International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / There are many applications for High-speed photography, and most rely on film as the primary medium of data acquisition. One such application of interest to the military services is the study of stores separation from aircraft. This type of testing has traditionally used high-speed film to gather data, however, there are many disadvantages to using film, such as the high cost of raw film, as well as the high processing expense after it has been exposed. In addition, there is no way to review data from film until it has been processed, nor is there any way to preview in real-time other conditions such as lighting which may affect the outcome of a test event. This paper discusses the characteristics of television systems with respect to motion picture systems, the challenges of recording and transmitting pictures, as well as the nature of what the first and eventual desired systems might be.

<p>'Image volumes' refer to realizations of images in other dimensions such as time, spectrum, and focus. Recent advances in scientific, medical, and consumer applications demand improvements in image volume capture. Though image volume acquisition continues to advance, it maintains the same sampling mechanisms that have been used for decades; every voxel must be scanned and is presumed independent of its neighbors. Under these conditions, improving performance comes at the cost of increased system complexity, data rates, and power consumption. </p><p>This dissertation explores systems and methods capable of efficiently improving sensitivity and performance for image volume cameras, and specifically proposes several sampling strategies that utilize temporal coding to improve imaging system performance and enhance our awareness for a variety of dynamic applications. </p><p>Video cameras and camcorders sample the video volume (x,y,t) at fixed intervals to gain understanding of the volume's temporal evolution. Conventionally, one must reduce the spatial resolution to increase the framerate of such cameras. Using temporal coding via physical translation of an optical element known as a coded aperture, the compressive temporal imaging (CACTI) camera emonstrates a method which which to embed the temporal dimension of the video volume into spatial (x,y) measurements, thereby greatly improving temporal resolution with minimal loss of spatial resolution. This technique, which is among a family of compressive sampling strategies developed at Duke University, temporally codes the exposure readout functions at the pixel level.</p><p>Since video cameras nominally integrate the remaining image volume dimensions (e.g. spectrum and focus) at capture time, spectral (x,y,t,\lambda) and focal (x,y,t,z) image volumes are traditionally captured via sequential changes to the spectral and focal state of the system, respectively. The CACTI camera's ability to embed video volumes into images leads to exploration of other information within that video; namely, focal and spectral information. The next part of the thesis demonstrates derivative works of CACTI: compressive extended depth of field and compressive spectral-temporal imaging. These works successfully show the technique's extension of temporal coding to improve sensing performance in these other dimensions.</p><p>Geometrical optics-related tradeoffs, such as the classic challenges of wide-field-of-view and high resolution photography, have motivated the development of mulitscale camera arrays. The advent of such designs less than a decade ago heralds a new era of research- and engineering-related challenges. One significant challenge is that of managing the focal volume (x,y,z) over wide fields of view and resolutions. The fourth chapter shows advances on focus and image quality assessment for a class of multiscale gigapixel cameras developed at Duke.</p><p>Along the same line of work, we have explored methods for dynamic and adaptive addressing of focus via point spread function engineering. We demonstrate another form of temporal coding in the form of physical translation of the image plane from its nominal focal position. We demonstrate this technique's capability to generate arbitrary point spread functions.</p> / Dissertation

In this thesis I explore how migratory properties of the model organism Dictyostelium discoideum are influenced by dimensionality and topology of the environment that surrounds the cell. Additionally, I sought to develop a microfluidic device able to measure mechanical properties of single cells with a sufficient throughput to account for the inherent heterogeneity of biological samples. Throughout this thesis I made use of microfabrication methods such as photo-lithography and soft-lithography, to develop ad hoc microstructured substrates. These tools enabled me to tackle different biological and biomedical questions related to cell migration and cell mechanics. Confining cells into channels with low dimensionality appeared to regulate the velocity of cellular locomotion, as well as the migration strategy adopted by the cell. Spatial confinement induced an altered arrangement of the acto-myosin cytoskeleton and microtubules. Moreover, the spatial constraint resulted in a simplified, mono-dimensional migration, characterised by constant average speed. Additionally, some cellular processes tended to occur in a periodic fashion, upon confinement. Interestingly, if Dictyostelium cells migrated through asymmetric bifurcating micro- channels, they appeared to be able to undergo a ’decision-making’ process leading to a directional bias. Although the biophysical mechanism underlying this response is yet to be understood, the data shown in this thesis suggest that Dictyostelium cells respond to differences in local concentrations of chemoattractants. The speed of a cell that crawls in a channel also depends on the cell’s stiffness, that in turn represents a measure of the density and structure of its cytoskeleton. To date, only a few methods have been developed to investigate cell mechanics with sufficient throughput. This motivated my interest in developing a microfluidic-based device that, exploiting the recording capabilities of a modern high speed camera, enabled me to assess the cellular mechanical properties at a rate greater than 10,000 cells per second, without the need for cell labelling. In this thesis I presented an example of how this method can be employed to detect differences between healthy and cancerous prostate cells, as well as to differentiate between prostate and bladder cancer cells based on their mechanical response. In conclusion, the work presented in this thesis highlights the interdisciplinarity required to investigate complex biological and biomedical problems. Specifically, the use of quantitative approaches that span from microtechnology, live imaging, computer vision and computational modelling enabled me to investigate novel biological processes as well as to explore new diagnostic technologies that aim to promote the improvement of the future healthcare.

