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Monday, March 2nd, 2015
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| 9:45a |
New analysis shows ion slowdown in fuel cell material Dislocations in oxides such as cerium dioxide, a solid electrolyte for fuel cells, turn out to have a property that is the opposite of what researchers had expected, according to a new analysis at MIT.
Researchers had thought that a certain kind of strain — specifically, strain caused by dislocations in the material’s atomic lattice — would speed the transport of oxygen ions through the material, potentially leading to the much faster diffusion that is necessary in high-performance solid oxide fuel cells, water-splitting, or oxygen-separation membranes. But the new atomic-level simulation of oxide ion transport has revealed that while these dislocations do greatly accelerate atom transport in metals, they can have the opposite effect in this metal-oxide material, and possibly in many others.
Instead of easing ion mobility, it turns out that dislocations in cerium dioxide cause a kind of “traffic jam” for the flowing ions, slowing them to a crawl, says MIT graduate student Lixin Sun, lead author of a paper describing the analysis in the journal Nature Communications.
In cerium dioxide, which is already used as an electrolyte material in solid oxide fuel cells, the simulation shows that “edge dislocations slow down oxide ion diffusion, contrary to the well-known fast diffusion of atoms along dislocations in metals,” says Bilge Yildiz, an associate professor of nuclear science and engineering and of materials science and engineering, who was the paper’s senior author. The surprising result suggests that researchers will need to pursue different approaches in trying to speed up the movement of these ions.
The work is part of ongoing studies by Yildiz and her team, which also includes co-author and research scientist Dario Marrocchelli, into how various kinds of strain in thin-film materials can be used to alter and improve the transport and surface reaction kinetics of those materials, often in dramatic ways.
“People have argued about the role of strain [in cerium dioxide],” Sun says. “Some say strain can enhance the oxide ion transport for devices like solid oxide fuel cells. But others say no, and the experimental results show orders-of-magnitude scatter.”
While there is extensive existing research on ion transport under elastic strain — such as when a rubber band stretches, but then returns to its original length when released — the same is not true of transport along dislocations resulting from plastic strain in oxides.
Plastic strain — such as when a stretched piece of taffy remains stretched — introduces extended defects called dislocations into crystalline structures; the accelerating effect that dislocations have on atom transport in metals has been widely studied, Yildiz says. “But in oxides, which are important in energy-conversion devices such as fuel cells, electrolyzers, and batteries, the dislocation effects remains largely understudied,” she adds. “It’s never been studied at the atomic level to reveal what an individual dislocation does to oxide ion transport, and that’s why we turned our attention to it.”
Because that kind of strain has been more difficult to simulate and measure, Sun says, “People speculated that it could enhance ionic transport,” since that’s what happens with metals.
While the new findings were based on a detailed analysis of the molecular structure of cerium dioxide, Sun says the results “should be general to those materials that have a high concentration of defects” — which include many, but not all, metal oxides.
Specifically, the results showed that dislocations accumulate too many oxygen vacancies and dopant metal cations, and as a result these ionic defects interact and trap each other, “like too many cars clogging a highway”, Sun says.
The research was supported by the U.S. Department of Energy and the National Science Foundation. | | 12:00p |
Six keys to sports analytics The ninth annual MIT Sloan Sports Analytics Conference (SSAC) was the biggest meeting yet of sports-data experts: More than 3,100 people attended the event last Friday and Saturday, including a notable number of 6-foot-8-inch former NBA forwards roaming around inside the Boston Convention and Exhibition Center. Founded by Houston Rockets general manager Daryl Morey SM ’00 and sports executive Jessica Gelman, SSAC illuminates the state of its high-profile industry. Here are some key takeaways from the 2015 event.
1. Sports analytics has made a big impact — sometimes
In 2006, Morey traded for Shane Battier, a forward averaging only 10 points per game. But advanced metrics showed Battier was an outstanding player due to his fine defense and shot selection. The Rockets soon started giving Battier an unprecedented level of statistical information about the opponents he had to guard.
“It was the first time someone was speaking my language in basketball,” Battier said at a Friday panel. “It wasn’t just [about] heart and grit.”
Battier, now retired, recalled this onstage with Morey; Jeff Van Gundy, his former Rockets coach; and author Michael Lewis, whose 2009 New York Times profile of Battier introduced several analytics concepts to the general public, such as the fact that the corner three-pointer is the most efficient shot in basketball.
