La conductivité électronique de l'éméraldine sel dépend des conditions de sa synthèse (solvant et dopant utilisés) et de son traitement après synthèse. L'objectif principal de cette thèse est de démontrer et d'interpréter les corrélations entre l'environnement et les propriétés de la forme conductrice de la polyaniline. Dans la partie théorique, nous avons examiné l'influence des différents dopants et solvants sur la structure et les propriétés de la polyaniline. Pour atteindre cet objectif, un large dispositif de méthodes de chimie quantique a été testé et une méthode appropriée a été choisie. Dans la partie expérimentale nous avons utilisé une nouvelle approche pour accéder aux propriétés intrinsèques de la polyaniline i.e. sans utiliser ni solvants ni dopants autres que ceux utilisés lors de la synthèse. Les calculs montrent que la description théorique de la polyaniline dépend fortement du choix de la méthode. La modélisation de l'effet de la polarité du solvant grâce à l'utilisation de la méthode PMC semble être cruciale pour une description fiable de l'interaction polyaniline-dopant. Les résultats obtenus démontrent pour la première fois que les interactions, de la polyaniline avec les dopants dépendent de la nature chimique du solvant et pas du dopant lui-même. De plus, nous avons montré que la stabilité de la forme polaronique (conductrice) augmente avec l'augmentation de la polarité du solvant. Ces conclusions correspondent parfaitement à nos résultats expérimentaux qui montrent le rôle crucial du solvant (et pas des dopants) sur les propriétés de la polyaniline. / The electric conductivity of the emeraldine salt depends on the conditions of its synthesis (solvents and dopants) and post-synthetic treatment. The main objective of the present thesis is to demonstrate and interpret the correlations between the environment and the properties of the conductive form of polyaniline. In order to achieve this goal a new theoretical approach is developed with reference to the experimental data. In the theoretical section, we examine the influence of different dopants and solvents on the structure and properties of polyaniline. To achieve this, a variety of quantum chemistry methods is tested and a proper method is chosen. In the experimental part we use a new method for tuning of the intrinsic polyaniline properties without using solvents or dopants other than those employed in the synthesis. The calculations show that the theoretical description of polyaniline depends strongly on the choice of the method. Modeling the effect of solvent polarity (in this case by the PCM method) seems to be crucial for the reliable description of the interaction polianiline-dopant. The obtained results demonstrate for the first time that interaction of polyaniline with dopants depends on the chemical nature of the solvent and not on the dopant itself. In addition, the stability of the polaronic form (conducting) grows with the increase of solvent polarity. These findings correspond well to our experimental results that show the crucial role of the solvent (and not of the dopants) for the properties of polyaniline.

Diferentes abordagens teóricas têm sido utilizadas em estudos de sistemas biomoleculares com o objetivo de contribuir com o tratamento de diversas doenças. Para a dor neuropática, por exemplo, o estudo de compostos que interagem com o receptor sigma-1 (Sig-1R) pode elucidar os principais fatores associados à atividade biológica dos mesmos. Nesse propósito, estudos de Relações Quantitativas Estrutura-Atividade (QSAR) utilizando os métodos de regressão por Mínimos Quadrados Parciais (PLS) e Rede Neural Artificial (ANN) foram aplicados a 64 antagonistas do Sig-1R pertencentes à classe de 1-arilpirazóis. Modelos PLS e ANN foram utilizados com o objetivo de descrever comportamentos lineares e não lineares, respectivamente, entre um conjunto de descritores e a atividade biológica dos compostos selecionados. O modelo PLS foi obtido com 51 compostos no conjunto treinamento e 13 compostos no conjunto teste (r² = 0,768, q² = 0,684 e r²teste = 0,785). Testes de leave-N-out, randomização da atividade biológica e detecção de outliers confirmaram a robustez e estabilidade dos modelos e mostraram que os mesmos não foram obtidos por correlações ao acaso. Modelos também foram gerados a partir da Rede Neural Artificial Perceptron de Multicamadas (MLP-ANN), sendo que a arquitetura 6-12-1, treinada com as funções de transferência tansig-tansig, apresentou a melhor resposta