A chemo-enzymatic process for the production of beta-thymidine, a key intermediate in antiretrovirol manufacture
- Authors: Gordon, Gregory Ernest Robert
- Date: 2010
- Subjects: HIV infections -- Treatment -- South Africa , HIV infections -- South Africa -- Prevention , Antiretroviral agents
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:10423 , http://hdl.handle.net/10948/d1016217
- Description: The socio-economic impact of HIV/AIDS on South Africa has resulted in lower gross domestic product, loss of skills in key sectors such as education, and increased health-care costs in providing access to treatment. Currently active pharmaceutical ingredients (API’s) such as stavudine (d4T) and azidothymidine (AZT) are imported from India and China, while formulation is conducted locally. A strategy was initiated between CSIR Biosciences and LIFElab under the auspices of Arvir Technologies to investigate the feasibility of local antiretroviral manufacture (d4T and AZT) or the manufacture of a key intermediate such as β- thymidine (dT). Several advantages associated with successful implementation of this strategy include ensuring a local supply of API’s, thus reducing reliance on procurement from foreign sources and reducing the effect of foreign exchange rate fluctuations on providing cost effective access to treatment. A local supply source would also reduce the imports and thus aid the balance of payments deficit, and in addition to this, provide stimulus in the local pharmaceutical manufacturing industry (which has been in decline for several decades), resulting in increased skills and employment opportunities. This thesis describes the development of a superior chemo-enzymatic process for the production of β-thymidine (72 percent yield, prior to isolation), a key intermediate in the preparation of anti-retrovirals. Alternative processes based purely on chemical or bioprocess transformations to prepare either 5-methyluridine (5-MU) or dT suffer from several disadvantages: lengthy transformations due to protection/deprotection strategies, low selectivties and product yields (30 percent in the chemical process) and isolation of the product from dilute process streams requiring the use of large uneconomical reactors (bioprocesss). This contributes significantly to the cost of d4T and AZT manufacture. Our novel chemoenzymatic process comprises of a biocatalytic reaction for the production of 5-MU, with subsequent chemical transformation into dT (3 steps) negating and circumventing the limitations of the chemical or bioprocess routes. During the course of this project development, the β-thymidine selling price declined from 175 $/kg (2005) to 100 $/kg (2008). However, the process described in this work is still competitive based on the current β- thymidine selling price of 100 $/kg. The process economics show that with further optimization and increasing the isolated dT yield from 70 percent to 90 percent, the variable cost decreases from 136 $/kg to 110 $/kg. The increase in isolated yield is highly probable, based on solubility data of β-thymidine. The decrease in β-thymidine selling price and technological improvement in dT manufacture should translate into lower API manufacture costs and more cost effective access to treatment. Our novel biocatalytic process producing 5-MU uses a coupled enzyme system employing PNP, Purine Nucleoside Phosphorylase and PyNP, Pyrimidine Nucleoside Phosphorylase. The overall transglycosylation reaction may be decoupled into the phosphorolysis reaction (PNP) and synthesis reaction (PyNP). During the phosphorolysis reaction, guanosine is converted into guanine and ribose-1-phosphate (R-1-P) in the presence of PNP enzyme. The reaction intermediate R-1-P is then coupled to thymine in the presence of PyNP enzyme during the synthesis reaction, producing 5-MU. The process was scaled up from lab-scale to bench-scale (10 - 20 L) and demonstrated to be robust and reproducible. This is evident from the average guanosine conversion (94.7 percent ± 2.03) and 5-MU yield (88.2 percent ± 6.21) and mole balance (104 percent ± 7.61) which were obtained at bench-scale (3 replicates, 10 L). The reaction was carried out at reactor productivities of between 7 – 11 g.L-1.h-1. The integration of the biocatalytic process and chemical processes was successfully carried out, showing that 5-MU produced using our novel biocatalytic process behaved similarly to commercially available 5- MU (ex. Dayang Chemicals, China). A PCT patent application (Ref. No. P44422PC01) on this chemo-enzymatic process has been filed and currently public private partnerships are being explored through Arvir Technologies to evaluate and validate this technology at one ton scale.
- Full Text:
- Date Issued: 2010
A critical analysis of organisational strategies for employee engagement
- Authors: Poisat, Paul
- Date: 2006
- Subjects: Employees -- Attitudes , Employee motivation , Personnel management
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9378 , http://hdl.handle.net/10948/466 , Employees -- Attitudes , Employee motivation , Personnel management
- Description: Organisations are continuously searching for ways to increase their competitiveness as a means to survive in the global economy. More recently approaches have focused on the role that people perform in bringing about competitive advantage. Research indicates that engaged employees contribute vastly to the financial bottom-line of the organisation (see section 3.2.2). The research problem in this study was to identify strategies that organisations can use to engage their employees. To achieve this objective a theoretical employee engagement model was presented. The presentation of the theoretical model consisted of the following sub-processes: § Firstly, a literature survey was conducted to determine the underlying drivers/constructs of employee engagement. Abstract iii § The second comprised surveying the literature dealing specifically with approaches for measuring employee engagement. § Thirdly, the literature was surveyed to identify strategies and models used by organisations for engaging employees. The theoretical employee engagement model served as a basis for the compilation of the survey questionnaire that determined the extent to which human resource practitioners and line managers agree with the theoretical model developed in this study. The questionnaire was administered to a random sample of individuals employed in the automotive cluster in the Nelson Mandela Metropolitan Municipality and the Buffalo City Metropole. The empirical results obtained from the survey indicated that respondents strongly concurred with the theoretical employee engagement model presented in the study. These results were included in the theoretical model, which lead to the development of the integrated organisational employee engagement model. The model comprises of four interrelated categories that all contribute to enhancing employees’ engagement. These categories are organisational leadership, organisational culture, organisational strategies and the manager’s role. From the literature survey and the study it became clear that the role of the manager, had the most significant impact on employee engagement of all the categories. In addition, the integrated organisational employee engagement model can be used by organisations as an applied strategy for the measurement of employee engagement. The main findings from this research are that 60 per cent of organisations that participated in the empirical study had implemented strategies to engage their employees. However, the majority of organisations reporting not having an engagement strategy were among organisations that employed less than 700 employees (smaller organisations). The study also highlighted certain variables that required special attention, especially when implementing employee engagement within the South African context. South African companies as compared to their overseas counterparts, rated organisational engagement variables such as remuneration, benefits and gain sharing lower. A further variable that was identified by the study requiring special attention was, ‘senior management shows a sincere interest in employees’ well-being’. A final point emanating from the study is that the implementation of employee engagement, as a strategy to enhance organisational competitiveness, must be viewed as a continuous process. Organisations should prior, to the implementation of an employee engagement strategy, consider whether they are prepared to share engagement results, take corrective action commensurate with the results and deal with employee expectations that may be incurred. The strategies espoused by the integrated organisational employee engagement model developed in this study, can be used by organisations to increase organisational competitiveness by improving their employees’ level of engagement.
