Effect of bound water on piezoelectric,dielectric, and elastic properties of wood

The interaction of water with wood, such as bamboo and cedar, is investigated by measuring their complex piezoelectric, dielectric, and elastic constants between -150 and 150°C at 10 Hz. Bamboo and cedar are found to have two hydration-dependent elastic loss peaks; one is observed at about -100°C and the other at about -40°C. The former loss peak is due to the adsorbed water in the hydration range between 0 and 4% moisture content (MC) and the latter to the adsorbed water above 4% MC. These two types of water are considered bound on different sites in the regions around crystalline cellulose, where molecules of one type associate with each other and molecules of the other are unassociated. We consider that the piezoelectric polarization of wood is attributed to the rotation of hydroxyl groups in the crystal lattice of cellulose. The piezoelectric constants are observed to decrease but the elastic and dielectric constants to increase with increasing hydration. The effect of adsorbed water on elastic losses in bamboo and cedar are found to be similar to that in collagenous substances.     

Electric field-induced piezoelectricity in polymer film

An apparatus is devised for measuring the real and imaginary components of the piezoelectric strain constant d = d′ ? id″ for polymer films with a d.c. bias field. Electric fieldinduced piezoelectricity is observed for films of several types of polymer. The ratio of the piezoelectric constant to the d.c. bias field gives (? + κ)/G where ? is the dielectric constant, κ is the electrostriction constant, and G is the elastic constant. The temperature dependence of the field-induced piezoelectricity gives, therefore, combined information of dielectric and elastic properties of polymers. After heating to about 95°C followed by cooling to room temperature, maintaining a constant d.c. basis on a poly(vinyl chloride) film, piezoelectricity is observed at null d.c. field, which suggests the introduction of a residual polarization in the films.     

Spatial clustering procedures for region analysis

This paper describes two clustering procedures for region analysis of image data and discusses the security of these algorithms theoretically. First our algorithms find kernels of regions and then classify pixels into regions using these kernels. The first algorithm distinguishes the regions that have far more distances than the given distance and the second algorithm distinguishes C regions that are great distances from each other in the feature space. These parameters are criteria which decide whether regions are similar or dissimilar. Examples are presented in order to show how these algorithms work for real image data.     

Kinetic study of thermostable L-threonine dehydrogenase from an archaeon Pyrococcus horikoshii

In the genome data base of the hyperthermophilic archaeon Pyrococcus horikoshii, an open reading frame with sequence homology to a gene encoding alcohol dehydrogenase was found. It was demonstrated that the encoded enzyme was a thermostable L-threonine dehydrogenase which can oxidize the hydroxy alkyl residue of L-threonine associated with the reduction of NAD+ or NADP+. This enzyme is a member of the zinc-containing L-threonine dehydrogenase family. One enzyme molecule contained one zinc atom, and this metal was considered to contribute to the hyperthermostablility of the enzyme. The reaction of the enzyme proceeded via a sequential mechanism. The Michaelis constants (Km) for L-threonine and NAD+ were 0.013 and 0.010 mM, respectively, and the maximum reaction rate (Vmax) was 1.75 mmol NADH formed/min/mg-protein at 65 degrees C. The Km values for both L-threonine and NADP+ were larger than those for L-threonine and NAD+ with a similar Vmax value. These results indicate that the enzyme has lower affinity to NADP+ than to NAD+, and the binding affinity for L-threonine depends on the coenzymes.     

Is atrial fibrillation resulting from rheumatic mitral valve disease a proper indication for the maze procedure?

