Testing the efficient market hypothesis in the cryptocurrency market
- Authors: Apopo, Natalya Camilla
- Date: 2019
- Subjects: Digital currency
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: http://hdl.handle.net/10948/42427 , vital:36662
- Description: Digital currencies are rising in popularity owing to their purported benefits and the speculative profits that investors are making in the market. These currencies, though decentralised in substance, can be purchased using digital wallets from cryptocurrency exchange platforms around the world. In Africa, these platforms are still at the nascent stages of growth and development, but evidence suggests a burgeoning potential in these markets. Volatility in these markets has been a topic of concern for many empirical investigations with most finding corroborative evidence of excess volatility in the digital currency market. However, there is a conflicting body of evidence when it comes to the studies evaluating the efficiency of the virtual currency market. The efficient market hypothesis ( EMH)is a controversial theory in finance. Proponents argue that it provides a basis for understanding financial markets whereas opponents suggest that the hypothesis is premature in its assumptions of the real functioning of these markets. Though not perfect, the efficient markets model provides a sufficient baseline against which capital markets may be analysed. Besides being one of the most empirically investigated theories in finance, its utility led to the development of later models such as the capital asset pricing model. In postulating that the prices of securities reflect all available information in capital markets, the efficient markets theory lends itself to testing the efficacy levels of the cryptocurrency market. For the purposes of this study, the weak version of the efficient markets theory was evaluated as itis considered the lowest possible form of efficiency attainable. Using both linear and nonlinear unit root testing methodologies, a significant subset of the cryptocurrency market was investigated for inefficiencies via the null hypothesis of non-stationarity. There were mixed results from the testing process, but a substantial portion of the currencies investigated rejected the null of a unit root in favour of stationarity, providing some evidence against weak form efficiency. For these reasons, it is recommended that further research be conducted in the virtual currency markets to offer more conclusive findings.
- Full Text:
- Date Issued: 2019
- Authors: Apopo, Natalya Camilla
- Date: 2019
- Subjects: Digital currency
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: http://hdl.handle.net/10948/42427 , vital:36662
- Description: Digital currencies are rising in popularity owing to their purported benefits and the speculative profits that investors are making in the market. These currencies, though decentralised in substance, can be purchased using digital wallets from cryptocurrency exchange platforms around the world. In Africa, these platforms are still at the nascent stages of growth and development, but evidence suggests a burgeoning potential in these markets. Volatility in these markets has been a topic of concern for many empirical investigations with most finding corroborative evidence of excess volatility in the digital currency market. However, there is a conflicting body of evidence when it comes to the studies evaluating the efficiency of the virtual currency market. The efficient market hypothesis ( EMH)is a controversial theory in finance. Proponents argue that it provides a basis for understanding financial markets whereas opponents suggest that the hypothesis is premature in its assumptions of the real functioning of these markets. Though not perfect, the efficient markets model provides a sufficient baseline against which capital markets may be analysed. Besides being one of the most empirically investigated theories in finance, its utility led to the development of later models such as the capital asset pricing model. In postulating that the prices of securities reflect all available information in capital markets, the efficient markets theory lends itself to testing the efficacy levels of the cryptocurrency market. For the purposes of this study, the weak version of the efficient markets theory was evaluated as itis considered the lowest possible form of efficiency attainable. Using both linear and nonlinear unit root testing methodologies, a significant subset of the cryptocurrency market was investigated for inefficiencies via the null hypothesis of non-stationarity. There were mixed results from the testing process, but a substantial portion of the currencies investigated rejected the null of a unit root in favour of stationarity, providing some evidence against weak form efficiency. For these reasons, it is recommended that further research be conducted in the virtual currency markets to offer more conclusive findings.
