• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.87.2-87.2
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• 2011

Proper motion of sunspots in several active regions was studied to detect their indicator on flare onset, using data from the Solar Flare Telescope at Mitaka (four flaring active regions), TRACE (e.g. NOAA 0424, M1.7 flare on 5 Aug. 2003) and Hinode (e.g. NOAA 10930, X3.4 flare on 13 Dec. 2006). The proper motion of individual sunspots was derived using a local correlation tracking method. As a result, we found that the sunspots that are located under or close to a part of chromospheric flaring patches showed a change in their moving direction prior to the flare onset. The change in their movements took place a half to two hours before the flare onset. On the other hand, sunspots in non-flaring areas or non-flaring active regions did not show this kind of change. It is likely, therefore, that if a sunspot shows the particular movement, a chromospheric flare is to occur in its nearby region. In the most active regions, the part of flare ribbons was located on an emerging bipolar pair of sunspots. The disturbance in the usual motion of the bipolar sunspots and in other sunspots as well can be interpreted as a sign of magnetic shear development leading to final magnetic energy buildup before its sudden release. We suggest that the change in sunspot motion in a short time scale prior to the flare onset can be regarded as a good indicator in predicting the onset timing and location of chromospheric flares.

• Steel and Composite Structures
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• v.37 no.2
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• pp.229-251
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• 2020

In this paper, dynamic buckling of a smart sandwich nanotube is studied. The nanostructure is composed of a carbon-nanotube with inner and outer surfaces coated with ZnO piezoelectric layers, which play the role of sensor and actuator. Nanotube is under magnetic field and ZnO layers are under electric field. The nanostructure is located in a viscoelastic environment, which is assumed to obey Visco-Pasternak model. Non-local piezo-elasticity theory is used to consider the small-scale effect, and Kelvin model is used to describe the structural damping effects. Surface stresses are taken into account based on Gurtin-Murdoch theory. Hamilton principle in conjunction with zigzag shear-deformation theory is used to obtain the governing equations. The governing equations are then solved using the differential quadrature method, to determine dynamic stability region of the nanostructure. To validate the analysis, the results for simpler case studies are compared with others reported in the literature. Then, the effect of various parameters such as small-scale, surface stresses, Visco-Pasternak environment and electric and magnetic fields on the dynamic stability region is investigated. The results show that considering the surface stresses leads to an increase in the excitation frequency and the dynamic stability region happens at higher frequencies.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09c
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• pp.37-46
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• 2010

Marine clays are soft soil deposits having complicated mineralogy and formation characteristics. Thus, characterization of its geotechnical behavior has been a main issue for geotechnical engineers. Nowadays, the importance and applications of geophysical exploration on marine clays are increasing significantly according to the accuracy, efficiency, and reliability of geophysical survey technology. For marine clays, seismic survey is effective for density and elasticity characterization, while electro-magnetic wave provides the information about the fluid conductivity phenomena inside soil. For practical applications, elastic wave technology can evaluate the consolidation state of natural marine clay layers and estimate important geotechnical engineering parameters of artificially reclaimed marine deposits. Electrical resistivity can provide geophysical characteristics such as particle cementation, pore geometry shape, and pore material phase condition. Furthermore, nondestructive geophysical monitoring is applicable for risk management and efficiency enhancement during natural methane gas extraction from gas hydrate-bearing sediments.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1144-1149
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• 2001

In this paper, a sliding mode controller of a fluid engine mount using MR (Magneto-Rheological) fluid was discussed When the MR fluid is applied to a fluid mount, resistance of MR fluid can be controlled by electro-magnetic valve installed in the inertia track. Since the rheological property of the MR fluid shows a function of shear rate, the damping characteristics of the mount will be change according to the frequency. Changing an applied magnetic field to the valve changes the property of the mount, such as the resistance of the MR fluid, the notch and the resonant frequencies due to the fluid passing, quantity of the fluid passing, the effective piston area of the volumetric damping and stiffness. Therefore, the fluid mount using MR fluid can be regarded as a variable structure system The sliding mode control known well as a particular type of variable structure control was introduced in this study. The sliding mode control, which has inherent robustness, is also expected to improve the control performance in the engine mount The sliding mode controller for the mount formatted by taking into account the response property with a time constant to MR fluid and the variable mount property. The motion equations of the fluid mount are derived from Newton's law of motion and used in numerical simulation. Numerical simulations illustrate the effectiveness of the sliding mode controller.

• Structural Engineering and Mechanics
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• v.78 no.5
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• pp.557-572
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• 2021

The current study considers free vibration of the spherical panel with magnetorheological (MR) fluids core and magneto-electro-elastic face sheets. The panel is subjected to electro-magnetic loads and also is located on an orthotropic visco-Pasternak elastic foundation. To describe the displacement components of the structure, the first-order shear deformation theory (FSDT) is used and the motion equations are extracted by employing Hamilton's principle. To solve the motion differential equations, Navier's method is selected as an exact analytical solution for simply supported boundary conditions. Effect of the most important parameters such as magnetic field intensity, loss factor, multi-physical loads, types of an elastic medium, geometrical properties of the panel, and also different material types for the face sheets on the results is considered and discussed in details. The outcomes of the present work may be used to design more efficient smart structures such as sensors and actuators.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.9
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• pp.52-60
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• 2017

