Dissertations / Theses on the topic 'Degradation modes'
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Diangha, Maurice Nkinyam Boh. "Punching shear modes of failure in impacted reinforced concrete beams." Thesis, University of Sheffield, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245559.
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Ivo, Ponky [Verfasser], and Günther [Akademischer Betreuer] Tränkle. "AlGaN/GaN HEMTs Reliability: Degradation Modes and Analysis / Ponky Ivo. Betreuer: Günther Tränkle." Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2012. http://d-nb.info/1026768551/34.
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Luengo, Cristina. "Photo-oxidative degradation of mechanisms and modes of stabilisation in SEBS triblock copolymer." Thesis, Manchester Metropolitan University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407530.
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Trunova, Olena. "Effect of thermal and mechanical loadings on the degradation and failure modes of APS TBCs." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=982570570.
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Yousif, Kamil Mansoor. "Studies of degradation modes of molybdenum black coatings in relation to their use as solar selective absorbers." Thesis, Brunel University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333363.
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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.
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Lu, Jin 1959. "Degradation processes and related reliability models." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39952.
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Reliability characteristics of new devices are usually demonstrated by life testing. When lifetime data are sparse, as is often the case with highly reliable devices, expensive devices, and devices for which accelerated life testing is not feasible, reliability models that are based on a combination of degradation and lifetime data represent an important practical approach. This thesis presents reliability models based on the combination of degradation and lifetime data or degradation data alone, with and without the presence of covariates. Statistical inference methods associated with the models are also developed.The degradation process is assumed to follow a Wiener process. Failure is defined as the first passage of this process to a fixed barrier. The degradation data of a surviving item are described by a truncated Wiener process and lifetimes follow an inverse Gaussian distribution. Models are developed for three types of data structures that are often encountered in reliability studies, terminal point data (a combination of degradation and lifetime data) and mixed data (an extended case of terminal point data); conditional degradation data; and covariate data.
Maximum likelihood estimators (MLEs) are derived for the parameters of each model. Inferences about the parameters are based on asymptotic properties of the MLEs and on the likelihood ratio method. An analysis of deviance is presented and approximate pivotal quantities are derived for the drift and variance parameters. Predictive density functions for the lifetime and the future degradation level of either a surviving item or a new item are obtained using empirical Bayes methods. Case examples are given to illustrate the applications of the models.
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Zhang, Yu-Jiang. "An integrated rail track degradation model." Thesis, Queensland University of Technology, 2000. https://eprints.qut.edu.au/36110/7/36110_Digitised%20Thesis.pdf.
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There has been a worldwide trend to increase axle loads and train speeds. This means that railway track degradation will be accelerated, and track maintenance costs will
be increased significantly. There is a need to investigate the consequences of increasing traffic load. The aim of the research is to develop a model for the analysis of physical
degradation of railway tracks in response to changes in traffic parameters, especially increased axle loads and train speeds. This research has developed an integrated track degradation model (ITDM) by integrating several models into a comprehensive framework. Mechanistic
relationships for track degradation hav~ ?een used wherever possible in each of the models contained in ITDM. This overcc:mes the deficiency of the traditional statistical track models which rely heavily on historical degradation data, which is generally not available in many railway systems. In addition statistical models lack the flexibility of incorporating future changes in traffic patterns or maintenance practices. The research starts with reviewing railway track related studies both in Australia and overseas to develop a comprehensive understanding of track performance under various traffic conditions. Existing railway related models are then examined for
their suitability for track degradation analysis for Australian situations. The ITDM model is subsequently developed by modifying suitable existing models, and
developing new models where necessary. The ITDM model contains four interrelated submodels for rails, sleepers, ballast and subgrade, and track modulus. The rail submodel is for rail wear analysis and is developed from a theoretical concept. The sleeper submodel is for timber sleepers damage prediction. The submodel is developed by modifying and extending an existing model developed elsewhere. The submodel has also incorporated an analysis
for the likelihood of concrete sleeper cracking. The ballast and subgrade submodel is evolved from a concept developed in the USA. Substantial modifications and
improvements have been made. The track modulus submodel is developed from a conceptual method. Corrections for more global track conditions have been made. The integration of these submodels into one comprehensive package has enabled the interaction between individual track components to be taken into account. This is done by calculating wheel load distribution with time and updating track conditions
periodically in the process of track degradation simulation.
A Windows-based computer program ~ssociated with ITDM has also been developed. The program enables the user to carry out analysis of degradation of individual track components and to investigate the inter relationships between these
track components and their deterioration.
The successful implementation of this research has provided essential information for prediction of increased maintenance as a consequence of railway trackdegradation. The model, having been presented at various conferences and seminars, has attracted wide interest. It is anticipated that the model will be put into practical use among Australian railways, enabling track maintenance planning to be optimized and potentially saving Australian railway systems millions of dollars in operating costs.
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Harris, David Wayne. "A degradation analysis methodology for maintenance tasks." Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/24867.
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Bi, Wu. "PEM fuel cell catalyst degradation mechanism and mathematical modeling." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/29756.
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Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2008.Committee Chair: Fuller, Thomas; Committee Co-Chair: Deng, Yulin; Committee Member: Gallivan, Martha; Committee Member: Kohl, Paul; Committee Member: Singh, Preet. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Robertson, Jennifer E. "Thermal Degradation Studies of Polycarbonate." Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/27704.
