Дисертації з теми "Lean condition"

Un moteur diesel faible puissance a était converti en A. C. Puis alimenté au gaz naturel. Les caractéristiques générales de la combustion (délais, durées de combustion, dispersion cyclique) ont été étudiées en fonction du rapport air-gaz, de l'avance à l'allumage, et du type de bougie ainsi que les performances du moteur. Pour le comportement en mélange très pauvre, nous avons déterminé les limites opératoires, analyse le déroulement de la combustion et observe les variations de pression. En utilisant un générateur de turbulence en forme de cône, nous avons reculé les limites pauvres et réduit la dispersion cyclique et la pollution estimée en fonction de la richesse du mélange, de l'avance à l'allumage, de la vitesse et de la charge du moteur. A la fin de l'étude, nous donnons les conditions opératoires optimum pour différentes charges et vitesses.

The issue of leakage within the water distribution system is one of importance not only at an economic level for the industry, but there is also a wider environmental agenda, addressing issues of water sustainability and resource management. Very little is known about the factors which lead to failure and ultimately leakage from lead-based assets encompassing both lead service pipes and lead-run joints in cast iron mains. This has led to many repairs being carried out on lead-based assets as a reactive measure, either as part of the mains renewal programme or as leaks are detected. The aim of the present project was to gain an understanding of the significant factors affecting the failure of lead pipes and joints, and the associated mechanisms of failure.

Bakgrund I den nutida forskningen är det essentiellt att företag tar hänsyn till medarbetarnas motivation så att de gynnas av det arbetssätt som tillämpas. En arbetsmetod som blivit allt vanligare är konceptet Lean som ursprungligen kommer från den japanska bilindustrin. Lean har idag utvecklats till ett allmängiltigt koncept som tillämpas i flertalet branscher världen över. Trots att konceptet innebär flertalet positiva aspekter har det fått utstå stark kritik när det kommer till de mänskliga aspekterna och forskare har ställt sig frågan om Lean är "Mean". Kritiken härleds främst till medarbetares arbetsmiljö i form av stress och brist på variation, självbestämmande, hälsa och välmående. Få empiriska studier har däremot genomförts som undersöker konsekvenserna som Lean får på medarbetares upplevda motivation. Syfte Vårt syfte är att undersöka och öka förståelsen för medarbetares upplevelser av motivationen i företag som tillämpar Lean. Vidare har studien för avsikt att utreda om det föreligger en paradox mellan Lean och vad som motiverar medarbetare på en arbetsplats. Metod Studien har utgått från en kvalitativ metod via intervjuer. För att göra en djupare undersökning och analysera hur vårt fenomen, motivation, upplevs i en kontext med Lean tillämpade vi Små-N-studier. Vi har även haft en iterativ forskningsansats som förenat den deduktiva och induktiva ansatsen där studien pendlat mellan teorier och empiriska observationer fram tills det slutgiltiga resultatet. Slutsatser Utefter medarbetarnas upplevelser har vi identifierat att det inte föreligger någon paradox mellan Lean och motivation eftersom övervägande antal medarbetare upplevde att de är motiverade även om företaget tillämpar Lean. Dock har studien kunnat urskilja både stödjande och motverkande faktorer när det kommer till medarbetarnas upplevda arbetsförhållanden som i sin tur inverkar på motivationen. De motverkande faktorerna menar vi främst beror på att arbetsförhållandena i somliga fall innehåller höga prestationskrav, målstyrning samt standardiseringar. Vidare upplevs motivationen överlag som mer positiv när företagen använder en mjukare form av Lean där samtliga medlemmars intressen beaktas.
Background In modern research, it is essential that companies consider employees’ motivation so that they benefit from the applied practices. A working method that has become increasingly common is the concept Lean, which has its origin in the Japanese automotive industry. Today, Lean has evolved into a universal concept that is applied in many industries worldwide. Although the concept involves numerous positive aspects it has endured strong criticism when it comes to the human aspects and researchers have raised the question if Lean is "Mean". Criticism is derived primarily to employees’ working conditions in terms of stress and lack, variation, autonomy, health and wellbeing. However, few empirical studies have been carried out that examines the impact that Lean has on employees’ experienced motivation. Aim The aim is to increase the understanding of employees’ experienced motivation in companies that practice Lean. Further on the study has the intention to investigate if there is a paradox between Lean and what motivates employees on work. Methodology The study has been conducted through a qualitative method by interviews and to be able to do a deeper examination and analyze how our phenomenon, motivation, is experienced in a Lean context we applied small-N-studies. Our strategy has been iterative, combining both a deductive and inductive approach, where the study has varied between theories and empirical observations until the final result. Conclusions We have identified that there is no paradox between Lean and motivation since the majority of employees’ experienced that they are motivated even though the company practice Lean. Nevertheless the study shows that there are both supportive and counteractive factors when it comes to the employees’ experienced working conditions. The counteractive factors consists foremost of high performance standards, goal steering and standardizations, and have in some cases a negative influence on the working conditions. Furthermore the experienced motivation is more positive overall when the companies use a softer form of Lean where all the members’ interests are taken into account.

Fossil fuels still account for a large percentage of global energy demand according to available statistics. Natural gas is increasingly gaining the share of these fuels due to the retired coal and nuclear plants. The more stringent emission standards have also put natural gas ahead of other fuels as a result of its efficiency, cost, environmental attributes as well as the operational efficiency of the gas turbine, an engine that uses this fuel. A standard low emission combustion technique in gas turbines is the dry low NOx combustion, with lean fuel and fuel-air premixed upstream of the flame holder. However, this condition is highly susceptible to combustion instabilities characterised by large amplitude oscillations of the combustor’s acoustic modes excited by unsteady combustion processes. These pressure oscillations are detrimental both to the efficiency of performance as well as the hardware of the system. Although the processes and mechanisms that result in instabilities are well known, however, the current challenges facing gas turbine operators are the precise understanding of the operational conditions that cause combustion instabilities, accurate prediction of the instability modes and the control of the disturbances. In a bid to expand this knowledge frontier, this study uses a 100kW swirl premixed combustor to examine the evolution of the flow structures, its influence on the flame dynamics, in terms of heat release fluctuation and the overall effects on the pressure field, under different, swirl, fuel and external excitation conditions. The aim is to determine the operational conditions whose pressure oscillation is reduced to the barest minimum to keep the system in an excellent running condition. The results of this study are expected to contribute towards the design of a new control system to damp instabilities in gas turbines.

