• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.7
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• pp.958-966
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• 2001

This study has examined the microstructural development in the Bridgman type directional solidification of hyper-peritectic Sn-Cd alloys, and the temperature and flow field have been numerically simulated to see if there is any change induced by convection. The directional solidification experiments carried out in quartz tubes with inside diameters of 0.4∼6mm showed that the resulting microstructures are clearly dependent on the size of tube diameters. The bigger ampoules where the effect of convection is highly expected produced saw-like structures resulting from the primary $\alpha$ and peritectic $\beta$ phase growing together at a planar solid-liquid front, with the former being surrounded by the latter. In the smaller ampoules, where the effect of convection is expected low however, the saw structure disappears, and as is understood from the theoretical prediction based on diffusion-controlled solidification the initial growth of the primary $\alpha$ phase is replaced by the nucleation of the peritectic $\beta$ phase whose growth continues to the end of the solidification.

• Journal of the Korean Institute of Telematics and Electronics
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• v.18 no.6
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• pp.23-29
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• 1981

By using a slot-line in combination with microstrip lines, a coplanar wide-band balun is designed and fabricated. The slot-line of balun junction is compensated to be operated in C-band(4~8GHz), and therefore the results are agreement with theoritical prediction. Experimental data are given for a 3-section Chebyshev transformer-matched balun with a balanced-to-unbalanced line impedance ratio of 2 : 1. A bandwidth from 3.5GHz to 7.0GHz is obtained with V.S.W.R. of below 1.2 : 1. Maximum insertion loss is measured as 0.9dB, and the phase difference varies linearlly within 180$^{\circ}$$\pm$5$^{\circ}$.

• YAKHAK HOEJI
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• v.10 no.4
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• pp.21-24
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• 1966

In order to confirm whether or not Acacia leaf inhibits the increase of serum total cholesterol content of rabbits administered with cholesterol, this paper is conducted. Thirty rabbits were equally divided into three groups: A, B and C. The group A was fed with the stock diet only throughout the experimental period of 42 days. The group B was fed with the stock diet and cholesterol for the first 21 days and then Acacia leaf was given to the rabbits in addition to the above diet for the remainder of the experimental period. The group C was fed with the stock diet, cholesterol and Acacia leaf for the first 21 days and then the Acacia leaf was removed from the diet for the latter part of 21 days. The results of the serum total cholesterol determination of each group were illustrated in the tables, 1-11, and figure 1. From the data, therefore, following conclusion might be drawn: 1. The Acacia leaf inhibits the increase of serum total cholesterol of rabbits administered with cholesterol. 2. It is not clear whether Acacia leaf expedites the excretion of the metabolites of the given cholesterol or blocks the transfer of the absorbed cholesterol into the blood stream.

• Journal of Korean Society on Water Environment
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• v.22 no.4
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• pp.706-710
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• 2006

To evaluate impacts of the construction noise, Trionyx sinensis, inland fishers aquacultural organism, were exposed to control groups (about 55 dB) and noise groups (80 dB). The survival, growth rate and feeding efficiency of the juvenile Trionyx sinensis were measured at 10, 20 and 30 days intervals (each 9 hours/day). No significant mortality occurred during the experiments, but growth rates (1.7 times) and feeding efficiency (1.83 times) showed significant reduction in time-dependent manner. Also, serum cortisol (6.7 times) and corticosterone levels (1.37 times) in noise groups significantly increased by the noise exposure, compared to the controls, In conclusion, this study may provide the fundamental knowledge on adverse effects Trionyx sinensis and apply to assessments on the impacts of aquaculture industry by construction noise.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.33B no.1
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• pp.153-160
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• 1996

In this paper, we propose an efficient digital architecture for the discrete-time cellular neural networks (DTCNN's). DTCNN's have the locality and the translation invariance in the templates which determine the patterns of the connection between the cells. Using distributed arithmetic (DA) and the characteristics of DTCNN, we propose a simple implementation of DTCNN. The bus width in the cell-to-cell interconnection is reduced to one bit because of DA's bitwise operation. We implemented the reconfigurable architecture of DTCNN using programmable FPGA.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.5
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• pp.16-22
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• 2001