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Polymeric materials are increasingly being used in diverse, very demanding applications. Either pre- or post- application environments may require exposures to conditions hostile to the polymer's integrity. Frequently, these demanding conditions result in degradation of the polymer and subsequent decreases in desirable properties. Clearly then, a methodology to predict important properties, such as Tg, molecular weight, and tensile strength, from knowledge of the environmental history of a polymeric-based specimen is beneficial.
The current study focuses on bisphenol A polycarbonate and tracks changes in the properties of this material as a function of the degree of degradation, t. For the purposes of the present research, the environmental effects have been limited to those associated with elevated temperature, although the methodology is general. This t parameter is a product of the kinetic rate constant, k, found from isothermal kinetics, and the time of degradation, t. Elucidation of t has been linked to measurement of the molecular weight distribution which in turn can be related to various properties to yield predictive relationships for these properties. Only the thermal history of the polymer and its initial properties are required for the model. This technique is not limited to a specific polymer or even to thermal degradation. As long as the kinetics of the process can be mathematically modeled, this approach should apply to a host of other situations, providing property prediction simply from knowledge of the material history.
The research seeks to better understand the thermal degradation of polycarbonate. Kinetics of the process was explored, and the chemical mechanisms were examined. A key part of the project was the determination of the molecular weights and molecular weight distributions at each level of degradation. Furthermore, mechanical stress-strain properties, glass transition temperatures, and melt viscosities were also measured. This information, together with the kinetic expressions, facilitated prediction of these types of material properties for a known thermal history.Ph. D.
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Fedeniuk, Ricky Wayne. "Oxytetracycline degradation in model meat processing systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ27404.pdf.
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Argyropoulos, Dimitris S. "Synthesis and degradation of model network polymers." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72032.
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Theoretical expressions essentially based on the Flory-Stockmayer statistics of gelation were experimentally examined for their applicability beyond the gel point. By studying the crosslinking process of a polyester network formed from 1,3,5-benzenetriacetic acid and 1,10-decamethylene glycol beyond the gel point, the validity of the expressions was quantitatively confirmed, and their limitations were delineated.On stepwise degradation of a similar network, increasingly large soluble fractions were obtained at each step, and their weight-average molecular weights increased as the degelation point was approached. The molecular weights and distributions of these fractions were in close quantitative agreement with theory, i.e., they represented a near-mirror image of the molecular weights of sol fractions obtained on crosslinking beyond the gel point. Similar results were obtained by degrading a network prepared by the random crosslinking of monodisperse primary chains of polystyrene.
Experimental support was thus obtained for treating random network degradation by reversing the statistics of the Flory-Stockmayer theory of gelation.
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Han, Xiaoxiao. "Degradation models for polyesters and their composites." Thesis, University of Leicester, 2011. http://hdl.handle.net/2381/10275.
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Intensive studies are being carried out to use devices made of bioresorbable polymers inside the human body to provide various temporary functions. Typical examples include scaffolds for tissue engineering, fixation screws for broken bones and drug-loaded matrices for controlled-release. The development is entirely based on trial and error. The degradation rate strongly depends on the shape and size of the devices, making it difficult to transfer experience from one device to another. The degradation time ranges from weeks to years; animal and ultimately human trials have to be carried out, making the trial and error approach time-consuming and expensive. The entire field would benefit enormously from mathematical models capable of predicting the degradation and property change of the devices. This PhD project will develop such models as following: a) A multi-scale model for degradation of bioresorbable polyesters was developed. Events that occur at the molecular scale are modelled at the molecular scale using the kinetic Monte Carlo schemes while events that occur at the device scale are modelled using macroscopic diffusion model. b) A phenomenological model for simultaneous crystallisation and biodegradation of biodegradable polymers was developed. This model completed the degradation theory developed by Wang et al. at University of Leicester. c) The model in (b) was improved and applied to the analysis of accelerated degradation data. Temperature effects were taking into account by using Arrhenius relations. d) A model for the biodegradation of composite materials made of polyesters and calcium phosphates was developed. A calcium phosphate effectiveness map is established to show the conditions under which incorporating calcium phosphates into polyesters is effective, saturated or ineffective. f) A phase field model was developed for drug release from a swelling Hydroxypropyl methylcellulose matrix. This model can be readily extended to full three dimensional problems.
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Heywood, Richard John. "The degradation models of cellulosic transformer insulation." Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/2129/.
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Cotton, Dale M. 1982. "Exploring issues for a cartilage degradation model." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32835.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references.
The primary goal of this work was to establish a model system wherein a controlled level of damage is induced to a sample of normal cartilage, such that damage and repair can be observed by the dGEMRIC method of MR imaging. Primarily this included the iterative design of a cartilage tissue holder and testing of its ability to approximate uniaxial diffusion, as well as observation of glycosaminoglycan degradation induced by ADAMTS using dGEMRIC and DMMB assays. The mean uniaxial degradation rate for 20nM ADAMTS was 0.17 mm/day ± 0.08 (1 [delta], n = 4). The shape of the diffusion front was mostly flat, with attributable factors such as vascular structures affecting the shape. These consistencies made ADAMTS an acceptable choice for a degradation agent in the model system. A final holder design was created that proved largely successful in limiting access of ADAMTS to a single surface, as demonstrated by the flat diffusion/degradation front. This led to a good approximation of uni-axial diffusion and fit well with simple mathematical models of diffusion and previously determined diffusivities of Gadolinium agents in cartilage. A model system using ADAMTS as a degradation agent and dGEMRIC methods of observation can now be implemented for exploration of cartilage's ability to repair itself.
by Dale M. Cotton.
