http://hdl.handle.net/1889/636 Thu, 20 Jun 2013 12:12:05 GMT 2013-06-20T12:12:05Z http://dspace-unipr.cilea.it:80/retrieve/1981/Logo fisica Melloni.jpg http://hdl.handle.net/1889/636 http://hdl.handle.net/1889/2137 Title: Correlators of Wilson loops on Hopf fibrations in the AdS_5/CFT_4 correspondence Authors: Mori, Stefano Abstract: We study at quantum level the correlators of supersymmetric Wilson loops lying on Hopf fibers of S^3. In N=4 SYM, the strong coupling analysis can be performed using AdS/CFT correspondence. A connected surface, linking two different fibers is presented. The string solution describes fibers with opposite orientations and thus supersymmetry is broken. We describe the appearance of a first order phase transition as a function of angular separation of the fibers, of the difference of scalar couplings and of the ratio of the radii of the fibers, between a connected phase, where a unique surface stretches between the two fibers, and a disconnected phase, where each fiber is attached to a distinct surface. Deeper investigations are carried on in particular limits, where supersymmetry is restored or a quark-antiquark static potential interpretation is given.; Studiamo a livello quantistico i correlatori di loop di Wilson supersimmetrici descritti da fibre di Hopf su una S^3. In N=4 SYM, l'analisi ad accoppiamento forte è condotta utilizzando la corrispondenza AdS/CFT. Presentiamo una soluzione connessa, che collega due differenti fibre. La soluzione di stringa descrive fibre con orientazioni opposte, perciò la supersimmetria è rotta. Descriviamo la comparsa di una transizione di fase tra la fase connessa, dove un'unica superficie si estende tra le due fibre, e una fase sconnessa, dove ogni fibra è descritta da una distinta superficie, al variare della separazione angolare delle fibre, della differenza tra gli accoppiamenti con gli scalari e del rapporto tra i raggi delle fibre. Ulteriori analisi permettono di evidenziare particolari limiti, in cui la supersimmetria è ripristinata o una interpretazione in termini di potenziale statico tra una coppia quark-antiquark è possibile. Mon, 11 Mar 2013 23:00:00 GMT http://hdl.handle.net/1889/2137 2013-03-11T23:00:00Z http://hdl.handle.net/1889/2136 Title: Mean field models: rigorous results on spin glasses and biological applications to cooperative systems Authors: Di Biasio, Aldo Abstract: This thesis is split in two main parts, having in common the study of mean field models in Statistical Physics and Complex Systems. The first part is dedicated to an application of some of the methods of this science to the analysis of cooperative phenomena in biological systems, while the second part deals with mean field spin glass models, focusing on more formal aspects. Cooperativity is a widespread phenomenon in biochemical reactions: many biological functions involve the interactions of small molecules with specific sites on larger biopolymers, and the formation of some kind on non-covalent bond between the small molecule, called ligand, and the proper binding site; the binding of a ligand to one site can influence the affinity of other sites for the same kind of ligand, and in this case the binding is said to be cooperative. Cooperativity is said to be positive if the affinity of other sites increases after a ligand has bound, viceversa it is said to be negative, functioning a device to sharpen or dampen the responsiveness of a system to the changes in a stimulus. In our approach, the cooperative system is mapped into a spin model, with couplings generated by binary strings associated to each site, similarly to the Hopfield model. The simple non-cooperative systems are mapped into models with zero interactions, while positive and negative cooperativity are described in terms of models with, respectively, ferromagnetic and antiferromagnetic interactions. Thus, many different cooperative behaviors, described by the related binding curves, can be analyzed, in an unified vision, in terms of properties of the free energy for the corresponding spin model, by properly tuning the couplings. We fitted the theoretical curves obtained in this way with some experimental data found in literature, extrapolating the values of the effective interactions between the binding sites, which can be put in direct correspondence with some of the most used coefficients that measure cooperativity. The second part focuses on mean field spin glass models. The purpose of this part of the work is to show the applications of some techniques recently introduced to give a more rigorous and firm ground to the beautiful heuristic results known in this field for many years, both to prove the validity of such powerful methods and to develop alternative mathematical tools to approach the study of complex systems. The rigorous proof that the Parisi formula for the free energy is