Superconducting Magnet to Probe Proton Structure

Researchers will use a 14-foot, doughnut-shaped superconducting magnet being tested at the University of Illinois to help unlock the innermost secrets of the proton.

Funded by the National Science Foundation, the $2.75 million magnet was designed for an upcoming experiment at the Thomas Jefferson National Accelerator Facility in Newport News, Va. The experiment, called G0 (pronounced "Gee Zero"), involves about 100 scientists from many institutions. Steve Williamson, a U of I physicist, is the experiment coordinator.

Over several months, researchers will meticulously inspect the magnet, cool it to liquid-helium temperatures, and turn it on for the first time. As the power is gradually increased, a robotic test rig will precisely monitor the growing magnetic-field strength in three-dimensional space and alert the researchers to potential problems. The principle designer of the magnet is former U of I physicist Ron Laszewski.

Late this year, with testing complete, the magnet will be shipped to the Jefferson facility. There it will serve as the centerpiece of the G0 experiment–a major effort to closely examine the role that the strange quark plays in generating proton structure and nuclear magnetism.

"We know that the proton’s structure–in particular, its magnetic moment–comes from the up, down, and strange quarks inside the proton," said U of I physicist Doug Beck, spokesperson for the experiment. "But exactly how it is put together is what we are trying to find out."

In the experiment, an intense beam of polarized electrons will scatter off liquid hydrogen and deuterium targets located in the magnet’s core. Detectors, mounted around the perimeter of the magnet, will record the number and position of the scattered particles.

The new magnet will provide a much broader view of the small-scale structure of the proton, compared to earlier "snapshots" obtained with other experiments, such as the SAMPLE apparatus at the MIT/Bates Linear Accelerator Center, Beck said.

"The new magnet should allow measurement of the anapole moment and other aspects of the proton structure with much greater precision over a wide range of momentum transfers," Beck said.

The 80,000-pound magnet was constructed by BWXT in Lynchburg, Va., and required three years to build. It was moved to the U of I in mid-December.

For someone with partial hearing loss, picking out a voice in a crowded social gathering can be hard, even with the help of a hearing aid. That’s about to change.

Scientists at the University of Illinois have signed an exclusive licensing agreement with Phonak Inc., a leading manufacturer of technologically advanced hearing aids, to commercialize an intelligent hearing aid system. The new hearing-aid technology will be able to spatially separate sounds and process them in a way much like the human brain. A key feature of the new system is its ability to integrate signals from each ear so that a listener can focus on a desired voice while canceling out background noise.

The concept for the intelligent hearing aid was developed by a team of 12 researchers at the university’s Beckman Institute for Advanced Science and Technology. Professors from the departments of physiology, electrical and computer engineering, and speech and hearing science contributed to the work.

By allowing the wearer to focus on a single conversation without excessive interference, the intelligent hearing aid will represent a significant improvement over conventional systems, said Albert Feng, a U of I professor of molecular and integrative physiology and leader of the Beckman team.

The intelligent hearing aid prototype consists of a pair of miniature microphones, a processor, an amplifier, and two earpieces. At the heart of the system is what is called a Binaurally Based Intelligent Auditory Processor, which filters the sounds and transmits only the desired voice to the amplifier.

The processor works by comparing signals from the microphones and detecting subtle differences in their time of arrival–much like the process that occurs in the human brain.

"Normal hearing exploits the fact that we have two ears," said Doug Jones, a U of I professor of electrical and computer engineering and a member of the Beckman team. "Our brains utilize both the time of arrival and the intensity of impinging sound waves to perform spatial processing and filtering. This allows us to focus our attention in the direction of the desired sounds and ignore the rest."

Phonak engineers and U of I researchers are now working to package the prototype into a miniature, self-contained system. Phonak is headquartered in Stäfa, Switzerland.

Ballistic Phonons Reveal Strange
Attenuation in Lead Superconductor

By measuring how long it takes phonons (lattice vibrations) to travel through a thin crystal, University of Illinois researchers have found experimental evidence of an unusual spin-density-wave ground state in lead superconductors.

"Lead is a conventional superconductor with not-so-conventional properties," said Jim Wolfe, a U of I professor of physics and a researcher at the university’s Frederick Seitz Materials Research Laboratory. "Anomalies in the lattice dynamics, specific heat, and acoustic attenuation in lead superconductors have puzzled researchers for several decades. Now, we are much closer to a viable explanation."

