APAM Faculty Featured in Columbia Engineering Magazine


APAM Professors Simon Billinge, Mark Cane, Richard Osgood, Lorenzo Polvani, Adam Sobel, and Marc Spiegelman were featured in the Fall 2010 Columbia Engineering Magazine: Impact on Sustainability. (Reprinted with permission from Columbia Engineering Magazine)



Simon Billinge: Characterizing Nanoparticles for Fuel Cells

The solid oxide fuel cell, which runs on hydrogen and oxygen to produce water as exhaust, is seen as a promising technology of the future for transportation. These fuel cells are now used on an experimental basis to power city buses. But the fuel cells have proved unreliable because the nanoparticles of platinum that serve as a catalyst for the chemical reaction sometimes do not function optimally, which results in inefficient operation.

“Scientists want to exploit the nanoparticle in the device but still don’t know that particle’s basic properties,” said Simon Billinge, Professor of Materials Science. “Sometimes it works, and sometimes it doesn’t.”

These catalysts, nanoparticles of platinum, are one-millionth of a millimeter in thickness. The properties of the metal change when they are so small, and scientists have yet to fully characterize their properties. By determining the nanoparticle’s structure and properties—its electrical conductivity, thermal conductivity, melting point, and stiffness—scientists will be better able to predict a fuel cell’s performance, based on what particular nanoparticle is used as the catalyst.

To help provide a solution, Billinge is developing new methods to characterize the structure of nanoparticles, figuring out the arrangements of atoms in particles that are made up of a few hundred to a few thousand atoms. He uses intense x-ray and neutron-source technology, carrying out his research in particle accelerators at the Brookhaven National Laboratory in Long Island, the Los Alamos National Laboratory in New Mexico, and the Argonne National Laboratory in Illinois.

In these accelerators, the nanoparticles of platinum circle at high energy, with the x-ray beam providing data on the defraction patterns revealed in the experiment. Billinge has made important breakthroughs by developing novel fourier transform methods to analyze the data.

He also has worked on measuring the surface energy of the platinum catalyst. The surface atoms, like those on the meniscus of a water droplet, have higher energy than those inside of the particle. And it’s the surface area of the nanoparticles that provides the reactivity for the hydrogen and oxygen that come together to produce the energy that propels the vehicle.
 


Mark Cane: Predicting El Niño

Mark Cane spent much of his early 20s protesting against the war in Vietnam and volunteering with the civil rights movement in the South. He remains a social activist, but today he does so from his position as one of the world’s top climate modelers. As science- based predictions of the weather a few days in advance were becoming routine, predicting the weather three or four months in advance was left to the likes of The Farmer’s Almanac.

All that began to change in 1985 when Mark Cane and his student, Steve Zebiak, published the results of a model they developed to predict the movement of warm water across the tropical pacific ocean in a cyclical phenomenon known as the El Niño southern oscillation, or ENSO. When it forms, El Niño’s meteorological reach spans the globe, causing a well-known pattern of extreme weather events. The 2009 El Niño, for example, resulted in deep droughts in India and the Philippines and deadly rains in Uganda. Aside from the regular progression of the seasons, no other phenomenon influences earth’s short-term climate as profoundly as ENSO.

The Zebiak-Cane model showed a moderate El Niño developing in late 1986. People in Peru, Australia, and elsewhere still had vivid memories of the devastating effects of the powerful El Niño that formed in 1982 and 1983, so many scientists opposed publishing forecasts they didn’t yet understand.

“People said, ‘What if you’re wrong?’” said Cane, the G. Unger Vetlesen Professor of Earth and Climate Sciences and a Professor in the Department of Applied Physics and Applied Mathematics and the Department of Earth and Environmental Sciences. “I said, ‘What if we’re right and we don’t tell anyone?’”

Cane and Zebiak published their forecast in Nature in June of that year, which gave anyone who cared to listen time to prepare. Despite a delay in its formation early in the forecast window, by the autumn of 1986, the predicted El Niño developed, bringing its associated weather patterns to much of the globe.

Most of Cane’s work since that time relates to the impacts of human-induced climate change and natural climate variability on people around the world, such as a seminal paper studying the implications of El Niño on maize yields in Zimbabwe. He has also created a highly successful master’s degree program in climate and society that prepares students to understand and cope with the impacts of climate variability and climate change on society and the environment.

“Science should be more than just an academic exercise,” said Cane. “We’re not just predicting this thing in the Pacific; we’re trying to predict all these consequences around the world that people care about.”
 


