Viscous cycle

Between Earth’s crust and its core lies the mantle. Although this rocky layer forms 84 percent of our planet’s total volume, much about it—including its viscosity—is unknown. A February Nature study, led by geophysicist Sunyoung “Sunny” Park, tackles that mystery using measurements of deep earthquakes to infer the mantle’s fluidity. These quakes, which occur hundreds of miles beneath Earth’s surface, seldom affect people or property, but they do have subtle geologic effects; the 2018 event Park studied has been causing the island of Tonga to sink about one centimeter per year. The researchers used that information to develop a model of how viscous the mantle must be to cause the observed changes in data. They now believe there is a slow-flowing layer—about 50 miles thick—at the bottom of the upper mantle that extends around the globe. This sheds light on how heat and geological materials mix and move through Earth.

Sleep on it

Millions of Americans experience obstructive sleep apnea—a condition characterized by interrupted breathing during sleep—and can awaken up to 30 times an hour. The crux of the problem is tongue position: sleep apnea sufferers’ tongues fall back in their mouths, whereas in people without the condition, the brain tells the tongue’s motor neurons to stay contracted and forward in the mouth to keep the airway open. But how does the brain know when to activate those motor neurons, and why does the system stop working for some people? New research from UChicago Medicine’s Alfredo Garcia and colleagues, published in eLife in January, shows that a system of gases acts as a signal in the region of the brain responsible for tongue position. When the system is unbalanced, the signal is interrupted and the tongue slides back, constricting the pharynx. By understanding the molecular underpinnings of sleep apnea, researchers hope to improve treatments and give patients the relief they need.

Emissions control

Keeping a comfortable indoor temperature comes at a serious cost: the energy expended to heat and cool buildings is both expensive and a major contributor to climate change. In a study published online January 26 in Nature Sustainability, Pritzker School of Molecular Engineering’s Po-Chun Hsu and colleagues developed a new smart building material that can address the problem by changing how much heat it absorbs or emits based on the outside temperature. The material includes a layer that, using a small amount of electricity, shifts between a heat-absorbing solid on cold days and a heat-emitting liquid on hot ones. According to the researchers’ models, the electricity required to power the changes in the material would be less than 0.2 percent of that used for a typical commercial building—and the material could reduce the energy consumption of the building’s climate control system by 8.4 percent each year.

Risk assessment

Between 2000 and 2020, suicide rates increased 30 percent, making suicide the 12th leading cause of death in the United States in 2020. Multiple studies have linked suicide rates to social and environmental factors such as exposure to violence, crime, and air pollution. A new study led by Robert Gibbons, PhD’81, and published April 26 in JAMA Network Open, has found stronger evidence for these links. The researchers measured the relationship between social vulnerability and suicide rates using the Social Vulnerability Metric. The SVM draws over 200 variables from 17 nationally representative databases focusing on factors such as age, education, employment, housing, transportation, and health insurance. The authors found that in 2016–20, the suicide rate in the most socially vulnerable communities was 82 percent higher than that in the least vulnerable communities. This suggests that interventions that decrease social vulnerability may also decrease suicide rates.