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Thursday, December 20th, 2018
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| 12:00a | Improving crop yields while conserving resources When it comes to the health of the planet, agriculture and food production play an enormous role. According to the Food and Agriculture Organization of the United Nations, roughly 37 percent of land worldwide is used for agriculture and food production, and 11 percent of the Earth’s land surface is used specifically for crop production. Finding ways to make agriculture more sustainable and efficient is crucial not only for the environment, but also for global food supply. Julia Sokol grew up far away from any farm. Born in Russia, Sokol and her family moved when she was 10 years old to New York City, where her father worked for the United Nations. These days, however, Sokol, a PhD student in mechanical engineering, spends a lot of her time thinking about agriculture. For the past two years, Sokol has been working on a drip irrigation project at MIT’s Global Engineering and Research (GEAR) Lab. After receiving her bachelor’s in mechanical engineering at Harvard University, Sokol spent some time in industry, first as a research assistant at Schlumberger, then working at a small sustainability consulting firm. Wanting a stronger technical foundation, she applied to MIT for graduate school. During her master’s program, Sokol took course 2.76 (Global Engineering), which was taught by associate professor and principal investigator of the GEAR Lab, Amos Winter. Having developed an interest in water-related issues, Sokol jumped at the opportunity to work with Winter on the GEAR Lab’s energy efficient drip irrigation project. “I was really excited to join the project,” says Sokol. “It perfectly combines my passion for sustainability with my interest in fundamental research in fluid mechanics and system design.” Rather than flood irrigation — in which water is pumped from a source to flood a field — drip irrigation has a central pump that moves water through a network of pipes. Emitters attached to the pipes release water uniformly throughout the field, resulting in higher crop yield and less water consumption when compared to flood irrigation.
The emitters used in drip irrigation disperse water evenly, as opposed to flood irrigation, which often causes crops to get water-logged. “These drip emitters need to provide a uniform flow rate throughout the field so all crops get the same amount of water,” adds Susan Amrose, a research scientist at the GEAR Lab. The research team first focused on the geometrical features of these emitters. They developed a mathematical model describing how the geometrical features interact with the membranes inside them. Based on this model, they optimized the emitters to get the lowest possible pressure required to ensure the water flows to crops at the right rate. Commercial emitters require minimum activation pressure of 1 bar to provide a constant flow rate for the crops. Thanks to the changes the team made inside the emitter, they lowered the activation pressure to just 0.15 bar. This reduction in the pressure needed to activate the drippers cut the power needed to operate the central pump in half. “Reducing the pressure lowers the cost of the system overall, which is beneficial to the farmer, and of course it also helps reduce greenhouse gas emissions,” says Sokol. For off-grid drip irrigation systems that operate via solar power, the use of the new emitters could reduce costs to the farmer by 40 percent. “For farmers in developing countries, this cost savings reduces the barrier to a water conserving and yield increasing technology,” adds Amrose. The team has conducted a number of field trials in Morocco and Jordan, where they work with NGO partners and private farmers to test the newly designed emitters and optimized irrigation system. “The biggest takeaway from these field trials was how much our system reduced energy and cost while providing high uniformity of flow rate to crops,” explains Sokol. According to Amrose, Sokol has been instrumental in the development and testing of these emitters. “She brings the whole package — she is an excellent designer, she can be in the field fixing hardware, and she is also incredibly good theoretically, working with models,” Amrose says. Sokol and the GEAR Lab team will continue to make improvements to the design of the emitters that both reduce costs, conserve resources, and improve crop yield. “The global population keeps growing, so we need greater agricultural productivity,” Sokol adds. “That’s our focus — to make that happen, especially in developing areas.” |
| 11:00a | New threat to ozone recovery Earlier this year, the United Nations announced some much-needed, positive news about the environment: The ozone layer, which shields the Earth from the sun’s harmful ultraviolet radiation, and which was severely depleted by decades of human-derived, ozone-destroying chemicals, is on the road to recovery. The dramatic turnaround is a direct result of regulations set by the 1987 Montreal Protocol, a global treaty under which nearly every country in the world, including the United States, successfully acted to ban the production of chlorofluorocarbons (CFCs), the main agents of ozone depletion. As a result of this sustained international effort, the United Nations projects that the ozone layer is likely to completely heal by around the middle of the century. But a new MIT study, published today in Nature Geoscience, identifies another threat to the ozone layer’s recovery: chloroform — a colorless, sweet-smelling compound that is primarily used in the manufacturing of products such as Teflon and various refrigerants. The researchers found that between 2010 and 2015, emissions and concentrations of chloroform in the global atmosphere have increased