• Journal of the Korean Ceramic Society
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• v.29 no.1
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• pp.65-73
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• 1992

The effect of grain size on the time-dependent piezoelectrice degradation of a poled PZT of MPB composition Pb0.988Sr0.012 (Zr0.52Ti0.48)O3 with 2.4 mol% of Nb2O5 was studied, and the degradation mechanism was discussed. Changes in the internal bias field and the internal stress both responsible for the time-dependent degradation of poled PZT were examined by the polarization reveral technique, XRD and Vickers indentation, respectively. The piezoelectric degradation increased with increasing time and grain size, and the internal bias field due to space charge diffusion decreased with increasing grain size of poled PZT. The internal bias field, however, was almost insensitive to the degradation time regardless of the grain size. On the other hand, both the x-ray diffraction peak intensity ratio of (002) to (200) and the fracture behavior including the crack propagation support that the ferroelectric domain rearrangement of larger grain size showed rapid relaxation of the internal stress compared with smaller one, which is thought the origin of the larger piezoelectric degradation in the former. In conclusion, the contribution of space charge diffusion on the piezoelectric degradation of PZT is strongly dependent on both the grain size and the composition. Thus, the relaxation of internal stress due to the ferroelectric domain rearrangement as well as the amount and time-dependence of the internal bias field due to space charge diffusion should be considered simultaneously in the degradation mechanism of PZT.

• Nuclear Engineering and Technology
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• v.43 no.3
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• pp.243-256
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• 2011

This paper considers the concept of analog computing based on a cellular neural network (CNN) paradigm to simulate nuclear reactor dynamics using a time-dependent second order form of the neutron transport equation. Instead of solving nuclear reactor dynamic equations numerically, which is time-consuming and suffers from such weaknesses as vulnerability to transient phenomena, accumulation of round-off errors and floating-point overflows, use is made of a new method based on a cellular neural network. The state-of-the-art shows the CNN as being an alternative solution to the conventional numerical computation method. Indeed CNN is an analog computing paradigm that performs ultra-fast calculations and provides accurate results. In this study use is made of the CNN model to simulate the space-time response of scalar flux distribution in steady state and transient conditions. The CNN model also is used to simulate step perturbation in the core. The accuracy and capability of the CNN model are examined in 2D Cartesian geometry for two fixed source problems, a mini-BWR assembly, and a TWIGL Seed/Blanket problem. We also use the CNN model concurrently for a typical small PWR assembly to simulate the effect of temperature feedback, poisons, and control rods on the scalar flux distribution.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.1
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• pp.1-12
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• 1994

This paper deals with the time-dependent analysis of reinforced and prestressed concrete beams. Based on the age-adjusted effective modulus method, the structural behavior in accordance with time is analyzed using the force equilibrium and strain compatibility condition within a typical section. Unlike most of presented approaches adopting some assumptions, such as non-cracking of concrete and consideration of steel effect as a transformed concrete area only, more accurate results can be obtained at all loading conditions since all materials are considered together so as to be maintained their given properties and the cracking effect is included at the same time. Several parameter studies are conducted with the objective to identify the significance of various effects on the time-dependent response of concrete members, i.e., stress re-distribution of each material and occurrance of long-term deflection, etc. Moreover, the obtained results can be used at design and/or construction stage for the purpose of more accurate prediction of structural response with time.

• Journal of Physiology & Pathology in Korean Medicine
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• v.18 no.3
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• pp.900-907
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• 2004

The antiproliferative effect of the water extract of the branch and root bark of Ulmi Pumilae Cortex(WEUPC) was investigated on the p53-negative human leukemia cell line (HL-60). A dose- and time-dependent inhibition of cell growth was observed; this effect appears to be due to induction of apoptosis. Involvement of oxidative stress is indicated by a dose-dependent increase in intracellular reactive oxygen species levels. In addition. anti-apoptic effect was observed in the cells simultaneously treated with WEUPC and the anti-oxidant N-acetylcysteine. WEUPC did not affect the anti-apoptotic Bcl-2 and the pro-apoptotic Bax, whereas p21/sup WAF1/CIPl/ was enhanced in a dose- and time-dependent fashion; this effect was partially inhibited by N-acetylcysteine. The increase in p21/sup WAF1/CIPl/ was accompanied by a parallel accumulation of cells in the G1 phase of the cycle. These results suggest that the p53-independent induction of p21/sup WAF1/CIP/ and the induction of apoptosis may mediate the anti proliferative effect of WEUPC at least in this study; on the basis of this observation, WEUPC could be proposed as an useful adjunct to the treatment of p53-deficient tumors, which are often refractory to standard chemotherapy.

