• Journal of Welding and Joining
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• 제18권1호
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• pp.83-90
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• 2000

It was attempted to improve seam-tracking performance by applying a new arc-sensing algorithm for FCAW(flux-cored arc welding) process in fillet joints. For this study the authors have introduced three different weight factors: $\circled1$ arc currents at the weaving end are more weighted, $\circled2$ arc currents are evenly weighted along the weaving, and $\circled3$ arc currents at the weaving center are more weighted. To evaluate the 3 factors the values of signal-to-noise(S/N) ratio has been measured. The values were obtained for various welding conditions with different gaps in horizontal and vertical fillet joints. The test results showed that the S/N ratio of the 1st case was highest which resulted in the best of seam tracking performance. In addition, the comparison between the seam tracking performance in horizontal fillet joints and that in vertical ones has been done, and the result showed that tracking performance in vertical joints was relatively better than that in horizontal joints.

• 조명전기설비학회논문지
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• 제26권6호
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• pp.16-28
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• 2012

This paper proposes a quasi Z-source converter(QZSC) with a diode-capacitor output filter to improve the output DC voltage boost ability. The proposed converter has the same quasi Z-source network topology compared with the conventional converter. But the proposed method is adopted a diode-capacitor filter as its output filter, since the conventional method is used an inductor-capacitor as its output filter. Under the condition of the same input-output DC voltage, the proposed method has more lower shoot-through duty ratio than the conventional method. Also, because the proposed converter has same voltage boost factor under lower shoot-through duty ratio compared with the conventional converter, the proposed converter can be operated with the lower capacitor voltage of Z-source network and the lower input current. To confirm the validity of the proposed method, PSIM simulation and a DSP based experiment were performed to acquire the output DC voltage 120[V] under the input DC voltage 80[V]. And the capacitor voltage and inductor current in Z-source network, the output voltage of each converter were compared and discussed.

• Journal of Welding and Joining
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• 제20권2호
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• pp.102-108
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• 2002

Resistance spot welding of aluminum alloys is based upon Joule heating of the components by passing a large current in a short duration. Since aluminum alloys have the potential to replace steels fur automobile body assemblies, it is important to study the process robustness of aluminum spot welding process. In order to evaluate the effects of process parameters on the weld quality, major process variables and abnormal process conditions were selected and analyzed. A newly developed two-stage, sliding-level experiment was adopted fur effective parameter design and analysis. Suitable ranges of welding current and button diameters were obtained through the experiment. The effects of the factors and their levels on the variation of acceptable welding current were considered in terms of main effects. From the results, it is concluded that any abnormal process condition decreases the suitable current range in the weld lobe curve. Pareto analysis of variance was also introduced to estimate the significant factors on the signal-to-noise (S/N) ratio. Among the six factors studied, fit-up condition is found to be the most significant factor influencing the SM ratio. Using a Pareto diagram, the optimal condition is determined and the SM ratio is significantly improved using the optimal condition.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.163-164
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• 2005

Round shape Bi2212/Ag is isotropic and can be fabricated Rutherford cable to transport high current. Bi2212/Ag round wires with various Ag ratio were fabricated using powder-in-tube process. Double stacked 385 (55\times$7) filamentary wire of various wire diameter was heat-treated at various melting temperature. Wires which have Ag ratio of 0.3 and 0.42 of Ag tube for monofilament show similar critical current density. As average filament diameter decreases from 33 to 16 \mu$m, critical current density of wires increase, and in case of 16 ${\mu}m$ and $T_m$ 890$^{\circ}C$, critical current density was 2,062 $A/mm^2$ at 4.2 K, 0 T.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표대회 논문집(III)
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• pp.668-673
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• 1998

The specimen of current study has the same type with the 3-span slabs of Burns et al used in the study by Mojtahedi/Gamble, which laid a ground for the revision of the ACI318-77 code to the ACI 318-83 code. But those specimens was failed prematurely before it reached the ultimate strength which the specimen had. The reason is that bonded reinforcements were cut off where there is no need for the flexural reinforcement. As results. the slabs failed ultimately where the reinforcements was cut off. Thus, the tendon stresses of failure may have been much smaller than the values which culd reach if the bonded reinforcements were extended beyond the theoretical cut off points. On the based on the fact mentioned above. the specimens which had the same conditions as the specimens of Burns et al were used in the current study, but in which the reinforcements were distributed in a sequence for the reinforcements not to be cut anywhere in the 3-span. As a results, it was known that the current ACI code, revised by the result of Mojtahedi/Gamble's study, overestimated the effect of span/depth ratio on the members with high span/depth ratio. Thus it was concluded that the effect of span/depth ratio on the ultimate stress of unbonded tendon regulated by the current ACI code must be reconsidered and reevaluated.

• 한국전기전자재료학회논문지
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• 제22권2호
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• pp.107-113
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• 2009

In order to improve air stability, we proposed a new active layer of an organic TFT by synthesizing P3HT/POSS conjugated polymer. P3HT/POSS OTFTs with the various P3HT/POSS volume ratios were fabricated and characterized. With the P3HT/POSS volume ratio of 1:1, we achieved the field-effect mobilities of ${\sim}1.19{\times}10^{-3}\;cm^2/v{\cdot}sec$ in the saturation region and the current on/off ratio of ${\sim}2.51{\times}10^2$. The resulting current on-off ratio was much higher than that of the P3HT-based OTFTs and resulted from the dramatic decrease of the off-current. Since the off-current can be reduced by preventing oxygen in atmosphere from doping the P3HT/POSS active layers, this new active layer shows its ability to avoid oxygen doping in atmosphere. Therefore, the improvement of the air stability can be achieved by employing the P3HT/POSS active layers.

