In this thesis we develop analytical models for boundary layer flow through a two dimensional group of obstacles , based on the "distributed force" model. An array of obstacles is represented as a region without solid obstructions but with distributed body forces resisting the flow. Linear analyses are presented of inviscid, laminar (or constant eddy viscosity) and turbulent flow through such force distributions. For any group of obstacles, we show how to calculate the model force distribution which becomes the input for the linear analyses. The entire procedure can be iterated to take account of non-linear upstream sheltering effects. In general the model distributed force integrates to equal the actual force exerted by obstacles on the flow divided by the fraction of the array volume not occupied by solid obstacles. Turbulent stresses are modelled using a mixing length that is uniform up to a specified height and increases linearly above. Our physical arguments for a displaced mixing length above the obstacles provide an explanation for the observed coincidence between displacement height and the level of mean momentum absorption. Comparisons of the turbulent analysis results with numerical simulations and experimental data show very encouraging agreement and so support both the distributed force model and the assumptions of the mathematical analysis. From the results of the turbulent flow analysis, effective roughness and displacement heights can be calculated for the flow above the obstacles. When the displacement of the turbulent mixing length is correctly taken into account, the calculated parameters are comparable with those obtained experimentally. An analysis of plume dispersion through a group of obstacles shows how the flow field results can be applied to practical situations, and highlights the dominant effect of enhanced perturbation shear stress, especially in the obstacle roof top layer, on changes to the downstream evolution of the plume.

La structure électronique, le spectre de phonons et les effets du couplage électron-phonon (e-p) sur les propriétés de transport de nanofils de Si (SiNW) ont été étudiés systématiquement sur la base de calculs en liaisons fortes et en champ de forces de valence. La structure électronique des nanofils dépend de leur orientation et de leur diamètre, changeant d’une bande interdite directe à indirecte. La largeur de bande interdite décroît et tend vers celle du Si massif quand le diamètre croît. Les spectres de phonons dépendent également de l’orientation et du diamètre. Ils présentent quatre modes acoustiques ce qui est typique des systèmes unidimensionnels. La mobilité et le temps de vie des électrons dans des nanofils orientés [110] ont été calculés. Les calculs confirment qu’à température ambiante les propriétés de transport dans les SiNWs dépendent fortement de la diffusion par les phonons, impliquant à la fois des modes acoustiques et optiques tous dérivant des modes acoustiques du Si massif. La mobilité augmente et tend vers celle du massif quand le diamètre augmente, et elle décroît quand la température passe de 77K à 300K. La relation entre la mobilité et la densité de porteurs est plus complexe. Pour des densités inférieures à 10 19 cm-3, la mobilité est pratiquement constante car elle ne dépend pas de la position du niveau de Fermi. Pour des densités supérieures, la mobilité dépend très fortement de la densité de porteurs car le niveau de Fermi est suffisamment haut pour croiser le minimum de bande de conduction et le transport multi-bandes devient important. Un autre travail entrepris dans la thèse a concerné la modélisation en liaisons fortes et en fonctions de Green hors équilibre du transport balistique dans des hétérojonctions de nanotubes de carbone (n1,m1)/(n2,m2)/(n1,m1). La conductance des jonctions semiconductrices décroît exponentiellement quand la longueur du nanotube (n2,m2) augmente. Cependant la conductance de (12,0)/(9,0)/(12,0) augmente avec la longueur du nanotube (9,0). Cet accroissement anormal de la conductance est expliqué par l’évolution du potentiel. De plus, la relation entre la conductance et la symétrie de rotation dans les jonctions métalliques est étudiée. Un comportement universel de conductance est démontré et est interprété par la différence de phase des électrons qui traversent deux interfaces de la jonction. Finalement, la conductance balistique de multi-jonctions est étudiée et la possibilité de réaliser des composants basés uniquement sur des nanotubes de carbone est proposée. / In this thesis, the electronic structure, the phonon spectrum, and the electron-phonon (e-p) coupling effect in transport properties of Silicon Nanowires (SiNW) have been studied systematically based on Tight-Binding (TB) model and Valence-Force-Field (VFF) model. The electronic structure of SiNW is strongly dependent on the orientation and the diameter, even changing from direct gap to indirect gap, and the gap of SiNWs decreases and tends to the bulk value as the diameter increases. The phonon spectra are also dependent on the orientation and the diameter. It’s a character of nanowires that there are four acoustic phonon modes. Based on the calculation of both low field mobility and lifetime of electrons in SiNWs along [110], it’s confirmed that at room temperature the transport of carriers in SiNWs strongly depends on the phonon scattering, involving both optical phonons and acoustic phonons. The mobility increases and tends to the bulk value when the diameter increases. The mobility decreases in power law when the temperature increases from 77K to 300K. The relationship between the mobility and the density of carrier is more complicated. For low density of carrier (<10 19/cm3), the mobility is almost constant because it is approximately independent on the Fermi level at low concentration. For higher concentration, the mobility is strongly dependent on the density of carrier because the Fermi level is high enough to cross the conduction band edge (CBE) and multi-band transport becomes important. In a second study undertaken in this thesis, TB model and Nonequilibrium Green's Function (NEGF) are used to calculate the ballistic transport properties of carbon nanotube (CNT) heterojunctions (n1,m1)/(n2,m2)/(n1,m1). The conductance of semiconducting junctions decreases exponentially when the length of the middle CNT (n2,m2) increases. However, the conductance of (12,0)/(9,0)/(12,0) increases when the length of the CNT (9,0) increases. This anomalous increase of conductance is explained and reproduced very well by an exponentially dropped potential. Furthermore, the relationship between the conductance and the rotation symmetry in metallic jonctions is studied. The conductance spectra change periodically, and there are three different spectra at most for a special type of jonction. This universal behavior of conductance can be well understood by the phase difference of electrons, which travel through two interfaces of a junction. Finally, the ballistic conductance of multi-Iead junctions is studied and the possibility of making pure CNT electronic device is revealed.

