• 한국태양에너지학회 논문집
• /
• 제26권3호
• /
• pp.71-78
• /
• 2006

Thermodynamic irreversibility analysis of an air-to-water heat pump system is analyzed in this study. This analysis shows the distribution of irreversibilities(true losses in thermodynamic sense) through the system components and informs us of a potential improvements with the irreversibility factor decreases. The results show that the largest irreversibilities occur in the motor-compressor unit. The remaining irreversibilities are distributed relatively uniformly through the other parts including utilization system. The increase of performance can be attained through either the improvement of adiabatic efficiency of motor-compressor unit(${\eta}_{mc}$) or the reduction of temperature difference(${\Delta}T$). With the decrease of utilization temperature($T_u$) COPH also increases but the exergetic efficiency decreases. The increase of COPH of about 0.05 can be accomplished with 1K decrease of ${\Delta}T$ or $T_u$.

• 한국통신학회논문지
• /
• 제16권9호
• /
• pp.819-827
• /
• 1991

국내 FM 방송채널을 기존의 200 KHz 간격으로 배치 했을 때와 100 KHz로 배치 했을 때, 송신출력, 지형굴곡계수, 송신 안테나 실효높이를 변수로 하여 효율 적인 방송망을 규정하고 채널을 배치하여 동일한 조건에서 스펙트럼의 이용효율을 산출·비교하였다. 그 결과 100 KHz 간격으로 채널을 배치하게 되면 200 KHz에 비해 사용가능한 채널 수는 두배로 늘어나고 스펙트럼의 이용효율은 최소 35.5%에서 최대 100%까지 증가시킬 수 있음을 알 수 있었다.

• Asia pacific journal of information systems
• /
• 제15권2호
• /
• pp.121-148
• /
• 2005

This study focuses on MRO e-Marketplace and attempts to research how companies select the structure of e-Marketplace governance and how it influences purchasing performance. Furthermore, a longitudinal study is conducted to analyze the dynamic relationship between variables in our research model. The research gives the following results. First, as the utilization level of e-Marketplace increases, the level of relational exchange between purchasing company and e-Marketplace increases. The increased utilization level enhances purchasing efficiency rather than reducing purchasing price. Secondly, as the level of relational exchange between purchasing companies and e-Marketplace increases, system integration increases, whereas supply externality decreases. Accordingly, system integration improves purchasing efficiency, whereas the low supply externality does not help lower purchasing price. Third, compared to the initial growth stage, the stable stage of e-Marketplace has the significantly increased level of relational exchange and purchasing efficiency through system integration, rather than the reduction of purchasing price by supply externality.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제10권5호
• /
• pp.1998-2014
• /
• 2016

In recent years, cloud computing services based on smart phones and other mobile terminals have been a rapid development. Cloud computing has the advantages of mass storage capacity and high-speed computing power, and it can meet the needs of different types of users, and under the background, mobile cloud computing (MCC) is now booming. In this paper, we have put forward a new classification-based virtual machine placement (CBVMP) algorithm for MCC, and it aims at improving the efficiency of virtual machine (VM) allocation and the disequilibrium utilization of underlying physical resources in large cloud data center. By simulation experiments based on CloudSim cloud platform, the experimental results show that the new algorithm can improve the efficiency of the VM placement and the utilization rate of underlying physical resources.

• Nuclear Engineering and Technology
• /
• 제55권7호
• /
• pp.2687-2696
• /
• 2023

The fuel operating ranges of fusion tokamak-based power plants are estimated using the improved engineering breakeven equation. The Lawson criterion equations are derived in the form of a triple product with a focus on engineering breakeven and the subbreakeven operating range. The relationship of fuel parameters to the power plant net efficiency is outlined. Analysis shows that the operating ranges of the suitable fuel parameters form a closed area, the size of which affects the net efficiency of the power plant. The obtained fuel operating ranges confirm the well-known fact that DT fuel is currently the only fusion fuel useable in tokamak-based fusion power plants. It is also shown that the energy utilization of pB fuel is possible in the subbreakeven operating range but is conditioned by the very high efficiency of the power plant equipment. For the utilization of DD, DHe3, and pB fuels, the required magnetic fields are indicatively estimated.

• 동력기계공학회지
• /
• 제20권6호
• /
• pp.87-92
• /
• 2016

This research dealt with performance characteristics of OTEC system applying an ejector and additional pump. Each system using five kinds of working fluids was analyzed, and primary parameters with respect to entrainment ratio were examined: Turbine gross power, evaporation capacity, pump work, efficiency and volume flow ratio. The primary results were as following. The efficiency of ejector-pump OTEC system was dependent on entrainment of the ejector. The degree of efficiency change was different from applied working fluid, and amount of pump work was turned out to be primary factor affected system efficiency. Meanwhile, optimized entrainment ratio was different from applied working fluid since their different vapor density. System efficiency at optimized entrainmet ratio of each working fluid was around 5%, showing minor difference each other.

