Through its interdisciplinary research, service-based learning, and innovative coursework, Georgia Tech’s School of Civil and Environmental Engineering is a leader in systems-level thinking and technological innovation at the interface of built, natural, information, and social systems. The school aims to not only define the challenges and complex problems facing humanity and the environment, but to catalyze the solutions to solve them.

This installment of the Faces of Research Q&A series is with Joe F. Bozeman III, assistant professor in the School of Civil and Environmental Engineering, the School of Public Policy, and director of the SEEEL.

What is your field of expertise and why did you choose it?
I research and develop ethical and culturally relevant climate change adaptation and mitigation strategies anchored in environmental engineering practice. My current focus areas are urbanization, food-energy-water, and circularity (e.g., circular materials and the circular economy). I chose this path because I felt that I could merge my lived experiences, having come from humble beginnings, with the technical aspects of engineering and public policy to realize more ethical infrastructure and policy outcomes.  

What makes Georgia Tech research institutes unique?
Georgia Tech’s research institutes have an existing system which allows for collaboration across scientific disciplines and with real community members. This is something that I think is uniquely beneficial for folks like me. That is, for my research to have real-world impact, I need access to faculty and community collaborators who share an equity-centered mindset. 

What impact is your research having on the world?
It has been wonderful to see my research enter broader community and academic spaces through mainstream media, scientific publications, regulatory deliberation, and even art. For instance, my work on U.S. food-consumption impacts — for example, greenhouse gas emissions, land, and water impact that come from what we eat — across sociodemographic subgroups (Black, Latinx, white, and socioeconomic status) was featured in a range of media outlets including NPR, the New York Post, Popular Science, Free Speech TV, and political radio programs. Other aspects of my research have established international research priorities for cities, or urban systems, and even inform some of the music you may have heard on network TV and streaming services. My lab, (SEEEL), is exploring other ways to merge ethics, engineering, and art in meaningful ways.     

What is the most challenging aspect of your research?
For SEEEL activities, acquiring and fairly distributing money, and time resources is the most challenging part. The concept of integrating a systemic ethical foundation into existing engineering practices is new. This is exciting in many ways. However, it also presents challenges when it comes to developing standards around flexible funding access, community-based research and development, and establishing criteria to evaluate how well ethical systems are being achieved in various domains (e.g., within research labs, within governmental bodies, and for actual community members). Through these types of efforts, I hope to play a role in regaining some of the public’s trust in academia.

If you weren't a researcher, what would you be?
If I weren’t a researcher, I probably would have continued as a music sound engineer, producer, and performer. As I previously mentioned, I hope to leverage my experience in the arts to help translate some of the technical engineering findings into content that all of us can easily digest (e.g., songs, video, film, and physical art). I’d even go as far as to say that I think there is room to make the technical engineering findings, in their original form, more accessible to the broader public. This has compelled SEEEL to master the art of effective writing and presentation delivery.

What was the first thing you remember wanting to be when you were a kid?
As a kid, I first wanted to be a NBA player. Ironically, I listed becoming an engineer as a very close second. Back then, I believe I thought of engineering as a means to video game and sound design.

This news release first appeared in the Chinese Academy of Sciences newsroom, and has been tailored for Georgia Tech readers.

Mycorrhizal symbiosis — a symbiotic relationship that can exist between fungi and plant roots — helps plants expand their root surface area, giving plants greater access to nutrients and water. Although the first and foremost role of mycorrhizal symbiosis is to facilitate plant nutrition, scientists have not been clear how mycorrhizal types mediate the nutrient acquisition and interactions of coexisting trees in forests.  

To investigate this crucial relationship, Lingli Liu, a professor at the Institute of Botany of the Chinese Academy of Sciences (IBCAS) led an international, collaborative team, which included School of Biological Sciences professor Lin Jiang. The team studied nutrient acquisition strategies of arbuscular mycorrhizae (AM) and ectomycorrhizal (EcM) trees in the Biodiversity–Ecosystem Functioning (BEF) experiment in a subtropical forest in China, where trees of the two mycorrhizal types were initially evenly planted in mixtures of two, four, eight, or 16 tree species.   