BACKGROUND: There are a few patients without detectable atrial contraction despite restoration of atrial rhythm after the maze procedure for atrial fibrillation (AF) associated with mitral valve disease. METHODS: From January 1995 to March 1997, 29 consecutive patients with AF associated with mitral valve disease underwent our modified maze procedure combined with mitral or other valve operations. The causes of mitral valve disease were rheumatic mitral stenosis (n = 22) and nonrheumatic mitral regurgitation (n = 7). The 17 patients with postoperative atrial rhythm were divided into group I with rheumatic mitral stenosis (n = 10), and group II with mitral regurgitation of nonrheumatic origins (n = 7). RESULTS: Seventeen patients regained atrial rhythm, 2 patients had junctional rhythm, and another 10 remained in AF. Between the group of patients with restoration of atrial rhythm and that of patients remaining in AF, significant differences were found in the percentage with rheumatic disease, history of AF, and maximum f-wave voltage. The postoperative peak velocity of the atrial filling wave to peak velocity of early filling wave ratio for the left atrium measured using Doppler echocardiography was 0.25 in group I, which was significantly lower than that (0.42) in group II. CONCLUSIONS: Reconsideration of the indications for the maze procedure for AF associated with rheumatic mitral stenosis may thus be reasonable, particularly for cases in which replacement using a prosthetic valve is necessary, but we believe that patients with nonrheumatic mitral valve disease, especially those able to undergo reconstructive operations, are the best candidates for the maze procedure.     

Fabrication of Lead-Free Piezoelectric (Na/sub 0.5/K/sub 0.5/)NbO/sub 3/Ceramics by a Modified Solid-State Reaction Method

Sodium potassium niobate, (Na_0.5K_0.5)NbO₃, fine powder has been successfully synthesized at the low temperature of 550degC through a modified solid-state reaction method, in which urea [CO(NH₂)₂] plays an important role. High-density (Na_0.5K_0.5)NbO₃ ceramics could be obtained by conventional sintering of the synthesized (Na_0.5K_0.5)NbO₃ fine powder with the addition of 0.03 mol% Co₃O₄ as a sintering additive. The crystal structure, microstructure, and dielectric and piezoelectric properties were characterized. The (Na_0.5K_0.5)NbO₃ ceramic showed a comparatively saturated P-E hysteresis loop. The (Na_0.5K_0.5)NbO₃ ceramic also displayed piezoelectricity with a piezoelectric constant d₃₃ of 126 pC/N and a planar electromechanical coupling factor k_p of 33%.     

Tritium diffusivity in crystal grain of Li2TiO3 and tritium release behavior under several purge gas conditions

It has been reported by the present authors that behavior of tritium release from solid breeder grain is consisted of diffusion in grain, tritium transfer at surface layer and surface reactions on grain surface such as adsorption or isotope exchange reactions. Tritium release curves estimated using the tritium release model gave good agreement with observed tritium release curves from Li₄SiO₄, Li₂ZrO₃ or LiAlO₂.

Tritium release behavior from Li₂TiO₃ under humid purge gas, dry purge gas and dry purge gas with hydrogen conditions is discussed in this study, tritium release curves using the release model that we proposed previously give a good agreements with experimental tritium release curves. Tritium effective diffusivity in the crystal grain of Li₂TiO₃ is also estimated in this study using a curve-fitting method applied to the release curves obtained under the humid purge gas condition. It is discussed that change of color of Li₂TiO₃ surface under hydrogen purge gas condition is observed and this phenomenon might affect tritium release behavior from Li₂TiO₃.     

Piezoelectricity of the Transmembrane Protein ba3 Cytochrome c Oxidase

Controlling the electromechanical response of piezoelectric biological structures including tissues, peptides, and amino acids provides new applications for biocompatible, sustainable materials in electronics and medicine. Here, the piezoelectric effect is revealed in another class of biological materials, with robust longitudinal and shear piezoelectricity measured in single crystals of the transmembrane protein ba₃ cytochrome c oxidase from Thermus thermophilus. The experimental findings from piezoresponse force microscopy are substantiated using a range of control measurements and molecular models. The observed longitudinal and shear piezoelectric responses of ≈ 2 and 8 pm V⁻¹, respectively, are comparable to or exceed the performance of commonly used inorganic piezoelectric materials including quartz, aluminum nitride, and zinc oxide. This suggests that transmembrane proteins may provide, in addition to physiological energy transduction, technologically useful piezoelectric material derived entirely from nature. Membrane proteins could extend the range of rationally designed biopiezoelectric materials far beyond the minimalistic peptide motifs currently used in miniaturized energy harvesters, and the finding of robust piezoelectric response in a transmembrane protein also raises fundamental questions regarding the molecular evolution, activation, and role of regulatory proteins in the cellular nanomachinery, indicating that piezoelectricity might be important for fundamental physiological processes.