[EN] In the current work, the characterization of the combustion process inside a stratified pre-chamber spark ignition (PCSI) system is performed. An extensive bibliographical review about the pre-chamber systems developed from the second half of the 20th century until modern times is presented. The review shows that the latest generation systems have the potential to accomplish the emissions limits while providing high performance and low fuel consumption. Nevertheless, many efforts of the scientific community are still needed to allow the large-scale application of the technology. Indeed, based on the outstanding challenges observed, the investigation plan is developed including both experimental and numerical parts. All experiments were performed by means of the rapid compressionexpansion machine (RCEM) in the CMT-Motores Térmicos laboratory. The original cylinder head layout was modified to allow the housing of the prechamber itself, fuel injectors, spark plug, pressure transducers in both chamber, and a thermocouple. The test methodology involved the acquisition of the pressure evolution in both main chamber and pre-chamber, the piston position (used to compute the instantaneous cylinder volume), the duration of the auxiliary injection, and the spark ignition point. These are used as input for the zero-dimensional thermodynamic model which simulates the fundamental parameters aims to characterize the PCSI system working cycle. Therefore, a deeper knowledge of the mass interchanged process, induced turbulence field, heat release rate, combustion speed, and flame regime is generated. Subsequently, to calibrate the zero-dimensional model coefficients under motoring conditions, several 3D CFD simulations were carried out by means of Converge software. Hence, the results of the simulations in terms of interchanged mass and pre-chamber turbulent kinetic energy have been used to calibrate the nozzle discharge coefficient and the turbulence sub-model coefficients for all the pre-chamber geometries. Furthermore, the 3D CFD simulations outputs are analysed to fully understand the flow field structure and the local effect induced by the different nozzles at the spark activation time. The turbulent kinetic energy in terms of intensity and orientation is investigated over several relevant pre-chamber sections. The results reveal a clear relationship between the turbulence developed within the pre-chamber and the orifices structure. Straight orifices or perpendicular jets impact, promote more intense local turbulence due to direct collision while tilted orifices guarantee more homogeneity due to the swirling motion. Additionally, increase the orifice numbers shows benefits on the fluid dynamic homogeneity. Thus, preceding the experimental campaign several fundamental aspects of the system are evaluated. The cycle-to-cycle dispersion is explored by means of the statistical assessment showing low pressure peak deviation. The auxiliary injection pressure and timing are optimized for avoiding wall wetting phenomena while ensuring proper air/fuel mixing. Finally, the spark activation point is chosen as a function of the theoretically maximum turbulent flame speed. Thereby, the experimental campaign is carried out according to tests matrix, in order to evaluate the effect of the equivalence ratio of both chambers, and how the orifices diameter, number, and distribution affect the combustion process. Moreover, chemiluminescence visualization tests, performed by means of the available optical access of the RCEM, are combined with zerodimensional and 3D CFD results to shed light on the work cycle. Conclusions suggest a slightly rich mixture inside the pre-chamber combined with the highest number of tilted orifices as the better configuration for improving combustion efficiency under lean and ultra-lean main chamber mixture conditions. Nevertheless, axial orifices should be considered for further investigations. Finally, the author proposes a series of developments considered interesting in both the experimental and numerical fields.
[ES] En el presente trabajo se realiza la caracterización del proceso de combustión dentro de un sistema de encendido por pre-cámara bajo carga estratificada. Por lo tanto, se presenta una extensa revisión bibliográfica sobre los sistemas de pre-cámara desarrollados desde la segunda mitad del siglo XX hasta los tiempos modernos. El resumen muestra que los sistemas de última generación tienen el potencial de cumplir con los límites de las emisiones, al tiempo que proporcionan un alto rendimiento y un bajo consumo de combustible. No obstante, todavía se necesitan muchos esfuerzos de la comunidad científica para permitir la difusión a gran escala de la tecnología. De hecho, sobre la base de los desafíos abiertos observados, se desarrolla el plan de investigación incluyendo tanto una parte experimental como numérica. Todos los experimentos se realizan mediante la máquina de compresión-expansión rápida (RCEM) de que dispone el laboratorio CMT-Motores Térmicos . La disposición original de la culata se modificó para permitir el alojamiento de la propia pre-cámara, los inyectores , la bujía, los sensores de presión y un termopar. La metodología de ensayo implica la adquisición de la evolución de la presión tanto en cámara principal como en pre-cámara, el volumen del cilindro, la duración de la inyección auxiliar y el punto de ignición de la bujía. Estos se utilizan como parámetros de entrada para el modelo termodinámico cero-dimensional que devuelve los parámetros fundamentales que caracterizan ciclo de trabajo del sistema PCSI. Por lo tanto, se genera un conocimiento más profundo del proceso de intercambio de masas, del campo de turbulencias inducidas, de la tasa de liberación de calor, de la velocidad de combustión y del régimen de la llama. Posteriormente, para calibrar los coeficientes del modelo cero-dimensional bajo condiciones de arrastre, se llevaron a cabo varias simulaciones CFD en 3D mediante el software Converge. Por lo tanto, los resultados de las simulaciones en términos de masa intercambiada y energía cinética turbulenta de la precámara se han utilizado para calibrar el coeficiente de descarga de la tobera y los coeficientes del sub-modelo de turbulencia para todas las geometrías de la pre-cámara. Además, se analizan los resultados de las simulaciones CFD para comprender plenamente la estructura del campo de flujo y el efecto local inducido por las diferentes geometriás en el tiempo de activación de la chispa. La energía cinética turbulenta en términos de intensidad y orientación se investiga en varias secciones relevantes de la pre-cámara. Los resultados revelan una clara relación entre la turbulencia desarrollada dentro de la pre-cámara y la estructura de los orificios. Los orificios rectos o los chorros perpendiculares, promueven una turbulencia local más intensa debido a la colisión directa mientras que los orificios inclinados del campo fluido y del dosado. Precedentemente al desarrollo de la campaña experimental se evalúan varios aspectos fundamentales del sistema. La dispersión ciclo a ciclo se explora por medio de la evaluación estadística que muestra una baja desviación de los picos de presión. La presión y el punto de inyección auxiliar se optimizan para evitar los fenómenos de mojado de las paredes, asegurando al mismo tiempo una mezcla adecuada de aire/combustible. Finalmente, el punto de activación de la chispa se elige en función de la velocidad máxima teórica de la llama turbulenta. De este modo, la campaña experimental se lleva a cabo de acuerdo con la matriz de pruebas, con el fin de evaluar el efecto del dosado equivalente de ambas cámaras, y cómo el diámetro, el número y la distribución de los orificios afectan al proceso de combustión. Además, las pruebas de visualización de quimioluminiscencia, realizadas mediante el acceso óptico disponible de la RCEM, se combinan con resultados de CFD y resultados del modelo cerodimen para arrojar luz sobre el ciclo de trabajo. Las conclusiones sugieren que una mezcla ligeramente rica dentro de la pre-cámaracombinadaconelmayornúmerodeorificiosdesfasadoseslamejor configuración para garantizar un elevada eficiencia de la combustión en condiciones de mezcla pobre y ultra-pobre de la cámara principal. No obstante, los orificios axiales deben ser considerados para investigaciones futuras. Por último, el autor propone una serie de desarrollos considerados interesantes tanto en el campo experimental como en el numérico.
[CA] En el present treball es realitza la caracterització del procés de combustió dins d'un sistema d'encesa de pre-cambra soto càrrega estratifi-cada. Per tant, es presenta una extensa revisió bibliogràfica sobre els sistemes de precambra desenvolupats des de la segona meitat del segle XX fins als temps moderns. El resum mostra que els sistemes d'última generació tenen el potencial de complir amb els límits de les emissions, al mateix temps que proporcionen un alt rendiment i un baix consum de combustible. No obstant això, encara es necessiten molts esforços de la comunitat científica per a permetre la difusió a gran escala de la tecnologia. De fet, sobre la base dels desafiaments oberts observats, es desenvolupa el pla d'investigació incloent tant una part experimental com numèrica. Tots els experiments es realitzen mitjançant la màquina de compressió-expansió ràpida (RCEM) de què disposa el laboratori CMT-Motors Tèrmics. La disposició original de la culata es va modificar per a permetre l'allotjament de la pròpia pre-cambra, els injectors , la bugia, els sensors de pressió i un termoparell. La metodologia d'assaig implica l'adquisició de l'evolució de la pressió tant en cambra principal com en pre-cambra, el volum del cilindre, la duració de la injecció auxiliar i el punt d'ignició de l'espurna. Aquests s'utilitzen com a paràmetres d'entrada per al model termodinàic zero-dimensional que retorna els paràmetres fonamen-tals que caracteritzen cicle de treball del sistema PCSI. Per tant, es genera un coneixement més profund del procés d'intercanvi de masses, del camp de turbulències induïdes, de la taxa d'alliberament de calor, de la velocitat de combustió i del règim de la flama. Posteriorment, per a calibrar els coefi-cients del model zerodimensional sota condicions d'arrossegament, es van dur a terme diverses simulacions CFD en 3D mitjançant el programari Converge. Per tant, els resultats de les simulacions en termes de massa intercanviada i energia cinètica turbulenta de la pre-cambra s'han utilitzat per a calibrar el coeficient de descàrrega de la tovera i els coeficients del sub-model de turbulència per a totes les geometries de la pre-cambra. A més, s'analitzen els resultats de les simulacions CFD per a comprendre plenament l'estructura del camp de flux i l'efecte local induït per les diferents geometries en el temps d'activació de l'espurna. L'energia cinètica turbulenta en termes d'intensitat i orientació s'investiga en diverses seccions rellevants de la pre-cambra. Els resultats revelen una clara relació entre la turbulència desenvolupada dins de la pre-cambra i l'estructura dels orificis. Els orificis rectes o els dolls perpendiculars, promouen una turbulència local més intensa a causa de la col·lisió directa mentre que els orificis inclinats garanteixen una major homogeneïtat a causa de la generació d'un macro-remolì. A més, l'augment del nombre d'orificis mostra beneficis en l'homogeneïtat fluid-dinàmica. Llavors, abans de la campanya experimental s'avaluen diversos aspectes fonamentals del sistema. La dispersió cicle a cicle s'explora per mitjà de l'avaluació estadística que mostra una baixa desviació dels pics de pressió. La pressió i el punt d'injecció auxiliar s'optimitzen per a evitar els fenòmens de mullat de les parets, assegurant al mateix temps una mescla adequada d'aire/combustible. Finalment, el punt d'activació de l'espurna es tria en funció de la velocitat màxima teòrica de la flama turbulenta. D'aquesta manera, la campanya experimental es duu a terme d'acord amb la matriu de proves, amb la finalitat d'avaluar l'efecte del dosatge equivalent de totes dues cambres, i com el diàmetre, el numero i la distribució dels orificis afecten el procés de combustió. A més, les proves de visualització de quimioluminescència, realitzades mitjançant l’accés òptic disponible de la RCEM, es combinen amb resultats de CFD i resultats del model zero-dimensional per a llançar llum sobre el cicle de treball. Les conclusions suggereixen que una mescla lleugerament rica dins de la pre-cambra combinada amb el major nombre d’orificis desfasats és la millor configuració per a garantir un elevada eficiència de la combustió en condicions de mescla pobra i ultra-pobre de la cambra principal. No obstant això, els orificis axials han de ser considerats per a investigacions futures. Finalment, l’autor proposa una sèrie de desenvolupaments considerats interessants tant en el camp experimental com en el numèric.
Pagano, V. (2020). Analysis of a stratified pre-chamber spark ignition system under lean mixture conditions [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/152486
TESIS