This study examined the structural stability of nonlocal magneto-electro-elastic nano plates on elastic foundations using first-order shear deformation theory. Navier's method has been used to solve the buckling loads for all edges simply supported boundary conditions. On the other hand, biaxial buckling analysis of nano-plates has beenrarely studied. According to the Maxwell equation and the magneto-electro boundary condition, the change inthe magnetic and electric potential along the thickness direction of the magneto-electro-elastic nano plate wasdetermined. To reformulate the elasticity theory of the magneto- electro-elastic nano plate, the differential constitutive equation of Eringen was used and the governing equation of the nonlocal elasticity theory was studied using variational theory. The effects of the elastic foundation arebased on Pasternak's assumption. The relationship between nonlocal theory and local theory was analyzed through calculation results. In addition, structural stability problems were investigated according to the electric and magnetic potentials, nonlocal parameters, elastic foundation parameters, and side-to-thickness ratio. The results of the analysis revealedthe effects of the magnetic and electric potential. These calculations can be used to compare future research on new material structures made of magneto-electro-elastic materials.

• Journal of the Korean Ceramic Society
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• v.42 no.2 s.273
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• pp.132-139
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• 2005

Sintering behavior of $BaO-Nd_{2}O_3-TiO_2$ with a Pb-based glassceramics frit were investigated in order to understand an effect of glassceramics as a low temperature sintering agent on dielectric ceramics. A green sheet form was fabricated through tape casting method with the glassceramic fut added $BaO-Nd_{2}O_3-TiO_2$. The dispersion properties, rheological properties and final density of dielectric composit slurry as a function of amount and composition of organic additives was examined. The dispersants' addition was effective in controlling dispersion of the ceramics in solution. The addition of excessive dispersant showed adverse effect on dispersion. The prepared slurries, containing ceramic : powders, glass-ceramics and various kinds of organic viechles, exhibited typical shear thinning behavior. The best properties of tape casting appeared powder to solvent ratio 65 : 35 and amount of the binder 6 wt$\%$ and plasticizer 3 wt$\%$. The viscosity of the slurry was 677 cps and green/sintered density in the tape was $3.3 g/cm^3,\;5.56 g/cm^3$ respectively.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.5
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• pp.405-413
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• 2017

In this paper, we study the biaxial buckling analysis of nonlocal MEE(magneto-electro-elastic) nano plates based on the first-order shear deformation theory. The in-plane electric and magnetic fields can be ignored for MEE(magneto-electro-elastic) nano plates. According to magneto-electric boundary condition and Maxwell equation, the variation of magnetic and electric potentials along the thickness direction of the MME plate is determined. In order to reformulate the elastic theory of MEE(magneto-electro-elastic) nano-plate, the nonlocal differential constitutive relations of Eringen is used. Using the variational principle, the governing equations of the nonlocal theory are discussed. The relations between nonlocal and local theories are investigated by computational results. Also, the effects of nonlocal parameters, in-plane load directions, and aspect ratio on structural responses are studied. Computational results show the effects of the electric and magnetic potentials. These computational results can be useful in the design and analysis of advanced structures constructed from MEE(magneto-electro-elastic) materials and may be the benchmark test for the future study.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.4
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• pp.365-373
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• 2008

Fiber Reinforced Polymer, FRP has a light weight, a high tensile strength based on design, non-electronic, non-magnetic, and rust-resistant feature, etc and many researches are being conducted recently on FRP in the construction area. Among them, GFRP (Glass Fiber Reinforced Polymer) is excellent in price competitiveness and is widely being used. However, since GFRP has a relative low modulus of elasticity and causes excessive deflection, the section must be large to be used as a structural component and an investigative review must be carried out in design to set the limit for deflection by the use load. Therefore, in order to solve the mentioned technical problems, this study suggested a section of a module form such that application of a large-scale section is possible. Also, to secure the low rigidity of FRP, this study developed a new FRP+ concrete composite girder form that confined the concrete. To identify the structural movement of the developed FRP+ concrete composite girder, shear strength test was carried out.

• Journal of the Korean Society of Radiology
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• v.82 no.6
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• pp.1556-1564
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• 2021

Purpose This study aimed to apply MR elastography (MRE) to achieve in vivo evaluation of the elastic properties of thigh muscles and validate the feasibility of quantifying the elasticity of normal thigh muscles using MRE. Materials and Methods This prospective study included 10 volunteer subjects [mean age, 32.5 years, (range, 23-45 years)] who reported normal activities of daily living and underwent both T2-weighted axial images and MRE of thigh muscles on the same day. A sequence with a motion-encoding gradient was used in the MRE to map the propagating shear waves in the muscle. Elastic properties were quantified as the shear modulus of the following four thigh muscles at rest; the vastus medialis, vastus lateralis, adductor magnus, and biceps femoris. Results The mean shear modulus was 0.98 ± 0.32 kPa and 1.00 ± 0.33 kPa for the vastus medialis, 1.10 ± 0.46 kPa and 1.07 ± 0.43 kPa for the vastus lateralis, 0.91 ± 0.41 kPa and 0.93 ± 0.47 kPa for the adductor magnus, and 0.99 ± 0.37 kPa and 0.94 ± 0.32 kPa for the biceps femoris, with reader 1 and 2, respectively. No significant difference was observed in the shear modulus based on sex (p < 0.05). Aging consistently showed a statistically significant negative correlation (p < 0.05) with the shear modulus of the thigh muscles, except for the vastus medialis (p = 0.194 for reader 1 and p = 0.355 for reader 2). Conclusion MRE is a quantitative technique used to measure the elastic properties of individual muscles with excellent inter-observer agreement. Age was consistently significantly negatively correlated with the shear stiffness of muscles, except for the vastus medialis.