No description available.

No description available.

No description available.

This paper presents the construction and evaluation of a DC to AC inverter with IGBT:s and the basic PCD-layout for the single IGBT drivers. The main work consisted of constructing a PCB-card for controlling a number of IGBT:s, simulate its properties and test driving it. The schematic of the card is an extension of the recommended use of the optocoupler HCPL316J with a few modulations made for the special demands on the Division of Electricity at Uppsala University. Even though, some basic changes were made in the schematic in this work, the main changes concerned choice of components due to economy and space and did not change the electrical properties of the card notably. Except several electrical properties that will be the main focus in this paper, size and price are two things that also have been taken under consideration during the work. In the paper, many parts and components will be described to fully explain the function of the cards properties. This is for future reference and documentation and was one of the goals of the project.

The behaviour of limited subassemblages with flexible beans and semi-rigid beam to column connections was studied using a computer program in which the finite element method was employed in a non-linear analysis which accounts for the presence of semi-rigid connections and the inelastic behaviour of frames. The program accounts for many other factors such as initial imperfections and residual stresses. The theoretical background to the present computer program has been presented along with the program layout. The program was used to simulate some of the experimental results obtained from tests on rigidly and flexibly connected frames with different combinations of beam and column loads. The analytical results were found to compare reasonably well with the experimental results. The program was also used to simulate a series of I-shaped subassemblages that were tested at the University of Sheffield. Comparisons were made between the analytical and experimental results characterized by the maximum loads, load-deflection curves and load- moment curves. Good agreement was obtained between the analytical and the experimental load-deflection curves for all of the cases considered. The general trends of the measured and calculated load- moment curves for most cases were found to be comparable. The recommendations given in B35950 for the design of columns in simple construction were applied to all cases in the last series and were found unconservative in the cases of balanced loading and conservative in the cases of unbalanced loads. A limited parametric study was conducted to study the effects of semi-rigid joints, bean flexibility and type of loading. In this study, an I-shaped subassemblage was analysed for different load types and different types of beam to column connections. A substantial effect was recognized due to the presence of semi-rigid connections whether or not a beam load was applied. Beam flexibility was also seen to affect the carrying capacity of the subassemblage under the action of column load only although this effect was less noticeable than that of the connection flexibility. The presence of beam load was found to result in an unexpected interaction curve which relates the total force in the column to the moment that is transmitted to the column's end. An almost linear relationship with negative gradient seems to exist between the column and beam loads. It is pointed out that all the findings of the present study are based on the range of cases considered in the parametric study but it is suggested that they serve as indicators to the behaviour of any the subassemblage under axial load oniy or axial load combined with beam loads. A few recommendations for future work are presented.

Particulate adsorption by Mucor flavus and Neurospora crassa is a physical property of the cell wall, independent of both cellular metabolism and the production of extracellular polymers. Initial attractive forces responsible for particulate adsorption by N. crassa are mainly electrostatic in nature and this mechanism probably holds for M. flavus also. The outer glucan layer of the cell wall of N. crassa, although able to adsorb particulates, was not as efficient as the underlying protein layer at particle adsorption. Young, growing mycelium generally adsorbs the , -, largest amount of particles, due to the continued production of adsorption sites and the entrapment of particulates by hyphae. Factors increasing adsorption include nutrient starvation of mycelium and incubation with low concentrations of magnesium ions. Relatively high concentrations of mercury and copper ions decrease adsorption perhaps due to the precipitation and adsorption of the corresponding metal sulphides on the mycelial surface thereby effectively physically interfering with further particulate adsorption. Optimum conditions for adsorption are a temperature of 250C and a slightly acid pH value. Also, small particles are more readily adsorbed than large particles. Mucor flavus can adsorb clays and this ability may be used to treat industrial effluents which contain large amounts of clay minerals. An acid pH and a temperature of 250C are optimum conditions for clay adsorption by the fungus. Low concentrations of montmorillonite and kaolinite increase biomass production by Aspergillus niger in submerged culture, due to the inhibition of pellet formation by the fungus. The clays cause A. niger to grow in a more filamentous form and presumably would affect other fungi in a similar way. The use of clays to control fungal morphology may be important in several industrial fermentations. Low concentrations of the fungicide thiram stimulated the growth of Aspergillus niger in the presence of montmorillonite. Immobilization of fungi by magnetic means is possible due to their ability to adsorb magnetite. This method could also be used to remove fungi from fermentation media as an alternative to filtration or centrifugation. Even though older hyphae of Penicillium chrysogenum are unable to adsorb magnetite, this fungus can still be magnetically immobilized if it is grown from a spore suspension in the presence of magnetite. Either the spores or young hyphae of this fungus adsorb magnetite, producing pellets with magnetic properties. Magnetite adsorption occurs optimally at a temperature of 250C and is constant over a wide range of pH values. Waste mycelium of A. niger from the surface fermentation method of citric acid production can be magnetically removed from solution after adsorbing magnetite. Dilute solutions of sodium hydroxide and sodium bicarbonate desorbed magnetite attached to mycelial surfaces. Silver is accumulated selectively by A. niger waste mycelium produced by the surface fermentation method of citric acid production. The process is rapid, maximum uptake occurring twenty minutes after initial exposure of the mycelium to a silver solution. Silver accumulation by the mycelium is relatively insensitive to changes in pH and temperature, a slight decrease in uptake only occurring at a temperature of 800C. Dilute solutions of H2S04 and HNO3 desorb silver from the mycelial surface. However, this process is relatively inefficient and more effective desorbents need to be found to make the silver accumulation process economically viable.

