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From physnews@aip.org Wed Jul 2 19:12:35 1997 Date: Wed, 2 Jul 97 11:02:31 EDT From: physnews@aip.org (AIP listserver) Message-Id: <9707021502.AA12498@aip.org> To: physnews-mailing@aip.org Subject: update.328
PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 328 July 2, 1997 by Phillip F. Schewe and Ben Stein THE MARS PATHFINDER spacecraft arrives July 4 at its destination where, after firing retrorockets and deploying a parachute and numerous airbags, it will bounce to a halt on what was probably an ancient floodplain. After this, its missionary rover will venture forth to taste rocks and make movies. The local weather forecast calls for blue skies and wispy clouds with a small chance of a dust storm (currently 600 miles to the south), in which case the sky will be pink. In September another craft, the Mars Global Surveyor, will take up orbit around Mars. (For the latest update, view the JPL website: mpfwww.jpl.nasa.gov/) STORING AN OPTIMUM AMOUNT OF INFORMATION IN A PHOTON or any other quantum particle is possible even in the presence of noise, researchers have concluded (B. Schumacher et al., Physical Review A, July 1997; A.S. Holevo, upcoming in IEEE Transactions on Information Theory). A photon has many different quantum states, each of which can be made to represent a different digit. Furthermore, one can store many digits simultaneously in a single photon by putting it into a combination or "superposition" of many states. However, quantum mechanics prevents a measuring device from perfectly distinguishing between all these different states. Previously, physicists discovered that the maximum amount of information that can be read from a photon can be no greater than the amount of entropy, or disorder, it acquires when a range of quantum states is created to represent different digits. Now, the researchers show that this upper limit can be reached, even in a noisy environment, by utilizing several strategies, such as employing only those quantum states that are most distinguishable. These findings provide insights into how little energy is required to store a message. (For more details, go to www.aip.org/physnews/preview; Ben Schumacher, Kenyon College, 614-427-5832) HOLLOW NANOPARTICLE LUBRICANTS, consisting of fullerene-like tungsten disulfide balls, have performed well in friction and durability tests, and may be superior to other solid-state lubricants, which usually come in powdered form. The 100-nm WS2 balls (much smaller than conventional powder grains, microns across) are nested like some carbon nanotubes, but flexible. This, their chemical inertness, and the tendency to roll rather than slide when pushed, should make the nanoparticles a good lubricant at the micron scale, or as an additive in other lubricants. Scientists working at the Weizmann Institute and at the Center for Technological Education in Israel are now able to make gram amounts of the lubricant. (L. Rapoport et al., Nature, 19 June 1997.) ONE MEASURE OF A NATION'S SCIENTIFIC STRENGTH is the number of papers it generates and the citations those papers receive. For the period 1992-96, these were the top producers of papers in a select set of journals: US (1.3 million), UK (300,000), Japan (281,000), and Germany (259,000). Ranked according to citations per paper, the order becomes Switzerland (5.66), US (5.03), Netherlands (4.46), Sweden (4.38), and UK (4.19). The EU nations lumped together and the US each have a 36% share of total citations. The general trend these past 15 years has been for the US citation rate to remain high but for its citation share to give ground to the EU and to Asian/Pacific nations. (ISI ScienceWatch, May/June; also Nature, 5 June 1997.)