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Silicon Nanowires the Route from Synthesis towards Applications
No full textThis work provides an overview on the silicon nanowires synthesis scenario by introducing the most employed bottom-up and top-down strategies, exploiting their main advantages and drawbacks. The impressive structural, optical and electrical properties of these nanostructures promote their implementation in low power consumption nanodevices with improved performances. Some representative examples of Si NW applications in field-effect transistors, broadband photodetectors, low-cost solar cells with improved light absorption and for selective and ultrasensitive biological detectors are reported.
The realization of Si NWs by metal assisted chemical etching (MACE) by the use of discontinuous Au layers and the relationship among structural features and growth conditions are here discussed in detail. Indeed, the NW length, diameter, crystalline structure and doping can be precisely defined by using this low cost and industrially compatible process. Si NWs with quantum confined size are realized by MACE leading to the observation of room temperature light emission from Si. According to quantum confinement theory, the emission wavelength can be red-shifted by tuning the NW diameter opening the routes towards low-cost, Si-based photonics. Moreover, the realization of innovative multiwavelength light sources operating at room temperature is investigated by embedding a carbon nanotube (CNT) dispersion inside Si nanowire arrays using a low cost and Si technology compatible technology. The NW/CNT hybrid system exhibits a tunable emission both in the visible and in the infrared which is strategic for telecommunication applications. The conditions leading to the prevalence of the visible or the IR signal have been identified and are herein discussed. The design of 2D random fractal arrays of Si nanowires is here described. Indeed, the structural arrangement of MACE synthesized Si NWs can be engineering by the deposition of a thin Au layer that superimposes its complimentary fractal arrangement onto the Si NW arrays. Si NW fractal arrays display strong self-similarities over a wide range of length scales and the correlation among the fractal parameters and the optical properties are demonstrated. In fact, the ability to control the scattering, absorption and emission properties is investigated as a function of fractal dimension and lacunarity for different designs. A strong light trapping behavior in the visible range due to the efficient in-plane multiple scattering occurring in the Si NW layer has a promising potential for both photovoltaics and photonics. Furthermore, the first experimental observation of a constructive interference effect in the backscattered Raman light from strongly diffusing Si nanowires is reported.
Coherent backscattering of light (CBS) is observed when electromagnetic waves undergo multiple scattering within a disordered optical medium. CBS effect arising from the interference of inelastic scattered Raman radiation has been demonstrated in random Si NW arrays.
The results are interpreted within the theoretical model of mixed Rayleigh-Raman random walks, exploiting the role of phase coherence in multiple scattering phenomena.
In conclusion, the decoration of MACE-synthesized Si NWs by Ag nanoparticles (NPs) produced by pulsed laser deposition (PLD) is an appealing strategy in order to couple the huge aspect ratio of NWs to plasmonic effects leading to the realization of ultrasensitive surface enhanced Raman spectroscopy (SERS) sensors.
PLD conditions have been optimized to guarantee the uniform decoration of NW sidewall along all their length without the need of any post-deposition annealing by using a low-cost and Si implementable technology.
The Ag NP morphology can be precisely tuned as a function of the NW length or the number of laser pulses and the correlation among the structural and optical properties of Si NWs decorated is reported, demonstrating a great potentiality for SERS applications
Multifunctional nanocomposites obtained by hierarchical structures
No full textIl presente lavoro è focalizzato sullo sviluppo di nanocompositi multifunzionali innovativi basati sull'uso di una struttura gerarchica. A questo scopo, nanofibre polimeriche sono state prodotte per electrospinning. Questo processo utilizza un' alta tensione (circa il 10-20 kV) per caricare elettricamente una soluzione polimerica per la produzione di fibre ultra-sottili. Due diverse applicazioni sono stati proposte per le membrane termoplastiche ottenute. Nella prima, esse sono state utilizzate per fabbricare laminati compositi tenacizzati e nanorinforzati (utilizzando MWCNT) mediante Resin Transfer Molding (RTM) e altre tecniche di infusione. Mentre nella seconda applicazione, tali membrane sono state modificate con nanoparticelle inorganiche e utilizzate come membrane attive per filtrazione dell'acqua.
La necessità di tenacizzare materiali compositi si pone perché essi sono soggetti a delaminazione lungo piani interlaminari. La soluzione proposta a questo problema è stato l'uso di nanofibre che possono essere abbastanza piccole da rinforzare regioni della matrice che si trovano tra strati adiacenti del laminato. A questo scopo sono stati elettrofilati diversi polimeri e sono stati utilizzati come tenacizzanti in laminati compositi. La caratterizzazione di questi laminati, modificati con nanofibre, mostra proprietà termo-meccaniche simili a quelle dei sistemi ottenuti utilizzando la procedura standard. Inoltre, al fine di conferire altre funzionalità quali resistenza al fuoco, lightining-strike, auto-sensing, ecc al composito, sistemi di resine epossidiche con nanocariche sono stati studiati e caratterizzati.
