The objective of this study is to determine the effects of carrier gas viscosity of hydrogen and helium on column efficiency; particularly when employing thin films. When using thin films, mass transfer in the stationary phase becomes negligible and mass transfer in the mobile phase predominates. It was envisioned that when employing thin films hydrogen would be the carrier gas of choice due to its higher diffusivity and lower viscosity. The combination of the previous factors should lead to faster analyses (isothermal) and higher column efficiency with hydrogen. Viscosity is the resistance of a liquid or gas to flow. The viscosity of a gas is determined by two factors: (1) the molecular weight of the gas; and (2) its temperature. When the temperature or molecular weight of the gas is increased its viscosity is also increased. In a chromatographic system, with a constant pressure drop, an increase in viscosity results in a decrease in the linear velocity of the carrier gas, ultimately resulting in lower column efficiency. / Master of Science

No description available.

Ph. D.

This thesis investigates the semi-blind channel estimation in uplink (UL) of Orthogonal Frequency Division Multiple Access (OFDMA) systems based on subspace decomposition. We exploit the orthogonality between signal subspace and noise subspace induced by virtual carriers (VCs) and cyclic prefix (CP) and the property of that the exclusive sub-carriers set is assigned to each user to estimate and identify the channels for each user individually. In OFDMA systems, when some users don¡¦t communicate with base station, the sub-carriers of non-active user provide extra redundancy for channel estimate to enhance the accuracy of channel estimation. Furthermore, the sufficient channel identifiability condition is developed. Furthermore, a novel scheme, called as virtual carriers recovery (VCR) scheme, is proposed to improve the performance of the subspace-based channel estimation method. It suppresses the noise interference by recovering the VCs to zeros at receiver. The simulation results illustrate that the enhancement of VCR scheme is particularly apparent for the partially loaded OFDMA system at low signal to noise ratio (SNR). In addition, the VCR scheme increases the convergence rate of the subspace-base semi-blind channel estimation.

While 3.3 billion people flew worldwide in 2014 a large number of these were from developed countries. It is emerging countries which offer the greatest potential for future air traffic growth, with forecasts suggesting that 7.3 billion people will fly by 2034. The greatest proportion of this traffic will be in the Asia-Pacific region where there is already high low-cost carrier penetration. Given increasing price-based competition within short-haul markets, there are many significant challenges in terms of how Asian network airlines respond to LCC competition, and a popular response is the use of low-cost subsidiaries. Thus, the aims of this research are to establish the sources of competitive advantage of Asian airlines generally, and to examine the competitive responses of Asian network airlines and the strategic capabilities of them in competing with low-cost carriers, with a particular focus upon the use of low-cost subsidiaries. This research is underpinned with competitive advantage theory, particularly the resource-based view which concerns the internal environment of firms where each firm possesses a collection of unique resources and capabilities that provide the foundation for competitive strategy. For this research, data were collected from 49 senior airline management personnel using questionnaire surveys, resource surveys, and semi-structured interviews. The data were then analysed using VRIN analysis, the importance and difficulty of 37 competitive responses, strategic capability analysis, and the product and organisational architecture model. The results found that both a strong strategy and stable leadership are crucial. The strategies of Asian network airlines must be flexible to respond appropriately to competitive threats as they materialise, with this responsiveness contributing to the attainment of competitive advantage. Out of an analysed 36 intangible resources, the top resources for competitive advantage and responding to competitive threats for Asian airlines generally are slots, brand, and product and service reputation, with the importance of these based more on being hard to copy than valuable. Each analysed airline business model has a relatively distinct core bundle of intangible resources which explains the internal sources of their competitive advantage. The need for Asian network airlines to strengthen their competitive advantage and their ability to compete is because low-cost carriers impact them in many ways, most notably through a reduction