Rapid and efficient initiation of hydrocarbon/air mixtures has been identified as one of the critical and enabling technologies for Pulse Detonation Engines (PDEs). Although the NPS Rocket Propulsion Laboratory has successfully demonstrated fuel/air detonations in a valveless pulse detonation engine using ethylene, propane, and JP-10 fuels, past engine designs have relied upon a sensitive fuel/oxygen initiator unit. To realize the increased thermodynamic efficiencies of PDEs and thus compete with ramjets and other supersonic platforms, it is imperative to eliminate any need for supplementary oxygen in an air-breathing PDE design. This thesis examined ignition technologies and initiator designs which did not require auxiliary oxygen, including capacitive discharge systems and the developing technology of Transient Plasma Ignition (TPI). The current NPS pulse detonation engine architecture was modified to evaluate the various ignition strategies in a PDE operating on an ethylene/air mixture at simulated supersonic cruising conditions. Comparisons were based upon ignition success rate, ignition delay time, detonation wave speed, and Deflagration-to-Detonation (DDT) distance. Reliability and performance of the TPI system proved to be superior to conventional ignition systems. Furthermore, successful initiation of a PDE operating at a frequency of up to 40 hertz was demonstrated without the use of supplementary oxygen.

The influence of sucrose as an important factor in the vase-life of cut flowers has been dually noted. Sucrose is actively transported across the cell membrane via a symport system and the membrane-imbedded ATPase enzyme generates the required energy and proton gradient for the process. The activity of this enzyme decreases during the senescence of Petunia petals, concomitant with a decrease in sucrose-uptake in the post-climacteric phase. However, ATP does not appear to be limiting, indicating that a change in proton gradients may be responsible for this phenomenon. In order to study the uptake of sucrose in Petunia corollas various inhibitors of ATPase enzyme activity (DES and sodium orthovanadate) were introduced. The effect of potassium ferricyanide on the disruption of the membranal electro-chemical gradient was also determined. In addition it was found that the plasma membrane redox system seems to be influential in creating the H+-gradient necessary for sucrose-uptake. These effects were also studied in relation to prior treatment of flowers with the hormone, ethylene, for 24 hours. The results obtained have shown the i) importance of a stable inter- and intracellular pH environment; ii) the imbedded ATPase enzyme’s dependence on the membrane stability; iii) the maintenance of the electro-chemical gradient across membranes; the active energy generated by the ATPase enzyme; and lastly, iv) the effect of ethylene directly on membrane integrity and indirectly on sucrose-uptake. / Prof. C.S. Whitehead

Thesis (M.Phil.)--Chinese University of Hong Kong. / Includes bibliographies.

