8,100 research outputs found
Space based microlensing planet searches
The discovery of extra-solar planets is arguably the most exciting
development in astrophysics during the past 15 years, rivalled only by the
detection of dark energy. Two projects unite the communities of exoplanet
scientists and cosmologists: the proposed ESA M class mission EUCLID and the
large space mission WFIRST, top ranked by the Astronomy 2010 Decadal Survey
report. The later states that: "Space-based microlensing is the optimal
approach to providing a true statistical census of planetary systems in the
Galaxy, over a range of likely semi-major axes". They also add: "This census,
combined with that made by the Kepler mission, will determine how common
Earth-like planets are over a wide range of orbital parameters". We will
present a status report of the results obtained by microlensing on exoplanets
and the new objectives of the next generation of ground based wide field imager
networks. We will finally discuss the fantastic prospect offered by space based
microlensing at the horizon 2020-2025.Comment: 8 pages, Proceedings to the ROPACS meeting "Hot Planets and Cool
Stars" (Nov. 2012, Garching), invited contributio
Explicit minimal Scherk saddle towers of arbitrary even genera in
Starting from works by Scherk (1835) and by Enneper-Weierstra\ss \ (1863),
new minimal surfaces with Scherk ends were found only in 1988 by Karcher (see
\cite{Karcher1,Karcher}). In the singly periodic case, Karcher's examples of
positive genera had been unique until Traizet obtained new ones in 1996 (see
\cite{Traizet}). However, Traizet's construction is implicit and excludes {\it
towers}, namely the desingularisation of more than two concurrent planes. Then,
new explicit towers were found only in 2006 by Martin and Ramos Batista (see
\cite{Martin}), all of them with genus one. For genus two, the first such
towers were constructed in 2010 (see \cite{Valerio2}). Back to 2009, implicit
towers of arbitrary genera were found in \cite{HMM}. In our present work we
obtain {\it explicit} minimal Scherk saddle towers, for any given genus ,
Sistema de plantio solteiro e consorciado na produção de hortaliças no Vale do São Francisco.
Suplemento. Edição dos Anais do 52 Congresso Brasileiro de Olericultura, Salvador, jul. 201
Quantum cosmological perfect fluid model and its classical analogue
The quantization of gravity coupled to a perfect fluid model leads to a
Schr\"odinger-like equation, where the matter variable plays the role of time.
The wave function can be determined, in the flat case, for an arbitrary
barotropic equation of state ; solutions can also be found for
the radiative non-flat case. The wave packets are constructed, from which the
expectation value for the scale factor is determined. The quantum scenarios
reveal a bouncing Universe, free from singularity. We show that such quantum
cosmological perfect fluid models admit a universal classical analogue,
represented by the addition, to the ordinary classical model, of a repulsive
stiff matter fluid. The meaning of the existence of this universal classical
analogue is discussed. The quantum cosmological perfect fluid model is, for a
flat spatial section, formally equivalent to a free particle in ordinary
quantum mechanics, for any value of , while the radiative non-flat case
is equivalent to the harmonic oscillator. The repulsive fluid needed to
reproduce the quantum results is the same in both cases.Comment: Latex file, 13 page
Hamiltonian Reduction and the Construction of q-Deformed Extensions of the Virasoro Algebra
In this paper we employ the construction of Dirac bracket for the remaining
current of deformed Kac-Moody algebra when constraints similar to
those connecting the -WZW model and the Liouville theory are imposed and
show that it satisfy the q-Virasoro algebra proposed by Frenkel and
Reshetikhin. The crucial assumption considered in our calculation is the
existence of a classical Poisson bracket algebra induced, in a consistent
manner by the correspondence principle, mapping the quantum generators into
commuting objects of classical nature preserving their algebra.Comment: 6 pages, late
Quantum critical 5f-electrons avoid singularities in U(Ru,Rh)2Si2
We present specific heat measurements of 4% Rh-doped U(Ru,Rh)2Si2 at magnetic
fields above the proposed metamagnetic transition field Hm~34 T, revealing
striking similarities to the isotructural Ce analog CeRu2Si2, suggesting that
strongly renormalized hybridized band models apply equally well to both
systems. The vanishing bandwidths as H --> Hm are consistent with a putative
quantum critical point close to Hm. The existence of a phase transition into an
ordered phase in the vicinity of Hm for 4% Rh-doped U(Ru,Rh)2Si2, but not for
CeRu2Si2, is consistent with a stronger super-exchange in the case of the U 5-f
system, with irreversible processes at the transition revealing a strong
coupling of the 5f orbitals to the lattice, most suggestive of orbital or
electric quadrupolar order.Comment: 4 pages, 4 figure
Qualitative analysis of a scalar-tensor theory with exponential potential
A qualitative analysis of a scalar-tensor cosmological model, with an
exponential potential for the scalar field, is performed. The phase diagram for
the flat case is constructed. It is shown that solutions with an initial and
final inflationary behaviour appear. The conditions for which the scenario
favored by supernova type Ia observations becomes an attractor in the space of
the solutions are established.Comment: Latex file, 9 pages, 1 figur
- …