November 8, 2011
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.
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TOPICS IN THIS ISSUE:
1. Researchers create extra-long electrical arcs using less energy
Researchers at the University of Canterbury, in New Zealand, have developed a new, lower-voltage method of generating extra-long, lightning-like electrical arcs. The arcs are created when an electrical impulse is applied to a thin copper wire that subsequently explodes. By jump-starting the arcs using exploding wires, as opposed to the traditional method of directly breaking down air, the researchers reduced the amount of voltage needed to create an arc of a given length by more than 95 percent. This photograph shows a 60-meter-long arc, thought to be the longest of its type ever created using this method. The researchers hope that the new method could have wide applications, including inducing real lightning from thunderclouds and creating novel new electrical machines that contain plasma conductors and coils.
Article: “Generating Extra Long Arcs Using Exploding Wires” is accepted for publication in the Journal of Applied Physics.
(1) University of Canterbury, New Zealand
2. ‘Noise’ tunes logic circuit made from virus genes
In the world of engineering, “noise” – random fluctuations from environmental sources such as heat – is generally a bad thing. In electronic circuits, it is unavoidable, and as circuits get smaller and smaller, noise has a greater and more detrimental effect on a circuit’s performance. Now some scientists are saying: if you can’t beat it, use it. Engineers from Arizona State University in Tempe and the Space and Naval Warfare Systems Center (SPAWAR) in San Diego, Calif., are exploiting noise to control the basic element of a computer – a logic gate that can be switched back and forth between two different logic functions, such as AND\OR – using a genetically engineered system derived from virus DNA. In a paper accepted to the AIP’s journal Chaos, the team has demonstrated, theoretically, that by exploiting sources of external noise, they can make the network switch between different logic functions in a stable and reliable way.
The scientists focused on a single-gene network in a bacteriophage λ (lamda). The gene they use regulates the production of a particular protein in the virus. Normally, there are biological reactions that regulate the creation and destruction of this protein; upsetting that balance results in a protein concentration that is either too high or too low. The scientists assigned a “1” to one concentration and a “0” to the other. By manipulating the protein concentration, the team could encode the logic gate input values and obtain the desired output values.
Article: “Logical stochastic resonance with correlated internal and external noises in a synthetic biological logic block” is accepted for publication in Chaos: An Interdisciplinary Journal of Nonlinear Science.
Authors: Anna Dari (1), Behnam Kia (2), Adi R. Bulsara (3), and William L. Ditto (3).
(1) School of Biological and Health Systems Engineering, Arizona State University, Tempe
3. For new microscope images, less is more
When people email photos, they sometimes compress the images, removing redundant information and thus reducing the file size. Compression is generally thought of as something to do to data after it has been collected, but mathematicians have recently figured out a way to use similar principles to drastically reduce the amount of data that needs to be gathered in the first place. Now scientists from the University of Houston and Rice University in Houston, Texas have utilized this new theory, called compression sensing, to build a microscope that can make images of molecular vibrations with higher resolution and in less time than conventional methods. The microscope provides chemists with a powerful new experimental tool.
The main concept behind compressive sensing is something called “sparsity.” If a signal is “sparse,” the most important information is concentrated in select parts of the signal, with the rest containing redundant information that can be mathematically represented by zero or near-zeros numbers. The sparse signal that the Texas researchers were looking at came from a sum frequency generation (SFG) microscope, which shines two different frequency lasers at a surface and then measures the return signal to gather information about the vibration and orientation of the molecules at the surface boundary.
Traditional SFG microscopes scan a sample by systematically moving across it, but the resolution of these traditional scans is limited because as resolution increases the strength of the signal decreases. Instead of systematically scanning the boundary, the compressive sensing microscope gathered a set of pseudo-randomly positioned sampling points. If the important information was captured in the sample, then a series of mathematical steps could be used to construct the entire image. The researchers tested their microscope by imaging stripes of gold deposited on a silicon background and then coated with a chemical called octadecanethiol. The device sensed the stretching of the carbon-hydrogen bonds in the octadecanethiol layer and created images with 16 times more pixel density than was possible with the traditional scanning techniques. The new microscope could find applications in biomolecular imaging and the scientific study of interfaces.
Article: “Sum Frequency Generation-Compressive Sensing Microscope” is accepted for publication in the Journal of Chemical Physics.
Authors: Xiaojun Cai (1), Bian Hu (1), Ting Sun (2), Kevin F. Kelly (2), and Steven Baldelli (1).
(1) Department of Chemistry, University of Houston
4. New hybrid detector monitors alpha, beta, and gamma radiation simultaneously
By combining three layers of detection into one new device, a team of researchers from Japan has proposed a new way to monitor radiation levels at power plant accident sites. The device would be more economical that using different devices to measure different types of radiation, and could limit the exposure times of clean-up workers by taking three measurements simultaneously. Radioactive decay produces three flavors of emissions: alpha, beta, and gamma. Alpha particles comprise 2 neutrons and 2 protons. Because of their large mass and relatively slow speed, alpha particles are the least penetrating of the three types of radiation, and can be stopped by a sheet of paper. Beta particles are electrons that can travel farther than alpha particles, but not as far as high-energy gamma photons, the third type of radiation. The researchers took advantage of the different penetrating properties of the three types of radiation to design their device. Their new radiation detector has three scintillators, which are sheets of material that light up when hit by radiation. Alpha particles strike only the first scintillator, beta particles travel on to the second scintillator, and gamma photons make it all the way through to the third scintillator. The scintillators were then coupled to a photomultiplier tube, a device that converts the light pulses into electrical current. Because the shape of a light pulse differs depending on which type of radiation produced it (alpha particles produce sharp peaks, gamma particles more broad pulses), the device could distinguish between the different radiation types and produce counts for all three simultaneously. The new device could be used for a range of applications in which scientists might need to determine the types of radioactive material present, the researchers write.
Article: “Development of an alpha/beta/gamma detector for radiation monitoring” is accepted for publication in Review of Scientific Instruments.
Authors: Seiichi Yamamoto (1) and Jun Hatazawa (2).
Upcoming Conference of Interest
APS/DFD Meeting: The American Physical Society/Division of Fluid Dynamics meeting will be held November 20 - 22, 2011, in Baltimore, Md.