Science by the Seat of the Pants

PASADENA, Calif. — Sliding down a sand dune on your derriere might at first take seem a bit undignified for a professor from the California Institute of Technology. But for mechanical engineering professor Melany Hunt, it's all in the name of science.

Hunt wants to know why many desert sand dunes give off sound--and a loud, droning sound to boot--whenever the dune avalanches, or a strong wind blows, or a scientist slides down its side. While the phenomenon has been known about for centuries (Hunt has a book, Tales of Travel, circa 1923, that mentions Marco Polo knew about it), what causes the sound remains a mystery. Most believe the answer is friction--tiny grains of sand rubbing together. But that's only part of the story, Hunt believes, noting that the sound continues even after the movement has stopped. And further, the sound a sand dune makes in winter differs from the sound it makes in summer.

Intriguing questions, says Hunt, and it ties into her research concerning the flow of particulates and granular materials, including the natural environment of both sand and debris flows. Which is why she has spent the last few summers investigating the phenomenon of sand dune sound as a mentor with Caltech's Summer Undergraduate Research Fellowships (SURF) program. (Every summer, the SURF program brings undergraduate students from various schools to Caltech to conduct independent research with faculty members.)

So several times each summer, Hunt, her research colleague, mechanical engineering professor Chris Brennen, and her students make the long drive to the Eureka Dunes in Death Valley, California, or the Dumont Dunes nearby, or to the Kelso Dunes in the Mojave National Preserve, CA. Once there, they slog up to the dune's crest line, carting a radar unit, geophones (a type of microphone), and lots of water to combat the common 100-plus degree temperatures.

The equipment is being used to confirm Hunt's theory about the loud sound that's generated--she believes it's a resonance effect, much like a string being plucked on a musical instrument. Over a long period of time, whatever rain that falls in this desert environment percolates into the sand dune, eventually forming a band of moisture some two meters (6.6 feet) down. In time this sand hardens, says Hunt, forming a hard, cement-like crust. When the sand on the surface is disturbed, friction between sand grains creates a noise that reverberates, back and forth, between the dry sand on the surface and the wet sand below.

"That may be why smaller dunes don't make sound," says Hunt, "because they haven't been around long enough to form that hard layer of sand." The minimum needed is about two meters of thickness, she says. The loudest dunes are the tallest and the steepest, those with a maximum 30-degree angle of repose; that is, the steepest the dune's face can be without collapsing. It's also the reason she believes the sound varies by the season, which affects how much moisture is in the sand.

Hunt and her students dragged the radar to the top of the dune and used it to confirm the existence of the band of wet, hard sand down below. The geophone was used to record the noise as the students slid down the dune.

Hunt plans at least one more trip to a sand dune sometime in September; intrepid reporters are invited to attend. Meanwhile, for a QuickTime movie, complete with sound, of students sliding down a dune, please see the website of Kathy Brantley, one of Hunt's former students, at http://www.prettypixel.net/Dunes/index.html.

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Jennings Named Caltech Provost

PASADENA, Calif.— Paul Jennings, professor emeritus in civil engineering and applied mechanics at the California Institute of Technology, has been named provost of the Institute. He takes the post on August 1.

Jennings, who has been on the Caltech campus as a student, professor, and administrator for 44 years, returns to the provost position after a nine-year hiatus. He served as vice president and provost from 1989 to 1995. Thus, he was the Institute's sixth, and is now its eighth, provost since the post was created in 1962.

"Paul is an exciting choice," said Caltech President David Baltimore. "At a time when so many things are happening on campus--the $1.4 billion capital campaign is in mid-stream, there are a number of building and renovation projects projected, there are budgetary challenges to be met--he brings a wealth of knowledge and experience to the office. He is an effective administrator, a great leader and an eloquent spokesman. I personally enjoyed very much working with Paul when he filled in as acting vice president for business and finance a few years ago, and I look forward to having the opportunity to work closely with him again."

Jennings is an expert in the design of earthquake-resistant structures and in how the earth moves during a temblor. He played an active role in investigating the effects of damaging earthquakes.

He was chair of Caltech's Division of Engineering and Applied Science from 1985 to 1989, served as the acting vice president for business and finance in 1995 and again in 1998-99, and as executive officer for civil engineering and applied mechanics from 1975 to 1980.

