Kwong, Kwok Kun. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 66-70) and index. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Saccadic eye movements are guided by attention. Indeed, some saccade trajectory effects serve as an index the attentional strength of visual objects in the map of visual space used to plan a saccade. One approach to understanding saccade planning relies on simple tasks in sparse displays (containing a single target and distractor object) to develop neurophysiologically plausible models of saccade behavior. Under tightly controlled conditions, saccade trajectories can be well predicted by representing displays of objects with simple visual features and their relative salience. But the world in which the saccade system typically operates is not sparse, and observer eye movements are guided by more than just salience. As such, another approach has been to examine saccadic behavior in complex scenes and complicated goals. Such scene context can drastically affect saccades in ways that are not well predicted by a context-free and expectation-free representation of visual salience. This dissertation starts to bridge this gap between these literatures by focusing on object surfaces. Covert shifts of attention operate on representations informed not just by stimulus salience and location-based expectations, but also by the perceptual organization of object surfaces. Covert attention can be guided by surface context, such that targets and distractors are processed differently as a function of whether they are on the same or different surface. These effects are fragile, however, and have previously only been demonstrated in relatively engaging tasks and with strong perceptions of objecthood. The present work tested the strength of the relationship between attention and saccades by testing whether surface context guides orienting eye movements. Observers made saccades to objects that could be organized with different surface structure. In four experiments (Chapters 2 and 3) I found no evidence that the saccade map encoded surface context. But in two experiments (Chapters 4 and 5) I demonstrate saccade trajectories are sensitive to surface context, independently of low or high task engagement. This demonstrates that object surface-based representations are not necessarily fragile and can affect the oculomotor map even for simple saccadic orienting for which the surface is task-irrelevant. This lends evidence to the theory that the nature of the representation of vision is one of object surfaces, and suggests that the strength of object encoding is stronger than has been previously demonstrated.

Random triangulated surfaces are created by taking an even number, n, of triangles and arbitrarily ”gluing” together pairs of edges until every edge has been paired. The resulting surface can be described in terms of its number of boundary cycles, a random variable denoted by h. Building upon the work of Nicholas Pippenger and Kristin Schleich, and using a recent result from Alex Gamburd, we establish an improved approximation for the expectation of h for certain values of n. We use a computer simulation to exactly determine the distribution of h for small values of n, and present a method for calculating these probabilities. We also conduct an investigation into the related problem of creating one connected component out of n triangles.

The purpose of this project was to study the differential geometry of curves and surfaces in three-dimensional Euclidean space. Some important concepts such as, Curvature, Fundamental Form, Christoffel symbols, and Geodesic Curvature and equations are explored.

Cell attachment is vital for the integration of biomaterials in the body. Surface modification using cell adhesive peptides, such as Arginine-Glycine-Aspartic (RGD), has showed promise for enhancing cell adhesion. Cell adhesion on glass and polyethylene glycol (PEGylated) surfaces modified with active RGD and Proline- Histidine-Serine-Arginine-Asparagine (PHSRN) peptides as well as inactive RDG and HRPSN control peptides was investigated in serum free conditions using three cell lines; NIH3T3 fibroblasts, MC3T3 pre-osteoblasts and C2C12 pre-myoblasts. Peptide attachment to glass surfaces was confirmed by x-ray photoelectron spectroscopy and contact angle measurements. Cell attachment and spreading was equivalent on all peptide and fibronectin coated glass surfaces and was significantly higher than on unmodified glass after 3 hours. Cell attachment to the peptide modified glass was reduced in the presence of soluble RGD and RDG peptides, indicating that cell attachment to these surfaces may be integrin mediated, but not specific for RGD. Inhibition of protein synthesis with cycloheximide revealed that endogenous protein synthesis did not influence the specificity of cell attachment to the peptide modified glass surfaces in all cell types within a 3 hour period. However, cycloheximide treatment inhibited cell spreading on the peptide modified glass surfaces, suggesting that proteins synthesis was required for spreading. Long term adhesion studies, within a 24 hour period, showed that all cell lines were able to remain attached to the peptide modified glass surfaces, while C2C12 and MC3T3 cells were also able to form focal adhesions during this period. Cell attachment to peptide modified PEGylated surfaces over a 3 hour period showed that NIH3T3 and C2C12 cells experienced significantly higher levels of cell attachment on the RGD modified surface compared to the other peptides. MC3T3 cells attached to all the peptide modified PEGylated surfaces to the same extent, suggesting that cell attachment to peptide modified PEGlyated surfaces, can be cell type dependent. In conclusion all the peptides were able to promote cell adhesion on glass surfaces in the absence of a PEG linker. In the presence of a PEG linker cellular response to the peptide surfaces was both peptide and cell type dependent.