The Asbestos Hazard Emergency Response Act (AHERA) requires public schools to manage asbestos containing materials. Twenty five years after AHERA was enacted public schools continue to struggle with documenting and managing asbestos containing material assets. In addition, the manufacturing of lead based paint (LBP) was banned over thirty years ago yet public schools continue to have to manage LBP assets with no guidelines specific to public schools. When compared to current civil infrastructure asset management systems, AHERA and the HUD guidelines lack a rating system based on visual inspection data. The development of a condition index algorithm and risk of failure model would provide school planners an efficient management tool to predict the future condition of asbestos containing material and lead based paint assets. As a result, school planners would be able to prioritize maintenance, repair, and abatement projects based on the risk to the indoor air quality of their facilities and more efficiently utilize their limited resources to mitigate such risks. This paper presents initial work toward the development of a visual condition index algorithm and a risk of failure model to support prioritization of maintenance, repair, and abatement projects. The condition assessment categories provided by AHERA and HUD were adapted and incorporated in an evaluation form created to assist in rating the various stages of accessibility, deterioration, and detection of typical ACM and LBP building components. The evaluation form can be utilized by inspection and school personnel when reclassifying ACM and LBP components during semi-annual inspections of their facilities and also ensure the repeatability of the condition assessment and risk of failure methodologies. A risk of failure model was developed utilizing the FMEA process, specifically the calculation of a risk priority number (RPN). Three schools were selected for a field pilot study to develop the accessibility, deterioration, detection, and RPN algorithms and evaluate for repeatability. The algorithms will provide a quantitative and consistent means for documenting the condition and RPN of asbestos containing material and lead based paint assets and allow the condition of these assets to be monitored and reclassified over a period of time.
Ph. D.

Thesis (M.S.)--West Virginia University, 2005.
Title from document title page. Document formatted into pages; contains vi, 39 p. : ill. Includes abstract. Includes bibliographical references (p. 37-39).

This research aims to understand the impact of lean manufacturing (Lean) on employee working conditions (EWC) in organisations operating in Nigeria, mainly from the managers’ and supervisors’ perspective. An exploratory study, the research adopts a case study research strategy to address the research aim. The case study organisations are a Complex Product Manufacturer, and a Power System Manufacturer, both located in Nigeria. The findings from this study provide insights into the Lean practices adopted by organisations operating in Nigeria, such as 5S, Total Preventive Maintenance (TPM), Just-in-Time (JIT) and Continuous Improvement (CI). Having determined the Lean practices adopted by Lean organisations operating in Nigeria, the research assesses the impact of these practices on EWC. Firstly, by the review of the literature to capture the possible impacts of Lean on EWC from a wider perspective, which led to the development of a conceptual model of the impact of Lean on EWC. The development of the conceptual model is followed by an assessment of the impact of Lean on EWC through the case studies, an area not hitherto considered by research into Lean in Nigeria. The findings of this research established that Lean has had a predominately positive rather than negative impact on EWC. The implementation of Lean has led to improved physical EWC, in terms of housekeeping, layout, and ergonomics. Furthermore, physiological EWC such as reduction in stress, increased autonomy, motivation, and teamwork, better interpersonal relationship, and lastly, increase in the presences and usage of polyvalence (multi-skilled workforce). They were also the physical and physiological impacts of better management of workload, and improvement in health and safety. More so, the negative features of Lean, although recorded at the initial stages of Lean implementation in the case organisations are physiological. They are: increase in stress, a greater sense of apprehension amongst employees. Physical and physiological negative features whereby employees experienced an increase in workload, work being tedious and employees working in pain, and an accident. Nevertheless, several recommendations were developed based on the research findings. For instance, the case study organisation needs to integrate job rotation and multifunctional working into their practice of Lean, to prevent the exposure of employees to monotonous jobs, including the chance of repetitive strain injuries (RSI) occurring. For other organisations working to implement Lean, the results of this study could assist them to learn best practices in the implementation of Lean and to understand its possible strength and weakness. Moreover, other contributions made by this research, are that, for Non-Lean manufacturers and intending Lean manufacturers, especially those in Nigeria in which this research observes a predominant unfavourable EWC, the findings of this research suggest that Lean leads to an improvement in EWC and provides an opportunity to produce at a lower cost. The improvement in EWC, while also producing at lower cost found in this research could serve as an incentive for these organisations to adopt Lean. Furthermore, this research other than being the first empirical study to identify the Lean practices adopted by organisations operating in Nigeria and to investigate their impact on EWC develops three models. The first was the conceptual model following the review of the literature, which captures the possible impact of Lean on EWC. The model was subsequently evaluated against the findings from the case studies, leading to the development of two more models. First, a model on Lean and its impact on EWC, second, a model of the Negative Features of EWC in organisations following the implementation of Lean. These models developed in this research can be used in the assessment of Lean and its impact on EWC by organisations and could serve as a reference for further research into Lean and EWC.

The thesis presents an investigation of the potential of measuring plant condition from hyperspectral reflectance data. To do this, some linear methods for embedding the high dimensional hyperspectral data and to perform regression to a plant condition space have been compared. A preprocessing step that aims at normalized illumination intensity in the hyperspectral images has been conducted and some different methods for this purpose have also been compared.A large scale experiment has been conducted where tobacco plants have been grown and treated differently with respect to watering and nutrition. The treatment of the plants has served as ground truth for the plant condition. Four sets of plants have been grown one week apart and the plants have been measured at different ages up to the age of about five weeks. The thesis concludes that there is a relationship between plant treatment and their leaves' spectral reflectance, but the treatment has to be somewhat extreme for enabling a useful treatment approximation from the spectrum. CCA has been the proposed method for calculation of the hyperspectral basis that is used to embed the hyperspectral data to the plant condition (treatment) space. A preprocessing method that uses a weighted normalization of the spectrums for illumination intensity normalization is concluded to be the most powerful of the compared methods.

A constant volume cylindrical combustion bomb of 100 mm diameter, and of variable length (from 250 mm to 1000 mm) has been built. The effect of charge stratification on the ignitability and subsequent flame propagation of lean (1 > 6) methane-oxygen mixtures has been investigated. The test mixtures were quiescent with initial conditions of 25°C and 1.5 bar absolute. The stratified charge was created by injecting small quantities of a relatively rich (λ = 4.57) premixed methane-oxygen mixture through a modified commercially available spark plug so that an easily ignitable mixture formed in the vicinity of the spark electrodes. The injector used was a commercially available Bosch gasoline injector, suitably modified for gas operation. The injection pressure was 5 bar gauge. The size of the injected puff could be altered by adjusting the duration (from 0-100 ms) for which the injector was opened, and the timing of the spark could be adjusted so that it occurred either before, after or at the end of injection. Results show that the injected premixed puff is an efficient high energy ignition source for very lean methane-oxygen mixtures. For the most reliable ignition performance a delay of 10 ms between the end of injection and the occurrence of the spark has been found to be desirable. This is attributed to the decay of the turbulence produced by the puff. Long injection durations (greater than 20 ms) also improved ignition reliability, due to the larger puff size. The use of charge stratification did not enable combustion to continue below the ideal flammability limit. It did extend the equipment lean limit of flammability from λ = 7.3 (spark alone) to λ = 8.35, and thus demonstrated that it could be useful as a limit extender in non-ideal combustion situations. Results from the longest bomb used (1000 mm) show that the flame dies out after successful ignition has been achieved, and that a distinct lean flammability limit does not exist. Experimental evidence suggests that the flame is generating turbulence as it propagates, and this turbulence causes the flame to become self accelerating. Further, it is thought that the flame generated turbulence is the primary cause of flame extinction (in the form of turbulence induced gas phase quenching) after successful ignition in the 1000 mm bomb.

An investigation of the combustion of lead sulphide .concentrates under controlled conditions has been carried out. A fast response, two-wavelength radiation pyrometer and a "laminar flow" furnace were constructed to facilitate the measurement of the temperature of individual particles during combustion. Chemical analysis and electron microscopy studies of the reaction products were also performed. The combustion of galena, pyrite, pyrrhotite, sphalerite and two commercial concentrates (Brunswick and Sullivan) at 1130K was investigated. The effects of particle size between 63-125μm and gaseous oxygen concentration between 10 and 100% were examined. For combustion in both air and oxygen a number of different combustion pulses were identified which corresponded to the combustion of different mineral species or to different physical phenomena. An analogous series of pulse classifications was identified for combustion in oxygen however they reflected the greater intensity and temperature of the reactions. The form of combustion was strongly dependent on oxygen concentration. From the results it was not possible to identify the effect of particle size on combustion behaviour. The vaporisation of lead sulphide appears important to the mechanism of galena combustion. In air the temperature of combustion appears limited to 1500-1700K (of boiling point PbS of 1609K); whereas in oxygen, massive vaporisation results in a heating arrest at 1700-2000K and disintegration into droplets which combust at 2000-2400K. Transition from air-type to oxygen-type combustion occurs at oxygen concentrations between 40 and 65% and is thought to be due to the transition from a liquid to gaseous phase PbO reaction product. The initial stage of pyrite reaction is thermal decomposition to porous pyrrhotite. The ignition of this porous pyrrhotite was more rapid than dense pyrrhotite, but once molten, the combustion of the two was indistinguishable and the peak temperature observed was very reproducible. In air the peak combustion temperatures of 2400-2600K appeared to coincide with a sudden expansion of the particle, possibly due to the inflation of thin-walled iron oxide cenospheres. In oxygen the reactions are more intense and disintegration typically occurs on reaching a peak temperature of 3000-3400K, Between ~10 and 35% oxygen the maximum combustion temperature increased linearly, but at higher concentrations remained constant at 3000-3400K. The results suggest the maximum temperature reached is limited by the occurrence of a physical phenomenum possibly associated with the vaporisation of iron. Sphalerite did not ignite at the temperatures considered, but shells of zinc oxide were observed in the reaction products. For the commercial concentrates pulses of intermediate combustion characteristics and a wide range of combustion temperatures (typically intermediate to those of PbS and FeS) were observed, as well as many pulses similar to those of the constituent minerals. The former were considered to be due to the combustion of agglomerations of many smaller individual particles. The effect of the mineral composition was evident in the combustion results, with increased quantities of iron sulphide tending to result in more intense reactions. The results suggest that metallic lead formation occurs during the initial stages of reaction, probably after melting as the result of reaction between the surface oxides/sulphates and unreacted PbS. A simple reaction model for iron sulphide combustion suggests that the reaction of the molten drop is controlled by gas-phase oxygen mass transfer with the measured heating rates consistent with the formation of wustite and sulphur dioxide.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

