• Korean Journal of Mathematics
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• 제4권1호
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• pp.39-43
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• 1996

Large-time asymptotic behavior of the solutions of interacting population reaction-diffusion systems are considered. Polynomial stability was proved.

• Journal of Ecology and Environment
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• 제44권3호
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• pp.162-177
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• 2020

Background: Ecologists have achieved much progress in the study of mechanisms that maintain species coexistence and diversity. In this paper, we reviewed a wide range of past research related to these topics, focusing on five theoretical bodies: (1) coexistence by niche differentiation, (2) coexistence without niche differentiation, (3) coexistence along environmental stress gradients, (4) coexistence under non-equilibrium versus equilibrium conditions, and (5) modern perspectives. Results: From the review, we identified that there are few models that can be generally and confidently applicable to different ecological systems. This problem arises mainly because most theories have not been substantiated by enough empirical research based on field data to test various coexistence hypotheses at different spatial scales. We also found that little is still known about the mechanisms of species coexistence under harsh environmental conditions. This is because most previous models treat disturbance as a key factor shaping community structure, but they do not explicitly deal with stressful systems with non-lethal conditions. We evaluated the mainstream ideas of niche differentiation and stochasticity for the coexistence of plant species across salt marsh creeks in southwestern Denmark. The results showed that diversity indices, such as Shannon-Wiener diversity, richness, and evenness, decreased with increasing surface elevation and increased with increasing niche overlap and niche breadth. The two niche parameters linearly decreased with increasing elevation. These findings imply a substantial influence of an equalizing mechanism that reduces differences in relative fitness among species in the highly stressful environments of the marsh. We propose that species evenness increases under very harsh conditions if the associated stress is not lethal. Finally, we present a conceptual model of patterns related to the level of environmental stress and niche characteristics along a microhabitat gradient (i.e., surface elevation). Conclusions: The ecology of stressful systems with non-lethal conditions will be increasingly important as ongoing global-scale climate change extends the period of chronic stresses that are not necessarily fatal to inhabiting plants. We recommend that more ecologists continue this line of research.

• 한국대기환경학회지
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• 제12권3호
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• pp.289-296
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• 1996

Effects of crustal species on the characteristics of ambient particles were studied by applying a gas-particle equilibrium model, SCAPE, to the measurements at Kosan, Cheju Island during the spring and summer, 1994. Two cases were simulated; the measured composition was used without any modification (case 1), and the metal ion concentrations originated from crust were subtracted from the measured particle composition (case 2). Total suspended particles (TSPs) were collected by an automatic high volume tape sampler during spring period and by high volume samplers during summer period. The fine particles, PM 2.5, and gaseous volatile species were collected using a filter pack smapler during summer period. The water soluble ion concentrations were analyzed from all the particle samples. According to the simulation results, the effect of crustal elements on the chemical composition of particles is negligible for both TSP particles and PM 2.5 particles. Acidity of particles measured at Kosan, however, is affected by the change of the concentrations of crustal species, stronger effects for TSP particles than for PM 2.5 particles during summer, and stronger effects during summer than spring for TSP particle. The average pH decrease due to the absence of crustal species was about 0.10 for PM 2.5 particle during summer and 1.51 and 0.85 for TSP particles during summer spring, respectively. Water contents of PM 2.5 particles for both cases are comparable to each other. Estimated water content of TSP particles for case 2 is higher than that for case 1 by about 4 $\sim 6 \mum/m^3$ because salts of metal ions are not hygroscopic.

• 한국입자에어로졸학회지
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• 제6권4호
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• pp.151-164
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• 2010

Inorganic ions and water are major components of ambient fine particles. Water content in fine particles is mainly determined by ambient meteorological conditions and the concentrations of hygroscopic species such as inorganic ions. Thus, to reduce fine particle mass concentration, it is important to accurately estimate the relationship between water content and the concentration of ions in fine particles. Water content in fine particles in Seoul are estimated by using a gas/particle equilibrium model to understand the characteristics of fine particle mass concentration. In addition, sensitivity of fine particle mass concentration to the changes of particulate ionic species (sulfate, nitrate, and ammonium) is estimated. It was found that water content in Seoul is mostly determined by the concentrations of the hygroscopic ionic species, especially, sulfate and ammonium, and ambient relative humidity.

