Isotopic fractionation study towards massive star-forming regions across the Galaxy

One of the most important tools to investigate the chemical history of our Galaxy and our own Solar System is to measure the isotopic fractionation of chemical elements. In the present study new astronomical observations devoted to the study of hydrogen and nitrogen fractionation (D/H and 14N/15N ratios) of molecules, towards massive star-forming regions in different evolutionary phases, have been presented. Moreover, a new detailed theoretical study of carbon fractionation, 12C/13C ratios, has been done. One of the main results was the confirmation that the 14N/15N ratio increases with the galactocentric distance, as predicted by stellar nucleosynthesis Galactic chemical evolution models. This work gives new important inputs on the understanding of local chemical processes that favor the production of molecules with different isotopes in star-forming regions

Studio di un sistema di distribuzione a geometria variabile per un motore a combustione interna ad uso motociclistico

Un sistema di distribuzione a geometria variabile è stato studiato per essere impiegato su un motore motociclistico esistente. Attraverso simulazioni CFD monodimensionali sono state individuate le variazioni migliori ed, in seguito ad una esauriente ricerca sullo stato dell'arte, è stato scelto il meccanismo in grado di realizzarle. Una trattazione analitica ed un'analisi cinematica numerica hanno consentito di adattare il meccanismo alle esigenze del motore in studio in modo da ottenere leggi d'alzata delle valvole che consentissero il conseguimento di incrementi delle prestazioni

Protonated CO2 in massive star-forming clumps

Interstellar CO2 is an important reservoir of carbon and oxygen, and one of the major constituents of the icy mantles of dust grains, but it is not observable directly in the cold gas because has no permanent dipole moment. Its protonated form, HOCO+, is believed to be a good proxy for gaseous CO2. However, it has been detected in only a few star-forming regions so far, so that its interstellar chemistry is not well understood. We present new detections of HOCO+ lines in 11 high-mass star-forming clumps. Our observations increase by more than three times the number of detections in star-forming regions so far. We have derived beam-averaged abundances relative to H2 in between 0.3 and 3.8 x 10^{-11}. We have compared these values with the abundances of H13CO+, a possible gas-phase precursor of HOCO+, and CH3OH, a product of surface chemistry. We have found a positive correlation with H13CO+, while with CH3OH there is no correlation. We suggest that the gas-phase formation route starting from HCO+ plays an important role in the formation of HOCO+, perhaps more relevant than protonation of CO2 (upon evaporation of this latter from icy dust mantles).Comment: 5 pages, 4 figures, 1 table, accepted for publication in MNRA

Le multinazionali in America Latina

Le imprese multinazionali costituiscono una componente fondamentale del processo di globalizzazione. Capitali, tecnologie e conoscenze, opportunità di lavoro, varietà di prodotti e accesso ai mercati internazionali concedono alle multinazionali un notevole potere contrattuale nei confronti delle imprese minori e delle autorità nei paesi in cui investono, vantando un forte “appeal” nelle decisioni politiche. Dopo un capitolo introduttivo illustrante effetti e determinanti degli investimenti all’estero di queste imprese, l’elaborato si concentra sul continente latino americano, analizzandone i tratti caratteristici della politica economica in età contemporanea. Ricca di risorse, materie prime e di mercati promettenti, con i suoi 500 milioni di consumatori, questa terra rappresenta un territorio ambito e spesso conteso, testimone negli ultimi cinquant’anni di fondamentali cambiamenti politici ed economici. Dopo un lungo periodo di protezionismo e dirigismo imposto dai locali governi, molte delle barriere fino ad allora imposte, si sgretolarono, permettendo l’ingresso e il successivo insediamento nel territorio di grandi imprese multinazionali. La maggior parte delle realtà locali dovette cedere alla concorrenza e divenne oggetto di acquisizioni da parte delle aziende estere; al contrario altre, storicamente legate a i propri mercati, riuscirono ad espandersi oltre i propri confini alla ricerca di nuove opportunità, trasformandosi in multilatinas. Molte di queste sono oggi multinazionali di livello mondiale, e costituiscono la base dello sviluppo e della crescita economica di paesi come il Brasile, il Cile ed il Messico. E proprio a quest’ultimo Stato viene dedicata la parte conclusiva della tesi, con un’ampia digressione sulle emergenti multinazionali messicane e sulla loro storia, meritevoli con la loro intraprendenza e con i loro successi di aver reso nuovamente grande questa nazione

Combined model for 15N\rm ^{15}N, 13C\rm ^{13}C, and spin-state chemistry in molecular clouds

We present a new gas-grain chemical model for the combined isotopic fractionation of carbon and nitrogen in molecular clouds, in which the isotope chemistry of carbon and nitrogen is coupled with a time-dependent description of spin-state chemistry. We updated the rate coefficients of some isotopic exchange reactions considered in the literature, and present here a set of new exchange reactions involving molecules substituted in $\rm ^{13}C$ and $\rm ^{15}N$ simultaneously. We apply the model to a series of zero-dimensional simulations representing a set of physical conditions across a prototypical prestellar core, exploring the deviations of the isotopic abundance ratios in the various molecules from the elemental isotopic ratios as a function of physical conditions and time. We find that the $\rm ^{12}C/^{13}C$ ratio can deviate from the elemental ratio by up to a factor of several depending on the molecule, and that there are highly time-dependent variations in the ratios. The $\rm HCN/H^{13}CN$ ratio, for example, can obtain values of less than 10 depending on the simulation time. The $\rm ^{14}N/^{15}N$ ratios tend to remain close to the assumed elemental ratio within $\sim$ ten per cent, with no clear trends as a function of the physical conditions. Abundance ratios between $\rm ^{13}C$-containing molecules and $\rm ^{13}C$+$\rm ^{15}N$-containing molecules show somewhat increased levels of fractionation due to the newly included exchange reactions, though still remaining within a few tens of per cent of the elemental $\rm ^{14}N/^{15}N$ ratio. Our results imply the existence of gradients in isotopic abundance ratios across prestellar cores, suggesting that detailed simulations are required to interpret observations of isotopically substituted molecules correctly, especially given that the various isotopic forms of a given molecule do not necessarily trace the same gas layers.Comment: Accepted to A\&A; abstract abridged to meet arXiv requirement

Production of large Bose-Einstein condensates in a magnetic-shield-compatible hybrid trap

We describe the production of large ${}^{23} \mathrm{Na}$ Bose-Einstein condensates in a hybrid trap characterized by a weak magnetic field quadrupole and a tightly focused infrared beam. The use of small magnetic field gradients makes the trap compatible with the state-of-the-art magnetic shields. By taking advantage of the deep cooling and high efficiency of gray molasses to improve the initial trap loading conditions, we produce condensates composed of as much as $7$ million atoms in less than $30 \; \mathrm{s}$.Comment: 8 pages, 3 figure