• Membrane Journal
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• 제11권2호
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• pp.74-82
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• 2001

By using a phenomenological approach, model equations incorporating the resistance-in¬series concept were established to evaluate quantitatively concentration polarization in the boundary layer in feed adjacent to the membrane surface in the vapor permeation and separation of volatile organic compounds (VOCS)/$N_2$ mixture through po]y(dimethylsiloxane) (PDMS) membrane. The vapor permeations of various VOCS/$N_2$ mixtures through PDMS membrane were carried out at various feed flow rates. Chlorinated hydrocarbons, such as, methylene chloride, chlorofonn, 1,2-clichloroethane and 1,1,2-trichloroethane were used as organic vapor. By fitting the model equations to the experimental penneation data. the model parameters were detennined. respectively. Both the mass transfer coefficient of VOC across tbe boundary layer and concentration polarization modulus as a measure of the extent of concentration polarization were eitimated Quantitatively by the mooe1 equations with the determined model parameters. From the analysis on the detennined model parameters, the boundary layer resistance due to the concentration polarization of VOCs component was found to be more significant when the condensability of voe was greater. This study seeks to emphasize the importance of the boundary resistance on the vapor penneation of the vapor/gas mixtures with high permeability and high selectivity towards the minor component VOC.

• Journal of the Korea Convergence Society
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• 제11권11호
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• pp.203-209
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• 2020

A hybrid mount featuring rubber element and piezoelectric actuator is devised to reduce vibration when starting a vehicle engine. As a first step, a passive mount adopting rubber element is manufactured and its dynamic characteristics are experimentally evaluated. After evaluating dynamic characteristics of the manufactured inertial piezoelectric actuator, the proposed hybrid mount is then established by integrating the piezoelectric actuator with the rubber element for performance improvement at non-resonant high frequencies. A mathematical model of the established active vibration control system is formulated and expressed in the state space form. Subsequently, sliding mode controller (SMC) is designed to attenuate the vibration transmitted from the base excitation. Finally, control performances of the proposed hybrid mount are evaluated such as transmissibility in frequency domain and time responses.

• Korean Journal of Construction Engineering and Management
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• 제10권1호
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• pp.136-145
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• 2009

The objective of the Intelligent Excavation System (IES) is to recognize the work environment and produce work plan and automatically control the excavator through integrating sensor and robot technologies. This paper discusses one of the core technologies of IES development project, development of 3D work environment modeling. 3D laser scanner is used for 3-dimensional mathematical model that can be visualized in virtual space in 3D. This paper describes (1) how the most appropriate 3D imaging system has been chosen; (2) the development of user interface and customization of the s/w to control the scanner for IES project; (3) the development of the mobile station for the scanner; (4) and the algorithm for the automatic registration of laser scan segments for IES project. The development system has been tested on the construction field and lessons learned and future development requirements are suggested.

• Korean Chemical Engineering Research
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• 제46권3호
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• pp.521-528
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• 2008

The micro-porous asymmetric PVDF hollow fiber membranes for gas-liquid contactor were prepared by the dry-jet wet phase inversion process and the characteristics of hollow fiber membranes were evaluated by the gas permeation method and scanning electron microscope. The chemical absorbent for removal of $SO_2$ gas was sodium hydroxide at bench scale hollow fiber membrane contactor. The experiments were performed in a counter-current mode of operation with gas in the shell side and liquid in the fiber lumen of the module to examine the effect of various operating variables such as concentration of absorbent, gas flow rate, L/G ratio and concentration of inlet $SO_2$ gas on the $SO_2$ removal efficiency using PVDF hollow fiber membrane contactor. Membrane mass transfer coefficient($k_m$) was calculated by mathematical modeling. The volumetric overall mass transfer coefficient increased with increasing the concentration of absorbent and L/G ratio. The increase of the absorbent concentration and L/G ratio not only provides more sufficient alkalinity but also decreases liquid phase resistance. The volumetric overall mass transfer coefficient increased with increasing gas flow rate due to decreasing the gas phase resistance.

