• Journal of the Korea Society for Simulation
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• v.30 no.1
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• pp.11-20
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• 2021

As unmanned underwater systems have recently emerged, a high-speed underwater channel modeling technique, which is one of the most important techniques in the system, has received a lot of attention. In this paper, we proposed a high-speed sound propagation model and verified the applicability through quantitative performance analyses. We used a high-order finite difference method (FDM) for wave propagation modeling in the water, and a domain decomposition method was adopted using multiple general-purpose graphics processing units (GPUs) to increase the calculation efficiency. We compared the results of the model we proposed with the analytic solution in the half-infinite media and results of the Virtual Timeseries Experiment (VirTEX) model, which is based on the ray method. Finally, we analyzed the performance of the model quantitatively using numerical examples. Through quantitative analyses of the improvement in computational performance, we confirmed that the computational speed increases linearly as the number of GPUs increases. The computation times are increased by 2 times and 8 times, respectively, when the domain size of computation and the maximum frequency are doubled. We expect that the proposed high-speed underwater channel modeling technique is able to contribute to the enhancement of national defense as an underwater communication channel model and analysis tool to develop the underwater communication technique for the unmanned underwater system.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.5
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• pp.249-257
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• 2022

This paper presents an improved computational framework for the direct-solution-based finite element tearing and interconnecting (FETI) algorithm. The FETI-local algorithm is further improved herein, and localized Lagrange multipliers are used to define the interface among its subdomains. Selective inverse entry computation, using a property of the Boolean matrix, is employed for the computation of the subdomain interface stiffness and load, in which the original FETI-local algorithm requires a full matrix inverse computation of a high computational cost. In the global interface computation step, the original serial computation is replaced by a parallel multi-frontal method. The performance of the improved FETI-local algorithm was evaluated using a numerical example with 64 million degrees of freedom (DOFs). The computational time was reduced by up to 97.8% compared to that of the original algorithm. In addition, further stable and improved scalability was obtained in terms of a speed-up indicator. Furthermore, a performance comparison was conducted to evaluate the differences between the proposed algorithm and commercial software ANSYS using a large-scale computation with 432 million DOFs. Although ANSYS is superior in terms of computational time, the proposed algorithm has an advantage in terms of the speed-up increase per processor increase.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.11
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• pp.1627-1634
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• 2021

This paper introduces a low-power compact ADC circuit for analog Convolutional filter for low-power neural network accelerator SOC. While convolutional neural network accelerators can speed up the learning and inference process, they have drawback of consuming excessive power and occupying large chip area due to large number of multiply-and-accumulate operators when implemented in complex digital circuits. To overcome these drawbacks, we implemented an analog convolutional filter that consists of an analog multiply-and-accumulate arithmetic circuit along with an ADC. This paper is focused on the design optimization of a low-power 8bit SAR ADC for the analog convolutional filter accelerator We demonstrate how to minimize the capacitor-array DAC, an important component of SAR ADC, which is three times smaller than the conventional circuit. The proposed ADC has been fabricated in CMOS 65nm process. It achieves an overall size of 1355.7㎛², power consumption of 2.6㎼ at a frequency of 100MHz, SNDR of 44.19 dB, and ENOB of 7.04bit.

• Journal of Preventive Medicine and Public Health
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• v.21 no.1 s.23
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• pp.21-30
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• 1988

