Top 12 in 2012

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Top 12 in 2012
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Credit: Benjamin Deverman/Caltech

Gene therapy for boosting nerve-cell repair

Caltech scientists have developed a gene therapy that helps the brain replace its nerve-cell-protecting myelin sheaths—and the cells that produce those sheaths—when they are destroyed by diseases like multiple sclerosis and by spinal-cord injuries. Myelin ensures that nerve cells can send signals quickly and efficiently.

Credit: L. Moser and P. M. Bellan, Caltech

Understanding solar flares

By studying jets of plasma in the lab, Caltech researchers discovered a surprising phenomenon that may be important for understanding how solar flares occur and for developing nuclear fusion as an energy source. Solar flares are bursts of energy from the sun that launch chunks of plasma that can damage orbiting satellites and cause the northern and southern lights on Earth.

Coincidence—or physics?

Caltech planetary scientists provided a new explanation for why the "man in the moon" faces Earth. Their research indicates that the "man"—an illusion caused by dark-colored volcanic plains—faces us because of the rate at which the moon's spin rate slowed before becoming locked in its current orientation, even though the odds favored the moon's other, more mountainous side.

Choking when the stakes are high

In studying brain activity and behavior, Caltech biologists and social scientists learned that the more someone is afraid of loss, the worse they will perform on a given task—and that, the more loss-averse they are, the more likely it is that their performance will peak at a level far below their actual capacity.

Credit: NASA/JPL-Caltech

Eyeing the X-ray universe

NASA's NuSTAR telescope, a Caltech-led and -designed mission to explore the high-energy X-ray universe and to uncover the secrets of black holes, of remnants of dead stars, of energetic cosmic explosions, and even of the sun, was launched on June 13. The instrument is the most powerful high-energy X-ray telescope ever developed and will produce images that are 10 times sharper than any that have been taken before at these energies.

Credit: CERN

Uncovering the Higgs Boson

This summer's likely discovery of the long-sought and highly elusive Higgs boson, the fundamental particle that is thought to endow elementary particles with mass, was made possible in part by contributions from a large contingent of Caltech researchers. They have worked on this problem with colleagues around the globe for decades, building experiments, designing detectors to measure particles ever more precisely, and inventing communication systems and data storage and transfer networks to share information among thousands of physicists worldwide.

Credit: Peter Day

Amplifying research

Researchers at Caltech and NASA's Jet Propulsion Laboratory developed a new kind of amplifier that can be used for everything from exploring the cosmos to examining the quantum world. This new device operates at a frequency range more than 10 times wider than that of other similar kinds of devices, can amplify strong signals without distortion, and introduces the lowest amount of unavoidable noise.

Swims like a jellyfish

Caltech bioengineers partnered with researchers at Harvard University to build a freely moving artificial jellyfish from scratch. The researchers fashioned the jellyfish from silicon and muscle cells into what they've dubbed Medusoid; in the lab, the scientists were able to replicate some of the jellyfish's key mechanical functions, such as swimming and creating feeding currents. The work will help improve researchers' understanding of tissues and how they work, and may inform future efforts in tissue engineering and the design of pumps for the human heart.

Credit: NASA/JPL-Caltech

Touchdown confirmed

After more than eight years of planning, about 354 million miles of space travel, and seven minutes of terror, NASA's Mars Science Laboratory successfully landed on the Red Planet on August 5. The roving analytical laboratory, named Curiosity, is now using its 10 scientific instruments and 17 cameras to search Mars for environments that either were once—or are now—habitable.

Credit: Caltech/Michael Hoffmann

Powering toilets for the developing world

Caltech engineers built a solar-powered toilet that can safely dispose of human waste for just five cents per use per day. The toilet design, which won the Bill and Melinda Gates Foundation's Reinventing the Toilet Challenge, uses the sun to power a reactor that breaks down water and human waste into fertilizer and hydrogen. The hydrogen can be stored as energy in hydrogen fuel cells.

Credit: Caltech / Scott Kelberg and Michael Roukes

Weighing molecules

A Caltech-led team of physicists created the first-ever mechanical device that can measure the mass of an individual molecule. The tool could eventually help doctors to diagnose diseases, and will enable scientists to study viruses, examine the molecular machinery of cells, and better measure nanoparticles and air pollution.

