13,246 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
Field Induced Supersolid Phase in Spin-One Heisenberg Models
We use quantum Monte Carlo methods to demonstrate that the quantum phase
diagram of the S=1 Heisenberg model with uniaxial anisotropy contains an
extended supersolid phase. We also show that this Hamiltonian is a particular
case of a more general and ubiquitous model that describes the low energy
spectrum of a class of {\it isotropic} and {\it frustrated} spin systems. This
crucial result provides the required guidance for finding experimental
realizations of a spin supersolid state.Comment: 4 pages, 4 figure
Energy transduction by respiratory complex I
Dissertation presented to obtain a PhD degree in Biochemistry at the Instituto de Tecnologia QuĂmica e BiolĂłgica, Universidade
Nova de LisboaThe aim of the work presented in this dissertation was to provide a contribution to the understanding of the energy transducing mechanism of respiratory complex I. This enzyme is present in most bacteria and in all mitochondrial systems and it is characterized by its large number of subunits, its prosthetic groups (flavin and iron-sulfur centers), and its NADH:quinone
oxidoreductase activity sensitive to specific inhibitors and coupled with
charge translocation across the membrane.(...
Spin Supersolid in Anisotropic Spin-One Heisenberg Chain
We consider an S=1 Heisenberg chain with strong exchange (Delta) and
single--ion uniaxial anisotropy (D) in a magnetic field (B) along the symmetry
axis. The low energy spectrum is described by an effective S=1/2 XXZ model that
acts on two different low energy sectors for a given window of fields. The
vacuum of each sector exhibits Ising-like antiferromagnetic ordering that
coexists with the finite spin stiffness obtained from the exact solution of the
effective XXZ model. In this way, we demonstrate the existence of a spin
supersolid phase. We also compute the full Delta-B quantum phase diagram by
means of a quantum Monte Carlo simulation.Comment: 4+ pages, 2 fig
Quantum Topology Change in (2 + 1)d
The topology of orientable (2 + 1)d spacetimes can be captured by certain
lumps of non-trivial topology called topological geons. They are the
topological analogues of conventional solitons. We give a description of
topological geons where the degrees of freedom related to topology are
separated from the complete theory that contains metric (dynamical) degrees of
freedom. The formalism also allows us to investigate processes of quantum
topology change. They correspond to creation and annihilation of quantum geons.
Selection rules for such processes are derived.Comment: LaTeX file, 33 pages, 10 postscript figures, some typos corrected,
references updated, and other minor change
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