Teses / dissertações sobre o tema "Interface potential"

A method is presented for the determination of interface topography of multi-layered crustal models from gravity or magnetic data. The technique is developed within the framework of discrete linear inverse theory and exploits the quasi-linearity of the problem to derive a simple cost-effective algorithm suitable for use on large gridded data sets.
Variation of auxiliary parameters allows a suite of acceptable models to be produced rapidly and appraised in the light of available geological and geophysical evidence. When independent knowledge concerning the behaviour of specified interfaces is available, the incorporation of such data in the form of linear equality constraints is outlined.
The proposed method is applied to Curie isotherm and Moho mapping in the Abitibi greenstone belt.

Les interfaces entre un conducteur et un isolant sont généralement supposées parfaites, c'est-à-dire que la longueur de Debye dans l'isolant est supposée très grande devant son épaisseur. Il est montré dans ce travail que ce n'est pas le cas et que des états d'interface produisent un potentiel de contact qui peut modifier grandement le comportement de l'interface lorsque le matériau est soumis à un champ électrique intense. En effet le dipôle d'interface à l'origine de la tension d'interface modifie la courbure des bandes d'énergie et donc favorise au au contraire contrarie l'injection ou l'extraction de charges. Une série d'expériences a été réalisée en utilisant la méthode d'onde de pression implémentée à l'aide d'un générateur acoustique de forte puissance sur des échantillons de polyéthylène de différents types, avec différentes électrodes et avec différentes conditions expérimentales. Les dipôles d'interface observés par la mesure influent effectivement sur l'injection de charges lorsque le matériau est sous haute tension. On peut remarquer que l'aluminium a une influence plus importante, notamment lorsqu'il est utilisé avec de l'huile silicone. Lorsque l'isolant ne possède pas d'électrodes, il est préférable de le coupler directement à un polymère chargé en carbone avec de l'huile silicone plutôt que de lui déposer des électrodes sous vide. Le dipôle d'interface observé est en effet plus proche de celui observé avec des électrodes en polymère chargé en carbone collées à chaud. Lors de la mise sous tension, on remarque que les charges pénètrent d'abord dans l'échantillon du fait du dipôle d'interface. La migration de ces charges produisent alors des injections secondaires dues à un effet de champ. La fluoration de la surface des échantillons n'a pas significativement amélioré la situation et n'opère donc pas comme un rempart aux charges, mais plutôt comme une barrière à la diffusion d'impuretés
The interfaces between a conductor and an insulator are generally assumed to be perfect, meaning that the Debye length in the insulator is considered to be much larger than its thickness. However, this work shows that this is not the case and that interface states generate a contact potential that can significantly alter the behavior of the interface when the material is subjected to a strong electric field. Indeed, the interface dipole responsible for the interface voltage modifies the curvature of the energy bands and thus either promotes or hinders charge injection or extraction. A series of experiments was conducted using the pressure wave method, implemented with a high-power acoustic generator on various polyethylene samples, with different electrodes and under various experimental conditions. The interface dipoles observed through measurement do indeed influence charge injection when the material is under high voltage. It is noteworthy that aluminum has a greater influence, particularly when used with silicone oil. When the insulator does not have electrodes, it is preferable to directly couple it with a carbon-filled polymer and silicone oil rather than deposit electrodes on it under vacuum. The interface dipole observed is indeed closer to that seen with carbon-filled polymer electrodes hot-bonded to the material. Upon applying voltage, charges initially penetrate the sample due to the interface dipole. The migration of these charges then leads to secondary injections caused by a field effect. Fluorinating the surface of the samples did not significantly improve the situation and thus does not act as a shield against charges, but rather as a barrier to the diffusion of impurities

Les charges à l'interface liquide/solide sont un élément originel majeur des phénomènes électrocinétiques observés en micro/nanofluidique. Elles sont donc la colonne vertébrale de mon manuscrit de thèse, qui se décompose en trois parties : Dans la première partie, un rappel des concepts de base sur les interfaces liquides/solides est proposé au lecteur. Il est suivi d'une description des différentes méthodes expérimentales permettant de mesurer le potentiel zeta de couples solide/électrolyte, puis d'une présentation des travaux de la littérature exploitant les charges aux interfaces pour la préconcentration de molécules biologiques dans des systèmes Micro-Nano-Micro (MNM) fluidiques. Ensuite, une deuxième partie est consacrée à la mesure du potentiel zeta par la méthode des courants d'écoulement. Nous y présentons l'amélioration du banc expérimental issu des travaux antérieurs à ma thèse, ainsi que le développement de nouveaux protocoles de préparation des surfaces permettant de rationaliser et de stabiliser les mesures. Une application à un détecteur original de molécules biologiques clos cette deuxième partie. Enfin, la troisième et dernière partie s'intéresse à la préconcentration de molécules biologiques. Une méthode originale de fabrication des dispositifs MNM et les résultats de préconcentration obtenus, très encourageants, sont décrits. Des premiers modèles numériques et phénoménologiques sont proposés, qui mettent en avant l'originalité de notre travail
The charges at liquid/solid interfaces are a key element for both understanding and exploiting the electrokinetic phenomena in micro/nanofluidics. The manuscript of my Ph.D thesis is dedicated to these phenomena, which is divided into three main parts: Above all, a simple overview of charges at the liquid/solid interface is proposed. Then, several common methods for measuring the zeta potential at the liquid/solid interface are described. Next, various effective methods to preconcentrate the biological molecules is presented with the help of the surface charges. Secondly, the streaming current, which is a standard method to measure the zeta potential in our laboratory, is detailed. It contains the upgrade of the experimental setup from the previous version and the development of new protocols, which improve dramatically the stabilization and the reproducibility of the measurements. In addition, an original biological sensor is briefly presented based on these advancements. Lastly, in the final part, we describe a method which is primitively utilised in the fabrication of Micro-Nano-Micro fluidic system. Based on this system, some favorable preconcentration results is obtained. Moreover, numerical simulations are presented to prove the originality of our work

Brain-computer interfaces (BCI) provide an alternative communication channel which does not rely on the brain's normal output pathway between patients suffering from neuromuscular diseases and their external environment. BCI requires at least one brain signal as input in order to interpret the intent of the user. Non-invasive electroencephalography (EEG) is the most common and favourite method for acquiring brain signals. In the last two decades, several EEG based BCIs have been developed to help these patients. The brain signals which can be recorded in EEG and used as the input for BCIs include motor sensory rhythm, slow cortical potential, P300 and steady-state visual evoked potential (SSVEP). Compared to the other EEG based BCI paradigms, SSVEP based BCI has the advantage of high information transfer rate, high detection rate, less user training time required and commands scalability. Furthermore, SSVEP based BCI is normally operated in the self paced mode which is more intuitive and practical for real world applications. Recently, SSVEP based BCIs have attracted great attention in the field of BCI research. While most SSVEP BCI studies focus on the improvement of signal detection and classification accuracy, there is a need to bridge the gap between BCI research and practice in the real world. SSVEP based BCI requires an external visual stimulator to elicit SSVEP response. Currently, for most SSVEP based BCIs the viewing distances between the visual stimulator and the users are less than 100cm, limiting the usability and flexibility of BCI and its potential applications and users. This study proposes a novel distance adaptable SSVEP BCI paradigm which allows its users to operate the system from a range of viewing distances between the user and the visual stimulator. Unlike the conventional SSVEP BCI where users can only operate the system when they are sitting in front of the visual stimulator at a fixed distance which is normally less than 100cm, in our proposed system, users can operate the BCI at any viewing distance within the range in this proposed BCI. It is hoped that the proposed BCI system can improve the usability and the flexibility of BCI and also broaden the range of potential applications and users. For example, it can be used by older people with degenerating mobility or by patients with impaired mobility in the care environment to support their independence. Moreover, it can also be used by healthy people in a smart home or for a game control environment. The primary goal of the present study is to investigate the feasibility of the proposed distance adaptable SSVEP based BCI. This study first investigates the impact of the viewing distance on SSVEP response and compensates the deteriorated SSVEP resulting from the viewing distance by changing the intensities of the visual stimuli. 10 healthy subjects participate in the experiment to assess the feasibility of the distance adaptable SSVEP based BCI. The feasibility of the system is evaluated by the classification performance of off-line experiments at different viewing distances. The classification accuracies of the proposed BCI are examined by different EEG time window lengths, number of SSVEP harmonics and the number of recording electrodes employed. This study also investigates the sources of deterioration of SSVEP detection in BCI setup and proposes an electrode ranking method to select the recording electrodes for the implementation of the real time on line system. The experimental results demonstrate that a distance adaptable SSVEP BCI is achievable and that electrodes chosen by the proposed electrode ranking method outperform electrodes chosen by random selection in classification performance.

Amyotrophic lateral sclerosis and other neurodegenerative disorders can cause individuals to lose control of their muscles until they are unable to move or communicate. The development of brain-computer interface (BCI) technology has provided these individuals with an alternative method of communication that does not require muscle movement. Recent research has shown the impact psychological factors have on BCI performance and has highlighted the need for further research. Working memory is one psychological factor that could influence BCI performance. The purpose of the present study is to evaluate the relationship between working memory and brain-computer interface performance. The results indicate that both working memory and general intelligence are significant predictors of BCI performance. This suggests that working memory training could be used to improve performance on a BCI task.

