Fine-tuning photosynthesis

A new analysis by MIT researchers could make it possible to design more efficient artificial systems that mimic the way plants harvest the energy of sunlight through photosynthesis.

The study is the latest in an ongoing series examining the process of photosynthesis and the different variables that determine its efficiency, conducted by Associate Professor of Chemistry Jianshu Cao and his postdocs and colleagues. The new work, which looks at artificial photosynthetic systems based on self-assembling molecules designed by researchers at of the University of California, Berkeley, follows a paper they published in October in the New Journal of Physics that examined the factors that determine the efficiency of natural photosynthesis.

Graphic: Christine Daniloff

The hope, being pursued by various research teams around the world, is to be able to eventually produce synthetic chemical systems that mimic nature’s process of photosynthesis and thereby produce a more efficient way of harnessing the sun’s energy than today’s photovoltaic panels, and that can be used to produce some kind of fuel that can be stored and used when needed, eliminating the intermittency problems of solar power. Understanding how to maximize the efficiency of the process is one step toward being able to create such a system.

The new research, by Cao and postdoctoral fellow Ji-Hyun Kim, found that there are many possible shapes that can be formed by bundles of chromophores — the reaction centers within molecules that actually absorb particles of light from the sun, or that transfer that energy or convert it into chemical forms that can be stored for later use. Among other configurations, the chromophores readily either adopt a helical shape (like a bedspring) or form a stack of disks. In their analysis, the stacked-disk configuration proved especially easy to fine-tune for optimal efficiency.

There are three basic types of chromophores: acceptors, which absorb the light’s energy; donors, which emit light; and bridges, which transfer the energy from one reaction center to another. In systems composed mainly of donors and acceptors, the addition of extra bridges can greatly increase the efficiency of the process, the researchers found. In addition, specific ratios of acceptor to donor sites lead to the most efficient transfer of energy. Their findings were published in The Journal of Physical Chemistry, and the work was supported by the MIT Energy Initiative, the Singapore-MIT Alliance for Research and Technology, the National Science Foundation and the MIT Center for Excitonics.

In the related work published last month, Cao, Class of 1942 Professor of Chemistry Robert Silbey, and their postdoctoral fellow, Jianlan Wu, had found that the efficiency of natural photosynthesis can be improved by adding just the right amount of noise — that is, random fluctuations. Since noise usually reduces efficiency, this finding was somewhat counter-intuitive. Adding more noise could also decrease the efficiency, they found. “There’s an optimum amount” of noise, Silbey explains, that produces the most efficient transfer of energy.

To explain why a certain amount of noise could be helpful, he offers the analogy of friction from the road while driving a car. Of course, friction slows the car somewhat, thus decreasing efficiency, and with too much friction the car could grind to a halt. But if there were no friction at all — such as on a perfectly smooth icy surface — the wheels would just spin and the car would not move at all. There is an optimum amount of friction somewhere in the middle, and that’s also the case with noise in a photosynthetic system. In the case of photosynthesis, energy is being transferred from one part of the molecule to the next, and random environmental fluctuations — or noise — can add a push to the moving electrons carrying the energy and help propel them along, up to a point; but too much of this extra push can have the opposite effect, scattering the excitons so they are less likely to make it to the reaction center where that energy is harnessed.

The specific photosynthetic systems the team studied included those from green sulfur bacteria, which have a very common type of multi-chromophoric aggregates that perform the energy conversion, Silbey says.

While many teams of researchers have studied the way photosynthesis takes place in different plants, algae and bacteria, this work looked at the underlying quantum-mechanical processes and calculated how a variety of different variables affected the efficiency of the system, Cao says. “We think we have a very general picture of it now, that can be used for optimal design” of new, synthetic light-harvesting systems. This could allow fine-tuning of the timescales, temperatures and molecular configurations to get the maximum energy output from a given amount of sunlight. The search for general optimization in light-harvesting systems is currently being pursued by several other groups, including those of MIT professor of mechanical engineering Seth Lloyd, Alan Aspuru-Guzik of Harvard University, and Martin Plenio of Ulm, Germany.

This theoretical analysis was triggered by experiments in the last few years, including those by Greg Engel, an assistant professor of chemistry at the University of Chicago, which demonstrated the quantum-mechanical basis for biological photosynthesis. “That’s what got the theorists all worked up,” Cao says, and led them to search for basic understandings that could lead to the most efficient possible systems. The next step will be for others to apply this understanding to the design of new synthetic systems.

