• Steel and Composite Structures
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• 제12권1호
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• pp.31-51
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• 2012

Local buckling can be ignored for hot-rolled ordinary strength steel equal angle compression members, because the width-to-thickness ratios of the leg don't exceed the limit value. With the development of steel structures, Q420 high strength steel angles with the nominal yield strength of 420 MPa have begun to be widely used in China. Because of the high strength, the limit value of the width-to-thickness ratio becomes smaller than that of ordinary steel strength, which causes that the width-to-thickness ratios of some hot-rolled steel angle sections exceed the limit value. Consequently, local buckling must be considered for 420 MPa steel equal angles under axial compression. The existing research on the local buckling of high strength steel members under axial compression is briefly summarized, and it shows that there is lack of study on the local buckling of high strength steel equal angles under axial compression. Aiming at the local buckling of high strength steel angles, this paper conducts an axial compression experiment of 420MPa high strength steel equal angles, including 15 stub columns. The test results are compared with the corresponding design methods in ANSI/AISC 360-05 and Eurocode 3. Then a finite element model is developed to analyze the local buckling behavior of high strength steel equal angles under axial compression, and validated by the test results. Following the validation, a finite element parametric study is conducted to study the influences of a range of parameters, and the analysis results are compared with the design strengths by ANSI/AISC 360-05 and Eurocode 3.

• 한국추진공학회지
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• 제11권5호
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• pp.60-71
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• 2007

액체로켓 엔진의 시동은 연소기와 가스발생기의 안정적인 점화는 물론 시동에 소요되는 시간을 단축하여 추력 발생과 상관없는 추진제 소모량을 줄이는 방향으로 전개되어야 한다. 특히 엔진시스템의 시동 순서나 규격을 모두 시험적으로 개발하는 데는 한계가 있으며, 안전상의 이유로 시험 조건이나 시동 cyclogram에 대한 해석적인 분석이 선행될 필요가 있다. 이에 본 연구에서는 가스발생기 사이클 액체로켓 엔진의 수학적 모델을 상용 1차원 유체시스템 해석 프로그램인 Flowmaster를 기반으로 개발하였으며, 이를 이용하여 안정된 엔진 시동을 위한 파이로시동기 규격이나 연소기 및 가스발생기 종단밸브의 열림시간 등을 구하는 방법론을 제시하였다. 아울러 해석 결과로 구한 시동특성을 해외 엔진의 시동 해석 결과와 정성적인 비교를 수행하여 비교적 잘 일치함을 파악하였다.

• 대한의용생체공학회:의공학회지
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• 제32권2호
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• pp.134-143
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• 2011

The selection of meaningful clinical tests and its reference values from a high-dimensional clinical data with imbalanced class distribution, one class is represented by a large number of examples while the other is represented by only a few, is an important issue for differential diagnosis between similar diseases, but difficult. For this purpose, this study introduces methods based on the concepts of both discernibility matrix and function in rough set theory (RST) with two discretization approaches, equal width and frequency discretization. Here these discretization approaches are used to define the reference values for clinical tests, and the discernibility matrix and function are used to extract a subset of significant clinical tests from the translated nominal attribute values. To show its applicability in the differential diagnosis problem, we have applied it to extract the significant clinical tests and its reference values between normal (N = 351) and abnormal group (N = 101) with either cholecystitis or cholelithiasis disease. In addition, we investigated not only the selected significant clinical tests and the variations of its reference values, but also the average predictive accuracies on four evaluation criteria, i.e., accuracy, sensitivity, specificity, and geometric mean, during l0-fold cross validation. From the experimental results, we confirmed that two discretization approaches based rough set approximation methods with relative frequency give better results than those with absolute frequency, in the evaluation criteria (i.e., average geometric mean). Thus it shows that the prediction model using relative frequency can be used effectively in classification and prediction problems of the clinical data with imbalanced class distribution.