para a predição da atividade biológica dos compostos (r²treinamento = 0,891, r²validação = 0,852 e r²teste = 0,793). Outra abordagem foi utilizada para simular o ambiente de membranas sinápticas utilizando bicamadas lipídicas compostas por POPC, DOPE, POPS e colesterol. Os estudos de dinâmica molecular desenvolvidos mostraram que altas concentrações de colesterol induzem redução da área por lipídeo e difusão lateral e aumento na espessura da membrana e nos valores de parâmetro de ordem causados pelo ordenamento das cadeias acil dos fosfolipídeos. As bicamadas lipídicas obtidas podem ser usadas para simular interações entre lipídeos e pequenas moléculas ou proteínas contribuindo para as pesquisas associadas a doenças como Alzheimer e Parkinson. As abordagens usadas nessa tese são essenciais para o desenvolvimento de novas pesquisas em Química Medicinal Computacional. / Different theoretical approaches have been used in the studies of biomolecular systems aiming to contribute with the treatment of several diseases. For neuropathic pain, for example, the study of compounds that interact with sigma-1 receptor (Sig-1R) can elucidate the main factors associated to their biological activities. For this purpose, studies of Quantitative Structure-Activity Relationships (QSAR) using Partial Least Squares (PLS) and Artificial Neural Network (ANN) methods were applied to 64 Sig-1R antagonists belong to 1-arylpyrazole class. PLS and ANN models were used in order to describe linear and nonlinear behavior, respectively, between a set of descriptors and the biological activity of the selected compounds. The PLS model was obtained with 51 compounds in the training set and 13 compounds in the test set (r² = 0.768, q² = 0.684 and r²test = 0.785). Leave-N-out tests, biological activity randomization and outliers detection confirmed the robustness and stability of the models and showed that they were not obtained by chance correlations. Models were also generated from Multilayer Perceptron Artificial Neural Network (MLP-ANN) and the 6-12-1 architecture, trained by tansig-tansig transfer functions, showed the best result for the biological activity prediction of the compounds (r²training = 0.891, r²validation = 0.852 and r²test = 0.793). Another approach was used to simulate synaptic membranes environment using lipid bilayers composed by POPC, DOPE, POPS and cholesterol. Performed molecular dynamics studies showed that high cholesterol concentration induces decrease of area per lipid and lateral diffusion and increase of membrane thickness and order parameter caused by ordering of phospholipids acil chains. The obtained lipid bilayers can be used to simulate interactions between lipids and small molecules or proteins contributing for researches associated to Alzheimer and Parkinson diseases. The approaches used in this thesis are essential for the development of new researches in Computational Medicinal Chemistry.

Ce mémoire présente diverses expériences d'amplification d'impulsions lumineuses brèves ou mono fréquences réalisées avec des milieux laser solides. Une étude théorique de l'amplification laser en régime de saturation est présentée dans la première partie. Les effets de déformation des profils spatial et temporel par la saturation du gain sont étudiés a partir d'un modèle théorique simple considérant le milieu comme un ensemble de cibles éphémères. Il est démontré par ailleurs que le temps de relaxation du niveau inférieur de la transition laser peut avoir une certaine incidence sur le rendement effectif de l'amplification. La deuxième partie est entièrement consacrée a la description d'un amplificateur régénératif nanoseconde utilisant du yag dope au néodyme ou de l'alexandrite comme milieux actifs. Ce dispositif permet de produire des impulsions monofréquences par injection d'une cavité esclave. Une étude détaillée de ce dispositif montre qu'un asservissement de la longueur de la cavité est inutile avec ce type de fonctionnement. Un nouveau matériau solide accordable aux propriétés exceptionnelles est présenté dans la dernière partie de ce mémoire: il s'agit du saphir dope titane. Une mesure précise de l'énergie de saturation a permis d'aborder l'amplification de plusieurs types de signaux lumineux et de réaliser divers oscillateurs aux caractéristiques variées. De nombreux amplificateurs utilisant le saphir dope titane comme milieu actif sont également présentés. Ils permettent d'amplifier des impulsions monomodes ainsi que des impulsions brèves.

