• Structural Engineering and Mechanics
• /
• v.53 no.5
• /
• pp.939-956
• /
• 2015

In this study, in order to propose an efficient model to predict the torque capacity of steel fiber reinforced concrete (SFRC) beams, the existing experimental data related to torsional response of beams is reviewed. It is observed that existing data neglects the effects of some parameters on the variation of torque capacity. Thus, an experimental research was also conducted to obtain the effects of neglected parameters. In the experimental study, a total of seventeen SFRC beams are tested against torsion. The parameters considered in the experiments are concrete compressive strength, steel fiber aspect ratio, volumetric ratio of steel fibers and longitudinal reinforcement ratio. The effect of each parameter is discussed in terms of torque versus unit angle of twist graphs. The data obtained from this experimental research is also combined with the data got from previous studies and employed in artificial neural network (ANN) analysis to estimate the ultimate torque capacity of SFRC beams. In addition to parameters considered in the experiments, aspect ratio of beam cross-section, yield strengths of both transverse and longitudinal reinforcements, and transverse reinforcement ratio are also defined as parameters in ANN analysis due to their significant effects observed in previous studies. Assessment of the accuracy of ANN analysis in estimating the ultimate torque capacity of SFRC beams is performed by comparing the analytical and experimental results. Comparisons are conducted in terms of root mean square error (RMSE), mean absolute error (MAE) and coefficient of efficiency ($E_f$). The results of this study revealed that addition of steel fibers increases the ultimate torque capacity of reinforced concrete beams. It is also found that ANN is a powerful method and a feasible tool to estimate ultimate torque capacity of both normal and high strength concrete beams within the range of input parameters considered.

• Asian Pacific Journal of Cancer Prevention
• /
• v.16 no.18
• /
• pp.8271-8279
• /
• 2016

Background: Hepato-carcinogenesis is multifaceted in its molecular aspects. Among the interplaying agents are altered gap junctions, the proteasome/autophagy system, and mitochondria. The present experimental study was designed to outline the roles of these players and to investigate the tumor suppressive effects of curcumin with or without mesenchymal stem cells (MSCs) in hepatocellular carcinoma (HCC). Materials and Methods: Adult female albino rats were divided into normal controls and animals with HCC induced by diethyl-nitrosamine (DENA) and $CCl_4$. Additional groups treated after HCC induction were: Cur/HCC which received curcumin; MSCs/HCC which received MSCs; and Cur+MSCs/HCC which received both curcumin and MSCs. For all groups there were histopathological examination and assessment of gene expression of connexin43 (Cx43), ubiquitin ligase-E3 (UCP-3), the autophagy marker LC3 and coenzyme-Q10 (Mito.Q10) mRNA by real time, reverse transcription-polymerase chain reaction, along with measurement of LC3II/LC3I ratio for estimation of autophagosome formation in the rat liver tissue. In addition, the serum levels of ALT, AST and alpha fetoprotein (AFP), together with the proinflammatory cytokines $TNF{\alpha}$ and IL-6, were determined in all groups. Results: Histopathological examination of liver tissue from animals which received DENA-$CCl_4$ only revealed the presence of anaplastic carcinoma cells and macro-regenerative nodules. Administration of curcumin, MSCs; each alone or combined into rats after induction of HCC improved the histopathological picture. This was accompanied by significant reduction in ${\alpha}$-fetoprotein together with proinflammatory cytokines and significant decrease of various liver enzymes, in addition to upregulation of Cx43, UCP-3, LC3 and Mito.Q10 mRNA. Conclusions: Improvement of Cx43 expression, nonapoptotic cell death and mitochondrial function can repress tumor growth in HCC. Administration of curcumin and/or MSCs have tumor suppressive effects as they can target these mechanisms. However, further research is still needed to verify their effectiveness.