significantly. They were able to trace the source of these emissions to East Asia, where it appears that production of products from chloroform is on the rise. If chloroform emissions continue to increase, the researchers predict that the recovery of the ozone layer could be delayed by four to eight years. “[Ozone recovery] is not as fast as people were hoping, and we show that chloroform is going to slow it down further,” says co-author Ronald Prinn, the TEPCO Professor of Atmospheric Science at MIT. “We’re getting these little side stories now that say, just a minute, species are rising that shouldn’t be rising. And certainly a conclusion here is that this needs to be looked at.” Xuekun Fang, a senior postdoc in Prinn’s group, is the lead author of the paper, which includes researchers from the United States, South Korea, Japan, England, and Australia. Short stay, big rise Chloroform is among a class of compounds called “very short-lived substances” (VSLS), for their relatively brief stay in the atmosphere (about five months for chloroform). If the chemical were to linger, it would be more likely to get lofted into the stratosphere, where it would, like CFCs, decompose into ozone-destroying chlorine. But because it is generally assumed that chloroform and other VSLSs are unlikely to do any real damage to ozone, the Montreal Protocol does not stipulate regulating the compounds. “But now that we’re at the stage where emissions of the more long-lived compounds are going down, the further recovery of the ozone layer can be slowed down by relatively small sources, such as very short-lived species — and there are a lot of them,” Prinn says. Prinn, Fang, and their colleagues monitor such compounds, along with other trace gases, with the Advanced Global Atmospheric Gases Experiment (AGAGE) — a network of coastal and mountain stations around the world that has been continuously measuring the composition of the global atmosphere since 1978. There are 13 active stations scattered around the world, including in California, Europe, Asia, and Australia. At each station, air inlets atop typically 30-foot-tall towers pull in air about 20 times per day, and researchers use automated instruments to analyze the atmospheric concentrations of more than 50 greenhouse and ozone-depleting gases. With stations around the world monitoring gases at such a high frequency, AGAGE provides a highly accurate way to identify which emissions might be rising and where these emissions may originate. When Fang began looking through AGAGE data, he noticed an increasing trend in the concentrations of chloroform around the world between 2010 and 2015. He also observed about three times the amount of atmospheric chloroform in the Northern Hemisphere compared to the Southern Hemisphere, suggesting that the source of these emissions stemmed somewhere in the Northern Hemisphere. Using an atmospheric model, Fang and his colleagues estimated that between 2000 and 2010, global chloroform emissions remained at about 270 kilotons per year. However, this number began climbing after 2010, reaching a high of 324 kilotons per year in 2015. Fang observed that most stations in the AGAGE network did not measure substantial increases in the magnitude of spikes in chloroform, indicating negligible emission rises in their respective regions, including Europe, Australia, and the western United States. However, two stations in East Asia — one in Hateruma, Japan, and the other in Gosan, South Korea — showed dramatic increases in the frequency and magnitude of spikes in the ozone-depleting gas.
MIT researchers have back-tracked chloroform in East Asia using AGAGE measurements and 3-dimensional atmospheric transport models. Courtesy of the researchers. The rise in global chloroform emissions seemed, then, to come from East Asia. To investigate further, the team used two different three-dimensional atmospheric models that simulate the movement of gases and chemicals, given global circulation patterns. Each model can essentially trace the origins of a certain parcel of air. Fang and his colleagues fed AGAGE data from 2010 to 2015 into the two models and found that they both agreed on chloroform’s source: East Asia. “We conclude that eastern China can explain almost all the global increase,” Fang says. “We also found that the major chloroform production factories and industrialized areas in China are spatially correlated with the emissions hotspots. And some industrial reports show that chloroform use has increased, though we are not fully clear about the relationship between chloroform production and use, and the increase in chloroform emissions.” “An unfortunate coherence” Last year, researchers from the United Kingdom reported on the potential threat to the ozone layer from another very short-lived substance, dichloromethane, which, like chloroform, is used as a feedstock to produce other industrial chemicals. Those researchers estimated how both ozone and chlorine levels in the stratosphere would change with increasing levels of dichloromethane in the atmosphere. Fang and his colleagues used similar methods to gauge the effect of increasing chloroform levels on ozone recovery. They found that if concentrations remained steady at 2015 levels, the increase observed from 2010 to 2015 would delay ozone recovery by about five months. If, however, concentrations were to continue climbing as they have through 2050, this would set a complete healing of the ozone layer back by four to eight years. The fact that the rise in chloroform stems from East Asia adds further urgency to the situation. This region is especially susceptible to monsoons, typhoons, and other extreme storms that could give chloroform and other short-lived species a boost into the stratosphere, where they would eventually decompose into the chlorine that eats away at ozone. “There’s an unfortunate coherence between