• Journal of Mechanical Science and Technology
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• v.20 no.7
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• pp.1077-1088
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• 2006

This paper describes a numerical investigation on the performance deteriorations of a low speed, single-stage axial turbine due to use of rough blades. Numerical calculations have been carried out with a commercial CFD code, CFX-Tascflow, by using a modified wall function to implement rough surfaces on the stator vane and rotor blade. To assess the stage performance variations corresponding to 5 equivalent sand-grain roughness heights from a transition ally rough regime to a fully rough regime, stage work coefficient and total to static efficiency were chosen. Numerical results showed that both work coefficient and stage efficiency reduced as roughness height increased. Higher surface roughness induced higher blade loading both on the stator and rotor which in turn resulted in higher deviation angles and corresponding work coefficient reductions. Although, deviation angle changes were small, a simple sensitivity analysis suggested that their contributions on work coefficient reductions were substantial. Higher profile loss coefficients were predicted by higher roughness heights, especially on the suction surface of the stator and rotor. Furthermore sensitivity analysis similar to the above, suggested that additional profile loss generations due to roughness were accountable for efficiency reductions.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.171-176
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• 2008

As one way of design optimization of two-stage two-cylinder rotary compressor used for R410A heat pump application, displacement volume ratio, being defined by the ratio of the second stage cylinder volume to that of the first stage, has been varied and its effect on the compressor performance has been investigated by a computer simulation program. For simplicity, only the cylinder height of the second stage was varied to change the volume ratio. With increasing the volume ratio in the range of VR=$0.55{\sim}0.9$, volumetric efficiency increased monotonically, but adiabatic efficiency showed a maximum at around VR=0.6. Mechanical efficiency was little influenced by the volumetric ratio. As a consequence, maximum improvement of the compressor performance was found at around VR=0.7. Compared to a one-stage two-cylinder rotary compressor with about the same cooling capacity, COP improvement was about 6.96%.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.422-427
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• 1999

This is the basic study on the evaluation of seismic performance for existing railway bridges. This study presents all evaluation items and a progressive method of seismic performance for existing railway bridges. In the evaluation of seismic performance, a two-stage is used. Firstly, according to the seismic performance evaluation categories, preliminary screening of bridges is recommended. And using tile seismic rating system, seismic rank of bridges is calculated. Secondly, for the selected bridges in the first stage, detailed evaluation is recommended.

• Journal of Power Electronics
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• v.7 no.1
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• pp.44-54
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• 2007

Ac-dc power conversion can either be done with two separate converter stages or with a single converter stage. Two-stage ac-dc converters, however, can be costly and complex, while the performance of single-stage converters is compromised due to a reduced number of components. Several researchers have therefore proposed adding some sort of auxiliary circuit consisting of a second switch and some passive elements to single-stage converters to improve their performance. Although these modified single-stage converters may have two converters, they are not two-stage converters as they do not have two separate and independently controlled converters that are always operating to convert power from one form to another. In this paper, the operation of ac-dc single-stage converters is first reviewed and their strengths and weaknesses are noted. The operation of several modified single-stage converters, including one proposed by the authors, is then discussed, and the paper concludes by presenting experimental results that confirm the feasibility of the proposed converter.

• Journal of Korean Elementary Science Education
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• v.21 no.2
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• pp.227-239
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• 2002

The purpose of this study was to improve the practice of performance assessment in elementary science education and to support it according to the levels teachers' concerns. So this study was conducted by applying CBAM which is based on teachers' concern, which was designed for the investigation of the elementary science teachers' concern, their performance level, intellectual understanding, status of performance. and stage oi awareness and the connections between these factors. The study involved 311 elementary school teachers in the city of Seoul. The result of this study was as follows: First, the stage of teachers’ concerns performance assessment in science marked 49.5％, indicating that about half of the teachers was staying on the informative stage which could be generally occurring in the beginning of performance the curriculum innovation. The level of performance marked 33.8%, which was regarded as the stage of elaboration. For the category of intellectual understanding, most of the teachers didn’t fully understood the performance assessment. Regarding the status performance, 90.4％ of the teachers were implementing the assessment at the state of knowing the purpose of it. However. 40.5% of the teachers didn't fully understand the specific characteristics of the assessment. Also, the results of analyzing the teachers’ awareness on science performance assessment indicated that they have slightly positive positions. Secondly, the result of analyzing the stages of concerns for the assessment, based on the elementary school teachers' personal background, levels of implementation, and their intellectual understanding showed that the concerns were significantly different with the categories of their workplaces(p<.05). Finally, the result of analyzing the relationship among the concerns for the science performance assessment, levels of implementation and intellectual understanding indicated that there were significant differences in levels of implementation with the degree of intellectual understanding (p<.001).