• 디지털정책학회지
• /
• 제1권2호
• /
• pp.9-15
• /
• 2022

2011년, 세계경제포럼(The World Economic Forum)은 물-에너지-식량을 세계 3대 위험군에 포함했다. 물-에너지-식량은 국가의 발전 전략과 국민의 삶과 관계된다. 본 연구에서는 SBM-Malmquist 지수를 기반으로 중국의 2011-2020년 물-에너지-식량 종합 이용 효율성을 계산한다. 측정 결과를 살펴보면, 중국 전체 물-에너지-식량의 종합 이용은 효율성이 낮으나 상승세를 보였다. 전국적으로 물-에너지-식량 종합 이용 효율성은 뚜렷한 차별성이 존재하며 전반적으로 동부> 중부> 서부의 지리적 분포 구도를 보인다. 전국에 Beijing과 Shanghai만 진정한 유효에 이르고 기타 각 성의 투입과 산출 사이에는 모두 비효율 상태가 존재한다. 물-에너지-식량 종합 이용 효율성의 Malmquist 지수는 1.136으로 상승세를 보이며 기술효율과 기술진보를 통해 중국의 물-에너지-식량 종합 이용 효율성의 향상을 이끌고 있다. 하루빨리 물-에너지-식량 문제에 있어 전략적높이를 끌어올려 그 발전에 대한 정책적 지원을 해야 한다. 각 지역은 지역 간 조율기구를 설립해야 하며 각 성의 식량 생산량, 수자원 분포 등 문제에 따라 맞춤형 조치를 제정해 경제가 조방형 발전에서 녹색 발전으로 전환되도록 조속히 추진해야 한다.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제11권3호
• /
• pp.1492-1509
• /
• 2017

The wireless sensor network (WSN) is a key technology to support the Internet of things (IoT) paradigm. The efficiency of the MAC protocol in WSN is very important to take scalability with restricted wireless resources. The DESYNC-TDMA has an advantage of simple distributed slot allocation inspired by nature, but there is a critical disadvantage of split slots by firing message. The basic split slot model has less efficiency for continuous packet transmitting because of wasting of the slots less than the packet size. In this paper, we propose a firing offset adjustment scheme to improve the efficiency of slot utilizations, which can manage the slot assigned to each node as a single large block, called the single slot model. The performance analysis models for both the existing and the proposed schemes are also derived. Experimental results show that the proposed method provide better efficiency of slot utilization than the existing schemes without any loss of the nature of the desynchronization.

• Advances in Energy Research
• /
• 제5권3호
• /
• pp.207-217
• /
• 2017

Energy consumption in agriculture is responsible for greenhouse gas emission but it can be reduced after efficient utilization of energy inputs. Therefore, the present study aims for the estimation of energy efficiency and extent of greenhouse gas reduction after benchmarking of inefficient farms in off-season tomato in Punjab province of Pakistan. Primary data were collected from 70 farmers with simple random sampling. By using data envelopment analysis, the average value of technical, pure technical and scale efficiency was 0.80, 0.92 and 0.87, respectively while increasing, constant and decreasing return to scale was observed in 33, 26 and 11 farmers, respectively. Total input energy was reduced by $12,688.91MJ\;ha^{-1}$ (13.89%) if inefficient farms used the energy inputs according to recommendations or benchmarking. A major portion of energy saving comes from fertilizers (68.79%) followed by diesel (15.70%), chemicals (5.91%), machinery (4.37%) and water (4.00%). Total greenhouse gases reduction was $499.17kg\;CO_2\;eq.ha^{-1}$ (14.57%) as a result of improvement in energy efficiency or benchmarking of inefficient farms. Agricultural extension staff should visit the vegetable farms on regular basis and give necessary information about efficient utilization of energy inputs. The government should create awareness about the optimum use of input through seminars and pamphlets.

• 한국초지조사료학회지
• /
• 제16권3호
• /
• pp.183-189
• /
• 1996

The productivity and utilization of four different grasdlegume pastures for grazing management were examined. The pasture mixtures used in this study were orchardgrass + ladino clover (Tl), orchardgrass + alfalfa (T2), perennial ryegrass + alfalfa (T3), and orchardgrass (T4, without legumes) respectively. The pastures were mtationally grazed 7 times with growing cow which had an initial weight of ca 243kg. The gmwth of pasture plants, dry matter (DM) yield, DM distribution, daily DM production, and pasture utilization were investigated at the NLRI, in Suwon, from April to October in 1991 and 1992. The average plant height at each grazing was 32-33m. The average DM content was 17.8%, wil the lowest in TI (16.4%) and highest in T3 and T4 (18.4%). The annual DM production were 9,609 kg (T3), 9,420 kg (Tl), 9,402 kg (T2), and 9,194 kgha (T4) in that order, but no significant differences were found in forage yield between treatments. Most of forage DM was produced in spring season, particularly in May. The daily DM production was highest in May (81.9kg), and lowest in August (33.0kg/ha). The average efficiency of pasture utilization was about 79%, with the lowest in TI (77%), and highest level of utilization was observed in T4 (82%). In this experiment, production and utilization of each pastures were observed similarly. However, the forage nutritive value, botanical composition, and animal performance as affected by different pasture mixtures for suitable grazing management are needed to ascertain.