Splitting water

This year, two separate Caltech research groups made key advances in the quest to extract hydrogen from water for energy use. In June, a team of chemical engineers devised a nontoxic, noncorrosive way to split water molecules at relatively low temperatures; this method may prove useful in the application of waste heat to hydrogen production. Then, in September, a group of Caltech chemists identified the mechanism by which some water-splitting catalysts work; their findings should light the way toward the development of cheaper and better catalysts.

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In 2012, Caltech faculty and students pursued research into just about every aspect of our world and beyond—from understanding human behavior, to exploring other planets, to developing sustainable waste solutions for the developing world.

In other words, 2012 was another year of discovery at Caltech. Here are a dozen research stories, which were among the most widely read and shared articles from Caltech.edu.

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H. Jeff Kimble to Receive Quantum Physics Award

The German Physical Society (Deutsche Physikalische Gesellschaft, or DPG) and the Optical Society of America (OSA) have selected Caltech physics professor H. Jeff Kimble to receive the Herbert Walther Award for his "pioneering experimental contributions to quantum optics, cavity quantum electrodynamics, and quantum information science."

"It is a special honor for me to receive this award since I have the greatest respect for Professor Walther, beginning when we first met when I was a graduate student and continuing over almost 30 years as scientific colleagues and competitors," says Kimble, William L. Valentine Professor and professor of physics at Caltech. "Walther made historic contributions to physics that have shaped the future that we now all enjoy."

The Herbert Walther Award highlights scientific contributions in quantum optics and atomic physics and recognizes individuals for their efforts to promote excellence in the international scientific community. Kimble will accept the award at the Laser World of Photonics Conference in Munich, Germany, in May 2013.

Kimble became a professor of physics at Caltech in 1989. He was named Valentine Professor in 1997 and director of the Institute for Quantum Information and Matter at Caltech in 2011. He has cemented his reputation in quantum optics through discoveries relating to quantum measurement and quantum information science.

Kimble's research has led to greater understanding of novel quantum states of the electromagnetic field, such as "squeezed" and "antibunched" light. His demonstration in 1995 of a quantum phase gate that operated at the single photon level and was suitable for the implementation of rudimentary quantum logic has been considered seminal in establishing the experimental foundations of quantum information science. Kimble and his colleagues have also made important contributions to theoretical physics, including a new paradigm for the realization of distributed quantum networks.

The Herbert Walther Award was first given by the DPG and OSA in 2007. The namesake of the award, Herbert Walther, was a well-known scientist and educator from the Max Planck Institute for Quantum Optics (of which he was founding director) and Ludwig Maximilians University, Munich, who made significant contributions to the field of laser physics and optics; he passed away in 2006. Past recipients of the award include Alain Aspect, Marlan O. Scully, Serge Haroche, and David J. Wineland.

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The Miracle and Beauty of Physics: An Interview with Cliff Cheung

When you lift a paper clip off a table with a small magnet, you're accomplishing a remarkable feat: the tiny magnet is overcoming the gravitational pull from the entire Earth. Why does gravity seem so weak compared to electromagnetism and the other fundamental forces of nature? This vast discrepancy in scale—how a small magnet can beat out a whole planet—is related to what physicists call the hierarchy problem.

Cliff Cheung—who joined Caltech this fall as an assistant professor of theoretical physics—is fascinated by this "very deep puzzle" (which may be solved through supersymmetry, a class of theories in which every fundamental particle has a partner particle, as well as by dark matter, the mysterious stuff that accounts for nearly a quarter of the universe). Recently, Cheung—who also plays guitar and piano, sings, and writes music—answered a few questions about coming to Caltech and his passion for physics.

What are you looking forward to about Caltech?

The environment here is fantastic. Caltech puts a lot of firepower behind a very small number of people. It's like having an academic steamroller on your side, so to speak. In my case, Caltech has been incredibly generous and supportive in all respects so far.

I'm super excited to be joining the theory group in particular, which is a powerhouse in a range of topics, including particle physics, cosmology, and string theory. Personally, it's surreal and humbling to be here given Caltech's legendary physics legacy.

