• JSTS:Journal of Semiconductor Technology and Science
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• 제3권1호
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• pp.47-54
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• 2003

New efficiency enhancement techniques have been devised and implemented to InGaP/GaAs HBT MMIC power amplifiers for W-CDMA mobile terminals applications. Two different types of bias current control circuits that select the efficient quiescent currents in accordance with the required output power levels are proposed for overall power efficiency improvement. A dual chain power amplifier with single matching network composed of two different parallel-connected power amplifier is also introduced. With these efficiency enhancement techniques, the implemented MMIC power amplifiers presents power added efficiency (PAE) more than 14.8 % and adjacent channel leakage ratio(ACLR) lower than -39 dBc at 20 dBm output power and PAE more than 39.4% and ACLR lower than -33 dBc at 28 dBm output power. The average power usage efficiency of the power amplifier is improved by a factor of more than 1.415 with the bias current control circuits and even up to a factor of 3 with the dual chain power amplifier.

• 조명전기설비학회논문지
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• 제21권6호
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• pp.102-108
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• 2007

원유가의 급등과 더불어 에너지자원에 대한 관심이 크게 증가 되었는데, 다양한 에너지관련 분야 중에서 먼저 선행되어야 하는 것은 기존의 설비에서 사용하고 있는 에너지가 효과적으로 사용되고 있는가를 판단하는 것이며, 이를 에너지 효율의 산정이라고 한다. 따라서 본 논문에서는 에너지의 주요 수요처중 하나인 제지 생산 플랜트의 한 공정에서 전력에너지와 열에너지에 대한 에너지효율을 계산하였다. 이때 전력에너지는 운전 중인 전동기의 부하에 따른 효율을 중심으로, 열에너지는 공정에서 입출력되는 열량을 중심으로 계산하였다. 즉 운전 중인 생산설비의 한 공정의 전력과 열에너지에 대해 각각 에너지효율을 산정하였으며 일부 에너지절감에 대한 방안도 제시하였다.

• 한국지반공학회지:지반
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• 제11권1호
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• pp.51-62
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• 1995

1985년 국내에 처음으로 TBM(tunnel boring machine) 공법이 도입된 이래, 최근 그 사용이 급격히 증가하여 전세계 TBM 보유율의 27%를 차지하게 되었으며 상당한 시공실적도 가지게 되었다. 그러나 TBM 공법에 의한 많은 시공실적에도 불구하고 TBM의 굴착효율을 증진시키기 위한 연구는 미흡한 편이다. TBM 공법의 굴착효율에 영향을 미치는 인자로는 기계적 요인, 지반공학적 요인과 현장운영 상의 요인을 들 수가 있다. 이때까지의 굴착효율을 높이기 위한 연구는 주로 기계적 요인의 개선방안에 대해서 중점적으로 다루이져 왔지만 지반공학적 요인도 매우 중요하며 암반이 갖고 있는 물리적 특성에 따라서 사전에 TBM 공법의 적용여부를 판단할 수 있으며, 또한 현장 암반조건에 적합한 TBM 종류를 선택할 수도 있다. 본 논문의 목적은 실제 TBM 공법 적용 현장에서 얻어진 암반에 대한 자료와 제반 TBM 굴착작업과의 관계를 분석하고, 암반조건에 따른 TBM 굴착효과를 구명하고자 하였다.

• 동아시아식생활학회지
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• 제23권6호
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• pp.862-870
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• 2013

This study examines the effect of communication type of food service employees on the self-efficiency and organizational commitment. To accomplish the purpose of the study, a survey was conducted to employees of food service companies located in Seoul, from August 5, 2013 to August 25, 2013 as a method of empirical study. The results of this study was analyzed using the SPSS WIN 12.0 and statistical reliability analysis, factor analysis, frequency analysis, correlation analysis and multiple regression analysis were conducted for hypothesis verification. The analysis results of this study are as follows. First, the R-square of regression result for 'communication type will have a positive effect on self-efficiency' was .220. Also, it was found that factors of consideration (Beta=.286, t=5.622), instruction (Beta=.303, t=5.970) and business (Beta=.214, t=4.217) had positive effects on self-efficiency. Values for factors of consideration and instruction were higher than business. Second, the R-square of regression result for 'communication type will have a positive effect on organizational commitment' was .429. Also, it was found that factors of consideration (Beta=.453, t=10.428), instruction (Beta=.380, t=8.749) and business (Beta=.282, t=6.477) had positive effects on organizational commitment. Values for factors of instruction and business were high but value of consideration factor turned out the highest. Third, the R-square of regression result for 'self-efficiency will have a positive effect on organizational commitment' was .334. Also, it was found that out of the factors of positivity (Beta=.369, t=8.423), confidence (Beta=.415, t=8.833) and negativity (Beta=-.072, t=-1.536), positivity and confidence had positive effects on organization commitment, and only positivity and confidence showed high values in organization commitment. Upon analyzing the effect of factors of self-efficiency (positivity, confidence, negativity) on organizational commitment, it was found that positivity and confidence showed high relevance but the negativity factor did not have any correlation.

• 수산경영론집
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• 제45권1호
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• pp.63-77
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• 2014

This study is to estimate the recent changes in total factor productivity of 15 Korean adjacent water fisheries based on Malmquist productivity indices. The study adopted both input and output oriented productivity measures utilizing a hyperbola distance function. In addition to this point, the study also calculated the 95% confidence interval for the various components of the productivities in order to access the statistical significance of estimates using 2000 times of re-sampling process through the smoothed bootstraping. The results of the study showed us that there was 18% reduction in the overall total factor productivity during the study period from 2007 to 2011, which turned out to be 5% of annual decrease in productivity. The study found that the main reason of this decrease in total productivity is about 22% downward shift of a fisheries production function due to recent conditions of a devastated fishing ground. When we evaluated the statistical significance of changes in technical efficiency combining both pure technical and scale efficiency based on the 95% confidence intervals, we could not find any evidence of changes in those components of total factor productivity. When we accessed the productivity of the each of 15 adjacent water fisheries methods, only the large danish seine fisheries showed us about 7% increase in productivity. Even though the large trawling and the large tow-boat trawling revealed no changes in productivity, all of the other 12 fisheries suffered the decreases in productivities.