Polymer samples of polytetrafluoroethylene (PTFE) and a PTFE-glass weave (RF- 35P) are exposed to low pressure, non-equilibrium glow discharge plasmas for enhanced wettability as measured by static contact angles. Plasma treatments are performed in two parallel plate RF plasma systems, a downstream microwave plasma and a barrel etcher using feed gases composed of H₂, N₂, Ar, He, and 0₂. Surface analysis of the topography and chemical composition of treated samples is performed by atomic force microscopy (AFM), attenuated total reflection infrared (ATR-IR) spectroscopy, x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF SIMS). Optical emission spectroscopy is used to correlate wettability to reactive species in the plasma, and plasma parameters to species emission. In the parallel plate plasma systems, the contact angle can change from approximately 95° to 5° with treatment while treatments in the downstream and barrel etcher systems do not result in a contact angle change. The difference in plasma performance is attributed to ion bombardment. Plasmas composed of 20 to 80% H₂O in (H₂ + N₂) give the best wettability improvement. Plasma exposure significantly reduces the surface fluorine content followed by incorporation of nitrogen, oxygen and hydrogen, apparently as amino, hydroxyl and carbonyl functional groups with evidence of an amide. The incorporation of oxygen likely originates through peroxy radicals subsequent to plasma exposure. It is proposed that using a higher applied power creates a more reactive surface. A larger percentage of H₂ in the plasma tends to passivate the surface, leading to a smaller wettability improvement which is correlated to the atomic hydrogen concentration in the plasma. The addition of He or Ar into the H₂/N₂ plasma tends to dilute or weaken the plasma effect on wettability. To a much greater extent, the addition of oxygen also decreases the wettability. This latter effect is attributed to etching reactions which result in a more hydrophobic surface. An etch rate of approximately 0.2 μ/min is observed, and this is the first report of PTFE etching with 0₂/H₂/N₂. The distance between the parallel plate electrodes (gap) is a significant factor for the wettability of treated polymers, while power, pressure and flow rate are not. The optimal storage conditions to retain the wettability of H₂/N₂ plasma-treated RF-35P are low pressure and low temperature. The following model of PTFE surface modification is proposed. Ion bombardment creates reactive sites that initiate surface reactions. Reactive species from the H₂/N₂ plasma modify the surface through incorporation of amino, hydroxyl and carbonyl surface groups. These new groups increase the polymer wettability. Atomic hydrogen in the mixture is required to improve the wettability, but too high of a concentration will passivate the surface and lessen the wettability improvement. If oxygen is present, the modified surface is etched away leaving a refreshed, more hydrophobic surface. / Graduation date:2006

Thesis (Ph. D.)--University of Chicago, Department of Mathematics, 1917. / "Private edition, distributed by the University of Chicago Libraries." Includes bibliographical references. Also available on the Internet.