Diferentes abordagens teóricas têm sido utilizadas em estudos de sistemas biomoleculares com o objetivo de contribuir com o tratamento de diversas doenças. Para a dor neuropática, por exemplo, o estudo de compostos que interagem com o receptor sigma-1 (Sig-1R) pode elucidar os principais fatores associados à atividade biológica dos mesmos. Nesse propósito, estudos de Relações Quantitativas Estrutura-Atividade (QSAR) utilizando os métodos de regressão por Mínimos Quadrados Parciais (PLS) e Rede Neural Artificial (ANN) foram aplicados a 64 antagonistas do Sig-1R pertencentes à classe de 1-arilpirazóis. Modelos PLS e ANN foram utilizados com o objetivo de descrever comportamentos lineares e não lineares, respectivamente, entre um conjunto de descritores e a atividade biológica dos compostos selecionados. O modelo PLS foi obtido com 51 compostos no conjunto treinamento e 13 compostos no conjunto teste (r² = 0,768, q² = 0,684 e r²teste = 0,785). Testes de leave-N-out, randomização da atividade biológica e detecção de outliers confirmaram a robustez e estabilidade dos modelos e mostraram que os mesmos não foram obtidos por correlações ao acaso. Modelos também foram gerados a partir da Rede Neural Artificial Perceptron de Multicamadas (MLP-ANN), sendo que a arquitetura 6-12-1, treinada com as funções de transferência tansig-tansig, apresentou a melhor resposta para a predição da atividade biológica dos compostos (r²treinamento = 0,891, r²validação = 0,852 e r²teste = 0,793). Outra abordagem foi utilizada para simular o ambiente de membranas sinápticas utilizando bicamadas lipídicas compostas por POPC, DOPE, POPS e colesterol. Os estudos de dinâmica molecular desenvolvidos mostraram que altas concentrações de colesterol induzem redução da área por lipídeo e difusão lateral e aumento na espessura da membrana e nos valores de parâmetro de ordem causados pelo ordenamento das cadeias acil dos fosfolipídeos. As bicamadas lipídicas obtidas podem ser usadas para simular interações entre lipídeos e pequenas moléculas ou proteínas contribuindo para as pesquisas associadas a doenças como Alzheimer e Parkinson. As abordagens usadas nessa tese são essenciais para o desenvolvimento de novas pesquisas em Química Medicinal Computacional. / Different theoretical approaches have been used in the studies of biomolecular systems aiming to contribute with the treatment of several diseases. For neuropathic pain, for example, the study of compounds that interact with sigma-1 receptor (Sig-1R) can elucidate the main factors associated to their biological activities. For this purpose, studies of Quantitative Structure-Activity Relationships (QSAR) using Partial Least Squares (PLS) and Artificial Neural Network (ANN) methods were applied to 64 Sig-1R antagonists belong to 1-arylpyrazole class. PLS and ANN models were used in order to describe linear and nonlinear behavior, respectively, between a set of descriptors and the biological activity of the selected compounds. The PLS model was obtained with 51 compounds in the training set and 13 compounds in the test set (r² = 0.768, q² = 0.684 and r²test = 0.785). Leave-N-out tests, biological activity randomization and outliers detection confirmed the robustness and stability of the models and showed that they were not obtained by chance correlations. Models were also generated from Multilayer Perceptron Artificial Neural Network (MLP-ANN) and the 6-12-1 architecture, trained by tansig-tansig transfer functions, showed the best result for the biological activity prediction of the compounds (r²training = 0.891, r²validation = 0.852 and r²test = 0.793). Another approach was used to simulate synaptic membranes environment using lipid bilayers composed by POPC, DOPE, POPS and cholesterol. Performed molecular dynamics studies showed that high cholesterol concentration induces decrease of area per lipid and lateral diffusion and increase of membrane thickness and order parameter caused by ordering of phospholipids acil chains. The obtained lipid bilayers can be used to simulate interactions between lipids and small molecules or proteins contributing for researches associated to Alzheimer and Parkinson diseases. The approaches used in this thesis are essential for the development of new researches in Computational Medicinal Chemistry.

