• Journal of Bio-Environment Control
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• v.22 no.2
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• pp.108-115
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• 2013

This study was conducted to suggest a model to calculate the overall heat transfer coefficient of single layer covering for various greenhouse conditions. There was a strong correlation between cover surface temperature and inside air temperature of greenhouse. The equations to calculate the convective and radiative heat transfer coefficients proposed by Kittas were best fitted for calculation of the overall heat transfer coefficient. Because the coefficient of linear regression between the calculated and measured cover surface temperature was founded to 0.98, the slope of the straight line is 1.009 and the intercept is 0.001, the calculation model of overall heat transfer coefficient proposed by this study is acceptable. The convective heat transfer between the inner cover surface and the inside air was greater than the radiative heat transfer, and the difference increased as the wind speed rose. The convective heat transfer between the outer cover surface and the outside air was less than the radiative heat transfer for the low wind speed, but greater than for the high wind speed. The outer cover convective heat flux increased proportion to the inner cover convective heat flux linearly. The overall heat transfer coefficient increased but the cover surface temperature decreased as the wind speed increased, and the regression function was founded to be logarithmic and power function, respectively.

• Steel and Composite Structures
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• v.36 no.5
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• pp.553-568
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• 2020

Steel-concrete composite structures have been extensively used in building, bridges, and other civil engineering infrastructure. Shear stud connectors between steel and concrete are essential in composite members to guarantee the effectiveness of their behavior in terms of strength and deformability. This study focuses on investigating the shear stiffness of headed studs embedded in several types of concrete with wide range of compressive strength, and their effects on the elastic behavior of steel-concrete composite girders were evaluated. Firstly, totally 206 monotonic push-out tests from the literature were reviewed to investigate the shear stiffness of headed studs embedded in various types of concrete (NC, HPC, UHPC etc.). Shear stiffness of studs is defined as the secant stiffness of the load-slip curve at 0.5V_u, and a formulation for predicting defined shear stiffness in elastic state was proposed, indicating that the stud diameter and the elastic modulus of steel and concrete are the main factors. And the shear stiffness predicted by the new formula agree well with test results for studs with a diameter ranging from 10 to 30 mm in the concrete with compressive strength ranging from 22.0 to 200.0MPa. Then, the effects of shear stiffness on the elastic behaviors of composite girders with different sizes and under different loading conditions were analyzed, the equations for calculating the stress and deformation of simply supported composite girders considering the influence of connection's shear stiffness were derived under different loading conditions using classical linear partial-interaction theory. As the increasing of shear stiffness, the stress and deflection at the most unfavorable section under partial connected condition tend to be those under full connected condition, but the approaching speed decreases gradually. Finally, the connector's shear stiffness was recommended for fully connection in composite girders with different dimensions under different loading conditions. The findings from present study may provide a reference for the prediction of shear stiffness for headed studs and the elastic design of steel-concrete composite girder.

• Journal of the Korean School Mathematics Society
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• v.8 no.3
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• pp.367-382
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• 2005

In this paper, we deal with various contents relating to the group concept in school mathematics and teaching of algebraic structures indirectly by combining these contents. First, we consider structure of knowledge based on Bruner, and apply these discussions to the teaching of algebraic structure in school algebra. As a result of these analysis, we can verify that the essence of algebraic structure is group concept. So we investigate the previous researches about group concept: Piaget, Freudenthal, Dubinsky. In our school, the contents relating to the group concept have been taught from elementary level indirectly. Tn elementary school, the commutative law and associative law is implicitly taught in the number contexts. And in middle school, various linear equations are taught by the properties of equality which include group concept. But these algebraic contents is not related to the high school. Though we deal with identity and inverse in the binary operations in high school mathematics, we don't relate this algebraic topics with the previous learned contents. In this paper, we discussed algebraic structure focusing to the group concept to obtain a connectivity among school algebra. In conclusion, the group concept can take role in relating these algebraic contents and teaching the algebraic structures in school algebra.