correct, in fact, was established only some years ago, split across two works by Guerra and Talagrand, and many important rigorous results, such as the existence of the thermodynamic limit for the free energy, or the correctness of the ultrametric hypothesis for low-temperature states, are quite recent. Most of the techniques used for these recent breakthroughs are based on interpolation and coupling the given system with an auxiliary, properly chosen, one. Some of these methods can be formulated through an interesting formal analogy with a mechanical system, governed by a proper Hamilton-Jacobi equation. The analysis of this associated mechanical problem, whose potential is related to the fluctuations of the order parameter, allowed us to reconstruct, in particular, the free energy for the Sherrington-Kirkpatrick model and the p-spin glass model, up to the first step of broken replica symmetry.; Questa tesi è divisa in due parti, che hanno in comune lo studio di modelli di campo medio in meccanica statistica e sistemi complessi. La prima parte è dedicata all'applicazione di alcuni metodi di queste scienze all'analisi di fenomeni cooperativi in sistemi biologici, mentre la seconda parte riguarda modelli di campo medio per vetri di spin, ed è focalizzata su aspetti più formali. La cooperatività è un fenomeno molto diffuso nelle reazioni biochimiche e, nel nostro approccio, i sistemi cooperativi sono mappati in un modello di spin interagenti con accoppiamenti generati da strighe binarie, in maniera simile al modello di Hopfield. In questo modo viene modellizzata una possibile eterogeneità nelle interazioni, e possono essere descritti effetti cooperativi ed anticooperativi a seconda del segno dell'accoppiamento medio. Nella seconda parte viene mostrata l'applicazione di alcune tecniche sviluppate di recente nell'ambito dello studio dei modelli di vetri di spin, inscritte in un approccio che ha consentito di dare una base rigorosa ai risultati euristici noti in questo contesto da molti anni (limite termodinamico, validità della soluzione di Parisi, ecc.). Queste tecniche, basate su un'analogia formale con sistemi meccanici, consentono di ricostruire l'energia libera per il modello di Sherrington-Kirkpatrick e per il p-spin glass utilizzando delle funzioni di partizione interpolanti con un sistema ausiliario, in cui agiscono una serie di campi esterni random. Thu, 28 Feb 2013 23:00:00 GMT http://hdl.handle.net/1889/2136 2013-02-28T23:00:00Z http://hdl.handle.net/1889/2135 Title: Nanostructured magnetic materials for sensors and biomedicine Authors: Chiesi, Valentina Abstract: In the last twenty years the discovery of new nanostructured materials and nanoscale physical effects have paved the way for several technologies; thanks to these discoveries nanotechnology is now a word used in our everyday language. In the nanoworld the properties of materials are completely different from the bulk and can give rise to new and surprising solutions to problems arising in very different fields, from medicine, to energy production or telecommunications. Nanotechnology allows, for instance, to have smaller, easier to use, more sensitive and lighter sensors. In medicine, the day when nano-vectors and nano-manipulators will become reality is not so far. The research activity presented in this thesis focuses on different magnetic nanostructures, i.e., thin films, nanoparticles and nanocomposites, characterised by physical properties which can fruitfully be exploited in sensors and biomedicine. Novel properties in magnetic nanostructures can arise for a number of reasons, such as confinement of the magnetic material into two- or one-dimensional structures and close proximity with other materials in layered or nanocomposite structures. When specific functional magnetic properties are due to size reduction, an in depth study of the correlation between magnetism and size reduction is mandatory for the nanostructured material optimisation for a given application. For this reason, we have followed the same methodological approach for each studied material: starting from the material design, passing through a complete structural and magnetic characterisation has allowed us, in the most prominent cases, to model the magnetic properties and give an answer to application requirements. This thesis is made up of six chapthers. In the first chapter basic elements of magnetism and magnetic materials are recalled, which are useful to understand the experimental results. In particular the attention is on the effect of size reduction on magnetic phenomenology and magnetisation processes, on surface effects in thin films and nanoparticles and on the effect of interactions between magnetic nanoparticles. In the second chapter the experimental techniques used to characterise thin films and nanoparticles are shown. In the third chapter the main