• Title, Summary, Keyword: Effect size

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Size effect study on compressive strength of SCLC

  • Karamloo, Mohammad;Roudak, Mohammad Amin;Hosseinpour, Hamed
    • Computers and Concrete
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    • v.23 no.6
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    • pp.409-419
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    • 2019
  • In the present study, effect of size and placement of cubic specimens on compressive strength of self-compacting lightweight concrete (SCLC) were considered. To do so, 81 specimens of different sizes (50 mm, 75 mm, 100 mm, and 150 mm) were prepared by using three different mixes of SCLC. Results of the cured specimens were then used in regression analyses to find predictive equations with regard to both the placement direction and the size. Test results showed that the strength ratio in cases in which the direction of loading and placement were parallel, were higher than those specimens, whose configurations were normal between loading and placement. In addition, strength ratios in SCLC mixes were slightly higher than those are for self-compacting normal weight concrete. In order to analyze the effect of size on compressive strength the conventional size effect law as well as the modified size effect law (MSEL) were used. Besides, the convergence criterion of nonlinear regression process of size effect study has been discussed. Analyses of the results showed that the unconstraint nonlinear regression in size effect study of SCLC mixes could lead to erroneous results.

A Meta-Analysis of the Effects of the Career Education Program for Students with Disabilities (장애 학생을 대상으로 한 진로교육 프로그램의 효과에 관한 메타분석)

  • Choi, Hea Young
    • Family and Environment Research
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    • v.55 no.3
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    • pp.289-301
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    • 2017
  • This study was to analyze the effects of the career education program for students with disabilities. The analysis was performed based on two research questions. First, the total effect size on the career program for students with disabilities was considered. Second, the difference of the effect size between the sub-groups regarding dependency variables, types of disabilities, types of schools, number of people, and number of sessions was also included for analysis. For this, the author reviewed a database and analyzed 12 previous studies, presented in five master thesis and seven Korean journals from 2005 to 2015 based on the author's selection criteria. Subsequently, 27 effect size was found. The publication bias was analyzed by Rosenthal's fail-safe N. The overall effect size for all studies on the random effect model was 1.717, which was positive and high in value. Given the heterogeneity among the effect size, the subgroup analysis was conducted, and indicated that the effect size was significantly high when the purpose of the program was related to the student's self-decision ability. The results demonstrated that the programs were specified for students with intellectual disabilities, when the schools were elementary, when the number of students in a group was 1-10, and when program sessions lasted more than 21 times, the effect size was high. Implication for the future research and program implication were discussed on these findings.

A meta-analysis on the effects of the differentiated instruction in mathematics (수학과 수준별 수업의 효과에 대한 메타분석)

  • Kim, Sun Hee
    • The Mathematical Education
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    • v.54 no.4
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    • pp.335-350
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    • 2015
  • The purpose of this study was to investigate the effectiveness of the differentiated instruction in mathematics by a meta-analysis. Among the studies conducted for last twenty three years, the relevant 49 research articles were selected, 80 effect sizes were calculated for the cognitive domain and 70 effect sizes for the affective domain. Effect sizes were analyzed with school levels, student level, group organization method such as homogeneous vs. heterogeneous, class transfer and adjusting class sizes for each cognitive domain and affective domain. The results are as the followings: In the cognitive domain, the overall effect size of the differentiated instruction produced a medium effect(effect size=0.68, U3=75.17%). The differentiated instruction showed the highest effect size on elementary school and middle school, mid level students, heterogeneous group, class transfer and not adjusted class size. And in the affective domain, the overall effect size of the differentiated instruction produced a low effect(effect size=0.36, U3=65.36%). The differentiated instruction showed the highest effect size on elementary school, mid level students, and heterogeneous group. Thus the differentiated instruction was proved to be effective in mathematics classes.

Studies on the Temperature Effect to Rosin Size in Paper Making (로진 싸이즈에 미치는 溫度의 影響에 關하여)

  • Dong Bum Chi
    • Journal of the Korean Chemical Society
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    • v.7 no.2
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    • pp.133-139
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    • 1963
  • It is well-known that high temperature hurts the sizing effect of rosin size in paper making, mainly owing to the particle size of rosin-aluminium complex in paper stock. In this experiments, author find, when the temperature of stock rises up. the particle size of rosin-aluminium complex of neutral rosin size increases and the degree of sizing decreases finally. However, the behavior of Bewoid size is quite opposite to former. This result showed that, Bewoid size is suitable in hot summer and neutral rosin size in cold winter for better sizing effect.

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Size Effect on Flexural Stress-Strain Relationship of Reinforced-Concrete Beams (철근콘크리트 보의 휨압축강도 및 변형률에 대한 크기효과)

  • 김민수;김진근;김장호
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.911-916
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    • 2002
  • It is important to consider the effect of depth when estimating the ultimate strength of a concrete flexural member because the strength always decreases with an increase of member size. In this study, the size effect of reinforced concrete beam was experimentally investigated. For this purpose, a series of beam specimens subjected to 2-point bending load were tested. More specifically, three different depth (d=15, 30, and 60 cm) of reinforced concrete beams were tested to investigate the size effect. The shear-span to depth ratio (a/d=3) and thickness (20 cm) of the specimens were kept constant where the size effect in out-of-plan direction is not considered. The test results are fitted using least square method (LSM) to obtain parameters for modified size effect law (MSEL). The analysis results indicate that the flexural compression strength and ultimate strain decreases as the specimen size increases. Finally, more general parameters for MSEL are suggested.

