3284 research outputs found
Sort by
Food web interactions in an ecological community model: Tomato plant, Tuta absoluta and its natural enemies
No full textThe introduction of an invasive pest in a new area often disrupts the ecological stability existing in a consolidated agricultural system. In this case, the knowledge of the mechanisms of interaction occurring among the species characterizing the food web becomes crucial. In my PhD research activity, I investigated the multitrophic interactions occurring in the ecological model of Tomato, Tuta absoluta and its natural enemies, referring particularly to the omnivorus predator Nesidiocoris tenuis. I conducted behavioral observations on potential intraguild interactions occurring between N. tenuis and the two T. absoluta parasitoids Necremnus tutae and Bracon nigricans. Direct behavioral observations on the mirid were carried out under a microscope supplying T. absoluta larvae parasitized by each of the two parasitoids. Another set of trials was conducted in microcosms to assess the effects of the mirid on the development of both parasitoids. Furthermore, to study the indirect plant responses triggered by the feeding behavior of N. tenuis on tomato plant, we assessed the attraction of the whitefly Bemisia tabaci and its parasitoid Encarsia formosa toward punctured plants by different N. tenuis instars.These data, obtained in olfactory studies, were also related to the analysis of the gene expression involved in the codification for the main phytohormones which lead plant defense and to the analysis of the levels of these phytohormones in healthy and punctured tomato plants. Finally, further studies on the plant-insect interactions were conducted comparing the different attraction of N. tenuis for healthy tomato, the potential companion plants Sesamum indicum and Dittrichia viscosa plants as well as tomato plants infested by T. absoluta eggs and larvae. At the same time gas chromatographic analysis was carried out in order to obtain the volatile profile of each plant to be related with the olfactory studies.
These three lines of research provided useful data in the understanding and in the management of the complex interactions in the chosen model. The key role played by the plant in directing these interactions and the competitiveness shown by the zoophytophagous mirid N. tenuis were highlighted. Data evidenced that this omnivorous predator showed to be able to compete with the two parasitoids B. nigricans and N. tutae performing intraguild interferences such as Kleptoparasitism and Intraguild Predation on them. All the feeding instars of N. tenuis were able to induce indirect plant defense in tomato through the activation of the Jasmonic acid pathway responsible for E. formosa attraction and the abscissic acid pathway involved in B. tabaci rejection. Finally in our study with alternative plants, the capability of the mirid to exploit plant biodiversity showing a positive orientation behavior toward potential companion plants of tomato such as sesame emerged; furthermore in these studies we identified volatile compounds emitted by plants potentially responsible for this attraction activity
Thermally induced effects in controlled atmosphere on Graphene and Molybdenum disulfide
No full textA wide interest has grown in recent years for the 2D materials. The graphene (Gr) is the 2D carbon material with a zero energy band gap, that turned out to be relevant due to its electrical, transport and optical properties and is considered the pioneer of emerging 2D solids. A key requirement for some applicative tasks is constituted by the need to open an energy gap in the Gr electronic levels distribution to induce, for example, a higher current modulation (i.e., on/off current ratio) in Gr-based field effect transistors. Another target is the doping to induce a shift of the Fermi level for the use of graphene in electronics devices and modulate the charge carriers. In this context, controllable and stable p- or n-type doping represent prominent goals to tailor Gr sheet resistance for specific electronics and optoelectronics applications, such as ultra-thin exible circuits and interconnects
transparent conductive electrodes for the next generation solar cells and/or touch screens. It is known that oxygen is a p-type dopant for graphene, active also by thermal treatments. The mechanisms responsible for p-type doping of substrate supported monolayer graphene
(Gr) by thermal treatments in oxygen ambient have been investigated by micro-Raman spectroscopy, atomic force microscopy (AFM), considering commonly employed dielectric substrates, such as SiO2 and Al2O3 thin films grown on Si. While a high p-type doping (~10^13 cm^-2) is observed for Gr on SiO2, no significant doping is found for Gr samples on the Al2O3 substrate, suggesting a key role of the Gr/SiO2 interface states in the trapping of oxygen responsible for the Gr p-type doping. Furthermore, we investigated the doping stability of Gr on SiO2 during subsequent thermal treatments in nitrogen (N2), carbon dioxide (CO2), water (H2O) or in vacuum controlled atmospheres. These processes induce only minor effects on the doping of Gr but for H2O and principally affect its defectiveness, suggesting that the literature reported air influence on the doping depends on water present in the atmosphere. Alongside the Gr, the MoS2 transition metal dichalcogenides is one of the stable 2D materials of interest. The potentiality to produce Van der Waals heterostructures combining Gr and MoS2, in particular, is pushing their study. Indeed, the non-null band gap, good chemical sensitivity and photo response of MoS2 pave the way for applications in optoelectronics, sensing and photovoltaic devices, for example. In this context, the possibility to tune the properties of MoS2 by opportune treatments is of interest, also to evaluate the thermal effects in the case of heterostructures. The MoS2 treatment in O2 has evidenced a progressive erosion of the flakes without relevant spectral changes in their central zone, during in-situ measurements, whereas the formation of MoO3 on the flakes edges is observed indicative of the oxygen activated transformation
