• Communications for Statistical Applications and Methods
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• v.26 no.6
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• pp.583-589
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• 2019

Counterexamples of a skew-normal distribution are developed to improve our understanding of this distribution. Two examples on bivariate non-skew-normal distribution owning marginal skew-normal distributions are first provided. Sum of dependent skew-normal and normal variables does not follow a skew-normal distribution. Continuous bivariate density with discontinuous marginal density also exists in skew-normal distribution. An example presents that the range of possible correlations for bivariate skew-normal distribution is constrained in a relatively small set. For unified skew-normal variables, an example about converging in law are discussed. Convergence in distribution is involved in two separate examples for skew-normal variables. The point estimation problem, which is not a counterexample, is provided because of its importance in understanding the skew-normal distribution. These materials are useful for undergraduate and/or graduate teaching courses.

• Progress in Superconductivity
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• v.13 no.2
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• pp.85-89
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• 2011

Using the density functional theory and its combination to the dynamical mean field theory (DMFT), we have studied the electronic and magnetic structures of Fe-based superconductors, $AFe_2As_2$ (A=Ca, Sr, Ba). Our results for the electronic structure agree well with existing angle resolved photoemission spectroscopy (ARPES) data. The temperature dependent magnetization has been calculated using DMFT, and the magnetic transition temperatures are reasonably consistent with the experimentally observed trend for three compounds.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.3
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• pp.121-130
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• 2001

This paper addresses a method for evaluating perceived velocities of the graphic module in a driving simulator. The major two graphic factors associated with perceived velocities are analyzed: they are the lateral distance between a virtual driver and an array of environmental objects and the textural density of these objects. A graphical representation of a vehicle and its surrounding environment are constructed by employing a three-dimensional tool, Pro/ENGINEER and a virtual environment, dVISE. Using the developed virtual driving environment, experiments have been carried out to formulate the relationship between velocity perception and each factor. Based on the experimental results, nonlinear regression equations are derived to show how the perceived velocities are dependent upon distance/density.

• Journal of Powder Materials
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• v.11 no.4
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• pp.341-347
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• 2004

In the study, a hybrid constitutive model for densification of metallic powders was applied to cold isostatic pressing. The model is based on a pressure-dependent plasticity model for porous materials combined with a dislocation density-based viscoplastic constitutive model considering microstructural features such as grain size and inter-particle spacing. Comparison of experiment and calculated results of microscale and nanoscale Cu powders was made. This theoretical approach is useful for powder densification analysis of various powder sizes, deformation routes and powder processing methods.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.10
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• pp.891-895
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• 2005

Novel structure ultrasonic motors which have cross type stator were designed and fabricated. Driving characteristics of the motors were analyzed and measured by changing the materials of the stator. This ultrasonic motor has stator with hollowed cross bar and the stator rotate the rotor using elliptical displacement of the inside tips. This motion is generated by lateral vibration mode of cross bars. This stator was analyzed by finite element analysis depandent on stator's materials. And the cross type ultrasonic motors were made by analyzed results. The larger displacements were obtained, when the density of material was decreased. But the stress was increased when the stator's material has large density and Young's modulus. The fabricated one has high speed and torque in large stress on contact point between rotor and stator. The stress was more effected on speed and torque than the displacement.

• Journal of the Korean Magnetics Society
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• v.4 no.2
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• pp.89-93
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• 1994

Effects of density, inner-stress, and grain size on B-H hysteresis loop properties of Mg-ferrite were investigated. As the sintered bulk density increase, coercive force($H_c$) decreasand squareness ratio increase. Coercive force was very dependent on inner-stress in sintered body, so coercive force increase from 1.95[Oe] to 4.35[Oe] when inner stress present in bulk, however, the squareness ratio was almost not changed Coercive force and squareness ratio were independent on grain size of sintered body which is between 6-11[$\mu\textrm{m}$]

• Journal of the Korean Ceramic Society
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• v.29 no.3
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• pp.241-251
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• 1992

The effects of slip composition and processing conditions on the fabrication of ceramic heat exchanger cores by doctor blade process were investigated. Since the effects of those two variables were inter-dependent, the effects of binder system, binder plus plasticizer, were extensively studied for a limited range of processing conditions and a pre-determined ceramic composition. The content of binder system and the ratio of binder to plasticizer were identified as main variables to affect densities and mechanical properties of green sheets, compressive properties and bond strengths of laminates, and shrinkages and their anisotropy of sintered laminates. However, sintered densities and water absorptions of laminates were not influenced by either the content of binder system or the ratio of binder to plasticizer, when the debinded laminates had a relatively high density (relative density of >55% in this study).

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.10a
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• pp.101-105
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• 1992

Machined graphite/epoxy composite surfaces were studied by using SEM(Scanning Electron Microscopy). surface profilometry and its analysis to determine suitable surface describing parameters for machined unidirectional and laminate composite surface. The surface roughness and profile are found to be highly dependent on the fiber layup direction and the measurement direction. Machined unidirectional and 0.deg. 45 .deg. 90 .deg. plies in laminate composite surface profiles are found to be Gaussian in the direction of machining. Since there exist bare fibers without matrix smearing in 0 .deg. ply, higher surface roughness values were found in this orientation. It was possible to machine 90 .deg. and -45 .deg. plies due to the adjacent plies, which were holding those plies. It was found that the microgeometrical variations in terms of roughness parameters Ra without Dy (maximum Damage Depth) region and Dy are better descriptors of the machined laminate composite surface than commonly used roughness parameters Ra and Ra. The characteristics of surface profiles in laminate composite are well represented in CHD (Cumulative Height Distribution) plot and PPD (Percentage Probability Density) plot. Also, the power spectral density function is shown to be capable of identifying the wavelength distribution of the machining damage.

• Laser Solutions
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• v.6 no.2
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• pp.27-33
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• 2003

A laser shock cleaning technology is a new dry cleaning methodology for the effective removal of small particles from the surface. This technique uses a plasma shock wave produced by a breakdown of air due to an intense laser pulse. In order to optimize the laser shock cleaning process, it needs to evaluate the cleaning performance quantitatively by using a monitoring technique. In this paper, an acoustic monitoring technique was attempted to investigate the laser shock cleaning process with an aim to optimize the cleaning process. A wide-band microphone with high sensitivity was utilized to detect acoustic signals during the cleaning process. It was found that the intensity of the shock wave was strongly dependent on the power density of laser beam and the gas species at the laser beam focus. As a power density was larger, the shock wave became stronger. It was also seen that the shock wave became stronger in the case of Ar gas compared with air and N$_2$ gas.

• Ocean Systems Engineering
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• v.1 no.3
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• pp.249-261
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• 2011

The stochastic nonlinear dynamic behavior and probability density function of ship rolling are studied using the nonlinear dynamical systems approach and probability theory. The probability density function of the rolling response is evaluated through solving the Fokker Planck Equation using the path integral method based on a Gauss-Legendre interpolation scheme. The time-dependent probability of ship rolling restricted to within the safe domain is provided and capsizing is investigated from the probability point of view. The random differential equation of ships' rolling motion is established considering the nonlinear damping, nonlinear restoring moment, white noise and colored noise wave excitation.