Scienze fisiche

Tissue loss or end-stage organ failure caused by injury or other types of damage is one of the most devastating and costly problems in human health care. Although surgical strategies have been developed to deal with these problems, and significant advances have been achieved in organ transplantation, it is extremely limited by a critical donor shortage and the necessity of lifelong immunosuppression and its serious complications. In the USA, more than 6,000 people die each year as a result of shortage of donor organs. Tissue engineering [TE] is seen by many as the only way to address this shortage. TE is an interdisciplinary field that draws from materials science, cell biology, biotechnology and chemistry, and strives to offer a new solution to tissue loss or organ failure through the use of synthetic, hybrid, or natural materials that have been designed and fabricated into a 3-dimensional scaffolds that provide support and allow cell attachment, proliferation, differentiation and function. However, Skin and cartilage are the only two tissues grown under laboratory conditions that have achieved successful clinical application. The main reason for this is that cartilage doesn’t require blood vessels or nerves and skin is sustained by nutrients that diffuse through the thickness of the cells that make up the graft. Attempts to grow more biologically challenging tissue and organs have been had mixed results. The obstacles and challenges that have to be overcome include: 1. Graft loss/failure due to at the cyto-incompatibility at the graft-biomaterial interface and bio-incompatibility host-biomaterial interface. 2. Inadequate neovascularization and nutrient channels to support cell survival deep in the interior of the scaffolds. 3. Immuno-rejection of allogenic graft. 4. Lack of healthy easily accessible cells for use in tissue engineering To this end we have developed “smart” biomaterials with nano-scale architecture to elicit desirable cell response (cytocompatibility) at the cell-biomaterial interface and desirable host response (biocompatibility) at the host biomaterial interface. We then designed and microfabricated an original scaffold that incorporated the “smart” architecture and microfluidic network to permit the flow of nutrient-rich media deep in the interior. The scaffold consists of two microporous hemi-membranes that are superimposed and aligned in such a way that the micropores are laterally offset. Sandwiched between these hemi-membranes is a microfluidic channel network that runs perpendicular to the micropore axis and permits interconnectivity between the laterally offset micropores. By decreasing the size of the channels from the micro- to the nano- scale the scaffold acquires a another “smart” characteristic as a immuno-isolating membrane. To examine the scaffold’s potential for tissue regeneration, muscle myoblast cells (mouse C2C12 cell-line), neuroblastomas (mouse PC12 cell-line) and embryonic stem cells (mouse TBV-2 cell-line) were seeded and cultured on the scaffolds. Biocompatibility was evaluated by subcutaneous implantation of the scaffold in mice. Results show that myoblast and neuroblastomas attached, proliferated and differentiated. The exponential cell proliferation associated with in vitro embryonic stem cell culture was controlled. In vivo studies demonstrated scaffold-host integration as evidenced by vascular colonisation of the scaffold.. By developing the ability to construct and control the following scaffold parameters; microporous architecture; microfluidic interconnectivity and canal size; the external and internal shape of the scaffold and it’s multi-scaled surface architectures, the “smart” scaffold developed in our laboratories have great potential as an ideal scaffold for tissue engineering.

Optical tweezers enable for non-destructive, contact-free manipulation of ultrasound contrast agent (UCA) microbubbles, which are used in medical imaging for enhancing the echogenicity of the blood pool and to quantify organ perfusion. Understanding the dynamics of ultrasound-driven contrast agent microbubbles from a fundamental physical standpoint is a first step for exploiting their acoustical properties and to develop new diagnostic and therapeutic applications. However, experiments on bubble dynamics presently suffer from a lack of control on bubble position, because of buoyancy, microstreaming and bubble clustering. In this respect, optical tweezers can be used to study UCA microbubbles under controlled and repeatable conditions, by positioning them away from interfaces and from neighboring bubbles. In addition, an ultra-high speed imaging system is required to record the dynamics of UCA microbubbles in ultrasound, as their oscillations occur on the nanoseconds timescale. In this thesis, optical tweezers and an ultra-high speed camera are integrated into an experimental setup to control the boundary conditions and record the oscillations of the microbubbles. Optical tweezers are commonly obtained by focusing a laser beam through a microscope objective, as the high intensity gradient in the focal region causes dielectric microparticles to be attracted in the focus. In the special case of microbubbles, which exhibit a lower refractive index than the surrounding liquid, the opposite situation arises: they are pushed away from the region of maximum intensity. Nevertheless, microbubbles can be trapped in the dark core of a donut-shaped trap, which can be obtained e.g. by focusing a Laguerre-Gaussian beam. In our setup, a Gaussian beam is converted to a Laguerre-Gaussian mode by using diffractive optical elements implemented on a spatial light modulator. This allows to trap and manipulate single or multiple microbubbles, and to control the distance from interfaces as well as the bubbleto- bubble distance. The “Brandaris 128” ultra-high speed camera is used, in combination with the optical tweezers, to recorded the bubble oscillations at a frame rate of 15 million frames per second. The influence of a rigid wall on the resonance frequency and oscillation amplitude was experimentally investigated. An experimental phospholipid-coated agent (BR-14, Bracco Research S.A., Geneva, Switzerland) was used throughout the experiments. A resonance frequency curve was recorded for the same bubble positioned at the wall and at controlled distance from the wall. The experiments show a drop in the resonance frequency for the bubble close to the ii Abstract wall, as expected from the theoretical models. These results are highly relevant for molecular imaging applications, where the response of targeted microbubbles needs to be discriminated from that of freely flowing ones. We also quantify the bubble-to-bubble interaction, in two ways: first, we compare the change of the radial oscillations of one bubble with and without a neighboring bubble. Second, we resolve the change in distance between two bubbles during ultrasonic insonation. This results from an acoustical, generally attractive, interaction force between the bubbles, termed secondary Bjerknes force. To understand this rich two-bubble dynamics, we couple a recent single-bubble model, accounting for both gas and monolayer properties with a model quantifying the mutual interaction of bubbles in their translation and oscillations. Experiments where optical tweezers are used as a force sensor to measure the binding force in an antigen-antibody complex at the single molecule level are also presented. In the future, the possibility of combining optical micromanipulation with the force-sensing capabilities of optical tweezers will open the way to a new class of experiments which will give us a deeper insight into fundamental bubble phenomena and find direct application to new ultrasound-assisted targeting strategies.

