Continuous-velocity lattice gas cellular automata for miscible binary fluid and its application to simulation of interface instability

Continuous-velocity lattice gas cellular automata (CVLGA) is extended to miscible binary fluid systems. A new parameter is introduced in order to control the diffusivity of the fluids. The correlation between the diffusivity and the new parameter proves that there exists the maximum value of the diffusivity. Quantitative verifications of the model are carried out with numerical simulations of the diffusion phenomena across a falling fluid film. The model is then applied to the simulations of Rayleigh-Taylor instability during the gravitational mixing phenomena. The qualitative tendency of the growth of the interface instability is the same as that obtained in conventional numerical methods.     

Uniformly Porous Composites with 3-D Network Structure (UPC-3D) for High-Temperature Filter Applications

Uniformly porous composites with 3-D network structure (UPC-3D) have been recently developed via a pyrolytic reactive sintering process, which takes advantage of the evolved CO₂ gas from a decomposing carbonate source (e.g., dolomite, CaMg(CO₃)₂) and does not require any additional pore-forming agent nor long-time burning-out process. Through liquid formation via LiF doping, strong necks are formed between constituent particles before completion of the pyrolysis of carbonate, resulting in the formation of a strong 3-D network structure. The pore size distribution is very narrow (with typical pore size: ∼1 μm), and the porosity was controllable (∼30–60%) by changing the sintering temperature. This article presents the development details of UPC-3D, and reports the recent findings in CaZrO₃/MgAl₂O₄ system, which will be one of the more promising systems for practical applications.     

Residues important for the function of a multihelical DNA binding domain in the new transcription factor family of Cam and Tet repressors

We report that some prokaryotic repressors including CamR andTetR belong to the same family. CamR and TetR bind to DNA usinga multihelical DNA binding domain (DBD) at the N-termini ofthe proteins, while the C-termini are important for regulatingthe DNA binding in a manner dependent on their co-factors (camphorfor CamR, tetracycline for TetR). In all, 11 important aminoacid positions have been identified in the CamR DBD by the systematicsubstitution of residues by Ala. Of the 11 positions, 10 areeither buried in the core, and thus important for creating thehydrophobic environment, or exposed on the surface, and thusimportant for binding to DNA. The eleventh residue, Gly, seemsto be important for a loop structure. The DNA binding mode ofthis type of DBD and a general mechanism of regulating theirDNA binding are discussed in reference to the crystal structureof TetR [Hinrichs et al., (1994) Science, 264, 418–420].     

Free energy perturbation study on a Trp-binding mutant (Ser88 ->Cys) of the trp-repressor

The Ser⁸⁸Cys mutant of the trp-repressor showed a lower affinityfor the corepressor than the wild-type repressor [G = 1.7 ±0.3 kcal/mol, Chou and Matthews (1989) J. Biol. Chem., 264,18314–18319].A molecular dynamics/free energy cycle perturbation study wasperformed to understand the origin of the decreased affinity.A value (G = 1.58 ± 0.28 kcal/mol) comparable with theexperimental value was obtained by the simulation. Free energycomponent analysis revealed that destabilization of the vander Waals interaction between Ser⁸⁸ and Trp¹⁰⁹ (corepressor)mainly contributed to the decreased affinity of the mutant.The rotational transition of the hydroxyl (sulfhydryl) groupof Ser⁸⁸ (Cys⁸⁸) during the simulations affected the contributionsof Arg⁸⁴ and water to the free energy change in the aporepressorand those of Arg⁸⁴ and Trp ¹⁰⁹ to that in the holorepressor.However, the contributions from different residues compensatedeach other, and the total free energy changes were almost invariablein the various simulations.     

Comparison of lipid composition ofCandida guilliermondii grown on glucose,ethanol and methanol as the sole carbon source

The carbon and energy source for aerobically grown cultures ofCandida guilliermondii profoundly influenced the neutral lipid content and the fatty acid composition of the individual lipid components. Methanol (0.80%, w/v) grown cells cultivated at 30 C in presence of 0.025% ammonium sulfate contained 12% total lipids, 67% of which was neutral lipids. Glucose (0.74%, w/v) or ethanol (0.53%, w/v) grown cells contained 21–22% total lipids, 80% of which was neutral lipids, under the same conditions. Methanol-grown cells contained a decreased 18∶1 acid (52–54% of total fatty acids) and an increased 18∶2 acid (23–25%), as compared with glucose- or ethanol-grown cells which contained 57–66% 18∶1 acid and 8–14% 18∶2 acid, in both neutral and polar lipid fractions. The relationship between methanol metabolism and desaturation of fatty acid in yeast was discussed.     