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.2
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• pp.25-32
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• 1994

The characteristics of the R-22 two-stage compression refrigeration systems were investigated. The apparatus consisted of 0.5HP and 1HP hermetic reciprocating compressors for the high and low stage sides respectively, a condenser, an evaporator, a heat exchanger, four expansion valves, and two intercoolers. The experiments covered a range of refrigerant flow rates from 24 to 84kg/h, and the inlet temperature of cooling water in the condenser and heat source water in the evaporator ranged from 20 to 30$^.\circ}C$The results Showed that the refrigerant flow rate had greater effect on the refrigerating capacities, the compression efficiency and the coefficient of performance of two-stage compression systems than the inlet temperature of heat source water. And all these values were decreased with increasing inlet temperatures of the cooling water. The pressure drops in the evaporator of two-stage compression systems were decreased in proportion to the increase in the inlet temperature of the heat source and cooling water, but it was increased by the refrigerant flow rate.

• Communications for Statistical Applications and Methods
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• v.28 no.5
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• pp.411-424
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• 2021

Inference following two-stage adaptive designs (also known as two-stage randomization designs) with survival endpoints usually focuses on estimating and comparing survival distributions for the different treatment strategies. The aim is to identify the treatment strategy(ies) that leads to better survival of the patients. The objectives of this study were to assess the performance three commonly cited methods for estimating survival distributions in two-stage randomization designs. We review three non-parametric methods for estimating survival distributions in two-stage adaptive designs and compare their performance using simulation studies. The simulation studies show that the method based on the marginal mean model is badly affected by high censoring rates and response rate. The other two methods which are natural extensions of the Nelson-Aalen estimator and the Kaplan-Meier estimator have similar performance. These two methods yield survival estimates which have less bias and more precise than the marginal mean model even in cases of small sample sizes. The weighted versions of the Nelson-Aalen and the Kaplan-Meier estimators are less affected by high censoring rates and low response rates. The bias of the method based on the marginal mean model increases rapidly with increase in censoring rate compared to the other two methods. We apply the three methods to a leukemia clinical trial dataset and also compare the results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1B
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• pp.24-33
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• 2002

The cell search scheme for W-CDMA consists of the following three stages: slot synchronization(1st stage), group identification and frame boundary detection(2nd stage), and long code identification(3rd stage). The performance of the cell search when a mobile station is switched on, which is referred to as initial cell search, is decreased by the initial frequency and timing error. In this paper, we propose the pipeline structured initial cell search scheme using time trackers to compensate for the impact of the initial timing error in the stage 2 and stage 3. The simulation results show that the performance of the proposed scheme is maximal 1.5dB better than that of the conventional one when the initial timing error is near ${\pm}T_c$/2.

• The Research Journal of the Costume Culture
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• v.19 no.1
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• pp.83-95
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• 2011

Today, a variety performance premiered in Korea, works of art as an advanced production planning and production system is becoming. Accordingly, the field of stage costume also increased collaboration with foreign producers and production systems and the advancement of the stage costume are required are becoming. The opening performance of the 30th anniversary of the Seoul Theater Festival was selected as Towol Theater Theater in 2009, April 16 to 26 of Picasso's women's costume is the study of production systems. This work directing and stage design by inviting domestic producers from foreign fields, and co-authored the work in the field of stage costumes in collaboration with foreign producers that are worth study and research work. In this study, this work has a practical study of costumes throughout the production system, an advanced stage costumes to contribute to the development of the field. The research methodology book data, collected papers, Internet resources through research and theoretical studies play 'Picasso's women's stage production of the award total to an empirical study was undertaken. The results of this study are as follows. First, the costume director for making a scholarly grasp of the direction of the investigation is ongoing throughout the process of creating the costumes. Second, foreign producers and co-author of the stage when the award, if other than purely domestic producers and create costumes to build production systems. Third, foreign producers and co-costume design and costume making coherent explanation for the processing of the list(Costume Breakdown List) are developed. Fourth, the actual performance over the director's intention to visualize the presentation was good enough, and the idea of the costume crew was taken to the director's idea of directing a play that reflected the will has a big meaning.

• Aerospace Engineering and Technology
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• v.7 no.2
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• pp.151-156
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• 2008

Numerical analyses of two-stage turbopump turbines were conducted. One of the candidates for the 1st rotor was selected based on the result of the numerical investigation. Besides, the effects of the stator height on the turbine performance were studied. Finally, the performance of the entire two-stage turbine was predicted by numerical calculation. The result showed that the two-stage turbine produces more specific power than a one-stage turbine.