- Full Text:
- Date Issued: 2006
A model for evaluating training and development initiatives in the Botswana public service
- Authors: Tshukudu, Theophilus Tebetso
- Date: 2009
- Subjects: Civil service -- Personnel management -- Botswana , Civil service -- Labor productivity -- Botswana , Civil service -- Botswana -- Evaluation , Employees -- Training of , Public administration
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9384 , http://hdl.handle.net/10948/879 , Civil service -- Personnel management -- Botswana , Civil service -- Labor productivity -- Botswana , Civil service -- Botswana -- Evaluation , Employees -- Training of , Public administration
- Description: The purpose of this study was to develop an integrated model for evaluating training and development initiatives used by the Botswana public service. To achieve this goal, the following actions were taken: A literature study was conducted to identify the scope and impact of an effective training and development initiative and its evaluation; A literature study was conducted to identify strategies for evaluating training and development initiatives. The theoretical study focused on effective training and development strategies and their evaluation and critical organisational factors that contribute to successful training evaluation; The findings from the literature study were integrated into a model for evaluating training and development initiatives to be used by the Botswana public service; and This model was used as the basis for the development of a survey questionnaire to determine whether trainers, training managers and supervisors who were responsible for training and development in the public service agreed with the effective strategies for evaluating training and development developed in the study. The survey was conducted in ministries and departments in the south east district of Botswana, mainly in Gaborone, where ministries and government departments are located. The empirical results from the study showed that the majority of respondents’ training and development activities were not evaluated and that there is no link between training and development and performance management. In particular, disagreements were shown with regard to ten strategies and critical organisational factors. Evaluation of training and development in general, is an issue that organisations are challenged with on a daily basis. Lack of skills by trainers on how to evaluate training and development is one major contributing factor to this problem. An integrated and strategic approach towards the evaluation of training and development is required to effectively and constructively train and development employees according to strategic organisational goals, rather than according to individual trainee’s goals.
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- Date Issued: 2009
A model to improve the effectiveness of the Occupational Health and Safety Inspectorate function relative to South African construction
- Authors: Geminiani, Franco Luciano
- Date: 2008
- Subjects: Construction industry -- Safety measures
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9695 , http://hdl.handle.net/10948/719 , Construction industry -- Safety measures
- Description: Irrespective of all the efforts made by the Department of Labour (DoL) and other relevant stakeholders to improve the performance of Occupational Health and Safety (OH&S) in construction. In the Construction Industry, there is still a very high level of accidents and fatalities in South Africa. Injuries and accidents to workers do not help a community in any nation. The construction industry in South Africa is generally known to be one of the most hazardous and has one of the most dismal OH&S records among all industrial segments with an unacceptably high level of injuries and fatalities resulting in considerable human suffering. A doctoral study was recently conducted with the aim of investigating the effectiveness and performance of the DoL OH&S Inspectorate in South Africa. The empirical study was conducted among a range of stakeholders: civil engineering and building contractors; OH&S consultants; project managers; DoL inspectors; and designers by means of a questionnaire survey. The methodology adopted in this study included the exploratory and descriptive methods, which entails the technique of observation including the use of questionnaires and data analysis. The salient findings of the study are presented and elucidate that the DoL OH&S Inspectorate is not effective in terms of OH&S relative to the construction industry in South Africa. Conclusions and recommendations included expound that the DoL OH&S Inspectorate is not effectively conducting their duties reinforcing the need for a reviewed OH&S Inspectorate model framework. The proposed structured normative model consists of fundamental elements which would improve the effectiveness of the DoL OH&S Inspectorate. The findings of the study with recommendations are included.
- Full Text:
- Date Issued: 2008
A strategy for the development of team leaders in the East Cape motor industry cluster : a competency based approach
- Authors: Melamed, Graham Morrison
- Date: 2006
- Subjects: Leadership , Teams in the workplace , Automobile industry and trade -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:8568 , http://hdl.handle.net/10948/419 , Leadership , Teams in the workplace , Automobile industry and trade -- South Africa -- Eastern Cape
- Description: The research undertaken in this study was to identify the strategy needed to be adopted by the East Cape Motor Industry Cluster (ECMIC) in order to develop the competencies of its Team Leaders. v Hamel and Prahalad (1994: 28) are of the opinion that the focus of a company must move from current market share, to the share of tomorrow’s opportunities that the company can reasonably expect to gain. The company must therefore consider what it can achieve with its existing set of competencies, and what new competencies need to be acquired in order to prosper in the future. The development of competencies is thus deemed to be critical to the South African economy as the various local automotive manufacturers enter the export field. The ECMIC has traditionally been considered the heart of the automotive industry in South Africa with three of the major manufacturers located in the Nelson Mandela and Buffalo City Metropoles. In order to support these manufacturers, a vast number of component manufacturers and service providers have been established to support the automotive manufacturers both in the ECMIC and in other areas of the country. Since the establishment of a democratic South Africa and the removal of sanctions, the automotive industry has started to establish itself globally. This study will undertake a literature study of the application of competencies in the workplace, teams and team leaders and how competencies are applied in the ECMIC. The results of an empirical study into core competencies in the ECMIC will be used to elucidate a set of competencies which will be used to develop a strategy utilising the competency approach in team leaders in the ECMIC.
- Full Text:
- Date Issued: 2006
An evaluation of leadership characteristics required to meet the demands of a strategic change process in the automative cluster in the Eastern Cape region
- Authors: Angloher, Sanette
- Date: 2010
- Subjects: Leadership , Organizational change
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9341 , http://hdl.handle.net/10948/1261 , Leadership , Organizational change
- Description: Against a backdrop of increasing globalisation, deregulation, the rapid pace of technological innovation, a growing knowledge workforce, and shifting social and demographic trends, the primary task of management today is the leadership of organisational change (Graetz, 2000:550). In the words of Lussier and Achua Abstract v (2001:9): “The companies that will survive in the new global competitiveness environment are those that can attract and maintain leaders”. The above emphasises the important role of managers during times when change take place in the organisation. Yet employees are often managed inappropriately in a period of change. There are two reasons for this: (1) managers managing change are under pressure which undermines their own performance, (2) organisations often do not possess managers who are skilful at handling change. It is this second reason that will form the focus of this study. Carnall (1999:105) states that managing change effectively requires an understanding of both what is and seems likely to happen and of how people react to change, and a skilful management performance. Leaders must take on more facilitative roles, as competencies in change management become critical to creating and sustaining effective organisations. The major technological advances of today rely heavily on leaders to facilitate change. Leaders need to encourage people to “collaborate, take risks, take responsibility and be accountable for the change process the organisation must continually undergo to maintain a leadership position in its industry”, according to Moran and Brightman (2000:3). They furthermore argue that “change leaders recognise that they are always trying to balance stability and change. It is a delicate balance to accomplish since employees desire order and stability, while organisations must be ready to adapt to changing conditions quickly”. In this rapidly changing world, organisations must become more flexible, more responsive, and more willing to change and adapt. They must create and assimilate new knowledge at an increasing pace, encourage innovation, and learn to compete in new ways. Dess and Picken (2000:30) argue that the leaders of these organisations must be proactive in facilitating organisational learning and encouraging positive adaptation to external changes. The above shows what an important role leaders/managers have to play in the strategic change process. They need to possess the requisite skills in leadership, problem solving, continuous improvement, team effectiveness, and customer service in order to ensure the long-term growth and stability in the organisation which change can bring about. This research project will identify the various skills needed to successfully manage a change initiative.