Engel, who was not involved in this MIT research, says it is “a beautiful piece of work.”  He adds that “for a long time we have known that photosynthesis has been optimized by evolution, but understanding the way it was optimized provides a way to move forward” in trying to design similarly optimized synthetic systems. “Now that we can take advantage of this and copy some of the underlying design principles” nature has used, he says, “it opens up many new opportunities for us to take advantage of the three-and-a-half billion years of R&D that nature has done.”

But this is just the beginning of a long process in terms of applying this understanding, Engel says: “There is still a great deal of work to be done. This is not the answer, this is the beginning of the roadmap, the first signpost along the way.”

MIT analysis shows how synthetic systems for capturing the sun’s energy could be made more efficient.

MIT researchers test automatic parallel parking

Any driver knows it can be hard to remain calm behind the wheel. But perhaps high-tech tools can help. A new study by MIT researchers, announced Thursday, suggests that driver-assistance technologies lower the amount of stress people feel when behind the wheel.

Associate Director of New England University Transportation Center Bryan Reimer, a research scientist at the MIT AgeLab, discusses how the self-parking car works. Photo: Melanie Gonick

The study, conducted over nine months by researchers in the MIT AgeLab in collaboration with the Ford Motor Company and the New England University Transportation Center (NEUTC), monitored drivers as they conducted two generally stress-inducing maneuvers: parallel parking, and backing out into cross-traffic in a parking garage. When using vehicles equipped with driver-assistance systems, however, drivers had lower heart rates, lower reported perceptions of stress, and in some cases operated vehicles more prudently, compared to the times when they operated vehicles entirely manually.

AgeLab researchers say these kinds of technological interventions are badly needed. “The driver behind the wheel has gotten increasingly stressed over time,” said Joseph Coughlin, the founder and director of the AgeLab, and director of the NEUTC, noting that the average one-way driving commute in the United States has risen to 29 minutes from 19 minutes in the last 10 years. For this reason, Coughlin, who teaches transportation policy in the MIT Engineering Systems Division, emphasized that it is vital to develop tools that make life on the road simpler. For drivers, “stress is a safety issue, and it is a quality-of-life issue,” Coughlin said, adding, “according to the Gallup-Healthways Well-Being Index, middle-aged Americans, who live and breathe in their cars, are reporting the lowest level of well-being compared to all other age groups.”

The study involved 84 participants, balanced by age and gender, who were divided into two groups, one for each driver-assistance tool. One set of 42 subjects had to execute a dozen parallel-parking maneuvers each on Massachusetts city streets. They drove a Lincoln MKS equipped with Ford’s Active Park Assist tool, which uses cameras and sensors to gauge the size of parking spots, then automatically turns the steering wheel — without the driver touching it — as the car backs into a spot.

While using Active Park Assist, the drivers’ heart rates were reduced by 12 beats per minute: they averaged 71 beats per minute, compared to an average of 83 beats per minute in the instances in which the drivers were asked to park without the tool. Moreover, the drivers’ subjective perceptions of their own stress levels, after parking, were 30 percent higher when they parked manually than when they used Active Park Assist.

“That’s quite surprising and quite a large magnitude,” said Bryan Reimer, a research scientist in the AgeLab. The AgeLab, a multi-disciplinary research program based within MIT’s Engineering Systems Division and the Center for Transportation and Logistics, seeks to design and use innovations that can increase health and wellness throughout people’s lives. The NEUTC is sponsored by the United States Department of Transportation.

Parallel parking, it turns out, produces a significant amount of fear and loathing among drivers. A poll conducted by Harris Interactive (and commissioned by Ford) shows that 31 percent of U.S. drivers avoid parallel parking whenever they can.

The other driver-assistance tool in the study was Ford’s Cross-Traffic Alert system, which notifies drivers who are backing out of parking sports of oncoming vehicles, via a warning sound and light. In a Boston-area parking garage, drivers had to both use the Cross-Traffic Alert system, and back out without it, a half-dozen times each. Overall, drivers had heart rates and reported levels of stress that were reduced less than 5 percent when they were using the system, compared to driving manually, a modest decrease. However, drivers were 33 percent more likely to yield to oncoming traffic when using the Cross-Traffic Alert tool, reducing the potential for accidents.

