THE INTERACTION OF IGNITION AND IN-CYLINDER FLOW ON FLAME KERNEL DEVELOPMENT AND ITS IMPACTS ON COMBUSTION IN AN OPTICALLY ACCESSIBLE DIRECT INJECTION ENGINE

A significant challenge facing spark-ignited (SI) engines to achieve higher efficiency via highly diluted combustion is the quickly increased combustion instability as the dilution level increases. The flow motion variation has been identified as a dominant factor that introduces combustion variability at highly diluted conditions. However, the detailed mechanism of how the variation in flow motion impacts the flame kernel development and introduces combustion instability is only partially understood. This research investigated the impacts of the in-cylinder flow on variability of the ignition and early flame kernel development in a single cylinder direct-injection spark-ignition (DI-SI) optically accessible engine and accessory test benches. Firstly, different types of spark plug electrode designs were studied on a spark plug flow fixture bench. The results showed that the impacts of incoming flow on the ignition output vary as the incoming flow direction is changed. The ignition energy drops and discharge duration prolongs as the incoming flow is blocked by any part of the electrodes. Secondly, the flow motion near the spark plug region was investigated in an optical engine through high-speed imaging of the spark discharge arc stretching and flow field measurement via particle imaging velocimetry. It was observed that at motored conditions there is a consistent trend that the flow can change direction from the bulk motion as the piston approaches the top dead center (TDC). The transition of flow direction near the spark plug is a source of variability in initial flame kernel convection and propagation. It was found that by increasing the tumble motion, the transition window can be retarded later in the cycle. Lastly, the impacts of the unstable incylinder flow motion on the flame kernel initiation and development was studied at both diluted and stoichiometric conditions. The 2D and 1D probability distribution functions of the flame kernel indicated that the reversed flow direction near the spark plug at ignition timing results in smaller and less stretched flame kernels, which are a source of combustion variability. As the tumble level is increased, the window where the transition of flow direction occurs near the spark plug also changes. This research indicates that, at the studied loads and speeds, higher tumble level helps maintain a consistent flow motion near the spark plug at the ignition timing, which results in faster growing flame kernels

Solid-state NMR and Electrochemical Dilatometry Study of Charge Storage in Supercapacitor with Redox-active Ionic Liquid Electrolyte

