Study of Aerosols Stands to Improve Climate Models

Aerosols, tiny particles in the atmosphere, play a significant role in Earth's climate, scattering and absorbing incoming sunlight and affecting the formation and properties of clouds. Currently, the effect that these aerosols have on clouds represents the largest uncertainty among all influences on climate change.

But now researchers from Caltech and the Jet Propulsion Laboratory have provided a global observational study of the effect that changes in aerosol levels have on low-level marine clouds—the clouds that have the largest impact on the amount of incoming sunlight that Earth reflects back into space. The findings appear in the advance online version of the journal Nature Geoscience.

Changes in aerosol levels have two main effects—they alter the amount of clouds in the atmosphere and they change the internal properties of those clouds. Using measurements from several of NASA's Earth-monitoring satellites from August 2006 through April 2011, the researchers quantified for the first time these two effects from 7.3 million individual data points.

"If you combine these two effects, you get an aerosol influence almost twice that estimated in the latest report from the Intergovernmental Panel on Climate Change," says John Seinfeld, the Louis E. Nohl Professor and professor of chemical engineering at Caltech. "These results offer unique guidance on how warm cloud processes should be incorporated in climate models with changing aerosol levels."

The lead author of the paper, "Satellite-based estimate of global aerosol-cloud radiative forcing by marine warm clouds," is Yi-Chun Chen (Ph.D. '13), a NASA postdoctoral fellow at JPL. Additional coauthors are Matthew W. Christensen of JPL and Colorado State University and Graeme L. Stephens, director of the Center for Climate Sciences at JPL. The work was supported by funding from NASA and the Office of Naval Research.

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Sink or Swim: Students Prep for RoboSub Competition

For the past year, a team of Caltech students has been meeting at the campus pool on Sunday afternoons to prepare for a competition—but they haven't been shooting for faster lap times or flip turns. Advised by professor Joel Burdick of the Division of Engineering and Applied Science, the students on the Caltech Robotics Team have been carefully crafting and optimizing their robotic submarine named Bruce—the team's entry in the 17th Annual International RoboSub Competition.

At the competition, which will take place in San Diego this week, Bruce and 38 competitors from around the world will be scored on how many tasks they can complete in 25 minutes. On their own, the tasks—pulling a lever, parking between two poles, and shooting little torpedoes at a target, for example—seem relatively simple. However, as a completely autonomous robot, Bruce is programmed to perform these tasks without the help of a human operator; when the competition begins, the team will hand Bruce over to a professional diver who will place the robot in the water and flip a switch.

The Caltech team is no stranger to competition—its robotic rover placed second in a 2012 NASA competition—but the contest this week will be Bruce's debut. And although the rookie robotic team member may get all the attention in San Diego, the 30 students who have been working to perfect Bruce are the team's real all-stars.

To learn more about Bruce—and the humans behind the robot—check out the roster of selected team leaders below:

 

Name: Bruce
Team title: robotic submarine
Year: 2014-?
Major: undecided
Summer plans: competing at the International RoboSub Competition in San Diego

A pair of unique attributes:
1. A pressurized hull. Like any watercraft, Bruce has to have a watertight body called a hull. Bruce's pressurized hull is pumped up with a bicycle pump the night before entering the water. If the pressure is the same in the morning, the team knows that Bruce is watertight and can safely enter the water without ruining expensive electronics.
2. A Doppler velocity logger (DVL). When you're driving a vehicle on land, the number of wheel rotations can tell you how fast and far a vehicle has traveled. Since this isn't possible in the water, a DVL sends out radar signals to the pool floor, measuring the Doppler shift of the return signals to determine the robot's position. DVLs are expensive, but the Caltech team was able to refurbish a broken one—a gift from a sponsor—for Bruce's upcoming competition.

 

Name: Solomon Chang
Team title: programming lead
Year: class of 2015
Major: computer science
Summer plans: interning at Google for the image search infrastructure team

What skills have you learned since joining the team?
On the robotics team, I have been able to channel the theoretical learning from my classes at Caltech into a practical form. In preparation for the competition, I've been working closely with a software team which involved working on 20,000 lines of code—something I'd never experienced in classes. Although it might sound cliché, I cannot begin to emphasize the usefulness of the robotics team in applying software concepts to the real world.

