The objective of this thesis is to investigate the flow conditions that lead to coarse grain entrainment at near incipient motion conditions. Herein, a new conceptual approach is proposed, which in addition to the magnitude of hydrodynamic force or flow power, takes into account the duration of the flow event. Two criteria for inception of grain entrainment, namely the critical impulse and critical energy concepts, are proposed and compared. These frameworks adopt a force or energy perspective, considering the momentum or energy transfer from each flow event to the particle respectively, to describe the phenomenon. A series of conducted mobile particle experiments, are analyzed to examine the validity of the proposed approaches. First a set of bench-top experiments incorporates an electromagnet which applies pulses of known magnitude and duration to a steel spherical particle in a controlled fashion, so as to identify the critical level for entrainment. The utility of the above criteria is also demonstrated for the case of entrainment by the action of turbulent flow, via analysis of a series of flume experiments, where both the history of hydrodynamic forces exerted on the particle as well as its response are recorded simultaneously. Statistical modeling of the distribution of impulses, as well as conditional excess impulses, is performed using distributions from Extreme Value Theory to effectively model the episodic nature of the occurrence of these events. For the examined uniform and low mobility flow conditions, a power law relationship is proposed for describing the magnitude and frequency of occurrence of the impulse events. The Weibull and exponential distributions provide a good fit for the time between particle entrainments. In addition to these statistical tools, a number of Adaptive Neuro-Fuzzy Inference Systems employing different input representations are used to learn the nonlinear dynamics of the system and perform statistical prediction. The performance of these models is assessed in terms of their broad validity, efficiency and forecast accuracy. Even though the impulse and energy criteria are deeply interrelated, the latter is shown to be advantageous with regard to its performance, applicability and extension ability. The effect of single or multiple highly energetic events carried by certain coherent flow structures (mainly strong sweep events) with regard to the particle response is also investigated. / Ph. D.

Le développement actuel des moteurs doit répondre à une volonté de réduction de la consommation et à des normes de plus en plus sévères. Les moteurs Diesel, bien que performants, présentent des émissions trop importantes d'oxydes d'azote (NOx) et de particules de suies. Ces émissions polluantes proviennent essentiellement de l'existence de zones riches en carburant ne permettant pas une combustion optimale. La préparation du mélange air / carburant, fortement conditionné par l'entraînement d'air par le spray est donc essentielle. La Vélocimétrie par Images de Particules sur traceurs Fluorescents, associée à un traitement spécifique des champs de vitesses instantanés de la phase gazeuse externe sont utilisés afin d'obtenir des mesures en proche frontière du spray. Dans la zone quasi statique du spray, un effet important de la densité ambiante sur le taux de mélange est mis en évidence. D'autre part, la diminution du diamètre de trou d'injecteur améliore sensiblement le taux de mélange local. Pour compléter cette analyse, un gain du taux de mélange entre les deux injecteurs est calculé pour chaque densité ambiante. Pour les fortes densités, le gain issu de la réduction du diamètre de trou peut at! teindre une valeur importante (> 60%). La phase gazeuse latérale dans la zone instationnaire du spray est ensuite investiguée et la méthodologie de la F-PIV est transposée à cette zone. Un lien entre la longueur de pénétration du spray et des longueurs d'entraînement est défini. La densité ambiante n'a pas d'effet sur ces longueurs d'entraînement. La diminution du diamètre de trou engendre une augmentation du gaz entraîné à une distance plus courte du nez de l'injecteur. Cependant, cette étude montre que les deux sprays n'engendrent pas un entraînement de gaz similaire. / The actual development of the engine must reply to a will of fuel consumption reduction and to stricter norms concerning the pollutant emissions. Although the Diesel engines are competitive, the NOx and soot particle emissions mainly come from the existence of wealthy fuel zone preventing an optimal combustion. Therefore, the air / fuel mixing preparation, highly controlled by the air entrainment in spray, is essential. Particle Image Velocimetry on fluorescent tracers, associated with a specific processing of the instantaneous velocity fields have been applied to obtain measurements in the near vicinity of the spray edge. In the "quasi- teady" region of the spray, the important effect of the ambient density on the mixing rate has been pointed out. On the other hand, an orifice diameter decrease significantly improves the local air / fuel ratio. To complete this analyse, a gain in mixing rate between two different injectors has! been calculated for each gas density. For high densities, the gain due to a reduction of the hole diameter can reach important value (> 60%). Then, lateral gaseous phase in no stationary zone of spray is studying and F-PIV method is transposed to this zone. A link between the penetration length and entrainment lengths is defined. Ambient density has not effect on entrainment lengths. The hole diameter decrease generates entrained gas increase at shorter distance of injector nozzle. However, this study shows two sprays do not generated the same gas entrainment

