• 한국기계가공학회지
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• 제18권8호
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• pp.51-59
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• 2019

Flow forming is an eco-friendly and high-efficiency plastic deformation process with fewer chips during a process which is specifically used to manufacture seamless tubular products like tire wheels, rocket motor cases etc. On the development of mortar barrel using Inconel718 tube, some flow formed products had dimensional errors on their thickness. In this study, our purpose is to optimize the process conditions with the smallest dimensional error. In order to find an optimum process condition, 2D axisymmetric FEM simulation analyses with Taguchi method were conducted. Geometric variables (attack angle, flatting angle, roller nose radius) and operating parameters (depth of forming, feed rate) are considered as control factors. Forward flow forming with single roller was first analyzed to determine the effective factors using AFDEX software and attack angle of the roller was identified as the most influential factor. Also, the nose radius of the rollers was confirmed as a significant factor in multi-rollers flow forming system. The effect of rollers offset values are also studied and finally, we proposed optimal conditions to improve the accuracy of flow forming process with Inconel718 tube for mortar barrel manufacturing.

• 한국컴퓨터정보학회논문지
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• 제7권1호
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• pp.137-146
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• 2002

본 논문은 물류의 소프트개발, 시장점유의 강화. 수익의 유지 및 기업의 존속을 위해 전문물류업체인 제3자 물류에 물류업무를 위임하여 화주기업과 고객인 소비자와의 관계를 공유·연계할 수 있는 3자간의 통합된 물류정보시스템 구현 방안을 제시하였다. 이에 물류기능의 한 분야인 수·배송에서 현실적으로 고객의 만족을 더욱 증진시키기 위해 첨단메카니즘을 이용하여 고객에 대한 고품질의 물류서비스에 가치를 두고 접근하여, 제3자 물류를 보다 전략적으로 활용하고, 서비스품질에 있어서도 고도의 능력을 보유할 수 있게 하는 방안으로 모델을 제시하였다.

• 드라이브 ㆍ 컨트롤
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• 제16권1호
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• pp.1-6
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• 2019

The use of micro bubbles in industrial fields has been increasing in the recent years., particularly micro-bubble sterilization and water purification effects. Various methods have been developed for the generation of micro-bubbles. Depending on the method of generating bubbles, the micro-bubbles can be roughly classified into saturation molding, cavitation and rotation flow types. The objective of this study was to use ventilated tube type as a method of generating micro-bubbles in order to purify large amount of water quality such as lakes and reservoirs. This method shows a difference in efficiency in which micro-bubbles are generated depending on the contact ratio of gas to liquid. The study also investigated the optimal gas liquid contact ratio by applying various orifice methods and investigated the optimum condition of micro-bubble generation by gas Based on this, a technology to develop a micro-bubble generator with a venturi type nozzle shape that has a high water purification effect was developed.

• Journal of Plant Biotechnology
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• 제48권2호
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• pp.93-99
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• 2021

This study was conducted to develop an Agrobacterium-mediated genetic transformation protocol for the carnation cv. "Jinju" to counteract its ethylene sensitivity. The new protocol involves the use of an improved shoot regeneration medium, optimized minimal concentrations of the selective agent, a pre-culture period, and co-cultivation periods. Silver nanoparticles (NAg) added at a concentration of 2.0 μM to the Murashige and Skoog (MS) basal shoot regeneration medium supplemented with 0.1 mg/L indole-3-butyric-acid (IBA) and 0.2 mg/L thidiazuron (TDZ) improved the shoot regeneration efficiency, number of shoots per explant, and plant growth compared to the control without the addition of NAg. The phosphinothricin (PPT) concentration of 1.0 mg/L was determined to be the minimal and optimal concentration for the selection of putative transgenic plants. When the explants were infected with Agrobacterium cells harboring the acdS gene, the explants that were pre-cultured for three days induced more putative transgenic plants than those that were co-cultivated for four days. Therefore, we expect that the results of this study will benefit researchers who are developing genetic transformations of carnations.

• 한국수소및신에너지학회논문집
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• 제32권1호
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• pp.1-10
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• 2021

Water electrolysis technology, which generates hydrogen using renewable energy resources, has recently attracted great attention. Especially, the polymer electrolyte membrane water electrolysis system has several advantages over other water electrolysis technologies, such as high efficiency, low operating temperature, and optimal operating point. Since research that analyzes performance characteristics using test bench have high cost and long test time, however, model based approach is very important. Therefore, in this study, a system model for water electrolysis dynamics of a polymer electrolyte membrane was developed based on MATLAB/Simulink®. The water electrolysis system developed in this study can take into account the heat and mass transfer characteristics in the cell with the load variation. In particular, the performance of the system according to the stack temperature control can be analyzed and evaluated. As a result, the developed water electrolysis system can analyze water pump dynamics and hydrogen generation according to temperature dynamics by reflecting the dynamics of temperature.

• 드라이브 ㆍ 컨트롤
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• 제18권4호
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• pp.84-90
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• 2021

Viscosity of hydraulic oils decreases due to loss reduction and efficiency increase of fluid power systems. However, low viscosity is not always appropriate due to the induction of large leakage and small lubricity. Therefore, a detailed study on the optimum viscosity of hydraulic oils is necessary. In this study, based on the thermohydrodynamic lubrication theory, numerical simulation was conducted using the slipper model of swashplate-type axial piston pumps and motors. The viscosity grades' (VG) effects of oils on power losses are mainly discussed numerically in fluid film lubrication, including changes in temperature and viscosity. The simulation results reveal that the flow rate increases and the friction torque decreases as VG decreases. The film temperature and power loss were minimised for a specific oil with a VG. The minimum conditions regarding the temperature and loss were different and closed. Under various operating conditions, the film temperature and power loss were minimised, suggesting that an optimum hydraulic oil with a specific VG could be selected for given operating conditions of pressure and speed. Otherwise, a preferable operating condition must be established to determine a specific VG oil.

