Thesis (M.S.)--University of Texas at Dallas, 2008. / Includes vita. Includes bibliographical references (leaves 63-65)

Thesis (MEng)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The purpose of this thesis is the description of the development of a QPSK demodulator for the Sunsat 1 groundstation. A general overview of the functioning and requirements of a typical QPSK demodulator system is given. Several methods or algorithms for clock and carrier recovery are discussed. Specific attention is given to the QPSK demodulator chipset from Philips used for the implementation of the demodulator. The digital decoding logic used to serialize the parallel I and Q datastream is explained. Finally measurement techniques for performance evaluation of QPSK systems are investigated. As part of this the implementation loss of the developed QPSK demodulator is measured. / AFRIKAANSE OPSOMMING: Die doelwit van hierdie tesis is om die ontwikkeling van 'n QPSK demodulator vir die Sunsat 1 grondstasie te beskryf. 'n Algemene oorsig oor die funksionering en vereistes van 'n tipiese QPSK demodulator stelsel word gegee. Verskeie algoritmes en tegnieke vir klok en draersein herwinning word ondersoek en bespreek. Spesifieke verwysing word telkens gemaak na die QPSK demodulasie vlokkie paar van Philips gebruik vir die implementering van die demodulator. Die digitale dekodering logika benodig vir die datastroom verpakking word ondersoek en beskryf. Laastens word daar gekyk na meettegnieke en evaluasie van QPSK demodulasie stelsels se prestasie. As deel hiervan word die implementasie verlies van die ontwikkelde QPSK demodulator stelsel gemeet.

This thesis is dedicated to developing novel photofunctional molecular materials for the applications in chemical sensing, bioimaging and electrochromic. To begin with, a brief introduction of photofunctional molecular materials and an overview of their applications in chemical sensing, bioimaging and electrochromic were presented in Chapter 1. In chapter 2, we have synthesized a series of water-soluble phosphorescent cationic iridium(III) solvato complexes (1-7) as multicolor cellular probes for imaging in living cells. All of these complexes can be dissolved in PBS. The emission of complexes can be tuned from green to red by changing the chemical structure of cyclomedtalating ligands. All complexes exhibit low cytotoxicity to living cells and exhibit cell membrane permeability and specific staining of cytoplasm. They enter the cells by the mechanism of energy-independent passive diffusion mechanisms. More importantly, complex 7 can act as a two-photon phosphorescent cellular probe, and fluorescence lifetime imaging microscopy is successfully applied for bioimaging in the presence of short-lived background fluorescence. We developed two excellent optical probes for CO2 detection in Chapter 3. The first one for the CO2 detection is a phosphorescent probe based on an iridium(III) complex with 2-phenylimidazo-[4,5-f][1,10]phenanthroline. After bubbling CO2 into the detection solution, the quenched phosphorescence by the addition of CH3COO can be recovered. Photobleaching experiment demonstrates that this phosphorescent CO2 probe shows higher photostability than some of the reported organic probes. More importantly, the time-resolved PL experiment demonstrates that this probe can be used to detect CO2 in the presence of strong background fluorescence, which improves the sensitivity and signal-to-noise ratio of the sensor in complicated media. The second one is a water-soluble fluorescent probe based on tetraphenylethene derivative. After bubbling CO2 into the detection solution, remarkable color change and fluorescence enhancement could be observed. The response of this probe to CO2 in aqueous solution is fast and the detection limit is about 2.4 × 106 M. To emphasize the practical application of this probe, a porous film was successfully fabricated by mixing the dye with sodium carboxymethyl cellulose in water, which can serve as an efficient CO2 gas sensor. More importantly, this probe exhibits low cytotoxicity towards live cells and has the ability to monitor the external CO2 concentration changes of living cells. Chapter 4 focused on the development of novel soft salt based phosphorescent probe. This type of probe consists of two oppositely charged ionic complexes with two distinguishable emission colors, which makes it a perfect candidate as a ratiometric probe. The emission color of 10 changes from blue to red with increasing pH value. 10 is cell-permeable and exhibits low cytotoxicity, and it has been successfully applied for ratiometric pH imaging with the use of confocal microscopy, demonstrating its great potential for intracellular environment monitoring. Furthermore, phosphorescence lifetime imaging experiments can detect intracellular pH variations by photoluminescence lifetime measurements, which allowed for eliminating background fluorescence and selecting long-lived phosphorescence images. Quantitative measurement of intracellular pH fluctuations caused by oxidative stress has been successfully carried out for 10 based on the pH-dependent calibration curve. A series of cationic Zn(II) complexes has been designed and synthesized in chapter 5. The photophysical properties of these Zn(II) complexes are affected by the counterions. By altering the counterions, the emission peak can be changed from 549 nm to 622 nm. Interestingly, the CIE coordinate and the emission colors can be simply tuned by adjusting the concentration of 11d in the polyether. Under an electric field of about 15 V applied onto the electrodes, the emission color of the solution of 11b-11d near the cathode changed its original emission color to sky blue. Based on this interesting electrochromic fluorescence of 11d, a quasi-solid information recording device has been successfully designed. Furthermore, data encryption has been realized by combining 1d with BODIPY, and information decoding processed has been accomplished, for the first time, by employing TPA excitation techniques, in which the large TPA cross section of 11d is differentiated from small TPA cross section of common organic dyes. Finally, Chapters 6 and 7 present the concluding remarksand the experimental details of the work described in Chapters 25