Jennings, who is highly regarded within the Caltech community for his energy, enthusiasm, and organizational skills, is also internationally renowned in the seismology and engineering fields. He has been the president of the Seismological Society of America and of the Earthquake Engineering Research Institute. He was a member of the National Science Foundation's advisory committee on earthquake engineering and a chairman of the National Research Council's committee on seismology.

Jennings earned a B.S. from Colorado State University in 1958, an M.S. from Caltech in 1960, and a Ph.D. from Caltech in 1963. He was a research fellow at Caltech in civil engineering in 1965 and swiftly moved up the academic ladder to become a full professor in 1972. He has been an emeritus professor since 2002. He also served on the teaching staff of the U.S. Air Force Academy from 1963 to 1965.

Jennings replaces Steve Koonin who served as provost from 1995 until early this year when he stepped down from the administrative role to become chief scientist of BP in London. Koonin is on a leave of absence from his faculty appointment as professor of theoretical physics.

Jennings is a hiker and avid fly fisherman. His wife is Missy and he has two grown daughters, Kathryn and Margaret.

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Media Contact: Jill Perry, Media Relations Director (626) 395-3226 jperry@caltech.edu

Visit the Caltech Media Relations Web site at: http://pr.caltech.edu/media

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Inaugural Wouk Lecture on Advanced Technology for Space Exploration

PASADENA, Calif.- Erik Antonsson, the chief technologist at the Jet Propulsion Laboratory and a professor of mechanical engineering at the California Institute of Technology, will give the inaugural Victor Wouk Lecture at 4 p.m. May 19 in Lees-Kubota Lecture Hall, 101 Guggenheim Laboratory of Aeronautics and Applied Science on the Caltech campus. Antonsson will discuss "Advanced Technology for Space Exploration" and will provide an overview of the JPL Strategic Technology Plan, along with highlights of recent successes and future missions. A wine and cheese reception will follow. The program is free and open to the public.

This new lectureship is named in honor of Caltech alumnus Victor Wouk, who received his master's and doctorate degrees in electrical engineering from Caltech in 1940 and 1942, respectively. He devoted himself largely to developing hybrid motor vehicles and using semiconductors in electric vehicles. He designed and built a high-performance electric vehicle and a high-performance, low-emission, improved-fuel-use hybrid. He continues to promote the continuing development of hybrid automobiles powered by both electricity and gasoline, such as the Toyota Prius, Honda Insight, and Ford Escape Hybrid.

The range of Wouk's activities is wide, and he has consulted for several institutions and the government on the problems of energy. A space-travel buff since childhood, he also worked with the team that developed fuel gauges for the "dune buggies" that roamed the surface of the moon during the Apollo program.

The Victor Wouk Lectureship was established by the Wouk family in December 2004 to bring to campus experts on the latest advances in science and technology.

Due to health limitations, Wouk himself will not be able to attend the lecture, but his brother Herman, the author, and Victor's son, Jonathan, will attend.

Antonsson is currently on leave from Caltech as he serves in his position at JPL, in which he has responsibility for planning, implementing, and leading JPL's technology strategy. He also serves as a member of JPL's executive council and as the senior representative for JPL basic technology research to NASA headquarters and other NASA centers and government agencies

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White House Names Three from Caltech Faculty as Presidential Early Career Award Winners

PASADENA, Calif.—Three members of the faculty at the California Institute of Technology have been named among the most recent winners of the prestigious Presidential Early Career Award for Scientists and Engineers (PECASE). The honor was announced today by the White House.

The three are Babak Hassibi, an electrical engineer who studies data transmission and wireless communications system; Mark Simons, a geophysicist who specializes in understanding the mechanical behavior of Earth using radar and other satellite observations of the motions of Earth's surface; and Brian Stoltz, an organic chemist who specializes in the synthesis of structurally complex, biologically active molecules.

Hassibi was cited by the White House for his "fundamental contributions to the theory and design of data transmission and reception schemes that will have a major impact on new generations of high-performance wireless communications systems. He has nurtured creativity in his undergraduate and graduate students by involving them in research and inspiring them to apply new approaches to communications problems."

