• Journal of Korean Society of Steel Construction
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• v.19 no.1
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• pp.15-27
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• 2007

Over the past decade, labor costs have increased relative to the cost of material hardware according to analysts in the construction industry. Therefore, the minimum weight design, which has been widely adopted in the literature for the optimal design of steel structures, is no longer the most economical construction approach. Presently, although connection- related costs is crucial in determining the most cost-effective steel structures, most studies on this subject focused on minimum-weight design or engaged in higher analysis. Therefore, in this study, we proposed a fabrication scheme for the most cost-effective moment-resisting steel frame structures that resist lateral loads without compromising overall stability. The proposed approach considers the cost of steel products, fabrication, and connections within the design process. The optimal design considered construction realities, with the optimal trade-off between the number of moment connections and total cost was achieved by reducing the number of moment connections and rearranging them using the combination of analysis that includes shear, displacement and interaction value based on the LRFD code and optimization scheme based on genetic algorithms. In this study, we have shown the applicability and efficiency in the examples that considered actual loading conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.207-214
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• 2021

This study aims to analyze the effect of the level of accounts receivable on firm profitability. It is possible to find the optimal level of accounts receivable that maximizes profitability. In this study, 6,632 samples were selected from manufacturing companies listed on the Korean Stock Exchange from 2001 to 2018. We used the fixed effect panel model to analyze the model equation. There is a positive (+) relationship between the profitability of a company, the Return on Assets (ROA), and accounts receivable (AR). Also, this relationship has a nonlinear relationship or a reverse-U shape. There is an optimal level of accounts receivables, which results in profitability increase up to a certain extent, but subsequently, profitability decreases when accounts receivables exceed this level. In the case of monopoly companies with a higher-than-average market share, the coefficient between accounts receivable and firm profitability is greater than that for competitors with a lower market share than average. It supports the hypothesis that Titman (1984) suggested, that trade credit is important for enhancing corporate profitability. It is confirmed that accounts receivables play an important role in enhancing firm profitability and it is necessary to understand this well from the corporate standpoint.

• Korean journal of applied entomology
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• v.52 no.4
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• pp.387-394
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• 2013

The developmental times of mealworm beetle larvae, Tenebrio molitor were studied at six temperatures ranging from 15 to $30^{\circ}C$ with 60~70% RH, and a photoperiod of 14L:10D. Mortality of larval period was very low at 17 and $20^{\circ}C$ but did not die over $22^{\circ}C$. Developmental time of larva was decreased with increasing temperature. The total developmental time of T. molitor larvae was longest at $17^{\circ}C$ (244.3 days) and shortest at $30^{\circ}C$ (110.8 days). Egg and larvae were not developed at $15^{\circ}C$. The lower developmental threshold and effective accumulative temperatures for the total larval stages were $6.0^{\circ}C$ and 2564.1 degree-days, respectively. The relationship between developmental rate and temperature was fitted by a linear model and nonlinear model of Logan-6($r^2$=0.95). The distribution of completion of each development stage was well described by the 2-parameter Weibull function ($r^2$=0.8502~0.9390).

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.138-145
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• 2017

The purpose of this study is to establish a reasonable analytical method for the estimation of overall behavior characteristic from cracking to yielding of rebar and crushing of concrete and seismic performance of reinforced concrete shear wall with high-strength reinforcing bar. A total of 8 specimens of reinforced concrete walls which have constant aspect ratio and a variety of variables such as reinforcement ratio, reinforcement yielding strength, reinforcement details, concrete design strength, section shape and whether lateral restraint hoop were selected and the analysis was performed by using a non-linear finite element analysis program (RCAHEST) applying the proposed constitutive equation by the authors. The mean and coefficient of variation for maximum load from the experiment and analysis results was predicted 1.04 and 8%. The mean and coefficient of variation for displacement corresponding maximum load from the experiment and analysis results was predicted 1.17 and 19% respectively. The analytical results were predicted relatively well the fracture mode and the overall behavior until fracture for all specimens. These results are expected to be used as basic data for application of high-strength reinforcing bar to design codes in the future.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.11
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• pp.1254-1264
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• 2008

This paper suggests an extended memory polynomial model that improves accuracy in modeling memory effects of RF power amplifiers(PAs), and verifies effectiveness of the suggested method. The extended memory polynomial model includes cross-terms that are products of input terms that have different delay values to improve the limited accuracy of basic memory polynomial model that includes the diagonal terms of Volterra kernels. The complexity of the memoryless model, memory polynomial model, and the suggested model are compared. The extended memory polynomial model is represented with a matrix equation, and the Volterra kernels are extracted using least square method. In addition, the structure of digital predistorter and digital signal processing(DSP) algorithm based on the suggested model and indirect learning method are proposed to implement a digital predistortion linearization. To verify the suggested model, the predicted output of the model is compared with the measured output for a 10W GaN HEMT RF PA and 30 W LDMOS RF PA using 2.3 GHz WiBro input signal, and adjacent-channel power ratio(ACPR) performance with the proposed digital predistortion is measured. The proposed model increases model accuracy for the PAs, and improves the linearization performance by reducing ACPR.