This thesis presents a simulation model of Stepped Frequency (SF) and Near Field BeamForming (NF BF) based stationary Through Wall Imaging (TWI) system to scan an object behind the wall for the reconstruction of 2D/3D image of it. The developed simulation model of TWI system requires neither the movement of the antenna array nor the object to reconstruct the image of the object behind the wall, thus overcoming the limitation of SAR/ISAR based TWI system. The simulation model of TWI system arrived at in this thesis facilitates the scan of the desired scenario in both azimuth and elevation to maximize the information available for more effective reconstruction of the Image of object behind the wall. The reconstruction of the image has been realized through conventional image processing algorithms which are devoid of inversion techniques to minimize the computational burden as well as the overall execution time of the TWI system. Contrary to the present TWI systems, the proposed simulation model has the capability for the reconstruction of the shape and contour of the object. In addition, the formulated simulation model of the TWI system overcomes the previously imposed constraints on the distances of separation between the object and the wall as well as the wall and the target. The simulation model of TWI of this thesis can handle arbitrary distances (far field or near field) between the antenna array and the wall as well as the wall and the object, which is not the case with the existing TWI systems. The thesis provides wave propagation analysis from the transmitting antenna array through the wall and the obstacle behind it and back to the receiver. Subsystems of TWI system like beamforming antenna arrays, wall and obstacles have been modeled individually. The thesis proposes a novel near field beamforming method that overcomes the usual requirement of 3D or volumetric near field radiation patterns of the beamforming array. Typical simulation results of NF BF with linear and planar arrays reveal the beam formation at a distance of one wavelength from the aperture of the array and which corresponds to the ratio of observation distance to aperture of array to be 0.2334. As a supplement to the presented NF BF a generic and versatile procedure to compute near field radiation patterns of antennas with prior knowledge of its either field or current distribution over the radiating aperture is also proposed. Examples of reconstruction of images of typical 2D and 3D objects are also illustrated in the thesis.

A Picture Archive and Communication System (PACS) is a health information technology that facilitates the electronic storage, transmission, presentation and processing of digital medical-imaging datasets. The benefits of PACS have been well-documented. It provides a means to replace traditional film-based workflows and their inherent limitations. Referring clinicians’ acceptance is a critical factor in the overall success of a PACS implementation; and given the financial implications of project failure, research into physician acceptance and meaningful use is crucial. Very few PACS acceptance studies have focused on the referring clinicians, and even less in the context of the private sector. Therefore, the problem that this research aims to address is: There is a lack of understanding on which factors influence PACS acceptance and the meaningful use thereof by referring clinicians in private practice. This explorative study follows an embedded mixed methodology approach in order to meet the research objectives, favouring a qualitative method of inquiry with the support of a quantitative strand. Electronic questionnaires were distributed to private practice referring clinicians to probe the aspects related to PACS acceptance and its meaningful use. The conceptual framework, as devised by Paré and Trudel (2007), was used as a theoretical lens to categorize and discuss the research results in terms of Project, Technological, Organizational and Behavioural factors that affect PACS acceptance and its meaningful use. The findings showed good acceptance rates, which is in line with other research conducted in this field, including research done in the public sector. Technical and Organizational factors were the most prevalent. An extension of the above-mentioned theoretical framework was proposed to assist in maintaining positive results after the project Implementation phase has been completed. This research expands the Information Technology PACS body of knowledge – by identifying both the technical and the non-technical factors that are crucial in private practice referring doctor acceptance and meaningful use. By addressing these factors, institutions can improve the likelihood of PACS project success in private practice settings. Maximising referring doctor acceptance and meaningful use could also give private practices a competitive advantage over their competitors.

