• Title/Summary/Keyword: the diffusion process

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Demand Forecasting for New Service using the Diffusion Model (확산모형 (Diffusion Model)을 이용한 새로운 서비스 수요예측)

  • Kim, Gyeong-Taek;Park, Se-Gwon
    • Journal of Korean Institute of Industrial Engineers
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    • v.13 no.1
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    • pp.25-29
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    • 1987
  • When the historical data are available, the diffusion model, which describes the time pattern of the adoption process of a new product or technology or service, has been used as a reasonable predictor in the telecommunication demand forecasting area. This paper shows that the diffusion model is applicable when the historical data are not available. The model used is in the form of a "logistic" function. The parameters of the function are estimated using the questionnaire and the historical data of reference products. From the questionnaire, an initial and an upper limit long run value of the market share are estimated, and the diffusion time to the upper limit value is determined by the relation between the investment and the utility.

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Theoretical Studies of Surface Diffusion : Multidimensional TST and Effect of Surface Vibrations

  • 곽기정;신석민;이상엽;신국조
    • Bulletin of the Korean Chemical Society
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    • v.17 no.2
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    • pp.192-198
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    • 1996
  • We present a theoretical formulation of diffusion process on solid surface based on multidimensional transition state theory (TST). Surface diffusion of single adatom results from hopping processes on corrugated potential surface and is affected by surface vibrations of surface atoms. The rate of rare events such as hopping between lattice sites can be calculated by transition state theory. In order to include the interactions of the adatom with surface vibrations, it is assumed that the coordinates of adatom are coupled to the bath of harmonic oscillators whose frequencies are those of surface phonon modes. When nearest neighbor surface atoms are considered, we can construct Hamiltonians which contain terms for interactions of adatom with surface vibrations for the well minimum and the saddle point configurations, respectively. The escape rate constants, thus the surface diffusion parameters, are obtained by normal mode analysis of the force constant matrix based on the Hamiltonian. The analysis is applied to the diffusion coefficients of W, Ir, Pt and Ta atoms on the bcc(110) plane of W in the zero-coverage limit. The results of the calculations are encouraging considering the limitations of the model considered in the study.

Fabrication of Low Temperature Cofired Ceramic (LTCC) Chip Couplers for High Frequencies ; II. Effect of Sintering Process on Ag Diffusion (고주파용 저온 동시소성 세라믹(LTCC)칩 커플러 제조: II. Ag 이온 확산에 대한 소결공정의 영향)

  • 이선우;김경훈;심광보;구기덕
    • Journal of the Korean Ceramic Society
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    • v.36 no.5
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    • pp.490-496
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    • 1999
  • The sintering behavior of LTCC (low temperature cofired ceramics) chip couplers was investigated in relation with Ag diffusion at the interface of glass ceramic substrate-Ag electrode. Sintering temperature was in the range of 825$^{\circ}C$-975$^{\circ}C$. The commercial green sheet and silver electrode were used. Below 875$^{\circ}C$ the diffusion of the Ag ion into the substrate and the penetration of glassy phases into the electrode occurred due to an increase of fluidity. Thus the lectrode line was severely deformed and damaged. At 975$^{\circ}C$ the transformation of crystalline phases into glassy phases and the melting of the Ag electrode resulted in the diffusion of the considerable amount of Ag ions.

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Calculation of Stretched Laminar Diffusion Flame Using the Coherent Flame Sheet Model (코히어런트 화염면 모델을 이용한 스트레치 층류 확산 화염의 수치 계산)

  • 정진은;진영욱
    • Transactions of the Korean Society of Automotive Engineers
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    • v.8 no.1
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    • pp.17-22
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    • 2000
  • The transient process simplified by the 1-D stretched laminar flame formed at the fuel-oxidizer interface was investigated using the coherent flame sheet model. Under the combustion environment of high temperatures and pressures the results show that the time required to reach the steady state was relatively short compared to the reverse of strain rate. Hence the employment of the tabulation of precalculated steady-flame results in the calculation of turbulent diffusion flames using the coherent flame sheet model is concluded valid, Also upstream temperatures were found to have only a minor effect on the nondimensional flame temperature and nondimensional fuel even through the letter is sensitive to pressure changes.

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Feature Scale Simulation of Selective Chemical Vapor Deposition Process

  • Yun, Jong-Ho
    • Journal of the Korean Vacuum Society
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    • v.4 no.S1
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    • pp.190-195
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    • 1995
  • The feature scale model for selective chemical vapor deopsition process was proposed and the simulation was performed to study the selectivity and uniformity of deposited thin film using Monte Carlo method and string algorithm. The effect of model parameters such as sticking coefficient, aspect ratio, and surface diffusion coefficient on the deposited thin film pattern was improved for lower sticking coefficient and higher aspect ratio. It was revealed that the selectivity loss ascrives to the surface diffusion. Different values of sticking coefficients on Si and on SiO2 surface greatly influenced the deopsited thin film profile. In addition, as the lateral wall angle decreased, the selectively deposited film had improved uniformity except the vicinity of trench wall. The optimum eondition for the most flat selective film deposition pattern is the case with low sticking coefficient and slightly increased surface diffusion coefficient.

