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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.
81

Aluminum Speciation Using Fluorescence Quenching

Smith, Donald Scott 02 May 1994 (has links)
<p> A noninvasive method using fluorescence quenching (FQ) to determine the conditional stability constants (logK') for aluminum with naturally occurring organic ligands has been developed. The method utilizes the Stern-Volmer equation to interpret data from ligand fluorescence suppression by aluminum. The total ligand concentration can also be determined using the measured stability constant and the Ryan-Weber equation. The method has been validated with the model ligand salicylic acid; logK' was found to be 3.5 ± 0.01 vs. 4.0 from the literature. The method was applied to the reference ligand Armadale fulvic acid and chemically realistic values were obtained. In addition, the expected trend of increasing stability constant with decreasing pH was observed. The method was further validated by determining the stability constant for Armadale fulvic acid using an independent technique, PCV colourimetry; the results agreed very well logK' = 4.7 vs. 4.65 for FQ analysis. Application of the method to whole filtered beaver pond water showed an increasing trend in the stability constant as the dissolved organic carbon (DOC) decreased. The Log of the stability constants were 3.15 ± 0.03, 3.26 ± 0.03, and 3.63 ± 0.02 for DOC concentrations 23, 14, and 10 ppm respectively. The method was also applied to size fractionated waters form lake Skjervatjern in Norway and the expected trend of increasing stability constant with increasing molecular weight was observed.</p> / Thesis / Bachelor of Science (BSc)
82

Non-linear flow, fracture, mechanical quenching, and computer modeling of a glass cylinder pressed between parallel plates

Sakoske, George Emil January 1992 (has links)
No description available.
83

Analysis of Methoxy-polyethylene Glycol-modified Human Serum Albumin

Houts, Frederick William 30 May 2006 (has links)
No description available.
84

Biochemical Characterization of hTRF1 and hTEP1, Two Proteins Involved in Telomere Maintenance

Tahmaseb, Kambiz 21 June 2007 (has links)
No description available.
85

Near-Field Cosmology and Star Formation Quenching with Local Dwarf Galaxies

Garling, Christopher Trent 10 August 2022 (has links)
No description available.
86

An Experimentally-validated Agent-based Model to Study the Emergent Behavior of Bacterial Communities

Leaman, Eric Joshua 03 February 2017 (has links)
Swimming bacteria are ubiquitous in aqueous environments ranging from oceans to fluidic environments within a living host. Furthermore, engineered bacteria are being increasingly utilized for a host of applications including environmental bioremediation, biosensing, and for the treatment of diseases. Often driven by chemotaxis (i.e. biased migration in response to gradients of chemical effectors) and quorum sensing (i.e. number density dependent regulation of gene expression), bacterial population dynamics and emergent behavior play a key role in regulating their own life and their impact on their immediate environment. Computational models that accurately and robustly describe bacterial population behavior and response to environmental stimuli are crucial to both understanding the dynamics of microbial communities and efficiently utilizing engineered microbes in practice. Many existing computational frameworks are finely-detailed at the cellular level, leading to extended computational time requirements, or are strictly population scale models, which do not permit population heterogeneities or spatiotemporal variability in the environment. To bridge this gap, we have created and experimentally validated a scalable, computationally-efficient, agent-based model of bacterial chemotaxis and quorum sensing (QS) which robustly simulates the stochastic behavior of each cell across a wide range of bacterial populations, ranging from a few to several hundred cells. We quantitatively and accurately capture emergent behavior in both isogenic QS populations and the altered QS response in a mixed QS and quorum quenching (QQ) microbial community. Finally, we show that the model can be used to predictively design synthetic genetic components towards programmed microbial behavior. / Master of Science
87

