Number 448, September 16, 1999 by Phillip F. Schewe and Ben Stein
LIQUID CRYSTAL ACOUSTICS. Penn State physicist Jay Patel seeks to understand the optical properties of liquid crystals which, consisting of rod shaped molecules with the ability to polarize light, are regularly employed in electronic displays; an applied voltage lines up the rods and shuts off or turns on transmitted light. So it came as a big surprise when Patel discovered that liquid crystals also have acoustic properties. To be precise, an applied voltage imparts energy to the rod molecules which in turn cause the cavity in which the liquid crystal resides to vibrate. The cavity resonates with an audible frequency that could be heard with the unaided ear. (An analogy: the strings of a violin aren't what make sound; rather they transmit the energy of the bow to the body of the violin whose vibrations are source of the music we hear.) Unsure of the implications of liquid crystal sound (tiny speakers, delay lines for circuits?), Patel and his colleagues suspect that this discovery will lead to a fruitful new research area. (Kim and Patel, Applied Physics Letters, 27 Sept. 1999; contact Patel at firstname.lastname@example.org; 814-863-8999.)
CLAY OSCILLONS. Nature often sorts energy into certain preferred forms such as the unique spectrum of colors emitted by heated atoms or the characteristic note sounded by an organ pipe. This energy sorting can even turn up in a granular material. For example, a few years ago (Update 286) scientists discovered that collections of tiny metal balls, when shaken slightly up and down, vested some of their energy in the form of tiny waterspout heaps called "oscillons" Now physicists at the Hebrew University in Jerusalem (Jay Fineberg, email@example.com) have observed a similar effect in a colloid, a fluid material (e.g., milk) in which tiny particles (in this case small bits of clay) are suspended in a solvent (see figure at Physics News Graphics). Granular media and suspensions are very different in nature---grains are discrete objects that collide directly with each other whereas the particles in colloids interact via the medium of the solvent fluid---so the appearance of oscillons in both materials might represent some universal manifestation of driven nonlinear systems. The researchers are not yet sure where localized oscillon states would turn up in the natural world. One possibility is earthquakes. Oscillon-like states may explain the localized and highly variable damage (or intense ground acceleration) which, in many cases, occurs in poorly consolidated sediments (in analogy to the clay sediments used in the experiments) at relatively large distances from an earthquake's epicenter. (Lioubashevski et al., Physical Review Letters, 18 Oct.)
VISUALIZING ELECTRONIC ORBITALS. The image of an atom is really the image of its outermost electrons or, to be more precise still, the image of the averaged likelihood that the electrons will be at various places. For any but the innermost electrons, the shape of this likelihood surface (or orbital) will be non-spherical in shape. Physicists at Arizona State have now actually imaged these orbitals for the first time and shown that they look just the drawings used in quantum textbooks for decades. Using a combination of x-ray diffraction and electron microscopy the ASU scientists produced a 3D map of the orbitals of copper atoms and their bonds with neighboring atoms in a cuprite (Cu2O) compound (see figure at Physics News Graphics). The images of Cu-O and Cu-Cu bonds might provide insight into the workings of high temperature superconductors, in which the whereabouts of electrons and holes (the voids left by vacated electrons) are crucial. (J.M. Zuo et al., Nature, 2 Sept. 1999.)
CORRECTION. Fermionic atoms (Update 447) are atoms with an odd number of constituents (electrons, protons, or neutrons), but it should be emphasized that these constituents are themselves fermions, namely half-integral-spin entities. Dysprosium (Update 443) is element 66, not element 62.