We present a Markov chain analysis for studying the performance of wireless ad hoc networks. The models presented in this dissertation support an arbitrary backoff strategy. We found that the most important parameter affecting the performance of binary exponential backoff is the initial backoff window size. Our experimental results show that the probability of collision can be reduced when the initial backoff window size equals the number of terminals. Thus, the throughput of the system increases and, at the same time, the delay to transmit the frame is reduced. In our second contribution, we present a new analytical model of a Medium Access Control (MAC) layer for wireless ad hoc networks that takes into account frame retry limits for a four-way handshaking mechanism. This model offers flexibility to address some design issues such as the effects of traffic parameters as well as possible improvements for wireless ad hoc networks. It effectively captures important network performance characteristics such as throughput, channel utilization, delay, and average energy. Under this analytical framework, we evaluate the effect of the Request-to-Send (RTS) state on unsuccessful transmission probability and its effect on performance particularly when the hidden terminal problem is dominant, the traffic is heavy, or the data frame length is very large. By using our proposed model, we show that the probability of collision can be reduced when using a Request-to-Send/Clear- to-Send (RTS/CTS) mechanism. Thus, the throughput increases and, at the same time, the delay and the average energy to transmit the frame decrease. In our third contribution, we present a new analytical model of a MAC layer for wireless ad hoc networks that takes into account channel bit errors and frame retry limits for a two-way handshaking mechanism. This model offers flexibility to address design issues such as the effects of traffic parameters and possible improvements for wireless ad hoc networks. We illustrate that an important parameter affecting the performance of binary exponential backoff is the initial backoff window size. We show that for a low bit error rate (BER) the throughput increases and, at the same time, the delay and the average energy to transmit the frame decrease. Results show also that the negative acknowledgment-based (NAK-based) model proves more useful for a high BER. In our fourth contribution, we present a new analytical model of a MAC layer for wireless ad hoc networks that takes into account Quality of Service (QoS) of the MAC layer for a two-way handshaking mechanism. The model includes a high priority traffic class (class 1) and a low priority traffic class (class 2). Extension of the model to more QoS levels is easily accomplished. We illustrate an important parameter affecting the performance of an Arbitration InterFrame Space (AIFS) and small backoff window size limits. They cause the frame to start contending the channel earlier and to complete the backoff sooner. As a result, the probability of sending the frame increases. Under this analytical framework, we evaluate the effect of QoS on successful transmission probability and its effect on performance, particularly when high priority traffic is dominant. / Graduate

The aim of this bachelor thesis was to investigate how local farmers of sunflower and local processors of sunflower oil in Babati, Tanzania perceive constraints and possibilities to value chain upgrading by conducting a case study. Open-ended interviews were conducted during a period of eight weeks with local sunflower farmers, local sunflower processors and other actors with knowledge of the sunflower value chain. The results from the study show that the main constraints perceived by farmers were lack of capital and incentive to buy new seeds, lack of knowledge of how to re-plant old seeds, their lack of bargaining position and market knowledge which together put restrains on their market access. The main constraints, perceived by local processors, were lack of access to credit, lack of market access with regard to sunflower cakes, a bi-product of sunflower oil production, and a shortage of sunflower seeds on the local market. With regard to the shortage of seeds produced in the area this was discussed further with the respondents as it seems to be connected with actors need for diversification as a form of risk aversion. The main upgrading options as perceived by farmers were value addition by also processing and selling the sunflower oil and different forms of horizontal integration. The main upgrading option perceived by local processors of sunflower oil was an insourcing of the labelling and packaging of sunflower oil which would create access to higher value markets.

