• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2161-2163
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• 1999

Generally, ZnO varistors have dynamic characteristics that the cut-off voltage increases as the time to crest of the varistor current decreases. Dynamic characteristics of ZnO varistor are the most important factor in region of the steep front discharge current particularly. Also, V-I characteristics of ZnO varistor have hysterisis loop in time domain and frequency dependency. This paper deals with ZnO varistor numerical equation and modeling method which takes the behavior of varying clamping voltage into consideration during the time to crest, in range of $1{\mu}m{\sim}50{\mu}m$, of impulse current applied to a ZnO varistor. The simulated results by the proposed model are compared with experimental results for each of the impulse current.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1995.10a
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• pp.258-265
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• 1995

For design of seismic isolated system the determination of isolated frequency is very important. In this paper the effects of seismic isolated frequency for cylindrical tank are investigated using the 1940 EL Centre earthquake(NS). From the results of analysis the seismic isolated frequencies significantly depend on input acceleration and displacement components in lower frequency regions. Therefore, the seismic isolated frequency should be determined by consideration of input ground motion characteristics. For the seismic analysis the modified hysteretic hi-linear model of seismic isolators which can consider the yield load variation, shape of hysterisis loop variation and hardening effects of isolators is proposed. The analyses using the proposed model give similar displacement responses but higher maximum acceleration responses than those using the simple hysteretic hi-linear model.

• Journal of Magnetics
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• v.2 no.3
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• pp.105-109
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• 1997

The Preisach model neds a density function or Everett function for the hysterisis operator to simulate the hysteresis phenomena. To obtain the function, many experimental data for the first order transition curves are required. However, it needs so much efforts to measure the curves, especially for the hard magnetic materials. By the way, it is well known that the density function has the Gaussian distribution for the interaction axis on the Preisach plane. In this paper, we propose a simple technique to determine the distribution function or Everett function analytically. The initial magnetization curve is used for the distribution of the Everett function for the coercivity axis. A major, minor loop and the initial curve are used to get the Everett function for the interaction axis using the Gaussian distribution function and acceptable results were obtained.

• Steel and Composite Structures
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• v.23 no.1
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• pp.17-29
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• 2017

The seismic performance of steel beam to concrete-encased composite column with unsymmetrical steel section joints is investigated and reported within this paper. Experimental and analytical evaluation were conducted on a total of 8 specimens with T-shaped and L-shaped steel section under lateral cyclic loading and axial compression. The test parameters included concrete strength, stirrup ratio and axial compression ratio. The response of the specimens was presented in terms of their hysterisis loop behavior, stress distribution, joint shear strength, and performance degradation. The experiment indicated good structural behavior and good seismic performance. In addition, a three-dimensional nonlinear finite-element analysis simulating was conducted to simulate their seismic behaviors. The finite-element analysis incorporated both bond-slip relationship and crack interface interaction between steel and concrete. The results were also compared with the test data, and the analytical prediction of joint shear strength was satisfactory for both joints with T-shaped and L-shaped steel section columns. The steel beam to concrete-encased composite column with unsymmetrical steel section joints can develop stable hysteretic response and large energy absorption capacity by providing enough stirrups and decreased spacing of transverse ties in column.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.5
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• pp.405-412
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• 2012

A flow control on airfoil installed a vortex cell for high efficiency wind turbine blade in stationary and dynamic stall conditions have been numerically investigated by solving the compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with Roe's flux-difference splitting and an implicit time-integration method coupled with dual time step sub-iteration. The computed result for the airfoil in the stationary showed that lift-drag ratio increases due to low pressure by the vortex cell. The oscillating airfoil with the vortex cell showed that the magnitude of hysteresis loop is reduced due to the enhanced vortex in the cell.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.11
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• pp.869-874
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• 2010

Magnetoelectric composites with compositions (1-x)[0.5PZT-0.25PNN-0.25PZN](ferroelectric) - x[$(Ni_{0.9}Zn_{0.1})Fe_2O_4$](ferrite) in which x varies as 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 were prepared by conventional ceramic process. The presence of two phases (ferroelectric phase with large grain and ferrite phase with small grain) in the particulate ceramic composites was confirmed by XRD, SEM and EDX. The ferroelectric and magnetic properties of the composites were studied by measuring the P-E and M-H hysterisis loop on the composite composition (x=0, 0.1, 0.2, 1), they were strongly affects of the phase content in composite. The magnetoelectric votage was measured as a function of DC magnetic field and the maximum magnetoelectric voltage coefficient of 14 mV/cm Oe was observed in x=0.2(80 mol% ferroelectric and 20 mol% ferrite phase).

• Journal of Pharmaceutical Investigation
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• v.35 no.4
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• pp.233-241
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• 2005

Ursolic acid (UA), a bioactive triterpene acid, has been known to increase collagen content in human skin in addition to other actions such as anti-inflammatory, skin-tumor prevention and anti-invasion. However, it is poorly soluble in water. Therefore, we firstly prepared microemulsion system with benzyl alcohol, ethanol and Cremophor EL, RH 40 and Brij 35 as surfactant in order to increase solubility of UA and then prepared microemulsion was dispersed in o/w cream base for the topical delivery of UA in an effort to improve anti-wrinkle effect. The pseudo-ternary phase diagrams were developed and various microemulsion formulations were prepared using benzyl alcohol as an oil, Cremophor EL, RH 40 and Brij 35 as a surfactant. The droplet size of microemulsions was characterized by dynamic light scattering. The accumulation of VA in the skin from topical cream was evaluated in vitro using hairless mouse skins. The mean droplet size was $26.8{\pm}6.6$ nm for microemulsions II with Cremophor EL. All UA creams showed pseudoplastic flow and hysterisis loop in their rheogram, depending on the type of materials added in topical creams. The in vitro accumulation data demonstrated the UA topical cream prepared with the combination of Poloxamer 407 and Xanthan gum as a copolymer showed higher accumulation percentage than those prepared with either Poloxamer 407 or Xanthan gum. These results suggest that UA topical cream using microemulsion systems may be promising for the topical delivery of UA.