205 research outputs found
Influence of hydrogen on paramagnetic defects induced by UV laser exposure in natural silica
Diffusion limited reactions of point defects were investigated in amorphous
SiO2 exposed to UV laser light. Electron spin resonance and in situ absorption
measurements at room temperature evidenced the annealing of E' centers and the
growth of H(II) centers both occurring in the post-irradiation stage and
lasting a few hours. These transients are caused by reactions involving
molecular hydrogen H2, made available by dimerization of radiolytic H0.Comment: Submitted to Physica Status Solid
H(II) centers in natural silica under repeated UV laser irradiations
We investigated the kinetics of H(II) centers (=Ge'-H) in natural silica
under repeated 266nm UV irradiations performed by a Nd:YAG pulsed laser. UV
photons temporarily destroy these paramagnetic defects, their reduction being
complete within 250 pulses. After re-irradiation, H(II) centers grow again, and
the observed recovery kinetics depends on the irradiation dose; multiple 2000
pulses re-irradiations induce the same post-irradiation kinetics of H(II)
centers after each exposure cycle. The analysis of these effects allows us to
achieve a deeper understanding of the dynamics of the centers during and after
laser irradiation.Comment: Submitted to Journal of Non Crystalline Solid
Influence of fluorine on the fiber performance studied through the NBOHC-related 1.9 eV microluminescence
The distribution of Non Bridging Oxygen Hole Centers (NBOHC) in Fluorine doped optical fibers was investigated by confocal microluminescence spectroscopy monitoring the characteristic 1.9 eV luminescence band. The results show that these defects are generated by the fiber drawing and their concentration further increases after \u3b3 irradiation.
The NBOHC profile along the fiber is anticorrelated to the fluorine content. This finding agrees with the role of
fluorine in the fiber toughness and is discussed from the microscopic point of view on the basis of previous works
Optical properties of Ge-oxygen defect center embedded in silica films
The photo-luminescence features of Ge-oxygen defect centers in a 100nm thick
Ge-doped silica film on a pure silica substrate were investigated by looking at
the emission spectra and time decay detected under synchrotron radiation
excitation in the 10-300 K temperature range. This center exhibits two
luminescence bands centered at 4.3eV and 3.2eV associated with its
de-excitation from singlet (S1) and triplet (T1) states, respectively, that are
linked by an intersystem crossing process. The comparison with results obtained
from a bulk Ge-doped silica sample evidences that the efficiency of the
intersystem crossing rate depends on the properties of the matrix embedding the
Ge-oxygen defect centers, being more effective in the film than in the bulk
counterpart.Comment: 10 pages, 3 figures, in press on J. Non cryst. solids (2007
Structural relaxation of E' gamma centers in amorphous silica
We report experimental evidence of the existence of two variants of the E'
gamma centers induced in silica by gamma rays at room temperature. The two
variants are distinguishable by the fine features of their line shapes in
paramagnetic resonance spectra. These features suggest that the two E' gamma
differ for their topology. We find a thermally induced interconversion between
the centers with an activation energy of about 34 meV. Hints are also found for
the existence of a structural configuration of minimum energy and of a
metastable state.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
Radiation hardening techniques for rare-earth based optical fibers and amplifiers
Er/Yb doped fibers and amplifiers have been shown to be very radiation sensitive, limiting their integration in space. We present an approach including successive hardening techniques to enhance their radiation tolerance. The efficiency of our
approach is demonstrated by comparing the radiation responses of optical amplifiers made with same lengths of different rare-earth doped fibers and exposed to gamma-rays. Previous studies indicated that such amplifiers suffered significant degradation for doses exceeding 10 krad. Applying our techniques significantly enhances the amplifier radiation resistance, resulting in a very limited degradation up to 50 krad. Our optimization techniques concern the fiber composition, some possible pre-treatments and the interest of simulation tools used to harden by design the amplifiers.
We showed that adding cerium inside the fiber phosphosilicate-based core strongly decreases the fiber radiation
sensitivity compared to the standard fiber. For both fibers, a pre-treatment with hydrogen permits to enhance again the fiber resistance. Furthermore, simulations tools can also be used to improve the tolerance of the fiber amplifier by
helping identifying the best amplifier configuration for operation in the radiative environment
Portuguese cacholeira blood sausage: A first taste of its microbiota and volatile organic compounds
Among typical Portuguese sausages, the cacholeira blood sausage undoubtedly represents one of the most popular preparations. To the authors’ knowledge, a lack of information on both the microbiota and the volatile organic compounds (VOCs) of this blood-containing sausage emerges from the available scientific literature. This study represents the first characterization of physico-chemical, microbiological and volatile traits of Portuguese cacholeira blood sausage. To this end, ready-to-eat cacholeira blood sausages were collected from two production batches manufactured in summer (batch 1) and autumn (batch 2). Viable counts showed active microbial communities mainly composed by lactic acid bacteria, coagulase negative cocci, enterococci and eumycetes. The metataxonomic approach showed a simple bacterial composition, which was dominated by Lactobacillus sakei in both the analyzed batches (1 and 2) considered. Carnobacterium, Enterococcus, Kluyvera, Lactococcus and Serratia were found as minor genera. The mycobiota varied according to the production season. Batch 1 was dominated by Starmerella apicola, Debaryomyces hansenii and Candida tropicalis, whereas batch 2 was dominated by D. hansenii. Moreover, Aspergillus spp., Kurtzmaniella zeylanoides, Saccharomyces cerevisiae, Kurtzmaniella santamariae, Brettanomyces bruxellensis and Pichia kluyveri were detected in both the batches as minority species. Seventy-two volatile compounds were identified, including esters, phenols, terpenoids, acids, alcohols, ketones, aldehydes, lactones, furans, sulphur and nitrogen compounds. Significant differences were seen in the amount of some compounds, as a feasible consequence of differences in the raw materials, artisan production and seasonality
Poorly differentiated neuroendocrine larynx carcinoma: Clinical features and mirnas signature—a new goal for early diagnosis and therapy?
Laryngeal neuroendocrine carcinomas (LNECs) are rare and highly heterogeneous malignancies presenting a wide range of pathological and clinical manifestations. Herein, we retrospectively characterize ten patients diagnosticated with LNEC, five of which were defined as well‐moderately differentiated neuroendocrine carcinomas, and five that were defined as poorly differentiated neuroendocrine carcinomas, according to the latest WHO classification. Clinical features were analyzed and compared between the two subgroups together with a microRNA study which evidenced a peculiar signature likely related to poorly differentiated larynx neuroendocrine carcinomas. These findings may offer new useful insights for clinicians to improve diagnosis efficiency, therapy response, and patients’ outcome for this aggressive neoplasm
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