• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1341-1346
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• 2001

In this study, the acoustic properties of steel-wire sound absorbing materials with different thickness and bulk density were investigated in terms of characteristic impedance, propagation constant, and absorption coefficient. The well-known two-cavity method was used for evaluating those acoustic parameter values in experiments. Also, in order to validate the experimentally measured values, the results were compared with the results obtained from Chung and Blaser's transfer function method and SWR method. The experimentally measured values of normal absorption coefficients were generally agreed well with the corresponding values from the transfer function method and the SWR method. Based on the experimental results, the following conclusions could be made. The magnitude of the absorption coefficient and the frequency range of the maximum absorption coefficient were controllable by changing the thickness and bulk density of the sound absorbing materials. Also, the magnitude of the absorption coefficient depended on the characteristic impedance and the propagation constant. As large as the air cavity depth at the rear side of the steel-wire sound absorbing materials, the maximum magnitude of the absorption coefficient occurred at the lower frequency ranges.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2023년도 학술발표회
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• pp.167-167
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• 2023

Soil organic carbon (SOC) is a critical component of soil health and is crucial in mitigating climate change by sequestering carbon from the atmosphere. Accurate estimation of SOC storage is essential for understanding SOC dynamics and developing effective soil management strategies. This study aimed to investigate the factors influencing the spatial distribution of SOC storage in South Korea, using bulk density (BD) prediction to estimate SOC stock. The study utilized data from 393 soil series collected from various land uses across South Korea established by Korea Rural Development Administration from 1968-1999. The samples were analyzed for soil properties such as soil texture, pH, and BD, and SOC stock was estimated using a predictive model based on BD. The average SOC stock in South Korea at 30 cm topsoil was 49.1 Mg/ha. The study results revealed that soil texture and land use were the most significant factors influencing the spatial distribution of SOC storage in South Korea. Forested areas had significantly higher SOC storage than other land use types. Climate variables such as temperature and precipitation had a relative influence on SOC storage. The findings of this study provide valuable insights into the factors influencing the spatial distribution of SOC storage in South Korea.

• 대한전자공학회논문지
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• 제23권2호
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• pp.236-242
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• 1986

The dependence of the current-voltage characteristics of hydrogenated amorphous silicon pin solar cells on the illumimination light intensity has been investigated. The open circuit voltage increases linearly with increasing the logarithm of light intensity up to AM 1, and nearly saturates above AM 1, indicating the open circuit voltage approaching the built-in potential of the pin solar cell above AM 1. The short circuit current density increase with light intensity in proportion to I**0.85 before and I**0.97 after light exposure. Since the series resistance devreses and shunt resistance increases with light intensily, the fill factor increases with light illumination. To increase the fill factor at high illumination in large area solar cells, t6he grid pattern on the ITO substrates should be made. Long light exposure on the solar cells gives rise to the increase of bulk resistance and defect states, resulting in the decrease of the fil factor and short circuit current density. The potential drop in the bulk of the a-Si:H pin solar cells at short circuit condition increases with decreasing temperature, and increases after long light exposure.

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
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• 제16권6호
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• pp.698-701
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• 2010

최근 차량 통신망에서는 차량 안전 및 도로 교통 서비스에 더하여, 차량 통신 사용자들에게 email, ftp, 비디오 스트리밍 등 인터넷을 통한 서비스를 제공하기 위한 기술을 개발 중이다. 특히 차량 통신망의 특수성을 고려한 IP 이동성 제공 기술의 연구가 필요하다. 차량의 이동성 관리를 위해 Proxy Mobile IPv6(PMIPv6)를 차량 통신망에 적용할 경우, 차량의 빠른 이동 속도로 위치 등록에 따른 신호비용이 증가되는 문제점을 가지고 있다. 특히 차량 밀도가 높은 도로에서 많은 차량들이 고속으로 이동을 하게 되면 위치등록에 따른 신호비용이 증가하기 때문에 본 논문에서는 이동하는 다수의 차량들을 한 번에 LMA(Local Mobility Anchor)에 등록할 수 있는 방법을 제안하여 신호 비용을 줄이는 것을 목표로 한다. 수치 분석 및 시뮬레이션을 통해, 제안방안이 기존의 PMIPv6를 적용한 방식보다 신호 비용 면에서 효율적인 것을 확인하였다.