By 2011, the secret was out: The Miami Heat signed Battier, and then other efficient players, such as Mike Miller and Ray Allen, to support stars LeBron James and Dwyane Wade; they promptly won two straight championships.
“The market for your services changed,” Lewis said to Battier: Sometimes, in sports, analytics has a large effect, quickly.
2. Still, most teams aren’t that analytical
Overall, however, it remains hard to get teams to accept data-driven ideas. NFL teams are still notoriously conservative on fourth-down plays, while football play-calling in general is too predictable.
“I think a Twister spinner could probably call a game better than some offensive coordinators,” said Brian Burke, founder of the web site Advanced Football Analytics, making the point that more randomization on offense would help.
Meanwhile, some basketball analytics, such as the statistic known as “win shares,” show the value of old-school virtues such as defense, rebounding, avoiding turnovers, and taking good shots. But many NBA teams still give huge contracts to players like Carmelo Anthony, a so-called “ball-stopper” because he does not pass enough.
“We are still stuck in [thinking] the best players are ball-stoppers … and it’s got to change,” former NBA coach Mike D’Antoni said on Friday.
3. Analysts need to explain themselves
To be useful, advanced analysis demands clear explanations for coaches, managers, and players. If analytics shows that a baseball team should alter its defensive positioning, or that long two-point shots in basketball are bad — and does it ever — this has to be explained in everyday language.
“It’s not what you know, it’s what you can impart on people,” Van Gundy said.
“It’s the message that’s important, but the messenger can be just as important,” New York Mets general manager Sandy Alderson added.
It does happen: Battier helped get James interested in analytics by giving him tips about guarding rival star Kevin Durant. James has since bought into shot-efficiency data, too.
“Once he had that little [bit], he wanted more,” Battier said. “If the greatest player of his generation is looking for an edge, I think other people would be wise to follow.”
4. Competition can hold analytics back
Commentators occasionally complain that SSAC panelists are not candid enough. But at this year’s soccer analytics panel, Michael Niemeyer, analytics head of German powerhouse Bayern Munich, divulged several insider insights. When Bayern Munich was preparing to play AS Roma this season, positional data showed that one of Roma’s three strikers, the longtime star Francesco Totti, played well behind the other two. So Bayern Munich could play just three defenders while still outnumbering Roma’s strike force. By contrast, Manchester City’s pattern of attacks convinced Bayern Munich’s manager, Pep Guardiola, to play four defenders.
Guardiola, a noted experimenter, “asks me for things,” Niemeyer said, adding, “It’s always about numeric advantage. … If you know that the coach wants to see this information, then you look for that.”
Analytics was once open, academic-style: Bill James, whose annual “Baseball Abstract” books launched the field in the 1980s, has always published his formulas. But teams do not, which may hurt the field’s long-term progress.
Yet Niemeyer’s openness at SSAC reflects the culture of German soccer: The analytics staffs of top-level German teams have league-wide meetings where they share their best practices, then return to working independently.
“That is the right way to do it,” Niemeyer said.
5. Look under the hood
It’s not just teams who can be secretive: Today, many independent analysts do not show their work, either. And some metrics shoot to prominence without being fully vetted, like baseball’s WAR (“wins above replacement”), a much-hyped attempt to sum up a player’s total contributions. But recently critics, including Bill James, have questioned the lack of transparency in some versions of WAR, the high value it places on defense, and more. Even WAR proponents at SSAC this year agreed it’s a work in progress.
“It’s a flawed metric,” conceded Dave Cameron, managing editor of the popular baseball analytics site FanGraphs, noting that WAR is composed of heterogeneous evaluations of offense and defense. Still, Cameron defended the general value of WAR, while saying he welcomed outside input: “We’re trying to improve it.”
Meanwhile, basketball has several advanced metrics for judging a player’s total contributions. For one, win shares highly values Battier-style efficiency, while PER (“player efficiency rating”) is kinder to gunners like Anthony.
Understanding the assumptions behind any statistic “makes you think” about your own views, Van Gundy noted on Friday. That’s the essence of analytics: Don’t trust, but verify — with data.
6. You, too, can be in this business
Let’s assume you watch sports with a keen analytical eye: How can you get into the sports analytics business?
“If you’re doing good work, it will get noticed,” said Chris Anderson, co-author of “The Numbers Game,” a leading soccer analytics book. The classic path for a professional analyst involves being noticed as writer or blogger, then making the leap to an analytics-minded franchise.
