Ho Sin Yee, Stella. / "August 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (p. 167-193). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Atrial Fibrillation (AF) is rare amongst young people whilst epidemic in the elderly. Whilst much is known about the pathophysiology of AF, the mechanisms underlying the vulnerability to AF amongst older people in incompletely understood. Young (< 18 months, first quintile of life) and old (> 8 years, last quintile of life) Welsh mountain sheep were used to investigate changes in atrial electrophysiology with age. Old sheep were more vulnerable to induced AF than young sheep. On the surface ECG, p-wave duration increased with age suggesting increasing atrial size. The corrected sinus node recovery time increased with age, suggesting deteriorating sinus node function. These findings confirmed the validity of sheep as a model for human ageing. In isolated atrial myocytes, action potentials (APs) were recorded using the perforated patch clamp technique. AP duration increased with age, and an increase in AP amplitude was also seen at the lowest stimulation rates. Right atrial AP durations were prolonged compared to those from left atrial myocytes, and the inter-atrial difference was similar between old and young. However, when right atrial monophasic APs were recorded from anaesthetised sheep in vivo, no difference in AP duration was seen between age groups. Alternans occurred at lower stimulation rates in old compared to young myocytes and was of greater magnitude. These age-related differences were present in isolated myocytes and in vivo. Alternans mechanisms were explored by simultaneously recording APs and intracellular calcium concentration. Atrial alternans was driven by alternans of Ca2+ cycling at low stimulation rates. However, despite disabling Ca2+ cycling using thapsigargin, alternans could still be elicited from myocytes during rapid stimulation. Right atrial conduction velocity (CV) was assessed in vivo and found to increase with age. A key determinant of CV, the Na+ current INa was investigated using the whole cell patch clamp technique. INa increased with age in left atrial myocytes and recovered faster from inactivation. Protein expression was investigated using Western blotting. Expression of the Na+ channel α-subunit did not change with age. The gap junction protein Cx43 was expressed less in older subjects, but Cx40 expression was similar. This work has cast light on several aspects of atrial electrophysiology in which the effects of age have not been thoroughly investigated. The longer cellular APs seen with age decrease the wavelength of potential re-entrant circuits which could be seen as protective against AF. However, AP prolongation is also associated with afterdepolarisations which could serve to trigger AF. The increase in alternans behaviour may set the stage for wavebreak, leading to re-entrant circuit formation. The increase in CV was surprising and might be seen as protective against AF as it increases arrhythmia wavelength, and is likely to be caused by the increased INa.

The master thesis studies the impact of the entropy gradient on the vorticity of ve- locity field, particularly by applying the linear momentum balances. These balances are formulated for Thermo-viscous fluids (later fluids) and Thermo-viscous-elastic ma- terial (later solids) with the other balances (energy, mass, etc.). In order to derive these balances, the Classical continuum mechanics approach is used along with the respec- tive Variational principles. The thesis emphasizes the Variational principles applica- tion representing the modification of the Bateman principle [Bat29] and its comparison with the Classical approach, linked to the L. Crocco work [Cro37], particularly in the case of vorticity generation. It is pointed that by the definition of the dissipative en- tropy sdis a harmony of both approaches can be achieved and that, in the case of an appropriate limit, the direct effect of the entropy gradient on the vorticity of velocity field can be demonstrated. By applying this conclusion the relationship between the change of circulation among a closed curve and released heat on the given geometry is indicated.

Sedimentation is one of many characterization tools used to test materials in nanotechnology. Characterization of settling behavior is complex as there are many variables which can affect sedimentation. In our research, we focused on sedimentation in colloidal systems with the aid of an optical turbidometer. Nanoparticles of CeO2 (Ceria Oxide) and TiO2 (Titanium Dioxide) are embedded onto a polymeric matrix of a thermally responsive microgel of poly(N-isopropylacrylamide) (PNIPAM) and interpenetrating chains of poly(acrylic acid) to create novel composites. The composites are loaded with the inorganic oxide nanoparticles at different weight percent from a low value of 10 weight % to 75 weight %. The loading of the colloidal particles affects the sedimentation rate. In this thesis a turbidomenter is used to characterize the settling rate, which is an important characteristic for application of these new composites. TiO2 is a key constituent in many industrial products; cosmetics, paints, ceramics and used in waste water remediation. It is a potent photocatalyst which breaks down almost any organic compound when exposed to ultraviolet light. By combining nanoparticles of TiO2 with microgels of a polymer, the composites can facilitate use and recovery of the catalyst. Gravity settling of these loaded composites provides an easy separation of TiO2 nanoparticles. In this context, characterization of settling plays an important role. CeO2 composites are used to polish oxide coatings in the semiconductor industry and sedimentation of the composite particles is important as it can affect the efficiency of the planarization process. Therefore, measuring sedimentation of these composites is necessary. In this study, the settling behavior is measured optically for a variety of conditions that differ in loading of inorganic nanoparticles within the microgels, temperature of the solution, and concentration of particles in solution. The overall goal is to understand the sedimentation behavior of these novel composites and facilitate their use in industrial processes.

