Nous présentons une caméra à balayage de fente intégrée basée sur un système de comptage de photon unique résolu en temps (TCSPC-SC) employant l'architecture linéaire « streak » pour surmonter la limitation de l'espace inhérent aux systèmes TCSPC bidimensionnels. Cette solution permet l'intégration de fonctionnalités électroniques complexes dans les pixels sans l'inconvénient d'un faible facteur de remplissage conduisant à une faible efficacité de détection. Le TCSPC-SC se compose de deux blocs principaux: une photodiode à avalanche (SPAD) et un bloc de mesure de temps, les deux blocs sont intégrés en technologie 180 nm CMOS standard. La structure de la SPAD utilisée a été sélectionnée parmi 6 structures différentes après un processus de caractérisation précise et approfondie. Le bloc de mesure du temps se compose d'un TOC hybride capable d'atteindre des résolutions de temps élevées et ajustables avec une large dynamique de mesure grâce à un système de conversion de temps (TOC) hybride qui combine l'approche analogique basée sur un convertisseur de temps vers amplitude(TAC), et les approches numériques utilisant une boucle à verrouillage de retard (DLL) et un compteur numérique. Le TOC hybride a été spécialement conçu pour être utilisé dans un système TCSPC qui intègre une ligne de TOC nécessitant ainsi une conception appropriée pour limiter la consommation d'énergie et la surface d'occupation et parvenir à une architecture flexible et facilement extensible. Suite à la conception et la réalisation de ces deux blocs dans une technologie180 nm CMOS standard, une structure de test de la caméra à balayage de fente (TCSPC-SC) qui englobe 8 unités a été réalisée dans le but final de mettre en œuvre un modèle TCSPC-SC complet et plus large. / In this work we present a TCSPC Streak Camera (TCSPC-SC) that takes advantage of the streak mode imaging ta overcome the space limitation inherent ta 20 TCSPC sensor arrays. This cost-effective solution allows the integration of complex functionalities in the pixel without the inconvenience of low fill factor that leads ta low detection efficiency. The TCSPC~SC consists of two main building blacks: a SPAD and a time measurement black bath integrated in 180 nm Standard CMOS technology. The SPAD was selected among 6 different SPAD structures following a thorough characterization process ta fully determine its performance figures. The time measurement black consists of a hybrid TOC capable of achieving high adjustable time resolutions with large dynamic range owing ta a time conversion scheme that combines traditional Analog Time to Amplitude Converter (TAC), Digital DLL-based and counter-based TOC. Furthermore, thehybrid TOC was especially designed ta be used in a TCSPC system that incorporates an array of TDCs which required a careful design ta limit power consumption and occupation area in order to achieve a flexible and easily scalable architecture. These two building blacks were bath fabricated in a 180 nm standard CMOS technology and employed ta demonstrate a TCSPC Streak Camera(TCSPC-SC) test structure that englobes 8 units in order ta demonstrate the system's operation principle with the final aim of implementing a complete and bigger TCSPC-SC model in the near future

<p>Hypersonic flow conditions, such as temperature, pressure, and flow velocity, are challenging to measure on account of the extreme conditions experienced by a craft moving above Mach 5. At Mach 5, the temperature in stratospheric air behind a normal shock wave exceeds temperatures of 1,300 K, and as the craft speed increases, so does the temperature. At these temperatures and conditions, traditional measurement techniques such as thermocouples and pressure transducers either alter the flow path, affecting the measurement, or they do not survive the external conditions. As such, there is interest in investigating alternative ways to measure flow properties. This thesis focuses on the implementation of several optical measurement techniques designed to determine the flow temperature, density gradient, and flow velocity in a detonation driven shock tube. A detonation driven shock tube was chosen for the project as it reliably creates high-speed, low-density, gas flows that are reminiscent of hypersonic conditions. </p><p>The first optical measurement technique implemented was background oriented schlieren, a measurement technique that quantitatively provides density gradient data. Experimental data obtained at pressures up to 3,000 psia resulted in density gradients at the exit of the detonation tube in good agreement with the literature.</p><p>The detonation tube was also fitted with two fiber optic ports to gather chemiluminescence thermometry data. Both a Stellarnet Black-Comet spectrometer and a Sydor Ross 2000 streak camera were used to capture spectroscopic data at these ports, in order to determine the detonation speed and the rotational temperature of the intermediate OH* combustion products. The Stellarnet spectrometer did not have a fast enough data capture rate to gather reliable data. While the streak camera captured data quickly, we had difficulty gathering enough light from the combustion event and the gathered data was very noisy. The streak camera did however capture the time duration of the full combustion event, so if the fiber connector ports are improved this data taking method could be used in the future to gather rotational temperature data. Both measurement techniques provided some unintrusive measurements of high-speed flows, and improvements to the data taking system could provide much needed information on hypersonic flow conditions. </p>

