Li-ion battery technologies have transformed the consumer electronics and electric vehicles landscape over the last few decades. Single-crystal cathode materials with controllable physical properties including size, morphology, and crystal facets can aid researchers in developing relationships between physical characteristics, chemical properties, and electrochemical performance. High-voltage LiNi_0.5Mn_1.5O₄ (LNMO) materials are desirable as cathodes due to their low cost, low toxicity, and high capacity and energy density making them promising to meet increasing consumer demands for battery materials. However, transition metal dissolution, interfacial instability, and capacity fading plague these materials when paired with graphite, limiting their commercial capability. Furthermore, variation in Ni/Mn ordering can lead to complex multiphase co-existence and changes in Mn oxidation state and electrochemical performance. These properties can be adjusted during synthesis using a facile and tunable molten salt synthesis method. This dissertation focuses on the investigation of chemical and structural heterogeneities of LNMO prepared under different synthetic conditions at different length scales. In Chapter 2, the influences of molten salt synthesis parameters on LNMO particle size, morphology, bulk uniformity, and performance are evaluated revealing the difficulty of reproducible cathode synthesis. We utilize the X-ray nanodiffraction technique throughout this work, which provides high-resolution structural information. We develop a method to measure and relate lattice strain to phase distribution at the tens of nanometers scale. In Chapter 3, mapping lattice distortions of LNMO particles with varying global Mn oxidation states reveals inherent structural defects and distortion heterogeneities. In Chapter 4, we examine lattice distortion evolution upon chemical delithiation, Mn dissolution behaviors, and evaluate the chemical delithiation method as a means to replicate electrochemical cycling conditions. We further investigate lattice distortion spatially via in situ nanodiffraction during battery cycling in Chapter 5, illustrating the capabilities of the measurement to provide practical understanding of cathode transformations. From intra-particle to electrode materials level, heterogeneities that arise in cathode materials can dictate performance properties and degradation mechanisms and are necessary for researchers to understand for the improvement of Li-ion battery systems. The development of the nanodiffraction measurements aids in our understanding of inherent and dynamic materials chemical and structural heterogeneities. / Doctor of Philosophy / The invention of rechargeable Li-ion batteries in the 1990s has undeniably revolutionized modern civilization. Cell phones, laptops, grid energy storage, and electric vehicles have become fundamental fixtures of the 21st century. As technologies improve and requirements for advanced renewable energy storage have increased, researchers have sought to design longer lasting, faster charging, and more lightweight batteries. Modifying and finding new positive electrode materials is one way to improve the capabilities of modern batteries as their properties are governed by fundamental chemistry. High-voltage LiNi_0.5Mn_1.5O₄ (LNMO) is one such material that can allow for fast charging and high energy storage capacity, but its commercialization is hindered by complex physical and chemical properties, which can limit its lifetime in batteries. Large, particles with well-defined shapes are desirable to improve the stability of the materials; however, understanding their defects and structural heterogeneities is vital to continued optimization and requires advanced characterization techniques. In this dissertation, we characterize the physical phases and chemical properties of LNMO samples prepared under different conditions resulting in different particle shapes, sizes, and chemical distributions. An advanced X-ray nanodiffraction technique is used to measure phase distributions within individual particles while lab-based analytical techniques and electrochemical testing can determine bulk properties and battery performance of materials. Overall, the aim of this work is to develop techniques to measure structural and chemical heterogeneities of cathode materials at different length scales and to understand how they influence properties and performance in batteries. This work provides valuable insights into the inherent and dynamic properties of high-voltage electrode materials useful to advance our understanding of how these materials fail and to aid researchers in creating design principles to develop stable, high-performing future generations of rechargeable batteries.

