Thesis (M. Optometry) -- University of Limpopo, 2019 / BACKGROUND The measurement of the refractive end point plays a major role in the assessment of the refractive status of the patient. Currently, there are very few techniques if not one that can measure the refractive end point of the patient. The current method which is the duochrome technique is based on chromatic aberration. Until now there is no test for refractive end point that is not based on chromatic aberration. Therefore, it was against this background that the current study was undertaken to investigate an alternative for the duochrome technique to measure the refractive end point. AIM OF THE STUDY The aim of this study was to establish the use of cross grid in conjunction with Jackson crossed cylinders at distance as a monocular refractive end point technique. METHODOLOGY A cross-sectional analytic and descriptive study design was used. Sixty-four subjects (31 males and 33 females) were included in this study. Their ages ranged from 18 to 37 years with a mean of 20.75 years (SD = ± 2.67 years). The participants were University of Limpopo Optometry students. Ethical approval to perform this study was obtained from the Turfloop Research Ethics Committee (TREC) of University of Limpopo. All participants were made aware of the purpose of the study, and signed consent was obtained from each participant. All investigations and measurements adhered to the tenets or principles, belief and requirements of the Declaration of Helsinki. Optometric procedures performed included visual acuity, subjective measurement of refractive error, monocular refractive end point using duochrome technique and monocular refractive end point measurement using gross grid in conjunction with the cross grid. Data analysis was done using the Statistical Package for Social Sciences (SPSS) Version 23. Paired sample t-test was performed on all the procedures. RESULTS The uncorrected distance VA for the right eyes (OD) ranged from -0.30 LogMAR to 1.00 LogMAR with a mean of -0.25 LogMAR (SD = ±0.32). The nearest equivalent spherical powers (NSE = sphere +0.5 cylinder) for the right eye ranged from -4.25 to +4.25D (mean = -0.13, SD= ±1.09D) and from -4.50D to +1.00D (mean = +0.07 ±0.94D) for the left eye. After the removal of outliers, the refractive end point measurements with the duochrome technique for the right eyes ranged from -4.50D to 3.50D with a mean of -0.269, SD (±1.037) in bright illumination and from -4.50D to 4.50D with a mean of -1.914 (±1.101) in dim illumination. Subsequently, the NSE with the crossed cylinder in conjunction with the cross grid technique for the right eyes in bright illumination ranged from -4.75D to 4.75D with a mean of -0.481, SD (±1.037) and from -4.25D to 0.50D with a mean of -0.427 (±0.860) in dim illumination. Sample Pearson correlation coefficients for end point with duochrome and crossed cylinder found that the highest correlation is between the duochrome in bright and cross grid in dim illumination (r = 0.701, p < 0.05), while duochrome in dim and cross grid in bright illumination had the lowest correlation (r = 0.659). The Bland–Altman plots showed that there was a good agreement between the duochrome methods and between the crossed cylinder method methods. CONCLUSION the refractive end point measurements obtained from duochrome and cross grid are well correlated and comparable, suggesting that they could be used interchangeably in most clinical settings. However, caution is needed when using measurements obtained by cross grid method in dim illumination.

Utilizing the higher capacity steel in design can provide additional advantages to the concrete construction industry including a reduction of congestion, improved concrete placement, reduction in the required reinforcement and cross sections which would lead to savings in materials, shipping, and placement costs. Using high-strength reinforcement is expected to impact the design provisions of ACI 318 code and other related codes. The Applied Technology Council (ATC-115) report "Roadmap for the Use of High-Strength Reinforcement in Reinforced Concrete Design" has identified key design issues that are affected by the use of high-strength reinforcement. Also, ACI ITG-6, "Design Guide for the Use of ASTM A1035 Grade 100 Steel Bars for Structural Concrete" and NCHRP Report 679, "Design of Concrete Structures Using High-Strength Steel Reinforcement" have made progress towards identifying how code provisions in ACI 318 and AASHTO could be changed to incorporate high-strength reinforcement. The current research aims to provide a closer investigation of the behavior of beams reinforced with high-strength steel bars (including ASTM A615 Grade 100 and ASTM A1035 Grades 100 and 120) and high-strength concrete up to 12000 psi. Focus of the research is on key design issues including: ductility, stiffness, deflection, and cracking. The research includes an extensive review of current literature, an analytical study and conforming experimental tests, and is directed to provide a number of recommendations and design guidelines for design of beams reinforced with high-strength concrete and high-strength steel. Topics investigated include: strain limits (tension-controlled and compression-controlled, and minimum strain in steel); possible change for strength reduction factor equation for transition zone (Φ); evaluation of the minimum reinforcement ratio (þmin); recommendations regarding limiting the maximum stress for the high-strength reinforcement; and prediction of deflection and crack width at service load levels. Moreover, this research includes long-term deflection test of a beam made with high grade concrete and high-strength steel under sustained load for twelve months to evaluate the creep deflection and to insure the appropriateness of the current ACI 318 time-dependent factor, λ, which does not consider the yield strength of reinforcement and the concrete grade.

