March2006
Raja Sengupta, a professor of Civil and Environmental Engineering, is a principal researcher with California PATH. |
In the last few years, the decreasing cost of wireless networking technology has untethered us from our Internet connections at home and at the office. Now UC Berkeley professor Raja Sengupta of the Department of Civil and Environmental Engineering is developing a system to bring WiFi into our cars. It’s not for Web browsing en route but rather a collision warning system that helps drivers keep their wits about them.
"Around 90 percent of crashes are caused by driver decision error or inattention," says Sengupta, who is affiliated with the Center for Information Technology Research in the Interest of Society (CITRIS). "Drivers fail to notice what's happening around them or they make a mistake reacting."
Sengupta's system, devised in collaboration with James Misener of the UC Berkeley-based California Partner for Advanced Transit and Highways (PATH), is based on an in-vehicle display that tracks your vehicle's location and those around you. For example, if you're tailgating someone, the screen might warn you to back off. Or an alert may sound if you're starting to change lanes and will likely hit another vehicle that's in your blind spot. The National Highway Traffic Safety Administration has been exploring such "active safety systems" for a decade or more. The problem though is that the ones that work are far too expensive to make it into the showrooms.
A screenshot from the collision warning system display (with a photo of the vehicles in a test run). The icon of the car on the screen becomes larger as the vehicle in front gets closer. Eventually, it turns red to indicate that a collision is imminent. (courtesy the researchers) |
"These systems require 360 degrees of coverage," Sengupta explains. "And the sensor-based systems with that capability use radar or cameras costing hundreds or thousands of dollars."
The new approach--developed with support from General Motors --employs technology that has already plummeted in price due to economies of scale. Each vehicle would be equipped with a GPS receiver and WiFi radio.
"Commercial WiFi radios sold for home and office networking can be easily modified to work on a frequency band that the FCC has allocated for short range safety communications use," Sengupta says. "The radios are already in the tens of dollars range and might even tumble to cost a single dollar."
The GPS enables a vehicle to monitor its own direction, location and velocity. Every 100 milliseconds, that data is transmitted via WiFi to all neighboring cars. Since the system doesn't use range-finding sensors like radar, it can even gather information about vehicles that may not be in direct line of sight. Essentially, the automobiles are constantly forming ad hoc wireless networks as they pass one another, but instead of accessing Web sites or email, they exchange information about their physical place on the road. Sengupta calls it a "Cooperative Collision Warning System."
Sengupta and his colleagues have already successfully demonstrated the technology with a fleet of five vehicles. Still, the researchers have a long road ahead before the cooperative collision warning system is ready for commercialization. For example, data transmission protocols and error correction algorithms must be improved so that occasional missed bits of data, a given due to the speed and volume of cars on a freeway, don't result in hazardous system errors.
Meanwhile, the researchers are exploring concerns around privacy and data authentication. How can you ensure, Sengupta asks, that the data received is accurate as opposed to a faulty system or malicious attack on the network?
Once the technical challenges are met though, the "chicken-and-egg" problem must be faced.
"The safety system can't deliver much value at low market penetration," Sengupta says. "Your radio is basically useless unless the cars around you have one."
The researchers believe that government subsidies could help bring such a system to critical mass, the tipping point where the marginal cost to include it in a vehicle is less than the marginal value. And once the public becomes used to backseat drivers in their dashboards, the sci-fi notion of automated vehicles could become a bit more real. Self-driving vehicles raise a host of liability issues, Sengupta says, but there may be valuable baby steps on the way to automation.
"Perhaps if you're getting too close to the car in front of you, the vehicle could gently brake or exert a little back pressure on the accelerator," he says. "Of course, you could easily override the system. You need to be responsible for your own vehicle."
Dan Fletcher with a custom Atomic Force Microscope designed and built by his research group to analyze the mechanisms of cell motility. Understanding how a cell moves could someday make it possible to engineer novel devices that take inspiration from cellular mechanisms, such as advanced drug delivery systems. (David Pescovitz photo) |
As cells move through the body, navigating through tissue and pushing against obstacles, they change shape. Understanding the dynamics of this process could someday lead to therapies that improve immune cells or fight cancer. To gain insight into cell motility, UC Berkeley bioengineering professor Daniel Fletcher and his students customized an atomic force microscope (AFM), a tool commonly used in nanoengineering. Their tricked-out instrument is helping reveal how the scaffolding that gives a cell its shape is affected by its environment.