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- Date Issued: 2010
Analysis processes as antecedents for decision-making related to growth strategies of South African Game Ranchers
- Authors: Van Eyk, Marlé
- Date: 2010
- Subjects: Tourism -- Marketing , Game farms -- South Africa
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9356 , http://hdl.handle.net/10948/1546 , Tourism -- Marketing , Game farms -- South Africa
- Description: Game ranching offers an economic alternative to conventional stock farming and is a means of supplementing income derived from agricultural activities. Competition is intensifying as ranchers continuously look for ways to improve and expand their businesses and gain a competitive advantage. Ranchers consequently have to find strategies that can ensure growth. Since a reciprocal relationship and dependency exists between a game ranch and the environment in which it operates, it is essential that ranchers take cognizance of aspects in the marketing environment that can either limit, and hence encumber the choice of growth strategy, or stimulate the growth potential of game ranches. As the objective of marketing is to offer customers superior value, it is pertinent for ranchers to know and understand the needs, requirements and motivations of visitors. Failure to do so will cause visitors to patronise other game ranches, or alternative tourism offerings that meet their expectations. A literature review was conducted to define strategy and assist in identifying growth strategies available to a game ranch. The literature review assisted in categorising elements in the external, internal and customer analysis phases of strategic marketing management. Surveys were conducted by means of self-completion questionnaires which were distributed throughout South Africa. Two sets of questionnaires were distributed - one to respondents with prior experience of a game ranch, and one to respondents with no-prior experience. A qualifying question directed the fieldworker to decide which questionnaire should be completed by the respondent. The surveys were constructed in such a way as to determine to what extent various factors would persuade respondents to visit a ranch or extend their stay. Based on a factor analysis, an eight factor structure emerged which represented the personal values of respondents and their levels of expectation for each of the factors. The eight factors were stimulation, universalism, tradition, security, hedonism, power, socialisation, and self-direction. The study revealed the following. - The majority of respondents with no-prior experience of a game ranch is either unaware of the offerings of game ranches, or perceives them as too expensive. - The sustainable use of natural resources is not only essential for the existence of a game ranch, but is also an important motivator for respondents to either visit a game ranch or extend their stay at a ranch. - Staff play a critical role in the overall experience of visitors and act as an important motivator to either visit/revisit a game ranch or extend their stay at the ranch. - Clean and comfortable overnight facilities are deemed important by all respondents. - Respondents have a strong desire to relax and spend time with family and friends. A decision-making framework from which game ranches can select applicable growth strategies resulted from the study. The decision-making framework comprises a three-phase process; phase 1 is the identification of a game ranch's target market; phase 2 is the use of a simplistic framework to determine a possible growth strategy for a game ranch; phase 3 is the identification of ways to implement the selected strategy. As the game ranch industry makes significant contributions to the economic, social and ecological welfare of South Africa, this study added to the body of knowledge of game ranching in South Africa, particularly with regard to the growth options available to game ranches. Recommendations for consideration of future research included the following. - As the current study investigated hunting and tourism, future research on growth strategies for game ranches could also include other aspects of game ranching such as the sale of live game and game products. - More focused empirical research into external and internal strategic analysis should be considered to supplement the empirical research into customer analysis resulting from the current study. - Finally, additional information obtained on the external and internal strategic analysis process could lead to expanding the decision-making framework developed in this study into a more holistic tool to be used in selecting a growth strategy, or combination of strategies for a game ranch3.
- Full Text:
- Date Issued: 2010
Causal determinants of the public's attitudes towards hunting as a basis for strategies to improve the social legitimacy of hunting
- Authors: Coetzer, Wentzel Christoffel
- Date: 2014
- Subjects: Hunting -- South Africa , Wildlife management -- South Africa , Wildlife conservation -- South Africa
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:10759 , http://hdl.handle.net/10948/d1021164
- Description: It is widely acknowledged that the organised wildlife and hunting industry in South Africa contributes significantly to the country’s economy, as well as to the effective management and conservation of wildlife on privately owned land. Despite this, hunting has come under increasing attack by anti-hunting proponents who wish to bring a ban on hunting. A number of broad shifts across society at large and lobbying against hunting by anti-hunting proponents have given rise to legitimate concerns regarding the social acceptability of hunting. To maintain the social legitimacy of hunting, it is imperative to put strategies in place to actively broaden the base of public acceptance of hunting. Towards this aim, this study is an empirical investigation of the causal determinants of the public’s attitudes towards hunting and of the implications it holds for improving the social legitimacy of hunting. The study commenced by building a sound theoretical foundation from the available literature on the measurement of attitudes, the structure and formation of attitudes, the instrumental and experiential aspects of attitudes, attitudinal ambivalence, the psychology of strong attitudes, as well as the phenomenon of cognitive dissonance. Thereafter, the study turned to identify an adequate and empirically valid research approach for investigating attitudes and its causal determinants. A popular attitude theory in social psychology, namely the theory of reasoned action, was identified as a suitable conceptual framework for conducting this study. According to the reasoned action model, the salient behavioural beliefs people associate with a particular behaviour form the informational foundation (or cognitive foundation) on which their attitudes towards the behaviour are based. More specifically, the model suggests that peoples’ overall attitude towards a behaviour is a function of their perceived probability that a behaviour will produce certain outcomes (belief strength), as well as the degree to which they judge the perceived outcomes of the behaviour as positive or negative (outcome evaluation). The methodological design of the study’s empirical component was strictly based on the standard procedures prescribed by the theory of reasoned action. Two consecutive and methodologically interrelated surveys were conducted amongst members of the public to collect the study’s primary data. The main salient behavioural beliefs on which different attitudes towards hunting are based were identified and further investigated. The results were analysed from the perspective of the theory of reasoned action and a clear understanding of the causal determinants of different attitudes towards hunting were attained. Based on the findings of the study, a number of conclusions and recommendations were made that may guide the development of future strategies to improve the social legitimacy of hunting. Amongst other things, it was suggested that public education programmes should be developed to address the public’s misconceptions of hunting; that public relation campaigns be undertaken to improve the public’s negative image of hunters; and that hunter education programmes be put in place to make hunters aware of the role they could play at community level to improve the social acceptability of hunting. Detailed guidelines regarding the contents of such education programmes and public relation campaigns were provided.
