Caltech Scientist Awarded Grant to Develop Solar-Powered Sanitation System

PASADENA, Calif.—Environmental scientist and engineer Michael Hoffmann of the California Institute of Technology (Caltech) has received a $400,000 grant from the Bill & Melinda Gates Foundation to build a solar-powered portable toilet that could help solve a major health problem in developing countries. The grant, announced July 19 at the AfricaSan 3 sanitation and hygiene conference in Rwanda, will be used to complete the initial design, development, and testing of the unique sustainable system. Designed for use by up to 500 people per day with minimal maintenance, the sanitation unit will have the added benefit of turning waste into fuel.

Hoffmann's concept, called a "Self-Contained, PV-Powered Domestic Toilet and Wastewater Treatment System," is one of eight projects funded through the foundation's "Reinvent the Toilet Challenge." The Bill & Melinda Gates Foundation announced this grant as part of more than $40 million in new investments launching its Water, Sanitation, & Hygiene strategy. According to the World Health Organization (WHO) and UNICEF, about 2.6 billion people—approximately 40 percent of the world's population—lack access to safe sanitation, and nearly half of them practice open defecation. In addition, WHO estimates that 1.5 million children die each year from diarrheal disease, which is often caused by poor sanitation.

"Life expectancy correlates to the accessibility of clean water and proper sanitation practices," says Hoffmann, the James Irvine Professor of Environmental Science at Caltech, who has been working for years on the electrochemical technology to create a sustainable toilet and waste-treatment system. "All of our efforts in biomedicine may go for naught if we don't take care of sanitation."

Hoffmann's toilet system could fit inside the typical portable sanitation unit often found at construction sites and recreation areas, but the comparison ends there. It starts with a photovoltaic or solar panel, which converts the sun's rays into enough energy to power an electrochemical reactor that Hoffmann designed to break down water and human waste material into hydrogen gas. The hydrogen gas can then be stored in hydrogen fuel cells to provide a backup energy source for nighttime operation or for use under low-sunlight conditions. Hoffmann also envisions equipping the units with self-cleaning toilets that would also be powered by the energy from the sun and fuel cells.

Hoffmann says that he can build a workable unit for $2,000, but that the cost would come down significantly if the toilets were produced in volume. Following production of a prototype under the Gates Foundation grant, Hoffmann hopes to continue the project to refine the system and reduce its cost. In August 2012, all "Reinvent the Toilet Challenge" grantees will present their prototypes, with winning projects to receive additional funding for product development, industrial production, and commercialization.

"To address the needs of the 2.6 billion people who don't have access to safe sanitation, we not only must reinvent the toilet, we also must find safe, affordable, and sustainable ways to capture, treat, and recycle human waste," says Sylvia Mathews Burwell, president of the Global Development Program at the Bill & Melinda Gates Foundation. "Most importantly, we must work closely with local communities to develop lasting sanitation solutions that will improve their lives."

A member of the Caltech faculty since 1980, Hoffmann was honored in 2010 by the National Taiwan University as a Distinguished Visiting Chair Professor and by the State of Kerala, India, as an Erudite Distinguished Scholar. Earlier this year, Hoffmann was elected to the National Academy of Engineering. He is the organizing chair of the upcoming International Conference on the Photochemical Conversion and Storage of Solar Energy, which will be held on the Caltech campus at the end of July 2012. 

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Michael Rogers
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Summer Construction of the SCI-Arc/Caltech Solar Decathlon House Hits High Gear

A joint team of students from Caltech and the Southern California Institute of Architecture (SCI-Arc) are working 60-plus-hour weeks this summer to complete construction of a state-of-the-art, energy-efficient house for the Solar Decathlon, a biennial competition sponsored by the U.S. Department of Energy (DOE) that will be held from September 23 to October 2 on the National Mall in Washington, D.C. The competition challenges 20 teams from around the world to create the most energy-efficient, affordable, and attractive house they can.

