42,227 research outputs found
Mixed and discontinuous finite volume element schemes for the optimal control of immiscible flow in porous media
We introduce a family of hybrid discretisations for the numerical
approximation of optimal control problems governed by the equations of
immiscible displacement in porous media. The proposed schemes are based on
mixed and discontinuous finite volume element methods in combination with the
optimise-then-discretise approach for the approximation of the optimal control
problem, leading to nonsymmetric algebraic systems, and employing minimum
regularity requirements. Estimates for the error (between a local reference
solution of the infinite dimensional optimal control problem and its hybrid
approximation) measured in suitable norms are derived, showing optimal orders
of convergence
Noncommutative Einstein-Maxwell pp-waves
The field equations coupling a Seiberg-Witten electromagnetic field to
noncommutative gravity, as described by a formal power series in the
noncommutativity parameters , is investigated. A large
family of solutions, up to order one in , describing
Einstein-Maxwell null pp-waves is obtained. The order-one contributions can be
viewed as providing noncommutative corrections to pp-waves. In our solutions,
noncommutativity enters the spacetime metric through a conformal factor and is
responsible for dilating/contracting the separation between points in the same
null surface. The noncommutative corrections to the electromagnetic waves,
while preserving the wave null character, include constant polarization, higher
harmonic generation and inhomogeneous susceptibility. As compared to pure
noncommutative gravity, the novelty is that nonzero corrections to the metric
already occur at order one in .Comment: 19 revtex pages. One refrence suppressed, two references added. Minor
wording changes in the abstract, introduction and conclusio
Atypical Thermonuclear Supernovae from Tidally Crushed White Dwarfs
Suggestive evidence has accumulated that intermediate mass black holes (IMBH)
exist in some globular clusters. As stars diffuse in the cluster, some will
inevitable wander sufficiently close to the hole that they suffer tidal
disruption. An attractive feature of the IMBH hypothesis is its potential to
disrupt not only solar-type stars but also compact white dwarf stars. Attention
is given to the fate of white dwarfs that approach the hole close enough to be
disrupted and compressed to such extent that explosive nuclear burning may be
triggered. Precise modeling of the dynamics of the encounter coupled with a
nuclear network allow for a realistic determination of the explosive energy
release, and it is argued that ignition is a natural outcome for white dwarfs
of all varieties passing well within the tidal radius. Although event rates are
estimated to be significantly less than the rate of normal Type Ia supernovae,
such encounters may be frequent enough in globular clusters harboring an IMBH
to warrant a search for this new class of supernova.Comment: 13 pages, 4 figures, ApJ, accepte
Search for the companions of Galactic SNe Ia
The central regions of the remnants of Galactic SNe Ia have been examined for
the presence of companion stars of the exploded supernovae. We present the
results of this survey for the historical SN 1572 and SN 1006. The spectra of
the stars are modeled to obtain Teff, log g and the metallicity. Radial
velocities are obtained with an accuracy of 5--10 km s. Implications for
the nature of the companion star in SNeIa follow.Comment: 8 pages, 2 Postscript figures. Appeared in "From Twilight to
Highlight: the Physics of Supernovae", ed. W. Hillebrandt & B. Leibundgut
(Springer), pp. 140-14
Instability of Amorphous Ru-Si-O Thin Films under Thermal Oxidation
Ternary films about 200 nm thick of composition Ru20Si15O65 have been synthesized by reactive rf magnetron sputtering of a Ru1Si1 target in an argon-oxygen gas. As-deposited, the films are X-ray-amorphous. Their atomic density is 8.9 × 10^22/cm^3 (5.1 g/cm^3), and their electrical resistivity is in the range of 2 mOmega cm. After annealing in dry oxygen at 600°C for 30 min, micron-sized grains of RuO2 grow out of the film and volatile RuO4 escapes. The significance of these results is discussed
A new scaling property of turbulent flows
We discuss a possible theoretical interpretation of the self scaling property
of turbulent flows (Extended Self Similarity). Our interpretation predicts
that, even in cases when ESS is not observed, a generalized self scaling, must
be observed. This prediction is checked on a number of laboratory experiments
and direct numerical simulations.Comment: Plain Latex, 1 figure available upon request to
[email protected]
Dark Matter, Sparticle Spectroscopy and Muon in
We explore the sparticle mass spectra including LSP dark matter within the
framework of supersymmetric (422)
models, taking into account the constraints from extensive LHC and cold dark
matter searches. The soft supersymmetry-breaking parameters at can be
non-universal, but consistent with the 422 symmetry. We identify a variety of
coannihilation scenarios compatible with LSP dark matter, and study the
implications for future supersymmetry searches and the ongoing muon g-2
experiment.Comment: 21 pages, 8 fig
A resonance without resonance: scrutinizing the diphoton excess at 750 GeV
Motivated by the recent diphoton excesses reported by both ATLAS and CMS
collaborations, we suggest that a new heavy spinless particle is produced in
gluon fusion at the LHC and decays to a couple of lighter pseudoscalars which
then decay to photons. The new resonances could arise from a new strongly
interacting sector and couple to Standard Model gauge bosons only via the
corresponding Wess-Zumino-Witten anomaly. We present a detailed recast of the
newest 13 TeV data from ATLAS and CMS together with the 8 TeV data to scan the
consistency of the parameter space for those resonances.Comment: 8 pages, 4 figures, extended discussion of underlying models, new
plots with varying mass of the heavy scalar, to appear in PL
Chiral Perturbation Theory, the expansion and Regge behaviour determine the structure of the lightest scalar meson
The leading behaviour of Unitarised Chiral Perturbation Theory
distinguishes the nature of the and the . At one loop order the
is a meson, while the is not. However, semi-local
duality between resonances and Regge behaviour cannot be satisfied for larger
, if such a distinction holds. While the at is inevitably
dominated by its di-pion component, Unitarised Chiral Perturbation Theory
beyond one loop order reveals that as increases above 6-8, the
has a sub-dominant fraction up at 1.2 GeV. Remarkably this ensures
semi-local duality is fulfilled for the range of , where the
unitarisation procedure adopted applies.Comment: 22 pages, 8 figures. Version to be published in Physical Review
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