• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.1
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• pp.40-48
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• 2000

1A novel bipolar linear transconductor and its application to operational transconductance amplifier(OTA) for low-voltage low-power signal processing is proposed. The transconductor consists of a npn differential-pair with emitter degeneration resistor and a pnp differential-pair connected to the npn differential-pair in cascade. The bias current of the pnp differential-pair is used with the output current of the npn differential-pair for wide linearity and temperature stability. The OTA consists of the linear transconductor and a translinear current cell followed by three current mirrors. The proposed transconductor has superior linearity and low-voltage low-power characteristics when compared with the conventional transconductor. The experimental results show that the transconductor with transconductance of 50 ${\mu}S$ has a linearity error of less than ${\pm}$0.06% over an input voltage range from -2V to +2V at supply voltage ${\pm}$3V. Power dissipation of the transconductor was 2.44 mW. A prototype OTA with a transconductance of 25 ${\mu}S$ has been built with bipolar transistor array. The linearity of the OTA was same as the proposed transconductor. The OTA circuit also exhibits a transconductance that is linearly dependent on a bias current varying over four decades with a sensitivity of 0.5 S/A.

• Journal of Biomedical Engineering Research
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• v.25 no.3
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• pp.189-194
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• 2004

Pixel values of contrast enhanced computed tomography (CE-CT) images are randomly changed. Also, the middle liver part has a problem to segregate the liver structure because of similar gray-level values of a pancreas in the abdomen. In this paper, an automatic liver segmentation method using a partial histogram threshold (PHT) algorithm is proposed for overcoming randomness of CE-CT images and removing the pancreas. After histogram transformation, adaptive multi-modal threshold is used to find the range of gray-level values of the liver structure. Also, the PHT algorithm is performed for removing the pancreas. Then, morphological filtering is processed for removing of unnecessary objects and smoothing of the boundary. Four CE-CT slices of eight patients were selected to evaluate the proposed method. As the average of normalized average area of the automatic segmented method II (ASM II) using the PHT and manual segmented method (MSM) are 0.1671 and 0.1711, these two method shows very small differences. Also, the average area error rate between the ASM II and MSM is 6.8339 ％. From the results of experiments, the proposed method has similar performance as the MSM by medical Doctor.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.99-112
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• 1999

By using 92 values of lateral earth pressure coefficient(K) measured in Korea, the tendency of K with varying depth is analyzed and compared with the range of K defined by Hoek and Brown. The horizontal stress is generally larger than the vertical stress in Korea : About 84 % of K values are above 1. In this study, the theory of elasto-plasticity is applied to analyze the variation of K values, and the results are compared with those of numerical analysis. This reveals that the erosion, sedimentation and weathering of earth crust are important factors in the determination of K values. Surface erosion, large lateral pressure and good rock mass increase the K values, but sedimentation decreases the K values. This study enable us to analyze the effects of geological processes on the K values, especially at shallow depth where underground excavation takes place. A neural network expert system using multi-layer back-propagation algorithm is developed to predict the K values. The neural network model has a correlation coefficient above 0.996 when it is compared with measured data. The comparison with 9 measured data which are not included in the back-propagation learning has shown an average inference error of 20% and the correlation coefficient above 0.95. The expert system developed in this study can be used for reliable determination of K values.

• Journal of Radiation Protection and Research
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• v.39 no.3
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• pp.150-158
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• 2014

Radiation-related practitioners and radiation-treated patients at medical institutions are inevitably exposed to radiation for diagnosis and treatment. Although standards for maximum doses are recommended by the International Commission on Radiological Protection (ICPR) and the International Atomic Energy Agency (IAEA), more direct and available measurement and analytical methods are necessary for optimal exposure management for potential exposure subjects such as practitioners and patients. Thus, in this study we developed a system for real-time radiation monitoring at a distance that works with existing portable device. The monitoring system comprises three parts for detection, imaging, and transmission. For miniaturization of the detection part, a scintillation detector was designed based on a silicon photomultiplier (SiPM). The imaging part uses a wireless charge-coupled device (CCD) camera module along with the detection part to transmit a radiation image and measured data through the transmission part using a Bluetooth-enabled portable device. To evaluate the performance of the developed system, diagnostic X-ray generators and sources of $^{137}Cs$, $^{22}Na$, $^{60}Co$, $^{204}Tl$, and $^{90}Sr$ were used. We checked the results for reactivity to gamma, beta, and X-ray radiation and determined that the error range in the response linearity is less than 3% with regard to radiation strength and in the detection accuracy evaluation with regard to measured distance using MCNPX Code. We hope that the results of this study will contribute to cost savings for radiation detection system configuration and to individual exposure management.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.3
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• pp.661-668
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• 2018

Biomedical signals using skin resistance have different characteristics according to stress diseases. Biological diagnostic devices for diagnosing stress diseases have been developed by using these characteristics, and devices have been developed so that the signals measured by the skin storage meter can be easily analyzed. Experts in the field will look directly at the output signal to determine the likelihood of any stress disorder. However, it is very difficult for a person to accurately determine whether a person to be measured has a stress disorder by analyzing a bio-signal measured by each person to be measured, and the result of the judgment is very likely to be wrong. In order to solve these problems, we implemented the function of determining the signal of a stress disorder by using the machine learning technique. SVM was used as a classification method in consideration of low computing ability of measurement equipment. Training data and test data were randomly generated for each disease using error range 5 based on 13 diseases. Simulation results showed more than 90% decision accuracy. In the future, if the measurement equipment is actually applied to the patients, we can retrain the classifier with the newly generated data.

