Dispersion Behavior of Barium Titanate Nanoparticles Prepared by Using Various Polycarboxylic Dispersants

The effects of the polycarboxylic dispersant structures on the crystallinity and sedimentation behavior of prepared BaTiO₃ nanoparticles were analyzed using four types of dispersants—ethylenediaminetetraacetic acid dipotassium salt (EDTA), trans -aconitic acid (TAA), ammonium acrylate–methyl acrylate co-polymer (PAA50), and sodium polyacrylate (PAA100). In the case of EDTA and TAA, the adsorbed ratio of the dispersants on BaTiO₃ nanoparticles was relatively low, and only slight improvement of sedimentation behavior was observed. On the other hand, in the case of PAA50 and PAA100, the adsorbed ratio was high, and the sedimentation behavior was gratefully improved. Next, in order to analyze the relationships among the additive amount of polycarboxylic dispersants, crystallinity, and sedimentation behavior, various amounts of PAA100 or PAA50 were treated in the synthesis solution. The sedimentation behavior of BaTiO₃ nanoparticles improved with increasing amounts of PAA100 and PAA50 while their crystal phase became amorphous. Adding PAA50 at a molar ratio of COO⁻/Ba²⁺=0.266 resulted in BaTiO₃ nanoparticles with the best dispersion stability in an aqueous media.     

Oxidative degradation of polyolefins. I. Thermal oxidative degradation of atactic polypropylene in solution

Atactic polypropylene was oxidized in solution with radical initiator in the absence and presence of metal catalyst to considerably high conversion over the temperature range of 70° to 125°C, and oxidation products and the change in molecular weight distribution were measured. The unoxidized polypropylene had no ultraviolet absorption at 253.7 nm, whereas the oxidized polypropylene showed distinct absorption over a wide range of molecular weights. It was found that oxygen was incorporated into the polymer chain as hydroperoxide, acid, carbonyl, and hydroxy groups. Much of the absorbed oxygen was found to be involved in smaller fraction of low molecular weight products. Although the average molecular weight of the oxidized polypropylene decreased significantly, the formation of low-boiling products was quite small.     

Preparation and Characterization of a Large-Scale YBa2Cu3O7−x Superconductor Prepared by Plastic Forming without a High-Pressure Molding: Effect of Polyvinyl Alcohol (PVA) Addition on the Superconducting Properties

The preparation of large-scale YBa₂Cu₃O_{7− x} superconductor samples was investigated. This method is based on plastic forming using a slurry consisting of YBa₂Cu₃O_{7− x} particles and a sol solution made up of multimetallic hydroxide particles (YBa₂Cu₃(OH) _x colloidal particles) and poly(vinyl) alcohol (PVA). The effects of adding PVA on the product, the crystallinity, and the superconducting properties of the sample were investigated. It was found that PVA acted as a protective colloid in the sol solution and stabilized YBa₂Cu₃(OH) _x colloidal particles, and that the role of PVA changed from a thickener to a flocculant during drying so that the formability/workability of the green sheet sample was improved and large samples (about 80 mm × 80 mm × 3 mm) without large cracks were obtained after firing. The samples became superconducting at 91.5±0.5 K ( T _con) and the full transition temperature ( T _coff) was 88.5±1.5 K. The critical current density ( J _c) of the sample prepared from the slurry containing 1 wt% PVA was 713±150 A/cm² at 77 K. This J _c value was improved to 2300 A/cm² by heat treatment at 773 K under an oxygen atmosphere.     

Preparation of Bi,Pb-Sr-Ca-Cu-O superconductor by the sol-gel method

The high -T _c superconducting phase in the Bi, Pb-Sr-Ca-Cu-O system has been prepared by the sol-gel method. The formation process of the low-T _c phase as well as the high-T _c phase has been examined by thermal analysis, infra-red measurements and X-ray diffraction, and compared with the conventional solid-state reaction. At a low heat-treatment temperature of 400 ° C, Bi₂O₃, CaCO₃ and CuO are precipitated from the gel. These oxides react with each other to form several double oxides above 600 ° C and yield the low-T _c phase as a main product at 800 ° C. The heat treatment at higher temperatures effectively leads to the formation of the high-T _c phase. In particular, the high-T _c phase is most predominantly formed in the specimen heat treated at 845 ° C for 48 h after calcination at 800 ° C for 12 h, which is reflected in the critical temperature of 104 K. The temperature at which the low-T _c phase is formed is lower in the sol-gel-derived sample than in the specimen prepared by the solid-state reaction. Further-more, the sol-gel method brought about a larger amount of the high-T _c phase than the solid-state reaction when the conditions for the heat treatment were identical. These facts clearly indicate the superiority of the sol-gel method for the formation of both high-T _c and low-T _c Bi, Pb-Sr-Ca-Cu-O superconducting phases.     