"The question we asked is, 'what happens physically when a cell pushes out and hits something?'" says Fletcher, who is affiliated with the UC San Francisco/Berkeley bioengineering graduate group and the UC Berkeley biophysics graduate group. "We wanted to figure out a way of quantifying that directly."
The researchers focused on the cytoskeleton, the network of filaments made from proteins like actin. This cytoskeletal actin network provides the cell's structure and mechanical integrity, even as its shape changes.
"When a cell crawls, its front extends forward," Fletcher says. "Actin helps power that forward motion."
A window into the cell reveals the actin network and organelles inside a macrophage as it pursues bacterial invaders. Actin forms long filaments that lie just beneath the surface of the cell, giving it structure and stability. As the immune cell crawls and looks for invaders, such as the bacterium E. coli, new actin growth helps to push the cell forward. (Nicolle Rager Fuller, National Science Foundation) [view larger image] |
The aim was to watch such an actin network grow in vitro under a microscope and study how it responds to opposing forces. But off-the-shelf microscopes wouldn't do. Instead, Fletcher and his graduate students built a custom atomic force microscope. In a standard AFM, a micron-sized cantilever physically scans a sample much like a needle travels across a record. As the probe moves over the surface of a cell, a cantilever at the end of the tip bends in response to the sample's topography and mechanical properties. That deflection is captured by a laser and translated into a measurement with nanometer (one-billionth of a meter) resolution.
"The problem is that unwanted agitation or drift over time can compromise the integrity of measurements taken," says graduate student Sapun Parekh. "So we added a second cantilever to compensate."
In their set-up, the cantilever doesn't scan the sample but rather bends like a diving board as the actin network beneath it grows and pushes against it. Meanwhile, the other cantilever acts as a reference point on the surface of the sample chamber. Using this technique, the surface can be kept at a constant position relative to the first cantilever, enabling the microscope to accurately measure the growth of the actin network.
"There haven't been many tools available to rigorously study the dynamics of these systems," says Ovijit Chaudhuri, another bioengineering graduate student involved in the research. "It's exciting to find out the interesting and complex aspects of this system now that we have the ability to probe it."
Actin in this fish cell is stained with a red fluorescent dye. The bright areas on the top edge depict growing actin networks. (courtesy the researchers) |
To conduct their experiments, the researchers used the cantilevered tip to provide an increasingly greater force to a growing network of actin for up to a half-hour. The force acts like a barrier that the cell might encounter in vivo. As the force became stronger, the speed of the actin's growth stayed constant. After a preiod of increasing force, they then reduce the force to its initial strength. Oddly though, when the pressure of the cantilever was reduced, the network grew faster than before against the same load.
"We found that the growth of the actin is dependent on its loading history, not just the load at the moment," Fletcher says. "That means the cell has some sort of 'memory' of how it has previously interacted with its environment."
The protein network seems to remodel its architecture based on the pressure it's experienced, he explains. The experiments suggest that the growing actin network adds more filaments to push back against resistance.
"Now, we'd like to determine whether the resistance causes the network to become denser," Chaudhuri says. "And if that's the case, we hope to elucidate the factors that govern those changes in the number of filaments which will help us understand how the protein network generates force."
According to Fletcher, this basic research could someday help the fight against certain diseases. For example, immune cells and cancer cells both depend on their ability to move through the body.
"If we can gain a fundamental understanding of how cells use the actin network, we have a better chance of improving an immune cell's ability to move or, in the case of cancer, removing that ability," Fletcher says.
Robert Ritchie has also explored the fracture mechanics of teeth. |
As we age, our bones become brittle. According to the National Institutes of Health, one in two women and one in four men over 50 will have an osteoporosis-related fracture in her or his remaining lifetime. Often these fractures require surgery. Sometimes they prove fatal. But what can be done to toughen bones? The first step, says UC Berkeley materials science professor Robert Ritchie, is to find out how they break.
"The only way to possibly treat the brittleness of bone is to understand the mechanisms that make it fracture," says Ritchie, who is also the chair of the Department of Materials Science and Engineering and a scientist at Lawrence Berkeley National Laboratory.
X-ray computed tomography of human bone performed at Berkeley Lab's Advanced Light Source and the Stanford Linear Accelerator Center reveals nanoscale damage. In this image, shapes that appear solid are actually spaces — the blue structures are canals that carry blood and lymph vessels and nerves through the bone, while the pale green shape is a propagating crack. (courtesy Berkeley Lab) [view larger image] |
Ritchie has spent his entire career analyzing the fatigue and fracture of various materials, from ceramics to silicon to exotic alloys. After "running out of materials to break and study," he jokes, he stumbled upon bone. Common knowledge said that an age-related reduction in the density of bone mineral is tied to brittleness. However, recent studies suggest that bone mineral density may only be a small part of the problem.