in market share and reduced yields given the key motivation of customers within short-haul markets and economy class is now price and value-for-money. Asian network airlines are most likely to respond to low-cost carriers if they focus upon their core markets, grow their market share, and target the core higher-yielding passengers on which network airlines rely. In such instances, Asian network airlines should respond by focusing more on their brands and meeting the needs of their core targeted market segments. There is a strong positive correlation between profit margin and the strategic capability to compete with low-cost carriers. Yet, Asian network airlines have relatively weak capabilities overall. While Vietnam Airlines, Malaysia Airlines, and Garuda Indonesia are reasonably well placed to compete, network airlines from Northeast Asia, in particular, must strengthen their capabilities especially as Japan, China, and Taiwan are witnessing fast low-cost carrier growth. However, the possession of a strong capability does not mean it is fully or properly leveraged. To compete more effectively with low-cost carriers, the most important competitive responses, based upon analysis of 37 responses, are the ability of management to quickly introduce changes, leveraging brand strength, and increasing aircraft utilisation. Based on the relationship between the importance and difficulty of responses, the most crucial responses for competitive advantage of Asian network airlines are reducing costs to within 30% of LCCs and increasing aircraft utilisation. If achieved, these should lead to meaningful sustained advantage. Low-cost subsidiaries are easier to implement than for network airlines to significantly reduce costs, change to one fleet, or reduce the use of direct distribution, which may explain their popularity within Asia and them being a borderline very essential competitive response. For network airlines, low-cost subsidiaries are a more effective way to compete with low-cost carriers, to participate in the growth of the budget segment, a means of operating uneconomic routes, and to remove unprofitable customers. Network airlines can then focus upon their core market segments and their core competencies. However, their creation is reactive and not proactive which undermines their effectiveness, likewise that low-cost subsidiaries suffer from poor profitability, higher costs, and much smaller size and scale than their key low-cost competitors. This research recommends that Asian network airlines strengthen their existing and primary sources of competitive advantage while pursuing new sources of advantage. While the strategic capabilities of Asian network airlines have strengthened over time, it is essential that they are further strengthened and fully acted upon given increasing competitiveness. The use of low-cost subsidiaries will continue, but it is crucial for themselves and their parent network airlines that they improve their ability to compete and thereby their performance.

The aim of this thesis is to analyze the changes to marketing strategy of airline companies in Europe due the proliferation of low-cost carriers in Europe. The thesis is divided into three parts. In the theoretical part the marketing strategy framework is established by reviewing the latest literature on marketing theory and its application to the airline industry. The second chapter provides the historical background and shows the specifics of the airline industry in order to determine when the proliferation of low-cost carriers in Europe occurred. It also analyzes the impact the proliferation had on the business operations of the network carriers by looking at the changes to different elements of the marketing mix. Finally the third chapter summarizes the authors research on consumer behavior in the airline industry. The research was conducted through a quantitative questionnaire and it investigates consumers perception of price and brand awareness.

Thesis (MScAgric)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Botrytis bunch rot of grape is caused by Botrytis cinerea Pers. :Fr. Conidia of the pathogen, which is dispersed by wind, water droplets and by insects, can penetrate the intact grape berry cuticle, but disease expression occurs only under predisposing conditions. Since relatively high infection rates often occur in vineyards, predisposing factors must play a fundamental role in primary infection and subsequent disease occurrence. Insects can play a very important role in this regard by depositing inocula at wound sites during feeding and by providing fresh wounds during their oviposition and feeding activities. The aim of this study was (i) to determine the potential of the Mediterranean fruit fly to transfer B. cinerea and other bunch and fruit rot fungi in natura, (ii) to investigate