- Full Text:
- Date Issued: 2014
Characterisation of dissimilar friction stir welds between 5754 Aluminium alloy and C11000 copper
- Authors: Akinlabi, Esther Titilayo
- Date: 2010
- Subjects: Friction stir welding , Aluminum alloys , Copper alloys
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9629 , http://hdl.handle.net/10948/1536 , Friction stir welding , Aluminum alloys , Copper alloys
- Description: Friction Stir Welding (FSW) is a solid state welding process invented and patented by The Welding Institute (TWI) in 1991, for joining ferrous and non-ferrous materials1. The FSW of Aluminium and its alloys has been commercialised; and recent interest is focused on joining dissimilar materials. However, in order to commercialise the process, research studies are required to characterise and establish process windows. This research work through material characterisation of the welded joints establishes a process window for the Friction Stir welding of 5754 Aluminium Alloy and C11000 Copper. Furthermore, preliminary studies83,85 on the FSW of aluminium and copper have revealed the presence of intermetallic compounds which are detrimental to the weld qualities. This research work is also aimed at establishing process parameters that will result in limited or no intermetallic formation in the weld. The joint integrity of the resulting welds will also be correlated with the input process parameters. Based on the preliminary investigations conducted, a final weld matrix consisting of twenty seven welds was produced by varying the rotational speed between 600 and 1200 rpm, and the feed rate between 50 and 300 mm/min using three different shoulder diameter tools – 15, 18 and 25 mm to compare the heat input into the welds and to achieve the best results. The welds were characterised through microstructural evaluation, tensile testing, microhardness profiling, X-Ray Diffraction analysis, electrical resistivity and statistical analysis – in order to establish the interrelationship between the process parameters and the weld qualities. viii Microstructural evaluation of the weld samples revealed that the interfacial regions are characterised by mixture layers of aluminium and copper; while 33 percent of the tensile samples are within the acceptable range (> 75 percent joint efficiency). High Vickers microhardness values were measured at the joint interfaces, which corresponded with the intermetallic compounds. The Energy Dispersive Spectroscopy analysis revealed the presence of thin layers of intermetallics in nanoscale at the interfacial regions. The diffractograms of the X-Ray Diffraction analysis showed small peaks for intermetallics in some of the welds. Low electrical resistivities were measured at the joint interfaces. The statistical analysis showed that the downward vertical force, (Fz) can significantly influence the resulting weld qualities. An overall summary of the analysis of the weld qualities - with respect to the shoulder diameter tools employed showed that the 18 mm shoulder diameter tool is most appropriate among the three shoulder diameters considered, and a process window of medium spindle speed of 950 rpm and low-to-medium feed rate between 50 and 150 mm/min is established for FSW of Aluminium and Copper. Welds produced at 1200 rpm and 300 mm/min with low heat input did not have intermetallics formed at the joint interface.
- Full Text:
- Date Issued: 2010
Continuous flow synthesis of silicon compounds as feedstock for solar-grade silicon production
- Authors: Chigondo, Fidelis
- Date: 2016
- Subjects: Silicon -- Synthesis , Homogeneous catalysis
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: http://hdl.handle.net/10948/4529 , vital:20613
- Description: This thesis describes the key steps in the production of high purity (solar-grade) silicon from metallurgical-grade silicon for use in the production of photovoltaic cells as alternative renewable, environmentally benign and cheap energy source. The initial part of the project involves the development and optimization of a small chemical production platform system capable of producing alkoxysilanes from metallurgical-grade silicon as green precursors to solar-grade silicon production. Specifically, the main aim of the study was to synthesize trialkoxysilanes in continuous flow mode, although the synthesis on monosilane was also done in batch mode. The alkoxylation reaction was carried out in a traditional slurry phase batch reactor, packed bed flow tubular reactor and also attempted in a continuous flow falling film tubular reactor. The effect of key parameters which affect the silicon conversion and selectivity for the desired trialkoxysilane were investigated and optimized using ethanol as a reagent model. The synthesis was then extended to the other alcohols namely methanol, n-propanol and n-butanol. Copper catalysts which were tested in the alkoxylation reaction included: CuCl, Cu(OH)2, CuO and CuSO4. CuCl and Cu(OH)2 showed comparable activity in the batch mode but the former was more efficient in the packed bed flow tubular reactor. Cu(OH)2 could be used as a non-halide catalyst but its activity is limited to short reaction cycles (<10 h). The uncatalysed reaction resulted in negligible reaction rates in both types of reactors. High temperature catalyst pre-heating (>500 oC) resulted in a lower rate of reaction and selectivity than when slightly lower temperatures are used (<350 oC) in both reactors, although much difference was noticed in the packed bed flow tubular reactor. Synthesis in the batch reactor needed longer silicon-catalyst activation time, higher pre-heating temperature and higher catalyst amounts as compare to the packed bed flow tubular reactor. Reaction temperature and alcohol flow rate influenced the reaction in both methods. The optimum reaction temperature range and alcohol flow rate was comparable in both reactors (230 to 240 oC) and 0.1mL/min respectively. The effect of alcohol R-group (C1 to C4) on the reaction revealed that conversion and selectivity generally decrease with an increase in carbon chain length in both methods. Ethanol showed highest selectivity (>95% in batch and >97% in flow) and conversion (about 88% in batch and about 64% in flow) as compared to all other alcohols studied showing that it could be the most efficient alkoxylation alcohol for this reaction. Overally, the packed bed flow tubular reactor resulted in higher selectivity to trialkoxysilanes than the batch system. Performing the reaction under pressure resulted in increased conversion but selectivity to the desire trialkoxysilane diminished. Synthesis in a continuous flow falling film tubular reactor was not successful as it resulted in very poor conversion and selectivity. Monosilane was successfully synthesized from the disproportionation of triethoxysilane using homogeneous and heterogeneous catalysts in batch mode. The results obtained from homogeneous catalysis showed that the reaction can be conducted at room temperature. The heterogeneous catalysis method resulted in slow conversion at room temperature but mild heating up to 55 oC greatly improved the reaction. Conducting the reaction under neat conditions produced comparable results to reactions which were carried out using solvents. The disproportionation reaction was best described by the first order kinetic model. The results obtained in this research indicate that the packed bed flow tubular reactor can be utilized with future modifications for continuous flow synthesis of alkoxysilanes as feedstock for the solar-grade silicon production.
