Watching Paint Dry and Colors Fade: The Intersection of Art and Science

Watson Lecture Preview

Conserving a museum's holdings is a blend of art and science. Analytical chemists have explained why a dramatic sky disappeared from Winslow Homer's For to Be a Farmer's Boy. Materials scientists have unearthed the sources of color in ancient Chinese jades. Environmental engineers have uncovered the reasons behind the faded brilliance of Georges Seurat's A Sunday on La Grande Jatte.

On Wednesday, May 20, at 8 p.m. in Caltech's Beckman Auditorium, Katherine T. Faber, the Simon Ramo Professor of Materials Science at Caltech, will examine how science serves art in a museum setting, and discuss how bridges to universities can be built.

 

Q: What do you do?

A: I am a materials scientist who focuses on the mechanical behavior of brittle materials. Ceramic materials are especially attractive for use at very high temperatures, such as those needed for energy-related applications—engine components, catalyst supports, or coatings for turbines in aerospace or power generation.

And when I say "mechanical behavior," I'm largely interested in how materials fracture. I'm pretty fortunate to be able to break things for a living. But I have also discovered through the years that some of the materials and structures that I want to study don't exist. That has forced me to move into ceramic processing as well. That way my students and I can understand the link between how the materials are made and how they respond.

Our recent work has focused on porous materials. Historically, one would not want pores in brittle materials, because they act as flaws, and therefore as sources of failure. More recently, porosity is desirable in ceramics, for high-temperature filters or for biomedical scaffolds that allow cell or bone ingrowth, to name just two examples.

 

Q: How does that relate to art conservation, which is the subject of your talk?

A: Conservation studies have actually become an important part of my career. Objects of cultural heritage are made up of the same materials that we study as materials scientists. The phenomena that occur in cultural heritage materials are of particular interest—one needs to understand degradation, such as fading or cracking, in order to preserve these objects. The merit of these studies reaches beyond the art community. We all benefit from these investigations. So will our children, if we continue to study and protect our cultural heritage.

Engineering disciplines are generally very forward thinking and future-oriented. We say, "What materials can we make that will improve our future?" But it is also of value to take our knowledge of materials and look back. One aspect of this art-related work that has been appealing to students is the realization that the expertise that they are developing can be used to solve many different kinds of problems. It's not just about the next photovoltaic or the next superalloy—their talents and skills can be put to use in technical art history. Ultimately, I would like to develop partnerships here in Southern California that will offer Caltech students the same opportunities that the students at Northwestern University have had with the Art Institute of Chicago. It's simply a matter of finding the right partners in the broad array of museums we have here.

 

Q: How did you get into this line of work?

A: Quite by chance. About 12 years ago, I was approached by staff from the Art Institute of Chicago, which had just been given funds to hire its very first conservation scientist. The museum had a very large conservation department, but it did not have a PhD-level scientist on board. The staff was trying to anticipate the needs of this person, who had yet to be named. They were hoping to identify contacts in the academic community for their future hire, and they had heard about my department's reputation. I was the chair of Northwestern's Department of Materials Science and Engineering at the time, so I was the natural person to visit. When asked if we might be a good link for their scientist, my response was an immediate "Yes!"

And indeed, a year later the Art Institute hired a fantastic conservation scientist, Francesca Casadio, and we started to work together immediately. We've collaborated on ancient Chinese jades and Meissen ceramics. I also became the matchmaker, if you will, who linked other engineering faculty at Northwestern to the Art Institute. In 2013, Francesca and I went on to found the Center for Scientific Studies in the Arts, a partnership funded by the Andrew W. Mellon Foundation, extending our research to museums around the U.S. But it was all serendipity.

 

Named for the late Caltech professor Earnest C. Watson, who founded the series in 1922, the Watson Lectures present Caltech and JPL researchers describing their work to the public. Many past Watson Lectures are available online at Caltech's iTunes U site.

