62,842 research outputs found
Fail-safe system for activity cooled supersonic and hypersonic aircraft
A fail-safe-system concept was studied as an alternative to a redundant active cooling system for supersonic and hypersonic aircraft which use the heat sink of liquid-hydrogen fuel for cooling the aircraft structure. This concept consists of an abort maneuver by the aircraft and a passive thermal protection system (TPS) for the aircraft skin. The abort manuever provides a low-heat-load descent from normal cruise speed to a lower speed at which cooling is unnecessary, and the passive TPS allows the aircraft skin to absorb the abort heat load without exceeding critical skin temperature. On the basis of results obtained, it appears that this fail-safe-system concept warrants further consideration, inasmuch as a fail-safe system could possibly replace a redundant active cooling system with no increase in weight and would offer other potential advantages
Extrasolar Planets in the Classroom
The field of extrasolar planets is still, in comparison with other
astrophysical topics, in its infancy. There have been about 300 or so
extrasolar planets detected and their detection has been accomplished by
various different techniques. Here we present a simple laboratory experiment to
show how planets are detected using the transit technique. Following the simple
analysis procedure describe we are able to determine the planetary radius to be
1.27 +/- 0.20 R_{J} which, within errors agrees with the establish value of
1.32 +/- 0.25 R_{J}.Comment: 7 pages, 2 figures, published in Physics Educatio
A warped kernel improving robustness in Bayesian optimization via random embeddings
This works extends the Random Embedding Bayesian Optimization approach by
integrating a warping of the high dimensional subspace within the covariance
kernel. The proposed warping, that relies on elementary geometric
considerations, allows mitigating the drawbacks of the high extrinsic
dimensionality while avoiding the algorithm to evaluate points giving redundant
information. It also alleviates constraints on bound selection for the embedded
domain, thus improving the robustness, as illustrated with a test case with 25
variables and intrinsic dimension 6
On the positive eigenvalues and eigenvectors of a non-negative matrix
The paper develops the general theory for the items in the title, assuming
that the matrix is countable and cofinal.Comment: Version 2 allows the matrix to have zero row(s) and rows with
infinitely many non-zero entries. In addition the introduction has been
rewritte
A preliminary evaluation of LANDSAT-4 thematic mapper data for their geometric and radiometric accuracies
Some LANDSAT thematic mapper data collected over the eastern United States were analyzed for their whole scene geometric accuracy, band to band registration and radiometric accuracy. Band ratio images were created for a part of one scene in order to assess the capability of mapping geologic units with contrasting spectral properties. Systematic errors were found in the geometric accuracy of whole scenes, part of which were attributable to the film writing device used to record the images to film. Band to band registration showed that bands 1 through 4 were registered to within one pixel. Likewise, bands 5 and 7 also were registered to within one pixel. However, bands 5 and 7 were misregistered with bands 1 through 4 by 1 to 2 pixels. Band 6 was misregistered by 4 pixels to bands 1 through 4. Radiometric analysis indicated two kinds of banding, a modulo-16 stripping and an alternate light dark group of 16 scanlines. A color ratio composite image consisting of TM band ratios 3/4, 5/2, and 5/7 showed limonitic clay rich soils, limonitic clay poor soils, and nonlimonitic materials as distinctly different colors on the image
Pressure-viscosity measurements for several lubricants to 5.5 x 10 to the 8th power Newtons per square meter (8 x 10 to the 4th psi) and 149 C (300 F)
A capillary viscometer was used to measure viscosity as a function of pressure, temperature, and shear stress for a number of lubricants. The conditions under which the measurements were made are specified. The results obtained for each material are analyzed. It was determined that all pressure-viscosity coefficients decreased with increasing temperature. Data from other techniques such as optical elastohydrodynamics, oscillating crystal, and low shear capillary viscometry were compared with the results obtained
Modulation of endoglin expression in islets of langerhans by VEGF reveals a novel regulator of islet endothelial cell function
