Thesis (M.S.M.E.)--University of Delaware, 2006. / Principal faculty advisor: Kausik Sarkar, Dept. of Mechanical Engineering. Includes bibliographical references.

This article presents an analysis of German nicht...sondern... (contrastive not...but...) which departs from the commonly held view that this construction should be explained by appeal to its alleged corrective function. It will be demonstrated that in nicht A sondern B (not A but B), A and B just behave like stand-alone unmarked answers to a common question Q, and that this property of sondern is presuppositional in character. It is shown that from this general observation many interesting properties of nicht...sondern... follow, among them distributional differences between German 'sondern' and German 'aber' (contrastive but, concessive but), intonational requirements and exhaustivity effects. sondern's presupposition is furthermore argued to be the result of the conventionalization of conversational implicatures.

Flicker defined form (FDF) is a temporally-dependent illusion created by the counterphase flicker of randomly positioned element dots, that preferentially stimulates the magnocellular system. Previous studies have found improvement with peripheral presentation, a resistance to blur and a dependence on high temporal frequencies. (Quaid & Flanagan, 2005a; Quaid & Flanagan, 2005b). Although it is seemingly very different from most luminance defined, static stimuli, it is still unknown in what ways it differs. The current study aimed to determine how FDF varies or is similar to static, luminance defined stimuli. Current results showed that FDF could be matched to particular spatial frequencies, and improved with increasing background structure and area. Shapes could be discriminated from each other and recognized. These results suggest that although FDF is dependent on motion pathways for temporal dynamic perception, it could also benefit from the input of form perception pathways, depending on the cues present in the stimulus (e.g. background structure, area). Results also showed that FDF does not benefit from Gestalt rules of contour closure, unlike some static stimuli, although related studies have shown that FDF could still be detected in spite of blur. These studies suggest that FDF appears to rely on motion perception pathways, areas such as MT, but is easier to perceive at times due to overlap in function with shape perception pathways, areas such as IT. As such FDF shares many characteristics with other motion-defined-form stimuli, but uniquely shares aspects of form vision.

In these days, nanomaterials are applied in a variety of biomedical applications including magnetic resonance imaging (MRI), cell imaging, drug delivery, and cell separation. Most MRI contrast agents affect the longitudinal relaxation time (T1) and transverse relaxation time (T2) of water protons in the tissue and result in increased positive or negative contrast. Here, we report the optimization of r1 (1/T1) or r2 (1/T2) relaxivity dynamics with diameter controlled gadolinium oxide nanocrystals (2~22 nm) and iron based magnetic nanocrystals (4 ~33 nm). The r1 and r2 MR relaxivity values of hydrated nanocrystals were optimized and examined depending on their core diameter, surface coating, and compositions; the high r1 value of gadolinium oxide was 40-60 S-1mM-1, which is 10-15 fold higher than that of commercial Gd (III) chelates (4.3~4.6 S-1mM-1). Moreover, in vitro toxicological studies revealed that polymer coated nanocrystals suspensions had no significant effect on human dermal fibroblast (HDF) cells even at high concentration. Towards multimodal imaging or multifunctional ability, we developed the iron oxide/QDs complexes, which consist of cores of iron oxide that act as nucleation sites for fluorescent QDs. The choice of variable QDs helped to visualize and remove large iron oxide materials in a magnetic separation. Additionally, diluted materials concentrated on the magnet could be fluorescently detected even at very low concentration. The designed MRI or multifunctional nanomaterials will give great and powerful uses in biomedical applications.

