Un conducteur est bien caractérisé par sa conductance donnée par la formule de Landauer. Toutefois, le bruit contient davantage d'informations. Il mesure les fluctuations temporelles du courant autour de sa valeur moyenne. De plus, le signe des corrélations croisées est lié à la statistique des porteurs de charge. Cette thèse aborde deux principaux thèmes à savoir le transport dans les liquides de Luttinger et dans les structures hybrides. Dans la première partie, nous commençons par donner une vision détaillée des liquides de Luttinger et des systèmes qu'ils modélisent. Nous parlons également du formalisme de Keldysh permettant de traiter des problèmes hors équilibre. Puis, nous rentrons dans le vif du sujet en étudiant l'effet de la largeur d'un contact ponctuel quantique sur le courant de rétrodiffusion entre les deux états de bords de l'effet Hall quantique. L'augmentation de la largeur du contact ponctuel quantique entraîne une forte diminution du courant de rétrodiffusion. Dans un autre chapitre, nous développons une technique permettant l'utilisation d'un circuit RLC couplé inductivement au circuit mésoscopique pour détecter les corrélations de courant en régime photo-assisté. La mesure de ces corrélations s'effectue à travers la charge aux bornes du condensateur. Dans une deuxième partie, nous consacrons notre étude au transport non-local dans les structures hybrides supraconductrices. L'étude de la réflexion d'Andreev croisée y est détaillée. Finalement, nous étudions une structure en double point quantique reliée à deux électrodes en métal normal et une supraconductrice. Nous mettons en avant la séparation des paires de Cooper en mesurant simultanément les courants de branchement et les corrélations croisées. Nous démontrons que dans le régime antisymétrique, c'est-à-dire lorsque les deux points quantiques ont des niveaux d'énergie opposés par rapport au potentiel chimique du supraconducteur, la réflexion d'Andreev croisée est optimisée. / The conductance is the most natural quantity to characterize a quantum conductor. It is given by the Landauer Formula. However, noise contains more information. It measures the current fluctuations around its average value. Moreover, the sign of the crossed correlations is related to the statistics of carriers. This thesis broaches two main topics which are the transport in the quantum Hall effect and in hybrid circuits.First, we start by introducing the Luttinger liquid and the systems which are modelized by them. Also, we discuss the Keldysh formalism in order to treat nonequilibrium problems. Then, we study the effect of the width of a quantum point contact on the backscattering current between two edge states of the quantum Hall effect. By increasing the width of the quantum point contact, we show that the backscattering current is strongly reduced. In another chapter, we develop a technique to use a RLC circuit inductively coupled to a mesoscopic circuit in order to measure the current correlations in the photo-assisted regime. The measurement of these correlations is performed through the charge on the capacitor plates.Secondly, we present the non-local transport in hybrid structures. The mechanism of Crossed Andreev Reflection is explained. Finally, we study a double quantum dot connected to two normal leads and a superconducting lead. We introduce the separation of the Cooper pair by measuring together the branching currents and the crossed correlations. We demonstrate that in the anti-symmetric regime (the energy level of the two quantum dots have opposite values with respect to the chemical potential of the superconducting lead), crossed Andreev reflection is optimized.

A cominuição de amostras geológicas envolve etapas para reduzir seus grãos garantindo sua representatividade, com o auxílio de vários equipamentos de moagem de amostras. São duas as contaminações que podem ser causadas durante o uso desses equipamentos. A primeira é a contaminação primária, pelo contato face a face entre a amostra e os componentes do sistema de moagem, e a segunda é a contaminação cruzada, derivada do material de outras amostras, previamente tratadas, que esteja depositado na superfície dos equipamentos de moagem. São limitadas as informações encontradas na literatura acerca das contaminações primárias, a maioria dos autores presumindo que a mesma seja maior na etapa final dos processos de tratamento. Ainda assim, se faz necessário um estudo sistemático sobre as possibilidades de contaminação primária, durante as diversas etapas de tratamento das amostras. Para esta pesquisa foram utilizadas amostras de quartzo puro, coletado na Fazenda Batatal, em Diamantina, Minas Gerais, com o exame da contaminação primária causada pelo uso dos equipamentos de fragmentação (britador de mandíbulas primário de aço manganês, britador de mandíbulas secundário de carbeto de tungstênio e prensa hidráulica com acessórios de fragmentação em aço) e, a seguir, os de pulverização (moinho de anéis de ágata, carbeto de tungstênio e aço-Cr). O quartzo, um dos materiais mais