To see the other types of publications on this topic, follow the link: Degradation and stabilization of ruthenium.
Dissertations / Theses on the topic 'Degradation and stabilization of ruthenium'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 23 dissertations / theses for your research on the topic 'Degradation and stabilization of ruthenium.'
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
Ahmad, Rihan Ahmed Irfan. "A study on space structure attitude stabilization and actuator degradation." Thesis, University of Leicester, 2012. http://hdl.handle.net/2381/27909.
Full textAbstract:
This thesis first addresses an important topic concerning space structure control systems, namely, attitude stabilization and control, which is followed by a study on subsystem interactions of general Multi Input Multi Output (MIMO) systems for better performance and actuator fault tolerance. A novel and simple output feedback stabilization approach is proposed for a space structure system characterized with kinematics and dynamics. The approach globally, asymptotically stabilizes the plant and the closed-loop stability is proved using Lyapunov analysis. The simplicity and robustness of the designed controller are demonstrated by investigating the closed-loop response after reducing the degree of freedom in control structure. The stability of the closed-loop system is further analyzed and the performance is compared with two other robust control approaches. The study carries on to another space plant, a Large Space Telescope (LST). Its dynamic model which is fitted with reaction wheels initially developed by NASA is analyzed and the fully coupled dynamics are derived by taking into account the nonlinear coupling phenomena and other terms neglected in their original (NASA) form. The dynamics are combined with Quaternion based kinematics to form an intricate yet realistic LST attitude model. The attitude of the nonlinear LST model is stabilized using a state feedback controller and the LST model is shown to track a time varying attitude reference. Structure configuration is an imperative task in the design of MIMO control systems. In order to make use of interactions between multiple channels so that the system can deal with vulnerability due to actuator degradation, a novel interaction measure is proposed. It is defined as Relative Dependency Index (RDI) and is based on H∞ norms. Such a measurement is effective in understanding the influence of the jth input on the ith output of a system. RDI based guidelines are outlined for configuring a system towards coupling/decoupling. RDI is further extended to the Input Impact Index (i.i.i.) which helps in determining how much an actuator degradation would affect the output of a system. The validity of RDI and i.i.i. is illustrated by simulation results and tested on the linearized spacecraft attitude model presented in the former part of the thesis.
2
Kann, Yelena. "Chemiluminescence studies of degradation and stabilization of plasticized poly(vinyl chloride)." Thesis, University of Sussex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398359.
Full text
3
Pejaver, Satish K. "Kinetics in liposomal systems : drug stabilization ; synthesis and degradation of liposome prodrugs /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487323583620435.
Full text
4
Saveleva, Viktoriia. "Investigation of the anodes of PEM water electrolyzers by operando synchrotron-based photoemission spectroscopy." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAF002/document.
Full textAbstract:
Le développement de catalyseurs de la réaction de dégagement de l’oxygène (OER) pour les électrolyseurs à membrane échangeuse de protons (PEM) dépend de la compréhension du mécanisme de cette réaction. Cette thèse est consacrée à l'application de la spectroscopie d’émission de photoélectrons induits par rayons X (XPS) et de la spectroscopie de structure près du front d'absorption de rayons X (NEXAFS) operando sous une pression proche de l'ambiante (NAP) dans le but d’étudier les mécanismes de la réaction d’oxydation de l’eau sur des anodes à base d’iridium et de ruthénium et leurs dégradation dans les conditions de la réaction. Cette thèse montre les mécanismes différents de la réaction OER pour les anodes à base d’Ir et de Ru impliquant respectivement des transitions anioniques (formation d’espèce OI- électrophile) ou cationiques (formation des espèces de Ru avec l’état d'oxydation supérieur à IV) quelle que soit la nature (thermique ou électrochimique) des oxydesDevelopment of oxygen evolution reaction (OER) catalysts for proton exchange membrane water electrolysis technology depends on the understanding of the OER mechanism. This thesis is devoted to the application of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and near edge X-ray absorption fine structure (NEXAFS) techniques for operando investigation of the Ir, Ru - based anodes. For Ru-based systems, we observe the potential-induced irreversible transition of Ru (IV) from an anhydrous to a hydrated form, while the former is stabilized in the presence of Ir. Regarding single Ir-based anodes, the analysis of O K edge spectra reveals formation of electrophilic oxygen OI- as an OER intermediate. Higher stability of Ir catalysts supported on antimony-doped tin oxide (ATO) is related to their lower oxidation. This work demonstrates different OER mechanisms on Ir, Ru-based anodes involving anion and cation red-ox chemistry, correspondingly, regardless the oxide nature
5
Ko, Sae Bom. "Identification of active agents for tetrachloroethylene degradation in Portland cement slurry containing ferrous iron." Texas A&M University, 2003. http://hdl.handle.net/1969.1/3861.
Full textAbstract:
Fe(II)-based degradative solidification/stabilization (Fe(II)-DS/S) technology is
the modification of conventional solidification/stabilization (S/S). Inorganic pollutants
are immobilized by Fe(II)-DS/S while organic pollutants are destroyed. Experimental
studies were conducted to identify the active agents for Tetrachloroethylene (PCE)
degradation as well as the conditions that enhance the formation of the active agents in
the Fe(II)-DS/S system. PCE was chosen as a model chlorinated aliphatic hydrocarbon
in this study.