• 한국산학기술학회논문지
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• 제12권6호
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• pp.2735-2738
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• 2011

본 실리콘 태양전지 셀을 제작하는데 있어서, 기판 표면에서의 광 흡수를 증가시키기 위한 texturing은 KOH+IPA+DI $H_2O$를 혼합한 에칭용액의 온도를 80도로 유지하면서 1~40분 동안 에칭시간을 각각 다르게 하고 태양전지 시료를 제작하였다. 셀의 특성분석은 SEM과 I-V 특성곡선을 이용하였으며, 실리콘 태양전지 셀의 효율과 texturing에 의한 표면 거칠기 사이의 상관성을 조사한 결과, Texturing이 표면 전체적으로 고르게 이루어진 샘플에서 효율이 높게 나타났다. 에칭이 과도하게 일어난 샘플에서는 효율이 오히려 감소하였다.

• 한국기계가공학회지
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• 제16권1호
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• pp.70-76
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• 2017

The pollution problem of fossil energy sources has caused the development of green energy harvesting systems. Piezoelectric energy harvesting technology has been developed under those external environmental factors. A piezoelectric energy harvester can be defined as a device which transforms mechanical vibration or impact energy into electrical energy. Most researches have focused on bender structures. However, these have a limitation on energy efficiency because of the small effective electromechanical coupling factor, around 10%. Therefore, we should look for a new design for energy harvesting. A cymbal energy harvester can be a good candidate for the high-power energy harvester because it uses a high amplification mechanism using endcaps while keeping a higher electromechanical coupling factor. In this research, we focused on energy efficiency improvements of the cymbal energy harvester by changing the polarization direction, because the electromechanical coupling factor of the k33 mode and the k15 mode is larger than that of the k31 mode. Theoretically, we checked the cymbal harvester with radial polarization and it could obtain 6 times larger energy than that with the k31 direction polarization. Furthermore, we verified the theoretical expectation using the finite element method program. Consequently, we could expect a more efficient cymbal harvester with the radial polarization by comparing two polarization directions.

• Current Photovoltaic Research
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• 제6권1호
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• pp.27-30
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• 2018

The dependency of the electrical characteristics of silicon solar-cells on the depth of damaged layer induced by wire-sawing process was investigated. To compare cell efficiency with residual sawing damage, silicon solar-cells were fabricated by using as-sawn wafers having different depth of saw damage without any damaged etching process. The damaged layer induced by wire-sawing process in silicon bulk intensely influenced the value of fill factor on solar cells, degrading fill factor to 57.20%. In addition, the photovoltaic characteristics of solar cells applying texturing process shows that although the initial depth of saw-damage induced by wire-sawing process was different, the value of short-circuit current, fill-factor, and power-conversion-efficiency have an almost same, showing ~17.4% of cell efficiency. It indicated that the degradation of solar-cell efficiency induced by wire-sawing process could be prevented by eliminating all damaged layer through sufficient pyramid-surface texturing process.

• Geomechanics and Engineering
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• 제10권5호
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• pp.617-633
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• 2016

A numerical study has been conducted to examine the improvement achieved in the ultimate pullout capacity of horizontal circular anchor plates embedded in undrained clay, by constructing granular columns of varying diameter over the anchor plates. The analysis has been carried out by using lower bound theorem of limit analysis and finite elements in combination with linear programming. The improvement in uplifting capacity of anchor plate is expressed in terms of an efficiency factor (${\xi}$). The efficiency factor (${\xi}$) has been defined as the ratio of ultimate vertical pullout capacity of anchor plate having diameter D embedded in soft clay reinforced by granular column to the vertical pullout capacity of the anchor plate with same diameter D embedded in soft clay only. The variation of efficiency factor (${\xi}$) for different embedment ratios and different diameter of granular column has been studied considering a wide range of softness of clay and different value of soil internal friction angle (${\phi}$) of the granular material. It is observed that ${\xi}$ increases with an increase in diameter of the granular column ($D_t$) and increase in friction angle of granular material. Also, the effectiveness of the usage of granular column increases with decrease in cohesion of the clay.

• 전력전자학회논문지
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• 제27권2호
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• pp.85-91
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• 2022

This study proposes a high efficiency bridgeless Power Factor Correction (PFC) converter with improved common mode noise characteristics. Conventional PFC has limitations due to low efficiency and enlarged heat sink from considerable conduction loss of bridge diode. By applying a Common Mode (CM) coupled inductor, the proposed bridgeless PFC converter generates less conduction loss as only a small magnetizing current of the CM coupled inductor flows through the input diode, thereby reducing or removing heat sink. The input diode is alternately conducted every half cycle of 60 Hz AC input voltage while a negative node of AC input voltage is always connected to the ground, thus improving common mode noise characteristics. With the aim to improve switching loss and reverse recovery of output diode, the proposed circuit employs Critical Conduction Mode (CrM) operation and it features a simple Zero Current Detection (ZCD) circuit for the CrM. In addition, the input current sensing is possible with the shunt resistor instead of the expensive current sensor. Experimental results through 480 W prototype are presented to verify the validity of the proposed circuit.