A criterion for existence of right-induced model structures

Suppose that $F: \mathcal{N} \to \mathcal{M}$ is a functor whose target is a Quillen model category. We give a succinct sufficient condition for the existence of the right-induced model category structure on $\mathcal{N}$ in the case when $F$ admits both adjoints. We give several examples, including change-of-rings, operad-like structures, and anti-involutive structures on infinity categories. For the last of these, we explore anti-involutive structures for several different models of $(\infty, 1)$-categories, and show that known Quillen equivalences between base model categories lift to equivalences

An examination of liquidity and investor sentiment in financial markets

This thesis is comprised of three main chapters. The first chapter, "Asymmetric Liquidity Persistence", is based on a working paper co-authored with Jianxin Wang. In this paper, we identify a new autoregressive property of daily liquidity that contributes to sudden liquidity dry-ups. While liquidity is generally highly persistent, this persistence is conditional on past market states. Large negative returns cause liquidity persistence to initially decrease and then increase in the longer-run. We call this Asymmetric Liquidity Persistence (ALP). We show that ALP is present in both market-level and stock-level liquidity. We demonstrate that our ALP model can generate more accurate in-sample and out-of-sample liquidity estimations. According to the predictions of the Amihud (2002) liquidity premium model, our ALP model provides for a superior characterisation of the daily liquidity process. The second chapter is titled "Discretionary Trading Surrounding Anticipated Distraction Events: the Case of the FIFA World Cup". This chapter demonstrates how anticipated market-orthogonal events can induce discretionary trading. Following Ehrmann and Jansen (2017), this study uses FIFA World Cup matches that occur during trading hours as an exogenous shock to the opportunity cost of monitoring markets. World Cup football matches have an impact on contemporaneous trading and an asynchronous impact on the rest of the trading day. In particular, when World Cup matches occur in the middle of the trading day, there is an abnormally large amount of trading between market open and kick-off time. Dollar trading volume between 120 to 90 minutes before kick-off is 23.4% of a standard deviation higher than normal levels. This is due to a temporal substitution effect whereby traders submit their orders prior to kick-off in order to avoid trading during match time. During this pre-match period, markets exhibit greater liquidity, volatility and price discovery. During matches, markets exhibit reduced liquidity, volatility and price discovery. The extraordinary market conditions that occur on match days follow the theoretical predictions of the Admati and Pfleiderer (1988) discretionary trading model. The third chapter, "Sports Sentiment and Stock Returns: An Intra-day Study", builds upon the behavioural finance literature and in particular, the influential study of Edmans, Garcia, and Norli (2007). Edmans et al. (2007) demonstrate that sporting results can predict overnight stock returns. The authors attribute this to a sports sentiment effect. In this thesis chapter, I demonstrate that the Edmans et al. (2007) daily sentiment effect is still present in a more recent sample of stock market data. In addition, I utilise all FIFA World Cup matches that have occurred during trading hours since 1998 to determine that there is an analogous intra-day sentiment effect. Winning full-time outcomes are associated with positive abnormal stock returns for the remainder of the trading day. Moreover, unexpected victories and victories over traditional rivals have a significant and positive marginal impact on abnormal stock returns. Using trade and quote data, this study also documents abnormal order imbalance and quote revision activity surrounding half-time match outcomes. Evidence suggests that both liquidity takers and providers are influenced by investor sentiment. Small trades exhibit the greatest sentiment effects. Following the three main thesis chapters, I provide concluding remarks and discuss limitations and future research opportunities for each research project

Methods for Prediction of High-Speed Reacting Flows in Aerospace Propulsion

Research to develop high-speed airbreathing aerospace propulsion systems was underway in the late 1950s. A major part of the effort involved the supersonic combustion ramjet, or scramjet, engine. Work had also begun to develop computational techniques for solving the equations governing the flow through a scramjet engine. However, scramjet technology and the computational methods to assist in its evolution would remain apart for another decade. The principal barrier was that the computational methods needed for engine evolution lacked the computer technology required for solving the discrete equations resulting from the numerical methods. Even today, computer resources remain a major pacing item in overcoming this barrier. Significant advances have been made over the past 35 years, however, in modeling the supersonic chemically reacting flow in a scramjet combustor. To see how scramjet development and the required computational tools finally merged, we briefly trace the evolution of the technology in both areas

Supersonic reacting internal flow fields

The national program to develop a trans-atmospheric vehicle has kindled a renewed interest in the modeling of supersonic reacting flows. A supersonic combustion ramjet, or scramjet, has been proposed to provide the propulsion system for this vehicle. The development of computational techniques for modeling supersonic reacting flow fields, and the application of these techniques to an increasingly difficult set of combustion problems are studied. Since the scramjet problem has been largely responsible for motivating this computational work, a brief history is given of hypersonic vehicles and their propulsion systems. A discussion is also given of some early modeling efforts applied to high speed reacting flows. Current activities to develop accurate and efficient algorithms and improved physical models for modeling supersonic combustion is then discussed. Some new problems where computer codes based on these algorithms and models are being applied are described

Supersonic combustor modeling

The physical phenomena involved when a supersonic flow undergoes chemical reaction are discussed. Detailed physical models of convective and diffusive mixing, and finite rate chemical reaction in supersonic flow are presented. Numerical algorithms used to solve the equations governing these processes are introduced. Computer programs using these algorithms are used to analyze the structure of the reacting mixing layer. It is concluded that, as in subsonic flow, exothermic heat release in unconfined supersonic flows retards fuel/air mixing. Non mixing is shown to be a potential problem in reducing the efficiency of supersonic as well as subsonic combustion. Techniques for enhancing fuel/air mixing and combustion are described

