M.Phil. (Optometry) / Previous studies of corneal and keratometric variation used incomplete or incorrect statistical methods. For the first time, proper multivariate statistical methods are applied to evaluate short-term keratometric variation in human eyes. Keratometric variation is represented graphically by means of stereo-pair scatter plots, trajectories of change in dioptric power, ellipsoidal confidence regions for mean dioptric power, as well as meridional profiles. Quantitative expressions of variation are given in terms of mean values, variance-covariance matrices and volumes of 95% distribution ellipsoids. Manual and automatic keratometry is compared, both on a steel ball and on an eye. It appears that the automatic keratometer exhibits less variation than the manual keratometer....

M.Phil. / Using newly developed statistical analysis methods for refractive error this study examines the difference between autorefraction and subjective refraction and how it is related to age. The term autorefractive excess refers to the amount obtained by subtracting the subjective refraction from the autorefraction. The clinical sample consisted of five groups of fifty subjects each. The subjects in group 1 ranged in age from 1 to 10 years, group 2 from 11 to 20 years, group 3 from 21 to 30 years, group 4 from 31 to 40 years and group 5 from 41 years and older. Only one examiner (the author) and one autorefractor (Allergan-Humphrey 580) were used. The study found that there was a difference between the mean autorefractive excesses for the different age groups and that the difference between autorefraction and subjective refraction was statistically significant in both the left and the right eyes of all age groups. Left and right eyes exhibited similar behavior. The autorefractive excess for both the left and the right eyes together of group 1 was approximately -0.25/-0.18 x180 in conventional and (-0.25 0.00 -0.43)' in h-notation. The autorefractive excess increases by approximately (0.10 0.00 0.10)' per decade. There is an astigmatic component of approximately -0.18 x180 in both eyes of all age groups. Approximately 60% of the subjects had sphere-equivalent strengths of autorefractive excesses of under 0.50 D. Therefore 60% of subjects might be content with a prescription given from the autorefractor reading. Approximately 50% of subjects had cylinderequivalent strengths of autorefractive excesses of under 0.50 D.

M.Phil. / The aim of this study was to use auto refraction to investigate both the short-term intra-ocular variation of refractive status among primary school children and the spread of refractive status across eyes. The sample consisted of 90 Caucasian school children from a primary school in a small town, Eloff, in the Mpumalanga province of South Africa ...

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M.Phil. / Keratometric readings on three subjects were taken both during pregnancy and postpartum. One subject was visually non-compensated and did not require refractive correction, one was a contact lens wearer and one had undergone radial keratotomy. Twenty readings were taken by means of an automatic keratometer on each eye, morning and afternoon, every fortnight. The recent matrix method of optometric statistical analysis was employed and the results graphically compared and analysed. Findings indicate diurnal variations including variation in corneal curvature and variance through the course of normal pregnancy. Most evident was an increase in keratometric variation in all three subjects at the time of birth and a substantial decrease in corneal refractive power in the subject who had before undergone radial keratotomy. This result may have far-reaching implications on the long term prognosis of refractive surgery especially for females of child bearing age. Outliers representing transient increases in curvature were most common in the vertical meridian (indicating possible lid interaction), while the presence of bimodal distributions suggests a sensitivity of the automatic keratometer to changes in head posture.

ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / This document is focused on the examination of the tracking angular error due to the radio refraction for the target in low altitude of less than 5km and in low elevation angle. The real measured data using the GPS and the tracking systems of C- and S-band frequency in NARO Space centre, Korea are used for the analysis. The analysis shows couple of conclusions on the radio refraction effects; there are angular errors due to the radio refraction which is not to be neglected comparing the accuracy of the tracking system but to be considered for the precise measurement of the target position. Also, the refraction errors are dependent on the target altitude, but not on the frequency.

A great number of the urban areas in Ethiopia are situated within the Great Rift Valley of Ethiopia, a system consisting of depressions and large faults. As a region with significant seismic activities, it is vital that careful planning is implemented to avoid constructing buildings on flat surfaces as they can amplify ground motion in the case of an earthquake.   This study was conducted in Adama, a city located within the rift system, to map and characterize the subsurface of a construction site with seismic refraction and investigate whether this is an optimal area to construct a building should an earthquake occur. Seismic refraction is based on Snell’s law, specifically the case of the critical angle, which is when the refracted angle is at 90 degrees and a number of the energy from the wave is rebounded back to the surface in accordance with Huygen’s Principle.       Seismic waves were generated with a sledgehammer and recorded with 24 vertical geophones. The acquired data was then analysed with SeisImager and produced a 2D-tomography of the site with the corresponding velocity layers for a P-wave. Comparing the P-wave velocities to a table of Seismic Velocities of Rocks and Various Materials, one could determine that the subsurface layers consisted of rock soils, sand and silt. These are incredibly loose materials that will amplify ground motion during earthquake crisis and are therefore not optimal or ideal for constructing buildings.

