A larval Devonian lungfish

Perhaps the most enduring of puzzles in palaeontology has been the identity of Palaeospondylus gunni Traquair, a tiny (5-60-mm) vertebrate fossil from the Middle Devonian period (approximately 385 Myr ago) of Scotland, first discovered in 1890 (refs 1-3). It is known principally from a single site (Achanarras Quarry, Caithness) where, paradoxically, it is extremely abundant, preserved in varved lacustrine deposits along with 13 other genera of fishes. Here we show that Palaeospondylus is the larval stage of a lungfish, most probably Dipterus valenciennesi Sedgwick and Murchison 1828 (ref. 5), and that development of the adult form requires a distinct metamorphosis. Palaeospondylus is the oldest known true larva of a vertebrate.     

Reticular synthesis and the design of new materials

The long-standing challenge of designing and constructing new crystalline solid-state materials from molecular building blocks is just beginning to be addressed with success. A conceptual approach that requires the use of secondary building units to direct the assembly of ordered frameworks epitomizes this process: we call this approach reticular synthesis. This chemistry has yielded materials designed to have predetermined structures, compositions and properties. In particular, highly porous frameworks held together by strong metal-oxygen-carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.     

REE geochemistry of suspended sediments from the rivers around the Yellow Sea and provenance indicators

Rare earth element (REE) compositions of the suspended sediments from the rivers around the Yellow Sea were different in that Korean river sediments (Han, Keum and Yeongsan Rivers) yield stronger fractionations than Chinese river sediments (Changjiang, Huanghe and Yalujiang), shown by obvious enrichments of LREE (light rare earth element) relative to UCC (upper continental crust).Variations of source rock compositions in the drainage basins are responsible for the differences of REE compositions between the river sediments. REE fractionation parameters including (La/Yb)ucc and (Gd/Yb)ucc as well as the ratios of La/Sc and Th/Sc can be treated as proper proxies for identifying the Chinese river sediments from those Korean river matters, and furthermore, for studying the provenances and paleoenvironmental changes of the marginal seas of China.     

Real-time detection of electron tunnelling in a quantum dot

Nanostructures in which strong (Coulomb) interactions exist between electrons are predicted to exhibit temporal electronic correlations. Although there is ample experimental evidence that such correlations exist, electron dynamics in engineered nanostructures have been observed directly only on long timescales. The faster dynamics associated with electrical currents or charge fluctuations are usually inferred from direct (or quasi-direct) current measurements. Recently, interest in electron dynamics has risen, in part owing to the realization that additional information about electronic interactions can be found in the shot noise or higher statistical moments of a direct current. Furthermore, interest in quantum computation has stimulated investigation of quantum bit (qubit) readout techniques, which for many condensed-matter systems ultimately reduces to single-shot measurements of individual electronic charges. Here we report real-time observation of individual electron tunnelling events in a quantum dot using an integrated radio-frequency single-electron transistor. We use electron counting to measure directly the quantum dot's tunnelling rate and the occupational probabilities of its charge state. Our results provide evidence in favour of long (10 micros or more) inelastic scattering times in nearly isolated dots.     

A class of compact dwarf galaxies from disruptive processes in galaxy clusters

Dwarf galaxies have attracted increased attention in recent years, because of their susceptibility to galaxy transformation processes within rich galaxy clusters. Direct evidence for these processes, however, has been difficult to obtain, with a small number of diffuse light trails and intra-cluster stars being the only signs of galaxy disruption. Furthermore, our current knowledge of dwarf galaxy populations may be very incomplete, because traditional galaxy surveys are insensitive to extremely diffuse or compact galaxies. Aware of these concerns, we recently undertook an all-object survey of the Fornax galaxy cluster. This revealed a new population of compact members, overlooked in previous conventional surveys. Here we demonstrate that these 'ultra-compact' dwarf galaxies are structurally and dynamically distinct from both globular star clusters and known types of dwarf galaxy, and thus represent a new class of dwarf galaxy. Our data are consistent with the interpretation that these are the remnant nuclei of disrupted dwarf galaxies, making them an easily observed tracer of galaxy disruption.     

Global anisotropy and the thickness of continents

For decades there has been a vigorous debate about the depth extent of continental roots. The analysis of heat-flow, mantle-xenolith and electrical-conductivity data all indicate that the coherent, conductive part of continental roots (the 'tectosphere') is at most 200-250 km thick. Some global seismic tomographic models agree with this estimate, but others suggest that a much thicker zone of high velocities lies beneath continental shields, reaching a depth of at least 400 km. Here we show that this disagreement can be reconciled by taking into account seismic anisotropy. We show that significant radial anisotropy, with horizontally polarized shear waves travelling faster than those that are vertically polarized, is present under most cratons in the depth range 250-400 km--similar to that found under ocean basins at shallower depths of 80-250 km. We propose that, in both cases, the anisotropy is related to shear in a low-viscosity asthenospheric channel, located at different depths under continents and oceans. The seismically defined 'tectosphere' is then at most 200-250 km thick under old continents. The 'Lehmann discontinuity', observed mostly under continents at about 200-250 km, and the 'Gutenberg discontinuity', observed under oceans at depths of about 60-80 km, may both be associated with the bottom of the lithosphere, marking a transition to flow-induced asthenospheric anisotropy.     

Cellular turnover and extracellular matrix remodeling in female reproductive tissues: functions of metalloproteinases and their inhibitors

Female reproductive tissues possess a unique ability to accommodate a remarkable amount of cell turnover and extracellular matrix (ECM) remodeling following puberty. Cellular structures within ovary, uterus, and mammary tissue not only change cyclically in response to ovarian hormones but also undergo differentiation during pregnancy, and eventually revert to that resembling the pre-pregnant stage. Cell proliferation, apoptosis, invasion, and differentiation are integral cellular processes that are precisely regulated in reproductive tissues, but become dysregulated in pathologies such as cancer. Explicit reorganization of ECM and basement membranes is also critical to preserve the form and function of these tissues. Here we review the evidence that coordinated spatiotemporal expression patterns of matrix metalloproteinase (MMP) genes and their tissue inhibitors (TIMPs) are important in cell and ECM turnover of the ovary, uterus, and mammary tissues. We discuss how perturbation in these gene families may impact the biology of these reproductive tissues and the factors implicated in the control of MMP and TIMP gene expression. The observed trends in MMP and TIMP expression involved in ovarian and mammary carcinomas are also presented.