• The Korean Journal of Physiology
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• v.21 no.1
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• pp.1-12
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• 1987

There is evidence that the effect of extracellular $Ca^{2+}$ on heart rate is temperature-dependent: at $38^{\circ}C$ excess $Ca^{2+}$ induces positive chronotropic response, whereas at $30^{\circ}C$ there is no significant chronotropic effect of $Ca^{2+}$. The cause of this temperature-dependency, however, remains still unclear. Therefore, this study was undertaken to investigate the chronotropic effect of external $Ca^{2+}$ at different temperature in the isolated rabbit atria and in the small strips of SA node cut perpendicularly to crista terminalis. In the isolated atria, the $Ca^{2+}$ effect was temperature-dependent: at $35^{\circ}C$ excess $Ca^{2+}$ evoked positive chronotropic response, while at $30^{\circ}C$ there was no significant changes in sinus rate. On the contrary, in the small SA strips external $Ca^{2+}$ induced negative chronotropic effect. At $35^{\circ}C$ changes in $Ca^{2+}$ concentration from 2 to 4, 6, and 10 mM decreased the sinus rate by $2.7{\pm}1.6%$, $11.2{\pm}3.7%$ and $23.2{\pm}8.1%$ respectively. Lowering the temperature to $30^{\circ}C$, the negative chronotropic effect of $Ca^{2+}$ became greater. With intracellular microelectrodes transmembrane potential was recorded in the small SA strips at $30^{\circ}C$, $35^{\circ}C$ and $38^{\circ}C$. As temperature increased from 30 to $38^{\circ}C$, sinus rate was accelerated by $13/min/^{\circ}C$, $APD_{50}$(action ptential duration from peak to 50% repolarization) decreased by $5\;msec/^{\circ}C$, and amplitude of action potential was slightly decreased. With an increase in $Ca^{2+}$ concentrations from 0.5 to 6 mM, overshoot increased and MDP decreased. These $Ca^{2+}$ effects on the overshoot and MDP of action potentials were not altered by temperature. But the $Ca^{2+}$ effects on the rates of diastolic depolarization, systolic depolarization and repolarization were modified by temperature. Discrpancy of the chronotropic effects of $Ca^{2+}$ between isolated atria and small SA strips was discussed.

• Journal of the Korean GEO-environmental Society
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• v.15 no.11
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• pp.67-75
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• 2014

In this study, the staged seismic performance evaluations were conducted to the 91 high speed railway tunnels in use for checking whether to comply with the recent design criteria or not. In addition, the seismic fragility functions of the tunnels were developed to allow the probabilistic risk assessment. The results of the staged seismic performance evaluations which consist of a preliminary assessment and a detailed assessment, show that the tunnels comply with the recent design criteria. With reference to the results of previous studies, a form of the proposed seismic fragility functions was set as a log-normal distribution by PGA, and the parameters of the functions were determined by using the probability of damage for the design PGA level. The seismic fragility functions were developed for each types (Cut & Cover, NATM) of tunnels. The seismic fragility functions from this study and the existing research results (FEMA, 2004) were compared to evaluate the seismic performance level of the tunnels, as a result the tunnels of this study were relatively superior to the ASSM tunnels on the seismic performance.

• Journal of Korean Society of Forest Science
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• v.94 no.4 s.161
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• pp.269-276
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• 2005

This research was carried out in order to make clear population and community structure of Berchemia berchemiaefolia forest surveyed from October 1998 to October 2004 which was located in Janggok-Ri Gunwi-Gun, Kyungpook province. B. berchemiaefolia community was classified into 3 groups such as Picrasma quassioides group, Carex ciliata-marginata group and Typical group using ZM methods. In case of floristic composition structure according to crown stories, B. berchemiaefolia occupied 42.82%, 34.43%, and 5.28%, in tree layer, subtree layer and shrub layer, respectively. Importance value of Quercus variabilis, Platycarya strobilacea and Quercus serrate species was generally high. Species diversity of Picrasma quassioides group indicated 1.6669 which was highest value among the 3 vegetation groups. Population of B. berchemiaefolia showed overall the structure of reverse J type in DBH class showing the peak between 6 cm and 10 cm and reached 14 meters in height class, and the age structure of the population ranged from 11 years to 60 years showing regular distribution type. Stump sprout or/and epicormic branch made numerous stems around original stump of previous generation which was considered to be cut and disappeared by residents. Seedlings or/and saplings of B. berchemiaefolia were intensively occurred in the opened areas of forest road. Those things could be certainly considered to establish management plan of B. berchemiaefolia forest.