the transport, deposition and subsequent disease expression on grape berries in vitro, and (iii) to investigate fruit fly activities and the nature of deposited conidia and mycelia of B. cinerea by aid of digital photography and epifluorescence microscopy, respectively. Two Sensus fruit fly traps containing the para-pheromone, Capilure, were installed in orchards and five neighboring vineyards on four farms in the Stellenbosch region. Ceratitis fruit flies were collected weekly, identified and counted to determine the fluctuations in fruit fly population. Following field collection, the fruit flies were plated on Kerssies' B. cinerea selective medium and the number of flies yielding the pathogen was recorded. Two fruit fly species, C. capitata and C. rosa, were captured during the study period. Ceratitis rosa numbers comprised only 1% of the total number of fruit flies captured. Ceratitis capitata numbers, and the percentage B. cinerea contaminated flies generally increased after harvest in the different orchards and vineyards. Following harvest, the percentage flies yielding B. cinerea was higher in vineyards compared to orchards. Furthermore, in each vineyard an increase in percentage B. cinerea contaminated fruit flies was preceded by a corresponding increase in its neighboring orchard. The levels of both Penicillium and Alternaria contaminated fruit flies stayed high throughout the investigation period, especially after harvest of the orchard cultivars. Low incidence of Aspergillus, Mucor and Rhizopus spp. were recorded on C. capitata. These findings suggest that the Mediterranean fruit fly may play an important role in the dispersal of inocula of fungi associated with postharvest decay from early-maturing stone fruit orchards to mid- and late-maturing wine grape vineyards, and in disease induction under conditions unfavourable for natural infection. Three experiments were conducted to determine the potential of fruit flies in provoking B. cinerea decay. In the first experiment, transport of conidia and disease expression were investigated on rachis segments bearing unwounded berries only. In the second experiment, the effect of wounding on disease expression was investigated. In the third experiment, the effect of inoculum type (mycelia and conidia) on transportation and disease expression was investigated on rachis segments bearing unwounded berries, and on segments with wounded berries. The table grape cultivar, Dauphine, and the wine grape cultivar, Shiraz, were used at véraison, two weeks before harvest and harvest, and the transport studies were conducted in ethanol-disinfected perspex cages. Disease expression was studied in dry (~56% RH), ethanol-disinfected perspex chambers incubated at 22°C. The isolations from berries revealed that the flies deposited, without preference, high amounts of B. cinerea at various positions on the grape berry's surface. The freezing studies showed that the deposited conidia germinated and penetrated the berry skin at various positions. However, B. cinerea developed more often at the pedicel end than on the cheek or style end, which indicated a peculiar interaction between B. cinerea, the fruit fly and host tissue at this part of the berry. This phenomenon was substantiated by the finding that B. cinerea also developed more often at the pedicel end of berries that were not frozen. Further evidence for this interaction was found on intact berries exposed to flies that carried mycelia after feeding on berries without sporulating colonies of the pathogen, but showing symptoms of slippery skin. Significantly more decay developed on wounded berries compared to the unwounded berries and more so at the wound site. In addition, female fruit flies were responsible for significantly more decay development than male fruit flies. The study thus proved that the Mediterranean fruit fly can promote B. cinerea disease development under conditions unfavorable to natural infection. The activities of the Mediterranean fruit fly, Ceratitis capitata, on grape berries were monitored by aid of digital photography. In addition, the deposition of conidia and mycelia of Botrytis cinerea at three sites (pedicel end, cheek and style end) on the grape berry, germination of the fungal structures after dry (±56% RH) and moist (±93% RH) incubation and wounds inflicted during ovipositioning were examined with an epifluorescence microscope. The observations revealed that the fruit fly's activities were generally restricted to the grape berry. They visited the grape berry cheek more often, but visitations to the pedicel end of berries increased substantially from véraison to harvest, indicating the possibility of nutrient leakages at this site. Microscopy revealed that the flies deposited conidia singular, in feeding packages and in faecal excrements on the berry surface. The