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Determining what information is transmitted across neural populations
No full textQuantifying the amount of information communicated between neural population is crucial to understand brain dynamics. To address this question, many tools for the analysis of time series of neural activity, such as Granger causality, Transfer Entropy, Directed Information have been proposed. However, none of these popular model-free measures can reveal what information has been exchanged. Yet, understanding what information is exchanged is key to be able to infer, from brain recordings, the nature and the mechanisms of brain computation. To provide the mathematical tools needed to address this issue, we developed a new measure, exploiting benefits of novel Partial Information Decomposition framework, that determines how much information about each specific stimulus or task feature has been transferred between two neuronal populations. We tested this methodology on simulated neural data and showed that it captures the specific information being transmitted very well, and it is also highly robust to several of the confounds that have proven to be problematic for previous methods. Moreover, the measure was significantly better in detection of the temporal evolution of the information transfer and the directionality of it than the previous measures. We also applied the measure to an EEG dataset acquired during a face detection task that revealed interesting patterns of interhemispheric phase-specific information transfer. We finally analyzed high gamma activity in an MEG dataset of a visuomotor associations. Our measure allowed for tracing of the stimulus information flow and it confirmed the notion that dorsal fronto-parietal network is crucial for the visuomotor computations transforming visual information into motor plans. Altogether our work suggests that our new measure has potential to uncover previously hidden specific information transfer dynamics in neural communication
Finding the missing connection: diffusion-based tractography reconstruction of the acoustic radiation and other applications
Get PDFMagnetic resonance diffusion-based tractography techniques have offered a real breakthrough in brain studies. These methods allow, for the first time, to explore the anatomical organization of white matter pathways in humans, in-vivo and non-invasively.
As any other method, diffusion-based tractography has limitations. The inherent limits related to the indirect measurement of the diffusion signal, and the strong dependence of this technique on acquisition, models and algorithm parameters, prevents the reliable reconstruction of some major white matter bundles. This dissertation targets the methods, limitations, improvements, and validation of tracking methods, with applications in neurobiological and clinical research. In particular, the main work focuses on a white matter bundle that represents a notable omission in tractography studies: the acoustic radiation (AR), a major projection sensory pathway conveying auditory information from the thalamus to the auditory cortex. Topographical knowledge of this bundle is scarce, and its in-vivo tractography reconstruction remains challenging, preventing the investigation of auditory and language functional mechanisms in humans. This dissertation investigates, for the first time, the topography of the AR using post-mortem blunt dissections and provides a detailed description of the trajectory of these fibres and their relationship with major neighbouring white matter bundles. The topographical information is then applied to conduct an investigation on the effects of different MRI acquisition and tractography parameters on the in-vivo tractography reconstruction of the AR. An optimal set of parameters is obtained for AR reconstructions and used to build the first tractography atlas of the acoustic radiation. The AR atlas is then applied to study congenital deaf patients. The optimized reconstruction parameters and the atlas generated in this dissertation may be used in future studies interested in identifying and characterizing the AR. The reliable 3D reconstruction of this bundle will improve our understanding of the functional mechanisms underlying hearing and language in healthy subjects and patients, as well as in neurosurgical applications
Memristor-Based Computing Architecture with Advanced Signal Processing Capabilities
No full textMemristor-based computing architecture with advanced signal processing capabilities investigates analogue applications of memristors, particularly in image processing, combining them with conventional electronic circuitry.
The concept of memristor (short for memory resistor) was first theorised in 1971 by Prof. Chua while reasoning on the theoretical grounds of of the symmetry of equations governing the fundamental passive circuit theory.
This thesis can be split into two parts as follows: i) Memristor Device, Modelling, Characterisation and Programming and ii) Memristor Circuit Applications. In the first part, an overview of the theory of memristors which gives an introductory background is discussed alongside the device modelling to fit experimental data. Electrical characterisation was carried out on fabricated memristors to validate the fundamental fingerprint of these devices and finally, the different programming techniques, particularly the pulse-based technique which was widely used in this work, was exhaustively treated.