Evolution of vulnerable carotid plaques are crucial reason for cerebral ischemic strokes and identifying them in the early stage can become very important in avoiding the risk of stroke. In order to improve the identification and quantification accuracy of infancy plaques better visualization techniques are needed. Improving the visualization and quantification of neovascularization in carotid plaque using contrast enhanced ultrasound imaging still remains a challenging task. In this thesis work, three optimization techniques are proposed, which showed an improvement in the sensitivity of contrast agents when compared to the conventional clinical settings and insonation strategies. They are as follows:1) Insonation at harmonic specific (2nd harmonic) resonance frequency instead of resonance frequency based on maximum energy absorption provides enhanced nonlinear contribution.2) At high frequency ultrasound imaging, shorter pulse length will provide improved harmonic signal content when compared to longer pulse lengths. Applying this concept to multi- pulse sequencing (Pulse Inversion and Cadence contrast pulse sequencing) resulted in increased magnitude of the remaining harmonic signal after pulse summations.3) Peak negative pressure optimization of Pulse Inversion and Cadence contrast pulse sequencing was showed to further enhance the nonlinear content of the backscattered signal from contrast microbubbles without increasing the safety limits, defined by the mechanical index.The results presented in this thesis are based on computational modeling (Bubblesim software) and as a future continuation we plan to verify the simulation results with vitro studies.

Flicker defined form (FDF) is a temporally-dependent illusion created by the counterphase flicker of randomly positioned element dots, that preferentially stimulates the magnocellular system. Previous studies have found improvement with peripheral presentation, a resistance to blur and a dependence on high temporal frequencies. (Quaid & Flanagan, 2005a; Quaid & Flanagan, 2005b). Although it is seemingly very different from most luminance defined, static stimuli, it is still unknown in what ways it differs. The current study aimed to determine how FDF varies or is similar to static, luminance defined stimuli. Current results showed that FDF could be matched to particular spatial frequencies, and improved with increasing background structure and area. Shapes could be discriminated from each other and recognized. These results suggest that although FDF is dependent on motion pathways for temporal dynamic perception, it could also benefit from the input of form perception pathways, depending on the cues present in the stimulus (e.g. background structure, area). Results also showed that FDF does not benefit from Gestalt rules of contour closure, unlike some static stimuli, although related studies have shown that FDF could still be detected in spite of blur. These studies suggest that FDF appears to rely on motion perception pathways, areas such as MT, but is easier to perceive at times due to overlap in function with shape perception pathways, areas such as IT. As such FDF shares many characteristics with other motion-defined-form stimuli, but uniquely shares aspects of form vision.

Magnetic resonance imaging (MRI) is one of the most powerful imaging techniques for research and clinical diagnosis. To expand upon the intrinsic capabilities of MRI, new contrast agents that can detect the presence of biomarkers in vivo are being developed. My Masters thesis research focuses on the design and synthesis of a new MRI contrast agent that can detect glutathione (GSH), a biomarker that has been implicated in a number of oxidative stress diseases. This new MRI contrast agent is based on chelated dysprosium (Dy), an inorganic metal, which provides negative contrast to surrounding tissue. Preliminary data has shown that attaching a poly(ethylene glycol) (PEG) chain to the Dy chelate, effectively increasing its molecular weight, enhances the contrast ability of Dy. Using this new information, the contrast agent was designed to have a large molecular weight PEG chain attached to the Dy chelate through a disulfide, creating a thiol-sensitive linkage. In the presence of a thiol-containing molecule such as GSH, the Dy will be dePEGylated through a disulfide exchange reaction, removing the molecular weight effect of the PEG, and allowing for the detection of GSH by MRI. This new MRI contrast agent could provide insight into the progression and diagnosis of oxidative stress pathologies associated with GSH.

In this study, a liquid-crystal display (LCD) with the capability of switchable viewing-angle is proposed. The contrast ratio of the LCD mainly depends on the transmittance of the bright state and the dark state. By using the improved structure of the pixel electrodes, the viewing angle of the LCD can be switched between the wide viewing-angle mode and the narrow-viewing angle mode. Based on the proposed three-electrode structure, the liquid-crystal orientation of the LCD is controlled to generate different light-leakage conditions at large viewing angles, thus, resulting in the switch of the viewing angle of the LCD. The proposed structure, which has the slim outline and low-cost of the LCD, is a simple way to control the viewing angle of the LCD. Potential applications for the protection of personal privacy are emphasized.

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Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references.