• Water for future
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• v.28 no.4
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• pp.185-194
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• 1995

The objective of this study is to explore scale problem and to analyze the relations between scale and geomorphologic parameters of the rainfall-runoff model. Generally, measurement and calculation of geomorphologic parameters rely on and are sensitive to the resolution of source information available. Therefore, rainfall-runoff models using geomorphologic parameters should take account of the effects of the map scale used in their development. The derived rainfall-runoff model considering scale problem in this research is the GIUH type model, that is a basin IUH consisting of the channel network response and hillslope response. The cannel network response is computed by means of the diffusion analogy transformed from linearized St. Venant equation and hillslope response is calculated by 2-parameter gamma distribution function. Representing geomorphologic structure of the channel network and initial distribution of its response is width function. This width function is derived by fractal theory and Melton's law to consider scale problems and is weighted by the source location function (SLF) proposed in this research to increase the applicability.

• Korean Membrane Journal
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• v.7 no.1
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• pp.1-18
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• 2005

The permeate flux decline due to membrane fouling can be addressed using a variety of theoretical stand-points. Judicious selection of an appropriate theory is a key toward successful prediction of the permeate flux. The essential criterion f3r such a decision appears to be a detailed characterization of the feed solution and membrane properties. Modem theories are capable of accurately predicting several properties of colloidal systems that are important in membrane separation processes from fundamental information pertaining to the particle size, charge, and solution ionic strength. Based on such information, it is relatively straight-forward to determine the properties of the concentrated colloidal dispersion in a polarized layer or the cake layer properties. Incorporation of such information in the framework of the standard theories of membrane filtration, namely, the convective diffusion equation coupled with an appropriate permeate transport model, can lead to reasonably accurate prediction of the permeate flux due to colloidal fouling. The schematic of the essential approach has been delineated in Figure 5. The modern approaches based on appropriate cell models appear to predict the permeate flux behavior in crossflow membrane filtration processes quite accurately without invoking novel theoretical descriptions of particle back transport mechanisms or depending on adjust-able parameters. Such agreements have been observed for a wide range of particle size ranging from small proteins like BSA (diameter ${\~}$6 nm) to latex suspensions (diameter ${\~}1\;{\mu}m$). There we, however, several areas that need further exploration. Some of these include: 1) A clear mechanistic description of the cake formation mechanisms that clearly identifies the disorder to order transition point in different colloidal systems. 2) Determining the structure of a cake layer based on the interparticle and hydrodynamic interactions instead of assuming a fixed geometrical structure on the basis of cell models. 3) Performing well controlled experiments where the cake deposition mechanism can be observed for small colloidal particles (< $1\;{\mu}m$). 4) A clear mechanistic description of the critical operating conditions (for instance, critical pressure) which can minimize the propensity of colloidal membrane fluting. 5) Developing theoretical approaches to account for polydisperse systems that can render the models capable of handing realistic feed solutions typically encountered in diverse applications of membrane filtration.

• Water for future
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• v.27 no.1
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• pp.123-131
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• 1994

A plunge pool is often employed as an energy-dissipating device at the end of a spillway or a pipe culvert. A jet from spillways or pipes frequently generates a scour hole which threatens the stability of the hydraulic structure. Existing scour prediction formulas of plunge pool of spillways or pipe culverts give a wide range of scour depths, and it is, therefore, difficult to accurately predict those scour depths. In this study, a new experimental method and new scour prediction formulas under submerged circular jet for large bed materials with shallow tailwater depths were developed. A major variale, which was not used in previous scour prediction equations, was the ratio of jet size to bed material size. In this study, jet momentum acting on a bed particle and jet diffustion theory were employed to derive scour prediction formulas. Four theoretical formulas were suggested for the two regions of jet diffusion, i.e., the region of flow establishment and the region of established flow. The semi-theoretically developed scour prediction formulas showed close agreement with laboratory experiments performed on a movable bed made of large spherical particles.

• Nuclear Engineering and Technology
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• v.22 no.4
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• pp.359-370
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• 1990

This study concerns with comparing low-dimensional reactor kinetics methods with a three-dimensional kinetics method to be used for safety analysis of light water reactors in order to suggest means of preparing input parameters required for low-dimensional methods. For this purpose a one-dimensional finite difference two-group diffusion theory code ODTRAN and a third-order Hermit polynomial-based point kinetics code POTRAN are developed and used to obtain low-dimensional solutions to the LRA-BWR kinetics benchmark problem. The results are compared with a three-dimensional modified Borresen's coarse-mesh solution of the kinetics problem by CMSNACK code. Through this comparison some simple but practical means of preparing input parameters of low-dimensional kinetics analysis methods are suggested.

• Nuclear Engineering and Technology
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• v.23 no.4
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• pp.374-386
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• 1991

Various factors affecting the teachability of Cs-137 in cement matrix have been investigated. Factors investigated include such as pressure curing, vibration curing, pressure leaching, the effect of the clay addition, ion-exchange resin(IRN-77) addition, and $CO_2$or air injection. Leaching experiments were conducted by the method recommended by IAEA. To analyze the experimental results, pore structure analysis of cement matrices was carried out by BET method. Cement matrices may not contact directly with underground water in real repository, since the surroundings of disposed drums are filled with backfill. Thus, the effect of backfill to the teachability has been investigated. The well-known diffusion theory was utilized to predict long term leach rate and cumulative fraction leached of Cs-137 or non-radioactive species.

