3,815 research outputs found
29Si Hyperfine Structure of the E'_\alpha Center in Amorphous Silicon Dioxide
We report a study by electron paramagnetic resonance (EPR) on the E'_\alpha
point defect in amorphous silicon dioxide (a-SiO2). Our experiments were
performed on gamma-ray irradiated oxygen-deficient materials and pointed out
that the 29Si hyperfine structure of the E'_alpha consists in a pair of lines
split by 49 mT. On the basis of the experimental results a microscopic model is
proposed for the E'_alpha center, consisting in a hole trapped in an oxygen
vacancy with the unpaired electron sp3 orbital pointing away from the vacancy
in a back-projected configuration and interacting with an extra oxygen atom of
the a-SiO2 matrix.Comment: 4 page
The reaction on p-shell nuclei
This letter is concerned with the study of the reaction in p-shell nuclei, i.e., , ,
and . The emission rates are
reported as a function of . These rates are discussed in comparison with
previous findings. The ratio in p-shell nuclei is
found to depart largely from that on hydrogen, which provides support for large
in-medium effects possibly generated by the sub-threshold . The
continuum momentum spectra of prompt pions and free sigmas are also discussed
as well as the missing mass behavior and the link with the
reaction mechanism. The apparatus used for the investigation is the FINUDA
spectrometer operating at the DANE -factory (LNF-INFN, Italy).Comment: 14 pages, 5 figures, accepted for publication in Phys. Lett.
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
Intrinsic point defects in silica for fiber optics applications
Due to its unique properties, amorphous silicon dioxide (a-SiO2 ) or silica is a key material in many technological fields, such as high-power laser systems, telecommunications, and fiber optics. In recent years, major efforts have been made in the development of highly transparent glasses, able to resist ionizing and non-ionizing radiation. However the widespread application of many silica-based technologies, particularly silica optical fibers, is still limited by the radiation-induced formation of point defects, which decrease their durability and transmission efficiency. Although this aspect has been widely investigated, the optical properties of certain defects and the correlation between their formation dynamics and the structure of the pristine glass remains an open issue. For this reason, it is of paramount importance to gain a deeper understanding of the structure–reactivity relationship in a-SiO2 for the prediction of the optical properties of a glass based on its manufacturing parameters, and the realization of more efficient devices. To this end, we here report on the state of the most important intrinsic point defects in pure silica, with a particular emphasis on their main spectroscopic features, their atomic structure, and the effects of their presence on the transmission properties of optical fibers
Coulomb corrections to low energy antiproton annihilation cross sections on protons and nuclei
We calculate, in a systematic way, the enhancement effect on
antiproton-proton and antiproton-nucleus annihilation cross sections at low
energy due to the initial state electrostatic interaction between the
projectile and the target nucleus. This calculation is aimed at future
comparisons between antineutron and antiproton annihilation rates on different
targets, for the extraction of pure isospin channels.Comment: 18 pages, 4 figures (latex format
Geographical and environment-related variations of essential oils in isolated populations of Thymus richardii Pers. in the Mediterranean basin
Composition of essential oils of different populations of Thymus richardii grex of six localities from Bosnia-Herzegovina (Konjic, Borci), Spain (Majorca, Ibiza, Valencia) and Italy (Marettimo, Sicily) were determined by GC/FID and GC/MS. The main constituents in most of the samples were aromatic monoterpenes corresponding to non-phenolic cyclic compounds (p-cymene, gamma-terpinene). The highest monoterpene concentrations were found in the Bosnian samples (70%), and the lowest in samples from the Balearic Islands ( 50%) in samples from Majorca with beta-bisabolene (>40%) being the principal constituent. Discriminant analysis (LDA) shows the differentiation of two chemotypes: A (phenol chemotype), with p-cymene and gamma-terpinene as characteristic compounds and B, with beta-bisabolene and carvacrol, as major and significative compounds. The occurrence of the chemotypes was related to summer positive precipitation and to deep of soils.Llorens, L.; Llorens Molina, JA.; Agnello, S.; Boira Tortajada, H. (2014). Geographical and environment-related variations of essential oils in isolated populations of Thymus richardii Pers. in the Mediterranean basin. Biochemical Systematics and Ecology. 56:246-254. doi:10.1016/j.bse.2014.05.0072462545
