Scienze fisiche

As technology advances, hearing aids can be packaged into increasingly smaller housings. Devices that fit entirely within the deeper portion of the external auditory canal have been developed, called completely-in-the-canal (CIC). These aids are custom moulded and have high cosmetic appeal because they are virtually undetectable. They also have several acoustic advantages: reduced occlusion effect, reduced gain requirements, and preservation of the natural acoustic properties of the pinna and external ear. However, CIC hearing aids require proper fitting of the hearing aid shell to the subject ear canal to achieve satisfactory wearing comfort, reduction in acoustic feedback, and unwanted changes in the electro-acoustic characteristics of the aid. To date, the hearing aid shell manufacturing process is fully manual: the shell is fabricated as a replica of the impression of the subject ear canal. Conventional impression acquisition method is very invasive and imprecise, moreover the typical post-impression processes made on the ear impression leaves room for error and may not accurately represent the structural anatomy of patient’s ear canal. There are some laser approaches able to perform a 3D laser scanning of the original ear impression but, the entire shell-making process is completely dependent on the ear impression and often is the sole cause of poor fitting shell. Therefore, direct ear canal scanning is the only way to perform accurate and repeatable measurements without the use of physical ear impression. The conventional optical elements are not able to enter in the inner part of the ear and perform a scanning of the cavity. This work is devoted to the direct scanning of human external auditory canal by using electromagnetically actuated torsion micromirror fabricated by micromachining technique as scanner. This is the first ever demonstration of actual scanning of human external auditory canal by a single integral Micro-Electro-Mechanical System (MEMS). A novel prototype 3D scanning system is developed together with surface reconstruction algorithm to obtain an explicit 3D reconstruction of actual human auditory canal. The system is based on acquisition of optical range data by conoscopic holographic laser interferometer using electromagnetically actuated scanning MEMS micromirror. An innovative fabrication process based on poly(methylmethacrylate) (PMMA) sacrificial layer for fabrication of free standing micromirror is used. Micromirror actuation is achieved by using magnetic field generated with an electromagnetic coil stick. Micromirror and electromagnet coil assembly composes the opto-mechanical scanning probe used for entering in ear auditory canal. Based on actual scan map, a 3D reconstructed digital model of the ear canal was built using a surface point distribution approach. The proposed system allows noninvasive 3D imaging of ear canal with spatial resolution in the 10 μm range. Fabrication of actual shell from in-vivo ear canal scanning is also accomplished. The actual human ear canal measurement techniques presented provide a characterization of the ear canal shape, which help in the design and refining of hearing aids fabrication approaches to patient personalized based.

The present work pertains to the surface science approach to heterogeneous catalysis. In particular model systems for CO2 hydrogenation to methanol, and NO selective catalytic reduction, are investigated by means of a combined approach, where the molecular-level insight provided by a low-temperature scanning tunneling microscope is complemented by density functional theory (DFT) calculations of their electronic structure. To this end, the Inelastic Electron Tunneling Spectroscopy (STM-IETS) technique was introduced for the first time in our laboratory, a recent development which allows to measure the vibrational spectrum of individual molecules adsorbed on a surface. Regarding CO2, we provide single molecule imaging and characterization of CO2/Ni(110), chemisorbed with high charge transfer from the substrate, in an activated state that plays a crucial role in the hydrogenation process. We obtain a detailed characterization of the adsorption geometries and an estimate of the energies corresponding to the different adsorbed states. A consistent picture of CO2 chemisorption on Ni(110) is provided on the basis of the newly available information, yielding a deeper insight into the previously existing spectroscopic and theoretical data. In the Selective Catalytic Reduction (SCR) process, nitrogen oxide is selectively transformed to N2 by reductants such as ammonia. The specificity of this reaction was tentatively attributed to the formation of NH3-NO coadsorption complexes, as indicated by several surface science techniques. Here we characterize the NH3-NO complex at the atomic scale on the (111) surface of platinum, investigating the intermolecular interactions that tune the selectivity. The structures that arise upon coadsorption of NH3 and NO are analyzed in terms of adsorption sites, geometry, energetics and charge rearrangement. An ordered 2 × 2 adlayer forms, where the two molecules are arranged in a configuration that maximizes mutual interactions. In this structure, NH3 adsorbs on top and NO on fcc-hollow sites, leading to a cohesional stabilization of the extended layer by 0.29 eV/unit cell. The calculated vibrational energies of the individually-adsorbed species and of the coadsorption structure fit the experimental values found in literature within less than 6%. The characterizations and optimizations that had to be tackled in order to successfully perform STM-IETS measurement are eventually presented, focusing in particular on an original method which allows to increase the achieved resolution. Namely, the modulation broadening associated to phase-sensitive detection is reduced by employing a tailored modulation function, different from the commonly-used sinusoid. This method is not limited to STM-IETS, but can be easily applied whenever a lock-in amplifier is used to measure a second derivative.

The Regional Climate Model RegCM4 (Giorgi et al., 2012) treats nonconvective clouds and precipitation following the Subgrid Explicit SUBEX param- eterization (Pal et al., 2000). This scheme includes a simple representation for the formation of raindrops and solves diagnostically the precipitation: rain forms when the cloud water content exceeds the autoconversion threshold, that is an increasing function of the temperature and assumes different values over the land and over the ocean to account for the difference in number of the cloud condensation nuclei over continental and oceanic regions. The SUBEX scheme does not account for the presence of clouds ice, and the fraction of ice is diagnosed as a function of temperature in the radiation scheme. Due to the increasing emphasis on cloud representations in the climate community and the forthcoming increasing resolution due to the inclusion, in the close future, of a non-hydrostatic compressible core, the treatment of the ice microphysics and a prognostic representation of the precipitation is required in RegCM4. This thesis presents the new parameterization for stratiform cloud microphysics and precipitation implemented in RegCM4. The approach of the new parameterization is based on an implicit numerical framework recently developed and implemented into the ECMWF operational forecasting model (Tiedtke, 1993). The new parameterization solves 5 prognostic equations for the water vapour, the liquid water, the rain, the ice and the snow mixing ratios. It allows a proper treatment of mixed-phase clouds and a more physically realistic representation of the precipitation as it is no more an instantaneous response to the microphysical processes occurring in clouds and is subjected to the horizontal advection. A first discussion of the results contains an evaluation of the vertical distributions of the main microphysical quantities, such as the liquid and ice water mixing ratios and the relative fractions. It also presents a series of sensitivity tests to understand how the moisture and radiation quantities respond to the variation of the microphysical parameters used in the scheme, such as the fall speeds of the falling categories, the autoconversion scheme and the evaporation coefficient. Cloud properties are afterwards evaluated through the implementation for RegCM4 of the new cloud evaluation COSP tool (Bodas-Salcedo et al., 2011), developed by the Cloud Feedback Model In- tercomparison Project (CFMIP), that facilitates the comparison of simulated clouds with observations from passive and active remote sensing by diagnosing from model outputs the quantities that would be observed from satellites if they were flying above an atmosphere similar to that predicted by the model. Different hypothesis are presented to explain the reasons for RegCM4 biases in representing different types of clouds over the tropical band and new prospectives for the future investigations designed to answer to the open questions are outlined.

