Physics News Update 442

Larry Klaes (
Tue, 10 Aug 1999 09:17:15 -0400

>Date: Mon, 9 Aug 1999 14:39:18 -0400 (EDT)
>From: AIP listserver <>
>Subject: update.442
>The American Institute of Physics Bulletin of Physics News
>Number 442 August 9, 1999 by Phillip F. Schewe and Ben Stein
>Laser Interferometer Gravitational-wave Observatory (LIGO),
>when fully deployed, will consist of two facilities (Hanford, WA
>and Livingston, LA). At each site laser beams pass up and down
>two perpendicular 4-km-long vacuum pipes, reflecting repeatedly
>from mirrors hung from wires. The presence of a passing
>gravitational wave would announce itself by a flexing of space-
>time which would very slightly lengthen the path of light in one
>arm and shorten the path in the other arm, causing a subtle change
>in the interference pattern made by the converging light beams
>from the two arms. The full LIGO, by about November 2001,
>should be able to detect a strain, defined as the fractional change in
>the position of the mirrors divided by the length of the arm (4 km),
>of 10^-21. This is the expected disturbance one expects from the
>gravity waves emitted by the coalescence of two solar-sized stars at
>a distance from Earth of 30-50 million light years. But before
>LIGO scientists possess their full instrument, they do have a 40-m
>prototype at Caltech, built for doing engineering studies but also
>capable of sensing gravity waves, albeit with the lesser strain
>sensitivity of a few times 10^-19. Thus the LIGO team, while
>testing methods for searching (directly via gravity waves) for
>binary coalescences, have thereby rendered an upper limit for such
>events of less than one every two hours in our galaxy. This result
>is useful for the test of the procedures, but is not significant for
>astronomers, who have previously established more stringent upper
>bounds with electromagnetic waves (visible and radio). (Contact
>Barry Barish at Caltech, 626-395-3853 or 818-601-2643; Stan
>Whitcomb 626-395-2131; or Bruce Allen, University of
>Wisconsin-Milwaukee, 626-893-2003 or 414-229-6439; Allen et
>al., Physical Review Letters, 16 August 1999.)
>July, the US team had its second-best showing since it started
>competing in 1986, with 3 gold medals and 2 silver medals brought
>home by the 5 high school students who participated. In informal
>rankings, the US placed 3rd out of the 62 countries that competed,
>after Russia and Iran. Taking place this year in Padua, Italy, where
>Galileo discovered the 4 Jupiter moons named after him, the
>Olympiad contains two days of grueling theoretical and
>experimental problems amounting to what is the world's most
>difficult high-school physics test. For example, the students had
>to compute the precise trajectory of a space probe that uses
>Jupiter's gravity as a slingshot--a technique used in real-life
>spacecraft such as Cassini. Gold medalists included Peter Onyisi
>(Arlington, VA), who had the tenth highest overall score out of the
>approximately 300 competitors at the Olympiad, Benjamin
>Mathews (Dallas, TX), and Andrew Lin (Wallingford, CT). Silver
>medalists include Jason Oh (Baltimore, MD) and Natalia Toro
>(Boulder, CO), who earlier this year also became the youngest
>person (at 14 years of age) ever to win the top prize of the Intel
>(formerly Westinghouse) Science Talent Search. (More
>information at
>IN-PLANE-GATE (IPG) TRANSISTORS can be excavated using
>nanomachining techniques. IPG transistors, in which the source,
>drain, and gate all lie in a plane rather than in a sandwich, might be
>especially useful for high-frequency applications. Scientists at the
>University of Hannover (Hans Werner Schumacher, 011-49-511-
>762-2523, have carved out an
>IPG structure in a semiconductor surface using the probe from an
>atomic force microscope (see figure at
> The probe makes an incision
>into the material extending down about halfway toward a buried
>interface where, lodged between GaAs and AlGaAs layers, a
>reservoir of electrons is confined to a plane. The incisions from
>above do not penetrate into this two-dimensional electron gas
>(2DEG) but they do shape (and can even pinch off) the conduction
>of the electrons. The Hannover researchers have also used their
>inscribing approach to make single-electron transistors (SETs),
>devices that register the coming and going of single electrons.
>(Schumacher et al., Applied Physics Letters, 23 August 1999.)