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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
241

Spermine Depresses NMDA, K/AMPA and GABA<sub>a</sub>-Mediated Synaptic Transmission in the Rat Hippocampal Slice Preparation

DiScenna, Pascal G., Ferchmin, Pedro A., Eterovic, Vesna A., Teyler, Timothy J. 06 June 1994 (has links)
The effects of spermine, an endogenous polyamine, were examined in area CA1 of the rat hippocampal slice preparation. Spermine, at low millimolar concentrations, rapidly and potently depressed NMDA and K/AMPA-mediated population EPSPs, and GABA-mediated monosynaptic population IPSPs. These effects contrast with its well-known potentiation of NMDA currents at lower concentrations. Our results raise the possibility that the large intracellular stores of spermine that are released after various neural insults could act as an endogenous neuroprotective mechanism by limiting excessive calcium entry.
242

Liquid-Liquid Equilibrium of Biodiesel Components

Bell, Joseph C. 07 December 2012 (has links) (PDF)
Biodiesel is produced from vegetable oils through transesterification. Triglyceride mixtures extracted from oilseed feedstocks are upgraded by reaction with an alcohol in the presence of a catalyst to produce fatty acid esters. This reaction produces a mixture of esters, glycerin, alcohol, and catalyst. Separation of the fatty acid esters (biodiesel) and glycerin can be accomplished through liquid-liquid extraction by water addition. Designing liquid-liquid extraction with water as the solvent requires ternary liquid-liquid equilibrium data for mixtures of water, glycerin, and fatty acid esters. Ternary mixture LLE data have been experimentally measured for several of these systems. Those measured include mixtures with the methyl esters of lauric, myristic, palmitic, stearic, and oleic acids. Data were collected at atmospheric pressure and 60°C. These ternary systems have been correlated using the NRTL equation. These data and correlation parameters can be used to improve separations efficiency in trans-esterified biodiesel fuels.
243

Thermodynamic Kinetics and Efficiency Analysis of Methyl Viologen

Chen, Chang 19 October 2012 (has links) (PDF)
Methyl Viologen (MV) is an electron mediator that has great possibilities to be used with an electrode system in which the electrode system provides electrons towards reducing MV species. MV has three redox states and they can be converted to each other via redox reactions on the surface of the electrode. The concentration of the three species of MV was related to the voltage potential applied to the system through a thermodynamic model. With the thermodynamic model the concentration of the three species can be predicted with different applied voltage potentials towards providing guidance for controlling the redox state of MV in a system. The kinetic rates of MV reduction were also assessed using a preliminary kinetic model. The kinetic model predicted all three species concentration changes with time although only the MV+ concentration was measured with time. Analysis revealed that the rate of MV reduction was three orders of magnitude slower than the rate of electrons required for bioethanol production. However, increasing the affinity of MV+ on the surface and blocking the H+ on the surface potentially can increase the reduction rate of MV by up to three orders of magnitude and can potentially enable MV to be used in commercial applications. As for the efficiency study, the coloumbic efficiency was less than 22% which was much lower than the efficiency of more than 85% observed in other studies for the direct electron transfer between electrode and bio organism. The efficiency was lowered mainly by the reduction of H+ and minimizing H+ on the electrode can largely increase the efficiency. Medium used for cell growth can also affect the efficiency through medium species consuming electrons provided by the electrode. Electron mediators, such as MV, have potential promise in applications such as microbial fuel cells, biofuel formation, and waste water treatment. However, engineering analysis of electron mediators is critical to provide better engineering control, design, and economic analysis for future applications.
244

An Evaluation Study Of The Effectiveness Of Using A Reaction-based Process For Hydrazine Waste Remediation