Traditional semiconductor technology will reach a size limit within the next few years. A possible solution could be the use of organic molecules in technological applications as single functional units in metal-organic based devices; the success of this approach strongly depends on the understanding of the behaviour of these molecules on metallic surfaces. The interaction with metallic substrates and the interaction between the molecules themselves determine the electronic and magnetic properties of the system, and it is thus of fundamental interest to study these metal-organic interfaces both in the case of single molecules and layer structures. In this thesis, an extensive study of the electronic and magnetic properties of tetra-phenyl-porphyrin (2H-TPP) molecules adsorbed on metal surfaces is reported. By means of scanning tunnelling microscopy (STM) we studied the adsorption geometry of these molecules on the Au(111), Ag(111) and Cu(100) surfaces. By using X-ray photoemission spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, a temperature-induced conformational adaptation reaction of the 2H-TPP molecules adsorbed on the Au(111) and Ag(111) surfaces, upon annealing at 550 K, is described. A possible dehydrogenation reaction, with the formation of new C-C bonds, could explain the rotation of the molecule phenyl rings parallel to the surface plane and the associated increasing in the molecule-substrate interaction. In-situ metalation of porphyrins in ultra-high vacuum is obtained by two methods: in the first one, the metalation of 2H-TPP on Ag(111) is achieved by direct metal evaporation (Mn, Rh and Fe) on the molecular layer; in the second case we report the self-metalation of 2H-TPP through the coordination with a metal atom from the Fe(110) and Al(111) substrates. In addition, we investigated the effects of metalation and temperature-induced conformational adaptation on the molecule-substrate interaction, by means of XPS and NEXAFS, in the case of CoTPP on Ag(111). The magnetic properties resulting from the metal coordination are studied by X-ray magnetic circular dichroism (XMCD). Here, a description of the magnetic coupling of a MnTPPCl single layer with a Fe(110) ferromagnetic substrate is disclosed. Moreover, we focused on the study of the magnetic properties and exchange coupling of two layer of molecule and a ferromagnetic thin film. In the case of a MnTPP layer on FeTPP/Fe(110) the magnetic coupling extends to the second layer of molecules, for which the magnetization is opposite with respect to the substrate.

Cantilever sensors have been the subject of growing attention in the last decades and their use as mass detectors proved with attogram sensitivity. The rush towards the detection of mass of few molecules pushed the development of more sensitive devices, which have been pursued mainly through downscaling of the cantilever-based devices. In the field of mass sensing, the performance of microcantilever sensors could be increased by using an array of mechanically coupled micro cantilevers of identical size. In this thesis, we propose three mechanically coupled identical cantilevers, having three localized frequency modes with well-defined symmetry. We measure the oscillation amplitudes of all three cantilevers. We use finite element analysis to investigate the coupling effect on the performance of the system, in particular its mass response. We fabricated prototype micron-sized devices, showing that the mass sensitivity of a triple coupled cantilever (TCC) system is comparable to that of a single resonator. Coupled cantilevers offer several advantages over single cantilevers, including less stringent vacuum requirements for operation, mass localization, insensitivity to surface stress and to distributed a-specific adsorption. We measure the known masses of silica beads of 1µm and 4µm in diameter using TCC. As it is difficult to obtain one single bead at the free end of the cantilevers, we choose to use the Focused Ion Beam. By sequential removing mass from one cantilever in precise sequence, we proved that TCC is also unaffected from a-specific adsorption as is, on the contrary, the case of single resonator. Finally, we proposed shown the use of TCC can be as micromechanical transistor device. We implemented an actuation strategy based on dielectric gradient force which enabled a separate actuation and control of oscillation amplitude, thus realizing a gating effect suitable to be applied for logic operation.

Il satellite Planck è il diretto successore europeo del satellite americano WMAP. Planck è lo strumento di terza generazione per lo studio del CMB dallo spazio ed è composto da una matrice di 74 ricevitori suddivisi in due strumenti, Low Frequency Instrument (LFI) e High Frequency Instrument (HFI), che osserva il cielo in nove frequenze nell'intervallo tra i 30 GHz ed 857 GHz. Tutti i ricevitori osservano il cielo contemporaneamente e continuamente con una risoluzione angolare che va dai ~30 arcominuti, alla frequenza più bassa, ai ~5 arcominuti, alla frequenza più alta, ed una sensibilità dell'odine di ~10^(-6). Planck è stato lanciato nel Maggio del 2009 e, prima del suo completo spegnimento nell'Ottobre del 2013, lo strumento LFI ha continuamente e stabilmente osservato il cielo per 1513 giorni operativi (OD), che corrispondono a otto complete mappe del cielo. I dati di Planck rilasciati nel 2013 includono le mappe di temperatura del CMB basate sul periodo nominale della missione, che copre gli OD dal 91 al 563. Questa tesi presenta la caratterizzazione degli effetti sistematici di LFI effettuata per i dati di Planck rilasciati nel 2013, con una particolare attenzione all'effetto spikes a 1 Hz. Dall'analisi effettuata, tutti gli effetti sistematici conoscuti di LFI risultano sotto controllo e il loro contributo nello spettro di potenza delle mappe di temperatura del cielo prodotte è sensibilmente inferiore al segnale delle anisotropie del CMB. Dai null test effettuati risulta inoltre che tutti gli effetti sono propriamente corretti. nell'analisi dei dati e che non è presente alcun indizio di ulteriori sistematici sconosciuti. L'effetto delle spikes a 1 Hz è causato da una inattesa interferenza tra le linee di acquisizione dei dati scientifici e quelle dell'housekeeping, che avviene nell'elettronica di lettura di LFI. Questo effetto, individuato per la prima volta durante i test a terra dello strumento, si manifesta come un'onda quadra alla frequenza di 1 Hz che si sovrappone alle tensioni in uscita da tutti i ricevitori di LFI. I ricevitori che più risentono di questo effetto sono quelli a 44 GHz. La tecnica di rimozione di questo disturbo nell'analisi dei dati effettuata per i dati di Planck rilasciati nel 2013 consiste nel sottrarre un template di onda quadra dalle tensioni prodotte dai ricevitori. Tra le diverse tecniche utilizzate per la costruzione del template descritte nella tesi, quella del template filtrato utilizzata nei dati del 2013 risulta essere la più efficiente. Nei canali a 44 GHz dove la rimozione è implementata, il contributo delle spikes nello spettro di potenza delle mappe di LFI è ridotto di due ordini di grandezza, sia in temperatura che in polarizzazione. L'utilizzo di un unico template da sottrarre per l'intera missione per ogni segnale misurato, cielo e riferimento per ogni ricevitore, è giustificato dall'estrema stabilità del template sia in fase che in ampiezza nell'arco di tutta la missione. Dopo la correzione dei dati, la stima del residuo del segnale di spikes nelle mappe dovuto a piccole fluttuazioni dell'ampiezza del template nel corso della missione permette di concludere che l'effetto delle spikes a 1 Hz di LFI è totalmente sotto controllo. Siccome il contributo del segnale di spikes nei canali a 30 GHz e 70 GHz è molto piccolo e siccome il template a queste frequenze sembra non essere molto stabile in ampiezza, la possibilità di rimuovere le spikes anche da questi canali è ancora in fase di studio. In particolare, è importante controllare la possibile introduzione di artefatti nei dati come risultato del processo di rimozione. Avendo a disposizione i dati di tutta la missione, nella tesi si è inoltre studiata la possibilità di aumentare la risoluzione dei template, con lo scopo di investigare la possibilità di ottenere dei template più stabili da utilizzare per i canali a 30 GHz e 70 GHz. I template ad alta risoluzione danno dei risultati identici ai template filtrati nei canali a 44 GHz, mentre nei canali a 30 Ghz e 70 GHz, nonostante la stabilità sia migliore, i template sono ancora dominati dal rumore. Nonostante questo, la produzione dei template ad alta risoluzione ha permesso di verificare la stabilità dello strumento fino a risoluzioni di 1/2^(16) s. Inoltre è stato possibile tracciare in dettaglio il comportamento dello strumento LFI sull'intera missione, osservando variazioni del template delle spikes ben al disotto della risoluzione utilizzata per la rimozione delle spikes dai dati di Planck rilasciati nel 2013. Questi nuovi template hanno idividuato 5 OD in tutta la missione dove lo strumento presenta un comportamento peculiare. In tutti questi casi si è scoperto che le variazioni osservate sono legate ad operazioni note effettuate sullo strumento. Da un confronto diretto dei template per i canali a 44 GHz, non si osservano cambiamenti incrementandone la risoluzione. L'effetto finale sulle mappe e sulla stima dei parametri cosmologici è ancora in fase di studio. Al momento non si rende necessario modificare i template utilizzati nella release di Planck del 2013 per la quella del 2014. L'analisi sull'effetto della rimozione dei template ad alta risoluzione dai canali dei 30 GHz e 70 GHz ed il loro possibile utilizzo in release future è ancora in corso.

