• Resources Recycling
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• v.19 no.6
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• pp.93-101
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• 2010

In this study, we have studied hydration properties and compressive strength of the electric arc furnace reduction slag as a cement admixture. The reduction slag is mainly consisted of 17.1% of f-CaO and rapid curing clinker minerals, 37.1% of $C_{11}A_7CaF_2$, and 21.0% of $C_3A$. When the substitution rate of the slag on OPC was 30%, the initial setting time and final setting time has been shortened from 305 min. and 425 min. to 10min. and 30min. When the substitution rate of the slag on OPC was 7%, the compressive strength of mixed cement mortars has been increased than that of OPC during all period. When the substitution rate of the slag on OPC was over 20%, the compressive strength of mortars has been reduced than that of OPC at initial and final compressive strength. As a result of hydration properties of reduction slag, $C_{11}A_7CaF_2$ transfer to $C_3AH_6$ but as the substitution rate of slag on OPC increases, increased f-CaO and the metastable hydrates $C_4AH_{13}$ increased. Therefore, we should control the substitution rate of the slag on OPC was under 7% in order to use EAF reduction slag as a cement admixture.

• Bulletin of the Society of Naval Architects of Korea
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• v.24 no.3
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• pp.25-34
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• 1987

Whereas the finite element method is well established today, the boundary element method is a fairly recent development. Both are general-purpose methods for the solution of various structural analysis problem. The B.E.M has several potential advantages relative to the F.E.M. One of them is that the number of unknowns in algebraic system obtained by discretization is proportional to the number of boundary nodes. Anothor advantage is the ease of discretization and input data preparation. However, the B.E.M. always leads to a fully populated and unsymmetric system of equations. Even though the number of degree-of-freedom is reduced as compared with F.E.M, since nodes exist on the boundary only in the B.E.M, to follow that the effort to solve the equations can be greater. It has been shown also that the time spent in setting up the coefficient matrix is a significant and can, in some cases, be greater than the time required to solve the equation. Thus, one can naturally consider the idea that two methods should be coupled, then the advantages of both methods can be taken. And further, by using this coupling method the HATCH CORNER was analyzed to give initial design data.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.5
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• pp.37-46
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• 2016

In this paper, we propose the beam-steering system using Rotman lens antenna operating at 2.442GHz which is to replace an expensive phase shifter. The overall system consists of the transmission antennas, Rotman lens and switch box. Setting the initial design conditions, it was designed and fabricated satisfying the requirements. From the result tested in the anechoic chamber, it was found that the beam can be steered using Rotman lens in the anechoic chamber. We also visually checked the beam-steering by turning on the LED of the rectenna showing the real-time beam receiving.

• International Commerce and Information Review
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• v.7 no.1
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• pp.95-117
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• 2005

The purpose of this study is to provide a conceptual understanding of ASP service for ERP implementation in small-to-medium enterprises under the current market situation in which the significance of information systems was standing out to respond to the rapid changes of managerial environment caused by the spread of Internet. In addition, it was to extract practical causes of introduction of ERP through ASP services by analyzing the causes and benefits considered by small-to-medium enterprises which use it. This study confirms that using ASP is better, faster and cheaper. Therefore, it is inevitable. The enterprises can reduce many risks of in-House ERP system such as excessive initial investment and operational expenses, lengthened constructional time, and the possibility of failure while achieving the benefit of ERP solution. However, there are many considerations which the enterprise carefully take into in order to implement the systems successfully such as selecting the system which is right for the enterprise's environment by setting the goal of implementing the system clearly, reducing the construction time by minimizing the customizing of the system, including the core people who knows the business process well, enough education before and after the implementation, and considering many aspect of ASP service provider. Also, the service provider should develop new way to provide customized service with cheap price while guaranteeing the reliability and supporting the customer's needs actively.

• Geophysics and Geophysical Exploration
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• v.24 no.4
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• pp.171-179
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• 2021

We outline a process for estimating Cole-Cole parameters from time-domain induced polarization (IP) data. The IP transients are all inverted to 2D Cole-Cole earth models that include resistivity, chargeability, relaxation time, and the frequency exponent. Our inversion algorithm consists of two stages. We first convert the measured voltage decay curves into time series of current-on time apparent resistivity to circumvent the negative chargeability problem. As a first step, a 4D inversion recovers the resistivity model at each time channel that increases monotonically with time. The desired intrinsic Cole-Cole parameters are then recovered by inverting the resistivity time series of each inversion block. In the second step, the Cole-Cole parameters can be estimated readily by setting the initial model close to the true value through a grid search method. Finally, through inversion procedures applied to synthetic data sets, we demonstrate that our algorithm can image the Cole-Cole earth models effectively.