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Caltech Students Named Goldwater Scholars

Two Caltech students, Saaket Agrawal and Paul Dieterle, have been awarded Barry M. Goldwater scholarships for the 2015–16 academic year.

The Barry Goldwater Scholarship and Excellence in Education Program was established by Congress in 1986 to award scholarships to college students who intend to pursue research careers in science, mathematics, and engineering.

Saaket Agrawal is a sophomore from El Dorado Hills, California, majoring in chemistry. Under Greg Fu, the Altair Professor of Chemistry, Agrawal works on nickel-catalyzed cross coupling, a powerful method for making carbon-carbon bonds. Specifically, Agrawal conducts mechanistic studies on these reactions, which involves elucidating the pathway through which they occur. After Caltech, he plans to pursue a PhD research program in organometallic chemistry—the combination of organic (carbon-based) and inorganic chemistry—and ultimately hopes teach at the university level.

"Caltech is one of the best places in the world to study chemistry. The faculty were so willing to take me on, even as an undergrad, and treat me like a capable scientist," Agrawal says. "That respect, and the ability to do meaningful work, has motivated me."

Paul Dieterle is a junior from Madison, Wisconsin, majoring in applied physics. He works with Oskar Painter, the John G. Braun Professor of Applied Physics, studying quantum information science.

"The quantum behavior of atoms has been studied for decades. We are researching the way macroscopic objects behave in a quantum mechanical way in order to manipulate them into specific quantum states," Dieterle says. Painter's group is studying how to use macroscopic mechanical objects to transform quantized electrical signals into quantized optical signals as part of the larger field of quantum computing, a potential next generation development in the field.

"The power of quantum computing would be immense," says Dieterle, who would like to attend graduate school to study quantum information science. "We could simulate incredibly complex things, like particles at the edge of a black hole. Participating in this physics revolution is so exciting."

Agrawal and Dieterle bring the number of Caltech Goldwater Scholars to 22 in the last decade.

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In Our Community

New Thin, Flat Lenses Focus Light as Sharply as Curved Lenses

Lenses appear in all sorts of everyday objects, from prescription eyeglasses to cell-phone cameras. Typically, lenses rely on a curved shape to bend and focus light. But in the tight spaces inside consumer electronics and fiber-optic systems, these rounded lenses can take up a lot of room. Over the last few years, scientists have started crafting tiny flat lenses that are ideal for such close quarters. To date, however, thin microlenses have failed to transmit and focus light as efficiently as their bigger, curved counterparts.

Caltech engineers have created flat microlenses with performance on a par with conventional, curved lenses. These lenses can be manufactured using industry-standard techniques for making computer chips, setting the stage for their incorporation into electronics such as cameras and microscopes, as well as in novel devices.

"The lenses we use today are bulky," says Amir Arbabi, a senior researcher in the Division of Engineering and Applied Science, and lead author of the paper. "The structure we have chosen for these flat lenses can open up new areas of application that were not available before."

The research, led by Andrei Faraon (BS '04), assistant professor of applied physics and material science, appears in the May 7 issue of Nature Communications.

The new lens type is known as a high-contrast transmitarray. Made of silicon, the lens is just a millionth of a meter thick, or about a hundredth of the diameter of a human hair, and it is studded with silicon "posts" of varying sizes. When imaged under a scanning electron microscope, the lens resembles a forest cleared for timber, with only stumps (the posts) remaining. Depending on their heights and thicknesses, the posts focus different colors, or wavelengths, of light.

A lens focuses light or forms an image by delaying for varying amounts of time the passage of light through different parts of the lens. In curved glass lenses, light takes longer to travel through the thicker parts of the lens than through the thinner parts. On the flat lens, these delays are achieved by the silicon posts, which trap and delay the light for an amount of time that depends on the diameter of the posts. With careful placement of these differently sized posts on the lens, the researchers can guide incident light as it passes through the lens to form a curved wavefront, resulting in a tightly focused spot.