This thesis explores the challenges and potential of technology integration in current ship management practices. While technology advancements were designed to be contributing to minimising task complexity, issues such as fatigue, increased administrative burden and technology assisted accidents still plague the industry. In spite of the clearly recognisable benefits of using modern technology in the management of ships, in practice its application appears lacking by a considerable margin. The main driver of the study was to appreciate the cause of this disparity. The study first reviewed a wide body of literature on issues involving the use of technology which included academic literature with empirical evidences and theoretical explanations of implementation of technology at work. With the help of the extant knowledge this research embarked on providing an explanation to the gap that existed in the application of technology in the shipping industry. By taking a case study approach the thesis looked into the induction and integration of technology in the management and operation of ships that primarily interfaced closely between the ship and its management unit on shore. Three companies with mutually diverse management setup were studied. The fourth case comprised of purposefully selected senior members of ships’ staff. The analysis of the data revealed that the manifestation of the gap in technology implementation is caused by deeper influences at work in the shipping industry. The un-optimised technology integration results in the seafarer, who is the keystone to the technology application, becoming a victim of the circumstances. The technology that was intended to ease operations and burdens ends up in controlling him, even leaving him under-resourced and causing fatigue.This was not an unintended outcome but the result of weak regulatory practices, short-term capital outlook and weakened labour practices in the shipping industry all caused by wider social and economic developments affecting not just this industry but businesses globally. The impact of such influences was however more acute in this industry resulting in such extreme consequence. By bringing to light the limited application of some fundamental principles of human-systems integration, this study has attempted to expand the boundaries of research on the subject and contributed to the holistic understanding of the various underlying factors that influence technology integration in ship management processes.

Os sedimentos aquáticos podem fornecer importantes subsídios na avaliação dos ecossistemas aquáticos lênticos, uma vez que grande parte dos nutrientes se encontra no estado sólido. A ocorrência de uma floração de cianobactérias tóxicas originada no Blang, segundo de três reservatórios em cascata do Sistema Salto de Hidrelétricas, localizado no município de São Francisco de Paula (RS), motivou a investigação das possíveis fontes de nutrientes, especialmente de fósforo (P) que foi identificado como limitante para a eutrofização. Foram investigadas fontes de origens difusas (solos, águas e sedimentos dos tributários) e pontuais (uso urbano e a carga interna representada pelo sedimento do leito dos reservatórios). Os resultados mostraram características oligotróficas nas fontes externas e a presença de P disponível em excesso no sedimento do leito, indicando que a carga interna poderia ser uma fonte significativa de nutrientes. A possibilidade de circulação da água hipolimnética foi investigada através de números adimensionais e características físicas do corpo de água, demonstrando que dificilmente ocorreria, uma vez que somente eventos climáticos extremos poderiam provocar a inversão da massa líquida. Excluídas as fontes externas, os resultados sugerem que a fertilização do reservatório Blang tenha sido causada pela abertura da comporta de fundo do reservatório Divisa, localizado imediatamente à montante, durante uma estiagem. O segundo objetivo desta pesquisa foi avaliar a importância dos agregados de partículas e da seleção granulométrica para a análise química de nutrientes em sedimentos aquáticos. Resultados obtidos em sedimentos de ambientes lóticos e lênticos (Sistema Salto, RS), demonstraram que os agregados maiores (465 - 63 μm) concentram nitrogênio nos ambientes lênticos, por isso a análise deve ser realizada, preferencialmente, na fração ≤ 465 μm em sedimentos de ambientes lênticos e na fração ≤ 63 μm dos ambientes lóticos. O último objetivo deste estudo foi testar os efeitos da oxidação sobre a capacidade e a velocidade da sorção de fosfato em sedimentos aquáticos orgânicos, identificando as melhores condições para retenção. Foram utilizados sedimentos aquáticos siliciclásticos de origens distintas, principalmente no que se refere ao clima e à origem do conteúdo orgânico, alóctone e autóctone, representados pelos tipos Dy (Reservatório Divisa, RS) e Sapropel (Reservatório de Tapacurá, São Lourenço da Mata, PE) respectivamente. O experimento foi realizado em suspensões de sedimentos mantidos sob níveis de potencial redox compreendidos entre - 200 mV e + 400 mV. Resultados demonstram que a sorção de fosfato é maior no sedimento tipo Dy em condições reduzidas e no Sapropel em condições oxidadas.
Water-borne sediments can provide important information for evaluating lentic aquatic ecosystems because a large proportion of their nutrients are found in the solid phase. A toxic algal bloom in the Blang Reservoir, the second of three in the Salto System chain of hydroelectric dams located in Sao Francisco de Paula in Rio Grande do Sul, Brazil, motivated the investigation of possible nutrient sources, especially phosphorus, which was identified as the limiting nutrient for eutrophization. Non-point sources, including soil, water and sediment carried by tributaries, and point sources, including urban areas and the internal load from the reservoir bottom, were examined. Results showed oligotrophic characteristics in the external sources and excess P availability in bottom sediments, indicating that the internal load may be a significant source of nutrients. The possible circulation of hypolimnic water was investigated using adimensional numbers and physical characteristics of the body of water, demonstrating that this is unlikely to occur, since only extreme climatic events could cause inversion of the liquid mass. By excluding external sources, results suggest that the fertilization of the Blang Reservoir was most likely caused by the opening of the floodgates from the Divisa Reservoir immediately upstream during a drought period. The second goal of this study was to evaluate the importance of particle aggregates and particle size selection for chemical analyses of nutrients and water-borne sediments. Results from sediments in lentic and lotic environments from the Salto System show that the larger aggregates (465 - 63 μm) concentrate nitrogen under lentic conditions and that, therefore, analyses should be performed on the fraction smaller than 465 μm in lentic environments and in the fraction ≤ 63 μm in lotic environments. The final objective of this study was to test the effects of oxidation on the phosphate sorption capacity and rate in organic aquatic sediments, identifying the best conditions for retention. Silicate aquatic sediments from different origins in terms of climate and source of organic content (allochtonous or autochtonous) were used, and were represented by the types Dy (Divisa Reservoir, RS) and Sapropel (Tapacurá Reservoir, São Lourenço da Mata, PE), respectively. The experiment was carried out in suspended sediment maintained under levels of redox potential between –200mV and +400mV. Results demonstrated that phosphate sorption is greatest in sediment type Dy under reduced conditions and in Sapropel under oxidized conditions.

This research set out to develop a novel technique to decompose Electroencephalograph (EEG) signal into sets of constituent peaks in order to better describe the underlying nature of these signals. It began with the question; can a localised, single stimulation of sensory nervous tissue in the body be detected in the brain? Flash Visual Evoked Potential (VEP) tests were carried out on 3 participants by presenting a flash and recording the response in the occipital region of the cortex. By focussing on analysis techniques that retain a perspective across different domains � temporal (time), spectral (frequency/scale) and epoch (multiple events) � useful information was detected across multiple domains, which is not possible in single domain transform techniques. A comprehensive set of algorithms to decompose evoked potential data into sets of peaks was developed and tested using wavelet transform singularity detection methods. The set of extracted peaks then forms the basis for a subsequent clustering analysis which identifies sets of localised peaks that contribute the most towards the standard evoked response. The technique is quite novel as no closely similar work in research has been identified. New and valuable insights into the nature of an evoked potential signal have been identified. Although the number of stimuli required to calculate an Evoked Potential response has not been reduced, the amount of data contributing to this response has been effectively reduced by 75%. Therefore better examination of a small subset of the evoked potential data is possible. Furthermore, the response has been meaningfully decomposed into a small number (circa 20) of constituent peaksets that are defined in terms of the peak shape (time location, peak width and peak height) and number of peaks within the peak set. The question of why some evoked potential components appear more strongly than others is probed by this technique. Delineation between individual peak sizes and how often they occur is for the first time possible and this representation helps to provide an understanding of how particular evoked potentials components are made up. A major advantage of this techniques is the there are no pre-conditions, constraints or limitations. These techniques are highly relevant to all evoked potential modalities and other brain signal response applications � such as in brain-computer interface applications. Overall, a novel evoked potential technique has been described and tested. The results provide new insights into the nature of evoked potential peaks with potential application across various evoked potential modalities.

Australia is free from canine rabies. The spread of the disease in Indonesia has increased the risk of rabies incursion in northern Australia. Remote Indigenous communities, such as those in the Northern Peninsula Area (NPA), contain large populations of free-roaming domestic dogs surrounded by dingo populations, creating optimal conditions for rabies establishment. A cross-sectional survey of NPA hunters revealed that hunting practices using domestic dogs create opportunities for dingo-dog interactions. Dingo purity analyses on scats of canine origin collected in the NPA region demonstrated that dingoes visit areas around the communities, increasing the likelihood of contact with roaming domestic dogs. A scoping review on the ecology of dingoes identified density, home range size and contacts between dingoes, three key ecological parameters for disease spread modelling, as major research gaps especially in northern Australia. Dingo population density and home range size in the NPA were estimated from spatially explicit mark-resight models based on data from a one-year camera-trap study. This study also revealed a substantial temporal overlap and spatial correlation in activity between dingoes and domestic dogs, further supporting the likelihood for disease spread at the wild-domestic interface. A novel spatial stochastic rabies spread model, which incorporated field-derived dingo ecological parameters and landscape heterogeneity specific to the NPA, predicted a high probability (59%) of spread to other packs following the introduction of the disease into the dingo population from a roaming or hunting domestic dog. Outbreaks were generally larger when rabies was introduced during the dry season and in areas around the communities. Overall, this research provides compelling evidence of the importance of improving Australia’s preparedness for a potential rabies incursion in high-risk areas, to prevent serious consequences in remote Indigenous communities.

