Le mécanisme élémentaire de l'électrodépôt de films de MnO2 fût étudié sur des électrodes de Pt massif dans des électrolytes aqueux. Il se révèle être une réaction multi-étapes sensible au pH et à la force ionique. La chronoampérométrie couplée à des électrolytes neutres peu concentrés favorise l'électrodépôt de films stables de MnO2. Le FTO est un meilleur substrat que l'ITO parce qu'il présente une activité électrochimique plus élevée et favorise la stabilité mécanique de films électrodéposés de MnO2. De plus, le potentiel d'électrodépôt influence à la fois la structure et la morphologie des films de MnO2. Les films amorphes de MnO2 obtenus à potentiel élevé possèdent une activité électrocatalytique et une stabilité plus élevées que la birnessite. Un traitement thermique peut améliorer amplement leur activité électrocatalytique et leur stabilité mécanique. Une transition de phase des films de MnO2 apparaît à 500 °C. Leur morphologie change de façon dramatique après chauffage au-delà de cette température. Les échantillons chauffés à 500 °C ont la meilleure activité électrocatalytique pour l'OER. Les cations Na+, K+, Ca2+ and Mg2+ sont insérés en petites quantités dans la structure des films de MnO2 au cours de la démarche d'électrodépôt, mais ils influencent néanmoins la structure et la morphologie des films. Finalement, les films de birnessite ou amorphes apparaissent comme des candidats prometteurs en tant que catalyseurs pour la dissociation photoélectrochimique de la dissociation de l'eau, puisqu'ils génèrent des photocourants considérables sous lumière solaire. Pour cela, des films de MnO2 épais, amorphes et recuits à 500 °C produisent les meilleures performances. / The basic electrodeposition mechanism of MnO2 films was studied first on bulk Pt electrodes in various aqueous electrolytes. It was revealed that MnO2 electrodeposition is a multi-step reaction that is sensitive to pH and ionic strength. Chronoamperometry coupled to low concentration neutral aqueous solutions favors the electrodeposition of stable MnO2 films. FTO was found to be a better substrate than ITO, because it has a higher electrochemical activity and could enhance the mechanical stability of electrodeposited MnO2 films. Moreover, the potential used for electrodeposition has great influence on both the structure and the morphology of MnO2 films. Amorphous MnO2 films obtained at high potential possess higher electrocatalytic activity and stability than the birnessite-type MnO2 variety. The heat treatment can greatly enhance the electrocatalytic activity and mechanical stability. A phase transition of MnO2 films appears at 500 °C. The morphology changes dramatically after heating above this temperature. Samples heated at 500 °C are found to have the best electrocatalytic activity towards OER. Na+, K+, Ca2+ and Mg2+ cations were found to be inserted in small amounts into the structure of MnO2 films during the electrodeposition procedure but they influence the structure and morphology of the films. Finally, birnessite type and amorphous MnO2 films appear to be promising candidates as catalysts for photoelectrochemical water splitting, as they are able to generate considerable photocurrents under solar light illumination. In this purpose, thick and amorphous films with 500 °C heat treatment are supposed to produce the best performances.

