• Geomechanics and Engineering
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• 제23권2호
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• pp.115-125
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• 2020

This study aims to explore practical and useful equations for rapid evaluation of uniaxial compressive strength of concrete (UCS-C) during the preliminary design stage of aggregate selection. For this purpose, aggregates which were produced from eight different intact rocks were used in the production of concretes. Laboratory experiments involved the tests for uniaxial compressive strength (UCS-R), point load index (PLI-R), P wave velocity (UPV-R), apparent porosity (n-R), unit weight (UW-R) and aggregate impact value (AIV-R) of the rock samples. UCS-C, point load index (PLI-C) and P wave velocity (UPV-C) of concrete samples were also determined. Relationships between UCS-R-rock parameters and UCS-C-concrete parameters were developed by regression analyses. In the simple regression analyses, PLI-C, UPV-C, UCS-R, PLI-R, and UPV-R were found to be statistically significant independent variables to estimate the UCS-C. However, higher coefficients of determination (R²=0.97-1.0) were obtained by multiple regression analyses. The results of simple regression analysis were also compared to the limited number of previous studies. The strength conversion factor (k) values were found to be 14.3 and 14.7 for concrete and rock samples, respectively. It is concluded that the UCS-C can roughly be estimated from derived equations only for the specified rock types.

• Journal of Advanced Marine Engineering and Technology
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• 제39권2호
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• pp.143-151
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• 2015

Recently, tidal current energy conversion is a promising way to harness the power of tides in order to meet the growing demands of energy utilization. A new concept of tidal current energy conversion device, named Vane Tidal Turbine (VTT), is introduced in this study. VTT has several special features that are potentially more advantageous than the conventional tidal turbines, such as propeller type tidal turbines. The purpose of this study on VTT is to analyze the possibility of extracting the hydrokinetic energy of tidal current and converting it into electricity, and evaluate the performance of turbines for various numbers of blades (six, eight and twelve) using Computational Fluid Dynamics (CFD). At various tip-speed ratios (TSR), the six-bladed turbine obtains the highest power and torque coefficients, power efficiency is up to 28% at TSR = 1.89. Otherwise, the twelve blade design captures the smallest portion of available tidal current energy at all TSRs. However, by adding more blades, torque extracted from the rotor shaft of twelve-bladed turbine is more uniform due to the less interrupted generation of force for a period of time (one revolution).

• The Journal of Asian Finance, Economics and Business
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• 제7권3호
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• pp.115-125
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• 2020

This paper investigates the impact of working capital management on the firm's profitability. The research sample includes 119 non-financial listed companies on Vietnam stock market over a period of 9 years from 2010 to 2018. Two statistical approaches include Ordinary least squares (OLS) and fixed effects model (FEM) are employed to address econometric issues and to improve the accuracy of the regression coefficients. The empirical results show the negative and significant impacts of the working capital management, which measured by cash conversion cycle (CCC) and three components of the CCC including accounts receivable turnover in days (ARD), inventory turnover in days (INVD), and accounts payable turnover in days (APD) on the firm's profitability measured by return on assets (ROA) and Tobin's Q. It implies that firms can increase profitability by keeping the optimization of the working capital management measured by the CCC, which includes shortening the time to collect money from clients, accelerating inventory flow and hold the low payment time to creditors. Besides, the profitability of firms was impacted by the sale growth rate, firm size, leverage, and age. Therefore, this paper provides a new insight to managers on how to improve the firm's profitability with working capital management.

• 대한전자공학회논문지
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• 제26권2호
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• pp.1-9
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• 1989

本 硏究에서는 多相回路와 高速 DCT를 利用한 12채널의 TDM/FDM 相互變煥 시스템의 單純化 方法 및 變煥時間을 短縮시키는 方法 다루었다. 多相回路의 原試型필터는 補間 FIR 필터의 設計技法을 適用하여 設計되었다. 그리고 DCT의 高速알고리듬과 補間 FIR 필터의 線型 位相特性 때문에 나타나는 係數間의 對稱性을 活用한 結果, 變煥時間의 大部分을 차지하는 곱셈回數가 $0.1640{\times}10^6$Multiplications/sec.channel로서 기존의 연구 結果보다 約 25% 以上 감소되는 效果를 얻었다. 복조시스템을 포함하는 全體 시스템의 컴퓨터 시뮬레이션을 통해 理論的인 結果의 타당성을 確認하였다.

