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Advanced models of supervised structural clustering
Get PDFThe strength and power of structured prediction approaches in machine learning originates from a proper recognition and exploitation of inherent structural dependencies within complex objects, which structural models are trained to output. Among the complex tasks that benefited from structured prediction approaches, clustering is of a special interest. Structured output models based on representing clusters by latent graph structures made the task of supervised clustering tractable. While in practice these models proved effective in solving the complex NLP task of coreference resolution, in this thesis, we aim at exploring their capacity to be extended to other tasks and domains, as well as the methods for performing such adaptation and for improvement in general, which, as a result, go beyond clustering and are commonly applicable in structured prediction.
Studying the extensibility of the structural approaches for supervised clustering, we apply them to two different domains in two different ways. First, in the networking domain, we do clustering of network traffic by adapting the model, taking into account the continuity of incoming data. Our experiments demonstrate that the structural clustering approach is not only effective in such a scenario, but also, if changing the perspective, provides a novel potentially useful tool for detecting anomalies. The other part of our work is dedicated to assessing the amenability of the structural clustering model to joint learning with another structural model, for ranking. Our preliminary analysis in the context of the task of answer-passage reranking in question answering reveals a potential benefit of incorporating auxiliary clustering structures.
Due to the intrinsic complexity of the clustering task and, respectively, its evaluation scenarios, it gave us grounds for studying the possibility and the effect from optimizing task-specific complex measures in structured prediction algorithms. It is common for structured prediction approaches to optimize surrogate loss functions, rather than the actual task-specific ones, in or- der to facilitate inference and preserve efficiency. In this thesis, we, first, study when surrogate losses are sufficient and, second, make a step towards enabling direct optimization of complex structural loss functions. We propose to learn an approximation of a complex loss by a regressor from data. We formulate a general structural framework for learning with a learned loss, which, applied to a particular case of a clustering problem – coreference resolution, i) enables the optimization of a coreference metric, by itself, having high computational complexity, and ii) delivers an improvement over the standard structural models optimizing simple surrogate objectives. We foresee this idea being helpful in many structured prediction applications, also as a means of adaptation to specific evaluation scenarios, and especially when a good loss approximation is found by a regressor from an induced feature space allowing good factorization over the underlying structure
A holistic multi-scale mathematical model of the murine extracellular fluid systems and study of the brain interactive dynamics
Get PDFRecent advances in medical science regarding the interaction and functional role of fluid compartments in the central nervous system have attracted the attention of many researchers across various disciplines. Neurotoxins are constantly cleared from the brain parenchyma through the intramural periarterial drainage system, glymphatic system and meningeal lymphatic system. Impairment of these systems can potentially contribute to the onset of neurological disorders. The goal of this thesis is to contribute to the understanding of brain fluid dynamics and to the role of vascular pathologies in the context of neurological disorders. To achieve this goal, we designed the first multi-scale, closed-loop mathematical model of the murine fluid system, incorporating: heart dynamics, major arteries and veins, microcirculation, pulmonary circulation, venous valves, cerebrospinal fluid (CSF), brain interstitial fluid (ISF), Starling resistors, Monro-Kellie hypothesis, brain lymphatic drainage and the modern concept of CSF/ISF drainage and absorption based on the {\em Bulat-Klarica-Orešković} hypothesis. The mathematical model relies on one-dimensional Partial Differential Equations (PDEs) for blood vessels and on Ordinary Differential Equations (ODEs) for lumped parameter models. The systems of PDEs and ODEs are solved through a high-order finite volume ADER method and through an implicit Euler method. The computational results are validated against literature values and magnetic resonance flow measurements. Furthermore, the model is validated against {\em in-vivo} intracranial pressure waveforms acquired in healthy mice and in mice with impairment of the intracranial venous outflow. Through a systematic use of our computational model in healthy and pathological cases, we provide a complete and holistic neurovascular view of the main murine fluid dynamics. We propose a hypothesis on the working principles of the glymphatic system, opening a new door towards a comprehensive understanding of the mechanisms which link vascular and neurological disorders. In particular, we show how impairment of the cerebral venous outflow might potentially lead to accumulation of solutes in the parenchyma, by altering CSF and ISF dynamics.
