Physics tip sheet #4 - March 13, 2002

March 13, 2002

1) Zettawatt to exawatt lasers and their applications
T. Tajima and G. Mourou
Physical Review Special Topics - Accelerators and Beams (March 2002)


Since its birth, the laser has been extraordinarily effective in study and applications at the atomic and molecular level. In its early life, the laser was associated with the physics of electron volts and of the chemical bond. Over the past fifteen years, however, there has been a surge in physicists' abilities to produce high intensities, 5 to 6 orders of magnitude higher than was possible before. This report suggests a path to new types of lasers with powers many orders of magnitude higher than current technology. Such a laser at extreme high intensity could accelerate particles to frontiers of high energy and would become a tool of fundamental physics encompassing particle physics, gravitational physics, nonlinear field theory, ultrahigh-pressure physics, astrophysics, and cosmology.

Journal article: http://link.aps.org/abstract/PRSTAB/v5/e031301

2) Biomolecular nanowires
A. Calzolari, R. Di Felice, E. Molinari, A. Garbesi
arXiv preprint server


What's twice as good as a double helix? A quadruple helix - especially when it forms a long stable wire that conducts electricity. A stable structure is formed when sets of four guanine molecules in a square are layered in the presence of potassium. The quadruple helix structure has a channel down the center that fills with potassium ions and has electronic properties like those of a semiconductor. Wires such as these may form the basis for nanoelectronics.

Preprint: http://www.arxiv.org/abs/cond-mat/0203139

3) Measuring gravity changes with atom interferometers
J. M. McGuirk, G. T. Foster, J. B. Fixler, M. J. Snadden, and M. A. Kasevich
Physical Review A (Print issue: March 2002)


Measuring very small changes in gravitational fields finds application in navigation, underground structure detection and oil and mineral exploration. However, most gravitometers suffer from the problem that vibrations can't be distinguished from changes in gravity. A device based on atom interferometry (in which two beams of cooled atoms are made to interfere with each other) is able to distinguish between vibrations and gravity changes by measuring local changes in the gravitational field. The device is sensitive to one part in one billion variations, sensitive enough to make useful geophysical measurements.

Journal article: http://link.aps.org/abstract/PRA/v65/e033608

4) Increase of Complexity from Classical Greek to Latin Poetry
R. Mansilla, E. Bush
ArXiv preprint server


A study of the scansion of ancient poetry using information theoretic tools shows an evolution from rigid, relatively simple structures in Greek to more relaxed forms in Latin. Using these tools for a comparison of the Odyssey and Iliad shows an unusually large difference in style for poems of the same period and may contribute to discussion of the authorship of "Homer's" epics.

Preprint: http://www.arxiv.org/abs/cond-mat/0203135

5) Gravitational waves kick back
Herman J. Mosquera Cuesta
Physical Review D (Print issue: March 15, 2002)


Most pulsars move through the galaxy at about 450 km/s, about 9 times faster than the average star. A proposed explanation for the higher speeds is that gravitational waves emitted at the pulsars' births involve a huge amount of energy and cause considerable recoil. If this proposed mechanism actually operates, it would provide a valuable example of the influence of gravitational waves on real astrophysical processes. Then the overwhelming population of high velocity pulsars would give great support to Einstein's theory of gravitation as the most likely theory realized in nature.

Journal article: http://link.aps.org/abstract/PRD/v65/e061503

6) Website popularity and growth
Chang-Yong Lee and Seungwhan Kim
Physical Review E (Print issue: March 2002)


A new model of the World Wide Web accounts for the observed growth and popularity distributions of websites. One of the characteristics of site popularity is a power law distribution. This means that a small number of sites are very popular and a large number of sites are not popular according to a certain distribution. The specifics of the distribution are different for each category of website, such as educational websites (.edu). However, the general rule is that the faster the number of sites in a category grows, the more extreme the distribution is (with fewer popular sites and more unpopular sites).

Journal article: http://link.aps.org/abstract/PRE/v65/e036132

7) Where could negative energy hide?
Arvind Borde, L. H. Ford and Thomas A. Roman
Physical Review D (Print issue: April 15, 2002)


Although all forms of observed matter have positive energies, quantum field theory allows for the possibility of negative energy densities in some areas of spacetime. If negative energy densities did exist, they would allow for the existence of traversable wormholes, faster-than-light travel, creation of naked singularities and violations of the second law of thermodynamics. This paper examines what constraints exist on possible configurations of spacetime with negative energy densities. In doing so, it provides examples of some possible configurations in two dimensions as a starting point for further exploration.

Journal article: http://link.aps.org/abstract/PRD/v65/e084002
-end-


American Physical Society

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