An associate professor of electrical engineering at Caltech and a faculty member since 2001, Hassibi earned his bachelor's degree from the University of Tehran in 1989, and his master's and doctorate degrees from Stanford in 1993 and 1996, respctively. He is the holder or coholder of four patents for communications technology, and is the winner of several awards, including the 2002 National Science Foundation Career Award, the 1999 American Automatic Control Council O. Hugo Schuck Best Paper Award, the 2003 David and Lucille Packard Fellowship for Science and Engineering, and the 2002 Okawa Foundation Grant for Telecommunications and Information Sciences.

Simons, an associate professor of geophysics, combines satellite data with continuum mechanical models of Earth to study ongoing regional crustal dynamics, including volcanic and tectonic deformation in Iceland, crustal deformation and the seismic cycle in California, Chile, and Japan, and volcanic and tectonic deformation in and around Long Valley, California. He also uses the gravity fields of the terrestrial planets to study the large-scale geodynamics of mantle convection and its relationship to tectonics.

Simons earned his bachelor's degree at UCLA in 1989, and his doctorate from MIT in 1995. He was a postdoctoral scholar at Caltech for two years before joining the faculty in 1997.

Stoltz has been an assistant professor of chemistry at Caltech since 2000. He earned his bachelor's degree at Indiana University of Pennsylvania in 1993, his master's and doctorate degrees at Yale University in 1996 and 1997, respectively. Before joining the Caltech faculty he spent two years at Harvard University as a National Institutes of Health (NIH) Postdoctoral Fellow. His work is aimed at developing new strategies for creating complex molecules with interesting structural, biological, and physical properties. The goal is to use these complex molecules to guide the development of new reaction methodology to extend fundamental knowledge and to potentially lead to useful biological and medical applications.

Stoltz, an Alfred P. Sloan Fellow, is the recipient of a Research Corporation Cottrell Scholars Award, the Camille and Henry Dreyfus New Faculty Award, and the Pfizer Research Laboratories Creativity in Synthesis Award. Additionally, he was named as an Eli Lilly Grantee in 2003 and has won a number of young faculty awards from pharmaceutical companies such as Merck Research Laboratories, Abbott Laboratories, GlaxoSmithKline, Johnson & Johnson, Amgen, Boehringer Ingelheim, and Roche. At Caltech he won the 2001 Graduate Student Council Teaching Award and Graduate Student Council Mentoring Award.

The PECASE awards were created in 1996 by the Clinton Administration "to recognize some of the nation's most promising junior scientists and engineers and to maintain U.S. leadership across the frontiers of scientific research." The awards are made to those whose innovative work is expected to lead to future breakthroughs.

 

 

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Researchers demonstrate existenceof earthquake supershear phenomenon

PASADENA, Calif.--As if folks living in earthquake country didn't already have enough to worry about, scientists have now identified another rupture phenomenon that can occur during certain types of large earthquakes. The only question now is whether the phenomenon is good, bad, or neutral in terms of human impact.

Reporting in the March 19 issue of the journal Science, California Institute of Technology geophysics graduate student Kaiwen Xia, aeronautics and mechanical engineering professor Ares Rosakis, and geophysics professor Hiroo Kanamori have demonstrated for the first time that a very fast, spontaneously generated rupture known as "supershear" can take place on large strike-slip faults like the San Andreas. They base their claims on a laboratory experiment designed to simulate a fault rupture.

While calculations dating back to the 1970s have predicted that such supershear rupture phenomena may occur in earthquakes, seismologists only recently began assuming that supershear was real. The Caltech experiment is the first time that spontaneous supershear rupture has been conclusively identified in a controlled laboratory environment, demonstrating that super-shear fault rupture is a very real possibility rather than a mere theoretical construct.

In the lab, the researchers forced two plates of a special polymer material together under pressure and then initiated an "earthquake" by inserting a tiny wire into the interface, which is turned into an expanding plasma by the sudden discharge of an electrical pulse. By means of high-speed photography and laser light, the researchers photographed the rupture and the stress waves as they propagated through the material.

The data shows that, under the right conditions, the rupture propagates much faster than the shear speed in the plates, producing a shock-wave pattern, something like the Mach cone of a jet fighter breaking the sound barrier.

The split-second photography also shows that such ruptures may travel at about twice the rate that a rupture normally propagates along an earthquake fault. However, the ruptures do not reach supershear speeds until they have propagated a certain distance from the point where they originated. Based on the experiments, a theoretical model was developed by the researchers to predict the length of travel before the transition to supershear.

