Tunable separation of single-walled carbon nanotubes by dual-surfactant density gradient ultracentrifugation

We present a systematic study of the effects of surfactants in the separation of single-walled carbon nanotubes (SWNTs) by density gradient ultracentrifugation (DGU). Through analysis of the buoyant densities, layer positions, and optical absorbance spectra of SWNT separation using the bile salt sodium deoxycholate (DOC) and the anionic salt sodium dodecyl sulfate (SDS), we clarify the roles and interactions of these two surfactants in yielding different DGU outcomes. The separation mechanism described here can also help in designing new DGU experiments by qualitatively predicting outcomes of different starting recipes, improving the efficacy of DGU and simplifying post-DGU fractionation.      

Stability of metal nanocomposites under heavy-ion bombardment of insulators

Optical transmission and ion-induced photon emission of SiO₂ (silica glass), LiNbO₃ and Al₂O₃ were measured during implantation of 60-keV Cu⁻ or Au⁻ ions. Conditions of stability of metal nanocomposites were determined and represented with the help of nonequilibrium phase diagrams. Formation of structures dynamically stable under ion bombardment diminished the efficiency of ion implantation for further accumulation of implants as in nanoparticles. Contributions from various radiation-induced processes (sputtering, radiation-induced diffusion, atomic collisions, electronic excitations, etc.) to formation of nanocomposites were evaluated.     

Optical nonlinearity of Cu:SrTiO3 composite fabricated by negative ion implantation

Optical nonlinearity and dispersion were studied for Cu nanoparticle composite. Negative Cu⁻ ions with 60 keV were applied for implanting into SrTiO₃ at a flux of 10 μA/cm² up to a total fluence of 1 × 10¹⁷ ions/cm². The steady-state optical spectrum of Cu-implanted SrTiO₃ showed a surface plasmon resonance resulting from the formation of nanoparticles. Transient transmission and reflection were measured by the pump–probe method with a femtosecond laser system. Optical nonlinearity originated from Cu:SrTiO₃ nanoparticle composite and from SrTiO₃ matrix overlap, in measured transient spectra. The nonlinear component of Cu:SrTiO₃ composite was extracted from the transient spectra with the difference of time response. Nonlinear dielectric coefficient and dispersion around the surface plasmon resonance were derived from extracted transient spectra. The dispersion was compared with a local electric field factor.     

用固体碳及CO/CO2还原电炉粉尘中氧化锌的研究

用化学试剂和实际电炉粉尘作试样，考察了利用固体碳和CO/CO2进行氧化锌还原的各种影响因素。研究发现，与固 固还原反应相比，气 固还原反应较快，但前者易受温度的影响。在CO/CO2＝10、温度控制在1〖KG-*9〗000～1〖KG-*9〗100 ℃时，可保证电炉粉尘中氧化锌的顺利还原与气化分离。本研究为开发利用移动焦炭层的电炉粉尘处理新工艺提供了理论依据。     

Gold nanoparticle distribution monitor for drug delivery system based on optically assisted ultrasonic velocity-change imaging

Optical absorption images of the tissue mimic phantom including gold nanoparticles were obtained by detecting the ultrasonic velocity-change caused by light irradiation. A series of experimental results showed the possibility as a nanoparticle distribution monitor for the drug delivery system.     

Trajectory tuning for the tracking problem of the underactuated mechanical systems: application to the PVTOL aircraft

The Planer vertical take-off and landing (PVTOL) aircraft is a typical example of an underactuated mechanical system and has a nonminimum-phase nature. When considering output tracking control, the Input/Output (I/O) linearization method is not appropriate since the stability of the internal dynamics is not guaranteed. Hauser et al. regarded this system as a slightly nonminimum-phase system which approximates to a minimum-phase one. Their control scheme yielded good results when the coupling factor was small, but the results were not acceptable when the coupling factor increased. In this article, we propose two approaches to improve the control performance. First, we consider the approximation error of Hauser's scheme as uncertainty, and apply the Linear Quadratic Regulator (LQR) method, which possesses robustness against uncertainty, to determine the stabilizing feedback coefficients. Second, from the fact that the tracking error is unavoidable, we use the “virtual reference trajectory” to design the tracking control law, and optimize this trajectory to reduce the tracking error between the “actual reference trajectory” and the “resulting trajectory”. This optimization also improves the control performance by choosing a suitable performance index. By using our approach, we achieve better performance even if the coupling factor is increased. We show these results by numerical simulation. This work was presented, in part, at the Seventh International Symposium on Artificial Life and Robotics, Oita, Japan, January 16–18, 2002     

Stabilization of linear time-invariant systems with periodic communication constraints by output sample hold control

This article considers feedback control systems wherein the control loops are closed through a real-time network, and expresses the linear time-invariant system with the constraint in an input or output as a periodic discrete time system. It is shown that this system is stabilized by using output sample hold contol. This method has the merit that the capacity of a sensor-controller communication bus is small. This work was presented, in part, at the 8th International Symposium on Artificial Life and Robotics, Oita, Japan, January 24–26, 2003     

Thermal behaviour and particle size evaluation of primary clusters in a water-based magnetic fluid

This paper reports the experimental research on thermal behaviour and particle size evaluation of primary clusters of ferromagnetic nano-particles in a water-based magnetic fluid. The magnetic fluids are suspensions of ultra fine particles coated with a molecular layer of dispersant in a liquid carrier such as water or kerosene. The particles are coated with single- or double-layer of surfactant to achieve stable dispersion. Numerous experimental studies have indicated the existence of the primary cluster of ferromagnetic nano-particles in a water-based magnetic fluid. The purpose of this research is to evaluate the particle size of the primary clusters by applying the Einstein's equation for Brownian motion assuming that the primary cluster has a spherical-shape. The thermal behaviour of ferromagnetic nano-particles in magnetic fluids is investigated through the micro visualization using the optical darkfield microscope system and particle tracking velocimetry data processing system. Real-time visualization of the Brownian motion of primary clusters in a water-based magnetic fluid was carried out. The experimental results clarified that the primary cluster size depends upon the concentration of the ferromagnetic nano-particle in the magnetic fluid.     

Contamination levels of PCDDs, PCDFs and Co-PCBs in commercial baby foods in Japan

To examine dioxin contamination in commercial baby foods in Japan, congener analyses of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and coplanar polychlorinated biphenyls (Co-PCBs) were performed on 102 varieties of baby foods obtained from supermarkets in 2001-2002. The toxic equivalent quantity (TEQ) levels for dioxins in samples ranged from < 0.001 to 0.135 pg-TEQ/g wet weight when undetected or trace levels of congeners were taken as zero. Among 102 samples tested, 26 samples exceeded 0.010 pg-TEQ/g. The highest TEQ value was for "sardine, vegetables" (0.135 pg-TEQ/g), followed by "Japanese radish (daikon), sardine" (0.080 pg-TEQ/g). Thus, dioxins were detected at low levels in baby foods containing animal products such as fishes and/or dairy products.