First, the conditions that lead to maximizing production of the active agents were
identified by measuring the ability of various chemical mixtures to degrade PCE. Results
showed that Fe(II), Fe(III), Ca, and Cl were the the important elements that affect
degradation activity. Elemental compositions of the mixtures and the conditions
affecting solid formation might be the important factors in determining how active solids
are formed. Second, instrumental analyses (XRD, SEM, SEM-EDS) were used to identify
minerals in chemical mixtures that have high activities. Results indicate that active
agents for PCE degradation in Portland cement slurries and in cement extracts might be
one of several AFm phases. However, systems without cement did not form the same
solids as those with cement or cement extract. Ferrous hydroxide was identified as a
major solid phase formed in systems without cement.
Finally, the effect of using different types of ordinary Portland cement (OPC) on
PCE degradation rate during Fe(II)-DS/S was examined and the solids were examined
by instrumental analyses (XRD, SEM, SEM-EDS). Four different OPC (Txi, Lehigh,
Quikrete, and Capitol) showed different PCE degradation behaviors. Pseudo first-order
kinetics was observed for Capitol and Txi OPC and second-order kinetics was observed
for Quikrete. In the case of Lehigh cement, pseudo first-order kinetics was observed in
cement slurry and second-order kinetics in cement extract. Calcium aluminum hydroxide
hydrates dominated solids made with Txi, Quikrete, and Lehigh cements and FriedelÂs
salt was the major phase found in solids made with Capitol cements. Fe tended to be
associated with hexagonal thin plate particles, which were supposed to be a LDH.
6
Hamati, Jida. "MuRF3 binds to the retromer subunit SNX5 inhibiting its MuRF2-mediated degradation and leading to its stabilization." Doctoral thesis, Humboldt-Universität zu Berlin, Lebenswissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17621.
Full textAbstract:
Die muskelspezifischen RING-Finger Ubiquitin E3 Ligasen MuRF1, MuRF2 und MuRF3 werden mit verschiedenen zellulären Prozessen in Verbindung gebracht. MuRF1 und MuRF3 beteiligen sich am Abbau mehrerer Muskelstrukturproteine über das Ubiquitin Proteasom System (UPS) und spielen somit eine wichtige Rolle bei der Aufrechterhaltung der Skelett- und Herzmuskelstruktur und -funktion. MuRF1 wurde als Atrophie-Marker identifiziert, da seine Expression während der Muskelatrophie ansteigt, und MuRF2 und MuRF3 wirken bei der Stabilisierung von Mikrotubuli und Differenzierung von Myozyten mit. Dennoch sind bisher viele Aspekte der Funktion von MuRF-Proteinen ungeklärt. Die Domänenstruktur der MuRF-Proteine zeigt mehrere hochkonservierte Domänen, die sich an Protein-Protein Interaktionen beteiligen. Die Identifizierung und Charakterisierung ihres Interaktoms ermöglicht ein besseres Verständnis ihrer Funktionen. Aus diesem Grund wurden quantitative massenspektrometrische Analysen durchgeführt, um neue Interaktionspartner und Substrate für MuRF1, 2 und 3 zu identifizieren. Sorting nexin 5 (SNX5), eine Untereinheit des Retromers in Säugetieren, wurde als Interaktionspartner von MuRF3 identifiziert. SNX5, das eine wichtige Rolle in subzellulären Transport-Signalwegen spielt, interagierte über seine BAR-Domäne mit MuRF3. SNX5 und MuRF3 co-lokalisierten und assoziierten mit vesikulären Strukturen des subzellulären Transport-Signalweges. SNX5 wurde außerdem als Substrat von MuRF2 identifiziert. MuRF2 band und ubiquitinierte SNX5 in vivo und vermittelte damit dessen Abbau über das UPS. MuRF3 stabilisierte SNX5 durch die Inhibierung dieses Abbaus. Somit konnten MuRF2 und MuRF3 mit einem in subzellulärem Transport aktiven Protein in Verbindung gebracht werden, das direkt mit Mikrotubuli assoziiert und funktionell von einem stabilen Mikrotubuli-Netzwerk abhängig ist. Dies legt eine mögliche regulatorische Rolle von MuRF2 und MuRF3 in Mikrotubuli-abhängigen subzellulären Transportwegen nahe.Muscle specific RING-Finger ubiquitin E3 ligases MuRF1, MuRF2 and MuRF3 have been implicated in several cellular functions. MuRF1 and MuRF3 have been shown to bind and degrade muscle contractile and structural proteins via the ubiquitin proteasome system (UPS), thus playing an important role in the maintenance of skeletal and cardiac muscle structure and function. MuRF1 is considered an atrophy marker since its expression increases during muscle atrophy. MuRF2 and MuRF3 are involved in myocyte differentiation and both bind to and stabilize microtubules. Nevertheless, many aspects of the functions of the MuRF-family are unknown. The domain structure of the MuRF family implicates several highly conserved domains involved in protein-protein interaction. Accordingly, one way to better understand the role of MuRF proteins in myocyte function and protein homeostasis is to identify and characterize their interactome. Therefore, quantitative mass spectrometric analysis was used to identify novel interaction partners and target proteins of MuRF1, 2 and 3. Sorting nexin 5 (SNX5), a mammalian retromer subunit which plays an important role in subcellular trafficking pathways, was identified as a novel interaction partner of MuRF3, with which it interacted via its Bin/Amphiphysin/Rvs (BAR)-domain. SNX5 and MuRF3 co-localized and associated with early endosomes, connecting the microtubule-binding MuRF3 to structures of subcellular trafficking pathway. SNX5 was also identified as a substrate of MuRF2, which interacted with and ubiquitinated SNX5 in vivo, mediating its degradation in a UPS-dependent manner. This MuRF2-mediated degradation was inhibited by MuRF3, which stabilized SNX5. Thus, MuRF2 and MuRF3 were linked to a subcellular trafficking protein, SNX5, which is directly associated with microtubules and functionally dependent on a stable microtubule network, suggesting a possible regulatory role of MuRF2 and MuRF3 in microtubule-dependent subcellular trafficking pathways.