puros encontrados na natureza, é o que apresenta dureza suficientemente alta para promover intensos processos de interação e contaminação mais extrema. Posteriormente, avaliou-se a possibilidade da contaminação cruzada em quartzo causada pelo tratamento prévio de amostras de basalto (o RS132, da Formação Serra Geral, Rio Grande do Sul) e de granito (o ITU-06.04A, da intrusão Salto, Salto, São Paulo), utilizadas como padrões nos laboratórios do Instituto de Geociências da Universidade de São Paulo, IGc-USP, com composições determinadas por fluorescência de raios X (FRX), no Laboratório de FRX do IGc-USP. As determinações químicas em soluções convenientemente preparadas de amostras de quartzo, utilizadas nas etapas de contaminação primária e cruzada, foram realizadas por espectrometria óptica com plasma indutivo acoplado (ICP-OES) e espectrometria de massa com plasma indutivo acoplado (ICP-MS) no Laboratório de Química e ICP-OES/MS do IGc-USP. Para estudos da contaminação primária foram geradas alíquotas Q1A, Q1B, Q1C, Q2A, Q2B, Q2C, Q3A, Q3B e Q3C (1 identifica tratamento por britador primário de ferro fundido, 2 o britador secundário de CW, 3 a prensa de aço-carbono; e A, B e C identificam os moinhos de anéis na moagem final: ágata, CW e aço-cromo). Nos estudos da contaminação cruzada foram geradas quatro alíquotas, Q4A-Gcc e Q4B-Gcc (quartzo pulverizado, respectivamente, em moinho de anéis de ágata e de CW, após pulverização do granito), e Q4A-Bcc e Q4B-Bcc (quartzo pulverizado nos mesmos moinhos, após tratamento do basalto). A única contaminação registrada foi causada pelos equipamentos durante cominuição primária do quartzo. A ambientação dos moinhos realizada após a moagem de granito ou basalto foi efetuada mediante limpeza rotineira, seguida de moagem com areia quartzosa (a seguir descartada), procedimento efetivo para evitar contaminação cruzada, por remover o material (basáltico ou granítico) aderido às superfícies dos equipamentos. O britador primário de aço manganês colabora com contaminações por Fe e Mn e elementos Cr, Mo, Cu, Sc e Nb, em teores menores. O britador de mandíbulas secundário de CW contaminou com W, provavelmente também com C (determinado por programa Total-Quant), e com algo de Al. A prensa em aço carbono contamina em níveis de 50 ppm de Fe, e teores menores de Cr e Mn. Moinhos pulverizadores de aço temperado contaminaram principalmente com Fe e Cr e, em teores menores, com Mn, W, Ni, Zn, Mo, e V. Cu e Sc aparecem também em níveis extremamente baixos nas amostras tratadas, e podem ser adicionados por estes moinhos. O moinho de anéis de CW contaminou com W (1000 ppm) e Co (70 ppm), aparecendo ainda C com teores apreciáveis; também contamina com Ta e Nb (em torno de 2 e 0,6 ppm, respectivamente). As determinações de vários elementos-traço no quartzo pulverizado em moinho de anéis de ágata ficaram muito próximas, ou abaixo, do limite de detecção das técnicas utilizadas, não se documentando nenhuma contaminação por efeito da utilização deste equipamento. / The grinding of geologic samples is performed to reduce grain size of the constituting minerals and to preserve a representative sample of the original material, with the help of several grinding and milling equipments. The primary and a secondary or crossed contamination are the possible effects that can be produced during these processes. The first is caused by the interaction between the components of the grinding equipments and the sample, the second derives from contamination by other geologic materials previously ground in those equipments. The information found in the previous literature on the subject is relatively limited, most authors assuming that the main contamination may be produced during the final stages of comminution, the one leading to the generation of fine powders. Thus, there is a need to conduct a systematic survey about extent and possibility of primary contaminations. The materials used are samples of pure quartz crystals from the Fazenda Batatal, city of Diamantina, Minas Gerais state, with research initially centered on the examination of primary contamination caused by the fragmentation equipment (manganese steel primary crusher, W carbide secondary crusher, hydraulic press with steel anvil) and then grinding to fine powder (ring grinders equipped with agate, W carbide or chrome-steel rings). Quartz, one of the purest substances found in nature, is a hard mineral that interacts vigorously with the grinding equipment, therefore causing more extreme contamination. A second round was performed testing crossed contamination in quartz caused by previous grinding of basalt (RS 132, Serra Geral Formation, Rio Grande do Sul state) and granite (ITU-06.04A, from the Salto intrusion, city of Salto, São Paulo state), used as standards at the chemistry laboratories of the Instituto de Geociências, Universidade de São Paulo (IGc-USP), with their compositions determined by XRF at Igc-USP. The other chemical determinations, performed on samples of quartz solutions, for checking primary as well as