Phatophysiological Mechanisms and cellular therapies in the Musculoskeletal Disorders
No full textOsteoarthritis (OA), one of the most commonly occurring musculoskeletal conditions, is a nearly universal, slowly progressive degenerative condition of articular cartilage, affecting of men and women as they age. Articular cartilage is characterized by its extreme fragility, due to the fact that it is neither innervated nor vascularized, so once injured it is not able to repair and it undergoes the degenerative process. Although a lot is known about this complex and multifactorial disease, the only existing therapy consists in the attenuation of its symptoms but no resolutory therapy is available. Considering numerous aspects and multifactorial nature of the OA disease, the aim of this research was to improve the knowledge of the morpho-molecular mechanisms occurring in the osteoarthritic and normal cartilage and to find the possible therapeutic solutions for this complicated disease. The present study focused on the most important aspects of OA. Primarily, we took into account its principal risk factor and triggering element represented by aging process, to pass subsequently to investigate about its main cause given by the inflammatory process and altered lubricating ability of the cartilage tissue, to end with the investigation of the solution to the problem given by the tissue engineering approach based on adipose tissue-derived MSCs. In conclusion, the present research highlights some important aspects concerning molecular alterations of articular cartilage tissue occurring in the pathological conditions and provides new insights for the treatments aimed to prevent, attenuate or solve the osteoarthritic process, as well as to restore the lost cartilage tissue
Symmetries, Equivalence and Decoupling of First Order PDE's
No full textThe present Ph.D. Thesis is concerned with first order PDE's and to the structural conditions allowing for their transformation into an equivalent, and somehow simpler, form.
Most of the results are framed in the context of the classical theory of the Lie symmetries of differential equations, and on the analysis of some invariant quantities.
The thesis is organized in 5 main sections. The first two Chapters present the basic elements of the Lie theory and some introductory facts about first order PDE's, with special emphasis on quasilinear ones.
Chapter 3 is devoted to investigate equivalence transformations, i.e., point transformations suitable to deal with classes of differential equations involving arbitrary elements.
The general framework of equivalence transformations is then applied to a class of systems of first order PDE's, consisting of a linear conservation law and four general balance laws involving some arbitrary continuously differentiable functions, in order to identify the elements of the class that can be mapped to a system of autonomous conservation laws.
Chapter 4 is concerned with the transformation of nonlinear first order systems of differential equations to a simpler form. At first, the reduction to an equivalent first order autonomous and homogeneous quasilinear form is considered. A theorem providing necessary conditions is given, and the reduction to quasilinear form is performed by constructing the canonical variables associated to the Lie point symmetries admitted by the nonlinear system.
Then, a general nonlinear system of first order PDE's involving the derivatives of the unknown variables in polynomial form is considered, and a theorem giving necessary and sufficient conditions in order to map it to an autonomous system polynomially homogeneous in the derivatives is established. Several classes of first order Monge-Ampere systems, either with constant coefficients or with coefficients depending on the field variables, provided that the coefficients entering their equations satisfy some constraints, are reduced to quasilinear (or linear) form.
Chapter 5 faces the decoupling problem of general quasilinear first order systems. Starting from the direct decoupling problem of hyperbolic quasilinear first order systems in two independent variables and two or three dependent variables, we observe that the decoupling conditions can be written in terms of the eigenvalues and eigenvectors of the coefficient matrix.
This allows to obtain a completely general result. At first, general autonomous and homogeneous quasilinear first order systems (either hyperbolic or not) are discussed, and the necessary and sufficient conditions for the decoupling in two or more subsystems proved. Then, the analysis is extended to the case of nonhomogeneous and/or nonautonomous systems. The conditions, as one expects, involve just the properties of the eigenvalues and the eigenvectors (together with the generalized eigenvectors, if needed) of the coefficient matrix; in particular, the conditions for the full decoupling of a hyperbolic system in non-interacting subsystems have a physical interpretation since require the vanishing both of the change of characteristic speeds of a subsystem across a wave of the other subsystems, and of the interaction coefficients between waves of different subsystems.
Moreover, when the required decoupling conditions are satisfied, we have also the differential constraints whose integration provides the variable transformation leading to the (partially or fully) decoupled system. All the results are extended to the decoupling of nonhomogeneous and/or nonautonomous quasilinear first order systems
RF Harvesting System for Remotely Powered Wireless Sensor Nodes
No full textWireless sensor networks (WSNs) based on batteryless nodes have been attracting an increasing attention in the scientific and industrial communities. Energy to replace battery can be extracted from environmental sources such as vibration, solar, thermal, or provided by RF carrier of a power transmitter.
