4,345 research outputs found
Water facilities in retrospect and prospect: An illuminating tool for vehicle design
Water facilities play a fundamental role in the design of air, ground, and marine vehicles by providing a qualitative, and sometimes quantitative, description of complex flow phenomena. Water tunnels, channels, and tow tanks used as flow-diagnostic tools have experienced a renaissance in recent years in response to the increased complexity of designs suitable for advanced technology vehicles. These vehicles are frequently characterized by large regions of steady and unsteady three-dimensional flow separation and ensuing vortical flows. The visualization and interpretation of the complicated fluid motions about isolated vehicle components and complete configurations in a time and cost effective manner in hydrodynamic test facilities is a key element in the development of flow control concepts, and, hence, improved vehicle designs. A historical perspective of the role of water facilities in the vehicle design process is presented. The application of water facilities to specific aerodynamic and hydrodynamic flow problems is discussed, and the strengths and limitations of these important experimental tools are emphasized
Color Measurement on Substrates with Optical Brightening Agents
Yellow and blue Pantone colors were printed on a substrate with high Optical Brightening Agent (OBA) levels and then measured under different measurement conditions as outlined in ISO 13655. Both colors exhibited large DEOO shifts with lighter screen tints, as more paper influenced the measurement. The Pantone colors were further analysed after being printed on two different substrates with varying OBAs. While the solids were color-matched to a DEOO of less than 1.0, the tints resulted in DEOO values above 7.0 due to more paper influence in the lighter screen tints
Herpetofaunal Inventory of Arkansas Post National Memorial, Arkansas County, Arkansas
The Arkansas Post National Memorial (ARPO) is a unique historical landmark with an interesting herpetofaunal community. We conducted an amphibian and reptile inventory of this national park from 2000-2002. We found eight amphibian and 21 reptilian species inhabiting the park. These included eight species not previously identified at ARPO. Overall species richness was highest at Alligator Slough, although the northern portion of ARPO was relatively rich. Aquatic trophic guilds included 7 (36.8%) piscivores, 7 (36.8%) omnivores, 4 (21.1%) insectivores, and one (5.3%) carnivore. The terrestrial trophic guilds included 13 (76.5%) insectivores, 2 (11.8%) carnivores, and 1 (5.9%) each of omnivores and generalized carnivores. We provide a species list, analysis of the distributions, diversity relationships and the trophic guilds present at ARPO, including management recommendations for the conservation of the herpetofauna community at ARPO
Following microscopic motion in a two dimensional glass-forming binary fluid
The dynamics of a binary mixture of large and small discs are studied at
temperatures approaching the glass transition using an analysis based on the
topology of the Voronoi polygon surrounding each atom. At higher temperatures
we find that dynamics is dominated by fluid-like motion that involves particles
entering and exiting the nearest-neighbour shells of nearby particles. As the
temperature is lowered, the rate of topological moves decreases and motion
becomes localised to regions of mixed pentagons and heptagons. In addition we
find that in the low temperature state particles may translate significant
distances without undergoing changes in their nearest neig hbour shell. These
results have implications for dynamical heterogeneities in glass forming
liquids.Comment: 12 pages, 7 figure
Creation and pinning of vortex-antivortex pairs
Computer modeling is reported about the creation and pinning of a magnetic
vortex-antivortex (V-AV) pair in a superconducting thin film, due to the
magnetic field of a vertical magnetic dipole above the film, and two antidot
pins inside the film. For film thickness , , and no pins,
we find the film carries two V-AV pairs at steady state in the imposed flux
range , and no pairs below. With two antidot
pins suitably introduced into the film, a single V-AV pair can be stable in the
film for . At pin separation , we find the
V-AV pair remains pinned after the dipole field is removed, and, so can
represent a 1 for a nonvolatile memory.Comment: 8 pages, 6 figure
Electronic properties of buried hetero-interfaces of LaAlO3 on SrTiO3
We have made very thin films of LaAlO3 on TiO2 terminated SrTiO3 and have
measured the properties of the resulting interface in various ways. Transport
measurements show a maximum sheet carrier density of 1016 cm-2 and a mobility
around 104 cm2 V-1 s-1. In situ ultraviolet photoelectron spectroscopy (UPS)
indicates that for these samples a finite density of states exists at the Fermi
level. From the oxygen pressure dependence measured in both transport as well
as the UPS, we detail, as reported previously by us, that oxygen vacancies play
an important role in the creation of the charge carriers and that these
vacancies are introduced by the pulsed laser deposition process used to make
the heterointerfaces. Under the conditions studied the effect of LaAlO3 on the
carrier density is found to be minimal.Comment: 19 pages, 6 figure
Kaluza-Klein electrically charged black branes in M-theory
We present a class of Kaluza-Klein electrically charged black p-brane
solutions of ten-dimensional, type IIA superstring theory. Uplifting to eleven
dimensions these solutions are studied in the context of M-theory. They can be
interpreted either as a p+1 extended object trapped around the eleventh
dimension along which momentum is flowing or as a boost of the following
backgrounds: the Schwarzschild black (p+1)-brane or the product of the
(10-p)-dimensional Euclidean Schwarzschild manifold with the (p+1)-dimensional
Minkowski spacetime.Comment: 16 pages, uses latex and epsf macro, figures include
An objective rationale for the choice of regularisation parameter with application to global multiple-frequency S -wave tomography
In a linear ill-posed inverse problem, the regularisation parameter (damping) controls the balance between minimising both the residual data misfit and the model norm. Poor knowledge of data uncertainties often makes the selection of damping rather arbit
Ozone Response to Aircraft Emissions: Sensitivity Studies with Two-dimensional Models
Our first intercomparison/assessment of the effects of a proposed high-speed civil transport (HSCT) fleet on the stratosphere is presented. These model calculations should be considered more as sensitivity studies, primarily designed to serve the following purposes: (1) to allow for intercomparison of model predictions; (2) to focus on the range of fleet operations and engine specifications giving minimal environmental impact; and (3) to provide the basis for future assessment studies. The basic scenarios were chosen to be as realistic as possible, using the information available on anticipated developments in technology. They are not to be interpreted as a commitment or goal for environmental acceptability
Hot gas and dust in a protostellar cluster near W3(OH
We used the IRAM Interferometer to obtain sub-arcsecond resolution
observations of the high-mass star-forming region W3(OH) and its surroundings
at a frequency of 220 GHz. With the improved angular resolution, we distinguish
3 peaks in the thermal dust continuum emission originating from the hot core
region about 6 arcsec (0.06 pc) east of W3(OH). The dust emission peaks are
coincident with known radio continuum sources, one of which is of non-thermal
nature. The latter source is also at the center of expansion of a powerful
bipolar outflow observed in water maser emission. We determine the hot core
mass to be 15 solar masses based on the integrated dust continuum emission.
Simultaneously many molecular lines are detected allowing the analysis of the
temperature structure and the distribution of complex organic molecules in the
hot core. From HNCO lines, spanning a wide range of excitation, two 200 K
temperature peaks are found coincident with dust continuum emission peaks
suggesting embedded heating sources within them.Comment: 12 pages, 3 figure
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