• Journal of the Korean Electrochemical Society
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• v.20 no.2
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• pp.27-33
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• 2017

Conventional lithium ion batteries suffer from notorious safety issues caused by inevitable lithium dendrite formation and proliferation during over/fast charging processes. The lithium dendrites or mechanical damage on the separator induce internal short circuit in LiB that generates extensive amount of heat within contacted electrode surfaces through the separator. During this heat generation, conventional polyolefin separators shrinks dramatically, and increasing short circuit pathway, that causes the battery to explode. To overcome this serious issue, ceramic coated separators are developed in commercial LiB to enhance thermal and mechanical stability. In this paper, various size(IL = 488.5 nm, I = 538.7 nm, S = 810.3 nm, D = 1533.3 nm) of $Al_2O_3$ particles are coated using styrene-butadiene rubber(SBR) / carboxymethyl cellulose(CMC) binder on PE separator to investigate its thermal stability and electrochemical effect on LiB coin cell with NCM cathode and Li metal anode.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.7
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• pp.563-567
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• 2011

The most widely used piezoelectric ceramics are lead oxide based ferroelectrics (PZT). However, the toxicity of lead oxide and its high vapor pressure during processing have led to a demand for alternative lead-free piezoelectric materials. We synthesized Lead-free piezoelectric ceramics of $0.96(K_{0.5}Na_{0.5})NbO_3-0.04SrZrO_3+x$ mol% $ZrO_2$ [KNN-SZ+$xZrO_2$; x= 0~0.10] doped with 0.1 wt% $MnO_2$ by a conventional solid state method. We investigated the piezoelectric properties and microstructures of these disk samples sintered in reduced atmosphere in order to evaluate the possibility of the multilayered piezoelectric ceramics having the base metal such as Ni as a internal electrode. All of these KNN-SZ samples sintered in 3%$H_2-97%N_2$ atmosphere at $1,140^{\circ}C$ exhibit pure perovskite structure irrespective of the content of $ZrO_2$. Meanwhile, the sintering denisty and piezoelectric properties such as $K_p$, $Q_m$ and $d_{33}$ of KNN-SZ samples as a function of $ZrO_2$ content show the maxima ($k_p$=28.07%, $Q_m$= 101.34, $d_{33}$= 156 pC/N) at x= 0.04 and it is likely that there is some morphotropic phase boundary(MPB) in this KNN-SZ+$xZrO_2$ composition system. These results indicate that the ceramic composition is a promising candidate material for applications in lead free multilayer piezoelectric ceramics.

• Journal of the Korean Magnetic Resonance Society
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• v.5 no.2
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• pp.99-109
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• 2001

Authors investigated neuronal changes of local cellular metabolism in the cerebral lesions of Parkinsonian symptomatic side between before and after stereotactic neurosurgery by follow-up 1H magnetic resonance spectroscopy (MRS). Patients with Parkinson's disease (PD) (n = 15) and age-matched normal controls (n = 15) underwen MRS examinations using a stimulated echo acquisition mode (STEAM) pulse sequence that provided 2${\times}$2${\times}$2 ㎤ (8ml) volume of interest in the regions of substantia nigra, thalamus, and lentiform nucleus. Spectral parameters were 20 ms TE, 2000 ms TR, 128 averages,2500 Hz spectral width, and 2048 data points. Raw data were processed by the SAGE data analysis package (GE Medical Systems). Peak areas of N-acetylaspartate (NAA), creatine (Cr), choline-containing compounds (Cho), inositols (Ins), and the sum (Glx) of glutamate and GABA were calculated by means of fitting the spectrum to a summation of Lorentzian curves using Marquardt algorithm. After blindly processed, we evaluated neuronal alterations of observable metabolite ratios between before and after stereotactic neurosurgery using Pearson product-moment analysis (SPSS, Ver. 6.0). A significant reduction of NAA/Cho ratio was observed in the cerebral lesion in substantia nigra of PD patient related to the symptomatic side after neurosurgery (P : 0.03). In thalamus, NAA/Cho ratio was also significantly decreased in the cerebral lesion including the electrode-surgical region (P : 0.03). A significant reduction of NAA/Cho ratio in lentiform nucleus was not oberved, but tended toward significant reduction after neurosurgery (P = 0.08). In particular, remarkable lactate signal was noted from the surgical thalamic lesions of 6 among 8 patients and internal segments of globus pallidus of 6 among 7 patients, respectively. Significant metabolic alterations of NAA/Cho ratio might reflect functional changes of neuropathological processes in the lesion of substantia nigra, thalamus, and lentiform nucleus, and could be a valuable finding fur evaluation of Parkinson's disease after neurosurgery. Increase of lactate signals, being remarkable in surgical lesions, could be consistent with a common consequence of neurosurgical necrosis. Thus, IH MRS could be a useful modality to evaluate the diagnostic and prognostic implications fur Parkinsons disease after functional neurosurgery.

