Caltech Researchers Reveal Three Distinct Modes of Dynamic Friction Rupture with Implications for Earthquake Behavior

PASADENA, Calif.-A new study by researchers at the California Institute of Technology has revealed important findings about the nature of ruptures and sliding behavior, which could impact how we respond to earthquakes and other disasters.

In the modeling of earthquake ruptures, researchers have, for some time, proposed that three primary modes of rupture may occur at a faultline during an earthquake. The experimental visualization of these ruptures or sliding modes, including the "self-healing" pulse rupture, has for the first time been achieved and demonstrated in the Graduate Aeronautical Laboratories of the California Institute of Technology (GALCIT) using dynamic high-speed photoelasticity and laser vibrometry.

Ares Rosakis, Director of GALCIT and the Theodore von Karman Professor of Aeronautics and Professor of Mechanical Engineering at Caltech, says, "The discovery of these rupture failure modes has never been directly confirmed. We are the first to create the conditions in the laboratory to generate and visualize these rupture and sliding phenomena. Utilizing ultrahigh-speed optical instrumentation, we have been able to see these modes in a laboratory-which has produced some rather counterintuitive results. The results of this research could have a significant impact on understanding earthquake behavior and ruptures, could validate existing theoretical and numerical methodologies currently used in seismology, and could one day help us to potentially mitigate massive earthquake damage."

In controlled laboratory conditions, Rosakis along with his collaborators, Guruswami Ravichandran, the John E. Goode, Jr. Professor of Aeronautics and Mechanical Engineering, and George Lykotrafitis, their former PhD student and currently a postdoctoral scholar at MIT, created rupture models propagating along "incoherent" or frictional interfaces separating identical materials. Combining high-speed photography with a new technique called laser vibrometry, the team conclusively confirmed the existence of the rupture mode types, the exact point of rupture, the sliding velocity, and the rupture propagation speed. Ultrahigh-speed photography, providing up to two million photographs per second, and dynamic photoelasticity were combined with laser vibrometry, to give an accurate measurement of the sliding velocities and to reveal the various modes of sliding.

Specifically, to conduct the research, the GALCIT team compressed two sheets of Homalite, a clear polymeric material. They then shot projectiles at various velocities into one of the two sheets. The high-speed camera and the interferometers were simultaneously triggered. Two laser vibrometers measured both the horizontal and the vertical particle velocities just above and below the sliding interface, thus providing a time record of the relative sliding and opening speeds as the dynamic rupture went by with speeds in excess of 1.0Km/sec. They also controlled the parameters of impact speed, confining pressure, and surface roughness to measure the dynamic sliding.

Theoretical models have predicted that shear ruptures assume either a sliding crack rupture mode; a pulse-like mode; a wrinkle-like opening pulse mode; or a mixed rupture combination of these modes. In earthquake faulting, a sliding crack mode would occur where a large section of the interface slides behind a fast-moving rupture front and continues to slide for a long time. In the "self-healing" slip pulse mode (first proposed in the early '90s by Thomas Heaton, professor of engineering seismology and civil engineering at Caltech) the rupture will actually slide or "crawl" along the fault in a pulse-like motion, and the fault will then recompress or "self-heal" behind the pulse. In this pulse-like sliding mode, the slip is confined to a finite distance behind the propagating rupture front, while the fault behind it relocks. The third mode, the wrinkle-like opening pulse mode, is similar to the sliding pulse but would actually create a vertical opening across the fault plane followed by self-healing (something like a ripple on a carpet). Through this new laboratory research technology, these phenomena were actually seen and verified.

This research may eventually provide new insights into how we view, react, and prepare for earthquakes. "In studying seismology and the physics of earthquakes, there is no way to internally visualize the earth's crust," comments team member Ravichandran. "In the lab, we have now confirmed the existence and behaviors of crack-like sliding, self-healing pulse-like sliding, and wrinkle-like opening pulse sliding. This research can provide vital information to help determine the behavior of earthquake ruptures and sliding. Now we have a way to 'see' these behaviors, which can provide new avenues of understanding for these occurrences."

