• Title/Summary/Keyword: Stability ratio

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Modification of Polyacrylonitrile Films by Hydroxylamine and Hydrazine Treatment (히드록실아민과 히드라진 처리에 의한 폴리아크릴로니트릴 필름의 개질)

  • Park, Hee Jung;Kim, Young Ho
    • Polymer(Korea)
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    • v.39 no.3
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    • pp.394-402
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    • 2015
  • Modification of polyacrylonitrile (PAN) films by using hydroxylamine (HA) and hydrazine to produce hydroxyl and amine groups, respectively, and to introduce cross-linking of PAN polymers was studied. Modified PAN films obtained by HA and/or hydrazine treatment including a successive or a simultaneous process were analyzed by the degree of conversion, water and N,N'-dimethylformamide (DMF) swelling ratio, FTIR spectra, atom content, and thermal analysis data. PAN films reacted with HA showed increased hydrophilicity and low dimensional stability in water. Hydrazine treatment gave PAN films high dimensional stability of low DMF swelling. Although the DMF swelling ratio of the modified PAN films was dramatically decreased by the successive treatment of hydrazine and HA, the introduction of the hydrophilic functional groups was limited due to the cross-linking. Simultaneous treatment of HA and hydrazine was the most effective method to increase hydrophilicity of PAN films with a high dimensional stability.

Effect of Different Pressing Processes and Density on Dimensional Stability and Mechanical Properties of Bamboo Fiber-based Composites

  • Zhang, Ya-Hui;Huang, Yu-Xiang;Ma, Hong-Xia;Yu, Wen-Ji;Qi, Yue
    • Journal of the Korean Wood Science and Technology
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    • v.46 no.4
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    • pp.355-361
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    • 2018
  • In this study, the dimensional stability and mechanical properties of bamboo fiber-based composites (BFBCs) were studied at two pressing manufacturing processes, i.e., hot- and cold- pressing, and were compared with three density parameters (1.0, 1.1, and $1.2kg/m^3$). Width swelling ratio (WSR), thickness swelling ratio (TSR), and water absorption ratio (WAR) were calculated for water immersions of 4 and 28 h. WSR, TSR, and WAR for specimens immersed for 28 h were higher than those for 4 h treatment, which shows that the immersion time has a significant influence on the dimensional stabilities of BFBCs. Moreover, the positive linear relations between density and dimensional were observed at both the pressing ways, indicating that the WSR, TSR, and WAR decreased with an increase in the density of BFBCs. The compressive strength, shear strength, modulus of rupture (MOR), and modulus of elasticity (MOE) were determined. The compressive strength, MOR, and MOE of hot-pressed specimens were significantly higher than those for the cold-pressed specimens, which are also directly proportional to density. Moreover, the samples with the highest density of $1.2kg/m^3$ performed high values on mechanical properties in both the manufacturing methods.

An Experimental Study on the Stability of Assembled Earth Retaining Wall in Sandy Ground (사질토 지반에 설치된 조립식 지주옹벽(AER)의 안정성에 관한 실험적 연구)

  • Yoo, Jae-Won;Im, Jong-Chul;Hwang, Sung-Pil;Kim, Chang-Young;Choi, Jung-Hyun;Kim, Hong-Sun
    • Journal of the Korean Geotechnical Society
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    • v.32 no.2
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    • pp.43-52
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    • 2016
  • Assembled Earth Retaining wall (AER-wall is used here) using back pile (back supporting beam is used from here) has been developed at Pusan National University. Both cost and time have been significantly reduced because AER-wall can be fabricated in a shop. Also its stability has been improved with a back supporting beam reducing earth pressure. In this study, the test results were analyzed after laboratory model tests were performed. The lateral displacement of AER-wall significantly decreased with both inclined wall and back supporting beams. As a result, the stability of AER-wall and effect of back supporting beam have been analyzed and verified.

Relationship Between the Postural Alignments and Spatio-temporal Gait Parameters in Elderly Woman (여성 노인의 자세 정렬과 시공간 보행 변수 사이의 연관성)

