Low, Ho Chi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 76-79). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.

Ma thèse consiste en une étude des cercles de contact et plus généralement des p-sphères de contact sous différents points de vue, topologique, géométrique et algébrique. Une p-sphère de contact est l'ensemble des combinaisons linéaires normalisées de p+1 formes de contact si toutes ces formes sont de contact.<br />Dans la première partie nous étudions des p-sphères de contact invariantes sur des fibrés principaux en cercles. Nous classifions les fibrés principaux de dimension 3 qui admettent des p-sphères de contact invariantes et nous construisons des exemples.<br />Dans la partie géométrique nous étudions l'ensemble des structures de contact associées aux éléments d'un cercle de contact. Nous définissons la notion de faisceau de contact et de toupie de contact (sur une variété riemannienne). Nous classifions les variétés de dimension 3 qui admettent des toupies de contact et nous caractérisons les métriques pour lesquelles il peut y avoir des toupies de contact sur une variété donnée.<br />Dans la partie algébrique, nous étudions les groupes de Lie de dimensions 3 et 7 qui admettent des p-sphères de contact invariantes à gauche. Nous obtenons des résultats de classification, ainsi qu'un certain nombre d'exemples. <br />Nous montrons également qu'il n'existe pas de p-sphère de contact sur les variétés de dimension 4n+1 (pour p 1) et que sur les (4n-1)-sphères il existe toujours une ( (4n)-1)-sphère de contact, où est le nombre d'Adams.

A number of scholars have identified a crisis in the field of education. Namely, students today are more self-absorbed and individualistic than ever before. In other words, they have few social commitments and lack a sense of community. This lack of social responsibility is particularly problematic in Colombia, where a privileged few enjoy all the spoils and the elite youth are groomed as the future leaders of the country. For many, hope is all but lost on these socially irresponsible students. On the other hand, some planners and critics believe that service-learning -- which connects community service to the classroom -- is a remedy for this lack of social solidarity. With this in mind, service-learning has become increasingly popular during the past decade all over the globe, and particularly in Latin American countries such as Colombia. This research project is an evaluation of the service-learning program at one of the most elite high schools in Colombia. The project has two specific aims: (1) to document the impact of the program on the attitudes and behaviors of the students and (2) to assess the quality of the implementation of the program. In order to achieve these aims, three data collection methods -questionnaires, interviews, and focus groups - were used to paint a holistic picture of the program. Furthermore, a theoretical model of service-learning was developed as a benchmark to evaluate the program. The results revealed that the service-learning program was having a minimal impact on students' attitudes and behaviors. In fact, the analysis showed that in many instances the program was simply reinforcing stereotypes and solidifying the social division in Colombia. The failure to achieve the desired outcomes may have been due to the fact that the program did not fulfill many of the required expectations of service-learning. In the final chapter, specific recommendations are given to improve the program.

Syfte:.Syftet med studien är att jämföra icare tonometri med NCT och se om de två metoderna får likvärdiga resultat. Studien ville även se vilken av metoderna som föredras av deltagarna. Metod: 85 personer deltog med medelålder 27 ± 9,2 år. Mätningarna utfördes på 82 av deltagarna i slumpmässig ordning på deras högerögon. I studien användes topcon CT-80A non-contact tonometer (topcon coroporation) och icare ® TA01i tonometer (icare Finland Oy). Resultat: Medelvärde för icare var 16,4 ± 3,9 mmHg. Medelvärdet för NCT var 15,6 ± 2,6 mmHg. Det var statistisk signifikant skillnad mellan metoderna (p = 0,001). Väldigt god positiv korrelation mellan icare och NCT (r = 0,85; y = 1,2905x - 3,7199). 91% av deltagarna föredrog icare framför NCT. Slutsats: Båda metoderna fungerar bra som screeningmetoder av IOP men icare har en tendens att ge högre värden än NCT. Icare tonometer var den metod som de flesta deltagarna föredrog. Det fanns en statistiskt signifikant skillnad mellan icare och NCT vilket tyder på att metoderna skiljer sig åt resultatmässigt.