Electrochemical Impedance Spectroscopy (EIS) has been largely employed for the study of reaction kinetics and condition monitoring of batteries during different operational conditions, such as: Temperature, State of Charge (SoC) and State of Health (SoH) etc. The EIS plot translates to the impedance profile of a battery and is fitted to an Equivalent Electric Circuit (EEC) that model the physicochemical processes occurring in the batteries. To precisely monitor the condition of the batteries, Kramers-Kronig relation: linearity, stability and causality as well as the appropriate perturbation amplitude applied during EIS should be adhered to. Regardless of the accuracy of EIS, its lengthy acquisition time makes it impracticable for online measurement. Different broadband signals have been proposed in literature to shorten EIS measurement time, with different researchers favouring one technique over the other. Nonetheless, broadband signals applied to characterize a battery must be reasonably accurate, with little effect on the systems instrumentation. The major objective of this study is to explore the differences in the internal chemistries of the lithium-ion and lead acid batteries and to reduce the time associated with their condition monitoring using EIS. In this regard, this study firstly queries the methodology for EIS experiments, by investigating the optimum perturbation amplitude for EIS measurement on both the lead acid and lithium-ion batteries. Secondly, this study utilizes electrochemical equations to predict the dynamics and operational conditions associated with batteries. It also investigates the effect of different operational conditions on the lead acid and lithium-ion batteries after EEC parameters have been extracted from EIS measurements. Furthermore, different broadband excitation techniques for rapid diagnostics are explored. An online condition monitoring system is implemented through the utilization of a DC-DC converter that is used to interface the battery with the load. The online system is applied alongside the different broadband signals. The deviation in the broadband impedance spectroscopy result is compared against the Frequency Response Analyzer (FRA) to determine the most suitable technique for battery state estimation. Based on the comparisons, the adoption of a novel technique – Chirp Broadband Signal Excitation (CBSE) is proposed for online condition monitoring of batteries, as it has the advantage of being faster and precise at the most important frequency decade of the impedance spectrum of batteries.

Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, in conjunction with the Leaders for Global Operations Program at MIT, 2018.
Thesis: M.B.A., Massachusetts Institute of Technology, Sloan School of Management, in conjunction with the Leaders for Global Operations Program at MIT, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 55).
As Dell seeks to continually improve customer experience, the company is identifying new and innovative ways to improve on-time delivery. Inventory shortages that occur prior to production account for approximately 35% of missed delivery dates. When these part shortages occur, demand planners must apply "extended" lead times to these parts to ensure that Dell's customers have the correct expectation for when their order will be delivered. This project focuses on part shortage problems and how to generate accurate lead times for customers commitments. Previous research on the topic on lead time setting has focused predominately on buffering and measuring uncertainty in supply chains, which detail the benefits of having appropriate levels of safety stock and flexibility. However, prior research does not adequately describe methods for adjusting product lead times under uncertain supply conditions. The project develops a deterministic model for identifying when parts in Dell's supply chain require lead time adjustments due to supply shortages and then for setting the new lead times. Additionally, this project includes a statistical analysis of previous extended lead time events. After a five-week testing period, the deterministic model was quite accurate in identifying what parts require extended lead times. This offers a 3% improvement in identifying when extended lead times are needed as it decreases human error in missed and late lead time extensions. Predominant sources of error resulted from backlog management issues, part deviations in production, and miscellaneous data errors. The statistical analysis yields two insights into part recovery in Dell's supply chain: (1) larger volume shortages take shorter time to recover than small volume shortages, and (2) approximately 80% of all part shortages recover within 10 days. This research offers valuable insight into the problems associated with lead times in Dell's supply chain and recommends ways to best mitigate these errors. As Dell develops more robust and comprehensive databases on its inventory, future research can identify methods to accurately and automatically update lead times in real-time.
by Zachariah Balent.
S.M.
M.B.A.

The aim of this work is an investigation on a series of Pd-doped cobalt spinels catalysts for the lean CH4 combustion reaction. All the catalysts were synthesized and fully characterized from the structural and surface point of view (XRD, XRF, RS, BET, XPS, and FESEM) and then tested towards the oxidation of CH4 in lean conditions. The work was divided into two parts. In the first part, different catalysts at powder level were screened to optimize the design of Pd-doped cobalt spinel catalysts. In the second part, the best performing Pd-based catalysts previously selected were coated on structures of various nature (ceramic monoliths and foams) and tested towards the lean methane combustion to simulate a possible real applications (abatement of unburned CH4 residues from compressed natural gas vehicles or ventilation air methane emissions in coal mines). This thesis is organized as a collection of papers, either published during the Ph.D. or submitted for publications. In the first part (catalysts at powder level), the influence of different synthesis methods on the preparation of Pd/Co3O4 catalysts was evaluated (Paper I). Next, the role of the Pd doping on Co3O4 was investigated to determine the optimal Pd loading (Paper II). Then the Pd/Co3O4 catalyst formulation was optimized: the important catalysts’ features determining the reactivity were exploited in a technologically relevant methane concentration range (Paper III). In the end, a series of cobalt iron spinels was investigated to synthesize active catalysts, with a lower content of Co, with the aim of reducing the production costs (Fe cheaper than Co) (Paper IV). As main results, the synthesis method influences the catalytic activity. Indeed, the undoped spinels synthesized by solution combustion synthesis exhibit a better activity respect to the undoped spinel synthesized via precipitation. Thus, evaluating all the informations coming from the various characterizations, the influence of the synthesis method on the catalytic activity of cobalt oxide seems to be related with its redox state. Palladium doping improves the catalytic activity independently of the synthesis method, palladium load, and CH4 inlet concentration. Indeed a complete CH4 oxidation can be reached at a temperature lower than 430 °C for undoped spinels. The addition of palladium led to the formation of a reduced cobalt oxide phase which could contribute to a generation of active oxygen species under reaction conditions. The optimal Pd load is 3wt.%, calculated as PdO. The benefit was due to the existence of well-dispersed Pd nanocrystals. At lower Pd concentrations (0.5% Pd) the amount of Pd was insufficient to catalyze CH4 combustion effectively in the applied conditions, while the specific activity was lost for higher Pd concentrations (5% Pd) because of the agglomeration of Pd nanoparticles. Finally, the addition of Fe to Co3O4 did not affect the catalytic activity of undoped catalysts, supposedly because the rate-determining step of the reaction is the activation of the C–H bond in the CH4 molecule, and apparently, Fe is not influencing the lattice oxygen stability. In the second part of the work, undoped and 3 wt.% Pd-doped cobalt spinel catalysts were deposited on monoliths and open cell foams via solution combustion synthesis using glycine as precursors. The catalyzed structures were impregnated with Pd via wetness impregnation. The catalytic activity were tested toward the methane oxidation in lean conditions, in a gas mixture containing 0.5 vol.% or 1 vol.% CH4 at three different weight hourly space velocity (30, 60, and 90 NL h–1 gcat–1). The addition of Pd improved the catalytic activity of all structures independently on the test conditions. The pressure drop and heat transfer properties were evaluated for monoliths and foams as well. The results show that the foams exhibit an higher catalytic activity than the monolith. Moreover, all the catalysts show better activity at lower weight hourly space velocity. The open cell foam based on zirconia, with the biggest average pore diameter, exhibits the best catalytic activity. In general, zirconia-based foams show a better activity than alumina and silicon carbide ones for all test conditions. In order to well understand the different behavior of the foams, pressure drop measurements and thermal conductivity tests were carried out. From these measurements, the zirconia-based foams have lower pressure drop and lower overall heat exchange coefficients than the monolith and alumina and silicon carbide foams. This aspect can be explained by the higher thermal conductivity of alumina and silicon carbide materials. In conclusion, the obtained results represent a promising scientific advance because they demonstrate the good and stable performance of a 3% Pd/Co3O4 catalyst on a zirconia-based structured support for methane combustion in adiabatic or quasi-adiabatic applications (Papers V and VI). Finally, the basic Co3O4 spinel, synthesized with different methods, was tested as an alternative anodic catalyst for the electrochemical oxygen evolution reaction, the typical reaction of an electrolyzer (Paper VII).

