Physics Tip Sheet #21 - July 10, 2002

Contact: David Harris
harris@aps.org
301-209-3238
American Physical Society

1) Holographic plankton tracking
P. R. Hobson, J. Watson
Journal of Optics A: Pure and Applied Optics (Print issue: July 2002)

Knowledge of the distribution and dynamics of marine organisms and particles is crucial to understanding aquatic ecosystems. However, most measurement techniques disrupt the system and prevent collection of good data. Researchers have shown how to record the three dimensional structure and dynamics of a plankton colony by recording a series of holographic images. They can be analyzed later by moving a detector through a holographic reconstruction of the plankton swarm, frozen in time. A large-scale implementation of the recording scheme has been deployed in Loch Etive, Scotland, and analysis of the images is under way.

Journal article: http://stacks.iop.org/1464-4258/4/S34

2) Artificial leaves to remove carbon dioxide
L. G. Wang, S. J. Pennycook, S. T. Pantelides
Physical Review Letters (To appear)

Artificial leaves, made from semiconductors, might one day help to remove excess airborne carbon dioxide and maybe even turn it into fuel. Artificial CO2 fixation needs several ingredients: light, a catalyst (such as CdS), and organic molecules. A new study suggests how this process can be made more efficient, a necessary step if artificial fixation is ever to be practical on a large scale. The authors suggest the possibility that nanocrystal doping might obviate the need for light, which would allow some fixation to take place in dark smokestacks.

Physics News Update: http://www.aip.org/enews/physnews/2002/split/597-3.html
Journal article: Available on request

3) Measuring fundamental constants with BECs
S. Gupta, K. Dieckmann, Z. Hadzibabic, D. E. Pritchard
arXiv preprint server

The precise determination of fundamental constants, down to parts-per-billion, impacts on many fields of physics. However, independent attempts to measure fundamental constants from diverse fields of physics can greatly increase precision and confidence in the measurements. A new experiment using Bose-Einstein condensates (BECs) shows how the fine structure constant, which sets the strength of electromagnetism, can be measured as precisely as in particle physics experiments. A BEC is split into three parts, which travel along different paths before recombining. The interference pattern created depends on the size of the fine structure constant. So far, the experiment has not broken the record for precision but a plausible extension that is being constructed should equal or beat the particle physics result.

Preprint: http://www.arxiv.org/abs/cond-mat/0202452

4) Nanotube diagnostic x-rays
G. Z. Yue, Q. Qiu, Bo Gao, Y. Cheng, J. Zhang, H. Shimoda, S. Chang, J. P. Lu, O. Zhou
Applied Physics Letters (Print issue: July 8, 2002)

Researchers have developed an x-ray source using a room-temperature array of carbon nanotubes to create electrons that deliver sufficient x-ray flux for doing practical medical imaging. The device is much smaller and cooler than other x-ray sources and the resultant x-ray pulse is more focused. Also, response time is sharper and the pulse shape can be programmed, which helps in the tracking of moving objects.

Physics News Update: http://www.aip.org/enews/physnews/2002/split/597-1.html
Journal article: http://link.aip.org/link/?apl/81/355
Graphics: http://www.aip.org/mgr/png/2002/157.html

5) Gamma knife improvements
J.-S. Tsai, et al.
American Association of Physicists in Medicine meeting

Gamma knife is the name for a machine in which high energy gamma-rays are used to irradiate intracranial tumor cells difficult to treat with other methods. An array of 201 gamma-emitting cobalt-60 sources is laid out in such a way that the rays converge on the target tumor, whose coordinates are carefully determined by CT and MRI scans. At the AAPM meeting in Montreal this week, a researcher reports on new methods for coordinating MRI and CT scans to obtain the best possible tumor location to insure proper dosages.

Physics News Update: http://www.aip.org/enews/physnews/2002/split/597-4.html
Abstract: http://www.aapm.org/meetings/02AM/pdf/7571-56076.pdf

6) Ultra-high energy cosmic rays and pulsars: a connection
A. D. Erlykin, A. A. Mikhailov, A. W. Wolfendale
Journal of Physics G: Nuclear and Particle Physics (Print issue: August 2002)

Ultra-high energy cosmic rays (UHECRs) are currently a mystery to astronomers. Many assume that they are coming from sources outside our galaxy but relatively little is known conclusively. A comparison of the direction from which UHECRs come and the distribution of objects within our galaxy shows a correlation between UHECRs and spun-up pulsars (pulsars spinning at high speeds) that is better than chance should allow. Although this does not imply pulsars are the source of UHECRs, it provides impetus not to dismiss galactic sources and to investigate pulsar dynamics for the creation of UHECRs.

Journal article: http://stacks.iop.org/0954-3899/28/2225

7) Element 118 Retraction
V. Ninov, et al.
Physical Review Letters (Print issue: July 15, 2002)

In 1999, physicists at Lawrence Berkeley National Lab reported observing three events amid high energy collisions in which it appeared that a nucleus corresponding to element 118 had been produced; in each case the nucleus had quickly decayed into daughter nuclei. Two years later these same researchers came to believe that their analysis of the events, and therefore their claim for discovery of the element, was doubtful.

Physics News Update: http://www.aip.org/enews/physnews/2002/split/597-2.html
Journal article: http://link.aps.org/abstract/PRL/v89/e039901

8) Background article: The Sloan Digital Sky Survey
J. Loveday, for the SDSS collaboration
arXiv preprint server

The Sloan Digital Sky Survey (SDSS) is making a multi-color, three-dimensional map of the nearby Universe. The map will be used to constrain models of cosmology and of galaxy formation and evolution. This article describes the goals and methods used by the SDSS, the current status of the survey, and highlights some discoveries made from data obtained in the first two years of survey operations.

Preprint: http://www.arxiv.org/abs/astro-ph/0207189

9) Now in print
BEC accelerator: TS#17.5: http://www.aps.org/media/tips/tips061202.html
Article: Journal of Physics B: http://stacks.iop.org/0953-4075/35/3095

For media assistance with these or other physics stories, contact:

David Harris
Head of Media Relations
American Physical Society
Ph: +1 301 209 3238
Fax: +1 301 209 3264
Email: harris@aps.org