This thesis also concerns the development of a high-order ADER-type numerical method for systems of hyperbolic balance laws in networks, based on a new implicit solver for the junction-generalized Riemann problem. The resulting ADER scheme can deal with stiff source terms and can be applied to non-linear systems of hyperbolic balance laws in domains consisting of networks of one-dimensional sub-domains. Also, we design a novel one-dimensional mathematical model for collecting lymphatics coupled with a Electro-Fluid-Mechanical Contraction (EFMC) model for dynamical contractions. The resulting mathematical model gives each lymphangion the autonomous capability to trigger action potentials based on local fluid-dynamical factors
Numerical Modelling of Braiding Processes in Gravel-Bed Rivers
Get PDFGravel-bed braided rivers are distinctive natural environments that provid a wide range of key environmental, economic and recreational services. There is, however,a growing concern that over the twentieth century, an increasing number of braided rivers have metamorphosed into wandering or single thread channels, representing a loss of key habitats, geodiversity and amenity. While in some situations, shifts in channel pattern may be unambiguously linked to abrupt changes in flow or sediment supply, the lack of a theoretical basis underpinning the development and maintenance of braiding makes identification of the cause and effect of channel metamorphosis hazardous. A growing body of research has suggested that the transition between channelpatterns may depend on the poorly understood interaction between the flow regime,sediment supply and vegetation colonisation. Such interactions are governed by critical thresholds, due to changes in flow resistance and bank strength associated with the distribution, form and intensity of vegetation colonisation. Subtle changes in flow or sediment supply that promote vegetation growth or indeed remove itthrough inundation or attrition. This can lead to complex non-linear shifts in the balance of forces that govern sediment transport and bedform morphodynamics, ultimately resulting in one-way changes in channel morphology. There is, therefore, a critical need to develop a quantitative understanding of these feedbacks in orderto design sustainable river management programmes that seek to optimize the ecological and socio-economic benefits these rivers offer.
In summary, this thesis aims to advance our understanding of the morphodynamics of braided rivers and the role numerical models may have in helping to interrogate their behavior and governing controls
Avoiding non-proliferation atrophy: the effectiveness of multilateral cooperation, regime dynamics and the case of nuclear non-proliferation
Get PDFThis project investigates the evolution multilateral nuclear non-proliferation arrangements to prevent state and non-state actors to access potentially destructive weapons and components thereof. While less scrutinized by political scientists and security experts, cooperative frameworks abound in practice. This begets questions as to the mechanisms and processes by which actors effectively cooperate in a crowded, complex and pluralist environment. Which factors determine the success and resilience of non-proliferation arrangements? How much explanatory power do cognitive beliefs and institutional practices command to understand and explain variance in governance effectiveness?
While previous studies have focused on the ‘front-end’ of cooperation by examining factors leading states to cut deals, others have focused on the ‘back-end’ by focusing on the role of military and diplomatic means, such as alliances, coercion and the role of law. In addition, while scholarship on cooperation neglects sovereignty-conscious issues, non-proliferation studies disregard what happens between the ‘front- and the backend’ of the cooperation loop.
This work analyzes three arrangements – the review process of the Nuclear Non- Proliferation Treaty, U.N. Security Council Resolution 1540 and the Nuclear Security Summits. Using case study analysis, elite interviews and participant observation, this study undertakes an investigation from a cognitivist perspective and examines the “principles, norms, rules, and decision-making procedures” governing non-proliferation.
While factors related to knowledge and learning affect actors' understandings of risks and their mitigation pathways, their impact is intertwined with idiosyncratic factors, with crisis as overarching and crosscutting thread. Theoretically, compared to neorealism and neoliberal institutionalism, cognitive approaches to international regimes provide the most cogent explanations to account for governance effectiveness, but cannot wholly explain a case. Operatively, effective and resilient nuclear non-proliferation governance should provide for permanent interaction whereby novel implementation and monitoring mechanisms are experimented in a sovereignty-respecting way
Gli interlocutori di Socrate nei Dialoghi di Platone
Get PDFQuesta tesi ha come obiettivo quello di definire il ruolo intratestuale degli interlocutori di Socrate in sei dialoghi di Platone: Alcibiade maggiore, Carmide, Teeteto, Gorgia, Repubblica (libri I, II e V), Filebo.
