A guest-free germanium clathrate

The challenges associated with synthesizing expanded semiconductor frameworks with cage-like crystal structures continue to be of interest. Filled low-density germanium and silicon framework structures have distinct properties that address important issues in thermoelectric phonon glass-electron crystals, superconductivity and the possibility of Kondo insulators. Interest in empty framework structures of silicon and germanium is motivated by their predicted wide optical bandgaps of the same magnitude as quantum dots and porous silicon, making them and their alloys promising materials for silicon-based optoelectronic devices. Although almost-empty Na(1-x)Si136 has already been reported, the synthesis of guest-free germanium clathrate has so far been unsuccessful. Here we report the high-yield synthesis and characteristics of germanium with the empty clathrate-II structure through the oxidation of Zintl anions in ionic liquids under ambient conditions. The approach demonstrates the potential of ionic liquids as media for the reactions of polar intermetallic phases.     

Proximity signal and shade avoidance differences between early and late successional trees.

Competitive interactions between plants determine the success of individuals and species. In developing forests, competition for light is the predominant factor. Shade tolerators acclimate photosynthetically to low light and are capable of long-term survival under the shade cast by others, whereas shade avoiders rapidly dominate gaps but are overtaken in due course by shade-tolerant, later successional species. Shade avoidance results from the phytochrome-mediated perception of far-red radiation (700-800 nm) scattered from the leaves of neighbours, provides early warning of shading, and induces developmental responses that, when successful, result in the overgrowth of those neighbours. Shade tolerators cast a deep shade, whereas less-tolerant species cast light shade, and saplings tend to have high survivorship in shade cast by conspecific adults, but high rates of mortality when shaded by more-tolerant species. Here we report a parallel relationship in which the shade-avoidance responses of three tree species are inversely proportional to proximity signals generated by those species. On this basis, early successional species generate small proximity signals but react strongly to them, whereas late successional species react weakly but generate strong signals.     

Remains of Homo erectus from Bouri, Middle Awash, Ethiopia

The genesis, evolution and fate of Homo erectus have been explored palaeontologically since the taxon's recognition in the late nineteenth century. Current debate is focused on whether early representatives from Kenya and Georgia should be classified as a separate ancestral species ('H. ergaster'), and whether H. erectus was an exclusively Asian species lineage that went extinct. Lack of resolution of these issues has obscured the place of H. erectus in human evolution. A hominid calvaria and postcranial remains recently recovered from the Dakanihylo Member of the Bouri Formation, Middle Awash, Ethiopia, bear directly on these issues. These approximately 1.0-million-year (Myr)-old Pleistocene sediments contain abundant early Acheulean stone tools and a diverse vertebrate fauna that indicates a predominantly savannah environment. Here we report that the 'Daka' calvaria's metric and morphological attributes centre it firmly within H. erectus. Daka's resemblance to Asian counterparts indicates that the early African and Eurasian fossil hominids represent demes of a widespread palaeospecies. Daka's anatomical intermediacy between earlier and later African fossils provides evidence of evolutionary change. Its temporal and geographic position indicates that African H. erectus was the ancestor of Homo sapiens.     

Signal recognition particle contains a 7S RNA essential for protein translocation across the endoplasmic reticulum

In addition to its previously characterized, six different polypeptide components, signal recognition protein--which functions in protein translocation across and integration into the endoplasmic reticulum membrane--contains a 7S RNA molecule. The RNA is closely identified with the small cytoplasmic 7SL RNA and is required for both structural and functional properties of signal recognition protein--which we therefore rename signal recognition particle.     

Records of exotic fishes from Idaho and Wyoming

One exotic poeciliid ( Xiphophorus helleri ) and two cichlids ( Cichlasoma nigrofasciatum and Tilapia mossambica ) are recorded as recently established in thermal springs and their outflows in southern Idaho. Misgurnus anguillicaudatus was collected and is considered as established in the Boise River system. Poecilia mexicana and juvenile hybrid tilapias are recorded from the Bruneau River at Bruneau Hot Springs, Idaho. A reproducing population of X. helleri was found in a spring within the boundaries of Grand Teton National Park, Wyoming. Poecilia reticulata , previously reported from one spring each in Idaho and Wyoming, is recorded from a second spring outflow in Idaho.