PHYSICS NEWS UPDATE A digest of physics news items prepared by Phillip F. Schewe, AIP Publ

Master Index Current Directory Index Go to SkepticTank Go to Human Rights activist Keith Henson Go to Scientology cult

Skeptic Tank!

PHYSICS NEWS UPDATE A digest of physics news items prepared by Phillip F. Schewe, AIP Public Information Number 171 April 1, 1994 FASTER TECHNIQUES FOR SEQUENCING DNA, described at the American Physical Society (APS) March Meeting in Pittsburgh, may contribute to the Human Genome Project. With the conventional technique, known as gel electrophoresis, in which DNA fragments are separated by electric fields, it would take 20,000 man-years to determine the complete sequence of 3 billion "base pairs" that make up the human genetic code. In a modification of electrophoresis that uses thinner gels and higher electric fields, Lloyd Smith of the University of Wisconsin can now sequence a 500 base-pair DNA fragment in an hour, as opposed to the 12-14 hours it takes normally. Brian Chait of Rockefeller University has devised a sequencing method that completely bypasses the use of a gel. In his method, a laser pulse would zap DNA fragments, converting them into gaseous ions which would then fly towards a detector to be analyzed. Once his technique is refined, Chait estimates that an amount of DNA code that normally takes several hours to sequence could be analyzed in less than a minute. Other researchers in Pittsburgh proposed sequencing methods based on photolithography techniques and single-molecule detection. PUNCTUATED EQUILIBRIUM is the name for Harvard paleontologist Stephen Jay Gould's theory that evolution comes about not just by gradual steps but sometimes because of catastrophic events, such as meteor impacts. Kim Sneppen of the Niels Bohr Institute in Denmark, speaking at the APS meeting, believes that evolutionary bursts may also occur because of the dynamics of ecological systems themselves. Sneppen and his colleague Per Bak of Brookhaven have proposed a model in which biological species can exhibit "self-organized criticality," according to which some systems, such as sand dunes or geological faults, can accommodate the gradual addition of energy or stress or small increments of matter until a certain threshold is crossed, after which a catastrophic reordering takes place, such as an earthquake or avalanche. Sneppin's model, employing various rates of mutation and interactions among species, seems to forecast such avalanches for biological systems. (Science News, 26 March 1994.) WOMEN IN PHYSICS account for only 15% of bachelor's degree recipients, 11% of new PhD's, and only 3% of tenured or tenure-track positions in the U.S. This compares poorly with the comparable numbers for many other nations with advanced physics establishments. For example, recent women physics PhD percentages were 18% in Germany, 21% in France, 12% in Britain, and 25% in the former Soviet Union. In the other direction, the number for Japan was only 4%. (Science, 11 March 1994.) NEUTRINO OSCILLATIONS, the transformation of one neutrino type (electron, muon, or tau) to another, is invoked to explain the solar neutrino problem: a detector designed to monitor electron-type neutrinos from the sun will fail in its job if, on the way to Earth, electron neutrinos are turning into muon neutrinos. A new generation of terrestrial experiments searching for neutrino oscillation are now being planned. All involve accelerator-produced neutrinos and the study of their fluxes at various points along a baseline. One scheme uses neutrinos from CERN in Switzerland and a detector at Gran Sasso in Italy, 732 km away. Another experiment involves shooting neutrinos from Fermilab, near Chicago, up to the Soudan II detector in Minnesota. (Science, 18 Feb.)


E-Mail Fredric L. Rice / The Skeptic Tank