conidia in feeding packages were ensheathed by salivical fluids and occurred in clusters of 10 to 50 conidia. An average of 60% of the conidia in feeding packages germinated under dry conditions (±56% RH). Conidia that passed through the intestinal tract of the fruit fly and that were deposited in faecal excrements were deformed and low in viability. These conidia did not occur in cluster format, but were proportionally spread with the faeces on the surface of the grape berry. Conidia that were deposited singular and in faecal excrements did not germinate unless incubated under moist conditions (± 93% RH). Wounds inflicted by female fruit flies during ovipositioning were most frequently observed on the cheek. This predisposition to B. cinerea infection of grape berries by the activities of fruit flies, suggested an important role for the flies in the initiation of Botrytis bunch rot epidemics in vineyards. / AFRIKAANSE OPSOMMING: DIE ROL VAN DIE MEDITERREENSE VRUGTEVLIEG, CERATITIS CAPITATA, IN BOTRYTIS CINEREA TROSVERROTTING VAN DRUIWE Botrytis-trosverrotting van druiwe word deur Botrytis cinerea Pers. :Fr. veroorsaak. Konidia van die patogeen wat deur wind, waterdruppels en insekte versprei word, kan die intakte druiweskil binnedring, maar siekte-uitdrukking vind slegs onder spesiale omstandighede plaas. Aangesien relatief hoë infeksie vlakke algemeen in wingerde voorkom, moet predisponerende faktore 'n fundamentele rol in die primêre infeksie, en die daaruit voortspruitende siektetoestand speel. Insekte kan 'n baie belangrike bydrae lewer deur inokuia tydens voeding by wonde te deponeer. Nuwe wonde kan ook tydens oviposisionering en voeding ontstaan. Die doel van hierdie studie was om (i) die potensiaal van die Mediterreense vrugtevlieg om B. cinerea en ander tros- en vrugverrottingswamme in natura oor te dra, te bepaal; om (ii) die verspreiding, deponering en daaropvolgende siekteuitdrukking op druiwekorrels in vitro te ondersoek; en om (iii) die aktiwiteite en aard van die gedeponeerde konidia en miselia met behulp van digitale fotografie sowel as epifluoressensiemikroskopie waar te neem. Twee Sensus-vrugtelokvalle met die paraferomoon, Capilure, IS In vrugteboorde en aangrensende wingerde in die Stellenbosch-omgewing aangebring. Ceratitis-vrugtevlieë is weekliks versamel, geïdentifiseer en getel om fluktuasies in die vrugtevliegpopulasie te bepaal. Na die veldversameling is die vrugtevlieë op Kerssies se B. cinerea-selektiewe medium uitgeplaat. Gedurende die studie is twee spesies vrugtevlieë, C. capitata en C. rosa, gevang. Na oesstyd het die aantal Ceratitis-vrugtevlieë en die persentasie vrugtevlieë, besmet met B. cinerea, in die verskillende boorde en wingerde toegeneem. Na oestyd was die persentasie vrugtevlieë wat B. cinerea gedra het, hoër in die wingerde as in die boorde. Elke toename in die persentasie B. cinerea-besmette vrugtevlieë in 'n wingerd is voorafgegaan deur 'n ooreenkomstige toename in die aangrensende vrugteboord. Die aantal vrugtevlieë besmet met Penicillium en Alternaria spp. het tydens die navorsingstydperk deurgaans hoog gebly, veral nadat die vrugteboord-kultivars geoes is. Die voorkoms van Aspergillus-, Mucor- en Rhizopus spp. op Ceratitis-vrugtevlieë was deurgaans laag. Hierdie bevinding wys daarop dat vrugtevlieë 'n belangrike rol speel in die verspreiding van swarninokula, wat met na-oes verrotting geassosieer word, van vroegrypwordende steenvrugteboorde na mid- en laatrypwordende wyndruifwingerde. Drie eksperimente is in vitro onderneem om vrugtevlieë se potensiaal om B. cinereaverrotting te veroorsaak te bepaal. In die eerste eksperiment is ragi met slegs ongewonde korrels gebruik om die oordrag van konidia en siekte-ontwikkeling te ondersoek. In die tweede eksperiment is die effek van verwonding op siekte-ontwikkeling ondersoek. In die derde eksperiment is die effek van inokulumtipe (miselia en konidia) op verspreiding en siekte-ontwikkeling ondersoek deur ragis-segmente met gewonde korrels sowel as ragissegmente met ongeskonde korrels te gebruik. Die tafeldruif-kultivar Dauphine en die wyndruif-kultivar Shiraz, by kleurbreuk, twee weke voor oes en by oestyd, is in die eksperimente gebruik. Die oordragstudies is in etanol-ontsmette perspex-hokke uitgevoer. Siekte-ontwikkeling is bestudeer in droeë (±56% RH), etanol-ontsmette perspex-kamers en geinkubeer by 22°C. By ondersoek is gevind dat vlieë, sonder voorkeur, groot hoeveelhede B. cinerea op verskeie dele op die druiwekorrel-oppervlak deponeer. Bevriesingstudies het aangetoon dat die gedeponeerde konidia op verskeie dele van die korrelontkiem en die skil binnedring. Botrytis cinerea het egter meer dikwels by die korrelsteelkant as by die stempelkant, of op die wang, ontwikkel. Hierdie bevinding het 'n eiesoortige interaksie tussen B. cinerea, die vrugtevlieg en gasheerweefsel by die