Convergence Issue 20

The magazine of engineering and the sciences at UC Santa Barbara

FOCUS ON: SSLEEC

Leading the way in gallium-nitride-based technologies

College of Enginee

A message from the Deans

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s winter slows things down in much of the nation, the UC Santa Barbara campus remains mostly sunny and as vibrantly active as the whales currently migrating along our shores. This issue of Convergence presents a small sample of what’s happening in engineering and the sciences.

After years of planning and construction, the BioEngineering building (page 10) opened in October. It's a spectacular new structure, where innovative cross-disciplinary research will link engineering and the sciences for decades to come.

ROD ALFERNESS Dean and Richard A. Auhll Professor, College of Engineering

PIERRE WILTZIUS Susan & Bruce Worster Dean of Science, College of Letters & Science

This issue inaugurates “FOCUS ON,” indicating a section or even an entire issue dedicated to a major theme. We begin on page 20 with coverage of UCSB’s Solid State Lighting and Energy Electronics Center, a unique industry-academia partnership that has produced life-changing breakthroughs in lighting and energy-efficient electronics.

Our alumni make us proud every day and in so many areas of endeavor. On page 14, you’ll meet Rory Cooper (PhD, Electrical and Computer Engineering '89), who exemplifies how far CoE graduates can go. Cooper, who sustained a spinal-cord injury in 1980, directs the Human Engineering Research Laboratories at the University of Pittsburgh, the world’s largest and most active center for assistive technology. He is as dedicated to the rights of those with disabilities as he is to creating technology that profoundly and positively impacts their lives.

Steve Cooper (no relation to Rory; BS ’68) is another stellar alumnus who spent many successful years as an executive and turnaround expert in the semiconductor industry, then returned to UCSB in 2000 as a major donor and a mentor to students, with particular support for the Technology Management Program. We feature a Q & A with Steve on page 8.

The cross-fertilization between the College of Engineering and the Division of Math, Life and Physical Sciences continues unabated and is behind several stories here. A new collaborative group has received NSF funding to develop state-of-theart brain-imaging techniques (page 38). Another group, led by biology professor Denise Montell, examines the dynamics of anastasis, which allows cells to return from the brink of death (page 13), and UCSB astrophysicists (page 39) are part of a group studying a supernova that breaks all known rules of how stars die. On page18, you’ll read about how, inspired by marine mussels, Professor Megan Valentine and a cross-disciplinary team of researches affiliated with UCSB’s Materials Research Lab have discovered a promising new approach to making stretchy materials stronger without sacrificing flexibility.

This issue also covers Professor M. Scott Shell (page 30), who creates algorithms that have made possible previously unattainable simulations of highly complex molecular systems. And on page 34, you’ll meet Professor Pradeep Sen, who has spent nearly a decade developing industry-changing approaches to the computing-intensive denoising process required to generate screen-ready images for animated film features films.

Convergence proves once again that UCSB engineering and science continue to surge — in every season.

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CONTENTS 4 Winners Circle Prestigious awards for CoE faculty.

6 News Briefs Breakthrough in Metallurgy From Materials Lab to High School Lab Switching Up to Enhance the Cloud.

donor q&A

8 Steve Cooper: 50-Year Connection He graduated in 1968, thrived in the corporate world, and then became a key CoE supporter and donor.

10 Building Bioengineering A dazzling new structure propels collaborative science into the future.

13 Resilient Cells Biologists explore how damaged cells recover from the verge of death.

alumnus profile

14 Rory Cooper: Built to Enable After incurring a spinal cord injury, he earned a PhD and created the world's leading center for adaptive technology.

18 Stretching with Strength Marine mussels inspire a new way to make stretchy polymers that are stronger and just as flexible.

20 COVER Image Artist's representation: themes of light and energy, the foundations of the SSLEEC. (See page 28.)

COVER STORY — Focus On:

20 Center of Light and Energy The Solid State Lighting and Energy Electronics Center leads the way in gallium-nitride-based technologies.

30 Shortcuts for Modeling Atomic Activity Professor M. Scott Shell's algorithms make possible previously unattainable simulations of complex systems.

34 Turning Down the Noise Professor Pradeep Sen's research has changed the animated-film industry.

38 Illuminating Brain Activity NSF grant makes UCSB a key player in national brain initiative.

39 A Star that Will Not Die A supernova challenges known theories of how stars end their lives.

The Magazine of Engineering and the Sciences at UC Santa Barbara Issue 20, Fall 2017 Editor in Chief: James Badham Creative Director: Peter Allen Design: Michelle Mak UCSB Public Affairs Contributor: Julie Cohen Artwork: Peter Allen, Brian Long Photography: Matt Perko, Ryder Rogers

College of Engineering 3

Winners circle Prestigious awards for College of Engineering Faculty

Brad Chmelka, Professor, Chemical Engineering; Director, Institute for Collaborative Biology, was elected a Foreign Member of the Royal Swedish Academy of Engineering, founded in 1919 as the world's first engineering academy.

John Bowers, Professor, Electrical and Computer Engineering; Director, UCSB Institute for Energy Efficiency, received a Central Coast Innovation Award from the Pacific Coast Business Times.

Larry Coldren, Professor, Electrical and Computer Engineering, received the 2017 Nick Holonyak, Jr. Award from the Optical Society of America, for significant contributions to semiconductor-based optical devices and materials.

Craig Hawker, Professor, Chemical Engineering and Materials, won the 2017 Overberger Prize from the American Chemical Society, recognizing his groundbreaking polymer research.

Carlos G. Levi, Professor, Materials and Mechanical Engineering, was named the inaugural recipient of a new UCSB professorship, the Mehrabian Endowed Chair in Materials.

Igor Mezic, Professor, Mechanical Engineering, received a 2017 Society for Industrial and Applied Mathematics (SIAM) Fellowship Award for his longterm contributions to applied mathematics..

Umesh Mishra, Professor, Electrical & Computer Engineering, received the 2017 Distinguished Educator Award from the Institute of Electrical and Electronics Engineers Microwave Theory and Techniques Society.

Sanjit Mitra, Professor Emeritus, Electrical and Computer Engineering, received the 2017 Institute of Electrical and Electronics Engineers Education Activities Board Vice President’s Award for his work in circuits, systems, and signal processing.

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Yasamin Mostofi, Professor, Electrical and Computer Engineering, received the Antonio Ruberti Young Researcher Prize from the Institute of Electrical and Electronics Engineers Control Systems Society, Shuji Nakamura, Nobel laureate and Professor, Materials, and Electrical and Computer Engineering, received the Mountbatten Medal from the Great Britain–based Institution of Engineering and Technology, in recognition of his pioneering work in developing LEDs. Michelle O’Malley, Assistant Professor, Chemical Engineering, was one of thirteen university faculty members in the United States to receive a 2017 Dreyfus Teacher-Scholar award from the Dreyfus Foundation.

Sumita Pennathur, Associate Professor, Mechanical Engineering, was one of only two scientists in the U.S. to receive a prestigious 2017 Visionary Award and a five-year, $1.635 million research grant from the American Diabetes Association (ADA).

Tresa Pollock, Professor, Materials, received one of thirteen 2017 Vannevar Bush Faculty Fellowships from the U.S. Department of Defense. The fellowship includes $3 million to fund five years of Pollock’s research to discover new materials that could operate in extreme environments.

Ram Seshadri, Professor, Materials, was named the first Linda R. Wudl Chair for Materials. The chair supports a CoE Materials faculty member whose interdisciplinary scholarship merits a joint appointment in the life sciences or physical sciences.

M. Scott Shell, Professor, Chemical Engineering, received the 2017 American Institute of Chemical Engineers Computational Molecular Science and Engineering Forum Impact Award, for “outstanding research in computational molecular science and engineering.”

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Welding the Unweldable, Printing the Unprintable PhD students in Tresa Pollock's lab co-lead a team that uses nanoparticles to solve an ages-old metallurgy problem High-strength alloys have been critical in developing aircraft wings and fuselages, and other highperformance applications where margins for error are small. Many alloys could also be useful in additive manufacturing, or 3D printing, which, at the highest level, makes it possible to fabricate complex, highprecision objects without the cost or geometric constraints of die-making and machining processes.

A few years ago, scientists at HRL, a research-and-development laboratory owned by The Boeing Company and General Motors, identified additive manufacturing as a technology that might provide a competitive advantage in the metallurgy space. But a decades-old hurdle stood in the way, which was, that of the roughly five thousand currently available alloys, only about ten can be used in 3D laser printing. That’s because, during the intense heating and ensuing cooling (solidification), most alloys experience something called “hot cracking,� which critically weakens the metal, to the point where it can be pulled apart like a flaky biscuit. Welding has the same effect, which is why airplane wings and fuselages made of such alloys are held together by rivets rather than welds.

Now the HRL team, which includes John H. (Hunter) Martin and Brennan Yahata, both PhD students working in the lab of CoE Alcoa Distinguished Professor of Materials Tresa Pollock, has achieved a breakthrough by developing a technique for eliminating hot cracking, thus opening the door to using high-strength aluminum alloys and a wide range of other engineering-relevant alloys for 3D printing.

The findings appear in the journal NATURE; find the complete version of this article at: engr.ucsb.edu/metallurgy.

