60,661 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
A New Waveform Consistency Test for Gravitational Wave Inspiral Searches
Searches for binary inspiral signals in data collected by interferometric
gravitational wave detectors utilize matched filtering techniques. Although
matched filtering is optimal in the case of stationary Gaussian noise, data
from real detectors often contains "glitches" and episodes of excess noise
which cause filter outputs to ring strongly. We review the standard \chi^2
statistic which is used to test whether the filter output has appropriate
contributions from several different frequency bands. We then propose a new
type of waveform consistency test which is based on the time history of the
filter output. We apply one such test to the data from the first LIGO science
run and show that it cleanly distinguishes between true inspiral waveforms and
large-amplitude false signals which managed to pass the standard \chi^2 test.Comment: 10 pages, 6 figures, submitted to Classical and Quantum Gravity for
the proceedings of the Eighth Gravitational Wave Data Analysis Workshop
(GWDAW-8
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
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
Competition between charge and spin order in the extended Hubbard model on the triangular lattice
Several new classes of compounds can be modeled in first approximation by
electrons on the triangular lattice that interact through on-site repulsion
as well as nearest-neighbor repulsion . This extended Hubbard model on a
triangular lattice has been studied mostly in the strong coupling limit for
only a few types of instabilities. Using the extended two-particle self
consistent approach (ETPSC), that is valid at weak to intermediate coupling, we
present an unbiased study of the density and interaction dependent crossover
diagram for spin and charge density wave instabilities of the normal state at
arbitrary wave vector. When dominates over and electron filling is
large, instabilities are chiefly in the spin sector and are controlled mostly
by Fermi surface properties. Increasing eventually leads to charge
instabilities. In the latter case, it is mostly the wave vector dependence of
the vertex that determines the wave vector of the instability rather than Fermi
surface properties. At small filling, non-trivial instabilities appear only
beyond the weak coupling limit. There again, charge density wave instabilities
are favored over a wide range of dopings by large at wave vectors
corresponding to superlattice in real space.
Commensurate fillings do not play a special role for this instability.
Increasing leads to competition with ferromagnetism. At negative values of
or , neglecting superconducting fluctuations, one finds that charge
instabilities are favored. In general, the crossover diagram presents a rich
variety of instabilities. We also show that thermal charge-density wave
fluctuations in the renormalized classical regime can open a pseudogap in the
single-particle spectral weight, just as spin or superconducting fluctuations
New South Wales Vegetation classification and Assessment: Part 3, plant communities of the NSW Brigalow Belt South, Nandewar and west New England Bioregions and update of NSW Western Plains and South-western Slopes plant communities, Version 3 of the NSWVCA database
This fourth paper in the NSW Vegetation Classification and Assessment series covers the Brigalow Belt South-/1(BBS) and Nandewar (NAN) Bioregions and the western half of the New England Bioregion (NET), an area of 9.3 million hectares being 11.6% of NSW. It completes the NSWVCA coverage for the Border Rivers-Gwydir and Namoi CMA areas and records plant communities in the Central West and Hunter–Central Rivers CMA areas. In total, 585 plant communities are now classified in the NSWVCA covering 11.5 of the 18 Bioregions in NSW (78% of the State). Of these 226 communities are in the NSW Western Plains and 416 are in the NSW Western Slopes. 315 plant communities are classified in the BBS, NAN and west-NET Bioregions including 267 new descriptions since Version 2 was published in 2008. Descriptions of the 315 communities are provided in a 919 page report on the DVD accompanying this paper along with updated reports on other inland NSW bioregions and nine Catchment Management Authority areas fully or partly classified in the NSWVCA to date. A read-only version of Version 3 of the NSWVCA database is on the DVD for use on personal computers. A feature of the BBS and NAN Bioregions is the array of ironbark and bloodwood Eucalyptusdominated shrubby woodlands on sandstone and acid volcanic substrates extending from Dubbo to Queensland. This includes iconic natural areas such as Warrumbungle and Mount Kaputar National Parks and the 500,000 ha Pilliga Scrub forests. Large expanses of basalt-derived soils support grassy box woodland and native grasslands including those on the Liverpool Plains; near Moree; and around Inverell, most of which are cleared and threatened. Wetlands occur on sodic soils near Yetman and in large clay gilgais in the Pilliga region. Sedgelands are rare but occupy impeded creeks. Aeolian lunettes occur at Narran Lake and near Gilgandra. Areas of deep sand contain Allocasuarina, eucalypt mallee and Melaleuca uncinata heath. Tall grassy or ferny open forests occur on mountain ranges above 1000m elevation in the New England Bioregion and on the Liverpool Range while grassy box woodlands occupy lower elevations with lower rainfall and higher temperatures. The vegetation classification and assessment is based on over 100 published and unpublished vegetation surveys and map unit descriptions, expert advice, extra plot sampling and data analysis and over 25 000 km of road traverse with field checking at 805 sites. Key sources of data included floristic analyses produced in western regional forest assessments in the BBS and NAN Bioregions, floristic analyses in over 60 surveys of conservation reserves and analysis of plot data in the western NET Bioregion and covering parts of the Namoi and Border Rivers- Gwydir CMA areas. Approximately 60% of the woody native vegetation in the study area has been cleared resulting in large areas of “derived” native grasslands. As of June 2010, 7% of the area was in 136 protected areas and 127 of the 315 plant communities were assessed to be adequately protected in reserves. Using the NSWVCA database threat criteria, 15 plant communities were assessed as being Critically Endangered, 59 Endangered, 60 Vulnerable, 99 Near Threatened and 82 Least Concern. 61 of these communities are assessed as part of NSW or Commonwealth-listed Threatened Ecological Communities. Current threats include expanding dryland and irrigated cropping on alluvial plains, floodplains and gently undulating topography at lower elevations; over-grazing of steep hills; altered water tables and flooding regimes; localized mining; and the spread of exotic species, notably Coolatai Grass (Hyparrhenia hirta)
Gravitational Waves in Open de Sitter Space
We compute the spectrum of primordial gravitational wave perturbations in
open de Sitter spacetime. The background spacetime is taken to be the
continuation of an O(5) symmetric instanton saddle point of the Euclidean no
boundary path integral. The two-point tensor fluctuations are computed directly
from the Euclidean path integral. The Euclidean correlator is then analytically
continued into the Lorentzian region where it describes the quantum mechanical
vacuum fluctuations of the graviton field. Unlike the results of earlier work,
the correlator is shown to be unique and well behaved in the infrared. We show
that the infrared divergence found in previous calculations is due to the
contribution of a discrete gauge mode inadvertently included in the spectrum.Comment: 17 pages, compressed and RevTex file, including one postscript figure
fil
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
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