APS News

STM Advances, Data Storage Mark 1995 March Meeting

More than 5,200 physicists converged on the San Jose Convention Center in California, 20-24 March, for the Society's annual March Meeting. Approximately 5,000 technical papers were presented, mostly on topics in condensed matter and materials physics, as well as related fields, making it one of the largest physics meetings ever. APS units represented at the meeting included biological physics, chemical physics, condensed matter physics, fluid dynamics, high polymer physics, and materials physics.

Among the technical highlights were sessions on the latest advances in scanning tunneling microscopy (STM) technology (see story below), the future of data storage (see page 4), and electric battery-powered vehicles (see page 5). Other technical sessions reported on the application of chaos control techniques to treat cardiac disease (see page 2), a new computer modeling technique for molecular biology (see page 8), and reports on the latest research on optoelectronics, liquid crystals, smart materials and neural networks, and superconductivity.

Nontechnical highlights included sessions on the changing role of physicists in industry (see page 5) and on the job market and graduate education (see page 3). Other nontechnical sessions were organized on topics such as new studies of Isaac Newton's works, climate issues, and an international perspective on physics education.

The traditional ceremonial session for the bestowal of prizes and awards was held Monday evening, followed by a reception hosted by APS President C. Kumar N. Patel (University of California, Los Angeles). Eleven prizes and awards were presented, and the winners gave lectures on their respective award-winning topics at various sessions throughout the week. Citations and brief biographical summaries of the recipients appeared in the March 1995 issue of APS NEWS.

Liquid Crystals. Exhibiting both the orderliness of crystalline solids and the freedom of molecules in a liquid, liquid crystals have important applications in biology. For instance, they form the membranes around the cells in human bodies and provide the basis for the multi-billion-dollar flat panel display industry, which depends on a phenomenon in which the rod-like molecules can rotate the polarization of light to create a shutter-like effect. Liquid crystals are also important for the study of pattern formation in nonequilibrium systems, and scientists hope to gain a better understanding of turbulence and possibly of morphogenesis.

Speaking at a Wednesday morning session, Patricia Cladis (AT&T Bell Laboratories) described how she uses liquid crystals as a miniature laboratory for studying phase transitions. By heating one end of a sample and cooling the other end, she has found that the phase interface between a pure liquid state and a liquid crystal state features spatial patterns: that is, stripes with a characteristic "wavelength". Furthermore, when the liquid crystal is chiral, the interface also oscillates with a characteristic frequency. Cladis hopes to explore the connection between biological systems and the spatial and temporal order of liquid crystal patterns.

Smart Materials. Smart materials are molecular-based structures that respond adaptively to changes in their environment, and are estimated to comprise a $500 million dollar annual industry. In a Tuesday morning session, Victoria Haynes (B.F. Goodrich) described such examples of smart materials as photochromic lenses, which automatically darken or lighten in response to changes in sunlight level, and electrorheological fluids, which alter their viscosity in response to electric fields. The latter are used in engine mounts in the automobile industry in order to keep engines balanced.

The HIV Protein Coat/Junk DNA Languages. Studies of the interactions between HIV's protein coat and surrounding water molecules have uncovered an intriguing pattern that seems to persist in the protein despite its frequent mutations, according to Arnold Mandell (Florida Atlantic University), who reported on his findings during a Thursday morning session. Although it frequently mutates to avoid antibodies, the HIV protein may preserve its deadly function by maintaining key electrical characteristics in water that remain the same despite mutations of its amino acids. And researchers at Boston University have found that the non-protein-coding "junk" DNA that makes up 97 percent of the human genome has similarities to natural languages when statistically-based linguistics tests were applied to the sequences of "letters" in the genetic code, providing further evidence that the poorly understood junk DNA may contain structured information.

Two-Dimensional DNA. Aided by a video showing individual DNA molecules traveling through a two-dimensional obstacle course, Wayne Volkmuth, a scientist at Stanford University, described his proposed design for separating the DNA by length -- a function that may prove useful in DNA fingerprinting and sequencing. Guided by electric fields, single DNA fragments in the video are sandwiched between a silicon floor and Pyrex ceiling as they travel between regularly spaced silicon posts about 150 nanometers tall. The "microlithographic arrays" can possibly become components of compact DNA diagnostic devices of the future and may be able to separate DNA fragments more quickly than traditional methods because of their smaller size.

