• Journal of Korean Biological Nursing Science
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• v.17 no.2
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• pp.211-217
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• 2015

Purpose: The purpose of this study is to identify factors influencing the pregnancy rate among unexplained infertile couples who received treatments of assisted reproductive technology (ART) and intra-uterine inseminations (IUI). Methods: The medical records of 24,201 cases of unexplained infertility among a total of 31,684 intrauterine insemination treatment cases, (which benefited by 'National Medical-aid Program for ART in 2011') were used for this analysis. Results: Woman's age (OR=0.94), frequency of IUI (OR=0.86), and treatment type (OR=1.54) were significant factors on pregnancy rates in the logistic regression analysis. Conclusion: Factors, such as the age of the infertile woman, frequency of IUI, and treatment type used to induce ovulation were shown to positively influence pregnancy rate. However, the age of the spouse was not a significant variable. Infertile couples having unprotected sexual intercourse with unexplained infertility had priority. The results demonstrated that about 70% of infertile Korean couples had unexplained infertility. This was a higher rate of unexplained infertility than that of the clinical standard. Therefore, we should assess for causes through future studies. In addition, affective or emotional factors influencing unexplained infertility need to be researched further.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.5
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• pp.731-737
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• 2011

The purpose of this study is to examine Internet users' psychological anxiety about the possibility of personal information leakage. The investigator examined the difference of psychological anxiety focusing on the possibility of personal information leakage according to the use amount of Internet, the number of joined sites and the frequency of e-commerce transaction. Study findings show that women felt more psychological anxiety than men did. In addition, people who used Internet more frequently felt more psychological anxiety. However, the number of joined sites and the average frequency of e-commerce transaction in a month had no significant influence upon users' psychological anxiety about the possibility of personal information leakage.

• Steel and Composite Structures
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• v.23 no.6
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• pp.691-714
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• 2017

Rotating fluid induced vibration and instability of embedded piezoelectric nano-composite separators subjected to magnetic and electric fields is the main contribution of present work. The separator is modeled with cylindrical shell element and the structural damping effects are considered by Kelvin-Voigt model. Single-walled carbon nanotubes (SWCNTs) are used as reinforcement and effective material properties are obtained by mixture rule. The perturbation velocity potential in conjunction with the linearized Bernoulli formula is used for describing the rotating fluid motion. The orthotropic surrounding elastic medium is considered by spring, damper and shear constants. The governing equations are derived on the bases of classical shell theory (CST), first order shear deformation theory (FSDT) and sinusoidal shear deformation theory (SSDT). The nonlinear frequency and critical angular fluid velocity are calculated by differential quadrature method (DQM). The detailed parametric study is conducted, focusing on the combined effects of the external voltage, magnetic field, visco-Pasternak foundation, structural damping and volume percent of SWCNTs on the stability of structure. The numerical results are validated with other published works as well as comparing results obtained by three theories. Numerical results indicate that with increasing volume fraction of SWCNTs, the frequency and critical angular fluid velocity are increased.

• Journal of the Korean Society of Safety
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• v.18 no.4
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• pp.98-104
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• 2003

Various nondestructive evaluation (NDE) techniques have been studied to locate steel rebars of dowel, and to detect invisible damage such as voids and cracks inside concrete and debonding between rebars and concrete caused by corrosions and earthquakes. In this study, the aurhors developed 3-dimensional (3D) electromagnetic (EM) imaging technology to detect such damage and to identify exact location of steel rebars of dowel. The authors have developed sub-surface two-dimensional (2D) imaging technique using tomographic antenna array in previous works. In this study, extending the earlier analytical and experimental works on 2D image reconstruction, a 3D microwave imaging system using tomographic antenna array was developed, and multi-frequency technique was applied to improve quality of the reconstructed image and to reduce background noises. This paper presents the analytical expressions of numerical focusing procedures for 3D image reconstruction and numerical simulation to study the resolution of the system and the effectiveness of multi-frequency technique. Also, the design of 4?4 antenna array with switching devices is introduced as a preliminary study for the final design of whole array.

• Journal of Power Electronics
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• v.15 no.2
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• pp.544-554
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• 2015

This paper presents a steady-state operation analysis of full-bridge series-resonant inverters focusing on the distorted load current due to low-quality-factor resonant circuits in induction heating and other applications. The regions of operation based on the zero-voltage switching (ZVS) and non-zero-voltage switching (NON-ZVS) operations of the asymmetrical voltage-cancellation control technique are identified. The effects of a distorted load current under a wide range of output powers are also analyzed for achieving a precise ZVS operating region. An experimental study is performed with a 1kW prototype. Simulation and experimental studies have confirmed the validity of the proposed method. An efficiency comparison between the variable frequency method and the conventional fixed-frequency method is provided.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.2
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• pp.75-82
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• 2021

Fields of high-precision positioning applications are growing fast across the mass market worldwide. Accordingly, the industry is focusing on developing methods of applying State-Space Representation (SSR) corrections on low-cost GNSS receivers. Among SSR correction types, this paper analyzes Safe Position Augmentation for Real Time Navigation (SPARTN) messages being offered by the SAfe and Precise CORrection DAta (SAPCORDA) company and validates positioning algorithms based on them. The first part of this paper introduces the SPARTN format in detail. Then, procedures on how to apply Basic-Precision Atmosphere Correction (BPAC) and High-Precision Atmosphere Correction (HPAC) messages are described. BPAC and HPAC messages are used for correcting satellite clock errors, satellite orbit errors, satellite signal biases and also ionospheric and tropospheric delays. Accuracies of positioning algorithms utilizing SPARTN messages were validated with two types of positioning strategies: Code-PPP using GPS pseudorange measurements and PPP-RTK including carrier phase measurements. In these performance checkups, only single-frequency measurements have been used and integer ambiguities were estimated as float numbers instead of fixed integers. The result shows that, with BPAC and HPAC corrections, the horizontal accuracy is 46% and 63% higher, respectively, compared to that obtained without application of SPARTN corrections. Also, the average horizontal and vertical RMSE values with HPAC are 17 cm and 27 cm, respectively.