Session ID: SA-B1-3
SCIS & ISIS 2010, Joint 5th International Conference on Soft Computing and Intelligent Systems and 11th International Symposium on Advanced Intelligent Systems. December 8-12, 2010, Okayama Convention Center, Okayama, Japan

Individuals who suffer from severe motor disabilities face the possibility of the loss of speech. A Brain-Computer Interface (BCI) can provide a means for communication through non-muscular control. Current BCI systems use characters that flash from gray to white (GW), making adjacent character difficult to distinguish from the target. The current study implements two types of color stimulus (grey to color [GC] and color intensification [CI]) and I hypotheses that color stimuli will; (1) reduce distraction of nontargets (2) enhance target response (3) reduce eye strain. Online results (n=21) show that GC has increased information transfer rate over CI. Mean amplitude revealed that GC had earlier positive latency than GW and greater negative amplitude than CI, suggesting a faster perceptual process for GC. Offline performance of individual optimal channels revealed significant improvement over online standardized channels. Results suggest the importance of a color stimulus for enhanced response and ease of use.

Cette etude porte sur les proprietes interfaciales du polycrylamide hydrolyse adsorbe sur un aluminosilicate de synthese. La cinetique d'adsorption resultant d'interactions attractives a courtes distances est fortement influencee par l'existence de potentiels electrostatiques a longue portee. L'adsorption induit la creation de charges positives en surface, charges instantanement compensees par un transfert d'anions de la solution vers la zone interfaciale

Damage to the central nervous system (CNS) leads to the generation of an immune response which culminates with the encapsulation of the damaged area. The encapsulation, known as a glial scar, essentially breaks neural signal pathways and blocks signal transmissions to and from the CNS. The effect is the loss of motor and sensory control for the damaged individual. One method that has been used successfully to treat this problem is the use of a brain-machine interface (BMI) which can intercept signals from the brain and use these signals to control a machine. Although there are many types of BMI devices, implantable devices show the greatest promise with the ability to target specific areas of the CNS, with reduced noise levels and faster signal interception, and the fact that they can also be used to send signals to neurons. The largest problem that has plagued this type of BMI device is that the materials that have been used for their construction are not chemically resilient, elicit a negative biological response, or have difficulty functioning for extended periods of time in the harsh body environment. Many of these implantable devices experience catastrophic failure within weeks to months because of these negative factors. New materials must be examined to advance the future utilization of BMI devices to assist people with CNS damage or disease. We have proposed that two semiconductor materials, cubic silicon carbide (3C-SiC) and nanocrystalline diamond (NCD), which should provide solutions to the material biocompatibility problems experienced by implantable BMI devices. We have shown in this study that these two materials show chemical resilience to neuronal cellular processes, and we show evidence which indicates that these materials possess good biocompatibility with neural cell lines that, in the worst case, is comparable to celltreated polystyrene and, in most cases, even surpasses polystyrene. We have utilized 3C-SiC within an electrode device and activated the action potential of differentiated PC12 cells. This work details our initial efforts to modify the surfaces of these materials in order to improve cellular interaction and biocompatibility, and we examine our current and future work on improving our implantable BMI devices.

The effects of neurodegenerative diseases such as amyotrophic-lateral sclerosis (ALS) eventually render those suffering from the illness unable to communicate, leaving their cognitive function relatively unharmed and causing them to be “locked-in” to their own body. With this primary function compromised there has been an increased need for assistive communication methods such as brain-computer interfaces (BCIs). Unlike several augmentative or alternative communication methods (AACs), BCIs do not require any muscular control, which makes this method ideal for people with ALS. The wealth of BCI research focuses mainly on increasing BCI performance through improving stimulus processing and manipulating paradigms. Recent research has suggested a need for studies focused on harnessing psychological qualities of BCI users, such as motivation, mood, emotion, and depression, in order to increase BCI performance through working with the user. The present studies address important issues related to P300-BCI performance: 1) the impact of mood, emotion, motivation, and depression on BCI performance were examined independently; and 2) pleasant, unpleasant, and neutral emotions were induced in order to determine the influence of emotion on BCI performance. By exploring psychological mechanisms that influence BCI performance, further insight can be gained on the best methods for improving BCI performance and increasing the number of potential BCI users. The results from Study 1 did not reveal a significant relationship between any of the four psychological factors and BCI performance. Since previous research has found a significant impact of motivation and mood on BCI performance, it may be the case that these factors only impact performance for some individuals. As this is the first study to directly investigate the impact of emotion and depression on BCI performance, future research should continue to explore these relationships. The results from Study 2 were inconclusive for the pleasant condition, since it appears the pleasant emotion manipulation was unsuccessful. The findings indicate that unpleasant emotions do not have a significant impact on BCI performance. This result is promising since it indicates that individuals should still be able to use the BCI system to communicate, even when they are experiencing unpleasant emotions. Future research should further explore the impact of pleasant emotions on BCI performance.

This thesis study focuses on the realization of an online cue based Motor Imagery (MI) Brain Computer Interface (BCI). For this purpose, some signal processing and classification methods are investigated. Specifically, several time-spatial-frequency methods, namely the Short Time Fourier Transform (STFT), Common Spatial Frequency Patterns (CSFP) and the Morlet Transform (MT) are implemented on a 2-class MI BCI system. Distinction Sensitive Learning Vector Quantization (DSLVQ) method is used as a feature selection method. The performance of these methodologies is evaluated with the linear and nonlinear Support Vector Machines (SVM), Multilayer Perceptron (MLP) and Naive Bayesian (NB) classifiers. The methodologies are tested on BCI Competition IV dataset IIb and an average kappa value of 0.45 is obtained on the dataset. According to the classification results, the algorithms presented here obtain the 4th level in the competition as compared to the other algorithms in the competition. Offline experiments are performed in METU Brain Research Laboratories and Hacettepe Biophysics Department on two subjects with the original cue-based MI BCI paradigm. Average prediction accuracy of the methods on a 2-class BCI is evaluated to be 76.26% in these datasets. Furthermore, two online BCI applications are developed: the ping-pong game and the electrical wheelchair control. For these applications, average classification accuracy is found to be 70%. During the offline experiments, the performance of the developed system is observed to be highly dependent on the subject training and experience. According to the results, the EEG channels P3 and P4, which are considered to be irrelevant with the motor imagination, provided the best classification performance on the offline experiments. Regarding the observations on the experiments, this process is related to the stimulation mechanism in the cue based applications and consequent visual evoking effects on the subjects.

This thesis is part of current research at Center for Intelligence Systems Research (CISR) at The George Washington University for developing new in-vehicle warning systems via Brain-Computer Interfaces (BCIs). The purpose of conducting this research is to contribute to the current gap between BCI and in-vehicle safety studies. It is based on the premise that accurate and timely monitoring of human (driver) brain's signal to external stimuli could significantly aide in detection of driver's intentions and development of effective warning systems. The thesis starts with introducing the concept of BCI and its development history while it provides a literature review on the nature of brain signals. The current advancement and increasing demand for commercial and non-medical BCI products are described. In addition, the recent research attempts in transportation safety to study drivers' behavior or responses through brain signals are reviewed. The safety studies, which are focused on employing a reliable and practical BCI system as an in-vehicle assistive device, are also introduced. A major focus of this thesis research has been on the evaluation and development of the signal processing algorithms which can effectively filter and process brain signals when the human subject is subjected to Visual LED (Light Emitting Diodes) stimuli at different frequencies. The stimulated brain generates a voltage potential, referred to as Steady-State Visual Evoked Potential (SSVEP). Therefore, a newly modified analysis algorithm for detecting the brain visual signals is proposed. These algorithms are designed to reach a satisfactory accuracy rate without preliminary trainings, hence focusing on eliminating the need for lengthy training of human subjects. Another important concern is the ability of the algorithms to find correlation of brain signals with external visual stimuli in real-time. The developed analysis models are based on algorithms which are capable of generating results for real-time processing of BCI devices. All of these methods are evaluated through two sets of recorded brain signals which were recorded by g.TEC CO. as an external source and recorded brain signals during our car driving simulator experiments. The final discussion is about how the presence of an SSVEP based warning system could affect drivers' performances which is defined by their reaction distance and Time to Collision (TTC). Three different scenarios with and without warning LEDs were planned to measure the subjects' normal driving behavior and their performance while they use a warning system during their driving task. Finally, warning scenarios are divided into short and long warning periods without and with informing the subjects, respectively. The long warning period scenario attempts to determine the level of drivers' distraction or vigilance during driving. The good outcome of warning scenarios can bridge between vehicle safety studies and online BCI system design research. The preliminary results show some promise of the developed methods for in-vehicle safety systems. However, for any decisive conclusion that considers using a BCI system as a helpful in-vehicle assistive device requires far deeper scrutinizing.

Con il termine Brain-Computer Interface (BCI) si indica un sistema hardware e software che permette, a partire da segnali di origine cerebrale, di tradurre le intenzioni dell’utente in comandi per il controllo di un dispositivo di output, come computer, sintetizzatori vocali, apparecchi di assistenza e neuroprotesi. Questa tipologia di applicazioni non richiede l’impiego di muscoli periferici, poiché sfrutta solamente specifici segnali generati dall’attività cerebrale. In particolare, il presente elaborato tratta le BCI-speller, ovvero sistemi che permettono la scrittura di un testo sfruttando le variazioni del segnale elettroencefalografico (EEG) suscitate attraverso un’interfaccia grafica (GUI). La GUI è costituita da lettere, simboli e numeri opportunamente presentati, così che, se il soggetto presta attenzione ad uno di essi, particolari potenziali cerebrali vengono elicitati nell’EEG e sfruttati per identificare e quindi selezionare tale simbolo. L’obiettivo dell’elaborato è introdurre l’emergente e promettente campo di ricerca delle BCI, facendo luce sulle caratteristiche dei componenti che le caratterizzano e sulle varie applicazioni a cui si prestano, concentrandosi sulle BCI-speller. A tal fine, sono state presentate BCI-speller basate su due particolari potenziali cerebrali (P300 e SSVEP), ponendo particolare attenzione sugli aspetti che possono portare ad un loro miglioramento. Maggiore enfasi è stata quindi posta sulle diverse GUI delle BCI-speller basate su questi potenziali, in quanto modifiche associate alla presentazione dello stimolo e alla facilità d’uso di queste interfacce possono migliorare in prima battuta il potenziale elicitato, e di conseguenza la prestazione generale della BCI. Infine, sono stati evidenziati i vantaggi e i limiti associati a queste tecnologie, nonché gli sviluppi futuri nella prospettiva di un impiego quotidiano di queste tecnologie da parte di pazienti affetti da disturbi neuromuscolari.