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As one of the world's leading metallurgists, Professor Tresa Pollock (Materials), shown above beside an electron microscope and equipment used for 3D printing of complex alloys, provided insights for two of her PhD students, (top, from left) John H. (Hunter) Martin and Brennan Yahata, who are also part of the HRL team that discovered a way to avoid the phenomenon of "hot cracking" in super-heated alloys.

Trained to Teach

Pho

rtesy of Levi Miller to cou

For PHD students, teaching comes with the territory. For Levi Miller (MEd 2017, MS 2014), it turned out to be the passion that led him from the PhD track to the high school classroom

Switching Up UCSB engineers aim to improve the speed and energy efficiency of cloud servers. A social media data center is likely to be the testing ground.

A couple of years ago, Levi Miller was a PhD student in the lab of CoE materials professor Micheal Chabynic. Like most PhD students, he taught, and the more he taught, the more he was attracted to teaching. Eventually, realizing "I enjoyed the functions of teaching I was doing as a TA more than I enjoyed research,” he made the difficult decision to leave the PhD program and pursue a Master of Science in materials and then a Master of Education at UCSB’s Gevirtz Graduate School of Education.

Now Miller, who is teaching this year at the highly regarded Engineering Academy at Dos Pueblos High School in Goleta, has received one of six Knowles Teacher Initiative Fellowships for 2017, which are given to promising math and science teachers across the nation who are beginning their teaching careers.

“Making the switch was one of the hardest things I’ve ever done, because the Materials Department was so good — and so good to me,” Miller recalls. “Michael Chabinyc was a kind and supportive advisor,” and one who fully supported Miller’s career decision. Because of that, Miller says, “I was able to have that conversation without burning any bridges. I really appreciated that, because it didn’t have to be that easy.”

Whenever you go onto your Facebook or LinkedIn page, banks of servers at enormous kilometer-long data centers that make up the cloud spring into action, gathering data. The various types of data live on different servers, so a tremendous amount of communication takes place between servers to assemble the package you’re presented as a user. Providing that service to billions of users requires many millions of servers and a great deal of energy.

Not surprisingly, digital giants are always looking for faster and more-efficient ways to store, fetch, and distribute all that data, which, for much of its journey, moves at the speed of light via fiber-optic cable. But there are bottlenecks in the data-storage-and-retrieval system created by copper-wired switches that link servers to each other and to the fiber-optic system. All that copper creates inefficiencies, which in turn produce heat, which requires more electricity to remove. The cumulative result is slower data transmission and higher cost.

Now, a team of researchers in the UCSB College of Engineering has received a Department of Energy (DOE) grant for $4.4 million to develop integrated technology that will make it possible to incorporate photonics right onto the switch chip, eliminating the need for comparatively inefficient copper wiring.

The team includes principal investigator Clint Schow and fellow electrical and computer engineering faculty members and co-PI’s Jim Buckwalter, Larry Coldren, Jonathan Klamkin, and Adel Saleh, plus about a dozen graduate students and postdoctoral researchers.

The team projects at least a 90-percent reduction in network power usage in both small- and large-scale systems, and a 200- to 600-percent increase in the overall efficiency of data-center transactions.

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A 50-year connection

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Steve Cooper graduated from the UCSB College of Engineering in 1968 with a degree in electrical engineering. He and his wife, Sue, met and married while they were students. He started at Intel when revenues were $50 million; now they're over $100 billion. He has spent much of his life as a manager and entrepreneur, primarily in the semiconductor field, leading startups and guiding corporate turnarounds. Since 2000, he has pledged $1 million to the CoE and dedicated thousands of hours to serving the university, as a member of the UCSB Foundation and as a current member of the CoE Dean’s Cabinet. Convergence caught up with him during the cabinet’s conference in November.

C: What made you decide to give to UCSB? SC: I was working on TMP and saw a real need there, so I decided to funnel some of my funds into it. I liked having the chance to reconnect with the university, and I felt the need to give back. I wasn't a great engineer, but I've done some pretty good things as a CEO, and my UCSB engineering degree is what allowed me to do that. There were a few turning points in my life, and UCSB was one of them.

C: Can you take us through your involvement with TMP? SC: TMP started in about 1998, and I've been involved with it since about 2000. There was a period when the university and the state were in a bad financial situation, and we didn't know if the program would continue. But we kept it running, and we can thank Chancellor Yang and [then-chair] Bob York for winning wide support for it, both across campus and in the UC Office of the President. Now it has a solid foundation, staff, and facilities. It attracts students from many departments. It has a master's program, and our first TMP PhD candidate will be starting soon. It offers students a great opportunity to form teams and learn how to work on projects with colleagues from other disciplines. It's not just research, technology, and engineering; it's a blend of everything, which is the direction the world is going.

C: How is it for you to mentor students and to be involved in their success?

SC: I find it really stimulating to interact with students here at UC Santa Barbara, whether they are in engineering or somewhere else. They're brilliant. I mean, I couldn't get into this school with the grades required today [laughs]. But also, I’m impressed by how much they know and how much they've traveled the world. And their technical expertise is just incredible. People sometimes disparage today's youth, but I'm so impressed by what I see at UCSB. C: Can you tell us a little about the Cooper Computer Lab? SC: In 2006 I was ready to give a sizable gift, and it was a naming opportunity. I can't tell you how rewarding it has been. At the time I thought, It's a computer lab; they'll put some computers in it and it will get some use. But in reality, it has been extremely well received.

It's used by many people on campus. And I've been especially pleased by the feedback from professors. They're so grateful to

have it. That's true of everything I've contributed to UCSB: I'm very satisfied with what's been accomplished.

C: What is it about UCSB that makes you want to continue to support it?

SC: The real strength of UC Santa Barbara is interdisciplinary cooperation. It's something other universities talk about, but it exists here unlike in any other place. I’ve worked at other elite California universities, and I saw that the silos were so formed, so tall, and so impenetrable that, despite the efforts of a lot of good professors, they've never been able to establish the kind of cross-disciplinary cooperation we have here. When I went here we had Quonset huts, and professors had to share space and share everything. There is a belief that that sharing is part of what has led to today's culture of cooperation and collaboration across campus.

C: What stands out to you about UCSB and the College of Engineering today?

SC: I believe that neither UCSB nor the College of Engineering gets the credit it deserves for what it accomplishes. I hope to see that change during my lifetime. The greater academic community knows where we stand and how we rank. But prospective students and parents may not recognize that we have Nobel laureates, or that students have the unique opportunity here to work on research as undergraduates.

C: What would you say to others who might be considering a gift to support the CoE? SC: The opportunity here is to identify what interests you — whether it's business, as it was for me with TMP, or technology or medicine, or something else — and have a one-on-one relationship with someone at the university who can keep you current on what's going on. Some of the most gratified donors I know have supported individual students, who have come to their houses and presented progress to them. It's a phenomenal experience and an opportunity to pursue one of your passions and see a tangible return on your donation.

FOR INFORMATION ON HOW TO GIVE TO UCSB CoE, VISIT

ENGR.UCSB.EDU/CHAMPIONSOFENGINEERING

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Photo by Tony Mastres

Building BioEngineering A dazzling new structure to help propel innovative, collaborative science into the future

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fter a decade of planning, a fundraising effort that included the obstacle of the Great Recession, and nearly two years of construction, the new $86 million BioEngineering Building at UC Santa Barbara had its grand opening on October 20. Chancellor Henry T. Yang and College of Engineering Dean Rod Alferness cut the ceremonial ribbon as faculty, staff, donors, members of the Dean’s Cabinet, and others in the UCSB community cheered.

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Building Bioengineering (continued) “This is the culmination of years of visionary work and the beginning of a new era of research collaboration on our campus,” the chancellor said.

The building is home to 15 faculty who, will mentor and guide some 165 graduate students and postdoctoral researchers on what Alferness described as “a journey of problem-solving and discovery in a shared 21st-century laboratory space, where new collaborations and cross-discipline directions will be forged as we continue to build on what is already a highly research-productive and impactful bioengineering community on this campus.”

The 45,000-square-foot glass, metal, and concrete building, designed by the architectural firm Moore Ruble Yudell, includes 17,200 square feet of laboratory space and a range of cutting-edge “smart” sustainability features.

Brad Chmelka, professor of chemical engineering and co-director of the Institute for Collaborative Biotechnology, said to the assembled crowd, “Buildings like this are crucial in that they allow people to come together from many different departments in order to talk and learn from each other, which provides a source of ideas, creativity, and applications that wouldn’t happen if people were in their respective silos of isolation.”

Kevin Plaxco, professor of chemistry and biochemistry and director of the Center for BioEngineering, who was one of the first to move into the new lab, said, “I’m excited by what this gorgeous building means to bioengineering at UCSB. We want to do revolutionary things here, to solve challenges that we'll face ten years from now, or thirty years from now.”

Executive Vice Chancellor David Marshall added, “As science learns how to imitate nature, we also discover how the principles and practices of engineering can give us new insights into the building blocks and fundamental processes of life, allowing us both to understand and reverse-engineer the principles and processes of biology.

