• 대한기계학회논문집A
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• 제40권9호
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• pp.791-799
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• 2016

최근 기계 시스템의 고속화가 진행됨에 따라 구조물 및 기계부품의 신뢰성 및 안전성 확보 측면에서, 충격하중하에서 구조용 재료의 동적변형거동에 대한 평가가 필요하다. 그러나 $10^4\;s^{-1}$를 넘는 고 변형률속도에서 실험적 기법을 사용한 구조용 재료의 변형거동의 파악은 용이하지 않은 실정이다. 본 연구에서는, 고 변형률속도역에서 금속재료의 동적변형거동을 조사하기 위해 Taylor 봉 충격시험을 실시하였다. 또한 고속영상촬영 시스템을 사용하여 Taylor 봉 충격시험 동안 변형거동을 관찰하였다. Taylor 봉 충격시, 경과시간에 따른 변형과정을 AUTODYN 상용 S/W를 사용한 수치해석을 수행하여 실험결과와 비교하여 고 변형률속도역에서 거동을 평가하였다.

• 한국건설관리학회논문집
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• 제16권1호
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• pp.101-109
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• 2015

투자에 의해 기대되는 경제적 효과는 실질할인율의 자승으로 매년 나누어서 현재가치로 전환된다. 따라서 실질할인율이 경제성 분석결과에 미치는 영향은 다른 요인들보다 크다. 실질할인율을 예측하는 기존의 일반적인 방법은 과거 특정기간의 평균값을 적용하는 것이다. 본 연구에서는 실질할인율의 예측 정확도를 향상시키기 위한 방법을 제안하였다. 먼저 실질할인율을 구성하는 기업대출 이자율과 소비자 물가지수에 영향을 미치는 경제변수들을 도출하였다. 기업대출 이자율에 영향을 주는 변수들로는 콜 금리와 환율, 소비자 물가지수에 영향을 주는 경제변수는 생산자 물가지수를 선정하였다. 다음으로 실질할인율과 선정된 변수들과의 영향관계를 검정하였다. 영향관계가 존재하는 것으로 분석되었다. 마지막으로 관련된 경제 변수들을 기반으로 2008년부터 2010년까지의 실질할인율을 예측하였다. 예측 결과의 정확도는 실측값과 평균값의 결과와 비교되었다. 실측값이 적용된 실질할인율은 -1.58%였으며, 예측 값은 -0.22%, 평균값은 6.06%으로 분석되었다. 본 연구에서 제안한 방법은 금융위기와 같은 특수 상황을 고려하지 않은 것이지만, 평균값보다 예측 정확도가 크게 우수한 것으로 분석되었다.

• 한국소음진동공학회논문집
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• 제13권5호
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• pp.334-340
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• 2003

Exponential window function Is widely used In impact hammer testing to reduce leakage error as well as to get a good S/N ratio. The larger its decaying rate is, the more effectively the leakage errors are reduced. But if the decay rate of the exponential window is too large, the FRF is distorted. And the modal parameters of the system can not be exactly identified by modal analysis technique. Therefore, it is a difficult problem to determine proper decay rate in impact hammer testing. In this paper, amount of the FRF distortion caused by exponential window is theoretically uncovered. A new circle fitting method is also proposed so that the modal parameters are directly extracted from impulse response spectrum distorted by the exponential-windowed impulse response data. The results by the conventional and proposed circle fitting method are compared through a numerical example.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.447-452
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• 2004

Vacuum interrupters in order to be used in various switch-gear components such as circuit breakers, distribution switches, contactors, etc. spread the arc uniformly over the surface of the contacts. The electrodes of vacuum interrupters are made of sinter-forged Cu-Cr materials for good electrical and mechanical characteristics. Since the closing velocity is 1-2m/s and impact deformation of the electrode depends on the strain rate at that velocity, the dynamic behavior of the sinter-forged Cu-Cr is a key to investigate the impact characteristics of the electrodes. The dynamic response of the material at intermediate strain rate is obtained from the high speed tensile test machine test and at the high strain rate is obtained from the split Hopkinson pressure bar test. Experimental results from both quasi-static and dynamic compressive tests are interpolated to construct the Johnson-Cook model as the constitutive relation that should be applied to simulation of the dynamic behavior of the electrodes. The impact characteristics of a vacuum interrupter are investigated with computer simulations by changing the amount of chromium content.

• The Journal of Asian Finance, Economics and Business
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• 제9권9호
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• pp.263-269
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• 2022

The global financial crisis of 2008-2009 and the COVID-19 pandemic that started in 2019 along with the slow and unstable recovery of the global economy have raised concerns about the impact of global uncertainty on the macroeconomics of the countries. The paper used the Structural Vector Autoregression (SVAR) model to examine the impact of global uncertainty shocks on Vietnam's economy from the period 2008-2022. We found that Vietnam's output dropped following the shock of global uncertainty, the peak was in the third month, and lasted for one year. Inflation in Vietnam had a rapid downturn in the first month, peaked in the seventh month, and took a long time to cease. When the economy experienced the shock of increased global uncertainty, Vietnam's policy interest rate was adjusted downward. Additionally, we included a long-term interest rate to consider the overall impact of monetary policy into account. A decreasing trend was also found with this rate. The global uncertainty shock effects acted as the aggregate demand shocks, reducing output and inflation as the uncertainty increases and vice versa, thus monetary policy can be used to regulate Vietnam's economy to deal with negative shocks without the trade-offs between output and inflation as aggregate supply shocks.

