46,592 research outputs found
Digital overlaying of the universal transverse Mercator grid with LANDSAT data derived products
Picture elements of data from the LANDSAT multispectral scanner are correlated with the universal tranverse Mercator grid. In the procedure, a series of computer modules was used to make approximations of universal transverse Mercator grid locations for all picture elements from the grid locations of a limited number of known control points and to provide display and digital storage of the data. The software has been written in FORTRAN 4 language for a Varian 70-series computer
An algorithm for automating the registration of USDA segment ground data to LANDSAT MSS data
The algorithm is referred to as the Automatic Segment Matching Algorithm (ASMA). The ASMA uses control points or the annotation record of a P-format LANDSAT compter compatible tape as the initial registration to relate latitude and longitude to LANDSAT rows and columns. It searches a given area of LANDSAT data with a 2x2 sliding window and computes gradient values for bands 5 and 7 to match the segment boundaries. The gradient values are held in memory during the shifting (or matching) process. The reconstructed segment array, containing ones (1's) for boundaries and zeros elsewhere are computer compared to the LANDSAT array and the best match computed. Initial testing of the ASMA indicates that it has good potential for replacing the manual technique
Quantum stabilization of a hedgehog type of cosmic string
Within a slightly simplified version of the electroweak standard model we
investigate the stabilization of cosmic strings by fermion quantum
fluctuations. Previous studies of quantum energies considered variants of the
Nielsen-Olesen profile embedded in the electroweak gauge group and showed that
configurations are favored for which the Higgs vacuum expectation value drops
near the string core and the gauge field is suppressed. This work found that
the strongest binding was obtained from strings that differ significantly from
Nielsen-Olesen configurations, deforming essentially only the Higgs field in
order to generate a strong attraction without inducing large gradients.
Extending this analysis, we consider the leading quantum correction to the
energy per unit length of a hedgehog type string, which, in contrast to the
Nielsen-Olesen configuration, contains a pseudoscalar field. To employ the
spectral method we develop the scattering and bound state problems for fermions
in the background of a hedgehog string. Explicit occupation of bound state
levels leads to strings that carry the quantum numbers of the bound fermions.
We discuss the parameter space for which stable, hedgehog type cosmic strings
emerge and reflect on phenomenological consequences of these findings.Comment: 34 page
Simplified system displays complex curves corresponding to input data
Cathode ray oscilloscope displays curves or contours of complex shapes corresponding to sets of x,y coordinates. It requires few storage facilities and produces a rapid display of complex curves with a fewer number of commands than previous systems
Attractive Electromagnetic Casimir Stress on a Spherical Dielectric Shell
Based on calculations involving an idealized boundary condition, it has long
been assumed that the stress on a spherical conducting shell is repulsive. We
use the more realistic case of a Drude dielectric to show that the stress is
attractive, matching the generic behavior of Casimir forces in
electromagnetism. We trace the discrepancy between these two cases to
interactions between the electromagnetic quantum fluctuations and the
dielectric material.Comment: Five pages, one figure, pdflatex, matches version to be pusblished in
Phys Lett
Stable charged cosmic strings
We study the quantum stabilization of a cosmic string by a heavy fermion
doublet in a reduced version of the standard model. We show that charged
strings, obtained by populating fermionic bound state levels, become stable if
the electro--weak bosons are coupled to a fermion that is less than twice as
heavy as the top quark. This result suggests that extraordinarily large fermion
masses or unrealistic couplings are not required to bind a cosmic string in the
standard model. Numerically we find the most favorable string profile to be a
simple "trough" in the Higgs vev of radius . The
vacuum remains stable in our model, because neutral strings are not
energetically favored.Comment: 5 pages, 3 figures, version to be published in Phys. Rev. Let
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