• Architectural research
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• v.2 no.1
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• pp.47-54
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• 2000

The critical load of a continuous compression member was determined by the beam-analogy method. The proposed method utilizes the stress-analysis results of the analogous continuous beam, where imaginary concentrated lateral load changing its direction is applied at each midspan. The proposed method gives a lower bound error of critical load and can predict the span that buckles first. The effective length factors for braced frame columns can be easily determined by the present method, but result in the upper bound errors in all cases, which can lead to a conservative structural design.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.11a
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• pp.493-505
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• 2006

Call center staffing problems have often relied upon queueing models, which are traditionally used to compute average call waiting time. However, the relationship between the in-bound call volume and call abandon rate is not directly explained even with the complex queueing formula while that relationship is a major interest to the hospital due to profitability. In this paper we provide a novel approach for the call center staffing problem by incorporating the relationship between the in-bound call volume and call abandon rate with a nonlinear integer programming, rather than using the traditional queueing model. We perform numerical analyses with actual data obtained from a reservation call center in a hospital.

• Journal of the Korean Mathematical Society
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• v.37 no.1
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• pp.31-44
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• 2000

We study a free boundary problem satisfying Bernoulli type boundary condition along which the gradient of a piecewise harmonic solution jumps zero to a given constant value. In such problem, the free boundary splits the domain into two regions, the zero set and the harmonic region. Our main interest is to identify the global shape and the location of the zero set. In this paper, we find the lower and the upper bound of the zero set. In a convex domain, easier estimation of the upper bound and faster disk test technique are given to find a rough shape of the zero set. Also a simple proof on the convexity of zero set is given for a connected zero set in a convex domain.

• Bulletin of the Korean Mathematical Society
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• v.51 no.6
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• pp.1649-1654
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• 2014

A tournament T is an orientation of a complete graph and an arc in T is called pancyclic if it is contained in a cycle of length l for all $3{\leq}l{\leq}n$, where n is the cardinality of the vertex set of T. In 1994, Moon [5] introduced the graph parameter h(T) as the maximum number of pancyclic arcs contained in the same Hamiltonian cycle of T and showed that $h(T){\geq}3$ for all strong tournaments with $n{\geq}3$. Havet [4] later conjectured that $h(T){\geq}2k+1$ for all k-strong tournaments and proved the case k = 2. In 2005, Yeo [7] gave the lower bound $h(T){\geq}\frac{k+5}{2}$ for all k-strong tournaments T. In this note, we will improve his bound to $h(T){\geq}\frac{2k+7}{3}$.

• Bulletin of the Korean Mathematical Society
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• v.50 no.6
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• pp.2001-2011
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• 2013

Cho and Kim [4] have introduced the concept of the competition index of a digraph. Similarly, the competition index of an $n{\times}n$ Boolean matrix A is the smallest positive integer q such that $A^{q+i}(A^T)^{q+i}=A^{q+r+i}(A^T)^{q+r+i}$ for some positive integer r and every nonnegative integer i, where $A^T$ denotes the transpose of A. In this paper, we study the upper bound of the competition index of a Boolean matrix. Using the concept of Boolean rank, we determine the upper bound of the competition index of a nearly reducible Boolean matrix.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.04a
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• pp.401-405
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• 2004

Column subtraction, originally proposed by Harche and Thompson(]994), is an exact method for solving large set covering, packing and partitioning problems. Since the constraint set of ship scheduling problem(SSP) have a special structure, most instances of SSP can be solved by LP relaxation. This paper aims at applying the column subtraction method to solve SSP which can not be solved by LP relaxation. For remained instances of unsolvable ones, we subtract columns from the finale simplex table to get another integer solution in an iterative manner. Computational results having up to 10,000 0-1 variables show better performance of the column subtraction method solving the remained instances of SSP than complex branch-and-bound algorithm by LINDO.

• Bulletin of the Korean Mathematical Society
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• v.54 no.4
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• pp.1323-1330
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• 2017

For a nondegenerate projective irreducible variety $X{\subset}{\mathbb{P}}^r$, it is a natural problem to find an upper bound for the value of $${\ell}_{\beta}(X)=max\{length(X{\cap}L){\mid}L={\mathbb{P}}^{\beta}{\subset}{\mathbb{P}}^r,\;{\dim}(X{\cap}L)=0\}$$ for each $1{\leq}{\beta}{\leq}e$. When X is locally Cohen-Macaulay, A. Noma in [10] proves that ${\ell}_{\beta}(X)$ is at most $d-e+{\beta}$ where d and e are respectively the degree and the codimension of X. In this paper, we construct some surfaces $S{\subset}{\mathbb{P}}^5$ of degree $d{\in}\{7,{\ldots},12\}$ which satisfies the inequality $${\ell}_2(S){\geq}d-3+{\lfloor}{\frac{d}{2}}{\rfloor}$$. This shows that Noma's bound is no more valid for locally non-Cohen-Macaulay varieties.

• Journal of Communications and Networks
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• v.8 no.2
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• pp.194-204
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• 2006

This contribution focuses on the maximum likelihood (ML) noncoherent synchronization of multi-antenna transceivers working in faded environments and employing ultra-wideband impulse radio (UWB-IR) transmit technology. In particular, the Cramer-Rao bound (CRB) is derived for the general case of multiple input multiple output (MIMO) UWB-IR systems and used to compare the ultimate performance of three basic transmit schemes, thereinafter referred to as single input multiple output (SIMO), MIMO equal signaling (MIMO-ES), and MIMO orthogonal signaling (MIMO-OS) ones. Thus, the noncoherent ML synchronizer is developed for the better performing transmit scheme (i.e., the SIMO one) and its performance is evaluated under both signal acquisition and tracking operating conditions. The performance gain in the synchronization of UWB- IR signals arising by the utilization of the multi-antenna technology is also evaluated.

• Journal of Communications and Networks
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• v.5 no.2
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• pp.174-183
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• 2003

Space-Time (ST) codes are known to provide high transmission rates, diversity and coding gains. In this paper, a tight upper bound on the error probability of ST codes over rapid fading channels is presented. Moreover, ST codes suitable for rapid fading channels are presented. These codes are designed using the QPSK and 16-QAM signal constellations. The proposed codes are based on two different encoding schemes. The first scheme uses a single trellis encoder, whereas the second scheme uses the I-Q encoding technique. Code design is achieved via partitioning the signal space such that the design criteria are maximized. As a solution for the decoding problem of I-Q ST codes, the paper introduces a low-complexity decoding algorithm. Results show that the I-Q ST codes using the proposed decoding algorithm outperform singleencoder ST codes with equal complexity. The proposed codes are tested over fading channels with different interleaving conditions, where it is shown that the new codes are robust under such imperfect interleaving conditions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12A
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• pp.1223-1228
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• 2006

Closed-form expressions for capacity bounds of multiuser diversity combined with maximum ratio transmission (MRT) and maximum ratio combining (MRC) at each link are presented under the assumption of independent and quasi-static flat multiple-input multiple-output (MIMO) Rayleigh fading channels. The analysis results precisely agree with the numerical verification results and clearly show the impact of MRT/MRC on multiuser diversity.