In the case of a strike-slip fault like the San Andreas, the lab results indicate that the rupture needs to rip along for about 100 kilometers and the magnitude must be about 7.5 or so before the rupture becomes supershear. Large earthquakes along the San Andreas tend to be at least this large if not larger, typically involving rupture lengths of about 300 to 400 kilometers.

"Judging from the experimental result, it would not be surprising if supershear rupture propagation occurs for large earthquakes on the San Andreas fault," said Kanamori.

Similar high-speed ruptures propagating along bimaterial interfaces in engineering composite materials have been experimentally observed in the past (by Rosakis and his group, reporting in an August 1999 issue of Science). These ruptures took place under impact loading; only in the current experiment have they been initiated in an earthquake-like set-up.

According to Rosakis, an expert in crack propagation, the new results show promise in using engineering techniques to better understand the physics of earthquakes and its human impact.

According to Kanamori, the human impact of the finding is still debatable. The most damaging effect of a strike-slip earthquake is believed to be caused by a pulse-like motion normal to the fault caused by the combined effect of the rupture and shear wave. The supershear rupture suppresses this pulse, which is good, but the persistent shock-wave (Mach wave) emitted by the supershear rupture enhances the fault-parallel component of motion (the ground motion that runs in the same direction that the plates slip) and could amplify the destructive power of ground motion, which is bad.

The outstanding question about supershear at this point is which of these two effects dominates. "This is still being debated," says Kanamori. "We're not committed to one view or the other." Only further laboratory-level experimentation can answer this question conclusively.

Several seismologists believe that supershear was exhibited in some large earthquakes, including those that occurred in Tibet in 2001 and in Alaska in 2002. Both earthquakes were located in a remote region and had little, if any, human impact, but analysis of the evidence shows that the fault rupture propagated much faster than would normally be expected, thus implying supershear.

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(Nearly) Autonomous Bob (Almost) Ready to Race

PASADENA, Calif. -- It's do-or-die time for Bob. Next week marks the final test for the Chevrolet truck with the human nickname, the California Institute of Technology's entry in the DARPA Grand Challenge autonomous ground vehicle race scheduled for March 13.

DARPA, the Defense Advanced Research Projects Agency, is offering a $1 million prize to a team whose vehicle can complete an off-road course of more than 200 miles that will start somewhere near Barstow, CA, and end somewhere near Las Vegas (the exact course won't be revealed until race day).

The challenge, of course, is that the 25 vehicles invited to race by DARPA (culled from an original 106 entries) will race without a driver and must be fully autonomous--not a remote-controlled vehicle driven by a student wielding a laptop at a distance, but a completely autonomous car that will drive and navigate itself. The vehicles will have to contend with such pitfalls as dirt roads and ditches, open water, rocks and boulders, underpasses, cattle guards, sandpits, and their fellow competitors.

Before that race, though, Bob and the other vehicles must meet a challenge that is almost as great--a Qualification, Inspection, and Demonstration (QID) test to take place at the California Speedway in Fontana. On Monday, March 8, from 10:30 to 11 a.m., and again on Wednesday, March 10, from 9:30 to 10 a.m., Bob will have to successfully navigate a mile-and-a-half-long course that will contain all the dire elements mentioned above. "We think of it as the precursor to the actual race," says Dave van Gogh, the project manager for Team Caltech. (QID General Opening Ceremony is scheduled for Monday, March 8, at 9 a.m., and continues on Tuesday and Wednesday, at 8 a.m.)

For a year now, van Gogh has shepherded between 18 and 23 Caltech undergraduates who receive academic credit for their work. Although they are receiving advice from scientists at Caltech, the Jet Propulsion Lab, and Northrop Grumman, it is ultimately the students' responsibility for the computing hardware, software coding, and designing and building Bob's mechanical infrastructure.

All of the hardware has been installed, and in tests, the truck has been able to navigate from one point to another by itself. What hasn't been accomplished yet is the autonomous avoidance of obstacles, which is--obviously--critical for Bob's success. Currently, several of the students are feverishly writing additional code and rooting out programming errors in preparation for the Monday QID.

