MIT Research News' Journal
[Most Recent Entries]
[Calendar View]
Thursday, September 21st, 2017
| Time |
Event |
| 12:00a |
New analysis explains role of defects in metal oxides Sometimes things that are technically defects, such as imperfections in a material’s crystal lattice, can actually produce changes in properties that open up new kinds of useful applications. New research from a team at MIT shows that such imperfections in a family of materials known as insulating metal oxides may be key to their performance for a variety of high-tech applications, such as nonvolatile memory chips and energy conversion technologies.
The findings are reported this week in the journal Physical Review Letters, in a paper by MIT Associate Professor Bilge Yildiz, Professor and Associate Provost Krystyn Van Vliet, and former postdoc Mostafa Youssef.
These metal oxide materials have been investigated by many researchers, Yildiz says, and “their properties are highly governed by the number and the kind of defects that are present.” When subjected to strong driving forces, such as strong electric fields, “the behavior of such defects had not been well-understood,” she says.
Researchers do have a well-established theoretical understanding of how perfectly structured versions of these insulating metal oxides function under a variety of conditions, such as in strong electric fields, but there was no such theory to describe the materials when they contain common types of defects, according to Yildiz. Understanding these effects quantitatively is important in order to develop this promising family of materials for potential applications including new types of low-energy computer memory and processing devices, electrically based refrigeration, and electro-catalytic energy-conversion devices such as fuel cells.
The team demonstrated a theoretical framework and showed how the stability and structure of a point defect is altered under strong electric fields. They took a common defect called a neutral oxygen vacancy — a place where an oxygen atom should appear in the lattice but instead two electrons are trapped. Their results have quantified the polarization behavior of the material with this defect, in an electric field.
“The oxygen vacancies in particular are very important in electronic and electrochemical applications,” says Yildiz, who holds joint appointments in the departments of Nuclear Science and Engineering and Materials Science and Engineering.
In many of these applications, she says, there can be an internal voltage gradient created within the thin-film material, and this “electric potential” gradient causes strong electric fields. Understanding the effects of those fields is essential for the design of certain new devices.
“Most of the work in this area is experimental,” Yildiz says. “You take a thin film, you put it in an electric field, and you do measurements.” But in such experiments, the effects of the local electric potential and the electric field are convoluted, making it very hard to understand the results. “It’s impossible to resolve them from each other, so you need to have a theory” to account for the effects, she adds.
The researchers have now devised a new theoretical framework that allows them to isolate the electric field effect from the electric potential effect, and quantify both independently. This allowed them to make very specific predictions that are different from those produced by classical theory and should make it possible to validate the new model experimentally within a year, Yildiz says.
The findings should help enable the development of some important potential applications, she says. One is in a new type of computer memory device known as resistive switching memory, which provides fast switching speeds using very little energy. These memory devices rely on the presence of defects.
“The way they switch their resistance state [to record data] depends on the defect type, content, and distribution,” she says. “In order to model the device behavior, you should be able to model how the applied strong electric fields alter the defect structure, concentration, and distribution.” That’s what this new work enables: “If you know quantitatively the effects of both the potential and the field, then you can design your operating conditions to benefit from these effects.”
Understanding these effects is also important for other applications such as splitting water molecules to produce hydrogen at solid-liquid interfaces, electronic devices that rely on oxide-oxide interfaces, or other electrochemical processes using these materials as catalysts, where defects serve as the sites that enable the interactions.
The materials the team studied belong to a class known as alkaline-earth-metal binary oxides, whose constituents are “among the most abundant class of materials on Earth,” Yildiz says. “[This class is] cheap, abundant, and has tunable properties,” making it promising for many applications. But she adds that the theoretical approach they took will now be applied much more broadly, to many other kinds of oxide materials and to other kinds of defects within them besides the neutral oxygen vacancies.
“This work establishes a new paradigm for the study of defects in semiconductors, by setting up the necessary mathematics for the calculation of the defect formation energy in electrically stimulated defective crystals,” says Cesare Franchini, an associate professor of computational materials physics at the University of Vienna, who was not involved in this work. “This work extends the current theories which connect thermodynamics with electric polarization, and will be beneficial for virtually all applications in which defects (and their tunability by electric stimuli) are an asset, including catalysis, electronics, and electrocaloric devices.”
