Studio e progettazione di dettaglio di un sistema elettro-idraulico per posizionamento angolare di precisione di particolari meccanici rotanti

Questa tesi di laurea, svolta in collaborazione con Oto Melara S.p.a, riguarda lo studio e la progettazione di un sistema per la graduazione meccanica di una tipologia di munizioni calibro 127mm. Lo studio si inserisce nella progettazione di un nuovo complesso navale che dovrà essere in grado di gestire, oltre a una tipologia innovativa di munizioni (programmabili a contatto), anche munizioni di tipo standard (provviste di una spoletta a graduazione meccanica)

Spin physics with CLAS and CLAS12

An extensive experimental program to measure the spin structure of the nucleon has been conducted in Hall B at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS) in the last decade. Using a longitudinally polarized beam scattering off longitudinally polarized NH3 and ND3 targets, inclusive Deep Inelastic Scattering (DIS), Semi‐Inclusive DIS (SIDIS) and DVCS experiments were carried out that make a significant contributions to the existing data. The inclusive double spin asymmetry A∥ was measured over a large range in Q2 and W, providing data of impressively high precision that give a better understanding of the structure of the nucleon in the DIS and the valence quarks regions. Using parameterizations A2 and F1 from world data, the virtual photon asymmetry A1 and the structure function g1 were extracted in a Q2 range from 0.05 to 5 GeV2 and a W range from 1.08 to 3.0 GeV. As a result of the extended kinematical range, first moments of structure functions were measured over a large range in Q2 and duality was tested. Furthermore, newly proposed experiments, using an upgraded accelerator at Jefferson Laboratory and an improved CLAS detector (CLAS12), are expected to increase the statistical precision of the current measurements and extend them to kinematic regions presently not accessible, such as high x. This will improve significantly our knowledge of the structure of the nucleon, including parton distribution functions, duality and higher twists contributions

Nucleon spin structure at Jefferson Lab

In the past decade an extensive experimental program to measure the spin structure of the nucleon has been carried out in the three halls at Jefferson Lab. Using a longitudinally polarized beam scattering off longitudinally or transversely polarized 3He, NH3 and ND3 targets, the double spin asymmetries A∥ and A⊥ were measured, providing data of impressively high precision that gives a better understanding of the structure of the nucleon in the deep inelastic scattering and the valence quarks regions. The virtual photon asymmetries A1,2 and polarized structure functions g1,2 were also extracted for the proton, neutron and deuteron over large kinematic ranges, allowing the extraction of first moments and the testing of sum rules and duality

Quantitative physiology of bacterial survival under carbon starvation and temperature stress