Per uno studio completo che parte dalla materia oscura e va all'origine e propagazione dei raggi cosmici, quello multi canale è uno degli approcci migliori per risolvere i quesiti irrisolti della fisica delle astroparticelle. GAMMA-400, grazie alla sua natura duale, dedita allo studio di raggi cosmici (elettroni fino alle energie del TeV e protoni e nuclei fino a 10^{15}-10^{16} eV) e raggi gamma (da 50 MeV fino a qualche TeV), si dedicherà allo studio di questi problemi. Lo scopo di questa tesi è lo studio delle prestazioni di GAMMA-400 per l'osservazione dei raggi gamma. Due diverse configurazioni della geometria sono state studiate: la "baseline" e la cosiddetta configurazione "enhanced". Le principali differenze tra queste due configurazioni si trovano nel tracciatore e nel calorimetro. Il tracciatore della "baseline" è composto da dieci piani di silicio, otto dei quali comprendono anche uno strato di ~0.1 X_0 di tungsteno. Il tracciatore della configurazione "enhanced" è invece composto da 25 piani di silicio inframezzati da uno strato di tungsteno di ~0.03 X_0. Il calorimetro della "baseline" è diviso in due sezioni: una parte composta da due piani di ioduro di cesio e silicio (chiamata "pre-shower") e una seconda parte composta da 28x28x12 cubi di ioduro di cesio. Il calorimetro della configurazione "enhanced" è invece composto solo da 20x20x20 cubi di ioduro di cesio. Per stimare le prestazioni ho sviluppato un algoritmo di ricostruzione della direzione del raggio gamma incidente. La ricostruzione può fare uso delle informazioni provenienti dal tracciatore, dal "pre-shower" o dal calorimetro, sia combinandole che singolarmente. Le direzioni ottenuta grazie alle informazioni del solo "pre-shower" o del solo calorimetro, anche se di minor risoluzione, possono essere utili per aumentare il numero di fotoni visti ad alta energia e per fornire le informazioni necessarie all'osservazione di transienti con i telescopi Cherenkov a terra. La risoluzione angolare utilizzando il tracciatore è migliore nel caso della configurazione "enhanced". A basse energie ciò è possibile grazie al minore tungsteno, e di conseguenza minor "scattering" multiplo, presente all'interno del tracciatore. Il calorimetro più piccolo, e più profondo, seppur ostacolando la ricostruzione dell'energia di fotoni ad alta energia, produce anche un numero minore di particelle di "backsplash" che peggiorano la ricostruzione delle tracce. L'area efficace totale della "baseline", potendo contare su un calorimetro più grande ed il "pre-shower", è più grande rispetto alla configurazione "enhanced". La risoluzione angolare, l'area efficace e la strategia di osservazione dello strumento contribuiscono alla sensitività per sorgenti puntiformi. La sensitività totale dello strumento è migliore per la "baseline" per energie maggiori di 5 GeV. Ho implementato un set prelminare di condizioni di "trigger" per lo studio dei raggi gamma tramite l'utilizzo delle informazioni del tracciatore. La necessità di rigettare la maggior parte delle particelle cariche deriva dall'elevato fondo presente in orbita (~10^6 protoni per raggio gamma) e una capacità di "downlink" limitata (~100 GB/day). Tra le due configurazioni si nota una differenza di meno dell'1% nel numero rimanente di protoni. Seppur promettente, tale risultato deve essere migliorato e possibili miglioramenti sono descritti nella tesi. Gli algoritmi di ricostruzione e "trigger" sono applicati all'analisi della possibilità di studiare "gamma-ray burst" (GRB) con la principale strumentazione a bordo di GAMMA-400. Una stima del numero di eventi non ricostruiti, perchè avvengono nel tempo morto tra due "trigger", è effettuata tramite la simulazione di un ipotetico GRB accoppiata ai tempi di arrivo dei fotoni presi dai dati reali di due GRB osservati da Fermi. In nessuna delle due configurazioni è visibile una percentuale significativa di "pile-up". Anche aumentando il flusso dei GRB la percentuale di eventi non ricostruiti non supera mai il 6%. Nonostante questo risultato, molto dipenderà dal disegno finale dell’elettronica di lettura dei rivelatori che potrebbe aumentare i tempi morti dello strumento.

