• Geophysics and Geophysical Exploration
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• v.5 no.3
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• pp.199-205
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• 2002

In the resistivity method, the potential difference between two grounded electrodes is measured and this can be positive or negative. The apparent resistivity and the potential difference have the same polarity. Since the electric field is the gradient of the potential, the polarity of the potential difference depends on the direction of the electric field. If the direction of the vector connecting two grounded electrodes is the same to that of the electric field, the measured potential difference and the apparent resistivity become positive. If the opposite is the case, they become negative. In general, the primary electric field and the vector connecting two potential electrodes have the same direction in a surface resistivity method. In this case, the measured potential difference is always positive because the primary electric field is greater than the secondary field. Therefore, the apparent resistivity is always positive if noise is free and topography is flat. The secondary field component, however, can be greater than the primary field component along the vector connecting two potential electrodes in the cross-hole resistivity method. Furthermore, if the secondary electric field and the vector connecting two potential electrodes have an opposite direction, the apparent resistivity become negative. Consequently, the apparent resistivity may be negative in the region where the primary electric field component along the vector connecting two potential electrodes is very small.

• Proceedings of the KSEEG Conference
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• 2002.04a
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• pp.110-112
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• 2002

• Geophysics and Geophysical Exploration
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• v.15 no.2
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• pp.75-84
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• 2012

The sea layer in marine Controlled-Source Electromagnetic (mCSEM) survey changes the conventional definition of apparent resistivity which is used in the land CSEM survey. Thus, the development of a new algorithm, which computes apparent resistivity for mCSEM survey, can be an initiative of mCSEM data interpretation. First, we compared and analyzed electromagnetic responses of the 1D stratified gas hydrate model and the half-space model below the sea layer. Amplitude and phase components showed proper results for computing apparent resistivity than real and imaginary components. Next, the amplitude component is more sensitive to the subsurface resistivity than the phase component in far offset range and vice versa. We suggested the induction number as a selection criteria of amplitude or phase component to calculate apparent resistivity. Based on our study, we have developed a numerical algorithm, which computes appropriate apparent resistivity corresponding to measured mCSEM data using grid search method. In addition, we verified the validity of the developed algorithm by applying it to the stratified gas hydrate models with various model parameters. Finally, by constructing apparent resistivity pseudo-section from the mCSEM responses with 2D numerical models simulating gas hydrate deposits in the Ulleung Basin, we confirmed that the apparent resistivity can provide the information on the geometric distribution of the gas hydrate deposit.

• Composites Research
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• v.23 no.2
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• pp.1-9
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• 2010

This study analyzes the apparent fracture toughness of a thick-walled cylinder with a functionally graded material (FGM) coating at the inner surface of the cylinder. The cylinder is assumed to have a single radial edge crack emanating from its inner surface. The crack surfaces and the inner surface of the cylinder are subjected to an internal pressure. The incompatible eigenstrain developed in the cylinder due to nonuniform coefficient of thermal expansion as a result of cooling from sintering temperature is taken into account. Based on a method of evaluating stress intensity factor introduced in our previous study, an approach is developed to calculate apparent fracture toughness. The approach is demonstrated for a cylinder with a TiC/$Al_{2}O_{3}$ FGM coating and some numerical results of apparent fracture toughness are presented graphically. The effects of material distribution profile, cylinder wall thickness, application temperature, and coating thickness on the apparent fracture toughness are investigated in details. It is found that all of these factors play an important role in controlling the apparent fracture toughness of the cylinder.

• Korean Journal of Food Science and Technology
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• v.21 no.6
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• pp.815-819
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• 1989

Rheological properties of chestnut starch suspensions (3 and 4%, db) and gelatinized starch (4%, db) were investigated with a capillary and rotational viscometer, respectively. Starch suspensions had no yield stress and showed dilatant flow behavior in the temperature ranges of $30-65^{\circ}C$. However, starch suspension showed pseudoplastic flow behavior at $70^{\circ}C\; and\;above\; 65^{\circ}C$ for 3 and 4% concentration, respectively Flow activation energy below $50^{\circ}C$ was 0.56 kcal/mole but increased to 51.9-80.8 kcal/mole at $60-70^{\circ}C$. The behavior of gelatinized starch (4%) was pseudoplastic regardless of heating temperature $(65-80^{\circ}C)$ and time (15-60 min). The apparent viscosity of the starch remained constant after heating at $80^{\circ}C$ for 45 min. The swelling power and log apparent viscosity showed similar pattern. The activation energy of the apparent viscosity of the geletinized starch at $70-80^{\circ}C$ was 13.09kcal/mole. The apparent viscosity of thermal-gelatinized $(90^{\circ}C)$ starch was lower than that of 15 psi-gelatinized starch.

• Geophysics and Geophysical Exploration
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• v.5 no.2
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• pp.108-117
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• 2002

We have introduced a new approach to obtain the conductivity information of subsurface using Cagniard impedance over two-dimensional (2-D) model in the presence of horizontal magnetic dipole source with the frequency range of $1\;kHz\~1\;MHz$. Firstly, we designed the method to calculate the apparent resistivity from the ratio between horizontal electric and magnetic fields, Cagniard impedance, considering the source effects when the plane wave assumption is failed in finite source EM problem, and applied it to several numerical models such as homogeneous half-space or layered-earth model. It successfully provided subsurface information even though it is still rough, while the one with plane wave assumption is hard to give useful information. Next, through analyzing Cagniard impedance and apparent resistivity considering source effect over 2-D models containing conductive- or resistive-block, we showed that the possibility of obtaining conductivities of background media and anomaly using this approach. In addition, the apparent resistivity considering source effect and phase pseudosections constructed from Cagniard impedance over the isolated conductive- and resistive block model well demonstrated outlines of anomalies and conductivity distribution even though there were some distortions came from sidelobes caused by 2-D body.

