Sensitivity of an anadically oxidized aluminium film on a surface acoustic wave sensor to humidity

The sensitivity, transient response and sensitivity mechanism of a surface acoustic wave humidity sensor using porous anodically oxidized aluminium (alumina) films as mechanical interfaces have been studied theoretically and experimentally. It is found that the sensitivity of alumina films of 1.0 μm thickness is -0.034 m/(s %RH) and is the same order as that of polyimide films. The transient response of alumina films to humidity is about one order faster than that of polyimide films. For the sensitivity mechanism, the phase-velocity change is attributed to the mechanical perturbation caused by the absorption of water molecules. The equivalent density change of alumina films between 0 and 100%RH is about 0.7%. In addition, the actual stiffness constants of alumina films are two orders less than those of bulk alumina.     

Preparation and characterization of porous and electrically conducting carbon-clay composites

Porous and electrically conducting carbon-clay composites were prepared by firing mixtures of carbon powder (0 to 20 wt%) and clay minerals. They showed porosity of 50 to 65% and had high mechanical strength (compressive strength = 130 to 400 kg cm^–2) as well as high resistance against thermal oxidation in air. Their electrical conductivity, , increased with increasing carbon content levelling off at about 20 wt% of carbon content to give a value of about 2 S cm^–1. Formation of carbon chains is considered to be responsible for the electrical conduction in the composite, and a model to correlate the electrical conductivity with the carbon content has been proposed by modifying a model previously proposed by Scarisbrick.     

Preparation of zirconia-toughened bioactive glass-ceramics

Bioactive glass-ceramics toughened by tetragonal zirconia polycrystal (TZP) were prepared by hot-pressing mixed powders of the MgO-CaO-P₂O₅-SiO₂ glass and TZP containing 20 to 80% alumina. The bending strength and the fracture toughness of the composite materials were improved compared with those of the material without TZP. These composites showed high bending strengths (400 to 500MPa) and high fracture toughness ( 2.8MPa m^1/2). The existence of a crack deflection mechanism was observed by scanning electron microscopy. After soaking in simulated physiological solution at 100 °C, no phase transformation from tetragonal to monoclinic of TZP in the composites and no degradation in bending strength occurred.     

Laser spectroscopic measurement of quenching and doublet mixing rates of the Na(3P(3/2, 1/2)) doublet in a propane-air flame

We have measured the quenching rate of the Na 3P level and the doublet mixing rates of the Na 3P(3/2) and 3P(1/2) levels in a propane-air flame at atmospheric pressure. To obtain these rates, subnanosecond time-resolved fluorescence measurements were made using a mode-locked dye laser and the time-correlated single-photon counting method. Our results are 1.4 x 10(9) s(-1) for the quenching rate and 3.0 x 10(9) s(-1) for the 3P(3/2) --> 3P(1/2) mixing rate.     

Local Epidermal Endocrine Estrogen Protects Human Melanocytes against Oxidative Stress,a Novel Insight into Vitiligo Pathology

As the outermost barrier of the body, skin is a major target of oxidative stress. In the brain, estrogen has been reported synthesized locally and protects neurons from oxidative stress. Here, we explored whether estrogen is also locally synthesized in the skin to protect from oxidative stress and whether aberrant local estrogen synthesis is involved in skin disorders. Enzymes and estrogen receptor expression in skin cells were examined first by quantitative real-time PCR and Western blot analyses. Interestingly, the estrogen synthesis enzyme was mainly localized in epidermal keratinocytes and estrogen receptors were mainly expressed in melanocytes among 13 kinds of cultured human skin cells. The most abundant estrogen synthesis enzyme expressed in the epidermis was 17β-hydroxysteroid dehydrogenase 1 (HSD17β1) localized in keratinocytes, and the most dominant estrogen receptor expressed in the epidermis was G protein-coupled estrogen receptor 1 (GPER1) in melanocytes. To investigate whether keratinocyte-derived estradiol could protect melanocytes from oxidative stress, cultured human primary epidermal melanocytes (HEMn-MPs) were treated with H₂O₂ in the presence or absence of 17β estradiol or co-cultured with HSD17β1 siRNA-transfected keratinocytes. Keratinocyte-derived estradiol exhibited protective effects against H₂O₂-induced cell death. Further, reduced expression of HSD17β1 in the epidermis of skin from vitiligo patients was observed compared to the skin from healthy donors or in the normal portions of the skin in vitiligo patients. Our results suggest a possible new target for interventions that may be used in combination with current therapies for patients with vitiligo.     

Corrosion rate of magnesium and its alloys in buffered chloride solutions

The effect of the buffer capacity of test solution on the corrosion rate of cast pure (>99.95 mass%) and high-purity (>99.9999 mass%) magnesium, and AZ31 and AZ91E has been studied. Their corrosion rates were measured gravimetrically in a pH 6.5 and a pH 9 borate buffer including chloride ions, and in a conventional chloride solution. Except for the AZ91E in the pH 6.5, the corrosion rates of all the examined materials depended solely on the pH of the test solution, although the materials had a variety of purity and alloying elements. Higher buffer capacity probably masked the detrimental effect of the “cathodic impurities”. The corrosion rates measured in the buffers were considered as giving the resistivity of the passive film to anodic reactions. The high-purity magnesium had a fair corrosion resistance even in conventional chloride solution.     

Humidity Sensor Characteristics of Woodceramics

The humidity sensor characteristics of Woodceramics were investigated. The Woodceramics used in this experiment were prepared at 650–900°C. The size of specimens selected was 1 × 1 × 10 mm . One was used as-cut and the other was polished. Above 700°C, the resistance of the specimen was below 50 and the decrease of resistance with increasing relative humidity was small. The specimen prepared at 650°C had a resistance of about 1 k. The resistance of as-cut specimens decreased with increase in relative humidity, but that of the polished specimen did not change significantly. The difference between as-cut and polished samples was explained by the differences in surface micro-structure.     

Laser-Sintered Barium Titanate

Laser sintering of alkoxy-derived ultrafine BaTiO₃ powders was investigated. The temperature increases of the sample with laser irradiation were measured with a thermocouple. It was found that laser irradiation could generate enough heat to sinter ceramics. A slurry was prepared by mixing an alkoxy-derived BaTiO₃ powder, binder additives, solvent, and plasticizer. The slurry was tape cast and dried to give a green sheet. The green sheet was laser sintered and was then characterized by SEM, XRD, and density measurements. The effect of burnout before laser irradiation and the characteristic microstructure of laser-sintered BaTiO₃ are described.     

Surface modification of tetrafluoroethylene–perfluoroalkyl vinylether copolymer (PFA) by plasmas for copper metallization

Tetrafluoroethylene–perfluoroalkyl vinylether copolymer (PFA) sheet surfaces were modified with argon, helium, oxygen, and hydrogen plasmas. How the four plasmas modified the PFA sheet surfaces was investigated. All plasmas modified the PFA surfaces and at the same time initiated degradation of the PFA polymer chains. The balance between modification and degradation was strongly influenced by the magnitude of the discharge current in the plasmas. Efficiency of the plasmas in modification was hydrogen plasma > oxygen plasma > argon plasma > helium plasma. The modification involved defluorination of CF₂ carbons into CHF and CH₂ carbons and oxidation into O? CH₂, O? CHF, and O? CF₂ groups. The surface‐modification technique (a combination of hydrogen plasma treatment and silane coupling treatment) proposed in this study was applied for copper metallization of the PFA surface. The utility of the technique was confirmed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1087–1097, 2002