La corretta valutazione del rischio finanziario è una delle maggiori attività nell'amibto della ricerca finanziaria, ed è divenuta ancora più importante dopo la recente crisi finanziaria. I recenti progressi dell'econofisica hanno dimostrato come la dinamica dei mercati finanziari può essere studiata in modo attendibile per mezzo dei modelli usati in fisica statistica. L'andamento dei prezzi azionari è costantemente monitorato e registrato ad alte frequenze (fino a 1ms) e ciò produce un'enorme quantità di dati che può essere analizzata statisticamente per validare e calibrare i modelli teorici. Il presente lavoro si inserisce in questa ottica, ed è il risultato dell'interazione tra il Dipartimento di Fisica dell'Università degli Studi di Trieste e List S.p.A., in collaborazione con il Centro Internazionale di Fisica Teorica (ICTP). In questo lavoro svolgeremo un analisi delle serie storiche finanziarie degli ultimi due anni relative al prezzo delle azioni maggiormente scambiate sul mercato italiano. Studieremo le proprietà statistiche dei ritorni finanziari e verificheremo alcuni fatti stilizzati circa i prezzi azionari. I ritorni finanziari sono distribuiti secondo una distribuzione di probabilità a code larghe e pertanto, secondo la Teoria delle Grandi Deviazioni, sono frequentemente soggetti ad eventi estremi che generano salti di prezzo improvvisi. Il fenomeno viene qui identificato come "condensazione delle grandi deviazioni". Studieremo i fenomeni di condensazione secondo le convenzioni della fisica statistica e mostreremo la comparsa di una transizione di fase per distribuzioni a code larghe. Inoltre, analizzaremo empiricamente i fenomeni di condensazione nei prezzi azionari: mostreremo che i ritorni finanziari estremi sono generati da complesse fluttuazioni dei prezzi che limitano gli effetti di salti improvvisi ma che amplificano il movimento diffusivo dei prezzi. Proseguendo oltre l'analisi statistica dei prezzi delle singole azioni, investigheremo la struttura del mercato nella sua interezza. E' opinione comune in letteratura finanziaria che i cambiamenti di prezzo sono dovuti ad eventi esogeni come la diffusione di notizie politiche ed economiche. Nonostante ciò, è ragionevole ipotizzare che i prezzi azionari possano essere influenzati anche da eventi endogeni, come le variazioni di prezzo in altri strumenti finanziari ad essi correlati. La grande quantità di dati a disposizione permette di verificare quest'ipotesi e di studiare la struttura del mercato finanziario per mezzo dell'inferenza statistica. In questo lavoro proponiamo un modello di mercato basato su prezzi azionari interagenti: studieremo un modello di tipo "integrate & fire" ispirato alla dinamica delle reti neurali, in cui ogni azione è influenzata da tutte gli altre per mezzo di un meccanismo con soglie limite di prezzo. Usando un algoritmo di massima verosimiglianza, applicheremo il modello ai dati sperimentali e tenteremo di inferire la rete informativa che è alla base del mercato finanziario.

Il Modello Standard delle particelle elementari è senza dubbio una delle teorie che hanno riscosso il maggior quantitativo di successo nella storia della fisica. La recente scoperta del bosone di Higgs, ad opera degli esperimenti ATLAS e CMS operanti presso il Large Hadron Collider (LHC) di Ginevra, è solamente l’ultima di una lunga serie di predizioni teoriche confermate dall’esperimento. Il meccanismo di produzione di quark b in associazione a bosoni vettori W e Z si inquadra all’interno della fenomenologia del Modello Standard, ma la sua predizione teorica presenta alcune interessanti sfide collegate alla complessità dei calcoli perturbativi nel campo della Cromodinamica Quantistica e alla descrizione del quark b all’interno del protone. Molti sviluppi sono stati fatti di recente in questo contesto tramite lo sviluppo di diversi modelli per la produzione del quark b. Questi risultati presuppongono diverse approssimazioni allo scopo di rendere il calcolo fattibile. La misura della sezione d’urto di produzione per questi processi costituisce quindi un ingrediente importante alla comprensioni di simili processi. Nel presente lavoro, la sezione d’urto per la produzione inclusiva di un bosone vettore W in associazione con una coppia di quark b è stata misurata sfruttando l’insieme di collisioni protone-protone prodotte da LHC ad un energia nel centro di massa pari a 8 TeV. Si è osservato il bosone vettore W tramite il suo decadimento in un elettrone o in un muone ed in un neutrino, mentre ciascun getto adronico originato da un b quark è stati identificato tramite la presenza di un adrone B associato ad un vertice di decadimento secondario. L’analisi è stata effettuata su un campione di collisioni consistente di una luminosità pari a 19.6/fb. La misura della produzione di eventi W+bb è inoltre importante in quanto essa costituisce un fondo irriducibile ad altri processi fisici di grande interesse quali la produzione di W in associazione al bosone di Higgs nel suo canale di decadimento in coppie di quark b. Altri processi del Modello Standard che producono uno stato finale simile al processo studiato nella presente tesi sono costituiti dalla produzione di coppie di quark top , quark top singoli o dalla produzione di coppie di bosoni vettori. Infine, lo stato finale del processo W+bb può costituire un fondo irriducibile per processi di nuova fisica oltre il Modello Standard, quali ad esempio la produzione di particelle supersimmetriche.

Phase-contrast X-ray imaging is an invaluable tool in medical diagnostics and biological sciences. It provides images where both absorption and refraction contribute. For quantitative analysis of these images, the phase needs to be retrieved numerically. There are many phase-retrieval methods available. My thesis aims to optimize the application of phase retrieval methods for different phase-contrast imaging situations. A quantitative comparison between phase contrast and phase retrieved images is also performed on some selected examples. We analyzed the two most-applied phase retrieval algorithms and outlined derivations, approximations and assumptions of each one. We implemented these algorithms on experimental data collected at the SYRMEP beam-line of ELETTRA, Italy. We used the algorithms based on Born approximation and transport-of-intensity equation (TIE) for different kinds of test objects and biological samples (high absorbing, homogeneous, low absorbing, etc.) at various experimental conditions (sample-to-detector distances, energies, detector resolutions). Their capability and restriction are evaluated in the visualization of the sample morphology up to its tiniest details. It was shown that Born method is highly depended on phase and intensity distributions in the object plane, being quite accurate in the case of small phase variations and low absorption materials. On the other side, the TIE approximation did not impose any direct limitations on phase and intensity distributions in the object-plane or image-plane but its application is restricted to near-filed region. The application of phase retrieval techniques on biological samples have been assessed the strong ability of these algorithms in improving the visualization of structures and details with a complex geometry. They also produced images with a better separation of the different phases of the sample for an easier and more efficient segmentation. On the other side, as expected, the application of phase retrieval algorithms on high absorbing sample didn’t give further useful information respect to the phase contrast imaging. The Signal to Noise Ratio (SNR) values obtained for phase retrieved images, either for the area-signal and edge-signal, were significantly improved with respect to conventional phase contrast images. For both algorithms, the noise has been significantly reduced. In general, the application of TIE method produced higher SNR in comparison to Born as it is not strongly limited by absorption of the sample. We were able to reduce the scattering contributions by increasing the sample-to-detector distance and, therefore, higher SNR values were achieved. Using phase retrieval algorithms, the tiny details were less defined than in the original phase contrast image because of blurring, but, on the final analysis, this was not significant since data were rendered and segmented more efficiently. For the future development of this work, we will consider the possibility to implement a mixed TIE+Born approach in order to overcome the limitation of Born approximation about the requirement for sample absorption, and restriction posed by TIE to the near-field region sample-to-detector working distances.

