Number 47, September 13, 1991 by Phillip F. Schewe and Ben Stein DNA MOLECULES CAN BE MANIPULATED with "optical tweezers." Steven Chu of Stanford, a pioneer in the cooling and trapping of neutral atoms, has been able to grasp individual biological molecules by attaching to them polystyrene spheres. This allows Chu, for example, to study the mechanical properties of a DNA molecule by stretching apart its ends using two independently focussed laser beams. In its stretched state, the molecule can be "spot welded" to a microscope slide, where it can be glimpsed by scanning probe microscopes. (Science, 23 August 1991.) QUASICRYSTAL SEMICONDUCTORS are being sought by scientists in Grenoble, France (T. Klein et al., Phys. Rev. Lett, 3 June 1991). They found that at a temperature of 1 K the electrical conductivity of a high-quality AlCuFe quasicrystal was much lower then for typical metals. Furthermore, the conductivity was found to be sensitive to small changes in the composition, a property characteristic of doped semiconductors. Lowering the temperature or increasing the quality of the sample further reduced (rather than enhanced as with metals) the conductivity. (Nature, 5 Sept. 1991.) THE LARGE HADRON COLLIDER , Europe's version of the SSC, has not been officially approved by CERN's constituent nations, but plans for the machine proceed. Like the SSC, the LHC would provide proton-proton collisions rather than proton-antiproton collisions (it takes 300,000 protons to produce one antiproton). LHC's maximum collision energy, 15 TeV, would be less than SSC's 40 TeV, but CERN's Director General Carlo Rubbia believes that their emphasis on high luminosity will enable them to harvest much of the new physics that may be waiting at TeV energies. Besides p-p interactions at 15 TeV, LHC may also be linked with the electron-positron machine LEP (in whose 27-km tunnel LHC would be built) to provide electron-proton collisions at energies up to 1.7 TeV, five times higher than will be available at the nearly completed HERA machine in Hamburg. Also, heavy-ion reactions with total energies up to 1250 TeV, will be possible. (LHC News, supplement to Aug. CERN Courier.) THE COLD NEUTRON RESEARCH FACILITY , a source of cold (energies less than 5 meV) neutrons at NIST, has begun operation. Neutron beams, although not as intense as x-ray beams, are better than x rays for probing certain properties of matter, such as magnetic structure. Cold neutrons, with wavelengths of 4 angstroms or more, are useful for resolving mesoscopic structures (hundreds or thousands of angstroms in size) that are pertinent to the study of polymers, composites, and thin-film interfaces. The CNRF provides a home for cold-neutron researchers in the U.S. who for some time had had to make the trip to Grenoble, France, home of the Institute Laue-Langevin; ILL is currently shut down for an indefinite period. (Physics Today, Sept 1991.) BUCKYBALLS CAN BE ORDERED BY MAIL for those who don't have the time or apparatus for making them. Several companies now market C-60-rich soot for about $10 to $20 a gram. The purer stuff costs more, typically $500 for a gram of mixed C-60 and C-70. (The Scientist, 19 August 1991.)