An effective co-design approach for RF harvesting systems is described, which is based on a CMOS differential drive rectifier and an inductively coupled loop (ICL) antenna. The proposed methodology acts on both rectifier and antenna, and aims at optimizing system performance in terms of efficiency and input sensitivity for a given load specification. Moreover, a rectifier solution is also proposed to enhance circuit performance by properly driving transistor bulks without additional components
Development of new Lithium-Transition Metals co-doped Nanotitania. A perspective for sustainable photocatalytic materials and a comparative study between benefits and health risks.
No full textDuring this century, rapid population growth has led to an increased exploitation of oil and nuclear power to satisfy energy demands. This situation has created a growing tension between the deteriorating condition of the natural environment and the needs of society. Several research projects have sought to improve the situation through the development of innovative products and eco-friendly technologies: for example, the purification of the gaseous emissions emitted by industrial sources, or the manufacture of vehicles using sunlight as a renewable and clean energy. In addition, newly created materials are able to reduce air pollutants (organic and inorganic) through the process of photocatalysis, which consists of using solid semiconductors able to oxidize harmful substances until complete mineralization. In this context, the production of photocatalytic building materials could constitute a very interesting solution, and become an integral part of the strategy to reduce environmental pollution. Titanium dioxide (TiO2) is one of the most common photocatalytic materials. It can be used in many fields of application, including the building industry. The combination of titanium dioxide with cement makes it possible to obtain a binder that has both traditional properties, such as mechanical strength and durability, and new properties allowing the preservation of the environment and the conservation of the aesthetic value of the buildings. For instance, researchers have managed to create a material capable of accelerating the oxidation of the organic pollutants that are deposited on the external walls of the buildings.
This dissertation focused on the design, synthesis and characterization of a new family of titanium dioxide 1D, 2D and 3D nano-systems, doped with lithium and some transition metals in order to decrease the band gap and to enable visible light photoactivation even in indoor conditions.
The NPs samples showed an increment of the relative surface areas that was better than the increments observed in all the nanosheet samples (446 m2/g-1). The use of lithium, cobalt, cerium, and tungsten ions as dopants was evaluated through the UV-Vis absorption technique. The results showed both an increased absorption in the visible range and a decrease of band gap for the doped samples in comparison to the sample of pure TiO2.
We used several methods to evaluate the photocatalytic efficiency of all the nanoparticles and nanosheets we produced. The Li-Co and Li-Ce doped nanoparticles showed very good results both in water solution and in gas phase. The photocatalytic activity of our nanosystems was comparable with the standard samples under UVb light, but the doped NPs, in particular those doped with Au@TiLi(5) and TiLi(5)Co(5), showed better results under visible light than the control samples.
Our new synthesis method achieved very interesting results. It allowed us to obtain nanoparticles, nanosheets, xerogels, and aerogels covered with Li+ ions in place of the H+ ion at the surface in order to maintain them in a good dispersion in solution.
In order to evaluate the toxicity of the NPs, a comparative study on human lung cells and E. coli cells was carried out in vitro. All the analyzed nanoparticles exhibited different photocatalytic activities for human cells and bacteria, in particular under irradiation. Some transition metal ions doped nanoparticles exhibited cytotoxicity even in absence of illumination, a phenomenon that was probably caused by their dopant content. The use of such systems could constitute a risk for human health; however, once inhaled, the lack of illumination within the human body could reduce such a risk, and for TiLi and Au@TiLi(5) groups the danger is virtually absent. The toxicity on E. coli cells is significantly higher in almost all cases. In the case of the TiLiCo group, in particular, there is a high contrast between the low toxicity for human cells and the high toxicity for E. coli
Effetti della fibrillazione atriale sulla riparazione mitralica percutanea mediante sistema MitraClip.
No full textBackground La fibrillazione atriale (FA) è un'aritmia di comune riscontro nei pazienti con insufficienza mitralica, associandosi spesso a malattia valvolare in stadio più avanzato e maggior numero di comorbidità. Tuttavia, i dati relativi all'impatto dell'aritmia sulla riparazione mitralica per via percutanea sono molto limitati.
Obiettivo La presente analisi si pone come obiettivo la valutazione degli effetti della FA sul trattamento di pazienti ad elevato rischio chirurgico con insufficienza mitralica di grado moderato-severo o severo, sottoposti a riparazione percutanea mediante sistema MitraClip.
