M.W.P. Strandberg. / "September 25, 1948." / Includes bibliographical footnotes. / Army Signal Corps Contract No. W-36-039-sc-32037 Project No. 102B. Dept. of the Army Project No. 3-99-10-022.

The trapping behavior of deuterium and helium in polycrystalline tungsten (PCW) under D+-only, He+-only, sequential and simultaneous irradiation was studied as a function of incident ion fluences and irradiation temperature. Deuterium implanted at 300 and 500 K gets trapped at surface adsorption sites, vacancy-related traps, or extended defects. No deuterium was trapped for 700 K implantations. Results were affected by tungsten-carbide impurities in PCW specimens. It is suggested that He trapping occurs via the formation of He clusters, at impurity sites, or as part of He-vacancy complexes. For sequential implantations, D and He were found to de-trap each other, with He impeding the trapping of D when implanted first at 300 K. Under simultaneous irradiation a decrease in D inventories was observed for all cases, and a re-distribution of He to higher energy traps (associated with He-vacancy complex formation) was observed for higher fluences and temperatures.

The trapping behavior of deuterium and helium in polycrystalline tungsten (PCW) under D+-only, He+-only, sequential and simultaneous irradiation was studied as a function of incident ion fluences and irradiation temperature. Deuterium implanted at 300 and 500 K gets trapped at surface adsorption sites, vacancy-related traps, or extended defects. No deuterium was trapped for 700 K implantations. Results were affected by tungsten-carbide impurities in PCW specimens. It is suggested that He trapping occurs via the formation of He clusters, at impurity sites, or as part of He-vacancy complexes. For sequential implantations, D and He were found to de-trap each other, with He impeding the trapping of D when implanted first at 300 K. Under simultaneous irradiation a decrease in D inventories was observed for all cases, and a re-distribution of He to higher energy traps (associated with He-vacancy complex formation) was observed for higher fluences and temperatures.

The use of the stable isotopes, 18O and 2H, has proven to be a valuable tool in determining the importance of various hydrological controls on the modern water balances of Slave River Delta lakes, NWT, Canada. Samples collected during the 2002 and 2003 field season have shown that delta lakes exhibit highly systematic isotopic variability over the entire delta. The major influences observed to be affecting Slave River Delta lakes include spring snowmelt runoff, flood events from the Slave River, seiche events from Great Slave Lake and thaw season precipitation events. An important component of Slave River Delta lake modern water balances is evaporation, the main controlling factor of water loss in the study lakes, as well as isotopic variability experienced throughout the entire delta during the ice-off season. Flood events from Great Slave Lake and the Slave River play a key role in controlling modern water balances and isotopic compositions of lakes in the delta. Levee height throughout the delta seems to strongly affect local hydrology, with areas having the greatest levee heights also having the most enriched lake water compositions, and areas having the lowest levee heights having the most depleted isotopic signatures. Outer delta and mid-delta lakes experience the greatest amount of flooding during the spring. Lakes that are affected by spring flood events have a more depleted isotopic signature than those lakes in the upper delta. Discrepancies between δ18O- and δ2H-derived E/I ratios have been effectively reconciled by incorporating site-specific information into the mass balance equations, and allowing mixing between Great Slave Lake (GSL) vapour δE, a large body of water adjacent to the delta and advected atmospheric vapour δA. The use of locally derived parameters also ensures a more accurate depiction of local conditions. Good correlation can be observed during July 2003, between mixing of GSL vapour and atmospheric moisture, when the lakes water balances were solely affected by evaporation. The mixing ratios obtained from two of the study lakes suggest that 5 – 16% of ambient atmospheric moisture was derived from Great Slave Lake.

