Individuals with high working memory capacity (WMC) appear to be particularly good at focusing their attention (McCabe, Roediger, McDaniel, Balota, & Hambrick, 2010). Therefore, we studied the correlation between WMC and the ability to suppress neurological activity from a task-irrelevant stimulus. The research question tests the foundations of Lavie’s perceptual load theory; that early selection occurs, by testing if higher WMC enhances people’s ability to inhibit processing of task-irrelevant stimuli from low versus high load (i.e. the difference from low to high load should be smaller for high WMC than for low WMC). This was operationalised by measuring the correlation of WMC and auditory processing under low versus high visual load. Auditory processing was measured with auditory steady state responses (ASSR), and WMC was measured with an operation-letter span task. The results showed no significant correlation between WMC and ability to suppress task-irrelevant stimuli. Based on the data, it is not possible to conclude with certainty that effects of load on auditory processing are unaffected by WMC, because confidence intervals were large.

Made available in DSpace on 2014-06-11T19:22:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-07-18Bitstream added on 2014-06-13T18:49:50Z : No. of bitstreams: 1 oliveira_mfm_me_rcla.pdf: 189165 bytes, checksum: a4bab800dd002ebdbcf3ba192de703c9 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O principal objetivo deste estudo foi comparar a velocidade, concentração de lactato sanguíneo e os índices técnicos correspondentes à máxima fase estável de lactato sanguíneo obtida de forma contínua e intermitente na natação. Participaram deste estudo, 5 nadadores fundistas e 8 triatletas (23 + 9 anos, 1,76 + 0,1 m e 71,3 + 9,8 kg), com pelo menos 3 anos de experiência nas respectivas modalidades. Os indivíduos realizaram em diferentes dias, os seguintes testes, em uma piscina de 25 m: 1) repetição máxima na distância de 400 m; 2) teste incremental para a determinação do limiar de lactato (LL) e limiar anaeróbio (LAn); 3) 2 a 4 repetições com duração de 30 min em diferentes intensidades, para a determinação da máxima fase estável de lactato sanguíneo contínua (MLSSC), e; 4) 2 a 4 tentativas de 12 x 150 s com intervalo de 30 s (5:1) em diferentes intensidades, para a determinação da máxima fase estável de lactato sanguíneo intermitente (MLSSI). O LAn foi determinado por meio de interpolação linear entre a velocidade e a concentração de lactato, considerando uma concentração fixa de lactato de 3,5 mM. O critério de determinação da MLSSC e da MLSSI foi um aumento menor ou igual a 1 mM de lactato entre o décimo e o trigésimo min de exercício. Os índices técnicos taxa de braçada (TB), comprimento de braçada (CB) e índice de braçada (IB) foram determinados em todos os testes. A TB foi calculada por meio de filmagem utilizando o tempo necessário para se realizar cinco ciclos completos de braçadas. O CB foi calculado dividindo a velocidade pela TB. O IB foi determinado pelo produto da velocidade e o CB. De acordo com os dados do presente estudo, a máxima fase estável de lactato sanguínea é atingida em uma velocidade maior quando esta é determinada de forma intermitente (1,17 + 0,09 m.s-1) do que de forma contínua (1,13 + 0,08 m.s-1)... / The main objective of this study was to compare the speed, blood lactate concentration and technical indexes corresponding to the maximal lactate steady state obtained with continuous and intermittent protocols. Thirteen endurance swimmers and triathletes (23.8 ± 9.5 yr., 1.76 ± 0.1 m and 71.3 ± 9.8 kg) participated of this study. The athletes had at least 3 years of experience in swimming. The individuals performed in different days, the following tests: 1) Maximal performance tests of 400 m; 2) Progressive test until exhaustion to determine the anaerobic threshold (AT); 3) 2 to 4 30-min repetitions in different intensities, to determine continuous maximal lactate steady state (MLSSC), and; 4) 2 to 4 trials of 12 x 150 s with 30 s of rest (5:1) at different intensities, to determine the intermittent maximal lactate steady state (MLSSI). The AT was determined trough linear interpolation between the speed and blood lactate concentration, considering a fixed blood lactate value of 3.5 mM. The criterion for the determination of MLSSC and MLSSI was an increase lower or equal to 1 mM of lactate between tenth and thirty min of exercise. Technical indexes stroke rate (SR), stroke length (SL) and stroke index (SI) were determined in all tests. The TB was calculated trough film using the time to perform five complete stroke cycles. The CB was calculated trough the quotient between the speed and SR. The SI was determined by the product of the speed and SL... (Complete abstract click electronic access below)

