This Week in Science

Science  19 Mar 2010:
Vol. 327, Issue 5972, pp. 1425
  1. Saturn's Secrets Probed

    The Cassini spacecraft was launched on 15 October 1997. It took it almost 7 years to reach Saturn, the second-largest planet in the solar system. After almost 6 years of observations of the series of interacting moons, rings, and magnetospheric plasmas, known as the Kronian system, Cuzzi et al. (p. 1470) review our current understanding of Saturn's rings—the most extensive and complex in the solar system—and draw parallels with circumstellar disks. Gombosi and Ingersoll (p. 1476; see the cover) review what is known about Saturn's atmosphere, ionosphere, and magnetosphere.

  2. A Fair Society

    Many of the social interactions of everyday life, especially those involving economic exchange, take place between individuals who are unrelated to each other and often do not know each other. Countless laboratory experiments have documented the propensity of subjects to behave fairly in these interactions and to punish those participants deemed to have behaved unfairly. Henrich et al. (p. 1480, see the Perspective by Hoff) measured fairness in thousands of individuals from 15 contemporary, small-scale societies to gain an understanding of the evolution of trustworthy exchange among human societies. Fairness was quantitated using three economic games. Various societal parameters, such as the extent to which food was purchased versus produced, were also collected. Institutions, as represented by markets, community size, and adherence to a world religion all predict a greater exercise of fairness in social exchange.

  3. At Sixes and Sevens

    CREDIT: CARNALL ET AL.

    Molecular synthesis and macroscopic aggregation have often been regarded as entirely separate processes. From the researcher's standpoint, once reagents have been mixed, synthesis is largely passive, whereas processes such as crystallization can be more actively manipulated. Carnall et al. (p. 1502) characterized an unusual system in which the formation of aggregated cyclic macromolecules (macrocycles) from small peptide-based building blocks was governed by intimately interdependent factors ranging from the scale of covalent bond formation all the way to micron scale fiber growth. As the macrocycles stacked against one another to form the fibers, they remained loosely bonded enough internally to incorporate or expel individual building blocks. Varying the type of mechanical force applied to the growing fibers (either through shaking or stirring the solution), alternately favored formation of either 6-membered or 7-membered covalent macrocycles.

  4. Ferrous Shape Memory Alloy

    So-called shape memory alloys “remember” the shape they are processed into, and can return to that shape after being deformed by heat. A limitation for most metal-based shape memory alloys is the extent to which they can be deformed elastically. Tanaka et al. (p. 1488; see the Perspective by Ma and Karaman) demonstrate an iron-based alloy that shows much higher levels of superelastic strain, surpassing the performance of nickel-titanium alloys. In addition to high superelastic strain, this ferrous shape memory alloy has much higher strength than NiTi and copper-based shape memory alloys and, consequently, a high-energy absorption capability. These properties may allow shape memory alloys to be exploited as strain sensors or energy dampers.

  5. Taming Turbulence

    When fluid flows through a pipe, if the inertial forces are increased or the viscosity is decreased, the flow will become increasing noisy and will shift from being laminar to turbulent. Turbulence can be triggered by roughness in the pipe or other irregularities, which cause local eddies that grow into full-scale disruption of the otherwise smooth flow. Hof et al. (p. 1491; see the Perspective by McKeon) show that a continuous turbulent eddy, downstream, eliminates the growth of upstream disturbances and can prevent the overall flow from becoming turbulent. Unlike many other control methods, the energy cost for implementing this strategy is less than the benefit gained by maintaining a laminar flow.

  6. Small Is Beautiful

    Shrinking the size of lasers is attractive because it generally leads to a reduction in power requirements, an increase in switching speed, and possibly a cleaner output. Walther et al. (p. 1495) combined patterned electronic components (inductor and capacitor) and an active gain material to develop a submillimeter laser that emits in the microwave regime at low temperature. The use of established patterning techniques and tunable superlattice structures offer the prospect of shrinking the size still further, as well as providing a route to designer laser output for high-speed information transport and optical processing.

  7. Messy Mountain Meandering

    CREDIT: JONATHAN R. BARBOUR

    Predicting the influence of climate on landscapes is sometimes straightforward; for example, river deposits might grow with increased rainfall because erosion rates and sediment transport increase. However, long-term tectonic processes complicate the geomorphic signatures of more gradual climate-related phenomena that reconfigure landscapes. By correlating a decades-long record of typhoon rainfall in Japan with digital elevation models, Stark et al. (p. 1497) show that climate directly influences the extent of river meandering. When expanded to a larger region of the western North Pacific, this analysis revealed a strong climatic imprint on the landscape of humid mountainous areas. The region-wide analysis also revealed that underlying bedrock strength, as opposed to tectonic uplift, acts as a secondary control.

