3,345 research outputs found
Localizing coalescing massive black hole binaries with gravitational waves
Massive black hole binary coalescences are prime targets for space-based
gravitational wave (GW) observatories such as {\it LISA}. GW measurements can
localize the position of a coalescing binary on the sky to an ellipse with a
major axis of a few tens of arcminutes to a few degrees, depending on source
redshift, and a minor axis which is times smaller. Neglecting weak
gravitational lensing, the GWs would also determine the source's luminosity
distance to better than percent accuracy for close sources, degrading to
several percent for more distant sources. Weak lensing cannot, in fact, be
neglected and is expected to limit the accuracy with which distances can be
fixed to errors no less than a few percent. Assuming a well-measured cosmology,
the source's redshift could be inferred with similar accuracy. GWs alone can
thus pinpoint a binary to a three-dimensional ``pixel'' which can help guide
searches for the hosts of these events. We examine the time evolution of this
pixel, studying it at merger and at several intervals before merger. One day
before merger, the major axis of the error ellipse is typically larger than its
final value by a factor of . The minor axis is larger by a factor
of , and, neglecting lensing, the error in the luminosity distance is
larger by a factor of . This large change over a short period of
time is due to spin-induced precession, which is strongest in the final days
before merger. The evolution is slower as we go back further in time. For , we find that GWs will localize a coalescing binary to within $\sim 10\
\mathrm{deg}^2$ as early as a month prior to merger and determine distance (and
hence redshift) to several percent.Comment: 30 pages, 10 figures, 5 tables. Version published in Ap
Measuring parameters of massive black hole binaries with partially aligned spins
The future space-based gravitational wave detector LISA will be able to
measure parameters of coalescing massive black hole binaries, often to
extremely high accuracy. Previous work has demonstrated that the black hole
spins can have a strong impact on the accuracy of parameter measurement.
Relativistic spin-induced precession modulates the waveform in a manner which
can break degeneracies between parameters, in principle significantly improving
how well they are measured. Recent studies have indicated, however, that spin
precession may be weak for an important subset of astrophysical binary black
holes: those in which the spins are aligned due to interactions with gas. In
this paper, we examine how well a binary's parameters can be measured when its
spins are partially aligned and compare results using waveforms that include
higher post-Newtonian harmonics to those that are truncated at leading
quadrupole order. We find that the weakened precession can substantially
degrade parameter estimation. This degradation is particularly devastating for
the extrinsic parameters sky position and distance. Absent higher harmonics,
LISA typically localizes the sky position of a nearly aligned binary a factor
of less accurately than for one in which the spin orientations are
random. Our knowledge of a source's sky position will thus be worst for the
gas-rich systems which are most likely to produce electromagnetic counterparts.
Fortunately, higher harmonics of the waveform can make up for this degradation.
By including harmonics beyond the quadrupole in our waveform model, we find
that the accuracy with which most of the binary's parameters are measured can
be substantially improved. In some cases, parameters can be measured as well in
partially aligned binaries as they can be when the binary spins are random.Comment: 18 pages, 16 figures, version accepted by PRD (with improved
distributions of partially aligned spins
Two-dimensional Hubbard-Holstein bipolaron
We present a diagrammatic Monte Carlo study of the properties of the
Hubbard-Holstein bipolaron on a two-dimensional square lattice. With a small
Coulomb repulsion, U, and with increasing electron-phonon interaction, and when
reaching a value about two times smaller than the one corresponding to the
transition of light polaron to heavy polaron, the system suffers a sharp
transition from a state formed by two weakly bound light polarons to a heavy,
strongly bound on-site bipolaron. Aside from this rather conventional bipolaron
a new bipolaron state is found for large U at intermediate and large
electron-phonon coupling, corresponding to two polarons bound on
nearest-neighbor sites. We discuss both the properties of the different
bipolaron states and the transition from one state to another. We present a
phase diagram in parameter space defined by the electron-phonon coupling and U.