 

Name: Erin Evans
Team title: mechanical engineering subteam member/fundraising and outreach lead
Year: class of 2015
Major: mechanical engineering
Summer plans: SURF research with Professor Sergio Pellegrino in the Space Structures Laboratory

In addition to implementing a robotic submarine design, what have you learned from your time on the team?
It has been an extremely useful learning experience that has given me skills in team management, leadership, and collaborating with people with a wide range of working styles, not to mention all the technical experience I have gained from the engineering aspect of the team along the way. It's also great to work with my teammates. It is easy to see that we've grown closer through the hours and hours of work we have put into this project over the years.

 

Name: David Flicker
Team title: electrical lead
Year: class of 2015
Major: computer science
Summer plans: hardware engineering intern for Airware, a startup that makes autopilot systems

What is one of the major victories you've experienced so far with Bruce?
The greatest success for me was fitting all of the electronics into the newly completed pressurized hull. The hull was finished on a Friday, and we really wanted to try running Bruce in the water on a Sunday, so we had one day to carefully stuff the hull full of the required electronics. Besides the number of parts and connections we needed to make in that short amount of time, the "bigger" problem was that the components were all too large. We almost didn't fit the electronics inside the hull, which would have stopped us dead in our tracks—but luckily, we found a way to make it work.

 

Name: Justin Koch
Team title: project manager
Year: class of 2015
Major: mechanical engineering
Summer plans: robotics research with Disney Imagineering

What's the main thing you've been prepping in the final months before the competition?
The main thing we will be focusing on before the competition is the reliability of our system. While we won't be able to do every task, the ones we do attempt need to be consistently successful. As a rookie team, we probably won't be the best vehicle in the competition, but we will be the best at what we can do. Once we're done competing for the first time this year, we plan to return to the competition and win.

The 17th Annual International RoboSub Competition will take place July 29-August 3, 2014, at the SSC Pacific TRANSDEC in San Diego. On July 30, the Caltech Alumni Association will be hosting an event in San Diego to celebrate the team's first RoboSub competition. Find more information about the event here.

The team is advised by Joel Burdick, the Richard L. and Dorothy M. Hayman Professor of Mechanical Engineering and Bioengineering.

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Future Electronics May Depend on Lasers, Not Quartz

Nearly all electronics require devices called oscillators that create precise frequencies—frequencies used to keep time in wristwatches or to transmit reliable signals to radios. For nearly 100 years, these oscillators have relied upon quartz crystals to provide a frequency reference, much like a tuning fork is used as a reference to tune a piano. However, future high-end navigation systems, radar systems, and even possibly tomorrow's consumer electronics will require references beyond the performance of quartz.

Now, researchers in the laboratory of Kerry Vahala, the Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics at Caltech, have developed a method to stabilize microwave signals in the range of gigahertz, or billions of cycles per second—using a pair of laser beams as the reference, in lieu of a crystal.

Quartz crystals "tune" oscillators by vibrating at relatively low frequencies—those that fall at or below the range of megahertz, or millions of cycles per second, like radio waves. However, quartz crystals are so good at tuning these low frequencies that years ago, researchers were able to apply a technique called electrical frequency division that could convert higher-frequency microwave signals into lower-frequency signals, and then stabilize these with quartz. 

The new technique, which Vahala and his colleagues have dubbed electro-optical frequency division, builds off of the method of optical frequency division, developed at the National Institute of Standards and Technology more than a decade ago. "Our new method reverses the architecture used in standard crystal-stabilized microwave oscillators—the 'quartz' reference is replaced by optical signals much higher in frequency than the microwave signal to be stabilized," Vahala says.

Jiang Li—a Kavli Nanoscience Institute postdoctoral scholar at Caltech and one of two lead authors on the paper, along with graduate student Xu Yi—likens the method to a gear chain on a bicycle that translates pedaling motion from a small, fast-moving gear into the motion of a much larger wheel. "Electrical frequency dividers used widely in electronics can work at frequencies no higher than 50 to 100 GHz. Our new architecture is a hybrid electro-optical 'gear chain' that stabilizes a common microwave electrical oscillator with optical references at much higher frequencies in the range of terahertz or trillions of cycles per second," Li says.  