Neighboring base damage induced by permanganate oxidation of 8-oxoguanine in DNA

We found that single-stranded DNA oligomers containing a 7, 8-dihydro-8-oxoguanine (8-oxo-G) residue have high reactivity toward KMnO4; the oxidation of 8-oxo-G induces damage to the neighboring nucleotide residues. This paper describes the novel reaction in detail, including experiments that demonstrate the mechanism involved in the induction of DNA damage. The results using DNAs of various base compositions indicated that damaged G, T and C (but not A) sites caused strand scissions after hot piperidine treatment and that the damage around the 8-oxo-G occurred at G sites in both single and double strands with high frequency. The latter substrates were less sensitive to damage. Further, kinetic studies of the KMnO4reaction of single-stranded oligomers suggested that thereactivity of the DNA bases at the site 5'-adjacent to the 8-oxo-G was in the order G >A >T, C. This preference correlates with the electron donating abilities of the bases. In addition, we found that the DNA damage at the G site, which was connected with the 8-oxo-G by a long abasic chain, was inhibited in the above order by the addition of dG, dA or dC. On the other hand, the damage reactions proceeded even after the addition of scavengers for active oxygen species. This study suggests the involvement of a redox process in the unique DNA damage initiated by the oxidation of the 8-oxo-G.     

Current status of acute respiratory infections in children under five years of age in Nairobi, Kenya

Two hundreds and twenty-six children under five years of age with pneumonia were recruited from an urban poor area in Nairobi, Kenya, and examined for pathogens for 1 year from February 1997. One hundred and twenty-eight of the 226 patients were pathogen-positive cases. The patients under 1-year-old were 61.8% of the pathogen-positive cases. A total 192 organisms were isolated from 128 pathogen-positive patients. Streptococcus pneumoniae had the highest prevalence rate of 31.3%, followed by respiratory syncytial virus with 10.4%, Candida albicans with 9.9%, Moraxella (B) catarrhalis with 7.8%. In S. pneumoniae, 66.7% of the organism was resistant to oxacillin. It was also shown that 51.1% and 65.1% of the S. pneumoniae strains were resistant to gentamicin and trimethoprim/sulfam, respectively. From these results, it is clear that a lot of multi-drug resistant S. pneumoniae strains including penicillin-resistant S. pneumoniae were frequently detected in an urban poor area.     

Oxidative degradation of polymers. II. Thermal oxidative degradation of atactic polypropylene in solution under pressure

Atactic polypropylene was oxidized in solution in the presence and absence of radical initiator over the temperature range of 140° to 200°C under oxygen pressure of 3.3 to 12.4 kg/cm², and the effects of metal catalyst and additives on the rate, products, and change in molecular weight distribution were measured. The synergistic effect was observed with cobalt and managanese salts. The deactivation of the metal catalyst was suppressed by the addition of acetic acid and acetic anhydride as solvent. The rate of oxidation increased with increasing temperature, but the decrease in molecular weight was nevertheless not so significant as to give many low-boiling products. However, the production of mixtures of acid, ketone, alcohol, and ester with molecular weights of several hundreds was promising. The refractive index of polypropylene decreased markedly as the oxidation proceeded, and the complications involved in the determination of the change in molecular weight distribution measured by gel permeation chromatography are discussed.     

Discrimination of Listeria monocytogenes contaminated commercial Japanese meats

Discrimination was attempted on 14 Listeria monocytogenes strains isolated from commercially available Japanese pork and chicken. Examination of the isolates was performed by restriction fragment length polymorphism (RFLP) analysis of the chromosomal DNA and amplified products and comparison of the nucleotide sequences of the amplified products. A polymorphism region containing the repeated sequences in the iap gene was amplified by the polymerase chain reaction (PCR). The genetic analyses could discriminate the 14 isolates in combination with traditional serotyping, and some strains isolated from different meats were confirmed to have a genetically close relationship. Genetic analyses used in the present study would be useful for the elucidation of the pathogen tracks from contaminated sources to humans and of the ecological niche in the food environment.     

Electrochromic properties of the n-heptyl viologen-ferrocyanide system

Electrochromic properties of the mixed solution of n-heptyl viologen dibromide (HV), Fe(CN) ₆ ^4– and NaH₂PO₂ or KBr were investigated by cyclic voltammetry and the transparency-time relation. When Fe(CN) ₆ ^4– is added to a HV solution the mixture colours violet without inputting any voltage. However, the colour fades gradually by further addition of NaH₂PO₂, and the transparency of the mixture increases with addition of larger amounts of NaH₂PO₂. The same effect was observed by addition of KBr to the HV-Fe(CN) ₆ ^4– solution. The input voltage required for the electrochromism of HV is lowered considerably by addition of Fe(CN) ₆ ^4– , when NaH₂PO₂ or KBr plays a role in controlling the colouringerasing phenomena. The HV-Fe(CN) ₆ ^4– -KBr system showed some HV residue in the cyclic voltammogram on an indium-tin oxide (ITO) electrode, while no such HV residue was observed in the HV-Fe(CN) ₆ ^4– -NaH₂PO₂ system. The HV-Fe(CN) ₆ ^4– -NaH₂PO₂ system is superior in colouring-erasing reproducibility and in response time to the HV solution or the HV-Fe(CN) ₆ ^4– system.     

‘Flaw matrix’ and its application to some ceramics

An improved method for the prediction of fatigue life and/or failure strength of ceramics is proposed, which is especially useful for ceramics whose failure strength does not follow Weibull statistics and for the prediction of failures with a low probability. It was shown that various types of failure data such as fatigue life, failure strength and short time failure strength are all useful for the prediction of failures. Experimental verification of the method is given for various types of ceramics and stressing processes.