• The Journal of Asian Finance, Economics and Business
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• 제9권5호
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• pp.285-294
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• 2022

Using the ARDL approach, this study examined the impact of macro factors on Vietnam's stock market in the short and long run from 2010 to 2021. The State Bank of Vietnam and the International Monetary Fund provided time series data for this study. Research results show that in the long run, money supply and exchange rate respectively affect the stock market. The money supply had a positive effect on the VN-Index, while the exchange rate showed the opposite effect. However, the study did not find a relationship between world oil price and interest rates on VN-Index in the long run. On the other hand, in the short term, there are relationships between variables; specifically, interest rates and exchange rates have a negative impact on the VN-Index, while the world oil price and the fluctuation of money supply M2 of the previous one and two months showed an impact in the same direction on this index. The differences in the regression results on the impact of exchange rate and oil price on the VN-Index compared to previous studies come from the characteristics of Vietnam's stock market, with the large capitalization of companies in the oil and gas sector, and the structure of Vietnam's economy with export heavily depends on FDI sector.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.7-9
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• 2014

An auditory experiment was conducted to establish annoyance criteria for floor impact noise in apartment buildings. Heavyweight floor impact sounds were recorded using an impact ball; the impact sound pressure level (SPL) together with the temporal decay rate (DR), which is quantified by the dB drop per second, was analyzed. For the experiment, A-weighted exposure levels of the heavy-weight floor impact sounds ranging 34~73 dB were evaluated at 3 dB intervals. Participants used a 7-point verbal scale to evaluate the level of annoyance from floor impact noise. The results show that the annoyance increases with increasing impact SPL and decreasing DR. Consequently, a classification and an acceptable level of floor impact sounds were proposed.

• 한국포장학회지
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• 제28권3호
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• pp.201-210
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• 2022

Expanded polystyrene (EPS) is the most commonly used fresh food refrigeration insulation in Korea and Europe. Moreover, as the use of disposable packaging materials has increased significantly along with non-face-to-face delivery services since the COVID-19 crisis, social issues related to waste disposal are also being raised. Therefore, in this study, the life cycle of EPS boxes for fresh food is focused on the factors that have a large difference between incineration and landfill including recycling in Europe and Korea in the disposal process after use, and raw materials and energy in the manufacturing process, which account for a large portion of the environmental impact value. We tried to compare the environmental impact of evaluation. Overall, the raw material production stage, box manufacturing stage, and packaging stage have similar processes in Europe and Korea, but unlike Europe, Korea, which lacks landfills and incineration facilities, has focused on expanding the recycling rate. It was necessary to do an environmental impact assessment. Data affecting the environment were derived based on 2019 and 2020 data for Korea and 2017 and 2020 data for Europe. In order to predict the future environmental impact assessment, assumptions about the disposal rate in 2025 and 2030 were introduced and evaluated. As a result of this study, it was found that the raw material production stage of EPS boxes, which have similar processes in both Korea and Europe, has the greatest effect on the global warming effect of Korean EPS boxes. However, Korea, which has a relatively high recycling rate in the disposal process compared to incineration and landfill, showed better environmental performance than Europe in most impact indicators except freshwater eutrophication. In particular, Korea has increased the overall recycling rate compared to Europe by replacing various recyclable materials such as building materials and sundries with XPS (extruded polystyrene) recycled materials. In conclusion, it was found that increasing the recycling rate rather than incinerating and landfilling EPS boxes for fresh food in the domestic EPS industry has relatively less environmental load compared to Europe.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2017년도 춘계 학술논문 발표대회
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• pp.214-215
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• 2017

Extreme loads such as impact and explosion have higher strain rate than static loading condition. Therefore, it is necessary to evaluate mechanical properties at high strain rate in order to apply fiber reinforced cement composites to ensure safety performance against impact and explosion. In this study, the compressive properties of fiber reinforced cement composites by strain rate were evaluated.

• 한국융합학회논문지
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• 제9권1호
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• pp.151-159
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• 2018

이 연구는 의원 간 경쟁이 급성중이염 총진료비와 항생제처방률에 미치는 영향을 분석하였다. 건강보험심사평가원 2015년 유 소아 급성중이염 평가 자료를 활용하여 기초통계, 상관분석, 회귀분석을 실시한 결과는 다음과 같다. 첫째, 총진료비와 의원 간 경쟁지수는 시 구 군별 큰 격차를 보였으나, 항생체처방룰은 차이를 보이지 않았다. 둘째, 의원 간 경쟁은 총진료비에 통계적으로 유의한 영향을 미쳤다. 셋째, 의원 간 경쟁은 항생제처방률에 통계적으로 유의한 영향을 미치지 않았다. 향후 연구에서 의료기관 경쟁정도가 진료행태에 미치는 다른 요인을 규명하기 위해 재진비율, 방문당 진료비 등에 대한 추가 연구가 필요하다.