• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.7
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• pp.557-564
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• 2002

To reduce unwanted vibrations in war ship which may be transmitted through underwater path, it is required to use high damping mounts to isolate the vibration. In this work, the beam structure with squeeze mode ER mount is proposed and response characteristics such as acceleration and force transmissibility of beam with constant voltage and optimal controller are experimentally analyzed. The controller is empirically realized and control responses are evaluates in frequency domains. Experiments show vibration reduction capability of squeeze mode ER mount.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.297-300
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• 2005

This paper presents vibration control of an engine mount for a passenger vehicle utilizing ER fluid and piezoelectric actuator. The proposed engine mount can be isolated the vibration of wide frequency range with many types of amplitude. The main function of ER fluid is to attenuate vibration for low frequency with large amplitude, while the piezoelectric actuator is activated in hish frequency range with small amplitude. A mathematical model of the engine mount is derived using Hydraulic model and mechanical model. After formulating the governing equation of motion, then field-dependent dynamic stiffness of the engine mount is evaluated for various engine speed and excitation amplitude conditions. Then robust controller is designed to attenuate vibration of wide range frequency component. Computer simulation is undertaken in order to evaluate the vibration control performance such as transmissibility magnitude in frequency domains.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.8 s.113
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• pp.822-829
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• 2006

This paper presents a robust and superior control performance of a quarter-vehicle electrorheological (ER) suspension system. In order to achieve this goal, a moving sliding mode control algorithm is adopted, and its moving strategy is tuned by fuzzy logic. As a first step, ER damper is designed and manufactured for a passenger vehicle suspension system, and its field-dependent damping force is experimentally evaluated. After formulating the governing equation of motion for the quarter-vehicle ER suspension system, a stable sliding surface and moving algorithm based on fuzzy logic are formulated. The fuzzy moving sliding mode controller is then constructed and experimentally implemented. Control performances of the ER suspension system are evaluated in both time and frequency domains.

• Proceedings of the Korean Society of Rheology Conference
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• 2000.11a
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• pp.56-60
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• 2000

• Molecules and Cells
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• v.19 no.2
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• pp.268-278
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• 2005

We investigated the effect of cytosolic and extracellular $Ca^{2+}$ on $Ca^{2+}$ signals in pancreatic acinar cells by measuring $Ca^{2+}$ concentration in the cytosol($[Ca^{2+}]_c$) and in the lumen of the ER($[Ca^{2+}]_{Lu}$). To control buffers and dye in the cytosol, a patch-clamp microelectrode was employed. Acetylcholine released $Ca^{2+}$ mainly from the basolateral ER-rich part of the cell. The rate of $Ca^{2+}$ release from the ER was highly sensitive to the buffering of $[Ca^{2+}]_c$ whereas ER $Ca^{2+}$ refilling was enhanced by supplying free $Ca^{2+}$ to the cytosol with $[Ca^{2+}]_c$ clamped at resting levels with a patch pipette containing 10 mM BAPTA and 2 mM $Ca^{2+}$. Elevation of extracellular $Ca^{2+}$ to 10 mM from 1 mM raised resting $[Ca^{2+}]_c$ slightly and often generated $[Ca^{2+}]_c$ oscillations in single or clustered cells. Although pancreatic acinar cells are reported to have extracellular $Ca^{2+}$-sensing receptors linked to phospholipase C that mobilize $Ca^{2+}$ from the ER, exposure of cells to 10 mM $Ca^{2+}$ did not decrease $[Ca^{2+}]_{Lu}$ but rather raised it. From these findings we conclude that 1) ER $Ca^{2+}$ release is strictly regulated by feedback inhibition of $[Ca^{2+}]_c$, 2) ER $Ca^{2+}$ refilling is determined by the rate of $Ca^{2+}$ influx and occurs mainly in the tiny subplasmalemmal spaces, 3) extracellular $Ca^{2+}$-induced $[Ca^{2+}]_c$ oscillations appear to be triggered not by activation of extracellular $Ca^{2+}$-sensing receptors but by the ER sensitised by elevated $[Ca^{2+}]_c$ and $[Ca^{2+}]_{Lu}$.

• Korean Journal of Materials Research
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• v.25 no.9
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• pp.480-486
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• 2015

$Pb_{1-x}MoO_4:Er^{3+}/Yb^{3+}$ phosphors with various doping concentrations of $Er^{3+}$ and $Yb^{3+}$ ($x=Er^{3+}+Yb^{3+}$, $Er^{3+}=0.05$, 0.1, 0.2, and $Yb^{3+}=0.2$, 0.45) are successfully synthesized using a microwave sol-gel method, and the up-conversion photoluminescence properties are investigated. Well-crystallized particles, which are formed after heat treatment at $900^{\circ}C$ for 16 h, exhibit a fine and homogeneous morphology with particle sizes of $2-5{\mu}m$. Under excitation at 980 nm, the $Pb_{0.7}MoO_4:Er_{0.1}Yb_{0.2}$ and $Pb_{0.5}MoO_4:Er_{0.05}Yb_{0.45}$ particles exhibit a strong 525 nm emission band, a weak 550 nm emission band in the green region, and a very weak 655 nm emission band in the red region. The Raman spectra of the doped particles indicate the presence of strong peaks at higher and lower frequencies induced by the disordered structures of $Pb_{1-x}MoO_4$ through the incorporation of the $Er^{3+}$ and $Yb^{3+}$ ions into the crystal lattice, which results in the unit cell shrinkage accompanying the new phase formation of the $MoO_{4-x}$ group.