Under physiological conditions in the brain, molecules are released with high spatial and temporal resolution. A lot of efforts have been done in the last years in order to develop techniques that mimic this situation. Among them, we mention the use of micropipettes for the ejection of fluids, the use of AFM (Atomic Force Microscopy), microfluidic devices and optical manipulation. The latter approach exploits light to manipulate the samples, e.g. to create transient pores in the cell membrane or to move small objects carrying a stimulus. This Thesis concerns with the development of new techniques for the local delivery of molecules based on optical manipulation technologies, and in particular on optical tweezers. Sub-micrometer particles in a compact trap, such as the single-beam gradient or optical tweezers, can be localized within a small fraction of a wavelength of light or moved over long distances of many centimeters without any mechanical contact. A three-dimensional trap is simply created by focusing a laser beam through a microscope objective with high numerical aperture. We studied three types of vectors for local delivery of molecules, which can be optically manipulated: microbeads, micron-sized liposomes and Quantum dots (Qdots). Silica microbeads can be covalently functionalized on their surface with the protein of interest and placed in contact with the desired part of a cell. In order to validate the technique, we functionalized beads with a secretory molecule, the neurotrophin Brain-derived neurotrophic factor (BDNF). BDNF is a key regulator of neuronal development and plasticity. We showed that single BDNF-coated microbeads can be extracted with optical tweezers from small reservoirs and positioned with submicrometric precision to specific sites on the dendrites of cultured hippocampal neurons. Localized contact of microbeads functionalized with BDNF induced focal increase of Calcium signaling in the stimulated dendrite, specific activation of the TrkB receptor pathway and influenced the development of growth cones. Remarkably, a single BDNF-coated bead positioned on a dendrite was found to be enough for TrkB phosphorylation, an efficient and long-lasting activation of Calcium signaling in the soma, and c-Fos signaling in the nucleus, comparable to bath stimulation conditions. Moreover, since BDNF is covalently cross-linked to the bead surface we could demonstrate that activation of some of the TrkB receptor pathway does not necessarily require BDNF endocytosis. In the case of liposomes, the molecules of interest were encapsulated within their lumen. Single liposomes were trapped and transported by means of optical tweezers to the site of stimulation on cultured neurons. Finally, the release of liposome content was induced by application of UV-pulses that broke the liposome membrane. In order to test the effect of the UV-induced release, liposomes with a diameter ranging from 1 to 10 μm (fL to pL volumes), were filled with KCl and tested on neuronal cells. Neuronal cultures, loaded with Ca2+ dye, were monitored by imaging intracellular Ca2+. An efficient release from the liposomes was demonstrated by detectable Calcium signals, indicating induced depolarization of the neuronal cells by KCl. Afterwards, this technique was used to address a biological issue, that is the effect of two proteins (Semaphorin 3A and Netrin-1) on growth cones. The growth cone is an intracellular apparatus located at the tip of the neurite of developing neurons. Its motility governs axonal path-finding and the construction of neuronal networks. Growth cones are highly dynamic structures that respond to external stimuli turning towards or away from the chemical gradient. We were able to demonstrate an attractive effect of Netrin-1 on the growth cones of primary hippocampal neurons. On the contrary, Semaphorin 3A showed a repellant behavior. To correlate the high resolution of vector manipulation with high resolution of imaging we used STimulated Emission Depletion (STED) to investigate the intimate organization of two main cytoskeleton components: actin and tubulin filaments. STED microscopy allowed imaging of actin bundles in the filopodia and organized network in lamellipodia with un-precedent resolution, beyond the diffraction barrier. Lastly, we used liposomes to encapsulate Quantum dots. Qdots are bright and photostable nanocrystals. Due to their small size, similar to that of proteins, Qdots may be endocyted along the receptor-mediated endocytosis pathway, when they are functionalized with the appropriate ligand. As case study we considered the BDNF-TrkB endocytotic pathway. We optimized the protocol for the direct binding of BDNF to Qdots and we demonstrated the possibility of encapsulating and releasing them from liposomes. Concluding, two different approaches for local stimulation of neurons, based on optical manipulation of microvectors, were presented and validated in this thesis. Indirect optical manipulation of nanovectors (Qdots) encapsulated in liposomes has been demonstrated as well. The techniques were then successfully applied to address some biological issues, that in turn required the optimization of other imaging tools (super resolution microscopy and Qdots).

