315 research outputs found
Composition of plasma-sprayed tungsten coatings on CuCrZr alloy
No full textMock-ups for the International Thermonuclear Experimental Reactor(ITER) were manufactured by depositing W coatings on tubular substrates of CuCrZr alloy via plasma spraying. An appropriate interlayer (of Ni, Al and Si) was optimised to increase the adhesion of W on the Cu alloy and to provide a soft interface with intermediate thermal expansion coefficient for better thermo-mechanical compatibility.
The distribution of chemical elements in the layered interface and in the coating was investigated by energy dispersive spectroscopy (EDS), XPS and AES in the as-preparedmaterial and after heat treatment of 24 h at 823 K. Moreover, the external Wlayer was examined by inductively coupled plasma emission spectrometry(ICP-ES).
The results showed that the as-prepared material does not exhibit macro-porosity. The layers forming the interface do not exhibit any long-range diffusion of the chemical species from layer to layer during the deposition process. The heat treatment does not seem to cause long-rangemigration of Al and Ni into theWcoating.
The presence of Ni (0.4wt%) in the as-deposited externalWlayer as shown by ICP-ES is only due to the low purity (commercial grade) of W powders used in spraying operations. It can be eliminated by using W powders of higher purity in the deposition process
Seismic Sustainability of a Contemporary Architectural Expression" Chapter on “Conceptual Approach to Structural Design
No full textA correct structural design should derive from the contemporary
contribution of the architectural and engineered components. The "architectural
concept" should account for the structural design criteria since the very beginning of
its development. This is especially true for an earthquake resistant structure, indeed
some resistance principles could conflict with some architectural composition
principles traditionally based on the consideration of only static actions. With this
aim, new seismic protection technologies can mitigate the apparent conflict between
architectural expression and structural requirements. The paper deals with the
sample design of a transportation intermodal building capable to distinguish itself
from the current anonymous industrial buildings. The design principle consists of
creating an internal flexible space with an exterior in-view structure contradicting the
traditional idea of structural frame. It starts on with a research of architectures in
nature: the external structural skeleton is conceived from textures derived from
images of trees. The design of the building accounts for up-to-date construction
technologies. Precast prestressed long-span thin slabs are provided. The full seismic
protection is achieved by means of a base isolation system, taking advantage of
having all the vertical loads carrying structures along the perimeter. An architectural
solution for eliminating the gap at the building base is also conceived
Micro-chemical inhomogeneity in eutectic Pb-Bi alloy quenched from melt
No full textThe liquid lead-bismuth eutectic (LBE) alloy is of great interest for applications in advanced nuclear systems, in particular it is considered to be a good candidate as a coolant and neutron spallation source material for MYRRHA, an accelerator driven system.
Investigations based on mechanical spectroscopy experiments and high temperature X-ray diffraction (HT-XRD) evidenced that the structure of the liquid alloy is not stable but undergoes relevant changes as the temperature increases. To understand whether such transformations, occurring in the liquid state involve elemental clustering, the alloy has been water-quenched from the liquid state at three different temperatures. After quenching, the samples have been investigated by standard XPS and scanning photoemission microscopy (SPEM) at the ELETTRA synchrotron. The SPEM results showed that the distribution of two metals is characterized by: 1) Pb enriched clusters; 2) Bi enriched clusters and 3) matrix in near eutectic composition. The statistics of clusters size was evaluated from the linescans of chemical Pb/Bi images. The average size of clusters is noticeably reduced by increasing quenching temperature: it is in the range of 1 ÷ 3 μm at 313 °C and passes to 0.5 ÷ 0.9 μm at 518 °C. Therefore, SPEM results evidenced a structural and micro-chemical re-arrangement of the atoms in the melt consisting in the evolution of cluster size and composition
XPS investigation of 5N purity Al thin foils for MEMS devices
No full textThin Al foils are promising materials for applications in devices of microelectromechanical systems (MEMS). In this work, three foils of high purity (5N) Al with different thickness (10, 50, and 125 μm) were analyzed by means of X-ray photoelectron spectroscopy (XPS), before and after annealing (720 K for 30 min). XPS surface analysis and depth profiling of chemical composition were performed to investigate the distribution of Al oxide. Electron energy loss spectroscopy (EELS) measurements were also carried out in order to identify the plasmon losses and chemical state of Al. The loss peaks in the 5N-Al thin foils were compared with those of an Al foil of commercial purity (99.95 wt%). The thickness of the oxide layer on the sample surface of all the samples is not constant and oxide is thicker in the samples of high purity than in those of commercial quality. Moreover, the thinnest foils of 5N-Al (10 μm) exhibit the thinnest oxide layer. These findings have been discussed by considering the size effect, that is, mechanical properties of thin foils are improving as the thickness decreases. The complex morphology of the metal-oxide interface may contribute to enhance the mechanical performances of Al foils with a thickness below ~50 μm, because the free dislocations pile up against the interface which represents an obstacle for their motion hindering plastic deformation. Obtained results suggest that Al foils to be used in MEMS devices should be of high purity and annealed to get a surface completely covered by the oxide layer
Thermoelectric analysis of ZnSb thin films prepared by ns-pulsed laser deposition
No full textZinc antimonide (ZnSb) is a promising thermoelectric material for the temperature range 300-600 K. ZnSb thin films were prepared by nanosecond Pulsed Laser Deposition (PLD) to evaluate the performance of nanostructured films for thermoelectric conversion by the determination of the Power Factor. A study of the influence of structural, compositional and thermoelectric properties of thin films is reported as a function of different deposition parameters, such as repetition rate, pulse energy, and substrate temperature. The evaluation of a thin film ZnSb compound with excess Sb has been performed to verify the variation of the thermoelectric properties. The obtained results are reported and discussed in the 300-600 K temperature range
Mitigation
No full textE' una sintesi aggiornata sulle ricerche condotte sulle strategie e sui mezzi linguistici con cui i parlanti attenuano i rischi connessi alle loro azioni linguistiche
Tecniche di Machine Learning per la classificazione di accelerazioni indotte da mezzi di trasporto
No full textIn questo elaborato si è raggiunto l'obiettivo di realizzare un algoritmo di Machine Learning per il riconoscimento di accelerazioni di mezzi di trasporto. Le accelerazioni sono state acquisite tramite un sensore accelerometrico situato all'interno degli smartphone, grazie all'applicazione Matlab Mobile.
