image: Low-packed projectiles produce simple shallow craters with a thin layer of the projectile material covering it. High packed ones produce deeper craters and central peaks surrounded by the sprayed material. view more
Credit: F. Pacheco-Vazquez and J.C. Ruiz-Suarez
Grainy asteroids and the craters they leave behind
F. Pacheco-Vazquez and J.C. Ruiz-Suarez
Physical Review Letters (forthcoming)
It's generally accepted that craters in the moons and planets were created by asteroid collisions. But, why are some craters completely flat while others show central peaks? New experiments involving projectiles made of globs of granular material appear to provide a solution to the long-standing mystery: loosely-packed projectiles completely spread after collision, leading to bowl-shaped craters, while tightly-packed globs give rise to central peaks in the craters they produce. The research suggests that the differences between crater types could have more to do with the composition of asteroids than the surfaces of the planets they strike.
Carnivorous plants snap shut in very different ways
Simon Poppinga and Marc Joyeux
Physical Review E (forthcoming)
The carnivorous aquatic Waterwheel Plant (Aldrovanda vesiculosa) and the closely related terrestrial Venus Flytrap (Dionaea muscipula) both feature elaborate snap-traps, which clamp shut when triggered by insects and small animals. However, videos of snapping traps from both species suggest completely different closure mechanisms. The modified leaves of the Venus Flytrap close by abruptly flipping their curvature, while the Waterwheel Plant relies on deformation of the midrib that connects the two halves of the trap, rather than changing the shape of its component parts. Poppinga and Joyeux present the first detailed mechanical models for these plants, which show how they achieve similar carnivorous ends with very different mechanical means.
Pair Creation Constrains Superluminal Neutrino Propagation
Andrew G. Cohen and Sheldon L. Glashow
Physical Review Letters (forthcoming)
Particles that exceed the speed of light in a material such as water or glass produce Cherenkov radiation, which is the source of the blue light often associated with nuclear reactors immersed in water. If neutrinos travel faster than light in a vacuum, they should produce similar sorts of radiation. Cohen and Glashow calculate the radiation that should have resulted if the startling announcement of faster-than-light neutrinos detected by the OPERA collaboration in Italy is correct, assuming that the neutrinos operate under accepted physical laws. The authors argue that their analysis casts serious doubts on the likelihood that neutrinos can exceed the speed of light.