This Week in Science

Science  20 Jul 2012:
Vol. 337, Issue 6092, pp. 267
  1. It's the Oxygens


    Scanning tunneling microscopy of cuprate high-temperature superconductors has revealed surprising inhomogeneity of the energy scales known as the superconducting gap, pseudogap, and the critical temperature. Some of these effects have been correlated with chemical disorder of the materials caused by doping, but, because of technical limitations, only the dopants in a limited energy range have been imaged. Zeljkovic et al. (p. 320) extend this range to reveal the positions of the remaining oxygen defects in Bi2+ySr2-yCaCu2O8+x.

  2. The Primordial Soup

    Protons and neutrons were originally thought to be indivisible, but we now know that they have constituent parts—quarks. Quarks are bound together tightly through gluons and can only come apart under extreme conditions—conditions believed microseconds after the Big Bang to have formed a hot, dense “soup” of quarks and gluons, called the quark-gluon plasma (QGP). QGP can be made experimentally in heavy ion colliders, where extremely high temperatures are reached. Jacak and Müller (p. 310) review the progress in this field and its unexpected ties to cold atomic gases and string theory.

  3. Crater Core

    The high-northern latitudes of the Arctic have an important influence on climate and constitute a region with a unique array of complex feedbacks that make it difficult to understand the workings of its climate. Melles et al. (p. 315, published online 21 June) developed a 2.8-million-year record of Arctic climate, using a sediment core from a lake in northeastern Russia that was formed more than 3.5 million years ago by a meteorite impact. Pronounced glacial episodes began 2.6 million years ago but did not achieve orbital pacing for another 700,000 years.

  4. A Different Spin Transistor

    A typical transistor consists of a source and a drain; the current that makes it to the drain is controlled by applying voltage to the third terminal, called the gate. In spin-based electronics, where spin current is used instead of charge, the source and the drain are ferromagnetic materials connected by a narrow semiconducting channel. This design, however, suffers from low efficiency. Betthausen et al. (p. 324; see the Perspective by Žutić and Lee) combined homogeneous and helical magnetic fields to change the orientation of the spin on its way to the drain, preserving spin information over distances many times the spin mean free path. The transistor is “on” when the transport is adiabatic—i.e., slow enough for the spin to be able to adapt to the local magnetic field—and “off” otherwise.

  5. Magnetically Bound

    At the macroscopic scale associated with daily life on Earth, magnetic attraction can seem fairly strong—think of the great loads moved by magnetized cranes. Microscopically, however, the field strengths attainable by human construction act as just a small perturbation on the Coulombic forces that bind atoms into molecules. Lange et al. (p. 327; see the Perspective by Schmelcher) used theoretical calculations to examine atomic behavior in environments very close to certain stars, where magnetic fields exceed those attainable on Earth by factors of 10,000 or more. The results predict a distinct type of chemical bonding in which spin-parallel hydrogen atoms or ground-state helium atoms are drawn together into pairs.

  6. Who Influences Who?

    A goal in social science is how to assess people's influence over one. Aral and Walker (p. 337, published online 21 June) describe a generalized method for identifying influential and susceptible members of social networks based on large-scale in vivo randomized experimentation. The method was used to estimate peer effects in consumer demand for a commercial Facebook application in a representative sample of 12 million Facebook users. Older users were more influential than younger users, women were more influential over men than men over women, and married individuals were the least susceptible to influence in the decision to adopt the product studied.

  7. Sex Chromosome Evolution

    The fly genus Drosophilia has repeatedly generated evolutionarily new sex chromosomes. To understand the changes shaping the X and Y chromosomes, Zhou and Bachtrog (p. 341), sequenced the genome of D. miranda, which formed neo-X and neo-Y chromosomes approximately 1 million years ago. The data illuminate the ongoing conflict between selection for male and female function on the sex chromosomes and show that Y chromosome evolution is characterized both by a loss of gene function and selection for male-specific adaptations in genes beneficial to male functions.