In terms of applications, starting from a novel memristor-based light to resistance encoder, a more complex architecture based on adaptive background subtraction for scene interpretation used for the analyses of motion and its association to a particular object in the scene is treated in this work.
Throughout this thesis, the intention of an overview on the application of memristors in image processing algorithm is emphasised and the last chapter discusses a neural network architecture based on memristors. The intended neural network architecture was trained to perform colour classification targeting applications based on gesture detection.
In essence, Memristor-based computing architecture with advanced signal processing capabilities gives an insight into the advantages to come having an hybrid system of standard CMOS image processing techniques with memristive devices particularly in computation-intensive applications requiring high speed and massive parallel signal processing. Typically the realisation of such powerful and dense networks in an integrated circuit with acceptable size which is not resource hungry by using the commonly encountered elements and conventional CMOS technology is becoming increasingly difficult to achieve. Computing architectures based on memristors present the advantages that could help overcome the limitations of an overall implementation with conventional electronic elements
Mechanochromic Photonic Crystals as Strain Sensors for structural Applications
Get PDFStructural Health Monitoring is an important aspect in civil engineering, dedicated to monitor and maintain the structural conditions of civil architecture objects. It results in extension of their life time and appropriateness for human use.
Present, commercially available sensors for SHM are complex, sophisticated and multicomponent systems. Although, they provide high precision of measurements, their total cost (the price and costs of exploitation) has been still too high to be commonly applicable. There are also other disadvantages such as distributed architecture, heavy cables or their sensitivity to electromagnetic interference like it is in case of conventional electrical sensors. Unlike them, more advance fiber optic sensors are robust to external fields. However, they involve the infrared light for data transmission, therefore they desire additional support of other devices for data processing.
Now a day, there is a lack of portable sensing instruments supporting more sophisticated technologies, whose applications can be reduced by failure assessing with those instruments.
Current investigations have been focused on development of structures that can be used as an independent sensing tool without a power supplier, such as mechanochromic photonic crystals with three-dimensional structure. Their mechanochromic properties are visible with naked eye as a color variation on their top surface stimulated by mechanical deformation of the structure. However, their fabrication desires high precision to obtain sample with the high sensitivity to stretching and omit some limitation corresponding to its composition (deeply described in chapter 4). Hence, there is need to find alternative solutions. One of them refers to two-dimensional photonic crystals, which were intensively investigated as a components of sensing systems such as MOEMSs (micro-opto-electro-mechanical microsystems). However, their main disadvantage is the fabrication that involves the lithography techniques, which are quiet expensive and time-consuming. Furthermore, the lithographic techniques desire clean room conditions. Hence, the number of produced specimens is limited.
In this thesis, there is proposed completely new approach to develop a strain sensor, including fabrication of strain-sensitive sample and methodology of measurements. The sample was fabricated as two-dimensional finite structure of hexagonally arranged voids on the PDMS substrate. The applied fabrication protocol was cost-effective and not time-consuming. The final product was a PDMS replica of monolayer colloidal crystal obtained by self-assembly of polystyrene colloidal spheres. Further investigations involved diffractive properties of its periodic structure. Its strain sensitivity was investigated by monitoring the parameters of diffracted (transmitted or reflected) light such as the diffracted wavelength (chapter 6) and the polarization (chapters 7 and 8), which vary by stretching the sample. Moreover, there was tested another approach, which involved shape changes in diffraction pattern. The diffraction pattern is a result of interaction between a periodic structure and an illuminating light.
The obtained data confirmed strong relationship between optical response and the geometry of diffractive structure. However, the experiments require further optimization of fabrication protocol, methodology (conditions of measurements, sample parameters, an appropriate arrangement of components in the experimental setups
La collezione predinastica del Museo Egizio di Torino: uno studio integrato di archivi e reperti
Get PDFThe Predynastic collection of the Museo Egizio (Turin) was mainly acquired by the Italian Egyptologist Ernesto Schiaparelli (1856-1928), leader of the M.A.I. (Missione Archeologica Italiana) through archaeological investigations and purchases on the antiquarian market.
