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Headwaters, which are the most common stream order in the landscape, are mostly dependent on energy produced in the terrestrial system, largely consisting of leaf litter from riparian vegetation. The aim of this study was to investigate the decomposition in headwaters of leaf litter from three native (alder, birch, spruce) and one non-native (lodgepole pine) species and how decomposition responds to changes in the environment. Further, microbial and shredder influences on leaf-litter decomposition and aquatic decomposer ability to adapt to non-native species was investigated. By using field-data from this study, calculations were made to assess if microbes and shredders are resource limited. Litterbags were placed in 20 headwater streams in northern Sweden that varied in water chemistry, stream physical characteristics and riparian vegetation. The results revealed that species litter decomposition of different plant species was affected differently by changes in environmental variables. Alder and birch decomposition were positively associated, whereas lodgepole pine deviated from the other species in decomposition and its relationship with important environmental variables, indicating that the ability of the boreal aquatic systems to decompose litter differs between introduced and native species. When including macroinvertebrates, shredder fragmentation generally increased decomposition, but was not significant for all sites. Resource availability for microbes and shredders was controlled by litter input, and no risk of resource limitations was evident during the study period. These findings highlight a complexity of the decomposition process that needs to be considered when predicting changes due to human activities.

Given a graph G, a K_3-decomposition of G, also called a triangle decomposition, is a set of subgraphs isomorphic to K_3 whose edges partition the edge set of G. Further, a rational K_3-decomposition of G is a non-negative rational weighting of the copies of K_3 in G such that the total weight on any edge of G equals one. In this thesis, we explore the problem of rational triangle decompositions of dense graphs. We start by considering necessary conditions for a rational triangle decomposition, which can be represented by facets of a convex cone generated by a certain incidence matrix. We identify several infinite families of these facets that represent meaningful obstructions to rational triangle decomposability of a graph. Further, we classify all facets on up to 9 vertices and check all 8-vertex graphs of degree at least four for rational triangle decomposability. As the study of graph decompositions is closely related to design theory, we also prove the existence of certain types of designs. We then explore sufficient conditions for rational triangle decomposability. A famous conjecture in the area due to Nash-Williams states that any sufficiently large graph (satisfying some divisibility conditions) with minimum degree at least 3/4v is K_3-decomposable; the same conjecture stands for rational K_3-decomposability (no divisibility conditions required). By perturbing and restricting the coverage matrix of a complete graph, we show that minimum degree of at least 22/23v is sufficient to guarantee that the given graph is rationally triangle decomposable. This density bound is a great improvement over the previously known results and is derived using estimates on the matrix norms and structures originating from association schemes. We also consider applications of rational triangle decompositions. The method we develop in the search for sufficient conditions provides an efficient way to generate certain sampling plans in statistical experimental design. Furthermore, rational graph decompositions serve as building blocks within certain design-theoretic proofs and we use them to prove that it is possible to complete partial designs given certain constraints. / Graduate / 0405

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No description available.

Let X be a simply connected, compact Riemannian symmetric space. We can represent X as the homogeneous space U/K, where U is a simply connected compact Lie group, and K is the fixed point set of an involution θ of U. Let G be the complexification of U. We consider the intersections of the image of the Cartan embedding Φ : U/K → U ⊂ G : uK → uu⁻ᶿ with the strata of the Birkhoff (or triangular, or LDU) decomposition G = ⫫(w∈W) ∑(G/w), ∑(G/w) = N⁻wHN⁺ relative to a θ-stable decomposition of the Lie algebra, g = n⁻ ⊕h ⊕ n⁺. For a generic element g in this intersection, g ∈ Φ(U/K) ∩ ∑(G/1), this yields a unique triangular factorization g = ldu. Our main contribution is to produce explicit formulas for the diagonal term d in classical cases, using Cayley coordinates (this choice of coordinate is motivated by considerations beyond sheer convenience). These formulas have several applications: 1) we can compute π₀(Φ(U/K) \ ∩ ∑(G/1) ) explicitly; 2) we can compute ʃ(Φ(U/K))ᵃΦ^-iλ (where ᵃΦ is the positive part of d) using elementary techniques in rank 1 cases; 3) they are useful in explicitly calculating Evens-Lu Poisson structures on U=K (see [Caine(2006)]). Our set-up involves choosing specific representations of the various u in su(n;C) that are compatible with θ; that is, θ fixes each of the subspaces n⁻; h; and n⁺ which, in our setup, always consist of strictly lower triangular, diagonal, and strictly upper triangular matrices, respectively. The formulas contain determinants such as det(1 + X), where X is in ip, the -1-eigenspace of θ acting on the Lie algebra u. Due to the relatively sparse nature of these matrices, these determinants are often easily calculable, and we illustrate this with many examples.

No description available.

