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Sviluppo di materiali nanostrutturati e apparati per applicazioni in catalisi eterogenea.
No full textThe doctoral research period was devoted to the development of new ideas in the field of heterogeneous catalysis, involving both the realisation of novel apparatus for the study of catalysts and the synthesis of new catalytic materials.
A new apparatus for the study of selectivity in oxidative dehydrogenation reaction was initially setup aiming at studying the performances of new saponite catalysts. These materials have been shown to lead to coke productivity during ODH reaction.
These data gave us the idea to use saponite materials as polymer flame retardant. The clay material flame retardant effect is due to two synergic effect: the creation of a protective inorganic layer on the surface of the polymer matrix and the formation of char laminar structures. Our purpose was to increase the catalytic conversion performances of propene to coke by exploiting both acid saponite sites and vanadium species. The catalytic performances of different saponite materials toward propene ODH reaction was studied. Different metal-free acidic saponites (containing different amount of Brønsted acid sites) and V-containing saponite both acidic and non-acidic were investigated.
We found that the synergic effect of acidic site and Vanadium presence allow to the system (HV-Sap) to reach the highest low temperature activities and it is the only system that still maintain a positive coke production at 773 K.
The second research field is the development of apparatus suitable for planar catalyst libraries tests. A reactor which is able to scan small active catalytic surfaces using very low gas flow was developed and successfully tested in our laboratories. The reactor is designed to allow a continuous scanning test on a reduced circular area without any sealing system. The system consists of two main parts: the sample holder and the reactor head. The sample holder is mounted on a movable XYZ stage to set the relative 3D position with respect the fixed reactor head position. The reactor head features a little open chamber at the bottom; the reactant gas mixture is fed by a hose in the middle of the chamber, whereas the reaction gases are extracted by a side hose.
The entire system (reactor head and sample holder) is located in a controlled argon atmosphere chamber. The product gas mixture is confined and diluted in-situ by a flow of inert leakage gas from the controlled external atmosphere. The product gas mixtures are analysed by a downstream quadrupole-based mass spectrometer. Two model reactions were used to develop the scanning reactor: the hydrogenation of 1-3 butadiene over Pd nano-structured and the CO oxidation reaction over gold supported on titania
Finally, the possibility to obtain hydrogen from the photoproduction of renewable chemicals is investigated. At present, hydrogen is mainly produced from fossil fuels; a very interesting hydrogen source is water-splitting but, in spite of the intense research activities registered in the last decades, pure water splitting is still far from any technological application due to the complexity of the process and its inherent drawbacks. In particular, the main issue is the fast recombination between H2 and O2 (thermodynamically favourable inverse reaction) or between photogenerated electrons and holes.
A different approach to photoproduction is the use of organic compound as sacrificial agent for the hole sequestration: this reaction is accordingly called photoreforming. In particular, the catalytic photoreforming of ethanol and glycerol is investigated in this study. The first is obtained from carbohydrates fermentation and glycerol is the main byproduct of trans-etherification reaction for biodiesel production, being both cheap and widely available chemicals.
We want to study bimetallic gold-platinum systems supported over titania; a number of application of monometallic system in photoreforming are known in the literature and bimetallic systems are known to show optimal performances as catalytic system for a large number of reactions but they have never been used as photocatalysts.
The bimetallic system showed the highest activity during the photoreforming reaction of ethanol but during the reactions with glycerol solution the presence of both metal didn’t improve the reactivity of the system. Also the activity of photodeposited system were investigated on glycerol photoreforming with UV-A light. The hydrogen production rate of photodeposited gold monometallic system is close to the impregnated bimetallic system; the photodeposited bimetallic system showed a hydrogen production rate of 3400 μmol g-1 h-1 after 6 reaction hours,1000 μmol g-1 h-1 higher than bimetallic impregnated system
Uso di statine e recidiva di fibrillazione atriale dopo ablazione transcatetere o cardioversione elettrica.
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X-ray telescope mirrors from surface profile to point spread function.
No full textX-ray astronomy was born on 1962 when Giacconi decided to put a Geiger counter onto a rocket, in hope of measuring the X-ray emission from the Sun. Even if the Sun emission was disappointing, he made the discovery that changed our view on the Universe. An unknown background of X-ray emission that later turned out to contain millions of X-ray sources, both galactic and extra-galactic. Owing to the development of increasingly sophisticated instruments, the sensitivity and the resolution to detect X-ray sources has improved significantly over the last 50 years.
