Dissertations / Theses on the topic 'Degradation'
To see the other types of publications on this topic, follow the link: Degradation.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Degradation.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Spain, Brock Colter. "Controlled degradation." Thesis, Montana State University, 2010. http://etd.lib.montana.edu/etd/2010/spain/SpainB1210.pdf.
Abstract:
On November 20, 1943 young Higgins landing craft operator Leon Cooper ferried U.S. Marines of the Second Division ashore on the island of Betio, Tarawa Atoll. The Tarawa landing was to be the first American amphibious assault in World War II and at Red Beach it challenged an entrenched force of 5,000 Japanese soldiers. The fighting lasted only seventy-six hours but it remains one of the bloodiest offenses during WWII. Nearly 1,700 Americans died and over 2,000 wounded during the battle at Tarawa. Most of the dead, both American and Japanese alike, were quickly buried in unmarked graves and cemeteries on the island. Since WWII, some American remains have been recovered, accounted for, and returned to the United States. However, the remains of 564 U.S. Marines and countless Japanese soldiers have yet to come home. Several years later... Leon Cooper had returned home and made a life as a computer company executive. Since retiring, the 89 year old Malibu veteran has stumbled upon a new fight in a familiar place. A few years ago he learned of a landfill covering the bodies of his fallen comrades at Red Beach. Outraged he began spending his own money and raising awareness about the build-up of garbage and debris on hallowed ground. His efforts have resulted in nationwide recognition and a documentary, Return to Tarawa: The Leon Cooper Story. However, the ultimate goal has yet to be realized. Leon has made it his last work to clean-up Red Beach. Apart from local and regional governments not cooperating, rising sea levels have also posed a threat to Leon's efforts. With an intending doom dictating the timeline, the clean-up of Red Beach pales in comparison to the relocation of 10,000 natives from their homes in one of the poorest regions on earth. If not addressed the issues at Red Beach will simply be underwater. The moral line made at this juncture divides right from wrong and outlines actions in each. Are mounds of trash atop soldier's remains simply 'out of sight and out of mind'? Or is their trash in our oceans atop forgotten hero's buried at sea? History tells a story of man's inhumanity to man; a tale of war that led men to kill other men for shared principals and the translation of that naivety into a nation dumping trash on a graveyard. It is the goal of this thesis to explore the qualities of humankind that are embodied in a soldiers sacrifice by creating an architecture that controls degrading conditions in spite of certain destruction. This, a municipal waste management facility, chooses to hold the sacrifices of soldiers above their deaths and carries their bodies from the trash into a memoriam that eases trauma into memory while instituting new possibilities, new activities, and new images for a hopeful future.
2
Kanungo, Tapas. "Document degradation models and a methodology for degradation model validation /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/5851.
3
Johansen, Maren Teresa. "Degradation of Amines." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for kjemi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23201.
Abstract:
In view of the rising amounts of greenhouse gases in the atmosphere, preventing CO2 emissions has become increasingly important. The combustion of fossil fuels for energy production and transportation is a large contributor to the problem. One of the ways to reduce the amounts of CO2 being released from combustion is carbon capture and storage (CCS). Post-combustion is the capturing method which has been deemed the easiest to apply to existing power plants in a short period of time. Absorption of CO2 by MEA is the most common method used in post-combustion carbon capture, but there are still many aspects of the process that are not fully understood. Understanding the absorption mechanisms will make it easier to make more economical and environmentally friendly choices in the future. In this thesis the oxidative degradation of monoethanolamine (MEA) has been studied using an open batch setup. The stability of MEA has been studied under different temperatures and concentrations of oxygen in the gas stream. These experiments give a matrix of experiments performed at 55, 65 and 75 °C, with oxygen concentrations of 6, 21, 50 and 98% in the gas stream. To monitor how well the experimental results could be trusted, the water balance was maintained throughout the experiments, and the pH was measured in the flasks capturing volatile degradation compounds.To get a detailed picture of the degradation, the weight percent of nitrogen and the CO2 concentration has been found in the end samples, and the alkalinity and MEA concentration was found for all the samples.11 known degradation compounds have been monitored for the different experiments, and the conditions these compounds are formed at have been compared with the suggested reaction mechanisms. 4 of the products were analyzed as anions using Ion chromatography (IC), and 7 secondary reaction products were analyzed as part of a degradation mix in LC-MS. The dependency of these compounds to temperature and oxygen conditions has been discussed. The primary degradation compounds seems to show a more direct correlation to oxygen flow or temperature, while the secondary degradation reaction shows a bigger variation of temperature and oxygen dependency relative to the conditions of the experiments. Various analytical methods for determination of the known compounds were used to determine the concentration of the degradation compounds in the experiments. The accuracy of these methods was investigated, and the results investigated for both LC-MS, GC-MS and IC-EC, showed large variations. Mixing experiments were performed to investigate the unknown mechanism of N-(2-hydroxyethyl) glycine.
4
Steele, Carolyn. "Tennis ball degradation." Thesis, Loughborough University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504041.
Abstract:
Despite anecdotal evidence of changes to tennis ball characteristics and play properties, little research has been directed towards understanding the causes and effects of tennis ball degradation. Improved racket technology and player fitness have contributed to an increase in the speed of the game, yet balls have seen few advancements over the same period. There are several obvious factors contributing to tennis ball degradation: natural pressure loss in pressurised balls, changes to the cloth covering due to court and racket impacts, and precipitation and environmental factors. As recent tennis research has focused on the new balls, there is a need to investigate other ball conditions present in the game of tennis. This thesis provides a structured investigation into the causes and effects of ball degradation, an objective assessment of the effects of degradation on ball performance, and incorporates subjective perceptions of all aesthetics and play properties noted by players. Particular attention is given to ball fuzziness. Excessive fuzziness can occur from manufacturing variability, court and racket interactions, and environmental conditions - though there is currently no standardised method to assess ball surface condition. An objective measure of ball fuzziness has been developed and used in the analysis of nearly 4000 individual ball images. The effects of court and racket impacts, precipitation, natural pressure loss, and repeated impacts have been analysed for their effects on ball degradation. An assessment of ball performance utilised ball impact and aerodynamic data to determine significant differences between balls and develop an improved ball trajectory model.
5
Solanky, S. S. "Controlled degradation of diene elastomers: photo-controlled degradation of natural rubber." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2002. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2807.
6
Polavarapu, Indira. "Optimal design of an accelerated degradation experiment with reciprocal Weibull degradation rate." [Tampa, Fla.] : University of South Florida, 2004. http://purl.fcla.edu/fcla/etd/SFE0000503.
7
Deneke, Carlus. "Theory of mRNA degradation." Phd thesis, Universität Potsdam, 2012. http://opus.kobv.de/ubp/volltexte/2012/6199/.
Abstract:
One of the central themes of biology is to understand how individual cells achieve a high fidelity in gene expression. Each cell needs to ensure accurate protein levels for its proper functioning and its capability to proliferate. Therefore, complex regulatory mechanisms have evolved in order to render the expression of each gene dependent on the expression level of (all) other genes. Regulation can occur at different stages within the framework of the central dogma of molecular biology. One very effective and relatively direct mechanism concerns the regulation of the stability of mRNAs. All organisms have evolved diverse and powerful mechanisms to achieve this. In order to better comprehend the regulation in living cells, biochemists have studied specific degradation mechanisms in detail. In addition to that, modern high-throughput techniques allow to obtain quantitative data on a global scale by parallel analysis of the decay patterns of many different mRNAs from different genes.
In previous studies, the interpretation of these mRNA decay experiments relied on a simple theoretical description based on an exponential decay. However, this does not account for the complexity of the responsible mechanisms and, as a consequence, the exponential decay is often not in agreement with the experimental decay patterns.
