• Korean Journal of Materials Research
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• v.29 no.8
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• pp.469-476
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• 2019

A lead-free bulk ceramic having a chemical formula $Ba_{0.8}Ca_{0.2}(Ti_{0.8}Zr_{0.1}Ce_{0.1})O_3$ (further termed as BCTZCO) is synthesized using mixed oxide route. The structural, dielectric, impedance, and conductivity properties, as well as the modulus of the synthesized sample are discussed in the present work. Analysis of X-ray diffraction data obtained at room temperature reveals the existence of some impurity phases. The natural surface morphology shows close packing of grains with few voids. Attempts have been made to study the (a) effect of microstructures containing grains, grain boundaries, and electrodes on impedance and capacitive characteristics, (b) relationship between properties and crystal structure, and (c) nature of the relaxation mechanism of the prepared samples. The relationship between the structure and physical properties is established. The frequency and temperature dependence of the dielectric properties reveal that this complex system has a high dielectric constant and low tangent loss. An analysis of impedance and related parameters illuminates the contributions of grains. The activation energy is determined for only the high temperature region in the temperature dependent AC conductivity graph. Deviation from the Debye behavior is seen in the Nyquist plot at different temperatures. The relaxation mechanism and the electrical transport properties in the sample are investigated with the help of various spectroscopic (i.e., dielectric, modulus, and impedance) techniques. This lead free sample will serve as a base for device engineering.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.5
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• pp.516-521
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• 2022

We investigated the microstructure, crystal structure, dielectric, and elecromechanical strain properties of lead-free BaTiO₃ (BT)-modified (Bi_1/2Na_1/2)TiO₃-SrTiO₃ (BNT-ST) piezoelectric ceramics. Samples were prepared by a conventional ceramic processing route. Temperature dependent dielectric properties confirmed that a phase transition from a nonergodic relaxor to an ergodic relaxor was induced when the BT concentration reached 1.5 mol%, interestingly, where the average grain size reached a maximum value of 4.5 ㎛. At the same time, enhanced electromechanical strain (S_max/E_max = 600 pm/V) was obtained. It is suggested that the induced ferroelectric-relaxor phase transition by the BT modification is responsible for the enhancement of electromechanical strain in 1.5 mol% BT-modified BNT-ST ceramics.

• Journal of Environmental Health Sciences
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• v.48 no.2
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• pp.106-115
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• 2022

Background: Current research suggests that humans are exposed to microplastics through consumption of foods and beverages, the airway route, and a variety of other means. Objectives: We evaluated oxidative stress and inflammation from polyethylene microplastics (PE-MPs) in the neonatal liver through intragastric administration or intratracheal instillation in pregnant mice. Methods: PE-MPs were administered from gestational day 9 to postnatal day 7. The intragastric administration group (0.01 mg/mouse/day or 0.1 mg/mouse/day) and intratracheal instillation group (6 ㎍/mouse/day or 60 ㎍/mouse/day) of PE-MPs were administered. After sacrifice, the oxidative stress and inflammation of the neonatal livers were measured. Results: As a result of the oxidative stress caused by PE-MPs in the neonatal livers, glutathione peroxidase decreased in a concentration-dependent manner in the intragastric administration group compared to the control group and intratracheal instillation decreased in high concentration PE-MPs. The catalase level increased at high concentrations of intragastric administration and intratracheal instillation. To confirm the level of inflammation caused by PE-MPs, monocyte chemoattractant protein-1 and tumor necrosis factoralpha were increased compared to the control group except for intratracheal intilation-high concentration PEMPs. The C-reactive protein level was decreased by intragastric administration compared to the control group and intratracheal instillation was increased compared to the control group. Conclusions: Despite the difficulty in comparing the toxic intensity between intragastric administration and intratracheal instillation of PE-MPs, our study revealed that oxidative stress and inflammation were induced in the neonatal liver. However, it is necessary to evaluate the toxic effects of microplastics on various organs as well. Overall, the present study indicates that the evaluation of toxic effects of long-term microplastic exposure, potential of microplastic toxicity on next-generation offspring and toxicity mechanism in human should be considered for further investigations.

• Korean Journal of Materials Research
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• v.32 no.5
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• pp.243-248
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• 2022

This study demonstrates a different approach method to fabricate antimony selenide (Sb₂Se₃) thin-films for the solar cell applications. As-deposited Sb₂Se₃ thin-films are fabricated via electrodeposition route and, subsequently, annealed in the temperature range of 230 ~ 310℃. Cyclic voltammetry is performed to investigate the electrochemical behavior of the Sb and Se ions. The deposition potential of the Sb₂Se₃ thin films is determined to be -0.6 V vs. Ag/AgCl (in 1 M KCl), where the stoichiometric composition of Sb₂Se₃ appeared. It is found that the crystal orientations of Sb₂Se₃ thin-films are largely dependent on the annealing temperature. At an annealing temperature of 250 ℃, the Sb₂Se₃ thin-film grew most along the c-axis [(211) and/or (221)] direction, which resulted in the smooth movement of carriers, thereby increasing the carrier collection probability. Therefore, the solar cell using Sb₂Se₃ thin-film annealed at 250 ℃ exhibited significant enhancement in J_SC of 10.03 mA/cm² and a highest conversion efficiency of 0.821 % because of the preferred orientation of the Sb₂Se₃ thin film.