The Caltech researchers found that their flat lenses focus as much as 82 percent of infrared light passing through them. By comparison, previous studies have found that metallic flat lenses have efficiencies of only around a few percent, in part because their materials absorb some incident light.

Although curved glass lenses can focus nearly 100 percent of the light that reaches them, they usually require sophisticated designs with nonspherical surfaces that can be difficult to polish. On the other hand, the design of the flat lenses can be modified depending upon the exact application for which the lenses are needed, simply by changing the pattern of the silicon nanoposts. This flexibility makes them attractive for commercial and industrial use, the researchers say. "You get exceptional freedom to design lenses for different functionalities," says Arbabi.

A limitation of flat lenses is that each lens can only focus a narrow set of wavelengths, representing individual colors of the spectrum. These monochromatic lenses could find application in devices such as a night-vision camera, which sees in infrared over a narrow wavelength range. More broadly, they could be used in any optical device involving lasers, as lasers emit only a single color of light.

Multiple monochromatic lenses could be used to deliver multicolor images, much as television and computer displays employ combinations of the colors red, green, and blue to produce a rainbow of hues. Because the microlenses are so small, integrating them in optical systems would take up little space compared to the curved lenses now utilized in cameras or microscopes.

Although the lenses currently are expensive to manufacture, it should be possible to produce thousands at once using photolithography or nanoimprint lithography techniques, the researches say. In these common, high-throughput manufacturing techniques, a stamp presses into a polymer, leaving behind a desired pattern that is then transferred into silicon through dry etching of silicon in a plasma.

"For consumer applications, the current price point of flat lenses is not good, but the performance is," says Faraon. "Depending on how many of lenses you are making, the price can drop down rapidly."

The paper is entitled "Subwavelength-thick lenses with high numerical apertures and large efficiency based on high-contrast transmitarrays." In addition to Arbabi and Faraon, other Caltech coauthors include graduate student Yu Horie, senior Alexander Ball, and Mahmood Bagheri, a microdevices engineer at JPL. The work was supported by the Caltech/JPL President's and Director's Fund and the Defense Advanced Research Projects Agency. Alexander Ball was supported by a Summer Undergraduate Research Fellowship at Caltech. The device nanofabrication was performed in the Kavli Nanoscience Institute at Caltech.

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Monday, May 18, 2015
Brown Gymnasium – Scott Brown Gymnasium

Jupiter’s Grand Attack

JCAP Receives a 5-Year, $75M Funding Renewal

On Monday, April 27, the Department of Energy (DOE) announced a five-year, $75 million renewal of the Joint Center for Artificial Photosynthesis (JCAP). JCAP's mission is to explore the science and technology of artificial photosynthesis to harness solar energy for the production of fuel.

JCAP is the nation's largest research program dedicated to the development of an artificial solar-fuel generation technology. Established in 2010 as a DOE Energy Innovation Hub, JCAP aims to create a low-cost generator to make fuel from sunlight 10 times more efficiently than plants. Such a breakthrough would have the potential to reduce our country's dependence on oil and enhance energy security.

The Hub is directed by Caltech, but it has its primary sites both at Lawrence Berkeley National Laboratory (LBNL) and at Caltech. JCAP brings together more than 150 scientists and engineers from Caltech and LBNL, and also draws on the expertise and capabilities of key partners at UC Irvine, UC San Diego, and the SLAC National Accelerator Laboratory at Stanford.

The funding renewal announcement was made at LBNL by Franklin Orr, under secretary for science and energy at DOE.

"JCAP's work to produce fuels from sunlight and carbon dioxide holds the promise of a potentially revolutionary technology that would put America on the path to a low-carbon economy," said Orr in a DOE press release. "While the scientific challenges of producing such fuels are considerable," the released noted, "JCAP will capitalize on state-of-the-art capabilities developed during its initial five years of research, including sophisticated characterization tools and unique automated high-throughput experimentation that can quickly make and screen large libraries of materials to identify components for artificial photosynthesis systems."   