• Journal of KIISE:Computer Systems and Theory
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• v.32 no.11_12
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• pp.692-704
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• 2005

With the improvement of computer hardware, GPUs(Graphics Processor Units) have tremendous memory bandwidth and computation power. This leads GPUs to use in general purpose computation. Especially, GPU implementation of compute-intensive physics based simulations is actively studied. In the solution of differential equations which are base of physics simulations, tridiagonal matrix systems occur repeatedly by finite-difference approximation. From the point of view of physics based simulations, fast solution of tridiagonal matrix system is important research field. We propose a fast GPU implementation for the solution of tridiagonal matrix systems. In this paper, we implement the cyclic reduction(also known as odd-even reduction) algorithm which is a popular choice for vector processors. We obtained a considerable performance improvement for solving tridiagonal matrix systems over Thomas method and conjugate gradient method. Thomas method is well known as a method for solving tridiagonal matrix systems on CPU and conjugate gradient method has shown good results on GPU. We experimented our proposed method by applying it to heat conduction, advection-diffusion, and shallow water simulations. The results of these simulations have shown a remarkable performance of over 35 frame-per-second on the 1024x1024 grid.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.23-30
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• 2003

In this study, the various load cases by specified by the IEC61400-1 international specification and GL Regulations for the wind energy conversion system were considered, and a specific composite structure configuration which can effectively endure various loads was proposed. In order to evaluate the structure, the structural analysis for the composite wind turbine blade was performed using the finite element method(FEM). In the structural design, the acceptable configuration of blade structure was determined through the parametric studies, and the most dominant design parameters were confirmed. In the stress analysis using the FEM, it was confirmed that the blade structure was safe and stable for all the considerd load cases. Moreover the safety of the blade root joint with insert bolts, newly devised in this study, was checked against the design loads and also the fatigue loads. The fatigue life for operating more than 20 years was estimated by using the well-known S-N linear damage rule, the load spectrum and Spera's empirical equations. The full-scale static test was performed under the simulated aerodynamic loads. from the experimental results, it was found that the designed blade had the structural integrity. Furthermore the measured results were agreed with the analytical results such as deflections, strains, the mass and the radial center of gravity. The studied blade was successfully certified by an international institute, GL, of Germany.

• Korean Journal of Food Science and Technology
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• v.18 no.4
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• pp.306-312
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• 1986

Color changes of a mixture of 0.8 M glucose, fructose or sucrose and 0.8 M glycine were evaluated by Hunter 'L', 'a', 'b' values during Maillard reaction at the temperature range of $70^{\circ}-100^{\circ}C$. The results suggested the reaction to be devided into three stages. In initial reaction the 'L' and 'a' values decreased slowely, and 'b' rapidly increased to maximum, which were followed by a rapid decrease in 'L' and 'b' and rapid increase in 'a' values at intermediate stage. At final reaction period the both 'L' and 'b' were slowed down in their reduction rate while 'a' decreased rapidly from its maximum point. All of the Hunter values were reached to nea. zero. Linear equations, which can be used for prediction of cole. change in Maillared reaction, of $1/\sqrt{(L_t-L_{\circ})^2\;+\;(a_t-a_{\circ})^2\;+\;(b_t-b_{\circ})^2}\;=\;a(1/t)\;+\;b$ for Hunter values and $1/\sqrt{X\;+\;Y\;+Z}\;=\;a(1/t)\;+\;b$ for CIE tristimulus values were found to have a very high correlation coefficient. Relationships between 'L' and 'a', 'L' and 'b' and 'a' and 'b' were also graphcally compared.

• International Journal of Highway Engineering
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• v.10 no.4
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• pp.151-159
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• 2008

Performances of retroreflectivity vary place to place, according to traffic volumes and time lengths after striping, depending on pavement marking materials and colors. The present paper uses the nation wide data of retroreflectivity, which has been collected from freeways and then tries to develop the regression curve setting traffic volume and service life as independent variables and retroreflectivities as dependent variables. The DB system includes two year's measurement in $2005{\sim}2006$ over Korean freeway pavement marking at an interval of three months for the period. The mobile measurement system, a laserlux, was employed for the purpose. The DB has provided a lot of information about materials and performance of the specific pavement marking such as geometric features, traffic volumes, material characteristics and the installation date. This study provides the comparison of pavement marking performances under diversified conditions. Based on accumulated pavement marking performances, this study provides performance curves based on the diversified factors. The goal of the retroreflectivity modeling is to develop equations that can be used to estimate an average retroreflectivity of pavement markings as a function time since application and traffic volume. After representing the variation of retroreflectivities and estimating regression curves by linear, exponential, logarithmic and power function, the regression curve which had the highest coefficient of determination and the value similar to the last field measurement was regarded as the retroreflectivity decay model. As a result of verification, the decay model showed the signification within the 90% confidence level and especially showed the clear relation with field data according to increase of cumulative vehicle exposure. Accordingly, these models can be used to determine service lives, retroreflectivity degradation rates, and retroreflectivity of new markings.