Building complex games like Grand Strategy Games for both PC and console is a costly endeavour. Normally, two different platforms imply two different User Interface (UI) and User Experience (UX) designs, even though it is the same game. If the game’s UI could have similar designs for both platforms, this costly obstacle could be overcome. This study aimed to take the first steps to look at “one UI to rule them all”. Due to the lack of existing research on this topic, this study had to begin from scratch. This led to a focus on existing strategy games on consoles, and an evaluation of the User Experience (UX) of these games. Considering the lack of Grand Strategy Games on consoles, eleven existing strategy games on console similar to Grand Strategy Games were chosen to be investigated further with the aim to find possible best practices and/or the most important aspects of the player’s experience in these games. Through discussion with game industry experts (experienced and senior UX designers), the UI and UX of strategy games on console were broken down and grouped as specific game interactions, with emphasis on the similarity to Grand Strategy Games. By using the defined game interactions, a quantitative survey was carried out to pinpoint the game interactions with the biggest impact on the player’s experience. The analysis of the results from the 864 respondents in the quantitative survey showed the importance of console first. It could be determined by looking at how well the only console first game of the survey did. Halo Wars 2 had the overall best-perceived experience in five out of the eight defined game interactions. Yet the participants preferred playing Halo Wars 2 on PC to an equal extent as they preferred to play it on consoles, concluding that console first seems to be the design approach to use when a game studio wants to ship a game simultaneously to both PC and consoles since it gives the overall best player experience. Furthermore, the pace, meaning the speed with which the player can execute specific in-game actions and reach their goals, was found to be a major factor in the player’s experience of the chosen strategy games on console. This led to a further developed definition of the pace through discussion and workshops with industry experts. Research then continued with remote and unmoderated playtests (qualitative usability testing) of two of the chosen games being most similar to Grand Strategy Games; Stellaris and Sid Meier’s Civilization VI. These playtests aimed to find what are the most important aspects of the pace and how the pace affects the player's experience. When the participants were asked to rank what they thought has the biggest impact on the pace in the game, game mechanical aspects were ranked higher than UI and UX aspects of the pace. This shows the game mechanics to be more important than the UI and UX aspects of the pace when designing the pace in a game like Stellaris and Sid Meier’s Civilization VI.

La modelisation du role des ions chlorures a l'interface acier inoxydable / solution necessite de connaitre la repartition des charges et des potentiels a travers toute l'interface. Des mesures de spectroscopie d'impedance electrochimique et de photoelectrochimie ont permis de connaitre ces repartitions dans le film passif. Les mesures de potentiel d'ecoulement effectuees dans ce travail ont pour but de proposer des repartitions a l'interface film passif / solution. Les mesures ont ete effectuees a l'abandon, c'est-a-dire sans imposer de perturbation electrique exterieure. Des l'immersion de l'acier en solution, il se developpe entre le film passif de l'acier et la solution une interphase. En milieu nacl, cette interphase est constituee notamment de cations metalliques hydrates du substrat et d'ions de l'electrolyte. Le developpement de l'interphase, qui se fait parallelement a son chargement en chlorures, est limitant durant les premieres heures d'immersion et depend, ainsi que les caracteristiques de l'interphase, de l'etat de surface de l'acier. L'interphase participe au signal de potentiel d'ecoulement, contrairement a ce qui est observe pour un materiau inerte comme le verre, qui nous a servi de reference tout au long de ce travail. Cette participation est a l'origine d'un comportement particulier des aciers inoxydables vis-a-vis de la pression imposee dans les mesures. Ici, nous proposons une nouvelle methode de calcul du potentiel zeta qui prend en compte l'existence de cette interphase. Nous avons etudie egalement les proprietes acido-basiques de surface de differents etats de surface d'aciers. Les ph isoelectriques determines varient, selon l'etat de surface, entre 2 et 5. Ils sont plus acides que les ph isoelectriques des oxydes de fer et de chrome. Les resultats de mesures xps ont mis en evidence que le rapport chrome sur fer dans la couche passive augmentait avec le ph isoelectrique.

Chemisorption of an organic monolayer to tune the surface properties of a transparent conductive oxide (TCO) electrode can improve the performance of organic electronic devices that rely on efficient charge transfer between an organic active layer and a TCO contact. Here, a series of perylene diimides (PDIs) was synthesized and used to study relationships between monolayer structure/properties and electron transfer kinetics at PDI-modified indium-tin oxide (ITO) electrodes. In these PDI molecules, one of the imide substituents is a benzene ring bearing a phosphonic acid (PA) and the other is a bulky aryl group that is twisted out of the plane of the PDI core. The size of the bulky aryl group and the substitution of the benzene ring bearing the PA were both varied, which altered the extent of aggregation when these molecules were absorbed as monolayer films (MLs) on ITO, as revealed by both attenuated total reflectance (ATR) and total internal reflection fluorescence spectra. Polarized ATR measurements indicate that, in these MLs, the long axis of the PDI core is tilted at an angle of 33-42 degrees relative to the surface normal; the tilt angle increased as the degree of bulky substitution increased. Rate constants for electron transfer (k(s,opt)) between these redox-active modifiers and ITO were determined by potential-modulated ATR spectroscopy. As the degree of PDI aggregation was reduced, k(s,opt) declined, which is attributed to a reduction in the lateral electron self-exchange rate between adsorbed PDI molecules, as well as the heterogeneous conductivity of the ITO electrode surface. Photoelectrochemical measurements using a dissolved aluminum phthalocyanine as an electron donor showed that ITO modified with any of these PDIs is a more effective electron-collecting electrode than bare ITO.

Individuals who suffer from amyotrophic lateral sclerosis (ALS) have a loss of motor control and possibly the loss of speech. A brain-computer interface (BCI) provides a means for communication through nonmuscular control. Visual BCIs have shown the highest potential when compared to other modalities; nonetheless, visual attention concepts are largely ignored during the development of BCI paradigms. Additionally, individual performance differences and personal preference are not considered in paradigm development. The traditional method to discover the best paradigm for the individual user is trial and error. Visual attention research and personal preference provide the building blocks and guidelines to develop a successful paradigm. This study is an examination of a BCI-based visual attention assessment in an ALS sample. This assessment takes into account the individual’s visual attention characteristics, performance, and personal preference to select a paradigm. The resulting paradigm is optimized to the individual and then tested online against the traditional row-column paradigm. The optimal paradigm had superior performance and preference scores over row-column. These results show that the BCI needs to be calibrated to individual differences in order to obtain the best paradigm for an end user.

This thesis explores how an Android application that is used in combination with tangible appcessories is capable of facilitating a learning experience for visually impaired students within the specific domain of geometry. This study’s approach illustrates how using an application in combination with a physical appcessory can provide information concerning geometry to the visually impaired. An application, called Invisible Tangible Geometry (ITG), was programmed using Android in conjunction with a 3D printed model. This thesis describes the application, the physical appcessory, as well as early stage user studies. The application enables visually impaired users to explore simple geometric forms displayed on a tablet through sound and vibrotactile feedback. A physical appcessory, that can be manipulated to adopt several forms and is dynamic, is used in addition. Its shape is sensed by the tablet adds an additional tactile layer to the application and experience. Within the thesis a methodological framework, as well as a user-centered design approach was applied. An expert interview and three user engagements with visually impaired individuals serve as early validations of the project and ideas and provide feedback that directs design and development of future work. Current avenues for the future work will include additional interaction modes in the application. For example, the ability to digitize real world forms, and improving the robustness of the tangible appcessory. The plan, for future development, is to establish an autonomous functioning application that enables the visually impaired to be able to explore, participate and interact with geometry smoothly and without the need of aid from others. The correlation of application and appcessory will allow for anything between a quick glance, through feeling the model, and gaining detailed information, by using the application. The application enhances provided information through the use of a model and enriched digital feedback.

This thesis illustrates how geophysical and geochemical methods can be combined to study archaeological sites and obtain enhanced interpretations of the results using the complementary information they provide. Whilst these two disciplines tend to be used independently, this thesis brings them together, with a view to exploring their relationships and developing strategies that lead to non-destructive and cost-effective surveys. The investigation focuses on the correlation of geophysical and geochemical results over common archaeological features and their analysis using soil geochemistry in order to understand the factors of contrast involved in their detection. Five case study sites in Scotland were selected, each one presenting a specific challenge to be assessed by the integrated methodology developed in this thesis. The research employed a range of geophysical (earth resistance, magnetometry, magnetic susceptibility, FDEM and GPR) and geochemical (total phosphate and multi-element analysis) techniques routinely used in archaeological prospection. The different geophysical responses obtained over targeted archaeological features were considered with respect to soil texture, organic matter content, pH, conductivity and chemical composition from archaeological deposits, topsoil and subsoil samples. The results not only provide a nuanced understanding of the character of the archaeological features surveyed, but begin to develop a better insight of how the setting of a site may affect geophysical and geochemical datasets at Scottish archaeological sites. This thesis concludes that the detection of archaeological anomalies depends upon inter-related and site-specific contrast factors including: general site settings (e.g. the effect of highly variable glacial drift deposits), the type of features to be detected (e.g. cut or impervious), and the effect of soil post-depositional processes inside archaeological features and surrounding matrix. For example, at the prehistoric site at Forteviot site (Perthshire) redox processes inside archaeological ditches contribute to their negative magnetic response. Also, chemical composition related to anthropogenic organic materials may enhance the conductivity of theoretical impervious features as illustrated at the Bay of Skaill site (Orkney).

