• 한국기계가공학회지
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• 제18권9호
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• pp.36-43
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• 2019

Turning, a main machining process, is a widespread process in metal cutting industries. Many researchers have investigated the effects of process parameters on the machining process. In the turning process, input variables including cutting speed, feed, and depth of cut are generally used. Surface roughness and electric current consumption are used as output variables in this study. We construct a simulation model for the turning process using a neural network, which predicts the output values based on input values. In the neural network, obtaining the appropriate set of weights, which is called training, is crucial. In general, back propagation (BP) is widely used for training. In this study, techniques such as ant colony optimization (ACO) and particle swarm optimization (PSO) as well as BP were used to obtain the weights in the neural network. Particularly, two combined techniques of ACO_BP and PSO_BP were utilized for training the neural network. Finally, the performances of the two techniques are compared with each other.

• East Asian Economic Review
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• 제25권3호
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• pp.310-336
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• 2021

We use iterative numerical procedures combined with analytical methods due to Rapach and Wohar (2009) to solve for the dynamic asset allocation strategy for optimal portfolio demand. We compare different optimal portfolio demands when investors in each country have different access to overseas and domestic investment opportunities. The optimal dynamic asset allocation strategy without foreign investment opportunities leads domestic investors in Korea, Hong Kong, and Singapore to allocate more funds to domestic bonds than to domestic stocks. However, the U.S. investors allocate more wealth to domestic stocks than to domestic bonds. Investors in all countries short bills at a low level of risk aversion. Next, we investigate dynamic asset allocation strategy when domestic investors in Korea have access to foreign markets. The optimal portfolio demand leads investors in Korea to allocate most resources to domestic bonds and foreign stocks. On the other hand, the portfolio weights on foreign bonds and domestic stocks are relatively low. We also analyze dynamic asset allocation strategy for the investors in the U.S., Hong Kong, and Singapore when they have access to the Korean markets as overseas investment opportunities. Compared to the results when the investors only have access to domestic markets, the investors in the U.S. and Singapore increase the portfolio weights on domestic stocks in spite of the overseas investment opportunities in the Korean markets. The investors in the U.S., Hong Kong, and Singapore short domestic bills to invest more than initial funds in risky assets with a varying degree of relative risk aversion coefficients without exception.

• Archives of Pharmacal Research
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• 제12권2호
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• pp.88-93
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• 1989

In order to obtain some informations about the effect of molecular weight on the release rate of drug from drug carrier, two types of poly-L-glutamic acid (PLGA)-cytarabine (ara-C) conjugates, PLGA-ara-C:I and PLGA-ara-C:II, were synthesized using two types of PLGA having different average molecular weight, 43,000 and 77,800, respectively. The PLGA-ara-C conjugates were synthesized by mixed anhydride method and found to be covalently linked. Both types of conjugates charged negatively at biological pH. The pH-dependent release rate of ara-C was observed in both cases, and the release rate was accelerated in basic, acidic conditions (the k values were 0.015 $day^{-1}$ at pH 7.0, 0.024 $day^{-1}$ at pH 5.0, and 0.059 $day^{-1}$ at pH 9.0 in the case of PLGA-ara-C:I) and in the presence of pretense. The time required for the release of 16.5% of ara-C from PLGA-ara-C:I were 8 hr and 144 hr in the presence and absence of protease, respectively. Although both types of conjugates showed similar drug substitution ratio, they showed different release rates. Between the two types of conjugates, PLGA-ara-C:II showed the faster release rate (0.030 vs 0.042 $day^{-1}$ in pH 7.4 phosphate buffer solution at $37^{\circ}C$) and the smaller activation energy for the release of drug (12.5 vs 7.7 Kcal/mol) than PLGA-ara-C:I. The characteristic effect of molecular weight on the release rates of PLGA-ara-C conjugates suggests that the drug release rate might be effectively controlled over a prolonged period of time by the combined use of the different types of PLGA-ara-C conjugates having different molecular weights.