This thesis reports the results of an experimental investigation of the effect of buoyancy forces on turbulent upflow of air in a vertical pipe under condit.io:1s of constant wall heat flux at Reynolds numbers of 5000 to 14000. Preliminary velocity and axial turbulence intensity measurements in isothermal flows for Reynolds numbers of 5000 to 32000 are also reported. Velocity and temperature distributions were measured over a range of heat fluxes at Reynolds numbers of approximately 5000 and 8000 and at a single heat flux at a Reynolds number of 14000.

The study of cycling biomechanics typically requires measurement of pedal loads through force transducer instrumentation. However, analysis of seated cycling often necessitates the additional measurement of the loads exerted on the rider by the seat and handlebars. A stationary exercise bicycle was instrumented with two commercial six-axis force transducers at both the seat and handlebar locations via a custom designed mounting system. The system was tested by applying known forces and moments to the fixtures and proved capable of accurately measuring the loads. Additional data collected from cycling tests were compared to values from the literature to add supporting evidence to the validity of the system. The instrumented stationary bicycle was further used to study the accuracy of modeling seated cycling in OpenSim. Five participants cycled at a moderate resistance level for three trials. Force and moment data were collected by seat, handlebar, and pedal load cells, while kinematic data were collected by an optical motion capture system. Participant data were analyzed with the OpenSim residual reduction algorithm (RRA) tool excluding seat and handlebar loads. The RRA pelvic residual was then compared to an experimentally determined handlebar and seat equivalent (HBSE) calculated from respective load cell data. Graphical comparisons of the RRA and HBSE results showed strong correlations in Anterior-Posterior (A-P) and Superior-Inferior (S-I) force directions and to a lesser degree, Medial-Lateral (M-L) force and S-I moment directions. M-L and A-P moment plots showed the least correlation between RRA and HBSE. Statistical comparisons showed RRA errors likely within 5.2% body weight (BW) for forces and 2.4% BW*height for moments. Considering the average participant height and weight of 167.7 cm and 63.6 kg, respectively, recommended error ranges for RRA are roughly ±4.0% BW for forces and ±7.2% BW*height for moments. This indicates that the OpenSim RRA tool can be used for cycling analysis.