One of the major technological improvement was the development of focusing telescope, which allowed to enhance the angular resolution and sensitivity of several orders of magnitude. The angular resolution of an X-ray imaging telescope is mainly determined by the quality of its focusing optics. These generally consist of a number of nested shells of grazing incidence mirrors. The typical configuration used, which minimizes the effect of coma aberration and reduces the focal length, is the so-called Wolter-I (paraboloid-hyperboloid mirror configuration). In order to keep the mass to levels comparable with the launcher (because X-ray absorption in the atmosphere prevents observation from ground) the optics have to be lightweight, hence the mirrors have to be thin.
The final performance of a mirror module is always subject to degradation, provided in the realization phase. During the different stages of production (under construction and integration) there may be distortions. In addition, the mirror surface is not ideally smooth but is characterized by a certain roughness topography. Both these types of imperfections combine to determine the degradation of the Point Spread Function (PSF), i.e. the annular integral of focused intensity around the focal spot, which generally characterizes the quality of the optics.
Regarding the characterization of an X-ray mirror, one of the basic objectives is to establish the relationship between the imperfections of the mirrors and their PSFas a function of the incident wave energy. The aimis to predict the angular resolution of a mirror, given measurements of profiles and microroughness, or to establish the level of tolerable imperfections of a mirror given a certain angular resolution required by the project specifications.
The study of the topography of the mirror surface is done through several methods.
It is generally divided into two different kinds of analysis: the study of the profile, i.e. large spatial wavelengths (comparable with the mirror length) and the study of microroughness, i.e. short spatial wavelengths.
The first ones, also called the figure errors, are often due to deformation of the mirror that occurs during construction and integration and are responsible for the degradation of the PSF and can be treated by geometrical optics. The second ones are due, for example, to the limits of the polishing mandrel methods, from which the shells are replicated, and the deposition technology of the reflective coating. These imperfections are responsible for a diffusion (called scattering), which degrades the PSF at increasing energy and can not be treated by geometrical optics, but using physical optics under some assumptions. This problem is much more important in Xray than in optical astronomy, because X-ray have a 1000 times smaller wavelengths and are sensitive to surface defects 1000 times smaller. The surface polishing is thereby a fundamental point in X-ray mirrors.
The characterization of the microroughness is made in terms of power spectrum as a function of the spatial frequency on the surface (PSD - Power Spectral Density).
The PSD is a fundamental quantity in the characterization of X-ray telescope optics because is proportional to the scattering. The measure of roughness is done with different instruments in order to have a range of spatial frequencies as more wide as possible, from a few millimetres to a few tens of nanometres.
There is also a range of intermediate frequencies, at the limit of microroughness, which generates a degradation of the PSF that can neither be predicted by geometrical optics and nor by the scattering theory. For this reason, it is difficult in general to predict accurately its effect on the PSF.
My PhD activity is included in the mission project NHXM financed by ASI and in the development of X-ray mirrors for ATHENA mission project financed by ESA.
The first part of my PhD project has been therefore aimed at the characterization of microroughness and reflectivity of the mirrors, at INAF/OAB, in order to determine the topography of the surface and to support the industry (Media Lario Technology, leader company of manufacturing optical components) in setting the process.
The second part of the project was instead dedicated to the development of a selfconsistent general method, based on physical optics, to compute the PSF of X-ray 2 mirrors from their profile metrology. The third part, which is the merging of these two parts of the project, consist in the applications to real cases through verifications with calibration tests.
My research work can be divided into three phases:
• First phase - I performed measurements of mirror profiles and roughness of several samples of mirrors for the missions NHXMand ATHENA, using different instruments available at INAF/OAB. The roughness measurements, at spatial scales smaller than 1 mm, can be achieved with different instruments that have different spatial wavelength ranges (i.e. optical interferometer WYKO and Atomic Force Microscope). However, the effects of roughness can also be directly observed by performing X-ray reflectivity measurements using an X-ray diffractometer. I used the X-ray diffractometer available at INAF/OAB for scattering measurements, with particular attention to the effects in large angle scattering and modulation interference introduced by the multilayer. By merging these different data I derived the complete roughness surface PSD.
Bymeans of the X-ray diffractometer Imade reflectivity measurements of samples of mirrors with multilayer coating, obtaining the reflectivity curve as a function of the angle of incidence and as a function of the energy. Using a program to fit the reflectivity curves (PPM), I estimated the thickness of the layers and their uniformity, then assessing the compliance with design specifications.
