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The present study investigates adsorption of taste substances to lipid membranes for the multichannel taste sensor. To clarify the mechanism of adsorption of taste substances to a lipid membrane, we measured adsorption quantities of taste substances, such as amino acids and quinine-HCl, with fluorometry, and the surface of the lipid membrane was analyzed with ESCA (Electron spectroscopy for chemical analysis). Furthermore, we measured potential responses of a lipid membrane and pH of monosodium glutamate and lipid solutions. The results showed that amino acids adsorb to the lipid membrane, but no specific adsorption site exists on the membrane. The adsorption occurred by weak interaction between a phosphoric acid group of lipid molecules and an amino group of amino acids. Quinine-HCl adsorbed to membrane with strong electrostatic coupling and weak hydrophobic effects to lipid molecules in the membrane.

An ethanol sensor using two chloride ion-selective polymeric membrane electrodes (Cl-ISEs) was developed. Two different polymeric membranes were used, one with o-nitro-phenyloctyl ether (NPOE) and the other with n-decylalcohol (DA) as the plasticizer. The electrical potential of the Cl-ISE fell linearly with increasing ethanol concentration at a given concentration of Cl-. The electrical potential equation is viewed as a function of the concentration of ethanol and Cl-. The responses to ethanol and Cl- differed between plasticizers. The two Cl-ISEs showed nearly Nernstean slopes for Cl- in ethanol solution (0-20%). In addition, each electrode had good linearity for ethanol with a slope of −2.51 mV/ethanol % (NPOE) and −1.01 mV/ethanol% (DA), respectively. The concentration of ethanol and Cl- can be estimated by solving the simultaneous equations derived from the electrical potentials of the two different Cl-ISEs. To decrease the interference from co-existing components, KCl solution was added to the sample until the total concentration was 30 mM. The ethanol sensor using the two Cl-ISEs showed good accuracy in the measurement of ethanol in sake and shochu.

This paper describes an application of taste sensor for detection of cyanide. The taste sensor consists of multichannel sensors with lipid membranes which are modeled on living organisms. One of characteristics of this sensor is a global selectivity. In this study, we have developed a new effective method which is able to control the charge of membranes for high sensitivity and selectivity of lipid membrane sensors. Using this method, sensors for free cyanide and complex cyanide were developed. We could detect total cyanide under the guideline limit. It was possible to detect free cyanide below the concentration 0.5ppm in river water. Measurement time is within five minutes. In conclusion, the taste sensor has a very powerful performance and advantage for real time monitoring of water quality.

A multichannel taste sensor can respond to many kinds of chemical substances simultaneously with high sensitivity. It has a possibility to measure various substances that remain in used food packages. The purpose of the present research is to detect chemical substances which were dissolved to aqueous solution from three materials such as raw materials of PET bottles (poly (ethyleneterephthalate)), used PET bottles and recycled egg packages. We found that there is no metalic ions in these samples and hydrophobic substances were dissolved from used PET bottles and recycled egg packages. Additionally, we used near-infrared spectroscopy to analyze the substances; however, no significant spectrum was not found. This result implies that the multichannel taste sensor can be used to evaluate the quality of recycled food packages.

A multichannel taste sensor, namely an electronic tongue, with global selectivity is composed of several kinds of lipid/polymer membranes for transforming information about substances producing taste into electrical signals, which are input to a computer. The sensor output exhibits different patterns for chemical substances which have different taste qualities such as saltiness, sourness and bitterness, whereas it exhibits similar patterns for chemical substances with similar tastes. The sensor responds to the taste itself, as can be understood from the fact that taste interactions such as the suppression effect, which appears for mixtures of sweet and bitter substances, can be reproduced well. The suppression of the bitterness of quinine and a drug substance by sucrose can be quantified. Amino acids can be classified into several groups according to their own tastes on the basis of sensor outputs. The tastes of foodstuffs such as beer, coffee, mineral water, milk, sake, rice, soybean paste and vegetables can be discussed quantitatively using the taste sensor, which provides the objective scale for the human sensory expression. The flavour of a wine is also discriminated using the taste-odour sensory fusion conducted by combining the taste sensor and an odour-sensor array using conducting polymer elements. The taste sensor can also be applied to measurements of water pollution. Miniaturization of the taste sensor using FET produces the same characteristics as those of the above taste sensor by measuring the gate-source voltage. Use of the taste sensor will lead to a new era of food and environmental sciences.