Several years ago, Albert Overhauser, a physicist at Purdue University, proposed a theory to account for some of this odd behavior. Overhauser suggested that the ground state for lead possessed an unusual spin-density-wave structure not normally found in superconductors.

"If spin-density waves did, indeed, exist in lead, they would create a large anisotropy in the superconducting gap," Wolfe said. "We thought this anisotropy might be revealed by imaging the transmission of phonons through a single crystal of high-purity lead."

Wolfe’s research group invented the method of phonon imaging in order to examine the propagation and scattering of high-frequency phonons in crystals at low temperatures. The technique, which measures the spatial pattern of heat flux emanating from a point source, can probe anisotropies in the superconducting gap of conventional superconductors.

To image phonons, Wolfe and graduate student Jonathan Short use a laser pulse to generate thermal energy at a point on the surface of a supercooled crystal. They record the arrival of the thermal energy after it propagates through the crystal lattice to a detector–a small, superconducting aluminum bolometer. Scanning the laser beam, they piece together many measurements to create a timelapse movie showing phonon movement.

"In our experiment, we found certain directions in which the phonons are attenuated, even though the usual expectation for lead is that the superconducting gap is very isotropic," Wolfe said. "This suggests there are directions in the superconductor where the energy gap is much lower than usual."

For a large energy gap, phonons can propagate ballistically–that is, without scattering off electrons. A significant reduction in the gap along specific directions will result in highly anisotropic attenuation of these phonons, producing a pattern of dark lines in a phonon image.

"Our experiment provides an interesting piece of evidence that seems to support Overhauser’s theory," Wolfe said. "The present theoretical challenge is to apply the spin-density-wave theory to the specific electronic structure of lead and see if the experimental results are reproduced in detail."

The U.S. Department of Energy funded this research.

By recognizing both visual and audio cues, a self-aiming camera being developed at the University of Illinois can tell the difference between an airplane and an albatross.

The camera system, which could find use as an intelligent sentinel in sensitive military applications, originally was built to demonstrate the versatility of a simulated neural network. The researchers modeled the network after the superior colliculus of the human brain.

"The superior colliculus serves as the visual reflex center of the brain," said Sylvian Ray, a U of I professor of computer science and a researcher at the Beckman Institute for Advanced Science and Technology. "It is the primary agent for deciding which direction to turn the head in response to sensory stimuli such as visual and auditory cues."

To demonstrate the effectiveness of their neural network, Ray and his colleagues, molecular and integrative physiology professor Thomas Anastasio, postdoctoral research associate Paul Patton, and graduate research assistants Samarth Swarup and Alejandro Sarmiento, constructed a camera and microphone system that supplies visual and auditory cues to the model and responds to its directives.

One camera looks for motion by comparing successive video frames while the system monitors audio signals from a pair of omnidirectional microphones. A sound-location algorithm analyzes the sounds and sends the information to the neural network. The model then determines the correct position and moves a second camera, equipped with a long-focus lens, to acquire the target. This target image can be transmitted to a human operator for further analysis.

"While the system can be attracted by either sight or sound, the combination of the two offers a much stronger stimulus," Ray said. "By using look-up libraries of sight and sound, the system can differentiate between an aircraft on the horizon and a flock of birds."

The work was originally funded by a U of I Critical Research Initiatives grant. Additional funding to develop the intelligent sentinel concept came from the Office of Naval Research.

This year’s anticipated launch of the Planetary Society’s "Cosmos 1" spacecraft may usher in the long-awaited age of solar sailing. The performance of such spacecraft could be optimized with a simple control strategy developed by scientists at the University of Illinois.

Powered by the sun, solar sails require no onboard propellant–making delivery of huge payloads across vast distances of interplanetary space possible. "For example, a solar-sail spacecraft could ferry provisions and equipment to Mars in advance of a manned expedition," said Victoria Coverstone, a U of I professor of aeronautical and astronautical engineering.

In a project funded by the Jet Propulsion Laboratory, Coverstone and John Prussing, also a professor of aeronautical and astronautical engineering at the U of I, investigated the feasibility of using a solar sail to escape Earth’s orbit and venture out to the planets.