7
Ndossi, Emanueli Mathayo [Verfasser]. "Composition, degradation and stabilization of soil organic matter along an elevation gradient of Mount Kilimanjaro / Emanueli Mathayo Ndossi." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/122410031X/34.
Full text
8
Salim, Md Wadud. "Deformation and degradation aspects of ballast and constitutive modelling under cyclic loading." Access electronically, 2004. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20050215.114659/index.html.
Full text
9
Herman, Stephanie. "Automatic detection of protein degradation markers in mass spectrometry imaging." Thesis, Uppsala universitet, Institutionen för biologisk grundutbildning, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-275072.
Full textAbstract:
Today we are collecting a large amount of tissue samples to store for future studies of different health conditions, in hopes that the focus in health care will shift from treatments to early detection and prevention, by the use of biomarkers. To make sure that the storing of tissue is done in a reliable way, where the molecular profile of the samples are preserved, we first need to characterise how these changes occur. In this thesis, data from mice brains were collected using MALDI imaging mass spectrometry (IMS) and an analysis pipeline for robust MALDI IMS data handling and evaluation was implemented. The finished pipeline contains two reduction algorithms, catching images with interesting intensity features, while taking the spatial information into account, along with a robust similarity measurement, for measuring the degree of co-localisation. It also includes a clustering algorithm built upon the similarity measurement and an amino acid mass comparer, iteratively generating combinations of amino acids for further mass comparisons with mass differences between cluster members. Availability: The source code is available at https://github.com/stephanieherman/thesis
10
Hamati, Jida Verfasser], Thomas [Gutachter] [Sommer, Jens [Gutachter] Fielitz, and Oliver [Gutachter] Daumke. "MuRF3 binds to the retromer subunit SNX5 inhibiting its MuRF2-mediated degradation and leading to its stabilization / Jida Hamati ; Gutachter: Thomas Sommer, Jens Fielitz, Oliver Daumke." Berlin : Lebenswissenschaftliche Fakultät, 2016. http://d-nb.info/1117638235/34.
Full text
11
Rumple, Amber C. "Sustainable chemistry solutions for industrial challenges: mechanisms of PVC degradation and stabilization; reversible ionic liquids for CO₂ capture; efficient Suzuki coupling of basic, nitrogen containing substrates." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53474.
Full textAbstract:
The thermal degradation of polyvinyl chloride (PVC) is a significant processing challenge which can lead to deleterious mechanical and optical properties in a wide range of products. Synergetic studies on PVC model compounds and blends of bulk PVC provide unique insights into the thermal degradation and stabilization pathways in the presence of common additives. Model PVC compounds were selected to replicate specific defects (e.g., allylic, vicinal and tertiary) and tacticity (i.e., utilizing stereochemistry to investigate tacticity) commonly found in PVC. Model studies were conducted neat (solvent-free) with metal carboxylates. Experimental results highlight that the allylic and tertiary defects are more reactive than pristine PVC and isotactic sites are more reactive than their syndiotactic counterparts. Zinc stearate was found to act not in the role of substituent, but as a Lewis acid by facilitating dehydrochlorination of labile chlorides. This prevents the accumulation of hydrogen chloride and autocatalytic chain unzipping. In contrast, calcium stearate delayed the formation of zinc chloride, a much stronger Lewis acid than zinc stearate, through an ion exchange process to form calcium chloride. Thermal weight loss studies using blends of bulk PVC proved critical in transferring mechanistic insights into the context of a polymeric matrix.
Post-combustion carbon capture has traditionally involved the use of aqueous alkanol amine solutions. The regeneration of such systems, however, can be costly and energy intensive. We have developed an alternative system utilizing silylated alkylamines to reversibly capture CO2 under near ambient conditions. The silyl amines developed capture CO2 through chemical reaction to form reversible ionic liquids (RevIL). RevILs utilize no added water and are tunable by molecular design allowing us to influence industrially relevant carbon capture properties such as viscosity, temperature of reversal, and enthalpy of regeneration, while maximizing overall CO2 capture capacity. We demonstrate a strong structure-property relationship among the silyl amines where minor structural modifications lead to significant changes in the bulk properties of the RevIL.