Parlando di membrane per la filtrazione dell'acqua, attualmente, membrane polimeriche sono per lo più utilizzate per applicazioni di filtraggio grazie alle loro buone proprietà e bassi costi rispetto alle membrane inorganiche. Di conseguenza, i meccanismi di filtrazione di queste membrane si basano principalmente sugli effetti meccanici come setacciatura, quindi nessuna rimozione chimica delle sostanze tossiche può essere realizzata, questo porta ad effetti di fouling che limitano le prestazioni della membrana. L'idea è stata quella di sviluppare le membrane attive per il filtraggio dell'acqua, caratterizzate da un effetto combinato, setacciatura, proprietà foto-catalitiche e proprietà antibatteriche. A questo scopo, nanofili di ZnO cristallino sono stati cresciuti con un processo chimico da un bagno di deposizione sulle fibre PES ES. Le membrane ibride ottenute mostrano una buona attività fotocatalitica. Inoltre, membrane di PES antibatteriche sono state ottenute da un procedimento one step a partire da una soluzione polimerica con nanoparticelle d'argento precursori. La conversione da precursori argento a nanoparticelle di argento è confermata dalla spettroscopia UV-vis
Study of agronomical and postharvest factors influencing qualitative and nutraceutical traits on blood orange and pomegranate fruits
No full textThe awareness of consumers on the importance of food safety and of potential benefits of many fruit and vegetable derived products are, more and more, driving the interest of research institutes and food industries to deepen the knowledge on the quality of raw materials for fresh or processed use or to design food products enriched with nutraceutical substances.
Several factors influence composition and quality of food products in pre- and post-harvest stages, such as cultivar and rootstock, agronomical techniques and storage conditions. The possibility to enhance the synthesis of some chemical compounds, in particular nutraceuticals (flavonoids, such as phenols and anthocyanins) is an important strategy in order to obtain foods with high functional activity.
The overall aim of the PhD thesis is the evaluation of agronomical and postharvest factors that can influence the qualitative and nutraceutical traits of two important fruit products i.e. blood oranges and pomegranates. These fruits are characterized by a high anthocyanin content greatly appreciated by the consumers for their nutraceutical properties.
The influence of several rootstocks on yield precocity and fruit quality and the effect of postharvest treatments on qualitative parameters were mainly considered in the case of blood oranges.
As concerning pomegranate the investigation was focused on nutraceutical and physicochemical evolution observed in different studies regarding the comparison of international cultivars grown in Italy and Spain and the characterization of several Sicilian pomegranate accessions.
On the whole, the results are interesting for their contribution to the comprehension of the many factors, from varietal choice up to fruit postharvest management, affecting the qualitative profiles of the products with a special emphasis on those compounds valuable for their nutraceutical properties
Aree urbane e acque meteoriche. Un approccio integrato per la pianificazione della città resiliente
No full textUrban pluvial flooding is stressing urban areas with increasing frequency, becoming a factor of great concern. Soil sealing resulting from urban development is one of the main reasons for changes in natural hydrological processes and related recurring failures of urban drainage systems, especially during heavy rainfall events. Today, several studies are looking at the concept of urban resilience as a new paradigm, for a better integration of issues of water and flood risk with urban planning. Resilience is viewed as a way to tackle risk, showing bonds with its different sections, among which the flood hazard. It is broadly agreed that spatial planning, by incorporating Sustainable urban Drainage Systems (SuDS) within tools and polices, helps to build urban flood resilience. In particular, SuDS, as alternative strategy for surface water management, could potentially address anthropogenically generated hazard, thanks to the water-flow regulating service and benefits they provide. This research explores the relationship between the risk of urban pluvial flooding, resilience and urban planning. Particularly, the concept of resilience is clarified in order to highlight how it contributes to both analyse urban systems by adding levels of knowledge, and steer planning and policy approaches towards the mitigation of pluvial flood risk. By applying a research methodology based on the use of EPA-Storm Water Management Model (SWMM), the main aim of the thesis was to define a proper methodology and to build-up an analytical tool in order to analyse and assess the urban system s response to rainfall events, and to be used during and for purposes of the planning process. The proposed methodology is open to be flexibly applied to aptly handle the previous issues. Accordingly, the purpose was twofold: to assess the impact of masterplan in terms of increase of flow peak releases from urban catchments concerned by planned urban developments; to examine the urban system s reaction to rainfall and to evaluate how the response is affected by SuDS implementation at the catchment level. Case study areas were selected in the cities of Catania and