September 2005
Now a professor in the Department of Materials Science and Engineering, Oscar Dubon is also an alum of the program. |
According to the US Department of Commerce, about one-third of this country's gross domestic product from private industry, approximately $3.5 trillion, is climate and weather sensitive. Industries like agriculture, air travel, and tourism are highly dependent on accurate forecasts while weather patterns are also intricately tied to pollution and even national security. The problem is that the models used for weather forecasting are incomplete. UC Berkeley environmental engineer Tina Katopodes Chow is helping fill the gaps.
Weather forecasting models are numerical systems that take observational data about factors like atmospheric pressure, temperature, wind speed and direction, and humidity and crunch those numbers in computer simulations of the atmosphere. At the heart of these simulations are complex equations that describe fluid dynamics, or flow, in the atmosphere. The region to be modeled, ranging from one city to the entire planet, is overlaid with a grid containing points where the equations are computed. The solutions to those equations are then output as a weather forecast. Faster computers have enabled higher resolution models to be used. The trick though is that a forecast model is only as good as the algorithms, or parametrizations, it uses.
"I work on improving the algorithms that go into those models so that the forecasts can be more accurate," says Chow, a newly-hired professor in the Department of Civil and Environmental Engineering.
Chow's work focuses on the atmospheric boundary layer (ABL), the region a mile or so above the Earth that most affects life on the planet. As the resolution of forecasting models improves, it sometimes becomes more difficult to predict the flow of the ABL, Chow says. That's because the details of the terrain, everything from mountains to skyscrapers, can shift the flow.
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"Solutions for solving the equations that govern fluid dynamics are developed in idealized worlds," she says. "But when you do environmental flow, you have rough terrain. Houses, trees, roads, and valleys have to be accounted for in some way."
Recently, Chow began looking at flow in the Sierra Nevada Mountains in Owens Valley , California . Under certain weather conditions, wind flowing over steep mountains sometimes stirs up an intense form of turbulence called a rotor. The phenomenon can be disastrous for airplanes and can also kick up massive amounts of dust, contributing to air pollution. Indeed, the dry Owens Lake bed is thought to be the largest single source of tiny dust particles in the western hemisphere. How the rotors form is not well understood.
Next year though, Chow and her colleagues will participate in a large multi-institution effort to study rotor waves using advanced sensors, meteorological towers, and aircraft. She hopes the data gathered as part of the Terrain-induced Rotor Experiment (T-REX) effort will inform the development of better algorithms to represent these kinds of phenomena in weather models.
"This will bring the numerical and observational sides of the problem together," she says.
This movie shows a simulation of atmospheric flow through the Riviera Valley during the two hours following sunrise. As the sun moves across the sky over the course of a day, shadows cover different parts of the Valley, affecting the heating of the ground and thereby the wind flow, represented by the moving arrows. In the video, the shaded surface represents the incoming solar radiation. Black is no sunlight and white is bright sun. (courtesy the researchers) [movie .avi file] |
Chow is also studying the atmospheric boundary layer in urban environments, where tall buildings and heat rising from sun-baked asphalt and industrial facilities can affect the flow. To tackle this complex "bottom topography," Chow and her colleagues are developing methods to simulate flows down streets between buildings, "urban canyons" comparable to the valleys found in the Sierra Nevadas. The trick is determining the boundary conditions, where the model begins and ends. After all, the flow moving through New York City doesn't just start at, say, Times Square . So in order to create an accurate high-resolution simulation, the urban flows must be combined with more traditional mesoscale models that simulate meteorological phenomena that can be spread across hundreds of miles, such as a system of thunderstorms.
"Urban and mesoscale models have never been truly coupled together before," Chow says.
Modeling the flow in complex urban terrains could lead to more accurate weather forecasts, especially in cities with microclimates. But it may also provide valuable insight about how materials are transported through the urban environment, from plumes of pollution and ash to possibly even more dangerous substances.
"We'd like to be able to predict in real time the dispersion of contaminants, either accidental or intentional, so that the effects might be controlled," says Chow, who previously worked in this area at Lawrence Livermore National Laboratory. "If we can get the flow model correct, the list of applications beyond weather forecasting becomes huge."
Modeling the Sound of Music
by David Pescovitz
Before entering UC Berkeley's PhD program, Cynthia Bruyns was a member of the NASA Ames Research Center's Biological Visualization, Imaging, and Simulation Laboratory. She now works part time with Apple Computer's audio research group and runs an electronic music record label. |
If a musical instrument has never been built before, how can you know what it will sound like? That's the question UC Berkeley graduate student Cynthia Bruyns is answering with Vibration Lab, software she's designing to simulate the sound of any percussive instrument, real or imagined, in a computer. Her system could someday enable musicians to play instruments that exist only on the screen, enable the interactive design of new physical instruments, and even boost the realism of immersive virtual environments for education and training.
"Every object's sound comes from the way it's vibrating, and every object vibrates differently depending on its shape and material," says Bruyns, a student of computer science professor Carlo Séquin, an affiliate of the Center for Information Technology Research in the Interest of Society (CITRIS). "Instruments like violins are shapes that have been perfected over many years to produce a certain tone."
