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Development of the glass slumping technology for the production of teh X-raymirrors aboard the international X-ray observatory optical module.
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The E-ELT adptive mirror: prototype and optical test
No full textGround-based optical-infrared 10m-class telescopes, such as Keck, Gemini, and Very Large Telescopes (VLT), are currently leading many of the astronomical research fields due to their unprecedented collecting areas. However, many new astrophysical quests arose from recent observations, justifying the need for even larger telescopes, with diameters > 30 m.
The European scientific community, led by the European Southern Observatory (ESO), takes part in this challenging competition whit the "European-Extremely Large Telescope" (E-ELT), a revolutionary project for a 40m-class telescope that will allow us addressing many of the most pressing unsolved questions about our Universe.
Building Extremely Large Telescopes asked for innovative technologies, from larger and repeatable optical manufacturing techniques to produce hundredths of aspherical off-axis hexagonal segments and large monolithic mirrors, or large thin optical shell mirrors, to better and faster controls (active and adaptive optics), together with more specialized focal plane instrumentations devoted to address specific astrophysical questions, more likely to large particle physics experiments.
Moreover the challenge of building extremely large telescope pushes forward the parallel ability to measure and test optical components of large sizes.
Adaptive Optics (AO) techniques allow to obtain enhanced ground-based astronomical observations, partially restoring diffraction-limited spatial resolutions, by compensating the degrading effects of the atmospheric turbulence. The delivered image quality of an AO-assisted telescope depends on the level of the correction of the wavefront error due to the atmosphere.
This work focuses on the adaptive deformable mirror unit (M4AU) of the E-ELT. During my Ph.D. study, I took part in the competitive "EELT-M4 project" study, led by an Italian-French consortium (Microgate, ADS, SAGEM, INAF-O.A.Brera).
Optical measurements were conceived, designed and performed on a similar, scaled-down, fully-representative prototype of the final system, to fully validate the proposed concept. Due to very stringent requirements in term of wavefront correction (10-100 nm rms), only interferometric optical setups were able to provide enough accuracy and sensitivity to carry out the work.
A set of three devices has been designed for the tests:
- a Ritchey-Common test setup (RCT), able to cover the full area of the M4AU DP optical surface with a single measurement, taken with a phase-shifting Fizeau interferometer;
- a Stitching Interferometric Setup (SIS), where a scanning smaller optical beam is able to reconstruct the same optical surface with increased capture range and spatial resolution, useful in the first steps of the calibration procedures;
- a piston sensing unit (PSU), which exploits the optical path difference between adjacent optical shells, after careful analysis of diffraction patterns.
Those devices, together with purposely designed control softwares and data reduction softwares,
were used during a 6-months measurement campaign, demonstrating the full compliance of the prototype system with the requirements to be obtained in the final system (flattening of each optical shell, co-phasing of the optical shells, optical stroke calibration, stability of calibration under time and changing environmental conditions).
Results have been positively reviewed by the EELT project office, and were used as feedback on the design of final optical test system, to be operated on the 2.5m M4AU unit
Role of UDP-GlcNAc and hyaluronan synthase 2 O-GlcNAcylation in the control of hyaluronan synthesis.
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Exploiting supramolecular interactions for asymmetric catalysis.
No full textSupramolecular chemistry refers to the area of chemistry beyond the molecules and focuses on the chemical systems made up of a discrete number of assembled molecular subunits or components. While traditional chemistry concentrates on the covalent bond, supramolecular chemistry examines the weaker and reversible non-covalent interactions between molecules. These forces include hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, pi-pi interactions and electrostatic effects. The aim of this thesis is the use of this type of interactions, in particular hydrogen bonding, for the development of new catalytic systems.
In the first part of the work the synthesis of a new class of supramolecular bis(oxazolines) named SupraBox using urea moiety as self-assembly inducer is reported. A library of 16 ligands, with different degree of structural diversity, were prepared by a 3-step modular synthesis starting from readily available starting materials. Palladium- and Copper-complexes were characterized by NMR spectroscopy, UV spectroscopy and mass spectrometry to investigate their structures and properties and used as catalysts in kinetic resolutions of racemic diols and in the desymmetrization of meso diols with good results.
In the second part, a new class of peptidomimetic organocatalysts starting from two bifunctional diketopiperazines was investigated. Four different organocatalysts were prepared and tested in the conjugate addition reaction of several aldehydes to beta-nitrostyrene and (E)-2-(furan-2-yl)nitroethene with good to excellent diastereo- and enantioselectivities. A rationale for the mechanism is also proposed: a Monte Carlo/Energy Minimization (MC/EM) conformational search by molecular mechanics methods was undertaken on the four catalysts proving the importance of hydrogen bonding between catalyst and substrate
Web content mining with multi-source machine learning for intelligent web agents.
