Takashi Oyabu

Characteristics of potted plants for removing offensive odors

Abstract Plants have the capability to remove indoor air pollutants and furthermore to decompose odor molecules in an indoor environment. Hydrogen sulfide (H2S), ammonia (NH3) and methyl mercaptan (CH3SH) are the three main offensive odors in a nursing home. It is strongly desired to develop an effective method for reducing those substances. In this study, the pollutant-removing characteristics of a potted plant for three substances, ammonia, formaldehyde and acetone, are examined using a tin oxide gas sensor. As for the results, it became obvious that the removing characteristics for ammonia gas could be indicated using an approximate function of y=a exp (−bx)+c . In this function, the coefficient b stands for the removing effect and c means the offset level of sensor output. The coefficient a stands for the intercept from that level. It can indicate the number of pots and the kind of plants to maintain the clean air quality in an indoor environment. The pothos plant is very available for putting this to practical use.

Odor sensing characteristics of a lavatory in a general domicile

Abstract Six odor sensors, which are of the metal-oxide semiconductor type, were installed in a lavatory of a residence. Features of sensor-output patterns were investigated by monitoring the odors. Frequency of lavatory-use was detected and kinds of excretion were also identified. As for the results, it appears clear that two or three sensors react to urine and four or five sensors react to feces. The patterns, for example degree of fluctuation and inclination of sensor characteristics, differ with subjects. This system can be applied effectively to homes for the aged to survey the residents’ behaviors. The odor sensor system is also effective for monitoring the indoor environment without an infringement of privacy.

An algorithm for evaluating disasters by fuzzy reasoning

Abstract Many sensors and systems have been developed for detecting disasters in domestic circumstances, such as gas leaks and fires. In general, only one sensor is used for detecting one kind of disaster. If there should be a malfunction in a sensor of this system, it will be immediately ineffective. A new type of system with improved reliability that can detect three kinds of disasters, gas leaks, generation of carbon monoxide gas and fires, has been constructed by the use of four kinds of sensors. Furthermore, the system adopts fuzzy reasoning, which has simple membership functions and can estimate the grade of each disaster.

Purification Capability of Tobacco Transformed with Enzymes from a Methylotrophic BACTERIUM for Formaldehyde

Plants have the ability to remediate environmental pollution. Especially, they have a high purification capability for airpollution. We have measured the purification characteristics of foliage plants for indoor airpollutants—for example, formaldehyde (HCHO), toluene, and xylene—using a tin oxide gas sensor. HCHO is an important intermediate for biological fixation of C1 compounds in methylotrophs. The ribulose monophosphate pathway of HCHO fixation is inherent in many methylotrophic bacteria, which can grow on C1 compounds. Two genes for the key enzymes, HPS and PHI, from the methylotrophic bacterium Mycobacterium gastri MB19 were introduced into tobacco. In this article, the HCHO-removal characteristic of the transformant was examined by using the gas sensor in order to evaluate quantitatively. The purification characteristics of the transformant for toluene, xylene, and styrene were also measured. The results confirmed an increase of 20% in the HCHO-removal capability. The differences of the purification capabilities for toluene, xylene, and styrene were not recognized.

Dynamic model to estimate the dependence of gas sensor characteristics on temperature and humidity in environment

Abstract A gas sensor using tin oxide changes its electrical resistance ( R s ) with a change in the concentration of a reducing gas ( C ). However, the R s vs. C correlation is affected significantly by the temperature ( t ) and relative humidity ( h ) of the surrounding atmosphere. We propose a dynamic model to describe the influences of t and h . As is well-known, the R s vs. C correlation was expressed satisfactorily by an equation, log 10 R s = α log 10 C + β ( α and β constant), under fixed conditions of t and h . Analysis of the observed data indicated that the values of α and β under various environmental conditions were distributed along a plane when plotted three-dimensionally against t and h . This fact allows to propose a simple model in which both α and β are linear functions of t and h , respectively. The three constants included in each function were determined experimentally. The resulting equation of α and β were found to describe the R s vs. C correlation well under various conditions of t and h .

