In a novel application of the temporal numerical simulation, an investigation ofturbulence modeling techniques is carried for the turbulent wall jet over aconvex surface (Coanda wall jet.) The simultaneous presence of multipleinstability mechanisms and the interaction with the turbulence dynamics at thesolid boundary produces a unique combination of different large turbulentcoherent structures that constitutes both a consistent challenge for numericalsimulations and an ideal test bed for turbulence models.The Temporal Direct Numerical Simulation (TDNS) of the Coanda wall jetrestricts the focus from the global turbulent Coanda wall jet to a smaller, localportion of the flow and offers a wide array of advantages to the present work. Inparticular, the size of the computational domain can be arbitrarily chosen inboth the spanwise and the streamwise directions. This allows to either suppressor enhance individual physical mechanisms and, consequently, to selectivelyreproduce different large coherent structures within the local flow. In the firstpart, temporal numerical simulations are employed to reproduce four differentflow scenarios of the local Coanda wall jet with a level of numerical resolutionthat, because of the reduced size of the computational domain, cannot be matchedby standard DNS of the entire physical flow (spatial DNS, or SDNS.)The TDNS of these four flow scenarios are then used in the second part for ana--posteriori analysis of different turbulence models in order to addresscommon shortcomings shown by Hybrid Turbulence Models (HTM). For each flowscenario, the turbulent flow field is deliberately decomposed in resolved andunresolved flows by the application of different filters in space correspondingto different grid resolution. The behavior of turbulence models can be reproducedfrom the resolved flow and compared to the turbulent stress tensor directlycalculated from the unresolved part of the flow field. Starting from the RANSlimit, turbulence models with different levels of complexity are studied.Successively, the performance of these models is analyzed at intermediatenumerical resolutions between RANS, LES, and DNS. Finally, an improvedformulation of the Flow Simulation Methodology (FSM) is proposed.

This thesis reports results from the investigation of optically-induced carrier dynamics in graphite and graphitic carbon nanostructures. In this first set of experiments, the dynamics of photo-excited carriers in exfoliated graphene and thin graphitic films are studied by optical pump-probe spectroscopy. Samples ranging in thickness from 1 to 260 carbon layers are deposited onto an oxidized silicon substrate. Time-resolved reflectivity and transmissivity are measured at 1300 nm, following excitation by 150 fs, 800 nm pump pulses at room temperature. Two time scales are identified over which the extracted transient dielectric function returns to its quiescent value. A fast decay time of ~200 fs in graphene is associated with hot phonon emission and increases to ~300 fs for thicknesses greater than only a few carbon layers. The slow decay time, associated with hot phonon interaction and/or carrier recombination, increases more gradually, from ~2.5 to 5 ps over ~30 layers. A simple model suggests the thickness dependence of the slow decay time is likely a result of thermal diffusion into the substrate. In the second set of experiments, coherently-controlled two-colour injection photocurrents are generated via quantum interference of single- and two-photon absorption in bulk graphite and a variety of single-walled carbon nanotube samples, such as a CVD-grown aligned forest of nanotubes (tube diameter dt = 2.5 ± 1.5 nm), and both arc discharge (dt = 1.44 ± 0.15 nm) and HiPco (dt = 0.96 ± 0.14 nm) nanotube films separated by electronic type (metallic vs. semiconducting). At pump wavelengths of 1500 and 750 nm, the emitted terahertz radiation is used to estimate a peak current density of ~12 kA/cm² in graphite and a peak current of ~8 nA per nanotube. From the dependence of the injected current on pump polarization, the relative values of the current injection tensor elements are measured, and information is gained on the alignment and birefringence of the nanotube samples. The dependence of the injected current on pump wavelength implies that the currents are likely based on band-band electronic transitions and not on excitonic effects, which govern most linear optical processes.