Amine containing substrates are important building blocks for a variety of biological and pharmaceutical compounds. However, application of the otherwise versatile Suzuki reaction to these substrates has proved challenging due to either ligation of the amine to the palladium or to electronic effects slowing the oxidative addition step. Conventional methods to overcome these challenges involve protection-deprotection strategies or the use of designer ligands to facilitate reaction. We have shown that application of CO2 pressure and adjusting the water content of the reaction system facilitate the Suzuki coupling of 4-amino-2-halopyridines in high yield with the simple Pd(TPP)2Cl2 catalyst. The protocol was expanded to 2-halopyridines. The results of these investigations will be discussed.
12
Hamati, Jida [Verfasser], Thomas [Gutachter] Sommer, Jens [Gutachter] Fielitz, and Oliver [Gutachter] Daumke. "MuRF3 binds to the retromer subunit SNX5 inhibiting its MuRF2-mediated degradation and leading to its stabilization / Jida Hamati ; Gutachter: Thomas Sommer, Jens Fielitz, Oliver Daumke." Berlin : Lebenswissenschaftliche Fakultät, 2016. http://d-nb.info/1117638235/34.
Full text
13
Campbell, Paul. "Utilising the solvation properties of ionic liquids in the size-controlled synthesis and stabilization of metal nanoparticles for catalysis in situ." Thesis, Lyon 1, 2010. http://www.theses.fr/2010LYO10212/document.
Full textAbstract:
Les liquides ioniques (LIs) à base d’imidazolium présentent une très grande organisation en réseaux 3D et sont constitués de microdomaines polaires et apolaires, dû à la présence des canaux ioniques et au regroupement des chaînes alkyles lipophiles. L’objectif de ce travail est d’utiliser leurs propriétés de solvatation, liées à cette organisation, pour générer et stabiliser in situ des nanoparticules métalliques (NPs) d’une taille contrôlée et prévisible. Cette approche a trouvé de nombreuses applications dans des domaines tels que la catalyse et la microélectronique. Le phénomène de croissance cristalline des NPs (ruthénium, nickel et tantale) générées in situ lors de la décomposition sous H2 des complexes organométalliques, est contrôlé i) par la taille des poches apolaires, dans lesquelles le complexe se dissout, ii) par les conditions expérimentales (température, agitation) et iii) par la nature du métal et du complexe précurseur. Le mécanisme de stabilisation des NPs, jusqu'alors mal compris, dépend du mécanisme de formation des NPs, qui pourrait entraîner la présence de ligands hydrures ou carbènes N-hétérocycliques (NHC) à leur surface. Cette présence a été démontrée par marquage isotopique et analysée en RMN ainsi qu’en spectrométrie de masse. Les LIs sont également des milieux intéressants en catalyse. Des études sur l’influence du LI sur l’activité des catalyseurs homogènes ont souligné l’importance cruciale des paramètres physico-chimiques des LIs, et particulièrement de la viscosité, qui intervient ainsi dans la loi cinétique. Enfin, une étude approfondie de l’effet de la taille des NPs sur l’activité catalytique et la sélectivité pour l’hydrogénation, réalisée en milieu LI, a confirmé l’importance du contrôle de la taille des NPs pour les applications catalytiquesImidazolium based ionic liquids (ILs) consist of a continuous 3-D network of ionic channels, coexisting with non polar domains created by the grouping of lipophilic alkyl chains, forming dispersed or continuous microphases. The aim of this work is to use the specific solvation properties of ILs, related to this 3-D organisation, to generate and stabilise in situ metal nanoparticles (NPs) of a controlled and predictable size. This approach has found application in fields such as catalysis and microelectronics. The phenomenon of crystal growth of NPs (ruthenium, nickel, tantalum) generated in situ in ILs from the decomposition of organometallic complexes under molecular hydrogen, is found not only to be controlled by i) the size of non-polar domains, in which the complexes dissolve, but also by ii) the experimental conditions (temperature, stirring) and iii) the nature of the metal and its precursor complex. The previously unexplained stabilisation mechanism of NPs in ILs is found to depend on the mechanism of formation of NPs, which may lead to the presence of either hydrides or N-heterocyclic carbenes (NHC) at their surface. These have both been evidenced through isotopic labelling experiments analysed by NMR and mass spectrometry. Another advantage of ILs is that they provide an interesting medium for catalytic reactions. Studies on the influence of the IL on the catalytic performance in homogeneous catalysis have highlighted the crucial importance of the physical-chemical parameters of ILs, in particular the viscosity, for which a term must be included in the kinetic rate law. Using these findings, a thorough investigation of the effect of the NP size on catalytic activity and selectivity in hydrogenation in ILs was undertaken, confirming the importance of controlling NP size for catalytic applications
14
Trifilieff, Sylvie. "Etude de la structure des fractions polaires de petroles (resines et asphaltenes) par degradations chimiques selectives." Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13026.
