Endogenous bioelectric fields guide morphogenesis during embryonic development and regeneration by directly regulating the cellular functions responsible for these phenomena. Although this role has been extensively explored in many peripheral tissues, the ability of electric fields to regulate wound repair and stimulate regeneration in the mammalian central nervous system (CNS) has not been convincingly established. This dissertation explores the role of electric fields in regulating the injury response and controlling the regenerative potential of the mammalian CNS. We place particular emphasis on their influence on astrocytes, as specific differences in their injury-induced behaviors have been associated with differences in the regenerative potential demonstrated between mammalian and non-mammalian vertebrates. For example, astrocytes in both mammalian and non- mammalian vertebrates begin migrating towards the lesion within hours and begin to proliferate after an initial delay of two days; subsequently, astrocytes in non-mammalian vertebrates support neurogenesis and assume a bipolar radial glia-like morphology that guides regenerating axons, whereas astrocytes in mammals do not demonstrate robust neurogenesis and undergo a hypertrophic response that inhibits axon sprouting. To test whether injury-induced electric fields drive the astrocytic response to injury, we exposed separate populations of purified astrocytes from the rat cortex and cerebellum to electric field intensities associated with intact and injured mammalian tissues, as well as to those electric field intensities measured in regenerating non-mammalian vertebrate tissues. Upon exposure to electric field intensities associated with uninjured tissue, astrocytes showed little change in their cellular behavior. However, cortical astrocytes responded to electric field intensities associated with injured mammalian tissues by demonstrating dramatic increases in migration and proliferation, behaviors that are associated with their formation of a glial scar in vivo; in contrast, cerebellar astrocytes, which do not organize into a demarcated glial scar, did not respond to these electric fields. At electric field intensities associated with regenerating tissues, both cerebellar and cortical astrocytes demonstrated robust and sustained responses that included morphological changes consistent with a regenerative phenotype. These results support the hypothesis that physiologic electric fields drive the astrocytic response to injury, and that elevated electric fields may induce a more regenerative response among mammalian astrocytes.

Ce travail porte sur l’amélioration de l’extraction des composés phénoliques à partir des raisins tout au long de la chaîne de la vinification en rouge. La qualité des vins rouges est en grande partie déterminée par les composés phénoliques. Parmi les composés phénoliques, les anthocyanes, qui sont responsables de la couleur, et les tanins, à l’origine de la sensation d’astringence. Pour augmenter la quantité des composés phénoliques présents dans le vin, un développement des procédés permettant d’améliorer la diffusion des composés phénoliques durant la vinification en rouge doit être mis en jeu. Nous avons entamé notre étude par un suivi de la maturité phénolique des raisins rouges appartenant à différentes parcelles de la société château KSARA localisées dans la vallée de la Békaa tout en se servant des méthodes Glories (1&2) et ITV. Quant à l’amélioration de l’extractibilité des composés phénoliques durant la vinification en rouge, différents prétraitements ont été appliqués dans le but d’améliorer la diffusion de ces composés. Parmi ces procédés, les technologies suivantes ont été abordées dans notre étude: les électrotechnologies (CEP), les ultrasons, le chauffage modéré, le traitement enzymatique, la macération préfermentaire à froid et la thermovinification. Ces techniques permettent d’endommager ou de fragiliser les membranes et/ou parois cellulaires facilitant ainsi la libération du contenu cellulaire vers le milieu extérieur. Les cinétiques d’extraction des composés phénoliques ont pu être modélisées par le modèle empirique de Peleg et le modèle cinétique simplifié afin d’estimer les rendements d’extraction. De plus, dans ce travail, l’accent a été mis sur les propriétés antiradicalaires et antimicrobiennes des composés phénoliques extraits de différentes variétés de raisins fournis par la société Château KSARA. Pour valoriser les co-produits de la vinification, le chauffage ohmique pulsé (COP) a été appliqué sur le marc du raisin dans le but d’améliorer l’extraction de ses composés phénoliques. L'optimisation du choix de la date des vendanges et l'amélioration des procédés d’extractions des composés phénoliques durant la vinification en rouge, pourraient nous conduire à élaborer un vin d'une meilleure qualité. Ce travail étant effectué, il sera intéressant comme projet à venir de valider ces différents pré-traitements à grande échelle pour une perspective d’application industrielle. / This study focuses on improving the extraction of phenolic compounds from grapes throughout the chain of red winemaking. The quality of wine is mainly determined by the phenolic compounds. From these phenolic compounds, the anthocyanins, which are responsible of the color and tannins, the responsible of the astringency. In order to increase the amount of phenolic compounds present in wine, a development