results obtained on amorphous thin films, showing soft magnetic properties, are reported. After a detailed investigation of the correlation between growth parameters and film properties, these have been optimised for exploiting the thin film as magnetic core in flux-gate and hall sensors. Chapter four presents the results on Iron oxide nanoparticles, which, after suitable surface functionalisation, have been studied as magnetic hyperthermia mediators and for magnetic separation. The mere effect of size reduction is here accompanied by other effects, such as aggregation, nanoparticles interactions, exchange-bias effect in core-shell nanoparticles, which enrich the systems phenomenology. Finally, chapter five summarises the results obtained on composite and multifunctional nanostructures, characterised by different functional properties. In particular, the superparamagnetic properties of magnetite nanoparticles are coupled to the semiconducting properties of Zinc oxide tetrapods and Silicon carbide nanowires. At the end of this chapter the results obtained on nanodisks of Ni-Mn-Ga Heusler alloy, which is an intrinsically multifunctional material, are reported. Mon, 31 Dec 2012 23:00:00 GMT http://hdl.handle.net/1889/2135 2012-12-31T23:00:00Z http://hdl.handle.net/1889/1801 Title: Ab-initio simulations of the Al/ZnO interface Authors: Bazzani, Mirco Abstract: This thesis is part of a broad effort aimed at gaining a better description of the active elements in functionalized nanostructures for energy applications, and a deeper understanding of charge and energy transfer mechanisms in these complex systems. In particular this work focused on Aluminum doped ZnO, recently proposed for interesting photovoltaic applications, and on the Al/ZnO interface since Metal/ZnO contacts are central to all ZnO electronic devices. Beside the fundamental interest in the challenging topics related to material science and nano structures, the control of the interactions at these interfaces offers a unique opportunity to unravel the interplay between structures and functionalities of increasing complexity and technological relevance. Our approach is based on ab initio Density Functional Theory (DFT) simulations to characterize microscopic properties and processes that constitute the fundamental building blocks of ideal structures and interfaces. Firstly we studied the effects of aluminum doping on the electronic and optical properties of ZnO, via DFT simulations. We discussed the bandstructure and absorption properties of Al:ZnO as a function of the dopant concentration, and compared with recent experimental data. Our results support the formation of a transparent conductive oxide compound up to an incorporation of Al of about 3% in substitutional Zn sites. We propose an explanation to the observed degradation of conductivity in terms of interstitial defects expected to occur at high doping concentrations, beyond the Al solubility limit. Finally, we addressed the problem of the Al/ZnO interface, the main target of the PhD project. For the first time, the Al/ZnO Schottky barrier was calculated on a reduced mismatch system, taking into account the macroscopic dipole field effects adapting well-established methods to the present case. Our results highlight the Ohmic character of contact, clearly showing the strong influence of the interface microscopic details on the barrier height.; Questa tesi è parte di un progetto volto a migliorare la descrizione degli elementi attivi in nanostrutture funzionalizzate per applicazioni energetiche, e una più profonda comprensione dei meccanismi di trasferimento di carica ed energia in questi sistemi complessi. In particolare questo lavoro si è concentrato sul drogaggio di ZnO mediante Alluminio (AZO), di recente proposto come candidato ottimale per applicazioni fotovoltaiche, e sull'interfaccia Al/ZnO inquanto il contatto metallo/ZnO contatti è fondamentale per tutti i dispositivi elettronici basati su ZnO. Oltre all'interesse fondamentale legato alla scienza dei materiali e nano strutture, il controllo delle interazioni di queste interfacce ha una notevole rilevanza tecnologica. In primo luogo sono stati studiati gli effetti del doping mediante Alluminio sulle proprietà elettroniche ed ottiche di ZnO, attraverso simulazioni ab-initio DFT. La nostra analisi si è focalizzata sulle proprietà elettroniche e sui meccanismi di assorbimento di Al da parte di ZnO in funzione della concentrazione di drogante, attraverso il confronto con i più recenti dati sperimentali. I nostri risultati supportano la formazione di un ossido conduttivo trasparente fino ad una incorporazione di Al (sostituzionale) di circa il 3%, fornendo una spiegazione in termini di difetti interstiziali al degrado di conducibilità osservato sperimentalmente. Infine, è stato affrontato il problema dell'interfaccia Al/ZnO, l'obiettivo