The electrocatalytic water decomposition has been investigated in this thesis by means of its two half standard reactions: the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). These reactions occur in different locations in a typical electrochemical cell: the anode and the cathode, respectively. Motivated by the lack of understanding about the reaction mechanisms occurring at the anodes and cathodes, we have proposed first: novel representations of typical TiO2 surfaces, based on small cluster systems, which can be used for a quick and more detailed assessment of the OER activities at modified TiO2 surfaces, and secondly we investigated the HER in two sets of model surfaces which represent recently synthesized materials, based on Mo2C and graphene with promising activities toward the HER. We have employed Density Functional Theory (DFT) based methods within both localized and extended basis sets, as implemented in GAMESS and VASP packages, respectively, to examine the structural, electronic and vibrational properties of the proposed models. We propose new reaction mechanisms for the OER on a number of molecular representations of TiO2 electrodes. For each reaction pathway, the free energy profile is computed, at different biases, from the DFT energies, the entropic and the zero-point energy contributions. The mechanisms explored in this thesis are found to be energetically more feasible than alternative reaction pathways considered in previous theoretical works based on molecular representations of the TiO2 surfaces. The representation of the surface of specific, commonly occurring, titanium dioxide crystals (e.g., rutile and anatase) within the small cluster approximation is able to reproduce qualitatively the rutile (110) outperforming of the anatase (001) surface. We subsequently investigate the influence of doping TiO2 surfaces with transition metals (TMs) on the performance of TiO2 -based electrodes for the water splitting electrochemical reaction. Two cluster models of the TM-doped active sites which resemble both the TiO2 anatase (001) and rutile (110) surfaces, respectively, are considered for the evaluation of the water decomposition reaction when a Ti is replaced by a TM atom. A set of TMs spanning from Vanadium to Nickel is considered. The late TMs explored here: Fe, Co and Ni are found to reproduce the observed experimental trends for the overpotentials in TiO2-doped electrodes. In the case of Cr and Mn, the present study predicts an enhancement of the OER activity for the anatase-like clusters while a reduction of this activity is found for the rutile-like ones. The vanadium-doped structures do not show relevant influence in the OER activity compared to pure TiO2-based cluster models. The last part of this work is devoted to the theoretical study of the HER on recently found materials based on the synergistic combination of molybdenum carbide and graphene layers. We propose two major structural models to describe the HER mechanism within the framework of DFT: Mo2C-based clusters adsorbed on carbon nanosheets and the Mo2C (001) surface covered by pure and nitrogen-doped graphene layers. The former system evaluates the influence of Mo2C nanoparticles adsorbed on carbon nanosheets towards the HER. The second one is employed to gain insight about the high HER activity observed in molybdenum carbide anchored on nitrogen-doped porous carbon nanosheets (Mo2C@2D-NPC), recently synthesized. The H-adsorption free energy has been used as a principal descriptor to asses the HER activity at the proposed model active sites. It resembles the value for the best state of the art catalyst for the HER (i.e., platinum at carbon substrate Pt@C) in some of the proposed structural models. Furthermore, a pH-correction is added within a simplified model, to the H-adsorption free energy barrier in every proposed structure. The pH dependence of the H-adsorption free energy barriers allows the assessment of the HER at acidic and alkaline conditions simultaneously. An overall agreement with experimental results is found and further predictions, promoting the development of better HER catalysts, have been done.

The purpose of this study is to describe the subjective psychological experience of relapse in cocaine/crack and heroin users with the aim of identifying the significant cognitive, emotional and social themes involved in relapse. A better understanding of relapse may aid in providing more effective treatment for substance users. Both the intra- and interpsychic factors involved in relapse that emerge from the study are viewed from within a broad systems theory approach. In this study, not only the whole system is of relevance, but also the subsystems. Various sub systems are also identified to allow for the recognition of patterns, functions and recursive feedback loops that maintain substance-using behaviour. Due to the qualitative nature of the study, the context surrounding substance abuse and the substance users assumes vital importance. The interrelationships between the various intrapsychic structures, the family unit, the social contexts, the drugs themselves and the physiological aspects of substance abuse are identified. A qualitative research design was applied. In-depth semi-structured interviews were used to gather data from the eight participants, who were crack and heroin users who attended the in-patient rehabilitation programme at Phoenix House. Seven of the participants were still in the in-patient rehabilitation programme at the time of the interview, while one participant was in the aftercare programme. All have been through a rehabilitation process before and were at Phoenix House due to a relapse. A thematic analysis was conducted and the process of analysis settled on eight overall themes. Extensive descriptions of these themes are provided. The discussion highlights the role of relapse in the cycle of self-destruction that constitutes substance abuse, in addition to the role relapse plays in the process of recovery. Connection seems to be the key to breaking the cycle of alienation that users experience. Falling into the trap of rejecting users without looking beyond their behaviour allows them to continue functioning in a way that confirms their view of themselves as unlovable, which, in turn, maintains their behaviour. Although systems theory is an independent approach in its own right, the nature of its view allows for the incorporation of other approaches. Where possible and relevant, other theories are incorporated into the discussion of the results, with the aim of gaining an integrated understanding of the findings of the study within the broader field of substance abuse. / Dissertation (MA (Clinical Psychology))--University of Pretoria, 2005. / Psychology / unrestricted