A few vertically integrated retail chains increasingly dominate South Africa’s agro-food supply chain. M+M Planet Retail (2004) placed the market concentration among retailers to be as high as 96% for the top four chains leaving only 4% to the small competitors. The onset of this trend has led to the demise of a large number of “mom and pop” general dealers in favour of the sleek new stores as they were either priced or bought out of business. Players in the fresh produce market have proved to be resilient to this onslaught. The green grocers and hawkers have survived the “category killers” and appear to be able to face this competition head on. It is this resilience that is of interest to this study. The review of literature revealed a dearth of studies and hence methodology into the nature of the interaction between the three forms of retail. A preliminary survey also revealed the lack of coherent and detailed information, particularly among the greengrocers and hawkers. Thus the established methods of modelling competition analysis, namely the Structure Conduct Performance and the New Empirical Industrial Organisation frameworks, were deemed inappropriate. The study therefore took an exploratory form that relied on measures of central tendency and the perceptions of leading industry practitioners to reveal the nature and magnitude of competition between supermarkets, green grocers and hawkers. The study primarily drew on ‘Porter’s forces’ competition model to structure the investigation. It also employed a chain analysis approach including supply and value chain analysis (VCA) tools to analyse this competition. The study therefore sought to unpack the retail sections of the three chains in terms of identifying role-players; their relationships and interaction; as well as to account for the relative values that different types of fresh produce retailers generated for the final consumer. Besides the contribution to the general body of knowledge about the nature of the system that feeds us, this study provides means for the competing channels to upgrade and improve efficiency. A developmental and empowerment point of view was emphasised in the research, as such, identifying possible measures to upgrade and improve the informal sector was given precedence. The objective was to describe and analyse the competitive environment in which FFV was retailed in the Tshwane through a determination of the competitive and strategic behaviour of retailers and a mapping the flow of value. It was hypothesised that fresh produce retailers competed by varying elements of their marketing mix to suit their niche markets. The investigation was conducted in two phases; a pilot study followed by a survey involving a six-step sampling frame targeting a total of 120 respondents including 15 supermarkets, 30 greengrocers and 75 hawkers. This analysis was limited to the bounds of the Tshwane metropolitan area, South Africa, and focused on six fresh fruits and vegetable lines concurrently traded by supermarkets, greengrocers and hawkers. The main findings of the investigation include that tri-dimensional FFV retail competition was most intense in the middle-income areas of the city. The low income areas were dominated by informal traders while the large supermarkets chains and the large format greengrocers dominated the high income areas. The non-syndicated greengrocers were confined to the middle-income areas where competition was most intense. When the marketing strategies and chain maps were compared it was concluded that the tridimensional competitive environment was facilitated by the existence of multiple niches; the equalising effect of produce market based pricing; the general upgrade in product quality offered by all retailers; characteristics of fresh produce itself as compared to other foodstuffs and the existence of multiple market niches in the sector. Concluding the study were recommendations to improve (upgrade) the marketing performance of each of the three channels. / Dissertation (MSc(Agric) (Agricultural Economics))--University of Pretoria, 2007. / Agricultural Economics, Extension and Rural Development / MSc(Agric) / unrestricted

It has been hypothesized that an increase in the ratio of plasma tryptophan (TRP) to branched-chain amino acid (BCAA) concentrations may mediate an increase in cerebral serotonin synthesis, through an increased cerebral tryptophan uptake. It is postulated that the increased brain serotonin content may induce central fatigue during prolonged exercise. Until present, this postulate had not been subject to rigorous scientific testing during prolonged exercise. Therefore the aim of this study was to investigate whether ingesting a BCAA supplement during prolonged exercise improves physical performance and central fatigue. The use of such a supplement during prolonged exercise could then be expected to have a large effect on performance. Eight trained cyclists (VO₂ max= 61.9 ± 4.3 ml 02/kg/min) ingested, in random order, a drink containing either 10% carbohydrate (CHO), 10% CHO and 0.16% branched-chain amino acid (BCAA) or 0.16% BCAA. Every hour, for the duration of the exercise (4 hours, 55% VO₂ max) blood samples were analysed for amino acids, ammonia, free fatty acids, glycerol, glucose and insulin concentrations. Urine was analysed for urea and creatinine concentrations. Heart rate, oxygen consumption (VO₂), respiratory exchange ratio (RER) and rating of perceived exertion were also analysed. Thereafter, subject's 40km time trial performance and RPE was assessed on a Velodyne windtrainer. Central fatigue following the time trial was quantified using the Sternberg reaction-time paradigm. The serum concentration of the BCAA's declined as a result of the exercise, in the BCAA only trial. Tryptophan concentration, however, did not change during the exercise. The serum TRP:BCAA ratio increased (0.16 ± 0.06 to 0.20 ± 0.10; p≤0.05) in the CHO trial only. The BCAA trial differed from the two trials in which CHO was ingested because plasma ammonia and glucose concentrations did not increase, while free fatty acids (FF A's) and glycerol concentrations increased significantly (p≤0.05). The lower RER in the BCAA trials suggests a higher proportion of fat was oxidised in these trials, compared to the other two trials. Cycling performance, over a 40km time trial, (CHO= 68.59 ± 6.02; CHO+ BCAA = 68.00 ± 3.01; BCAA = 69.43 ± 5.35 min/sec), ratings of perceived exertion, submaximal or maximal heart rates, and mental performance were not different between trials. Data from this study appears to refute the thesis hypothesis that an increase in serum TRP:BCAA decreases physical performance and central fatigue, during prolonged exercise.