S.B.
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Foch, Bethany J. (Bethany Joy). "Integrated degradation models for polymer matrix composites." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10520.
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Al-Haj, Ebrahem Mohammed. "Nonparametric accelerated degradation models in life-testing /." Search for this dissertation online, 2003. http://wwwlib.umi.com/cr/ksu/main.
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Geddes, Daniel J. "Alkaline degradation of amylose: a kinetic mode." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/5524.
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Ji, Yizhen. "Degradation Analysis for Heterogeneous Data Using Mixture Model." Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1363310469.
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Mason, Sharon Leeanne. "Polyphenolic degradation and turnover in model and natural systems." Thesis, University of Newcastle Upon Tyne, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.578291.
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Concerns for soil carbon stocks with increasing global temperature have recently been raised. Adopting a multidisciplinary, reductionist approach and investigating the degradation and turnover of individual compound classes is essential in order to gain a greater knowledge of soil carbon dynamics and address the issue of soils becoming sources of carbon dioxide rather than sinks. The second most abundant natural biopolymer on earth is lignin and therefore its contribution to soil organic matter (SOM) is significant. The physical recalcitrance of lignin, together with its stability in laboratory studies has led many to assume that its degradation in soils must be slow. However, recent findings suggest that it is more easily degraded than conventionally perceived. This thesis investigates the molecular mechanisms involved in the degradation and turnover of lignin in the model system and the natural environment, linking together the associated biological and geochemical changes. White rot fungi are the primary degraders of lignin, secreting a complex array of extracellular enzymes that result in an oxidative attack of the biopolymer. Laboratory based, time-dependent growth experiments were performed and investigated the key enzymatic changes associated with lignin breakdown by the white rot fungus Pleurotus ostreatus cultivated on wheat straw (Triticum aestivum [L.]), ash (Fraxinus excelsior [L]) and Sitka spruce (Picea sitchensis [Bong.] Carr). The corresponding geochemical changes to lignin structure were also analysed using on- line thermally assisted hydrolysis and methylation (THM) in the presence of tetramethylammonium hydroxide (TMAH). Fungal growth, enzyme activity and lignin breakdown were substrate dependent, with higher levels of enzyme activity, lignin oxidation and side chain cleavage in the angiosperm (wheat straw and ash) systems than the gymnosperm (Sitka spruce) system. Early peaks in manganese dependent peroxidase and laccase activity were followed by a more gradual increase in lignin oxidation and side chain cleavage. On-line thermally assisted hydrolysis and methylation (THM) in the presence of 13C_ labelled/unlabelled tetramethylammonium hydroxide (TMAH) was used to investigate the phenolic distributions and their quantitative changes in soils beneath a Sitka spruce afforested moorland, an unforested moorland and an unimproved lowland grassland. \3C-labelled TMAH was successfully employed to distinguish between lignin- and non-lignin- derived (particularly tannin) phenols. Afforestation had a significant effect on phenolic degradation dynamics in these peaty gley soils. The Sitka spruce afforested moorland recorded a change in input and land preparation either as a result of changing vegetation input or due to land preparation prior to planting. Changes to soil carbon stocks were also investigated in these three soils and afforestation appeared to result in the accumulation of organic carbon in mineral horizons.
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Emzivat, Yrvann. "Safety System Architecture for the Design of Dependable and Adaptable Autonomous Vehicles." Thesis, Ecole centrale de Nantes, 2018. http://www.theses.fr/2018ECDN0009.
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L’automatisation de la tâche de conduite s’inscrit dans un contexte de développement d’une mobilité durable. Il s’agit d’une solution prometteuse qui pourrait bien contribuer à la création de nouveaux moyens de transports sûrs et respectueux de l’environnement. Cependant, concevoir un véhicule autonome reste un défi majeur. C’est pour cette raison qu’il incombe aujourd’hui à l’utilisateur de reprendre le contrôle du véhicule à chaque fois que les circonstances s’y prêtent. Il semble pourtant peu judicieux de confier une telle responsabilité à un être humain dont l’implication dans la tâche de conduite est moindre. Les travaux menés dans le cadre de cette thèse portent sur la conception de véhicules autonomes agiles et sûrs. C’est plus précisément le développement d’un système capable de gérer de potentielles défaillances seul, d’élaborer des stratégies de repli par lui-même et de s’adapter à un environnement complexe qui est abordé iciDriving automation is often presented as a viable solution to the prevailing challenges of sustainable mobility. It has the potential to create a paradigm shift in transportation technology, by providing a medium for cleaner, safer and more efficient means of transportation, while providing a better user experience overall. However, designing a dependable Automated Driving System is a challenge in itself. Current systems lack common sense and have trouble behaving in a truly cautionary manner, which is why a fallback-ready user is expected to take over in the event of a performance-relevant system failure affecting the dynamic driving task. Yet it seems unwise to rely on human drivers to act as a safety net for the purpose of offsetting the lack of maturity of Automated Driving Systems, for automation changes their active involvement into a monitoring role and creates new challenges, such as complacency, automation dependency, lack of understanding and misuse. The work places emphasis on the design of dependable and adaptable Automated Driving Systems. In particular, the thesis addresses the problem of designing a new ADS primary subsystem, whose role it is to monitor the state of the ADS, supervise its actions and respond as needed to guarantee the safety of its occupants and of others
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Namor, Omar G. "Sorbic acid interaction with sulphur dioxide in model food systems." Thesis, University of Surrey, 1987. http://epubs.surrey.ac.uk/847780/.