The optical reference used by the researchers is a laser that, to the naked eye, looks like a tiny disk. At only 6 mm in diameter, the device is very small, making it particularly useful in compact photonics devices—electronic-like devices powered by photons instead of electrons, says Scott Diddams, physicist and project leader at the National Institute of Standards and Technology and a coauthor on the study.

"There are always tradeoffs between the highest performance, the smallest size, and the best ease of integration. But even in this first demonstration, these optical oscillators have many advantages; they are on par with, and in some cases even better than, what is available with widespread electronic technology," Vahala says.

The new technique is described in a paper that will be published in the journal Science on July 18. Other authors on this paper include Hansuek Lee, who is a visiting associate at Caltech. The work was sponsored by the DARPA's ORCHID and PULSE programs; the Caltech Institute for Quantum Information and Matter (IQIM), an NSF Physics Frontiers Center with support of the Gordon and Betty Moore Foundation; and the Caltech Kavli NanoScience Institute.

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Future Electronics May Depend on Lasers
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Friday, October 10, 2014
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Frederick B. Thompson

1922–2014

 

Frederick Burtis Thompson, professor of applied philosophy and computer science, emeritus, passed away on May 27, 2014. The research that Thompson began in the 1960s helped pave the way for today's "expert systems" such as IBM's supercomputer Jeopardy! champ Watson and the interactive databases used in the medical profession. His work provided quick and easy access to the information stored in such systems by teaching the computer to understand human language, rather than forcing the casual user to learn a programming language.

Indeed, Caltech's Engineering & Science magazine reported in 1981 that "Thompson predicts that within a decade a typical professional [by which he meant plumbers as well as doctors] will carry a pocket computer capable of communication in natural language."

"Natural language," otherwise known as everyday English, is rife with ambiguity. As Thompson noted in that same article, "Surgical reports, for instance, usually end with the statement that 'the patient left the operating room in good condition.' While doctors would understand that the phrase refers to the person's condition, some of us might imagine the poor patient wielding a broom to clean up."

Thompson cut through these ambiguities by paring "natural" English down to "formal" sublanguages that applied only to finite bodies of knowledge. While a typical native-born English speaker knows the meanings of 20,000 to 50,000 words, Thompson realized that very few of these words are actually used in any given situation. Instead, we constantly shift between sublanguages—sometimes from minute to minute—as we interact with other people.

Thompson's computer-compatible sublanguages had vocabularies of a few thousand words—some of which might be associated with pictures, audio files, or even video clips—and a simple grammar with a few dozen rules. In the plumber's case, this language might contain the names and functions of pipe fittings, vendors' catalogs, maps of the city's water and sewer systems, sets of architectural drawings, and the building code. So, for example, a plumber at a job site could type "I need a ¾ to ½ brass elbow at 315 South Hill Avenue," and, after some back-and-forth to clarify the details (such as threaded versus soldered, or a 90-degree elbow versus a 45), the computer would place the order and give the plumber directions to the store.

Born on July 26, 1922, Thompson served in the Army and worked at Douglas Aircraft during World War II before earning bachelor's and master's degrees in mathematics at UCLA in 1946 and 1947, respectively. He then moved to UC Berkeley to work with logician Alfred Tarski, whose mathematical definitions of "truth" in formal languages would set the course of Thompson's later career.

On getting his PhD in 1951, Thompson joined the RAND (Research ANd Development) Corporation, a "think tank" created within Douglas Aircraft during the war and subsequently spun off as an independent organization. It was the dawn of the computer age—UNIVAC, the first commercial general-purpose electronic data-processing system, went on sale that same year. Unlike previous machines built to perform specific calculations, UNIVAC ran programs written by its users. Initially, these programs were limited to simple statistical analyses; for example, the first UNIVAC was bought by the U.S. Census Bureau. Thompson pioneered a process called "discrete event simulation" that modeled complex phenomena by breaking them down into sequences of simple actions that happened in specified order, both within each sequence and in relation to actions in other, parallel sequences.

Thompson also helped model a thermonuclear attack on America's major cities in order to help devise an emergency services plan. According to Philip Neches (BS '73, MS '77, PhD '83), a Caltech trustee and one of Thompson's students, "When the team developed their answer, Fred was in tears: the destruction would be so devastating that no services would survive, even if a few people did. . . . This kind of hard-headed analysis eventually led policy makers to a simple conclusion: the only way to win a nuclear war is to never have one." Refined versions of these models were used in 2010 to optimize the deployment of medical teams in the wake of the magnitude-7.0 Haiti earthquake, according to Neches. "The models treated the doctors and supplies as the bombs, and calculated the number of people affected," he explains. "Life has its ironies, and Fred would be the first to appreciate them."