DARPA is sponsoring the challenge to encourage innovation in driverless technology, which the Department of Defense believes will be critical to future military endeavors. The idea for the race itself was suggested by former Caltech provost Steve Koonin, now on leave from the Institute. At the time he chaired the JASONs, an elite core of academic scientists that provides the federal government with advice on national security issues. DARPA had approached the group for advice on how best to advance research into autonomous vehicles.

The immediate goal of Team Caltech is to pass Monday's QID. The other primary goal, says van Gogh, has already been met--providing the students with a unique educational opportunity. "All of the students are really motivated and excited about this," he says. "That was our goal from the beginning--to create a unique learning experience for them."

The QID is free and open to the public. The California Speedway is located at 9300 Cherry Avenue in Fontana. More information on attending the QID and race can be found at http://www.darpa.mil/grandchallenge/spectators.htm.

Media Contact:Mark Wheeler (626) 395-8733 wheel@caltech.edu

Visit the Caltech Media Relations website at http://pr.caltech.edu/media

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Caltech Engineers Design a Revolutionary Radar Chip

PASADENA, Calif. -- Imagine driving down a twisty mountain road on a dark foggy night. Visibility is near-zero, yet you still can see clearly. Not through your windshield, but via an image on a screen in front of you.

Such a built-in radar system in our cars has long been in the domain of science fiction, as well as wishful thinking on the part of commuters. But such gadgets could become available in the very near future, thanks to the High Speed Integrated Circuits group at the California Institute of Technology.

The group is directed by Ali Hajimiri, an associate professor of electrical engineering. Hajimiri and his team have used revolutionary design techniques to build the world's first radar on a chip--specifically, they have implemented a novel antenna array system on a single, silicon chip.

Hajimiri notes, however, that calling it a "radar on a chip" is a bit misleading because it's not just radar. Having essentially redesigned a computer chip from the ground up, the technology is revolutionary enough to be used for a wide range of applications.

The chip can, for example, serve as a wireless, high-frequency communications link, providing a low-cost replacement for the optical fibers that are currently used for ultrafast communications. Hajimiri's chip runs at 24 GHz (24 billion cycles in one second), an extremely high speed, which makes it possible to transfer data wirelessly at speeds available only to the backbone of the Internet (the main network of connections that carry most of the traffic on the Internet).

Other possible uses:

* In cars, an array of these chips--one each in the front, the back, and each side--could provide a smart cruise control, one that wouldn't just keep the pedal to the metal, but would brake for a slowing vehicle ahead of you, avoid a car that's about to cut you off, or dodge an obstacle that suddenly appears in your path.

While there are other radar systems in development for cars, they consist of a large number of modules that use more exotic and expensive technologies than silicon. Hajimiri's chip could prove superior because of its fully integrated nature. That allows it to be manufactured at a substantially lower price, and makes the chip more robust in response to design variations and changes in the environment, such as heat and cold.

* The chip could serve as the brains inside a robot capable of vacuuming your house. While such appliances now exist, a vacuum using Hajimiri's chip as its brain would clean without constantly bumping into everything, have the sense to stay out of your way, and never suck up the family cat.

* A chip the size of a thumbnail could be placed on the roof of your house, replacing the bulky satellite dish or the cable connections for your DSL. Your picture could be sharper, and your downloads lightning fast.

* A collection of these chips could form a network of sensors that would allow the military to monitor a sensitive area, eliminating the need for constant human patrolling and monitoring.

In short, says Hajimiri, the technology will be useful for numerous applications, limited only by an entrepreneur's imagination.

Perhaps the best thing of all is that these chips are cheap to manufacture, thanks to the use of silicon as the base material. "Traditional radar costs a couple of million dollars," says Hajimiri. "It's big and bulky, and has thousands of components. This integration in silicon allows us to make it smaller, cheaper, and much more widespread."

Silicon is the ubiquitous element used in numerous electronic devices, including the microprocessor inside our personal computers. It is the second most abundant element in the earth's crust (after oxygen), and components made of silicon are cheap to make and are widely manufactured. "In large volumes, it will only cost a few dollars to manufacture each of these radar chips," he says.

"The key is that we can integrate the whole system into one chip that can contain the entire high-frequency analog and high-speed signal processing at a low cost," says Hajimiri. "It's less powerful than the conventional radar used for aviation, but, since we've put it on a single, inexpensive chip, we can have a large number of them, so they can be ubiquitous."

