Effect of grain size on creep of Ti-53.4mol%Al intermetallics at 1100 K

Constant stress creep under compression stress, 100 to 316 MPa, at 1100 K was investigated on single-phase TiAl intermetallics. The material was ingot-cast, isothermally forged, and then annealed to produce stable equi-axed grain structures, whose average grain diameters were 25, 42 and 70m. Creep curves were very similar among the three specimens with different grain diameters and the creep rates at a given strain, as well as the minimum creep rates, depended little on grain size. Two regimes were observed on the stress dependence of the minimum creep rate. The stress exponent under high stresses was about 4.5, independent of grain size. Under stresses lower than about 150 MPa it became about 8.     

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.     

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.     

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     

Properties of aqueous solutions of several salts of α,ω-alkanediol disulfates

Several salts of α,ω-sulfates, MO₃SO(CH₂)_n OSO₃M(n=12, 14, 16, 18, and M=Li, Na, and K) were prepared from the corresponding α,ω-alkane diols. The Krafft points of these α,ω-sulfates with common counterion as estimated by electroconductivity measurements increased with the increase of the hydrocarbon chain length, and the effect of the counterions on the Krafft points of the α,ω-sulfates with the same hydrocarbon chain length was in the order : Li<Na<K. Solutions of the α,ω-sulfates, except disodium dodecanediol disulfate, showed two break points corresponding to the first and second critical micelle concentration in each plot of the electroconductivity as a function of the concentration. The existence of the second break point suggested that another aggregation of rearrangement of the existing aggregates occurs in α,ω-sulfate solutions in addition to the usual micelle formation. The first and second break points of α,ω-sulfates with sodium counterion decreased logarithmically with increasing total number of methylene groups. The relationships were given as follows: log(first break point)=−0.138Nc−0.095; log(second break point)=−0.104Nc−0.251. The effect of the counterions upon the break points of α,ω-sulfates with the same hydrocarbon chain length was in accordance with their positions in the lyotropic series.     

Measurement of internal stresses in coatings using time resolved fluorescence

This paper describes a new nondestructive technique for detecting internal stresses in coatings using time resolved fluorescence. The measurement principle is based upon an experimental result that the decay time of fluorescence from poly(3-octylthiophene), P3OT, dispersed in uniaxially-stretched polymer films decreases with increasing tensile stress acting on the films. Internal stresses in the clear coat and in the base coat of a multilayer structure, which was composed of electrodeposited coat, surface coat, base coat, and clear coat, were estimated from the decay time of fluorescence from P3OT in both coats. The order of internal stresses in the clear coat and base coat of the multilayer system was 1 MPa. When the coatings were piled up, the internal stress decreased as the distance from a metal substrate was increased. It was found that moisture and temperature influenced internal stresses in the clear coat rather than in the base coat. Internal stress in the clear coat, which was one layer coated on a metal substrate, was measured by the traditional bimetallic method or by the time resolved fluorescence technique. Comparing both methods, it was concluded that the time resolved fluorescence technique gave reliable values for internal stresses in coatings.     

Studies on the nuclear magnetic resonance spectra of olefinic protons of conjugated fatty acid methyl esters

The NMR spectra of olefinic protons in the four representative conjugated fatty acid methyl esters, methylcis-9,trans-11-octadecadienoate, methyltrans-9,trans-11-octadecadienoate, methyl α eleostearate, and methyl β eleostearate, were studied. The chemical shift of each olefinic proton in these compounds was determined by considering their intramolecular environment. Coupling constants were also obtained as the results of spectral analysis.