1,564 research outputs found
Computational Confirmation of AN Abnormal Mach Reflection Wave Configuration
No full textFor the Mach reflection (MR) of symmetric shock waves of opposite families, only the wave configuration of an overall Mach reflection (oMR) consisting of two direct Mach reflections (DiMR+DiMR) is theoretically admissible. For asymmetric shock waves, an oMR composed of a DiMR and an inverse Mach reflection (InMR) is possible if the two slip layers assemble a converging-diverging stream tube, while an oMR including two inverse Mach reflections (InMR+InMR) is absolutely impossible. In this paper, an overall Mach reflection configuration with double inverse MR patterns is computationally confirmed using the computational fluid dynamics technique. The aerodynamic mechanism behind such an abnormal wave pattern is illustrated. Classical two- and three-shock theories are also applied for the theoretical analysis. (C) 2009 American Institute of Physics. [DOI:10.1063/1.3073006
Peter M. Mach
No full textabstract: Peter was 12 years old when he heard gunshots and bombing at his village.
“Lost Boys Found” is an ongoing, interdisciplinary project that is collecting, recording and archiving the oral histories of the Lost Boys/Girls of Sudan. The collection is a work-in-progress, seeking to record the oral history of as many Lost Boys/Girls as are willing, and will be used in a future book.Age: 28Region: Upper NileThis picture and bio was donated to the Lost Boys Found project from The Arizona Lost Boys Cente
John Mach Nhial
No full textabstract: John witnessed the Arab military shooting people in his villages. When he attended school in Payido he used charcoal from burned trees to write on cardboard.
“Lost Boys Found” is an ongoing, interdisciplinary project that is collecting, recording and archiving the oral histories of the Lost Boys/Girls of Sudan. The collection is a work-in-progress, seeking to record the oral history of as many Lost Boys/Girls as are willing, and will be used in a future book.Age: 27Region: Upper NileThis picture and bio was donated to the Lost Boys Found oral history project from The Arizona Lost Boys Cente
Effects of initial conditions and Mach number in the evolution of Richtmyer-Meshkov instabilities
No full textWe present an experimental study of the effects of shock intensity and initial conditions on the evolution of Richtmyer-Meshkov Instabilities (RMI). This study is carried out in a vertical shock tube with a single interface of sulfur-hexafluoride and air. We use combined particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) to obtain simultaneous measurements of velocity and density. These measurements enable us to determine single- and multi-point statistics of vector, scalar, and combined fields. We use these statistical descriptors to study the evolution of turbulence mixing in RMIs under different Mach numbers and initial conditions
Lattice Boltzmann method for compressible flows with high Mach numbers
No full textIn this paper we present a lattice Boltzmann model to simulate compressible flows by introducing an attractive force. This scheme has two main advantages: one is to soften sound speed effectively, which greatly raises the Mach number (up to 5); another is its relative simple procedure. Simulations of the March cone and the comparison between theoretical expectations and simulations demonstrate that the scheme is effective in the simulation of compressible flows with high Mach numbers, which would create many new applications
Direct activation of Ca2+ and voltage-gated potassium channels of large conductance by anandamide in endothelial cells does not support the presence of endothelial atypical cannabinoid receptor
No full textEndocannabinoid anandamide induces endothelium-dependent relaxation commonly attributed to stimulation of the G-protein coupled endothelial anandamide receptor. The study addressed the receptor-independent effect of anandamide on large conductance Ca(2+)-dependent K(+) channels expressed in endothelial cell line EA.hy926. Under resting conditions, 10 microM anandamide did not significantly influence the resting membrane potential. In a Ca(2+)-free solution the cells were depolarized by ~10 mV. Further administration of 10 microM anandamide hyperpolarized the cells by ~8 mV. In voltage-clamp mode, anandamide elicited the outwardly rectifying whole-cell current sensitive to paxilline but insensitive to GDPbetaS, a G-protein inhibitor. Administration of 70 microM Mn(2+), an agent used to promote integrin clustering, reversibly stimulated whole-cell current, but failed to further facilitate the anandamide-stimulated current. In an inside-out configuration, anandamide (0.1-30 microM) facilitated single BKCa channel activity in a concentration-dependent manner within a physiological Ca(2+) range and a wide range of voltages, mainly by reducing mean closed time. The effect is essentially eliminated following chelation of Ca(2+) from the cytosolic face and pre-exposure to cholesterol-reducing agent methyl-beta-cyclodextrin. O-1918 (3microM), a cannabidiol analog used as a selective antagonist of endothelial anandamide receptor, reduced BKCa channel activity in inside-out patches. These results do not support the existence of endothelial cannabinoid receptor and indicate that anandamide acts as a direct BKCa opener. The action does not require cell integrity or integrins and is caused by direct modification of BKCa channel activity
