• Smart Structures and Systems
• /
• v.3 no.1
• /
• pp.51-68
• /
• 2007

High-strength concrete (HSC) is becoming increasingly attractive for various construction projects since it offers a multitude of benefits over normal-strength concrete (NSC). Unfortunately, current design provisions for shear capacity of RC slender beams are generally based on data developed for NSC members having a compressive strength of up to 50 MPa, with limited recommendations on the use of HSC. The failure of HSC beams is noticeably different than that of NSC beams since the transition zone between the cement paste and aggregates is much denser in HSC. Thus, unlike NSC beams in which micro-cracks propagate around aggregates, providing significant aggregate interlock, micro-cracks in HSC are trans-granular, resulting in relatively smoother fracture surfaces, thereby inhibiting aggregate interlock as a shear transfer mechanism and reducing the influence of compressive strength on the ultimate shear strength of HSC beams. In this study, a new approach based on genetic algorithms (GAs) was used to predict the shear capacity of both NSC and HSC slender beams without shear reinforcement. Shear capacity predictions of the GA model were compared to calculations of four other commonly used methods: the ACI method, CSA method, Eurocode-2, and Zsutty's equation. A parametric study was conducted to evaluate the ability of the GA model to capture the effect of basic shear design parameters on the behaviour of reinforced concrete (RC) beams under shear loading. The parameters investigated include compressivestrength, amount of longitudinal reinforcement, and beam's depth. It was found that the GA model provided more accurate evaluation of shear capacity compared to that of the other common methods and better captured the influence of the significant shear design parameters. Therefore, the GA model offers an attractive user-friendly alternative to conventional shear design methods.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.24 no.2
• /
• pp.76-88
• /
• 1982

The stream morphological characteristics of a basin have important influence upon the analysis of runoff. In this study, the laws of stream morphology-the law of average stream fall and the law of least rate of potential energy expenditure-which were derived based on the analogy of entropy in thermodynamics are introduced and their validity is analysised with the data taken from the topographic maps covering the whole Geum River system. The first law is the Law of Average Stream Fall which states that under the dynamic equilibrium condition the ratio of average fall between any two different order stream in the same river basin in unity. The second law is the law of least rate of energy expenditure which states that all natural streams are intended to choose their own course of flow such that the rate of potential energy loss per unit mass of water this course is a minimum. The parameters representing the morphological characteristics of 13 tributaries in the Geum River system such as stream bifurcation ratio and stream concavity were Computed from the Horton-Strahler's laws and are used to check the law of average stream fall. The result showed that the law of average stream fall agrees reasonably well with law of Horton-Strahler. Concavity of a river basin is shown to be the determinative factor to the formation of a stream system. Concavity of a river basin is shown to be the determinative factor to the formation of a stream system. Based on Horton's Law and the law of average stream fall, longitudinal stream profiles can be calculated.

• Journal of Biosystems Engineering
• /
• v.36 no.5
• /
• pp.355-360
• /
• 2011

This study was carried out to analyze the installation effect of an anti-wind net on reducing wind velocity which was used to protect orchards as well as single-span plastichouses. The pressure drop through three types of anti-wind net was measured in a subsonic wind tunnel. The wind reduction through the anti-wind facility for several sets in respect to three types of the net and heights of the facility ranging from 3 to 11 m was analyzed by using computational fluid dynamics (CFD). The measured data showed that the pressure drop increased as an equation of the second degree of the inlet wind velocity. Numerical computations exhibited that the effect of wind reduction definitely augmented as the net size became smaller and increased with the height of the facility being heightened to some extent. For the typical and widely used anti-wind facility with a height of 5 m and a net size of 4mm, the amount of wind reduction came up to 5.1 m/s for the inlet wind velocity of 20 m/s, and also 7.6 and 10.1 m/s for the inlet wind velocities of 30 and 40 m/s, respectively. In case for the orchard's longitudinal length to be within about 200 m, the appropriately effective height of the facility was predicted to be 5 m. Finally, the negative total pressure on the top face of the single-span plastichouse certainly reduced for all the cases with the anti-wind facility being installed. In particular, the reduction of the negative total pressure was more considerable as the inlet wind velocity increased.

