January 2003

From American Physical Society

Physics tip sheet #30 - January 9, 2003

1) Non-invasively estimating the strength of bone to aid osteoporosis management
G. H. Gunaratne
Physical Review E (Print issue: December 2002)

Osteoporosis is a major socioeconomic problem in western societies. Since excessive use of therapeutic agents often has adverse effects on patients, noninvasive diagnostic tools to determine their need are essential for effective management of the disease. The new technique proposed here examines how bones respond to vibrations of various frequencies, with healthy bone responding differently to weak bone.

Journal article: http://link.aps.org/abstract/PRE/v66/e061904

2) Deconstructing birdsong
R. Laje, G. B. Mindlin
Physical Review Letters (Print issue: December 31, 2002)

The complex chirping and warbling of a bird's song may be the product of a relatively simple circuit in its brain. Researchers modeled a part of the bird brain that can generate diverse song elements. They found that a single arrangement of cells showed behavior complex enough to produce much of the variety in a sparrow's tune.

Physical Review Focus: http://focus.aps.org/story/v11/st1
Journal article: http://link.aps.org/abstract/PRL/v89/e288102

3) Getting more from MRI
V. G. Kiselev, D. S. Novikov
Physical Review Letters (Print issue: December 30, 2002)

A new analysis technique could get micron-scale data out of MRI scans of blood, brain cells, and even buried minerals--without having to re-engineer anything in the machines themselves. Standard MRI imagers today can resolve down to about half a millimeter on a live human, but now a team describes a way of analyzing MRI data to squeeze out information on the average shapes and sizes of particles only a few microns across.

Physical Review Focus: http://focus.aps.org/story/v10/st28
Journal article: http://link.aps.org/abstract/PRL/v89/e278101

4) Fine writing with atoms
W. H. Oskay, S. D. Steck, M. G. Raizen
Physical Review Letters (Print issue: December 31, 2002)

The possibility of using light forces to control the deposition of atoms on surfaces is the basis for the emerging field of atom lithography. Interfering laser beams can focus atoms into very small regions as they deposit, thereby building nanostructures on a surface. This focusing has become even sharper with a new technique in which atoms are manipulated by a series of kicks from a light wave. This leads to a spatial array of atoms, which is of interest for atomic lithography. By depositing atoms in an array, massively parallel nanoconstruction could be accomplished.

Journal article: http://link.aps.org/abstract/PRL/v89/e283001

5) Explaining mortality plateaus
J. B. Coe, Y. Mao, M. E. Cates
Physical Review Letters (Print issue: December 31, 2002)

Theories of biological aging predict a steady increase in mortality with age. However, some species show a mortality plateau when individuals reach a certain age, their chance of dying stops increasing. A new model is able to reproduce this surprising feature of aging by more realistically incorporating the effects of both genetic and environmental factors.

Journal article: http://link.aps.org/abstract/PRL/v89/e288103

6) Hot spots in Venusian atmosphere
V. P. Goncharov, V. M. Gryanik, V. I. Pavlov
Physical Review E (Print issue: December 2002)

The atmosphere of Venus sustains localized "hot spots" unlike Earth's. Models of these hot spots show they are vortices that only exist under certain conditions and at certain locations. This paper explains how the twin hot spots at Venus' pole come into being and how they rotate around each other.

Journal article: http://link.aps.org/abstract/PRE/v66/e066304

7) A minimal model for genome evolution and growth
L.-C. Hsieh, L. Luo, F. Li, H. C. Lee
Physical Review Letters (Print issue: January 10, 2003)

When a genome is viewed as a series of letters A, G, T, and C, it seems quite random. However, the organization of the letters has a complex statistical structure very different from a random sequence. One characteristic is that a typical real genome has similar statistical properties to DNA sequences of much shorter length. This is essentially due to the repetitive nature of DNA, especially in the "junk" sections of the genome. But why so much repetition and how did it come about? In this paper, physicists have developed a minimal model of genome evolution and growth that matches the statistics of real DNA quite well. In their model, either single letter mutations are allowed, or a random length of DNA can be copied from somewhere in the string and inserted somewhere else at random. By repeating this process many times from a short DNA strand, long DNA strands that resemble real genomes are created.

Journal article: http://link.aps.org/abstract/PRL/v90/e018101

8) Deducing neutrino recipes on the desktop
M. Trinczek, et al.
Physical Review Letters (Print issue: January 10, 2003)

Recent experimental results show conclusively that different types of neutrinos mix together. However, the details of the mixing are still uncertain. A new technique using tabletop equipment has put some of the best direct bounds on how neutrinos mix for certain energy ranges. This paper describes how a radioactive potassium atom is trapped with magnets and lasers to watch it decay. By carefully analyzing the paths of the decay products, details about the neutrino can be deduced.

Journal article: http://link.aps.org/abstract/PRL/v90/e012501

This article comes from Science Blog. Copyright 2004

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