To measure the fertility rate and pregnancy wastage of women in rural area, 3,780 married women under 50 years old who were not sterilized either woman or husband in Gunwee county were followed up for 2 years. Seventeen Myun health workers visited these women periodically to check the status of their family planning practice and menstruation. Pregnant women were interviwed for their past obstetric history and followed up to the time of delivery. Family planning was practiced in 51.6% of the 6,826 women-years observed during the period from April 1, 1985 to March 31, 1987. Pregnancy, abortion and delivery covered 7.6% of the observed women-years and family planning was not practiced in 36.5% of the women-years. When sterilized women at the beginning of the study were included, the family planning practice rate was 72.1% which was slightly higher than the national family planning practice rate. However, 28% of the women of 30-39 years old had not practiced family planning although they had 2-3 children and they used more such less effective methods as safe-period method and condom than the women of 20-29 years old. Overall pregnancy rate was 14.3 per 100 woman-years. Women of 25-29 years old had the highest pregnancy rate of 27.4 per ,100 woman-years. Pregnancy wastage including spontaneous and induced abortions and still births was 22.0% of all pregnancies and it increased with the age of women; 15.8% in women less than 30 years old and 43.7% in women of 30 years and over. Women who terminated the pregnancy with induced abortion had more pregnancies, more previous induced and spontaneous abortions and shorter pregnancy interval than those women who terminated with live birth. Pregnant women terminated with a live birth had received 4.2 prenatal cares on the average. Eighty-five percent of deliveries occurred at a medical facility and 15% at home which was substantially lower home delivery rate than the other rural area of Korea. This may be due to the effects of the demonstration project for the primary health care in 1970s in Gunwee county. These findings suggest that family planning service in rural area should be strengthened by promoting the use of more effective contraceptive method among women over 30 years of age.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.4 s.334
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• pp.19-28
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• 2005

In this paper, we proposed a parallel fast 2-D discrete wavelet transform hardware architecture based on lifting scheme. The proposed architecture improved the 2-D processing speed, and reduced internal memory buffer size. The previous lifting scheme based parallel 2-D wavelet transform architectures were consisted with row direction and column direction modules, which were pair of prediction and update filter module. In 2-D wavelet transform, column direction processing used the row direction results, which were not generated in column direction order but in row direction order, so most hardware architecture need internal buffer memory. The proposed architecture focused on the reducing of the internal memory buffer size and the total calculation time. Reducing the total calculation time, we proposed a 4-way data flow scheduling and memory based parallel hardware architecture. The 4-way data flow scheduling can increase the row direction parallel performance, and reduced the initial latency of starting of the row direction calculation. In this hardware architecture, the internal buffer memory didn't used to store the results of the row direction calculation, while it contained intermediate values of column direction calculation. This method is very effective in column direction processing, because the input data of column direction were not generated in column direction order The proposed architecture was implemented with VHDL and Altera Stratix device. The implementation results showed overall calculation time reduced from $N^2/2+\alpha$ to $N^2/4+\beta$, and internal buffer memory size reduced by around $50\%$ of previous works.

• Journal of Preventive Medicine and Public Health
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• v.23 no.1 s.29
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• pp.87-97
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• 1990

We followed up all the infants born to the married women under 50 years of age residing in Gunwee county, Kyungpook Province, between 1 April 1985 and 31 March 1987, and those born to the married women under 50 years residing in Hapchun County, Kyungnam Province, between 1 March 1987 and 28 February 1988, to their first birthday. Likewise, we followed up the infants born to the women who visited the MCH Center of South District Health Center in Taegu City for delivery between 1 April 1985 and 31 March 1987 to the 27th day after birth and obtained the infant mortality rate and the neonatal mortality rate, respectively. There were 17 infant deaths among 1,359 live births in Gunwee and Hapchun Counties and the infant mortality rate was 12.5 per 1,000 live births. Out of 17 infant deaths, 82.4 percent were neontal death and 17.6 percent were postnonatal deaths. Out of the 6,001 live births born to the women visited the MCH Center, 4,834 infants (80.6%) were followed up to the 27th day after birth. Of these 4,834 infants, 36 infants died before the 28th day after birth and thus the neonatal mortality rate was 7.4 per 1,000 live births. Comparison of the maternal characteristics and the birth weight between infants who were followed up and those who were lost to follow-up showed no significant differences. Assuming that the neonatal and postneounatal mortality ratio had been 6:4, the infant mortality rate for the infants born at the MCH Center would have been 12.3 per 1,000 live births. Taking such findings into consideration as the infant mortality rate observed in Gunwee and Hapchun Counties, the neonatal mortality rate at the MCH Center, the causes of infant deaths, and the low birth weight incidence rate, a conservative estimate of infant mortality rate of Korea would be between 12 and 15 per 1,000 live births in $1985{\sim}1988$.

