Fenomeni di miscelamento del boro nel lower plenum del reattore IRIS

L'obiettivo di questa tesi è quello di fornire, con l’ausilio di un codice di fluidodinamica computazionale, un supporto agli studi attualmente in corso presso l’università di Pisa riguardanti i fenomeni di miscelamento del boro nel lower plenum del reattore IRIS, in previsione della prossima realizzazione di un’apparecchiatura in scala. In particolare, sono state considerate configurazioni geometriche del reattore di diversa complessità e accuratezza, prendendo come condizioni operative di riferimento quella nominale e quella incidentale (con perdita di refrigerante primario e iniezione di acqua borata di emergenza). Le simulazioni sono state fatte sul reattore sia in piena scala che in scala ridotta (1:5), considerando in quest’ultimo caso differenti valori di portata in ingresso, dipendentemente dal parametro conservato nel processo di scala (numero di Reynolds, tempo di residenza)

Synergy and Other Interactions between Polymethoxyflavones from Citrus Byproducts

The citrus by-products released from citrus processing plants may contain high levels of potentially bioactive compounds such as flavonoids, which are a widely distributed group of polyphenolic compounds with health-related properties based on their antioxidant activity. In the study reported here, the potential bioactivities and antioxidant activities of extracts, fractions and compounds from citrus by-products were evaluated along with the chemical interactions of binary mixtures of compounds and complex mixtures. The bioactivities and interactions were evaluated in wheat coleoptile bioassays and the antioxidant activity was evaluated by the al DPPH (2,2-diphenyl-1-picrylhdrazyl radical) radical scavenging assay. The extracts, fractions and most of the isolated compounds (mainly polymethoxyflavones) showed high activity in the wheat coleoptile bioassay. However, the antioxidant activity was not consistently high, except in the acetone extract fractions. Moreover, a study of the interactions with binary mixtures of polymethoxyflavones showed the occurrence of synergistic effects. The complex mixtures of fractions composed mainly of polymethoxyflavones caused a synergistic effect when it was added to a bioactive compound such as anethole. The results reported here highlight a new application for the wheat coleoptile bioassay as a quick tool to detect potential synergistic effects in compounds or mixtures

Spin vortices and vacancies: interactions and pinning on a square lattice

The study gives a decisive answer to the recently risen question about the type and origin of interaction between spin vortices and spin vacancies in 2D spin models. The approach is based on the low-temperature approximation of the 2D XY model known as the Villain model and does not involve any additional approximations, thus preserving the lattice structure. The exact form of the Hamiltonian describing a system of topological charges and a vacant site supports the attractive type of interaction between the vacancy and the charges. The quantitative difference between the characteristics of the vortex behavior in the 2D XY and Villain models due to the different energy of the vortex "cores" in the two models is pointed out. This leads to a conclusion that the interaction between a vortex and a spin vacancy and between a vortex and the antivortex differs quantitatively for small separations in the two mentioned models.Comment: 13 pages, 5 figure

A scale for assessing the severity of diseases and adverse drug reactions: Application to drug benefit and risk

Physicians were interviewed to assess their willingness to risk adverse drug reactions among patients. These untoward reactions were ranked according to severity and weighted against the primary illness being treated. A specially designed questionnaire in the form of a matrix was used. Severity was divided into seven classes denoted by progressively increasing numerical scores, W1 to W7, whose values could be calculated from analysis of the completed questionnaires. The questionnaires presented several cases, in each of which an illness of specified severity was to be treated with a drug whose untoward reactions differ in severity from that of the primary illness. Each case involved a different permutation of the severities. Analysis of the completed questionnaires yielded the mean values of the scores which were found to range from W1 = 1.00 (the mildest case) to W7 = 817 (the most serious case). It is our opinion that this type of scale is preferable to nonnumerical descriptions of severity such as mild or serious, since, when combined with data on frequency of occurrence, a numerical scale permits a determination of expectation of both benefit and risk

« Il tacco a coda » : comment ne pas perdre pied avec ses talons

Vendredi soir, 18 h 30, je reçois un mail de mon agence préférée me demandant de traduire, de l’italien vers le français, 7 316 mots pour le lundi matin 11 h. Je consulte le document et constate que c’est encore pour cette grande marque de mode italienne que j’aime tant. Après une semaine passée à traduire des contrats commerciaux et des polices d’assurance, voilà qui va me changer les idées ! J’accepte donc le défi et l’idée de ne pas avoir de repos ce week-end-là. Il s’agit d’une formation..

Electronic states in arsenic-decapped MnAs (1100) films grown on GaAs(001): A photoemission spectroscopy study

3 pages, 2 figures.We examine the arsenic bonding in the near-surface region of initially arsenic-capped MnAs(1100) films grown on GaAs(001) as it evolves upon arsenic decapping. Line-shape analyses of high-resolution As 3d photoelectron emission spectra recorded at room temperature RT allow us to identify electronically distinct As-bonding states associated to bulk MnAs phases, bulk arsenic, and interfacial environments. Stable MnAs phases appear to be affected by the presence of a thin arsenic coating, an effect that could be advantageously used to enhance the ferromagnetic properties of MnAs films around RTWe thank the BESSY staff for support. This work has been supported by the Spanish Ministry of Education and Science (“Ramón y Cajal” and “Materials” Programs, 2005 call and MAT2004-05348 Grant, respectively) and by the German Federal Ministry for Education and Research.Peer reviewe

Anisotropic Electronic Structure of the Two-Dimensional Electron Gas at the AlOx/KTaO3(110) interface

Oxide-based two-dimensional electron gases (2DEGs) have generated significant interest due to their potential for discovering novel physical properties. Among these, 2DEGs formed in KTaO3 stand out due to the recently discovered crystal face-dependent superconductivity and large Rashba splitting, both of which hold potential for future oxide electronics devices. In this work, angle-resolved photoemission spectroscopy is used to study the electronic structure of the 2DEG formed at the (110) surface of KTaO3 after deposition of a thin Al layer. Our experiments revealed a remarkable anisotropy in the orbital character of the electron-like dispersive bands, which form a Fermi surface consisting of two elliptical contours with their major axes perpendicular to each other. The measured electronic structure is used to constrain the modeling parameters of self-consistent tight-binding slab calculations of the band structure. In these calculations, an anisotropic Rashba splitting is found with a value as large as 4 meV at the Fermi level along the [-110] crystallographic direction. This large unconventional and anisotropic Rashba splitting is rationalized based on the orbital angular momentum formulation. These findings provide insights into the interpretation of spin-orbitronics experiments and help to constrain models for superconductivity in the KTO(110)-2DEG system

Atom-specific identification of adsorbed chiral molecules by photoemission

The study of chiral adsorbed molecules is important for an analysis of enantioselectivity in heterogeneous catalysis. Here we show that such molecules can be identified through circular dichroism in core-level photoemission arising from the chiral carbon atoms in stereoisomers of 2,3-butanediol molecules adsorbed on Si(100), using circularly polarized x rays. The asymmetry in the carbon 1s intensity excited by right and left circularly polarized light is readily observed, and changes sign with the helicity of the radiation or handedness of the enantiomers; it is absent in the achiral form of the molecule. This observation demonstrates the possibility of determining molecular chirality in the adsorbed phase