In summary, from one hand surface roughness (from direct topography measurements and scattering measurements) to obtain the PSD, on the other hand, measurements of reflectivity (as a function of both the incidence angle and the energy) for the characterization of the structure of the multilayer. The feedback provided to the industry in a commons way and the isolation of the critical points has lead to the deposition of coatings with excellent reflectivity.
I performed reflectivity measurements also within the study of the crystallization of gold during the evaporation process, which contributes to worsen the surface roughness. The gold layer is deposited on the mandrel, which is then electroformed a Nickel-Cobalt shell (the mirror). The gold layer serves to detach the shell from mandrel and it should minimize the microroughness increasing.
In this regard, I performed diffraction measurements of different gold deposits with different thickness. Studying the Bragg peaks I obtained an estimation of the size of the gold crystallites as a function of the thickness.
Larger are the crystallites, higher is the value of the microroughness. The conclusion is that more the gold layer is thick, larger are the crystallites and larger crystallites means microroughness increasing.
• Second phase - I developed a new method to calculate the PSF of an X-ray mirror (e.g. Wolter-I configuration, in double reflection) at any energy by applying the principle of Huygens-Fresnel from real profile and roughness data.
In other words, the X-ray reflection is treated by the undulatory theory, building the wavefront deformed by the mirror imperfections. In this interpretation, even the deformed geometry are treated by the physical optics. This allows to obtain the PSF determined from both contributions (figure error and scattering) at any energy in a self-consistent way, without considering different separated energy regimes treated with different methods. This method, never used before, ultimately solves the problem of PSF computation, starting from the complete surface topography of an X-ray mirror.
• Third phase - I performed several calibrations over mirror shells in different configurations as demonstrator for the NHXM hard X-ray imaging telescope (0.3 - 80 keV). Prototypes of NHXM mirror modules with a few mirror shells were manufactured, aiming at demonstrating the feasibility of mirrors. Imade the direct performance verification by measuring the X-ray PSF (Point Spread Function) up to 50 keV in full-illumination setup at PANTER (MPE, Germany) and in pencil-beam set up at monochromatic X-ray energies from 15 to 63 keV at the BL20B2 beamline of the SPring-8 synchrotron radiation facility. Moreover, I simulated PSF from the metrology profile of mirror shell using Fresnel diffraction method. The calibration measured data and the simulated data (obtained with my Fresnel method) match perfectly. This provide the experimental proof of the correctness of the method, that therefore will represent, from now on, a powerful prediction tool in X-ray optics.
The Fresnel diffraction method is easily extendible to other optical systems, also out of astrophysical applications, even with a number of more than two reflections, e.g Syncrotron and FEL facilities.
For the future, I plan to implement the Fresnel diffraction method improving the simulations of mirrors coated with multilayer. In this case in order to increase the prediction accuracy, we have to taking into account the scattering from multilayer interfaces
Molecular physiological studies on the peptide transporter-1, PepT1.
No full textThe peptide transporter-1, PepT1, is responsible for the uptake of peptides in the mammalian intestine after protein digestion. It has also been shown to transport a wide range of pharmacological agents; thus making it important in drug design and delivery. Many studies have addressed structure-function relationships in the transporter, using biochemical and uptake assays; however PepT1 is an electrogenic transporter whose activities could be more clearly studied using electrophysiological methods.
In this work therefore, the transporter has been studied using the two electrode voltage clamp technique on the transporter expressed in Xenopus laevis oocytes.
Temperature effects on the kinetics of the three isoforms studied (rabbit, zebrafish, seabass) is reported here with a suggestion of a possible structural adaptation in the transporter. Since the transporter is also of interest in animal feed formulation, transport characteristics of a range of dipeptide combinations are also presented; with a recommendation on the possible optimal lysine supplementation in feeds that require essential amino acids supplementation.
Reverse operation in transporters may be the result of or lead to pathophysiological states. Experimental data here show that mutants in Arginine 282 and aspartate 341 exhibit properties that make them suitable as models to study possible reverse operation in PepT1. To understand the physiological significance of reverse operation, the structural and functional basis of this phenomenon was also explored
Definition of hydrologic regimes in regulated rivers for aquatic biodiversity conservation.
No full textNegative ecological effects of water withdrawal activities from lotic systems have led to the need for the restoration of naturally shaped flow schemes. As a first step in this direction, individuation of sustainable minimum flow volumes can limit extreme alteration of ecosystem structure and functionality. The definition of such minimum flow values, to be released downstream each water diversion structure, must follow the understanding and the quantification of ecological alteration related to flow reduction.
