Electromagnetic shock tubes were used to generate plasmas having a number density of the order of 10¹⁷ per cm³ and an energy per particle of 1-3 ev. In the shock tubes employed, the driving current was passed via electrodes through a discharge at one end of the tube. The discharge gases that were driven down the shock tube plus the ambient gas that was picked up and heated constituted the plasma that was studied. Many workers have assumed that shock equations can describe the discontinuity at the front of the plasma. An investigation into the effects of changes in the geometry of the driver mechanism has disclosed that the luminosity structure that can be attributed to the discharge gases stays very close to the luminosity front. The amount of ambient gas that is entrained in front of the discharge gases is thus small. Therefore, some doubt exists about the applicability of the shock equations both in the present shock tube and in the electromagnetic shock tubes of other workers. The shape of the luminosity front of the plasma was found to be affected by the properties of the driving discharge, even at a time long after the driving current had ceased to flow. Instabilities of the discharge and contamination by electrode material were found to drastically affect the homogeneity of the plasma. The homogeneity and reproducibility of the plasma produced by a small-cathode driver were found to be fairly good. However, there was a large amount of contamination in the plasma. The plasma was used to investigate the electro-dynamic response of an inductive magnetohydrodynamic power generator. Expressions for the output power were derived and compared with the experimental results. The electrodynamical response of a novel electrode-type Bɵ magnetohydrodynamic power generator was calculated. In an experiment performed with this generator a magnetohydrodynamic Interaction was observed indicating that the plasma was transporting an azimuthal magnetic field. No output power was obtained. The probable cause for this was that the applied magnetic field was insufficient to break down the sheath on the electrodes. A low pressure spark gap switch suitable for use as a main switch and as a "crowbar" switch on a capacitor bank was developed. The switch was operated over a voltage range of 0.5 to 25 kV, at energies up to 4 kJ and currents up to 500 kA. Under normal operating conditions the triggering time was 40 nsec and the jitter approximately 10 nsec. The inductance of the main switch was 4 nH and the inductance of the crowbar switch was about 1 nH. Other contributions are presented on a wide-voltage-range open-air spark gap switch, high voltage trigger circuits and on the dynamics of the plasma in an electromagnetic shock tube. The latter consists of an elementary treatment of the electromagnetic acceleration processes and a proposal of a model for the decelerating plasma. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Memoria para optar al Título Profesional de Ingeniero en Recursos Naturales Renovables / La actividad agrícola es una importante fuente de emisión y captura de gases de efecto invernadero a la atmósfera, existiendo una alta variación de emisiones en función de los factores ambientales, del tipo de manejo del suelo e insumos agrícolas utilizados. En la actualidad existen escasos estudios a nivel local sobre emisiones agrícolas que diferencien sistemas de manejo. El propósito del presente estudio fue comparar la emisión entre dos cultivos locales de cero labranza (CL) y labranza convencional (LC). Se estimó el potencial de calentamiento global, expresado como emisión en equivalentes de CO2 en sistemas de manejo del suelo de cero labranza y convencional, en una rotación trigo – maíz sin quema de residuos, en un suelo de la serie Santiago en la zona Central de Chile. Se incluyó en este análisis desde la producción de insumos hasta la cosecha. Se estudiaron los registros de carbono orgánico del suelo (0 a 15 cm), rendimiento y biomasa de trigo y maíz, fertilizantes y maquinaria utilizada durante siete años de ensayo en la Estación Experimental Antumapu de la Universidad de Chile. La comparación entre los sistemas agrícolas analizados, indica que en CL se produce una menor emisión de gases de efecto invernadero que en LC. En CL se produce una emisión de 2.556 kg ha-1 año-1 en equivalentes de CO2 y en LC de 5.282 kg ha-1 año-1. La emisión por unidad de producto (kg eq-CO2 kg-1 grano) es de 0,26 y 0,51 en CL y LC respectivamente. La captación de CO2 del suelo registrada en CL es de 1.270 kg ha-1 año-1, mientras en LC se produce una emisión directa del suelo de 1.030 kg CO2 ha-1 año-1 teniendo una alta incidencia en la emisión del sistema. El uso de fertilizantes nitrogenados tuvo una alta incidencia en la emisión de ambos sistemas agrícolas, tanto en sus emisiones de N2O como en su fabricación.

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Evidence has shown that changes in land-use can affect the potential of the soil to act as a methane sink. The Lakenheath site consists of drained fenland peat, which is being re-converted to wetland. At the time of this study the site consisted of four land-use types, an intensively cultivated plot, unmanaged grassland, woodland, and wetland. Peat cores were taken from the four plots and compared for their ability to act as a methane sink. CH4 uptake was measured throughout the depth profiles using gas chromatography. Clear differences in methane oxidation rates were recorded with depth and land-use. The woodland soil showed the highest capacity for atmospheric methane oxidation, and the wetland soil was only profile that had a distinct peak of methane oxidation activity (just above the water table). Despite the change in land-use, all four soils had the capacity to oxidise both high and low concentrations of methane and so acted as a methane sink. The only exception to this was the wetland soil after persistent rainfall. The uppermost layers were water saturated and all soil sections failed to oxidise methane. Methanotroph diversity in the four soils was compared using molecular biological and enrichment techniques. Total DNA was extracted from depth profiles of the four soils and PCR amplified with 16S rRNA methanotroph group-specific primers and primers specific to subunits of the pMMO and AMO (pmoA and amoA), sMMO (mmoX) and MDH (methanol dehydrogenase, mxaF). In addition, DNA was extracted from the top 5 cm of the cultivated (drained) and flooded soil and PCR amplified with primers specific to subunits of the pMMO and AMO. These PCR products were cloned and gene libraries constructed for each soil. No significant differences were observed in retrieved methanotroph sequences from these two soils, suggesting that the methanotroph population had not altered after flooding. The sequences obtained in the molecular study were predominantly amoA sequences from nitrifiers and pmoA sequences from type II methanotrophs. No type I pmoA sequences were retrieved. Type I methanotrophs, however, were isolated directly from the peat soil in the enrichment study.

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