The researchers found that as the diversity of species increased, the net primary production (NPP) of EcM trees rapidly decreased, but the NPP of AM trees progressively increased, leading to the sheer dominance (>90%) of AM trees in the highest diversity treatment. 

The team's analyses further revealed that differences in mycorrhizal nutrient-acquisition strategies, both nutrient acquisition from soil and nutrient resorption within the plant, contribute to the competitive edge of AM trees over EcM ones.  

In addition, analysis of soil microbial communities showed that EcM-tree monocultures have a high abundance of symbiotic fungi, whereas AM-tree monocultures were dominated by saprotrophic and pathogenic fungi.  

According to the researchers, as tree richness increased, shifts in microbial communities, particularly a decrease in the relative abundance of Agaricomycetes (mainly EcM fungi), corresponded with a decrease in the NPP of EcM subcommunities, but had a relatively small impact on the NPP of AM subcommunities.  

These findings suggest that more efficient nutrient-acquisition strategies, rather than microbial-mediated negative plant-soil feedback, drive the dominance of AM trees in high-diversity ecosystems.  

This study, based on the world’s largest forest BEF experiment, provides novel data and an alternative mechanism for explaining why and how AM trees usually dominate in high-diversity subtropical forests.

These findings also have practical implications for species selection in tropical and subtropical reforestation—suggesting it is preferable to plant mixed AM trees, as they have a more efficient nutrient-acquisition strategy than EcM trees.  

This study was published as an online cover article in Sciences Advances on Jan. 19 and was funded by the Strategic Priority Research Program of CAS and the National Natural Science Foundation of China.

The $1.3 billion research enterprise at Georgia Tech is the embodiment of a commitment the advancement of technology and betterment of the human condition. Georgia Tech's research enterprise through offerings such as the Enterprise Innovation Institute, the Georgia Tech Research Institute, Commercialization, and Interdisciplinary Research Institutes, to solve the most pressing challenges in a host of sectors, including computing, engineering, design, the sciences, liberal arts, and business.

This installment of the Faces of Research Q&A series is with Chaouki T. Abdallah, Executive Vice President for Research at Georgia Tech.

What is your field of expertise and why did you choose it?
My field of expertise is Systems Theory, and my degrees are all in Electrical Engineering. I chose it because it was heavily mathematical but can also be applied across multiple fields (aerospace, chemical, mechanical, electrical, biology, etc.).

What makes Georgia Tech research institutes unique?
Our IRIs (Interdisciplinary Research Institutes) connect research across colleges but what makes them even more impactful is their intra-connectivity. Problems that are even too big for one IRI, are being solved by researchers across multiple ones. 

What impact is your research having on the world?
My own research impact has been mostly through my students. However, I did use my research in systems and network science to study and improve the complexity of college curricula, leading to 150% improvement in the four-year graduation rate and tens of millions of dollars in savings for students.

What is the most profound advice you ever received?
Pick the hill you’re willing to die on.

What is something you wished you knew as a budding researcher that everyone considering research as a career should know?
The joy of knowing something is eclipsed by the joy of explaining it to others.

What song or album best describes you?
"With a Little Help From My Friends" by The Beatles.

Akanksha Menon, assistant professor in the George W. Woodruff School of Mechanical Engineering, has been awarded a prestigious Faculty Early Career Development (CAREER) Award from the National Science Foundation’s (NSF) Division of Chemical, Bioengineering, Environmental and Transport Systems (CBET).

Menon directs the Water–Energy Research Lab (WERL) at Georgia Tech, which focuses on applying thermal science and functional materials to develop sustainable energy and water technologies.

"I am incredibly honored to receive an NSF CAREER award," said Menon. "I remember attending the College of Engineering panel on writing a successful NSF proposal wondering if I would be able to do this, and here I am with a CAREER award on my first try!"

