Cyclopontadienylides (e.g, (III)) were prepared from dibromocyclopentene (l) b the action of cyclic organic bases followed by treatment with caustic alkali. The intermediate was shown to be the dibromide of the diquaternary salt (e.g. (II)), and the reaction scheme may be represented, in the case of pyridine, by the equations: (See full file abstract for equation) These ylides are brown-red crystalline solids, which impart strong colours to their solutions. The colour varied with polarity of the solvent, e.g. from orange-red in alcohol to a slightly purplish-red in benzene. The reactions of various organic bases with dibromocyclopentene were investigated but satisfactory products were obtained only from pyridine and substituted pyridines. However, rod materials of uncertain composition were obtained from aniline and ammonia. Also a compound from dimethyl sulphide was obtained, probably having the structure (IV) although satisfactory analysis results were not obtained in this case. (See full file Abstract for equation) The structure of the ylide from pyridine was established by catalytic hydrogenation to N-cyclopontylpiperidine and comparison of derivatives obtained therefrom with those from an authentic sample. Tetraphenylcyclopentaoienylides were prepared from 1-brom-2:3:5-tetraphenylcyclopentadiene by allowing this bromo compound to stand with the bases at room temperature, and removing the elements of hydrogen bromide with sodium hydroxide. Ylides formed in this way were blue to blueish- purple crystalline solids, showing a corresponding range of colour in organic solvents. The unphenylated ylides decomposed fairly rapidly on exposure to the air in the solid state, but more slowly in solution. The phenylated derivatives were quite stable as solids, but the colour of their solution faded quickly, Stability was enhanced in each case by storing the samples under nitrogen or in vacuo. Derivatives were generally difficult to isolate, but compounds were obtained with picric acid (from phenylated ylides) and benzene diazonium chloride (from unphenylated ylides, including that from dimethyl sulphide), a preliminary investigation was also made into the possibility of preparing many membered carbon rings by pinacone reduction of a-w-diketones. a-w-heptadecane dicarboxyclic acid was prepared as an intermediate.

No description available.

The subject matter of this thesis is concerned with the stability of fluid flows; more particularly , with the stability of liquid films which have an interface with air. We will therefore begin by formulating the basic equations and ideas which pertain to this class of problems. Later in this chapter, a summary will be given of the topics dealt with in this dissertation.

The retrieval of information from explicit memory has been associated with three temporally and topographically dissociable ERP correlates, an early bilateral and late right frontal component as well as a left parietal effect. The three studies in this thesis investigated that material-specificity of these ERP old/new effects to address the question whether the ERP correlates of memory retrieval vary according to the nature of the information that is retrieved. The studies compared the ERP correlates for retrieval of pictures and words, when presented in the same modality at study and test and when presented across modalities (i.e., words at study - pictures at test or vice versa) in the two phases. Results provided little evidence for the engagement of different neural generators for the retrieval of the different types of stimuli. The topographic differences that emerged, suggested the engagement of a common set of generators activated at different levels and with a different time-course, depending on the type of encoding stimulus and retrieval cue. However, the results did provide further evidence regarding the functional interpretations of the established old/new effects. All experimental conditions revealed a left parietal effect which was largest when the encoding stimuli were presented in pictorial form. Given that the rich perceptual information inherent in pictures leads to a greater incidence of episodic retrieval for pictures (picture superiority effect) the current finding provides further support for the functional interpretation of this effect as the neural correlate of recollection. All experimental conditions also revealed a late right frontal effect which showed no differences in magnitude or topography between the different conditions. This insensitivity to the type of encoded material and the type of retrieval cue supports the interpretation of the effect as the neural correlate of post-retrieval monitoring processes. New functional properties of the early bilateral frontal effect emerged. The effect was only present when stimuli were presented in the same modality at study and test. Thus, the effect appears to be highly sensitive to the perceptual similarity of an item between study and test, which suggests a functional correlation to perceptual data-driven processes, proposed to be one of the bases of familiarity-driven recognition.

No description available.

The magnetic field greatly influences the plasma in the solar atmosphere and in this thesis we consider the effect of the field on the stability of the plasma. The many observations that have been made suggest that two types of field structure play a major role. Firstly a current sheet - this has field lines which change direction in a thin, current forming region, but are fairly uniform outside. We consider the case where the field strength is zero along the neutral line so that a gas pressure gradient is required across the sheet to balance the magnetic pressure gradient. Secondly a force-free field - here the magnetic force is zero, which requires the magnetic pressure to be much larger than the gas pressure. In the neutral current sheet we examine the thermal instability and the tearing-mode instability. While in the force-free magnetic arch system we look for a thermal instability which can occur when the foot points of the arch are sheared. When we investigated the thermal stability of the current sheet we found that as its length increases it passes through a series of stable equilibria until a value, L[sub]max, is reached when the sheet cools down to a max new stable equilibrium. For coronal conditions, values for L[sub]max and max cooling time are in fair agreement with the observed values for quiescent prominences. We calculate the growth rate of the tearing-mode instability in a neutral current sheet with no energy sources or sinks and find that the maximum growth rate can be significantly larger in the current sheet than in the sheared field of constant magnitude considered by others. Also the growth rate decreases when the ratio of gas to magnetic pressure is reduced. We find that the growth rate is significantly inhibited if the current sheet has a transverse magnetic field which is large enough. Lastly we examine the thermal balance in a sheared, force-free magnetic field and show that thermal instability can occur if the field is sheared enough. We assume thermal equilibrium between radiative loss and thermal conduction and we take gravity balanced by a pressure gradient. If, for example, the density at the base of the field is ten times larger than the normal coronal value, as it may be in coronal condensations, then there is instability if the shear angle is greater than 63 °. The presence of a large enough mechanical heating is found to prevent the instability occurring.