Hajimiri's radar chip, with both a transmitter and receiver (more accurately, a phased-array transceiver) works much like a conventional array of antennas. But unlike conventional radar, which involves the mechanical movement of hardware, this chip uses an electrical beam that can steer the signal in a given direction in space without any mechanical movement.

For communications systems, this ability to steer a beam will provide a clear signal and will clear up the airwaves. Cell phones, for example, radiate their signal omnidirectionally. That's what contributes to interference and clutter in the airwaves. "But with this technology you can focus the beams in the desired direction instead of radiating power all over the place and creating additional interference," says Hajimiri. "At the same time you're maintaining a much higher speed and quality of service."

Hajimiri's research interest is in designing integrated circuits for both wired and wireless high-speed communications systems. (An integrated circuit is a computer chip that serves multiple functions.) Most silicon chips have a single circuit or signal path that a signal will follow; Hajimiri's innovation lies in multiple, parallel circuits on a chip that operate in harmony, thus dramatically increasing speed and overcoming the speed limitations that are inherent with silicon.

Hajimiri says there's already a lot of buzz about his chip, and he hasn't even presented a peer-reviewed paper yet. He'll do so next week at the International Solid State Circuit Conference in San Francisco.

Note to editors: Color pictures of the tiny chip, juxtaposed against a penny, are available.

Media Contact: Mark Wheeler (626) 395-8733 wheel@caltech.edu

Visit the Caltech Media Relations website at http://pr.caltech.edu/media

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Caltech engineers announce new, more promising type of electrolyte for fuel cells

PASADENA, Calif.—The quest for a cheap and robust fuel cell for future cars may be a bit closer this week to the "grail" moment. Scientists at the California Institute of Technology have announced that they're getting promising results with a new material that solves various limitations of previously tested fuel cells.

In an article published online November 20 by the journal Science on the Science Express Website, associate professor of materials science and chemical engineering Sossina Haile and her colleagues report that they have created a new phosphate-based electrolyte to go inside the fuel cells. The new substance, formally named cesium dihydrogen phosphate is, for a variety of reasons, better than the team's previously favored electrolyte, which was based on a sulfate.

"It's a whole new way of doing fuel cells that opens up tremendous possibilities for system simplification," says Haile, a leading authority on fuel cell technology. Haile's most spectacular results in recent years have been with the "solid acid" electrolytes, such as both the phosphate and the sulfate materials, that ferry current along the fuel cell in a way that minimizes the use of expensive parts that rapidly wear out.

Fuel cells have for some time been promoted as a way to help wean global society away from its addiction to gasoline and internal-combustion engines. Like a combustion engine, a fuel cell uses some sort of chemical fuel as its energy source, but like a battery, the chemical energy is directly converted to electrical energy, without a messy and inefficient combustion step.

The components in a fuel cell that make this direct electrochemical conversion possible are an electrolyte, a cathode, and an anode. In the simplest example hydrogen fuel is brought into the anode compartment and oxygen is brought into the cathode compartment. There is an overall chemical force driving the oxygen and the hydrogen to react to produce water.

In the fuel cell, however, the direct chemical reaction is prevented by the electrolyte that separates the fuel (H2) from the oxidant (O2). The electrolyte serves as a barrier to gas diffusion, but it will let protons migrate across it. In order for the reaction between hydrogen and oxygen to occur, the hydrogen molecules shed their electrons to become protons. The protons then travel across the electrolyte and react with oxygen atoms at the cathode, where they also pick up electrons to produce neutral water. An additional requirement for these electrochemical reactions to occur is that there be some external path through which the electrons migrate; it is precisely this electron motion that provides usable electricity from the fuel cell.

Traditional fuel cells, which utilize polymer electrolytes, are hampered by a number of problems. The most notable are the cells' inability to operate at high temperatures, their requirement for complicated water regulation systems, and their failure to control fuel diffusion.

Haile and her associates have addressed these shortcomings by creating a novel fuel cell with a solid-acid electrolyte. Solid acids have unique properties that lie between those of normal acids and normal salts. Importantly, solid acids are very efficient at conducting protons when they are heated to "warm" temperatures.

