Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

Browse

Filters

2011 - 20192

Settings

Subject: search.filters.subject.Nitric Oxide

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    SALMONELLA ENTERICA STRATEGIES FOR PERSISTENCE ON TOMATO (SOLANUM LYCOPERSICUM) AND SEROVAR DYNAMICS IN SURFACE AND RECLAIMED WATER
    (2019) Ferelli, Angela Marie Cecelia; Micallef, Shirley A.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    While select aspects of Salmonella enterica subspecies enterica persistence in agricultural matrices have been illustrated, serovar specific survival strategies in surface water, transmission, and persistence on plants are multifaceted and remain only partially examined. In the present work, we utilized an interdisciplinary approach to illustrate novel mechanisms by which S. enterica may adapt to plants as an alternative host. Furthermore, we leveraged the wealth of diversity in S. enterica serovars to investigate specific dynamics and drivers of persistence in water and transfer onto produce crops. Through biochemical, gene expression, and plant challenge assays of both tomato (Solanum lycopersicum) vegetative and fruit organs, we found that plant-derived NO was generated in response to S. Newport recognition. Furthermore, bacterial gene expression on both leaves and fruit was indicative of adaptation to a novel environment including upregulation in NO detoxification machinery, indicating plant-derived NO as a novel bacterial stress. NO tolerance of various S. enterica was then evaluated to investigate drivers of “produce associated’ S. enterica adaptation to the plant niche. We identified that plant derived NO can negatively affect titers of all S. enterica serovars tested and that serovar specific tolerance to NO in vitro was apparent in a concentration and exposure time dependent manner. Finally, the survival of various S. enterica in surface and reclaimed water was investigated while evaluating the potential for transition to viable but non-culturable (VBNC) organisms. Furthermore, surface water used for irrigation, a common water environment for S. enterica, was investigated as a priming reservoir for various S. enterica serovars for enhanced transmission onto tomato crops. Persistence in water included VBNC subpopulations and was driven by water type. Transfer success onto tomato was driven by serovar, and prolonged incubation in water increased the transfer ability of serovars that initially transferred poorly onto tomato. Finally, attachment to polystyrene and water oxidation-reduction potential were identified as possible indicators of foodborne pathogen transfer success onto tomato. Moving forward, a greater understanding of the environmental queues used by S. enterica subspecies enterica responding to the agricultural environment will aid researchers in developing S. enterica targeted on-farm management techniques to ensure safe yet sustainable fresh produce cultivation practices.
  • Thumbnail Image
    Item
    INVESTIGATION OF JP-8 AUTOIGNITION UNDER VITIATED COMBUSTION CONDITIONS
    (2011) Fuller, Casey Charles; Jackson, Gregory S.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Limited data on jet fuel ignition and oxidation at low-O2, vitiated conditions has hindered the validation of kinetic models for combustion under such conditions. In this study, ignition delay time experiments of JP-8 have been performed with vitiated air at low pressures. Initially, the effects of temperature, equivalence ratio, and mole fractions of vitiated components on JP-8 ignition at 1 atm were screened to discover that temperature, O2 and NO have the largest significance. A following detailed investigation examined the effect on JP-8 ignition of larger concentrations of NO (0 - 1000 ppm) at lower temperatures (700 - 900 K), pressure (0.5 - 1.0 atm) and O2 mole fractions (12 - 20%). Results show that even trace amounts of NO dramatically enhance the oxidation of JP-8 with reduction in ignition delay time of up to 80%. Significant coupling exists between NO and the other design variables (temperature, oxygen level and pressure) as related to the effect of NO on ignition. An empirical model relating temperature, O2 and NO to ignition delay time of JP-8 has also been developed.