Automated Guided Vehicle Systems (AGVSs) have been widely adopted by many low to medium manufacturing operations, particularly in Flexible Manufacturing Systems (FMS). The high degree of flexibility and control offered in vehicle routing has made AGVS a proven and viable material handling technology in today's manufacturing systems [Bozer91]. An important aspect in maintaining flexibility in an AGVS is its control architecture. A control architecture provides the backbone of the physical and the informational infrastructure of a system. This research has identified three types of control architectures. They are the centralized, hierarchical, and heterarchical control architectures. When designing an AGVS, most designers do not consider control architecture as a design factor, and do not analyze its effect on the system's performance. The objective of this research is to analyze the effect of control architectures on the relative performance of the AGVS. This research uses simulation to study the effect of control architectures on the AGVS. The simulation model for each control architecture contains two parts -- an AGV controller and a shop floor controller. Both models are programmed in C language. The AGV controller consists of three basic components – vehicle scheduling, vehicle routing, and traffic control. Each of these three components is modeled according to the nature and characteristics of the corresponding control architecture. Two different flow path layouts are considered for the shop floor model. The two layouts are different in size and number of work stations. Performance measures chosen for this study are intended to reflect the responsiveness of the system and the overall system performance under the impact of different control architectures. / Master of Science

No description available.

This thesis investigates physiological mechanisms underlying temperature adaptations in perennial grasses. A comparative approach was employed by using pairs of species that have been collected from lowland sites in thermally contrasting habitats up to 2000 km apart on a north-south direction. The population samples from northern latitudes, i.e. from cooler climates, had higher growth rates at 12°C than southern provenances. Dark respiration rates between 5 and 25°C did not differ between provenances; but acclimatization at 10°C increased the respiration rate in all northern population samples, whereas some southern population samples reduced their respiration rate as a response to acclimatization at 10°C. Northern provenances showed a greater activity of carbohydrate formation in light after periods of 48 hours starvation in darkness. This property could be attributed to the higher activity of RuBP-carboxylase in northern genotypes. No evidence was found that the higher activities are due to higher enzyme concentrations in these genotypes. The enzyme exhibited lower energies of activation in northern provenances in the range 5 - 15°C Activation energies for succinate dehydrogenase in isolated mitochondria were higher for northern population samples in the range 10 - 25°C. Higher specific activities were found for malate dehydrogenase from northern plants between 5 and 25°C. In this temperature range the apparent energies of activation were lower for northern plants. The enzyme displayed positive thermal modulation in both northern and southern provenances. Temperature changes had generally a greater effect on northern provenances. The significance of these findings is discussed in the light of previous reports in the literature and in relation to a possible advantage in the plant's native habitat.

Factors affecting the survival of over-wintering tree roots during waterlogging were investigated. Die-back of roots covered by high Winter water tables results in shallow rooted trees susceptible to wind-throw. Such is the scale of the problem in Britain, this research is considered to be of practical relevance. Sitka spruce (Picea sitchensis (Bong.) Carr.) and Lodgepole pine (Pinus contorta Douglas ex Loudon) were chosen, being the most predominant species planted and showing differing susceptibility to flooding. Sitka spruce is considered flood-intolerant (Crawford 1982) and Lodgepole pine highly-tolerant (Minore 1968). In both species, waterlogging the whole root system for 3 months severely reduced the carbohydrate content of the distal 15cm root, reflecting almost total depletion of starch reserve and varying degrees of glucose depletion. In Sitka spruce, depletion depended on the date of flood-initiation, being most severe after flooding from October when root respiration rate was higher, rather than November as the roots became dormant. Flooding injury was reflected in decreased tri-phenyl tetrazolium chloride reduction and loss of respiratory capacity. Greater loss of aerobic (as compared to anaerobic) respiration capacity after flooding suggested damage to the aerobic pathway, either directly through anoxia or indirectly due to depletion of sugars important in cell maintenance. Injury appeared to be greater when respiratory activity at flood-initiation was high. Aeration from stem lenticels ameliorated flood-injury and carbohydrate depletion in Lodgepole pine, although the roots appeared to have no metabolic adaptation to anoxia. Increased soil temperature during Winter flooding increased carbohydrate depletion in the distal root and reduced viability relative to seedlings flooded at ambient temperature. Carbohydrate depletion during cold storage and its effect on survival of soil waterlogging at out-planting was determined in Sitka spruce. Cold storage leads to increased root growth and slightly superior flood-tolerance when compared to nursery over-wintered seedlings, presumably due to the more dormant state of stored seedlings.