Characterization of alicyclic polyimides based on cyclobutane ring dianhydride and aromatic diamine

Films of alicyclic polyamic acid and polyimide containing cyclobutane ring in dianhydride moiety and aromatic ring with p- or m-linkages in diamine moiety were characterized by infrared (IR) spectroscopy, dynamic viscoelasticity, differential-scanning calorimetry (DSC), density, and wide-angle X-ray diffraction analyses. Partially and fully imidized polyimides were obtained by varying the imidization temperature, e.g., 150°C, 250°C, and 350°C. It was found from the results of IR spectra, dynamic viscoelasticity, and DSC measurements that the imidization of alicyclic polyamic acid was reduced at about 150°C and needed a higher imidization temperature than aromatic polyamic acid. Alicyclic polyimide with m-linkage in the diamine moiety had a higher density and a much more ordered structure than with p-linkage. © 1994 John Wiley & Sons, Inc.     

Secondary neutral and ionized particle measurements under MeV-energy ion bombardment

We have measured both secondary neutral and ionized particles from an InSb target under 3.0 MeV Si ion bombardment. Measurements of both ions and neutrals have not been carried out so far in the MeV-energy range. The mass spectra and axial emission energy distributions of secondary particles were investigated. Secondary ions were measured with a linear- and a reflective-type time-of-flight technique, whereas secondary neutral particles were photo-ionized by a UV pulsed laser (ArF: 193 nm) and measured with a reflective-type time-of-flight technique. Different results were obtained for neutral particles in comparison with ionized particles. The mean energy of neutral Sb atoms was much lower than that of neutral In atoms, whereas the mean energies of secondary In and Sb ions were nearly equal.     

Sources of nitrate and ammonium contamination in groundwater under developing Asian megacities

The status of nitrate (NO(3)(-)), nitrite (NO(2)(-)) and ammonium (NH(4)(+)) contamination in the water systems, and the mechanisms controlling their sources, pathways, and distributions were investigated for the Southeast Asian cities of Metro Manila, Bangkok, and Jakarta. GIS-based monitoring and dual isotope approach (nitrate delta(15)N and delta(18)O) suggested that human waste via severe sewer leakage was the major source of nutrient contaminants in Metro Manila and Jakarta urban areas. Furthermore, the characteristics of the nutrient contamination differed depending on the agricultural land use pattern in the suburban areas: high nitrate contamination was observed in Jakarta (dry fields), and relatively lower nutrients consisting mainly of ammonium were detected in Bangkok (paddy fields). The exponential increase in NO(3)(-)-delta(15)N along with the NO(3)(-) reduction and clear delta(18)O/delta(15)N slopes of NO(3)(-) ( approximately 0.5) indicated the occurrence of denitrification. An anoxic subsurface system associated with the natural geological setting (e.g., the old tidal plain at Bangkok) and artificial pavement coverage served to buffer NO(3)(-) contamination via active denitrification and reduced nitrification. Our results showed that NO(3)(-) and NH(4)(+) contamination of the aquifers in Metro Manila, Bangkok, and Jakarta was not excessive, suggesting low risk of drinking groundwater to human health, at present. However, the increased nitrogen load and increased per capita gross domestic product (GDP) in these developing cities may increase this contamination in the very near future. Continuous monitoring and management of the groundwater system is needed to minimize groundwater pollution in these areas, and this information should be shared among adjacent countries with similar geographic and cultural settings.     

Gas permeation properties of a composite membrane filled with poly(ethylene oxide) into a porous membrane

The permeability coefficients of O₂, N₂, and CO₂ gases at 25°C were examined for composite membranes that were prepared by filling poly(ethylene oxide)(PEO) with different molecular weights into a porous membrane. The permeability coefficients of O₂, N₂, and CO₂ were 2 × 10⁻¹⁰ – 4 × 10⁻¹⁰, 5 × 10⁻¹¹ – 9.5 × 10⁻¹¹, and 6 × 10⁻¹⁰ – 1 × 10⁻⁹ (cm³ STPcm/cm² s cmHg), respectively. The higher permeability coefficients of CO₂ are explained in terms of high solubility of CO₂ in filled PEO. The permeability coefficient of CO₂ was affected by the degree of crystallinity of PEO in the composite. On the other hand, there was little effect of crystallinity on O₂ and N₂ permeability coefficients. Some probable relationships between selectivities of O₂ to N₂ and CO₂ to N₂ and the degree of crystallinity of PEO were observed. The CO₂ gas permeability coefficients of the composite membrane for PEO50000 (M_w = 5 × 10⁴) showed a marked change due to melting or crystallization of PEO. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2733–2738, 1999     

