The research activities described in the present thesis have been oriented to the design and development of components and technological processes aimed at optimizing the performance of plasma sources in advanced in material treatments. Consumables components for high definition plasma arc cutting (PAC) torches were studied and developed. Experimental activities have in particular focussed on the modifications of the emissive insert with respect to the standard electrode configuration, which comprises a press fit hafnium insert in a copper body holder, to improve its durability. Based on a deep analysis of both the scientific and patent literature, different solutions were proposed and tested. First, the behaviour of Hf cathodes when operating at high current levels (250A) in oxidizing atmosphere has been experimentally investigated optimizing, with respect to expected service life, the initial shape of the electrode emissive surface. Moreover, the microstructural modifications of the Hf insert in PAC electrodes were experimentally investigated during first cycles, in order to understand those phenomena occurring on and under the Hf emissive surface and involved in the electrode erosion process. Thereafter, the research activity focussed on producing, characterizing and testing prototypes of composite inserts, combining powders of a high thermal conductibility (Cu, Ag) and high thermionic emissivity (Hf, Zr) materials The complexity of the thermal plasma torch environment required and integrated approach also involving physical modelling. Accordingly, a detailed line-by-line method was developed to compute the net emission coefficient of Ar plasmas at temperatures ranging from 3000 K to 25000 K and pressure ranging from 50 kPa to 200 kPa, for optically thin and partially autoabsorbed plasmas. Finally, prototypal electrodes were studied and realized for a newly developed plasma source, based on the plasma needle concept and devoted to the generation of atmospheric pressure non-thermal plasmas for biomedical applications. / L’attività di ricerca svoltasi durante il Dottorato è stata orientata alla progettazione e allo sviluppo di componenti e processi tecnologici innovativi atti ad ottimizzare le prestazioni di sorgenti plasma nel trattamento avanzato di materiali. Sono stati in particolare studiati e sviluppati consumabili di torce al plasma termico per il taglio di materiali metallici (PAC, plasma arc cutting), nell’ambito della cosiddetta alta definizione. L’attività di tipo sperimentale in ambito PAC si è concentrata sulla valutazione e realizzazione di modifiche dell’inserto emettitore, rispetto alla configurazione attuale di elettrodi standard, che prevede un inserto piatto in afnio (Hf) inserito per interferenza in un corpo elettrodo in rame (Cu). Le soluzioni proposte per l’attività di ricerca sono state basate su un’approfondita analisi bibliografica e brevettuale. Il comportamento di inserti in Hf operanti ad alte correnti (250A) in torce PAC è stato sperimentalmente analizzato, ottimizzando la forma iniziale della superficie emittente per incrementarne la vita utile. Sono inoltre state studiate le modificazioni microstrutturali dell’inserto emettitore al fine di comprendere i fenomeni coinvolti nel processo di erosione. Infine, l’attività di ricerca su elettrodi PAC si è concentrata sulla produzione, caratterizzazione e test di inserti compositi prototipali, realizzati unendo polveri ad alta conduttività termica (Cu, Ag) e polvere ad alta emissività termoionica (Hf, Zr). La complessità del sistema torcia ha inoltre richiesto un approccio integrato, che affiancasse attività di simulazione modellistico-computazionale con le valutazioni sperimentali, di natura chimico-fisica e microstrutturale. È stato in questo senso implementato un modello per il calcolo del coefficiente di emissione netto (NEC) del plasma di Argon in funzione di temperatura (1000-25000 K) e pressione (50-200 kPa), per plasmi otticamente sottili o parzialmente auto-assorbiti. Sono infine stati inoltre studiati e realizzati elettrodi prototipali per sorgenti di plasma non termico, finalizzate in particolare ad applicazioni biomedicali, nella configurazione detta plasma needle.

