Soil particle-size distribution (PSD) is one of the most important physical attributes due to its great influence on soil properties related to water movement, productivity, and soil erosion. The multifractal measures were useful tools in characterization of PSD in soils with different taxonomies. Land-use type largely influences PSD in a soil, but information on how this occurs for different land-use types is very limited. In this paper, multifractal Rényi dimension was applied to characterize PSD in soils with the same taxonomy and different land-use types. The effects of land use on the multifractal parameters were then analyzed. The study was conducted on the hilly-gullied regions of the Loess Plateau, China. A Calcic Cambisols soil was sampled from five land-use types: woodland, shrub land, grassland, terrace farmland and abandoned slope farmland with planted trees (ASFP). The result showed that: (1) entropy dimension (D 1 ) and entropy dimension/capacity dimension ratio (D 1 /D 0 ) were significantly positively correlated with finer particle content and soil organic matter.

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Graphene quantum dots (GQDs) have recently emerged as a promising type of low‐toxicity, high‐biocompatibility, and chemically inert fluorescence probe with a high resistance to photobleaching. They are a prospective substitution for organic materials in light‐emitting devices (LED), enabling the predicted concept of much brighter and more robust carbon LED (CLED). However, the mechanism of GQD emission remains an open problem despite extensive studies conducted so far, which is becoming the greatest obstacle in the route of technical improvement of GQD quantum efficiency. This problem is solved by the combined usage of femtosecond transient absorption spectroscopy and femtosecond time‐resolved fluorescence dynamics measured by a fluorescence upconversion technique, as well as a nanosecond time‐correlated single‐photon counting technique. A fluorescence emission‐associated dark intrinsic state due to the quantum confinement of in‐plane functional groups is found in green‐fluorescence graphene quantum dots by the ultrafast dynamics study, and the two characteristic fluorescence peaks that appear in all samples are attributed to independent molecule‐like states. This finding establishes the correlation between the quantum confinement effect and molecule‐like emission in the unique green‐fluorescence graphene quantum dots, and may lead to innovative technologies of GQD fluorescence enhancement, as well as its broad industrial application.

Here we report an electrochemiluminescence (ECL) self-interference spectroscopy technique (designated as ECLIS) with spatial resolution in the normal direction of the electrode surface. Self-interference principally originates from the superposition of ECL emitted directly by luminophores and that reflected from electrode surfaces, resulting in a spectrum consisting of orderly distributed peaks. On the basis of this spectrum and theoretical analysis by the matrix propagation model, the distance between luminophores and the electrode surface can be probed with a vertical resolution on the nanometer scale. We demonstrated first in this work that the height of ECL luminophores assembled on the electrode surface using different molecular linkers, such as double-stranded DNA, could be determined, as well as the possible conformation of linker molecules at the surface. Moreover, the thickness of the ECL emitting layer adjacent to the electrode surface was estimated for the classical coreactant ECL systems involving freely diffusing Ru­(bpy)3 2+ and tri-n-propylamine in solutions. The thickness was found to vary from ∼350 nm to nearly 1 μm depending on the concentration of Ru­(bpy)3 2+. We believe that ECLIS with a high vertical resolution will provide an easy way to collect molecular conformation information and study ECL reaction mechanisms at electrode interfaces.

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a b s t r a c t a r t i c l e i n f oSoil organic carbon (SOC) is one of the key components for assessing soil quality. Meanwhile, the changes in the stocks SOC may have large potential impact on global climate. It is increasingly important to estimate the SOC stock precisely and to investigate its variability. In this study, Yangjuangou watershed was selected to investigate the SOC distribution under different land uses. We found that SOC concentration decreased with increasing soil depth under all land uses and was significantly different across the vertical soil profile (P b 0.01). However, considering effect of land use on SOC, it is only significant (P b 0.01) in the topsoil (0-5 cm) layer. This indicated that land use has a large effect on the stocks of SOC in the surface soil. The stratification ratio of SOC N 1.2 may mean that soil quality is improving. The order of the SOC density (0-30 cm) under different land uses is forestland N orchard land N grassland N immature forestland N terraced cropland. The SOC stock is found to be as large as 2.67 × 10 3 t (0-30 cm) in this watershed. Considering time effect of restoration, the slope cropland just abandoned is more efficient for SOC accumulation than trees planted in the semi-arid hilly loess area.

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Semiconductor quantum dots (QDs) composed of multiple components are playing an important role in solar energy conversion as light harvesting materials. Electron extraction dynamics in CdSe and core/shell CdSe/CdS/ZnS colloidal QDs are studied by femtosecond transient absorption spectroscopy in this Article. Our study demonstrates that, in the presence of the commonly used electron acceptor, methyl viologen (MV2+), electrons in the 1S state of CdSe QDs can be effectively extracted with a time constant less than 150 fs. With regard to type I core/shell CdSe/CdS/ZnS QDs, 400 nm excitation will mainly populate the CdS first, due to its large absorption cross section at around that wavelength. Electrons from the conduction band of CdS then can be directly extracted by MV2+ before transferring to core CdSe. Therefore, MV2+ can serve as an efficient bridge to extract electrons from the shell of type I QDs. As compared to the bare QDs, core/shell QDs have slower charge separation and much slower recombination rates. Thus, the core/shell QDs are beneficial for designing solar cells.