Within the framework of the AdS5/CFT4 correspondence, the GKP string living on a AdS5 x S5 background finds a counterpart in the anti-ferromagnetic vacuum state for the spin chain, fruitfully employed to investigate the dual N=4 SYM superconformal gauge theory. The thesis mainly deals with the excitations over such a vacuum: dispersion relations and scattering matrices are computed, moreover a set of Asymptotic Bethe Ansatz equations is formulated. Furthermore, the survey of the GKP vacuum within the AdS4/CFT3 duality between a string theory on AdS4 x CP 3 and N=6 Chern-Simons reveals intriguing connections relating the latter to N=4 SYM, in a peculiar high spin limit.

The thesis reports the results of an experimental research on rare earth ion-doping effects on the structural, chemical, optical and near-infra-red photoluminescence properties of wide band gap oxide films. The aim of the work was to develop materials with good photoluminescence properties, which can be applied to increase the photovoltaic conversion efficiency of crystalline Si-based solar cells, through the increase of the most efficient and useful fraction of the solar spectrum which hits the cells, thanks to a photon frequency down-shifting process. Neodymium trivalent ion (Nd3+) was used as dopant of TiO2 and ZnO thin films. The films, with different Nd concentrations were grown onto quartz by RF plasma co-sputtering and annealed at different temperatures (400°-800°C). Different film architectures were investigated for their photoluminescence properties. Structural changes such as phase transformation from anatase to rutile, internal strain building and lattice distortion due to Nd3+ incorporation in titania, correlated with optical changes, were evidenced. Exciting titania and zinc oxide matrices with optimal Nd concentrations, with ultra-violet (UV) light energies equal to or above their gap values resulted in an efficient frequency down-shifting from UV to near-infra-red emission. The joint study of the vibrational, chemical and structural properties of the doped films allows the understanding of the excitation energy transfer process between the matrix to the ion, where self-trapped excitons can be involved. To conclude this study, the doped films were tested as down-shifter layers onto a Si-solar cell where they gave promising results. They were also tested for their photoactivity with methylene blue, showing their inhibitor effect on the photo-degradation of this organic dye molecule. Keywords: Co-Sputtering, rare earth doping, Neodymium, Titanium dioxide, Zinc oxide thin films, Photoluminescence

The present thesis deals with the study of nuclear reactions of weakly-bound few-body nuclei with stable targets at energies around the Coulomb barrier. A weakly-bound nucleus is characterized by having low binding energy and thus large probability to undergo a breakup during the interaction with another nucleus. The effect of breakup on other reactions such as fusion is still not well understood and represents an interesting issue to study in detail. Among weakly-bound nuclei, there are some which are particularly interesting to study because of their peculiar structure and the key role they play in astrophysics: the halo nuclei.

Catalysts are of great importance in many different fields, including the energy and the environmental sectors. It is important to produce them with simple preparation technique and to enhance the catalysts surface-to-volume ratio. The work undertaken in this thesis concerns the synthesis of nanostructures by Pulsed Laser Deposition (PLD) and R.F. sputtering deposition and the tailoring of their structures by varying deposition parameters. We synthesized Cobalt oxide nanoparticles (NPs) by PLD and studied the influence of the deposition parameters (i.e. substrate temperature, target-to-substrate distance and partial pressure of Oxygen in the chamber) on the final structure and crystalline phase of the NPs. The deposited NPs can be divided in two main categories: small NPs having a diameter of about 5 nm, and big NPs of size ranging from 50 to 400 nm. Depending on the value chosen for the deposition parameters, small NPs have CoO- or Co3O4 crystalline phase, and NPs can have a core/shell structure. The phase composition of the core and of the shell also vary according to the deposition conditions. We synthesized thin film of Co-B NPs by PLD. Depending on the energy density, the laser process is able to produce well-dispersed spherical Co NPs partially embedded within B-based film matrix in a single-step deposition. The small size, the polycrystalline nature of Co NPs, and the presence of Boron matrix is important for catalytic performance of the Co-B film. The catalytic activity of the Co-B has been tested in hydrolysis of chemical hydrides (ammonia borane and sodium borohydride). PLD deposition of C-film, to serve as support for Co-B NPs, was performed at different Ar pressures (from 10 to 50 Pa) to tailor film roughness in order to investigate the role of porous and irregular C- surface on supporting Co-B NPs acting as catalysts. The measured hydrogen generation rate attained with C-supported Co-B catalyst film is higher than both unsupported-Co-B film and conventional Co-B powder. Multilayer ITO/Cr-doped-TiO2 thin films have been synthesized by radiofrequency magnetron sputtering in order to sensitize TiO2 in visible light and to lower the charge recombination rate in the Cr-doped-TiO2. When the multilayer films were exposed to visible light, we observed that the photocurrent increases as function of the number of bilayers by reaching the maximum with 6-bilayers of ITO/Cr-doped- TiO2. The superior photocatalytic efficiency of the 6-bilayers film implies higher hydrogen production rate through water-splitting. Spontaneous growth of Lead nanowires (NWs) have been observed in composite Al-Pb film deposited by R.F. sputtering deposition. The parameters of deposition and the storage of the Al-Pb films after deposition has been changed in order to understand the growth process of NWs. Evolution of NWs growth was also observed inside a SEM chamber. We propose that a stress-driven mechanism and the corrosion occurring on the films surface in environment atmosphere are the cause of NWs growth.

