• Applied Chemistry for Engineering
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• v.27 no.4
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• pp.444-448
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• 2016

Hollow silicon/carbon (H-Si/C) composites as anode materials for lithium ion batteries were investigated to overcome the large volume expansion. H-Si/C composites were prepared as follows; hollow $SiO_2\;(H-SiO_2)$ was prepared by adding $NaBH_4$ to $SiO_2$ synthesized using $st{\ddot{o}}ber$ method followed by magnesiothermic reduction and carbonization of phenolic resin. The H-Si/C composites were analyzed by XRD, SEM, BET and EDX. To improve the capacity and cycle performance, the electrochemical characteristics of H-Si/C composites synthesized with various $NaBH_4$ contents were investigated by charge/discharge, cycle, cyclic voltammetry and impedance tests. The coin cell using H-Si/C composite ($SiO_2:NaBH_4=1:1$ in weight) in the electrolyte of $LiPF_6$ dissolved in organic solvents (EC : DMC : EMC = 1 : 1 : 1 vol%) has better capacity (1459 mAh/g) than those of other composition coin cells. It is found that the coin cell ($SiO_2:NaBH_4=1:1$ in weight) has an excellent capacity retention from 2nd cycle to 40th cycle.

• Journal of the Korean Electrochemical Society
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• v.4 no.4
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• pp.139-145
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• 2001

Various compositions of iron oxide based materials as a cathode of lithium secondary battery have been fabricated and tested with electrochemical method. A layered form of $LiFeO_2$ was synthesized by mixing and heating the initial materials of $FeCl_3\;6H_2O,\;LiOH$ and NaOH at low temperature. The effect of changing the precursors composition was investigated. As a result, when increasing the additive amount of NaOH, the capacity of the electrode is decreased but the performance and declining rate of capacity became smaller. $LiFeO_2$ synthesized with the weight ratio of $NaOH/FeCl_3/LiOH,\;2/1/7$ showed the largest capacity, but the discharging efficiency was sharply decreased after 30 cycles. Charge-discharge tests of lithium cells with $LiFeO_2$ cathode having the layer structure were performed. This cell showed the reversibility in the range of 1.5-4.5V of cell voltage. By using CPR method, chemical diffusion coefficients were measured in 1M $LiPF_6/EC/DEC$ solution. The value of chemical diffusion coefficient decreased with increasing the lithium content x, In 0.5$10^{-11}^cm^2/s$.

• Journal of the Korean Association of Geographic Information Studies
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• v.17 no.3
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• pp.160-174
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• 2014

The purpose of this paper is to develop a meso-scale grid-based continuous hydrological model and apply to assess the future watershed hydrology by climate change. The model divides the watershed into rectangular cells, and the cell profile is divided into three layered flow components: a surface layer, a subsurface unsaturated layer, and a saturated layer. Soil water balance is calculated for each grid cell of the watershed, and updated daily time step. Evapotranspiration(ET) is calculated by Penman-Monteith method and the surface and subsurface flow adopts lag coefficients for multiple days contribution and recession curve slope for stream discharge. The model was calibrated and verified using 9 years(2001-2009) dam inflow data of two watersheds(Chungju Dam and Soyanggang Dam) with 1km spatial resolution. The average Nash-Sutcliffe model efficiency was 0.57 and 0.71, and the average determination coefficient was 0.65 and 0.72 respectively. For the whole Han river basin, the model was applied to assess the future climate change impact on the river bsain. Five IPCC SRES A1B scenarios of CSIRO MK3, GFDL CM2_1, CONS ECHO-G, MRI CGCM2_3_2, UKMO HADGEMI) showed the results of 7.0%~27.1 increase of runoff and the increase of evapotranspiration with both integrated and distributed model outputs.

• Journal of the Korean Electrochemical Society
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• v.11 no.4
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• pp.268-272
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• 2008

$LiFePO_4$ material was synthesized by electrospinning method to obtain optimal particle size($50{\sim}100\;nm$) without carbon coating or ball milling. This material showed an orthorthombic structure with Pnma space group without any impurities, such as FeP or $Fe_2P$, in the XRD pattern. The particle morphology and particle shape were observed by SEM analysis. Li/$LiFePO_4$ cell showed a high initial discharge capacity of 135 mAh/g, at current density of $0.1\;mA/cm^2$ with a cut-off voltage of 2.8 to 4.0V. This cell exhibited a perfect cycle performance over 99.9% cycle retention rate up to 50 cycles.