• 한국세라믹학회지
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• 제20권3호
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• pp.211-216
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• 1983

This work aims at characterizing silicon grains and its compacts. In order to remove iron silicon grains were washed with 5N hydrochloride at 60-7$0^{\circ}C$ for 170 hrs, and then followed the chemical analysis by atomic absorption spectrophotometer X-ray diffraction analysis SEM observation and specific surface area determination by B. E. T. Mixtures of graded silicon particles with two or three different sizes were made into packings by mechanical vibration. The mixtures were used to make compacts with 10 mm in diameter and 70mm in length by isostatically pressing at 1, 208 kg/$cm^2$ (20 kpsi) and 4, 255kg/$cm^2$ (60 kpsi) respectively. Bulk densities of packings and compacts were measured. A slip made of magnesium nitrate solution and fine silicon particles was spray-dried and then decomposed at 30$0^{\circ}C$ for the purpose of coating the uniform layer of magnesium oxide on the surface of particles. The results obtained are as follows: (1) About two thirds of iron content could be removed from silicon by washing silicon powders with hydrochloride. (2) Uniform layer of magnesium oxide on the surface of silicon could be prepared by spray-drying suspension and by decomposing it. (3) B. E. T. specific surface area of fine silicon particles was 2, 826.753$m^3$/kg. (4) In the binary system with two sizes of 40-53$\mu\textrm{m}$ particles and <10$\mu\textrm{m}$ particles the maximum bulk density of packing was 55% of theoretical value and that of compacts made at the pressure of 4, 255 kg./$cm^2$ (60 kpsi) was 73% of theoretical value. (5) In the ternary system with three sizes the maximum bulk density of packing was 1.43 g/$cm^3$and that of compacts was 1.80g/$cm^3$which is equivalent to 77.6% of theoretical value. The composition of the closest compact was consisted of 50% of 40-53$\mu\textrm{m}$ particles 20% of 10-30$\mu\textrm{m}$ particles and 30% of <10$\mu\textrm{m}$ parti-cles.

• 한국전기전자재료학회논문지
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• 제15권9호
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• pp.783-787
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• 2002

In recent year, B $i_{4-}$x L $a_{x}$ $Ti_3$ $O_{12(BLT)}$ is one of promising substitute materials for the ferroelectric random access memory(FRAM) applications. But the systematic composition is still insufficient, so this experiment was carried out in ceramic ambient sintering process which has the very excellent ferroelectric property. Samples were prepared by a bulk and the purpose which was estimated with a suitability of thin films applications. The density of B $i_{3.75}$ L $a_{0.25}$ $Ti_3$ $O_{12}$ was high and the XRD pattern showed that the intensity of main peak (117) was increased at the argon ambient sintering. Controlling the quantity of oxygen, crystallization showed a thin, long plate like type, and we obtained the excellent dielectric and polarization properties at the argon atmosphere sintering. Also this sintering process was effective at the bulk sample. Argon ambient sintered sample produced higher permittivity of 154, the remanent polarization(2Pr) of 6.8 uC/$\textrm{cm}^2$ compared with that sintered in air and oxygen ambient. And this sintering process showed a possibility which could be applied to thin films process..

• Journal of Biosystems Engineering
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• 제43권4호
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• pp.426-439
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• 2018

Purpose: To continuously monitor soil and climatic properties, a data acquisition system (DAQ) was developed and tested in plum farms (Gyewol-ri and Haechang-ri, Suncheon, Korea). Methods: The DAQ consisted of a Raspberry-Pi processor, a modem, and an ADC board with multiple sensors (soil moisture content (SEN0193), soil temperature (DS18B20), climatic temperature and humidity (DHT22), and rainfall gauge (TR-525M)). In the laboratory, various tests were conducted to calibrate SEN0193 at different soil moistures, soil temperatures, depths, and bulk densities. For performance comparison of the SEN0193 sensor, two commercial moisture sensors (SMS-BTA and WT-1000B) were tested in the field. The collected field data in Raspberry-Pi were transmitted and stored on a web server database through a commercial communications wireless network. Results: In laboratory tests, it was found that the SEN0193 sensor voltage reading increased significantly with an increase in soil bulk density. A linear calibration equation was developed between voltage and soil moisture content depending on the farm soil bulk density. In field tests, the SEN0193 sensor showed linearity (R = 0.76 and 0.73) between output voltage and moisture content; however, the other two sensors showed no linearity, indicating that site-specific calibration is important for accurate sensing. In the long-term monitoring results, it was observed that the measured climate temperature was almost the same as website information. Soil temperature information was higher than the values measured by DS18B20 during spring and summer. However, the local rainfall measured using TR 525M was significantly different from the values on the website. Conclusion: Based on the test results obtained using the developed monitoring system, it is thought that the measurement of various parameters using one device would be helpful in monitoring plum growth. Field data from the local farm monitoring system can be coupled with website information from the weather station and used more efficiently.

