Image of the Day: Yersinia pestis

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This is a scanning electron micrograph depicting a mass of yersinia pestis bacteria–the cause of bubonic plague–in the foregut of the flea vector. The bubonic plague is a zoonotic disease, circulating mainly in fleas on small rodents, and is believed to be the cause of the Black Death that devastated Europe in the 14th century. Because the plague killed so many of the working population, wages rose with the demand for labor. Some historians have seen this as a turning point in European economic development.

Image credit: NIAID

Larry Linden: Big changes needed to avert possible climate “catastrophe”

After a career that included work as a White House advisor in the Carter administration and as a partner at Goldman Sachs, Larry Linden SM ’70, PhD ’76 has turned his attention to what he says is the most critical issue facing humanity today: the threat of catastrophic global climate change.

Linden, speaking on campus Wednesday in the opening event of the MIT Climate Change Conversation, urged his audience to join him in making the issue a top priority — and in pushing elected leaders to take concrete action now, before changes to the world’s atmosphere and oceans become irreversibly damaging. And the most effective approach, he emphasized, is by putting a price on carbon emissions from fossil fuels.

That could take a number of forms: an outright tax on carbon, a cap-and-trade arrangement, or a revenue-neutral combination of fees and rebates. While the present political climate in the United States may make any such agreement an uphill battle, Linden stressed that his foundation — the Linden Trust for Conservation — and other groups are working hard to find centrist, bipartisan approaches that could lead toward the goal of limiting global climate change.

Pointing to unexpectedly rapid changes in public opinion in other areas, Linden said that while the prospects for political action on climate may now appear bleak, “We can be surprised, and I hope we will. This is an idea that could go from impossible to inevitable overnight.”

Linden, a board member of the World Wildlife Fund and former chairman of the board of directors of Resources for the Future, described the evolution of his thinking on climate change. He said his awareness of environmental issues started early: As a child in Pasadena, Calif., he personally experienced the terrible, pre-Clean Air Act smog of the Los Angeles basin. Now, he said, “I’m doing everything in my power to move our country to act [on climate change] at the scale that’s required.”

Unpredictable changes

At the current pace, Linden said, we face a rise in temperature of as much as 4 to 6 degrees Celsius by 2100 — and the carbon dioxide humans are now adding to the air will stay there for centuries or even millennia. This could lead, he said, “to abrupt, unpredictable and potentially irreversible changes” — such as the release of frozen methane, or the death of the Amazon rainforest — that could greatly amplify the impacts. If such large changes do occur, Linden said, “I don’t think it’s an overstatement to call this a planetary catastrophe.”

While Linden said the fossil fuel industry will fiercely resist any proposed regulations or fees aimed at limiting carbon emissions, he added that past experience gives reason to treat industry’s claims with some skepticism: Proposals to limit automobile pollution to deal with California’s smog problems faced similar objections, which proved unfounded.

“The financial system is an extremely complex, interrelated system — just like the climate system,” Linden said. While companies never like to be told what to do, he said, if federal rules constrain their actions, they will abide by the law.

In 2009, when federal cap-and-trade legislation was proposed in Congress and passed in the House, Linden was encouraged, thinking that this would be a be “a great start.” But when the proposed law was dropped without even being brought to a vote in the Senate, “I practically fell off my chair,” he said. In the years since, the idea has not resurfaced in Congress.

Slashing emissions

But something along those lines is exactly what is needed now, Linden said. Research has shown that to avert the most drastic climate consequences, greenhouse gas emissions must be cut by about 80 percent over the next four or five decades. In addition, massive new investment in research and development on alternative energy sources is needed, he said.

The most essential change in policy, Linden said, is a mechanism for “internalizing the externalities”: capturing the great societal costs of fossil fuel emissions in the costs of the fuels themselves. “It could be a cap-and-trade system, or a tax or a fee on carbon, or a limit on emissions,” he said.

