• 한국경영과학회지
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• 제4권1호
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• pp.25-31
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• 1979

We consider the optimal ordering policy for a single-product two-stage inventory system where the main assumptions are as follows: (i) constant continuous demand only at stage 2, (ii) constant input (production) rate at stage 1, (iii) instantaneous delivery (transportation) from stage 1 to stage 2, (iv) backlogging is allowed only at stage 2, (v) an infinite planning horizon. Costs considered are ordering and linear holding costs at both stages, and linear shortage cost only at stages 2. By solving 9 different case problems, we have observed the general from of the optimal ordering policies for our model which minimizes the total cost per unit time. It is noticeable from this observation that the questionable but more often than not adopted assumption by many authors in determining the optimal potimal policy for multistage inventory systems, that the ordering (lot) sizes at each stage remain constant thruout the planning horizon, is not valid.

• 대한수학회보
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• 제46권1호
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• pp.135-146
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• 2009

In the present note we study the properties of weak Armendariz rings, and the connections among weak Armendariz rings, Armendariz rings, reduced rings and IFP rings. We prove that a right Ore ring R is weak Armendariz if and only if so is Q, where Q is the classical right quotient ring of R. With the help of this result we can show that a semiprime right Goldie ring R is weak Armendariz if and only if R is Armendariz if and only if R is reduced if and only if R is IFP if and only if Q is a finite direct product of division rings, obtaining a simpler proof of Lee and Wong's result. In the process we construct a semiprime ring extension that is infinite dimensional, from given any semi prime ring. We next find more examples of weak Armendariz rings.

• Korean Journal of Mathematics
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• 제29권3호
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• pp.483-492
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• 2021

This article concerns the property that for any element a in a ring, if a²ⁿ = aⁿ for some n ≥ 2 then a² = a. The class of rings with this property is large, but there also exist many kinds of rings without that, for example, rings of characteristic ≠2 and finite fields of characteristic ≥ 3. Rings with such a property is called reduced-over-idempotent. The study of reduced-over-idempotent rings is based on the fact that the characteristic is 2 and every nonzero non-identity element generates an infinite multiplicative semigroup without identity. It is proved that the reduced-over-idempotent property pass to polynomial rings, and we provide power series rings with a partial affirmative argument. It is also proved that every finitely generated subring of a locally finite reduced-over-idempotent ring is isomorphic to a finite direct product of copies of the prime field {0, 1}. A method to construct reduced-over-idempotent fields is also provided.

• 대한수학회지
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• 제60권5호
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• pp.1087-1107
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• 2023

Let E be an elliptic curve defined over ℚ of conductor N, c the Manin constant of E, and m the product of Tamagawa numbers of E at prime divisors of N. Let K be an imaginary quadratic field where all prime divisors of N split in K, P_K the Heegner point in E(K), and III(E/K) the Shafarevich-Tate group of E over K. Let 2u_K be the number of roots of unity contained in K. Gross and Zagier conjectured that if P_K has infinite order in E(K), then the integer c · m · u_K · |III(E/K)| $\frac{1}{2}$ is divisible by |E(ℚ)_tor|. In this paper, we prove that this conjecture is true if E(ℚ)_tor ≅ ℤ/2ℤ or ℤ/4ℤ except for two explicit families of curves. Further, we show these exceptions can be removed under Stein-Watkins conjecture.

• 대한기계학회논문집B
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• 제28권6호
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• pp.713-725
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• 2004