After a presentation by AgeLab and Ford researchers on Thursday, reporters tried out the Active Park Assist system on an MIT roadway, near the Wright Brothers Wind Tunnel. Under the guidance of Jarrod Orszulak, a research engineer in AgeLab, this driver activated the parking system by pressing a button, and — arms away from the wheel — let the car smoothly angle into a parking spot. Only one thing produced stress: some daydreaming pedestrians, a problem engineers probably cannot solve.

AgeLab study: Driver-assistance systems can increase wellness and safety behind the wheel

A link between air travel and deaths on the ground

Study suggests pollution from airplanes flying at ‘cruise’ altitudes contributes to 8,000 deaths per year globally.

The atmosphere is full of natural and man-made chemicals, including emissions from fuel combustion and byproducts of living organisms. Many of these chemicals combine in the atmosphere to form tiny solid and liquid particles known as “fine particulate matter” that are 2.5 micrometers or smaller (the average human hair is about 70 micrometers in diameter, by comparison). While it’s not clear whether all of these particles may be harmful, some are; the danger to humans comes when they are inhaled and trapped in the lungs, where they can then enter the bloodstream.

An Airbus A380, the world's largest passenger airliner

In 2004, the World Health Organization estimated that about one million deaths per year are caused by air pollution, and several epidemiological studies have linked air pollution to the development of cardiovascular and respiratory illnesses, including lung cancer. Those studies tracked thousands of adults over many years to measure their exposure to air pollution while monitoring their health. Once the data were statistically analyzed to correct for other risk factors like smoking, the results indicated that increased exposure to fine particulate matter caused by air pollution is linked to health problems like chronic bronchitis and decreased lung function, as well as premature death.

Air India Airbus A310-304

Aviation emissions contribute to this health problem, according to a new study that suggests that airplanes flying at a cruise altitude of around 35,000 feet emit pollutants that contribute to about 8,000 deaths per year globally. The research, reported online this month in the journal Environmental Science and Technology, provides the first estimate of premature deaths attributable to aircraft emissions at cruise altitudes. Aircraft emit nitrogen oxides (NOx) and sulfur oxides (SOx), which react with gases already existing in the atmosphere to form harmful fine particulate matter.

Tracking emissions

Current worldwide regulations target aircraft emissions only up to 3,000 feet. That’s because regulators have assumed that anything emitted above 3,000 feet would be deposited into a part of the atmosphere that has significantly smoother air, meaning pollutants wouldn’t be affected by turbulent air that could mix them toward the ground. Thus, even though 90 percent of aircraft fuel is burned at cruise altitudes, only those pollutants that are emitted during takeoff and landing are regulated by measuring emissions during tests of newly manufactured engines in simulated takeoff and landing conditions.

Aeroflot Il-76TD

“Anything above that [altitude] really hasn’t been regulated, and the goal of this research was to determine whether that was really justified,” says lead author Steven Barrett, the Charles Stark Draper Assistant Professor of Aeronautics and Astronautics in MIT’s Department of Aeronautics and Astronautics.

To study the effects of cruise emissions, Barrett used a computer model that combined data about plane trajectories, the amount of fuel burned during flights and the estimated emissions from those flights. He combined that with a global atmospheric model that accounts for air-circulation patterns in different parts of the globe and the effect of emissions to determine where aviation emissions might cause an increase in fine particulate matter. He then used data related to population density and risk of disease in different parts of the world to determine how the change in particulate matter over certain regions might affect people on the ground — specifically, whether the air pollutants would lead to an increased risk of death.

Saab Gripen, a Swedish multi-role fighter aircraft.

Analysis of these data revealed that aircraft pollution above North America and Europe — where air travel is heaviest — adversely impacts air quality in India and China. That is, even though the amount of fuel burned by aircraft over India and China accounts for only 10 percent of the estimated total amount of fuel burned by aircraft across the globe, the two countries incur nearly half — about 3,500 — of the annual deaths related to aircraft cruise emissions. The analysis also revealed that although every country in the Northern Hemisphere experienced some number of fatalities related to these emissions, almost none of the countries in the Southern Hemisphere had fatalities.

That’s because the majority of air traffic occurs in the Northern Hemisphere, where planes emit pollutants at altitudes where high-speed winds flowing eastward, such as the jet stream, spread emissions to other continents, according to the study. Part of the reason for the high percentage of premature deaths in India and China is that these regions are densely populated and also have high concentrations of ammonia in their atmosphere as a result of farming. This ammonia reacts with oxidized NOx and SOx to create fine particulate matter that people inhale on the ground. Although agriculture is abundant in Europe and North America, the ammonia levels aren’t as elevated above those regions.