  8. More than a Dash of Sea Salt


    The cycling of major elements, such as sulfur, in the oceans depends on a number of processes, from bacterial respiration of organic matter to venting of gases from hydrothermal vents on the seafloor. Over geologic time, sediment deposited on the seafloor preserves chemical records of major changes in sulfur cycling and seawater chemistry (see the Perspective by Hurtgen). Halevy et al. (p. 331) observed swings in sulfur isotopes in a stratigraphic database covering North America and the Caribbean that, when modeled, corresponded to variable evaporite preservation and high turnover of sedimentary pyrite. Wortmann and Paytan (p. 334) modeled the two most recent major swings in sedimentary sulfur isotopes over the last 130 million years and suggest that short periods of rapid fluxes in sulfur cycling were at least in part caused by the growth and dissolution of evaporite deposits.

  9. Redox Status Incites Gametogenesis

    Germ cells differ from somatic cells in their chromosomal complement, being haploid rather than diploid. In animals, the germ cells are generally produced by a separate lineage set aside early in development. Plants, however, lack a reserved germ cell lineage. Kelliher and Walbot (p. 345; see the Perspective by Whipple) now show that, in maize, the key signal for germ cell production is hypoxia, which triggers differentiation of anther germ cells from a generalized field of progenitors. The specializing germ cells then induce differentiation of supportive somatic cells.

  10. Diversity of Interactions

    The diversity in interactions that occur between different species—such as predation, competition, and mutualism—is a fundamental feature of natural ecological systems. Using a theoretical model, Mougi and Kondoh (p. 349; see the Perspective by Boyd) show that the diversity of ecological relationship helps a biological community to be stable and thus may be key to the maintenance of biodiversity itself.

  11. Lysosomal Amino Acid Transporter


    Cystinosis is characterized by intralysosomal accumulation of free cystine, which results in age-dependent problems in the kidney, muscle, retina, and central nervous system. The disease-causing gene encodes a lysosomal cystine transporter. The most effective therapeutic agent for cystinosis, cysteamine, depletes lysosomal free cystine by converting it to cysteine and the mixed disulfide cysteine-cysteamine, which can then be exported from lysosomes as a lysine analog through a putative lysine/cationic amino acid transporter. Using an unbiased genetic screen for Caenorhabditis elegans mutants with increased accumulation of apoptotic cells or autophagosomes, Liu et al. (p. 351) now reveal the molecular identity of a lysosomal lysine/arginine transporter that plays a role in maintaining lysosome function and amino acid homeostasis and that can explain how cysteamine alleviates a lysosomal storage disease.

  12. Never Let Me Go

    Kinetochores are the structures within chromosomes that interact with the microtubules of the mitotic spindle during mitosis. By measuring the deformation of individual kinetochores in live mammalian cells, Dumont et al. (p. 355, published online 21 June) asked, how do kinetochores harness the free energy of microtubule depolymerization without losing grip of microtubules? Kinetochores contacted microtubules using two distinct mechanical interfaces: an active, force-generating interface near the microtubule tip, and a passive, frictional interface at least 20 nanometers away along the microtubule lattice. The separate active and passive interfaces allowed for intermittent force generation and persistent microtubule attachment—both required for accurate chromosome segregation.

  13. Born to Stay Together

    For as many neurons as there are in the brain, there are many more astrocytes. These backstage workers perform a variety of functions, such as sustaining the blood-brain barrier and providing a stabilized environment for neurons. Diversity of astrocyte function is reflected in different molecular expression profiles. Tsai et al. (p. 358, published online 28 June) selectively labeled astrocytes that originated from different domains of the mouse spinal cord and found that not all astrocytes are created equal: Neighborhoods of astrocytes were defined by shared birthplaces.

  14. Size Matters Less

    X-ray crystallography is a central research tool for uncovering the structures of proteins and other macromolecules. However, its applicability typically requires growth of large crystals, in part because a sufficient number of molecules must be present in the lattice for the sample to withstand x-ray–induced damage. Boutet et al. (p. 362, published online 31 May) now demonstrate that the intense x-ray pulses emitted by a free-electron laser source can yield data in few enough exposures to uncover the high-resolution structure of microcrystals.