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Dynamical excitations in low-dimensional condensates: sound, vortices and quenched dynamics
Full text linkThe dynamics of systems out of equilibrium, such as the phase transition process, are very rich, and related to largely scalable problems, from very small ultracold gases to large expanding galaxies. Quantum low-dimensional systems show interesting features, notably different from the canonical three-dimensional case. Bose-Einstein condensates are very good platforms to study macroscopic quantum phenomena. These three points describe well the motivation behind the study presented in this work.
In this thesis, some dynamical problems of trapped and uniform condensates are studied, both at zero and finite temperature. In particular, we focus on the analysis of the propagation of linear and nonlinear excitations in a quasi-1D and in quasi-2D systems. In the first case, we are able to correctly describe the dynamics of a solitonic vortex in an elongated condensate, as measured by Serafini et al. [Phys. Rev. Lett. 115, 170402 (2015)]. In the second case, we reproduce the decay rate of a phase-imprinted soliton (collaboration with Birmingham), and assess its dependence on the temperature. We also replicate the propagation speed of sound waves over a wide range of temperatures as in Ville et al. [arXiv:1804.04037] (collaboration with Collège de France). The result of this analysis is included in Ota et al. [arXiv:1804.04032], which is currently under revision.
In uniform low-dimensional systems Bose-Einstein condensation is technically not possible, and in two dimensions it is replaced by the Berezinskii-Kosterlitz-Thouless superfluid phase transition. We study its critical properties by analysing the spontaneous generation of vortices during a quench, produced via the Kibble-Zurek mechanism. This procedure predicts, for any dimension, the scaling for the density of defects formed during a fast transition, when the system is not adiabatically following the control parameter, and regions of phase inhomogeneity are formed. We address the role of reduced dimensionality on this process. All finite temperature simulations are performed by means of the stochastic (projected) Gross-Pitaevskii equation, a model fully incorporating density and phase fluctuations for weakly interacting Bose gases
Economic and Management issues of firms in Vietnam: Productivity, multinational profit shifting, and ownership changes
Full text linkThis thesis is comprised of three essays which explore economic and management issues of firms in Vietnam. The issues being addressed here are varied but connected to highlight (partly) how firms are doing business in the transition economy of Vietnam. The first essay examines ownership differential (i.e. state-owned, private-owned, and foreign-owned) and competition effect on firm total factor productivity (TFP) as consequences of mixed economic reforms in Vietnam (Chapter 2). It describes the big picture: the whole transition process/institutional changes in Vietnam and how such changes are reflected in competition effect on firm TFP and comparative performance (in terms of TFP) of firms with different ownership types. The next two essays deal specifically with foreign firms' subsidiaries in Vietnam. One essence of the economic reform of Vietnam is its “open-door policy” to foreign direct investment (FDI) and international trade. While many benefits of FDI have been identified, in the second essay, an unwanted consequence of FDI is dealt with instead. Specifically, it examines whether foreign multinational firms undertake tax-avoidance profit shifting out the country (Chapter 3). Using a newly developed identification approach in the literature, the essay examines how corporate income tax-rate differentials between the home country and Vietnam determine a foreign wholly-owned subsidiary’s under-reporting of the profit obtained from an exogenous income shock in Vietnam. The third essay then investigates post-formation conversion of international joint ventures (JVs) to either wholly-owned subsidiaries (WOSs– 100% foreign ownership) or domestic firms (DOMs– 100% domestic ownership) in Vietnam. In this essay, both the drivers of such ownership transfers and their performance implications are investigated (Chapter 4)
An Innovative Learning-by-Example Methodological Strategy for Advanced Reflectarray Antenna Design
Full text linkReflectarray antennas are reflector structures which combine characteristics of both reflector and array antennas. They exhibit electrically large apertures in order to generate significant gain as conventional metallic reflector antennas. At the same time they are populated by several radiating elements which can be controlled individually like conventional phased array antennas. They are usually flat and can be folded and deployed permitting important saving in terms of volume. For these reasons they have been
considered since several years for satellite applications. Initially constituted by truncated metallic waveguides and mainly considered for radar applications, they are now mainly constituted by a dielectric substrate, backed by a metallic plane (groundplane) on which microstrip elements with variable shape/size/orientation are printed. These elements are illuminated by the primary feed. The reflected wave from each element has a phase that can be controlled by the geometry of the element itself. By a suitable design of the elements that make up the reflectarray, it is therefore possible to compose the phase front of the reflected waves in the desired direction (steering direction),
