Program Highlights

In designing new motile materials, much can be learned by studying the physical mechanisms underlying cell crawling. One important form of cell crawling is driven by self-assembly of the protein actin. In this process, energy is supplied and various proteins cooperate to assemble actin from small proteins into a branched network. We have conducted the first physically-consistent simulations of this process and have discovered that the mechanism driving motion of the cell boundary (modeled in our case by a flat disk) is very simple: the buildup of the branched actin network behind the disk drives the disk forwards because the disk is repelled by actin. This is reminiscent of the old joke about why bagpipe players always walk while they play (to get away from the noise). Understanding of this mechanism opens the way to the development of new materials that can move, such as asymmetrically-coated beads in self-generated concentration gradients.

Silicon/silicon dioxide is arguably the most important technological interface. With the end of Moore’s law scaling for silicon fast approaching, alternatives to silicon dioxide could enable new electronic device architectures. MRSEC researchers have recently achieved ferroelectric functionality in intimate contact with silicon by growing SrTiO3 films in an intricate growth process using oxide molecular-beam epitaxy, producing fully strained SrTiO3 layers in direct contact with silicon with no interfacial silicon dioxide. Piezo-force microscopy sees ferroelectricity in the ultra-thin SrTiO3 layers. Stable ferroelectric nanodomains, observed at temperatures as high as 400 K, may form the basis of a new class of ferroelectric memories, bistable field-effect transistor devices, and low-power devices operating at room temperature.

The NYU team, led by Jasna Brujic, an assistant professor in NYU’s Department of Physics, developed an innovative way to tabulate the number of spheres-they created a method for determining how spheres pack from inside the jar, making it easier to more accurately count them.

To answer the question of how particles pack in general, the NYU researchers made a transparent, fluorescent packing of oil droplets in water, which allowed it to record three-dimensional images and examine the local geometry of each member of the pack. In other words, what does a packing look like from the point of view of a grain within-i.e., a “granocentric” view?