Industry reaction

Funded by the UK Research Councils with help from the U.S. Department of Transportation, the study recommends that cruise emissions be “explicitly considered” by international policymakers who regulate aviation engines and fuels. Steve Lott, a spokesman for the International Air Transport Association, a trade group that represents 230 airlines, says that aviation is “a small part of a big problem,” particularly when compared to other transportation sources of emissions, such as those caused by shipping, which a 2007 study linked to 60,000 premature deaths per year.

NASA test aircraft

Lourdes Maurice, the chief scientific and technical adviser for environment at the Federal Aviation Administration, says that if the agency can confirm Barrett’s findings through additional research, then it will work with the Environmental Protection Agency and the International Civil Aviation Organization to consider appropriate regulatory action. The FAA will continue to fund research to address uncertainties highlighted by Barrett’s work, she adds.

Cargolux Boeing 747-400F

Barrett concedes that there are many uncertainties, including how accurately the model reflects how air travels vertically from high altitudes to low altitudes. To address this, he is collaborating with researchers at Harvard to study an isotope of the element beryllium that is produced naturally at high altitudes and attaches to atmospheric particles that eventually reach the ground through air or rain. Researchers have a general idea of how much beryllium is concentrated in the atmosphere, and Barrett and his colleagues are currently analyzing ground measurements of the element to quantify the extent to which his model “gets vertical transport right.”

Barrett is a member of the Partnership for AiR Transportation Noise and Emissions Reduction (PARTNER), a cooperative research organization that completed the study. Sponsored by the FAA, NASA and Transport Canada, PARTNER has its operational headquarters at MIT.

International prize for solar cooker

Low-cost portable device developed at MIT wins major prize in Netherlands competition.

One Earth Designs, a company spawned by an MIT student team to produce a low-cost portable solar cooker for use in developing countries, won the top prize last week in the Netherlands Green Challenge. Scot Frank ’08, who is CEO of the company, accepted the prize of 500,000 euros (about $667,000).

SolSource is a lightweight solar energy device that provides users with a low-cost and portable means of cooking, heating and electricity generation. Image: One Earth Designs

The company will use the money to help scale up production of the solar cookers in China. The umbrella-shaped device, made of yak wool and a thin reflective coating, is expected to sell for about $13. In addition to cooking food and boiling water, the portable device, which can be folded up and carried in a canvas bag, can be used to provide home heating and to generate power for lights or cellphones.

The company has begun testing of energy use and air quality in 400 homes in Tibet to establish a baseline, after which it will test the impact of introducing the solar device to those homes. Most cooking and heating in the region is presently provided by burning wood and yak dung, which can cause serious problems of indoor air pollution, Frank says. Senior Amy Qian was the company’s chief engineer, and the team also includes other MIT alumnae, as well as students from Harvard and Wellesley.

“I feel incredibly honored, on behalf of our whole team,” Frank said in accepting the prize from His Royal Highness Prince Friso of Orange-Nassau, the honorary jury chair. The prize will help to “make our dream come true,” he said.

Ability to recharge rapidly could make electric cars more acceptable to consumers, says MIT student team

A team of MIT students has been working on testing a rapid-recharging system that could help to change public perceptions about electric vehicles and their practicality. They have already done extensive testing of the system with an individual battery cell and with a motorcycle they converted to all-electric operation, and in coming months they hope to be able to demonstrate the system on a full-sized sedan they converted.

MIT Electric Vehicle Team member Radu Gogoana works on the conversion of a 2010 Mercury Milan to an all-electric powertrain. Photo: Patrick Gillooly

The goal is to demonstrate that recharging can be accomplished routinely in under 30 minutes without severely reducing the operating lifetime of the batteries or causing other problems. In the year since the MIT Electric Vehicle Team started working on the project, new and established companies have begun to offer commercial rapid-recharging systems, and Japan has officially adopted a new standard for the connectors for such systems and has begun installing the systems in more than 100 locations. The Nissan Leaf, a pure electric five-passenger car to be introduced in the U.S. later this year, is already capable of rapid recharging in 30 minutes in places that have the necessary “Level III” charging system. (So far, there is just one such station in the U.S., in Portland, Oregon).

Next week, Lennon Rodgers, a doctoral student in mechanical engineering and a member of the MIT Electric Vehicle Team, will present a paper on the team’s rapid-charging tests at the 12th International Conference on Advanced Vehicle and Tire Technologies in Montreal. The paper was co-authored by fellow team members Radu Gogoana ’10, a master’s student in mechanical engineering, Paul Karplus (an undergraduate at Stanford) and Michael Nawrot ’11.