Why do you think physics is exciting?

It works. When I was a student seeing the Standard Model [the theory of how all fundamental particles behave and interact] for the first time, I remembering thinking, this theory is very strange and very alien. But then you actually start calculating and you see what it predicts—and it works! There's a certain miracle in being able to write down something on a piece of paper which explains almost every experiment on record. That miracle is what excites a lot of us.

When someone writes down a formula or a theory, any physicist worth his salt can judge: is this beautiful or is this ugly? Equations that describe the universe can have a certain kind of elegance or they may not. In this sense, the ideas that we discuss have an intrinsic beauty.

That sense of beauty seems to emphasize the point that science, and physics in particular, is a very human endeavor.

That's right. It's much less cold than you think. This isn't meant to detract from what we do, but there is a certain subjectivity that I think is a very good thing. The fact that there are experiments to keep us honest is essential—at least for a particle physicist like myself. But at the same time we can enjoy the beauty of the models we write down

How did you become interested in physics?

I've had a couple of formative experiences. When I was in high school there was this wonderful program at Columbia University where you took a test and if you passed they let you take a class on the weekends. It's what nerds do. Anyway, I remember taking this class on special relativity, which to a high-school student is eye opening, but not so foreign as to be disconcerting. Special relativity is really just mechanics, but with a twist. Seeing these ideas for the first time made me think, I want to do this

This experience connected with me because I felt like I could really see the history as I learned the physics. I imagined Einstein in a room, writing down the equations for his gedanken [thought] experiments and I realized that just by thinking, it was possible to determine tangible and deep facts about the world around us. That's a pretty powerful thing. Learning that this was possible—that you could come up with the rules without actually playing the game—was absolutely amazing to me. You just had to use your brain. 

Born in Cleveland, Cheung grew up in the suburbs of New York City. He went on to Yale, where he received his BS in 2004. He finished his PhD from Harvard in 2009, before spending the past few years at UC Berkeley and Lawrence Berkeley National Laboratory as a postdoc.

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A Sky Full of Planets

Think back to the last time you saw the Milky Way—that faint stripe of stars that thickens and brightens as you get farther from city lights. At least 200 billion stars fill the Milky Way, our galaxy. How many planets might orbit those stars? What would those worlds be like? Twenty years ago, it was anybody's guess.  

In the 1990s, astronomers began to discover planets around other stars—so-called exoplanets. Since then, the confirmed count of exoplanets has skyrocketed to more than 850, with thousands of candidates awaiting follow-up. Astronomers now estimate that the stars in our Milky Way have an average of at least one planet each. (The next time you look up into the night sky, think about that.)

The sudden prospect of characterizing so many solar systems in our own galaxy has brought together two once-isolated camps: planetary scientists, who generally focus on the inside of our solar system, and astronomers, who mostly look beyond it. Planetary scientists see an opportunity to learn about our solar system and its origins by putting it into the context of a huge ensemble of other solar systems, and astronomers have a keen interest in what planetary scientists might help them discover about planet formation on a galactic or even larger scale.

To those ends, nine Caltech astronomers and planetary scientists are forming a Center for Planetary Astronomy. Joining together in a single research center will help them maintain fruitful collaborations, collectively attract research funding and fellowships for young scholars, and recruit top students and postdoctoral scholars.

The nascent center's members bring complementary perspectives to the characterization of our newly discovered neighbors. Planetary science professor Geoff Blake, astronomy professor Lynn Hillenbrand, and senior research associate John Carpenter study planet-forming disks of gas and dust around young stars. Mike Brown, the Richard and Barbara Rosenberg Professor and professor of planetary astronomy, and Caltech's infamous Pluto-killer, studies fossil rubble from just such a disk—a fantastic array of thousands of planetesimals and chunks of rock and ice on the fringes of our solar system, known as the Kuiper belt, that yields clues to the primordial solar system. The remaining scientists are focused more on the planets themselves. John Johnson, an assistant professor of planetary astronomy, focuses on the detection and characterization of exoplanets, searches for worlds like Earth, and investigates how stars' masses affect planet formation by studying the relationships between exoplanets and the very different types of stars that they orbit. Heather Knutson, an assistant professor of planetary science, characterizes exoplanets' compositions, temperatures, atmospheres, and even their weather. Yuk Yung, the Smits Family Professor of Planetary Science, studies the atmospheres of planets, and Dave Stevenson, the Marvin L. Goldberger Professor of Planetary Science, studies planetary interiors and how they evolve. Gregg Hallinan, an assistant professor of astronomy, is trying to detect radio signals from exoplanets, which would indicate the presence of magnetic fields that could be a signature of habitability.