Neste trabalho apresentamos e comparamos diferentes técnicas de tomografia bidimensional por RMN implementados num sistema de tomografia de campo magnético ultra-baixo (O.05T). A partir da seqüência convencional \"Spin Echo\" (SE), utilizada rotineiramente, implementamos a seqüência \"Gradient Recalled Echo\" (GRE) e duas seqüências que utilizam o principio de Steady-State Free Precession (SSFP), sendo \"Fast Low Angle Shot\" (FLASH) e \"Fast Acquisition Double Echo\" (FADE). Com as seqüências de SSFP conseguimos diminuir drasticamente a duração de um exame de tomografia convencional (seqüência SE). A seqüência FADE ainda permite adquirir duas imagens com contrastes claramente diferentes sem aumentar significativamente a duração do exame. Desenvolvemos procedimentos de calibração indispensáveis para as técnicas de SSFP que também melhoraram a relação sinal ruído de 15 por cento na técnica SE . Analisamos teórica e experimentalmente o comportamento do contraste das seqüências apresentadas. Fizemos ainda uma serie de imagens de um phantom e da cabeça de um voluntário com as diferentes seqüências e sugerimos algumas combinações dos parâmetros (protocolos) como tempo de repetição, tempo ao eco e angulo de excitação. Um destes protocolos esta sendo testado em casos clínicos para comparar a utilidade das seqüências apresentadas no diagnóstico medico. Com este trabalho ganhamos uma experiência na utilização de técnicas rápidas indispensáveis para a elaboração de uma metodologia para obter imagens tridimensionais / In this work we present and compare different techniques for bidimensional tomography in NMR which were implemented on a ultra low magnetic field (O.05T) tomographic system. Based on the conventional spin echo pulse sequence (SE), which is routinely used, we implemented the gradient recalled echo (GRE) pulse sequence and two sequences that use the principle of Steady-State Free Precession (SSFP) being \"Fast Low Angle Shot\" (FLASH) and \"Fast Acquisition Double Echo\" (FADE). With the SSFP sequences we shorten drastically the duration of the conventional SE tomography sequence. Besides this the FADE sequence gives two images with clearly different contrast without extending significantly the duration of the experiment. Needed for the SSFP techniques, we developed calibration procedures, which improved as well the SE sequence signal to noise ratio of about 15 percent. We analyzed theoretically and experimentally the behavior of the contrast of the presented sequences. Moreover we acquired various images of a phantom and the human brain of a normal volunteer using the different sequences and proposed some combinations of the parameters (protocols) repetition time, time to echo and flip angle. One of these protocols is being tested in clinical cases to compare the usefulness of the presented techniques for medical diagnostic. With this work we gained a wide experience in using SSFP techniques that will be indispensable in the elaboration of three-dimensional tomography methodologies

Os aços de alta resistência e baixa liga são amplamente utilizados em dutos transportadores de óleo e gás e, atualmente, o desenvolvimento de novos projetos de liga e o uso de técnicas altamente avançadas de fabricação e processamento dos aços se tornaram essenciais para obtenção de estruturas que resistam aos danos provocados por H, principal motivo de falha de oleodutos e gasodutos em meios ricos em H2S. No presente trabalho, avaliou-se o efeito de características microestruturais na difusividade do H em dois aços grau API X65, com diferentes teores de Mn. Uma das chapas ainda está em fase experimental de desenvolvimento, tem baixo teor de Mn e foi produzida para aplicação em ambientes sour. A outra chapa tem alto teor de Mn, já é usada comercialmente há alguns anos e foi desenvolvida para trabalho em ambientes doces. Os dois materiais passaram por caracterização microestrutural nas três seções da chapa: longitudinal e transversal à direção de laminação e do topo da chapa (paralela à direção de laminação). Após a caracterização, amostras de cada seção dos aços foram submetidas a ensaios de permeabilidade ao H; o aço baixo Mn passou por análises de EBSD (Difração de Elétrons Retroespalhados), para determinação de textura. O aço baixo Mn tem microestrutura homogênea ao longo da espessura da chapa, composta por ferrita refinada e pequenas ilhas de perlita. O aço alto Mn, por sua vez, apresenta microestrutura heterogênea ao longo da espessura, formada por bandas de ferrita e perlita, com marcada presença de segregação central de elementos de liga. Os ensaios de permeabilidade ao H mostraram que os coeficientes de difusão efetiva do H, Deff, do