Les liquides ioniques électroactifs se distinguent comme nouveaux électrolytes prometteurs pour les supercapacités électrochimiques en permettant notamment d’atteindre des densités énergétiques plus élevées qu’en milieux organiques ou avec des liquides ioniques traditionnels. Cet accroissement est dû aux réactions de transfert électronique (faradiques) qui y prennent place en plus de ceux dans la double-couche qui sont purement capacitifs. Les études fondamentales sur les mécanismes menant au stockage d’énergie dans des supercapacités à base de liquides ioniques électroactifs sont, bien qu’essentielles, peu nombreuses en comparaison avec les systèmes classiques. Le développement d’approches basées sur la spectroscopie de résonance magnétique nucléaire à l’état solide (SS-NMR) permet l’obtention d’information sur l’environnement local au sein des matériaux d’électrodes qui est nécessaire pour comprendre les mécanismes de stockage dans les supercapacités. Elle permet notamment de suivre l’adsorption et la désorption des ions dans la microstructure du carbone activé utilisé pour les électrodes. Ces approches ont jusqu’à maintenant été utilisées uniquement pour l’étude de systèmes classiques où le stockage n’est effectué que par les mécanismes non-faradiques (double-couche électrigue). Dans ce mémoire je présenterai l’utilisation de la SS-NMR en combinaison avec la dilatométrie électrochimique pour l’étude approfondie des mécanismes de stockage dans des supercapacités constituées d’électrodes à base de carbone activé et utilisant un électrolyte à base de liquide ionique électroactif. La capacité de cette approche pour la détermination de la contribution faradique à la charge emmagasinée a été démontrée pour la première fois. Cette étude a permis de démontrer que le mécanisme de stockage avec un électrolyte électroactif diffère en fonction du voltage appliqué aux électrodes. À l’électrode positive, la désorption des co-ions dans les micropores du carbone activé domine à bas voltage alors que l’adsorption des contre-ions devient importante à haut voltage où elle est accompagnée de l’oxydation du groupement électroactif présent sur le liquide ionique. À l’électrode négative, l’adsorption du contre-ion est le mécanisme principal peu importe le voltage appliqué. L’utilisation de la dilatométrie électrochimique qui permet de mesurer le changement d’épaisseur d’une électrode en fonction du potentiel appliqué a confirmé ces observations. Les résultats de ce mémoire ont permis de mieux comprendre le stockage d’énergie par les supercapacités électrochimiques et l’approche développée pourra être appliquée aux systèmes d’électrolytes électroactifs afin d’en améliorer les performances.Redox-active ionic liquids are emerging as promising new electrolytes for supercapacitors, providing higher capacitance and energy density than organic or ionic liquid electrolytes. Fundamental studies of the charge storage mechanism in supercapacitors are of critical importance for the development and application of devices. Solid-state NMR (SS-NMR) methodology having the ability to provide local environment information within electrodes at the molecular level has been recently developed to study the mechanism of charge storage in supercapacitors. The charge storage in supercapacitors with organic or ionic liquid electrolytes has been studied by SS-NMR. The charge storage in supercapacitors with redox-active species that involves faradaic processes is different from those of electrochemical double-layer capacitors comprising organic solvents or ionic liquids as electrolytes. However, there are until now no published findings on charge storage mechanisms in supercapacitors with redox-active electrolytes. Therefore, fundamental studies of the charge storage mechanism in supercapacitors with redox-active ionic liquid electrolytes are needed. In this thesis, SS-NMR techniques combined with electrochemical dilatometry were used to investigate in depth the charge storage in supercapacitors comprising redox-active ionic liquid electrolytes. The charge contributed from the faradaic reaction of the redox-active species is determined for the first time by the NMR measurements. Moreover, it is revealed that the charge storage mechanism of supercapacitors with the redox-active ionic liquid electrolyte EMIm FcNTf/ACN (1-ethyl-3-methylimidazolium ferrocenylsulfonyl (trifluoromethylsulfonyl) imide/acetonitrile) is driven by different charge regimes for different voltages. More specifically, charge storage on the positive electrode occurs via co-ion desorption in the low voltage range and subsequently counter-ion adsorption in the high voltage range, whereas charging on the negative electrode occurs exclusively by counter-ion adsorption over the studied voltage range. The electrochemical dilatometry measurements show macroscopic dimensional changes of the electrodes during charging, further confirming the proposed mechanism suggested by SS-NMR. The results give a detailed picture of the charge storage of supercapacitors with a redox-active ionic liquid electrolyte, providing new insights on the charge storage in supercapacitors

Chinese WeChat Users and Their Behavioural Features: A Case Study Based on the Grounded Theory

WeChat is a social medium for mobile phones developed by the Chinese company Tencent in 2011. By March 2018, there were one billion active WeChat users, making it the social software with the fastest development in China. Most Chinese WeChat users share WeChat Moments, establish WeChat groups, send WeChat red envelopes, and become WeChat Businessman on WeChat. This paper probes the features of WeChat user behavior in light of the Grounded Theory. The findings revealed four behavioral features: the expression of personality, the connection between individuals, group establishment by individuals, and the connection between individual and group. From the perspective of interpretivism, this paper analyzed such behavior and found that WeChat users are individuals with different characters. Sharing WeChat Moments enables users to become unique individuals and express their personalities in certain social circles. In addition, people through WeChat Moments and WeChat red envelopes enhance the connections among individuals. WeChat Businessman also develops via the connection between individuals. Different individuals can form WeChat groups according to other contexts, and individuals in different groups can have something in common. The connection between individual and group is also a social need. The virtual world established in WeChat can be called the “WeChat world.

Regulation of the heat shock response by thiol-reactive compounds in the yeast Saccharomyces cerevisiae