La dynamique d'un difféomorphisme d'une variété compacte est essentiellement concentrée sur l'ensemble récurrent par chaînes, qui est partitionné en classes de récurrence par chaînes, disjointes et indécomposables. Le travail de Bonatti et Crovisier [BC] montre que, pour les difféomorphismes C¹-génériques, une classe de récurrence par chaînes ou bien est une classe homocline, ou bien ne contient pas de point périodique. Une classe de récurrence par chaînes sans point périodique est appelée classe apériodique.Il est clair qu'une classe homocline hyperbolique ni contient d'orbite périodique faible ni supporte de mesure non hyperbolique.Cette thèse tente de donner une caractérisation des classes homoclines non hyperboliques en montrant qu'elles contiennent des orbites périodiques faibles ou des mesures ergodiques non hyperboliques. Cette thèse décrit également les décompositions dominées sur les classes apériodiques.Le premier résultat de cette thèse montre que, pour les difféomorphismes C¹-génériques, si les orbites périodiques contenues dans une classe homocline H(p) ont tous leurs exposants de Lyapunov bornés loin de zéro, alors H(p) doit être (uniformément) hyperbolique. Ceci est dans l'esprit des travaux sur la conjecture de stabilité, mais il y a une différence importante lorsque la classe homocline H(p) n'est pas isolée. Par conséquent, nous devons garantir que des orbites périodiques "faibles'', crées par perturbations au voisinage de la classe homocline, sont contenues dans la classe. En ce sens, le problème est de nature "intrinsèque'', et l'argument classique de la conjecture de stabilité est impraticable.Le deuxième résultat de cette thèse prouve une conjecture de Díaz et Gorodetski [DG]: pour les difféomorphismes C¹-génériques, si une classe homocline n'est pas hyperbolique, alors elle porte une mesure ergodique non hyperbolique. C'est un travail en collaboration avec C. Cheng, S. Crovisier, S. Gan et D. Yang. Dans la démonstration, nous devons appliquer une technique introduité dans [DG], et qui améliore la méthode de [GIKN], pour obtenir une mesure ergodique comme limite d'une suite de mesures périodiques.Le troisième résultat de cette thèse énonce que, génériquement, une décomposition dominée non-triviale sur une classe apériodique stable au sens de Lyapunov est en fait une décomposition partiellement hyperbolique. Plus précisément, pour les difféomorphismes C¹-génériques, si une classe apériodique stable au sens de Lyapunov a une décomposition dominée non-triviale Eoplus F, alors, l'un des deux fibrés est hyperbolique: soit E contracté, soit F dilaté.Dans les démonstrations des résultats principaux, nous construisons des perturbations qui ne sont pas obtenues directement à partir des lemmes de connexion classiques. En fait, il faut appliquer le lemme de connexion un grand nombre (et même un nombre infini) de fois. Nous expliquons les méthodes de connexions multiples dans le Chapitre 3. / The dynamics of a diffeomorphism of a compact manifold concentrates essentially on the chain recurrent set, which splits into disjoint indecomposable chain recurrence classes. By the work of Bonatti and Crovisier [BC], for C¹-generic diffeomorphisms, a chain recurrence class either is a homoclinic class or contains no periodic point. A chain recurrence class without a periodic point is called an aperiodic class.Obviously, a hyperbolic homoclinic class can neither contain weak periodic orbit or support non-hyperbolic ergodic measure.This thesis attempts to give a characterization of non-hyperbolic homoclinic classes via weak periodic orbits inside or non-hyperbolic ergodic measures supported on it. Also, this thesis gives a description of the dominated splitting on Lyapunov stable aperiodic classes.The first result of this thesis shows that for C¹-generic diffeomorphisms, if the periodic orbits contained in a homoclinic class H(p) have all their Lyapunov exponents bounded away from 0, then H(p) must be (uniformly) hyperbolic. This is in spirit of the works of the stability conjecture, but with a significant difference that the homoclinic class H(p) is not known isolated in advance. Hence the "weak'' periodic orbits created by perturbations near the homoclinic class have to be guaranteed strictly inside the homoclinic class. In this sense the problem is of an "intrinsic" nature, and the classical argument of the stability conjecture does not pass through.The second result of this thesis proves a conjecture by Díaz and Gorodetski [DG]: for C¹-generic diffeomorphisms, if a homoclinic class is not hyperbolic, then there is a non-hyperbolic ergodic measure supported on it. This is a joint work with C. Cheng, S. Crovisier, S. Gan and D. Yang. In the proof, we have to use a technic introduced in [DG], which developed the method of [GIKN], to get an ergodic measure by taking the limit of a sequence of periodic measures.The third result of this thesis states that, generically, a non-trivial dominated splitting over a Lyapunov stable aperiodic class is in fact a partially hyperbolic splitting. To be precise, for C¹-generic diffeomorphisms, if a Lyapunov stable aperiodic class admits a non-trivial dominated splitting Eoplus F, then one of the two bundles is hyperbolic: either E is contracted or F is expanded.In the proofs of the main results, we construct several perturbations which are not simple applications of the connecting lemmas. In fact, one has to apply the connecting lemma several (even infinitely many) times. We will give the detailed explanations of the multi-connecting processes in Chapter 3.

