12,000 research outputs found
Evolution of X-ray spectra of Cygnus X-3 with radio flares
Cygnus X-3, among the X-ray binaries, is one of the brightest in the radio
band, repeatedly exhibiting huge radio flares. The X-ray spectra shows two
definite states, low (correspondingly hard) and high (correspondingly soft).
During the hard state the X-ray spectra shows a pivoting behaviour correlated
to the radio emission. In the high state the X-ray spectra shows a gamut of
behaviour which controls the radio flaring activity of the source. The complete
evolution of the X-ray spectra along with the radio flaring activity is
reported here, for the first time for this source.Comment: Bibliography has been correctly adde
Post-Double Hopf Bifurcation Dynamics and Adaptive Synchronization of a Hyperchaotic System
In this paper a four-dimensional hyperchaotic system with only one
equilibrium is considered and its double Hopf bifurcations are investigated.
The general post-bifurcation and stability analysis are carried out using the
normal form of the system obtained via the method of multiple scales. The
dynamics of the orbits predicted through the normal form comprises possible
regimes of periodic solutions, two-period tori, and three-period tori in
parameter space.
Moreover, we show how the hyperchaotic synchronization of this system can be
realized via an adaptive control scheme. Numerical simulations are included to
show the effectiveness of the designed control
Phase-field modeling of equilibrium precipitate shapes under the influence of coherency stresses
Coherency misfit stresses and their related anisotropies are known to
influence the equilibrium shapes of precipitates. Additionally, mechanical
properties of the alloys are also dependent on the shapes of the precipitates.
Therefore, in order to investigate the mechanical response of a material which
undergoes precipitation during heat treatment, it is important to derive the
range of precipitate shapes that evolve. In this regard, several studies have
been conducted in the past using sharp interface approaches where the influence
of elastic energy anisotropy on the precipitate shapes has been investigated.
In this paper, we propose a diffuse interface approach which allows us to
minimize grid-anisotropy related issues applicable in sharp-interface methods.
In this context, we introduce a novel phase-field method where we minimize the
functional consisting of the elastic and surface energy contributions while
preserving the precipitate volume. Using this method we reproduce the
shape-bifurcation diagrams for the cases of pure dilatational misfit that have
been studied previously using sharp interface methods and then extend them to
include interfacial energy anisotropy with different anisotropy strengths which
has not been a part of previous sharp-interface models. While we restrict
ourselves to cubic anisotropies in both elastic and interfacial energies in
this study, the model is generic enough to handle any combination of
anisotropies in both the bulk and interfacial terms. Further, we have examined
the influence of asymmetry in dilatational misfit strains along with
interfacial energy anisotropy on precipitate morphologies
Investigating Neutron Polarizabilities through Compton Scattering on He
We examine manifestations of neutron electromagnetic polarizabilities in
coherent Compton scattering from the Helium-3 nucleus. We calculate He elastic scattering observables using chiral perturbation theory to
next-to-leading order (). We find that the unpolarized
differential cross section can be used to measure neutron electric and magnetic
polarizabilities, while two double-polarization observables are sensitive to
different linear combinations of the four neutron spin polarizabilities.
[Note added in 2018] An erratum for this paper has been posted as
arXiv:1804.01206. Overall conclusions are unchanged, but quantitative results
are affected appreciably.Comment: 4 pages, 4 figures; version published in Phys. Rev. Let
Iterative methods for elliptic finite element equations on general meshes
Iterative methods for arbitrary mesh discretizations of elliptic partial differential equations are surveyed. The methods discussed are preconditioned conjugate gradients, algebraic multigrid, deflated conjugate gradients, an element-by-element techniques, and domain decomposition. Computational results are included
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