• Structural Engineering and Mechanics
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• v.73 no.5
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• pp.565-584
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• 2020

The nonlinear thermo-electro-elastic buckling behavior of viscoelastic nanoplates under magnetic field is investigated based on nonlocal elasticity theory. Employing nonlinear strain-displacement relations, the geometrical nonlinearity is modeled while governing equations are derived through Hamilton's principle and they are solved applying semi-analytical generalized differential quadrature (GDQ) method. Eringen's nonlocal elasticity theory considers the effect of small size, which enables the present model to become effective in the analysis and design of nano-sensors and nano actuators. Based on Kelvin-Voigt model, the influence of the viscoelastic coefficient is also discussed. It is demonstrated that the GDQ method has high precision and computational efficiency in the buckling analysis of viscoelastic nanoplates. The good agreement between the results of this article and those available in literature validated the presented approach. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of the several parameters such as electric voltage, small scale effects, elastomeric medium, magnetic field, temperature effects, the viscidity and aspect ratio of the nanoplate on its nonlinear buckling characteristics. It is explicitly shown that the thermo-electro-elastic nonlinear buckling behavior of viscoelastic nanoplates is significantly influenced by these effects. Numerical results are presented to serve as benchmarks for future analyses of viscoelastic nanoplates as fundamental elements in nanoelectromechanical systems.

• Advances in nano research
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• v.12 no.3
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• pp.231-251
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• 2022

Dynamic behavior of temperature-dependent Reddy functionally graded (RFG) nanobeam subjected to thermomagnetic effects under the action of moving point load is carried out in the present work. Both symmetric and sigmoid functionally graded material distributions throughout the beam thickness are considered. To consider the significance of strain-stress gradient field, a material length scale parameter (LSP) is introduced while the significance of nonlocal elastic stress field is considered by introducing a nonlocal parameter (NP). In the framework of the nonlocal strain gradient theory (NSGT), the dynamic equations of motion are derived through Hamilton's principle. Navier approach is employed to solve the resulting equations of motion of the functionally graded (FG) nanoscale beam. The developed model is verified and compared with the available previous results and good agreement is observed. Effects of through-thickness variation of FG material distribution, beam aspect ratio, temperature variation, and magnetic field as well as the size-dependent parameters on the dynamic behavior are investigated. Introduction of the magnetic effect creates a hardening effect; therefore, higher values of natural frequencies are obtained while smaller values of the transverse deflections are produced. The obtained results can be useful as reference solutions for future dynamic and control analysis of FG nanobeams reinforced nanocomposites under thermomagnetic effects.

• International Journal of Aerospace System Engineering
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• v.2 no.1
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• pp.12-17
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• 2015

Aero-optical effects induced by the flow around the optical window degrade the performance of the IR seeker, especially for the hypersonic flow. For the thermochemical non-equilibrium flow, index of refraction model and optical transmission calculation method are developed to predict the aero-optical effects. The optical distortion is discussed for the typical optical widow shape and flow condition. The influence on aero-optical effects is analyzed.

• Journal of the Optical Society of Korea
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• v.1 no.1
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• pp.23-25
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• 1997

In this paper we will show theoretically that a refractive index grating exhibits a retro-self-focusing effect and an accompanying pinholing effect under the Gaussian intensity distribution of an incident optical field. Those effects result from an effective wave number change of the medium due to the intense optical field.

• Journal of Korean Institute of Industrial Engineers
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• v.23 no.3
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• pp.533-544
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• 1997

Among numerous factors that have an effect on visual field, the effects of background condition on the size of the visual field were investigated to obtain more practical visual field that can be readily applicable to industrial settings. A visual experiment was conducted, in which the subject was instructed to search a target with distinct orientations. Size contrast, meridian, nontarget density, and subject's gender showed a significant effect on the size of the visual field at $\alpha=0.01$. The size of the visual field was linearly proportional to size contrast, and inversely proportional to density. Female's visual fields were found to be significantly larger than male subjects', The size of the visual field on horizontal axis was larger than that on vertical axis, and the size of the head & eye field on right meridian was also larger than that on left meridian. The shape was found to be horizontally oriented oval and statistically asymmetric with respect to horizontal and vertical axes. The regression equations to predict the visual fields on the given background condition were suggested. The visual fields suggested in this study would be valuable to the design of visual displays and the panel layout of various displays and controls.

