This Week in Science

Science  13 Jan 2012:
Vol. 335, Issue 6065, pp. 144
  1. Structured Memories


    High-density magnetic memory is generally produced by using ferromagnetic materials. As the density increases and the memory elements become closer together, stray fields can result in cross-talk and a corruption of the stored information. Antiferromagetic structures, however, are expected to be relatively insensitive to magnetic fields and so should, in principle, allow the elements to be packed in even closer. Loth et al. (p. 196) carried out low-temperature experiments to construct antiferromagnetic structures atom by atom. Electrical switching of the magnetic states was observed, and data could be robustly stored on the structure for several hours, albeit at low temperature.

  2. Why Wait?


    Tropospheric ozone can be dangerous to human health, can be harmful to vegetation, and is a major contributor to climate warming. Black carbon also has significant negative effects on health and air quality and causes warming of the atmosphere. Shindell et al. (p. 183) present results of an analysis of emissions, atmospheric processes, and impacts for each of these pollutants. Seven measures were identified that, if rapidly implemented, would significantly reduce global warming over the next 50 years, with the potential to prevent millions of deaths worldwide from outdoor air pollution. Furthermore, some crop yields could be improved by decreasing agricultural damage. Most of the measures thus appear to have economic benefits well above the cost of their implementation.

  3. TACE Trafficking

    The cytokine tumor necrosis factor (TNF) is a major driver of inflammation and contributes to the immune pathology seen in a variety of diseases, including inflammatory bowel disease, rheumatoid arthritis, and sepsis. Soluble TNF is produced by cleavage of its ectodomain by the ADAM family metalloprotease, TNFα-converting enzyme (TACE). However, the molecular regulation of TACE is not understood (see the Perspective by Lichtenthaler). Adrain et al. (p. 225) and McIlwain et al. (p. 229) now show that the rhomboid family member iRhom2 interacts with TACE in macrophages and is required for its proper intracellular trafficking and activation. In the absence of iRhom2, TACE was not released from the endoplasmic reticulum, and active protease did not reach the cell surface. Because of an inability to produce TNF, iRhom2-deficient mice were more resistant to lipopolysaccharide-induced septic shock but could not adequately control a Listeria monocytogenes infection.

  4. Binary Revelation

    Binary star systems that contain a neutron star or a black hole are expected to emit gamma rays. These gamma-ray binaries are a rare class of objects, which are also expected to emit x-rays. Indeed, several such systems were initially detected through their x-ray emission. The Fermi LAT Collaboration (p. 189; see the Perspective by Mirabel) reports the detection of a gamma-ray binary that was previously unknown as an x-ray source. Follow-up observations reveal that the system is also a source of x-rays and that the companion star is a class O star, a type that is very hot and very luminous.

  5. Breaking Up the Indivisible

    The famous Millikan oil drop experiment demonstrated that electric charge is quantized and cannot be divided into parts smaller than that of an electron. Decades later, the fractional quantum Hall effect was discovered that could only be explained through the existence of quasi-particles of fractional charge. Now, Isakov et al. (p. 193) numerically demonstrate the existence of an even more exotic object, a fractionalized quantum critical point (QCP), in the so-called Kagome lattice of bosons. Quantum Monte Carlo simulations were used to measure the critical exponents and revealed the fractionalization by comparison with a QCP of real bosons.

  6. Dispersal in 3D

    The fabrication of composites containing small proportions of nanoparticles is limited by the ability to disperse the particles uniformly in all three dimensions. Erb et al. (p. 199; see the Perspective by Fratzl) describe a process for creating nanoparticle composites in which a magnetic field is used to align the nanoparticles. Surprisingly, the magnetic alignment of iron-oxide functionalized nanorods and discs was enabled using very small magnetic fields and low-volume fractions of magnetic nanoparticles, which allowed control of the orientation of the nanorods and discs three-dimensionally.

  7. Fluoride Riboswitch

    Riboswitches are found in prokaryote and eukaryote messenger RNAs (mRNAs), where they regulate expression of the linked mRNA through ligand binding and conformational change. Baker et al. (p. 233, published online 22 December) analyzed the binding properties of the “crcB motif” found in the noncoding RNA at the 5′ end of a diverse collection of prokaryotic genes. A crcB motif from Pseudomonas syringae was capable of selectively sensing the very small and highly charged fluoride ion. Some of the crcB and eriC genes associated with the fluoride riboswitch showed evidence of being fluoride transporters. The bacterium Methylobacterium extorquens DM4, which can use halogenated hydrocarbons as an energy source, was found to encode at least 10 fluoride riboswitches in its genome.