Menon’s NSF CAREER project, “Nonequilibrium effects in thermochemical energy storage: linking microstructure to thermal transport,” aims to bridge our understanding of structure-property relationships in thermochemical materials across different lengths and timescales.

Currently, thermal loads (e.g., space conditioning and hot water) account for 50% of the energy consumption in buildings. To match energy demand with supply especially from renewables, a thermal battery can be used that stores and releases energy as heat. Among the different storage materials, thermochemical salt hydrates are promising as they have a higher energy density compared to phase change or sensible storage materials. However, these salt hydrates experience mechanical stress and hygrothermal instabilities that reduce their energy density as the thermal battery is cycled (charge-discharge).

Menon aims to provide a mechanistic understanding of the key factors governing thermochemical phase transitions and their impact on coupled heat-and-mass transport, which will eventually enable the development of reversible thermal batteries with long-term stability to decarbonize buildings.

Menon's research will be complemented by two education and outreach efforts. She will provide interdisciplinary and experiential learning opportunities for traditionally underrepresented students in Science, Technology, Engineering, and Mathematics (STEM) from the high school to graduate levels, as well as curriculum development for teachers to increase knowledge about energy storage broadly.

Menon’s award of $607,000 over five years will provide support for both her research and education and outreach efforts.

"The funding allows me to bring on a Ph.D. student to grow our efforts in decarbonizing heat, and it also supports my educational and outreach goals – all of which is what motivated me to become a faculty member," she said.

The CAREER Program offers the NSF’s most prestigious awards in support of early-career faculty who have the potential to serve as academic role models in research and education and to lead advances in the mission of their department or organization.

Menon joined Georgia Tech as an assistant professor in 2021. Prior, she was a Rosenfeld Postdoctoral Fellow at Lawrence Berkeley National Laboratory, where she worked on hybrid membrane-thermal desalination processes using solar energy. She also contributed to the development of thermal energy storage materials for high-temperature industrial process heat. Menon completed her Ph.D. at Georgia Tech, where she developed semiconducting polymers and new device architectures for thermoelectric energy harvesting. She holds a bachelor's degree from Texas A&M University at Qatar and a master’s degree in mechanical engineering from Georgia Tech.

Coral reef conservation is a steppingstone to protect marine biodiversity and life in the ocean as we know it. The health of coral also has huge societal implications: reef ecosystems provide sustenance and livelihoods for millions of people around the world. Conserving biodiversity in reef areas is both a social issue and a marine biodiversity priority.

In the face of climate change, Annalisa Bracco, professor in the School of Earth and Atmospheric Sciences at Georgia Institute of Technology, and Lyuba Novi, a postdoctoral researcher, offer a new methodology that could revolutionize how conservationists monitor coral. The researchers applied machine learning tools to study how climate impacts connectivity and biodiversity in the Pacific Ocean’s Coral Triangle — the most diverse and biologically complex marine ecosystem on the planet. Their research, recently published in Nature Communications Biology, overcomes time and resource barriers to contextualize the biodiversity of the Coral Triangle, while offering hope for better monitoring and protection in the future.

“We saw that the biodiversity of the Coral Triangle is incredibly dynamic,” Bracco said. “For a long time, it has been postulated that this is due to sea level change and distribution of land masses, but we are now starting to understand that there is more to the story.”

Connectivity refers to the conditions that allow different ecosystems to exchange genetic material such as eggs, larvae, or the young. Ocean currents spread genetic material and also create the dynamics that allow a body of water — and thus ecosystems — to maintain consistent chemical, biological, and physical properties. If coral larvae are spread to an ecoregion where the conditions are very similar to the original location, the larvae can start a new coral.

Bracco wanted to see how climate, and specifically the El Niño Southern Oscillation (ENSO) in its phases — El Niño, La Niña, and neutral conditions — impacts connectivity in the Coral Triangle. Climate events that move large masses of warm water in the Pacific Ocean bring enormous changes and have been known to exacerbate coral bleaching, in which corals turn white due to environmental stressors and become vulnerable to disease.