As operárias de Melipona quadrifasciata exercem diferentes funções na colônia, segundo sua faixa etária. No interior da colônia, os indivíduos mais jovens, nutrizes, ficam localizados na região mais interna e aproximam-se progressivamente das regiões periféricas à medida que envelhecem. Os indivíduos mais velhos, forrageiras, saem da colônia diariamente. Ritmos biológicos estão presentes nas operárias de todas as idades, mas apenas os ritmos das forrageiras estão bem caracterizados. Neste trabalho, o objetivo foi detectar mudanças no sistema temporal que ocorrem ao longo do desenvolvimento ontogenético de abelhas operárias. O ritmo monitorado foi aquele de consumo de O2, empregando um ciclo claro/escuro como agente sincronizador. O consumo de O2 foi registrado em nutrizes com 24 horas de vida e em forrageiras, sendo que as nutrizes foram divididas em dois grupos: Nutri_BOD, indivíduos colocados em condições constantes de temperatura e iluminação assim que emergiam do favo, e NUTRI_Col, indivíduos devolvidos à colônia por 24 horas antes dos testes. O protocolo experimental foi dividido em três fases: Fase1, forrageiras e Nutriz_BOD eram mantidos em condição constante de iluminação e temperatura durante 24 horas. Nutriz_Col era devolvida a colônia de origem durante esse mesmo intervalo; Fase2, exposição a ciclo claro/escuro 12:12h durante 48 horas; Fase3, todos os indivíduos voltavam às condições ambientais constantes. Em Fase2 e Fase3 foram feitas as medidas de consumo de O2. Os resultados da Fase2 não mostraram arrastamento, período significativo do ritmo difere de 24h. A média de consumo na fotofase apresenta diferença significativa da média de consumo na escotofase, para o grupo das forrageiras e Nutri_Col, sendo o consumo maior na fotofase. Ritmos em livre curso foram encontrados em todas as forrageiras e em 25% das nutrizes de ambos os grupos. Os resultados indicam a existência de um processo de maturação do sistema circadiano, bem como na capacidade de lidar com a luz, que representa uma situação desfavorável à sobrevivência das nutrizes. Como os dois grupos de nutrizes apresentaram ritmos endógenos, o surgimento deles independe da influência da colônia. A colônia, porém, parece modular a velocidade do estabelecimento do ritmo e sua capacidade de sincronizar-se com o ciclo claro/escuro ambiental. / The workers of the stingless bee, Melipona quadrifasciata, assume different tasks during their adult life. Newly emerged individuals - nurses - remain inside the nest, without contact with the external environment. As the workers mature, they migrate to more peripheral regions but only the oldest - foragers - leave the nest. Foragers have strong daily rhythms. Biological rhythms have already been detected in all the workers, but only the rhythms of foragers are well characterized. This work aimed to detect changes in temporal biological system during post-embryonic development. For this, the rhythm of oxygen consumption was measured and light/dark cycle was used as the synchronizing agent. Oxygen consumption was monitored in foragers and in nurses 24 hours after the emergence. The nurses were divided into two groups: 1-Nutri_BOD: the bees were kept in constant conditions of temperature and illumination. 2- NUTRI_Col: newly emerged workers were transferred back to the colony for 24 hours before the experiment. The experimental protocol was divided into three parts: 1- Forager and Nutriz_BOD were kept in constant conditions of illumination and temperature for 24 hours. Nutriz_Col were returned to the colony during the same interval. 2- Animals were exposed to a light/dark cycle, 12:12h, for 48 hours. 3- All the bees returned to constant conditions, for 4 days. Mesurements of O2 consumption were taken during the second and third parts of the experiment. There was not entrainment of the individual\'s rhythms. The period was different from 24h. In foragers and Nutri_Col there were significant differences between the average consumption in the photophase and the average consumption in the scotophase. A free running rhythm was present in all foragers and in 25% of Nutri_Col and Nutri_BOD. Results indicate the existence of a process of maturation running in the circadian system, and an increasing ability to respond to light. Presence of light is a non-permissive condition for the nurses\' survival. Endogenous rhythms are present in both groups of nurses. The presence of the colony is not necessary to the development of the rhythm. However, the colony seems to modulate the rate of to the development and the ability to synchronize with the light/dark cycle.