In an effort to develop more efficient and practical interventions for athletic performance, some behavioral researchers have incorporated a variety of technological innovations. In sports research, only a few studies have examined the effects of video feedback on athletic skill development. The effects of combining expert video modeling with self video feedback as an adjunct to standard coaching techniques were analyzed in this study. Participants in this study were four 7-10 year old competitive gymnasts. During the intervention, each gymnast performed a specific gymnastics skill and then viewed a pre-recorded video segment showing an expert gymnast performing the same skill. The gymnast then viewed a video replay of her own performance of the skill. Next she saw a side by side slow motion with freeze frame comparison of her performance with that of the expert model. Lastly, in normal time, the gymnast viewed the expert video clip again, followed by her own performance of the skill. The effect of expert video modeling with self video feedback on gymnastics skill performance was evaluated in a multiple baseline across behaviors research design. The results showed that the gymnasts' skills increased in performance following exposure to video feedback.

Abstract not available

Steel corrosion in reinforced concrete is a major concern to transportation agencies nationwide because of the expenses incurred for repair and ultimate shortening of bridge life. Cathodic protection (CP), as a remedy, has been applied to reinforced bridges in the US since 1974. However, application of this technique is largely empirical, lacking fundamental understanding. In order to optimize the performance of a CP system, it is important to monitor the rebar potential with respect to a reliable reference electrode. Moreover, because of potential variation in the concrete, reference cell placement is fundamental to ensure effective protection. The work plan was divided into two parts: laboratory scale experimentation and computer simulation. In the experimentation section, the response of graphite probes was compared to that of an Orion silver-silver chloride electrode. Graphite probes behaved as well as the standard electrode. Furthermore, the home-made graphite probes behaved the same as the commercial ones. This will allow much greater experimental latitude since the home-made probes are much more economical than the commercial ones. A finite difference code was developed to assess the performance of cathodic protection. The potential distribution in a two dimensional geometry of a concrete block with a sprayed zinc anode at one boundary and an iron cathode at the other side was calculated under cathodic protection. The equations were solved by means of a Gauss-Seidel iterative method with the help of an overrelaxation factor. An interval halving method was used to solve for nonlinear boundary condition at the iron. The effects of concrete pore saturation, concrete cover, and applied potential were studied to determine the degree of protection and proper placement of the reference electrode in concrete. Furthermore, a sensitivity analysis was performed versus input parameters: concrete conductivity, oxygen mass transfer coefficient, and oxygen reduction polarization parameters. The results of the simulation showed that the center of the rebar is less protected than the other locations. Therefore, the reference electrode should be located as close to the center as possible. / Graduation date: 1995