When attempting to communicate with another person, the success or failure that a communicator perceives, he or she interprets as understanding or misunderstanding. Research has shown that "perceived understanding" or the "feeling of being understood" is important in self-concept development. However, for some time researchers have focused on the listener's needs and the speaker's needs have been given less attention. Yet, the listener's role in meeting the speaker's needs, particularly in providing feedback to the speaker, is of utmost importance if the speaker is to have the "feeling of being understood." This research examined the concept of the "feeling of being listened to," as it relates to the "feeling of being understood." Eye contact, vocalics, and head nods were examined as listener behaviors that affect "perceived listening." Alone, in a private room, each subject viewed a randomly-assigned videotape, imagining him- or herself as the speaker, thus, taking the speaker's perspective. The videotape showed the listener, who responded to the speaker with none, one, or all three nonverbal behaviors being tested. Immediately after viewing the videotape, subjects completed two instruments that identified the probability of eye contact, vocalics, and head nods, as pre-conditions of "perceived listening" and "perceived listening" as a pre-condition of "perceived understanding." Tests of the first four hypotheses about the relationship between nonverbal behaviors and perceived listening were non-significant. The test of the fifth hypothesis about the correlation between perceived listening and perceived understanding was significant, but there was some indication that these two concepts may be redundant. A post-hoc analysis of the relationship between nonverbal behaviors and perceived understanding yielded nonsignificant results, supporting the concern that perceived listening and perceived understanding may be redundant concepts.

Brass couplings are used in most piping systems for tap water. The alloy contain a variety of metal composition, amongst these metals lead is included. Lead is a toxic metal that can leach from brass when it is in contact with aqueous solutions. There are several physical and chemical conditions that affect the leaching of lead. Stagnation time, material composition and water quality are some of these conditions. The aim of this project is to generate a dataset that can be used for evaluation of the leaching of heavy metals from brass couplings during different hydrochemical conditions. By exposing brass couplings to synthetic waters various properties, analyse the results and comparing these to limits set by approval procedures it is possible to obtain a prediction on how the brass couplings might leach lead when installed in tap water systems. Results shows that at least one of the brass couplings included in this test could be unfit for usage in drinking water system installations.

Doctor of Philosophy
Department of Plant Pathology
Erick D. DeWolf
Stripe rust (caused by Puccinia striiformis f. sp. tritici) and leaf rust (caused by Puccinia triticina) are the top two diseases of winter wheat (Triticum aestivum) with a 20-year average yield loss of 4.9% in Kansas. Due to the significant yield losses caused by these diseases, the overall objective of this research was to identify environmental variables that favor stripe and leaf rust epidemics. The first objective was to verify the environmental conditions that favor P. triticina infections in an outdoor field environment. Wheat was inoculated with P. triticina and exposed to ambient weather conditions for 16 hours. Number of hours with temperature between 5 to 25°C and relative humidity >87% were highly correlated and predicted leaf rust infections with 89% accuracy. The results of this outdoor assay were used to develop variables to evaluate the association of environment with regional leaf rust epidemics. Before regional disease models can be developed for a forecast system, suitable predictors need to be identified. Objectives two and three of this research were to identify environmental variables associated with leaf rust and stripe rust epidemics and to evaluate these predictors in models. Mean yield loss on susceptible varieties was estimated for nine Kansas crop reporting districts (CRD’s). Monthly environmental variables were evaluated for association with stripe rust epidemics (>1% yield loss), leaf rust epidemics (>1% yield loss), severe stripe rust epidemics (>14% yield loss) and severe leaf rust epidemics (>7% yield loss) at the CRD scale. Stripe rust and leaf rust epidemics were both strongly associated with soil moisture conditions; however, the timing differed between these diseases. Stripe rust epidemics were associated with soil moisture in fall and winter, and leaf rust epidemics during winter and spring. Severe stripe rust and leaf rust epidemics were associated with favorable temperature (7 to 12°C) and temperature (15 to 20°C) with relative humidity (>87%) or precipitation in May using tree-based methods of classification, respectively. The preliminary models developed in this research could be coupled with disease observations and varietal resistance information to advise growers about the need for foliar fungicides against these rusts in Kansas winter wheat.

The objective of this study is to examine lean production and its effects on general working conditions and occupational health and safety. Lean production is considered either as a humane way of production with positive effects on workers or to have negative consequences for workers'
and their job quality. This study investigates the increasing workload of the workers as a result of the unlimited performance demands of lean production as the first hypothesis. Secondly, there is the question of whether lean production provides a reduction in the number of occupational accidents because of the fact that occupational accidents are seen as waste, thus eliminated at all costs. The last hypothesis which will be assessed is that the number of occupational diseases increases after the implementation of lean production. To that end, a case study was carried out in an automotive plant by a qualitative research method using tools of observation, document analysis, in depth interview and structured interview. As a conclusion, the implementation of lean production in a plant in automotive industry has resulted in the reduction of the occupational accidents and improvement of ergonomic conditions even though the main incentive for these improvements is to reduce the wastes and costs and to increase the profitability and competitiveness. Based on the interviews, workers do not consider that their workload is increased after the implementation of lean production. Besides, workers feel work autonomy and job satisfaction. They also claim that they do not feel job stress in contrast to the literature.

L'ouvrage se propose d'aborder l'economie, la societe et les mentalites castillanes au dix-huitieme siecle, a partir de l'etude d'un cas particulier, la ville de leon et sa juridiction. Le cadre spatial retenu permet d'envisager une approche globale d'une ville et de sa campagne. L'ensemble represente quatre-vingt dix villages et environ quinze mille habitants. La premiere partie est consacree au cadre geographique et institutionnel que constituent la ville et sa juridiction. Une analyse de la structure et de l'evolution de la population entre mille cinq cent quatre-vingt dix et mille huit cent vingt completent cette premiere partie. La seconde partie analyse les structures socio-professionnelles de la ville et de sa campagne du seizieme au dix-huitieme siecle. L'economie de la ville et de sa campagne, les structures generales de la propriete et la propriete fonciere urbaine au dix-huitieme siecle font l'objet d'une etude plus detaillee. Les mentalites au dix-huitieme siecle sont enfin evoquees dans une troisieme partie organisee autour de deux themes : le poids de la religion que revelent testaments et representations (tableaux, sculptures, etc. ) et la penetration des lumieres dans la vieille castille du dix-huitieme siecle. Ce dernier aspect se fonde sur la mesure de l'alphabetisation et sur l'analyse des lecteurs et des lectures leonais
The purpose of this work is to approach eighteenth-century castilian economy, society and mentalities through the study of a particular case, the town of leon and its jurisdiction. The choice of these spatial limits allows a global approach of a town and of its countryside, which as a whole represent ninety villages and about fifteen thousand people. The first part deals with the geographical and institutional limits of the town and its jurisdiction. This is completed by an analysis of the structure and evolution of the population between fifteen-ninety and eighteen-twenty. The second part analyses the socio-professional structures of the town and of its countryside from the sixteenth until the eighteenth century. The economy of the town and of its countryside, the general structure of property, and urban landel property in the eighteenth century are studied in greater detail. The mentalities in the eighteenth century are analysed in a third part which is organized along two themes : the weight of religion which is revealed in wills and representations (pictures, sculptures, etc. ), and the penetration of the enlightenment in eighteenth-century old castile, this last aspect being based on a measure of literacy and on an analysis of leonese readers and readings

Ferroelectric materials have received lots of attention thanks to their intriguing properties such as the piezoelectric and pyroelectric effects, as well as the large dielectric constants and the spontaneous polarization which can potentially be used for information storage. In particular, perovskite crystal has a very simple unit cell structure yet a very rich phase transition diagram, which makes it one of the most intensively studied ferroelectric materials. In this dissertation, we use effective Hamiltonian, a first-principles-based computational technique to study the finite-temperature properties of ferroelectric perovskites. We studied temperature-graded (BaxSr1-x )TiO3 (BST) bulk alloys as well as the dynamics of nanodomain walls (nanowalls) in Pb(ZrxTi1-x )O3 (PZT) ultra-thin films under the driving force of an AC field. Our computations suggest that, for the temperature-graded BST, the polarization responds to the temperature gradient (TG), with the "up" and "down" offset observed in polarization components along the direction of TG, in agreement with the findings from experiments. For the nanowalls in PZT, the dynamics can be described by the damped-harmonic-oscillator model, and we observed a size-driven transition from resonance to relaxational dynamics at a critical thickness of 7.2 nm. The transition originates from the change in the effective mass of a nanowall as a film thickness increases. Some of the findings may find potential applications in various devices, such as thermal sensors, energy converters, or novel memory units.

