Thursday, January 2nd, 2014

Time	Event
10:00a	Making silicon devices responsive to infrared light Researchers have tried a variety of methods to develop detectors that are responsive to a broad range of infrared light — which could form imaging arrays for security systems, or solar cells that harness a broader range of sunlight’s energy — but these methods have all faced limitations. Now, a new system developed by researchers at five institutions, including MIT, could eliminate many of those limitations. The new approach is described in a paper published in the journal Nature Communications by MIT graduate student Jonathan Mailoa, associate professor of mechanical engineering Tonio Buonassisi, and 11 others. Silicon, which forms the basis of most semiconductor and solar-cell technology, normally lets most infrared light pass right through. This is because the material’s bandgap — a fundamental electronic property — requires an energy level greater than that carried by photons of infrared light. “Silicon usually has very little interaction with infrared light,” Buonassisi says. Various treatments of silicon can mitigate this behavior, usually by creating a waveguide with structural defects or doping it with certain other elements. The problem is that most such methods have significant negative effects on silicon’s electrical performance; only work at very low temperatures; or only make silicon responsive to a very narrow band of infrared wavelengths. The new system works at room temperature and provides a broad infrared response, Buonassisi says. It incorporates atoms of gold into the surface of silicon’s crystal structure in a way that maintains the material’s original structure. Additionally, it has the advantage of using silicon, a common semiconductor that is relatively low-cost, easy to process, and abundant. The approach works by implanting gold into the top hundred nanometers of silicon and then using a laser to melt the surface for a few nanoseconds. The silicon atoms recrystallize into a near-perfect lattice, and the gold atoms don’t have time to escape before getting trapped in the lattice. In fact, the material contains about 1 percent gold, an amount more than 100 times greater than silicon’s solubility limit: Normally, this is as if one put more sugar into a cup of coffee than the liquid could absorb, leading to accumulation of sugar at the bottom of the cup. But under certain conditions, materials can exceed their normal solubility limits, creating what’s called a supersaturated solution. In this case, the new processing method produces a layer of silicon supersaturated with gold atoms. “It’s still a silicon crystal, but it has an enormous amount of gold near the surface,” Buonassisi says. While others have tried similar methods with materials other than gold, the MIT team’s work is the first clear demonstration that the technique can work with gold as the added material, he says. “It’s a big milestone, it shows you can do this,” Mailoa says. “This is especially attractive because we can show broadband infrared response in silicon at room temperature.” While this is early-stage work, for some specialized purposes — such as a system for adjusting infrared laser alignment — it might be useful relatively quickly. This use of gold was a surprise: Usually gold is incompatible with anything involving silicon, Buonassisi says. Even the tiniest particle of it can destroy the usefulness of a silicon microchip — so much so that in many chip-manufacturing facilities, the wearing of gold jewelry is strictly prohibited. “It’s one of the most dangerous impurities in silicon,” he says. But at the very high concentrations achieved by laser doping, Buonassisi says, gold can have a net positive optoelectronic impact when infrared light shines on the device. While this approach might lead to infrared imaging systems, Buonassisi says, its efficiency is probably too low for use in silicon solar cells. However, this laser processing method might be applicable to different materials that would be useful for making solar cells, he says. The research was funded by the U.S. Army Research Office, the National Science Foundation, the U.S. Department of Energy, and the MIT-KFUPM Center for Clean Water and Energy, a joint project of MIT and the King Fahd University of Petroleum and Mining. (Comment on this)
7:00p	Study: Having Medicaid increases emergency room visits Adults who are covered by Medicaid use emergency rooms 40 percent more than those in similar circumstances who do not have health insurance, according to a unique new study, co-authored by an MIT economist, that sheds empirical light on the inner workings of health care in the U.S. The study takes advantage of Oregon’s recent use of a lottery to assign access to Medicaid, the government-backed health-care plan for low-income Americans, to certain uninsured adults. The research examines emergency room records for roughly 25,000 people over 18 months. “When you cover the uninsured, emergency room use goes up by a large magnitude,” says Amy Finkelstein, the Ford Professor of Economics at MIT and a principal investigator of the study, along with Katherine Baicker, a professor at the Harvard School of Public Health. The study, which is being published today in the journal Science, also documents that having Medicaid consistently increases visits to the emergency room across a range of demographic groups, types of visits, and medical conditions, including types of conditions that may be