1,721,263 research outputs found
Sintesi, Caratterizzazione e Applicazioni di Carbon Nanodots
No full textRecentemente i Carbon Nanodots – nanoparticelle a base di carbonio – si sono affermati come nuova tipologia di nanomateriale. Essi mostrano proprietà chimico-fisiche molto interessanti, come la fotoluminescenza, solubilità in acqua, facilità di funzionalizzazione, fotostabilità e biocompatibilità.
Grazie a queste caratteristiche, i Carbon Nanodots potrebbero essere impiegati in diversi campi che vanno dalla biologia alla catalisi.
Questa Tesi è basata sull’investigazione delle proprietà di superficie dei Carbon Nanodots, preparati da differenti precursori e approcci sintetici, in aggiunta alle loro applicazioni organocatalitiche e fotoniche.
Nel capitolo 1 viene presentata una panoramica delle metodologie sintetiche e di purificazione dei Carbon Nanodots. Inoltre, vengono descritte le loro caratteristiche fisico-chimiche. Si riporta anche una breve discussione sui loro utilizzi applicativi.
Nel capitolo 2 sono state studiate le proprietà superficiali di diversi Carbon Nanodots, in particolare quelli drogati con azoto. In collaborazione con il gruppo della Prof. Bonchio dell'Università di Padova, è stato sfruttato il loro contenuto amminico superficiale per condurre trasformazioni amminocatalitiche in acqua.
Nel capitolo 3 viene presentata una famiglia di Carbon Nanodots da precursori ricchi di gruppi amminici, attraverso approcci mono e multicomponente. I nanomateriali ottenuti sono stati caratterizzati mediante tecniche spettroscopiche, morfologiche e analitiche. In seguito, le loro prestazioni catalitiche sono state confrontate utilizzando come modello una reazione aldolica.
Nel capitolo 4 sono presentati nuovi Carbon Nanodots chirali e drogati con azoto, preparati in un solo passaggio sintetico senza ricorrere a reazioni di post-funzionalizzazione con agenti chirali. Utilizzando precursori ricchi in azoto è stata ottenuta una coppia di nanoparticelle enantiomeriche, oltre alla corrispondente forma meso.
Infine, nel capitolo 5, è stata esplorata la luminescenza allo stato solido dei Carbon Nanodots incorporati in alcune matrici (polimerica, di silice e amminosilanica), dimostrando il potenziale delle matrici prodotte come sensori di pH, oltre al loro impiego come additivi per celle solari e diodi ad emissione di luce.Recently, Carbon Nanodots emerged as a nanomaterial with attractive physicochemical properties such as photoluminescence, aqueous solubility, ease of functionalization, photostability and biocompatibility. Owing to these characteristics, Carbon Nanodots could be conveniently employed in several fields ranging from biology to catalysis.
This Thesis is focused on the investigation of the surface properties of Carbon Nanodots prepared from different precursors and synthetic approaches, facilitating and demonstrating their application in organocatalysis and photonic devices.
In chapter 1 an overview of the synthetic and purification methodologies of Carbon Nanodots is presented, in addition to their physical-chemical characteristics. A brief discussion on their potential applications is also reported.
In chapter 2 the surface properties of different Carbon Nanodots are presented. In particular, the focus is on nitrogen-doped Carbon Nanodots. In collaboration with the group of Prof. Marcella Bonchio at the University of Padova, their superficial amino-groups were exploited to perform aminocatalytic transformations in water.
In chapter 3 a family of nitrogen-doped Carbon Nanodots is described. The novel materials have been synthesized from amino-rich precursors via both mono- and multi-component approaches. The nanomaterials were characterized by means of spectroscopic, morphological, and analytical techniques. Subsequently, their catalytic performances were compared toward an aldol reaction model.
