8,122 research outputs found
Comparison of post-Newtonian templates for compact binary inspiral signals in gravitational-wave detectors
The two-body dynamics in general relativity has been solved perturbatively
using the post-Newtonian (PN) approximation. The evolution of the orbital phase
and the emitted gravitational radiation are now known to a rather high order up
to O(v^8), v being the characteristic velocity of the binary. The orbital
evolution, however, cannot be specified uniquely due to the inherent freedom in
the choice of parameter used in the PN expansion as well as the method pursued
in solving the relevant differential equations. The goal of this paper is to
determine the (dis)agreement between different PN waveform families in the
context of initial and advanced gravitational-wave detectors. The waveforms
employed in our analysis are those that are currently used by Initial
LIGO/Virgo, that is the time-domain PN models TaylorT1, TaylorT2, TaylorT3,
TaylorT4 and TaylorEt, the effective one-body (EOB) model, and the
Fourier-domain representation TaylorF2. We examine the overlaps of these models
with one another and with the prototype effective one-body model (calibrated to
numerical relativity simulations, as currently used by initial LIGO) for a
number of different binaries at 2PN, 3PN and 3.5PN orders to quantify their
differences and to help us decide whether there exist preferred families that
are the most appropriate as search templates. We conclude that as long as the
total mass remains less than a certain upper limit M_crit, all template
families at 3.5PN order (except TaylorT3 and TaylorEt) are equally good for the
purpose of detection. The value of M_crit is found to be ~ 12M_Sun for Initial,
Enhanced and Advanced LIGO. From a purely computational point of view we
recommend that 3.5PN TaylorF2 be used below Mcrit and EOB calibrated to
numerical relativity simulations be used for total binary mass M > Mcrit.Comment: 27 pages, 8 figures, 4 tables, submitted to PR
Density Matrix Renormalization Group Applied to the Ground State of the XY-Spin-Peierls System
We use the density matrix renormalization group (DMRG) to map out the ground
state of a XY-spin chain coupled to dispersionless phonons of frequency . We confirm the existence of a critical spin-phonon coupling for the onset of the spin gap bearing the signature of
a Kosterlitz-Thouless transition. We also observe a classical-quantum crossover
when the spin-Peierls gap is of order . In the classical
regime, , the mean-field parameters are strongly renormalized
by non-adiabatic corrections. This is the first application of the DMRG to
phonons.Comment: 10 pages, 5 figures. To be published in PR
Contrasting carbonate depositional systems for Pliocene cool-water limestones cropping out in central Hawke's Bay, New Zealand
Pliocene limestone formations in central Hawke's Bay (eastern North Island, New Zealand) accumulated on and near the margins of a narrow forearc basin seaway within the convergent Australia/Pacific plate boundary zone. The active tectonic setting and varied paleogeographic features of the limestone units investigated, in association with probable glacioeustatic sea-level fluctuations, resulted in complex stratigraphic architectures and contrasting types of carbonate accumulation on either side of the seaway. Here, we recognise recurring patterns of sedimentary facies, and sequences and systems tracts bounded by key physical surfaces within the limestone sheets. The facies types range from Bioclastic (B) to Siliciclastic (S) end-members via Mixed (M) carbonate-siliciclastic deposits. Skeletal components are typical cool-water associations dominated by epifaunal calcitic bivalves, bryozoans, and especially barnacles. Siliciclastic contents vary from one formation to another, and highlight siliciclastic-rich limestone units in the western ranges versus siliciclastic-poor limestone units in the eastern coastal hills. Heterogeneities in facies types, stratal patterns, and also in diagenetic pathways between eastern and western limestone units are considered to originate in the coeval occurrence in different parts of the forearc basin of two main morphodynamic carbonate systems over time
Integrated simulation of ground motion mitigation, techniques for the future compact linear collider (CLIC)
CLIC is a proposal of CERN for a future high-energy particle collider. CLIC will collide electron and positron beams at a centre of mass energy of 3TeV with a desired peak luminosity of 2x10^3^4cm^-^2s^-^1. The luminosity performance of CLIC is sensitive to ground motion. Ground motion misaligns accelerator components, most importantly quadrupole magnets, which leads to emittance growth and beam-beam offset at the interaction point. This paper discusses the beam based feedback strategies currently used together with mechanical stabilization systems to address the above mentioned issues. These strategies consist of an Interaction Point Feedback (IPFB) and an Orbit Feedback (OFB). The two feedbacks have been designed independently and the main objective of this paper is to show how they interact. A simulation program is used in order to simulate the whole collider, it includes the behaviour of the beams, magnets, supports, ground attenuators, sensors, and actuators. Beam-offset feedback optimization and integrated simulations have been performed and results show that despite a detrimental coupling of both feedbacks at high frequency, it is possible to decrease the beam-beam offset and maintain the desired luminosity
Active stabilization studies at the sub-nanometer level for future linear colliders
The next collider which will be able to contribute significantly to the comprehension of matter is a high energy linear collider. The luminosity of this collider will have to be of 1035cm-2s-1, which imposes a vertical beam size of 0,7nm. The relative motion between the last two focusing magnets should not exceed a third of the beam size above 4Hz. Ground motion and acoustic noise can induce vibrations that have to be compensated with active stabilisation. In this paper, we describe the three aspects needed for such a development. We have assessed sensors capable of measuring sub-nanometre displacements, performed numerical calculations using finite element models to get the dynamic response of the structure, and developed a feedback loop for the active stabilisation. Combining the expertise into a mecatronics project made it possible to obtain a displacement RMS at 5Hz of 0.13nm at the free end of our prototype