Purpose: To examine the variables that influence lipid deposition on conventional and silicone hydrogel contact lens materials and to build a physiologically relevant in vitro model of lipid deposition on contact lenses. Methods: Lipid deposition on contact lens materials can lead to discomfort and vision difficulty for lens wearers. Using a variety of radiochemical experiments and two model lipids (cholesterol and phosphatidylcholine), a number of clinically significant parameters that may influence lipid deposition were examined. • The optimization and characterization of a novel artificial tear solution (ATS) was examined (Chapter 3) • Optimization of an extraction system to remove deposited cholesterol and phosphatidylcholine from various contact lens materials (Chapter 4) • The influence of different tear film components on lipid deposition was researched (Chapter 5) • The efficiency of hydrogen peroxide disinfecting solutions to remove deposited lipid from contact lenses was investigated (Chapter 6) • The effect of intermittent air exposure on lipid deposition was examined through the use of a custom built “model blink cell” (Chapter 7) Results: A novel complex ATS designed for in-vial incubations of contact lens materials was developed. This solution was stable and did not adversely affect the physical parameters of the contact lenses incubated within it. An efficient extraction protocol for deposited cholesterol and phosphatidylcholine was optimized based on chloroform and methanol with the addition of water and acetic acid for phosphatidylcholine extraction. Overall, cholesterol and phosphatidylcholine deposition is cumulative over time and found to deposit in greater masses on silicone-containing hydrogels. Cholesterol and phosphatidylcholine deposition is influenced by the composition of the incubation medium and air exposure which occurs during the inter-blink period. Hydrogen peroxide disinfecting solutions were able to remove only marginal amounts of lipid from the contact lenses, with the surfactant containing solution removing more. Conclusion: This thesis has provided hitherto unavailable information on the way in which lipid interacts with conventional and silicone hydrogel contact lens materials and the in vitro model built here can be utilized in various ways in the future to assess other aspects and variables of lipid and protein deposition on a variety of biomaterials.

Contact lens success is primarily driven by comfort of the lens in eye. Over the years, many modifications have been made to the lens surface and bulk material to improve comfort of the lens, however 50% of contact lens wearers still report dry eye symptoms while wearing their lenses. Wettability of the lens material plays a large role in lens comfort, primarily due to its influence in tear film stability. In vitro wettability of contact lenses has typically been assessed by measuring the water contact angle on the lens surface. Currently there are three techniques to measure the in vitro wettability of contact lenses, the sessile drop technique, captive bubble technique, and the Wilhelmy balance method. To date, there is much published on assessing wettability using the sessile drop and captive bubble technique, however there is no data published looking at the in vitro wettability of hydrogel contact lenses measured by the Wilhelmy balance method. Accumulation and deposition of tear components on the lens surface can also affect lens performance, by altering the wettability of the lens surface and causing lens spoilage. The majority of in vitro studies looking at deposition of tear components on the lens surface dope the lenses in tear solutions for a set period of time. None of these studies have investigated the impact of exposing the lenses to tear solutions, then exposing them to the air and then back into the tear solution, which mimics the process during blinking. In Chapter 2, an evaluation of the influence of lens preparation on the wettability of contact lenses measured by the sessile drop technique was conducted. The wettability of 6 silicone hydrogel and one conventional lens material was assessed. Lenses were blot dried on either a microfiber cloth or lens paper for different drying periods and contact angles were measured using the sessile drop technique. There were large variations in results using the microfiber cloth after all drying periods, but there was little variation in results after lenses were blot dried on lens paper for approximately 20 seconds. Thus, it was determined that for future contact angle analysis using the sessile drop technique that lenses should be blot dried for roughly 20 seconds on lens paper. This method was used consistently for the rest of the experiments in which the sessile drop technique was used to measure contact angles. The remainder of Chapter 2 compared the contact angles of different lens materials measured by the sessile drop technique and Wilhelmy balance method. The wettability of five different silicone hydrogel lens materials was assessed directly