and to ensure that the obtained overall radiation pattern exhibits a secondary lobe profile which meets the design specifications. Reflectarrays may be used to synthesize pencil or shaped beams. The synthesis methods commonly used to achieve this goal are based on three different steps: (a) calculation of the nearfield “phase distribution” that the wave reflected by the reflectarray must exhibit
to get the desired far-field behaviour; (b) discretization of such distribution into cells of size comparable to that of the elements of interest (i.e., the patches); (c) calculation of the geometry of each elementary cell that will provide the desired reflection coefficient. The first step (a) is a Phase Only approach and permits already to achieve fast preliminary indications on the performance achievable. Accurate results require the implementation of the steps (b) and (c) as well and it is thus of fundamental importance to have techniques capable of efficiently and accurately calculating the reflection coefficient associated with a given geometry of the element [in order to efficiently solve the step (c)]. This coefficient is mathematically represented by a 2x2 complex matrix, which takes into account the relationships between co-polar and cross-polar components of the incident (due to the feed) and reflected field. This matrix naturally depends on the geometry of the element, the direction of incidence of the wave (azimuth and elevation) and the operating frequency of the system. The computation of the reflection coefficient is usually performed using electromagnetic full-wave (FW) simulators; the computation is however time consuming and the generation of the unit cells scattering response database becomes often unfeasible.
In this work, an innovative strategy based on an advanced statistical learning method is introduced to efficiently and accurately predict the electromagnetic response of complex-shaped reflectarray elements. The computation of the scattering coefficients of periodic arrangements, characterized by an arbitrary number of degrees-of-freedom, is firstly recast as a vectorial regression problem, then solved with a learning-by-example strategy exploiting the Ordinary Kriging paradigm.
A set of representative numerical experiments dealing with different element geometries is presented to assess the accuracy, the computational efficiency, and the flexibility of the proposed technique also in comparison with state-of-the-art machine learning methods
Surface Patterned Ceramics Via Breath Figures Method With Potential Application As Implant Coatings
Full text linkSurface porous silicon based ceramics are a class of materials with excellent mechanical, physical and chemical properties and for this reason they are widely used in different fields of application. The resultant properties of these material are due principally to the combination of the chemical composition (coordination with the Si atom) and the specific geometry of the pattern. These parameters are able to influence phenomena such as the biological activity, the exposed surface area and the thermal, mechanical and chemical resistance. Techniques used nowadays to synthesize these ceramics with a specific patter are usually really complicated, expensive and time-consuming with limitations for the large-scale industrial application. The Breath Figure method is a new fast and highly controllable technique that allows to decorate the surface of polymer films with different porous patterns. A large variety of starting materials can be used to perform this process, obtaining porous films with different characteristics and with a specific control on the entire process. In this work we used a UV cross-linkable polysiloxane as precursor for the Breath Figure process in order to combine the pattern procedure with the polymer derived ceramic method. Initially, the effects of the process variables on the final surface porosity was evaluated, identifying the parameters which most influence the final material. After the patterning, materials with different characteristics were pyrolyzed under different atmospheres in order to induce simultaneously the ceramic conversion and the chemical modification of the silicone structure. Three different porous silicon-based ceramics were obtained using flowing air, nitrogen and ammonia during the heat treatments, respectively: silicon dioxide, silicon oxycarbide and silicon oxynitride. All these material have been proposed as implant coating for different body districts, but recent studies demonstrated the potential application of silicon oxynitrides as bone implant coatings due to the enhanced bioactivity and osteoinductivity of the ceramic. For this reason in the second part of this work we evaluated the potential bioactivity of surface porous silicon oxynitrides in terms of bioactive silicon ions release capability and effects of different porosity degrees on cells behavior. Four different surface pattern were applied on titanium alloy disks and used for an in vitro characterization using human Mesenchymal Stem Cells and compared with uncoated titanium. The results indicated that the silicon ions release from the coating surface leads to an increase of the cellular activity with the porous pattern influencing the hMSC initial adhesion and proliferation
Il riscatto delle lacrime. Il tema della solitudine e della violenza in opere scelte di Ljudmila Petrushevskaja e Svetlana Vasilenko. Un'analisi tematica.