Full textAbstract:
Oxydation des asphaltenes de quatre petroles lourds avec du tetroxyde de ruthenium et identification des molecules d'acides formees par spectrometrie de masse. L'etude de la ou des fonction(s) acide(s) sur chaque produit, associee a une experience de simulation de maturation sur argile, a conduit a proposer un mecanisme d'incorporation de ces molecules dans les asphaltenes. Il s'agirait de reactions de type fridel-crafts, catalysees par la matrice minerale. L'etude de la structure des resines a ete etudiee par hydrogenolyse avec du nickel de raney et les molecules formees par chromatographie en phase gazeuse couplee a de la spectrometrie de masse
15
Nugroho, Robertus Wahyu Nayan. "Modification of polymeric particles via surface grafting for 3D scaffold design." Doctoral thesis, KTH, Polymerteknologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-174295.
Full textAbstract:
Surface modification techniques have played important roles in various aspects of modern technology. They have been employed to improve substrates by altering surface physicochemical properties. An ideal surface modifying technique would be a method that is applicable to any kind of materials prepared from a wide range of polymers and that can occur under mild reaction conditions. The work in this thesis has utilized four main concepts: I) the development of a ‘grafting-from’ technique by covalently growing polymer grafts from particle surfaces, II) the presence of steric and electrosteric forces due to long-range repulsive interactions between particles, III) a combined surface grafting and layer-by-layer approach to create polyelectrolyte multilayers (PEMs) on particle surfaces to fabricate strong and functional materials, and IV) the roles of hydrophilic polymer grafts and substrate geometry on surface degradation. A non-destructive surface grafting technique was developed and applied to polylactide (PLA) particle surfaces. Their successful modification was verified by observed changes to the surface chemistry, morphology and topography of the particles. To quantify the aggregation behavior of grafted and non-grafted particles, force interaction measurements were performed using colloidal probe atomic force microscopy (AFM). Long-range repulsive interactions were observed when symmetric systems, i.e., hydrophilic polymer grafts on two interacting surfaces, and asymmetric system were applied. Electrosteric forces were observed when the symmetric substrates interacted at pH 7.4. When PEMs were alternately assembled on the surface of poly(L-lactide) (PLLA) particles, the grafted surfaces played a dominated role in altering the surface chemistry and morphology of the particles. Three-dimensional scaffolds of surface grafted particle coated with PEMs demonstrated high mechanical performance that agreed well with the mechanical performance of cancellous bone. Nanomaterials were used to functionalize the scaffolds and further influence their physicochemical properties. For example, when magnetic nanoparticles were used to functionalize the scaffolds, a high electrical conductivity was imparted, which is important for bone tissue regeneration. Furthermore, the stability of the surface grafted particles was evaluated in phosphate buffered saline (PBS) solution. The nature of the hydrophilic polymer grafts and the geometry of the PLLA substrates played central roles in altering the surface properties of films and particles. After 10 days of PBS immersion, larger alterations in the surface morphology were observed on the film compared with microparticles grafted with poly(acrylic acid) (PAA). In contrast to the PAA-grafted substrates, the morphology of poly(acrylamide) (PAAm)-grafted substrates was not affected by PBS immersion. Additionally, PAAm-grafted microparticulate substrates encountered surface degradation more rapidly than PAAm-grafted film substrates.QC 20151002
16
Monin, Guillaume. "Stabilisation chimique des électrolytes polymères pour pile à combustible." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00728176.
Full textAbstract:
La dégradation accélérée des membranes conductrices protoniques en pile est en partie due à une oxydation induite par la production d'H2O2. Cette étude présente une stratégie originale de stabilisation chimique d'une matrice de sPEEK par l'inclusion de nano-charges stabilisantes. Quatre nano-charges ont été préparées par fonctionnalisation de nanoparticules de silice avec des fonctions chimiques organosoufrées (disulfure, tétrasulfure et thiourée). Un protocole spécifique de mise en forme des membranes hybrides a permis d'obtenir des composites présentant des propriétés mécaniques et une conductivité protonique compatibles avec l'application pile. Les fonctions polysulfures permettent de ralentir la dégradation de la matrice de sPEEK durant l'étape de mise en œuvre et d'augmenter sa conductivité au cours d'un vieillissement ex-situ (H2O2). En présence de fonctions tétrasulfures, la membrane sPEEK ne se dégrade pas durant un test de 1200h en OCV à 70°C et 100%HR.
17
Wilson, Gregory J. "Photocatalysis with a Heterosupramolecular Assembly." Queensland University of Technology, 2006. http://eprints.qut.edu.au/16290/.
