American Institute of Physics
SEARCH AIP
home contact us sitemap
Physics News Update
Number 406, December 11, 1998 by Phillip F. Schewe and Ben Stein

JOSEPHSON EFFECT IN A BOSE-EINSTEIN CONDENSATE. Mark Kasevich and Brian Anderson at Yale have loaded a Bose-Einstein condensate of rubidium atoms (occupying a single quantum state) into the grip of an optical lattice, a series of energy wells established by the electric field of a laser beam. With the help of gravity, atoms from one part of the condensate can tunnel to another (spatially separated) part but retain their coherent relation to the rest of the condensate, analogous to the Josephson effect, in which part of a supercurrent can tunnel across an insulator from one superconductor to another. The spaced-out drops of atoms constitute a pulsed atom laser beam. (Science, 27 November 1998.)

MRI OF SINGLE MAMMALIAN CELLS has been demonstrated by Carnegie Mellon researchers (Chien Ho, 412-268-3395), opening possibilities for improving treatment of organ rejection and studying how natural killer cells attach to tumors. In the present work, the researchers took pictures of rat T cells (components of the immune system) embedded in a gelatin solution. To prepare the cells for MR imaging, they added magnetic iron-oxide particles coated with dextran, a glucose-based molecule. Through a natural process known as endocytosis, the particles were absorbed by each cell and taken up in a fluid-filled region known as the vacuole. Many such particles entered each vacuole, and collectively they produced a detectable magnetic signal over a region 50 times greater than the vacuole's 1 micron size. Therefore, an MRI scanner with 50-micron resolution could detect a single vacuole in a T cell, itself only 7-10 microns in size. Previous studies have shown that dextran-coated iron-oxide particles do not affect a T cell's function and could act as a safe "MRI contrast agent" inside bodies. While this technique may not be able to track single cells in a living body, owing to its less favorable environment for MR imaging, the researchers believe the method can be developed into a sensitive, noninvasive means of detecting unwanted accumulation of T cells in transplanted organs, a sign of tissue rejection. More generally, this technique may enable MRI to detect the presence and movement of any other type of cell (including tumor-killing cells) in living things, as long as one can design a suitable MRI contrast agent that can enter the cell without affecting its function. (Dodd et al., Biophysical Journal, January 1999; images at Physics News Graphics.)

SPACE WEATHER EXERTS ITSELF IN SEVERAL WAYS. Here are two examples, from reports given at this week's "American Geophysical Union (AGU) meeting in San Francisco, of how a hurricane of particles from the sun can push things around here at Earth. First, Geoffrey Reeves of Los Alamos described new data recorded by a number of orbiting spacecraft which suggests that Earth's own magnetic field is more important than the solar wind in supplying electrons and whipping them to high speeds in the Van Allen belts. Electron energies and densities in the belts change too quickly, Reeves argued, to be responding directly to solar eruptions. Another report, delivered by Thomas Moore of NASA Goddard, confirmed with new observations by the Polar satellite the idea that blasts of solar wind can greatly enhance the escape of oxygen, helium, and hydrogen ions from Earth's upper atmosphere. This exodus of ions contributes to near-Earth space storms and promotes a charge buildup on nearby spacecraft.

[an error occurred while processing this directive]