Application of Optical Fiber Sensors for Quenching Temperature Measurement

Hurley, Paul Raymond 17 June 2020 (has links)
The critical heat flux (CHF) point for a reactor core system is one of the most important factors to discuss in regards to reactor safety. If this point is reached, standard coolant systems are not enough to handle the temperature increase in the cladding, and the likelihood of meltdown greatly increases. While the nucleate boiling and film boiling regimes have been well-investigated, the transition boiling regime between the point of departure from nucleate boiling (DNB) and the minimum film boiling temperature (T<sub>min</sub>) remains difficult to study. This is due to both the complexity of the phenomena, as well as limitations in measurement, where experiments typically utilize thermocouples for temperature data acquisition. As a result of technological advancement in the field of fiber optics, it is possible to measure the quenching temperature to a much higher degree of precision. Optical fiber sensors are capable of taking many more measurements along a fuel simulator length than thermocouples, which are restricted to discrete points. In this way, optical fibers can act as an almost continuous sensor, calculating data at a resolution of less than one millimeter where a thermocouple would only be able to measure at one point. In this thesis, the results of a series of quenching experiments performed on stainless steel, Monel k500, and Inconel 600 rods at atmospheric pressure, with different subcooling levels and surface roughnesses, will be discussed. The rewetting temperature measurement is performed to compare results between thermocouples and optical fiber sensors in a 30 cm rod. These results are further discussed with regard to future application in two-phase flow experiments. / Master of Science / There are multiple types of boiling that can occur depending on the heat transfer capabilities of the system and the power applied to the coolant. The most common is nucleate boiling, where vapor produced at the surface forms bubbles and move away from the surface due to buoyancy. At a high enough power, the bubbles can coalesce into a film and lead to a point at which the liquid coolant can no longer contact the surface. Since vapor is not as effective at transferring heat from the surface, the temperature will increase drastically. In nuclear reactors, this situation (known as departure from nucleate boiling), can quickly lead to a meltdown of the fuel rods. Another important safety parameter in nuclear reactors is the minimum temperature at which this vapor film can be maintained, T<sub>min</sub>. This parameter is a source of significant concern with regard to accident scenarios such as LOCA (loss of coolant accident), where reintroducing coolant to the rods efficiently is of top priority. While much research has been done on nucleate and film boiling, it has been difficult to study the transition period between the two regimes due to both its transient nature and the lack of continuous measurement capabilities. Typically, temperature is measured using thermocouples, which are point-source sensors that do not allow for high spatial resolution over a large area. This thesis deals with the utilization of optical fibers for temperature measurement, which are capable of calculating data at every millimeter, potentially a much more precise measurement system than with the thermocouples. The experiments performed in this paper are quenching experiments, where a rod embedded with thermocouples and an optical fiber is heated to well above T<sub>min</sub> and quickly plunged into a volume of water, in order to view the transition from film to nucleate boiling.
88

Effects of Metallic Nanoalloys on Dye Fluorescence

Dorcéna, Cassandre Jenny 15 October 2007 (has links)
Metallic nanoparticles (NPs) are exploited for their ability to interact with organic compounds and to increase significantly the fluorescence intensity and the photostability of many fluorescent dye molecules. Metal enhanced fluorescence (MEF) is therefore widely investigated for biosensing applications. When used in immunoassays, silver island films (SIFs) could augment the fluorescence intensity of fluorescein by a factor of seventeen; SIFs were also able to double or triple the emission intensity of cyanine dyes which are commonly used in (deoxyribonucleic acid) DNA microarrays. The emission intensity of indocyanine green — widely used as a contrast agent in medical imaging — was about twenty times higher in the proximity of SIFs. This enhancement phenomenon — due to the surface plasmon polaritons associated with the metallic NPs — can be explained by energy transfer from the metal NPs to the fluorescent dye molecules or by a modified local electromagnetic field experienced by the fluorophores in the vicinity of metal surfaces. Our research focused on the optical characterization of colloidal gold-silver alloy NPs containing different ratios of gold and silver (Au<sub>1.00</sub>-Ag<sub>0.00</sub>, Au<sub>0.75</sub>-Ag<sub>0.25</sub>, Au<sub>0.50</sub>-Ag<sub>0.50</sub>, and Au<sub>0.25</sub>-Ag<sub>0.75</sub>), as well as their interaction with three fluorophores: rose bengal, rhodamine B, and fluorescein sodium. Depending upon the dye quantum yield and its concentration in solution, enhancement or quenching of fluorescence was obtained. Thus, a three to five times increase in fluorescence intensity was observed in a 2.0 mM solution of rose bengal with all nanoalloys, a slight enhancement of fluorescence (1.2 – 1.6 times) was noticed in a 0.13 mM solution of rhodamine B with all four types of NPs, and fluorescence quenching occurred in all the fluorescein-NP solutions regardless of the dye concentration. / Master of Science
89

Molecular mechanisms involved in the bacterial talking and maize growth promotion / Mecanismos moleculares envolvidos na comunicação bacteriana e na promoção de crescimento de milho

