APS News

2005 March Meeting Gears Up for Showtime in the City of Angels

The latest research results on the spin Hall effect, new chemistry with superatoms, and several sessions celebrating all things Einstein are among the expected highlights at the 2005 APS March meeting, to be held later this month in Los Angeles, California. The conference is the largest physics meeting of the year, featuring some 6500 talks covering a wide variety of research topics—many of which directly impact technologies that help to define the nature of modern culture.

Examples of cutting-edge work to be discussed at the meeting that might convert basic knowledge into useful devices include bio-logical computing, magnetic resonance force microscopy, fuel cells and other uses for hydrogen fuel, superconducting diamond, condensates of utlracold Fermi atoms, gene chips, amorphous steel, solid-state qubits, and circuit QED. A special plenary session will focus on ways in which changing attitudes can recrystallize an entire field, often called a "paradigm shift." Topics to be covered include the advent of single-molecule biology; the discovery of a black hole at the center of the Milky Way, and strongly-correlated electron systems, including the quantum Hall effect.

However, physics research doesn't exist in a vacuum, but is linked in many ways to social issues. Several sessions will focus on such nontechnical issues as the status of women in physics research, human rights of scientists in China and Iran, paper citations in Physical Review Letters, journal refereeing, scientific collaborations between developed and developing countries, and alternative careers for physicists.

Celebrating All Things Einstein.
This year marks the centenary of Albert Einstein's famous year of physics breakthroughs, when he published papers on the photoelectric effect, Brownian motion, and special relativity. Appropriately, 2005 has been recognized as the World Year of Physics (http://www.physics2005.org), and there are numerous sessions at the meeting devoted to Einstein's ideas and activities. For instance, these sessions showcase Einstein's many fruitful collaborations with other scientists. These include such well-known figures as Millikan, Lorentz, Bohr, Born, Planck, Boltzmann, and Ehrenfest, but also Emmy Noether, one of the rare women physicists of that era, who proved two deep theorems on the connection between symmetries and conservation laws-an achievement that greatly impressed Einstein.

Einstein's discoveries aren't simply relegated to the dusty annals of physics history: his ideas are still having an impact on cutting-edge research in condensed matter physics today, according to speakers at a special Wednesday evening session. For instance, Alex Zettle of the University of California, Berkeley, will discuss how Einstein's doctoral thesis work in 1905 concerned the size, geometry and interactions of nanoparticles, which are in turn of fundamental relevance to the design and creation of next- generation nano-electromechanical systems (NEMS). Moses Chan (Pennsylvania State University) will talk about evidence of Bose-Einstein condensation in solid helium, while Stanford University's Zhixun Shen will discuss how photoemission spectroscopy has emerged as a leading tool to push the frontier of condensed matter physics-a full 100 years since Einstein first explained the photoelectric effect at the heart of the technology.

Another session focuses on Einstein's activities in the social sphere, including his involvement with such ticklish issues as racism, pacifism, Zionism, and the dropping of the atom bomb during World War II. There will also be papers presented on Einstein in China, Einstein and diversity in physics, and a special World Year of Physics public lecture by 1996 Nobel Laureate Douglas Osheroff (Stanford University).

Spins in the Hall.
Physicists at the meeting will be buzzing over a newly observed phenomenon, the spin Hall effect, whose origin is still being hotly debated. It has the potential of leading to extremely low- power memory chips and computer processors. The classical Hall effect is created by the deflection of electric current as it traverses a conductor in a magnetic field. In contrast, the spin Hall effect is the deflection of an electron in a semiconductor in a direction that depends on the electron's spin. Speakers at two separate sessions will discuss the experiment and theory underlying this effect, including two research groups that recently demonstrated it. Originally proposed in 1971, theoretical interest in the phenomenon languished until quite recently, but has since revived: over 60 theoretical papers have been published in the past two years.

Superatom Chemistry.
Researchers have discovered that clusters of aluminum atoms can behave as "superatoms" that mimic the chemical properties of different elements depending upon the size of the cluster. Starting with iodine-based compounds called polyiodides, a team of scientists from Penn State and Virginia Commonwealth University removed a single iodine atom and replaced it with an aluminum cluster made of either 13 or 14 atoms. As a result, the clusters exhibited chemistry similar to halogen atoms, such as iodine, and alkaline earth elements such as magnesium. But there were some differences, too, leading in one case to the creation of an entirely new class of polyiodide structures. These results provide further evidence of an underlying "periodic table" of cluster elements. The work may also lead to novel materials such as aluminum-based compounds that wouldn't rust.

