Effect of anisotropy on acoustoelastic birefringence in wood

The ultrasonic velocity of shear waves propagating through radial direction of a wood plate specimen, transversely to the loading direction, was measured. By rotating an ultrasonic sensor, the oscillation direction of the shear waves was varied with respect to the wood plate axis and loading direction. The relationship between shear wave velocity and oscillation direction was examined to discuss the effect of anisotropy on the acoustoelastic birefringence in wood. The results obtained were summarized as follows. When the oscillation direction of the shear wave corresponded to the tangential direction of the wood specimen regardless of the stress direction, shear wave velocity decreased markedly and the relationship between shear wave velocity and rotation angle tended to become discontinuous. That is, when the shear waves oscillated in the anisotropic axis of the wood, the shear wave velocity peaked unlike in the case of oscillation in the stress direction. In an isotropic material (acrylic, aluminum 5052), on the contrary, when the shear waves oscillated in the stress direction of the specimen, the shear wave velocity peaked regardless of the main-axis direction of the specimen. On the basis of the discussion of these results, the ultrasonic shear wave propagating in wood under stress is confirmed to be polarized in the anisotropic axis of the wood.     

Effect of cholesterol and other additives on viscosity, self-diffusion coefficient, and intramolecular movements of oleic acid

It has been empirically known that cholesterol largely increases the viscosity of oleic acid. To clarify the mechanism of the effect of cholesterol on the intermolecular and the intramolecular (segmental) movements of oleic acid in the liquid state, we measured density, viscosity, IR, 1H NMR chemical shift, self-diffusion coefficient, and 13C NMR spin-lattice relaxation time for the liquid samples of oleic acid containing a small amount of cholesterol. Furthermore, the above measurements were also carried out for the samples of oleic acid containing a small amount of cholestanol, cholestane, cholesteryl oleate, ethanol, or benzene. Cholesterol, possessing one OH group and one double bond in its molecular structure, largely increased the viscosity and reduced the self-diffusion and the intramolecular movement of oleic acid. Cholestanol, possessing one OH group but not a double bond, and cholesteryl oleate, not possessing an OH group, also reduced the self-diffusion and the intramolecular movement; cholestane, not possessing an OH group, slightly reduced the self-diffusion and the intramolecular movements. In contrast with these sterols, ethanol and benzene reduced the viscosity and increased the self-diffusion and the intramolecular movements. In addition, cholesterol and ethanol, both having one OH group, promoted the upfield shift of the 1H NMR signal of the carboxyl group of oleic acid; IR difference spectra for the cholesterol/oleic acid system quite resemble those for the ethanol/oleic acid system. These results suggest that oleic acid makes a complex with cholesterol as well as with ethanol. On the basis of the formation of the complex, we have revealed the role and the functional mechanism of cholesterol to the intermolecular and the intramolecular movements of oleic acid in the liquid state.     

Determination of dimethyl sulfoxide and dimethyl sulfone in urine by gas chromatography–mass spectrometry after preparation using 2,2‐dimethoxypropane

A method for routinely determination of dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO₂) in human urine was developed using gas chromatography–mass spectrometry. The urine sample was treated with 2,2‐dimethoxypropane (DMP) and hydrochloric acid for efficient removal of water, which causes degradation of the vacuum level in mass spectrometer and shortens the life‐time of the column. Experimental DMP reaction parameters, such as hydrochloric acid concentration, DMP–urine ratio, reaction temperature and reaction time, were optimized for urine. Hexadeuterated DMSO was used as an internal standard. The recoveries of DMSO and DMSO₂ from urine were 97–104 and 98–116%, respectively. The calibration curves showed linearity in the range of 0.15–54.45 mg/L for DMSO and 0.19–50.10 mg/L for DMSO₂. The limits of detection of DMSO and DMSO₂ were 0.04 and 0.06 mg/L, respectively. The relative standard deviations of intra‐day and inter‐day were 0.2–3.4% for DMSO and 0.4–2.4% for DMSO₂. The proposed method may be useful for the biological monitoring of workers exposed to DMSO in their occupational environment. Copyright © 2009 John Wiley & Sons, Ltd.     

Electrical conduction in undoped and yttrium-doped Na2SO4

The electrical conductivity of undoped and yttrium-doped Na₂SO₄ has been measured by the ac two-terminal method at temperatures between 540 and 1075 K in air or in SO₂O₂SO₃ atmospheres. At high temperatures such as 1075 K, doping of 1.7 at% yttrium (Y) decreases the conductivity, which indicates that the Frenkel defect of sodium ions is pre-dominant in Na₂SO₄ and that the mobility of the interstitial ions is higher than that of the vacancies. However, the vacancy concentration is high enough to increase the conductivity in the samples doped with 2.0–3.8 at% Y. A further addition of yttrium decreases the electrical conductivity again, suggesting the appeareance of defect interactions such as ordering or clustering of the defects. The electrical conductivity of the undoped and the 4 at% Y-doped Na₂SO₄ is independent of the SO₃ partial pressure. The complex impedance analysis shows that the grain boundary resistance increases with sintering time. This is probably caused by a decrease in the contact area between grains during sintering.     