We have developed an improved and more general theory of mRNA degradation which provides a general framework of mRNA expression and allows describing specific degradation mechanisms. We have made an attempt to provide detailed models for the regulation in different organisms. In the yeast S. cerevisiae, different degradation pathways are known to compete and furthermore most of them rely on the biochemical modification of mRNA molecules. In bacteria such as E. coli, degradation proceeds primarily endonucleolytically, i.e. it is governed by the initial cleavage within the coding region. In addition, it is often coupled to the level of maturity and the size of the polysome of an mRNA. Both for S. cerevisiae and E. coli, our descriptions lead to a considerable improvement of the interpretation of experimental data. The general outcome is that the degradation of mRNA must be described by an age-dependent degradation rate, which can be interpreted as a consequence of molecular aging of mRNAs. Within our theory, we find adequate ways to address this much debated topic from a theoretical perspective.
The improvements of the understanding of mRNA degradation can be readily applied to further comprehend the mRNA expression under different internal or environmental conditions such as after the induction of transcription or stress application. Also, the role of mRNA decay can be assessed in the context of translation and protein synthesis.
The ultimate goal in understanding gene regulation mediated by mRNA stability will be to identify the relevance and biological function of different mechanisms. Once more quantitative data will become available, our description allows to elaborate the role of each mechanism by devising a suitable model.Ein zentrales Ziel der modernen Biologie ist es, ein umfassendes Verständnis der Genexpression zu erlangen. Die fundamentalen Prozesse sind im zentralen Dogma der Genexpression zusammengefasst: Die genetische Information wird von DNA in Boten-RNAs (mRNA) transkribiert und im Prozess der Translation von mRNA in Proteine übersetzt. Zum Erhalt ihrer Funktionalität und der Möglichkeit von Wachstum und Fortpflanzung muss in jeder Zelle und für jedes Gen die optimale Proteinkonzentration akkurat eingestellt werden. Hierzu hat jeder Organismus detaillierte Regulationsmechanismen entwickelt. Regulation kann auf allen Stufen der Genexpression erfolgen, insbesondere liefert der Abbau der mRNA-Moleküle einen effizienten und direkten Kontrollmechanismus. Daher sind in allen Lebewesen spezifische Mechanismen - die Degradationsmechanismen - entstanden, welche aktiv den Abbau befördern. Um ein besseres Verständnis von den zugrunde liegenden Prozessen zu erlangen, untersuchen Biochemiker die Degradationsmechanismen im Detail. Gleichzeitig erlauben moderne molekularbiologische Verfahren die simultane Bestimmung der Zerfallskurven von mRNA für alle untersuchten Gene einer Zelle. Aus theoretischer Perspektive wird der Zerfall der mRNA-Menge als exponentieller Zerfall mit konstanter Rate betrachtet. Diese Betrachtung dient der Interpretation der zugrunde liegenden Experimente, berücksichtigt aber nicht die fundierten Kenntnisse über die molekularen Mechanismen der Degradation. Zudem zeigen viele experimentelle Studien ein deutliches Abweichen von einem exponentiellen Zerfall. In der vorliegenden Doktorarbeit wird daher eine erweiterte theoretische Beschreibung für die Expression von mRNA-Molekülen eingeführt. Insbesondere lag der Schwerpunkt auf einer verbesserten Beschreibung des Prozesses der Degradation. Die Genexpression kann als ein stochastischer Prozess aufgefasst werden, in dem alle Einzelprozesse auf zufällig ablaufenden chemischen Reaktionen basieren. Die Beschreibung erfolgt daher im Rahmen von Methoden der stochastischen Modellierung. Die fundamentale Annahme besteht darin, dass jedes mRNA-Molekül eine zufällige Lebenszeit hat und diese Lebenszeit für jedes Gen durch eine statistische Lebenszeitverteilung gegeben ist. Ziel ist es nun, spezifische Lebenszeitverteilungen basierend auf den molekularen Degradationsmechanismen zu finden. In dieser Arbeit wurden theoretische Modelle für die Degradation in zwei verschiedenen Organismen entwickelt. Zum einen ist bekannt, dass in eukaryotischen Zellen wie dem Hefepilz S. cerevisiae mehrere Mechanismen zum Abbau der mRNA-Moleküle in Konkurrenz zueinander stehen. Zudem ist der Abbau durch mehrere geschwindigkeitsbestimmende biochemische Schritte charakterisiert. In der vorliegenden Arbeit wurden diese Feststellungen durch ein theoretisches Modell beschrieben. Eine Markow-Kette stellte sich als sehr erfolgreich heraus, um diese Komplexität in eine mathematisch-fassbare Form abzubilden. Zum anderen wird in Kolibakterien die Degradation überwiegend durch einen initialen Schnitt in der kodierenden Sequenz der mRNA eingeleitet. Des Weiteren gibt es komplexe Wechselwirkungen mit dem Prozess der Translation. Die dafür verantwortlichen Enzyme - die Ribosomen - schützen Teile der mRNA und vermindern dadurch deren Zerfall. In der vorliegenden Arbeit wurden diese Zusammenhänge im Rahmen eines weiteren spezifischen, theoretischen Modells untersucht. Beide Mechanismen konnten an experimentellen Daten verifiziert werden. Unter anderem konnten dadurch die Interpretation der Zerfallsexperimente deutlich verbessert und fundamentale Eigenschaften der mRNA-Moleküle bestimmt werden. Ein Vorteil der statistischen Herangehensweise in dieser Arbeit liegt darin, dass theoretische Konzepte für das molekulare Altern der mRNAs entwickelt werden konnten. Mit Hilfe dieser neuentwickelten Methode konnte gezeigt werden, dass sich die Komplexität der Abbaumechanismen in einem Alterungsprozess manifestiert. Dieser kann mit der Lebenserwartung von einzelnen mRNA-Molekülen beschrieben werden. In dieser Doktorarbeit wurde eine verallgemeinerte theoretische Beschreibung des Abbaus von mRNAMolek ülen entwickelt. Die zentrale Idee basiert auf der Verknüpfung von experimentellen Zerfallsmessungen mit den biochemischen Mechanismen der Degradation. In zukünftigen experimentellen Untersuchungen können die entwickelten Verfahren angewandt werden, um eine genauere Interpretation der Befunde zu ermöglichen. Insbesondere zeigt die Arbeit auf, wie verschiedene Hypothesen über den Degradationsmechanismus anhand eines geeigneten mathematischen Modells durch quantitative Experimente verifiziert oder falsifiziert werden können.
8
Viger, Marie-Élise. "Photoelectrochemical degradation of ciprofloxacin." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=92310.
Abstract:
Conventional wastewater treatment plants have been found to only partially degrade pharmaceuticals. As a result, antibiotics have been detected in the aquatic environment, causing an increase in bacteria resistance.In this research a photoelectrochemical reactor with a TiO2-RuO2 working electrode was built to study its possible application for the treatment of antibiotic-containing wastewaters. Ciprofloxacin was chosen as a model antibiotic.
Degradation of ciprofloxacin was carried out photocatalitically, electrochemically and photoelectrochemically. All three methods were successful in degrading the antibiotic. However, photoelectrochemical degradation was found to be significantly more efficient than the other two techniques due to a synergetic factor. For instance after one hour at a current of 0.4A for 1mM of ciprofloxacin, photoelectrochemical process degrades 56% while electrochemical and photocatalytic process only degrades 41% and 3% respectively.
Overall, it was demonstrated that photoelectrochemical degradation represents possibly a viable method for the treatment of antibiotic-containing industrial wastewaters.
Les produits pharmaceutiques sont seulement partiellement dégradés dans les centres de traitement des eaux usées. Des antibiotiques se retrouvent donc dans les ruisseaux et rivières. Leur présence cause une résistance grandissante des bactéries aux traitements antibiotiques.