where chloroform is being emitted and where there are frequent storms that puncture the top of the troposphere and go into the stratosphere,” Prinn says. “So, a bigger fraction of what’s released in East Asia gets into the stratosphere than in other parts of the world.” Fang and Prinn say that the study is a “heads-up” to scientists and regulators that the journey toward repairing the ozone layer is not yet over. “Our paper found that chloroform in the atmosphere is increasing, and we identified the regions of this emission increase and the potential impacts on future ozone recovery,” Fang says. “So future regulations may need to be made for these short-lived species.” “Now is the time to do it, when it’s sort of the beginning of this trend,” Prinn adds. “Otherwise, you will get more and more of these factories built, which is what happened with CFCs, where more and more end uses were found beyond refrigerants. For chloroform, people will surely find additional uses for it.” This research was supported by NASA, the National Institute of Environmental Studies in Japan, the National Research Foundation of Korea, the U.K. Natural Environment Research Council, the Commonwealth Scientific and Industrial Research Organization of Australia, the Department for Business, Energy & Industrial Strategy, and other organizations. |
| 1:29p | Gut-brain connection signals worms to alter behavior while eating When a hungry worm encounters a rich food source, it immediately slows down so it can devour the feast. Once the worm is full, or the food runs out, it will begin roaming again. A new study from MIT now reveals more detail about how the worm’s digestive tract signals the brain when to linger in a plentiful spot. The researchers found that a type of nerve cell found in the gut of the worm Caenorhabditis elegans is specialized to detect when bacteria are ingested; once that occurs, the neurons release a neurotransmitter that signals the brain to halt locomotion. The researchers also identified new ion channels that operate in this specialized nerve cell to detect bacteria. “In terms of a precise mechanism of how the gut signals back up to the brain, it was unclear what was going on,” says Steven Flavell, an assistant professor of brain and cognitive sciences and a member of MIT’s Picower Institute for Learning and Memory. “Food is something that really motivates this animal, so people have studied this for a long time, but the mechanism of how food ingestion is detected by the nervous system to drive a behavioral change, that had really been missing.” Flavell is the senior author of the study, which appears in the Dec. 20 issue of Cell. Jeffrey Rhoades, a former technical assistant in the Picower Institute, is the paper’s first author. Gut-brain connection In all animals, the gut and the brain have a strong connection. Signals from our gastrointestinal tract let us know when we’re full and help to control our appetite, via hormones such as leptin and ghrelin. The GI tract is also the source of most of the body’s serotonin, which also play a role in appetite. Additionally, the digestive tract has its own semi-independent nervous system, known as the enteric nervous system. This system of neurons governs GI functions such as contraction of the digestive organs and the secretion of hormones and digestive enzymes. While the full complexities of the human enteric nervous system have yet to be fully understood, many researchers use C. elegans, which has a much simpler nervous system, as a model to study feeding behavior. Researchers have previously shown that food greatly influences the locomotion of C. elegans. The worm’s diet consists mainly of bacteria, and scientists found that whenever the worms encounter a large patch of food, they slow down to consume it. When they are satiated, Flavell and his colleagues found that the animals begin wandering around their environment again. Thanks to their recent study, we are beginning to understand why. “There was behavioral evidence that C. elegans’ nervous system is receiving information about the food in the environment, but we didn’t know how that worked,” Flavell says. The researchers knew that serotonin release was driving the slowdown, but they didn’t know what was triggering that release. To try to figure that out, they decided to study a type of serotonin-producing enteric neurons called neurosecretory-motor (NSM) neurons, which are located in the lining of the C. elegans digestive organ, known as the pharynx. Through a series of experiments, the researchers found that NSM neurons become active immediately when worms eat bacterial food. NSM neurons have a single long extension, or neurite, that projects into the worms’ gut. The researchers also discovered that this neurite acts as a sensory ending for NSM neurons, playing a key role in activating the neurons when the animal eats bacterial food. Further studies revealed two new ion channels, called DEL-3 and DEL-7, that are located at the very tip of this neurite and are required for NSM neurons to be activated by bacterial food. These channels are part of a family of proteins called acid-sensing ion channels (ASICs), which are found in all animals including humans. Some of these channels have roles in taste and in pain detection, while others’ functions are still unknown. Intriguingly, these channels are also expressed in enteric neurons in the mammalian gut. Flavell speculates that ASICs may play a general role in sensing bacterial populations present along the digestive tract and potentially elsewhere. “A particularly intriguing aspect of this work is the identification of the putative food sensors in NSM,” says Piali Sengupta, a professor of biology at Brandeis University who was not involved in the study. “These turn out to be members of the ASIC ion channel family, which are activated by multiple stimuli in other