of methods used to improve the extraction of phenolic compounds during the red vinification should be discussed. We began our study by using two methods Glories (1&2) and ITV to monitor the phenolic maturity of red grapes grown in the vineyards in the province of Bekaa-Château KSARA S.A.L. Whereas for the improvement of the extractibility of phenolic compounds during the vinification, different pre-treatments were applied in order to ameliorate the diffusion of these compounds. Among these process, the following technologies were discussed in our study: the electrotechnologies (PEF), the ultrasound, the moderate heat treatment, the enzymatic treatment, the cold maceration and the thermovinification. These techniques are able to weaken the cell walls and facilitate the diffusion of grape’s phenolic compounds during vinification. Peleg’s equation and the simplified kinetic model were shown to be suitable for describing the extraction kinetics for phenolic compounds and for the estimation of the extraction yield of polyphenols. Furthermore, in this study, the antiradical and antimicrobial activities of phenolic compounds extracted from grapevine varieties of Château KSARA-Bekaa-Lebanon were analyzed. To valorize the by-products of the vinification, the pulsed ohmic heating (POH) was applied on the grape pomace in order to ameliorate the extraction of the phenolic compounds. The optimization of the choice of the harvesting date and the amelioration of the extraction of phenolic compounds during the red vinification, will conduce to elaborate a high quality of wine. After this study, it will be interesting to validate the different pre-treatments at large scale for a perspective of an industrial application.

Métodos de produção eficientes que economizam tempo e energia são sempre exigidos e novos processos de sinterização de baixo custo têm sido desenvolvidos para materiais cerâmicos e implementados por empresas e pesquisadores em todo o mundo. Com este objetivo, uma nova abordagem conhecida como Flash Sintering está atraindo grande interesse. Esta nova técnica de sinterização envolve a aplicação de campo elétrico através de uma amostra durante o aquecimento, gerando assim aceleração abrupta da cinética de densificação, diminuindo o tempo de sinterização de horas para segundos e diminuindo o aquecimento do forno em até centenas de graus Celsius. Frequentemente descritas para cerâmicas policristalinas e compósitos de cerâmica e vidro, a sinterização auxiliada por campo elétrico com apenas vidro não foi encontrado na literatura. A sinterização assistida por campo elétrico foi controlada com sucesso, sem que ocorresse o escoamento da amostra, obtendo uma elevada densidade relativa do vidro comercial. Um vidro de janela soda-cal-sílica não estequiométrica foi usado na pesquisa devido à sua importância comercial, por ser um material de partida de baixo custo, por apresentar condução iônica e haver na literatura dados de propriedades físicas e de cinética de sinterização convencional. O campo elétrico também influencia fortemente a cinética de sinterização do vidro soda-cal-sílica. Os resultados experimentais foram comparados com cálculos analíticos realizados a partir do modelo de Clusters não-isotérmico de sinterização de vidro por fluxo viscoso com cristalização concorrente. O aumento de temperatura nos compactos de pó de vidro durante o aquecimento do forno e aplicação de campo elétrico foi estimado usando um modelo de radiação de corpo negro. Preliminarmente, o aumento da temperatura devido ao efeito Joule pode explicar a diminuição da temperatura de amolecimento em comparação com a temperatura do forno e a sinterização rápida do vidro estudado. / Efficient production methods saving time and energy are always demanded and novel reduced-cost sintering processes have being developed for ceramic materials and implemented by companies and researchers of all over the world. With this aim, a new sintering approach generally known as flash sintering is attracting great interest. This new sintering technique involves the application of electric field through a sample while heating, thereby generating abrupt acceleration of the densification kinetics, decreasing the sintering time from hours to seconds and decreasing the oven heating in up to hundreds of degrees Celsius. Well described for polycrystalline ceramics and ceramic-and-glass composites, the sintering of pure glass aided by electric field is still lacking in the literature. The sintering assisted by electric field, was successfully controlled, without sample flow, achieved a high relative density of a commercial glass. A non-stoichiometric soda-lime-silica window glass was used due to its commercial importance, low cost starting material, ionic conduction, and literature on physical properties and conventional sintering kinetics. Electric field was observed to also strongly influence window glass sintering kinetics. The experimental results were compared with analytical calculations obtained from the non-isothermal Clusters model of glass sintering by viscous flow with concurrent crystallization. The temperature increase in the glass powder compacts during oven heating and electric field application was estimated by using a black-body radiation model. Preliminary, the temperature increase due to Joule effect can explain the softening temperature decrease compared with the oven temperature, and the fast sintering of the studied glass.