Schiaparelli never published extensively the results of his excavation in Predynastic sites as Gebelein, Heliopolis and Hammamiya, and great part of the excavation records are still unedited. This study aims at tracing back the history of the formation of the Predynastic collection stored in the Museo Egizio and at defining its quantitative and qualitative nature by means of an integrated study of artefacts and archives
Stefan George e Friedrich Hoelderlin: due ciclicità a confronto
No full textLo studio affronta il problematico argomento della ciclicità in relazione a due grandi lirici tedeschi, Stefan George e Friedrich Hoelderlin, misurandosi con una vasta tradizione critica e con non agevoli dettati ermeneutici. Il lavoro è scandito in sette capitoli, dei quali il primo analizza il termine 'ciclo', partendo dal suo significato etimologico di cerchio, circolo e ruota, per poi soffermarsi sul significato di successione di eventi memorabili all'interno di un'epoca. Il ciclo è inteso quale categoria estetico-semantica che, incardinata nella dimensione riflessiva del linguaggio, permette di leggere le liriche sia come singoli testi autonomi sia come testi poetici inseriti in un insieme più vasto. Nel secondo capitolo si analizza la nozione di rituale ciclico in Stefan George nel contesto della Germania guglielmina, lacerata dalla frattura fra Bourgeoise e Bildungsbuergertum. Da questo prospettiva il rituale ciclico georgeano è concepito come mito che mira a creare una tradizione culturale funzionale ai bisogni della Germania, legittimandone i caratteri di specificità, eccellenza ed esclusività rispetto alle altre nazioni, nonché esorcizzando lo stereotipo tedesco di "verspaetete Nation", condannata a restare in uno stato di frammentazione territoriale fino al 1871. Il mito carente, capace di tradurre in realtà una volontà di potenza di stampo nietzscheano, viene incarnato dal poeta come esponente di una realtà potenziata che si colloca in un punto di scissura tra finito e infinito. Fondandosi sulla ripetizione di un'azione, il rituale estetico garantisce stabilità e continuità e offre un efficace antidoto contro la fugacità del tempo, mentre l'espressione poetica diviene una totalità in sé conchiusa. In Stefan George il culto della bellezza genera un cerchio magico, nel quale egli si trasforma da esteta in vate che preconizza la palingenesi dell'umanità. Oggetto di indagine sono state, a titolo di esempio, le strutture cicliche di Der Teppich des Lebens und die Lieder von Traum und Tod mit einem Vorspiel. Infine il lavoro volge a contemplare il rapporto tra Friedrich Hoelderlin e Stefan George, a partire dall'analisi del contributo di George e dei suoi sodali per la riscoperta dell'opera tarda di Hoelderlin per poi estendersi alle fonti utilizzate nel processo ermeneutico della poesia georgeana, nonché alle analogie tematiche rintracciabili tra i due poeti tedeschi che mantengono inalterata la propria singolarità sul piano stilistico e linguistico. Ciò avviene attraverso l'analisi di testi esemplari come gli hoelderliniani Fragment philosophischer Briefe e Verfahrungsweise des poetischen Geistes oltre agli inni Patmos, Friedensfeier, Brot und Wein e Der Zeitgeist e le loro ricadute entro l'opera georgeana, a fronte dello specifico paradigma della ciclicità
Security Risk Assessment Methods: An Evaluation Framework and Theoretical Model of the Criteria Behind Methodsâ Success
Get PDFOver the past decades a significant number of methods to identify and mitigate security risks have been proposed, but there are few empirical evaluations that show whether these methods are actually effective. So how can practitioners decide which method is the best for security risk assessment of their projects? To this end, we propose an evaluation framework to compare security risk assessment methods that evaluates the quality of results of methods application with help of external industrial experts and can identify aspects having an effect on the successful application of these methods. The results of the framework application helped us to build the model of key aspects that impact the success of a security risk assessment. Among these aspects are i) the use of catalogues of threats and security controls which can impact methods' actual effectiveness and perceived usefulness and ii) the use of visual representation of risk models that can positively impact methods' perceived ease of use, but negatively affect methods' perceived usefulness if the visual representation is not comprehensible due to scalability issues. To further investigate these findings, we conducted additional empirical investigations: i) how different features of the catalogues of threats and security controls contribute into an effective risk assessment process for novices and experts in either domain or security knowledge, and ii) how comprehensible are different representation approaches for risk models (e.g. tabular and graphical)
Methods for Analyzing the Information Content of Large Neuronal Populations