• International Journal of Oral Biology
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• v.32 no.3
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• pp.113-118
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• 2007

Treatment of oral cancers with chemotherapeutic agents become evaluated as an effective method to reduce cancer cell proliferation. Anti-proliferative and anti-oral cancer activities of momordin I on oral cancer cells were evaluated in this study. Momordin I was originally purified from a natural product, Ampelopsis radix and showed the antiproliferative activity against oral carcinoma, KB cells. Obtained $IC_{50}$ value was approximately $10.4{\mu}g/ml$. Time-and dose-dependent chromosomal DNA fragmentations were observed in momordin I-treated KB cells. Flow cytometry analysis showed time-dependent apoptotic cell appearance after treatment of momordin I. Approximately 18.6% apoptotic cells were observed at 72 hours after $20{\mu}g/ml$ of momordin I treatment. These observation were consistent with the results obtained in DNA fragmentation analysis. These data suggest that momordin I has anti-proliferative effect and induces cell death in KB cells through apoptosis.

• Biomedical Science Letters
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• v.22 no.4
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• pp.211-214
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• 2016

House dust mite is an essential allergen in the pathogenesis of allergic diseases. Abnormal regulation of neutrophil apoptosis is an important pathogenic process in allergic diseases. In the present study, we investigated the effects of house dust mites on spontaneous apoptosis of neutrophils and its associated mechanisms. Extract of Dermatophagoides pteronissinus (DP) inhibited neutrophil apoptosis in a time-dependent manner. Cycloheximide (CHX), an inhibitor of translation, increased apoptosis of DP-treated neutrophils as well as control cells. The pro-apoptotic effect of CHX was blocked by DP in neutrophils. In addition, DP increased the phosphorylation of Bad in a time-dependent manner, indicating that it exerted an inhibitory effect on the function of Bad. These results suggest that DP has anti-apoptotic effects of neutrophils and may regulate protein synthesis and activation of Bad. Moreover, these findings may shed light on elucidation of allergy pathogenesis due to house dust mites.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.906-909
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• 2005

In this study, the dynamic flying characteristics of the worn head sliders are investigated theoretically due to the change in head geometry caused by head and disk contact. The film shapes can be approximated as taper- truncated cycloidal-flat film. Two-dimensional time dependent modified Reynolds equation included molecular slip effect are formulated with neglected the roughness effect. The motion of head slider was assumed to have two degree of freedom in this work. Finite difference approximation with Newton Raphson iterative technique and the fourth order Runge-Kutta method were implemented to obtain the transient response of the slider head with various change in head geometry numerically and compared with the transient response of the IBM3380 type head slider. The simulation results show the film shape has affects significantly on the static and dynamic characteristic of slider head in magnetic storage systems.

• Journal of Korea Society of Industrial Information Systems
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• v.17 no.3
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• pp.27-34
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• 2012

This paper presents the impact of time dependent dielectric breakdown (TDDB, also called as gate oxide breakdown) failure on nanoscale digital CMOS Circuits. Recently, TDDB for ultra-thin gate oxides has been considered as one of the critical reliability issues which can lead to performance degradation or logic failures in nanoscale CMOS devices. Also, leakage power in the standby mode can be increased significantly. In this paper, TDDB aging effects on large CMOS digital circuits in the 45nm technology are analyzed. Simulation results show that TDDB effect on MOSFET circuits can result in more significant increase of power consumption compared to delay increase.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1998.11a
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• pp.142-142
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• 1998

This study has been undertaken to examine the effect of biphenyl dimethyl dicarboxylate (DDB) on rat liver drug metabolizing enzyme in order to understand the mechanism of DDB on improving hepatic toxicity in rat liver. After DDB was administered into male rats for different periods of time, mRNA level of CYP1A1 and CYP2B1 was measured by polymerase chain reaction (PCR). DDB treatment resulted in increase in CYP2B1 mRNA level whereas there was no change in CYP1A1 mRNA level. This effect of DDB was time dependent reaching maximal level by 2-day treatment. DDB dose response study showed that 50mg/kg DDB induced CYP2B1 mRNA to maximal level and DDB icreased CYP2B1 gene expression with dose-dependent manner. Based on studies of lipid peroxidation, serum ALT and AST levels and histopathologic examination showed DDB protection on CCl4 induced hepatotoxiccity.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.164-164
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• 2016

Radar rainfall estimates have been widely used in calculating rainfall amount approximately and predicting flood risks. The radar rainfall estimates have a number of error sources such as beam blockage and ground clutter hinder their applications to hydrological flood forecasting. Moreover, it has been reported in paper that those errors are inter-correlated spatially and temporally. Therefore, in the current study, we tested influence about spatio-temporal errors in radar rainfall estimates. Spatio-temporal errors were simulated through a stochastic simulation model, called Multivariate Autoregressive (MAR). For runoff simulation, the Nam River basin in South Korea was used with the distributed rainfall-runoff model, Vflo. The results indicated that spatio-temporal dependent errors caused much higher variations in peak discharge than spatial dependent errors. To further investigate the effect of the magnitude of time correlation among radar errors, different magnitudes of temporal correlations were employed during the rainfall-runoff simulation. The results indicated that strong correlation caused a higher variation in peak discharge. This concluded that the effects on reducing temporal and spatial correlation must be taken in addition to correcting the biases in radar rainfall estimates. Acknowledgements This research was supported by a grant from a Strategic Research Project (Development of Flood Warning and Snowfall Estimation Platform Using Hydrological Radars), which was funded by the Korea Institute of Construction Technology.