  8. Sperm Wars

    Some female insects mate on only one day of their life, but then they may mate with multiple males and store the sperm, sometimes for years. But as the mates compete for mates, so their sperm compete for ova, and competition between ejaculates can result in the destruction of sperm inside multiply mated females. But females need to select the sperm they want and to maintain stores of viable sperm to ensure a lifetime's fertility. Den Boer et al. (p. 1506) compared species of bees and ants with queens that either mate once or mate multiple times, and found that sperm competition has driven the evolution of compounds in the male accessory gland that protect a male's own sperm while damaging another male's sperm. To counteract the male effect, queens produce compounds that mitigate sperm destruction and maximize the number of her offspring.

  9. Diversity Gradients

    Latitudinal gradients in species abundance, with relatively few occurring at the poles and many at the equator, are well known for macroorganisms. It is a matter of controversy, fueled by a lack of observational data, whether such gradients also occur among microorganisms. Barton et al. (p. 1509, published online 25 February) have built on a global marine circulation model to predict the dynamics of phytoplankton populations. In silico, they obtain patterns of latitudinal gradation for plankton that are interspersed with hotspots of amplified diversity, which point to plausible natural explanations for the phenomenon that can be tested in the future by systematic metagenomic surveys.

  10. Puberty Impairs Plasticity

    CREDIT: SHEN ET AL.

    While the existence of a period of reduced learning coinciding with the onset of puberty in mice is well characterized, the underlying cellular and molecular mechanisms remain unclear. Shen et al. (p. 1515) assessed the role of specific γ-aminobutyric acid type A (GABAA) receptors for restricting hippocampal plasticity during puberty. At puberty, but not in adults or the very young, GABA receptors containing the α4 and δ subunits were targeted perisynaptically to excitatory synapses, shunting the depolarizing current necessary for N-methyl-d-aspartate (NMDA) receptor activation. As a consequence, signal transmission was affected and spatial learning reduced.

  11. Dancing with AMPARs

    A type of transmembrane receptor for glutamate, known as AMPAR, mediates most of the fast excitatory transmission in the mammalian central nervous system. Their function is regulated by the composition of their subunits, posttranslational modifications, and protein-protein interactions. Recently, several proteins that interact with AMPARs have been identified that affect their subcellular localization, synaptic stabilization, and kinetics. Using proteomic analysis, immunohistochemistry, and electrophysiology, von Engelhardt et al. (p. 1518, published online 25 February; see the Perspective by Farrant and Cull-Candy) identified a protein, CKAMP44, which modulates postsynaptic AMPA receptor gating, deactivation, and desentization.

  12. Cycle Entrainment

    Cells manage many cyclic processes that must coordinate with each other for best cellular performance. Yang et al. (p. 1522) present a general theoretical framework that quantitatively describes coupled cyclic processes and then apply this to the interaction between the circadian and cell-division cycles in single cyanobacteria. Simultaneously tracking individual cell divisions and circadian phases and fitting the data with the model suggest that cell-cycle progression slows down dramatically during a specific circadian interval, whereas cell-cycle progression is independent of the cell-cycle phase.

  13. Dying by Design

    To make optical-switching applications a reality, losses from scattering and other absorption processes have to be minimized. Hales et al. (p. 1485, published online 18 February; see the Perspective by Haque and Nelson) present a strategy to explore the refraction and absorption properties of a group of cyanine dyes for designing materials that have properties corresponding to technologically interesting telecommunications windows. The optical properties of the cyanine molecule was controlled by adding heavy chalcogen atoms (selenium) into the end groups of the molecular structure. While producing a series of molecules meeting criteria for feasible application, the work also demonstrates a route to improve the performance of nonlinear optical materials.

  14. Partial View

    Skilled billiard players can easily predict how spinning of one ball will affect the trajectory of the second ball it strikes in a collision. In principle, quantum mechanics can be used to predict the analogous impact of the angular momentum of reagents on the outcome of a chemical reaction. In practice, however, observation of most chemical reactions—even in the confines of a molecular beam apparatus—encompasses a vast number of collisions over multiple angular momentum distributions. Dong et al. (p. 1501; see the Perspective by Althorpe) have honed their spectroscopic resolution sufficiently to distinguish the impact of subtle angular momentum variations on the reactivity of fluorine with hydrogen atoms. Their data agree with theory and reveal oscillating peaks in reaction probability, termed partial wave resonances.

  15. Oceanic Nitrogen Fixation

    Nitrogen fixation in the oceans is important in sustaining global marine productivity and balances carbon dioxide export to the deep ocean. It was previously believed that marine nitrogen fixation was due to a single genus of filamentous cyanobacteria, Trichodesmium. The recent discovery of unicellular open-ocean cyanobacteria has raised the question of how they contribute to global ocean nitrogen fixation and how they compare in distribution and activity to Trichodesmium. Using data collected from the southwest Pacific Ocean, Moisander et al. (p. 1512, published online 25 February) show that the unicellular nitrogen-fixing cyanobacteria (UCYN-A and Crocosphaera watsonii) have distinct ecophysiologies and distinct oceanic distributions from each other, and from Trichodesmium. These data can be incorporated into models to retune estimates of the global rates of oceanic nitrogen fixation and carbon sequestration.

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