• The Korean Journal of Physiology
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• v.17 no.1
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• pp.1-11
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• 1983

1) The two microelectrode method was used to voltage clamp small preparations of rabbit sinoatrial node. The kinetics of hyperpolarization activated inward current, $i_f$ were analysed. 2) The hrperpolarization pulses activated $i_f$ current in the presence of $10^{-7}g/ml$ TTX and 2 mM $Mn^{2+}$. The activation range was in between -45 mV to -75 mV. The current magnitude was increased and time course was faster by strong hyperpolarization pulses. 3) Standard envelope tests indicated that this current is exponentially controlled by single gate. 4) Semilogarithmic plot of $i_f$ activation versus time was found to be linear in the activation range. The decrease in current magnitude and the shifts in activation curve and rate constants curve to the hyperpolarizing direction were obtained with $Ba^{2+}$, indicating that $Ba^{2+}$ shifts the voltage dependence of the gating kinetics, were partially reversed by 24 mM $K^+$.

• Journal of the Korean Electrochemical Society
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• v.9 no.2
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• pp.95-99
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• 2006

Electrochemical properties were studied for a single particle of active material of hydrogen storage alloy $(MmNi_{3.55}Co_{0.75}Mn_{0.4}Al_{0.3})$ and nickel hydroxides $(NiOH)_2$ for the secondary Nickel Metal Hydride (Ni-MH) batteries using the microelectrode, which was manipulated to make electrical contact with an active material particle for cyclic voltammograms (CV) and potential-step experiments. As a result of CV test, it was found that three kinds of hydrogen oxidation peaks at -0.9, -0.75 and -0.65 V and hydrogen evolution peak at -0.98 V for hydrogen storage alloy were separately observed and two kinds of peaks of proton oxidation/reduction at 0.45 and 0.32 V and oxygen evolution reaction (OER) at 0.6 V for nickel hydroxides were also more clearly observed. Furthermore hydrogen diffusion coefficient within a single particle was also found to vary the order between $10^{-9}\;and\;10^{-10}cm^2/s$ over the course of hydrogenation and dehydrogenation process for potential-step experiments.

• The korean journal of orthodontics
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• v.44 no.3
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• pp.128-135
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• 2014

Objective: This study evaluated the cytotoxicity and genotoxicity of fixed orthodontic treatment with three different light-cured orthodontic bonding composites by analyzing micronucleus (MN) formation in the buccal mucosa during a 6-month period. Methods: Thirty healthy volunteers were selected from consecutive patients referred for orthodontic treatment. Equilibrium 2 brackets and molar tubes (Dentaurum) were bonded with three different lightcured orthodontic bonding composites-Transbond XT (3M Unitek), Kurasper F (Kuraray Europe), or GrenGloo (Ormco Corporation)- to all teeth in both arches. Exfoliated buccal epithelial cells were scraped from the middle part of the inner cheeks with sterile cement spatulas before treatment and at 1, 3, and 6 months after treatment. MNs and nuclear alterations, such as karyorrhexis (KR), karyolysis (KL), and binucleated cells (BNs), were scored under a light microscope. Repeated measure ANOVA was used to calculate statistical differences in degenerative nuclear abnormalities. Results: MN rates did not significantly differ among different time points within the same cell type (p > 0.05). In contrast, the number of BNs in buccal epithelial cells significantly increased in all composite groups (p < 0.01, Transbond XT; p < 0.001, Kurasper F and GrenGloo). KL frequency significantly increased between the beginning and end of the study in the Kurasfer F ($0.80{\pm}0.79$ to $1.90{\pm}1.10$; p < 0.05) and GrenGloo ($1.30{\pm}1.06$ to $2.40{\pm}1.08$; p < 0.05) groups. Conclusions: After 6 months of fixed orthodontic treatment with different light-cured composites, morphological signs of cytotoxicity were observed but genotoxic effects were absent.

• Journal of Ocean Engineering and Technology
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• v.10 no.2
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• pp.77-87
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• 1996

The estimation of the remaining life for the aged components in power plant as well as chemical and peroleum plants has been recently coberned. The raw materials used in this syudy are the 1Cr-1Mo-0.25V rotor steel which intensified P and S compositions along with the nominal compositions of ASTM A470 standard. Five kinds of specimens with the different degradation levels were prepared by isothermal aging teat treatment at $630^{\circ}C$ The mechanical properties and fatigue strength of virgin and aged 1Cr-1Mo-0.25V rotor steel have been inbestigated through the hardness, tensile, fatigue test, SEM fractograph and EDS analysis at room temperature. Thus, the data of aged specimens were compared with those of virgin specimen to evaluate the aging effects. The main results obtained in this study are as follows; The decrease of the hardness due to degradation was distinguished until 50, 000hrs simulated service time. And is was confirmed that the considerable amount of P, Mn, Cr and S was precipitated at the grain boundary of aged material through the SEM and EDS analysis. The fatigue strength of 25, 000, 50, 000, 75, 000 and 100, 000hrs aged material was decreased 29.5%, 24.4%, 28.6%, 35.7% than that of virgin material at $10^7$ cycles of room temperature. The major cracks of virgin and aged materials initiated at the inclusions including Si, P and Mn compositions which were located at the outer periphery of the specimen.

