Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 34-38). Also available via the Internet.

Thesis (doctoral)--Technische Universiteit Eindhoven, 1999. / "SPIE digital library." Originally published: Knegsel : HV Press, 1999. Includes bibliographical references and index. Also available in print version.

No / Contrast constancy is the ability to perceive object contrast independent of size or spatial frequency, even though these affect both retinal contrast and detectability. Like other perceptual constancies, it is evidence that the visual system infers the stable properties of objects from the changing properties of retinal images. Here it is shown that perceived contrast is based on an optimal thresholding estimator of object contrast, that is identical to the VisuShrink estimator used in wavelet denoising.

<p> This thesis is concerned with the improvement of the contrast ratio of flexible display devices, which are Sphere Supported Thin Film Electroluminescent (SSTFEL) devices. A two-layer coating system was selected as anti-reflection (AR) coatings to be deposited on the surface of SSTFEL devices to reduce the reflection of the ambient light from the surface of devices based on the interference concept. This AR coating was composed of an ITO layer and an ultra-thin gold layer. In order to maximize destructive interference in the visible wavelength range, the optical properties, including refractive index, transmittance and reflection of ITO films and ultra-thin gold films related to sputtering conditions have been studied. The electrical conductance of these two films has also been explored because these two layers work not only as AR coatings but also as a conductive and transparent electrode of SSTFEL devices. AFM images show that the surface morphology of ultra-thin gold films on Si substrates is similar to that on an ITO layer and on polypropylene sheets. The measurements of specular and diffuse reflectance of AR coatings on the propylene sheets and devices have been performed in detail. Results show that AR coatings have better performance on the devices when the thickness of ultra-thin gold layers and ITO layers are 3.43 to 4.01nm, and 42.5 to 45.0nm respectively. Specular and diffuse reflectance of SSTFEL devices with AR coatings are around 1.3% and 13.6% respectively, which is 6.3 times less than that of devices without AR coatings. The contrast ratio of devices with AR coatings is up to 47.9:1 at the ambient illumination level of 52.6Lux. At the ambient illumination level of 200 Lux, the contrast ratio of SSTFEL devices is 5 times higher than that of SSTFEL devices without AR coatings. </p> <p> During the research on the properties of ultra-thin gold films, it has been observed that the ultra-thin gold film has unreported optical and electric properties when its thickness is around 3nm. Its reflectance spectrum is similar to the reflectance spectrum of the substrate, whether the substrate is a glass slide or a wafer of silicon, and follows the reflectance spectrum of the substrates with an increase of several percent in visible wavelength range. The conductance of the ultra-thin gold film decreases by exponential decay as its thickness decreases for the conductance is based on tunneling effects. However, the conductance suddenly increases while the thickness of the ultra-thin gold layer is decreased at around 3 to 4 nm. This behavior has not been reported and explained. </p> / Thesis / Master of Applied Science (MASc)

This thesis compares theoretical models of ultrasound contrast agents to the acoustic response from single Microbubbles(MBs). The acoustic response was compared using a range of driving parameters. A rigid shelled contrast agent and a lipid shelled contrast agent were used in the comparison. While attempts to model the behaviour of some contrast agents at low mechanical index (MI) have been successful at higher MI the behaviour of MBs is still not well understood. Understanding and predicting the response ofMBs to medical ultrasound can lead to improvements in the clinical use of MBs through improved contrast agent design or improved signal processing. Numerical models were developed to compare to three specific cases; 1) Rigid shelled contrast agents 2) Lipid shelled contrast agents 3) Responses from lipid shelled contrast agents that are hit by subsequent driving pulses. Three models were used to compare to the responses from single rigid shelled contrast agents. Two of these models have been used before and the third was developed based on the optical observations of the responses of these rigid shelled agents at these MI. Two shelled models were used to compare to the response of single lipid shelled MBs. Using statistical methods the parameters defining the shell properties were found. The parameters that gave best agreement with the lipid shelled data was then used with a model to account for the molecular diffusion of gas from a MB and a new model to account for the optically observed shedding of the shell from a MB to compare to the multiple response from single MBs. While the theoretical prediction of an acoustic response of a suspension of MBs or the radial oscillation of single MBs has been compared before to experimental data, the successful comparison of the acoustic response of single MBs to the theoretical prediction is the first of it’s kind known to the author. The new theoretical model of the rigid shelled MB that was developed in this thesis gave better agreement with the experimental data than the other previously used models. The shell parameters of the lipid shelled MB were determined for the lowest driving amplitude and were in agreement with those measured previously from optical observations. Finally, the model for the shedding of the shell was shown to give quantitative agreement with the multiple acoustic responses from single MBs. When shedding of the shell was included the choice of constitutive equation for the shell was shown to strongly affect subsequent responses from the MB.

The search to directly image and characterize exoplanets that are initially hidden below the stellar and instrumental noise relies on the use of both extreme adaptive optics (AO) and a subsequent point spread function (PSF) subtraction pipeline. In this thesis I present my research on both real-time AO techniques and post-processing PSF subtraction techniques. First, I present a new PSF subtraction algorithm designed to image the HR 8799 debris disk using the Hubble Space Telescope. I find an over-luminosity after PSF subtraction that may be from the inner disk and/or planetesimal belt components of this system, but ultimately conclude that this is likely a non-detection as a result of telescope stability and broadband chromatic effects. Thus, assuming a non-detection, I derive upper limits on the HR 8799 dust belt mass in small grains, consistent with measurements of other debris disk halos. This important result suggests that a detection may not be possible until the rise of future, more stable space telescopes. Next, I present a new PSF subtraction algorithm applied to current campaign data from the Gemini Planet Imager (GPI), designed to optimize the GPI planet detection sensitivity of narrow orbit planets. My results, while still being investigated, seem to show that current algorithms are already optimized, and that limited gains can be achieved with my new algorithm. Finally, I apply a new real-time AO nulling technique, called super-Nyquist wavefront control (SNWFC), to be used on future 30 m class telescopes to image wide-orbit exoplanets. I demonstrate application of SNWFC in both a deterministic laboratory experiment and coronagraphic simulations using an interferometric nulling technique, suggesting that this technique would allow higher SNR characterization of wide-orbit exoplanets on future telescopes. / Graduate / 0606, 0752

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Multi-modality imaging is a possible solution for overcoming individual modality limitations. With the use of modality specific contrast agents, contrast-enhanced multi-modality imaging may provide a more comprehensive evaluation of tumour characteristics. This may be possible by combining ultrasound and magnetic resonance imaging, whose contrast agents behave differently within the microvasculature. A novel, microvascular, and leaky phantom is presented that permits ultrasound contrast agents to remain entirely within the mimicking vascular compartment while the magnetic resonance contrast agents may freely diffuse between the mimicking vasculature and tissue compartments. The results show that the phantom is a useful tool for investigating the combination of contrast-enhanced ultrasound and magnetic resonance imaging. This work motivates further combined contrast-enhanced imaging studies, with future work to incorporate additional modalities.