New Uses of Neural Networks. Operating on the principle that a relationship exists between a material's structure and its properties, researchers can "teach" neural networks to predict properties on the basis of the structural characteristics of molecules, according to Robert Sumpter of Oak Ridge National Laboratory, who described the process during a Thursday morning session. They are also able to design a material with desirable properties into the network and produce suitable structures. For example, as an alternative to ozone-destroying CFCs, the network came up with a chlorine-free fluorohydrocarbon compound.

Currently, scientists at Florida State University's Center for Complex Systems are exploring the possibility of using neural networks to encode the structure of a molecule in the values of different elements of a neural network. The changing values of the elements and connections between them are in turn related to the movements and contortions of complex molecules.

Optoelectronics. Optical devices such as lasers are being integrated into electronic microcircuitry at an ever-increasing rate, and several scientists presented examples of such applications during a Monday morning session. Topics included new materials and fabrication techniques, such as selected-area epitaxy; more efficient lasers emitting at wavelengths suitable for long-range data transmission; components like photoreceiveds, which perform almost as well as the best single test models when integrated onto chips; modulation rates approaching 20Gbits per second; and multiplexing, which combines lasers and detectors operating at slightly different wavelengths in order to increase the number of signals in a single fiber.

Scanning SQUID Microscopy. Scientists at the University of Maryland's Center for Superconductivity Research have obtained images of superconductors, ferromagnets, paramagnets, normal metals, and current flowing in electrical circuits using a high-temperature scanning SQUID microscope and liquid nitrogen as the cryogen. Speaking at a Tuesday afternoon session, group leader Randall Black described how the microscope uses a superconducting quantum interference device as a probe to image extremely weak variations in magnetic fields at microscopic length scales.

Because of the SQUID's large bandwidth, Black's team has also been able to image alternating fields from rf circuits and eddy currents induced in metals at frequencies as high as 200 GHz. The highest frequencies were obtained by a technique that uses circulating Josephson currents in the SQUID's body to induce eddy currents in the sample.

Microscopic Quantum Pinball. Researchers at Harvard University have discovered that if a device is small enough (1 micron) and cold enough (1 K), an electron sent into the device will move ballistically; that is, it will move in straight lines and reflect elastically off the walls. The properties of the device depend on its shape, which can be a stadium, a circle, or a "pacman"-- that is, a circle with a bar extending from the center to the edge. According to Michael Berry, who spoke in a Monday morning session, scientists can study chaos in the quantum realm with these miniature pinball machines.

Sticky Materials. In a Thursday morning session, Stacy Bike, a chemical engineer at the University of Michigan, described her research on the physical forces that control whether or not tiny colloidal particles suspended in a solution will stick to a flat surface or to each other. To measure the weak interaction forces, Bike developed a technique called total internal reflection microscopy (TIRM), in which a low-powered laser beam is bounced off a microscope slide supporting a dilute dispersion of the particles. While most of the light is reflected, some penetrates through the solution in an evanescent wave and is scattered as beams of visible light, which can be measured under the microscope, in order to calculate the potential energy of interactions.

Bike's research could eventually lead to synthetic membranes for artificial red blood cells and scratch-proof finishes on automobiles. "Once we understand the process, we should be able to either promote or discourage particle adhesion, depending on how we manipulate the forces involved," she said.

Visualization and Simulation. The combination of powerful personal and workstation computers with modern application software has driven the development of the field of visualization, according to Tom Wickham-Jones (Wolfram Research), who spoke at a Friday morning session on new applications of visualization. His company has developed a computer program, Mathematica, which is used to collect technical material in electronic documents that combine computations, text, graphics, animations, and sound. "This synthesis of visualization with electronic information delivery helps researchers communicate their work in an effective manner," said Wickham-Jones. "Such documents are stored in a machine independent format that makes them straightforward to share with other workers."

Researchers at Lawrence Livermore National Laboratory have performed large-scale molecular dynamics simulations of processes at surfaces, including growth and surface deformation. "Visualization has become an integral tool in understanding these simulations," said LLNL's James Belak, who showed simulations of indentation and scraping of metal and ceramic surfaces. "It enables us to characterize the films in terms of simple concepts such as local coordination, porosity, and stress."