Full text linkLa tesi si pone l'obiettivo di analizzare, attraverso un confronto principalmente tematico, una serie di opere scelte delle due scrittrici di lingua russa Ljudmila Stefanovna Petrushevskaja (Mosca, 1938) e Svetlana Vladimirovna Vasilenko (Kapustin Jar, 1956). L'intento è quello di individuare l'esistenza di un complesso di motivi legati al tema della violenza e della solitudine. I motivi per indagare in questa direzione sono essenzialmente legati all'idea che, grazie allo sviluppo costante della letteratura femminile russa negli ultimi decenni, unitamente ad una maturazione del pensiero femminista e a una maggiore consapevolezza da parte della società circa i diritti delle donne, alcune delle problematiche sociali, psicologiche, familiari presenti in seno al popolo russo, vengono dunque trattate con un particolare punto di vista, quello femminile appunto (lo zhenskij vzor). Ciò implica non solo una differente visione del mondo e della realtà rispetto ad un punto di vista maschile, ma anche un diverso modo di trattare determinati problemi, riflettere su dilemmi, proporre soluzioni. Il periodo scelto per la nostra indagine che va dalla Perestrojka alla Russia post-sovietica ci è sembrato calzante non solo perché le autrici hanno prodotto alcune delle loro maggiori opere, riuscendo tra l'altro a vederle pubblicate, ma anche perché essendo una fase storica di cambiamenti, riforme radicali, stravolgimenti e tentativi di sostenere un'entità statale ormai in crisi, la società russa ha sviluppato e subito determinate problematiche che sono il frutto di decenni di una cupa dittatura precedente, di scelte azzardate e non ponderate da parte dello stato centrale, del dramma dei conflitti bellici e, non ultime, delle crisi e del periodo sopraindicato. Solitudine e violenza emergono dunque dalle opere petrushevskiane e vasilenkiane non tanto come scelte tematiche inventate e scevre dalla realtà da parte delle scrittrici, bensì come rappresentazioni (in chiave artistico letteraria) di quanto già presente nel quotidiano della vita russa di quei decenni. La tesi tratta sia i movimenti letterari vicini alle due autrici (la drugaja proza e la zhenskaja proza), sia lo sviluppo della letteratura femminile in Russia e le costanti tematiche del byt, della poshlost' e della chernucha. In una delle appendici troviamo un possibile spunto per un lavoro comparatistico in ambito americanista, con esponenti della letteratura statunitense (Afro American Literature), avente come scopo l'individuazione dell'esistenza dei due temi qui studiati anche nel panorama letterario d'oltreoceano; in questa sede è stata proposta una possibile comparazione con una coppia di autrici come Toni Morrison (1931) ed Alice Malsenior Walker (1944), delle quali sono state brevemente analizzate alcune opere che possiedono, secondo chi scrive, tratti di similarità con il tema della solitudine e quello della violenza espressi in ambito russofono dalla Petrushevskaja e dalla Vasilenko; tuttavia ci si auspica che eventuali lavori da parte di esperti in studi letterari anglo-americani, possano trarre spunto dalla presente tesi per ampliare anche ad altre autrici d'oltreoceano la comparazione, pur mantenendo ben presenti le differenze culturali, storiche, sociali e letterarie tra le due realtà. Concludendo desideriamo segnalare come Ljudmila Petrushevskaja e Svetlana Vasilenko, allo stadio attuale della produzione critica scientifica, non siano mai state trattate in coppia con un'analisi approfondita delle loro opere, né in ambito russo né in quello statunitense (da dove provengono molti studi su di loro): ciò significa che esistono numerosi, notevoli ed articolati testi critici su entrambe che sono stati indubbiamente di grande ausilio per la composizione della presente tesi, ma un testo che le consideri in coppia, cercando di sondare e scoprire eventuali punti in comune (l'esistenza dei due temi ricercati nelle loro opere) e punti di divergenza, ancora non c'era. Pertanto, una delle sfide di questo lavoro, oltre a quella di aver provato ad individuare la risposta delle scrittrici alla problematica connessa alla violenza e alla solitudine,è stata proprio quella di averle studiate in coppia, quali due delle più alte rappresentanti della letteratura russa contemporanea, capaci di esprimere un punto di vista letterario così peculiare da poter essere inteso come uno specchio per comprendere una realtà sociale in continuo divenire
Wettability of graphitic materials and development of graphene layer as barriers to prevent the surface degradation induced by water.