• Child Health Nursing Research
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• v.3 no.2
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• pp.142-153
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• 1997

Empathy is an essential factor for establishing therapeutic relationship. Especially for pediatric nursing, the nurses need to know how to perceive children's feeling and thought and to express her understanding about them affectively. So, empathy is considered as an important concept in pediatric nursing. This study was attempted to measure the empathic ability of pediatric nurses by pediatric nurses and mothers of hospitalized children. The subject of this study consisted of 83 pediatric nurses and 106 mothers of hospitalized children in 4 hospitals in Seoul and 1 hospital in Kyung-Gi. Data were collected from Jan. 14 to Feb. 6, 1997, by the questionnair method. The instrument for this study was the Empathic Construct Rating Scale : ECRS(60-item, 5 point scale). Data were analyzed by descriptive statistics, t-test and ANOVA. Results of this study are summarized as follows 1. Pediatric nurses perceived their empathic ability to be moderately high (Mn=3.71). The level of perceived empathic ability of the pediatric nurses showed no significance by general characteristics. 2. The mothers of hospitalized children perceived nurses' empathic ability to be moderate(Mn=3.27). The level of perceived nurses' empathic ability of the mothers of hospitalized children showed significant differences by the experience of hospitalization of the children and the age of the mothers. 3. The perceived nurses' empathic ability of the mothers was significantly low than of the pediatric nurses(t=6.50, P<.001). From the above results, it can be concluded, that the empathic ability of the pediatric nurses is not sufficient for caring children and mothers of ficiently. So, the pediatric nurses' empathic ability is needed to improve through facilitative relationship training as refreshment in-service education program.

• Nuclear Engineering and Technology
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• v.40 no.3
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• pp.225-232
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• 2008

To understand the effect of the cyclic strain rate on the environmentally assisted cracking behaviors of SA508 Gr.1a low alloy steel in deoxygenated water at $310^{\circ}C$, the fatigue surface and a sectioned area of specimens were observed after low cycle fatigue tests. On the fatigue surface of the specimen tested at a strain rate of 0.008 %/s, unclear ductile striations and a blunt crack tip were observed. Therefore, metal dissolution could be the main cracking mechanism of the material at this strain rate. On the other hand, on the fatigue surfaces of the specimens tested at strain rates of 0.04 and 0.4 %/s, brittle cracks and flat facets, which are evidences of the hydrogen induced cracking, were observed. In addition, a tendency of linkage between the main crack and the micro-cracks was observed on the sectioned area. Therefore, at higher strain rates, the main cracking mechanism could be hydrogen induced cracking. Additionally, evidence of the dissolved MnS inclusions was observed on the fatigue surface from energy dispersive x-ray spectrometer analyses. Thus, despite the low sulfur content of the test material, the sulfides seem to contribute to environmentally assisted cracking of SA508 Gr.1a low alloy steel in deoxygenated water at $310^{\circ}C$.

• Journal of Korea Foundry Society
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• v.20 no.2
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• pp.122-128
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• 2000

Strip casting process is a new technology that makes a near net shape thin strip directly from molten metal. With this process, a large amount of energy and casting cost could be decreased from the abbreviation of reheating and/or hot rolling process. Ductile cast iron which has spheroidal graphite in the matrix is the most commercial and industrial material, because of its supreme strength, toughness, and wear resistance etc. But it cannot be produced to the thin strip owing to difficulty in rolling of ductile cast iron. In this study, ductile cast iron strips are produced by the twin roll strip caster, with different chemical compositions of C, Si, and Mn contents. And then heat-treated, microstructures and mechanical properties are examined. The microstructures of as-cast strip are that of white cast iron which consists of the mixture of cementite and pearlite, but the equiaxed crystal zone of the pearlite or segregation zone of cementite exists in the center region of the strip thickness, which cannot be observed in the rapidly solidified metallic mold cast specimens. This structure is supposed to be formed from the thermal distribution of strip and the rolling force. Comparing with the structures of each strips after heat treatment, increasing Si content makes smaller spheroidal graphite and more compact in the matrix, furthermore the less of Mn content makes the ferrite matrix be obtained clearer and easier. As a result of the tensile test of graphitization heat-treated strips, the yield strengths are about 250 MPa, the tensile strengths are about $430{\sim}500$ MPa, and the elongations are about $10{\sim}13%$. In the case of the strip which has the smaller and more compact spheroidal graphite in the ferrite matrix, the higher tensile strength and better drawability could be obtained.

