Stacking of conical molecules with a fullerene apex into polar columns in crystals and liquid crystals

Polar liquid crystalline materials can be used in optical and electronic applications, and recent interest has turned to formation strategies that exploit the shape of polar molecules and their interactions to direct molecular alignment. For example, banana-shaped molecules align their molecular bent within smectic layers, whereas conical molecules should form polar columnar assemblies. However, the flatness of the conical molecules used until now and their ability to flip have limited the success of this approach to making polar liquid crystalline materials. Here we show that the attachment of five aromatic groups to one pentagon of a C(60) fullerene molecule yields deeply conical molecules that stack into polar columnar assemblies. The stacking is driven by attractive interactions between the spherical fullerene moiety and the hollow cone formed by the five aromatic side groups of a neighbouring molecule in the same column. This packing pattern is maintained when we extend the aromatic groups by attaching flexible aliphatic chains, which yields compounds with thermotropic and lyotropic liquid crystalline properties. In contrast, the previously reported fullerene-containing liquid crystals all exhibit thermotropic properties only, and none of them contains the fullerene moiety as a functional part of its mesogen units. Our design strategy should be applicable to other molecules and yield a range of new polar liquid crystalline materials.     

Malaria risk: estimating clinical episodes of malaria

Estimates of the disease burden caused by malaria are crucial for informing malaria control programmes. Snow and colleagues claim that their estimate of 515 million cases of malaria caused by Plasmodium falciparum globally is up to 50% higher than that reported by the World Health Organization (WHO), and 200% higher for areas outside Africa. However, this comparison refers to the WHO's estimates from 1990 and 1998, and not to the range of 300 million to 500 million that the WHO has used since 2000 (ref. 2). Both groups agree that the burden of malaria disease outside Africa, especially in South Asia, is greater than was estimated in the 1990s.     

Conventional taxonomy obscures deep divergence between Pacific and Atlantic corals

Only 17% of 111 reef-building coral genera and none of the 18 coral families with reef-builders are considered endemic to the Atlantic, whereas the corresponding percentages for the Indo-west Pacific are 76% and 39%. These figures depend on the assumption that genera and families spanning the two provinces belong to the same lineages (that is, they are monophyletic). Here we show that this assumption is incorrect on the basis of analyses of mitochondrial and nuclear genes. Pervasive morphological convergence at the family level has obscured the evolutionary distinctiveness of Atlantic corals. Some Atlantic genera conventionally assigned to different families are more closely related to each other than they are to their respective Pacific 'congeners'. Nine of the 27 genera of reef-building Atlantic corals belong to this previously unrecognized lineage, which probably diverged over 34 million years ago. Although Pacific reefs have larger numbers of more narrowly distributed species, and therefore rank higher in biodiversity hotspot analyses, the deep evolutionary distinctiveness of many Atlantic corals should also be considered when setting conservation priorities.     

Unusually large earthquakes inferred from tsunami deposits along the Kuril trench

The Pacific plate converges with northeastern Eurasia at a rate of 8-9 m per century along the Kamchatka, Kuril and Japan trenches. Along the southern Kuril trench, which faces the Japanese island of Hokkaido, this fast subduction has recurrently generated earthquakes with magnitudes of up to approximately 8 over the past two centuries. These historical events, on rupture segments 100-200 km long, have been considered characteristic of Hokkaido's plate-boundary earthquakes. But here we use deposits of prehistoric tsunamis to infer the infrequent occurrence of larger earthquakes generated from longer ruptures. Many of these tsunami deposits form sheets of sand that extend kilometres inland from the deposits of historical tsunamis. Stratigraphic series of extensive sand sheets, intercalated with dated volcanic-ash layers, show that such unusually large tsunamis occurred about every 500 years on average over the past 2,000-7,000 years, most recently approximately 350 years ago. Numerical simulations of these tsunamis are best explained by earthquakes that individually rupture multiple segments along the southern Kuril trench. We infer that such multi-segment earthquakes persistently recur among a larger number of single-segment events.     

Fabrication and characterization of TiO2 -based dye-sensitized solar cells

Dye-sensitized solar cells TiO_2 with were fabricated.The phase composition and microstructures of the solar cells were examined by X-ray diffractometry and transmission electron microscopy,and the energy levels of the present solar cells were also discussed.The results show that a solar cell mixed with xylenol orange and rose Bengal shows a higher conversion efficiency compared to solar cells with a single dye.An introduction of amorphous TiO_2 layers results in an improvement of the conversion efficien...     

High-resolution carbon dioxide concentration record 650,000-800,000 years before present

Changes in past atmospheric carbon dioxide concentrations can be determined by measuring the composition of air trapped in ice cores from Antarctica. So far, the Antarctic Vostok and EPICA Dome C ice cores have provided a composite record of atmospheric carbon dioxide levels over the past 650,000 years. Here we present results of the lowest 200 m of the Dome C ice core, extending the record of atmospheric carbon dioxide concentration by two complete glacial cycles to 800,000 yr before present. From previously published data and the present work, we find that atmospheric carbon dioxide is strongly correlated with Antarctic temperature throughout eight glacial cycles but with significantly lower concentrations between 650,000 and 750,000 yr before present. Carbon dioxide levels are below 180 parts per million by volume (p.p.m.v.) for a period of 3,000 yr during Marine Isotope Stage 16, possibly reflecting more pronounced oceanic carbon storage. We report the lowest carbon dioxide concentration measured in an ice core, which extends the pre-industrial range of carbon dioxide concentrations during the late Quaternary by about 10 p.p.m.v. to 172-300 p.p.m.v.     

应用于高精度伺服机构的牵曳传动设计

介绍了牵曳传动的原理，特点及设计理论，分析了高精度牵曳传动伺服机构中传动轮的适宜形状，并设计制作成一种牵曳传动恒速伺服机构，达到了了预期的高精度。