• Journal of the Korean Chemical Society
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• v.45 no.6
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• pp.570-576
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• 2001

The europium doped yttrium oxybromide phosphors were synthesized by solid-state reaction method. The YOBr: $Eu^{3+}$ phosphor showed a strong and narrow red emission band at 621 nm and maximum emission intensity obtained when 0.05 mol Eu ions were doped. The red emission of $Eu^{3+}$ originated from $^5D_0$ ${\rightarrow}$ $^7F_2$electric dipole transition. In order to investigate on photoluminescence behavior, several experimental skills and numerical fittings are conducted to the YOBr: $Eu^{3+}$ phosphor. The emission spectrum was measured in the UV range and then decay curve of $^5D_0$ ${\rightarrow}$ $^7F_j$transitions was examined. The energy interaction type of YOBr: $Eu^{3+}$ phosphor was dipole-dipole interaction. In addition to the calculating by critical concentration, the critical distance ($R_0$) was calculated by decay curve fitting parameter from Inokuti-Hirayamas equation, and spectral overlap method. The critical distance was 17.03, 10.51 and 7.18$\AA$ for those methods, respectively. As considering systematic error of measurements, these values are within the same order, so that the above fitting methods are plausible and recommendable.

• Journal of the Korea Institute of Building Construction
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• v.17 no.4
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• pp.305-312
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• 2017

To evaluate the reliability of fly ash quality supplied to ready-mixed concrete plant using mass cylinder and hydrometer, in this research, the correlationship between the fly ash properties provided from certification and density measurement with suspension was evaluated. As a result, the reliability of the certification, except fineness and loss on ignition, all properties had a discord. Additionally, in the case of density, fineness, and L.O.I, the relation with the density measured using hydrometer showed high correlation, especially fineness was strongly related with the density measured using hydrometer. Furthermore, according to the comparative analysis with previous research, the fly ash used in this research was similar measurement with raw powder without any refining process, it is considered that the constant error of blaine test or using raw ash sample as a fly ash. In current standard regarding fly ash, the fineness range of class 2 can be changed from $3,000-4,500cm^2/g$ to $3,500-4,500cm^2/g$ for improved quality of fly ash in fineness aspect.

• Journal of Korean Society of Forest Science
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• v.105 no.4
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• pp.429-434
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• 2016

Slope failures in forest roads often result in social and economic loss as well as environmental damage. This study was carried out to assess susceptibility of slope failures of forest roads in Hongcheon-gun, Gangwon-do where many slope failures occurred after heavy rainfall in 2013 using GIS and logistic regression analysis. The results showed that sandy soil (6.616) in soil texture type had the highest susceptibility to slope failures while medium class (-3.282) in tree diameter showed the lowest susceptibility. A error matrix for both slope failure and non-slope failure area was made and a model was developed showing a classification accuracy of 74.6%. Non-slope failures area in the forest roads were classified mostly in the range of >0.7 which was higher values than the classification criteria (0.5) used by the logistic regression model. It is suggested that considering forest environment and site factors related to forest road failures would improve the accuracy in predicting susceptibility of slope failures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.4
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• pp.95-103
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• 1984

This paper is a study on improving the accuracy of control points by suggesting angular requirements which make geometric conditions to be optimum. For this purpose, a equation, by which the accuracy of control point coordinates measured in an arbitrary station can be estimated, is derived. This equation is integrated and average standard error of the coordinates is computed, so that the optimum location of observatory station is determined. In the case of triangulation, a regular triangle has been generally considered as the best geometric condition, but because the precision of each side is different, the $52.77^{\circ}$ isosceles triangle is founded to be the best one. Also in trigonometric leveling, the geometric condition is founded to be optimum when the base angle of a isosceles triangle is $45^{\circ}$. In control surveying for close-range photogrammetry the optimum relation between base length($B_0$) and object distance($D_0$) can be founded to be as follow; $D_0=0.357587-0.357967B_0+0.308555B_0{^2}$.

• Ecology and Resilient Infrastructure
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• v.3 no.3
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• pp.177-181
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• 2016

In order to prevent the fragmentation of animal habitat due to road construction, the most widely applied solution is building animal passes worldwide. In Korea, animal passes were introduced in the early 2000s, and through trial and error, the national guidelines for them and their design standards were published in 2010. These were criticized by politicians because of their relative inefficiency considering their high construction cost and their lack of animal usage. This study investigated the extent to which animals used the facilities. For this study, two types of animal passes, eco-bridges and ecoducts, were considered and the test sites were chosen from the Baekdu Mountains. The animal usage data was captured using infra-red CCTV cameras. The results showed that various types of animals used eco-bridges and ecoducts. Interestingly various types of birds were captured by cameras and endangered animals were also in them. The season, weather, and their surrounded vegetation also had effects on their usages. The infrared CCTV allowed detailed captures of animals but the electricity shortage was one disadvantage. During the last decades, a number of eco-bridges were constructed throughout the country and now we need to focus on their monitoring and maintenance for their successful efficiency and application.