• Applied Chemistry for Engineering
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• v.19 no.5
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• pp.484-490
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• 2008

Electrospun of PVP (polyvinylpyrrolidone) ultra fine fibers were fabricated using various solvents including methanol, ethanol, 2-propanol, butanol, acetone, methylene chloride, and DMF, which possess different properties such as boiling point, dielectric constant, and dipole moment. Electrospun PVP fiber was influenced by viscosity, conductivity, and surface tension of spinning solution. Therefore, the electrospun PVP fiber was successfully prepared under critical conditions of viscosity > $0.114kg/m{\cdot}s$, conductivity > 1.02 mS/m, surface tension < 30.0 mN/m. In case of an ethanol solvent system, average diameter of PVP fiber increased from 1701 nm to 5454 nm as increased the applied voltage from 10 kV to 20 kV.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1499-1508
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• 2013

Freeze-thaw tests were performed on gneiss samples collected from Terra Nova Bay, Antarctica in order to examine the engineering properties of rocks with slightly weathered (SW) and moderately weathered (MW). The tests were conducted under temperature ranging from $20{\pm}2^{\circ}C$ to $-20{\pm}2^{\circ}C$. A cycle of test consisted of 5 hours of freezing followed by another 5 hours of thawing under full saturation. In this paper, total 200 cycles of freeze-thaw test were performed with measurements of porosity, absorption, ultrasonic velocity, and shore hardness per each 20 cycle and that of uniaxial compressive strength (UCS) per each 50 cycle. The UCS of the SW rocks approximately decreased 0.07 MPa per a single cycle, while that of MW rocks decreased around 0.2 MPa per a single cycle. During the 200 cycles of SW rocks, the absorption increased from 0.23% to 0.39%, the P-wave velocity decreased from 4,054 m/s to 3,227 m/s and S-wave velocity decreased from 2,519 m/s to 2,079 m/s. Similarly, those of MW rocks changed from 0.65% to 1.6%, 3,207 m/s to 2,133 m/s and 2,028 m/s to 1,357 m/s. In conclusion, it was inferred that the properties of SW rocks experienced approximately 200-300 cycles of freeze-thaw process become close to those of MW rocks.

• Journal of Periodontal and Implant Science
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• v.30 no.2
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• pp.389-405
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• 2000

The purpose of this study is to evaluate the effect of IGF-I for DNA synthetic activity and the mRNA expression of bone matrix protein, type I collagen and osteopontin in prolifetation and differentiation of MC3T3-E1 cells. To evaluate DNA synthetic activity, cells were seeded at $2{\times}10^4cells/ml$ in 24 well plates and to evaluate mRNA of type I collagen and osteopontin cells were seeded at $5{\times}10^5cells/ml$ in 100mm culture dishes. These cells were cultured in alpha-minimum essential medium(${\alpha}-MEM$) containing 10% fetal bovine serum at $37^{\circ}C$, 5% $CO_2$ incubator. For DNA synthetic activity test 1, 10, 100ng/ml IGF-I were added to the cells which had been cultured for 3 days before 24 hours. For type I collagen mRNA expression 1, 10ng/ml IGF-I were added to the cells which had been cultured for 5, 10 days and for osteopontin mRNA expression 0.1, 1, 10ng/ml IGF-I were added to the cells which had been cultured for 5, 15, 20 days. Cell proliferaton was measured by the incorporation of [$^3H$]-thymidine into DNA and expression for type I collagen and osteopontin were measured by northern blot analysis. The results were as follows : DNA synthetic activity were generally higher in experimental group than control group. Expressions of type I collagen mRNA were higher at 5 day group and much lower at 10 day group in the control groups. In the experimental groups, mRNA expressions were slightly increased when 1 ng/ml IGF-I were added to 5 day group and decreased in all experimental 10 day groups. Expressions of osteopontin mRNA were higher at 20 day groups and lower at 15 day groups than the control groups. In the experimental groups, mRNA expressions were incereased when 0.1, 1 ng/ml IGF-I were added to 5 day group and in all the 15 day groups, but decreased when 0.1, 1, 10 ng/ml IGF-I were added to 20 day groups. IGF-I stimulated DNA synthetic activity of MC3T3-E1 cells during proliferation stage significantly, did not greatly changed effects on type I collagen mRNA expression and stimulated osteopontin mRNA expression at 15 day especially. In conclusion, we suggests that IGF-I have a tendency of stimulation effect of DNA synthetic activity but do not stimulate type I collagen mRNA in proliferation stage of MC3T3-E1 cell cultures, and stimulate osteopontin mRNA in differentiation stage of MC3T3-E1 cell cultures.