The center's members are excited about its potential contribution to the major discoveries that are sure to come in this field. "The unique combination of Caltech's top-ranked astronomical facilities, astronomy program, and planetary science program will allow us to access the deep and broad knowledge about planets and planetary systems that only comes from such a joint endeavor," says Brown.

Says Knutson, "I was trained as an astronomer, but what I do is planetary science. Caltech is one of the few places where we have great conversations between the two groups. And Caltech's resources, in terms of telescopes, give us the opportunity to move quickly and think big." 

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High-Energy Physicists Smash Records for Network Data Transfer

New methods for efficient use of long-range networks will support cutting-edge science

PASADENA, Calif.—Physicists led by the California Institute of Technology (Caltech) have smashed yet another series of records for data-transfer speed. The international team of high-energy physicists, computer scientists, and network engineers reached a transfer rate of 339 gigabits per second (Gbps)—equivalent to moving four million gigabytes (or one million full length movies) per day, nearly doubling last year's record. The team also reached a new record for a two-way transfer on a single link by sending data at 187 Gbps between Victoria, Canada, and Salt Lake City.

The achievements, the researchers say, pave the way for the next level of data-intensive science—in fields such as high-energy physics, astrophysics, genomics, meteorology, and global climate tracking. For example, last summer's discovery at the Large Hadron Collider (LHC) in Geneva of a new particle that may be the long-sought Higgs boson was made possible by a global network of computational and data-storage facilities that transferred more than 100 petabytes (100 million gigabytes) of data in the past year alone. As the LHC continues to slam protons together at higher rates and with more energy, the experiments will produce an even larger flood of data—reaching the exabyte range (a billion gigabytes).

The researchers, led by Caltech, the University of Victoria, and the University of Michigan, together with Brookhaven National Lab, Vanderbilt University, and other partners, demonstrated their achievement at the SuperComputing 2012 (SC12) conference, November 12–16 in Salt Lake City. They used wide-area network circuits connecting Caltech, the University of Victoria Computing Center in British Columbia, the University of Michigan, and the Salt Palace Convention Center in Utah. While setting the records, they also demonstrated other state-of-the-art methods such as software-defined intercontinental networks and direct interconnections between computer memories over the network between Pasadena and Salt Lake City.

"By sharing our methods and tools with scientists in many fields, we aim to further enable the next round of scientific discoveries, taking full advantage of 100-Gbps networks now, and higher-speed networks in the near future," says Harvey Newman, professor of physics at Caltech and the leader of the team. "In particular, we hope that these developments will afford physicists and students throughout the world the opportunity to participate directly in the LHC's next round of discoveries as they emerge."

As the demand for "Big Data" continues to grow exponentially—both in major science projects and in the world at large—the team says they look forward to next year's round of tests using network and data-storage technologies that are just beginning to emerge. Armed with these new technologies and methods, the Caltech team estimates that they may reach 1 terabit-per-second (a thousand gbps) data transfers over long-range networks by next fall. 

More information about the demonstration can be found at http://supercomputing.caltech.edu/.
 

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Tuesday, April 9, 2013
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Caltech Faculty Named AMS Fellows

Nine members of Caltech's faculty have been named to the inaugural class of Fellows of the American Mathematical Society (AMS). According to the AMS, the distinction recognizes members of the society "who have made outstanding contributions to the creation, exposition, advancement, communication, and utilization of mathematics." There are 1,119 Fellows in the inaugural class from more than 600 institutions.

