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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
91

Examining facts, finding ugly truths : the historical and political forces that shaped the critical reception of Alice Walker's The third life of Grange Copeland

Sims, Mary Hughes January 1999 (has links)
The purpose of this study has been to determine what extraliterary forces--cultural, historical, political, social--shaped the critical reception of Alice Walker's first novel, The Third Life of Grange Copeland (1970). The philosophies of Hans Robert Jauss, as espoused in Toward an Aesthetic of Reception (1971), guided this study. Particular interest was placed on Jauss's claim that every work has its own specific, historically, and sociological determinable audience, that every writer is dependent on the milieu, view, and ideology of that audience and that literary success presupposes a book which presents what the audience expects, a book which presents the audience with its own image. (26)The Third Life of Grange Copeland appeared at the end of the Civil Rights Movement, in the midst of a Black Arts Movement (a movement that presented black artist with a criteria for representing their people), and on the cusp of a black feminist movement which moved black women from the object to the subject position in black literary discourse.The politically charged context in which Walker's first novel appeared determined her first audience's reception to her work. The reception from black civic leaders, literary critics, scholars and the black community was largely negative. This initial negative response has followed Walker throughout her literary career despite the fact that she has won both the American Book Award and the Pulitzer Prize for fiction. / Department of English
92

Rat brain Walker tumor implantation model / Modelo de implante de tumor de Walker em cÃrebro de ratos

