This Week in Science

Science  18 Sep 2009:
Vol. 325, Issue 5947, pp. 1471
  1. Monitoring Massive Microbial Dispersal


    Quantifying the relative influence of present-day environmental conditions and geological history on the spatial distribution of species represents a major challenge in microbial ecology. Ecological approaches to distinguish between these two biogeographic controls are limited by environmental variability both in space and through time (see the Perspective by Patterson). Using a 1.5-million-year fossil record of marine diatoms, Cermeño and Falkowski (p. 1539) show that, even at the largest (global) spatial scale, the dispersal of marine diatoms is not very limited. Environmental factors are the primary control shaping the global biogeography of marine diatom morphospecies. Thermophilic microorganisms are routinely detected in permanently cold environments from deep sea sediments to polar soils. Hubert et al. (p. 1541) provide a quantitative analysis of a potentially large-scale dispersion of thermophilic bacteria in the ocean. Approximately 108 thermophilic spores are deposited each year on every square meter of Arctic sediment.

  2. Corkscrew Polarizer

    Strong optical activity, measured in terms of a material's ability to polarize light, usually requires a material several hundred wavelengths thick. Gansel et al. (p. 1513, published online 20 August; see the cover) show that the tunable electromagnetic response of metamaterials may offer a route to reduce the amount of material required for strongly optically active materials. Based on the standard metamaterials design of the splitring resonator, photolithography was used to define an array of three-dimensional gold nanocorkscrews. Just a single wavelength thickness of the corkscrew design was required for a circular polarizer operating over an octave of bandwidth.

  3. Cold Atom Magnetism

    Magnetic ordering arises from the strong interactions between atoms, with its origins deeply rooted in quantum mechanics. How the ordering comes about, however, has long been a topic of debate because most condensed-matter systems are limited by a somewhat fixed parameter space. Cold atom systems, by comparison, provide the ability to tune the magnitude and sign of the atom-atom interaction, as well as the density. Jo et al. (p. 1521; see the Perspective by Zwerger) exploit this flexibility to use an ensemble of ultracold fermionic atoms as a “quantum simulator” to explore the possibility of magnetic ordering. As the repulsive interaction between atoms is increased, an instability occurs in the free two-component Fermi gas (or jellium), which results in a phase transition and the ferromagnetic ordering of the atoms.

  4. The Meteorite Who Fell to Earth

    Orbital data is available for only a handful of meteorites. Some are found long after they fell to Earth. Others are recovered after they have been observed falling through the atmosphere, but their trajectories are rarely recorded. Bland et al. (p. 1525) used a photographic camera network located in the Australian desert to track a fireball in the sky, find the meteorite, and establish its orbit. The meteorite is a basaltic achondrite; most such rocks have been traced to the major asteroid Vesta. In this case, the meteorite's isotopic composition and orbital properties suggest a distinct parent asteroid—a different source of basaltic material residing in the innermost main belt.

  5. Predicting Terrorism?

    Terrorists may be extremists whose opinions do not reflect the mainstream views in their country. Alternatively, public opinion could provide a useful indicator of the likelihood of terrorism. Krueger and Malečková (p. 1534) used data from the Gallup World Poll of public opinion and the National Counter Terrorism Center to demonstrate a positive relationship between the percentage of people in a country who disapprove of the leadership of another country and the number of terrorist attacks carried out by people or groups from the former country against the latter. Although the data do not demonstrate causality, they do suggest that public opinion can provide an “early warning signal” of future terrorist threats.

  6. Transistors Switch onto Spin


    Using the spin of an electron in addition to, or instead of, the charge properties is believed to have many benefits in terms of speed, power-cost, and integration density over conventional electronic circuits. At the heart of the field of spintronics has been a proposed spin-analog of the electronic transistor, the spin field effect transistor. Koo et al. (p. 1515) demonstrate the injection and detection of spin between two ferromagnetic contacts and show how the magnitude of the spin-current between the source and drain contacts can be controlled by a voltage applied to a gate. The results present an experimental realization of the concepts described for the spin-transistor.

  7. Oblique Reasoning

    In Milankovich theory, the canonical theory of glaciation and deglaciation, ice sheets wax and wane in response to the amount of summer insolation at a latitude of 65°N, which is consistent with the observed timing of the last deglaciation. The penultimate glaciation behaved quite differently, however. Now, Drysdale et al. (p. 1527, published online 13 August) offer firmer constraints on the timing of the penultimate deglaciation, by correlating a difficult-to-date marine record of ocean volume to a precisely datable nearby speleothem (terrestrial stalagmite). Ocean volume began to increase about 141,000 years ago, thousands of years before the rise in 65°N summer insolation. Thus, instead of the forcing mechanism proposed by Milankovich, variations in Earth's obliquity may be mostly responsible for the disappearance of ice sheets.