“Situated at the intersection of science and nature, of biology and engineering, this new BioEngineering building stands for the interdisciplinary and collaborative culture that has made UC Santa Barbara a great research university,” he continued. “It also represents the entrepreneurial spirit of the campus and the insistence that in times of decreased government support, we find ways to pursue the acts of discovery that illustrate how a great public university can contribute to society.”

New opening for bioengineering (from top): Chancellor Henry T. Yang and CoE Dean Rod Alferness cut the ribbon, a student happily eyes new lab digs, and other students unpack research necessities on moving day.

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Biologists explore how damaged cells return from the verge of death

Photo courtesy of Denise Montell

resilient cells

Dying human cancer cells are labeled with fluorescent dyes to show DNA (blue), actin (red) and active caspase 3 (green).

A new collaboration between two UC Santa Barbara labs explores the underlying molecular mechanism of a remarkable process called anastasis, a Greek word meaning “rising to life.” Building on earlier work showing that cells can return from the brink of death, the new study demonstrates that anastasis is an active process composed of two distinguishable stages. The team’s findings appear in the Journal of Cell Biology.

“We knew already that cells need to transcribe new genes in order to recover,” explains corresponding author Denise Montell, UCSB’s Duggan Professor of Molecular, Cellular, and Developmental Biology. “So we profiled every molecule of mRNA in the cells as they started to die and then as they recovered.”

First, the biologists added a toxin to the growth medium to induce apoptosis — a form of programmed cell suicide that is an integral part of almost every disease — and took the cells to the brink of death. They then exchanged the medium to remove the inducer and allowed the cells to recover for one, two, three, four, eight or twelve hours. At every step, the researchers collected millions of cells and sequenced their RNAs to discover how their genetic profile changed during this process. UCSB’s Kosik Molecular and Cellular Neurobiology Lab conducted the RNA analysis.

The data from the RNA profiles not only demonstrated the active nature of the anastasis process, but also showed its two distinct phases. Patterns of gene expression resembled each other at the one-, two-, three-, and four-hour intervals, as did those at eight and twelve hours of recovery. Both groups were much different from untreated cells.

“We also found that even when cells are at the brink of death, they are secretly enriching survival RNAs,” Montell said. “The cells don’t know if things are going to get better or worse, so they hold on to some survival molecules just in case. The cells are poised to recover even while they’re dying.”

The team focused on one particular pro-survival RNA, called “snail,” which is enriched at the brink of death. The cells don’t make protein out of the RNA or degrade it; rather, they hold on to it. When the scientists prevented the expression of snail, the cells were unable to survive.

They also discovered that RNAs induced in the early phase of anastasis promote transcription of other genes, which allows cells to recover and start dividing. In the later phase, RNAs change what they make and acquire the ability to migrate.

“Some things are expressed during the whole recovery process, including angiogenesis inducers that make new blood vessels,” Montell notes. “This looks a lot like wound healing — cell proliferation or migration to fill in the gap and the creation of new blood vessels to nourish the recovery.

“That’s all fine in a normal beneficial process,” she adds. “For example, it's good news that cells deprived of oxygen during a heart attack can recover. But when cancer cells do the same thing, it’s bad news. Chemotherapy drugs and radiation are known to induce cancer cells to undergo apoptosis. But anastasis may give them a way to bounce back after treatment.”

Now that the researchers have described this molecular mechanism, they are particularly interested in the earliest phases of recovery before cells begin transcribing new genes. They also would like to better understand the long-term cellular effects of anastasis. “We want to know whether a cell recovering from the brink of death retains a permanent epigenetic memory of the experience,” Montell said. “We also want to find out whether cells that have experienced one round of anastasis are more or less resilient to a subsequent round. And most importantly, does the mechanism we describe in this paper underlie relapse after chemo and radiation therapy?”

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Photo by Joe Appel

BUILT to Enable 14 Fall 2017

Alumnus Rory Cooper heads the world's leading center for wheelchair and adaptive technology

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uring a Skype interview with UCSB alumnus and University of Pittsburgh professor Rory Cooper (PhD Electrical and Computer Engineering, '89), a foldable steel Everest & Jennings wheelchair, circa 1950, is visible behind him in his office. It weighs 80 pounds.

Cooper himself, who is Distinguished Professor and FISA/PVA Chair of the Department of Rehabilitation Science and Technology and has multiple professorial appointments at the university, sits in a more recent chair of his own design. Made of titanium, it weighs just 18 pounds. The wheels are removable, and it’s easy to lift them and the 10-pound frame into the car. Cooper’s aluminum racing chair weighs 12 pounds. He used one like it to earn a bronze medal at the 1988 Paralympic Games.

Thanks largely to the advances resulting from research and engineering led by Cooper at Pitt’s Human Engineering Research Laboratories (HERL), which he started in 1994 after being recruited as an associate professor, millions of people have wheelchairs that are light, ergonomic, and efficient. They play basketball, tennis, rugby, volleyball

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registers several new patents and negotiates several licenses per year.

“It's a big operation that keeps me rather busy,” Cooper says in the understated manner that quickly becomes familiar, as does his commitment to ensuring that his fellow wheelchair users are able to participate fully in all aspects of life. “The goal is full autonomy and full participation as equal partners in society, and respect for people with disabilities,” he says.

HERL and Cooper’s efforts on behalf of those with disabilities were born of his own experience after experiencing a spinal cord injury while an army sergeant stationed in Germany in 1980. As soon as he began using one of the heavy steel chairs of the time, he knew he had to do something to improve it.

After returning to the U.S. from Germany, he enrolled as an engineering student at Cal Poly San Luis Obispo, where he not only earned bachelor’s and master’s degrees in electrical and computer engineering, but also started his own company, Cooper Engineering, which he ran for three years as an undergraduate before selling it.

The goal is full autonomy and full participation as equal partners in society, and respect for people with disabilities.

— about seventy sports in all — in chairs designed especially for those activities, and for specific positions. The chairs require less energy to move, and their design reduces injury. Those with more severe disabilities have access to an ever-expanding range of high-tech features.

Roughly 70 people — and up to 100 when summer interns are present — work in the 40,000-square-foot facility, which includes a fully outfitted shop where engineers can build what they design. About one-third of HERL staff members have a disability. The lab is home to about 70 research projects, and it turns out 35 to 50 published papers, and

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“I’ve always been a man on a mission,” he says.

Cooper had been an athlete all his life, and the fact that he could no longer walk did nothing to diminish his competitive spirit.

While at Cal Poly, he collaborated with a group of designers and inventors to share concepts and evolve the technology that led to the first racing wheelchair.

He pursued lighter-weight materials. He was one of the first to introduce a three-wheeler, and was the first to introduce the solid frame to replace the traditional folding frame. At UCSB, he also designed the Smart Wheel,

a feedback mechanism to measure the force and movements on the push rims and inform redesigns to reduce the risk of carpal tunnel and rotator cuff injuries. The data it provided led him to move the axle forward on the racing chair, arguably the single most revolutionary and broadly beneficial advance in manual-wheelchair design history.

When he started racing, Cooper recalls, “I realized that you needed two separate things — a racing chair and an everyday chair. It’s funny, because the everyday chair I use now is much like the racing chairs I tried to design in the early eighties.”

He also noticed that athletes who were pushing so many hard miles on the lighter, axle-forward chairs were not incurring higher rates of wrist or shoulder injuries, while others in heavy everyday chairs were frequently injured.“ So it was clear we should put racing technology and design into everyday chairs,” he says. Doing so took a problem that happened to eighty percent of users down to twenty percent, not only reducing pain and suffering for wheelchair users, but also saving tens of millions of dollars in health-care costs.

Cooper has always innovated. He was the first to put fenders over the wheels on his racing chair to prevent the tires from burning his underarms when racing. “People laughed, but you can’t find a racing chair today that doesn’t have them,” he says.

Wheelchair racers also suffered from compensating for the crown on roads, which tended to send them off to one side or the other and led to crashes. Cooper developed a crown-compensation mechanism to keep the chair going straight.

THE SOCIAL SIDE OF DISABILITIES Those who incur injuries that create longterm or lifelong physical disabilities face challenges on multiple levels. They must heal their bodies and then relearn nearly every aspect of life. After overcoming all that, they face another obstacle in the form of societal indifference and even outright discrimination.

It is one thing to face a physical challenge that distinguishes one from the mainstream population; it is another to be considered, 15

unjustly and by assumption, somehow incapable of contributing to society as a result.

The Americans with Disabilities Act was not passed until 1990, so at the time of his injury, Cooper, like millions of others with disabilities, had few legal protections against discrimination. In fact, when he applied to the UCSB Engineering PhD program, Cooper’s application was rejected initially, because some on the admissions review board believed his outstanding grades had been artificially inflated to compensate for his disability. It was a different time.

Cooper was eventually admitted, and he entered UCSB excited about the prospect of gaining a multidisciplinary perspective, which wasn’t possible at many universities.

After graduating, he planned to work for NASA, or for Disney, “designing rides or animatronics.” But a key advisor, Stephen Horvath, mentioned to Cooper that he was a talented engineer who had an obviously strong affinity for the problems facing people with disabilities, and suggested he consider making a career of designing better wheelchairs and related devices to serve them.

the social barrier. People, especially kids, read the story at breakfast, and they see that disabled people can be multifaceted and are just people.”