O presente trabalho teve como objetivo o desenvolvimento de um equipamento capaz de gerar e captar o efeito corona em alimentos de forma automatizada e instantânea. Para isto, foi desenvolvido um gerador de alta tensão e alta frequência, um sistema de captação com eletrodo e câmera digital e um software de gerenciamento do sistema, que recebe e trata os dados coletados através da câmera digital. Para comprovar a eficiência do sistema, foram feitos vários testes com frutas (maçã, limão, ameixa, uva e pera) e os resultados obtidos foram comparados com imagens geradas por um sistema kirlian e com simulações computacionais através de algoritmo genético e elementos finitos e permitem assim, concluir que o sistema proposto foi capaz de captar imagens que contém informações das características físico-químicas do alimento. / This study aimed to develop a device capable of generating and acquiring the corona effect on food automatically and instantaneously. In order to make it possible, a high voltage and high frequency generator was developed, with a system with electrodes and digital camera controlled by a software that receives and handles incoming data from a digital camera. To test de system, experiments where made with fruits (apples, lemons, plums, grapes and pears) and the results where compared to a standard system and with computational simulation made with Genetic Algorithm and Finite Elements and it was conclude that the system is able to acquire images that contain information on the physical-chemical proprieties of the material.

O grande acúmulo de saponinas nos frutos imaturos de erva mate permite considerá-los uma fonte de matéria prima abundante e ainda não explorada para obtenção de saponinas. As saponinas são conhecidas como tensoativos naturais, sendo utilizadas pelas suas propriedades emulsificantes e farmacológicas. O presente estudo teve como principal objetivo avaliar o uso de técnicas de extração emergentes, como Extração assistida por Ultrassom (US), Campo Elétrico Moderado (CEM) e Extração por Fluido Supercrítico (EFS) para a extração seletiva de saponinas a partir de frutos imaturos de erva mate. Foram investigadas três condições de intensidade de ultrassom (565, 423 e 282 W cm-²) e de intensidade de campo elétrico (50, 37,5 e 25 V cm-1) associadas a diferentes temperaturas de operação. A interação das intensidades de ultrassom e de campo elétrico com diferentes temperaturas foi avaliada através do método de superfície de resposta. Para as extrações por fluido super e sub crítico foram utilizadas três condições de pressão (10, 20 e 30 MPa) e posteriormente sua correlação com diferentes vazões de solvente (1,62; 2,22 e 2,78 x10-4 kg s-1) e temperatura (30, 40 e 50 °C) foi investigada através do métodos de superfície de resposta. Curvas de rendimento das extrações em função do tempo foram levantadas para as condições ótimas de campo elétrico e intensidade de ultrassom (37,5 V cm-1 e 565 W cm-², respectivamente) a 40°C. As curvas foram modeladas matematicamente, com ajuste satisfatório, por modelos cinéticos de 1ª e 2ª ordem e também por um modelo difusivo baseado na 2ª Lei de Fick. Para extração supercrítica, foi construída a curva de extração para a condição de 10 MPa e 40 °C e esta curva foi modelada matematicamente. Assim, foram estimados parâmetros relacionados à transferência de massa, importantes para a compreensão fenomenológica dos processos extrativos. Nesse estudo, a extração com CO2 supercrítico mostrou-se tecnicamente viável para a obtenção de saponinas, sendo mais seletiva em relação aos processos por campo elétrico e ultrassom. Os ensaios com ultrassom e campo elétrico conseguiram gerar extratos brutos com até 68,30 e 64,26 μgilexmg-1extrato em massa de equivalente de saponina por massa de extrato, respectivamente. Os extratos obtidos com fluido supercrítico apresentaram elevada seletividade para saponinas, gerando extratos brutos com até 100,9 μgilex mg-1 extrato de saponina por massa de extrato. A pressão de operação não apresentou efeito tanto no rendimento global de extrato quanto no de saponina. / Considering the substantial amount of saponins in unripe yerba mate fruits, they are an abundant source of raw material not exploited yet. Saponins are known as natural surfactants, being used by their emulsifier and pharmacological properties. This study aimed to evaluate emergent extraction techniques such as Ultrasound (US), Moderate Electric Field (MEF) and Supercritical Fluid Extraction (SFE) for the selective extraction of saponins from unripe fruits of yerba mate. Three power conditions (565, 423 and 282W cm-2), electric field intensities (50, 37.5 and 25 V cm-1) and pressure conditions (10, 20 and 30 MPa) were initially assayed for US, MEF and SFE respectively at 40 °C. Power and electric field intensity were found to affect the saponins yields, thus, their correlation with different temperatures were evaluated with a factorial design. At the optimal condition, US and MEF saponins yields were 6.42% and 6.83% (%gilex gextract-1). Extraction yield curves were raised for optimum conditions of