• Honam Mathematical Journal
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• v.9 no.1
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• pp.113-119
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• 1987

Random variables $X_1$, $X_1$, ..., $X_m$ are said to be weakly associated if whenever $\pi$ is a permutation of {1, 2,..., m}, $1{\leq}k<m$, and f: $R^{k}{\rightarrow}R$, g: $R^{m-k}{\rightarrow}R$ are coordinatewise nondecreasing functions then Cov $[f(X_{x(1)},...,\;X_{\pi(k)},\;g(X_{x(k+1)},...,\;X_{x(m)})]{\geq}0$, whenever the covariance is defined. An infinite collection of random variables is weakly associated if every finite subcollection is weakly associated. The basic properties of weak association and central limit theorem for weakly associated random variables are derived. We also extend this idea to point random fields and prove that a Cox process with a stationary weakly associated intensity rardom measure is weakly associated. Another inequalities and the fact that positive correlated normal random variables are weakly associated are also proved.

• Journal of the Optical Society of Korea
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• v.20 no.6
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• pp.698-703
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• 2016

We report a new all-optical flip-flop (AOFF) with a quite simple structure, using optical beating in an injection-locked Fabry-Perot laser diode (FP-LD) with optical bistability. While conventional AOFF methods using an injection-locked FP-LD require additional devices such as secondary FP-LDs or polarization controllers for reset operation, the proposed method can be implemented using only a single commercially available FP-LD with set and reset signals. The optical beating induces intensity fluctuations inside the FP-LD, and releases the locking state to the reset state. Even though we demonstrated the AOFF at 100 Mbit/s, we expect that its operation rate could extend to 10 Gbit/s, according to the limit of the FP-LD's frequency response.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.343-350
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• 2002

The structural stability of pressure housing of SMART CEDM forming pressure boundary must be evaluated. In this paper, the stress and thermal analyses of the upper pressure housing of CEDM are performed for design pressure, hydraulic test pressure and thermal loading. Finite element and boundary condition were generated from the model which is made by I-DEAS program and the stress and thermal analyses were performed by ANSYS Program. The upper Pressure housing was analysed using 2D axisymmetric model because it is symmetry about an axis. The stress values obtained by analysis were compared with the stress intensity limit of ASME and KEPIC MNB standard.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.6
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• pp.260-264
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• 2002

We developed LD Pumped Nd:$VVO_4$ microchip laser with the cavity length of 1mm. The microchip laser output was 87.5㎽ at the wavelength of 1063.9nm with the input power of 241㎽ at the wavelength of 809nm. The slope efficiency was 40.7% and the threshold input power was 31.1㎽. We have also defined input power limit for the single longitudinal mode operation theoretically. It was 2.5 times larger than that of threshold input intensity. According to the results of simulation, the Nd:YVO$_4$ microchip laser can be operated with the maximum output of 15㎽ for the single longitudinal mode up to the input power of 77.75㎽.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.5
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• pp.429-434
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• 2003

The magnetic field sensor was fabricated with superconducting ceramics of BiPbSrCaCuO system. The sensor at liquid nitrogen temperature showed the increase of electrical resistance by applying magnetic field. Actually, the voltage drop across the sensor was changed from zero to a value more than 100 $\mu\textrm{V}$ by the applied magnetic field. The change of electrical resistance depended on magnetic field. The sensitivity of this sensor was 2.9 $\Omega$/T. The sensing limit was about 1.5${\times}$10$\^$-5/ T. The increase of electrical resistance by the magnetic field was ascribed to a modification of the Josephson junctions due to the penetrating magnetic flux into the superconducting material. Considering the observed properties of the superconductor with trapped magnetic flux, a magnetic sensor was fabricated to detect simultaneously both the intensity and the direction of the magnetic field.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.150-151
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• 2006

Laser pyrolysis is a very suitable method for the synthesis of a wide range of nanoparticles. A pilot unit based on this process has been recently developed at CEA. This paper reports results showing the possibility to produce SiC and $TiO_2$ nanoparticles at rates of respectively 1 and 0.2 kg/h and also the possibility to adjust the mean grain size of the particles and their structure by changing the laser intensity and reactants flow rates. First tests of liquid recovery have been also successfully performed to limit the risks of nanoparticles dissemination in the environement during their recovery.

• Journal of the Korean Society of Tobacco Science
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• v.23 no.1
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• pp.90-93
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• 2001

In order to save hanging labor hours and reduce work intensity for bulk curing of the flue-cured tobacco, and electric hoist was developed. It consists of a pair of square steel frames with side plates and rolling casters to move back and forth on the second tire of bulk barn, and wire rope type lift was attached to the beneath of its top center. The lift driven by DC motor could be controlled by operating switch with one limit switch and control box, and a scissors shaped gripper was deviced to grip tobacco rack to the end of wire rope. As the results of experiments with electric hoist, labor hours for hanging could be saved by 30 to 40% as compared with those in conventional method. With simple and light structure, it was possible for even woman to load the harvested tobacco, and it could be recommended for farmers to use this device with reasonable price.

• Journal of the korean society of oceanography
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• v.38 no.2
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• pp.45-51
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• 2003

Recent observations reveal that the Tsushima Current has a double-cored structure downstream of the Tsushima Island. To explain this, a simple analytical model is proposed based on the assumption of small lateral eddy viscosity. This model suggests that an otherwise uniform current becomes to have a stream core immediately after it enters a channel due to the action of lateral friction. The core is initially broad but becomes sharper downstream. The speed at which the core develops depends on the intensity of lateral eddy viscosity. Likewise, a single-cored stream changes rapidly to a double-cored stream when it passes through an island located in the center of the channel. When the stream leaves the island behind, the reverse process from the double-to single-cored structures takes place. In this case, however, the double-cored structure is retained for a significant distance from the island. Overall, this model suggests that the double-cored structure of the Tsushima Current observed downstream of the Tsushima Island Is created by the lateral friction exerted by the Tsushima Island.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.03a
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• pp.465-472
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• 2003

The main concept of base isolation system is to reduce the member forces by decreasing the earthquake forces transmitted to superstructure instead of the conventional techniques of strengthening the structural members. There are two important advantages in friction pendulum systems. The functions of carrying the vertical load and of providing horizontal stiffness are effectively separated. This results in a more stable system that eliminates the need of a fail-safe mechanism. Friction pendulum systems are less sensitive to variations in the frequency content of ground excitation and tend to limit the intensity of the farce imparted to the superstructure. This study investigates the friction coefficients on the FPS test specimens according to the velocity, bearing pressure and test waveform.

• Journal of the Optical Society of Korea
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• v.7 no.2
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• pp.119-125
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• 2003

We demonstrate parametric resonance in a magneto-optical trap. When we modulate the intensity of the cooling laser at about twice the resonant frequency of the trap, the atoms in the trap are divided into two parts and oscillate with 180 degree phase difference with the finite length due to nonlinearity of the trap potential. These are the effects of general nonlinear dynamics, called the Hopf bifurcation, or limit cycle motion. The amplitude and the phase of the oscillations are measured and compared with the theoretical calculations based on simple Doppler cooling theory. The experimental results are in excellent agreement with the simulation results based on the simple Doppler cooling theory.