In chapter 4 are presented chiral nitrogen-doped Carbon Nanodots prepared via one-step synthesis, i.e. without employing post-functionalization reactions with chiral agents. Starting from nitrogen-rich precursors, a pair of nanoparticles with intrinsic chirality (enantiomers) were obtained, as well as their meso counterpart.
Finally, in chapter 5 the solid-state luminescence of Carbon Nanodots embedded in several matrices (polymeric, silica, and aminosilane) was explored. The application of Carbon Nanodots composites was demonstrated as pH-sensors, in addition to their use as additives for solar cells and light-emitting diodes
Finite-time control of discrete-time linear systems
No full textIn this note, we consider the finite-time stabilization of discrete-time linear systems subject to disturbances generated by an exosystem. Finite-time stability can be used in all those applications where large values of the state should not be attained, for instance in the presence of saturations. The main result provided in the note is a sufficient condition for finite-time stabilization via state feedback. This result is then used to find some sufficient conditions for the existence of an output feedback controller guaranteeing finite-time stability. All the conditions are then reduced to feasibility problems involving linear matrix inequalities (LMIs). Some numerical examples are presented to illustrate the proposed methodology. © 2005 IEEE
Photonics-based environment monitoring system for an enhanced prevention of landslide and structural failure risks
No full textElezioni europee 2019: cosa ci dicono i flussi di voto
No full textAnalisi dei flussi di voto verificatisi tra elezioni politiche 2018 ed elezioni europee 2019 in un campione di collegi elettorali delle diverse aree geografiche del Paese
Conditions for annular finite-time stability of Itô stochastic linear time-varing systems with Markov switching
No full textIn this study, the authors tackle some control problems related to the class of continuous-time, stochastic linear time-varying systems with Markov switching. First, the annular stochastic finite-time stability problem is considered, and two sufficient conditions are derived by considering the Itô formalism. Both conditions require the solution of a feasibility problem based on differential linear matrix inequalities. The former turns out to be less conservative and, therefore, is exploited in the analysis context; however, it cannot be converted into a computationally tractable condition for feedback purposes. The latter, which is based on a more conservative assumption, allows us to solve the state-feedback design problem. They show that the proposed approach obtains less conservative results with respect to the previous literature. Moreover, the application of the methodology to the finite-time control of a satellite illustrates the effectiveness of the proposed approach when facing engineering problems
An Observer-Based Output Feedback Controller for the Finite-Time Stabilization of Markov Jump Linear Systems
No full textIn this letter, we investigate the finite-time output
feedback control problem for continuous-time Markov
jump linear systems. In this context, the first result is
a sufficient condition for stochastic finite-time stability,
requiring the solution of a feasibility problem constrained
by differential linear matrix inequalities. Afterward, we
consider the stabilization problem via output feedback
dynamical controllers. The usual machinery pursued in the
deterministic case would lead to stabilization conditions
depending on differential bilinear matrix inequalities, that
cannot be solved in practice. Therefore, a different methodology,
based on the separation approach provided by
Amato et al., is exploited to design an observer-based output
feedback controller, which can be computed by solving
an optimization problem depending on linear constraints.
A non-trivial application example, involving the finite-time
stabilization of the longitudinal dynamics of a helicopter,
is presented in order to illustrate the effectiveness of the
proposed technique
Finite-time stabilization via dynamic output feedback
No full textIn this paper the finite-time stabilization of continuous-time linear systems is considered; this problem has been previously solved in the state feedback case. In this work the assumption that the state is available for feedback is removed and the output feedback problem is investigated. The main result provided is a sufficient condition for the design of a dynamic output feedback controller which makes the closed loop system finite-time stable. Such sufficient condition is given in terms of an LMI optimization problem; this gives the opportunity of fitting the finite-time control problem in the general framework of the LMI approach to the multi-objective synthesis. In this context an example illustrates the design of a controller which guarantees, at the same time, finite-time stability together with some pole placement requirements. © 2005 Elsevier Ltd. All rights reserved
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