1,859 research outputs found
PyCBC Live: Rapid Detection of Gravitational Waves from Compact Binary Mergers
We introduce an efficient and straightforward technique for rapidly detecting
gravitational waves from compact binary mergers. We show that this method
achieves the low latencies required to alert electromagnetic partners of
candidate binary mergers, aids in data monitoring, and makes use of
multidetector networks for sky localization. This approach was instrumental to
the analysis of gravitational-wave candidates during the second observing run
of Advanced LIGO, including the period of coincident operation with Advanced
Virgo, and in particular the analysis of the first observed binary neutron star
merger GW170817, where it led to the first tightly localized sky map
() used to identify AT 2017gfo. Operation of this analysis
also enabled the initial discovery of GW170104 and GW170608 despite non-nominal
observing of the instrument.Comment: 10 pages, 5 figures, submitted to Physical Review
Detecting binary compact-object mergers with gravitational waves: Understanding and Improving the sensitivity of the PyCBC search
We present an improved search for binary compact-object mergers using a
network of ground-based gravitational-wave detectors. We model a volumetric,
isotropic source population and incorporate the resulting distribution over
signal amplitude, time delay, and coalescence phase into the ranking of
candidate events. We describe an improved modeling of the background
distribution, and demonstrate incorporating a prior model of the binary mass
distribution in the ranking of candidate events. We find a and
increase in detection volume for simulated binary neutron star and
neutron star--binary black hole systems, respectively, corresponding to a
reduction of the false alarm rates assigned to signals by between one and two
orders of magnitude.Comment: 7 pages, 3 figures, as accepted by Ap
Complex Conjugate Pairs in Stationary Sturmians
Sturmian eigenstates specified by stationary scattering boundary conditions
are particularly useful in contexts such as forming simple separable two
nucleon t matrices, and are determined via solution of generalised eigenvalue
equation using real and symmetric matrices. In general, the spectrum of such an
equation may contain complex eigenvalues. But to each complex eigenvalue there
is a corresponding conjugate partner. In studies using realistic
nucleon--nucleon potentials, and in certain positive energy intervals, these
complex conjugated pairs indeed appear in the Sturmian spectrum. However, as we
demonstrate herein, it is possible to recombine the complex conjugate pairs and
corresponding states into a new, sign--definite pair of real quantities with
which to effect separable expansions of the (real) nucleon--nucleon reactance
matrices.Comment: (REVTEX) 8 Pages, Padova DFPD 93/TH/78 and University of Melbourn
Isoscalar off-shell effects in threshold pion production from pd collisions
We test the presence of pion-nucleon isoscalar off-shell effects in the
reaction around the threshold region. We find that these
effects significantly modify the production cross section and that they may
provide the missing strength needed to reproduce the data at threshold.Comment: 6 pages, REVTeX, twocolumn, including 3 figures (Postscript), uses
psfig, updated and extended versio
The importance of few-nucleon physics at low energy
This manuscript originated from the discussion at the workshop on the "Future
of Few-body Low Energy Experimental Physics" (FFLEEP), which was held at the
University of Trento on December 4-7, 2002 and has been written in its present
form on March 19, 2003. It illustrates a selection of theoretical advancements
in the nuclear few-body problem, including two- and many-nucleon interactions,
the three-nucleon bound and scattering system, the four-body problem, the
A-body (A4) problem, and fields of related interest, such as reactions of
astrophysical interest and few-neutron systems. Particular attention is called
to the contradictory situation one experiences in this field: while theory is
currently advancing and has the potential to inspire new experiments, the
experimental activity is nevertheless rapidly phasing out. If such a trend will
continue, advancements in this area will become critically difficult.Comment: 29 pages, 21 figures. Manuscript originated from the discussion at
the workshop on the "Future of Few-body Low Energy Experimental Physics"
(FFLEEP), University of Trento, December 4-7, 2002, written in its present
form on March 19, 2003, circulated mainly among the participants to the
FFLEEP workshop. Since the authors have been repeatedly solicited to make the
manuscript accessible to a larger audience potentially interested in its
scientific content, they have decided to post it on this archiv
The one-pion-exchange three-nucleon force and the puzzle
We consider a new three-nucleon force generated by the exchange of one pion
in the presence of a 2N correlation. The underlying irreducible diagram has
been recently suggested by the authors as a possible candidate to explain the
puzzle of the vector analyzing powers and for nucleon-deuteron
scattering. Herein, we have calculated the elastic neutron-deuteron
differential cross section, , , , , and
below break-up threshold by accurately solving the Alt-Grassberger-Sandhas
equations with realistic interactions. We have also studied how evolves
below 30 MeV. The results indicate that this new 3NF diagram provides one
possible additional contribution, with the correct spin-isospin structure, for
the explanation of the origin of this puzzle.Comment: revised version: We have also studied how Ay evolves below 30 MeV, 4
Pages (twocolumn), 2 figures, uses psfig, RevTe
Why is the three-nucleon force so odd?