The recent development of extreme ultraviolet (EUV) sources has increased the need for diagnostic tools, and has opened up a previously limited portion of the spectrum. With ultrafast laser systems and spectroscopy moving into shorter timescales and wavelengths, the need for nanosecond scale imaging of EUV is increasing. EUV’s high absorption has limited the number of imaging options due to the many atomic resonances in this spectrum. Currently EUV is imaged with photodiodes and X-ray CCDs. However photodiodes are limited in that they can only resolve intensity with respect to time and X-ray CCDs are limited to temporal resolution in the microsecond range. This work shows a novel approach to imaging EUV light over a nanosecond time scale, by using an EUV scintillator to convert EUV to visible light imaged by a conventional streak camera. A laser produced plasma, using a mass-limited tin based target, provided EUV light which was imaged by a grazing incidence flat field spectrometer onto a Ce:YAG scintillator. The EUV spectrum (5 nm-20 nm) provided by the spectrometer is filter by a zirconium filter and then converted by the scintillator to visible light (550 nm) which can then be imaged with conventional optics. Visible light was imaged by an electron image tube based streak camera. The streak camera converts the visible light image to an electron image using a photocathode, and sweeps the image across a recording medium. The streak camera also provides amplification and gating of the image by the means of a micro channel plate, within the image tube, to compensate for low EUV intensities. The system provides 42 ns streaked images of light with a iii temporal resolution of 440 ps at a repetition rate of 1 Hz. Upon calibration the EUV streak camera developed in this work will be used in future EUV development.

Fluorescence lifetime imaging microscopy (FLIM) is an imaging modality that is able to provide key insights into subcellular processes. When used to measure Förster resonance energy transfer (FRET), for instance, it can discern protein-protein interactions and conformational changes. This kind of information is highly useful in the drug screening process in order to determine the effectiveness of drug leads and their mechanisms of action. FLIM has yet to be successfully translated to high-content screening (HCS) platforms due to the high throughput and fine temporal and spatial resolution requirements of HCS. Our prototype HCS FLIM system uses a time-resolving instrument called a streak camera to multiplex the FLIM scanning process, allowing for 100 confocal spots to be simultaneously scanned across a sample. There have been a few major advancements to the prototype. First the fiber array used to connect the fluorescence channels to the streak camera was characterized. Its alternating fiber delay scheme was successful in greatly reducing optical crosstalk between adjacent channels. Next, an optical beam scanner for parallel excitation beams was designed and implemented, greatly improving the possible scan speeds of the system. The streak camera was upgraded to a higher repetition rate sweep, and modifications to system components and reconstruction procedures were made to accommodate the new sweep unit. A single-photon avalanche diode array was also tested as a possible replacement for the streak camera, and was found to offer photon detection efficiency advantages. Finally, improvements were made to the excitation power and optical throughput of the system in order to reduce the required exposure time. These advances to the prototype system bring it closer to realizing the requirements of HCS FLIM, and provide a clear picture for future improvements and research directions. / Thesis / Doctor of Philosophy (PhD) / Fluorescent proteins are commonly used to tag subcellular targets so that they can easily be distinguished with a fluorescence microscope. While this can help visualize where different organelles and proteins are located in the cell, a great deal more information can be gained by measuring the fluorescence lifetime at each point in the sample, which is highly sensitive to the microenvironment. Fluorescence lifetime imaging microscopy (FLIM) has the potential to be a powerful technique for testing drug leads in the drug discovery process, although current FLIM systems are not able to provide the high throughput speeds and high temporal resolution required for drug screening. This thesis project has succeeded in improving a highly parallel FLIM microscope by reducing inter-channel crosstalk, implementing an optical scanner, improving power and optical throughput, and investigating future time-resolving instruments. This progress has brought the prototype setup closer to being used in a drug screening environment.

