• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.9
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• pp.31-37
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• 2004

We have proposed a design methodology for large active-area single-mode VCSELS, which have higher reliability and output power, and are well-suited for high-speed operation. The key idea underlying the design methodology is to reduce the effective index difference between active and cladding regions by controlling the thickness and position of the oxide layer. The idea is confirmed by the self-consistent effective index method. By placing the oxide layer position properly, we can increase the radius of the oxide aperture for single-mode operation by 3 times.

• Geomechanics and Engineering
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• v.13 no.2
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• pp.285-300
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• 2017

Shallow coal resources are increasingly depleted, the mining has entered the deep stage. Due to "High stress, high gas, strong adsorption and low permeability" of coal seam, the gas drainage has become more difficult and the probability of coal and gas outburst accident increases. Based on the flow solid coupling theory of coal seam gas, the coupling model about stress and gas seepage of coal seam was set up by solid module and Darcy module in Comsol Multiphysics. The gas extraction effects were researched after applying hydraulic technology to increase permeability. The results showed that the effective influence radius increases with the expanded borehole radius and drainage time, decreases with initial gas pressure. The relationship between the effective influence radius and various factors presents in the form: $y=a+{\frac{b}{\left(1+{(\frac{x}{x_0})^p}\right)}}$. The effective influence radius with multiple boreholes is obviously larger than that of the single hole. According to the actual coal seam and gas geological conditions, appropriate layout way was selected to achieve the best effect. The field application results are consistent with the simulation results. It is found that the horizontal stress plays a very important role in coal seam drainage effect. The stress distribution change around the drilling hole will lead to the changes in porosity of coal seam, further resulting in permeability evolution and finally gas pressure distribution varies.

• Transactions of Materials Processing
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• v.3 no.4
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• pp.454-467
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• 1994

The drawbead restraining forces for the various radius of drawbead and die corner are analyzed by the belt theory, and they are compared with the experimental results. During this procedure, the drawing angles are also varied from $0^{\circ}$ to $60^{\circ}$, and the near part of the drawed die corner are divided into fur steps for the theoretical analysis. The stress distributions through the sheet thickness for these steps are also suggested theoretically. The wide range of experimental data of the drawing forces and strain distributions for the various dimension and blank holding forces are presented. It is concluded that the theoretical assumption for the restraining force analysis is very useful from the comparison with the experimental results.

• Bulletin of the Korean Mathematical Society
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• v.60 no.5
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• pp.1181-1199
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• 2023

For solving complex symmetric positive definite linear systems, we propose a single step real-valued (SSR) iterative method, which does not involve the complex arithmetic. The upper bound on the spectral radius of the iteration matrix of the SSR method is given and its convergence properties are analyzed. In addition, the quasi-optimal parameter which minimizes the upper bound for the spectral radius of the proposed method is computed. Finally, numerical experiments are given to demonstrate the effectiveness and robustness of the propose methods.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.04a
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• pp.227-234
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• 2003

In this study, an equivalent continuum model for single wall carbon nanotube is proposed. The model links interatomic potentials and atom structure of a materials to a constitutive model on the continuum level. The Young's modulus and shear modulus were predicted by the model. The predictions were in good agreement with the prior experimental results available in the literatures. Also, the strain energy of the carbon nanotube was predicted as a function of the radius of the carbon nanotube.

• Journal of the Korean Society of Safety
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• v.22 no.5
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• pp.41-49
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• 2007

In general, the curved structures have the engineering efficiency as well as a fine view compared with straight member. Also, composite materials are composed of two or more different materials to produce desirable properties for structural strength as compared to single ones. Shell structures with composite materials have many advantages in strength and weight reduction. Therefore, composite laminated conical shells are analyzed in this study. To solve differential equations of conical shells, this paper used finite difference method. Various parametric study according to the change of radius ratio, vertex angle and subtended angle are examined. The change of radius ratio, vertex angle and subtended angle mean the change from conical shells to cylindrical shells, conical shells to circular plates and open shells closed shells, respectively.

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1226-1233
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• 2003

Experimental heat transfer data for single-phase water flow in the annuli with corrugated inner tubes are presented. In the annuli with parallel flow, ten different annular arrangements are considered. For water flow rate in 1,700${\gamma}$$\^$*/). As P/e becomes closer to 8 in the range below the radius ratio (${\gamma}$$\^$*/) of 0.5, Nusselt numbers increase. However, Nusselt numbers decrease in the range above the radius ratio (${\gamma}$$\^$*/) of 0.5 because flow reattachment position becomes farther in the narrower clearance.

• Journal of Korea Society of Industrial Information Systems
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• v.25 no.1
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• pp.1-11
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• 2020

Wireless sensor networks consist of a large number of tiny sensor nodes which have limited battery life. In order to maximize the network life span, we propose an optimal transmission radius, R, for control messages. We analyze the transmission radius as a function of the energy consumption of cluster head nodes and the energy consumption of member nodes to find the optimal value of R. In simulations we apply our proposed optimization of transmission range to LEACH-based single-hop and multi-hop networks to show that our proposed scheme outperforms other existing routing algorithms in terms of network life span.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.77.1-77.1
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• 2016

We investigate the properties and detection conditions for the planetary caustic perturbation of close-separation planets. To find the properties of the planetary caustic perturbation, we construct deviation maps by subtracting the single-lensing magnification of the lens star from the planetary lensing magnification for various lensing parameters. We find that each deviation area of the positive and negative perturbations disappears at the same normalized source radius according to a given deviation threshold regardless of mass ratio but disappears at a different normalized source radius according to the separation. We also estimate the upper limit of the normalized source radius to detect the planetary caustic perturbation. We find simple relations between the upper limit of the normalized source radius and the lensing parameters. From the relations, we obtain an analytic condition for the detection limit of the planet, and which show that we can sufficiently discover a planet with the mass of sub-Earth for typical microlensing events. Therefore, we expect to add the number of low-mass planets in the next-generation microlensing experiments and conclude that our detection condition of the planet can be used as a important criteria for maximal planet detections considering the source type and the photometric accuracy.

• Geomechanics and Engineering
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• v.21 no.3
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• pp.289-300
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• 2020

Estimating the damage induced by an explosion around a blast hole has always been a challenging issue in geotechnical engineering. It is difficult to determine an exact dimension for damage zone since many parameters are involved in the formation of failures, and there are some uncertainties lying in these parameters. Thus, the present study adopted a probabilistic approach towards this problem. First, a reliability model of the problem was established and the failure probability of induced damage was calculated. Then, the corresponding exceedance risk curve was developed indicating the relation between the failure probability and the cracked zone radius. The obtained risk curve indicated that the failure probability drops dramatically by increasing the cracked zone radius so that the probability of exceedance for any crack length greater than 4.5 m is less than 5%. Moreover, the effect of each parameter involved in the probability of failure, including blast hole radius, explosive density, detonation velocity, and tensile strength of the rock, was evaluated by using a sensitivity analysis. Finally, the impact of the decoupling ratio on the reduction of failures was investigated and the location of its maximum influence was demonstrated around the blast point.