"We are honored and delighted to receive renewed support from the Department of Energy for JCAP," says JCAP director Harry A. Atwater, Howard Hughes Professor of Applied Physics and Materials Science at Caltech. "Thanks to this renewal, JCAP will continue to push the scientific frontiers of artificial photosynthesis, with an emphasis on selective carbon dioxide reduction under mild temperature and pressure conditions. Carbon dioxide reduction is at the core of natural photosynthesis, and understanding the science and technology of this reaction is also central to society's efforts to mitigate carbon dioxide emission. It is an enormous challenge, but just the sort of problem that is worthy of sustained scientific investment. We are excited for the work ahead."

In its first five years of research, JCAP has made significant advances in a number of areas, including the automated and rapid discovery and characterization of new catalysts and light absorbers, the development of techniques for protecting the light-absorbing components in solar-fuels generators, and the creation of experimental protocols for objective evaluations of the activity and stability of materials. All of these technologies are critical to the development of solar-driven water splitting and the reduction of carbon dioxide to produce fuel.

For more information about JCAP, please visit http://solarfuelshub.org/.

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Tuesday, May 19, 2015
Guggenheim 101 (Lees-Kubota Lecture Hall) – Guggenheim Aeronautical Laboratory

Science in a Small World - Short Talks

Tuesday, May 19, 2015
Dabney Hall, Garden of the Associates – The Garden of the Associates

Science in a Small World - Poster Session #2

Tuesday, May 19, 2015
Dabney Hall, Garden of the Associates – The Garden of the Associates

Science in a Small World - Poster Session #1

Space-Based Solar Power Project Funded

A sponsored research agreement with Northrop Grumman Corporation will provide Caltech up to $17.5 million over three years for the development of the Space Solar Power Initiative (SSPI). The SSPI will develop the scientific and technological innovations necessary to enable a space-based solar power system—consisting of ultralight, high-efficiency photovoltaics, a phased-array system to produce and distribute power dynamically, and ultralight deployable space structures—that ultimately will be capable of generating electric power at a cost comparable to that from fossil-fuel power plants.

The project was conceived and will be led jointly by three professors in Caltech's Division of Engineering and Applied Science (EAS): Harry A. Atwater, Howard Hughes Professor of Applied Physics and Materials Science and director of the Resnick Sustainability Institute; Ali Hajimiri, Thomas G. Myers Professor of Electrical Engineering; and Sergio Pellegrino, Joyce and Kent Kresa Professor of Aeronautics, professor of civil engineering, and a senior research scientist at Caltech's Jet Propulsion Laboratory.

Atwater's group will design and demonstrate ultralight, high-efficiency photovoltaics optimized for space conditions and compatible with an integrated, modular power conversion/transmission system.

Hajimiri's team will develop the integrated circuits and the antenna design for the system's large-scale phased array, timing control, and conversion of direct current to radio frequency power. "The three groups are working closely to take a holistic approach to the design of the entire system," he says.

Through a modular approach power will be generated, converted, and radiated locally at the same place in space using a distributed power conversion and transmission solution created with modern integrated electronics that eliminates inter- and intramodule power wiring in the system. "This significantly reduces the system mass, and thereby its cost," he adds.

"This space-based, highly adaptive power generator will enable versatile on-demand power anywhere on the planet and will be able to almost instantly distribute the power to different locations," Hajimiri says. "This is enabled through an agile phased-array system that can dynamically direct the power to the desired locations on Earth and simultaneously provide power to multiple destinations on demand. This can substantially reduce the need and the cost associated with the power distribution network across the globe."

Any such system must first be able to collect the solar energy that is then converted and distributed. "One of the key barriers to the realization of cost-competitive space-based solar power systems is the deployment in space of large surface area structures to collect solar power, at low cost," says Pellegrino. "The cost and complexity of launching and deploying conventional deployable structures would be unacceptable for many applications." To circumvent this barrier, his team is developing novel architectures for multifunctional deployable space structures with an overall areal density on the order of 100 grams per square meter, equivalent to one or two sheets of paper. "The concepts that we are investigating build on over 10 years of research on deployable thin-shell structures, which most recently had resulted in the development of low-cost fiber-composite booms and reflectors in which elastic hinges are created simply by making small cuts in the wall of a shell structure," he says.