• Journal of Navigation and Port Research
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• v.28 no.6
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• pp.481-489
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• 2004

Ship collisions and grounding continue to occur regardless of continuous efforts to prevent such accidents. With the increasing demand for safety at sea and for protection of the environment, it is of crucial importance to be able to reduce the probability of accidents, assess their consequences and ultimately minimize or prevent potential damages to the ships and the marine environment. Numerical simulations for actual collision problem are conducted with a special attention with respect to finite element size, fracture criteria and material properties, which require a careful consideration to improve the accuracy. A parametric analysis varying colliding speed, angle, design loading condition is conducted using nonlinear finite element analysis method for 46,00 dwt Product/chemical carrier. The relationship between the absorbed energy and indentation are derived quantitatively using the insights observed from this study, and a novel design concept for assessing the anti-collision performance are proposed.

• Journal of the Korea Organic Resources Recycling Association
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• v.21 no.1
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• pp.62-68
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• 2013

The effect of organic substance on its degradation rate in burial site was investigated using batch tests. Substrate were swine and cattle with the initial concentrations of 2, 4, 6, 8, and 10 g VS(volatile solids)/L, respectively. The highest methane production rates of swine and cattle were found at 2 g VS/L as 46.3 and 48.4 ml CH4/g VS.d, respectively. As substrate concentration increased, the methane production rate decreased. The inhibition constants were n and m that were estimated using nonlinear inhibition model. The values of n and m were inhibition constants of methane production rate and ultimate methane yield, respectively. The values of n and m were 4.9 and 0.6 on swine and 1.1 and 0.4 on cattle. The methane production rate was responded sensitively by increase and decrease of substrate concentration, whereas ultimate methane yield do not relatively. From a relation between n and m, inhibitory effect of substrate concentration was confirmed as uncompetitive inhibition.

• Journal of the Korean Society for Marine Environment & Energy
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• v.13 no.2
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• pp.112-120
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• 2010

In this paper time series wave data measured continuously for 24 hours during a storm in Yura Sea Area are used to investigate statistical characteristics of nonlinear waves. The exceedance probability of wave height is compared using the Rayleigh distribution and the Edgeworth-Rayleigh (ER) distribution. Wave data which show stationary state for 10 hours contain 4600 waves approximately. The Gram-Chalier distribution fits the probability of wave elevation better than the Gaussian distribution. The Rayleigh ($H_{rms}$) distribution follows the exceedance probability of wave height in general and predicts the probability of freak waves well. The ER distribution overpredicts the exceedance probability of wave heights and the occurrence of freak waves. If wave data measured for 30 minute period which contains 250 waves are used, the ER distribution can predict the occurrence probability of freak waves well. But it overpredicts the probability of overall wave height If no freak wave occurs, the Rayleigh ($H_{rms}$) distribution agrees well with wave height distribution for the most of wave height ranges. The wave height distribution of freak waves of which height are less than 10 m shows similar tendency compared with freak waves greater than 10 m. The value of $H_{max}/H_{1/3}$ is related to the kurtosis of wave elevation. It seems that there exists threshold value of the kurtosis for the occurrence of freak waves.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.697-703
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• 2017

This paper examines the flexure behavior of FRP-concrete composite structure that can replace conventional reinforced concrete structure types. In order to investigate the structural performance and behavioral characteristics in numerical analysis means, ABAQUS, a general purpose finite element analysis program, was utilized for nonlinear finite element analysis, and the various variables and their influences were analyzed and compared with experimental results to suggest values optimized to this composite structure. The concrete damage plasticity model and Euro code for concrete were used. In the implicit finite element analysis, the convergence was ambiguous when geometrical and material nonlinearity were large, so the explicit finite element analysis used in this study was deemed to be appropriate. From the comparison with the experiment about concrete damaged plasticity model, 20mm for the mesh size, $30^{\circ}$ for the dilation angle, $100Nmm/mm^2$ for the value of fracture energy, 0.667 for Kc value, and the consideration of damage parameter were suggested believed to be appropriate. The numerical model suggested in this study was able to imitate the ultimate load and cracking pattern very well; therefore, it is expected to be utilized in research of various new material composite structures.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.5
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• pp.59-66
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• 2002

Long-rails in railways and high-speed railway are subjected to additional stresses resulted from the displacements inconsistence between upper structures, and this phenomenon is more remarkable in continuous bridges than in simple bridges. For the sake of safety, railways have to guarantee trains to stop safely without derailment even in the event of earthquake. The influences of acceleration, braking, and temperature were analyzed by static nonlinear method. But earthquake loads that require dynamic nonlinear analysis are not considered in these methods. Because linear relation between relative displacements of decks and rail stresses is not guaranteed at the nonlinear systems such as long rails on the bridges, it is required compute to rail stresses considering both braking and earthquake load by nonlinear dynamic analysis method. In this study, dynamic analysis method with material non-linearity for rails on continuous bridges according to the Taiwan High Speed Railway(THSR) Design Specification volume 9 was developed. And additional stresses and displacements of long rails for acceleration, braking, and earthquake loads were analyzed by this method.