Theoretical description with a potential is made for inhomogeneous structures of high field domain and current filament in semiconductors with a negative differential conductivity (NDC) appearing under voltage- and current-controlled conditions, respectively. The potential proposed here can describe systematically a route from homogeneous state to the patterned state through the instability of homogeneous state, whereas previously proposed potentials can describe only the patterned state. The potential is constructed from two internal variables: one is the variable dependent on the spatial coordinate which exhibits the spatial pattern in the NDC region, while another remains constant spatially but changes discontinuously its value when the patterned state bifurcates from a thermodynamic branch of the homogeneous state. The bifurcation to spatial pattern is examined in a similar way to the first-order phase transition in equilibrium systems. At the same time, the property of the resulting pattern is discussed from analogy with the phase separation.

Spatio-temporal patterns of electric potential produced by a root of azuki bean were investigated. It was found that the electric potential of a root shows a banding pattern surrounding the root and also a spontaneous oscillation. This electro-magnetic circumstance has a relation to its growth.

A nonperturbative method is presented for describing approximately the behavior of a self-oscillation of electric voltage in the Van der Pol equation over a wide range of the value of external parameter µ. To express an appreciably distorted wave form for the steady self-oscillation at µ1, a phase F of the voltage x, defined by x2A cos F (ωt), is approximated by a combination of several straight lines as a function of ωt from 0 to 2π with several numerical coefficients determined mainly from asymptotic behaviors of x for µ1 and µ1. It is shown that the resultant expression for x can describe well the numerical result over the wide range of µ. A bursting phenomenon induced by an oscillation of µ with a long period is also discussed on the basis of the present method, and the analytical results are in good agreement with the numerical ones.

Two-dimensional pattern of an electric potential around a horizontally-placed root of adzuki bean was detected by a multi-electrode measuring system. The vectors of electric current calculated from the electric potential pattern show a long route from the basal part of the root to the apical part.

The growth of a primary root was studied for adzuki beans incubated under an external electric field. An electric current was applied to the solution around the root, which was laid horizontally. The electric potential and pH patterns were measured along the root. The change of the growth speed was observed when the electric field, corresponding to a current of 1-10 µA/cm2, was applied for a period of 15 to 60 min. The application of the electric field in the direction from the base to the tip of a root activated the growth of the root, whereas the growth was inhibited by applying the electric field of the reverse polarity. The changes of the growth rates were both about 20% for the currents of 10 µA/cm2. The root was generating an electric current pattern in the aqueous solution around its surface with the maximum current density of the order of 1 µA/cm2. In the activation of the growth, the amplitude of the electric potential pattern and the acidification around the root were found to be increased. The opposite tendency was obtained in the growth inhibition. The degree of acidification corresponds to the change of the growth rate by a well-known acid growth mechanism.

There are methods used to test the optical purity of enantiomers; however, most of the simple methods are not precise and more complicated methods are better. As a result, these methods cannot be widely used for industrial purposes. The aim of this research is to design a sensor which can discriminate D-amino acids from L-amino acids. The designed sensor has chiral membranes and uses the technique of impedance change of these chiral membranes to discriminate the amino acids. We used a noise-FFT (Fast Fourier Transform) technique to determine the membrane impedance. When an enantiomer membrane resides in a chiral environment, (E*), diastereomeric interactions (E*-D) and (E*-L) are created, which may differ sufficiently in the arrangement of molecules of the membranes so as to permit the discrimination of optical substances due to the change in membrane characteristics. With increasing concentrations of the amino acids, the membrane resistance changes depended on the optical activity of the amino acids. The results suggest that the impedance changes of the chiral membrane with diastereomeric reaction can be used for the high-performance chemical sensor to measure the optical purity of different substances.

Saltiness elicited by salt is one of the basic tastes. However, components of salt on the market differ depending on manufacturing processes and its taste as well. Salt manufactured by ion-exchange membrane process is composed of more than 99% pure sodium chloride, while bay salt contains trace coexisting components. Despite reports on sensory evaluation, the differences in taste are still uncertain because of a small amount of coexisting components. We studied the taste of salt with trace coexisting components; the bittern ("nigari" in Japanese) was evaluated objectively and quantitatively using a multichannel taste sensor with lipid/polymer membranes. A taste sensor is comprised of several types of lipid/polymer membranes for transforming information of taste substances into electric signals. The model samples were composed of sodium chloride and trace coexisting components such as magnesium sulfate, magnesium chloride, calcium chloride and sodium chloride. The taste sensor clearly discriminated each sample according to the response patterns. Based on the sensor outputs, we evaluated the taste by means of the combination of principal component analysis and ionic strength. The results show the taste of salt with nigari has a correlation with ionic strength.

Primary roots of adzuki bean were incubated under an external electric field in the transverse direction across the root. A root was laid horizontally in a aqueous solution, and the electric field was generated by flowing the electric current in the solution. Roots bent to the side of the positive electrode. This bending tendency increased with increasing the electric field. The surface-electric potential and pH distributions were measured under the electric field and the normal condition. The application of electric field caused the asymmetries of the electric potential pattern and the acidification. At the activated side in the growth, corresponding to the electrically negative side of the root, the amplitudes of the potential and the acidification were found to increase whereas the opposite tendency was observed at the opposite side. The results with a theoretical consideration suggest that the symmetry of the growth was broken by an asymmetrical H+ re-distribution made by the external electrical force.

Chemical sensor which can be used for a multi-purpose chemical measurement to detect various chemical substances with a small number of a sensor array was investigated. It was confirmed that chemical compounds adsorbed strongly and irreversibly on a platinum surface using conventional electrochemical methods and an instrumental surface analysis. The adsorbates were also analyzed by means of an electrochemical impedance spectroscopy under dynamic potential scan; measured impedance reflects CPE (constant phase element) properties of the electrode surface. The method provides a convenient technique for the surface analysis of adsorbing chemicals. The CPE response profile was modified through chemical adsorption/desorption and the interaction between the polarized surface and chemical substances. Consequently, various profiles depending on chemical substances were obtained and it had quantitative and qualitative information about chemicals interacting with the surface. The present method which does not require a specific electrochemical reaction can be applied for multi-purpose chemical sensors and also simple chemical analyses.