systems, including mechanical stimuli and pH. In C. elegans, these channels appear to be activated by an as yet unidentified component of bacteria, the food source of C. elegans.” The researchers are now trying to figure out how DEL-3 and DEL-7 detect bacteria. One possibility is that the channels directly detect a compound secreted by bacteria. Alternatively, a bacterial compound may interact with a nearby receptor that then activates the ion channels, Flavell says. Many neurons Flavell’s lab is also planning to study other C. elegans neurons that also have extensions into the gut, to see if they play a similar role to the NSM neurons, possibly detecting other components of bacteria or other food cues. “With the tools that we now have in place, it should be straightforward for us to go into these other cell types and ask if they are activated by food ingestion, and if so, what kinds of channels do they express,” Flavell says. “There are about 30 other ion channels that are closely related to DEL-3 and DEL-7 in the worm, and they might be detecting other bacterial signals.” The researchers are also exploring in more detail the effects of serotonin on the rest of the animals’ brain. Once the ion channels in the NSM cells are activated, the cells begin releasing serotonin, which can then be detected by nearby neurons that express serotonin receptors. “We’re trying to really look at the whole rest of the nervous system to see how serotonin changes the activity of many downstream cells to ultimately lead to this behavioral change,” Flavell says. Another unanswered question is whether this basic mechanism for bacterial sensing that the Flavell lab has discovered also operates in humans. The human gut contains a diverse array of bacteria, referred to as the microbiome. In addition, the gut is lined with neuron-like cells called enterochromaffin cells that make serotonin and release it to sensory neurons that carry information to the brain. Researchers are only just beginning to understand the channels and receptors that might allow these cells to detect the contents of the gut, and how serotonergic gut-to-brain signaling might alter behavior in mammals. These new mechanisms worked out in the worm may guide future studies in this area. The research was funded by the JPB Foundation, the Picower Institute Innovation Fund, the Picower Neurological Disorders Research Fund, the NARSAD Young Investigator program, the National Institutes of Health, the Howard Hughes Medical Institute, and the National Science Foundation. |
| 6:00p | Modeling climate risk where it hits home Long-term assessment of likely regional and local climate impacts is critical to enabling municipalities, businesses, and regional economies to prepare for potentially damaging and costly effects of climate change — from prolonged droughts to more frequent and intense extreme events such as major storms and heatwaves. Unfortunately, the tools most commonly used to project future climate impacts, Earth-system models (ESMs), are not up to the task. ESMs are too computationally time consuming and too expensive to run at sufficient resolution to provide the detail needed at the local and regional level. To that end, a new MIT-led study in the journal Earth and Space Science uses a regional climate model of the northeastern United States to downscale the middle and end-of-century climate projections of an ESM under a high-impact emissions scenario to a horizontal resolution of 3 kilometers. Through downscaling, output from the ESM was used to drive the regional model at a higher spatial resolution, enabling it to simulate local conditions in greater detail. The resulting high-resolution climate projections consist of more than 200 climate variables at an hourly frequency. Among other things, the study projects that between now and the end of the century, the region will experience significantly more days per year in which mean and maximum temperatures exceed 86 degrees Fahrenheit, and fewer days per year in which the minimum temperature falls below freezing. Over that period in Boston, the annual number of days the mean temperature exceeds 86 F increases from three to 22, and the number of days the daily maximum temperature exceeds 86 F increases from 49 to 78. “Our approach allows for analysis of changes in temperature, precipitation, and other climate variables within a single 24-hour period,” says Muge Komurcu, the lead author of the study and a research scientist with the MIT Joint Program on the Science and Policy of Global Change and Department of Earth, Atmospheric and Planetary Sciences (EAPS). “The aim of these projections is to support further assessments of climate change impacts and sustainability studies in the region.” Downscaling of climate projections provides climate variables at the resolution needed to assess climate change impacts at regional and local scales. As a result, the variables produced in the study may be used as input to other models and analyses to assess the likely future impact of climate change on extreme precipitation and heat wave events, regional ecosystems, agriculture, the spread of infectious diseases (e.g. Lyme disease), hydrology, the economy, and other concerns. To produce the study’s climate variables, the researchers used a high-resolution regional climate model, the Weather Research and Forecasting (WRF) model, to downscale middle and end-of-century climate projections of the Community Earth System Model (CESM) under a high greenhouse gas emissions scenario to a horizontal resolution of 3 kilometers for the northeastern U.S. To ensure that their method is reliable, Komurcu and her co-authors — MIT EAPS professor of atmospheric science Kerry Emanuel and Purdue University Professor Matthew Huber and PhD student Rene Paul Acosta — simulated the process using historical climate observations. They showed that their technique reproduced observed historical mean and extreme climate events over a 10-year period. The study’s 200-plus, 3-kilometer-resolution climate variables cover 55 years, encompassing middle and end-of-century time periods. “To our knowledge, this is the first and only study that has downscaled global model projections to such a high resolution for a long time period for this region,” says Komurcu. To assist regional assessments of climate change impacts and sustainability studies in the northeastern U.S., the researchers plan to make all model input and output files from this study publicly available through the University of New Hampshire’s Data Distribution Center. The study was supported by the National Science Foundation through the New Hampshire Established Program to Stimulate Competitive Research. |