Transcriptional control plays a major role in regulating hypoxic responses in plants. However, the transcriptional regulatory networks associated with hypoxia remain to be constructed. By transcriptomic analysis I show here that a novel systemic transcriptional reprogramming, which is mediated via the interplay of hormones, facilitates the survival of plants under flooding. A feasible strategy for identifying downstream targets of transcription factors (TFs) was developed. The downstream pathways of a hypoxia-responsive TF, WRKY22, were constructed. The results also show that AtERF73/HRE1 (Arabidopsis thaliana Ethylene Response Factor 73/Hypoxia Responsive ERF 1) modulate ethylene-dependent and -independent responses during hypoxia. Transcriptomic analysis of Arabidopsis in both root and shoot tissues during flooding of roots indicates the existence of a systemic communication through transcriptional reprogramming. By functional classification of affected genes, a comprehensive managing program of carbohydrate metabolism was observed. Through transcriptional profiling in ethylene and abscisic acid (ABA) signaling mutants, ein2-5 and abi4-1, an alteration of long-distance hypoxic regulation was uncovered in ein2-5 and abi4-1. Moreover, genes involved in ABA biosynthesis were also found to be differentially regulated between shoots and roots. Many members of the WRKY TF family were highly induced by hypoxia. One of the early-induced WRKYs, WRKY22, which has the highest induced level, was chosen for identifying its downstream targets. Anoxic tolerance was affected in WRKY22 overexpressing (WRKY22-OX) and knock-out (wrky22-ko) lines. Comparison of differential gene expression profiles between the wild-type and WRKY22-OX and between the wild-type and wrky22-ko lines by microarray analysis identified novel hypoxia-responsive genes as WRKY22 targets. Chromatin immunoprecipitation (ChIP) followed by microarray hybridization (ChIP-chip) and ChIP followed by quantitative PCR (ChIP-qPCR) were utilized to analyze in vivo interactions. To study the role of ethylene during hypoxia, I characterized an AP2/ERF (APETALA2/ethylene response factor) AtERF73/HRE1 that is specifically induced during hypoxia. I showed that the expression of AtERF73/HRE1 can be induced by exogenous 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor of ethylene. Its hypoxic induction was reduced but not completely abolished in ethylene-insensitive mutants and in the presence of inhibitors of ethylene biosynthesis and responses. Increased ethylene sensitivity and exaggerated triple responses were observed in HRE1-RNAi knock-down lines. By comparing expression differences between the wild-type and HRE1-RNAi lines, I found that hypoxic induction of glycolytic and fermentative genes was reduced by the HRE1-RNAi knock-down mutations, whereas induction of a number of peroxidase and cytochrome P450 genes was increased. Collectively, these results show that AtERF73/HRE1 is involved in modulating ethylene responses under both normoxia and hypoxia.

No description available.

Protein disulfide isomerase (PDI), a member of the thioredoxin superfamily, contains two domains with significant sequence homology to the active sites in thioredoxin. PDI facilitates the folding of nascent proteins in the endoplasmic reticulum (ER), binds hormones and Ca�����, catalyzes the glutathione dependent reduction of dehydroascorbate, serves as a major chaperone molecule in the ER and serves as a subunit for prolyl-4-hydroxylase and microsomal triglyceride transferase. Because of its abundance in the ER and association with disease and chemically induced toxicity, the goal of this research was to investigate the relative susceptibility of PDI thiols to alkylation. The sensitivity of PDI to 1-chloro-2,4-dinitrobenzene (CDNB), iodoacetamide (IAM) and biotinoylated iodoacetamide (BIAM) was explored. The relative susceptibility of the thiolate anions present in the two active sites of PDI each containing the -CGHC- sequence was investigated with mass spectrometric techniques. PDI was inactivated by CDNB but was not found as sensitive as thioredoxin reductase as shown by Amer and coworkers (1995). IAM and BIAM were used as model alkylating agents to explore the two active sites of PDI and determine the residues most susceptible to alkylation. Alkylation by IAM and BIAM was first detected at the N-terminal cysteine in each active site (-C*GHC-) followed by alkylation at the second cysteine residue (-C*GHC*-) as shown by tandem mass spectrometry. Mass spectroscopy showed that the episulfonium ion derived from the glutathione conjugate of 1,2-dichloroethane, S-(2-chloroethyl)glutathione (CEG), decreased activity and protein thiols of PDI. CEG produced two protein adducts at very low excesses of CEG over PDI; however, higher concentrations resulted in several protein adducts. Only one modification in each active site at the N-terminal cysteine residue can be identified, indicating that while these thiolate anions of PDI are susceptible, it would appear that the episulfonium ion may present itself to other sites as well. This may have important toxicologic significance regarding the mechanism of 1,2-dichloroethane toxicity and the role of PDI in the redox status of the cell. / Graduation date: 2003

