Study explains why some materials shrink under stress

When a conventional soft material is placed between two surfaces that then move across each other in opposite directions, the material tends to bulge out at right angles to the motion of the surfaces. However, there are some gel-like materials such as blood clots that do the opposite when under stress – and understanding why has puzzled physicists for some time. Now, Daniel Bonn at the University of Amsterdam and colleagues have performed calculations and experiments that they say can explain the phenomenon. Materials that shrink under stress tend to comprise networks of filaments that also contain water. When the team modelled such materials they found that when the gaps between the filaments were small, the water could not easily move within the gel – and the materials bulged when stressed. When the pores are larger, however, the water can flow more easily when stressed. This allows the network to shrink in the directions perpendicular to the stress as the water flows away from the stressed regions. The team was also able to observe this behaviour in the lab and the results – which are reported in Physical Review Letters – could prove useful to scientists developing artificial tissues.

Women discouraged by masculine culture in physics

An analysis of more than 1000 papers on gender disparity in science, technology, engineering and mathematics subjects has revealed three main reasons why women are underrepresented in those subjects at undergraduate level in the US. The research, led by Sapna Cheryan, a psychologist at the University of Washington in Seattle, found that the key factors are a lack of sufficient early experience in these subjects, the existence of masculine cultures and gender gaps in self-belief. The research focused on the six science and engineering fields with the highest numbers of undergraduate degrees: biology, chemistry, mathematics, physics, engineering and computer science. In the US, biology, chemistry and mathematics are studied by almost equal numbers of men and women, while physics, engineering and computer science are male dominated, with less than 20% of undergraduate degrees being awarded to women. The analysis revealed three overarching reasons why women participate less in physics, engineering and computer science, the most significant of which was the existence of masculine cultures. Cheryan says that there are three main characteristics of the masculine cultures they identified: male-oriented stereotypes about the people in these fields, negative stereotypes about women’s abilities and few female role models. “These signal to girls and women that they do not belong to the same extent as their male peers,” Cheryan told Physics World. The research is described in Psychological Bulletin.

Cosmologist Carlos Frenk wins 2017 Max Born Medal

The 2017 Max Born Medal for outstanding contributions to physics has been won by the cosmologist Carlos Frenk. Originally from Mexico, Frenk is director of the Institute of Computational Cosmology at the University of Durham in the UK. He bagged the medal for his pioneering work on the theory of cold dark matter (CDM), which explains the formation of galaxies and other large structures in the universe. The medal is given jointly by the Institute of Physics and the German Physical Society and includes a prize of €3000. In odd-numbered years the award is given to a physicist based in the UK or Ireland and presented in Germany. In even-numbered years the winner is based in Germany and travels to the UK or Ireland to accept the prize. In 2015 Frenk was a consultant on The World Machine, which was a science-themed sound-and-light show projected onto the façade of Durham Cathedral. He speaks about that experience in “The cathedral and the cosmos“.

 

• You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on how physics research is improving in China.