The effect of natural herbivory on the secondary metabolism of Myrica gale was investigated. In a field experiment herbivory was found to elicit changes in both the leaf phenolics and the density of volatile oil glands. Lygocoris spinolai, a capsid bug, accounted for most of the observed herbivory. One set of plants (the controls) were kept free of insect herbivores while a second set sustained capsid bug herbivory. The terpenoid and phenolic profile of leaves from each set was obtained on a weekly basis using GLC and IIPLC respectively. GC-MS was used to identify constituents of the volatile oil. UV, ¹H and ¹³C NMR, El-MS and FAB-tlS were used to identify the phenolics. Capsid bug damage induced a cpialitative change in the phenolic content of the leaves. This induction revealed a new compound, kaempferol-3-(2,3-diacetoxy-4-p-coumaroyl)rhamnoside, which was isolated and identified. The leaves also proved to contain other flavonoids, the concentrations of which were not affected by herbivory. Artificial damage was observed to elicit a quantitative change in leaf phenolics, thus having a different effect than herbivore damage. Herbivore damage also induced quantitative changes in the volatile oil by eliciting gland production whilst having no effect on the composition of the oil. The induced flavonoid and the volatile oil were tested for fungal growth inhibitory properties. Both were found to have marked antifungal activity at low concentrations when tested against fungal species isolated from the leaves of M. gale in the field. The observed phenomena are discussed in terms of defenses against herbivores and pathogens. The relationship between the nitrogen economy of M. gale and leaf chemistry is also discussed.

No description available.

No description available.

Hepatoma Tissue Culture (HTC) cells grown in the presence of 60µM arachidonic acid for 24, 36 and 48 hours became progressively more thermosensitive than control cells. However, this difference in thermal sensitivity was only detectable with the clonogenic assay and not with the colorimetric assay. Attempts were also made to manipulate cellular cholesterol levels. Firstly, some cells were incubated with phosphatidylcholine liposomes to deplete the plasma membrane of cholesterol: Secondly, another group of cells were treated with 25 hydroxycholesterol, an inhibitor of cholesterol synthesis, to lower cholesterol levels: Finally, a third group of cells were supplemented with cholesterol hemisuccinate, a hydrophilic ester of cholesterol. The first two approaches did not enhance the thermal sensitivity of HTC cells. Supplementation with cholesterol hemisuccinate, which was predicted to partition in to the plasma membrane and reduce membrane fluidity, resulted in increased thermal sensitivity of the cells. Thus, the thermal sensitivity of HTC cells could be enhanced by supplementation with either arachidonate or cholesterol hemisuccinate. A rapid plasma membrane isolation procedure was developed which generated plasma membranes in relatively high yield and purity. The plasma membrane- enriched fraction was also assayed for contaminating intracellular membranes by determining marker enzyme activities associated with these membranes. Using this method, plasma membranes were prepared from HTC cells grown m 60µM arachidonic acid for 36 hours and from cells grown in normal medium. Analysis of the plasma membrane showed that the arachidonic acid content of the phospholipid fatty acyl groups had been significantly increased in cells grown in the presence of this fatty acid. There was no change in the cholesterol/phospholipid molar ratio or cholesterol concentration relative to amount of protein in the plasma membranes from the two cell populations. The measurement of fluidity using DPH fluorescence polarisation revealed that the increase in the arachidomc acid content of the plasma membrane phospholipid acyl groups was associated with enhanced plasma membrane fluidity when compared to control plasma membranes. This increase in plasma membrane fluidity correlated with the enhanced thermal sensitivity of the cells grown in arachidonic acid-containing medium when compared to cells grown in normal medium. Furthermore, the thermal sensitivity of Na(^+), K(^+) –ATPase and alkaline phosphodiesterase I were assessed in plasma membranes derived from arachidonic acid-supplemented and control cells. The enhanced fluidity of plasma membranes derived from arachidonate-supplemented cells also correlated with increased thermosensitivity of alkaline phosphodiesterase I.