A dynamical system approach to data assimilation in chaotic models

The Assimilation in the Unstable Subspace (AUS) was introduced by Trevisan and Uboldi in 2004, and developed by Trevisan, Uboldi and Carrassi, to minimize the analysis and forecast errors by exploiting the flow-dependent instabilities of the forecast-analysis cycle system, which may be thought of as a system forced by observations. In the AUS scheme the assimilation is obtained by confining the analysis increment in the unstable subspace of the forecast-analysis cycle system so that it will have the same structure of the dominant instabilities of the system. The unstable subspace is estimated by Breeding on the Data Assimilation System (BDAS). AUS- BDAS has already been tested in realistic models and observational configurations, including a Quasi-Geostrophicmodel and a high dimensional, primitive equation ocean model; the experiments include both fixed and“adaptive”observations. In these contexts, the AUS-BDAS approach greatly reduces the analysis error, with reasonable computational costs for data assimilation with respect, for example, to a prohibitive full Extended Kalman Filter. This is a follow-up study in which we revisit the AUS-BDAS approach in the more basic, highly nonlinear Lorenz 1963 convective model. We run observation system simulation experiments in a perfect model setting, and with two types of model error as well: random and systematic. In the different configurations examined, and in a perfect model setting, AUS once again shows better efficiency than other advanced data assimilation schemes. In the present study, we develop an iterative scheme that leads to a significant improvement of the overall assimilation performance with respect also to standard AUS. In particular, it boosts the efficiency of regime’s changes tracking, with a low computational cost. Other data assimilation schemes need estimates of ad hoc parameters, which have to be tuned for the specific model at hand. In Numerical Weather Prediction models, tuning of parameters — and in particular an estimate of the model error covariance matrix — may turn out to be quite difficult. Our proposed approach, instead, may be easier to implement in operational models.

Creazione e sviluppo di corpora multimediali. Nuove metodologie di ricerca nella traduzione audiovisiva

The construction and use of multimedia corpora has been advocated for a while in the literature as one of the expected future application fields of Corpus Linguistics. This research project represents a pioneering experience aimed at applying a data-driven methodology to the study of the field of AVT, similarly to what has been done in the last few decades in the macro-field of Translation Studies. This research was based on the experience of Forlixt 1, the Forlì Corpus of Screen Translation, developed at the University of Bologna’s Department of Interdisciplinary Studies in Translation, Languages and Culture. As a matter of fact, in order to quantify strategies of linguistic transfer of an AV product, we need to take into consideration not only the linguistic aspect of such a product but all the meaning-making resources deployed in the filmic text. Provided that one major benefit of Forlixt 1 is the combination of audiovisual and textual data, this corpus allows the user to access primary data for scientific investigation, and thus no longer rely on pre-processed material such as traditional annotated transcriptions. Based on this rationale, the first chapter of the thesis sets out to illustrate the state of the art of research in the disciplinary fields involved. The primary objective was to underline the main repercussions on multimedia texts resulting from the interaction of a double support, audio and video, and, accordingly, on procedures, means, and methods adopted in their translation. By drawing on previous research in semiotics and film studies, the relevant codes at work in visual and acoustic channels were outlined. Subsequently, we concentrated on the analysis of the verbal component and on the peculiar characteristics of filmic orality as opposed to spontaneous dialogic production. In the second part, an overview of the main AVT modalities was presented (dubbing, voice-over, interlinguistic and intra-linguistic subtitling, audio-description, etc.) in order to define the different technologies, processes and professional qualifications that this umbrella term presently includes. The second chapter focuses diachronically on various theories’ contribution to the application of Corpus Linguistics’ methods and tools to the field of Translation Studies (i.e. Descriptive Translation Studies, Polysystem Theory). In particular, we discussed how the use of corpora can favourably help reduce the gap existing between qualitative and quantitative approaches. Subsequently, we reviewed the tools traditionally employed by Corpus Linguistics in regard to the construction of traditional “written language” corpora, to assess whether and how they can be adapted to meet the needs of multimedia corpora. In particular, we reviewed existing speech and spoken corpora, as well as multimedia corpora specifically designed to investigate Translation. The third chapter reviews Forlixt 1's main developing steps, from a technical (IT design principles, data query functions) and methodological point of view, by laying down extensive scientific foundations for the annotation methods adopted, which presently encompass categories of pragmatic, sociolinguistic, linguacultural and semiotic nature. Finally, we described the main query tools (free search, guided search, advanced search and combined search) and the main intended uses of the database in a pedagogical perspective. The fourth chapter lists specific compilation criteria retained, as well as statistics of the two sub-corpora, by presenting data broken down by language pair (French-Italian and German-Italian) and genre (cinema’s comedies, television’s soapoperas and crime series). Next, we concentrated on the discussion of the results obtained from the analysis of summary tables reporting the frequency of categories applied to the French-Italian sub-corpus. The detailed observation of the distribution of categories identified in the original and dubbed corpus allowed us to empirically confirm some of the theories put forward in the literature and notably concerning the nature of the filmic text, the dubbing process and Italian dubbed language’s features. This was possible by looking into some of the most problematic aspects, like the rendering of socio-linguistic variation. The corpus equally allowed us to consider so far neglected aspects, such as pragmatic, prosodic, kinetic, facial, and semiotic elements, and their combination. At the end of this first exploration, some specific observations concerning possible macrotranslation trends were made for each type of sub-genre considered (cinematic and TV genre). On the grounds of this first quantitative investigation, the fifth chapter intended to further examine data, by applying ad hoc models of analysis. Given the virtually infinite number of combinations of categories adopted, and of the latter with searchable textual units, three possible qualitative and quantitative methods were designed, each of which was to concentrate on a particular translation dimension of the filmic text. The first one was the cultural dimension, which specifically focused on the rendering of selected cultural references and on the investigation of recurrent translation choices and strategies justified on the basis of the occurrence of specific clusters of categories. The second analysis was conducted on the linguistic dimension by exploring the occurrence of phrasal verbs in the Italian dubbed corpus and by ascertaining the influence on the adoption of related translation strategies of possible semiotic traits, such as gestures and facial expressions. Finally, the main aim of the third study was to verify whether, under which circumstances, and through which modality, graphic and iconic elements were translated into Italian from an original corpus of both German and French films. After having reviewed the main translation techniques at work, an exhaustive account of possible causes for their non-translation was equally provided. By way of conclusion, the discussion of results obtained from the distribution of annotation categories on the French-Italian corpus, as well as the application of specific models of analysis allowed us to underline possible advantages and drawbacks related to the adoption of a corpus-based approach to AVT studies. Even though possible updating and improvement were proposed in order to help solve some of the problems identified, it is argued that the added value of Forlixt 1 lies ultimately in having created a valuable instrument, allowing to carry out empirically-sound contrastive studies that may be usefully replicated on different language pairs and several types of multimedia texts. Furthermore, multimedia corpora can also play a crucial role in L2 and translation teaching, two disciplines in which their use still lacks systematic investigation.