In 1957, Thompson joined General Electric Corporation's computer department. By 1960 he was working at GE's TEMPO (TEchnical Military Planning Operation) in Santa Barbara, where his natural-language research began. "Fred's first effort to teach English to a computer was a system called DEACON [for Direct English Access and CONtrol], developed in the early 1960s," says Neches.

Thompson arrived at Caltech in 1965 with a joint professorship in engineering and the humanities. "He advised the computer club as a canny way to recruit a small but dedicated cadre of students to work with him," Neches recalls. In 1969, Thompson began a lifelong collaboration with Bozena Dostert, a senior research fellow in linguistics who died in 2002. The collaboration was personal as well as professional; their wedding was the second marriage for each.

Although Thompson's and Dostert's work was grounded in linguistic theory, they moved beyond the traditional classification of words into parts of speech to incorporate an operational approach similar to computer languages such as FORTRAN. And thus they created REL, for Rapidly Extensible Language. REL's data structure was based on "objects" that not only described an item or action but allowed the user to specify the interval for which the description applied. For example:

                        Object: Mary Ann Summers

                        Attribute: driver's license

                        Value: yes

                        Start time: 1964

                        End time: current

"This foreshadowed today's semantic web representations," according to Peter Szolovits (BS '70, PhD '75), another of Thompson's students.

In a uniquely experimental approach, the Thompsons tested REL on complex optimization problems such as figuring out how to load a fleet of freighters—making sure the combined volumes of the assorted cargoes didn't exceed the capacities of the holds, distributing the weights evenly fore and aft, planning the most efficient itineraries, and so forth. Volunteers worked through various strategies by typing questions and commands into the computer. The records of these human-computer interactions were compared to transcripts of control sessions in which pairs of students attacked the same problem over a stack of paperwork face-to-face or by communicating with each other from separate locations via teletype machines. Statistical analysis of hundreds of hours' worth of seemingly unstructured dialogues teased out hidden patterns. These patterns included a five-to-one ratio between complete sentences—which had a remarkably invariant average length of seven words—and three-word sentence fragments. Similar patterns are heard today in the clipped cadences of the countdown to a rocket launch.

The "extensible" in REL referred to the ease with which new knowledge bases—vocabulary lists and the relationships between their entries—could be added. In the 1980s, the Thompsons extended REL to POL, for Problem Oriented Language, which had the ability to work out the meanings of words not in its vocabulary as well as coping with such human frailties as poor spelling, bad grammar, and errant punctuation—all on a high-end desktop computer at a time when other natural-language processors ran on room-sized mainframe machines.

"Fred taught both the most theoretical and the most practical computer science courses at the Institute long before Caltech had a formal computer science department. In his theory class, students proved the equivalence of a computable function to a recursive language to a Turing machine. In his data analysis class, students got their first appreciation of the growing power of the computer to handle volumes of data in novel and interesting ways," Neches says. "Fred and his students pioneered the arena of 'Big Data' more than 50 years ahead of the pack." Thompson co-founded Caltech's official computer science program along with professors Carver Mead (BS '56, MS '57, PhD '60) and Ivan Sutherland (MS '60) in 1976.

Adds Remy Sanouillet (MS '82, PhD '94), Thompson's last graduate student, "In terms of vision, Fred 'invented' the Internet well before Al Gore did. He saw, really saw, that we would be asking computers questions that could only be answered by fetching pieces of information stored on servers all over the world, putting the pieces together, and presenting the result in a universally comprehensible format that we now call HTML."

Thompson was a member of the scientific honorary society Sigma Xi, the Association for Symbolic Logic, and the Association for Computing Machinery. He wrote or coauthored more than 40 unclassified papers—and an unknown number of classified ones.

Thompson is survived by his first wife, Margaret Schnell Thompson, and his third wife, Carmen Edmond-Thompson; two children by his first marriage, Mary Ann Thompson Arildsen and Scott Thompson; and four grandchildren.

Plans for a celebration of Thompson's life are pending.

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