  • Kim, Sung-Hyeon;Shin, Ho-Jin;Suh, Hye-Rim;Jung, Kyoung-Sim;Cho, Hwi-Young
    • Journal of the Korean Society of Physical Medicine
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    • v.15 no.3
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    • pp.117-125
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    • 2020
  • PURPOSE: Aging causes changes in the postural alignment and gait due to changes in the nervous and musculoskeletal systems. On the other hand, the relationship between the changes in posture alignment and gait is unclear. This study examined the relationship between the postural alignment and spatiotemporal gait parameters in Korean elderly women. METHODS: Thirty-two-healthy elderly women participated in this study. All subjects were assessed for their posture alignment and gait ability. Stepwise multiple linear regression was performed to determine to what extent the postural alignments could explain the spatiotemporal gait parameters. RESULTS: Coronal head angle was moderately correlated with the velocity (r = -.51), normalized velocity (r = -.46) and gait-stability ratio (r = .58) (p < .05). The trunk angle was moderately correlated with the normalized velocity (r = -.32) and gait-stability ratio (r = .32) and weakly correlated with the velocity (r = -.28) (p < .05). The coronal shoulder angle was moderately correlated with the swing phase (r = -.57), stance phase (r = .56), single limb stance (r = -.56) and double limb stance (r = .51) (p < .05). The coronal head angle and trunk angle accounted for 36% of the variance in velocity, 33% variance in normalized velocity and 46% variance in the gait-stability ratio (p < .05). The coronal shoulder angle accounted for 32% variance in the swing phase, 32% variance in the stance phase, 31% variance in the single limb stance and 26% variance in the double limb stance (p < .05). CONCLUSION: Changes in posture alignment in elderly women may serve as a biomarker to predict a decrease in walking ability due to physical aging.

A Study on Future System Construction Using WSCR Strengthness Index based on Python (Python 기반 WSCR 강건 지수를 이용한 미래계통 구축에 관한 연구)

  • Park, Seong-Jun;Hur, Jin;Kim, Hyun-Jin;Cho, Yoon-Sung
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.67 no.8
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    • pp.994-1001
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    • 2018
  • In this paper, to studied about future power system construction using PSS / E-Python API. Python-based future system automatical construction methods and modeling of renewable sources. it confirmed the stability of the powert system for each renewable area by calculating the weighted short circuit ratio (WSCR) index. it calculated the short circuit ratio (SCR) and selected the transmission line linkage scenario to improve the stability of vulnerable areas. it confirmed the WSCR index improvement through the selected transmission line linkage of scenario, and analyzed the stability of the renewable power system applying the scenario. It describes Facts and Shunt devices adjustment for the load flow convergence. It describes the stable methed of the bus voltage through the transformer Ratio Tap adjustment. By performing PSS/E ASCC using the Python it was performed three-phase short circuit fault capacity analysis, it is confirmed whether excess of the fault current circuit breaker capacity. In order to contingency accident analysis, it have described the generation of one or two line list of each areas using the Python. The list is used to contingency analysis and describe the soluted of the transmission line overload through comparison before and after adding the scenario line.

Experimental and numerical study on the stability of slurry shield tunneling in circular-gravel layer with different cover-span ratios

  • Liu, Xinrong;Liu, Dongshuang;Xiong, Fei;Han, Yafeng;Liu, Ronghan;Meng, Qingjun;Zhong, Zuliang;Chen, Qiang;Weng, Chengxian;Liu, Wenwu
    • Geomechanics and Engineering
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    • v.28 no.3
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    • pp.265-281
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    • 2022
  • A set of slurry shield test system capable of cutter cutting and slurry automatic circulation is used to investigate the deformation characteristics, the evolution characteristics of support resistance and the distribution and evolution process of earth pressure during excavating and collapsing of slurry shield tunneling in circular-gravel layer. The influence of cover-span ratio on surface subsidence, support resistance and failure mode of excavation face is also discussed. Three-dimensional numerical calculations are performed to verify the reliability of the test results. The results show that, with the decrease of the supporting force of the excavation face, the surface subsidence goes through four stages: insensitivity, slow growth, rapid growth and stability. The influence of shield excavation on the axial earth pressure of the front soil is greater than that of the vertical earth pressure. When the support resistance of the excavation face decreases to the critical value, the soil in front of the excavation face collapses. The shape of the collapse is similar to that of a bucket. The ultimate support resistance increase with the increase of the cover-span ratio, however, the angle between the bottom of the collapsed body and the direction of the tunnel excavation axis when the excavation face is damaged increase first and then becomes stable. The surface settlement value and the range of settlement trough decrease with the increase of cover-span ratio. The numerical results are basically consistent with the model test results.

Experiments on Stability of Armor Rocks on Rear Slope of Rubble Mound Structures under Wave Overtopping Condition with Rectangular Crest Element (월파조건에서 직사각형 상치콘크리트가 설치된 경사제 항내측 사면에 거치된 피복석의 안정성 실험)

  • Young-Taek Kim;Jong-In Lee
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.35 no.5
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    • pp.102-108
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    • 2023
  • In this study, hydraulic model tests were performed to investigate the stability of armor units at harbor side slope for rubble mound structures. The armor units on the rear slope were rocks. The Korean design standard for harbor and fishery port suggested the design figures that showed the ratio of the armor weight for each location of rubble mound structures and it could be known that the same weight ratio was needed to the sea side and rear side slope of rubble mound structures. The crest elements were commonly applied to the design process of rubble mound structures in Korea and the investigation of the effects of super structures would be needed. The damage rate (S =2) was applied and the stable wave height was measured for each test condition. The results were suggested as the armor weight ratio of the rear side slope(armor rock) to the sea side slope (tetrapod) in relation to the relative crest height.