• Journal of Periodontal and Implant Science
• /
• v.50 no.5
• /
• pp.327-339
• /
• 2020

Purpose: The purpose of this study was to examine the local tissue reactions associated with 3 different poly(lactic-co-glycolic acid) (PLGA) prototype membranes and to compare them to the reactions associated with commercially available resorbable membranes in rats. Methods: Seven different membranes-3 synthetic PLGA prototypes (T1, T2, and T3) and 4 commercially available membranes (a PLGA membrane, a poly[lactic acid] membrane, a native collagen membrane, and a cross-linked collagen membrane)-were randomly inserted into 6 unconnected subcutaneous pouches in the backs of 42 rats. The animals were sacrificed at 4, 13, and 26 weeks. Descriptive histologic and histomorphometric assessments were performed to evaluate membrane degradation, visibility, tissue integration, tissue ingrowth, neovascularization, encapsulation, and inflammation. Means and standard deviations were calculated. Results: The histological analysis revealed complete integration and tissue ingrowth of PLGA prototype T1 at 26 weeks. In contrast, the T2 and T3 prototypes displayed slight to moderate integration and tissue ingrowth regardless of time point. The degradation patterns of the 3 synthetic prototypes were similar at 4 and 13 weeks, but differed at 26 weeks. T1 showed marked degradation at 26 weeks, whereas T2 and T3 displayed moderate degradation. Inflammatory cells were present in all 3 prototype membranes at all time points, and these membranes did not meaningfully differ from commercially available membranes with regard to the extent of inflammatory cell infiltration. Conclusions: The 3 PLGA prototypes, particularly T1, induced favorable tissue integration, exhibited a similar degradation rate to native collagen membranes, and elicited a similar inflammatory response to commercially available non-cross-linked resorbable membranes. The intensity of inflammation associated with degradable dental membranes appears to relate to their degradation kinetics, irrespective of their material composition.

• Korean Journal of Occupational Health Nursing
• /
• v.26 no.3
• /
• pp.142-150
• /
• 2017

Purpose: The purpose of this descriptive, cross-sectional study was to identify the factors affecting health-related quality of life by examining the relationships among posttraumatic stress, health-related work limitations, and family support in firefighters. Methods: The data were collected from 390 firefighters working in four fire stations located in the G district using self-report questionnaires. The collected data were analyzed using descriptive statistics, t-test, one-way ANOVA along with the $Scheff{\acute{e}}$ test, and multiple regression. Results: As per the results of multiple regression analysis, the factors affecting health-related quality of life in firefighters were posttraumatic stress, health-related work limitations, and family support. This model explained 31% of the variance in health-related quality of life (F=30.03, p<.001). Conclusion: Considering the findings of this study, there is a need to reduce posttraumatic stress and health-related work limitations and develop family support toward firefighters.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.2
• /
• pp.66.2-66.2
• /
• 2017

The Korea Astronomy and Space Science Institute plans to develop a coronagraph in collaboration with National Aeronautics and Space Administrative (NASA) and install it on the International Space Station (ISS). The coronagraph is an externally occulted one stage coronagraph with a field of view from 2.5 to 15 solar radii. The observation wavelength is approximately 400 nm where strong Fraunhofer absorption lines from the photosphere are scattered by coronal electrons. Photometric filter observation around this band enables the estimation of 2D electron temperature and electron velocity distribution in the corona. Together with the high time cadence (< 12 min) of corona images to determine the geometric and kinematic parameters of coronal mass ejections, the coronagraph will yield the spatial distribution of electron density by measuring the polarized brightness. For the purpose of technical demonstration, we intend to observe the total solar eclipse in 2017 August for the filter system and to perform a stratospheric balloon experiment in 2019 for the engineering model of the coronagraph. The coronagraph is planned to be installed on the ISS in 2021 for addressing a number of questions (e.g. coronal heating and solar wind acceleration) that are both fundamental and practically important in the physics of the solar corona and of the heliosphere.

• The Mathematical Education
• /
• v.44 no.2 s.109
• /
• pp.307-323
• /
• 2005

The purpose of this study was to develop a program to cultivate mathematical creativity based on open-ended problem and to investigate its effect. The major features of this innovative program are (a) breaking up fixations, (b) multiple answers, (c) various strategies, (d) problem posing, (e) exploring strategies, (f) selecting and estimating, (g) active exploration through open-ended problems. 20 units for 7th grade mathematics were developed. This study hypothesizes that experimental students may develop more divergent thinking abilities than their traditional counterparts. The participants were 7th grade students attending middle schools in Seoul. Instruments were pre and post tests to measure mainly divergent thinking skills through open-ended problems. The results indicated that the experimental students achieved better than the comparison students on overall and each component of fluency, flexibility, and originality of divergent thinking skills, when deleting the effect of covariance of the pretest. The developed program can be a useful resource for teachers to use in enhancing their students' creative thinking skills. Further this open-ended approach can be served as a model to implement in classes. This study suggests that further investigations are needed in order to examine effects on affective domains such as motivation and task perseverance which are also considered as important factors of creativity.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.1
• /
• pp.34-42
• /
• 1986