BACKGROUND: Endoglin/CD105 is an auxiliary receptor for transforming growth factor-β with established roles in vascular remodelling. It has recently been shown that heterozygous endoglin deficiency in mice decreases insulin secretion in an animal model of obesity, highlighting a potential role for endoglin in the regulation of islet function. We have previously identified two different populations of endoglin expressing cells in human and mouse islets which are: (i) endothelial cells (ECs) and (ii) islet mesenchymal stromal cells. The contribution of islet EC endoglin expression to islet development and sensitivity to VEGF is unknown and is the focus of this study. RESULTS: In vitro culture of mouse islets with VEGF164 for 48 h increased endoglin mRNA levels above untreated controls but VEGF did not modulate VEGFR2, CD31 or CD34 mRNA expression or islet viability. Removal of EC-endoglin expression in vivo reduced islet EC area but had no apparent effect on islet size or architecture. CONCLUSION: EC-specific endoglin expression in islets is sensitive to VEGF and plays partial roles in driving islet vascular development, however such regulation appears to be distinct to mechanisms required to modulate islet viability and size
Combining phytoremediation with bioenergy production: developing a multi‑criteria decision matrix for plant species selection
The use of plants to extract metal contaminants from soils has been proposed as a cost-effective means of remediation, and
utilizing energy crops for this phytoextraction process is a
useful way of attaining added value from the process. To simultaneously attain both these objectives successfully, selection of an appropriate plant species is crucial to satisfy a number of important criteria including translocation index, metal
and drought tolerance, fast growth rate, high lignocellulosic content, good biomass production, adequate calorific value, second generation attribute, and a good rooting system. In this study, we proposed a multi-criteria decision analysis (MCDA) to aid decision-making on plant species based on information generated from a systematic review survey. Eight species Helianthus annuus (sunflower), Brassica juncea (Indian mustard), Glycine max (soybean), Salix spp. (willow), Populus spp. (poplar), Panicum virgatum (switchgrass), Typha latifolia (cattails), and Miscanthus sinensis (silvergrass) were examined based on the amount of hits on a number of scientific search databases. The data was normalized by estimating their min–max values and their suitability. These criteria/indicators were weighted based on stipulated research objectives/priorities to form the basis of a final overall utility scoring. Using the MCDA, sunflower and silvergrass emerged as the top two candidates for both phytoremediation and bioenergy production. The multi-criteria matrix scores assist the process of making decisions because they compile plant species options quantitatively for all relevant criteria and key performance indicators (KPIs) and its weighing process helps incorporate stakeholder priorities to the selection process
Geometric, electronic properties and the thermodynamics of pure and Al--doped Li clusters
The first--principles density functional molecular dynamics simulations have
been carried out to investigate the geometric, the electronic, and the finite
temperature properties of pure Li clusters (Li, Li) and Al--doped
Li clusters (LiAl, LiAl). We find that addition of two Al
impurities in Li results in a substantial structural change, while the
addition of one Al impurity causes a rearrangement of atoms. Introduction of
Al--impurities in Li establishes a polar bond between Li and nearby Al
atom(s), leading to a multicentered bonding, which weakens the Li--Li metallic
bonds in the system. These weakened Li--Li bonds lead to a premelting feature
to occur at lower temperatures in Al--doped clusters. In LiAl, Al
atoms also form a weak covalent bond, resulting into their dimer like behavior.
This causes Al atoms not to `melt' till 800 K, in contrast to the Li atoms
which show a complete diffusive behavior above 400 K. Thus, although one Al
impurity in Li cluster does not change its melting characteristics
significantly, two impurities results in `surface melting' of Li atoms whose
motions are confined around Al dimer.Comment: 9 pages, 7 figure
Error tolerance in an NMR Implementation of Grover's Fixed-Point Quantum Search Algorithm
We describe an implementation of Grover's fixed-point quantum search
algorithm on a nuclear magnetic resonance (NMR) quantum computer, searching for
either one or two matching items in an unsorted database of four items. In this
new algorithm the target state (an equally weighted superposition of the
matching states) is a fixed point of the recursive search operator, and so the
algorithm always moves towards the desired state. The effects of systematic
errors in the implementation are briefly explored.Comment: 5 Pages RevTex4 including three figures. Changes made at request of
referees; now in press at Phys Rev
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