The team is nearing completion of the house's heating and air conditioning, plumbing, and electrical systems; polyurethane insulation was blown into the ceiling joists on July 14, and now team members are busy piecing together 1/2" construction-grade plywood as finish sheeting on the ceiling.

Once finished, the two-story SCI-Arc/Caltech house will sport a soft "skin" of white architectural vinyl—typically used in tent halls—and a central computer, connected to the Internet, to control everything from heating to lighting based on weather forecasts and other data, optimizing energy use.

To follow a blog documenting the SCI-Arc/Caltech team's progress and view pictures of the build, go to http://www.chip2011.com/blog.

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Kathy Svitil
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Wind-turbine Placement Produces Tenfold Power Increase, Caltech Researchers Say

PASADENA, Calif.—The power output of wind farms can be increased by an order of magnitude—at least tenfold—simply by optimizing the placement of turbines on a given plot of land, say researchers at the California Institute of Technology (Caltech) who have been conducting a unique field study at an experimental two-acre wind farm in northern Los Angeles County.

A paper describing the findings—the results of field tests conducted by John Dabiri, Caltech professor of aeronautics and bioengineering, and colleagues during the summer of 2010—appears in the July issue of the Journal of Renewable and Sustainable Energy.

Dabiri's experimental farm, known as the Field Laboratory for Optimized Wind Energy (FLOWE), houses 24 10-meter-tall, 1.2-meter-wide vertical-axis wind turbines (VAWTs)—turbines that have vertical rotors and look like eggbeaters sticking out of the ground. Half a dozen turbines were used in the 2010 field tests.

Despite improvements in the design of wind turbines that have increased their efficiency, wind farms are rather inefficient, Dabiri notes. Modern farms generally employ horizontal-axis wind turbines (HAWTs)—the standard propeller-like monoliths that you might see slowly turning, all in the same direction, in the hills of Tehachapi Pass, north of Los Angeles.

In such farms, the individual turbines have to be spaced far apart—not just far enough that their giant blades don't touch. With this type of design, the wake generated by one turbine can interfere aerodynamically with neighboring turbines, with the result that "much of the wind energy that enters a wind farm is never tapped," says Dabiri. He compares modern farms to "sloppy eaters," wasting not just real estate (and thus lowering the power output of a given plot of land) but much of the energy resources they have available to them.

Designers compensate for the energy loss by making bigger blades and taller towers, to suck up more of the available wind and at heights where gusts are more powerful. "But this brings other challenges," Dabiri says, such as higher costs, more complex engineering problems, a larger environmental impact. Bigger, taller turbines, after all, mean more noise, more danger to birds and bats, and—for those who don't find the spinning spires visually appealing—an even larger eyesore.

The solution, says Dabiri, is to focus instead on the design of the wind farm itself, to maximize its energy-collecting efficiency at heights closer to the ground. While winds blow far less energetically at, say, 30 feet off the ground than at 100 feet, "the global wind power available 30 feet off the ground is greater than the world's electricity usage, several times over," he says. That means that enough energy can be obtained with smaller, cheaper, less environmentally intrusive turbines—as long as they're the right turbines, arranged in the right way.

VAWTs are ideal, Dabiri says, because they can be positioned very close to one another. This lets them capture nearly all of the energy of the blowing wind and even wind energy above the farm. Having every turbine turn in the opposite direction of its neighbors, the researchers found, also increases their efficiency, perhaps because the opposing spins decrease the drag on each turbine, allowing it to spin faster (Dabiri got the idea for using this type of constructive interference from his studies of schooling fish).

In the summer 2010 field tests, Dabiri and his colleagues measured the rotational speed and power generated by each of the six turbines when placed in a number of different configurations. One turbine was kept in a fixed position for every configuration; the others were on portable footings that allowed them to be shifted around.

The tests showed that an arrangement in which all of the turbines in an array were spaced four turbine diameters apart (roughly 5 meters, or approximately 16 feet) completely eliminated the aerodynamic interference between neighboring turbines. By comparison, removing the aerodynamic interference between propeller-style wind turbines would require spacing them about 20 diameters apart, which means a distance of more than one mile between the largest wind turbines now in use.