• Restorative Dentistry and Endodontics
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• v.12 no.1
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• pp.39-49
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• 1986

The purpose of this study was to observe characteristic properties through the polarization curves and SEM images from 4 different types of amalgam obtained by using the potentiostats (Princeton EG & G) & SEM (Jeol/35), and to investigate the degree of corrosion on the oxidation peak of the each phase of amalgam. After each amalgam alloy and Hg was triturated as the direction of the manufacturer by means of the mechanical amalgamator (Shofu Co.), the triturated mass was inserted into the cylindrical metal mold which was 12mm in diameter and 10.0mm in height and was condensed by using routine manner. The specimen was removed from the mold and stored at room temperature for about 24 hours. The standard surface preparation was routinely carried out. Anodic polarization measurement was employed to confirm the corrosion behaviour of the amalgams in a 0.9% saline solution (P.H: 6.8-7.0) at $37^{\circ}C$. The initial rest potential (corrosion potential) was determined after 30 minutes of immersion of specimen in electrolyte, and the potential scan was begun at the point of 100mV cathodic from the corrosion potential. The scan rate was 0.17mV/sec. in the study to observe the degree of corrosion of each phase. SEI and EPMA images on the determined oxidation peaks of each amalgam were observed. The results were as follows: 1. In the four anodic polarization curves, low copper amalgams have three oxidation peaks and high copper amalgams have two oxidation peaks, -270mV, +26mV and +179mV(SEC) in the low copper lathe cut, and -300mV, +39mV and +163mV(SEC) in the low copper spherical. -4mV and +154mV(SEC) in the Dispersalloy, and +17mV and +180mV(SEC) in the Tytin as high copper amalgams. 2. ${\gamma}_2$ phase in the low copper amalgam and ${\eta}$ phase in the high copper amalgam were the most corrodible phases and Ag-Cu eutectic in high copper amalgam was the most slowly corroded phase. 3. Low copper amalgam was more susceptible in corrosion than high copper amalgam.

• Journal of the Korean Magnetics Society
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• v.9 no.5
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• pp.251-255
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• 1999

NiFe(60 $\AA$)/Co(0$\AA$$\leq$x$\AA$$\leq$15$\AA$)/Cu(60$\AA$)/Co(30$\AA$) spin valve thin films were prepared on 4$^{\circ}$ tilt-cut Si(111) substrates with a 50 $\AA$ thick Cu underlayer without applying any external magnetic field during the deposition, and the effects of inserted ultrathin Co layer on magnetic anisotropy and GMR properties of the NiFe(60 $\AA$)/Cu(60$\AA$)/Co(30$\AA$) spin valves were investigated. As the ultrathin Co layer was inserted into the NiFe/Cu interface of the spin valves, GMR ratio was increased from about 1.5% to 3.5%, and the easy axis of NiFe(60 $\AA$) layer was rotated by 90$^{\circ}$. Accordingly, it was aligned along the same direction with the easy axis of Co(30 $\AA$)layer. Therefore, squared R-H curves was obtained in the spin valves, which is favorable properties for the digital GMR devices such as MRAM. In order to investigate the change of magnetic anisotropy of NiFe layer of the spin valves in more details,XRD measurement was performed using NiFe(500 $\AA$) and NiFe(500 $\AA$)/Co(10 $\AA$) thin films on the same templates. Strong (220) NiFe peak was observed in both films regardless of the inserted Co layer, so it was thought that the variation of magnetic anisotropy of NiFe layer is from the interface effect, the change of interface from NiFe/Cu to NiFe/Co, rather than the volume effect such as the change of magnetocrystalline effect.

