• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.32-40
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• 2002

The study of nonlinear gas transport in rarefied condition or associated with the microscale length of the geometry has emerged as an interesting topic in recent years. Along with the DSMC method, several fluid dynamic models that come under the general category of the moment method or the Chapman-Enskog method have been used for this type of problem. In the present study, on the basis of Eu's generalized hydrodynamics, computational models for diatomic gases are developed. The rotational nonequilibrium effect is included by introducing excess normal stress associated with the bulk viscosity of the gas. The new models are applied to study the one-dimensional shock structure and the multi-dimensional rarefied hypersonic flow about a blunt body. The results indicate that the bulk viscosity plays a considerable role in fundamental flow problems such as the shock structure and shear flow. An excellent agreement with experiment is observed for the inverse shock density thickness.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.5
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• pp.110-116
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• 2003

With the growth of aircraft performance and needs for light aircraft, the problems associated with hail impacts on aircraft during flights and grounding become and important issue. These hail encounters can cause severe damages to aircraft and result in major concerns in safety and cost. Since nearly all external components of the commercial and military aircraft-in particular, the nose section and the leading edge of the wing and tail-are subject to damages, much effort has been put into understanding of this problem. However, most of the previous studies have focused on the composite components and few results have been reported for the metallic components. In this paper, we study the ice impacts on the aluminum component with the finite element analysis method utilizing commercial non-linear dynamics solver LS-DYNA. The results are compared with the experimental data and a simple measure of the ice impact effects is proposed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.2
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• pp.118-124
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• 2015

The design of radar absorbing structures(RAS) is a discrete optimization problem and is usually processed by stochastic optimization methods. The calculation of radar cross section(RCS) should be decreased to improve the efficiency of designing RAS. In this paper, an efficient method using impedance matching is studied to design RAS for minimizing RCS. Input impedance of the minimal RCS for the specified wave incident conditions is obtained by interlocking physical optics(PO) and optimizations. Complex permittivity and thickness of RAS are designed to satisfy the calculated input impedance by a discrete optimization. The results reveal that the studied method attains the same results as stochastic optimization which have to conduct numerous RCS analysis. The efficiency of designing RAS can be enhanced by reducing the calculation of RCS.

• Journal of Broadcast Engineering
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• v.1 no.1
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• pp.7-13
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• 1996

MASF is a kind of temporal filter proposed for noise reduction and temporal band limitation. MASF uses motion vectors to extract temporal information in spatial domain. Therefore, inaccurate motion information causes some distortions in MASF operation. Currently, bilinear interpolation after BMA(Block Matching Algorithm) is used for the motion estimation sheme of MASF. But, this method results in unreliable estimation when the object in image sequence has larger movement than the maximum displacement assumed in BMA or the input images are severely corrupted with noise. In order to i:;olve this problem, we analyse the effect of inaccurate motion on MASF and propose a hierarchical motion estimation algorithm based on the analysis results. Experimental results show that the proposed method produces reliable output under large motion and noisy situations.

• Journal of Labour Economics
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• v.27 no.2
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• pp.139-159
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• 2004

This paper explores the determinants of re-employment of retired military personnel who served more than ten years in Korea. Recently, the re-employment rate of veterans is less than 30%. Considering the reduction in military forces in future, this very low rate of re-employment may be one of important social and economic problem. Using a survey and econometric analyses, we generate several important results. First, spouses' income is higher in the group who chose to run their own business than in the group who decided to become salary workers. Second, those who gave economic activities had longer the period of military service, higher ranks, and higher rate of being in bad health. Third, the longer the military service period is, the shorter the period of job search. And those who not taking the program of vocational guidance have short search period. If, however, one was more educated or one served longer in Seoul area, then she is more likely to have a longer search period. These results imply that the current important factors in government policies for veterans such as vocational guidance programs, information for employment, and military experience should be improved to be more oriented to the requirements of employers.

• The Journal of the Korea Contents Association
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• v.19 no.11
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• pp.445-450
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• 2019

This study proves that syringe reuse of automated injection system entails a risk of contrast media reflux and saline solution contamination which are pumped by a piston into the patients' venous cannula in the dynamic MR images, we will be aware of the serious problem. To quantify the contrast media contamination effect on the saline solution, identical volume of the saline solution was collected before and after the contrast injection to the patients' venous cannula following T1 weighted image scanning to verify whether signal intensities differences are observed. The signal intensity of saline solution after the contrast injection was significantly higher than that of saline before injection by 523.43%. This result is due to the backflow that contaminates the saline solution on the opposite side when the contrast agent is injected. In conclusion, the syringe used to inject contrast medium. causes cross-contamination due to contrast reflux. Therefore, even if the same patient's examination is used for quantitative analysis, the error should be avoided by changing the acquisition sequence or replacing the syringe.

