• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1997.10a
• /
• pp.7-11
• /
• 1997

직경 3.5 cm, 길이 1.5 m 의 석영관 내에서 염화제1철 증기를 수소로 환원하여 철 초미립자를 제조하였다. 염화제1철의 증발조건, 염화제1철 증기와 수소의 혼합방법, 반응물의 예비가열온도, 반응온도, 염하제1철의 농도, 반응기내 체류시간이 생성된 철 입자의 크기 및 크기분포에 미치는 영향을 조사하였다. 철 입자의 평균직경은 40-88 cm 이고, 기하표준편차는 1.4 정도로 나타났다. 철 입자들은 자기적 성질에 의해 서로 연결되어 체인을 형성하였으며, 전자회절분석 결과 단결정이었다. 평균입경 55nm 철 입자들의 항자력은 900 Oe, 포화자화값은 130 emu/g 이었다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2002.04a
• /
• pp.77-77
• /
• 2002

초소형 공중발사체 설계 시 하이브리드 모터의 적용가능성에 대한 연구를 실시하였다. HTPB/LOX를 추진제로 하여 마차바퀴형 연료 그레인, 산화제 탱크 가압방식을 사용하였고, 성능특성을 계산하기 위하여 하이브리드 연료의 연소율이 일정하다고 가정 하였다. 본 연구에 사용된 임무는 중량 3.5kg의 나노위성을 근지점 고도 200km, 원지점 고도 1,500km의 타원궤도로 진입시키는 것을 목적으로 하는 로켓의 1단 부분에 관한 것으로 1단의 발사속도는 M=1.3, 발사고도는 12km, 연소종료 고도는 40km이다. 1단에 대한 페이로드 중량은 127.5kg이고, 속도증가분($\Delta$V)은 3,330m/s이다. 모선은 F-4E를 사용하였고 모선의 특성상 발사체의 총 중량이 1,000kg이하로 제한되고 길이와 직경이 5m${\times}$5m로 제한되나 1단에 대한 길이의 제한조건은 현재까지 명확히 정립되지 않은 상태이다. 설계과정에서의 변수는 연료 그레인 포트 개수, 초기 산화제 플럭스, 연소실 압력을 사용했고, 설계 제한조건은 추진제 중량, 평균 비추력, 평균 추력, 연소시간, 1단 길이, 직경, 연소시간이고, 이들의 범위는 모선의 특성과 초소형 공중발사체의 임무특성에 맞게 설정하였다.

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2003.11a
• /
• pp.405-406
• /
• 2003

현재 우리나라 입자상물질에 대한 대기환경기준은 공기역학적 직경 10 $\mu\textrm{m}$ 이하인 PM$_{10}$ 기준이 연평균 70 $\mu\textrm{g}$/㎥ 및 일평균 150 $\mu\textrm{g}$/㎥이다. 그러나 영국의 PM$_{10}$ 기준은 24시간 평균 50 $\mu\textrm{g}$/㎥로 강화하여 입자상물질에 의한 건강피해를 줄이기 위해 노력하고 있다(EPAQS, 1995). 분진은 공기역학적 직경 2.5 $\mu\textrm{m}$를 기준으로 미세입자와 거대입자로 나누어지는 쌍극분포의 형태(Whitby et al., 1972)를 나타내며, 분진이 인체에 미치는 영향에 관한 많은 연구를 통해 10 $\mu\textrm{m}$ 이하의 입자가 호흡성 분진으로 인체에 더 유해한 영향을 미치고 있음이 밝혀졌다(Emison, 1988). (중략)

• Journal of agriculture & life science
• /
• v.53 no.6
• /
• pp.23-33
• /
• 2019

In accordance with a change in the management information system containing the management record and planning for the entire national forest in South Korea by an amendment of the relevant law (The national forest management planning and methods, Korea Forest Service), in this study, average, the maximum, and the minimum values for DBH were presented while only average values were required before the amendment. In this regard, there is a need for an estimation algorithm by which all the existing values for DBH established before the revision can be converted to the highest and the lowest ones. The purpose of this study is to develop an estimation equation to automatically show the minimum and the maximum values for DBH for 12 main tree species from the data in the national forest management information system. In order to develop the estimation equation for the minimum and the maximum values for DBH, there was exploited the 6,858 fixed sample plots of the fifth and the sixth national forest inventory between in 2006 and 2015. Two estimation models were applied for DBH-tree age and DHB-tree height using such growth variables as DBH, tree age, and height, to draw the estimation equation for the maximum and the minimum values for DBH. The findings showed that the most suitable model to estimate the minimum and the maximum values for DBH was Dmin=a+bD+cH, Dmax=a+bD+cH with the variables of DBH and height. Based on these optimal models, the estimation equation was devised for the minimum and the maximum values for DBH for the 12 main tree species.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.3 no.3
• /
• pp.31-39
• /
• 1999