electric field and ultrasound power (37.5 V cm-1 and 565 W cm-², respectively). Three different kinetic models were used to model mathematically the overall extraction curves, namely a first-order, second-order, and a mass transfer model based on Fick’s Law. The operating pressure had no effect on either the overall brute extract or saponins yield for SFE. Although the extracts obtained with supercritical fluid showed low brute extracts yields, it was highly selective for saponins yielding up to 10.09%. For supercritical extraction, the extraction curve for 10 MPa and 40 °C was assayed and the experimental data fitted by a mathematical model. Parameters related to mass transfer, important for understanding of the extractive processes, were successfully estimated. In this study, the extraction with ultrasounds, electric field and supercritical CO2 were shown to be technically viable to obtain saponins from unripe yerba mate fruits, being EFS more selective than the other technics studied.

Dans cette thèse, différentes techniques de microscopie électronique à transmission et à balayage (STEM : scanning transmission electron microscopy) ont été améliorées et appliquées à plusieurs structures essentiellement à base de semiconducteurs. La création de nouveaux matériaux et dispositifs a été à l'origine du développement des civilisations et des méthodes de caractérisation expérimentales sont nécessaires pour étudier les nouvelles structures afin de les comprendre et de les améliorer. Avec le développement des nanotechnologies, la microscopie électronique est devenu un outil indispensable du fait de sa grande résolution spatiale et de la pléthore d'information qu'elle permet d'obtenir.Dans la première partie de cette thèse, les nombreux développements réalisés sont présentés. Plusieurs sous-techniques du STEM ont été améliorés : création de moirés obtenus par balayage (SMF : scanning moiré fringes), nano-diffraction électronique en mode précession (NPED : nano-beam precession diffraction) et haute résolution en STEM (HR-STEM). Ces développements permettent d'obtenir des cartographies quantitatives sur les déformations et les champs électriques et indirectement des informations chimiques.Dans la deuxième partie, les techniques développés sont utilisés pour étudier différentes structures et les résultats sont comparés à ceux d'autres techniques comme l'holographie et le contraste de phase différentielle (DPC : differentail phase contrast). Dans une structure photovoltaïque à base de matériaux II-VI, une accumulation d'un matériau II a été détectée aux interfaces grâce aux mesures des déformations. Des champs de déformations très faibles capitaux pour le fonctionnement des isolants topologiques à base de HgTe ont été mesurés. Des cartographies de déformation très précises ont été obtenues dans des transistors SiGe. Dans des couches AlN/GaN des cartographies de déformation et de champs électriques ont pu être réalisés simultanément révélant l'importance des dislocations. Des domaines d'inversion coeur-coquille ont été mis en évidence pour la première fois. Ils ont été observés dans de nombreux fils de GaN élaborés par épitaxie par jet moléculaires. Les positions des atomes dans un domaine d'inversion ont pu être mesurés à quelques picomètres près et comparés à des calculs ab-initio. / In this work, different scanning transmission electron microscopy (STEM) techniques have been developed and applied to several material systems. The creation of novel materials and devices has been a backbone of society’s development and characterization methods are needed to investigate these materials in order to understand and improve them. With the advent of nanotechnology, electron microscopy has become an invaluable tool, as it is able to visualize the atomic structure of thin samples and produces a plethora of quantifiable signals.In a first part, the numerous developments realized in this thesis are presented. Several STEM based techniques have been improved: scanning moiré fringes (SMF), nano-beam precession diffraction (NPED) and high-resolution STEM (HR-STEM). These developments allow for more accurate strain measurements, the quantitative mapping of electric fields and to realize accurate chemical profiles.In a second part, the developed methods are applied to different material systems and compared to more classical techniques, like holography and differential phase contrast (DPC). In a II/VI solar cell structure the interface chemistry is determined from strain with atomic resolution. Very faint strain gradients that are vital for the topological insulator properties of HgTe are measured. Accurate two-dimensional strain maps are obtained of a SiGe transistor. Simultaneous strain and electric field maps of m-plane AlN/GaN reveal the influence of dislocations in the material. Core-shell type inversion domains are described for the first time in GaN nanowires. They were found in many samples grown by molecular beam epitaxy. Thanks to quantitative analysis the exact atomic structure of inversion domains in GaN is described and compared to simulations.