Richard Osgood: Looking at Light

Sometimes, to solve big problems, you have to think small. Richard Osgood thinks very small. One of the biggest energy questions today is how to make solar cells more efficient and more affordable. This is particularly important for the billion or so people who live in poverty and, in most cases, entirely off the grid.

Osgood and the other members of the surface group in his research laboratory for fundamental and applied science study the basic processes that allow some materials to convert light to electricity. It is a phenomenon that makes photovoltaic cells and fuel cells possible and that lies at the foundation of many hopes for a more sustainable future. But for all its promise, the process is surprisingly not well understood.

“This is a very basic question we’re trying to address,” said Osgood, Higgins Professor of Electrical Engineering and a Professor in the Department of Applied Physics and Applied Mathematics. “We need to know more about the fundamentals that limit the efficiency of charge transfer.”

He and his team use ultrashort bursts of laser light to watch individual molecules of titanium dioxide accept or reject electrons. they also have made some of the first studies of titanium dioxide nanoparticles using the atomic-level resolution of a scanning tunneling microscope (stM) to understand how these novel structures can be used to improve solar cells.

Titanium dioxide is of particular interest because it is used in graetzel cells, a type of low-cost photovoltaic cell that is easy to manufacture from readily available materials. Most low-cost cells are sensitive to only a narrow band of sunlight. The graetzel cell, however, contains a layer of organic dye that produces free electrons from a wide spectrum of sunlight, much like chlorophyll does in plants. These electrons are then taken up by the titanium dioxide semiconductor to produce a current. The trouble is, graetzel cells are only about 7 to 10 percent efficient, meaning that, at best, only one out of ten free electrons produces a current. Osgood and others would like to improve on this, but the reasons why one electron is captured and another is not remain elusive. By firing extremely short (10–15 femtosecond) bursts of laser light at a titanium dioxide crystal and simultaneously watching with an STM, Osgood and his team are nearing the ability to observe individual electrons being taken up or rejected by the crystal matrix.

The rise of far-reaching, basic science studies like his—that span physics, chemistry, and engineering—gives Osgood hope that, by focusing on the small stuff, answers to the big questions are not far off. “The world is changing in the way things are done,” he said. “The number of people doing interdisciplinary work is growing every day. It’s an exciting time.”
 


Lorenzo Polvani: Reevaluating the Hole in the Ozone

We don’t hear much about the hole in Earth’s ozone layer these days, and for good reason. Collective international action has been successful in reversing a decades-long deterioration of the protective layer in the stratosphere. The hole, which grows and shrinks seasonally over antarctica, is expected to close by sometime midcentury.

Now, however, models and observations of Earth’s atmosphere are showing that the ozone hole may be having an effect on global climate patterns that may be masking the full impact of global warming. “The ozone hole has been ignored for the past decade as a solved problem,” said Lorenzo Polvani. “But we’re finding it has caused a great deal of the climate change that’s been observed.”

Polvani, who holds appointments in the Department of Applied Physics and Applied Mathematics as well as the Department of Earth and Environmental Sciences, has studied atmospheric dynamics from the surface to the upper stratosphere and from both poles to the equator. In the last few years, he has focused on understanding the effects that ozone depletion, and its eventual recovery, has on Earth’s climate.

Ozone - a molecule made up of three atoms of oxygen - absorbs much of the sun’s UVB radiation. In the mid-1980s, it was discovered that chlorofluorocarbons, a chemical used as aerosol propellants, were collecting in the stratosphere over Antarctica, where they were very quickly breaking down the planet’s ozone. in 1987, world governments signed the Montreal protocol to ban the manufacture and use of chlorofluorocarbons, and the success of the agreement has been held up as a model for an eventual international climate treaty.

Ozone warms the stratosphere when it absorbs UV radiation. Its relative absence over Antarctica for the past 40 years has had a cooling effect on the upper atmosphere over the South Pole that is as much as ten times as strong as the warming effect associated with increasing carbon dioxide concentrations.

The effects of this cooling already appear to be affecting the location of the Southern Hemisphere’s mid-latitude jet stream. Like its twin in the north, the southern jet stream is associated with the formation and movement of weather patterns around the globe. Cooling of the upper troposphere - the highest part of the lower atmosphere - has been connected to a shift of the southern mid-latitude jet stream toward the south by a few degrees.

This shift has resulted in precipitation patterns moving south as well, and in the tropical dry zones expanding. The evidence is not yet conclusive, but Australia’s lengthy drought may be the result of this rearrangement of southern hemisphere weather patterns. If so, Polvani’s next task is to find out what will happen as the ozone hole closes and the full brunt of global warming is felt throughout the
atmosphere.

