Number 92, August 19, 1992 by Phillip F. Schewe and Ben Stein|
THE LANDSCAPE OF DNA MAY BE FRACTAL . Several studies of DNA reveal unexplained relationships between nucleotides distant from each other. A Rockefeller/Tokyo team of scientists found such correlations in the genes regulating blood coagulation (Europhysics Letters, 7 Feb). Researchers at Boston University transformed sequences of nucleotide into a series of "random walks" and discovered correlations over many scales---1000, 10000, and 100000 nucleotide---suggesting a fractal pattern (Nature, 12 Mar.). Self-similarity on a scale of 50 million nucleotides has showed up in a study at IBM (Phys. Rev. Lett., 22 June). Long-range correlations did not appear in DNA sequences where introns, little-understood intervals of apparently noncoding DNA, were absent, a fact which had frustrated earlier attempts to find correlations in bacterial DNA which did not contain introns. (Science, 7 August 1992.)
THE ELECTRICAL CHARGE OF ANTIPROTONS AND POSITRONS has been studied using data from cyclotron-frequency experiments (which monitor the behavior of particles in a magnetic field) comparing protons with antiprotons and electrons with positrons, as well as spectroscopic measurements of short-lived states containing antimatter, such as positronium and antiprotonic atoms. Richard Hughes of Los Alamos and B.I. Deutch of the University of Aarhus in Denmark have calculated that the charges of the positron and electron are equal to about one part in 10**8, while the charge of the antiproton equals that of the electron to about one part in 10**5 (Phys. Rev. Lett., 27 July). The precision of these calculations would improve if researchers could study antihydrogen, an atom consisting entirely of antimatter. (Science News, 15 August 1992.)
PHOTONS FROM SONOLUMINESCENCE MAY PEAK IN THE ULTRAVIOLET. Sonoluminescence (SL) is a phenomenon in which sound waves create bubbles in a sample of water and cause them to oscillate. The excited bubbles in turn emit light. Last year, Seth Putterman (213-825-2269) and his group at UCLA discovered that the light pulses were very short, only 50 psec, and that the conversion of sound energy into light energy represented in effective energy concentration of 12 orders of magnitude. Now the UCLA scientists have studied the spectra of SL photons and found that if a peak exists it must be at an energy above 6 eV; detection of photons with energies above this value could not be calibrated. The UCLA researchers believe SL can be used for producing a broadband light source in the wavelength range of 190-750 nm. (Robert Hiller et al., 24 August, Physical Review Letters.)
"SEAGEL" IS THE LIGHTEST SOLID . Produced by Robert Morrison at Lawrence Livermore National Lab, Seagel is made of agar from kelp, and contains only 40 to 50 mg of material per cubic centimeter of solid. (New Scientist, 15 August 1992.)
PHYSICS NEWS UPDATE will recess for three weeks while the editor explores the physics of Yosemite and Sequoia National Parks.