Novel optical fibre based laser sources for spectral and temporal versatility

As laser amplifiers and oscillators continue to see widespread use in all branches of science and engineering, they continue to develop in terms of operating parameters to keep pace with their applications. Importantly, the temporal and spectral characteristics of laser systems must be carefully tailored to match application requirements. This thesis reports advances in the development of laser systems, based upon optical fibre technology, which demonstrate the flexibility of optical fibre and fibre integrated devices to cover a wide range of temporal and spectral characteristics. First, the principle of spectrally masked phase modulation for short pulse generation is explored. Here, a phase modulator is used to generate a time dependent optical frequency shift, which can be turned into an effective amplitude modulation by the introduction of an optical band pass filter. This method is combined with nonlinear compression techniques based on solitonic propagation in optical fibre to generate optical pulses with duration of a few hundreds of femtoseconds and repetition rates of tens of gigahertz. Increasing the range of wavelengths over with doped fibre amplifier systems will operate requires the development of laser/amplifier systems based on new active dopants. To this end amplifier systems based upon bismuth activated alumosilicate fibre were evaluated. The amplifier stages were then incorporated into a master oscillator power fibre amplifier (MOPFA) scheme, demonstrating the applicability of bismuth doped silica fibre to advanced laser configurations. Finally, the development of a novel laser source for use in fluorescent microscopy is detailed. The source was based on a gain switched diode which is amplified in a two stage Raman fibre amplifier system, subsequently frequency doubled in a periodically poled lithium tantalate crystal. Nonlinearity and optical filtering are exploited to re-shape the output pulse's temporal profile.Open Acces

Why You Love Me Then As Now?

https://digitalcommons.library.umaine.edu/mmb-vp/2761/thumbnail.jp

Impossibilities proved by Galois theory

I studied three areas in my paper:1. The basic field theory needed to prove the impossibility of three goals of Ruler and Compass construction. Here I found the results flowed rather easily. I found that the level of material needed to prove these problems was, for the most part, not out of reach for any undergraduate mathematics student.2. I studied the step into Galois theory and the necessary material needed to prove the impossibility of solving the general Quintic with radicals. This was the biggest step. The jump from the basic field theory I studied in 1. to the Galois theory needed for 2. is extreme. I spent most of my time studying this material so that I may understand it well enough to present it.3. I studied the rational distance problem, specifically how its arguments are extremely similar to those of the problems in 1. and 2. I found that the main argument lies in drawing an equality between the geometry of the problem, and then using this relation to prove equivalent field extensions. This can only happen for some polygons, and that is the conclusion in the paper.More generally, I found that independent study, no matter how expository and non novel, in the area you're interested in is extremely fascinating. I was motivated and intrigued to continue studying well beyond the normal hours, and certainly this project has cemented in me the will to pursue a Ph.D in mathematics

Luring houseflies (Musca domestica Diptera: Muscidae) to traps: Do cuticular hydrocarbons and visual cues increase catch?

Houseflies (Musca domestica L.) are a major pest species of livestock units and landfill sites used for the disposal of domestic waste. Of the many methods used to limit housefly populations, the most common are chemical control and lure-and-kill trap systems. Insecticide resistance has seen increased emphasis on lure-and-kill, but the success of this method relies on effective attraction of houseflies using olfactory or visual stimuli. Here we examine the efficacy of olfactory (cuticular hydrocarbons) or visual (colours and groups of flies) attractants in a poultry unit. Despite simulating the cuticular hydrocarbon profiles of male and female houseflies, we found no significant increase in the number of individuals lured to traps, or any sex-specific responses. Similarly the use of target colours selected to match the three peaks in housefly visual spectral sensitivity yielded no improvement in catch rate. We also demonstrate that male and female flies have significantly different spectral reflectance (males are brighter between 320-470nm; females are brighter between 470-670nm). An experiment incorporating groups of recently killed flies from which cuticular hydrocarbons were either removed by solvent or left in-tact also failed to show any evidence of olfactory or visual attraction for houseflies of either sex. Thus variations on the most commonly applied methods of luring houseflies to traps in commercial livestock units failed to significantly increase capture rates. Our results support commonly observed inconsistencies associated with using olfactory or visual stimuli in lure-and-kill systems, possibly because field conditions lessen the attractant properties observed in laboratory experiments

The urinary metabolites of testosterone: An index of testicular function in children

The evaluation of testicular Leydig cell function is of considerable clinical value in the investigation of gonadal problems in childhood, and adolescence. Testicular function was assessed in the patients in this thesis by the estimation of the basal plasma testosterone concentration, the basal daily urinary excretion of testosterone and the individual androgen metabolites and the changes in these parameters to administered HOG. This method therefore not only gives an index of testosterone production but also allows investigation of actual testosterone utilization by the patient. Following the addition of [1,2,6,7-3H] testosterone for recovery purposes, aliquots of plasma were made alkaline by the addition of sodium hydroxide and the testosterone extracted with diethyl ether. Purification of the extracted residues was effected by partition and thin layer chromatography. The dried residues were dissolved in dichloromethane and esterified with heptafluorobutyric anhydride for 30 minutes at room temperature. Following subsequent purification by thin layer chromatography, quantitation of testosterone-17-heptafluorobutyrate was made by electron capture detection on a Pye 104 gas liquid chromatograph. A correction was made for the recovery rate of radioactively labelled testosterone added initially to plasma samples. A near total hydrolysis of urinary conjugates of testosterone was effected by incubation with beta-glucuronidase (750 F.u. per ml urine) at 3

Curvature suppresses the Rayleigh-Taylor instability

The dynamics of a thin liquid film on the underside of a curved cylindrical substrate is studied. The evolution of the liquid layer is investigated as the film thickness and the radius of curvature of the substrate are varied. A dimensionless parameter (a modified Bond number) that incorporates both geometric parameters, gravity, and surface tension is identified, and allows the observations to be classified according to three different flow regimes: stable films, films with transient growth of perturbations followed by decay, and unstable films. Experiments and theory confirm that, below a critical value of the Bond number, curvature of the substrate suppresses the Rayleigh-Taylor instability