Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode

Seafloor spreading centres show a regular along-axis segmentation thought to be produced by a segmented magma supply in the passively upwelling mantle. On the other hand, continental rifts are segmented by large offset normal faults, and many lack magmatism. It is unclear how, when and where the ubiquitous segmented melt zones are emplaced during the continental rupture process. Between 14 September and 4 October 2005, 163 earthquakes (magnitudes greater than 3.9) and a volcanic eruption occurred within the approximately 60-km-long Dabbahu magmatic segment of the Afar rift, a nascent seafloor spreading centre in stretched continental lithosphere. Here we present a three-dimensional deformation field for the Dabbahu rifting episode derived from satellite radar data, which shows that the entire segment ruptured, making it the largest to have occurred on land in the era of satellite geodesy. Simple elastic modelling shows that the magmatic segment opened by up to 8 m, yet seismic rupture can account for only 8 per cent of the observed deformation. Magma was injected along a dyke between depths of 2 and 9 km, corresponding to a total intrusion volume of approximately 2.5 km3. Much of the magma appears to have originated from shallow chambers beneath Dabbahu and Gabho volcanoes at the northern end of the segment, where an explosive fissural eruption occurred on 26 September 2005. Although comparable in magnitude to the ten year (1975-84) Krafla events in Iceland, seismic data suggest that most of the Dabbahu dyke intrusion occurred in less than a week. Thus, magma intrusion via dyking, rather than segmented normal faulting, maintains and probably initiated the along-axis segmentation along this sector of the Nubia-Arabia plate boundary.     

Lithium isotope evidence for subduction-enriched mantle in the source of mid-ocean-ridge basalts

'Recycled' crustal materials, returned from the Earth's surface to the mantle by subduction, have long been invoked to explain compositional heterogeneity in the upper mantle. Yet increasingly, problems have been noted with this model. The debate can be definitively addressed using stable isotope ratios, which should only significantly vary in primitive, mantle-derived materials as a consequence of recycling. Here we present data showing a notable range in lithium isotope ratios in basalts from the East Pacific Rise, which correlate with traditional indices of mantle heterogeneity (for example, 143Nd/144Nd ratios). Such co-variations of stable and radiogenic isotopes in melts from a normal ridge segment provide critical evidence for the importance of recycled material in generating chemical heterogeneity in the upper mantle. Contrary to many models, however, the elevated lithium isotope ratios of the 'enriched' East Pacific Rise lavas imply that subducted ocean crust is not the agent of enrichment. Instead, we suggest that fluid-modified mantle, which is enriched during residency in a subduction zone, is mixed back into the upper mantle to cause compositional variability.     

iASPP oncoprotein is a key inhibitor of p53 conserved from worm to human

We have previously shown that ASPP1 and ASPP2 are specific activators of p53; one mechanism by which wild-type p53 is tolerated in human breast carcinomas is through loss of ASPP activity. We have further shown that 53BP2, which corresponds to a C-terminal fragment of ASPP2, acts as a dominant negative inhibitor of p53 (ref. 1). Hence, an inhibitory form of ASPP resembling 53BP2 could allow cells to bypass the tumor-suppressor functions of p53 and the ASPP proteins. Here, we characterize such a protein, iASPP (inhibitory member of the ASPP family), encoded by PPP1R13L in humans and ape-1 in Caenorhabditis elegans. iASPP is an evolutionarily conserved inhibitor of p53; inhibition of iASPP by RNA-mediated interference or antisense RNA in C. elegans or human cells, respectively, induces p53-dependent apoptosis. Moreover, iASPP is an oncoprotein that cooperates with Ras, E1A and E7, but not mutant p53, to transform cells in vitro. Increased expression of iASPP also confers resistance to ultraviolet radiation and to cisplatin-induced apoptosis. iASPP expression is upregulated in human breast carcinomas expressing wild-type p53 and normal levels of ASPP. Inhibition of iASPP could provide an important new strategy for treating tumors expressing wild-type p53.     

Observation of rare-earth segregation in silicon nitride ceramics at subnanometre dimensions

Silicon nitride (Si3N4) ceramics are used in numerous applications because of their superior mechanical properties. Their intrinsically brittle nature is a critical issue, but can be overcome by introducing whisker-like microstructural features. However, the formation of such anisotropic grains is very sensitive to the type of cations used as the sintering additives. Understanding the origin of dopant effects, central to the design of high-performance Si3N4 ceramics, has been sought for many years. Here we show direct images of dopant atoms (La) within the nanometre-scale intergranular amorphous films typically found at grain boundaries, using aberration corrected Z-contrast scanning transmission electron microscopy. It is clearly shown that the La atoms preferentially segregate to the amorphous/crystal interfaces. First-principles calculations confirm the strong preference of La for the crystalline surfaces, which is essential for forming elongated grains and a toughened microstructure. Whereas principles of micrometre-scale structural design are currently used to improve the mechanical properties of ceramics, this work represents a step towards the atomic-level structural engineering required for the next generation of ceramics.     

UK pharmaceuticals: a matter of Life

A British anti-abortion organization, Life, has challenged the legality of an abortion clinic's prescribing of post-coital hormone treatment (PCHT), the so-called "morning-after pill." Life contends that, contrary to its classification by the Department of Health and Social Security, PCHT is an abortifacient rather than a contraceptive. Even if Life wins the case, successful prosecution of the abortion clinic appears unlikely because British law would require proof of intention to procure miscarriage.     

Litter decomposition by arthropods in undisturbed and intensively managed mountain brush habitats

The population dynamics and decomposition activities of litter arthropods in an unmanaged sagehrush/bitterbrush habitat in southeastern Wyoming were assessed in 1986. The effects of sagebrush/bitterbrush management practices on litter arthropod communities and the role of these communities in decomposition were also assessed. Insecticide applications were used to selectively exclude arthropods in order to determine the ecological impact of these detritivores. Application of a herbicide, 2,4-D, was associated with increased arthropod populations for 30 days following treatment. Mowing increased arthropod densities at two different times, 10-30 days and 50 days post treatment, perhaps as a result of functional and numerical responses by litter arthropods. Elimination of arthropods from otherwise undisturbed shrub habitats by the use of broad-spectrum insecticides reduced the rate of litter decomposition during the growing season, indicating that these organisms play an important role in decomposition and nutrient cycling.     

Preliminary mammal survey of Fossil Butte National Monument, Wyoming

The mammalian community of Fossil Butte National Monument, Wyoming, consisted of at least 45 species. Snap trap sampling of the smaller species combined with sight and sign observations of the larger species formed the basis of this preliminary survey in the summers of 1974 and 1975. Snap - trapping samples (2880 trap days) yielded 44 least chipmunks and 89 deer mice. The distribution of all species was characterized by plant community occupancy. Heavy domestic livestock use of the communities nearest water has resulted in severe alteration in community structure; this has probably affected the distribution and abundance of at least some of the smaller mammals.