principale del progetto di dottorato. Per la prima volta è stata calcolata la barriera Schottky del contatto Al/ZnO su un sistema a mismatch reticolare ridotto, tenendo conto degli effetti del campo di polarizzazione macroscopico ZnO. I nostri risultati evidenziano il carattere Ohmico del contatto, mostrando chiaramente la forte influenza dei dettagli microscopici d'interfaccia sulla barriera Schottky. Sun, 29 Jan 2012 23:00:00 GMT http://hdl.handle.net/1889/1801 2012-01-29T23:00:00Z http://hdl.handle.net/1889/1795 Title: Pure spinor superstring in AdS_4xCP^3 Authors: Camobreco, Alessio Abstract: We study a formulation of the Pure Spinor superstring in the superspace AdS_4xCP^3. In this formulation the ghost constraint is solved and it allows to compute the central charge of the action up to one-loop. We compute also the operator product expansion of the Lorentz currents with themselves. Wed, 29 Feb 2012 23:00:00 GMT http://hdl.handle.net/1889/1795 2012-02-29T23:00:00Z http://hdl.handle.net/1889/1794 Title: Dynamical and rheological characterization of 2D architectures at the air/water interface Authors: Orsi, Davide Abstract: This Thesis reports the characterization of the mechanical response and of the internal microscopic dynamics of 2D Langmuir films, performed and interpreted within the theoretical framework provided by fluctuation-response function theorems. The mechanical shear modulus of Langmuir films has been measured by means of the Interfacial Shear Rheology technique (ISR). X-ray photon correlation spectroscopy (XPCS) experiments were performed to characterize the slow microscopic dynamics of samples either at the air/water interface or transferred on solid substrate. Two kind of systems have been investigated: polymeric films made of a photosensitive azobenzene-polyacrylate (PA4), and films of gold nanoparticles (GNPs) forming a 2D gel. Langmuir films of PA4 present an elastic shear response, which can be controlled at will by suitable illumination, induceing photoisomerisation of the azobenzene and therefore a transformation from an elastic to a viscous film. This process is accompanied by an acceleration, of more than one order of magnitude, of the internal dynamics, without a change in any thermodynamic parameter (temperature or surface pressure). Also, back isomerization with blue light acts on the system as an “optical quench”. All this allows the polymer to be brought out of equilibrium- and its dynamics being studied- in a novel and unconventional way. GNPs films are characterized by an heterogeneous morphology, with a foam-like structure at low concentration, and a Levy-distribution of sizes, which is deemed to be at the origin of the elastic, gel-like mechanical response observed. The slow dynamics of the films, observed by XPCS on the spatial scale of hundreds of nanometers, has an hyper-diffusive character which has been found in many arrested systems. Dynamical heterogeneities have been observed and characterized by means of higher order correlation functions -in particular, four times correlation functions have been experimentally accessed for the first time in an XPCS experiment in the course of this work. The GNPs 2D gel dynamics is characterized by two distinct time scales; both fast and slow motions are confined to the surface plane (2D) and have similar dependencies on the exchanged momentum, and on the coverage fraction. The degree of heterogeneity increases with concentration; at the same time, it seems that the motion involves a hierarchy of spatial scales. These results are compatible with theoretical results and simulations of the dynamics of colloidal gels.; Questa Tesi riporta la caratterizzazione della risposta meccanica e della dinamica microscopica di film di Langmuir bidimensionali, eseguita e interpretata nell'ambito del quadro teorico fornito dai teoremi fluttuazione-funzione di risposta. Il modulo meccanico di scorrimento di tali film è stato misurato mediante reologia interfacciale di Shear (ISR). La dinamica microscopica lenta dei campioni è stata caratterizzata tramite misure di spettroscopia di fotocorrelazione di raggi X (XPCS), sia all'interfaccia aria/acqua che su film trasferiti su substrato solido. Sono stati studiati due diversi tipi di sistemi: film polimerici di un poliacrilato fotosensibile contenente azobenzene (PA4), e film di nanoparticelle di oro (GNP) costituenti un gel 2D. I Film di Langmuir di PA4 presentano una risposta di shear elastica, controllabile a piacimento mediante illuminazione con luce UV. Essa induce una fotoisomerizzazione dell'azobenzene che causa il passaggio da un comportamento meccanico elastico ad uno maggiormente viscoso. Questo processo è accompagnato da un'accelerazione, di più di un ordine di grandezza, della dinamica interna, senza che venga modificato alcun parametro termodinamico (temperatura o pressione