No description available.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work aimed to analyze floristic and structure variations in a Montane Mixed Ombrophylous Forest remnant, in the county of Nova Prata, RS. It was inventoried 71 parcels with dimensions of 10 x 100 m, using the process of systematic sampling in Two Stages. It were identified and measured all individuals with circumference at breast height ≥ 30,0 cm. The dissertation was divided into two chapters, with specific objectives to analyze the presence of floristic groups (Chapter I) and diagnostic and diagnose structural variations between clusters (Chapter II). The plots were classified by cluster analysis, using the Ward connection method. The plots were classified into four distinct floristic groups that present differences in specific diversity, composition and floristic similarity. The group 3 included the largest area of forest remaining and it had the highest diversity values and species number between groups, and greater floristic similarity with the forest in general. It was observed that different species dominate ecological groups in relation to the structure, favoring the development of specific populations. The aggregate (clustered) distribution pattern was the main pattern of spatial distribution of species obtained in the groups, indicating that the species forming denser spots in the vegetation. The diameter and hypsometric structures proved to be different between groups indicating they have good capacity for renewal and a denser canopy bottom. In summary, the floristic groups of the Montane Mixed Ombrophylous Forest remnant had floristic and structural variations. These variations evidence the need to consider different arboreous communities in the case of an intervention. / O presente trabalho teve como objetivo geral analisar as variações florísticas e estruturais de um remanescente de Floresta Ombrófila Mista Montana, localizado no município de Nova Prata, RS. Para isso, foram inventariadas 71 parcelas, com dimensões de 10 x 100 m, pelo processo de Amostragem Sistemática em Dois Estágios. Foram identificados e mensurados todos os indivíduos com circunferência à altura do peito ≥ 30,0 cm. A dissertação foi dividida em dois capítulos, com os objetivos específicos de analisar a presença de grupos florísticos (Capítulo I) e diagnosticar variações estruturais entre os agrupamentos (Capítulo II). Por meio da análise de agrupamento, utilizando o método de ligação Ward, as parcelas foram classificadas em quatro grupos florísticos distintos, que apresentam diferenças de diversidade específica, composição e similaridade florística. O Grupo 3, que englobou a maior área do remanescente florestal, possui os maiores valores de diversidade e número de espécies entre os grupos, e a maior similaridade florística com a floresta em geral. Em relação à estrutura, constatou-se que diferentes espécies dominam ecologicamente os grupos, favorecendo o desenvolvimento de populações específicas. O principal padrão de distribuição espacial das espécies nos grupos obtidos foi o agregado (agrupado), indicando que as espécies ocorrem formando manchas mais densas na vegetação. As estruturas diamétrica e hipsométrica mostraram-se distintas entre os grupos, e indicam que estes possuem boa capacidade de renovação e um dossel inferior mais denso. Em síntese, os grupos florísticos do remanescente de Floresta Ombrófila Mista Montana apresentam variações florísticas e estruturais, as quais evidenciam a necessidade de se considerar as diferentes comunidades arbóreas no caso de uma intervenção.

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No. of bitstreams: 2 Dissertação - Edilson Gonçalves de Aguiais - 2013.pdf: 1092088 bytes, checksum: 17ed1418e4743c6af8c42894c26771cb (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2013-09-04 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The purpose of this study is to understand to what extent the phenomenon of structural heterogeneity existing in Goiás industrial economy has affected the structure of earnings and employment in the state of Goiás in the interregnum from 2000 to 2010 . The hypothesis put forward is that, in Goiás, the process of growth of industrial production and the number of companies has developed so as to increase productivity gap and labor income among different segments of the manufacturing industry in the period 2000-2010. To perform the proposed work goal, we used the technical resources of literature and documents and adopted the descriptive analytical method. The first analysis is a comparison between the structure of the transformation of Goiás and São Paulo industry and the results indicated a reduction in structural heterogeneity, both indicators of labor productivity as in the structure of earnings and employment. The second test checks the industrial conformation as the level of technology embodied in the production process. At this point, the segments of low technological intensity remained the largest share of the value added by the manufacturing industry, indicating that driving the dynamic axis of Goiás economy facing the external sector, deepening into a process of specialization in some technologically advanced segments. There, in this period, a process of reduction of intra-sectoral