Rapid charging, also known as Level III, requires much higher voltages and current than what is supplied by conventional household circuits. The Japanese rapid-charging standard, called CHAdeMO, provides DC power at up to 500 volts with a current of 125 amps. Typical chargers operate on standard AC power, using either 110 volt household current (Level I), which generally can recharge an electric car’s batteries overnight, or special systems (similar to those needed for electric stoves or clothes dryers) that use 220 volts (Level II), which can cut the charging time in half. “Rapid charging” systems typically refer to those that can charge the batteries to at least 80 percent of capacity within 30 minutes.

Because of the large power requirements, this is not something you’d ever do in your home garage. Rather, this fast-recharge technology might be installed in central recharging stations comparable to today’s gas stations, where the cost of the necessary infrastructure could be warranted and where a fast turnaround is necessary. In many cases, rapid charging systems can provide a 50 percent charge — typically enough to travel 50 miles — in under 5 minutes, comparable to the time it takes to fill a gas tank.

While rapid charging — largely being promoted by companies with long commercial experience with recharging industrial fork lifts and similar vehicles — is beginning to attract attention, there has been relatively little testing on the effects of repeated rapid charging on battery life and performance. “Is it damaging over time? That’s the issue we wanted to study,” says Rodgers. That’s the kind of data the MIT team was collecting in an attempt to prove the potential for this technology.

Rodgers says that the chemistry used in lithium-ion batteries made by the MIT spinoff company A123 Systems is the best suited for rapid charging, and the company’s website declares that the batteries are capable of being fully recharged in 15 minutes. These batteries, based on research carried out at MIT in the lab of Yet-Ming Chiang, professor of materials science and engineering, have been selected for several planned new electric vehicles including cars from Fisker Automotive and buses and trucks from Daimler and Navistar.

In the team’s tests, they ran one of these battery cells through 1,500 charge and discharge cycles, using an automated system. After 1,500 cycles, the battery had lost less than 10 percent of its initial power capacity, Rodgers says. The team used a fan to prevent overheating, which by stressing the chemical and mechanical components can lead to degradation.

To test a rapid-charging system under realistic conditions, the team converted a motorcycle to all-electric operation, and then performed a successful rapid-charging test, reaching more than 80 percent charge within 10 minutes.

The MIT EV Team has also completed the conversion of a 2010 Mercury Milan hybrid (donated by Ford) into a pure electric vehicle. The initial conversion was successfully completed last summer, and this summer they have been making major improvements — reinstalling the 8,000 lithium ion phosphate battery cells provided by A123, rewiring the system with a new control system, adding a powerful cooling system for the batteries, and making changes to make the car street-legal. They hope to use the car for testing of rapid charging technology, although they are still looking for funding to get the necessary equipment. Commercial rapid-charging systems can cost tens of thousands of dollars.

Kristen Helsel, vice president of EV Solutions for Aerovironment, a company that makes charging systems for electric vehicles, says that it’s unlikely anyone will start installing rapid-charging stations in the U.S. in substantial numbers until the country adopts an official standard, and “I don’t expect it in the near term. There are still multiple designs under consideration.” But a rapid charging capability is going to be crucial for widespread acceptance of electric vehicles, no matter what their driving range is on a full charge, because people will always want the possibility of being able to go farther, she says. In the meantime, research such as that being carried out by the MIT EV Team can play a useful role, she says. “Better batteries are coming, and because of that the ability to charge at any level is going to be a constantly evolving thing. We need to continually evolve the technology, and to better understand the effects of different things” on battery life and other factors, she says. “There’s all sorts of good work that needs to be done.”

For car designers, Rodgers says, there is a tradeoff they need to consider: They can include larger battery packs that provide a longer driving range, but are more difficult to recharge rapidly, or smaller packs that give a shorter range but cost less and can more easily be charged rapidly.

In addition to analyzing battery performance, the team analyzed the impact that rapid charging of electric vehicles might have on the electric grid. They concluded that spikes of usage that might present problems for the grid could be eliminated by using an intermediate battery system. Instead of directly charging the vehicle from the grid, a large battery pack — perhaps using batteries recycled from other cars — could be slowly charged using a “trickle charge” from the grid, thus using low-cost, off-peak power, and then rapidly transfer its charge to the vehicle’s batteries.

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