A large number of the bacteria on Earth live for long periods in states of very low metabolic activity and little or no growth due to starvation and other environmental stresses. Within millions of years, bacteria have developed several strategies to adapt to many different environments, where they survive and evolve to optimize their fitness and to undergo rapid division cycles when conditions become favourable. However, many of these survival strategies are still a puzzle and relatively little is known about the mechanisms that underpin the dominant modes of bacterial existence. This is particularly alarming, as the growth-arrest phase has become crucial to understand the contribution of microorganisms to human physiology and predisposition to disease as well as microbial tolerance and resistance to antibiotics. The dearth of information is mainly due to the difficulties in defining, reproducing and measuring bacterial behaviours in growth-arrest states, which may often seem erratic and unpredictable, while cell physiology is similarly diverse and often specific to the particular environmental conditions. Thus, determining how molecular contributions affect survival is challenging. This explains why, in the last century, bacteria have been mainly studied during the exponential growth phase, which is, on the contrary, a well-defined and reproducible steady state of constant growth, gene expression and molecular compositions. As a result, an increasing combined use of experiments and predictive models focused on this phase has provided a deep understanding of bacterial physiology and gene regulation during growth. A similar quantitative approach that focuses on the growth-arrest phase is largely missing. In this thesis, we contribute to fill this gap by developing new quantitative approaches to investigate bacterial physiology in hostile environments where stresses, such as lack of nutrients and additional environmental perturbations, like temperature increase, force the cells to activate strategies of survival. To do so, we choose to work with the bacterium Escherichia coli (E. coli) that, among the estimated 10^12 microbial species living in our planet, is one of the most studied thanks to its hardiness, versatility and ease of handling. In Chapter 1, we provide an overview of the physiology of E. coli life cycle and of the main quantitative methods so far used to study it, especially focusing on its behaviour during the growth-arrest phase. In Chapter 2, we establish the missing quantitative approach to study E. coli physiology in the death phase. We show that in carbon starvation, an exponential decay of viability emerges as a collective phenomenon, with viable cells recycling nutrients from dead cells to maintain viability. The observed collective death rate is determined by the maintenance rate of viable cells and the amount of nutrients recovered from dead cells, the yield. Using this relation, we study the cost of a wasteful enzyme during starvation and the benefit of the stress response sigma factor RpoS. While the enzyme activity increases maintenance and thereby the death rate, RpoS improves biomass recycling, decreasing the death rate. Our approach thus enables quantitative analyses of how cellular components affect the survival of non-growing cells. In Chapter 3, we use the quantitative approach developed in the previous chapter to study how survival of E. coli in carbon starvation depends on the previous culture conditions. We show that environments that support only slow growth lead to longer survival in starvation because of a decrease of maintenance rate, meaning that slower growing cells need less energy to survive. Our results suggest a physiological trade-off between the ability to proliferate fast and the ability to survive long that could shed light on the long-standing question of why bacteria outside of laboratory environments are not optimized for fast growth. In Chapter 4, we study E. coli physiology under the combined stresses of carbon starvation and high temperatures, characterizing a thermal fuse that leads to a dormant and antibiotic persistent sub-population. This fuse is implemented by a thermally unstable enzyme, MetA, in the methionine synthesis pathway. The combination of a positive feed-back in the methionine system and a dual-use of methionine for protein synthesis and as a methyl-donor results in the bacterial population splitting into two distinct states at elevated temperatures, growing and dormant. We then reveal that these dormant bacteria not only survive antibiotic treatment, but also heat shocks, suggesting that the thermal fuse has originally evolved as a ''bet-hedging'' strategy to ensure survival in heat shocks. Our findings, summarized in Chapter 5, pave the way for the development of a new theoretical framework and experimental approach to understand bacterial physiology in the growth-arrest phase, by linking phenomenological modeling to molecular mechanisms.Eine große Anzahl der Bakterien auf der Erde lebt über große Zeiträume in einem Zustand mit sehr geringer Stoffwechselaktivität und nur geringem oder keinem Wachstum. Ein Grund dafür sind widrige Umwelteinflüsse und die damit einhergehenden Belastungen wie beispielsweise Ressourcenmangel. Innerhalb von Millionen von Jahren haben Bakterien diverse Strategien zur Anpassung an verschiedene Umgebungen, in denen sie überleben und sich weiterentwickeln, entwickelt, um ihre Fitness zu optimieren und bei günstigen Bedingungen schnelle