• 한국분말재료학회지
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• 제30권2호
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• pp.140-145
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• 2023

Although the Ti-6Al-4V alloy has been used in the aircraft industry owing to its excellent mechanical properties and low density, the low formability of the alloy hinders broadening its applications. Recently, laser-powder bed fusion (L-PBF) has become a novel process for overcoming the limitations of the alloy (i.e., low formability), owing to the high degree of design freedom for the geometry of products having outstanding performance used in high-tech applications. In this study, to investigate the effect of bulk shape on the microstructure and mechanical properties of L-PBFed Ti-6Al-4V alloys, two types of samples are fabricated using L-PBF: thick and thin samples. The thick sample exhibits lower strength and higher ductility than the thin sample owing to the larger grain size and lower residual dislocation density of the thick sample because of the heat input during the L-PBF process.

• 대한기계학회논문집A
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• 제34권11호
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• pp.1659-1666
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• 2010

WBD(wire-woven bulk diamond)라고 명명한 와이어로 직조된 다공질 금속의 새로운 형태를 소개한다. WBD 는 기계적 열 특성과 공학적 응용면에서 몇 년 전에 소개되어진 WBK(wire-woven bulk Kaogme)와 같이 나선형 와이어로 구성된다. WBK 에서는 각 교차점에서 3 개의 와이어가 접하나 WBD 에서는 4 개의 와이어가 서로 접하여 배열된다. 압축하중 하에서 WBD 의 기계적 거동을 조사하고 그 결과를 WBK 와 비교하였다. 같은 세장비(d/c)에서 WBD 의 밀도 및 강도는 WBK 의 약 2 배이나, WBD 의 강성도는 WBK 보다 그만큼 높지 않다.

• 한국식품영양과학회지
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• 제41권9호
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• pp.1320-1325
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• 2012

건조방법에 따른 품종별 고춧가루의 물리적 특성을 알아보기 위하여 집단밀도, 압축특성, 쌓임각, 비회복성 일 및 응력이완 특성을 살펴보았다. 이완집단밀도는 0.4197~0.4274$g/cm^3$ 범위로 열풍건조 한반도품종이 큰 밀도를, 청양품종열풍건조가 작은 밀도를 나타내었다. 충격집단밀도는 0.523~0.586 $g/cm^3$ 범위로 원적외선건조 한반도 품종이 큰 밀도를 나타내었고 한반도품종 천일건조가 0.523 $g/cm^3$로 작았다. 하우스너 비는 1.225~1.370의 범위를 보였으며, 두 품종모두 원적외선 건조에서 큰 값을 나타내었다. 압축성은0.00157~0.00225 범위로 한반도품종 원적외선건조가 큰 압축성을 나타내었다. 압축비는 0.971~1.032의 범위로 열풍건조가 크게 나타났으며, 품종에 따라서는 한반도품종이 큰값을 나타내었다. 안식각은 37.47{\sim}$42.38^{\circ}$ 범위로 열풍건조가 큰 값을 나타내었으며, 비회복성 일은 76.0~81.7%의 범위로 건조방법에 따른 차이는 작았지만 한반도품종이 청양품종에 비해 큰 값을 보였다. $k_2$값은 1.20~1.24 범위로 건조방법 및 품종 간 차이는 작았으며, 이완성은 13.41~24.31%범위로 원적외선 건조가 큰 값을 보였고 건조 방법별로 청양품종이 큰 값을 나타내었다.