The development of improved models of seismic diffraction is assisted by the availability of accurate scattering data. An acoustic scatter-mapping system was developed for the purpose of providing such data rapidly and at low cost. This system uses a source-receiver pair suspended on a trolley over the structure to be mapped. Signal generation, acquisition, processing, and plotting are performed on an AT-compatible microcomputer and a laser printer. The entire process can be performed in an automated manner within five hours, generating scatter-mapping plots in a format familiar to the geophysical industry. The system hardware was similar to those of Hilterman [1] and others referenced by him, but used a controlled source transducer. The available processing power of a microcomputer allowed the use of a 1 to 15 KHz swept-frequency source signal, similar to that used in Vibroseis and Chirp Radar, which is later crosscorrelated with received signal to provide precise scatter-mapping data for the target structure. Several examples of theoretical and experimental acoustic scatter-mappings are provided for comparison. The novelty of this system lies in its use of a swept frequency source signal. While common in the fields of seismology and radar, swept frequency source signals are new to the area of acoustic scatter mapping. When compared to a similar system using a pulsed source signal, this system produces a better controlled source signal of greater energy, resulting in a more useful resultant signal and better mapping characteristics. The system was able to map scattering from features in the target structure smaller than one percent of the crosscorrelated source signal's 37 mm dominant wavelength. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Vibrational imaging approaches including Raman microscopy and IR-absorption micro-spectroscopy can provide rich chemical information about biological samples. This dissertation contributes to improve the capabilities of vibrational microscopy in three aspects each with corresponding biological applications. First, along the line of combining electronic resonant effect with stimulated Raman scattering (SRS), we studied the spectroscopic characteristics for on-resonant SRS case and demonstrated the utility of electronic pre-resonant SRS on super-multiplexed imaging for live cells and tissue sections. Second, we provided a new light-matter interaction as a hybrid technique of Raman and fluorescence, called stimulated Raman excited fluorescence (SREF), bringing the long-sought-after goal of detecting single-molecule Raman scattering without plasmonic enhancement into view. Coupling SREF with vibrational sensing, local electric field and hydrogen-bonding environment can thus be visualized in situ. Third, we brought small vibrational probes into mid-infrared imaging for the goal of rich-information-content, high-throughput metabolic imaging. Chapter 1 introduces some basis of Raman scattering, and provides an overview of state-of-art SRS microscopy. Chapter 2 explores on the rigorous electronic resonant region with SRS (er-SRS) through suppression of electronic background and subsequent retrieval of vibrational peaks. In agreement with theoretical prediction, changing of vibrational band shapes from normal Lorentzian, through dispersive shapes, to inverted Lorentzian is observed when approaching electronic resonance. As large as 10-23 cm2 of resonance Raman cross section is estimated in er-SRS. In Chapter 3, a new light-matter interaction called stimulated Raman excited fluorescence (SREF) is studied. Through stimulated Raman pumping to an intermediate vibrational eigenstate followed by an upconversion to an electronic fluorescent state, SREF encodes vibrational resonance into the excitation spectrum of fluorescence emission. By leveraging superb sensitivity of SREF, we achieved all-far-field single-molecule Raman spectroscopy and imaging without plasmonic enhancement. Chapter 4 details the development of SREF into a novel water-sensing tool, by coupling with vibrational solvatochromism of environment-sensitive Raman mode. This new technique allows direct visualization on spatially-resolved distribution of water states inside single mammalian cells. Interesting intracellular heterogeneity of water states between nucleus and cytoplasm has been revealed. Chapter 5 demonstrates the utility of epr-SRS in super-multiplexed imaging with either commercial fluorophores in lives cells or our MARS probes on tissue sections. Multiplex protein-based tissue imaging is completed with newly-designed functional MARS dye with up to 12 channels simultaneously. Chapter 6 focus on metabolic imaging by mid-infrared (MIR) microscopy with vibrational probes. Raman scattering microscopy has made a major advance in metabolic imaging utilizing vibrational probes, yet is limited to relatively low throughput. As an alternative solution, MIR microscopy provides significantly higher cross section and exhibits as a rich-information-content, high-throughput technique with recent rapid technical advances. We introduced three types of small vibrational probes as azide, 13C and carbon-deuterium for studying dynamic metabolic activities of protein, lipids and carbohydrates in cells, small organisms and mice for the first time. Two MIR microscopy platforms as Fourier transform infrared (FTIR) absorption microscopy and discrete frequency mid-infrared (DFIR) microscopy were utilized to validate the generality of our vibrational probes and applicability for single-cell metabolic profiling and metabolism study on large-scale tissues.