aço baixo Mn são ligeiramente superiores aos do aço alto Mn. Outros dois importantes parâmetros que foram calculados para os dois aços são a concentração de H na sub-superfície do material, C0, e o número de traps por unidade de volume, Nt. Contrariando expectativas, o aço baixo Mn apresentou maiores valores de C0 e Nt do que o aço alto Mn. Ensaios preliminares de dessorção térmica realizados nos dois aços mostraram os mesmos resultados: o aço baixo Mn aprisiona mais H do que o aço alto Mn. Estes resultados contraditórios de C0 e Nt foram atribuídos à presença de nanoprecipitados de microadições de liga no aço baixo Mn, não detectáveis por microscopia óptica e eletrônica de varredura. Ainda, para os dois aços, os valores de Deff variaram em função da seção analisada da seguinte maneira: Deff longitudinal ? Deff transversal > Deff topo. Para entender melhor o comportamento anisotrópico da difusão do H nos dois aços calculou-se um novo coeficiente de difusão, que foi chamado de coeficiente de difusão no estado estacionário, Dss. O Dss considera que todos os traps do aço estão saturados, permitindo, assim que se avalie somente o efeito de obstáculos físicos à difusão do H. No aço alto Mn, o Dss variou da mesma maneira que o Deff: Dss longitudinal ? Dss transversal > Dss topo; este comportamento foi atribuído ao bandeamento presente no material. No aço baixo Mn, o Dss variou de forma diferente do Deff: Dss transversal > Dss longitudinal >= Dss topo, indicando que a difusão do H pode ser auxiliada por contornos de grão enquanto os traps estão sendo saturados, e que a textura cristalográfica pode influenciar a difusão após o estado estacionário ser atingido. / High strength low alloy steels are widely applied as pipelines for crude oil and natural gas transportation and, currently, new approaches to alloy design, in addition to the use of advanced steelmaking and processing techniques, have become essential for obtaining structures that resist to hydrogen damage, which is the main cause of pipelines failure in H2S-rich environments. The main objective of the present work is to evaluate the influence of microstructural features on hydrogen diffusivity in two API X65 steels, with different Mn contents. One of the steel plates has been recently developed for usage in sour environments, is on its experimental stage and has a low Mn content. The other one is a commercial plate steel, with high Mn content, developed for sweet applications. Both steel plates were characterized in its three sections, in relation to the rolling direction: longitudinal, transverse and top surface of the plate (parallell to the rolling direction). After that, samples obtained from each section of the plates were submitted to hydrogen permeation tests; the low Mn steel was also analysed with EBSD, for texture determination. The low Mn steel presents a homogeneous microstructure through plate thickness, composed of refined ferrite and small pearlite islands. The high Mn steel has a heterogeneous microstructure through the plate thickness, composed of ferrite and pearlite bands, and presents centerline segregation. Hydrogen permeation tests showed that the Deff obtained for the low Mn steel sections are slightly higher than for the high Mn steel. Another two important parameters that were calculated for both steels are the subsurface hydrogen concentration, C0, and the number of traps per unit volume, Nt. Contrary to what was expected, the low Mn steel presented the higher C0 and Nt values. Thermal dessorption spectroscopy analysis confirmed that the low Mn steel traps more H atoms than the high Mn one. These results, along with the similar Deff values, were related to the presence of nanoprecipitates of microalloying elements, that cannot be detected via optical and scanning electron microscopy. Additionally, also for both steels, the Deff values varied in function of the analyzed section as it follows: Deff longitudinal ? Deff transverse > Deff top. In order to better understand this anisotropic behavior, a new diffusion coefficient, which was called diffusion coefficient at the steady state, Dss, was determined. Dss considers that all the trapping sites are saturated, enabling, thus, the evaluation of physical obstacles to H diffusion. For the high Mn steel, the Dss varied in the same matter as the Deff: Dss longitudinal ? Dss transverse > Dss top; this behavior was associated with the microstructural banding present in the material. For the low Mn steel, the Dss exhibited a different behavior: Dss transverse > Dss longitudinal >= Dss top, suggesting that H diffusion can be aided by grain boundaries while the trapping sites are being filled and that crystallographic texture may play its role after the steady state is reached.