- Full Text:
- Date Issued: 2019
Tribocorrosion properties of friction stir welded and laser welded titanium alloy
- Authors: Davoren, Brandon Hilton
- Date: 2017
- Subjects: Chemistry, Technical -- Research Materials -- Mechanical properties , Aluminum alloys
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/33250 , vital:32605
- Description: Titanium alloy Ti6Al4V has extensive uses in aerospace, dentistry and the biomedical industry. When used in these applications there is often a need to weld two or more pieces of titanium alloy together. This can be done by either friction stir weld or laser weld methods. These welded regions are often exposed to corrosive environments in addition to factors such as induced additional mechanical wear. Thus to accurately report on the viability of the material in a specific application, the corrosion, wear and their synergistic effects need to be studied. Friction stir welding, which is a well-suited method for joining plates of Ti6Al4V, creates regions in the material that are affected differently. These regions can be described as the parent material, advancing side, retreating side and the weld zone. The tribological properties of the different friction stir weld regions were analysed in air using different loads, frequencies, experimental duration and surrounding environments. When the applied load was increased some of the weld regions showed an increase in the specific wear rate. For example, the weld zone region showed a decrease when compared to the parent material. In this tribology study the effect of the counter material was evaluated. E52100, Si3N4, SS 316 and alumina counter materials were used in the test procedure which was conducted in air on the weld regions. The parent material was found to have the highest average specific wear rates with the four counter materials when compared to the weld zone samples. The regions affected by the friction stir weld process all showed, on average, lower specific wear rates than the parent material. For the various tested samples, the coefficient of friction and material compatibility that was found to be the most stable, was the alumina ball. Owing to this as well as its chemical stability, alumina was determined to be the best material for further tribocorrosion studies. The friction stir welded samples, that were cut from a cross section of a friction stir weld plate, were analyzed in 3.5% NaCl and dilute Harrison’s solution respectively. The effect of wear on the electrochemical properties was studied under open circuit voltage (OCV) and fixed 0.2 V and 0.4 V applied potential conditions respectively. The effect of wear on the corrosion properties was studied using potentiodynamic polarization. From analyzing the friction stir weld regions in both a wear and wear-free environment, the synergistic properties, namely the effect of wear on corrosion and the effect of corrosion on wear, were able to be calculated. The first electrochemical study was performed under OCV conditions. In the presence of applied wear, the open circuit potential of the friction stir weld samples, in both 3.5% NaCl and dilute Harrison’s solution, was found to decrease from the initial stabilized value. Of interest was the rate at which the OCV recovered. It was found to follow a second order repassivation growth model which was explained in terms of an initial film growth stage, followed by a film thickening stage that results in a new OCV. The second synergized electrochemical-wear study was under fixed 0.2 V and 0.4 V applied potential conditions. In both solutions, 3.5% NaCl and dilute Harrison’s solution, a large increase in the current was observed during the applied wear experiment. The samples submerged in 3.5% NaCl were found to have higher average currents during the wear experiment than those in dilute Harrison’s solution. The rapid decrease in the current, after the applied wear ceased, was found to also follow the second order repassivation model. The electrochemical-wear synergism was done by using potentiodynamic polarization tests. The friction stir weld regions as well as the laser samples were analysed in a wear as well as a wear-free environment in order to determine the effect that wear had on the corrosion properties. In both 3.5% NaCl and dilute Harrison’s solution the corrosion rates were found to increase by 100-fold when the wear was present. The effect of the wear process on corrosion could also be described by synergistic factor, where values close to 1 would imply that applied wear had little effect on the corrosion properties and vice versa. The synergistic factors showed that the corrosion rate was greatly affected by the presence of wear with corrosion synergistic factors of 20 and upward for the friction stir welded samples. The results showed that the weld zone region had a lower corrosion rate than the parent material. This implied that the main weld zone was shown to have the least effect of wear on corrosion and would therefore show the lowest likelihood of failure due to corrosion when compared to the parent material. The wear synergistic factor was found to be between 1 and 1.6 for the friction stir weld regions. This implied that the wear rates of the friction stir welded samples were slightly affected by the presence of a corrosive environment and that the wear properties of the laser welded samples were enhanced by the presence of a corrosive environment. Similar studies performed on laser welded samples showed unusually different results due to the small nature of the laser weld region, with inconclusive results when compared to the friction stir welded samples.
- Full Text:
- Date Issued: 2017
- Authors: Davoren, Brandon Hilton
- Date: 2017
- Subjects: Chemistry, Technical -- Research Materials -- Mechanical properties , Aluminum alloys
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/33250 , vital:32605
- Description: Titanium alloy Ti6Al4V has extensive uses in aerospace, dentistry and the biomedical industry. When used in these applications there is often a need to weld two or more pieces of titanium alloy together. This can be done by either friction stir weld or laser weld methods. These welded regions are often exposed to corrosive environments in addition to factors such as induced additional mechanical wear. Thus to accurately report on the viability of the material in a specific application, the corrosion, wear and their synergistic effects need to be studied. Friction stir welding, which is a well-suited method for joining plates of Ti6Al4V, creates regions in the material that are affected differently. These regions can be described as the parent material, advancing side, retreating side and the weld zone. The tribological properties of the different friction stir weld regions were analysed in air using different loads, frequencies, experimental duration and surrounding environments. When the applied load was increased some of the weld regions showed an increase in the specific wear rate. For example, the weld zone region showed a decrease when