407 research outputs found
Effective-Hamiltonian parameters for \emph{ab initio} energy-level calculations of SrCl:Yb and CsCaBr:Yb
Calculated energy levels from recent \emph{ab initio} studies of the
electronic structure of SrCl:Yb and CsCaBr:Yb are
fitted with a semi-empirical "crystal-field" Hamiltonian, which acts within the
model space . Parameters are obtained for the
minima of the potential-energy curves for each energy level and also for a
range of anion-cation separations. The parameters are compared with published
results parameters fitted to experimental data and to atomic calculations. The
states with significant character give a good approximation of the
impurity-trapped exciton states that appear in the \emph{ab initio}
calculations.Comment: Minor revisio
Cytogenetic evidences on the evolutionary relationships between the tetraploids of the section Rhizomatosae and related diploid species (Arachis, Leguminosae).
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Previous issue date: 2017-07-27bitstream/item/181202/1/Ortiz2017-Article-CytogeneticEvidencesOnTheEvolu.pd
Preliminary Experience With the Use of Electromagnetic Navigation for the Diagnosis of Peripheral Pulmonary Nodules and Enlarged Mediastinal Lymph Nodes
Electromagnetic navigation is a new technique that can be
used with bronchoscopy to obtain samples of small peripheral
nodular lesions and enlarged mediastinal lymph nodes. It is
very versatile in that it enables both transbronchial biopsies
and fine-needle aspiration to be performed. We describe
2 cases in which navigation with the superDimension/
Bronchus system combined with traditional diagnostic
techniques facilitated a definitive diagnosis by bronchoscopy.
Electromagnetic navigation can obviate the need for more
invasive diagnostic procedures such as surgery, thus saving
time and money and avoiding complications
Sida cabreriana Krapov.
Ruta prov. 56. Cuesta de las Lajitas, 12 a 14 km SW de La Mendieta.publishedVersio
Yb2+-doped SrCl2: electronic structure of impurity states and impurity-trapped excitons
First-principles electronic structure calculations of the excited states of Yb2+-doped Sr Cl2 crystals up to 65 000 cm-1 reveal the existence of unexpected excited states with double-well potential energy surfaces and dual electronic structure lying above and very close in energy to the 4f 135d manifold, with which they interact strongly through spin-orbit coupling. The double-well energy curves result from avoided crossings between Yb-trapped exciton states (more stable at short Yb–Cl distances) and 4f 136s impurity states (more stable at long Yb–Cl distances); the former are found to be preionization states in which the impurity holds the excited electron in close lying empty interstitials located outside the YbCl8 moiety. Spin-orbit coupling between the double-well states and the lower lying 4f 135d impurity states spreads the dual electronic structure character to lower energies and, hence, the instability of the divalent oxidation state is also spread. To some extent, the dual electronic structure (impurity-trapped exciton–impurity state) of some excited states expresses and gives support to hypotheses of interaction between Yb2+ and Yb3+ pairs proposed to understand the complex spectroscopy of the material and conciliates these hypotheses with interpretations in terms of the existence of only one type of Yb2+ defect. The results presented confirm the presence of impurity states of the 4f 136s configuration among the 4f 135d manifolds, as proposed in literature, but their energies are very different from those assumed. The Yb-trapped excitons found in this chloride host can be seen as precursors of the luminescent Yb-trapped excitons characterized experimentally in the isomorphous SrF2 crystals
Hyperleptinaemia, respiratory drive and hypercapnic response in obese patients
Leptin is a powerful stimulant of ventilation in rodents. In humans, resistance
to leptin has been consistently associated with obesity. Raised leptin levels
have been reported in subjects with sleep apnoea or obesity-hypoventilation
syndrome. The aim of the present study was to assess, by multivariate analysis,
the possible association between respiratory centre impairment and levels of
serum leptin. In total, 364 obese subjects (body mass index >or=30 kg.m(-2))
underwent the following tests: sleep studies, respiratory function tests,
baseline and hypercapnic response (mouth occlusion pressure (P(0.1)), minute
ventilation), fasting leptin levels, body composition and anthropometric
measures. Subjects with airways obstruction on spirometry were excluded. Out of
the 346 subjects undergoing testing, 245 were included in the current analysis.
Lung volumes, age, log leptin levels, end-tidal carbon dioxide tension,
percentage body fat and minimal nocturnal saturation were predictors for baseline
P(0.1). The hypercapnic response test was performed by 186 subjects; log leptin
levels were predictors for hypercapnic response in males, but not in females.
Hyperleptinaemia is associated with a reduction in respiratory drive and
hypercapnic response, irrespective of the amount of body fat. These data suggest
the extension of leptin resistance to the respiratory centre
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