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.

This thesis describes a measurement of a CP violating asymmetry in neutral B meson decays, B0->D(*)0h0, where D(*)0 is a charmed meson and h0 is a light meson such like a pi0, eta, eta' or omega, performed on data collected by the BABAR experiment at the Stanford Linear Accelerator Center (SLAC) asymmetric-energy electron-positron collider PEP-II. In this accelerator electrons and positrons collide at an energy in the center of mass frame of s = (10.58 GeV)^2, equal to the Upsilon(4S) resonance mass. The analysis reported in this thesis is the first measurement of CP-violation in B0->D(*)0h0 decays. A possible manifestation of CP violation in neutral B meson decays appears in final states accessible to both B0 and B0bar; a B0 can mix into a B0bar and this gives an extra phase that translates into a CP violating effect. If the D0 (D0bar) meson decays into a CP eigenstate, then both B0 and B0bar can contribute to the final state, realizing the condition for possible CP violation. The interesting point in measuring CP violation using B0->D(*)0h0 modes is that theoretical uncertainties are well under control since SM contributions other than leading amplitude are highly suppressed. Observation of a sizeable difference from the SM expectation in CP violating asymmetries for this decay would be an evidence for New Physics contributions. CP-violation was well established in B meson physics looking at b->ccs transitions; the predicted theoretical uncertainties for these modes are relatively small. Once the CP-violation is established, it is crucial to test its mechanism and its agreement with SM expectations, measuring other decays. The b->s channels are interesting because they have only penguin diagrams contribuiting to decay amplitude. On the contray, the B0->D(*)0h0 amplitude receive no contribution from any penguin diagram; measuring CP-asymmetry in B0->D(*)0h0 decays is therefore an independent test of the avor sector of the Standard Model. The results of measured CP-asymmetry using b->ccs, b->sqq and B0->D(*)0h0 decays could indicate a pattern that allows to determine which New Physics is likely to be correct. We analyzed about 384x10^6 BBbar pairs (corresponding to a luminosity of 349 fb^(-1)). Useful decay chains, and background sources that could mimic our signal were identifed, together with discriminant variables enhancing signal significance over background. The analysis selected B0B0bar pairs in which one neutral B meson was reconstructed in our decay modes and the other one was tagged as B0 or B0bar in an inclusive way. We eventually selected roughly 1100 events, with an estimated signal yield of 340+-32 signal events. The fit to time-dependent CP-asymmetry indicated that: C = -0.23 +- 0.16 +- 0.04 S = -0.56 +- 0.23 +- 0.05 where the first error is statistical and the second is systematic. Assuming S = -sin2(beta), then sin2beta = 0.56 +- 0.23 +- 0.05. This is the first measurement for these decay modes. The result is consistent with the Standard Model expectation and is 2.5 standard deviation away from CP-conserved hypothesis C = S = 0. This result is consistent with world average ("WA"): sin2beta = 0.675 +- 0.026. The results presented in this thesis are dominated by statistical uncertainties, therefore there is room to improve the analysis using more data. BABAR data taking will continue until the end of 2008 with the plans to increase peak luminosity and to almost triplicate the dataset used in this analysis. On the other hand one can also envisage the possibility of including more channels. For example B0->D0h0 with D0->KSpi0 might be added, trading the large D0->K0Spi0 branching ratio against the poorer primary vertex information. Overall, a decrease of the statistical uncertainty by a factor between 1.5 and 2. can be envisaged in the near future. Measurements at the proposed future "SuperB factory", with very large luminosity should be able to push the uncertainty to the systematic limit. In any case, a comparison of statistical uncertainties with the other measurements using b->c transitions shows that this channel is one of the most promising in this domain. The B0->D(*)0h0 decays can shed some light into the present situation for the flavor sector of the Standard Model, adding an independent measurement of the mixing phase beta that will contribute to constrain contributions to physics beyond the Standard Model.