An interface of a circular arc formed by two isotropic, homogeneous elastic materials is investigated. It is shown that L integral satisfies the conservation law for the interface if it is perfectly bonded, in frictionless contact or separated such as in a crack with the origin of the coordinate system being located at the center of the circular arc. The property of path independence of the L integral is applied to an interfacial crack problem, to obtain the stress intensity factors, where the interfacial crack is located along the arc of the circular inclusion embedded in infinite matrix. It is assumed here that the contact zone exist as in the model proposed by Comninou, thus removing the overlapping of the materials along the interface. Another example is shown for case of a circular interfacial crack in the matrix of finite size, where the stress intensity factors are determined by computing a value of the L integral numerically along the path far from the crack tip.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.1 no.2
• /
• pp.74-83
• /
• 1997

The definition of burning admittance and conventional n-$\tau$ stability rating technique are combined to investigate the high frequency combustion instabilities inside the cylindrical combustion chamber. Perturbed flow variables are written as the sum of fluctuating and time-averaged mean quantities on the assumption that the terms of the order higher than unity are sufficiently small, hence linearized governing equations could be formulated. Chamber admittances up and downstream of the flame front calculated with appropriate boundary conditions result in the burning admittance and corresponding n-$\tau$ neutral stability curve. Configurational and operational design factors are tested to detect the unstable wave-induced LOX-RP1 combustion instabilities. Operational design factors, e.g. pressure or O/F ratio, appear less influential to drive high frequency instability while the location of the flame front and configurational factors enhance or deteriorate the stabilities strongly. Conclusively, LOX-RP1 combustion inside the cylindrical combustion chamber is apt to be unstable against long residence time and shortened chamber length.

• Journal of the Society of Naval Architects of Korea
• /
• v.39 no.2
• /
• pp.34-44
• /
• 2002

Approximately 70 percent of shop's hull plate consists of three-dimensional curved shell. Concerning with the research on the automation of plate forming many studies have been carried out for the last decade. The purpose of this study is to develop the simulator of heating on the basis of the reasonable mechanical model representing a heating phenomenon. The beating experiment has been carried out with varying parameters influencing on the results of heating information at the kinematics analysis, simulatorestimate the shape of deformed plate that process along the processing information. When we get the initial shape and the object shape, we calculate the processing information first, using kinematics analysis. In a simulator we estimate deformed shape from the processing information. After this we compare deformed shape and object shape. If the error of deformed shape and object shape is in the proper limits, that information is determined the final processing information. Else we repeat the process changing variable.

• Journal of Families and Better Life
• /
• v.9 no.1 s.17
• /
• pp.81-94
• /
• 1991

The Purpose of this study is to determine how Korean and United Sates families manage resourcese. Further, socioeconomic and social psychological determinants of frequency of family resoures management will be investigated for each country. Comparision of results well be made to find similarities and differences between Korea and the U.S. Most studies of family resource management have used urban samples, so this study adds to understanding of another segment of the populations. Family resource management variables, as dependent variables, were measured by asking respondents how often they used a variety of wasys to handle finances and time. Independent variables were : (a) total household income, (b) respondents education, (c) respondents ages, (d) householder size, (e) family adaptability, (f) family cohesion, and (g) interpersonal communications. Data for the Korean sample were collected in rural areas of South Korea during summer 1989, U.S. data were collected in two counties of Illinois. The data used in this study include 473 Korean samples and 301 U.S. families. In both samples, the respondent was the financial manager, the person who usually handled the finances and paid the bills. The data were analyzed by frequencys, t-test, and multiple regression analysis methods. As a results, U.S. respondents tended to engage in family resource management more frequently than Korean respondents. This could be attributed to a longer history of consumer education and financial management education taught in the public schools and through the Cooperative Extension Service in the U.S. Social-psycological variables were significant predictors of frequency of family financial management in both samples. the differences in both samples are that, in Korea, frequency of family financial management increased as household size and educational years increased, however, in the United States, the relationships of these variables were not significant. Some similarities and differences were found in Korea and the U.S. families, and this results represents that interpersonal communications are important determinants, even in different cultures. One hadn, the difference of socio-cultural factors result as the difference of some statisical differences. Findings from this study have important implications for research and education, and can be applicated to study of family resource management in other rural areas.