Experimental analysis of coaxial jets: instability, flow and mixing characterization

The velocity and mixing field of two turbulent jets configurations have been experimentally characterized by means of cold- and hot-wire anemometry in order to investigate the effects of the initial conditions on the flow development. In particular, experiments have been focused on the effect of the separation wall between the two streams on the flow field. The results of the experiments have pointed out that the wake behind a thick wall separating wall has a strong influence on the flow field evolution. For instance, for nearly unitary velocity ratios, a clear vortex shedding from the wall is observable. This phenomenon enhances the mixing between the inner and outer shear layer. This enhancement in the fluctuating activity is a consequence of a local absolute instability of the flow which, for a small range of velocity ratios, behaves as an hydrodynamic oscillator with no sensibility to external perturbations. It has been suggested indeed that this absolute instability can be used as a passive method to control the flow evolution. Finally, acoustic excitation has been applied to the near field in order to verify whether or not the observed vortex shedding behind the separating wall is due to a global oscillating mode as predicted by the theory. A new scaling relationship has been also proposed to determine the preferred frequency for nearly unitary velocity ratios. The proposed law takes into account both the Reynolds number and the velocity ratio dependence of this frequency and, therefore, improves all the previously proposed relationships.

Modeling hydrothermal system: deriving observables and hydrothermal instability in volcanic and non-volcanic setting

Hydrothermal fluids are a fundamental resource for understanding and monitoring volcanic and non-volcanic systems. This thesis is focused on the study of hydrothermal system through numerical modeling with the geothermal simulator TOUGH2. Several simulations are presented, and geophysical and geochemical observables, arising from fluids circulation, are analyzed in detail throughout the thesis. In a volcanic setting, fluids feeding fumaroles and hot spring may play a key role in the hazard evaluation. The evolution of the fluids circulation is caused by a strong interaction between magmatic and hydrothermal systems. A simultaneous analysis of different geophysical and geochemical observables is a sound approach for interpreting monitored data and to infer a consistent conceptual model. Analyzed observables are ground displacement, gravity changes, electrical conductivity, amount, composition and temperature of the emitted gases at surface, and extent of degassing area. Results highlight the different temporal response of the considered observables, as well as the different radial pattern of variation. However, magnitude, temporal response and radial pattern of these signals depend not only on the evolution of fluid circulation, but a main role is played by the considered rock properties. Numerical simulations highlight differences that arise from the assumption of different permeabilities, for both homogeneous and heterogeneous systems. Rock properties affect hydrothermal fluid circulation, controlling both the range of variation and the temporal evolution of the observable signals. Low temperature fumaroles and low discharge rate may be affected by atmospheric conditions. Detailed parametric simulations were performed, aimed to understand the effects of system properties, such as permeability and gas reservoir overpressure, on diffuse degassing when air temperature and barometric pressure changes are applied to the ground surface. Hydrothermal circulation, however, is not only a characteristic of volcanic system. Hot fluids may be involved in several mankind problems, such as studies on geothermal engineering, nuclear waste propagation in porous medium, and Geological Carbon Sequestration (GCS). The current concept for large-scale GCS is the direct injection of supercritical carbon dioxide into deep geological formations which typically contain brine. Upward displacement of such brine from deep reservoirs driven by pressure increases resulting from carbon dioxide injection may occur through abandoned wells, permeable faults or permeable channels. Brine intrusion into aquifers may degrade groundwater resources. Numerical results show that pressure rise drives dense water up to the conduits, and does not necessarily result in continuous flow. Rather, overpressure leads to new hydrostatic equilibrium if fluids are initially density stratified. If warm and salty fluid does not cool passing through the conduit, an oscillatory solution is then possible. Parameter studies delineate steady-state (static) and oscillatory solutions.

Dynamic stabilization of Rayleigh-Taylor instability of ablation fronts in inertial confinement fusion

One of the most important problems in inertial confinement fusion is how to find a way to mitigate the onset of the Rayleigh-Taylor instability which arises in the ablation front during the compression. In this thesis it is studied in detail the possibility of using for such a purpose the well-known mechanism of dynamic stabilization, already applied to other dynamical systems such as the inverted pendulum. In this context, a periodic acceleration superposed to the background gravity generates a vertical vibration of the ablation front itself. The effects of different driving modulations (Dirac deltas and square waves) are analyzed from a theoretical point of view, with a focus on stabilization of ion beam driven ablation fronts, and a comparison is made, in order to look for optimization.