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Sorbic acid and sulphur dioxide are often used together, as preservatives,in many foods. Sorbic acid is known to undergo degradation in aqueous solutions, and this degradation appears to be accelerated in the presence of sulphur dioxide. The interaction between sorbic acid and sulphur dioxide is the subject of this thesis. The work is subdivided into five chapters, as follows: The first chapter deals with the chemistry of sorbic acid acid and sulphur dioxide. The second chapter describes a study of the degradation products of sorbic acid, in aqueous systems, in the presence of sulphur dioxide and a possible mechanism for the occurrence of these products is proposed. Chapter three deals with the preparation and degradation of 6-[[13]C] sorbic acid in order to find evidence for, or against, the mechanism proposed in chapter two. It also gives details of syntheses attempted in order to obtain 6-[[13]C] sorbic acid. The interaction of sorbic acid and sulphur dioxide in real food systems is the subject of the fourth chapter. The food systems studied were mayonnaise, tomato puree, orange juice and cottage cheese. The effect of packaging on the rate of degradation of sorbic acid was also investigated. The final chapter deals with a microbiological study of two homologues of sorbic acid, 2,4-heptadienoic acid, 2,4-octadienoic acid. The fungicidal activity of these two compounds, towards selected fungi, was analysed. 4-0xobut-2-enoic acid, a degradation product of sorbic acid in aqueous systems, was also analysed as a possible fungistat.
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Raghunathan, Uppili Srinivasan. "TCAD modeling of mixed-mode degradation in SiGe HBTs." Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54315.
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Barkhau, Robert A. "The preparation, characterization, and condensation reactions of polymer-supported lignin models." Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/5643.
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Orifici, Adrian Cirino, and adrian orifici@student rmit edu au. "Degradation Models for the Collapse Analysis of Composite Aerospace Structures." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080619.090039.
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Lawrence, Bryce T. "Recreation related degradation in Kansas state parks : applying GIS models." Thesis, Manhattan, Kan. : Kansas State University, 2005. http://hdl.handle.net/2097/74.
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Masiulaitytė, Inga. "Regression and degradation models in reliability theory and survival analysis." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2010. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20100527_134956-15325.
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In doctoral thesis redundant systems and degradation models are considered. To ensure high reliability of important elements of the system, the stand-by units can be used. These units are commuted and operate instead of the main failed unit. The stand-by units can function in the different conditions: “hot”, “cold” or “warm” reserving. In the thesis systems with “warm” stand-by units are analyzed. Hypotheses of smooth commuting are formulated and goodness-of-fit tests for these hypotheses are constructed. Nonparametric and parametric point and interval estimation procedures are given. Modeling and statistical estimation of reliability of systems from failure time and degradation data are considered.Daktaro disertacijos tyrimo objektai yra rezervuotos sistemos ir degradaciniai modeliai. Norint užtikrinti svarbių sistemos elementų aukštą patikimumą, naudojami jų rezerviniai elementai, kurie gali būti įjungiami sugedus šiems pagrindiniams elementams. Rezerviniai elementai gali funkcionuoti skirtinguose režimuose: „karštame“, „šaltame“ arba „šiltame“. Disertacijoje yra nagrinėjamos sistemos su „šiltai“ rezervuotais elementais. Darbe suformuluojama rezervinio elemento „sklandaus įjungimo“ hipotezė ir konstruojami statistiniai kriterijai šiai hipotezei tikrinti. Nagrinėjami neparametrinio ir parametrinio taškinio bei intervalinio vertinimo uždaviniai. Disertacijoje nagrinėjami pakankamai bendri degradacijos modeliai, kurie aprašo elementų gedimų intensyvumą kaip funkciją kiek naudojamų apkrovų, tiek ir degradacijos lygio, kuri savo ruožtu modeliuojama naudojant stochastinius procesus.
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Makris, Dimitrios. "Non-enzymic and enzymic degradation of flavonols in model systems." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246805.
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Östling, Erik. "Model on degradation of PEM fuel cells in marine applications." Thesis, KTH, Kemiteknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-299446.