Caltech's Fellows are

Tom Apostol, Professor of Mathematics, Emeritus

Michael Aschbacher, Shaler Arthur Hanisch Professor of Mathematics

Danny Calegari, Richard Merkin Distinguished Professor of Mathematics

Yizhao Thomas Hou, Charles Lee Powell Professor of Applied and Computational Mathematics

Alexander Kechris, Professor of Mathematics

Wilhelmus Luxemburg, Professor of Mathematics, Emeritus

Hirosi Ooguri, Fred Kavli Professor of Theoretical Physics and Mathematics

Dinakar Ramakrishnan, Taussky-Todd-Lonergan Professor of Mathematics

Barry Simon, International Business Machines Professor of Mathematics and Theoretical Physics

"I'm delighted that the American Mathematical Society has recognized so many of our mathematics faculty for inclusion in their first class of Fellows," says Tom Soifer, chair of the Division of Physics, Mathematics and Astronomy. "This is a clear recognition of the quality and stature of our mathematics faculty by the world's largest and most influential society for mathematical research and education."

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Caltech Mourns the Passing of Wallace L. W. Sargent

 

Wallace "Wal" Sargent passed away on October 29 at the age of 77. He was the Ira S. Bowen Professor of Astronomy, Emeritus, at Caltech. He was an outstanding observational astronomer at the forefront of spectroscopy for over 50 years during an immensely productive and distinguished career. He began his career at the Institute as a research fellow in Astronomy from 1959 to 1962. He returned as an assistant professor in 1966, becoming full professor in 1971 and Bowen Professor in 1981. Sargent served as Caltech's executive officer of astronomy from 1975 to 1981 and again from 1996 to 1997 and as the director of Palomar Observatory from 1997 to 2000.

Sargent was born in 1935 in Elsham, United Kingdom, and he was the first pupil of the Scunthorpe Technical High School to go to a university. He entered the University of Manchester in 1953, where he earned his bachelor's, master's, and PhD degrees, as well as becoming a lifelong supporter of Manchester United. It was shortly after graduation that Sargent came to Caltech as a research fellow. From 1962 to 1964 he was a senior research fellow at the Royal Greenwich Observatory, where he met and married astronomer Anneila Sargent (née Cassells), now the Benjamin M. Rosen Professor of Astronomy at Caltech and the vice president for student affairs.

Perhaps the most remarkable aspect of Sargent's contributions to astrophysics is the range of subjects in which he made fundamental advances. Among his accomplishments were the demonstration that most of the helium in the universe was produced in the Big Bang with which the universe began (with Leonard Searle), the first dynamical evidence for the presence of supermassive black holes at the centers of galaxies (with his student Peter Young), the measurement of the mass of the Milky Way Galaxy using the radial velocities of outer satellites, the discovery that most nearby galaxies harbor low-luminosity nuclear activity, and illuminating studies on the emission from quasars and Seyfert galaxies.

As varied as Sargent's scientific accomplishments have been, there is one area of astrophysics where he both pioneered the field and has remained in the forefront to this day: the astrophysics of the diffuse intergalactic medium and the chemical history of the universe. This field gave us the first glimpses of the high-redshift universe at a time when normal galaxies could only be seen to small cosmological distances.

Sargent is considered the father of quasar absorption line spectroscopy. Using innovative new astronomical detectors developed by his collaborator, Alec Boksenberg, Sargent explored the gas permeating the high-redshift universe. Sargent had the foresight to recognize the advantages for faint-object spectroscopy of a new kind of  electronic detector, the Image Photon Counting System, developed by Boksenberg at University College London. The Sargent-Boksenberg partnership—"Boksenberg's Flying Circus" as Sargent affectionately dubbed it—revolutionized the field by carrying out the first statistically rigorous surveys of  quasar absorption systems. Sargent, with Boksenberg and their collaborators, gave us a key physical insight into the nature of the material between galaxies and brought to the fore the importance of this technique for observational cosmology. They used this information to understand how the material of which we are made has evolved since the first galaxies formed.

Sargent led the second Palomar Observatory Sky Survey, a photographic survey of the entire northern sky that was converted to a digital image format so that it could be analyzed via computers. This process produced a catalog of over 50 million galaxies and half a billion stars, including tens of thousands of quasars, and was a model for the many surveys that have followed using CCDs.