Seventy-four methicillin-resistant Staphylococcus aureus (MRSA) from two Malaysian hospitals were characterised by both phenotypic and genotypic techniques. These isolates were collected over an 18 year time period in the years, 1982, 1989, 1994 and 2000. All of the Malaysian MRSA isolates were found to be multiresistant and resistant to at least five different antimicrobial agents. Over 30% of them were non-typable by the International Basic Set of bacteriophages. The majority of the typable isolates were susceptible to the group III phages, especially phage 85. The majority of the isolates carried one to six plasmids. Only two isolates were plasmid free. The plasmid profiles of these isolates, other than the 1982 isolates, were very similar to each other. Contour-clamped homogeneous electric field (CHEF) gel electrophoresis was used to examine the genetic relatedness of the isolates. Twenty-six CHEF patterns were found among the isolates. These CHEF patterns were closely related to each other. The predominant CHEF pattern A was found in the 1982, 1989 and 1994 isolates. The CHEF patterns of the year 2000 isolates were different to CHEF pattern A, but still closely related. All of the isolates were found to carry the Allotype III SCCmec and have coagulase-gene type 24. Multilocus sequence typing was preformed on the isolates with CHEF pattern A collected in different years. These isolates were found to have either sequence type 239 (ST239), or its single locus variant. The predominant Malaysian clone belongs to the pandemic clone ST239-MRSA-III that is pandemic in Asian countries. (Enright, 2003, Ko et al., 2005). / A 1.5 kb cryptic plasmid found in Malaysian isolates was indistinguishable from a cryptic plasmid found in an Australian isolate. A 3.0 kb cryptic plasmid found in Malaysian isolates was undistinguishable from a 3.0 kb plasmid found in Singaporean isolates. Class II multiresistance plasmids of 28, 30.5 and 35 kb were commonly found together in many Malaysian MRSA isolates. Both the 28 and 30.5 kb plasmids encode resistance to the heavy-metals and nucleic acid-binding (NAB) compounds. The 35 kb plasmid carries heavy-metal and NAB resistance but also encodes β-lactamase. Structurally these three plasmids are almost identical and probably have the same origin. The differences observed between these plasmids is probably due to excision or partial deletion of the β-lactamase transposon of the original plasmid. The 28 kb plasmid is identical to the 28 kb plasmid of Singaporean and some Australian isolates. A 20 kb plasmid in Indonesian isolates was found to be closely related to these three plasmids. A conjugative plasmid, pWBG707, conferring trimethoprim-resistance was found in Malaysian isolates. It did not carry either of the two staphylococcal trimethoprim-resistance genes, dfrA and dfrD. (Lyon and Skurray, 1987, Dale et al., 1995b) It either encodes a novel resistance gene or the recently discovered dfrG gene. (Sekiguchi et al., 2005) pWBG707 was also found to mobilise a small 3.0 kb kanamycin-resistance plasmid during conjugation. / The mecR1 and mecI genes regulating the transcription of the methicillin-resistance gene, mecA, were also examined in the isolates. The Malaysian isolate, WBG7422, with the predominant CHEF pattern A has a nonsense mutation in its mecI gene that disables