• 한국지리정보학회지
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• 제3권4호
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• pp.33-49
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• 2000

본 논문은 도시지역의 폐기물 매립지의 적지선정에 GIS기법을 적용한 사례연구를 제시한 것이다. 폐기물 매립지의 적지분석을 위한 여러 가지 평가인자들을 결정하고 데이터의 수집, 입력, 변환을 통하여 데이터베이스가 구축되었다. 또한 위성영상의 처리에 의해 대상지역의 최근 토지피복 분류와 식생활력도(NDVI) 데이터가 평가인자로서 GIS데이터에 통합되었다. 사회경제적 인자와 자연환경적 인자로 구분되는 1차 분류 평가인자들의 가중치를 이원비교법에 의해 결정된 2차분류 평가인자들의 가중치와 조합하여 분석하였다. 사례연구의 결과, 여러 가지 평가기준에 따른 적합성 분석이 가능하였으며, 사회경제적 인자를 중요하게 간주하는 관점에서 2차 분류 평가인자들의 가중치를 중요도에 따라 다르게 부여한 경우에서 가장 높은 적합도가 얻어졌다.

• Journal of the Korean Data and Information Science Society
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• 제21권6호
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• pp.1021-1029
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• 2010

중소기업의 조사부담 완화를 위하여 2009년부터 기존의 "중소기업실태조사", "중소기업인력실태 조사" 및 "중소기업사업전환실태조사"를 통합하여 하나의 조사로 수행하게 되었다. 통합 중소기업실태조사를 위한 새로운 표본설계에서 중소제조업과 지식기반서비스업 부문이 너무 상이하므로 별개의 모집단을 구성하였으며, 전체 표본수는 10,000개로 하였다. 변동계수를 사용한 배분공식으로 1차 층인 종사자규모 산업분류별로 표본을 배분하고 루트비례배분을 사용하여 2차 층인 지역별로 표본의 크기를 결정하였다. 새로운 표본설계에서는 가중치를 계산하였고 이를 이용한 추정량과 추정오차 공식을 유도하여 기존의 단순집계를 벗어나 종사자 규모별, 업종별 그리고 지역별 추정과 추정의 정도에 대한 평가를 가능하게 하였다.

• 한국환경보건학회지
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• 제30권2호
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• pp.71-78
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• 2004

This study was performed to evaluate developmental and estrogenic activity of bisphenol A (BPA) and butyl benzyl phthalate (BBP) to the second generation of Sprague-Dawley rats ingested during gestational or lactational periods. Rats were given BPA 20$\mu\textrm{g}$/kg BBP 100mg/kg of pregnancy or lactation periods. Maternal body weight and neonatal body weight were recorded. The rats were sacrificed on day 21 after birth. Reproductive organs of dam and neonate were utilized for receptor binding assay. The plasma concentrations of BPA and MBep, one of the major metabolites of BBP were analyzed with HPLC. The co-administration of BPA and BBP induced slow weight gain compared with single administration in dams. Also, such mixture induced low neonatal body weights in next generation. The dams treated with BPA and BBP during lactational periods showed significant organ weight changes in liver and spleen. The dams exposed during lactational periods showed significant organ weight changes not only in liver and spleen but also in kidney, uterus and ovary. The F1 female rats exposed during lactation periods showed significant organ weight changes in liver, spleen, ovary. The F1 male rats showed significant organ weight changes in liver, kidney, epididymis, vesicular glands, prostate. However, no clear synergistic effects of BPA and BBP were noted. There was no significantly different ER$\alpha$ expression pattern between control and treated groups. However, ER$\alpha$ expression were increased in F1 male testis and female uterus. PI male showed distinct ER$\alpha$ expression, especially in the group of lactational combined exposure. Synergistic ER$\alpha$ expression was found by combined treatment of BPA and BBP. We could not find any evidences of synergistic effects on BPA and/or BBP combined administration on dams and their fetuses, except in ER$\alpha$ expression of F1 male.

• Asian-Australasian Journal of Animal Sciences
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• 제24권3호
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• pp.414-420
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• 2011

A study was conducted to investigate the effects of the combined stressor induced by high stocking density with feed restriction on immunological parameters such as leukocyte differential counts and cytokine expression in laying hens. A total of forty White Leghorn laying hens were randomly allotted into the control (12 kg of body weight/$m^2$) and the stress (44 kg of body weight/$m^2$) groups, and then birds of the stress group were given 75% of voluntary intake of the control birds for 12-d on a daily basis. There was a significant decrease in body weight without affecting the relative weights of the liver and spleen after 12-d of the combined stressor. In hematological values, no significant difference in leukocyte differential counts including heterophils (H), lymphocytes (L), monocytes and H:L ratio was observed between the two groups. In cytokines, hepatic lipopolysaccharide-induced tumor necrosis factor-${\alpha}$ (LITNF-${\alpha}$) and inducible nitric oxide synthase (iNOS) expression levels in the stress group were significantly (p<0.05) higher compared with those in the control group. However, the expression levels of interleukin (IL)-4 and IL-6 in the liver were not affected by the combined stressor. Splenic LITNF-${\alpha}$ expression in the combined stressor group was significantly (p<0.05) up-regulated compared with that in the control birds. However, the combined stressor did not affect splenic IL-4, IL-6 and iNOS expression. In conclusion, the combined stressor caused by high stocking density with feed restriction enhanced some pro-inflammatory cytokines including LITNF-${\alpha}$ and iNOS in lymphoid and non-lymphoid organs of birds, suggesting that altered cytokine expression to given stressors can be another parameter that can be used in assessing stress responses of birds.