The present work of thesis is situated within the framework of the study of disordered systems as liquids and glasses. A liquid is a system characterized by long range translational invariance and by a short range ordered structure. In the liquid state, contrarily to the crystalline one, there is not structural periodicity and all we learnt from solid state physics (Block’s theorem, phonons, Brillouin’s zones, eigen-states of plane waves, etc.) must be fully revised. The macroscopic collective properties of condensed matter are the result of inter and intra-molecular interactions that are typified by characteristic time and space scales. A longstanding and powerful tool to investigate the collective nature of the microscopic processes inside the system is the acoustic spectroscopy. While in the case of crystalline phase we could take advantage of the periodical structure of the system, limiting our investigation to the so called first Brillouin zone, in order to characterize a disordered system we need to explore a widest as possible spectral range to access the all time and space scales in which the dynamical phenomena occur. This approach can be called Broad Band Acoustic Spectroscopy . My PhD activity was devoted to the development of new experimental methods and techniques allowing the exploration with continuity of dynamics evolving with timescales from tenth’s of ns’s to ps’s. I could test such Broad Band Acoustic Spectroscopy on a prototypical sample: acetonitrile, the liquid with highest dipole moment, known for its many different inter- and intra-molecular dynamics. Using several experimental and computational approaches I could characterize the main dynamical processes for such compound in its whole liquid phase. Thanks to the crossing of the all acquired information, it was possible to identify a mutual influence between different relaxations whose behaviour otherwise was not possible to correctly understand. After a brief introduction to contextualize the Broad Band Acoustic Spectroscopy in disordered systems, in Chapter 1 is presented an overview of the experimental techniques used to perform the measurements within this work. In this chapter, the first my original contribution to the extension of acoustic spectral range finds the place. Thanks to the design and realization of particular spatial filters it is now possible to perform Brillouin Light Scattering experiments with angle tunabil- ity without incurring in annoying spurious contributions issues. In the chapter are also recalled the main physical principles at the ground of every presented tech- nique, in particular stressing the complementarity of the energy and time resolved spectroscopies. Because all the information from the inner dynamics of the sample are mediated by the acoustic modes interaction, Chapter 2 is dedicated to the formalism of the density fluctuations, highlighting the differences between the hydrodynamic model, valid at macroscopic length-scales, and the memory functions approach, necessary to describe the mesoscopic region where the characteristic length-scales of the acoustic modes are comparable to the inter-particles distances. In Chapter 3 are shown the experimental results obtained thanks to the Broad Band Spectroscopy in the whole temperature range of the liquid phase of acetoni- trile. We could first measure some thermodynamical quantities by a non linear spectroscopy named Transient Grating, shedding light on the literature debate on them. Among the obtained results, we appreciated a temperature dependency of the heat capacity ratio which is usually considered a constant. Starting from these results and using the filtering approach introduced in Chapter 1, we could profitably study the vibrational relaxation of acetonitrile discovering some relevant discrepan- cies with previous studies. In this way we demonstrated the importance to avoid eventual spurious contributions and to have complementary information from dif- ferent spectral domains. Then there will be shown the results for the so called structural relaxation, obtained in the high energy domain by Inelastic X-ray Scat- tering. A really interesting correlation has been found with the result obtained by the ultrafast response of the Transient Grating method. Once again, to obtain such comparison was necessary to combine the information arising from many different spectral ranges, fact that highlights the utility and endorses the multi-techniques broad band acoustic spectroscopy method. The temperature dependence of the aforementioned relaxation processes sug- gested to evaluate if any coupling there exist between the two. This is exactly what we were able to appreciate in the deep-UV domain and we proposed a phenomeno- logical model to give a picture of the occurring interaction. To further investigate such dynamics coupling effect, could be extremely useful to explore the soft-UV spectral range but so far any technique was able to access such energy domain. In Chapter 4 we thus present our innovative solution to the problem: a novel table top Fabry-Perot interferometer conceived to operate with UV laser source and with only reflecting optics. The last chapters of the thesis describe my contribution to the forthcoming Free Electron Laser (FEL) based experiment to further increase the accessible spectral range to the acoustic spectroscopy: the TIMER project. In particular I will show the result obtained with the pilot experiment named “mini-TIMER” in which we could demonstrate the feasibility of a Transient Grating experiment in the Extreme Ultra Violet (EUV) domain. When TIMER will be operative it will be the first experimental setup able to probe the EUV mesoscopic region of crucial importance for the study of glasses and nano-structures. This result paves the way to a new class of intriguing experiments only matter of theoretical considerations so far: the so called four wave mixing experiments with elemental selectivity.

The chemistry of carbon dioxide has recently become of great interest both for technological and environmental issues. Indeed, carbon dioxide is one of the most problematic greenhouse gases and is also a fundamental ingredient for the industrial catalytic organic synthesis of many compounds like, for example, methanol. Recent investigations have shown that, while the common industrial process for methanol synthesis is carried out on Cu catalysts, Ni-Cu model catalysts show a particularly high e ciency. In order to understand the origin of such increase in the catalyst activity, a thorough characterization of the CO2-Ni interaction and the atomic-scale description of the hydrogenation process are mandatory. This thesis is focused on the study of the adsorption and activation of carbon dioxide mainly on pure Ni(110) surface and of its reactions with atomic and molecular hydrogen by means of accurate quantum mechanical rst principles numerical simulations. The interaction of the CO2 molecule with the surface is characterized in terms of adsorption geometries, energetics, vibrational and electronic properties, including charge transfer, core-level shifts and scanning tunneling microscopy images, obtained from electronic structure calculations and compared with original experimental results achieved mainly by the Surface Structure and Reactivity Group active at the TASC laboratory. A consistent picture of CO2 chemisorption on Ni(110) is provided on the basis of the newly available information, yielding a deeper insight into the previously existing spectroscopic and theoretical data. We nd that CO2 molecule can be chemisorbed in diff erent, almost energetically equivalent adsorption confi gurations on a Ni(110) surface,with high charge transfer from the substrate. The molecule, that in gas phase is linear and unreactive, is chemisorbed in a bent and activated state on the nickel surface and can react with the hydrogen. The atomic-scale investigation sheds light also on the long-standing debate on the actual reaction path followed by the reactants. Di fferent hydrogenation channels have been explored to determine the reaction network: using molecular hydrogen, only a Langmuir-Hinshelwood process (both reactants are adsorbed) is possible, resulting in the production of formate which is just a 'dead-end' molecule; with atomic hydrogen, instead, the reaction proceeds also through parallel Eley-Rideal channels (only one of the molecules adsorbs and the other one reacts with it directly from the gas phase, without adsorbing), where hydrogen-assisted C-O bond cleavage in CO2 yields CO already at low temperature.

The first part of this thesis work concerns the development of an ultra–high–vacuum experimental system, hosting a commercial Low Temperature Scanning Tunneling Microscope (LT-STM), that has been built for characterizing and manipulating single molecules and molecular complexes adsorbed on metal surfaces. The design from scratch, the commissioning and the performance tests of the various components of the system are presented. The preparation chamber that has been developed provides the fundamental surface preparation and analysis instruments, combining the STM analysis with other experimental techniques and allowing for easy setup of additional preparation/analysis instruments. The manipulator sample stage allows for a wide temperature range, needed for the preparation of a variety of surfaces to be investigated in the LT-STM. In the second part of this work, we present two examples of how molecules and molecular complexes can be studied and manipulated with the LT-STM technique. In the first example, within a collaboration established with the group of Dr. Leonhard Grill at the Freie Universität in Berlin, we have characterized an azobenzene derivative adsorbed on the Au(111) surface, a known molecular switch based on a trans–cis isomerization, which can be reversibly induced by the tip of the STM with controlled voltage pulses. We could show how the molecule–molecule interactions play a critical role in determining the switching abilities of the molecules between different self–assembled molecular islands, and how the molecule–substrate interaction can efficiently determine two different spatial periodicities of the switching molecules. In the second example, we have presented preliminary results regarding the characterization of the NH3-NO complex which forms on the Pt(111) surface, showing that by exploiting the manipulation and spectroscopic tools of the LT-STM, it will be possible to investigate at the atomic scale the properties of the hydrogen bond most likely involved the complex.

