12,663 research outputs found
Aerodynamic characteristics of the 40- by 80/80- by 120-foot wind tunnel at NASA Ames Research Center
The design and testing of vane sets and air-exchange inlet for the 40 x 80/80 x 120-ft wind tunnel at NASA Ames are reported. Boundary-layer analysis and 2D and 3D inviscid panel codes are employed in computer models of the system, and a 1/10-scale 2D facility and a 1/50-scale 3D model of the entire wind tunnel are used in experimental testing of the vane sets. The results are presented in graphs, photographs, drawings, and diagrams are discussed. Generally good agreement is found between the predicted and measured performance
Multiple-electron losses of highly charged ions colliding with neutral atoms
We present calculations of the total and m-fold electron-loss cross sections
using the DEPOSIT code for highly charged U(q+) ions (q=10,31,33) colliding
with Ne and Ar targets at projectile energies E=1.4 and 3.5 MeV/u. Typical
examples of the deposited energy T(b) and m-fold ionization probabilities Pm(b)
used for the cross-section calculations as a function of the impact parameter b
are given. Calculated m-fold electron-loss cross sections are in a good
agreement with available experimental data. Although the projectile charge is
rather high, a contribution of multiple-electron loss cross sections to the
total electron-loss cross sections is high: about 65% for the cases mentioned.Comment: 6 pages, 4 figure
Coherent and Incoherent Vortex Flow States in Crossed Channels
We examine vortex flow states in periodic square pinning arrays with one row
and one column of pinning sites removed to create an easy flow crossed channel
geometry. When a drive is simultaneously applied along both major symmetry axes
of the pinning array such that vortices move in both channels, a series of
coherent flow states develop in the channel intersection at rational ratios of
the drive components in each symmetry direction when the vortices can cross the
intersection without local collisions. The coherent flow states are correlated
with a series of anomalies in the velocity force curves, and in some cases can
produce negative differential conductivity. The same general behavior could
also be realized in other systems including colloids, particle traffic in
microfluidic devices, or Wigner crystals in crossed one-dimensional channels.Comment: 5 pages, 4 postscript figure
On orientational relief of inter-molecular potential and the structure of domain walls in fullerite C60
A simple planar model for an orientational ordering of threefold molecules on
a triangular lattice modelling a close-packed (111) plane of fullerite is
considered. The system has 3-sublattice ordered ground state which includes 3
different molecular orientations. There exist 6 kinds of orientational domains,
which are related with a permutation or a mirror symmetry. Interdomain walls
are found to be rather narrow.
The model molecules have two-well orientational potential profiles, which are
slightly effected by a presence of a straight domain wall. The reason is a
stronger correlation between neighbour molecules in triangular lattice versus
previously considered square lattice
A considerable reduction (up to one order) of orientational interwell
potential barrier is found in the core regions of essentially two-dimentional
potential defects, such as a three-domain boundary or a kink in the domain
wall. For ultimately uncorrelated nearest neighbours the height of the
interwell barrier can be reduced even by a factor of 100.Comment: 11 pages, 13 figures, LaTeX, to appear in Low Temperature Physic
An N-body Tree Algorithm for the Cray T3D
We describe in this paper an algorithm for solving the gravitational N-body problem using tree data structures on the Cray T3D parallel supercomputer. This implementation is an adaptation of previous work where this problem was solved using an SIMD, fine-grained parallel computer. We show here that this approach lends itself, with small modifications, to more coarse-grained parallelism as well. We also show that the performance of the algorithm on the Cray T3D parallel architecture scales adequately with the number of processors (up to 256). Specific levels to be reached using the Cray T3D parallel architecture. A peak performance level of 9.6 Gflop/s is reached on 256 processors for the time critical gravity computation
Ratchet Cellular Automata
In this work we propose a ratchet effect which provides a general means of
performing clocked logic operations on discrete particles, such as single
electrons or vortices. The states are propagated through the device by the use
of an applied AC drive. We numerically demonstrate that a complete logic
architecture is realizable using this ratchet. We consider specific
nanostructured superconducting geometries using superconducting materials under
an applied magnetic field, with the positions of the individual vortices in
samples acting as the logic states. These devices can be used as the building
blocks for an alternative microelectronic architecture.Comment: 4 pages, 3 figure
Functional Landscape Connectivity Of Greater Sage Grouse Habitat In A Multiple Use Landscape
Maintaining connectivity of sage-grouse habitat is critical to managing sage-grouse populations in the presence of widespread human disturbance. We used an empirical approach to model connectivity of a landscape based on resource selection of free-ranging GPS-collared greater sage-grouse (Centrocercus urophasianus) in a natural gas field in central Wyoming. We analyzed resource selection during three movement states (encamped, traveling, and relocating) and incorporated turning angle to identify features that functioned as barriers or conduits to movement. To illustrate application of the results we used the resource selection model to create spatially-explicit predictive maps identifying areas that generally provided large amounts of high quality ‘movement habitat.’ We found that both males and females selected for vegetation variables at multiple spatial scales. When traveling or relocating, males and females tended to avoid natural gas and oil wells and associated infrastructure and avoided areas with high topographic roughness within 800m. High topographic roughness was a barrier for traveling males. Relocating females were more likely to travel in a straight direction through areas of high road density and steep slopes. The predictive maps validated well using independent GPS location data. These results provide insight into habitat preferences of sage-grouse and can be used for both general and site-specific guidance on identifying habitats preferred or avoided during moderate and long distance movements of sage-grouse. When combined with critical seasonal use maps, e.g., nesting/brooding habitat and winter range, land managers could delineate areas of high value for connectivity of critical seasonal use areas
Selenium in Rocks, Soils, and Plants
The selenium which is found in the soils of the Great Plains has been derived from geological formations, especially those formations deposited during Cretaceous time. The sedimentary rocks which make up the Cretaceous formations are the most important selenium bearers. The selenium which was laid down in these sedimentary formations has been carrie3d through the soil-forming processes and is found in the soils of certain areas. Plants growing ion these soils absorb the selenium which further finds its way into the tissues of animals that happen to feed upon the plants
Domain Walls Motion and Resistivity in a Fully-Frustrated Josephson Array
It is identified numerically that the resistivity of a fully-frustrated
Josephson-junction array is due to motion of domain walls in vortex lattice
rather than to motion of single vortices
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