The research was supported by the MRSEC Program of the National Science Foundation and used resources of the National Energy Research Scientific Computing Center, a Department of Energy Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy. | | 10:30a |
Projects make inroads on global food and water challenges With goals that include finding better ways to purify and desalinate water, improving fertilizer production, and preventing food contamination, nearly two dozen research teams presented updates on their work at a day-long event on Sept. 15. The workshop featured the recipients of grants from the Abdul Latif Jameel World Water and Food Security Lab (J-WAFS) program at MIT.
John H. Lienhard V, the Abdul Latif Jameel Professor of Water and Food and the director of J-WAFS, introduced the workshop by reporting that the program has received and funded grant proposals from all five of MIT’s schools, provided 24 seed grants and nine “Solutions” commercialization grants, and attracted industrial partners including the $4 billion water technology company Xylem.
J-WAFS has been awarding seed grants since its founding in 2014. The reports at the workshop included presentations on work that is just getting started under the latest grants, as well as progress reports from grants awarded over the past three years.
Among the newly awarded grants, three relate to improving water supplies for drinking and irrigation. Two others involve ways of providing low-cost, locally sourced fertilizers for crop production, and one is for a method to grow algae in bioreactors for use as animal feed or feedstock for biofuels.
Among the new water sector projects is one by Gail E. Kendall Professor of Mechanical Engineering Evelyn Wang and chemistry professor Mircea Dinca, who are developing a practical, low-cost device to extract potable water directly from the air, even in low-humidity regions. This project builds on technology previously developed in Wang’s lab and potentially could triple or quadruple the water output of the previous version, Wang said.
Another, led by Stephen Graves, the Abraham J. Siegel Professor of Management Science at the Sloan School of Management, and Bish Sanyal, the Ford International Professor of Urban Development in the Department of Urban Studies and Planning, will focus on agricultural extension services in Senegal and why the current services do not reach small farmers. This research will probe to what extent private firms with knowledge of irrigation technology can supplement public efforts. In particular, the research will analyze the current barriers to privately provided irrigation and identify ways in which the benefits of such irrigation practices can be channeled toward small firms.
The fertilizer projects included a concept for deriving potassium fertilizer from feldspar, a mineral that is abundant in Africa and other regions, instead of importing such fertilizers at high cost. The idea is being developed by Associate Professor Antoine Allanore of the Department of Materials Science and Engineering.
Another project, led by Karthish Manthiram, the Warren K. Lewis Assistant Professor in Chemical Engineering, seeks to develop an electrochemical method for producing nitrogen fertilizer using smaller, lower-cost systems than the huge industrial facilities currently used for such production.
“In sub-Saharan Africa, one of the major factors holding back a ‘green revolution’ is a lack of fertilizer use,” said Davide Ciceri, a research scientist on Allanore’s research team. These projects could help to address that lack and increase productivity on farms in Africa, which presently lag far behind those of other continents. “Africa has the lowest yields in the world and the lowest nitrogen fertilizer use,” Manthiram said.
Among the projects nearing the end of their two-year grant term was one that aims to entirely eliminate the need for nitrogen fertilizers, in this case by using biological engineering to create cereal grain species capable of producing their own fertilizer, as some leguminous plants already do. This project, led by professor of biological engineering Christopher Voigt, received a second J-WAFS seed grant this year to further develop the work.
Another concluding project, led by professors Noelle Selin of the Institute for Data, Systems, and Society and the Department of Earth, Atmospheric and Planetary Sciences and Valerie Karplus, the Class of 1943 Career Development Assistant Professor of Global Economics and Management, examined the prevalence of mercury pollution of rice in China and its correlation with emissions from potential contributing sources such as coal plants. These results could help bring about policy changes that focus on both legacy soil contamination and future emissions from the power sector.
Other projects studied ways of using climate change projections to help guide water and agriculture policy in the developing world, and opportunities for increasing food production in these areas. J-WAFS-supported researchers are also studying water systems, including how water percolates into the soil under different conditions — a crucial factor for the recharging of aquifers. Others are investigating how to detect and remediate various sources of pollution in water systems, and ways of detecting specific kinds of pathogens in food, fish, and aquaculture systems, and throughout global food supply chains.
Principal investigators of concluding projects reported that their seed grants have helped them to secure substantial follow-on funding, including a multimillion dollar award for a project on food safety and supply chains, led by MIT Sloan School of Management professors Retsef Levi, Tauhid Zaman, and Yanchong Zheng.