The two-dimensional motion of a freely falling circular cylinder in an infinite fluid is investigated numerically using combined formulation. The effect of vortex shedding on the motion of a freely falling cylinder is clearly seen: as the streamwise velocity of the cylinder increases due to gravity, the periodic vortex shedding induces a periodic motion of the cylinder. This motion in turn affects the flow field, which is manifested by the generation of the angular velocity vector of the cylinder parallel to the cross product of the gravitational acceleration vector and the transverse velocity vector of the cylinder. A correlation of St-Re relationship for a freely falling circular cylinder is drawn from the present results. The Strouhal number for a freely falling circular cylinder is found to be smaller than that for a fixed circular cylinder when the two Reynolds numbers based on the streamwise terminal velocity of a freely failing circular cylinder and the free stream velocity of a fixed one are the same. From "thought experiments", it is shown that the transverse motion of the cylinder plays a crucial role in reducing the Strouhal number and has an effect of reducing the Reynolds number from the viewpoint of the pressure coefficient. The mechanism of this reduction in the Strouhal number is revealed by the fact that the freely falling cylinder experiences a smaller lift force than the fixed one due to the transverse motion resulting in the retardation of the vortex shedding.

• Journal of Radiation Protection and Research
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• 제11권2호
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• pp.91-103
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• 1986

가압 경수로형 원자로에서 발생하는 증발기 저부 폐액에서의 Cs-137의 용출에 대한 실험을 수행하였다. IAEA에 의해 제안된 용출실험 방법에 근거를 두고, ANS 방법의 일부를 채용하였다. 용출에 영향을 미치는 여러 인자들로서, 시료채취방법, 양생온도, 양생기간, 용출액 온도, Vermiculite 첨가와 체적 대 표면적비 등이 고려되었다. 준 무한 격판(Semi-infinite Slab)에 대한 확산 모델은 4주간 경화된 시료의 실험치와 좋은 일치를 보이고 있다. 4주간 $25^{\circ}C$에서 양생된 시료의 표면적 확산 계수는 $1.20{\sim}1.47{\times}10^{-11}cm^2/sec$가 됨을 확인했으며, 이 계수에 의해 Cs-137의 장기 용출을 예측을 유한 격판 근사(Finite-slab Approximation) 방법을 이용하여 수행하였다. 또한, 계산 결과로부터 Cs-137은 용출 개시후 약 25년이 되면 초기량의 0.66%인 최대치가 되며 100년 후에는 약 0.25%가 잔류한다.

• 패션비즈니스
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• 제20권6호
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• pp.79-93
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• 2016

Since the development of patterns using tessellation is applied to a wide range of fields such as clothing, architecture, environment, and products, etc. and its expression principle is also found in various fields such as mathematics and science, etc. However, this pattern is mostly used as a math material with little studies on fashion and culture. In addition, it is thought that Korean traditional culture products need more various and modern design development methods and pattern through preliminary investigation which is simple copy of traditional items, simple copy of Korean Alphabet, Chinese character, and folk paintings. Therefore, it will present the method to make more design cases using Tessellation. Tessellation that combines mathematics and art will be the infinite form of designing of designers as well as creative training way to understand the composition principles of old culture and to raise sense of modern design. Tessellation of regular triangle, regular square, and regular hexagon was performed on the patterns which have meaning of wealth and prosperity of Korean traditional patterns. As the concrete method, first, each side of the regular triangle is developed symmetrically with patterns of fish, turtle, and cicadas. Second, rotational movement after symmetry movement about middle point of one side ${\times}$ 1 symmetry movement about middle point ${\times}$ 1 using crane and cloud, of the regular triangle was performed. Third, the regular square was tessellated parallel movement ${\times}$ 2 with "Da(multi)" and dragon pattern as the source image. Fourth, the sitting tiger was tessellated with symmetry movement about middle point ${\times}$ 2 and parallel movement ${\times}$ 1. Fifth, three bat patterns are tessellated by again rotational movement of two sides after rotational movement of one side and rotational movement of the other side. In addition, It developed traditional culture product design of the scarf, umbrella, aprons, neckties.

