Mon projet porte sur l'elaboration d'un microscope optique en champ proche (SNOM) sans ouverture fonctionnant dans le domaine de l'infrarouge et utilisant le rayonnement synchrotron de l'ESRF comme source de lumiere infrarouge. Ce rayonnement a deux particularites bien adaptees aux etudes spectroscopiques: c'est une source de lumiere blanche couvrant la bande du proche infrarouge de 5 a 15 microns alors que les sources lasers accordables sont encore en developpement. Il est tres brillant et stable, a la fois dans le temps et dans l'espace. Une fois elaboree, le microscope sera appliquee a la spectroscopie infrarouge - essentiellement vibrationelle - et le diagnostic des materiaux et des nanostructures qui sont d'inter^et actuel pour l'industrie micro et nanoelectronique [RCB+02]. Comme mon projet est tres instrumental, le debut a ete consacre a la conception de tout un systeme de microscopie, a partir du zero et avec tout le materiel necessaire disponible a la n de la premiere annee. La seconde annee a ete consacree a l'integration et la mise en oeuvre du dispositif experimental, a la comprehension de ses fonctionnalites et a des essais de validation du nouveau outil. Apres nous nous sommes pleinement engages dans la recherche et la comprehension de cet outil unique. Nous avons commence par quelques resultats preliminaires, puis cela a ete essentiellement une question de temps experimental alloue pour obtenir les resultats que nous avions vises. Notre conguration est unique et donc les travaux que nous avons pour reference sont ceux de groupes utilisant les m^emes techniques d'exploitation dans des conditions tres dierentes. Notre principale diculte est de detecter un signal faible. Je montrerai plus loin quelques calculs qui nous y ont fait croire. Notre groupe de reference a reussi a le faire dans des conditions plus simples que les notres, mais il est utile de rappeler que cela leur a pris 3 ans pour adapter leur sensibilite a l'installation, ce qui conrme que ce sont des techniques tres dur. Notre idee de depart etait d'utiliser le rayonnement synchrotron comme source de lumiere dans l'infrarouge en raison de ses caracteristiques. Il s'agit d'une source de lumiere blanche, avec toutes les longueurs d'onde presentes en meme temps, nous permettant d'eectuer une spectroscopie, ce qui signie que nous obtiendrons une information chimique sur l'echantillon [Hil04; MGCS04]. Telle est la grande nouveaute en comparison avec les autres travaux. Il s'est avere que la lumiere est assez faible ce qui rend la recherche du signal dicile. Notre installation doit alors etre testee avec un laser, qui est de plusieurs ordres de grandeur plus puissant que le rayonnement synchrotron, et qui pourrait etre un bon outil de debogage. Cela semble une bonne alternative pour mieux comprendre les points essentiels qui doivent etre ameliores dans notre systeme. Les lasers a utiliser pourraient etre visible, infrarouge (CO2), ou accordable. Pour la spectroscopie, les lasers accordables sont non seulement moins stables mais ils sont aussi plus limites dans la gamme spectrale sur la partie infrarouge proche du spectre, que le rayonnement synchrotron. Le synchrotron de l'ESRF est mon laboratoire d'accueil, et j'ai travaille en collaboration avec le CEA-LETI pour le developpement de cet outil.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 194-202).

Afin de progresser dans la compréhension de la structure de vibration-rotation de l'acétylène dans son état électronique fondamental, un modèle global a été développé avec succès pour trois de ses isotopologues, permettant d'attribuer de nouvelles données de spectres enregistrés sous diverses conditions expérimentales. L'ensemble des programmes d'analyse rovibrationnelle globale conçus à l'Université Catholique de Louvain par le Pr. A. Fayt et al. ont été utilisés pour répondre aux demandes de collaborateurs tels que les Prs. A. Campargue, A. Jolly ou encore R. Georges dans le cadre de plusieurs problèmes de type spectroscopique, notamment pour des applications astrophysiques. Le modèle global et son pouvoir prédictif mis ainsi à l'épreuve, nous avons démontré la validité de nos jeux de paramètres pour ces trois molécules. Concernant l'isotopologue principal, $H^{12}C^{12}CH$, 14 nouvelles bandes ont été mises à jour à partir de spectres enregistrés en CRDS à Grenoble par A. Campargue et al. Une analyse rovibrationnelle globale a été effectuée jusqu'à une énergie de 8600 cm$^{-1}$. 10750 raies ont été ajustées simultanément sur les 12137 attribuées dans la littérature. 266 paramètres ont été déterminés par la méthode de moindres-carrés. La déviation standard sans dimension du fit est de 0.92. La bande $ u_{5}$-$ u_{4}$, centrée vers 117 cm$^{-1}$ a été simulée. La valeur du moment de transition associé, $|mu_{5 leftarrow 4}|$, a été estimé à partir des informations existant dans la littérature exploitant par ailleurs les résultats issus du modèle global. 163 nouvelles bandes du $H^{12}C^{13}CH$ ont été analysées bande par bande à partir de spectres enregistrés sur BOMEM DA3.002 FT à Bologne et sur FTS IFS120HR à Bruxelles. Les spectres enregistrés ont été analysés région par région, produisant ainsi plus de 8300 raies de rotation-vibration non encore répertoriées. Elles enrichissent une base de données qui a servi à effectuer une analyse rovibrationnelle globale jusque 9500 cm$^{-1}$. 16250 raies ont été ajustées sur les 18010 disponibles. 317 paramètres ont été déterminés dans le processus de moindres-carrés. La déviation standard sans dimension du fit est de 1.1. Le troisième isotopologue qui a retenu notre attention est le $H^{12}C^{12}CD$. La découverte de cette molécule dans l'atmosphère de Titan a orienté notre travail. Lors de l'analyse globale des niveaux de bending, 4347 raies ont été fittées à l'aide des 62 paramètres endéans la précision expérimentale de 5 10$^{-4}$ cm$^{-1}$. La déviation standard sans dimension du fit est de 0.79. Une simulation des niveaux de bending avec un profil de raie associé a été effectuée permettant la création d'une base de données spectroscopiques contenant 7472 raies et destinée aux astrophysiciens.