The J-WAFS program funds work in both the developing and developed worlds, Lienhard said. Its researchers have been studying not just new technologies but also the social, economic, and political factors needed to allow such improvements to move toward widespread implementation. “It isn’t enough to have a great invention that works in a lab here in Cambridge. It has to work on site,” he said.
The program was “formed to catalyze research around MIT in the areas of water and food,” Lienhard said. “We’re really interested to see how we can bring the unique strengths of the Institute, in technology and science and business innovation and urban planning and social science, to bear on the urgent challenges that we face around water and food, going into the future.”
“We’ve gotten a lot of great proposals, and we don’t have enough money to fund them all,” he said. “But we’re doing our best to make the money go as far as we can.” J-WAFS will issue a new call for seed research proposals to the MIT community this fall. | | 1:59p |
Babies can learn that hard work pays off If at first you don’t succeed, try, try again.
A new study from MIT reveals that babies as young as 15 months can learn to follow this advice. The researchers found that babies who watched an adult struggle at two different tasks before succeeding tried harder at their own difficult task, compared to babies who saw an adult succeed effortlessly.
The study suggests that infants can learn the value of effort after seeing just a couple of examples of adults trying hard, although the researchers have not studied how long the effect lasts. Although the study took place in a laboratory setting, the findings may offer some guidance for parents who hope to instill the value of effort in their children, the researchers say.
“There’s some pressure on parents to make everything look easy and not get frustrated in front of their children,” says Laura Schulz, a professor of cognitive science at MIT. “There’s nothing you can learn from a laboratory study that directly applies to parenting, but this does at least suggest that it may not be a bad thing to show your children that you are working hard to achieve your goals.”
Schulz is the senior author of the study, which appears in the Sept. 21 online edition of Science. Julia Leonard, an MIT graduate student, is the first author of the paper, and MIT undergraduate Yuna Lee is also an author.
Putting in the effort
Many recent studies have explored the value of hard work. Some have found that children’s persistence, or “grit,” can predict success above and beyond what IQ predicts. Other studies have found that children’s beliefs regarding effort also matter: Those who think putting in effort leads to better outcomes do better in school than those who believe success depends on a fixed level of intelligence.
Leonard and Schulz were interested in studying how children might learn, at a very early age, how to decide when to try hard and when it’s not worth the effort. Schulz’ previous work has shown that babies can learn causal relationships from just a few examples.
“We were wondering if they can do similar fast learning from a little bit of data about when effort is really worth it,” Leonard says.
To do that, they designed an experiment in which 15-month-old babies first watched an adult perform two tasks: removing a toy frog from a container and removing a key chain from a carabiner. Half of the babies saw the adult quickly succeed at the task three times within 30 seconds, while the other half saw her struggle for 30 seconds before succeeding.
The experimenter then showed the baby a musical toy. This toy had a button that looked like it should turn the toy on but actually did not work; there was also a concealed, functional button on the bottom. Out of the baby’s sight, the researcher turned the toy on, to demonstrate that it played music, then turned it off and gave it to the baby.
Each baby was given two minutes to play with the toy, and the researchers recorded how many times the babies tried to press the button that seemed like it should turn the toy on. They found that babies who had seen the experimenter struggle before succeeding pressed the button nearly twice as many times overall as those who saw the adult easily succeed. They also pressed it nearly twice as many times before first asking for help or tossing the toy.
“There wasn’t any difference in how long they played with the toy or in how many times they tossed it to their parent,” Leonard says. “The real difference was in the number of times they pressed the button before they asked for help and in total.”
The researchers also found that direct interactions with the babies made a difference. When the experimenter said the infants’ names, made eye contact with them, and talked directly to them, the babies tried harder than when the experimenter did not directly engage with the babies.
“What we found, consistent with many other studies, is that using those pedagogical cues is an amplifier. The effect doesn’t vanish, but it becomes much weaker without those cues,” Schulz says.
A limited resource
A key takeaway from the study is that people appear to be able to learn, from an early age, how to make decisions regarding effort allocation, the researchers say.
“We’re a somewhat puritanical culture, especially here in Boston. We value effort and hard work,” Schulz says. “But really the point of the study is you don’t actually want to put in a lot of effort across the board. Effort is a limited resource. Where do you deploy it, and where do you not?”