crossed contamination, were performed on ICP-OES and ICPMS equipments, at the Chemistry and ICP-OES/MS Laboratory of Igc-USP. For the testing of primary contamination, the quartz aliquots Q1A, Q1B, Q1C, Q2A, Q2B, Q2C, Q3A, Q3B, and Q3C were prepared (1, 2 and 3 identify, respectively, primary jaw crusher with iron jaws, the secondary crusher with W carbide jaws and the hydraulic press with carbon steel anvil; A, B and C stand for the three used ring grinders, respectively equipped with agate, W carbide and chrome steel rings). Crossed contamination was tested with the aliquots Q4A-Gcc and Q4B-Gcc (quartz samples powdered, respectively, in the agate ring grinder and the CW ring grinder, after grinding of granite), and Q4A-Bcc and Q4B-Bcc (the same procedures as before, now with previous grinding of basalt). The only contamination registered in this study was caused during primary crushing and grinding of the quartz samples. Cleansing of equipment performed after grinding of basalt or granite using conventional cleaning techniques followed by grinding of quartzose sand (later discarded), is a procedure that erases the previous (basaltic or granitic) material from the used equipment; no significant crossed contamination was registered. The primary manganese steel crusher adds principally Fe and Mn to quartz, and elements as Cr, Mo, Cu, Sc and Nb, in lesser amounts. The secondary W carbide jaw crusher contaminates with W, probably also with C (determined with the TotalQuant program), and also with some Al. The carbon steel press contributes with contamination of about 50 ppm Fe, and lesser amounts of Cr and Mn. Powdering mills with tempered steel add mainly Fe and Cr and, to lesser extents, also Mn, W, Ni, Zn, Mo, and V to the quartz; Cu and Sc are present as possible contaminants in very low levels. The W carbide ring mill contaminates quartz with W (around 1000 ppm) and Co (around 70 ppm), adding significant levels of C. This mill contributes also with Ta and Nb additions (2 and 0.6 ppm, respectively). The determination of trace elements in quartz powdered with the agate ring mills does not register significant increases in the analyzed amounts, with levels that remain close to, or below, the respective detection limits, thus possibly precluding any contamination with the use of these mills.

O presente trabalho é uma apresentação de aplicações de estruturas da álgebra de dimensões altas para a teoria de homotopia. Mais precisamente mostramos que existe uma equivalência entre as categorias dos cat$^n$-grupos e a dos $n$-cubos cruzados de grupos, ambas equivalentes a categoria das $n$-categorias estritas internas à categoria de grupos, e uma certa subcategoria da categoria dos $n$-cubos fibrantes, os chamados $n$-cubos de Eilenberg-MacLane. Além disso existe uma equivalência entre uma localização dessa subcategoria e a categoria homotópica dos $(n+1)$-tipos homotópicos, o que sugere a utilidade de usar as estruturas algébricas apresentadas como invariantes topológicas. O teorema central dessa teoria, o teorema generalizado de Seifert-van Kampen, diz que o funtor dos $n$-cubos de fibração aos cat$^n$-grupos usado para mostrar a equivalência mencionada preserva o colimite de certos diagramas e que nesses casos conectividade é preservada, o que permite certas computações. Apresentaremos definições das estruturas algébricas mencionadas além de como calcular certos colimites na categoria de $n$-cubos cruzados de grupos, demonstraremos os teoremas principais da teoria e mostramos como usar esses resultados para generalizar resultados clássicos da topologia algébrica como o teorema de Blakers-Massey, o teorema de Hurewicz e a fórmula de Hopf para homologia de grupos. / The present work is a presentation of applications to homotopy theory of structures in higher dimensional algebra. More precisely we show how the categories of crossed $n$-cubes of groups and of cat$^n$-groups, both equivalent to the category of strict $n$-categories internal to the category of groups, are equivalent to a subcategory of the category of fibrant $n$-cubes, namely the Eilenberg-MacLane $n$-cubes. There is also an equivalence between a localization of the category of Eilenberg-MacLane $n$-cubes and the homotopy category of homotopy $(n+1)$-types, which suggests the usefulness of the presented algebraic structures as topological invariants. The central theorem of this theory, the generalized Seifert-van Kampen theorem, states that the functor from $n$-cube of fibrations to the cat$^n$-groups used to show the aforementioned equivalence preserves the colimit of certain diagrams, and in these cases connectivity is preserved, which permits some computations. We present definitions of the relevant algebraic structures and also how to calculate certain colimits in the category of crossed $n$-cubes of groups, we demonstrate the main theorems of the theory and then we show how to generalize classical results in algebraic topology like the Blakers-Massey theorem, Hurewicz theorem and Hopf\'s formula for the homology of groups.

