• 생물환경조절학회지
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• 제1권2호
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• pp.162-168
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• 1992

As the automation of nutrient solution management proceeds in the field of hydroponics, effective supporting systems to manage the nutrient solution by computer become needed. This study was attempt to predict the EC of nutrient solution using the neural networks. The multilayer perceptron consisting of 3 layers with the back propagation learning algorithm was selected for EC prediction, of which nine variables in the input layer were the concentrations of each ion and one variable in the output layer the EC of nutrient solution. The meq unit in ion concentration was selected fir input variable in the input layer. After the 10,000 learning sweeps with 108 sample data, the comparison of predicted and measured ECs for 72 test data showed good agreements with the correlation coefficient of 0.998. In addition, the predicted ECs by neural network showed relatively equal or closer to the measured ones than those by current complicated models.

• 대한설비공학회지:설비저널
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• 제15권3호
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• pp.283-291
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• 1986

An experimental study has been conducted to investigate characteristics of the flow patterns, its transitions and the mean local void fraction obtained from which the probe was traversed diametrically from center to wall of the test section in the vertical upward air-water flow for isothermal condition using the electrical conductivity probe. It has been shown that the probability density function of the mean local void fraction measured statistically from a Fast Fourier Transform becomes a criterion for the flow patterns and the mean local void fraction profile is a highly function of the flow patterns.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
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• pp.260-265
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• 1996

Polyproplyene Fibers have many advantages such as light weight, low cost, chemical stability and duragbility. It has been reported that polypropylene fiber can increase the toughness of concrete and the resistance to crack formation. This study has been performed to investigate the dirability related properties such as permeability and diffusivity of polypropylene fiber reinforced concrete. The permeability and diffusivity were measured with GWT, Poroscope, and electrical conductivity of concrete. From the test result, it is found that the addition of the polypropylene fiber improved the permeability and diffusivity of concrete, when the workability reduction was corrected by water reducer. The relationships between the permeability and diffusivity, and other properties of polypropylene fiber reinforced concrete showed that the tesst results are interrelated each other.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 B
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• pp.1096-1099
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• 1996

In this paper, the eddy current flowmeter with 4-coil is designed and made on the basis of theory, and its characteristics is considered through dry test and flow experiments. The biggest output signal varied with wave wave form frequency, and 900Hz in rectangular wave, 27.12kHz in sine wave. The conductivity is bigger, the output signal is bigger and has a linearity between both relation, and also The Magnetic Reynolds Number and output characteristics The flow faster and the output signal is bigger.

• 대한수학회지
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• 제61권4호
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• pp.621-657
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• 2024

In this study, the numerical solution of a space-fractional Burgers' equation with initial and boundary conditions is considered. This equation is the simplest nonlinear model for diffusive waves in fluid dynamics. It occurs in a variety of physical phenomena, including viscous sound waves, waves in fluid-filled viscous elastic pipes, magneto-hydrodynamic waves in a medium with finite electrical conductivity, and one-dimensional turbulence. The proposed QBS/CNG technique consists of the Galerkin method with a function basis of quadratic B-splines for the spatial discretization of the space-fractional Burgers' equation. This is then followed by the Crank-Nicolson approach for time-stepping. A linearized scheme is fully constructed to reduce computational costs. Stability analysis, error estimates, and convergence rates are studied. Finally, some test problems are used to confirm the theoretical results and the proposed method's effectiveness, with the results displayed in tables, 2D, and 3D graphs.

• Transactions on Electrical and Electronic Materials
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• 제7권1호
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• pp.7-11
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• 2006

The changes of the electrical conductivity in chalcogenide amorphous semiconductors, $Ge_{1}Se_{1}Te_{2}$, have been studied. A phase change random access memory (PRAM) device without an access transistor is successfully fabricated with the $Ge_{1}Se_{1}Te_{2}$-phase-change resistor, which has much higher electrical resistivity than $Ge_{2}Sb_{2}Te_{5}$ and its electric resistivity can be varied by the factor of $10^5$ times, relating with the degree of crystallization. 100 nm thick $Ge_{1}Se_{1}Te_{2}$ thin film was formed by vacuum deposition at $1.5{\times}10^{-5}$ Torr. The static mode switching (DC test) is tested for the $100\;{\mu}m-sized$ $Ge_{1}Se_{1}Te_{2}$ PRAM device. In the first sweep, the amorphous $Ge_{1}Se_{1}Te_{2}$ thin film showed a high resistance state at low voltage region. However, when it reached to the threshold voltage, $V_{th}$, the electrical resistance of device was drastically reduced through the formation of an electrically conducting path. The pulsed mode switching of the $20{\mu}m-sized$ $Ge_{1}Se_{1}Te_{2}$ PRAM device showed that the reset of device was done with a 80 ns-8.6 V pulse and the set of device was done with a 200 ns-4.3 V pulse.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 봄 학술논문 발표대회
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• pp.43-44
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• 2023

