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Number 376, June 11, 1998 by Phillip F. Schewe and Ben Stein
THE BURGESS SHALE OF COLLOIDS. Like the rocky hillside in the Canadian Rockies which harbored a trove of animal phyla not seen before (see SJ Gould's book "Wonderful Life"), a range of new colloid structures has been created by scientists at Brandeis in suspensions of tiny rod-like (viruses) and sphere-like (e.g., polystyrene balls) particles. Demonstrating again the principle that the inexorable increase in entropy in the universe needn't preclude localized order (i.e., order in part of a system can result if this creates the opportunity--in the form of a greater free volume--for greater disorder in the rest of the system), the Brandeis experiment has turned up a variety of never-before-seen rod-ball structures in which the main architectural force is not inter-particle interactions but rather entropy-driven phase transitions. (For example, in one odd structure, planes of stacked rods were separated by sheets of balls, with extra columns of balls appearing at regular intervals--- see figure at Physics News Graphics). It's as if in a sea of otherwise non-interacting billiard balls and cues the influence of entropy had caused the particles to acquire an effective size-and- shape-dependent attractive potential which obliges the particles to take up their novel configurations. The appearance of this spontaneous self-assembled order would seem to be important in a number of colloid systems, such as the segregation of DNA molecules inside prokaryotic cells (cells without a distinct nucleus). (Nature, 28 May 1998; contact Seth Fraden, seth@smectic.elsie.brandeis.edu.)
WEIGHING NEUTRINOS WITH GALAXY SURVEYS. Unlike recent neutrino oscillation experiments (which measure the mass difference between neutrino species: Update 375), cosmological measurements might be able to probe neutrino mass directly. This is because the teeming neutrinos in the universe would, with even a pinch of mass, play an important shepherding role in the behavior of galaxies: heavier neutrinos (through their gravitational exertions) would tend to suppress galaxy clustering. Scientists at the Institute for Advanced Study (Daniel Eisenstein, 609-734-8013, eisenstein@ias.edu) have proposed a way in which accurate maps of galaxies (such as will be furnished by the Sloan Digital Sky Survey) and accurate maps of the cosmic microwave background (such as will be provided by the Microwave Anisotropy Probe) can be combined to yield the neutrino mass if it exceeds about 1 eV. (Hu, Eisenstein, and Tegmark, Physical Review Letters, 15 June 1998.)
THE FIRST PRACTICAL, COHERENT SOFT X RAY SOURCE has been devised by scientists at the University of Michigan. They convert laser light at a wavelength of 800 nm into light at x-ray wavelengths of 17-32 nm by sending it through a channel of gas. Until now the task of producing x rays by the "harmonic conversion" process has been hampered by the fact that the nonlinear crystals used to double the light frequency in the visible and ultraviolet soak up x rays, while the gas media more hospitable to x rays cause the x-ray beam to fall out of phase with the laser- light beam as they co-propagate through the conversion medium. The Michigan researchers succeed in preserving the phase match with the additional use of a fiber waveguide, thereby increasing the x-ray yield by a factor of 100 to 1000 over previous devices. (Rundquist et al., Science, 29 May 1998.)
CORRECTION. The diameter of the Earth is 12,700 km, not 20,000 km (Update 375). The research on the tumble of paper (Update 374) will appear in a forthcoming Phys. Rev. Lett.
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