Linden said that his foundation is supporting a revenue-neutral carbon tax as the next major national policy step. Studies have shown, he said, that an initial tax of $15 per ton of carbon emitted, with significant annual increases, could cut emissions in half by 2050.

The key, he said, lies in public action to force politicians to act. But the very nature of the issue — requiring strong action now to avoid consequences many years hence — makes action difficult: “If you designed a problem to maximize the political difficulty of addressing it, you couldn’t do much better,” Linden said. “We will therefore need extraordinary political leadership.”

“Bipartisan support is needed,” he added, noting that the Linden Trust is actively working to build support across the political spectrum. “We’re looking for centrist solutions,” he said. Like the climate itself, “our political system is an extremely complicated, interrelated system. There are possible positive feedback loops, and many nonlinear thresholds that can produce irreversible impacts. … That’s what we need to look for now.”

While the process might take years, Linden said, “We have to fight the political fight.” In the meantime, he said, state initiatives might provide useful “working examples” for national action.

Maria Zuber, MIT’s vice president for research, introduced this kickoff event of MIT’s Climate Change Conversation, an effort to involve the MIT community in seeking ways in which the Institute might contribute to addressing the threat of global climate change. The proposals arising from this process, Zuber said, would be “rooted in science, would be bold, would encourage personal engagement.”

Zuber added that while this has been “a divisive issue on many campuses, of the many things that we could possibly do, there must be some things that we can all agree on that would be useful to do, and maybe we should start with doing those.”

Linden’s talk was sponsored by the Committee on the MIT Climate Change Conversation, which will organize a series of events during the spring semester to engage the community in thinking about how the Institute can contribute to confronting climate change.

By David L. Chandler | MIT News Office

Image of the Day: Bald eagles roost

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Several bald eagles roost in a snowcapped tree. Both the national bird and national animal of the United States, the bald eagle’s range includes most of Canada and Alaska, all of the contiguous U.S., and northern Mexico. It is found near large bodies of open water with an abundant food supply and old-growth trees for nesting.

Image credit: USFWS

Image of the Day: Pu’u ‘O’o lava on fire

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Pu‘u ‘O‘o lava flows and burns near Pahoa, Hawaii as a result of Kilauea Volcano eruption in June 2014. A cinder/spatter cone in the eastern rift zone of the Kilauea volcano of the Hawaiian Islands, Pu’u ‘O’o has been erupting continuously since January 3, 1983, making it the longest-lived rift-zone eruption of the last two centuries.

Image credit: Kelly Hudson

Sequestration on shaky ground

Carbon sequestration promises to address greenhouse-gas emissions by capturing carbon dioxide from the atmosphere and injecting it deep below the Earth’s surface, where it would permanently solidify into rock. The U.S. Environmental Protection Agency estimates that current carbon-sequestration technologies may eliminate up to 90 percent of carbon dioxide emissions from coal-fired power plants.

While such technologies may successfully remove greenhouse gases from the atmosphere, researchers in the Department of Earth, Atmospheric and Planetary Sciences at MIT have found that once injected into the ground, less carbon dioxide is converted to rock than previously imagined.

The team studied the chemical reactions between carbon dioxide and its surroundings once the gas is injected into the Earth — finding that as carbon dioxide works its way underground, only a small fraction of the gas turns to rock. The remainder of the gas stays in a more tenuous form.

“If it turns into rock, it’s stable and will remain there permanently,” says postdoc Yossi Cohen. “However, if it stays in its gaseous or liquid phase, it remains mobile and it can possibly return back to the atmosphere.”

Cohen and Daniel Rothman, a professor of geophysics in MIT’s Department of Earth, Atmospheric, and Planetary Sciences, detail the results this week in the journal Proceedings of the Royal Society A.

Current geologic carbon-sequestration techniques aim to inject carbon dioxide into the subsurface some 7,000 feet below the Earth’s surface, a depth equivalent to more than five Empire State Buildings stacked end-to-end. At such depths, carbon dioxide may be stored in deep-saline aquifers: large pockets of brine that can chemically react with carbon dioxide to solidify the gas.