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Reinforcement of soil enables a soil slope or wall to be retained at angles steeper than the soil material’s angle of repose. Geosynthetic Reinforced Soil (GRS) systems enable shortened construction time, lower cost, increased seismic performance and potentially improve aesthetic benefits over their conventional retaining wall counterparts such as gravity and cantilever type retaining walls. Experience in previous earthquakes such as Northridge (1994), Kobe (1995), and Ji-Ji (1999) indicate good performance of reinforced soil retaining walls under high seismic loads. However, this good performance is not necessarily due to advanced understanding of their behaviour, rather this highlights the inherent stability of reinforced soil against high seismic loads and conservatism in static design practices. This is an experimental study on a series of seven reduced-scale GRS model walls with FHR facing under seismic excitation conducted using a shake-table. The models were 900 mm high, reinforced by five layers of stiff Microgrid reinforcement, and were founded on a rigid foundation. The soil deposit backfill was constructed of dry dense Albany sand, compacted by vibration (average Dr = 90%). The influence of the L/H ratio and wall inclination on seismic performance was investigated by varying these important design parameters throughout the testing programme. The L/H ratio ranged from 0.6 – 0.9, and the walls were primarily vertical except for one test inclined at 70o to the horizontal. During testing, facing displacements and accelerations within the backfill were recorded at varying levels of shaking intensity. Mechanisms of deformation, in particular, were of interest in this study. Global and local deformations within the backfill were investigated using two methods. The first utilised coloured horizontal and vertical sand markers placed within the backfill. The second utilised high-speed camera imaging for subsequent analysis using Geotechnical Particle Image Velocimetry (GeoPIV) software. GeoPIV enabled shear strains to be identified within the soil at far smaller strain levels than that rendered visible by eye using the coloured sand markers. The complementary methods allowed the complete spatial and temporal development of deformation within the backfill to be visualised. Failure was predominantly by overturning, with some small sliding component. All models displayed a characteristic bi-linear displacement-acceleration curve, with the existence of a critical acceleration, below which deformations were minor, and above which ultimate failure occurs. During failure, the rate of sliding increased significantly. An increase in the L/H ratio from 0.6 to 0.9 caused the displacement-acceleration curve to be shallower, and hence the wall to deform less at low levels of acceleration. Accelerations at failure also increased, from 0.5g to 0.7g, respectively. A similar trend of increased seismic performance was observed for the wall inclined at 70o to the horizontal, when compared to the other vertical walls. Overturning was accompanied by the progressive development of multiple inclined shear surfaces from the wall crest to the back of the reinforced soil block. Failure of the models occurred when an inclined failure surface developed from the lowest layer of reinforcement to the wall crest. Deformations largely confirmed the two-wedge failure mechanism proposed by Horii et al. (2004). For all tests, the reinforced soil block was observed to demonstrate non-rigid behaviour, with simple shearing along horizontal planes as well as strain localisations at the reinforcement or within the back of the reinforced soil block. This observation is contrary to design, which assumes the reinforced soil block to behave rigidly.

