49,375 research outputs found
Waveforms for Gravitational Radiation from Cosmic String Loops
We obtain general formulae for the plus- and cross- polarized waveforms of
gravitational radiation emitted by a cosmic string loop in transverse,
traceless (synchronous, harmonic) gauge. These equations are then specialized
to the case of piecewise linear loops, and it is shown that the general
waveform for such a loop is a piecewise linear function. We give several simple
examples of the waveforms from such loops. We also discuss the relation between
the gravitational radiation by a smooth loop and by a piecewise linear
approximation to it.Comment: 16 pages, 6 figures, Revte
Spinor Parallel Propagator and Green's Function in Maximally Symmetric Spaces
We introduce the spinor parallel propagator for maximally symmetric spaces in
any dimension. Then, the Dirac spinor Green's functions in the maximally
symmetric spaces R^n, S^n and H^n are calculated in terms of intrinsic
geometric objects. The results are covariant and coordinate-independent.Comment: 7 page
Analytic Results for the Gravitational Radiation from a Class of Cosmic String Loops
Cosmic string loops are defined by a pair of periodic functions and
, which trace out unit-length closed curves in three-dimensional
space. We consider a particular class of loops, for which lies along
a line and lies in the plane orthogonal to that line. For this class
of cosmic string loops one may give a simple analytic expression for the power
radiated in gravitational waves. We evaluate exactly in
closed form for several special cases: (1) a circle traversed
times; (2) a regular polygon with sides and interior vertex angle
; (3) an isosceles triangle with semi-angle .
We prove that case (1) with is the absolute minimum of within
our special class of loops, and identify all the stationary points of
in this class.Comment: 15 pages, RevTex 3.0, 7 figures available via anonymous ftp from
directory pub/pcasper at alpha1.csd.uwm.edu, WISC-MILW-94-TH-1
Data documentation for the 1981 summer vegetation experiment
The mobile agricultural radar sensor was used to collect data from 31 fields in the floodplain of the Kansas River east of Lawrence, Kansas during the summer of 1981. Corn, soybeans, and wheat crops were observed from May 1 to November 11. Radar backscattering measurements were acquired at 10.2 GHz for VV and VH polarizations at 50 deg incidence angles for all fields and at 30 deg, 40 deg, 50 deg, 60 deg, and 70 deg for nine of the 31 fields. Target parameters describing the vegatation and soil characteristics, such as plant moisture, plant height, soil moisture, etc., were also measured. The methodology, radar backscatter data and associated ground-truth data obtained during this experiment are documented
The Weyl tensor two-point function in de Sitter spacetime
We present an expression for the Weyl-Weyl two-point function in de Sitter
spacetime, based on a recently calculated covariant graviton two-point function
with one gauge parameter. We find that the Weyl-Weyl two-point function falls
off with distance like r^{-4}, where r is spacelike coordinate separation
between the two points.Comment: 9 pages, no figure
An approach to the multidimensional assessment of food security and environmental sustainability: a vulnerability framework for the Mediterranean region
Poster presented at First International Conference on Global Food Security. Noordwijkerhout (The Netherlands), 29 Sep - 2 Oct 201
Multidimensional assessment of food security and environmental sustainability: a vulnerability framework for the Mediterranean Region [Poster]
Poster presented at Tropentag 2013. International Research on Food Security, Natural Resource Management and Rural Development. "Agricultural development within the rural-urban continuum". Stuttgart-Hohenheim (Germany), Sep 17-19 2013
An approach to the multidimensional assessment of food security and environmental sustainability: a vulnerability framework for the Mediterranean region
Poster presented at First International Conference on Global Food Security. Noordwijkerhout (The Netherlands), 29 Sep - 2 Oct 201
Stochastic background from extra-galactic double neutron stars
We present Monte Carlo simulations of the extra galactic population of
inspiralling double neutron stars, and estimate its contribution to the
astrophysical gravitational wave background, in the frequency range of ground
based interferometers, corresponding to the last thousand seconds before the
last stable orbit when more than 96 percent of the signal is released. We show
that sources at redshift z>0.5 contribute to a truly continuous background
which may be detected by correlating third generation interferometers.Comment: 13 pages, 7 figures - proceeding of a talk given at the 11th GWDAW,
to appear in CQ
Recovering hidden Bloch character: Unfolding Electrons, Phonons, and Slabs
For a quantum state, or classical harmonic normal mode, of a system of
spatial periodicity "R", Bloch character is encoded in a wavevector "K". One
can ask whether this state has partial Bloch character "k" corresponding to a
finer scale of periodicity "r". Answering this is called "unfolding." A theorem
is proven that yields a mathematically clear prescription for unfolding, by
examining translational properties of the state, requiring no "reference
states" or basis functions with the finer periodicity (r,k). A question then
arises, how should one assign partial Bloch character to a state of a finite
system? A slab, finite in one direction, is used as the example. Perpendicular
components k_z of the wavevector are not explicitly defined, but may be hidden
in the state (and eigenvector |i>.) A prescription for extracting k_z is
offered and tested. An idealized silicon (111) surface is used as the example.
Slab-unfolding reveals surface-localized states and resonances which were not
evident from dispersion curves alone.Comment: 11 pages, 7 figure
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