heterogeneity caused by the reduction in labor productivity in sectors with a higher share in the value added of the manufacturing industry and the structure of jobs. Finally, the third analysis captures the structural heterogeneity according to company size, demonstrating an important change since the micro ceases to be the main source of jobs in the Goiás’s manufacturing while indicating a process of increase in average incomes work in the 2000-2010 period. There is, therefore, in this period, an intense process of incorporating labor to the industrial structure, especially in large companies, consortiums to increase our level of average labor compensation, indicating a process of reducing the heterogeneity structure in the manufacturing industry state of Goiás. / O intuito deste trabalho é compreender em que medida o fenômeno da heterogeneidade estrutural existente na economia industrial goiana afetou a estrutura de rendimentos do trabalho e emprego do estado de Goiás no interregno 2000-2010. A hipótese defendida é que, em Goiás, o processo de crescimento da produção industrial e no número de empresas se desenvolveu de modo a ampliar hiato de produtividade e rendimento do trabalho entre os diferentes segmentos da indústria de transformação no período 2000-2010. Para a realização do objetivo proposto no trabalho, utilizaram-se dos recursos técnicos da pesquisa bibliográfica e documental e adotou-se o método analítico descritivo. A primeira análise faz uma comparação entre a estrutura da indústria de transformação de Goiás e São Paulo sendo que os resultados indicaram uma redução na heterogeneidade estrutural, tanto nos indicadores de produtividade do trabalho quanto na estrutura de rendimentos do trabalho e emprego. A segunda análise verifica a conformação industrial conforme o nível de tecnologia incorporada ao processo produtivo. Nesse ponto, os segmentos de baixa intensidade tecnológica mantiveram a maior participação no valor adicionado pela indústria de transformação, indicando a condução do eixo dinâmico da economia goiana voltado para o setor externo, aprofundando-se em um processo de especialização em segmentos pouco avançados tecnologicamente. Há, neste período, um processo de redução da heterogeneidade intra-setorial provocada pela redução da produtividade do trabalho nos setores com maior participação no valor adicionado da indústria de transformação e na estrutura de empregos. Por fim, a terceira análise resgata a heterogeneidade estrutural de acordo com o porte das empresas, demonstrando uma importante mudança visto que a microempresa deixa de ser a principal fonte de empregos da manufatura goiana ao mesmo tempo em que indica um processo de aumento dos rendimentos médios do trabalho no período 2000-2010. Há, portanto, neste período, um intenso processo de incorporação de mão de obra à estrutura industrial goiana, principalmente nas grandes empresas, consorciada com ampliação do nível da remuneração média do trabalho, indicando um processo de redução da heterogeneidade estrutura na indústria de transformação do estado de Goiás.

Cette thèse se propose d’étudier à la lumière des théories traditionnelles et modernes de l’optimalité les facteurs de blocage du processus de convergence au sein de la communauté économique et monétaire d’Afrique centrale. Cette entité régionale voit ses chances de converger à long terme compromises par l’existence d’hétérogénéités au niveau des mécanismes de demande de monnaie d’une part, et de ceux garants de la stabilité des prix d’autre part. Sans renier l’intérêt des critères de convergence nominale, cette étude démontre qu’il serait une erreur de les considérer comme capables de prémunir la zone contre les asymétries. Ces critères, qui sont certes essentiels au fonctionnement de la zone économique et monétaire, offrent de faibles garanties en termes d’ajustement aux chocs asymétriques. En somme, cette thèse s’intéresse aux interconnections entre d’une part les variables nominales et réelles, et les variables structurelles qui les sous-tendent d’autre part. Elle conclut en définitive que l’union régionale formée par la CEMAC ne pourra être viable à terme qu’à condition que les structures tendent à s’homogénéiser. / This thesis proposes to study in the light of the traditional and modern theories of optimality the factors of blocking of the process of convergence within the economic and monetary community of Central Africa. This regional entity sees its chances to converge in the long run compromised by the existence of heterogeneities on the level of the mechanisms of request for currency on the one hand, and those guaranteeing price stability on the other hand. Without disavowing the interest of the convergence criteria nominal, it shows that it would be an error to regard them as able to secure the zone against asymmetries. These criteria, which are certainly essential with the operation of the economic and monetary zone, offer weak warranties in terms of adjustment to the asymmetrical shocks. All in all, this thesis is interested on interconnections between on the one hand the nominal and real variables, and the structural variables which underlie them. It concludes that the regional union formed by the CEMAC could not be viable in the long term, except if the structures tend to be homogenized.