out-of-blister and after a 48 hour soak in saline. There were significant differences in contact angles for the lens materials between the two techniques. There were also significant differences in contact angles directly out-of-blister and after the 48 hour soak. Results from this study suggested that different methods of measuring wettability can produce different results and that blister pack solutions can alter the wettability of lens materials. Chapter 3 measured the physical properties of blister pack solutions of silicone hydrogel lenses. The pH, osmolality, surface tension, and viscosity of the blister solutions for 9 silicone hydrogel lenses, 2 conventional lenses, and 2 saline solutions were measured. The osmolality of the blister solutions followed a trend, in that blister solutions manufactured by the same company had the same osmolality. Products produced by Johnson & Johnson had the highest osmolality. Blister solutions that contained additional wetting agents had higher viscosities compared to blister solutions without added wetting agents. The main conclusion from this study was that adding wetting agents to blister solutions could alter the physical properties of the blister solutions. The purpose of Chapter 4 was to measure the physical properties of the blister pack solutions of daily disposable lenses and to evaluate the wettability of the lens materials and substantivity of the blister solutions, using a method in which lenses were cycled through 5 minute soaks in saline to mimic blinking. Five daily disposable lens materials were evaluated, one of which was shipped in a blister solution with added surfactants and wetting agents. The wettability of the lenses was assessed using the sessile drop technique and Wilhelmy balance method. The lens with the modified blister solution had a lower surface tension and higher viscosity compared to all the other blister solutions. The same trend in osmolalties as those reported in Chapter 3, were found with blister solutions made by the same manufacturer having the same osmolality. The wettability varied across lens materials. Overall, the lens material with the added components to the blister solution had the lowest contact angle. Chapter 5 investigated the deposition of tear components onto the surface of conventional and silicone hydrogel lens materials and looked at the impact of this on changes in wettability. Three lens materials used in Chapter 4 were exposed to a saline solution, lysozyme solution, and a complex tear solution for 5 minutes, 1 hour, 4 hours, and 8 hours. The wettability was assessed after each time point using the sessile drop and Wilhelmy balance methods. There was little to no deposition on the lens materials that had the highest in vitro CAs in Chapter 4, exemplified by no change in wettability after being soaked in the lysozyme and complex tear solutions. There was deposition on the lens materials with the lowest CAs in Chapter 4, exemplified by a significant increase in wettability after being soaked in the lysozyme and complex tear solutions. Results indicate that there is some deposition onto one lens material, as shown by the change in wettability of the lens surface. These results were further used to validate a method used in Chapter 6. The experiment conducted in Chapter 6 was similar to the experiment in Chapter 5, except that the lenses were not soaked in the three solutions but rather exposed to the solutions in a “model blink cell”. The model blink cell moves lenses in and out of solution at a set time interval, in an attempt to mimic blinking. The interval was set so the lenses would be placed for 1 second in solution and 5 seconds exposed to the air. The same lens materials used in Chapter 5 were used in for this experiment. The lenses were exposed to a saline solution, lysozyme solution and complex tear solution for 5 minutes, 1 hour, 4 hours, and 8 hours. Much like in Chapter 5, deposition on the lens materials was determined by a change in the lens wettability. There were differences in the results of this chapter and that of Chapter 5, with deposition occurring on two of the lens materials rather than just one. This result indicates that the drying of the lens surface for 5 seconds out of solution has an effect on the deposition of tear components on certain lens materials. Thus, the model blink cell may be a useful tool for future deposition studies. Overall this thesis demonstrated that preparation of the lens material can cause variation in contact angles. Different methods of measuring in vitro wettability of contact lenses can produce different results and thus the method used to assess wettability should always be stated. The physical properties of blister pack solutions can change with added wetting agents and surfactants, and components from blister solutions can alter the initial wettability of contact lenses. In vitro deposition of proteins onto the lens surface can vary with techniques, and finally, deposition of tear components onto the surface of contact lenses can alter the lens wettability.