“Biologists collect data in situ, which is extremely important,” Bracco said. “But it’s not possible to monitor enormous regions in situ for many years — that would require a constant presence of scuba divers. So, figuring out how different ocean regions and large marine ecosystems are connected over time, especially in terms of foundational species like coral, becomes important.”

Machine Learning for Discovering Connectivity

Years ago, Bracco and collaborators developed a tool, Delta Maps, that uses machine learning to identify “domains,” or regions within any kind of system that share the same dynamic. Bracco initially used it to analyze domains of climate variability in models but also suspected it could be used to study ecoregions in the ocean.

For this study, they used the tool to map out domains of connectivity in the Coral Triangle using 30 years of sea surface temperature data. Sea surface temperatures change in response to ocean currents over scales of weeks and months and across distances of tens of kilometers. These changes are relevant to coral connectivity, so the researchers built their machine learning tool based on this observation, using changes in surface ocean temperature to identify regions connected by currents. They also separated the time periods that they were considering into three categories: El Niño events, La Niña events, and neutral or “normal” times, painting a picture of how connectivity was impacted during major climate events in particular ecoregions.

Novi then applied a ranking system to the different ecoregions they identified. She used rank page centrality, a machine learning tool that was invented to rank webpages on the internet, on top of Delta Maps to identify which coral ecoregions were most strongly connected and able to receive the most coral larvae from other regions. Those regions would be the ones most likely sustain and survive through a bleaching event.

Climate Dynamics and Biodiversity

Bracco and Novi found that climate dynamics have contributed to biodiversity because of the way climate introduces variability to the currents in the equatorial Pacific Ocean. The researchers realized that alternation of El Niño and La Niña events has allowed for enormous genetic exchanges between the Indian and Pacific Oceans and enabled the ecosystems to survive through a variety of different climate situations.

“There is never an identical connection between ecoregions in all ENSO phases,” Bracco said. “In other parts of the world ocean, coral reefs are connected through a fixed, often small, number of ecoregions, and if you eliminate this fixed number of connections by bleaching all connected reefs, you will not be able to rebuild the corals in any of them. But in the Pacific the connections are changing all the time and are so dynamic that soon enough the bleached reef will receive larvae from completely different ecoregions in a different ENSO phase.”

They also concluded that, because of the Coral Triangle’s dynamic climate component, there is more possibility for rebuilding biodiversity there than anywhere else on the planet. And that the evolution of biodiversity in the Coral Triangle is not only linked to landmasses or sea levels but also to the evolution of ENSO through geological times. The researchers found that though ENSO causes coral bleaching, it has helped the Coral Triangle become so rich in biodiversity.

Better Monitoring Opportunities

Because coral reef survival has been designated a priority by the United Nations Sustainable Development Goals, Bracco and Novi’s research is poised to have broad applications. The researchers’ method identified which ecoregions conservationists should try hardest to protect and also the regions that conservationists could expect to have the most luck with protection measures. Their methodology can also help to identify which regions should be monitored more and the ones that could be considered lower priority for now due to the ways they are currently thriving.

“This research opens a lot of possibilities for better monitoring strategies, and especially how to monitor given a limited amount of resources and money,” Bracco said. “As of now, coral monitoring often happens when groups have a limited amount of funding to apply to a very specific localized region. We hope our method can be used to create a better monitoring over larger scales of time and space.”

 

CITATION: Novi, L., Bracco, A. “Machine learning prediction of connectivity, biodiversity and resilience in the Coral Triangle.” Commun Biol 5, 1359 (2022). 

DOI: https://doi.org/10.1038/s42003-022-04330-8

A new type of solar technology has seemed promising in recent years. Halide perovskite solar cells are both high performing and low cost for producing electrical energy – two necessary ingredients for any successful solar technology of the future. But new solar cell materials should also match the stability of silicon-based solar cells, which boast more than 25 years of reliability. 