The user interface for Vibration Lab with a virtual representation of a metal model of the letter "G." (courtesy the researcher) [view larger image] |
Bruyns' software enables users to take a computer-generated 3D model of a complex object and, essentially, bang it with a virtual stick to hear how it vibrates. For example, thin and flat metal objects sound very different from thick, curved wooden instruments. This is a giant leap in ease-of-use compared to state-of-the-art virtual instrument software.
Previously, Bruyns explains, some computer musicians have created virtual instruments from shapes like circles, squares, and rectangles that are relatively easy to model on a computer. The software then calculates how a vibration wave propagates through the shape, resulting in a tone. More commonly, electronic musicians create instrument sounds by manipulating digital oscillators and tweaking a host of other parameters until they hear the tone they're after. Someday, Bruyns hopes her software could lead to a user-friendly library of 3D instrument models that a composer could modify without much programming knowledge.
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To test the Vibration Lab software, Bruyns compared the sound of striking a real square of metal (left) with that of a virtual 3D model of the same object (right). (courtesy the researcher)
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Bruyns' software is based on techniques of modal analysis, the mathematical process of breaking a vibration down into its component parts, such as frequency and damping. Beginning with a 3D model built with commercially-available software, the Vibration Lab system adds mass and stiffness properties that mimic the characteristics of a real material like wood or bronze. The frequencies of the object are then calculated. Users can then "strike" the object in various places by hitting keys on an electronic piano keyboard connected to the computer using a standard digital music interface.
To test the system, Bruyns recorded the sound of striking real world objects she fabricated and compared that frequency spectrum with a hit on the object's virtual counterpart. The structures were metal letters that spelled out SIGGRAPH, the name of a scientific conference where she presented her work last year. The difference in frequency between the real and virtual objects ranged from just seven to 10 percent. Room acoustic effects can also be added using additional pieces of software.
Along with applications in electronic music, Bruyns hopes that her software could be used as a tool for real world instrument designers. She was inspired by the work of Séquin's friend Steve Reinmuth, an Oregon artist who sculpts exotic bells out of bronze.
"These sculptors make futuristic shapes that look like alien instruments and have very pretty tones," she says. "But a lot of that is trial and error. It would be nice to give the artists a tool to predict what their shapes will sound like."
Eventually, the system could also add realistic audio to an immersive computer-generated environment in development within CITRIS. The idea of the project, led by former CITRIS director Ruzena Bajcsy, is to enable individuals in remote places to gather via the Internet in a shared virtual environment created with digital cameras, computer graphics, and synthesized sound.
Not surprisingly, Bruyns has already been approached by companies interested in commercializing Vibration Lab. Right now though, she's focused on completing her PhD, probably in the next year or so. The next stage in the research is to simulate how air enclosed in the body of an instrument will affect its sound. To start, she's studying the timpani, a large drum with a sealed enclosure full of air.
"In the future, the software might enable me to take a 3D model of a tabla drum, for example, and know what it would sound like if it was made from solid gold."
Professor Xiang Zhang (ME '96) is the director of the National Science Foundation's Nano-scale Science and Engineering Center (NSEC) based at UC Berkeley. |
UC Berkeley mechanical engineering professor Xiang Zhang is taking a close look at the nanoworld. Very close. He's building an optical microscope that's nearly ten times more powerful than today's best comparable systems. The superlens at the heart of the scope could someday be used to observe the tiniest machinations of living cells, fabricate much faster and smaller computer processors, and manufacture DVDs with thousands of movies on each disk. Already, it cast a new light on a centuries-old barrier faced by optical physicists and engineers.
A nanometer is one-billionth of a meter. State-of-the-art optical microscopes can only reveal details bigger than about 400 nanometers, the size of a very large virus. The superlens produces images with resolutions of approximately 60 nanometers.
"That's just the beginning," says Zhang, who built the lens with two graduate students and a research scientist in his group. "We're looking to move from 60 nanometers to 20 and possibly even 10."
At left (A) is an image of an array of nanowires 60 nanometers wide created with the silver superlens. The center distance between each nanowire is 120 nanometers. To the right (B) is an image of the same nanowires. In this image, created without the superlens, the individual nanowires are not distinct. The scale bar on both images is 1 micrometer. (Cheng Sun, UC Berkeley) |
With a scope capable of such great resolution, biologists could zoom in on proteins moving along the microtubule fibers that form the skeleton of the cellular factory. Currently, that level of detail is captured using scanning electron microscopes and atomic force microscopes. While the electron microscopes produce valuable images, they work by scanning point by point just above the surface of the sample. As a result, they can take several minutes to generate a single image. Meanwhile, atomic force microscopes physically scan a sample much like a phonograph needle travels across a record. The problem is that as the sharp probe touches the sample, it can perturb it. On the other hand, the Berkeley researchers' superlens enables a single snapshot to be taken in a fraction of a second without any contact.