- Full Text:
- Date Issued: 2016
Customer satisfaction with the guesthouse experience in Ghana
- Authors: Amoah, Felix
- Date: 2016
- Subjects: Consumer satisfaction -- Ghana , Hospitality industry -- Ghana -- Management , Tourism -- Ghana -- Marketing
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: http://hdl.handle.net/10948/6073 , vital:21036
- Description: Guesthouse accommodation plays an important role in Ghana’s hospitality industry and was therefore the focus of this study as little research dealing with guesthouses in Ghana could be found. The number of guesthouses in Ghana continues to grow and they thus represent an important alternative to hotels. However, these establishments seem to perform poorly and face several challenges such as lack of managerial knowledge, insufficiently skilled employees, poor interaction with customers, and criticisms of the provision of low quality service. The main reason for undertaking this research was to provide guesthouse managers in Ghana with information that might assist them in making decisions about the experience they offer. Such knowledge could make this type of accommodation more competitive and eventually help the hospitality sector in Ghana attract tourists and grow. It is imperative that guesthouses focus on the experience they offer, because contemporary tourism and hospitality literature suggest that successful businesses require a shift from functional and financial interests to a more profound focus on total experiences which embody emotional aspects. It is thus argued that, if guesthouse managers in Ghana do not know how their guests perceive their guesthouse experience, they might make costly mistakes and allocate resources to aspects that already provide quality and value in a functional sense, instead of those elements perceived as providing quality and value in the total experience. Two dominating concepts, namely experience quality and experience value, formed the basis of the examination of guests’ experience with the guesthouses in Ghana. In addition, the relationships between the experience and satisfaction were also investigated. Four experience quality dimensions, namely hedonics, peace of mind, involvement, and recognition, and seven value dimensions were examined. The experience value dimensions included atmospherics, enjoyment, entertainment, efficiency, excellence, escape, and economic value. A proportional stratified random sampling procedure was followed to select the guesthouses for the study. Thereafter, a structured questionnaire was distributed to the guesthouse guests selected by means of convenience sampling. Five hundred and forty one useable questionnaires were received. The guesthouse guests formed the primary sampling unit for this study. The results of the empirical study showed a strong positive correlation between all the dimensions of experience quality and experience value, while the factor analysis confirmed that all these dimensions loaded on a single factor. Therefore, experience quality and experience value cannot be separated, and the resulting single multi-dimensional factor was subsequently renamed, overall experience. The results also indicated a positive relationship between hedonics, peace of mind, involvement, recognition, atmospherics, enjoyment, entertainment, efficiency, excellence, escape, economic value, and overall satisfaction. The inferentially established rank-order of the dimensions contributing to satisfaction can guide managers when allocating resources. Overall, atmospherics was ranked first, followed by economic value. Escape was the lowest ranked dimension. In addition, it was found that, except for escape, all the experience dimensions were perceived as basic satisfiers. This implies that guests will be dissatisfied when provision of these dimensions is inadequate. With regard to escape, listed as a performance factor, guests will be satisfied when performance is improved and dissatisfied when performance is low. A positive relationship was also found between overall experience and overall satisfaction. The latter include the likelihood of return and recommending the guesthouse to others. Finally, structural equation modelling confirmed a model representing the 11 experience dimensions (hedonics, peace of mind, involvement, recognition, atmospherics, enjoyment, entertainment, escape, efficiency, excellence, and economic value) and the relationships between overall experience and overall satisfaction pertaining to guesthouses in Ghana.
- Full Text:
- Date Issued: 2016
Development of a process for the preparation of linalool from CIS-2-pinanol
- Authors: Buddoo, Subash Ramnarain
- Date: 2009
- Subjects: Odors , Perfumes -- History , Perfumes -- Formulae , Fermentation
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:10425 , http://hdl.handle.net/10948/d1016219
- Description: Linalool is a key intermediate for the production of important fragrance chemicals such as geraniol, nerol, geranial, and neral. Linalool can be produced via a two-step process from α-pinene which is a major component of crude sulphated turpentine (CST) a foul-smelling, volatile waste product of the pulp and paper industry. The key step in this process is the pyrolysis step which involves the isomerisation of cis-2-pinanol to linalool and requires high temperatures (600-650°C) and is not very selective due to the decomposition of the product itself under these conditions. A client of the CSIR, Teubes Pty. Ltd., is a manufacturer of flavour and fragrance compounds for the local and international fragrance market and expressed an interest in producing linalool since the company would then gain access to other valuable fragrance chemicals via relatively simple processes. Earlier work conducted by AECI, R & D did not meet with much success since the selectivity to linalool was very poor and the process could hardly be deemed as scalable. The main objective of this project was therefore to develop a process for the selective isomerisation of cis-2-pinanol to linalool with minimum by-product formation and using process equipment that could be scaled to full-scale production. Since cis-2- pinanol could not be purchased in sufficient quantities for process development, a process had to be developed for the bench-scale preparation of kilogram quantities of cis-2-pinanol from α-pinene obtained from the client. Although this synthesis formed a minor part of this investigation, several process improvements and innovations were introduced to produce high quality cis-2-pinanol, in very good yields at kilogram scale. A major part of this investigation was the design and set up of a pyrolyis rig capable of operating at elevated temperatures (400 - 750°C) for the evaluation of various process parameters. Various vaporizer, reactor, and condensation systems were evaluated for their ability to cope with the demanding conditions on a consistent basis. The initial part of the investigation was a screening exercise to evaluate various process parameters as well as solvents, materials of construction, catalysts, etc. A comprehensive statistical design was also conducted to determine the critical process parameters and the model obtained was used to predict the optimum conditions required for the preparation of in-specification product on a consistent basis. These conditions were used in the preparation of a 1kg sample which was required by theclient for market evaluation purposes. The use of a novel microreactor system was also evaluated for the pinanol pyrolysis reaction. To our knowledge, this is the first time that a microreactor has been successfully used for this type of reaction in the Fragrance industry and a patent application is being filed by the CSIR. The kinetics of the reaction in both the tubular reactor system and the microreactor system was investigated. Computer modelling studies on both the systems were also conducted. The raw material cost to produce a kilogram of linalool is $1.40. There is a significant margin of 60.8 percent between the raw material cost of linalool and the current selling price ($3.57/kg). This clearly indicates that the project is potentially feasible from an economic point of view and we can now proceed with confidence to the next stage which is the engineering design, building and commissioning of the large scale pyrolysis rig. The rest of the process steps will be conducted on existing equipment currently present at the CSIR’s large scale facility (Imbiza in Isando, Gauteng).