This technology also has potential applications for any composite structure containing coherent and incoherent interfaces; for example, the durability of the new generation of high- speed naval vessels that are constructed with layered structures in their hulls and are subject to dynamic wave slamming or underwater threats can be studied by such techniques. Ravichandran is the director of a newly established Multidisciplinary University Research Initiative sponsored by the Office of Naval Research at GALCIT whose purpose is the study of such phenomena as they pertain to the reliability of the new generation of naval vessels.

The findings from the GALCIT team are being published in the September 22 issue of the journal Science. The title of their article is "Self-Healing Pulse-Like Shear Ruptures in the Laboratory."

This work has been sponsored by the National Science Foundation, the U.S. Department of Energy, and the Office of Naval Research.


Contact: Deborah Williams-Hedges (626) 395-3227

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Caltech Researchers Announce Invention of the Optofluidic Microscope

PASADENA, Calif.—The old optical microscopes that everyone used in high-school biology class may be a step closer to the glass heap. Researchers at the California Institute of Technology have announced their invention of an optofluidic microscope that uses no lens elements and could revolutionize the diagnosis of certain diseases such as malaria.

Reporting in the journal Lab on a Chip, Caltech assistant professor of electrical engineering professor Changhuei Yang and his coauthors describe the novel device that combines chip technology with microfluidics. Although similar in resolution and magnifying power to a conventional top-quality optical microscope, the optofluidic microscope chip is only the size of a quarter, and the entire device—imaging screen and all—will be about the size of an iPod.

"This is a new way of doing microscopy," says Yang, who also has a dual appointment in bioengineering at Caltech. "Its imaging principle is similar to the way we see floaters in our eyes. If you can see it in a conventional microscope and it can flow in a microfluidic channel, we can image it with this tiny chip."

That list of target objects includes many pathogens that are most dangerous to human life and health, including the organism that causes malaria. The typical method of diagnosing malaria is to draw a blood sample and send it to a lab where the sample can be inspected for malaria parasites. A high-powered optical microscope with lens elements is far too big and cumbersome for inspection of samples in the field.

With a palm-sized optofluidic microscope, however, a doctor would be able to draw a drop of blood from the patient and analyze it immediately. This process would be much simpler and faster than the current method, and the equipment would be far cheaper and more readily available to physicians in third-world countries.

The device works by literally flowing a target sample across a tiny fluid pathway. Normally, the image would be low in resolution because the target would interrupt the light on a single pixel, thus limiting the resolution to pixel size.

However, the researchers have avoided this limitation by attaching an opaque metal film to a microfluidic chip. The film contains an etched array of submicron apertures that are spaced in such a way that adjacent line scans overlap and all parts of the target are imaged.

The new optofluidic microscope is one of the first major accomplishments to come out of Caltech's Center for Optofluidic Integration, which was begun in 2004 with funding from the federal Defense Advanced Research Projects Agency (DARPA) for development of a new generation of small-scale, highly adaptable, and innovative optical devices.

"The basic idea of the center is to build optical devices for imaging, fiber optics, communications, and other applications, and to transcend some of the limitations of optical devices made out of traditional materials like glass," says Demetri Psaltis, who is the Myers Professor of Electrical Engineering at Caltech and a coauthor of the paper. "This is probably the most important result so far showing how we can build very unique devices that can have a broad impact."

Xin Heng, a graduate student in electrical engineering at Caltech, performed most of the experiments reported in the paper. The other Caltech authors are David Erickson, a former postdoctoral scholar who is now a mechanical-engineering professor at Cornell University; L. Ryan Baugh, a postdoctoral scholar in biology; Zahid Yaqoob, a postdoctoral scholar in electrical engineering; and Paul W. Sternberg, the Morgan Professor of Biology.

Robert Tindol

Researchers Announce New Way to Assess How Buildings Would Stand Up in Big Quakes

PASADENA, Calif.—How much damage will certain steel-frame, earthquake-resistant buildings located in Southern California sustain when a large temblor strikes? It's a complicated, multifaceted question, and researchers from the California Institute of Technology, the University of California, Santa Barbara, and the University of Pau, France, have answered it with unprecedented specificity using a new modeling protocol.

The results, which involve supercomputer simulations of what could happen to specific areas of greater Los Angeles in specific earthquake scenarios, were published in the latest issue of the Bulletin of the Seismological Society of America, the premier scientific journal dedicated to earthquake research.