Teilungszyklen zu durchlaufen. Viele dieser Überlebensstrategien sind jedoch immer noch ein Rätsel und es ist nur relativ wenig über die Mechanismen bekannt, die den dominanten Formen der bakteriellen Existenz zu Grunde liegen. Dies ist von besonderer Bedeutung, da die Phase unterdrückten Wachstums entscheidend ist, um den Beitrag von Mikroorganismen zur menschlichen Physiologie und Anfälligkeit für Krankheiten, sowie zur mikrobiellen Verträglichkeit und Antibiotikaresistenz zu verstehen. Der Mangel an Informationen ist hauptsächlich auf die Schwierigkeiten bei der Definition, Reproduktion und Messung des Verhaltens von Bakterien in Zuständen des Wachstumsstillstands zurückzuführen, die oft unberechenbar und unvorhersehbar erscheinen, während die Zellphysiologie ähnlich vielfältig und oft spezifisch für die jeweiligen Umgebungsbedingungen ist. Daher ist es schwierig zu bestimmen, wie sich molekulare Mechanismen auf das Überleben auswirken. Dies erklärt, warum im letzten Jahrhundert Bakterien hauptsächlich während der exponentiellen Wachstumsphase untersucht wurden, die im Gegenteil ein genau definierter und reproduzierbarer Gleichgewichtszustand des konstanten Wachstums, der Genexpression und der molekularen Zusammensetzung ist. Infolgedessen hat eine zunehmende Kombination von Experimenten und Vorhersagemodellen, die sich auf diese Phase konzentrieren, ein tiefes Verständnis der bakteriellen Physiologie und Genregulation während des Wachstums geliefert. Ein ähnlicher quantitativer Ansatz, der sich auf die Phase der Stagnation konzentriert, fehlt weitgehend. In dieser Doktorarbeit tragen wir dazu bei, diese Lücke durch die Entwicklung neuer quantitativer Ansätze zur Untersuchung der bakteriellen Physiologie in ungünstigen Umgebungen zu füllen, in denen Stressfaktoren, wie beispielsweise Nährstoffmangel, auftreten und zusätzliche umweltbedingte Störungen, wie eine Temperaturerhöhung, die Zellen zwingen, Strategien zum Überleben zu aktivieren. Dazu arbeiten wir mit dem Bakterium Escherichia coli (E. coli), das unter den circa 10^12 mikrobiellen Spezies, die auf unserem Planeten leben, wegen seiner Widerstandsfähigkeit, Vielseitigkeit und einfachen Handhabung eines der am besten untersuchten Bakterien darstellt. In Kapitel 1, geben wir einen Überblick über die Physiologie des Lebenszyklus von E. coli und über die wichtigsten bisher verwendeten quantitativen Methoden, wobei wir uns auf das Verhalten während der Wachstumsphase konzentrieren. In Kapitel 2, stellen wir den fehlenden quantitativen Ansatz zur Untersuchung der Physiologie von E. coli während der Sterbephase fest. Wir zeigen, dass bei Kohlenstoffmangel ein exponentieller Zerfall der Lebensfähigkeit als kollektives Phänomen auftritt, wobei lebensfähige Zellen Nährstoffe aus toten Zellen recyceln, um die Lebensfähigkeit aufrechtzuerhalten. Die beobachtete kollektive Sterberate wird durch die Erhaltungsrate lebensfähiger Zellen und die Menge an Nährstoffen, die aus toten Zellen als Ertrag gewonnen werden, bestimmt. Unter Verwendung dieser Beziehung untersuchen wir die Kosten einer verschwenderischen Enzymaktivität während des Hungerns und den Nutzen des Sigma Faktors RpoS für die Stressreaktion. Während diese Aktivität die Instandhaltung und damit die Sterblichkeitsrate erhöht, verbessert RpoS das Recycling der Biomasse und senkt die Sterblichkeitsrate. Unser Ansatz ermöglicht daher quantitative Analysen darüber, wie sich zelluläre Komponenten auf das Überleben nicht wachsender Zellen auswirken. In Kapitel 3, verwenden wir den im vorherigen Kapitel entwickelten quantitativen Ansatz, um zu untersuchen, wie das Überleben von E. coli bei Kohlenstoffmangel von den vorherigen Kulturbedingungen abhängt. Wir zeigen, dass Umgebungen, die nur langsames Wachstum unterstützen, aufgrund einer verringerten Erhaltungsrate zu einem längeren Überleben führen, was bedeutet, dass langsamer wachsende Zellen weniger Energie zum Überleben benötigen. Unsere Ergebnisse legen einen physiologischen Kompromiss zwischen der Fähigkeit, sich schnell zu vermehren, und der Fähigkeit, lange zu überleben, nahe, der Auschluss darüber geben könnte, warum Bakterien außerhalb von Laborumgebungen nicht für schnelles Wachstum optimiert sind. In Kapitel 4, untersuchen wir die Physiologie von E. coli unter dem kombinierten Stress von Kohlenstoffmangel und hohen Temperaturen und charakterisieren eine thermische Sicherung, die zu einer ruhenden und antibiotisch persistierenden Subpopulation führt. Diese Sicherung wird durch ein thermisch instabiles Enzym, MetA, im Methioninsyntheseweg implementiert. Die Kombination aus einer positiven Rückkopplung im Methioninsystem und einer doppelten Verwendung von Methionin für die Proteinsynthese und als Methyldonor führt dazu, dass sich die Bakterienpopulation bei erhöhten Temperaturen in zwei verschiedene Zustände aufspaltet, wobei jeweils eine Subpopulation wächst und die Andere schläft. Wir zeigen dann, dass diese ruhenden Bakterien nicht nur eine Antibiotikabehandlung, sondern auch Hitzeschocks überstehen, was darauf hindeutet, dass sich die thermische Sicherung ursprünglich als eine ''bet-hedging'' Strategie entwickelt hat, um das Überleben bei Hitzeschocks sicherzustellen. Unsere Ergebnisse, die in Kapitel 5 zusammengefasst sind, ebnen den Weg für die Entwicklung eines neuen theoretischen Rahmens und experimentellen Ansatzes zum Verständnis der Bakterienphysiologie in der Phase des Wachstumsstopps, indem phänomenologische Modelle mit molekularen Mechanismen verknüpft werden

