45,529 research outputs found
Hierarchical analysis of gravitational-wave measurements of binary black hole spin-orbit misalignments
Binary black holes may form both through isolated binary evolution and
through dynamical interactions in dense stellar environments. The formation
channel leaves an imprint on the alignment between the black hole spins and the
orbital angular momentum. Gravitational waves from these systems directly
encode information about the spin--orbit misalignment angles, allowing them to
be (weakly) constrained. Identifying sub-populations of spinning binary black
holes will inform us about compact binary formation and evolution. We simulate
a mixed population of binary black holes with spin--orbit misalignments
modelled under a range of assumptions. We then develop a hierarchical analysis
and apply it to mock gravitational-wave observations of these populations.
Assuming a population with dimensionless spin magnitudes of , we
show that tens of observations will make it possible to distinguish the
presence of subpopulations of coalescing binary black holes based on their spin
orientations. With observations it will be possible to infer the relative
fraction of coalescing binary black holes with isotropic spin directions
(corresponding to dynamical formation in our models) with a fractional
uncertainty of . Meanwhile, only observations are
sufficient to distinguish between extreme models---all binary black holes
either having exactly aligned spins or isotropic spin directions.Comment: 12 pages, 9 figures. Updated to match version published in MNRAS as
10.1093/mnras/stx176
Distributed Reasoning in a Peer-to-Peer Setting: Application to the Semantic Web
In a peer-to-peer inference system, each peer can reason locally but can also
solicit some of its acquaintances, which are peers sharing part of its
vocabulary. In this paper, we consider peer-to-peer inference systems in which
the local theory of each peer is a set of propositional clauses defined upon a
local vocabulary. An important characteristic of peer-to-peer inference systems
is that the global theory (the union of all peer theories) is not known (as
opposed to partition-based reasoning systems). The main contribution of this
paper is to provide the first consequence finding algorithm in a peer-to-peer
setting: DeCA. It is anytime and computes consequences gradually from the
solicited peer to peers that are more and more distant. We exhibit a sufficient
condition on the acquaintance graph of the peer-to-peer inference system for
guaranteeing the completeness of this algorithm. Another important contribution
is to apply this general distributed reasoning setting to the setting of the
Semantic Web through the Somewhere semantic peer-to-peer data management
system. The last contribution of this paper is to provide an experimental
analysis of the scalability of the peer-to-peer infrastructure that we propose,
on large networks of 1000 peers
Electronic spin precession and interferometry from spin-orbital entanglement in a double quantum dot
A double quantum dot inserted in parallel between two metallic leads allows
to entangle the electron spin with the orbital (dot index) degree of freedom.
An Aharonov-Bohm orbital phase can then be transferred to the spinor
wavefunction, providing a geometrical control of the spin precession around a
fixed magnetic field. A fully coherent behaviour is obtained in a mixed
orbital/spin Kondo regime. Evidence for the spin precession can be obtained,
either using spin-polarized metallic leads or by placing the double dot in one
branch of a metallic loop.Comment: Final versio
An effective Hamiltonian for phase fluctuations on a lattice: an extended XY model
We derive an effective Hamiltonian for phase fluctuations in an s-wave
superconductor starting from the attractive Hubbard model on a square lattice.
In contrast to the common assumption, we find that the effective Hamiltonian is
not the usual XY model but is of an extended XY type. This extended feature is
robust and leads to essential corrections in understanding phase fluctuations
on a lattice. The effective coupling in the Hamiltonian varies significantly
with temperature.Comment: 2 figure
On the structure of spectra of travelling waves
The linear stability of the travelling wave solutions of a general reaction-diffusion system is investigated. The spectrum of the corresponding second order differential operator is studied. The problem is reduced to an asymptotically autonomous first order linear system. The relation between the spectrum of and the corresponding first order system is dealt with in detail. The first order system is investigated using exponential dichotomies. A self-contained short presentation is shown for the study of the spectrum, with elementary proofs. An algorithm is given for the determination of the exact position of the essential spectrum. The Evans function method for determining the isolated eigenvalues of is also presented. The theory is illustrated by three examples: a single travelling wave equation, a three variable combustion model and the generalized KdV equation
Detection of 84-GHz class I methanol maser emission towards NGC 253
We have investigated the central region of NGC 253 for the presence of
84.5-GHz (E) methanol emission using the Australia
Telescope Compact Array. We present the second detection of 84.5-GHz class~I
methanol maser emission outside the Milky Way. This maser emission is offset
from dynamical centre of NGC 253, in a region with previously detected emission
from class~I maser transitions (36.2-GHz E and 44.1-GHz
A methanol lines) . The emission features a narrow
linewidth (12 km s) with a luminosity approximately 5 orders of
magnitude higher than typical Galactic sources. We determine an integrated line
intensity ratio of between the 36.2 GHz and 84.5-GHz class I
methanol maser emission, which is similar to the ratio observed towards
Galactic sources. The three methanol maser transitions observed toward NGC 253
each show a different distribution, suggesting differing physical conditions
between the maser sites and that observations of additional class~I methanol
transitions will facilitate investigations of the maser pumping regime.Comment: Accepted into ApJL 12 October 2018. 10 pages, 3 Figures and 2 Table
Critical Behavior of Coupled q-state Potts Models under Weak Disorder
We investigate the effect of weak disorder on different coupled -state
Potts models with using two loops renormalisation group. This study
presents new examples of first order transitions driven by randomness. We found
that weak disorder makes the models decouple. Therefore, it appears that no
relations emerge, at a perturbation level, between the disordered -state Potts model and the two disordered , -state Potts models
(), despite their central charges are similar according to recent
numerical investigations. Nevertheless, when two -state Potts models are
considered (), the system remains always driven in a strong coupling
regime, violating apparently the Imry-Wortis argument.Comment: 7 pages + 1 PS figure (Latex
Detecting nonlocal Cooper pair entanglement by optical Bell inequality violation
Based on the Bardeen Cooper Schrieffer (BCS) theory of superconductivity, the
coherent splitting of Cooper pairs from a superconductor to two spatially
separated quantum dots has been predicted to generate nonlocal pairs of
entangled electrons. In order to test this hypothesis, we propose a scheme to
transfer the spin state of a split Cooper pair onto the polarization state of a
pair of optical photons. We show that the produced photon pairs can be used to
violate a Bell inequality, unambiguously demonstrating the entanglement of the
split Cooper pairs.Comment: 11 pages, 9 figures, v3 with added reference
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