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Sjöfarten står för 3 % av världens totala växthusgaser och är idag högst beroende av fossila bränslen. Ett alternativ för att gå över till en fossilfri flotta är användning av bränsleceller och vätgas som drivmedel. Om vätgasen produceras från elektrolys med förnyelsebara energikällor så är driften utsläppsfri och koldioxidneutral. Bränsleceller kan användas i många olika sammanhang, men har ännu inte slagit igenom med full kraft. En anledning till detta är livslängden som är för kort. För att sjöfarten ska kunna implementera bränslecellsdrift behöver nedbrytningen av bränslecellen bli vidare utforskad och motverkad. Syftet med detta examensarbete var att hitta de mest signifikanta nedbrytningsmekanismerna för sjöfarten samt att bygga en modell för att förutspå livslängden utifrån lastprofiler från fartyg. Rapportens avgränsningar var att enbart studera PEM-bränsleceller tack vare dess höga energitäthet och att teknologin är närmast marknaden för mobila applikationer. En litteraturstudie genomfördes för att fastställa de viktigaste nedbrytningsmekanismerna samt de faktorer som begränsar livslängden. Dessa bestämdes till start/stop cykler samt lastcykler vilka försämrar konduktiviteten i membranet samt minskar den elektrokemiska ytarean. En empirisk modell från experiment från litteraturen etablerades för att hitta relationen mellan parametrarna konduktivitet och elektrokemisk ytarea som funktion av start/stop cykler respektive lastcykler. En Comsol-modell användes för att utvärdera bränslecellens prestanda med dessa försämrade parametrar. Två lastprofiler analyserades och tolkades som antal start/stop cykler samt lastcykler för att utvärdera prestandan som funktion av antal år i drift. Båda fallen var i drift till dess att prestandan minskat med 20 % utvärderat vid strömtätheten 0.6 A/cm2. Båda lastprofilerna var utvärdera med olika körstrategier för att jämföra den modellerade livslängden beroende på ingångsvärden. Den första lastprofilen delades in i Case 1a och Case 1b där antalet start/stop cykler och lastcykler varierade. Resultatet visade att antalet timmar i drift mer än tredubblades i Case 1b där båda ingående indata hade minskats. Case 2 delades upp i tre olika körstrategier där Case 2a var en referens som jämfördes mot Case 2b respektive Case 2c. Skillnaden mot Case 2b var att antalet start/stop cykler per dag multiplicerades med faktor 4. Resultatet från modellen var att livstiden minskade från 6 till 4 år. Vidare utvärderades Case 2c där istället antalet lastcykler dividerades med faktor 4, allt annat identiskt med Case 2a. Utfallet var en ökad livslängd från 6 år till 11 år, med totalt 32 032 timmar i drift. Denna livslängd kan jämföras med kommersialiserade marina produkter från Ballard och Powercell, där livslängden är 30 000 respektive 20 000 timmar i drift. Sammanfattningsvis kan det konstateras att både start/stop cykler och lastcykler bryter ner bränslecellen och därmed minskar dess prestanda. Lastcykler var den faktor som var mest förödande gällande livslängden. Den modellerade livslängden på 32 032 timmar indikerar att den empirisk modellen tillsammans med Comsol-modellen genererade realistiska resultat. Slutligen kan sägas att ett område för framtida forskning inom ämnet innefattar lastcykler eftersom denna hade störst påverkan på modellen. Att särskilja olika typer av lastcykler och koppla till olika degradering skulle skapa än mer förståelse för livslängden. Då denna studie genomfördes på bränslecellsnivå skulle framtida studier kunna inkludera att analysera degradering på systemnivå för att få mer insikt i dessa processer.The shipping industry emits 3 % of the global GHG-emissions and is highly dependent on fossil fuels. One alternative to decarbonise the sector is by utilising hydrogen in fuel cells. The propulsion is free from emissions if hydrogen is produced from renewables. The fuel cell technology can be applied in various applications but have not been fully commercialised. One of the biggest bottlenecks for fuel cell technology is the durability that needs to be improved. In order for marine vessels to implement hydrogen propulsion, the degradation need to be further understood and mitigated. The purpose of this thesis was to assess the most significant degradation mechanisms for marine applications and to build a model to evaluate the lifetime depending on load profiles. The scope of the thesis was to include PEMFCs since they have the highest power density and are closest to commercialisation for transport applications. A literature review was conducted to assess the most important degradation mechanisms and operating conditions that limits the lifetime, which concluded in start/stop cycling and load cycling. These conditions deteriorate the membrane conductivity and the electrochemical surface area. An empirical model based on experimental data from the literature was conducted to find relationships for conductivity and ECSA as function of start/stop cycling and load cycling, respectively. A Comsol model was established to evaluate performance reduction with degraded parameters. Two different load cycles were interpreted as number of start/stop cycles and load cycles in order to simulate the degradation. The output was polarization curves as function of operating years. Each case was operated until a performance reduction of 20 % was obtained at the current density of 0.6 A/cm2. Both load profiles were analysed with different operation strategies to compare the resulting lifetime. The first load curve was divided into Case 1a and Case 1b where start/stop cycles and load cycles were altered. The results showed that the lifetime in operation hours was more than three-folded in Case 1b when the number of start/stop cycles and load cycles was reduced. Case 2 was divided into three operating strategies. For comparison with Case 2a, the number of start/stop cycles per day in Case 2b was increased by a factor of 4. The result was that the lifetime declined from 6 to 4 years. Furthermore, Case 2c evaluated the lifetime if the number of load cycles per day decreased by a factor of 4, all else being equal to Case 2a. The outcome was an increment in lifetime from 6 to 11 years, with a total of 32 032 hours of operation. This lifetime can be compared to commercialised products from Ballard and Powercell with lifetimes of 30 000 and 20 000 operating hours, respectively. Conclusively, the simulations showed that both start/stop cycling and load cycling deteriorates the fuel cell performance. Load cycling is the operating condition that cause the most severe degradation. Moreover, the modelled lifetime of 32 032 hours indicates that the empirical model in combination with the Comsol model generate realistic lifetimes. Finally, since load cycling had the most vital impact on the lifetime, one of the topics for future research would be to distinguish different types of load cycles and connect to separate degradation outcomes. Since the model was on fuel cell level, future work could also include systems effects such as ripple current or distributions within fuel cell stacks.
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Kawai, Shingo. "DEGRADATION MECHANISMS OF LIGNIN SUBSTRUCTURE MODEL COMPOUNDS BY CORIOLUS VERSICOLOR." Kyoto University, 1989. http://hdl.handle.net/2433/78223.