Un réacteur photoélectrochimique avec une électrode RuO2-TiO2 fut construit pour déterminer s'il pouvait être utilisé pour le traitement des eaux usées contenant des antibiotiques. La ciprofloxacine fut choisie comme modèle antibiotique.
Les procédés photochimique, électrochimique et photoélectrochimique peuvent tous dégrader la ciprofloxacine. Le meilleur résultat est obtenu avec la dégradation photoélectrochimique grâce à un phénomène synergétique. Par exemple pour la dégradation d'une solution de 1mM de ciprofloxacine avec un courant de 0.4A, le procédé photoélectrochimique dégrade 56% tandis que les procédés électrochimique et photochimique dégradent respectivement 41% et 3%.
La dégradation photoélectrochimique s'avère donc prometteuse pour le traitement des eaux usées contenant des antibiotiques.
9
Wang, Chun-hung, and 王俊雄. "Land degradation in Wuzhou." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50704485.
10
Mason, Francis Gerard. "Bacterial degradation of thiocyanate." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282235.
11
Puttanlek, Chureerat. "Microbial degradation of dichlobenil." Thesis, University of Kent, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314268.
12
Auer, Nadja. "Fungal degradation of nitrocellulose." Thesis, University of Westminster, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251569.
13
Caswell, R. C. "Bacterial degradation of alginates." Thesis, Bucks New University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234705.
14
Seth-Smith, Helena Margaret Brabazon. "Microbial degradation of RDX." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619689.
15
Alberts, Johanna Francina. "Microbial degradation of mycotoxins." Thesis, Stellenbosch : Stellenbosch University, 2007. http://hdl.handle.net/10019.1/19429.
Abstract:
Dissertation (PhD)--University of Stellenbosch, 2007.ENGLISH ABSTRACT: Aflatoxins are mycotoxins predominantly produced by the filamentous fungi Aspergillus flavus and Aspergillus parasiticus. Aflatoxin B1 (AFB1), the most abundant aflatoxin, is highly mutagenic, toxic, carcinogenic and teratogenic to humans and animals and is particularly correlated with the incidence of hepatocellular carcinoma in parts of Africa, China and South East Asia. In this regard aflatoxin is classified as a type I human carcinogen by the International Agency for Research on Cancer. Furthermore, aflatoxin contamination of food and feed is responsible for extensive economic losses due to loss of crops and farm animals. In spite of regulations regarding acceptable levels of aflatoxin in food, aflatoxin contamination remains a serious worldwide problem, especially in developing countries where it occurs predominantly in dietary staples. Inactivation of aflatoxin by physical and chemical methods has not yet proved to be effective and economic. However, biological detoxification offers an attractive alternative for eliminating toxins as well as safe-guarding the desired quality of food and feed. In this study, the biological degradation of AFB1 by bacteria and fungi was investigated. Several bacteria, including Rhodococcus spp., as well as white rot fungi have the potential to degrade a wide range of polycyclic hydrocarbon compounds due to the large repertoire of enzymes they produce and therefore the ability of some of these microorganisms to degrade AFB1 was investigated. Effective degradation of AFB1 by intracellular extracts of Mycobacterium fluoranthenivorans sp. nov. DSM 44556T, Nocardia corynebacterioides DSM 20151 and N. corynebacterioides DSM 12676 was demonstrated. Furthermore, AFB1 was effectively degraded by liquid cultures as well as intra- and extracellular extracts of Rhodococcus erythropolis DSM 14303. Significant (P<0.001) reduction in AFB1 was observed following treatment with R. erythropolis extracellular extracts with only 33.20% residual AFB1 after 72 h. Results indicated that the degradation by R. erythropolis DSM 14303 is enzymatic and that the enzymes are constitutively produced. The degradation of AFB1 when treated with R. erythropolis DSM 14303 extracellular extract coincided with a total loss of mutagenicity. In addition, treatment of AFB1 with culture fractions containing recombinant 2,3-dihydroxybiphenyl dioxygenase, which was produced through extracellular expression of the bphC1 gene of R. erythropolis DSM 14303 in Escherichia coli BL21, resulted in significant (P<0.0001) degradation (49.32%) and reduced mutagenic potency (42.47%) of the molecule. Significant (P<0.0001-0.05) degradation of AFB1 was obtained following treatment with culture extracts containing laccase enzyme produced by white rot fungi (17.10- 76.00%), purified fungal laccase from Trametes versicolor (1 U/ml, 87.34%) as well as with recombinant laccase produced by Aspergillus niger (118 U/L, 55.00%). Furthermore, treatment of AFB1 with purified fungal laccase enzyme (1 U/ml) resulted in loss of the mutagenic potency of the molecule. The decrease in the fluorescence and mutagenic properties of AFB1 following treatment with the microbial preparations imply changes to the furofuran- and/or lactone rings of the molecule. The current study contributes towards developing genetic engineered microbial strains which could be applied as an important bio-control measure. Such strains could exhibit multifunctional technological properties including degradation of AFB1, to significantly improve the quality, safety and acceptability of food.
AFRIKAANSE OPSOMMING: Aflatoksiene is mikotoksiene wat hoofsaaklik deur die filamentagtige fungi, Aspergillus flavus en Aspergillus parasiticus geproduseer word. Die algemeenste aflatoksien, aflatoksien B1 (AFB1), is hoogs mutagenies, toksies, karsinogenies en teratogenies vir mense en diere. Veral in sekere dele van Afrika, China en Suid-Oos Asië bestaan daar `n korrelasie tussen aflatoksien en die voorkoms van hepatosellulêre karsinoom en gevolglik word aflatoksiene as `n tipe I menslike karsinogeen deur die Internasionale Agentskap vir Kankernavorsing geklassifiseer. Aflatoksien kontaminasie in voedsel het ook `n ekonomiese impak as gevolg van verlies aan landbougewasse en diere. Ten spyte van maatreëls betreffende die toelaatbare vlakke van aflatoksiene in voedel, is aflatoksien kontaminasie steeds `n groot probleem wêreldwyd, veral in ontwikkelende lande waar dit hoofsaaklik in stapelvoedsel voorkom. Huidiglik is die inaktivering van aflatoksiene deur fisiese en chemiese metodes nie effektief en ekonomies nie. Daarteenoor bied biologiese tegnieke `n gunstige opsie vir die eliminering van die toksiene, terwyl die organoleptiese eienskappe van die voedsel steeds behoue bly. Hierdie studie fokus op die biologiese afbraak van AFB1 deur bakterieë en fungi. Verskeie bakterieë, insluitend Rhodococcus spp., sowel as witvrot fungi produseer `n verskeidenheid ensieme wat hulle in staat stel om `n wye reeks polisikliese hidrokoolstofverbindings af te breek en gevolglik is afbraak van AFB1 deur sommige van hierdie mikroörganismes bestudeer. Effektiewe afbraak van AFB1 deur intrasellulêre ekstrakte van Mycobacterium fluoranthenivorans sp. nov. DSM 44556T, Nocardia corynebacterioides DSM 20151 en N. corynebacterioides DSM 12676 is aangetoon. AFB1 is ook effektief in vloeibare kulture sowel as intra- en ekstrasellulêre ekstrakte van Rhodococcus erythropolis DSM 14303 afgebreek. `n Beduidende (P<0.001) afbraak van AFB1 is waargeneem na behandeling met R. erythropolis DSM 14303 ekstrasellulêre ekstrakte, met slegs 33.20% oorblywende AFB1 na 72 h. Resultate het getoon dat die afbraak deur R. erythropolis DSM 14303 ensimaties is en dat die ensieme konstitutief geproduseer word. Afbraak van AFB1 deur R. erythropolis DSM 14303 het ook tot `n totale verlies aan mutagenisiteit gelei. Verder het behandeling van AFB1 met rekombinante 2,3-dihidroksiebifenieldioksiginase fraksies wat geproduseer is deur ekstrasellulêre uitdrukking van die bphC1 geen van R. erythropolis DSM 14303 in Escherichia coli BL21, beduidende (P<0.0001) afbraak (49.32%) en vermindering in mutagenisiteit (42.47%) van die molekuul teweeggebring. Beduidende (P<0.0001-0.05) afbraak van AFB1 is verkry na behandeling met witvrot fungus kultuurekstrakte wat lakkase-ensiem bevat (17.10-76.00%), gesuiwerde lakkase geproduseer deur Trametes versicolor (1 U/ml, 87.34%), sowel as rekombinante lakkase geproduseer deur Aspergillus niger (118 U/L, 55.00%). Verder het die behandeling van AFB1 met gesuiwerde lakkase-ensiem (1 U/ml) gelei tot verlies aan mutagenisiteit van AFB1. Die afname in fluoressensie en mutageniese eienskappe van die AFB1-molekuul na behandeling met die onderskeie mikrobiese preparate dui op struktuurveranderings aan die furofuraan- en/of laktoonringe van die molekuul. Hierdie studie lewer `n bydrae tot die ontwikkeling van geneties gemanipuleerde mikrobiese rasse wat as `n belangrike biokontrole kan dien. Sulke rasse met multifunksionele tegnologiese eienskappe, insluitend die afbraak van AFB1, kan die kwaliteit, veiligheid en aanvaarbaarheid van voedsel verbeter.
