Letters in 2009

Age and compositional data for the newly discovered, paired and differentiated meteorites Graves Nunatak (GRA) 06128 and GRA 06129 are reported. These meteorites are feldspar-rich, with andesite bulk compositions. Their age of 4.52 Gyr demonstrates formation early in Solar System history, and their composition is most consistent with an origin as partial melts from a volatile-rich, oxidized asteroid.

Diatoms constitute a vital part of the oceanic ecosystem. As they are dependent on silica, they are thought to have risen to prominence alongside grasslands in the Miocene epoch, when the first large-scale weathering of grassland-derived silica took place. A new analysis of an ocean-bed database contradicts that scenario; it is shown that diatom diversity peaked at the Eocene–Oligocene boundary, long before grasslands became prominent.

The magnetic fields of Earth and Jupiter, along with those of rapidly rotating, low-mass stars, are generated by convection-driven dynamos that may operate similarly, although the field strengths vary. The critical factor unifying field generation in such different objects, while still causing a large variation, has been unclear. This paper reports an extension of a scaling law derived from geodynamo models to rapidly rotating stars. The unifying principle is that the energy flux available for generating the magnetic field sets the field strength.

The spectral location of terahertz radiation, between optical and microwave frequencies, has hindered the development of compact semiconductor terahertz sources. One approach is to make use of photonic-crystal structures, which allows surface emission of radiation so that the spectral and spatial modes can be simultaneously engineered. To fabricate electrically-driven devices, it is necessary to define boundary structures around the active, pumped area and this paper now demonstrates a general technique to implement such boundaries.

Aromatase cytochrome P450 is the only enzyme in vertebrates known to catalyse the biosynthesis of all oestrogens from androgens. This paper solves the X-ray crystal structure of the first natural mammalian, full-length P450, human placental aromatase.

This paper reports a novel link between calcium signalling and salicylic-acid-mediated responses (both important for plant immunity). AtSR1, a calcium/calmodulin-binding transcription factor, is shown to be a negative regulator of plant immunity by suppressing biosynthesis of salicylic acid.

Quantum measurements are subject to an uncertainty that is usually distributed equally between pairs of complementary properties (such as position and momentum). However, a technique known as 'squeezing' can be used to reduce the uncertainty of one desired property at the expense of increasing that of the other. Squeezing may have a critical role in high precision applications such as atomic clocks and optical communications. This paper demonstrates the ultimate squeezing limit for the polarization of a composite optical system.

In human societies, altruistic behaviour can evolve because those who fail to co-operate are lumbered with a bad reputation. This study explores the circumstances under which punishment is favoured using a game theory model in which all individuals observe the interactions between others and assess their reputation under various social norms. It is shown that punishment is only a successful strategy under a narrow set of parameters, including the relative costs of punishment and cooperation, the reliability of reputations and the spread of gossip.

This study models converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the Cascadia continental margin to its intersection with the forearc mantle. The observations suggest that water is pervasively present in fluid form at high pore pressures, indicating that the megathrust is a low-permeability boundary. These results may hold important implications for our understanding of seismogenesis, subduction-zone structure and the mechanism of episodic tremor and slip.

Self-gravity plays a decisive role in the final stages of star formation, where dense cores inside molecular clouds collapse to form star-plus-disk systems. But the role of self-gravity at earlier times is unclear. This paper reports a dendogram analysis that reveals that self-gravity plays a significant role over the full range of scales traced by ¹³CO observations in L1448, but not everywhere in the observed region.

Lung carcinoma cells were found to secrete the extracellular matrix proteoglycan versican. Versican directly activates the TLR2 receptor complex on macrophages, which in turn promotes tumour metastasis by producing TNF-?. Thus cancer cells utilize signalling pathways of the innate immune system to support metastatic spread.

This study presents the structure of gp23-chaperonin complexes showing gp23 encapsulated in the folding chamber. The folding chamber is distorted to enclose a large substrate, and this is the first study that visualizes of a newly folded physiological substrate trapped inside the folding chamber of GroEL.

This paper describes the combination of near-field optical forces (such as those used in optical traps) to confine nanoscopic matter inside a liquid core-slot waveguide and photon scattering forces to transport them. The waveguide overcomes the diffraction limits of conventional optical trapping systems to manipulate objects down to tens of nanometres in scale. As the waveguide is linear, it can also manipulate extended biomolecules demonstrated by trapping and transporting DNA molecules.