The biological membrane surrounding the living cell provides a sealed barrier that tightly regulates the interactions with the outside environment. A large number of integral membrane proteins mediate these interactions and are involved in a wide variety of biological processes. An increasing number of studies have led to the conclusion that lipids provide more than a hydrophobic solvent for membrane proteins, and that interactions between lipids and proteins are required to allow protein function. ABC transporters are one of the most important family of membrane proteins. However, the importance of their lipidic environment is largely unknown. Only a few studies showed that their activity was dependent on the lipidic composition of the surrounding bilayer. The bacterial ABC transporter HorA was used as a model to probe the influence of the lipidic environment on that class of membrane proteins. HorA is a multidrug transporter expressed in Lactobacillus brevis, a Gram-positive beer spoilage bacterium. It turned out that phosphatidylethanolamine (PE) was indispensable to maintain both the activity and the structural integrity of HorA. Surprisingly, replacement of PE by the chemically related PC (phosphatidylcholine) did not led to the suppression of HorA activity, but to an unexpected phenotype. Whereas the cytoplasmic domains of HorA were still able to hydrolyze ATP, the membrane parts of the transporter were unable to use that energy to mediate substrate transport. Using several biophysical methods particularly adapted to the study of reconstituted systems, we showed that the structure of HorA is strongly altered by this lipid replacement. In particular, the structural organization of the transmembrane domains of the protein is strongly affected.

Brain-computer interface (BCI) technologies allow users to control external devices through brain activity alone, circumventing the somatic nervous system and the need for overt physical movement. BCIs may potentially benefit individuals with severe neuromuscular disorders who experience significant, and often total, loss of voluntary muscle control (e.g. amyotrophic lateral sclerosis, multiple sclerosis, brainstem stroke). Though a majority of BCI research to date has focused on electroencephalography (EEG) for brain signal acquisition, recently researchers have noted the potential of an optical imaging technology called near-infrared spectroscopy (NIRS) for BCI applications. This thesis investigates the feasibility of a practical, online optical BCI based on conscious modulation of prefrontal cortex activity through the performance of different cognitive tasks, specifically mental arithmetic (MA) and mental singing (MS). The thesis comprises five studies, each representing a step toward the realization of a practical optical BCI. The first study demonstrates the feasibility of a two-choice synchronized optical BCI based on intentional control states corresponding to MA and MS. The second study explores a more user-friendly alternative - a two-choice system-paced BCI supporting a single intentional control state (either MA or MS) and a natural baseline, or "no-control (NC)", state. The third study investigates the feasibility of a three-choice system-paced BCI supporting both MA and MS, as well as the NC state. The fourth study examines the consistency with which the relevant mental states can be differentiated over multiple sessions. The first four studies involve healthy adult participants; in the final study, the feasibility of optical BCI use by a user with Duchenne muscular dystrophy is explored. In the first study, MA and MS were classified with an average accuracy of 77.2% (n=10), while in the second, MA and MS were differentiated individually from the NC state with average accuracies of 71.2% and 62.7%, respectively (n=7). In the third study, an average accuracy of 62.5% was obtained for the MA vs. MS vs. NC problem (n=4). The fourth study demonstrated that the ability to classify mental states (specifically MA vs. NC) remains consistent across multiple sessions (p=0.67), but that there is intersession variability in the spatiotemporal characteristics that best discriminate the states. In the final study, a two-session average accuracy of 71.1% was achieved in the MA vs. NC classification problem for the participant with Duchenne muscular dystrophy.