Simple but still realistic physical models suitable for structural design of flat concrete plates and column footings with respect to punching are presented. Punching of a flat plate is assumed to occur when the concrete compression strain at the column edge due to the bending moment in the slab reaches a critical value that is considerably lower than the generally accepted ultimate compression strain 0.0035 for one-way structures loaded in bending. In compact slabs such as column footings the compression strength of the inclined strut from the load to the column is governing instead. Both the strain limit and the inclined stress limit display a size-effect, i.e. the limit values decrease with increasing depth of the compression zone in the slab. Due respect is also paid to increasing concrete brittleness with increasing compression strength. The influence of the bending moment means that flat plates with rectangular panels display a lower punching capacity than flat plates with square panels – a case that is not recognized by current design codes. As a consequence, punching shall be checked for each of the two reinforcement directions separately if the bending moments differ. Since the theory can predict the punching load as well as the ultimate deflection of test specimens with good precision, it can also treat the case where a bending moment, so called unbalanced moment, is transferred from the slab to the column. This opens up for a safer design than with the prevailing method. It is proposed that the column rotation in relation to the slab shall be checked instead of the unbalanced moment for both gravity loading and imposed story drift due to lateral loads. However, the risk for punching failure is a great disadvantage with flat plates. The failure is brittle and occurs without warning in the form of extensive concrete cracking and increased deflection. Punching at one column may even initiate punching at adjacent columns as well, which would cause progressive collapse of the total structure. A novel reinforcement concept is therefore presented that gives flat plates a very ductile behaviour, which eliminates the risk for punching failure. The performance is verified by tests with monotonic as well as cyclic loading. / QC 20100929

No description available.

Esta tesis se dedica en un estudio de estabilidad no lineal de la morfodinàmica de la zona de rompientes de playas de arena. El modelo numérico MORFO55 resuelve las ecuaciones de aguas someras no lineales para la hidrodinámica y actualiza la topografía a partir del transporte de sedimento. En primer lugar, se aplica en el caso de playas complejas longitudinalmente no uniformes con objeto de probar sus distintas formulaciones. En secundo lugar, se usa para estudiar la generación de estructuras rítmicas en playas longitudinalmente uniformes. Entre estos patrones se distinguen las barras transversales y oblicuas, las barras crescenticas y los sistemas de barras/surcos (ridges/runnels). La hipótesis de que emergen a partir de inestabilidades internas del acoplamiento entre la topografía y la hidrodinámica se investiga. Los estudios previos de modelización numérica se limitaban a las etapas iniciales de la generación de las barras. En particular, mostraban que las barras transversales y oblicuas pueden formarse en playas planas mientras que las barras crecenticas aparecen en playas con barra. La formación de los sistemas de barras/surcos se explica con modelos conceptuales de la observación mediante satélite según los cuales emergerán a partir de la deformación de la barra intermareal. Esta tesis estudia el régimen no lineal de la evolución de todos estos sistemas. Particularmente se obtiene un estado 'nal de equilibrio. Los resultados generales coinciden cualitativamente con las barras observadas en la naturaleza. Se da una interpretación física de la formación, de la evolución y de la saturación del crecimiento de las barras. / This thesis performs a nonlinear stability study of the surf zone morphodynamics of sandy beaches. To this end the MORFO55 model based on a wave and depth averaged nonlinear shallow water equations solver with wave driver, sediment transport and bed updating is presented. It is first applied to complex longitudinally non-uniform beaches in order to test different model formulations. Second, it is applied to study the generation of surf zone rhythmic features on alongshore uniform beaches. Shore-attached transverse or oblique bars, crescentic bars and ridge and runnel systems are well known examples of such features. The hypothesis that they emerge by self organisation of the coupling between topography, waves and currents is here tested. In absence of shore-parallel bars, the initial formation of transverse and oblique bars had been shown by previous modelling studies of linear stability analysis but is now extended to the finite amplitude regime. In most of barred beaches, crescentic bars and ridge and runnel systems appear. Conceptual models based on field observations suggest that ridges and runnels could emerge by the deformation of the alongshore intertidal bar intercepted by crescentic bars. Up to now, only the formation of crescentic bars had numerically succeeded with linear and non linear models. This study shows that a dynamical equilibrium state of each of these rhythmic bar systems may be described with a numerical model. General results are in qualitative agreement with the bar systems observed in nature. A physical explanation for their formation, their evolution and the saturation of their growth is given.