Almeida, Jaqueline Raquel de 06 September 2018 (has links)
With the increase of agricultural production, there is an improvement in the use of mineral fertilizers, which may cause different environmental problems, besides the soil salinization. A possible alternative for reducing the application of these products is the use of plant growth-promoting bacteria (PGPB), that can be used alone or in co-inoculation, resulting in an alternative environmentally and economically feasible. Better results can be obtained if the interaction among bacteria-bacteria and bacteria-plant be elucidated, and strategy developed to optimize these interactions. Thus, the plant growth-promoting Bacillus sp. RZ2MS9, previous described as a potential PGPB in maize and soybean, was GFP-tagged and monitored alone and co-inoculated with Azospirillum brasilense (Ab-v5::pWM1013) during maize colonization. The interaction of tagged strains in maize were monitored by fluorescent microscopy (FM) and quantitative PCR (qPCR), demonstrating an endophytic behavior of Bacillus sp. RZ2MS9. Although the non-detection of Ab-v5::pWM1013, the co-inoculation resulted in the best increase in root and shoot dried weight, root volume and in root diameter, showing that inoculation with more than one strain can be a good choice to development of bio-fertilizers. One important system to bacterial interaction is the quorum sensing (QS). The QS is an important cell-cell communication system that allows bacterial cells to recognize their own population and modulate their gene expression. This, system is also involved in the interspecific communication, including other bacterial species and plants. In the other hand, enzymes able to detect and degrade these molecules evolved, the called quorum quenching (QQ) system, that has been evolved in some bacteria as competitive advantage for niches colonization. The aiiA gene, was one of the first gene related with the QQ in Bacillus. The aiiA was found in Bacillus sp. RZ2MS9 genome. Through construction of a new QQ biosensor, Agrobacterium tumefaciens At11006, and validated by A. tumefaciens NTL4, the ability of RZ2MS9 to degrade QS molecules was confirmed. The knockout of aiiA gene was performed using the CRISPR-Cas9 system, confirming this gene function. By these results, the influence of QQ system of Bacillus sp. RZ2MS9 during maize colonization and RZ2MS9 - A. brasilense - maize can be better investigated, opens the possibility to better understand the role of QQ system in the interaction among PGPB and plants. / Concomitantemente ao aumento da produção agrícola, há o aumento do uso de fertilizantes minerais, que pode acarretar no desenvolvimento de diferentes problemas ambientais, além de causar a salinização dos solos. Uma possível alternativa para tentar reduzir a aplicação desses produtos é o uso de bactérias promotoras de crescimento de plantas (BPCPs), que podem ser usadas isoladamente ou em co-inoculação com outras bactérias, tornando-as uma alternativa ambientalmente e economicamente viável. Melhores resultados podem ser obtidos se a interação bactéria-bactéria e bactéria-planta for elucidada, permitindo que estratégias sejam desenvolvidas para otimizar essas interações. Em vista disso, a bactéria Bacillus sp. RZ2MS9, previamente descrita como uma potencial BPCP em milho e soja, foi marcada com GFP e monitorada durante a colonização de milho inoculada sozinha, bem como em co-inoculação com Azospirillum brasilense (Ab-v5::pWM1013). A interação dessas linhagens marcadas em milho, foi monitorada por microscopia de fluorescência (FM) e PCR quantitativo (qPCR), revelando um comportamento endofítico de Bacillus sp. RZ2MS9. Em plantas co-inoculadas, apesar da linhagem Ab-v5::pWM1013 não ter sido detectada por qPCR, a co-inoculação resultou no aumento do peso seco das raízes e da parte aérea, no volume e no diâmetro do sistema radicular, demonstrando que a inoculação com mais de uma linhagem bacteriana pode ser uma boa alternativa para o desenvolvimento de bio-fertilizantes. O quorum sensing (QS) é um importante sistema de comunicação célula-célula que permite que as bactérias reconheçam sua própria população e modulem sua expressão gênica. Este sistema também está envolvido na comunicação interespecífica, incluindo outras espécies bacterianas e plantas. Co-evolutivamente, enzimas capazes de detectar e degradar essas moléculas evoluíram, dando origem ao chamado quorum quenching (QQ), sistema que evoluiu em algumas bactérias como uma vantagem competitiva para a colonização de nichos. O gene aiiA, foi um dos primeiros genes relacionados ao sistema QQ descrito no gênero Bacillus, gene este que foi anotado no genoma de RZ2MS9. Através da construção de uma nova linhagem biossensora de QQ, Agrobacterium tumefaciens At11006, e validada através da linhagem A. tumefaciens NTL4, a capacidade de RZ2MS9 de degradar moléculas de QS foi confirmada. O knockout do gene aiiA foi realizado utilizando o sistema CRISPR-Cas9, confirmando a função desse gene. Através dos resultados obtidos neste trabalho, a influência do sistema QQ de Bacillus sp. RZ2MS9 durante a colonização do milho, bem como a interação RZ2MS9 - A. brasilense - milho pode ser melhor investigada, abrindo a possibilidade de uma melhor compreensão do papel do sistema QQ na interação entre bactérias promotoras de crescimento e plantas.
90