• Restorative Dentistry and Endodontics
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• v.35 no.6
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• pp.445-452
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• 2010

Objectives: The aim of this study was to compare apical sealing ability and physical properties of MTA, MTA - AH-plus mixture (AMTA) and experimental Portland cement - Epoxy resin mixture (EPPC) for a development of a novel retro-filling material. Materials and Methods: Forty-nine extracted roots were instrumented and filled with gutta-percha. Apical root was resected at 3 mm and the retro-filling cavity was prepared for 3 mm depth. Roots were randomly divided into 3 groups of 15 roots each. The retro-filling was done using MTA, AMTA, and EPPC as the groups divided. Four roots were used as control groups. After setting in humid condition for 24 hours, the roots were immersed in 1% methylene blue dye solution for 72 hours to test the apical leakage. After immersion, the roots were vertically sectioned and photos were taken to evaluate microleakage. Setting times were measured with Vicat apparatus and digital radiographs were taken to evaluate aluminum equivalent thickness using aluminum step wedge. The results of microleakage and setting time were compared between groups using one-way ANOVA and Scheffe's post-hoc comparison at the significance level of 95%. Results: AMTA and EPPC showed less microleakage than MTA group (p < 0.05). AMTA showed the highest radio-opacity than other groups and the novel EPPC showed 5 mm aluminum thickness radio-opacity. EPPC showed the shortest initial and final setting times than other groups while the MTA showed the longest (p < 0.05). Conclusions: Under the condition of this study, the novel composite using Portland cement-Epoxy resin mixture may useful for retro-filling with the properties of favorable leakage resistance, radio-opacity and short setting time.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1116-1122
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• 2009

As a result of this study, we reached the following conclusions. With appropriate setting of oil pressure and flow rate, it operated same rotation speed with existing cooler by electrical transmission. In initial operation, a temperature of a cold storage is lower rapidly. As an internal temperature of a cold storage is lower, a decreasing rate of temperature is lower. As a result of comparing the both type, the cooler of oil pressure type showed the following results. The decreasing rate of temperature was more faster and shorter operating time was more shorter than existing cooler of electric type. The actual case of a cold storage, the cooler of oil pressure type can prevent quality deterioration and decrease power consumption. As an internal temperature of a cold storage is lower, power consumption increased rapidly, the oil pressure type showed lower power consumption. COP of two of these types decreased continuously as the internal temperature of a cold storage being reach setting temperature, and that of oil pressure type showed higher amount about 25%. As a setting temperature is lower, the number of refrigerator's operating times are less and operating time is longer, so power consumption is increased in the maintenance of a cold storage's internal temperature, power consumption of hydraulic type showed lower amount about 21~25% in two of these types.

• Journal of the Korean Geotechnical Society
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• v.39 no.9
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• pp.5-11
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• 2023

In analyzing geotechnical structures, the analysis fields are becoming increasingly diversified. In particular, the need for predicting the thermal behavior of ground materials has become important in fields related to soil freezing. To ensure a reliable assessment of the freezing behavior of the ground, considering the variation in the effective thermal conductivity of soil specimens under various conditions is crucial. In this study, probe experiments were conducted by varying the porosity, initial degree of saturation, and read time settings of the meter. Next, the factors influencing the effective thermal conductivity of the frozen sandy soil were evaluated. The experimental results conducted under different porosity conditions showed a tendency for the effective thermal conductivity of frozen soil to increase as the specimen's porosity decreased. However, as the degree of saturation of the specimen increased, the effective thermal conductivity also increased. The sensitivity of the meter's read time setting to the measurement of effective thermal conductivity was observed. When the read time was set to 1 min, the measured values were in a range similar to that obtained in previous studies conducted in Korea with the same soil specimen.

• Journal of the Korea Institute of Building Construction
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• v.20 no.4
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• pp.321-330
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• 2020

The addition of a limestone filler(LF) to fill into the voids between cement and aggregate particles can reduce the cementitious paste volume. In previous studies, it has been found that the addition of LF to reduce the cementitious paste volume would substantially increase the compressive strength, and reduce the heat generation. This paper aim to evaluate the influence of LF contents on the hydration kinetics and compressive strength. Hydration kinetics were evaluate using heat of hydration, ignition loss and thermal analysis. The heat of hydration was measured using Isothermal Calorimetry. The degree of hydration was measured using ignition loss. Hydration product analysis was carried out by Thermal Gravimetric and Differential Thermal Analysis. The results show that the addition of LF reduces not only the initial setting time and heat of hydration peak, also degree of hydration and rate of strength development at early age increase with the addition of LF. It can be concluded the LF fills the pore between cement particles due to formation of carboaluminate, which may accelerate the setting of cement pastes.

• Journal of the Korea Institute of Building Construction
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• v.15 no.1
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• pp.25-33
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• 2015

In this study, initial crack index was evaluated by FEM analysis to find the crack propagation from hydration heat in precast concrete. As results, as the usage of hardening accelerator increased, initial compressive strength increased and setting time was shortened. Additionally, as amounts of hardening accelerators increased, the central temperature of concrete increased and the time to reach the highest temperature was shortened. It was demonstrated that the hardening accelerators accelerated the hydration reaction of cement, and caused the increase of hydration heat within the short period of time. Furthermore, the crack index for evaluating the heat level was performed by FEM. As results, there was no problem about the cracks, despite of the growth of initial high hydration heat. This is because of the increased tensile strength that is large enough to sustain the thermally induced-stress.