This thesis focuses on the study of instream ecological effects of water withdrawal from lowland rivers (Ticino and Adda rivers), with the purpose to define adequate indicators for the identification of ecological effects of hydrological alteration. The application of such indicators should be useful for the definition of environmentally sustainable minimum flow schemes.
For this purpose, national protocols for the study of biological communities were applied and critically analyzed. These monitoring criteria and tools appeared inadequate for addressing the hydrological assessment as postulated in this work and for the studied geographical context.
Alternative sampling and analysing methods are proposed, following two different directions: (1) a different approach in the use of a common and well known structural indicator (macroinvertebrate fauna) and (2) the integration of such structural descriptors with a functional approach that considers the river quality through ecosystem methabolism measures.
Although their widespread use, connected to simple field and laboratory application, macroinvertebrates appeared to be an inadequate tool for hydrological alteration monitoring. However, interesting considerations about relationship between community density and richness and environmental disturbance could be made.
Presented data about physico-chemical parameters, collected through the open-channel method, show an influence of flow on ecosystem functional processes, mainly related to influence on aquatic vegetation. Collected data were useful to define an easy method to assess general response of the ecosystem to hydrological modifications, which future application could lead to interesting results and to an alternative approach for the application of WFD (Dir. 2000/60/EC) requirements
Searching for molecular markers of quality in fish reared in aquaculture.
No full textOne of the most unique characteristics of fish as food is that it is highly perishable. Consequently, freshness is fundamental to the quality of fish, and the time that has passed after catching it and the temperature ‘‘history” of fish are very often the key factors in determining the ultimate quality characteristics of such products. Therefore, the development of reliable methods to assess the freshness of fish, as well as the evaluation of quality, has been the goal of fish research for many years.
During post mortem storage, fish muscle degrades and the flesh quality decreases rapidly, depending on the fish species. Loss of freshness, followed by spoilage, is the result of complex biochemical and microbiological processes that begin with a metabolic shift from an aerobic to an anaerobic state. This is followed by transformation of glycogen into lactic acid and the consequent reduction in pH and activation of different proteolytic reactions catalyzed by endogenous enzymes, which produce nutrients that promote subsequent bacterial proliferation. Post mortem tenderization is one of the most unfavourable quality changes in fish muscle and contrasts with mammalian and avian meats in which post mortem degradation of myofibrillar and cytoskeletal proteins is often desired to obtain a tender product.
Previous studies on fish have investigated post mortem phenomena using chemical, physical, histological, and microbiological methods by focusing on indicators such as pH, lactic acid, adenine nucleotides and their degradation products, texture, firmness, and elasticity. Only few studies in the current literature have included a combination of molecular and proteomic investigation. Therefore the objective of the present Thesis was to investigate by molecular biology and proteomic techniques on how different methods of slaughtering and post mortem storage conditions influence the freshness quality of fish filet. The target species was cultured European sea bass (Dicentrarchus labrax) which is a marine teleost of great interest for Mediterranean aquaculture, representing an excellent fishfood product of high commercial value.
Firstly, microfluidic capillary electrophoresis and real-time PCR were successfully applied to investigate the post mortem alterations in RNA extracted from sea bass muscular tissue in relation to three parameters: slaughtering method, and post mortem time and storage temperature (Chapter 3). In the course of this study, we first identified the sea bass cDNA sequences coding for endogenous proteases such as calpains and cathepsins which are assumed to play a major role in post mortem degradation of fish muscle. Then we determined the total RNA and ì-calpain- and cathepsin-L-specific mRNAs integrity over 5 days of storage at two different temperatures (1°C and 18°C) in sea bass slaughtered by three different methods (asphyxia in air, hypothermia/asphyxia in ice, and spinal cord transection). The results of this study showed that, RNA degradation is a slow process under the conditions investigated and, although post mortem storage temperature negatively affects the integrity of total RNA (higher degradation at 18°C), the transcripts of ì-calpain and cathepsin L are present for up to 5 days post mortem in the muscle of sea bass stored at either 1°C or 18°C without showing any significant slaughtering method-related degradation rates.