Aging in skeletal muscle is characterized by a loss in muscular performance. This is in part related to the direct loss of muscle mass due to senescence, known as sarcopenia. With age, skeletal muscles lose force production, contractile speed, and power production. The force velocity relationship of muscle is a product of force production and contraction speed, both of which decline with age; however, the mechanisms and trajectory of this decline are not well understood. Exercise has positive effects on muscle, and thus may assist in maintaining performance in old age. However, few long-term studies have been performed to examine the effects of life-long exercise on muscle contractile performance. In order to test the potential for life-long exercise to reduce the effects of again on muscle contractile performance, muscle performance was determined in control mice and mice selected for high voluntary wheel running at baseline, adult, and old ages. Peak isometric force declined with age in control (C) mice without exercise (P

The purpose of this study was to assess the acute effects of static stretching on foot velocity at impact with a soccer ball. Eighteen Division I female soccer athletes underwent two test conditions separated by 48 hr. Each condition was randomly assigned and began by placing four retro-reflective markers on bony landmarks of the ankle (total of eight markers, four on each ankle). One condition was the no-stretch condition, in which each participant performed a self-paced jog for 5 min as a warm-up, and then sat quietly for 6 min before performing three maximal instep kicks into a net. The second condition was the stretch condition, which was identical to the no-stretch condition, except the participants performed a series of six randomly ordered stretches instead of sitting quietly for 6 min. Three-dimensional motion analysis was used to quantify the resultant velocity of the head of the 5th metatarsal immediately prior to foot impact with a soccer ball. The results of a dependent t test indicated that there was no significant difference between the no-stretch (18.34 ± 1.29 m/s) and stretch conditions (17.96 ± 1.55 m/s; p = .102, d = .3) Based on these findings, acute stretching performed one time for 30 s before maximal instep soccer kicking has no effect on the resultant foot velocity of Division 1A university female soccer players. Pre-event stretching performed in a like manner may best be prescribed at the discretion of the athlete.