Oropeza, Cristina M 01 January 2011 (has links)
Hydrazine (HZ) and monomethylhydrazine (MMH) are used extensively as hypergolic propellants at Kennedy Space Center. These highly reactive fuels are considered highly toxic, and potentially carcinogenic. Consequently, the transport, handling, and disposal of hydrazines is strictly regulated to protect personnel and the environment. Currently, KSC generates large volumes of hydrazine-laden wastewater for disposal. This waste is contained and shipped on public highways for subsequent disposal by incineration presenting a potentially catastrophic threat to the environment and the general public in the event of an accidental release. Other existing remediation methods include oxidative and reductive pathways as well as biodegradation in fixed film reactors. Each of these methods has associated drawbacks and limitations that make them unsuitable for industrial use. Recently, hydrazine neutralization by reaction with alpha-ketoglutaric acid (AKGA) to form the stabilized pyridazine derivatives PCA and mPCA has been explored. The applicability of this technique for use at KSC has been established and procedural considerations for implementation have been addressed. Experimental evidence based on worst case scenario decontamination processing simulations and reaction characterization has suggested that AKGA can cost effectively function as a drop-in replacement for current neutralizers with minimal modification to existing infrastructure and operating procedures. Further work will be necessary to satisfy permitting iv requirements and verify that the reaction product stream is non-hazardous in light of limited toxicity data.
245

Degenerate and Nondegenerate Rearrangements in 8,8-Dimethylbenzohomotropylium Cations

Sivapalan, Manjula 12 1900 (has links)
<p> Investigations on the stability and reactions of various isomers of the benzohomotropylium/bridged [11]-annulene system are presented in this thesis. As 1,6-methano-[11]-annulenium cations are isomeric with benzohomotropylium cations in principle it is possible for these systems to be interconverted by a circumambulatory migration of the 'bridging' methano group. If this reaction were to proceed to equilibrium it would allow the examination of the thermodynamic stability of the various isomers.</p> <p> Homotropylium cations with two methyl groups at C8 are known to undergo facile circumambulatory rearrangements. Thus in this work the 1-hydroxy 8,8-dimethyl-2,3-benzohomotropylium and 1-hydroxy 8,8-dimethyl-4,5-benzohomotropylium cations have been prepared by protonation of the corresponding 2,3- and 4,5- benzohomotropones in FSO3H. On the basis of their 1H NMR spectra it is concluded that they can properly be regarded as homoaromatic cations. The thermal isomerizations of these cations have been studied in detail. The thermal isomerization of these cations led to the formation of a series of products but does not yield the corresponding [11]-annulenium isomer. In addition the barriers to ring inversion in these cations were found to be much lower than those of other homotropylium cations. This suggests that the former cations have a very open structure. Besides this experimental approach, the relative stability of these isomers has been explored using MNDO calculations. The calculated heats of formation (ΔHf) showed that the 1-benzohomotropylium cation is more stable than the corresponding [11]-annulenium ion by 21 kcal/mol.</p> / Thesis / Master of Science (MSc)
246

Effects Of Various Fumigants And Alternative Processing Methods On The Safety, Volatile Composition, And Sensory Quality Of Dry Cured Ham

Sekhon, Ramandeep Kaur 11 December 2009 (has links)
Randomized complete block designs with three replications were utilized to evaluate the effects of fumigation with sulfuryl fluoride (SF) (0, 12, 24, 36 and 72 mg/L), phosphine (PH3) (0, 200 and 1000 ppm at 48 hr), methyl bromide (MB) (0, 4, 8, 16, and 32 mg/L for 48 hr), carbon dioxide (CO2) (0, 60% at 48 hr and 60% at 96 hr) and ozone (O3) (0 ppm and 175 ppm for 48 hr) on the volatile flavor compound concentrations in dry cured ham. Fluoride and SF concentrations increased (P < 0.05) in dry cured hams as SF fumigation concentration increased, but all samples contained fluoride and SF concentrations below the legal limits of 20 and 0.01 ppm, respectively. Also, as phosphine fumigation concentration increased, the residual concentration of phosphine also increased in the hams (P < 0.05), but all samples contained levels that were lower than the legal limit of phosphine in stored food products (0.01 ppm). Minimal differences existed in the presence and concentration of aroma active compounds in fumigated hams when compared to the control. Triangle tests indicated that consumers could not discern (P > 0.75) between the control hams and the fumigated hams. This study revealed that there were minimal aroma/flavor differences among control hams and hams that were fumigated with SF, PH3, MB, CO2 or O3 and that fumigation of dry cured ham with SF and PH3 were safe and met legal requirements for consumption. This reveals that SF, PH3, CO2 and O3 could be tested at the industrial level to determine their efficacy as potential alternatives to methyl bromide to treat dry cured hams for insect pests.
247