• Electronics and Telecommunications Trends
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• v.37 no.5
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• pp.11-21
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• 2022

GaN (Gallium-Nitride) is a promising candidate material in various radio frequency applications due to its inherent properties including wide bandgap, high carrier concentration, and high electron mobility/saturation velocity. Notably, AlGaN/GaN heterostructure field effect transistor exhibits high operating voltage and high power-density/power at high frequency. In next-generation radar systems, GaN power transistors and monolithic microwave integrated circuits (MMICs) are significant components of transmitting and receiving modules. In this paper, we introduce technological trends for C-/X-/Ku-band GaN MMICs including power amplifiers, low noise amplifiers and switch MMICs, focusing on the status of GaN MMIC fabrication technology and GaN foundry service. Additionally, we review the research for the localization of C-/X-/Ku-band GaN MMICs using in-house GaN transistor and MMIC fabrication technology. We also discuss the results of C-/X-/Ku-band GaN MMICs developed at Defense Materials and Components Convergence Research Department in ETRI.

• Human Ecology Research
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• v.59 no.2
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• pp.245-259
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• 2021

The purpose of this study was to analyze big data to identify the sub-dimensions of ethical consumption, as well as the consumption value associated with ethical consumption that changes over time. For this study, data were collected from Naver and Daum using the keyword 'ethical consumption' and frequency and matrix data were extracted through Textom, for the period January 1, 2016, to December 31, 2018. In addition, a two-way mode network analysis was conducted using the UCINET 6.0 program and visualized using the NetDraw function. The results of text mining show increasing keyword frequency year-on-year, indicating that interest in ethical consumption has grown. The sub-dimensions derived for 2014 and 2015 are fair trade, ethical consumption, eco-friendly products, and cooperatives and for 2016 are fair trade, ethical consumption, eco-friendly products and animal welfare. The results of deriving consumption value keywords were classified as emotional value, social value, functional value and conditional value. The influence of functional value was found to be growing over time. Through network analysis, the relationship between the sub-dimensions of ethical consumption and consumption values derived each year from 2014 to 2018 showed a significantly strong correlation between eco-friendly product consumption and emotional value, social value, functional value and conditional value.

• Journal of Information Technology Services
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• v.21 no.3
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• pp.89-103
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• 2022

The purpose of this study is to explore professors' perception of blended learning. For this purpose, the reflective journals written by 56 university professors was analyzed using the keyword network analysis method. The results of this study are as follows: First, as a result of keyword frequency analysis for the blended learning, the keywords showed the highest frequency in the order of (1) 'instructional design', 'student', 'instructional method', 'learning objective' in the area of learning, (2) 'importance', 'instruction', 'feeling', 'student' in the area of feeling, and (3) 'semester', 'plan', 'weekly', and 'instruction' in the area of action plan. Second, the results of analyzing the degree, closeness centrality, and betweenness centrality of network connection are as follows. (1) The keywords 'instruction', 'instructional method', 'instructional design', and 'learning objective' in the area of learning, (2) the keywords 'instruction', 'importance', and 'necessity' in the area of feeling, and (3) 'instruction', 'plan', and 'semester' in the area of action plan showed high values in degree, closeness centrality, and betweenness centrality. Based on the research results, implications for blended learning and professors' perception were discussed.

• Journal of Fashion Business
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• v.26 no.3
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• pp.138-154
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• 2022

The purpose of this study is to identify the characteristics of domestic American casual fashion trends using big data text mining analysis. 108,524 posts and 2,038,999 extracted keywords from Naver and Daum related to American casual fashion in the past 5 years were collected and refined by the Textom program, and frequency analysis, word cloud, N-gram, centrality analysis, and CONCOR analysis were performed. The frequency analysis, 'vintage', 'style', 'daily look', 'coordination', 'workwear', 'men's wear' appeared as the main keywords. The main nationality of the representative brands was Japanese, followed by American, Korean, and others. As a result of the CONCOR analysis, four clusters were derived: "general American casual trend", "vintage taste", "direct sales mania", and "American styling". This study results showed that Japanese American casual clothes are influenced by American casual clothes, and American casual fashion in Korea, which has been reinterpreted, is completed with various coordination and creative styles such as workwear, street, military, classic, etc., focusing on items and brands. Looks were worn and shared on social networks, and the existence of an active consumer group and market potential to obtain genuine products, ranging from second-hand transactions for limited edition vintages to individual transactions were also confirmed. The significance of this study is that it presented the characteristics of American casual fashion trends academically based on online text data that the public actually uses because it has been spread by the public.