In April, Zhang and his colleagues published a paper outlining their technique in the journal Science. Lead author on the paper was Zhang's former PhD student Nicholas Fang-- now an assistant professor of mechanical engineering at the University of Illinois at Urbana-Champaign--graduate student Hyesong Lee, and research scientist Cheng Sun.
At top (A) is the higher resolution image of the word NANO created with a silver superlens. Below that (B) is an image created during a control experiment in which the superlens is replaced by spacer layer. The averaged line width is 89 nanometers in image A with the superlens, and 321 nanometer in image B without the superlens. The scale bar in both images is 2 micrometers. (Cheng Sun, UC Berkeley) |
To prove their concept, the researchers focused a beam of ultraviolet light through the superlens, a silver film three thousand times thinner than a human hair. Employing a photolithography process like those used in microchip fabrication, the researchers then recorded crisp images of nanowires and the word "nano" spelled out on a layer of polymer. A similar approach could be used by the semiconductor industry to pack many more transistors on a chip than currently possible. The speed and power of a computer processor is determined in large part by the density of the transistors.
"The work we published demonstrated the physics principle of the lens," Zhang says. "Our next objective is to make an optical microscope that could be used in biomedical imaging and other applications."
The previous experiment was based on near-field microscopy, meaning the sample was placed very close to the light source and detector to achieve the high resolution. Now, the researchers are honing a superlens-equipped microscope where the distance between the sample and the detector (your eye in a standard microscope) is comparable to traditional optical microscopes. They expect to publish their results in the next several months.
Schematic drawing of nano-scale imaging using a silver superlens that achieves a resolution beyond the optical diffraction limit. The red line indicates the enhancement of "evanescent" waves as they pass through the superlens. (Cheng Sun, UC Berkeley) |
The April publication made waves in the physics community not only because of the technology's promise but because it demonstrated that a well-known constraint in optical resolution, called the diffraction limit, could be beaten. When an object emits or reflects light, it produces two kinds of waves: propagation waves and evanescent waves. Conventional lenses such as those in eyeglasses capture the propagating waves of lights and focus them on a receptor, your eyeball for example. However, evanescent waves carry a great deal more detail about the object. The problem is that these waves decay very rapidly. For years, optical scientists and engineers have focused on capturing those waves to possibly produce a perfect image of an object. Two years ago, Zhang's group confirmed that a silver superlens could enhance optical evanescent waves. Now, they've shown how to build an optical microscope that does just that. The system doesn't capture all of the evanescent waves necessary for a perfect image, but it gets close.
"Between the diffraction limit and a perfect image, there is a huge land to look around in," Zhang says. "The superlens enables you to recover the lost treasures of the evanescent waves and build a sharper image."
Andy Schuler (Ph.D.98 CEE), an assistant professor of civil engineering at Duke University |
Hey there little buddy. If you could play a character on Gilligans Island, who would you be? The Skipper? Ginger? For Andy Schuler (Ph.D.98 CEE), an assistant professor of civil engineering at Duke University, it was the professor, of course. After a fortuitous phone call, he found himself in TBSs reality show The Real Gilligans Island on an uncharted island off Mexico. He was cast as none other than the professor, played by actor Russell Johnson in the original series which ran from 1964-1967.
"The professor really was one of my heroes growing up, and how many people get the chance to walk in their heros shoes, particularly when that hero was on a cheesy sixties sitcom?" says Schuler.
Schuler says his journey from engineering professor to TV professor and back again was a fun, but surreal experience. It all started last summer when he read an email about the shows call for auditions. It sounded interesting and I was curious, so I responded within a few minutes, he recalls. I thought it would be a fun and different thing to do. He called the phone number and was encouraged to send in digital photos and a video. They liked what they saw and heard so they flew me out to L.A. for a screen test. The next thing he knew, he had a plane ticket to Mexico and 10 days off work for the filming.
I didnt know what to expect, he says. I thought we might be shipwrecked and have to build huts and trap animals so I brushed up on my survival skills. But when we got there, theyd built a whole set just like Gilligans Island.
On the reality show, two complete sets of castaways -- two real-life skippers, first mates, millionaire couples, movie stars, farm girls, and professors -- competed as teams, then individually, to be the only castaway left on the island and the winner of a quarter million dollars.
Schuler didnt win -- he lost in a catapult game, but he says he was in it mostly for the experience. During his run, Schuler found himself in a love triangle (one of the Gilligans liked one of the Mary Anns, who liked him), and he became good friends with Gilligan Zach, one of his teammates. They hung out on the beach together and made traps to catch fish. It was a blast, he says.
It was also strange. We were all in costume walking around the set trying to act normal, but there are movie crews, cameramen, and sound guys everywhere. You have a conversation with someone, but youre miked so its all recorded. It was big brother watching you every moment. The whole reality thing is a mix of real moments and edited moments. I was pretty happy with how I was portrayed on it. At the end of the day, it is a business.
Schuler is now back on the job. He says his students and colleagues teased him a little when he got back, though most were interested in his experience. But Schuler says his flirtation with TV is probably over. I dont have an agent and am not planning to try out for anything else, he says. Being a [real] professor is one of the greatest jobs in the world.