"Bone quality, rather than quantity, seems to be a bigger part of the problem," Ritchie says. "And I realized I could quantify this using fracture mechanics. Our approach is that the mechanisms of fracture depend on the structure of the bone, and that structure changes with age, disease or clinical treatment."
To conduct the research, Ritchie and his colleagues use advanced 3D visualization techniques such as X-ray computed tomography, made possible by Berkeley Lab's Advanced Light Source, to study the bones of cadavers. They examine the bone across a spectrum of size scales, from the macroscale to the nanoscale. The critical dimension, Ritchie says, is surprisingly quite large—on the scale of hundreds of microns. This is the dimension of osteons, channels that surround the blood vessels passing through the bone. When a large crack reaches the edge of an osteon, it's often deflected. That mechanism can toughen the material. These regions are also prone to microcracking, which surprisingly can also lead to toughening in bone.
Two-dimensionaly tomographs show fewer and smaller bridges in older bone. (courtesy the researchers) [view larger image] |
"The small cracks actually open up ahead of any major crack," Ritchie says. "And between the microcracks are regions of unbroken bone. So when a major crack tries to open, these unbroken regions act as 'bridges' across the crack that sustain load and prevent the larger crack from propagating."
With age though, the number of osteons increases. And that's "too much of a good thing," Ritchie says. Too many microcracks actually defeats the toughening mechanism. So armed with their newfound knowledge, the researchers are collaborating with groups at the UC San Francisco and UC Davis to determine whether therapeutic treatments can be developed to help offset this deterioration in the fracture resistance of bone as one ages.
"It fascinates me that you might be able to explain things as complicated as disease and aging in terms of mechanical factors," Ritchie says. "Indeed, it's doubly intriguing because we can also use nature's inspiration to develop new materials based on these mechanisms."
Cool Alumni: Matt Fritzinger
by Rachel Shafer
Matt Fritzinger (B.S.'95 ME) |
The first thing you see when you walk into Matt Fritzinger's office at Berkeley High School is a mountain bike resting against the wall. Fritzinger (B.S.'95 ME) is executive director of the NorCal High School Mountain Bike Racing League, a non-profit organization he founded in 2001 that is now the largest youth cycling program in the country. The league includes 20 teams and 300 riders from Northern California.
"I never imagined that I could turn a hobby into something full-time," he says. "Never."
Fritzinger began racing in track and road cycling competitions as an eighth grader. At Cal, he rode with the Cal Cycling Team. "Some of my best college memories are from the cycling team," he says. "I met almost all my good friends there. I'm still really close to some of them today."
After he graduated, Fritzinger wasn't sure what he wanted to do. He decided that he wasn't a talented enough rider to pursue a professional career.
He moved to Durango to take advantage of Colorado's outdoors, waiting tables to support himself. He returned to the Bay Area in the spring of 1996 and landed a job as a mechanical engineer for a company that built industrial cranes.
"I was a mouse jockey," he says of his computer-driven responsibilities. "I hated it. But I needed to make some money." For six months he saved everything, then left.
During this time, Fritzinger was pondering a teaching career. He wanted a job where he could work with people and wasn't chained to a desk. Math was his forte, he says, and in 1997, Fritzinger was hired as a math teacher by Berkeley High School. In 1998, he started a mountain biking team there.
Fritzinger says he's always dreamed of participating in Italy's racing circuit, and in the summer of 2000, he made it happen. There, he observed Italians and their love of cycling, and particularly how they fostered and taught it to their children. Bay Area students deserved the same, he thought.
When he came back, he founded the league. He organized and ran a six-race series and coaxed four new teams into existence. He convinced corporations and individuals to donate. He worked 80-hour weeks -- 40 as a teacher and 40 for the league. It was manic, he says, but the reward was smile after brilliant smile from young, mud-spackled riders as they crossed the finish line of a tough race.
In 2005, Fritzinger stopped teaching to run things full-time. He expanded the program to include winter workshops, summer camps, and coaches training. He's working to recruit more low-income riders and even hire a dietician part-time to teach riders about nutrition strategies. The league continues to grow.
With success in his pocket, Fritzinger says an engineering career could be down the road. But there's that bike against the wall and so, for now, he'll ride.