This thesis aims to analyze how interfacing affects viewer experiences and viewer positions, and how glitch art online makes that effect visible. Glitch art is concerned with disruptions in the systems that govern how for instance photography is produced, circulated and displayed in a digital image flow. The system’s usually undisrupted operation emerges through the friction created between the key components of the study: the viewer, the photo-based mediation, and the inter­face where the two meet. These components are encircled by the relation between individual and system, whose increased integration with one another requires a sharper eye: a tactical spectatorship in response to how the interface of the image flow can turn the individual into a part of the system. The unfolding of such a spectatorship is in­vestigated through three questions: What can a viewer see and do by interfacing with the web­site, and with what means? How is the photo-based material on the web­site produced, dis­played and concept­ualized? How does the website and its photo-based material – glitched and not glitched – position the viewer haptically and epistemologically? With a cross disciplinary approach, three media phenomenological case studies present glitch artworks­ in an online environment. The case study on Phillip Stearns’s project Year of the Glitch concerns the web­site’s index and archive pages as well as still images with a focus on camera reconstruction, verbal con­cept­ualization, and image materiality. The case study on Rosa Menkman’s website Sunshine in My Throat includes index and artwork pages, two art­works with still and moving images as well as a thema­ti­za­tion of the entire online environ­ment being glitched. The case study on Evan Meaney’s project Ceibas Cycle focuses on the index page and an interface-based artwork, two video works as well as a portfolio of photo­graphs that are not glitched. The timeliness of the case study materials – created between 2004 and 2012 – is anchored in systems aesthetics, in which technical problems are explored as a cultural critique since the 1960s. The quali­tative analysis both emphasizes and problem­atizes experience, as a complement to quantitative studies about images in relation to a digital flow. The study analyzes how glitch art shapes experiences both by follow­ing the interface and by disrupting it. The effect of the underlying system thus appears in a material that has not yet been given an in-depth art historical analysis with a particular focus on the individual viewer. With such a focus, glitch is conceptualized as systemic friction in this study, which clarifies how the artworks online produce knowledge about the interface by providing the individual with a possibility of creating tactical breaks into the image flow. The results of the study consist of the ways of seeing that develop such a possibility – and they gain relevance as they make visible how the flow usually operates in invisible ways. These results point out that the experience of the artworks – and by ex­ten­sion, other experiences of images online – can alert viewers to their own activity within the image flow. If the system sets boundaries for experiences of and through the interface, a tactical spectatorship becomes possible when a glitch gives the individual an opportunity to try different positions towards these boundaries.

L'étude par neuro-imagerie de l'activité de plusieurs cerveaux en interaction (hyperscanning) permet d'étendre notre compréhension des neurosciences sociales. Nous proposons un cadre pour l'hyperscanning utilisant les interfaces cerveau-ordinateur multi-utilisateur qui inclut différents paradigmes sociaux tels que la coopération ou la compétition. Les travaux de cette thèse comportent trois contributions interdépendantes. Notre première contribution est le développement d'une plateforme expérimentale sous la forme d'un jeu vidéo multijoueur, nommé Brain Invaders 2, contrôlé par la classification de potentiels évoqués visuels enregistrés par électroencéphalographie (EEG). Cette plateforme est validée par deux protocoles expérimentaux comprenant dix-neuf et vingt-deux paires de sujets et utilise différentes approches de classification adaptative par géométrie riemannienne. Ces approches sont théoriquement et expérimentalement comparées et nous montrons la supériorité de la fusion des classifieurs indépendants sur la classification d'un hypercerveau durant la seconde contribution. L'analyse de coïncidence des signaux entre les individus est une approche classique pour l'hyperscanning, elle est pourtant difficile quand les signaux EEG concernés sont transitoires avec une grande variabilité (intra- et inter-sujet) spatio-temporelle et avec un faible rapport signal-à-bruit. En troisième contribution, nous proposons un nouveau modèle composite de séparation aveugle de sources physiologiquement plausibles permettant de compenser cette variabilité. Une solution par diagonalisation conjointe approchée est proposée avec une implémentation d'un algorithme de type Jacobi. A partir des données de Brain Invaders 2, nous montrons que cette solution permet d'extraire simultanément des sources d'artéfacts, des sources d'EEG évoquées et des sources d'EEG continues avec plus de robustesse et de précision que les modèles existants
The study of several brains interacting (hyperscanning) with neuroimagery allows to extend our understanding of social neurosciences. We propose a framework for hyperscanning using multi-user Brain-Computer Interfaces (BCI) that includes several social paradigms such as cooperation or competition. This dissertation includes three interdependent contribution. The first contribution is the development of an experimental platform consisting of a multi-player video game, namely Brain Invaders 2, controlled by classification of visual event related potentials (ERP) recorded by electroencephalography (EEG). The plateform is validated through two experimental protocols including nineteen and twenty two pairs of subjects while using different adaptive classification approaches using Riemannian geometry. Those approaches are theoretically and experimentally compared during the second contribution ; we demonstrates the superiority in term of accuracy of merging independent classifications over the classification of the hyperbrain during the second contribution. Analysis of inter-brain synchronizations is a common approach for hyperscanning, however it is challenging for transient EEG waves with an great spatio-temporal variability (intra- and inter-subject) and with low signal-to-noise ratio such as ERP. Therefore, as third contribution, we propose a new blind source separation model, namely composite model, to extract simultaneously evoked EEG sources and ongoing EEG sources that allows to compensate this variability. A solution using approximate joint diagonalization is given and implemented with a fast Jacobi-like algorithm. We demonstrate on Brain Invaders 2 data that our solution extracts simultaneously evoked and ongoing EEG sources and performs better in term of accuracy and robustness compared to the existing models

La formation contrôlée de cocristaux est un objectif important dans le developpement de médicaments. Ce travail a utilisé l'électrochimie à l'interface entre deux liquides non miscibles (ITIES) pour contrôler la formation de cocristaux. Dans la première partie, le comportement électrochimique de la caféine a été étudié au moyen de la voltampérométrie cyclique (CV) et de la voltampérométrie à courant alternatif (ACV). La caféine est un cation hydrophile donc, elle a été transférée à un potentiel hautement positif. Le transfert de la caféine (CaffH+) a été vérifié à différents pH et le pH 2 a été choisi comme étant le plus optimal pour la formation de cocristaux. L'expérience de contrôle a prouvé que le 1-hydroxy-2-naphtoïque (1H2N) ne transfére pas à l'ITIES. L'ACV a fourni des informations sur l'influence de la composition de la phase aqueuse et organique. Les valeurs ont changé lorsque CaffH+ seul, 1H2N seul et 1H2N et CaffH+ étaient présents dans la phase aqueuse. Ces résultats suggèrent que ces deux molécules sont actives au niveau interfacial. Dans la deuxième partie, la cocristallisation de Caff et 1H2N a été étudiée à l'ITIES sous polarisation chimique. L'interface a été polarisée par l'ajout d'anions hydrophobes à la phase organique. De cette façon, une cocristallisation sélective a été obtenue, comme vérifié par la diffraction des rayons X et la spectroscopie Raman. Des potentiels interfaciaux positifs ont favorisé la formation d'une forme polymorphe de cocristal de Caff : 1H2N et un potentiel négatif a inhibé la cocristallisation à l'interface liquide-liquide. Cette approche du contrôle électrochimique de la cocristallisation ouvre de nouvelles possibilités pour le développement de médicaments. Dans la troisième partie, la mesure simultanée des variations de potentiel (∆E) et de courant (I) aux ITIES, qui ont été polarisées en utilisant des cations tétraalkylammonium comme ion commun a été rapportée. Divers rapports de concentration de tétraméthyl-, tétraéthyl- et tétrapropylammonium ont été dissous dans les deux phases. Ces systèmes biphasiques ont ensuite été utilisés pour vérifier que la différence de potentiel interfacial mesurée correspondait aux calculs théoriques. Ce dispositif expérimental a ensuite été utilisé pour étudier le processus de cocristallisation interfaciale de CaffH+ hydrophile et cationique avec 1H2N lipophile. La présence de caféine dans la phase aqueuse a conduit à des valeurs de courant plus élevées, causées par le transfert de charge interfacial. De telles variations de courant ont été observées aussi bien en l'absence qu'en présence de 1H2N dans la phase organique. L'analyse du bruit du courant électrochimique a montré une nette différence entre les cellules dans lesquelles les cocristaux sont formés et celles dans lesquelles la cocristallisation est entravée, soit par un potentiel négatif, soit par un changement de pH. La méthode ECN est un outil puissant pour suivre les changements qui se produisent aux ITIES dans les expériences sur les ions communs par la mesure simultanée du potentiel et du courant. Dans la dernière partie, des cocristaux ont été formés sur les ITIES selon les conditions choisies par la méthode des plans d'expériences (DoE). Différents facteurs ont été testés : électrolytes en phase aqueuse, divers solvants et sels appliquant un potentiel positif. L'analyse XRD a montré les conditions permettant d'obtenir une phase I et une phase II presque pures. L'étude des ∆E et I simultanés et de la tension interfaciale a prouvé que le potentiel appliqué influence la cinétique du processus de cocristallisation. La méthode DoE a indiqué que le sel organique est le facteur ayant un impact actif sur la cocristallisation aux ITIES
Controlled formation of cocrystals is an important objective in drug development. This work used the electrochemistry at interface between two immiscible liquids (ITIES) to control the formation of cocrystals. In the first part, the electrochemical behaviour of caffeine was investigated by the means of cyclic voltammetry (CV) and alternating current voltammetry (ACV). The caffeine is the hydrophilic cation thus, it transferred at highly positive potential. Transfer of caffeine (Caff) was verified at various pH and the pH 2 was chosen to be the most optimal for the cocrystals formation. The control experiment proved that 1-hydroxy-2-naphthoic (1H2N) did not transfer at ITIES. ACV provided the information about the influence of the aqueous and organic phase composition. Values have changed when CaffH+ alone, 1H2N alone and both 1H2N and CaffH+ were present in the aqueous phase. These suggest that these two molecules are interfacially active. In the third part the simultaneous measurement of potential (∆E) and current (I) variations at the ITIES, which were polarised using tetraalkylammonium cations as a common ion was reported. Various concentration ratios of tetramethyl-, tetraethyl-, and tetrapropylammonium were dissolved in both phases. Such biphasic systems were then used to verify that the interfacial potential difference measured fit the theoretical calculations. This experimental set-up was next used to probe the interfacial cocrystallisation process of hydrophilic and cationic CaffH+ with lipophilic 1H2N. The presence of caffeine in the aqueous phase led to higher current values, caused by interfacial charge transfer. Analysis of the electrochemical current noise showed a clear difference between cells in which cocrystals are formed and those in which cocrystallisation is hindered, either by a negative potential or by a change in pH. The EN method is a powerful tool to follow the changes occurring at ITIES in common ion experiments by simultaneous measurement of potential and current. In the last part, cocrystals were formed on the ITIES according to the conditions chosen by the design of experiments (DoE) method. Various factors were tested: electrolytes in the aqueous phase, various solvents and salts applying positive potential. The XRD analysis showed the conditions to obtain almost pure Phase I and almost pure phase II. Study of simultaneous ∆E and I and the interfacial tension proved that the applied potential influences the kinetics of the cocrystallization process. DoE method indicated organic salt as the factor having an active impact on cocrystallization at ITIES