A estrutura a termo como previsor da atividade econômica real

TCC (graduação) - Universidade Federal de Santa Catarina. Centro Sócio-Econômico. Economia.O objetivo deste trabalho é a analisar o poder de previsão da estrutura a termo da taxa de juros sobre o produto, investimento, gasto do governo, consumo das famílias, exportações, importações e IBC-BR. Será utilizada a análise de componentes principais para estimar os fatores nível, inclinação e curvatura da estrutura termo. O modelo estimado foi o de mínimos quadrados ordinários e o arcabouço usado para a análise dos dados estará relacionado principalmente aos mecanismos de transmissão da política monetária. O R2 ajustado de todos os modelos estimados foi consideravelmente alto. A curvatura foi determinante na estimação dos melhores modelos selecionados, apresentando significância em praticamente todos os modelos específicos. A inclinação teve significância em alguma defasagem apenas para o consumo das famílias, investimento e gasto do governo. Houve a evidência de um ciclo de juros de curto prazo para o produto, investimento, consumo das famílias, importações, e IBCB

DVCS with longitudinally polarized target using CLAS at 6 GeV

Deeply Virtual Compton Scattering (DVCS) is one of the simplest processes that can be described in terms of Generalized Parton Distributions (GPDs). The target single‐spin asymmetry (target SSA) in the reaction ep⃗→epγ is directly proportional to the imaginary part of the DVCS amplitude, and gives access to a combination of GPDs namely H̃, H, and E. This asymmetry will be measured in a dedicated experiment at Jefferson Lab using the CEBAF 6‐GeV polarized electron beam, a polarized solid‐state 14NH3 target, and the CEBAF Large Acceptance Spectrometer (CLAS) together with the Inner Calorimeter (IC). The expected asymmetry from leading‐order calculations is in the range of 20% to 40%, depending on the kinematics and on the GPD model used. The DVCS amplitude will be mapped out in the Q2 region from 1 to 4 GeV2, xB from 0.15 to 0.55 and −t from 0.1 to 2 GeV2 providing new constraints on the GPDs

First measurement of target and double spin asymmetries for e [over→] p [over→]→ epπ^{0} in the nucleon resonance region above the Δ (1232)

The exclusive channel p→(e→,e′p)π0 was studied in the first and second nucleon resonance regions in the Q2 range from 0.187 to 0.770 GeV2 at Jefferson Lab using the CEBAF Large Acceptance Spectrometer. Longitudinal target and beam-target asymmetries were extracted over a large range of center-of-mass angles of the π0 and compared to the unitary isobar model MAID, the dynamic model by Sato and Lee, and the dynamic model DMT. A strong sensitivity to individual models was observed, in particular for the target asymmetry and in the higher invariant mass region. This data set, once included in the global fits of the above models, is expected to place strong constraints on the electrocoupling amplitudes A1/2 and S1/2 for the Roper resonance N(1400)P11 and the N(1535)S11 and N(1520)D13 states

Photodisintegration of He4 into p+t

The two-body photodisintegration of 4He into a proton and a triton has been studied using the CEBAF Large-Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Real photons produced with the Hall-B bremsstrahlung-tagging system in the energy range from 0.35 to 1.55 GeV were incident on a liquid 4He target. This is the first measurement of the photodisintegration of 4He above 0.4 GeV. The differential cross sections for the γ4He→pt reaction were measured as a function of photon-beam energy and proton-scattering angle and are compared with the latest model calculations by J.-M. Laget. At 0.6-1.2 GeV, our data are in good agreement only with the calculations that include three-body mechanisms, thus confirming their importance. These results reinforce the conclusion of our previous study of the three-body breakup of 3He that demonstrated the great importance of three-body mechanisms in the energy region 0.5-0.8 GeV