ENABLING TECHNOLOGY Cooper’s work has earned him worldwide recognition, not only for his groundbreaking technology, but equally for his character and qualities as a person. His CV lists pages of awards and proclamations, each a variation on a theme introduced with such phrasing as “For exceptionally meritorious service…,” “For a highly prolific spirit of innovation…,” “For transformative achievement…,” “For inspirational leadership…,” and For selfless service.”

He recently added two more. He won a 2017 Samuel J. Heyman Service to America medal in the Science and Environment category, and he was one of 396 members

In 2009, Cooper (#4 on side panel below) appeared on a box of Cheerios as part of a two-year General Mills campaign to celebrate athletes who were veterans.

After attending a few conferences and realizing “there was a profession in that,” Cooper changed the focus of his dissertation from robotics to the control aspects of wheelchairs. He completed his degree in 1989, after only three years, while finding time to train for the 1988 Paralympic Games in Seoul, South Korea, where he won a bronze medal in the 4x400-meter relay race and competed in four other events, including the marathon.

The Paralympics, he says, “changed my life,” and he has worked relentlessly to make physically competitive experiences a reality for more people with disabilities.

In industry jargon, such endeavors are referred to as “adaptive reconditioning.” Participating in them, Cooper says, “helps to improve your psychological perception of yourself; builds strength, flexibility, and coordination; introduces you to other people with disabilities and helps with social integration; and increases the visibility of people with disabilities and society’s appreciation for what they can do.”

Cooper himself has been part of a growing body of positive imagery associated with those who have a disability. In 2009, General Mills selected him to appear on a Cheerios box as part of a special two-year campaign to recognize veterans who were athletes.

“It was cool that Cheerios would put a vet with a disability on the box,” he says. “That can help to overcome the biggest barrier to having a disability — Photo used with permission of General Mills Marketing, Inc.

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of the American Association for the Advancement of Science to be named a 2017 Fellow.

The center has developed a series of assistive robotic arms, including one currently being tested that receives signals directly from the brain, and another, the STRONGARM, which mounts to the chair and replaces a lift for assistance with transfers. It folds behind the chair when not in use.

The Personal Mobility and Manipulation Appliance (PerMMA), incorporates two robotic arms controlled by touchpad, microphone, or joystick, depending on the users’ needs, to help with everyday tasks. The MEBot is a lightweight electric wheelchair that can climb curbs and self-level on uneven pavement. (Cooper puts the MEBot through its paces on the first page of this article.)

The Virtual Coach onboard coaching system is a breakthrough using data communication to support people ("without being a nag") who have advanced chairs in using them correctly, thus avoiding problems with ulcers, swelling of the limbs, and other medical conditions.

Photo courtesy of Rory Cooper

Much of HERL’s wheelchair research explores strong yet lightweight composite materials, power and computer-controlled innovations, and advances in propulsion and mobility.

Depending on the user’s needs, a chair may incorporate laser sensors, abundant software, and machine learning.

Rory Cooper (seated at center) and fellow HERL researchers examine a frame for a wheelchair being developed at the lab.

PARTICIPATORY DESIGN, CHALLENGES, AND THE LONG VIEW HERL is a highly collaborative, deeply interdisciplinary operation that includes medical doctors, physical and occupational therapists, and mechanical, computer, and bio-engineers. In what Cooper refers to as “participatory action engineering,” the lab constantly engages with veterans and others who use assistive devices. “Ever since its inception, I’ve wanted to include veterans in HERL as employees and trainees,” he notes.

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And HERL adaptive technologies go beyond wheelchair applications. The Cueing Kitchen, for example, was designed for people who may struggle with food preparation and other daily activities because of cognitive impairments resulting from traumatic brain injury, dementia, or Alzheimer’s disease.

The Cueing Kitchen is a basic residential kitchen cabinet layout modified with portable or wireless sensing and cueing technologies that recognize, for example, if an individual is using the correct appliance and for the correct duration, has opened the correct cabinets or appliances, has retrieved or stored the correct item, or is working in the correct region of the kitchen.

The key is to get different perspectives, and it’s another way veterans can contribute so that we’re solving real problems — their problems.

"

Despite dramatic advances in technology and expanded insurance coverage of adaptive technologies that incorporate it, challenges remain, especially in overcoming the social stigma related to having a disability.

“As successful and known as I am now, I still get people who basically tell me to my face that I’m wasting my time working on these problems,” Cooper explains. “They’ll say, ‘They have all the technology they need.’

No, they don’t, not until they have equal participation and standing in society.”

Cooper is in it for the long haul. “This is my calling, my passion,” he says. “I consider myself fortunate to apply my engineering talents to help people with disabilities and people in general, and change society just a bit for the good. Sometimes I go up to a vet I see using something we created and ask about the new backrest or wheels, and they say, ‘It’s unbelievable. It’s changed my life.’

How can anything be better than that?”

As we spoke, Cooper was preparing to compete in a marathon to be held at Fort Bragg the following weekend. “The vast majority of the people will be runners, but now they respect us for how hard we train,” he says. He finished in 1:40, about 22 minutes faster than the world record for a running marathon. Average bicyclists can't keep up with fast wheelchair athletes.

And average humans can’t keep up with Cooper, because he’s always moving, always racing to serve — and change — the world.

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It's challenging to make a material both stretchier and stronger. Natural polymers in the rugged mollusk seem to offer a conceptual blueprint.

18 Fall 2017

One challenge with such materials is that making them stronger usually involves the trade-off of making them more brittle. That’s because structurally, elastomers are rather shapeless networks of polymer strands — often compared to a bundle of disorganized spaghetti noodles — held together by a few chemical cross-links. Strengthening a polymer requires increasing the density of cross-links between the strands by creating more such links. That causes the elastomer’s strands to resist stretching away from each other, giving the material a more organized structure, but also making it stiffer and more prone to failure.

Inspired by the tough, flexible polymeric byssal threads that marine mussels use to secure themselves to surfaces in the rugged intertidal zone, a team of researchers affiliated with the UCSB Materials Research Laboratory (MRL) and colleagues beyond it has developed a method for overcoming

Photo courtesy of Megan Valentine

Elastomers constitute a wide range of polymer-based materials — from tire rubber and wet suit Neoprene to Lycra clothing and Silicone — that are valued for their ability to flex and stretch without breaking and return to their original form.

Cross-link colleagues: Associate Professor Megan Valentine (above) and co-lead authors (top), Emmanouela Filippidi, a postdoctoral researcher in Valentine's lab, and Thomas R. Cristiani, a PhD student in Professor Jacob Israelachvili's lab.

the inherent trade-off between strength and flexibility in elastomeric polymers.

Project researchers affiliated with the MRL's Interdisciplinary Research Group on Bio-inspired Wet Adhesion are co-authors Professor Megan Valentine (Mechanical Engineering), Professor Jacob Israelachvili (Chemical Engineering and Materials), both in the UCSB College of Engineering, and Professor Herbert Waite (Department of Molecular, Cellular, and Developmental Biology). Kollbe Ahn, of the UCSB Marine Science Institute, and Professor Claus Eisenbach, of the University of Stuttgart, also collaborated on the project. An article describing the new research, titled “Toughening elastomers using mussel-inspired ironcatechol complexes,” and leadauthored by UCSB postdoctoral researcher Emmanouela Filippidi and PhD student Thomas R. Cristiani, appeared in the October 27 issue of the journal Science.

Similar previous efforts, also inspired by the mussel’s cuticle chemistry, were limited to wet, soft systems such as hydrogels. Here, though, the researchers incorporated iron coordination bonds into a dry polymeric system of a type that could potentially be substituted for stiff but brittle materials, especially in impact- and torsion-related applications.

“A material having that characteristic, called an ‘energy-dissipative plastic,’ is useful for coatings,” says Cristiani, a PhD student in Israelachvili’s lab.

“It would make a great cell-phone case because it would absorb a large amount of energy, so your phone would be protected and less likely to break upon impact with the floor.”

Not only did it maintain its stretchiness, but it also became eight hundred times stiffer and one hundred times tougher in the presence of these reconfigurable ironcatechol bonds!

“In the past decade, we have made tremendous advances in understanding how biological materials maintain strength under loading,” says Valentine, the corresponding author.

"In fact, this work builds on Israelachvili and Waite's longstanding collaboration to better understand structure-function relationships in mussel adhesion. That work, says Waite, has allowed "synthetic and theoretical partners to adopt those insights for their translation of nature into technology." In this paper, Valentine adds, "we exploit our understanding of mussel bonding to create new strong, stretchable polymer materials that hold promise for many industrial applications, ranging from construction to robotics."

To achieve networks having architecture and performance similar to those of the mussel byssal cuticle, the team synthesized an amorphous, loosely cross-linked epoxy network, then treated it with iron to form dynamic iron-catechol cross-links.

The dry system is important for a couple of reasons. In a wet system, the network absorbs water, causing the polymer chains to stretch, so that not much extra flexibility remains. But with a dry material, the amorphous strands are initially very compact, with a lot of room to stretch. When the iron cross-links are added to strengthen the polymer, the stretchiness of the dry material is not compromised, because those bonds can break, so the polymer chains are not locked in place. Additionally, removing the water from the network results in the catechol and iron being closer together and able to form regions of high connectivity, which improves the mechanical properties.