• 한국CDE학회논문집
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• 제5권3호
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• pp.276-284
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• 2000

Usual practice of the transformation of a B-spline curve into a set of piecewise polynomial curves in a power form is done by either a knot refinement followed by basis conversions or applying a Taylor expansion on the B-spline curve for each knot span. Presented in this paper is a new algorithm, called a direct expansion algorithm, for the problem. The algorithm first locates the coefficients of all the linear terms that make up the basis functions in a knot span, and then the algorithm directly obtains the power form representation of basis functions by expanding the summation of products of appropriate linear terms. Then, a polynomial segment of a knot span can be easily obtained by the summation of products of the basis functions within the knot span with corresponding control points. Repeating this operation for each knot span, all of the polynomials of the B-spline curve can be transformed into a power form. The algorithm has been applied to both static and dynamic curves. It turns out that the proposed algorithm outperforms the existing algorithms for the conversion for both types of curves. Especially, the proposed algorithm shows significantly fast performance for the dynamic curves.

• 농촌계획
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• 제26권3호
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• pp.25-38
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• 2020

The purpose of this study is constructing a regional-level crop acreage choice model incorporating the impacts of producer risk aversion, and applying the constructed model to the Korean policy that promotes rice paddy conversion into non-rice crop fields. The study adopts the approach of Paris (2018) which estimates the absolute risk aversion coefficient inside of a positive mathematical programming model. A panel data set of 143 cities/counties is used for the empirical study where agricultural land in each region is allocated to 8 crops. Our estimated absolute risk aversion coefficients are smaller than those of Paris (2018), but are a little bit larger than those of the existing Korea studies based on survey or econometric methods. We found that there are close relationships among the estimated risk aversion, regional characteristics, and farming patterns. We also found that incorporating the estimated risk attitudes results in substantial differences in the impacts of the rice paddy conversion policy.

• Asian-Australasian Journal of Animal Sciences
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• 제16권11호
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• pp.1666-1672
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• 2003

The objective of this study was to evaluate the potential of an alumninosilicate clay, marketed under the trade name Biotite V, to improve growing-finishing pig performance and to determine its effects on nutrient digestibility and excretion. Sixty crossbred pigs (22.3${\pm}2.7kg$, Camborough 15 Line female${\times}$Canabred sire) were assigned on the basis of sex, weight and litter to one of four dietary treatments in a $2{\times}4$ (two sexes and four treatments) factorial design experiment. The experimental diets were based on barley and soybean meal and contained 0, 0.25, 0.5 or 0.75% biotite during the growing period (22.3-60.5 kg) and 0, 0.5, 1.0 or 1.5% biotite during the finishing period (60.5-110.3 kg). Each pig was allowed access to its own individual feeder for 30 min twice daily (07:00 and 15:00 h). Individual pig body weight, feed consumption and feed conversion were recorded weekly. The pigs were slaughtered at a commercial abattoir when they reached an average weight of 110.3 kg. Carcass weight was recorded and dressing percentage calculated. Carcass fat and lean measurements were obtained with a Destron PG 100 probe between the 3rd and 4th last ribs, 70 mm of the midline. Total tract digestibility coefficients for dry matter, energy, nitrogen and phosphorus were determined using three males and three females per treatment starting at an average weight of $52.2{\pm}3.8kg$. These pigs were housed under identical conditions as those used in the growing stage and were fed the same diets modified only by the addition of 0.5% chromic oxide as a digestibility marker. Over the entire experimental period (22.3-110.3 kg), daily gain was unaffected (p>0.05) by the inclusion of biotite in the diet. There was a cubic response for feed intake (p=0.06) and a quadratic response (p=0.07) for feed conversion due to biotite. Feeding biotite produced no significant (p>0.05) linear or quadratic effects on any of the carcass traits measured. Dry matter digestibility decreased linearly (p=0.02) with increasing levels of biotite in the diet. However, digestibility coefficients for energy, nitrogen and phosphorus were unaffected (p<0.05) by biotite inclusion. Lactobacilli and enterobacteria numbers were unaffected by inclusion of biotite while Salmonella was not detected in any of the fecal samples. The overall results of this experiment indicate that biotite inclusion did not reduce fecal excretion of nitrogen or phosphorus and failed to improve nutrient digestibility. Neither growth rate nor carcass quality was improved while a modest improvement in feed conversion was observed at lower levels of inclusion. Based on the results of this experiment, it would be difficult to justify the routine inclusion of biotite in diets fed to grower-finisher pigs. Whether or not a greater response would have been obtained with pigs of a lower health status is unknown.

