• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.20-29
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• 1995

A theoretical model for film condensation of a vapor including a relatively lighter noncondensable gas on a horizontal tube has been formulated on the basis of the conservation laws and other fundamental physical principles. The model is applied to the prediction of the condensation heat transfer characteristics for the Freon vapor in the presence of air on a horizontal tube. Calculated results for the mean heat transfer coefficient, which is shown to depend strongly on the bulk concentration of air, are in good agreement with the available experimental results for a range of operating conditions. The distributions of physical quantities along the surface of tube are also calculated, such as the boundary layer thickness and local heat transfer coefficient. The present model is readily reduced to the Nusselt model as the bulk concentration of air decreases to zero. Therefore, the transition from the condensation of pure vapor to that of vapor-air mixture occurs continuously not abruptly.

• Journal of Electrical Engineering and information Science
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• v.2 no.6
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• pp.208-211
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• 1997

We have fabricated a single-electron-tunneling(SET) transistor with a dual gate geometry based on the SOI structure prepared by SIMOX wafers. The split-gate is the lower-gate is the lower-level gate and located ∼ 100${\AA}$ right above the inversion layer 2DEG active channel, which yields strong carrier confinement with fully controllable tunneling potential barrier. The transistor is operating at low temperatures and exhibits the single electron tunneling behavior through nano-size quantum dot. The Coulomb-Blockade oscillation is demonstrated at 15mK and its periodicity of 16.4mV in the upper-gate voltage corresponds to the formation of quantum dots with a capacity of 9.7aF. For non-linear transport regime, Coulomb-staircases are clearly observed up to four current steps in the range of 100mV drain-source bias. The I-V characteristics near the zero-bias displays typical Coulomb-gap due to one-electron charging effect.

• ETRI Journal
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• v.38 no.5
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• pp.934-940
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• 2016

In this paper, secure multicasting with the help of cooperative decode-and-forward relays is considered for the case in which a source securely sends a common message to multiple destinations in the presence of a single eavesdropper. We show that the secrecy rate maximization problem in the secure multicasting scenario under an overall power constraint can be solved using semidefinite programing with semidefinite relaxation and a bisection technique. Further, a suboptimal approach using zero-forcing beamforming and linear programming based power allocation is also proposed. Numerical results illustrate the secrecy rates achieved by the proposed schemes under secure multicasting scenarios.

• Wind and Structures
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• v.23 no.1
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• pp.59-73
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• 2016

In this paper, a hyperbolic shear deformation beam theory is developed for free vibration analysis of functionally graded (FG) sandwich beams. The theory account for higher-order variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. The material properties of the functionally graded sandwich beam are assumed to vary according to power law distribution of the volume fraction of the constituents. The core layer is still homogeneous and made of an isotropic material. Based on the present refined beam theory, the equations of motion are derived from Hamilton's principle. Navier type solution method was used to obtain frequencies. Illustrative examples are given to show the effects of varying gradients and thickness to length ratios on free vibration of functionally graded sandwich beams.

• Proceedings of the IEEK Conference
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• 2000.07b
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• pp.1041-1044
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• 2000

The enhancement to the back-propagation algorithm presented in this paper has resulted from the need to extract sparsely connected networks from networks employing product terms. The enhancement works in conjunction with the back-propagation weight update process, so that the actions of weight zeroing and weight stimulation enhance each other. It is shown that the error measure, can also be interpreted as rate of weight change (as opposed to ${\Delta}W_{ij}$), and consequently used to determine when weights have reached a stable state. Weights judged to be stable are then compared to a zero weight threshold. Should they fall below this threshold, then the weight in question is zeroed. Simulation of such a system is shown to return improved learning rates and reduce network connection requirements, with respect to the optimal network solution, trained using the normal back-propagation algorithm for Multi-Layer Perceptron (MLP), Higher Order Neural Network (HONN) and Sigma-Pi networks.

• JSTS:Journal of Semiconductor Technology and Science
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• v.11 no.2
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• pp.111-120
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• 2011

A two-dimensional analytical model for deriving the threshold voltage of a short channel fully depleted (FD) cylindrical/surrounding gate MOSFET (CGT/SGT) is suggested. By taking into account the lateral variation of the surface potential, introducing the natural length expression, and using the Bessel functions of the first and the second kinds of order zero, we can derive potentials in the gate oxide layer and the silicon core fully two-dimensionally. Making use of these potentials, the minimum surface potential can be obtained to derive the threshold voltage as a closed-form expression in terms of various device parameters and applied voltages. Obtained results can be used to explain the drain-induced threshold voltage roll-off of a CGT/SGT in a unified manner.

• International Journal of Advanced Culture Technology
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• v.7 no.4
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• pp.268-273
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• 2019

The apparent soil resistivity is used for estimating multilayer soil parameters, such as, layer's depth and soil resistivity. The soil parameters are estimated by continuously revising those parameters until the error between the measured and calculated apparent soil resistivity reaches to allowable level. The equation for calculating the apparent soil resistivity is complicated and time consumed, because it is composed of an infinite integral which includes a zero order Bessel's function of the first kind. In this paper, a fast algorithm for calculating the apparent soil resistivity of horizontal multilayer earth structure is proposed using exponential sampling method.

• Smart Structures and Systems
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• v.17 no.1
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• pp.59-72
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• 2016

The Impact Echo method can be used to measure the thickness of concrete plate like structures. Measurements are based on the identification of a clear thickness resonance frequency which can be difficult in very thick or highly attenuative plates. In this study the detectability of the measured resonant frequency is enhanced by time domain summation of signals with different source receiver spacing. The proposed method is based on the spatial and temporal properties of the first higher symmetric zero group velocity Lamb mode (S1-ZGV) which are described in detail. No application dependent tuning or filtering is needed which makes the method robust and suitable for implementation in automatic IE thickness measurements. The proposed technique is exemplified with numerical data and field data from a thick concrete wall and a highly attenuative asphalt concrete layer.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.11
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• pp.2139-2146
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• 2011

In this paper, a robust adaptive controller is proposed for trajectory tracking of robot manipulators with the unknown friction coefficient and bounded disturbance. A new adaptive control law is developed based on sliding mode and derived from the Lyapunov stability analysis. The introduction of a boundary layer solves the problem of chattering. The proposed adaptive controller is globally asymptotically stable and guarantees zero steady state error for joint positions. The estimated friction coefficients can also approach the actual coefficients asymptotically. A simulation example is provided to demonstrate the performance of the proposed algorithm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.4
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• pp.293-297
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• 1998

The influence of ion implantation on surface properties of polymers was studied. We investigated microhardness, friction, wear and wettablility of polyimide. Energies of 50, 200keV were used with doses range from $1{\times}10^{13} to 1{\times}10^{16} [ions/cm^2]$. The implanted ion species were B, N and Ar. The microhardness of polyimide was increased after implantation for doses of $1{\times}10^{15}\; [ions/cm^2]$. A reduction of the friction coefficient was in most case correlated with a reduction of wear. The contact angles of water for $B^+,N^+$ implanted polyimide decreased from $76^{\circ}C$ to zero, as the fluencies increased at energies of 50 and 200 KeV. However, the contact angle of Ar ion implanted polyimide did not change under ambient room conditions even if the time elapsed. SEM measurement was performed to characterize the modified surface layer.