Image of the Day: Global perspectives on a comet

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Photographers from around the globe received awards for their stunning images of comet C/2012 S1 (ISON) at the Northeast Astronomy Forum held at Rockland Community College recently. The National Science Foundation’s Division of Astronomical Sciences, Astronomy magazine and Discover magazine co-sponsored the photo contest.
Shown here is People’s Choice award winner Eric Cardoso’s photo, “Comet ISON,” from Setúbal, Portugal.

Image credit: Eric Cardoso

3 Questions: Michael Greenstone on the experimental method in environmental economics

How can scholars get traction on environmental problems, particularly those relating to pollution? In an essay appearing in this week’s issue of the journal Science, MIT economist Michael Greenstone, along with co-authors Francesca Dominici and Cass Sunstein of Harvard University, make the case for “quasi-experiments,” or “natural experiments,” which have gained prominence in other domains of the social sciences. Environmental economics, they suggest, can rely increasingly on quasi-experiments to sharpen its conclusions about which kinds of environmental action are most cost-effective. Greenstone sat down with MIT News to discuss the subject.

Q. Why should quasi-experiments be in the environmental economics toolbox?

A. The single best way to learn about the world is through randomized controlled trials (RCTs). Now, some problems are not directly amenable to RCTs. In the case of climate change, we don’t have a second planet to randomly assign climate change to, or not. And that means to learn about a lot of environmental problems, such as climate change or air quality, we have to turn to other methods.

The conventional approach to doing that has been to rely on comparisons of places that are more polluted to places that are less polluted. [But] places that are more polluted might have other things that are different about them, besides the pollution. In this paper we have highlighted a potential solution, the use of quasi-experimental evaluation techniques, which mimic some of the features of an experiment, in the sense that there is a group that receives the treatment and a [very similar] group that doesn’t. But [this] is based on nature or politics or some other accident, rather than being done through random assignment.

In the case of environmental questions, there has been great progress in the last 10 to 15 years applying quasi-experiments to environmental questions. This same revolution has been occurring in other fields — labor economics, development economics, public finance, statistics, and criminology. This “credibility revolution,” as some people refer to it, tries to move beyond simple comparisons.

Q. What are some kinds of topics or findings that attest to the value of quasi-experiments in environmental economics?

A. One is a comparison of what happened to air pollution-related diseases during the Beijing Olympics, when the Chinese government shut down, by fiat, many sources of air pollution. Others have been taking advantage of the way the Clean Air Act was implemented in the U.S., using places that were otherwise similar, some of which were regulated stringently and others were much less so, [and measuring] what happens to air quality, infant mortality rates, housing prices, and manufacturing activity in those places.

More recently I [co-authored] a paper [with Yuyu Chen, Avraham Ebenstein, and Hongbin Li], on air pollution and life expectancy, by looking at a region in China where there were very large increases in particulate air pollution relative to otherwise seemingly similar places. If you go back to the planning period in China, they didn’t have enough money to heat all of China during the winter, so they implemented an arbitrary rule, which is often the hallmark of quasi-experiments. This arbitrary rule was that all places north of the Huai River were to receive free winter heating, largely derived from coal combustion, and in places to the south, no heating was allowed.

The first result of that paper is that there are dramatic differences in particulate air pollution [between the] north and south [sides] of the river, due to the Huai River heating policy. The second result is: That appears to be matched by sharp declines in life expectancy, just to the north of the river, and just to the south. If you were unfortunate enough to be an intended beneficiary of this policy, the consequences appear substantial: The people who live to the north have a life expectancy of about five years less than people just to the south. If you took those estimates literally, it would suggest the half a billion people in the north are losing 2.5 billion years of life expectancy, which is a staggering figure.

There is another remarkable thing about particulates that motivated us to write the Science paper: We just went back into old [Office of Management and Budget] reports on the benefits of regulation, and somewhere between one-third and one-half of all benefits from all regulations come from the regulation of pollution — and one [form of] air pollution in particular, particulates in air pollution.

Q. When we talk about cost-benefits analyses regarding health, it can create trepidation among those who think focusing on limiting costs may lead to less emphasis on benefits. Quasi-experiments may be sharper tools, but are they also policy-neutral in this sense?