“These next couple of decades are going to be interesting times,” said Polvani. “We’re going to see these climate changes play out in our lifetimes.
 


Adam Sobel: Modeling Monsoons

Adam Sobel once bought a plane ticket to the city of Darwin in Australia’s tropical north based on a colleague’s weather prediction. That in itself is nothing new, but the prediction he followed was for the start of the monsoon rains three weeks hence, a prediction that was virtually unheard of just a decade earlier for the length of its foresight. When he got off the plane, no one was happier to see the sky open up and the rain begin right on schedule.

“We had half a meter of rain in ten days,” said Sobel, who holds a dual appointment in the Department of Applied Physics and Applied Mathematics and the Department of Earth and Environmental Sciences. “It was exciting.”

For more than one billion people, the seasonal monsoons are both a life-giving annual event and a potential disaster. Although much is known about how the monsoons occur, very little is understood about how they vary. The monsoons are an atmospheric circulation pattern that develops in the tropics at fairly well-defined times of year. The sun warming Earth’s surface draws moisture from ocean waters and forms the iconic, seasonal rains of south and southeast Asia or sub-tropical Africa and South America. The people who live in these regions, particularly the rural poor, rely on the monsoon rains to water crops and recharge aquifers.

When the monsoons are weak, drought and famine can result; if they come with too much gusto, flooding and disease occur. The fine line between life and death makes monsoon forecasting one of the most important topics within climate
modeling these days. Sobel is trying to develop models to predict the variations within a monsoon season, known as “active” and “break” cycles, which have so far been beyond the ability of climate modeling. Recently, he helped demonstrate the central importance of heat stored in the oceans, particularly in the so-called mixed layer that encompasses the top 10 to 50 meters of water, on the formation of active and break cycles.

The atmospheric patterns that drive the monsoon - the Madden Julian Oscillation in particular - are also responsible for spawning tropical storms in distant ocean basins and may influence the formation of El Niño and La Niña cycles in the Western Pacific. As a result, Sobel’s work may one day have an impact on people who live well beyond the reach of the monsoon rains.

“We need a central theory that can be stated simply that explains the variations we see,” said Sobel. “Weather prediction can look two weeks in the future, max. Climate models can give us the probability for a strong or weak monsoon a year in advance. This is in between. It’s kind of the Holy Grail right now.”
 


Marc Spiegelman: Studying Earth’s Mantle and Crust

Growing up, Marc Spiegelman dreamed of one day being the next Jacques Cousteau. The only problem was he enjoyed hiking more than diving and he excelled at math and physics rather than oceanography. Two summers spent work- ing as a ranger for the U.S. Forest Service and the discovery that the planet often reveals its secret inner workings through calculus sealed his future.

Today, Spiegelman studies the interior of the planet using the tools of a computational physicist - computer models and equations describing fluids and solids deforming far beyond human eyes and time scales. In combining his love of dry land with his interest in physics and math, Spiegelman treats the planet as one, big physics problem and, at the same time, is helping advance understanding of how Earth’s crust and mantle behave in tectonically active regions of the world - places dominated by volcanoes and earthquakes. More recently, he has begun considering a problem that has traditionally attracted scientists with a more airy focus: what to do with all the carbon dioxide in the atmosphere.

Spiegelman’s principal expertise involves applying theories that describe the migration of magma and fluids in the solid earth, and the behavior of solid materials under the immense heat and stress of the deep earth. His efforts are helping create a more general understanding of the interactions between solids and fluids in the mantle and crust. This work has applications to understanding the behavior and output of volcanoes around the globe like Eyjafjal-lajökull, the volcano in Iceland that erupted in early 2010 and shut down air travel over much of Europe for nearly one month. His work also provides insights into such problems such as the interactions between reactive fluids and a variety of minerals found in the earth.

His expertise is attracting attention from new circles because it turns out that one of the more promising ideas for dealing with excess carbon emissions involves the solid earth. Geological carbon sequestration, a problem that Spiegelman’s colleagues at the Lamont-Doherty Earth Observatory are actively investigating, entails injecting carbon dioxide into certain mineral formations found in many places around the world.

Spiegelman’s ability to work between the worlds of observation and modeling may one day prove crucial in understanding what happens when carbon dioxide under immense pressure reacts with mineral formations containing magnesium. Such reactions produce extreme heat, which cracks the rock, and form solid magnesium carbonate, locking the carbon dioxide away safely and permanently.

It is this ability to model unobservable interactions between solids, fluids, and heat deep underground that gives him a leg up on his old hero, Jacques Cousteau. Instead of a view into the depths of the ocean, Spiegelman has been able to see through his equations and models into deepest recesses of the upper earth.


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