Number 90, August 4, 1992 by Phillip F. Schewe and Ben Stein|
1/F NOISE HAS 1/F NOISE. Certain signals, such as the light coming from quasars or the current flowing through a resistor, exhibit small fluctuations which, although seemingly random, actually possess an underlying structure. When studying this problem, scientists often transform their data from the time domain---the raw signal, consisting of fluctuations around some mean value, as a function of time---into the frequency domain, in which the fluctuation "power" (essentially the fluctuation likelihood) is plotted as a function of frequency. Such a plot typically shows that the fluctuation power is proportional to the inverse of the frequency; hence the name "1/f noise." The data is Fourier-transformed in this way because it better reveals the fact that all time scales are involved in the physical process at work. In other words, fluctuations occurring now are related to fluctuations at various times in the past, and are anything but random. Scientists at the University of Minnesota (contact James Kakalios, 612-624-9856) have carried this process one step further and have shown that a 1/f noise spectrum can itself be characterized by 1/f noise. Studying the fluctuations of current flowing through hydrogenated amorphous silicon, the Minnesota researchers formed a power spectrum, which they monitored as a function of time. This time dependence in turn furnished a "second spectrum," which proved itself to be 1/f in nature. (C.E. Parman, N.E. Israeloff, and J. Kakalios, 17 August 1992 issue of Physical Review Letters.)
ACTIVITY AT ACCELERATORS around the world: At HERA in Hamburg, 27-GeV electrons and 820-GeV protons were colliding as of June 1. The initial luminosity was 1.5 x 10**27 particles per sec per sq cm. At Stanford's SLC, electron beams with polarizations at high as 25% were colliding with positrons. Polarizations of 46% are expected by the end of the year. Meanwhile, at the Beijing Electron-Positron Collider (BEPC) a new value for the mass of the tau lepton (1776.9 MeV) has been obtained with ten times the precision of previous measurements. (CERN Courier, July 1992.)
PHYSICAL REVIEW AND PHYSICAL REVIEW LETTERS continue to grow. Together these physics journals received 14,600 submissions in 1991, 8% more than in 1990. Foreign submissions accounted for 56% of the 1991 total; the chief contributors from abroad were Germany, Japan, France, China, India, and Canada. The growth of submissions has necessitated an increase from two to three in the median number of articles per year referred to referees. Referees increasingly use electronic mail (29% of responses) and faxes (20% of responses). Only 6.7% of articles were submitted by e-mail, but this was an increase of 138% over 1990. (APS News, August 1992.)
THE ASTROPHYSICAL JOURNAL now has a video adjunct. The printed version of the 10 July issue of ApJ is accompanied by a VHS cassette containing several segments related to certain articles in the journal. Thus you can read about and also see the simulated collisions of galaxies. Future use of videotape material will depend on its usefulness to authors, who pay an extra fee for the service.