A. Let’s start with the [opposite] case, where we rule out quantitative analysis as being too easily politicized. I think what happens in that vacuum is that people with vested interests rush in. And by definition they do not have the welfare of the full country at heart; they have the welfare of the interest groups or businesses they’re running or representing, be they pro-environment or anti-environment. And I think quantification is absolutely central to being able to constrain those arguments. There is no question that quantification can be abused like anything else can be abused. But I think the role of the university and the academy is to put out, as best they can, credible answers, and what I have observed in the political process is that high-level academic research does not always drive policy decisions, but it puts bounds on the policy discussion. Those bounds constrain the policy decisions to a region around the best evidence. And that can be very valuable.

By Peter Dizikes | MIT News Office

A river of plasma, guarding against the sun

The Earth’s magnetic field, or magnetosphere, stretches from the planet’s core out into space, where it meets the solar wind, a stream of charged particles emitted by the sun. For the most part, the magnetosphere acts as a shield to protect the Earth from this high-energy solar activity.

But when this field comes into contact with the sun’s magnetic field — a process called “magnetic reconnection” — powerful electrical currents from the sun can stream into Earth’s atmosphere, whipping up geomagnetic storms and space weather phenomena that can affect high-altitude aircraft, as well as astronauts on the International Space Station.

Now scientists at MIT and NASA have identified a process in the Earth’s magnetosphere that reinforces its shielding effect, keeping incoming solar energy at bay.

By combining observations from the ground and in space, the team observed a plume of low-energy plasma particles that essentially hitches a ride along magnetic field lines — streaming from Earth’s lower atmosphere up to the point, tens of thousands of kilometers above the surface, where the planet’s magnetic field connects with that of the sun. In this region, which the scientists call the “merging point,” the presence of cold, dense plasma slows magnetic reconnection, blunting the sun’s effects on Earth.

“The Earth’s magnetic field protects life on the surface from the full impact of these solar outbursts,” says John Foster, associate director of MIT’s Haystack Observatory. “Reconnection strips away some of our magnetic shield and lets energy leak in, giving us large, violent storms. These plasmas get pulled into space and slow down the reconnection process, so the impact of the sun on the Earth is less violent.”

Foster and his colleagues publish their results in this week’s issue of Science. The team includes Philip Erickson, principal research scientist at Haystack Observatory, as well as Brian Walsh and David Sibeck at NASA’s Goddard Space Flight Center.

Mapping Earth’s magnetic shield

For more than a decade, scientists at Haystack Observatory have studied plasma plume phenomena using a ground-based technique called GPS-TEC, in which scientists analyze radio signals transmitted from GPS satellites to more than 1,000 receivers on the ground. Large space-weather events, such as geomagnetic storms, can alter the incoming radio waves — a distortion that scientists can use to determine the concentration of plasma particles in the upper atmosphere. Using this data, they can produce two-dimensional global maps of atmospheric phenomena, such as plasma plumes.

These ground-based observations have helped shed light on key characteristics of these plumes, such as how often they occur, and what makes some plumes stronger than others. But as Foster notes, this two-dimensional mapping technique gives an estimate only of what space weather might look like in the low-altitude regions of the magnetosphere. To get a more precise, three-dimensional picture of the entire magnetosphere would require observations directly from space.

Toward this end, Foster approached Walsh with data showing a plasma plume emanating from the Earth’s surface, and extending up into the lower layers of the magnetosphere, during a moderate solar storm in January 2013. Walsh checked the date against the orbital trajectories of three spacecraft that have been circling the Earth to study auroras in the atmosphere.

As it turns out, all three spacecraft crossed the point in the magnetosphere at which Foster had detected a plasma plume from the ground. The team analyzed data from each spacecraft, and found that the same cold, dense plasma plume stretched all the way up to where the solar storm made contact with Earth’s magnetic field.

A river of plasma

Foster says the observations from space validate measurements from the ground. What’s more, the combination of space- and ground-based data give a highly detailed picture of a natural defensive mechanism in the Earth’s magnetosphere.

“This higher-density, cold plasma changes about every plasma physics process it comes in contact with,” Foster says. “It slows down reconnection, and it can contribute to the generation of waves that, in turn, accelerate particles in other parts of the magnetosphere. So it’s a recirculation process, and really fascinating.”

