• 전자공학회논문지
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• 제49권12호
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• pp.45-55
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• 2012

센서 네트워크는 센서가 설치된 지역에서 감지된 데이터를 무선으로 전달하는 기술로서, 기존 방식과 달리 에너지 효율이 매우 중요한 성능요소이다. 이러한 특성에 따라 많은 WSN MAC 프로토콜에서는 Wakeup과 Sleep을 반복하여 수행하는 Duty Cycle 기법을 활용하고 있지만, 고정적인 Wakeup 구간의 설정에 따라 획일화된 에너지 성능과 수신 성공률로 인하여 성능이 제한적이다. 본 논문에서는 이러한 Duty Cycle 기반의 MAC 프로토콜을 개선하기 위하여, 채널 환경에 따라 동적으로 Wakeup 구간을 가변화시키는 기법을 제안한다. 제안하는 방식은 트래픽이 높은 환경에서 Wakeup 구간을 증가시켜 수신 성공률을 높이고, 트래픽이 낮은 환경에서 Wakeup 구간을 줄여 에너지 성능을 향상시켰다. 또한 본 논문에서는 제안하는 방식의 성능에 대한 효율적인 평가를 위하여 기존 동기식 및 비동기식 MAC의 결과와 제안방식을 적용한 MAC의 결과를 비교하고 이를 분석하였다.

• 정보처리학회논문지A
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• 제19A권3호
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• pp.121-128
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• 2012

본 논문은 다양한 해상도에서의 초음파 영상 처리를 위한 최적의 프로세싱 엘리먼트 구조를 제안한다. 이를 위해 본 논문에서는 각 프로세싱 엘리먼트(processing element, PE)당 처리되는 영상 데이터(data-per-processing element, DPE) 수를 변화시키는 실험을 통해 시스템의 성능(system performance), 에너지 효율(energy efficiency), 면적 효율(area efficiency)을 각각 측정하고, 측정된 결과를 바탕으로 최적의 매니코어 프로세서 구조를 선택하였다. 모의실험 결과, 에너지 효율은 $256{\times}256$, $768{\times}1,024$, $1,024{\times}1,280$ 해상도를 갖는 영상에서 PE 개수가 각각 1,024개, 4,096개, 16,384개일 때 가장 높았다. 또한 면적 효율은 $256{\times}256$ 해상도의 영상에서는 PE 개수가 256개, $768{\times}1,024$와 $1,024{\times}1,280$ 해상도의 영상에서는 4,096개에서 가장 높은 효율을 보였다.

• Journal of Forest and Environmental Science
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• 제31권1호
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• pp.1-6
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• 2015

Microwave assisted biodiesel production from crude Pongamia pinnata oil using homogeneous base catalyst (KOH) was unsuccessful because of considerable soap formation. Therefore, a two step process of biodiesel production from high free fatty acid (FFA) oil was investigated. In first step, crude P. pinnata oil was acid catalyzed using $H_2SO_4$ and acid value of oil was reduced to less than 4 mg KOH/g. Effect of sulfuric acid concentration, alcohol-oil molar ratio and microwave irradiation time on acid value of oil was studied. Result suggested that 1.5% $H_2SO_4$ (w/w), 6:1 methanol oil molar ratio and 3 min microwave irradiation time was sufficient to reduce the acid value of oil from 12 and 22 mg KOH/g to 2.9 and 3.9 mg/KOH/g, respectively. Oil obtained after pretreatment was subsequently used for microwave assisted alkali catalyzed transesterification. A higher biodiesel yield (99.0%) was achieved by adopting two step processes. Microwave energy efficiency during alkali catalyzed transesterification was also investigated. The results suggested a significant energy saving because of reduced reaction time under microwave heating.

• 한국인터넷방송통신학회논문지
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• 제14권5호
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• pp.67-72
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• 2014

본 논문에서는 협력 통신에 에너지 하베스팅 기법을 적용할 경우 발생되는 잡음을 최소화하고 성능을 개선시킬 수 있는 방안을 제안하였다. 제안된 기법은 에너지 하베스팅 노드에서 수집된 전력을 저장하고 저장된 전력을 바탕으로 중계기를 사용한다. 이때, 중계기에서는 복호 후 전송(Decode and Forward) 기법을 적용하여 잡음의 영향을 최소화하였고, 수신단에서는 최대비 결합(Maximal Ratio Combining) 기법을 적용하여 다이버시티 이득을 얻었다. 따라서 제안된 기법을 일반적인 네트워크 환경에 적용할 경우 중소형 중계기의 구동에 필요한 전력을 제거할 수 있으며, 전력의 수집으로 인해 단말기 및 네트워크의 효율성을 증가시킬 수 있다. 마지막으로, 제안한 프로토콜을 레일리 페이딩 환경에서 전력 수집 효율 및 비트오류율(Bit Error Rate), 아웃티지 확률(Outage Probability)을 통해 시스템의 성능을 평가한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.980-982
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• 2001

