• Journal of Korean Institute of Industrial Engineers
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• v.3 no.1
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• pp.39-47
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• 1977

Most of the current literature on inventory theory has been devoted to the study of single stage models. A class of inventory problems which is of great interest is the multistage inventory system which involves a series and hierarchical sequence of stations. This study analyzes some aspect of the series type and multi-stage inventory system, using the fixed cycle ordering which bas a modificatory control function in the system equations. The objective of this study is to clarify the dynamic behavior of the system. The author has derived the theoretical formulas of variation of ordering quantity and stock fluctuation of each stage due to power spectral density function. Influence of parameters such as, (1) intensity of autocorrelation of demand sequence ($\lambda$), (2) forecasting exponential smoothing factors of each stage (${\alpha}_1,\;{\alpha}_2,\;{\alpha}_3$) and (3) production control factor of the 3rd stage ($\gamma$), as operators of the system on the variation of ordering quantity and stock fluctuation of the system. is also clarified. As a result of this study, the relations between the variation of ordering quantity, stock fluctuation and the parameters of the system, have been found. The principles and the theorical analysis presented here will be applicable to more complex type of discrete control systems in constructing the specific condition of the system to minimize inventory variances.

• International Journal of Advanced Culture Technology
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• v.11 no.2
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• pp.170-177
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• 2023

In quantum mechanics, uncertainty refers to the uncertainty of a measurement physical quantity, because some mechanical quantity can only be in its eigenstate under certain conditions, and the values shown are discrete.The exact value can only be obtained by measuring it in the eigenstate of this mechanical quantity.Uncertainty is like a double-edged sword, which has both advantages and disadvantages in art itself and in the process of artistic creation. In this study, it is divided into three main parts. First, the existence of uncertainties in contemporary art is sorted out in two broad parts, the definition of the uncertainties in art and the specific expression in contemporary art, respectively, with examples from four aspects of psychological impact, accidental presentation effect, expression form and connection with the viewer. The purpose is to understand how uncertainties are expressed in the process of artistic creation. Second, the role of the uncertainties in artistic creation is analyzed through examples, and then it is proposed that artists should use uncertainties to serve art with a scientific and rational attitude. Thirdly, the application of uncertainties in my creative practice and their influences on my painting creation. In summary, every artistic creator should take art seriously and sincerely. The relationship among the creative subject, society and life is an eternal and continuous interaction, and art is a carrier of reflection. For the problems brought by uncertainties in artistic creation, from choosing new certainty by thinking to the emergence of uncertainties, such a cycle is the process of art sublimating from life and being closely related to life.

• Journal of the Korean Operations Research and Management Science Society
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• v.22 no.1
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• pp.51-58
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• 1997

In this paper, we propose a stochastic LP model for determining an optimal input quantity in a single-product multi-stage production system with random yields. Due to the random yields in our model, each stage of the production system can result in defective items, which can be re-processed or scrapped at certain costs. We assume that the random yield at each stage follows an independent discrete empirical distribution. Compared to dynamic programming models that prevail in the literature, our model can easily handle problems of larger sizes.

• Wind and Structures
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• v.27 no.4
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• pp.213-221
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• 2018

In the desert and Gobi regions with strong wind and large sediment discharge, sand transporting engineering is more effective than sand blocking and sand fixing measures in sand prevention. This study uses the discrete phase model of 3D numerical simulation to study the motion trail, motion state and distribution rule of sand particles with different grain diameters when the included angle between the main shaft of the feather-row lateral transportation sand barrier and the wind direction changes, and conducts a comparison in combination with the wind tunnel test and the flow field rule of common sand barrier. According to the comparison, when wind-sand incoming flow passes through a feather-row sand barrier, sand particles slow down and deposit within the deceleration area under the resistance of the feather-row sand barrier, move along the transportation area formed by the transportation force, and accumulate as a ridge at the tail of the engineering. With increasing wind speed, the eolian erosion of the sand particles to the ground and the feather-row sand barrier is enhanced, and the sand transporting quantity and throw-over quantity of the feather-row sand barrier are both increased. When sand particles with different grain diameters bypass the feather-row sand barrier, the particle size of the infiltrating sands will increase with the included angle between the main shaft of the feather-row sand barrier and the wind direction. The obtained result demonstrates that, at a constant wind speed, the flow field formed is most suitable for the lateral transportation of the wind-drift flow when the included angle between the main shaft of the feather-row sand barrier lateral transportation engineering and the wind speed is less than or equal to $30^{\circ}$.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.41 no.4
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• pp.59-69
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• 2018

This study deals with the case study on the pallet quantity determination problem for the flexible manufacturing system producing 32 different types of aircraft wing ribs which are major structures of an aircraft wings. A Korean company has constructed the WFMS (wing rib flexible manufacturing system) that is composed of several automated equipments such as the 5-axis machining centers, the RGV (rail guided vehicles)s, the AS/RS (automated storage and retrieval system), the loading/unloading stations, and so on. Pallets play a critical role in the WFMS to maintain high system utilization and continuous work flow between 5-axis machining machines and automated material handling devices. The discrete event simulation method is used to evaluate the performance of the WFMS under various pallet mix alternatives for wing rib manufacturing processes. Four performance measures including system utilization, throughput, lead-time and work in process inventory level are investigated to determine the best pallet mix alternative. The best pallet mix identified by the simulation study is adopted in setting up and operating a real Korean aircraft parts manufacturing shop. By comparing the real WFMS's performances with those of the simulation study, we discussed the cause of performance difference observed and the necessity of developing the CPS (cyber physical system).

