• Geophysics and Geophysical Exploration
• /
• v.10 no.3
• /
• pp.203-210
• /
• 2007

As a part of basic studies on monitoring of landslides and slope stability using SP measurements, micro-electric potentials of rock samples were measured accompanied with the rock failure by a uniaxial loading test were measured. The measurement system consists of a 8 channel A/D converter with 24 bit resolution, uniaxial loading tester, strain gages and 4 sets of electrode attached to a rock sample. Rock samples of granite, limestone, and sandstone were tested. Also, mortar samples were tested in order to monitor electric-potentials of a uniform sample. Micro-electric potentials were detected in all saturated samples and the strength of them increased as the loading force increased. Sandstone samples showed the largest strength of micro-electric potential and it followed limestone and granite samples, which indicates a positive relationship with porosity of rocks. The mechanism generating these micro-electric potential can be explained in terms of electro-kinetics. In case of dry samples, micro-electric potential could be observed only in sandstone samples, where piezoelectric effect played main role due to high contents of quartz in sandstone samples. We found that biggest micro-electric potentials were observed at the electrodes near the crack surface of rock samples. This is very encouraging result that SP monitoring can be applied to predicting landsliding or to estimate collapsing position combining with monitoring of acoustic emissions.

• The Journal of Engineering Geology
• /
• v.16 no.2 s.48
• /
• pp.179-187
• /
• 2006

Two specimens of mortar containing artificial slit and Geochang granite containing the straight notch were selected to be used in this research. Source mechanism of micro-crack by radiation pattern based on dislocation the-ory was estimated by the first motion of longitudinal wave and spatial distribution between the location of transducers for monitoring acoustic emission and source coordinates determined by the application of the least square method. Result of analysis showed that the orientation of dislocation surfaces due to shear dislocation and tensile dislocation squares considerably with crack direction visually observed. The ultimate goal of this study is to provide fundamental information for source mechanism of micro-crack within materials.

• Journal of Korean Society of Environmental Engineers
• /
• v.28 no.11
• /
• pp.1148-1153
• /
• 2006

Signal measuring system to analyze ion concentrations in biofilm was constructed with ion selective microeleclrode and electrometer. In order to evaluate the performance and applicability of signal measuring system, the following characteristics, such as slope of calibration curve, detection limit, variation of response according to the time, and potentiometric selectivity coefficient, were investigated. The slope of calibration curve showed high degree of association for primary ion concentration. The response of the system was log-linear in standard solution down to $10{\mu}M$ and signal measuring system was not sensitive for interfering ions. In comparison with commercial electrometer, the fabricated electrometer system had similar tendencies for the slope of calibration curve, detection limit, and response time. Therefore the signal measuring system could be used to investigate ion profiles in biofilm as a cost effective and reliable measuring system.

• Korean Journal of Materials Research
• /
• v.11 no.6
• /
• pp.483-491
• /
• 2001

The recovery and recrystallization behavior of cold-rolled Zr-based alloys during isothermal annealing at temperatures from $575^{\circ}C$ to $650^{\circ}C$ was studied by thermoelectric power and Vickers microhardness measurement. The recovery and recrystallization resulted in the increase of TEP doe to the extinction of lattice defect, vacancy, dislocation and stacking fault during isothermal annealing after cold- rolling. The completion of recrystallization could be determined much clearly by TEP behavior than by microhardness change in Zr-based alloys. Especially, the recovery and recrystallization were classified separately by TEP behavior in Zr-0.4Nb-xSn alloys. From the analysis of TEP behavior and microhardness, the addition of Sn caused to form the interaction between stain field and dislocation, which resulted in the delay of recovery in Zr-based alloys. The precipitation due the addition of Nb suppressed the grain growth after recrystallization effectively in Zr-based alloys.

• Journal of Korean Society of Environmental Engineers
• /
• v.22 no.10
• /
• pp.1833-1841
• /
• 2000

Microelectrode probe was made and applied to the biofilm in the biological treatment process as the state-of-art technology in order to actually measure the biofilm thickness, ionic concentration gradient, and material transport, etc. instead of classical theoretical approach. The working microelectrode, one of the main components of microelectrode probe, was easily contaminated and broken when determining the differences in the ionic concentrations through the measurement of biofilm's EMF (electromotive force). As a demonstration, two microelectrode probes were constructed in our lab for the measurement of the pH and $NO_3{^-}$ concentration in denitrifying biofilm. The microelectrode probe through the inner biofilm ($350{\mu}m$ from the surface of biofilm) showed that the pH was increased from pH 8 in the bulk solution to pH 8.3, on the other hand, the $NO_3{^-}$ concentration was decreased from 30 fig N/L in the bulk solution to 4 fig N/L.