The taste sensor showed a similar pattern for chemical substances producing the same taste qualities, while quite different patterns were obtained for substances with different taste qualities. In fact, similar outputs were obtained for, e.g., NaCl, KCl and KBr eliciting saltiness, whereas their patterns differed clearly from those for other basic taste qualities. The taste of amino acids was also classied into several groups in accordance with the human taste sense. The taste sensor has a new concept of global selectivity. What is important in recognition of taste is not discrimination of minute difference in molecules but to transform molecular information contained in interactions with biological membranes into several kinds of groups, i.e., taste intensities and qualities. This function is of a high level, where intelligent sensing is required. In this sense, the taste sensor is essentially an intelligent sensor to reproduce the taste sense, which is a complex, comprehensive sense of humans. Several kinds of commercial drinks such as coffee, beer and mineral water were discriminated easily using the taste sensor. The taste sensor has a sensitivity, reproducibility and durability higher than those of humans. Human taste expressions such as ‘bitterness’ and ‘sourness’ were quantied, and also the physico-chemical indices for food production such as alcohol concentration and titratable acidity were shown to be measured by the taste sensor. Improvements in the membranes and measurement methods have also been made for the purpose of measurements, e.g., by adopting the Langmuir�Blodgett method [38], a monolayer of thiol-containing lipids [39] or impedance measurements [40]. The taste sensor will be applicable for quality control in the food industry and will help the automation of production. The sense of taste is vague and largely depends on subjective factors of human feelings. If we compare the standard index measured by means of the taste sensor with sensory evaluation, we will be able to assess taste objectively. Moreover, the mechanism of information processing of taste in the brain as well as the reception at taste cells will also be claried by developing a taste sensor which has output similar to that of the biological gustatory system. In fact, a recent study [19] has shown that astringency is a taste expressed by bitterness and sourness, whereas astringency has so far been considered not as a taste sense but a tactile sense. The result using the taste sensor indicates that the reception mechanism of taste substances in biological systems should be reconsidered. Objective scales of physical quantities such as length and time were proposed over two thousand years ago. We are now familiar with quantitative, objective scales, although there exists subjective feeling as well. As for taste, however, we have had no scale so far. The taste sensor provides a quantitative, objective measure of taste. ‘Deliciousness’ will be measured simultaneously using other sensors. Excellent odor or gas sensing systems based on various principles have also been developed [41—47]. We are now standing on the threshold of a new age of food culture.

A multichannel taste sensor whose transducer is composed of several kinds of lipid/polymer membranes with different characteristics can detect taste in a manner similar to human gustatory sensation. Taste information is transformed into a pattern composed of electric signals of membrane potentials of the receptor part. In the present study, it was shown that the suppression of the bitterness of quinine and a drug substance by sucrose can be quantified using a multichannel taste sensor. The present method can be expected to provide a new automated method to measure the strength of bitterness of drug substance in the place of sensory evaluation.

We have developed a multichannel taste sensor with lipid membranes which can detect and quantify the basic taste substances in aqueous solution. The aim of the present study is to increase selectivity to adsorptive taste substances (bitter, umami and astringent taste substances) for quantification of taste by improving measuring methods. High selectivity to adsorptive taste substances is obtained by CPA measurement algorithm (CPA: Change of membrane Potential caused by Adsorption). High repeatability is also obtained by developing a cleaning technique of taste sensor.

Response mechanism of a membrane made of trioctylmethylammonium chloride (TOMA) to ethanol was studied. The response of the TOMA membrane to ethanol increased linearly with increasing ethanol concentration (0-20%) at constant KCl concentration. The slope of response to ethanol was-1.73 (mV/ethanol%) using the multiple regression analysis (0-20% ethanol, 1-100 mMKCI). The value of this slope calculated using the transfer activity coefficient of chloride ion from water to ethanol showed a good agreement with the experimental value. On the other hand, the results obtained in AgCl and anion exchange membrane disagreed with the theoretical values.