In this paper, numerical experiment is attempted to analyze and compare the combustion efficiency of the burning sprays due to OFO, FOF triplet / FOOF split doublet injectors. Preconditioned Wavier-Stokes equation system with low Reynolds number $\kappa$-$\varepsilon$ model for turbulence closure, is LU-SGS time-integrated. Spray processes are modeled by DSF analysis with experimentally determined injection characteristics. n-heptane/air global reaction model approximates the combustion for simplicity, and the influence of turbulence on the chemical reaction is included using eddy dissipation model. The results showed the FOF triplet injector of highest combustion efficiency, whereas the OFO type of poet performance. It was also observed that the droplet mean diameter and the average gas temperature due to the mixing efficiency, are the representative parameters for the performance design of combustion.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.2
• /
• pp.209-213
• /
• 2016

The characteristics of fluidization in a centrifugal fluidized bed with a 184 mm inner diameter, 50 mm width of the gas distributor was observed by photographs and experimental works using Cu-ZSM-5 zeolite catalysts with a mean diameter of $26{\mu}m$ and $32{\mu}m$ as bed materials at a rotor at 400rpm and 600rpm. Under these experimental ranges, the experimental results clearly showed the effects of the number of rotation of the rotor on the behavior of bubbles in the centrifugal fluidized bed. As the number of rotations of the rotor increased, the gas velocity at which bubbles begin to be formed also increased but the diameter of the bubbles decreased. In addition, the size of the bubbles in the centrifugal fluidized bed were relatively smaller than those in the conventional bubbling fluidized bed.

• Korean Chemical Engineering Research
• /
• v.57 no.1
• /
• pp.105-110
• /
• 2019

Effect of height on the size and shape of carbon nanotube (CNT) aggregates in the freeboard region of a bubbling fluidized bed ($0.15m\;i.d.{\times}2.6m\;high$) has been determined. Feret diameter and Heywood diameter of the CNT aggregates in the freeboard region of fluidized bed increased with increasing gas velocity. The average aggregate diameters and CNT particle number in the aggregates decreased with increasing of height in the freeboard. Aspect ratio increased as the location was closer to the surface of the dense phase, but decreased at the highest location. Solidity did not show any significant changes with height. The results showed the aggregates formation process is affected by the height in the freeboard. A correlation was proposed to predict the Heywood diameter of the CNT aggregates.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.25 no.2
• /
• pp.48-58
• /
• 2022

This study tried to assess the applicability of a hand-held LiDAR for measuring the geometric structures of forest trees including diameters at a breast height(DBH) and tree height(H). A traditional method using tapelines was conducted to analyze the accuracy of the LiDAR instrument in the Taebaeksan national park in South Korea. Four statistical indices which are bias, root mean square error, mean absolute error, and correlation coefficient were employed to compare the measurements by the LiDAR instrument and traditional method. The DBHs from the LiDAR were very similar to those from the traditional method. And it indicated that the LiDAR is sufficient to be a alternative of a traditional method. However, there was a limitation in assessing the accuracy of LiDAR for measuring tree height by comparing the measurements by observer's eyes since they included different error sources. Further study is needed to assess the accuracy of LiDAR instrument for tree height through more reliable measurements.

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.10 no.1
• /
• pp.9-16
• /
• 2008

In this study we investigated the effects of the microclimatic conditions on tree growth in different site types for natural deciduous forests in Korea. First, we classified all the sites into 36 types according to their aspect (east, west, south, and north), elevation (higher than 1,000 m, 700$\sim$1,000 m, and lower than 700 m), and topographical conditions (ridge, slope, and valley). For each site type, we measured diameter growth with increment borer, and then estimated periodic annual increment of diameter, height and volume. We applied a topoclimatological technique for estimating microclimatic conditions, and produced monthly climatic estimates from which 17 weather variables (including indices of warmth, coldness, and aridity) were computed for each site type. The periodic annual increments of diameter, height, and volume were then correlated by regression analysis with those weather variables to examine effects of microclimate on tree growth by site type. We found that the correlation of diameter growth by site type was significantly correlated with most weather variables except daily photoperiod. Water condition was the most important factor for the height growth. For volume growth, on the other hand, the conditions such as relatively high temperature and low humidity provided favorable environment. Our regression analysis shows that aridity index is a good predictor for tree growth including diameter, height and volume increments.

• Journal of the Korean Wood Science and Technology
• /
• v.43 no.1
• /
• pp.52-59
• /
• 2015

Cross-cut disks from small diameter oak logs were thermally modified and developed to make accessories such as a brooch. However it is known that domestic oaks are refractory and it is hard to dry their cross-cut disks without any drying defects. The cross-cut disks of Quercus variabilis (7 mm long in the longitudinal direction) were forced to dry in air at two different air velocities in summer and fall season, and their drying yields were investigated. Under the same condition, the average final moisture contents (MCs) of the specimens dried in the fall were lower than those dried in the summer. The average final MCs of the small diameter specimens dried at higher air velocity were slightly lower than those at lower air velocity while those of the large diameter specimen were not influenced by the air velocity. The number of the large diameter specimens with cross checkings was higher than that of the small diameter specimen. This discrepancy between two different diameters was twice in the fall, while it was more than four times in the summer. The large diameter specimens dried at low air velocity in Summer were cross-checked most, which was attributed to repeated water condensation and evaporation due to high humidity and low air velocity.