• Transactions of Materials Processing
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• v.28 no.1
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• pp.34-42
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• 2019

In this study, various alloying elements (Cr, Sr, Ca, Cd) were added to improve the mechanical properties of ADC12 fabricated by a die casting process. The effect of alloying elements on the microstructure and mechanical properties were investigated. The phase analysis results of the modified ADC12 alloy with conventional ADC12 alloy, showed the similar characteristics of Al matrix, Si phase, $CuAl_2$ phase and the Fe intermetallic phase. As a result of the microstructure observation, the secondary dendrite arm spacing (SDAS) was shown to have decreased after the addition of the alloying elements. The eutectic Si phase, which existed as flake form in the conventional ADC12 alloy, was modified finely as a fiber form in the modified ADC12 alloy. It was observed that the $CuAl_2$ phase as the strengthening phase was relatively finely distributed in the modified ADC12 alloy. The Fe intermetallic appeared as a Chinese script shaped $Al_6$ (Mn,Fe) which is detrimental to mechanical properties in conventional ADC12 alloy. On the other hand, in the modified ADC12 alloy, polyhedral ${\alpha}-Al_{15}Si_2$ $(Fe,Mn,Cr)_3$ was observed. The tensile properties were improved in the modified ADC12 alloy. The yield strength and tensile strength increased by 12.4% and 10.0%, respectively, in the modified ADC12 alloy, and the elongation was also seen to have been increased. As a result of the pin on disk wear test, the wear resistance properties were also improved by up to about 7% in the modified ADC12 alloy. It is noted that the wear deformation microstructures were also observed, and it was found that the fine eutectic Si and strengthening phases greatly improved abrasion resistance.

• Annals of Occupational and Environmental Medicine
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• v.35
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• pp.53.1-53.15
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• 2023

Background: Plastics are high-molecular-weight materials composed of long carbon chains. They are prevalent in daily life, present in various items such as food containers and microwavable packaging. Phthalates, an additive used to enhance their flexibility, are endocrine-disrupting chemicals. We utilized the data from the Korean National Environmental Health Survey (KoNEHS) cycle 3, representing the general South Korean population, to investigate the relationship between the use of plastics in refrigerator food storage and phthalate exposure. Methods: We assessed 3,333 adult participants (aged ≥ 19 years) including 1,526 men and 1,807 women, using data from KoNEHS cycle 3. Using the 75th percentile concentration, urine phthalate metabolites were categorized into high and low-concentration groups. χ² test was conducted to analyze variations in the distribution of each variable, considering sociodemographic factors, health-related factors, food intake, the use of plastics, and the concentration of urine phthalate metabolites as the variables. To calculate odds ratios (ORs) for the high-concentration group of urine phthalate metabolites based on the use of plastics in refrigerator food storage, logistic regression analysis was conducted. Results: In men, the use of plastics in refrigerator food storage had significantly higher adjusted ORs compared to those using the others. The adjusted ORs were calculated as follows: mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) had an OR of 1.35 (95% confidence interval [CI]: 1.05-1.72), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) had an OR of 1.48 (95% CI: 1.16-1.88), mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP) had an OR of 1.32 (95% CI: 1.04-1.66), ∑di(2-ethylhexyl) phthalate (∑DEHP) had an OR of 1.37 (95% CI: 1.08-1.74) and mono-n-butyl phthalate (MnBP) had an OR of 1.44 (95% CI: 1.13-1.84). Conclusion: The concentrations of urine phthalate metabolites (MEHHP, MEOHP, MECPP, ∑DEHP, and MnBP) were significantly higher in men who used plastics in refrigerator food storage compared to those using the others.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.04a
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• pp.98-103
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• 2001

In order to understand the characteristics of leachate at the Seokdae municipal waste landfill in the Pusan city, the correlation between leachate pollution loading and volume of gas production. concentration of gas and subsidence of ground, the characteristical methos, geochemical analyses and laboratory column tests using samples of gases, leachate and surface soil of Seokdae waste landfill area. Through the analysis of water balance, leachate flow rate and pollution loading were estimated. Geistatistical analysis of four gas components ( $O_2$, C $H_4$, $H_2$S and CO) shows the possibility of ground subsidence around the group of a site with high concentration of gas. From geochemical analyses of leachate, EC and Total-Alkalinity of ground subsidence around the group of a site with high concentration of gas. From geochemical analysis of leachate, Ec and Total-Alkalinity were increased, and Cl, Cr, Mn, Cu, Zn, Cd and Pb were decreassed comparing to the part, and the type of water quality was Na-HC $O_3$ in trilinear diagram. It shows that biodecomposition of municipal wastes continues actively. From the analysis of water balance, the total leachate flow rate is about 465.11㎥/day and pure pollution loading of Cl, Mn and Fe are estimated to 223.8kg/day, 0.2kg/day, 0.3kg/day, respectively. The laboratory column test of residual soil and landfill soil shows 0.206cm and 0.019cm for linear velocity(equation omitted), 0.234 $\textrm{cm}^2$/min and 0.018$\textrm{cm}^2$/min for diffusion coefficient ( $D_{ι}$), and 1.136cm and 0.095cm longitudinal dispersion index ($\alpha$$_{ι}$), respective]y. It demonstrates that the delay time of contamination for residual soil is shorter than that of landfill soil.