• Steel and Composite Structures
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• 제45권6호
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• pp.775-796
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• 2022

In this study, a new type of energy absorbers with a functionally graded thickness is investigated, these type of absorbers absorb energy through expanding-folding processes. The expanding-folding absorbers are composed of two sections: a thin-walled aluminum matrix and a thin-walled steel mandrel. Previous studies have shown higher efficiency of the mentioned absorbers compared to the conventional ones. In this study, the effect of thickness which has been functionally-graded on the aluminum matrix (in which expansion occurs) was investigated. To this end, initial functions were considered for the matrix thickness, which was ascending/descending along the axis. The study was done experimentally and numerically. Comparing the experimental data with the numerical results showed high consistency between the numerical and experimental results. In the final section of this study, the best energy absorber functionally graded thickness was introduced by optimization using a third-order genetic algorithm. The optimization results showed that by choosing a minimum thickness of 1.6 mm and the exponential coefficient of 3.25, the most optimal condition can be obtained for descending thickness absorbers.

• 한국항공운항학회지
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• 제31권2호
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• pp.66-71
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• 2023

In the case of the Navy, if some of the co-pilots are included in the long-term promotion process due to the limited number of co-pilots, operational flight and administrative tasks will be added to the co-pilots not included in the rest of the Pilot in commander process. Therefore, to solve this problem, the co-pilot who has passed the PQS step-by-step process minimizes the personnel gap in the flight operation unit through a system that evaluates whether it is possible to perform its duties as a co-pilot through actual flight after entering the school. The advantage of the PQS course is that you can control flight plans on your own and minimize gaps in flight and ground work while carrying out the curriculum, but you can't focus on education or improve your skills due to irregular training flight cycles. Therefore, in this study, after collecting opinions on effective flight cycles through a survey of pilots of P-3C, the Navy's fixed-wing aircraft representative, we will analyze the association of aircraft volume performance by flight cycle to derive the optimal flight cycle of the P-3C pilot course.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제18권7호
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• pp.2027-2046
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• 2024

Reconfigurable Intelligent Surface (RIS) is an innovative technique to precisely control the phase of incident signals with the help of low-cost passive reflective elements. It shows excellent potential in the sixth generation of mobile communication systems, which not only extends wireless coverage but also boosts channel capacity. Considering that multipath propagation and a high number of antennas are involved in RIS in assisted mega multiple-input multiple-output (MIMO) systems, it suffers from severe channel fading and multipath effects, which in turn lead to signal instability and degradation of transmission performance. To overcome this obstacle, this essay suggests an improved gradient optimization algorithm to dynamically and optimally adjust the phase of the reflective elements to counteract channel fading and multipath effects as a strategy. In order to overcome the optimization problem of falling into local minima, this paper proposes an adaptive learning rate algorithm based on Adagrad improvement, which searches for the global optimal solution more efficiently and improves the robustness of the optimization algorithm. The suggested technique helps to enhance the estimate of channel efficiency of RIS-assisted large MIMO systems, according to simulation results.

• 생물환경조절학회지
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• 제30권4호
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• pp.367-376
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• 2021

우리나라 딸기 재배는 시설 재배로 이루어지고 있으며, 대부분 농가의 급액 관리는 재배자의 경험을 토대로 타이머 제어 방식으로 이루어지고 있다. 타이머 급액 방법은 재배 환경, 작물의 생육 단계, 배지 수분 함량 등을 고려하기 어려워 작물을 최적 수준으로 관리하지 못하고, 급액 관리의 정확성이 결여되는 문제점이 있다. 적산 일사량과 배지 수분함량을 이용한 급액 방법은 작물의 생육 상태에 따라 정밀하게 양액을 공급하는 친환경적인 방법이다. 본 연구는 코이어배지를 이용한 딸기 수경재배에서 적산일사량과 배지 수분함량을 이용한 복합 급액 제어와 타이머 제어 급액 방법을 비교하고 복합 급액 제어 시 최적의 적산 일사량 기준을 설정하고자 수행하였다. 적산일사량 급액 방법은 외부 일사량을 기준으로 100, 150, 250J·cm^-2에 도달하면 자동으로 급액하며 배지 수분함량이 60% 미만이면 강제 급액하고, 1회 급액량은 50mL로 공급하였다. 타이머 제어는 대조구로 설정하였다. 급액을 개시하는 적산 일사량 기준이 작을수록 일일급액량이 많았으며 100J·cm^-2 기준 급액 시 급액량은 250J·cm^-2 처리구 대비 46% 많았다. 지상부 생체중과 건물중 모두 복합 급액 제어 방법이 타이머 제어보다 높았으며, 100, 150J·cm^-2 처리구에서 지상부 생체중이 높았고 100J·cm^-2 처리구에서 건물중이 유의하게 높은 값을 나타냈다. 수량 또한 타이머 제어 방법보다 복합 제어 방법에서 유의하게 높았으며 적산 일사량 기준이 작을수록 초기 수량이 증가하였다. 평균 과중은 타이머 제어 급액 시 가장 낮았다. 본 연구 결과 딸기의 정밀 급액 관리를 위하여 적산 일사량과 배지 수분 함량 센서를 이용한 복합 제어 활용 가능성을 확인하였다.