Institutional Processes and Discursive Strategies: Rhetoric and Vocabulary Analysis of CSR and Sustainability

The candidate tackled an important issue in contemporary management: the role of CSR and Sustainability. The research proposal focused on a longitudinal and inductive research, directed to specify the evolution of CSR and contribute to the new institutional theory, in particular institutional work framework, and to the relation between institutions and discourse analysis. The documental analysis covers all the evolution of CSR, focusing also on a number of important networks and associations. Some of the methodologies employed in the thesis have been employed as a consequence of data analysis, in a truly inductive research process. The thesis is composed by two section. The first section mainly describes the research process and the analyses results. The candidates employed several research methods: a longitudinal content analysis of documents, a vocabulary research with statistical metrics as cluster analysis and factor analysis, a rhetorical analysis of justifications. The second section puts in relation the analysis results with theoretical frameworks and contributions. The candidate confronted with several frameworks: Actor-Network-Theory, Institutional work and Boundary Work, Institutional Logic. Chapters are focused on different issues: a historical reconstruction of CSR; a reflection about symbolic adoption of recurrent labels; two case studies of Italian networks, in order to confront institutional and boundary works; a theoretical model of institutional change based on contradiction and institutional complexity; the application of the model to CSR and Sustainability, proposing Sustainability as a possible institutional logic.

Institutional Complexity and Technology Transfer: A Theoretical and Empirical Analysis

This Doctoral Thesis unfolds into a collection of three distinct papers that share an interest in institutional theory and technology transfer. Taking into account that organizations are increasingly exposed to a multiplicity of demands and pressures, we aim to analyze what renders this situation of institutional complexity more or less difficult to manage for organizations, and what makes organizations more or less successful in responding to it. The three studies offer a novel contribution both theoretically and empirically. In particular, the first paper “The dimensions of organizational fields for understanding institutional complexity: A theoretical framework” is a theoretical contribution that tries to better understand the relationship between institutional complexity and fields by providing a framework. The second article “Beyond institutional complexity: The case of different organizational successes in confronting multiple institutional logics” is an empirical study which aims to explore the strategies that allow organizations facing multiple logics to respond more successfully to them. The third work “ How external support may mitigate the barriers to university-industry collaboration” is oriented towards practitioners and presents a case study about technology transfer in Italy.

A threshold hypothesis of institutional change: collective action in the Italian Alps during the 13th - 19th centuries.

This dissertation is about collective action issues in common property resources. Its focus is the “threshold hypothesis,” which posits the existence of a threshold in group size that drives the process of institutional change. This hypothesis is tested using a six-century dataset concerning the management of the commons by hundreds of communities in the Italian Alps. The analysis seeks to determine the group size threshold and the institutional changes that occur when groups cross this threshold. There are five main findings. First, the number of individuals in villages remained stable for six centuries, despite the population in the region tripling in the same period. Second, the longitudinal analysis of face-to-face assemblies and community size led to the empirical identification of a threshold size that triggered the transition from informal to more formal regimes to manage common property resources. Third, when groups increased in size, gradual organizational changes took place: large groups split into independent subgroups or structured interactions into multiple layers while maintaining a single formal organization. Fourth, resource heterogeneity seemed to have had no significant impact on various institutional characteristics. Fifth, social heterogeneity showed statistically significant impacts, especially on institutional complexity, consensus, and the relative importance of governance rules versus resource management rules. Overall, the empirical evidence from this research supports the “threshold hypothesis.” These findings shed light on the rationale of institutional change in common property regimes, and clarify the mechanisms of collective action in traditional societies. Further research may generalize these conclusions to other domains of collective action and to present-day applications.

Flessibilità e controllo sindacale nel mercato del lavoro contemporaneo: il caso del contratto a tempo determinato

Il lavoro di ricerca che si presenta è suddiviso in tre capitoli nei quali, da altrettanti punti di osservazione, è analizzato il tema della instabilità del lavoro. Nel primo capitolo, il candidato evidenzia le cause che hanno determinato il vorticoso aumento di utilizzo dei contratti di lavoro flessibili e, a tal proposito, da un prospettiva extra-nazionale, analizza le direttive europee e, i principi comuni e le guidelines che, nel percorso di sviluppo della strategia europea per l’occupazione, hanno posto la flexicurity come modello di mercato europeo tipico; dalla medesima prospettiva, prendendo spunto dai cambiamenti del mercato globale, si pone attenzione all’analisi economica del diritto del lavoro e, in particolare, alle conseguenze che le trasformazioni economiche generano sulla capacità di questa materia di tenere elevato il grado di sicurezza occupazionale connesso alla stipula dei contratti di lavoro. Il secondo capitolo è dedicato al ruolo svolto in Italia dai sindacati sul tema della flessibilità. In tal senso, l’autore evidenzia come la funzione “istituzionale” cui sono chiamate anche le organizzazioni dei lavoratori abbia caratterizzato le scelte di politica sindacale in materia di lavori temporanei; è così preso in esame il concetto di flessibilità “contrattata”, come già emerso in dottrina, e si teorizza la differenza tra rinvii “aperti” e rinvii “chiusi”, quali differenti forme di delega di potere normativo alle parti sociali in materia di flessibilità. Nel terzo ed ultimo capitolo l’autore tenta di evidenziare i vantaggi e le funzioni che derivano dall’utilizzo del contratto a termine, quale principale forma di impiego flessibile del nostro mercato del lavoro. Premessi tali benefici viene formulato un giudizio critico rispetto al grado di liberalizzazione che, con le ultime riforme, è stato ammesso per questo istituto sempre più strumento di arbitrio del datore di lavoro nella scelta della durata e delle condizioni di svolgimento della prestazione di lavoro.