• Journal of Korea Water Resources Association
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• v.31 no.4
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• pp.363-373
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• 1998

In this study, random flow field in a nonstationary porous formation is characterized through cross covariances of the velocity with the log conductivity and the head. The hydraulic head and the velocity in saturated aquifers are found through stochastic analysis of a steady, two-dimensional flow field without recharge. Expression for these cross covariances are obtained in quasi-analytic forms all in terms of the parameters which characterize the nonstationary conductivity field and the average head gradient. The cross covariances with a Gaussian correlation function for the log conductivity are presented for two particular cases where the trend is either parallel or perpendicular to the mean head gradient and for separation distances along and across the mean flow direction. The results may be of particular importance in transport predictions and conditioning on field measurements when the log conductivity field is suspected to be nonstationary and also serve as a benchmark for testing nonstationary numerical codes. Keywords : cross covariance, nonstationary conductivity field, saturated aquifer, stochastic analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.3
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• pp.199-206
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• 2014

In this paper, a scheme to evaluate the response variability for functionally graded material (FGM) beam with varying sectional area is presented. The randomness is assumed to appear in a spatial domain along the beam axis in the elastic modulus. The functionally graded material categorized as composite materials, however without the drawbacks of delamination and occurrence of cracks due to abrupt change in material properties between layers in the conventional composite materials. The functionally graded material is produced by the gradual solidification through thickness direction, which endows continuous variation of material properties, which makes this material performs in a smooth way. However, due to difficulties in tailoring the gradients, to have uncertainty in material properties is unavoidable. The elastic modulus at the center section is assumed to be random in the spatial domain along the beam axis. Introducing random variables, defined in terms of stochastic integration, the first and second moments of responses are evaluated. The proposed scheme is verified by using the Monte Carlo simulation based on the random samples generated employing the spectral representation scheme. The response variability as a function of correlation distance, the effects of material and geometrical parameters on the response variability are investigated in detail. The efficiency of the proposed scheme is also addressed by comparing the analysis time of the proposed scheme and MCS.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.627-637
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• 2009

Composite materials have been employed in the various engineering applications due to high mechanical performances including high strength-weight ratio and high degree of free formability. Due to complex manufacturing process, however, it can have intrinsic randomness in the material constants which affect the deterministic behavior of the composite structures. In this study, we suggest a formulation for stochastic finite element analysis considering the spatial randomness of Poisson's ratio. Considering the reciprocal relation between elastic moduli and Poisson's ratios in the two mutually orthogonal axes, one of two values of Poisson's ratio can be expressed in terms of the other. Using this, the relation between stress resultants and strains is derived in the ascending order of power of the stochastic field function, which can be directly used in the formulation to obtain the coefficient of variation of responses. The adequacy of the proposed scheme is demonstrated by comparison with the results of Monte Carlo analysis.

• Journal of the Korean association of regional geographers
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• v.6 no.2
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• pp.57-69
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• 2000

The purpose of this study is to identify distributional characteristics of autumn droughts in occurrence frequency and to analyze synoptic characteristics on the surface pressure fields and 500hPa levels for autumn droughts in Korea. The regional distributions of autumn droughts in occurrence frequency vary according to the monthly regional distributions of the precipitation variabilities in Korea. In september, the southwestern and the mid western parts of Korean Peninsula have high rate of drought frequency, while the eastern coast regions have low rate of it. It means that the regional distribution of the drought frequency in september indicates west-high and east-low pattern. In October, the regional distribution of the drought frequency shows low variations on regions, but in November the inland areas have low rate of drought frequency, whereas the coastal areas have high rate of it. Negative anomalies appear on the surface and 500hPa level, around Korean Peninsula during the drought period of early autumn. Positive height anomalies areas are extended from the Sea of Okhotsk to the central part of the North Pacific Ocean. It indicates that the occurrence frequencies of blocking high and ridge are high around the Sea of Okhotsk. When the pressure system, such as migratory anticyclone, stays around the Korean Peninsula, a drought occurs. In late autumn drought, the positive anomalies appear in the west and the negative anomalies in the east are generated, respectively and therefore, zonal wind is strong around Korean Peninsula. In consequence, occurrences of droughts in early autumn have a different mechanism from those of late autumn.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.4
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• pp.523-527
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• 1997

Population analysis of the common squid, Todarodes pacificus identified three seasonal cohorts in the Korean waters. They were significantly separable in terms of spawning period and fecundity, and they were slightly different in frequency distribution of egg size, while they are not significantly different in mantle length at $50\%$ maturity.

