• Journal of Educational Research in Mathematics
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• v.9 no.2
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• pp.419-438
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• 1999

This paper explored the impact of dynamic geometry software such as CabriII, GSP on student's understanding deductive justification, on the assumption that proof in school mathematics should be used in the broader, psychological sense of justification rather than in the narrow sense of deductive, formal proof. The following results have been drawn: Dynamic geometry provided positive impact on interacting between empirical justification and deductive justification, especially on understanding the necessity of deductive justification. And teacher in the computer environment played crucial role in reducing on difficulties in connecting empirical justification to deductive justification. At the beginning of the research, however, it was not the case. However, once students got intocul-de-sac in empirical justification and understood the need of deductive justification, they tried to justify deductively. Compared with current paper-and-pencil environment that many students fail to learn the basic knowledge on proof, dynamic geometry software will give more positive ffect for learning. Dynamic geometry software may promote interaction between empirical justification and edeductive justification and give a feedback to students about results of their own actions. At present, there is some very helpful computer software. However the presence of good dynamic geometry software can not be the solution in itself. Since learning on proof is a function of various factors such as curriculum organization, evaluation method, the role of teacher and student. Most of all, the meaning of proof need to be reconceptualized in the future research.

• Wind and Structures
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• v.19 no.3
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• pp.233-247
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• 2014

Vortex-induced oscillation is a type of aeroelastic phenomenon, to which extended structures such as long-span bridges are most susceptible. The vortex-induced vibration (VIV) behaviors of a concerned bridge were investigated conventionally in virtue of wind tunnel tests on string-mounted sectional models. This necessitates the building of a linkage between the response of the sectional model and that of the prototype structure. Although many released literatures have related to this issue and provided suggestions, there is a lack of consistency among them. In this study, some theoretical models describing the vortex-induced structural motion, including the linear empirical model, the nonlinear empirical model and the modified (or generalized) nonlinear empirical model, are firstly reviewed. Then, the concept of equivalent mass density is introduced based on the principle that an equal input of energy should result in identical structural amplitudes. Based on these, the theoretical linkages between the amplitude of a section model and that corresponding to the prototype bridge are discussed with different analytical models. Theoretical derivation indicates that such connections are dependent mainly on two factors, one is the presupposed shape of deformation, and the other is the theoretical VIV model employed. The theoretical analysis in this study shows that, in comparison to the nonlinear empirical models, the linear one can result in obvious larger estimations of the full bridges' responses, especially in cases of cable-stayed bridges.

• The Journal of Asian Finance, Economics and Business
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• v.3 no.4
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• pp.5-16
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• 2016

Prior literature expects a lower marginal cash value for weaker governance firms. We test this empirical hypothesis by using the sample of publicly traded Korean firms from 2005 to 2013. To measure the quality of governance structures, we employ the corporate governance scores provided by Korean Corporate Governance Services. The empirical model of Faulkender and Wang (2006) is adopted to estimate the marginal value of cash. Our empirical analysis shows a higher marginal value of cash for the good governance firms in the examination of the total governance score. This finding is consistent to the agency view of cash policy predicting a larger marginal value of cash for the firms with higher governance scores. However, this positive relationship is not robust for a subset of detailed governance scores; a lower marginal cash value is observed for the firms with better qualities of board structure, auditing, dividend policies. Moreover, our empirical analysis verifies a quite low level of marginal cash value for Korean firms, which supports the existence of severe agency conflicts in Korean corporations. Our results verify the significant role of agency conflicts between a manager and shareholders in the determination of marginal cash values in the Korean firms.

• The Journal of Asian Finance, Economics and Business
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• v.3 no.4
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• pp.67-79
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• 2016

Prior literature expects a lower marginal cash value for weaker governance firms. We test this empirical hypothesis by using the sample of publicly traded Korean firms from 2005 to 2013. To measure the quality of governance structures, we employ the corporate governance scores provided by Korean Corporate Governance Services. The empirical model of Faulkender and Wang (2006) is adopted to estimate the marginal value of cash. Our empirical analysis shows a higher marginal value of cash for the good governance firms in the examination of the total governance score. This finding is consistent to the agency view of cash policy predicting a larger marginal value of cash for the firms with higher governance scores. However, this positive relationship is not robust for a subset of detailed governance scores; a lower marginal cash value is observed for the firms with better qualities of board structure, auditing, dividend policies. Moreover, our empirical analysis verifies a quite low level of marginal cash value for Korean firms, which supports the existence of severe agency conflicts in Korean corporations. Our results verify the significant role of agency conflicts between a manager and shareholders in the determination of marginal cash values in the Korean firms.

