• Steel and Composite Structures
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• v.50 no.5
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• pp.563-581
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• 2024

This paper presents a novel finite element model for the free vibration analysis of variable-thickness functionally graded porous (FGP) microplates resting on Pasternak's medium in the hygro-thermal environment. The governing equations are established according to refined higher-order shear deformation plate theory (RPT) in construction with the modified couple stress theory. For the first time, three-node triangular elements with twelve degrees of freedom for each node are developed based on Hermitian interpolation functions to describe the in-plane displacements and transverse displacements of microplates. Two laws of variable thickness of FGP microplates, including the linear law and the nonlinear law in the x-direction are investigated. Effects of thermal and moisture changes on microplates are assumed to vary continuously from the bottom surface to the top surface and only cause tension loads in the plane, which does not change the material's mechanical properties. The numerical results of this work are compared with those of published data to verify the accuracy and reliability of the proposed method. In addition, the parameter study is conducted to explore the effects of geometrical and material properties such as the changing law of the thickness, length-scale parameter, and the parameters of the porosity, temperature, and humidity on the free vibration response of variable thickness FGP microplates. These results can be applied to design of microelectromechanical structures in practice.

• Geomechanics and Engineering
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• v.38 no.2
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• pp.125-137
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• 2024

In paste backfill mining, cemented coal gangue-fly ash backfill (CGFB) can effectively utilize coal-based solid waste, such as gangue, to control surface subsidence. However, given the pressurized water accumulation environment in goafs, CGFB is subject to coupling effects from water pressure and chloride ions. Therefore, studying the influence of pressurized water on the chlorine salt erosion of CGFB to ensure green mining safety is important. In this study, CGFB samples were soaked in a chloride salt solution at different pressures (0, 0.5, 1.5, and 3.0 MPa) to investigate the chloride ion transport characteristics, hydration products, micromorphology, pore characteristics, and mechanical properties of CGFB. Water pressure was found to promote chloride ion transfer to the CGFB interior and the material hydration reaction; enhance the internal CGFB pore structure, penetration depth, and chloride ion content; and fill the pores between the material to reduce its porosity. Furthermore, the CGFB peak uniaxial compression strain gradually decreased with increasing soaking pressure, whereas the uniaxial compressive strength first increased and then decreased. The resulting effects on the stability of the CGFB solid-phase hydration products can change the overall CGFB mechanical properties. These findings are significant for further improving the adaptability of CGFB for coal mine engineering.

• Journal of the Korean School Mathematics Society
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• v.5 no.2
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• pp.71-82
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• 2002

This study purported to develop the learning materials for the optional activities of mathematics, apply them to the students, and examine the effect on the learner's interest and attitude to mathematics. In order to conduct this study, the learning materials for the mathematics optional activities were developed according to the units of grade 8-Ga and the developed learning materials of the mathematics optional activities were inputted in two classes for 18 units after the second grade middle school students in Daejeon area received the questionnaire regarding the learning attitude and the interest in the mathematics. After that, the questionnaire regarding the learning attitude and the interest in the mathematics and the examination regarding the response to the application of the learning materials for mathematics optional activities were conducted and did t-test. The results of the study as follows : First The learning materials applied exciting games for mathematics optional activities aroused interest in mathematics and made the learners have confidence in mathematics learning. Second, There was affirmative change in the interest and attitude to the mathematics learning with the application of the mathematics optional learning materials. Third The leaning materials of the mathematics optional activities made the learners think mathematical questions connected with the real life and try various ways to solve the questions. Here are some suggestions to study the development of the learning materials such as story, game, quiz and craft. First it is necessary to develop the learning materials applied the games or the real life matters connected with mathematics for all grade middle school students and use them in the mathematics optional activities. Second, many students feel a great interest in animation. moving picture, sound graphic, etc. If the multimedia learning materials included the real life matters or the games are developed, the learners will feel more interest in mathematics. Third, the systematic and economical support is continuously needed in order that teachers are given much time to study and the opportunity to attend the training course for the understanding of the optional activities and the development of the various learning materials.

