Delaunay triangulations of hyperbolic surfaces

Triangulations are among the most important and well-studied objects in computational geometry. A triangulation is a subdivision of a surface into triangles. This allows the use of computer algorithms to analyze the geometry of the surface or perform simulations. A Delaunay triangulation is a particular kind of triangulation that is often used because of its favorable properties. In this thesis we studied Delaunay triangulations of hyperbolic surfaces. Hyperbolic surfaces are surfaces with a constant negative curvature and can be used to model shapes or structures that, intuitively speaking, cannot be "flattened" in the Euclidean plane. In the thesis we describe the properties of a specific class of hyperbolic surfaces that allow a well-known algorithm for computing Delaunay triangulations to be generalized to these surfaces. In particular, we compute the systole of these surfaces, which is an important parameter in the algorithm. Moreover, we provide upper and lower bounds for the minimal number of vertices of Delaunay triangulations of hyperbolic surfaces and show that these bounds are asymptotically optimal

Spiral diffusion of rotating self-propellers with stochastic perturbation

Translationally diffusive behavior arising from the combination of orientational diffusion and powered motion at microscopic scales is a known phenomenon, but the peculiarities of the evolution of expected position conditioned on initial position and orientation have been neglected. A theory is given of the spiral motion of the mean trajectory depending upon propulsion speed, angular velocity, orientational diffusion and rate of random chirality reversal. We demonstrate the experimental accessibility of this effect using both tadpole-like and Janus sphere dimer rotating motors. Sensitivity of the mean trajectory to the kinematic parameters suggest that it may be a useful way to determine those parameters

Chemical and electrical modification of polypropylene surfaces

Although many multi-component polymer systems are well characterised, the surface properties of polymers mixed with low surface energy additives have received little attention. In addition, the new branches of scanning probe microscopy that enable high resolution mapping and modification of surface charge distributions have been infrequently applied to polymer surfaces. The surface segregation of a fluorochemical additive directly from a polypropylene host matrix has been investigated by AFM and other surface analysis techniques. The level of surface enrichment was found to be governed by the temperature and duration of annealing. Further investigation revealed that the speed and extent of surface enrichment of the additive increases with polymer molecular weight. The effect of additive structure on surface segregation has also reported. A method of depositing charge onto polypropylene substrates from a high potential scanning AFM tip was developed. The relation between AFM tip- voltage and the level of charge deposited on the substrate suggested that a localised corona discharge was generated. AFM scanning parameters were found to effect the deposition of charge. The charging behavior of fluorochemical doped polypropylene surfaces was investigated on macroscopic scales using a scanning electrometer probe, and on microscopic scales using EFM. Fluorochemical domains at the surface have been found to preferentially accumulate both positive and negative charge. Surface charge distributions were found to become more uniform during annealing. Sub-micron particle capture by charged surfaces was investigated using EFM. In addition, spatially confined amine beads were deposited onto a patch of localised charge and subsequently functionalised to produce a metallic gold coating

Glancing angle metal evaporation synthesis of catalytic swimming Janus colloids with well defined angular velocity

The ability to control the degree of spin, or rotational velocity, for catalytic swimming devices opens up the potential to access well defined spiralling trajectories, enhance cargo binding rate, and realise theoretically proposed behaviour such as chiral diffusion. Here we assess the potential to impart a well-defined spin to individual catalytic Janus swimmers by using glancing angle metal evaporation onto a colloidal crystal to break the symmetry of the catalytic patch due to shadowing by neighbouring colloids. Using this approach we demonstrate a well-defined relationship between the glancing angle and the ratio of rotational to translational velocity. This allows batches of colloids with well-defined spin rates in the range 0.25 to 2.5 Hz to be produced. With reference to the shape and thickness variations across the catalytically active shapes, and their propulsion mechanism we discuss the factors that can lead to the observed variations in rotational propulsion

Changes in Professional and Community Perceptions Following Physical Therapy Graduate Student Participation in a Student Led Inter-professional Outreach Clinic