• Nuclear Engineering and Technology
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• v.21 no.3
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• pp.193-204
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• 1989

This paper develops a new method for reconstructing neutron flux distribution, that is based on the maximum entropy Principle in information theory. The Probability distribution that maximizes the entropy Provides the most unbiased objective Probability distribution within the known partial information. The partial information are the assembly volume-averaged neutron flux, the surface-averaged neutron fluxes and the surface-averaged neutron currents, that are the results of the nodal calculation. The flux distribution on the boundary of a fuel assembly, which is the boundary condition for the neutron diffusion equation, is transformed into the probability distribution in the entropy expression. The most objective boundary flux distribution is deduced using the results of the nodal calculation by the maximum entropy method. This boundary flux distribution is then used as the boundary condition in a procedure of the imbedded heterogeneous assembly calculation to provide detailed flux distribution. The results of the new method applied to several PWR benchmark problem assemblies show that the reconstruction errors are comparable with those of the form function methods in inner region of the assembly while they are relatively large near the boundary of the assembly. The incorporation of the surface-averaged neutron currents in the constraint information (that is not done in the present study) should provide better results.

• Magazine of the Korea Concrete Institute
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• v.9 no.2
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• pp.153-161
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• 1997

In the concrete st~uctures exposed to the environmental condition, the water movement is occurred by thc moisture difilsion, and the rnoisturrt distribution in concwt.c is nonunifhrm. Such a non-unif'orm moisture distribution causes tht. diflbrent.ia1 drying shrinkage in concrete structures. From this typc. of' dif'fercntial drying shrinkagr' tensiit-1 stress is occurred in exposure surface of concrete structures. and may result in crack formation. This residual stress is significantly affected by the creep of concrete, and the differential creep is also occurred at the cross section of concrete structures due to moisture difference at each locations. In this study, based on the moisture diffusion theory, a finite element program which is capable of simulating the moisture distribution in concrete was developed. And the analysis method for the differential drying shrinkage was suggested, in which the differential creep was considered. The differential drying shrinkage strain was also measured at various positions of concrete. Finally the validity of analysis method was proved by comparing test results with analytical results.

• Korean Chemical Engineering Research
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• v.56 no.5
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• pp.679-686
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• 2018

Reverse osmosis (RO) concentration of sodium chloride, sodium acetate, and sodium citrate solutions has been performed by polyamide RO membrane. Concentration polarization phenomena was also studied by changing pressure, solute kinds, and initial solution concentration. Pressure effect on permeation flux was that the increase of flux was accompanied by the increase of pressure. Flux increase was observed by the decrease of initial solution concentration. Surface concentration on the RO membrane increases and so flux declines due to the concentration polarization. In the later phase of concentration, concentration polarization effect was decreased by the back diffusion of solute from the polariztion layer. In case of sodium citrate, its large ion size and charge density resulted in the discrepancy between theory and experimental data of concentration polarization. It may be due to electric repulsion on the membrane surface.

• The Journal of Information Systems
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• v.17 no.3
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• pp.175-204
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• 2008

Ubiquitous computing is enhancing computer use by making many computers available throughout the physical environment without being noticed to the users. To facilitate successful adoption and diffusion of ubiquitous systems, it is important to find out the factors affecting their uses. Although researches related to ubiquitous computing have been vigorously conducted from the aspect of system and service provider, there have been very few studies that focus on the user's perspective. This study attempts to find out major factors which are dedicated to the development of ubiquitous systems and services and the relationships between these factors and user satisfaction factors. This study derived the specific factors that characterize ubiquitous services, such as ubiquity, contextual offer, user affinity, privacy, reliability, responsiveness, assurance, and empathy. We also considered service quality factors of ubiquitous services. Then these factors were combined with the Expectation Confirmation Theory (ECT) model and the path analysis was applied to find out the factors affecting user satisfaction and the intention to use the systems. The research findings indicate that ubiquity, contextual offer, privacy, reliability, and responsiveness affect the perceived usefulness. The perceived ease of use and confirmation were found to affect the perceived usefulness. The perceived usefulness, perceived ease of use, and confirmation fumed out to influence the satisfaction. It turned out that the result of this study on the relationship between the perceived usefulness and user satisfaction was identical with the findings in previous related ECT researches. We think this study makes two significant contributions to the development of ubiquitous services. First, this study provides basic implications for better ubiquitous services by considering important characteristics of ubiquitous systems as services. Second, this study also suggests important factors that need to be considered when ubiquitous service providers develop new ubiquitous services to improve user satisfaction and the intention to use the services.

• The Journal of Korean Association of Computer Education
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• v.5 no.1
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• pp.35-43
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• 2002

By entering the information society, the trend of increasing use of the cyber education to deliver high-Quality educational programs is likely to continue. For instance, supported by the government agencies, central officials training institute is expending vast amounts of money for the installation of cyber education programs. However, much of the research that has been done concerns the discrepancy between the potential and the actual use of technology in the field of education and training. The intent of this study was to identify the decision of the adoption of cyber education among national officials who had just peceived the existence the cyber education programs which would be used for their professional training and development, and to investigate the relationships between the Rogers' five attributes of innovation (relative advantage, compatibility, easy of use, observability, trialiability) and their decision of adoption. The results of the study generally concurred with Rogers diffusion of innovation theory revealing that perceived compatibility, easy of use, and observability of cyber education are significant predictors of decision to participate in cyber education.