This thesis presents a combined numerical and experimental study on the response of kidney cells to shock waves. The motivation was to develop a mechanistic model of cell deformation in order to improve the clinical use of shock waves, by either enhancing their therapeutic action against target cells or minimising their impact on healthy cells. An ultra-high speed camera was used to visualise individual cells, embedded in tissue-mimicking gel, in order to measure their deformation when subject to a shock wave from a clinical shock wave source. Advanced image processing was employed to extract the contour of the cell from the images. The evolution of the observed cell contour revealed a relatively small deformation during the compressional phase and a much larger deformation during the tensile phases of a shock wave. The experimental observations were captured by a numerical model which describes the volumetric cell response with a bilinear Equation of State and the deviatoric cell response with a viscoelastic framework. Experiments using human kidney cancer cells (CAKI-2) and noncancerous kidney cells (HRE and HK-2) were compared to the model in order to determine their mechanical properties. The differences between cancerous and noncancerous cells were exploited to demonstrate a design process by which shock waves may be able to improve the specificity on targeted cancer cells while having minimal effect on normal cells. The cell response to shock waves was studied in a more biophysically realistic environment to include influence of cell size, shape and orientation, and the presence of neighbouring cells. The most significant difference was predicted when cells were in a cluster in which case the presence of neighbouring cells resulted in a four-fold increase on the von Mises stress and the membrane strain. Finally the numerical model was extended to capture the effect of cell damage using one of two paradigms. In the first paradigm the model captured microdamage during one shock wave but then assumed that the cell recovered by the time the next shock wave arrived. The second model allowed microdamage to accumulate with increasing number of shock waves. These models may be able to explain the strong effect that shock wave loading rate has on tissue damage. In conclusion a validated numerical model has been developed which provides a mechanistic understanding of how cells respond to shock waves. The model has application in suggesting improved strategies for current uses of shock waves, e.g., lithotripsy, as well as opening up new indications such as cancer treatment.

The development of ultrasound contrast agents, or microbubbles, over the past 40 years has increased the possibilities for diagnostic imaging, although, more recently they have been proposed as a new vehicle for delivery of drugs and genes. However, there yet remains a considerable lack of fundamental understanding of microbubble behaviour under ultrasound excitation which has restricted their translation to therapeutic use. This project focussed on three key areas relating to the generation, observation, and bioeffects of microbubbles and the ultrasound used in their excitation. The experimental endeavour involved first, a full characterisation of the performance of a rotating mirror high-speed camera (Cordin 550-62) that was previously used by our group [and others] to investigate microbubble dynamics. Specifically, the investigation begins with an assessment of the frame-rate reporting accuracy of the system, a key aspect to the robustness of quantitative measurements extracted from recorded image sequences. This is then followed by the demonstration of a novel method of analysis for examining the image formation process in this type of camera, which facilitates a sensor-by-sensor assessment of performance that was not previously realised. Consolidating with previous work from within the group, this new analysis method was used to clarify previous data, and in the process suggested the presence of a temporal anomaly embedded within recorded images. In addition, the analysis also revealed empirical evidence for the mechanisms leading to this anomaly. Following on, a holographic optical tweezer system was developed for the purpose of exercising precise spatial control over microbubbles within their experimental environment. By positioning microbubbles in specific arrangements, interesting behaviours that were not previously achieved experimentally in the context of shelled microbubbles, were observed. Furthermore, by careful positioning of microbubbles within the imaging plane, it was possible to exploit the temporal anomaly present in the camera to greatly improve the integrity of data recorded, and to also operate in an enhanced imaging mode. Group aspirations to accelerate the development of therapeutic microbubbles had previously generated some early work on the in-house generation of bespoke bubble populations using microfluidic lab-on-a-chip techniques. In order to facilitate further development in this area, a finite-element computational model was herein developed to aid next generation chip design. Finally, in a slightly different context, considering not only the mechanical effect a microbubble may effect in a therapeutic treatment, a single biological cell assay was developed in order to probe any mechanical effects that were induced by the excitation ultrasound itself. Capitalising on the precise force control possible with atomic force spectroscopy, the elastic moduli of cells pre- and post-ultrasound insonation (sans microbubbles) were recorded. These new developments have extended the group capability and expertise in the areas of high-speed imaging, experimental observations of microbubble dynamics and with microfluidic generation of microbubbles. Additionally, the insights garnered have both served to consolidate the group's previous and as yet unpublished data, opening the way for circulation with absolute confidence in the integrity of that data.