The aim of this PhD thesis is the study of the properties of the Inter-Galactic Medium (IGM) through Quasi Stellar Objects (QSOs) absorption lines at redshifts z~2-4. The study of the IGM provides a unique picture of the Universe in the early phases of structure formation and is crucial to test cosmological models. Furthermore, the metal content of the IGM can be used to constrain the nature of the enrichment mechanisms at high redshifts. Two main mechanisms have been proposed predicting different distribution of metals in the IGM: a late enrichment, due to the observed galaxies at redshift ~3, and an early enrichment, due to a population of very massive first stars (the so called popIII stars), not yet observed, at higher redshift. The existing observations are not sufficient to discriminate between the two mechanisms. QSO spectra show interesting features to study the IGM: 1. The Lyman-alpha (Lya) forest : the forest of absorption lines blue-ward of the Lya emission arising in large scale neutral hydrogen density fluctuations of moderate amplitude in the warm photo-ionized IGM. Since the dynamical state of the low density IGM is governed mainly by the Hubble expansion, gravitational instabilities and photo-ionization, the involved physics is quite simple and mildly non-linear. The Lyman forest is then a fair tracer of the underlying matter density field. 2. Metal absorptions: many absorption features due to ionic transitions in chemical elements heavier than He (``metals'') are clearly present red-ward of the Lya emission. Some of them are associated with the QSO itself but the majority are tracers of intervening metals belonging to structures of different nature, from diffuse gas to galaxies. Chapter 1 of the thesis presents in detail how the physics of the IGM can be understood studying QSO absorption lines, and the classical results obtained in this field. Then the thesis focuses on the work done during the PhD, which has addressed three research areas: 1. Study of lines of sight (LOSs) to isolated QSOs (Chapter 2,3): (i) a sample of 22 high-resolution QSO spectra has been studied. Classical statistics have been applied: all the absorption features in the spectra have been fit with Voigt profiles to extract physical parameters associated with the absorbing material; quantities like the evolution in redshift of the number density of the lines and the two-point correlation function of the line distribution along the spectra have been studied and compared with measurements available in the literature; (ii) a new method to analyze the Lya forest has been implemented. Traditionally, absorption spectra are resolved in a collection of discrete absorption systems. This method instead reconstructs the underlying density field processing the lines on the basis of the physical properties of the IGM. Therefore, a continuous density field is built and the main drawbacks of the Voigt fitting approach are overcome. (iii) the new algorithm has been tested with N-body hydrodynamical simulations of the IGM; (iiii) the new algorithm has been applied to the observational data sample to study the hydrogen density field ( its evolution with redshift and its clustering properties ) and the so called proximity effect of QSO, estimating the overdensity around the object. 2. Study of lines of sight to multiple QSOs (Chapter 4,5): The thesis presents also the work done studying multiple QSO LOSs, i.e. studying the properties of the IGM not only with the spectrum of a single object, by trying to get transversal informations comparing different LOSs, close both in angular separation and in the emission redshift of the source. A sample of 15 QSO forming 21 pairs have been studied to get the transverse correlation function, using the statistics of the transmitted flux of the objects. Furthermore, we have observed a pair of close QSO during two nights (7-8 august 2007) with UVES, the high resolution spectrograph at the ESO Very Large Telescope (VLT) located at Cerro Paranal, in Chile. These two objects have been observed to study the correspondence between metal absorptions and galaxies in the field; preliminary results and the description of the work in progress are presented in detail in the thesis (Chapter 5). 3. New instrumentation (Chapter 6): Looking ahead to new possibilities of advance in this field of research, an important role will be played by the high sensitivity and medium resolution spectrograph X-shooter. It will receive first light at the ESO VLT in July 2008 and will start operating in early 2009. When in operation, its wide spectral-range observing capability will be unique at very large telescopes and extremely relevant for the study of QSO spectra. The thesis describes the Science Case "Tomography of the IGM" for the instrument, and the work done at ESO within the X-shooter project. For the operation of this instrument we have carried out laboratory measurements of calibration sources for the Near-InfraRed arm and I participated to an observational project to build a spectro-photometric flux catalogue of standard stars for the instrument.

The main focus of the work presented in this Thesis is the study of the potentiality and possible systematics in combining observations of the thermal Sunyaev-Zeldovich effect (tSZ) and of the X–ray emission in galaxy clusters. The great advantage of the combination of this two types of observations is that they have a different dependence on the properties (density and temperature) of the Intra Cluster Medium (ICM). Also the behavior with redshift is completely different: X–rays provide very bright images of nearby clusters, but decline rapidly with redshift, while the tSZ signal is independent of redshift and is more suitable for observations of distant objects. At present, the X–ray data have far better resolution than the tSZ ones. For this reason, our attention is mainly directed to the present and upcoming generation of tSZ telescopes, which should produce high resolution images. In this perspective, we analyze a sample of galaxy clusters extracted from a set of cosmological hydrodynamical simulations, which have been carried out with the GADGET-2 code. These simulations include the effects of radiative cooling, star formation and supernovae feedback and, as such, they provide a realistic description of the ICM.