Sargent was a leader in the development of the W. M. Keck Observatory, coleading its science steering committee during the observatory's crucial formative years. With the advent of the Keck telescopes, he capitalized on the new powerful instruments on the world's largest telescopes to extend his research to probe the material between galaxies to the farthest reaches of the universe. Sargent established the existence of metals, the products of stellar nucleosynthesis, in the intergalactic medium only a billion years or so after the Big Bang. This research is helping us to identify and understand the first stars to form in the infant universe, which will be the targets of the next generation of telescopes.

In addition to his research, Sargent had a major influence on astronomy as an educator, particularly through the string of brilliant, accomplished graduate students that he mentored during his career.

Chuck Steidel (PhD '90), the Lee A. DuBridge Professor of Astronomy at Caltech, was a graduate student of Sargent's in the late 1980s and remembers his ability to inject humor into any situation that was in danger of becoming overly serious. "This was quite necessary for calming a young graduate student such as myself," admits Steidel. "Our conversations would almost always end up on a topic other than my thesis—baseball, music, literature, sumo wrestling. Looking back it is hard to recall ever receiving direct advice from Wal, and yet somehow he profoundly influenced the way I view science. As a colleague, Wal has been just as important to me," continues Steidel. "Wal will be missed for much more than his scientific accomplishments."

Alex Filippenko (PhD '84), a professor of astronomy at the University of California, Berkeley, was also mentored by Sargent during his graduate studies at Caltech. At the end of a five-night observing run at Palomar Observatory in 1985 they made a chance discovery of a new type of supernova, and although Sargent had studied supernovae many years earlier, Filippenko recalls that Sargent gave him the lead in the analysis and publication of their results. "This literally changed my career," Filippenko says. "Wal always encouraged his students to capitalize on exciting opportunities that came their way."

Sargent has received many honors—he was named a fellow of the American Academy of Arts and Sciences in 1977, a fellow of the Royal Society in 1981, and a member of the National Academy of Sciences in 2005. He was awarded the Helen B. Warner Prize of the American Astronomical Society in 1969, gave the George Darwin Lecture of the Royal Astronomical Society in 1987, received the Dannie Heineman Prize of the American Astronomical Society and the American Institute of Physics in 1991, received the Catherine Wolfe Bruce Medal of the Astronomical Society of the Pacific in 1994, and was the Henry Norris Russell Lecturer of the American Astronomical Society in 2001. Sargent was a member of more than 30 review and prize committees over the span of his career and a visiting fellow at observatories around the world, from Australia to Europe to Berkeley, California.

Sargent is survived by his wife, Anneila Sargent; two daughters, Lindsay Eleanor Berg and Alison Clare Hubbs; sons-in-law Henry Berg and Dan Hubbs; and four grandsons—Patrick and Charlie Hubbs and Angus and Eric Berg. A public memorial reception will be held at a later date.

Donations can be made in memory of Wallace L. W. Sargent here.

 

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Two Faculty Members Named Packard Fellows

Two Caltech faculty members have been awarded Packard Fellowships for Science and Engineering. Biologist Alexei Aravin and astronomer John Johnson each were awarded $875,000, to be distributed over five years.

"I'm very excited about this fellowship," says Aravin, an assistant professor of biology. "It will allow my lab to pursue new, ambitious goals that are difficult to fund using traditional sources."

Aravin studies RNA molecules, which encode the information contained in genes to help create proteins. His lab is probing the mechanisms that determine the stability and fate of RNA. He's also trying to figure out how noncoding RNA—which doesn't encode information but nevertheless plays crucial roles in the cell—functions and is produced.

Johnson's research focuses on discovering and characterizing planets around other stars. "My broad goals," he says, "are to gain a better understanding of planet formation, place our solar system in a broader galactic context, and eventually find places in the galaxy where other life forms might reside." He plans to use the money to help support postdocs in his research group and to start a visitor program in which scientists from other institutions are invited to brainstorm and collaborate.

