Convective instabilities in the advanced stages of nuclear shell burning can play an important role in neutrino-driven supernova explosions. In our previous work, we studied the interaction of vorticity and entropy waves with the supernova shock using a linear perturbations theory. In this paper, we extend our work by studying the effect of acoustic waves. As the acoustic waves cross the shock, the perturbed shock induces a field of entropy and vorticity waves in the post-shock flow. We find that, even when the upstream flow is assumed to be dominated by sonic perturbations, the shock-generated vorticity waves contain most of the turbulent kinetic energy in the post-shock region, while the entropy waves produced behind the shock are responsible for most of the density perturbations. The entropy perturbations are expected to become buoyant as a response to the gravity force and then generate additional turbulence in the post-shock region. This leads to a modest reduction of the critical neutrino luminosity necessary for producing an explosion, which we estimate to be less than ∼ 5%.
Efficient nanoscale light sources are sought after for applications such as sensing, imaging, and the development of photonic circuits. In particular, free electron light sources have gained much attention due to their ability to tune and direct light emission. Here, we show that radiation from free electrons passing through a 100 nm wide nanohole can reach as high as 90% of the theoretical limit. This is accomplished through the introduction of a circular nanoridge around the hole to form a structure we call the nanowell. The power radiated from the nanowell exceeds that of a regular nanohole by over 100 times and that of nanoholes surrounded by other features, such as bullseyes, by similar enhancement factors. Upon varying the structural parameters of the nanowell, the peak output wavelength can be tuned over a broad frequency range from the visible to the near-infrared. This reveals a route to extracting power from free electrons via material nanopatterning.
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