Avola, in Sicily, for which masterplans design has been recently proposed by local planning authorities. Simulation of scenarios were carried out for a number of design storm events of selected return periods. Input parameters for the modelling were derived from urban analyses and hydrologic analyses and processing. Firstly, the methodology was based on the comparison between pre- and post-development catchment release scenarios and was applied to a case study catchment in the southern part of Catania. The study showed the need of careful consideration of the hydraulic invariance principle in land use planning practices. In particular, a set of flow release restrictions were determined for new areas of development, achieving the condition of unvaried flow peaks at the sub-catchment level, for different return periods of the storm-water event. Secondly, the methodology was applied to selected urban catchments in the centre of Avola. SWMM was used to track the quantity of runoff generated within each sub-catchment, and the flow rate and flow depth of water in each pipe in order to profile the system response to rainfall-runoff simulation. A dual-drainage approach was used to simulate the interaction between the minor and the major drainage systems and to obtain local flood characteristics to be mapped. Moreover, different effectiveness of selected SUDS measures were demonstrated in terms of improved water-flow regulation service and flood hazard mitigation, by comparing scenarios of pre- and post-implementation. Thesis discussion reflects the need for planning emphasis on mitigation and translating the understanding about risk, resilience and sustainable drainage into decisions via effective policy mechanisms. Suitable tools are needed to encourage a drainage-sensitive urban development and retrofitting
Some selective and monotone versions of covering properties and some results on the cardinality of a topological space
No full textThis thesis consists of two chapters. In the first
one, we investigate some selective and monotone versions of
covering properties; in particular we study two selective properties: the selective absolute
star-Lindelöfness, defined by S. Bhowmik, and the selective strong star-
Menger property. Furthermore, we define and study several properties related to monotone
normality. In the second chapter, we give some bounds to the cardinality of particular classes of topological spaces
Role of pentazocine in an in vitro model of hypoxia/reoxygenation
No full textExperimental research is making considerable efforts to understand the rules that regulate
the balance between toxic and protective brain innate immunity. Sigma-1 receptor is
expressed in both neurons and glia is a unique class of intracellular proteins and is
involved in neurodegeneration. Our aim was to evaluate the biological effects of sigma-1 selective ligands, and bifunctional sigma-1 selective ligands conjugated with lipoil
function in microglia following hypoxia/reoxygenation condition. BV2 cells were exposed
to 3 hours of hypoxia and 24h of reoxygenation. Cells were treated with sigma-1 agonist
(+)-Pentazocine, various bifunctional sigma-1 agonists conjugated with lipoil function and
with lipoic acid alone. We assessed cell viability, apoptosis, reactive oxygen species (ROS)
formation, mitochondria membrane potential, and total thiol groups content (GSH). Our
results showed that 24h of reoxygenation resulted in a significant decrease of cell viability
and increase in apoptosis when compared to control. No significant effect of (+)Pentazocine and tested compounds was observed on cell viability following 24h of
reoxygenation. Furthermore, all treatments resulted in a significant decrease of ROS
formation when compared to untreated cells. Finally, pharmacological treatments restored
mitochondrial membrane potential when compared to the untreated group. Consistently
with these results we also showed that GSH content was restored following
pharmacological treatments. Our results showed that newly synthetized bifunctional
sigma-1 compounds exhibited significant antioxidant activity and induce apoptosis in
activated microglia thus providing a new tool for effective manipulation of brain
inflammation, with the specific aim of favoring its protective arm and boosting innate
neuroprotective mechanisms
6
GENERAL INTRODUCTION MICROGLIA
The concept of microglia was introduced by Pio del Rio-Hortega as a defined cellular
elemen
Surface engineering of oxide systems for energy and molecular electronics applications
No full textThis thesis work was focused on oxide surfaces modification through the anchoring of functional molecular systems, for perspective applications in the fields of molecular electronics and energy. The main goal was the development of an effective experimental strategy for the robust anchoring of functional molecules onto oxide substrates of technological interest, such as transparent (semi)conducting oxides (TCOs). The strategy exploited for the modification involved a preliminary stepwise surface priming based on the chemistry of zirconium phosphates/phosphonates (ZP-priming), consisting in the deposition on a zirconium-phosphate layer directly at the oxide surface. Experimental evidences are presented that this preliminary surface treatment provides a stable and robust platform for the subsequent anchoring of functional molecules, bearing a phosphonic group, onto oxides of different chemical nature and morphology.