This study evaluated the mechanical and electrical properties of low-cement mortar using a large amount of industrial by-products to reduce carbon emissions from the cement industry. As types of industrial by-products, blast furnace slag and fly ash, which are representative materials, were used, and ultra-high fly ash was mixed and evaluated to solve the problem of initial strength loss. In addition, in order to evaluate the electrical properties, 1% of MWCNT was incorporated relative to the powder mass. As experimental items, the compressive strength was measured on the 1st, 3rd, 7th and 28th days of age, and the rate of change in electrical resistance was measured on the 28th day of age. As a result of the experiment, the initial strength of the test specimen mixed with blast furnace slag and fly ash was significantly lower than that of 100% cement, and the specimen mixed with blast furnace slag showed strength equal to that of cement at 28 days of age. As an electrical characteristic, the electrical resistance was reduced when the load was loaded, and this reason is judged to be the effect of improving the conductivity as the connection between CNTs is narrowed by the compressive load.

• 전기학회논문지
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• 제59권6호
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• pp.1087-1094
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• 2010

We have developed a cylindrical multi-terminal capacitive-conductive sensor that could be attached to the internal surface of cooling system pipe to evaluate capacitance and conductivity of heat transfer fluid. It was used as measuring system to diagnose insulating condition, by which was kept a insulating resistance of inner stack and at the same time was cooled electrochemical heat of reaction of FCEV(fuel cell electric vehicle) stack that used a compressed hydrogen gas reacting with oxygen in accordance with variation on thermal degradation of nonconductive heat transfer fluid. Also to assess diagnosis characteristics of heat transfer fluid, i.e. coolant, we have performed accelerated aging test using developed sensor attached to cooling system. Consequently, it was measured dielectric and electric resistance of coolant to estimate and analyse for dielectric properties by degradation condition.

• Transactions on Electrical and Electronic Materials
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• 제3권2호
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• pp.32-37
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• 2002

This paper gives the basic mechanical properties of indium-tin-oxide (ITO) films on polymer substrates which are exposed to externally and thermally induced bending force. By using modified Storney formula including triple layer structure and bulge test measuring the conductive changes of patterned ITO islands as a function of bending curvature, the mechanical stability of ITO films on polymer substrates was intensively investigated. The numerical analyses and experimental results show thermally and externally induced mechanical stresses in the films are responsible for the difference of thermal expansion between the ITO film and the substrate, and leer substrate material and its thickness, respectively. Therefore, a gradually ramped heating process and an organic buffer layer were employed to improve the mechanical stability, and then, the effects of the buffer layer were also quantified in terms of conductivity-strain variations. As a result, it is uncovered that a buffer layer is also a critical factor determining the magnitude of mechanical stress and the layer with the Young's modulus lower than a specific value can contribute to relieving the mechanical stress of the films.

• Carbon letters
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• 제13권4호
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• pp.230-235
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• 2012

In this study, reduced graphene oxide/polyimide (r-GO/PI) composite films, which showed significant enhancement in their electrical conductivity, were successfully fabricated. GO was prepared from graphite using a modified Hummers method. The GO was used as a nanofiller material for the preparation of r-GO/PI composites by in-situ polymerization. An addition of 20 wt% of GO led to a significant decrease in the volume resistivity of composite films by less than nine orders of magnitude compared to that of pure PI films due to the electrical percolation networks of reduced GO created during imidization within the films. A tensile test indicated that the Young's modulus of the r-GO/PI composite film containing 20 wt% GO increased drastically from 2.3 GPa to 4.4 GPa, which was an improvement of approximately 84% compared to that of pure PI film. In addition, the corresponding tensile strength was found to have decreased only by 12%, from 113 MPa to 99 MPa.