Number 103, November 17, 1992 by Phillip F. Schewe and Ben Stein
DO QUARKS HAVE CONSTITUENTS? The issue of quark substructure can be addressed by studying the production of jets of particles in high-energy proton-antiproton collisions. The CDF (Collider Detector at Fermilab) collaboration recently published an analysis of two-jet events produced at the Tevatron collider. Finding no direct evidence, the researchers concluded that any quark substructure would only become evident at energies of 1 TeV or more. (F. Abe et al., Phys. Rev. Lett., 16 Nov.)
VORTICES IN HEAVY-FERMION SUPERCONDUCTORS have been imaged for the first time. In certain materials---in this case, a uranium-platinum compound---superconductivity can occur at temperatures below 1 K through the interactions of inner-shell electrons which, because they are tightly bound, move as if they were heavier than normal electrons. Like the high-temperature superconductors, the heavy-fermion superconductors can respond to the presence of an external magnetic field by producing vortices, little loops of current flowing around the magnetic flux lines. Studies of vortices in other superconductors indicate that they can form a sort of "lattice" configuration. Now a group of scientists at AT&T Bell Labs (David J. Bishop, 908-582-3927) and the RISO National Lab in Denmark have used neutron diffraction to show that vortices in a heavy-fermion material, UPt3, assume an oblique hexagonal structure. (R.N. Kleiman et al., Phys. Rev. Lett., 23 Nov. 1992.)
AN ANTENNA MOUNTED ON A PHOTONIC CRYSTAL has been demonstrated by scientists at the MIT Lincoln Lab and Bellcore. Photonic crystals are the recently introduced structures that reject electromagnetic radiation lying in certain frequency ranges or "bands" in the same way that semiconductors reject electrons in certain energy bands. Elliott Brown of Lincoln Lab (617-981-4713) and his colleagues built a photonic crystal-antenna setup which can couple microwave radiation to devices on integrated circuits. This configuration allows integrated-circuit devices to receive microwave radiation, or conversely, convert electric current to microwave signals. The configuration traditionally used for this purpose, antennas on semiconductor substrates, transmits only a few percent of their total power into the air; the rest is radiated into the semiconductor. The Lincoln Lab-Bellcore antenna, which has a planar bow-tie geometry, has much higher efficiency because the photonic crystal on which it is mounted has a sizeable energy gap in the microwave region. (Optics & Photonics News, November 1992; also upcoming article in "Physics News in 1992," to be published by the AIP Public Information Division.)
THE KNOWN SHAPE OF THE MILKY WAY keeps changing as new information comes to light. At a recent conference devoted to the subject, data from COBE, IRAS, Rosat, and other sources added to or modified the traditional view of our galaxy. Examples include the observation of 100-light-year-wide bubbles of hot, low-density gas and of other worm-shaped filaments of hot gas (up to 1000 light years long) sticking up out of the galactic plane. Meanwhile, COBE observations of the galactic center support an earlier assertion by Maryland astronomer Leo Blitz that the Milky Way is not a classic pinwheel but actually a barred spiral. (Science, 6 Nov. 1992.)
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