Synthesis and Fragmentation Reactions of Linoleic Acid-Derived Hydroperoxides

Zhang, Wujuan January 2008 (has links)
No description available.
248

The kinetics of a methyl methacrylate polymerization initiated by the stable free radicals in irradiated polytetrafluoroethylene and properties of the resultant graft polymer

Donato, Karen Ann Ehnot January 1987 (has links)
No description available.
249

Metabolic Engineering Techniques to Improve Methylation in the Psilocybin Biosynthesis Pathway in E. Coli

Kaplan, Nicholas Allen 27 July 2022 (has links)
No description available.
250

A Generic Smell Generating Enzymatic Biosensor

Xu, Yaqin 10 1900 (has links)
<p>This thesis describes a new type of biosensor, which reports the presence of a target by generating a smell that can be easily detected by the human nose. This approach is radically different from, but complementary to, colorimetric based reporting and it paves the way for the development of multi-sensory biosensors that can be used in a variety of fields, such as diagnostic device, food processing and environmental monitoring</p> <p>Biosensors typically consist of two parts: a bio-recognition element and a signal transducer. The biorecognition element is the component that can specifically interact with its cognate target, while the transducer produces a signal that can be easily identified. The key element of the smell generating biosensor is the enzyme tryptophanase (TPase), which was used as the signal transducer. This enzyme uses either L-tryptophan or S-methyl-L-cysteine as substrates, to produce either indole or methyl mercaptan as final products- both molecules are easily detectable by the human nose. Proof-of-concept for this biosensor was achieved by performing an enzyme-linked immunosorbent assay (ELISA) on magnetic beads with detection of IgG from rabbit serum (the target) in a sample and reporting the presence of the target through the generation of a smell (either indole or methyl mercaptan, depending on the substrate used).</p> <p>The potential use of TPase for biosensing was further expanded by creating a bienzyme system that allows specifically detecting of adenosine-5’-triphosphate (ATP) and reporting its presence by generating a smell. This bienzyme system is based on the fact that TPase activity is greatly affected by the concentration of pyridoxal phosphate (PLP)- which acts as a cofactor that modulates enzyme activity. The enzyme pyridoxal kinase PKase catalyzes the phosphorylation of pyridoxal to PLP in the presence of ATP. The more ATP presents, the more PLP is produced per unit time. If this occurs in the presence of TPase, larger concentrations of ATP in samples will result in higher amounts and faster rates of PLP formation, leading to increased activity of TPase, hence faster generation of either indole or methyl mercaptan is achieved. This bienzyme was used for the detection of DNA molecules with a specific sequence as well as for the detection of microbial cells through smell generation.</p> <p>Most widely used biosensors require immobilization of the biologically active elements on a stable surface. Paper, being a cheap and easy accessible substrate, was used for fabrication of the olfactory-based biosensor. Poly(N-isopropylacrylamide-co-vinylacetic acid) (PNIPAM-VAA) microgels with functional groups present on their surface were modified by biotinylation and loaded with streptavidin/avidin (to be prepared as a platform for further biomolecule immobilization). The microgels were then used as a supporter for the bienzyme system on filter paper to construct a paper-based smell-generating biosensor, which opens the way for the creation of printable smell-reporting printable bio-inks.</p> / Doctor of Philosophy (PhD)

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