ABSTRACT EFFECTS OF WILDLAND-URBAN INTERFACE FUEL TREATMENTS ON POTENTIAL FIRE BEHAVIOR AND ECOSYSTEM SERVICES IN THE CENTRAL SIERRA NEVADA MOUNTAINS OF CALIFORNIA Christopher C. Hamma For the past several decades, the wildland-urban interface (WUI) has been expanding in the low- to mid-elevation mixed-conifer belt of California’s Sierra Nevada mountain range. Concurrently, the effects of fire exclusion and shifting climatic patterns in this region have led to increases in wildfire size and severity, posing an ever-greater risk to life and property. As a result, the need for implementation of fuel treatments to reduce fire hazard is generally recognized to be urgent. However, by removing vegetation, these treatments may also diminish the ability of forest ecosystems to provide valuable ecosystem services to society. Forest managers, landowners, and other WUI stakeholders would therefore benefit from a better understanding of the effects of various fuel treatment types on both fire hazard reduction and ecosystem benefits. The present study examined the effects of four commonly-used fuel treatment types on stand-level forest structural characteristics, surface and canopy fuel loading, potential fire behavior, air pollution removal, and carbon sequestration and storage. Fuel treatments involving thinning and/or prescribed burning were largely successful at reducing live and dead fuel loading, with corresponding reductions in predicted fire behavior. The little-studied but increasingly popular practice of mastication (chipping or shredding small trees and brush and leaving the debris on the ground) was associated with significantly increased surface fuel loading, although deleterious effects on potential fire behavior were not found. Overall, the findings from the fire and fuels portion of the present research largely match those reported in other, similar studies in Sierra Nevada mixed-conifer forest. However, the current analysis found little in the way of significant treatment effects on stand-level air pollution removal or carbon dynamics. This study was affected by challenges including small sample size and high variability in the data; nonetheless, the results underscore the general validity of fuel treatment implementation in central Sierra Nevada WUI areas for moderating wildfire severity and effects, with the recognition that the efficacy of such treatments may be limited under extreme weather conditions.

Considerons l'experience d'electro-mouillage : une goutte de liquide mouille partiellement un film polymere. On applique une difference de potentiel entre cette goutte et une contre-electrode placee sous le polymere isolant. L'equilibre de la goutte chargee resulte des forces de tension superficielle, gravitationnelle et electrostatique. Un raisonnement simple prevoit un etalement de grande amplitude de la goutte sur le polymere lorsque la difference de potentiel est elevee. Cependant, apres un etalement sensible, l'experience fait apparaitre un blocage inattendu de la goutte soumise a un potentiel superieur a une valeur critique. Ce travail consiste en la modelisation mathematique et la simulation numerique de l'experience d'electro-mouillage, dans le but de determiner l'origine de ce blocage. Le modele est formule comme un probleme d'optimisation de forme tridimensionnelle. L'energie a minimiser est definie par l'intermediaire du gradient de la solution d'un probleme elliptique exterieur, qu'on resout par une methode d'equations integrales. La difficulte principale reside dans le caractere infini de la solution de l'equation integrale, au voisinage de la ligne de mouillage de la goutte. Pour la traiter, on etudie a priori le comportement du potentiel, puis on developpe une methode specifique faisant intervenir des fonctions de base singulieres ; l'utilisation de ces fonctions souleve des difficultes de derivation de forme. Ensuite, les simulations numeriques permettent de mettre en valeur le phenomene physique preponderant dans le blocage.

Being completely lost in an unfamiliar environment can be inconvenient, stressful and, at times, even dangerous. Maps are the traditional tools used for guidance but many people find maps difficult to use. In recent years, new tools like outdoor Augmented Reality (AR) have become available which allow virtual navigation cues to be directly overlaid on the real world, potentially overcoming the limitations of maps. However, it has been hypothesized that lower effort invested in processing navigation guidance may lead to diminished spatial knowledge (SK) thereby making users of such navigation tools far more vulnerable to getting lost should the tools fail for any reason. This thesis explores the research question of how AR and maps compare as tools for pedestrian navigation guidance as well as for SK acquisition and if there is a potential for AR tools be developed that would balance the two. We present a series of studies to better understand the consequences of using AR in a pedestrian navigation tool. The first two studies compared time-on-task performance and user preferences for AR and Map navigation interfaces on an outdoor navigation task. The results were not aligned with expectations, which led us to build a controlled testing environment for comparing AR and map navigation. Using this simulated setting, our third study verified the assumption that AR can indeed result in more efficient navigation performance and it supported the hypothesis that this would come at the cost of weaker SK. In our fourth study, we used a dual task design to compare the relative cognitive resources required by map and AR interfaces. The quantitative data collected indicated that users could potentially accept additional workload designed to improve SK without incurring significantly more effort. Our fifth and final study explored an interface with additional AR cues that could potentially balance navigation guidance with SK acquisition. The contributions of this thesis include insights into performance issues relating to AR, a classification of user types based on navigation tool usage behavior, a testbed for simulating perfect AR tracking in a virtual setting, objective measures for determining route knowledge, the capacity that pedestrian navigation tool users may have for performing additional tasks, and guidelines that would be helpful in the design of pedestrian navigation tools.

Thesis (M.S.)--Boston University
PURPOSE: Tbis study will look at the feasibility of Steady State Visually Evoked Potential (SSVEP) brain-computer interfaces (BCI) as possible augmentative and alternative communication (AAC) systems for individuals who are severely disabled such as those with Locked-in Syndrome (LIS). The study intended to test whether there is a difference in BCI performance between healthy and impaired individuals and why. Specifically, the study focused on the operational competency, such as ocular motor function, ofthe impaired individuals as it relates to performance. Further, the study also attempted to explore the contributions of environmental distracts to performance. The results oftbis investigation will provide insights valuable for future BCI-AAC development and the potential for their acceptance by the AAC and LIS communities. METHODS: The study consisted of 12 healthy adults and 5 severely disabled adults presenting with 4 different neurological disorders. Tbis study consisted to two parts. The first part was an assessment ofthe communicative abilities ofthe impaired subjects. The assessment was conducted through a video recorded interview, from which communication rates were calculated and behavioral observations of each impaired subject's communicative behaviors were made with a focus on ocular motor behavior. The second part involved testing of the SSVEP BCI. All subjects performed selection tasks from a choice of four directions in the UDLR task. For each trial, the subject was prompted to attend to a specific SSVEP stimulus. Each stimulus was selected at random to flash at one of four frequencies (12, 13, 14, or 15Hz) (Lorenz, 2012). After 4 seconds, the BCI predicted the attended cue direction (Up, Down, Left, Right). If the prediction was correct, a "thumbs-up" feedback signal was shown to the subject; a "thumbs-down" was shown for incorrect predictions. The UDLR data collected for each trial consisted of a table with two columns: one column recorded the ground truth, which was the target direction, and one column recorded the decoded, or classified direction. Two additional columns were added. One column indicated whether the subject had any ocular motor impairment with a 1 or 0. A binary logistic regression was completed to investigate the main effect of age, subject group, and ocular motor impairment with respect to BCI accuracy. Additionally, observations regarding the affect of environmental distractions were also made. [TRUNCATED]