• Tribology and Lubricants
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• v.26 no.1
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• pp.7-13
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• 2010

This experimental study presents tribological characteristics under boundary lubrication contacts associated with electrorheolocal (ER) fluid. ER fluid is prepared by using phosphorated starch particles and silicone oil. Experimental apparatus of tribological tester is designed and constructed to evaluate tribological characteristics of pin specimens. Wear tests under boundary lubrication of ER fluid are experimentally performed under consideration of several operational factors such as normal load, sliding distance, sliding speed and specimen materials: steel, copper and aluminum. After wear test, microscopic surface changes of the worn pin specimens are analyzed in order to investigate measured wear characteristics by using the scanning electron microscope (SEM) as well as surface profilometer. In addition, the chemical wear characteristics are investigated by using energy dispersive x-ray spectroscopy (EDS). Moreover, friction coefficient measurements under different materials of pin specimens are conducted for the tribological investigations. In order to verify the effect of starch phosphate particles in ER fluid, the wear test results with ER fluid are compared with test results with only silicone oil. The results clearly present that the phosphorated starch based ER fluid shows the stabilized wear as well as friction characteristics after run-in operations, but the wear rate under ER fluid is increased.

• Development and Reproduction
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• v.22 no.3
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• pp.235-244
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• 2018

We investigate the effect of endoplasmic reticulum (ER) stress inhibitor treatment during parthenogenetic activation of oocytes on the ER stress generation, apoptosis, and in vitro development of parthenogenetic porcine embryos. Porcine in vitro matured oocytes were activated by 1) electric stimulus (E) or 2) $E+10{\mu}M$ Ca-ionophore (A23187) treatment (EC). Oocytes were then treated by ER stress inhibitors such as salubrinal (200 nM) and tauroursodeoxychloic acid (TUDCA, $100{\mu}M$) for 3 h prior to in vitro culture. Parthenogenetic embryos were sampled to analyze ER stress and apoptosis at the 1-cell and blastocyst stages. The x-box binding protein 1 (Xbp1) mRNA and ER stress-associated genes were analyzed by RT-PCR or RT-qPCR. Apoptotic gene expression was analyzed by RT-PCR. At the 1-cell stage, although no difference was observed in Xbp1 splicing among treatments, BiP transcription level in the E group was significantly reduced by salubrinal treatment, and GRP94 and ATF4 transcription levels in EC group were significantly reduced by all treatments (p<0.05) compared to control. In the EC group, both apoptotic genes were reduced by ER stress inhibitor treatments compared to control (p<0.05) except Caspase-3 gene by TUDCA treatment. These results suggest that the treatment of ER stress inhibitor during parthenogenetic activation can reduce ER stress, and thereby reduce apoptosis and promote in vitro development of porcine parthenogenetic embryos.

• Journal of Microbiology and Biotechnology
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• v.18 no.6
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• pp.1197-1202
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• 2008

Recent studies provide some evidence that the HtrA2 protein is intimately associated with the pathogenesis of neurodegenerative disorders and that endoplasmic reticulum (ER) quality control and ER stress-associated cell death play critical roles in neuronal cell death. However, little is known about the intimate relationship between HtrA2 and ER stress-associated cellular responses. In the present study, we have demonstrated that the HtrA2 protein level was gradually and significantly increased by up to to-fold in the mitochondria under tunicamycin (Tm)-induced ER stress, which eventually promoted cell death through the release of HtrA2 into the cytoplasm. Using an ecdysone-inducible mammalian expression system, we demonstrate that the extent of cell death in 293-HtrA2 cells was approximately 20 times higher under Tm-induced ER stress, indicating that the increase in the HtrA2 protein level in the mitochondria itself is necessary but not sufficient for the promotion of cell death. Taken together, these results suggest that HtrA2 may serve as a mediator of ER stress-induced apoptosis and ER-mitochondrial cross-talk in some cellular processes.

• Korean Journal of Agricultural and Forest Meteorology
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• v.7 no.1
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• pp.98-106
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• 2005

Groundwater plays an important role in water and carbon cycles in Gwangneung forest watershed located in a complex landscape. Because groundwater affects electrical resistivity (ER) of underground materials, the depth to water table and water content in subsurface can be investigated through measuring ER. Accordingly, the ER survey has been employed more frequently in recent hydrological investigations. Quantitative applications of the results of ER survey will contribute significantly to the examination of water budget closure at various spatiotemporal scales. This paper presents the preliminary results of the ER survey conducted at Gwangneung forest watershed to determine proper locations and depths of monitoring wells. Such use of ER survey, in conjunction with an integrated geophysical investigation and geographic information system, can provide more effective examination of underground structure and optimal locations of monitoring wells to further our understanding of the role of groundwater.