• 한국정밀공학회지
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• 제12권5호
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• pp.98-107
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• 1995

The in-process detection of drill wear and breakage is one of the most importnat technical problems in unmaned machining system. In this paper, the monitoring system is developed to monitor abnormal drilling states such as drill breakage, drill wear and unstable cutting using motor current. Drill breakage is detected by level monitoring. Tool wear is classified by fuzzy pattern recognition. The key feature for classification of tool wear is the estimated flank wear which is calculated by the proposed flank wear model. The characteristic of the model is not sensitive to the variation of cutting conditions but is sensitive to drill wear state. Unstable cutting states due to the unsmooth chip disposal and the overload are monitored by the variance/mean ratio of spindle motor current. Variance/mean ratio also includes the information about the prediction of drill wear and drill breakage. The evaluation experiments have shown that the developed system works very well.

• 디지털융복합연구
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• 제14권10호
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• pp.107-117
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• 2016

본 연구는 유가증권시장의 제조업을 대상으로 재무정보의 효율성이 기업가치에 미치는 영향에 대해 정보가 반영되는 시기를 중심으로 검증하고자 하였다. 이를 위해 재무제표 공시를 기준으로 분석기간을 당해(t)년도, 재무제표 공시 전 90일, 차기년도(t+1)로 구분하였다. 실증분석에 사용된 재무변수는 수익성, 성장성, 안정성, 활동성 및 시장가치 비율이며 재무정보가 분석기간 동안의 주식수익률에 미치는 영향을 단계적 회귀분석(stepwise regression)을 이용해 검증하였다. 실증분석 결과, 성장성과 수익성에 관한 정보는 당기의 주식수익률에 반영되는데 비해 안정성과 활동성에 관한 정보는 차기의 주식수익률에 정보를 반영하고 있는 것으로 나타났다. 총자산증가율은 당기 및 차기의 주식수익률에 부(-)의 유의적인 영향을 주는 것으로 나타났으며, 이는 재무정보가 산출된 동기간에 정보가 반영될 뿐만 아니라 차기에도 지속적으로 정보를 반영하는 것으로 판단된다. 본 연구는 재무정보의 성격에 따라 기업가치에 반영되는 시기가 달라지는 것을 발견하였다.

• 보건행정학회지
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• 제12권2호
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• pp.43-75
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• 2002

This study focuses on the factors that make the financial structure of hospitals in Korea different, and on recommended courses of action that could be very helpful to hospitals in maintaining a sound financial structure. Data used in this study were collected from 132 hospitals with complete general data of present conditions as well as financial statements. They were chosen from the 174 hospitals that passed the standardization audit undertaken by the Korean Hospital Association from 1996 to 2000 for the purpose of accrediting training hospitals. The dependent variable in this study is financial structure. It consists of liabilities as against total assets (total liabilities to total assets, short-term liabilities to total assets, long-term liabilities to total assets, short-term borrowings to total assets, long-term borrowings to total assets). The independent variables are ownership type, hospital type, location, whether or not a representative is a director of the hospital, the possibility of changing a hospital director, bed size, period of establishment, asset structure, profitability, growth, tax shields, business risk, competition. The factors that appear to have the strongest impact on the liabilities to total assets of all the hospitals sampled are ownership type, hospital type, profitability, tax shields, and business risk. It was found that not-for-profit private hospitals and for-profit private hospitals have more liabilities than public hospitals, and tertiary medical institutions have less liabilities than the secondary general hospitals. Moreover, hospitals earning more at the expense of high business risk have a distinct tendency to lower liabilities. Concerning the current ratio, it was found that factors such as ownership type, hospital type, period of establishment, asset structure, and business risk are the more significant variables. The current ratio of public hospitals is higher than that of both not-for-profit private hospitals and for-profit private hospitals, and the current ratio of tertiary medical institutions is higher than that of general hospitals. As business risk is higher in hospitals compared to other businesses, the current ratio becomes higher; this is because it is assumed that for fear of bankruptcy, hospitals lessen liabilities to total assets. On the other hand, as hospitals become older, the fixed assets to total assets become lower. It is remarkable that in hospitals, the factors affecting liabilities to total assets have an opposite regression coefficient sign against factors affecting current ratio. It brings out the same results borne out by the old financial theories and researches, in which a lot of the liabilities of hospitals are considered as the cause of worsening liquidity. Therefore, it is very important for hospitals to maintain a sound financial structure in order to survive using the rational acquisition and maintenance of capital.

• 전력전자학회논문지
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• 제21권5호
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• pp.434-441
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• 2016

This paper deals with transformer turns ratio design with the consideration of loss minimization in isolated bidirectional DC-DC converter. Generally, the rms value of current, magnitude of current at switching instance, and duty ratio of a converter vary according to the turns ratio of an isolation transformer in the converter under the same voltages and output power level. Therefore, the transformer turns ratio has an effect on the total loss in a converter. The switching and conduction losses of IGBTs and MOSFETs consisting of dual-active bridge converter are analyzed, and iron and copper losses in an isolation transformer and inductor are calculated. Total losses are calculated and measured in cases of four different transformer turns ratios through simulation and experiment with 3-kW converter, and an optimum turns ratio that provides minimum losses is found. The usefulness of the proposed transformer turns ratio design approach is verified through simulation and experimental results.