superficiale). Inoltre, illuminando i film con luce blu si ottiene l'isomerizzazione inversa, paragonabile ad un "quench ottico". Tutto questo permette di portare fuori equilibrio la dinamica interna del polimero in un modo innovativo e anticonvenzionale. I film di GNP sono caratterizzati da una morfologia eterogenea, con una struttura simile a schiuma a basse concentrazioni, e una struttura caratterizzata da distribuzione alla Lévy delle dimensioni caratteristiche alle concentrazioni più elevate. Si ritiene che tale struttura sia all'origine del comportamento di tipo elastico (gel) osservato nella risposta meccanica del sistema. La dinamica lenta del film, osservata mediante XPCS sulla scala spaziale delle centinaia di nanometri, ha un carattere iper-diffusivo, già osservato in molti altri sistemi arrestati. Eterogeneità dinamiche sono stati osservate e caratterizzate mediante funzioni di correlazione di ordine superiore -in particolare, funzioni di correlazione a quattro tempi sono stati misurate sperimentalmente per la prima volta in un esperimento XPCS nel corso di questo lavoro. La dinamica dei gel 2D di GNP è caratterizzata da due scale temporali distinte: entrambi i movimenti (veloci e lenti) sono confinati all'interfaccia (2D) e hanno dipendenze simili in funzione del momento trasferito e della concentrazione. Il grado di eterogeneità aumenta con la concentrazione e, al tempo stesso, sembra che tali moti coinvolgano una gerarchia di scale spaziali. Questi risultati sono compatibili con la teoria e le simulazioni della dinamica di gel colloidali riportate in letteratura. Thu, 15 Mar 2012 23:00:00 GMT http://hdl.handle.net/1889/1794 2012-03-15T23:00:00Z http://hdl.handle.net/1889/1793 Title: Wilson Loops and Scattering Amplitudes in Supersymmetric Field and String Theories Authors: Marmiroli, Daniele Abstract: The long-standing problem of finding weak-strong coupling interpolating observables for supersymmetric Chern-Simons theories in three dimensions is analysed from the point of view of BPS Wilson loop operators.; Analizziamo l'annoso problema della determinazione di funzioni interpolanti tra i regimi di accoppiamento debole e accoppiamento forte in teorie di Chern-Simons supersimmetriche in tre dimensioni dal punto di vista di operatori di Wilson BPS. Wed, 29 Feb 2012 23:00:00 GMT http://hdl.handle.net/1889/1793 2012-02-29T23:00:00Z http://hdl.handle.net/1889/1682 Title: Numerical Stochastic Perturbation Theory for Lattice QCD: computation of renormalization constants and prospects for the study of the Dirac operator spectrum Authors: Brambilla, Michele Abstract: This thesis accounts for my research project in NSPT. From a technical point of view, it actually covers three quite different fields. As in any numerical investigation, my research project required an extensive programming work. My PhD activity was the chance for what is technically known as a refactoring of Parma group LGT (and in particular NSPT) codes. This was in particular true in a phase in which the group was moving to the usage of new multi-cores architectures and (even more) of a new parallel platform (Aurora). As it is often the case for such a work, there is no obvious way to account for this in a thesis without letting this numerical work actually take over Physics. The solution which I chose is to give a brief methodological account of the package which is the result of my activities (PRlgt). I would regard the computation of three loop renormalization constants as the core business of this work. Perturbative versus non-perturbative renormalization has been an issue for quite a long time. As a matter of fact, such a comparison has always been limited by the low order at which perturbative results were available. The ambitious goal of my work was to get to three loop results for quark bilinears (in a given regularization) with a fair account of all the systematics. This in turn enables us to better assess the level of confidence of non-perturbative results. The bottom line is that there are in general more indeterminations in non-perturbative determinations than it is usually stated: truncation errors are not the end of the story. As a last subject, the work pins down the prospects for an NSPT study of the Dirac operator spectrum. The spirit is to investigate the pattern of chiral symmetry breaking from Banks-Casher relation: can one inspect thereshuffling of Dirac operator eigenvalues due to color interactions? This part of the work has by far a different status with respect to renormalization constants computation. While I put the technical basis for a computation that has not even been attempted before with traditional techniques, there is a long way to go to get quantitative results. I try to give a qualitative account of what emerges from one loop bare perturbation theory: eigenvalues do repel each other and the spectrum is