• Journal of Power Electronics
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• v.13 no.2
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• pp.296-303
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• 2013

This paper proposes a high efficiency three-phase cascaded phase shifted H-bridge multi-level inverter without DC/DC converters for grid-tied multi string photovoltaic (PV) applications. The cascaded H-bridge topology is suitable for PV applications since each PV module can act as a separate DC source for each cascaded H-bridge module. The proposed phase shifted H-bridge multi-level topology offers advantages such as operation at a lower switching frequency and a lower current ripple when compared to conventional two level topologies. It is also shown that low ripple sinusoidal current waveforms are generated with a unity power factor. The control algorithm permits the independent control of each DC link voltage with a maximum power point for each string of PV modules. The use of the controller area network (CAN) communication protocol for H-bridge multi-level inverters, along with localized PWM generation and PV voltage regulation are implemented. It is also shown that the expansion and modularization capabilities of the H-bridge modules are improved since the individual inverter modules operate more independently. The proposed topology is implemented for a three phase 240kW multi-level PV power conditioning system (PCS) which has 40kW H-bridge modules. The experimental results show that the proposed topology has good performance.

• ETRI Journal
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• v.36 no.6
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• pp.924-930
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• 2014

This paper presents a $0.13{\mu}m$ CMOS 3-level envelope delta-sigma modulation (EDSM) RF signal generator, which synthesizes a 2.6 GHz-centered fully symmetrical 3-level EDSM signal for high-efficiency power amplifier architectures. It consists of an I-Q phase modulator, a Class B wideband buffer, an up-conversion mixer, a D2S, and a Class AB wideband drive amplifier. To preserve fast phase transition in the 3-state envelope level, the wideband buffer has an RLC load and the driver amplifier uses a second-order BPF as its load to provide enough bandwidth. To achieve an accurate 3-state envelope level in the up-mixer output, the LO bias level is optimized. The I-Q phase modulator adopts a modified quadrature passive mixer topology and mitigates the I-Q crosstalk problem using a 50% duty cycle in LO clocks. The fabricated chip provides an average output power of -1.5 dBm and an error vector magnitude (EVM) of 3.89% for 3GPP LTE 64 QAM input signals with a channel bandwidth of 10/20 MHz, as well as consuming 60 mW for both channels from a 1.2 V/2.5 V supply voltage.

• Journal of Electrical Engineering and Technology
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• v.2 no.3
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• pp.373-378
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• 2007

Soft switching was applied to the multi-level inverter to enhance the performance of the high-intensity discharge (HID) ballast used in vehicle headlights. The electrical properties were investigated and the available modeling of ballast in steady state was calculated using mathematical methods. The result was used in analyzing the power characteristics. The modeling was confirmed by the experiment.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.1
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• pp.42-49
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• 2006

In this research. the diesel cycle was thermodynamically interpreted to evaluate the possibility of high efficiency by converting diesel engines to the high expansion diesel cycle, and general cycle features were analyzed after comparing these two cycles. Based on these analyses. an experimental single cylinder a long stroke with high expansion-diesel engine. of which S/B ratio was more than 3, was manufactured. After evaluating the base engine through basic experiments, a diesel engine was converted into the high expansion diesel engine by establish VCR device and VVT system Accordingly, the high expansion diesel cycle can be implemented when the quantity of intake air is compensated by supercharge and the effective compression ratio is maintained at its initial level through the reduction of the clearance volume. In this case, heat efficiency increased by $5.0\%$ at the same expansion-compression ratio when the apparent compression ratio was 20 and the fuel cut off ratio was 2. As explained above, when the atkinson cycle was used for diesel cycle, heat efficiency was improved. In order to realize high expansion through retarding the intake value closing time, the engine needs to be equipped with variable valve timing equipment, variable compression ratio equipment and supercharged pressure equipment. Then a high expansion diesel cycle engine is realized.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.172-178
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• 2011

This paper presents an optimization procedure for high-efficiency design of a mixed-flow pump. Optimization techniques based on a weighted-average surrogate model are used to optimize a vane diffuser of a mixed-flow pump. Validation of the numerical results is performed through experimental data for head, power and efficiency. Three-level full factorial design is used to generate nine design points within the design space. Three-dimensional Reynoldsaveraged Navier-Stokes equations with the shear stress transport turbulence model are discretized by using finite volume approximation and solved on hexahedral grids to evaluate the efficiency as the objective function. In order to reduce pressure loss in the vane diffuser, two variables defining the straight vane length ratio and the diffusion area ratio are selected as design variables in the present optimization. As the results of the design optimization, the efficiency at the design flow coefficient is improved by 7.05% and the off-design efficiencies are also improved in comparison with the reference design.