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Lima, Camila Santos de Figueiredo. "Do Cabeço ao Saramém : um ensaio sobre degradação ambiental e economia da produção social em um município do baixo São Francisco sergipano." Universidade Federal de Sergipe, 2016. https://ri.ufs.br/handle/riufs/5931.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESThis work is the result of reflections on the conditions that shape, in modernity, the relationship of contemporary man and his environment. In a city in the Lower São Francisco Sergipe, a place used for socio-cultural analysis which handles this dissertation, where emphasizes the environment as the scene of disputes and transformation of this area, involving the power of capital over the domination of nature and the human resources that are allocated there. We're talking about the New Housing Complex Saramém in the municipality of Brejo Grande, Sergipe, which has its formation a decade and a half and stood on a tragic event occurred at the end of the 90s in the twentieth century: the old-sea invasion island Cabeço, in the same municipality, causing the Saramém were territory for its homeless. This work is concerned by sketching constituent elements of sociability and ways of life in Cabeço Island, Brejo Grande / SE, in relation to the ways of life and production material and symbolic present in the XXI century in Saramém set in the same city, under the sign of the capitalist promise of "development, progress and quality of life." This dissertation is the result of a work based on ethnographic practice, not only the author but also by some co-authors who conducted their research on site and are here, enriching the reflections and adding information to this work. Ethnomethodological of inspiration, lays bare the marks of these ideologies in discourses illuminating the daily practices in the region and revealing the distortions between the logic of capital and the logic of beiradeiro (Golobi, s / d). Also counts with the immeasurable help of recently produced custom expert's report of the Federal Court of the state of Sergipe, which aimed to clarify critical points in lawsuit filed by the Association of Village Cabeço in Brejo Grande, against the Hydroelectric Company San Francisco (Chesf), on the grounds that the installation of the Xingó Hydroelectric power plant would have drastically affected the natural flow of the river, causing the water of the power loss of this at the expense of the strength of the sea that lies at the mouth of the river where is located the island of Cabeço. In addition to the veracity of this claim, we will put into question the domination that these actions, transformation and commercialization of natural and human resources by man eventually mold into sociabilities levels in times of strong appeal to capital.
Este trabalho é fruto de reflexões acerca das condições que moldam, na modernidade, as relações do homem contemporâneo com o seu meio. Em um município do Baixo São Francisco sergipano, um lugar serve para a análise sócio-cultural da qual se encarrega esta dissertação, onde se privilegia o meio ambiente como palco de disputas e transformações deste espaço, que envolvem a força do capital sobre a dominação da natureza e dos recursos humanos que lá se alocam. Estamos falando do Novo Conjunto Habitacional Saramém, no município de Brejo Grande, em Sergipe, que tem sua formação há uma década e meia e se ergueu sobre um trágico acontecimento ocorrido ao fim da década de 90 no século XX: a invasão do mar à antiga ilha do Cabeço, no mesmo município, fazendo com que o Saramém fosse território para os seus desabrigados. Este trabalho se ocupa por esboçar elementos constitutivos das sociabilidades e modos de vida na Ilha do Cabeço, Brejo Grande/SE, em relação aos modos de vida e de produção material e simbólica presentes no século XXI no Conjunto Saramém, no mesmo município, sob o signo da promessa capitalista de “desenvolvimento, progresso e qualidade de vida”. Esta dissertação é fruto de um trabalho baseado na prática etnográfica, não apenas da autora, mas também por parte de alguns coautores que realizaram suas pesquisas no local e que estão, aqui, enriquecendo as reflexões e agregando informações a este trabalho. De inspiração etnometodológica, põe a descoberto as marcas das ideologias presentes nos discursos iluminando as práticas cotidianas na região e a desvelando as distorções entre a lógica do capital e a lógica do beiradeiro (Golobi, s/d). Também conta-se com o incomensurável auxílio do recentemente produzido laudo da pericial sob encomenda da Justiça Federal do estado de Sergipe, que teve como objetivo de esclarecer pontos decisivos em ação movida pela Associação do Povoado Cabeço, em Brejo Grande, contra a Companhia Hidrelétrica do São Francisco (CHESF), sob a alegação de que a instalação da Usina Hidrelétrica de Xingó teria afetado drasticamente o fluxo natural do rio, ocasionando a perda de força das águas deste em detrimento da força do mar que o encontra na foz do rio São Francisco, onde se localizava a ilha do Cabeço. Para além da veridicidade desta alegação, poremos em questão o que estas ações de dominação, transformação e mercantilização dos recursos naturais e humanos pelo próprio homem acabam por moldar em níveis de sociabilidades em tempos de forte apelo ao capital.
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Huang, Xue Ning. "Mode I and mode II intralaminar fracture of unidirectional composites." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304092.
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Xie, Yimeng. "Advancements in Degradation Modeling, Uncertainty Quantification and Spatial Variable Selection." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/71687.