Francisco HÃlder Cavalcante Felix 14 September 2001 (has links)
Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / The disabling effects of central nervous system (CNS) tumors are out of proportion to their low incidence. Theyâre second only to stroke as neurologic mortality causes. Brain metastases are the commonest intracranial tumors in adults, almost 10 times more frequent than primary brain tumors. Their diagnosis and treatment have met significant advances, although much more research about drug resistance and new treatment modalities are needed. New and even better brain tumor animal models will help to evaluate novel drug regimens and adjuvant therapies for CNS neoplasms. In the present work, the author presents a simple and easily reproducible brain tumor model utilizing the tumor cell line W256 transplanted to Wistar rats. They tested a drug widely used for palliative treatment of tumoral brain edema (dexamethasone), for survival impact. They also have tested the effects of a drug newly proposed as multidrug resistance reversal agent (cyclosporin â CS). Wistar albino rats had stereotaxic intracranial tumor inoculation after the surgical installation of a permanent canulla on the area of interest (right subfrontal caudate). The brain tumor model, as a model of metastatic brain disease, was successful, with reproducible tumor growth (95%), low incidence of extracranial tumor implantation (21% local, no distant metastasis) and few evidence of surgical site infection (21%). The median survival of the animals was 12.5 days (control), 13 days (CS vehicle treated), 11 days (CS treated), 9.5 and 9 days (dexamethasone 0.3 and 3.0 mg/kg/day). These differences were not significant, although the survival rates on the 12th day post-inoculation have showed a significant survival decrease for the case of dexamethasone 3,0 mg/kg/day (p < 0.05), but not for CS treatment (Fischerâs Exact Test). The estimated tumor volume was 17.08  6.7 mm3 (control) and 12.61  3.6 mm3 (CS treatment, not significant, Studentâs t-test). The tumor volume in the 9th day post-inoculation was estimated in 67,25  19,8 mm3. The doubling time was 24.25 h. This model behaved as an undifferentiated tumor, with local invasiveness features compared with that of primary brain tumors. It fits well, in this way, for the study of tumor cell migration on CNS parenchyma. Phenomena like neuronal degeneration, neuron cell edema and death, and gliosis, as well as perivascular cell infiltrates, were seen frequently. One could find, also, neoangiogenesis, satellite tumor growth, and tumor cell migration in normal brain parenchyma. Besides heavy parenchymatous infiltration, it was also disclosed markedly tumor cell migration along white matter tracts, such as callosal fibers and infiltration in the Virchow-Robins perivascular space. The model presents as a dual brain tumor and leptomeningeal carcinomatosis model. It could be used for the study and treatment test in the scenario of these two pathologies. The intracerebral tumor growth induced peripheral blood neutrophil count elevation (ANOVA, p < 0.01), higher chance for neutrophilia (Fischerâs Exact Test, p < 0.01), higher chance for lymphopenia (Fischerâs Exact Test, p < 0.01) and brain weight increase (Studentâs t-test, p < 0.001) comparing to control. There was no significant change in any of the other hematologic, biochemical and biological parameters tested. CS treatment did not alter any of the tests, as compared to non-treated brain tumor animals. The only exception was the mean animal weight on the first week post-inoculation (ANOVA, p < 0.05). CS, in this way, was responsible for an early cachexia in the brain tumor inoculated animals. CS treatment of brain tumor animals did show non-significant effects indicating a volume (26%) and weight tumor decrease, and tumor infiltrating neutrophil increase (odds ratio - OR = 5.6). This indicates the necessity to further study morphologically and functionally the local inflammation in brain tumor inoculated animals, as well the effects of CS administration. In conclusion, the W256 intracerebral tumor model is simple, easily performed, reproducible and of great potential utility. In this model, tumor inoculation can lead to hematologic and biologic modifications in the experimental animals. CS could apparently lead to early tumor caquexia in this tumor model. However, CS treatment did not modify the survival chance of the brain tumor animals, in sharp contrast to dexamethasone 3.0mg/kg/day, a much-used drug in the treatment of brain tumors, which decreased the animal survival. / Os importantes efeitos incapacitantes dos tumores do sistema nervoso central (SNC) sÃo desproporcionais a sua baixa incidÃncia. Mesmo assim, entre as doenÃas neurolÃgicas, ficam atrÃs apenas dos acidentes vasculares do SNC como causa de morte. MetÃstases cerebrais constituem os tumores intracranianos mais comuns do adulto, ocorrendo atà 10 vezes mais freqÃentemente que tumores primÃrios. AvanÃos significativos