Philosophiae Doctor - PhD / Investigation of the acoustic impedance variations in the upper shallow marine sandstone reservoirs was extensively studied from 10 selected wells, namely: F-O1, F-O2, E-M4, E-CN1, E-G1, E-W1, F-A10, F-A11, F-A13, and F-L1 in the Bredasdorp Basin, offshore, South Africa. The studied wells were selected randomly across the upper shallow marine interval with the purpose of conducting a regional study to assess the variations in the acoustic impedance across the reservoirs using wireline log and core data. The datasets used in this study were geophysical wireline logs, conventional core analysis, geological well completion reports, core plugs, and core samples. The physical rock properties such as lithology, fluid type, and hydrocarbon bearing zone were identified while different parameters like the volume of clay, porosity, and water saturation were quantitatively estimated. The reservoirs were penetrated at a different depth ranging from a shallow depth of 2442m at well F-L1 to a deeper depth of 4256.7m at well E-CN1. The average volume of clay, average effective porosity from wireline log, and average water saturation ranged from 8.6%- 43%, 9%- 16% and 12%- 68%, respectively. Porosity distribution was fairly equal across the field from east to west except in well F-A10, F-A13, and F-A11 where a much higher porosity was shown with F-A13 showing the highest average value of 16%. Wells E-CN1, E-W1, F-O1, F-L1 and E-G1 had lower porosity with E-CN1 showing the lowest average value of 9%. The acoustic properties of the reservoirs were determined from geophysical wireline logs in order to calculate acoustic impedance and also investigate factors controlling density and acoustic velocities of these sediments. The acoustic impedance proved to be highest on the central to the western side of the field at E-CN1 with an average value of 11832 g/cm3s whereas, well F-A13 reservoir in the eastern side of the field proved to have the lowest average acoustic impedance of 9821 g/cm3s. There was a good linear negative relationship between acoustic impedance and porosity, compressional velocity vs porosity and porosity vs bulk density. A good linear negative relationship between acoustic impedance and porosity was obtained where the reservoir was homogenous, thick sandstone. However, interbedded shale units within the reservoir appeared to hinder a reliable correlation between acoustic impedance and porosity. The cross-plots results showed that porosity was one of the major factors controlling bulk density, compressional velocity (Vp) and acoustic impedance. The Gassmann equation was used for the determination of the effects of fluid substitution on acoustic properties using rock frame properties. Three fluid substitution models (brine, oil, and gas) were determined for pure sandstones and were used to measure the behaviour of the different sandstone saturations. A significant decrease was observed in Vp when the initial water saturation was substituted with a hydrocarbon (oil or gas) in all the wells. The value of density decreased quite visibly in all the wells when the brine (100% water saturation) was substituted with gas or oil. The fluid substitution affected the rock property significantly. The Vp slightly decreases when brine was substituted with water in wells F-A13, F-A10, F-O2, F-O1 F-A11, F-L1, and E-CN1. Wells E-G1, E-W1, and E-M4 contain oil and gas and therefore showed a notable decrease from brine to oil and from oil to gas respectively. Shear velocity (Vs) remained unaffected in all the wells. The acoustic impedance logs showed a decrease when 100% water saturation was replaced with a hydrocarbon (oil or gas) in all the wells. Clay presence significantly affects the behaviour of the acoustic properties of the reservoir rocks as a function of mineral type, volume, and distribution. The presence of glauconite mineral was observed in all the wells. Thirty-two thin sections, XRD and SEM/EDS from eight out of ten wells were studied to investigate lithology, diagenesis and the effect of mineralogy on porosity and acoustic properties (Compressional velocity and bulk density) within the studied reservoir units. Cementation (calcite and quartz), dissolution, compaction, clay mineral authigenesis, and stylolitization were the most significant diagenetic processes affecting porosity, velocity, and density.Well E-CN1 reservoir quality was very poor due to the destruction of intergranular porosity by extensive quartz and illite cementation, and compaction whereas well F-A13 show a highly porous sandstone reservoir with rounded monocrystalline quartz grain and only clusters of elongate to disc-like, authigenic chlorite crystals partly filling a depression within altered detrital grains. Overall, the results show that the porosity, lithology mineralogy, compaction and pore fluid were the major factors causing the acoustic impedance variations in the upper shallow marine sandstone reservoirs. / 2021-09-01

Music appears to have advantageous effects during exercise as it has been shown to increase motivation, decrease ratings of perceived exertion (RPE), and improve exercise performance. The improvement of running performance in particular, is the main effect recreational runners want to focus on as many want to improve their time in road races. Running velocity, indicated by a faster time to completion is thought to improve with an increase in step frequency, step length, or a combination of these variables. Currently, there is limited research that observes methods to help increase step frequency or step length. The manipulation of music cadence may be considered an effective training method that influences step frequency. The purpose of this study was to observe the effect of music cadence on step frequency in the recreational runner. A total of 30 recreational runners (15 male, 15 female) with a mean age of 31.0 ± 5.8 (range= 20-39), a BMI of 24.0 ± 3.3 (range= 19-32), and an estimated VO2 max of 49.6 ± 5.4 (range= 41-60) participated in this study. Individually, runners completed four 1600-meter time trials on an outdoor track at maximal effort. The first trial was a familiarization trial where participants ran 1600 meters with no music. Two music conditions were then created for each runner based on their natural step frequency obtained during the familiarization trial. The first condition represented music at natural step cadence and the second condition represented music at increased step cadence. The next three 1600 meter time trials were randomized and included a control condition of no music, a natural cadence music condition at the runner's natural step frequency, and an increased cadence music condition of 10-20 beats per minute (bpm) above the natural cadence music condition. Results indicated that step frequency was significantly higher during the increased cadence music condition compared to both the natural cadence music and no music conditions (p < 0.05). Additionally, time to completion was significantly lower in the increased cadence music condition compared to both the natural cadence music and no music conditions (p < 0.05). Lastly, there was no significant difference in step length among music conditions. These results indicate that music cadence had a positive influence on running performance as it was able to increase step frequency and improve time to completion in a group of recreational runners. Therefore, for practical application, recreational runners can alter music cadence to help improve running performance.