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Multicellular spheroids have emerged as a promising tool for drug delivery, cancer therapy, and tissue engineering. Compared to 2D monolayers, spheroids provide a more realistic representation of the 3D cellular environment, enabling better understanding of the signaling cascades and growth factors involved in vivo. The formation of in vitro spheroids involves the aggregation of several cells that proliferate to grow into larger spheroids. Biophysical cues provide crucial information for the cells to assemble into 3D structures. We used suspended fiber networks to demonstrate a new way to form and spatially pattern spheroids comprised of human pericytes. We show that fiber architecture (aligned vs. crosshatched), diameter (200, 500, and 800 nm), and contractility influence spheroids in their spontaneous formation, growth, and maintenance, and report a dynamic trade of cells between adjacent spheroids through remodeled fiber networks. We found that aligned fiber networks promoted spheroid formation independent of fiber diameter, while large-diameter crosshatched networks abrogated spheroid formation, promoting growth of 2D monolayers. Thus, a mixture of diameters and architectures allowed for spatial patterning of spheroids and monolayers within a single system. We further quantified various dynamic interactions and describe the forces involved during spheroid formation, cell efflux from spheroids, and show the loss and recovery of spheroid forces with pharmacological perturbation of Rho-associated protein kinase (ROCK). Thus, we develop new insights on the dynamics of spheroids using suspended fiber networks of varying diameters and architectures, with the potential to connect matrix biology with developmental, disease, and regenerative biology. / Master of Science / In recent years, studies involving multicellular spherical aggregates or 'spheroids' have gained popularity since they capture the 3D cellular environments seen within the body more realistically when compared to 2D cell culture systems (such as monolayers) traditionally used for biological studies. These spheroids resemble organs and tissues in terms of their structure and function better and are increasingly being studied for an array of applications such as drug delivery, cancer therapy, as implants and in tissue regeneration and tissue engineering. The cellular microenvironment consists of fibrous proteins of varying diameter arranged in various geometric patterns, which can influence the growth and culture of spheroids. Here, we use our Spinneret-Based Tunable Engineered Parameters (STEP) technique to fabricate fibrous networks with precise control over fiber diameter and architecture and study how biophysical cues can influence the formation and culture of spheroids. Using aortic pericytes, we show that fiber architecture (aligned vs. crosshatched) and diameter (200, 500, and 800 nm) can control how pericytes aggregate into either 2D monolayers or 3D spheroids. We study the effect of each of these parameters to show that stiffer, denser fibers are robust networks which the cells refrain from remodeling, and thus lead to monolayers while more compliant and sparser networks are easily remodeled to promote spheroid formation. Thus, we spatially pattern a mixture of 3D spheroids and 2D monolayers in a single system by varying the parameters at different regions. We quantify various interactions such as spheroid formation, spheroid merging, spheroid migration, cell efflux from spheroids and the dynamic contractile forces exerted on the matrix by spheroids during these interactions. We also show that contractility has a major role in spheroid formation and to maintain their structure and look at the changes in the gene expressions associated with contractility during the formation and growth of spheroids. Thus, we develop new knowledge in controlling the growth of pericytes into 2D and 3D structures and show that our fiber networks can be an essential platform for studying spheroids.

In the shot put throw, the primary power is generated in the form of ground reaction forces as a result of action of the lower extremities (Coh, Stuhec, & Supej, 2008). The purpose of this study was to determine how the ground reaction force and ground contact time during the delivery phase of rotational shot put relates to the predicted distance of the throw. This will allow us to determine the optimal approach of force application for maximum throwing distance (Linthorne, 2001). Eight male subjects were used in this study (age 23 ± 4 y; body mass 123 ± 14 kg; height 190 ± 4 cm; all right handed). Subjects threw three attempts in a custom-built shot put ring where two force plates were located where both feet were expected to land in the delivery. The throws were also filmed using two high-speed cameras at 120 frames/s. These videos gave us the speed, angle and height of release for predicting distance thrown. Results: Peak right leg force during delivery was correlated with throwing distance (R2 = 0.450, p = 0.001). Also, left leg ground time was significant with predicted throwing distance (R² = 0.516, p < 0.001). Because increased strength leads to greater throwing distances (Zaras et al., 2013) and peak right leg force was significant, it would be useful to perform proper strength training exercises that can increase a thrower's ability to increase the peak ground forces during a throw. If the thrower can produce greater peak force into the ground with the right leg during the delivery phase, this should cause the thrower to come off their left leg sooner, resulting in greater speed of release and thus distance thrown.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

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