• 한국정보시스템학회지:정보시스템연구
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• 제32권3호
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• pp.133-150
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• 2023

Purpose This study aims to develop classification models using a decision tree algorithm to identify core keywords and rules influencing online consumer review evaluations for the robot vacuum cleaner on Amazon.com. The difference from previous studies is that we analyze core keywords that affect the evaluation results by dividing the subjects that evaluate online consumer reviews into self-evaluation (star ratings) and peer evaluation (helpfulness votes). We investigate whether the core keywords influencing star ratings and helpfulness votes vary across different products and whether there is a similarity in the core keywords related to star ratings or helpfulness votes across all products. Design/methodology/approach We used random under-sampling to balance the dataset. We progressively removed independent variables based on decreasing importance through backwards elimination to evaluate the classification model's performance. As a result, we identified classification models that best predict star ratings and helpfulness votes for each product's online consumer reviews. Findings We have identified that the core keywords influencing self-evaluation and peer evaluation vary across different products, and even for the same model or features, the core keywords are not consistent. Therefore, companies' producers and marketing managers need to analyze the core keywords of each product to highlight the advantages and prepare customized strategies that compensate for the shortcomings.

• Nuclear Engineering and Technology
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• 제29권5호
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• pp.399-405
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• 1997

In this study a new phase separated spectral analysis algorithm is proposed to identify CSB vibration mode directly from ex-core neutron signals. Ex-core neutron signals can be decomposed into the global, core support barrel (CSB) beam mode, and CSB shell mode components by the new phase separation algorithm based on the characteristics of Fourier transform. By using the proposed algorithm and the conventional spectral analysis the vibration mode of the CSB and the fuel assembly of Ulchin-1 NPP were identified from measured ex-core neutron signals.

• Nuclear Engineering and Technology
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• 제44권2호
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• pp.151-160
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• 2012

The advantages for using Monte Carlo methods to analyze full-core reactor configurations include essentially exact representation of geometry and physical phenomena that are important for reactor analysis. But this substantial advantage comes at a substantial cost because of the computational burden, both in terms of memory demand and computational time. This paper focuses on the challenges facing full-core Monte Carlo for keff calculations and the prospects for Monte Carlo becoming a routine tool for reactor analysis.

• 대한기계학회논문집A
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• 제25권9호
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• pp.1334-1340
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• 2001

In this paper, the experimental modeling of the force between permanent magnet and iron-core solenoid is suggested for more accurate control of 3 D.O.F. motor using the electromagnetic force. In the case of iron-core solenoid, the general equation of solenoid cant be used simply because of its nonlinearity. Therefore, the magnetic flux density is estimated through the concept of equivalent permanent magnet. The force distribution between permanent magnet and iron-core solenoid is more dependent on the magnetization of iron core caused by the permanent magnet than any other parameters. Therefore, the equation of the force estimation between these magnetic systems can be modeled by the experimental function of the magnetization of iron core. Especially, if the distance between iron-core solenoid and permanent magnet is far enough, the force equation through experiment can be expressed from only the current of coil and the distance between iron-core solenoid and permanent magnet. It means that Coulombs law can be used for magnetic systems and it is validated through the experiment. Therefore, force calibration is performed by the concept of Coulombs law.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제4B권2호
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• pp.54-58
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• 2004

This paper presents the iron core design method of a high temperature superconducting (HTS) transformer considering voltages per turn (V/T). In this research, solenoid type HTS coils were selected for low voltage (LV) winding and double pancake coils for high voltage (HV) winding, just as in conventional large power transformers. V/T is one of the most fundamental elements used in designing transformers, as it decides the core cross sectional area and the number of primary and secondary winding turns. By controlling the V/T, the core dimension and core loss can be changed diversely. The leakage flux is another serious consideration in core design. The magnetic field perpendicular to the HTS wire causes its critical current to fall rapidly as the magnitude of the field increases slowly. Therefore in the design of iron core as well as superconducting windings, contemplation of leakage flux should be preceded. In this paper, the relationship between the V/T and core loss was observed and also, through computational calculations, the leakage magnetic fields perpendicular to the windings were found and their critical current decrement effects were considered in relation to the core design. The ％ impedance was calculated by way of the numerical method. Finally, various models were suggested.