To achieve all of these goals, Atwater, Hajimiri, and Pellegrino already have assembled a team of students, postdoctoral scholars, and senior researchers that will eventually exceed 50 members. In addition, the EAS division is in the process of building specialized laboratory facilities to support the team. Meanwhile, Northrop Grumman engineers and scientists will collaborate with the Caltech researchers to develop solutions, build prototypes, and obtain experimental and numerical validation of concepts that will allow for the eventual implementation of the system.

"This initiative is a great example of how Caltech engineers are working at the leading edges of fundamental science to invent the technologies of the future," says Ares Rosakis, Otis Booth Leadership Chair of the EAS division and the Theodore von Kármán Professor of Aeronautics and Mechanical Engineering. "The Space Solar Power Initiative brings together electrical engineers, applied physicists, and aerospace engineers in the type of profound interdisciplinary collaboration that is seamlessly enhanced at a small place like Caltech. I believe it also demonstrates the value of industry and academic partnerships. We are working on extremely difficult problems that could eventually provide the world with new, and very cost-competitive technology for sustainable energy."

"By working together with Caltech, Northrop Grumman extends its long heritage of innovation in space-based technologies and mission solutions," said Joseph Ensor, vice president and general manager, Space Intelligence, Surveillance and Reconnaissance (ISR) Systems, Northrop Grumman, in a press release. "The potential breakthroughs from this research could have extensive applications across a number of related power use challenges."

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Tracking Photosynthesis from Space

Watching plants perform photosynthesis from space sounds like a futuristic proposal, but a new application of data from NASA's Orbiting Carbon Observatory-2 (OCO-2) satellite may enable scientists to do just that. The new technique, which allows researchers to analyze plant productivity from far above Earth, will provide a clearer picture of the global carbon cycle and may one day help researchers determine the best regional farming practices and even spot early signs of drought.

When plants are alive and healthy, they engage in photosynthesis, absorbing sunlight and carbon dioxide to produce food for the plant, and generating oxygen as a by-product. But photosynthesis does more than keep plants alive. On a global scale, the process takes up some of the man-made emissions of atmospheric carbon dioxide—a greenhouse gas that traps the sun's heat down on Earth—meaning that plants also have an important role in mitigating climate change.

To perform photosynthesis, the chlorophyll in leaves absorbs sunlight—most of which is used to create food for the plants or is lost as heat. However, a small fraction of that absorbed light is reemitted as near-infrared light. We cannot see in the near-infrared portion of the spectrum with the naked eye, but if we could, this reemitted light would make the plants appear to glow—a property called solar induced fluorescence (SIF). Because this reemitted light is only produced when the chlorophyll in plants is also absorbing sunlight for photosynthesis, SIF can be used as a way to determine a plant's photosynthetic activity and productivity.

"The intensity of the SIF appears to be very correlated with the total productivity of the plant," says JPL scientist Christian Frankenberg, who is lead for the SIF product and will join the Caltech faculty in September as an associate professor of environmental science and engineering in the Division of Geological and Planetary Sciences.

Usually, when researchers try to estimate photosynthetic activity from satellites, they utilize a measure called the greenness index, which uses reflections in the near-infrared spectrum of light to determine the amount of chlorophyll in the plant. However, this is not a direct measurement of plant productivity; a plant that contains chlorophyll is not necessarily undergoing photosynthesis. "For example," Frankenberg says, "evergreen trees are green in the winter even when they are dormant."

He adds, "When a plant starts to undergo stress situations, like in California during a summer day when it's getting very hot and dry, the plants still have chlorophyll"—chlorophyll that would still appear to be active in the greenness index—"but they usually close the tiny pores in their leaves to reduce water loss, and that time of stress is also when SIF is reduced. So photosynthesis is being very strongly reduced at the same time that the fluorescence signal is also getting weaker, albeit at a smaller rate."

