1,720,986 research outputs found
Laser-Driven Neutron Generation with Near-Critical Targets and Application to Materials Characterization
Full text linkLaser-driven neutrons arouse outstanding interest because of their promising uses in several fields, from basic science to materials inspection. Many experiments achieved neutron yields [108 - 1010 n/(sr s)] suitable for applications. These results were obtained by exploiting high-energy (approximately 10-100 J) lasers working at low repetition rates. Instead, adopting advanced target configurations like near-critical double-layer targets (DLTs) and compact, commercial lasers was slightly considered. Here, a theoretical study is performed to address neutron generation with commercial (40-400 TW, 1-15 J) systems and DLTs. We investigate proton acceleration and interaction with various materials to induce (p, n) reactions. DLTs allow achieving 1-2 orders of magnitude larger neutron yields and maximum energies 3 times higher than with single-layer targets. Then, the feasibility of two materials characterization techniques, namely fast neutron activation analysis and pulsed fast neutron resonance radiography, is assessed. The results indicate that they can be performed with commercial lasers and DLTs
Le concept de fonction dans less écoles italienne; usage de l'épistemologie et de l'histoire des mathématiques pour en clarifier le sens
No full textSecante: Chi è costei? - Interpretazioni di studenti della scuola secondaria superiore sul limite tra analisi e geometria
No full textUna molto frequente pratica didattica relativa al Calcolo evoca il lato informale della derivata facendo ricorso alla retta tangente, definita sbrigativamente come 'limite delle rette secanti'. La nostra ricerca vuole contribuire al dibattito sulle potenziali conseguenze di questa tipologia di interpretazione 'grafica' tramite l'analisi di un questionario, somministrato a studenti di scuola secondaria superiore italiana nella fascia di età 16 - 18 anni. In particolar modo abbiamo deciso di focalizzare la nostra attenzione sugli aspetti linguistici, indagando sui significati attribuiti dagli allievi ai termini 'limite' e 'secante'. Sul piano epistemologico è emerso un sorprendente rapporto di carattere simbiontico tra tangente e secante, che riteniamo rivesta un ruolo non trascurabile nello sviluppo di modelli non coerenti di secante nella 'terra di mezzo' tra Geometria ed Analis
Reference-free evaluation of thin films mass thickness and composition through energy dispersive X-ray spectroscopy
Full text linkIn this paper we report the development of a new method for the evaluation of thin films mass thickness and composition based on the Energy Dispersive X-Ray Spectroscopy (EDS). The method exploits the theoretical calculation of the in-depth characteristic X-ray generation distribution function (φ(ρz))in multilayer samples, where φ(ρz)is obtained by the numerical solution of the electron transport equation. Once the substrate composition in known, this method gives reliable measurements without the need of a reference sample and/or multiple voltage acquisitions. The electron transport model is derived from the Boltzmann transport equation and it exploits the most updated and reliable physical parameters in order to obtain an accurate description of the phenomenon. The method for the calculation of film mass thickness and composition is validated with benchmarks from standard techniques. In addition, a model uncertainty and sensitivity analysis is carried out and it indicates that the mass thickness accuracy is of the order of 10 μg/cm2, which is comparable to the nuclear standard techniques resolution. We show the technique peculiarities in one example model: two-dimensional mass thickness and composition profiles are obtained for a ultra-low density, high roughness, nanostructured film
Activités didacticques à caractère vertical pour la construction du concept de limite
No full textAbstract: This paper concerns the activities of a research group in mathematics education about the concept of limit. The main characteristic of this group is that all stages in schooling (primary – 6 to 10 years; middle school – 11 to 13 years, and high school – 14 to 19 years) are represented, both within the group itself and as regards the pupils involved. This vertical cross-section is a resource which is as rare as it is precious. It allows us, indeed, to propose similar activities at different levels, check the evolution of the ideas, techniques and errors of the schoolchildren over time, and observe the effect of the teaching methods on them. With the support of research in mathematics education, we chose some issues, in particular measurement and approximation, which, in our opinion, can favour the gradual early development of the concept of limit. In this context, we would emphasise the importance of approximation as a resource for the long way to build the concept of the limit
La Scuola di Specializzazione per l'Insegnamento Secondario. Il punto di vista dei matematici di Parma
No full textCuriosità per la matematica 'inutile' - Uno strumento per migliorare il pensiero critico
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