Electronic noses combine an array of cross-selective gas sensors with a pattern recognition engine to identify odors. Pattern recognition of multivariate gas sensor response is usually performed using existing statistical and chemometric techniques. An alternative solution involves developing novel algorithms inspired by information processing in the biological olfactory system. The objective of this dissertation is to develop a neuromorphic architecture for pattern recognition for a chemosensor array inspired by key signal processing mechanisms in the olfactory system. Our approach can be summarized as follows. First, a high-dimensional odor signal is generated from a chemical sensor array. Three approaches have been proposed to generate this combinatorial and high dimensional odor signal: temperature-modulation of a metal-oxide chemoresistor, a large population of optical microbead sensors, and infrared spectroscopy. The resulting high-dimensional odor signals are subject to dimensionality reduction using a self-organizing model of chemotopic convergence. This convergence transforms the initial combinatorial high-dimensional code into an organized spatial pattern (i.e., an odor image), which decouples odor identity from intensity. Two lateral inhibitory circuits subsequently process the highly overlapping odor images obtained after convergence. The first shunting lateral inhibition circuits perform gain control enabling identification of the odorant across a wide range of concentration. This shunting lateral inhibition is followed by an additive lateral inhibition circuit with center-surround connections. These circuits improve contrast between odor images leading to more sparse and orthogonal patterns than the one available at the input. The sharpened odor image is stored in a neurodynamic model of a cortex. Finally, anti-Hebbian/ Hebbian inhibitory feedback from the cortical circuits to the contrast enhancement circuits performs mixture segmentation and weaker odor/background suppression, respectively. We validate the models using experimental datasets and show our results are consistent with recent neurobiological findings.

Electronic noses combine an array of cross-selective gas sensors with a pattern recognition engine to identify odors. Pattern recognition of multivariate gas sensor response is usually performed using existing statistical and chemometric techniques. An alternative solution involves developing novel algorithms inspired by information processing in the biological olfactory system. The objective of this dissertation is to develop a neuromorphic architecture for pattern recognition for a chemosensor array inspired by key signal processing mechanisms in the olfactory system. Our approach can be summarized as follows. First, a high-dimensional odor signal is generated from a chemical sensor array. Three approaches have been proposed to generate this combinatorial and high dimensional odor signal: temperature-modulation of a metal-oxide chemoresistor, a large population of optical microbead sensors, and infrared spectroscopy. The resulting high-dimensional odor signals are subject to dimensionality reduction using a self-organizing model of chemotopic convergence. This convergence transforms the initial combinatorial high-dimensional code into an organized spatial pattern (i.e., an odor image), which decouples odor identity from intensity. Two lateral inhibitory circuits subsequently process the highly overlapping odor images obtained after convergence. The first shunting lateral inhibition circuits perform gain control enabling identification of the odorant across a wide range of concentration. This shunting lateral inhibition is followed by an additive lateral inhibition circuit with center-surround connections. These circuits improve contrast between odor images leading to more sparse and orthogonal patterns than the one available at the input. The sharpened odor image is stored in a neurodynamic model of a cortex. Finally, anti-Hebbian/ Hebbian inhibitory feedback from the cortical circuits to the contrast enhancement circuits performs mixture segmentation and weaker odor/background suppression, respectively. We validate the models using experimental datasets and show our results are consistent with recent neurobiological findings.