well rearranged with respect to the free field. Mon, 28 Feb 2011 23:00:00 GMT http://hdl.handle.net/1889/1682 2011-02-28T23:00:00Z http://hdl.handle.net/1889/1679 Title: Models in Statistical Physics on Infinite Graphs Authors: Campari, Riccardo Abstract: Physicists and mathematicians love regularity, mainly for the reason that it makes things simple, clear and, primely, computable; nature, on the other hand, has its own way of deciding what’s the right way to behave, and although it presents the attentive observer with beautifully ordered crystals, impressive fractals and perfectly spherical soap bubbles, the vast majority of matter we interact with every day has no definite structural order: wood, plastic, cloth, all are microscopically complex structures which do not enjoy neither translational nor scale invariance, nor any other form of symmetry. However, even when the spatial disposition of the constituents of matter is highly irregular, what determines the physical properties of the system are not so much the details of the distribution, as the topological structure of their interactions, which can usually be safely reduced to nearest neighbour or next-nearest neighbour relations. As a consequence, both regular and complex matter are well described by means of graphs, which represent in a compact form the interactions among their constituents. When paired with an underlying mathematical model, a graph is able to describe many physical systems in an approximate yet effective way. Furthermore, a graph can equally well model a network of interacting agents, as one often finds in economic literature, or computers - the Internet is the prime example - or abstract data structures in IT, or a deluge of other possibilities. Given their broad applicability, it is not surprising that a great wealth of scientific literature in many fields regards physical and mathematical models defined on graphs. In particular, during my doctoral period I focused on two different general purpose models, which enjoy a wide diffusion: discrete random walks and the Ising model. Random Walks. Regarding random walks, my current research focuses on the statistics of multiple agents simultaneously travelling on an infinite graph, and their collective properties. Several degrees of technical difficulty accompany this endeavour, associated with keeping track of multiple positions, on the one hand, and with the non-linearity of collective properties, on the other. A simplifying picture can be sometimes achieved by means of the distance graph, each vertex of which corresponds to a relative position of the particles, so that, for example, simultaneous encounters of all the particles correspond to a return to the origin in the distance graph. Constructing the distance graph proves however impossible in general, so that case specific methods need to be used to calculate the same quantities. While further work is in progress, the results I obtained up to date regard three particles moving on an infinite line: owing to the homogeneity of the structure, a distance graph exists, which corresponds to the triangular 2-d lattice, so that the probability of finding the particles at given relative distances can be straightforwardly calculated by means of a standard Fourier transform and saddle point approximation. As a further step, we computed the probability that the minimum and maximum distances among the particles are lower than some constant d, and found that asymptotically they scale as a function of d^2/t, implying that the surfaces of fixed probability undergo a regular diffusion. The results have been submitted for publication. The Ising Model. The second area of research I investigated revolves around the magnetization properties of the ferromagnetic Ising model on arbitrary graphs. More specifically, my aim was to find a relationship between the long range topology of a graph and its spontaneous magnetization. Several results are present in literature for regular lattices, fractals and a few more general graphs, and an extension of the Mermin-Wagner theorem states that transient on the average graphs show indeed spontaneous magnetization; however, a very wide set of graphs was still uncovered, and no sufficiently general criterion for assessing the existence of long range correlation existed. The approximate direction of exploration was clear since the beginning: on the one side, the number of different paths present in a graph is a first measure of the quality of the correlation between far away points; in turn, the transmission of information from one vertex to another is strongly inhibited when all the paths connecting them must cross just a small number of edges of the graph. These considerations formed the basis from which we proceeded to the construction of two theorems: a necessary condition for the presence of spontaneous