Cryogenic Particle Detectors. The development of cryogenic elementary particle detectors with higher resolution and lower thresholds is motivated by searches for dark matter in the form of weakly interacting massive particles (WIMPs) and by reactor neutrino experiments. Recent significant improvements in the sensitivity of these detectors have been made using low impedance SQUID-based phonon sensors, according to B. Cabrera of Stanford University, who plans to use this sensor technology in a dark matter experiment currently being assembled at Stanford Underground Facility.

New Studies of Isaac Newton's Works. Historians have long been in disagreement about how Isaac Newton progressed from the mythical falling apple to his laws of motion and gravitation. But Michael Nauenberg (University of California, Santa Cruz), who spoke at a Monday morning session, has rigorously scrutinized Newton's early work in orbital dynamics to discover an unacknowledged contribution from rival scientist Robert Hooke. He believes that one diagram in the margin of a letter from Newton to Hooke demonstrates that Newton may have understood orbital dynamics much earlier than historians have assumed, at least eight years prior to the 1687 publication of the Principia.

Alan Shapiro of the University of Minnesota described the influence of Renaissance artists' new conceptions of colors -- they discovered the three primary colors and rejected Aristotle's idea that chromatic tones are mixtures of white and black, or light and darkness --on Newton's discovery that sunlight is a mixture of all the simple spectral colors, from which he derived new physical properties of sunlight.

"His synthesis of the two fundamentally different concepts of primary color affected the reception and understanding of his theory in the 18th century," said Shapiro. "Placing Newton's theory in the context of the artists' tradition helps to explain why it took until the mid-19th century to develop the distinction between the additive mixing of lights and the subtractive mixing of pigments."

Science Climate Issues. The physical sciences have traditionally had the lowest number of women and people of color, and efforts to increase their ranks have to date met with only modest success. The University of California, Berkeley's Center for Particle Astrophysics (CfPA), one of 25 NSF-funded Science and Technology centers, established a program in 1991 to address these and other issues pertaining to the climate of scientific workplaces. During a Monday afternoon session, CfPA Director Bernard Sadoulet gave an overview of the program's objectives and efforts to date, which was followed by an open panel discussion between CfPA scientists, staff, and students.

Globalizing Physics Education. With well over 40 percent of physics graduate students at U.S. universities hailing from other countries, it has become increasingly important for educators to gain an understanding and appreciation of their varied cultural and educational backgrounds, according to E. Leonard Jossem (Ohio State University), who kicked off a Tuesday morning session exploring the differences between the American educational systems and those of other countries, as well as some of the problems most frequently encountered.

Other speakers explored such topics as the need to evaluate foreign courses in light of their acceptability to North American institutions, particularly for students from Latin American and the former Soviet Union, whose numbers have increased substantially in the last few years. And while Indian students constituted the largest international group in U.S. physics departments until the 1980s, K.R. Subbaswamy (University of Kentucky) believes that historic changes in global relations, the tight physics job market, and India's changing economic factors will have important implications for the selection and mentoring of Indian physics students in the U.S.

Special thanks to Philip F. Schewe and Benjamin Stein of the American Institute of Physics' Public Information Office for contributing to the coverage of technical sessions in this issue.

1995 MARCH MEETING PROGRAM COMMITTEE Chair: John Clem, Iowa State University Hassan Aref, University of Illinois, Urbana-Champaign (Division of Fluid Dynamics) Dan Barnes, Los Alamos National Laboratory (Division of Computational Physics) Charles Duke, Xerox (Committee on Applications of Physics) Elizabeth Garber, SUNY-Stony Brook (Forum on History of Physics) J. Murray Gibson, University of Illinois (Division of Materials Physics) Charles Han, National Institute of Standards and Technology (Division of High Polymer Physics) Klaus Jaeger, Lockheed Missiles & Space (Instrument and Measurement Science Topical Group) Stuart M. Lindsay, Arizona State University (Division of Biological Physics) W. Carl Lineberger, University of Colorado/JILA (Laser Science Topical Group) Ken Lyons, AT&T Bell Laboratories (Forum on Education) Roberto Merlin, University of Michigan (Forum on International Physics) Robert C. Richardson, Cornell University (Division of Condensed Matter Physics) Alvin M. Saperstein, Wayne State University (Forum on Physics and Society) Giacinto Scoles, Princeton University (Division of Chemical Physics)

APS encourages the redistribution of the materials included in this newspaper provided that attribution to the source is noted and the materials are not truncated or changed.

Editor: Barrett H. Ripin