korrelsteelkant van die korrel aangetoon. Die verskynsel is gestaaf deur die bevinding dat B. cinerea ook meer dikwels by die korrelsteelkant van die korrels wat nie gevries is nie, ontwikkel het. Verdere bewys van hierdie interaksie is gevind by ongeskonde korrels wat aan die vlieë wat miselia gedra het blootgestel is. Die siekte het beduidend meer dikwels op gewonde as ongewonde korrels en verder aansienlik meer dikwels op die wondoppervlakte ontwikkel. Dit was ook duidelik dat vroulike vrugtevlieë baie meer vir verrotting verantwoordelik was as manlike vrugtevlieë. Die studie bewys dus dat Mediterreense vrugtevlieë die ontwikkeling van B. cinerea kan bevorder in omstandighede wat ongunstig is vir natuurlike infeksie. Die aktiwiteite van die Mediterreense vrugtevlieg C. capitata op die druiwekorrels is met behulp van digitale fotografie waargeneem. Verder is die deponering van konidia en miselia van B. cinerea op die verskillende dele (korrelsteelkant, wang en stempelkant) van die korrel, ontkieming van die swamstrukture na droeë (±56% RH) en nat (±93% RH) inkubasie en wonde wat tydens oviposisionering veroorsaak is, met epifluoressensie-mikroskopie ondersoek. Die waarnemings het onthul dat die vrugtevlieg se aktiwiteite gewoonlik tot die druiwekorrel beperk is. Hulle het korrelwange meer dikwels besoek. Besoek aan die korrelsteelkant het aansienlik toegeneem van kleurbreuk tot oestyd, wat op die moontlikheid van voedingstof-lekkasie by die deel aandui. Mikroskoopstudies het aangedui dat vlieë konidia enkel, in voedingspakkies en in fekale uitskeidings op die korreloppervlakte deponeer. Die konidia in die voedingspakkies is deur speekselvloeistof omhul en het in groepe van 10 tot 50 konidia voorgekom. Gemiddeld 60% van die konidia in voedingspakkies het in droeë omstandighede (±56% RH) ontkiem. Konidia wat deur die spysverteringskanaal van die vrugtevlieg gegaan het en in die fekale ekskresie gedeponeer is, was misvorm en het lae lewensvatbaarheid gehad. Laasgenoemde konidia was nie in groepe gedeponeer nie, maar is proporsioneel met die feces op die oppervlak van die druiwekorrel versprei. Konidia wat enkel en in feces gedeponeer is, het nie ontkiem nie, tensy toestande vogtig (±56% RH) was. Wonde wat deur die vroulike vrugtevlieë tydens oviposisionering veroorsaak is, is meer dikwels op die wang van die korrelopgemerk. Hierdie predisposisie van druiwekorrels tot B. cinerea-infeksie, meegebring deur die aktiwiteit van die vrugtevlieg, dui daarop dat die rol wat die vrugtevlieg in die inisiëring van Botrytis trosverrottingepidemies in wingerde speel, van beduidende belang is.

Mitochondria from Xenopus laevis and Ambystoma mexica- num embryos between fertilization and the beginning of feeding were studied: the former with respect to metabolic behaviour, enzyme pattern and carrier activity, and the latter with respect to morphological parameters. The metabolic behaviour of mitochondria was studied by assessing the rates of oxygen uptake in presence of various substrates. The rates of oxidation of most substrates change during development. The only substrate to be readily metabolized is glutamate (in presence of malate), whose rate of oxidation presents a peak during gastrulation and declines during larval development. The high rate of oxidation of glutamate and a high aspartate aminotransferase activity indicate that the glutamate- aspartate cycle may be predominant in early embryonic mitochondria. The activity of enzymes from the matrix, the inner membrane and the outer membrane were studied. During early development activities of enzymes in the various compartments change independently of each other. Furthermore, enzymes within one compartment may vary independently. Measurements of carrier activity reveal that the carrier for dicarboxylic acids displays a high activity before gastrulation and decreases thereafter, while the tricarboxylic acid, pyruvate and glutamate/OH carriers show the opposite pattern of change, their activities being low or undetectable during early development. This implies that a mitochondrial differentiation takes place ' during development, beginning at gastrulation when the first differentiated cells appear. In order to correlate mitochondrial and cellular differentiation, morphological parameters of mitochondria from undifferentiated and differentiated cells - Ruffini cells and epidermal cells - were analyzed. Mitochondria from the differentiated cells are significantly different from those in undifferentiated cells. Thus the processes of cell differentiation are accompanied by morphological and biochemical differentiation of the mitochondria. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1981, härtill 5 uppsatser</p> / digitalisering@umu

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / abstract / Microbiology / Master / Master of Philosophy