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Size Effect of Axial Compressive Strength of Concrte in Notched Specimens (노치가 있는 콘크리트 공시체의 축압축강도에 대한 크기효과)

  • 김민욱;김진근;김봉준
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.135-140
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    • 1999
  • The size effect of axial compressive strength of concrete in notched specimens was experimentally investigated. Based on the concept of the fracture mechanics and size effect law, theoretical studies for axial compressive failure of concrete were reviewed, and two failure modes of concrete specimen under compression were discussed. In this study, experiment of axial compressive failure, which is one of the two failure modes, was carried out by using double cantilever fracture specimens. By varying the slenderness of cantilevers and the eccentricity of applied loads with respect to the axis of each cantilever, the size effect of axial compressive strength of concrete was investigated, and predicted by Bazant's size effect law. The test results show that size effect appears conspicuously for all series of specimens. For the eccentricity of loads, the influence of tensile and compressive stress at the notch tip are significant and so that the size effect is varied. In other words, if the influence of tensile stress at the notch tip grows up, the size effect of concrete increases. And the fact that the fracture process zone must be sufficiently secured for more accurate experiment was affirmed.

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A Theoretical and Experimental Study on the Tribological Size Effect in Microforming Processes (마이크로 성형에서 마찰거동의 크기효과에 대한 이론적 및 실험적 연구)

  • Kim, H.S.
    • Transactions of Materials Processing
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    • v.22 no.7
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    • pp.394-400
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    • 2013
  • Microforming is a very efficient and economical technology to fabricate very small metallic parts in various applications. In order to extend the use of this forming technology for the production of microparts, the size effect, which occurs with the reduction of part size and affects the forming process significantly, must be thoroughly investigated. In this study, the tribological size effect in microforming was studied using modeling and scaled ring compression experiments. A micro-scale friction approach based on the slip-line field theory and lubricant pocket model was used to understand the friction mechanism and explain the tribological size effect. Ring compression tests were performed to analyze the interfacial friction condition from the deformation characteristics of the ring specimens. In addition, finite element analysis results were utilized to quantitatively determine the size-dependent frictional behavior of materials in various process conditions. By comparing theoretical results and experimental measurements for different size factors, the accuracy and reliability of the model were verified.

Size Effect on Axial Compressive Strength of Notched Concrete Specimens

  • Yi, Seong-Tae;Kim, Jin-Keun
    • KCI Concrete Journal
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    • v.14 no.1
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    • pp.43-50
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    • 2002
  • In this study, size effect tests were conducted on axial compressive strength of concrete members. An experiment of Mode I failure, which is one of two representative compressive failure modes, was carried out by using dimensionally proportional cylindrical specimens (CS). An adequate notch length was taken from the experimental results obtained from the compressive strength experiment of various initial notch lengths. Utilizing the notch length, specimen sizes were then varied. In addition, new parameters for the modified size effect law (MSEL) were suggested using Levenberg-Marquardt's least square method (LSM). The test results show that size effect was apparent for axial compressive strength of cracked specimens. Namely, the effect of initial notch length on axial compressive strength size effect was apparent.

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Effects of Grain Size Distribution on the Mechanical Properties of Polycrystalline Graphene

  • Park, Youngho;Hyun, Sangil
    • Journal of the Korean Ceramic Society
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    • v.54 no.6
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    • pp.506-510
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    • 2017
  • One of the characteristics of polycrystalline graphene that determines its material properties is grain size. Mechanical properties such as Young's modulus, yield strain and tensile strength depend on the grain size and show a reverse Hall-Petch effect at small grain size limit for some properties under certain conditions. While there is agreement on the grain size effect for Young's modulus and yield strain, certain MD simulations have led to disagreement for tensile strength. Song et al. showed a decreasing behavior for tensile strength, that is, a pseudo Hall-Petch effect for the small grain size domain up to 5 nm. On the other hand, Sha et al. showed an increasing behavior, a reverse Hall-Petch effect, for grain size domain up to 10 nm. Mortazavi et al. also showed results similar to those of Sha et al. We suspect that the main difference of these two inconsistent results is due to the different modeling. The modeling of polycrystalline graphene with regular size and (hexagonal) shape shows the pseudo Hall-Petch effect, while the modeling with random size and shape shows the reverse Hall-Petch effect. Therefore, this study is conducted to confirm that different modeling is the main reason for the different behavior of tensile strength of the polycrystalline structures. We conducted MD simulations with models derived from the Voronoi tessellation for two types of grain size distributions. One type is grains of relatively similar sizes; the other is grains of random sizes. We found that the pseudo Hall-Petch effect and the reverse Hall-Petch effect of tensile strength were consistently shown for the two different models. We suspect that this result comes from the different crack paths, which are related to the grain patterns in the models.

A Convergence Study about Meta-Analysis on the Effects of ACT Intervention Program (수용전념치료(ACT)프로그램 효과의 메타분석에 대한 융합연구)

  • Kim, Kyung Hee
    • Journal of the Korea Convergence Society
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    • v.7 no.5
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    • pp.145-153
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    • 2016
  • The purpose of this study was using a meta-analysis to estimate effect size ACT intervention program. Using a statistical method, meta-analysis has advantages that prove intervention's amount and direction. Meta-analysis facilitates comprehensive analysis. Through the data collection, 43studies were selected and 183 effect size were calculated as analysis objects. Using a 183 effect size, the overall effect size, Effect Size of categorical Factor, meta-regression result were suggested. The overall effect size of ACT program was 0.704. In the effect area of ACT, the affective domain had the largest effect size. Next were the cognitive domain, the behavioral domain. Analysis on gender of participant, mixed group had the largest effect size. Next were the female grouop, male group. Analysis on age of participant, adult group had the largest effect size. Next were the undergraduate grouop, adolescent group. Based on the findings, implications for future study were discussed.