• International Journal of Highway Engineering
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• v.9 no.4
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• pp.193-204
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• 2007

Deformation strength($S_D$) is a property which shows relatively good correlation with rut resistance of asphalt mixtures at high temperature. The Asphalt Pavement Analyzer (APA) is widely used as an equipment for estimating rut resistance of asphalt mixtures. The APA was used as corresponding property of the $S_D$ to estimate rutting resistance of asphalt mixtures. Many data were collected to establish the correlation of $S_D$ with APA. For $S_D$ test, the specimen is submerged into the $60^{\circ}C$ water for 30 minutes before applying a vertical load at the speed of 50mm/min to obtain peak load (P) and deformation (y) for $S_D$ calculation. For the same materials, APA test was performed. Relation of the $S_D$ with APA rut depth was evaluated using regression analysis. The $R^2$ value was 0.76, indicating this simple test procedure being a possible method for predicting deformation resistance of asphalt concretes at high temperature. It was also shown that, using the regression model, minimum value(s) of $S_D$ of surface course asphalt mixture or binder course for a particular road level can be determined. The limit values may be possible to use as cut-off value(s) of asphalt mixtures for the layer after further elaborated studies.

• Journal of Adhesion and Interface
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• v.20 no.1
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• pp.9-14
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• 2019

The change of three different reagents for electrical conductive paint using aircraft coating with elapsing time of exposure to different condition was investigated. Three different reagents were poured into the vial bottles, stored in air condition and room temperature and observed with elapsing days. In addition, adhesion property of paint was tried using cross cut tape test after storage of $N_2$ atmosphere. The weight of each different reagent was measured along with elapsing time. To confirm the change of chemical component with exposure of air atmosphere, FT-IR was performed. The weight of part A and Part B decreased slightly whereas the weight of part C decreased rapidly and the precipitation was remained. The part B was cured after exposure of $N_2$ atmosphere and the 2250 cm-1 from FT-IR peak decreased slowly at the same time. It was considered that the water contained in air accelerated the reaction of -NCO functional groups and it caused the curing whereas $N_2$ atmosphere not contained water and it resulted in the retardancy of curing.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4102-4110
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• 2022

Aiming at high-power and long-pulse operation up to 1000 s, some improvements have been made for both 2.45 GHz and 4.6 GHz lower hybrid (LH) systems during the recent 5 years. At first, the guard limiters of the LH antennas with graphite tiles were upgraded to tungsten, the most promising material for plasma facing components in nuclear fusion devices. These new guard limiters can operate at a peak power density of 12.9 MW/m². Strong hot spots were usually observed on the old graphite limiters when 4.6 GHz system operated with power >2.0 MW [B. N. Wan et al., Nucl. Fusion 57 (2017) 102019], leading to a reduction of the maximum power capability. With the new limiters, 4.6 GHz LH system, the main current drive (CD) and electron heating tool for EAST, can be operated with power >2.5 MW routinely. Long-pulse operation up to 100 s with 4.6 GHz LH power of 2.4 MW was achieved in 2021 and the maximal temperature on the guard limiters measured by an infrared (IR) camera was about 540 ℃, much below the permissible value of tungsten material (~1200 ℃). A discharge with a duration of 1056 s was achieved and the 4.6 GHz LH energy injected into the plasma was up to 1.05 GJ. Secondly, the fully-active-multijunction (FAM) launcher of 2.45 GHz system was upgraded to a passive-active-multijunction (PAM), for which the density of optimum coupling was relatively low (below the cut-off value). Good coupling with reflection coefficient ~3% has been achieved with plasma-antenna distance up to 11 cm for the new PAM. Finally, in order to eliminate the effect of ion cyclotron range of frequencies (ICRF) wave on 4.6 GHz LH wave coupling, the location of the ICRF launcher was changed to a port that is located 157.5° toroidally from the 4.6 GHz LH system and is not magnetically connected.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.98-105
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• 2017

