Probing electronic transitions in individual carbon nanotubes by Rayleigh scattering

Rayleigh scattering spectra were obtained from individual single-walled carbon nanotubes with the use of a laser-generated visible and near-infrared supercontinuum. This diagnostic method is noninvasive and general for nanoscale objects. The approach permits clear identification of excited states in arbitrary metallic and semiconducting nanotubes. We analyzed spectral lineshapes in relation to the role of excitonic effects and correlated the results with Raman scattering data on individual tubes. The nanotube structure remained the same over distances of tens of micrometers. Small nanotube bundles retained distinct Rayleigh spectroscopic signatures of their component nanotubes, thus allowing the probing of nanotube-nanotube interactions.     

Impact of land‐use changes on soil hydraulic properties of Calcaric Regosols on the Loess Plateau,NW China

Vegetation restoration efforts (planting trees and grass) have been effective in controlling soil erosion on the Loess Plateau (NW China). Shifts in land cover result in modifications of soil properties. Yet, whether the hydraulic properties have also been improved by vegetation restoration is still not clear. The objective of this paper was to understand how vegetation restoration alters soil structure and related soil hydraulic properties such as permeability and soil water storage capacity. Three adjacent sites with similar soil texture, soil type, and topography, but different land cover (black locust forest, grassland, and cropland) were selected in a typical small catchment in the middle reaches of the Yellow River (Loess Plateau). Seasonal variation of soil hydraulic properties in topsoil and subsoil were examined. Our study revealed that land‐use type had a significant impact on field‐saturated, near‐saturated hydraulic conductivity, and soil water characteristics. Specifically, conversion from cropland to grass or forests promotes infiltration capacity as a result of increased saturated hydraulic conductivity, air capacity, and macroporosity. Moreover, conversion from cropland to forest tends to promote the creation of mesopores, which increase soil water‐storage capacity. Tillage of cropland created temporarily well‐structured topsoil but compacted subsoil as indicated by low subsoil saturated hydraulic conductivity, air capacity, and plant‐available water capacity. No impact of land cover conversion on unsaturated hydraulic conductivities at suction > 300 cm was found indicating that changes in land cover do not affect functional meso‐ and microporosity. Our work demonstrates that changes in soil hydraulic properties resulting from soil conservation efforts need to be considered when soil conservation measures shall be implemented in water‐limited regions. For ensuring the sustainability of such measures, the impact of soil conversion on water resources and hydrological processes needs to be further investigated.     

European seasonal and annual temperature variability, trends, and extremes since 1500

Multiproxy reconstructions of monthly and seasonal surface temperature fields for Europe back to 1500 show that the late 20th- and early 21st-century European climate is very likely (>95% confidence level) warmer than that of any time during the past 500 years. This agrees with findings for the entire Northern Hemisphere. European winter average temperatures during the period 1500 to 1900 were reduced by approximately 0.5 degrees C (0.25 degrees C for annual mean temperatures) compared to the 20th century. Summer temperatures did not experience systematic century-scale cooling relative to present conditions. The coldest European winter was 1708/1709; 2003 was by far the hottest summer.