Individuals with limited motor control are often unable to interact with their environment. Recently, near-infrared spectroscopy (NIRS) systems have been investigated as potential brain-computer interfaces (BCI). Previous studies examined data offline, preventing users from understanding how their thoughts triggered the NIRS system. This thesis focused on understanding the short-term effects of feedback on user’s ability to learn how to control BCIs. Data were collected from control and experimental groups over seven sessions, as they performed fast singing imagery or mental arithmetic. Significant differences were observed between the control group’s results in non-feedback sessions and the experimental group’s results in feedback sessions. Qualitative results from 3 of the 10 participants suggested they had control of the feedback system. They performed the task with online accuracies of 61% - 88% in the final 2 sessions with feedback. These results suggest that continued investigation of NIRS feedback systems is warranted.

Near-infrared spectroscopy (NIRS) is an emerging non-invasive brain-computer interface (BCI) modality that measures changes in hemoglobin concentrations in neurocortical tissue. Previous NIRS studies have not employed real-time feedback with online classification, a combination which would allow users to alter their mental strategy on the fly. This thesis reports the results of two online studies. The first study contrasted online classification of prefrontal hemodynamics using an artificial neural network (ANN) and a hidden Markov model-based (HMM) classifier. The second study measured the accuracy of an online linear discriminant classifier. In study 1, only the ANN classifier facilitated online classification rates greater than chance (p=0.0289). In study 2, a new feedback system and experimental protocol led to improved classification rates over those of the first study (p=5.1*10^(-5)). While control over instantaneously generated feedback in online NIRS-BCIs has been demonstrated, factors such as user frustration, mental fatigue, and restrictions on ambient lighting may compromise performance.

Near-infrared spectroscopy (NIRS) is an emerging non-invasive brain-computer interface (BCI) modality that measures changes in hemoglobin concentrations in neurocortical tissue. Previous NIRS studies have not employed real-time feedback with online classification, a combination which would allow users to alter their mental strategy on the fly. This thesis reports the results of two online studies. The first study contrasted online classification of prefrontal hemodynamics using an artificial neural network (ANN) and a hidden Markov model-based (HMM) classifier. The second study measured the accuracy of an online linear discriminant classifier. In study 1, only the ANN classifier facilitated online classification rates greater than chance (p=0.0289). In study 2, a new feedback system and experimental protocol led to improved classification rates over those of the first study (p=5.1*10^(-5)). While control over instantaneously generated feedback in online NIRS-BCIs has been demonstrated, factors such as user frustration, mental fatigue, and restrictions on ambient lighting may compromise performance.

Switchable surfaces, also called smart surfaces or controllable surfaces, respond to changes in their local environment resulting in altered surface properties. There are various environmental perturbations that can cause changes to the surface properties but the focus of this thesis is on the affect of electrostatic potential. Significant evidence is provided from previous reports on electrochemical and infrared spectroscopic experiments suggesting that self-assembled monolayers (SAMs) of 4-mercaptobenzoic acid (4-MBA) undergo protonation-deprotonation by the application of an electric field. However, there are plenty of aspects of this electric field driven protonation-deprotonation mechanisms using carboxylic acid terminated SAMs that are not well understood. Most importantly, there is a lack of model independent measurements to validate this process. As such, experimental techniques utilizing infrared spectroscopy were employed to correlate electrochemical measurements and models.<p> This body of work demonstrates the importance of the intermolecular hydrogen bonding network on the measured voltammetric peak associated with the protonation-deprotonation of these SAMs. The voltammetric peak height diminishes with increasing exposure to an electrolyte solution. This behaviour is attributed to the replacement of the carboxylic acid protons with electrolyte cations and ultimately the disruption of the hydrogen bonded network.<p> We attempted to further our ex-situ infrared measurements by using an in-situ spectroelectrochemical technique. We had some initial successes, presented within, but more work is needed to complete this picture and is beyond the scope of this thesis. To summarize, the protonated state of SAMs of 4-MBA can be driven by the application of an electric field providing a potential platform to build a controllable smart surface.

Individuals with limited motor control are often unable to interact with their environment. Recently, near-infrared spectroscopy (NIRS) systems have been investigated as potential brain-computer interfaces (BCI). Previous studies examined data offline, preventing users from understanding how their thoughts triggered the NIRS system. This thesis focused on understanding the short-term effects of feedback on user’s ability to learn how to control BCIs. Data were collected from control and experimental groups over seven sessions, as they performed fast singing imagery or mental arithmetic. Significant differences were observed between the control group’s results in non-feedback sessions and the experimental group’s results in feedback sessions. Qualitative results from 3 of the 10 participants suggested they had control of the feedback system. They performed the task with online accuracies of 61% - 88% in the final 2 sessions with feedback. These results suggest that continued investigation of NIRS feedback systems is warranted.