Cohen and Rothman sought to model the chemical reactions that take place after carbon dioxide is injected into a briny, rocky environment. When carbon dioxide is pumped into the ground, it rushes into open pockets within rock, displacing any existing fluid, such as brine. What remains are bubbles of carbon dioxide, along with carbon dioxide dissolved in water. The dissolved carbon dioxide takes the form of bicarbonate and carbonic acid, which create an acidic environment. To precipitate, or solidify into rock, carbon dioxide requires a basic environment, such as brine.

The researchers modeled the chemical reactions between two main regions: an acidic, low-pH region with a high concentration of carbon dioxide, and a higher-pH region filled with brine, or salty water. As each carbonate species reacts differently when diffusing or flowing through water, the researchers characterized each reaction, then worked each reaction into a reactive diffusion model — a simulation of chemical reactions as carbon dioxide flows through a briny, rocky environment.

When the team analyzed the chemical reactions between regions rich in carbon dioxide and regions of brine, they found that the carbon dioxide solidifies — but only at the interface. The reaction essentially creates a solid wall at the point where carbon dioxide meets brine, keeping the bulk of the carbon dioxide from reacting with the brine.

“This can basically close the channel, and no more material can move farther into the brine, because as soon as it touches the brine, it will become solid,” Cohen says. “The expectation was that most of the carbon dioxide would become solid mineral. Our work suggests that significantly less will precipitate.”

Cohen and Rothman point out that their theoretical predictions require experimental study to determine the magnitude of this effect.

“Experiments would help determine the kind of rock that would minimize this clogging phenomenon,” Cohen says. “There are many factors, such as the porosity and connectivity between pores in rocks, that will determine if and when carbon dioxide mineralizes. Our study reveals new features of this problem that may help identify the optimal geologic formations for long-term sequestration”

This research was funded in part by the U.S. Department of Energy.

By Jennifer Chu | MIT News Office

Image of the Day: Sea spider in McMurdo Sound

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Sea spiders are marine arthropods of class Pycnogonida. They are cosmopolitan, found especially in the Mediterranean and Caribbean Seas, as well as the Arctic and Antarctic Oceans. There are over 1,300 known species, ranging in size from 1 millimeter (0.039 inches) to over 90 centimeters (35 inches) in some deep water species. Most are toward the smaller end of this range in relatively shallow depths, however, they can grow to be quite large in Antarctic waters. Although sea spiders are not true spiders, or even arachnids, their traditional classification as chelicerates would place them closer to true spiders than to other well-known arthropod groups, such as insects or crustaceans. However, even this is in dispute, as genetic evidence suggests they may even be an ancient sister group to all other living arthropods.

Image credit: Steve Rupp, National Science Foundation

Image of the Day: Digging clams

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A coastal brown bear sow and her two cubs dig for clams on the Lake Clark coast in Alaska. Pulled from the U of ALA Alaskan Native Language Center: Qizhjeh Vena, meaning “a place where people gathered” in Dena’ina Athabascan, is the original name of Lake Clark. The Athabascan people known as Dena’ina have lived in the Lake Clark region for thousands of years. The land and water supports, shapes and sustains their culture.

Image credit: NPS Photo / K. Jalone

Professor emeritus Richard Schafer, former deputy head of mathematics at MIT, dies at 96

Richard D. Schafer, emeritus professor and former deputy head of the MIT Department of Mathematics, died on Dec. 28, 2014. He was 96.

Schafer joined the MIT mathematics faculty in 1959 as deputy head under department head William Ted Martin. The department had seen a period of rapid growth of faculty and postdoctoral programs in the ’50s, with expanding demands in teaching and graduate supervision. As deputy head, Schafer was instrumental in organizing the application and review processes of the relatively new CLE Moore Instructorship program, and in systemizing the assignment of teaching and the scheduling of classes with the Office of the Registrar. He stepped down as deputy head when Ted Martin ended his tenure as department head in 1968, but he stayed on at MIT until his retirement in 1988 as professor emeritus.

