Light as a Feather, Stiffer Than a Board
Julia R. Greer, Assistant Professor of Materials Science and Mechanics, and colleagues have developed the world’s lightest solid material, with a density of 0.9 milligrams per cubic centimeter. The new material, called a micro-lattice, relies, on a lattice architecture: tiny hollow tubes made of nickel-phosphorous are angled to connect at nodes, forming repeating, asterisklike unit cells in three dimensions. "We're entering a new era of materials science where material properties are determined not only by the microscopic makeup of the material but also by the architecture of the constituents," Greer says. [Caltech Feature]
Compaction Bands in Sandstone are Permeable
José E. Andrade, Associate Professor of Civil and Mechanical Engineering, and colleagues have analyzed X-ray images of Aztec sandstone and revealed that compaction bands are actually more permeable than earlier models indicated. Their paper provides the first permeability calculations based on actual rock samples taken directly from the field in the Valley of Fire, Nevada. They conclude that these formations are not as impermeable as previously believed, and that therefore their ability to trap fluids—like oil, gas, and CO2—should be measured based on 3D images taken from the field. [Caltech Press Release]
Stimulating Electrode Array Assists Paraplegic Man to Stand and Move Legs Voluntarily
Joel W. Burdick, Professor of Mechanical Engineering and Bioengineering, and colleagues including Yu-Chong Tai, Professor of Electrical Engineering and Mechanical Engineering, have used a stimulating electrode array to assist a paralyzed man to stand, step on a treadmill with assistance, and, over time, to regain voluntary movements of his limbs. Using a combination of experimentation, computational models of the array and spinal cord, and machine-learning algorithms, Professor Burdick and his colleagues are now trying to optimize the stimulation pattern to achieve the best effects, and to improve the design of the electrode array. Further advances in the technology should lead to better control of the stepping and standing processes.