The ALICE experiment at CERN will study the medium formed in very high energy lead-lead collisions at the LHC. According to the Quantum Chromo Dynamics theory of the strong interaction, a phase transition to a state where quarks and gluons are not confined into hadrons (Quark-Gluon Plasma) can occur in these collisions. Heavy quarks (charm and beauty) are produced in hard scattering processes in the first stages of the collisions. While travelling through the medium they can lose energy by means of gluon radiation. This affects the momentum spectra of the hadrons produced in the subsequent hadronization. To study the energy loss mechanism and its dependence on the parton nature (quark/gluon) and mass (light/heavy quark), hadron momentum spectra observed in heavy-ion collisions are compared to the same spectra observed in proton-proton collisions, where the formation of a thermalized medium is not expected. In this thesis, the measurement of charm production in proton-proton collisions via the exclusive reconstruction of the D0 meson (cū) decay in the D0->Kπ channel is presented. An invariant mass analysis of selected pairs of particles with opposite charges is performed, exploiting the high spatial resolution of the Inner Tracking System silicon detector, that assures the tracking precision needed to resolve the D0 decay vertices from the interaction point of the colliding protons (primary vertex). The estimate of the fraction of secondary D0 mesons coming from the decay of B mesons, if based on theoretical calculations, introduces a relevant systematic error. A method to extract this contribution directly from data, via the analysis of the impact parameter distribution, i.e. the distance between the reconstructed meson trajectory and the primary vertex, is presented. The presence of the ITS assures the possibility to highlight the different shape of the impact parameter distribution typical of secondary D0 mesons, influenced by the relative long lifetime of B mesons (cτ~460-490 μm). Due to construction and mounting finite precision, the modules composing the ITS can be displaced from their designed positions by large amounts if compared with the expected spatial resolutions, of the order of tens of micron. This deteriorates the detector performances, in particular the tracking spatial and momentum resolutions. The alignment of the ITS, that is, the a posteriori determination of more than 13000 parameters defining the real position and orientation in space of the modules, is extensively discussed. The results obtained with 2008 cosmic-ray data are presented. The promising alignment status allowed to test the analysis for the D0 reconstruction on proton-proton collision data simulated with realistic detector properties.

The aim of this thesis work is to explore coherently different aspects related to the properties of the Intergalactic Medium (IGM) and to its chemical and physical evolution from high to low redshift, especially regarding metal enrichment and the impact of different feedback processes. In the last years, high resolution spectroscopic observations have shown that the neutral hydrogen (HI) in the IGM at redshift around three, traced by the Lyman-alpha forest lines in absorption, is subjected to metal pollution down to very low column density (10^13 atoms cm^-2) with a metallicity of about 10^-3 in solar units. Since metals are produced only by stars inside galaxies, the diffuse metals in the IGM retain an important trace of the star formation and of the feedback processes from the galaxies to the IGM. The purpose of the thesis is to identify the mechanisms responsible of the enrichment, propose some physically motivated theoretical models and compare the prediction of the models with the latest observational data. In particular we focussed on two different type of enrichment: galactic (energy and momentum driven) winds produced by "starburst" galaxies at redshift z=1.5-4 and AGN feedback associated to the energy released by gas accretion onto super-massive black holes. We analysed in detail the following aspects: dynamic and energetic of wind and AGN feedbacks, IGM contamination efficiency as a function of different astrophysical and cosmological parameters, temperature and chemical composition of the metal systems, nature of the ultraviolet ionizing background (UVB). In the first part of the thesis we investigated the properties of a particular class of cosmological objects, the so called Damped Lyman-alpha systems (DLAs). These are defined as quasar (QSO) absorption systems with neutral hydrogen column density N_HI > 2 x 10^20 atoms cm^-2 (Wolfe et al. 1986). DLAs are considered as an important reservoir and/or sink of gas for the galaxy formation process in the high redshift Universe and their HI content dominate the total neutral hydrogen budget over a large fraction of the cosmic history. The interplay between DLAs and galaxies is thereby fundamental and should be addressed by any galaxy formation model. Using parallel national and internationals supercomputers, we ran high-resolution and large box-size cosmological hydrodynamical simulations of a LambdaCDM model. The numerical code used is a modified version of the Tree Particle-Mesh Smoothed Particle Hydrodynamics code GADGET-2 (Springel 2005). The main modification consists in an accurate modelling of the chemical evolution which allow us to follow the metal release from Type II and Type Ia supernovae (SNII, SNIa), along with low and intermediate mass stars (LIMS) (see Tornatore et al. 2007). We explored the numerical convergence of some relevant physical quantities and we vary the parameters describing: the properties of galactic winds, the initial stellar mass function, the linear dark matter power spectrum and the metal enrichment pattern of the IGM around DLAs. We focussed on the properties of dark matter haloes that are likely to be the hosts of DLAs systems: we predict relatively low star formation rates (0.01-0.1 M_sun/year) and metallicities around 0.1 Z_sun, at least for the bulk of our haloes of masses between 10^9 and 10^10 h^-1 M_sun hosting DLAs. For more massive haloes metallicities and star formation rates depend on the specific wind model. We found that strong galactic winds with speed of about 600 km/s, in an energy-driven wind scenario, are needed in order to match the observed column density distribution function for DLAs and the evolution of the neutral hydrogen content with redshift. The momentum-driven implementation of the galactic wind model, that relates the speed and mass load in the wind to the properties of the dark matter haloes, shows a behaviour which is intermediate between the energy-driven galactic winds of small (100 km/s) and large (600 km/s) velocities. At z=3 the contribution of haloes of masses between 10^9 and 10^10 h^-1 M_sun, for DLAs below 10^20.8 atoms cm^-2, to the column density distribution function, is significant. By interpolating physical quantities along line-of-sights through massive haloes we qualitatively showed how different galactic wind models impact on the IGM around DLAs. Furthermore, we analysed statistics related to the velocity widths of SiII associated to DLAs: while the expanding shells of gaseous matter associated to the wind can account for the observed velocities, the metallicity in the wind seems to be rather clumpy and this produces an underestimation of the observed velocity widths. We outlined possible solutions to this problem. These results are published in the paper Tescari et al. (2009, MNRAS, 397, 411). In the second part of the thesis we turned our attention to the cosmic evolution of the CIV, i.e. triply ionized carbon. Most studies of the high redshift IGM have focussed on CIV absorption, because it is strong and lies redward of the Lyman-alpha forest. Moreover the absorption line is actually a doublet with rest frame wavelengths 1548.204 and 1550.781 Angstrom, so its identification in the observational spectra is easier because of the fixed ratio between the wavelengths of the two components. The cosmological mass density of CIV, Omega_CIV, observed as a function of redshift is a fundamental quantity closely related to the metal enrichment of the IGM. Its apparent lack of evolution in the redshift interval z=[1.5,5] (Songaila 2001; Pettini et al. 2003; Boksenberg et al. 2003) is puzzling since both the physical conditions of the IGM and the properties of the ionizing background are thought to evolve between these epochs. The most recent measurements of CIV absorptions in spectra of QSOs at z=6 seem to indicate a downturn in the CIV mass density at z>5 (Becker et al. 2009; Ryan-Weber et al. 2009). At z<1, recent results based on HST UV data (Cooksey et al. 2009) give Omega_CIV=(6 +- 1) x 10^-8 corresponding to a 2.8 +- 0.5 increase over the 1.5