Plant growth, development, and environmental responsiveness are dependent on hormone-induced gene expression. This dissertation reports multiple interactions between the plant hormones auxin and ethylene and investigates their contribution to the gravitropic response, elongation growth, adventitious root formation, callus and tracheary element initiation and growth, and flower development. Four mutants of tomato (Lycopersicon esculentum, Mill.) altered in either hormone production or hormone response were used to test the involvement of ethylene and auxin. These mutants included diageotropica (dgt) which is auxin-resistant, Never-ripe (Nr), which is ethylene-resistant, epinastic (epi), which overproduces ethylene and lazy-2 (lz-2), which exhibits a phytochrome-dependent reversed-gravitropic response. Additionally, a double mutant between Nr and dgt was constructed and tested. Gravitropism was studied as an exemplary process involving both auxin and ethylene. Mutant analysis demonstrated that ethylene does not play a primary role in the gravitropic response via the currently known ethylene response pathways. However, ethylene can modify the gravitropic response, e.g. the delayed gravitropic response of the dgt mutant can be restored with exceedingly low concentrations of ethylene and ethylene synthesis- and ethylene-action inhibitors can partially inhibit the graviresponse. The role of gravity in tracheary element (TE) production was tested in microgravity (during a space shuttle flight) and in hypergravity (centrifugation). A correlation was found between gravitational force and the production of TEs, with decreased numbers of TEs produced in microgravity and increased numbers produced in response to hypergravity. Increased production of TEs by dgt in both increased and reduced gravity indicates that gravity regulates vascular development via a DGT-dependent pathway involving auxin. Combination of both the Nr and dgt mutations in a double mutant leads to plants which exhibit the reduction of auxin-sensitivity typical of dgt as well as a delay in fruit ripening typical of Nr. The reduced gravitropic response of the dgt mutant was restored to wild-type levels in the double mutant confirming a complex role for ethylene in the gravitropic response. Abnormal floral organ development was observed in a subset of double mutant flowers.These data demonstrate multiple connections between auxin and ethylene during development and provide further insight into their cellular interactions. / Graduation date: 2001

This microcosm study demonstrated the enhanced anaerobic transformation of vinyl chloride (VC) to ethylene. A previous microcosm study from Point Mugu site showed the accumulation of VC due to the slow transformation step of VC to ethylene. To overcome the rate-limiting step, two laboratory experiments tested the effect of trichloroethylene (TCE) additions on the rate enhancement, repeated low TCE additions and high TCE concentration additions. TCE (2 ��mol) was repeatedly added over a two week interval. In a parallel study, an equal amount of VC was added to another set of microcosms. TCE addition increased VC transformation to ethylene, with nearly 19% VC conversion to ethylene compared to 4% VC conversion in the VC added controls. However, the increased VC transformation rates were not sufficient enough to avoid VC accumulation. Rate of VC transformation decreased once TCE addition was stopped. This indicated the mixed culture required the transformation of TCE to maintain VC transformation rates. With TCE added at high concentrations (100 mg/L and 200 mg/L), nearly complete transformation of TCE to ethylene was observed. After the addition of high TCE concentrations, low concentration TCE (3 ��mol) was added and near 95% transformed to ethylene in 45 days. Two different low hydrogen yielding substrates, butyrate and propionate, were tested. Both were equally effective in promoting TCE dechlorination. Methanogenesis was inhibited at high TCE concentration with both substrates. Kinetic analysis of VC transformation data showed VC transformation followed the first order kinetics with respect to concentrations using a modified Monod equation. First-order kinetic constants increased after the addition of high ICE concentrations. After 200 mg/L of TCE addition, the first-order kinetic constant increased by factor of six compared to the rate obtained from the earlier low TCE concentration addition. However, reintroduction of TCE at low concentration maintained similar enhanced kinetic constants, as achieved at high concentration. This indicated the enhancement of VC transformation to ethylene was likely due to the growth of microorganisms using TCE as a terminal electron acceptor. These microorganisms were likely responsible for the transformation of VC to ethylene. / Graduation date: 2001

