• 한국재료학회지
• /
• 제29권7호
• /
• pp.412-424
• /
• 2019

Global fitting functions for Fe-selective chlorination in ilmenite($FeTiO_2$) and successive chlorination of beneficiated $TiO_2$ are proposed and validated based on a comparison with experimental data collected from the literature. The Fe-selective chlorination reaction is expressed by the unreacted shrinking core model, which covers the diffusion-controlling step of chlorinated Fe gas that escapes through porous materials of beneficiated $TiO_2$ formed by Fe-selective chlorination, and the chemical reaction-controlling step of the surface reaction of unreacted solid ilmenite. The fitting function is applied for both chemical controlling steps of the unreacted shrinking core model. The validation shows that our fitting function is quite effective to fit with experimental data by minimum and maximum values of determination coefficients of $R^2$ as low as 0.9698 and 0.9988, respectively, for operating parameters such as temperature, $Cl_2$ pressure, carbon ratio and particle size that change comprehensively. The global fitting functions proposed in this study are expressed simply as exponential functions of chlorination rate(X) vs. time(t), and each of them are validated by a single equation for various reaction conditions. There is therefore a certain practical merit for the optimal process design and performance analysis for field engineers of chlorination reactions of ilmenite and $TiO_2$.

• 한국정보과학회논문지:데이타베이스
• /
• 제35권6호
• /
• pp.518-532
• /
• 2008

모바일 환경에서는 상향링크와 하향링크의 대역특이 비대칭적이며 전력이 한정되어 있기 때문에 보다 효율적인 데이타 전송기술인 브로드캐스팅 방법이 연구되어 왔다. 브로드캐스트에서 인덱스를 사용하면 원하는 데이타가 언제 방송되는지를 알 수 있어 튜닝 시간을 줄이고, 전력의 소비를 줄일 수 있다. 지금까지 연구된 싱글 채널 인덱스 기법들은 모든 데이타 아이템이 동일한 확률로 접근되는 flat 브로드캐스트에 적합한 인덱스 기법들이다. 데이타 아이템에 대한 접근 확률이 편향되는 경우에는 멀티디스크 방송기법을 사용해야 효과적인 전송이 가능하나, 기존의 인덱스 기법들은 인덱스가 한 방송 주기 내에서 반복되어 방송되는 데이타 아이템을 가리킬 수 없기 때문에 멀티디스크 방송 기법에는 효과적이지 않다. 본 논문에서는 싱글 채널 인덱스 기법으로서 멀티디스크 방송에 적용되는 인덱스 기법인 MDEI (Multi-disk Exponential Index) 기법을 제안한다. 본 논문에서 제안하는 MDEI 기법은 각 디스크 별로 인덱스를 구성하기 때문에, 데이타에 대한 접근확률이 편향되는 경우에 flat 브로드캐스트를 사용하는 다른 인덱스 기법들보다 평균 접근 지연시간 시간을 크게 줄일 수 있다. 실험 결과는 데이타에 대한 접근 확률이 편향된 환경에서 MDEI가 평균 접근 지연시간에 있어서 매우 좋은 성능을 갖는 것을 보여준다.

• 한국산림과학회지
• /
• 제86권1호
• /
• pp.17-24
• /
• 1997

지구(地球)의 잠재자연식생분포(潛在自然植生分布)를 추정(推定)하기 위한 첫단계로서 자연식생분포(自然植生分布)와 밀접(密接)한 관계가 있는 기온(氣溫)과 강수량(降水量)에 대한 최적구면보간방법(最適球面補間方法)을 개발하기 위해, Light Climatic Dataset로 명명(命名)한 전세계에 분포(分布)된 1,060점의 측후소(測候所)의 실측자료(實測資料)를 보간용(補間用)과 검정용(檢定用)으로 무작위(無作爲) 2등분(等分)하고, 검정용(檢定用) 측후소(測候所)에 있어서 관측치(觀測値)와 보간용(補間用)에 의한 추정치(推定値)와의 오차(誤差)를 보간방법(補間方法)과 파라메타가 틀린 조합(組合)에 대해 상호비교(相互比較)하였다. 보간용(補間用)에 의한 추정치(推定値)는, 측후소(測候所)의 선택법(選擇法)으로 전점(全点), 정점(定点), 안반경(安半徑)의 3가지 방법, 거리에 대한 하중(荷重)으로 n승 반비례(反比例), 부(負)의 지수함수(指數函數)의 2가지 방법, 방위(方位)에 관한 하중(荷重)으로 타원하중법(楕圓荷重法), 각각에대해 상호조합(相互組合)하여 산출(算出)되었다. 그 결과, 측후소(測候所)의 선택법(選擇法)은 정반경법(定半徑法), 거리(距離)에 관한 하중식(荷重式)은 부(負)의 지수함수(指數函數), 방위(方位)에 관한 하중법(荷重法)은 타원하중법(楕圓荷重法)을 조합(組合)하는 것이 기온(氣溫)과 강수량(降水量)의 보간(補間)에 적합(適合)하였으며, 그에 관한 파라메타 값은 기온(氣溫)에 있어서 정반경(定半徑) $30^{\circ}$, -0.78의 지수함수(指數函數), 타원하중(楕圓荷重) 0.4로, 강수량(降水量)에 있어서는 각각 $35^{\circ}$, -0.53, 1.2로 나타났다.