Full textAbstract:
Supramolecular chemistry has asserted itself as a significant multidisciplinary field concerned with molecular effects afforded through non-covalent molecular interactions. The increased interest in the literature towards nanoscale devices, through modulation of molecular function, has seen the renaissance of supramolecular chemistry as function progresses from solution to surface. Heterosupramolecular chemistry follows the architectural principles of supramolecular chemistry and embraces both covalent and non-covalent interactions of condensed phase surfaces and molecular components. A modular approach to device architecture was applied as a novel method of performing photocatalysis under visible light illumination. The application of heterosupramolecular assembly to the design of photoelectrochemical cells capable of visible light induced charge separation allowed the study of interfacial processes by means of electrochemical observations. Preparation of a series of supramolecular components was undertaken as specific molecular species within a photochemical system. Starting from a synthesised bidentate ligand that incorporated an acidic functional group, 4,4'-bis(methyl)phosphonate-2,2'-bipyridine (dmpbpy) as its ethyl ester, was chelated to give the surface sensitisers, bis-(2,2'-bipyridine)-(4,4'-bis(methyl)phosphonato-2,2'-bipyridine)ruthenium(II) dichloride ([Ru(bpy)2(dmpbpy)]Cl2) and cis-bis-(4,4'-bis-(methyl)phosphonato-2,2'-bipyridine)(2,2'-bipyridine)ruthenium(II) dichloride ([Ru(dmpbpy)2(bpy)]Cl2). An electron relay moiety with an acidic functional group, 1-ethyl-1'-(2-phosphonoethyl)-4,4'-bipyridinium dichloride (EVP), was also prepared using a procedure developed by the candidate. The electronic properties of the prepared photosensitisers were examined by theoretical quantum chemical TD-DFT calculations on the molecular structures and singlet excitations were discussed in relation to experimental data. This identified that the lowest lying LUMO states were consistently occupied by 2,2'-bipyridine (bpy) and this was speculated to be a factor affecting quantum injection yields. The effect of microwave modification of colloidal TiO2 suspensions under extended periods of treatment was investigated. Nanoparticles of TiO2 were compared and contrast to similar convection hydrothermally treated TiO2 and a commercial titania product, namely Degussa P25, both of which are utilised in device fabrication. The investigation identified that extended periods of microwave hydrothermal treatment do not greatly enhance the crystallinity and primary grain size of TiO2. The heterosupramolecular assembly of a multi-component photochemical system was constructed from prepared molecular and condensed phase components. It was demonstrated that this device was capable of inducing a photochemical reaction in H2O under irradiation with > 420 nm in the absence of an organic electron donor. Interpretation of the photocurrents obtained from this assembly provided understanding of photochemical reactions under low light intensities. Optimised conditions for the photochemical reaction was determined to be pH = 5 and illumination yielded = 0.0036% with an apparent quantum yield (AQY) = 1.6%. Photocatalytic decomposition of organic compounds in a dye-sensitised photoelectrocatalytic cell was investigated for the complete mineralisation of EDTA into CO2, H2 and simple amines and interpreted through photocurrent observations. This was extended to a broad range of organic compounds of various solution concentrations as a simulated industrial waste stream. Photooxidation gave unique photocurrent-time profiles which identified two distinct interfacial processes by mathematical treatment of photocurrent transients with a kinetic model. Kinetic parameters were proposed as a factor for qualitative discrimination of the organic compounds. The implications of these results for heterogeneous catalysis were discussed and the formation of Host-Guest complexes as a method of molecular sensing and as specific photocatalytic receptors was proposed.
18
Lee, Lok Yan. "Study of the photodegradation and photostability of anti-cancer drugs in different media towards the development of both new actinometers and liquid formulations." Thesis, De Montfort University, 2016. http://hdl.handle.net/2086/12188.
Full textAbstract:
This study aims at tackling some of the problems often encountered in photostability testing and liquid formulation development. Three anti-cancer drugs will be employed as models; Dacarbazine (DBZ) has well established photostability issues, Axitinib (AXI) and Sunitinib (SUT) are two new drugs only commercially available in solid dosage forms. In ethanol, the photokinetics of these drugs were well described by the newly proposed Φ-order kinetic mathematical model. This has confirmed the photoreversible character of AXI and SUT’s and unimolecular photoreaction of DBZ’s photodegradations. Also, the Φ-order kinetics is proven to describe them better than the usually used classic thermal reaction orders. In aqueous solution, the drugs were found to undergo thermal and photochemical complex degradations, involving at least 3 photoproducts. A new photokinetic approach has been proposed in this work to solving and unravelling the attributes of such complex mechanisms. For the first time, the quantum yields (QY) of the three drugs were determined and found to increase with irradiation wavelength. SUT’s QY were comparable in ethanol and water (QY460 = 0.02), DBZ was found to be more photoefficient in water (QY330 = 0.04 and 0.1, respectively) and AXI in water (QY330 = 0.06 and 0.03). Φ-order kinetics’ potential for the development of reliable actinometers of the three drugs, without prior knowledge of unknown reaction parameters, has also been established. A general equation to describe the isotherm of a (Gn:Hm) guest-host multicomponent complex was proposed in this work to palliate the lack of a strategy for characterising nanosponge-drug complexes. It provides information on both stiochiometry and association constant of the complex. The results indicate that hydrophobic AXI forms a 1:0.8 complex, indicating the possibility of multiple association sites and/or different types of binding. The newly developed AXI/nanosponge liquid formulation has significantly increased solubility (5000-fold) and thermal stability. Furthermore, the photostability of DBZ and SUT were considerably improved by using a strategy based on light-absorption competitors. Their initial velocities reduced from 10 and 3 s-1 (respectively) to 1 and 0.13 s-1. The successful application of these methods to the model anti-cancer drugs has set out new approaches that might be found useful for future treatments of photodegradation data, development of drug-actinometers and liquid formulations of drugs.