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This dissertation focuses on three research projects: 1) construction of simultaneous prediction intervals/bounds for at least k out of m future observations; 2) semi-parametric degradation model for accelerated destructive degradation test (ADDT) data; and 3) spatial variable selection and application to Lyme disease data in Virginia. Followed by the general introduction in Chapter 1, the rest of the dissertation consists of three main chapters. Chapter 2 presents the construction of two-sided simultaneous prediction intervals (SPIs) or one-sided simultaneous prediction bounds (SPBs) to contain at least k out of m future observations, based on complete or right censored data from (log)-location-scale family of distributions. SPI/SPB calculated by the proposed procedure has exact coverage probability for complete and Type II censored data. In Type I censoring case, it has asymptotically correct coverage probability and reasonably good results for small samples. The proposed procedures can be extended to multiply-censored data or randomly censored data. Chapter 3 focuses on the analysis of ADDT data. We use a general degradation path model with correlated covariance structure to describe ADDT data. Monotone B-splines are used to modeling the underlying degradation process. A likelihood based iterative procedure for parameter estimation is developed. The confidence intervals of parameters are calculated using the nonparametric bootstrap procedure. Both simulated data and real datasets are used to compare the semi-parametric model with the existing parametric models. Chapter 4 studies the Lyme disease emergence in Virginia. The objective is to find important environmental and demographical covariates that are associated with Lyme disease emergence. To address the high-dimentional integral problem in the loglikelihood function, we consider the penalized quasi loglikelihood and the approximated loglikelihood based on Laplace approximation. We impose the adaptive elastic net penalty to obtain sparse estimation of parameters and thus to achieve variable selection of important variables. The proposed methods are investigated in simulation studies. We also apply the proposed methods to Lyme disease data in Virginia. Finally, Chapter 5 contains general conclusions and discussions for future work.Ph. D.
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Gazzarri, Javier Ignacio. "Impedance model of a solid oxide fuel cell for degradation diagnosis." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/218.
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A numerical model of the steady state and alternating current behaviour of a solid-oxide fuel cell is presented to explore the possibilities to diagnose and identify degradation mechanisms in a minimally invasive way using impedance spectroscopy. This is the first report of an SOFC impedance model to incorporate degradation, as well as the first one to include the ribbed interconnect geometry, using a 2-D approximation. Simulated degradation modes include: electrode/electrolyte delamination, interconnect oxidation, interconnect/electrode interface detachment, and anode sulfur poisoning. Detailed electrode-level simulation replaces the traditional equivalent circuit approach, allowing the simulation of degradation mechanisms that alter the shape of the current path. The SOFC impedance results from calculating the cell response to a small oscillatory perturbation in potential. Starting from the general equations for mass and charge transport, and assuming isothermal and isobaric conditions, the system variables are decomposed into a steady-state component and a small perturbation around the operating point. On account of the small size of the imposed perturbation, the time dependence is eliminated, and the original equations are converted to a new linear, time independent, complex-valued system, which is very convenient from a numerical viewpoint. Geometrical and physical modifications of the model simulate the aforementioned degradation modes, causing variations in the impedance. The possibility to detect unique impedance signatures is discussed, along with a study of the impact of input parameter inaccuracies and parameter interaction on the presented results. Finally, a study of pairs of concurrent degradation modes reveals the method’s strengths and limitations in terms of its diagnosis capabilities.
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Ozbek, Murat Olus. "Inferential Model Predictive Control Of Poly(ethylene Terephthalate) Degradation During Extrusion." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/12607497/index.pdf.
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Poly(ethylene terephthalate), PET, which is commonly used as a packaging material, is not degradable in nature. As an issue of sustainable development it must be recycled and converted into other products. During this process, extrusion is an important unit operation. In extrusion process, if the operating conditions are not controlled, PET can go under degradation, which results in the loss of some mechanical properties.
In order to overcome the degradation of recycled PET (RPET), this study aims the control of the extrusion process. Dynamic models of the system for control purposes are obtained by experimental studies. In the experimental studies, screw speed, feed rate and barrel temperatures are taken as process variables in the ranges of 50 &ndash500 rpm, 3.85 &ndash
8.16 g/min and 270 &ndash
310 oC respectively. Singular value decomposition (SVD) technique is used for the best pairing between the manipulated &ndash
controlled variables, where screw speed is taken as the manipulated variable and molecular weight of the product is taken as the controlled variable. PID and model predictive controller (MPC) are designed utilizing the dynamic models in the feedback inferential control algorithm. In the simulation studies, the performance of the designed inferential control system, where molecular weight (Mv) of the product is estimated from the measured intrinsic viscosity ([&
#951
]) of the product, is investigated. The controller utilizing PID and MPC control algorithms are found to be robust and satisfactory in tracking the given set points and eliminating the effects of the disturbances.
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Kaylor, Rosann Matthews. "The high-temperature, alkaline degradation of a new cellulose model compound." Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/27286.
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Chan, Wing-yu Tori, and 陳詠茹. "Mouse model with impaired matrix degradation at the chondro-osseous junction." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B41758055.
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Miwa, Hazuki Eleanor. "A Recombinant System to Model Proteoglycan Aggregate Interactions and Aggrecan Degradation." Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1130857836.
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Gok, Abdulkerim. "Degradation Pathway Models of Poly(ethylene-terephthalate) Under Accelerated Weathering Exposures." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1449244610.
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Chan, Wing-yu Tori. "Mouse model with impaired matrix degradation at the chondro-osseous junction." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B41758055.
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Nguyen, Quynh Hoa. "Risk assessment for drug degradation products using physiologically-based pharmacokinetic models." Diss., University of Iowa, 2014. https://ir.uiowa.edu/etd/1993.
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Degradation product toxicity is a critical quality issue for a small group of useful drug products--e.g. lidocaine, isoniazid, chlorhexidine, gabapentin. In the traditional risk assessment approaches, a no-observed-adverse-effect level (NOAEL) derived from animal data is determined with the use of generic (and arbitrary) uncertainty factors to obtain an acceptable daily intake. The effects of compound-specific biological complexities and pharmacokinetics are typically not part of the risk calculations. The selection of uncertainty factors that account for interspecies or intraspecies difference concerning biokinetics and biodynamics has also generally failed to consider chemical-specific mechanism information or pharmacokinetics data. The use of combining in-vitro biopharmaceutical characterization methods and physiologically-based pharmacokinetic modeling has undergone extensive study and validation for predicting clinical drug blood level time profiles. The rationale for the proposed research is that a PBPK modeling utilizing rat to human scaling for target tissue toxicity in combination with the Monte Carlo method for estimating human target exposure distributions provides a rational basis for assessing drug stability safety issues for drug substances that potentially degrade to toxic compounds.