• 전자공학회논문지B
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• 제33B권1호
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• pp.79-86
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• 1996

본 논문은 가변길이코드의 encoding/decoding를 위한 간단하고도 메모리 측면에서 효율적인 구조를 제안한다. MPEG1 DCT계수를 encoding/decoding함으로써 구현한 본 구조에서 114개의 DCT계수를 메모리 매핑하는데 최소인 7비트의 어드레스가 할당되도록 하였고, 직렬-병렬 및 병렬-직렬 변환용 쉬프트 레지스터와 code mapping ROM을 결합시킨 구조로써 최소의 플립플롭 및 메모리를 사용하여 구현하였다. 속도측면에선 COMPASS tool(0.8${\mu}m$ CMOS technology standard cells)을 사용해서 시뮬레이션 해본 결과 encoding/decoding의 경우 모두 50Mbps의 동작속도를 얻을 수 있었다.

• 한국통신학회논문지
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• 제33권12C호
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• pp.1039-1045
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• 2008

H.264/AVC 비디오 부호화 표준은 높은 부호화 효율을 보여주지만, 그에 따른 부호기의 복잡도가 증가하는 단점이 있다. 특히 비트율-왜곡 최적화 기법을 이용하여 인트라 모드를 결정하는 방법은 부호기의 복잡도를 증가시키는 가장 큰 원인이다. 따라서 부호화 효율을 유지하면서 부호기의 복잡도를 감소시키는 여러 가지 방법이 제안되고 있다. 본 논문에서는 MPEG-2에서 H.264로의 변환 과정에서 $4{\times}4$ 정수 변환 계수를 이용하여 효율적으로 인트라 예측 모드를 결정하는 방법을 제안한다. 제안하는 알고리듬을 적용한 모의실험 결과는 영상의 부호화 성능을 유지하면서 복잡도 및 부호화 수행 시간을 감소시킬 수 있었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.569-577
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• 2020

Based on laboratory experiments and numerical simulations, the scale effect of Internal Solitary Wave (ISW) loads on spar platforms is investigated. First, the waveforms, loads, and torques on the spar model at a laboratory obtained by the experiments and simulations agree well with each other. Then, a prototype spar platform is simulated numerically to elucidate the scale effect. The scale effect for the horizontal forces is significant owing to the viscosity effect, whereas it is insignificant and can be neglected for the vertical forces. From the similarity point of view, the Froude number was the same for the scaled model and its prototype, while the Reynolds number increased significantly. The results show that the Morison equation with the same set of drag and inertia coefficients is not applicable to estimate the ISW loads for both the prototype and laboratory scale model. The coefficients should be modified to account for the scale effect. In conclusion, the dimensionless vertical forces on experimental models can be applied to the prototype, but the dimensionless horizontal forces of the experimental model are larger than those of the prototype, which will lead to overestimation of the horizontal force of the prototype if direct conversion is implemented.