This thesis examines the catalytic characteristics of two materials with respect to the decomposition of Formic Acid. The decomposition of formic acid proceeds via two principal reaction pathways: dehydration and dehydrogenation. Dehydrogenation is a valuable reaction producing Hydrogen suitable for use in fuel cells whereas the dehydration pathway produces carbon monoxide, a poison for many fuel cell materials. One of the surface species, the formate ion, is also implicated in other important chemical reactions, most notably the water gas shift and the decomposition of methanol. The author seeks to document various intermediate surface species associated with the two reaction pathways with hope to use this information to future tailoring of catalysts for greater selectivity.

The next generation of miniaturized satellites (“nanosats”) feature dramatically reduced thrust and impulse requirements for purposes of spacecraft attitude control and maneuvering. E↵orts at the University of Vermont have concentrated on developing a MEMS-based chemical micropropulsion system based on a rocket grade hydrogen peroxide (HTP) monopropellant fuel. A key component in the micropropulsion system is the catalytic reactor whose role is to chemically decompose the monopropellant, thereby releasing the fuel’s chemical energy for thrust production. The present study is a joint computational and experimental design e↵ort at developing a MEMS-based micro-reactor for incorporation into a monopropellant micropropulsion system. Numerically, 0D and simplified 2D models have been developed to validate the model and characterize heat and mass di↵usion in the channel. This model will then be extended to a 2D model including all geometric complexities of the catalyst bed geometry with the goal of optimization. Experimentally, both meso and micro scale catalyst geometries have been constructed to prove the feasibility of using RuO2 nanostructures as an in situ in a microchannel.

Orientador: Massao Ionashiro / Banca: João Oimpio Tognolli / Banca: Eder Tadeu Gomes Cavalheiro / Banca: Lázaro Moscardini D'Assunção / Banca: Maria Inês Gonçalves Leles / Resumo: Foram sintetizados no estado sólido os compostos Ln-2-MeO-Bz, sendo que Ln representa os lantanídeos trivalentes e Y (III) e 2-MeO-Bz representa o 2-methoxibenzoato. Os compostos foram sintetizados por adição estequiométrica, sob agitação, do ligante nas respectivas soluções de cloretos ou nitratos de lantanídeos. A precipitação dos compostos só ocorreram quando as soluções foram parcialmente evaporadas em banho maria. A caracterização dos compostos foi realizada utilizando-se de métodos convencionais: difratometria de raios X pelo método do pó, espectroscopia de absorção na região do infravermelho, análise elementar e as técnicas termoanalíticas TG/DTG (termogravimetria / termogravimetria derivada simultânea) e TG - DTA (termogravimetria - análise térmica diferencial simultânea) e DSC (Calorimetria exploratória diferencial). Estas técnicas puderam dar informações sobre desidratação, modos de coordenação, comportamento térmico, estequiometria e estrutura dos compostos sintetizados. Com os resultados das curvas TG e da complexometria, pôde-se estabelecer a fórmula geral de cada composto sintetizado. Pela análise dos difratogramas de raios X foi observado que todos os compostos sintetizados são cristalinos e que os compostos de lutécio e itérbio são isomorfos. A observação dos espectros de infravermelho teórico e experimental sugerem uma coordenação bidentada sem equalização de cargas entre o 2-metoxibenzoato e os seus respectivos centros metálicos. As curvas TG-DTA e DSC forneceram informações inéditas e importantes sobre o comportamento e a decomposição térmica dos compostos sintetizados. / Abstract: Solid state Ln 2-MeO-Bz compounds, where Ln stands for trivalent La to Lu and Y (III) and 2-MeO-Bz is 2-methoxybenzoate, have been synthesized. The solid state compounds were prepared by stoichiometric relation adding slowly, with continuous stirring the ligand solution to the respective metal chloride or nitrate solutions. No precipitate was observed during the addition of sodium 2-methoxybenzoate; however the precipitate was obtained when the solution was evaporated in a water bath. Simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), X-ray powder diffraction, infrared spectroscopy, elemental analysis and complexometry, were used to characterize and to study the thermal behaviour of these compounds. The results led to information about composition, dehydration, coordination mode, structure, thermal behaviour and thermal decomposition of the isolated compounds. From TG curves and complexometry results, a general formula could be established for these compounds in the solid state. The X-ray powder patterns pointed out that the synthesized compounds have a crystalline structure without evidence concerning to the formation of isomorphous series, except the ytterbium and lutetium compounds. The experimental and theoretical infrared spectroscopy data suggest that 2-metoxibenzoate acts as a bidentate bond with an incomplete equalization of bond lenghts in the carboxylate anion. The TG-DTA and DSC curves provided previously unrerported information concerning the thermal behaviour and thermal decomposition of these compounds. / Doutor