Johnson, an assistant professor of astronomy, was meeting with a student when he got the phone call notifying him of the award. "I don't remember my exact reaction, but it certainly startled the poor student," he says. "I spent the rest of the day grinning like an idiot."

According to the Packard Foundation, the fellowships were established in 1988 to allow promising professors to pursue research early in their careers with few funding and reporting constraints. Each year, presidents from 50 universities each nominate two early-career professors for the fellowship. A panel of scientists and engineers then select 16 fellows. To date, there have been more than 400 professors who have received Packard Fellowships. Aravin and Johnson join 26 members of current and past Caltech faculty who have been named Packard Fellows.

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Noted Physicist Robert F. Christy Dies

Robert F. Christy, one of the last people alive to have worked on the Manhattan Project—which created the atomic bomb during World War II—and whose later research in astrophysics contributed to our understanding of the size of the universe, passed away on October 3 at his home in Pasadena. The former provost and acting president of the California Institute of Technology (Caltech), where he was a longtime professor, was 96 years old.

Christy was credited with designing the explosive core of the first atomic bomb.

"Robert Christy was one of the founders of a very important area of astrophysical research and a major figure at Caltech in the postwar era," says B. Thomas Soifer, professor of physics and chair of the Division of Physics, Mathematics and Astronomy (PMA) at Caltech. "Bob was an outstanding theoretical physicist; his contributions to scientific research, to public policy—and his leadership—helped in shaping what Caltech is today."  

Christy was born in Vancouver, British Columbia, and entered the University of British Columbia (UBC) in 1932 as a 16-year-old sophomore. He graduated in 1935 at the age of 19 with a bachelor's degree in physics, then stayed for two more years at UBC to earn a master's degree in physics and mathematics in 1937, after which he moved to the UC Berkeley, where he studied physics as a graduate student of J. Robert Oppenheimer, also known as the "father of the atomic bomb."

After earning his degree in 1941, Christy was hired to teach at the Illinois Institute of Technology. In the fall of 1941 he was invited to join the Manhattan Project; he started in January of 1942, working with Eugene Wigner at the University of Chicago on the theory of atomic chain reactions. When Enrico Fermi and his team moved to the University of Chicago in March, he asked Christy to work with him on experimental "exponential piles" (chain-reacting systems that were too small to fully chain-react). In the winter of 1942, Christy helped build the first nuclear reactor, Chicago Pile-1, before being invited to Los Alamos by Oppenheimer in early 1943. He also helped design the reactors at Hanford where the plutonium was to be made.

Notably, Christy was involved in the creation of the plutonium core ("pit") of the implosion weapon designed at Los Alamos. The Los Alamos team's idea for the plutonium bomb was to embed a mass of nuclear fuel (specifically, plutonium) within a hollow sphere of high-explosive lenses; when the explosives were detonated, the nuclear fuel would implode into a dense "critical" mass, triggering a chain reaction that would lead to a nuclear explosion. However, the team soon realized, if the shape of the core became unstable and deviated from a perfect sphere, the bomb might fizzle out and fail to explode.

Christy's design of the Pu core consisted of a nearly solid sphere of plutonium metal of slightly less than critical mass, with a small central cavity containing an "initiator" that supplied neutrons to get the fission reaction started as the core imploded. When compressed hard enough, the atoms would be forced close enough together to achieve critical mass, through a process known as fast criticality, triggering the chain reaction and a nuclear blast. This is the design (referred to as the "Christy Gadget" at Los Alamos at the time; the word "bomb" wasn't used by Manhattan Project scientists) that was used in the Trinity bomb test and in the weapon ("Fat Man") dropped on Nagasaki on August 9, 1945.

Following the war, Christy initially returned to the University of Chicago. In 1946, on the recommendation of Oppenheimer, he was hired at Caltech as an associate professor of physics, doing work in theoretical physics and nuclear physics, including the study of cosmic rays. He became a professor of theoretical physics in 1950; Institute Professor of Theoretical Physics in 1983; and Institute Professor, Emeritus, in 1986.