• 환경생물
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• 제18권2호
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• pp.237-246
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• 2000

섬 생물지리학에서 평형설(equilibrium theory)은 섬의 면적과 본토에서 떨어진 거리에 따른 이입율과 절멸율의 작용에 의해 섬에 분포하고 있는 종 수가 결정된다는 이론이다. 본 연구는 한반도 부속도서에서 여러 생태학적인 요인들인 섬의 면적, 격리정도, 위도 및 섬의 최고 고도로 표시한 서식지 다양성과 나비의 종 수에 관한 상관관계를 파악하기 위하여 71개의 섬에서 기록된 나비의 종 수와 이들 요인들 사이의 상관분석 및 회귀분석을 실시하였다. 그 결과 나비 종 수는 섬 면적($r^2$=0.405, P<0.005) 및 고도로 표시한 서식지 다양성($r^2$=0.341, P<0.005)과는 유의한 상관관계를 보였으나 본토와의 거리 ($r^2$=0.018, P>0.05)및 섬 위도($r^2$=0.040, P>0.05)와는 유의한 상관관계를 나타내지 않았다. 본 연구와 이전의 연구결과를 종합해보면 한반도 부속도서의 나비 종 수는 섬의 면적, 식생 그리고 최고 고도와 같은 생태적 변수에 영향을 받는 것으로 요약된다.

• 한국토양비료학회지
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• 제34권3호
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• pp.213-236
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• 2001

토양용액의 이온조성은 작물의 양분흡수와 밀접한 관계를 가지고 있으며 양분의 이온조성을 추정하기 위하여 많은 모델이 개발되어 사용되고 있다. 토양용액 중 분석되는 양분의 몰농도는 insoluble 이온쌍과 평형을 이루고 있는 soluble 이온과 이온쌍 그리고 complex등의 농도로 간주하고, 양이온과 음이온을 동시에 고려한 양분의 이온조성을 추정하기 위하여 분석된 양분의 몰농도에 따른 선정된 평형식의 평형상수에 대한 conditional equilibrium constant를 구하여 모든 평형식이 만족되는 이온과 이온쌍의 몰농도를 구하는 모델을 설정하였다. 본 모델 이용시 기본적으로 필요한 성분은 pH, Eh, EC, 양이온 8종(K, Ca, Mg, Na, Fe, Mn, Al, $NH_4{^+}$, 음이온 6종(Si, 5, p Cl, $NO_3{^-}$, $HCO_3{^-}$)이며 다른 성분도 추가할 수 있도록 하였다. 토양과 토양용액이 평형조건인 경우 추정된 이온과 이온쌍의 조성과 이에 따른 존재 가능한 침전량과 mineral 종류별 함량을 계산하였다.

• 한국항공우주학회지
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• 제34권7호
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• pp.89-96
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• 2006

액체 로켓의 가스발생기의 연소 온도는 터빈 깃의 열 손상을 방지하기 위하여 1,000K 이하로 유지되며 이를 위하여 농후 연소 또는 산화제 과다 연소를 유지한다. 이러한 이유로 연소는 비평형 화학반응이 주로 발생하며 연소반응을 예측하기가 매우 어렵다. 한편 케로신은 여러 가지 탄화수소 연료로 이루어진 혼합연료로 화학반응 메커니즘에 대한 모델이 매우 어려운 실정이다. 본 연구에서는 Dagaut가 개발한 207 화학종, 1592 화학반응 단계를 이용하였으며 완전혼합반응기 연소모델을 적용하여 계산하였다. 계산결과와 실험결과를 비교하여 보면 사용된 화학반응 기구가 검댕 예측을 하지 않고 있음에도 불구하고 계산 결과는 연소가스 온도 뿐 아니라 가스 물성치 등을 매우 잘 예측하고 있음을 확인하였다.

• 수산경영론집
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• 제29권2호
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• pp.77-96
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• 1998

Fisheries products in Korea generally go through three markets, namely the wholesale market at production site (Market A), the wholesale market at consumption site (Market B), and the retail market (Market C), from producers to end consumers. As the products move from Market A through Market B to Market C, the marginal gap of prices asked in these markets demonstrates an apparent relationship. The producers, middlemen, consumers, and governmental departments concerned may influence the marketing prices of fisheries products. This study employing the cointegration theory tries to investigate whether causality of the price-setting among these markets exists and, if any, what it is. The authors have focused their attention on fisheries markets in Pusan, analyzing the long-run equilibrium relationship and causality between the prices of hairtail and squid among markets at different levels. Data used in this study cover the period f개m August 1984 to December 1997 fer hairtail, and the period from May 1989 to December 1997 for squid. The main findings of the study may be summarized as follows: First, regardless of the price time-series of hairtail and squid in individual market, the first difference is necessary fur satisfying the stationary conditions since each time-series is a first integration. This means homogeneous integration of time-series, which is a requirement of the long-run equilibrium of prices at different markets, is satisfied. Second, the study of the long-run equilibrium relationship between the prices at Market A and Market B shows that a long-run equilibrium relationship does exist for selling prices of the two species at Market A and Market B. Third, the ECM (error correction model ) used here to describe the long- and short-run dynamics of price change demonstrates that, in the case of squid, the price change in Market A will lead to a corresponding price change in Market B in the long-run period. In the short-run, however, the price at Market H is not only influenced by the price change in Market A but influence the price at Market A as well, that is, the Prices between Market A and Market B have a feedback effect. It should be stressed that the limitation in data collection, which cover only two species of hairtail and squid, is likely to cause a sampling bias. Nonetheless, we may conclude that a dynamic relation in the formation of prices does exist in view of the transaction amount of species at different markets. It is believed that the conclusion drawn from this study would not only contribute to a long-lasted debate on the direction of causality of price-setting among academic circle and fishing community, but would provide a useful standard for the policy makers in charge of the price-setting of fisheries products as well.