- Full Text:
- Date Issued: 2009
Development of a reciprocating aerofoil wind energy harvester
- Authors: Phillips, Russell Leslie
- Date: 2008
- Subjects: Windmills , Wind power , Wind turbines
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9622 , http://hdl.handle.net/10948/899 , Windmills , Wind power , Wind turbines
- Description: Cross flow wind turbines are not unique. The performance of Savonius and Darrieus turbines is well documented. Both share the advantage of being able to accept fluid flow from any direction. The Savonius is drag based and hence has poor power output while the Darrieus is lift based. Due to the fact that the Darrieus has fixed blades the fluid flow through the rotor does not result in optimal lift being generated at all points in the rotation circle. A drawback of the Darrieus system is that it has to operate at a high tip-to wind-speed ratio to obtain reasonable performance with the fixed blades. Deviation from a small optimal range of tip speed ratios results in poor performance. The Darrieus also has poor starting torque. The research conducted in this project focused on overcoming the shortcomings of other turbines and developing an effective cross flow turbine capable of good performance. A number of different concepts were experimented with, however all were based on a symmetrical aerofoil presented to the actual relative airflow at an angle that would produce the highest lift force at all times. The lift force was then utilized to generate movement and to do work on an electrical generator. All concepts contemplated were researched to ascertain their appropriateness for the intended application. During development of the final experimental platform and after lodging of a provisional patent (RSA 2007/00927) it was ascertained that the design shared some similarities with an American patent 5503525 dated 28/4/1994. This patent employed complex electronic sensing and control equipment for control of blade angle. This was thought to be overly complex and costly, particularly for small scale wind energy generation applications and a simpler mechanical solution was sought in the design of the final experimental platform used in this project. The design of the mechanical control system was refined in an attempt to make it simpler, more durable and employ the least number of moving parts. Literature studies and patent searches conducted, suggested that the mechanical control system as developed for the final experimental platform was unique. The enormous variation in the power available from the wind at the different wind speeds likely to be encountered by the device necessitated some means of control. In high wind conditions control of the amount of wind power into the device was deemed to be the preferable means of control. A number of different concepts to achieve this were devised and tested. The final concept employed limited the tail angle deflection and hence the lift produced by the aerofoils. This resulted in a seamless “throttle” control allowing the device to be used in any wind strength by adjusting the control to a position that resulted in the device receiving a suitable amount of power from the wind. The outcome of performance tests conducted indicated that the device has the potential to be developed into a viable wind turbine for both small and large scale applications. The ability to control the power input from the wind to the machine from zero to a maximum is considered to be one of the most beneficial outcomes of this project and together with the quiet operation and low speed, are considered the main advantages of the device over existing wind turbine designs. The possibilities of using the device to compress air for energy storage are exciting avenues that warrant further research.
- Full Text:
- Date Issued: 2008
Factors influencing survivor qualities after downsizing
- Authors: Chipunza, Crispen
- Date: 2009
- Subjects: Downsizing of organizations -- South Africa , Organizational change -- South Africa , Cost control , Unemployment -- Psychological aspects
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9381 , http://hdl.handle.net/10948/1219 , Downsizing of organizations -- South Africa , Organizational change -- South Africa , Cost control , Unemployment -- Psychological aspects
- Description: Today organisations all over the world have to cope with the ever-increasing rate of local and global change. Those in developing countries have to cope with the inefficiencies engendered by state-led economic, developmental and political strategies, such as new government regulations. These have had an impact on the management of human resources and are exemplified by an increasing adoption of strategies meant to reduce pressure on costs and margins. An increasing popular management response to these challenges has been to engage in some form of organisational restructuring such as downsizing. Often employees who remain (survivors) after downsizing are not given much attention, yet the achievement of new strategic goals depends on the survivors having positive attitudes, relentless commitment and high motivation. Research indicates that employees who are motivated and committed contribute vastly to the financial-bottom-line of the organisation. Therefore, downsizing organisations should continuously search for ways to increase such qualities among their survivors. The objective of this study was to identify the factors that influence the attitudes, commitment and motivation of survivors in a developing economy with a volatile environment. To achieve this objective, a theoretical survivor quality model was presented. In order to present the model, firstly, a literature survey on the importance of survivor quality in terms of attitudes, commitment, and motivation among survivors was conducted. Secondly, literature survey pertaining to the drivers of survivor quality was done, and thirdly, literature dealing with strategies to deal with survivor quality was surveyed. The theoretical survivor quality model was used to compile the research instrument that determined the attitudinal, commitment and motivational levels of survivors, how the three constructs are related after downsizing, as well as the factors influencing the observed levels. The questionnaire was randomly distributed among survivors in the selected manufacturing organisations in Zimbabwe. The empirical results obtained from the study showed that survivors in a developing economy with a volatile environment had moderate levels of attitudes, commitment ad motivation. Two categories of factors were identified as important in influencing these levels. They were downsizing strategy and demographic factors. The downsizing strategy factors were communication and victim support, while education, age, and number of years employed emerged as the demographic factors. The study further highlighted that older survivors with less education contributed more to the moderate levels of attitude, commitment and motivation observed. The study highlights that these variables must be taken into consideration when implementing downsizing in an economically volatile environment in order to manage survivor quality. A further point emanating from the study is that prior to downsizing, organisations should adopt effective communication strategies throughout the process. The key factors identified as influencing survivor quality in this study were integrated into the survivor quality model which can be used by other organisations in a similar context to manage survivor quality in order to increase their efficiency, effectiveness, iv and competitive advantage after downsizing.
- Full Text:
- Date Issued: 2009
Histopathological changes in male wistar rats maintained on a water-based sutherlandia frutescens extract
- Authors: Wickens, Nicolas John
- Date: 2012
- Subjects: Rats -- Physiology , Rats as laboratory animals
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: http://hdl.handle.net/10948/4742 , vital:20670
- Description: In this study a standardized 46 week chronic drinking water toxicity protocol was used to elucidate the toxic potential of Sutherlandia frutescens (S. frutescens) using histopathologic, morphometric and transmission electron microscopic analysis. The histopathologic changes in the duodenum, heart, kidney, liver, lung, pancreas and spleen of male Wistar rats were evaluated. Fifty-four rats were randomly divided into four groups: Group 1 – Normal diet control (ND control), n=7, Group 2 – Normal diet + plant extract (ND + p), n=9, Group 3 – High fat diet control (HFD control), n=19Group 4 – High fat diet + p (HFD + p), n=19In the high fat group male Wistar rats were fed ±55 g/day of a specialised high fat diet over a 46 week period to induce obesity and an insulin resistant state. The treatment groups (groups 2 and 4) received a dose concentration of a tea extract of the S. frutescens plant in their drinking water daily. This study showed that the consumption of S. frutescens significantly reduces weight gain in male Wistar rats on a chronic high fat diet (p≤0.001 vs. HFD control group). S. frutescens appears to propagate periportal and centrilobular glycogen storage in rat hepatocytes in the experimental groups as exemplified by a significantly (p≤0.0001 vs. control groups) increased incidences of Periodic Acid Schiff (PAS) positive staining S. frutescens also reduced intracellular lipid accumulation as made evident by the significantly lower incidence of epicardial adipose tissue (EAT), hepatic steatosis and pancreatic interstitial fat. Obesity was associated with increased fibrotic lesions such as myocardial perivascular fibrosis, centrilobular hepatic fibrosis and pancreatic periductal fibrosis. Obesity associated hypertension contributed to the widespread and significant increase in the average lesion severity of arterial congestion in all organs in the HFD control group. Pulmonary infection was equally prevalent in all rats. Despite the complex histopathology in all groups, differences in the control groups, such as, the presence of a conservative polymorphonuclear leukocyte (PMNL) infiltration, substantial intra-alveolar oedema and focal arterial wall hypertrophy in the control groups was highly suggestive of Sendai viral infection. However histopathologic evidence, in the treatment groups, suggested chronic recurrent viral infection with superimposed Mycoplasma pulmonis (M. pulmonis) bacterial infection. The impact of advanced suppurative pulmonary infection was widespread and exemplified by increased lesion incidences of spontaneous murine progressive cardiomyopathy (MCP) and spontaneous chronic progressive nephropathy (CPN) among others. In conclusion S. frutescens administered for 46 weeks to male Wistar rats significantly lowered intracellular lipid accumulation and obesity associated myocardial, renal, hepatobiliary, pulmonary and pancreatic histopathology. Moreover, duodenal, cardiovascular, hepatobiliary, pulmonary, renal, pancreatic and splenic tissue did not show histopathologic evidence of direct plant extract associated toxicity or carcinogenicity.
