We present a study of the metal sites of different proteins through X-ray Absorption Fine Structure (XAFS) spectroscopy. First of all, the capabilities of XAFS analysis have been improved by ab initio simulation of the near-edge region of the spectra, and an original analysis method has been proposed. The method subsequently served ad a tool to treat diverse biophysical problems, like the inhibition of proton-translocating proteins by metal ions and the matrix effect exerted on photosynthetic proteins (the bacterial Reaction Center, RC) by strongly dehydrate sugar matrices. A time-resolved study of Fe site of RC with μs resolution has been as well attempted. Finally, a further step aimed to improve the reliability of XAFS analysis has been performed by calculating the dynamical parameters of the metal binding cluster by means of DFT methods, and the theoretical result obtained for MbCO has been successfully compared with experimental data.

No description available.

Nowadays alternative energies are an extremely important topic and the possibility of using hydrogen as an energy carrier must be explored. Many problems infer the technological application of this abundant and powerful resource, one of them the possibility of storage. In the framework of suitable materials for hydrogen storage, magnesium has been the center of this study because it is cheap and the amount of stored hydrogen that it achieves (7.6 wt%) is extremely appealing. Nanostructure helps to overcome the slow hydrogen diffusion and the functionalization of surfaces with transition metals or oxides favors the hydrogen molecule dissociation/recombination. The aim of this research is the investigation of the metal-hydride transformation in magnesium nanoparticles synthesized by inert-gas condensation, exploiting the fact that they are a simple model system. The so produced nanostructured powder has been analyzed in response to nanoparticles surface functionalization by transition metal clusters, specifically palladium, nickel and titanium, chosen on the basis of their completely different Mg-related phase diagrams. The role of the intermetallic phases formed upon heating and hydrogenation treatments will be presented to provide a comprehensive picture of hydrogen sorption in this class of nanostructured storage materials.

No description available.

The possibility of combining different functionalities in a single device is of great relevance for further development of organic electronics in integrated components and circuitry. Organic light-emitting transistors (OLETs) have been demonstrated to be able to combine in a single device the electrical switching functionality of a field-effect transistor and the capability of light generation. A novel strategy in OLET realization is the tri-layer vertical hetero-junction. This configuration is similar to the bi-layer except for the presence of a new middle layer between the two transport layers. This “recombination” layer presents high emission quantum efficiency and OLED-like (Organic Light-Emitting Diode) vertical bulk mobility value. The key idea of the vertical tri-layer hetero-junction approach in realizing OLETs is that each layer has to be optimized according to its specific function (charge transport, energy transfer, radiative exciton recombination). Clearly, matching the overall device characteristics with the functional properties of the single materials composing the active region of the OFET, is a great challenge that requires a deep investigation of the morphological, optical and electrical features of the system. As in the case of the bi-layer based OLETs, it is clear that the interfaces between the dielectric and the bottom transport layer and between the recombination and the top transport layer are crucial for guaranteeing good ambipolar field-effect electrical characteristics. Moreover interfaces between the bottom transport and the recombination layer and between the recombination and the top transport layer should provide the favourable conditions for the charge percolation to happen in the recombination layer and form excitons. Organic light emitting transistor based on the tri-layer approach with external quantum efficiency out-performing the OLED state of the art has been recently demonstrated [Capelli et al., Nat. Mater. 9 (2010) 496-503] widening the scientific and technological interest in this field of research.

Many studies on the morphology, molecular orientation, device performance, substrate nature and growth parameter dependence have been carried out since the proposal of Sexithiophene (6T) for organic electronics [ ] However, these studies were mostly performed on films thicker than 20nm and without specifically addressing the relationship between morphology and molecular orientation within the nano and micro structures of ultrathin films of 0-3 monolayers. In 2004, the observation that in OFETs only the first few monolayers at the interface in contact with the gate insulator contribute to the charge transport [ ], underlined the importance to study submonolayer films and their evolution up to a few monolayers of thickness with appropriate experimental techniques. We present here a detailed Non-contact Atomic Force Microscopy and Scanning Tunneling Microscopy study on various substrates aiming at the investigation of growth mechanisms. Most reported similar studies are performed on ideal metals in UHV. However it is important to investigate the details of organic film growth on less ideal and even technological surfaces and device testpatterns. The present work addresses the growth of ultra thin organic films in-situ and quasi real-time by NC-AFM. An organic effusion cell is installed to evaporate the organic material directly onto the SPM sample scanning stage.

During the last decade advances in the field of sensor design and improved base materials have pushed the radiation hardness of the current silicon detector technology to impressive performance. It should allow operation of the tracking systems of the Large Hadron Collider (LHC) experiments at nominal luminosity (1034 cm-2s-1) for about 10 years. The current silicon detectors are unable to cope with such an environment. Silicon carbide (SiC), which has recently been recognized as potentially radiation hard, is now studied. In this work it was analyzed the effect of high energy neutron irradiation on 4H-SiC particle detectors. Schottky and junction particle detectors were irradiated with 1 MeV neutrons up to fluence of 1016 cm-2. It is well known that the degradation of the detectors with irradiation, independently of the structure used for their realization, is caused by lattice defects, like creation of point-like defect, dopant deactivation and dead layer formation and that a crucial aspect for the understanding of the defect kinetics at a microscopic level is the correct identification of the crystal defects in terms of their electrical activity. In order to clarify the defect kinetic it were carried out a thermal transient spectroscopy (DLTS and PICTS) analysis of different samples irradiated at increasing fluences. The defect evolution was correlated with the transport properties of the irradiated detector, always comparing with the un-irradiated one. The charge collection efficiency degradation of Schottky detectors induced by neutron irradiation was related to the increasing concentration of defects as function of the neutron fluence.