• Progress in Medical Physics
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• v.19 no.2
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• pp.102-112
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• 2008

We developed a high-resolution micro-CT system based on rotational gantry and flat-panel detector for live mouse imaging. This system is composed primarily of an x-ray source with micro-focal spot size, a CMOS (complementary metal oxide semiconductor) flat panel detector coupled with Csl (TI) (thallium-doped cesium iodide) scintillator, a linearly moving couch, a rotational gantry coupled with positioning encoder, and a parallel processing system for image data. This system was designed to be of the gantry-rotation type which has several advantages in obtaining CT images of live mice, namely, the relative ease of minimizing the motion artifact of the mice and the capability of administering respiratory anesthesia during scanning. We evaluated the spatial resolution, image contrast, and uniformity of the CT system using CT phantoms. As the results, the spatial resolution of the system was approximately the 11.3 cycles/mm at 10% of the MTF curve, and the radiation dose to the mice was 81.5 mGy. The minimal resolving contrast was found to be less than 46 CT numbers on low-contrast phantom imaging test. We found that the image non-uniformity was approximately 70 CT numbers at a voxel size of ${\sim}55{\times}55{\times}X100\;{\mu}^3$. We present the image test results of the skull and lung, and body of the live mice.

• Journal of Energy Engineering
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• v.23 no.4
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• pp.88-94
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• 2014

In this paper, Thermal Shock tests were performed varying the composition of the solder and ribbon thickness (A-type:0.2mm/60Sn40Pb, B-type:0.25mm/60Sn40Pb, C-type:0.2 /62Sn36Ag2Pb, D-type:0.25mm/62Sn36Ag2Pb) for evaluating the long-term reliability about Ribbon junction of Silicon solar cells. Thermal Shock test condition was performed during the 600cycles having $-40^{\circ}C{\sim}85^{\circ}C$ temperature range each 15 minutes; One cycle time was 30min. As a result, the initial efficiency of the A-type, B-type, and C, D-type were showed 15.0%, 15.4% and 15.8% respectively. After thermal shock test, the efficiency decreasing-rate of each type were as follow that A-type was 13.8%, B-Type was 15.4%. C-Type and D-Type was 15.3% and 16.2%, respectively. Also, degradation of surface changes and I-V characteristic curves were showed that the series resistance of the A, C-type was increased. Also, current lowering starting point of C-type shown 0.05volt[v] earlier than that of A-type. And B, D-type shown characteristics of composite lowering efficiency such as increase of series resistance, decrease of parallel resistance and cell damage. Therefore Initial solderability and efficiency of specimens using the solder with SnAgPb were superior. But, It has inferior the long-term reliability. The test was confirmed that as the ribbon thickness increases, long-term reliability of solar cell will decrease.

• Journal of the Korean GEO-environmental Society
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• v.15 no.5
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• pp.5-11
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• 2014

In this study, greenhouse gas emission for small scale landfill (H and Y landfill) was investigated to deduce special the methane generation rate constant(k). To achieve the purpose, the data of physical composition was collected and amount of LFG emission was calculated by using FOD method suggested in 2006 IPCC GL. Also, amount of LFG emission was directly measured in the active landfill sites. By comparing the results, the methane generation rate constant(k), which was used as input variable in FOD method suggested in 2006 IPCC GL, was deduced. From the results on the physical composition, it was shown that the ranges of DOC per year in H (1997~2011) and Y (1994~2011) landfill sites were 13.16 %~23.79 % ($16.52{\pm}3.84%$) and 7.24 %~34.67 % ($14.56{\pm}7.30%$), respectively. The DOC results showed the differences with the suggested values (= 18 %) in 2006 IPCC GL. The average values of methane generation rate constant(k) from each landfill site were $0.0413yr^{-1}$ and $0.0117yr^{-1}$. The results of methane generation rate constant(k) was shown big difference with 2006 IPCC GL defualt value (k = 0.09). It was confirmed that calculation results of greenhouse gas emission using default value in 2006 IPCC GL show excessive output.