• 경영과정보연구
• /
• 제12권
• /
• pp.53-75
• /
• 2003

The Internet is flourishing and the World Wide Web is growing at an exponential rate. A fundamental concept of Intranet, the so-called second wave, was introduced only a few years ago. Intranets have been embraced by corporate users of information services and made substantial inroads in strategic vision documents and procurement practices. Business organizations have come to the conclusion that they require an extensive data repository in order to acquire a competitive advantage in a dynamically change market. This rich assortment of data must further be delivered and deliverable enterprise-wide in a secure and cost-efficient manner. Information technology(IT) has created the Intranet as a vitally important mechanism for the storage, dissemination, and even the analysis data. The present study is an attempt to develop a more through understanding of the potential and actual impact of the Intranet on organizational functions and activities. Expecially, it also consists of an effort to assess the impact of the Intranet on communication. The research also addresses the issue of how the Intranet affects communication and shapes or modifies business activities. The results of literature review and study revealed that middle managers believe that the extent of the Intranet use is significantly related to improvements in overall organizational functions and activities. While communication, decision-making, productivity, work collaboration, and business activities are all enhanced by Intranet use, communication appears to be most dramatically improved by Intranet use.

• Smart Structures and Systems
• /
• 제16권4호
• /
• pp.641-665
• /
• 2015

In this paper, a simple and efficient phenomenological macroscopic one-dimensional model is proposed which is able to simulate main features of shape memory alloys (SMAs) particularly ferro-elasticity effect. The constitutive model is developed within the framework of thermodynamics of irreversible processes to simulate the one-dimensional behavior of SMAs under uniaxial simple tension-compression as well as pure torsion+/- loadings. Various functions including linear, cosine and exponential functions are introduced in a unified framework for the martensite transformation kinetics and an analytical description of constitutive equations is presented. The presented model can be used to reproduce primary aspects of SMAs including transformation/orientation of martensite phase, shape memory effect, pseudo-elasticity and in particular ferro-elasticity. Experimental results available in the open literature for uniaxial tension, torsion and bending tests are simulated to validate the present SMA model in capturing the main mechanical characteristics. Due to simplicity and accuracy, it is expected the present SMA model will be instrumental toward an accurate analysis of SMA components in various engineering structures particularly when the ferro-elasticity is obvious.

• 한국산학기술학회논문지
• /
• 제10권12호
• /
• pp.3702-3707
• /
• 2009

본 논문은 Gray 부호화된 QAM (Quadrature Amplitude Modulation) 신호를 I 축 상에서 M개의 심벌을 갖는 M-PAM (Pulse Amplitude Modulation)과 Q 축 상에서 N개의 심벌을 갖는 N-PAM으로 분리한다. 수신된 심벌 신호를 비트 연판정 값으로 변환하기 위하여 Euclidean 거리를 이용한 근사화된 MAP (Maximum a Posteriori) 알고리듬을 제시한다. 기존의 Max-Log-MAP 방식은 일반 MAP 방식에서 사용하는 지수함수 혹은 로그함수 대신 심벌간 거리 비교를 통하여 구현 복잡도를 낮추었다. 그러나 심벌의 수가 증가 할수록 비교대상이 많아지므로 구현 복잡도가 증가하게 된다. 제안된 알고리듬은 사칙 연산에 의해 계산이 되기 때문에 직관적으로 구현복잡도가 낮아짐을 알 수 있다.