"This study has brought together state-of-the-art 3-D-simulation tools used in the fields of earthquake engineering and seismology to address important questions that people living in seismically active regions around the world worry about," says Swaminathan Krishnan, a postdoctoral scholar in geophysics at Caltech and lead author of the study.

"What if a large earthquake occurred on a nearby fault? Would a particular building withstand the shaking? This prototype study illustrates how, with the help of high-performance computing, 3-D simulations of earthquakes can be combined with 3-D nonlinear analyses of buildings to provide realistic answers to these questions in a quantitative manner."

The publication of the paper is an ambitious attempt by the researchers to enhance and improve the methodology used to assess building integrity, says Jeroen Tromp, the McMillan Professor of Geophysics and director of the Seismological Laboratory at Caltech. "We are trying to change the way in which seismologists and engineers approach this difficult interdisciplinary problem," Tromp says.

The research simulates the effects that two different 7.9-magnitude San Andreas earthquakes would have on two hypothetical 18-story steel frame buildings located at 636 sites on a grid that covers the Los Angeles and San Fernando basins. An earthquake of this magnitude occurred on the San Andreas on January 9, 1857, and seismologists generally agree that the fault has the potential for such an event every 200 to 300 years. To put this in context, the much smaller January 17, 1994, Northridge earthquake of 6.7 magnitude caused 57 deaths and economic losses of more than $40 billion.

The simulated earthquakes "rupture" a 290-kilometer section of the San Andreas fault between Parkfield in the Central Valley and Southern California, one earthquake with rupture propagating southward and the other with rupture propagating northward. The first building is a model of an actual 18-story, steel moment-frame building located in the San Fernando Valley. It was designed according to the 1982 Uniform Building Code (UBC) standards yet suffered significant damage in the 1994 Northridge earthquake due to fracture of the welds connecting the beams to the columns. The second building is a model of the same San Fernando Valley structure redesigned to the stricter 1997 UBC standards.

Using a high-performance PC cluster, the researchers simulated both earthquakes and the damage each would cause to the two buildings at each of the 636 grid sites. They assessed the damage to each building based on "peak interstory drift."

Interstory drift is the difference between the roof and floor displacements of any given story as the building sways during the earthquake, normalized by the story height. For example, for a 10-foot high story, an interstory drift of 0.10 indicates that the roof is displaced one foot in relation to the floor below.

The greater the drift, the greater the likelihood of damage. Peak interstory drift values larger than 0.06 indicate severe damage, while values larger than 0.025 indicate that the damage could be serious enough to pose a serious threat to human safety. Values in excess of 0.10 indicate probable building collapse.

The study's conclusions include the following:

o A 7.9-magnitude San Andreas rupture from Parkfield to Los Angeles results in greater damage to both buildings than a rupture from Los Angeles to Parkfield. This difference is due to the effects of directivity and slip distribution controlling the ground-motion intensity. In the north-to-south rupture scenario, peak ground displacement is two meters in the San Fernando Valley and one meter in the Los Angeles basin; for the south-to-north rupture scenario, ground displacements are 0.6 meters and 0.4 meters respectively. o In the north-to-south rupture scenario, peak drifts in the model of the existing building far exceed 0.10 in the San Fernando Valley, Santa Monica, and West Los Angeles, Baldwin Park and its neighboring cities, Compton and its neighboring cities, and Seal Beach and its neighboring cities. Peak drifts are in the 0.06-0.08 range in Huntington Beach, Santa Ana, Anaheim, and their neighboring cities, whereas the values are in the 0.04-0.06 range for the remaining areas, including downtown Los Angeles. o The results for the redesigned building are better than for the existing building. Although the peak drifts in some areas in the San Fernando Valley still exceed 0.10, they are in the range of 0.04-0.06 for most cities in the Los Angeles basin. o In the south-to-north rupture, the peak drifts in both the existing and redesigned building models are in the range of 0.02-0.04, suggesting that there is no significant danger of collapse. However, this is indicative of damage significant enough to warrant building closures and compromise human safety in some instances.

Such hazard analyses have numerous applications, Krishnan says. They could be performed on specific existing and proposed buildings in particular areas for a range of types of earthquakes, providing information that developers, building owners, city planners, and emergency managers could use to make better, more informed decisions.

