Third-order optical nonlinearity of the carbon nanotubes was investigated with both 30-ps-wide and 8-ns-wide Nd:YAG laser beams. Both 1064 and 532 nm were used in each case. The nonlinear optical temporal response was obtained both on the picosecond scale and on the nanosecond scale, and the corresponding mechanism is discussed. Finally, we have compared the average contribution of one carbon atom to the third-order optical nonlinearity in the carbon nanotubes with that in C60, finding some enhancement of the third-order optical nonlinearity in the carbon nanotubes.

ABSTRACT:A new type of carbon nanotube (CNT) (diameter of Ͻ100 nm) coated by conducting polypyrrole (PPY) was synthesized by in situ polymerization on CNTs. The structure of the resulting complex nanotubes (CNT-PPY) was characterized by elemental analysis, X-ray photoelectron spectroscopy, Raman spectra, and X-ray diffraction. These indicated no significant chemical interaction between PPY and the CNT. The electrical, magnetic, and thermal properties of the complex nanotubes were measured and showed the physical properties of the CNTs were modified by conducting PPY.

It is widely recognized that lake sediment grain‐size distributions tend to be polymodal and consist of two or more grain‐size components. However, for specific cases, the genesis of each component usually is poorly understood. In this study, the grain‐size components of the surface sediments of Hulun Lake, Inner Mongolia, were partitioned using the log‐normal distribution function method and the relationship between the identity of each grain‐size component and the hydraulic condition of the lake was investigated in order to relate the constituent components to specific depositional processes in the lake. The data indicate that the modern clastic sediments of Hulun Lake contain six distinct unimodal grain‐size distributions representing six grain‐size components. Each of the components retains its identity including modal size, manner of transportation and environment of deposition, although the relative percentage varies with the hydraulic conditions throughout the lake. These components are specified from fine to coarse modes as long‐term suspension clay, offshore‐suspension fine silt and medium to coarse silt, and nearshore‐suspension fine sand, saltation medium sand and traction coarse sand. The percentage contribution of several grain‐size components interpreted as being indicative of nearshore environments is shown to be correlated negatively with water depth across the modern lake bed; this suggests that the proportion of these components in core data might be useful as a proxy for water depth. This possibility was tested using a sediment core from Hulun Lake where high percentages of the nearshore grain‐size components were found to be correlated with low regional precipitation reconstructed from the pollen profile of the same core. The coincidence of two independent proxies does not only demonstrate the validity of log‐normal distribution function in partitioning polymodal sediments but reveals the potential of lake sediment grain‐size components for the research of lake‐level fluctuations during the geological past.

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