In this thesis, we solve for (equivariant) Gromov-Witten theories of some important classes of surfaces and threefolds, and study their relationships to other brances of mathematics. The first object is the class of P2-bundles over a smooth curve C of genus g. Our bundles are of the form P(L0 + L1 +L2) for arbitrary line bundles L0, L1 and L2 over C. We compute the partition functions of these invariants for all classes of the form s + nf, where s is a section, f is a fiber and n is an integer. In the case where the class is Calabi-Yau, i.e., K • (s + nf) = 0,the partition function is given by 3g (2sin u/2) 2g-2 As an application, one can obtain a series of full predictions for the equivariant Donaldson Thomas invariants for this family of non-toric threefolds. Secondly, we compute the C-equivariant quantum cohomology ring of Y, the minimal resolution of the DuVal singularity C2 /G where G is a finite subgroup of SU(2). The quantum product is expressed in terms of an ADE root system canonically associated to G. We generalize the resulting Frobenius manifold to non-simply laced root systems to obtain an n parameter family of algebra structures on the affine root lattice of any root system. Using the Crepant Resolution Conjecture, we obtain a prediction for the orbifold Grornov-Witten potential of [C2 /G]. Thirdly, for a polyhedral group G, that is a finite subgroup of S0(3), we completely determine the Gromov-Witten theory of Nakamura's G- Hilbert scheme, which is a preferred Calabi-Yau resolution of the polyhedral singularity C3/G. The classical McKay correspondence determines the (classical) cohomology of this resolution in terms of the representation theory of G. We express the Cromov-Witten potential in terms of an ADE root system associated to G. As an application, we use the Crepant Resolution Conjecture to provide a full prediction for the orbifold Grornov-Witten invariants of [C3/G]. Finally, in the case that G is the group A4 or Z2 x Z2, we compute the integral of Ag on the Hurwitz locus HG C Mg of curves admitting a degree 4 cover of P1 having monodromy group G. We compute the generating functions for these integrals and write them as a trigonometric expression summed over the positive roots of the E6 and D4 root systems respectively. As an application, we prove the Crepaut Resolution Conjecture for the orbifolds [C3/A4] and [C3/(Z2 x Z2)].

In an effort to understand the resuspension phenomena, interactions of spherical micro-meter particles (glass beads (GB) and Stainless steel (SS)) were investigated experimentally on different surfaces (glass, ceramic, hardwood, metal and chemical agent resistant coated metal (CARC)). Particles were deposited on the lower surface of a 10 cm square wind tunnel by gravitational settling. Air flows were imposed from an open entrance at average velocities up to 16 m/s. Individual particle trajectories obtained by high-speed imaging reveal three different types of motion: rolling/bouncing, immediate liftoff and complex motion. Surface roughness significantly affects the particle initial motion prior to liftoff. The majority of particle trajectories from the glass substrate were parallel to the surface with complex motion, covering 25% of the total distance traveled in rolling/bouncing motion before liftoff. Hardwood substrates took the longest time for initial particle movement (t >1 s) causing a more rapid liftoff. The ceramic substrate showed the most rolling/bouncing motion, for 80% of the particles. Additionally, single layer detachment showed that the detachment percentage initially follow an exponentially increasing trend for a period of ~ 1 s, followed by a plateau phase for a period of 5 s. Changing velocity, substrate and particle size significantly affects GB particle detachment. Furthermore, detachment from the metal substrate was consistently higher than the CARC substrates. However, particle density is not a significant difference in the bigger particle size studied. Initial 3-D particle tracking showed that particles seem to travel in a constant angle to the left rather than going straight in the flow direction. A detachment mode model showed that the detachment by direct liftoff required a much higher speed than rolling motion with a minimum of 14 m/s for both GB70 and SS70 on glass and metal surface, and the velocity increased to 21 m/s for the smaller particle. Incorporating the different types of particle motion prior to liftoff into resuspension models, and how their relative contributions change with different particle and substrate materials, can potentially yield improved predictive capabilities.

Thesis (doctoral)--Physics--Göteborg university, 2001. / Notes bibliogr.