16
Shields, Andrew James. "Discharge degradation of mica." Thesis, Glasgow Caledonian University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370768.
17
Wilsby, Astrid. "Insight in cellulose degradation." Thesis, KTH, Fiber- och polymerteknologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-302670.
Abstract:
I strävan efter att minska textilindustrins omfattande miljöpåverkan utvecklas nya metoder för textilåtervinning. Idag återvinns bomullstyg av Renewcell på deras anläggning i Kristinehamn. Den återvunna produkten, Circulose®, är en dissolvingmassa som kan användas för att spinna nya viskosfibrer som man i sin tur kan använda för att göra nya kläder. Föreliggande arbete är en förstudie om möjligheten att optimera Renewcellls återvinningsprocess. Arbetet inkluderar en optimering av massaprocessen vilket resulterar i en mer effektiv process som minskar förbrukningen av processkemikalier.To reduce the extensive environmental impact of the textile industry, new methods for textile recycling are being developed. Today, cotton-based fabric is recycled by Renewcell at their facility in Kristinehamn. The recycled product, Circulose®, is a dissolving pulp that can be used to spin new viscose fibers, which in turn can be used to make new clothes. The present work is a feasibility study on the possibility of optimizing Renewcell's recycling process. The work includes an optimization of the pulp process, which results in a more efficient process with a reduced consumption of process chemicals.
18
Leong-Lim, Linda Wei Chin. "Degradation of penicillin sulphoxide." Thesis, University of Surrey, 1986. http://epubs.surrey.ac.uk/847636/.
Abstract:
The thesis describes three principle investigations of the alkaline and enzymic degradation of penicillin V beta-sulphoxide. (i) Penicillin V beta-sulphoxide was observed to undergo epimerisation at C-6 on treatment with mild aqueous base: the direct epimerisation of the sulphoxide has only previously been observed using esters in non-aqueous solutions. (ii) 3-phenoxyacetamido-1-phenoxyacetylpyrrole was isolated as an alkaline hydrolysis product of VSO: this appears to be the first reported example of the direct degradation of a penicillin derivative to a pyrrole. This compound was then synthesised and compared with the isolated product. (iii) Comparative studies of the degradation of penicillin V sulphoxide by beta-lactamase and alkali indicated the possible operation of different pathways: this contrasts with the corresponding degradations of penicillin V which were indistinguishable. These investigations are discussed in the context of earlier studies of beta-lactam degradation which are reviewed in an introductory chapter.
19
Holec, Sarah Gagliardi Dominique. "Polyadenylation and RNA degradation." Strasbourg : Université Louis Pasteur, 2008. http://eprints-scd-ulp.u-strasbg.fr:8080/987/01/HOLEC_Sarah_2008.pdf.
20
Wang, Haibo. "Hydroxyapatite degradation and biocompatibility." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1087238429.
Abstract:
Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xiv, 190 p.; also includes graphics. Includes bibliographical references (p. 166-190).
21
Allen, David Peter. "Photocatalytic degradation of atrazine." Thesis, University of Bath, 1995. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296324.
22
Purdy, K. R. "Aspects of chlorhexidine degradation." Thesis, University of Bath, 1987. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376334.
Abstract:
This thesis examines the factors affecting the stability of chlorhexidine salts (principally gluconate) in dilute aqueous solution (0.001 to O.05%w/v). Such studies are pertinent to the use of chlorhexidine as a preservative in aqueous pharmaceutical products. The introduction details the factors affecting the stability of pharmaceuticals in solution. Published work on the physico-chemical properties of chlorhexidine and structurally related compounds is then reviewed together with methods available for the quantitative analysis of chlorhexidine. The experimental section describes the evaluation of a HPLC stability indicating method for the quantitative determination of chlorhexidine in terms of sensitivity, precision, reproducibility and selectivity. Comparison is made between this method and the more conventional colorimetric methods based on the Holbrook technique and 4-chloroaniline determination. The degradation kinetics of dilute aqueous solutions of chlorhexidine gluconate have been examined by a pH-stat.ting technique. Over the range pH 2 to 10, 0.002% w/v chlorhexidine gluconate fohowed a pH of maximum stability around pH 5 (at 90°C) with regions uf specific acid/base catalysis presen~. Modifications attributable to a water catalysed reaction (pH 3.5 to 6.5) and presence of unionised chlorhexidine base (pH> 8.5) were also apparent. Concentration dependency was noted at both alkaline and neutral pH. Linear Arrhenius relationships were observed producing -1 apparent activation energies varying from 69.5 to 96.1 kJ.mol •Degradation rate dependence upon ionic strength was consistent with a negative salt effect in alkaline solution. Variable effects on rate were observed in the presence of buffers and with different types of surfactant. Limited studies indicated chlorhexidine solutions are photochemically stable at netural pH but are not amenable to y-irradiation sterilisation. Quantitative analysis of 4-chloroaniline has shown that this compound is not, as previous literature might suggest, the major degradation product of chlorhexidine. HPLC analysis indicates that up to six degradation products may occur. In the discussion an interpretation of kinetic data is presented. Qualitative information from chromatographic studies is used to support a proposed degradation pathway for chlorhexidine. Finally the kinetic data has been used to assess the stability of chlorhexidine to heat sterilisation processes and on long term storage.
23
Gallet, Guillaume. "From Fast to Slow Degradation : Different Strategies to Characterise Polymer Degradation by Chromatographic Techniques." Doctoral thesis, KTH, Polymer Technology, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3262.
24
Jones, Samantha. "Deconstructing the degradation debate : a study of land degradation in the Uluguru Mountains, Tanzania." Thesis, University of East Anglia, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338943.
25
Ning, Shuluo. "Bayesian Degradation Analysis Considering Competing Risks and Residual-Life Prediction for Two-Phase Degradation." Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1339559200.
26
Johansson, Erik. "Free radical mediated cellulose degradation." Doctoral thesis, KTH, Chemistry, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3477.
Abstract:
This thesis addresses the mechanisms involved in cellulosedegradation in general and Totally Chlorine Free (TCF) bleachingof pulp in particular. The thesis shows that the cellulosedegradation during high consistency ozone bleaching is explainedby free radical chain reactions.