Get PDFDeciphering how neurons represent the external world is a fundamental goal in neuroscience. This requires identifying which features in the population response in a single trial are informative about the stimulus. Neurons can code stimuli using both space and time. Individual neurons show differential selectivity to certain stimuli across space at coarse time scales while representing others by modulating their activity at fine time scales. The information content in the population is modified from neural interactions across space and time. While this emphasizes the need to examine population responses across space and time, analyzing a population of hundreds of neurons is challenging when only a limited number of trials are available due to the high dimensionality of the joint spatiotemporal response space. We addressed this by introducing a novel method called space-by-time non-negative matrix factorization. The method describes the population activity with a low dimensional representation consisting of spatial modules, groups of neurons that are coactivated, and temporal modules, patterns that describe how these neurons modulate their spiking across time. The population activity in each trial is described by a set of coefficients, that indicate the level of activation of each spatial and temporal module in the trial. We used this method to analyze datasets from auditory, visual and somatosensory modalities. It identified physiologically meaningful spatial and temporal modules that described how each population coded stimuli in space and time. It further indicated the differential contributions of spatial and temporal dimensions for the population code. Particularly, the first spike latency was demonstrated to be informative at the population level. We refined the method to model the sub-Poisson, Poisson and supra-Poisson variability typically observed in spike counts. This refinement demonstrated enhanced capacity in identifying spatial and temporal modules from empirical data and indicated that the activity of a neural population code stimuli using multiple representations. Our findings indicate that our method is scalable to large populations of neurons and has the capacity to efficiently identify biologically meaningful and informative low dimensional representations
Il sindacato di legittimità costituzionale sulla misura delle pene detentive: un'indagine comparata The constitutional review of excessive prison terms: a comparative study
Get PDFThe study focuses on the jurisprudential development of the concept of proportionality of punishment in the Italian and american systems. The most important decisions dealing with such a issue, both of the Italian constitutional court and the SCOTUS are analyzed in detail. There is also an in depth analysis of lower federal courts' and state courts' proportionality jurisprudence, and a focus on the most significant theoretical perspectives elaborated by U.S. scholars, who strongly criticize the proportionality jurisprudence developed in the Suprem Court decisions, especially in the non-capital context
Desiree - a Refinement Calculus for Requirements Engineering
No full textThe requirements elicited from stakeholders suffer from various afflictions, including informality, incompleteness, ambiguity, vagueness, inconsistencies, and more. It is the task of requirements engineering (RE) processes to derive from these an eligible (formal, complete enough, unambiguous, consistent, measurable, satisfiable, modifiable and traceable) requirements specification that truly captures stakeholder needs. We propose Desiree, a refinement calculus for systematically transforming stakeholder requirements into an eligible specification. The core of the calculus is a rich set of requirements operators that iteratively transform stakeholder requirements by strengthening or weakening them, thereby reducing incompleteness, removing ambiguities and vagueness, eliminating unattainability and conflicts, turning them into an eligible specification. The framework also includes an ontology for modeling and classifying requirements, a description-based language for representing requirements, as well as a systematic method for applying the concepts and operators in order to engineer an eligible specification from stakeholder requirements. In addition, we define the semantics of the requirements concepts and operators, and develop a graphical modeling tool in support of the entire framework. To evaluate our proposal, we have conducted a series of empirical evaluations, including an ontology evaluation by classifying a large public requirements set, a language evaluation by rewriting the large set of requirements using our description-based syntax, a method evaluation through a realistic case study, and an evaluation of the entire framework through three controlled experiments. The results of our evaluations show that our ontology, language, and method are adequate in capturing requirements in practice, and offer strong evidence that with sufficient training, our framework indeed helps people conduct more effective requirements engineering