1. The plastic deformation of crystals occurs through the nucleation and motion of lattice defects known as dislocations. Here an atomistic Monte Carlo simulation of compression in two dimensions demonstrates how geometrically necessary dislocations spontaneously coalesce to form grain boundaries. This work explores the complex relationship between size effects and strain rate effects in plasticity at the nanoscale. Single crystal under compression between confining walls, with an imposed strain gradient Physics of Dislocation Patterning and Size Effects in Plasticity Robin Selinger, Catholic University, DMR-0116090

2. Low-angle tilt boundaries formed via spontaneous coalescence of dislocations The plastic deformation of crystals occurs through the nucleation and motion of lattice defects known as dislocations. Here an atomistic Monte Carlo simulation of compression in two dimensions demonstrates how geometrically necessary dislocations spontaneously coalesce to form grain boundaries. This work explores the complex relationship between size effects and strain rate effects in plasticity at the nanoscale. Physics of Dislocation Patterning and Size Effects in Plasticity Robin Selinger, Catholic University, DMR-0116090

3. Education : Participants include Scott Weingarten, a full-time physics teacher and Chair of the Science Division at St. Johns College High School, Washington, DC. He is also a graduate student, part-time, at Catholic University, and expects to complete his Ph.D. in 2005. Scott holds guest researcher status at the National Institute of Standards and Technology in Gaithersburg, MD and spent summer 2004 as a visiting researcher at Sandia National Laboratory in Livermore, CA. Additional participants include Julie Kaufman, a high school student at Montgomery Blair High School, Montgomery County, MD; Weidong Luo and Bryan Armentrout, physics graduate students at Catholic University; and Matthew Davidson, an undergraduate physics major at Catholic University. Physics of Dislocation Patterning and Size Effects in Plasticity Robin Selinger, Catholic University, DMR-0116090