• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.05a
• /
• pp.217-220
• /
• 2008

The most important properties in the rubber for a flexible seal are the shear modulus, shear stress, reproducibility of rubber properties from lot to lot and shear modulus variation as aging. This study was conducted to confirm a rubber characteristic for the flexible seal. As a test result, the shear modulus is the range of 0.4310 ${\sim}$ 0.4997MPa, and failure shear stress is above 2.5MPa. After 1 year, the shear modulus of rubber as aging increased about 11.8%.

• Wind and Structures
• /
• v.25 no.4
• /
• pp.397-413
• /
• 2017

When bridges are constructed with lower heights from the ground, the formed channel between the deck and the ground will inevitably hinder or accelerate the air flow. This in turn will have an impact on the aerodynamic forces on the deck, which may result in unexpected wind-induced responses of bridges. This phenomenon can be referred to "ground effects." So far, no systematic studies into ground effects on the wind-induced responses of closed box girders have been performed. In this paper, wind tunnel tests have been adopted to study the ground effects on the aerodynamic force coefficients and the wind-induced responses of a closed box girder. In correlation with the heights from the ground in two ground roughness, the aerodynamic force coefficients, the Strouhal number ($S_t$), the vortex-induced vibration (VIV) lock-in phenomena over a range of wind velocities, the VIV maximum amplitudes, the system torsional damping ratio, the flutter derivatives, the critical flutter wind speeds and their variation laws correlated with the heights from the ground of a closed box girder have been presented through wind tunnel tests. The outcomes show that the ground effects make the vortex-induced phenomena occur in advance and adversely affect the flutter stability.

• Korean Journal of Optics and Photonics
• /
• v.5 no.2
• /
• pp.245-251
• /
• 1994

The charateristics of switching between two modes in a ring dye laser has been analyzed by the Monte-Carlo computer simulation. The effect of including pump fluctuations in the first-passage-time (FPT) distributions was compared with the distribution with the quantum fluctuation. The results show the same tendency in both cases, such as steep increases from 0 to peak an exponential decrease in long time range. However the introduction of pumping fluctuation is turned out to shorten the mean FPT. The variation of the mean FPT is examined for the various fluctuationrelated parameters. The mean FPT is lengthened when pump parameter a is increased while it is shorted when Q. $\GAMMA$ are decreased. eased.

• Proceedings of the KSRS Conference
• /
• 2007.10a
• /
• pp.156-158
• /
• 2007

The radiance observed from the ocean depends on the illumination and viewing geometry along with the water properties, and this variation is called the bidirectional effect which is important to be considered in ocean color remote sensing. In the present study, as a preliminary step, the spectral-angular radiances in coastal water were investigated with experiments for a range of viewing geometric conditions $(0-70^{\circ})$. Over a phytoplankton-dominated water surface the upward radiance for visible and near-infrared wavelengths (example, SeaWiFS and GOCI) increased at nadir and decreased toward the near-horizon, becoming dependent of viewing angles (with higher radiance at nadir view angle and lower radiance at near-horizon viewing angle). This variations were better expressed by the Q-factor, which relates upwelling radiance to the upwelling irradiance (i.e., $Q=E_u/L_u$, also dependent on Sun's position). The Q-factor for this case was more non-uniform with the considered wavelengths and was dependent on viewing geometric conditions. These experimental results confirm the previous similar findings in other coastal waters.

• Journal of Energy Engineering
• /
• v.10 no.3
• /
• pp.243-252
• /
• 2001

Combustion characteristics of domestic anthracite coal were observed by high-pressure thermogravimetric analyzer with variation of pressure (1~16 atm) and heating rate (15, 20, $25^{\circ}C$/min) with non-iso-thermal method (temperature range : 25~100$0^{\circ}C$). Measured combustion reaction rate increased with increasing pressure. This result could be explained by the fact that the activation energy of coal combustion decreased with increasing pressure. Reaction order of coal combustion determined by Freeman and Carroll$^{[11]}$ method linearly increased from 1.04 to 1.30 and activation energy decreased from 47.37 to 14.42 Kcal/mol as pressure increased from 1 to 16 attn.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.11 no.2
• /
• pp.166-176
• /
• 2000

