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Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Recent experimental data on dijet cross section in diffractive photoproduction at HERA collider are analyzed with an emphasis on QCD factorization breaking effects. The possible sources of the contradiction in conclusions of H1 and ZEUS collaborations such as different hadronization corrections and different phase space of both analysis are studied.

Cover crops are typically sown between cash crops and can suppress weed emergence and growth. If cover crops are sown after cash crop harvest the system is left susceptible to weed emergence while they establish. Interseeding cover crops into a standing cash crop may limit this bare period by allowing cover crops to become established, go into dormancy, and then revive around cash crop senescence. Studies were conducted in Princeton and Lexington, KY, to determine (i) which corn pre-emergent herbicides and mixtures of herbicide active ingredients commonly used by Kentucky growers would impact interseeded cover crop density and biomass, (ii) which grass entries that are adapted to Kentucky would be best to interseed in corn, and (iii) if interseeded cover crops would suppress weeds similar to a cover crop planted after cash crop harvest. There were few reductions in interseeded cover crop density and biomass from the pre-emergent herbicides tested. Among the entries interseeded in four site-years, the tall fescue pre-cultivars generally performed the best but none were consistently able to survive the summer when interseeded into corn. Compared to a cereal rye cover crop seeded after corn harvest, interseeded cover crops produced less biomass and therefore suppressed fewer weeds.

Deep seismic exploration in the Gippsland Basin is hindered by strong, unidentified noise below the Latrobe Group coal sequence. Low velocity events that appeared in field data semblance analyses suggested that an elastic wave modelling study was required to understand the subcoal reflection response. The modified reflectivity method (Kennet, 1980) provided a means for constructing detailed and accurate synthetic seismograms from realistic depth models, under the assumption of an isotropic, plane-layered earth. A study into the effect of each part of an elastic depth model (upon an elastic depth model (upon an elastic synthetic seismogram) resulted in a set of guidelines for obtaining a field data comparison. Excellent ties were obtained at several wells, often using little more than a partial sonic log. The noise contributions to the synthesis were interpreted using additional synthetics computed from variations upon the depth model and by exercising control over the wave types modelled. Subsequent processing of the synthetics revealed three types of persistent noise in progressively deeper parts of the subcoal image: 1) mode converted interbed multiples (generated within the coal sequence); 2) S-wave reflections and long period multiples (generated between the coal sequence and the Miocene carbonates and 3) surface related multiples.

Deep seismic exploration in the Gippsland Basin is hindered by strong, unidentified noise below the Latrobe Group coal sequence. Low velocity events that appeared in field data semblance analyses suggested that an elastic wave modelling study was required to understand the subcoal reflection response. The modified reflectivity method (Kennet, 1980) provided a means for constructing detailed and accurate synthetic seismograms from realistic depth models, under the assumption of an isotropic, plane-layered earth. A study into the effect of each part of an elastic depth model (upon an elastic depth model (upon an elastic synthetic seismogram) resulted in a set of guidelines for obtaining a field data comparison. Excellent ties were obtained at several wells, often using little more than a partial sonic log. The noise contributions to the synthesis were interpreted using additional synthetics computed from variations upon the depth model and by exercising control over the wave types modelled. Subsequent processing of the synthetics revealed three types of persistent noise in progressively deeper parts of the subcoal image: 1) mode converted interbed multiples (generated within the coal sequence); 2) S-wave reflections and long period multiples (generated between the coal sequence and the Miocene carbonates and 3) surface related multiples.

Residual vibrations degrade the performance of many systems. Due to the lightweight and flexible nature of space structures, controlling residual vibrations is especially difficult. Also, systems such as the Space Shuttle remote Manipulator System have frequencies that vary significantly based upon configuration and loading. Recently, a technique of minimizing vibrations in flexible structures by command input shaping was developed. This document presents research completed in developing a simple, closed- form method of calculating input shaping sequences for two-mode systems and a system to adapt the command input shaping technique to known changes in system frequency about the workspace. The new techniques were tested on a three-link, flexible manipulator.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Fire suppression in the southern and central Appalachian Mountains has resulted in an alteration to vegetation structure and composition. For this research the dominant species, abundance, density and age structure of the ericaceous shrub layer is characterized on four sites across the southern and central Appalachian Mountains. Fire histories for each of the sites varied, and were determined in previous research using dendroecological techniques. Over 800 ericaceous shrubs were collected, species included Pieris floribunda (Pursh) Bentham & Hooker f., Rhododendron maximum L. and Kalmia latifolia L.. Basal area of ericaceous shrubs was significantly different between sites. Age structures show that when fire suppression started Ericaceae began to establish. A few Ericaceae cross-sections displayed scars, that are likely associated with fire events, suggesting they probably survived mild fire events. Ericaceous shrub age structures were also compared to SPB outbreaks and PDSI. There were no significant correlations, but field observations suggest that SPB may be providing conditions suitable for Ericaceae establishment. Topographic patterns reveal that Kalmia latifolia is most abundant at mid-slope positions and decreases at higher and lower slope positions. There were significant differences in the density between slope positions averaged across all sites. Sites with the most recent and frequent fires did not have any of the three ericaceous shrubs collected at the slope bottom or ridge-top. At the most fire-suppressed site Ericaceae are present at every slope position. Age structures reveal that the oldest Ericaceae are found at the mid-slope positions while the age of thickets appears to decrease away from the mid-slope position. This pattern suggests that Ericaceae are moving into slope positions where they were previously less abundant. Sites with the most recent frequent fire regime seem to have prevented Ericaceae from heavily inhabiting high and low topographic positions while also reducing the overall basal area and density of Ericaceae.