By simulation, it has been shown that the number, weight andviscosity average of liner polymer chain length can be used tocalculate the number of random scissions in a linear polymer ofany molecular weight distribution, provided that there is acalibrated Mark-Houwink equation. A model describing partialdegradation of molecular weight distributions of linear polymersmeasured with viscometry was developed and verifiedexperimentally. The model predicts viscometric measurement ofchemical cellulose degradation by a rapidly reacting reagent tobe strongly dependent on cellulose accessibility.
The role of free radical reactions in cellulose degradationwas studied by varying the amount of ferrous ions and ozone addedto the cotton linters. The result was compared to the resultsobtained from cellulose of lower crystallinity (cellulose beads)by measuring average chain length. When a ferryl ion reacted withcotton linters in the presence of ozone, the very formation ofone glycosidic radical was more significant to degradation thanthe final step of forming one oxidised glycoside. The inefficientdegradation observed of the oxidation step is explainable by theamount of accessible glycosides being too small to influenceviscometry. The efficient degradation observed in associationwith the glycosidic radical formation is explained by initiationof free radical chain reactions that are propagated as long asthere is ozone in the system. As none of these phenomena werefound in the less crystalline cellulose, cellulose structureappears to be important for how free radical mediated cellulosedegradation develops.
The theory of free radical chain reactions coupled withdiffusion suggests a concentric expansion of the chain reactionsoutwards from the initial site of radical formation duringozonation of carbohydrates. This was confirmed by demonstratingfree radical chain reactions spreading from a spot of initiationoutwards during ozonation of a filter paper, using a pH-indicatorto monitor acid formation. Furthermore, the interior and exteriorof cellulose fibres doped with initiator were shown to bepermeated by small holes after ozonation.
Ethylene glycol was shown to improve the selectivity duringozone bleaching of oxygen bleached kraft pulp at pH 3. Optimalconditions were obtained at pH 3 for 25 wt% ethylene glycol. Theinfluence of ethylene glycol on selectivity is explained by aproportion of the free radical chain reactions being carried bythe ethylene glycol instead of the cellulose during ozonebleaching. The observations were summarised in the form of amodel where the observed degradations for pulp, bleached pulp andcotton fibres during both ozone bleaching and ethylene glycolassisted ozone bleaching were shown to agree with each other.
From g-irradiation of ozonised aqueous solutions of alcohol,the rate constant of superoxide formation from the peroxylradical of methanol was estimated to be 10 s-1. Rate constants of the reactions between ozone andalkylperoxyl radicals were determined to be around 104M-1s-1. The possibility of the reaction betweenalkylperoxyl radicals and ozone contributing significantly tofree radical chain reactions during ozonation of carbohydratesand alcohols could therefore be ruled out.
Cellulose, degradation, free radical, ozone, selectivity,ethylene glycol, alcohol, bleaching, kraft pulp, cotton linters,delignification, fibre, fibril, crystallinity, ferryl ion, freeradical chain reactions, TCF, viscometry, molecular weightdistributions, random scissions.
27
Zundel, Michael. "Ribosome Degradation in Escherichia coli." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_dissertations/152.
Abstract:
Upon termination of translation, the fate of ribosomes is determined largely by the rate at which cells are growing. During periods of exponential growth, ribosomes are rapidly recycled, translation is re-initiated, and the ribosomes are extremely stable. However, when nutrient sources become limiting, and ribosomes are not actively translating, they may become substrates for degradation. While this phenomenon is well known, details of how the process is initiated and what are the signals for degradation have, until now, remained elusive. Here, I present in vitro and in vivo data showing that free ribosome subunits are the targets of degradative enzymes, whereas 70S particles that remain associated are protected from such degradation. Conditions that increase the formation of subunits both in vitro and in vivo lead to enhanced degradation. Thus, the simple presence of free 50S and 30S subunits is sufficient to serve as the mechanism that initiates ribosome degradation. In order to identify RNases involved in ribosome degradation, both in vitro and in vivo assays were developed. Together, they have provided evidence for a multi-step degradation process involving both endo- and exoribonucleases. Examination of extracts from strains deficient in known RNases revealed that the endoribonucleases, RNase E and RNase G, may be involved in the initial cleavages. The resulting fragments, some of which are small enough oligoribonucleotides that they remain part of the acid-soluble fraction are degraded to mononucleotides primarily by the 3'-5' exoribonucleases, RNase R and polynucleotide phosphorylase.
28
Solano, Alvarez Wilberth. "Microstructural degradation of bearing steels." Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/249201.
Abstract:
The aim of the work presented in this thesis is to clarify one of the most fundamental aspects of fatigue damage in bearings steels through critical experiments, in particular whether damage in the form of cracks precedes hard “white-etching matter" formation, which is carbon supersaturated nanoscaled ferrite. Heat treatments have been designed to create four different crack types and distributions: scarce martensite plate cracks, fine grain boundary cracks, abundant martensite plate cracks, and surface cracks. Subsequent rolling contact fatigue experiments showed that the amount of hard white-etching matter is higher in pre-cracked samples compared to those without prior damage and that its formation mechanism is the frictional contact of disconnected surfaces within the bulk that elevate the temperature and localise deformation. These key experiments indicate that hard white-etching matter is the consequence, not the cause, of damage. Therefore, one way to avoid white-etching matter is by increasing the toughness of the material. The macroscopically homogenous distribution of microcracks proved also to be a useful rolling contact fatigue life enhancer due to damage deflection via crack branching and a powerful trap for diffusible hydrogen. Successful trapping was corroborated by the inability of hydrogen to cause crack propagation via embrittlement or accelerate white-etching matter generation during rolling contact fatigue. By also studying the behaviour of a nanostructured bainitic steel under rolling contact fatigue, it was found that its degradation mechanism is ductile void formation at bainitic ferrite/stress-induced martensite interfaces, followed by growth and coalescence into larger voids that lead to fracture along the direction of the softer phase as opposed to the conventional damage mechanism in 52100 steel of crack initiation at inclusions and propagation. Given the relevance of phase quantification in nanobainite and the possible surface artefacts introduced by preparation, alternative methods to X-ray diffraction such as magnetic measurements were also investigated. The lack of hard white-etching matter obtained in the carbide-free nanostructured bainite led to conclude that an alternative route to mitigate hard white-etching matter could be by eliminating pre-eutectoid carbides from the microstructure, therefore restricting their dissolution and ultimate carbon supersaturation of the mechanically deformed and homogenised nanoferrite.
29
Ayixiamuguli, Nueraimaiti. "Lignin degradation using lignolytic enzymes." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/35262/.