"When I first arrived at Caltech in September 1949," recalls Ward Whaling, Caltech professor of physics, emeritus, and Christy's colleague for more than six decades, "fall classes had not started and the PMA division office could find no one to show me around the Kellogg Radiation Laboratory except a young theoretical physicist named Christy. I had never heard of him—his Los Alamos achievements would remain classified for years—but the prospect of being shown the lab by a theoretical physicist was depressing. Boy, was I wrong! I quickly learned that Bob Christy was quite familiar with that part of the new lab that had already been installed—to replace the wartime weapons-testing facility and an earlier X-ray therapy clinic—and he also knew what was being planned for the future. Later, when I began my own research using the accelerators he had shown me that first day, I learned that he regularly visited the lab, maybe two or the times a week, in the afternoon, with his hands clasped behind his back, just looking, sometimes asking a question, but taking care not to interrupt serious work." As Christy noted in a 1994 oral history interview with the Caltech Archives, "I was an unusual theorist in that my greatest strength was . . . in seeing how theory and experiment related."

In 1960, Christy turned his attention Cepheid variable stars, which had long been used as a so-called standard candle with which to measure distances to other galaxies because their pulsation rate varies with their intrinsic brightness.

At the time "it was unknown why they varied, what made them vary," explained Christy in his oral history. "It was known that they were apparently spherical pulsators. That is, they expanded and contracted—a regular expansion and contraction in spherical symmetry. I thought: Well, this is very much like the spherical hydrodynamics in implosion," he said. "It's basically the same equations we had used—of course, with different substances—but the mathematical approach was very similar to what we had been working on at Los Alamos." The mathematical model that Christy developed helped explain why the stars vibrated and earned him the Royal Astronomical Society's Eddington Medal in 1967. He was elected to the National Academy of Sciences in 1965.

"Christy's analysis of how Cepheid stars pulsate enabled him to say definitively, when a star pulsates at a certain rate, just how bright it would be if we were close to it," says Kip S. Thorne, Richard P. Feynman Professor of Theoretical Physics, Emeritus, at Caltech. "Astronomers could then compare that with how bright the star looks through their telescopes and deduce how far away the star is—the dimmer it appears, the farther it must be. This was crucial in determining the size of our galaxy and thence, combined with much other data, the size of the universe."

Christy held several administrative posts during his tenure at Caltech, including as executive officer for physics from 1968 to 1970, Caltech's faculty chair from 1969 to 1971, vice president and provost from 1970 to 1980, and, when Institute president Harold Brown left to become secretary of defense under Jimmy Carter, as acting president of the Institute from 1977 to 1978.

Because of his wartime experience, Christy was a longtime opponent of the further development of nuclear weapons. In the summer of 1945, he became one of the founding members of the Association of Los Alamos Scientists (ALAS) and helped draft a statement about educating the public on how to manage atomic energy for peaceful uses. He was one of 10 Caltech physicists who had participated in the bomb-building at Los Alamos who signed and paid for a full-page ad that ran in the Los Angeles Times on October 14, 1956, calling for an end to nuclear weapons tests.

In the mid-1980s, Christy became a member of the National Research Council's Committee on Dosimetry, which studied the radiation effects of the Hiroshima and Nagasaki bombs. "He worked on the bomb in good faith, because he wanted to save lives, and he was proud that the work that he'd done helped the war come to an end," says Christy's widow, I.-Juliana Sackmann Christy. "But he later referred to nuclear weapons as 'killing machines.' He was a man of principle."

A skilled dancer who loved to sing, Christy was an avid horseman and learned to ride from Robert Oppenheimer, who gave him his first "half a horse" to lure him to join the Manhattan Project, says Mrs. Christy. "Another scientist owned the other half, and the two often argued about who had the front and who had the back," she says. Christy continued to ride until he was well into his 90s—and after losing his eyesight—on his 240-acre ranch in Ventura County.

Christy is survived by Juliana, his second wife; two daughters, Ilia Juliana Christy and Alexandra Roberta Christy; two sons from his first marriage to Dagmar Elizabeth von Lieven, Thomas Edward "Ted" Christy and Peter Robert Christy; and five grandchildren. Services will be held at 1:30 p.m. on October 20, 2012, at Mountain View Cemetery in Altadena, California.

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Kathy Svitil
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Caltech Mourns the Passing of Robert Christy
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