  8. Criegee Sighting

    Standard mechanistic models for the reaction of ozone with unsaturated hydrocarbons implicate a transient carbonyl oxide compound, termed the “Criegee intermediate,” which has largely eluded detection. Welz et al. (p. 204; see the Perspective by Marston) have now detected the compound by using mass spectrometry, following the low-pressure photolytic reaction of oxygen with diiodomethane, and measured its decay kinetics in the presence of nitric oxide, nitrogen dioxide, and sulfur dioxide. Reaction rates were higher than expected, suggesting that the intermediate may play a more prominent role in atmospheric chemistry than previously assumed.

  9. Riding the Wind

    Pelagic seabirds rely on wind to move between breeding and foraging areas, and albatrosses—which travel thousands of kilometers over sea—are well-known wind riders. Weimerskirch et al. (p. 211; see the cover) monitored foraging and reproduction in wandering albatrosses over 40 years and found that a change in wind patterns, probably induced by climate change, had a notable impact on important life history traits. Greater wind strength increased the rate of travel for the birds and shortened their foraging trips. These shorter trips improved breeding success and resulted in an increase in adult mass. Thus, over the past half-century, environmental changes have improved conditions for the albatross.

  10. Parasite Invasion Strategy

    Exocytosis is essential to the lytic cycle of apicomplexan parasites and is required for the pathogenesis of toxoplasmosis and malaria. DOC2 proteins recruit the membrane fusion machinery required for exocytosis in a Ca2+-dependent fashion. Farrell et al. (p. 218) describe the phenotype of a Toxoplasma gondii conditional mutant impaired in host cell invasion and egress. The phenotype was explained by a defect in secretion of the micronemes, an apicomplexan-specific organelle that contains adhesion proteins. A T. gondii Doc2 gene was identified, by whole-genome sequencing, to be involved in the secretion defect, and a conditional allele of the orthologous gene engineered into the malaria parasite, Plasmodium falciparum, also caused defects in microneme secretion.

  11. That Sweet Sensation


    Photosynthesis in the leaf generates sucrose that must be transported via the phloem to other parts of the plant in order, for example, to be incorporated into harvestable produce. Studying Arabidopsis and rice, Chen et al. (p. 207, published online 8 December; see the Perspective by Braun) identified the SWEET family of sucrose efflux transporters that are responsible for carrying sucrose out of the leaf cells. When the transporters were disabled, sucrose accumulated in the leaves. Functioning properly, the SWEET transporters carry sucrose across the plasma membrane and other transporters move it further into the phloem.

  12. Doing the Side Step

    The molecular motor, dynein, contains two ring domains responsible for its movement along the microtubule. However, how the rings move relative to each other during processive motility and whether dynein processivity requires interhead coordination are unclear. To directly observe how dynein “walks” along microtubules, DeWitt et al. (p. 221, published online 8 December) performed advanced fluorescence-imaging studies to follow both motor domains of a single dynein motor at nanometer resolution. The data suggest that the two heads do not cooperate during movement, which suggests a fundamentally different mechanism of motility from that observed for other microtubule-based motors.

  13. Long-Lasting Pain Killers

    Opioids are among the most widely used and extensively studied drugs in the world. A continuous application of relatively low opioid doses is thought to be necessary to maintain synaptic depression in pain pathways. Drdla-Schutting et al. (p. 235) found that a single opioid application could produce lasting reversal of synaptic long-term potentiation in pain pathways. Chronic pain is often associated with synaptic potentiation in nociceptive pathways. A brief, high-dose application of opioids depotentiated long-term potentiation in spinal pain pathways. The same dose also reversed hyperalgesia in behaving animals. Thus, opioids not only attenuate pain but also may eradicate a significant cause for chronic pain.

  14. Global Ecosystem Analysis

    The relationship between species richness and the functional properties of their ecosystems has often been studied at small scales in experimental plots. Maestre et al. (p. 214; see the Perspective by Midgley) performed field measurements at 224 dryland sites from six continents and assessed 14 ecosystem functions related to carbon, nitrogen, and phosphorus cycling. Positive relationships were observed between perennial plant species richness and ecosystem functionality. The relative importance of biodiversity was found to be as large as, or larger than, many key abiotic variables. Thus, preservation of plant biodiversity is important to buffer negative effects of climate change and desertification in drylands, which collectively cover 41% of Earth's land surface and support over 38% of the human population.