I dati accelerometrici sono stati successivamente caricati sul pc per essere studiati ed elaborati attraverso Matlab.
Sono state individuate le differenze tra dati di accelerazioni di mezzi di trasporto e accelerazioni di attività motorie.
Poi si è potuto procedere con l'identificazione della feature, caratteristica idonea la quale permette la distinzione dei vari dati e permette la realizzazione dell'algoritmo.
L'algoritmo utilizzato come modello di classificazione è il K-Nearest-Neighbour. Infine le prestazioni di questo modello di classificazione sono state valutate mediante la Matrice di Confusione
Combined use of SA-XPS, XRD and SEM + EDS for the micro-chemical characterisation of Ag-based archaeological artefacts
No full textThe precious metallic artefacts are particularly interesting from a historical, artistic and economical point of view because they were used as jewels, amulets or artistic items and also for currency,mediumof exchange and formof saving. By means of the combined use of XPS, X-ray diffraction, SEM+ energy dispersive spectrometry and optical microscopy, the micro-chemical surface structure of the corrosion products grown on archaeological Ag-based artefacts has been investigated in the present work. The obtained results allowed the identification of the corroding agents coming fromthe surrounding environmentwhere the artefacts have been found, stored or exhibited. The experimental findings highlight the role of chloride ions that are present in the patina as chloroargyrite or corrode the copper islands scattered in the alloy giving rise to the formation of the dangerous species such as atacamite and paratacamite. Furthermore, the results shown different corrosion behaviours with the outermost layers enriched of S, Ca, Al, Si and Fe demonstrating the relationship between some soil constituents and surface alloy corrosion products giving rise to the formation of different compound
ZnSb-based thin films prepared by ns-PLD for thermoelectric applications
No full textZinc antimonide-based nanostructured thin films were produced by Pulsed Laser Deposition (PLD) using a ns-ArF laser (193 nm) and a multi-target deposition system. The films were prepared according to a multi-layer structure, obtained by adding different dopants (Cr, Ag) within the ZnSb matrix. The influence of the dopant introduction on the structural, compositional and electronic properties of the deposited films was studied in the temperature range 300–600 K. The power factor (PF) of films with dopant concentration of 5 at.% resulted significantly increased up to 100–200 μW/mK² at 600 K with respect to that of undoped films
Mezzi di comunicazione e modernità. Una teoria sociale dei media
No full textTroppo spesso lo studio sui mezzi di comunicazione prescinde dal considerare l’inevitabile intreccio tra il loro sviluppo e le trasformazioni istituzionali del contesto in cui si trovano ad operare. E’ immune da questa omissione il nuovo libro di John B. Thompson, Mezzi di comunicazione e modernità. Una teoria sociale dei media (Bologna, il Mulino, 1998; tit. orig. The Media and Modernity. A Social Theory of the Media, Cambridge, Polity Press, 1995).
Ambizione dell’autore è fornire un contributo alla comprensione delle trasformazioni culturali associate alla nascita delle società moderne, riconoscendo un ruolo di centrale importanza allo sviluppo dei mezzi di comunicazione e al loro impatto. Una delle tesi centrali del libro consiste infatti nella considerazione che l’organizzazione sociale del potere simbolico non si limiti a trasmettere informazioni e contenuti culturali – lasciando immutate le relazioni tra individui - ma contribuisca a creare nuove forme di azione e interazione nel mondo sociale, nuovi modi di rapportarsi agli altri e a se stessi, nuove forme e modalità di esercizio del potere.Too often the study of the means of communication is independent from considering the inevitable intertwining of their development and the transformation of the institutional context in which they operate. And 'immune from this omission the new book by John B. Thompson, Media and modernity. A social theory of the media (Bologna, Il Mulino, 1998, tit. Orig. The Media and Modernity. A Social Theory of the Media, Cambridge, Polity Press, 1995). Ambition of the author is to provide a contribution to the understanding of cultural transformations associated with the birth of modern societies, recognizing a role of central importance to the development of the media and their impact. One of the central theses of the book consists in the fact that consider the social organization of symbolic power does not merely convey information and cultural content - leaving unchanged the relationships between individuals - but it helps to create new forms of action and interaction in the social world, new ways of relating to others and to themselves, new forms and methods of exercise of power
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