In this study, the fiber blending ratio and strain rate effect on the tensile behavior of hybrid fiber reinforced cement composite was evaluated. Hooked steel fiber and polyvinyl alcohol fiber were used for reinforcing fiber. The fiber blending ratio of HSF+PVA were 1.5+0.5, 1.0+1.0 and 0.5+1.5vol.%. As a results, the tensile strength, strain capacity and fracture toughness of the hooked steel fiber reinforced cement composites were improved by the increase of the bond strength of the fiber and the matrix according to increase of strain rate. However, the tensile stress sharply decreased after the peak stress because of the decrease in the number of straightened pull-out fibers by micro cracks in the matrix around hooked steel fiber. On the other hand, PVA fiber showed cut-off fracture at strain rate $10^{-6}/s$ with multiple cracks. However, at the strain rate $10^1/s$, the multiple cracks and strain capacity were decreased because of the pull-out fracture of PVA fiber. The HSF1.5PVA0.5 shown the highest tensile strength because the PVA fiber suppressed the micro cracks in the matrix around the hooked steel fiber and improved the pull-out resistance of hooked steel fiber. Thus, DIF of strain capacity and fracture toughness of HSF1.5PVA were greatly improved. In addition, the synergistic response of fracture toughness was positive because the tensile stress was slowly decreased after the peak stress by improvement of the pull-out resistance of hooked steel fiber at strain rate $10^1/s$.

• Tuberculosis and Respiratory Diseases
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• v.43 no.4
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• pp.547-557
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• 1996

Background : An excessive accumulation of neutrophils in lung tissue has been known to play an important role in mediating the tissue injury among the adult respiratory distress syndrome, idiopathic pulmonary fibrosis and cystic fibrosis by releasing toxic oxygen radicals and proteolytic enzymes. Therefore, it is important to understand a possible mechanism of neutrophil accumulation in lung tissue. In many species, exposure to hyperoxic stimuli can cause changes of lung tissues very similar to human adult respiratory distress syndrome and neutrophils are also functioning as the main effector cells in hyperoxic lung injury. The purpose of the present study was to examine whether neutrophils function as a key effector cell and to study the nature of possible neutrophil chemotactic factors found in bronchoalveolar lavage fluid from the hyperoxia exposed rats. Methods : We exposed the rats to the more than 95% oxygen for 24, 48, 60 arid 72 hours and bronchoalveolar lavage(BAL) was performed. Neutrophil chemotactic activity was measured from the BAT- fluid of each experimental groups. We also evaluated the molecular weight of neutrophil chemotactic tractors using fast performance liquid chromatography and characterized the substances by dialyzer membrane and heat treatment. Results : 1) The neutrophil proportions in bronchoalveolar lavage fluid began to rise from 48 hours after oxygen exposure, and continued to be significantly increased with exposure times. 2) chemotactic index for neutrophils in lung lavages from rats exposed to hyperoxia was significantly higher in 48 hours group than in control group, and was significantly increased with exposure time. 3) No deaths occured until after 48 hours of exposure. However, mortality rates were increased to 33.3 % in 60 hours group and 81.3 % in 72 fours group. 4) Gel filtration using fast performance liquid chromatography disclosed two peaks of neutrophil chemotactic activity in molecular weight of 104,000 and 12,000 daltons. 5) Chemotactic indices of bronchoalveolar lavage fluid were significantly deceased when bronchoalveolar lavage fluid was treated with heat ($56^{\circ}C$ for 30 min or $100^{\circ}C$ for 10 min) or dialyzed (dialyzer membrane molecular weight cut off : 12,000 daltons). Conclusion : These results suggested that the generation of neutrophil chemotactic factor and subsequent neutrophil influx into the lungs are playing an important roles in hyperoxia-induced acute lung injury. Neutrophil chemotactic factor in the lung lavage fluids consisted of several distinct components having different molecular weight and different physical characteristics.