Physics tip sheet #37

Understanding how high energy materials explode on a molecular level is extremely challenging. Everything happens so fast, on a small scale and with a variety of chemical and physical processes playing a part. New simulations modeled Nitramine RDX, found in many military explosives. The simulations show how shock waves cause primary chemical reactions, creating further mechanical stresses and more complex chemical reactions. Importantly, this work shows that computer simulations are now capable of examining the complex processes of explosions from first principles - information that is vital in the development of safe and effective explosives.

Journal article: http://link.aps.org/abstract/PRL/v91/e098301

2) Crackle sounds in the lungs
A. Alencar, et al.
Physical Review E (Published online: July 21, 2003)

Crackle sounds have long been used as a qualitative diagnostic tool for certain pulmonary dysfunctions. However, analysis of lung crackle sounds has not had a solid theoretical basis. A new model of crackle sounds accurately predicts what sounds are heard as airways open and close during breathing. The work may have clinical application because various lung diseases change the anatomical and physiological features that cause the crackle sounds.

Journal article: http://link.aps.org/abstract/PRE/v68/e011909

3) Anatomy of a bathtub vortex
A. Andersen, et al.
Physical Review Letters (Published online: September 5, 2003)

Although the vortex that drains a bathtub is the best-known vortex, it has been the focus of surprisingly little research. The few previous studies have made unrealistic assumptions in their models. A new analysis is able to reproduce most of the observed features of bathtub vortices bringing us closer to properly understanding just how a bathtub drains. Some of the more surprising features of bathtub drainage that may be new to you are that bubbles often detach from the bottom tip of the vortex before it reaches all the way down to the plughole. These bubbles occur because the tip of the vortex is unstable when rotation is fast. The air bubble is usually sucked straight down the drain after detaching. The flow around the plughole itself has some unusual behavior. Most of the water on the bottom of the tub flows toward the hole but about one centimeter before the hole, jumps upward before turning around and going down the hole.

Journal article: http://link.aps.org/abstract/PRL/v91/e104502

4) Wave nature of biomolecules
L. Hackermuller, et al.
Physical Review Letters (Published online: August 28, 2003)

The wave nature of biomolecules has been shown for the first time in tetraphenylporphyrin (TPP) and quantum interference has been shown for the largest molecules yet. These experiments showed that when the molecules passed through two slits, they formed interference patterns on a screen, just like two rocks thrown into a pond show interference patterns of waves on the surface. The porphyrin structure in TPP is at the heart of many biomolecules and is the color center of chlorophyll and hemoglobin. The largest molecule to exhibit interference is the fluorofullerene C60F48. Experiments showed that the interference happens exactly as predicted by quantum mechanics, despite the molecules consisting of 78 and 108 atoms each.

Journal article: http://link.aps.org/abstract/PRL/v91/e090408

5) Superfluid gyroscope
E. Hodby, et al.
Physical Review Letters (Published online: August 27, 2003)

A gyroscope usually consists of a solid disk that spins at a high speed and resists being turned to face a different direction. However, a new experiment has demonstrated a gyroscope made of a superfluid Bose-Einstein condensed gas. The ellipsoidal glob of supercold Rubidium atoms moves just like a children's toy spinning top (a common form of gyroscope). It spins on its own axis but also precesses, or has the axis rotate about, just as a spinning top does as it begins to fall over.

Journal article: http://link.aps.org/abstract/PRL/v91/e090403