Impedance changes in phospholipid LB (Langmuir-Blodgett) and protein-mixed phospholipid LB films by several taste substances were measured. The resistance of the phospholipid LB film increased by bitter and sweet substances, whereas the resistance decreased for salty, sour and umami substances. For sweetness the larger change was observed in the protein-mixed phospholipid LB film, and hence discrimination between sweetness and bitterness was possible.

Detection of some toxic substances in water is a time consuming process because large number of substances need to be analyzed. When some toxic substances in the drains flow into the river, they cause environmental destruction. Accurate detection of substances which have serious effects on living organism is required as well as short measurement time. Although a sensing system employing living fish is devised, there are some problems in reliability, maintenance and evaluation because they are living thing. It is possible to measure the influence of pollutant for living organism directly by a sensor which is similar to biological systems. So we investigate a method of detection of toxic substances by multichannel lipid membrane sensors which are modeled on living organism.SA401 has multichannel sensor with lipid membranes which are modeled on living organism. It is able to detect some toxic substances in the water. For the reason, this system has been applied to measure water quality, such as, mineral water, tap water, contaminated river water and factory drains. We have found this method is effective and many pollutants (e. g. CN-, Fe3+, Cu2+, etc.), in factory drains, have been measured in a few minutes, the detection limits are lower than regulations of drain. It is possible to detect cyanide of factory drains selectively in short time by applying lipid membrane sensor. In conclusion, it is an effective mean to use multichannel lipid membrane sensors for observation of water quality especially for factory drains.

Interactions between a lipid-protein membrane and taste substances were investigated using SPR (surface plasmon resonance). The used membrane was the LB (Langmuir-Blodgett) multi-layered film composed of DHP (dihexadecyl phosphate) and the sugar-binding protein ConA. The LB membrane including ConA showed larger responses to almost all the taste substances, such as quinine, caffeine, sucrose and NaCl than the LB membrane without ConA. Suggestion was also made on the interactions of astringent and pungent substances with the charged lipid LB membrane.

Taste can be quantified using a multichannel taste sensor with lipid/polymer membranes. Its sensitivity and stability are superior to those of humans. A present study is concerned with the first step of miniaturization and integration of the taste sensor with lipid/polymer membranes using FET. As a result, it was found that gate-source voltage of the taste sensing FET showed the same behaviours as the conventional taste sensor utilizing the membrane-potential change due to five kinds of taste substances. Discrimination of foodstuffs was very easy. A thin lipid membrane formed using LB technique was also tried. These results will open doors to fabrication of a miniaturized, integrated taste sensing system.

The taste of milk with homogenization treatment was discriminated using a taste sensor. The transducer is composed of seven electrodes with lipid/polymer membranes. Sensory evaluations by humans for expressing taste characteristics of “richness” showed that there were no significant differences among the milk samples, which were treated with different homogenization pressure; on the contrary, it was possible to discriminate the slight differences in quality of milk with the taste sensor. The response electric potential pattern was much different below and above 100 kg cm −2 of homogenization pressure. The electric potential decreased systematically with increasing homogenization pressure higher than 100 kg cm −2 . The distribution of fat globule size had two peaks with homogenization pressure below 100 kg cm −2 , but had one peak over 100 kg cm −2 . Thus, the taste sensor responds to some physico-chemical changes accompanied by change in globule size and has the discrimination ability superior to humans. The present result will contribute to automated real-time control of homogenization of milk.