Antifreeze Proteins.
More than 35 years ago, scientists discovered special proteins in the bloodstream of certain fish that prevented them from freezing. These antifreeze proteins (AFPs) have also been found in insects, plants, fungi, bacteria, and even vertebrates. They either keep the organism from freezing or, if crystallization has occurred, help to mitigate structural damage, caused by large ice grains growing at the expense of small grains, irrevocably breaking some tissue structures. Scientists think that AFPS are able to work by binding to (and limiting further growth of) ice crystals. The first direct observations of AFP on newly-formed ice crystals will be reported at the meeting.

Integrating Strained Silicon.
The silicon chip industry is turning to strained silicon as a means to make faster, low-power computer chips with conventional technology. Physicists have long known that strained silicon contains electrons that travel up to twice the maximum speed of electrons in ordinary silicon. While the original motivation for strained silicon was to make chips with speedier electrons, researchers now realize that using reduced-strength electric fields to turn on and off transistors could get electrons moving at conventional speeds, while dissipating lower levels of power as they travel through dense networks of transistors. Strained silicon technology has already begun to appear in the product lines of major chip manufacturers such as AMD, Intel, Texas Instruments, and IBM. Several speakers from industry and academia will be on hand to discuss some of the latest discoveries and challenges of implementing this promising new technology.

How Frogs Get Perfect Pitch.
Clawed frogs in South Africa depend for dinner on their ability to sense the floundering of insects on the surface of the pond they inhabit. They must not only detect, but discriminate: the frog can discern between water waves at, for example, a frequency of 14 Hz and 14.5 Hz, respectively. J. Leo van Hammen and colleagues at the Technical University of Munich study what happens at the synapse level to allow the frog to accomplish this. The frog can "hear" with its skin and detect motions in the pond as slow as 0.1 mm/sec through an underlying "lateral-line" system. Human touch sensors simply aren't sensitive enough to "hear" with their skin. Van Hemmen will report on how the frog develops effective "wetware" (neuronal software and hardware) for catching prey by resolution.

Terahertz Technology.
The terahertz portion of the electromagnetic spectrum (300 GHz to 10 THz) spans the region between microwaves and light. THz radiation is non-ionizing and can penetrate many materials, leading to several new inventions in areas ranging from medicine to homeland security. At the March meeting, Michael Kemp of TeraView Ltd. will discuss the use of THz radiation in medical imaging to detect cancer, while David Zimdars of Picometrix will present a THz scanning system that has been deployed to scan space shuttle fuel tanks for defects. NIST's Erich Grossman will round out the session by describing the design of an imager for concealed weapons detection.

Looking Deeper with 3D Imaging.
Ordinary x-ray crystallography yields the structure of a biomolecule like a protein simply by providing averaged information from scattering from a large number of identical unit cells. In contrast, UCLA physicist John Miao forms high-resolution images of non-crystal-line samples. He and his colleagues use the SPring-8 synchrotron in Japan—the most powerful continuous x-ray source in the world—to reveal layered images with spatial resolution as good as 7 nm. These layers are then stacked up to provide the best 3D images yet obtained for targets such as E.coli and yeast. Microscopic methods with similar spatial resolution, like scanned probe microscopes or electron microscopes, can't form 3D images.

Artificial Sight.
Age-related macular degeneration (AMD) and retinitis pigmentosa (RP) are the leading causes of blindness around the world. Although the neural "wiring" from eye to brain is intact, these patients lack photoreceptor activity. Scientists now realize that electrical stimulation of the retina can produce visual percepts in blind patients suffering from these diseases, and are developing retinal implants to do just that. Thus far, such implants have had only a few electrodes; several thousand pixels would be required to restore meaningful sight. Speakers will discuss their work on various elements of the next generation of retinal prosthetic devices. Closing out the session will be Oak Ridge National Labora-tory's Elias Greenbaum, who is developing a method for inserting purified spinach protein reaction centers and other photoreactive agents into retinal cells to restore photoreceptor function.

Fast Cancer Detection.
Many cancer-detection devices still use staining and fluorescence techniques. Researchers at Sandia National Laboratories have developed a newer approach, using single cells as waveguides within special optical cavities. The way in which the laser light in the cavity is scattered or absorbed depends on the internal state of the cell, especially the structure of the cell's mitochondria, which in turn depends on malignant conditions. According to Sandia scientist Paul Gourley, the new laser method is fast (with picosecond sampling times) and less prone to misinterpretation. It is well suited to cell types with lots of mitochondria, such as brain, muscle and liver cells.

Scratching the Surface.
What, exactly, is happening when you scratch your skin with a needle? It triggers a physiological response, sending substances that create vasodilation in order to repair the scratch. But we still don't understand completely what mechanical processes are behind this response. Now, researchers have devised a method that obtains the contraction state of smooth and very small muscles situated around blood vessels, which they have used to describe the entire mechanical response to skin irritation, They will report on their findings at the meeting.

James Riordon, Ben Stein and Phil Schewe contributed to this article.

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Editor: Alan Chodos
Associate Editor: Jennifer Ouellette