• Advances in nano research
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• v.15 no.4
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• pp.339-353
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• 2023

This work aims to present a solution for the buckling behavior of perforated nano/microbeams with deformable boundary conditions using nonlocal strain gradient theory (NLSGT). For the first time, a solution that can provide buckling loads based on the non-local and strain gradient effects of perforated nanostructures on an elastic foundation, while taking into account both deformable and rigid boundary conditions. Stokes' transformation and Fourier series are used to realize this aim and determine the buckling loads under various boundary conditions. We employ the NLSGT to account for size-dependent effects and utilize the Winkler model to formulate the elastic foundation. The buckling behavior of the perforated nano/microbeams restrained with lateral springs at both ends is studied for various parameters such as the number of holes, the length and filling ratio of the perforated beam, the internal length, the nonlocal parameter and the dimensionless foundation parameter. Our results indicate that the number of holes and filling ratio significantly affect the buckling response of perforated nano/microbeams. Increasing the filling ratio increases buckling loads, while increasing the number of holes decreases buckling loads. The effects of the non-local and internal length parameters on the buckling behavior of the perforated nano/microbeams are also discussed. These material length parameters have opposite effects on the variation of buckling loads. This study presents an effective eigenvalue solution based on Stokes' transformation and Fourier series of the restrained nano/microbeams under the effects of elastic medium, perforation parameters, deformable boundaries and nonlocal strain gradient elasticity for the first time.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.5
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• pp.2259-2266
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• 2012

This study was analyzed the 119 rescuers' image of citizens to provide a fundamental material to improve 119 rescuers' image effectively. This research design was a descriptive study. Data were collected from November 9, 2011 to December 9, 2011, and analyzed by SPSS PASW statistics 18.0 program. Among the 4 subcategories of the image, occupational image was found the highest value($3.17{\pm}0.36$), and the social image($2.81{\pm}0.48$) was found the lowest. There were statistical different between age($p$ <.001), occupation($p$ <.001), whether or not the emergency first response education is completed($p$ <.05), and whether or not 119 emergency service is received($p$ <.05). In the result of multivariate regression analysis, adjusted $R^2$ value was 0.120. The model fit 12.0%. Occupation (students, housewives and office workers) and those who completed emergency first response education were showed a positive image of 119 rescuers. There is a need to compare and analyze the image of 119 rescuers in accordance with whether or not 119 emergency service is received and the satisfaction with the emergency service under the control of the general characteristics(sex, age, occupation, economic level, etc.) of subjects.

• 대한공업교육학회지
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• v.39 no.1
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• pp.128-142
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• 2014

The purpose of this study was to provide a basis information for the education direction of 'creative engineering design' lesson to highschool students and pre-technology teachers by analyzing pre-experienced the d epartment of technology professors' recognitions, according to the newly opened unit 'creative engineering design' in 2009 revised highschool technology home economics education curriculum. The survey questionnaire was composed of 34 questions and collected from 16 department of technology education professors. The data was analyzed by SPSS program. The results of study were as follows : First, in 'creative engineering design' educational objectives, the highest average level(M) of response was problem solving ability, the opportunity of engineering experience and creativity improvement were followed. In the response about 'creative engineering design' educational contents, the average level(M) of the creative thinking method education was the highest(3.94). and the following important level was the write training education for presentation. Second, in the 'creative engineering design' educational areas, the professors preferred the idea conception, design, and production manufacturing area. In the teaching learning method, the average level(M) of design-based learning method was the first. and PBL, problem solving method were favored Third, in the 'creative engineering design' lesson manage, the secure of practice room and material cost, and the check of the progress situations were needed preferentially. In the education assessments, various and combined assessment preferred such as production, portfolio, and presentation. Fourth, in the pre-technology teachers' lesson of the university course, the product manufacturing level was preferred production to improve uncomfortable thing in life. The major difficulty in product manufacturing was the lack of major knowledge and product conception.

• Korean Journal of Environmental Agriculture
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• v.34 no.4
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• pp.294-302
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• 2015

BACKGROUND: Chemical accidents have increased owing to chemical usage, human error and technical failures during the last decades. Many countries have organized supervisory authorities in charge of enforcing related rules and regulations to prevent chemical accidents. A very important part in chemical accidents has been coping with comprehensive first aid tool. Therefore, the present research has provided information with the initial applications concern to the rapid analysis of hazardous material using instruments in vehicle of field mode after chemical accidents. METHODS AND RESULTS: Mobile measurement vehicle was manufactured to obtain information regarding field assessments of chemical accidents. This vehicle was equipped with four instruments including gas chromatography with mass spectrometry (GC/MS), Fourier Transform Infrared Spectroscopy (FT-IR), Ion Chromatography (IC), and UV/Vis spectrometer (UV) to analyses of accident preparedness substances, volatile compounds, and organic gases. Moreover, this work was the first examined the evaluation of applicability for analysis instruments using 20 chemicals in various accident preparedness substances (GC/MS; 6 chemicals, FT-IR; 2 chemicals, IC; 11 chemicals, and UV; 1 chemical) and their calibration curves were obtained with high linearity ( r ² > 0.991). Our results were observed the advantage of the high chromatographic peak capacity, fast analysis, and good sensitivity as well as resolution. CONCLUSION: When chemical accidents are occurred, the posted measurement vehicle may be utilized as tool an effective for qualitative and quantitative information in the scene of an accident owing to the rapid analysis of hazardous material.