| 7:00p | How different types of knowledge impact the growth of new firms Diversifying into new industries is vital to an economy’s ability to grow and generate wealth. But to branch out into new industrial activities, a city, region or country must first have a pool of people with the right mix of knowledge and experience to make those pioneering firms a success. So how do local economies ensure they have the right mix of experience to allow new ventures to thrive? In a paper published this week in the Proceedings of the National Academy of Sciences, a team led by César A. Hidalgo, director of the Collective Learning Group in the MIT Media Lab, studied the effects of occupation-specific, industry-specific, and location-specific knowledge on the success of pioneer firms. These are firms operating in an industry that has not previously been present in a region. They found these pioneering firms were significantly more likely to survive and grow when their first hires were people with experience in the same or a related industry, rather than those who had experience carrying out the same type of job. The notion that knowledge is central to driving growth, for which economist Paul Romer was awarded the Nobel Prize in economics earlier this year, is already well-established. The new paper also builds on previous work by Hidalgo’s group over the past decade, including a paper in Science in 2007, in which the researchers developed measures of how economies are able to successfully move into new products based on how closely related they are to their existing product base. “We know these diversification events are more likely to happen when you have related activities at a location, but someone must still be the first to enter,” Hidalgo says. “That pioneer has to get their knowledge from somewhere.” To understand where this knowledge comes from, and what type of knowledge is likely to lead to the greatest success, the team, who also included lead author and MIT PhD student Cristian Jara-Figueroa, MIT post doc Bogang Jun, and Edward Glaeser, the Fred and Eleanor Glimp Professor of Economics at Harvard University, investigated the different types of experience that workers carry with them when they join a new firm. They used data from 2002 to 2013 from Brazil’s Annual Social Security Information Report (RAIS). The RAIS dataset covers around 97 percent of the country’s formal labor market, and includes fine-grained information on individual workers. Using this dataset, they studied the workforce hired by new pioneer firms within a region, to identify the industry, occupation and location of their previous jobs. “So for a nurse in a hospital, their knowledge of nursing is their occupation-specific knowledge, while their experience in a hospital is their industry-specific knowledge,” Hidalgo says. They found that it is far better for pioneer firms to hire people with industry-specific knowledge, even if those workers had a very different occupation in their previous job. They then compared these results with those of new firms in a region that were not pioneers, but instead were involved in an industry that was already present in the area. They found that industry-specific knowledge was significantly more important for pioneer than nonpioneer firms. Location-specific knowledge proved to be the second most important type of experience, while occupation-specific knowledge was not significant at all for pioneer firms, and provided a small boost for nonpioneers. “These results strongly suggest that when regions try to develop new industries, they should focus on accumulating industry-specific knowledge that entrepreneurs can leverage,” Jara-Figueroa says. “Once the industry has been developed in the place, both types of knowledge become important.” It may be that knowledge of an industry can only be acquired while working within it, making it harder to pass on to others than occupation-based skills and ideas that can be taught, says Hidalgo. What’s more, industry knowledge is important because it includes a familiarity with the social network within that sector. So, for example, someone who has worked in a particular industry for some time will have a better understanding of both the suppliers and customers within the sector, and the firm’s competitors, Hidalgo adds. The research has particular implications for governments in the developing world, according to Glaeser. “This is related to the broad question of whether the developing world needs foreign direct investment, or whether it can succeed with home-grown entrepreneurship,” Glaeser says. “Our paper supports the view that domestic entrepreneurship can work, as long as it has access to the relevant forms of industry-specific capital.” The research also suggests there may be a need for governments to develop more industry-specific, rather than occupation-based, education programs, Hidalgo says. The research team now plan to investigate how this demand for industry-specific knowledge varies from industry to industry. |
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