Cones of silence, complex rays and catastrophes: high-frequency flow–acoustic interaction effects

In this paper we develop a novel ray solver for the time-harmonic linearized Euler equations used to predict high-frequency flow–acoustic interaction effects from point sources in subsonic mean jet flows. The solver incorporates solutions to three generic ray problems found in free-space flows: the multiplicity of rays at a receiver point, propagation of complex rays and unphysical divergences at caustics. We show that these respective problems can be overcome by an appropriate boundary value reformulation of the nonlinear ray equations, a bifurcation-theory-inspired complex continuation, and an appeal to the uniform functions of catastrophe theory. The effectiveness of the solver is demonstrated for sources embedded in isothermal parallel and spreading jets, with the fields generated containing a wide variety of caustic structures. Solutions are presented across a large range of receiver angles in the far field, both downstream, where evanescent complex rays generate the cone of silence, and upstream, where multiple real rays are organized about a newly observed cusp caustic. The stability of the caustics is verified for both jets by their persistence under parametric changes of the flow and source. We show the continuation of these caustics as surfaces into the near field is complicated due to a dense caustic network, featuring a chain of locally hyperbolic umbilic caustics, generated by the tangency of rays as they are channelled upstream within the jet.

Ethnic Riots and Other Myths

This chapter examines what was described as the worst “ethnic rioting” in Malaysia in decades. In 2001, Malays and Indians clashed in an area known as Kampung Medan. Many analysts, academics, and politicians were quick to ascribe blame, drawing on the ethnic “myths” or stereotypes. Others invoked the purported and inevitable frustrations caused by anomie and squalor in squatter areas. The recounting of the violent events by witnesses and victims demonstrates that the respective figures of the Indian and Malay increasingly silence complex exchanges and intimacies between the two groups. These figures, in turn, are also produced out of a particular developmentalism driven by ethnonationalist impulses. The chapter also studies the symptoms of cultural and ethnic uncertainty generated by the bureaucratization of ethnic privilege.