This thesis reports results from the investigation of optically-induced carrier dynamics in graphite and graphitic carbon nanostructures. In this first set of experiments, the dynamics of photo-excited carriers in exfoliated graphene and thin graphitic films are studied by optical pump-probe spectroscopy. Samples ranging in thickness from 1 to 260 carbon layers are deposited onto an oxidized silicon substrate. Time-resolved reflectivity and transmissivity are measured at 1300 nm, following excitation by 150 fs, 800 nm pump pulses at room temperature. Two time scales are identified over which the extracted transient dielectric function returns to its quiescent value. A fast decay time of ~200 fs in graphene is associated with hot phonon emission and increases to ~300 fs for thicknesses greater than only a few carbon layers. The slow decay time, associated with hot phonon interaction and/or carrier recombination, increases more gradually, from ~2.5 to 5 ps over ~30 layers. A simple model suggests the thickness dependence of the slow decay time is likely a result of thermal diffusion into the substrate. In the second set of experiments, coherently-controlled two-colour injection photocurrents are generated via quantum interference of single- and two-photon absorption in bulk graphite and a variety of single-walled carbon nanotube samples, such as a CVD-grown aligned forest of nanotubes (tube diameter dt = 2.5 ± 1.5 nm), and both arc discharge (dt = 1.44 ± 0.15 nm) and HiPco (dt = 0.96 ± 0.14 nm) nanotube films separated by electronic type (metallic vs. semiconducting). At pump wavelengths of 1500 and 750 nm, the emitted terahertz radiation is used to estimate a peak current density of ~12 kA/cm² in graphite and a peak current of ~8 nA per nanotube. From the dependence of the injected current on pump polarization, the relative values of the current injection tensor elements are measured, and information is gained on the alignment and birefringence of the nanotube samples. The dependence of the injected current on pump wavelength implies that the currents are likely based on band-band electronic transitions and not on excitonic effects, which govern most linear optical processes.

Controlling the quantum states of charge (excitons) or spin-polarized carriers in semiconductor quantum dots (QDs) has been the focus of a considerable research effort in recent years due to the strong promise of using this approach to develop solid state quantum computing hardware. The long-term scalability of this type of quantum computing architecture is enhanced by the use of QDs emitting in the telecom band, which would exploit the established photonic infrastructure. This thesis reports the use of all optical infrared experimental techniques to control exciton dynamics in two different QD samples consisting of InAs/GaAs QDs and InAs/InP QDs within a planar microcavity. An infrared quantum control apparatus was developed and used to apply optimized shaping masks to ultrafast pulses from an optical parametric oscillator. Pulse shaping protocols designed to execute a two-qubit controlled-rotation operation on an individual semiconductor QD were demonstrated and characterized. The quantum control apparatus was then implemented in simultaneous single qubit rotations using two uncoupled, distant InAs/GaAs QDs. These optimal control experiments demonstrated high fidelity optical manipulation of exciton states in the two QDs using a single broadband laser pulse, representing a step forward on the path to a scalable QD architecture and showcasing the power of pulse shaping techniques for quantum control on solid state qubits. As an alternative to single QDs, which have very low optical signals, subsets of QDs within an ensemble can be used in quantum computing applications. To investigate the mediation of inhomogeneities in a QD ensemble, pump-probe experiments were performed on InAs/InP QDs within a dielectric Bragg stack microcavity. Two different excitation geometries showed that the angle dependence of the microcavity transmission allowed for the spectral selection of QD subsets with transition energies resonant with the cavity mode. The microcavity mitigated inhomogeneities in the ensemble while providing a basis for addressing QD subsets which could be used as distinguishable quantum bits. This thesis work shows significant advances towards an optical computing architecture using quantum states in semiconductor QDs.

The spatial and temporal structure of the flow, vorticity and stress over equilibrium orbital-scale sand ripples are investigated at turbulence-resolving scales with a wide-band coherent Doppler profiler (MFDop) in an oscillating tray apparatus. The oscillation period and horizontal excursion were 10 s and 0.5 m. Velocity profiles were acquired with 3 mm vertical resolution and at a 42 Hz sampling rate. Ripple wavelength and amplitude were 25 cm and 2.2 cm. The MFDop measurements are used to investigate the development of the lee vortex as a function of phase, and the co-evolution of turbulent kinetic energy, Reynolds stress and turbulence production. Shear stress is determined from the vertically-integrated vorticity equation and using the double-averaging approach. Friction factors obtained from the two methods are comparable and range from 0.1 to 0.2.