• Journal of Agricultural Extension & Community Development
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• v.20 no.2
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• pp.315-339
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• 2013

This study aims to suggest methods to estimate the agriculture related added value created in the agricultural production sector and the up/downstream agribusiness of Chungcheongnam-do by using the transaction table at producer's price, the domestic transaction table, the wholesale-retail profit table and the freight charge table in the input-output tables, and further aims to estimate regional and industrial agriculture related added values created in the agricultural production sector and the agribusiness of Chungcheongnam-do by using the input-output tables of the year 2005. This thesis suggests the consideration of overall and holistic policy regarding public welfare facilities in healthcare, commission sale market places for fishery products, fishery processing factories, processing factories for medicines, cosmetics, feedstuff, and tobacco leaves and the innovative distribution system with regard to wholesale/retail that Chungnam lacks in. It is also proposed to make comprehensive and cohesive policy to enhance growth and competitiveness of agricultural, forestry and fishery industry.

• Journal of Korea Water Resources Association
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• v.33 no.2
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• pp.159-167
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• 2000

The purpose of this study is to estimate the stochastic monthly runoff model for the Kunwi south station of Wi-stream basin in Nakdong river system. This model was based on the theory of Box-Jenkins multiplicative ARlMA and the state-space model to simulate changes of monthly runoff. The forecasting monthly runoff from the pair of estimated effective rainfall and observed value of runoff in the uniform interval was given less standard error then the analysis only by runoff, so this study was more rational forecasting by the use of effective rainfall and runoff. This paper analyzed the records of monthly runoff and effective rainfall, and applied the multiplicative ARlMA model and state-space model. For the P value of V AR(P) model to establish state-space theory, it used Ale value by lag time and VARMA model were established that it was findings to the constituent unit of state-space model using canonical correction coefficients. Therefore this paper confirms that state space model is very significant related with optimization factors of VARMA model.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.20 no.4
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• pp.180-191
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• 2015

Marine environmental characteristics and primary productivity of phytoplankton were investigated in seaweed bed of northwestern coast of Jeju Island during Autumn, 2014. The trophic state based on dissolved inorganic nitrogen and phosphorus was mesotrophic. The Redfield ratio was less than 16, indicating that nitrogen was the limiting factor for the growth of phytoplankton. Dissolved organic nitrogen and phosphorus accounts for 63 and 46% of the dissolved total nitrogen and phosphorus, respectively. Light utilization efficiency (${\alpha}$) and maximum photosynthetic capacity ($P_m{^B}$) were highest in the Donggwi (third-year marine forest), followed by Gonae (one-year marine forest), Biyangdo (natural seaweed bed) and Geumneung (whitening area). The primary productivity of phytoplankton in the Donggwi, Gonae and Biyangdo also was higher than that in the Geumneung. Although nitrogen is the limiting factor, enriched dissolved organic nitrogen might play an important role to maintain primary productivity. In addition, phytoplankton community through photosynthesis could produce about 14% of phytoplankton carbon in one hour. These results will be able to use the important information for material cycle and ecological valuation of seaweed bed.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.28 no.2
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• pp.163-173
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• 1995

Populations of the common squid, Todarodes pacifirus in the Korean waters were analyzed using the samples taken monthly from February, 1991 to July, 1992. Summer, Autumn and Winter cohorts were arbitrarily established based on frequency distributions of mantle lengths and maturation stages. As cohorts were seperated in mantle length distributions on the basis of accumulated information of size and maturation of T. pacificus, cohorts seperated by the present method were mostly in accord with those by Tanaka's method. But they were not consistent with those by Bhattacharya's and Cassie's methods.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.18 no.3
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• pp.131-141
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• 2013

Stock identification of Todarodes pacificus collected in the East Sea, Yellow Sea and East China Sea during the period from September to December in 2011 was analyzed by morphometric characters and mitochondrial DNA (mtDNA) cytochrome oxidase subunit I (COI) gene nucleotide variations. Frequency distributions of mantle length was analyzed by morphological method with measuring size of T. pacificus. Then each stock was estimated to confirm their maturation for mean mantle length comparing with mean mature mantle length 20-22 cm. According to morphologic stock identification, it is estimated that the northern part of East Sea is categorized as summer stock and the rest parts, including mid /southern part of the East Sea, northern part of the East China Sea and northern part of the West Sea were autumn stock. For genetic analysis, a total 49 haplotypes were defined by 33 variable nucleotide sites. From the extensive haplotype diversity, limited nucleotide diversity and star-like shape of haplotype network, T. pacificus appears to have undergone rapid population expansion from an ancestral population with a small effective population size. Although pair-wise Fst estimates which represent genetic difference among groups were low, there are relatively remarkable difference of Fst between middle and southern part of the East Sea. Although middle part of the East Sea and southern part of the East Sea were situated at the East Sea, genetically separated groups were appeared.