January 4, 2012
Physics News Highlights of the American Institute of Physics (AIP) contains summaries of interesting research from the AIP journals, notices of upcoming meetings, and other information from the AIP Member Societies. Copies of papers are available to journalists upon request.
AIP Media Services Contacts:
Follow us on Twitter: @AIPPhysicsNews
TOPICS IN THIS ISSUE:
Graphene, the ultra-durable carbon material that holds promise for a range of applications, has yet another trick up its single-atom-thick sleeve. Engineers at the University of Houston have used quantum mechanical calculations to show that, merely by creating holes of a certain configuration in a sheet of graphene, they can coax graphene into behaving like a piezoelectric material. Piezoelectric substances generate electricity in response to physical pressure, and vice versa, and scientists can use these materials for applications such as energy harvesting and artificial muscles, as well as to make precise sensors. Graphene itself is not naturally piezoelectric. But the Houston engineers reasoned that if they took either a semiconducting or insulator form of graphene, punched triangle-shaped holes into it, and applied a uniform pressure to the material, they could make that material act as though it were piezoelectric. The team’s calculations showed that triangular holes did indeed result in piezoelectric behavior, while circular holes – as they predicted – did not. They also found that graphene’s pseudo-piezoelectricity was almost as strong as that of well-known piezoelectric substances such as quartz. The authors suggest that triangular pores could be created in real graphene using electron-beam radiation in a lab, which means these calculations can be tested using existing methods. “Nature has dealt humankind … a very limited choice of effective electromechanical materials” that exhibit piezoelectricity, write the authors in their paper, accepted to the AIP’s Applied Physics Letters. Adding graphene to the list “could potentially open new avenues” of use, both for graphene and for applications that rely on piezoelectricity.
Authors: Swapnil Chandratre (1) and Pradeep Sharma (1, 2).
(1) Department of Mechanical Engineering, University of Houston, Texas
In an effort to make data storage more cost-effective, a group of researchers from National Tsing Hua University in Taiwan and the Karlsruhe Institute of Technology in Germany have created a DNA-based memory device that is “write-once-read-many-times” (WORM), and that uses ultraviolet (UV) light to make it possible to encode information. The device, described in a paper accepted to the AIP’s Applied Physics Letters, consists of a thin film of salmon DNA that has been embedded with silver nanoparticles and then sandwiched between two electrodes. Shining UV light on the system enables a light-triggered synthesis process that causes the silver atoms to cluster into nano-sized particles, and readies the system for data encoding. In some cases, using DNA may be less expensive to process into memory devices than using traditional, inorganic materials like silicon, the researchers say.
At first, when no voltage or low voltage is applied through the electrodes to the UV-irradiated DNA, only a low current is able to pass through the composite; this corresponds to the “off” state of the device. But the UV irradiation makes the composite unable to hold charge under a high electric field, so when the applied voltage exceeds a certain threshold, an increased amount of charge is able to pass through. This higher state of conductivity corresponds to the “on” state of the device.
The team found that this change from low conductivity (“off”) to high conductivity (“on”) was irreversible: once the system had been turned on, it stayed on, no matter what voltage the team applied to the system. And once information is written, the device appears to retain that information indefinitely: the researchers report that the material’s conductivity did not change significantly during nearly 30 hours of tracking. The authors hope the technique will be useful in the design of optical storage devices and suggest that it may have plasmonic applications as well.
Article: “Photoinduced write-once read-many-times memory device based on DNA biopolymer nanocomposite” is accepted for publication in Applied Physics Letters.
Authors: Yu-Chueh Hung (1), Wei-Ting Hsu (1), Ting-Yu Lin (1), and Ljiljiana Fruk.
(1) Institute of Photonics Technologies, National Tsing Hua University, Taiwan
3. Paddlefish sensors tuned to detect signals from zooplankton prey
In 1997, scientists at the Center for Neurodynamics at the University of Missouri - St. Louis demonstrated that special sensors covering the elongated snout of paddlefish are electroreceptors that help the fish detect prey by responding to the weak voltage gradients that swimming zooplankton create in the surrounding water. Now some of the same researchers have found that the electroreceptors contain oscillators, which generate rhythmical firing of electrosensory neurons. The oscillators allow the electroreceptors to create a dynamical code to most effectively respond to electrical signals emitted naturally by zooplankton. The results are presented in a paper appearing in the AIP’s journal Chaos. To test the response of paddlefish electroreceptors to different stimuli, the researchers recorded signals from electrosensory neurons of live fish, while applying weak electric fields to the water in the form of computer-generated artificial stimuli or signals obtained previously from swimming zooplankton. The team then analyzed the power contained in different frequency ranges for the noisy input signals and the corresponding electroreceptor responses, and compared the two. In addition to finding that the paddlefish sensors best encode the signals emitted by zooplankton, the team also found that as the strength of the input signal was raised, the firing of the fish’s sensory neurons transitioned from a steady beat to a noisy pattern of intermittent bursts. This bursting pattern became synchronized across different groups of electroreceptors, increasing the likelihood of the signal reaching higher-order neurons. This provides a plausible mechanism to explain how reliable information about the nearness of prey is transferred to the fish’s brain, the researchers write.
Article: “Sensory Coding in Oscillatory Electroreceptors of Paddlefish” is accepted for publication in Chaos: An Interdisciplinary Journal of Nonlinear Science.
Authors: Alexander B. Neiman (1) and David F. Russell (2).
(1) Neuroscience Program, Department of Physics and Astronomy, Ohio University
Upcoming Conferences of Interest
Physics Today: January Articles
1. Recent developments in U.S. patent law: Legislation making the United States the last country to abandon the first-to-invent patent system should have a significant effect on the way scientists approach patenting.
AIP Science Communication Awards: Call for Entries
Entries are requested for the American Institute of Physics’ 2012 Science Communication Awards, which recognize effective science communication, both in print and new media, that improves the general public's appreciation of physics, astronomy, and allied science fields.
Categories: Science Writing (books), Children’s Writing, New Media
More information and an entry form are available at http://www.aip.org/aip/writing.
To receive Physics News Highlights by email, please contact Catherine Meyers at email@example.com.