No description available.

A series of recent studies using Drosophila melanogaster suggest that while males may benefit from having access to many partners, female fitness is reduced by extended cohabitation and sexual interaction with males. Yet, even if repeated sexual interactions are harmful to females, limited male exposure will ultimately be detrimental due to sperm-depletion and infertility. Females are therefore expected to balance mating opportunities and sperm storage capacity to maximize lifetime reproductive success. I introduced extended mating deprivation as a selective pressure to experimentally evolve lines of D. melanogaster for characters related to mating and postcopulatory sexual selection. Evolution of the mate-deprived lines over several dozen generations demonstrated that restricted sexual access was indeed a potent selective pressure. I consistently found that when males were removed for an extended time period, female fitness declined substantially, suggesting that mate-deprivation over nine days was harmful. Under these conditions, selected-line males responded to mate-reduced conditions and demonstrated a 13% increase in reproductive success compared to controls. Experimental females had a 15% increase in fertility compared to controls. I investigated a series of developmental characteristics that may have been altered by the selection regime, and while there was some evidence of evolved change, these results were not consistent. Although the data at hand do not substantiate a detailed characterization, both sexes in the experimental populations demonstrated increased fitness after extended mate-deprivation, thus evolutionary change appears to have occurred via selection on one or both relevant male ejaculate characteristics: sperm number and survival, and factors affecting female late-life fertility. / Thesis (Master, Biology) -- Queen's University, 2008-04-28 23:05:42.835

This thesis investigated a potential improvement to hydrogen storage for fuel cells using a thermally efficient hydrogen storage method. The efficiency of the storage system was improved using a metal hydride system to act as a thermal control unit for an exothermic chemical hydrogen storage system. A cylindrical shaped “hybrid” reactor was created to allow hydrogen production from a sodium borohydride packed bed reactor and the metal hydride. Additionally, a custom built pressure-composition-temperature apparatus was built to record the amount of hydrogen desorption from the metal hydride while isolating the metal from potential poisons such as oxygen. Before using the chemical hydride packed bed, heat transfer through the reactor was studied using circulating water. The water experiments showed that an increase in heat flux to the reactor led to a faster desorption rate of hydrogen from the metal hydride resulting in a larger temperature drop throughout the reactor. After the operating characteristics of the hybrid reactor were studied, a 10 wt% solution of sodium borohydride was created and pumped through the packed bed to produce enough hydrogen for a 300 W fuel cell. The amount of heat produced from the packed bed portion of the reactor was significant, but temperatures levelled to around 80 °C. As expected, temperature control was directly proportional to the rate of hydrogen release from the metal hydride. On average, approximately 10% of the available heat energy was transferred to the metal hydride, and the hybrid reactor operated with gravimetric and volumetric energy densities of 0.27 kWh·kg-1 and 1.29 kWh·L-1 respectively. If the hybrid reactor is used solely to control peak temperatures, the amount of metal hydride necessary for thermal control could be decreased. Additionally, improvements in heat transfer as well as the hydrogen storage materials themselves would increase the energy density values further. When compared to other energy storage devices, the hybrid reactor without improvements is competitive as a backup power generator due to its silent operation and large volumetric energy density. Since the hybrid reactor can provide quiet and cool energy storage in a relatively small volume, it may become an effective and efficient means for hydrogen storage with limited improvements. / Thesis (Master, Mining Engineering) -- Queen's University, 2007-12-06 14:45:56.551 / AUTO21

No description available.

Advanced research in Controlled/Modified Atmosphere storage systems has shown that open channels of different lengths and cross sectional areas, connected to an air tight storage chamber, are able to maintain variable stable gas concentrations which could be near optimal concentrations for CA/MA storage of various commodities. / This study was geared towards assessing the suitability of the diffusion channels in maintaining a desired gas concentration for CA storage of spinach. Initially, the respiratory behaviour of spinach was studied in gas sealed chambers (replicated four times) stored at four different temperatures, 2$ sp circ$C, 8$ sp circ$C, 15$ sp circ$C and 23$ sp circ$C. The respiration rate of spinach was 20 mgCO$ sb2$/kg.h, 66 mgCO$ sb2$/kg.h, 163 mgCO$ sb2$/kg.h and 271 mgCO$ sb2$/kg.h for 2$ sp circ$C, 8$ sp circ$C, 15$ sp circ$C and 23$ sp circ$C, respectively. A model was developed based on principles of enzymatic kinetics which could reliably predict the respiration rate of spinach at any given storage temperature. / Two other sets of experiments were carried in a cold room set at 2$ sp circ$C. (Abstract shortened by UMI.)

The seed storage fungi (xerotolerant) species of the genera Aspergillus and Penicillium} are renowned for their devastating effects on stored grain and grain products. In view of the fact that most of these fungi Iiberate toxins which can be harmful to both man and his livestock this problem is becoming increasingly relevant, particularly in developing countries. The seed storage fungi are said to be saprophytes and opportunistic invaders of dead or naturally dried organic matter, and as such no direct host-pathogen relationship has been ascribed to them. This dissertation reports aspects of an investigation into the modes/pathways utilised by these fungi in their infection of maize caryopses (seeds) and plants. The work involved studies on: the effects of protracted storage on maize seeds; the morphology of storage fungi; extra-cellular enzymes of storage fungi; the pathways utiIised by the storage fungi in invasion of seed tissues; and the effects of the storage fungi on the seeds. Correlations have been made on a species basis between the extent of seed deterioration and fungal aggressiveness. The results of these investigations indicated that apart from affecting seed vigour and viability, these fungi can also affect plant vigour. This latter aspect was further investigated to determine whether a seed storage fungus could infect germinating maize seeds, and remain an internal contaminant of the tissues during plant growth and development. These latter studies revealed that Aspergillus flavus var. columnaris is capable of systemic transmission from one seed generation to the next. This hitherto unrecognised phenomenon apart from indicating that the fungal species is in fact a biotroph as well as a saprophyte, also has implications In control measures. / Thesis (Ph.D.)-University of Natal, Durban, 1990.

