• 전기학회논문지
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• 제59권11호
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• pp.1996-2005
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• 2010

This paper proposes a new method for constant control of the output AC voltage of a voltage-fed three phase Z-source inverter (ZSI), in case of Z-network DC voltage variation or heavy change of load. The modulation index for the reference output AC voltage of ZSI can be calculated by the basic definition of ZSI, the input DC voltage and capacitor voltage of Z-network. And, the output AC voltage of ZSI is controlled by the modified space vector modulation (SVM) with the calculated modulation index. By the proposed method, the modulation index of output AC voltage is closely following in the reference modulation index. The validity of the proposed method is verified using PSIM simulation. In case which the input DC voltage of ZSI is heavily changed from 100[V] to 70[V] (or to 150[V]) and in case which load is changed from $30[\Omega]$ to $10[\Omega]$, we confirmed that the output AC voltage of ZSI is constantly controlled by the proposed method because the modulation index of ZSI is also simultaneously changed. Finally, FFT and %THD of the output voltage and current of ZSI by the proposed method are analyzed.

• Current Optics and Photonics
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• 제3권5호
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• pp.423-428
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• 2019

Visibility of road-surface markings is one of the critical issues that should be secured for self-driving cars as well as human drivers. Glass beads are taking on the role of retroreflectors, and therefore are considered a necessity in modern pavements. In this context, retroreflectance is sensitively dependent not only on the refractive index of glass beads but also on that of the surrounding medium. This implies that the optimum refractive index of glass beads immersed in water, i.e. under wet conditions, is different from that of glass beads surrounded by air, i.e. under dry conditions. A refractive index of approximately 1.9, which is known to maximize retroreflectance under dry conditions, actually exhibits much poorer retroreflectance under wet conditions. This suggests that glass beads with optimal refractive index for wet conditions need to be installed together with those for dry conditions. We propose a facile but practical model capable of calculating retroreflectance of glass beads surrounded by an arbitrary medium, here water in particular, and experimentally verify its capability of assessing the refractive index of commercial glass beads. Changes in retroreflectance according to the mixing ratio of glass beads with different refractive indices are also discussed, in an effort to propose the proper use of glass beads produced for dry and wet conditions.

• 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.

• 통상정보연구
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• 제12권4호
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• pp.171-192
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• 2010

In general, a stock index and its individual stocks are assumed to follow a random walk. A stock index is an important source of information and one that is seen by people everyday, regardless of their investment intentions. This paper examines the correlation between the KOSPI-the index that best reflects the Korean stock market and the macro - economic variables that have been found to influence the index by previous studies. The sample period considers the years after 2000 when the Korean stock market matured as restrictions on foreign investors were removed. For this purpose, a Vector Error Correction Model (VECM) and KOSPI equation with a general pacific approach were used. This paper aims at verifying the factors that determined the KOSPI after 2000 and at examining whether there was structural change in the investment environment. It also investigates changes in the factors determining the KOSPI's performance as a result of structural changes in the investment environment. The V AR (Vector Autoregressive) model including the nine variables was selected as a baseline model whose stability was tested using the unit root test. The results from the VECM and the structural changes in the investment environment can be summarized by the following Inner story points.

• 대한기계학회논문집A
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• 제26권1호
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• pp.74-82
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• 2002

In this paper the start fuel index was developed to estimate ride quality of a forklift truck during the start motion. Through the consultation with test drivers, definition of start feel was made, and three parameters were selected to describe the start motion. They are engagement shock in the forwarding direction, vertical and pitch vibration respectively. To find out the relation between the measured motion and the subjective fueling, both the subjective rating and the measurement of vehicle motions were performed simultaneously. The correlation analysis between the two kinds of results showed start fuel was expressed by the measured accelerations with accuracy and reliability, Use of the new index has advantages of not only evaluating start fuel only by the measured signals but providing the consistent results which are not affected by physical and mental state of a test driver. Usefulness of the new index was confirmed by verification test on four new forklift trucks of a same model, which showed the order of preference by the index was coincided that by subjective evaluation.