Materiais vítreos com propriedades similares às do cristal germanato de bismuto de composição Bi4Ge3O12, material cintilador que possui estrutura do tipo eulitita, são de interesse devido as suas propriedades luminescentes, que os tornam promissores para aplicação como dispositivos ópticos. Vidros do sistema GeO2-Bi2O3 (BGO) também tem sido tema de inúmeras pesquisas por combinarem um típico formador vítreo (GeO2) a um formador condicional composto intermediário (Bi2O3), o que os proporciona características estruturais únicas, resultantes da mudança de coordenação dos átomos de germânio (fenômeno de anomalia do germânio) e também dos átomos de bismuto. Neste trabalho, estudou-se a influência da adição de CeO2, comumente conhecido como agente oxidante, nas propriedades físico-químicas de vidros de germanato de bismuto do sistema [100-x].[(1-y)GeO2-yBi2O3]:xCeO2 (para x = 0,2 ou 1 e y = 0,2 ou 0,3 % em mol), preparados pelo método de fusão e moldagem. O escurecimento inomogêneo das amostras, associado à termoredução do íon Bi3+, foi evitado com a adição de céria, que se mostrou um modificador da estrutura local dos vidros, mesmo para uma dopagem de 0,2 % em mol. Foi observada, pela primeira vez, a cristalização da fase de estrutura eulitita cintiladora induzida pela presença de Ag na superfície do vidro de composição 99,8[0,8GeO2- 0,2Bi2O3 ]:0,2CeO2 % em mol, referido pela sigla 80BGO:0,2Ce, abaixo da temperatura de transição vítrea (Tg). A difusão de Ag no vidro é condição necessária para que o fenômeno da cristalização aconteça, uma vez que esse elemento pode ser considerado um efetivo agente nucleante para a fase cintiladora. A cristalização induzida é favorecida pela tensão gerada na interface cristal/vidro, devido a uma diferença de volume molar entre essas duas fases, o que permite que o fenômeno da cristalização seja observado em temperturas inferiores à Tg. / Glassy materials with similar properties to those of the bismuth-germanate crystal in the composition of Bi4Ge3O12, a scintillator material with the eulytite structure, are of interest due to their luminescent properties that makes them promising materials to application as optical devices. Glasses from the system GeO2-Bi2O3 (BGO) has also being subjects of numerous studies, by combining a typical glass former oxide (GeO2) with the conditional one intermediate compound (Bi2O3). The presence of these two oxide compounds in the glass composition provides them a unique structural characteristic resulting from the coordination changes of germanium atoms (germanium anomaly phenomenon) and also of the bismuth atoms. In the present work, it was studied the influence of CeO2 addition, commonly known as an oxidant agent, in the physical-chemical properties of the bismuth-germanate glasses up to the system [100-x].[(1-y)GeO2-yBi2O3 ]:xCeO2 (for x = 0.2 or 1 and y = 0.2 or 0.3 mol %), prepared by the melting/molding method. The inhomogeneous darkening of the samples, associated to the thermal reduction of the Bi3+ ions, was avoided by the ceria addition that acts as a local modifier of the glass structure even for concentrations of 0.2 mol %. It was observed, by the first time, the crystallization of the eulytite scintillator phase, induced by the presence of Ag in the surface of the glass in the 99[0.8GeO2- 0.2Bi2O3 ]:0.2CeO2 mol % composition, referred to as 80BGO:0.2Ce, below the glass transition temperature (Tg). The Ag diffusion into the glass is a necessary condition to the crystallization phenomenon since this element can be considered as an effective nucleating agent to the scintillator phase. The crystallization is favored by the tension generated in the crystal/glass interface, due to a difference in molar volume of these two phases, allowing that the crystallization phenomenon be observed at temperatures below Tg.

Materiais vítreos com propriedades similares às do cristal germanato de bismuto de composição Bi4Ge3O12, material cintilador que possui estrutura do tipo eulitita, são de interesse devido as suas propriedades luminescentes, que os tornam promissores para aplicação como dispositivos ópticos. Vidros do sistema GeO2-Bi2O3 (BGO) também tem sido tema de inúmeras pesquisas por combinarem um típico formador vítreo (GeO2) a um formador condicional composto intermediário (Bi2O3), o que os proporciona características estruturais únicas, resultantes da mudança de coordenação dos átomos de germânio (fenômeno de anomalia do germânio) e também dos átomos de bismuto. Neste trabalho, estudou-se a influência da adição de CeO2, comumente conhecido como agente oxidante, nas propriedades físico-químicas de vidros de germanato de bismuto do sistema [100-x].