Numerical Investigation of Chemical Reactivity Effects on the Formation of Gaseous Oblique Detonation Waves

The concept of using oblique detonation waves for high efficiency propulsion systems have recently generated great interest in the development of air-breathing hypersonic aircraft due to their potential increased thermal efficiency through detonative combustion. However, for the proper design of an Oblique Detonation Wave Engine (ODWE), it is critical to predict the necessary conditions and understand the formation mechanism of oblique detonation waves. In this study, numerical simulations using a Graphics Processing Unit (GPU)-based solver are performed to investigate oblique detonations induced by a two-dimensional, semi-infinite wedge using the reactive Euler equations coupled with one-step Arrhenius or two-step induction-reaction kinetics. The novelty of this work lies in the analysis of chemical reaction sensitivity on the two types of oblique detonation formation, namely, the abrupt onset with a multi-wave point and a smooth transition with a curved shock. Scenarios with various inflow Mach number regimes M0 and wedge angles θ are considered. The conditions for these two formation types are described quantitatively by the obtained boundary curves in M0-Ea and M0-kR spaces. At a low M0, the critical conditions for the transition are independent of the wedge angle. At a high flow Mach number regime with M0 above approximately 9.0, the boundary curves for the three wedge angles deviate substantially from each other. The overdrive effect induced by the wedge becomes the dominant factor on the transition type. For large Ea the flow in the vicinity of the initiation region and subsequent ODW surface also exhibit more complex features

Where does Pseudo-cleft Construction Come from in Taiwan Southern Min?

PACLIC 21 / Seoul National University, Seoul, Korea / November 1-3, 200

El e-commerce reemplaza la compra presencial en tiendas por departamento: Saga Falabella

En medio de un complejo entorno de incertidumbre empresarial, causado por la pandemia del coronavirus, nace el tema central del presente artículo, el cual busca demostrar si el comercio electrónico logrará reemplazar la compra presencial en Saga Falabella. Por otro lado, se describen las medidas a implementar dentro del canal online de Saga Falabella. Esto con el fin de lograr eficiencia y así poder satisfacer la creciente demanda y tendencia de seguridad de los consumidores. Cabe resaltar que el análisis se realiza únicamente en las tiendas de Lima Metropolitana, Perú

Evolutionary conservation of DNA-contact residues in DNA-binding domains

<p>Abstract</p> <p>Background</p> <p>DNA-binding proteins are of utmost importance to gene regulation. The identification of DNA-binding domains is useful for understanding the regulation mechanisms of DNA-binding proteins. In this study, we proposed a method to determine whether a domain or a protein can has DNA binding capability by considering evolutionary conservation of DNA-binding residues.</p> <p>Results</p> <p>Our method achieves high precision and recall for 66 families of DNA-binding domains, with a false positive rate less than 5% for 250 non-DNA-binding proteins. In addition, experimental results show that our method is able to identify the different DNA-binding behaviors of proteins in the same SCOP family based on the use of evolutionary conservation of DNA-contact residues.</p> <p>Conclusion</p> <p>This study shows the conservation of DNA-contact residues in DNA-binding domains. We conclude that the members in the same subfamily bind DNA specifically and the members in different subfamilies often recognize different DNA targets. Additionally, we observe the co-evolution of DNA-contact residues and interacting DNA base-pairs.</p

Critical Tube Diameter for Quasi-Detonations

The critical tube diameter problem for quasi-detonations is studied via experiments and two-dimensional numerical simulations based on the reactive Euler equations. In the experiments, quasi-detonation in stoichiometric acetylene-oxygen mixtures is generated in rough-walled tubes with three different diameters, where the wall roughness is introduced by using spiral inserts with different wire diameters. Photodiodes are placed along the rough tubes to record the detonation time-of-arrival to deduce the velocity, and a high-speed schlieren system is used to observe the diffraction processes. Near the critical regime of detonation diffraction, the quasi-detonation emerging from the rough tube is again shown to first fail and subsequently re-initiate from a local explosion center in the spherical deflagration reaction zone. For quasi-detonations, stronger turbulence and instabilities produce stronger local hot spots, which balances the significant velocity deficit as much as approximately 15% in the rough tube, resulting in the critical pressure remaining relative constant. The cell sizes for quasi-detonation in rough tubes are directly measured, and the ratio of critical tube diameters (dc) to these determined cell sizes (λ) is used to quantify the critical criterion of detonation initiation. In rough tubes with coil springs, the previous criterion of dc/λ ≧ 13 for detonation re-initiation appears invalid, and the critical initiation regime for quasi-detonation in rough tubes is found approximately as dc/λ ≧ 8. Despite the cell enlargement and the lower propagation velocity for quasi-detonation, it is hypothesized that the increase in cell irregularities or instabilities can in turn benefit the transmission process. These unstable features of quasi-detonation are supported by the two-dimensional numerical simulations, also showing a higher degree of cell irregularities, a wider spectrum of induction rate, and the generation of shocked reactive pockets

The Effect of Chemical Reactivity on the Formation of Gaseous Oblique Detonation Waves

High-fidelity numerical simulations using a Graphics Processing Unit (GPU)-based solver are performed to investigate oblique detonations induced by a two-dimensional, semi-infinite wedge using an idealized model with the reactive Euler equations coupled with one-step Arrhenius or two-step induction-reaction kinetics. The novelty of this work lies in the analysis of chemical reaction sensitivity (characterized by the activation energy Ea and heat release rate constant kR) on the two types of oblique detonation formation, namely, the abrupt onset with a multi-wave point and a smooth transition with a curved shock. Scenarios with various inflow Mach number regimes M0 and wedge angles &theta; are considered. The conditions for these two formation types are described quantitatively by the obtained boundary curves in M0&ndash;Ea and M0&ndash;kR spaces. At a low M0, the critical Ea,cr and kR,cr for the transition are essentially independent of the wedge angle. At a high flow Mach number regime with M0 above approximately 9.0, the boundary curves for the three wedge angles deviate substantially from each other. The overdrive effect induced by the wedge becomes the dominant factor on the transition type. In the limit of large Ea, the flow in the vicinity of the initiation region exhibits more complex features. The effects of the features on the unstable oblique detonation surface are discussed