, time marching Navier-Stokes code is validated for unsteady airfoil motion by comparing results with those from classical potential flow. The Navier-Stokes code is then analyzed for calculation of primitive and exact estimates of eigenvalues and eigenvectors associated with fluid-airfoil interaction. A variational formulation for the Euler equations and Navier-Stokes equations will be the basis for reduction of order through an eigenvector transformation
Dynamical model of sequential spatial memory: winnerless competition of patterns
We introduce a new biologically-motivated model of sequential spatial memory
which is based on the principle of winnerless competition (WLC). We implement
this mechanism in a two-layer neural network structure and present the learning
dynamics which leads to the formation of a WLC network. After learning, the
system is capable of associative retrieval of pre-recorded sequences of spatial
patterns.Comment: 4 pages, submitted to PR
Spin interactions of interstitial Mn ions in ferromagnetic GaMnAs
The recently reported Rutherford backscattering and particle-induced X-ray
emission experiments have revealed that in low-temperature MBE grown GaMnAs a
significant part of the incorporated Mn atoms occupies tetrahedral interstitial
sites in the lattice. Here we study the magnetic properties of these
interstitial ions. We show that they do not participate in the hole-induced
ferromagnetism. Moreover, Mn interstitial double donors may form pairs with the
nearest substitutional Mn acceptors - our calculations evidence that the spins
in such pairs are antiferromagnetically coupled by the superexchange. We also
show that for the Mn ion in the other, hexagonal, interstitial position (which
seems to be the case in the GaMnBeAs samples) the p-d interactions with the
holes, responsible for the ferromagnetism, are very much suppressed.Comment: 4 pages, 3 figures, submitted to PR
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Scintillating glass fiber neutron sensors: 2, Light transmission in scintillating fibers
The capture and transmission of light from an event through a scintillating fiber is somewhat different than in conventional optical waveguide applications. A theoretical all-ray model that depends on surface and bulk loss factors is developed for this transmission. The capture fraction can be significantly greater than that predicted on the basis of meridional rays alone and the gross loss is nonexponential for short distances (less than or of the order of one 1/e distance). The latter phenomenon occurs because high-angle and skew rays are more rapidly attenuated than meridional rays
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Delivery of Functional Anti-miR-9 by Mesenchymal Stem Cell–derived Exosomes to Glioblastoma Multiforme Cells Conferred Chemosensitivity
Glioblastoma multiforme (GBM), the most common and lethal tumor of the adult brain, generally shows chemo- and radioresistance. MicroRNAs (miRs) regulate physiological processes, such as resistance of GBM cells to temozolomide (TMZ). Although miRs are attractive targets for cancer therapeutics, the effectiveness of this approach requires targeted delivery. Mesenchymal stem cells (MSCs) can migrate to the sites of cancers, including GBM. We report on an increase in miR-9 in TMZ-resistant GBM cells. miR-9 was involved in the expression of the drug efflux transporter, P-glycoprotein. To block miR-9, methods were developed with Cy5-tagged anti-miR-9. Dye-transfer studies indicated intracellular communication between GBM cells and MSCs. This occurred by gap junctional intercellular communication and the release of microvesicles. In both cases, anti-miR-9 was transferred from MSCs to GBM cells. However, the major form of transfer occurred with the microvesicles. The delivery of anti-miR-9 to the resistant GBM cells reversed the expression of the multidrug transporter and sensitized the GBM cells to TMZ, as shown by increased cell death and caspase activity. The data showed a potential role for MSCs in the functional delivery of synthetic anti-miR-9 to reverse the chemoresistance of GBM cells
Serum kynurenic acid is reduced in affective psychosis
A subgroup of individuals with mood and psychotic disorders shows evidence of inflammation that leads to activation of the kynurenine pathway and the increased production of neuroactive kynurenine metabolites. Depression is hypothesized to be causally associated with an imbalance in the kynurenine pathway, with an increased metabolism down the 3-hydroxykynurenine (3HK) branch of the pathway leading to increased levels of the neurotoxic metabolite, quinolinic acid (QA), which is a putative Nmethyl- D-aspartate (NMDA) receptor agonist. In contrast, schizophrenia and psychosis are hypothesized to arise from increased metabolism of the NMDA receptor antagonist, kynurenic acid (KynA), leading to hypofunction of GABAergic interneurons, the disinhibition of pyramidal neurons and striatal hyperdopaminergia. Here we present results that challenge the model of excess KynA production in affective psychosis. After rigorous control of potential confounders and multiple testing we find significant reductions in serum KynA and/or KynA/QA in acutely ill inpatients with major depressive disorder (N = 35), bipolar disorder (N = 53) and schizoaffective disorder (N = 40) versus healthy controls (N = 92). No significant difference was found between acutely ill inpatients with schizophrenia (n = 21) and healthy controls. Further, a post hoc comparison of patients divided into the categories of non-psychotic affective disorder, affective psychosis and psychotic disorder (non-affective) showed that the greatest decrease in KynA was in the affective psychosis group relative to the other diagnostic groups. Our results are consistent with reports of elevations in proinflammatory cytokines in psychosis, and preclinical work showing that inflammation upregulates the enzyme, kynurenine mono-oxygenase (KMO), which converts kynurenine into 3-hydroxykynurenine and quinolinic acid
Annealing-Dependent Magnetic Depth Profile in Ga[1-x]Mn[x]As
We have studied the depth-dependent magnetic and structural properties of
as-grown and optimally annealed Ga[1-x]Mn[x]As films using polarized neutron
reflectometry. In addition to increasing total magnetization, the annealing
process was observed to produce a significantly more homogeneous distribution
of the magnetization. This difference in the films is attributed to the
redistribution of Mn at interstitial sites during the annealing process. Also,
we have seen evidence of significant magnetization depletion at the surface of
both as-grown and annealed films.Comment: 5 pages, 3 figure
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