Yes / The Molecular Stress Function (MSF) constitutive model with convective constraint release mechanism has been shown to accurately fit a large range of viscometric data, and also shown to give strong vortex growth in flows of LDPE through planar and axisymmetric contractions. This work compares simulation and experimental results for 3-D flows of Lupolen 1840H LDPE through a contraction slit; 3-D effects are introduced by using a slit with a low upstream aspect ratio of 5:3. Comparisons are made with vortex opening angles obtained from streak photography, and also with stress birefringence measurements. The comparisons are made with two versions of the convective constraint release (CCR) mechanism. The simulated vortex angles for one version of the CCR mechanism are found to approach what is seen experimentally. The best-fit value for the stress optical coefficient was found to vary between CCRs and to decrease with flow rate. This is partially explained by different centreline elongational rates with the two CCRs, which in turn is related to different opening angles. A 3-D simulation is compared to the corresponding 2-D simulation. It is shown that both velocity vectors and birefringence show only small changes to around 60% of the distance to the side wall.

All members of the genus Xanthomonas are considered to be plant pathogenic, with specific pathovars infecting several high value agricultural crops. One of these pathovars, X. campestris pv. zeae (as this is only a proposed name it will further on be referred to as Xanthomonas BLSD) the causal agent of bacterial leaf steak of maize, has established itself as a widespread significant maize pathogen within South Africa. Insufficient information about the present distribution of the pathogen is available. The main aim of the study was thus to isolate and characterise the pathogen using molecular methods. Results demonstrated that the causal agent of bacterial leaf streak disease (Xanthomonas BLSD: potentially X. campestris pv. zeae) was widely distributed within the major maize cultivation regions of South Africa. Most of the isolates collected originated from the Highveld maize production provinces (North West, Free State, Gauteng and Mpumalanga provinces) as well as from irrigated maize fields in the Northern Cape province. The XgumD gene marker was used to determine if the isolates belonged to the genus Xanthomonas. The gumD gene fragment is located within the gumB-gumM region of the operon and is conserved among Xanthomonas species. This gene fragment is partially responsible for xanthan production. This marker was amplified from all isolates and a selected number were sequenced. The marker was only able to confirm that the causal agent was a member of the genus Xanthomonas. PCR methods were used for the characterisation of the isolates. This included PCR and sequencing of ribosomal RNA- gyraseB and gumD genes. A fingerprinting method BOX-PCR was also employed. Good quality DNA of sufficient quantities was obtained from the various isolates. Amplification produced no non-specific amplification products. This resulted in good quality sequences that could be analysed using bioinformatics tools. Phylogenetic analyses of the ribosomal RNA and gyraseB genes could not detect differences amongst the 47 Xanthomonas BLSD isolates. However, these genes were able to distinguish between the type strain of these isolates and various Xanthomonas species and pathovars. From all three neighbour joining trees the Xanthomonas BLSD isolates had close association with X. axonopodis pv. vasculorum strain ATCC 35938. For the 16S rRNA gene there exists no sequence differences between Xanthomonas BLSD and X. axonopodis pv. vasculorum strain ATCC 35938. A single nucleotide difference was observed between Xanthomonas BLSD and X. axonopodis pv. vasculorum strain ATCC 35938 for the 23S rRNA gene. The gyraseB gene detected a total of six nucleotide variations between these two Xanthomonas species. For all of the phylogenetic trees there was no clustering of Xanthomonas BLSD with X. campestris pathovars. Genetic profiling (via BOX-PCR) based on present/absent analysis revealed no variations amongst the Xanthomonas BLSD isolates. All isolates shared an identical pattern produced by 12 distinct PCR products. This profiling technique did differentiate between the isolates of Xanthomonas BLSD and X. axonopodis pv. vasculorum strain ATCC 35938. Their profiles shared common bands, but differed in the number and overall pattern of the bands. These results suggest two main conclusions: (i) Xanthomonas BLSD has a clonal origin with geographical separation not impacting genetic variation. The fact that all the isolates appear to be clonal may imply that when resistant maize cultivars are developed these should be resistant to all isolates of the pathovar irrespective of their geographical origin. This is a suggestion that will have to be corroborated using more isolates and additional genetic fingerprinting techniques (ii) the Xanthomonas BLSD isolates from this study may not belong to X. campestris. Further studies using other markers should be conducted to determine the real identity of Xanthomonas BLSD. / MSc Environmental Sciences, North-West University, Potchefstroom Campus, 2015