SRM has different characteristics according to their control methods. Therefore, A new magnetizing method with a low-frequency increasing the energy conversion ratio that is related to the efficiency of motor is proposed. As results, it improved the efficiency about 2(%) and decreased the noise level up to 5[dB]. And a torque ripple is also sufficiently reduced compared with that of the conventional switching angle magnetizing approach.

• 설비공학논문집
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• 제11권4호
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• pp.542-548
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• 1999

Instead of testing split air conditioners, an empirically based calculation procedure may be used to estimate the Energy Efficiency Ratio at ARI A test conditions. Typically, the system involving the indoor unit well sold and the given outdoor unit is called the matched system. All other systems involving a given outdoor unit and other indoor units are called the mixed systems. To estimate the EER(A) for the mixed systems, EER(A) for the matched system must be known, Generally, the EER(A) for the matched system is known. This procedure relies on independent measurements and calculations made on an outdoor unit in conjunction with a matched indoor and a mixed indoor coil. A heat pump simulation model was used to quantify the effects of individual system components on the system performance. The procedure is applicable to all air-conditioning units having rated cooling capacities less than 19,000W and charged with refrigerant 22.

• 설비공학논문집
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• 제13권1호
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• pp.66-71
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• 2001

In the air-conditioning industry, the refrigerant charging amount is one of the most important parameters affecting the energy efficiency ratio of heat pumps. An experimental study was performed on the characteristics of an inverter driven air-to-air heat pump system with a variation of compressor frequency and charging amount of refrigerant. The frequency was altered from 40Hz to 70Hz and the charging amount was changed from 1.6kg to 2.8kg in tests. The variation of performance was measured with switching of the expansion valve on each frequency and charging amount. All the tests were performed at the Korean Standard and test conditions of the air conditioners. As results, it was found that there existed the charging amount and the level of the suction gas superheat which provided the highest energy efficiency ratio at all the frequency bands.

• 한국수소및신에너지학회논문집
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• 제6권1호
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• pp.23-34
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• 1995

In order to realize the ultra lean burn, the method of hydrogen supplement in gasoline engine has been examined and analyzed. A small quantity of hydrogen gas was supplied and mixed with gasoline fuel in the intake manifold. As the results, lean limit was extended to fuel-air equivalence ratio 0.35 which normal combustion was impossible by gasoline fuel. The NO and CO were remarkably decreased, and thermal efficiency and torque were increased. It was also found that by considering cycle variation, emission characteristics, torque and thermal efficiency, suitable operate region of hydrogen supplemented gasoline engine was equivalence ratio 0.5.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.108.2-108.2
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• 2011

This presentation shows energy-efficiency of microwave-accelerated esterification of free fatty acid with a heterogeneous catalyst by net microwave power measurement. In the reaction condition of 5wt% sulfated zirconia and 1:20 molar ratio of oil to methanol at $60^{\circ}C$ and atmospheric pressure, more than 90% conversion of the esterification was achieved in 20 minutes by microwave heating, while it took about 130 minutes by conventional heating. Electric energy consumption for the microwave heating in this accelerated esterification was only 67% of estimated minimum heat energy demand because of significantly reduced reaction time.

• 한국수산과학회지
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• 제30권6호
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• pp.929-935
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• 1997

The total energy of fish movement and the maximum burst swimming speed were estimated and formulated in accordance with body length and water temperature for several species in fisheries by empirical methods and also by using published results. Under the assumption of swimming energy reserve of a fish at the initial rest state, the swimming endurance of fish with different body lengths, swimming speeds and angular velocity was calculated using the relevant equations under similar conditions in tank experiments as well as natural conditions in field. Relative swimming energy efficiency or the transition swimming speed between red and white muscle for energy consumption was represented as a trigonometric function of swimming speed ratio. Therefore, this model does closely approach the actual swimming abilities and their limits especially in relation to the fishing gear operation and allow for the greater vitality of the wild fish in the fields.