"We have shown that these questions can be answered, and they can be answered in a very quantitative way," Krishnan says.

The research paper is "Case Studies of Damage to Tall Steel Moment-Frame Buildings in Southern California during Large San Andreas Earthquakes," by Swaminathan Krishnan, Chen Ji, Dimitiri Komatitsch, and Jeroen Tromp. Online movies of the earthquakes and building-damage simulations can be viewed at

Contact: Jill Perry (626) 395-3226


Physicists Devise New Technique for Detecting Heavy Water

PASADENA, Calif.—Scientists at the California Institute of Technology have created a new method of detecting heavy water that is 30 times more sensitive than any other existing method. The detection method could be helpful in the fight against international nuclear proliferation.

In the June 15 issue of the journal Optics Letters, Caltech doctoral student Andrea Armani and her professor Kerry Vahala report that a special type of tiny optical device can be configured to detect heavy water. Called an optical microresonator, the device is shaped something like a mushroom and was originally designed three years ago to store light for future opto-electronic applications. With a diameter smaller than that of a human hair, the microresonator is made of silica and is coupled with a tunable laser.

The technique works because of the difference between the molecular composition of heavy water and regular water. An H2O molecule has two atoms of hydrogen that each are built of a single proton and a single electron. A D2O molecule, by contrast, has two atoms of a hydrogen isotope known as deuterium, which differs in that each atom has a single neutron in addition to a proton and an electron. This makes a heavy-water molecule significantly more massive than a regular water molecule.

"Heavy water isn't a misnomer," says Armani, who is finishing up her doctorate in applied physics and will soon begin a two-year postdoctoral appointment at Caltech. Armani says that heavy water looks just like regular water to the naked eye, but an ice cube made of the stuff will sink if placed in regular water because of its added density. This difference in masses, in fact, is what makes the detection of heavy water possible in Armani and Vahala's new technique. When the microresonator is placed in heavy water, the difference in optical absorption results in a change in the "Q factor," which is a number used to measure how efficiently an optical resonator stores light. If a higher Q factor is detected than one would see for normal water, then more heavy water is present than the typical one-in-6,400 water molecules that exists normally in nature.

The technique is so sensitive that one heavy-water molecule in 10,000 can be detected, Armani says. Furthermore, the Q factor changes steadily as the heavy-water concentrations are varied.

The results are good news for those who worry about the escalation of nuclear weapons, because heavy water is typically found wherever someone is trying to control a nuclear chain reaction. As a nuclear moderator, heavy water can be used to control the way neutrons bounce around in fissionable material, thereby making it possible for a fission reactor to be built.

The ongoing concern with heavy water is exemplified by the fact that Armani and Vahala have received funding for their new technique from the Defense Advanced Research Projects Agency, or DARPA. The federal agency provides grants to university research that has potential applications for U.S. national defense.

"This technique is 30 times better than the best competing detection technique, and we haven't yet tried to reduce noise sources," says Armani. "We think even greater sensitivities are possible."

The paper is entitled "Heavy Water Detection Using Ultra-High-Q Microcavities" and is available online at

Robert Tindol

Jerry Marsden Elected to Royal Society

PASADENA, Calif.—Jerry Marsden, the Carl F. Braun Professor of Engineering and Control and Dynamical Systems at the California Institute of Technology, has been named a member of the Royal Society of the United Kingdom. Marsden joins 43 other scientists as the new inductees of a society that through the years has counted Isaac Newton, Charles Darwin, Albert Einstein, and Stephen Hawking among its members.

Marsden was cited by the Royal Society for "his fundamental contributions to a very wide range of topics such as Hamiltonian systems, fluid mechanics, plasma physics, general relativity, dynamical systems and chaos, nonlinear elasticity, nonholonomic mechanics, control theory, variational integrators and solar system mission design. Some of his recent research has contributed to understanding and designing NASA missions to the moons of Jupiter."

Marsden earned his bachelor's degree in applied mathematics from the University of Toronto and his doctorate in applied mathematics from Princeton University. He taught at UC Berkeley from 1968 to 1995 and then came to Caltech as a professor of control and dynamical systems, becoming the Carl F. Braun Professor in 2003. In the early 1970s, he was one of the original founders of reduction theory for mechanical systems with symmetry. Marsden received the 1990 AMS-SIAM Norbert Wiener Prize and the SIAM John von Neumann Prize in 2005. He is also a recipient of the Research Award for Natural Sciences of the Alexander von Humboldt Foundation in 1992 and 1999 and the 2000 Max Planck Research Award for Mathematics and Computer Science.

