• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.9 no.6
• /
• pp.735-745
• /
• 1998

The method of moments has been widely used in the analysis of TM scattering problems. Recently, significant advances in the development of fast and efficient techniques for solving large problems have been reported. In such methods, iterative matrix solvers are preferred by virtue of their speed and low memory requirements. But for near resonant and strong multiple scattering problems, e.g., involving an aircraft engine inlet, a large number of iterations is required for convergence. In this paper, an efficient approximate inverse based preconditioner is used to reduce this number of iterations. By using the matrix partitioning method, the computational is used to reduce this number of iterations. By using the matrix partitioning method, the computational cost for obtaining the approximate inverse is reduced to O(N). We apply this preconditioner to an O(NlogN) algorithm, the multilevel fast multipole algorithm, for the aircraft engine inlet problem. The numerical results show the efficiency of this preconditioner.

• Korean Journal of Health Education and Promotion
• /
• v.33 no.1
• /
• pp.49-60
• /
• 2016

Objectives: This study aims to assess the relationships between individual, social and physical environmental correlates and physical activity (PA) and sedentary behavior (SB) in Korean children. Methods: A total of 1,134 elementary school students (512 boys, $5^{th}$ and $6^{th}$ graders) in Seoul participated in the survey including self-reported moderate and vigorous intensity PA and SB as well as demographic and psychological correlates. These data were matched them with school- and community-level environmental data from the government sources. The relationships of the multilevel correlates with PA and SE were analyzed using gender-specific hierarchical regression analysis. Results: Boys were more active than girls, but there was no gender difference in SB. Students with higher levels of self-efficacy were more likely to participate in moderate and vigorous PA. There were gender-specific associations between social and physical environments correlates and PA. Boys with higher levels of self-esteem and self-efficacy were less likely to involve in SB. Girls in the $6^{th}$ grade were more likely to involve in SB. Conclusions: In order to encourage PA and discourage SB in children, school- and community-level environmental support should be considered along with programs to improve self-efficacy and self-esteem.

• Journal of Korean Neurosurgical Society
• /
• v.59 no.4
• /
• pp.374-378
• /
• 2016

Objective : A modified surgical technique of posterior cervical foramintomy called posterior cervical inclinatory foraminotomy (PCIF) was introduced in previous preliminary article. PCIF allows better preservation of facet joint and capsule than conventional techniques. The authors conducted a study to investigate long-term outcomes of PCIF. Methods : We retrospectively reviewed demographic, radiologic, and clinical data from the patients who underwent PCIFs at our institution. Criteria included a minimum of 48 month follow-up and PCIFs for patients with radiculopathy from foraminal stenosis (C2-T1; single or multilevel) with persistent or recurrent root symptoms despite conservative treatment for more than 3 months. Patients who had undergone previous cervical operation were excluded. The visual analogue scale (VAS) score was used for clinical follow-up, and radiologic follow-up was performed to compare the changes of cervical sagittal alignment, focal angle and disc-space height of treated segment. Results : The PCIFs were performed between April 2007 and March 2011 on 46 patients (32 males and 14 females) with a total of 73 levels affected. The average duration of follow-up was 74.4 months. Improvements in radiculopathic pain were seen in 39 patients (84.7%), and VAS score decreased from $6.82{\pm}1.9$ to $2.19{\pm}1.9$. Posterior neck pain also improved in 25 patients (71.4%) among 35 patients, and VAS score decreased from $4.97{\pm}2.0$ to $2.71{\pm}1.9$. The mean disc-space heights of treated segment were $5.41{\pm}1.03mm$ preoperatively and decreased to $5.17{\pm}1.12mm$ postoperatively. No statistically significant changes in cervical sagittal alignment, focal angle were seen during the follow-up period (Cox proportional hazards analysis and Student t-test, p>0.05). Conclusion : The PCIF is highly effective in treating patients with cervical spondylotic radiculopathy, leading to long-lasting relief in pain. Long-term radiologic follow-up showed no significant spinal angular imbalance.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.2
• /
• pp.351-360
• /
• 2016

The purpose of this research is to suggest directions for urban planning and policies for the creation of a happy urban environment. To achieve this objective, this study extracted the urban environment characteristic elements that were expected to affect the levels of individual happiness and empirically analyzed the factors that affect the happiness levels of people. To determine the elements of the urban environment, this research analyzed the variables, urban environment characteristics, such as physical environment, natural environment, social environment, and individual characteristics. Regarding the physical environment of the city, a lower population density and a higher level of walking environment satisfaction showed a high level of individual happiness. In terms of the natural environment of the city, more spacious park areas and higher green area satisfaction showed a high level of individual happiness. Finally, regarding the social environment of the city, social trust was found to affect the happiness levels.

• Safety and Health at Work
• /
• v.11 no.2
• /
• pp.228-234
• /
• 2020

Background: The concept of social capital has its focus on cooperative relations in the workplace. This study investigates the association between social capital and sickness absence among workers in 41 work groups in the Danish dairy industry and examines the possible effects of an intervention on social capital in the workplace on sickness absence. Methods: A sample of 791 dairy workers working in 41 work groups that participated in an intervention study on social capital filled in a questionnaire on four subtypes of social capital, and social capital scores from individual participants were aggregated to the level of work groups. Sickness absence was measured at the level of work groups in company registers as the two-year average percentage of working time lost to sickness absence. Group-level associations between social capital and sickness absence were analyzed using multilevel linear regression analysis. Analyses were adjusted for age, gender, group size, and random effects at the workplace level. Results: We found statistically significant associations between social capital within work groups, social capital in relation to the immediate manager, and social capital toward the workplace as a whole on the one side and sickness absence on the other side. We found no support for any effects of the intervention on sickness absence. Conclusion: The work group level of social capital is associated with the work group level of sickness absence. However, the intervention to enhance group-level social capital had no effect on reducing sickness absence in the intervention group.