[(1-y)GeO2-yBi2O3]:xCeO2 (para x = 0,2 ou 1 e y = 0,2 ou 0,3 % em mol), preparados pelo método de fusão e moldagem. O escurecimento inomogêneo das amostras, associado à termoredução do íon Bi3+, foi evitado com a adição de céria, que se mostrou um modificador da estrutura local dos vidros, mesmo para uma dopagem de 0,2 % em mol. Foi observada, pela primeira vez, a cristalização da fase de estrutura eulitita cintiladora induzida pela presença de Ag na superfície do vidro de composição 99,8[0,8GeO2- 0,2Bi2O3 ]:0,2CeO2 % em mol, referido pela sigla 80BGO:0,2Ce, abaixo da temperatura de transição vítrea (Tg). A difusão de Ag no vidro é condição necessária para que o fenômeno da cristalização aconteça, uma vez que esse elemento pode ser considerado um efetivo agente nucleante para a fase cintiladora. A cristalização induzida é favorecida pela tensão gerada na interface cristal/vidro, devido a uma diferença de volume molar entre essas duas fases, o que permite que o fenômeno da cristalização seja observado em temperturas inferiores à Tg. / Glassy materials with similar properties to those of the bismuth-germanate crystal in the composition of Bi4Ge3O12, a scintillator material with the eulytite structure, are of interest due to their luminescent properties that makes them promising materials to application as optical devices. Glasses from the system GeO2-Bi2O3 (BGO) has also being subjects of numerous studies, by combining a typical glass former oxide (GeO2) with the conditional one intermediate compound (Bi2O3). The presence of these two oxide compounds in the glass composition provides them a unique structural characteristic resulting from the coordination changes of germanium atoms (germanium anomaly phenomenon) and also of the bismuth atoms. In the present work, it was studied the influence of CeO2 addition, commonly known as an oxidant agent, in the physical-chemical properties of the bismuth-germanate glasses up to the system [100-x].[(1-y)GeO2-yBi2O3 ]:xCeO2 (for x = 0.2 or 1 and y = 0.2 or 0.3 mol %), prepared by the melting/molding method. The inhomogeneous darkening of the samples, associated to the thermal reduction of the Bi3+ ions, was avoided by the ceria addition that acts as a local modifier of the glass structure even for concentrations of 0.2 mol %. It was observed, by the first time, the crystallization of the eulytite scintillator phase, induced by the presence of Ag in the surface of the glass in the 99[0.8GeO2- 0.2Bi2O3 ]:0.2CeO2 mol % composition, referred to as 80BGO:0.2Ce, below the glass transition temperature (Tg). The Ag diffusion into the glass is a necessary condition to the crystallization phenomenon since this element can be considered as an effective nucleating agent to the scintillator phase. The crystallization is favored by the tension generated in the crystal/glass interface, due to a difference in molar volume of these two phases, allowing that the crystallization phenomenon be observed at temperatures below Tg.

Les télescopes terrestres et spatiaux recueillent une énorme quantité d'informations dans le domaine infrarouge en provenance d'objets astrophysiques ''chauds'' (500-3000 K) tels que les atmosphères d'exoplanètes (Jupiters chauds), de naines brunes et les enveloppes circumstellaires d'étoiles AGBs. Cette thèse s'inscrit dans une approche d'astrophysique de laboratoire s'attachant à reproduire in situ certains aspects des conditions extrêmes rencontrées au sein de ce type d'environnements afin notamment de produire des données haute température de molécules clefs. Le nouveau dispositif mis en place à Rennes couple une Source Haute Enthalpie à un spectromètre par temps de déclin d'une cavité optique (CRDS). Le gaz étudié, chauffé dans le réservoir à une température avoisinant 2000 K, est expulsé dans une chambre basse pression au travers d'un injecteur circulaire. Le jet libre hypersonique ainsi formé est sondé en tout point et avec une très haute sensibilité. La simulation de nos écoulements stationnaires (CFD) associée à la modélisation du spectromètre a abouti à des spectres synthétiques en très bon accord avec les spectres expérimentaux. Ces données numériques ont été utilisées pour expliquer l'origine des profils de raie atypiques et plus généralement pour comprendre la structure des jets hypersoniques axisymétriques. Le cœur isentropique de ces écoulements est caractérisé par de fortes conditions hors équilibre. Une température de vibration très élevée (1350 K) et une température de rotation très basse (10 K) ont été obtenues à partir d’un jet de CO et d’argon. Ce découplage des degrés de liberté internes permet de simplifier la structure rotationnelle des spectres enregistrés et facilite l’étude des états vibrationnels excités des molécules en révélant la structure des bandes chaudes, absentes des bases de données spectroscopiques pour la plupart des molécules polyatomiques. Une approche complémentaire consiste à sonder la couche de choc produite par l'ajout d'un obstacle sur le trajet de l'écoulement. La température rotationnelle est brutalement élevée donnant ainsi accès aux transitions rotationnelles de hautes valeurs du nombre quantique J. Ces deux méthodes ont été appliquées avec succès au méthane qui joue un rôle majeur dans de nombreux environnements astrophysiques chauds. Enfin, outre la production de données spectroscopiques, ce dispositif expérimental a permis de mettre en évidence la relaxation des degrés de liberté internes du CO dans différents gaz porteurs (He et Ar) en suivant l’évolution des températures de rotation et vibration le long de l'écoulement hypersonique, aussi bien dans le cœur isentropique qu'au sein des couches limites. Ces températures sont comparées aux températures d'excitation obtenues par des méthodes ab initio afin de valider des calculs de taux de collision. Les données obtenues