Experimental and theoretical progress has been made toward the production and manipulation of novel atomic and molecular states. The design, construction and characterization of a driver for an acousto-optic modulator is presented which achieves a maximum diffraction efficiency of 54 % at 200 MHz, using a commercial modulator. A novel design is presented for a highly sensitive optical spectrum analyzer for displaying laser mode structure in real time. Utilizing programmable microcontrollers to read data from a CMOS image sensor illuminated by the diffraction pattern from a Fabry-Perot interferometer, this device can operate with beam powers as low as 3.3 micro-watts, at a fraction of the cost of equivalent products. Computational results are presented analyzing the behaviour of a model quantum system in the vicinity of an avoided crossing. The results are compared with calculations based on the Landau-Zener formula, with discussion of its limitations. Further computational work is focused on simulating expected conditions in the implementation of the STIRAP technique for coherent control of atoms and molecules in the beam experiment. The work presented provides tools to further the aim of producing large, mono-energetic populations of heavy Rydberg systems. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2007-10-03 17:17:56.841

This thesis concerns the occurrence of the large-scale bed and plan forms known as alternate bars and meandering, and the internal structures of the flow associated with their formation. The work is to be viewed as an extension of previous work by da Silva (1991), Yalin (1992), and Yalin and da Silva (2001). As a first step in this work, the criteria for occurrence of alternate bars and meandering of Yalin and da Silva (2001) is re-considered in view of additional field and laboratory data from the recent literature and data resulting from two series of experimental runs carried out in two sediment transport flumes. This leads to a number of modifications of the boundary-lines in the related existence-region diagram of Yalin and da Silva. The size of the largest horizontal coherent structures (HCS’s) of an alternate bar inducing flow was then investigated experimentally on the basis of three series of flow velocity measurements. These were carried out in a 21m-long, 1m-wide straight channel, conveying a 4cm-deep flow. The bed consisted of a silica sand having a grain size of 2mm; its surface was flat. The measurements were carried out using a Sontek 2D Micro ADV. The horizontal burst length was found to be between five and seven times the flow width. The effect of the HCS’s on the mean flow was also investigated. A slight internal meandering of the flow caused by the superimposition of burst-sequences on the mean flow was clearly detectable. Finally, with the aid of three new series of measurements in the same channel, an attempt was made to penetrate the dynamics and life-cycle of the HCS’s. For this purpose, quadrant analysis was used; the cross-sectional distribution of relevant statistical turbulence-related parameters was investigated; and cross-correlations of flow velocity along the flow depth and across the channel were performed. The analysis indicates that the HCS’s originate near the channel banks, with the location of ejections and sweeps being anti-symmetrically arranged with regard to the channel centreline, and then evolve so as to occupy the entire depth of the water and the entire width of the channel. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2010-03-09 10:20:53.596

Laser micromachining has become increasing prominent in various industries given its speed, lack of tool wear, and ability to create features on the order of micrometres. Inherent stochastic variations from thermal ablation along with detrimental heat effects, however, limit the feasibility of achieving high precision. The high number of control parameters that make laser micromachining versatile also hinders optimization due to high exploration time. The introduction of high intensity nonlinear ablation leads to more precise cuts but at a much higher, often restrictive, cost. The work here shows that by combining an imaging technique frequently used in ophthalmology called optical coherence tomography (OCT) with a machining platform, in situ observation of ablation can be made. This combination, known as in-line coherent imaging (ICI), allows information to be gathered about the dynamics of the ablation process. Experimental results show that quality cutting of silicon can be achieved with thermal ablation and at a wavelength of 1070 nm. This result is surprising as silicon absorbs this wavelength very weakly at room temperature. It is shown here that a nonlinear thermal dependence in absorption allows a cascaded absorption effect to enable machining. With the aid of ICI, the model shown here is able to accurately predict the thermal ablation rate and help understand the ablation process. The high quality cutting achieved allows for a more cost efficient alternative to current techniques using ultraviolet diode-pumped solid state (UV DPSS) systems. Where thermal effects such as heat-affected zones (HAZ) cannot be overcome, high intensity nonlinear ablation allows the processing of lead zirconate titanate (PZT) for high frequency arrays (used in ultrasound applications) at speeds two orders of magnitude greater than found in the literature, and potential feature sizes (< 100 µm) in polymethyl methacrylate (PMMA) unachievable by thermal ablation. The ablation mechanism here is Coulombic explosion (CE), which is a non-thermal process. Coupled with demonstrated manual and automatic feedback abilities of ICI, the processes shown here may open up new avenues for fabrication. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2011-05-31 15:02:55.547

