Search results for "Ultra"
showing 10 items of 4451 documents
Spectral heterogeneity of oxygen-deficient centers in Ge-doped silica
2004
Abstract We report an experimental investigation of the emission spectra of a 1000 mol ppm sol–gel Ge-doped silica by fine tuning the excitation energy in the ultraviolet (UV) range, around 5 eV , and in the vacuum-UV range, around 7.3 eV , at room temperature and at 10 K . The sample is characterized by a blue (centered at ∼3.2 eV ) and an UV (centered at ∼4.3 eV ) bands. We have found that the ratio between the area of the blue and the UV bands depends on the temperature and on the excitation energy in both the vacuum-UV and the UV range. At both temperatures the spectral features of the blue and the UV bands are weakly affected when the excitation is varied in the vacuum-UV. At variance,…
Bulk sensitive photo emission spectroscopy of compounds
2007
This work reports about bulk-sensitive, high energy photoelectron spectroscopy from the valence band of CoTiSb excited by photons from 1.2 to 5 keV energy. The high energy photoelectron spectra were taken at the KMC-1 high energy beamline of BESSY II employing the recently developed Phoibos 225 HV analyser. The measurements show a good agreement to calculations of the electronic structure using the LDA scheme. It is shown that the high energy spectra reveal the bulk electronic structure better compared to low energy XPS spectra.
Role of ΔpH in the mechanism of zeaxanthin-dependent amplification of qE
1995
Abstract The influence of zeaxanthin on the high-energy-state fluorescence quenching (qE) and the pH dependence of the maximum chlorophyll fluorescence yield (Fm) was examined in spinach thylakoids. High contents of zeaxanthin were achieved using different pretreatments. A pronounced, zeaxanthin-dependent amplification of non-photochemical quenching (NPQ) was exclusively found in thylakoids containing zeaxanthin, synthesized in the dark via the buildup of an artificial ΔpH. These thylakoids also showed a significant quenching of chlorophyll fluorescence in the range pH 5.5–6.3, where no or only slight quenching was visible in zeaxanthin-free thylakoids. Thylakoids containing high amounts of…
A Preliminary Estimation of the Direct Ultraviolet Spectral Irradiance in Valencia (Spain): Comparison with Measured Values
2000
UVSPEC and SMARTS2 models have been used to estimate the UV spectral irradiance values in Valencia, Spain, and the results of these estimations have been compared with experimental measurements of direct irradiance at normal incidence obtained using an Optronic OL 754 in the 300-400 nm range. The relative RMSD and MBD parameters have been used to estimate the deviations of the modelled values with respect to the experimental values. The results indicate that the deviations are smaller when the SMARTS2 model is used with the appropriate aerosol coefficients.
Radical scavenging activity of ultrasound-treated Carbon Nanotubes
2016
Carbon nanotubes (CNTs) having controlled radical activity have been achieved tuning the content of their lattice defects induced by an ultra-sound (us) treatment.
Trap Spectroscopy by the Glow Rate Technique using Bleaching of Colour Centres
2002
An application of the glow rate technique (GRT) for analysis of the parameters of thermostimulated decay of colour centres is presented using the data on the decay of radiation defects in LiBaF 3 :Fe crystals created by X rays at 300 K. The GRT offers a procedure for evaluation of the mean activation energy as a function of temperature in the case of arbitrary thermostimulated relaxation kinetics represented by the trap distribution function. The experimental procedure involves at least two subsequent measurements of thermostimulated decay kinetics at different heating rates. It is shown that the decay of the F type centres is governed by interaction of mobile anion vacancies with F A and F…
Pb–Pb age, stable isotope and chemical composition of Archaean magnesite, Barberton Greenstone Belt, South Africa
2010
International audience; Trace-element, carbon, oxygen and lead-isotope analyses were carried out to determine the formation mode and crystallization age of magnesite from the Budd ultramafic complex of the Archaean Barberton Greenstone Belt, South Africa. Its significantly high Ti contents probably relate to a soluble Ti-rich accessory mineral, probably dissolved during magnesite precipitation. Primitive mantle-normalized REE patterns of the magnesite show negative Ce and Eu anomalies induced by two events: (1) the Eu anomaly indicates reducing conditions probably induced by the emplacement of the ultramafic source rock; (2) the Ce anomaly implies oxidizing conditions, probably during a hyd…
Ultrapotassic volcanism from the waning stage of the Neotethyan subduction: a key study from the Izmir-Ankara-Erzincan suture belt, central northern …
2016
Upper Cretaceous volcano-sedimentary successions in the Central Pontides of Turkey, related to the closure of the Tethys Ocean, include a variety of alkaline ultrapotassic igneous rocks that have been classified as leucititic, lamprophyric and trachytic based on their mineral paragenesis. Although the ultrapotassic rocks display a range of K 2 O contents (0·9–8·4 wt %) that may partly reflect alteration processes, they display subduction-related trace element signatures characterized by significant enrichment of large ion lithophile elements and light rare earth elements relative to high field strength elements and heavy rare earth elements and depletion of Nb and Ta. However, their initial…
Visual abstract for Abdominal Radiology: what it is, why we need it and how to make it
2021
Visual abstract for Abdominal Radiology: what it is, why we need it and how to make it
La diagnostica delle malattie infettive: Tra metafora del passato e itinerario nel futuro
1993
A global emergency is threatening mankind, awakening dead ghosts and causing alarm about our present and future: it is the apparently irreversible spread of infectious diseases.This critical and worrying situation should be acknowledged and carefully followed by the radiological profession since all of us – teachers, specialists, professionals – have to deal with imaging diagnostic modalities deriving information from a deceitful and camouflageing anatomo-functional substratum.The increasing spread of infectious diseases is due to a wide range of concomitant factors: HIV infection, drug addiction, migration fenomena and the related opportunistic infections combined with poor hygienic, physi…