• Parasites, Hosts and Diseases
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• v.35 no.4
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• pp.259-264
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• 1997

This study was carried out to determine whether dermal mast cell responses to Parasoninn westemoni in an abnormal host, the mouse, were dependent on the site of metacercarial inoculation. In mice during subcutaneous infection, the number of der- mal mast cells were increased significantly (p<0.05) at the first week ($38.3/\textrm{mm}^2$) and then persisted at a high level until the sixth week ($45.2/\textrm{mm}^2$) of infection compared with PBS- injected (control) mice (range: $19.4-25.1/\textrm{mm}^2$). In mice during oral infection, the number of dermal mast cells were increased significantly (p<0.05) at two weeks ($33.5/\textrm{mm}^2$) after infection and remained at these levels thereafter compared loth non-infected (control) mice (range: $17.4-22.3/\textrm{mm}^2$). In mice both during subcutaneous and oral infection, the recruited dermal mast cells showed extensive degranulation at the second week (68.4%) and 60.7%, respectivelyl, reached a peak at the third week (81.4%, and 92.1%, respectively) and then declined slightly thereafter. By contrast, in both control mice, about 10% of dermal mast cells were degranulated. In conclusion, this study suggests that dermal mast cell responses to p. westemcni in mice are dependent on cutaneous sensitization by larval excretory-secretory antigens, irrespective of infection route.

• Journal of Korean Society of Transportation
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• v.27 no.1
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• pp.143-155
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• 2009

A dynamic traffic assignment (DTA) has recently been implemented in many practical projects. The core of dynamic model is the inclusion of time scale. If excluding the time dimension from a DTA model, the framework of a DTA model is similar to that of static model. Similar to static model, with given exogenous travel demand, a DTA model loads vehicles on the network and finds an optimal solution satisfying a pre-defined route choice rule. In most DTA models, the departure pattern of given travel demand is predefined and assumed as a fixed pattern, although the departure pattern of driver is changeable depending on a network traffic condition. Especially, for morning peak commute where most drivers have their preferred arrival time, the departure time, therefore, should be modeled as an endogenous variable. In this paper, the authors point out some shortcomings of current DTA model and propose an alternative approach which could overcome the shortcomings of current DTA model. The authors substitute a traditional definition for time-dependent OD table by a new definition in which the time-dependent OD table is defined as arrival time-based one. In addition, the authors develop a new DTA model which is capable of finding an equilibrium departure pattern without the use of schedule delay functions. Three types of objective function for a new DTA framework are proposed, and the solution algorithms for the three objective functions are also explained.

• The Korean Journal of Physiology
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• v.24 no.1
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• pp.27-37
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• 1990

The extrafetal transfer of $Li^{+}$ in amniotic fluid was studied in 45 pregnant rabbits. LiCl solution was administered either intravenously to mother or directly into the amniotic sac and monitored the appearance and disappearance of $Li^{+}$ in the amniotic fluid, then calculated the transfer rate of $Li^{+}$ of extrafetal origin. To study the transplacental $Li^{+}$ transfer, a solution of 150 mM LiCl was infused continuously via maternal vein (initial dose: 0.7 mmol/kg, maintaining dose: 0.03 mmol/kg/min) and the $Li^{+}$ concentration was measured in maternal blood and amniotic fluid after 60 and 120 minutes of infusion. Change in the volume of aminotic fluid was determined by Congo red dilution method at the same time. Effects of duration of gestation was not considered in this study. Extrafetal transport of $Li^{+}$ into the amniotic fluid was estimated by comparing the $Li^{+}$ concentration and volume of amniotic fluid determined before and after ligating the placental vessels. Extrafetal $Li^{+}$ transport from the amniotic fluid was determined by observing the time dependent disappearance of $Li^{+}$ and Congo red in amniotic fluid after injecting 0.5 ml solution of 15 mM or 90 mM LiCl and 50 mg/ml Congo red. Following are the results obtained: 1) During infusion of LiCl through maternal vein the ratio of the aminotic $Li^{+}$/maternal plasma $Li^{+}$ increased significantly along with the increment of fetal weight. 2) The volume of amniotic fluid of larger fetuses than 20.5 gm increased significantly during administration of LiCl while that of smaller fetuses did not change. 3) After umbilical cord ligation the $Li^{+}$ concentration of amniotic fluid of larger fetuses than 20.5 gm was decreased to $59.9{\pm}10.3%$ and $56.9{\pm}42.9%$ $(mean{\pm}S.D.)$ of those of control group after 60 and 120 minutes of LiCl infusion respectively. In amniotic fluid of smaller fetuses than 20.5 gm, there was no significant difference between control and ligation groups. 4) The disappearance rate of Congo red in the amniotic fluid was $45.2{\pm}8.2%/hr$. 5) The disappearance rate of $Li^{+}$ after intraamniotic injection of LiCl depended on the amount injected. On injecting $7.5\;{\mu}mol$ LiCl, $Li^{+}$ disappeared rapidly from the amniotic fluid and the rates after 60 min and 90 min were $97.0{\pm}2.8,\;98.5{\pm}2.0%$ respectively. On injecting $45\;{\mu}mol$ LiCl, the rates were $56.0{\pm}15.4,\;78.9{\pm}14.5%$ at 60 and 90 min. 6) From the above results it was concluded: a) $Li^{+}$ transfer into the amniotic fluid increased along with the fetal growth and one half of $Li^{+}$ influx is through the extrafetal route even after the maturation of fetal kidney. b) One half of the $Li^{+}$ transfer from the amniotic fluid was through swallowing of fetus, while the remaining half was transfered rapidly through amniotic membrane, which was concentration limited.