Cells govern their activities and modulate their interactions with the environment to achieve homeostasis. The heat shock response (HSR) is one of the most well studied fundamental cellular responses to environmental and physiological challenges, resulting in rapid synthesis of heat shock proteins (HSPs), which serve to protect cellular constituents from the deleterious effects of stress. In addition to its role in cytoprotection, the HSR also influences lifespan and is associated with a variety of human diseases including cancer, aging and neurodegenerative disorders. In most eukaryotes, the HSR is primarily mediated by the highly conserved transcription factor HSF1, which recognizes target hsp genes by binding to heat shock elements (HSEs) in their promoters. In recent years, significant efforts have been made to identify small molecules as potential pharmacological activators of HSF1 that could be used for therapeutic benefit in the treatment of human diseases relevant to protein conformation. However, the detailed mechanisms through which these molecules drive HSR activation remain unclear. In this work, I utilized the baker\u27s yeast Saccharomyces cerevisiae as a model system to identify a group of thiol-reactive molecules including oxidants, transition metals and metalloids, and electrophiles, as potent activators of yeast Hsf1. Using an artificial HSE-lacZ reporter and the glucocorticoid receptor system (GR), these diverse thiol-reactive compounds are shown to activate Hsf1 and inhibit Hsp90 chaperone complex activity in a reciprocal, dose-dependent manner. To further understand whether cells sense these reactive compounds through accumulation of unfolded proteins, the proline analog azetidine-2-carboxylic acid (AZC) and protein cross-linker dithiobis(succinimidyl propionate) (DSP) were used to force misfolding of nascent polypeptides and existing cytosolic proteins, respectively. Both unfolding reagents display kinetic HSP induction profiles dissimilar to those generated by thiol-reactive compounds. Moreover, AZC treatment leads to significant cytotoxicity, which is not observed in the presence of the thiol-reactive compounds at the concentrations sufficient to induce Hsf1. Additionally, DSP treatment has little to no effect on Hsp90 functions. Together with the ultracentrifugation analysis of cell lysates that detected no insoluble protein aggregates, my data suggest that at concentrations sufficient to induce Hsf1, thiol-reactive compounds do not induce the HSR via a mechanism based on accumulation of unfolded cytosolic proteins. Another possibility is that thiol-reactive compounds may influence aspects of the protein quality control system such as the ubiquitin-proteasome system (UPS). To address this hypothesis, β-galactosidase reporter fusions were used as model substrates to demonstrate that thiol-reactive compounds do not inhibit ubiquitin activating enzymes (E1) or proteasome activity. Therefore, thiol-reactive compounds do not activate the HSR by inhibiting UPS-dependent protein degradation. I therefore hypothesized that these molecules may directly inactivate protein chaperones, known as repressors of Hsf1. To address this possibility, a thiol-reactive biotin probe was used to demonstrate in vitro that the yeast cytosolic Hsp70 Ssa1, which partners with Hsp90 to repress Hsf1, is specifically modified. Strikingly, mutation of conserved cysteine residues in Ssa1 renders cells insensitive to Hsf1 activation by cadmium and celastrol but not by heat shock. Conversely, substitution with the sulfinic acid and steric bulk mimic aspartic acid led to constitutive activation of Hsf1. Cysteine 303, located in the nucleotide-binding/ATPase domain of Ssa1, was shown to be modified in vivo by a model organic electrophile using Click chemistry technology, verifying that Ssa1 is a direct target for thiol-reactive compounds through adduct formation. Consistently, cadmium pretreatment promoted cells thermotolerance, which is abolished in cells carrying SSA1 cysteine mutant alleles. Taken together, these findings demonstrate that Hsp70 acts as a sensor to induce the cytoprotective heat shock response in response to environmental or endogenously produced thiol-reactive molecules and can discriminate between two distinct environmental stressors

Motivating Millennial Bank Employees in Wenzhou, China from Financial and Non-financial Perspectives

As Generation X retires, Millennial professionals are becoming more involved in the workforce. Numerous skilled individuals from the Wenzhou banking industry have migrated to non-banking financial firms, and banks should seriously consider the job satisfaction of Millennial employees (Sun, 2017). This dissertation focuses on how Wenzhou's banking sector may better motivate its entry-level Millennial staff. This dissertation used semi-structured interviews as a qualitative research method to interview three Millennial grassroots employees of a bank in Wenzhou. As a comparison, three Generation X grassroots employees of the same bank were interviewed. According to this research, Millennial workers' essential employment guarantees were wages and bonuses. They preferred non-monetary benefits and desired participation in courses for professional development and the ability to place a strong focus on career prospects. This finding was consistent with the theory of employees' demand for achievement. The theory's claim that workers only cared about a sense of accomplishment for conquering challenges was refuted by Millennials' frustration with bonuses that were tough to attain. Millennials' job satisfaction was affected by their friendly relationships with colleagues, which contradicted the theory that referred to hygiene factors as irrelevant to motivating employees. There were no obvious variations between the two generations, X and Y. This research provided some recommendations for improvement that were presented correspondingly. Keywords: Motivation, Financial Rewards, Non-Financial Rewards, Millennial