it. However, its mecR1 gene is intact. The eastern Australia MRSA (EA MRSA), WBG525, has a CHEF pattern that is closely related to the Malaysian predominant CHEF pattern A and its mecI gene has a mutation identical to the Malaysian isolate. Unlike the Malaysian isolate however, its mecR1 gene has a 166 bp deletion. Both WBG7422 and WBG525 express Class III heterogeneous methicillin resistance. However, WBG525 has more highly resistant cell in its population than WBG7422. The loss of aminoglycoside resistance, together with c. 114 kb of chromosomal DNA, was observed in some Malaysian isolates. The deleted segment was found to carry the aacA-aphD gene that encodes a bifunctional aminoglycoside-modifying enzyme conferring resistance to many of the aminoglycosides. The Malaysian isolates were compared with MRSA from different countries. These MRSA included 18 epidemic MRSA (EMRSA) from the United Kingdom, 15 Australian nosocomial MRSA, five classical MRSA, 22 community-acquired MRSA (CMRSA) from Australia and New Zealand and 46 nosocomial MRSAs from eight Asian-Pacific countries and South Africa. These Asian-Pacific countries were Australia, PR China, Hong Kong, Indonesia, Japan, Philippines, Singapore and Taiwan. / The CHEF patterns of most of the Asian-Pacific and South African isolates were closely related to the Malaysian isolates. Isolates from Singapore, Indonesia and Philippines were found to have an identical CHEF pattern to the Malaysian CHEF patterns A5. The Asian-Pacific and South African isolates, including the Malaysian isolates, were found to be closely related to EMRSA-1, -4 and -7. These EMRSA belong to the ST239-MRSA-III clone and are coagulase-gene type 24. The isolates from Japan were the only Asian-Pacific isolates not related to the other Asian-Pacific isolates and EMRSAs. EMRSA-1 and EA MRSA have the same 166 bp deletion in their mecR1 gene. Both of these strains have closely related CHEF patterns, the same sequence type, coagulase-gene type and SCCmec. These results indicate that these two strains belongs to the same clone and confirms the international spread of this clone in the early 1980s. However, the Malaysian isolates have CHEF patterns that are more closely related to EMRSA-4 than to EMRSA-1. Similar to the Malaysian isolates EMRSA-4 has an intact mecR1 gene. The CMRSA isolates were not related to any of the nosocomial MRSA. They also have very diverse genetic backgrounds but carry less diverse SCCmec allotypes. Most of the CMRSA carry either Allotype IV or V SCCmec These results show that the spread of Malaysian MRSA is due to a single clonal expansion. Infection control measures would have to have been more efficient if this clone was to have been contained. The Malaysian epidemic clone is the Asian pandemic clone, ST239-MRSA-III. The Malaysian isolates and EMRSA-4 probably share the same ancestor. / The presence of the same MRSA strain in Malaysian hospitals and in the hospitals of neighbouring countries indicates that the inter-hospital spread of an epidemic MRSA has occurred. This observation also suggests that the infection control measures in Malaysian hospitals have not been totally effective. The ineffectiveness of infection control has left Malaysian hospitals vulnerable to the future importation of new pandemic clones and/or highly virulent or resistant clones.