Man vill förkorta betongs bindetid dvs. den tid då betongytan kan behandlas så att betongytan blir slät efter gjutning. Det är en stor utmaning för företag som tillverkar fabriksbetong vintertid, eftersom bindetiden förlängs ju kallare klimatet är. Syftet med denna labboration var att visa hur Kalciumnitrart fungerar som bindetidsaccelerator i betong, och om Kalciumnitrart påverkar betongens fysikaliska egenskaper.  Följande faktorer har studerats för att se hur dessa faktorer påverkar betongens bindetid i kombination med användning av Kalciumnitrat. Betongens utgångstemperartur Typ av flyttillsatsmedel i betongen Betongens utgångskonsistens Betongens lagringsklimat Även hitta rätt dosering för att denna produkt ska vara lönsamt att användas i praktiken. Alla underökningar har utförts hos Sika AB laboratorium. All data har noggrant undersökts och använts i Excel program för framtagning av tabeller och diagram. Resultaten/slutsats i underökningarna visade följande. Bindetiden kan förkortas med Kalciumnitrat utan att behöva riskera betongens fysikaliska egenskaper. Enligt bindetidsdiagram noterades att 2,0 % och 2,5 % doseringarna gav bästa resultat gällande bindetid dvs. de gav kortast bindetid. Observera att +5 graders lagringsklimat gav ologiska resultat dvs. referensbetongen utan acceleratorn gav kortast bindetid. Tryckhållfastheten påverkas inte av acceleratorn dvs. man kan använda denna produkt utan att riskera betongens bärförmåga. Resultaten visade att betongens utgångskonsistens har stor betydelse för bindetiden, ju högre konsistens värde desto längre bindetid. Även betongens utgångstemperatur har påverkan på bindetiden, ju högre betongtemperatur desto kortare bindetid. / You want to reduce the concrete’s initial setting i.e.  the time the concrete surface can be treated so that surface gets plane after molding. It’s a big challenge for the companies that produce mill concrete in winter. Since the colder the climate gets the binding process will be extended. The purpose of this lab was to show how Calcium Nitrate functions as bonding time accelerator in concrete and if Calcium Nitrate affects the physical features of the concrete. The following elements have been studied to see how these elements affect the initial setting of the concrete in combination with the use of Calcium Nitrate. The initial temperature of the concrete The type of super plasticizer in the concrete The initial consistency Concrete storage climate Even finding the right dose so that this product will be profitable to use in the practice. All investigations have been made at Sika AB laboratory. All the data have been investigated and used in excel program for the product of chart and diagram. The results of the investigations showed the following:   Bond time can be reduced with Calcium Nitrate without needing to risk the physical features of the concrete.  According to bonding time diagram it was noted that 2.0 % and 2.5% doses gave the best result valid the initial setting i.e. that gave the shortest time of initial setting, Observe that +5 degrees storage climate gave illogical results i.e. reference concrete without the accelerator gave the shortest initial setting. Compressive strength does not get affected by the accelerator i.e. you can use this product without risking the concretes carrying capacity.  The results showed that the concrete initial consistency has a big importance to bond time, the higher consistency value the longer time of initial setting. Even concrete initial temperature has influence on the bond time, the higher concrete temperature, the shorter time of initial setting.

As a direct consequence of the misuse of antibiotics since its first discovery, bacteria have developed extensive resistance mechanisms making them once again potential lethal threats. This eventuality has triggered a vast research effort from scientists worldwide to find solutions to mitigate antimicrobial resistance. One such option is the identification of new potential antimicrobial agents, like for example antimicrobial peptides (AMPs). Various methods have been applied to evaluate the properties and determine the complex mechanism of AMPs. However, the details of the mechanism remain unknown and hence the work in this project seeks to examine the suitability of using TIR Raman, a vibrational spectroscopy technique which is sufficiently surface sensitive to study the interaction of AMPs in contact with lipid bilayers, which are just a few nanometres thick. In order to evaluate the information that could be extracted from TIR Raman, measurement of solid supported lipid bilayers in the absence of peptides were first carried out. In particular, the lipid DMPC with a phase transition close to room temperature, was measured at various temperatures to determine spectral changes associated with the transition. For the peptide-membrane interactions, the AMP LL37 was put into contact with solid supported lipid bilayers modelling the cell membranes of bacteria (DOPE, DOPG) or humans (DOPC) respectively. The data clearly indicates that the membrane composition, and specifically the lipid head group charge, play an important role in the peptide-membrane interactions. In the bilayers mimicking bacteria cell membranes, the peptide either absorbed onto or inserted into the bilayer. In contrast, for the bilayer modelling a human cell membrane, no significant variations were detected, indicating no interaction with LL37. The findings presented in this work generally