Brass components are widely used in drinking water distribution systems as valves, faucets and other fixtures. They can be corroded by â dezincification,â which is the selective leaching of zinc from the alloy. Dezincification in potable water systems has important practical consequences that include clogged water lines, premature system failure and leaks, and release of contaminants such as lead. Brass failures attributed to dezincification are known to occur at least occasionally all over the world, and have emerged as a significant problem in the U.S. recently due to the use of inexpensive high zinc brass fittings in cross-linked polyethylene (PEX) plumbing systems. As PEX systems gain popularity and leaded brass is recognized as an important source of lead in potable water systems, it is important to examine dezincification corrosion in more detail.

An in-depth literature review revealed that conventional wisdom about dezincification was no longer adequate in explaining failures observed in modern water systems. Little research has been conducted since the landmark work of Turner et al. nearly half a century ago. The potential role of chloramines, phosphate inhibitors, and modern understanding of water chemistry need evaluation. The role of physical factors including stirring, heating and galvanic connections are also potentially influential.

A mechanistic study of zinc solubility and corrosion of copper: zinc couples provided insight to factors that might mitigate and exacerbate zinc leaching from brass. Zinc solubility and corrosion was reduced by higher pH and bicarbonate, but was enhanced by higher chloride. Hardness ions including Mg+2 and Ca+2 had little effect.

Alloys with higher zinc content had a greater propensity for dezincification corrosion. Stirring and galvanic connections caused brass to leach more metals and have higher weight loss. Heating may contribute to corrosion scale accumulation.

A comprehensive examination of dezincification as a function of water chemistry used numerous techniques that include measurement of galvanic currents, metal leaching, and weight loss. In general, as would be predicted based on results of the study of solubility and corrosion of pure zinc, chloride emerged as an aggressive ion whereas bicarbonate was beneficial to brass corrosion. Hardness had little impact, and phosphates, silicates and Zn+2 inhibitors had a significant short-term benefit but little long-term benefit.

The relationship between dezincification corrosion, lead leaching from brass, and water chemistry was investigated in Chapter 5. Surprisingly, lead and zinc leaching from a range of brasses were found to be negatively correlated. Hence, use of brasses that minimize dezincification problems might increase lead leaching.

This thesis represents a comprehensive analysis of factors that are influential for dezincification and lead leaching from brass in premise water distribution systems through literature reviews, mechanistic investigations, bench-scale experiments, and case studies. Results can be used by water utilities, plumbing engineers, manufacturers and home owners to better prevent, recognize, and mitigate brass and dezincification corrosion problems.
Master of Science

Maintaining due diligence on safety practices at the workplace of battery technicians is the most cost-effective intervention against lead-related hazards. The safety practice on lead poisoning in Nigeria is below average, and the compliance level is far from the expected target of 90%. Using Dejoy's workplace self-protective behavior theory, this study investigated multilevel factors that influence safety practices on lead poisoning and compared the rate of utilization of personal protective equipment by battery technicians in the organized and roadside settings. The study was a quantitative, cross-sectional survey design, and a multistage and systematic sampling technique was used to select 293 adult battery technicians aged 18 years and above. Hypotheses were tested with chi-square and multivariate logistic regressions at the significant level of p < 0.05 and 95% confidence interval. The outcome of the safety practice status of battery technicians is 20%, and the rate of utilization of personal protective equipment is 18% in Lagos, Nigeria. Findings revealed that workplace conditions, blood lead levels, knowledge, education, and the rate of utilization of personal protective equipment are predictors of the safety practice status of battery technicians. There was no significant difference between battery technicians in the organized and roadside setting considering the perceived risk of lead poisoning and utilization of personal protective equipment. The positive social change implications of this study include recommendations for battery technicians to use the evolved alternative safety approaches to reduce lead-related hazards. Public health professional and policymakers should invest resources towards reducing the impact of lead poisoning on battery technicians at the workplace.

Reduction of the pollutant emissions is a challenge for the gas turbine industry. A solution to this problem is to employ the low swirl burner which can operate at lower equivalence ratios than a conventional swirl burner. However, flames in the lean regime of combustion are susceptible to flow perturbations and combustion instability. Combustion instability is the coupling between unsteady heat release and combustor acoustic modes where one amplifies the other in a feedback loop. The other method for significantly reducing NOx and CO2 is increasing fuel reactivity, typically done through the addition of hydrogen. This helps to improve the flammability limit and also reduces the pollutants in products by decreasing thermal NOx and reducing CO2 by displacing carbon. In this work, the flammability limits of a low swirl burner at various operating conditions, is studied and the effect of pressure, bulk velocity, burner shape and percent of hydrogen (added to the fuel) is investigated. Also, the flame structure for these test conditions is measured using OH planar laser induced fluorescence and assessed. Also, the OH PLIF data is used to calculate Rayleigh index maps and to construct averaged OH PLIF intensity fields at different acoustic excitation frequencies (45-155, and 195Hz). Based on the Rayleigh index maps, two different modes of coupling between the heat release and the pressure fluctuation were observed: the first mode, which occurs at 44Hz and 55Hz, shows coupling to the flame base (due to the bulk velocity) while the second mode shows coupling to the sides of the flame. In the first mode, the flame becomes wider and the flame base moves with the acoustic frequency. In the second mode, imposed pressure oscillations induce vortex shedding in the flame shear layer. These vortices distort the flame front and generate locally compact and sparse flame areas. The local flame structure resulting from these two distinct modes was markedly different.

Thesis (M.S.) -- University of Maryland, College Park, 2008.
Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

We examined the claim that equivalence classes contain all positive elements in a reinforcement contingency by asking whether negative stimuli in a reinforcement contingency will also form an equivalence class, based on their shared function as S-minus stimuli. In Experiment 1, 5 subjects were tested for equivalence for positive and negative stimuli. Testing of positive stimuli preceded testing of negative stimuli. Two of five subjects demonstrated equivalence for positive stimuli, and three subjects demonstrated equivalence for negative stimuli. In Experiment 2, order of testing was reversed. Four of six subjects demonstrated equivalence for positive stimuli, and none demonstrated equivalence for negative stimuli. In Experiment 3, positive and negative stimuli were tested together. Only one of five subject demonstrated equivalence for positive and negative stimuli. These data suggest that negative stimuli may enter an equivalence class, and so Sidman paradigm should be expanded. Order of testing was found as a meaningful variable.

In this study, catalytic activity of the Co and/or Pb-SBA-15 mesoporous catalysts in methane partial oxidation reaction was investigated. By using sol-gel, incipient wetness impregnation and post grafting method, SBA-15 samples are incorporated with Co and/or Pb at different weight loadings to provide a controlled geometry in nanometer scale. The characterization of the synthesized samples was done by XRD, N2 adsorption isotherms, FTIR, TEM images, Raman and XPS analysis. In the present study also, gas phase methane partial oxidation modeling and the synthesizing of mesoporous SBA-15 silica with different pore sizes were investigated. For the samples prepared by sol-gel method, XRD analysis showedthat cobalt exists in the form of Co3O4and Pb exist in the form of PbO. BET surface areas of the Co loaded catalysts are in the range of 479.5-640.1 m2/g. However, in Pb loaded samples, higher metal loading decrease the surface area up to 4.63 m2/g. Considering the both Co and Pb containing bi-metallic samples, TEM and BET results revealed that the ordered hexagonal mesostructure was fully destroyed. The samples prepared by incipient wetness impregnation and post grafting method characterized by using BET, TEM, Raman and XPS analysis. According to the BET results all the samples show ordered mesostructure in agreement with TEM results for all Co and/or SBA-15 mesoporous samples. TEM results also revealed that, the Co(5%) Pb(5%)-SBA-15 catalyst prepared by incipient wetness impregnation method possess big cobalt and lead oxide crystallines on the mesoporous structure. Raman analysis results indicated that cobalt exist in Co3O4 form. According to XPS results all samples containing cobalt include Co3O4. The partial oxidation of methane was carried out in a fixed bed flow-type reactor in a temperature range of 50&ndash
850°
C under atmospheric pressure.According to the reaction test results, the 0.5%Rh-Co-SBA15 catalyst shows the highest methane conversion (82%) and H2 selectivity. The non-precious metal show lower reactivities, addition of Pb to the Co-SBA-15 catalyst increases the catalytic activity and decrease the H2 production temperature.

Two Pore domain K+ channels (K2P) are a specific family of channels whose functionality is finely tuned by a rich ensemble of chemical and physical stimuli. The ionic currents produced by these proteins are usually referred as ‘’leak’’ or ‘’background’’ potassium currents because they stabilize the resting potential of membranes to highly negative values close to the K+ equilibrium potential. In particular, the human TRAAK channel (Twik Related Arachidonic Acid K+ channel) is influenced by chemicals (anesthetics or drugs), and physical agents (pH, temperature, membrane stretching or bending). Although the firsts experimental findings date back to early ‘00 a full comprehension of the gating mechanism and ion transport is still missing. Among the most influential theories on gating, we mention the two states hypothesis suggested by MacKinnon thanks to the crystal structure availability. The existence of an atomistic model paved the way to furthers investigations, as well by using theoretical approaches. In this context, exploiting in silico techniques belonging to computational biophysics, we provided a comprehensive characterization of the channel behaviour. Advanced simulating conditions were used, with the purpose of mimicking as close as possible the real protein behaviour, and some of those key-biases playing a modulation role of channel activity. By using Molecular Dynamics simulations, several protocols were applied to simulate hTRAAK in presence of different conditions: i) membrane stretching, ii) ions concentration gradients, iii) applied electrostatic potential. These strategies were chosen to gain new insights into the putative conductive state of the channel, promoting the translocation of K+ ions through it.

