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1

A queueing system with heterogeneous impatient customers and consumable additional items

Baek J., Dudina O., Kim C.

International Journal of Applied Mathematics and Computer Science

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2017

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Vol. 27, no. 2

367--384

EN

A single-server queueing system with a marked Markovian arrival process of heterogeneous customers is considered. Type-1 customers have limited preemptive priority over type-2 customers. There is an infinite buffer for type-2 customers and no buffer for type-1 customers. There is also a finite buffer (stock) for consumable additional items (semi-products, half-stocks, etc.) which arrive according to the Markovian arrival process. Service of a customer requires a fixed number of consumable additional items depending on the type of the customer. The service time has a phase-type distribution depending on the type of the customer. Customers in the buffer are impatient and may leave the system without service after an exponentially distributed amount of waiting time. Aiming to minimize the loss probability of type-1 customers and maximize throughput of the system, a threshold strategy of admission to service of type-2 customers is offered. Service of type-2 customer can start only if the server is idle and the number of consumable additional items in the stock exceeds the fixed threshold. Stationary distributions of the system states and the waiting time are computed. In the numerical example, we show some interesting effects and illustrate a possibility of application of the presented results for solution of optimization problems.

2

Bringing Kano’s perspective to AHP: the 2D-AHP decision model

Jung U., Yim S., Lim S., Kim C.

Management and Production Engineering Review

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2016

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Vol. 7, No. 4

16--26

EN

AHP and the Kano model are such prevalent TQM tools that it may be surprising that a true hybrid decision-making model has so far eluded researchers. The quest for a hybrid approach is complicated by the differing output perspective of each model, namely discrete ranking (AHP) versus a multi-dimensional picture (Kano). This paper presents a hybrid model of AHP and Kano model, so called two-dimension AHP (2D-AHP). This paper first compares the two approaches and justifies a hybrid model based on a simple conceit drawn from the Kano perspective: given a decision hierarchy, child and parent elements can exhibit multi-dimension relationships under different circumstances. Based on this premise, the authors construct a hybrid two-dimension AHP model whereby a functionaldysfunctional question-pair technique is incorporated into a traditional AHP framework. Using the proposed hybrid model, this paper provides a practical test case of its implementation. The 2D-AHP approach revealed important evaluation variances obscured through AHP, while a survey study confirmed that the 2D-AHP approach is both feasible and preferred in some respects by respondents. Although there have been rich research efforts to combine AHP and Kano model, most of them is simply about a series of individual usage of each methodology. On the other hand, the type of hybridization between AHP and Kano model in this paper is quite unique in terms of the two dimensional perspective. The model provides a general approach with application possibilities far beyond the scope of the test case and its problem structure, and so calls for application and validation in new cases.

3

Analysis of an MMAP/PH1, PH2/N/∞ queueing system operating in a random environment

Kim C., Dudin A., Dudin S., Dudina O.

International Journal of Applied Mathematics and Computer Science

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2014

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Vol. 24, no. 3

485--501

EN

A multi-server queueing system with two types of customers and an infinite buffer operating in a random environment as a model of a contact center is investigated. The arrival flow of customers is described by a marked Markovian arrival process. Type 1 customers have a non-preemptive priority over type 2 customers and can leave the buffer due to a lack of service. The service times of different type customers have a phase-type distribution with different parameters. To facilitate the investigation of the system we use a generalized phase-type service time distribution. The criterion of ergodicity for a multi-dimensional Markov chain describing the behavior of the system and the algorithm for computation of its steady-state distribution are outlined. Some key performance measures are calculated. The Laplace–Stieltjes transforms of the sojourn and waiting time distributions of priority and non-priority customers are derived. A numerical example illustrating the importance of taking into account the correlation in the arrival process is presented.

4

Statistical analysis of welding industry of South Korea

Kim C., Kang M., Bae S.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 36, nr 2

207-211

EN

Purpose: This paper represents the current status of welding industry of South Korea - how much the welding industry accounts for in monetary terms in the manufacturing industry of South Korea. Design/methodology/approach: We classify welding industry into welding equipment industry and materials & the welding engineering sub-industry. To decide the portion of the welding industry in other engineering industry, we adopt the Welding-Related Expenditures, Investments, and Productivity Measurement in U.S. Manufacturing, Construction, and Mining Industries, a report published by AWS in 2002. The statistical analysis was performed based on the NSO and KITA data. Findings: In South Korea, the welding-related portion in the engineering industry showed much higher figures - about 9 times higher in production amount and over 5 times in export amount - than the welding equipment and materials industry. In addition, the total production of the welding industry amounted to 2.6 billion $, indicating that the welding industry holds a very important place in the entire domestic industries. Research limitations/implications: The welding industry of South Korea was statistically analyzed using the welding related expenditure of the manufacturing industries. Research limitations/implications: This research quantitatively showed the relative importance of the welding industry in South Korea. Originality/value: Due to the nature of welding industry, it is difficult to identify the boundary of welding industry. In addition, monetary impact of welding industry was not revealed in practical manner. In this paper, we categorize the welding industry into two sub-industries and analyze the statistical data with our framework to reveal monetary impact of welding industry. With our results, it is possible to estimate the economical effects of welding industry in South Korea.