A cominuição de amostras geológicas envolve etapas para reduzir seus grãos garantindo sua representatividade, com o auxílio de vários equipamentos de moagem de amostras. São duas as contaminações que podem ser causadas durante o uso desses equipamentos. A primeira é a contaminação primária, pelo contato face a face entre a amostra e os componentes do sistema de moagem, e a segunda é a contaminação cruzada, derivada do material de outras amostras, previamente tratadas, que esteja depositado na superfície dos equipamentos de moagem. São limitadas as informações encontradas na literatura acerca das contaminações primárias, a maioria dos autores presumindo que a mesma seja maior na etapa final dos processos de tratamento. Ainda assim, se faz necessário um estudo sistemático sobre as possibilidades de contaminação primária, durante as diversas etapas de tratamento das amostras. Para esta pesquisa foram utilizadas amostras de quartzo puro, coletado na Fazenda Batatal, em Diamantina, Minas Gerais, com o exame da contaminação primária causada pelo uso dos equipamentos de fragmentação (britador de mandíbulas primário de aço manganês, britador de mandíbulas secundário de carbeto de tungstênio e prensa hidráulica com acessórios de fragmentação em aço) e, a seguir, os de pulverização (moinho de anéis de ágata, carbeto de tungstênio e aço-Cr). O quartzo, um dos materiais mais puros encontrados na natureza, é o que apresenta dureza suficientemente alta para promover intensos processos de interação e contaminação mais extrema. Posteriormente, avaliou-se a possibilidade da contaminação cruzada em quartzo causada pelo tratamento prévio de amostras de basalto (o RS132, da Formação Serra Geral, Rio Grande do Sul) e de granito (o ITU-06.04A, da intrusão Salto, Salto, São Paulo), utilizadas como padrões nos laboratórios do Instituto de Geociências da Universidade de São Paulo, IGc-USP, com composições determinadas por fluorescência de raios X (FRX), no Laboratório de FRX do IGc-USP. As determinações químicas em soluções convenientemente preparadas de amostras de quartzo, utilizadas nas etapas de contaminação primária e cruzada, foram realizadas por espectrometria óptica com plasma indutivo acoplado (ICP-OES) e espectrometria de massa com plasma indutivo acoplado (ICP-MS) no Laboratório de Química e ICP-OES/MS do IGc-USP. Para estudos da contaminação primária foram geradas alíquotas Q1A, Q1B, Q1C, Q2A, Q2B, Q2C, Q3A, Q3B e Q3C (1 identifica tratamento por britador primário de ferro fundido, 2 o britador secundário de CW, 3 a prensa de aço-carbono; e A, B e C identificam os moinhos de anéis na moagem final: ágata, CW e aço-cromo). Nos estudos da contaminação cruzada foram geradas quatro alíquotas, Q4A-Gcc e Q4B-Gcc (quartzo pulverizado, respectivamente, em moinho de anéis de ágata e de CW, após pulverização do granito), e Q4A-Bcc e Q4B-Bcc (quartzo pulverizado nos mesmos moinhos, após tratamento do basalto). A única contaminação registrada foi causada pelos equipamentos durante cominuição primária do quartzo. A ambientação dos moinhos realizada após a moagem de granito ou basalto foi efetuada mediante limpeza rotineira, seguida de moagem com areia quartzosa (a seguir descartada), procedimento efetivo para evitar contaminação cruzada, por remover o material (basáltico ou granítico) aderido às superfícies dos equipamentos. O britador primário de aço manganês colabora com contaminações por Fe e Mn e elementos Cr, Mo, Cu, Sc e Nb, em teores menores. O britador de mandíbulas secundário de CW contaminou com W, provavelmente também com C (determinado por programa Total-Quant), e com algo de Al. A prensa em aço carbono contamina em níveis de 50 ppm de Fe, e teores menores de Cr e Mn. Moinhos pulverizadores de aço temperado contaminaram principalmente com Fe e Cr e, em teores menores, com Mn, W, Ni, Zn, Mo, e V. Cu e Sc aparecem também em níveis extremamente baixos nas amostras tratadas, e podem ser adicionados por estes moinhos. O moinho de anéis de CW contaminou com W (1000 ppm) e Co (70 ppm), aparecendo ainda C com teores apreciáveis; também contamina com Ta e Nb (em torno de 2 e 0,6 ppm, respectivamente). As determinações de vários elementos-traço no quartzo pulverizado em moinho de anéis de ágata ficaram muito próximas, ou abaixo, do limite de detecção das técnicas utilizadas, não se documentando nenhuma contaminação por efeito da utilização deste equipamento. / The grinding of geologic samples is performed to reduce grain size of the constituting minerals and to preserve a representative sample of the original material, with the help of several grinding and milling equipments. The primary and a secondary or crossed contamination are the possible effects that can be produced during these processes. The first is caused by the interaction between the components of the grinding equipments and the sample, the second derives from contamination by other geologic materials previously ground in those equipments. The information found in the previous literature on