Denna systematiska litteraturstudie syftar till att med hjälp av forskning identifiera avgörande faktorer för framgångsrika undervisningsstrategier av stambråk i grundskolans matematikundervisning. Studien baseras på elva vetenskapliga artiklar som bearbetats systematiskt med hjälp av innehållsanalys för att besvara forsknings-frågorna om vilka avgörande faktorer som forskningen visar för undervisningen av stambråk samt vilka framgångsrika undervisningsstrategier som finns. Forskningen visar att areamodellen som representationsform dominerar undervisningen av bråk vilket innebär att stambråk får lite plats i undervisningen. Stambråket är en viktig del för att kunna tillägna sig avgörande faktorer av bråk. Resultatet visar att en undervisning med linear measurement (linjära representationsformer) betonar stambråkets roll som tolkningsverktyg för att kunna jämföra andra bråk samt det omvända förhållandet där en större nämnare utgör en mindre andel. Resultatet visar också att undervisningen av stambråk etablerar grundläggande principer för rationella tal och mer avancerade matematiska områden som proportionalitet och algebra. Därmed är lärares val av undervisningsstrategier och representationsformer samt deras kunskaper inom dessa områden vitala för vad eleverna kan tillägna sig i samband med bråkundervisningen.

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The master thesis done within the master study programme Transport vehicles and handing machinery presents a design of a wood splitting machine. The first part of the thesis is a literary review focused on current state in the field of wood splitting machines and on the overview of the most common wood species including their technical parameters. In the second part of the thesis, suitable machine components were chosen for the conceptual design of the wood splitter, taking into account predefined parameters. Then a machine frame was designed and its strength was verified by analytical and FEM method. Finally, drawing documentation for the machine, machine frame and splitting tool was created.

The thesis focuses on the computational simulation of wedge splitting test of a concrete specimen by using finite element method. Different levels of numeric model for different notch depth and for different position of support are solved. Depending on the depth of a notch and difference of configuration, the crack paths and responses to an exterior load on a crack mouth opening displacement are evaluated.

Optická odezva BiTeX (X = I, Cl, Br) polovodičových materiálů s obřím spinovým štěpením Rashbova typu je studována za nízkých teplot do vysokých magnetických polí, kde je směr magnetické indukce kolmý na povrch vzorku (Faradayova konfigurace). Na rozdíl od reflexního uspořádání nám transmisní uspořádání umožňuje přímé pozorování přechodů mezi Landauovými hladinami v blízkosti křižiště vodivostních pásů - Diracův bod. Optická odezva BiTeX sloučenin je srovnána s teoretickým modelem spočteným v rámci Kubo-Greenwoodova formalismu z Rashbova hamiltonianu.

L’objectif principal de ce travail de thèse était de mettre en évidence et de mesurer l’effet co-catalytique de complexes moléculaires organo-métalliques à base de métaux de transition adsorbés sur des semi-conducteurs dopés photo-actifs vis-à-vis des réactions de photo-dissociation de l’eau et de photo-réduction du dioxyde de carbone, en en vue d’applications dans des cellules photochimiques et photo-électrochimiques. Nous avons tout d’abord identifié et sélectionné les matériaux (deux semi-conducteurs photo-actifs et deux co-catalyseurs moléculaires électroactifs) les plus adaptés (les résultats sont présentés dans le chapitre I). Nous avons ensuite conçu, développé et mis au point un bâti expérimental permettant la détection et le dosage en continu des produits de réaction lors des réactions d’intérêt (les résultats sont présentés dans le chapitre II). La détection des produits de réaction se fait à l’aide d’un chromatographe en phase gazeuse couplé au réacteur. Nous avons ensuite élaboré/synthétisé et mesuré les propriétés intrinsèques des matériaux sélectionnés (les résultats sont présentés dans le chapitre III). Finalement, nous avons mis en évidence l’activité co-catalytique des complexes utilisés et mesuré un ensemble d’indicateurs de performance tels que les cinétiques de réaction et les fréquences de « turn-over » (les résultats sont présentés dans le chapitre IV). / The main objective of this research work was to put into evidence the co-catalytic effect of organo-metallic molecular complexes containing transition metals as reactive centers, adsorbed at the surface of doped semiconductors with photo-activity with regard to water photo-dissociation and carbon dioxide photo-reduction, in view of practical applications in photochemistry and photo-electrochemistry. First, appropriate materials (two photoactive semiconductors and two molecular co-catalysts) have been identified and selected (results are presented in chapter I). Then, we have designed, constructed and optimized a specific test bench that can be used for the continuous detection and titration of reaction products (results are presented in chapter II). Product analysis was achieved by coupling a gas-phase chromatograph to the photo-electrochemical reactor. Then, photoactive semiconductors and molecular co-catalysts have been elaborated/synthesized and their intrinsic properties have been measured (results are presented in chapter III). Finally, the co-catalytic activity of molecular complexes has been put into evidence and several performance indicators such as reaction kinetics and turn-over frequency have been measured (results are presented in chapter IV).