Recent developments in chiral dynamics of hadrons and hadrons in a nuclear medium
In this talk I present recent developments in chiral dynamics of hadrons and
hadrons in a medium addressing the following points: interaction of the octet
of pseudoscalar mesons with the octet of baryons of the nucleon, showing recent
experimental evidence on the existence of two states, the
interaction of the octet of pseudoscalar mesons with the decuplet of baryons of
the , with particular emphasis on the resonance,
dynamically generated by this interaction. Then I review the interaction of
kaons in a nuclear medium and briefly discuss the situation around the claims
of deeply bound states in nuclei. The large renormalization of the
in the nuclear medium is shown as another example of successful
application of the chiral unitary techniques.Comment: Talk at the Fifth International Conference on Perspectives in
Hadronic Physics: Particle-Nucleus and Nucleus-Nucleus Scattering at
Relativistic Energies, Trieste, May 200
A computational study on temperature variations in mrgfus treatments using prf thermometry techniques and optical probes
Structural and metabolic imaging are fundamental for diagnosis, treatment and follow-up in oncology. Beyond the well-established diagnostic imaging applications, ultrasounds are currently emerging in the clinical practice as a noninvasive technology for therapy. Indeed, the sound waves can be used to increase the temperature inside the target solid tumors, leading to apoptosis or necrosis of neoplastic tissues. The Magnetic resonance-guided focused ultrasound surgery (MRgFUS) technology represents a valid application of this ultrasound property, mainly used in oncology and neurology. In this paper; patient safety during MRgFUS treatments was investigated by a series of experiments in a tissue-mimicking phantom and performing ex vivo skin samples, to promptly identify unwanted temperature rises. The acquired MR images, used to evaluate the temperature in the treated areas, were analyzed to compare classical proton resonance frequency (PRF) shift techniques and referenceless thermometry methods to accurately assess the temperature variations. We exploited radial basis function (RBF) neural networks for referenceless thermometry and compared the results against interferometric optical fiber measurements. The experimental measurements were obtained using a set of interferometric optical fibers aimed at quantifying temperature variations directly in the sonication areas. The temperature increases during the treatment were not accurately detected by MRI-based referenceless thermometry methods, and more sensitive measurement systems, such as optical fibers, would be required. In-depth studies about these aspects are needed to monitor temperature and improve safety during MRgFUS treatments
Synthesis and functionalization of casein nanoparticles with aptamers for triple-negative breast cancer targeting
This work shows the synthesis of a drug delivery system made of casein nanoparticles able to host hydrophobic molecules and be functionalized with aptamers targeting the epidermal growth factor receptor. In vitro cell viability and uptake analyses, performed on triple-negative breast cancer cells, confirmed the safety profile and the target selectivity
Investigation by raman spectroscopy of the decomposition process of HKUST-1 upon exposure to air
We report an experimental investigation by Raman spectroscopy of the decomposition process of Metal-Organic Framework (MOF) HKUST-1 upon exposure to air moisture (T=300 K, 70% relative humidity). The data collected here are compared with the indications obtained from a model of the process of decomposition of this material proposed in literature. In agreement with that model, the reported Raman measurements indicate that for exposure times longer than 20 days relevant irreversible processes take place, which are related to the occurrence of the hydrolysis of Cu-O bonds. These processes induce small but detectable variations of the peak positions and intensities of the main Raman bands of the material, which can be related to Cu-Cu, Cu-O, and O-C-O stretching modes. The critical analyses of these changes have permitted us to obtain a more detailed description of the process of decomposition taking place in HKUST-1 upon interaction with moisture. Furthermore, the reported Raman data give further strong support to the recently proposed model of decomposition of HKUST-1, contributing significantly to the development of a complete picture of the properties of this considerable deleterious effect
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