the subject is relatively limited, most authors assuming that the main contamination may be produced during the final stages of comminution, the one leading to the generation of fine powders. Thus, there is a need to conduct a systematic survey about extent and possibility of primary contaminations. The materials used are samples of pure quartz crystals from the Fazenda Batatal, city of Diamantina, Minas Gerais state, with research initially centered on the examination of primary contamination caused by the fragmentation equipment (manganese steel primary crusher, W carbide secondary crusher, hydraulic press with steel anvil) and then grinding to fine powder (ring grinders equipped with agate, W carbide or chrome-steel rings). Quartz, one of the purest substances found in nature, is a hard mineral that interacts vigorously with the grinding equipment, therefore causing more extreme contamination. A second round was performed testing crossed contamination in quartz caused by previous grinding of basalt (RS 132, Serra Geral Formation, Rio Grande do Sul state) and granite (ITU-06.04A, from the Salto intrusion, city of Salto, São Paulo state), used as standards at the chemistry laboratories of the Instituto de Geociências, Universidade de São Paulo (IGc-USP), with their compositions determined by XRF at Igc-USP. The other chemical determinations, performed on samples of quartz solutions, for checking primary as well as crossed contamination, were performed on ICP-OES and ICPMS equipments, at the Chemistry and ICP-OES/MS Laboratory of Igc-USP. For the testing of primary contamination, the quartz aliquots Q1A, Q1B, Q1C, Q2A, Q2B, Q2C, Q3A, Q3B, and Q3C were prepared (1, 2 and 3 identify, respectively, primary jaw crusher with iron jaws, the secondary crusher with W carbide jaws and the hydraulic press with carbon steel anvil; A, B and C stand for the three used ring grinders, respectively equipped with agate, W carbide and chrome steel rings). Crossed contamination was tested with the aliquots Q4A-Gcc and Q4B-Gcc (quartz samples powdered, respectively, in the agate ring grinder and the CW ring grinder, after grinding of granite), and Q4A-Bcc and Q4B-Bcc (the same procedures as before, now with previous grinding of basalt). The only contamination registered in this study was caused during primary crushing and grinding of the quartz samples. Cleansing of equipment performed after grinding of basalt or granite using conventional cleaning techniques followed by grinding of quartzose sand (later discarded), is a procedure that erases the previous (basaltic or granitic) material from the used equipment; no significant crossed contamination was registered. The primary manganese steel crusher adds principally Fe and Mn to quartz, and elements as Cr, Mo, Cu, Sc and Nb, in lesser amounts. The secondary W carbide jaw crusher contaminates with W, probably also with C (determined with the TotalQuant program), and also with some Al. The carbon steel press contributes with contamination of about 50 ppm Fe, and lesser amounts of Cr and Mn. Powdering mills with tempered steel add mainly Fe and Cr and, to lesser extents, also Mn, W, Ni, Zn, Mo, and V to the quartz; Cu and Sc are present as possible contaminants in very low levels. The W carbide ring mill contaminates quartz with W (around 1000 ppm) and Co (around 70 ppm), adding significant levels of C. This mill contributes also with Ta and Nb additions (2 and 0.6 ppm, respectively). The determination of trace elements in quartz powdered with the agate ring mills does not register significant increases in the analyzed amounts, with levels that remain close to, or below, the respective detection limits, thus possibly precluding any contamination with the use of these mills.

We report on conductance measurements in carbon nanotube based double quantum dots connected to two normal electrodes and a central superconducting finger. By operating our devices as Cooper pair beam splitters, we provide evidence for Crossed Andreev Reflection (CAR). We inject Cooper pairs in the superconducting electrode and measure the differential conductance at both left and right arm. The contacts split the device into two coupled quantum dots. Each of the quantum dots can be tuned by a lateral sidegate. If the two sidegates are tuned such that both quantum dots are at a transmission resonance, a considerable part of the injected Cooper pairs splits into different normal contacts. On the contrary, if only one of the two dots is at resonance, nearly all pairs tunnel to the same normal contact. By comparing different triple points in the double dot stability diagram, we demonstrate the contribution of split Cooper pairs to the total current. In this manner, we are able to extract a splitting efficiency of up to 50% in the resonant case. Carbon Nanotubes ensure ballistic transport and long spin-flip scattering lengths. Due to these properties they are promising candidates to investigate EPR-type correlations in solid state systems.