The Royal Society was established in England in 1660 and is the world's oldest scientific academy in continuous existence. The society's objectives are to recognize excellence in science, to support leading-edge scientific research and its applications, to stimulate international interaction, and to promote education and the public's understanding of science.

Robert Tindol
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Aerospace Engineers and Biologists Solve Long-Standing Heart Development Mystery

PASADENA, Calif.—An engineer comparing the human adult heart and the embryo heart might never guess that the former developed from the latter. While the adult heart is a fist-shaped organ with chambers and valves, the embryo heart looks more like tube attached to smaller tubes. Physicians and researchers have assumed for years, in fact, that the embryonic heart pumps through peristaltic movements, much as material flows through the digestive system.

But new results in this week's issue of Science from an international team of biologists and engineers show that the embryonic vertebrate heart tube is indeed a dynamic suction pump. In other words, blood flows by a dynamic suction action (similar to the action of the mature left ventricle) that arises from wave motions in the tube. The findings could lead to new treatments of certain heart diseases that arise from congenital defects.

According to Mory Gharib, the Liepmann Professor of Aeronautics and Bioengineering at the California Institute of Technology, the new results show once and for all that "the embryonic heart doesn't work the way we were taught.

"The morphologies of embryonic and adult hearts look like two different engineers designed them separately," says Gharib, who has worked for years on the mechanical and dynamical nature of the heart. "This study allows you to think about the continuity of the pumping mechanism."

Scott Fraser, the Rosen Professor at Caltech and director of the MRI Center, adds that the study shows the promise of advanced biological imaging techniques for the future of medicine. "The reason this mechanism of pumping has not been noticed in the heart tube is because of the limitations of imaging," he says. "But now we have a device that is 100 times faster than the old microscopes, allowing us to see things that previously would have been a blur. Now we can see the motion of blood and the motions of vascular walls at very high resolutions."

The lead author of the paper is Gharib's graduate student Arian Forouhar. He and the other researchers used confocal microscopes in the Beckman Institute's biological imaging center on campus to do time-lapse photography of embryonic zebrafish. According to Fraser, embryonic zebrafish were chosen because they are essentially transparent, thus allowing for easy viewing, and since they develop completely in only a few days.

The time-lapse photography showed that peristalsis, an action similar to squeezing a tube of toothpaste, was not the pumping mechanism, but rather that valveless pumping known as "hydroelastic impedance pumping" takes place. In this model fewer active cells are required to sustain circulation.

Contraction of a small collection of myocytes, usually situated near the entrance of the heart tube, initiates a series of forward-traveling elastic waves that eventually reflect back after impinging on the end of the heart tube. At a specific range of contraction frequencies, these waves can constructively interact with the preceding reflected waves to generate an efficient dynamic-suction region at the outflow tract of the heart tube.

"Now there is a new paradigm that allows us to reconsider how embryonic cardiac mechanics may lead to anomalies in the adult heart, since impairment of diastolic suction is common in congestive heart-failure patients," says Gharib.

"The heart is one of the only things that makes itself while it's working," Fraser adds. "We often think of the heart as a thing the size of a fist, but it likely began forming its structures when it was a tiny tube with the diameter of a human hair."

"One of the most intriguing features of this model is that only a few contractile cells are necessary to provide mechanical stimuli that may guide later stages of heart development," says Forouhar. According to Gharib, this simplicity in construction will allow us to think of potential biomimicked mechanical counterparts for use in applications where delicate transport of blood, drugs, or other biological fluids are desired.

In addition to Forouhar, Gharib, and Fraser, the authors are Michael Liebling, a postdoctoral scholar in the Beckman Institute's biological imaging center; Anna Hickerson (BS '00; PhD '05) and Abbas Nasiraei Moghaddam, graduate students in bioengineering at Caltech; Huai-Jen Tsai of National Taiwan University's Institute of Molecular and Cellular Biology; Jay Hove of the University of Cincinnati's Genome Research Institute; and Mary Dickinson of the Baylor College of Medicine.