ocorreram em seu diagnÃstico e tratamento, embora mais pesquisa sobre os fenÃmenos que diminuem o efeito de drogas em metÃstases cerebrais e tratamentos eficazes para estas patologias sejam cada vez mais necessÃrios. O desenvolvimento de melhores modelos animais de tumores do SNC serà necessÃrio para a avaliaÃÃo in vivo de novas formas de quimioterapia (QT) e terapia adjuvante para tumores cerebrais. No presente trabalho, o autor objetivou desenvolver um modelo de tumor cerebral simples e de fÃcil reproduÃÃo utilizando a linhagem W256, alÃm de testar o efeito na sobrevida animal de uma droga largamente usada para o tratamento de efeitos secundÃrios a edema cerebral (dexametasona). O autor tambÃm testou uma droga envolvida numa nova proposta de reversÃo de multirresistÃncia a drogas anti-neoplÃsicas em tumores cerebrais (ciclosporina â CS). Ratos albinos (Wistar) tiveram o tumor inoculado atravÃs de estereotaxia, apÃs a instalaÃÃo cirÃrgica de uma cÃnula no ponto escolhido (caudato subfrontal direito). O modelo de tumor implantado no cÃrebro de ratos, simulando uma metÃstase cerebral, mostrou-se bem sucedido e reprodutÃvel (95% de crescimento tumoral), com baixa incidÃncia de disseminaÃÃo tumoral extracraniana local (21%), baixa evidÃncia de infecÃÃo local (21%), ausÃncia de metÃstases à distÃncia e ausÃncia de sinais de infecÃÃo sistÃmica. Os animais sobreviveram uma mediana de 12,5 dias (grupo controle), 13 dias (tratados com veÃculo da CS), 11 dias (tratados com CS), 9,5 e 9 dias (dexametasona 0,3 e 3,0 mg/kg/dia, respectivamente). As diferenÃas entre estas medianas nÃo foram significantes (teste de Kruskal-Wallis), embora as diferenÃas entre as taxas de sobrevida no 12o dia apÃs a inoculaÃÃo tenham mostrado reduÃÃo significante no grupo que recebeu dexametasona 3,0 mg/kg/dia (p < 0,05), mas nÃo no grupo tratado com CS (teste de Fischer). O volume tumoral estimado (VTE) no sÃtimo dia pÃs-inoculaÃÃo (7DPI) foi de 17,08  6,7 mm3 no controle e 12,61 3,6 mm3 apÃs tratamento com CS, sem diferenÃa significante (teste t-Student). O VTE no 9DPI de animais do grupo Tumor foi de 67,25  19,8 mm3. O tempo de duplicaÃÃo foi de 24,25 h. O modelo comportou-se como um tumor de caracterÃsticas indiferenciadas, apresentando invasividade local comparada à de tumores primÃrios do SNC, prestando-se ao estudo da migraÃÃo de cÃlulas tumorais no SNC. Observaram-se fenÃmenos como degeneraÃÃo neuronal hidrÃpica, edema celular neuronal, sinais de morte celular neuronal e gliose, alÃm da presenÃa de infiltrados celulares tumorais e inflamatÃrios perivasculares. Observaram-se, tambÃm, neoformaÃÃo vascular, formaÃÃo de nÃdulos tumorais satÃlites ao tumor principal e migraÃÃo celular tumoral no parÃnquima cerebral normal. Observou-se, alÃm da infiltraÃÃo parenquimatosa, marcante migraÃÃo celular tumoral ao longo de tratos de substÃncia branca (corpo caloso) e ao longo dos espaÃos perivasculares de Virchow-Robins. O modelo apresenta-se como um misto de tumor cerebral intraparenquimatoso e carcinomatose leptomenÃngea, podendo ser utilizado para estudar o comportamento e testar formas de tratamento para ambas as patologias. O crescimento tumoral intracerebral induziu aumento do nÃmero de neutrÃfilos no sangue perifÃrico (ANOVA, p < 0,01), maior chance de apresentar neutrofilia (teste de Fischer, p < 0,01), maior chance de apresentar linfopenia (teste de Fischer, p < 0,01) e aumento do peso dos cÃrebros dos animais experimentais (teste t-Student, p < 0,001) em relaÃÃo ao controle. Nenhum dos outros valores hematolÃgicos, bioquÃmicos e biolÃgicos foi alterado de maneira significante. O tratamento de animais inoculados com tumor com a CS, nÃo alterou nenhuma das medidas hematolÃgicas, bioquÃmicas ou biolÃgicas em relaÃÃo aos animais inoculados com tumor e nÃo tratados, exceto o peso dos animais na primeira semana apÃs inoculaÃÃo tumoral (ANOVA, p < 0,05). A CS, dessa forma, induziu significantemente uma caquexia precoce nos animais inoculados com tumor cerebral. O tratamento com CS de animais inoculados com tumor mostrou tendÃncias nÃo significantes a diminuir volume (26%) e massa (7%) tumorais e aumentar nÃmero de neutrÃfilos infiltrantes de tumor (razÃo de chance - RC = 5,6) e necrose tumoral, indicando a necessidade de posteriores estudos para caracterizar morfolÃgica e funcionalmente a resposta inflamatÃria local em animais inoculados com tumor e a influÃncia da CS neste processo, alÃm do efeito da CS na angiogÃnese tumoral. Concluindo, o modelo de W256 intracerebral mostrou-se simples, de fÃcil execuÃÃo, reprodutÃvel e Ãtil. Neste modelo, a inoculaÃÃo tumoral induz modificaÃÃes hematolÃgicas e biolÃgicas nos animais. A CS pareceu exarcebar a caquexia tumoral neste modelo. A CS, todavia, nÃo alterou a chance de sobrevida de animais inoculados com tumor cerebral, ao contrÃrio da dexametasona 3,0 mg/kg/dia, que reduziu esta chance. A CS, assim, parece ser mais segura neste modelo tumoral que uma droga largamente utilizada para tratamento de pacientes com metÃstase cerebral.
93

