This Week in Science

Science  28 Feb 1997:
Vol. 275, Issue 5304, pp. 1237
  1. Siberian outpost

    Artifacts were discovered at the Diring Yuriakh archaeological site in northeast Asia in 1982, yet their age has been difficult to determine because of lack of suitable material for dating; estimates have varied from 15,000 years to more than several million years ago. This site may mark the early migration of peoples into northeast Asia, an expansion that eventually led to migration into North America. Waters et al. (p.1281; see the news story by Holden, p. 1268) show that the artifacts are associated with windblown deposits and were thus able to date the deposits and bounding strata using thermoluminescence to more than 260,000 years ago.

  2. Filling in the band gap

    Materials that can totally reflect electromagnetic radiation propagating in any direction for specific frequency bands, so-called photonic band-gap structures (PBGs), have potential applications in the fabrication of perfect mirrors, optical wave guides, and lasers. The current challenge is the fabrication of three-dimensional PBGs with band gaps in the infrared and visible range. Wanke et al.(p.1284) show that laser-induced direct-write deposition from the gas phase allows construction of periodic structures with transmission minima in the infrared. Dopants or defects can be introduced easily, and structures can be grown around existing devices.

  3. Methane chemistry (I)

    Several routes for converting methane to higher hydrocarbons have been proposed that involve oxidation, a route that competes with total oxidation to CO and CO2. A low-temperature route (400o to 600oC) for incorporating methane into higher hydrocarbons makes use of alkenes or higher alkanes as coreactants is described by Choudhary et al.(p.1286). An H-galloaluminosilicate zeolite catalyst was used to help facilitate hydrogen-transfer reactions.

  4. Methane chemistry (II)

    The giant outer planets, Uranus and Neptune, have a middle icy layer composed of methane, ammonia, and water, stable at high pressures (20 to 300 gigapascals) and high temperatures (2000 to 6000 kelvin). These extreme conditions are difficult to reproduce in the laboratory but were simulated in molecular dynamics calculations by Ancilotto et al.(p.1288; see the Perspective by Hubbard, (p.1279).They found that methane will form more complex hydrocarbons, such as ethane, before it dissociates into hydrogen and carbon (precipitated as diamond). This additional mechanism for producing ethane may help explain the estimated overabundance of ethane on Neptune's surface if convection carries this ethane from the interior to the surface.

  5. Volcanic boom

    An explosive volcanic eruption results when gas bubbles form in a magma chamber and conduit and rapidly expand as pressure drops. Obtaining accurate measurements of this process has been difficult but is a key test for models and theory and inferring the size of eruptions in remote areas. Morrissey and Chouet (p.1290; see the cover and also the Perspective by Vergniolle, p.1278) show that gas concentrations in the magma and burst pressures can be inferred from remote measurements of the atmospheric shock waves produced by the eruption.

  6. In the know

    Reasoning our way through a new situation where we learn through experience, such as a complex game or puzzle, requires us to develop strategies for winning. Bechara et al.(p.1293; see the news story by Vogel, p.1269) found that normal individuals, when learning a gambling task, were using effective strategies (winning money) before they were consciously aware of it. Well before they verbally reported a strategy (knowing which deck to pick cards from), they had sweated (showed a skin conductance response, or SCR) before making a high-risk move in the game. Patients who had suffered prefrontal cortex damage and who suffered from decision-making defects did not develop anticipatory SCRs, even when they knew consciously that they were making risky choices.

  7. Heart in the right place

    On the outside, vertebrates exhibit bilateral symmetry, but on the inside some organs, like the heart, must develop asymmetrically—thus the tube in embryos that becomes the heart loops around to the right. Before such looping occurs, signaling molecules, such as Nodal, a member of the transforming growth factor-name family, are expressed on only one side of the embryo. Isaac et al. (p.1301; see the Perspective by Robertson, p.1280) show that in the chick embryo, cSnR, a member of the Snail zinc finger proteins, is expressed opposite of Nodal (on the right side). Interruption of its expression randomized heart development, indicating that it operates downstream of these other signals.

  8. Proteolysis and cell division

    Recent evidence indicates that regulated proteolysis is a key mechanism by which cellular processes are controlled. A complex of proteins that mediates such controlled destruction is known as the anaphase-promoting complex (APC) for its role in regulating the exit of cells from mitosis. However, few of the key targets of the APC are known. Juang et al.(p.1311) report that one such target is the protein Ase1, a microtubule-binding protein that is a component of the mitotic spindle. Degradation of Ase1 is apparently necessary for normal assembly and disassembly of the spindle. The results indicate that, like phosphorylation mediated by the cyclin-dependent kinases, proteolysis mediated by the APC is a critical regulatory mechanism for multiple steps in the cell division cycle.

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