• Bulletin of the Korean Chemical Society
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• v.13 no.6
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• pp.665-669
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• 1992

We consider the problem of a random walker on a one-dimensional lattice (N sites) confronting a centrally-located deep trap (trapping probability, T=1) and N-1 adjacent sites at each of which there is a nonzero probability s(0 < s < 1) of the walker being trapped. Exact analytic expressions for < n > and the average number of steps required for trapping for arbitrary s are obtained for two types of finite boundary conditions (confining and reflecting) and for the infinite periodic chain. For the latter case of boundary condition, Montroll's exact result is recovered when s is set to zero.

• Journal of the Korean Chemical Society
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• v.10 no.1
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• pp.25-31
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• 1966

It is well known that the coloration and structural changes in thermal treatment of polyacrylonitrile are due to the formation of partly hydrogenated naphthylidine-type ring involving the pendant nitrile groups. Any quantitative study of the reaction, in the sense of kinetics and/or statistics, however, has never been reported. This paper presents that, at first, the disappearance of the nitrile groups follows the first order kinetics, which indicates clearly that nitrile groups do not disappear by a long chain reaction-the kinetic chain length is very short. This observation rules out the long intramolecular and intermolecular propagation chain through which most of the nitrile groups disappear. From the evidence that a similar reaction occurs in propylene carbonate solutions without gel formation, one may conclude that the coloration and structural changes are not necessarily intermolecular reaction. Secondly, a finite amount of nitrile groups remains unreacted at the extrem of reaction-not contributed to the formation of naphthylidine-type ring. The concentration of this unreacted nitrile groups is 19∼22% which is good agreement with the statistically calculated value of 19.2%.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.7
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• pp.52-59
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• 2020

Automatic tool changers (ATCs) can be divided into drum and chain types. Drum-type ATCs contain a magazine, where the tools are mounted, and a cam gearbox, which swaps the tools via roller gear and grooved plate cams. Drum-type ATCs are advantageous in that the operating time for the tool magazine is more rapid than that of chain-type ATCs and the length of the unit is shorter. Thus, drum-type ATCs can be fabricated into various shapes and forms depending on the number of tools and the magazine size in accordance with machining center requirements and consumer demand. In particular, the price competitiveness of a machining center with a drum-type ATC is higher, while drum-type ATCs are more rigid with fewer parts, possibly reducing the need for regular servicing. This study aims to verify the structural stability and design validity of the magazine base, which is the main structure of a drum-type ATC, using finite element analysis. This study kinematically verifies the specifications of the selected drive motor and reducer and assessed the design of the cam gearbox. It also conducts a structural analysis of the roller camp, which is the core component of the cam gearbox, based on the results of the kinetodynamic analysis, thus validating the structural design.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.88-92
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• 2009

When exposed to uniform magnetic fields externally applied, paramagnetic particles acquire dipole moments and the induced moments interacting with each other lead to the formation of chainlike structures or clusters of particles aligned with the field direction. A direct simulation method, based on the Maxwell stress tensor and a fictitious domain method, is applied to solve flows with magnetic chains in simple shear flow. We assumed that the particles constituting the chains are paramagnetic, and inertia of both flow and magnetic particles is negligible. The numerical scheme enables us to take into account both hydrodynamic and magnetic interactions between particles in a fully coupled manner, enabling us to numerically visualize breakup and reformation of the chains by the combined effect of the external field and the shear flow. Simple shear flow with suspended magnetic chains is solved in a periodic domain for a given magnetic field. Dynamics of interacting magnetic chains is found to be significantly affected by a dimensionless parameter called the Mason number, the ratio of the viscous force to the magnetic force in the shear flow. The effect of particle area fraction on the chain dynamics is investigated as well.

• Bulletin of the Korean Mathematical Society
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• v.55 no.4
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• pp.1189-1208
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• 2018

The aim of this paper is to study the class of ${\Lambda}$-constacyclic codes of length $2p^s$ over the finite commutative chain ring ${\mathcal{R}}_a=\frac{{\mathbb{F}_{p^m}}[u]}{{\langle}u^a{\rangle}}={\mathbb{F}}_{p^m}+u{\mathbb{F}}_{p^m}+{\cdots}+u^{a-1}{\mathbb{F}}_{p^m}$, for all units ${\Lambda}$ of ${\mathcal{R}}_a$ that have the form ${\Lambda}={\Lambda}_0+u{\Lambda}_1+{\cdots}+u^{a-1}{\Lambda}_{a-1}$, where ${\Lambda}_0,{\Lambda}_1,{\cdots},{\Lambda}_{a-1}{\in}{\mathbb{F}}_{p^m}$, ${\Lambda}_0{\neq}0$, ${\Lambda}_1{\neq}0$. The algebraic structure of all ${\Lambda}$-constacyclic codes of length $2p^s$ over ${\mathcal{R}}_a$ and their duals are established. As an application, this structure is used to determine the Rosenbloom-Tsfasman (RT) distance and weight distributions of all such codes. Among such constacyclic codes, the unique MDS code with respect to the RT distance is obtained.