In this thesis I develop a chemical evolution model which takes advantage of the most recent high-quality abundance observations in the Galactic bulge to put constraints on its formation and evolution and to obtain a baseline model for bulges in general. I adopt updated massive star nucleosynthesis and follow the evolution of several alpha-elements and Fe by varying the evolutionary parameters. The [alpha/Fe] ratios in the bulge are correctly predicted to be supersolar for a wide range in [Fe/H], and the stellar metallicity distribution is reproduced assuming a short formation timescale, a high star formation efficiency and an initial mass function flatter than the disk. Metallicity-dependent oxygen yields with stellar mass loss are included in the chemical evolution models for the bulge and the solar neighbourhood. The agreement between predicted and observed [O/Mg] trends above solar metallicity is significantly improved; a normalisation problem probably indicates that the adopted semi-empirical yields need adjustment. The difference between [O/Fe] and the other [alpha/Fe] ratios in the bulge and solar neighbourhood is explained. I test the so-called universal initial mass function, suitable for ellipticals and disks, to see if the bulge stellar metallicity distribution can be reproduced by varying the yields for very massive stars, and included M31 in my analysis. I show that assuming a flatter initial mass function than the universal one is necessary, and that a variation exists in the initial mass function among different environments. Finally, I investigate the evolution of spiral bulges hosting Seyfert nuclei, with detailed calculations of the galactic potential and of the feedback from the central supermassive black hole in an Eddington-limited accretion regime. New spectro-photometrical evolution codes covering a wide range of stellar ages and metallicities allowed to model the photometric features of local bulges. I successfully predict the observed black hole-host bulge mass relation. The observed present-day nuclear bolometric luminosity is achieved only for the most massive bulges, otherwise a rejuvenation is necessary. The observed high star formation rates and metallicities, constancy of chemical abundances with the redshift and bulge present-day colours are reproduced, but a steeper initial mass function is required to match the colour-magnitude relation and the present K-band bulge luminosity.

The increasing energy crisis has induced science and technology world to drive a lot of efforts in the study of new materials suitable to develop renewable and with a low environmental impact energy sources as an alternative to petroleum. In this context photo-voltaic cells are a good solution, nevertheless the high costs and the low light-to-current efficiency still inhibits a large production and a common usage. The employment of organic based materials, i.e. the materials inspired by biological processes, finds a place in this research field. The wide availability of these materials in nature, the ease in material processing and the intriguing chemical and physical properties places the organics as good candidates in the production of photovoltaic devices. Moreover, their electronic properties allow a usage as charge injector to enhance the light-to-current efficiency in inorganic-based photovoltaic devices (Gratzel-cells). The aim of this thesis is to study the growth, the electronic properties, and the chargetransfer dynamic in thin and ultra-thin film(single molecular layer) composed by zinc-tetraphenylporphyrin and C70 and thicker melanin films. We choose these molecules both because of their high visible light sensitivity and because porphyrins are electron donor and fullerenes are electron acceptors. In fact, it is well know in biology that the chlorophyll (Mg-poprhyrin) when illuminated with visible light, act as an electron injector in the biochemical environment supplying the amount of energy needed to activate the production of glucose starting from water and carbon dioxide (chlorophyll synthesis). The fullerene C70 consist in an arrangement of 70 carbon atoms in a closed cage structure and is a good electron acceptor. Then, the our purpose is to use the different electronic properties of these molecules to generate donor/acceptor junctions at the molecular scale. Melanin is a natural pigment present in living beings responsible, in human body, of the colour of skin and of its variation due to the exposition to the sun light; it is a semiconductor with electron donor properties. The combined usage of the properties of these molecules opens the way to the production of complexes to realize high-efficiency and low cost photovoltaic devices. In this context, and at the present state of the art in the production of organic-based photovoltaic devices, investigations about the basic mechanism of molecular interaction and electronic properties are needed to clarify the problems that are still open. In fact the light-tocurrent conversion is just one of the possible processes successive to the absorption of a visible photon in a material. In fact the large number of dissipative processes dissipates the charges excited by the light and inhibits the light-to-current conversion efficiency. In this context, two aspect are fundamental: the presence of empty states in the conduction band that are not allowed for dipole transitions from the valence band but energetically favourable with respect to the first allowed ones, in order to brake the excitonic bond and a good charge mobility in order to transport the excited charges up to the collecting electrodes of the device. because the mobility is higher in ordered systems instead of non ordered ones, the molecular interaction and the growth condition have a fundamental role because they determine the molecular packing in the film. In this sense we used soft X-rays and UV-rays photoemission to study the interaction between ZnTPP and C70 and between these molecules and the Si(111)7x7 surface, one of the most common substrate used to produce electronic devices. We studied the order in the various films in the sense of “orientational order” using Near Edge Absorption Fine structure Spectroscopy at SuperESCA and ALOISA beamlines at ELETTRA synchrotron radiation facility in Trieste. Because the NEXAFS spectra, obtained with linearly polarized radiation, are sensitive to the direction of the chemical bonds, the dependence of the absorption structures intensity on the angle between the electrical field of the incoming radiation and the direction of the empty states yields informations about the geometrical (orientational) arrangements of the molecules in the film. The films were produced by sublimation in ultra-high-vacuum in order to obtain a film as pure as possible. We produced a melanin film via “drop casting”, by in air deposition of a suspension of synthetic melanin powder in mineral free water on a polycristal copper surface and drying the water. We obtained the first photoemission data available in literature about this system. A particular attention was dedicated to the ultra-fast delocalization processes of the excited charges. We used Resonant Photoemission technique (SuperESCA beamline at ELETTRA) to study the excitation de-excitation processes: a core electron is pumped to an empty state in the conduction band, the following decay of the core hole (scale of fs) reveals time scale of the excited charge delocalization with a chemical sensitivity typical of core spectroscopies