Atividade física e suplementação nutricional de leucina associadas ao crescimento tumoral = estudo do perfil hormonal de ratos implantados com carcinossarcomia de Walker 256 / Physical activity and nutritional supplementation with leucine associated with tumor growth : study of hormonal profile in Walker 256

Inocêncio, Aline Tatiane Toneto, 1983- 20 August 2018 (has links)
Orientador: Maria Cristina Cintra Gomes Marcondes / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-20T04:03:57Z (GMT). No. of bitstreams: 1 Inocencio_AlineTatianeToneto_M.pdf: 4201268 bytes, checksum: d04253942aceb6648e341e3f059a1864 (MD5) Previous issue date: 2012 / Resumo: O câncer-caquexia é caracterizado pelo desenvolvimento de anorexia, astenia, perda de peso, saciedade prematura, anemia e principalmente alteração no metabolismo de carboidratos, gorduras e proteínas dos pacientes com neoplasia. O aminoácido leucina atua promovendo a sinalização celular, inibindo o processo de catabolismo protéico e estimulando o processo de síntese protéica no músculo esquelético, principalmente em animais experimentais. O exercício físico proporciona alterações metabólicas voltadas, principalmente, à síntese protéica. Desse modo, estudamos os efeitos do treinamento físico associado à dieta rica em leucina sobre o processo de adaptação metabólica e hormonal durante a evolução do tumor de Walker em ratos. Ratos Wistar foram submetidos ao treinamento físico (natação por 45 minutos diários, 5 dias por semana) durante 6 semanas e após esse período receberam implante de células do carcinossarcoma de Walker 256, no subcutâneo. Após 21 dias de crescimento tumoral, os ratos foram sacrificados para obtenção de soro para determinação de glicocorticoides e catecolaminas e ressecção de tecidos e órgãos (adrenais, fígado, coração e músculo). Avaliação da cultura primária da glândula adrenal desses animais pôde-se observar a síntese de catecolaminas e liberação de citocinas, no meio de cultura, em função do crescimento tumoral modulados pelos efeitos da dieta rica em leucina associada ao exercício físico. O crescimento tumoral promoveu alterações metabólicas, bioquímicas e hormonais no hospedeiro do câncer como perda de peso e aumento de hormônios catabólicos como ACTH e glucagon. O exercício promoveu diminuição de IL-6 e INF-? no meio de cultura e aumento sérico de IL-4 e IL-10. O exercício e a suplementação com leucina proporcionaram a manutenção das concentrações plasmáticas de proteínas totais séricas e albumina, provavelmente em função da leucina, que é aminoácido conhecido como sinalizador celular e estimulador do metabolismo protéico. Nos animais tumor leucina exercitado (WLE), observamos manutenção de proteinas totais e albumina, manutenção dos níveis de ACTH e glucagon, além de diminuição nos níveis séricos de catecolaminas, em relação ao grupo LE. As análises bioquímicas, hormonais e de cultura de células mostraram que o exercício e a suplementação de leucina proporcionaram à melhora do estado caquético desses animais / Abstract: The cancer-cachexia is characterized by the development of anorexia, asthenia, weight loss, early satiety, anaemia and especially changes in the metabolism of carbohydrate, fat and protein in these cancer patients. The amino acid leucine acts promoting cell signalling by inhibiting the protein catabolism and stimulating the protein synthesis in skeletal muscle, especially in experimental animals. The exercise provides metabolic changes mainly in protein turnover. Thus studies that concern cancer-cachexia, physical exercise and nutritional supplementation can come up with best ways to support cancer treatment. In this work we evaluated the effects of physical training associated with leucine-rich diet on the metabolic processes and hormonal changes during Walker tumour growth in rats. Wistar rats (45 days-old) were submitted to physical training (swim section for 45 minutes daily, five days a week for 6 weeks). After 6 weeks of training, the rats received subcutaneous implant of Walker carcinoma cells. After 21 days of tumour growth, animals were sacrificed and collected blood, tissues and organs (adrenal, liver, heart and muscle). Cell primary culture of adrenal gland analysed the catecholamine synthesis and cytokines release in the culture medium, which was altered under tumour growth effects and modulated by the effects of leucine-rich diet associated with exercise physical. Tumour growth promoted metabolic, biochemical and hormonal changes in host such as weight loss and increased catabolic hormones release (ACTH and glucagon). The exercise decreased IL-6 and IFN-? content in culture medium and increased IL-4 and IL-10 serum content. Exercise and leucine supplementation provided maintenance of total serum protein and albumin, probably due to leucine which is known as cell signalling and stimulates protein metabolism. In addition, tumour-bearing-exercised animals (WLE) maintained serum protein and albumin, and also the ACTH and glucagon levels, and reduced serum catecholamine levels, in relation to LE group. The biochemical analyses, hormonal and cell culture have shown that exercise and leucine supplementation could improve the cachectic state in experimental animals / Mestrado / Fisiologia / Mestre em Biologia Funcional e Molecular
94

