• 대한기계학회논문집B
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• 제23권9호
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• pp.1185-1191
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• 1999

Radiation-induced oscillatory instability in diffusion flames is numerically investigated with nonlinear dynamics considered. As the simplest flame model, a diffusion flame established in the stagnant mixing layer is employed with optically thin gas-phase radiation and unity Lewis numbers for all species. Attention is focused on the radiation-induced extinction regime, which occurs at large $Damk\ddot{o}hler$ number. Once the steady flame structure is obtained for a prescribed value of the initial $Damk\ddot{o}hler$ number, transient solution of the flame is calculated after a finite amount of the $Damk\ddot{o}hler$-number perturbation is imposed on the steady flame. Transient evolution of the flame exhibits three types of flame-evolution behaviors, namely decaying oscillatory solution, diverging solution to extinction and stable limit-cycle solution. A dynamic extinction boundary is identified for laminar flamelet library.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2002년도 제24회 KOSCO SYMPOSIUM 논문집
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• pp.95-98
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• 2002

A numerical investigation on the flame propagation and extinction in a micro combustor is described. Previous measurements of $H_2-air$ flame propagation in a submilimeter scale combustor exhibited significance of wall effects on burning velocity and extinction. The heat transfer to wall becomes important not only in the cooling of burnt gases but also during the flame ropagation, which has be by and large ignored in macro scale combustor calculations. In order to take the heat loss into account the combustion calculation, we developed a numerical code with a heat transfer model that was determined empirically from measured data. PISO algorithm was used for differencing of conservation equations. $H_2-air$ reaction was modeled with 10 species - 16 steps. Comparison with measured data showed good agreement in flame propagation speed. Also the pressure decrease after flame extinction was accurately predicted by the model. A further study is desirable for a better quenching model that can predict the quenching location.

• 한국어류학회지
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• 제21권sup1호
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• pp.29-37
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• 2009

The tiny fragment of freshwater body is providing home for huge biodiversity and resources for the existence of human. The competing demand for freshwater have been increased rapidly and it caused the declination of biodiversity in recent decades. Unlike the natural process of extinction in gradual progress, the current species extinction is accelerated by human activity. As a result many fish species are already extinct or alive only in captivity in the world and about fifty eight animal species are in endangered in Korea including eighteen freshwater species. Conservation of biodiversity is the process by which the prevention of loss or damage is attained, and is often associated with management of the natural environment. The practical action is classified into in-situ, or ex-situ depending on the location of the conservation effort. Recovery means the process by which the status of endangerment is improved to persist in the wild by re-introduction of species from ex-situ conservation population into nature or translocation of some population. However there are a lot of restrictions to complete it and successful results are known very rare in case. In this article the authors explore some strategies for conservation and restoration of freshwater fish species conducted in Korea for few years. The major causes are discussed in relation with the decline of freshwater fish diversity during few decades and some strategies are evaluated to advance the process of conservation. A study on the Korean bullhead, Pseudobagrus brevicorpus, is introduced as a case for ex-situ conservation and restoration in freshwater ecosystem.

• 한국어류학회지
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• 제30권3호
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• pp.155-160
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• 2018

우리나라 멸종위기어류 한둑중개 Cottus hangiongensis의 분포양상 및 멸종위협 등급을 평가하기 위해 2011년부터 2017년까지 분포조사를 실시하였다. 한둑중개의 분포 결과를 1954~1985년, 1981~2003년, 2004~2012년, 2011~2017년으로 나누어 비교한 결과, 분포하천 수는 각각 30개, 24개, 10개, 19개 하천으로 나타나 점차적으로 감소하는 경향을 보였다. 본 조사(2011~2017)에서 새롭게 확인된 하천은 아야진천과 척산천 2개였으며, 과거에 출현하였으나 본 조사에서 확인되지 않은 하천은 15개였다. 한둑중개의 서식지는 공통적으로 하천 하류부의 물이 맑고 유속이 빠르며 하상은 돌과 큰돌이 있는 여울부였다. IUCN 적색목록 기준지침서에 따라 멸종위협 등급을 평가하면, 한둑중개 개체수는 1981~2003년에 비해 보의 축조와 하천공사, 서식지의 질적 하락 등의 이유로 30% 이상 감소한 것으로 추정되어 취약 (VU, A2ac)으로 평가하였다.

• 대한기계학회논문집B
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• 제27권2호
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• pp.243-250
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• 2003

The extinction behavior and the unsteady response of augmented reduced mechanism(ARM) have been investigated by adopting an OPPDIF code and a numerical solver for the flamelet equations. By comparing the performance of the ARM based on Miller and Bowman's mechanism(MB-ARM) with that of the ARM based on GRI-Mech 3.0(GRI-3.0-ARM), it is identified that the MB-ARM is more suitable for the unsteady calculation because it is relatively less stiff than GRI-3.0-ARM during an ignition process. The steady results using the MB-ARM, which is modified to predict reasonably the extinction point of experiment, are in excellent agreement with those from full mechanism. Under the sinusoidal transient disturbances of scalar dissipation rate, the unsteady responses of the flame temperature and species concentrations using a modified MB-ARM show in very close agreement with those from full mechanism. It is presumed that above modified MB-ARM is very suitable for the unsteady simulation of turbulent flames because it gives not only a low computational cost but also a good prediction performance for flame structure, extinction point and unsteady response.