[Truncated abstract] Seismic tomography has been extensively used in geophysics for different purposes such as geological mapping and prospecting for oil and gas. In geophysics, ultrasound or electromagnetic waves are normally used to provide the tomographic information. In the geotechnical area, seismic tomography is emerging as a promising technique that can be used to determine the spatial variability of shear wave velocities and hence the small strain stiffness of geomaterials. Although some studies have been undertaken to incorporate seismic measurement into centrifuge modelling, there has been to date no attempt to build a complete seismic tomography facility with high resolution for use in a geotechnical centrifuge. Such a powerful facility can help in better understanding of soil behaviour by providing a complete picture of the spatial variation of the soil property of concern. The main aim of this study was to develop a high-resolution seismic tomography (ST) system for the beam centrifuge at the University of Western Australia (UWA) by which the shear wave velocity and hence maximum shear modulus could be determined anywhere in the centrifuge model. ... This limitation was the requirement to use an a priori model. The exact solutions in the different examples presented in this chapter were known, and they were used as a priori models into the inversion process. However, in practice the exact solution is unknown, and the aim of the tomographic inversion is to obtain a solution that best describes the measured data. Carrying out inversion without using an a priori model can yield an output model that hints at the nature of the model. This output can then be used as the starting point in an iterative process, in which the output from one step is used as an a priori model for reinverting the original data in a subsequent step. In this case, this process slightly improved the output tomogram and decreased the value of root mean squares of travel time residuals (Rrms). An alternative inversion strategy was proposed based on the results obtained in this study. It involves using a searching algorithm. A searching process can be carried out based on the output from the first iteration (without using an a priori model). The search can involve varying the parameters that describe buried anomalies, such as the size of the anomaly, the velocity value in the anomaly, and the location of the anomaly. The aim is to search for the combination of anomaly parameters that minimises the resulting error parameters (mainly Rrmx, but also the average error and the standard deviation of the error). For more subtle cases, such as the velocity model under a footing, where inversion without using an a priori model did not recover the input model, a searching algorithm involving applying perturbations to the exact Boussinesq model can be performed. Not only can the searching procedure involve adding perturbation to the velocity values in the Boussinesq model, but it can also add perturbation to the shape of the velocity distribution below the footing. The searching process can continue until a model that fits the data with a minimum error is found, i.e., minimising Rrms.

The relationships between selected sprint specific bounding exercises and sprint performance were analysed using fourteen sprint athletes (7 elite performers, 7 sub-elite performers). Subjects were required to perform sprints over 60m, Counter Movement Jumps with and without loading (20kg), High Speed Alternate Leg Bounding over 30m and High Speed Single Leg Hopping over 20m. All athletes were subject to anthropometric measurement (Height, Weight and Leg Length). Of all variables measured, the Elite group were significantly better (p<0.001) in Counter Movement Jump, Time to 60m, Time from 30m to 60m and in their Maximal Running Velocity. Linear regressions were carried out on all variables that correlated with Time to 30m (Acceleration Phase) and Maximal Running Velocity at both the pO.OOl and p<0.01 level of significance. This allowed several prediction tables to be compiled that had performance measures (sprints and jumps) that could be used as testing measures for sprint athletes to determine their Acceleration Phase and Maximal Running Velocity. A stepwise multiple regression demonstrated that Time to 60m was the best predictor of Maximal Running Velocity. Time to 60m, Leg length, High Speed Alternate Leg Bounding and Sprint Stride Rate were the best predictors of the Acceleration Phase. A Stepwise cross-validation linear discriminant function analysis was used to determine the best predictors from both sprint and jump measures that would distinguish an athlete as an elite or sub-elite performer. From sprint variables, Time to 60m and Time to 30m were the two variables that best placed a sprint subject in either the Elite or Sub-elite group. From the bounding variables, Counter Movement Jump and the Ground Contact Time of the High Speed Alternate Leg Bounding were the two variables that best placed a sprint subject in either the Elite or Sub-elite group. The present study suggests that Time to 60m is the best predictor of Maximal Running Velocity and Acceleration Phase. Counter Movement Jumping and High speed Alternate Leg Bounding are also useful tools in developing and testing elite sprint athlete performance.