• Journal of Acupuncture Research
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• v.18 no.5
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• pp.60-69
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• 2001

Objective : Recent studies Suggested that there is a strong correlation between acupuncture stimulation and its related cortical activation. Anther study showed that either positive or negative BOLD effects could be observed depending on anatomical structure in acupuncture. Material and Methods : 1) Subjects and paradigms : Two separate stimulation paradigms were performed on five healthy (aged 22-23 yrs) in this study. First, the paradigm of acupuncture stimulation was that the acupuncture needle was inserted in acupoints KI6(照海), which is located in lateral side of the foot and then continuously twisted(補瀉를 除外한 捻轉法) for 70 seconds for 10 cycles of activation. During rest period (70 seconds), the needle was completed removed from acupoint. Total 60 cycles were performed and 10 images were obtained per cycle. Second, non-acupoint was randomly selected and the same paradigm was performed as acupoint stimulation. The stimulation protocol comprised 10 cycles of alternating activation and rest (10 images per cycle). Total 60 cycles were performed and each cycle take about 1.5 sec for motor task. Subjects take an at least 15 minutes break before starting anther paradigm. Conclusion : In this study, I investigated a new acupoint KI6(照海) which was known as motor - related acupoint and obtained an evidence that the stimulation of KI6(照海) resulted in negative BOLD response to stimulation.

• Korean Chemical Engineering Research
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• v.47 no.6
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• pp.715-719
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• 2009

The phase change electrode board for the bio-information detection through electrical property response of phase change material was developed in this study. We manufactured the electrode board using Aluminum first that is widely used in conventional semiconductor device process. Without further treatment, these aluminum electrodes tend to contain voids in PETEOS(plasma enhanced tetraethyoxysilane) material that are easily detected by cross-sectional SEM(Scanning Electron Microscope). The voids can be easily attacked and transformed into holes in between PETEOS and electrodes after etch back and washing process. In order to resolve this issue of Al electrode board, we developed a electrode board manufacturing method using low resistivity TiN, which has advantages in terms of the step-coverage of phase change($Ge_2Sb_2Te_5$, GST) thin film as well as thermodynamic stability, without etch back and washing process. This TiN material serves as the top and bottom electrode in PRAM(Phase-change Random Access Memory). The good connection between the TiN electrode and GST thin film was confirmed by observing the cross-section of TiN electrode board using SEM. The resistances of amorphous and crystalline GST thin film on TiN electrodes were also measured, and 1000 times difference between the amorphous and crystalline resistance of GST thin film was obtained, which is well enough for the signal detection.

• Journal of the korean academy of Pediatric Dentistry
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• v.35 no.3
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• pp.427-436
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• 2008

Purpose. The objective of this study was to evaluate the behavioral response and assess the effectiveness of additional intranasal (IN) and submucosal (SM) administration of midazolam during pediatric sedation for dental procedure. Material and methods. Thirty-three cases of healthy (ASAⅠ), uncooperative children aged from 24 to 72 month old at pediatric dental clinic of Ewha Womans University Hospital were selected for this study. Children received oral chloral hydrate 50 mg/kg with hydroxyzine 1.0 mg/kg. After waiting for 45 minutes, midazolam 0.2 mg/kg was administrated via IN route and via SM route randomly maintaining 50% of $N_2O$. A pulse oximeter and a capnograph were used for measuring vital signs ($SpO_2$, PR, RR, $EtCO_2$) throughout the sedation. Behavioral response was evaluated as Quiet (Q), Crying (C), Movement (M) or Struggling (S) in every 2 minutes for 40 minutes. Results. There were also no statistically significant differences in vital signs of the two groups. The behavioral response for the first ten minutes during sedation was a statistically significant difference (P < 0.05) between the two groups. After the first ten minutes, it was revealed that there was no significant difference. Conclusion. This study demonstrated that the addition of IN midazolam to the combination of oral chloral hydrate with hydroxyzine and nitrous oxide/oxygen inhalation is as safe and effective as that of SM midazolam in pediatric sedation for dental procedure.