By considering a class of diagrams which has been overlooked also in the most
recent literature on three-body forces, we extract a new contribution to the
three-nucleon interaction which specifically acts on the triplet odd states of
the two nucleon subsystem. In the static approximation, this 3N-force
contribution is fixed by the underlying 2N interaction, so in principle there
are no free parameters to adjust. The 2N amplitude however enters in the 3NF
diagram in a form which cannot be directly accessed or constrained by NN
phase-shift analysis. We conclude that this new 3N-force contribution provides
a mechanism which implies that the presence of the third nucleon modifies the
p-wave (and possibly the f-wave) components of the 2N subsystem in the
triplet-isotriplet channels.Comment: 10 Pages, 7 figures, RevTeX, twocolumn, epsf (updated version with
minor changes
Practical approximation scheme for the pion dynamics in the three-nucleon system
We discuss a working approximation scheme to a recently developed formulation
of the coupled piNNN-NNN problem. The approximation scheme is based on the
physical assumption that, at low energies, the 2N-subsystem dynamics in the
elastic channel is conveniently described by the usual 2N-potential approach,
while the explicit pion dynamics describes small, correction-type effects.
Using the standard separable-expansion method, we obtain a dynamical equation
of the Alt-Grassberger-Sandhas (AGS) type. This is an important result, because
the computational techniques used for solving the normal AGS equation can also
be used to describe the pion dynamics in the 3N system once the matrix
dimension is increased by one component. We have also shown that this
approximation scheme treats the conventional 3N problem once the pion degrees
of freedom are projected out. Then the 3N system is described with an extended
AGS-type equation where the spin-off of the pion dynamics (beyond the 2N
potential) is taken into account in additional contributions to the driving
term. These new terms are shown to reproduce the diagrams leading to modern
3N-force models. We also recover two sets of irreducible diagrams that are
commonly neglected in 3N-force discussions, and conclude that these sets should
be further investigated, because a claimed cancellation is questionable.Comment: 18 pages, including 5 figures, RevTeX, Eps
Heat flux measurements and modelling in the RFX-mod experiment
The knowledge of edge plasma transport parameters and plasma edge phenomena is a key element in the design of the first wall for a magnetically confined fusion experiment. In RFX-mod heat flux measurement and edge transport modelling have been done to improve the understanding of this aspect. Heat flux deposition profiles have been evaluated from infrared temperature measurements of insertable graphite limiters. They were inserted up to 12 mm into the reversed field pinch plasma of ohmically heated discharges with Ip=â0.6Ă·1.0 MA, ne=â0.5Ă·3·1019 mâ3 (n/nG<â0.7) and total power of about 10Ă·15 MW. Strong asymmetries in heat flux deposition have been measured in poloidal direction at low density between the electron and the ion drift side and smaller ones in toroidal direction when q(a)â 0. The poloidal asymmetry has been associated to the presence of superthermal electrons [1] while the toroidal one has been less clearly identified as due to the small toroidal extension of the limiters. To account for the 2D deposition nature of heat load on the surface of the employed limiters, a simple 3D code has been developed to evaluate heat flux from temperature data. In this way at the deeper limiter insertions a heat flux decay length of about 2 mm and 2.5 mm has been evaluated in electron and ion drift sides. Modelling of the evaluated heat fluxes has been done using the SOLEDGE2D-EIRENE edge code [2]. This fluid code is well suited for the RFX-mod wall limiter configuration because, thanks to the implemented penalization technique, the computational domain can be extended up to the entire first wall. Edge modelling has shown that measured decay lengths are compatible with energy diffusion coefficients in Scrape Off Layer (SOL) smaller than those commonly evaluated at plasma edge; the cause of the reduced diffusion in the SOL will be discussed in the paper
Book Reviews
Reviews of the following books: Greater Portland Celebration 350: A Commemorative Edition, edited by Albert F. Barnes; Portsmouth-Built: Submarines of the Portsmouth Naval Shipyard by Richard E. Winslow, III; A Glimpse of Sionâs Glory: Puritan Radicalism in New England, 1620-1660 by Philip R. Gura; The Socialist Alternative: Utopian Experiments and the Socialist Party of Maine, 1895-1914 by Charles Scontras; Restitution: The Land Claims of the Mashpee, Passamaquoddy, and Penobscot Indians of New England by Paul Brodeur
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