Le ragioni di interesse per questo argomento sono almeno due. Alcuni di questi personaggi individuano gli antagonisti di Socrate e rappresentano sfide per la riflessione platonica. In questo senso la loro presenza risulta importante per osservare in che modo i Dialoghi siano più la messa in scena di un metodo e di un diverso atteggiamento verso il sapere che l’esposizione di una dottrina, permettendo così di definire e contrario la φιλοσοφία. Ad essi è dedicato il primo capitolo (Il sapere ricevuto: gli interlocutori secondo l’Apologia), usando come traccia la lista che Socrate fa nell’Apologia.
Prima di intraprendere l’analisi dei personaggi è stato però necessario definire che cosa si intenda per interlocutore (Che cos’è un interlocutore socratico?). L’interazione o la presenza nei Dialoghi presenta molte sfumature, ma la definizione dei tratti che caratterizzano un interlocutore, in positivo e in negativo, sarà alla base della successiva lettura dei testi. Sulla base della caratterizzazione e della loro interazione dialogica si analizzeranno alcuni personaggi del corpus (La rifondazione platonica del sapere: il ruolo degli interlocutori). Le osservazioni sulla lista dell’Apologia e la disamina terminologica consentiranno di analizzare i dialoghi con una griglia interpretativa il più possibile ricavata dai testi. Si potrà perciò notare che sia gli interlocutori “impossibili” che i personaggi con i quali Socrate può costruire positivamente alcune tesi possiedono caratteristiche caratteriali e sociali ben precise. Infine, si analizzeranno alcuni fenomeni discorsivi che ostacolano il dialogo: se in questo modo Platone vuole mostrare l’impossibilità di «tessere un discorso comune in mancanza di un mondo di valori condiviso» (Fussi), è anche forse perché riconosce che la persuasione filosofica si esercita al di fuori della finzione dialogica
Understanding and Exploiting Language Diversity
Get PDFLanguages are well known to be diverse on all structural levels, from the smallest (phonemic) to the broadest (pragmatic). We propose a set of formal, quantitative measures for the language diversity of linguistic phenomena, the resource incompleteness, and resource incorrectness. We apply all these measures to lexical semantics where we show how evidence of a high degree of universality within a given language set can be used to extend lexico-semantic resources in a precise, diversity-aware manner. We demonstrate our approach on several case studies: First is on polysemes and homographs among cases of lexical ambiguity. Contrarily to past research that focused solely on exploiting systematic polysemy, the notion of universality provides us with an automated method also capable of predicting irregular polysemes. Second is to automatically identify cognates from the existing lexical resource across different orthographies of genetically unrelated languages. Contrarily to past research that focused on detecting cognates from 225 concepts of Swadesh list, we captured 3.1 million cognate pairs across 40 different orthographies and 335 languages by exploiting the existing wordnet-like lexical resources
Physiological and pathological role of serine 96 phosphorylation in the regulation of androgen receptor
Get PDFSpinal and bulbar muscular atrophy (SBMA) is an X-linked neuromuscular disorder characterized by the progressive dysfunction and loss of lower motor neurons. SBMA is caused by the expansion of a CAG tandem repeat encoding a polyglutamine (polyQ) tract in the androgen receptor (AR) gene. SBMA belongs to the family of polyQ diseases, which includes eight other neurological diseases caused by the same mutation in unrelated genes. PolyQ diseases share common features, such as that polyQ proteins are typically expressed throughout the body, yet they cause specific neuronal loss. It remains to be clarified why specific sub-populations of neurons degenerate in each polyQ disease. The well-known structure and function of AR make SBMA a good model to investigate polyQ disease pathogenesis. Androgen binding to AR results in its nuclear translocation and binding to androgen-responsive elements (AREs) to regulate gene expression. Moreover, AR is highly phosphorylated. Recently, we obtained evidence that phosphorylation of polyQ-AR by cyclin-dependent kinase 2 (CDK2) at serine 96 increases toxicity. This post-translational modification was enriched in neurons. Therefore, we hypothesized that phosphorylation of polyQ-AR at serine 96 modulates its function in response to activation of neuronal activity, a level of regulation altered in SBMA. We carried out a microarray analysis in resting and stimulated neurons in which AR was activated by androgens. Our preliminary results suggest that AR activation drives a differential gene expression program in stimulated neurons. In order to analyze the role of CDK2 and serine 96 phosphorylation in vivo, we deleted one or both CDK2 alleles in SBMA mice. Modulation of CDK2 expression reduced polyQ-AR phosphorylation at serine 96, decreased polyQ-AR accumulation in neurons, and attenuated disease manifestations in SBMA mice. Finally, we carried out an unbiased high-throughput screening of phosphatase and kinase inhibitors. As read-out, we analyzed polyQ-AR nuclear translocation induced by testosterone, in order to identify compounds to lower polyQ-AR toxicity. We isolated 6 phosphatase and 17 kinase inhibitors as modifiers of polyQ-AR nuclear shuttling. Among them, we found two compounds targeting Cdc25, a known activator of CDK2. Cdc25 modulation altered serine 96 phosphorylation, toxicity and transcriptional activity of polyQ-AR in cells. Our results support the idea that Cdc25 represents a potential candidate to develop new therapeutic strategies for SBMA. In summary, our findings show that serine 96 phosphorylation modifies AR physiological functions in neurons and polyQ-AR toxicity in SBMA