Tamis lyrique / Lyric sieve

Tenu, Claire 17 November 2016 (has links)
« Lyrisme : jeu qui lie et délie les noms et les corps – tous les noms et tous les corps. Son terrain est celui de la vie et de la mort entrelacées, un festin offrant formes, déformations, transformations. Sa matière est l’air, souvent irrespirable, son milieu est l’image, parfois invisible, sa réalité est la voix, presque inaudible. » L’exposition Tamis Lyrique, préparée et prolongée par l’ouvrage éponyme, présente un ensemble d’œuvres déployant une pratique lyrique et spéculative de la photographie, au croisement de diverses formes et disciplines : composition et montage, caractérisation topographique et récit filmique, écriture et installation. Certaines œuvres sont extraites des travaux récents accomplis au cours de l’élaboration de la thèse (photographies de Cherbourg, et le livre La ville que nous voyons ; L’air de l’accordéon, film co-réalisé avec Fanny Béguery en Corrèze). Dix pièces diverses parleurs sujets et leurs formes (vues photographiques, assemblages, objets, séquence de film) sont inédites. Quelques œuvres, plus anciennes, complètent cet ensemble, faisant l’objet de développements écrits particuliers dans le livre Tamis lyrique et permettant de repérer des variations ou d’apprécier une épaisseur temporelle des processus qui structurent le travail. / “ Lyricism is binding and unbinding names and bodies,playing in between all of the names and the bodies. Itsground is made of life and death together interweaved :a feast offering forms, deformations, transformations. Its material is the air, often unbreathable, its milieu is the image, invisible sometimes, its reality is the voice,almost inaudible.” The exhibition Tamis lyrique and the eponymous book present a group of works of art stemming from a lyric and speculative experience of photography, interbreeding diverse forms: tableau and montage, topographical characterization and filmic sequencing, writing and installation. Some of the works were produced during the doctoral thesis elaboration period, such as the photographs taken in Cherbourg, along with the book La ville que nous voyons, or the film L’air de l’accordéon, codirected with Fanny Béguery in Corrèze. Ten other various works are previously unseen. Some more works are older and were the subject of specific writings in the book Tamis lyrique, or enable to perceive variations or to appreciate a temporal density in the construction of the work.
95

Papel da suplementação nutricional com leucina e/ou ácido graxo poli-insaturado ômega-3 na modulação do efeitos do câncer na prole de ratas / Effects of nutritional supplementation with leucine and/or polyunsaturated fatty acid omega-3 as a modulatory on cancer evolution in the rats offspring

Miyaguti, Natália Angelo da Silva, 1989- 03 November 2015 (has links)
Orientador: Maria Cristina Cintra Gomes Marcondes / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-27T06:12:33Z (GMT). No. of bitstreams: 1 Miyaguti_NataliaAngelodaSilva_M.pdf: 7149513 bytes, checksum: e738b40c2027a8507e7b5ae2e65321e8 (MD5) Previous issue date: 2015 / Resumo: O Resumo poderá ser visualizado no texto completo da tese digital / Abstract: The Abstract is available with the full electronic digital document / Mestrado / Fisiologia / Mestra em Biologia Funcional e Molecular
96

