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Thursday, April 28th, 2016
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| 12:00a |
There’s something in the air Winds that blow across the Sahara desert in North Africa pick up particles of soil and sand, and typically carry them westward. Many of these grains travel across the Atlantic, leading to poor-visibility days in the southern U.S. and Caribbean, transporting nutrients to far-flung ecosystems in South America, and impacting hurricane formation in the Atlantic.
That’s just one example of the myriad ways that the behavior of tiny particles blown by the wind can have large-scale local, regional, and even global effects on the complex systems that govern Earth’s atmosphere. For Colette Heald, trying to unravel the intricate patterns of the atmosphere’s composition and chemistry, and the way these affect ecosystems, air quality, and even the climate itself, has been the driving force of her career.
Heald, who earned tenure at MIT last year, is the Mitsui Career Development Associate Professor in the Department of Civil and Environmental Engineering and also holds an appointment in the Department of Earth, Atmospheric and Planetary Sciences. Originally from Canada, she was born in Montreal and grew up in Ottawa, where her father was a paper industry executive and her mother a nurse. An older sister, who still lives in Canada, is an aerospace engineer.
Heald earned her BS in engineering physics at Queen’s University in Kingston, Ontario, and while there started doing summer research projects with faculty members at the University of Toronto. That’s when she got introduced to the field of atmospheric science. “I was so excited,” she says, to discover the deep connections between the kind of technical engineering research she had studied and the global environment. That led her to pursue a doctorate in atmospheric chemistry at Harvard University.
Coming from all directions
“That seemed like a flip from physics,” she recalls, “and I was concerned that I didn’t have the chemistry background for it.” But she soon discovered that the field “is so interdisciplinary; people come from a variety of directions” and bring different perspectives to the research.
She immediately became fascinated by the use of satellite data to study the atmosphere and its interactions. The timing was good: The first satellites measuring atmospheric pollution had been launched just a few years earlier.
One of the things measured by satellites was the concentration of carbon monoxide in the air. That compound “is produced from all kinds of combustion processes, and it’s a nice indicator because it stays in the atmosphere for about a month,” she says, “so we can use it to investigate the transport of plumes from sources to continents down-wind.”
Heald describes her current work as “trying to understand the sources, transformation, and impact of gases and particles in the atmosphere, which is very dynamic with a lot of chemical compounds that interact.” In a sense, she says, her focus is on figuring out what’s missing — where the holes are in models of the atmosphere, and how to fill those gaps. “I take an endpoint perspective,” she says. “I integrate the knowledge we have, and look for new ways to analyze the data to see what’s missing in our models.”
The effects are often subtle and hard to tease out from the chaotic mix of atmospheric processes. For example, in summer months the plumes of dust that constantly waft away from the Sahara desert end up in the North Atlantic and can make landfall in the United States and contribute to poor air quality in Florida. In the winter months winds blow the dust, which bears a complex load of assorted minerals, across to South America.
Trans-Atlantic fertilizer
One of those minerals is phosphorus, which happens to be a key limiting element for the growth of plants in the Amazon basin — so those African breezes are actually contributing to the Amazon’s fertility. That’s the kind of complex interaction, she explains, that would never be derived solely from theoretical modeling or experimental observation but requires the integration of different disciplines and approaches. “That gives you a sense of the challenge,” she says.
“There needs to be a strong coupling between observational work and modeling,” Heald says, “and these are models that take decades of development and a large community of scientists.” Much of her research focuses on aerosols, particles of matter so small that they virtually defy gravity and can stay aloft for weeks. Another major area of her research is the complex interaction between the atmosphere and the biosphere.
One thing that makes the modeling difficult is that many of the important processes in atmospheric chemistry involve transport across ocean basins, and “there are not a lot of observations available” over vast stretches of ocean. For example, for dust “we have long-term records in Barbados and in Florida, but we have to connect the dots” to extrapolate to the missing areas. Satellite data are helping to fill in the blanks, but careful calibration is required to make sure these measurements dovetail with the ground-based records.