All members of the genus Xanthomonas are considered to be plant pathogenic, with specific pathovars infecting several high value agricultural crops. One of these pathovars, X. campestris pv. zeae (as this is only a proposed name it will further on be referred to as Xanthomonas BLSD) the causal agent of bacterial leaf steak of maize, has established itself as a widespread significant maize pathogen within South Africa. Insufficient information about the present distribution of the pathogen is available. The main aim of the study was thus to isolate and characterise the pathogen using molecular methods. Results demonstrated that the causal agent of bacterial leaf streak disease (Xanthomonas BLSD: potentially X. campestris pv. zeae) was widely distributed within the major maize cultivation regions of South Africa. Most of the isolates collected originated from the Highveld maize production provinces (North West, Free State, Gauteng and Mpumalanga provinces) as well as from irrigated maize fields in the Northern Cape province. The XgumD gene marker was used to determine if the isolates belonged to the genus Xanthomonas. The gumD gene fragment is located within the gumB-gumM region of the operon and is conserved among Xanthomonas species. This gene fragment is partially responsible for xanthan production. This marker was amplified from all isolates and a selected number were sequenced. The marker was only able to confirm that the causal agent was a member of the genus Xanthomonas. PCR methods were used for the characterisation of the isolates. This included PCR and sequencing of ribosomal RNA- gyraseB and gumD genes. A fingerprinting method BOX-PCR was also employed. Good quality DNA of sufficient quantities was obtained from the various isolates. Amplification produced no non-specific amplification products. This resulted in good quality sequences that could be analysed using bioinformatics tools. Phylogenetic analyses of the ribosomal RNA and gyraseB genes could not detect differences amongst the 47 Xanthomonas BLSD isolates. However, these genes were able to distinguish between the type strain of these isolates and various Xanthomonas species and pathovars. From all three neighbour joining trees the Xanthomonas BLSD isolates had close association with X. axonopodis pv. vasculorum strain ATCC 35938. For the 16S rRNA gene there exists no sequence differences between Xanthomonas BLSD and X. axonopodis pv. vasculorum strain ATCC 35938. A single nucleotide difference was observed between Xanthomonas BLSD and X. axonopodis pv. vasculorum strain ATCC 35938 for the 23S rRNA gene. The gyraseB gene detected a total of six nucleotide variations between these two Xanthomonas species. For all of the phylogenetic trees there was no clustering of Xanthomonas BLSD with X. campestris pathovars. Genetic profiling (via BOX-PCR) based on present/absent analysis revealed no variations amongst the Xanthomonas BLSD isolates. All isolates shared an identical pattern produced by 12 distinct PCR products. This profiling technique did differentiate between the isolates of Xanthomonas BLSD and X. axonopodis pv. vasculorum strain ATCC 35938. Their profiles shared common bands, but differed in the number and overall pattern of the bands. These results suggest two main conclusions: (i) Xanthomonas BLSD has a clonal origin with geographical separation not impacting genetic variation. The fact that all the isolates appear to be clonal may imply that when resistant maize cultivars are developed these should be resistant to all isolates of the pathovar irrespective of their geographical origin. This is a suggestion that will have to be corroborated using more isolates and additional genetic fingerprinting techniques (ii) the Xanthomonas BLSD isolates from this study may not belong to X. campestris. Further studies using other markers should be conducted to determine the real identity of Xanthomonas BLSD. / MSc Environmental Sciences, North-West University, Potchefstroom Campus, 2015

No description available.