The six VAWTs generated from 21 to 47 watts of power per square meter of land area; a comparably sized HAWT farm generates just 2 to 3 watts per square meter.

"Dabiri's bioinspired engineering research is challenging the status quo in wind-energy technology," says Ares Rosakis, chair of Caltech's Division of Engineering and Applied Science and the Theodore von Kármán Professor of Aeronautics and professor of mechanical engineering. "This exemplifies how Caltech engineers' innovative approaches are tackling our society's greatest problems."

"We're on the right track, but this is by no means 'mission accomplished,'" Dabiri says. "The next steps are to scale up the field demonstration and to improve upon the off-the-shelf wind-turbine designs used for the pilot study." Still, he says, "I think these results are a compelling call for further research on alternatives to the wind-energy status quo."

This summer, Dabiri and colleagues are studying a larger array of 18 VAWTs to follow up last year's field study. Video and images of the field site can be found at http://dabiri.caltech.edu/research/wind-energy.html.

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Kathy Svitil
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Linde + Robinson Lab Making Headlines for Extraordinary Renovations

The world is taking note of the innovative work being done at Caltech—not just in the labs, but also in the unique renovations of our research spaces. The spring issue of Solutions Journal, a magazine of the Rocky Mountain Institute (RMI), features an in-depth profile of the Linde + Robinson Laboratory, an astronomy lab built in 1932 that has undergone extensive renovations and will be the nation's first LEED Platinum laboratory.

RMI is a nonprofit organization dedicated to efficient and sustainable use of resources. Several of the institute's staff members participated in the design process of the building, which will house the Ronald and Maxine Linde Center for Global Environmental Science when it re-opens later this month.

"Many newer buildings incorporate many green features and advanced technologies," said Foster Stanback, a green building enthusiast and RMI supporter, in the article. "The real challenge, though, is to retrofit many of the existing structures that can't simply be torn down. The final design plan that emerged … resulted in a building that will truly inspire others about the possibilities for the green retrofitting of older buildings."

To read the full article, click here

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Katie Neith
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Alternative Energy Expert Frances Arnold Profiled in the LA Times

For biochemist and chemical engineer Frances Arnold, the road to success has not been straight and narrow. In fact, she has often bucked the academic tradition of rigorous, time-consuming pre-experiment methodology for a more fast and furious approach to research.

"I said 'OK, if one experiment doesn't work I'm going to do a million experiments, and I don't care if 999,999 don't work. I'm going to find the one that does,'" said Arnold, the Dickinson Professor of Chemical Engineering, Bioengineering and Biochemistry at Caltech, in a profile published online and in the July 3 print edition of the Los Angeles Times.

Her unconventional approach has paid off. She is co-founder of a company that develops liquid fuel from plants and oversees a lab of 20 students and researchers dedicated to alternative energy.

To learn more about Arnold's career path, including a stint as a cab driver, read the full profile here

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Katie Neith
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Going with the Flow: Caltech Researchers Find Compaction Bands in Sandstone are Permeable

Findings could aid in the development of better technologies for hydraulic fracturing and other fluid extraction techniques from the earth

PASADENA, Calif.—When geologists survey an area of land for the potential that gas or petroleum deposits could exist there, they must take into account the composition of rocks that lie below the surface. Take, for instance, sandstone—a sedimentary rock composed mostly of weakly cemented quartz grains. Previous research had suggested that compaction bands—highly compressed, narrow, flat layers within the sandstone—are much less permeable than the host rock and might act as barriers to the flow of oil or gas. 

Now, researchers led by José Andrade, associate professor of civil and mechanical engineering at the California Institute of Technology (Caltech), have analyzed X-ray images of Aztec sandstone and revealed that compaction bands are actually more permeable than earlier models indicated. While they do appear to be less permeable than the surrounding host rock, they do not appear to block the flow of fluids. Their findings were reported in the May 17 issue of Geophysical Research Letters.