Interruption de la communication bactérienne dans la rhizosphère par la dégradation enzymatique des signaux quorum sensing / Disruption of bacterial communication in rhizosphere by enzymatic degradation of quorum sensing signals

Tannières, Mélanie 23 March 2012 (has links)
L’identification, chez divers organismes, d’enzymes de dégradation des N-acyl homosérineslactones (NAHLs) impliquées dans la signalisation QS pose la question de leurs rôles dans lesinteractions bactéries-eucaryotes. Dans une première partie, une synthèse bibliographique analyse lesconnaissances acquises sur ces enzymes dégradant les NAHLs. Dans une seconde partie, la croissancedes bactéries dégradant les signaux NAHLs a été stimulée par l’application de g-caprolactone (GCL)dans la rhizosphère de plants de pommes de terre à des fins de phytoprotection. L’effet de cetraitement sur la diversité des communautés bactériennes rhizosphériques a été évalué en combinantdifférentes approches d’écologie microbienne moléculaire comme la DGGE, le pyroséquençaged’amplicons rrs, et la métagénomique fonctionnelle. Cette dernière approche appliquée à une banquede 30 000 clones environ a conduit à l’identification d’un gène qsdB codant la dégradation des signauxNAHL. Ce travail révèle ainsi l’existence d’une nouvelle classe d’enzymes de dégradation des NAHLsappartenant à la famille des enzymes possédant une signature amidase (AS) dont des membres sontpar ailleurs impliqués dans la dégradation de composés xénobiotiques. Dans une troisième partie, unsystème expérimental a été développé afin de mesurer le transfert conjugatif du plasmide de virulenceTi (tumor inducing) chez des dérivés du pathogène Agrobacterium tumefaciens, appelés «tricheurs»,incapables de produire des signaux NAHLs mais utilisateurs de ceux produits par les autres bactéries.Ce modèle a permis de montrer l’effet modérateur de lactonases dégradant les NAHLs exprimées chezdes agrobactéries produisant les NAHLs, chez des bactéries réceptrices du plasmide Ti, ou des planteshôtes des agrobactéries sur le transfert conjugatif initié par les tricheurs. L’ensemble de ce travailrévèle à la fois une nouvelle famille d’enzymes impliquées dans la dégradation des NAHLs, ainsiqu’un nouveau rôle de ces enzymes dans la modulation des flux de gènes entre bactériesphytopathogènes en interaction avec une plante hôte. / Identification of bacterial and eukaryotic enzymes that degrade N-acyl homoserine lactones(NAHLs) involved in QS signaling raises the question of their roles in bacteria-eucaryotesinteractions. In a first part of this study, a bibliographic report analyzes the current data on thoseNAHL-degrading enzymes. In a second part, the growth of NAHL-degrading bacteria was stimulatedby g-caprolactone (GCL) amendment in potato rhizosphere to protect this plant against the soft-rotpathogen Pectobacterium. The effect of the GCL treatment on rhizospheric bacterial communities wasevaluated by a combination of different molecular microbial ecology techniques such as DGGE,pyrosequencing and functional metagenomic. This last approach was applied to generate ametagenomic library of ca. 30,000 clones and lead to the identification of the qsdB gene that encodesNAHL degradation, This work revealed the occurrence of a novel class of NAHL-degrading enzymesthat belong to the amidase signature (AS) family, some members of which being involved inxenobiotic compound degradation. In a third part, an experimental system was developed to measurethe conjugative transfer of Ti plasmid in various strains of the pathogen Agrobacterium tumefaciens,including “cheaters”, i.e. bacteria unable to produce NAHL signals but capable to use signals producedby other bacteria. Using this model; variations of the plasmid transfer of cheaters were measured whenNAHL-degrading lactonases were expressed in agrobacteria that produce NAHL signals, in recipientbacteria of Ti plasmid, or in agrobacterial host plant. Taken together, thesis experiments revealed anovel class of enzymes involved in NAHL-degradation and a new role for thoses enzymes in themodulation of gene transfer between pathogenic bacteria interacting with host plants.

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