19
Gao, Li. "On the oxidative degradation and stabilization of future jet fuels." 2005. http://etd1.library.duq.edu/theses/available/etd-07132005-154910/.
Full text
20
Santos, Raquel Miriam Barbosa dos. "Photo-oxidative degradation and stabilization of acrylonitrile-butadiene-styrene (ABS)." Doctoral thesis, 2013. http://hdl.handle.net/1822/23760.
Full textAbstract:
Tese de doutoramento
Ciência e Engenharia de Polímeros e CompósitosAcrylonitrile-butadiene-styrene (ABS) is a polymeric material used in many applications due to its outstanding properties and relative low cost for an engineering polymer. However, a common drawback of polymers with polydiene sequences, such as ABS, is their susceptibility to photo-oxidative degradation when exposed to ultraviolet (UV) radiation in the presence of oxygen. This work is dedicated to the study of the influence of weathering under natural and accelerated conditions on chemical structure and properties of ABS, aiming understands its degradation mechanism and enhancing its performance against UV radiation. Unstabilized and stabilized ABS samples obtained by extrusion were exposed to natural and accelerated weathering conditions. Natural exposure was carried out at Lisbon (Mediterranean climate) and accelerated weathering in a Xenotest 150S chamber. Chemical modifications of unstabilized ABS, evaluated by infrared spectroscopy with an ATR accessory, showed that under accelerated conditions the formation rate of photoproducts is higher than in natural weathering, although chain scission occurred mainly during natural exposure. During both types of weathering, optical, mechanical and rheological properties are considerable affected. Results obtained by DMA and spectrophotometry showed that titanium dioxide (TiO2) and carbon black (CB) have an important influence on photochemical stability of ABS exhibiting a protective effect against UV radiation, under accelerated conditions. The best results were achieved for ABS samples containing CB. Stabilized ABS samples with hindered amines light stabilizers and ultraviolet absorbers, primary and secondary antioxidants and a combination of both indicated that all stabilizers induced a decrease on the degradation rate of ABS during accelerated weathering experiments, although synergetic effects were achieved for samples containing physical mixtures of light and thermal stabilizers. The study of the interaction between light stabilizers, antioxidants and a combination of both with CB and TiO2 on the photostability of ABS reveled that while TiO2 efficiency is enhanced with the incorporation of light and thermal stabilizers, an antagonistic effects were found for pigmented-ABS samples with CB.
O Acrilonitrilo-butadieno-estireno (ABS) é um material polimérico utilizado numa ampla gama de aplicações devido às suas excelentes propriedades e baixo custo para um polímero de engenharia. Todavia, um dos problemas associados à utilização de polímeros contendo dieno, como o ABS, é a sua elevada suscetibilidade à degradação foto-oxidativa quando exposto à radiação ultravioleta (UV) na presença de oxigénio. Este trabalho é dedicado ao estudo da influência do envelhecimento sob condições naturais e aceleradas na estrutura química e propriedades do material, tendo como objetivo compreender o seu mecanismo de degradação e melhorar a sua estabilidade à radiação UV. Amostras de ABS, não estabilizadas e estabilizadas, obtidas por extrusão foram submetidas a envelhecimento natural e acelerado. As amostras foram expostas em ambiente natural na cidade de Lisboa (Clima Mediterrânico) e em ambiente acelerado numa câmara Xenotest 150S. Alterações químicas à superfície de amostras de ABS não estabilizado, avaliadas por espectroscopia de infravermelho com um acessório (ATR), mostraram que sob condições aceleradas a formação dos produtos de degradação é maior do que nas amostras submetidas a envelhecimento natural, embora a cisão da cadeia molecular ocorra preferencialmente sob condições naturais. O estudo realizado mostrou que o envelhecimento acelerado e natural de amostras de ABS têm uma importante influência sobre as suas propriedades óticas, mecânicas e reologicas. Resultados obtidos por DMA e espectrofotometria mostram que o dióxido de titânio (TiO2) e negro de fumo (CB) contribuem de forma significativa para uma maior estabilidade do material sob condições aceleradas, protegendo o material da radiação UV. Os melhores resultados foram obtidos para as amostras de ABS contendo negro de fumo Amostras de ABS estabilizadas com aminas estéricamente impedidas e absorvedores de UV, antioxidante primário e secundário e uma combinação entre ambos mostraram que embora os estabilizantes inibam o processo degradativo, embora efeitos sinergéticos foram alcançados para amostras de ABS contendo misturas físicas de estabilizantes à radiação e térmicos. O estudo das interações entre o TiO2 e CB com os sistemas de estabilização indicou que podem existir efeitos antagónicos e sinergéticos dependendo da estrutura molecular, das características químicas da superfície e, consequentemente, resultando em interações diferentes entre os materiais incorporados.
21
Trout, Bernhardt L. "Molecular Computations for the Stabilization of Therapeutic Proteins." 2003. http://hdl.handle.net/1721.1/3932.