The ZP-priming strategy was successfully applied to the treatment of nanostructured, micrometres-thick TiO2 and SnO2 substrates, and its efficacy in providing a uniform priming along the entire nanostructured layer was studied and assessed by ToF-SIMS depth profiling measurements. ZP-TiO2 and ZP-SnO2 were subsequently used as substrate for the preparation of photoactive electrodes with perspective application in dye-sensitised cells for solar energy conversion. It was demonstrated that the preliminary ZP treatment provides a suitable anchoring platform for the sensitisation with photoactive dye RuP (a ruthenium tepryridyl-triazin complex bearing a phosphonic group). ToF-SIMS depth profiling showed that the sensitisation involved the whole thickness of the oxides layers, and by means of UV-Vis spectroscopy it was possible to demonstrate that the preliminary ZP-priming has several benefits on the substrate sensitisation, namely an improvement of the binding stability and a greater amount of dye molecules adsorption. Photoelectrochemical measurements (JV characteristics upon irradiation) showed that the presence of the zirconium-phosphate layer at the interface between oxide and dye molecule does not negatively affect the dye-to-oxide charge injection, and, as a consequence, the functionality of the electrode.
The use of ZP-primed TCOs was also explored in the preparation of conductive molecular wires of metal-polypyridinic molecules through stepwise metal-coordination reactions directly at the oxide surface. A surface functionalised with a layer of terpyridinic units was obtained by anchoring onto a ZP-FTO substrate the ditopic molecule PPTP (terpyridyl-benzenephosphonic acid); the free terpyridinic groups at the surface were afterwards used as anchoring sites for the integration of ditopic RuDT2 molecules (ruthenium(II) phenylene bis-terpyridine complex) through direct metal-coordination by iron(II) of the terpyridine groups at the surface and one of the two free tepryridine units of RuDT2. By the stepwise iteration of the metal-coordination reaction, molecular wires were prepared with different numbers of Fe-RuDT2 units, as confirmed by ToF-SIMS measurements and UV-Vis. Data on the electrical behaviour of the wires were obtained by liquid-metal EGaIn junction technique, with results that show a good electrical conduction along the wires, similar to that of similar wires assembled on gold surfaces. The feasibility of the integration of these metal-polypyridinic conductive wires at the surface of a transparent and conductive oxide by means of the ZP-PPTP platform, and the evidence for good electrical conduction could allow perspective applications within the field of nanoscale molecular electronics, with possible extension to photoresponsive molecular electronics, given the presence of metal-terpyridinic centres (which are well-known photoactive sites)
Plant secondary compounds in ruminant feeding: implication and effect on meat fatty acid.
No full textAccording to FAO, about 9 billion of people will ask for food by 2050. The agriculture challenge is to increase food production by preserving food quality and natural resources.
According to WHO, red meat can favor the onset of cardiovascular disease and colon-rectal cancer; however, they are also an important source of vitamin, protein and functional fatty acids (CLA, EPA, DHA).
Future animal breeding techniques aims will be improving food nutritional profile and reducing environmental impact at the same time.
Rumen lipolysis and bio-hydrogenation allow the synthesis of a pool of fatty acids; this process is affected by animal diet. Pasture feeding increase omega-3 and CLA content in food; however, the problems related to pasture availability ask for innovative techniques that promote their synthesis even if green herbage is not present. The use of plants, or plant-extracts, containing bioactive compounds represents an achievable prospect.
The aim of this PhD was to deepen how different plants bioactive compounds affect fatty acid composition in lamb meat.
In the first experiment, the use of Trifolium pratensis (containing polyphenol oxidase enzyme, PPO) and Onobrychis viciifolia (containing condensed tannins, CT) silages were tested. The effect of PPO and CT on rumen lipid profile was comparable and even additive when silages were supplied as a mixture. In this case, meat fatty acid profile was similar to pasture-fed animals.
In the second experiment, three plants extract were added to lambs diet: hydrolizable tannins from chestnut (Castanea sativa), CT from mimosa (Acacia dealbata) and from gambier (Uncaria gambir). The effect of the different source of tannins on meat fatty acid composition was not very strong; however, multivariate analysis allowed discriminating the different groups
Sviluppo di un sistema di controllo per lo spettrografo CAOS
No full textLo scopo della mia attività è quello di realizzare una nuova interfaccia tra il telesco-pio da 91 cm e lo spettropolarimetro CAOS, situati all osservatorio M.G. Fracastoro di Serra La Nave (SLN).