• Clean Technology
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• v.23 no.3
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• pp.308-313
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• 2017

In this study, we investigated the electrocatalytic effects of the N and O co-doping of Graphite Felt (GF) electrode for the vanadium redox flow battery (VRFB) at the cathode and the anode reaction, respectively. The electrodes were prepared by chemical vapor deposition (CVD) with $NH_3-O_2$ at 773 K, and its effects were compared with an electrode prepared by an O doping treatment. The surface morphology and chemical composition of the electrodes were characterized by scanning electron microscopy (SEM) and photoelectron spectroscopy (XPS). The electrocatalytic properties of these electrodes were characterized in a VRFB single cell comparing the efficiencies and performance of the electrodes at the cathode, anode, and single cell level. The results exhibited about 2% higher voltage and energy efficiencies on the N-O-GF than the O-GF electrode. It was found that the N and O co-doping was particularly effective in the enhancement of the reduction-oxidation reaction at the anode.

• Applied Chemistry for Engineering
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• v.10 no.3
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• pp.415-418
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• 1999

The characteristics of VRLA (valve regulated Iead-acid) battery with the tubular positive plate and gel type electrolyte were examined as a function of active material filling density. The filling density of positive plate was 3.2 g/mL, 3.4 g/mL, and 3.6 g/mL, respectively. These VRLA batteries were cycled with 100% DOD (depth of discharge) at the $C_5/5$ rate, followed by IU-type recharge with $I_{max}=0.2C_{10}/10$ and a final voltage V=2.40 V/cell. The test was performed in a thermostatic room at $25{\pm}1^{\circ}C$. The result indicated that the initial capacity was independent of active material filling density, i.e., the highest initial capacity was 3.4 g/mL of filling density and the lowest was 3.6 g/mL. On aspect of the cycle-life performance of the VRLA battery, the filling density of 3.6 g/mL was similar to that of 3.4 g/mL in the positive plate, and both were higher than that of 3.2 g/mL. Water-loss and degradation of the VRLA battery were decreased according to an increase of the filling density in the positive plate. The optimum filling density of the active material was 3.4~3.6 g/mL.

• Korean Chemical Engineering Research
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• v.58 no.1
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• pp.142-149
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• 2020

In this study, the electrochemical performance of Graphite/Silicon/Pitch composites as anode material was investigated to improve the low theoretical capacity of artificial graphite. Spherical artificial graphite surface was coated with polyvinylpyrrolidone (PVP) amphiphiles material to synthesize Graphite/Silica material by silica islands growth. The Graphite/Silicon/Pitch composites were prepared by petroleum pitch coating and magnesiothermic reduction. The Graphite/Silicon/Pitch composite electrodes manufactured using poly(vinylidene fluoride) (PVDF), carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) binders. The coin type half cell was assembled using various electrolytes and additives. The Graphite/Silicon/Pitch composites were analysed by X-ray diffraction (XRD), scanning electron microscope (SEM) and a thermogravimetric analyzer (TGA). The electrochemical characteristics of Graphite/Silicon/Pitch composite were investigated by constant current charge/discharge, rate performance, cyclic voltammetry and electrochemical impedance spectroscopy. The Graphite/Silicon/Pitch composites showed high cycle stability at a graphite/silica/pitch ratio (1:4:8 wt%). When the electrode is prepared using PAA binder, the high capacity and stability is obtained. The coin type half cell assembled using EC: DMC: EMC electrolyte showed high initial capacity (719 mAh/g) and excellent cycle stability. The rate performance has an capacity retention (77%) at 2 C/0.1 C and an capacity recovery (88%) at 0.1 C / 0.1 C when the vinylene carbonate (VC) was added.