It is well known that communication systems employing multiple transmit and multiple receive antennas provide high data rates along with increased reliability. It has been shown that coding across both spatial and temporal domains together, called Space-Time Coding (STC), achieves, a diversity order equal to the product of the number of transmit and receive antennas. Space-Time Block Codes (STBC) achieving the maximum diversity is called full-diversity STBCs. An STBC is called information-lossless, if the structure of it is such that the maximum mutual information of the resulting equivalent channel is equal to the capacity of the channel. This thesis deals with high-rate and information-lossless STBCs obtained from certain matrix algebras called Crossed-Product Algebras. First we give constructions of high-rate STBCs using both commutative and non-commutative matrix algebras obtained from appropriate representations of extensions of the field of rational numbers. In the case of commutative algebras, we restrict ourselves to fields and call the STBCs obtained from them as STBCs from field extensions. In the case of non-commutative algebras, we consider only the class of crossed-product algebras. For the case of field extensions, we first construct high-rate; full-diversity STBCs for arbitrary number of transmit antennas, over arbitrary apriori specified signal sets. Then we obtain a closed form expression for the coding gain of these STBCs and give a tight lower bound on the coding gain of some of these STBCs. This lower bound in certain cases indicates that some of the STBCs from field extensions are optimal m the sense of coding gain. We then show that the STBCs from field extensions are information-lossy. However, we also show that the finite-signal-set capacity of the STBCs from field extensions can be improved by increasing the symbol rate of the STBCs. The simulation results presented show that our high-rate STBCs perform better than the rate-1 STBCs in terms of the bit error rate performance. Then we proceed to present a construction of high-rate STBCs from crossed-product algebras. After giving a sufficient condition on the crossed-product algebras under which the resulting STBCs are information-lossless, we identify few classes of crossed-product algebras that satisfy this sufficient condition and also some classes of crossed-product algebras which are division algebras which lead to full-diversity STBCs. We present simulation results to show that the STBCs from crossed-product algebras perform better than the well-known codes m terms of the bit error rate. Finally, we introduce the notion of asymptotic-information-lossless (AILL) designs and give a necessary and sufficient condition under which a linear design is an AILL design. Analogous to the condition that a design has to be a full-rank design to achieve the point corresponding to the maximum diversity of the optimal diversity-multiplexing tradeoff, we show that a design has to be AILL to achieve the point corresponding to the maximum multiplexing gain of the optimal diversity-multiplexing tradeoff. Using the notion of AILL designs, we give a lower bound on the diversity-multiplexing tradeoff achieved by the STBCs from both field extensions and division algebras. The lower bound for STBCs obtained from division algebras indicates that they achieve the two extreme points, 1 e, zero multiplexing gain and zero diversity gain, of the optimal diversity-multiplexing tradeoff. Also, we show by simulation results that STBCs from division algebras achieves all the points on the optimal diversity-multiplexing tradeoff for n transmit and n receive antennas, where n = 2, 3, 4.

Le principal rôle du corps calleux est d’assurer le transfert de l’information entre les hémisphères cérébraux. Du support empirique pour cette fonction provient d’études investiguant la communication interhémisphérique chez les individus à cerveau divisé (ICD). Des paradigmes expérimentaux exigeant une intégration interhémisphérique de l’information permettent de documenter certains signes de déconnexion calleuse chez ces individus. La présente thèse a investigué le transfert de l’information sous-tendant les phénomènes de gain de redondance (GR), de différence croisé– non-croisé (DCNC) et d’asynchronie bimanuelle chez les ICD et les individus normaux, et a ainsi contribué à préciser le rôle du corps calleux. Une première étude a comparé le GR des individus normaux et des ICD ayant subi une section partielle ou totale du corps calleux. Dans une tâche de détection, le GR consiste en la réduction des temps de réaction (TR) lorsque deux stimuli sont présentés plutôt qu’un seul. Typiquement, les ICD présentent un GR beaucoup plus grand (supra-GR) que celui des individus normaux (Reuter-Lorenz, Nozawa, Gazzaniga, & Hughes, 1995). Afin d’investiguer les conditions d’occurrence du supra-GR, nous avons évalué le GR en présentation interhémisphérique, intrahémisphérique et sur le méridien vertical, ainsi qu’avec des stimuli requérant une contribution corticale différente (luminance, couleur équiluminante ou mouvement). La présence d’un supra-GR chez les ICD partiels et totaux en comparaison avec celui des individus normaux a été confirmée. Ceci suggère qu’une section antérieure du corps calleux, qui perturbe le transfert d’informations de nature motrice/décisionnelle, est suffisante pour produire un supra-GR chez les ICD. Nos données permettent aussi d’affirmer que, contrairement au GR des individus normaux, celui des ICD totaux est sensible aux manipulations sensorielles. Nous concluons donc que le supra-GR des ICD est à la fois attribuable à des contributions sensorielles et motrices/décisionnelles. Une deuxième étude a investigué la DCNC et l’asynchronie bimanuelle chez les ICD et les individus normaux. La DCNC réfère à la soustraction des TR empruntant une voie anatomique « non-croisée » aux TR empruntant une voie anatomique « croisée », fournissant ainsi une estimation du temps de transfert interhémisphérique. Dans le contexte de notre étude, l’asynchronie bimanuelle réfère à la différence