Heald’s modeling work has showed, for example, that in recent decades winds have been slowing over Africa, and that could reduce the flow of those aerosols to the Americas. Since those particles have an overall cooling effect, by radiating back incoming sunlight, their reduction leads to an overall warming, she explains.
Heald says she has always been interested in many different subjects and had a hard time initially in college deciding what she wanted to major in, even considering art history. “My sister told me, you’ll always be able to experience art and literature, but it’s hard to pursue science and engineering as a hobby!”
While acknowledging that many women have experienced discrimination in their scientific education and careers, “I feel very fortunate,” Heald says, about the support and encouragement she received throughout her education and early career. “I was never discouraged, always only encouraged. I never felt that any doors were closed to me.”
The community of atmospheric chemists, she says, “is very collegial, and I’m grateful for the smooth path I’ve had and the friendly collaborations I’ve developed along the way. I know not all fields are like that, so when I have a chance to help or give back, I try to get involved.” | | 2:00p |
Spotting hidden activity in cells Inside every living cell, internal structures are continuously moving about. Under a microscope, organelles such as the nucleus, mitochondria, transport vesicles, or even external flagella wobble and twitch. This may happen spontaneously as these tiny structures are passively jostled inside a cell. But that’s not necessarily all there is to it. Often a cell invests extra energy into these motions to enhance cell functions in ways we don’t yet understand.
At the microscopic scale, particles in a fluid or a gas can move about in response to bombardment by the surrounding molecules. Such passive, thermally-induced motions are often very hard to distinguish from actively driven movements, and it can be impossible to tell just by looking whether particular motions inside a cell are simply thermal or pushed by some extra input of energy.
Now scientists at MIT, the University of Göttingen, Ludwig Maximilians University of Munich, the Free University Amsterdam, and Yale University have developed a noninvasive data analysis technique that can discern whether an object’s random motion is actively or thermally driven. After tracking the conformations or locations that a structure within the cell or a particle passes through as it moves, and observing how the particle transitions back and forth between such states, the researchers apply a fundamental principle of statistical physics to determine whether the random motions are active or thermal.
Nikta Fakhri, assistant professor in MIT’s Department of Physics, says the results will help scientists to uncover “hidden” active processes that drive a cell’s constituents to move in seemingly random ways.
“We want to see if particular dynamics in living systems — be those cells or tissues or whole organisms — that look at first glance like random thermal motion are indeed actively driven,” says Fakhri, who is a first co-author on the paper. “This is important because there must be a vital function connected with the process if the cell spends energy on it. Our work provides a practical experimental method to identify active, nonequilibrium processes in observations of biological systems.”
Fakhri and her colleagues have published their results today in the journal Science.
Shaking things up
Observations of the movements of microscopic particles date back to 1827, when Scottish botanist Robert Brown was looking through a microscope at pollen grains in water. He noticed that the grains contained tiny particles that jiggled vigorously, and at first glance believed that their motion meant the particles were somehow alive and moving on their own. Eventually, Brown retired this theory when he observed the same jiggling with inert particles from rocks, realizing that just seeing a particle moving doesn’t necessarily mean it is alive.
Scientists now know that such particles are being pushed around by even smaller water molecules, which themselves are jiggling. At elevated temperatures, water molecules possess kinetic energy and can remain forever restless. At microscopic scales, these tiny molecules and atoms can “bombard” other much larger particles. This phenomenon is now known as Brownian motion. Scientists today are so used to seeing Brownian motion that they often assume that a particle moving in a random fashion is likely to be at thermal equilibrium — a state in which a system is not dissipating any energy, and therefore inanimate.
In living cells, of course, many organelles or particles tend to move in a “ballistic” fashion, traveling across some distance, with a clearly directed or oscillatory trajectory. These types of motions, Fakhri says, represent an animated state that must be out of equilibrium, requiring a system to expend energy. What is interesting, however, are situations where particles jiggle randomly and seem to be in equilibrium, but in reality move actively.