alimenteront à terme des bases de données, matière première au développement de codes de transfert radiatif permettant d'interpréter les observations en provenance des milieux astrophysiques ''chauds''. / A huge quantity of infrared spectra is collected by terrestrial and space telescopes from cool astrophysical objects (500-3000 K) like exoplanet (hot Jupiter) and brown dwarf atmospheres or circumstellar envelop of AGB stars. The main purpose of this thesis connected to experimental astrophysics is to provide high temperature data of key molecules by reproducing in the laboratory some aspects of such environments. A new setup built in Rennes couples a High Enthalpy Source to a highly sensitive Cavity Ring-Down Spectrometer. The gas studied, heated in the reservoir up to 2000 K, is expanded in a vacuum chamber through a circular nozzle and the resulting hypersonic jet can be probed at any location. Computational flow dynamics (CFD) calculations associated to a modeling of the infrared absorption lead to synthetic lines which are in very good agreement with the observed spectra. These numerical data were used to attribute the unusual double peak line shapes to the particular flow structure of axisymmetric hypersonic jets. Strong out-of-equilibrium conditions were evidenced in the isentropic core of the expansion. High vibrational temperature (1350 K) and rotational temperature lower than 10 K were recorded inside a jet of CO seeded in Ar. This degrees-of-freedom decoupling greatly simplifies the rotational structure of the recorded infrared spectra and unveils the presence of hot bands stemming from highly excited vibrational states which are significantly populated at high temperature. Our approach is therefore well suited for the study of rotationally cold hot bands of polyatomic molecules which are virtually missing in spectroscopic databases. A complementary approach consists in probing the shock layer formed upstream of an obstacle set perpendicularly to the hypersonic flow axis. Rotational temperature raises abruptly downstream the shock, revealing transitions associated with high J quantum numbers. These two methods were successfully applied to methane which plays an important role in numerous astrophysical environments. In addition to the acquisition of infrared spectroscopic data, the relaxation of internal degrees-of-freedom of CO seeded in different carrier gases (Ar and He) was studied by following the evolution of rotational and vibrational temperatures along the flow, in the isentropic core as well as in the peripheral viscous layers. These temperatures were compared to excitation temperatures calculated by an ab initio method in order to validate collision rates. These data will feed databases needed for the development of radiative transfer codes with a view to a better modeling of spectra observed from "hot" astrophysical environments.

No description available.

Hlavním předmětem této diplomové práce jsou elektromagnetické simulace pomocí metody konečných prvků (FEM) k vyšetření vlivu grafenu na hrotem zesílenou Ramanovu spektroskopii (TERS) a povrchem zesílenou infračervenou absorpční spektroskopii (SEIRA) a k prozkoumání citlivosti sondy skenovacího optického mikroskopu blízkého pole (SNOM) ke složkám elektromagnetického pole v závislosti na parametrech sondy (průměru apertury v pokovení). Nejprve je proveden výpočet TERS systému složeného ze stříbrného hrotu nacházejícího se nad zlatým substrátem s tenkou vrstvou molekul, jehož účelem je porozumění principů TERS. Poté je na molekuly přidána grafenová vrstva, aby se prozkoumal její vliv ve viditelné (TERS) a infračervené (SEIRA) oblasti spektra. Druhá část práce se zabývá výpočty energiového toku SNOM hrotem složeným z pokoveného skleněného vlákna interagujícím s blízkým polem povrchových plasmonových polaritonů. Zde uvažujeme zlatou vrstvu se čtyřmi štěrbinami uspořádanými do čtverce na skleněném substrátu sloužícími jako zdroj stojatého vlnění povrchových plasmonů s prostorově oddělenými maximy složek elektrického pole orientovanými rovnoběžně či kolmo na vzorek. Ve výpočtech hrotem zesílené spektroskopie zjišťujeme, že grafen přispívá pouze malým dílem k zesílení pole ve viditelné oblasti spektra, ovšem v infračervené oblasti má grafen vliv pro záření s energií menší než dvojnásobek Fermiho energie grafenu, pro kterou je hodnota zesílení pole větší než v případě výpočtu bez grafenu. Avšak pro velmi vysoké vlnové délky zesílení pole v přítomnosti grafenu klesá pod (konstantní) hodnotu pro případ bez grafenu. Při studiu citlivosti SNOM hrotu k jednotlivým složkám pole shledáváme, že pro hrot se zlatým pokovením je energiový tok skleněným jádrem hrotu kombinací příspěvků energie prošlé aperturou a periodické výměny energie mezi povrchovým plasmonem šířícím se po vnějším okraji pokovení a mody propagujícími se v jádře. Dále zjišťujeme, že hroty s malou aperturou (či bez apertury) jsou více citlivé na složku elektrického pole orientovanou kolmo ke vzorku (rovnoběžně s osou hrotu), zatímco hroty s velkou aperturou sbírají spíše signál ze složky rovnoběžné s povrchem vzorku. V případě hrotu s hliníkovým pokovením jsou hroty citlivější ke složce pole rovnoběžné s povrchem, což je způsobeno slabším průnikem pole skrze pokovení.