• Korean Journal of Materials Research
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• v.5 no.4
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• pp.426-432
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• 1995

윤활제인 zinc stearate의 첨가량 (0~4wt%)을 변화시켜 U$O_{2}$분말의 겉보기밀도, 성형시의 분말입자간 마찰과 입자/다이벽 마찰간의 상관관계를 조사하였다. 소량의 윤활제 첨가시에는 U$O_{2}$분말입자간 박막의 윤활제 도포층이 형성되어 겉보기밀도가 증가한 반면 다량의 윤활제를 첨가한 경우에는 U$O_{2}$ 분말입자에 두꺼운 윤활제 도포층이 형성되고 미혼합된 윤활제가 존재하여 겉보기밀도는 감소하는 경향을 보였다. 윤활제를 첨가혼합한 상태에서 다이벽 윤활도포 유무에 따라 구한 U$O_{2}$ 성형체의 성형압력/성형밀도 자료로부터 분말입자간 마찰, 입자/다이벽 마찰 그리고 성형시 lubrication/inhibition등의 상대적 중요성을 조사하였다. 입자/다이벽 마찰에 의한 압력손실은 입자간 마찰에 의한 압력손실보다 크게 나타났다. 입자/다이벽 마찰에 의한 압력손실은 다이벽 윤활제 도포에 의해 최소화될 수 있지만 상대적으로 바람직하지 않은 성형시의 inhibition이 야기되는 것으로 나타났다.

• The Korean Journal of Rheology
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• v.8 no.3_4
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• pp.199-206
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• 1996

산마와 재배마에서 점질다당류를 추출하여 리올러지 및 열특성을 연구하였다. D.I.W 에서 산마와 재배마 점질다당류의 고유점도(η)는 각각 16.1 이/g. 25.1 이/g 이고 pH7일 때 최대값을 나타내었고 염을 가했을 때 (η)가 급격히 감소하다가 일정한 값을 나타내었으며 urea 용액에서 NaCl, MaCl2 용액에서보다 (η)가 높았다. 마 점질다당류의 chain stiffness는 0,0050이고 Overlap parameter는 산마와 재배마 점질다당류가 각각 0.06 g/이. 0.04 g/이였 다. 마 점질 다당류는 shear rate가 증가함에 따라 겉보기 점도가 감소하여꼬 농도가 증가함 에따라 yield stress 와 점조성 지수는 증가하고 shear index가 감소하는 가소성유동체였다. 산마 점질다당류는 35$^{\circ}C$까지 온도에 대하여 비교적 안정하였지만 그이상의 온도에서는 겉보 기 점도가 급격히 감소하였고 재배마 점질다당류는 온도가 증가할수록 겉보기 점도가 점차 적으로 감소하였다. 겉보기 점도는 1가 염가 2가 염 사이에 큰 차이가 없었고 염농도가 증 가함에 따라 겉보기 점도가 감소하였으나 urea를 첨가했을 때 겉보기 점도가 약간 감소하다 가 다시 증가하는 것을 알수 있었다. DSC로 산마와 재배마 점질다당류의 "true melting"을 측정했을 때 각각 92$^{\circ}C$, 93$^{\circ}C$였고, enthalpy는 67.06 cal/g, 75.83 cal/g였다. 겔화에 소요된 enthalpy는 pH가 증가할수록 큰 값을 나타냈고 NaCl을 첨가했을 때 감소하다가 염농도 증 가에는 영향을 받지 않았으며 Urea와 glycerol을 각각 첨가했을 때 D. I. W.오세보다 감소 하였다. TGA로 열분해 현상을 측정했을 때 분해 온도는 산마와 재배와 점질다당류가 각각 219~332$^{\circ}C$, 229~341$^{\circ}C$ 범위였다.TEX> 범위였다.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.10
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• pp.897-904
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• 2011

When whole-body is exposed to vertical vibration, asymmetry shape of human body affects the response on the translational(fore-aft, lateral, vertical) and rotational(roll, pitch, yaw) motion. While the translational motion has been studied with various titles, it has been rare to study the rotational motion of human body exposed to vertical excitation because of lack of experimental equipment. This study was performed by using a 6-axis force plate installing strain gage type sensors for the rotational response. Sixteen male subjects were exposed to vertical vibration on rigid seat in order to investigate apparent mass of three translational motion and apparent eccentric mass of three rotational motion. Random signal was generated to make excitation vibration which was on an effective frequency range of 3~40 Hz, and magnitude of 0.224 m/$s^2$ r.m.s. The frequency range and magnitude used was selected for the vibration of passenger vehicle on idling condition. As the result, cross-axis apparent masses of fore-and-aft and lateral direction were not significant showing 20 % and 3 % of vertical apparent mass relatively. And apparent eccentric mass of pitch motion was dominant when compared to that of roll and yaw motion, which is reasoned by asymmetry direction of human body sitting on a seat.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.237-243
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• 2001

The prediction model is proposed to estimate the variation of compressive strength of fly ash concrete with aging. After analyzing the experimental result with the model, the regression results are presented according to fly ash replacement content and water-cement ratio. Based on the regression results, the influence of fly ash replacement content and water-cement ratio on apparent activation energy was investigated. According to the analysis, the model provides a good estimate of compressive strength development of fly ash concrete with aging. As the fly ash replacement content increases, the limiting relative compressive strength and initial apparent activation energy become greater. The concrete with water-cement ratio smaller than 0.40 shows that the limiting relative compressive strength and apparent activation energy are nearly constant according to water-cement ratio. But, the concrete with water-cement ratio greater than 0.40 has the increasing limiting relative compressive strength and apparent activation energy with increasing water-cement ratio.