3,957 research outputs found
Steady-state negative Wigner functions of nonlinear nanomechanical oscillators
We propose a scheme to prepare nanomechanical oscillators in nonclassical
steady states, characterized by a pronounced negative Wigner function. In our
optomechanical approach, the mechanical oscillator couples to multiple laser
driven resonances of an optical cavity. By lowering the resonance frequency of
the oscillator via an inhomogeneous electrostatic field, we significantly
enhance its intrinsic geometric nonlinearity per phonon. This causes the
motional sidebands to split into separate spectral lines for each phonon number
and transitions between individual phonon Fock states can be selectively
addressed. We show that this enables the preparation of the nanomechanical
oscillator in a single phonon Fock state. Our scheme can for example be
implemented with a carbon nanotube dispersively coupled to the evanescent field
of a state of the art whispering gallery mode microcavity
The population of M-type supergiants in the starburst cluster Stephenson 2
The open cluster Stephenson 2 contains the largest collection of red
supergiants known in the Galaxy, and at present is the second most massive
young cluster known in the Milky Way. We have obtained multi-epoch,
intermediate-resolution spectra around the CaII triplet for more than 30 red
supergiants in Stephenson~2 and its surroundings. We find a clear separation
between a majority of RSGs having spectral types M0-M2 and the brightest
members in the NIR, which have very late spectral types and show strong
evidence for heavy mass loss. The distribution of spectral types is similar to
that of RSGs in other clusters, such as NGC 7419, or associations, like Per
OB1. The cluster data strongly support the idea that heavy mass loss and maser
emission is preferentially associated with late-M spectral types, suggesting
that they represent an evolutionary phase.Comment: Contribution to the Betelgeuse workshop, November 2012, Paris. To be
published in the European Astronomical Society Publications Series, editors:
Pierre Kervella, Thibaut Le Bertre & Guy Perri
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An Astrophysical Laboratory: Understanding and Exploiting the Young Massive Cluster Westerlund 1
Westerlund 1 provides a unique opportunity to probe the physics of massive stars, from birth to death and beyond, as well as the formation and evolution of a super star cluster that appears destined to evolve into a globular cluster. We highlight the result of current studies of this cluster, its diverse stellar constituents and immediate environment, concluding with a summary of future research avenues enabled by ESO facilities
Westerlund 1 as a Template for Massive Star Evolution
With a dynamical mass M_dyn ~ 1.3x10e5 M_sun and a lower limit M_cl>5x10e4
M_sun from star counts, Westerlund 1 is the most massive young open cluster
known in the Galaxy and thus the perfect laboratory to study massive star
evolution. We have developed a comprehensive spectral classification scheme for
supergiants based on features in the 6000-9000A range, which allows us to
identify >30 very luminous supergiants in Westerlund 1 and ~100 other less
evolved massive stars, which join the large population of Wolf-Rayet stars
already known. Though detailed studies of these stars are still pending,
preliminary rough estimates suggest that the stars we see are evolving to the
red part of the HR diagram at approximately constant luminosity.Comment: To be published in Proceedings of IAU Symposium 250: Massive Stars as
Cosmic Engines, held in Kaua'i (Hawaii, USA), Dec 2007, edited by F.
Bresolin, P.A. Crowther & J. Puls (Cambridge University Press
Population structure of the broad-snouted caiman (Caiman latirostris) in natural and man-made water bodies associated with a silvicultural landscape
The broad-snouted caiman (Caiman latirostris) is a South American crocodilian with a wide geographical distribution. Water bodies originally occupied by the species have suffered extreme anthropogenic pressure; however, the broad-snouted caiman has a high adaptive capacity to colonize man-made habitats such as decanting pounds and artificial reservoirs for agriculture or livestock. In this context, the present study aimed at identifying the population structure of the broad-snouted caiman in a silvicultural landscape in southeastern Brazil. Fifty-two caimans of various classes were captured with baited traps and steel cable snares at night. The estimated population size was 51 individuals. The population density was estimated to be 2.6 individuals/ha with a linear density of 11.3 individuals/km. The intermediate values of linear density estimates herein compared with other areas, suggesting that silvicultural landscapes can be relevant for broadsnouted caiman conservation. Therefore, the role of silvicultural landscapes in crocodilian conservation should be taken into consideration for environmental certification processes related to forestry in the Neotropics.Fil: Marques, Thiago Simon. Universidade de Sao Paulo; BrasilFil: Bassetti, Luís Antonio Bochetti. Universidade de Sao Paulo; BrasilFil: Lara, Neliton Ricardo Freitas. Universidade de Sao Paulo; BrasilFil: Millan, Cristian Honora. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Piña, Carlos Ignacio. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Verdade, Luciano Martins. Universidade de Sao Paulo; Brasi
Multiwavelength study of the fast rotating supergiant high-mass X-ray binary IGR J16465-4507
Since its launch, the X-ray and gamma-ray observatory INTEGRAL satellite has
revealed a new class of high-mass X-ray binaries (HMXB) displaying fast flares
and hosting supergiant companion stars. Optical and infrared (OIR) observations
in a multi-wavelength context are essential to understand the nature and
evolution of these newly discovered celestial objects. The goal of this
multiwavelength study (from ultraviolet to infrared) is to characterise the
properties of IGR J16465-4507, to confirm its HMXB nature and that it hosts a
supergiant star. We analysed all OIR, photometric and spectroscopic
observations taken on this source, carried out at ESO facilities. Using
spectroscopic data, we constrained the spectral type of the companion star
between B0.5 and B1 Ib, settling the debate on the true nature of this source.