Schafer was an algebraist, an expert in non-associative algebras. He did collaborative work with fellow mathematician Claude Chevalley on Lie algebras and extensive work on Jordan algebras. In 1966, Schafer published “Introduction to Nonassociative Algebras” (Academic Press), a book that has served as a standard reference for many years.

Schafer was born in Buffalo, New York, in 1918. He received both a BA and an MA from the University of Buffalo, and a PhD in mathematics from the University of Chicago in 1942. Between 1942 and 1945 he served in the U.S. Naval Reserve.

Upon his return to academia in 1945, Schafer took a yearlong appointment as an instructor at the University of Michigan. He was a member of the Institute for Advanced Study from 1946-48 and later from 1958-59. He joined the faculty at the University of Pennsylvania in 1948, and moved to the University of Connecticut as a full professor in 1953, where he served as department head until joining MIT in 1959. From 1955-58, Schafer also served as associate secretary of the eastern region of the American Mathematical Society.

In 2013, Schafer was elected to join the inaugural class of fellows of the American Mathematical Society. He had been active for 50 years in the Mathematical Association of America and Phi Beta Kappa.

A lifelong opera fan, Schafer regularly traveled to the Metropolitan Opera in New York City and to the Salzburg Festival in Germany. For 67 years, he was married to the late Alice T. Schafer — a fellow mathematician and longtime professor at Wellesley College, and a co-founder of the Association for Women in Mathematics.

Schafer is survived by sons John D. Schafer of Turner, Maine, and Richard S. Schafer of Concord, Massachusetts; grandson Scott D. Schafer of Philadelphia, Pennsylvania; granddaughters Tania Murray of Frankfort, Illinois and Stephanie Altavilla of Chelsea, Massachusetts; and two great-grandchildren, Mikayla and Grant Murray.

By Department of Mathematics

Image of the Day: Binary star formation

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Binary star formation through disk fragmentation starts with a young star surrounded by a rotating disk of gas and dust. The disk fragments, with a second star forming within the disk, surrounded by its own disk. The two stars form an orbiting pair.

Image credit: B. Saxton, NRAO/AUI/NSF

Rainfall can release aerosols, study finds

Ever notice an earthy smell in the air after a light rain? Now scientists at MIT believe they may have identified the mechanism that releases this aroma, as well as other aerosols, into the environment.

Using high-speed cameras, the researchers observed that when a raindrop hits a porous surface, it traps tiny air bubbles at the point of contact. As in a glass of champagne, the bubbles then shoot upward, ultimately bursting from the drop in a fizz of aerosols.

The team was also able to predict the amount of aerosols released, based on the velocity of the raindrop and the permeability of the contact surface.

The researchers suspect that in natural environments, aerosols may carry aromatic elements, along with bacteria and viruses stored in soil. These aerosols may be released during light or moderate rainfall, and then spread via gusts of wind.

“Rain happens every day — it’s raining now, somewhere in the world,” says Cullen R. Buie, an assistant professor of mechanical engineering at MIT. “It’s a very common phenomenon, and it was intriguing to us that no one had observed this mechanism before.”

Youngsoo Joung, a postdoc in Buie’s lab, adds that now that the group has identified a mechanism for raindrop-induced aerosol generation, the results may help to explain how certain soil-based diseases spread. 

“Until now, people didn’t know that aerosols could be generated from raindrops on soil,” Joung says. “This finding should be a good reference for future work, illuminating microbes and chemicals existing inside soil and other natural materials, and how they can be delivered in the environment, and possibly to humans.”

Buie and Joung have published their results this week in the journal Nature Communications.

Capturing a frenzy, in microseconds

Buie and Joung conducted roughly 600 experiments on 28 types of surfaces: 12 engineered materials and 16 soil samples. In addition to acquiring commercial soils, Joung sampled soil from around MIT’s campus and along the Charles River. He also collected sandy soil from Nahant Beach in Nahant, Massachusetts.