Cette thèse est dédiée au développement d’un modèle mathématique multi-échelle pour la régulation du cycle cellulaire par l’horloge circadienne. Ceci est motivé par le fait que plusieurs études ont montré un lien direct entre certains cancers et un dysfonctionnement du mécanisme de l’horloge circadienne. Le but est de comprendre l’effet des rythmes circadiens et leur perturbation sur la prolifération d’une population de cellules / This thesis is dedicated to the development of a multiscale mathematical model that describes the regulation of the cell cycle by the circadian clock. What motivated this work is the fact that several tumorigenic diseases are linked to circadian rhythms disruption. We would like to understand the effect of circadian rhythms on the proliferation of a cell population and hence give plausible explanation for diseases that arise form circadian clock disruption. The mammalian cell cycle and the circadian clock are two molecular processes that operate in a rhythmic manner and exquisite precision. On one hand, the cell cycle is driven by the rhythmic activity of cyclin dependent kinases which dictate the time a cell must engage mitosis and the time it must divide giving birth to two daughter cells. On the other hand, the circadian clock is a system of transcriptional and translational feedback-loops that generates sustained oscillations of different mRNAs and proteins with a period of approximately 24 h. It turns out that several components of the circadian clock regulates various cyclin-dependent kinases at different stages of the cell cycle. This makes the circadian clock a key player of the temporal organization of the cell cycle and makes these two biological processes act as two tightly coupled oscillators. Our modeling approach consists of using a molecular-structured partial differential equation that describes the proliferation of a cell population. Proliferation depends on the coupled cell cycle-circadian clock molecular state of cells. Due to the large number of molecular components involved in the cell cycle-circadian clock system, the problem becomes of high-dimensionality and specific numerical techniques are needed to solve the equation

This thesis describes research carried out to investigate techniques for (i) rapidly assessing the reactivity of fly ash; and (ii) evaluating its interaction with air-entraining admixtures (AEAs), both with regard to use in concrete. The materials considered for the project included, 54 fly ashes from 8 UK sources, and an additional three materials from Bangladesh, covering a range of fineness, loss-on-ignition (LOI) and production conditions (run-of-station, carbon removed, air-classified, co-combustion, oxy-fuel technology); Portland Cements (PCs) from five UK sources with various properties (strength classes 32.5 R, 42.5 N and 52.5 N); laboratory grade hydrated and quick limes; and three commercial AEAs and a standard laboratory grade reagent (surfactant). The research examining fly ash reactivity considered activity index tests to BS EN 450 (BSI, 2005c) as the reference and investigated tests covering fly ash properties/providing measures of fly ash behaviour to rapidly assess this. These included (i) fly ash fineness (45 µm sieve residue, or LASER particle size distribution (PSD) parameters), LOI and flow properties; (ii) accelerated curing of PC and lime-based mortars (iii) lime consumption by fly ash when combined with PC in paste or suspension (Frattini) or from a saturated lime solution; (iv) various measures of fly ash chemical composition (based on oxide/mineralogical analysis); and (v) a quicklime slaking test. The test results were validated by strength tests with 100 mm concrete cube. Results of the above indicated good correlations between fly ash fineness, mortar flow/water requirement and (pozzolanic) activity index (standard or accelerated curing). However, fly ash reactivity and fresh properties appeared to be influenced by the properties of the test PC (e.g. chemical composition and fineness) and there is a need to take this into account during assessment. Generally, finer fly ashes gave better flow; however, there is an optimum fineness (d90 ~40 µm) for best performance, and which is similar to the fineness of the test PC. Strong correlations between the accelerated and standard cured PC-based mortar indicate the latter can be used to estimate the former taking account of the fly ash properties. In view of eliminating the effect of PC properties on reactivity, mortar tests with laboratory grade hydrated lime suggested potential for this. However, for better assessment, this approach requires further work to address issues relating to slower rates of strength gain and increased time requirements, although high temperature conditions were used for curing. Measuring Ca(OH)2 consumption from fly ash/PC paste or suspension agreed with the behaviour in mortar, but needs