Foster likens this plume phenomenon to a “river of particles,” and says it is not unlike the Gulf Stream, a powerful ocean current that influences the temperature and other properties of surrounding waters. On an atmospheric scale, he says, plasma particles can behave in a similar way, redistributing throughout the atmosphere to form plumes that “flow through a huge circulation system, with a lot of different consequences.”

“What these types of studies are showing is just how dynamic this entire system is,” Foster adds.

Tony Mannucci, supervisor of the Ionospheric and Atmospheric Remote Sensing Group at NASA’s Jet Propulsion Laboratory, says that although others have observed magnetic reconnection, they have not looked at data closer to Earth to understand this connection.

“I believe this group was very creative and ingenious to use these methods to infer how plasma plumes affect magnetic reconnection,” says Mannucci, who was not involved in the research. “This discovery of the direct connection between a plasma plume and the magnetic shield surrounding Earth means that a new set of ground-based observations can be used to infer what is occurring deep in space, allowing us to understand and possibly forecast the implications of solar storms.”

By Jennifer Chu, MIT News Office

Image of the Day: ALMA sees a baby solar system

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Observations made with the Atacama Large Millimeter/submillimeter Array (ALMA) telescope of the disc of gas and cosmic dust around the young star HD 142527 show vast streams of gas flowing across the gap in the disc. These are created by giant planets guzzling gas as they grow. The dust in the outer disc is shown in red. Dense gas in the streams flowing across the gap, as well as in the outer disc, is shown in green. Diffuse gas in the central gap is shown in blue. The gas filaments can be seen at the three o’clock and ten o’clock positions, flowing from the outer disc towards the center.

Image credit: ALMA (ESO/NAOJ/NRAO), S. Casassus et al.

Image of the Day: Cambrian embryo fossil

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The Cambrian Period is a time when most phyla of marine invertebrates first appeared. Also dubbed the “Cambrian explosion,” fossilized records from this time provide glimpses into evolutionary biology. Most fossils show the organisms’ skeletal structure, which may give researchers accurate pictures of these prehistoric organisms. Now, researchers at the University of Missouri have found rare, fossilized embryos they believe were undiscovered previously. Their methods of study may help with future interpretation of evolutionary history. This image shows the Cambrian embryo fossil exposed by acid etching on rock surface. The polygonal structure on the surface is indicative of blastula-stage of development.

Image credit: Broce, et al.

A river of plasma, guarding against the sun

The Earth’s magnetic field, or magnetosphere, stretches from the planet’s core out into space, where it meets the solar wind, a stream of charged particles emitted by the sun. For the most part, the magnetosphere acts as a shield to protect the Earth from this high-energy solar activity.

But when this field comes into contact with the sun’s magnetic field — a process called “magnetic reconnection” — powerful electrical currents from the sun can stream into Earth’s atmosphere, whipping up geomagnetic storms and space weather phenomena that can affect high-altitude aircraft, as well as astronauts on the International Space Station.

Now scientists at MIT and NASA have identified a process in the Earth’s magnetosphere that reinforces its shielding effect, keeping incoming solar energy at bay.

By combining observations from the ground and in space, the team observed a plume of low-energy plasma particles that essentially hitches a ride along magnetic field lines — streaming from Earth’s lower atmosphere up to the point, tens of thousands of kilometers above the surface, where the planet’s magnetic field connects with that of the sun. In this region, which the scientists call the “merging point,” the presence of cold, dense plasma slows magnetic reconnection, blunting the sun’s effects on Earth.

“The Earth’s magnetic field protects life on the surface from the full impact of these solar outbursts,” says John Foster, associate director of MIT’s Haystack Observatory. “Reconnection strips away some of our magnetic shield and lets energy leak in, giving us large, violent storms. These plasmas get pulled into space and slow down the reconnection process, so the impact of the sun on the Earth is less violent.”

Foster and his colleagues publish their results in this week’s issue of Science. The team includes Philip Erickson, principal research scientist at Haystack Observatory, as well as Brian Walsh and David Sibeck at NASA’s Goddard Space Flight Center.

Mapping Earth’s magnetic shield

For more than a decade, scientists at Haystack Observatory have studied plasma plume phenomena using a ground-based technique called GPS-TEC, in which scientists analyze radio signals transmitted from GPS satellites to more than 1,000 receivers on the ground. Large space-weather events, such as geomagnetic storms, can alter the incoming radio waves — a distortion that scientists can use to determine the concentration of plasma particles in the upper atmosphere. Using this data, they can produce two-dimensional global maps of atmospheric phenomena, such as plasma plumes.