This Ph.D. work is dedicated to advancements in burst-mode laser technology and their applications in MHz-rate high-speed gas-phase environments. A comprehensive computational model for simulating experimental burst-mode systems is discussed. Direct comparison of the modeled results to the output of a constructed nanosecond (ns) burst-mode laser shows agreement within a factor of 2 for output energy, the temporal domain skews positively in an appropriate manner, and the spectral domain correctly remains unchanged. The modeled output of a femtosecond (fs) burst-mode laser displays near perfect agreement with its hardware, generating only a 1.7% deviation for output energy, an 11% deviation in spectral bandwidth, and a temporal profile that correctly remains unchanged. The experimental ns to fs burst-mode lasers systems used to compare with the aforementioned model are described in detail and demonstrated for use in measurements of temperature, species, and velocity at high repetition rates. In the ns regime, a compact-footprint (0.18 m2 ) flashlamp-pumped, burst-mode Nd:YAGbased master-oscillator power-amplifier (MOPA) laser is developed with a fundamental 1064 nm output of over 14 J per burst. This portable laser system uses a directly modulated diode laser seed source to generate 10 ms duration arbitrary sequences of 500 kHz doublet or MHz singlet pulses for flow-field velocity or species measurements, respectively. In the fs regime, a flashlamp-pumped burst-mode laser system with high peak power and a broad spectral bandwidth of >10 nm is constructed without the use of nonlinear compression techniques. A mode-locked, 1064.6 nm fundamental-wavelength broadband master oscillator, a fiber amplifier/pulse stretcher, and four Nd:glass power amplifiers are used to generate a sequence of high-repetition-rate, transform-limited 234 fs pulses over a 1 ms burst duration at a 0.1 Hz burst repetition rate. The generated peak powers are 1.24 GW at 100 kHz and 500 MW at 1 MHz with M2∼1.5. An adaptation of the fs burst-mode laser is used for femtosecond laser electronic excitation tagging (FLEET) of nitrogen for tracking the velocity field in high-speed flows at kilohertz– megahertz (kHz–MHz) repetition rates without the use of added tracers. The fs burst-mode laser is used to produce 500 pulses per burst with pulses having a temporal separation as short as 1 µs, an energy of 120 µJ, and a duration of 274 fs. This enables 2 orders of magnitude higher measurement bandwidth over conventional kHz-rate FLEET velocimetry. 15 The fs burst-mode system was further improved to include a picosecond (ps) leg for hybrid fs/ps rotational coherent anti-Stokes Raman scattering (RCARS) at MHz rates. Using a common fs oscillator, the system simultaneously generates time synchronized 1061 nm, 274 fs and 1064 nm, 15.5 ps pulses with peak powers of 350 MW and 2.5 MW, respectively. The system is demonstrated for two-beam fs/ps RCARS in N2 at 1 MHz with a signal-to-noise ratio of 176 at room temperature. This repetition rate is an order of magnitude higher than previous CARS using burst-mode ps laser systems and two to three orders of magnitude faster than previous continuously pulsed fs or fs/ps laser systems. As a continuation of the above advances in fs regime, a regenerative fs burst-mode laser is discussed in detail with motivations, design layouts, and cavity physics laid out. Preliminary construction of the system with a ns seed source is underway to assess the detailed system design and evaluate the potential for optical damage due to Kerr lensing or other nonlinear effects. This system and other potential follow-on research topics are discussed.