No description available.

Contact lens success is primarily driven by comfort of the lens in eye. Over the years, many modifications have been made to the lens surface and bulk material to improve comfort of the lens, however 50% of contact lens wearers still report dry eye symptoms while wearing their lenses. Wettability of the lens material plays a large role in lens comfort, primarily due to its influence in tear film stability. In vitro wettability of contact lenses has typically been assessed by measuring the water contact angle on the lens surface. Currently there are three techniques to measure the in vitro wettability of contact lenses, the sessile drop technique, captive bubble technique, and the Wilhelmy balance method. To date, there is much published on assessing wettability using the sessile drop and captive bubble technique, however there is no data published looking at the in vitro wettability of hydrogel contact lenses measured by the Wilhelmy balance method. Accumulation and deposition of tear components on the lens surface can also affect lens performance, by altering the wettability of the lens surface and causing lens spoilage. The majority of in vitro studies looking at deposition of tear components on the lens surface dope the lenses in tear solutions for a set period of time. None of these studies have investigated the impact of exposing the lenses to tear solutions, then exposing them to the air and then back into the tear solution, which mimics the process during blinking. In Chapter 2, an evaluation of the influence of lens preparation on the wettability of contact lenses measured by the sessile drop technique was conducted. The wettability of 6 silicone hydrogel and one conventional lens material was assessed. Lenses were blot dried on either a microfiber cloth or lens paper for different drying periods and contact angles were measured using the sessile drop technique. There were large variations in results using the microfiber cloth after all drying periods, but there was little variation in results after lenses were blot dried on lens paper for approximately 20 seconds. Thus, it was determined that for future contact angle analysis using the sessile drop technique that lenses should be blot dried for roughly 20 seconds on lens paper. This method was used consistently for the rest of the experiments in which the sessile drop technique was used to measure contact angles. The remainder of Chapter 2 compared the contact angles of different lens materials measured by the sessile drop technique and Wilhelmy balance method. The wettability of five different silicone hydrogel lens materials was assessed directly out-of-blister and after a 48 hour soak in saline. There were significant differences in contact angles for the lens materials between the two techniques. There were also significant differences in contact angles directly out-of-blister and after the 48 hour soak. Results from this study suggested that different methods of measuring wettability can produce different results and that blister pack solutions can alter the wettability of lens materials. Chapter 3 measured the physical properties of blister pack solutions of silicone hydrogel lenses. The pH, osmolality, surface tension, and viscosity of the blister solutions for 9 silicone hydrogel lenses, 2 conventional lenses, and 2 saline solutions were measured. The osmolality of the blister solutions followed a trend, in that blister solutions manufactured by the same company had the same osmolality. Products produced by Johnson & Johnson had the highest osmolality. Blister solutions that contained additional wetting agents had higher viscosities compared to blister solutions without added wetting agents. The main conclusion from this study was that adding wetting agents to blister solutions could alter the physical properties of the blister solutions. The purpose of Chapter 4 was to measure the physical properties of the blister pack solutions of daily disposable lenses and to evaluate the wettability of the lens materials and substantivity of the blister solutions, using a method in which lenses were cycled through 5 minute soaks in saline to mimic blinking. Five daily disposable lens materials were evaluated, one of which was shipped in a blister solution with added surfactants and wetting agents. The wettability of the lenses was assessed using the sessile drop technique and Wilhelmy balance method. The lens with the modified blister solution had a lower surface tension and higher viscosity compared to all the other blister solutions. The same trend in osmolalties as those reported in Chapter 3, were found with blister solutions made by the same manufacturer having the same osmolality. The wettability varied across lens materials. Overall, the lens material with the added components to the blister solution had the lowest contact angle. Chapter 5 investigated the deposition of tear components onto the surface of conventional and silicone hydrogel lens materials and looked at the impact of this on changes in wettability. Three lens materials used in Chapter 4 were exposed to a saline solution, lysozyme solution, and a complex tear solution for 5 minutes, 1 hour, 4 hours, and 8 hours. The wettability was assessed after each time point using the sessile drop and Wilhelmy balance methods. There was little to no deposition on the lens materials that had the highest in vitro CAs in Chapter 4, exemplified by no change in wettability after being soaked in the lysozyme and complex tear solutions. There was deposition on the lens materials with the lowest CAs in Chapter 4, exemplified by a significant increase in wettability after being soaked in the lysozyme and complex tear solutions. Results indicate that there is some deposition onto one lens material, as shown by the change in wettability of the lens surface. These results were further used to validate a method used in Chapter 6. The experiment conducted in Chapter 6 was similar to the experiment in Chapter 5, except that the lenses were not soaked in the three solutions but rather exposed to the solutions in a “model blink cell”. The model blink cell moves lenses in and out of solution at a set time interval, in an attempt to mimic blinking. The interval was set so the lenses would be placed for 1 second in solution and 5 seconds exposed to the air. The same lens materials used in Chapter 5 were used in for this experiment. The lenses were exposed to a saline solution, lysozyme solution and complex tear solution for 5 minutes, 1 hour, 4 hours, and 8 hours. Much like in Chapter 5, deposition on the lens materials was determined by a change in the lens wettability. There were differences in the results of this chapter and that of Chapter 5, with deposition occurring on two of the lens materials rather than just one. This result indicates that the drying of the lens surface for 5 seconds out of solution has an effect on the deposition of tear components on certain lens materials. Thus, the model blink cell may be a useful tool for future deposition studies. Overall this thesis demonstrated that preparation of the lens material can cause variation in contact angles. Different methods of measuring in vitro wettability of contact lenses can produce different results and thus the method used to assess wettability should always be stated. The physical properties of blister pack solutions can change with added wetting agents and surfactants, and components from blister solutions can alter the initial wettability of contact lenses. In vitro deposition of proteins onto the lens surface can vary with techniques, and finally, deposition of tear components onto the surface of contact lenses can alter the lens wettability.

This thesis utilized the concept of an optically stimulated Contact Potential Difference (osCPD) sensor to monitor oil properties. The osCPD technique is a variant of the contact potential difference (CPD) method used to obtain surface properties of materials. The technique uses modulated light to stimulate electron charge carriers in silicon coated with a layer of oil. Demonstration of this oil monitoring design was done by placing different oil samples on the silicon surface and monitoring the corresponding electrical signal with the osCPD sensor. Experiments showed that the osCPD sensor produced an electrical signal that was related to the amount of time an oil sample was aged in an engine (or mileage). Further, a linear relationship was found between the relative conductivity of these oils and the osCPD signal. It is theorized that this osCPD signal is dependant on the charge transfer at the silicon and oil interface. Investigation of this interaction was carried out. Experiments showed that adding a silicon nitride passivation layer on the silicon surface eliminated the change in osCPD signal with oil properties. A model of this charge interaction was developed.

No description available.