Thesis (MAgricAdmin.)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The South African wine industry produces a million tons of grapes annually and supports approximately 300 000 people, including dependants. For the biggest part of the zo" century the industry was governed by a system of statutory control, being isolated from the international market by politically-induced sanctions. As a result the main focus of the industry was on the domestic market and the value chain was structured to produce volume. In the 1990's, the removal of sanctions and statutory control, together with the global shift towards free international trade, created a new operational environment for the South African wine industry. New opportunities and threats emerged for the industry. This dissertation starts by creating a theoretical base for the value chain, including value chain management and the transaction costs that influence the economics of the value chain. The domestic wine market is stable, thus future growth of this industry will depend on exports. Chapter three identifies the characteristics of the international wine market, as well as the major trends in global wine consumption. This is followed by a discussion on the four primary drivers in the international wine industry along with an overview of the value chains of leading wine-producing countries. Chapter four commences with a historical overview of the development of the South African liquor industry. This is followed by a discussion on how the reopening of the international market, influenced the structure and composition of the value chain in the South African wine industry. The purpose of this chapter is to outline the value chain of the South African wine industry, stress problems and to investigate the international competitiveness of the chain. It is concluded by identifying the strengths and weaknesses in the value chain. The strengths in the chain were then used to create opportunities, while the weaknesses were used to highlight threats that give rise to transaction costs. The ownership structure and composition within the value chain of the South African wine industry, is the product of the current institutional structure of the industry. The current structure creates transaction costs in the respective links of the value chain. Chapter five identifies 34 problems that cause transaction costs, along with the implications for the wine industry. From these problems, strategies are derived that will enhance the international competitiveness·of the chain, inducing a greater focus on the market. Chapter five concludes by looking at five international markets, with practical suggestions for the future vision of the value chain in the South African wine industry. / AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse wynbedryf produseer jaarliks gemiddeld 'n miljoen ton druiwe en voorsien 'n bestaan aan ongeveer 300 000 persone. Die bedryf het vir die grootste gedeelte van die 20ste eeu gefuksioneer onder 'n stelsel van statutêre beheer en was as gevolg van politieke sanksies ge-isoleer van die internasionale mark. Die waardeketting van die wynbedryf was gestruktureer om volume te produseer en hoofsaaklik gefokus op die binneland as mark. Met die verwydering van statutêre beheer en sanksies, gepaardgaande met die globale verskuiwing na vrye internasionale handel gedurende die 1990's, het die waardeketting van die Suid-Afrikaanse wynbedryf skielik 'n nuwe operasionele omgewing betree. Dit het aan die bedryf nuwe geleenthede en bedreigings gebied. Die tesis begin deur 'n teoretiese basis te skep van 'n waardeketting, die bestuur daarvan en transaksiekostes wat die ekonomie van 'n waardeketting beïnvloed. Die plaaslike mark vir wyn het gestabiliseer en toekomstige groei van die Suid-Afrikaanse wynbedryf is afhanklik van uitvoere. In hoofstuk drie word na die kenmerke van die internasionale wynomgewing waarin die Suid-Afrikaanse wynbedryf meeding, en die belangrikste globale wynverbruiks tendense gekyk. Die vier primêre drywers in die internasionale wynbedryf word bespreek gevolg deur 'n kort oorsig oor die waardekettings van leier produserende wynlande. Hoofstuk vier begin deur 'n historiese oorsig oor die ontwikkeling van die Suid-Afrikaanse drankbedryf te gee. Dit word gevolg deur na die invloed te gaan kyk wat die heropening van internasionale markte op die struktuur en samestelling van die waardeketting in die Suid- Afrikaanse wynbedryf gehad het. Die doel van die hoofstuk is om 'n beskrywing van die waardeketting in die Suid-Afrikaanse wynbedryf te gee, probleme te identifiseer en die mededingendheid van die ketting internasionaal te ondersoek. Die hoofstuk word afgesluit deur sterk- en swakpunte in die waardeketting van die Suid-Afrikaanse wynbedryf af te lei. Uit die sterkpunte is geleenthede vir die bedryf geïdentifiseer, en vanuit die swakpunte is bedreigings wat aanleiding gee tot transaksiekostes, geïdentifiseer. Eienaarskapstrukture en eiendomsverhoudings binne die waardeketting van die Suid- Afrikaanse wynbedryf is die gevolg van die institusie waarbinne die bedryf oor tyd ontwikkel het. Die manier wat die ketting egter tans gestruktureer is bring transaksiekostes binne die onderskeie skakels in die ketting mee. In hoofstuk vyf word 34 probleme wat transaksiekostes genereer, met die onderskeie implikasies vir die bedryf, geïdentifiseer. Vanuit die probleme word strategiese opsies geïdentifiseer wat die ketting internasionaal meer mededingendheid sal maak, met grootter markgerigtheid. Die hoofstuk word afgesluit deur na vyf markte te gaan kyk, met praktiese voorstelle, waar die waardeketting van die Suid- Afrikaanse wynbedryf homself behoort te fokus.

