1,920 research outputs found
Estudio desde tierra y con el IUE de la atmósfera extendida de λ Pavonis
Se describe el comportamiento de la estrella Be, λ Pavonis, en base espectrogramas tomados en Bosque Alegre, Cerro Tololo y La Silla y a imágenes obtenidas con el satélite IUE. Las observaciones de La Silla y con el IUE son prácticamente simultáneas.Asociación Argentina de Astronomí
A terahertz-driven non-equilibrium phase transition in a room temperature atomic vapour
There are few demonstrated examples of phase transitions that may be driven directly by terahertz frequency electric fields, and those that are known require field strengths exceeding 1MV cm−1. Here we report a non-equilibrium phase transition driven by a weak (≪1 V cm−1), continuous-wave terahertz electric field. The system consists of room temperature caesium vapour under continuous optical excitation to a high-lying Rydberg state, which is resonantly coupled to a nearby level by the terahertz electric field. We use a simple model to understand the underlying physical behaviour, and we demonstrate two protocols to exploit the phase transition as a narrowband terahertz detector: the first with a fast (20 μs) non-linear response to nano-Watts of incident radiation, and the second with a linearised response and effective noise equivalent power ≤1 pWHz−1/2. The work opens the door to a class of terahertz devices controlled with low-field intensities and operating in a room temperature environment
Ultraviolet Study of the Active Interacting Binary Star R Arae using Archival IUE Data
The eclipsing and strongly interacting binary star system R Arae (HD149730)
is in a very active and very short-lived stage of its evolution. R Ara consists
of a B9V primary and an unknown secondary. We have collected the International
Ultraviolet Explorer (IUE) archival data on R Ara, with most of the data being
studied for the first time. There are 117 high resolution IUE spectra taken in
1980, 1982, 1985, 1989, and 1991. We provide photometric and spectroscopic
evidence for mass transfer and propose a geometry for the accretion structure.
We use colour scale radial velocity plots to view the complicated behavior of
the blended absorption features and to distinguish the motions of hotter and
cooler regions within the system. We observed a primary eclipse of R Ara in
2008 and have verified that its period is increasing. A model of the system and
its evolutionary status is presented.Comment: 13 pages, 15 figures, accepted for publication in MNRA
Two-body Förster resonance involving Rb nD states in a quasi-electrostatic trap
In this work, we excite nD5/2 Rydberg states in a dense and cold Rb atomic sample held in a 10.6 μm quasi-electrostatic trap using narrow-bandwidth laser pulses. Our goal is to study the Förster resonance process nD5/2+nD5/2→(n-2)F+(n+2)P3/2 at zero electric field as a function of the total atomic density using pulsed-field ionization in the range n=37-47. Such a process is almost degenerate for n=43. Younge and coworkers studied this process [K. C. Younge, A. Reinhard, T. Pohl, P. R. Berman, and G. Raithel, Phys. Rev. A 79, 043420 (2009)] and attributed the observed saturation to many-body effects. Our results show that as the ground-state atomic density increases, the nD5/2 state population and the population transfer starts to saturate, which is consistent with the onset of Rydberg atom blockade and previously published results. However, since our experiment allows the independent measurement of the nD5/2 and (n+2)P3/2 state populations, we were able to obtain the (n+2)P3/2 state population density dependence. Our results clearly show that the (n+2)P3/2 state population depends quadratically on the total Rydberg atomic population, and consequently, the Förster resonance is a two-body process for a ground-state atomic density below 3×1011 cm-3.FAPESP (12/19342-6; 13/02816-8)AFOSR (FA9550-12-1-0434)INCT-IQCNP
The Density Matrix Renormalization Group for finite Fermi systems
The Density Matrix Renormalization Group (DMRG) was introduced by Steven
White in 1992 as a method for accurately describing the properties of
one-dimensional quantum lattices. The method, as originally introduced, was
based on the iterative inclusion of sites on a real-space lattice. Based on its
enormous success in that domain, it was subsequently proposed that the DMRG
could be modified for use on finite Fermi systems, through the replacement of
real-space lattice sites by an appropriately ordered set of single-particle
levels. Since then, there has been an enormous amount of work on the subject,
ranging from efforts to clarify the optimal means of implementing the algorithm
to extensive applications in a variety of fields. In this article, we review
these recent developments. Following a description of the real-space DMRG
method, we discuss the key steps that were undertaken to modify it for use on
finite Fermi systems and then describe its applications to Quantum Chemistry,
ultrasmall superconducting grains, finite nuclei and two-dimensional electron
systems. We also describe a recent development which permits symmetries to be
taken into account consistently throughout the DMRG algorithm. We close with an
outlook for future applications of the method.Comment: 48 pages, 17 figures Corrections made to equation 19 and table
Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC
The uncertainty on the calorimeter energy response to jets of particles is
derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the
calorimeter response to single isolated charged hadrons is measured and
compared to the Monte Carlo simulation using proton-proton collisions at
centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009
and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter
response to specific types of particles (positively and negatively charged
pions, protons, and anti-protons) is measured and compared to the Monte Carlo
predictions. Finally, the jet energy scale uncertainty is determined by
propagating the response uncertainty for single charged and neutral particles
to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3%
for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table,
submitted to European Physical Journal
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