special instruments (e.g. TGA or XRF). A similar approach with saturated lime did not work well, despite several measures being taken to try and improve this. The oxide and mineralogical analysis results of fly ash did not give good correlations with activity index, but improved when a factor combining them with fineness was considered. The test results were validated in concrete and with air-classified fly ashes from single sources which gave clear trend/behaviour. The lime slaking test was found to be ineffective for identifying fly ash reactivity. The reactivity assessment results were validated by carrying out concrete strength tests. In general, more consistent trends were obtained for fly ash from single source as noted with mortar earlier. Methods adopted/developed to assess the interaction of fly ash with AEA included (i) the foam index test; (ii) acid blue 80 (AB80) dye adsorption test (spectroscopic method); and (iii) methylene blue test. High variability in foam index test results between different operators were noted, which reflected differences in the degree of shaking applied and difficulties in identification of the test end point. Adoption of an automatic shaker and determination of suitable test conditions reduced this by more than 50%. Reliable test procedures were also established for the AB80 dye adsorption method. The results obtained from these tests gave very good correlations with fly ash specific surface area and the AEA dose required (both with commercial AEAs and standard reagent) for achieving target air contents in mortar and concrete. The methylene blue dye test also gave good correlations with these parameters, but was less effective for low LOI fly ashes. Between laboratory tests were carried out at three UKQAA members and considered, LOI, fineness (45 µm sieve and LASER PSD), and activity index. The results gave good agreement with those obtained at the Concrete Technology Unit for this work and again emphasized the role of fly ash fineness on its reactivity. Overall, fly ash fineness was found to be the best means of rapidly assessing its reactivity. Some of the other methods considered gave promising behaviour but require further refinements. Therefore, it is suggested that in addition to 45 µm sieve residue, other types of fineness measurement (e.g. sub 10 µm quantities, d50 and d90) can be considered suitable alternatives to activity index. Similarly, foam index tests with the automatic shaker or the AB80 test method could both be used as fly ash physical requirement tests, or in production control for air-entrained concrete.

In mammalian hearts, initiation of the heartbeat occurs in a region of specialised pacemaker cells known as the sinoatrial node (SAN). The SAN is a highly complex spatially distributed structure which displays considerable cellular heterogeneity and is subject to complex electrotonic interactions with the surrounding atrial tissue. In this study, biophysically detailed ionic models of central and peripheral SAN pacemaker cells are described. These models are able to accurately reproduce experimental recordings of the membrane potential from central and peripheral SAN tissue. These models are used to investigate frequency synchronisation of electrically coupled cardiac pacemaker cells. Based on simulation results presented, it is proposed that cellular heterogeneity in the SAN plays an important role in achieving rhythm coordination and possibly contributes to the efficient activation of the surrounding atrial myocardium. This represents an important, previously unexplored, mechanism underlying pacemaker synchronisation and cardiac activation in vivo. A spatial-gradient model of action potential heterogeneity within the SAN is then formulated using a large-scale least squares optimisation technique. This model accurately reproduces the smooth spatial variation in action potential characteristics observed in the SAN. One and two dimensional models of the intact SAN are then formulated and three proposed models of SAN heterogeneity are investigated: 1) the discrete-region model, in which the SAN consists of a compact central region surrounded by a region of transitional pacemaker cells, 2) the gradient model, in which cells of the SAN exhibit a smooth variation in properties from the centre to the periphery of the SAN, and 3) the mosaic model, in which SAN and atrial cells are scattered throughout the SAN region with the proportion of atrial cells increasing towards the periphery. Simulation results suggest that the gradient model achieves frequency entrainment more easily than the other models of SAN heterogeneity. The gradient model also reproduces action potential waveshapes and a site of earliest activation consistent with experimental observations in the intact SAN. It is therefore proposed that the gradient model of SAN heterogeneity represents the most plausible model of SAN organisation.