• International Journal of Aeronautical and Space Sciences
• /
• v.18 no.2
• /
• pp.197-205
• /
• 2017

We investigate the slat noise generation mechanism by using large-eddy simulation (LES) and simple source modeling based on linearized Euler equations. An incompressible LES of an MD 30P30N three-element airfoil in the high-lift configuration is conducted at $Re_c=1.7{\times}10^6$. Using the total derivative of the hydrodynamic pressure (DP/Dt) acquired from the incompressible LES, representative noise sources in the slat cove region are characterized in terms of simple sources such as frequency-specific monopoles and dipoles. Acoustic radiation around the 30P30N multi-element airfoil is effectively computed using the Brinkman penalization method incorporated with the linearized Euler equation. The directivity pattern of $p^{\prime}_{rms}$ at $r=20c_{slat}$ in the multiple sources is closely compared to that obtained by the application of the LES/Ffowcs-Williams and Hawking's methods to the entire flow field. The power spectrum of p' at ${\theta}=290^{\circ}$ is in good agreement with the data reported in BANC-III, especially the broadband part of the spectrum with a decaying slope ${\propto}f^{-3}$.

• The Journal of the Korea Contents Association
• /
• v.16 no.6
• /
• pp.323-333
• /
• 2016

This study aimed at specifically validating the mediating effect of the elderly's leisure participation with regards to the impact of socio-economic factors on the elderly's satisfaction with life. This paper analyzed the data of 7,486 people who participated in the 4th research of the 2012 Korean Longitudinal Study of Ageing (KLoSa) by Korea Labor Institute. The outcome is as follows. First, among socio-economic factors, educational background, total household income and net asset were found to have positive impact on the elderly's satisfaction with life. When the level of the three factors was higher, the satisfaction with life was also greater. Second, the three socio-economic factors (educational background, total household income and net asset) affected the elderly's satisfaction with life through mediating effect of leisure participation. Those with higher educational background, total household income and net asset showed more leisure participation, leading to greater satisfaction with life.

• The Journal of the Korea Contents Association
• /
• v.15 no.8
• /
• pp.226-235
• /
• 2015

This study aims to explore effects of social exclusion on poverty of people who are 45 years old and over with disability. It also analyzed the difference between the urban and the rural area in relation to the effects of social exclusion on poverty. The researchers conducted a secondary data analysis using the fourth wave of Korean Longitudinal Study of Ageing. The sample included in this study was 640 people who were 45 years old and over with disability. Logistic regression results showed that urban residents who were younger, did not live with a spouse, were not at workforce, and lived in a rented house tended to be on welfare. For rural residents, on the other hand, only age and marital status were significantly related to poverty. Based on the findings, the researchers indicated political implications to diminish social exclusion and poverty of people with disability.

• The Journal of the Korea Contents Association
• /
• v.20 no.10
• /
• pp.458-469
• /
• 2020

Geriatric depression is associated with pathological changes in the brain and increases the risk of cognitive impairment or dementia. However, high cognitive reserve, such as high education, can delay or minimize clinical manifestations of pathologies involving the brain, so the effect of geriatric depression on cognitive impairment or dementia may vary depending on the education level. In this study, the author analyzed data from the Korean Longitudinal Study of Aging (KLoSA) to examine whether the effect of geriatric depression on cognitive function differed depending on education level. Among the 10,254 subjects registered in the KLoSA, the 4,905 subjects who met the inclusion criteria were analyzed by stepwise regression analysis. The results were as follows: first, depressive symptoms predicted low cognitive function after 12 years; second, the negative effect of depressive symptoms on cognitive function after 12 years was higher in the old adult group than in the young adult group; and third, the effect of age was significant only in the low-educated group. These results suggest that depressive symptoms in low-educated old adults may increase the risk of development of dementia in the long term.