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.

The need of coherent and intense pulsed radiation is spread among many research disciplines, such as biology, nanotechnology, physics, chemistry and medicine. The synchrotron light from traditional sources only partially meets these characteristics. A new kind of light source has been conceived and developed in the last decades: the Free-Electron Laser (FEL). The FEL process relies on the interaction between a relativistic electron beam and an electromagnetic wave in presence of a static and periodic magnetic field, produced by a device called undulator. This interaction generates coherent radiation at a fundamental frequency and its higher harmonics. In the standard configuration, the electron beam is generated by a linear accelerator and the interaction occurs in a single passage through one or several undulators. An alternative configuration can be obtained if the electrons are supplied by a storage ring. This work has been carried out at the Elettra laboratory within the ``new light sources'' group. My thesis focuses on both numerical and experimental issues about the generation of coherent harmonics on storage-ring FELs. The Elettra SRFEL has been originally designed to operate in ``oscillator configuration'' where the radiation is stored in an optical cavity (made of two mirrors). This process also drives the emission of radiation in the harmonics. In this work, different experimental methods have been implemented at Elettra to concentrate the power in giant pulses, both for the fundamental wavelength and its harmonics. Using this technique, it has been possible to generate fundamental radiation at 660 nm and 450 nm with (intra-cavity) power of few mJ and third harmonic radiation at 220 nm and 150 nm with few nJ of power. This process has been studied numerically by using a tri-dimensional simulation which also accounts for the re-circulation of the beam. The results of simulations are in good agreement with experimental measurements and allow to investigate the inner structure of the light below the picoseconds scale, where the instrumentation resolution reaches its limit. Structures of hundreds of femtoseconds inside the laser pulse have been found and this implies a higher peak power. Moreover, the numerical results have been confirmed by spectral measurements. By removing the optical cavity and focusing an external laser in the first undulator, a ``seeded single-pass'' configuration has been implemented. In the first undulator, the interaction with the external laser (``seed'') modulates the electron energy which is converted to spatial modulation (``bunching''). A Fourier analysis of the bunched electron-beam shows the presence of components at all harmonics (even and odd) and this explains why electrons in the second undulator can emit at any harmonic. To implement this configuration a design and layout plus tri-dimensional simulations were performed. Followed by the installation of the seed laser (Ti:Sapphire, lambda = 796 nm), the timing and the diagnostics. The commissioning focused on optimizing the spatial overlap and the synchronization between the electrons and the seed laser. Coherent harmonic radiation has been obtained at 265 nm, the third harmonic of the seed laser. After the characterization of this light, the seed frequency has been doubled by means of a nonlinear crystal. With this setup, radiation down to 99.5 nm (the fourth harmonic of the seed) has been generated. The shot-to-shot stability is comparable to the stability of the synchrotron radiation (fluctuations of few %) but the number of photons per pulse (~10^9) is about two-three orders of magnitude bigger than the synchrotron one. Thus this coherent radiation can be used for experiments similar to those suggested for the next generation FELs. Summarizing, the light source developed during my thesis is a unique facility able to generate coherent radiation with variable polarization, variable duration (between 100 fs and 1 ps), with peak power of the order of mega-Watts in a wide spectral VUV range. In the latest implementation, this radiation source has been used for two different kind of experiments, one in gas-phase, the other of solid state. The obtained results demonstrate the appealing of this source for user experiments. In perspective, there is a plan to extend the wavelength range below 100 nm and to improve the tunability of the source.