  8. Now Shown in 3D

    With the advent of systems-wide technologies and the development of analytical methods, data produced by analyzing individual or small groups of molecular components can be integrated to reassemble whole biological systems. Zhang et al. (p. 1544) have undertaken a major technological challenge: to integrate biochemical data with experimentally determined or predicted three-dimensional structures of all proteins involved in the central metabolism of a bacterial cell. This integration of large-scale data sets provides evolutionary and functional insights and furthers our understanding of the molecular assembly of complex biological networks.

  9. A Separate System for Itch Processing


    It has been a long-standing question if itch is a subquality of pain involving the same neuronal elements or if distinct, so-called labeled lines exist in the nervous system for both sensations. To address this question directly, Sun et al. (p. 1531, published online 6 August) destroyed neurons in the superficial spinal dorsal horn that express the gastrin-releasing peptide receptor. This receptor is known to be involved in mediating itch but not pain sensations. In various animal models, ablation of gastrin-releasing peptide receptor-expressing spinal dorsal horn neurons reduced itch without changing pain perception. Thus, itch and pain indeed appear to be mediated by distinct labeled lines in the central nervous system.

  10. Locust Wing Aerodynamics

    Insect wings function as deformable aerofoils, but the precise aerodynamic benefits of the observed deformations have remained obscure. Previous models have treated the wing as a flat plate, lacking any deformation, even though it is clear that the locust wing can twist and rotate along its length. Young et al. (p. 1549) validate a computational fluid dynamic model, using particle imaging velocimetry and smoke visualization of the flow around actual locusts, and use the model to investigate the effect of measured changes in wing shape during a stroke cycle. The complexity of insect wing venation directly affects the aerodynamics of flight via the intermediary of wing deformation.

  11. Anyone for d?

    The chemistry of amino acids comes in two chirally distinct flavors—so-called l- and d-enantiomers. By far the most commonly used form of amino acids in all kingdoms of life is the l-form. Now Lam et al. (p. 1552; see the Perspective by Blanke) present the unanticipated observation that diverse bacteria release large amounts of various d-amino acids into the environment in a population density–dependent fashion and that d-amino acids act as extracellular effectors that regulate the composition, structure, amount, and strength of peptidoglycan, the major stress-bearing component of the bacterial cell wall.

  12. Desperately Seeking Glucose

    Mutations in oncogenes and tumor suppressor genes allow cancer cells to outgrow their neighboring healthy cells. What microenvironmental conditions provide a selective growth advantage to these cells? Yun et al. (p. 1555, published online 6 August) identify low glucose availability as a microenvironmental factor driving the acquisition of KRAS oncogenic mutations that allow cancer cells to survive and grow. In genetically matched colorectal cancer cells that differed only in the mutational status of the KRAS oncogene, mutant cells selectively overexpressed glucose transporter-1 and exhibited enhanced glucose uptake and glycolysis. When cells with wild-type KRAS were placed in a low-glucose environment, very few cells survived but most of the survivors expressed high levels of glucose transporter-1, and a small percentage of the survivors had acquired new KRAS mutations. Thus, glucose deprivation may help to drive the acquisition of cell growth–promoting oncogenic mutations during tumor development.

  13. Tunable Metamaterials

    The electromagnetic response of metamaterials gives rise to exciting phenomena such as cloaking, negative refraction, and perfect lensing. Their response, however, tends to depend strongly on resonant effects, thereby limiting the application bandwidth. Driscoll et al. (p. 1518, published online 20 August) combine a split ring resonator array with the phase change material, VO2, to form a metamaterial in which the response can be tuned. The heat-induced phase change of VO2 from an insulator to a metal alters the response of split-ring resonator, and, because it displays a hysteresis, the device can retain a “memory” of the induced change. The results may lead to a flexible method for achieving metamaterials operating over a wide bandwidth and to novel switching applications.

  14. Limits to Invasion Predictions

    Using mathematical models linked to experiments on laboratory insect populations, Melbourne and Hastings (p. 1536) show that current models seriously underestimate variability in spatial spread. Genetic founder effects resulting from small population sizes are probably responsible for the surprising increase in variability and for increased uncertainty of ecological forecasts. Thus, even without exogenous sources of variability such as weather, fundamental uncertainties arise biologically from inherent differences among individuals and small population sizes.