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Characterization of the complex(B+C+N) Diffusion Layers Formed on Tool Steels (공구강에 형성된 복합(B+C+N) 확산층의 특성 연구)

  • Lee, Jong-Hun;Yu, Wi-Do;Im, Yeong-Mok;Gwon, Gi-Hyeon
    • 연구논문집
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    • s.33
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    • pp.175-182
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    • 2003
  • In this study, the wear resistance of the complex powder diffusion treated KS STD 61 has been investigatived. KS STD 61 tool steel was pretreated in quenching and tempering processes to obtain the tempered martensitic microstructure. The samples were packed with complex powder in steel pot($\Phi$90x60mm) and heated in a box furnace. the complex powder diffusion treatment are carried out at $540^{\circ}C$, $520^{\circ}C$, $500^{\circ}C$ for 40min, 1.5hr and 2.5hr. The microstructure, microhardness, wear resistance, and coating layer thickness of the complex powder diffusion treated samples were investigation. The weight loss of as heat treated sample was 0.4mg and that of the complex powder treated at $540^{\circ}C$ for 2.5hr was 0.17mg. These result means that the wear resistance of tool steels can be easily improved by the powder diffusion process at conventional tempering treatment temperature.

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Two-Step Diffusion of Boron into silicon by Spin-on source (스핀온 쏘스에 의한 실리콘내의 붕소의 이단계 확산)

  • 정태원
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.17 no.5
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    • pp.22-27
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    • 1980
  • The two-step diffusion process of boron into silicon has been investigated using a new diffusion source coiled "Spin-on Source". A simple method is proposei which can estimate the junction depth after the two -step diffusion for the cases where the junction depth after the predeposition is not negligible compared with the junction depth after the two-step diffusion. The estimated junction depths are, then, compared with the experimental measurements.surements.

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Term Structure Estimation Using Official Rate

  • Rhee, Joon Hee;Kim, Yoon Tae
    • Communications for Statistical Applications and Methods
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    • v.10 no.3
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    • pp.655-663
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    • 2003
  • The fundamental tenn structure model is based on the modelling of the short rate. It is well-known that the short rate depends on the interest rate policy of monetary authorities, especially on the official rate. Babbs and Webber(1994) modelled the tenn structure of interest rates using the official rate. They assume that the official rate follows a jump process. This reflects that the official rate infrequently changes. In this paper, we test this official tenn structure model and compare the jump-diffusion model with the pure diffusion model.

Fabrication and Testing of Injection Mold for Cosmetic Container with Conformal Cooling Channels Using Vacuum Diffusion Bonding (진공확산접합을 이용한 형상적응형 냉각채널을 가진 화장품 용기용 사출금형의 제작 및 시험사출)

  • Yu, Man-Jun;Park, Jong-Cheon
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.19 no.3
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    • pp.92-98
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    • 2020
  • In this study, an injection mold with conformal cooling channels was designed and manufactured for use in the production of a thick plastic cosmetic container that required high gloss surfaces. A cooling analysis verified the design of the conformal cooling channel for the cosmetic container, and also showed that the cooling efficiency was superior to that of the straight cooling channel. Slide cores designed with the conformal cooling channel were manufactured using the Layers Parting method and vacuum diffusion bonding. Subsequent test injection and quality inspection showed no problem in the appearance and dimensional accuracy of the produced product. The cycle time for product production was about 110 seconds, sufficient for mass production.

A study on the stress dependence of diffusion coefficient at the elevated tenperature and the structural characterictics of 12% Cr rotor steel. (12% Cr강의 고온 확산계수의 응력의존성과 조직의 특성에 관한 연구)

  • 장윤석;김태형
    • Journal of Ocean Engineering and Technology
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    • v.11 no.2
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    • pp.39-47
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    • 1997
  • Creep rate the elevated temperature is known to be controller by the softening process of microstructure especially in the solid solution alloys such as 125 Cr rotor steel. The change of structure is a decreasing process of the free energy of the state including stress, diffusivity of the material, and tmeperature. This study shows that diffusion coefficient, D of 12% Cr rotor steel at 953K with 74.8 MPa is 1.084~3.140*$10^{15}mm^2sec^1$ compared to $1.658*10^{24}mm^2sec^1$at 963K without stress. During creep, the growth of martensite laths accelerates the diffusion coefficient under stress due to incoherency of interface between carbides and matrix.

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