Superconduttori bulk in MgB2, ottenuti con tecnologia Mg-RLI brevettata da Edison Spa, sono stati oggetto di un'approfondita analisi in termini di forze di levitazione. Questo studio è stato preliminare per la progettazione di un innovativo sistema di levitazione lineare. I risultati ottenuti sperimentalmente sono stati validati attraverso modelli numerici sviluppati ad hoc. I campioni oggetto dello studio sono tre bulk in MgB2 rappresentativi delle tipiche forme usate nelle applicazioni reali: un disco, un cilindro, una piastra. I bulk sono stati misurati con un sistema di misura per le forze di levitazione realizzato a tale scopo. Un protocollo sperimentale è stato seguito per la caratterizzazione di base, sia in condizioni Field Cooling sia Zero Field Cooling, al quale sono state affiancate prove specifiche come la possibilità di mantenere inalterate le proprietà superconduttive attraverso la giunzione di più campioni con la tecnologia Mg-RLI. Un modello numerico è stato sviluppato per convalidare i risultati sperimentali e per studiare l'elettrodinamica della levitazione. Diverse configurazioni di rotori magnetici sono state accoppiate con un cilindro in MgB2 con lo scopo di valutare la soluzione ottimale; questo tema è stato apporofondito attraverso lo sviluppo di un software di simulazione che può tenere conto sia del numero di magneti sia della presenza di anelli in materiale magneti intercalati fra di essi. Studi analoghi sono stati portati avanti su una piastra di MgB2 per simulare il comportamento di una geometria piana. Un sistema di raffreddamento innovativo basato sull'azoto solido è stato studiato per poterlo accoppiare con un sistema di levitazione. Il criostato progettato è costituito da due dewar, uno dentro l'altro; quello interno ha lo scopo di raffreddare l'MgB2 mentre quello esterno di limitare delle perdite verso l'esterno. Il criopattino così ottenuto è accoppiato in condizioni FC ad una rotaia formata da magneti permanenti in NdFeB. / A complet analysis about the superconduction levitaton forces of various MgB2 samples has been performed as preliminary study for an innovative linear levitating system. MgB2 bulks are produced by the Reactive Liquid Infiltration (Mg-RLI) method developed by Edison SpA. The experimental results are also evaluated by means of numerical models. A new measurement system have been developed to perform an evaluation of the levitation forces of three MgB2 bulks as case study: a disc, a cylinder and a slab. The possibility to joint different pieces of bulk has been proved, such as the optimal relaxation time of this material (S=0.009 @ 33K). A numerical model has been developed to evaluate the experimental results of the MgB2 disc and to investigate the electrodynamics of levitation. Several types of permant magnets (PM) configuration have been coupled with a MgB2 cylinder to tentatively determine the best configuration; that has been also numerical evaluated by means of a numerical model which take into account the number of the PMs and the presence of rings of magnetic material between them to form a rotor. Similar studies has been carried out on a planar geometry by a MgB2 slab and different PM configuration. An innovative refrigeration method based on solid nitrogen has been studied to be coupled with a levitation system. The cryostat consists of two nested dewars, built by differents materials; the internal one lodge four MgB2 slabs while the external one reduce the thermal losses. A guideway made of NdFeB permanent magnets has been realized to test in Field Cooling configuration the possibility to use MgB2 – RLI for levitating systems.

This thesis has investigated and recorded sites of Archaeological interest in Randolph County, Indiana. An earlier survey, conducted by Frank M. Setzler in 1930, investigated and recorded 20 sites. These were revisited by the writer and comments on their present condition are included in the paper. In addition, 46 new sites were located, recorded and categorized according to the developmental stage suggested by surface finds and/or test pits. Finally the thesis discusses the spatial and temporal relationships of the sites to sites in other areas.

More efficient water treatment technologies would decrease the water bodies’ pollution and the actual intake of water resource. The aim of this thesis is an in-depth analysis of the magnetic separation of pollutants from water by means of a continuous-flow magnetic filter subjected to a field gradient produced by permanent magnets. This technique has the potential to improve times and efficiencies of both urban wastewater treatment plants and drinking water treatment plants. It might also substitute industrial wastewater treatments. This technique combines a physico-chemical phase of adsorption and a magnetic phase of filtration, having the potential to bond magnetite with any conventional adsorbent powder. The removal of both Magnetic Activated Carbons (MACs) and zeolite-magnetite mix with the addition of a coagulant was investigated. Adsorption tests of different pollutants (surfactants, endocrine disruptors, Fe(III), Mn(II), Ca(II)) on these adsorbents were also performed achieving good results. The numerical results concerning the adsorbent removals well reproduced the experimental ones obtained from two different experimental setups. In real situations the treatable flow rates are up to 90 m3/h (2000 m3/d).