coincide with similar research of LL37 using other techniques. At hand of the herein presented data, TIR Raman has proven suitable and effective in detecting effects of antimicrobial peptides in contact with model lipid bilayers, and hence can be recommended for further studies. / Som en direkt följd av missbruket av antibiotika sedan det först upptäcktes, har bakterier utvecklat omfattande resistensmekanismer vilket föranlett dem att återigen utgöra potentiellt dödlig hot. Denna situation har manat fram en väsentlig forskningsinsats från forskare världen över att hitta lösningar för att minska antimikrobiell resistens. Ett sådant alternativ har varit identifieringen av nya potentiella antimikrobiella substanser, så som till exempel antimikrobiella peptider. Ett flertal metoder har använts för att både evaluera peptiders egenskaper och fastställa deras komplexa mekanism. Detta till trots förblir de exakta detaljerna i mekanismen okända, vilket föranlett arbetet i detta projekt att undersöka lämpligheten i att använda TIR Raman, en vibrational-spektroskopisk metod som är tillräckligt ytkänslig för att studera interaktionen hos antimikrobiella peptider i kontakt med lipidmembran, vilka endast är några få nanometer tjocka. För att evaluera informationen som kan utvinnas med TIR Raman, utfördes först mätningar av lipidmembran, skapade på ett solitt underlag, utan tillägg av peptider. Mer noggrant, har lipiden DMPC med en fasövergång nära vid rumstemperatur, mätts vid olika temperaturer för att fastställa spektrala variationer associerade till övergången. För peptid-membran interaktionerna, sattes den antimikrobiella peptiden LL37 i kontakt med lipidmembran som modellerar cellmembranet hos bakterier (DOPE, DOPG) respektive människor (DOPC). Mätdatan indikerar tydligt att membrankompositionen, och där specifikt laddningen av lipidens huvudgrupp, spelar en viktig roll i membran-peptid interaktionerna. För lipidmembranen som imiterar bakteriella cellmembran, adsorberade peptiden till membranet eller integrerades in i det. Till skillnad från detta, kunde inga signifikanta variationer detekteras för lipidmembranet som modellerade ett mänskligt membran vilket indikerar att det inte interagerar med peptiden LL37. Upptäckterna som presenteras i detta arbete sammanfaller generellt med andra, liknande studier där andra instrument använts för att undersöka LL37. Det kan ur materialet som presenterats här utläsas att TIR Raman visat sig lämpligt och effektivt i detekteringen av antimikrobiella peptider i kontakt med modeller av lipidmembran, och kan därav rekommenderas för fortsatta studier.

La thèse de Giovanni BETTI BENEVENTI portes sur la caractérisation électrique et la modélisationphysique de dispositifs de mémoire non-volatile à changement de phase. Cette thèse a été effectuée dans le cadre d'une cotutelle avec l'Università degli Studi di Modena e Reggio Emilia (Italie).Le manuscrit en anglais comporte quatre chapitres précédés d'une introduction et terminés par uneconclusion générale.Le premier chapitre présent un résumé concernant l'état de l'art des mémoires a changement de phase. Le deuxième chapitre est consacré aux résultats de caractérisation matériau et électrique obtenus sur déposition blanket et dispositifs de mémoire à changement de phase (PCM) basées sur le nouveau matériau GeTe dopé carbone (GeTeC).Le chapitre trois s'intéresse à l'implémentation et à la caractérisation expérimentale d'un setup demesure de bruit a basse fréquence sur dispositifs électroniques a deux terminaux développé auxlaboratoires de l'Università degli Studi di Modena e Reggio Emilia en Italie.Enfin, dans le dernier chapitre est présentée une analyse rigoureuse de l'effet d'auto-chauffage Joulesur la caractéristique I-V des mémoires a changement de phase intégrant le matériau dans la phase polycristalline.

The neural circuitry responsible for memory consists of complex components with dynamic interactions. In hippocampal area CA1, interactions between excitatory pyramidal cells and inhibitory interneurons shape ensemble activity which encodes sequential experience. An extremely diverse set of inhibitory interneurons, with variation in gene expression, synaptic targeting, state-dependent activity, and connectivity, contribute substantially to circuit activity, such as theta and sharp wave-ripple oscillations. The precise roles of each interneuron group is not well understood, though characterization of their activity reveals mechanisms underlying hippocampal circuit computation. In this dissertation, I aim to identify and disrupt interactions between pyramidal cells and local interneurons to clarify their role in shaping cell assembly activity. We characterized axo-axonic cell activity in sharp wave-ripples, and compared their control of pyramidal cell activity and ripple events to parvalbumin expressing neurons. We identified pyramidal cell-interneuron interactions during ripples, suggesting they serve as lateral inhibitors between cell assemblies. We additionally developed and implemented a novel neural device to explore the role of cannabinoid disruption of hippocampal oscillations and organization of assemblies in vivo in awake animals. We demonstrate that cannabinoid receptor type 1 within CA1 is responsible for suppression of theta and SPW-Rs. We also found that cannabinoid activation within CA1 circuitry, regardless of muted input from CA3, was sufficient to disrupt sharp wave-ripples, likely through interference of pyramidal cell-interneuron