Our numerical method does not use any artificial approximation and can be
easily modified to other bipolaron models with longer range electron-phonon
and/or electron-electron interaction.Comment: 14 pages, 12 figure
Suggestion, hypnosis and hypnotherapy: a survey of use, knowledge and attitudes of anaesthetists
Publisher's copy made available with the permission of the publisher © Australian Society of AnaesthetistsClinical hypnosis is a skill of using words and gestures (frequently called suggestions) in particular ways to achieve specific outcomes. It is being increasingly recognised as a useful intervention for managing a range of symptoms, especially pain and anxiety. We surveyed all 317 South Australian Fellows and trainees registered with ANZCA to determine their use, knowledge of, and attitudes towards positive suggestion, hypnosis and hypnotherapy in their anaesthesia practice. The response rate was 218 anaesthetists (69%). The majority of respondents (63%) rated their level of knowledge on this topic as below average. Forty-eight per cent of respondents indicated that there was a role for hypnotherapy in clinical anaesthesia, particularly in areas seen as traditional targets for the modality, i.e. pain and anxiety states. Nearly half of the anaesthetists supported the use of hypnotherapy and positive suggestions within clinical anaesthesia. Those respondents who had experience of clinical hypnotherapy were more likely to support hypnosis teaching at undergraduate or postgraduate level when compared with those with no experience.http://www.aaic.net.au/Article.asp?D=200408
Linear iterated pushdowns
This paper discusses variants of nondeterministic one-way S-automata and context-free S-grammars where S is a storage type. The framework that these systems provide can be used to give alternative formulations of embedded pushdown automata and linear indexed grammars. The embedded pushdown automata is obtained by means of a linear version of a class of storage types called iterated pushdowns. Linear indexed grammar is obtained by using the pushdown storage type and restricting the way in which the grammar uses its storage
SRMS as a Novel Therapeutic Target in Gastric Cancer Peritoneal Metastases
https://openworks.mdanderson.org/sumexp21/1233/thumbnail.jp
Advanced localization of massive black hole coalescences with LISA
The coalescence of massive black holes is one of the primary sources of
gravitational waves (GWs) for LISA. Measurements of the GWs can localize the
source on the sky to an ellipse with a major axis of a few tens of arcminutes
to a few degrees, depending on source redshift, and a minor axis which is 2--4
times smaller. The distance (and thus an approximate redshift) can be
determined to better than a per cent for the closest sources we consider,
although weak lensing degrades this performance. It will be of great interest
to search this three-dimensional `pixel' for an electromagnetic counterpart to
the GW event. The presence of a counterpart allows unique studies which combine
electromagnetic and GW information, especially if the counterpart is found
prior to final merger of the holes. To understand the feasibility of early
counterpart detection, we calculate the evolution of the GW pixel with time. We
find that the greatest improvement in pixel size occurs in the final day before
merger, when spin precession effects are maximal. The source can be localized
to within 10 square degrees as early as a month before merger at ; for
higher redshifts, this accuracy is only possible in the last few days.Comment: 11 pages, 4 figures, version published in Classical and Quantum
Gravity (special issue for proceedings of 7th International LISA Symposium
Neutral hydrogen surveys for high redshift galaxy clusters and proto-clusters
We discuss the possibility of performing blind surveys to detect large-scale
features of the universe using 21cm emission. Using instruments with approx.
5'-10' resolution currently in the planning stage, it should be possible to
detect virialized galaxy clusters at intermediate redshifts using the combined
emission from their constituent galaxies, as well as less overdense structures,
such as proto-clusters and the `cosmic web', at higher redshifts. Using
semi-analytic methods we compute the number of virialized objects and those at
turnaround which might be detected by such surveys. We find a surprisingly
large number of objects might be detected even using small (approx. 5%)
bandwidths and elaborate on some issues pertinent to optimising the design of
the instrument and the survey strategy. The main uncertainty is the fraction of
neutral gas relative to the total dark matter within the object. We discuss
this issue in the context of the observations which are currently available.Comment: 10 pages, 6 figure
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