• Applied Chemistry for Engineering
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• v.18 no.5
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• pp.522-526
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• 2007

Structural features and electrochemical performances of cokes pyrolized from oxidized cokes were examined, and compared with KOH-activated coke. Needle cokes ($d_{002}=3.5{\AA} $), having a graphene layer structure, were changed to a single phase of graphite oxide after oxidation treatment with an acidic solution having an $NaCLO_3$/needle coke composition ratio of above 7.5, and the inter-layer distance of the oxidized coke was expanded to $6.9{\AA} $ with increasing oxygen content. After heating at $200^{\circ}C$, the oxidized coke was pyrolized to the graphene layer structure with inter-layer distance of $3.6{\AA} $. However, the change of the inter-layer distance of the needle coke was not observed in the KOH activation process. On the other hand, an intercalation of electrolyte ions into the pyrolized coke, observed at first charge, occurred at 1.0 V, in which the value was lower than that of KOH-activation coke. The cell capacitor using pyrolized coke exhibited a lower internal resistance of $0.57{\Omega}$ in 1 kHz, and a larger capacitance per weight and volume of 30.3 F/g and 26.9 F/ml at the two-electrode system in the potential range 0~2.5 V than those of the cell capacitor using KOH-activation of coke. This better electrochemical performance may be associated with structure defects in the graphene layer derived from the process of the inter-layer expansion and shrinkage.

• The Journal of Korean Medicine
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• v.20 no.3 s.39
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• pp.36-44
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• 1999

Objectives: It has been well known that electroacupuncture(EA) has an analgesic effect and there is a pain control system in the central nervous system(CNS). The pain control system is composed of three major nuclei, which are periaqueductal gray(PAG), raphe nuclei, and the pain inhibitory complex located in the spinal cord. It has been suggested that the analgesic effect of EA might be the result of activation of the pain control system in the CNS. However, there may be a possibility that other nuclei are also involved in this pain modulation. Thus, we investigated whether the posterior intralaminar thalamic nuclei (PTIN) are involved in the pain modulation. Methods: To measure the level of pain, the jaw opening reflex (JOR) was used as a pain index. The magnitude of JOR is estimated by averaging the area of 10 successive responses. JOR was evoked by tooth-pulp stimulation with bipolar electrode carrying stimulus with the following parameters: intensity ranging from 420uA to 680ulA, 0.3ms duration of square pulse, and 0.5 Hz. Hapkog($LI_4$) and Taechung ($LR_3$) were the chosen acupoints. The Hapkog point was stimulated ipsilaterally at 5V, 3 Hz, for 15min in total, and the Taechung was stimulated at 2-3 V, 3 Hz, and for a total of 15 or 30 minutes. Different intensities of stimulation were given the PITN; one was given at $300{\mu}A$ and the other was at 500uA. The position stimulated in these nuclei by Paxinos Atlas was AP; from bregma $-4.0{\sim}-4.3mm,\;L; 0.5{\sim}1.8mm,\;D;\;4.8{\sim}6.3mm$. Results: The Hapkog point had a significant analgesic effect (P<0.05). However, the Taechung point had no effect. Both types of stimulation in the PITN did not reveal any analgesic effects. Conclusions: From these results, it was suggested that the posterior intralaminar thalamic nuclei are not involved in the modulation of pain.