interactions. The work in this dissertation provides insight suggesting that interneuron activity must be studied at the spiking timescale to characterize their control over cell assembly activity. / Doctor of Philosophy / Understanding how the brain creates memory remains one of the greatest questions in the field of neuroscience. Coordinated brain activity serves to build communication on large and small scales, across brain regions and within circuits consisting of small groups of neurons. Precise coordination of activity and communication across neurons and regions is thought to build salient experience, which is achieved through the timing of neuron action potentials, or spikes. Neurons receive thousands of inputs that control their spiking activity. "Go and stop" signals from excitatory and inhibitory interneurons act to conduct synchronized activity, which is required for proper circuit function. Importantly, coordinated spiking across large groups of neurons is responsible for observed "brain waves", or oscillations, which reflect organized activity. In CA1 of the hippocampus, there are >20 subtypes of interneurons that all make distinct contributions to memory function, and the roles of these interneurons have not been fully studied within behaving animals. As engineers develop new tools, new methods become available to study and classify how unique groups of interneurons play a part in circuit activity. Thus, we sought to characterize the role of axo-axonic cells, a specialized interneuron with strong control over spiking activity, in hippocampal oscillations that are responsible for memory encoding and consolidation. We identified a new role for axo-axonic cells in the regulation of pyramidal cell spiking in sharp wave-ripple oscillations. Additionally, we developed a novel neural device that allowed us to investigate the mechanisms that underlie cannabinoids, molecules found in Cannabis sativa, and memory dysfunction. We leveraged the multifunctionality of our T-DOpE probe to focally deliver synthetic cannabinoid into the hippocampus in combination with optical control of circuits, with simultaneous recording of activity. We found that cannabinoids acting within CA1 sufficiently disrupt hippocampal oscillations, likely through hindering pyramidal cell-interneuron interactions. Together, these findings suggest that the spatial and temporal resolution required to study diverse roles of interneurons is high, and experiments designed to explore interneuron activity should especially emphasize fine time-scales.

Dans la course aux materiaux pour l'optique non-lineaire, les matrices dopees, solides et transparentes obtenues, a temperature ambiante, par procede sol-gel, prennent une importance toujours croissante. Ainsi, en soumettant un gel de silice, dope par des molecules organiques, aux impulsions breves, polarisees rectilignement, issues d'un laser a colorant, on induit une birefringence locale, de relaxation extremement lente. Ce phenomene, qui presente une dependance quadratique par rapport au champ electrique optique, peut s'expliquer par la conjonction d'un alignement moleculaire par effet kerr optique et de l'etablissement de liaisons hydrogene entre le gel et ses dopants. La nature et la structure des especes dopantes, de leur matrice hote ou encore des impulsions lumineuses jouent ici chacune un role essentiel. Les molecules dopantes doivent ainsi presenter une forte polarisabilite, et offrir un nombre important de sites d'ancrage par liaison hydrogene. Il en est de meme pour les pores de la matrice hote. La composition du gel affecte grandement le nombre de ces sites. Une maniere, toutefois, de favoriser l'alignement remanent des dopants consiste a les greffer, des la synthese, aux pores du gel, via des liaisons covalentes. La structure temporelle des impulsions est egalement cruciale. On y distingue deux composantes. L'une, d'une duree d'une centaine de femtosecondes, brise les liaisons hydrogene et libere les dopants. L'autre, plus longue (une dizaine de nanosecondes), les aligne. Mathematiquement descriptibles par une equation de diffusion rotationnelle modifiee, ces mecanismes ont donne lieu a quelques premieres applications experimentales (inscription d'une image et d'un reseau de diffraction). Le choix, enfin, de nanoparticules magnetiques comme dopants, permet de les orienter et non plus seulement de les aligner sous champ magnetique statique des la formation du gel. Les materiaux ainsi obtenus presentent une birefringence uniforme, mais aussi une non-centrosymetrie propice aux non-linearites optiques du second ordre.

The structures of AgSin (n = 1 ¡V 16) clusters are investigated using first-principles calculations. Our studies suggest that AgSin clusters with n = 7, 10, and 15 are relatively stable isomers and that these clusters prefer to be exohedral rather than endohedral. Moreover, doping leaves the inner core structure of the clusters largely intact. Additionally, the plot of fragmentation energies as a function of silicon atoms shows that the AgSin are favored to dissociate into one Ag atom and Sin clusters. Alternative pathways exist for n > 7 (except n = 11 and 16) in which the AgSin cluster dissociates into a stable Si7 and a smaller fragment AgSin􀀀7. The AgSi11 and AgSi16 cluster dissociates into a stable Si10 and a small fragment AgSi. Lastly, our analysis indicates that doping of Ag atom significantly decreases the gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital for n > 7.