The project presents the interesting sights and places in Indianapolis using both pictures and German texts. It would be possible for German visitors in Indianapolis to enjoy their visit more by means of this project. Also included is the history of 'the city with interesting comments on the German contribution to the development of Indianapolis. In the appendix the reader finds the history of the three German societies still active in the city.All pictures were also taken by the degree candidate.

The quench characteristics of second generation (2 G) YBCO Coated Conductor (CC) tapes are of fundamental importance for the design and safe operation of superconducting cables and magnets based on this material. Their ability to transport high current densities at high temperature, up to 77 K, and at very high fields, over 20 T, together with the increasing knowledge in their manufacturing, which is reducing their cost, are pushing the use of this innovative material in numerous system applications, from high field magnets for research to motors and generators as well as for cables. The aim of this Ph. D. thesis is the experimental analysis and numerical simulations of quench in superconducting HTS tapes and coils. A measurements facility for the characterization of superconducting tapes and coils was designed, assembled and tested. The facility consist of a cryostat, a cryocooler, a vacuum system, resistive and superconducting current leads and signal feedthrough. Moreover, the data acquisition system and the software for critical current and quench measurements were developed. A 2D model was developed using the finite element code COMSOL Multiphysics R . The problem of modeling the high aspect ratio of the tape is tackled by multiplying the tape thickness by a constant factor, compensating the heat and electrical balance equations by introducing a material anisotropy. The model was then validated both with the results of a 1D quench model based on a non-linear electric circuit coupled to a thermal model of the tape, to literature measurements and to critical current and quench measurements made in the cryogenic facility. Finally the model was extended to the study of coils and windings with the definition of the tape and stack homogenized properties. The procedure allows the definition of a multi-scale hierarchical model, able to simulate the windings with different degrees of detail.

CdTe and Cu(In,Ga)Se2 (CIGS) thin film solar cells are fabricated, electrically characterized and modelled in this thesis. We start from the fabrication of CdTe thin film devices where the R.F. magnetron sputtering system is used to deposit the CdS/CdTe based solar cells. The chlorine post-growth treatment is modified in order to uniformly cover the cell surface and reduce the probability of pinholes and shunting pathways creation which, in turn, reduces the series resistance. The deionized water etching is proposed, for the first time, as the simplest solution to optimize the effect of shunt resistance, stability and metal-semiconductor inter-diffusion at the back contact. In continue, oxygen incorporation is proposed while CdTe layer deposition. This technique has been rarely examined through R.F sputtering deposition of such devices. The above experiments are characterized electrically and optically by current-voltage characterization, scanning electron microscopy, x-ray diffraction and optical spectroscopy. Furthermore, for the first time, the degradation rate of CdTe devices over time is numerically simulated through AMPS and SCAPS simulators. It is proposed that the instability of electrical parameters is coupled with the material properties and external stresses (bias, temperature and illumination). Then, CIGS materials are simulated and characterized by several techniques such as surface photovoltage spectroscopy is used (as a novel idea) to extract the band gap of graded band gap CIGS layers, surface or bulk defect states. The surface roughness is scanned by atomic force microscopy on nanometre scale to obtain the surface topography of the film. The modified equivalent circuits are proposed and the band gap graded profiles are simulated by AMPS simulator and several graded profiles are examined in order to optimize their thickness, grading strength and electrical parameters. Furthermore, the transport mechanisms and Auger generation phenomenon are modelled in CIGS devices.

There is no abstract available for this dissertation.