• 대한치위생과학회지
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• 제5권2호
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• pp.155-164
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• 2022

Background: By regulating the factors that contribute to oral diseases in a healthy way, oral health can be maintained and prevented. Methods: The general characteristics, PHP index, oral health behavior, and clinical periodontal index of each group were calculated by frequency analysis, and a cross-analysis (χ² test) was conducted to assess the homogeneity of the general characteristics, oral health behavior, and clinical periodontal index of the study subjects. An Oral bacteriological examination was performed by gargling with saliva. Results: The expert periodontal prevention group showed a decrease in the copy number of periodontal disease causative bacteria, and A. actinomycetemcomitans, P. gingivalis, T. forsythus, andT. denticolashowed a significant difference before and after treatment (p=0.021). In the periodontal treatment group, A. actinomycetemcomitans, P. gingivalis, T. forsythus, andT. denticolaall showed a decrease in copy number, but there was no significant difference. Conclusions: This study showed professional periodontal prevention management had some effect on periodontal bacterial reduction.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제13권1호
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• pp.19-30
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• 2013

Recently, the constrained index tracking problem, in which the task of trading a set of stocks is performed so as to closely follow an index value under some constraints, has often been considered as an important application domain for control theory. Because this problem can be conveniently viewed and formulated as an optimal decision-making problem in a highly uncertain and stochastic environment, approaches based on stochastic optimal control methods are particularly pertinent. Since stochastic optimal control problems cannot be solved exactly except in very simple cases, approximations are required in most practical problems to obtain good suboptimal policies. In this paper, we present a procedure for finding a suboptimal solution to the constrained index tracking problem based on approximate dynamic programming. Illustrative simulation results show that this procedure works well when applied to a set of real financial market data.

• 한국소음진동공학회논문집
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• 제15권8호
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• pp.939-944
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• 2005

In this paper, a sound quality index for the evaluation of the vehicle intake noise was developed through a correlation analysis of the objective measurement and the subjective evaluation. First, intake orifice noise was measured at the wide-open throttle sweep condition. And then, the acoustic transfer function between intake orifice noise and interior noise was measured. Simultaneously, subjective evaluation was carried out with a 10-scale score by 8 special engineers. The correlation analysis between the psychoacoustic parameters derived from the measurement and the subjective evaluation was performed. The most critical factor was determined and the corresponding sound quality index for intake noise was obtained from the multiple factor regression analysis method. Finally, the effectiveness of the proposed index was validated.

• 한국기계가공학회지
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• 제10권3호
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• pp.7-12
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• 2011

In the recent field of 5-axis machine tools, it is necessary to improve machining ability. The tilting index table is a key unit in order to manufacture some non-rotational and 3-dimensional parts by using conventional machining centers. In this study, the structural analysis of a tilting index table is carried out and the displacement and distribution of stress in the tilting index table is analysed to design the table safely. The modal analysis is performed in order to confirm the frequency response about the vibration having a large effect on the machine tools. The dynamic analysis is performed in order to confirm the rigidity, and the structural stability has been verified.

• Current Optics and Photonics
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• 제4권1호
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• pp.44-49
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• 2020

In this paper, a new method is presented to measure the refractive index of single plain glass or multilayered materials, based on a laser frequency-shifted confocal feedback microscope. Combining the laser frequency-shifted feedback technique and the confocal effect, the method can attain high axial-positioning accuracy, stability and sensitivity. Measurements of different samples are given, including N-BK7 glass, Silica plain glass, and a microfluidic chip with four layers. The results for N-BK7 glass and Silica plain glass show that the measurement uncertainty in the refractive index is better than 0.001. Meanwhile, the feasibility of this method for multilayered materials is tested. Compared to conventional methods, this system is more compact and has less difficulty in sample processing, and thus is promising for applications in the area of refractive-index measurement.