The seeds of Trichilia dregeana, Trichilia emetica, Podocarpus henkelii and Syzygium cuminii display the characteristics typical of recalcitrant seeds. It is the phenomena of ongoing metabolic activity and desiccation sensitivity that render them unsuitable for storage by the conventional methods used for orthodox seeds. Investigations on the storage responses of 'sub-imbibed' (partially dried) and fully hydrated seeds of all four species were carried out to study the effects of partial drying on viability and subsequent storage lifespan; i.e. to assess whether 'sub-imbibed' storage is feasible for these species. The outcome of this investigation was proposed to contribute to the resolution of the argument that storing recalcitrant seeds at lowered water contents might extend their longevity; i.e. storage at a relatively high water content but below the fully hydrated level, might prevent germination but would not be sufficient to be injurious to the seed. Seeds of T. dregeana, T. emetica, P. henkelii and S. cuminii were dried to various target moisture contents (which were determined for each species in the initial drying experiment) and then subjected to storage for 3-22 weeks at 6, 16 and 25°C (in sealed containers). In parallel, seeds of each species were stored at the shedding water content. The seeds were periodically removed for sampling, and assessed for water content, germination, respiration, electrolyte leakage and microscopical features. Storage temperature appeared to affect viability of seeds of T. emetica and T. dregeana which displayed characteristics of chilling sensitivity. Storage at 6°C was detrimental (when compared with seeds stored under the same conditions at 16 and 25°C), but regardless of whether the seeds were undried or partially dried prior to storage. The seeds of P. henkelii did not demonstrate chilling sensitivity, the viability not being compromised at 6°C compared with those seeds stored at 16 and 25°C. Syzygium cuminii seeds were not subject to storage at 6°C because previous work indicated that they would be chilling-sensitive. Storage of 'sub-imbibed' seeds of T. dregeana, T. emetica, P. henkelii and Syzygium cuminii does not to confer any benefit over seeds stored in the fully hydrated state; rather it appears to be deleterious to seed survival during storage. This was apparent from the assessment of viability, electrolyte leakage and respiration. Vigour and viability of the 'sub-imbibed' seeds of all species declined more rapidly than the fully hydrated seeds. The only exception was P. henkelii seeds stored at 25°C, the fully hydrated seeds showed no survival after 11 weeks in storage, while 88% of the 'sub-imbibed' seeds survived this period. These results were, however, attributed to the proliferation of fungi on the fully hydrated seeds at 25°C. Although ultrastructural observations were made only on the T. emetica seeds, it was apparent that the cells from the 'sub-imbibed' seeds (after storage at 16 and 25°C) showed extensive degradation, with the intra-cellular components being largely unrecognisable. The cells from the seeds stored in the fully hydrated condition at 16 and 25°C maintained integrity and appeared metabolically active. In keeping with the suggestion that T. emetica seeds are chilling sensitive, the ultrastructure of the cells from both the 'sub-imbibed' and fully hydrated seeds showed deteriorative changes. All the results of the present study indicated that storage in the 'sub-imbibed' state is deleterious to seed survival. It is apparent that the removal of water, however small a proportion, accelerates seed deterioration during storage. Thus 'sub-imbibed' storage has no practical application for the storage of recalcitrant seeds. / Thesis (M.Sc)-University of KwaZulu-Natal, 2007.

Farber disease is a fatal inherited disorder of lipid metabolism. It is characterized by a deficiency of the lysosomal enzyme acid ceramidase (AC), resulting in the buildup of the bio-effector molecule ceramide. A previous attempt to generate a Farber mouse model by Asah1 knockout was unsuccessful owing to embryonic lethality in homozygous embryos. Here, we successfully generated viable homozygotes that developed Farber disease by introducing a single-nucleotide human patient mutation into a conserved region of murine Asah1 (P361R). Indeed, homozygotes manifested Farber disease symptoms and died within 7-13 weeks. Furthermore, treatment of neonatal pups with intravenous injections of AC lentiviral vectors (LVs) yielded homozygotes with intermediate Farber phenotypes highlighted by reduced symptoms and increased longevity. Therefore, this first model of Farber disease can facilitate the advancement of experimental therapies and offer mechanistic insights into the integral roles of acid ceramidase, ceramide, and related sphingolipids in cell signaling, growth, and oncogenesis.

Farber disease is a fatal inherited disorder of lipid metabolism. It is characterized by a deficiency of the lysosomal enzyme acid ceramidase (AC), resulting in the buildup of the bio-effector molecule ceramide. A previous attempt to generate a Farber mouse model by Asah1 knockout was unsuccessful owing to embryonic lethality in homozygous embryos. Here, we successfully generated viable homozygotes that developed Farber disease by introducing a single-nucleotide human patient mutation into a conserved region of murine Asah1 (P361R). Indeed, homozygotes manifested Farber disease symptoms and died within 7-13 weeks. Furthermore, treatment of neonatal pups with intravenous injections of AC lentiviral vectors (LVs) yielded homozygotes with intermediate Farber phenotypes highlighted by reduced symptoms and increased longevity. Therefore, this first model of Farber disease can facilitate the advancement of experimental therapies and offer mechanistic insights into the integral roles of acid ceramidase, ceramide, and related sphingolipids in cell signaling, growth, and oncogenesis.

No description available.