Problem of the Nth degree

Although first identified in 1995 as a top unsolved theoretical problem in chemical physics by the National Research Council, the N-representability problem has eluded scientists for 60 years. That is, until UChicago chemistry professor David Mazziotti published his approach in the June 27 Physical Review Letters. The problem centers around the fact that molecules may have several thousand electrons, and modeling them becomes increasingly complicated as the number grows, because the statistics governing one electron’s motion depends on the motion of all the others. After ten years, Mazziotti has built a two-electron model that represents large, multielectron molecules more accurately than traditional quantum-mechanics equations. The model allows scientists to predict the behavior of electrons in a range of chemical reactions.

The Pace of Evlolution

After a mass extinction, an evolutionary explosion follows. Then what? Scientists long supposed that evolutionary rates returned to normal. But a study by geophysicist David Jablonski and research assistant Andrew Krug suggests otherwise. Mass extinctions, they reported in the August Geology, affect evolutionary rates  for millions of years, until the next mass extinction sets a new pace. Analyzing data from bivalves, a group including clams, oysters, and scallops, they traced the organisms’ evolution from the Jurassic period to the Pleistocene epoch (in other words, from  about 200 million years ago to 10,000 years ago).  The researchers found that millions of years of steady evolution were disrupted by sudden increases or decreases in the rate at which new species appeared. These shifts marked mass extinctions, and after each, the altered rate became the new settled pace.

Addicted to Calories

Some scientists have proposed that obesity is a byproduct of our primitive brains’ inability to adjust to nearly unlimited access to food; tasty, calorie-rich foods release dopamine and generate compulsive behaviors. But is it the taste or the nutritional value (i.e., calories) that’s more addictive? A series of experiments comparing rodents’ preference of caloric sucrose with the calorie-free sweeteners sucralose or saccharin by Chicago biologist Jeff Beeler, neurobiologist Xiaoxi Zhuang, and their collaborators, indicates that the strongest motivator is nutrition, not flavor. In one experiment, mice were forced to work for their food. Early on, the mice worked equally hard for sucrose and sucralose. But on subsequent days, their appetite for sucralose dropped off, while their enthusiasm for sucrose remained high. The findings appear in the June European Journal of Neuroscience.

Planetary candidate

Using data from NASA’s Spitzer Space Telescope, UChicago astrophysics postdoc Kevin Stevenson and researchers from the University of Central Florida have discovered a planet smaller than Earth and covered entirely in molten lava. Called UCF-1.01, it is the first discovery attributed to the telescope, which launched nine years ago to study known planets. Located in the constellation Leo, 194 trillion miles away, UCF-1.01 has no atmosphere and a surface temperature of about 1,000 degrees Fahrenheit. It is one of only a handful of exoplanet candidates smaller than Earth. The study is published in the August 1 Astrophysical Journal.

Crime stoppers

Using group counseling and sports activities, researchers at the University of Chicago Crime Lab tried strengthening social-cognitive skills in 800 boys from 18 Chicago public schools. Called “Becoming a Man—Sports Edition,” the program spanned the 2009–10 academic year and addressed self-regulation and impulse control in young males, based on the hypothesis that most Chicago homicides result from the escalation of a relatively minor incident. Results showed a 44 percent decrease in violent-crime arrests among participants. After the study’s July release, Crime Lab director Jens Ludwig said the data suggested that prosocial progamming can prevent youth violence, and “the returns on investments are extremely high.” The program costs $1,100 per participant, but the drop in crime saves society an estimated $3,600 to $34,000 per student.