- Full Text:
- Date Issued: 2012
Impact of ambient air pollution on human health health in the Nelson Mandela Bay Municipality
- Authors: Nodwele, Mzoxolo Patrick , Strumpher, J
- Date: 2017
- Subjects: Environmental health -- South Africa -- Nelson Mandela Bay Municipality Air -- Pollution -- Meteorological aspects -- South Africa -- Nelson Mandela Bay Municipality
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: http://hdl.handle.net/10948/20142 , vital:29134
- Description: The aim of this study was to assess whether ambient-air pollution contributed negatively to ambient-air quality, and subsequently to human health in the Nelson Mandela Bay Municipality (the study area). A research design that is descriptive and explorative in nature was followed. The research methodology conformed to the following procedure. Firstly, an emission inventory of one hundred and fifty (150) emission sources listed on the data base of the Nelson Mandela Bay Municipality was compiled (“N” and “n” = 150) in a quantitative research approach. Emission data from these sources, together with the relevant meteorological data from the weather stations in the study area (“N” and “n” = 5) were collected and used as input into a geographical information system-software program to quantify the contribution of each emission source to ambient air pollution. The said software program was also used to simulate the dispersion of emissions over the study area. The emission inventory was compiled in consultation with a focus group of experts in the field of air-pollution control in a qualitative-research approach. Secondly, health records of the patients who attend the clinics in the said municipality (“N” and “n” = 49) were assessed for air pollution-related health outcomes. Nineteen (19) of the forty-nine (49) clinics were situated in Sub-District A; fifteen (15) clinics were situated in Sub-District B. The last fifteen of the clinics were situated in Sub-District C, which was also the least-industrialised sub-district. Sub-districts A and B were found to be the most industrialised of the three Sub-districts. Air pollution related health statistics were compiled for the following air-pollution-related health outcomes, namely: lower respiratory tract infections in children under five (5) years of age, as well as pneumonia and asthma in the general population.
- Full Text:
- Date Issued: 2017
Material characterisation of laser formed dual phase steel components
- Authors: Els-Botes, Annelize
- Date: 2005
- Subjects: Steel -- Fatigue , Bending , Lasers , Sheet-steel -- Effect of lasers on
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9609 , http://hdl.handle.net/10948/176 , Steel -- Fatigue , Bending , Lasers , Sheet-steel -- Effect of lasers on
- Description: The nature and scope of this thesis can be divided into four categories: • FORMING PARAMETERS • Identification of various laser forming parameters in order to produce specimens of similar dimension (radius of curvature). • TEMPERATURE AND MICROSTRUCTURE • To study the effect of maximum temperature reached during the forming operation on the microstructure of the various specimens. • FATIGUE LIFE • Compare the fatigue life of the specimens produced by various laser parameters to that of the original material, and also the fatigue life of mechanical formed specimens. • RESIDUAL STRESS PROFILE Determine if the laser forming process induces detrimental residual stress magnitudes in the specimens. The main objective of this thesis was to gain an understanding of the way in which laser forming affects the fatigue performance and residual stress magnitude / distribution of dual phase steel. Although lasers have been used successfully in various manufacturing processes (welding, cutting, marking, etc.), little information is available on the influence of laser forming on many automotive alloys such as dual phase steel. The first part of the work involved a literature review of the process and factors affecting the laser forming process. It became clear from the literature overview that laser forming of sheet material thicker than 1mm is complex in nature. The variables that can influence the process are complicated and their interaction with each other is not easily controlled. The main parameters that were thus controlled in this study are as follows: • Laser power (P) • Laser head travel speed (v) • Laser beam size (mm) The chapters that follow the literature review, deals with the laser forming process of dual phase steel and the production of fatigue specimens using various laser parameters. It was found that the following laser parameters resulted in specimens with approximately the same radius of curvature: Laser power KW Beam diameter mm Interval spacing % Overlap Scanning velocity m/min Line Energy J/m 5 20 10 50 2,5 2000 3,1 14 10,5 25 2 1550 1,5 7,5 7,5 0 1,2 1250 From the results obtained from fatigue testing specimens produced with the above settings, it is clear that the laser forming process has the potential to be employed as a production stage in the manufacture of wheel centre discs while maintaining adequate fatigue strength. Large beam diameters which cause heat penetration through the thickness of the specimen and hence microstructure breakdown should be avoided, since it was shown that these specimens exhibited impaired mechanical properties than those produced with a smaller laser beam diameter. The microstructural changes observed during the forming process needs to be considered since the mechanical properties of the material changes with a change in microstructure. A dramatic change in microstructure was observed; therefore it is of crucial importance that microstructural evaluation plays an important part in deciding optimum laser parameters for the forming process of ferrous alloys. During residual stress analysis, trends were observed between measurements taken at the same location of the samples; regardless whether measurements were taken on the laser irradiated side or the reverse side of the specimen. The only difference was the magnitude of the relieved residual stress. In most cases the obtained relieved residual stress was much smaller in magnitude than that of the original plate (in the bulk of the material). The surface indicated a slight tensile residual stress for most samples evaluated. A good correlation in distribution profile was obtained between microhardness and relieved residual stress distribution at the ‘middle of sample’ location. This indicates that an increase in hardness indicates an increase in residual stress magnitude for the laser formed specimens. In conclusion, this research has proved that it is possible to deform metal plate of a 3,5mm thickness with a CO2 laser system. The research also established the effect of process parameters on the final product’s shape/bend angle and characterised the effect of the laser forming process on the material’s mechanical properties and structural integrity.
