Abstract:Located in the Loess Plateau of China, the Wuding River basin (30 261 km 2 ) contributes significantly to the total sediment yield in the Yellow River. To reduce sediment yield from the catchment, large-scale soil conservation measures have been implemented in the last four decades. These included building terraces and sediment-trapping dams and changing land cover by planting trees and improving pastures. It is important to assess the impact of these measures on the hydrology of the catchment and to provide a scientific basis for future soil conservation planning. The non-parametric Mann-Kendall-Sneyers rank test was employed to detect trends and changes in annual streamflow for the period of 1961 to 1997. Two methods were used to assess the impact of climate variability on mean annual streamflow. The first is based on a framework describing the sensitivity of annual streamflow to precipitation and potential evaporation, and the second relies on relationships between annual streamflow and precipitation. The two methods produced consistent results. A significant downward trend was found for annual streamflow, and an abrupt change occurred in 1972. The reduction in annual streamflow between 1972 and 1997 was 42% compared with the baseline period (1961)(1962)(1963)(1964)(1965)(1966)(1967)(1968)(1969)(1970)(1971). Flood-season streamflow showed an even greater reduction of 49%. The streamflow regime of the catchment showed a relative reduction of 31% for most percentile flows, except for low flows, which showed a 57% reduction. The soil conservation measures reduced streamflow variability, leading to more uniform streamflow. It was estimated that the soil conservation measures account for 87% of the total reduction in mean annual streamflow in the period of 1972 to 1997, and the reduction due to changes in precipitation and potential evaporation was 13%.

ZIF-8 films were deposited on silicon wafers and characterized to assess their potential as future insulators (low-κ dielectrics) in microelectronics. Scanning electron microscopy and gas adsorption monitored by spectroscopic ellipsometry confirmed the good coalescence of the crystals, the absence of intergranular voids, and the hydrophobicity of the pores. Mechanical properties were assessed by nanoindentation and tape tests, confirming sufficient rigidity for chip manufacturing processes (elastic modulus >3 GPa) and the good adhesion to the support. The dielectric constant was measured by impedance analysis at different frequencies and temperatures, indicating that κ was only 2.33 (±0.05) at 100 kHz, a result of low polarizability and density in the films. Intensity voltage curves showed that the leakage current was only 10 −8 A cm 2 at 1 MV cm −1 , and the breakdown voltage was above 2 MV cm −1 . In conclusion, metal-organic framework ZIF-8 films were experimentally found to be promising candidates as low-κ dielectrics in microelectronic chip devices. This opens a new direction for research into the application of metal-organic frameworks.

A functional monomer with a pendant azide moiety, 2‐azidoethyl methacrylate (AzMA), was polymerized via reversible addition‐fragmentation chain transfer (RAFT) polymerization with excellent control over the molecular weight distribution (PDI = 1.05–1.15). The subsequent copper‐catalyzed Huisgen 1,3‐dipolar cycloadditions of phenyl acetylene with polyAzMA was achieved at room temperature with high conversion. The resulting functional polymer exhibited identical 1H NMR and IR spectra with the polymer of the same molecular structure but prepared by a prefunctionalization approach, confirming the retention of the azide side chains during the RAFT polymerization of AzMA. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4300–4308, 2007

We grow ultra-high mass density carbon nanotube forests at 450 °C on Ti-coated Cu supports using Co-Mo co-catalyst. X-ray photoelectron spectroscopy shows Mo strongly interacts with Ti and Co, suppressing both aggregation and lifting off of Co particles and, thus, promoting the root growth mechanism. The forests average a height of 0.38 μm and a mass density of 1.6 g cm−3. This mass density is the highest reported so far, even at higher temperatures or on insulators. The forests and Cu supports show ohmic conductivity (lowest resistance ∼22 kΩ), suggesting Co-Mo is useful for applications requiring forest growth on conductors.

Atom transfer radical polymerization (ATRP) catalyzed by N,N′,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA)/CuBr was performed to synthesize poly(tert-butyl acrylate) with predictable molecular weight, low polydispersities, and well-defined bromine end groups. The bromine end groups have been substituted by azides. Then C 60 end-capped poly(tert-butyl acrylate) was synthesized by the reaction of C60 with PtBA-N3 in DMF. GPC measurement showed that C60 was chemically bonded to the end chain of poly(tert-butyl acrylate); i.e., the final products (PtBA-C60) were monosubstituted. 1 H NMR, FTIR, and UV-vis measurements confirmed that the water-soluble, monosubstituted C60 derivatives of poly(acrylic acid) (PAA-C60) have been obtained by hydrolysis of PtBA-C60. The photoconductivities of PtBA-C60 and PAA-C60 were measured by photoinduced xerographic discharge technique. Experimental results showed that C60 bonded in the polymers is the headstream of the photoconductivity, and an increase of the C60 content in C60 polymeric derivatives could improve the photoconductivity dramatically. The microstructures of CGL are very important for the photoconductive properties, and perfect hole-transport channels in the CGL will improve the photoconductivity notably.