5

Bead-on-plate weldability of Al 5052 alloy using a disk laser

Kim J., Lim S., Cho J. H., Kim C.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 28, nr 2

187-190

EN

Purpose: The paper presents the effect of the laser welding parameters of the laser focal position and beam angle on the weldability of an Al 5052 thick plate using a 4kW disk laser. Design/methodology/approach: Bead-on-plate welding was conducted on a 10mm-thick Al 5052 plate. Aspects of the bead, including the bead surface and cross sections, were evaluated with various laser welding parameters. The porosity formation was also examined in an X-ray transmission tests. Findings: Although the penetration depth decreased as the focal point moves away from the surface, the appearance of the bead improved and the porosity decreased. The weldability according to the inclination angle of the laser beam was also investigated. It was found that a forward inclination of the laser beam (when the inclination angle is an acute angle) could enhance the weldability compared with a backward inclination. Research limitations/implications: The results of the thick plate BOP welding experiments can be expanded to optimizing the Al alloy welding of thin sheets. Practical implications: It is applicable as a ground technique for the laser welding of aluminium alloy to increase the productivity and quality using the recently developed disk laser. Originality/value: The outcome of the research shows the influence of the welding parameters on weldability aspects in disk laser welding of an Al alloy.

6

On BG-algebras

Kim C., Kim H.

Demonstratio Mathematica

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2008

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Vol. 41, nr 3

497-505

EN

In this paper we introduce the notion of BG-algebras which is a generalization of BG-algebras. We construct a BG-algebra from a non-empty set, which is non-group-derived. Moreover, using the notion of normal subalgebra, we obtain several isomorphism theorems of BG-algebra and related properties.

7

Another axiomatization of B-algebras

Kim C., Kim H.

Demonstratio Mathematica

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2008

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Vol. 41, nr 2

259-262

EN

In this paper we introduce the notion of a BA-algebra, and show that the class of BA-algebras is equivalent to the class of B-algebras.

8

Structure analysis and local magnetic parameters of magnetoresistance tunnel junctions

Kim C., Kim C. O., Hu Y., Kanak J., Stobiecki T., Ogata S., Tsunoda M., Takahashi M.

Materials Science

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2003

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Vol. 21, No. 1

9-23

EN

The Magnetoresistance Tunnel Junctions (MTJ) were deposited by DC magnetron sputtering method in the following layer sequence: Ta(50A)/Cu(100A)/Ta(50A)/Ni80Fe20(20A)/Cu(50A)/Mn75Ir25(100A)/Co70Fe30(25A)/Al-O/Co70Fe30(25A)/Ni80Fe20(t) /Ta(50A)/, with t = 0A, 100A and 1000A. X-ray diffraction analysis revealed that highly oriented fcc-(111) of IrMn3, Cu, Ni80Fe20 and Co70Fe30 crystal planes are stacked parallel to the substrate plane. The improvement of (111) texture and crystallinity was observed after annealing. The tunneling magnetoresistance ratio of patterned junction with electrode layer of Ni80Fe20 (t = 1000A), deposited on the free layer of Co70Fe30 (25A) exceeds 40% at room temperature after annealing at 200°C in magnetic field 1kOe. The local hysteresis loops were measured using the magneto-optical Kerr effect system. The relatively irregular variations of coercive force Hc and unidirectional anisotropy field Hua in as-deposited sample are revealed. After 200°C annealing Hc decreases but Hua increases with smooth local variations. Two-dimensional plots of Hc and Hua show the symmetric saddle shapes with their axes aligned with the pinned layer. The distribution of surface roughness is symmetric with respect to the center of MTJ. Correlation between surface roughness and the variation of Hua suggests that the Hua variation of the free layer is well described by dipole interactions in the form of socalled Néel "orange peel" coupling.

9

Design and implementation of infrared readout circuit using a new input circuit of current mirroring direct injection (CMDI)

Yoon N., Kim B., Lee H., Kim C.

Opto-Electronics Review

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1999

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Vol. 7, No. 4

321-326

EN

A new readout structure for infrared (IR) focal plane arrays (FPA) is presented in this paper. By applying a new input circuit of current mirroring direct injection (CMDI), we realised a high-performance readout circuit for IRFPA. It was found from the SPICE simulation that the CMDI inherently makes the detector bias stable as well as has almost 100% injection efficiency to the readout circuit from the detector even for low RDA values because it has almost zero input impedance. Compared with previous other input circuits, it has also many advantages such as small area and low power consumption. A readout chip including the CMDI inputt circuit has been designed and fabricated for MWIR 1x128 staggered linear HgCdTe infrared detector arrays using 1.2 um single-poly-double-metal N-well CMOS technology. From the measurement results of the fabricated chip, the readout function was successfully verified at 77 K with 5 V supply voltage.