• 한국수소및신에너지학회논문집
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• 제28권6호
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• pp.663-668
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• 2017

SOFC anode fabricated core-shell using machano-fusion method using core with submicron size Ni, nano size YSZ for shell. Using prepared core-shell, depending on the thickness of the shell, we studied how the characteristics of sintering and SOFC cell change by sintering the anode. The Ni-YSZ core-shell has a Ni core of 0.5 to $1.2{\mu}m$ over 2 to 7 YSZ of 15 to 20 nm is, and as the high speed mixing time increases, the YSZ number increases and the shell thickness becomes uniform increased. When the fuel electrode is manufactured with core-shell, it has superior sintering property, has grain of uniform size compared with the one synthesized by general mixing, the falling path is short, the conductors (electrons and ions) connection is excellent, the electrical conductivity has become excellent. The thicker the shell, the lower the electrical conductivity. When the thickness of shell ranged from 46 to 139 nm and 61 to 81 nm, the performance was the highest and the ASR was the smallest.

• Elastomers and Composites
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• 제51권4호
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• pp.275-279
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• 2016

Additive manufacturing or 3D printing is a new manufacturing process and its application is getting growth. However, the product qualities such as mechanical strength, dimensional accuracy, and surface quality are low compared with conventional manufacturing process such as molding and machining. In this study not only mechanical characteristics of polymer sandwich panel having three dimensional core layer but also mechanical characteristics of core layer itself were analyzed. The shape of three dimensional core layer was pyramidal kagome structure. This core layer was fabricated by two different methods, injection molding with PP resin and material jetting type 3D printing with acrylic photo curable resin. The material for face sheets in the polymer sandwich panel was PP. Maximum load, stiffness, and elongation at break were examined for core layers fabricated by two different methods and also assembled polymer sandwich panels. 3D printed core showed brittle behavior, but the brittleness decreased in polymer sandwich panel containing 3D printed core. The availability of 3D printed article for the three dimensional core layer of polymer sandwich panel was verified.

• Nuclear Engineering and Technology
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• 제49권1호
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• pp.134-140
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• 2017

A well-performed core power control to track load changes is crucial in pressurized water reactor (PWR) nuclear power stations. It is challenging to keep the core power stable at the desired value within acceptable error bands for the safety demands of the PWR due to the sensitivity of nuclear reactors. In this paper, a state-space model predictive control (MPC) method was applied to the control of the core power. The model for core power control was based on mathematical models of the reactor core, the MPC model, and quadratic programming (QP). The mathematical models of the reactor core were based on neutron dynamic models, thermal hydraulic models, and reactivity models. The MPC model was presented in state-space model form, and QP was introduced for optimization solution under system constraints. Simulations of the proposed state-space MPC control system in PWR were designed for control performance analysis, and the simulation results manifest the effectiveness and the good performance of the proposed control method for core power control.

• 대한수학교육학회지:학교수학
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• 제19권3호
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• pp.495-511
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• 2017

본 연구는 수학 교육과정에서의 핵심 개념에 대한 향후의 연구 방향을 제시하고자, 핵심 개념의 의미를 고찰하고 국가별 수학과 교육과정에서의 핵심 개념을 비교하였다. 그 결과, 학교 수학에서의 핵심 개념은 학교 수학에서 배워야 하는 수학의 주요 내용 영역, 수학 개념의 기저 및 내용 간의 핵심 원리, 교수 학습의 초점 등의 관점에서 제시되어 왔으며, 우리나라, 미국, 캐나다, 호주, 뉴질랜드 등의 교육과정에서 다양한 방식으로 제시된 것을 알 수 있었다. 본 연구는 향후 미래를 살아갈 학생들을 위한 수학과 교육과정을 위하여 수학과의 핵심 개념이 무엇인지에 대한 중장기 연구와 수학과 교육과정에서 핵심 개념의 제시 방식에 대한 연구의 방향을 논의하였다.

• Nuclear Engineering and Technology
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• 제37권1호
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• pp.79-90
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• 2005

In this paper are reviewed the current status of nuclear fuel management and reactor operational aid tools. In addition, we indicate deficiencies in current capabilities and what future research is judged warranted. For the nuclear fuel management review the focus is on light water reactors and the utilization of stochastic optimization methods applied to the lattice, fuel bundle, core loading pattern, and for BWRs the control rod pattern/core flow design decision making problems. Significant progress in addressing separately each of these design problems on a single cycle basis is noted; however, the outstanding challenge of addressing the integrated design problem over multiple cycles under conditions of uncertainty remains to be addressed. For the reactor operational aid tools review the focus is on core simulators, used to both process core instrumentation signals and as an operator aid to predict future core behaviors under various operational strategies. After briefly reviewing the current status of capabilities, a more in depth review of adaptive core simulation capabilities, where core simulator input data are adjusted within their known uncertainties to improved agreement between prediction and measurement, is presented. This is done in support of the belief that further development of adaptive core simulation capabilities is required to further significantly advance the utility of core simulators in support of reactor operational aid tools.