• Applied Microscopy
• /
• v.36 no.3
• /
• pp.155-163
• /
• 2006

The defects in a synthesized crystal of ${\alpha}-Al_2O_3$ used as substrate for growing of semi-conductor materials such as GaN were examined by the conventional transmission electron microscopy (TEM), Large Angle CBED and High-Angle Annular Dark Field (HAADF) STEM methods. The dominant defects found in the specimen are basal microtwins with the thickness of ${\sim}2\;to\;32 nm$ and the associated strong strain field at the interface of microtwin/matrix, basal dislocations and complex dislocations in the one of {$2\bar{1}\bar{1}3$} pyramidal slip plane. All these basal and pyramidal dislocations seem to be strong related to basal microtwins. It was also found that the density of defects is very uneven. In the certain area with the dimension of a few fm, the dislocation density is quite high as an order of ${/sim}10^{10}/cm^2, but the average density is roughly estimated to be less than ${\sim}10^5/cm^2, as is usually expected in general synthesized crystals.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.9 no.4
• /
• pp.7-16
• /
• 1972

A prototype of photoelectric photometer has been developed by all solid state operational amplifiers. The amplification of low-level anode currents from photomultiplier tube corresponding to a given incident light intensity and logarithmic transfer for star's magnitude nleasurements are achieved by the same operational amplifier. It is important to select low input bias currents for stable performance because the resolution is primarily limited by the bias currents. As such, they offer a higher reliable and economical for a large number of electrometer amplifier applications which have traditionaly been fulfilled by vacuum electrometer tubes or vibrating reed electrometers.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1995.05b
• /
• pp.675-680
• /
• 1995

원자로 압력용기 재료인 SA508-3 강의 인장소성변형에 따른 자기적 성질변화를 연구하였다. 소성변형에 따른 보자력, 잔류자화, 자기이력손실 및 Barkhausen Noise의 변화를 측정하였으며, 변형에 따른 자기적성질의 변화를 자구와 전위와의 상호작용으로 설명하였다. 강자성체의 자기적 성질과 기계적 성질 사이는 밀접한 관련이 있으며, 이를 이용하면 압력용기강의 조사효과 평가에 적용 할 수 있을 것으로 보인다.

• Journal of the Korean Chemical Society
• /
• v.34 no.4
• /
• pp.340-344
• /
• 1990

The pressure effect of voltammetric parameters for the oxidation of Bilirubin in 0.1 M TEAP-DMSO solution at micro Pt electrode has been investigated. With increasing the pressure from 1 to 1,800 bars, the peak potential of oxidation wave shifted to the more positive potential. The peak current becomes considerably smaller with increasing the pressure. The oxidation currents of Bilirubin was found to be diffusion controlled over all pressure ranges. The reversibility of oxidation step did not change with increasing pressure. The linear relationships were observed over all pressure ranges (1-1,800 bars).

• Journal of the Korean Society for Nondestructive Testing
• /
• v.20 no.1
• /
• pp.54-61
• /
• 2000

In order to determine the mode I stress intensity factor ($K_I$) by means of the alternating current potential drop(ACPD) technique, the change in potential drop due to load for a paramagnetic material containing a two-dimensional surface crack was examined. The cause of the change in potential drop and the effects of the magnetic flux and the demagnetization on the change in potential drop were clarified by using the measuring systems with and without removing the magnetic flux from the circumference of the specimen. The change in potential drop was linearly decreased with increasing the tensile load and was caused by the change in conductivity near the crack tip. The reason of decreasing the change in potential drop with increasing the tensile load was that the increase of the conductivity near the crack tip due to the tensile load caused the decreases of the resistance and internal inductance of the specimen. The relationship between the change in potential drop and the change in $K_I$ was not affected by demagnetization and was independent of the crack length.