• Korean Journal of Agricultural Science
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• v.33 no.2
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• pp.179-193
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• 2006

Technical efficiency of semiforcing watermelon growers is 0.8248 on average, and distributed between 0.6744 and 0.9268. The result showed that semiforcing watermelon growers had by 18% of technical inefficiency and could be assumed that increasing technical efficiency could induce watermelon production more increase. Consequently, if growers' technical efficiency were improved while other environments were constant, watermelon production could be increased. Following the results from the inefficiency effect model, all assumption coefficient such as growers age etc, are significant at 10% level. Estimate of dispersion parameter ${\gamma}$ is 0.89, which confirms those differences between practical output and frontier output were derived from the technical efficiencies among growers. Differences of production system between high and low level growers in production efficiency were showed at side altitude, ventilation and heat-retaining in section of facilities and automation, soil test and calcium application in section of environment management, transplant preparation and duration of pollination in section of crop management and shipment place, sorting degree and management record analysis in section of business management respectively. As a result of analyzing consulting data by using standard diagnosis table of watermelon cultivation under structure which cultivated on semi-forced watermelon growers, gap between high and low level growers was 7.0 points in facility automation section, 7.1 points in environment section, 8.8 points in crop management section and 13.6 points in business management section, respectively, which were the biggest one among them. In case of excluding information-related items from the evaluation index of business management section, changes of business achievement are to occur. Therefore, it is recommended for us to review the standard diagnostic table of watermelon cultivation under structure by dividing evaluation index of management section into management and information.

• The Journal of Asian Finance, Economics and Business
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• v.9 no.3
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• pp.355-364
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• 2022

The effect of technological innovation on the high-quality development of the producer services industry depends on whether or not technical innovation efficiency plays a key role. This study looks at the impact of technological innovation and financial technology (fintech) on the development of high-quality producer services in Fujian Province from 2010 to 2019. The efficiency of technological innovation is measured using Data Envelopment Analysis (DEA) and the Malmquist productivity index. The mean overall innovation efficiency score is 0.639, meaning that Fujian accounts for 36.1% of resource utilization inefficiencies and that there are significant differences in technological innovation efficiency between cities. The findings show that high-quality producer services industries benefited from innovation efficiency, but that the influence of technological innovation efficiency is insignificant. This demonstrates that financial innovation has not been able to completely enhance the development level of the producer services industry. This may be due to the unreasonable output structure of technological innovation and the low industrial transformation rate of technological achievements. This study advocates that the R&D fund allocation structure be optimized. That technological innovation can improve the high-quality development of the producer services industry is a consensus within the academic community.

• The Mathematical Education
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• v.41 no.2
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• pp.139-155
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• 2002

In this paper we represented the results of surveying on the present condition of mathematics education and the contents of the mathematics text books that are usually taught in Art High Schools interest in mathematics subjects and to achieve the higher level of mathematical abilities. We would like to raise their interest in mathematics and to improve the efficiency of teaching level on the basis of the 7th Mathematics Curriculum Revision. Some suggestions are of offered by considering the level of their mathematical abilities in Art High Schools and the present contents of the mathematical subjects from following views ⑴ the aspect of studying method ⑵ the aspect of revising contents of mathematics textbooks for them ⑶ the aspect of educational policies for Art High Schools

• Health Policy and Management
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• v.6 no.1
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• pp.191-210
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• 1996

This study purported to acquire information necessary to improve the operational efficiency of general hospitals. It tried to determine major indices which represent managerial performance of general hospitals and to identify the managerial characteristics of general hospital which affect the major financial indices. 201 hospitals which were subject to standardization audit by the Korean Hospital Association were investigated and 80 hospitals were finally chosen for this study. Their financial and managerial data during the period between January 1991 and December 1991 were collected. Considering financial indices in this study were the ration of net income to total asset, income growth rate, and quick ration. The results of study are summarized as followings. First. The ration of net income to total assets and quick ration were highly related to managerial characteristics of general hospitals. Therefore, the standardization of three financial indices should be needed to systematically check the operational efficiency of general hospitals. Second, the sample hospitals can be classified as four groups on the basis of their financial indices' level. 4 of those hospitals(5.0%) showed high level of performance in terms of three financial indices and 27 of them(33.7%) showed that they are highly related to only two financial indices. 34 hospitals(42.5%) showed they have high level of relationship with only one indices and 15 hospitals(18.8%) showed very weak performance level with three indices. In addition, there is no hospitals to show mid-range level of managerial performance in relation to all three financial indices. Third, there is no significant relationship between three financial indices and the managerial characteristics of hospitals such as the number of beds, type of operation, location of hospitals, and etc. However, in the case of hospitals which have high level of managerial performance, they have more specialists and medical support personnel in comparison to low performance hospitals. They also have high level of bed occupancy rate and average length of stay(ALOS). In conclusion, the study showed the standardization of 3 financial indices are necessary to systematically evaluate the managerial performance of general hospitals and provide more accurate operational information for each hospital. To do so, it is necessary to focus on management side of hospital such as the effective human resource management and quality enhancement of medical treatment.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.1120-1123
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• 2008

Efficient, color stable multi-EML WOLED have been fabricated using newly synthesized yellowish green dopant Ir(chpy)3 or Ir(mchpy)3. The devices have high external quantum efficiency of 11.7%, color rendering index of 87, variation of CIE coordinate of (0.02, 0.01) between 10 to 5000 cd/m2, and low roll-off in efficiency with increasing brightness.