In this study, numerical simulations of a low emission lab-scale non-premixed combustor are conducted and analyzed. The objectives are to provide new insight into the physical phenomena in the SPRF (Stagnation Point Reverse Flow) combustor built in the Georgia Tech Combustion Lab, and to compare three Large Eddy Simulation (LES) combustion models (Eddy Break-Up [EBU], Steady Flamelet [SF] and Linear Eddy Model [LEM]) for non-premixed combustion. The nominal operating condition of the SPRF combustor achieves very low NOx and CO emissions by combining turbulent mixing of exhaust gases with preheated reactants and chemical kinetics. The SPRF numerical simulation focuses on capturing the complex interaction between turbulent mixing and heat release. LES simulations have been carried out for a non-reactive case in order to analyze the turbulent mixing inside the combustor. The LES results have been compared to PIV experimental data and the code has been validated. The dominating features of the operational mode of the SPRF combustor (dilution of hot products into reactants, pre-heating and pre-mixing) have been analyzed, and results from the EBU-LES, SF-LES and LEM-LES simulations have been compared. Analysis shows that the LEM-LES simulation achieves the best agreement with the observed flame structure and is the only model that captures the stabilization processes observed in the experiments. EBU-LES and SF-LES do not predict the correct flow pattern because of the inaccurate modeling of sub-grid scale mixing and turbulence-combustion interaction. Limitations of these two models for this type of combustor are discussed.

Increasing differences in United States energy consumption and production has influenced the passing of legislation for biomass fuel production. To determine feasibility of energy crops for alternative fuels, research is needed to investigate dry matter yield over an extended harvest season; physical characteristics need to be described for potential harvesting problems; chemical characteristics described to identify selective harvest potential, optimal harvest timing, losses during harvest and storage; various harvest techniques investigated to identify potential cost savings; and impact of various storage techniques on quantity and quality of deliverable biomass. This study investigated the use of two sorghum varieties as a potential bioenergy feedstock where 20 ha were planted for three years. Standing crop samples were collected from August through January to document changes in dry matter yield, moisture, height, fiber content, proximate and ultimate analysis. The sorghum was cut and conditioned – as a two-cutting ratoon or single-cutting – using various mower-conditioners and windrow samples taken daily to determine best method of field drying, quantify dry matter loss and soil entrainment. Two storage methods were utilized – baling with wrapping in a tubeline, and chopping and compressing in bag using a modified cotton module builder – to determine best method of storage for reduced dry matter loss. The optimal time of harvest for maximum dry matter occurred with the November once-cut where 30 Mg ha^-1 was documented, but comparable yields were observed with the two-cutting scenario. Fiber content increased with maturity, peaked, and declined, while ash content and moisture decreased with maturity. The achievement of 55% moisture in January shows field curing to be necessary for transportation at any significant distance, but soil entrainment – as measured by ash concentration – was not found to be a significant problem after conditioning, multiple windrow inversions, and harvesting. The geometric mean length of particle was determined to be 1.4 to 3.7 times lower than nominal chop length, indicating potential cost savings in comminution. Dry matter loss estimates during storage proved difficult due to mobility of moisture throughout the packages, where losses were documented up to 40%. Module packages tended to have lower dry matter and constituent losses than bales.

