• Journal of the Korean Operations Research and Management Science Society
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• v.39 no.4
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• pp.137-152
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• 2014

In this paper, I suggest several techniques to estimate covariance matrix and compare the performance of the global minimum variance portfolio (GMVP) in terms of out of sample mean standard deviation and return. As a result, the return differences among the GMVPs are insignificant. The mean standard deviation of the GMVP using historical covariance is sensitive to the estimation window and the number of assets in the portfolio. Among the model covariance, the GMVP using constant systematic risk ratio model or using short sale restriction shows the best performance. The performance difference between the GMVPs using historical covariance and model covariance becomes insignificant as the historical covariance is estimated with longer estimation window. Lastly, the implied volatilities from ELW prices do not lead to superior performance to the historical variance.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.2
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• pp.161-166
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• 2012

The estuarine Gobiidae $Tridentiger$ $trigonocephalus$, $Chasmichthys$ $dolichognathus$ and $Favonigobius$ $gymnauchen$ were exposed to various heavy metals. As a measure of acute toxicity, the 96h-$LC_{50}$ in the three species exposed to copper, lead, zinc and chromium was 740-990, 1,660-1,980, 6,180-8,490 and 8,830-11,296 ${\mu}gL^{-1}$, respectively. In order of toxicity, the heavy metals were ranked copper>lead>zinc>chromium. The Gobiidae $C.$ $dolichognathus$ was more sensitive to heavy metals than $T.$ $trigonocephalus$ and $F.$ $gymnauchen$.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.04a
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• pp.11-14
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• 2001

In this study, the relationship between metals (Cu, Cr, Cd, Zn. Pb, and Fe) 5 fractions and toxicity of soil samples from various contaminated sites in Korea were investigated. Metal toxicity of soils was tested using MetPLATE$^{TM}$ test kit, which is known as metal sensitive and organic insensitive. Significant amount of Fe was found in soils, and metal contents were in the order of Fe>Zn>Pb>Cu>Cr>Cd. Metal levels in organic fraction were rather high for all metals except Fe, and quite high percentages (35~79%) for residual fraction were observed for all metals. There were no significant relationships between the content of each metal fraction and toxicity which showed regression $R^2$in the range of 0.0003~0.414. However, correlation between toxicity and total metal contents showed regression coefficient $R^2$= 0.72. These results showed that the risk evaluation of metals in contaminated sites should be difficult to assess only by the contents of metal distribution because of the complexity of mixture of various metals.s.

• Journal of electromagnetic engineering and science
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• v.15 no.3
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• pp.167-172
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• 2015

Research results on possible effects caused by radiofrequency fields in children are limited because most of the studies published so far have focused on adults, rather than children. Mobile phone use is now widespread, even among younger children. If a biological risk due to mobile phone exposure is found, it might be greater in children because their bodies might be more sensitive to radiofrequency energy. The issue of a possible difference in sensitivity between adults and children begins with whether any difference exists physically in terms of electromagnetic absorption. This paper presents a review of recent publications on dosimetric comparisons between children and adults with respect to radiation from mobile phones. The issue of the health effects of mobile phone use is beyond the scope of the present review. Most of the dosimetry research on possible differences in power absorption between children and adults has been based on numerical modeling and analysis. The understanding of the results so far is presented and needed studies are described.

• Asian Pacific Journal of Cancer Prevention
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• v.16 no.15
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• pp.6177-6186
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• 2015

Sensitivity and specificity are the two most important indicators in selection of medical imaging devices for cancer screening. Breast images taken by conventional or digital mammography, ultrasound, MRI and optical mammography were collected from 2,143,852 patients. They were then studied and compared for sensitivity and specificity results. Optical mammography had the highest sensitivity (p<0.001 and p<0.006) except with MRI. Digital mammography had the highest specificity for breast cancer imaging. A comparison of specificity between digital mammography and optical mammography was significant (p<0.021). If two or more breast diagnostic imaging tests are requested the overall sensitivity and specificity will increase. In this literature review study patients at high-risk of breast cancer were studied beside normal or sensitive women. The image modality performance of each breast test was compared for each.

• Toxicological Research
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• v.24 no.4
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• pp.235-243
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• 2008

While in some instances, loss of diversity results from acute toxicity (e.g. major pollution incidents), in most cases it results from long-term sub-lethal effects that alter the relative competitive ability and fitness of certain organisms. In such cases the sub-lethal effects will cause a physiological response in the organism that ultimately leads to community level changes. Very sensitive tools are now available to study sub-lethal responses at the molecular level. However, relating such laboratory measurements to ecological effects represents a substantial challenge that can only be met by investigation at all scales (molecular, individual organism and community level) with an appropriate group of organisms. Among the various in vertebrates which can be used as model organisms in such a way, the soil nematode, Caenorhabditis elegans appear to be a promising biological model to diagnose environmental quality. This paper reviews the current status of multilevel biomarkers in environmental toxicology, and C. elegans as promising organisms for this approach.

• Knowledge Management Research
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• v.19 no.1
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• pp.19-39
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• 2018

With the development of information technology, social network services (SNS) such as Facebook and Twitter became popular and many users disclose their personal and sensitive information like private story, photographs and location information through posting and sharing. Despite the privacy concerns in SNSs, individuals continue to disclose their identity online. This phenomenon is called 'privacy paradox'. The purpose of this study is to examine the role of collective efficacy on self-disclosure in SNS context and to explain privacy paradox phenomenon. Drawing upon the communication privacy management theory, research model was developed and empirically tested with cross-sectional data from 306 individuals. Results revealed that collective efficacy has a direct positive effect on self-disclosure while privacy risk is negatively related to self-disclosure. However, privacy concern is not directly related to self-disclosure. The relationship between privacy concern and self-disclosure was moderated by collective efficacy.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.3
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• pp.127-133
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• 2006

This Paper describes a dual bands PD measurement method which has two different bandwidths. The one bandwidth is 0.5 - 2 GHz and the other is 1 - 2GHz. This method is used for GIS diagnosis. In the experiment, it shows that the ratios between two PD quantities in dual bands depend on the defect types and gas pressures. The variations of ratios in different pressures are more sensitive than ones in defect types. And These ratios increase with increasing SF6 gas pressures. As these ratios give us additive information of PD we can analyze the defect type as well as risk assessment for the GIS reliably. Therefore the above result shows that these ratios are one of parameters for diagnosing GIS.

• 한국정보컨버전스학회:학술대회논문집
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• 2008.06a
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• pp.59-62
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• 2008

When performing a project, the most important thing is building a result with planned quality within development period. Particularly, if the project is delayed or has no good quality in the case of the mobile game development project which is sensitive to the release time and quality, it is immediately connected to the failure of the project. Extreme Programming is a methodology that divides the development cycle into smaller units for reducing the risk factor of the project in which the development period is important. In this paper, we suggest the Expanded Extreme Programming for mobile game development environment in which the development period and quality are important

• Special Issue of the Society of Naval Architects of Korea
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• 2007.09a
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• pp.94-98
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• 2007

The latest development of the submarine oil field and the deep-sea explorer, FPSO is commonly proposed and used for offshore oil production. And because the fundamental requirement of FPSOs to remain moored at their position, they are unable to avoid severe weather and environment. FPSO normally operates head to the weather, and sensitive equipment located the exposed area will be influenced by green water damages, the damages may occur to both onboard equipment and topside structures with resulting risk to personnel. In this paper, the main focus considers the physical structures of green water protector in order to preserve topside structures, equipment and personnel from green water.