• Journal of Astronomy and Space Sciences
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• v.34 no.1
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• pp.7-17
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• 2017

In South Korea, there are about 80 Global Positioning System (GPS) monitoring stations providing total electron content (TEC) every 10 min, which can be accessed through Korea Astronomy and Space Science Institute (KASI) for scientific use. We applied the computerized ionospheric tomography (CIT) algorithm to the TEC dataset from this GPS network for monitoring the regional ionosphere over South Korea. The algorithm utilizes multiplicative algebraic reconstruction technique (MART) with an initial condition of the latest International Reference Ionosphere-2016 model (IRI-2016). In order to reduce the number of unknown variables, the vertical profiles of electron density are expressed with a linear combination of empirical orthonormal functions (EOFs) that were derived from the IRI empirical profiles. Although the number of receiver sites is much smaller than that of Japan, the CIT algorithm yielded reasonable structure of the ionosphere over South Korea. We verified the CIT results with NmF2 from ionosondes in Icheon and Jeju and also with GPS TEC at the center of South Korea. In addition, the total time required for CIT calculation was only about 5 min, enabling the exploration of the vertical ionospheric structure in near real time.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.949-959
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• 2006

Despite of the popularity of using empirical methods for support design, empirical rules suffer from the inherent problem of providing no indication of the safety degree of the design. For the support design of large span tunnel, it was considered that the empirical design guidelines should be augmented by more explicit design methods. This paper presents an overview of the analytical support design methodology that is used to refine initial empirical recommendations. The initial support design supplemented by analytical methods is validated by probabilistic and deterministic approach applied to stress-induced and structurally controlled gravity-driven instability problem each. As a result, the extent of the potential failure zone is sorted out and numerical parametric studies were performed to gain insight into the overall behavior of tunnel in the potential failure zone. Concequently, it was decided that additional conservation techniques have to be planed as a reserved support pattern.

• Journal of the Korean Data and Information Science Society
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• v.8 no.1
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• pp.21-30
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• 1997

In accelerated life tests, the failure time of an item is observed under a high stress level, and based on the time the performances of items are investigated at the normal stress level. In this paper, when the mean of the prior of a failure rate is known in the exponential lifetime distribution with censored accelerated failure time data, we utilize the empirical Bayesian method by using the moment estimators in order to estimate the parameters of the prior distribution and obtain the empirical Bayesian predictive density and predictive intervals for a future observation under the normal stress level.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.11
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• pp.1475-1484
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• 1997

A new empirical formula for instantaneous heat transfer coefficients was determined. The determination of this formula is in need for prediction of instantaneous value of heat transfer coefficients to analyze in more detail the time variation of heat transfer rate from gas to wall in combustion chamber of a spark ignition engine. As the result, following formula was determined. h=687 $p^{0.75}$ $U^{0.75}$ $D^{0.25}$ - $T^{-0.465}$ U(.theta.)=O.494 $V_{p}$ +0.73*10$^{6}$ (1.35 p dV/d.theta.+V dp/d.theta.) Using this empirical formula, the instantaneous heat transfer coefficients of gas in the combustion chamber of spark ignition engine was predicted and compared with experimental values.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.1 s.256
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• pp.91-98
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• 2007

Air-conditioners use a spirally coiled capillary tube as an expansion device to enhance compactness of the unit. However, most empirical correlations in open literature were developed for straight capillary tubes without considering coiled effects on the mass flow rate. The objectives of this study are to investigate the flow characteristics of coiled capillary tubes and to develop a generalized correlation for mass flow rate through coiled capillary tubes. The mass flow rates through the coiled capillary tubes and straight capillary tubes were measured by varying operating conditions and tube geometry. The condensing temperatures varied at 40.5, 47.5 and $54.5^{\circ}C$, and subcoolings altered at 3.5, 6.5 and $11.5^{\circ}C$. The mass flow rates of the coiled capillary tubes decreased by 5 to 16% compared with those of the straight capillary tubes at the same operating conditions. An empirical correlation was developed by introducing equivalent length of capillary tube with non-dimensional parameters for coiled shape. The present correlation predicts the data with average and standard deviations of 0.33% and 3.24%, respectively.

• Ocean Science Journal
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• v.41 no.2
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• pp.97-104
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• 2006

A useful radiance-converting method was developed to convert the Landsat-7 ETM+thermal-infrared (TIR) band's radiance ($L_{{\lambda},L7/ETM+}$) to that of Landsat-5 TM TIR ($L_{{\lambda},L5/TM+})$ as: $L_{{\lambda},L5/TM}=0.9699{\times}L_{{\lambda},L7/ETM+}+0.1074\;(R^2=1)$. In addition, based on the radiance-converting equation and the linear relation between digital number (DN) and at-satellite radiance, a DN-converting equation can be established to convert DN value of the TIR band between Landsat-5 and Landsat-7. Via this method, it is easy to integrate Landsat-5 and Landsat-7 TIR data to retrieve the sea surface temperature (SST) in coastal waters on the basis of local empirical algorithms in which the radiance or DN of Lansat-5 and 7 TIR band is usually the only input independent variable. The method was employed in a local empirical algorithm in Daya Bay, China, to detect the thermal pollution of cooling water discharge from the Daya Bay nuclear power station (DNPS). This work demonstrates that radiance conversion is an effective approach to integration of Landsat-5 and Landsat-7 data in the process of a SST retrieval which is based on local empirical algorithms.