• The Journal of the Korea Contents Association
• /
• v.20 no.10
• /
• pp.326-337
• /
• 2020

The purpose of this study is to analyze the effect of social participation types on cognitive impairment degree(normal, mild, severe cognitive function) by urban and rural difference. The research was performed by multinomial logistic regression with the data of elderly 5,668 over 55 years of age from the sixth wave(2016) and the seventh wave(2018) of the Korean Longitudinal Study of Ageing. Results show that social participation reduces the risk of cognitive impairment on both urban and rural older adults regardless of types, but the types of social participation, which are effective to reduce the risk of cognitive impairment, are different between urban and rural area. According to residential area, types of social participation, which are effective to decline the risk of being mild or severe cognitive impairment and the risk of being severe cognitive impairment relative to mild, are different. These findings suggest that, in order to prevent cognitive impairment and reduce the severity, social participation is strongly recommended and appropriate supports are required. This implies policy and intervention efforts considering the urban and rural difference are needed.

• The Journal of the Korea Contents Association
• /
• v.20 no.10
• /
• pp.726-737
• /
• 2020

This study analyzed 4,284 elderly people aged 65 or older by SPSS 22.0 in the 7th data of 「2018 Korean Longitudinal Study of Ageing(KLoSA)」 to confirm the effect of the health-promoting behavior of the elderly on life satisfaction through cognitive function. The cognitive function level of the subjects was 13.8% doubtful about dementia, 23.8% cognitive decline, and 62.4% normal, and the satisfaction level of life was 59.304 points. The results of the study were as follows: First, the difference in cognitive function according to demographic characteristics was significant in gender, age, education, religion, and marriage factors. Second, the satisfaction of the elderly's life according to demographic characteristics was confirmed to have significant differences in gender, age, education, religion, and marriage factors. Third, the satisfaction of the elderly's life was significantly positive in drinking and regular exercise factors among independent variable the health-promoting behavior when cognitive function was mediated. On the other hand, The significant negative effect of the restriction of daily life activities was confirmed. In this way, the mediating effect of cognitive function was verified in the effect of the health-promoting behavior on the satisfaction of the elderly life.

• Journal of Korean Neurosurgical Society
• /
• v.41 no.4
• /
• pp.224-229
• /
• 2007

Objective : Despite improvement of therapeutic regimen, incidence of stroke increases and it remains a leading cause of death. Our study aims at offering variable data on recurrent strokes. Methods : There were 59 patients who admitted from Jan. 2002 to Dec. 2004 due to recurrent strokes. A retrospective longitudinal cohort study was done. Results : Four-hundred-seventy five patients, diagnosed with acute stroke, experienced 491 strokes in 3 years, and there were 75 recurrent strokes [15.3%] in 59 patients. These 59 patients were included in the study. First hemorrhagic cases [H] were 19 [32%], and the first infarction cases [I] were 40 [68%]. Subsequent strokes after first stroke were as follows : $H{\to}H$ 14 [23.7%] cases, $H{\to}I$ 5 [8.5%], $I{\to}H$ 8 [13.6%], $I{\to}I$ 32 (54.2%]. A Cox regression analyses showed that the first type of stroke was a significant factor to the second stroke as follows : if one has had a hemorrhagic stroke, the possibility of second hemorrhagic attack ($H{\to}H$ attack) increase 3.2 times than ischemic type and in ischemic stroke [$I{\to}I$ attack] 3.6 times increased incidence of second ischemic attack. Conclusion : The recurrence rate of stroke was 12.4% [59 of 475 patients]. If the first stroke is hemorrhage or infarction, the next stroke would have high potentiality of hemorrhage, or infarction. The possibility of same type in second stroke Increase over 3 times. In $H{\to}H$ group, the time interval between first and second stroke was shorter and the age of onset was earlier than in $I{\to}I$ group. Moreover, the infarction was more frequent than hemorrhage in multiple strokes. There was a correlation in lacunar type infarction between first and second attack.