Frame by frame
Fakhri and her colleagues set out to develop a statistical physics technique that would enable them to tell, just by imaging a particle, whether its random motions are thermal or active in nature.
Using video microscopy, they studied, frame by frame, the oscillatory motion of the flagellum of a Chlamydomonas algae. They deconstructed the backbone of the flagellum into a series of shapes, thus creating a phase space of the states the flagellum passes through as it completes an oscillatory cycle. They then counted the transitions between states. In thermal equilibrium, the back-and-forth transitions between all states must be balanced. However, they observed a clear imbalance in these transitions, confirming the already known fact that the flagellum expends energy for this active oscillatory motion.
Next, they analyzed the motions of a kidney cell’s cilium — an antenna-like appendage that at first glance appears to be jiggling back and forth passively. By tracking the cilium’s orientation and curvature, and counting transitions between states, they observed a slight imbalance in the transitions, pointing to an unexpected active process that drives the cilium, despite its passive appearance.
“This is a great paper, and somewhat a proof of principle,” says Gavin Crooks, senior scientist at Lawrence Berkeley National Laboratory. “Their method has the potential to be applicable to lots of cellular processes — we'll get deeper insights into the flow of information and energy through the cell, and what makes these molecule machines tick. You could imagine using these methods to examine if a piece of cellular machinery is working the way that it's meant to.”
Fakhri says the new method will help scientists to uncover new ways in which cells dissipate energy — which, ultimately, is the key to sustaining life. After all, as the Austrian physicist Erwin Schrödinger noted, “Living matter evades the decay to thermal equilibrium.”
“Almost a century later, through the work of this collaboration, we can now go further and find out how cells budget their energy and particularly why they often expend a lot of energy to create these apparently random motions,” Fakhri says.
This research was funded, in part, by the International Human Frontier Science Program. | | 2:30p |
Apollo 13 commander James Lovell: “Crises don’t bother me anymore” On April 14, 1970, 56 hours after the Apollo 13 spacecraft launched into space en route to the moon, commander James Lovell began filming inside the spacecraft’s command module as part of a live television program to be beamed down to three major U.S. networks. The broadcast was meant to give people on Earth a glimpse into the mission, which was to be NASA’s third landing on the moon, following its first historic and much celebrated Apollo 11 mission, and later, the equally successful Apollo 12.
“But this was the third lunar landing flight,” says Lovell, who spoke at MIT on Wednesday to a rapt audience, packed and overflowing in Room 10-250. “All three networks received the signal — nobody carried it. There was the Dick Cavett show … a rerun of ‘I Love Lucy,’ and a ballgame — even people in the control center were watching the ballgame.”
As there seemed to be little interest, NASA’s mission control suggested Lovell cut the program short.
“I said goodnight to everybody, turned off the camera, and was coming down the tunnel, when suddenly there was a ‘hiss, bang!’ and the spacecraft rocked back and forth, jets were firing, and there was noise all over,” Lovell recalled.
Of course, the cascade of system failures that would follow, and the ingenuity in getting the crew safely back to Earth is a story that has since been retold and aired many times over, on radio, television, and on the silver screen, with the 1995 Hollywood blockbuster “Apollo 13,” with Tom Hanks as Lovell.
“That explosion was the best thing to ever happen to NASA,” Lovell told the MIT crowd. “It showed, really, the talent that NASA people had, in mission control and throughout the organization, that turned an almost complete catastrophe into a successful recovery.”
Incident-free
Lovell spoke as a special guest invited to MIT by the Department of Aeronautics and Astronautics (AeroAstro). He recalled a similar visit to MIT, back in the summer of 1968, when he had recently been selected as the navigator for Apollo 8, which was to be the first crewed mission to orbit the moon. At the time, Institute Professor Charles “Doc” Draper and his team at the Instrument Lab — later renamed the Draper Lab — were leading the development of the guidance system for Apollo 8, which would navigate the spacecraft from Earth to the moon. Working with Draper’s team, Lovell learned to use the system to align the spacecraft with respect to Earth, and navigate to the moon using a map of 37 stars.