The Evolutionary Development of Compositional Technique and Style in the Piano Sonatas of George Walker: A Study of the Sonata No. 4 and Analytical Comparison of the Four Sonatas, Together With Three Recitals of Selected Works of f.j. Haydn, l.V. Beethoven, F. Schubert, F. Chopin, F. Liszt, J. Brahms, C Debussy, Z. KodáLy and F. Poulenc

Boe, Dennis Leonard 08 1900 (has links)
George Walker, pianist, composer and pedagogue, composed piano sonatas in 1953, 1957, 1975, and 1984. The Sonata No. 4 demonstrates the composer's continued fascination with a relaxation of traditional forms, coloristic effects of persistent interval combinations, incorporation of folk elements into his thematic material, and harmonic and rhythmic underpinnings as structural bases to his work.
97

Whole because of, not in spite of, our fragments: holistic survival in Walker's The color purple and The temple of my familiar

Keaton, Hetty 01 January 1991 (has links)
In this thesis, I will argue that the characters and groups in Walker's The Color Purple and The Temple of My Familiar, who practice holistic survival, remain or become whole, which is the key to living a meaningful life. For Walker, holistic survival entails embracing the fragments of our past, present, and future experiences. The past is made up of knowing about our personal experiences and remembering our heritage. The present is made up of healing the past by taking responsibility for the pain we have caused and valuing fellow life, and the future is made by using the past and present to create hope. It is not enough to merely survive, to continue breathing;rather, in order to survive whole, we must also successfully paste together the fragments that make up our past, present, and future. However, the consequences of neglecting any fragment can cause us to become lost. We can either collect and come to terms with our many fragments in order to become whole, or our experiences will remain scattered, leaving us fragmented beings.
98

A Comparison of the Educational Opportunities of the Whites and the Negroes of Walker County

Kuykendall, Ralph B. 08 1900 (has links)
This thesis is written on the subject, state fully, "A Comparison of the Education Opportunities of the Whites and Negores of Walker County." The study is based, as far as possible, on a per-pupil comparison. The writer found Walker County an excellent county in which to make such a study for the simple reason that there was not another county in the state of Texas where there was such an equal balance of negro and white approved scholastics. The counties of Harrison, Marion, San Jacinto, Walker, and Waller were the only ones in the state of Texas that had more approved negro scholastics than white approved scholastics. In Walker county during the year 1937-1938 there were 2,498 white scholastics and 2,505 negro scholastics. This shows that there were only seven more negro approved scholastics than white approved scholastics.
99

Investigations on Dynamics and Control of a Rimless Wheel Based 2D Dynamics Walker using Pulsed Torque Actuation