Abstract:
Lignin is the only plant biomass that contains aromatic groups in its structure and can provide a wide range of low molecular weight aromatic chemicals if its depolymerisation can be achieved successfully. Currently, lignin is mainly produced as a waste by-product by the paper and pulp industry and biorefineries. Therefore, the transformation of the phenolic-rich lignin into value added aromatic platform chemicals can be regarded of primary concern to improve the economic profitability of biorefining. Moreover, being a renewable resource, the consumption of fossil fuels will be reduced if lignin can be utilised efficiently. Between chemical degradation and enzymatic degradation, the latter could be a more sustainable method to break down lignin due to its enhanced substrate specificity and ability to preserve the aromatic ring structure compared with chemical processing. Therefore, laccase from Trametes versicolor (LTV), lignin peroxidase (LiP) and manganese peroxidase (MnP) were studied to determine the scope to depolymerise both water-soluble and insoluble lignins nder mild reaction conditions. The enzymatic activity and stability of all three enzymes was investigated and optimum assay conditions were achieved. LTV was found to be the most stable enzyme as it maintained 55 % of its activity at least for the first 6 h at 30 °C whereas LiP was deactivated after 2 h at 25 °C, and MnP was deactivated after 1 h at 28 °C. However, LTV stability decreased at higher temperatures during the oxidation of 2,2’-azino-bis (3- ethylbenthiazoline-6-sulphonic acid (ABTS)). One of the non-phenolic lignin model compounds, veratryl alcohol, was oxidised by LTV in the presence of ABTS, thus confirming the published data. The enzymatic degradation of Organosolv lignin (OSL) by LTV resulted in the formation of 2,6-dimethoxy-1,4-benzoquinone (DBQ). The OSL degradation by LTV was not improved by ethanol addition as a co-solvent although ethanol could stabilise LTV at 40 % (v/v). LTV catalysed the degradation of Kraft lignin although it indicated little effect on lignosulphonates. Lastly, the effect of varying the concentrations of 92 ionic liquids (ILs) and their equivalent metal salts on LTV activity was investigated to find a suitable co-solvent to improve the poor mass transfer in OSL degradation. The study showed that 62 ILs were laccase compatible at an IL concentration of 6 % (w/v) and more than 50 % laccase activity was retained in 18 ionic liquids up to 10 % (w/v), and 80 % (v/v) of dioctyl sulfosuccinate quaternary ammonium salt, [N4,4,4,4][AOT]. However, there was a progressive loss of activity when the concentrations of the ILs increased. Further study on the enzymatic degradation of ILs-pre-treated OSL is currently ongoing in our research group so that the decomposition of water-insoluble lignin will be understood more comprehensively.
30
Kay, Martin John. "Microbial degradation of polyester polyurethane." Thesis, University of Central Lancashire, 1992. http://clok.uclan.ac.uk/20311/.
Abstract:
During the course of these studies, polyester polyurethane foam has been found to be readily degraded in soil and marine environments. The incorporation of the formulation biocide Vinyzene E.P. reduced the rate and extent of degradation in test material exposed to soil conditions, but was found to be ineffective in preventing degradation when exposed to the marine environment. As a result of these studies, a number of fungi, representing a range of genera, have been isolated, identified, and shown using Kochian principles to degrade polyester polyurethane as a sole source of carbon. A list of isolates is submitted. In addition, a number of bacteria, hitherto unreported as deteriogens of polyester polyurethane, have been isolated and also shown, again using Kochian principles, to degrade polyester polyurethane. In order to effect degradation, the bacteria were found to require supplementation of the basal mineral salts medium with non-defined, complex sources of organic nitrogen, such as yeast extract. Chemical analysis of degraded test material, using FT-IR spectroscopy has provided evidence to suggest that the ester linkage of the polymer was hydrolysed during degradation by a bacterial isolate studied, resulting in marked reductions in the physical properties recorded. No degradation, either in terms of chemical composition or in the physical properties of the polymer was recorded where the test material was inoculated with this isolate in a mineral salts medium supplemented with glucose, suggesting that the enzymes involved in the degradation process were catabolically suppressed and therefore inducible. Extracellular esterase enzyme activity was detected in cellfree supernatants where the mineral salts medium was supplemented with yeast extract, but not in the case where glucose was used. However the addition of the test material did not enhance the level of esterase activity detected. Purification/concentration of these enzymes and characterisation studies using gel filtration chromatography, SDS-PAGE and PAGE were found to support these findings. The results of the present studies suggest that the test material was degraded by the bacterial isolate as a result of co-metabolism.
31
Van, Bouwelen Franciscus Maria. "Mechanically induced degradation of diamond." Thesis, University of Cambridge, 1996. https://www.repository.cam.ac.uk/handle/1810/251599.
32
Johansson, Erik E. "Free radical mediated cellulose degradation /." Stockholm : Department of Chemistry, Nuclear Chemistry, Royal Institute of Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3477.
33
Wedlake, Michael Douglas. "The thermal degradation of polynorbornene." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/9362.
34
Lahdou, Gilbert. "Microbial degradation of dibenzoate plasticizers." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=98983.
Abstract:
Earlier work with the dibenzoate plasticizers, di(propylene-glycol) dibenzoate (D(PG)DB) and di(ethylene-glycol) dibenzoate (D(EG)DB), had shown that one yeast could hydrolyze one of the ester bonds of these compounds resulting in an accumulation of the monoesters, di(propylene-glycol) monobenzoate or di(ethylene-glycol) monobenzoate, respectively. These monoesters exhibited an acute toxicity greater than that of the parent compounds and greater than the metabolites of the widely used phthalate and adipate plasticizers.In the present study, it was shown that the degradation of dibenzoate plasticizers is a common phenomenon among soil microorganisms. In most examples, the degradation was incomplete leading to the accumulation of the expected monoesters. However, the biodegradation of these monoesters was shown to be possible even if the rates of biodegradation were much slower than the rates of hydrolysis of the parent compounds. In addition, it was found that di(ethylene-glycol) monobenzoate was easier to biodegrade than di(propylene-glycol) monobenzoate. This difference was attributed to the methyl substituents on the di(propylene-glycol) monobenzoate. The very fast rates of degradation of simpler benzoate esters such as methyl and ethyl benzoate confirmed that steric effects could be important.
The rate of biodegradation of 1,6-hexanediol dibenzoate was much faster than that of either of the dibenzoate plasticizers. From this, it was hypothesized that the stability of the monoesters of the plasticizers was due to the presence of an ether function. It was also shown that the presence of the monoester of D(PG)DB was shown to increase the rate of hydrolysis of the parent di-ester. This was attributed to the ability of the monoester to enhance the bioavailability di-ester.
Collectively, these results do not support the use of dibenzoate plasticizers as environmentally friendly alternatives to phthalate and adipate plasticizers.
35
Evangelista, Sarah. "Microbial degradation of chlorophenoxy acids." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32352.
Abstract:
Clofibric acid, a pharmaceutical, and MCPP and MCPA, two herbicides, are structurally similar compounds. They are classified as chlorophenoxy acids and are found as organic contaminants in the aquatic environment. Their presence and fate in the environment has been of great concern. Microorganisms are ubiquitous in the environment and can play an important role in influencing the persistence of these contaminants because of their capacity to degrade them. Comparative biodegradation studies of the three compounds were performed using axenic cultures of bacteria. All microorganisms tested on clofibric acid were incapable of degrading it save for Rhodococcus rhodochrous which, instead of degrading it, transformed clofibric acid into its ethyl ester, ethyl clofibrate. MCPP and MCPA were degraded by Sphingomonas herbicidovorans at approximately the same rate, however, different metabolites were observed depending on the set of conditions used. More specifically, different biomass concentrations used in the experiments altered the emergence pattern of the metabolites seen during the degradation. Despite the fact that Sphingomonas herbicidovorans was capable of degrading MCPP and MCPA within a couple of days, results indicated that it was incapable of degrading clofibric acid under the same conditions. This suggests that the recalcitrance of clofibric acid is due to the additional methyl group adjacent to the ether bond.L'acide clofibrique, un produit pharmaceutique, le MCPP et le MCPA, deux herbicides, sont des composés similaires en structure. Ils font tous partie du groupe des acides chlorophénoxiques. La présence de ces contaminants organiques et leur sort dans l'environnement aquatique sont maintenant des sujets de préoccupations. Les microorganismes sont omniprésents dans l'environnement et jouent un grand rôle dans la possible dégradation de ces contaminants. La présente étude, portant sur leur biodégradation, a été menée avec des cultures pures. Tous les microorganismes testés furent incapables de dégrader l'acide clofibrique, à l'execption de la bactérie Rhodococcus rhodochrous qui menait à sa transformation en clofibrate, son ester éthylique. Le MCPP et le MCPA furent dégradés par la bactérie Sphingomonas herbicidovorans. Malgré le fait que leur taux de dégradation était similaires, les métabolites observés étaient différents selon le composé et les conditions employés. La concentration de biomasse employée pour débuter les expériences influençait les tendances d'apparition des métabolites. Malgré le fait que Sphingomonas herbicidovorans pouvait dégrader le MCPP et le MCPA en quelques jours, les résultats indiquent que ces bactéries sont incapables de degrader l'acide clofibrique dans les mêmes conditions. Cela suggère que la récalcitrance à la biodégradation de l'acide clofibrique est liée à la présence d'un groupe méthyle supplémentaire adjacent au lien éther.