Kiley Hamlin, an associate professor of psychology at the University of British Columbia, described the study as “a lovely demonstration that something we have long thought critical to older childrens’ and adults' likelihood of achieving success in school and in life — persistence on task — can be influenced in infants in the first half of the second year.”
Hamlin, who was not involved in the study, said the findings suggest two important things: “First, infants seem to be learning something about persistence in general, rather than on how to best solve task A or task B specifically. Second, influencing our infants' persistence, at least in the short term, might (ironically) take relatively little effort on our part.”
The researchers hope to investigate how long this effect might last after the initial experiment. Another possible avenue of research is whether the effect would be as strong with different kinds of tasks — for example, if it was less clear to the babies what the adult was trying to achieve, or if the babies were given toys that were meant for older children.
The research was funded by the National Science Foundation Graduate Research Fellowship Program, the MIT Center for Brains, Minds and Machines, and the Simons Center for the Social Brain. | | 4:30p |
Kerry Emanuel: This year’s hurricanes are a taste of the future In a detailed talk about the history and the underlying physics of hurricanes and tropical cyclones, MIT Professor Kerry Emanuel yesterday explained why climate change will cause such storms to become much stronger and reach peak intensity further north, heightening their potential impacts on human lives in coming years.
“Climate change, if unimpeded, will greatly increase the probability of extreme events,” such as the three record-breaking hurricanes of recent weeks, he said.
In Houston, Hurricane Harvey, which devastated parts of the Texas coastline and produced more total rainfall than any U.S. hurricane on record, would have been considered a one-in-2,000-years event during the 20th century, according to the best available reconstructions of the past record of such storms, Emanuel said. But in the 21st century, that probability could drop to one in 100 years, given the likely trajectory of climate change conditions. Hurricane Irma, with its record-breaking duration as a Category 5 storm, will go from being a one-in-800-years event in the area of the Caribbean that suffered a direct hit, to a one-in-80-years event by the end of this century, he said.
Emanuel, the Cecil and Ida Green Professor of Atmospheric Science and co-director of the Lorenz Center at MIT, has long been considered one of the leading researchers on tropical storms including hurricanes and cyclones (which is the name for such storms in the Pacific Ocean), the physical mechanisms that generate them, and the reconstruction of their past frequency and intensity. Ron Prinn, the TEPCO Professor of Atmospheric Science and director of the Center for Global Change Science, said in introducing Emanuel’s talk, “I can’t think of a better person in the world to address this issue of hurricanes,” including what he called the “2017 hurricane train” with its succession of huge storms.
In fact, although his talk had been titled “What Do Hurricanes Harvey and Irma Portend?” Emanuel pointed out that now there was “a tragic irony in presenting this lecture just hours after another hurricane [Maria] has devastated Puerto Rico.” At such a time, he said, “it is natural to ask if these are just natural events.” Referring to Environmental Protection Agency Administrator Scott Pruitt’s recent comments that it was inappropriate to talk about climate change in relation to hurricanes Harvey and Irma, Emanuel wondered aloud “if after 9/11 he would have said that now is not a good time to talk about terrorism?”
Already, over the last four decades, he said, hurricanes and cyclones globally have caused an average of $700 billion in damages annually since 1971. Meanwhile, thanks to population growth and the development of oceanfront property, “the global population exposed to hurricanes has tripled since 1970,” he said.
While hurricanes, like earthquakes and volcanoes, “are part of nature,” Emanuel said, “what we’re talking about are unnatural disasters — disasters we cause by building structures” in places that are inherently vulnerable to such devastating forces.
Because of policies, including the current system of federally provided flood insurance that gives private insurers little motivation to study countermeasures, he said, “we’re going to be having Harveys, Irmas, and Marias as far as the eye can see.”
While much of the news coverage of hurricanes focuses on the powerful winds, which have indeed been a major cause of damage and loss of life in the islands pummeled by Irma and Maria, Emanuel said that overall it is water, not wind, that causes the vast majority of damage from such storms, though most people underestimate the severity of the water impact. To illustrate the point, he showed a short, dramatic video of a hurricane-produced storm surge striking a building. “It is hydrodynamically the same thing as a tsunami,” he explained, as the clip showed water rushing steadily in and quickly engulfing an entire house.
