• 한국지하수토양환경학회지:지하수토양환경
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• 제28권6호
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• pp.45-57
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• 2023

To assess land subsidence estimation and preparedness in the Geum River basin, this study applied GIS techniques and identified six key areas. The Geum River basin has experienced an increase in heavy rainfall since late 2010, and four study areas have shown an increase in groundwater levels. Land subsidence primarily occurred from June to September, with higher rainfall years in 2020 and 2023. Approximately 83.6% of land subsidence in Chungcheongbuk-do province occurred in Cheongju-si, mainly attributed to aging sewage pipes. The regions experiencing population growth have likely led to the construction of underground infrastructures and sewer pipes. Thus, it is considered that various factors, including sewage pipe leaks, precipitation, slope gradient, low drainage density, and groundwater level fluctuations, have contributed to land subsidence. Improving land subsidence estimation involves incorporating additional natural factors and human activities.

• 한국표면공학회지
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• 제28권4호
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• pp.207-218
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• 1995

Tungsten(W) metal has excellent properties in heat-resistance, corrison-resistance and impact-resistance but W-Metal is hard to sinter because higher than $2,000^{\circ}C$ is required to sinter W-powder. Con-sequently, a deposit technique of Nikel Phosphorus(NiP) on W-powber by the liquid reduction precipitation method was performed. Sintering temperature of the resulting W-NiP composite was lowered around to $1,000^{\circ}C$, and the mechanical properties of the sintered body was studied. The most suitable conditions for NiP thin film deposit on W-Powder by the liquid reduction precipitation method, which are composition, concentration, pH and temperature of the liquid reduction solution, were considered. The activated sintering was carried out in a reducing condition furnace. Components and properties of the sintered body were investigated by the density and the hardness measurements, X- ray diffraction analysis, and microscopic photographs of the surface. Quantity of NiP thin film on W-powder could be varied by the change of the liquid reduction solution composition. The sintering temperature of W-NiP composite powder is lowered to $950^{\circ}C$ from $2,000^{\circ}C$ and the hardness is increased (ca. 720 Hv). Large shrinkage could be observed since density was increased from 5.5 to 11.0 g/$cm^2$ which 86.2% of theoretical density. W metal and $Ni_3P$ crystal were detected through X-ray diffraction on the sintered body. Perfectly activated sintering was observed by microscopic photographs.

• 한국분말재료학회지
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• 제23권2호
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• pp.136-142
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• 2016

As precursors of cathode materials for lithium ion batteries, $Ni_{1/3}Co_{1/3}Mn_{1/3}(OH)_2$ powders are prepared in a continuously stirred tank reactor via a co-precipitation reaction between aqueous metal sulfates and NaOH in the presence of $NH_4OH$ in air or nitrogen ambient. Calcination of the precursors with $Li_2CO_3$ for 8 h at $1,000^{\circ}C$ in air produces dense spherical cathode materials. The precursors and final powders are characterized by X-ray diffraction (XRD), scanning electron microscopy, particle size analysis, tap density measurement, and thermal gravimetric analysis. The precursor powders obtained in air or nitrogen ambient show XRD patterns identified as $Ni_{1/3}Co_{1/3}Mn_{1/3}(OH)_2$. Regardless of the atmosphere, the final powders exhibit the XRD patterns of $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ (NCM). The precursor powders obtained in air have larger particle size and lower tap density than those obtained in nitrogen ambient. NCM powders show similar tendencies in terms of particle size and tap density. Electrochemical characterization is performed after fabricating a coin cell using NCM as the cathode and Li metal as the anode. The NCM powders from the precursors obtained in air and those from the precursors obtained in nitrogen have similar initial charge/discharge capacities and cycle life. In conclusion, the powders co-precipitated in air can be utilized as precursor materials, replacing those synthesized in the presence of nitrogen injection, which is the usual industrial practice.