The use of the stable isotopes, 18O and 2H, has proven to be a valuable tool in determining the importance of various hydrological controls on the modern water balances of Slave River Delta lakes, NWT, Canada. Samples collected during the 2002 and 2003 field season have shown that delta lakes exhibit highly systematic isotopic variability over the entire delta. The major influences observed to be affecting Slave River Delta lakes include spring snowmelt runoff, flood events from the Slave River, seiche events from Great Slave Lake and thaw season precipitation events. An important component of Slave River Delta lake modern water balances is evaporation, the main controlling factor of water loss in the study lakes, as well as isotopic variability experienced throughout the entire delta during the ice-off season. Flood events from Great Slave Lake and the Slave River play a key role in controlling modern water balances and isotopic compositions of lakes in the delta. Levee height throughout the delta seems to strongly affect local hydrology, with areas having the greatest levee heights also having the most enriched lake water compositions, and areas having the lowest levee heights having the most depleted isotopic signatures. Outer delta and mid-delta lakes experience the greatest amount of flooding during the spring. Lakes that are affected by spring flood events have a more depleted isotopic signature than those lakes in the upper delta. Discrepancies between δ18O- and δ2H-derived E/I ratios have been effectively reconciled by incorporating site-specific information into the mass balance equations, and allowing mixing between Great Slave Lake (GSL) vapour δE, a large body of water adjacent to the delta and advected atmospheric vapour δA. The use of locally derived parameters also ensures a more accurate depiction of local conditions. Good correlation can be observed during July 2003, between mixing of GSL vapour and atmospheric moisture, when the lakes water balances were solely affected by evaporation. The mixing ratios obtained from two of the study lakes suggest that 5 – 16% of ambient atmospheric moisture was derived from Great Slave Lake.

In dieser Arbeit wird beschrieben, wie sich die in situ-IR-Spektroskopie zur Charakterisierung von CVD-Prozessen einsetzen läßt. Es werden Modellreaktoren vorgestellt, deren Konstruktion an die spektroskopische Verfolgung thermisch aktivierter Gasphasenreaktionen angepaßt ist. Ausgehend von Referenzmessungen, mit deren Hilfe Möglichkeiten und Grenzen der FT-IR-Spektroskopie in Bezug auf die CVD-Prozeßanalytik aufgezeigt werden, können auftretende Species im untersuchten System sicher bestimmt werden. Im Mittelpunkt der Arbeit steht die Untersuchung der Gasphase bei der Thermolyse von Methyltrichlorsilan in Abhängigkeit von den Prozeßparametern Temperatur und Eduktgaszusammensetzung. Die gefundenen Korrelationen werden durch Thermolysen einzelner, nachgewiesener Verbindungen bestätigt. Eine weitere Absicherung der Ergebnisse erfolgt durch Isotopenmarkierung mit Deuterium. Untersuchungen zur Schichtbildung ergänzen die Gasphasenanalytik. Auf Grundlage der nachgewiesenen stabilen und instabilen Species und deren Abhängigkeit von den Prozeßparametern wird ein Mechanismus vorgeschlagen und diskutiert, der die Thermolyse von Methyltrichlorsilan zur Abscheidung von Siliciumcarbid vollständig beschreibt.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--University of Michigan, 1935. / Cover title. By Paul F. Bartunek and E.F. Barker. "Reprinted from the Physical review, vol. 48, no. 6, September 15, 1935."

Not available / text

Three aspects of the Habitability of the Northern Plains of Mars to organics and terrestrial-like microbial life were assessed. (1) Protection offered by small surface features and (2) the breakdown of rocks to form soils were examined using a radiative transfer computer model. Two separate sublimation experiments provided a basis to improve (3) estimates of the amount of available water today and in the past by determining the fractionation of HDO between present-day reservoirs.(1) UV radiation sterilizes the hardiest of terrestrial organisms within minutes on the Martian surface. Small surface features including pits, trenches, flat faces and overhangs may create "safe havens" for organisms by blocking much of the UV flux. In the most favorable cases, this flux is sufficiently reduced such that organic in-fall could accumulate beneath overhanging surfaces and in pits and cracks while terrestrial microorganisms could persist for several tens of martian years.(2) The production of soils on the surface is considered by analogy with the arid US Southwest. Here differential insolation of incipient cracks of random orientations predicts crack orientation distributions consistent with field observations by assuming that only crack orientations which shield their interiors, minimizing their water loss, can grow, eventually disrupting the clast.(3) Disaggregated water ice to simulate the polar caps was produced by flash freezing in liquid nitrogen and crushing. When dust was added to the mixtures, the D/H ratio of the sublimate gas was seen to decrease with time from the bulk ratio. The more dust was added to the mixture, the more pronounced was this effect. The largest fractionation factor observed during these experiments was 2.5. Clean ice was also prepared and overlain by dust to simulate ground ice. Here, the movement of water vapor was modeled using an effective diffusivity that incorporated both adsorption on grains and diffusion. For low temperatures (<-55°C) a significant difference between the diffusivities of H2O and HDO was observed. This suggests adsorptive-control within the regolith as energies of interaction are 60-70kJmol-1. This ability of the martian regolith to preferentially adsorb HDO decouples the ice table and polar caps from the atmosphere and allows for geographic variations in the D/H ratio on Mars.