2,626 research outputs found
Prospects for observing ultra-compact binaries with space-based gravitational wave interferometers and optical telescopes
Space-based gravitational wave interferometers are sensitive to the galactic
population of ultra-compact binaries. An important subset of the ultra-compact
binary population are those stars that can be individually resolved by both
gravitational wave interferometers and electromagnetic telescopes. The aim of
this paper is to quantify the multi-messenger potential of space-based
interferometers with arm-lengths between 1 and 5 Gm. The Fisher Information
Matrix is used to estimate the number of binaries from a model of the Milky Way
which are localized on the sky by the gravitational wave detector to within 1
and 10 square degrees and bright enough to be detected by a magnitude limited
survey. We find, depending on the choice of GW detector characteristics,
limiting magnitude, and observing strategy, that up to several hundred
gravitational wave sources could be detected in electromagnetic follow-up
observations.Comment: 6 pages, 3 figures Updated to include new results. Submitted to MNRA
Space missions to detect the cosmic gravitational-wave background
It is thought that a stochastic background of gravitational waves was
produced during the formation of the universe. A great deal could be learned by
measuring this Cosmic Gravitational-wave Background (CGB), but detecting the
CGB presents a significant technological challenge. The signal strength is
expected to be extremely weak, and there will be competition from unresolved
astrophysical foregrounds such as white dwarf binaries. Our goal is to identify
the most promising approach to detect the CGB. We study the sensitivities that
can be reached using both individual, and cross-correlated pairs of space based
interferometers. Our main result is a general, coordinate free formalism for
calculating the detector response that applies to arbitrary detector
configurations. We use this general formalism to identify some promising
designs for a GrAvitational Background Interferometer (GABI) mission. Our
conclusion is that detecting the CGB is not out of reach.Comment: 22 pages, 7 figures, IOP style, References Adde
Copper cable theft: revisiting the price–theft hypothesis
Objectives: To test the commonly espoused but little examined hypothesis that fluctuations in the price of metal are associated with changes in the volume of metal theft. Specifically, we analyze the relationship between the price of copper and the number of police recorded 'live’ copper cable thefts from the British railway network (2006 to 2012)
The Roles of Dopamine and Related Compounds in Reward-Seeking Behavior Across Animal Phyla
Motile animals actively seek out and gather resources they find rewarding, and this is an extremely powerful organizer and motivator of animal behavior. Mammalian studies have revealed interconnected neurobiological systems for reward learning, reward assessment, reinforcement and reward-seeking; all involving the biogenic amine dopamine. The neurobiology of reward-seeking behavioral systems is less well understood in invertebrates, but in many diverse invertebrate groups, reward learning and responses to food rewards also involve dopamine. The obvious exceptions are the arthropods in which the chemically related biogenic amine octopamine has a greater effect on reward learning and reinforcement than dopamine. Here we review the functions of these biogenic amines in behavioral responses to rewards in different animal groups, and discuss these findings in an evolutionary context
Australian Wheat Varieties: Grain Quality Data on Recently Registered Varieties
Established and supported under the Australian Government’s Cooperative Research Centre Progra
The Challenges in Gravitational Wave Astronomy for Space-Based Detectors
The Gravitational Wave (GW) universe contains a wealth of sources which, with
the proper treatment, will open up the universe as never before. By observing
massive black hole binaries to high redshifts, we should begin to explore the
formation process of seed black holes and track galactic evolution to the
present day. Observations of extreme mass ratio inspirals will allow us to
explore galactic centers in the local universe, as well as providing tests of
General Relativity and constraining the value of Hubble's constant. The
detection of compact binaries in our own galaxy may allow us to model stellar
evolution in the Milky Way. Finally, the detection of cosmic (super)strings and
a stochastic background would help us to constrain cosmological models.
However, all of this depends on our ability to not only resolve sources and
carry out parameter estimation, but also on our ability to define an optimal
data analysis strategy. In this presentation, I will examine the challenges
that lie ahead in GW astronomy for the ESA L3 Cosmic Vision mission, eLISA.Comment: 12 pages. Plenary presentation to appear in the Proceedings of the
Sant Cugat Forum on Astrophysics, Sant Cugat, April 22-25, 201
Collective Modes in a Dilute Bose-Fermi Mixture
We here study the collective excitations of a dilute spin-polarized
Bose-Fermi mixture at zero temperature, considering in particular the features
arising from the interaction between the two species. We show that a
propagating zero-sound mode is possible for the fermions even when they do not
interact among themselves.Comment: latex, 6 eps figure
Casimir energy in a small volume multiply connected static hyperbolic pre-inflationary Universe
A few years ago, Cornish, Spergel and Starkman (CSS), suggested that a
multiply connected ``small'' Universe could allow for classical chaotic mixing
as a pre-inflationary homogenization process. The smaller the volume, the more
important the process. Also, a smaller Universe has a greater probability of
being spontaneously created. Previously DeWitt, Hart and Isham (DHI) calculated
the Casimir energy for static multiply connected flat space-times. Due to the
interest in small volume hyperbolic Universes (e.g. CSS), we generalize the DHI
calculation by making a a numerical investigation of the Casimir energy for a
conformally coupled, massive scalar field in a static Universe, whose spatial
sections are the Weeks manifold, the smallest Universe of negative curvature
known. In spite of being a numerical calculation, our result is in fact exact.
It is shown that there is spontaneous vacuum excitation of low multipolar
components.Comment: accepted for publication in phys. rev.
Chaotic behavior in a Z_2 x Z_2 field theory
We investigate the presence of chaos in a system of two real scalar fields
with discrete Z_2 x Z_2 symmetry. The potential that identify the system is
defined with a real parameter r and presents distinct features for r>0 and for
r<0. For static field configurations, the system supports two topological
sectors for r>0, and only one for r<0. Under the assumption of spatially
homogeneous fields, the system exhibts chaotic behavior almost everywhere in
parameter space. In particular a more complex dynamics appears for r>0; in this
case chaos can decrease for increasing energy, a fact that is absent for r<0.Comment: Revtex, 13 pages, no figures. Version with figures in Int. J. Mod.
Phys. A14 (1999) 496
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