However, their use for any application was largely ignored because they are water-soluble and difficult to fabricate into useful forms. In previous work, Haile explored the applicability of the solid acid CsHSO4 as a fuel cell electrolyte and demonstrated the successful operation of such a fuel cell. She found that the key to creating a functional solid-acid fuel cell is an operation temperature above 100 degrees C, which ensures that water in the system, which would otherwise dissolve and leach away the solid acid, is present as harmless steam.

The CsHSO4 electrolyte fuel cell suffered from a serious problem that prohibited its use for power generation. Specifically, the output of the fuel cell decreased over time as the hydrogen fuel reacted with the solid acid in the presence of the catalyst. As reported in their Science paper, Haile and her colleagues circumvented this problem by replacing the CsHSO4 solid acid with CsH2PO4, which does not react with hydrogen.

According to Haile, they were initially hesitant to use this material because it decomposes via dehydration into a nonuseful salt. However, they found that humidifying the fuel cell anode and cathode chambers with a relatively low level of water vapor could prevent the dehydration reaction and thereby maintain the fuel cell for long-term power generation.

Haile's humidity-stabilized CsH2PO4 fuel cells solve several critical problems that have plagued polymer fuel cell development. First, these solid-acid fuel cells can be operated at higher temperatures than those built with polymer electrolytes, which are limited to temperatures less than 100 degrees C. Operation at "warm" temperatures, 100-–300 degrees C, brings a number of benefits to fuel cell technology. Most directly, catalyst activity is enhanced, resulting in higher-efficiency fuel cells and allowing one to use less of the expensive catalyst.

In addition, the susceptibility of the catalyst to poisoning from carbon monoxide contamination of the fuel decreases. As a consequence, the fuel stream need not be purified as thoroughly as for polymer fuel cells, reducing the overall system complexity. Perhaps most significantly, operation at warm temperatures opens up the possibility of using less-expensive base-metal catalysts, which are not active enough to be considered for low temperature applications.

Additional system simplifications come about from the fact that the radiator necessary for maintaining a fuel cell at about 200 degrees C is much smaller than the one required for maintaining a temperature of about 90 degrees C. This has significant implications for automotive applications. Warm-temperature operation can furthermore be easily integrated with onboard hydrogen-generation systems that produce hydrogen also at warm temperatures. For a polymer electrolyte fuel cell, the hydrogen stream from these generators has to be cooled before it can be introduced into the cell.

Solid-acid fuel cells can be operated in the temperature range of 100–300 degrees C because, unlike polymers, they do not rely on water molecules to transport protons from one side of the membrane to the other. This "dry" proton transport results in additional advantages. In particular, there is no longer a need to remove water that accumulates at the cathode and replenish it at the anode. As a consequence, the overall system is, again, significantly simplified.

In the case of CsH2PO4, a small amount of water partial pressure, equivalent to about 10 percent relative humidity at 100 degrees C, is required in order to prevent dehydration of the material, but no water recirculation is necessary. The dry, solid-acid electrolytes are furthermore much less corrosive than their hydrated, polymer counterparts. This allows for much more flexibility in the choice of materials for the other components of the fuel cell system.

Where solid-acid fuel cells have tremendous advantages over polymer electrolyte fuel cells is in the use of alcohol (e.g., methanol) fuels. Hydrogen "stored" as methanol results in a liquid fuel with a high energy density, which is much easier to transport, store, and carry on board than hydrogen, says Haile. Polymer-based fuel cells do not work well with alcohol fuels because the fuel diffuses across the electrolyte, consuming fuel without generating electrical output. The solid-acid electrolytes are entirely impermeable to methanol, which means very high power outputs are possible—much higher than from polymer fuel cells running on methanol.

While the solid-acid fuel cells solve many of the problems of polymer fuel cells, there are still a few obstacles standing in the way of extensive fuel cell use. A continuing problem of the solid-acid fuel cells is the water solubility of the electrolytes. Haile suggests that clever engineering could circumvent this drawback. However, she plans to solve this problem by developing new solid-acid materials that are water-insoluble.

In developing humidity-stabilizing CsH2PO4 fuel cells, Haile was assisted by the lead author Dane Boysen, a graduate student in materials science; and Tetsuya Uda and Calum Chisholm, both postdoctoral scholars in Haile's lab.