“Find ways to make it actionable,” added Tyler Dellow, a former hockey blogger who is now a consultant for the NHL’s Edmonton Oilers. “Find ways to help coaches.”
“Do good work,” said Dallas Eakins, a former coach of the Oilers. “Have an opinion. And be able to back up your opinion.”
Kyle Dubas, a young assistant general manager of the NHL’s Toronto Maple Leafs, expressed the most reassuring view.
“Be yourself, and everything will be fine,” Dubas said. | | 3:00p |
New nanodevice defeats drug resistance Chemotherapy often shrinks tumors at first, but as cancer cells become resistant to drug treatment, tumors can grow back. A new nanodevice developed by MIT researchers can help overcome that by first blocking the gene that confers drug resistance, then launching a new chemotherapy attack against the disarmed tumors.
The device, which consists of gold nanoparticles embedded in a hydrogel that can be injected or implanted at a tumor site, could also be used more broadly to disrupt any gene involved in cancer.
“You can target any genetic marker and deliver a drug, including those that don’t necessarily involve drug-resistance pathways. It’s a universal platform for dual therapy,” says Natalie Artzi, a research scientist at MIT’s Institute for Medical Engineering and Science (IMES), an assistant professor at Harvard Medical School, and senior author of a paper describing the device in the Proceedings of the National Academy of Sciences the week of March 2.
To demonstrate the effectiveness of the new approach, Artzi and colleagues tested it in mice implanted with a type of human breast tumor known as a triple negative tumor. Such tumors, which lack any of the three most common breast cancer markers — estrogen receptor, progesterone receptor, and Her2 — are usually very difficult to treat. Using the new device to block the gene for multidrug resistant protein 1 (MRP1) and then deliver the chemotherapy drug 5-fluorouracil, the researchers were able to shrink tumors by 90 percent in two weeks.
Overcoming resistance
MRP1 is one of many genes that can help tumor cells become resistant to chemotherapy. MRP1 codes for a protein that acts as a pump, eliminating cancer drugs from tumor cells and rendering them ineffective. This pump acts on several drugs other than 5-fluorouracil, including the commonly used cancer drug doxorubicin.
“Drug resistance is a huge hurdle in cancer therapy and the reason why chemotherapy, in many cases, is not very effective”, says João Conde, an IMES postdoc and lead author of the PNAS paper.
To overcome this, the researchers created gold nanoparticles coated with strands of DNA complementary to the sequence of MRP1 messenger RNA — the snippet of genetic material that carries DNA’s instructions to the rest of the cell.
These strands of DNA, which the researchers call “nanobeacons,” fold back on themselves to form a closed hairpin structure. However, when the DNA encounters the correct mRNA sequence inside a cancer cell, it unfolds and binds to the mRNA, preventing it from generating more molecules of the MRP1 protein. As the DNA unfolds, it also releases molecules of 5-fluorouracil that were embedded in the strand. This drug then attacks the tumor cell’s DNA, since MRP1 is no longer around to pump it out of the cell.
“When we silence the gene, the cell is no longer resistant to that drug, so we can deliver the drug that now regains its efficacy,” Conde says.
When each of these events occurs — sensing the MRP1 protein and releasing 5-fluorouracil — the device emits fluorescence of different wavelengths, allowing the researchers to visualize what is happening inside the cells. Because of this, the particles could also be used for diagnosis — specifically, determining if a certain cancer-related gene is activated in tumor cells.
Controlled drug release
The DNA-coated gold nanoparticles are embedded in an adhesive gel that stays in place and coats the tumor after being implanted. This local administration of the particles protects them from degradation that might occur if they were administered throughout the body, and also enables sustained drug release, Artzi says.
In their mouse studies, the researchers found that the particles could silence MRP1 for up to two weeks, with continuous drug release over that time, effectively shrinking tumors.
This approach could be adapted to deliver any kind of drug or gene therapy targeted to a specific gene involved in cancer, the researchers say. They are now working on using it to silence a gene that stimulates gastric tumors to metastasize to the lungs.
“This is an impressive study that harnesses expertise at the interface of materials science, nanotechnology, biology, and medicine to enhance the efficacy of traditional chemotherapeutics,” says Jeffrey Karp, an associate professor of medicine at Harvard Medical School and Brigham and Women’s Hospital, who was not involved in the research. “Hopefully this approach will perform in studies beyond 14 days and be translatable to patients, who are desperate for new and more effective treatment regimens.”