These ground-based observations have helped shed light on key characteristics of these plumes, such as how often they occur, and what makes some plumes stronger than others. But as Foster notes, this two-dimensional mapping technique gives an estimate only of what space weather might look like in the low-altitude regions of the magnetosphere. To get a more precise, three-dimensional picture of the entire magnetosphere would require observations directly from space.

Toward this end, Foster approached Walsh with data showing a plasma plume emanating from the Earth’s surface, and extending up into the lower layers of the magnetosphere, during a moderate solar storm in January 2013. Walsh checked the date against the orbital trajectories of three spacecraft that have been circling the Earth to study auroras in the atmosphere.

As it turns out, all three spacecraft crossed the point in the magnetosphere at which Foster had detected a plasma plume from the ground. The team analyzed data from each spacecraft, and found that the same cold, dense plasma plume stretched all the way up to where the solar storm made contact with Earth’s magnetic field.

A river of plasma

Foster says the observations from space validate measurements from the ground. What’s more, the combination of space- and ground-based data give a highly detailed picture of a natural defensive mechanism in the Earth’s magnetosphere.

“This higher-density, cold plasma changes about every plasma physics process it comes in contact with,” Foster says. “It slows down reconnection, and it can contribute to the generation of waves that, in turn, accelerate particles in other parts of the magnetosphere. So it’s a recirculation process, and really fascinating.”

Foster likens this plume phenomenon to a “river of particles,” and says it is not unlike the Gulf Stream, a powerful ocean current that influences the temperature and other properties of surrounding waters. On an atmospheric scale, he says, plasma particles can behave in a similar way, redistributing throughout the atmosphere to form plumes that “flow through a huge circulation system, with a lot of different consequences.”

“What these types of studies are showing is just how dynamic this entire system is,” Foster adds.

Tony Mannucci, supervisor of the Ionospheric and Atmospheric Remote Sensing Group at NASA’s Jet Propulsion Laboratory, says that although others have observed magnetic reconnection, they have not looked at data closer to Earth to understand this connection.

“I believe this group was very creative and ingenious to use these methods to infer how plasma plumes affect magnetic reconnection,” says Mannucci, who was not involved in the research. “This discovery of the direct connection between a plasma plume and the magnetic shield surrounding Earth means that a new set of ground-based observations can be used to infer what is occurring deep in space, allowing us to understand and possibly forecast the implications of solar storms.”

By Jennifer Chu, MIT News Office

Image of the Day: Meandering Mississippi

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In the picture at left, small, blocky shapes of towns, fields and pastures surround the graceful swirls and whorls of the Mississippi River. Countless oxbow lakes and cutoffs accompany the meandering river south of Memphis, Tennessee, on the border between Arkansas and Mississippi, USA. The “mighty Mississippi” is the largest river system in North America.

Image credit: USGS / NASA

MIT students dominate Putnam Mathematical Competition, winning team event

The recently announced results of the annual William Lowell Putnam Mathematical Competition, the prestigious undergraduate mathematics contest that this year included more than 4,100 students from 557 colleges and universities across the U.S. and Canada, represented a sweeping victory for MIT.

The Institute not only won the team competition — placing ahead of runners-up Carnegie Mellon University and Stanford University — but also placed four students in the top five individual spots, an achievement that earns those contestants designation as “Putnam Fellows”: sophomore Mitchell Lee, junior Zipei Nie, freshman Bobby Shen, and freshman David Yang.

A large number of other MIT students also delivered strong performances on the famously challenging six-hour, 12-question exam.

“The Putnam exam is brutally graded,” explains Henry Cohn, an adjunct professor of applied mathematics who helped students prepare for the Putnam by teaching — along with Abhinav Kumar, an associate professor of applied mathematics — 18.A34 (Problem Solving Seminar). “There’s almost no partial credit given, so, for example, on question B6 this year, exactly zero students received full credit. This year’s median score was around one point out of 120 points available, so even students who scored zero were in good company.”

“There were 87 MIT students in the top 442 this year, which is amazing,” Cohn adds. “No other school had even half that many.”

Cohn and members of MIT’s team first learned of the Putnam triumph via Wikipedia.