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The Future of Really Big Computers

PASADENA, Calif. – Supercomputers are the gleam in every scientist's eye, useful for such data-intensive research as simulating global climate or unraveling the human genome. They work by a concept known as "parallel processing," whereby multiple computer chips execute parts of a program simultaneously. The more chips, the bigger the problem the computer can handle and the faster it can do it.

Over the last decade, says Thomas Sterling, a faculty associate in the Center for Advanced Computing Research at the California Institute of Technology, the performance of supercomputers has increased almost one thousand times, from less than 70 gigaflops, or one billion calculations per second, in 1993, to over 35 teraflops, or one trillion calculations per second, in 2003. And yet, many of today's largest systems often demonstrate disappointing efficiency, even though their size, cost, and power consumption continue to escalate. Current design strategies won't work for the next generation of supercomputers, making it unlikely they will be able to achieve the future potential speed of multi-petaflop computing (a quadrillion calculations per second).

On Wednesday, November 5, Sterling, a leader in the field of high-performance computer architecture, will discuss the challenges and the possible solutions for supercomputers in his talk "From PCs to Petaflops--The Future of Really Big Computers," the second of the 2003-2004 Earnest C. Watson Lecture Series at Caltech.

New research at Caltech, JPL, and other institutions, he says, is pushing the frontiers of supercomputers. By the end of the decade this work may revolutionize the way in which such computers are built and operated, and solve the problem of performance degradation. Sterling's talk will describe the very biggest computers ever built, and predict what future supercomputers will look like and what they may be able to achieve.

Sterling's lecture will take place at 8 p.m. in Beckman Auditorium, near Michigan Avenue south of Del Mar Boulevard, on Caltech's campus in Pasadena. Seating is available on a free, no-ticket-required, first-come, first-served basis. Caltech has offered the Watson Lecture Series since 1922, when it was conceived by the late Caltech physicist Earnest Watson as a way to explain science to the local community.

For more information, call 1(888) 2CALTECH (1-888-222-5832) or (626) 395-4652.

Media Contact: Mark Wheeler (626) 395-8733 wheel@caltech.edu

Visit the Caltech Media Relations website at http://pr.caltech.edu/media

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MW
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National Medal of Technology awardedby President Bush to Caltech's Carver Mead

Carver Mead, a renowned inventor and longtime faculty member of the California Institute of Technology, has been named by President George W. Bush as a recipient of the National Medal of Technology. The announcement was made by the White House today.

Mead, who is the Gordon and Betty Moore Professor of Engineering and Applied Science, Emeritus, at Caltech, is known by the high-tech community for many contributions in microelectronics and information technology. His major innovations include pioneering work on the very large-scale integration (VLSI) design for complex circuitry at the microscopic level; and an amplifying device known as the high electron mobility transistor (HEMT), used in microwave communications that is also an integral component of the Internet. He has also been a pioneer in computer animation, microchip design, neuromorphic electronic systems, and other computer interfaces.

His laboratory led an effort to create silicon models of specific areas of the nervous system. Early experiments have shown that the elementary operations of the nervous system can be emulated by analog circuits for the creation of novel devices.

In short, his work is aimed at technologies that will eventually result in human-machine interfaces. The devices his group has experimented on in the past include a cochlear chip, which is modeled after human hearing, as well as devices modeled after vision and learning.

A graduate of Caltech, Mead has been a member of the faculty for 45 years. He holds more than 50 U.S. patents, and has written more than 100 scientific publications.

Mead was presented the award "for pioneering contributions to the microelectronics field, that include spearheading the development of tools and techniques for modern integrated-circuit design, laying the foundation for fabless semiconductor companies, catalyzing the electronic-design automation field, training generations of engineers that have made the United States the world leader in microelectronics technology, and founding more than 20 companies including Actel Corporation, Silicon Compilers, Synaptics, and Sonic Innovations," according to the White House statement.

In announcing the award, the White House also cited the National Medal of Technology for its recognition of individuals and organizations that "embody the spirit of American innovation and have advanced the nation's global competitiveness. Their groundbreaking contributions commercialize technologies, create jobs, improve productivity and stimulate the nation's growth and development."

The award was established by Congress in 1980, and complements the older National Medal of Science. The National Medal of Technology is administered by the Department of Commerce. To date, there have been 146 recipients of the honor, 12 medals having gone to Caltech faculty, alumni, and trustees.

Additional information is available at http://www.technology.gov/medal.

 

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RT

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