PBPK models for rats and humans were developed to simulate drug exposure time profiles after oral administration of model compounds including aniline, p-chloroaniline, 2,6-dimethylaniline, o-toluidine and p-aminophenol. The PBPK models were parameterized using a combination of literature values, computational models and standard in vitro experiments. Microsomal and hepatocyte metabolism studies were used to estimate the metabolic constants, and ultrafiltration was used to measure protein binding. Intestinal permeability was predicted using a set of related compound data to correlate measured Caco-2 permeability with molecular descriptors by multivariate regression. Sensitivity analyses were conducted to evaluate the impact of PBPK model parameters on plasma level predictions. To evaluate patient population effects on exposure profiles, the PBPK model parameters were varied in meaningful ways using Monte Carlo methods. Based on population PBPK models, distributions of target tissue exposure in rats and humans were simulated and compared to derive human safe dose.
As results, rat PBPK model-predicted aniline concentration time profiles were in reasonable agreement with published profiles. Distributions of target tissue exposure in rats and humans were generated and compared based on a criterion. A human reference dose was then selected at a value of 1% criteria. This approach was compared to traditional risk assessment calculations. In conclusion, the PBPK modeling approach resulted in drug degradation product risk specifications that were less stringent than those estimated by conventional risk assessment approach. The PBPK modeling approach provides a rational basis for drug instability risk assessment by focusing on target tissue exposure and leveraging physiological, biochemical, biophysical knowledge of compounds and species.
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Addai, Obeng A. "Regulated Feedback Networks with Degradation." Youngstown State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1444046732.
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Gonzalez, de Frutos Jorge Verfasser], Regine [Akademischer Betreuer] [Willumeit-Römer, and Mikhail [Gutachter] Zheludkevich. "Local surface environment and degradation processes of degradable magnesium biomaterials under simulated physiological conditions / Jorge Gonzalez de Frutos ; Gutachter: Mikhail Zheludkevich ; Betreuer: Regine Willumeit-Römer." Kiel : Universitätsbibliothek Kiel, 2020. http://nbn-resolving.de/urn:nbn:de:gbv:8-mods-2020-00233-3.
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Haque, Ekram. "The synthesis of novel benzophenones and their mode of action as stabilisers in polyolefins." Thesis, Manchester Metropolitan University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277915.
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Davenport, James Charles William. "Mixed mode elastic-plastic fracture." Thesis, University of Bristol, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357788.
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Ingram, Kevin D. (Kevin Dean). "The Development of Predictive Models for the Acid Degradation of Chrysotile Asbestos." Thesis, University of North Texas, 1993. https://digital.library.unt.edu/ark:/67531/metadc279343/.
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The purpose of this study was to determine the factors affecting the acid degradation of chrysotile asbestos (Mg_3Si_2O_5(OH_4)) . Millions of tons of asbestos have found use in this country as insulative or ablative material. More than 95 percent of the asbestos in use is of the chrysotile variety. The remaining 5 percent is composed of various types of fibrous amphiboles. The inhalation of asbestos can lead to several diseases in humans. Asbestosis, lung cancer and mesothelioma are the most common afflictions associated with asbestos inhalation, and they may occur up to 40 years after the initial exposure. It has previously been reported that if more than 50 percent of the magnesium is removed from a chrysotile sample its carcinogenicity is reduced to nil. Several inorganic acids were studied to determine their ability to leach magnesium from chrysotile. It was found that the ability to leach magnesium was dependent upon the acidic anion in addition to the concentration of the acid. The ordering of the efficiency of the acids in their ability to remove magnesium from chrysotile was found to be HCl > H_2SO_4 > H_3PO_4 > HNO_3. Predictive equations were developed to allow the calculation of the amount of magnesium removed under various acid concentrations as a function of time and acid species. The effects of temperature and dissolved spectator cations upon the degradation process were also examined. There was no major effect on the amount of magnesium removed as a function of spectator cation concentration. An infrared method was also developed to allow the determination of the percent degradation of a chrysotile sample directly. The shifts in the positions of three silicate stretching peaks (1068 cm^-1, 948 cm^-1 and 715 cm^-1) and one magnesium oxygen stretching peak (415 cm"1) as a function of the percent magnesium removed were correlated to allow this determination.
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MURASE, Hiroshi, Yoshito MEKADA, Ichiro IDE, Tomokazu TAKAHASHI, and Hiroyuki ISHIDA. "Generation of Training Data by Degradation Models for Traffic Sign Symbol Recognition." Institute of Electronics, Information and Communication Engineers, 2007. http://hdl.handle.net/2237/14958.
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Amerinatanzi, Amirhesam. "Magnesium-based Biomedical Implants: Towards a Mathematical Model for Degradation and Design." University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1533048186717968.
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Katayama, Takeshi. "DEGRADATION OF LIGNIN SUBSTRUCTURE MODEL COMPOUNDS BY FUSARIUM SOLANI M-13-1." Kyoto University, 1989. http://hdl.handle.net/2433/78212.
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