Metodi - Sono stati inclusi nello studio i pazienti arruolati nel registro prospettico GRASP (Getting Reduction of Mitral Insufficiency by Percutaneous Clip Implantation) eleggibili ad un anno di follow-up. Endpoint primario per efficacia è stato considerato il composito di morte da tutte le cause, re-intervento per disfunzione valvolare mitralica ed insufficienza mitralica di grado 3+ o 4+ ad un anno di follow-up. Sono stati considerati endpoints secondari i singoli componenti dell'endpoint primario, il tasso di re-ospedalizzazione per scompenso cardiaco e la classe funzionale NYHA (New York Heart Association). Sono stati presi in esame anche i parametri ecocardiografici basali ed al follow-up.
Risultati - Sono stati inclusi nell'analisi 289 pazienti: 121 (41.8%) con FA e 168 (58.2%) senza. L'insufficienza mitralica aveva un'eziologia funzionale in 237 pazienti (82%). Le caratteristiche cliniche ed ecocardiografiche di base erano paragonabili nelle due coorti esaminate ad eccezione dell'età, della pregressa rivascolarizzazione miocardica percutanea, dell'STS score e del volume atriale sinistro. Ad un anno di follow-up non si registravano differenze significative in termini di endpoint primario (20.7% nei pazienti con FA vs. 22.6% nei pazienti senza FA, p= 0.875). Non si osservavano significative differenze neanche per quanto riguarda gli endopints secondari. Ad un anno di follow-up si registrava inoltre una significativa riduzione delle dimensioni del ventricolo sinistro, a prescindere dalla presenza di FA; non venivano riportate variazioni di rilievo in termini di dimensioni atriali.
Conclusioni - I pazienti affetti da FA ed insufficienza mitralica, pur presentando un carico di malattia maggiore rispetto ai pazienti non affetti dall aritmia, possono essere sottoposti a riparazione mitralica mediante sistema MitraClip con successo procedurale, sicurezza ed efficacia a medio termine del tutto paragonabili alla popolazione generale
Superalgebras with superinvolution
No full textThe purpose of this thesis is to present in the setting of superalgebras with superinvolution some of the most interesting and challenging problems of combinatorial PI-theory (the theory of polynomial identities), which have already been addressed in the field of associative algebras or of algebras with involution.
More precisely, I shall characterize the varieties of superalgebras with superinvolution of polynomial growth and along the way I shall classify the subvarieties of the varieties of almost polynomial growth. Finally I shall find standard identities of minimal degree in the setting of matrix superalgebras with superinvolution and in this way I shall show that the Amitsur-Levitzki theorem can be improved by considering only certain kinds of matrices
Quantum confinement effects on light absorption in Germanium for solar energy conversion
No full textThe world demand for energy is continuously increasing with a rate that will soon become unsustainable given the current exploitation of energy sources (such as fossil fuels). In addition, it should be figured out that most of commonly used energy resource are limited and that humankind has liberated a quantity of carbon (as CO2) in the past 250 years that it took our planet about 250 million of years to sequester. In this context, a wide and exciting range of possible solutions to provide enough and cleaner energy is represented by nanotechnologies offering innovative materials with interesting effects exploitable for energy production, distribution and saving. Among other materials, Group-IV semiconductors have been deeply investigated since they allow the fabrication of abundant, non-toxic, mono-elemental nanostructures (as Si quantum dots, C nanotubes, Ge nanowires, et al.) thanks to high purity and mature technology. Moreover, fascinating effects due to quantum confinement in this nanostructures can be effectively exploited for energy production in photovoltaics devices. Among them, Ge reveals interesting optical properties due to its quasi-direct bandgap, higher absorption coefficient and larger exciton Bohr radius with respect to Si, giving the chance to easily tune the optical properties by exploiting quantum confinement effect (QCE). However, the properties of Ge quantum dots (QDs) depends not only on the size as many other parameters can concur in controlling their optical behavior, especially for what concerns the optical bandgap. For this reason, the aim of this thesis is devoted to a detailed investigation of the optical properties of Ge QD, with particular emphasis on the light absorption properties and its modulation by QCE
Strategie di riduzione del pregiudizio verso i gruppi stigmatizzati. Coming out diretto e indiretto: effetti sugli atteggiamenti nei confronti delle persone omosessuali.
No full textIl presente studio ha esplorato gli effetti delle diverse modalità di coming out, diretto (attraverso una comunicazione esplicita, ad esempio Io sono Gay ) o indiretto (attraverso una comunicazione implicita, ad esempio attraverso la condivisione di informazioni sul proprio partner) sugli atteggiamenti verso una persona omosessuale. Nello specifico, tre esperimenti hanno analizzato se una modalità diretta di coming out abbia effetti negativi sugli atteggiamenti delle persone eterosessuali. I risultati supportano l ipotesi che una modalità diretta di coming out abbia effetti negativi sugli atteggiamenti verso una persona gay (Esperimenti I e II), attraverso l aumento della salienza della categoria orientamento sessuale (Esperimento II), e che tali effetti dipendano dai livelli di pregiudizio verso le persone gay (Esperimento III)