• Journal of the Institute of Electronics Engineers of Korea CI
• /
• v.45 no.5
• /
• pp.15-24
• /
• 2008

For high-dimensional classification tasks, such as face recognition, the number of samples is smaller than the dimensionality of the samples. In such cases, a problem encountered in linear discriminant analysis-based methods for dimension reduction is what is known as the small sample size (SSS) problem. Recently, to solve the SSS problem, a way of employing a dissimilarity-based classification(DBC) has been investigated. In DBC, an object is represented based on the dissimilarity measures among representatives extracted from training samples instead of the feature vector itself. In this paper, we propose a new method of optimizing DBCs using multi-level fusion strategies(MFS), in which fusion strategies are employed to represent features as well as to design classifiers. Our experimental results for benchmark face databases demonstrate that the proposed scheme achieves further improved classification accuracies.

• Journal of Korean Neurosurgical Society
• /
• v.30 no.2
• /
• pp.180-185
• /
• 2001

Objectives : We retrospectively studied the efficacy of anterior cervical discectomy and interbody fusion without plate fixation in degenerative cervical disease. Methods : Thirty two consecutive patients with degenerative cervical disease treated by decompression and interbody fusion(Smith-Robinson technique) without anterior cervical plating were studied for postoperative complication rate as well as the clinical and radiologic outcomes and were compared the result of ours with other reported series where the anterior cervical plating was used. Results : All cases were reviewed after average period of 13 months for the purpose of this study. There were 4 postoperative complications related to grafting. A solid fusion was obtained in all cases with single-level fusion(n=21) and 81.8 % of the cases with a two-level fusion(n=11). The overall fusion rate was 93.8 % and fusion rate per level fused was 95.3%. The clinical outcome of the patients was comparable with that in the literature, with one patient having a poor result. Comparing the result of this study with others of the anterior cervical plating, clinical outcome and fusion rate were not superior in plate fixation group in single-level fusion, but increased fusion rate and decreased graft-related complication rate were noted in multilevel fusion with plate fixation. However, the clinical outcome was not superior to noninstrumented fusion group of this study. Conclusion : These results demonstrate that anterior cervical discectomy and interbody fusion(Smith-Robinson technique) without instrumentation is safe and reliable method of single-level fusion in degenerative cervical disease. Plate fixation system doesn't seem necessary in single level fusion in degenerative cervical disease.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.15 no.8
• /
• pp.2900-2922
• /
• 2021

In this paper, the power spectral density(PSD) for Multilevel Minimum Shift Keyed signal with modulation index h = 1/2 (M-ary MSK) are derived using the mathematical method of the Markov Chain model. At first, according to an essential requirement of the phase continuity characteristics of MSK signals, a complete model of the whole process of signal generation is built. Then, the derivations for autocorrelation functions are carried out precisely. After that, we verified the correctness and accuracy of the theoretical derivation by comparing the derived results with numerical simulations using MATLAB. We also divided the spectrum into four components according to the derivation. By analyzing these figures in the graphic, each component determines the characteristics of the spectrum. It is vital for enhanced spectral characteristics. To more visually represent the energy concentration of the main flap and the roll-down speed of the side flap, the specific out-of-band power of M-ary MSK is given. OMLCD(Optimum Maximum Likelihood Coherent Detection) of M-ary MSK is adopted to compare the signal received with prepared in advance in a code element T to go for the best. And M-ary MSK BER(Bit Error Rate) is compared with the same ary PSK (Phase Shift Keying) with M=2,4,6,8. The results show the detection method could improve performance by increasing the length of L(memory inherent) in the phase continuity.

• 한국노년학
• /
• v.41 no.3
• /
• pp.397-420
• /
• 2021

The paper tried to determine relationships between volunteering and hypertension risks, symptom betterment, activity difficulty occurrences, and medicine treatment among middle-aged and older adults, with a prospective cohort study. Multilevel mixed-effects generalized linear models were used for the analysis of longitudinal panel data collected over 10 years from 2008 to 2018, using 5,867 cohort samples. The results showed that those who volunteered at least 200 hours per year were 3.4 times more lower than not-volunteering in risks of hypertension, those who volunteered yearly 50~99 hours were a lot more improved than not-volunteering in the symptom betterment, those who volunteered yearly at least 200 hours were 7.7 times lower than not-volunteering in activity difficulty occurrences, and those who volunteered yearly 50~99 hours were 2.5 times lower than not-volunteering in the occurrences of medicine treatment. These indicate that volunteering among middle-aged and older adults may have health benefits against incident hypertension. Finally the thesis discusses the study limitations, future directions of studies, and the practices implications.

• Applied Chemistry for Engineering
• /
• v.33 no.4
• /
• pp.402-407
• /
• 2022

Statistical design of experiments was used to optimize the MOF-5 synthesis process. A mixture design was employed to optimize precursor concentration. The optimal composition of three chemical materials, terephthalic acid, zinc acetate dihydrate, and N,N-dimethylformamide for MOF-5 synthesis was determined by extreme vertices design methods as follows; 1 mol : 2.7 mol : 40 mol. A multilevel factorial design was selected to screen the significance of synthesis reaction conditions such as temperature, time, and stirring speed. Statistical analysis results suggested excluding stirring speed from further investigation. Using a central composition design, the synthesis time and temperature were optimized. The quadratic model equation was derived from 13 synthesis experiments. The model predicted that MOF-5 synthesized at 119 ℃ for 10.4 h had the highest crystallinity.