In this paper, the LEO system signal degradation is mainly due to fading and doppler shift, so that the analysis of the signal degradation and compensation techniques are very important. This paper propose a Kalman filter based two step Automatic Frequency Control(AFC) to combat large and time variant frequency offset in low earth orbit satellite communication systems. The proposed Kalman AFC method estimates a frequency offset in two steps, I. e., coarse and fine estimations, extending the frequency acquisition range to even for than the symbol rate. Furthermore, it can track well a time variation of frequency offset. It is shown that the proposed compensator is able to compensate for doppler shift more than several KHz.

• Journal of computational fluids engineering
• /
• v.16 no.3
• /
• pp.29-36
• /
• 2011

The natural convection in a horizontal enclosure heated from the bottom wall, cooled at the top wall, and having a square adiabatic body at its centered area was studied. Three different Prandtl numbers (0.01, 0.7 and 7) were considered for an effect of the Prandtl number on natural convection. A two-dimensional solution for unsteady natural convection was obtained, using Chebyshev spectral methodology for different Rayleigh numbers varying over the range of $10^4$ to $10^6$. It had been experimentally and numerically reported [1,2] that the heat transfer mode becomes oscillatory when Pr is out of a specific Pr band beyond the critical Ra. In this study, we reproduced this phenomenon numerically. The variation of time- and surface-averaged Nusselt numbers on the hot and cold walls for different Rayleigh numbers and Prandtl numbers was presented to show the overall heat transfer characteristics in the system. And also, the isotherms and streamline distributions were presented in detail to compare the physics related to their thermal behavior.

• Asian-Australasian Journal of Animal Sciences
• /
• v.16 no.11
• /
• pp.1599-1603
• /
• 2003

The physical feature, physiological character and behavior studies were conducted with fifteen newly collected gayals in Bandarban hill tract area of Bangladesh. Their morphology is different from domestic cattle. The range of pulse rate, body temperature and respiration rate were 47 to 75 per minute, 37.78 to $38.88^{\circ}C$ and 20 to 40 per minute, respectively. These physiological values vary with different age group and seasonal variation. In hematological feature, the average findings were RBC $7.01{\pm}0.52$ million/cu.mm, WBC $14.3{\pm}3.69$ thousand/cu.mm, hemoglobin concentration $9.81{\pm}2.25gm%$, PCV $35.86{\pm}3.68%$. In differential WBC count neutrophils $28.23{\pm}1.75%$, lymphocytes $62{\pm}2.05%$, monocytes $4.4{\pm}1.34%$, eosinophils $5{\pm}2.49%$ and basophils $0.4{\pm}0.51%$. In behavior study, the animal shows browsing nature on hill slopes. They are watchful in new environment, become excited and nervous with strangers. Heated female gayals response for mating with domestic bull.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.4 no.5
• /
• pp.985-996
• /
• 2000

In the coastal zone, to draw up short and medium range weather forecasts, mesoscale pluviogenic systems coming from the sea have to be observed in real time. These observations use remote sensing. However, satellite remote sensing is not sufficient to describe pluviogenic systems; reference to radar long distance observations is indispensable. This paper deals with the corrections, which must be made to long distance radar data if the rainfall field is to be both accurately and quantitatively defined. The error due to vertical variation in the reflectivity factor can be corrected from estimation of the mean profiles or by a climatic adjustment method. Atten-uation in the propagation can be corrected by an iterative polarimetric method. These various correc-tions permit the distance validity limits of radar data to be extended.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.11a
• /
• pp.559-562
• /
• 2004

A 2.2-inch QCIF+ $(176{\times}RGB{\times}220)$ TFT-LCD with integrated row driver was developed using a standard amorphous silicon TFT technology. At low temperature $({\sim}-20^{\circ}C)$, the integrated row driver operation is dramatically effected by the electron drift mobility variation $({\sim}50%)$ and the threshold voltage shift $({\sim}1V)$ of the a-Si TFT. We studied the temperature dependency of the circuit design and found that higher on-current circuit is important to guarantee good operation in wide temperature range.