"The solar sail does not sail on the solar wind–the stream of charged particles that produces the familiar glow of auroras," Coverstone said. "Instead, the solar sail uses sunlight in much the same way as a sailboat uses wind. Sunlight striking the sail will apply a force, which can be directed by tilting the sail."

When launched into Earth orbit, the Cosmos 1 spacecraft will unfurl a solar sail consisting of 600 square meters of lightweight, aluminized mylar. The sail will be divided into eight "blades" or "pedals" roughly triangular in shape.

The actual mission–the first solar-sail flight of its kind–is scheduled for launch between October and December of this year.

Headquartered in Pasadena, Calif., the Planetary Society was co-founded by Carl Sagan, Bruce Murray, and Louis Friedman in 1980 to advance the exploration of the solar system. With more than 100,000 members in 140 countries, the society is the largest space interest group in the world.

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Researchers Design
Safer Canoe Chutes

When the weather warms, many outdoor enthusiasts take to the water in canoes and kayaks.

Some boaters, blocked in their travels by one of the myriad dams that dot the nation’s waterways, may attempt to navigate the spillway–a dangerous practice that could result in death by drowning in the strong undertow that forms at the base of a dam. Scientists at the University of Illinois have a safer alternative: properly designed passageways called canoe chutes.

"For well over a century, low-head dams have been constructed for such purposes as flood control, crop irrigation, and to provide power for mills and factories," said Marcelo Garcia, a U of I professor of civil and environmental engineering.

"With the recent rise in recreational use of our rivers and streams, these structures must now be modified to accommodate safe passage for boaters."

By using a combination of computational fluid dynamics and laboratory experiments, Garcia and graduate students Marjorie Caisley and Fabian Bombardelli are creating safe and efficient designs for retrofitting dams with canoe chutes.

Erected in an existing spillway, the basic design of a canoe chute consists of a series of steps or rapids connected by larger pools of slow-moving water. Each pool must be long enough to allow the water to slow sufficiently so that a boater can recover from the previous drop and prepare for the next. The pools also must be deep enough for a kayaker to roll over without the risk of head injury.

To create better guidelines for the construction of canoe chutes, Garcia’s team subjected a basic chute design to intensive testing with a powerful three-dimensional numerical model called Flow-3D, developed by Flow Science Inc. The researchers then built a physical model of the optimized design and compared its performance with their numerical predictions.

Properly designed canoe chutes also can serve as fish ladders, facilitating the migration of fish, Garcia noted.

The Illinois Department of Natural Resources, Office of Water Resources, funded Garcia’s work.

– James E. Kloeppel, University of Illinois News Bureau

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Sensors Detect Damaged
Rails, Faulty Wheels

Broken rails or damaged wheels can cause train accidents with potential loss of life, injury, or property damage. Researchers at the University of Illinois are fabricating fiber-optic sensors that can improve train safety by detecting flaws in rails and wheels.

"We use fiber optics to sense an environmental change–such as the weight of a passing train or the strain created by a cracked, broken, or buckled rail," said Shun-Lien Chuang, a U of I professor of electrical and computer engineering.

In projects sponsored by the Association of American Railroads and the Transportation Research Board at the National Academy of Sciences, Chuang and his research assistants are developing different sensor designs for specific applications.

In one sensor design, the weight of a passing train causes strain in the rail, which is transferred to the attached fiber. The intensity of light that is transmitted through the fiber will depend upon the condition of the rail and the amount of induced strain. In addition to detecting damaged rails, this sensor also can be used for detecting a train’s position and speed.

"The device uses an optical time domain reflectometry system, which measures the signal loss in the optical fiber as a function of distance using a time-gated pulse detection technique," Chuang said. "A moving train creates perturbations in the fiber’s optical transmission, so the system takes several scans and measures the distance to the perturbations in order to pinpoint the train’s location and speed."

Another sensor design is based on the "microbending" effect. "Fiber optics operate on total internal reflection–so when the fiber is bent, some of the light leaks out," Chuang said.

By introducing a certain amount of microbending into the fiber, the researchers can measure any additional pressure, including the weight of passing rail cars. The palm-sized sensor also offers a fast and cost-effective method to detect deformities–particularly flat spots–in rail-car wheels.

The sensors were field-tested locally in cooperation with the Canadian National Illinois Central Railroad. They are currently being tested at the AAR’s Transportation Technology Center in Pueblo, Colo.

–James E. Kloeppel, University of Illinois News Bureau