The propagation of light through an ultracold atomic gas is the main topic of the present work. The thesis consists of two parts. In Part I (Chapters 1,2,3), we give a complete description of the 1D photonic bands of a MI of two-level atoms paying attention to both band diagrams and reflectivity spectra. The role of regular periodicity of the system is addressed within a polariton formalism. The scattering on defects inside lattices of three-level atoms is also studied in view of optical detection of impurities in such structures. The light is used as a probe of systems engineered by the use of other laser beams. Part II (Chapters 4,5) is devoted to the development of a general framework for the time-dependent processing of a propagating slow Dark Polariton in a spatially inhomogeneous system. The coherently tunable atomic gas acts as a Dynamic Photonic Structure. Applications of this concept concerning wavelength conversion and reshaping of the pulse are also discussed for realistic experimental situations.

Using quantum Monte Carlo Methods, we compute the differential cross sections for elastic scattering of dark matter (DM) particles off light nuclei, up to $A=6$ (d, $^3$H, $^3$He, $^4$He, and $^6$Li). DM-nucleon one- and two-body currents are obtained to next-to-leading order in chiral effective theory, and they are derived from a DM-quark and DM-gluon effective interaction. The nuclear ground states wave functions are obtained from a phenomenological nuclear Hamiltonian, composed of the Argonne $v_{18}$ two-body interaction and the three-body Urbana IX. In this framework, we study the impact of one- and two-body currents and discuss the size of nuclear uncertainties. This work evaluates for the first time two-body effects in $A=4,6$ systems and provides the nuclear structure input that can be used to assess the sensitivity of future experimental searches of (light) dark matter, especially relevant for possible experimental targets such as $^3$He and $^4$He.

Graphitic materials, thanks to the lamellar structure and chemical stability, are of particular interest to realize barriers against the degradation of surface properties induced by water. Many studies showed that water could be a source of degradation of surface properties. To develop a method to overcome the problem related to the deterioration of the surface it is fundamental to study the water- material interaction. For this reason, in this thesis, the water-surface interaction of graphitic- materials and the use of graphitic materials as impermeable barriers against water were explored. Different experimental set up were realized to study the liquid-gas-solid interaction, such as time evolution of the sessile water drop contact angle, captive bubble contact angle and contact angle measurements in a controlled atmosphere. Moreover, a method of deposition of protective graphene-based films using a Meyer rod to apply graphene-inks onto a surface was developed. To understand the intrinsic wettability of graphitic materials a detailed study of the gas-liquid-solid interactions of graphite was conducted in a wide range of experimental conditions. The surface chemical properties and morphology were studied by X-ray photoelectron spectroscopy (XPS), profilometry and atomic force microscopy(AFM), sessile drop contact angle, captive bubble and secondary emission microscopy (SEM). The results of the gas-liquid–surface interaction study indicated that HOPG surface was sensitive to experimental conditions like airborne contamination and the presence of gases. Similarly, a detailed study of the interaction of water with PDMS surface in various experimental conditions (in the air and immersed in water) were conducted. The findings showed that when PDMS was immersed in water, its surface changed. In fact, the volume of air bubbles in contact with the surface of PDMS increased by increasing immersion time in the water. The experimental results indicated that such dynamic evolution of the air bubbles was related to the rearrangement of surface polymer chains via the migration of the polar groups. This phenomenon induced a degradation of the surface properties of PDMS when it is immersed in water. When graphene monolayer was added to PDMS surface, it acted as a barrier against water, suppressing the dynamic evolution of the bubble. We studied the protective properties also of graphene-based films deposited on lead (Pb). We observed that Pb surface degradation occurred when Pb was in contact with a drop of water. The results showed that degradation of Pb surface in contact with water happened very rapidly but graphene-based films, in particular, graphene oxides films, were able to reduce degradation of the surface significantly.

