PHYSICS NEWS UPDATE A digest of physics news items by Phillip F. Schewe, American Institut

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PHYSICS NEWS UPDATE A digest of physics news items by Phillip F. Schewe, American Institute of Physics Number 187 July 11, 1994 physnews@aip.org A CIRCUMSTELLAR DUST RING, made from asteroid debris, may exist and might be centered at a radius just outside Earth's orbit around the sun. Astronomers at the University of Florida reach this conclusion using a combination of numerical simulations of dust particles migrating from the asteroid belt (between Mars and Jupiter) in toward the sun and using observations made by the Infrared Astronomical Satellite (IRAS) of features in the zodiacal cloud, the thin fog of dust pervading the inner solar system. The Florida scientists suggest that the resonance effects that shuttle dust into and out of the heliocentric ring may also be important in building planets in star systems (such as Beta Pictoris) with circumstellar dust disks. (Stanley F. Dermott et al., Nature, 30 June 1994.) THE INTERGALACTIC MEDIUM (IGM) MAY HAVE BEEN DETECTED, at least that part of it consisting of singly ionized helium. Using the Hubble Space Telescope (HST), a Dutch-British- French-US team of astronomers have sampled the light coming from the quasar Q0302-003 (redshift of 3.286). They notice that ultraviolet light at a wavelength of 304 angstroms is being absorbed along the way, supposedly by the singly ionized helium making up part of the IGM. (Another presumed IGM component, singly ionized hydrogen, cannot be observed since, consisting of bare protons, it exhibits no atomic transitions.) Using the quasar approach to inferring the presence of the IGM is difficult because the quasar must be far away, so that the ultraviolet radiation can be redshifted into a range that can be detected by HST, and because it is rare for such a quasar not to lie behind several foreground neutral-hydrogen clouds, which could also absorb the ultraviolet. (P. Jakobsen et al., Nature, 7 July 1994.) THREEFOLD INCREASED DETAIL IN THE STRUCTURE OF A BIOMOLECULE was obtained when researchers applied a combination of several powerful techniques to x-ray crystallography. Wladek Minor (317-494-0879) of Purdue University and his colleagues used the Cornell High Energy Synchrotron Source to determine the atomic structure of crystallized L-1 lipoxygenase enzyme, a protein involved in polyunsaturated fatty acid metabolism in both mammals and plants. The synchrotron radiation's high intensity, combined with a special CCD detector, allowed the researchers to obtain data rapidly and with a very high signal-to-noise ratio. Cooling the crystal to near-liquid nitrogen temperatures preserved the crystalline order for hours of synchrotron beam exposure, permitting three times the number of observations than the best previous data set for this protein. Analysis of the data yielded crystal structure information with a resolution of 1.4 Angstroms, the best yet for such a large protein (containing 839 amino acids). Minor says this combination of techniques can be applied to learn new structural details of other proteins and viruses. (Paper at the meeting of the American Crystallographic Association in Atlanta, June 27-July 1.) PHYSICS NEWS UPDATE will presently recess for three weeks. -END OF FILE- =============

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