The importance of heterogeneous catalysis in chemical industry and its economic impact in today’s society motivate the continuous research effort in this field. Transition metals are among the main ingredients of commercial catalysts due to their chemical properties which depend on their surface morphological and electronic structure. It is well known that their catalytic properties can be further improved by tuning particle size in the nanometre range or by alloying different transition metals. Nowadays it is possible to predict the variation of surface chemical properties on the basis of the d-band centre energy position, which is actually considered as one of the most promising depicters of chemical reactivity. This physical quantity cannot be easily accessed in the experiment and is typically calculated using a theoretical approach. A promising approach to establish an experimental relationship between electronic structure and chemical reactivity relies on the use of X-ray Photoelectron Spectroscopy with third generation synchrotron radiation sources. Indeed, the high resolution achieved in the recent years has allowed identification in the core level photoemission spectra, the photoemission contribution originated from bulk and surface atoms thus determining what is usually named Surface Core Level Shift (SCLS). It has been shown that SCLS is a valuable probe of surface electronic structure, since the core level binding energy of an atom depends strongly on the local structural and chemical environment. In this thesis, the electronic structure modification induced by reduced coordination, surface strain, atomic rearrangement and ligand effects are investigated in different systems by means of High Energy Resolution Core Level Spectroscopy experiments and Density Functional Theory calculations. With this approach, highly under-coordinated Rh and Pt atoms, namely adatoms and addimers, on homo-metallic surfaces (Rh(100), Rh(111) and Pt(111)) has been probed. Rh-Pt mixed systems are also investigated in order to test the changes in Rh catalytic properties induced by interaction with the underlying Pt substrate. Surface atomic coordination changes can be induced also by surface reconstruction processes. Pt(100) represents a formidable example of how the same substrate can exhibit completely different catalytic properties by changing its surface structure from the more open high-reactivity (1  1) bulk termination to the strained low-reactivity reconstructed quasi-hexagonal (HEX) surface. In this thesis the (1  1) (HEX) phase transition on a clean Pt(100) surface was investigated. Another example was the reconstruction of O(2  2)pg/Rh(100). In this case the surface atomic rearrangement is caused by the presence of an atomic adsorbate. The understanding of the reconstructed phase is a fundamental step towards the understanding of the microscopic mechanisms, which permits the subsurface oxygen penetration during oxide formation. Finally, the structure of the Ni3Al(111) surface is examined by means of X-ray Photoelectron Diffraction. This is a preliminary study towards the investigation of the oxidation process which is responsible for the formation of a thin well-ordered alumina film in UHV conditions.

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.

Next-generation DNA detection arrays are expected to achieve unprecedented sensitivity, reducing the minimum amount of genetic material that can be directly (PCR-free and label-free) and quantitatively detected, up to the single cell limit. To realize these goals, we propose a new method for the miniaturization of DNA arrays to the nano-scale, which has the unique capability of controlling the packing quality of the deposited bio- molecules. We used NanoGrafting, a nano-lithography technique based on atomic force microscopy (AFM), to fabricate well ordered thiolated single stranded (ss)-DNA nano-patches within a self-assembled monolayer (SAM) of inert thiols on gold surfaces. By varying the “writing” parameters, in particular the number of scan lines, we were able to vary the density of the supported DNA molecules inside the nano-patches in a controlled manner. Our findings can be resumed in two parts: 1) Combining accurate height and compressibility measurements, before and after hybridization, we demonstrate that high-density ss-DNA nanografted patches hybridize with high efficiency, and that, contrary to current understanding, is not the density of probe molecules to be responsible for the lack of hybridization observed in high density ss-DNA SAMs, but the poor quality of their structure. 2) Dpn II enzymatic reactions were carried out over nanopatches with different molecular density and different geometries. Using nanopatch height measurements we are able to show that the capability of the Dpn II enzyme to reach and react at the recognition site significantly depends on the molecular density in the nanopatches. In particular the inhibition of the reaction follows a step-wise fashion at relatively low DNA densities. These findings suggest that, due to the enzyme size, it is possible to tune the efficiency of an enzymatic reaction within surface-bound DNA nanostructures by changing only the crowding of DNA on the surface and without introducing any further physical or chemical variable.

CT-AFM (Conductive Tip AFM) is commonly used for electrical characterization of organic and inorganic surface systems. Understanding electron transfer at the molecular level may lead to the development of molecular assemblies with unique properties and is of great importance for the advancement of both organic, molecular and bio-electronics. In this work we follow an approach to the study of Metal-molecule-Metal surface junctions that uses a combination of different AFM-based techniques. We first use nanografting to build nanopatches of the molecules of interest into a hosting reference self assembled monolayer (SAM) typically made of alkane and aromatic thiols. After the tip is changed to a conductive one, CT-AFM is used to characterize electrically the whole system recording, at the same time, the system topography. Some of the advantages of this approach are the possibility to build and study a wide range of different monolayers side-by-side on the same sample and the in-situ control of the quality both of the hosting monolayer and that of the grafted patches. Results will be presented on saturated and unsaturated thiols self-assembled and nanografted on Au(111) surfaces. We will also show a clear correlation between the contrast in current images and the quality of molecular packing inside the nanopatches.