Thesis (MEng)--Stellenbosch University, 2004.
ENGLISH ABSTRACT: This thesis presents the design of a DSP based controller system for an auxiliary converter for generic energy storage connection to a line-interactive power compensator. The aim is to utilize a wide range of energy storage systems and incorporate them into the existing power compensator. This was done by adding a second converter to the system. The new controller was developed to control this converter and thereby the energy storage. A study was done on lead acid batteries, flow batteries and flywheels in order to gain a basic understanding of these systems and identify the requirements for their control. Based on these findings, a new DSP based controller and measuring system was developed. To test the new system a dc to dc converter was implemented for the control of lead acid and flow batteries. A dc to ac converter was also tested for the control of flywheel energy storage.
AFRIKAANSE OPSOMMING: Die tesis handeloor die ontwerp van'n DSP gebaseerde beheerstelsel vir 'n Iyninteraktiewe on-onderbreekbare kragbron met drywings-kompensasie met 'n hulp omsetter vir algemene enegiestoor koppeling. The doel is om 'n wye verskeindheid energie store in die huidige drywings elektroniese stelsel te inkorporeer. 'n Tweede omstetter is by die stelsel gevoeg om die energie stelsel te beheer. 'n Nuwe beheerder is ontwikkel om die omsetter te beheer en daardeur die energie stoor. Loodsuur batterye, vloei batterye en vliegwiele is ondersoek om 'n basiese begrip te vorm en te identifiseer wat nodig is vir die beheer van sulke energie store. Die nuwe DSP beheerder en meetstelsel is ontwikkel gebaseer op hierde ondervindings. Om die nuwe beheerstelsel te toets is 'n gs na gs omsetter geïmplementeer vir die beheer van loodsuur en floei batterye. Die omsetter is geherkonfigureer na 'n gs na ws opstelling en getoets. Die konfigurasie word gebruik vir die beheer van vliegwiele.

Doctor of Philosophy
Department of Biology
David A. Haukos
Mottled ducks (Anas fulvigula) are dabbling waterfowl species native to coastal wetlands of the Gulf of Mexico of the United States and Mexico. Although closely related to common waterfowl species such as the mallard (A. platyrhynchos) and American black duck (A. rubripes), the mottled duck exhibits unique behavior, mainly in its life history as a non-migratory species. As such, because of population declines caused by predation, habitat destruction, and environmental contaminants, this species requires specialized conservation concerns and species-specific management to protect population numbers. The goal of this study was to assess ongoing effect of observed lead (Pb) contamination and exposure issues in mottled ducks and their habitats, which I achieved by conducting assessments that will provide managers habitat and organism level metrics to detect and mitigate lead in mottled ducks and their environments. My field study was conducted at the Texas Chenier Plain National Wildlife Refuge Complex (TCPC), which was the area of greatest mottled duck density on the Texas Coast. I first created a body condition index to provide managers a tool to monitor population health, and a proxy for lead exposure and avian health without destructively sampling individuals. I then used presence-only maximum entropy (MaxENT) and multivariate statistical modeling procedures in conjunction with mottled duck movement data to elucidate sets of habitat conditions that were conducive to predicting the occurrence of mottled ducks and environmental lead “hot spots”. MaxENT analyses suggested that lead in the top portion of the soil column is similarly related to all environmental variables considered, may be increasingly available after large-scale environmental disturbances. Lack of variation in coarse-scale habitat use between breeding and non-breeding seasons may further point to a food-based exposure pathway for lead as mottled ducks switch from an invertebrate to plant diet, either as a result of changing age classes or normal adult phenology, during the period of increased lead exposure. Using stable isotope ratio analysis, I then tested environmental samples of soil and vegetation as well as mottled duck blood to determine isotopic signatures that were consistent with particular sources of lead deposition (e.g., lead shot pellets, leaded fossil fuel combustion, industrial effluents). Comparisons suggested a great deal of similarity to lead shot reference values in vegetation and blood samples, especially in blood samples with higher concentrations of lead present. Last, I conducted a formal Ecological Risk Assessment (ERA) procedure to quantify the risk to mottled ducks from lead exposure in their current habitat and direct managers towards effective mitigation and habitat management strategies to reduce exposure in the future. One scenario suggested that mottled ducks were at greatest risk from eating an invertebrate-based diet, but lead content values at the TCPC suggest that a plant-based diet may provide a higher lead exposure risk for mottled ducks, depending on true levels of bioavailability in environmental media. Overall, I determined that mottled ducks experience greatest lead exposure risk from lead shot pellets on the TCPC or in nearby habitat, while potentially also experiencing low levels of exposure from several other sources. Additionally, management efforts that focus on plants that do not provide food resources for mottled ducks as a potential environmental sink for lead contamination, such as phytoremediation, may prove effective in reducing the overall lead load from historical activities that likely deposited much of the lead in this ecosystem.

This thesis is the final assignment for the program master of science in Industrial Design Engineering at luleå university of technology. The timespan is September of 2017 and early January 2018 and is equivalent to 30 high school credits. The work was performed at Martinsons Såg in Bygdsiljum, Sweden.Martinsons is Sweden’s largest producer of cross-laminated timber, crosslam. The staff is divided into two shifts with nine workers each. The production consists of three sections, gluing, CNC and shipping. The factory was expanded in early 2017 but did not achieve planned output. The last section, the shipping, is a bottleneck. The object of this thesis is to find a layout that solves the bottleneck and improve the working conditions in the shipping, and the pace of the system should be determined by the first process, the pressing. The production starts with the planks. Planks are cut to the right dimensions by a saw and placed in layers. Glue is then applied, and more layers are placed and moved to a press while the glue dries. It results in panels. The maximum size of the panels is 16x3 m. A CNC saw cuts the panels to litteras, custom order parts used to build everything from houses to public areas. The workers pack the littera manually. When the litteras are packed, the packages are loaded on trucks for delivery to the customers. The theoretical background of this thesis consists of three major subjects: industrial design engineering, ergonomic and lean production, with a focus on waste reduction. To understand the system the flows and working procedures were documented with observations, interviews, a survey and some filming. An OWAS were used to observed the ergonomic risks and analyse how they can be avoided. Later in the project were a brainstorming session and workshop used to generate concepts to solve the problems. The concepts were evaluated with a value matrix. The results from the examination of the system showed that the real bottleneck in the system was the crane. It was slow and is also used in the waste flows. Two packaging stations for the litteras cannot be used because of the flow of the sawdust, lowering the capacity and flexibility in the packaging. Summarised, the crane could not deal with the demands from the rest of the system. The ergonomic problems consisted of bent and twisted backs while the workers pack the littera. This thesis proposes an investment plan to solve these problems. It consists of two investments that expand the building and expand conveyors, thus removing much of the lifting much lifting with the crane. The waste and littera flows are separated to allow the crane to focus on the main flow of littera.Two new kinds of packaging stations are implemented to help with the packaging: standard stations that pack the littera on lifts and wall packaging stations that packs littera meant for walls that have many weaknesses. The standard stations consist of scissor lift tables that help reduce the time spent with a bent back while packaging. The temperature is maintained at comfortable levels with an airlock to the outside.

Numerous food-borne outbreaks of Escherichia coli O157:H7 have been linked to leafy greens in recent years. An overwhelming amount of lettuce and spinach on the market is sold in modified atmosphere packaging as ready to eat salad mixes. The objectives of this study were to determine the effects of modified atmosphere, storage temperature, and inoculum size on survival of E. coli O157:H7 on cut and whole leaf lettuce and spinach. E. coli O157:H7 H1730 was inoculated onto cut and whole leaves of leaf lettuce and spinach. Samples were held under normal atmospheric conditions or in a modified atmosphere package at either 4ºC or 10ºC to simulate display and abuse temperatures. Leaves were sampled at Days 0, 1 and every other day until visual spoilage occurred (7 days for lettuce, 9 days for spinach). E. coli O157:H7 was able to survive at 4° and 10°C regardless of atmosphere and inoculum size for 7 days on cut and whole lettuce and 9 days on cut and whole spinach. Overall, numbers of E. coli O157:H7 increased (1 log) throughout the storage period on spinach, and decreased on lettuce (1-1.5 log). Significantly higher (P < 0.05) numbers of E. coli O157:H7 were found on lettuce and spinach stored at 10ºC than when stored at 4ºC. There were no significant differences (P > 0.05) in Numbers of E. coli O157:H7 with respect to atmosphere, leaf type or inoculum size. If contamination of lettuce or spinach with E. coli O157:H7 occurred, the pathogen may survive well under typical packaging and storage conditions.
Master of Science in Life Sciences