Full textAbstract:
Molecular computations based on quantum mechanics and statistical mechanics have been applied to the understanding and quantification of processes leading to the degradation of therapeutic proteins. In particular, we focus on oxidation and aggregation. Specifically, two reactions, hydrogen transfer of hydrogen peroxide to form water oxide and the oxidation of dimethyl sulfide (DMS) by hydrogen peroxide to form dimethyl sulfoxide, were studied as models of these processes in general. Reaction barriers of the hydrogen transfer of H₂O₂ are in average of 10 kcal/mol or higher than the oxidation of DMS. Therefore, a two step oxidation mechanism in which the transfer of hydrogen atom occurs first to form water oxide and the transfer of oxygen to substrate occurs as the second step, is unlikely to be correct. Our proposed oxidation mechanism does not suggest a pH dependence of oxidation rate within a moderate range around neutral pH (i.e. under conditions in which hydronium and hydroxide ions do not participate directly in the reaction), and it agrees with experimental observations over moderate pH values. In the field of aggregation, we have developed a relatively simple approach for computing the change in chemical potential of a protein upon addition of an excipient (cosolute) to the protein solution. We have also developed a general approach to the design of excipients to prevent aggregation and are currently testing it experimentally.Singapore-MIT Alliance (SMA)
22
Ndossi, Emanueli Mathayo. "Composition, degradation and stabilization of soil organic matter along an elevation gradient of Mount Kilimanjaro." Doctoral thesis, 2019. http://hdl.handle.net/21.11130/00-1735-0000-0005-152F-0.
Full text
23
"A study of trail degradation along the Pat Sin Range, North New Territories, Hong Kong." Chinese University of Hong Kong, 1992. http://library.cuhk.edu.hk/record=b5887009.
Full textAbstract:
by Leung, Yu-fai.Thesis (M.Phil.)--Chinese University of Hong Kong, 1992.
Includes bibliographical references (leaves 167-178).
abstract --- p.ii
acknowledgements --- p.iv
table of contents --- p.vi
list of tables --- p.ix
list of figures --- p.xi
list of plates --- p.xiii
Chapter CHAPTER I --- introduction
the problem --- p.1
The Country Parks of Hong Kong --- p.1
Resource Impacts of Country-Park Recreation --- p.3
Trail Degradation --- p.4
objectives of the study --- p.5
scope of the study --- p.6
Chapter CHAPTER II --- literature review
introduction --- p.8
research approaches --- p.9
physical degradation on trails --- p.11
Compaction
Widening and Incision
Erosion --- p.16
FACTORS CONTRIBUTING TO TRAIL DEGRADATION --- p.17
Use Characteristics --- p.19
Environment --- p.20
RECREATION IMPACT STUDIES IN HONG KONG --- p.21
Chapter CHAPTER III --- study area
introduction --- p.24
the pat sin leng country park --- p.24
"Topography,Geology and Soils" --- p.25
Climate and Vegetation --- p.29
Recreational Use and Management --- p.31
the pat sin range trail --- p.35
Chapter CHAPTER IV --- research methodology
introduction --- p.41
research design --- p.41
hypotheses --- p.43
SAMPLING SCHEME --- p.44
VARIABLES INCLUDED IN THE STUDY --- p.46
FIELD MEASUREMENTS --- p.49
Degradation-Indicator Variables --- p.49
Site Condition Variables --- p.58
LABORATORY ANALYSIS --- p.63
DATA MANIPULATION AND ANALYSIS --- p.65
Chapter CHAPTER V --- SITE AND DEGRADATION CONDITION OF THE PAT SIN RANGE TRAIL
INTRODUCTION --- p.67
SITE CONDITION OF THE TRAIL --- p.67
Parent Material --- p.67
Topography --- p.72
TREAD SURFACE MATERIAL --- p.80
COMPACTION OF TRAIL TREAD --- p.82
MORPHOLOGY OF TRAIL TREAD --- p.90
Tread width --- p.91
Incision Depth --- p.94
Tread Cross-Section Area --- p.96
Multiple Treads --- p.96
Other Morphology Variables --- p.98
OVERALL EVALUATION --- p.98
Other Evidence of Degradation --- p.98
Summary Rating --- p.101
REMARKS --- p.106
Chapter CHAPTER VI --- ENVIRONMENTAL INFLUENCES ON TRAIL DEGRDATION
INTRODUCTION --- p.107
BRANCHING EFFECT OF TRAILS --- p.108
PARENT MATERIAL --- p.112
Parent Rock --- p.112
Soil Properties --- p.115
LOCATIONAL FACTORS --- p.120
Aspect --- p.120
Slope Steepness --- p.124
Trail Position on Slope --- p.136
OVERALL EVALUATION --- p.145
Chapter CHAPTER VII --- MANAGEMENT IMPLICATIONS
INTRODUCTION --- p.151
MANAGEMENT CONSIDERATIONS --- p.152
THE CASE OF PAT SIN RANGE TRAIL --- p.153
MONITORING TRAIL USE AND IMPACTS --- p.159
Chapter CHAPTER VIII --- CONCLUSION
SUMMARY OF FINDINGS --- p.162
LIMITATION OF THE STUDY --- p.164
SUGGESTIONS FOR FUTURE RESEARCH --- p.164
BIBLIOGRAPHY --- p.167
APPENDIX
DESCRIPTIONS OF SELECTED DEGRADED SITES --- p.179