Science Concentrates MODELING
Ice forms from disordered seeds Modeling study contradicts classical view that ice nuclei have ordered hexagonal structure The conventional view among scientists about how ice forms is that it begins from seeds in which water molecules are packed together in a hexagonal structure and maintains this structure as it grows. But a new modeling study suggests that the nanoscopic ice seeds actually begin as a mix of hexagonal and cubic layers known as a “stacking disordered” structure (Nature 2017, DOI: 10.1038/ nature24279). These eventually grow to form bulk ice with the traditional hexagonal structure. The findings have implications for weather models that consider how fast ice forms in clouds. “Classical nucleation theory assumes that the nucleus is like a piece of the bulk phase,” says Valeria Molinero, a chemistry professor at the University of Utah who led the study. Molinero’s group found, however, that stacking disordered ice seeds are entropically favored over the hexagonal
form. “What we’re seeing is that cubic ice is less stable than hexagonal ice, but mixing of the two favors cubic ice,” she says. According to Tianshu Li, an associate professor in the department of civil and
Modeling shows that ice nuclei are stacking disordered with a mix of cubic (red) and hexagonal (blue) lattices. environmental engineering at George Washington University who studies ice nucleation, researchers had experimentally observed these stacking disordered seeds before but assumed they formed because of
kinetic effects and weren’t thermodynamically stable. “This finding has remained puzzling,” he adds, but this new modeling study “now shows that the observed behavior is in fact a natural outcome of thermodynamics rather than kinetics.” The new simulations show that stacking disordered ice nucleation rates are more than three orders of magnitude as fast as those predicted by classical nucleation theory. And the effect is size and temperature dependent. The classical theory needs to incorporate that size and temperature dependence so that extrapolations from lab experiments will accurately predict conditions in clouds, Molinero says. The new starting point will have a significant effect on cloud models, Molinero says, especially in remote areas without aerosols that aid ice seed growth. Although the amount of radiation that clouds absorb depends strongly on how much ice they contain, she cautions that these new findings may not have a large impact on climate models.—CELIA ARNAUD
DIVERSITY
How gender diversity affects medical research Women are more likely than men to consider the effects of gender and sex in their research that women are more likely than men to Every cell in our bodies has a sex. And perform such analyses (Nat. Hum. Behav. that sex influences our cells’ biology, con2017, DOI: 10.1038/s41562-017-0235-x). tributing to differences between men and Social scientists have investigated how women in terms of incidence of disease gender diversity in teams affects perforand reactions to drugs. Yet biomedical remance and cooperation, but searchers still often study the Mathias W. Nielsen of Aarhus mechanisms of disease only University and his colleagues in male research animals. The wanted to see if it could afU.S. National Institutes of Health recently implementof medical studies that fect the types of scientific questions asked in a study. ed guidelines to encourage did NOT analyze sex To do so, Nielsen and his scientists to consider the and gender had women coworkers analyzed the geninfluence of sex and gender in as last authors der composition of the autheir research. thors of research papers deA new study of 1.5 million posited in PubMed between medical research papers 2008 and 2015. They used an suggests that increasing the existing computer algorithm gender diversity of scientists of medical studies that assigns a gender to an might lead to more analysis that analyzed sex and author based on their first of gender and sex differences. gender had women as name and country. Then the The study’s authors found last authors
C R E D I T: NAT UR E
27%
35%
team turned to the GenderMed Database to identify medical studies from that time period that performed gender and/or sex analyses. Through a statistical analysis, Nielsen and his colleagues found that teams with more women were more likely to include gender or sex analysis in their studies. The largest effect was when the last author of a paper was a woman. Nielsen says this finding suggests that women taking a leadership role in planning research was what mattered most in whether or not a study would examine gender or sex as a variable. “It’s an amazing example of the importance of promoting gender diversity in the workforce,” says Kathryn Sandberg, the director of the Center for the Study of Sex Differences in Health, Aging & Disease at Georgetown University. She says another interesting analysis could look at how the gender of grant reviewers affects decisions about funding research involving analysis of sex differences.—MICHAEL TORRICE NOVEMBER 13, 2017 | CEN.ACS.ORG | C&EN
7