Il presente elaborato si prefigge di analizzare il processo di liberalizzazione, comunitario e nazionale, del mercato del trasporto ferroviario di merci e di passeggeri, unitamente all'approfondimento della normativa dettata ai fini della tutela della sicurezza in ambito ferroviario. / The present study aims to analyze the process of liberalisation, both in EU and national market, with reference to rail freight and passengers, together with the deepening of the rule drawn up for the protection of safety in the railway sector.

In this thesis I studied La0.7Sr0.3MnO3/Alq3/AlOx/Co organic spin valves, which are multifunctional devices showing an interesting interplay between magnetoresistive effects and memristive switching. In particular this work aims at elucidating the elusive mechanisms for spin injection and transport in this archetypal structure. While spin injection in organic materials was demonstrated by different spectroscopic techniques, the origin of magnetoresistive effect in organic spin valves is still debated. In fact, the Hanle effect, considered to be the only reliable proof for spin transport across the organic spacer layer, has not been observed in such a device, yet. I investigated the thickness and temperature dependence of charge transport and magnetoresistive properties, and demonstrated the absence of the Hanle effect. Moreover I studied how the resistance and magnetoresistance of our devices were affected by memristive switching, which turned out to be a fundamental tool to enlighten the comprehensive picture. Two clearly distinguishable conduction regimes have been found for non magnetoresistive and magnetoresistive devices. The former is compatible with models for charge transport in organic materials, the latter can be described by an equivalent circuit where metallic paths and hopping channels act in parallel. In the framework of this model, a coherent description for the interplay between MR and memristive switching can be given. SV signals can be explained as tunnel magnetoresistance (TMR) or ballistic magnetoresistance (BMR) occurring across shortened regions of the organic bulk, which is an explanation compatible with the absence of Hanle effect. This work demonstrates that SV signals can be explained without resorting to spin injection and transport into the organic layer.

<p>Bioactive gibberellins (GAs) are phytohormones with various effects on plant development, from seed germination through fruit development. The signaling pathway of GA is centered on DELLA proteins (DELLAs), a group of growth repressors degraded upon perception of GA. Previous studies demonstrated that DELLAs administrate global regulation of gene expression. However, given that DELLAs do not contain any canonical DNA-binding domain and that DELLAs only have a moderate association to their target promoters, the nuclear-localized DELLAs are believed to interact with transcription factors for function. Indeed, quite a few transcription factors have been identified as DELLA interactors in the plant model Arabidopsis thaliana, some of which are well-known downstream transcription regulators involved in other signaling pathways. Nevertheless, the molecular mechanisms how DELLAs inhibit so many aspects of plant growth cannot be fully explained by the known DELLA interactors. </p><p>Recently, our lab discovered that INDETERMINATE DOMAIN 1 (IDD1), a C2H2 zinc-finger protein in Arabidopsis, and its closest homolog IDD2, have a strong physical interaction with DELLAs, revealing the potential involvement of these two IDD genes in GA signaling. Hence, the objectives of my doctoral research are (1) to evaluate the roles of IDD1 and IDD2 in GA-responsive phenotypes, (2) to investigate the genetic interaction between IDD1, IDD2 and DELLAs and (3) to identify the function of IDD1 and IDD2 and the significance of IDD-DELLA interaction in transcriptional regulation of IDD/DELLA targets. First, we found that both IDDs redundantly promote GA-induced hypocotyl elongation, and that they also play a positive role in stem elongation and floral initiation. Secondly, epistasis analyses exhibit that REPRESSOR OF ga1-3 (RGA) and GA INSENSITIVE (GAI), two DELLAs with a predominant role in vegetative growth, antagonize IDD1 and IDD2 in hypocotyl elongation, and that GAI also opposes IDD2 in stem elongation and floral initiation. These results entail an antagonistic relationship between IDDs and DELLAs via protein-protein interaction. We then showed that IDD1 and IDD2 repress the expression of canonical DELLA direct targets, including GA20ox2, GA3ox1, GID1b and SCL3. IDD1 also inhibits transcription of CAPRICE (CPC) and GLABRA2 (GL2), two crucial regulators of root epidermal cell patterning. Taking into account that IDD1 and RGA associate with the same region in CPC promoter, we conclude that CPC is a direct target of the IDD1/RGA complex. In addition, transient expression assays suggested that IDD1 and RGA counteract each other's effects on expression of GA20ox2, GID1b, SCL3, CPC and GL2, providing evidence that IDDs and DELLAs function antagonistically in transcriptional regulation of downstream genes in general. Although both IDDs bear a putative repression motif GLGLGL in their C termini, mutation of this motif did not affect the repressive activity of IDD1 in our transient expression system. On the other hand, fusion of the viral protein 16 (VP16) transcriptional activation domain to IDD1 seems to override the original repressive activity of IDD1. Together, these results uncover a new branch of GA signaling pathway through IDD1 and IDD2, shed light on the interplay of the two IDDs and DELLAs in GA feedback regulation and give insights into the molecular mechanism underlying IDD-mediated GA repression of root hair development.</p> / Dissertation