Well balanced Arbitrary-Lagrangian-Eulerian Finite Volume schemes on moving nonconforming meshes for non-conservative Hyperbolic systems
Get PDFThis PhD thesis presents a novel second order accurate direct Arbitrary-Lagrangian-Eulerian (ALE) Finite Volume scheme for nonlinear hyperbolic systems, written both in conservative and non-conservative form, whose peculiarity is the nonconforming motion of interfaces. Moreover it has been coupled together with specifically designed path-conservative well balanced (WB) techniques and angular momentum preserving (AMC) strategies. The obtained result is a method able to preserve many of the physical properties of the system: besides being conservative for mass, momentum and total energy, also any known steady equilibrium of the studied system can be exactly maintained up to machine precision. Perturbations around such equilibrium solutions are resolved with high accuracy and minimal dissipation on moving contact discontinuities even for very long computational times. The core of our ALE scheme is the use of a space-time conservation formulation in the construction of the final Finite Volume scheme: the governing PDE system is rewritten at the aid of the space-time divergence operator and then a fully discrete one-step discretization is obtained by integrating over a set of closed space-time control volumes. In order to avoid the typical mesh distortion caused by shear flows in Lagrangian-type methods, we adopt a nonconforming treatment of sliding interfaces, which requires the dynamical insertion or deletion of nodes and edges, and produces hanging nodes and space-time faces shared between more than two cells. In this way, the elements on both sides of the shear wave can move with a different velocity, without producing highly distorted elements, the mesh quality remains high and, as a direct consequence, also the time step remains almost constant in time, even for highly sheared vortex flows. Moreover, due to the space-time conservation formulation, the geometric conservation law (GCL) is automatically satisfied by construction, even on moving nonconforming meshes.
Our nonconforming ALE scheme is especially well suited for modeling in polar coordinates vortical flows affected by strong differential rotation: in particular, the novel combination with the well balancing make it possible to obtain great results for challenging astronomical phenomena as the rotating Keplerian disk. Indeed, we have formulated a new HLL-type and a novel Osher-type flux that are both able to guarantee the well balancing in a gas cloud rotating around a central object, maintaining up to machine precision the equilibrium between pressure gradient, centrifugal force and gravity force that characterizes the stationary solutions of the Euler equations with gravity. To the best knowledge of the author this work is original for various reasons: it is the first time that the little dissipative Osher scheme is modified in order to be well balanced for non trivial equilibria, and it is the first time that WB is coupled with ALE for the Euler equations with gravity; moreover the use of a well balanced Osher scheme joint with the Lagrangian framework allows, for the first time within a Finite Volume method, to maintain exactly even moving equilibria. In addition, the introduced techniques demonstrate a wide range of applicability from steady vortex flows in shallow water equations to complex free surface flows in two-phase models. In the last case, studied on fixed Cartesian grids, the new well balanced methods have been implemented in parallel exploiting a GPU-based platform and reaching the very high efficiency of ten million of volumes processed per seconds. Finally, in the case of vortical flows we propose a preliminary analysis on how to increase the accuracy of the method by exploiting the redundant conservation law that can be written for the angular momentum, as proposed in Després et al. JCP 2015. Indeed, an easy manipulation of the Euler equations allows to write its additional conservation law: clearly it does not add any supplementary information from the analytical point of view, but from a numerical point of view it provides extra information in particular in the case of rotating systems. We present both a master-slave approach, to deduce a posteriori a more precise approximation of the velocity, and some coupled approaches to investigate how the entire process can take advantage from considering directly the angular momentum during the computation within a strong coupling with other variables. A large set of different numerical tests has been carried out in order to check the accuracy and the robustness of the new methods for both smooth and discontinuous problems, close and far away from the equilibrium, in one and two space dimensions. Many of the presented results show a great enhancement with respect to the state of the art