The technique using the phenomenon called surface plasmon resonance can make it possible to detect the change of refractivity (or dielectric constant) of a solution in a thin local region (the typical thickness of the region is about 1 μm), which is very close to the surface of a thin basal metal plate. Interactions between lipid molecules and flavor substances were investigated by using the surface plasmon resonance. In this study, the effects of various kinds of flavor substances—which can be regarded as representative of the five kinds of basic tastes (sweet, salt, sour, savory, and bitter)—on the lipid membranes were examined. The lipid membrane utilized as a receptor for taste substances was the LB (Langmuir-Blodgett) multilayered film composed of dihexadecyl phosphate. It was found that almost no flavor substances had any observable interactions to the lipid membrane system, while quinine hydrochloride, the representative of bitterness, was found to be strongly adsorbed to the lipid membrane. It was shown by doing measurements for various numbers of layers of the membrane system that the quinine hydrochloride is absorbed not only onto the surface but into the internal region of the lipid layers. It was observed that the sweet substance or salty substance suppressed the adsorption of the bitter substance. Similar suppression effects can also be found in biological systems. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 2, 80(4): 1–8, 1997

It is shown that an artificial excitable lipid membrane exhibits chaotic oscillations under periodic electrical stimulation. Effect of chemical substances on the oscillatory dynamics was investigated. It was found that the structure of attractor representing the state of the oscillation changed considerably if the oscillation was chaotic. The possibility of the taste sensing and recognition system by using the chaotic dynamics is also discussed.

The taste of beer was measured using a taste sensing system with eight kinds of lipid membrane. The output from the sensor has high discriminating power and high correlation with taste substances in beer and sensory test by human. The estimation of the concentration of taste substances by multiple regression analysis was fairly well. The taste sensor also well estimated the result of sensory test of many keywords concerning beer taste.

日本古来の調味料である醤油の味の客観的評価を目指し,味覚センサを用いた醤油の測定を行った.(1) 合成基準液を作ることにより,識別能力ならびに再現性のよい測定法を確立することができた.(2) 各地から集めた25種の醤油を測定したところ,濃い口,うす口,さしみの3種に分類できなかったが,同一メーカーの醤油は味が比較的似ていることを示唆する結果が得られた.(3) 同一メーカーの醤油の類似性は,アミノ酸分析や官能検査でも確かめることができた.それぞれの醤油メーカーの味の独自性が強いのは醤油製造の伝統に基づくものと考えられる.今後,味覚センサを用いて醤油の製造工程の管理や最終製品の品質管理の簡易迅速化が可能になるものと期待される.

We have developed a multichannel taste sensor with artifical lipid membranes and have applied it to quantification of taste of green tea. We used multiple regression analysis and found high correlations of outputs of the taste sensor with the results of sensory test (taste, flavor and color) and chemical analyses (amino acids and tannin that are main taste substances in green tea). It is concluded that the taste sensor has a potential for quantification of taste of green tea. The taste sensor responds not only to amino acids and tannin, but also to many other taste substances, and hence it contains much more taste information than conventional chemical analyses.

We have developed a new portable taste sensor with a lipid/polymer membrane and conducted experiments to evaluate the sensor’s performance. The fabricated sensor consists of a taste sensor chip (40 mm × 26 mm × 2.2 mm) with working and reference electrodes and a portable sensor device (80 mm × 25 mm × 20 mm). The working electrode consists of a taste-sensing site comprising a poly(hydroxyethyl)methacrylate (pHEMA) hydrogel layer with KCl as the electrolyte layer and a lipid/polymer membrane as the taste sensing element. The reference electrode comprises a polyvinyl chloride (PVC) membrane layer with a small hole and a pHEMA layer with KCl. The whole device is the size of a USB memory stick, making it suitable for portable use. The sensor’s response to tannic acid as the standard astringency substance showed good accuracy and reproducibility, and was comparable with the performance of a commercially available taste sensing system. Thus, it is possible for this sensor to be used for in-field evaluations and it can make a significant contribution to the food industry, as well as in various fields of research.

A recently developed multichannel taste sensor with global selectivity is being reviewed. This sensor is composed of several kinds of lipid/ polymer membranes for transforming information of taste substances into electric signals, which are analysed by a computer. The sensor output shows different patterns for chemical substances which have different taste qualities such as saltiness and sourness, while it shows similar patterns for chemicals with similar tastes. The sensor responds to taste in itself, as can be understood from the fact that taste interactions such as the suppression effect, which appears between sweet and bitter substances, can be well reproduced. Amino acids can be classified into several groups according to their own tastes with sensor outputs. The taste of foodstuffs such as beer, coffee, mineral water and vegetables can be discussed quantitatively using the taste sensor, which provides the objective scale for the human sensory expression. The taste sensor will open the door to a new stage of food culture.