• 대한기계학회논문집
• /
• 제18권12호
• /
• pp.3287-3296
• /
• 1994

For the numerical computation of three-dimensional compressible flow field within a blade row in a centrifugal compressor, a quasi 3-dimensional solver which combines a reversible B-B flow and an irreversible H-S flow using finite element methods was developed. In a reversible B-B flow, the governing coordinates are modified in order to be applied to any type of turbomachinery, and two kinds of stream functions are introduced in order to make the Kutta condition exactly satisfied. In an irreversible H-S flow, the changes of entropy in the irreversible governing equations are determined not by empirical source but by the theoretical treatment of dissipation forces. The dissipation forces are obtained from the distribution of shear stresses in the flow passage which are given from the wall shear stresses using the exponential functions. A more accurate quasi-3-dimensional solver is established where the effect of body forces is involved in the non-axisymmetric H-S flow. Some numerical results obtained from authors' previous studies for axial flow machines assure that the present method is able to predict well as long as the flow is subsonic and not under strong viscous effect.

• Journal of Electrical Engineering and Technology
• /
• 제10권5호
• /
• pp.1940-1949
• /
• 2015

This paper presents an Enhanced Particle Swarm Optimization (EPSO) to solve short-term hydrothermal scheduling (STHS) problem with non-convex fuel cost function and a variety of operational constraints related to hydro and thermal units. The operators of the conventional PSO are dynamically controlled using exponential functions for better exploration and exploitation of the search space. The overall methodology efficiently regulates the velocity of particles during their flight and results in substantial improvement in the conventional PSO. The effectiveness of the proposed method has been tested for STHS of two standard test generating systems while considering several operational constraints like system power balance constraints, power generation limit constraints, reservoir storage volume limit constraints, water discharge rate limit constraints, water dynamic balance constraints, initial and end reservoir storage volume limit constraints, valve-point loading effect, etc. The application results show that the proposed EPSO method is capable to solve the hard combinatorial constraint optimization problems very efficiently.

• 통상정보연구
• /
• 제7권2호
• /
• pp.49-74
• /
• 2005

E-business has received much attention from entrepreneurs, executives, investors, and industry observers recently. The Internet is flourishing and the World Wide Web is growing at an exponential rate In recent years, information has become the critical commodity needed for success in the changing global economic order. Accordingly, business organizations have come to the conclusion that they require an extensive data repository in order to acquire a competitive advantage in a dynamically change market. This rich assortment of data must further be delivered and deliverable enterprise-wide in a secure and cost-efficient manner. Information technology(IT) has created the E-business as a vitally important mechanism for the storage, dissemination, and even the analysis data. The E-business has become increasingly important to a growing number of organizations in Korea in relatively short order. The present study is an attempt to develop a more through understanding of the potential and actual impact of the E-business on organizational functions and activities. Expecially, it also consists of an effort to assess the impact of the E-business on productivity. The research also addresses the issue of how the E-business affects productivity and shapes or modifies business activities. The results of literature review and study revealed that middle managers believe that the extent of the E-business use is significantly related to improvements in overall organizational functions and activities. While communication, decision-making, productivity, work collaboration, and business activities are all enhanced by E-business use, productivity appears to be most dramatically improved by Intranet use.

• Structural Engineering and Mechanics
• /
• 제9권3호
• /
• pp.269-288
• /
• 2000

The governing differential equations for free vibration of multi-step orthotropic shear plates with variably distributed mass, stiffness and viscous damping are established. It is shown that a shear plate can be divided into two independent shear bars to determine the natural frequencies and mode shapes of the plate. The jk-th natural frequency of a shear plate is equal to the square root of the square sum of the j-th natural frequency of a shear bar and the k-th natural frequency of another shear bar. The jk-th mode shape of the shear plate is the product of the j-th mode shape of a shear bar and the k-th mode shape of another shear bar. The general solutions of the governing equations of the orthotropic shear plates with various boundary conditions are derived by selecting suitable expressions, such as power functions and exponential functions, for the distributions of stiffness and mass along the height of the plates. A numerical example demonstrates that the present methods are easy to implement and efficient. It is also shown through the numerical example that the selected expressions are suitable for describing the distributions of stiffness and mass of typical multi-storey buildings.