In this work I present a novel approach to the analysis of biomolecules, and a study on two derived practical applications to evaluate its constraints, limits, and potential benefits, namely a biosensing device and a selective transport through membrane. The new approach is based on a 100-800 nm pore etched in a silicon nitride membrane. A linear target molecule, such as DNA, is inserted in the pore and linked at both termini with anchors, one on each side of the pore. Since the complex is stable and the linked objects have a size that is much larger than the target molecule, manipulation, pore closure/opening, possible interactions, stretching and other forces, and in general several characteristics and behaviours of the molecules can be studied at the pore interface. The realization of such a device is preliminary to the development of novel pore-based analytical tools. The principle was applied for the development of a biosensing device. Biosensing devices that perform electrical signal detection are facing the need of being both extremely small and highly sensitive, that is particularly challenging for conventional biosensors where the signal produced is proportional to the surface detecting area. Here, I report the production of a sensor device based on DNA specific displacement of a stable blockade in a synthetic pore section, due to objects associated with the interacting molecules. Thus the signal is proportional to the pore size and not to the surface containing the target/probe molecule. First, I report the setting up of the single components of the device: a complex made of a DNA linker and two particles –the anchors-, the synthetic nanopored membrane and an electrophoretic cell together with an electromagnet -the sensing tools-. Then I show the results of trans-membrane interactions between the objects both outside and inside the sensor device. The applications results related to the biosensor operation are then shown, reporting the detection of the hybridization or the strand-displacement between probes and targets DNA molecules. Finally, I show the operation of a trans-membrane transporter mediated by particles carriers, where the system is exploited to capture and import target molecules through the membrane.

Noise is often the main factor limiting the performance of detector systems. In this work a detailed study of the noise contributions in different types of silicon microstrip sensors is carried on. We investigate three sensors with double-sided readout fabricated by different suppliers for the ALICE experiment at the CERN LHC, in addition to detectors including an integrated JFET Source-Follower as a first signal conditioning stage. The latter have been designed as an attempt at improving the performance when very long strips, obtained by gangling together several sensors, are required. After a description of the strip sensors and of their operation, the “static” characterization measurements performed on them (current and capacitance versus voltage and/or frequency) are illustrated and interpreted. Numerical device simulation has been employed as an aid in interpreting some of the measurement results. The commonly used models for expressing the noise of the detector-amplifier system in terms of its relevant parameters are then presented. Two configurations of the first signal processing stage are considered and confronted: the usual charge-sensitive amplifier and the Source-Follower. Next, the noise measurements performed and their results are illustrated. Curves of the equivalent input noise charge versus shaping time of the filtering amplifier, for several values of the leakage current, have b een obtained. The leakage current has been varied by photogeneration, illuminating the sensor with a LED, or alternatively by injecting it into the strip from an external current source, through a high-value resistor. The noise measured with the strip sensors read-out by a charge- sensitive amplifier generally agrees well with the common model, but in some operating conditions unexpected contributions have been found. These have been interpreted by correlating them with some peculiar features of the capacitance-voltage measurements. The noise measured on the detectors with integrated JFET source-follower complies with the prediction of the model, using the measured values of the relevant parameters. Finally, the performances of the two different approaches are confronted.

In this thesis we report and discuss the results for the first complete calcula- tion of the one-loop electroweak corrections for the two dominant processes of single Top production at the Large Hadron Collider: the tW-associated pro- duction and the t-channel process. We calculate the corrections working both in the Standard Model (SM) and in the minimal supersymmetric extension of the Standard Model (MSSM, as- suming a mSUGRA scenario), analysing the effect of the corrections on several observables and trying to understand whether deviations from the Standard Model prediction could be observable. The single Top production is the main source of information about the Top weak interaction, and a privileged laboratory to understand the symmetry breaking in the weak sector. Moreover at the hadronic colliders the single Top processes provide the only known way to measure directly the Vtb element of the CKM matrix, providing a fundamental test of the Standard Model struc- ture. For the tW production process we present the complete calculation of the one- loop electroweak effect, including the effect of the hard real photon emission; we combine our results with the available calculation for the QCD and SUSY QCD corrections, providing a complete one loop description of the process. Our interest has been concentrated on the particular quantities that we have defined as partial rates, with special emphasis on the low (400 GeV) final in- variant mass. In this region with the addition of SUSY QCD one-loop terms, the genuine SUSY contribution reaches an interesting 10% size. The analysis of t-channel process is limited to the pure electroweak componet (adding the soft photon emission only, to cancel the infrared divergences aris- ing from diagrams with virtual photon). The electroweak corrections for the t-channel are less sensitive to the presence of the SUSY particles: this conclusion holds for all the four examined bench- mark points in themSUGRA scheme. In addition, considering the small contri- bution of the known SUSY QCD corrections, we conclude that in themSUGRA scenario it will be probably impossible to detect at the LHC any deviation from the SM predictions. In the SMcontext the size of the electroweak correctionswithout the hard emis- sion seems to be very large, but we expect that the total effect should be con- siderably reduced adding the hard emission part.

