Dynamics and control of an activated sludge process as a mixed culture system

One of the difficulties encountered in the operation of an activated sludge process is the phenomenon of bulking sludge. In an activated sludge process which is composed of a completely mixed aeration tank and a sedimentation vessel, the dynamic behavior of the system can be analyzed using a mathematical model. The model developed here is based on the kinetics and settleability of the combination of floc-forming sludge and bulking sludge. The operating conditions that cause the bulking phenomenon are clarified on the phase plane. It is also shown that a type of nonlinear state feedback regulator makes the system stable.     

Preparation of Dense BaTiO3 Ceramics from Sol-Gel-Derived Monolithic Gels

Dense, small-grained BaTiO₃ ceramics, with a grain size around 1 μm and a relative sintered density >98%, were obtained at 1100°C from sol-gel-derived gel monoliths without using any sintering additives. The monolithic gels asprepared had a relative density of about 50% and consisted of ultrafine pseudo-cubic BaTiO₃ particles (<50 nm). These gels, with a significantly high density compared with that of previous ones (∼30%), have been synthesized at room temperature from a sol solution with a concentration of equimolar mixture of titanium isopropoxide and barium ethoxide (0.8 mol/L), using the methanol/2-methoxyethanol mixed-solvent system. Microstructural development of the gel monoliths with increasing sintering temperature and the dielectric properties of the obtained dense BaTiO₃ ceramic have been investigated.     

Relations between molecular mixing state and conductive property in blends composed of polyaniline and aliphatic copolymer having acid groups

Blend films composed of polyaniline and aliphatic copolymer having carboxylic acid groups were prepared by vaporizing a solvent from a solution of both polymers. Poly(methyl methacrylate‐co‐methacrylic acid) and poly(1‐vinylpyrrolidone‐co‐acrylic acid) were used as the copolymers in this work. Conductivity of the blend film increased with decreasing concentration of polyaniline and then decreased in the region of low concentration. The N_1s peak in the ESCA spectrum of the blend film was shifted to higher binding energy with decreasing concentration of polyaniline and then was done to lower the binding energy in the region of low concentration. Polyaniline chains in the blend films become conductive by being oxidized with the carboxylic acid groups, which are the constituents of the copolymers. Through strong intermolecular interactions such as ionic bonding and hydrogen bonding between polyaniline and the copolymer, densities of the blend films are always higher than those predicted on the basis of the additive law. Blend films with higher density and higher conductivity are able to be prepared with a higher vaporizing rate, given that phase separation occurring during vaporizing process can be depressed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1113–1117, 2002     

Hydrogen production from the gasification of lignin with nickel catalysts in supercritical water

Hydrogen production from the gasification of lignin with Ni/MgO catalysts in supercritical water was conducted using stainless steel tube bomb reactor. Ni/MgO catalysts were prepared by impregnation method and were calcined at 773–1173 K in air for 8 h. The results of characterization for reduced Ni/MgO catalysts showed that Ni metal and NiO–MgO phase are formed after the reduction of calcined catalyst by _H2${\mathrm{H}}_2$. Furthermore, Ni metal surface area, which was calculated by CO chemical adsorption technique, decreased with increase in calcination temperatures. It was found that the carbon yield of gas products was increased with increase in Ni metal surface area except 10 wt% Ni/MgO (773 K) catalyst. Thus, it can be supposed that there is an optimal Ni particle size for the gasification of lignin in supercritical water. It should be noted that 10 wt% Ni/MgO (873 K) catalyst showed the best catalytic performance (carbon yield 30%) under reaction condition tested. It was concluded that Ni/MgO catalyst is a promising system for the gasification of lignin in supercritical water.     

Magnetic force-based cell patterning using Arg-Gly-Asp (RGD) peptide-conjugated magnetite cationic liposomes

Micropatterning of target cells is highly desired for tissue engineering and cell biology. Although recent progress in surface chemistry has enabled the spatial control of cell adhesion onto substrates, conventional methods usually require specialized devices and time-consuming processes to fabricate the substrate. In this study, we demonstrate a simple and rapid cell-patterning procedure using magnetite nanoparticles and magnetic force. To label the target cells magnetically, magnetite nanoparticles were encapsulated in cationic liposomes (magnetite cationic liposomes; MCLs). To promote cell attachment, an Arg-Gly-Asp (RGD)-motif-containing peptide was coupled to the phospholipid of MCLs (RGD-MCLs). A human keratinocyte cell line, HaCaT, which has a high anchorage dependency, was used as a model. The RGD-MCLs were added to an ultralow-attachment plate, whose culture surface is modified with a covalently bound hydrogel layer that is hydrophilic and neutrally charged, and then HaCaT cells were seeded to the plates. The RGD-MCLs induced cell adhesion, spreading, cytoskeletal organization, and fibronectin expression. When steel plates with a 200 microm width placed on a magnet were set under a culture surface, magnetically labeled cells aligned on the surface where the steel plate was positioned, resulting in cell patterning. Furthermore, various cell patterns using a computer-aided design were successfully fabricated. These results suggest that cell patterning using RGD-MCLs is a promising approach to tissue engineering and studies in cell biology.     