Increase in the γ-linolenic acid content by solvent winterization of fungal oil extracted fromMortierella genus

The fungal oil extracted fromMortierella ramanniana var.angulispora (IFO 8187) was solvent winterized in order to raise the content of γ-linolenic acid (GLA). Effects of winterization conditions (solvent, oil concentration in the solvent and temperature) and changes of glyceride compositions were discussed. The fungal oil was separated into four diglycerides and 17 triglycerides (TG) with high performance liquid chromatography. The predominant species were POO, POP and LOP, whose contents were 24.4, 22.9 and 9.4% of the total TG, respectively. Ethanol at 4°C gave the highest GLA content of 10.5% in spite of lower yield than with acetone at −20°C. The highest separation efficiency for GLA (η_GLA) was 0.27 with acetone at −20°C and 10% oil concentration, resulting in 8.3% of GLA from the fungal oil at 5.7% LGA. In case of lower oil concentration at 5–20%, η_GLA showed higher in the following order: acetone (−20°C)>n-hexane (−20°C)>acetone (4°C)>petroleum ether (−20°C). The winterization process also proved to be effective for the separation of TG type, Sa₂U (Sa; saturated fatty acid; U, unsaturated fatty acid) into the crystallized fraction and SaU₂ into the liquid fraction. Acetone at −20°C showed higher separation efficiency for triunsaturated TG than the other solvents.     

Thraustochytrid as a potential source of carotenoids

Thraustochytrids, marine protists whose dominant genera are Thraustochytrium and Schizochytrium, belong to the kingdom Chromista and are known as an industrial source of DHA. We describe here that thraustochytrid strain KH105, isolated as a DHA producer, also accumulates significant levels of β-carotene and xanthophylls including canthaxanthin and astaxanthin. A4-d cultivation using a medium composed of 10% glucose and less than 0.3% of nitrogen sources in a half-concentration of seawater gave an astaxanthin production up to 6.1 mg/L, and canthaxanthin content reached more than 10 mg/L under conditions where a higher concentration of nitrogen sources (6%) was employed. It might be advantageous in mass production systems for these carotenoids to be extracted readily by simply suspending the cells with organic solvents such as acetone and chloroform. Analyses on the morphological and life history features of the KH105 strain revealed that it belongs to the genus Schizochytrium. This particular species of thraustochytrids is thus considered to be a promising source of xanthophylls as well as DHA for use in the food industry.     

Reaction of sodium perborate with a chlorinated cyclic hindered amine (TMP-Cl): I. Quantitative evaluation of active oxygen species in fabric bleaching

The reaction of N-chloro-4-hydroxy-2,2,6,6-tetramethylpiperidine (TMP-Cl) with sodium perborate (PB) was investigated with special reference to the generation of singlet oxygen and the possible application to a new oxidative bleaching process. Generation of the singlet oxygen (¹O₂), the hydroxyl radical (HO·) and superoxide anion radical (O₂·⁻) in the PB/TMP-Cl mixed solution was confirmed by the trapping reagent method. From the results of another experiment, in which the bleaching abilities of each active oxygen species were confirmed, the main active oxygen species contributing to the bleaching of purpurogallin, the skeleton of black tea pigment, in the PB/TMP-Cl system was concluded to be¹O₂.     

Dehydrogenative Cracking of n-Butane over Modified HZSM-5 Catalysts

Dehydrogenative cracking reaction of n-butane was studied using HZSM-5 catalyst modified with various metal oxides. Alkaline earth (magnesium), transition metal (cobalt) and rare earth (lanthanum) elements are used for the modification. The selectivity of the products was studied at low conversion (20%). Methane, ethane, ethylene, propylene, butenes and butadiene were the main products. With the use of the cobalt- or magnesium-containing HZSM-5, dehydrogenative cracking was observed and the selectivity of ethylene was much larger than that of ethane. On the other hand, the selectivity of ethylene and ethane were almost the same in the reaction using the lanthanum-containing HZSM-5. It is considered that the cobalt- and magnesium-loaded sites on HZSM-5 played an important role in the dehydrogenative cracking.     

Some properties of Sb2Te3−xSex for nonvolatile memory based on phase transition

Composition dependence of properties of Sb₂Te_3–x Se _x in the range 0x<3 were studied using differential thermal analysis and X-ray diffraction. Sb₂Te_3–x Se _x form solid solution for 0<x1.25 and 2.75x<3. A systematic study of crystallization temperature in Sb₂Te_3–x Se _x (0x2.75) thin films prepared by flash evaporation was carried out. In preliminary experiments for some compositions, more than 10³ repetitions between amorphous and crystalline states were attained by the application of electric pulses.