The article is titled "The Embryonic Vertebrate Heart Tube is a Dynamic Suction Pump," and appears in the May 5 issue of Science.

Robert Tindol

Candes Receives Waterman Award

PASADENA, Calif.--Emmanuel Candes, an applied mathematician in the Division of Engineering and Applied Science at the California Institute of Technology, has been selected to receive the National Science Board's prestigious Alan T. Waterman Award, the highest honor awarded by the National Science Foundation.

The board cited Candes's development of new mathematical tools that allow efficient digital representation of wave signals, together with his discovery of new methods to economically translate analog data into already compressed digital form--work that promises to improve the digital processing of signals in a vast array of modern technologies.

The annual Waterman Award recognizes an outstanding young researcher in any field of science or engineering supported by the NSF. Candidates may not be more than 35 years old or seven years beyond receiving a doctorate. In addition to a medal, the awardee receives a grant of $500,000 over a three-year period for scientific research or advanced study in the mathematical, physical, medical, biological, engineering, social, or other sciences at the institution of the recipient's choice.

"Candes's work is nothing short of revolutionary," said John Cozzens, the program officer in NSF's Directorate for Computer and Information Science and Engineering who oversees Candes's grants. NSF has supported Candes's work since 2002.

"It promises to take the field to a whole new level and have many applications in everyday technologies, especially in medical imaging," Cozzens said.

At age 35, Candes is a leader in the field of "harmonic analysis," a branch of mathematics that teases apart signal waves for analysis and processing. The term comes from the observation that multiple waves in a complex system--whether from outer space, a cell phone, the Internet, or a DNA molecule--make up a chorus of individual "songs" singing in harmony with the others. Candes worked out the mathematics of wave snippets known as ridgelets, curvelets, chirplets and noiselets--small templates that provide powerful systems for processing and analyzing complex waves. The work allows researchers to listen more closely to the unique songs and understand and enhance the information they contain. By sharpening the details, harmonic analysis bestows order on the cacophony of complex systems and drowns out unwanted noise.

"My work is focused on finding good representations. We use representations all the time, and good ones make common tasks more simple," said Candes. For example, it is easier to perform additions or multiplications with the Arabic numbering system rather than with Roman numerals, he says, and easier still with the binary system a digital computer uses. "Harmonic analysis searches for convenient representations of more complicated objects to make tasks such as compressing image data, performing large calculations rapidly, and enhancing biomedical images much simpler."

We benefit from advances in signal processing and harmonic analysis in electronic devices, medical technology, aircraft safety, DNA analysis, knowledge about the universe, and even in finding oil. Wavelets, for example, form the basis of the JPEG image compression technology and high-end computer graphics.

With the advent of digital technologies, translating analog information faithfully into digital representations has been a major challenge. The translating method, called sampling, requires that enough information is selected from the analog object to adequately reproduce it in digital form. If the wrong amount is selected, key information may be lost.

Recently, Candes developed a new sampling mechanism that allows the faithful recovery of signals and images from far fewer data bits than traditional methods use. This new sampling theory may come to underlie procedures for sampling and compressing data simultaneously and much faster. "In practice," Candes said, "this means one could obtain super-resolved signals from just a few sensors."

A professor of applied and computational mathematics at Caltech, Candes studied in his native France before receiving a doctorate in statistics at Stanford University in 1998. He has received numerous awards for his work, including the Vasil Popov Prize in approximation theory, the Department of Energy Young Investigator Award, the James H. Wilkinson Prize in numerical analysis and scientific computing, and the Best Paper Award of the European Association for Signal, Speech and Image Processing. He was selected as an Alfred P. Sloan Research Fellow in 2001. He has also been invited to give plenary addresses at major international conferences. ### Contact: Jill Perry (626) 395-3226

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Fluid Mechanics Experts Come Up with New Test for Heart Disease

PASADENA, Calif.—Building on years of research on the way that blood flows through the heart valves, researchers from the California Institute of Technology and Oregon Health Science University have devised a new index for cardiac health based on a simple ultrasound test. The index is now ready for use, and provides a new diagnostic tool for cardiologists in searching for the very early signs of certain heart diseases.