Applicability of sodium sulfate as a solid electrolyte for a sulfur oxides sensor

The electromotive force (EMF) has been measured on SO₂O₂SO₃ concentration cells using undoped and 4 at.% yttrium-doped Na₂SO₄ as solid electrolytes at temperatures between 920 and 1120 K. Two types of electrolytes prepared by sintering and infiltration have proven to work basically well above 973 K. The observed EMF's are consistent with the values calculated from the Nernst equation in the wide concentration range of SO_x, showing that the ionic transference number is unity both in the undoped and yttrium-doped Na₂SO₄. A large difference in SO_x pressures between the anode and the cathode leads to the lowering of the EMF because of the permeation of gases through the macroscopic defects such as pores and cracks in the electrolyte. The experimental results suggest that improvement of the sinterability and the stabilization of the high temperature phase are the indispensable problems to solve for the practical application of Na₂SO₄ as a solid electrolyte to an SO_x sensor.     

Parametric simplex algorithms for solving a special class of nonconvex minimization problems

It is shown that parametric linear programming algorithms work efficiently for a class of nonconvex quadratic programming problems called generalized linear multiplicative programming problems, whose objective function is the sum of a linear function and a product of two linear functions. Also, it is shown that the global minimum of the sum of the two linear fractional functions over a polytope can be obtained by a similar algorithm. Our numerical experiments reveal that these problems can be solved in much the same computational time as that of solving associated linear programs. Furthermore, we will show that the same approach can be extended to a more general class of nonconvex quadratic programming problems.     

The effect of pressure on gas permeation through semicrystalline polymers above the glass transition temperature

A method is proposed to analyze the effect of pressure on permeation of gases through semicrystalline polymers above the glass transition temperature. The method utilizes similarities in molecular diameters of the gases and differences in their solubilities. Two polymers, polyethylene and polypropylene, and a series of gases are chosen for an application of the method, and the effect of pressure on the permeabilities for 10 gases is measured in the pressure range 1–130 atm at 25°C. For polymers, the logarithm of the permeability coefficient is linear in the pressure for each gas, with negative slope for slightly soluble gases (He, Ne, H₂, N₂, O₂, and Ar) and positive slope for highly soluble gases (CH₄, Kr, CO₂, and N₂O). Analyzing these slopes by the method proposed permits contributions of hydrostatic pressure and concentration to the pressure dependence of permeation to be evaluated. On the basis of the results, the mechanism of gas permeation in rubbery films under high pressures is discussed.     

Sorption and dilation in poly(ethyl methacrylate)–carbon dioxide system

Sorption and dilation in the system poly(ethyl methacrylate) (PEMA) and carbon dioxide are reported for pressures up to 50 atm over the temperature range 15–85°C. The sorption isotherms were obtained gravimetrically. The dilation accompanying sorption was measured directly with a cathetometer. At low temperatures the sorption and dilation isotherms were concave toward the pressure axis in the low-pressure region and turned to convex with increasing pressure. As the experimental temperature approached and exceeded the glass transition temperature of 61°C, both isotherms became convex or linear over the whole range of pressure. Partial molar volumes of CO₂ in PEMA were obtained from sorption and dilation data, which were described well by the extended dual-mode sorption and dilation models developed recently. The temperature dependence of the dual-mode parameters and the isothermal glass transition are discussed.     

Sorptive dilation of polysulfone and poly(ethylene terephthalate) films by high-pressure carbon dioxide

Dilation of polysulfone (PSUL) and crystalline poly(ethylene terephthalate) (PET) films accompanying sorption of carbon dioxide is measured by a cathetometer under high pressure up to 50 atm over the temperature range of 35–65°C. Sorptive dilation isotherms of PSUL are concave and convex to the pressure and concentration axes, respectively, and both isotherms exhibit hysteresis. Each dilation isotherm plotted versus pressure and concentration for the CO₂-PET system shows an inflection point, i.e., a glass transition point, at which the isotherm changes from a nonlinear curve to a straight line. Dilation isotherms of PET below the glass transition point are similar to those of the CO₂-PSUL system, whereas the isotherms above the glass transition point are linear and exhibit no hysteresis. Partial molar volumes of CO₂ in these polymers are determined from data of sorptive dilation. On the basis of the extended dual-mode sorption model and the current data, primitive equations for gas-sorptive dilation of glassy polymers are proposed.