magnetization, in zero external field and no boundary conditions, and a sufficient condition for its absence. These two theorems represent the most encompassing criteria to date for what regards the magnetizability of graphs: all the known structures enter the hypothesis of either of the theorems, even though no sufficient and necessary condition is known. The gap left between the hypotheses of the two theorems regards a very small class of pathological graphs whose existence is not even acknowledged. The theorems have been published as two different research papers. A part of my study was cast into an analysis of the different ways in which spontaneous magnetization can be defined, as either a spin expectation value or a long range order, for a single spin or averaged over the graph, under an external field or boundary conditions or neither. A chapter has been devoted to a thorough discussion of the matter. Thu, 17 Mar 2011 23:00:00 GMT http://hdl.handle.net/1889/1679 2011-03-17T23:00:00Z http://hdl.handle.net/1889/1560 Title: An organic memristor as the building block for bio-inspired adaptive networks Authors: Smerieri, Anteo Abstract: This thesis reports the research path I followed during my PhD course, which i followed from January 2008 to December 2010 working at the University of Parma, in the Laboratory of Molecular Nanotechnologies, under the supervision of Prof. Marco P. Fontana and Dr. Victor Erokhin, within the framework of an interdisciplinary, international research project called BION – Biologically inspired Organized Networks. The keystone of my research is an organic memristor, a two terminal polymeric electronic device recently developed in our research group at the university of Parma. A memristor is a passive electronic device in which the electrical resistance depends on the electrical charge that has passed through it, and hence is adjustable by applying the appropriate electric potential or sequence of potentials. As of the beginning of my PhD, the device was in its early characterization stages, but it was already clear that it could be used to mimic the kind of plasticity found in synapses within neuronal circuits. In the thesis I show some further characterization work, used for engineering the device to maximize its more useful characteristics and to deepen our understanding of the functioning of the device, as well as the work done on. The knowledge of computational neuroscience acquired during this side project has proved very useful to better coordinate research in the material science side of the project, whose ultimate goal is the realization of a new, highly innovative technology for the production of functional molecular assemblies that can perform advanced tasks of information processing, involving learning and decision making, and that can be tailored down to the nanoscale.; Questa tesi riporta il percorso di ricerca seguito durante il mio dottorato di ricerca, che ho svolto da gennaio 2008 a dicembre 2010 lavorando nel Laboratorio di Nanotecnologie Molecolari, presso l'Università di Parma, , sotto la supervisione del Prof. Marco P. Fontana e del Dott. Victor Erokhin, nel quadro di un approccio interdisciplinare, progetto di ricerca internazionale denominato BION - Biologically ispired Organized Networks . La chiave di svolta della mia ricerca è un memristor organico, un dispositivo a due terminali elettronici polimerici recentemente messo a punto nel nostro gruppo di ricerca presso l'università di Parma. Un memristor è un dispositivo elettronico passivo in cui la resistenza elettrica dipende dalla carica elettrica che è passata attraverso di essa, e quindi è regolabile applicando il potenziale elettrico appropriato o una sequenza di potenziali. A partire dall'inizio del mio dottorato di ricerca, il dispositivo è stato nelle sue fasi di caratterizzazione iniziale, ma era già chiaro che poteva essere usata per simulare il tipo di plasticità trovato in sinapsi all'interno di circuiti neuronali. Nella tesi ho mostrato un ulteriore lavoro di caratterizzazione, utilizzato per l'ingegneria del dispositivo al fine di massimizzare le sue caratteristiche più utili e di approfondire la nostra comprensione del funzionamento del dispositivo, così come il lavoro svolto. La conoscenza delle neuroscienze computazionali acquisite nel corso di questo progetto parallelo si è rivelato molto utile per meglio coordinare la ricerca per quanto riguarda il materiale scientifico del progetto, il cui scopo ultimo è la realizzazione di una nuova tecnologia altamente innovativa per la produzione di composti molecolari funzionali in grado di eseguire attività avanzate di elaborazione delle informazioni, che coinvolgano l'apprendimento e il processo decisionale, e che può essere adattata fino alla scala nanometrica. Wed, 16 Feb 2011 23:00:00 GMT http://hdl.handle.net/1889/1560 2011-02-16T23:00:00Z