This dissertation presents the theory and the conducted activity that lead to the construction of a high voltage high frequency arbitrary waveform voltage generator. The generator has been specifically designed to supply power to a wide range of plasma actuators. The system has been completely designed, manufactured and tested at the Department of Electrical, Electronic and Information Engineering of the University of Bologna. The generator structure is based on the single phase cascaded H-bridge multilevel topology and is comprised of 24 elementary units that are series connected in order to form the typical staircase output voltage waveform of a multilevel converter. The total number of voltage levels that can be produced by the generator is 49. Each level is 600 V making the output peak-to-peak voltage equal to 28.8 kV. The large number of levels provides high resolution with respect to the output voltage having thus the possibility to generate arbitrary waveforms. Maximum frequency of operation is 20 kHz. A study of the relevant literature shows that this is the first time that a cascaded multilevel converter of such dimensions has been constructed. Isolation and control challenges had to be solved for the realization of the system. The biggest problem of the current technology in power supplies for plasma actuators is load matching. Resonant converters are the most used power supplies and are seriously affected by this problem. The manufactured generator completely solves this issue providing consistent voltage output independently of the connected load. This fact is very important when executing tests and during the comparison of the results because all measures should be comparable and not dependent from matching issues. The use of the multilevel converter for power supplying a plasma actuator is a real technological breakthrough that has provided and will continue to provide very significant experimental results.

L’attività di ricerca della presente tesi di dottorato ha riguardato sistemi tribologici complessi di interesse industriale per i quali sono stati individuati, mediante failure analysis, i meccanismi di usura dominanti. Per ciascuno di essi sono state studiate soluzioni migliorative sulla base di prove tribologiche di laboratorio. Nella realizzazione di maglie per macchine movimentazione terra sono ampiamente utilizzati i tradizionali acciai da bonifica. La possibilità di utilizzare i nuovi microlegati a medio tenore di carbonio, consentirebbe una notevole semplificazione del ciclo produttivo e benefici in termini di costi. Una parte della tesi ha riguardato lo studio del comportamento tribologico di tali acciai. E’ stato anche affrontato lo studio tribologico di motori idraulici, con l’obiettivo di riuscire a migliorarne la resistenza ad usura e quindi la vita utile. Sono state eseguite prove a banco, per valutare i principali meccanismi di usura, e prove di laboratorio atte a riprodurre le reali condizioni di utilizzo, valutando tecniche di modificazione superficiale che fossero in grado di ridurre l’usura dei componenti. Sono state analizzate diverse tipologie di rivestimenti Thermal Spray in termini di modalità di deposizione (AFS-APS) e di leghe metalliche depositate (Ni,Mo,Cu/Al). Si sono infine caratterizzati contatti tribologici nel settore del packaging, dove l’utilizzo di acciai inox austenitici è in alcuni casi obbligatorio. L’acciaio inossidabile AISI 316L è ampiamente utilizzato in applicazioni in cui siano richieste elevate resistenze alla corrosione, tuttavia la bassa resistenza all’usura, ne limitano l’impiego in campo tribologico. In tale ambito, è stata analizzata una problematica tribologica relativa a macchine automatiche per il dosaggio di polveri farmaceutiche. Sono state studiate soluzioni alternative che hanno previsto sia la completa sostituzione dei materiali della coppia tribologica, sia l’individuazione di tecniche di modificazione superficiale innovative quali la cementazione a bassa temperatura anche seguita dalla deposizione di un rivestimento di carbonio amorfo idrogenato a-C:H / The research focused on complex tribological systems of industrial interest for which the dominant wear mechanisms have been identified, through failure analysis. Therefore alternative solutions were studied on the basis of tribological laboratory test. For the tracks of high power excavators are widely used conventional Q&T steels. The possibility of using the new microalloyed medium carbon steels, allow a considerable reduction of manufacturing costs. This section focused on the study of the tribological behavior of these steels. It was also addressed the tribological study of hydraulic motors, in order to improve the wear resistance and the durability of this motors. Bench tests were carried out to assess the main wear mechanisms, and tribological laboratory test were performed to reproduce the real conditions, evaluating surface modification techniques that were able to reduce the wear of the components. Various types of thermal spray coatings, in terms of deposition mode (AFS -APS ) and metal alloys used (Ni, Mo, Cu/Al), were analyzed. Tribological contacts were finally characterized in the packaging sector, where the use of austenitic stainless steel is required in many cases. The AISI 316L stainless steel is widely used in applications where high corrosion resistance are required, however, the low wear resistance, limit the use of this steel in the tribology field. In this context, a tribological issue has been analyzed related to automatic machines for dosing of pharmaceutical powders. Alternative solutions have been studied: the complete replacement of the materials of the tribological pair, and the identification of innovative surface modification techniques, such as low temperature carburizing followed by the deposition of hydrogenated amorphous carbon a-C:H coating(DLC)