Factors affecting the oxidative activity of laccase towards biphenyl derivatives in homogeneous aqueous-organic systems

Catalytic oxidation of biphenyl derivatives was investigated using laccase in a homogeneous aqueous-organic system. A thermostable laccase from Trametes sp. showed the highest catalytic activity for the oxidation of 4-hydroxybiphenyl (4-HB) at a reaction temperature of 60 degrees C when dimethylsulfoxide (DMSO) was employed as a co-solvent. Furthermore, the catalytic performance was successfully enhanced by the incorporation of a laccase mediator system (LMS) into the aqueous-DMSO media. The catalytic performance strongly depended on the type of mediator, and the highest activity was observed with 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as mediator, suggesting the importance of the selection of a suitable mediator. It was verified that this mediator system is applicable to the oxidation of several biphenyl derivatives with hydroxyl groups.     

Disintegration process of yttria-stabilized zirconia ceramics using hydrothermal conditions

Capability of the recycling of high strength and high fracture toughness yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) sintered body utilizing “low-temperature annealing degradation” phenomenon was investigated. Hydrothermal treatment was employed to induce the phase transformation from tetragonal to monoclinic zirconia and to disintegrate the Y-TZP sintered body. 3 mol% Y₂O₃–ZrO₂ specimens sintered at 1,550 °C and more were disintegrated without leaving the original appearances when the treatment temperature was between 200 °C and 400 °C. The size of the disintegrated fragments of Y-TZP sintered body was much affected by hydrothermal treatment conditions. Only with hydrothermal treatment and simple ball milling, the sintered body was pulverized into the primary particle level. This technique is expected to apply to a sustainable recycling system for the zirconia ceramics, which restrains an energy consumption compared to crushing zirconia using mechanical procedures.     

The influence of matrix on the quantum size effect of CdSe microcrystals-doped thin films

CdSe microcrystals were successfully dispersed in GeO₂ glass andCaF₂ crystal thin films by rf-sputtering. All films preparedshowed the blue shift of absorption edge in visible spectra due toquantum size effect. The amount of the blue shift of the filmsincreased with decreasing the size of the microcrystals. Comparingthe amount of the particle size–depending blue shift of CdSemicrocrystals dispersed in between the GeO₂, CaF₂ and SiO₂ matricies, the influence of the matrix on the shift was found.Therefore, it can be said that there is an influence of the matrix onthe quantum size effect. From the modified theoretical calculation,the influence of matrix was considered to appear through Coulombinteraction between electrons and holes.     

Strength and failure behavior of stitched carbon/epoxy composites

This article presents a study of the effect of through-the-thickness stitching yarns upon the strength and failure behavior of multidirectionally reinforced composites. The in-plane yarns were placed in four directions (0,±45, 90) to form a quasi-isotropic preform, which had open spaces between adjacent yarns. These interyarn spaces allowed easy insertion of the through-the-thickness stitching yarns without significant damage of the in-plane fibers. Fiber volume fractions of over 54 pct were obtained by this method. The through-the-thickness yarn sizes used in this study were 2, 4, and 6 kilo-filament (kf). Non-stitched performs were also manufactured with the same fiber content and by the same procedure as the stiched preforms for the control experiments. All preforms were infiltrated with epoxy resin by the resin transfer molding (RTM) technique. In-plane tensile and compressive strength, interlaminar shear strength, and mode I fracture toughness of the carbon/epoxy composites were measured at three through-the-thickness yarn contents. Although the through-the-thickness yarns significantly enhanced the mode I fracture toughness, they tended to degrade the in-plane tensile and compressive strength. The failure process under interlaminar shear loading by double notch shear tests showed two distinct stages: the fiber-matrix interfacial failure followed by the breakage/debonding of the through-the-thickness yarns. The through-the-thickness yarns caused a reduction of the initial failure load in the first stage but could enhance the final failure load in the second stage. In composites with 6 kf through-the-thickness yarns, the final failure load could exceed the initial failure load. Scanning electron microscope (SEM) and optical microscopic examinations were also conducted for observing the failure mechanisms and fracture surfaces. This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October 11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite-Materials Committee.     

Stability of a-Si:H solar cells deposited by Ar-treatment or by ECR techniques

Stability against light soaking was studied for amorphous silicon (a-Si:H) solar cells using three different i-layers; (a) device-quality a-Si:H (standard a-Si:H) with bandgap of 1.75 eV, (b) narrow bandgap (1.55 eV) a-Si:H fabricated by Ar* chemical annealing and (c) a-Si:H(Cl) fabricated from SiH₂Cl₂. Both the narrow bandgap a-Si:H and the a-Si:H(Cl) solar cells showed much improved stability than that of the standard a-Si:H solar cells: e.g., fill factor of the narrow bandgap a-Si:H cell only slightly decreased from 56% to 53%, while that of the standard a-Si:H cell degraded from 62% to 51%. In addition, mobility–lifetime products of the a-Si:H(Cl) cell also exhibited improved stability than that of the standard a-Si:H solar cell.     

Noninvasive Measurement of the Volume Elastic Modulus in Finger Arteries Using Photoelectric Plethysmography

A method for the nonivasive measurement of the volume elastic modulus (Ev) in human finger arteries was developed. The volume change ratio and pulse pressure in the arteries were simultaneously determined by a transmittance type infrared photoelectric plethysmograph and a volume oscillometric sphygmomanometer using an occlusive cuff. The Ev values could be obtained at a desired transmural pressure level of the arteries which was controlled by the cuff. A clear difference was revealed between the Ev values obtained in the fingers of two male subjects of 33 and 65 years old. The values determined by this method were compared to those calculated from pulse wave propagation velocity (Evp) obtained simultaneously in the fingers of 11 subjects. The linear regression equation was Ev = 1.31 Evp ?0.117 with a correlation coefficient r = 0.893 (n = 39). These results suggest that this should be a useful and noninvasive method of evaluating changes in arterial elasticity accompanying aging and perhaps influenced by accompanying hypertension or arteriosclerosis.