La geometria, e la topologia in particolare, rivestono un profondo ruolo in molti campi della fisica ed in particolare in materia condensata ove è possibile identificare diversi stati quantistici della materia attraverso proprietà topologiche. L'invariante di Chern è un invariante topologico che caratterizza lo stato isolante dei cristalli. Esso è definito attraverso la descrizione in spazio reciproco di un cristallo perfetto, per cui è necessario considerare un sistema infinito oppure finito ma con condizioni periodiche al bordo. In questa tesi il concetto di invariante di Chern viene generalizzato definendo un opportuno marcatore locale di Chern in spazio reale. Infatti se si considera un cristallo perfetto infinito oppure finito e con condizioni periodiche al bordo, la media sulla cella elementare di questo marcatore restituisce il consueto invariante di Chern. Tuttavia, grazie al suo carattere locale, il marcatore di Chern è ben definito e può essere utilizzato per identificare il carattere locale di Chern anche di un sistema microscopicamente disordinato o macroscopicamente disomogeneo (ad esempio etorogiunzioni di diversi cristalli) e con qualsiasi tipo di condizioni al bordo (periodiche o aperte). Nella seconda parte della tesi l'invariante locale di Chern viene utilizzato per fornire una descrizione locale in spazio reale della magentizzazione orbitale. Questa descrizione è utilizzabile sia con condizioni al bordo aperte che periodiche e quindi unifica i due separati approcci utilizzati in questi due casi. La nuova formula permette, inoltre, di ottenere anche una migliore comprensione del ruolo che gli stati di bordo rivestono nella magnetizzazione di un sistema. In entrambi i casi vengono presentati i risultati di simulazioni numeriche che confermano i risultati teorici derivati.

Advanced nanotechnologies allow the manipulation of molecules with nanoscale precision, and can be used for the production of sensitive devices for protein or nucleic acids detection for clinical use. DNA nano-assemblies are an excellent route for ultrasensitive DNA/RNA detection and for DNA-protein conjugated immobilization, for bio interaction studies, through the careful detection of single strand DNA (ssDNA) hybridization with complementary target sequences. For DNA nanoscale devices, the control of DNA surface density and conformation is crucial in order to achieve the highest reproducibility and to optimize the sensitivity. An improved understanding of the chemical and physical properties of the nanoscale DNA assemblies and of the recognition process is necessary for device performance optimization. In this framework, we first focused on the understanding of the mechanisms that optimize and limit hybridization efficiency in variable density DNA monolayers. We performed Atomic Force Microscopy (AFM) assisted-Nanografting and AFM measurements to realize reference patches into a DNA self-assembled monolayer, and to carefully monitoring DNA hybridization. We then performed molecular dynamics (MD) simulations, in collaboration with a theoretical group, to capture the energetic hybridization limit in high dense DNA monolayers. We found that no more than 44% of the substrate ssDNA can be successfully hybridized, limited by molecular and electrostatic crowding effect connected to the highly charged nature of DNA. To further capture the conformational properties of DNA monolayers, and their relation to biorecognition, we characterized the ionic strength effect on ssDNA nano-assembled of different density by careful AFM topography measurements in liquid environment. We confined ssDNA brushes with controlled surface densities within a bio-repellent self-assembled monolayer. We then monitored the topographic brush height variation upon changing salt type (NaCl, KCl, CaCl2 and MgCl2 ) and concentration inside the liquid cell. We showed that the measured height is related to scaling law of salt concentration, in agreement with the theory of polyelectrolyte brush. Using this scaling model to fit our experimental data, we quantified structural parameters such as the average internucleotide distance (d) for ssDNA brushes of different, estimated surface density σ, featuring a strong dependence of d on different salts species. This result is crucial for the structural designing of synthetic nucleic acids and, more generally, nucleic acid-based devices with controlled physical behaviors. In the last part of the work, we apply all knowledge learned on hybridization mechanism to a clinical problem. We studied the hybridization mechanism to distinguish single base mismatch and to detect at high sensitivity, without any labeling and amplification, microRNAs (miRNAs) connected to hearth failure disease. Our results demonstrate that the AFM nanolithography can serve as a sensitive and selective readout system to discriminate single nucleotide polymorphism. Also, our device allows for the detection of more than one sequence of miRNAs on a same assay with target in picomolar (100pM) range concentration.

The microscopic origin of the glass-transition represents a long-standing open problem in condensed matter physics. Recent theoretical advances and the increasing amount of experimental and simulation data demonstrate the activity of this field of research. In this thesis we address, through molecular dynamics simulations of model glass-forming liquids, a key and yet unsolved issue concerning the description of the glass-transition: the connection between the unusual dynamical properties of glass-formers, their structural properties, and the features of the intermolecular interactions. Toward this end, we consider a broad range of models based on pair interactions. Such models are able to describe both fragile and strong glass-formers and to reproduce different types of local order, including icosahedral and prismatic structures (typical of metallic glasses) as well as tetrahedral ones (typical of network glasses). For these models we provide a systematic characterization of the structure, dynamics, and potential energy surface. The first part of the thesis briefly introduces the theoretical framework concerning the connection between structure and dynamics in fragile and strong glass-formers, as well as the main experimental and simulation results. The state of the art of the description in terms of the potential energy surface is critically reviewed on the basis of recent simulation results. The simulation methods and the optimization algorithms employed in the thesis are then presented, focusing on the stage of object-oriented analysis of the problem of molecular simulations of classical interacting systems. Such analysis constitutes an original aspect of the thesis and provided a unified and effective framework for the development of simulation software. The second part focuses on the main results obtained. The variations of dynamical properties in different systems, with particular reference to the Angell's fragility and to dynamic heterogeneities, are traced back first to the features of the locally preferred structures, then to the properties of the potential energy surface. In particular, we show that the variation of fragility in the models considered can be rationalized in terms of the formation of stable domains formed by locally preferred structures. The analysis of the properties of stationary points (local minima and saddle points) in the potential energy surface allows us to establish a direct connection between fragility, structurally stable domains and energy barriers. On the other hand, the spatial localization features of the unstable modes display qualitative variations in the models considered. The study of the correlation between the spatial localization of the unstable modes and the propensity of motion reveals that the dynamical influence of such modes is typical of the late beta-relaxation - time scale within which the effect of dynamic heterogeneity is maximum. It appears to be easier to identify such connection in fragile, rather than strong, systems. This provides indications on the possible qualitative differences concerning the metabasin structure of the potential energy surface in fragile and strong glass-formers.

This Ph.D. Thesis is devoted to the derivation of cosmological constraints by using clusters of galaxies as probes. Clusters of galaxies provide potentially powerful means to measure the growth of cosmic structures, as well as excellent astrophysical laboratories. As such they have played an important role in establishing the current cosmological paradigm. On one hand, the results presented in this Thesis provide cosmological constraints from the best X-ray surveys of distant galaxy clusters available at present. On the other hand, the techniques developed to forecast constraints from future survey represent a flexible tool to optimize the design of future surveys of galaxy clusters to shed light on the content of the "Dark Sector" of the Universe and on the nature of gravity.