Contexte et objectifs : Les tentatives pour expliquer les variations des paramètres foliaires fondées uniquement sur les facteurs environnementaux, ce qui conduira à des erreurs importantes si la plante montre des variations ontogénétiques substantielles des propriétés foliaires. Nous avons évalué les variations des 27 traits morpho-anatomiques des feuilles de Dipterocarpus alatus durant six stades de développement architectural et entre les axes à un stade de développement donné sous deux conditions lumineuses différentes.Méthodologies:Une analyse architecturale a été réalisée pour distinguer précisément et objectivement des catégories d'axes et stades de développement de Dipterocarpus alatus. Les feuilles ont été collectées sur l'unité de croissance plus récente et complète sur la partie supérieure du tronc et sur la partie plus externe de la branche du milieu couronne des arbres qui poussent sous deux différentes conditions lumineuses. Vingt-deux traits foliaires ont été mesurées et calculées sur des images de tracés feuilles et de sections transversaux à l'aide de logiciel ImageJ. Densité stomatal a été calculée sur l'impression de vernis à ongles de la surface inférieure des feuilles. Quatre traits de chlorophylle ont été déterminées. Les tests d'ANOVA et Tukey ont été utilisés pour déterminer les différences entre les stades de développement et des axes. La contribution relative lmg a été calculée avec package R relaimpo et comparées avec l'analyse bootstrap pour déterminer le stade ontogénétique, catégorie axe ou l'intensité lumineuse, ce qui est expliqué plus les variations de l'anatomie des feuilles.Résultats:La morphologie et l'anatomie des feuilles diffère fortement durant l'ontogenèse pour les quatre axes en terme d'ordre et de catégorie deux sous des conditions lumineuses. L'effet de l'axe a été présentée au stade B, C, D et F, mais ont tendance à être insignifiante au stade E. Ontogenèse de l'arbre expliqué plus de variations dans la morphologie des feuilles et de l'anatomie que l'intensité lumineuse. Catégorie d'axe expliqué plus de variations dans la morphologie des feuilles, mais pas dans l'anatomie des feuilles que l'ontogenèse de l'arbre. Conclusions:Fortes et significatives variations intra-spécifiques (pendant l'ontogenèse et entre axes) peuvent influencer les variations inter-spécifiques, et donc contestent la validité de la valeur moyenne des traits foliaires entre les espèces. Ontogenèse de l'arbre contribué plus que l'intensité de la lumière dans l'explication de la variabilité dans la morphologie et l'anatomie des feuilles à la fois sur le tronc et deuxième l'ordre l'axe recommande fortement que les études sur les réponses de la morphologie et l'anatomie des feuilles à l'environnement doivent corriger l'effet de l'ontogenèse
Background and Aims:Attempts to explain variations in leaf parameters based solely on environmental factors, this will lead to significant errors if the plant shows substantial ontogenetic variations in leaf properties. We evaluated variations in 27 morpho-anatomical leaf traits of Dipterocarpus alatus over six architectural development stages and between axes at a given development stage under two different light conditions. Methods:An architectural analysis was conducted to distinguish precisely and objectively axis categories and developmental stages of Dipterocarpus alatus. Leaves were collected on the most recent complete growth unit on the top of the trunk and the outermost part of the middle-crown branch with branchlet and twig from trees growing under two different light conditions. Twenty two leaf traits were measured and calculated using ImageJ on images of leaf tracings and cross-sections. Stomatal density was calculated on nail varnish impression of the leaf lower surface. Four chlorophyll traits were determined. One-way ANOVA and Tukey post-hoc tests were used to determine differences between development stages and axes. The lmg relative contribution was calculated with R package relaimpo and compared with bootstrap analysis to determine ontogenetic stage, axis category or light intensity, which explained more the variations in leaf anatomy.Key results:Leaf morphology and anatomy differed strongly during ontogeny for all four axes in term of order and category under both light conditions. The axis effect was displayed at stages B, C, D and F but tend to be insignificant at stage E. Tree ontogeny explained more variations in leaf morphology and anatomy than light intensity. Axis category explained more variations in leaf morphology but not in leaf anatomy than tree ontogeny. Conclusions: Strong and significant intraspecific variations (during ontogeny and between axes) may influence the interspecific variations, and thus challenge the validity of the mean value of leaf traits between species. Tree ontogeny contributed more than light intensity in explanation of the variability in leaf morphology and anatomy both on the trunk and second axis order strongly recommends that studies on the responses of leaf anatomy to the environment need to correct for the ontogeny effect

The medicinal plants are included within the wide diversity of the MaciÃo de Baturità ecosytem and they are an important component of traditional medicine of this region. However, scientific information that may contribute to the increase in the cultivation of these plants are still rare, particularly at conditions of the State of CearÃ. The overall objective of this project is to evaluate the development and the production of alecrim pimenta (Lippia origanoides) at conditions of MaciÃo de BaturitÃ, CearÃ. Two experiments were conducted, the first during the dry season of 2013 (August to November) and the second during the rainy season of 2014 (February to May). The experiment was corned out in completely randomized design with split plots, being the plots defined by two seasons (drought and rainy), the subplot formed by light conditions (greenhouse and full sun), and the subsubplots formed by four evaluation times (0, 40, 80 and 120 days after transplanting). Five replications were used, each one represented by a pot of 20 L containing a plant. The following variables were evaluated: leaf area, plant height, stem diameter, dry matter production, leaf gas exchange, chlorophyll content, mineral nutrients, organic solutes, and essential oils. The alecrim pimenta grows well in the Baturità region, with yields of biomass and essential oil similar to those observed in other studies. The cultivation in greenhouse (50% of solar radiation) changed the pattern of development of alecrim pimenta, resulting in plants with better overall appearance, taller, with larger leaves, higher specific leaf area, less developed root system, and lower root/shoot ratio, regardless of the season of cultivation. The production of dry biomass of leaves and total did not differ between the two environments (light conditions) after 120 days cultivation, regardless of the period of year. During the drought season there was a strong influence of the light condition on stomatal conductance and transpiration, with the values being lower in full sun environment, suggesting stomatal sensitivity to climate conditions in this species. Plants grown in greenhouse showed, in general, higher levels of nutrients and nitrogen compounds (N-aminossolÃveis), compared to plants under full sunlight, regardless of the cropping season.
Dentre os vegetais que compÃem ampla diversidade do MaciÃo de Baturità se inserem as plantas medicinais, sendo estas, principais componentes da medicina tradicional. No entanto, informaÃÃes cientÃficas que possam contribuir para o incremento do cultivo dessas plantas ainda sÃo raras, particularmente nas condiÃÃes edafoclimÃticas do Estado do CearÃ. Objetivou-se com o presente trabalho, avaliar o desenvolvimento e o potencial produtivo do alecrim pimenta (Lippia origanoides) nas condiÃÃes edafoclimÃticas do MaciÃo de BaturitÃ, CearÃ. Foram realizados dois experimentos, sendo o primeiro durante o perÃodo seco de 2013 (agosto a novembro) e o segundo durante o perÃodo chuvoso de 2014 (fevereiro a maio). O experimento foi conduzido seguindo um delineamento inteiramente casualizados com parcelas subsubdivididas, sendo as parcelas definidas pelas duas estaÃÃes (seca e chuvosa), as subparcelas formadas pelas condiÃÃes de luminosidade (telado e pleno sol), e as subsubparcelas pelas quatro Ãpocas de avaliaÃÃo (0, 40, 80 e 120 dias apÃs o transplantio). Foram utilizadas cinco repetiÃÃes, sendo cada repetiÃÃo representada por um vaso de 20 litros contendo uma planta. Foram avaliadas as seguintes variÃveis: Ãrea foliar, altura da planta, diÃmetro do caule, massa seca dos diferentes ÃrgÃos vegetais, trocas gasosas, teores de clorofila, teores de minerais, solutos orgÃnicos e rendimento do Ãleo essencial. O alecrim pimenta desenvolveu-se bem na regiÃo do MaciÃo de BaturitÃ, com produtividades de biomassa e de Ãleo essencial similares Ãs observadas em outros estudos. O cultivo em telado alterou o padrÃo de desenvolvimento do alecrim pimenta, resultando em plantas com melhor aparÃncia geral, mais altas, com folhas maiores, maior Ãrea foliar especÃfica, menor desenvolvimento do sistema radicular e menor relaÃÃo raiz/parte aÃrea, independentemente da Ãpoca de cultivo. A produÃÃo de massa seca de folhas e total nÃo diferiu entre os dois ambientes apÃs 120 dias de cultivo, independentemente do perÃodo do ano. Houve forte influÃncia do ambiente de cultivo no perÃodo seco, sobre a condutÃncia estomÃtica e a transpiraÃÃo, com os valores sendo menores no ambiente a pleno sol, sugerindo a sensibilidade estomÃtica da espÃcie Ãs condiÃÃes atmosfÃricas do perÃodo. As plantas cultivadas em telado apresentaram, de forma geral, maiores teores de nutrientes minerais e de compostos nitrogenados (N-aminossolÃveis), em comparaÃÃo Ãs plantas submetidas a pleno sol, independente do Ãpoca de cultivo.