Ultrasound, applied in combination with microbubbles, has potential as a means to enhance the uptake of therapeutic agents, which could include drugs and nucleic acids, into biological cells. This process is commonly referred to as 'sonoporation', and the enhanced uptake can be caused through the incident ultrasonic pressure fi eld causing radial oscillations (cavitation) in the microbubbles, amongst other possibilities. However, the mechanisms responsible for any resultant increase in cell membrane permeability are not yet fully understood. This project focussed on achieving a more fundamental understanding of these salient processes by building on a platform of previous work within the group. One strand of the project involved a complete characterisation of the performance of a rotating mirror high speed camera (Cordin 550-62) that was previously used by our group [and others] to investigate microbubble cavitation phenomena and interactions with proximal cell membranes. Speci cally, I present herein an investigation into the image formation process with this type of camera, the essence of which stymied previous data interpretations. I demonstrate that an inherent asynchrony in the exposure of pixels within individual image frames leads to a temporal anomaly. This was achieved using low cost, flashing LED lights and resulted in the extraction of an algorithm to correct for the temporal anomaly. In a slightly diff erent context, the delivery of suitable ultrasonic fields is necessary to achieve a uniform treatment across a therapeutic target. This thesis also reports on a study on the design of ultrasonic lenses to alter the focal region of a focussed ultrasound transducer with the aim of producing focal regions that can enable sonoporation of tumours of varying sizes. We show that the use of lenses can be an inexpensive alternative to more complex systems such as phased array transducers. Design modelling and experimental testing of lens prototypes are presented along with preliminary results with tissue mimicking polyacrylamide gel phantoms. The target environment in which the process of sonoporation will be clinically useful (i.e. in the physiological circulation) can be simpli ed as a microfluidic system. One strategy for bubble mediated therapy involves the use of a pro-drug approach, that is, when two otherwise benign ingredients are loaded onto separate microbubble populations, but can become mixed at the anatomical target site by the action of focussed ultrasound whereupon a potent drug is produced. The required mixing can be achieved by the violent coalescence of nearby cavitating bubbles, their reaction product then being released and di ffused into the interiour of nearby cells through sonoporation. A study related to this field is presented here where laser induced thermocapillary flows are shown to cause mixing of the content of a drop in a microfluidic channel in a bid to understand the mixing process at a level that may assist future microbubble engineering strategy. To summarise then, the work presented in this thesis has consolidated earlier unpublished data sets achieved by the group, providing new and exacting experimental evidence and an accurate algorithm that will facilitate post-processing of that earlier data (Chapters 2-3). Moreover, group aspirations to translate earlier in-vitro work on sonoporation towards next phase medical-phantom exposures have been boosted through the provision of a new direction involving acoustic lensing, the experimental data from which was used to completely validate existing models for our own design scenarios (Chapter 4). Finally, previous unpublished observations on microbubble coalescence undertaken by the group suggested a means to implement pro-drug delivery with direct in-situ mixing. Such suggestions were explored within microfluidic contexts using lasers to control and visualise the mixing processes that might arise in such situations (Chapter 5). All of these new insights have served to consolidate the group's previous and as yet unpublished data, opening the way for dissemination with confidence in the integrity of that data, and have also extended group capability and expertise in the areas of MHz-rate high speed framing cameras, the fabrication of acoustic lenses, and with microfluidic mixing.

This study presents quantitative results on the effect on individual fiber length during fiber flocculation. Flocculation was induced by a cationic polyacrylamide (cPAM). A high speed camera recorded 25 second video clips. The videos were image-analyzed and the fiber length and the amount of fiber in each sample were measured. Prior to the flocculation process, fibers were fractionated into short and long fibers. Trials were conducted using the unfractionated fiber, short fiber, and long fiber. The short and long fibers were mixed in several trials to study the effect of fiber length. The concentration of cPAM was varied as well as the motor speed of the impeller (RPM). It was found that the average fiber length decreased more rapidly with increasing motor speed. Increasing the concentration of cPAM also led to a greater decrease in average fiber length. A key finding was that a plateau was reached where further increasing the amount of cPAM had no effect. Hence, fibers below a critical length resisted flocculation even if the chemical dose or shear was increased. This critical length was related to the initial length of the fiber.

Understanding the physics governing primary atomization of high pressure fuel sprays is of paramount importance to accurately model combustion in direct injection engines. The small length and time scales of features that characterize this process falls below the resolution power of typical grids in CFD simulations, which necessitates the inclusion of physical models (sub-models) to account for unresolved physics. Unfortunately current physical models for fuel spray atomization used in engine CFD simulations are based on significant empirical scaling because there is a lack of experimental data to understand the governing physics. The most widely employed atomization sub-model used in current CFD simulations assumes the spray atomization process to be dominated by aerodynamically-driven surface instabilities, but there has been no quantitative experimental validation of this theory to date. The lack of experimental validation is due to the high spatial and temporal resolutions required to simultaneously to image these instabilities, which is difficult to achieve. The present work entails the development of a diagnostic technique to obtain high spatial and temporal resolution images of jet breakup and atomization in the near nozzle region of Gasoline Direct Injection (GDI) sprays. It focuses on the optical setup required to achieve maximum illumination, image contrast, sharp feature detection, and temporal tracking of interface instabilities for long-range microscopic imaging with a high-speed camera. The resolution and performance of the imaging system is characterized by evaluating its modulation transfer function (MTF). The setup enabled imaging of GDI sprays for the entire duration of an injection event (several milliseconds) at significantly improved spatial and temporal resolutions compared to historical spray atomization imaging data. The images show that low to moderate injection pressure sprays can be visualized with a high level of detail and also enable the tracking of features across frames within the field of view (FOV)