Numerical models of trench migration for lateral heterogeneous subducting plates

The aim of this Thesis is to investigate the effect of heterogeneities within the subducting plate on the dynamics of subduction. In particular, I study the motion of the trench for oceanic and continental subduction, first, separately, and, then, together in the same system to understand how they interact. The understanding of these features is fundamental to reconstruct the evolution of complex subduction zones, such as the Central Mediterranean. For this purpose, I developed 2D and 3D numerical models of oceanic and continental subduction where the rheological, geometrical and compositional properties of the plates are varied. In these models, the trench and the overriding plate move self-consistently as a function of the dynamics of the system. The effect of continental subduction on trench migration is largely investigated. Results from a parametric study showed that despite different rheological properties of the plates, all models with a uniform continental crust share the same kinematic behaviour: the trench starts to advance once the continent arrives at the subduction zone. Hence, the advancing mode in continental collision scenarios is at least partly driven by an intrinsic feature of the system. Moreover, the presence of a weak lower crust within the continental plate can lead to the occurrence of delamination. Indeed, by changing the viscosity of the lower crust, both delamination and slab detachment can occur. Delamination is favoured by a low viscosity value of the lower crust, because this makes the mechanical decoupling easier between crust and lithospheric mantle. These features are observed both in 2D and 3D models, but the numerical results of the 3D models also showed that the rheology of the continental crust has a very strong effect on the dynamics of the whole system, since it influences not only the continental part of plate but also the oceanic sides.

Land use management in mountainous areas: combining ground-based and EO (Earth Observation) data to investigate the shallow landsliding susceptibility in the Duron valley (Trento, Italy).

Throughout the alpine domain, shallow landslides represent a serious geologic hazard, often causing severe damages to infrastructures, private properties, natural resources and in the most catastrophic events, threatening human lives. Landslides are a major factor of landscape evolution in mountainous and hilly regions and represent a critical issue for mountainous land management, since they cause loss of pastoral lands. In several alpine contexts, shallow landsliding distribution is strictly connected to the presence and condition of vegetation on the slopes. With the aid of high-resolution satellite images, it's possible to divide automatically the mountainous territory in land cover classes, which contribute with different magnitude to the stability of the slopes. The aim of this research is to combine EO (Earth Observation) land cover maps with ground-based measurements of the land cover properties. In order to achieve this goal, a new procedure has been developed to automatically detect grass mantle degradation patterns from satellite images. Moreover, innovative surveying techniques and instruments are tested to measure in situ the shear strength of grass mantle and the geomechanical and geotechnical properties of these alpine soils. Shallow landsliding distribution is assessed with the aid of physically based models, which use the EO-based map to distribute the resistance parameters across the landscape.

Dynamics of coastal aquifers: data-driven forecasting and risk analysis

This work is focused on the study of saltwater intrusion in coastal aquifers, and in particular on the realization of conceptual schemes to evaluate the risk associated with it. Saltwater intrusion depends on different natural and anthropic factors, both presenting a strong aleatory behaviour, that should be considered for an optimal management of the territory and water resources. Given the uncertainty of problem parameters, the risk associated with salinization needs to be cast in a probabilistic framework. On the basis of a widely adopted sharp interface formulation, key hydrogeological problem parameters are modeled as random variables, and global sensitivity analysis is used to determine their influence on the position of saltwater interface. The analyses presented in this work rely on an efficient model reduction technique, based on Polynomial Chaos Expansion, able to combine the best description of the model without great computational burden. When the assumptions of classical analytical models are not respected, and this occurs several times in the applications to real cases of study, as in the area analyzed in the present work, one can adopt data-driven techniques, based on the analysis of the data characterizing the system under study. It follows that a model can be defined on the basis of connections between the system state variables, with only a limited number of assumptions about the "physical" behaviour of the system.