• 지능정보연구
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• 제15권1호
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• pp.31-50
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• 2009

유비쿼터스 컴퓨팅 환경에서는 정적 및 동적인 상황 정보의 양이 무한대로 늘어나게 됨에 따라, 추천서비스에 있어서 정보 과부하 문제와 프라이버시 침해 문제가 중요한 문제로 대두되고 있다. 따라서 본 연구에서는 이러한 문제점을 해결하기 위하여 서버와의 교신 없이 고객 중심의 자체적인 정보처리와 고객들간 직접 커뮤니케이션을 통하여, 효율적이고 안전한 정보 획득이 가능하도록 P2P방식의 협업을 통하여 선호도가 유사한 다른 고객들의 상품에 대한 평가정보가 전달되는 추천서비스를 제안하였다. 제안한 추천방식은 협업필터링의 기본 법칙을 따르고 있지만, 현재 센서 네트워크에 접속해 있는 전체 고객를 대상으로 이웃 고객을 탐색하는 방법대신에 목표 고객 주위의 가까운 이웃을 지역적으로 탐색하는 방법을 채택하여 성능의 저하없이 유비쿼터스 컴퓨팅 환경에서 실시간 추천이 가능하도록 하였다. 또한 유비쿼터스 컴퓨팅 환경에서 적용가능한 프로토타입의 통합 네트워크 시스템의 구현을 통해 실세계 상점에서 유비쿼터스 컴퓨팅 기술의 활용 가능성을 제시하였다. 마지막으로 실제 모바일 회사의 데이터를 이용한 실험을 통하여 그 특징을 제시함으로써 향후 유비쿼터스 서비스 애플리케이션의 범용적인 추천모델을 제공하고자 한다.

• 한국정보전자통신기술학회논문지
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• 제9권2호
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• pp.171-177
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• 2016

소프트웨어 개발과정에서 소프트웨어 신뢰성은 매우 중요한 이슈이다. 소프트웨어 고장분석을 위한 무한고장 비동질적인 포아송과정에서 고장발생률이 상수이거나, 단조 증가 또는 단조 감소하는 패턴을 가질 수 있다. 본 연구에서는 소프트웨어 제품 테스팅 과정에서 고장 수명분포의 형상모수를 고려한 소프트웨어 신뢰성 비용 모형에 대하여 연구 하였다. 소프트웨어 신뢰성 분야에서 많이 사용되는 Lomax-NHPP 신뢰 성장 모형에 대한 비용 비교 문제를 제시하였다. 소프트웨어 고장모형은 무한고장 비동질적인 포아송과정을 이용하고 모수추정법은 최우추정법을 이용 하였다. 따라서 본 논문에서는 형상모수를 고려한 소프트웨어 비용모형 분석을 위하여 소프트웨어 고장시간 자료를 적용하여 비교 분석하였다. 대용량 소프트웨어가 수정과 변경하는 과정에서 결함의 발생을 거의 피할 수 없는 상황이 현실이다. 신뢰성 요구를 만족하고 총비용을 최소화하는 상황이 최적방출시간이다. 경우에 따라서는 왜도와 첨도 측면에서 효율적인 카파분포, 지수화지수분포 등 업데이트된 분포에 대한 방출 시기 문제를 비교 분석하는 연구도 가치 있는 일이라 판단된다. 이 연구를 통하여 소프트웨어 개발자들은 최적방출시간과 경제적 개발 비용을 파악 하는데 도움을 줄 수 있으리라 사료 된다.

• 패션비즈니스
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• 제22권2호
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• pp.88-106
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• 2018

The domestic fashion industry is not able to exceed the level of fashion that exists in advanced countries due to the relatively weak design competitiveness and the differentiated capability of product development. In order for the domestic fashion industry to become a growth industry that is valued in the world market of infinite competition, a step-by-step support system that can demonstrate and maintain the creative ability of designers is needed. Therefore, this study proposes a template - based 3D virtual fashion technology and a digital fashion platform based on it. The proposed template - based 3D virtual fashion technology is designed to clearly communicate the intention of designers and to be able to instantaneously view the results, thereby reducing the time and cost of producing prototypes. In addition, the digital fashion platform based on the template is designed as a collaborative platform based on idea sharing, which dramatically improves the process of confirming the prototype and initiating the product planning and manufacturing stages. This new technology can contributes to the formation of a business environment and a new area within the existing fashion industry and can be utilized for the development of the fashion industry in the future.