“We noticed a day or two before we received the ‘official’ results in the mail that somebody had altered the Wikipedia entry for the Putnam Competition to reflect that MIT had won, but we didn’t know if it was a prank,” he says. “When the ‘official’ results finally came, I was thrilled.”

Winning MIT team of Lee, Nie, and Gunby

The three members of MIT’s winning team — Lee, Nie, and junior Benjamin Gunby, also a mathematics major — competed in Putnam for a variety of reasons.

“I find the Putnam Competition to be a fun experience,” explains Lee, a mathematics major and two-time Putnam Fellow. “Besides that, I hope that my performance will help me if I apply for graduate school. I also appreciate the prize money.” (Lee won $3,500 for his efforts.)

Lee also enjoys the team camaraderie. He attributes MIT’s performance this year to “the overall strength of the math community here at MIT.”

“We enjoy talking about math,” he says. “We all support each other and congratulate each other. The things I have learned from other competitors undoubtedly played a role in my own performance.”

Nie, also a mathematics major and two-time Putnam Fellow, says that math contests provide a sense of belonging. As a high school student in China, Nie says, he felt “pessimistic day after day, so I decided to let math be the meaning of my life. Math and the support of my high school teachers cured me. Math Olympiad training became my main work during those years. Fortunately, I made great progress.”

Gunby, a Putnam Fellow last year and a member of the winning MIT trio this year, says math contests represent an intellectual challenge. “Math competitions have played a big part of my life,” he says, “especially during high school. Before college, math classes didn’t do much to improve my problem-solving skills. But everyone in college can find a math class that’s interesting and challenging.”

Michael Sipser, the Barton L. Weller Professor of Mathematics, head of the Department of Mathematics, and interim dean of the School of Science, says: “I’m proud that our department has attracted such a high caliber of student. We had an extraordinary number of top performers on the Putnam: 80 percent of the top five and 60 percent of the top 25.”

“Word has gotten out that MIT is the place to be for competitive math,” Sipser says, “and success breeds even more success. Winning helps us attract even more strong students, and not just math competitors, but smart kids in general.”

Sipser hopes that attention on events like the Putnam Competition can trigger larger public conversations about math. “It helps us celebrate math in a playful way,” he says.

Contest math vs. research math

How well does success at “contest math,” like the Putnam Competition, correlate with later achievement in math? As Sipser puts it, comparing time-limited contest math to research math “is like comparing regular chess to blitz chess.”

Bjorn Poonen, the Claude E. Shannon Professor of Mathematics and one of just eight students ever to be a four-time Putnam Fellow (as an undergraduate at Harvard University), agrees: “The Putnam differs from math research in that it rewards speed more than the ability to develop deep insights over time. There is some overlap in the skills, but there are many excellent mathematicians who didn’t do well on the Putnam. Also, as far as content goes, math majors at MIT learn much more than what is covered on the Putnam.”

Cohn, who received his SB in mathematics from MIT in 1995 and who participated in the Putnam Competition as an undergraduate, says: “While we rightfully celebrate these clever and quick problem-solvers who did so well on the Putnam, there are amazing MIT students who don’t even take the exam, as well as wonderful students who are going to accomplish fantastic things in mathematics even though they scored one point on the Putnam. The mathematics department doesn’t value students who win contests any more than we value the rest of our great students.”

By Chuck Leddy, MIT News correspondent

Image of the Day: Growing & glowing

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This map shows photosynthetic activity across North America during the growing season, with the United States Midwest proving to be the most active spot on the continent. The pink glow in the satellite photo represents fluorescence measured from land plants in early July, from 2007 to 2011. Plants convert light into energy in a process known as photosynthesis. During this process, vegetation emits a difficult-to-detect fluorescent glow that is invisible to the naked eye. The magnitude of the glow indicates the amount of photosynthesis within a given region, NASA officials said in a statement.

Image credit: NASA’s Goddard Space Flight Center / (description) LiveScience Staff

Image of the Day: Mapping polarization of ferroelectric materials

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At the atomic scale, engineering researchers at the University of Michigan (U-M) have for the first time, mapped the polarization of a cutting-edge material for memory chips. The researchers found a way to improve the performance of ferroelectric materials.

Image credit: Chris Nelson and Xiaoqing Pan, Department of Materials Science and Engineering, University of Michigan

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