To see how iron-enhanced cross-links used in the dry network would behave in a wet network, the researchers measured the mechanical properties of an iron-treated hydrogel. The wet network was 25 times less stiff and broke at five times shorter elongation than a similar dry network.

"That's an interesting but expected result," Filippidi says. “What’s striking is what happened when we compared the dry network before and after adding iron. Not only did it maintain its stretchiness, but it also became eight hundred times stiffer and one hundred times tougher in the presence of these reconfigurable iron-catechol bonds. That was unexpected.”

Valentine concludes: “This difference between responses in wet and dry systems is huge and makes our approach a game-changer in terms of synthesizing useful engineering materials for high-impact applications.”

In the absence of iron, when one of the covalent cross-links breaks, it is broken forever, because there is no mechanism for it to heal itself. But when the reversible iron-catechol coordination bonds are present, any of those broken iron-containing crosslinks can reform, not necessarily in the same place but nearby, thus maintaining the material’s resiliency even as its strength increases. The material is both stiffer and tougher than similar networks lacking iron-containing coordination bonds.

Further, as the iron-catechol network is stretched, it doesn’t store the energy, so when the tension is released, the material doesn’t bounce back like a rubber band, but rather, dissipates the energy slowly. The material recovers to re-assume its original shape, much like a viscoelastic material, such as memory foam, does after the pressure on it is released.

Iron-enhanced cross-links can make materials (like the one shown) stronger and stretchier.

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21

Center of Light and EnErgy

The Solid State Lighting and Energy Efficiency Electronics Center

Ever since the the Solid State Lighting and Energy Electronics Center (SSLEEC) opened in 2001 (as the Solid State Lighting Display Center), a group of highly collaborative, world-leading scientists has been working to push the limits of materials science and develop life-changing semiconductor technologies. Many are patented and now provide indispensable functionality in a wide array of consumer products.

The research ties the center to the future while building on the UCSB past, particularly the work of Professor Emeritus Herbert Kroemer, whose pioneering research oin semiconductors helped launch the Digital Age while earning him a Nobel Prize.

Today, SSLEEC brings together faculty, graduate students, and postdoctoral researchers from the Materials, Chemistry, Physics, and Electrical & Computer Engineering Departments at UCSB. The center is focused on developing new semiconductor-based technologies for energy-efficient lighting and its applications, power electronics, and the bulk growth of gallium nitride (GaN) crystals.

Equally important are the center’s strong industry connections, which ensure that valuable new products and technologies reach the marketplace, where they can positively impact the world.

“SSLEEC brings particular pride to UCSB Engineering and the Sciences based on the prowess of its faculty and researchers, and the many breakthroughs that have resulted from their efforts,” says Rod Alferness, CoE dean and a member of the SSLEEC Board of Directors. “The center stands for so much of what we value most at the college, and at UCSB as a whole: cutting-edge science, creative long-term collaborations involving people from multiple departments and disciplines; and a dedication to training graduate students who are ready to lead.”

In the following pages, you will learn about the SSLEEC and its indisputabe role in launching a new era of lighting and energy efficiency.

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Gallium Nitride: The Material that Made the Difference

FOCUS ON: SSLEEC

Professor Shuji Nakamura

SSLEEC researchers Steven DenBaars, Umesh Mishra, and James Speck began working with gallium nitride (GaN) in 1993, but research funding was largely unavailable, because, as DenBaars recalls, “GaN was thought to be useless as a semiconductor.”

That was because GaN is a highly imperfect crystal.

Typical LED semiconductors exhibit fewer than 100,000 defects (known as “dislocations”) in the crystal structure/cm2, and a silicon crystal may have as few as 0.1 defect/cm2. But in 2000, no one had yet made a GaN substrate that had fewer than 1 billion defects/cm2. When GaN is layered with other materials, those defects propagate in the crystal lattices, impeding performance of the semiconductor.

LEDs were the first technology to benefit from GaN. Early LEDs had poor brightness and were limited in color range and quality. In 1993 Shuji Nakamura and two colleagues in Japan used a GaN-based semiconductor to invent the blue LED. It made possible the white LED, which revolutionized the lighting industry.

DenBaars, Mishra, and Speck immediately launched a series of studies to better understand GaN crystal growth and determine why Nakamura’s

methods had succeeded. Nakamura came to UCSB in 2000, and since then, GaN has been at the center of SSLEEC technologies.

The GaN layer for early GaN semiconductors was grown on a sapphire substrate, but SSLEEC researchers discovered that GaN grown on a GaN substrate can have as few as 100 to 1000 defects/ cm2 in the crystal. Fewer dislocations mean much greater efficiency, so much so that a single GaNon-GaN chip could replace ten GaN-on-sapphire chips.

GaN-on-GaN semiconductors became possible in 2015, when Mitsubishi Chemicals developed a technique for producing GaN crystals in bulk.

Since then, GaN on GaN has become an SSLEEC signature. Says Nakamura: “It lets us develop new devices that others can’t make.”

The GaN-on-GaN semiconductor was the key to developing brighter LEDs and creating the first high-efficiency LEDs in 2005. It has made possible continued increases in efficiency ever since, and it shows promise for developing high-efficiency electronics for electric cars.

The once “unusable” semiconductor has become a defining point of disctinction.

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Theoretically Speaking: The Physics of Semiconductor Science Breakthrough-yielding laboratory experiments are pursued in parallel with theoretical work that informs and guides the hands-on science. Theory can suggest promising pathways and indicate that others might be dead ends. At the SSLEEC, that means having a thorough grasp of the physics behind the technologies. Professor Chris Van de Walle, who works in computational material science, has spent his thirteen years at UCSB laying the theoretical track to deliver scientific payloads at the SSLEEC. Van de Walle’s work requires “figuring out the properties of materials for electrical and optoelectrical applications. We are doing that at the most basic level, the level of atoms, which means quantum mechanics,” he says. His group has performed calculations required to solve problems related to various semiconductor materials, including gallium nitride (GaN), the common element in a wide range of SSLEEC innovations.

“In my group, we try to put fundamental knowledge in place to help other people make better materials and devices.” he says. “We basically solve the quantum-mechanical problem of how electrons and atoms behave in a solid, and are able to calculate materials properties from first principles.”

As an example, one problem with LEDs is that they are very small and only 30-percent efficient. That’s high compared to other forms of light, and SSLEEC researcher Shuji Nakamura achieved an LED with 50-percent efficiency in 2016, but it is still not nearly 100 percent. That’s a problem because the energy that is not emitted as light is released as heat, and because the semiconductor is so small, it doesn’t have enough surface area to carry the heat away, so a heat sink has to be attached to the bottom of the bulb, making it bigger and more expensive.

Figuring out why the LED has limited efficiency is therefore important, but, according to Van de Walle, “It’s difficult to establish, experimentally, what goes on inside an LED.” So around 2007, he began calculating what happens to the electrons and holes that are injected into the semiconductor material to produce light. The majority of them should combine and generate light but, given the limited efficiency, some of them had to be doing something else. He wondered what that was.

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Artist's rendering of radiative recombination (the pair of green and orange balls with light around them at bottom right) and nonradiative, Auger recombination (the two green balls and single orange ball with dark around them).

One important breakthrough was discovering that a process known as “Auger recombination” can be an important loss mechanism, impeding efficiency in a GaN LED. Sometimes when an electron combines with a hole and a certain amount of energy is generated, instead of being emitted as light, the energy is used by another electron to raise itself to a higher energy state. “That’s a loss mechanism, because it doesn’t result in light being emitted,” Van de Walle explains.

Until that discovery, the conventional wisdom had been that Auger recombination, recognized as a loss mechanism in other semiconductors that emit longer-wavelength, red or infrared, light would not occur in GaN–based semiconductors emitting shorter-wavelength green and blue light.

Calculations performed by Van de Walle’s group showed that assumption to be false, demonstrating not only that Auger recombination also affects the efficiency of green and blue LEDS, but that it becomes increasingly important “as you crank up the current in an LED.”

LED Lighting: Material Brilliance

FOCUS ON: SSLEEC

But for years no one had been able to develop the positive, P-type, GaN. Nakamura and his colleagues were the first to do it, enabling them to produce blue light. The blue LED enabled the white LED, which appeared two years later and has since revolutionized the lighting industry.

Since coming to UCSB in 2000, Nakamura has worked closely with his SSLEEC colleagues to develop brighter and more efficient LEDs. His first GaN LEDs were very bright but only 2-percent efficient. Now, blue LEDS are 84-percent efficient, red LEDs are at about 60 percent, and green are at 30 percent, while the incandescent bulb they are rapidly replacing is still only about 3-percent efficient.

Photo courtesy of SSLEEC

A blue LED glows at the center of a cone encapsulant.

In the early 1990s, few people were thinking about semiconductors as a lighting source, because what had captured their attention was light as a conduit for communication. Infrared was the source of communications used for the internet and for telephone connections. Red LEDs were used in traffic lights and as power indicators in electronic devices, but for little else.

