Number 101, October 30, 1992 by Phillip F. Schewe and Ben Stein|
CARBON ONIONS , quasi-spherical nested fullerene structures as large as 47 nm, have been synthesized by Daniel Ugarte of the Federal Polytechnic School in Lausanne, Switzerland. He used the beam in a powerful electron microscope both to create and to image a myriad of carbon objects. The largest have 70 concentric shells. The work of Ugarte and others seems to demonstrate that the most stable allotrope of carbon (at least for small objects) is not planar graphite but closed shells, owing chiefly to the need for satisfying the dangling bonds at the edge of the network. (Nature, 22 October 1992.)
A NEW DETERMINATION OF THE RYDBERG CONSTANT gives a value of 109237.315683 cm**-1 with an uncertainty of 2.9 parts in 10**11. Denoted by the letter R, the Rydberg Constant is the constant of proportionality in the formula (first derived by Balmer in 1885) prescribing the wavelengths of an atom's spectrum. (The number refers to hydrogen, but R can be calculated for the other elements.) The new value for R was obtained in an experiment comparing the frequencies of three transition lines in atomic hydrogen. The work was carried out by scientists at the National Institute of Metrology in Paris (F. Nez et al., Physical Review Letters, 19 Oct. 1992.) A more precise R will help in various tests of quantum electrodynamics.
STRAINED-LAYER SEMICONDUCTOR LASERS exploit rather than try to avoid the crystallographic mismatch between different semiconductor materials in a multilayer structure. Basically, scientists use the strain that arises from the mismatch to alter the electronic (bandgap) properties of the composite material. Experiments at the Philips lab in the Netherlands and at Bellcore in New Jersey have shown that when an InGaAs layer is grown on an InP substrate, the presence of a compressive or a tensile strain of 1.5% between the layers actually reduces the threshold current density necessary for laser light emission from 500 down to below 100 A/cm**2. The strain also tends to reduce the laser linewidth and the amount of fluctuation (chirp) in the frequency. (Physics World, October 1992.)
LUNAR ECLIPSES HAVE SWAYED HISTORICAL EVENTS. Armed with a table of upcoming eclipses, Christopher Columbus (shipwrecked during his 4th voyage) confidently predicted to the hostile native Jamaicans that God would send a messenger. The darkening of the moon duly occurred and Columbus got his way with the local residents. Other historically important eclipses include those of 431 BC, which influenced the decisive battle of the Peloponnesian War, at Syracuse; instead of retreating at a strategic moment, the superstitious Athenian general Nicias, intimidated by the ominous dark moon, delayed, causing the loss of his fleet and army. In 1453 the Byzantines were steadfastly defending Constantinople against the Ottomans, buoyed by an ancient prophecy that the city would not fall during a waxing moon. An eclipsed full moon on May 22 helped to break morale and the city fell a week later. Centuries later the Ottomans fell afoul of an eclipse which influenced the Arabian campaign in World War I. Lawrence of Arabia and his Bedouin followers captured the Ottoman fort at Aqaba by attacking while defenders were banging pots in an effort to bring back the eclipsed moon. (Sky & Telescope, December 1992.)