19,953 research outputs found
Effect of Target Material Yield Strength on Hypervelocity Perforation and Ballistic Limit
Viscoplastic flow theory in hypervelocity projectile perforation analyses of thin plate
The Photonic Lantern
Photonic lanterns are made by adiabatically merging several single-mode cores
into one multimode core. They provide low-loss interfaces between single-mode
and multimode systems where the precise optical mapping between cores and
individual modes is unimportant.Comment: 45 pages; article unchanged, accepted for publication in Advances in
Optics and Photonic
Velocity, energy and helicity of vortex knots and unknots
In this paper we determine the velocity, the energy and estimate writhe and
twist helicity contributions of vortex filaments in the shape of torus knots
and unknots (toroidal and poloidal coils) in a perfect fluid. Calculations are
performed by numerical integration of the Biot-Savart law. Vortex complexity is
parametrized by the winding number , given by the ratio of the number of
meridian wraps to that of the longitudinal wraps. We find that for vortex
knots and toroidal coils move faster and carry more energy than a reference
vortex ring of same size and circulation, whereas for knots and poloidal
coils have approximately same speed and energy of the reference vortex ring.
Helicity is dominated by the writhe contribution. Finally, we confirm the
stabilizing effect of the Biot-Savart law for all knots and unknots tested,
that are found to be structurally stable over a distance of several diameters.
Our results also apply to quantized vortices in superfluid He.Comment: 17 pages, 8 figures, 2 table
Remote sensing in Iowa agriculture: Identification and classification of Iowa's crops, soils and forestry resources using ERTS-1 and complimentary underflight imagery
The author has identified the following significant results. Springtime ERTS-1 imagery covering pre-selected test sites in Iowa showed considerable detail with respect to broad soil and land use patterns. Additional imagery has been incorporated into a state mosaic. The mosaic was used as a base for soil association lines transferred from an existing map. The regions of greatest contrast are between the Clarion-Nicollet-Webster soil association area and adjacent areas. Landscape characteristics in this area result in land use patterns with a high percentage of pasture, hay, and timber. The soil association areas of the state that have patterns interpreted to be associated with intensive row crop production are: Moody, Galva-Primghar-Sac, Clarion-Nicollet-Webter, Tama-Muscatine, Dinsdale-Tama, Cresco-Lourdes, Clyde, Kenyon-Floyd-Clyde, and the Luton-Onawa-Salix area on the Missouri River floodplain. Forestland estimates have been attained for an area in central Iowa using wintertime ERTS-1 imagery. Visual analysis of multispectral, temporal imagery indicates that temporal analysis for cropland identification and acreage analyses procedures may be a very useful tool. Combinations of wintertime, springtime, and summertime ERTS-1 imagery separate most vegetation types. Timing can be critical depending upon crop development and harvesting times because of the dynamic nature of agricultural production
Mid-infrared spectral broadening in an ultrafast laser inscribed gallium lanthanum sulphide waveguide
Resonant Processes in a Frozen Gas
We present a theory of resonant processes in a frozen gas of atoms
interacting via dipole-dipole potentials that vary as , where is
the interatomic separation. We supply an exact result for a single atom in a
given state interacting resonantly with a random gas of atoms in a different
state. The time development of the transition process is calculated both on-
and off-resonance, and the linewidth with respect to detuning is obtained as a
function of time . We introduce a random spin Hamiltonian to model a dense
system of resonators and show how it reduces to the previous model in the limit
of a sparse system. We derive approximate equations for the average effective
spin, and we use them to model the behavior seen in the experiments of Anderson
et al. and Lowell et al. The approach to equilibrium is found to be
proportional to ), where the constant is explicitly related to the system's parameters.Comment: 30 pages, 6 figure
GSM-enabled remote monitoring of rural handpumps: A proof-of-concept study
The continued expansion of mobile network coverage in rural Africa provides an opportunity for simple and low-cost hydroinformatic innovations to measure and transmit data on handpump use for policy and management improvements. We design, build and test a Waterpoint Data Transmitter to determine its robustness, functionality and scalability. Results demonstrate that this novel application using simple microprocessor, accelerometer and global system for mobile communications (GSM) components has significant potential in recording graduated time-step information flows of lever pumps which can be modelled into a reasonable water volume use approximation. Given the systemic informational deficit for rural waterpoints in Africa, where one in three handpumps is likely to be non-functioning, this innovation has the potential to provide universal, low-cost and immediate data to guide timely maintenance responses and planning decisions, as well as drive greater accountability and transparency in donor and government behaviour. Ā© IWA Publishing 2012
Extremely low longāterm erosion rates around the Gamburtsev Mountains in interior East Antarctica
The high elevation and rugged relief (>3 km) of the Gamburtsev Subglacial Mountains (GSM) have long been considered enigmatic. Orogenesis normally occurs near plate boundaries, not cratonic interiors, and largeāscale tectonic activity last occurred in East Antarctica during the PanāAfrican (480ā600 Ma). We sampled detrital apatite from Eocene sands in Prydz Bay at the terminus of the Lambert Graben, which drained a large preāglacial basin including the northern Gamburtsev Mountains. Apatite fissionātrack and (UāTh)/He cooling ages constrain bedrock erosion rates throughout the catchment. We doubleādated apatites to resolve individual cooling histories. Erosion was very slow, averaging 0.01ā0.02 km/Myr for >250 Myr, supporting the preservation of high elevation in interior East Antarctica since at least the cessation of Permian rifting. Longāterm topographic preservation lends credence to postulated highāelevation mountain ice caps in East Antarctica since at least the Cretaceous and to the idea that coldābased glaciation can preserve tectonically inactive topography
Remote sensing in Iowa agriculture: Identification and classification of Iowa's crops, soils and forestry resources using ERTS-1 and complimentary underflight imagery
There are no author-identified significant results in this report
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