• ETRI Journal
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• v.40 no.4
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• pp.531-536
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• 2018

The weighted K-nearest neighbor (WKNN) algorithm is used to reduce positioning accuracy, as it uses a fixed number of neighbors to estimate the position. In this paper, we propose a dynamic threshold location algorithm (DH-KNN) to improve positioning accuracy. The proposed algorithm is designed based on a dynamic threshold to determine the number of neighbors and filter out singular reference points (RPs). We compare its performance with the WKNN and Enhanced K-Nearest Neighbor (EKNN) algorithms in test spaces of networks with dimensions of $20m{\times}20m$, $30m{\times}30m$, $40m{\times}40m$ and $50m{\times}50m$. Simulation results show that the maximum position accuracy of DH-KNN improves by 31.1%, and its maximum position error decreases by 23.5%. The results demonstrate that our proposed method achieves better performance than other well-known algorithms.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.218-221
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• 2004

Dry sliding wear behavior of electro-pressure sintered Co, $Co-20\;wt.\%$ CuSn and $Co-20\;wt.\%$ WC composites were investigated. Wear tests of the materials were carried out using a pin-on-disk wear tester at various loads of 10N-100N under a constant sliding speed condition of 0.38m/s against glass ($83\%\;SiO_2$) beads. Sliding distances were varied with a range of $100m{\sim}600m$. A scanning electron microscopy was used to examine morphologies of worn surfaces, cross-sections, and wear debris. The $Co-20\;wt.\%$ WC composite had the highest and the $Co-20\;wt.\%$ CuSn composite showed the lowest wear resistance among the tested materials. All specimens exhibited low friction coefficients ranging from 0.12 to 0.4 at the applied load of 100N.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.141-161
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• 1998

The depth and patterns of demineralization according to the difference in concentration and application time of phosphoric acid were observed through the transmission electron microscope, and shear bond strengths to the acid -conditioned dentin were then measured and compared with the TEM results. To investigate the influence of polymer addition into the phosphoric acid and the effect of difference in concentration and application time of the acid, the specimens were randomly divided into 9 groups. Among the specimens, the exposed dentin surfaces were acid-conditioned with 10% polymer-thickened phosphoric acid(All Bond 2, Bisco, U.S.A.) and aqueous 10%, 20%, 30%, 40% phosphoric acid for 20 seconds, The rest of the specimens were acid-conditioned with 10% phosphoric acid for 15s, 30s, 60s, 120s respectively. The specimens were immersed in 4% glutaraldehyde in 0.1M sodium cacodylate buffer and postfixed with 1 % osmium tetroxide without decalcification and then observed under a JEOL Transmission Electron Microscope(JEM 1200 EX II, Japan). After the specimens were acid-conditioned as the above, primer and adhesive resin were applied to blot-dried dentin and shear bond strengths were then measured and analysed. The results were as follows : 1. The intertubular demineralization depth of 4.0-$5.0{\mu}m$ in 10% polymer-thickened phosphoric acid gels was similar or slightly deeper than that of 4.0-$4.5{\mu}m$ in aqueous 10% phosphoric acid solution. 2. The intertubular demineralization depth of aqueous 20%, 30% and 40% phosphoric acid solution was 6.5-$7.0{\mu}m$, 6.5-$7.5{\mu}m$ and 9.0-$15.0{\mu}m$ respectively. It showed that the depth of dentin demineralization is partly related to the concentration of phosphoric acid solution. 3. The intertubular demineralization depth of aqueous 10% phosphoric acid solution in application time for 15s, 30s, 60s and 120s was 2.5-$3.0{\mu}m$, 4.0-$6.0{\mu}m$, 6.5-$7.0{\mu}m$ and 8.5-$14.0{\mu}m$ respectively. It showed that the depth of dentin demineralization is directly related to the application time of phosphoric acid solution. 4. The partially demineralized dentin layer between demineralized collagen layer and unaffected dentin was showed to a width of 0.5-$1.0{\mu}m$ in lower concentration groups treated with aqueous 10% phosphoric acid for 20s, 60s, 120s and 20% phosphoric acid for 20s. 5. The demineralization effect at the border of intertubular-peritubular junction was less evident than that in the peritubular and intertubular dentin. The collagen fibers in the intertubular dentin had a random orientation, whereas those that lined the tubules were circumferentially aligned. The cross-linkage of dentinal collagen in demineralized collagen layer was clearly seen. 6. A statistically significant difference of bond strengths according to the difference in phosphoric acid concentration did not exist among the groups treated with 10%, 20%, 30% and 40% acid solution (P>0.05). However, bond strengths to the treated dentin with 10% phosphoric acid solution for 30s were significantly higher than that for 120s (P<0.05).