The study includes the first observations and calculations that show fluids have the ability to flow in sandstone that has compaction bands. Prior to this study, there had been inferences of how permeable these formations were, but those inferences were made from 2D images. This paper provides the first permeability calculations based on actual rock samples taken directly from the field in the Valley of Fire, Nevada. From the data they collected, the researchers concluded that these formations are not as impermeable as previously believed, and that therefore their ability to trap fluids—like oil, gas, and CO2—should be measured based on 3D images taken from the field.

"These results are very important for the development of new technologies such as CO2 sequestration—removing CO2 from the atmosphere and depositing it in an underground reservoir—and hydraulic fracturing of rocks for natural gas extraction," says Andrade. "The quantitative connection between the microstructure of the rock and the rock's macroscopic properties, such as hydraulic conductivity, is crucial, as physical processes are controlled by pore-scale features in porous materials. This work is at the forefront of making this quantitative connection."

Compaction bands at multiple scales ranging from the field scale to the specimen scale to the meso and grain scale. At the field scale, picture shows the presence of narrow tabular structures within the host rock in the Valley of Fire. At the grain scale, images show clear differences in porosity (dark spots) density. This research aims at quantifying the impact of grain scale features in macroscopic physical properties that control behavior all the way to the field scale.
Credit: Jose Andrade/Caltech

The research team connected the rocks' 3D micromechanical features—such as grain size distribution, which was obtained using microcomputed tomography images of the rocks to build a 3D model—with quantitative macroscopic flow properties in rocks from the field, which they measured on many different scales. Those measurements were the first ever to look at the three-dimensional ability of compaction bands to transmit fluid. The researchers say the combination of these advanced imaging technologies and multiscale computational models will lead to unprecedentedly accurate measurements of crucial physical properties, such as permeability, in rocks and similar materials. 

Andrade says the team wants to expand these findings and techniques. "An immediate idea involves the coupling of solid deformation and chemistry," he says. "Accounting for the effect of pressures and their potential to exacerbate chemical reactions between fluids and the solid matrix in porous materials, such as compaction bands, remains a fundamental problem with multiple applications ranging from hydraulic fracturing for geothermal energy and natural gas extraction, to applications in biological tissue for modeling important processes such as osteoporosis. For instance, chemical reactions take place as part of the process utilized in fracturing rocks to enhance the extraction of natural gas."

Other coauthors of the paper, "Connecting microstructural attributes and permeability from 3D tomographic images of in situ shear-enhanced compaction bands using multiscale computations," are WaiChing Sun, visiting scholar at Caltech; John Rudnicki, professor of civil and environmental engineering at Northwestern University; and Peter Eichhubl, research scientist in the Bureau of Economic Geology at the University of Texas at Austin.

The work was partially funded by the Geoscience Research Program of the U.S. Department of Energy.

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Katie Neith
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Caltech Researchers Develop High-Performance Bulk Thermoelectrics

PASADENA, Calif.—Roughly 10 billion miles beyond Neptune's orbit, and well past their 30th birthdays, Voyagers 1 and 2 continue their lonely trek into the Milky Way. And they're still functioning—running on power gleaned not from the pinprick sun, but from solid-state devices called thermoelectric generators, which convert heat energy into electricity.

The same technology can be applied here on Earth to recover waste heat when fuel is burned. "Cogeneration," or the production of electricity as a by-product of a heat-generating process, already provides as much as 10 percent of Europe's electrical power. Systems for this purpose typically operate best at very high temperatures, are costly to build and operate, and suffer from substantial inefficiencies. That's why they can be found in spacecraft and power plants but not, say, in cars.

But recently, scientists have concocted a recipe for a thermoelectric material that might be able to operate off nothing more than the heat of a car's exhaust. In a paper published in Nature this month, G. Jeffrey Snyder, faculty associate in applied physics and materials science at the California Institute of Technology (Caltech), and his colleagues reported on a compound that shows high efficiency at less extreme temperatures.