• Journal of Power Electronics
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• 제18권1호
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• pp.234-250
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• 2018

This paper presents a new load sharing control for use between paralleled three-phase inverters in an islanded microgrid based on the online line impedance estimation by the use of a Kalman filter. In this study, the mismatch of power sharing when the line impedance changes due to temperature, frequency, significant differences in line parameters and the requirements of the Plug-and-Play mode for inverters connected to a microgrid has been solved. In addition, this paper also presents a new droop control method working with the line impedance that is different from the traditional droop algorithm when the line impedance is assumed to be pure resistance or pure inductance. In this paper, the line impedance estimation for parallel inverters uses the minimum square method combined with a Kalman filter. In addition, the secondary control loops are designed to restore the voltage amplitude and frequency of a microgrid by using a combined nominal value SOGI-PLL with a generalized integral block and phase lock loop to monitor the exact voltage magnitude and frequency phase at the PCC. A control model has been simulated in Matlab/Simulink with three voltage source inverters connected in parallel for different ratios of power sharing. The simulation results demonstrate the accuracy of the proposed control method.

• Safety and Health at Work
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• 제8권4호
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• pp.364-370
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• 2017

Background: Labeled noise reduction (NR) data presented by manufacturers are considered one of the main challenging issues for occupational experts in employing hearing protection devices (HPDs). This study aimed to determine the actual NR data of typical HPDs using the objective fit testing method with a microphone in real ear (MIRE) method. Methods: Five available commercially earmuff protectors were investigated in 30 workers exposed to reference noise source according to the standard method, ISO 11904-1. Personal attenuation rating (PAR) of the earmuffs was measured based on the MIRE method using a noise dosimeter (SVANTEK, model SV102). Results: The results showed that means of PAR of the earmuffs are from 49% to 86% of the nominal NR rating. The PAR values of earmuffs when a typical eyewear was worn differed statistically (p < 0.05). It is revealed that a typical safety eyewear can reduce the mean of the PAR value by approximately 2.5 dB. The results also showed that measurements based on the MIRE method resulted in low variability. The variability in NR values between individuals, within individuals, and within earmuffs was not the statistically significant (p > 0.05). Conclusion: This study could provide local individual fit data. Ergonomic aspects of the earmuffs and different levels of users experience and awareness can be considered the main factors affecting individual fitting compared with the laboratory condition for acquiring the labeled NR data. Based on the obtained fit testing results, the field application of MIRE can be employed for complementary studies in real workstations while workers perform their regular work duties.

• Steel and Composite Structures
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• 제36권1호
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• pp.75-86
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• 2020

The grid structures with welded hollow spherical joint (WHSJ) have gained increasing popularity for use in industrial buildings with suspended cranes, and usually welded with steel tube (ST). The fatigue performance of steel tube-welded hollow spherical joint (ST-WHSJ) is however not yet well characterized, and there is little research on fatigue life prediction methods of ST-WHSJ. In this study, based on previous fatigue tests, three series of specimen fatigue data with different design parameters and stress ratios were compared, and two fatigue failure modes were revealed: failure at the weld toe of the ST and the WHSJ respectively. Then, S-N curves of nominal stress were uniformed. Furthermore, a finite element model (FEM) was validated by static test, and was introduced to assess fatigue behavior with the hot spot stress method (HSSM) and the effective notch stress method (ENSM). Both methods could provide conservative predictions, and these two methods had similar results. However, ENSM, especially when using von Mises stress, had a better fit for the series with a non- positive stress ratio. After including the welding residual stress and mean stress, analyses with the local stress method (LSM) and the critical distance method (CDM, including point method and line method) were carried out. It could be seen that the point method of CDM led to more accurate predictions than LSM, and was recommended for series with positive stress ratios.

• 한국어류학회지
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• 제33권2호
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• pp.64-73
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• 2021

본 연구는 2015년 1월부터 12월까지 한국 주변해역에서 대형선망어업으로 어획된 고등어의 성장과 연령구조를 분석하였다. 연령분석을 위해 총 459개의 이석이 사용되었고, 가랑이체장의 범위는 19.6~46.0 cm였다. 연령은 투명대의 수, 채집일, 이석 가장자리 형태, 1월 1일의 명목생일에 대한 정보를 이용하여 판독하였다. 윤문은 고등어의 산란시기인 5월에 형성되었다. 연령은 0세부터 6세까지 추정되었고, von Bertalanffy 성장식은 성별 간 유의한 차이가 나타나지 않았다. 암컷과 수컷을 모두 합한 성장식은 FL_t=39.3×{1-exp[-0.90×(t+0.033)]}으로 도출되었다. 2015년 대형선망 어획물의 연령구조를 살펴본 결과, 2세군의 어획비율이 30.9%로 가장 높았고, 0~2세군은 전체 어획물의 88.5%로 대부분을 차지하였다.