Les accumulateurs LiNi0.4Mn1.6O4 (LNMO)/Li4Ti5O12 (LTO), permettent d’atteindre théoriquement les densités de puissance et d’énergie fournissant une autonomie suffisante aux véhicules électriques. Cependant, deux problèmes majeurs liés à LNMO limitent leurs performances : l’oxydation prononcée des électrolytes à base de carbonates d’alkyles et la dissolution d’ions de métaux de transition (Mn2+, Ni2+). Les formulations à base de carbonate d’éthylène (EC) ont une aptitude à former des films polymères couvrant la matière active. Les cyclages galvanostatiques, faisant suite ou non à un stockage, confirment la supériorité de ces électrolytes, conduisant à des pertes de capacité réduites de l’électrode LNMO. D’autre part, les sulfones sont des composés prometteurs pour une utilisation dans les batteries LNMO/LTO. L’emploi de cellules symétriques et asymétriques démontre que les sulfones sont non-réactives vis-à-vis des interfaces LNMO/électrolyte et LTO/électrolyte. Cependant, cette non-réactivité ne permet pas le dépôt de films polymères qui auraient permis de stopper la dissolution d’ions Mn2+ et Ni2+ à partir de l’électrode positive. Ceci résulte en des performances dégradées à 30°C des accumulateurs par rapport à ceux employant EC dans les électrolytes
LiNi0.4Mn1.6O4 (LNMO)/Li4Ti5O12 (LTO) accumulators should theoretically achieve the power and energy densities that provide sufficient autonomy to electric vehicles. However, two major issues related to the use of LNMO limit their performances: the pronounced oxidation of the alkylcarbonate-based electrolytes and the transition metal ion (Mn2+, Ni2+) dissolution. The ethylene carbonate (EC)-based formulations get an ability to form polymer-covering films onto the active material. The galvanostatic cycling tests, after storage or not, confirm the superiority of these electrolytes, leading to reduced capacity losses of the LNMO electrode. Furthermore, sulfones are promising compounds to be applied to LNMO/LTO batteries. The use of symmetric and asymmetric cells demonstrates that sulfones are non-reactive towards the LNMO/electrolyte and LTO/electrolyte interfaces. However, this non-reactivity does not allow the deposition of polymer films, which would have enabled to stop the Mn2+ and Ni2+ dissolution from the positive electrode. This results in degraded performances of batteries at 30°C compared to those using EC in electrolytes

Neuronal networks are at the base of information processing in the brain. They are series of interconnected neurons whose activation defines a recognizable linear pathway. The main goal of studying neural ensembles is to characterize the relationship between the stimulus and the individual or general neuronal responses and the relation amongst the electrical activities of neurons within the network, also understanding how topology and connectivity relates to their function. Many techniques have been developed to study these complex systems: single-cell approaches aim to investigate single neurons and their connections with a limited number of other nerve cells; on the opposite side, low-resolution large-scale approaches, such as functional MRI (Magnetic Resonance Imaging) or electroencephalography (EEG), record signal changes in the brain that are generated by large populations of cells. More recently, multisite recording techniques have been developed to overcome the limitations of previous approaches, allowing to record simultaneously from huge neuronal ensembles with high spatial resolution and in different brain regions, i.e. by using implantable semiconductor chips. Local Field Potentials (LFPs), the part of electrophysiological signals that has frequencies below 500 Hz, capture key integrative synaptic processes that cannot be measured by analyzing the spiking activity of few neurons alone. Several studies have used LFPs to investigate cortical network mechanisms involved in sensory processing, motor planning and higher cognitive processes, like memory and perception. LFPs are also promising signals for steering neuroprosthetic devices and for monitoring neural activity even in human beings, since they are more easily and stably recorded in chronic settings than neuronal spikes. In this work, LFP profiles recorded in the rat barrel cortex through high-resolution CMOS-based needle chips are presented and compared to those obtained by means of conventional Ag/AgCl electrodes inserted into glass micropipettes, which are widely used tools in electrophysiology. The rat barrel cortex is a well-known example of topographic mapping where each of the whiskers on the snout of the animal is mapped onto a specific cortical area, called a barrel. The barrel cortex contains the somatosensory representation of the whiskers and forms an early stage of cortical processing for tactile information, along with the trigeminal ganglion and the thalamus. It is an area of great importance for understanding how the cerebral cortex works, since the cortical columns that form the basic building blocks of the neocortex can be actually seen within the barrel. Moreover, the barrel cortex has served as a test-bed system for several new methodologies, partly because of its unique and instantly identifiable form, and partly because the species that have barrels, i.e. rodents, are the most commonly used laboratory mammal. The barrel cortex, the whiskers that activate it and the intervening neural pathways have been increasingly the subject of focus by a growing number of research groups for quite some time. Nowadays, studies (such this one) are directed not only at understanding the barrel cortex itself but also at investigating issues in related fields using the barrel cortex as a base model. In this study, LFP responses were evoked in the target barrel by repeatedly deflecting the corresponding whisker in a controlled fashion, by means of a specifically designed closed-loop piezoelectric bending system triggered by a custom LabView acquisition software. Evoked LFPs generated in the barrel cortex by many consecutive whiskers' stimulations show large variability in shapes and timings. Moreover, anesthetics can deeply affect the profile of evoked responses. This work presents preliminary results on the variability and the effect of commonly used anesthetics on these signals, by comparing the distributions of evoked responses recorded from rats anesthetized with tiletamine-xylazine, which mainly blocks the excitatory NMDA receptors, and urethane, which conversely affects both the excitatory and inhibitory system, in a complex and balanced way yet preserving the synaptic plasticity. Representative signal shape characteristics (e.g., latencies and amplitude of events) extracted from evoked responses acquired from different cortical layers are analyzed and discussed. Statistical distributions of these parameters are estimated for all the different depths, in order to assess the variability of LFPs generated by individual mechanical stimulations of single whiskers along the entire cortical column. Preliminary results showed a great variability in cortical responses, which varied both in latency and amplitude across layers. We found significant difference in the latency of the first principal peak of the responses: under tiletamine-xylazine anesthetic, the responses or events of the evoked LFPs occurred later than the ones recorded while urethane was administered. Furthermore, the distributions of this parameter in all cortical layers were narrower in case of urethane. This behavior should be attributed to the different effects of these two anesthetics on specific synaptic receptors and thus on the encoding and processing of the sensory input information along the cortical pathway. The role of the ongoing basal activity on the modulation of the evoked response was also investigated. To this aim, spontaneous activity was recorded in different cortical layers of the rat barrel cortex under the two types of anesthesia and analyzed in the statistical context of neuronal avalanches. A neuronal avalanche is a cascade of bursts of activity in neural networks, whose size distribution can be approximated by a power law. The event size distribution of neuronal avalanches in cortical networks has been reported to follow a power law of the type P(s)= s^-a, with exponent a close to 1.5, which represent a reflection of long-range spatial correlations in spontaneous neuronal activity. Since negative LFP peaks (nLFPs) originates from the sum of synchronized Action Potentials (AP) from neurons within the vicinity of the recording electrode, we wondered if it were possible to model single nLFPs recorded in the basal activity traces by means of only one electrode as the result of local neuronal avalanches, and thus we analyzed the size (i.e. the amplitude in uV) distribution of these peaks so as to identify a suitable power-law distribution that could describe also these single-electrode records. Finally, the results of the first ever measurements of evoked LFPs within an entire column of the barrel cortex obtained by means of the latest generation of CMOS-based implantable needles, having 256 recording sites arranged into two different array topologies (i.e. 16 x 16 or 4 x 64, pitches in the x- and y-direction of 15 um and 33 um respectively), are presented and discussed. A propagation dynamics of the LFP can be already recognized in these first cortical profiles. In the next future, the use of these semiconductor devices will help, among other things, to understand how degenerating syndromes like Parkinson or Alzheimer evolve, by coupling detected behaviors and symptoms of the disease to neuronal features. Implantable chips could then be used as 'electroceuticals', a newly coined term that describes one of the most promising branch of bioelectronic medicine: they could help in reverting the course of neurodegenerative diseases, by constituting the basis of neural prostheses that physically supports or even functionally trains impaired neuronal ensembles. High-resolution extraction and identification of neural signals will also help to develop complex brain-machine interfaces, which can allow intelligent prostheses to be finely controlled by their wearers and to provide sophisticated feedbacks to those who have lost part of their body or brain functions.
Le reti neuronali sono alla base della codifica dell'informazione cerebrale. L'obiettivo principale dello studio delle popolazioni neuronali è quello di caratterizzare la relazione tra uno stimolo e la risposta individuale o globale dei neuroni e di studiare il rapporto tra le varie attività elettriche dei neuroni appartenenti ad una particolare rete, comprendendo anche come la topologia e la connettività della rete neuronale influiscano sulla loro funzionalità. Fino ad oggi, molte tecniche sono state sviluppate per studiare questi sistemi complessi: studi a singola cellula mirano a studiare singoli neuroni e le loro connessioni con un numero limitato di altre cellule; sul lato opposto, approcci su larga scala e a bassa risoluzione, come la risonanza magnetica funzionale o l'elettroencefalogramma, registrano segnali elettrofisiologici generati nel cervello da vaste popolazioni di cellule. Più recentemente, sono state sviluppate tecniche di registrazione multisito che mirano ad abbattere le limitazioni dei precedenti approcci, rendendo possibile la misurazione ad alta risoluzione di segnali generati da grandi ensamble neuronali e da diverse regioni del cervello simultaneamente, ad esempio mediante l'uso di chip impiantabili a semiconduttore. I potenziali di campo locali (LFP) catturano processi sinaptici chiave che non possono essere estratti dall'attività di spiking di qualche neurone isolato. Numerosi studi hanno utilizzato gli LFP per studiare i meccanismi corticali coinvolti nei processi sensoriali, motori e cognitivi, come la memoria e la percezione. Gli LFP rappresentano anche dei segnali interessanti nell'ambito delle applicazioni neuroprotesiche e per monitorare l'attività cerebrale negli esseri umani, dal momento che possono essere registrati più stabilmente e facilmente in impianti cronici rispetto agli spike neuronali. In questo studio, sono riportati dei profili LFP registrati dalla barrel cortex di ratto tramite chip ad ago ad alta risoluzione basati su tecnologia CMOS e confrontati con quelli ottenuti tramite elettrodi convenzionali in Ag/AgCl inseriti in micropipette di vetro, strumenti comunemente usati in elettrofisiologia. La barrel cortex di ratto è un esempio ben noto di mapping topografico, nel quale ogni baffo sul muso dell'animale è mappato in una specifica area corticale, chiamata barrel. La barrel cortex contiene la rappresentazione sensoriale dei baffi dell'animale e rappresenta uno dei primi stadi di elaborazione dell'informazione tattile, insieme al ganglio del trigemino e al talamo. Essa è un'area di primaria importanza per lo studio del funzionamento della corteccia cerebrale, visto che le colonne corticali che formano i blocchi di base della neocorteccia possono essere visualizzati facilmente all'interno della barrel cortex. La barrel cortex inoltre è utilizzata come sistema di test in numerose metodologie innovative, grazie alla sua struttura unica ed istantaneamente identificabile, e grazie anche al fatto che le specie dotate di barrel, i roditori, sono gli animali da laboratorio più comuni. La barrel cortex e le sue interconnessioni neuronali sono stati oggetto delle ricerche più disparate in questi ultimi decenni. Attualmente, alcuni studi (come questo) non mirano solamente a comprendere meglio la barrel cortex, ma anche ad analizzare problematiche in campi scientifici collegati, utilizzando la barrel cortex come modello base. In questo lavoro, sono stati evocati segnali LFP nella barrel cortex tramite deflessioni ripetute dei baffi dell'animale, realizzate in modo controllato tramite un sistema di deflessione piezoelettrica a closed-loop innescato da un sistema di acquisizione LabView. Le risposte evocate generate nella barrel dalla stimolazione ripetuta dei baffi presentano elevata variabilità nella forma e nelle latenze temporali. Inoltre, il tipo di anestesia utilizzata può influenzare profondamente il profilo della risposta evocata. Questo studio riporta i risultati preliminari sulla variabilità della risposta neuronale e sull'effetto di due anestetici di uso comune su questi segnali, confrontando le distribuzioni delle risposte evocate in ratti anestetizzati con tiletamina-xylazina (il quale agisce prevalentemente sui recettori eccitatori di tipo NMDA) e uretano (che agisce in modo più bilanciato e complesso su entrambi i sistemi eccitatori ed inibitori, preservando la plasticità sinaptica). Sono state analizzate e discusse alcune caratteristiche rappresentative del segnale evocato (ad esempio, le latenze temporali e l'ampiezza degli eventi), registrato a varie profondità corticali. Per tutte le prondità corticali acquisite, sono state stimate le distribuzioni statistiche di tali parametri, in modo da valutare la variabilità degli LFP evocati dalle stimolazioni meccaniche individuali delle vibrisse del ratto lungo l'intera colonna corticale. I primi risultati presentano una grande variabilità nelle risposte corticali, sia in latenza che in ampiezza. Inoltre, è stata riscontrata una differenza significativa nella latenza del primo picco principale delle risposte evocate: gli LFP evocati in animali anestetizzati con tiletamina-xylazina presentavano una latenza più lunga di quelli registrati in ratti anestetizzati con uretano. Inoltre, le distribuzioni dei parametri analizzati erano più strette e piccate in uretano, in corrispondenza di tutte le profondità corticali. Questo comportamento è sicuramente da attribuire al differente meccanismo d'azione dei due anestetici su specifici recettori sinaptici, e quindi nell'elaborazione e nella trasmissione dell'informazione sensoriale lungo tutto il percorso corticale. E' stato inoltre discusso il ruolo della attività basale nella modulazione della risposta evocata. A questo proposito, è stata registrata l'attività spontanea in corrispondenza dei vari layer corticali ed analizzata nel contesto statistico delle 'valanghe neuronali'. Una valanga neuronale è una cascata di attività elettrica in una rete neuronale, la cui distribuzione statistica dei parametri principali (dimensione e vita media) può essere approssimata da una legge di potenza. La distribuzione delle dimensioni di una valanga in una rete neuronale segue una legge di potenza del tipo P(s)=s^-a, con a=1.5. Tale esponente è un riflesso delle correlazioni spaziali a lungo raggio nell'attività neuronale spontanea. Dal momento che i picchi negativi (nLFPs) nelle tracce elettrofisiologiche originano dalla somma di potenziali d'azione sincronizzati generati da neuroni posti nelle vicinanze dell'elettrodo di registrazione, ci siamo chiesti se fosse possibile modellizare i singoli nLFP registrati nell'attività basale tramite un singolo elettrodo come il risultato di valanghe neuronali locali. Pertanto, abbiamo analizzato la distribuzione della dimensione (cioè l'ampiezza in uV) di tali picchi, in modo da identificare una distribuzione power-law appropriata, che potesse descrivere anche le registrazioni a singolo elettrodo. Infine, sono presentate e discusse le prime registrazioni in assoluto degli LFP evocati lungo un'intera colonna corticale ottenute tramite l'ultima generazione di chip impiantabili a tecnologia CMOS. Questi ultimi presentano una matrice di 256 siti di registrazione, organizzata secondo due possibili topologie, 16 x 16 o 4 x 64, e avente una distanza tra gli elettrodi pari a 15 um o 33 um rispettivamente. Una precisa dinamica di propagazione dei potenziali evocati può già essere riconosciuta in questi primissimi profili corticali. Nel prossimo futuro, l'uso di questi dispositivi a semiconduttore potrà aiutare a comprendere il decorso di sindromi neurodegerative come il Parkinson o l'Alzheimer, associando sintomi e comportamenti tipo della malattia a specifiche caratteristiche neuronali. I chip impiantabili potranno anche essere utilizzati come 'electroceuticals', ossia potranno aiutare a rallentare (o addirittura a capovolgere) il decorso delle malattie neurogenerative, costituendo le basi di protesi neuronali in grado di sostenere fisicamente o allenare funzionalmente le popolazioni neuronali danneggiate. L'identificazione e il rilevamento di segnali neuronali ad alta risoluzione aiuterà anche a sviluppare complesse interfacce cervello-macchina, che consentiranno il controllo di protesi intelligenti e che forniranno sofisticati meccanismi di feedback a chi ha perso l'uso di alcune parti del proprio corpo o determinate funzioni cerebrali.