• Korean Chemical Engineering Research
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• 제52권3호
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• pp.395-401
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• 2014

In this work, the reaction characteristics for the non-catalytic esterification of palm fatty acid distillate were analyzed. The esterification reaction was assumed as the pseudo homogeneous $2^{nd}$ order reversible reaction and 'reaction effectiveness factor (${\eta}$)' was used to take accounts into evaporation and reaction of water and methanol, which take place simultaneously in the liquid phase. The nonlinear programming was used to derive appropriate kinetic parameters, the reaction rate constant and mass transfer coefficient, minimizing the error between experimental data and the numerical values. Based on these parameters, the apparent activation energy was calculated to be 43.98 kJ/mol.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제27권1B호
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• pp.1-12
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• 2002

In the multimedia CDMA mobile communication service, it is required to support various applications, such as voice, video, file transfer, e-mail, and Internet access, with guaranteed QoS. In the mixed traffic environment ,which consists of voice, stream data, and packet data, we analyze the network where preemptive priority is granted to delay-intolerant voice service and a buffer is offered to delay-tolerant stream data service. And, for best-effort packet data service, the access control by transmission permission probability is applied to obtain prominent throughput. To analyze the multimedia CDMA mobile communication system, we build a 2-dimensional markov chain model about prioritized-voice and stream data services and accomplish numerical analysis in combination with packet data traffic based on residual capacity equation.

• Journal of the Korean Data and Information Science Society
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• 제28권1호
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• pp.153-161
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• 2017

Branching processes which is used for epidemic dispersion as stochastic process model have advantages to estimate parameters by real data. We have to estimate both mean and dispersion parameter in order to use the negative binomial distribution as an offspring distribution on branching processes. In existing studies on biology and epidemiology, it is estimated using maximum-likelihood methods. However, for most of epidemic data, it is hard to get the best precision of maximum-likelihood estimator. We suggest a Bayesian inference that have good properties of statistics for small-sample. After estimating dispersion parameter we modelled the posterior distribution for 2015 Korea MERS cases. As the result, we found that the estimated dispersion parameter is relatively stable no matter how we assume prior distribution. We also computed extinction probabilities on branching processes using estimated dispersion parameters.

• Journal of the Korea Convergence Society
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• 제9권6호
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• pp.39-44
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• 2018

The application of deep neural networks to finance has received a great deal of attention from researchers because no assumption about a suitable mathematical model has to be made prior to forecasting and they are capable of extracting useful information from large sets of data, which is required to describe nonlinear input-output relations of financial time series. The paper presents a new deep neural network model where single layered autoencoder and 4 layered neural network are serially coupled for stock price forecasting. The autoencoder extracts deep features, which are fed into multi-layer neural networks to predict the next day's stock closing prices. The proposed deep neural network is progressively learned layer by layer ahead of the final learning of the total network. The proposed model to predict daily close prices of KOrea composite Stock Price Index (KOSPI) is built, and its performance is demonstrated.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제13권2호
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• pp.279-285
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• 1993

It is important to understand the interrelationship between adsorption, equilibrium and mass transport in efficient design and operation of the granular activated carbon(GAC) adsorption systems. In this study, the micro-diameter-depth adsorption system(MIDDAS) technique was developed to estimate equilibrium and mass transport parameters, which were utilized to simulate adsorption and mass transport phenomena dynamically and mathematically. The homogeneous surface diffusion model(HSDM) utilizing the estimated equilibrium and mass transport parameters including the film transfer coefficients and surface diffusivities from the MIDDAS technique, successfully predicted competitive adsorption, desorption and chromatographic displacement effects. In the binary solute system of p-chlorophenol(PCP) and p-nitrophenol(PNP), PCP was displaced by PNP and the HSDM could predict successfully. While the HSDM described the desorption breakthrough curves for PCP, PNP and PTS well when complete reversible adsorption was assumed, the desorption breakthrough curves for DBS could be predicted after subsequent incorporation of the degree of irreversibility into the model simulations.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제35권7호
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• pp.773-778
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• 2011

Accelerometers are widely used to measure the lateral vibrations of pipe-like structures such as a gun tube under impulse loads. Stress waves that precede the lateral vibrations due to the explosion within a gun contribute little to the vibrations, but saturate the accelerometer input. A mechanical filter eliminates this high-frequency stress wave and only transmits the signal corresponding to the lateral vibrations. The mechanical filter consists of a mechanical structure for mounting the accelerometers and a damping material. The low-pass filter characteristics are determined from the equivalent damping and stiffness property of this damping material. In this paper, we tested nine commercially available damping materials for their vibration characteristics by using a test rig. We also observed the change in the vibration characteristics while compressing the material. We designed and manufactured a mechanical filter and verified its filtering performance.