Graduate student Nuria Oliva is also an author of the paper. The research was funded by the National Cancer Institute and a Marie Curie International Outgoing Fellowship. | | 3:00p |
Mystery solved: Why seashells’ mineral forms differently in seawater For almost a century, scientists have been puzzled by a process that is crucial to much of the life in Earth’s oceans: Why does calcium carbonate, the tough material of seashells and corals, sometimes take the form of calcite, and at other times form a chemically identical form of the mineral, called aragonite, that is more soluble — and therefore more vulnerable to ocean acidification?
Researchers had previously identified variations in the concentration of magnesium in the water as a key factor in that process, but had never been able to explain why that produced such a dramatic effect. Now scientists at MIT and Lawrence Berkeley National Laboratory (LBNL) have carried out a detailed, atomic-level analysis of the process. The new explanation, they say, could be a step toward enabling the directed synthesis of new materials on demand in the lab.
The findings are published this week in the Proceedings of the National Academy of Science by graduate student Wenhao Sun; Gerbrand Ceder, the Richard P. Simmons Professor in Metallurgy at MIT; and three others.
“The big-picture problem is about materials formation,” Sun explains. “When solids crystallize in solution, you expect them to make the lowest-energy, [most] stable crystal structure.”
Many materials perform better when they are metastable: stable under ordinary conditions, but subject to transformation to a more stable state over time. For example, metastable forms are more soluble, which can be beneficial for pharmaceuticals because it means they can more easily be taken up by the body. Other technologies, such as battery materials and water-splitting photocatalysts, require long-term stability and therefore do better as the stable phase.
Sun explains that the team chose to explore metastability using calcium carbonate because many decades of good experimental data are available, making it a good case for study of why some chemical reactions preferentially produce one of several possible forms of a compound.
Calcium carbonate can take the form of two different minerals: Calcite is the stable form, whereas aragonite is metastable: Over time, or when heated, it can ultimately transform into calcite. Another familiar example of such materials, Sun explains, is diamond versus graphite, the material of pencil lead: While both have the same composition — pure carbon — diamond is the metastable form, and over time will ultimately turn to graphite.
Calcium carbonate usually crystallizes as calcite, but surprisingly, it forms aragonite in seawater. The outcome affects many different processes — including the global carbon cycle, neutralizing carbon dioxide in the atmosphere into a stable mineral and limiting its buildup in the air. It also affects the formation of shells and corals, whose aragonite shells are vulnerable to the ocean acidification associated with climate change.
While scientists have known that different concentrations of magnesium in the surrounding water affect the fate of calcium carbonate, they have had no explanation for this. The MIT team’s analysis shows that the ratio of calcium to magnesium in the water affects the surface energy of the nucleating crystals; when that ratio passes a specific value, it tips the balance from forming calcite to forming aragonite.
“The surface energy is the barrier to nucleation,” Sun says. “We were able to calculate the effect of magnesium on the surface energy.” Though this surface energy is difficult to measure experimentally, the team was able to determine it through atomic-level calculations, he says: “We discovered that this was the mechanism of how magnesium stops the formation of the stable phase.”
If there is no magnesium in the solution, the stable calcite forms quickly, Sun says. “But as you increase the magnesium concentration, the calcite surface energy increases, and its nucleation rate drops by orders of magnitude,” he adds. “Eventually the nucleation of calcite gets frozen out, and you’re stuck with the metastable aragonite phase.”
The researchers’ calculated results closely match the proportions of the two forms seen experimentally when the magnesium ratios are varied, Sun says, showing that the analysis provides a tool to predict how other compounds will form from a solution.
Ultimately, the MIT team’s goal is to predict and control which materials form under various chemical solutions, making it possible to control the formation of new materials whose characteristics — such as hardness, chemical reactivity, transparency, or conductivity — are useful for technological applications.
The research is an outgrowth of the MIT- and LBNL-based Materials Project, conceived by Ceder, which has created an online database and tools to allow researchers to explore possible combinations of elements and discover new materials for specific purposes. These tools allow people to find chemical compounds that may never have been tried before, but which should exhibit the desired properties.
“So far, computational materials science has been very useful at predicting which materials might possess desirable technological properties,” Sun says, “This work enables us to predict how to reliably make them.”
The research team also included Saivenkataraman Jayaraman from MIT and Wei Chen and Kristin Persson of LBNL. The work was supported by the U.S. Department of Energy and the National Science Foundation. |
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