No full textThe web is recognized as the largest data source in the world. The nature of such data is characterized by partial or no structure, and even worse there exist no standard data schema for the even low-volumed structured data. Web Mining aims to extract useful knowledge from the Web by using a variety of techniques that have to cope with the heterogeneity and lack of a unique and fixed way of representing information.
An important aspect in Web Mining is played by the automation of extraction rules with proper algorithms. Machine Learning techniques have been successfully applied toWeb Mining and Information Extraction tasks thanks to the generalization and adaptation capabilities that are a key requirement on general content, heterogeneous web pages.
The World Wide Web is a graph, more precisely a directed labeled graph where the nodes are represented by the pages and the edges are represented by links between them. Recent works propose the exploitation of the web structure (Link Analysis) for content extraction, for example one can leverage the content category of neighbor pages to categorize the contents of difficult web pages where word-frequency-based techniques are not robust enough.
In this thesis we propose an automated method suitable for a wide range of domains based on Machine Learning and Link Analysis. In particular we propose an inductive model able to recognize content pages where structured information is located after being trained with proper input data. In order to keep the recognition speed high enough for real-world applications an additional algorithm is proposed which lets the approach to boost both in speed and quality. The proposed method has been tested with controlled dataset in a classic train-and-test scenario and in a real-world web crawling system
Categorical algebras for the compositional construction of probabilistic and distributed systems.
No full textStructured transition systems have been widely used in the formal specification of computing systems, including concurrent and probabilistic systems. In this thesis we extend the span of graphs algebra introduced in [40] to describe concurrent systems in a compositional way, in order to model probabilistic distributed systems.
The span algebra of [40] may be regarded as an extension of various automata models of computation based on distributed automata. With the introduction of both parallel and sequential operations, this extension allows the compositional description of concurrent, distributed and mobile systems. An important aspect of span graph model is that there is also a geometric characterization associated with the algebra along the lines of Penrose’s algebra of tensors.
The algebra of transition systems we describe is a well-supported compact closed category - a symmetric monoidal category for which every object has a separable algebra structure (satisfying Frobenius equation) - whose arrows are automata in which the actions have probabilities. The operations of the category permit the compositional description of probabilistic processes and in particular of classical finite Markov chains. The systems we can model with our algebra are distributed, hierarchical and with an evolving geometry.
We also extend the span algebra of [40] in order to permit the inclusion of quantum components. Again, this algebra is a well-supported compact closed category. This extension permits a compositional description of quantum protocols, in which quantum components interact with classical finite state components. In our view, the inclusion of explicit components of finite state classical control adds conceptual clarity and precision to quantum protocols
Approximation and spectral analysis for large structured linear systems.
No full textIn this work we are interested in standard and less standard structured linear systems coming from applications in various _elds of computational mathematics and often modeled by integral and/or di_erential equations. Starting from classical Toeplitz and Circulant structures, we consider some extensions as g-Toeplitz and g-Circulants matrices appearing in several contexts in numerical analysis and applications. Then we consider special matrices arising from collocation methods for di_erential equations: also in this case, under suitable assumptions we observe a Toeplitz structure. More in detail we _rst propose a detailed study of singular values and eigenvalues of g-circulant matrices and then we provide an analysis of distribution of g-Toeplitz sequences. Furthermore, when possible, we consider Krylov space methods with special attention to the minimization of the computational work. When the involved dimensions are large, the Preconditioned Conjugate Gradient (PCG) method is recommended because of the much stronger robustness with respect to the propagation of errors. In that case, crucial issues are the convergence speed of this iterative solver, the use of special techniques (preconditioning, multilevel techniques) for accelerating the convergence, and a careful study of the spectral properties of such matrices. Finally, the use of radial basis functions allow of determining and studying the asymptotic behavior of the spectral radii of collocation matrices approximating elliptic boundary value problems
Essays on development economics.
No full textThis thesis consists of four essays in empirical development economics. The first three essays focus on macroeconomic topics, examining issues related to the business cycle, fiscal and monetary policy, whereas the last one is focusing on a microeconomic topic, namely the relationship between schooling and child labor.
The first contribution investigates the effectiveness of macroeconomic policies in the recoveries periods in the Middle East, North Africa and Pakistan (MENAP). It is found that fiscal policy played a key role during the recoveries to potential output, although with weaker effects for the countries in the region that are more open to trade; monetary policy is found to have been less effective. The second essay explores the effects of the Medium-Term Expenditure Framework (MTEF) adoption on the main fiscal performance indicators, finding a positive and encouraging impact on fiscal discipline, allocative efficiency and technical efficiency, although the last one is not always robust. The third essay aims at identify the nexus between the excess of liquidity and commodity prices; in particular, it assesses whether the commodity prices react more powerfully than the consumer goods’ prices to changes in real money balances. The results show a positive relationship between real money and real commodity prices and provide empirical evidence for a stronger response of commodity prices with respect to consumer goods’ prices.