Les interfaces cerveau-ordinateur (Brain-Computer Interface ou BCI) permettent la communication entre l’utilisateur et la machine, grâce à la traduction de l’activité cérébrale en commandes qui servent à contrôler différents dispositifs. De nombreuses limitations empêchent la diffusion des systèmes BCI dans des applications réelles, telles que la phase de calibration qui résulte de la variabilité entre sessions et entre sujets. Cette phase est fondamentale car elle permet de régler les paramètres nécessaires pour le bon fonctionnement du système, mais elle est considérée beaucoup trop longue et fatigante pour le sujet.L'objectif de cette thèse est de surmonter ces limites par de nouvelles méthodes basées sur l’amélioration ou le remplacement de la phase de calibration traditionnelle, en proposant le développement d'une BCI centrée sur l'utilisateur.D’abord, nous proposons deux systèmes BCI adaptés au sujet. Le premier concerne un clavier virtuel basé sur des potentiels évoqués modulés par code-modulated Visual Evoked Potential (c-VEP) où la phase de calibration traditionnelle est remplacée par une phase dans laquelle les paramètres de stimulation sont réglés de manière adaptée au sujet. Le deuxième concerne le développement d'un système basé sur l’imagination mentale (MI-BCI) pour un sujet à déficience motrice sévère (tétraplégie), dans le cadre d'une compétition internationale BCI en direct.Ensuite, nous proposons une auto-calibration pour le c-VEP BCI qui utilise les propriétés fondamentales de la réponse VEP pour prédire les mots à l'aide d'un dictionnaire, éliminant la phase de calibration.Les méthodes proposées ont montré des résultats prometteurs et ouvrent de nouvelles perspectives pour la diffusion des systèmes BCI plus adaptables à l'utilisateur
Brain-Computer Interface (BCI) allows communication between a user and a machine, by converting the user's brain activity into commands that control external devices. Many limitations prevent the diffusion of BCI systems in real applications, such as the calibration phase that is a consequence of the issue of variability across sessions and among users. The calibration phase is fundamental because it allows to set the main parameters to extract the relevant information from the electroencephalograpy (EEG) signal of the subject, but it is considered time consuming and tedious for the user.The objective of this thesis is to overcome these limitations by novel methods based on the improvement or even replacement of the traditional calibration phase, proposing the development of a user-centered BCI system.Firstly, we present a design to develop an adaptive BCI system for two different applications. The former deals with a code-modulated Visual Evoked Potential (c-VEP) speller where an adaptive parameter setting phase is proposed to replace the standard calibration phase. The latter application concerns the development of a Mental Imagery (MI) BCI for a disabled user, characterized by a long user-centered multi-stage training phase, in the context of a international BCI competition.Secondly, we propose an auto-calibration c-VEP BCI system exploiting the language information. In our model the fundamental properties that characterize the VEP response are used to predict the full word using a dictionary, eliminating the traditional calibration phase.The proposed methods showed promising results and open new perspectives to the diffusion of BCI

Le profil position-orientation donne par les approximations type msa, lhnc. . . Est identique a celui des spheres dures. Il est montre que, meme dans ce cas, il existe des orientations privilegiees. Loin de la surface, seul le potentiel image classique subsiste. Au voisinage de celle-ci, le resultat est plus complique et ne peut etre prevu par la theorie classique. Il est montre aussi qu'un potentiel anisotrope faible ( equiv. A kt) suffit pour produire des effets observables sur le plan experimental. Deux approximations ont ete comparees: blip et l'inegalite de gibbs-bogolioubov. Enfin, etude des fonctions de correlation de paire: il est montre que, sur la surface et loin de celle-ci, ces fonctions sont decrites par les potentiels direct et image. Dans la region intermediaire, la solution est plus compliquee