Modeling raccoon (Procyon lotor) habitat connectivity to identify potential corridors for rabies spread
The United States Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS), Wildlife Services National Rabies Management Program has conducted cooperative oral rabies vaccination (ORV) programs since 1997. Understanding the eco-epidemiology of raccoon (Procyon lotor) variant rabies (raccoon rabies) is critical to successful management. Pine (Pinus spp.)-dominated landscapes generally support low relative raccoon densities that may inhibit rabies spread. However, confounding landscape features, such as wetlands and human development, represent potentially elevated risk corridors for rabies spread, possibly imperiling enhanced rabies surveillance and ORV planning. Raccoon habitat suitability in pine-dominated landscapes in Massachusetts, Florida, and Alabama was modeled by the maximum entropy (Maxent) procedure using raccoon presence, and landscape and environmental data. Replicated (n = 100/state) bootstrapped Maxent models based on raccoon sampling locations from 2012â2014 indicated that soil type was the most influential variable in Alabama (permutation importance PI = 38.3), which, based on its relation to landcover type and resource distribution and abundance, was unsurprising. Precipitation (PI = 46.9) and temperature (PI = 52.1) were the most important variables in Massachusetts and Florida, but these possibly spurious results require further investigation. The Alabama Maxent probability surface map was ingested into Circuitscape for conductance visualizations of potential areas of habitat connectivity. Incorporating these and future results into raccoon rabies containment and elimination strategies could result in significant cost-savings for rabies management here and elsewhere
Gravitational waves about curved backgrounds: a consistency analysis in de Sitter spacetime
Gravitational waves are considered as metric perturbations about a curved
background metric, rather than the flat Minkowski metric since several
situations of physical interest can be discussed by this generalization. In
this case, when the de Donder gauge is imposed, its preservation under
infinitesimal spacetime diffeomorphisms is guaranteed if and only if the
associated covector is ruled by a second-order hyperbolic operator which is the
classical counterpart of the ghost operator in quantum gravity. In such a wave
equation, the Ricci term has opposite sign with respect to the wave equation
for Maxwell theory in the Lorenz gauge. We are, nevertheless, able to relate
the solutions of the two problems, and the algorithm is applied to the case
when the curved background geometry is the de Sitter spacetime. Such vector
wave equations are studied in two different ways: i) an integral
representation, ii) through a solution by factorization of the hyperbolic
equation. The latter method is extended to the wave equation of metric
perturbations in the de Sitter spacetime. This approach is a step towards a
general discussion of gravitational waves in the de Sitter spacetime and might
assume relevance in cosmology in order to study the stochastic background
emerging from inflation.Comment: 17 pages. Misprints amended in Eqs. 50, 54, 55, 75, 7
Inspiral, merger and ring-down of equal-mass black-hole binaries
We investigate the dynamics and gravitational-wave (GW) emission in the
binary merger of equal-mass black holes as obtained from numerical relativity
simulations. Results from the evolution of three sets of initial data are
explored in detail, corresponding to different initial separations of the black
holes. We find that to a good approximation the inspiral phase of the evolution
is quasi-circular, followed by a "blurred, quasi-circular plunge", then merger
and ring down. We present first-order comparisons between analytical models of
the various stages of the merger and the numerical results. We provide
comparisons between the numerical results and analytical predictions based on
the adiabatic Newtonain, post-Newtonian (PN), and non-adiabatic resummed-PN
models. From the ring-down portion of the GW we extract the fundamental
quasi-normal mode and several of the overtones. Finally, we estimate the
optimal signal-to-noise ratio for typical binaries detectable by GW
experiments.Comment: 47 pages, 34 figures, full abstract in paper, revtex4, accepted by
PRD, miscellaneous revisions throughout pape
Vibration stabilization for a cantilever magnet prototype at the subnanometer scale
In the future linear colliders, the size of the beams is in the nanometer range, which requires stabilization of the final magnets before the interaction point. In order to guarantee the desired luminosity, an absolute displacement lower than 1/3 of the beam size, above a few hertz, has to be obtained. This paper describes an adapted instrumentation, the developed feedback loops dedicated to the active compensation and an adapted modelling able to simulate the behaviour of the structure. The obtained results at the subnanometer scale at the free end of a cantilever magnet prototype with a combination of the developed active compensation method and a commercial active isolation system are described
Active stabilization of a mechanical structure
This article [1] refers to a particular stage of our attempt to reach the stabilization of the linear collider final focus quadrupole. All along this final focus, an absolute displacement has to be lower than the third of nanometre above a few hertz. The presented intermediary step consists in doing active vibrations control of an elemen-tary mechanical structure in cantilever mode which is similar to the final focus. We consider mainly the active compensation and the latest results on a large prototype. Other aspects are also treated such as modelling, active isolation and instrumentation dedicated to the ground motion
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