• Journal of Korean Society of Transportation
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• v.24 no.6 s.92
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• pp.89-102
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• 2006

The purpose of this paper is to develop a dynamic OD estimating model to overcome the limitation of depicting teal situations in dynamic simulation models based on static OD trip. To estimate dynamic OD matrix we used the hybrid discrete choice model(called the 'Demand Simulation Model'), which combines travel departure time with travel mode and travel path. Using this Demand Simulation Model, we deduced that the traveler chooses the departure time and mode simultaneously, and then choose his/her travel path over the given situation In this paper. we developed a hybrid simulation model by joining a demand simulation model and the supply simulation model (called LiCROSIM-P) which was Previously developed. We simulated the hybrid simulation model for dependent/independent networks which have two origins and one destination. The simulation results showed that AGtt(Average gap expected travel time and simulated travel time) did not converge, but average schedule delay gap converged to a stable state in transportation network consisted of multiple origins and destinations, multiple paths, freeways and some intersections controlled by signal. We present that the hybrid simulation model can estimate dynamic OD and analyze the effectiveness by changing the attributes or the traveler and networks. Thus, the hybrid simulation model can analyze the effectiveness that reflects changing departure times, travel modes and travel paths by demand management Policy, changing network facilities, traffic information supplies. and so on.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.8
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• pp.86-92
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• 2009

In order to minimize ac mutual coupling, the auxiliary electrode are located at a right angle in measuring ground impedance. In case that the measurement space is limited, the alternative method is employed. At that time, it is necessary to investigate the measurement errors due to ac mutual coupling and earth mutual resistance in measuring the ground impedances. 'This paper presents the measurement accuracy according to the location of the current and potential auxiliary electrodes in measuring ground impedance of vertically or horizontally buried ground electrode. The measurement errors due to ac mutual coupling were evaluated Consequently, the effect of ac mutual coupling on the measurement accuracy for horizontally buried ground electrode is greater than that for vertically buried ground electrode. Measurement errors due to ac mutual coupling is the largest when the current and potential auxiliary electrodes are located in parallel. The 61.8[%] rule is inappropriate in measuring ground measurement. Theoretically, in case that the angle between the current and potential auxiliary electrodes is 90$[^{\circ}]$, there is no ac mutual coupling. If it is not possible to route the current and potential auxiliary electrodes at a right angle with limitation of measurement space, the location of these electrodes with an obtuse angle is preferred to that with an acute angle in reducing the measurement errors due to ac mutual coupling.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.3
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• pp.215-226
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• 2015

In this study, with variables the cross section area ($97m^2$, $58m^2$, $38m^2$) and the wind velocity(0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 m/s), the time of getting off train dependent on the way of itself and the width of the evacuation route was analyzed, and also fire and evacuation characteristics is reviewed by cross section area of each wind velocity. As the result, if cross section become smaller, the density of harmful gases in the tunnel increased more than the ratio of decreasing cross section area. In the case of small cross sectional area, the surrounding environment from initial fire is indicated to exceed the limit criteria suggested in performance based design. In the analysis of effective evacuation time for evacuation characteristics, the effective evacuation time was the shortest in the case of evaluating effective evacuation time by the visibility. Also, there was significant difference between the effective evacuation time on the basis of performance based evaluation and the effective evacuation time obtained by analyzing FED (Fractional effective dose), one of the analysis method obtaining the point that deaths occur, against harmful gases.