A two-dimensional numerical simulation of a supersonic, chemically reacting mixing layer

Research has been undertaken to achieve an improved understanding of physical phenomena present when a supersonic flow undergoes chemical reaction. A detailed understanding of supersonic reacting flows is necessary to successfully develop advanced propulsion systems now planned for use late in this century and beyond. In order to explore such flows, a study was begun to create appropriate physical models for describing supersonic combustion, and to develop accurate and efficient numerical techniques for solving the governing equations that result from these models. From this work, two computer programs were written to study reacting flows. Both programs were constructed to consider the multicomponent diffusion and convection of important chemical species, the finite rate reaction of these species, and the resulting interaction of the fluid mechanics and the chemistry. The first program employed a finite difference scheme for integrating the governing equations, whereas the second used a hybrid Chebyshev pseudospectral technique for improved accuracy

Coextension of scalars in operad theory

The functor between operadic algebras given by restriction along an operad map generally has a left adjoint. We give a necessary and sufficient condition for the restriction functor to admit a right adjoint. The condition is a factorization axiom which roughly says that operations in the codomain operad can be written essentially uniquely as operations in arity one followed by operations in the domain operad

Comparison of Mixing Characteristics for Several Fuel Injectors at Mach 8, 12, and 15 Hypervelocity Flow Conditions

CFD analysis is presented of the mixing characteristics and performance of three fuel injectors at flight Mach numbers of 8, 12, and 15. The Reynolds-averaged simulations (RAS) were carried out using the VULCAN-CFD solver. The high Mach number flow conditions match those of the experiments conducted as a part of the Enhanced Injection and Mixing Project (EIMP) at the NASA Langley Research Center. The EIMP aims to investigate scramjet fuel injection and mixing physics, improve the understanding of underlying physical processes, and develop enhancement strategies relevant to flight Mach numbers greater than 8. The injectors include a fuel placement device, a strut, and a fluidic vortical mixer, a ramp. These fuel injectors accomplish the necessary task of distributing and mixing fuel into the supersonic cross-flow, albeit via different strategies. For comparison, a flush-wall injector is also included. This type of injector generally represents the simplest method of introducing fuel into a scramjet combustor. The three injectors represent the baseline configurations of the EIMP experiments. The mixing parameters of interest, such as mixing efficiency and total pressure recovery, are computed from the RAS and compared for the three flight conditions and injector configurations. In addition to mixing efficiency and total pressure recovery, the combustion efficiency and thrust potential are also computed for the reacting simulations. Plotting the total pressure recovery and thrust potential as a function of mixing efficiency provides added insight into critical aspects of combustor performance as the flight condition and injector type are varied

The Effect of Turbulence Modeling on the Mixing Characteristics of Several Fuel Injectors at Hypervelocity Flow Conditions

CFD analysis is presented on the effects of turbulence modeling choices on the mixing characteristics and performance of three fuel injectors at hypervelocity flow conditions. The analyses were carried out with the VULCAN-CFD solver using Reynolds-Averaged Simulations (RAS). The hypervelocity flow conditions match the high Mach number flow of the experiments conducted as a part of the Enhanced Injection and Mixing Project (EIMP) at the NASA Langley Research Center. The three injectors are the baseline configurations used in the experiments and represent three categories of injectors typically considered individually or in combination for fueling high-speed propulsive devices. The current work discusses the impact of the turbulence model and the turbulent Schmidt number on the mixing flow field behavior and the mixing performance as described by the one-dimensional values of the Mach number, total pressure recovery, and the mixing efficiency. Because planar laser induced fluorescence (PLIF) images are available from the EIMP experiments, the sensitivity of the synthetic LIF signal to turbulence modeling choices is also examined to determine whether PLIF can be extended beyond its intended qualitative visualization purpose and used to guide CFD turbulence model and parameter selections. It is found that the mixing performance, as quantified using mixing efficiency, exhibits a strong sensitivity to both turbulence model choice and turbulent Schmidt number value. However, the synthetic LIF signal only demonstrates a modest level of sensitivity, which suggests that PLIF is of limited use for guiding CFD turbulence model and parameter selections

DIVERSITY OF ARCHAEA FROM THREE FORESTED ECOSYSTEMS IN GSMNP

Prokaryotes are vital to the survival of all life on Earth since they control the cycles of many elements including carbon, nitrogen, sulfur, etc. The study of the Archaea has resulted in numerous novel metabolic discoveries, most from extreme environments; however, little is known about archaea and their roles intemperate ecosystems. DNA was extracted directly from soil from three forested ecosystems in Great Smoky Mountains National Park and was used to characterize community structure using molecular techniques including PCR followed by molecular cloning and restriction fragment length polymorphism(RFLP) analysis, denaturing gradient gel electrophoresis (DGGE) and DNA sequencing. Seventeen archaea were sequenced, including species aligned to the phylum Crenarchaea, which so far contains only one organism cultured from a non-extreme environment. Overlap was seen between clones sampled from multiple sites and from DGGE banding patterns, indicating that some archaeal species are widespread . The extent of archaeal diversity is unknown and is thought to be dwarfed by bacteria; however, our understanding of archaea is limited due to their resistance to being cultivated. Obtaining a baseline of diversity in this group should ultimately help yield isolated species for further study of their unique metabolisms and biochemical properties