Projetos de reatores para tratamento de águas de abastecimento e águas residuárias envolvem o conhecimento da hidrodinâmica do escoamento e das reações químicas e bioquímicas que ocorrem em seu interior. A variável hidrodinâmica pode interferir de modo significativo na eficiência da unidade, visto que ela influencia diretamente no desempenho da cinética das reações. Existem muitos reatores que operam em regime não-permanente de vazão, entretanto, são poucos os trabalhos disponíveis na literatura científica que sugerem o desenvolvimento de métodos para a avaliação da hidrodinâmica desse tipo de escoamento. A aplicação de modelos convencionais para avaliações hidrodinâmicas desses reatores é conceitualmente errada, visto que os mesmos são desenvolvidos considerando-se um regime permanente de vazão. Nesse contexto apresenta-se nesse trabalho um modelo matemático voltado para a avaliação hidrodinâmica de reatores que operam em regime não-permanente de vazão, com intuito de subsidiar as análises e previsões de seu comportamento. Foi utilizada a técnica DTR para levantamento de dados experimentais e um software de simulação numérica, o Vensim 6.3 da Ventana Systems, para auxiliar no desenvolvimento do modelo. Após a sua calibração e validação, com as devidas restrições, o modelo demonstrou ser comparativamente mais adequado para a avaliação do comportamento hidrodinâmico de reatores em condições de regime não-permanente com variação senoidal cíclica de vazão, principalmente para escoamentos que possuem tempo de detenção hidráulica relativamente baixo e amplitude de variação de vazão relativamente elevada. / Reactor designs for water supply and wastewater treatment require the knowledge of hydrodynamic and chemical reactions that occur in its interior. The hydrodynamics is very important as it interferes the efficiency of an treatment unit, since it directly influences the chemical reactions. There are many non-steady state reactors, but there are little studies about their hydrodynamic evaluation in the literature. The use of conventional models is conceptually wrong because they have been developed for steady state conditions. This work presents a mathematical model for hydrodynamic evaluation in non-steady state reactors to support analisys of these flows. The RTD technique to get experimental data and a numerical software simulation have been used as well as the Vensim 6.3 program, of Ventana Systems, to support the model development. After its the calibration and validation, the model proved to be suitable for the experimental conditions, especially for flows that have relatively low hydraulic retention time and relatively high amplitude of flow variation.

The impact of refrigeration systems on the environment can be reduced by the use of alternative reffigerants which are less harmful to the atmosphere and the optimisation of systems and control strategies to deliver increased levels of energy efficiency. Mathematical modelling offers the opportunity to test the performance of systems under different operating conditions and with alternative refrigerants. Dynamic models allow comparison of both transient and steady-state behaviour and this is of particular importance for liquid chillers, since these systems can operate under transient conditions for long periods. This thesis details the development of a general dynamic model for the simulation of liquid chillers. Mathematical models of the reciprocating compressor, expansion valve, evaporator and condenser are presented. The models are integrated to form the overall system model by passing conditions from one component to another. A series of steady-state and transient experimental tests were carried out on a liquid chiller and the model was used to simulate these tests. Validation was carried out by comparison of these measured results to those predicted by the simulation for both the steady-state and transient tests. Once validated, the model was used to investigate the steady-state and dynamic performance of liquid chillers operating with various refrigerants. The effect of the mass of the system refrigerant charge was examined for a number of refrigerants. The steady-state performance for a range of evaporator and condenser coolant temperatures was also investigated. Finally, the effect of different system refrigerants on start-up transients was examined and the losses in cooling capacity due to cycling quantified. The effect of the expansion valve's initial superheat spring setting on the dynamic response and transient losses was also investigated.