The dynamics of retrieval processes in a system composed of coupled circle maps is studied by means of a statistical method and numerical simulations. Phase patterns are embedded in coupling parameters so that the system may work as an associative memory system. A parameter, which is an amplification factor multiplied to all the coupling strengths, is introduced for investigating the effect of the strength of the coupling nonlinearity on the behavior of the system concerned. The statistical method provides a set of time evolution equations representing the macroscopic behavior. It is found that the storage capacity is considerably enhanced by the introduced amplification factor. It is also shown that the system exhibits macroscopic chaotic oscillations when the strength of the coupling is sufficiently large. Moreover, the clustering is observed, as in other types of the globally coupled nonlinear systems.

The taste of Japanese sake was investigated using a taste sensor with eight kinds of lipid membranes and an enzymatic glucose sensor. The electric-potential pattern constructed of eight outputs from the taste sensor has information on the taste quality and intensity. A standard solution for sake measurement was synthesized. Therefore, chemical meanings were assigned to two perpendicular axes transformed from the nine variables of outputs from the two sensors; commercial brands of sake were scattered on this plane. The taste of sake was discussed objectively.

The titrable acidity of and the ethanol concentration in sake mash were measured using a multichannel taste sensor system. A positively charged membrane responded to ethanol and the electric response of the membrane showed good agreement with those determined by gas chromatography in the measurement of sake mash. It was considered that the responses were induced by a change in the activity coefficient of anions. The titrable acidity of sake mash was measured using an electrode with a negatively charged membrane, because the electric response of the membrane showed a strong correlation with the titrable acidity of sake. The result showed good agreement with the value determind by titration, and the agreement was slightly increased by multiple regression together with the electric response of the positively charged membrane. Therefore, it is concluded that this method is useful for determination of the ethanol concentration in and the titrable acidity of sake mash. The results show that the taste sensor can be used for monitoring of those values in sake fermentation.

Electric characteristics of hybrid polymer membranes composed of two lipid species were studied, where one lipid species is positively charged in aqueous solution and the other is negatively charged. As a result, it was found that the hybrid membranes responded to taste substances in different ways according to the molar mixing ratio of these two kinds of lipids, and also showed different response characteristics from those of the single-lipid membranes. The membranes with the mixing ratio around 50% exhibited the largest responses to HCl (sourness) and monosodium glutamate (umami). Moreover, good quantitative agreements with the observed data on the response electric potential were obtained using a theory describing both the changes in surface electric potential and surface charge density with taste substances.

It is clarified that the coupled oscillator system, which has the output of the phase coherency, can learn mapping from specified phase patterns to specified phase coherencies. The system considered here has the output unit which is a group of oscillators coupled both to the other oscillators of the system and also to the mean field generated by the output unit itself. It is analytically and numerically shown that the system can learn the above specified mapping. The effect of the distribution of the natural frequency of oscillators on the dynamics of the system is also investigated. It is shown that the system exhibits oscillatory and complex (chaotic) output when the phase pattern sufficiently different from the learned patterns is input into the system.

Raw egg white undergoes sol–gel transition by heat treatment, which changes it to an elastic gel. Here, protease treatment to render a new texture to heated egg white gel was applied. Protease-treated gels exhibited ductile flow without obvious rupture points. Transmission electron microscopy analysis showed that in protease-treated gels, protein aggregates were distributed more homogeneously compared with that observed in the untreated control, probably because ovalbumin was digested into small peptides as revealed by SDS-PAGE. The properties of the gel were evaluated by sensory tests and by measuring the movement of the masseter muscle, using surface electromyography. Results showed that maximum bite force and mastication duration were decreased for the protease-treated gels, which were evaluated as being softer, smoother, less elastic and better textured. Overall, our results indicate that protease-treated egg white gel has superior qualities and is easier to swallow than the untreated gel. Practical Applications In the food industry, the use of egg white is limited compared with that of egg yolk and whole eggs. In this study, we performed protease treatment to generate a new food material with smoother and softer texture compared with heat treated egg white. Our findings may expand the consumption of egg white, which can be consumed by people with mastication and swallowing disorders, and reduce the waste of egg white as a surplus product.