La nuova interfaccia al telescopio dello spettropolarimetro CAOS nasce da due di-verse esigenze:
1. Rendere più efficiente il sistema di autoguida.
2. Aumentare il grado di automazione dell interfaccia al telescopio.
I passi seguiti per la realizzazione del progetto sono i seguenti:
1) Valutazione dei requisiti da raggiungere in termini di precisione da parte di ogni singolo motore e conseguente scelta dell hardware sia relativo ai moduli Beckhoff sia relativo ai motori stessi.
2) Implementazione delle procedure ad hoc che permettano ad ogni singolo sottosi-stema di espletare le funzioni definite per la nuova interfaccia.
3) Realizzazione di un interfaccia grafica in ambiente TwinCAT 3 o pannello di vi-sualizzazione interattivo per ogni singolo motore.
4) Implementazione di un interfaccia grafica utente (GUI) in linguaggio Java per la realizzazione di un Client per ogni singolo motore.
Nel primo capitolo vengono descritte le caratteristiche di uno spettrografo in gene-rale e di seguito le specifiche dello spettrografo CAOS, entrando nei dettagli per ogni sin-gola parte di cui lo spettrografo è composto. Poi viene descritta l attuale interfaccia tra il telescopio e lo spettrografo CAOS e le sue funzioni, infine viene proposta la descrizione di una nuova interfaccia con i suoi sottosistemi.
Nel secondo capitolo vengono illustrate le funzioni delle movimentazioni della nuova interfaccia e l hardware utilizzato per ogni singolo sottosistema.
Inoltre verranno dati dei cenni sull ambiente TwinCAT 3 utilizzato per lo sviluppo del software Server e sul protocollo ADS, messo a disposizione della ditta Beckhoff per mettere in comunicazione un Client, realizzato con un linguaggio ad alto livello, con il Server TwinCAT.
Nel terzo capitolo vengono descritte le tecniche adoperate per la configurazione dei parametri elettrici e meccanici relativi ad ogni singola movimentazione che compone un sottosistema.
A partire da tali configurazioni è stata realizzata, per ogni singolo motore, un inter-faccia grafica ingegneristica in ambiente TwinCAT 3, che permette di conoscere le infor-mazioni sullo stato del motore e di verificare le funzioni implementate con il linguaggio IEC 61131-3. In un scenario reale di comunicazione a distanza, in rete, tale software rap-presenta la parte Server .
Infine è stata realizzata un Client grafico in Java, per ogni singolo motore, con lo scopo di testare il corrispondente Server e fornire un primo interfacciamento con il Server stesso.
Per la realizzazione della nuova interfaccia tra il telescopio 91 cm e lo spettrografo CAOS sono stati selezionati dei prodotti che, attualmente, rappresentano lo stato dell'arte nell ambito del controllo e dell automazione industriale, in modo da avere il massimo delle prestazioni tecnologiche con la massima compattezza di assemblaggio, alta affidabilità e ridotta manutenzione.
In riferimento alla precisione, considerando che l immagine di una stella sul piano focale del telescopio dovuta all atmosfera è dell ordine di 2 (secondi d arco) e che le dimensioni proiettate in cielo dalla fibra ottica sono minori di 5 secondi d arco, lo scopo dell attività relativamente al tip-tilt è stato il raggiungimento di una precisione tale da seguire un moto apparente della stella pari a 0.5 , pertanto la precisione richiesta per il riposizionamento dell oggetto da osservare nella posizione di riferimento, per la movimentazione dello specchietto tip-tilt, è pari a 0.5 equivalente a 2.4 µrad
Fully Integrated Data and Power Transfer Systems with Galvanic Isolation
No full textMy principal activity was focused on the design of galvanically isolated integrated systems as a part of a research project at the RF ADC by exploiting STMicroelectronics technology platforms providing on chip galvanic isolation. This technology was previously addressed to the implementation of isolated data transfer and it is currently used for mass production. In this context, the principal purpose of my work was the investigation on a fully integrated dc-dc power converter with half-duplex data communications providing on chip galvanic isolation in silicon technologies. This research is mainly interested in increasing the level of integration for the next generation of power converters with data transfer and several other applications requiring galvanic isolation. Autonomous sensors and/or control circuits, typically require a few tens of Mbps for data communication and an output power from tens to hundreds of mW. In this context, fully integrated interfaces can provide several advantages, including higher reliability, lower PCB area, lower system complexity and lower costs, especially if only silicon technology is exploited