Minature Heat Engine and Refrigerator

Piezoresistive heat engine and refrigerator

Heat engines provide most of our mechanical power and are essential for long-range transportation. However, whereas significant progress has been made in the miniaturization of motors driven by electrostatic forces, it has proven difficult to reduce the size of conventional liquid or gas driven heat engines below 10^7 um^3. Here we demonstrate an all-silicon reciprocating heat engine with a volume of less than 0.5 um^3. The device draws heat from a DC current using the piezoresistive effect and converts it into mechanical energy by expanding and contracting at different temperatures. It is shown that the engine can even increase the mechanical energy of a resonator when its motion is governed by random thermal fluctuations. When the thermodynamic cycle of the heat engine is reversed, it operates as a refrigerator or heat pump that can reduce motional noise in mechanical systems. In contrast to the Peltier effect, the direction of the thermal current does not depend on the direction of the electrical current.

Dense Stars

Dense matter in compact stars - A pedagogical introduction

Cold and dense nuclear and/or quark matter can be found in the interior of compact stars. It is very challenging to determine the ground state and properties of this matter because of the strong-coupling nature of QCD. I give a pedagogical introduction to microscopic calculations based on phenomenological models, effective theories, and perturbative QCD. I discuss how the results of these calculations can be related to astrophysical observations to potentially rule out or confirm candidate phases of dense matter.