The argument of the thesis is the transverse spin physics, and the work done is in the framework of the COMPASS experiment, a fixed target experiment at the CERN SPS. COMPASS investigation of the nucleon spin structure is made by means of Deep Inelastic Scattering (DIS), obtained using a muon beam of 160 GeV/c scattering off a polarized deuterium target. In order to study the transverse spin effects, the target nucleons are polarized transversally with respect to the beam direction. The data collected by COMPASS with this target configuration in the years 2003-2004 have been analyzed in order to extract transverse spin asymmetries yielding information about the nucleon spin structure. In the data the DIS events with at least one hadron in the final state have been selected. The hadrons have been identified as pions or kaons using the RICH detector of the spectometer, and to this end a work of calibration of the detector has been performed. The main result of the analysis is the measurement of the Collins and the Sivers asymmetries on identified hadrons, for the first time measured on a deuterium target. The Sivers asymmetries bring information about the Sivers parton distribution function, describing the distribution of the transverse momentum of the quark inside a transversally polarized nucleon. Collins asymmetries are related to the transversity distribution function of the nucleon, giving the probability of finding a quark with the spin parallel or antiparallel to the nucleon spin, and on the Collins fragmentation function, describing the spin dependent part of the fragmentation process. The Sivers, Collins and transversity functions are not known, and their knowledge is of big importance in order to understand the nucleon spin structure. These functions have been extracted fitting the Collins and Sivers asymmetries measured in this thesis together with asymmetries from other experiments: the Collins and Sivers asymmetries measured from the HERMES experiment on a proton target, and the azimuthal asymmetries in hadron pair production in electron-positron annhihilation measured by the Belle Collaboration. As a result of the fit, the unknown functions for different quark flavor, in particular for the u and d valence quark, have been obtained. In the fit, different parametrizations for the unknown functions have been used, and the role of the asymmetries measured in this thesis has been studied. Due to the fact that both HERMES and Belle in the first part of 2007 have provided new set of measured asymmetries with respect to those analyzed in the existing works, the compatibility between the different set of data has also been studied.

We present a study of the charmless Bs to phiphi decay performed with the CDFII detector at the Fermilab Tevatron Collider. Charmless Bs meson decays currently can be studied only at the Tevatron and represent a field still to be fully explored that offers additional ways to test our present theoretical understanding. The Bs to phiphi belongs to a particular class of these decays: the Bs meson decays into a pair of vector particle and the final state is self-conjugate. It can be used to measure the Bs decay width difference (Delta Gamma_s), CKM studies, and tests of decay polarization predictions.

La presente tesi descrive le attivita' di ricerca legate alla costruzione, la caratterizzazione e la validazione del rivelatore a micro-strisce di silicio (SSD) per il sistema di tracciamento dell'esperimento ALICE presso il collisionatore LHC al CERN. Nel primo capitolo della tesi si introduce la fisica delle collisioni fra ioni pesanti e si descrivono le principali osservabili che saranno utilizzate dall'esperimento ALICE per studiare la formazione e la successiva evoluzione del Plasma di Quark e Gluoni. Nel secondo capitolo e' presentata una descrizione del rivelatore di ALICE e sono discusse in particolare le caratteristiche del sistema di tracciamento, di cui l'SSD e' parte integrante, e le sue prestazioni in relazione alla fisica di ALICE. La terza parte della tesi riguarda le attivita' correlate alla costruzione e alla caratterizzazione dell'SSD: dopo la produzione e i test di accettazione, e' stata condotta un'indagine estensiva ed approfondita sui moduli difettosi, al fine di comprendere l'origine delle problematiche riscontrate e di elaborare soluzioni appropriate. Il lavoro effettuato ha permesso di recuperare numerosi moduli e di innalzare la qualita' globale del rivelatore. Dopo le operazioni di assemblaggio, il rivelatore nella configurazione finale e' stato completamente caratterizzato prima dell'installazione nel sito sperimentale. Una volta installato, le funzionalita' dell'SSD e la sua integrazione in ALICE sono state infine verificate durante la fase di commissioning, attraverso un elevato numero di acquisizioni di dati di rumore e di raggi cosmici. La caratterizzazione del rivelatore completo ha dimostrato l'importanza di un' efficace correzione hardware del common mode per l'efficienza e la qualita' globali dell'SSD. A tal fine, gli effetti di questa particolare fonte di rumore sono stati studiati attraverso una serie di simulazioni. I risultati di questo studio sono presentati nel quarto capitolo della tesi e due algoritmi sono proposti per un efficiente trattamento e reiezione del rumore di common mode. Infine, nell'ultimo capitolo viene descritto uno studio di fattibilita' della misura della molteplicita' di particelle cariche con l'SSD. In vista della prima fase di acquisizione dati dell'esperimento ALICE, e' stato simulato un campione di eventi protone-protone a 900 GeV di energia; l'efficienza di ricostruzione dei segnali di particella e' stata studiata e misurata in funzione delle caratteristiche funzionali del detector. Infine, la correlazione tra i segnali ricostruiti nell'SSD e le osservabili fisiche simulate dal Monte Carlo e' stata usata per caratterizzare l'interazione primaria.