<p>Transition from laminar to turbulent flow has beentraditionally studied in terms of exponentially growingeigensolutions to the linearized disturbance equations.However, experimental findings show that transition may occuralso for parameters combinations such that these eigensolutionsare damped. An alternative non-modal growth mechanism has beenrecently identified, also based on the linear approximation.This consists of the transient growth of streamwise elongateddisturbances, mainly in the streamwise velocity component,called streaks. If the streak amplitude reaches a thresholdvalue, secondary instabilities can take place and provoketransition. This scenario is most likely to occur in boundarylayer flows subject to high levels of free-stream turbulenceand is the object of this thesis. Different stages of theprocess are isolated and studied with different approaches,considering the boundary layer flow over a flat plate. Thereceptivity to free-stream disturbances has been studiedthrough a weakly non-linear model which allows to disentanglethe features involved in the generation of streaks. It is shownthat the non-linear interaction of oblique waves in thefree-stream is able to induce strong streamwise vortices insidethe boundary layer, which, in turn, generate streaks by thelift-up effect. The growth of steady streaks is followed bymeans of Direct Numerical Simulation. After the streaks havereached a finite amplitude, they saturate and a new laminarflow, characterized by a strong spanwise modulation isestablished. Using Floquet theory, the instability of thesestreaks is studied to determine the features of theirbreakdown. The streak critical amplitude, beyond which unstablewaves are excited, is 26% of the free-stream velocity. Theinstability appears as spanwise (sinuous-type) oscillations ofthe streak. The late stages of the transition, originating fromthis type of secondary instability, are also studied. We foundthat the main structures observed during the transition processconsist of elongated quasi-streamwise vortices located on theflanks of the low speed streak. Vortices of alternating signare overlapping in the streamwise direction in a staggeredpattern.</p><p><strong>Descriptors:</strong>Fluid mechanics, laminar-turbulenttransition, boundary layer flow, transient growth, streamwisestreaks, lift-up effect, receptivity, free-stream turbulence,nonlinear mechanism, streak instability, secondary instability,Direct Numerical Simulation.</p> / QC 20100518

This thesis examines the response of a representative agent investor to sequences (streaks) of quarterly earnings surprises over a period of twelve quarters using the United States S&P500 constituent companies sample frame in the years 1991 to 2006. This examination follows the predictive performance of the representative agent model of Rabin (2002b) [Inference by believers in the law of small numbers. The Quarterly Journal of Economics. 117(3).p.775 816] and Barberis, Shleifer, and Vishny (1998) [A model of investor sentiment. Journal of Financial Economics. 49. p.307 343] for an investor who might be under the influence of the law of small numbers, or another closely related cognitive bias known as the gambler s fallacy. Chapters 4 and 5 present two related empirical studies on this broad theme. In chapter 4, for successive sequences of annualised quarterly earnings changes over a twelve-quarter horizon of quarterly earnings increases or falls, I ask whether the models can capture the likelihood of reversion. Secondly, I ask, what is the representative investor s response to observed sequences of quarterly earnings changes for my S&P500 constituent sample companies? I find a far greater frequency of extreme persistent quarterly earnings rises (of nine quarters and more) than falls and hence a more muted reaction to their occurrence from the market. Extreme cases of persistent quarterly earnings falls are far less common than extreme rises and are more salient in their impact on stock prices. I find evidence suggesting that information discreteness; that is the frequency with which small information about stock value filters into the market is one of the factors that foment earnings momentum in stocks. However, information discreteness does not subsume the impact of sequences of annualised quarterly earnings changes, or earnings streakiness as a strong candidate that drives earnings momentum in stock returns in my S&P500 constituent stock sample. Therefore, earnings streakiness and informational discreteness appear to have separate and additive effects in driving momentum in stock price. In chapter 5, the case for the informativeness of the streaks of earnings surprises is further strengthened. This is done by examining the explanatory power of streaks of earnings surprises in a shorter horizon of three days around the period when the effect of the nature of earnings news is most intense in the stock market. Even in shorter windows, investors in S&P500 companies seem to be influenced by the lengthening of negative and positive streaks of earnings surprises over the twelve quarters of quarterly earnings announcement I study here. This further supports my thesis that investors underreact to sequences of changes in their expectations about stock returns. This impact is further strengthened by high information uncertainties in streaks of positive earnings surprise. However, earnings streakiness is one discrete and separable element in the resolution of uncertainty around equity value for S&P 500 constituent companies. Most of the proxies for earnings surprise show this behaviour especially when market capitalisation, age and cash flow act as proxies of information uncertainty. The influence of the gambler s fallacy on the representative investor in the presence of information uncertainty becomes more pronounced when I examine increasing lengths of streaks of earnings surprises. The presence of post earnings announcement drift in my large capitalised S&P500 constituents sample firms confirms earnings momentum to be a pervasive phenomenon which cuts across different tiers of the stock markets including highly liquid stocks, followed by many analysts, which most large funds would hold.