A novel microstrip circular slot antenna fed by a spiral line is presented in this paper. This antenna is a planar equivalent structure of an eccentric spiral antenna generates a circularly-polarized wave. We have investigated the input impedance and radiation characteristics of this antenna by using an EM (electromagnetic) simulator, and obtained a design method [or optimum structure. The main characteristic of the antenna is that the main beam direction is off-normal to the antenna plane and moves linearly into ${\theta }$ and ${\phi }$ direction as the frequency increases. This feature allows one to predict the main beam direction easily for a given operating frequency. This antenna has axial ratio lower than 3 dB in the direction of main beam over one octave bandwidth.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.4
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• pp.509-517
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• 1997

Results of flat plate compressible boundary layer calculation, based on discrete formulation of DSMC method, are presented in low Mach number and low Knudsen number range. The free stream is a uniform flow of pure nitrogen at various Mach numbers in low pressures (i.e. rarefied gas). Complete thermal accommodation and diffuse molecular reflections are used as the wall boundary condition, replacing unreal no-slip condition used in continuum calculations. In the discrete formulation of DSMC method, there is no need to use ad hoc assumptions on transport properties like viscosity and thermal conductivity, instead viscosity is calculated from values of other field variables (velocity and shear stress). Also the results are compared with existing self-similar continuum solutions. In all Mach number cases computed, velocity slip is most pronounced in regions near the leading edge where continuum formulation renders the solution singular. As the boundary layer develops further downstream, velocity slips asymptote to values that are between 10 to 20% of the magnitude of free stream velocity. When the free stream number density is reduced, so the gas more rarefied, the velocity slip increases as expected.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.976-982
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• 2002

In this study, smoke movement in tunnel fire with natural ventilation shaft has been investigated with various size of fire source. Gasoline pool fire with different size of diameter - 73mm, 100mm, 125mm and 154mm - was used to describe fire source. Experimental data is obtained with 1/20 model tunnel test and its results are compared with numerical results. The computation were carried out using FDS 1.0 which is a field model of fire-driven now. Temperature profiles between measured and predicted data are compared along ceiling and near the ventilation shaft. Both results are in good agreement with each other. In order to evaluating a safe egress time in tunnel fire, horizontal smoke front velocity was measured in model tunnel fire tests and those are compared with numerical results. According to the presence or absence of natural ventilation shaft, ventilation effect are estimated quantitatively. Finally, this paper shows that computational fluid dynamics(CFD) is applicable to predict fire-induced flow in tunnel.

• The Journal of Korean Medicine
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• v.22 no.4
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• pp.45-57
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• 2001

Objectives : The water extract of Gwibitang (GBT) has been traditionally used for treatment of psychologic disease and brain damage in Oriental Medicine, This study was designed to investigate the effect of GBT on the glutamate-induced toxicity of rat C6 glial cells. Methods : The cultured cells were pretreated with GBT and exposed to glutamate, The cell damage was assessed by using MTT assay and Hoechst, IC-l staining, Results : GBT had protective effects in glutamate-induced cytotoxicity, which was revealed as apoptosis characterized by chromatic condensation and the loss of mitochondrial membrane potential in C6 glial cells. However, GBT and glutamate had no effect in the activation of caspase family cysteine proteases including caspase-3, -8 and -9 proteasesin C6 glial ce]]s, GBT significantly recovered the depletion of GSH and inhibited the generation of $H_2O_2$ by glutamate in C6 glial cells. In addition, both GBT and antioxidants such as GSH and NAC protected the glutamate-induced cytotoxicity in C6 glial cells, indicating that GBT possibly has antioxidative effect. Moreover, GBT also inhibited the glutamate-induced degradation of $IkB{\alpha}$ in C6 glial cells, This result suggest that GBT has some inhibitory effects on the transcriptional activation of $NF-_{k}B$. Conclusions : GBT has protective effects in glutamate-induced cytotoxicity via an antioxidative mechanism.

• Korean Journal of Mathematics
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• v.20 no.3
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• pp.273-284
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• 2012

A ring R is called reversibly Armendariz if $b_ja_i=0$ for all $i$, $j$ whenever $f(x)g(x)=0$ for two polynomials $f(x)=\sum_{i=0}^{m}a_ix^i,\;g(x)=\sum_{j=0}^{n}b_jx^j$ over R. It is proved that a ring R is reversibly Armendariz if and only if its polynomial ring is reversibly Armendariz if and only if its Laurent polynomial ring is reversibly Armendariz. Relations between reversibly Armendariz rings and related ring properties are examined in this note, observing the structures of many examples concerned. Various kinds of reversibly Armendariz rings are provided in the process. Especially it is shown to be possible to construct reversibly Armendariz rings from given any Armendariz rings.