The heart of a thermoelectric generator is a flat array of semiconductor material. In operation, heat from an external source is directed against one side of the array, while the other side is kept cool. Like air molecules in a hot oven, the material within the array flows along the induced temperature gradient: away from the hot side and toward the cool side. But in the crystalline lattice of a semiconductor, there's only one "material" that isn't rigidly fixed: the charge carriers. Consequently, the only things that move in response to the thermal nonequilibrium are these charge carriers and the result is an electrical flow. Build up a circuit by laying out small semiconductor bricks side by side and wiring them together, and you've got a steady electric current.

The lead telluride (PbTe) family of compounds is commonly used in these applications, but regardless of the underlying technology, scientists designing new thermoelectric materials are continually constrained by structural issues at the most microscopic levels. Those moving charge carriers can run afoul of many complex effects, including electrical interactions, heat-induced vibrations (called phonons), and scattering caused by impurities and imperfections within the crystal structure.

The Caltech researchers began with lead telluride and then added a fractional amount of the element selenium, a concoction first proposed by Soviet scientists A. F. Ioffe and A. V. Ioffe in the 1950s. Because any semiconductor's properties are highly sensitive to the exact type and placement of each of its atoms, this small alteration in the formula produces important changes in the crystal's electronic structure.

Specifically, certain regions called "degenerate valleys" arrange themselves in such a way as to provide a more favorable pathway for charge carriers to follow, a trail of equal-energy stepping stones through the material. In addition, adding the selenium creates multiple regions called point defects. "They're like air bubbles trapped in window glass," says Snyder, "and they tend to scatter vibrations. The result is that heat dissipates more slowly through the material."

That dissipation is important, because in order for a material to be efficient, charge carriers should flow much more easily than heat. In other words, electrical resistance should be low, to maximize current, while thermal resistance should be high, to maintain the temperature gradient that causes the charge carriers to flow in the first place. "It's a delicate tradeoff," says Snyder. "Something like trying to blow ice cream through a straw. If the straw's very narrow, the ice cream moves slowly. But if you widen it to help the ice cream move faster, you'll find that you also run out of air faster."

To make sense of these tradeoffs, scientists speak of a quantity known as the "thermoelectric figure of merit," a dimensionless value that can be used to compare the relative efficiency of materials at specific temperatures. The temperature at which peak efficiency is seen depends on the material: each of the Voyager twins, for instance, produces enough juice to power a medium-sized refrigerator, but to do so it must draw heat from decaying radioisotopes. "These new materials are roughly twice as effective as anything seen before, and they work well in a temperature range of around 400 to 900 degrees Kelvin," says Snyder. "Waste heat recovery from a car's engine falls well within that range."

In other words, the heat escaping out your car's tailpipe could be used to help power the vehicle's electrical components—and not just the radio, wipers, and headlights. "You'll see applications wherever there's a solid-state advantage," Snyder predicts. "One example is the charging system. The electricity to keep your car's battery charged is generated by the alternator, a mechanical device driven by a rubber belt powered by the crankshaft. You've got friction, slippage, strain, internal resistance, wear and tear, and weight, in addition to the mechanical energy extracted to make the electricity. Just replacing that one subsystem with a thermoelectric solution could instantly improve a car's fuel efficiency by 10 percent."

As more automotive systems continue their gradual migration from mechanical or hydraulic to electrical—power steering and brakes, for instance, can both be made to run on electricity—the vehicle of the future will sport more than a passing commonality with the spacecraft of the 1970s. "The future of automobiles is electric," says Snyder. "What we're doing now is looking at how to make it all more efficient."

Snyder's coauthors on the paper, "Convergence of electronic bands for high performance bulk thermoelectrics," are Yanzhong Pei, Aaron LaLonde, and Heng Wang of Caltech; and Xiaoya Shi and Lidong Chen of the Shanghai Institute of Ceramics, Chinese Academy of Sciences. The work was supported by NASA-JPL, the DARPA Nano Materials program, and the Chinese Academy of Sciences.