Self consolidating concrete (SCC) is widely used in the construction industry. SCC is a high performance concrete with high workability and consistency allowing it to flow under its own weight without vibration and making the construction of heavily congested structural elements and narrow sections easier. Fiber reinforced polymer (FRP) reinforcement, with its excellent mechanical properties and non-corrosive characteristic, is being used as a replacement for conventional steel reinforcement. In spite of the wide spread of SCC applications, bond and flexural behaviour of SCC beams reinforced or prestressed with FRP bars has not been fully studied. Furthermore, the ACI 440.1R-06 equation for determining the development length of FRP bars is based on Glass FRP (GFRP) bars and may not be applicable for Carbon FRP (CFRP) bars. This research program included an experimental and analytical study to investigate the flexural and bond behaviour of SCC beams reinforced with FRP bars and SCC beams prestressed with CFRP bars. In the experimental phase, fifty-six beams were fabricated and tested. Sixteen of these beams were prestressed with CFRP bars and forty beams were reinforced with non-prestressed GFRP or CFRP bars. Four concrete batches were used to fabricate all the specimens. Three mixes were of self consolidating concrete (SCC) and one mix was of normal vibrated concrete (NVC). The test parameters for the non-prestressed beams were the concrete type, bar type and bar diameter, concrete cover thickness and embedment length while the test parameters for the prestressed beams were the concrete type and the prestressing level (30%, 45% and 60%). The transfer length of the prestressed CFRP bars was determined by means of longitudinal concrete strain profile and draw-in methods. All beams were tested in four-point bending to failure. Measurements of load, midspan deflection, bar slip if any at the beam ends, strain in reinforcing FRP bar at various locations, and strain in concrete at the beam midspan were collected during the flexural test. The concrete compressive strength at flexural tests of SCC mix-1, mix-2, and mix-3 were 62.1MPa, 49.6MPa and 70.9MPa, respectively and for the NVC mix was 64.5MPa. The material test results showed that SCC mixes had lower modulus of elasticity mechanical properties than the NVC mix. The modulus of elasticity of the SCC mixes ranged between 65% and 82% of the NVC mix. The modulus of rupture of the SCC mixes was 86% of the NVC mixes. The test results for beams prestressed with CFRP bars revealed that the variation of transfer length of CFRP bars in SCC versus their prestressing level was nonlinear. The average measured transfer lengths of 12.7mm diameter CFRP bars prestressed to 30%, 45% and 60% was found to be 25db, 40db, 54db, respectively. Measured transfer lengths of the 12.7mm diameter CFRP bar prestressed to 30% in SCC met the ACI440.4 prediction. However, as the prestressing level increased, the predicted transfer length became unconservative. At a 60% prestress level, the measured/prediction ratio was 1.25. Beams prestressed with CFRP bars and subjected to flexural testing with shear spans less than the minimum development length had local bar slippage within the transmission zone. Beams that experienced local bond slip, their stiffness was significantly decreased. A modification to the existing model used to calculate the transfer and development lengths of CFRP bars in NVC beams was proposed to account for the SCC. The test results for beams reinforced with FRP bars indicated that the average bond strength of CFRP bars in NVC concrete is about 15% higher than that of GFRP bars in NVC. The ACI 440.1R-06 equation overestimated the development length of the CFRP bars by about 40%, while CAN/CSA-S6-06 equation was unconservative by about 50%. A new factor of (1/1.35) was proposed to estimate the development length of the CFRP bars in NVC when the ACI440.1R-06 equation is used. Beams made from SCC showed closer flexural crack spacing than similar beams made from NVC at a similar loading. The deflection of beams made from SCC and reinforced with CFRP bars was found to be slightly larger than those made from NVC. The average bond stresses of GFRP and CFRP bars in SCC were comparable to those in NVC. However, FRP bars embedded in SCC beams had higher bond stresses within the uncracked region of the beams than those embedded in NVC beams. In contrast, FRP bars in SCC had lower bond stresses than FRP bars in NVC within the cracked region. The average bond strength of GFRP in SCC was increased by 15% when the concrete cover thickness increased from 1.0db to 3.0db. Cover thicknesses of 2db and 3db were found to be sufficient to prevent bond splitting failure of GFRP and CFRP bars in SCC, respectively. Bond splitting failure was recorded when the cover thickness dropped to 1.5db for the GRP bars and to 2.0db for the CFRP bars. An insignificant increase in average bond stress was found when the bar diameter decreased from 12.7mm to 6.3mm for the CFRP bars, and a similar increase occurred in GFRP bars when the bar diameter decreased from 15.9mm to 9.5mm. New models to calculate the development length of GFRP and CFRP bars embedded in SCC were proposed based on the experimental results. These models capture the average bond stress profile along the embedment length. A good agreement was found between the proposed model and the experimental results. Analytical modeling of the load-deflection response based on the effective moment of inertia (ISIS Canada M5) was unconservative for SCC beams reinforced with CFRP bars by 25% at ultimate loading. A new model for bond stress versus Ma/Mcr (applied moment to cracking moment) ratio was developed for GFRP and CFRP bars in SCC and for CFRP bars in NVC. These bond stress models were incorporated in a new rigorous model to predict the load-deflection response based on the curvature approach. The FRP bar extension and bond stress models were used to calculate the load-deflection response. With these models 90% of the calculated deflections were found to be within ± 15% of the experimental measured results for SCC beams reinforced with FRP bars. Analytical modeling of the load-deflection for NVC and SCC beams prestressed with CFRP bars are proposed done. The moment resistance was calculated using Sectional Analysis approach. The deflection was calculated using simplified and detailed methods. The simplified method was based on the effective moment of inertia while the detailed method was based on effective moment of inertia and effective centroid. The experimental results correlated well with the detailed method at higher loads range. This study provided an understanding of the mechanism of bond and flexural behaviour of FRP reinforced and prestressed SCC beams. The information presented in this thesis is valuable for designers using FRP bars as flexural reinforcement and also for the development of design guidelines for SCC structures.