poster abstractOver the past six months, Indiana University physical therapy students have organized a student run clinic as part of a larger medical school led inter-professional outreach initiative. As participants in this initiative, 1st, 2nd, and 3rd year students have engaged in patient care as well as inter-professional activities. The purpose of this study was to evaluate how student participation influenced their perceptions of professional and social responsibility. Professionalism within physical therapy encompasses multiple attributes that include clinical competency as well as professional and social responsibility. An open-ended questionnaire with reflection prompts was designed to capture student thoughts relative to these constructs. Data collection occurred following a four hour voluntary clinical commitment. Data evaluations were conducted by several researchers who independently reviewed the responses for common themes. The results indicate that students are having positive influential experiences that focus on three distinct areas: professional competency, professional responsibility, and civic identity. Student responses demonstrating professional responsibility included an appreciation for the importance of “treating the patient as a whole” as well as a desire to mentor future students in this setting. Professional responsibility was seen in comments made about the opportunity to apply what they had learned as well as “advocating for community wellness.” Students expressed surprise in learning about their potential impact in the community, which caused many to indicate a desire to be more civically engaged. These findings parallel the physical therapy profession’s core values of excellence, professional duty, and social responsibility. By using their current knowledge and promoting effective physical therapy services to those of different socioeconomic statuses, students are experiencing and developing the professional constructs required of their chosen field. Students also clearly expressed a desire to continue to serve this community supporting the importance of this inter-professional clinic as an opportunity to positively shape student professional development

Preparation and 3D Tracking of Catalytic Swimming Devices

We report a method to prepare catalytically active Janus colloids that "swim" in fluids and describe how to determine their 3D motion using fluorescence microscopy. One commonly deployed method for catalytically active colloids to produce enhanced motion is via an asymmetrical distribution of catalyst. Here this is achieved by spin coating a dispersed layer of fluorescent polymeric colloids onto a flat planar substrate, and then using directional platinum vapor deposition to half coat the exposed colloid surface, making a two faced "Janus" structure. The Janus colloids are then re-suspended from the planar substrate into an aqueous solution containing hydrogen peroxide. Hydrogen peroxide serves as a fuel for the platinum catalyst, which is decomposed into water and oxygen, but only on one side of the colloid. The asymmetry results in gradients that produce enhanced motion, or "swimming". A fluorescence microscope, together with a video camera is used to record the motion of individual colloids. The center of the fluorescent emission is found using image analysis to provide an x and y coordinate for each frame of the video. While keeping the microscope focal position fixed, the fluorescence emission from the colloid produces a characteristic concentric ring pattern which is subject to image analysis to determine the particles relative z position. In this way 3D trajectories for the swimming colloid are obtained, allowing swimming velocity to be accurately measured, and physical phenomena such as gravitaxis, which may bias the colloids motion to be detected

Effects of temperature and radiation on lettuce growing.

Lettuces were planted in the spring at 20 X 25 cm in glasshouses with several temperature regimes and differing light transmission (43-76%), and the effects were determined of air temperature and radiation on the percentage soil cover and yield. With heated, lightly heated and unheated glasshouses the time from planting to almost 100% soil cover was 33, 47 and 54 days, respectively, equivalent to about 600 degree-days. Variations in the total radiation received during these periods were marked. Growth in terms of fresh weight increase was slow initially under all conditions, but when the plants had attained about 60 g fresh weight they grew rapidly, and subsequent fresh weight increases were closely correlated with total radiation. (Abstract retrieved from CAB Abstracts by CABI’s permission

Preparation and 3D Tracking of Catalytic Swimming Devices

We report a method to prepare catalytically active Janus colloids that "swim" in fluids and describe how to determine their 3D motion using fluorescence microscopy. One commonly deployed method for catalytically active colloids to produce enhanced motion is via an asymmetrical distribution of catalyst. Here this is achieved by spin coating a dispersed layer of fluorescent polymeric colloids onto a flat planar substrate, and then using directional platinum vapor deposition to half coat the exposed colloid surface, making a two faced "Janus" structure. The Janus colloids are then re-suspended from the planar substrate into an aqueous solution containing hydrogen peroxide. Hydrogen peroxide serves as a fuel for the platinum catalyst, which is decomposed into water and oxygen, but only on one side of the colloid. The asymmetry results in gradients that produce enhanced motion, or "swimming". A fluorescence microscope, together with a video camera is used to record the motion of individual colloids. The center of the fluorescent emission is found using image analysis to provide an x and y coordinate for each frame of the video. While keeping the microscope focal position fixed, the fluorescence emission from the colloid produces a characteristic concentric ring pattern which is subject to image analysis to determine the particles relative z position. In this way 3D trajectories for the swimming colloid are obtained, allowing swimming velocity to be accurately measured, and physical phenomena such as gravitaxis, which may bias the colloids motion to be detected

Minimal Delaunay Triangulations of Hyperbolic Surfaces

Motivated by recent work on Delaunay triangulations of hyperbolic surfaces, we consider the minimal number of vertices of such triangulations. First, we show that every hyperbolic surface of genus g has a simplicial Delaunay triangulation with O(g) vertices, where edges are given by distance paths. Then, we construct a class of hyperbolic surfaces for which the order of this bound is optimal. Finally, to give a general lower bound, we show that the ?(?g) lower bound for the number of vertices of a simplicial triangulation of a topological surface of genus g is tight for hyperbolic surfaces as well