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Dave Zobel
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Jorgensen Renovation Kicks into Gear

Those fences you'll soon see sprouting up around Jorgensen Laboratory are among the less classic signs of spring—and yet, they are very much a symbol of growth and rebirth. Now that the interior demolition of the building has been completed, with some 90 percent of the materials removed being reused or recycled, Jorgensen Lab's much-anticipated renovation is about to begin in earnest.

Once completed in spring of 2012, the building will house two of Caltech's key sustainability research efforts: the Resnick Institute and the Joint Center for Artificial Photosynthesis, or JCAP. The lab's structure and infrastructure will embody the sort of innovative work that will be done within its walls, with a low-energy plant design, building energy information systems, and exhibits showcasing Caltech's energy research.

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Lori Oliwenstein
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Working Toward a Greener Future

Celebrate Earth Day with the Caltech community today from 11 a.m. to 2 p.m. along San Pasqual Walk in front of Chandler and the Red Door.

Chevrolet will have its Volt electric car on display, as well as its new fuel-cell car. Visitors will be able to take a look under the hoods and learn more about the cars. Alternative energy exhibitors at the event include Bloom Energy, a company that builds on-site fuel-cell power generators; Suntech and Verengo, manufacturers of solar energy solutions; and Seesmart LED lights, among others.

Student clubs, including the 2011 Solar Decathlon team, will also be exhibiting at Earth Day. Representatives from Engineers for a Sustainable World—an organization dedicated to sustainable development, scientific problem solving, and social entrepreneurship—will have a display at the event, as will members of the Caltech Community Garden Project.

The popular Kogi Truck will be serving up tacos and other Korean BBQ treats from noon until 2 p.m., with Coolhaus providing architectural-themed ice-cream sandwiches for dessert. Arroyo Food Coop and LifeSource Water will also be on hand for lunch options.

For more information about Caltech's year-round sustainability efforts, visit sustainability.caltech.edu.

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Katie Neith
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Solar Decathlon Team Breaks Ground

The joint Solar Decathlon team of Caltech and the Southern California Institute of Architecture (SCI-Arc) will show off their state-of-the-art, energy-efficient house tomorrow in a groundbreaking ceremony at 2 p.m. at the SCI-Arc campus in Los Angeles. After a year of designing and prototyping, the team will start construction on the house, which will travel to the National Mall in Washington, D.C., this fall for the biennial competition. At the ceremony, the team will raise the first wall.

Student team members will also give tours of a full-sized mock-up of the house and talk about its many engineering and design features. At 3 p.m., Eric Owen Moss, the director of SCI-Arc, and Harry Atwater, Caltech's Howard Hughes Professor and professor of applied physics and materials science and director of the Resnick Institute, will also speak. All are welcome and refreshments will be served.

The Solar Decathlon is a competition sponsored by the U.S. Department of Energy (DOE) in which 20 teams from around the world are selected to design and build the most energy-efficient, affordable, and attractive house they can. Taking place on the National Mall, the Solar Decathlon is a high-profile event that's intended to inspire policymakers, industry leaders, and the public to pursue a sustainable future with cutting-edge design and technology.

Somewhat resembling a giant white pillow, the SCI-Arc/Caltech house features a unique shape and a soft, exterior insulation. As the only two-story building in the competition, the house has a spacious interior, despite an area of only about 800 square feet (contest rules limit the area to between 600 and 1,000 square feet). A central computer controls everything from heating to lighting, optimizing energy use. For example, waste heat from the air-conditioning unit is used to provide hot water. Connected to the Internet, the house can even receive weather-forecast data, allowing it to anticipate cloudy skies and conserve the power generated by its solar panels. To learn more about these and other features of the house, you can attend the groundbreaking ceremony at

SCI-Arc Campus
Solar Decathlon Construction Site
350 Merrick Street
Los Angeles, CA 90013

If you would also like to help the team's outreach efforts—one of the 10 challenges on which the team will be judged—you can visit its Facebook page and click "like."

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Marcus Woo
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