The properties of a broad range of materials are due to processes which occur at the nanoscale. Recently, an increasing interest has been devoted to nanostructured materials, in which the basic components are nanoscopic, and low-dimensional nanomaterials such as nanoparticles, nanowires and layered materials, in which one or more dimensions are confined. This thesis deals with nanostructured materials, in particular based on graphene, such as Graphene Nanofoams and Pillared Graphene Frameworks, and low dimensional nanomaterials such as SiC/SiO2 core/shell nanowires and graphene layers. The work is divided in four parts treating four different topics with the underlying theme of material modeling, the first two parts deal with mechanical properties and gas treatment applications, for which a description at the atomistic level is adequate, while the third and the forth focus on X-ray spectra and electron holography simulations for which electronic structure calculations are needed. The present thesis gives a general overview on various computational approaches that are useful in modeling novel low dimensional and nanostructured materials, using these approaches in dealing with specific systems.

The aims of this dissertation are twofold. Firstly, the study of superfluidity, presented in the first part, has more a fundational character, since we investigate some well known problems, already raised in the context of superfluid helium, in order to gain a deeper understanding, by exploiting the cleannes of dilute BECs systems, as well as analyzing the new features emerging from the unique dilute BECs properties. We study the BEC flow through weak-links, first analyzing the various regimes of transport by the current-phase relation and the Josephson plasma oscillations, and then turning to the superfluid instability, determining critical velocities and examining the dissipation dynamics in different geometries and dimensionalities. Secondly, the analysis of quantum interferometry, given in the second part, has instead a more technological character, since we propose two possible implementation of interferometric protocols in double-well traps, with application to the measurement of weak-forces, and study their sensitivity in detail, especially in relation to its possible quantum enhancement.

Although protein folding has been studied for decades many open issues still resist, and we yet lack a clear and general description of the mechanisms leading from the unfolded to the folded state. In particular, it is still under debate whether proteins fold through few well-defined pathways or trough a large multitude of independent ways. Answering these questions is made difficult by the fact that standard molecular dynamics (MD) simulations are very computationally expensive and often impracticable. Moreover, often even experimental techniques lack the necessary resolution to give a definitive answer. We will introduce and develope the Dominant Reaction Pathway (DRP), which is an approach that permits to efficiently study the thermally activated conformational dynamics of bio-molecules in atomistic detail. In particular, it can be used to characterize and portray the folding pathways of a protein once the unfolded and folded configurations are given. We firstly applied the DRP to a realistic protein studying the folding pathways of the Fip35 WW Domain, a 35 amino-acids long protein. Performing all atom simulations we were able to show that this small protein folds following only two pathways, defined by the order of formation of secondary structures. Notably, our results are compatible with ultra long MD simulations and consistent with the analysis of the experimental available data on the folding kinetics of the same system. Exploiting the efficiency of the DRP formalism, computing a folding trajectory of this protein only required about one hour on 48 CPU’s. We applied then our simulation scheme to a much more challenging task: performing an all-atom folding simulation of a 82 amino-acids long protein displaying a topological knot in its native conformation. We were able to portray the folding mechanism and to identify the essential key contacts leading to the proper formation of this knot. Interestingly, we showed that non native contacts, i.e., transient contacts formed during the folding of the protein but absent in its native state, can sensibly enhance the probability of correctly forming the knot.