de TR entre la main gauche et la main droite, sans égard à l’hémichamp de présentation. Les effets de manipulations sensorielles et attentionnelles ont été évalués pour les deux mesures. Cette étude a permis d’établir une dissociation entre la DCNC et l’asynchronie bimanuelle. Précisément, les ICD totaux, mais non les ICD partiels, ont montré une DCNC significativement plus grande que celle des individus normaux, alors que les deux groupes d’ICD se sont montrés plus asynchrones que les individus normaux. Nous postulons donc que des processus indépendants sous-tendent la DCNC et la synchronie bimanuelle. De plus, en raison de la modulation parallèle du GR et de l’asynchronie bimanuelle entre les groupes, nous suggérons qu’un processus conjoint sous-tend ces deux mesures. / The main role of the corpus callosum is the transfer of information across the cerebral hemispheres. Evidence for this function comes from studies investigating the interhemispheric communication of split-brain individuals. Specific experimental paradigms requiring interhemispheric integration have enabled the documentation of disconnection symptoms for split-brain individuals. Along those lines, the present thesis investigated the transfer of information underlying the redundant target effect (RTE), the crossed-uncrossed difference (CUD), and bimanual asynchrony of normal and split-brain individuals, and therefore contributed to further our knowledge of the role of the corpus callosum. The first study investigated the RTE of partial split-brain (anterior section), total split-brain, and normal individuals. The RTE occurs when reaction times (RTs) to multiple stimuli are faster than RTs to a single stimulus. Split-brain individuals typically exhibit an enhanced RTE as compared to normal individuals (Reuter-Lorenz et al., 1995). In order to investigate the conditions in which the enhanced RTE occurs, we tested the RTE in interhemispheric, intrahemispheric, and midline conditions, as well as with stimuli requiring different cortical contributions (stimuli defined by luminance, equiluminant colour, or motion). Our data supported the occurrence of an enhanced RTE for partial and total split-brain individuals as compared to normal individuals. This suggests that an anterior section of the corpus callosum, which disrupts the transfer of motor/decisional information, suffices to produce an enhanced RTE in split-brain individuals. In addition, in contrast with the RTE of normal individuals, that of total split-brain individuals was modulated as a function of a sensory manipulation. We therefore conclude that the enhanced RTE of split-brain individuals is attributable to both sensory and motor/decisional contributions. The second study investigated the CUD and the bimanual asynchrony of normal, partial split-brain, and total split-brain individuals. The CUD refers to the subtraction of mean RTs of uncrossed hand-visual hemifield combination from mean RTs of crossed hand-visual hemifield combination. In the context of our study, the asynchrony reflected the difference between the left-hand RT and the right-hand RT on each trial, irrespective of the side of presentation. The effect of sensory and attentional manipulations was assessed for both measures. Our study contributed to dissociate the CUD and bimanual asynchrony. Specifically, total split-brain individuals, but not partial split-brain individuals, showed a larger CUD than normal individuals, whereas both split-brain groups were less synchronous than normal individuals. We therefore postulate that independent processes underlie the CUD and bimanual asynchrony. Furthermore, the parallel modulation of the RTE and bimanual asynchrony across groups suggest common underlying processes for these two measures.

Nel presente lavoro vengono suggerite nuove strategie di lettura per un’opera che costituisce un unicum, non solo nella produzione narrativa di Italo Calvino, ma certamente anche nella storia letteraria del Novecento. Il castello dei destini incrociati (1973) viene interpretato in senso cartografico, come il tentativo di mappare un mondo labirintico, dai significati inesauribili e comunque destinato a farsi inghiottire dal gorgo della modernità. Pur conservando i tratti del romanzo enciclopedico, viene messo in luce come il Castello si sottragga al desiderio di rappresentare la totalità, scegliendo piuttosto la strada del potenziale e della metamorfosi, nel tentativo di individuare i fattori primi di ogni storia narrabile. Un po’ torre di Babele e un po’ arca dell’alleanza, emerge nel lavoro come il libro nasca dal bisogno di verificare le ragioni della letteratura e di rivisitare il ruolo dell’intellettuale: sul finire degli anni sessanta, Calvino allestisce in chiave allegorica e figurale un’allarmata riflessione sulla convivenza, profetizzando l’apocalisse di un mondo che è chiamato a recuperare l’antica fiducia nella progettazione e nell’utopia. / This work suggests new reading strategies for a novel that represents a singular event, not only in Italo Calvino’s narrative production, but also in the history of Nineteenth-Century literature. The Castle of Crossed Destinies (1973) is approached in a cartographical way, as an attempt to give the map of a labyrinthine world, complicated by inexhaustible meanings and, in any case, destined to be swallowed by Modernity’s wheel. Though conserving the features of the encyclopaedic novel, the Castle is shown as a book that tries to dodge the desire to represent the world as a whole, as a totality: on the contrary, it chooses to go through the paths of potentiality and metamorphosis, seeking the prime factors of every possible story. The Castle is a sort of Tower of Babel, an Ark of the Covenant: Savio’s thesis underlines that this novel grows out of the need to check the reasons of literature and to rethink the role of intellectuals: in the end of the Sixties, allegorically and figurally, Calvino sets up an alarmed reflection about the coexistence of mankind, foretelling the apocalypse of a world that is called to rescue its old faith in planning and utopia.

