37,138 research outputs found
Time-resolved photometry of the nova remnants DM Gem, CP Lac, GI Mon, V400 Per, CT Ser and XX Tau
We present the first results of a photometric survey of poorly studied nova remnants in the Northern Hemisphere.
The main results are as follows: DM Gem shows a modulation at 0.123 d (probably linked to the orbit) and rapid variations at ∼22 min. A moderate resolution spectrum taken at the time of the photometric observations shows intense He II λ4686 and Bowen emission, characteristic of an intermediate polar or a SW Sex star. Variability at 0.127 d and intense flickering (or quasi-periodic oscillations) are the main features of the light curve of CP Lac. A 0.1-mag dip lasting for ∼45 min is observed in GI Mon, which could be an eclipse. A clear modulation (probably related to the orbital motion) either at 0.179 d or 0.152 d
is observed in the B-band light curve of V400 Per. The results for CT Ser point to an orbital period close to 0.16 d. Intense flickering is also characteristic of this old nova. Finally, XX Tau shows a possible periodic signal near 0.14 d and displays fast variability at ∼24 min. Its brightness seems to be modulated at ∼5 d. We relate this long periodicity to the motion of an eccentric/tilted accretion disc in the binary
N=1 Supergravity and Maxwell superalgebras
We present the construction of the supergravity action from the minimal
Maxwell superalgebra , which can be derived from the
superalgebra by applying the abelian
semigroup expansion procedure. We show that , pure supergravity can
be obtained alternatively as the MacDowell-Mansouri like action built from the
curvatures of the Maxwell superalgebra . We extend this
result to all minimal Maxwell superalgebras type . The
invariance under supersymmetry transformations is also analized.Comment: 22 pages, published versio
Maxwell Superalgebras and Abelian Semigroup Expansion
The Abelian semigroup expansion is a powerful and simple method to derive new
Lie algebras from a given one. Recently it was shown that the -expansion of
leads us to the Maxwell algebra
. In this paper we extend this result to superalgebras, by proving
that different choices of abelian semigroups lead to interesting
Maxwell Superalgebras. In particular, the minimal Maxwell superalgebra
and the -extended Maxwell superalgebra recently found by the Maurer Cartan expansion procedure, are
derived alternatively as an -expansion of . Moreover we show that new minimal Maxwell superalgebras type
and their -extended generalization can be obtained
using the -expansion procedure.Comment: 31 pages, some clarifications in the abstract,introduction and
conclusion, typos corrected, a reference and acknowledgements added, accepted
for publication in Nuclear Physics
Chern-Simons and Born-Infeld gravity theories and Maxwell algebras type
Recently was shown that standard odd and even-dimensional General Relativity
can be obtained from a -dimensional Chern-Simons Lagrangian invariant
under the algebra and from a -dimensional Born-Infeld
Lagrangian invariant under a subalgebra respectively. Very
Recently, it was shown that the generalized In\"on\"u-Wigner contraction of the
generalized AdS-Maxwell algebras provides Maxwell algebras types
which correspond to the so called Lie algebras. In this article we
report on a simple model that suggests a mechanism by which standard
odd-dimensional General Relativity may emerge as a weak coupling constant limit
of a -dimensional Chern-Simons Lagrangian invariant under the Maxwell
algebra type , if and only if . Similarly, we show
that standard even-dimensional General Relativity emerges as a weak coupling
constant limit of a -dimensional Born-Infeld type Lagrangian invariant
under a subalgebra of the Maxwell algebra type, if and
only if . It is shown that when this is not possible for a
-dimensional Chern-Simons Lagrangian invariant under the
and for a -dimensional Born-Infeld type Lagrangian
invariant under algebra.Comment: 30 pages, accepted for publication in Eur.Phys.J.C. arXiv admin note:
text overlap with arXiv:1309.006
Formation of corner waves in the wake of a partially submerged bluff body
We study theoretically and numerically the downstream flow near the corner of a bluff body partially submerged at a deadrise depth Δh into a uniform stream of velocity U, in the presence of gravity, g. When the Froude number, Fr=U/√gΔh, is large, a three-dimensional steady plunging wave, which is referred to as a corner wave, forms near the corner, developing downstream in a similar way to a two-dimensional plunging wave evolving in time. We have performed an asymptotic analysis of the flow near this corner to describe the wave's initial evolution and to clarify the physical mechanism that leads to its formation. Using the two-dimensions-plus-time approximation, the problem reduces to one similar to dam-break flow with a wet bed in front of the dam. The analysis shows that, at leading order, the problem admits a self-similar formulation when the size of the wave is small compared with the height difference Δh. The essential feature of the self-similar solution is the formation of a mushroom-shaped jet from which two smaller lateral jets stem. However, numerical simulations show that this self-similar solution is questionable from the physical point of view, as the two lateral jets plunge onto the free surface, leading to a self-intersecting flow. The physical mechanism leading to the formation of the mushroom-shaped structure is discussed
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