This Week in Science

Science  27 Sep 2013:
Vol. 341, Issue 6153, pp. 1429
  1. The Overeating Connection


    Obesity has become a major global health problem. Working in mice, Jennings et al. (p. 1517) identified an important brain circuit within the lateral hypothalamus that modulates food intake. The findings reveal the neuronal connections that drive the consumption of highly palatable food even when energy needs are satisfied. Inhibition of this circuit suppressed feeding.

  2. Observing Earth's Magnetotail

    Magnetic reconnection is a process that converts magnetic energy to kinetic energy, thermal energy, and particle acceleration. The process operates in Earth's magnetotail, the narrow and elongated region of the magnetosphere that extends away from the Sun, and is believed to power Earth's auroras and other space physics phenomena. Angelopoulos et al. (p. 1478) present an observational study of energy conversion in the magnetotail and the associated transport of magnetic flux during a geomagnetic substorm.

  3. Shape Memory Ceramics

    Shape memory materials convert heat into strain and vice versa. These materials are often made from metal alloys, which can generate large stresses with small shape changes. Ceramics have certain characteristics that underlie shape memory transformation, but generally crack under strain. Lai et al. (p. 1505; see the Perspective by Faber) introduce a modified ceramic structure with limited crystal grains that can withstand comparable cyclic strains to shape memory metals.

  4. Diurnal Immunology

    Like most organ systems in the body, several components of the immune system appear to be regulated in a diurnal manner. However, the cell populations affected, the underlying molecular mechanisms controlling these processes, and the functional consequences of such regulation are poorly understood. Now, Nguyen et al. (1483, published online 22 August; see the Perspective by Druzd and Scheiermann) have found that trafficking of monocytes to sites of inflammation is regulated in a diurnal manner in mice. Mice harboring a myeloid cell-specific deletion in the clock protein, BMAL1, showed reduced fitness in response to both acute and chronic inflammation.

  5. Half-Massless


    Certain materials, such as topological crystalline insulators (TCIs), host robust surface states that have a Dirac (graphene-like) dispersion associated with massless carriers; the breaking of protective symmetry within such materials should cause the carriers to acquire mass. Okada et al. (p. 1496, published online 29 August) used scanning tunneling microscopy to map out the energies of the electronic levels of the TCI Pb1-xSnxSe as a function of the strength of an external magnetic field. The massless Dirac fermions coexisted with massive ones, presumably as a consequence of a distortion of the crystalline structure affecting only one of the two mirror symmetries.

  6. Making the Grain

    Most metals contain a large number of ordered crystalline regions that are separated by disordered grain boundaries. If the material is annealed at elevated temperatures, the larger grains will grow uniformly at the expense of the smaller ones. This process slows down over time, making it hard to create very large grains. Abnormal grain growth, in which a few of the crystalline regions grow much faster and larger than the others, can occur if the material is put through a complex annealing process involving straining of the samples. Omori et al. (p. 1500; see the Perspective by Taleff and Pedrazas) find that a much simpler and shorter annealing process can trigger abnormal grain growth in copper-based shape-memory alloys. Thermal cycling between a high-temperature single-phase region and a lower-temperature two-phase region generated dislocations at low temperatures and grain growth on heating. Because this method does not require external straining of the sample, it is not limited to thin sheets or wires.

  7. Futile Forest Fragments

    Most of the planet's terrestrial biodiversity is found in tropical forests, but much of this critical habitat now persists as fragmented patches surrounded by agriculture. Smaller forest patches sustain fewer species than larger patches or contiguous forest. However, the numbers of species that will disappear from a forest fragment—and the rate of species loss—remain poorly understood. Gibson et al. (p. 1508) surveyed islands in a reservoir in Thailand to measure the rate of loss of small mammals from small forest fragments. Collapse of the entire native community (up to 12 species) from 16 forest fragments was observed after 25 years of isolation. Thus, small forest fragments hold little value for mammalian biodiversity, and conservation efforts should instead focus on the preservation of large forest expanses.

  8. Sourcing Antibiotic Resistance

    It is widely assumed that antibiotic resistance in farm animals contributes in a major way to antibiotic resistance in humans. Mather et al. (1514, published online 12 September; see the Perspective by Woolhouse and Ward) analyzed hundreds of genome sequences from Salmonella isolates collected from both livestock and patients in Scotland between 1990 and 2004. The relative contributions of animal-derived and human-derived sources of infection were quantified and the phylogenetic diversity of resistance profiles was matched with bacterial phylogenies. The results suggest that most human infections are caught from other humans rather than from livestock and that humans harbor a greater diversity of antibiotic resistance.

  9. Finally Out

    Last summer, it was not clear if the Voyager 1 spacecraft had finally crossed the heliopause—the boundary between the heliosphere and interstellar space. Gurnett et al. (p. 1489, published online 12 September) present results from the Plasma Wave instrument on Voyager 1 that provide evidence that the spacecraft was in the interstellar plasma during two periods, October to November 2012 and April to May 2013, and very likely in the interstellar plasma continuously since the series of boundary crossings that occurred in July to August 2012.

  10. Assessing Brown Dwarfs

    The last 2 years have seen the detection of dozens of very cold brown dwarfs. At temperatures around 300 to 500 kelvin, brown dwarfs are expected to have masses comparable to those of gas-giant planets, but because their distances are unknown, it has not been possible to estimate their masses. Dupuy and Kraus (p. 1492, published online 5 September) used data from the Spitzer Space Telescope to measure accurate distances to very cold brown dwarfs, which allowed them to determine the dwarfs' luminosities, temperatures, and masses. The results strengthen the connection between the coolest brown dwarfs and gas-giant exoplanets.

  11. Keeping Cells Cooperating


    Multicellular organisms have certain advantages over those that are single-celled. To evolve, however, they must surmount a persistent challenge: ensuring that their constituent cells cooperate with one another rather than “cheat” or compete with each other for resources. Dejosez et al. (p. 1511, published online 12 September) performed a genome-wide screen in induced pluripotent stem cells to search for genes that promote cell cooperation. A number of genes were identified of which knockdown allowed competitive behavior to dominate. These genes formed a network centered on p53, topoisomerase 1, and olfactory receptors. Thus, a genetic mechanism may promote cooperation in the developing embryo.

  12. Drugs, Dopamine, and Disinhibition

    Drugs often change the neuronal circuitry in the brain and thereby cause a long-lasting change in behavior. Using a wide range of in vivo and in vitro techniques in mice, Bocklisch et al. (p. 1521) observed that cocaine profoundly altered dopamine neuron function and that drug-evoked synaptic plasticity in a specific set of neurons represents a crucial step in circuit remodeling.

  13. Toward Titanium Carbide Batteries

    Many batteries and capacitors make use of lithium intercalation as a means of storing and transporting charge. Lithium is commonly used because it offers the best energy density, but also because there are difficulties in storing larger cations without disrupting the crystal structure of the host. Lukatskaya et al. (p. 1500 developed a series of MX compounds, where M represents a transition metal and X is carbon or nitrogen.The compound Ti3C2 forms a two dimensional layered structure, which is capable of accommodating a wide range of cations, including multivalent ones, either spontaneously or electrochemically