The Mach reflection of a detonation based on soot track measurements
No full textThis paper presents a series of soot tracks formed by gaseous detonation waves diffracting around wedges with different wedge angles. These cellular structure patterns describe the Mach-reflection processes of a detonation and reveal some unique characteristics. They can be used to analyze the relationship between the trajectory angle of the triple point, wedge angle, and initial pressure in Mach reflection. Compared to the Mach-reflected one-dimensional shock wave in nonreactive air, all these unique characteristics for a Mach-reflected detonation should be attributed to the transverse-wave structure of the detonation front; meanwhile, the precursor shock wave and transverse wave influence the Mach-reflected detonation, respectively. The experimental results support the recently published numerical simulation of this complex phenomenon
Shock Mach number influence on reaction wave types and mixing in reactive shock–bubble interaction
No full textAbstractWe present numerical simulations for a reactive shock–bubble interaction with detailed chemistry. The convex shape of the bubble leads to shock focusing, which generates spots of high pressure and temperature. Pressure and temperature levels are sufficient to ignite the stoichiometric H2–O2 gas mixture. Shock Mach numbers between Ma=2.13 and Ma=2.90 induce different reaction wave types (deflagration and detonation). Depending on the shock Mach number low-pressure reactions or high-pressure chemistry are prevalent. A deflagration wave is observed for the lowest shock Mach number. Shock Mach numbers of Ma=2.30 or higher ignite the gas mixture after a short induction time, followed by a detonation wave. An intermediate shock strength of Ma=2.19 induces deflagration that transitions into a detonation wave. Richtmyer–Meshkov and Kelvin–Helmholtz instability evolutions exhibit a high sensitivity to the reaction wave type, which in turn has distinct effects on the spatial and temporal evolution of the gas bubble. We observe a significant reduction in mixing for both reaction wave types, wherein detonation shows the strongest effect. Furthermore, we observe a very good agreement with experimental observations
Experimental investigation of shock–shock interactions with variable inflow Mach number
No full textExperiments on shock–shock interactions were conducted in a transonic–supersonic wind tunnel with variable free-stream Mach number functionality. Transition between the regular interaction (RI) and the Mach interaction (MI) was induced by variation of the free-steam Mach number for a fixed interaction geometry, as opposed to most previous studies where the shock generator angles are varied at constant Mach number. In this paper, we present a systematic flow-based post-processing methodology of schlieren data that enables an accurate tracking of the evolving shock system including the precise and reproducible detection of RI⇄ MI transition. In line with previous experimental studies dealing with noisy free-stream environments, transition hysteresis was not observed. However, we show that establishing accurate values of the flow deflections besides the Mach number is crucial to achieve experimental agreement with the von Neumann criterion, since measured flow deflections deviated significantly, up to 1. 2 ∘, from nominal wedge angles. We also report a study conducted with a focusing schlieren system with variable focal plane that supported the image processing by providing insights into the three-dimensional side-wall effects integrated in the schlieren images.Aerodynamic
The roles of transverse waves in Mach reflection of detonation wave
No full textExperiments were conducted with smoke foil techniques in a detonation tube to study the roles of transvers waves in Mach reflection of H-2/O-2/Ar detonation waves. We had observed changes of transverse tracks through Mach reflection and we had also observed that triple trajectory showing different shapes with the increase of wedge angle. The analyses showed the interaction between reflection wave and transverse wave deciding Mach reflection configurations and effecting the properties of transverse tracks after Mach reflection at different wedge angle
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