• Applied Chemistry for Engineering
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• v.32 no.6
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• pp.613-620
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• 2021

A flow channel shape of PEMFC has an influence on the internal flow uniformity. If the reactant distribution in a flow path is not uniform during operation, both catalyst deactivation and mechanical damage of membrane could occur resulting in decreasing the membrane electrode assembly (MEA) durability. Numerous studies concerning flow design have been conducted to make smooth supply and uniform distribution of reactants in fuel cells. The baffle of flow path could improve fuel cell performance through the forced convection effect. A sub-channel, as an additional air flow path, could increase the reactant concentration and reduce the mass transfer loss via a smooth water discharge. In this study, computational fluid dynamics (CFD) was used to analyze the effect of blocks and sub-channels on the current density and oxygen concentration of the fuel cell. As a result, the limit current density and oxygen concentration at a rear block increased when using blocks and sub-channels in a flow channel. In particular, the current density increased significantly when the sub-channel was placed between two blocks. Also, the sub-channel position was optimized by analyzing the oxygen concentration, and the oxygen concentration was recovered at a rear block in the fuel cell.

• Composites Research
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• v.36 no.1
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• pp.37-41
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• 2023

The treated water inside the ballast electrolytic cell creates a highly alkaline atmosphere due to hydroxide generated at the DSA(Dimension Stable Anode) electrode during electrolysis. In this study, a composite material that can replace the weakness of the PE-coated steel pipe used in the existing ballast pipe was prepared. The test samples are BRE(Basalt fiber reinforced epoxy), BRP(Basalt fiber reinforced unsaturated polyester), GRE(Glass fiber reinforced epoxy), and GRP(Glass fiber reinforced unsaturated polyester). And then it was immersed in NaOH for 720 hours. The friction test of each specimen was conducted. The Friction coefficient analysis according to material friction depth and interfacial adhesion behavior between resin and fiber were analyzed. As a result, the mechanism of interfacial separation between resin and fiber could be analyzed. In the case of the unsaturated polyester resin with low interfacial bonding strength the longer the immersion time in the alkaline solution, the faster the internal deterioration caused by the deterioration that started from the surface, resulting in a decrease in the friction coefficient. It is hoped that this study will help to understand the degradation behavior of composite materials immersed in various chemical solutions such as NaOH, acid, and sodium hypochlorite in the future.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.4
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• pp.249-255
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• 2009

The performance of microbial fuel cell (MFC) can be affected by many factors including the rate of organic matter oxidation, the electron transfer to electrode by electrochemical bacteria, proton diffusion, the concentration of electron acceptor, the rate of electron acceptor reduction and internal resistance. the performance of MFC using oxygen as electron acceptor can be influenced by oxygen concentration as limit factors in cathode compartment. Many studies have been performed to enhance electricity production from MFC. The series or parallel stacked MFC connected several MFC units can use to increase voltages and currents produced from MFCs. In this study, a single MFC (S-MFC) and a stacked MFC (ST-MFC) using acetate as electron donor and oxygen as electron acceptor were used to investigate the influence of dissolved oxygen (DO) concentrations in cathode compartment on MFC performance. The power density (W/$m^3$) of S-MFC was in order DO 5 > 3 > 7 > 9 mg/L, the maximum power density (W/$m^3$) of S-MFC was 42 W/$m^3$ at DO 5 mg/L. The power density (W/$m^3$) of ST-MFC was in order DO 5 > 7 > 9 > 3 mg/L and the maximum power density (W/$m^3$) of STMFC was 20 W/$m^3$ at DO 5 mg/L. These results suggest that the DO concentration of cathode chamber should be considered as important limit factor of MFC operation and design for stacked MFC as well as single MFC. The results of ST-MFC operation showed the voltage decrease of some MFC units by salt formation on the surface of anode, resulting in decrease total voltage of ST-MFC. Therefore, connecting MFC units in parallel might be more appropriate way than series connections to enhance power production of stacked MFC.