Pungent and astringent substances have been studied using a multichannel taste sensor. The electric-potential pattern made up of eight outputs from the membranes of the sensor has information about taste quality and intensity. Pungent substances including capsaicin, piperine and allyl isothiocyanate have no effect on the electric potentials of the liquid membranes. On the other hand, astringent substances such as catechin, tannic acid, chlorogenic acid and gallic acid change the potentials remarkably. A principal-component analysis of the patterns in electric-potential change caused by the taste substances reveals that the taste quality of astringency is located between bitterness and sourness. A model for astringency is presented.

Lipid membranes are useful materials to transform information about taste substances into electric signals. A lipid monolayer membrane for a taste sensor has been prepared by adsorbing lipid materials to the hydrophobic surface of a polymer membrane. The lipid-modified membranes respond to such electrolytic taste substances as HCl (sourness) or NaCl (saltiness) with large response magnitudes and such non-electrolytic substances as caffeine (bitterness) or sugar (sweetness) with high sensitivities. Thus the present membrane has a high ability to detect taste.

A taste sensor that uses lipid/polymer membranes can evaluate aftertastes felt by humans using Change in membrane Potential caused by Adsorption (CPA) measurements. The sensor membrane for evaluating bitterness, which is caused by acidic bitter substances such as iso-alpha acid contained in beer, needs an immersion process in monosodium glutamate (MSG) solution, called "MSG preconditioning". However, what happens to the lipid/polymer membrane during MSG preconditioning is not clear. Therefore, we carried out three experiments to investigate the changes in the lipid/polymer membrane caused by the MSG preconditioning, i.e., measurements of the taste sensor, measurements of the amount of the bitterness substance adsorbed onto the membrane and measurements of the contact angle of the membrane surface. The CPA values increased as the preconditioning process progressed, and became stable after 3 d of preconditioning. The response potentials to the reference solution showed the same tendency of the CPA value change during the preconditioning period. The contact angle of the lipid/polymer membrane surface decreased after 7 d of MSG preconditioning; in short, the surface of the lipid/polymer membrane became hydrophilic during MSG preconditioning. The amount of adsorbed iso-alpha acid was increased until 5 d preconditioning, and then it decreased. In this study, we revealed that the CPA values increased with the progress of MSG preconditioning in spite of the decrease of the amount of iso-alpha acid adsorbed onto the lipid/polymer membrane, and it was indicated that the CPA values increase because the sensor sensitivity was improved by the MSG preconditioning.

The purpose of this study is the development of a multichannel taste sensor chip for use in a portable taste sensor. The chip comprises a set of Ti/Ag patterned electrodes with lipid/polymer membranes and a reference electrode. The electrodes are formed on a polycarbonate substrate, which is attached to a polycarbonate sheet by double-sided adhesive tape (polyimide). The polycarbonate sheet has a number of holes in it that give access to the electrodes thus forming multichannel taste sensing sites. A sensor chip was fabricated and evaluated for its performance in tasting samples with basic tastes. The reference electrode did not interact with the basic taste samples, thus providing a stable potential. The outputs from the sensor chip for the various taste samples were at the same levels as those from a conventional taste sensor, indicating that this new taste sensor could provide the key element in the development of a portable taste sensor.

The relationship between gravitropism and surface electrical potentials was studied using etiolated epicotyls of adzuki bean (Phaseolus angularis). Early downward curvature (or transient positive gravitropic response) was observed about 1 min after gravistimulation. The downward curvature was closely related to the speed of the subsequent upward curvature. Surface electrical potentials decreased cooperatively in a limited region on the upper side within only 0.5 to 2 min. This is the earliest event found so far to follow gravistimulation of intact epicotyls. The rapid change in the potential had a high correlation with the early downward curvature and also the subsequent negative gravitropism. It is suggested that the rapid potential change plays an important role in gravity perception.