Numerical Analysis on the Behavior of Revetment Reinforced by Sand Compaction Pile According to Area Replacement Ratio (수치해석을 이용한 모래다짐말뚝 치환율에 따른 호안 구조물의 거동 분석)

  • Kim, Byoung-Il;Bong, Tae-Ho;Han, Jin-Tae;Jang, Young-Eun
    • Journal of the Korean Geosynthetics Society
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    • v.17 no.3
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    • pp.1-8
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    • 2018
  • Sand compaction pile (SCP) is a ground improvement method which is used to secure the stability of the soft ground by using a type of replacement pile filled with coarse grained material. The behavior characteristics of the SCP, which is frequently used for improving both the onshore and offshore ground, is governed by the ground condition, the installation method, and replacement ratio. Therefore, the stability of the SCP in terms of the bearing capacity and displacement needs to be evaluated considering both the design values and in-situ conditions of construction site. In this study, numerical analysis is carried out based on the conditions of 00 revetment construction site in South Korea where unexpected displacement occurred during construction of SCP. Based on the analysis results, the displacement of the revetment structure according to the replacement ratio of the SCP was compared to the result calculated from design formulas. The results showed that the lateral displacement can be exceeded the reference value from proposed criteria regardless of increased replacement ratio of SPC. It is also confirmed that the behavior of the structure according to the replacement ratio of SPC in not reflected in the existing calculation methods. Therefore, the stability of the SCP composite ground should be examined through the site inspection after the SCP construction.

Optimum Mixing Ratio of Epoxy for Glass Fiber Reinforced Composites with High Thermal Stability (에폭시 배합비에 따른 내열성 복합재료 최적조건)

  • Shin, Pyeong-Su;Wang, Zuo-Jia;Kwon, Dong-Jun;Choi, Jin-Yeong;Sung, Ill;Jin, Dal-Saem;Kang, Suk-Won;Kim, Jeong-Cheol;Park, Joung-Man
    • Composites Research
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    • v.27 no.4
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    • pp.168-173
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    • 2014
  • The optimum condition of glass fiber/epoxy composites was investigated according to mixing ratio of two epoxy matrices. Novolac type epoxy and isocyanate modified epoxy were used as composites matrix. Based on chemical composition of mixing matrix, optimum mixing ratio of epoxy resins was obtained through various experiments. In order to investigate thermal stability and interface of epoxy resin, glass transition temperature was observed by DSC instrument, and static contact angle was measured by reflecting microscope. Change of IR peak and $T_g$ was conformed according to different epoxy mixing ratio. After fabrication of glass fiber/epoxy composites, tensile, compression, and flexural properties were tested by UTM by room and high temperature. The composites exhibited best mechanical properties when epoxy mixing ratio was 1:1.

A Study of Dynamic Behavior of Segmental U-shaped Prestressed Concrete Girder Applied with Integrated Tensioning Systems (복합긴장방식이 적용된 세그멘탈 U형 거더 동적 거동 특성 연구)

  • Hyunock Jang;Ilyoung Jang
    • Journal of the Society of Disaster Information
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    • v.20 no.2
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    • pp.369-378
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    • 2024
  • Purpose: This study aims to verify structural stability by manufacturing a 40m full-scale specimen composed of a segmental U-shaped PSC girder with integrated tensioning systems and a concrete slab, proceeding dynamic behavior tests, and compare the results of the tests with the results of numerical analysis. Method: Dynamic behavior tests were conducted on a full-scale, undamaged specimen using an impact hammer, and the natural frequency and damping ratio were measured and compared with numerical analysis techniques and the general damping ratio of the facilities. Result: The natural frequency of the numerical analysis model consisting of a girder and slab composite section was calculated to be 2.561Hz, the natural frequency of the full-scale specimen was measured to be 2.670Hz, and the damping ratio was calculated to be 0.42~0.68%. Conclusion: The natural frequency of the full-scale specimen was found to be 4.3% larger than that of the numerical analysis model. Since the masses of the full-scale specimen and the numerical analysis model are the same as 99.97%, it can be derived that the stiffness of the full-scale specimen has secured structural safety and stability. As a result, the dynamic behavior stability of the specimen was verified. The measured damping ratio of 0.42~0.68% was found to be a stable dynamic behavior compared to the PSC structures damping ratio of 0.5~1.0% in the elastic region.