Concrete which is manufactured in a mixing plant to be delivered to construction site in unhardened and plastic stage is called ready-mixed concrete. Because of technical and economical reasons, many mineral and chemical admixtures are used in ready-mixed concrete production. As a result of extra mixing and delayed placing of ready-mixed concrete (especially at hot weather conditions), there can be many problems about concrete, like slump loss. Addition of water for retempering concrete is the usual procedure, but addition of water without proper adjustment in mixture proportions, adversely affects compressive strength. During this study, effects of prolonged mixing and retempering with superplasticizer on properties of fresh and hardened concrete at hot weather conditions are observed. Some of the properties of concrete inspected are compressive strength, splitting tensile strength, slump and air content. All mixes contain air entrainer and water reducer at a standard amount. The difference between mixes comes from kind and amount of mineral admixture which cement is replaced by. During the study, fly ash, blast furnace slag, ground clay brick and natural pozzolan are used at amounts, 25% and 50% of cement. Also, a mixture of pure cement is prepared as control concrete. 15 cm initial slump is planned in the experimental work. After five minutes and at the end of first, second, third and fourth hours of mixing process, if needed retempering process is proceeded with superplasticizer and samples are taken. As a result of retempering with superplasticizer, the aimed slump values are obtained. The effects are than, observed. As a result of this study, it has been observed that replacing Portland cement with certain mineral admixtures, especially fly ash at certain amounts, can be a solution for slump loss problem, by retarding the slump loss effect of prolonged mixing. Also it has been seen that ground clay brick causes better performance for slump values at lateral stages of mixing with respect to pure Portland cement. Another important observation has been about the increase in the amount of air caused by air entraining admixtures in fresh concrete based on prolonged mixing at hot weather conditions.

Le but de ce travail de recherche est de contribuer à une meilleure compréhension de la dynamique de propagation et de la miscibilité de jets gravitaires au-dessous d’un liquide ambiant. Des expériences ont été réalisées en laboratoire à l’aide d’une plateforme expérimentale constituée d’un bassin parallélépipédique contenant de l’eau douce et d’un canal d’injection de section rectangulaire de jets gravitaires de concentration constante initiale fixée. Les calculs mathématiques et numériques sont basés sur les modèles RANS (Reynolds-Averaged Navier Stokes equations), k-ε (K-epsilon) et DCE (Diffusion-Convective Equation) de la fraction volumique de l’eau salée pour décrire la propagation et le mélange du jet gravitaire. L’évolution du front du jet obtenue expérimentalement est utilisée pour valider le modèle numérique. Par ailleurs, la comparaison des résultats obtenus sur l’écoulement moyen (z⁄z0.5 =U/Umax) avec ceux des études 2D expérimentales et numériques antérieures ont montré des similarités. La simulation numérique des champs hydrodynamiques montre que la vitesse maximale est atteinte à la position 0.18 z0.5, où z0.5 est la hauteur d’eau pour laquelle la vitesse moyenne u est égale à la moitié de la vitesse maximale Umax. / The aim of this investigation is to contribute to a better understanding of the propagation dynamics and the mixing process of dense gravity currents. The Laboratory experiments proceeded with a fixed initial gravity current concentration in one experimental set-up. The gravity currents are injected using a rectangular injection channel into a rectangular basin containing the ambient lighter liquid. The injection studied is said in unsteady state volume, as the Reynolds number lies in the range 1111 - 3889. The experiments provided the evolution of the boundary interface of the jet, and it is used to validate the numerical model. The numerical model depends on the Reynolds-Averaged Navier Stokes equations (RANS). The k-ε (K-epsilon) and the Diffusion-Convective Equation (DCE) of the saline water volume fraction were used to model the mixing and the propagation of the gravity current jet. On the other hand, comparison of the mean flow (z⁄z0.5 =U/Umax) with previous two-dimensional numerical simulations and experimental measurements have shown similarities. The numerical simulations of the hydrodynamic fields indicate that the velocity maximum at 0.18 z0.5, where z0.5 is the height at which the mean velocity u is the half of the maximum velocity Umax.