Full text linkGraphitic materials, thanks to the lamellar structure and chemical stability, are of particular interest to realize barriers against the degradation of surface properties induced by water. Many studies showed that water could be a source of degradation of surface properties. To develop a method to overcome the problem related to the deterioration of the surface it is fundamental to study the water- material interaction. For this reason, in this thesis, the water-surface interaction of graphitic- materials and the use of graphitic materials as impermeable barriers against water were explored. Different experimental set up were realized to study the liquid-gas-solid interaction, such as time evolution of the sessile water drop contact angle, captive bubble contact angle and contact angle measurements in a controlled atmosphere. Moreover, a method of deposition of protective graphene-based films using a Meyer rod to apply graphene-inks onto a surface was developed. To understand the intrinsic wettability of graphitic materials a detailed study of the gas-liquid-solid interactions of graphite was conducted in a wide range of experimental conditions. The surface chemical properties and morphology were studied by X-ray photoelectron spectroscopy (XPS), profilometry and atomic force microscopy(AFM), sessile drop contact angle, captive bubble and secondary emission microscopy (SEM). The results of the gas-liquid–surface interaction study indicated that HOPG surface was sensitive to experimental conditions like airborne contamination and the presence of gases. Similarly, a detailed study of the interaction of water with PDMS surface in various experimental conditions (in the air and immersed in water) were conducted. The findings showed that when PDMS was immersed in water, its surface changed. In fact, the volume of air bubbles in contact with the surface of PDMS increased by increasing immersion time in the water. The experimental results indicated that such dynamic evolution of the air bubbles was related to the rearrangement of surface polymer chains via the migration of the polar groups. This phenomenon induced a degradation of the surface properties of PDMS when it is immersed in water. When graphene monolayer was added to PDMS surface, it acted as a barrier against water, suppressing the dynamic evolution of the bubble. We studied the protective properties also of graphene-based films deposited on lead (Pb). We observed that Pb surface degradation occurred when Pb was in contact with a drop of water. The results showed that degradation of Pb surface in contact with water happened very rapidly but graphene-based films, in particular, graphene oxides films, were able to reduce degradation of the surface significantly
Predispositions of Conscious Perception: from Correlation to Causation
Full text linkHuman mental life is accompanied by oscillatory signals that send information across distributed neural
networks. Whether a stimulus reaches or escapes our conscious experience is influenced by the state of the
brain in that moment, reflected in cerebral electrophysiology. Our understanding of this brain activity has grown vastly in recent years, thanks to leading advances in electro- and magneto-encephalography (EEG and MEG, or M-EEG, which enable us to monitor the electric brain signal) and recent developments allowing the direct modulation of endogenous oscillatory components that underlie cortical functions. Transcranial current stimulation, particularly the variant with alternating current (tACS), putatively lets us assess and gauge the role of oscillations on cognition. Several studies have confirmed that tACS can influence neural mechanisms and behavior, even conscious access. Until recently, cerebral activity during stimulation could not be assessed and observations were limited to the aftereffects. The aim of the project described in this dissertation is to investigate the validity of a pioneering procedure that can recover brain signal during simultaneous MEG and tACS. Then, exploiting this approach, we furthered our grasp of how the neural system is altered by transcranial stimulation and the complex relationship between the external current and the internal mechanisms of the brain. The overall goal is to explore our ability to manipulate neural signatures in ongoing activity and the conscious perception of an upcoming stimulus. Chapter 1 provides the reader with a general introduction of current studies and theories behind tACS influence on cognition and behavior. After a description of what tACS is and what it does, the focus is mostly on cutting-edge methods combining tACS and M-EEG, network connectivity and graph theoretical
frameworks to study cognitive processes. At the end of the introductory chapter, we indulge on applications
and consequences of these approaches, as well as open questions about our understanding of the prerequisites
of conscious perception that drove the experiments described in the following chapters.
