748 research outputs found
Black-hole kicks from numerical-relativity surrogate models
Binary black holes radiate linear momentum in gravitational waves as they
merge. Recoils imparted to the black-hole remnant can reach thousands of km/s,
thus ejecting black holes from their host galaxies. We exploit recent advances
in gravitational waveform modeling to quickly and reliably extract recoils
imparted to generic, precessing, black hole binaries. Our procedure uses a
numerical-relativity surrogate model to obtain the gravitational waveform given
a set of binary parameters, then from this waveform we directly integrate the
gravitational-wave linear momentum flux. This entirely bypasses the need of
fitting formulae which are typically used to model black-hole recoils in
astrophysical contexts. We provide a thorough exploration of the black-hole
kick phenomenology in the parameter space, summarizing and extending previous
numerical results on the topic. Our extraction procedure is made publicly
available as a module for the Python programming language named SURRKICK. Kick
evaluations take ~0.1s on a standard off-the-shelf machine, thus making our
code ideal to be ported to large-scale astrophysical studies.Comment: More: https://davidegerosa.com/surrkick - Source:
https://github.com/dgerosa/surrkick - pypi:
https://pypi.python.org/pypi/surrkick - Published in PR
On the small weight codewords of the functional codes C_2(Q), Q a non-singular quadric
We study the small weight codewords of the functional code C_2(Q), with Q a
non-singular quadric of PG(N,q). We prove that the small weight codewords
correspond to the intersections of Q with the singular quadrics of PG(N,q)
consisting of two hyperplanes. We also calculate the number of codewords having
these small weights
Coherent supercontinuum generation in a silicon photonic wire in the telecommunication wavelength range
We demonstrate a fully coherent supercontinuum spectrum spanning 500 nm from a silicon-on-insulator photonic wire waveguide pumped at 1575 nm wavelength. An excellent agreement with numerical simulations is reported. The simulations also show that a high level of two-photon absorption can essentially enforce the coherence of the spectral broadening process irrespective of the pump pulse duration.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
High-accuracy mass, spin, and recoil predictions of generic black-hole merger remnants
We present accurate fits for the remnant properties of generically precessing
binary black holes, trained on large banks of numerical-relativity simulations.
We use Gaussian process regression to interpolate the remnant mass, spin, and
recoil velocity in the 7-dimensional parameter space of precessing black-hole
binaries with mass ratios , and spin magnitudes .
For precessing systems, our errors in estimating the remnant mass, spin
magnitude, and kick magnitude are lower than those of existing fitting formulae
by at least an order of magnitude (improvement is also reported in the
extrapolated region at high mass ratios and spins). In addition, we also model
the remnant spin and kick directions. Being trained directly on precessing
simulations, our fits are free from ambiguities regarding the initial frequency
at which precessing quantities are defined. We also construct a model for
remnant properties of aligned-spin systems with mass ratios , and spin
magnitudes . As a byproduct, we also provide error
estimates for all fitted quantities, which can be consistently incorporated
into current and future gravitational-wave parameter-estimation analyses. Our
model(s) are made publicly available through a fast and easy-to-use Python
module called surfinBH.Comment: 6+5 pages. Matches PRL version. Python implementation available at
https://pypi.org/project/surfinBH
Observation of an optical event horizon in a silicon-on-insulator photonic wire waveguide
We report on the first experimental observation of an optical analogue of an event horizon in integrated nanophotonic waveguides, through the reflection of a continuous wave on an intense pulse. The experiment is performed in a dispersion-engineered silicon-on-insulator waveguide. In this medium, solitons do not suffer from Raman induced self-frequency shift as in silica fibers, a feature that is interesting for potential applications of optical event horizons. As shown by simulations, this also allows the observation of multiple reflections at the same time on fundamental solitons ejected by soliton fission.SCOPUS: ar.jhttp://www.opticsexpress.org/abstract.cfm?URIinfo:eu-repo/semantics/publishe
Observations of spatiotemporal instabilities in the strong-driving regime of an AC-driven nonlinear Schr\"odinger system
Localized dissipative structures (LDS) have been predicted to display a rich
array of instabilities, yet systematic experimental studies have remained
scarce. We have used a synchronously-driven optical fiber ring resonator to
experimentally study LDS instabilities in the strong-driving regime of the
AC-driven nonlinear Schr\"odinger equation (also known as the Lugiato-Lefever
model). Through continuous variation of a single control parameter, we have
observed a string of theoretically predicted instability modes, including
irregular oscillations and chaotic collapses. Beyond a critical point, we
observe behaviour reminiscent of a phase transition: LDSs trigger localized
domains of spatiotemporal chaos that invade the surrounding homogeneous state.
Our findings directly confirm a number of theoretical predictions, and they
highlight that complex LDS instabilities can play a role in experimental
systems.Comment: 6 pages, 4 figure
Measurement and tuning of the chromatic dispersion of a silicon photonic wire around the half band gap spectral region
We demonstrate the measurement and tuning of second-to-fourth order dispersion of a silicon wire waveguide in a spectral region of low nonlinear losses. Using white light interferometry we extract the chromatic dispersion of our waveguide from 1950 to 2300 nm. Moreover we demonstrate tuning of the zero dispersion wavelength over more than 100 nm, pushing it to longer wavelength by partially underetching the waveguide. © 2014 Optical Society of America.info:eu-repo/semantics/publishe
View Selection in Semantic Web Databases
We consider the setting of a Semantic Web database, containing both explicit
data encoded in RDF triples, and implicit data, implied by the RDF semantics.
Based on a query workload, we address the problem of selecting a set of views
to be materialized in the database, minimizing a combination of query
processing, view storage, and view maintenance costs. Starting from an existing
relational view selection method, we devise new algorithms for recommending
view sets, and show that they scale significantly beyond the existing
relational ones when adapted to the RDF context. To account for implicit
triples in query answers, we propose a novel RDF query reformulation algorithm
and an innovative way of incorporating it into view selection in order to avoid
a combinatorial explosion in the complexity of the selection process. The
interest of our techniques is demonstrated through a set of experiments.Comment: VLDB201
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