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.)

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