36
Connell, Richenda K. "Tropospheric degradation of halogenated compounds." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320615.
37
Lin, Yao. "Control of DAPK-1 degradation." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/4189.
Abstract:
DAPK-1 is calcium-calmodulin regulated protein kinase involved in multiple cellular pathways including apoptosis, autophagy, cell survival and motility. The cytokine TNF-α has been reported to induce the degradation of DAPK-1. Here I identified the protease cathepsin B as a novel binding partner of DAPK-1 that protects DAPK-1 from TNF-α induced degradation. Using deletion mutants of DAPK-1, I mapped the cathepsin B binding domain on DAPK-1 to amino acids 836-947. Overexpression of this mini-protein DAPK-1(836-947) facilitated degradation of full-length DAPK-1 and apoptosis induced by TNFR-1. Moreover, siRNA mediated knock-down of DAPK-1 enhanced TNF-α induced apoptosis, confirming the role of DAPK-1 as a survival factor in the TNF-α signalling pathway. In addition, a splice variant of DAPK-1, which I have called s-DAPK-1, was discovered. s-DAPK-1 shares part of DAPK-1’s ankyrin repeats region and cytoskeletal binding domain, and possesses an unique tail region, which contains a cleavage site at its first two amino acids. Unlike DAPK-1, s-DAPK-1 does not contribute to apoptosis induced by high level of MEK/ERK signalling, but it does mimic DAPK-1’s function to induce membrane blebbing. The proteolytically processed form of s-DAPK-1 is more active in the induction of membrane blebbing, which may be due to its higher stability compared to that of full-length s-DAPK-1, suggesting that the tail region can control s-DAPK-1 stability and activity. Co-transfection of s-DAPK-1 and DAPK-1 leads to reduction in DAPK-1 expression level, suggesting a role for s-DAPK-1 to regulate DAPK-1 stability. The kinase domain of DAPK-1 is the region required for s-DAPK-1 to promote DAPK-1 degradation. Surprisingly, s-DAPK-1 does not bind directly to DAPK-1, suggesting that the interaction is indirect and mediated by as yet unidentified accessory proteins. Finally, the experiments with proteasome and lysosome inhibitors indicated that s-DAPK-1 induces DAPK-1 degradation via both lysosome and proteasome pathways.
38
Mohammadian, Mehrdad. "Environmental degradation of poly(ethyleneterephthalate)." Thesis, Manchester Metropolitan University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317574.
Abstract:
The degradation of amorphous and orientated PET is investigated by several analytical methods. In this study, samples of both amorphous and orientated PET material were exposed to wet and dry soil, various humidities and temperature as well as UV irradiation. Results of accelerated ageing studies indicate that the amorphous sheet and biaxially orientated bottles degrade mainly due to de-esterification and oxidative chain scission due to their low crystallinity. At high temperatures (70-90) breakdown, as characterisedb y viscosity and chain scission measurements,is indicative of significant polymer deterioration. Breakdown is enhanced by increasing temperature, increasing relative humidity and UV irradiation. In this regard the polyester bottles are more stable than sheet due to a greater degree of orientation and hence higher degree of crystallinity. However, the rate of degradation is also a function of the surrounding environment. During the course of degradation, an increase in crystallinity was observed for both sheet and bottles. The rate of increase in crystallinity is initially rapid and is associated with plasticization by moisture and subsequent annealing. The dry conditions and UV irradiation cause negligible increase in crystallinity . An increase in the number of end groups was observed which is due to chain scission. Whilst the carboxyl and hydroxyl end groups were increased at the same rate asthermally degraded samples, the increase of carboxyl end groups for UV degraded samples was significantly higher than hydroxyl end groups. This increase is initially sharp and then more gradual with almost the same rate as hydroxyl end groups. A higher level of carboxyl end groups is due to the release of carbon dioxide and carbon monoxide mainly on the surface of the polymer. In this work two methods were used to introduce stability to the polymer. The first was preconditioning the polymer in an inert atmosphere for 48 hours at 600C which had a better effect for bottles This stabilizing effect was observed for both thermal degradation and UV irradiation of polyester materials. The second method was stabilizing polyester against UV irradiation by the incorporation of naphthalenea nd benzophenoned erivatives to the structure of the polyester. In this case the dihydroxybenzophenone showed the greatest stabilizing effect. Hydroperoxide formation during hydrolytic degradation is found to be both temperature and humidity dependent and appears to play a secondary role in thermal oxidation.
39
Jenkins, Andrew Tobias Aveling. "Electrochemical studies of coating degradation." Thesis, University of Newcastle Upon Tyne, 1995. http://hdl.handle.net/10443/967.
Abstract:
The polymer coatings considered in this thesis work principally by creating a barrier, in order to prevent a corroding medium such as water and / or oxygen from contacting the surface of the underlying metal. Such coatings are subject to attack from the environment in which they are placed. This attack can lead to failure of the coating and corrosion of the underlying metal. In this thesis, three principle means of coating degradation, leading to subsequent corrosion of the substrate have been considered: Mechanical damage of the coating, the effect of ultra-violet light weathering and filiform corrosion. Electrochemical measurements have been made in order to attempt to quantify both the degree of coating breakdown and the extent of corrosion of the substrate. The principle method for measuring coating breakdown and substrate corrosion utilised in the work for this thesis was Electrochemical Impedance Spectroscopy (EIS). EIS, in principle, allows both changes in coating porosity resulting from coating breakdown, and the extent of corrosion of the substrate to be measured. The extent of delamination under polymer coatings on defects of different sizes and on different substrates has been measured. The effect of ultra-violet light weathering of polymer coatings was measured using EIS and correlated with measurements of light reflection of the coating. Filiform corrosion was induced on two different substrates, coated with various coatings. The effect of substrate and coating on filiform corrosion growth rate and mechanism has been considered.
40
Jones, Melainie Susan. "The degradation of building stone." Thesis, University of Manchester, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318264.
41
Colquhoun, K. O. "Microbial degradation of xenobiotics chemicals." Thesis, Nottingham Trent University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383652.
42
Stratford, Jane. "The microbial degradation of thiocyanate." Thesis, University of Kent, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240134.
43
Mitchell, Jean Ann. "Enhanced degradation of dicarboximide fungicides." Thesis, University of Newcastle Upon Tyne, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386698.
44
Kafienah, Wa'el Zaki. "Mechanisms of fibrillar collagen degradation." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286510.
45
Pedlar, Louise. "The microbial degradation of lignin." Thesis, University of York, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333707.
46
El-Turki, Adel Abdulrazag. "Environmental degradation of construction materials." Thesis, University of Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310656.
47
Gajdacsi, Attila. "High accuracy ultrasonic degradation monitoring." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/55164.