Process planning is a task comprising a broad range of activities to design and develop an appropriate manufacturing process for producing a part. Interpretation of the part design, selection of manufacturing processes, definition of operations, operation sequences, machining datums, geometrical dimensions and tolerances are some common activities associated with the task. Process planning is also “the link between product design and manufacturing” with the supplementary commission to support design of competitive products. Process planning is of a complex and dynamic nature, often managed by a skilled person with few, or no, explicit methods to solve the task. The work is heuristic and the result is depending on personal experiences and decisions. Since decades, there have been plenty of attempts to develop systems for computer-aided process planning (CAPP). CAPP is still awaiting its breakthrough and one reason is the gap between the functionality of the CAPP systems and the industrial process planning practice. This thesis has an all-embracing aim of finding methods that cover essential activities for process planning, including abilities to predict the outcome of a proposed manufacturing process. This is realised by gathering supporting methods suitable to manage both qualitative and quantitative characterisation and analyses of a manufacturing process. The production research community has requested systematisation and deeper understanding of industrial process planning. This thesis contributes with a flow chart describing the process planning process (PPP), in consequence of the methodological studies. The flow chart includes process planning activities and information flows between these activities. The research has been performed in an industrial environment for high volume manufacturing of gear parts. Though gear manufacturing has many distinctive features, the methods and results presented in this thesis are generally applicable to precision manufacturing of many kinds of mechanical parts. / <p>QC 20140522</p>

O presente estudo, de abordagem qualitativa e descritiva, investiga as relações entre as teorias sobre Economia Criativa, Vantagem Competitiva, Cadeia de Valor e Qualidade no Mercado de Luxo objetivando identificar a contribuição do Programa do Polo de Joias do Pará para a criação de valor na indústria de joias do referido estado brasileiro. O método de pesquisa utilizado abrangeu a construção de proposições a partir da literatura revisada e reduzida, a realização de entrevistas com profissionais do setor joalheiro brasileiro, análise de conteúdo das entrevistas e análise da cadeia de valor do Polo de Joias do Pará com base na observação participante. Os resultados apontam que as estruturas teóricas empregadas neste estudo estão presentes na Cadeia de Valor do Programa do Polo de Joias do Pará, destacando a criação de valor por meio do benefício percebido pelo consumidor. O incipiente estudo cria oportunidade para a realização de novas relações com outros clusters criativos ou para a identificação de atitudes e intenções de compra dos clientes do Polo. / This qualitative and descriptive study investigate the relationship between theories about Creative Economy, Competitive Advantage, Value Chain and Quality in Luxury Market aiming to identify the contribution of the Pará Jewelry Cluster Program for creating value in jewelry industry of that Brazilian state. The research method included the construction of propositions from the literature reviewed and reduced, conducting interviews with professionals in the Brazilian Jewelry Industry, content analysis of the interviews and analysis of value chain of Pará Jewelry Cluster based on observation participant. The results show that the theoretical frameworks used in this study are present in the Value Chain of the Pará Jewelry Cluster Program, highlighting the creation of value through benefit perceived by consumers. The study creates opportunity for the realization of new relationships with other creative clusters or to identify attitudes and purchase intentions of customers from Polo.