Then, in 1993, after more than a decade of work, Shuji Nakamura and two colleagues in Japan used gallium nitride (GaN), a problematic semiconductor that was out of favor with most LED researchers, to create the first blue LED.

A comparison helps to put the dramatic gains in LED efficiency into perspective. During the past two decades, solar-cell efficiency improved impressively, from 30 percent to just over 40 percent. During the same period, LEDs improved from 2-percent efficiency to a maximum of 84 percent for the most efficient blue LED. A white 50-percent-efficient LED for home use was introduced at Costco in 2014.

In 2007, two new technologies — the first iPhone, which had a color display screen lit by LEDs that were built on GaN-based semiconductor technology developed at UCSB, and LED televisions — drove tremendous new demand, accelerating LEDs into lighting and resulting in multi-billion-dollar markets that drove down the lights’ cost. The same LED light bulb that cost $300 in 2007 costs just $3 today.

“We built our center on solid-state lighting,” DenBaars said in 2017. That decision has proved immensely valuable, in terms of both driving new technology and doing so with immense savings in energy use.”

Emitting light from an LED requires injecting current from both sides of the device. On one side are negatively charged electrons; on the other are positively charged holes. When they meet in the middle, they interact, and the electrons release energy as light.

25 25

The Art of Extraction: Freeing Light from Semiconductors

It seems straightforward enough: materials are combined according to a precise recipe to make a semiconductor light-emitting diode (LED), a current is run through it, and light is emitted. But it’s not as simple as that, mainly because it is extremely difficult to achieve high levels of efficiency in converting electricity to light in an LED. That key parameter of performance has two main components: internal quantum efficiency (IQE), which refers to how effectively electron energy is transformed into photons inside the material; and lightextraction efficiency (LEE), the percentage of photons emitted inside the LED material that make it to the outside as visible light.

Lacking specific architecture, in any LED made of any material and emitting light at any wavelength, LEE is only around ten percent. The rest of the photons remain trapped due to a refraction phenomenon that can cause them to bounce back and forth repeatedly within the LED until the energy is dissipated. The semiconductor boundaries must be engineered to release light to the outside. Achieving that has been the life’s work of Claude Weisbuch, a permanent part-time faculty member who came to UCSB as part of a Regents Professors program in 2002.

As of 2017, Weisbuch had spent 25 years — 15 at UCSB — working to increase the light-extraction efficiency of LEDs. His book on the physics and performance of semiconductor materials, titled Quantum Semiconductor Structures, published in 1991, became a widely used university text. While at Bell Labs from 1979-81, he explained the theory of light emission from quantum wells in semiconductorbased optical devices.

Weisbuch then turned to addressing efficiency “droop,” which refers to the fact that IQE decreases as the current to an LED increases. In short, working with Jim Speck, as well as with colleagues at Ecole Polytechnique in France, his base when not at UCSB, he was able to prove experimentally the existence of the droop mechanism.

Having significantly increased understanding of blueLED performance and its limits, in 2017 Speck and Weisbuch received funding to do the same for green LEDs. They are also seeking new semiconductor structures to address another challenge, which is that higher indium content required for green light produces more powerful internal electric fields, which, in turn, diminish the recombination rate of electrons and holes so that fewer photons are generated and, thus, less light emitted.

“We have the challenge of modeling the electronic and photonic activities, diminishing the electric fields, and then putting those two things together to optimize the structures,” Weisbuch says. “It’s quite complicated but it's also very exciting.”

Phot o co ur

In the late 1990s, thanks to the breakthrough work of fellow SSLEEC researcher Shuji Nakamura, the IQE of blue LEDs was high, but lighting extraction efficiency was 20 percent at best, so only one in five photons generated in the semiconductor material was being emitted as light.

At UCSB, Weisbuch worked to improve LEE by addressing the fact that photons bouncing around in the quantum well of a semiconductor can escape as visible light only by following certain angles of refraction. He developed various techniques to ensure that photons traveled in the right direction.

A green LED fabricated on patterned sapphire.

26 Fall 2017

tesy

of S SLE

EC

FOCUS ON: SSLEEC

Phosphors: Turning Blue Light White

Since 2008, Professor Ram Seshadri, director of the Materials Science Laboratory at UCSB, has worked to ensure that the phosphor is not a source of inefficiency, since efficiency is the whole reason to use an LED. “We want every blue photon that hits the phosphor to be converted to a yellow photon,” he says.

He worked on that for several years, while also developing codified rules for identifying good phosphor materials, to avoid having to test multiple materials that would likely not work.

More recently, Seshadri has been using a blue laser, rather than a blue LED, to excite the phosphors. “The goal is stadium lighting,” he says, “and you can’t do that currently with LEDs.”

Photo courtesy of SSLEEC

One key component for generating white light from an LED is the phosphor, which has nothing to do with the element phosphorus. Rather, it is a material that is applied over the surface of a blue LED. When the blue light source hits the phosphor, some of it is transformed to appropriate complementary colors that enable the totality of the emission to appear white.

A phosphor is a coating applied to a blue LED (like the one shown) to turn blue light white.

By now, Seshadri continues, “The existing materials for LED phosphors are so good that LEDs actually have to catch up with the phosphors. The original goal was to match the way colors are rendered under sunlight. We’ve accomplished that.”

GaN Lasers and Laser-Enabled Technologies Photo courtesy of SSLEEC

A series of edge-emitting laser structures, backlit to make them visible.

The first CD technology used an infrared laser to read the disc. Then Shuji Nakamura and his partners invented the violet laser. It had a shorter wavelength and correspondingly higher frequency and could therefore read much more information much faster.

The violet laser empowered the slightly misnamed BluRay technology. Later, Nakamura, Steve DenBaars, and James Speck found that by doping GaN — adding about 10-percent indium to change the crystal chemistry and add more electrons at the crystal interface — they could change the color of the laser from violet to blue and green.

The optical capacity of early GaN lasers was limited by inherent electric fields related to internal polarization on the GaN crystal. In 2001 Speck began developing non-polar and semi-polar GaN lasers and then worked closely with Nakamura on the problem over the next

several years. They wanted to create GaN-based laser diodes grown on nonpolar planes of the crystal, the so-called “B” and “C” planes, which are free from polarization-related electric fields.

At first, Nakamura recalled in 2017, “The results were very poor; light emission was close to zero.” But in 2006, the team produced the first highly functional non-polar and semi-polar GaN LEDs, fueling an ongoing string of breakthroughs in laser optics.

They also created high-efficiency blue lasers by developing GaN-on-GaN semiconductors (see article on page 23), which had far fewer defects than GaN crystals grown on other substrates. Fewer defects resulted in longer-lasting laser diodes that had ten times the capacity of then-commercially available Bluray players.

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GaN Lasers and Laser-Enabled Technologies (continued) A good amount of current SSLEEC research focuses on developing laser lighting in the expectation that it will eventually replace LED lighting. The first commercial products have appeared in the past few years. One of them, the laser headlight on BMW cars, increases night visibility by seven hundred meters, to a full kilometer. Laser projectors, enabled by laser technology developed at SSLEEC, are now being used in theaters in China and Japan, and laser-based projector televisions are undergoing trials. Projector TVs appeared in the 1990s, but failed because they

were too big and not bright enough. Lasers are incredibly bright. And while current LED TVs can be no thinner than the LED bulbs behind the screen, a laser television is only a screen with an image projected onto it, so it can be wafer thin.

In the not-distant future, large outdoor displays like those in stadiums and city centers will likely be based on laser light rather than LED technology.

Seeking Ultra-Efficient Electric Vehicles In 2017, Professor Umesh Mishra predicted that by 2037, twenty percent of all vehicles on the road would be electric. “When the price of solar panels dropped, solar energy took off,” he said. “When the price of batteries in electric vehicles (EVs) drops, EVs will take off, especially in Brazil, China, and India.”

Mishra is taking a GaN-based approach to enhancing EV efficiency. He uses the Tesla as an example embodying a main challenge — heat — that results from inefficiency in its electrical system, which converts DC power to AC power.

He explains that a 100-watt light bulb generates enough heat to burn your hand, and that ten times that — 100 kilowatts (kW) — is required to power a Tesla or other full-size EV sedan. The energy comes from the battery’s DC current, which is transformed into AC current to drive the motor. At today’s 95-percent efficiency, it generates 5 kW of heat, which will cause parts of the car and the electronics to degrade if not managed effectively.

The current solution to all that heat is a large, heavy cooling system. But, Mishra explained, if it were possible to use GaN transistors to perform DC-to-AC conversion at, say, 99-percent efficiency and, thus, decrease the resulting heat, a car could be designed differently, with air cooling replacing water cooling.

Professor Umesh Mishra

And that, Mishra says, would be a triple win: “The more-efficient battery creates more energy and less heat, which allows the cooling system to be smaller and lighter. That makes the car lighter, so it requires less energy, further extending battery range.”

Research conducted by Mishra and his collaborators has enabled 99.5-percent efficiency to be achieved in EV subsystems, an encouraging indicator that reaching the ambitious goal of designing a 99-percent-efficient system is on the horizon.