- Full Text:
- Date Issued: 2005
MISSTEV : model for information security shared tacit espoused values
- Authors: Thomson, Kerry-Lynn
- Date: 2007
- Subjects: Computer security -- Management , Management information systems -- Security measures , Data protection
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9787 , http://hdl.handle.net/10948/717 , Computer security -- Management , Management information systems -- Security measures , Data protection
- Description: One of the most critical assets in most organisations is information. It is often described as the lifeblood of an organisation. For this reason, it is vital that this asset is protected through sound information security practices. However, the incorrect and indifferent behaviour of employees often leads to information assets becoming vulnerable. Incorrect employee behaviour could have an extremely negative impact on the protection of information. An information security solution should be a fundamental component in most organisations. It is, however, possible for an organisation to have the most comprehensive physical and technical information security controls in place, but the operational controls, and associated employee behaviour, have not received much consideration. Therefore, the issue of employee behaviour must be addressed in an organisation to assist in ensuring the protection of information assets. The corporate culture of an organisation is largely responsible for the actions and behaviour of employees. Therefore, to address operational information security controls, the corporate culture of an organisation should be considered. To ensure the integration of information security into the corporate culture of an organisation, the protection of information should become part of the way the employees conduct their everyday tasks – from senior management, right throughout the entire organisation. Therefore, information security should become an integral component of the corporate culture of the organisation. To address the integration of information security into the corporate culture of an organisation, a model was developed which depicted the learning stages and modes of knowledge creation necessary to transform the corporate culture into one that is information security aware.
- Full Text:
- Date Issued: 2007
Monitoring and intelligent control for complex curvature friction stir welding
- Authors: Hua, Tao
- Date: 2006
- Subjects: Friction welding , Fuzzy systems
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9612 , http://hdl.handle.net/10948/420 , Friction welding , Fuzzy systems
- Description: A multi-input multi-output system to implement on-line process monitoring and intelligent control of complex curvature friction stir welding was proposed. An extra rotation axis was added to the existing three translation axes to perform friction stir welding of complex curvature other than straight welding line. A clamping system was designed for locating and holding the workpieces to bear the large force involved in the process between the welding tool and workpieces. Process parameters (feed rate, spindle speed, tilt angle and plunge depth), and process conditions (parent material and curvature), were used as factors for the orthogonal array experiments to collect sensor data of force, torque and tool temperature using multiple sensors and telemetry system. Using statistic analysis of the experimental data, sensitive signal features were selected to train the feed-forward neural networks, which were used for mapping the relationships between process parameters, process conditions and sensor data. A fuzzy controller with initial input/output membership functions and fuzzy rules generated on-line from the trained neural network was applied to perceive process condition changes and make adjustment of process parameters to maintain tool/workpiece contact and energy input. Input/output scaling factors of the fuzzy controller were tuned on-line to improve output response to the amount and trend of control variable deviation from the reference value. Simulation results showed that the presented neuro-fuzzy control scheme has adaptability to process conditions such as parent material and curvature changes, and that the control variables were well regulated. The presented neuro-fuzzy control scheme can be also expected to be applied in other multi-input multi-output machining processes.
- Full Text:
- Date Issued: 2006
Practical and scalable synthesis of N-Alkyl-N,N'Diacylhydrazines
- Authors: Gouws, Melissa Claire
- Date: 2008
- Subjects: Chemistry, Organic , Acylation , Insecticides
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:10406 , http://hdl.handle.net/10948/696 , Chemistry, Organic , Acylation , Insecticides
- Description: The work presented in this thesis is concerned with the evaluation of potential synthetic routes for the diacylhydrazine group of compounds, and particularly, unsymmetrical diacylhydrazines. Diacylhydrazines form the basis for a relatively new group of insecticides that have molt accelerating properties, and which are considered to offer substantial advantages over other insecticides used for the control of certain insects. The overall objective for this study is to evaluate different potential synthetic routes for a model diacylhydrazine with the view to define potentially scaleable routes. The compound selected for this study was the unsymmetrical diacylhydrazine, N-[N-(tertbutyl) phenylcarbonylamino](4-methylphenyl)-carboxamide since it offers the same range of challenges that would be expected for the synthesis of other similar unsymmetrical diacylhydrazines. Thus, the synthesis of unsymmetrical diacylhydrazines require two reaction steps: The first step is the synthesis of the intermediate mono-acylhydrazine, while the second step is the synthesis of the desired diacylhydrazine from the intermediate mono-acylhydrazine. The most important factor in the two-step reaction sequence is to obtain a high degree of selectivity for the desired mono-acylhydrazine isomer. Acylation of t-butylhydrazine using 4-methylbenzoyl chloride can produce the desired product N-[(tert-butyl)amino](4-methylphenyl)carboxamide in yields above 90 percent, but this reaction produces a variety of by-products, including the “wrong” isomer (N-amino-N- (tert-butyl)(4-methylphenyl)carboximide). Unexpected byproducts for this particular acylation reaction, not previously reported in the literature have also been identified during this investigation. This includes a de-butylated diacylhydrazine, (4-methylphenyl)- N-[(4-methylphenyl)carbonylamino] carboxamide. Although the reaction between tert-butylhydrazine and 4-methylbenzaldehyde is very selective giving near quantitative yields of the desired hydrazone, the subsequent conversion of the hydrazone into the desired mono-acylhydrazine is problematic. The most promising route appears via bromination to form the hydrazidic bromide, followed by hydrolysis of the hydrazidic bromide. Yields for the bromination reaction during this investigation were somewhat higher than that reported previously in literature. Hydrolysis of the hydrazidic bromide, apparently also results in the hydrolysis of the reaction product to give an ester of the free acid (when an ester solvent is used). The synthesis of N-[N-(tert-butyl)phenylcarbonylamino](4-methyl phenyl)carboxamide was only briefly considered to evaluate essentially two approaches, namely: · The conversion of the monoacylhydrazine, N-[(tert-butyl)amino](4- methylphenyl)carboxamide, by acylating with either benzoyl chloride or methylbenzoate (gave 86 percent N-[N-(tert-butyl)phenylcarbonylamino](4-methyl phenyl)carboxamide when benzoyl chloride was used as acylating agent); and · The one-pot conversion of the hydrazone, [(1E)-2-(4-methylphenyl)-1- azavinyl](tert-butyl)]amine, by bromination/hydrolysis and acylation. In this case, benzoyl chloride (2 percent N-[N-(tert-butyl)phenylcarbonylamino](4-methyl phenyl)carboxamide), benzoic acid (80.67 percent N-[N-(tertbutyl) phenylcarbonylamino](4-methylphenyl)carboxamide) were evaluated as potential acylating agents.
- Full Text:
- Date Issued: 2008