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Garamond} This paper presents an approach for modelling a commercial dinitrotoluene (DNT) production process using the CHEMCAD simulation software. A validation of the model was performed based on results of an experimental study carried out at Chematur Engineering AB, Sweden.  Important parameters such as fluid properties, temperature profile and other operating conditions for CHEMCAD steady state model were selected so as to obtain the crude DNT yield as well as the acid –and organic phase compositions within the same range as the reference values from the experimental study. The results showed that the assumption of the steady state model was correct, and that acid –and organic phase compositions were in good agreement, although with a slightly lower sulphuric acid concentration than that observed in the experimental study.  Also, a detailed study was carried out to analyse the effects of physicochemical conditions on the desired product yield. Both the results from the experimental study and the simulated model agree that the effects of mixed acids or heats of mixing acids contribute significantly to the energy balance.  For the appropriateness of the thermodynamics, a NRTL model was chosen and the reactor system was optimized by an equilibrium based approach, producing MNT in 99.8% yield and crude DNT in 99.9% yield. An 80.1/19.9 DNT isomer ratio of the main isomers was achieved and a reduction of by-products in the crude DNT shows a good agreement between the model and the experimental study. / p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Garamond} I denna rapport presenteras en metod för att modellera en kommersiell nitreringsprocess för tillverkning av dinitrotoluen (DNT) med simuleringsprogrammet CHEMCAD. En validering av modellen gjordes baserat på resultat från en experimentell studie utförd hos Chimärer Engineering AB, Sverige.  CHEMCAD-modellen utgår från ”steady-state” drift av anläggningen. Viktiga parametrar såsom fluidegenskaper, temperaturprofil och andra driftsbetingelser i CHEMCAD-modellen valdes för att erhålla ett utbyte av DNT samt sammansättningar av såväl syrafas som organisk fas i god överensstämmelse med referensvärdena från den experimentella studien.  Resultaten visade att antagandena i modellen var korrekta och sammansättningarna för syrafasen och den organiska fasen överensstämde med data från den experimentella studien.  Det genomfördes också en detaljerad studie för att analysera effekterna av fysikalisk-kemiska betingelser på det önskade produktutbytet. Både resultaten från den experimentella studien och data från anläggning i drift överensstämde med den simulerade modellen avseende utspädningsvärmens bidrag till energibalansen.  För att erhålla en lämplig beskrivning av reaktionssystemets termodynamik valdes en NRTL-modell och reaktorsystemet optimerades, vilket gav 99,8 % utbyte av MNT och 99,9 % DNT utbyte. Ett förhållande på 80,1 / 19,9 mellan de två huvudisomererna av DNT uppnåddes och en minskning av biprodukter i DNT produktblandningen. Detta är två exempel på en bra överensstämmelse mellan modellen och experimentstudien.

I denna studie har jämförelse gjorts mellan Interacoustics Eclipse och GSI Audera i samband med Auditory Steady-State Respons (ASSR) mätningar. Syftet med studien var att undersöka ASSR som metod, att utvärdera dess tillförlitlighet i jämfö­relse med tonaudiometri för personer med normal hörsel och personer med hörsel­nedsätt­ning. Avsikten var dessutom att undersöka om elektrod­placering­ på örsnibb eller på mastoid påverkade mät­resultatet, försökspersonens upplevelse av instrumen­­t­ens ljudstimuli, om de estimerade ASSR-värdena påverkades av att mättillfället påbörjades eller avslutades med Interacoustics Eclipse samt undersöka tiden för mätningarna. En experimentell studie genomfördes. Mätningarna som utfördes var tonaudiometri och ASSR, den senare uppmättes med Interacoustics Eclipse och GSI Audera på (n=20) vuxna med normal hörsel och (n=4) vuxna med hörselnedsättning. För personer med normal hörsel påvisades en god överensstämmelse mellan estimerade ASSR-värden och tonaudiometri för Interacoustics Eclipse, något sämre överensstämmelse för GSI Audera. Genomsnittlig mättid för båda instrumenten var ca 40 min. Resultaten visade att elektrodplaceringen inte har någon påverkan på ASSR-värden för Interacoustics Eclipse. Hälften av försökspersonerna upplevde att Interacoustics Eclipse hade ett behagligare ljudstimuli att slappna av till och den andra hälften upplevde GSI Audera som behagligast. De estimerade ASSR-värdena påverkades minimalt beroende på om mättillfället påbörjades eller avslutades med Interacoustics Eclipse.