Analysis of the impact of hydrological alterations and multiple stress factors on the ecological status of Alpine freshwater ecosystems
Get PDFFreshwater ecosystems are severely undergoing degradation due to the presence of multiple stressors that are undermining their biodiversity. In this sense, quantifying these effects on Alpine regions is challenging, due to the lack of tailored field measurements of hydrological, biological and chemical variables. This work aims to touch some of these aspects, with particular attention to hydrological dynamics and their effects on macroinvertebrates. Field activities have been conducted within the Adige catchment which has been selected as a case study in the FP7 project GLOBAQUA. Collected data have been analyzed by means of statistical tools and results showed a seasonal and spatial variability of biological communities related to hydrological and chemical variables. In particular, it has been observed that richness, diversity and relative composition of macroinvertebrates community are chiefly affected by hydrological alteration and urban pollution. Available literature confirmed that hydrological alteration is one of the most important factors affecting riverine ecosystems. In Alpine regions, most of the hydrological alterations observed are due to hydropower that represents the major source of energy in the Trentino-Alto Adige region. Since the introduction of the free energy market in Italy, hydropower production shows large fluctuations at the daily and larger temporal scales, as the managers aim at producing when the energy price is high. This increased the variability of streamflow downstream the restitution of the power plants. Changing climate is an additional stressor that can enhance the effects of these anthropogenic influences. Thereby, in this work hydrological alterations have been distinguished between those forced by climate change and those caused by the presence of hydropower plants and have been analysed in detail. The former have been analysed downstream of the Careser glacier, which has long-term observations of climatic variables, mass balances and streamflow. The main purpose of this study was finding a direct relationship linking biological indicators to streamflow variations related mainly to hydropower operations. Quantifying these effects is challenging due to the fact that the behaviour by which macroinvertebrates respond remains largely unexplained. However, analyses of similarities and independence, performed at the basin scale with data provided by the local Environmental Protection Agencies, showed evident differences in the biological communities between impacted and non-impacted sites. These results bring us to believe that a relationship between biological data and hydrological alteration is expected to exist, but that is not clearly explicated by simple correlations. Giving a quantitative interpretation of this correlation could help hydropower manager to improve and optimize the energy production with a more realistic scenario of the effects on the biological community, with also a perspective of the combined effects caused by the presence of multiple reservoirs within the basin
A Cognitively Inspired Framework to Support the Driving Task of Vehicles of the Future
No full textIn this work an artificial driving agent able to adapt its behavior depending on the specific situation and to generate human-like maneuvers was developed. The agent,
called co-driver, was designed with a bio-inspired architecture, with an approach that takes advantage of ideas from cognitive science. In fact the decision process is based on the affordance competition hypothesis: the agent generates a representation of all possible actions given what is perceived in the environment and then chooses the optimal maneuver after inhibiting all the dangerous ones.
In the first stage of the development process, atomic actions, called motor primitives, were identified. Then the co-driver was implemented with a layered architecture, where these motor primitives were combined in the upper levels in order to obtain
more complex behaviors. Thanks to this particular architecture, the development process of the final artificial driver was split in two parts: initially an advanced driver assistance system (ADAS) was implemented and tested, and finally the architecture was extended in order to have an artificial driving agent for automated driving. In the first case the system was
successfully tested on public roads and was able to warn the driver in case of dangerous scenarios, such as blind intersections. In the latter case, the co-driver
could manage several challenging test cases in urban scenarios, from car following to cut-in scenario and curves. Finally, it was compared with a state-of-art driver model of CarMaker simulation software used by the main car manufacturers.
Due to the achieved results, this work can be considered a valid potential solution for automated driving. In fact, the artificial driver was used as starting point for a European project (“Dreams4Cars”) that is currently in progress