Study of titanium nitride deposition by supersonic plasma spraying

In this study, titanium nitride (TiN) deposition by reactive spraying was carried out under a low-pressure environment using a DC arc plasma jet generator with a supersonic expansion nozzle. Titanium powders were injected using a hollow cathode with argon gas, and nitrogen or nitrogen and hydrogen mixture was used as the plasma gas. Microstructure and properties of the coatings were examined using scanning electron microscope and X-ray diffraction. A dense TiN coating with a Vickers hardness of 2000 Hv was formed at a substrate temperature of 700 °C with a low input power of 5.3 kW. The results showed that the supersonic plasma jet in thermodynamic and chemical nonequilibrium state exhibits high potentials for reactive spraying.     

Mutagenicity of eluent by hot water extraction of various coals: Effect of chlorination

Six kinds of powdery coals (two bituminous coals, two sub-bituminous coals, and two lignites) were extracted by hot water, and the eluents obtained were analyzed for total organic carbon (TOC), absorbance at 260 nm (A₂₆₀), and pH. The TOC in the eluents decreased in the order, lignites > sub-bituminous coals > bituminous coals. The eluents of lignite gave high A₂₆₀/TOC values and fairly low pH compared to other coals. Chemical structure of the organic matter eluted from coals was discussed with the aid of FTIR analysis. The coal eluents were analyzed by the Ames mutagenicity assay using Salmonella typhimurium TA100 and TA98 strains, and no mutagenicity was observed for all of the six coals. However, especially for the lignites, chlorination of the eluents produced an appreciable mutagenicity, and the expression of mutagenicity was dependent upon the type of coal. The mutagenicity was extinguished when metabolic activation (rat liver homogenate, +S9) was applied.     

pH-independent fluorescent chemosensor for highly selective lithium ion sensing

Since lithium salts are used as pharmaceutically active compounds against manic-depressive psychosis, there is a demand to monitor the lithium concentration in blood in the narrow range of 0.6-1.2 mM effectively and safely. Here we report on an optical sensor approach for the determination of Li+, based on the design and synthesis of a novel lithium fluoroionophore KLI-1 and its polymer immobilizable derivative KLI-2, and the application to an optode. The novel lithium fluoroionophores rely on a tetramethyl "blocking subunit" bearing 14-crown-4 as a Li+-selective binding site and 4-methylcoumarin as a fluorophore, intramolecularly connected to show ICT-type wavelength shift for ratiometric fluorescence measurements. The fluoroionophores showed high selectivity for Li+ with binding-induced blue shift in the fluorescence spectra, no response to major biological interfering cations (K+, Ca2+, Mg2+), a selectivity of log kLi+,Na+ = -2.4 over Na+ in solution, and no response to pH in the range of pH 3-10. A hydrophilic optode membrane with KLI-2 immobilized also showed good selectivity for Li+, pH independence in the physiological range (pH 6-8), and fully reversible signal changes. KLI-1 and KLI-2 are excellent Li+ fluorescent chemosensors that can be applied to quantitative measurements of lithium in clinical samples, although possible interference from Na+ has to be considered at the lower therapeutic level of Li+.     

Growth condition dependence of structural and electrical properties of Mg2Si layers grown on silicon substrates

Mg₂Si layers were grown on Si substrates by thermal treatment of the substrates in a Mg vapor, and the growth condition dependence of the structural and electrical properties of the layers was investigated. The layers were grown by an interdiffusion process between the deposited Mg atoms and the substrates. The structural and electrical properties of the layers depend on the combinations of the Si substrate and Mg source temperatures during the heat treatment. Any deviation from the isothermal treatment conditions causes degradation of the structural and/or electrical properties of the Mg₂Si layers. It was confirmed that the layers with the optimum structural and electrical properties were obtained when the layers were grown under isothermal growth conditions.