Physics tip sheet #36 - July 30, 2003

Physicists working at UCLA have created a 30-cm diameter plasma laser. This was accomplished by applying a nonuniform magnetic field to a type of plasma region, resulting in a frequency-selective Alfven wave resonator and then injecting current into the resonator. When a current threshold is exceeded, the result is a highly coherent, large amplitude wave that propagates into an adjacent plasma column.

Journal article: http://link.aps.org/abstract/PRL/v91/e035004

2) New dark matter observation methods
K. Abazajian, S. Dodelson
Physical Review Letters (print issue: 24 July 2003)

Recent rapid advances in astronomical observations have shed some light on the dark sector of the universe, including both dark matter and dark energy. Some of the dark matter is in the form of massive neutrinos, but the range of allowed masses is such that neutrinos could contribute anywhere from .3 percent to 20 percent of the matter density in the universe. Remarkably, both neutrino masses and dark energy leave similar signatures in the matter distribution of the universe, and a new paper examines how scientists might use weak gravitational lensing experiments to measure both signatures simultaneously.

Journal article: http://link.aps.org/abstract/PRL/v91/e041301

3) Emerging behavior in electronic bidding
I. Yang, H. Jeong, B. Kahng, A.L. Barabasi
Physical Review E (print issue: July 2003)

Recently, the self-organizing principles of complex systems have drawn the attention of the statistical physics community, and the complex system that is human behavior is no exception. A recently published paper in Physical Review E examines the behavior of consumers at the online auction site eBay and finds that the total number of bids placed by a consumer follows a power law distribution, as does the number of items individuals look at. This also implies that a few powerful and active individuals exert a strong influence on the final prices of items.

Journal article: http://link.aps.org/abstract/PRE/v68/e016102

4) Topology of the world trade web
Ma Angeles Serrano and Marian Boguna
Physical Review E (print issue: July 2003)

Economy and trade are fundamental parts of human social organization, but they have not traditionally been studied within the network modeling framework. A paper recently published in Physical Review E presents the first characterizations of the world trade web - the network built upon the trade relationships between different countries in the world. This network displays the typical properties of complex networks, including scale-free degree distribution, the small-world property and a high clustering coefficient.

Journal article: http://link.aps.org/abstract/PRE/v68/e015101

5) Relativistic submarine
G.E.A. Matsas
Physical Review D (print issue: July 2003)

Imagine a submarine moving at near-light speed. Observers on land should see the submarine get shorter and denser, causing it to sink. But the sailors on board would see the water getting denser, and the sub should float. A paper recently published in Physical Review D examines and solves for the first time this so-called submarine paradox by using a general relativistic extension of the Archimedes law of moving bodies to show that the submarine will sink.

Journal article: http://link.aps.org/abstract/PRD/v68/e027701
Physical Review Focus: http://focus.aps.org/story/v12/st4

6) H2O a misnomer?
C.A. Chatzidimitriou-Dreismann, M. Vos, C. Kleiner, T. Abdul-Redah
Physical Review Letters (to appear, issue of 8 August 2003)

Although most people will tell you that the chemical formula for water is H2O, a process called neutron Compton scattering (NCS) showed the H:O ratio is more like 1.5:1. But was that result due to some quirk of the measurement technique or is the ratio really not 2:1? Researchers have now extended the NCS measurements in a crucial way, demonstrating for the first time that the weird short-term effect of invisible protons is also observable with electron-proton Compton scattering (ECS). Although NCS and ECS operate in the same attosecond time window, ECS employs the electromagnetic force and NCS the strong force, which shows the observations are independent.

Journal article: Available to journalists on request

7) Noise can be good for you
R. Soma, D. Nozaki, S. Kwak, Y. Yamamoto
Physical Review Letters (to appear)

Researchers in Japan have found that a type of noise known as 1/f noise more effectively sensitizes the human brain than white noise. Working with nine human subjects, the team studied the human "baroreflex" system, in which an increase (or decrease) in blood pressure triggers a decrease (or increase) in heart rate. Their results mark the first demonstration of a functional link between fractal noise and the sensitivity of the physiological control system.

Journal article: Available to journalists on request

8) Natural nanostructures
M. Kawamura, N. Paul, V. Cherepanov, B. Voigtlander
Physical Review Letters (to appear)

Nanometer-sized electronic structures are highly desirable for the future miniaturization of electronic devices. Recent experiments have shown that it is possible to grow silicon and germanium nanowires with a thickness of one atomic layer by using the natural self-organization of atoms at surfaces. More complex structures, such as nanorings, are also possible, and researchers hope to be able to one day use these methods to build complex semiconductor devices.

Journal article: Available to journalists on request