In newly published research, a team led by Juan-Pablo Correa-Baena, assistant professor in the School of Materials Sciences and Engineering at Georgia Tech, shows that halide perovskite solar cells are less stable than previously thought. Their work reveals the thermal instability that happens within the cells’ interface layers, but also offers a path forward towards reliability and efficiency for halide perovskite solar technology. Their research, published as the cover story for the journal Advanced Materials in December 2022, has immediate implications for both academics and industry professionals working with perovskites in photovoltaics, a field concerned with electric currents generated by sunlight.

Lead halide perovskite solar cells promise superior conversion of sunlight into electrical power. Currently, the most common strategy for coaxing high conversion efficiency out of these cells is to treat their surfaces with large positively charged ions known as cations.

These cations are too big to fit into the perovskite atomic-scale lattice, and, upon landing on the perovskite crystal, change the material’s structure at the interface where they are deposited. The resulting atomic-scale defects limit the efficacy of current extraction from the solar cell. Despite awareness of these structural changes, research on whether the cations are stable after deposition is limited, leaving a gap in understanding of a process that could impact the long-term viability of halide perovskite solar cells. 

“Our concern was that during long periods of solar cell operation the reconstruction of the interfaces would continue,” said Correa-Baena. “So, we sought to understand and demonstrate how this process happens over time.”

To carry out the experiment, the team created a sample solar device using typical perovskite films. The device features eight independent solar cells, which enables the researchers to experiment and generate data based on each cell’s performance. They investigated how the cells would perform, both with and without the cation surface treatment, and studied the cation-modified interfaces of each cell before and after prolonged thermal stress using synchrotron-based X-ray characterization techniques.

First, the researchers exposed the pre-treated samples to 100 degrees Celsius for 40 minutes, and then measured their changes in chemical composition using X-ray photoelectron spectroscopy. They also used another type of X-ray technology to investigate precisely what type of crystal structures form on the film’s surface. Combining the information from the two tools, the researchers could visualize how the cations diffuse into the lattice and how the interface structure changes when exposed to heat. 

Next, to understand how the cation-induced structural changes impact solar cell performance, the researchers employed excitation correlation spectroscopy in collaboration with Carlos Silva, professor of physics and chemistry at Georgia Tech.  The technique exposes the solar cell samples to very fast pulses of light and detects the intensity of light emitted from the film after each pulse to understand how energy from light is lost. The measurements allow the researchers to understand what kinds of surface defects are detrimental to performance.

Finally, the team correlated the changes in structure and optoelectronic properties with the differences in the solar cells’ efficiencies. They also studied the changes induced by high temperatures in two of the most used cations and observed the differences in dynamics at their interfaces.

“Our work revealed that there is concerning instability introduced by treatment with certain cations,” said Carlo Perini, a research scientist in Correa-Baena’s lab and the first author of the paper. “But the good news is that, with proper engineering of the interface layer, we will see enhanced stability of this technology in the future.”

The researchers learned that the surfaces of metal halide perovskite films treated with organic cations keep evolving in structure and composition under thermal stress. They saw that the resulting atomic-scale changes at the interface can cause a meaningful loss in power conversion efficiency in solar cells. In addition, they found that the speed of these changes depends on the type of cations used, suggesting that stable interfaces might be within reach with adequate engineering of the molecules.

“We hope this work will compel researchers to test these interfaces at high temperatures and seek solutions to the problem of instability,” Correa-Baena said. “This work should point scientists in the right direction, to an area where they can focus in order to build more efficient and stable solar technologies.”

 

CITATION: Perini, C. A. R., Rojas-Gatjens, E., Ravello, M., Castro-Mendez, A., Hidalgo, J., An, Y., Kim, S., Lai, B., Li, R., Silva-Acuña, C., Correa-Baena, J.-P., Interface Reconstruction from Ruddlesden–Popper Structures Impacts Stability in Lead Halide Perovskite Solar Cells. Adv. Mater. 2022, 34, 2204726.

 

DOI: https://doi.org/10.1002/adma.202204726