Dans l’optique de produire de maîtriser les conditions d’expansion ex vivo de greffons hématopoïétiques produits à partir de sang périphérique en homéostasie, l’objectif de ce projet a été de caractériser fonctionnellement, métaboliquement et transcriptomiquement les cellules souches hématopoïétiques (CSH). Compte tenu de l’impossibilité technique de sélectionner spécifiquement les CSH humaines, nous avons utilisé un modèle cellulaire enrichi en CSH, le modèle Side Population(SP). Dans un premier temps, nos travaux ont confirmé que les CSH du sang périphérique étaient majoritairement dans la population SP et qu’elles possédaient des caractéristiques fonctionnelles proches des CSH des autres compartiments hématopoïétiques. Nous avons également démontré l’implication des basses concentrations d’O2 sur le maintien des CSH du sang périphérique. Dans un second temps, nos résultats ont prouvé que les CSH du sang périphérique utilisaient à la fois la glycolyse et la phosphorylation oxydative pour produire l’énergie nécessaire à leur maintien. Enfin, ce projet a permis d’apporter des résultats préliminaires concernant les régulations transcriptomiques des CSH du sang périphérique. Ces données montrent donc que le sang périphérique en homéostasie pourrait constituer une source potentielle de cellules pour la production de greffons hématopoïétiques tout en apportant les premiers éléments de compréhension de la physiologie de ces cellules, afin, dans un plus long terme de maîtriser leur maintien ou leur différenciation ex vivo. / To evaluate the possibility to control ex vivo expansion conditions, a key point to produce hematopoietic graft from steady state peripheral blood (SSPB), the objective of this project to characterize the functional properties, the metabolism and the transcriptomic regulations of hematopoietic stem cell (HSC) from SSPB. Due to the lack of strong HSC’s marker in human, we choose to use the Side Population (SP) model, previously described as enriched in HSC in other hematopoietic compartments. In a first part of our work, we showed that HSC from SSPB are mainly inside the SP population. Indeed, SP cells from SSPB exhibit functional properties very closed from HSC. In addition, we found they strongly affected by low O2 concentrations, as HSC from bone marrow. In a second part, our results showed that HSC from SSPB use as much glycolysis as oxidative phosphorylation to produce energy they need to maintain their properties. All together, these data give some interesting information about HSC regulation and needs. They also suggest that HSC from SSPB could be considering as a potential source of hematopoietic graft for therapy.

The ageing population has become more active and live longer, these patients require hip replacement surgery at a younger age. Artificial hip implants, consisting of the acetabular cup and femoral head, affect the lives of many people, and the longevity of these implants pose significant concerns (rarely longer than 17 years). To help understand the lubricating performance of such a system, a hip joint model was built based on the Reynolds equation; the model developed simulated hydrodynamic lubrication. A steady-state angular rotation model was built whereby it was concluded that such motion would not support any load due to the anti-symmetric nature of the resultant pressure distribution (anti-symmetric about the axis of rotation). The pressure distribution from the steady-state rotation simulation contained a pressure source and sink which converged to the centre of the cup and whose pressure value increased in magnitude, as the eccentricity ratio increased. Infeasible results were obtained when the intermediary pressure constraint, allowing only positive pressure values, was implemented. The results obtained were not representative of the problem and it is recommended that this constraint not be implemented. The transient walking cycle model showed that a fluid with viscosity of 0.0015Pa.s is not sufficient to support a load in the walking cycle under conditions representative of hydrodynamic lubrication. Increasing the fluid viscosity promoted better results in the hydrodynamic model. Increasing the femoral head radius and decreasing the radial clearance between the components also improves the possibility of hydrodynamic lubrication. It is recommended that the model should be extended to investigate elasto-hydrodynamic lubrication. If possible, the effects of a boundary lubrication model should be investigated, as it is believed to be a major contribution to the lubrication of hip joints. / Dissertation (MEng)--University of Pretoria, 2008. / Chemical Engineering / unrestricted