• The Mathematical Education
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• v.58 no.1
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• pp.1-20
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• 2019

As the importance of algebraic thinking in elementary school has been emphasized, the links between fraction knowledge and algebraic thinking have been highlighted. In this study, we analyzed the solution methods and characteristics of thinking by fifth graders who have not yet learned fraction division when they solved 'reverse fraction problems' (Pearn & Stephens, 2018). In doing so, the contexts of problems were extended from the prior study to include the following cases: (a) the partial quantity with a natural number is discrete or continuous; (b) the partial quantity is a natural number or a fraction; (c) the equivalent fraction of partial quantity is a proper fraction or an improper fraction; and (d) the diagram is presented or not. The analytic framework was elaborated to look closely at students' solution methods according to the different contexts of problems. The most prevalent method students used was a multiplicative method by which students divided the partial quantity by the numerator of the given fraction and then multiplied it by the denominator. Some students were able to use a multiplicative method regardless of the given problem contexts. The results of this study showed that students were able to understand equivalence, transform using equivalence, and use generalizable methods. This study is expected to highlight the close connection between fraction and algebraic thinking, and to suggest implications for developing algebraic thinking when to deal with fraction operations.

• School Mathematics
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• v.4 no.4
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• pp.643-655
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• 2002

In this paper we emphasize the introduction of ‘incommensurability’ on the teaching and learning the irrational number because we think of the origin of number as ‘ratio’. According to Greek classification of continuity as a ‘never ending’ divisibility, discrete number and continuous magnitude belong to another classes. That is, those components were dealt with respectively in category of arithmetic and that of geometry. But the comparison between magnitudes in terms of their ratios took the opportunity to relate ratios of magnitudes with numerical ratios. And at last Stevin coped with discrete and continuous quantity at the same time, using his instrumental decimal notation. We pay attention to the fact that Stevin constructed his number conception in reflecting the practice of measurement : He substituted ‘subdivision of units’ for ‘divisibility of quantities’. Number was the result of such a reflective abstraction. In other words, number was invented by regulation of measurement. Therefore, we suggest decimal representation from the point of measurement, considering the foregoing historical development of number. From the perspective that the conception of real number originated from measurement of ‘continuum’ and infinite decimals played a significant role in the ‘representation’ of measurement, decimal expression of real number should be introduced through contexts of measurement instead of being introduced as a result of algorithm.

• Journal of Elementary Mathematics Education in Korea
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• v.18 no.2
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• pp.319-339
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• 2014

Recently, the discussion about division and partition of fraction increases in Korea's national curriculum documents. There are varieties of assertions arranging from the opinion that both interpretations are unintelligible to the opinion that both interpretations are intelligible. In this paper, we investigated a possibility that division and partition interpretation of fraction become valid. As a result, it is appeared that division and partition interpretation of fraction can be defined reasonably through expansion of interpretation of natural number. Besides, division and partition interpretation of fraction can be work in activity, such as constructing equation from sentence problem, or such as proving algorithm of fraction division.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.393-396
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• 2008

Propellant consumption control for space launch vehicle can be achieved by propellant utilization system (PUS) and tank depletion system (TDS). In the course of developing new space launch vehicles, the main target of design is on reducing of space launch vehicle weight, which results in increasing both specific impulse and payload weight. The weights of space launch vehicles are generally allocated to structure, propulsion system, and propellants loaded. The quantity of propellants filled in propellant tanks may be estimated with the propellants actually consumed by propulsion system to complete its mission and the propellants left on-board at the time of engine shut-off. To minimize the remaining quantity of propellants on-board the supplying propellants' O/F ratio should be controlled from the certain time before engine shutdown. To control an O/F ratio, a control system, which accurately measures and compares the remainder of propellants in tanks and pipes, should be needed. This paper solely dedicates its contents to explore the merits and demerits of various level sensor, which is one of the important elements for PUS and TDS, and the transmission and control of signals within space launch vehicle.

• Geomechanics and Engineering
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• v.16 no.1
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• pp.21-34
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• 2018

Discontinuities considerably affect the mechanical and hydraulic properties of rock mass. These properties of the rock mass are influenced by the geometry of the discontinuities to a great extent. This paper aims to render an account of the geometrical parameters of several discontinuity sets related to the surrounding rock mass of Rudbar Lorestan Pumped Storage Power Plant powerhouse cavern making use of the linear and areal (circular and rectangular) sampling methods. Taking into consideration quite a large quantity of scanline and the window samplings used in this research, it was realized that the areal sampling methods are more time consuming and cost-effective than the linear methods. Having corrected the biases of the geometrical properties of the discontinuities, density (areal and volumetric) as well as the linear, areal and volumetric intensity accompanied by the other properties related to four sets of discontinuities were computed. There is an acceptable difference among the mean trace lengths measured using two linear and areal methods for the two joint sets. A 3D discrete fracture network generation code (3DFAM) has been developed to model the fracture network based on the mapped data. The code has been validated on the basis of numerous geometrical characteristics computed by use of the linear, areal sampling methods and volumetric method. Results of the linear sampling method have significant variations. So, the areal and volumetric methods are more efficient than the linear method and they are more appropriate for validation of 3D DFN (Discrete Fracture Network) codes.