Purification Characteristics of Golden Pothos for Atmospheric Gasoline

Previous studies have shown that plants have the ability to purify various atmospheric chemicals. Gasoline is one of the more serious pollutants. Soil and atmospheric pollution caused by gasoline is increasing due to the widespread use of automobiles. In this article, the purification characteristic of the pothos plant for atmospheric gasoline is investigated using a tin oxide gas sensor. The purification rate (P r ), defined as the purification ability per hour as described by a differential coefficient, has a maximum value at longer time intervals as the pollutant concentration becomes higher. P r can be represented by an exponential function of lapsed time and its characteristic in soil is similar. A golden pothos plant growing in a 30-cm diameter pot of was placed in a 300-l experimental chamber to examine its purification ability. P r had a maximum value 40 h after a 0.04-ml injection of gasoline into the chamber. The total purification ability (P a ) is also used in this study and is derived using the peak value (h) and the full width (t w ) at half maximum of the tin oxide gas-sensor characteristic, namely P a = h/t w × 100. The P a of the pothos for gasoline was about 7, with the value decreasing as the pollutant concentration increased.

A Novel Formaldehyde-Degrading Fungus, Trichoderma virens: Isolation and Some Properties

We succeeded in isolating two formaldehyde-degrading fungi, the strains BDF001 and 002, from the rhizospheric soil of formaldehyde-exposed potted golden pothos (Epipremnum aureum), and from the formaldehyde-exposed cultivation soil without plants, respectively. Sequence analysis of the ITS-5.8S rDNA regions confirmed that both fungi were of the same species, Trichodenna virens. These two strains, however, obviously differed from each other in formaldehyde resistance and formaldehyde-degrading ability. The formaldehyde concentration allowing a growth during cultivation for 10 days for the strain BDF001 was up to 0.6%, and that for the strain BDF002 was up to 0.35%. The strain BDF001 showed a formaldehyde-degrading activity 2.3 times higher than that of the strain BDF002. Ranges of the possible growth pH and temperature in the presence of 0.21% formaldehyde were between 4 and 9, and around 25°C, respectively.

Proposition of a survey device with odor sensors for an elderly person

Three types of metal oxide gas sensors were adopted to detect the degree of breath odor. Various sorts of information are included in the odor. Each sensor has different sensitivities to gaseous chemical substances and the sensitivities also differ according to human behaviors, for example taking a meal, teeth brushing and drinking something. There is also a possibility that the sensor can detect degrees of daily fatigue. Sensor sensitivities were low for the expiration of the elderly when the subject drank green tea. In this study, it is thought that the odor system can be incorporated into a healing robot. The robot can communicate with the elderly using several words and also by connecting to the Internet. As for the results, the robot can identify basic human behaviors and recognize the living conditions of the resident. Moreover, it can also execute a kind of information retrieval through the Internet. Therefore, it has healing capabilities for the aged, and can also receive and transmit information.

Feature extraction of multi-gas sensor responses using Genetic Algorithm

Abstract It is an established technique in the field of privacy protection to use a gas sensor to monitor indoor environments. In this paper, we propose a method for recognizing human activities in an indoor environment by using several kinds of high-sensitivity gas sensors. The feature of the method is estimating the signals with Genetic Algorithm (GA). The results showed that the proposed method effectively worked for the recognition of human activities. This paper demonstrates a significant result through utililization of the proposed technique in this research.

Detection of human activities by inverse filtration of gas sensor response

Abstract In an approach to identifying human activities in an indoor space from the response signals of a combustible gas sensor, an indoor space model was presented in which the response signal and the gas generation due to the human activities were correlated linearly through an indoor gas transfer function. Analysis indicated that: (1) the gas transfer by diffusion can describe essential features of the transfer function in the indoor space, and (2) the inverse filtration based on the space transfer characteristics thus estimated enables one to restore or extract the gas-generation function from the sensor signal output. The model was applied to identify daily human activities in a domestic house. The sensor response output consisted of heavily overlapping signals due to human actions taking place in succession. However, the inverse filtration could eliminate the overlapping (residual) components from the overall output to single out each human action associated with causing gas generation in the indoor space.