• 한국세라믹학회지
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• 제40권11호
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• pp.1120-1126
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• 2003

알루미나 분말을 분쇄하면서 Y 수화물을 동시에 침전시켜 YAG 분말을 합성하였다. 하소 분말 (l20$0^{\circ}C$, 4 h)에는 YAG 외에 소량의 YAM이 남아 있었다. 그러나 평균 입경 0.57 $\mu$m으로 분쇄한 분말 성형체에서는 산화물 혼합법에서 YAG 단일상이 얻어지는 온도 (l500∼1$600^{\circ}C$) 보다 훨씬 낮은 130$0^{\circ}C$ 에서 YAG 단일상이 이미 형성되었다. 분말의 소결성은 우수하여 소결조제 SiO$_2$(350 ppm Si) 의 첨가에 관계없이 치밀화가 잘 일어났다. SiO$_2$를 첨가하지 않은 경우, 1$600^{\circ}C$에서 98%의 손결밀도를 얻었다. SiO$_2$를 첨가한 경우에는 150$0^{\circ}C$에서 치밀화가 더 잘 일어나 97.7%의 소결밀도가 얻어졌으며, 1$600^{\circ}C$에서는 SiO$_2$의 소결촉진 효과가 나타나지 않아 밀도는 SiO$_2$를 첨가하지 않은 시편과 비슷하였다.

• 대한토목학회논문집
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• 제34권4호
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• pp.1117-1123
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• 2014

물은 인류와 동식물의 필요조건으로, 물 부족 상태 즉 가뭄은 전 세계적으로 가장 두려워하는 재해 중 하나이다. 본 연구는 지역적인 특성을 고려하여 가뭄을 판단하고 대응하기 위해 목표재현기간을 설정하고 한반도 전역을 대상으로 시 군 구 단위의 지역별 목표 표준강수지수를 산정하였다. 먼저 한반도에 위치한 30년 이상의 자료기간을 보유한 88개 기상관측소의 강우자료에서 월별강우자료를 추출하고 SPI (3)가뭄지수를 산정하였다. 산정된 SPI (3)에서 연도별 최저치를 추출하여 매개변수적 빈도해석과 경계핵밀도 함수를 이용한 비매개변수적 빈도해석을 실시하였다. 또한, 목표재현기간을 30년으로 설정하고 비매개변수적 빈도해석 결과에 티센비 적용하여 시 군 구 단위로 목표 표준강수지수를 산정하였다. 분석결과 가뭄의 심도와 빈도가 지역별로 크게 다르게 나타남을 확인 할 수 있었으며, 이는 한반도 가뭄의 판단과 대응을 위한 기초자료로 국가적인 수자원계획과 방재대책에 기여하고자 한다.

• 한국세라믹학회지
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• 제25권5호
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• pp.465-472
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• 1988

Alpha alumina powder with fine particle size and narrow particle size distribution was prepared by precipitation method using Al2(SO4)3.18H2O as a starting material. The alpha alumina powder was prepared by calcining aluminum hydroxide which was formed under various pH values. The sinterabilityof alpha alumina powder and the effect of MgO on the sinterability of alpha alumina powder were investigated. The sinterability of alpha alumina powder was the order of pH=10≒pH11>pH=7≒pH9, and alpha alumina obtained from boehmite which was prepared by precipitation method reached to 97.5% of theoretcal density by the pressureless sintering. The effect of MgO on volume shrinkage of alumina was very slight in the initial sintering stage but remarkable in the final sintering stage. It was also found that MgO controlled effectively the grain growth of alumina.

• 연구논문집
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• 통권28호
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• pp.39-47
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• 1998

Industrial electrostatic precipitation is a very complex process, which involves multiple-way interaction between the electric field, the fluid flow, and the particulate motion. This paper describes a strongly coupled calculation procedure for the rigorous computation of particle dynamics during electrostatic precipitation. The turbulent gas flow and the particle motion under electrostatic forces are calculated by using the commercial computational fluid dynamics (CFD) package FLUENT linked to a finite-volume solver for the electric field and ion charge. Particle charge is determined from both local electrical conditions and the cell residence time which the particle has experienced through its path. Particle charge density and the particle velocity are averaged in a control volume to use Lagrangian information of the particle motion in calculating the gas and electric fields. The turbulent particulate transport and the effects of particulate space charge on the electrical current flow are investigated. The calculated results for poly-dispersed particles are compared with those for mono-dispersed particles, and significant differences are demonstrated.

