4,312 research outputs found
Nonlinear static and dynamic analysis of mixed cable elements
This paper presents a family of finite elements for the nonlinear static and dynamic analysis of cables based on a mixed variational formulation in curvilinear coordinates and finite deformations. This formulation identifies stress measures, in the form of axial forces, and conjugate deformation measures for the nonlinear catenary problem. The continuity requirements lead to two distinct implementations: one with a continuous axial force distribution and one with a discontinuous. Two examples from the literature on nonlinear cable analysis are used to validate the proposed formulation for St VenantKirchhoff elastic materials. These studies show that displacements and axial forces are captured with high accuracy for both the static and the dynamic case
Matched-filter study and energy budget suggest no detectable gravitational-wave 'extended emission' from GW170817
Van Putten & Della Valle (2018) have reported a possible detection of
gravitational-wave 'extended emission' from a neutron star remnant of GW170817.
Starting from the time-frequency evolution and total emitted energy of their
reported candidate, we show that such an emission is not compatible with the
current understanding of neutron stars. We explore the additional required
physical assumptions to make a full waveform model, for example, taking the
optimistic emission from a spining-down neutron star with fixed quadrupolar
deformation, and study whether even an ideal single-template matched-filter
analysis could detect an ideal, fully phase-coherent signal. We find that even
in the most optimistic case an increase in energy and extreme parameters would
be required for a confident detection with LIGO sensitivity as of 2018-08-17.
The argument also holds for other waveform models following a similar
time-frequency track and overall energy budget. Single-template matched
filtering on the LIGO data around GW170817, and on data with added simulated
signals, verifies the expected sensitivity scaling and the overall statistical
expectation.Comment: 9 pages, 6 figures, updated version as accepted by MNRA
A geometric approach to dense Cayley digraphs of finite Abelian groups
We give a method for constructing infinite families of dense (or eventually likely dense) Cayley digraphs of finite Abelian groups. The diameter of the digraphs is obtained by means of the related minimum distance diagrams. A dilating technique for these diagrams, which can be used for any degree of the digraph, is applied to generate the digraphs of the family. Moreover, two infinite families of digraphs with distinguished metric properties will be given using these methods. The first family contains digraphs with asymptotically large ratio between the order and the diameter as the degree increases (moreover it is the first known asymptotically dense family). The second family, for fixed degree d = 3, contains digraphs with the current best known density.Peer ReviewedPostprint (author's final draft
LISA observations of supermassive black holes: parameter estimation using full post-Newtonian inspiral waveforms
We study parameter estimation of supermassive black hole binary systems in
the final stage of inspiral using the full post-Newtonian gravitational
waveforms. We restrict our analysis to systems in circular orbit with
negligible spins, in the mass range 10^8\Ms-10^5\Ms, and compare the results
with those arising from the commonly used restricted post-Newtonian
approximation. The conclusions of this work are particularly important with
regard to the astrophysical reach of future LISA measurements. Our analysis
clearly shows that modeling the inspiral with the full post-Newtonian waveform,
not only extends the reach to higher mass systems, but also improves in general
the parameter estimation. In particular, there are remarkable improvements in
angular resolution and distance measurement for systems with a total mass
higher than 5\times10^6\Ms, as well as a large improvement in the mass
determination.Comment: Final version. Accepted for publication in Phys. Rev.
Abelian Cayley digraphs with asymptotically large order for any given degree
Abelian Cayley digraphs can be constructed by using a generalization to Z(n) of the concept of congruence in Z. Here we use this approach to present a family of such digraphs, which, for every fixed value of the degree, have asymptotically large number of vertices as the diameter increases. Up to now, the best known large dense results were all non-constructive.Peer ReviewedPostprint (author's final draft
Emission spectrum of quasi-resonant laterally coupled quantum dots
We calculate the emission spectrum of neutral and charged excitons in a pair
of laterally coupled InGaAs quantum dots with nearly degenerate energy levels.
As the interdot distance decreases, a number of changes take place in the
emission spectrum which can be used as indications of molecular coupling. These
signatures ensue from the stronger tunnel-coupling of trions as compared to
that of neutral excitons.Comment: 7 pages, 7 figure
Volatility and dividend risk in perpetual American options
American options are financial instruments that can be exercised at any time
before expiration. In this paper we study the problem of pricing this kind of
derivatives within a framework in which some of the properties --volatility and
dividend policy-- of the underlaying stock can change at a random instant of
time, but in such a way that we can forecast their final values. Under this
assumption we can model actual market conditions because some of the most
relevant facts that may potentially affect a firm will entail sharp predictable
effects. We will analyse the consequences of this potential risk on perpetual
American derivatives, a topic connected with a wide class of recurrent problems
in physics: holders of American options must look for the fair price and the
optimal exercise strategy at once, a typical question of free absorbing
boundaries. We present explicit solutions to the most common contract
specifications and derive analytical expressions concerning the mean and higher
moments of the exercise time.Comment: 21 pages, 5 figures, iopart, submitted for publication; deep
revision, two new appendice
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