• Smart Structures and Systems
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• v.21 no.5
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• pp.601-609
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• 2018

The estimated probabilistic model of wind data based on the conventional approach may have high discrepancy compared with the true distribution because of the uncertainty caused by the instrument error and limited monitoring data. A sequential quadratic programming (SQP) algorithm-based finite mixture modeling method has been developed in the companion paper and is conducted to formulate the joint probability density function (PDF) of wind speed and direction using the wind monitoring data of the investigated bridge. The established bivariate model of wind speed and direction only represents the features of available wind monitoring data. To characterize the stochastic properties of the wind parameters with the subsequent wind monitoring data, in this study, Bayesian inference approach considering the uncertainty is proposed to update the wind parameters in the bivariate probabilistic model. The slice sampling algorithm of Markov chain Monte Carlo (MCMC) method is applied to establish the multi-dimensional and complex posterior distribution which is analytically intractable. The numerical simulation examples for univariate and bivariate models are carried out to verify the effectiveness of the proposed method. In addition, the proposed Bayesian inference approach is used to update and optimize the parameters in the bivariate model using the wind monitoring data from the investigated bridge. The results indicate that the proposed Bayesian inference approach is feasible and can be employed to predict the bivariate distribution of wind speed and direction with limited monitoring data.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.11
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• pp.4436-4452
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• 2015

The IEEE 802.15.6 standard is introduced to satisfy all the requirements for monitoring systems operating in, on, or around the human body. In this paper, analytical models are developed for evaluating the performance of the IEEE 802.15.6 CSMA/CA-based medium access control protocol for wireless body area networks (WBAN) under unsaturation condition. We employ a three-dimensional Markov chain to model the backoff procedure, and an M/G/1/K queuing system to describe the packet queues in the buffer. The throughput and delay performances of WBAN operating in the beacon mode are analyzed in heterogeneous network comprised of different user priorities. Simulation results are included to demonstrate the accuracy of the proposed analytical model.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2002.05a
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• pp.363-370
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• 2002

This paper presents a production planning algorithm for minimizing the costs of production and subcontracting in SCM (supply chain management) environment. In our SCM environment, the several local plants that aye dispersed geographically produce parts and products. In this environment, we have to decide the production volumes of both parts and products considering the BOM (bill-of-material) structure to meet the fixed order quantity or forecasted demand quantity. Each plant produces the specified parts of product with finite production capacity. There exist subcontracting decisions relevant to the production capacity of each plant except the core process plant, and when we use the subcontractor's capacities we should be charged for the fixed subcontracting fees. The objective of this study is to solve the production planning problem, which minimizes the total costs of production, inventory, setup, and subcontracting under constraints of production and subcontracting capacity. For this problem, an integrated production planning model based on the multi-level capacitated lot sizing problem was formulated, and efficient decomposition algorithm was proposed. The experimental investigation shows that the proposed heuristic generates quite good solutions at very low computational costs.

• The Journal of the Acoustical Society of Korea
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• v.16 no.2
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• pp.49-57
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• 1997

In this paper, we propose the stochastic pronunciation lexicon model for large vocabulary continuous speech recognition system. We can regard stochastic lexicon as HMM. This HMM is a stochastic finite state automata consisting of a Markov chain of subword states and each subword state in the baseform has a probability distribution of subword units. In this method, an acoustic representation of a word can be derived automatically from sample sentence utterances and subword unit models. Additionally, the stochastic lexicon is further optimized to the subword model and recognizer. From the experimental result on 3000 word continuous speech recognition, the proposed method reduces word error rate by 23.6% and sentence error rate by 10% compare to methods based on standard phonetic representations of words.

• Journal of Ocean Engineering and Technology
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• v.31 no.4
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• pp.299-307
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• 2017

The design of the mooring line to maintain the position of an offshore structure in rough marine environments is recognized as a very important consideration. Conventional fatigue evaluation of a mooring line was performed by considering the tensile force acting on the mooring line, but the mooring line broke after 238 days in the girassol area even though the expected fatigue life was expected to be longer. The causes of this event are known to be due to OPB/IPB (out-of-plane bending/in-plane bending) caused by chain link friction due to the excessive tensile strength of the mooring line. In this study, three models with different boundary conditions were proposed for fatigue analysis of a mooring line considering OPB/IPB. Interlink stiffness was calculated by nonlinear structure analysis and a stress concentration factor was derived. In addition, the sensitivity of interlink stiffness according to the magnitude of tensile force, large deformation effect, and coefficient of friction was analyzed, and the effect of critical elastic slip and bending moment calculation position on interlink stiffness was confirmed.