This dissertation describes the synthesis and characterization of fluorescent semiconductor nanoparticles (NPs) in order to optimize their biomedical utility for imaging and sensing applications. While both direct and indirect bandgap semiconductor NPs have been studied, control over their emission properties vary. Quantum confinement (QC), which primarily controls the emission wavelength of nanosized semiconductors, dictates that as the size of semiconductor NPs decrease, the magnitude of the bandgap increases, resulting in changes in the observed emission wavelength: smaller NPs have a larger bandgap, and thus a bluer emission. However, surface, interfacial, or shell defects can act as non-radiative or radiative recombination sites for excitons formed within the NP; the latter results in emission competition with the bandgap transition, as described Chapters 1 and 2. Because the emission wavelengths of direct bandgap semiconductor NPs correlate with size according to the expectations of QC, and are stable in aqueous environments with high quantum efficiencies (quantum yield, QY), current research focuses on their potential biomedical applications. Chapter 3 describes red-emitting CdSe/ZnS quantum dots (QDs) that exhibit a concentration-dependent decrease in fluorescence intensity in response to the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT). A mechanistic study was performed to understand a 5-HT-dependent decrease in QD emission and calibration curves relating QD intensity loss to 5-HT concentration in ensemble and single QD studies were generated. Unfortunately, the known toxicity of CdSe-based QDs has generated interest in more benign semiconductor NPs to replace these QDs in biological applications, while maintaining the same degree of control over the emission color and QY. Bulk indirect bandgap semiconductors, such as Si, have low efficiency inter-band transitions, and Si NPs are known to contain radiative defects that can alter the emission wavelength from QC-based size expectations; these competitive emission pathways must be controlled in order for Si NPs to be successfully used in biological applications. In general, synthetic methods that gives precise control over both the particle size and surface termination are needed in order to produce emission controlled Si NPs. Relative to groups II and VI QDs, synthetic routes to prepare Si NPs are few in numbers, and the size vs. defect emission events are difficult to assign. Not only do these assignments vary amongst reports, but they also vary with particle size, solvent, sample age, and identities of the surface ligands. Si NPs have been prepared through two synthetic routes using the Zintl salt, sodium silicide (NaSi) and ammonium bromide (NH4Br) as precursors. Chapter 4 describes the synthesis performed in the solvent N,N,-dimethylformamide (DMF). This reaction produces blue-emitting Si NPs (5.02 ± 1.21 nm) that bear partial hydride surface termination. However, it was determined that the solvent was able to interact with the Si NP surface, and prevent subsequent functionalization. This observation was used advantageously, and Chapter 5 describes a one-pot Zintl salt metathesis of Si NPs (3.9 + 9.8 nm) performed in a bi-functional (amine or carboxylic acid) solvent ligand, where the observations indicated that the solvent ligands coordinate to the Si NP. The emission maxima of the Si NPs prepared from the Zintl salt metathesis exhibited a dependence on the excitation energy, and is indicative of emission that is influenced by QC, which likely originates from deeply oxide embedded 1-2 nm crystalline cores. The Si NPs prepared from the one-pot Zintl salt metathesis were exposed to metals salt ions of varying reduction potentials to determine the band edges by what will or will not be reduced (Chapter 6). By monitoring the emission intensity of the Si NPs, in addition to the UV-Vis of the metal ions, the band edge of Si NPs may be determined. The value of the band edge may lend insight into the origin of Si NP emission. To utilize fluorescent Si NPs for biological applications, red emission is strongly preferred. Unfortunately, when preparing aqueous Si NPs, red emission usually changes to blue, likely from the oxidation of the Si NP surface. Therefore, the red emission needs to be efficiently protected from surface oxidants. Because both increased chain lengths and steric modalities have been found to protect the emission properties of Si NPs, red-emitting, ester-functionalized Si NPs (5.51+1.35 nm) with varying chain lengths and ester termination moieties were prepared to determine the best method of preserving the observed red emission in the presence of potential alcoholic oxidants. By determining the best was to protect Si NPs emission, the red-emission from Si NPs may be preserved for biological applications.

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