“I wish everyone who lives in zones subject to these storms could see films like this,” he said, adding that the scene depicted was clearly not survivable. “Water is the big killer.”
Part of the difficulty in providing strong, clear documentation of the increasing intensity of hurricanes is the sparsity of the historical records. “Prior to 1943, everything we know about hurricanes on the planet comes from anecdotal accounts,” he said, especially those provided by ships’ logs and news accounts in coastal cities. Still, Emanuel and others have devised a variety of ingenious ways of deducing the hurricane record over much longer periods, using techniques such as taking cores from coastal lagoons to reveal periods when storm surges drove quantities of beach sand far inland, and analyzing the annual rates of shipwrecks over a period of centuries.
Meanwhile, the use of new methods, including a technique for deriving wind speed information from the radio signals from GPS navigational satellites, are starting to provide an unprecedented degree of detail of the internal dynamics of these storms, which should enable researchers to continue to refine their models and may ultimately allow for more accurate forecasting of hurricanes. While projecting of hurricane tracks has already improved greatly, he said, the ability to predict the strength of coming storms is not yet as good.
Emanuel said his calculations of the physics behind the formation and growth of hurricanes indicate that the storms’ strength will continue to increase as the climate warms, but that there are inherent limits to that growth. At some point the maximum size of such storms will begin to level off, he said.
But those limits are still far off. For the near term, Emanuel said that U.S. rainfall events as intense as that produced by hurricane Harvey, which had about a 1 percent annual likelihood in the 1990s, has already increased in likelihood to about 6 percent annually, and by 2090 could be about 18 percent. | | 4:55p |
MIT Nuclear Reactor Laboratory launches seed grant program The MIT Reactor (MITR), built in the 1950s and a long-time presence in Cambridge, Massachusetts, serves as a valuable test bed for research that might have significant impacts on the future. The mission of this nuclear fission reactor is not to generate electricity; rather, it serves as an experimental environment to irradiate materials and characterize their modified properties — critical steps in the development of materials that can withstand radiation for many applications. The current version of the six-megawatt reactor (MITR-II), redesigned and rebuilt in the 1970s, is the second-largest university research reactor in the U.S. and the only one located on the campus of a major research university.
The reactor is operated by the MIT Nuclear Reactor Laboratory (NRL), an interdepartmental center that has long supported education and research in areas such as nuclear fission engineering, materials science, radiation effects in biology and medicine, neutron physics, geochemistry, and environmental studies.
Lin-wen Hu, NRL director of research and services and senior research scientist, says that although the reactor is available to MIT researchers — she used it for her own doctoral thesis research, for example — the majority of current users are from industry, national labs, and other academic institutions.
“We’re very fortunate that the MIT administration has supported the reactor since its inception,” says Hu. “We want to broaden the user base of the reactor — including increasing access for the MIT community.”
The new NRL Seed Program will give a few selected projects of MIT faculty and research staff cost-free access to the reactor’s experimental facilities, instruments, and technical support. This program has two main goals: to cultivate new research areas and to generate data in support of pursuing externally funded research proposals. The ability to use the reactor free-of-cost is a tremendous opportunity, as running an experiment in a nuclear reactor can cost from hundreds of thousands to millions of dollars.
Hu says that the NRL research and services group she started to assist users for research projects “has reached critical mass,” and has the infrastructure and expertise in place to work with more MIT faculty and research staff.
Four different categories of experiments, described in detail on the program webpage, will be considered for funding. These include: small-scale dedicated irradiation experiments, shared use in-core experiments, neutron beams and instruments, and materials characterization and post-irradiation evaluation.
A variety of different research applications might benefit from experiments using the reactor. For example, it could be used for testing a wide range of materials or sensors — such as those proposed for a next-generation reactor or for a robot that might be built to clean up after a nuclear incident — to understand how their properties change in a radiation environment. Research might involve using a neutron beam port, which provides neutrons to probe a material structure, or neutron activation analysis to detect even very small amounts of an element in a material.
Research submitted for the grant program can be done in collaboration with industry, national labs, or other universities, but the lead researcher submitting the project must be an MIT faculty or research staff member. Projects should demonstrate that early results or data will lead to proposals for external funding. Submission deadlines are Oct. 15, 2017 and April 15, 2018, and selected proposals will be announced a few weeks after each deadline. |
|