Abstract:
This thesis is concerned with maximising the precision of permanently installed ultrasonic time of flight sensors. Numerous sources of uncertainty affecting the measurement precision were considered and a measurement protocol was suggested to minimise variability. The repeatability that can be achieved with the described measurement protocol was verified in simulations and in laboratory corrosion experiments as well as various other experiments. One of the most significant and complex problems affecting the precision, inner wall surface roughness, was also investigated and a signal processing method was proposed to improve the accuracy of estimated wall thickness loss rates by an order of magnitude compared to standard methods. It was found that the error associated with temperature effects is the most significant among typical experimental sources of uncertainty (e.g. coherent noise and coupling stability). By implementing temperature compensation, it was shown in laboratory experiments that wall thickness can be estimated with a standard deviation of less than 20 nm when temperature is stable (within 0.1 C) using the signal processing protocol described in this thesis. In more realistic corrosion experiments, where temperature changes were of the order of 4 C), it was shown that a wall thickness loss of 1 micron can be detected reliably by applying the same measurement protocol. Another major issue affecting both accuracy and precision is changing inner wall surface morphology. Ultrasonic wave reflections from rough inner surfaces result in distorted signals. These distortions significantly affect the accuracy of wall thickness estimates. A new signal processing method, Adaptive Cross-Correlation (AXC), was described to mitigate the effects of such distortions. It was shown that AXC reduces measurement errors of wall thickness loss rates by an order of magnitude compared to standard signal processing methods so that mean wall loss can be accurately determined. When wall thickness loss is random and spatially uniform, 90% of wall thickness rates measured using AXC lie within 7.5 ± 18% of the actual slope. This means that with mean corrosion rates of 1 mm/year, the wall thickness estimate with AXC would be of the order of 0.75-1.1 mm/year. In addition, the feasibility of increasing the accuracy of wall thickness loss rate measurements even further was demonstrated using multiple sensors for measuring a single wall thickness loss rate. It was shown that measurement errors can be decreased to 30% of the variability of a single sensor. The main findings of this thesis have led to 1) a solid understanding of the numerous factors that affect accuracy and precision of wall thickness loss monitoring, 2) a robust signal acquisition protocol as well as 3) AXC, a post processing technique that improves the monitoring accuracy by an order of magnitude. This will benefit corrosion mitigation around the world, which is estimated to cost a developed nation in excess of 2-5% of its GDP. The presented techniques help to reduce response times to detect industrially actionable corrosion rates of 0.1 mm/year to a few days. They therefore help to minimise the risk of process fluid leakage and increase overall confidence in asset management.
48
Wong-Pascua, David Han Yen. "Kinetic studies of carotenoid degradation." Thesis, Durham University, 2017. http://etheses.dur.ac.uk/12389/.
Abstract:
Carotenoids are a diverse family of naturally occurring pigments that are produced by plants, photosynthetic bacteria and certain fungi. Their biological roles within these organisms include the quenching of reactive oxygen species, acting as accessory pigments in photosystems and the colouration of flowers and fruits. Although mammals do not produce carotenoids, they may be obtained through the diet. Numerous health benefits in humans have been found to be associated with carotenoid containing diets, such as the maintenance of cardiovascular health and protection against degenerative eye diseases. These discoveries have led to an interest in ways to increase the stability of carotenoids within foodstuffs. Contrary to the vast majority of studies involving carotenoids, the detergency industry is interested in finding solutions to decolourise carotenoid containing stains. Carotenoid stains are usually composed of oily hydrophobic soils that adhere strongly to fabrics and sequester away from water. Due to the difficulty in complete removal of carotenoid stain material from fabric and the strong colouration of carotenoids, the detergency industry has adopted the approach of making the stain less perceivable through bleaching rather than attempting to eliminate all stain material. Although processes involved in the oxidative degradation of carotenoids are well established and there are numerous investigations of carotenoid decomposition in foodstuffs, quantitative studies of factors influencing the bleaching of carotenoids under conditions relevant to an aqueous washing environment are scarce. We have performed a quantitative study of the effect of fatty acid, surfactant and pH on the bleaching of β-carotene in oil-in-water emulsions. Experiments were monitored using UV-Vis spectrophotometry and focussed on quantifying initial rates of oxidation of fatty acid (a process closely related to carotenoid oxidative degradation) and the bleaching of β-carotene. Linoleic acid was found to autoxidise faster at lower pH while the bleaching of β-carotene in the presence of linoleic acid was found to proceed more faster at neutral pH. Experiments were performed in the absence and presence of lipoxygenases (LOXs) from soybean. These enzymes promote the bleaching of carotenoids by accelerating the formation of hydroperoxide bleaching species from polyunsaturated fatty acids. LOXs are known to be relatively slow, however, a study in the literature has reported that a bleaching synergy exists between two isozymes, LOX1 and LOX3. The activities of LOX1 and LOX3 linoleic acid oxidation and β-carotene degradation were quantified and found to be pH and surfactant dependent. Combinations of these enzymes were used to quantified this synergy under a range of conditions. To complement bleaching experiments in microemulsion solutions, work was performed at P&G Newcastle to investigate factors influencing the bleaching of carotenoid stains on fabrics. Stain decolourisation was quantified by stain removal index (SRI) values obtained by DigiEye. The effect of concentration of linoleic acid and α-tocopherol (a powerful antioxidant) in stain material was found to show correlation with results obtained from solution bleaching experiments and confirmed that the majority of fatty acid dependent bleaching of carotenoids on fabric is reliant on a radical mechanism. A study of the effect of fabric type and treatment discovered that stain removal in the wash was more facile on hydrophilic fabric, however, bleaching of carotenoid stain material after the wash appeared to be faster on hydrophobic materials. In experiments monitoring the bleaching of carotenoid containing microemulsions in the presence of fabric, cotton and polycotton were found to strongly inhibit the bleaching process while polyester slowed the rate but not the extent of bleaching. A side project, involved the preliminary study of the hydrolysis of triethyloxonium tetrafluoroborate, a commercially available alkylating agent, usually restricted to use in dry organic solvents. Preliminary results showed a pH independent region from pH 2 to 10. A pH dependent region was discovered above pH 10, however, reactions proceeded too rapidly to quantify rate constants. Hydrolysis rate constants were also measured in 50% acetonitrile with rate constants almost identical to those in 100% water.
49
Blanchard, Roxann Russell. "Hydrogen degradation on InP HEMTs." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/80077.
Abstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (p. 125-133).
by Roxann Russell Blancard.
Ph.D.
50
Gornall, Tina. "Catalytic degradation of waste polymers." Thesis, University of Central Lancashire, 2011. http://clok.uclan.ac.uk/4886/.
Abstract:
Plastics have become an integral part of our lives. However, the disposal of plastic waste poses an enormous problem to society. An ideal solution would be to break down a polymer into its monomer, which could then be used as the building-blocks to recreate the polymer. Unfortunately, the majority of plastics do not degrade readily into their monomer units. Thermal degradation of polymers usually follows a radical mechanism (which is of high energy and requires high temperatures) and produces a large proportion of straight chain alkanes, which have low relative octane number (RON) and so cannot be used in internal combustion engines. However, a suitable catalyst can help to branch straight alkane chains and so give high RON fuels that can be blended into commercial fuels. An extensive thermogravimetric study of polymer-catalyst mixtures was undertaken and produced dramatic reductions in the onset temperature of degradation and significant changes in the activation energy, suggesting a change to a desirable Brønsted- or Lewis-acid catalysed degradation mechanism in many cases. For example, GC-MS analysis of low-density polyethylene (LDPE) degraded with Fulcat 435 clay showed the polymer forming a large number of C6-C7 single-branched alkanes of intermediate RON value. In comparison, degradation of LDPE in the presence of a ZSM-5 zeolite (280z) resulted in the production of a large aromatic content (41% of Total Mass at 450ºC) together with branched C6-C8 hydrocarbons (40%). This formation of a large proportion of high RON components from polyethylene and other polymers could move us one step closer to tackling the enormous problem of plastic waste disposal that the world faces today.