• Journal of the Korean Wood Science and Technology
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• 제10권3호
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• pp.4-12
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• 1982

1. 이 실험은 미국 Dept. of Navy의 위촉(委囑)을 받아 School of Forestry, Yale University에서 실시중인 열대산(熱帶産) 재목(材木)이 물리적(物理的) 기계적(機械的) 성질(性質) 연구계획(硏究計劃)의 일부(一部)로써 동대학(同大學) 목재공예연구실(木材工藝硏究室)에서 실시(實施)하였다. 2. 이 실험은 연구소에 장치(裝置)된 적은 실험설비를 이용(利用)하여 일정(一定)한 관계습도(關係濕度)(21%, 53%, 61% 그리고 83%등(等))를 조절하면서 各 관계습도(關係濕度) 밑에서 각(各) 시험편을 가질 수 있는 평형합수량(平衝含水量) equilibrium moisture content와 hysteresis loop 즉 relative humidity moisture content curve을 결정(決定)하기 위하여 실시하였다. 3. 이 실험을 통(通)하여 목적(目的)한 바 열대재(즉(卽) Ocotea, Tabebuia 그리고 Hymenaea)의 관계 습도에 따라 equilibrium moisture content와 이때에 일어나는 hysteresis loop를 알게 되었으며 각(各) 수종의 관계습도에 따른 equilibrium moisture content는 Table 4과 같으며 hysteresis loop 관계(關係)는 Fig. 2.3.4와 같다. 4. 이 실험을 통(通)하여서도 과거(過去) 모는 실험결과에서 보는 것과 같이 각(各) 수종에 따라 같은 관계습도에서 가질 수 있는 equilibrium moisture content에 상당(相當)한 차이(差異)를 볼 수 있었으며 그 차이(差異)는 관계습도가 높을수록 큰 경향(傾向)을 띠우고 따라서 hysteresis loop의 shape 에도 각기(各其) 그 고유(固有)한 특징(特徵)을 볼 수 있다. 5. 대기중(大氣中)에 있는 큰 재목(材木)이 가질 수 있는 평형함수량(乎衝含水量)(E M C) 은 Table 6와 같으며 이것 역시(亦是) 적은 시험편(試驗片)으로 시험(試驗)하여 얻은 결과(結果)와 같이 나무 종류(種類)에 따라 차이(差異)가 있고 그 차이(差異)는 관계습도(關係濕度)가 높으면 높을수록 크다는 것을 알게 되었다. 6. 재목(材木)의 생산지(生産地)가 다르면 즉 남방(南方) 열대지역(熱帶地方)에서 생산(生産)하는 것과 온대지방(溫帶地方)에서 생산(生産)되는 나무사이에는 나무 종류(種類)가 달라서 직접(直接) 비교(比較)는 안되나 나무 종류별(種類別)로 보면 역시(亦是) 이와같은 목재(木材)의 물리적(物理的) 성질(性質)에 확실(確實)히 차이(差異)가 있었다는 것을 알게 되었다.(참조(參照) Table 5) 7. 이 실험결과를 발표(發表)함에 있어 친(親)히 충고(忠告) 지도(指導)하여 주신 Wangaard와 Dickinson 양(兩) 교수님과 재과(材科) 주선(周旋)에 수고(受苦)를 아끼지 않고 전심(全心) 도와 주신 Mr. R. C. Claneh 씨(氏)등에게 충심(衷心)으로 감사(感謝)의 뜻을 표(表)하는 바이다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.84-91
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• 2008

Generalized hydrodynamic (GH) theory for multi-species gas and the computational models are developed for the numerical simulation of hypersonic rarefied gas flow on the basis of Eu's GH theory. The rotational non-equilibrium effect of diatomic molecules is taken into account by introducing excess normal stress associated with the bulk viscosity. The numerical model for the diatomic GH theory is developed and tested. Moreover, with the experience of developing the dia-tomic GH computational model, the GH theory is extended to a multi-species gas including 5 species; O$_2$, N$_2$, NO, O, N. The multi-species GH model includes diffusion relation due to the molecular collision and thermal phenomena. Two kinds of GH models are developed for an axisymmetric flow solver. By compar-ing the computed results of diatomic and multi-species GH theories with those of the Navier-Stokes equations and the DSMC results, the accuracy and physical consistency of the GH computational models are examined.