by Maksudul Islam. / Publication date from spine. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 58-65). / Questionaire also in Chinese. / Chapter CHAPTER1 --- ABSTRACT --- p.1 / Chapter CHAPTER2 --- INTRODUCTION --- p.3 / Chapter CHAPTER3 --- OBJECTIVES --- p.7 / Chapter CHAPTER4 --- LITERATURE REVIEW --- p.8 / Chapter 4.1.1 --- BACKGROUND --- p.8 / Chapter 4.1.2 --- GENETIC AND ENVIRONMENTAL STUDY --- p.9 / Chapter 4.1.3 --- EPIDEMIOLOGY OF MYOPIA --- p.14 / Chapter 4.1.4 --- RELATIONSHIP BETWEEN MYOPIA & OPTICAL COMPONENTS --- p.18 / Chapter 4.1.5 --- AXIAL LENGTH --- p.19 / Chapter 4.1.6 --- VITREOUS LENGTH --- p.20 / Chapter 4.1.7 --- CHANGES OF REFRACTION IN SCHOOL CHILDREN --- p.21 / Chapter 4.1.8 --- DEVELOPMENT OF MYOPIA --- p.23 / Chapter 4.1.9 --- EMMETROPIZATION --- p.26 / Chapter 4.1.10 --- SEX --- p.27 / Chapter 4.1.11 --- FACTORS --- p.29 / Chapter CHAPTER5 --- METHODS --- p.34 / SUBJECTS --- p.34 / PROCEDURE --- p.35 / Chapter CHAPTER6 --- RESULTS --- p.37 / Chapter 6.1.1 --- THE DISTRIBUTION OF REFRACTION --- p.37 / Chapter 6.1.2 --- THE RELATION BETWEEN AGE WITH REFRACTION AND OPTICAL COMPONENTS --- p.38 / Chapter 6.1.3 --- RELATION BETWEEN SEX AND REFRACTION --- p.39 / Chapter 6.1.4 --- RELATION BETWEEN REFRACTION AND OPTICAL COMPONENTS --- p.39 / Chapter 6.1.5 --- RELATION BETWEEN REFRACTION AND VISUAL TASK --- p.40 / Chapter 6.1.6 --- RELATION BETWEEN OCULAR COMPONENTS AND VISUAL TASK --- p.42 / Chapter 6.1.7 --- RELATION BETWEEN OCULAR COMPONENTS AND REFRACTION TO PARENTAL MYOPIA AND EDUCATION --- p.44 / Chapter CHAPTER7 --- DISCUSSION --- p.47 / Chapter CHAPTER8 --- REFERENCES --- p.58 / TABLES --- p.66 / FIGURES --- p.86 / APPENDIX I-II QUESTIONNAIRE IN CHINESE --- p.100 / APPENDIX III-IV QUESTIONNAIRE IN ENGLISH TRANSLATION --- p.110

The refraction convolution section (RCS) is a simple and efficient method for full trace processing of shallow seismic refraction data. It facilitates improved interpretation of shallow seismic refraction data through the convenient use of amplitudes as well as traveltimes. The RCS is generated by the convolution of forward and reverse shot records. The convolution operation effectively adds the first arrival traveltimes of each pair of forward and reverse traces and produces a measure of the depth to the refracting interface in units of time which is equivalent to the time-depth function of the generalized reciprocal method (GRM). The convolution operation also multiplies the amplitudes of first arrival signals. This operation compensates for the large effects of geometric spreading to a very good first approximation, with the result that the convolved amplitude is essentially proportional to the square of the head coefficient. The head coefficient is approximately proportional to the ratio of the specific acoustic impedances in the upper layer and in the refractor, where there is a reasonable contrast between the specific acoustic impedances in the layers. The RCS can also include a separation between each pair of forward and reverse traces in order to accommodate the offset distance in a manner similar to the XY spacing of the GRM. Lateral variations in the near-surface soil layers can effect amplitudes thereby causing 'amplitude statics'. Increases in the thickness of the surface soil layer correlate with increases in refraction amplitudes. These increases are adequately described and corrected with the transmission coefficients of the Zoeppritz equations. The minimum amplitudes, rather than an average, should be used where it is not possible to map the near surface layers. The use of amplitudes with 3D data effectively improves the spatial resolution by almost an order of magnitude. Amplitudes provide a measure of refractor wavespeeds at each detector, whereas the analysis of traveltimes provides a measure over several detectors, commonly a minimum of six. The ratio of amplitudes obtained with different shot azimuths provides a detailed qualitative measure of azimuthal anisotropy. Dip filtering of the RCS removes 'cross-convolution' artifacts and provides a convenient approach to the study of later events. The RCS facilitates the stacking of refraction data in a manner similar to the CMP methods of reflection seismology. It can improve signal-to-noise ratios.