• 한국연소학회지
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• 제10권4호
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• pp.33-40
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• 2005

The propagation rates of advancing and retreating non-premixed edge flames in a slot-jet counterflow were measured as a function of strain rate for varying jet spacing, mixture strength, stoichiometric mixture fractions $(Z_{st})$ and Lewis numbers (Le). Methane and propane fuels were tested and nitrogen and carbon dioxide were used as inerts. As results, we could identify igniting fronts, retreating fronts, two total extinction limits, and short-length edge flames. A burner separation affected to a low extinction limit only. Regimes for advancing and retreating edges together with total extinction were mapped in terms of normalized flame thickness and heat loss factor for $CH_4/O_2/N_2$ mixtures. Edge flames for $Z_{st}$ > 0.5 behaved like a stronger mixture while for $Z_{st}$ < 0.5 showed deteriorated feature, because of relative locations of a non-premixed flame and intermediate species such as CO and $H_2$. Furthermore, due to the relative importance of heat loss, propagating speeds of edge flames were significantly enhanced in $CH_4/O_2/CO_2$ mixtures (Le < 1) demonstrating increasing stability limits. However $C_3H_8/O_2/N_2$ mixtures (Le > 1) showed opposite result.

• 한국대기환경학회지
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• 제22권6호
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• pp.863-875
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• 2006

Intensive visibility monitoring was conducted to investigate physical and chemical characteristics of visibility impairment by airborne pollen. Light attenuation coefficients were optically measured by a transmissometer, a nephelometer, and an aethalometer. Elemental, ionic, and carbonaceous species were chemically analyzed on the filters collected by $PM_{2.5}$ and $PM_{10}$ samplers. Aerosol size distribution was analyzed using a cascade impactor during airborne pollen period. Airborne pollen count was calculated using a scanning electron microscope. Airborne pollen was emitted into the atmosphere in springtime and funker degraded visibility through its scattering and absorbing the light. Average light extinction coefficient was measured to be $211{\pm}36Mm^{-1}$ when airborne pollen was not observed. But it increased to $459{\pm}267Mm^{-1}$ during the airborne pollen period due to increase of average $PM_{2.5}$ and $PM_{10}$ mass concentration and relative humidity and airborne pollen count concentration for $PM_{10}$, which were measured to be $46.5{\pm}29.1{\mu}g\;m^{-3},\;97.0{\pm}41.7{\mu}g\;m^{-3},\;54.1{\pm}11.6%$, and $68.2{\pm}89.7m^{-3}$, respectively. Average light extinction efficiencies for $PM_{2.5}$ and $PM_{10}$ were calculated to be $5.9{\pm}0.9$ and $4.5{\pm}0.8m^2 g^{-1}$ during the airborne pollen period. Light extinction efficiency for $PM_{10}$ increased further than that for $PM_{2.5}$. The average light extinction budget by airborne pollen was estimated to be about 24% out of the average measured light extinction coefficient during the airborne pollen period.

• Genomics & Informatics
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• 제21권1호
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• pp.10.1-10.6
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• 2023

The fishes of the Chiasmodontidae family, known as swallower fishes, are species adapted to live in deep seas. Several studies have shown the proximity of this family to Tetragonuridae and Amarsipidae. However, the phylogenetic position of this clade related to other Pelagiaria groups remains uncertain even when phylogenomic studies are employed. Since the low number of published mitogenomes, our study aimed to assemble six new mitochondrial genomes of Chiasmodontidae from database libraries to expand the discussion regarding the phylogeny of this group within Scombriformes. As expected, the composition and organization of mitogenomes were stable among the analyzed species, although we detected repetitive sequences in the D-loop of species of the genus Kali not seen in Chiasmodon, Dysalotus, and Pseudoscopelus. Our phylogeny incorporating 51 mitogenomes from several families of Scombriformes, including nine chiasmodontids, recovered interfamilial relationships well established in previous studies, including a clade containing Chiasmodontidae, Amarsipidae, and Tetragonuridae. However, phylogenetic relationships between larger clades remain unclear, with disagreements between different phylogenomic studies. We argue that such inconsistencies are not only due to biases and limitations in the data but mainly to complex biological events in the adaptive irradiation of Scombriformes after the Cretaceous-Paleogene extinction event.

• 한국어류학회지
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• 제33권3호
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• pp.177-183
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• 2021

우리나라 멸종위기어류 버들가지 Rhynchocypris semotilus의 분포양상과 멸종위협을 평가하기 위해 강원도 고성군에서 2020년 6월에 분포조사를 실시하였다. 분포조사는 모두 12개 지점을 조사하여 6개 지점에서 268개체를 채집하였는데, 하천별로는 송현천(3개 지점), 고진동(2개), 오소동(1개) 순으로 지점수가 많았다. 버들가지 서식지는 하천 최상류 또는 상류(하천형 Aa type)의 유폭 3~15 m, 수심은 0.3~1.3 m로 하상은 큰돌과 작은돌의 비율이 높은 곳이었다. 전장빈도분포도(6월)로 연령을 추정한 결과, 전장 6~27 mm는 당년생, 38~59 mm는 만 1년생, 60~75 mm 만 2년생, 78~93 mm는 만 3년생, 96~125 mm는 만 4년생 이상으로 추정되었고, 생식소가 성숙되는 연령은 만 2년생 이상이었다. 버들가지의 멸종위협 등급을 IUCN 평가기준에 따라 평가하면, 개체군 크기는 크게 감소하지 않았으나, 성숙개체수는 1,000개체 이하로 추정되고, 적은 출현범위(39.668 km²)와 점유면적(16 km²), 지소수(3지소)를 보여 멸종위협 범주인 취약(VU D2)으로 평가되었다.

• Journal of applied mathematics & informatics
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• 제27권5_6호
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• pp.1097-1107
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• 2009

In this paper, three species stage-structured predator-prey model with time delayed and periodic constant impulsive perturbations of predator at fixed times is proposed and investigated. We show that the conditions for the global attractivity of prey(pest)-extinction periodic solution and permanence of the system. Our model exhibits a new modelling method which is applied to investigate impulsive delay differential equations. Our results give some reasonable suggestions for pest management.