In the April 18 issue of the journal Proceedings of the National Academy of Sciences (PNAS), the researchers show how ultrasound imaging can be used to create an extremely detailed picture of the jet of blood as it squirts through the cardiac left ventricle. Previous work by the Caltech team members has shown that there is an ideal length-to-diameter ratio for jets of fluid passing through valves, which means that any variation from this ratio is indicative of a heart that pumping in an abnormal manner.

According to Mory Gharib, Liepmann Professor of Aeronautics and Bioengineering at Caltech, the ideal stroke ratio for cardiac function is four. This means that the length of a jet of fluid is ideal in power efficiency if it is four times the diameter of the valve it is traveling through. Since pioneering the study of vortices in biological fluid transport, Gharib has worked at applying it to biomedical applications. The PNAS article presents the latest breakthrough.

"Vortex formation defines the optimal output of the heart," says Gharib. "The size and shape of the vortex is a diagnostic tool because the information can reveal whether a patient's heart is healthy or if there are problems that will lead to enlargement."

In vivo and in vitro images taken by the Caltech team and Oregon collaborators show that a healthy heart tends to form vortex rings in the blood as it passes through the left ventricle. If the valve is too large in diameter, the blood tends not to form strong vortices, and if it is too narrow, the heart has much less energy efficiency and must work harder in order to produce the effect of a healthy heart. In either case, the result of a non-optimal vortex formation is indicative of a malfunctioning heart.

The index that the researchers have created is a guide for cardiologists, who will be able to use a noninvasive ultrasound machine to image the heart, just as obstetricians use ultrasound devices to image developing fetuses. Thus, the technique can be used when the patient is at rest, unlike treadmill tests that can themselves pose a certain danger because they require patients to exert themselves.

"We're not saying that this technique replaces traditional diagnostic tools, but that it is another way of confirming if something is wrong," Gharib adds.

"We want to give people an earlier warning of disease with a new method that is non-invasive and relatively inexpensive," says John Dabiri, an assistant professor of aeronautics and bioengineering at Caltech and coauthor of the paper.

Continuing in vitro studies led by Arash Kheradvar, a medical doctor and graduate student in bioengineering at Caltech, are focused on correlating the new diagnostic index with specific symptoms of heart failure.

In addition to Gharib, the lead author, and Dabiri and Kheradvar, the authors are Edmond Rambod, a former postdoctoral researcher at Caltech, and David J. Sahn, a cardiologist at Oregon Health Science University.

The title of the PNAS paper is "Optimal vortex formation as an index of cardiac health."


Robert Tindol

Murray Awarded Feynman Teaching Prize

PASADENA, Calif.-Richard M. Murray was a freshman attending frosh camp at Camp Fox on Catalina Island when he first encountered famed physicist Richard Feynman. "I was sitting down, looking across a field, and a professor sat down next to me and started talking about some shells he had found while he was swimming. Lo and behold, it was Richard Feynman-although I was an engineering student and not in physics, and I'm not sure I knew who he was at the time. That willingness to talk to a student typified his approach to teaching."

Such willingness to engage and encourage students also typifies Murray's own approach, and now Murray, recently named the Thomas E. and Doris Everhart Professor of Control and Dynamical Systems at the California Institute of Technology, has been awarded the Richard P. Feynman Prize for Excellence in Teaching. The prize, handed out annually, is Caltech's most prestigious teaching honor. With it comes a $3,500 cash award, plus an equivalent raise in annual salary.

The Feynman Prize Selection Committee singled out Murray for his "enthusiasm, responsiveness, and innovation" in the classroom and for his "contribution to the undergraduate experience through teaching outside the conventional classroom."

"I think the field I do research in is very exciting, so I try to teach in a way that conveys the flavor of why I find it exciting," says Murray, whose work includes high-confidence control of cooperative systems and nonlinear control theory.

Murray was also commended for his determination to make sure his students understand the material he teaches. For example, he encourages students to anonymously fill out index cards, dubbed "Mud" cards, at the end of each class, asking questions about anything they found confusing (or 'muddy '). Answers to the students' questions are posted on the class website the same day.

"You have to be willing to take questions, because you know you are going to miss the mark sometimes," Murray says. This commitment to learning is not lost on Murray's students. "In all my classes I have never before had a professor that was so dedicated to answering students' questions and making sure that students understood the material," wrote one undergraduate in nominating Murray for the award. The student, who also praised Murray's "special creativity, innovation, and dedication to the classroom," added, "I can think of no other professor more deserving of this award."