In the light of these results, and in order to shed light on the influence of temperature on the status of sea bass muscle proteins during post mortem storage, a 2-D DIGE (2 Dimensional Difference Gel Electoforesis) and mass spectrometry study was performed on fish (Chapter 4). As expected, the greatest alterations in sea bass filet protein composition were observed upon post mortem storage at 18°C, with distinct changes appearing in the 2-D protein profile after 5 days of storage at this temperature. In particular, degradation of the myofibrillar protein myosin heavy chain and of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase, among the most abundant muscle proteins, could be clearly observed upon storage at higher temperatures. Although to a lesser extent, however, several proteins were observed to vary in abundance also upon storage for 5 days at 1°C. In particular, one of the most interesting observations was the rapid and significant decrease in the abundance of nucleoside diphosphate kinase B and phosphoglycerate mutase 2, which was observed also at low storage temperatures and appeared to be temperature-independent. The results of this study offer new knowledge on changes occurring in sea bass muscle proteins during post mortem storage at different temperatures and provide indications on protein degradation trends that might be useful for monitoring freshness of fish and quality of storage conditions.
Thirdly, 2D DIGE and mass spectrometry were applied to investigate the impact of slaughtering on the post mortem integrity of muscle tissue proteins in European sea bass (Chapter 5). Three different slaughtering techniques were evaluated: asphyxia in air (AA), asphyxia in ice (AI), and spinal cord severance (SCS). Principal components analysis (PCA) revealed a significant divergence of SCS samples, whereas AA and AI samples, although grouped separately, were less divergent and could be included in a single asphyxia cluster. In terms of single proteins, the most significant impact was seen on nucleoside diphosphate kinase B, which was consistently less affected when fish were slaughtered by SCS as compared to asphyxia. Integrity of the sarcomeric proteins myosin heavy chain and myosin binding protein C and of the cytosolic proteins fructose biphosphate aldolase, glyceraldehyde 3-phosphate dehydrogenase, and enolase 1 was also better preserved upon SCS slaughtering. Most interestingly, the influence on muscle protein integrity could be detected since the early post mortem phase. The results of this study demonstrated that slaughtering by SCS preserves protein integrity better than death by asphyxia, either in ice or in air. Both asphyxia conditions are comparably more adverse than SCS to muscle protein integrity, although a general trend favoring AI over AA is observed.
The last objective of this Thesis was to realize a proteome map of the sea bass muscle (Chapter 6) for use in traceability and species authenticity studies, and as a reference for identification of possible freshness and quality markers.
In the last study of this Thesis, the proteome profile of European sea bass (D.labrax) muscle was analyzed using 2-DE and tandem mass spectrometry (MS/MS) with the aim of providing a more detailed characterization of its specific protein expression profile. A highly populated and well resolved 2-DE map of the sea bass muscle tissue was generated, and the corresponding protein identity was provided for a total of 54 abundant protein spots. Upon Ingenuity Pathway Analysis, the proteins mapped in the sea bass muscle profile were mostly related to glycolysis and to the muscle myofibril structure, together with other biological activities crucial to fish muscle metabolism and contraction, and therefore to fish locomotor performance. The data obtained in this study provide important and novel information on the sea bass muscle tissue-specific protein expression, which can be useful for future studies aimed to improve seafood traceability, food safety/risk management and authentication analysis.
In conclusion, the results of this Thesis indicate that, storage conditions are important for post mortem deterioration of fish muscle, and temperature is one of the factors with the strongest impact on this process.
Pre-slaughter and slaughter stressful practices can have an important effect on the fish flesh quality. Therefore, the reduction of stress at slaughter might be a satisfactory strategy for both animal welfare and product quality.
The molecular and proteomic methods used in this Thesis helped to identify nucleoside diphosphate kinase B and phosphoglycerate mutase 2 as candidate biomarkers for the evaluation of sea bass fillet freshness quality
Pulse shaping and ultrashort laser pulse filamentation for applications in extreme nonlinear optics.
No full textThis thesis deals with numerical studies of the properties and applications of spatio-temporally coupled pulses, conical wavepackets and laser filaments, in strongly nonlinear processes, such as harmonic generation and pulse reshaping.
We study the energy redistribution inside these wavepackets propagating in gases and condensed media, in the linear and nonlinear regime. The energy flux constitutes a diagnostic for space-time couplings that we applied to actual experimental results. We analyze the spectral evolution of filaments in gases and derive the conditions for the generation of ultrashort pulses in the UV range. We study high harmonic generation in a gas from ultrashort conical wavepackets. In particular, we show how their propagation properties influence the harmonic output. We also study the interference of different electron trajectories. Finally, we derive the shape of stationary Airy beams in the nonlinear regime. For each topic, we present experimental results that motivated our works or were motivated by our simulations