2,559 research outputs found
Actinide chemistry using singlet-paired coupled cluster and its combinations with density functionals
Singlet-paired coupled cluster doubles (CCD0) is a simplification of CCD that
relinquishes a fraction of dynamic correlation in order to be able to describe
static correlation. Combinations of CCD0 with density functionals that recover
specifically the dynamic correlation missing in the former have also been
developed recently. Here, we assess the accuracy of CCD0 and CCD0+DFT (and
variants of these using Brueckner orbitals) as compared to well-established
quantum chemical methods for describing ground-state properties of singlet
actinide molecules. The actinyl series (UO, NpO,
PuO), the isoelectronic NUN, and Thorium (ThO, ThO) and
Nobelium (NoO, NoO) oxides are studied.Comment: 8 page
Developing a Data Acquisition System for Use in Cold Neutral Atom Traps
The rising interest in quantum computing has led to new quantum systems being developed and researched. Among these are trapped neutral atoms which have several desirable features and may be configured and operated on using lasers in an optical lattice. This work describes the development of a new data acquisition system for use in tuning lasers near the precise hyperfine transition frequencies of Rb 87 atoms, a crucial step in the functionality of a neutral atom trap. This improves on previous implementations that were deprecated and limited in laser frequency sweep range. Integration into the experiment was accomplished using an Arduino microcontroller and Python for real-time data acquisition and visualization
Dynamical star-disk interaction in the young stellar system V354 Mon
The main goal of this work is to characterize the mass accretion and ejection
processes of the classical T Tauri star V354 Mon, a member of the young stellar
cluster NGC 2264. In March 2008, photometric and spectroscopic observations of
V354 Mon were obtained simultaneously with the CoRoT satellite, the 60 cm
telescope at the Observat\'orio Pico dos Dias (LNA - Brazil) equipped with a
CCD camera and Johnson/Cousins BVRI filters, and the SOPHIE \'echelle
spectrograph at the Observatoire de Haute-Provence (CNRS - France). The light
curve of V354 Mon shows periodical minima (P = 5.26 +/- 0.50 days) that vary in
depth and width at each rotational cycle. From the analysis of the photometric
and spectroscopic data, it is possible to identify correlations between the
emission line variability and the light-curve modulation of the young system,
such as the occurrence of pronounced redshifted absorption in the H_alpha line
at the epoch of minimum flux. This is evidence that during photometric minima
we see the accretion funnel projected onto the stellar photosphere in our line
of sight, implying that the hot spot coincides with the light-curve minima. We
applied models of cold and hot spots and a model of occultation by
circumstellar material to investigate the source of the observed photometric
variations. We conclude that nonuniformly distributed material in the inner
part of the circumstellar disk is the main cause of the photometric modulation,
which does not exclude the presence of hot and cold spots at the stellar
surface. It is believed that the distortion in the inner part of the disk is
created by the dynamical interaction between the stellar magnetosphere,
inclined with respect to the rotation axis, and the circumstellar disk, as also
observed in the classical T Tauri star AA Tau and predicted by
magnetohydrodynamical numerical simulations.Comment: Accepted by Astronomy and Astrophysic
Profiles of Strong Permitted Lines in Classical T Tauri Stars
We present a spectral analysis of 30 T Tauri stars observed with the Hamilton
echelle spectrograph over more than a decade. One goal is to test
magnetospheric accretion model predictions. Observational evidence previously
published supporting the model, such as emission line asymmetry and a high
frequency of redshifted absorption components, are considered. We also discuss
the relation between different line forming regions and search for good
accretion rate indicators.
In this work we confirm several important points of the models, such as the
correlation between accretion and outflow, broad emission components that are
mostly central or slightly blueshifted and only the occasional presence of
redshifted absorption. We also show, however, that the broad emission
components supposedly formed in the magnetospheric accretion flow only
partially support the models. Unlike the predictions, they are sometimes
redshifted, and are mostly found to be symmetric. The published theoretical
profiles do not have a strong resemblance to our observed ones. We emphasize
the need for accretion models to include a strong turbulent component before
their profiles will match the observations. The effects of rotation, and the
outflow components, will also be needed to complete the picture.Comment: 25 pages including 9 figures, 3 tables, accepted for publication in
the Astronomical Journa
Índice de produção ponderado de atividades de bibliotecas: uma abordagem multicriterial.
O artigo propõe um índice de produção ponderado de atividades de bibliotecas
Avaliação e manejo do solo com a tecnologia de corte e trituração visando a sustentabilidade do sistema de produção da agricultura familiar, com ênfase em alternativas ao uso do fogo na Amazônia.
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Proposição de um índice de produção para bibliotecas com uso do Método MACBETH.
O artigo apresenta o uso de um método multicritério (MACBETH) para propor um índice de produção ponderado para bibliotecas
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