• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.12
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• pp.1855-1869
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• 1993

For the traditional ALOHA system without capture, the Markov chain obtained using the number of backlogged users at each slot if shown to be non-ergodic. So the infinite population ALOHA with fixed retransmission probabilities is unstable for any choice of the arrival rates and retransmission probabilities. The capture ALOHA system of also shown to be unstable for any arrival rate unless it has perfect. In this paper, we study a stabilization policy for capture ALOHA system that controls the retransmission probabilities and prove the stability of its multidimensional Markovian model by empolying a continuous Lyapunov function, and thus identify the stability region. We also study a delay performance through computer simulation th show the stability for any input rate below the maximum achievable channel throughput.

• Communications for Statistical Applications and Methods
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• v.11 no.1
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• pp.161-168
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• 2004

A single-index model is useful in fields which employ multidimensional regression models. Many methods have been developed in parametric and nonparametric approaches. In this paper, posterior inference is considered and a wavelet series is thought of as a function approximated to a true function in the single-index model. The posterior inference needs a prior distribution for each parameter estimated. A prior distribution of each coefficient of the wavelet series is proposed as a hierarchical distribution. A direction $\beta$ is assumed with a unit vector and affects estimate of the true function. Because of the constraint of the direction, a transformation, a spherical polar coordinate $\theta$, of the direction is required. Since the posterior distribution of the direction is unknown, we apply a Metropolis-Hastings algorithm to generate random samples of the direction. Through a Monte Carlo simulation we investigate estimates of the true function and the direction.

• Journal of the Korean Society for Precision Engineering
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• v.6 no.3
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• pp.109-119
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• 1989

This paper discusses the system layout of flexible manufacturing system. A definition of flexible manufacturing system has not been necessarily classified yet. An understanding, and an objective of its application are different in a variety of industries. It could be treated as the system adopting flexble-Automation and FMS has been improving as a form of parts maching system. It was thought that the problems of machining function and transfer function were important. This paper introduces parts family and machine groups to increase machining function and transfer function. Parts family and machine tool groups were made up by means of multidimensional dizitizing analysis. A new software algorithm for forming parts family and machine groups has been proposed. Flexible manufacturing system was layout according to the FMS transfer function classification.

• The Korean Journal of Applied Statistics
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• v.16 no.1
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• pp.55-69
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• 2003

In this article, we propose the weighted LAD (least absolute deviations) estimators for multi-dimensional contingency tables and drive an estimation method to estimate the proposed estimators. To illustrate the robustness of the estimators, simulation results are presented for several models Including log-linear models and models for ordinal variables in multidimensional contingency tables. Examples were also introduced.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.7
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• pp.1515-1522
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• 1997

Several image coding algorithms have been developed for the telecommunication and multimedia systems with high image quality and high compression ratio. In order to achieve low entropy and distortion, the system should pay great cost of computation time and memory. In this paper, the uniform cubic lattice is chosen for Lattice Vector Quantization (LVQ) because of its generic simplicity. As a transform coding, the Discrete Wavelet Transform (DWT) is applied to the images because of its multiresolution property. The proposed algorithm is basically composed of the biorthogonal DWT and the uniform cubic LVQ. The multiresolution property of the DWT is actively used to optimize the entropy and the distortion on the basis of the distortion-rate function. The vector codebooks are also designed to be optimal at each subimage which is analyzed by the biorthogonal DWT. For compression efficiency, the vector codebook has different dimension depending on the variance of subimage. The simulation results show that the performance of the proposed coding mdthod is superior to the others in terms of the computation complexity and the PSNR in the range of entropy below 0.25 bpp.

• Nuclear Engineering and Technology
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• v.49 no.1
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• pp.17-28
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• 2017

The modified power method has been studied by many researchers to calculate the higher eigenmodes and accelerate the convergence of the fundamental mode. Its application to multidimensional problems may be unstable due to degenerated or near-degenerated eigenmodes. Complex eigenmode solutions are occasionally encountered in such cases, and the shapes of the corresponding eigenvectors may change during the simulation. These issues must be addressed for the successful implementation of the modified power method. Complex components are examined and an approximation method to eliminate the usage of the complex numbers is provided. A technique to fix the eigenvector shapes is also provided. The performance of the methods for dealing with those aforementioned problems is demonstrated with two dimensional one group and three dimensional one group homogeneous diffusion problems.

• Journal of Korean Society for Quality Management
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• v.27 no.1
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• pp.101-110
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• 1999

Products are often evaluated on rating scales to measure and quantify their attributes of interest. In case that one wishes to compare multiple rating datasets simultaneously, there must be a standardized scale with which one can discriminate relative differences among corresponding scale means. In this regard, the concept of Thurstonian modeling applied to various discrimination tests including the triangular method has been recently being reconsidered. In this paper we extend previous researches on the triangular method and evaluate the effect of unequal variances and correlated variables upon the probability of correct response using Monte-Carlo simulation. We observed that the probability of correct response depends on dimensionality, variances, and correlation structure of stimulus sets. But it does not depend on the relative orientation in a multidimensional space.

• Journal of the Korean Institute of Telematics and Electronics
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• v.24 no.1
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• pp.60-66
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• 1987

This paper proposes an automatic image segmentation system for machine vision. In this an algorithm using the topological property on the multidimensional feature space for thresholding each primary segment in the image without prior information is presented. Also an effective filter for the removal of regional noises in a code valued image which are artifacts of the thresholding is presented. This method also may be applied for image enhancement or classification, which we show the possibility and the efficiency through computer simulation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.7
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• pp.1127-1140
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• 1997

With the study for identifying the transmission characteristics of vibration and noise generated by operating engine system of a vehicle, recently many engineers have studied actively the reduction of vibration and noise inducing uncomfortableness to the passenger. In this study, output noise was analyzed by multi-dimensional spectral analysis and vector synthesis method. The multi-dimensional analysis method is very effective in case of identification of primary source, but this method has little effect on suggestion for interior noised reduction. For compensation of this, vector synthesis method was used to obtain effective method for interior noise reduction, after identifying primary source for output noise. In this paper, partial coherence function of each input was calculated to know which input was most coherent to output noise, then with simulation of changes for input magnitude and phase by vector synthesis diagram, the trends of synthesized output vector was obtained. As a result, the change of synthesized output vector could be estimated.

• International Journal of Automotive Technology
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• v.6 no.6
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• pp.579-584
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• 2005

Unsteady state free natural gas jets injected from several types of injectors were numerically simulated. Simulations showed good agreements with the schlieren experimental results. Moreover, injections of natural gas in intake manifolds of a single-valve engine and a double-valve engine were predicted as well. Predictions revealed that large volumetric injections of natural gas in intake manifolds led to strong impingement of natural gas with the intake valves, which as a result, gave rise to pronounced backward reflection of natural gas towards the inlets of intake manifolds, together with significant increase in pressure in intake manifold. Based on our simulations, we speculated that for engines with short intake manifolds, reflections of the mixture of natural gas and air were likely to approach the inlets of intake manifolds and subsequently be inbreathed into other cylinders, resulting in non-uniform mixture distributions between the cylinders. For engines with long intake manifolds, inasmuch as the degrees of intake interferences between the cylinders were not identical in light of the ignition sequences, non-uniform intake charge distributions between the cylinders would occur.