• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.5
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• pp.532-541
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• 2001

Developments of nondestructive evaluation techniques for reduction of strength or toughness by aging of material have been carried out, and the method using electrical resistivity is one of them. In this study, to examine the application of electrical resistivity to the evaluation of degradation of metallic alloy, ten different non-magnetic materials were selected as test materials. Electrical resistivities measured by DC two-point probe method and those measured by non-contact type eddy current method were compared with each other. In addition, to examine the application possibility of four-point probe technology in field, the electrical resistivities for 1Cr-lMo-0.25V steel measured by DC two-point probe method and four-point probe method were compared with each other Differences between two measured values for the 1Cr-1Mo-0.25V steel were 0.6%. Therefore, the four-point probe method can be applied to the estimation of the degradation of metallic alloy. ect.

• Journal of the Korean Mathematical Society
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• v.43 no.6
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• pp.1253-1268
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• 2006

We develop the upper and lower solutions method for the four point problem relative to second order differential equations in order to obtain the existence of solution.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.4 s.175
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• pp.874-880
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• 2000

In this paper, a DC potential drop measurement system was used to find the position of the flaw on a simple thin plate. Four-point probe test was evaluated and used for this study. In the four-point probe test, the more distance between current pins provides the more measurable scope, the less voltage difference, and the more voltage difference rate. In the other hand, the more distance between voltage pins provides the less voltage difference and the less voltage difference rate. An optimized four-point probe was applied to measure the relation between voltage and the relative position of flaw to the probe. The Maxwell 21) simulator was used to analyze the electromagnetic field, and it showed that the analytical result was similar to the experimental result within 11.4% maximum error.

• Journal of Mechanical Science and Technology
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• v.14 no.3
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• pp.314-319
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• 2000

Back-face strain compliance (BFS compliance) for the four-point bend specimen has been calibrated for various crack length ratios. Finite element technique was employed to simulate four-point loading and calculate back-face strain of the bend specimen. The numerically determined strain variation along the back face indicates that the sensitivity to gage placement increases with crack length and back-face strain at the gage length less than O.2W, where W is the width of the bend specimen, can be measured within 5% deviation of the maximum BFS. Non-dimensional back-face strain compliance, -E'BCW, was calibrated with FE analysis and experiment. The experimentally determined compliance indicates good agreement with the numerical compliance and can be expressed as a function of crack length ratio.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.173-174
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• 2008

The four-point bending test is a widely used method to determine material parameters. The aim of the present study was to evaluate the flexural strength (or modulus of rupture) and the Weibull modulus of cordierite ceramic substrate by means of four-point bending tests. The strength data from experiments followed Weibull statistics. These data indicate that the fatigue effects are more severe when the substrate temperature in the peripheral region is near $200^{\circ}$. At temperatures well above $200^{\circ}C$ the available design strength can be as high as 65% as substrate's initial strength.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.7
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• pp.1434-1437
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• 2011

Precision measurement of silicon wafer resistivity has been using single-configuration Four-Point Probe(FPP) method. This FPP method have to applying sample size, shape and thickness correction factor for a probe pin spacing to precision measurement of silicon wafer. The deference for resistivity measurement values applied correction factor and not applied correction factor was about 1.0 % deviation. The sample size, shape and thickness correction factor for a probe pin spacing have an effects on precision measurement for resistivity of silicon wafer.

• Journal of Acupuncture Research
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• v.17 no.4
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• pp.18-27
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• 2000

There is a acupuncture method which make a difference according to the four seasons, according to body region or depth in skin. We call it Acupuncture follow the four seasons(四時刺法). In several chapters of Huangdineijing(黃帝內經) introduced Acupuncture follow the four seasons. Acupuncture follow the four seasons has two kinds of acupuncture method that is to acupuncture at body region and to acupuncture at five Su points(五兪穴). To use five Su points(五兪穴) according to Yongchu(靈樞) disagree with Nanjing(難經). In Yongchu(靈樞), the five phases property disagree with five Su points(五兪穴), but in Nanjing(難經) the five phases property agree with five Su points(五兪穴). Even if we can acupuncture the same point, there will be the different effect according as what is the purpose of doing acupuncture, and when we do acupuncture. That is to say, we can use apucupuncture for the purpose of prevention in Yongchu(靈樞), and for the purpose of healing the disease in Nanjing(難經). Therefore, because we select the point on the base of meridian Kis origin which spring out, we have to acupuncture Chong point(井穴) in winter according to Yongchu(靈樞). Because we select the point on the base of meridian Kis origin which flowing, we have to acupuncture Chong point(井穴) in spring according to Nanjing(難經). And in the base of five phases' property, the purpose of selecting five Su points(五兪穴) is the prevention according to Yongchu(靈樞), and the healing according to Nanjing(難經). So even though we acupuncture the exactly same Chong point(井穴), we can expect the effect that acupuncture method supply Ki for liver in winter. and the effect that it extract pathogenic Ki(邪氣) from the liver in spring.

• Journal of applied mathematics & informatics
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• v.28 no.3_4
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• pp.679-686
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• 2010

This paper is concerned with the following fourth-order four-point Sturm-Liouville boundary value problem $u^{(4)}(t)=f(t,\;u(t),\;u^{\prime\prime}(t))$, $0\;{\leq}\;t\;{\leq}1$, ${\alpha}u(0)-{\beta}u^{\prime}(0)={\gamma}u(1)+{\delta}u^{\prime}(1)=0$, $au^{\prime\prime}(\xi_1)-bu^{\prime\prime\prime}(\xi_1)=cu^{\prime\prime}(\xi_2)+du^{\prime\prime\prime}(\xi_2)=0$. Some sufficient conditions are obtained for the existence of at least one positive solution to the above boundary value problem by using the well-known Guo-Krasnoselskii fixed point theorem.

• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1471-1483
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• 2017

The low-frequency characteristics of four-switch three-phase (FSTP) inverter are investigated in this paper. Firstly, a general space vector pulse width modulation (SVPWM) directly involved the neutral point voltage of DC-link is proposed, where no sector identifications and trigonometric function calculations are needed. Subsequently, to suppress the DC offset in the neutral point voltage, the relationship between the neutral point voltage and the ${\beta}-axis$ component of the load current is derived, and then a new neutral point voltage control scheme is proposed where no low pass filter is adopted. Finally, the relationship between the load power factor and the maximum linear modulation index of the FSTP inverter is revealed. Since the operational region for the FSTP inverter in low frequency is reduced by the enlarged amplitude of the neutral point voltage, a linear modulation range enlargement scheme is proposed. A permanent magnet synchronous motor with preset rotary speed serves as the low-frequency load of the FSTP inverter. Experimental results verify that the new neutral point voltage control scheme is effective in the deviation suppression of the neutral point voltage, and the proposed scheme is able to provide a larger linear operational region in low frequency.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.5
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• pp.1-8
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• 2006

The Five Point Method of KS and Four Point Method of IES are generally used to measure and compute the average illuminance in residential areas. Such methods of measurement should be used exactly according to the characteristics of the space and activities. Therefore, this study evaluated computation methods of the average illuminance in terms of comparing the measured values with simulated ones. The Five Point Method of KS is very closed to evaluate task illuminancefor appreciating activities at the center while the Four Point Method of IES is very closed to a concept of the average illuminance over the space excluding the possible maximum and minimum illuminance values.