• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.473-479
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• 2000

The nanocrystalline Fe$_{84}$Zr$_{7}$B$_{6}$Cu$_{1}$ $Al_{2}$ alloy was annealed at 450 $^{\circ}C$ and 550 $^{\circ}C$ for l hour to achieve the ultra-soft magnetic properties such as large magnetoimpedence ratio(MIR), the incremental permeability ratio(PR), nearly zero coercivity, zero magnetostriction, etc. The PR and MIR of the sample were measured from 100 kHz to 10 MHz at a cryogenic chamber where the temperature can be varie from 10 K to 300 K. The increment of MIR value is proportional to increasing temperature. The maximum PR values measured at high frequency above 1 MHz remain almost same despite of the temperature variation from 10 K to 300 K except the sharpness in PR curves. However, the maximum PR values measured below 1 MHz show drastic increment at above 150K due to thermal activation of magnetic domains.s.s.

• Korean Journal of Materials Research
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• v.13 no.8
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• pp.531-536
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• 2003

The electromagnetic properties and microstructures of the ferrites based on ($Ni_{0.2}$ $Cu_{0.2}$ $Zn_{0.6}$)$_{1.085}$($Fe_2$$O_3$)$_{0.915}$ were investigated by changing the amount of additive SnO$_2$and CaO and the sintering temperatures. Addition of $SnO_2$caused pores in the specimen. There was no variation of grain size by changing the amount of additives. Total loss was reduced when ($Ni_{0.2} $Cu_{0.2}$ $Zn_{ 0.6}$)$_{1.085}$ ($Fe_2$$O_3$)$_{0.915}$ composition was sintered at $1150^{\circ}C$ rather than $1300^{\circ}C$. Addition of CaO was useful to reduce the total loss because it increased the sintering density. The lowest total loss was obtained when 0.06 wt% $SnO_2$and 0.4 wt% CaO were added at the same time.

• Journal of Korean Society on Water Environment
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• v.20 no.3
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• pp.296-300
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• 2004

The rejection properties of 6 aromatic pesticides were evaluated by a continuous flow system equipped with a hollow fiber NF membrane. Different from the separation experiment of batch cell, the rejection and the removal could be calculated exactly because the concentration of feed, permeate and retentate was separately obtained. The lowest and the highest rejection were found in carbaryl(54.8%) and methoxychlor(99.2%), respectively, and the removals were always shown higher than rejections. This may be caused by some reasons such as the solute adsorption on the membrane, the variation of feed concentration. Although molecular weight, molecular width regarded as solute characteristics and log P(n-octanol/water partition coefficient) as hydrophobicity could be applied to explain the rejection property, these factors should be considered together for better analysis. According to the higher relationship between log B(solute permeability) and molecular weight, it was revealed that the solute separation with this membrane was influenced more by molecular weight.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2004.12a
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• pp.43-51
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• 2004

Input impedance of the inverted L antenna which is modified from a monopole antenna varies to very high input impedance value when the ration of vertical height to horizontal length is reduced. So its impedance matching becomes very difficult. In this paper, we analyzed the input impedance variation range depending on the ratio of vertical height to horizontal length in the normal and ferrite thin film added configuration for the input impedance control. For the exact analysis involving the permittivity, permeability and conductivity of ferrite material, FDTD numerical method is used.

• Geotechnical Engineering
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• v.8 no.2
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• pp.59-70
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• 1992

This work is to study experimentally the measurment of pore air pressure according to rainfall in colluvium model and the characteristics of pore water pressure according to increasement of artesian ground water head. After modeling a geological feature of the Tertiary formation, the experiment was performed about sixty times on three kinds of soil. This experimental results showed the variation of pore water and pore air pressures with time, the change of void ratio and appling pressure head in the nonsaturated soil. It can be also expressed by the final pore water and the air reaction ratios and then formularizing the relationship between the permeability coefficient and the void ratio. In the results of this experiment, the patterns of the pore water pressure reaction are classified by the step-type and the wave-type, and the time-lag to reach final point of pore water pressure is in order sand, sandy silt and clayey sand.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.764-766
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• 1998

An evaluation method for oxygen permeable characteristics of the membrane covering to each cathode of multiple cathode - single anode type dissolved oxygen sensor, which has high reproducibility and is capable of measuring multiple components in solutions. For this purpose, a measuring circuit for the multiple cathode type DO sensor was designed to lower the noise signal by adapting a digital LPF to readout the sensor output accurately. Digital LPF is designed by setting up the transfer function to set the cutoff frequency to 10Hz, and the transfer function is programmed by C language, and then the filtering characteristics are evaluated with the simulation and experiments. Using this LPF added measuring circuit for the multiple cathode type DO sensor, we have obtained the calibration factor for each cathode to calibrate the variation of the output signals. The calibration factor was obtained by measuring the sensor output signal followed by oxygen partial pressure, using the same oxygen permeable membrane at each cathode of the multiple cathode type DO sensor.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.615-624
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• 2010

In this paper, the applicability of cement grout has been studied as an alternative to bentontite grout to backfill ground heat exchangers. To provide an optimal mixture design, the groutabilty and thermal conductivity of cement grouts with various mixture ratios were experimentally evaluated and compared. The unconfined compression strength of cement grout specimen was measured, which are exposed to cyclic temperature variation ranging from $50^{\circ}C$ to $-5^{\circ}C$. In addition, the integrity of the interface between circulating HDPE pipes and cement grout by performing equivalent hydraulic conductivity tests, in which a pipe locates at the center of the specimen.

• Geomechanics and Engineering
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• v.10 no.3
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• pp.325-334
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• 2016

Rock salt is a near-perfect material for gas storage repositories due to its excellent ductility and low permeability. Gas storage in rock salt layers during gas injection and gas production causes the stress redistribution surrounding the cavity. The triaxial cyclic loading and unloading tests for rock salt were performed in this paper. The elastic-plastic deformation behaviour of rock salt under cyclic loading was observed. Rock salt experienced strain hardening during the initial loading, and the irreversible deformation was large under low stress station, meanwhile the residual stress became larger along with the increase of deviatoric stress. Confining pressure had a significant effect on the unloading modulus for the variation of mechanical parameters. Based on the theory of elastic-plastic damage mechanics, the evolution of damage during cyclic loading and unloading under various confining pressure was described.

• Resources Recycling
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• v.13 no.6
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• pp.26-30
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• 2004

Input impedance of the inverted L antenna which is modified from a monopole antenna varies to very high input impedance value when the ratio of vertical height to horizontal length is reduced. So its impedance matching becomes very difficult. In this paper, we analyzed the input impedance variation range depending on the ratio of vertical height to horizontal length in the normal and ferrite thin film added configuration for the input impedance control. For the exact analysis involving the permittivity, permeability and conductivity of ferrite material, FDTD numerical method is used.

• Progress in Superconductivity and Cryogenics
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• v.9 no.3
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• pp.32-36
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• 2007

On the contrary of a conventional motor with very narrow air-gap. it is difficult to calculate the accurate magnetic field distribution and the performance of an air-cored superconducting motor by 2 dimensional analysis. which does not use high permeability material except outer machine shield. This paper aims to do analysis of magnetic field and force distribution from the 3 dimensional modelling of a 1MW class superconducting synchronous motor. Especially. the field coil composed of Bi-2223 high-temperature superconductor and the outer machine shield are modelled by finite element analysis software according to their structures and the self-inductance and Lorentz force are calculated based on the 3 dimensional magnetic field calculation. Moreover. the influence of an important parameter, synchronous reactance, has been analyzed on the machine performances such as voltage variation and output power.