The purpose of this research is to explore the communication and interaction between westerners and Chinese people in western bars in the touristic town of Yangshuo in southern China. Yangshuo is worldly famous for its breath-taking Karst Mountains, rice fields and water buffalos. It has attracted millions of visitors annually, both domestic and international. The tourist center of Yangshuo consists of a main street, West Street, and many other small streets around it. In recent years, bars and night clubs have been established, bringing a more modern and western atmosphere to the main tourist streets that are paved in marble and lined with ancient buildings. This research is focused on bars, western bars in particular, as a unique setting for intercultural communication and interaction. First of all, this research introduces a background of intercultural communication definitions, the link between bars and tourism in China, as well as international tourism in China. With the goal of understanding the intercultural phenomena in bars through conversations and observations, I explored the role of bars in the community, the social and intercultural situations in bars, and the reflection and outcome of those communication and interaction. Field work was conducted in July and August 2010, by using both qualitative and quantitative research methods: questionnaire survey and ethnographic participant observation. I was able to obtain a broad perception of the subject as well as detailed description from participants, including myself. A broad range of literature related to bars and spaces in leisure and tourism, as well as in the fields of intercultural communication, intercultural host-guest relationship in tourism, tourism and cultural understanding, and tourist experience were reviewed. The gaps in the literature were identified. Limited research was done by addressing the actual situations of intercultural communication and linking the social and intercultural theories with actual practice, especially in a tourism context. Also, the role of western bars, as a new form of recreational, cultural and social space in China needed more attention. Chapter four and five present major findings of this research. Informants were divided into five groups: western tourists, local westerners (westerners who have become residents), Chinese tourists, Chinese students studying English in Yangshuo, and local residents. Preliminary findings from questionnaire survey indicate that westerners and Chinese people have difference reasons for visiting Yangshuo and going to bars. Bars have both social and recreational functions for westerners but are of less interest to and have more limited functions as attractions to Chinese tourists. Local residents have the least interest in western bars but Chinese students often go to them, mainly to practice English with foreigners. Detailed analysis of qualitative data suggests intercultural communication and interaction have difference purposes and styles for the different groups. Students, locals who work in the bars and local westerners have most contact with western tourists. Chinese tourists tend to interact with westerners in non-verbal ways, such as in games and photo-taking. Language is a major communication barrier but westerners made more effort to overcome this, reflecting both desire and need as visitors in a foreign land. The research findings can seek theoretical explanation through many social and intercultural theories. They suggest tourist-host interaction and communication has been overrated, especially when tourists are travelling in a different culture. The level of contact and cultural understanding is relatively superficial, but more meaningful than mere commercial exchanges. The trend of globalization and cultural homogeneity was well recognized by both cultural groups. The acknowledgement of cultural difference and interaction between customers should be encouraged and facilitated in bars, in order to create an authentic bar experience and nurture effective intercultural communication.