In the lab, the researchers measured each soil sample’s permeability by first pouring the material into long tubes, then adding water to the bottom of each tube and measuring how fast the water rose through the soil. The faster this capillary rise, the more permeable the soil.

In separate experiments, the team deposited single drops of water on each surface, simulating various intensities of rainfall by adjusting the height from which the drops were released. The higher the droplet’s release, the faster its ultimate speed.

Joung and Buie set up a system of high-speed cameras to capture raindrops on impact. The images they produced revealed a mechanism that had not previously been detected: As a raindrop hits a surface, it starts to flatten; simultaneously, tiny bubbles rise up from the surface, and through the droplet, before bursting out into the air. Depending on the speed of the droplet, and the properties of the surface, a cloud of “frenzied aerosols” may be dispersed.

“Frenzied means you can generate hundreds of aerosol droplets in a short time — a few microseconds,” Joung explains. “And we found you can control the speed of aerosol generation with different porous media and impact conditions.”

From their experiments, the team observed that more aerosols were produced in light and moderate rain, while far fewer aerosols were released during heavy rain.

Buie says this mechanism may explain petrichor — a phenomenon first characterized by Australian scientists as the smell released after a light rain.

“They talked about oils emitted by plants, and certain chemicals from bacteria, that lead to this smell you get after a rain following a long dry spell,” Buie says. “Interestingly, they don’t discuss the mechanism for how that smell gets into the air. One hypothesis we have is that that smell comes from this mechanism we’ve discovered.”

From the ground up

Buie and Joung looked further into the relationship among raindrop velocity, surface properties, and aerosol generation, and came up with two dimensionless parameters that can be used to describe the relationship: the Weber number, which is a function of the impact speed of a droplet, and a modified Péclet number, which is used to contrast impact velocity and surface wettability.

Based on their calculations, the researchers found that aerosol generation is greatest when the ratio between the Weber and Péclet numbers is balanced, around 1 — a ratio that Buie and Joung expressed as the Washburn-Reynolds number. When this ratio is balanced,  raindrops are neither too fast nor too slow, and the surface is neither too wet nor too dry.

“When moderate or light rain hits sandy or clay soils, you can observe lots of aerosols, because sandy clay has medium wetting properties,” Joung says. “Heavy rain [has a high] impact speed, which means there’s not enough time to make bubbles inside the droplet.”

James Bird, an assistant professor of mechanical engineering at Boston University, says that scientists have long observed that raindrops can trap and release aerosols when falling on water. This paper, he says, is the first to show this effect on soil.

“I’m impressed by the extent [to which] the authors have unraveled the underlying physics,” says Bird, who was not involved in the research. “The aspect of this paper that I find most exciting is that it brings the conversation of bubble-induced aerosol formation from the ocean over to the land. Microbes from soil have been observed high in the atmosphere; this paper provides an elegant mechanism by which these microbes can be propelled past the stagnant layer of air around them to a place where the breeze can take them elsewhere.”

Joung and graduate student Zhifei Ge are now conducting similar experiments, with surfaces containing soil bacteria and pathogens such as E. coli, to observe whether such contaminants can be spread significantly via rainfall. In the current paper, he and Buie performed initial experiments using dyed liquid droplets on certain surfaces containing fluorescent dye. In those experiments, they observed through microscopy that the aerosols released from raindrops contained the dye — a finding that suggests such aerosols may also carry other contaminants, such as soil-based viruses and bacteria.

“Aerosols in the air certainly could be resulting from this phenomenon,” Buie says. “Maybe it’s not rain, but just a sprinkler system that could lead to dispersal of contaminants in the soil, for perhaps a wider area than you’d normally expect.”

Adds Joung: “To prevent transmission of microorganisms from nature to humans, we need to know the exact mechanism. In this work, we provide one possible way of transmission.”

By Jennifer Chu | MIT News Office

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