The last essay investigates the determinants of primary school enrollment, attendance and child labor in Bolivia, with a special attention at identifying the substitution and complementary relationships between schooling and working. The empirical findings reveal that the increase in enrollment is led by indigenous children and those living in urban areas. Moreover, contrary to common belief, being extremely poor and indigenous are the main determinants of school attendance; while extremely poor children increased their school attendance, they were not able to reduce child labor. On the other hand, indigenous children made them substitutes increasing schooling and reducing child labor.
Different econometric techniques have been used, among which Ordinary Least Squares, Fixed Effects, Instrumental Variables, Generalized Methods of Moments estimations, Stochastic Frontier Analysis, Cointegrated Vector Autoregression and Multivariate Probit models
Structure-function relationships in the oligopeptide transporter PepT1.
No full textThe proton-dependent di- and tripeptide transporter PepT1 represents the major route of dietary amino acid intake in the intestine of many species. This transporter belongs to the solute carrier family SLC15 and because of its electrogenic properties it may be studied both through electrophysiological and radiotracer uptake experiments.
In this work some functional and structural aspects of PepT1 have been investigated at the molecular level. In addition to the physiological relevance, understanding of the details of its mechanisms of operation is important since PepT1 appears to be involved in the absorption of many important, orally administered, drugs such as antibiotics, angiotensin-converting inhibitors, and antiviral agents.
The electrophisyiological and biophysical properties of PepT1 expressed in Xenopus oocytes were investigated with two-electrode voltage-clamp.
Most of the above functional observations were derived from uptake data, in absence of control of the membrane voltage, or from electrophysiological measurement of steady transport currents, in the presence of a dipeptide substrate. Important additional informations regarding the transport mechanism may arise from measurement of presteady-state currents, the electrophysiological signals that can be observed in absence of organic substrate, and that represent the first steps in the transport cycle. A unified kinetic model for PepT1 has been devised that can describe the different characteristics of the isoforms of different species, with respect to both presteady-state and transport-associated currents.
Mutational studies have provided significant evidence for the functional role of some residues in PepT1. Particularly Arg282 and Asp341, in the transmembrane domain 7 and 8 of the transporter, have been reported to form a charge pair that may break and reform during the transport cycle. The attention has been focused on these two oppositely charged aminoacids to better understand their functional role in the absorption pathway.
Finally, the functional and structural basis of reverse operation of wild-type and mutated forms of PepT1 have been studied. Mutants in the putative charge pair residues Arg282 and Asp341 of rabbit PepT1 have been shown exhibit properties useful to better understand the possibility of reverse transport. This reversed mode of operation may be either the effect or the cause of abnormal or pathological conditions
Temporal and spatial dynamics of organic chemicals in the environment with a multimedia fate model.
No full textOnce chemicals are released into the environment, their environmental fate is determined by their usage and discharge, partitioning tendencies, and by transport and transformation processes, which may vary greatly in space and time. In the last three decades, an increasing number of models based on the concept of “communicating media” have been developed to understand and predict the fate of chemicals in the environment. The tendency emerging from recent experimental and modelling efforts is to consider the fate of chemicals more closely related to the dynamics characterizing the “environmental scenario”. This thesis aims to give a contribution to the investigation of the role played by temporal and spatial dynamics of key chemodynamic processes and environmental properties in influencing the fate of chemicals in the environment. The focus of the thesis was the development of a new, dynamic and site specific multimedia fate model (MFM) of organic chemicals in the air-soil system. The model, named SoilPlus, is described in Chapter 1 and includes two dynamic air compartments, a multicompartmental litter, acting as an “intermediate” compartment between the air and a multicompartmental soil. The model also performs a complete water balance, accounting also for dissolved organic carbon (DOC) fluxes in the litter/soil system. The model underwent a process of benchmarking and then was used to investigate the role of the litter as a buffer compartment between soil and air, modelling hexachlorobenzene as an example of persistent organic pollutant (POP). SoilPlus uses the same two air compartments developed for the AirFug model, described in Chapter 2. AirFug integrates a new MFM, characterized by two dynamic-air compartments and a single soil compartment, and a meteorological preprocessor; after the model benchmarking, it was evaluated against experimental data from the literature regarding diel (less than 24 hours) variations of PCBs concentrations in urban air. The process of development of these two models prompted to investigate a suitable numerical solution for the equation system describing the chemical mass balance. Chapter 3 is focused on a critical evaluation of the performance of three different numerical methods suitable for models based on adjacent compartments. One of the tested methods was then implemented in the spatial-explicit version of SoilPlus developed and described in Chapter 4. This version of the model was applied to a geographic explicit scenario (a small agricultural basin) for which measured concentrations of pesticides in water were available, in order to evaluate the benefits arising from considering a more spatially resolved scenario (up to the field-scale) on the calculation of environmental concentrations.
Chapter 5, finally, summarizes the results of a recent workshop held at the University of Lancaster in 2009 focused on the need to consider cross-fertilization between the POP-cycle and C-cycle communities in order to more accurately predict future exposure scenarios for POPs