• Journal of the Korean Statistical Society
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• v.31 no.2
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• pp.143-152
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• 2002

In an effort to make a right choice among ratio estimation strategies and PPS sampling strategies, we conduct an empirical investigation of the relative performances of three ratio estimation strategies and four PPS estimation strategies using a set of 12 natural populations. The quality of a strategy is measured in the traditional way, namely with the consideration of efficiency, achieved coverage rate of the nominal 99% confidence interval and approach to normality (asymmetry).

• Corrosion Science and Technology
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• v.2 no.1
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• pp.1-6
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• 2003

A comprehensive coverage of corrosion in batteries is rendered difficult by the wide choice of materials, environments and physical features as obtained in practical settings. Understanding of the complex processes that occur in these electrochemical systems gets clearer as new theoretical approaches backed by sophisticated analytical and characterization techniques continue to provide valuable insights which aid in controlling/mitigating wasteful corrosion reactions which affect battery shelf-life, cycle life, rate capability and capacity. In the light of the above, I limit myself to a discussion on corrosion aspects in representative system such as conventional Leclanche, lead-acid battery and magnesium batteries, and advanced lithium systems.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.688-693
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• 2000

Recently great efforts and investment have been made in order to evaluate concrete durability by steel corrosion. But most of study is relatively or qualitatively estimated, therefore it has a great limitation in evaluating a remaining service life of concrete. In this research, steel corrosion rate was measured quantitatively by polarization resistance method and multi-regressed considering chloride, carbonation, coverage depth, relative humidity, W/C, and the use of deicing salts. And a half cell potential method was used at th same time for the purpose of comparing with polarization resistance method.

• Journal of the Korean Vacuum Society
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• v.1 no.1
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• pp.190-197
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• 1992

In this study we have investigated physical and electrical properties of high temperature oxide (HTO) thin film using dichlorosilane (DCS) gas. This film had low etch rate and excellent step coverage, and its characteristics of Si-O bond were similar to those of thermal oxide. I-V curves also showed similar electrical properties to those of thermally grown oxide (SiO2) while time dependent dielectric breakdown (TDDB) results revealed 1/4 value of thermal oxide. However, defect density was measured to be much lower value than that of thermal oxide.

• Journal of The Korean Society of Agricultural Engineers
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• v.53 no.6
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• pp.121-128
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• 2011

Long-term water treatment performance analysis was conducted for the constructed wetland treating agricultural tailwater. Studied wetland was established in 2001 and operated from June, 2002 to November, 2010. Wetland vegetation cover was shown over 90 % coverage after 2005. According to vegetation development, accumulation of sediment nutrient was observed; Organic Carbon, T-P and T-N. In addition, DO concentration and temperature was decreased in the constructed wetland output. An infiltration rate also significantly decreased due to compaction of wetland soil. A runoff coefficient was increased due to the low infiltration rate after 2005. A T-N, TSS and Chl.a removal rate was maintained constantly. However, the T-P removal rate was slightly decreased along to wetland operation because low DO concentration could increase elution of phosphorus from sediment. After constructing open water, the T-P removal rate was increased. This is because open water could accelerate the reaearation process. Consequently, over three years of vegetation development could be helpful for wetland performance. In addition, DO concentration is important factor to maintain the T-P treatment.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.12 no.5
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• pp.1-12
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• 2009

This research was initiated to investigate the revegetation characteristics under the seeding amount treatments of cool-season turfgrasses on the disturbed slope. 4 different seeding amounts of cool-season turfgrasses (0.0 $g/m^2$, 1.5 $g/m^2$, 3.0 $g/m^2$, 6.0 $g/m^2$) with the same seeding amounts of native woody (Rhus chinensis, Albizzia julibrissin) and herbaceous plants (Lotus corniculatus var. japonicus, Dianthus sinensis, Aster yomena) were treated with 3 replications on the experimental disturbed slope. Data such as soil hardness (mm), moisture content (%), surface coverage rate (%), the number of each germinating plant and plant height were analyzed. There were no statistic differences observed in the soil hardness and the soil moisture content while a significant difference was observed in the surface coverage rates. The surface coverage rates were higher in 3.0 $g/m^2$ and 6.0 $g/m^2$ plots compared to the rest two plots of cool-season turfgrasses. However, the emergence of native woody and herbaceous plants was relatively low in 3.0 $g/m^2$ and 6.0 $g/m^2$ plots of high seeding amounts of cool-season turfgrasses. This result indicated that high seeding amounts of cool-season turfgrasses could decrease the emergence of native woody and herbaceous plants. We concluded that 1.5 g~3.0 $g/m^2$ seeding amounts of cool-season turfgrasses was optimum level for the balanced emergence of cool-season turfgrasses, native woody and herbaceous plants in the viewpoint of the ecological disturbed slope revegetation.