The critical current density, Jc, is discussed theoretically to explain the exponential dependence of Jc on the flux density, B, given typically by Jc∝exp( −B B 0 (T) ), which has been widely observed for single crystals of high-Tc superconductors in an external magnetic field parallel to the crystal c-axis. It is pointed out that Jc shows an exponential-type dependence, Jc∝exp( −ƒf(B, T) ), when the tilt modulus, C44, of fluxoids shows a remarkable softening for higher values of the wave number. It is also shown that the present expression of Jc is reduced to the observed B dependence of ƒ(B, T)⋍ B B 0 (T) by taking account of th e effects of the layered crystal structure on C44 and the correlation length, l44.

Responses to periodic signals in the oscillator network are studied numerically. The network used here is globally coupled oscillators with distributed natural frequencies of the oscillatory elements. The ability of the temporal-pattern recognition in the system is studied using the learning rule which changes the distribution of the natural frequencies. It is found that the coherency representing the order of the system exhibits the periodic and complex behaviors. The periodic response of the coherency is observed in the case where the input signal is similar to the learned signal. The behavior of the coherency becomes complex; i.e., the number of the degrees of freedom of the behavior increases with the decrease in the similarity of the input signal to the learned signal. Moreover, the long transient process is observed after turning off the input.

Astringent substances and pungent substances were studied using a multichannel taste sensor with lipid membranes. The electric-potential pattern constructed of eight outputs from the membranes has information of taste quality and intensity. Pungent substances, such as capsaicin, piperine and allyl isothiocyanate, had no effect on the membrane potentials of the lipid membranes. On the other hand, astringent substances such as tannic acid, catechin, gallic acid and chlorogenic acid changed the potentials remarkably. A principal component analysis of the patterns in electric potential changes caused by the taste substances revealed the astringency is located between bitterness and sourness.

A taste sensor with a multichannel electrode was developed by using lipid membranes as a transducer of taste substances. The sensor can detect the taste in a similar manner to the human gustatory sensation by response patterns of electric potential to taste substances. The sensitivity, reproducibility and durability were superior to those of humans. The same taste as that elicited by some commercial aqueous drink was reproduced by making aqueous solution mixed from four kinds of basic taste substances, the concentrations of which were determined so that the electric-potential pattern of this mixed solution could agree well with the pattern by the drink. Different brands of beer were easily distinguished by the electric-potential patterns.

A theoretical model is presented for reproducing chaotic behaviors observed experimentally in the DOPH (dioleyl phosphate) membrane system with external periodic stimulation. The model describes the self-sustained oscillation of the membrane potential of the DOPH membrane by taking into account the effect of applied AC electric current. The route to chaos was classified as break-down of quasi-periodicity, although it was unclear experimentally. Effects of the change in the phenomenological parameters in the theoretical model on the attractor were also investigated. It was shown that some dynamic bifurcation properties can change much more sensitively than average quantities as the mean frequency. The change of the attractor was discussed in relation to the interaction of DOPH molecules with taste substances by comparing with experimental results.

The expression for the thermal-fluctuation-induced depinning line, T = TP (Be), is derived theoretically for weakly pinning high-Tc superconductors. In the derivation, it is shown that the thermal displacement of pinned fluxoids, uth reduces the critical current density as J c = J c0 ( − 〈u 2 th 〉/d 2 p ) 3 2 , where J c0 is the critical current density in the absence of u th and d p is the effective half width of the summed-up pinning potential. Then T p (itB e) is determined as the temperature at which Jc becomes zero due to the increase of 〈u2th〉 with the increase of T in the external flux density of Be. The relation of Tp(Be) with the irreversibility line of Ti(Be) and the flux melting line of Tm(Be) is also discussed.

The mechanism of the oscillatory electric potential of a dioleyl phosphate (DOPH) layer in a single hole sandwiched by two KCl solutions, 100 mM and 5 mM, was investigated using two types of cells for axial and transverse observations. It was discovered that the electrical oscillation was related to a macroscopic behavior of the interfaces between DOPH and KCl solutions caused by a chemically driven surface tension effect.