Chapter 2 reports the first study in which we addressed the feasibility of concurrent tACS and MEG, the
prerequisite for the rest of the project. Chapter 3 and 4 present studies that better delineated what happens in
the brain in terms of oscillatory phase, connectivity and the dependency of tACS effects with the ongoing brain
state during electrical stimulation. We addressed some key issues on the mechanisms of action of tACS and its
sensitivity to in-vivo brain networks.
Chapter 5 provides preliminary results of a study employing a near-threshold task paired with tACS and MEG
in the context of conscious perception. We stimulated prestimulus brain rhythms in sensory cortices to see if
their strength and connectedness with the rest of the brain could determine whether a stimulus will be
perceived or not. Chapter 6, after a recapitulation of the main results in a broader perspective, discusses the meaning and the limitations of the experimental findings and how these extend our current knowledge
How input modality and visual experience affect the representation of categories in the brain
Full text linkThe general aim of the present dissertation was to participate in the progress of our understanding of how sensory input and sensory experience impact on how the human brain implements categorical knowledge. The goal was twofold: (1) understand whether there are brain regions that encode information about different categories regardless of input modality and sensory experience (study 1); (2) deepen the investigation of the mechanisms that drive cross-modal and intra-modal plasticity following early blindness and the way they express during the processing of different categories presented as real-world sounds (study 2).
To address these fundamental questions, we used fMRI to characterize the brain responses to different conceptual categories presented acoustically in sighted and early blind individuals, and visually in a separate sighted group.
In study 1, we observed that the right posterior middle temporal gyrus (rpMTG) is the region that most reliably decoded categories and selectively correlated with conceptual models of our stimuli space independently of input modality and visual experience. However, this region maintains separate the representational format from the different modalities, revealing a multimodal rather than an amodal nature. In addition, we observed that VOTC showed distinct functional profiles according to the hemispheric side. The left VOTC showed an involvement in the acoustical categorization processing at the same degree in sighted and in blind individuals. We propose that this involvement might reflect an engagement of the left VOTC in more semantic/linguistic processing of the stimuli potentially supported by its enhanced connection with the language system. However, paralleling our observation in rpMTG, the representations from different modalities are maintained segregated in VOTC, showing little evidence for sensory-abstraction. On the other side, the right VOTC emerged as a sensory-related visual region in sighted with the ability to rewires itself toward acoustical stimulation in case of early visual deprivation.
In study 2, we observed opposite effects of early visual deprivation on auditory decoding in occipital and temporal regions. While occipital regions contained more information about sound categories in the blind, the temporal cortex showed higher decoding in the sighted. This unbalance effect was stronger in the right hemisphere where we, also, observed a negative correlation between occipital and temporal decoding of sound categories in EB. These last results suggest that the intramodal and crossmodal reorganizations might be inter-connected. We therefore propose that the extension of non-visual functions in the occipital cortex of EB may trigger a network-level reorganization that reduce the computational load of the regions typically coding for the remaining senses due to the extension of such computation in occipital regions
Lo stato di necessità è il suo fondamento. Uno studio comparato.
Full text linkLa presente ricerca analizza le due impostazioni più note all’interno del dibattito penalistico in tema di fondamento dello stato di necessità giustificante, ovvero la teoria dell’interesse prevalente e la tesi della solidarietà. Nella prima parte di questa indagine si assume come premessa concettuale e dogmatica l’importanza pratica che ha il compito di individuare il fondamento dello stato di necessità, il quale, inoltre, costituisce un concetto giuridico generale, che è possibile riconoscere in altri settori dell’ordinamento giuridico.