• 국제지역연구
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• 제14권1호
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• pp.3-29
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• 2010

본 논문의 목적은 해외에서 발생하는 화폐교란과 실물교란이 중간재를 수입하는 소국경제에 어떤 영향을 미치는지 알아보고, 또한 소국에서의 물가상승에 대한 명목임금연동정도가 해외경제교란이 소국경제에 전파되는 과정에 어떤 영향을 미치는지 알아보는데 있다. 이를 위해 본 논문에서는 변동환율제 하에서 자본이동이 완전하며, 합리적 기대가정 하에서 2국 2재화 모형을 채택하였다. 본 논문의 분석결과에 의하면 해외에서 발생하는 화폐교란과 실물교란은 가격효과, 해외승수효과, 자본이동을 통한 이자효과, 물가와 환율변동에 의한 상대가격효과, 그리고 실질잔고효과를 통하여 소국경제에 영향을 미치는 것으로 나타났다. 본 논문에서는 한국과 미국의 통계자료를 사용하여 실증분석을 하였다. 이를 통해 미국에서 발생하는 화폐교란과 실물교란이 한국경제에 어떤 영향을 미치는지, 그리고 한국에서의 임금연동지수가 미국에서 발생하는 경제교란이 한국경제에 전파되는 과정에 어떤 영향을 미치는지 알아보았다.

• 국제지역연구
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• 제15권2호
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• pp.101-123
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• 2011

본 연구는 한국, 미국, 및 일본간의 상호무역에서 요소가격균등화가 성립되는가를 ARDL모형에 의한 bounds test로 분석하여 요소가격균등화(factor price equalization, FPE)의 동일성(equality)과 수렴성(convergence)을 검정하려는 시도이다. 실증분석결과에 의하면 국제화가 심화됨에 따라 국가간 무역에서 시현될 가능성이 높아진 요소가격균등화는 무역규모에 있어서 상대적으로 대국인 미국이나 일본보다는 한국과 같은 소국에서 나타나며, 실질변수 보다는 명목변수를 통한 조정과정이 용이한 것으로 분석되었다. 그리고 국가간에 노동이나 자본과 같은 생산요소가 직접적으로 이동하는 단기적인 효과가 요소가격균등화에 미치는 영향은 미미한 것으로 분석되어 요소가격균등화가 장기적인 경제현상임을 알 수 있다. 따라서 우리나라의 경우 교역비중이 높은 미국, 일본, 중국, 및 EU 등과의 무역정책과 기타 국가와의 무역정책은 선별적으로 수립해야 하고, 또한 보다 장기적인 차원에서 시행하여야 할 것이다.

• 대한금속재료학회지
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• 제49권4호
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• pp.281-290
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• 2011

In order to gain better understanding of the selective surface oxidation and its influence on the galvanizability of a transformation-induced plasticity (TRIP) assisted steel containing 1.5 wt.% Si and 1.6 wt.% Mn, a model experiment has been carried out by depositing Si and Mn (each with a nominal thickness of 10 nm) in either monolayers or bilayers on a low-alloy interstitial-free (IF) steel sheet. After intercritical annealing at $800^{\circ}C$ in a $N_2$ ambient with a dew point of $-40^{\circ}C$, the surface scale formed on 590 MPa TRIP steel exhibited a microstructure similar to that of the scale formed on the Mn/Si bilayer-coated IF steel, consisting of $Mn_{2}SiO_{4}$ particles embedded in an amorphous $SiO_{2}$ film. The present study results indicated that, during the intercritical annealing process of 590 MPa TRIP steel, surface segregation of Si occurs first to form an amorphous $SiO_{2}$ film, which in turn accelerates the out-diffusion of Mn to form more stable Mn-Si oxide particles on the steel surface. During hot-dip galvanizing, particulate $Fe_{3}O_{4}$, MnO, and Si-Mn oxides were reduced more readily by Al in a Zn bath than the amorphous $SiO_{2}$ film. Therefore, in order to improve the galvanizability of 590 TRIP steel, it is most desirable to minimize the surface segregation of Si during the intercritical annealing process.