• Korean Business Review
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• v.20 no.1
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• pp.145-168
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• 2007

Recommender system helps customers to find easily items and helps the e-biz companies to set easily their target customer by automated recommending process. Recommender systems are being adopted by several e-biz companies and from these systems, both of customers and companies take some benefits. This study sets several thresholds to the similarity weight, which indicates a degree of similarity of two customers' preference, to improve the performance of prediction accuracy. According to the threshold, the accuracy of prediction is being improved but some threshold setting shows the reduction of the prediction rate, which is the coverage. This coverage reduction has male effect on the prediction accuracy of customers, so more study on the prediction accuracy of recommender system and to maximize the coverage are needed.

• Journal of Preventive Medicine and Public Health
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• v.27 no.4 s.48
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• pp.807-814
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• 1994

This study is to find out changes in medical practice at a university hospital before and after covering intraocular lens (IOL) from the health insurance benefit. The coverage started on March 1, 1993 and a total of 596 cases who were discharged from July 1 to December 31, 1992 and 580 cases who were discharged from July 1 to December 31, 1993 were analyzed. Since the standard reimbursement scheme was changed from March 1, 1993, the charges for 1992 were transformed into 1993 scheme. Major findings are as follows: Average length of stay was statistically significantly decreased from 8.24 days in 1992 to 6.86 days in 1993. Charges except IOL has been statistically significantly decreased from 501,000 Won in 1992 to 444,000 Won in 1993. Charges for drugs and injection have been reduced. However, charge per day for them was not much different. This is due to decrease in length of stay. Charges for laboratory tests and radiologic examination were quite the same. Charges which are not covered by the insurance remained the same. The revenue of the hospital was reduced as expected. However, the hospital reduced the length of stay and increase the turnover rate In order to compensate the potential loss of revenue due to the difference of reimbursement between the out-of-pocket expense and the insurance coverage. By introducing the IOL benefit in the insurance, the insured pays less, hospital generates more revenue through shortening the hospital stay, and the total medical care cost becomes less nationwidely.

• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.162-165
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• 2017

In an effort to compensate the rising of the data throughput demand nowadays, there have been many research works to optimize the radio resource and increase the capacity of the network. At the present, small cell network, mmWave band and beamforming technology are leading the trend and becoming the core solutions of the fifth generation (5G) cellular networks. Since the propagation characteristics of radio wave in the mmWave band is quite different from the conventional bands, the communication systems which work in these bands have to be redesigned. In this paper, a 3D simulation model is discussed for cellular network at 60 GHz in outdoor environments. Coverage analysis and system performance is carried out for a small cell system in the typical urban environment including street canyon simulation scenario. In addition, the beamforming technique is considered to evaluate the throughput improvement. Simulation results show that the mmWave small cell systems is expected to be one of the major candidate technologies to satisfy the requirements of 5G in terms of data rate.

• Journal of Satellite, Information and Communications
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• v.2 no.2
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• pp.53-58
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• 2007

The Satellite Mobile Communication System holds several advantages, such as wide coverage that guarantees the communication in a huge area. It is suitable in the ocean and forest and especially in emergency situation. However, the licensed frequency is not always occupied within all coverage and all the time. The actual utilization rate is relatively low compared to other wireless communications such as cellular systems. There are a large amount of white spaces in its coverage. Therefore, it is necessary to consider introducing additional services such as data communication, in order to increase the spectrum utilization as well as the revenue of the Satellite service provider. In this paper, we first analyze the possibility to implement new services in the licensed band of satellite mobile phone by its provider. Then we address the most significant issue for the implementation of current service, which is how to accurately detect the satellite mobile terminals. Finally, we suggest two new possible solutions namely, eigenvalue detection based methods to find out the existence of transmitted signal from the satellite mobile terminals.