Number 426, May 3, 1999 by Phillip F. Schewe and Ben Stein
MARS MAGNETISM. The Mars Global Surveyor spacecraft has discovered patterns of magnetized surface rockóbroad stripes of magnetic material pointing in one direction alternating with magnetic material pointing in the opposite direction, somewhat like the patterns seen at mid-ocean rift zones on Earth. On our planet the alternating stripes testify to the changing nature of Earth's magnetic field and to the recurring upwelling of magma resulting from the movement of tectonic plates above a seething molten planetary core. The conclusion: Mars too might have experienced tectonic activity. (Science, 30 April 1999.)
HIGH-PRECISION STUDIES OF ANTIPROTONS can be carried out in an ion trap. Harvard physicist Gerald Gabrielse takes antiprotons from a beam at CERN, reduces their energy by a factor of 10 billion (in a series of slowing and cooling steps), and then inserts them into the final trap, where their motions are compared with commonplace protons. Strictly speaking what is measured is q/m, the ratio of the particle's charge to its mass. In this respect q/m proves to be identical for protons and antiprotons to within an uncertainty of 90 parts per trillion, a tenfold improvement over Gabrielse's previous best measurement. (Gabrielse et al., Physical Review Letters, 19 April 1999; for a dossier on other antiproton properties see the article by John Eades in Review of Modern Physics, 1 Jan 1999.)
PATTERNED NANOTUBE ARRAYS. Nanometer-wide tubes of carbon atoms, made amid fiery arc discharges, have been used in a number of ways, such as for tips in scanned probe microscopes. Researchers at ATMI, a company in Danbury, CT, produce films of nanotubes in a chemical process that uses catalysts carefully deposited on large-area substrates. Mats of nanotubes grow only atop the catalyst in pre-determined places to form desired nanotube patterns. The tubes are good emitters of electrons and thus the process lends itself to the job of enabling flat-panel displays, and is, fortunately, compatible with silicon processing. (Xu and Brandes, Applied Physics Letters, 26 April.).
WRITING THE WORD "OPTICS" ON A SINGLE ATOM is possible, scientists have shown, demonstrating the huge information capacity that exists even in an individual hydrogen atom. The trick is to sculpt the electron cloud surrounding an atom into the letters of this word. Shining an ultrashort UV laser pulse and lower-frequency electromagnetic waves on an atom can send one of its electrons to a high-lying "Rydberg state," in which it no longer exists as a cloud of charge enshrouding the nucleus but instead becomes a "wavepacket" that circles the atomic nucleus like a planet around a sun (Update 234). Applying a series of pulses can create a set of wavepackets that combine with each other like water waves and cancel each other out at specific places to form patterns around the atom, such as the word "optics," in which points on each letter correspond to possible places for finding the electron after measurement. Although neither this feat, nor the act of accurately measuring such spatial patterns, can yet be achieved technologically, Carlos Stroud of the University of Rochester (716-275-2598) and Michael Noel of the University of Virginia (804-924-6599) point out that an electron in an n=50 Rydberg state (49 energy levels higher than the lowest state) has 2,500 possible states of angular momentum, and have shown that the states can be combined in many ways, such as to form this word. (Optics & Photonics News, April 1999; See figure at Physics News Graphics.)