InGaN based blue and near-ultraviolet light emitting diodes and laser diodes have been successfully commercialized for many applications such as general lighting, display backlighting and high density optical storage devices. Despite having a comparably high defect density, these devices are known for their efficient operation, which is attributed to localization in potential fluctuations preventing carriers from reaching the centers of nonradiative recombination. Nitride research is currently headed towards improving deep ultraviolet AlGaN and green InGaN emitters with higher Al and In molar fractions. The efficiency of these devices trails behind the blue counterparts as the carrier localization does not seem to aid in supressing nonradiative losses. In addition, the operation of ternary nitride heterostructure based devices is further complicated by the presence of large built-in electric fields. Although the problem can be ameliorated by growing structures in nonpolar or semipolar directions, the step from research to production still awaits. In this thesis, carrier dynamics and localization effects have been studied in three different nitride ternary compounds: AlGaN epitaxial layers and quantum wells with high Al content, nonpolar m-plane InGaN/GaN quantum wells and lattice matched AlInN/GaN heterostructures. The experimental methods of this work mainly consist of spectroscopy techniques such as time-resolved photoluminescence and differential transmission pump-probe measurements as well as spatial photoluminescence mapping by means of scanning near-field microscopy. The comparison of luminescence and differential transmission measurements has allowed estimating the localization depth in AlGaN quantum wells. Additionally, it has been demonstrated that the polarization degree of luminescence from m-InGaN quantum wells decreases as carriers diffuse to localization centers.What is more, dual-scale localization potential has been evidenced by near-field measurements in both AlGaN and m-InGaN. Larger scale potential fluctuation have been observed directly and the depth of nanoscopic localization has been estimated theoretically from the recorded linewidth of the near-field spectra. Lastly, efficient carrier transport has been observed through AlInN layer despite large alloy inhomogeneities evidenced by broad luminescence spectra and the huge Stokes shift. Inhomogeneous luminescence from the underlying GaN layer has been linked to the fluctuations of the built-in electric field at the AlInN/GaN interface. / <p>QC 20121101</p>

The results of a systematic 35Cl, 81Br, and 127I SSNMR spectroscopic study of a series of halogen-substituted anilinium halide salts are presented. Solid-state NMR of these nuclides, bromine-/81 and iodine-127 in particular, is not well established. Twenty-one compounds thought to exhibit halogen bonding were prepared based on modified literature procedures, and two crystal structures were solved. Experiments show that collection of SSNMR spectra of the anions is feasible, though ultrahigh magnetic fields (21.1 T) and variable offset data acquisition were found to be essential. Electric field gradient and chemical shift tensors are measured experimentally for all 21 compounds, significantly expanding the body of data for the quadrupolar halogen nuclei. Quadrupolar coupling constants for chlorine-35 ranged from 2.12 to 6.04 MHz, for bromine-81 from 12.3 to 45.3 MHz, and for iodine-127 from 57.50 to 152.50 MHz. Gauge-including projector-augmented wave density functional theory (GIPAW-DFT) calculations were used to provide insight as to how the NMR parameters vary with local environment and long-range crystal packing. Overall, calculations reproduced the experimental trends in quadrupolar coupling constants and chemical shift tensor span (Ω) but failed to provide quantitative agreement within experimental error. Experimental and computational data were analyzed in order to provide insight into how halogen bonding influences NMR parameters. Several trends were elucidated from this study, including an inverse correlation between Ω and the length of the shortest halogen-halide contact (d). In selected bromine compounds, for example, Ω (81Br) was measured to increase from 120 to 240 ppm as d decreased from 3.838 to 3.443 Å. In summary, this study has demonstrated the feasibility and utility of quadrupolar halogen SSNMR, and that these techniques may prove useful in characterizing halogen bonding interactions in solids.

The results of a systematic 35Cl, 81Br, and 127I SSNMR spectroscopic study of a series of halogen-substituted anilinium halide salts are presented. Solid-state NMR of these nuclides, bromine-/81 and iodine-127 in particular, is not well established. Twenty-one compounds thought to exhibit halogen bonding were prepared based on modified literature procedures, and two crystal structures were solved. Experiments show that collection of SSNMR spectra of the anions is feasible, though ultrahigh magnetic fields (21.1 T) and variable offset data acquisition were found to be essential. Electric field gradient and chemical shift tensors are measured experimentally for all 21 compounds, significantly expanding the body of data for the quadrupolar halogen nuclei. Quadrupolar coupling constants for chlorine-35 ranged from 2.12 to 6.04 MHz, for bromine-81 from 12.3 to 45.3 MHz, and for iodine-127 from 57.50 to 152.50 MHz. Gauge-including projector-augmented wave density functional theory (GIPAW-DFT) calculations were used to provide insight as to how the NMR parameters vary with local environment and long-range crystal packing. Overall, calculations reproduced the experimental trends in quadrupolar coupling constants and chemical shift tensor span (Ω) but failed to provide quantitative agreement within experimental error. Experimental and computational data were analyzed in order to provide insight into how halogen bonding influences NMR parameters. Several trends were elucidated from this study, including an inverse correlation between Ω and the length of the shortest halogen-halide contact (d). In selected bromine compounds, for example, Ω (81Br) was measured to increase from 120 to 240 ppm as d decreased from 3.838 to 3.443 Å. In summary, this study has demonstrated the feasibility and utility of quadrupolar halogen SSNMR, and that these techniques may prove useful in characterizing halogen bonding interactions in solids.