Physics tip sheet #26 - August 21, 2002

August 21, 2002

1) How the planets got their stripes
S. Sukoriansky, B. Galperin, N. Dikovskaya
Physical Review Letters (to appear)

Stripes observed on the disks of gaseous giant planets (Jupiter, Saturn, Uranus and Neptune) are formed by trains of clouds transported by organized, steady atmospheric currents. Typically, atmospheric turbulence would break the clouds down into smaller and smaller features until no large features were visible. However, in thin atmospheres the effect is opposite. The rotation of the planets combines with the turbulence to create the large-scale structures we see as rings, stripes and spots.

Journal article: Available on request
Lay-language summary: Available on request

2) Avalanches: How tough is snow?
H. O. K. Kirchner, G. Michot, J. Schweizer
Physical Review E (Print issue: August 2002)

Snow slab avalanches can occur when cracks form between snow layers with different properties. Understanding the properties of snow, in this case the fracture toughness, is essential to better modeling when and how avalanches occur. An experiment directly measures the fracture toughness and determines when snow structures will fail. The research also shows how increasing friction between snow layers decreases the risk of avalanches.

Journal article:

3) Photon mass gets a boost
T. Prokopec, O. Törnkvist, R. Woodard
Physical Review Letters (Print issue: September 2, 2002)

Simple physics principles might explain the mysterious magnetic fields that seem to permeate the cosmos. Researchers have suggested that the magnetism might have arisen if normally massless photons possessed mass during the Universe's early moments of expansion. Now they finally show that massive photons could have existed.

Physical Review Focus:
Journal article:

4) Independent confirmation of dark energy
K.-H. Chae, et al.
Physical Review Letters (to appear)

Astronomers looking at how heavy galaxies bend light moving past them (gravitational lensing) have obtained estimates of the dark energy content of the universe (responsible for the universe's accelerating expansion). The significance of this measurement is that it is independent of the cosmic microwave background data previously used to characterize dark energy. The two techniques agree very well.

Journal article: Available on request

5) Quantum physics builds better heat engines
T.E. Humphrey, R. Newbury, R. P. Taylor, H. Linke
Physical Review Letters (Print issue: September 9, 2002)

Brownian heat engines use local fluctuations in temperature to do something useful. Although this might, at first glance, seem like it breaks the second the law of thermodynamics, it is actually allowed if you drive the whole thing with a couple of different temperature heat baths. This paper shows how using quantum physics principles allows you to build a heat engine that operates as close as you want to the maximal efficiency. (Thermodynamics dictates a maximum efficiency for any engine, depending on the temperatures of the two baths. It is called the Carnot efficiency.)

Journal article: Available on request

6) "Zoom-whirl" orbits of bodies around black holes
K. Glampedakis, D. Kennefick
Physical Review D (Print issue: August 15, 2002)

Objects orbiting a black hole may have a peculiar type of orbit that will have an identifiable signature for gravity wave detectors. The type of orbit, called a "zoom-whirl" involves a body falling close to a black hole (the zoom) and then doing a few rapid rotations (the whirl) around the hole before moving further away again.

Journal article:

7) Now in print: CP violation measurements
Belle collaboration
arXiv preprint server

Recently reported results of charge-parity violation in particle physics have now been published as a preprint. The value of sin(2*beta) has been measured as 0.719 +/- 0.074, in agreement with the Standard Model.


8) Now in print: Muon magnetic moment measurements
Muon (g-2) collaboration
Physical Review Letters (Print issue: September 2, 2002)

Recently reported measurements of the anomalous magnetic moment of the muon have now been published. The experimental result is 2.6 standard deviations from the Standard Model prediction although there is currently debate over the accuracy of the theoretical value.

Journal article:

American Physical Society

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