• Journal of Technologic Dentistry
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• v.44 no.3
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• pp.81-88
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• 2022

Purpose: This study was conducted to verify the effects of self-esteem and critical thinking disposition on dental laboratory technology students' field practice stress. Methods: The subjects of the study were 198 dental laboratory technology students with clinical practice experience located in Gyeongsangbuk-do and Gyeongsangnam-do. The collected data were analyzed by t-test, ANOVA, correlation analysis, and linear regression analysis using IBM SPSS Statistics ver. 22.0 (IBM). Results: The average self-esteem, critical thinking disposition, and field practice stress scores were 3.76, 3.50, and 2.40, respectively. There was a significant correlation between self-esteem, critical thinking disposition, and field practice stress. It was found that the higher the self-esteem, the lower was the field practice stress. On the contrary, among the sub-items of critical thinking disposition, when intellectual fairness increased, the field practice stress decreased; however, when healthy skepticism increased, the field practice stress increased. Conclusion: Self-esteem and critical thinking disposition were both found to have a substantial effect on field practice stress. Therefore, various educational programs need to increase self-esteem and cultivate critical thinking skills for a successful field practice and field practice stress relief of laboratory technology students.

• Communications of Mathematical Education
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• v.30 no.2
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• pp.139-159
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• 2016

This study is the field of mathematics education on the assumption that they can extend outside the classroom. Recent mathematics education is increasing the importance of field experience and various activities based on real-life math education. Thus, it is necessary to consider this situation in pre-service teacher's education. The purpose of this study is to apply the 'Mathematics Field Trips Activities' in the pre-mathematics teacher education. So the specific case of 'Mathematics Field Trips Activities' was analyzed. Mathematics teachers conducted preliminary exploration activities on the historical cultural property which were effective in the following four aspects. First, cognitive effects and second, definitive effect. Third, cultural-mathematical effect. Fourth, the effect on improving math class. Finally they were summarized and divided into classes target content knowledge and teaching knowledge both sides. As a result, the 'Mathematics Field Trips Activities' were found to have significant effects on pre-service math teacher. Finally, ongoing research is needed to settle into a new teaching and learning methods.

• Korean Journal of Materials Research
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• v.9 no.7
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• pp.680-687
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• 1999

Fe-Al intermetallic compounds were manufactured by using the field-activated combustion synthesis process. Effects of chemical composition(Fe:Al= 3: 1,2:1, 1:1, 1:2, 1:3), Compaction pressure(150, 250, 350MPa) and electrical resistance on the reaction were investigated in this system. As the molar ratio of Al, compaction pressure and electric field increased, the combustion temperature and velocity were increased. The influences for reaction with current adjust way were investigated in this system. But in the absence of a electric field, the reaction could sustain a nonsteady combustion wave and was not completed. The reaction products were characterized with X-ray, SEM and EDXS to determine the structure and composition.

• Journal of Magnetics
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• v.7 no.2
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• pp.45-50
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• 2002

A magnetic field annealing is firstly used for nanostructured Sm-Co/Co films, prepared by magnetron sputtering method. The effects of magnetic field annealing on single-layered Sm-Co films are different from those on multi-layered Sm-Co/Co films. A detailed analysis of microstructures and magnetic properties is made by means of HRTEM, Auger electron spectroscopy, XRD and Physical Property Measurement System (PPMS). From magnetic properties and microstructure analysis, it was confirmed that these differences originate from the effects of magnetic field annealing on crystallization behavior of the films. The relationship between magnetic properties and microstructures explains a different demagnetization process of single-layered and multilayered films. For the single-layered Sm-Co films, magnetic-field-annealing makes the main phases change from $CaCu_5/ to Zn_2Th_{17}$ structure, resulting in a decrease of coercivity. The results show that the magnetic-field-annealing is useful to improve the properties of nanostructured Sm-Co(30 nm)/Co(10 nm) films, which ascribe to improving the pinning effectiveness in coercivity mechanism and decreasing the magnetostatic interaction of films. A very high coercivity about 0.7 T was obtained from nanoscaled multi-layered Sm-Co(30 nm)-/Co(10 nm) films.

• Korean Journal of Metals and Materials
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• v.49 no.6
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• pp.505-513
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• 2011

A magnetic device which enables the application of a strong and uniform magnetic field to thin film during sputtering was designed for controlling the magnetic anisotropy using a three dimensional finite element method, and the effects of the external magnetic field on the magnetic properties of sputtered thin films were investigated. Both the intensity and the uniformity of the magnetic flux density in the sputter zone (50 mm ${\times}$50 mm) was dependent on not only the shape and size of the magnet device but also the magnitude of stray fields from the magnet. For the magnet device in which the distance between two magnets or two pure iron bars was 80-90 mm, the magnetic flux density along the direction normal to the external magnetic field direction was minimum. The two row magnets increased the magnetic flux density and uniformity along the external magnetic field direction. An Fe thin film sputtered using the optimized magnet device showed a higher remanence ratio than that fabricated under no external magnetic field.