<div>Multi-model inference covers a wide range of modern statistical applications such as variable selection, model confidence set, model averaging and variable importance.</div><div>The performance of multi-model inference depends on the availability of candidate models, whose quality has been rarely studied in literature. In this dissertation, we study genetic algorithm (GA) in order to obtain high-quality candidate models. Inspired by the process of natural selection, GA performs genetic operations such as selection, crossover and mutation iteratively to update a collection of potential solutions (models) until convergence. The convergence properties are studied based on the Markov chain theory and used to design an adaptive termination criterion that vastly reduces the computational cost. In addition, a new schema theory is established to characterize how the current model set is improved through evolutionary process. Extensive numerical experiments are carried out to verify our theory and demonstrate the empirical power of GA, and new findings are obtained for two real data examples. </div>

Installed photovoltaic nameplate power have been growing rapidly around the worldin the last few years. But how much energy is returned to society (i.e. net energy) by this technology, and which factors contribute the most to the amount of energy returned? The objective of this thesis was to examine the importance of certain inputs and outputs along the solar panel production chain and their effect on the energy return on (energy) investment (EROI) for crystalline wafer-based photovoltaics. A process-chain model was built using publicly available life-cycle inventory (LCI) datasets. This model has been kept simple in order to ensure transparency. Univariate sensitivity analysis for processes and multivariate case studies was then applied to the model. The results show that photovoltaic EROI values are very sensitive to assumptions regarding location and efficiency. The ability of solar panels to deliver net energy in northern regions of the earth is questionable. Solar cell wafer thickness have a large impact on EROI, with thinner wafers requiring less silicon material. Finding an alternative route for production of solar-grade silicon is also found to be of great importance, as is introduction of kerf loss recycling. Equal system sizes have been found to yield an primary EROI between approximately 5.5-19 depending on location and assumptions. This indicates that a generalized absolute EROI for photovoltaics may be of little use for decision-makers. Using the net energy cliff concept in relation to primary EROI found in this thesis shows that primary EROI rarely decreases to less than the threshold of 8:1 in univariate cases. Crystalline photovoltaics under similar system boundaries as those in the thesis model does not necessarily constrain economic growth on an energetic basis.

In the trend of international development, multinational corporations should face three major international challenges: global integration and coordination, regional differences and responses and global innovation and learning. The backgrounds and motivations that enterprises adopt the strategy of internationalization are different. Whereas, enterprises to implement international strategies will inevitably involve the design and layout of channels. Therefore, ¡§Distribution Channel Strategies¡¨ are the major business strategies of the overseas subsidiaries of multinational corporations. Today is the era of ¡§who controlling the channels will win.¡¨ Besides providing superior quality products or service, enterprises should have adequate channels to, with lower cost or shorter transferring time, give customers convenient points to purchase and send the products to the target market, therefore, to create a good business performance. This thesis focuses on the distribution channel strategies of multi-national companies and gives a case study of ¡§Taiwan Furukawa.¡¨ We investigate internal and external environments and the business performances of two distribution channel strategies, and use case study method to the empirical analysis, which belonging to a single case design with a single design pattern of the subject. Three industry analysis methods, including value chain analysis, SWOT analysis, and five force analysis, is adopted to analyze the internal and external environments. We find that the sharp drop in revenue alerted Taiwan Furukawa to investigate the agencies and corporate customers in the sales network. They found the problem is that the business objectives of the agencies and Taiwan Furukawa are inconsistent, causing a significant reduction in sales volume. Then, the revenue has grown significantly after Taiwan Furukawa adopting ¡§direct sales¡¨ and ¡§zero-stage channel¡¨ substituting for ¡§indirect sales¡¨ and ¡§one-stage channel,¡¨ respectively. Above all, we find the ¡§zero-stage channel¡¨ has three functions, including direct sales, information channel, and customer service.