Climate and Conflict
Knowledge silos can hinder attempts to explore questions of interest across many disciplines. Hsiang et al. (p. 1235367, published online 1 August) provide a meta-analysis of data from disciplines as disparate as archaeology and psychology to examine the relation between climate and conflict. Overall, warmer temperatures or extremes of rainfall can be causally associated with changes in interpersonal violence and in civil war.
Tick, Tick, Tick…
Many aspects of everyday life from communication to navigation rely on the precise ticking of the microwave transitions of the atoms in atomic clocks. Optical transitions occur at much higher frequency and so offer the opportunity to reduce the scale of the ticks even more. Hinkley et al. (p. 1215, published online 22 August; see the Perspective by Margolis) compare the ticking of two optical clocks and report an instability near the 10−18 level. Such performance will improve tests of general relativity and pave the way for a redefinition of the second.
Sticking with DNA
One strategy for creating superlattices from nanoparticles is to coat the particles with DNA strands that have sticky ends that can be exploited to control the assembly of the lattice. This method can create binary lattices, but now Macfarlane et al. (p. 1222, published online 22 August) have succeeded in inserting a third type of nanoparticle into a predetermined site by tuning the strength of the relative DNA binding interactions.
Small organic molecules have emerged as catalysts as versatile as transition metal complexes. However, industrial application of such organocatalysts has been hampered by technical challenges. Now Lee et al. (p. 1225) have succeeded in tethering a diverse set of high-performance organocatalysts to nylon fabric through ultraviolet photochemistry, making them easy to isolate and reuse.
While the character of slow earthquakes has been approximated for some time, precise slip histories and the underlying mechanisms have remained elusive. Kaproth and Marone (p. 1229; published online 15 August) have made laboratory observations of repetitive, slow stick-slip in fault-zone materials and developed a mechanical explanation for how earthquake-like dynamic slip nucleation could start and then arrest so as to produce slow slip. As preseismic slip is a precursor to rupture, temporal variations in elastic wave speeds should be monitored in regions of high seismic hazard.
Many small insects are impressive jumpers, but large leaps and small bodies pose biomechanical challenges. Burrows and Sutton (p. 1254) show that the nymphal planthopper Issus has interlocking gears on their hindleg trochanters that act together to cock the legs synchronously before triggering forward jumps. At the final molt, the gears are swapped for a high-performance friction-based mechanism because the risk of breaking a gear is high, the options for repair during molting are gone, and, moreover, the animal is bigger and stronger.
Early responses of species to climate change seemed to predict a general poleward response (or upward in mountains and downward in the ocean). Pinsky et al. (p. 1239) test an alternative hypothesis that relates more to the nature of climate change than to changes in temperature. Using nearly 50 years of coastal survey data on >350 marine taxa, they found that climate velocity was a much better predictor of patterns of change than individual species' characteristics or life histories. The findings suggest that responses to climate change largely track changes in local conditions.
Move Over, TLR4
The innate immune system senses bacterial lipopolysaccharide (LPS) through Toll-like receptor 4 (TLR4) (see the Perspective by Kagan). However, Kayagaki et al. (p 1246, published online 25 July) and Hagar et al. (p. 1250) report that the hexa-acyl lipid A component of LPS from Gram-negative bacteria is able to access the cytoplasm and activate caspase-11 to signal immune responses independently of TLR4. Mice that lack caspase-11 are resistant to LPS-induced lethality, even in the presence of TLR4.
From Soil to Sky
Trace gases emitted either through the activity of microbial communities or from abiotic reactions in the soil influence atmospheric chemistry. In laboratory column experiments using several soil types, Oswald et al. (p. 1233) showed that soils from arid regions and farmlands can produce substantial quantities of nitric oxide (NO) and nitrous acid (HONO). Ammonia-oxidizing bacteria are the primary source of HONO at comparable levels to NO, thus serving as an important source of reactive nitrogen to the atmosphere.
Ensuring the light-weight and high-strength properties of carbon-fiber composite materials is costly. Cheung and Gershenfeld (p. 1219, published online 15 August; see the Perspective by Schaedler et al.) have mass-produced cross-sectional parts that can be assembled into strong, ultralight lattices. Carbon-fiber composites are sliced into cross-shaped pieces that can be independently tested and reliably assembled into rigid and reversible cuboctahedral lattices.
How, exactly, does warm ocean water erode an ice shelf? In a field study of an ice shelf at Pine Island, Antarctica, Stanton et al. (p. 1236) collected data from radar, seismic surveys, and oceanographic sensors inserted in holes bored through the ice shelf. The results show that localized, intensive melting occurs in a complex network of discreet channels that are formed on the underside of the shelf. This pattern of melting may limit the absolute rate of ice-shelf mass loss.
Quantum many-systems, such superfluids, are difficult to study in equilibrium, and thus understanding their dynamics poses a particular challenge. When the strength of interactions was suddenly changed in a two-dimensional gas of cesium atoms, Hung et al. (p. 1213, published online 1 August; see the Perspective by Schmiedmayer and Berges) observed oscillations in the time and space domains analogous to the peaks in the spectrum of the cosmic microwave background.
At a Stretch
Insect flight muscles are operationally similar to vertebrate skeletal muscles in many ways; however, they are specialized for high-speed, small amplitude oscillations and are activated not by the release and re-uptake of calcium, but rather through stretch-activation. Iwamoto and Yagi (p. 1243, published online 22 August) use a pair of ultrafast cameras to record diffraction patterns and wing beats in the flight muscles of bumblebees and find that stretch activation is a result of myosin and actin dynamics.