• The Korean Journal of Nuclear Medicine
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• v.28 no.1
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• pp.69-74
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• 1994

Authors retrospectively analysed 20 cases of follow-up $^{99m}Tc$-DMSA renal scans to evaluate renal function recovery after treatment in urologic disorders of infants and children. There were 20 cases with both $^{99m}Tc$-DMSA renal scans prior to and after therapy in 15 patients below 9 years old. Among them, 10 patients underwent ureteroneocystostomy under the diagnosis of vesicoureteral reflux, two patients pyeloplasty because of obstructive uropathy and one was treated with antibiotics even diagnosis of UPJ stricture. We have got the quantified uptake rate of $^{99m}Tc$-DMSA renal scan by using the regression equation as "y=0.591x-2.105" (y=the quantified uptake rate, x=the simple uptake rate). The number of kidneys performed proper therapy were 29, and the cases with more increased radiotracer uptake rate in the follow-up $^{99m}Tc$-DMSA renal scans were 20 in number as 69% in frequency. 19 cases with improved renal function on $^{99m}Tc$-DMSA renal scans didn't show any significant difference related to aging or recovery duration after therapy. The $^{99m}Tc$-DMSA renal scans were not useful to evaluate renal function recovery in infants and children, but could be good tests to assess residual renal function prior to or after treatment.

• Journal of environmental and Sanitary engineering
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• v.20 no.4 s.58
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• pp.9-20
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• 2005

The purpose of the study was characteristics of secondary pollutants of $PM_{10}$ collected in pocheon between August 2002 and June 2003. The ambient concentrations of $PM_{10}$ mass, 9 water-soluble anions and cations, and 13 bulk composition trace elements were determined from filter samples collected by $PM_{10}$ high volume air sampler(UV-15H, Graseby-Anderson Co., USA). During this period average $PM_{10}$ mass concentration was $83.8{\mu}g/m^3(49.8{\mu}g/m^3\~111.6{\mu}g/m^3)$ in Pocheon. Mechanism for transformation of secondary pollutants by soluble ion components is divided into two categories; $NaNO_3$ type by the reaction of sea salt and $HNO_3$ in the atmosphere, and nitrate salt or phosphate salt type such as $(NH_4)_2SO_4,\;NH_4NaSO_4,\;and\;(NH_4)_2SO_4(2NH_4O_3)$.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.5
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• pp.269-274
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• 2013

To proportionally control the electronic valve position of the actuator, we designed and fabricated PCU, CPT, and rotary absolute optical encoder for the detection of absolute angular position in the actuator. We also designed and constructed the test system by using DAQ hardware and Labview. We designed PCU to convert 1-5 V, 0-5 V, 0-10 V, 2-10 V voltage signals and 4-20 mA current signals to the voltage signals in the common 0.5-2.5 V range. We designed CPT to output 4-20 mA current signals corresponding to the valve positions based on the PWM signal input from the MCU. We also designed 20 bit optical encoder by using infrared LED and infrared transistor and made the serial communication with the main board possible. When we tested PCU and CPT with DAQ hardware and Labview software, they operated correctly with the small errors within ${\pm}0.003$ V and ${\pm}0.01$ mA, respectively, showing that our actuator has the excellent performance to employ as the industrial proportional-valve-actuator. The resolution of the encoder was $11.25^{\circ}$ and the maximum revolution to detect was 32,768.

• The Journal of the Acoustical Society of Korea
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• v.28 no.3
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• pp.198-207
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• 2009

Distribution of cavitation bubbles relative to change of the sound speed and attenuation in the water was estimated using acoustic signal from 20 to 300 kHz in two cases that cavitation bubbles exist and do not exist. To study generation and extinction property of cavitation bubble, bubble distribution was estimated in three cases: change of rotation speed (3000-4000 rpm), surface area of blade ($32-98\;mm^2$) and elapsed time (30-120 sec). As a result, the radii of the generated bubbles ranged from 10 to $60{\mu}m$, and bubble radius of $10-20{\mu}m$ and $20-30{\mu}m$ was accounted for 45 and 25% of the total number of cavitation bubbles, respectively. And generation bubble population correlated closely with the rotating speed of the blades but did not correlate with the surface area of blade. It was observed that 80% of total bubble population disappeared within 2 minutes. Finally, acoustic data of bubble distribution was compared with optical data.