compared to the parent material. In this tribology study the effect of the counter material was evaluated. E52100, Si3N4, SS 316 and alumina counter materials were used in the test procedure which was conducted in air on the weld regions. The parent material was found to have the highest average specific wear rates with the four counter materials when compared to the weld zone samples. The regions affected by the friction stir weld process all showed, on average, lower specific wear rates than the parent material. For the various tested samples, the coefficient of friction and material compatibility that was found to be the most stable, was the alumina ball. Owing to this as well as its chemical stability, alumina was determined to be the best material for further tribocorrosion studies. The friction stir welded samples, that were cut from a cross section of a friction stir weld plate, were analyzed in 3.5% NaCl and dilute Harrison’s solution respectively. The effect of wear on the electrochemical properties was studied under open circuit voltage (OCV) and fixed 0.2 V and 0.4 V applied potential conditions respectively. The effect of wear on the corrosion properties was studied using potentiodynamic polarization. From analyzing the friction stir weld regions in both a wear and wear-free environment, the synergistic properties, namely the effect of wear on corrosion and the effect of corrosion on wear, were able to be calculated. The first electrochemical study was performed under OCV conditions. In the presence of applied wear, the open circuit potential of the friction stir weld samples, in both 3.5% NaCl and dilute Harrison’s solution, was found to decrease from the initial stabilized value. Of interest was the rate at which the OCV recovered. It was found to follow a second order repassivation growth model which was explained in terms of an initial film growth stage, followed by a film thickening stage that results in a new OCV. The second synergized electrochemical-wear study was under fixed 0.2 V and 0.4 V applied potential conditions. In both solutions, 3.5% NaCl and dilute Harrison’s solution, a large increase in the current was observed during the applied wear experiment. The samples submerged in 3.5% NaCl were found to have higher average currents during the wear experiment than those in dilute Harrison’s solution. The rapid decrease in the current, after the applied wear ceased, was found to also follow the second order repassivation model. The electrochemical-wear synergism was done by using potentiodynamic polarization tests. The friction stir weld regions as well as the laser samples were analysed in a wear as well as a wear-free environment in order to determine the effect that wear had on the corrosion properties. In both 3.5% NaCl and dilute Harrison’s solution the corrosion rates were found to increase by 100-fold when the wear was present. The effect of the wear process on corrosion could also be described by synergistic factor, where values close to 1 would imply that applied wear had little effect on the corrosion properties and vice versa. The synergistic factors showed that the corrosion rate was greatly affected by the presence of wear with corrosion synergistic factors of 20 and upward for the friction stir welded samples. The results showed that the weld zone region had a lower corrosion rate than the parent material. This implied that the main weld zone was shown to have the least effect of wear on corrosion and would therefore show the lowest likelihood of failure due to corrosion when compared to the parent material. The wear synergistic factor was found to be between 1 and 1.6 for the friction stir weld regions. This implied that the wear rates of the friction stir welded samples were slightly affected by the presence of a corrosive environment and that the wear properties of the laser welded samples were enhanced by the presence of a corrosive environment. Similar studies performed on laser welded samples showed unusually different results due to the small nature of the laser weld region, with inconclusive results when compared to the friction stir welded samples.
- Full Text:
- Date Issued: 2017
A systematic review of the influence of parenting on the development of antisocial behaviour
- Authors: Jacobs, Philencia Daniela
- Date: 2013
- Subjects: Antisocial personality disorders , Parenting , Child psychology , Conduct disorders in children
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:9961 , http://hdl.handle.net/10948/d1020144
- Description: The role that parenting plays in the development of antisocial behaviour has been, and is still widely researched. International studies on this topic are vast. In South Africa, however, very little has been researched within this area. This study aimed to systematically review literature on the role of parenting in the development of antisocial behaviour. International literature published between 2000 and 2013 was reviewed in order to gain a better idea of the current state of knowledge on this topic. All of the articles included in the review examined some aspect of parenting behaviour, parenting practices and/or parenting styles related to the development of antisocial behaviour, conduct disorder, and/or oppositional defiant disorder. The articles were systematically assessed, and eight themes emerged which include: effective parenting behaviours; the moderating effects of callous unemotional traits on parenting; parental warmth; parental discipline; parental knowledge and monitoring; parental psychopathology; parenting styles; and parenting during infancy.
- Full Text:
- Date Issued: 2013
- Authors: Jacobs, Philencia Daniela
- Date: 2013
- Subjects: Antisocial personality disorders , Parenting , Child psychology , Conduct disorders in children
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:9961 , http://hdl.handle.net/10948/d1020144
- Description: The role that parenting plays in the development of antisocial behaviour has been, and is still widely researched. International studies on this topic are vast. In South Africa, however, very little has been researched within this area. This study aimed to systematically review literature on the role of parenting in the development of antisocial behaviour. International literature published between 2000 and 2013 was reviewed in order to gain a better idea of the current state of knowledge on this topic. All of the articles included in the review examined some aspect of parenting behaviour, parenting practices and/or parenting styles related to the development of antisocial behaviour, conduct disorder, and/or oppositional defiant disorder. The articles were systematically assessed, and eight themes emerged which include: effective parenting behaviours; the moderating effects of callous unemotional traits on parenting; parental warmth; parental discipline; parental knowledge and monitoring; parental psychopathology; parenting styles; and parenting during infancy.
- Full Text:
- Date Issued: 2013
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