• Journal of Biomedical Engineering Research
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• v.31 no.4
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• pp.328-334
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• 2010

Over the past few years, a considerable number of methods have been proposed and applied for the classification of photoplethysmography (PPG). Most of the previous studies, however, focused on the qualitative description of the pulse type according to specific disease and thus provided ambiguous criteria to interpreters. In order to screen out this problem, we present a quantitative method for the pulse type classification including the second derivative of photoplethysmography (SDPTG). In the PPG signal, we have classified the signal as 4 types using the position and the presence of the dicrotic wave. In addition, we have categorized the SDPTG signal as 7 types using the position and the presence of "c" and "d" wave and the sign of "c" wave. In order to check the efficacy of the proposed pulse type classification rule, we collected pulse signals from 155 subjects with different ages and sex. From the correlation analysis, Class 1(p<0.01) and Class 2(p<0.01) in the PPG signal are significantly correlated with ages. In a similar manner Class A(p<0.01), Class C(p<0.05), Class D(p<0.01), and Class F(p<0.01) in the SDPTG signal are considerably correlated with the ages. From these observations, and some earlier ones [4], [5], we can conclude that since the newly proposed method has objectivity and clarity in pulse type classification, this method can be used as an alternative of previous classification rules including similar age-related characteristics.

• Journal of Biomedical Engineering Research
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• v.34 no.2
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• pp.80-90
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• 2013

Recently, functional insoles of wedge-type it is for the young to raise their height inserted between insole and heel cause foot pain and disease. Additionally, these have a problem with stability and excessively load-bearing during gait like high-heel shoes. In this study, we compared the changes in biomechanical characteristics of foot with different insole thickness then we will utilize for the development of the insole with the purpose of relieving the pain and disease. Subjects(male, n = 6) measured COP(center of pressure) and PCP(peak contact pressure) on the treadmill(140cm/s) using F-scan system and different insole thickness(0~50 mm) between sole and plantar surface during gait. Also, we computed changes of stresses at the foot using finite element model with various insole thickness during toe-off phase. COP moved anterior and medial direction and, PCP was increased at medial forefoot surface, $1^{st}$ and $2^{nd}$ metatarsophalangeal, ($9%{\uparrow}$) with thicker insoles and it was show sensitive increment as the insole thickness was increased from 40 mm to 50 mm. Change of the stress at the soft-tissue of plantar surface, $1^{st}$ metatarsal head represents rapid growth($36%{\uparrow}$). Also, lateral moments were increased over the 100% near the $1^{st}$ metatarsal as the insole thickness was increased from 0 mm to 30 mm. And it is show sensitive increment as the insole thickness changed 10 mm to 20 mm. As a result, it was expected that use of excessively thick insoles might cause unwanted foot pain at the forefoot region. Therefore, insole thickness under 30 mm was selected.

• Journal of Satellite, Information and Communications
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• v.11 no.2
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• pp.29-35
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• 2016

High-availability seamless redundancy (HSR) is a fault-tolerant protocol for Ethernet networks that provides two frame copies for each frame sent. Each copy is forwarded on a separate physical path. HSR is a potential candidate for several fault-tolerant Ethernet applications, including smart-grid communications. However, the major drawback of the HSR protocol is that it generates and circulates unnecessary frames within connected rings regardless of the presence of a destination node in the ring. This downside degrades network performance and can deplete network resources. Two simple but efficient approaches have previously been proposed to solve the above problem: quick removing (QR) and port locking (PL). In this paper, we will present a hybrid approach, QRPL, by combining QR with PL, resulting in further traffic reductions. Our analysis showed that network traffic is significantly reduced for a large-sized HSR connected ring network compared to the standard HSR protocol, QR, and PL.

• The Plant Pathology Journal
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• v.36 no.2
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• pp.111-120
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• 2020

Powdery mildew of Indian mustard (Brassica juncea), caused by Erysiphe cruciferarum, is emerging as major problem in India. All the Indian mustard cultivars presently grown in India are highly susceptible to powdery mildew and so far no resistance source has been reported. In this study, with an aim to identify resistant source, 1,020 Indian mustard accessions were evaluated against E. cruciferarum PMN isolate, at Wellington, The Nilgiris, Tamil Nadu, India under natural hot spot conditions. The study identified one accession (RDV 29) with complete resistance against E. cruciferarum PMN isolate for the first time, which was consistent in five independent evaluations. Genetic analysis of F₁, F₂ and backcross populations obtained from the cross RSEJ 775 (highly susceptible) × RDV 29 (highly resistant) for two season revealed that the resistance is governed by two genes with semi-dominant and gene dosage effect. Further, a new disease rating system using six scales (0, 1, 2, 3, 4, and 5) has also been proposed in this study to score powdery mildew based on progress of fungal growth in different plant parts of the F₂ population. The outcome of this study viz. newly identified powdery mildew-resistant Indian mustard accession (RDV 29), information on inheritance of resistance and the newly developed disease rating scale will provide the base for development of powdery mildew-resistant cultivars of Indian mustard.