Patnaik, Lalit January 2014 (has links) (PDF)
Wheeled systems are energy efficient on prepared surfaces like roads and tracks. Legged systems are capable of traversing different terrains but can be lossy. At low speeds and on off-road surfaces, legged systems using dynamic walking can be energy efficient. Towards this objective, the dynamics of the walker needs to be modelled and controlled. In addition, the braking and ground impact losses need to be minimized. This thesis presents analysis and experiments on the dynamics and control of a rimless-spoked-wheel based mobile robot (Chatur ∗) that belongs to a category between wheeled and legged systems. This rolling rimless wheel is effectively a 2D dynamic walker that serves as a platform for investigating the dynamics and energetics of inverted pendulum walking with constant step angle. A pulsed actuation torque is proposed for the system resulting in four torque regimes defined by the ratio of energy losses to available actuator torque. Five physical constraints that impose fundamental limits on the choice of operating points of a generic inverted pendulum walker are expounded and a method for locating optimal operating points is discussed. Chatur’s hardware design is elaborated and a control topology is proposed for pulsed actuation of the dual brushless dc (BLDC) motor driven platform with wheel synchronization. Various actuator torque profiles can be used to achieve dynamic ‘walking’ in a hub-actuated rimless wheel. The proposed pulsed actuation torque gives rise to four torque regimes that achieve sustained walking and a fifth regime where the walker keeps slowing down with each step. The regimes can be identified based on the fraction of stance phase for which the actuator is energized. Theoretical analysis and experimental results are presented. A simple closed-form analytical solution, using hyperbolic functions, is proposed for the stance phase inverted pendulum dynamics considering planar motion. Ground impacts are assumed to cause abrupt drop in velocity. A constant braking torque that lumps together the effect of several loss phenomena is also considered. Based on whether the CoM is rising or falling and whether or not there is an actuating torque, a stance phase can have four types of sub-phases — actuated rise, unactuated rise, actuated fall, unactuated fall. These are concatenated in four different ways to form repeating cycles yielding the four regimes. The experimental set-up is a fixed step-angle walker constructed using two synchronized adjacent rimless wheels independently actuated at the hub. Varying the magnitude and duty ratio of the torque pulse, the four proposed regimes are experimentally shown. The mechanical power consumption and cost of transport are computed from measured motor currents for different average forward speeds. Videos of the walks are also taken. The space of operating points for an inverted pendulum based bipedal dynamic walker in terms of constraints and optimality is investigated. The operating point of the walker can be specified by the combination of initial mid-stance velocity (v0) and step angle (φm) chosen for a given walk. Not all operating points lead to a realizable steady-state gait. Using basic mechanics, a framework of physical constraints that limit the choice of operating points is proposed. The constraint lines thus obtained delimit the valid region of operation of the walker in the v0–φm plane. Within this allowable region, sub-regions that result in various regimes of walking are identified. A given average forward velocity vx,avg can be achieved by several combinations of v0 and φm. Only one of these combinations results in the minimum mechanical power consumption and can be considered the opti-mum operating point for the given vx,avg. A method is proposed for obtaining this optimal operating point based on tangency of the power and velocity contours. Putting together all such operating points for various vx,avg, a family of optimum operating points, called the optimal locus, is obtained. For the energy loss and internal energy models chosen, the optimal locus obtained has a largely constant step angle with increasing speed but tapers off at non-dimensional speeds close to unity. Thus, choosing the right step angle and keeping it fixed over a broad range of speeds could lead to an inverted pendulum walker that is close to optimal from a mechanical energy perspective. The complete hardware design for Chatur and the caveats associated with reliable performance of the mechanical and electrical subsystems are elaborated. In order to en-sure lateral stability, the system uses two contralateral wheels each driven by a separate BLDC hub motor. From a motor drive perspective, the mechanical load belongs to a unique class of dynamic loads whose reflected torque has a characteristic cyclic varia-tion that repeats several times within a mechanical revolution. The proposed control topology has two hierarchical levels, an inner loop for torque control of BLDC motor implemented using a standard proportional-integral controller, and an outer loop for torque reference generation that uses the information on the ground impact instants and the motor position feedback. Ground impacts of the spokes are detected by an accelerometer to initiate the application of torque. The torque pulse magnitude can be set internally or by a manual operator via radio control. The pulse duration is programmable and enables attainment of various torque regimes at different steady state speeds. The wheels are synchronized so that corresponding spokes on both wheels move in unison. This is achieved by including a wheel synchronization loop that compensates for any lag between the wheels. Lag is detected based on number of sector changes in the hall-effect position sensor data received from both motors. An improved BLDC motor drive is developed wherein non-commutating current feedback is used to reduce current spikes during sector transitions. Experimental waveforms for controller validation are shown.
100

The Texas Press and the Filibusters of the 1850s: Lopez, Carvajal, and Walker

Zemler, Jeffrey A. (Jeffrey Allen) 05 1900 (has links)
The decade of the 1850s saw the Texas press separate into two opposing groups on the issue of filibustering. The basis for this division was the personal beliefs of the editors regarding the role filibustering should have in society. Although a lust for wealth drove most filibusters, the press justified territorial expansion along altruistic lines. By 1858, however, a few newspapers discarded this argument and condemned filibusters as lawless bands of ruffians plundering peaceful neighbors. Throughout the decade, the papers gradually drifted from a consensus in 1850 to discord by the date of William Walker's third attempt on Nicaragua in 1858.

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