Ce travail de thèse a démontré la possibilité de mesurer la relaxation d’un complexe biomoléculaire ainsi que son hétérogénéité structurale, en associant la microfluidique et la fluorescence résolue en temps (FRT). Je présente de quelle façon la FRT permet d’obtenir une information sur la structure d’une molécule et comment on la mesure, notamment grâce à une caméra à balayage de fente. J’introduis ensuite la microfluidique de gouttes, permettant de mélanger deux réactifs en quelques millisecondes et de suivre la relaxation du complexe au cours de la propagation des micro-réacteurs. Puis, la mesure d’une cinétique avec un couple de molécules modèle démontre la preuve de principe, faisant l’objet d’un article soumis. Enfin la mesure de FRT par comptage de photons uniques dans des gouttes uniques est décrite. Elle ouvre une perspective d’application pour le criblage à haut débit : un brevet a été déposé. / This thesis has proven the feasibility of measuring the relaxation of a biomolecular complex as well as its structural heterogeneity, by associating microfluidics and time resolved fluorescence (TRF). I present in which way TRF allows for probing the structure of a molecule and how it is measured, in particular by using a streak camera. I then introduce droplet microfluidics, which enables to mix two reagents in a few milliseconds and to follow the relaxation of the complex, along propagation of the micro-reactors. Next, the measurement of a kinetics with test molecules validates the proof of concept, reported in a submitted article. Finally, the measurement of TRF by single photon counting in single droplets is described. It opens a perspective for an application in high-throughput screening: a patent has been registered.

The world-wide intensification of agriculture has led to a decline in species richness due to land use change, isolation, and fragmentation of natural and semi-natural habitats in agricultural and forestry landscapes. As a consequence, there is a current landscape management focus on the importance of green infrastructure to mitigate biodiversity decline and preserve ecosystem functions e.g. pollination services and pest control. Even though intensification in agriculture has been ongoing for several hundreds of years, remnant habitats from earlier management practices may still be remaining with a surprisingly high plant richness. Preserving these habitats could help conserving plant species richness in agricultural landscapes, as well as other organisms that are dependent on plants for food and shelter. In this thesis I focus on two small remnant habitats; midfield islets and borders between managed forest and crop field in southeastern Sweden. In the past, both habitats were included in the grazing system and therefore often still have remnant population of grassland specialist species left today. I have used these two remnant habitats as model habitats to investigate the effect of landscape factors and local factors on species richness of plants, flower morphologies and plants with fleshy fruits. Additively, I analysed the effect of surrounding landscape and local openness on the functions; pollination success, biological pest control of aphids and seed predation on midfield islets. One of my studies showed that spatial distribution and size of the habitat affected plant species richness. Larger habitat size and higher connectivity between habitats increased species richness of plants in the habitats. Openness of the habitats was shown to be an important factor to increase species richness and richness of flower morphologies, both on midfield islets and in forest borders. Even though midfield islets had the highest species and morphology richness, both habitat types are needed for habitat complementary as forest borders have more plants with fleshy fruits and a higher richness of plant species that flowers in spring/early summer. It was also shown that a more complex forest border, not just with gaps in the canopy, but also with high variation in tree stem sizes increases plant species richness in the field layer. The conclusion is that by managing small remnant habitats to remain or become more semi-open and complex in their structure, would increase species richness of plants, grassland specialist species, and flower morphologies. It would also increase some ecosystem functions as seed predation and biologic pest control of aphids are more effective close to trees. If both midfield islets and forest borders would be managed to be semi-open, the area and connectivity of semi-open habitat would increase in the agricultural landscape, which may also improve pollination success as the connectivity between populations has a possibility to increase. Grassland specialist species are clearly abundant in the small remnant habitats. As the decline of semi-natural grasslands is causing a decline in grassland specialists’ species, not only plants, I recommend that small remnant habitats are included in conservation and management plans and strategies to improve habitat availability and connectivity for grassland species in agricultural landscapes. / <p>Research funder Ekoklim. Project:4339602.</p><p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>