Jammed States of Matter

Almost any system composed of discrete pieces large enough that thermal fluctuations can be ignored can have a jamming transition: a point at which fluid flow is impeded by a change of state into a stable amorphous solid.  The behavior is general enough to explain a pile of sand, a jar of candies, or cars in a traffic jam.  Professor Andrea Liu was involved in recent theoretical breakthroughs in the study of this phenomenon.

 

PAPER Experiment

The Precision Array for Probing the Epoch of Reionization is a radio interferometer designed to detect 21 cm Hydrogen (HI) fluctuations occuring when the first galaxies ionized intergalactic gas at around 500 million years after the Big Bang.  The Penn PAPER team is led by Professor James Aguirre.

 

Alternatives to Dark Energy

Perhaps the deepest mystery in physics today is the origin of the accelerating expansion of the universe.  Professors Khoury and Trodden work, among other things, on the possibility that it is due to a dark sector with new light degrees of freedom.  Screening mechanisms, such as chameleon and symmetron, may explain why such scalars, if light, have escaped detection.

 

Dark Excitons

Excitons are electrically neutral excited states of a material consisting of a bound state of an electron and a hole.  Prof. Jay Kikkawa explores previously unseen "dark exciton" states in carbon nanotubes and shows their dependence on geometry of the nanotube.

 

Bio-optics and bio-optical materials

Prof. Alison Sweeney and her colleagues believe that the reflective structures in giant clams help them grow algae. The clams use sub-wavelength structures formed from a protein called reflectin to optimize the photosynthesis of the algae living in the clam tissues.