In the present doctoral work we have developed and tested a model for dissolved oxygen (DO) transfer from water to underlying flat and cohesive sediment beds populated with DO-absorbing bacteria. The model couples Large-Eddy Simulation (LES) of turbulent transport in the water-column, a biogeochemical model for DO transport and consumption in the sediment, and Darcy’s Law for the pore water-driven solute dispersion and advection. The model’s predictions compare well against experimental data for low friction-Reynolds numbers (Re). The disagreement for higher Re is investigated by progressively increasing the complexity of the model. A sensitivity analysis shows that the sediment-oxygen uptake (or demand, SOD) is approximately proportional to the bacterial content of the sediment layer, and varies with respect to fluid dynamics conditions, in accordance to classic high-Schmidt-number mass-transfer laws. The non- linear transport dynamics responsible for sustaining a statistically steady SOD are investigated by temporal- and-spatial correlations and with the aid of instantaneous visualizations: the near-wall coherent structures modulate the diffusive sublayer, which exhibits complex spatial and temporal filtering behaviours; its slow and quasi-periodic regeneration cycle determines the streaky structure of the DO field at the sediment-water interface (SWI), retained in the deeper layers of the porous medium. Oxygen depletion dynamics are then simulated by preventing surface re-areation with turbulent mixing driven by an oscillating low-speed current — an idealization of hypolimnetic DO depletion in the presence of a non-equilibrium periodic forcing. The oxygen distribution exhibits a self-similar pattern of decay with, during the deceleration phase, oscillations modulated by the periodic ejection of peaks of high turbulent mass flux (pumping oxygen towards the SWI), generated at the edge of the diffusive sublayer at the end of the acceleration phase. These fronts of highly turbulent mixing propagate away from the SWI, at approximately constant speed, in layers of below-average oxygen concentration. Finally, the model has been tested in a real geophysical framework, reproducing published in-situ DO measurements of a transitional flow in the bottom boundary layer of lake Alpnach. A simple model for the SOD is then derived for eventual inclusion in RANSE biogeochemical management-type models for similar applications. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2012-07-04 11:13:24.936

Aseptic loosening of artificial joints is caused by an osteolytic reaction to wear debris mediated by macrophages and other cells. Imaging these wear particles within cells can be a key process in understanding particle-cell interactions. However, the compounds used in surgical implants are not easily visualised as no tagging molecule can be added without altering the properties of the material. We were interested in using a label free optical technique known as coherent anti-Stokes Raman scattering spectroscopy (CARS) to image these particles in cells. In this thesis we studied how to use CARS to image physiologically relevant wear particles within cells. We characterised the responses from our CARS system and found them to be in good agreement to the Raman spectra we obtained for the same materials. We showed that the forward scattered CARS signal was consistently larger than the backwards scattered signal for the same size particles, and also generated a larger contrast, especially between sub-micron sized particles and the non-resonant background. Wear particles of polyethylene isolated from a pin-on-plate wear simulator were shown to be in a similar size range to those retrieved from revision tissue. When incubated in our model macrophage cells we were able to image areas of CARS signal that indicated the location of these particles in the cell. Furthermore, using multiple CARS images taken at different Raman resonances we were able to distinguish between three different polymeric compounds added to cells, showing the specificity of the technique. The inherent 3D sectioning capabilities of multiphoton microscopy were used to generate projected images of the cells and contents, as well as estimating the particle loads within cells. These results show that CARS could be an important tool in imaging intra-cellular polyethylene and characterising the interactions of wear particles with cells and the surrounding tissue.