• Korean Journal of Food Science and Technology
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• v.22 no.6
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• pp.681-685
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• 1990

Changes in the physicochemical characteristics and trans acid of cottonseed oil under the condition of selective hydrogenation, temperature$210^{\circ}C,\;H_2\;pressure\;0.3\;kg/cm^2$ Ni catalyst amount 0.12% (in oil), agitation speed 280 rpm, were investigated. The saturated fatty acid such as palmitic acid and stearic acid did not show any difference, while linoleic acid($50.03%{\rightarrow}9.38%$) were transformed to oleic acid ($20.65%{\rightarrow}60.35%$) during hydrogenation. In linoleic acid isomers, cc form were reduced significantly, but ct, tc, tt form showed little change, respectively. In oleic acid isomer, t form increased markedly, whereas there was no significant difference in c form. Meanwhile, melting point(MP) and solid fat content (SFC) were linearly increased, but iodine value(IV) linearly decreased as hydrogenation proceeded. From these results, linear regression equations were obtained as follows. MP & IV : Y= 1.59-2.36X(r=-0.96, p<0.05), SFC($at\;20^{\circ}C$) & MP : Y=2.81+2.01X(r=0.96, p<0.05), SFC($at\;20^{\circ}C$) & IV : Y=9.40-5.16X(r=-0.99, p<0.01), SFC($at\;20^{\circ}C$) & 18 : 1t : Y=6.25+8.48X(r=0.97, p<0.05)

• Journal of Oral Medicine and Pain
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• v.34 no.3
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• pp.277-294
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• 2009

The purpose of this study was to evaluate the soft tissue changes of class II adolescents and adults in respect to extraction or nonextraction. The study included 68 patients from Wonkwang Dental Hospital were categorized to adolescent extraction group, adolescent nonextraction group, adult extraction group, adult nonextraction group. Cephalometric tracing of each patient was done to compare pretreatment and posttreatment of each group, to compare the changes between groups. And among the variables that showed significancy, correlation analysis and simple linear regression were done. The results were as follows. 1. In both adolescents and adults after extraction treatment, nasolabial angle significantly increased and in both subjects after non extraction treatment, nasolabial angle significantly decreased. 2. In extraction subjects, there were positive correlation between the amount of treatment changes of vertical-U1 and E line-upper lip, the changes of vertical-L1 and E line-lower lip, the changes of vertical-L1 and vertical-Li. 3. In extraction subjects, simple regression equations of E line-upper lip, E line-lower lip, Li were calculated by regression analysis. According to the results above, it could be considered that the effect of the extraction or nonextraction treatment was greater than the effect of growth.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.38-52
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• 1991

In this paper, a semi-Lagrangian method is used to solve the nonlinear hydrodynamics of a three-dimensional body beneath the free surface in the time domain. The boundary value problem is solved by using the boundary integral method. The geometries of the body and the free surface are represented by the curved panels. The surfaces are discretized into the small surface elements using a bi-cubic B-spline algorithm. The boundary values of $\phi$ and $\frac{\partial{\phi}}{\partial{n}}$ are assumed to be bilinear on the subdivided surface. The singular part proportional to $\frac{1}{R}$ are subtracted off and are integrated analytically in the calculation of the induced potential by singularities. The far field flow away from the body is represented by a dipole at the origin of the coordinate system. The Runge-Kutta 4-th order algorithm is employed in the time stepping scheme. The three-dimensional form of the integral equation and the boundary conditions for the time derivative of the potential Is derived. By using these formulas, the free surface shape and the equations of motion are calculated simultaneously. The free surface shape and fille forces acting on a body oscillating sinusoidally with large amplitude are calculated and compared with published results. Nonlinear effects on a body near the free surface are investigated.