Preparation and properties of antimony-doped SnO2 films by thermal decomposition of tin 2-ethylhexanoate

Transparent Sb-doped SnO₂ films were prepared at 600° C on glass substrates by thermal decomposition of tin 2-ethylhexanoate and antimony tributoxide. The films 100 to 300 nm thick, which are composed of fine particles, were very smooth. The films showed no preferred orientation. The minimum resistivity (2.1×10^–2 cm) was attained at a concentration of 8 at% Sb on the substrate precoated with SiO₂. The transmission of these films was about 80% over a wavelength range from 0.4 to 2.0 m.     

Characterization and transport properties of a novel aliphatic polyamide with an ethyl branch

The CO₂ gas and water vapor transport properties of a novel aliphatic polyamide with an ethyl branch were investigated. The polymer was characterized with density measurements, differential scanning calorimetry, thermogravimetric analysis, and wide‐angle X‐ray diffraction analyses, and the amorphous and glassy nature of the polymer at the ambient temperature were confirmed. The CO₂ sorption isotherm of the polymer appeared to obey the dual‐mode sorption isotherm, which was characteristic of the glassy state. The water vapor sorption below a relative humidity of 0.4 or 0.5 was explained in terms of the Brunauer–Emmett–Teller sorption mechanism, whereas that at a high relative humidity demonstrated a dissolution type of water vapor into the polyamide. The permeability coefficients of He, CO₂, O₂, and N₂ gases through the membrane were as follows: P(He) > P(CO₂) > P(O₂) > P(N₂). The novel polyamide membrane was more permeable to CO₂, O₂, and N₂ gases than nylon 6 and nylon 66 membranes, containing a crystalline and hydrogen‐bonding nature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1955–1960, 2005     

Essential Cys-Pro-Cys motif of Caenorhabditis elegans copper transport ATPase

Caenorhabditis elegans putative copper ATPase (CUA-1) had been functionally expressed in a yeast delta ccc2 mutant (copper ATPase gene disruptant). We found that CUA-1 with Cys-Pro-Cys to Cys-Pro-Ala mutation could not rescue the yeast delta ccc2 mutant, suggesting that the carboxyl terminal cysteine residue in the conserved Cys-Pro-Cys motif is essential for copper transport.     

Debittering of enzymatic hydrolysates using an aminopeptidase from the edible basidiomycete Grifola frondosa

Bitter peptide solutions, prepared by the enzymatic hydrolysis of soy protein and milk casein, were treated with an aminopeptidase from the edible basidiomycete Grifola frondosa. As the incubation time elapsed, the amount of free amino acids released increased and the bitterness of the enzyme reaction mixtures decreased. However, the debittering of the milk casein hydrolysate by the aminopeptidase was less effective than that observed for the soy protein hydrolysate. Hydrophobic amino acids such as valine, leucine, phenylalanine, tyrosine, and isoleucine were preferentially released from the bitter solutions by the action of the aminopeptidase.     

Total sputtering yields of solids under MeV-energy Si ion bombardment

Total sputtering yields have been measured for SiO₂ and Cu targets bombarded with Si ions at an incident energy between 500 keV and 5.0 MeV using a quartz crystal microbalance technique. In order to measure total yields accurately, we have developed a beam modulation technique to avoid the effect of thermal drift. In the MeV energy range, an ion penetrates through thin SiO₂ and Cu targets and is implanted into a quartz crystal. Therefore, the thickness of these layers deposited on quartz crystals was carefully controlled to avoid damage of quartz crystal by incident ions. As a result, total sputtering yields of SiO₂ increased with incident Si ion energy, while those of the Cu target decreased. The total yields of the SiO₂ target were represented well by a power low of the electronic stopping power.