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FOCUS ON: SSLEEC

The Industry Connection

“It’s rare to find a center where a group of professors is working closely together on what is effectively a single material system [GaN–based optical electronics and power electronics], and where a group of companies find the research sufficiently applied to be relevant to their business enterprises,” says Tal Margalith (PhD Materials ’02), SSLEEC’s executive director of technology. “We’re working on technology that’s five to ten years out, so companies can look at something in advance and see whether it might make their current technology obsolete.”

Research topics are chosen through a collaborative process. “We’re continually looking to see what is most relevant to our membership,” Margalith says. “We may increase research in one area and then attract membership to enable that. For example, one promising area right now is micro LEDs. The word is out, and companies are coming to us to see where we are on that.”

Engineering II, home to the SSLEEC.

In the SSLEEC’s unique operating model, every dollar of funding comes from a rotating consortium of industry partners. Member companies gain access to faculty researchers and students, and can place a visiting researcher at UCSB, with costs covered by membership fees. They can also acquire intellectual property rights.

“Establishing industrial relevance is great,” he adds. “It brings money for research and ensures that what we're working on is important for someone. We want to make things that people care about.”

LiFi: Lighting Up Data Transfer Speeds Fiber-optic cables carry data at the speed of light. But SSLEEC collaborator John Bowers, director of the UCSB Institute for Energy Efficiency, says that the next chapter in rapid data transmission will be closer to home — i.e. in our light sockets — “as we move from a tethered existence to a wireless one.”

Wi-Fi has advanced tremendously since a rudimentary form of it was introduced in 1991, and the 5G network, expected in 2020, will be a significant next step in terms of bandwidth and download speed. But Li-Fi, which uses LED lights or lasers to transmit wireless communications at blazing-fast speeds, would be much faster, Bowers says.

Because light waves have a much higher frequency than the electromagnetic waves used by Wi-Fi, they transmit faster and can carry more information. A standard LED lightbulb in a Li-Fi system could move data at a up

to 100 megabits per second (Mbps). Laser-based LiFi could reach speeds up to 100 gigabits (Gbps) per second. The relatively snail-like 5G network should boost streaming speeds from 4G’s current 1 or 2 Gbps to 10 Gbps.

“The bottleneck,” Bowers notes, “is getting that high capacity out of the fiber and into the wireless space between the end of the fiber and your laptop, cellphone, or other device.”

The connector to a device used to transmit data at 1 Gbps. Now it’s 10 Gbps. Newer versions will run at 50 and 100 Gbps. Bowers adds, “The antenna in electronic devices does not have that capacity, but we can use Lif-Fi to transmit to our electronic devices at 100 Gbps or higher, and the return path could be wireless.” So you could download a movie in seconds.

Read the full Focus On: SSLEEC articles at:

engr.ucsb.edu/ssleec 29

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Modeling the Movements of Atoms Professor M. Scott Shell's algorithms make it possible to simulate highly complex systems

S

cientists rely heavily on simulations to understand the nature and behavior of molecular systems. Professor M. Scott Shell, in the Department of Chemical Engineering, develops computer simulations to describe how atoms and molecules generate forces that cause them to attract or repel each other and, thus, determine how they rotate, move, and evolve over time. That collective activity gives rise to the properties of everyday materials like water and allows biological molecules to perform their unique and complex functions. Simulations provide a virtual microscope to understand how such complexity emerges, and in turn, how the same biologically inspired behaviors can be used to create novel synthetic materials for a wide range of applications.

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An artist's interpretation of peptides composed of molecular groups in specific patterns self-assembling into functional structures.

Computer simulations provide a detailed picture of every atom in every molecule, as long as the system is small enough. “Sometimes you need only a thousand- or ten-thousand-atom simulation, as in liquid water, because if you simulate more than that, the system starts to look like a sea of the same without providing any new information,” Shell explains.

"Even with supercomputers, computing the activity of a million atoms is a heroic kind of simulation. And there are millions or billions of atoms in many systems we want to study."

But real limits to computing power, and the extensive time required to calculate the dynamic forces between atoms, constrain the ability to simulate systems having millions or billions of atoms.

“For every atom, the program must remember its location and speed, and calculate its interactions with all other atoms [and it must do this repeatedly for incredibly small increments of time], so you quickly start running out of computing power,” Shell explains. “Even with supercomputers, computing the activity of a million atoms is a heroic kind of simulation.”

As an example, Shell says that in a month of 24/7 computing time using the most advanced hardware, it is normally possible to simulate the atomic activity that occurs during only about a millionth of a second in a billionth of a billionth of a liter of water.

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That level of simulation, as incomplete as it may seem, turns out to be sufficient for understanding a wide range of molecular properties, but many more systems of interest — particularly complex molecules that perform biological functions — could be characterized if those limits could be expanded.

Shell went to work on that challenge and for his efforts received the American Institute of Chemical Engineers Computational Molecular Science and Engineering Forum Impact Award in 2017. He was recognized for developing algorithms that allow researchers to move well past the traditional limits of computational modeling and simulate molecular structures and systems that are significantly more complex. The work is based on a theoretical concept called “relative entropy,” for which his group is now well known.

“I’m extremely happy about this award, especially because it comes from a community of people who know my work well and therefore can actually evaluate it in great detail,” Shell said of the recognition.

“When I began as an assistant professor, this idea for relative entropy theory was new and, perhaps, risky. There were three to four years when I didn’t know if it was something people would care about.”

Early Research When Shell arrived at UCSB in 2007, the field of peptides — biological polymer chains of two or more amino acids — was burgeoning.

“Unlike conventional synthetic polymers, such as plastics, you can arrange the sequence of molecular groups along a peptide in a precise pattern,” Shell says. “That’s how nature does it.”

He noted that the ability to control sequences enables substantial control over behavior, because when peptides composed of a particular pattern of molecular groups are dissolved in water, as in the human body, they self-assemble into structures whose shape, properties, and functionality are determined by that pattern. In recent years, efforts have emerged to create biological molecules that are like peptides and have novel sequences that leverage those unique self-assembly properties to program-in new structures.

As an example, he adds, “Say I’ve made a peptide sequence and wonder what nanomaterial shape it will form in solution, or, even more desirable but significantly

In the early 2000s, researchers discovered special patterns of synthetic peptides that, when dissolved in water, self-assemble to form nanomaterials of various shapes — hollow tubes, square platelets, fibers, and spheres, for example. “The systems selfassemble based on the precise patterning that balances all the interactions,” Shell explains. “Understanding the relationship between the sequence patterns and the resulting structures would offer insight into how to engineer nanomaterials precisely.”

more challenging, I want a specific shape and wonder what sequence I should use to achieve it. Tackling that experimentally through trial and error is a long process, so a computational method for understanding what sequences become which structures would be valuable and establish what engineers refer to as ‘design rules.’

"Tackling that experimentally through trial and error is a really long process, so a computational method for understanding what sequences become which structures would be valuable."

“There wasn’t a good theory for how all that worked,” he continues, “and since chemical engineers think about how to predict and

understand soft materials that are driven by thermodynamics and self-assembly processes, and since I had just completed a postdoc in protein-folding simulations, I thought that working to understand some of the underlying design principles would allow us to develop theory to advance the field.”

Given limitations of computing power, Shell realized that to simulate large-scale processes like those associated with selfassembled peptide systems or even the natural molecular processes inside cells would require a new approach. He developed a strategy based on the idea that it’s not necessary to keep track of every atom in a system. His theory allows for a process called “coarse-graining,” in which only the most important atomic motions are identified and simulated, eliminating the need to compute the behavior of millions of individual atoms, without sacrificing accuracy. The secret was figuring out how to get rid of unnecessary details, and a key discovery was realizing that he would need to measure exactly how much information is lost when removing atoms to simplify a system for simulation.

Shell explains: “When a system is coarsegrained, inevitably some information is lost, because you no longer know where all the atoms are. It turns out that the loss can be quantified as a number. The higher the number, the more severe the loss and the more potentially inaccurate the coarsegraining approximation becomes.”

He realized that relative entropy was the correct way to measure information loss in coarse-grained molecular simulations.

Eventually, he was able to create algorithms that minimized relative entropy and, thus, information loss. He could then design accurate coarse-grained models that made it far easier to simulate complex systems.

Professor M. Scott Shell

“That was our hook,” Shell recalls. “We had this thermodynamic perspective that allowed us to simplify systems automatically so that we didn’t have to model the behavior of every atom, and we could therefore achieve significantly more thorough simulations of complicated systems without sacrificing fidelity or realism.” Those approaches, plus other simulation techniques developed by Shell and his students, have broadened understanding of synthetic peptide materials.

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Professor Pradeep Sen (left) and PhD student Steve Bako have worked to reduce the kind of noise that diminishes this image.

Turning Down

34 Fall 2017

The Noise

In 2008, Professor Pradeep Sen began a journey that would forever change digital filmmaking

M

odern films and TV shows are filled with spectacular computer-generated sequences.

Today, those scenes are typically computed (rendered) with a Monte Carlo path-tracer, a program that simulates the paths light follows through a virtual three-dimensional (3D) scene, to produce twodimensional (2D) image frames for the final film. To achieve accurate colors, shadows, and lighting, however, millions of light paths must be computed, which can take a lot of time, up to a week to compute a single frame. It's possible to render images in only a few minutes using just a few light paths, but doing so causes inaccuracies that show up as objectionable “noise� in the final 2D image.

