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This dissertation is an exploration of the effects of the collision of large asteroids and comets on the atmosphere of the Earth and Earthlike planets. The first task undertaken is the characterization of the impact rates in the inner solar system during the present time, and during the first billion years of Solar System history when the flux was changing rapidly. Once defined, these fluxes are used to model the long term cumulative effect of multiple impacts on planetary atmospheres. The implications of cometary impacts on evolution of the water and deuterium abundances on Venus are examined. The short lifetime of water on Venus suggests that the water abundance is in a quasi-steady-state balance between loss by escape and replenishment by infall. In addition, the observed deuterium-to-hydrogen ratio on Venus is consistent with a steady state and does not necessarily imply a past water excess. Results are presented of a model incorporating a stochastic cometary source and nonthermal escape of hydrogen that produces the observed water abundance and D/H ratio. The stochastic variability of each of these quantities is shown to be large. Water on Venus is likely to be in a near steady state mediated by large comet impacts. The early history of water on the planet has been obscured by a history of random impacts. A study of the effects of impact-generated dust clouds on the primitive Earth leads to the conclusion that such clouds were significant perturbers of the early climate. The Earth was shrouded by an optically-thick dust cloud for ≈ 150-250 m.y. During this time the surface temperature was equal to the planetary equilibrium temperature unless significant heating by impacts or surface heat flow existed beneath the dust cloud. An admixture of a few per cent of organic materials in the cloud may have significantly lowered the planetary bond albedo, thereby raising the equilibrium temperature. The epoch of continuous dust shrouding was followed by a period of stochastically intermittent dust clouds occuring at greater intervals as the early intense bombardment subsided towards the present day flux.

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The noble gas abundances and isotopic ratios of the terrestrial planets differ from each other and from the average of chondritic meteorites. These different abundance patterns result from primordial heterogeneities or different degassing histories. Magmatic transport is the only degassing mechanism that can be demonstrated to occur on Venus, Earth, and Mars, and is presently the dominant form of volatile transport to a planet's free surface. An alternative technique was developed to determine the partitioning and solubility of noble gases in mineral/melt systems. Natural end member minerals and synthetic melts known to be in equilibrium were held in separate crucibles in a one bar flowing noble gas atmosphere. Experiments were run 7-18 days at 1300 or 1332°C, in 99.95% Ar or a Ne-Ar-Kr-Xe mix. Gas concentrations were measured by mass spectrometry. The solubility of noble gases in minerals was surprisingly high, and individual samples of a particular mineral composition are distinct in their behavior. The data is consistent with lattice vacancy defect siting. Noble gas solubility in the minerals increases with increasing atomic number; this may be related to polarizability. Noble gas solubilities in melts decrease with increasing atomic number. Solubility is directly proportional to melt molar volume; values overlap the lower end of the range defined for natural basalts. The lower solubilities are related to the higher MgO and CaO concentrations and lower degree of polymerization and Fe³⁺ concentration in synthetic vs. natural melts. Partition coefficient patterns show a clear trend of increasing compatibility with increasing noble gas atomic number, but many individual values are > 1. Calculations show that the terrestrial planet atmospheres cannot have formed from partial melting of a common chondritic source. When results are examined with isotopic constraints and MOR and hot-spot activities, there is no compelling evidence that the Earth is substantially outgassed of its primordial or even its radiogenic volatiles. If volcanic degassing was mostly responsible for the atmospheres, then initial volatile abundances were Mars < Earth < Venus. Alternatively, roughly equal abundances could have been modified by catastrophic processes.

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This thesis focuses on diffusion channel design for broccoli storage, an important cash crop and consumer commodity in Canada. Experiments were first conducted to determine the respiration rate of broccoli in modified atmosphere conditions created by the produce metabolic activity inside closed chambers, at four different temperatures in the cold room of 3, 7, 13, and 24$ sp circ$C. The respiration rate decreased with a reduction of O$ sb2$ concentration inside the chamber. A model to predict the respiration rate of broccoli as a function of O$ sb2$ concentration at different temperatures was developed. Experiments were then carried out to determine the cross sectional area and length of diffusion channel leading to various final O$ sb2$ (steady-state) concentrations during the storage of broccoli. Combinations of cross sectional area of 0.04, 0.18, and 1.15 cm$ sp2$ and length of 0.6, 3, 7, 12, 18, and 25 cm were tested. The carbon dioxide produced through respiratory process was absorbed by placing hydrated lime inside the chambers such that the two-component molecular diffusion model by Ratti et al. (1993) could be evaluated. The length and cross sectional area of diffusion channel have a significant effect on the final level of O$ sb2$ (steady-state) concentration. The Ratti model then served as a basis for a modified model for predicting the length of diffusion channel required to obtain a given O$ sb2$ concentration as a function of the mass of stored broccoli and the cross sectional area of the diffusion channel. (Abstract shortened by UMI.)

This Thesis is concerned with the physical nature of the outer atmospheres of the 'hybrid' bright giants. These stars show C IV emission and evidence of cool, fast winds - unlike giants of similar effective temperature, which possess only cool chromospheres. The K3 II star ι Aur is studied in detail. Chapter 1 discusses the importance of these stars in the context of the HR diagram. Chapter 2 examines the evolutionary status of the 'hybrid' bright giants and sets out the physical parameters which are adopted in the atmospheric modelling. In Chapter 3, the high and low resolution IUE data extracted for ι Aur are discussed. In Chapter 4, the emission line fluxes and profiles are analysed and an emission measure distribution is calculated. Simple hydrostatic models of the transition region and corona are constructed. Chapter 5 describes the methodology employed to construct model chromospheres using non-LTE radiative transfer. In Chapter 6, computations of the chromospheric structure of a 'hybrid' star are presented for the first time. Calculations made for the first time show that the excitation of the Fe I y⁵G^o₃ level by the Mg II k line can produce the observed emission in other transitions from the J = 3 level. In Chapter 7, non-isothermal Alfvén wave driven wind models are calculated. It is shown that ι Aur proves to be a severe test of these models and that the transition region and the cool wind are physically separate. A brief resumé, and possible future research topics are given Chapter 8.