We measured a high rotation velocity of v = 320 +/- 8 km/s from fitting
absorption and emission lines in a stellar spectral model. We then built a
spectral energy distribution from photometric observations to evaluate the
origin of the different components radiating at each energy range. We finally
show that, having accurately determined the spectral type of the early-B
supergiant in IGR J16465-4507, we firmly support its classification as an
intermediate supergiant fast X-ray transient (SFXT).Comment: A&A in press, 14 pages, 15 tables, 13 figure
Exploring the Kondo model in and out of equilibrium with alkaline-earth atoms
We propose a scheme to realize the Kondo model with tunable anisotropy using
alkaline-earth atoms in an optical lattice. The new feature of our setup is
Floquet engineering of interactions using time-dependent Zeeman shifts, that
can be realized either using state-dependent optical Stark shifts or magnetic
fields. The properties of the resulting Kondo model strongly depend on the
anisotropy of the ferromagnetic interactions. In particular, easy-plane
couplings give rise to Kondo singlet formation even though microscopic
interactions are all ferromagnetic. We discuss both equilibrium and dynamical
properties of the system that can be measured with ultracold atoms, including
the impurity spin susceptibility, the impurity spin relaxation rate, as well as
the equilibrium and dynamical spin correlations between the impurity and the
ferromagnetic bath atoms. We analyze the non-equilibrium time evolution of the
system using a variational non-Gaussian approach, which allows us to explore
coherent dynamics over both short and long timescales, as set by the bandwidth
and the Kondo singlet formation, respectively. In the quench-type experiments,
when the Kondo interaction is suddenly switched on, we find that real-time
dynamics shows crossovers reminiscent of poor man's renormalization group flow
used to describe equilibrium systems. For bare easy-plane ferromagnetic
couplings, this allows us to follow the formation of the Kondo screening cloud
as the dynamics crosses over from ferromagnetic to antiferromagnetic behavior.
On the other side of the phase diagram, our scheme makes it possible to measure
quantum corrections to the well-known Korringa law describing the temperature
dependence of the impurity spin relaxation rate. Theoretical results discussed
in our paper can be measured using currently available experimental techniques.Comment: 22 pages, 12 figure
Toward Quantum Superposition of Living Organisms
The most striking feature of quantum mechanics is the existence of
superposition states, where an object appears to be in different situations at
the same time. The existence of such states has been tested with small objects,
like atoms, ions, electrons and photons, and even with molecules. More
recently, it has been possible to create superpositions of collections of
photons, atoms, or Cooper pairs. Current progress in optomechanical systems may
soon allow us to create superpositions of even larger objects, like micro-sized
mirrors or cantilevers, and thus to test quantum mechanical phenomena at larger
scales. Here we propose a method to cool down and create quantum superpositions
of the motion of sub-wavelength, arbitrarily shaped dielectric objects trapped
inside a high--finesse cavity at a very low pressure. Our method is ideally
suited for the smallest living organisms, such as viruses, which survive under
low vacuum pressures, and optically behave as dielectric objects. This opens up
the possibility of testing the quantum nature of living organisms by creating
quantum superposition states in very much the same spirit as the original
Schr\"odinger's cat "gedanken" paradigm. We anticipate our essay to be a
starting point to experimentally address fundamental questions, such as the
role of life and consciousness in quantum mechanics.Comment: 9 pages, 4 figures, published versio
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