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<jats:p> Some volcanoes erupt explosively, with magma rapidly expelled as a hot jet of gas. The processes by which the magma is converted into the hot jet are still poorly understood. As discussed in the Perspective by Vergniolle, recent research reported by Morrissey and Chouet in the same issue (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1290" related-article-type="in-this-issue" vol="275" xlink:href="10.1126/science.275.5304.1290" xlink:type="simple">1290</jats:related-article> ) may shed light on these violent events. Data obtained with a network of microbarographs, or pressure sensors, can be used to estimate the pressure of the exiting gas jet. </jats:p>

<jats:p> Molecules such as C <jats:sub>2</jats:sub> H <jats:sub>2</jats:sub> and C <jats:sub>2</jats:sub> H <jats:sub>6</jats:sub> have been observed in the atmosphere of Neptune, one of the giant planets composed mostly of hydrogen and helium. Planetary scientists have puzzled over whether these hydrocarbons are formed as ultraviolet light from the sun induces photochemical reactions in atmospheric methane. In his Perspective, Hubbard discusses simulations reported in the same issue by Ancilotto <jats:italic>et al</jats:italic> . (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1288" related-article-type="in-this-issue" vol="275" xlink:href="10.1126/science.275.5304.1288" xlink:type="simple">1288</jats:related-article> ) suggesting that C <jats:sub>2</jats:sub> H <jats:sub>6</jats:sub> may be produced by high-pressure chemical reactions deep within the planet. </jats:p>

<jats:p> Although vertebrates appear symmetrical on the surface, their viscera show pronounced left-right asymmetry. In an illustrated Perspective, Robertson summarizes what has been found to date about the molecular underpinnings of the asymmetry set up during embryogenesis, including a report in this week's issue by Isaac <jats:italic>et al</jats:italic> . (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1301" related-article-type="in-this-issue" vol="275" xlink:href="10.1126/science.275.5304.1301" xlink:type="simple">1301</jats:related-article> ) on the asymmetric expression of the transcription factor cSnR in the chick embryo. </jats:p>

<jats:p>Lower Paleolithic artifacts have been recovered from a single occupation surface within stratified deposits at Diring Yuriakh, an archaeological site in central Siberia. Thermoluminescence age estimates from eolian sediments indicate that the cultural horizon is greater than 260,000 years old. Diring Yuriakh is an order of magnitude older than documented Paleolithic sites in Siberia and is important for understanding the timing of human expansion into the far north, early adaptations to cold climates, and the peopling of the Americas.</jats:p>

<jats:p>Three-dimensional periodic microstructures of aluminum oxide, which are important for creating photonic band-gap structures (PBGs), were fabricated by laser rapid prototyping by means of laser-induced direct-write deposition from the gas phase. The structures consisted of layers of parallel rods forming a face-centered tetragonal lattice with lattice constants of 66 and 133 micrometers. These structures showed transmission minima centered around 4 terahertz (75 micrometers) and 2 terahertz (150 micrometers), respectively. PBGs will allow precise control of the optical properties of materials, including lasers without threshold.</jats:p>

<jats:p> Conversion of methane to higher hydrocarbons by its low-temperature activation without forming undesirable carbon oxides is of great scientific and practical importance. Methane can be highly activated, yielding high rates of conversion to higher hydrocarbons and aromatics (10 to 45 percent) at low temperatures (400° to 600°C), by its reaction over <jats:italic>H</jats:italic> -galloaluminosilicate ZSM-5 type (MFI) zeolite in the presence of alkenes or higher alkanes. The methane activation results from its hydrogen-transfer reaction with alkenes. </jats:p>

<jats:p>Constant-pressure, first-principles molecular dynamic simulations were used to investigate the behavior of methane at high pressure and temperature. Contrary to the current interpretation of shock-wave experiments, the simulations suggest that, below 100 gigapascals, methane dissociates into a mixture of hydrocarbons, and it separates into hydrogen and carbon only above 300 gigapascals. The simulation conditions (100 to 300 gigapascals; 4000 to 5000 kelvin) were chosen to follow the isentrope in the middle ice layers of Neptune and Uranus. Implications on the physics of these planets are discussed.</jats:p>

<jats:p>Explosive volcanic eruptions generate pressure disturbances in the atmosphere that propagate away either as acoustic or as shock waves, depending on the explosivity of the eruption. Both types of waves are recorded on microbarographs as 1- to 0.1-hertz N-shaped signals followed by a longer period coda. These waveforms can be used to estimate burst pressures and gas concentrations in explosive volcanic eruptions and provide estimates of eruption magnitudes.</jats:p>

<jats:p>Deciding advantageously in a complex situation is thought to require overt reasoning on declarative knowledge, namely, on facts pertaining to premises, options for action, and outcomes of actions that embody the pertinent previous experience. An alternative possibility was investigated: that overt reasoning is preceded by a nonconscious biasing step that uses neural systems other than those that support declarative knowledge. Normal participants and patients with prefrontal damage and decision-making defects performed a gambling task in which behavioral, psychophysiological, and self-account measures were obtained in parallel. Normals began to choose advantageously before they realized which strategy worked best, whereas prefrontal patients continued to choose disadvantageously even after they knew the correct strategy. Moreover, normals began to generate anticipatory skin conductance responses (SCRs) whenever they pondered a choice that turned out to be risky, before they knew explicitly that it was a risky choice, whereas patients never developed anticipatory SCRs, although some eventually realized which choices were risky. The results suggest that, in normal individuals, nonconscious biases guide behavior before conscious knowledge does. Without the help of such biases, overt knowledge may be insufficient to ensure advantageous behavior.</jats:p>

<jats:p>Recent developments in piconewton instrumentation allow the manipulation of single molecules and measurements of intermolecular as well as intramolecular forces. Dextran filaments linked to a gold surface were probed with the atomic force microscope tip by vertical stretching. At low forces the deformation of dextran was found to be dominated by entropic forces and can be described by the Langevin function with a 6 angstrom Kuhn length. At elevated forces the strand elongation was governed by a twist of bond angles. At higher forces the dextran filaments underwent a distinct conformational change. The polymer stiffened and the segment elasticity was dominated by the bending of bond angles. The conformational change was found to be reversible and was corroborated by molecular dynamics calculations.</jats:p>