most readily treatable in primary-care situations. “In no case were we able to find any subpopulations, or type of conditions, for which Medicaid caused a significant decrease in emergency department use,” Finkelstein adds. “Although one always needs to be careful generalizing to other settings, these results suggest that other Medicaid expansions are unlikely to decrease emergency room use.” What’s the policy upshot? The study is highly relevant to the current landscape in the U.S.: With the implementation of the Affordable Care Act, Medicaid is expanding in many states to cover a population similar to the one that gained Medicaid through Oregon’s lottery. The results in this paper, however, suggest nuances to the current debates over the expansion of Medicaid, medical costs, and the role of emergency rooms in providing care. On one level, the results accord with a traditional economics framework suggesting that insurance, by lowering out-of-pocket costs, would increase the use of medical care. Or, as Finkelstein observes, “If we’ve lowered the price of the emergency department, we would expect people to use it more.” However, Medicaid also lowers the out-of-pocket costs of other types of health care, such as primary-care doctors. Some policy analysts have suggested that expanding Medicaid could reduce emergency department visits by the formerly uninsured by bringing them into more regular contact with primary-care doctors and clinics for preventive care. In theory, that could also reduce overall system costs, since urgent care is expensive. Indeed, prior work by Finkelstein, Baicker, and others on Oregon’s lottery applicants showed that people who obtain Medicaid increase their use of primary and preventive care. But as Finkelstein points out, the net effect of Medicaid in the study was to also increase use of emergency services. Hypothetically, Finkelstein notes, the results “could have gone either way, which makes empirical work all the more important.” Other scholars in the field say the study opens the way for further scrutiny of emergency room use. Amitabh Chandra, an economist and professor at the Harvard Kennedy School who has read the paper, praises the study as “exemplary social science,” and says the results underscore our need to learn more about the circumstances in which people use emergency rooms. “People are going to want to find out how sick they are,” Chandra says. “The emergency room is a great place to find out. We should not view [use of] the emergency room as a failure of our health-care system.” Instead, he adds, “The big unanswered question is, ‘Which effect is causing them to go to the emergency room?’” Lottery numbers The study’s rigor derives from a unique policy the state of Oregon implemented in 2008. State officials, recognizing that they had Medicaid funds for about 10,000 additional low-income adults, developed a lottery to fill those slots, for which about 90,000 Oregonians applied. From the viewpoint of academic researchers, the lottery system presented the opportunity for a randomized controlled evaluation of Medicaid, since it created a group of state residents obtaining Medicaid coverage who were otherwise similar, on aggregate, to the applicants who continued to lack coverage. “It’s not that we’re the first to look at the effects of Medicaid empirically, but we are the very first to have a randomized controlled trial of the effect of covering the uninsured with Medicaid,” Finkelstein says. In Oregon, uninsured adults are eligible for the lottery-based Medicaid program when their annual income falls below the federal poverty level established by the U.S. Department of Health and Human Services, which in 2013 is roughly $11,490 for a single person or $23,550 for a family of four. In addition to Finkelstein and Baicker, the co-authors of the Science paper, titled “Medicaid Increases Emergency Department Use: Evidence from Oregon’s Health Insurance Experiment,” were lead author Sarah Taubman of the National Bureau of Economic Research, Heidi Allen of Columbia University’s School of Social Work, and Bill Wright of the Center for Outcomes Research and Education at Providence Health and Services in Portland, Ore. It is the latest paper to emerge from an ongoing study, led by Finkelstein and Baicker, of the lottery applicants in Oregon’s Medicaid system. In a 2011 paper published in the Quarterly Journal of Economics, they showed that Medicaid coverage increases doctor visits, prescription drug use, and hospital admissions; reduces out-of-pocket expenses or unpaid medical debt; and increases self-reported good health. In a 2013 paper published in the New England Journal of Medicine, they showed that Medicaid coverage reduces the incidence of depression but does not produce measured improvements in physical health. Finkelstein says she has been motivated by the Oregon study, and its reception, to create a new research group, J-PAL North America. Co-founded with Harvard economist Lawrence Katz, the group is meant to encourage randomized evaluations on policies and social issues in the U.S. It is the newest branch of MIT’s Abdul Latif Jameel Poverty Action Lab, which was founded in 2003 to support randomized trials in development economics globally. “It’s relatively rare to have this kind of randomized controlled trial on a major [policy] issue,” Finkelstein says. “And I’d like that to become less the exception, and closer to the norm.” (Comment on this)

<< Previous Day

2014/01/02 [Calendar]

Next Day >>