• 한국수자원학회논문집
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• 제38권8호
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• pp.595-604
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• 2005

관측자료의 보완이나 확충을 위한 강수량 모의발생은 수문분석에 있어서 중요한 과제라고 할 수 있다. 강수량을 모의하는 방법은 크게 기존의 매개변수적 방법과 비매개변수적 방법 두 가지로 나눌 수 있고, 강수량 모의의 시간간격에 따라 일강수량 자료의 모의 또는 시간강수량 자료의 모의 등으로 구분할 수 있다. 지금까지, Markov모형은 일강수량 모의발생에 많이 이용되어왔다. 이러한 대부분 Markov모형들은 동질성모형으로 상태벡터를 구축하는데 있어서 자료의 크기가 작으면 모형구축의 어려움이 따르고 같은 월에 대한 상태벡터의 동질성을 가정하는 등의 문제가 있다. 실제 강수발생의 과정은 비정상적(nonstationary)이므로 이를 보완하기 위해, 된 논문에서는 일강수량을 기존의 매개변수적인 방법이 아닌 단변량과 다변량에 대하여 비매개변수적인 방법으로 접근하여 모의하는 방법에 대하여 분석하였다.

• 대한토목학회논문집
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• 제30권5B호
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• pp.471-477
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• 2010

본 연구에서는 개념적인 토양수분수지 모형을 구성하여 유역에서의 물의 기화량과 유역의 습윤량의 비인 Horton 지수의 변동성을 살펴보고 있다. 제안된 모형으로부터 다양한 수문기상학적 변수들 및 유역 특성변수를 반영한 토양수분 확률밀도함수가 유도되며, 강수현상을 구성하는 두 가지 주요 인자인 강수발생빈도와 우기일의 평균 강수량의 변화에 따른 Horton지수의 민감도가 탐색된다. 수치모의결과를 통하여 Horton 지수는 강수량의 연간변동성보다 약 절반가량 낮았으며 둘 사이에는 강한 역 상관관계가 있음을 살펴볼 수 있다. 또한 강수량이 일정하더라도 강수발생빈도와 우기일 강수량 평균에 따라 서로 다른 Horton 지수를 가질 수 있음이 보여진다. 마지막으로 Horton 지수와 강수 프로세스를 구성하는 두 가지 주요 성분과는 어떤 한계점을 기준으로 비례/반비례 관계가 전환되는 비선형적인 관계를 가지고 있음을 살펴볼 수 있다.

• Journal of Ginseng Research
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• 제8권1호
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• pp.65-74
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• 1984

This experiment was carried out to study the effects of light intensity and soil water regimes on the growth of ginseng seedling. The results were as follows: 1. The maximum light intensity and optimum temperature in 1,le photosynthesis of ginseng seedling were 10,000 lux and 23 $^{\circ}C$. Respiration rate was increased at high temperature. 2. Air and soil temperature under the shading were increased as the increase of light intensity but soil water contents were decreased as the increase of light intensity, whereas air and soil temperature were decreased as the increase of precipitation under the shade b5: soil water contents were increased as the increase of precipitation under the shade. 3. The higher the transmittance of the shade, the greater the specific leaf weight (S.L.W.) and stomatal density. In contrast, however, the contents of total chlorophyll, chlorophyll a and b, and stomatal length was decreased. There was no any significant difference light intensity of the a/b ratio of chlorophyll. 4. The highest photosynthesis was occurred in ginseng leaves grown under the shade 5% L.T.R. and net photosynthesis rates increased with increasing soil water contents. 5. Optimum condition for usable seedling yield were 5% L.T.R. and 3.3% precipitation under the shade. Useless seedling increased with increasing precipitation under the shade.