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In 2008, Pradeep Sen, now associate professor in the Electrical and Computer Engineering Department at the UCSB College of Engineering (CoE), saw the problem first-hand while spending a portion of the summer at Sony Pictures Imageworks (SPI). SPI was one of the first studios to try using Monte Carlo path-tracers for film-production, initially on Monster House, and again for Cloudy with a Chance of Meatballs. Sometimes, the Monte Carlo noise was so overwhelming that it was difficult to see what was going on in the scene.

Sen began to think of solutions to the problem.

Although there had been more than two decades

foundation of every high-quality MC denoiser that followed: 1) Rather than using only the final noisy pixel colors for denoising, which makes it hard to distinguish between actual noise and detail, a lot of additional information that was calculated during rendering could be leveraged to improve denoising and 2) The filter would need to be adjusted and this information processed differently for each pixel in order to remove the different kinds of noise that can occur in complex scenes.

Based on these ideas, Sen and Darabi spent the next two years developing what they called Random Parameter Filtering (RPF), the first high-

MC denoising was not something anyone was really studying so this came out of left field and caught many by surprise. of research on ways to reduce this noise, previous approaches were either impractical or ineffective.

Sen was particularly intrigued by the idea of applying a filter to the final image to clean up the Monte Carlo noise, a process now known as Monte Carlo (MC) denoising. Although MC denoising was introduced in the early 1990s, the results were so unsatisfactory that the entire area of research was essentially dropped.

Sen knew that if he could build a filter to remove most of the MC noise from an image rendered in just a few minutes, to produce a high-quality image that looked as if it had been rendered over many days, it would be a game-changer in feature-film production. But when he asked people at SPI and top researchers elsewhere about the potential of MC denoising, everyone said that it would never work, for many reasons. The biggest concern was that, in trying to remove the noise, the filter would blur desired image detail. For high-quality film production, this was unacceptable.

Undeterred, Sen returned to his lab at the University of New Mexico, where he was working, and, with graduate student Soheil Darabi, soon developed the two key ideas that would form the

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quality MC denoiser. When the findings were made public in 2011, they generated a tremendous amount of interest. “People were excited,” Sen recalls. “MC denoising was not something anyone was really studying, so this came out of left field and caught many by surprise.”

Suddenly, MC denoising became a hot area of research, and people around the country began working on systems. Sen, by then at UCSB, and two PhD students, Nima Khademi Kalantari and Steve Bako, began working on the nextgeneration MC denoiser. Their idea was to use machine learning, which had been used to address standard image denoising. But could it be used for Monte Carlo denoising?

Initially, the team considered training an end-toend system to remove MC noise from a rendered image automatically. But that would have required a lot of training data — in this case 3-D scenes — which they did not have. So they simplified the problem by using the filter from the RPF system and replacing the statistical calculations they had used to adjust the RPF filter with a new machinelearning model. The resulting algorithm, called Learning-Based Filtering (LBF), offered a big

Photo courtesy of Pradeep Sen

An image divided into two sectors showing before (top left) and after Monte Carlo noise reduction.

improvement in denoising quality and was published at SIGGRAPH 2015, the leading digital graphics conference. It caught the attention of Disney’s Pixar Animation Studios, which hired Bako as an intern.

“Steve was one of the main architects of the LBF system, which was state-of-the-art at the time,” Sen says. “That made him was one of the world’s leading experts on implementing high-quality MC denoising systems. It’s no wonder Pixar wanted to hire him.”

Together, UCSB and Disney/Pixar built upon the LBF system to develop a deep-learning system that would take in noisy rendered images and directly compute high-quality noise-free images suitable for feature-film production. To train the system, they used millions of examples from the Pixar film Finding Dory, and then tested it on scenes from Cars3 and Coco. Their MC denoiser was able to produce highquality results that were comparable to the final frames in the films, and a paper on that work was published at SIGGRAPH 2017.

Thanks to the work of Sen and his team, MC denoising is now a well-established technique for dramatically reducing Monte Carlo rendering times. The graphics hardware giant NVIDIA recently released an MC denoiser for their interactive Iray path-tracer, and the startup company Innobright was established to develop and market high-end MC denoising algorithms. Most feature-film studios and effects houses have migrated to using path-traced rendering, coupled with MC denoising to reduce render times. In fact, Monte Carlo denoising has been recently credited as one of the two main reasons that Monte Carlo path-tracing has become ubiquitous in feature-film production.

But Sen isn’t satisfied.

“There is still a lot more progress we can make, particularly when dealing with renderings that have very few samples per pixel,” he says. “Improving results in that domain would drastically impact real-time rendering, which is used in video games,” thus improving the interactive experience. Nearly ten years on, Sen continues to turn down the volume on Monte Carlo noise.

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illuminating the Brain

A collaborative group seeks to use long-wavelength light as part of a new optical approach to understanding brain activity Not long ago, a major challenge to understanding brain function was simply gathering and processing the necessary data. Andvanced technology and big data have changed that.Today, says, B. N. Queenan, associate director of the UCSB Brain Initiative,“ The fundamental barrier is the ability to see the brain in action. As neuroscientists, we would love to record all the cells all the time, but that’s not possible with existing technologies, so we need to invent new ways of seeing what brains are up to.”

Now, a multidisciplinary team of researchers including UCSB professors John Bowers and Luke Theogarajan (Electrical and Computer Engineering) and Michael Goard (Molecular, Cellular, and Developmental Biology; Psychological and Brain Sciences) has been awarded $9 million from the National Science Foundation (NSF) to develop and share state-of-the-art optical brain-imaging techniques.

The group of neuroscientists, electrical engineers, molecular biologists, neurologists, bioengineers, and physicists was recognized for its collaborative NEMONIC (NExt generation MultiphOton NeuroImaging Consortium) project, which will push the boundaries of brain imaging by using light to measure brain activity.

The wavelengths of light that the human eye processes do not pass through brain tissue easily. Instead, they bounce off the surface of the brain, the skull, or the skin — which appear opaque — limiting our ability to see internal brain activity. But light with longer wavelengths, can pass through the surfaces unobstructed. NEMONIC employs combinations of longer-wavelength light to reach deeper into the brain and image the activity of cells that have been engineered to glow when stimulated.

The project is one 17 Next Generation Networks for Neuroscience (NeuroNex) awards supported this year within the federal government's BRAIN (Brain Research through Advancing Innovative Neurotechnologies) Initiative. With this award, UCSB becomes a designated NeuroNex Neurotechnology Hub, and a critical part of the national neuroengineering network.

Researchers in the three-part NEMONIC project will develop and share streamlined multiphoton imaging approaches to promote acquisition and exchange of data across the international neuroscience community.

"Current multiphoton microscopy systems are expensive and require significant expertise to build and use," Goard said. "We want to make the process easier, cheaper, and more robust.”

The NEMONIC team will capitalize on UCSB’s expertise in photonics and super-resolution techniques to push the boundaries of optical neuroimaging.

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The Star That Would Not Die Long-lived supernova challenges known theories of how stars die Humans have witnessed the supernova phenomenon thousands of times, and in every case the explosion has signaled the death of a star. Now, astrophysicists at UC Santa Barbara and astronomers at Las Cumbres Observatory (LCO) report a remarkable exception: a star called iPTF14hls that has exploded multiple times over more than fifty years.

The observations, published in the journal Nature, are challenging existing theories of these cosmic catastrophes.

“This supernova breaks everything we thought we knew about how they work,” said lead author Iair Arcavi, a NASA Einstein postdoctoral fellow in UCSB’s Department of Physics and at LCO. “It’s the biggest puzzle I’ve encountered in studying stellar explosions.”

Scientists at the CalTech–led Palomar Transient Factory discovered the supernova in September 2014. Initially, it appeared to be an ordinary supernova, which would be expected to rise to peak brightness and then fade within the span of about a hundred days. The team, observed, however, that after fading, iPTF14hls again grew brighter, and it repeated that behavior at least five times over three years in a phenomenon that had never been seen before.

Examining archival data, the scientists were astonished to find evidence of an explosion at the same location in 1954.

“For me, the most remarkable aspect of this supernova was its long duration,” said co-author Lars Bildsten, director of UCSB’s Kavli Institute for Theoretical Physics. “It certainly puzzled all of us.”

Since the discovery, Bildsten has worked with UC Berkeley astrophysicist Dan Kasen to find an explanation. One possibility is that iPTF14hls is the first observed example of a “pulsational pair instability” supernova. According to theory, the cores of massive stars become so hot that energy is converted into matter and antimatter, causing an explosion that blows off the star’s outer layers but leaves the core intact. The process can repeat over decades before the final explosion, when the star collapses into a black hole.

But, said co-author Andy Howell, a UCSB adjunct faculty member who leads the supernova research group at LCO, “These explosions were expected to be seen only in the early universe and should be extinct now. This is like finding a dinosaur still alive today.”

Artist's representation of a supernova, normally the final act for a star. But iPTF14hls is different.

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The atrium of the new BioEngineering building is home to several functional artworks by Aaron Kramer, who wove together coffee stirrers and thin strips of recycled hardwood to create lamps in the biomorphic shapes of red blood cells.

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