Another student praised Murray for his "infectious and boundless enthusiasm and perseverance for everything he is involved in and an exceptional talent for leadership." Yet another said that Murray is "without a doubt one of the most talented teachers I have ever met."

Murray also served as leader of Team Caltech, the group of about 50 undergraduate students who created "Alice," Caltech's entry in the Defense Advanced Research Projects Agency Grand Challenge autonomous robot race through the southern California desert. In a letter recommending Murray to the prize selection committee, Antony Fender, a lecturer in engineering and also a member of Team Caltech, said, "The students involved in this project received an education unlike anything I've ever seen before," adding that they would "carry this experience with them for their entire lives."

Murray says that he was surprised and "very honored" to receive the Feynman award. "I've known many faculty who received it and always looked up to them as being great teachers. It's a big honor to be among them."

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Caltech Scientist Creates New Method for Folding Strands of DNA to Make Microscopic Structures

PASADENA, Calif.—In a new development in nanotechnology, a researcher at the California Institute of Technology has devised a way of weaving DNA strands into any desired two-dimensional shape or figure, which he calls "DNA origami."

According to Paul Rothemund, a senior research fellow in computer science and computation and neural systems, the new technique could be an important tool in the creation of new nanodevices, that is, devices whose measurements are a few billionths of a meter in size.

"The construction of custom DNA origami is so simple that the method should make it much easier for scientists from diverse fields to create and study the complex nanostructures they might want," Rothemund explains.

"A physicist, for example, might attach nano-sized semiconductor 'quantum dots' in a pattern that creates a quantum computer. A biologist might use DNA origami to take proteins which normally occur separately in nature, and organize them into a multi-enzyme factory that hands a chemical product from one enzyme machine to the next in the manner of an assembly line."

Reporting in the March 16th issue of Nature, Rothemund describes how long single strands of DNA can be folded back and forth, tracing a mazelike path, to form a scaffold that fills up the outline of any desired shape. To hold the scaffold in place, 200 or more DNA strands are designed to bind the scaffold and staple it together.

Each of the short DNA strands can act something like a pixel in a computer image, resulting in a shape that can bear a complex pattern, such as words or images. The resulting shapes and patterns are each about 100 nanometers in diameter-or about a thousand times smaller than the diameter of a human hair. The dots themselves are six nanometers in diameter. While the folding of DNA into shapes that have nothing to do with the molecule's genetic information is not a new idea, Rothemund's efforts provide a general way to quickly and easily create any shape. In the last year, Rothemund has created half a dozen shapes, including a square, a triangle, a five-pointed star, and a smiley face-each one several times more complex than any previously constructed DNA objects. "At this point, high-school students could use the design program to create whatever shape they desired,'' he says.

Once a shape has been created, adding a pattern to it is particularly easy, taking just a couple of hours for any desired pattern. As a demonstration, Rothemund has spelled out the letters "DNA," and has drawn a rough picture of a double helix, as well as a map of the western hemisphere in which one nanometer represents 200 kilometers.

Although Rothemund has hitherto worked on two-dimensional shapes and structures, he says that 3-D assemblies should be no problem. In fact, researchers at other institutions are already using his method to attempt the building of 3-D cages. One biomedical application that Rothemund says could come of this particular effort is the construction of cages that would sequester enzymes until they were ready for use in turning other proteins on or off.

The original idea for using DNA to create shapes and structures came from Nadrian Seeman of New York University. Another pioneer in the field is Caltech's Assistant Professor of Computer Science and Computation and Neural Systems Erik Winfree, in whose group Rothemund works.

"In this research, Paul has scored a few unusual `firsts' for humanity," Winfree says. "In a typical reaction, he can make about 50 billion 'smiley-faces.' I think this is the most concentrated happiness ever created.

"But the applications of this technology are likely to be less whimsical," Winfree adds. "For example, it can be used as a 'nanobreadboard' for attaching almost arbitrary nanometer-scale components. There are few other ways to obtain such precise control over the arrangement of components at this scale."

The title of the Nature paper is "Folding DNA to create nanoscale shapes and patterns."

Robert Tindol


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