• 한국약용작물학회지
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• 제12권3호
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• pp.226-230
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• 2004

재배 생력용으로 많이 이용되고 있는 멀칭 방법이 삽주의 생육에 미치는 효과를 구명하여 최적 멀칭방법을 확립하고자 무멀칭, 볏짚, 투명비닐, 흑색비닐, 이들 비닐과 왕겨를 혼용한 멀칭이 삽주의 어린싹, 초기 및 후기 생장과 수량에 미치는 영향을 조사하였던 바 그 결과를 요약하면 다음과 같다. 1. 삽주의 어린싹 무게는 투명 비닐을 이용한 멀칭에서 가장 많았던 반면, 어린싹과 관련된 형질중에서는 엽수, 어린싹의 길이는 볏짚을 이용한 멀칭에서 가장 작았다. 2. 생장초기에는 볏짚을 이용한 멀칭시 엽수, 근수, 경수, 엽폭, 지상부 및 근경의 생체중이 가장 적었던 반면, 왕겨와 흑색비닐 혼합멀칭시 뿌리 관련 형질인 근수, 근경중 및 근중이 가장 많았다. 3. 생장후기에는 지온이 낮았던 생장초기의 멀칭효과가 고온기를 경과하면서 그 효과가 사라져 생장 및 형태적 형질에서는 멀칭처리간 차이가 거의 없었다. 4. 단위면적당 수량과 상품 수량은 볏짚 단독멀칭과 왕겨와 흑색비닐의 혼합멀칭 에서 가장 높았다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.233-236
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• 2002

An efficient method was developed in this study to obtain optimal stacking sequences, thicknesses, and minimum weights of stiffened laminated composite shells under combined loading conditions and stiffener layouts using genetic algorithms (GAs) and finite element analyses. Among many parameters in designing composite laminates determining a optimal stacking sequence that may be formulated as an integer programming problem is a primary concern. Of many optimization algorithms, GAs are powerful methodology for the problem with discrete variables. In this paper the optimal stacking sequence was determined, which gives the maximum critical buckling load factor and the minimum weight as well. To solve this problem, both the finite element analysis by ABAQUS and the GA-based optimization procedure have been implemented together with an interface code. Throughout many parametric studies using this analysis tool, the influences of stiffener sizes and three different types of stiffener layouts on the stacking sequence changes were throughly investigated subjected to various combined loading conditions.

• Macromolecular Research
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• 제12권5호
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• pp.451-458
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• 2004

Water-soluble polyacrylamides hydrophobically modified with small amounts of N,N-dialkylacrylamides [N,N-dihexylacrylamide (DHAM) and N,N-dioctylacrylamide (DOAM)] have been prepared through free radical solution polymerizations using two hydrophobic initiators derived from 4,4' -azobis(4-cyanopentanoic acid) (ACVA) and long linear chains consisting of 12 and 16 carbon atoms (C12 and C16). This procedure resulted in polyacrylamides containing hydrophobic groups along the chain as well as at the chain ends. We compare the properties of this class of polymers, termed "combined associative polymers", with those of the multisticker (with hydrophobic groups along the polymer chain) and telechelic (with hydrophobic groups at the chain ends) associative polymers. These materials were prepared using DHAM or DOAM and a hydrophobic initiator (ACVA) modified with alkyl chains of two different lengths. Polymers having molecular weights (M$\_$w/) of ca. 175,000 and hydrophobic contents [H] of ca. 0.8 mol% were prepared using 0.07 mol% of initiator relative to the total monomer feed. We investigated the effects that the type, localization, and concentration of the hydrophobic groups have on the viscosities of the associative polymer solutions.