O presente trabalho é uma apresentação de aplicações de estruturas da álgebra de dimensões altas para a teoria de homotopia. Mais precisamente mostramos que existe uma equivalência entre as categorias dos cat$^n$-grupos e a dos $n$-cubos cruzados de grupos, ambas equivalentes a categoria das $n$-categorias estritas internas à categoria de grupos, e uma certa subcategoria da categoria dos $n$-cubos fibrantes, os chamados $n$-cubos de Eilenberg-MacLane. Além disso existe uma equivalência entre uma localização dessa subcategoria e a categoria homotópica dos $(n+1)$-tipos homotópicos, o que sugere a utilidade de usar as estruturas algébricas apresentadas como invariantes topológicas. O teorema central dessa teoria, o teorema generalizado de Seifert-van Kampen, diz que o funtor dos $n$-cubos de fibração aos cat$^n$-grupos usado para mostrar a equivalência mencionada preserva o colimite de certos diagramas e que nesses casos conectividade é preservada, o que permite certas computações. Apresentaremos definições das estruturas algébricas mencionadas além de como calcular certos colimites na categoria de $n$-cubos cruzados de grupos, demonstraremos os teoremas principais da teoria e mostramos como usar esses resultados para generalizar resultados clássicos da topologia algébrica como o teorema de Blakers-Massey, o teorema de Hurewicz e a fórmula de Hopf para homologia de grupos. / The present work is a presentation of applications to homotopy theory of structures in higher dimensional algebra. More precisely we show how the categories of crossed $n$-cubes of groups and of cat$^n$-groups, both equivalent to the category of strict $n$-categories internal to the category of groups, are equivalent to a subcategory of the category of fibrant $n$-cubes, namely the Eilenberg-MacLane $n$-cubes. There is also an equivalence between a localization of the category of Eilenberg-MacLane $n$-cubes and the homotopy category of homotopy $(n+1)$-types, which suggests the usefulness of the presented algebraic structures as topological invariants. The central theorem of this theory, the generalized Seifert-van Kampen theorem, states that the functor from $n$-cube of fibrations to the cat$^n$-groups used to show the aforementioned equivalence preserves the colimit of certain diagrams, and in these cases connectivity is preserved, which permits some computations. We present definitions of the relevant algebraic structures and also how to calculate certain colimits in the category of crossed $n$-cubes of groups, we demonstrate the main theorems of the theory and then we show how to generalize classical results in algebraic topology like the Blakers-Massey theorem, Hurewicz theorem and Hopf\'s formula for the homology of groups.

M.Tech. / OBJECTIVE: To determine the most effective treatment protocol in the treatment of Lower-Crossed Syndrome by comparing objective results gained from a Rehabilitation program (group one), Spinal Manipulative Therapy (group two) and a combination of these therapies (group three) directed at the sacroiliac joints and lumbar spine. DESIGN: The study was a clinical trial in which three experimental groups of sixteen participants each were compared to each other. These participants were recruited from the local general population and were selected on the basis of inclusion and exclusion criteria, presenting with Lower-Crossed Syndrome and demonstrating unremarkable clinical and radiological findings. INTERVENTION AND DURATION: After randomisation, group one received a Rehabilitation program which consisted of a stretching and strengthening program only, group two received Spinal Manipulative Therapy only whereas group three received a combination of Spinal Manipulative Therapy and a Rehabilitation program. The frequency of the follow up consultations for this study was two consultations over the first two weeks of the trial and once a week for the following four weeks of the trial. MEASUREMENTS: Objective measurements included lumbar spine flexion and extension ranges of motion, hip flexor flexibility (hip extension), active and passive hamstring flexibility, gluteus maximus and abdominal strength tests and Sorenson’s Test (static back extensor strength test). Subjective measurements were the Oswestry Low Back Pain and Disability Index and McGill’s Questionnaire. Measurements were taken before (pre-) and after (post-) the first (initial), third, fifth and eighth (last) consultations. CONCLUSIONS: The aim of the study was to determine the most effective treatment protocol in the management of Lower Back Pain in athletes presenting with Lower-Crossed Syndrome. Although the combined group (group three) showed the greatest improvement these findings were statistically no greater than the statistical findings in group one and group two. All groups showed a statistically significant improvement over the trial period. This illustrates that both Spinal Manipulative Therapy and a Rehabilitation program (including stretching and strengthening) was effective in the management of Lower-Crossed Syndrome. From this study it can therefore be concluded that one treatment protocol did not prove to be more effective than that of the others.