Laboratory scale microcosm studies were conducted using site specific groundwater and aquifer solids to assess the feasibility of stimulating indigenous microorganisms in-situ to biologically transform Trichloroethylene (TCE) and its lesser chlorinated daughter products dichloroethylene (DCE) and vinyl chloride (VC). Three different treatments were conducted to determine the best approach for biologically remediating TCE under site specific conditions: anaerobic reductive dechlorination, aerobic cometabolism and sequential anaerobic/aerobic stimulation. Studies were conducted in batch serum bottles containing aquifer solids, groundwater and a gas headspace. Long-term (302 days) TCE anaerobic reductive dechlorination studies compared lactate, benzoate and methanol as potential anaerobic substrates. Site characteristic sulfate concentrations in the microcosms averaged 1,297 mg/L and TCE was added to levels of 2.3 mg/L. Substrates were added at one and a half times the stoichiometric electron equivalent of sulfate. Nutrient addition and bioaugmentation were also studied. Both benzoate and lactate stimulated systems achieved complete sulfate-reduction and prolonged dechlorination of TCE to VC and ethylene. Dechlorination was initiated between 15 to 20 days following lactate utilization and sulfate-reduction in the presence of approximately 300 mg/L sulfate. Benzoate amended microcosms did not initiate dechlorination until 120 to 160 days following the complete removal of available sulfate. After 302 days of incubation lactate and benzoate amended microcosms completely transformed TCE to VC with 7 to 15% converted to ethylene. Re-additions of TCE into both systems resulted in its rapid transformation to VC. The dechlorination of VC to ethylene was very slow and appeared to be dependent on VC concentration. Hydrogen addition at 10����� and 10������ atmospheres had no effect on the transformation of VC. Rapid methanol utilization resulted in its nearly stoichiometric conversion to methane and carbon dioxide without significant sulfate-reduction or dechlorination occurring. Nutrient addition slightly enhanced dehalogenation with lactate but inhibited it with benzoate. Bioaugmentation with a TCE dechlorinating culture from a previous benzoate amended Point Mugu microcosm effectively decreased lag-times and increased overall dechlorination. Aerobic cometabolism studies evaluated methane, phenol and propane as cometabolic growth substrates. Methane and phenol amended microcosms were able to remove only 50 to 60% of the added TCE after four stimulations, while propane utilizers were unable to cometabolize any TCE. Primary substrate utilization lag-times of 4 to 5 days, 0 to 0.5 days and 40 to 45 days were observed for methane, phenol and propane, respectively. Cometabolism of VC was possible in the presence of methane. Complete removal of 210 ��g/L VC was achieved after 2 stimulations with methane under strictly aerobic conditions. Methane utilization and VC oxidation required nitrate addition, indicating that the system was nitrate limited. A sequential anaerobic/aerobic microcosm study failed to achieve methane utilization and VC transformation likely due to oxygen being utilized to re-oxidize reduced sulfate in the system. / Graduation date: 1999

Since decades, nucleation, or the ability of certain organic or inorganic substances to trigger the crystal growth, has been empirically used in the plastics industry. Talc, for instance, is a well-known nucleating agent of poly(ethylene terephthalate) (PET) and other polymers, that allows one to enhance the crystallisation rate of the polymer material and to control its spherulites size. The exact mechanism involved in this nucleation had however remained unknown at the onset of this thesis. Through electron diffraction, performed on thin PET films nucleated by macroscopic talc particles as model samples, this work demonstrates an epitaxial relationship between polymer and substrate and thus confirms the seemingly ubiquitous role of epitaxy in the nucleation of polymers. However, in order to compare the talc-nucleated morphology of PET with the virgin one, new methods of sample preparation for transmission electron microscopy (TEM) have also been developed. Coupled with theoretically justified image analysis techniques, they allow the direct observation of PET crystalline lamellae, both in the bulk and in thin films. Analyses of the semicrystalline structure in the reciprocal and direct spaces were performed from small-angle X-ray scattering (SAXS) data and from observations by TEM on melt-crystallised samples. These independent results were shown to be in good agreement and bring strong evidence in favour of a semicrystalline space-filling model, where the average crystalline thickness is slightly smaller than the average width of the amorphous regions. Discrepancies between characteristic distances derived by several methods from the same experimental results were attributed to the broad distribution of thicknesses, in contrast with the ideal linear stack model commonly used to analyse the data.