Per quanto riguarda la tesi dell’interesse prevalente, questa indagine analizza la sua evoluzione storica e dogmatica. Tale analisi si svolge con lo scopo di valutare se le critiche che da qualche tempo le vengono mosse siano fondate o meno. In particolare, quella riguardante il presunto collettivismo del principio derivato dal fatto che esso sarebbe manifestazione di un utilitarismo incompatibile con la struttura e funzione attribuita al diritto «moderno». Per contro, la tesi sostenuta in questo lavoro consiste nel ritenere che l’interesse prevalente è la manifestazione di una norma di cultura, nozione del resto collegata ad una tradizione filosofica tutt’altro che omologabile all’utilitarismo. La determinazione degli interessi che predominano nei confronti di altri non viene determinata dall’alto, ma è l’esito di un rapporto di tipo orizzontale che sussiste tra i singoli appartenenti ad una data comunità.
Nella parte dedicata al principio di solidarietà, questa indagine svolge una sintesi della sua evoluzione in quanto concetto o principio giuridico, con l’obiettivo di rendere ancora più evidente la critica che viene svolta nella parte finale, ovvero l’essere un concetto che per principio presuppone un rapporto di tipo verticale, cioè un rapporto di potere, il quale risulta piuttosto incompatibile con un diritto penale di stampo liberale. Da questa critica si comprende come il concetto che si propone per dotare di contenuto assiologico il principio dell’interesse prevalente sia quello di «fraternità», ritenuto, d’altronde, un valore essenziale, in un diritto concepito in termini personalistici.
Nell’ultima parte si analizza l’impatto di queste due teorie all’interno del dibattito italiano e cileno
Impact of Internationalization on the Cognitive Configuration of Industrial Districts. Learning, Forgetting, and Unlearning Effects.
Full text linkThe increasing internationalization of Industrial Districts (IDs) is affecting the system’s production organization and the institutional context surrounding it, raising concerns about the role of localized industries for the development of local societies. To explore the impact of international openness on IDs, we focus on the endogenous cognitive processes occurring within the local system and resulting from the absorption and transformation of internal and external knowledge inputs. Using a conceptual and empirical approach, we contribute to enhance the current understanding of the issue by analyzing the transformations of IDs in terms of the variations on the stock of knowledge embedded into the system, namely the stock of systemic knowledge. In the First Chapter, we develop a conceptual frame to describe the endogenous cognitive processes determined by internationalization. We define three types of processes affecting systemic knowledge: “learning”, contributing to the increase of systemic knowledge; “forgetting”, determining the decrease of systemic knowledge; and “unlearning”, corresponding to the case in which the changes of the ID knowledge endowment lead to both learning and forgetting processes. In the Second Chapter, we apply the conceptual frame to a quantitative analysis referred to a dataset of Italian industrial firms between 2008 and 2015. The aim of the analysis is to measure how the type of internationalization undertaken by the mass of firms in the region, affects the innovation strategies of the ID firms located in the same territory. Based on the distinction between knowledge-seeking and knowledge-exploiting internationalization strategies, the analysis confirms that internationalization affects the innovation strategies of ID firms in different ways. We expect this is because, by modifying the system’s endowment of knowledge, internationalization can either support or constrain the emergence of external economies of learning, affecting local innovation. Chapter Three presents another application of the conceptual frame based on the case study of the Macerata-Fermo footwear IDs. The analysis has the purpose to explore the endogenous cognitive processes triggered by international openness, and to disentangle the potential development paths that the systems are undertaking. In so doing, we also consider the contextual factors affecting the system’s development path, such as the institutional background. In addition to informing us about the learning, forgetting and unlearning effects in the Macerata-Fermo IDs, the findings highlight that the degree of industrial diversification within the system is key to define its development path, favoring unlearning processes towards other industries in response to structural shocks