“This was the first time this system would be used to go to the moon,” Lovell said. “There are probably people here who know it better than I do.”
Lovell described Apollo 8 as the high point of his space career, recalling moments when he had the chance to look out the spacecraft’s windows, back toward Earth.
“The Earth was a place out there that you could put your thumb on and hide it completely,” Lovell recalled. “Everything you’ve ever known — all the problems that you have — if you put up your thumb, they all disappear. It was really mind-boggling to me. It was one of the most successful, incident-free Apollo flights that we had.”
Lead weight
Lovell’s next and final spaceflight, Apollo 13, was expected to be similarly smooth. Two weeks before launch, the spacecraft underwent its last test.
“As the countdown went on, we could see the whole spacecraft come to life,” Lovell said. “The test was successful — everything looked perfect.”
When the ground crew came by to empty the liquid oxygen tanks, which would be refilled before launch, they were unable to do so. It would take a month to replace the tanks, which would have delayed the mission. However, they noticed that one of the tanks was an old design, meant for Apollo 10, that was configured with an oxygen-emptying tube and a heater.
“They figured, why not turn on the heater and boil the oxygen out, and therefore save time? Not a bad idea, so that’s what they did,” Lovell said. “The day before liftoff, they filled it up once more with liquid oxygen. It was a bomb waiting to go off” because the fix actually damaged the internal elements of the tank.
And go off it did, with a ‘hiss, bang!’ that shook the spacecraft, shortly after Lovell ended the television broadcast on April 14. Checking the instrument gauges, he found that one oxygen tank was completely empty, while another was being rapidly depleted. As he looked out a side window, he witnessed a “gaseous substance, at high speed,” shooting out into space.
“That’s when that old lead weight went down in the bottom of my stomach,” Lovell said. “Because we needed oxygen for electricity, the third fuel cell would die, and because we used electricity to control our rocket engine, we’d lose the entire propulsion system. We were in serious trouble.”
“A square peg through a round hole”
The crew, including NASA astronauts Jack Swigert and Fred Haise, scrambled to find a fix, quickly realizing they would have to abort the lunar mission and attempt to fly home not in the main service module, but in the much smaller lunar module (originally equipped for two men to explore the surface of the moon), before re-docking with the main spacecraft.
“We used it as a life raft,” Lovell said. “It’s a fragile device, with skin so thin you could probably punch a hole through it.”
The crew worked with mission control to redirect the severely compromised craft back toward Earth, with its limited reserves of power and oxygen. Just as everything appeared to be on course for a successful return, the module’s carbon dioxide light blinked on, indicating the cabin, designed for two people, was saturated with the breathing of three men.
“If we weren’t going to do anything, we would be poisoned by our own exhalations,” Lovell said.
The crew would have to transfer canisters of lithium hydroxide from the dead command module to the lunar module, to remove the excess carbon dioxide. The only problem: those canisters were square, whereas the lunar module’s canisters were round.
In a moment that the film “Apollo 13” has since made famous, the team would have to “invent a way to put a square peg in a round hole.” They did so using a piece of plastic Lovell recalled that he had stored underwear in, a cardboard cover from a manual, an old sock, and duct tape.
Lovell described several more harrowing moments of resetting the craft’s course, before finally splashing down on Earth.
“If you come in too shallow, it’ll be like skipping a stone across water, and you’re gone,” Lovell said. “If you come in too steep, the sudden deceleration will put you on fire like a meteorite and that will be it. … I guess I wouldn’t be here if that last maneuver wasn’t successful.”
Before closing his talk, Lovell took several questions from the audience, including one from an AeroAstro PhD candidate, who asked his advice for anyone dealing with stress.
“You have to have a positive attitude and look ahead,” Lovell responded. “If we got curled up in some sort of attitude, waiting for a miracle to happen, I’d still be up there. And one other thing: Crises don’t bother me anymore. I just look at them and figure out how to get out of them, and that’s it.” |
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