Physics tip sheet #28 -- October 17, 2002

Whether company directors sit on several boards together has a significant influence on how individual boards come to decisions and whether minority lobby groups can win over an entire board. Another factor that influences decisions is the order of speakers in a board meeting. The authors apply their model of corporate board dynamics to data from Fortune 1000 companies.

Preprint: http://www.arxiv.org/abs/cond-mat/0209590

2) 3D ink
J. Lewis, et al.
74th Annual Society of Rheology Meeting

Researchers are perfecting "inks" that carry tiny particles made of metals, ceramics, plastics, or a variety of other materials instead of pigments. The inks are deposited with a machine similar to an ink jet printer. But unlike most inks, the fluid that the printer deposits is a gel that can be built up, layer by layer, into three-dimensional structures.

Physics News Update: http://www.aip.org/enews/physnews/2002/split/608-2.html
Meeting site: http://www.rheology.org/sor/annual_meeting/2002Oct/

3) Evaluating land for use without needing to dig
K. Oleschko, G. Korvin, A. S. Balankin, R. V. Khachaturov, L. Flores, B. Figueroa, J. Urrutia, F. Brambila
Physical Review Letters (Print issue: October 28, 2002)

Researchers can use microwaves to learn the structure of soil without disturbing it. In the new technique, ground-penetrating radar captures the soil's distribution of solid particles and pores, up to depths of 10 meters. The technique could give agriculturists and environmental scientists a fast and simple way to measure soil properties, which can determine the land's suitability for crops, say the researchers.

Physical Review Focus: http://focus.aps.org/v10/st17.html
Journal article: http://link.aps.org/abstract/PRL/v89/e188501

4) Black holes in your bathtub
R. Sch�tzhold, W. G. Unruh
Physical Review D (Print issue: August 15, 2002)

Unfortunately for physicists, black holes can't be tamed in the lab and studied. However, the behavior of a black hole can be modeled using nothing more than a tub of water. By putting blocks in the water to change the depth, the conditions around a black hole or multiple interacting black holes can be simulated. It seems that quantum mechanical effects won't show up in the analogue system but most of the large scale and astronomical properties of black holes should be testable in this system. (Note on terminology: "Gravity wave" refers to a wave in water in which gravity plays in role in propagation. "Gravitational wave" refers to waves in the gravitational field itself, a phenomenon predicted by Einstein's general relativity.)

Journal article: http://link.aps.org/abstract/PRD/v66/e044019

5) Car condensation in parking garages
M. Ha, M. den Nijs
Physical Review E (Print issue: September 2002)

Physicists have examined how a parking garage influences traffic on a road leading to it. They discover various types of traffic patterns including one type where the garage essentially controls the traffic levels on the road. The dynamics is similar to that found in ultracold atomic systems.

Journal article: http://link.aps.org/abstract/PRE/v66/e036118

6) Where have all the nuclei gone?
R. B. Wiringa, S. C. Pieper
Physical Review Letters (Print issue: October 28, 2002)

The nucleus of an atom can, in principle, have any number of protons and neutrons in it. However, certain combinations just don't appear. In some cases this is easily understood because it would take too much energy to make them or they would be unstable. However, there are surprising absences among the extended family of nuclei. For example, there are no nuclei found in nature with either 5 or 8 particles. The absence of these particular nuclei has had great significance in the evolution of the universe. For example, it accounts for why the Sun hasn't burnt out yet. New research shows how the laws of physics conspire to preclude 5- or 8-particle nuclei from existing.

Physical Review Focus: http://focus.aps.org/v10/st16.html
Journal article: http://link.aps.org/abstract/PRL/v89/e182501/

7) The sound of paper tearing
L. I. Salminen, A. I. Tolvanen, M. J. Alava
Physical Review Letters (Print issue: October 28, 2002)

Listening to a piece of paper being torn may provide clues as to how to strengthen it. From an analysis of the sounds, researchers could tell that rips in paper are quite different to cracks propagating through more solid substances. The researchers suspect that one component of the noise is characteristic of fibers in the paper pulling free from their surroundings, rather than being broken. If all the clues can be pieced together, there is a possibility of creating stronger materials with fibrous structures.

Journal article: http://link.aps.org/abstract/PRL/v89/e185503

8) Random vibrations help humans balance
A. Priplata, J. Niemi, M. Salen, J. Harry, L. A. Lipsitz, J. J. Collins
Physical Review Letters (to appear)

Random vibrations can help humans balance better. Experiments that involved subjects standing on a vibrating platform showed that their balance improved noticeably. The authors suggest that devices such as randomly vibrating shoe inserts could help elderly people balance as well as youngsters.

Journal article: Available on request
Related paper: How to balance a stick on your finger, http://www.aps.org/media/tips/tips091202.html