The Caltech and JPL team, as well as colleagues from NASA Goddard, discovered that they could measure SIF from orbit using spectrometers—standard instruments that can detect light intensity—that are already on board satellites like Japan's Greenhouse Gases Observing Satellite (GOSAT) and NASA's OCO-2.

In 2014, using this new technique with data from GOSAT and the European Global Ozone Monitoring Experiment–2 satellite, the researchers scoured the globe for the most productive plants and determined that the U.S. "Corn Belt"—the farming region stretching from Ohio to Nebraska—is the most photosynthetically active place on the planet. Although it stands to reason that a cornfield during growing season would be actively undergoing photosynthesis, the high-resolution measurements from a satellite enabled global comparison to other plant-heavy regions—such as tropical rainforests.

"Before, when people used the greenness index to represent active photosynthesis, they had trouble determining the productivity of very dense plant areas, such as forests or cornfields. With enough green plant material in the field of view, these greenness indexes can saturate; they reach a maximum value they can't exceed," Frankenberg says. Because of the sensitivity of the SIF measurements, researchers can now compare the true productivity of fields from different regions without this saturation—information that could potentially be used to compare the efficiency of farming practices around the world.

Now that OCO-2 is online and producing data, Frankenberg says that it is capable of achieving higher resolution than the preliminary experiments with GOSAT. Therefore, OCO-2 will be able to provide an even clearer picture of plant productivity worldwide. However, to get more specific information about how plants influence the global carbon cycle, an evenly distributed ground-based network of spectrometers will be needed. Such a network—located down among the plants rather than miles above—will provide more information about regional uptake of carbon dioxide via photosynthesis and the mechanistic link between SIF and actual carbon exchange.

One existing network, called FLUXNET, uses ground-based towers to measure the exchange of carbon dioxide, or carbon flux, between the land and the atmosphere from towers at more than 600 locations worldwide. However, the towers only measure the exchange of carbon dioxide and are unable to directly observe the activities of the biosphere that drive this exchange.

The new ground-based measurements will ideally take place at existing FLUXNET sites, but they will be performed with a small set of high-resolution spectrometers—similar to the kind that OCO-2 uses—to allow the researchers to use the same measurement principles they developed for space. The revamped ground network was initially proposed in a 2012 workshop at the Keck Institute for Space Studies and is expected to go online sometime in the next two years.

In the future, a clear picture of global plant productivity could influence a range of decisions relevant to farmers, commodity traders, and policymakers. "Right now, the SIF data we can gather from space is too coarse of a picture to be really helpful for these conversations, but, in principle, with the satellite and ground-based measurements you could track the fluorescence in fields at different times of day," he says. This hourly tracking would not only allow researchers to detect the productivity of the plants, but it could also spot the first signs of plant stress—a factor that impacts crop prices and food security around the world.

"The measurements of SIF from OCO-2 greatly extend the science of this mission", says Paul Wennberg, R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Science and Engineering, director of the Ronald and Maxine Linde Center for Global Environmental Science, and a member of the OCO-2 science team. "OCO-2 was designed to map carbon dioxide, and scientists plan to use these measurements to determine the underlying sources and sinks of this important gas. The new SIF measurements will allow us to diagnose the efficiency of the plants—a key component of the sinks of carbon dioxide."

By using OCO-2 to diagnose plant activity around the globe, this new research could also contribute to understanding the variability in crop primary productivity and also, eventually, the development of technologies that can improve crop efficiency—a goal that could greatly benefit humankind, Frankenberg says.

This project is funded by the Keck Institute for Space Studies and JPL. Wennberg is also an executive officer for the Environmental Science and Engineering (ESE) program. ESE is a joint program of the Division of Engineering and Applied Science, the division of Chemistry and Chemical Engineering, and the Division of Geological and Planetary Sciences.

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