• Journal of Veterinary Clinics
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• v.27 no.5
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• pp.622-625
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• 2010

Inflammatory polyps in feline ear are nonneoplastic, inflammatory growths that arise from the middle ear or the eustachian tube and extended into the pharynx or external ear canal. Two 2-year-old female Russian blue cats showed 2-3 weeks history of aural discharge, crust formation in external ear, and head or ear shaking. Two masses were surgically excised from ear canal, and submitted for diagnosis. Histopathologically, these masses were covered with hyperplastic ciliated epithelium or nonkeratinizing squamous epithelium with partial erosion and ulceration. The core of masses was consisted of proliferated connective tissue and massive infiltration of mononuclear cells. Immunohistochemically, about 90% of infiltrated mononuclear cells demonstrated CD3 positive T cell. According to both polymerase chain reaction (PCR) and reverse transcriptase-PCR, tissues samples were negative for feline viral pathogens. Based on the clinical, gross, histopathologic findings, these two cases were diagnosed as inflammatory polyps originated from the middle ear in cats.

• Bulletin of the Korean Space Science Society
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• 2007.10a
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• pp.139-143
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• 2007

Electric propulsion has become a cost effective and sound engineering solution for many space applications. The success of SMART-1 and MUSES-C developed by European Space Agency (ESA) and Japan Aerospace Exploration Agency (JAXA) each proved that even small spacecraft could accomplish planetary mission with electric propulsion systems. A small electric propulsion system which is Hall effect thruster like SMART-1 is under development by SaTReC and GDPL (Glow Discharge Plasma Lab.) in KAIST for the next microsatellite, STSAT-3. To achieve optimized propulsion system, it is very necessary to understand plasma motions of Hall effect thruster. In this paper, we try to approach comprehensive plasma model with the particle simulation complementary to Particle In Cell (PIC) simulation. We think these two different approaches will help experimenters to optimize Hall effect thruster performances.

• Journal of Periodontal and Implant Science
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• v.28 no.2
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• pp.291-310
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• 1998

This study was performed to evaluate the effects of extracts of Drynariae Rhizoma on the characteristics of rat calvaria cells(RCV) and bone marrow cells(RBM) which have the important role on the bone formation in vitro. Drynariae Rhizoma has been known as the useful herbal medicament for treatment of the wound healing including regeneration of bone fracture, and also has been used to treat the periodontal lesions, tooth mobility, gingival bleeding and pus discharge via sulcus in Oriental Medicine. In control group, the cells were cultured alone with Dulbeco's Modified Eagle's Medium contained with 10% fetal bovine serum, 100U/ml penicillin, $100{\mu}g/ml$ streptomycin, $0.5{\mu}g/ml$ amphotericin-B. In experimental group, extracts of Drynariae Rhizoma(0.1, 1, 5, 10, $50{\mu}g/ml$) were added into the above culture condition. And then each group was characterized by examing the cell proliferation at 1, 3, 7, 14, 21, 30th day, the amount of total protein synthesis and alkaline phosphatase activity of RCV at 2,4th day and those of RBM at 3, 6th day. And also, the calcified nodule of RCV was examed at 3, 5th day in three goup, control, experimental, culture with the PDGF group. The results were as follow ; 1. Both RCV and RBM cells in Drynariae Rhizoma-treated experimental group proliferated more rapidly than nontreated control group. The experimental group below $5{\mu}g/ml$ Drynariae Rhizoma-treated showed more prominent cell proliferation from the 7th day to the 21st day than the control group and above $10\;{\mu}g/ml$ treated group in RCV. 2. Amount of total protein synthesis was more increased in Drynariae Rhizomatreated group than in control group. In $5{\mu}g/ml$ Drynariae Rhizoma-treated group showed most prominent protein synthesis of the any other exrperimental group and control group. 3. Alkaline phosphatase activity also more increased in Drynariae Rhizomatreated group than control group. 4. Mineralized nodules in Drynariae Rhizoma-treated group were more than not in control group but also in PDGF-treated group. From the above results, Drynariae Rhizoma appeared to enhanced the proliferation, protein synthesis, alkaline phosphatase activity and cellular ability of mineralized nodule formation than PDGF. So that, we conclude that Drynariae Rhizoma enhances the activities of bone cells which have the important role on the periodontal regeneration and optimal application of Drynariae Rhizoma was thought to be useful as the means in bone regeneration.