Measurements of density, temperature, and their fluctuations in turbulent supersonic flow using UV laser spectroscopy

Nonintrusive measurements of density, temperature, and their turbulent fluctuation levels were obtained in the boundary layer of an unseeded, Mach 2 wind tunnel flow. The spectroscopic technique that was used to make the measurements is based on the combination of laser-induced oxygen fluorescence and Raman scattering by oxygen and nitrogen from the same laser pulse. Results from this demonstration experiment are compared with previous measurements obtained in the same facility using conventional probes and an earlier spectroscopic technique. Densities and temperatures measured with the current technique agree with the previous surveys to within 3 percent and 2 percent, respectively. The fluctuation amplitudes for both variables agree with the measurements obtained using the earlier spectroscopic technique and show evidence of an unsteady, weak shock wave that perturbs the boundary layer

Laser-spectroscopic measurement techniques for hypersonic, turbulent wind tunnel flows

A review is given of the nature, present status, and capabilities of two laser spectroscopic methods for the simultaneous measurement of temperature, density, and their fluctuations owing to turbulence in high speed wind tunnel flows. One method is based on the two frequency excitation of nitric oxide seeded into a nitrogen flow, using tunable dye lasers. The second, more recent method relies on the excitation of oxygen in air flows using a tunable, ArF excimer laser. Signal are obtained from both the laser induced fluorescence and from Raman scattering of the same laser pulse. Measurements are demonstrated in the turbulent boundary layer of a Mach-2 channel flow

Coherence of Associativity in Categories with Multiplication

The usual coherence theorem of MacLane for categories with multiplication assumes that a certain pentagonal diagram commutes in order to conclude that associativity isomorphisms are well defined in a certain practical sense. The practical aspects include creating associativity isomorphisms from a given one by tensoring with the identity on either the right or the left. We show, by reinspecting MacLane's original arguments, that if tensoring with the identity is restricted to one side, then the well definedness of constructed isomorphisms follows from naturality only, with no need of the commutativity of the pentagonal diagram. This observation was discovered by noting the resemblance of the usual coherence theorems with certain properties of a finitely presented group known as Thompson's group F. This paper is to be taken as an advertisement for this connection.Comment: 8 pages, to appear in Journal of Pure and Applied Algebr

Quantum entanglement and fixed-point bifurcations

How does the classical phase space structure for a composite system relate to the entanglement characteristics of the corresponding quantum system? We demonstrate how the entanglement in nonlinear bipartite systems can be associated with a fixed point bifurcation in the classical dynamics. Using the example of coupled giant spins we show that when a fixed point undergoes a supercritical pitchfork bifurcation, the corresponding quantum state - the ground state - achieves its maximum amount of entanglement near the critical point. We conjecture that this will be a generic feature of systems whose classical limit exhibits such a bifurcation.Comment: v2: Structure of the paper changed for clarity, reduced length, now 9 pages with 6 figure

Numerical simulation of dark lanes in post-flare supra-arcade

We integrate the MHD ideal equations to simulate dark void sunwardly moving structures in post--flare supra--arcades. We study the onset and evolution of the internal plasma instability to compare with observations and to gain insight into physical processes and characteristic parameters of these phenomena. The numerical approach uses a finite-volume Harten-Yee TVD scheme to integrate the 1D1/2 MHD equations specially designed to capture supersonic flow discontinuities. The integration is performed in both directions, the sunward radial one and the transverse to the magnetic field. For the first time, we numerically reproduce observational dark voids described in Verwichte et al. (2005). We show that the dark tracks are plasma vacuums generated by the bouncing and interfering of shocks and expansion waves, upstream an initial slow magnetoacoustic shock produced by a localized deposition of energy modeled with a pressure perturbation. The same pressure perturbation produces a transverse to the field or perpendicular magnetic shock giving rise to nonlinear waves that compose the kink--like plasma void structures, with the same functional sunward decreasing phase speed and constancy with height of the period, as those determined by the observations.Comment: Accepted MNRAS, 6 pages, 7 figure

Agent Provocateur

Background: ‘Agent Provocateur’ is the major textual work to document Felix Ruckert’s 2011 Australian visit in which he offered workshops for Xplore Festival (Sydney) and Strutdance (Perth). Ruckert is a Berlin-based dancer and choreographic artist whose work explores the edges of dance by demanding that audiences be complicit in risky performances. The article investigates Ruckert’s work as it relates to contact improvisation and questions of sexual overtones that trouble that performance form. As a dancer and researcher I use archival and field research and self-reflection to ask: does physical and emotional risk in a workshop lead to better performance outcomes? Contribution: The article advances research on emotion in dance by illustrating how Ruckert’s approach to contact improvisation enriches the emotional repertoire of dance artists via the abject categories of pain and discomfort. In addition I investigate his unique view on contact improvisation as a form of folk dance. This moves the question of sexuality and risk beyond technical considerations and makes it also an ethnographic consideration, building on Novak’s seminal study Sharing the Dance: an ethnography of contact improvisation (1986). Significance: First published by contact improvisation, new dance, movement improvisation in 2011, the magazine republished the article in 2012 with a statement illustrating how it extends research in the field: ‘[it] asks that uncomfortable question about the limits of CI: as a community, how do we draw the line between sexuality and sensuality in the dance, and are we fooling ourselves to imagine there is one? These liminal spaces at the edge of contact feed the development of the tradition, but how do you sustain a practice?