Aktuelle Meldungen bei MM-Physik
18. Dezember 2001 © Schulphysik">email: Schulphysik
"The American Institute of Physics Bulletin of Physics News" AIP Auswahl Nov/Dez 2001 by Phillip F. Schewe and Ben Stein, and James Riordon
OCEANS MIGHT BE COMMON AND DIVERSE
in our solar system and in other solar systems, according to David Stevenson of Caltech, who regards the old notion of a narrow "habitable zone" (Venus too hot, Mars too cold, Earth just right) for liquid water oceans as erroneous. Stevenson spoke earlier this week in San Francisco at a meeting of the American Geophysical Union ( http://www.agu.org/meetings/fm01top.html ) at a session intended to bring together two scientific communities that scrutinize very different realms the planets and the seafloor on Earth. The connection? Observations from the bottom of the ocean show that microbes thrive both in near-freezing seawater and in near-boiling effusions from thermal vents. These conditions might turn up in many other planetary environments. For example, the Galileo spacecraft has provided evidence for watery oceans on three of Jupiter's moons Callisto, Ganymede, and Europa. Subsurface oceans could be kept liquid by warmth from tidal forces (Jove wringing its satellites) or from radioactivity. Torrance Johnson of JPL, also speaking that the meeting, said that Europa's ocean might be 75-150 km thick and could thus harbor twice the water in Earth's oceans. Stevenson added that observations also hint at oceans on Titan, Triton, and Pluto. In the case of Titan (soon to get the Galileo treatment when the Cassini spacecraft reaches Saturn in 2004) an ocean would be a mixture of water and ammonia (acting as antifreeze). Under some circumstances water might even be found inside Uranus and Neptune.
A NANO-ELECTRON-VOLT NEUTRAL-ATOM STORAGE RING,
built and tested by physicists at Georgia Tech, should help the development of atom fiber optics. Generally, storage rings not only store particles but also serve to define an energy and trajectory insofar as the particles are guided around a prescribed track by some kind of magnet system; particles with the wrong energy would fly away. Normally the magnets exert themselves by grabbing onto the particles' electric charge. Neutral atoms don't have a net charge but they can possess a net dipole moment which, if the atom is moving slowly enough, is sufficient for guidance (see figure at http://www.aip.org/mgr/png ). The Georgia Tech experiment (Michael Chapman, firstname.lastname@example.org, 404- 894-5223, Jacob Sauer, email@example.com, Murray Barrett, firstname.lastname@example.org) is much more modest than your typical particle accelerator: it's only 2 cm across and corrals neutral rubidium atoms moving at speeds of 1 meter/sec (equivalent energy=nano-eV, temperature=microkelvins). So far swarms of one million atoms have made as many as seven circuits around the ring (see figure at http://www.aip.org/mgr/png ). The same researchers produced the first all-optical generation of a Bose Einstein condensate (Update 545), and they hope to load the atoms from a condensate with their new storage ring (dubbed the "Nevatron"). Possible goals include ultra sensitive gyroscopes and atom lasers. (Sauer et al., Physical Review Letters, 31 December 2001;
|14 Dez 2001
ULTRASOUND SCANS ARE AUDIBLE TO A FETUS,
MOTION WITH PICOMETER ACCURACY.
||29 Nov 2001
ATTOSECOND PHYSICS HAS
|21 Nov 2001
HIDDEN OBJECTS REVEALED
WITH QUANTUM HOLOGRAPHY.
|14 Nov 2001
SINGING LIKE A