• Restorative Dentistry and Endodontics
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• v.29 no.3
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• pp.249-266
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• 2004

The purpose of this study was to determine whether pH and time has any influence on the degradation behavior of composite restoration by analyzing the leached monomers of dental composites qualitatively and quantitatively after storage in acetate buffer solution as a function of time using high performance liquid chromatography (HPLC) / mass spectrometer. Materials and Methods：Three commercial composite restorative resin materials (Z-250, Heliomolar and Aeliteflo) with different matrix structure and filler composition were studied. Thirty specimens (7mm $diameter{\times}2mm$ thick) of each material were prepared. The cured materials were stored in acetate buffer solution at different pH (4, 7) for 1, 7 and 45days. As a reference, samples of unpolymerized composite materials of each product were treated with methanol (10mg/ml). Identification of the various compounds was achieved by comparison of their mass spectra with those of reference compound, with literature data. and by their fragmentation patterns. Data were analysed statistically using ANOVA and Duncan's test. Results：1. Amounts of leached TEGDMA in Aeliteflo were significantly larger than those of UDMA in Z-250 and Heliomolar at experimental conditions of different storage time and pH variation (p<0.001). 2. As to comparison of the amounts of leached monomers per sorage time, amounts of leached TEGDMA in Aeliteflo and UDMA in Z-250 and Heliomolar were increased in the pH 4 solution more significantly than in the pH 7 solution after 1day, 7days and 45days, respectively (p<0.001). 3. In total amounts of all the leached monomers with storage times, the overall amounts of pH 4 extracts were larger than those of pH 7 extracts for all resin groups, but there was no significant difference (p>0.05).

• Bulletin of the Korean Chemical Society
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• v.28 no.5
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• pp.745-750
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• 2007

An isotope dilution-liquid chromatography/tandem mass spectrometric method was developed as a candidate reference method for the accurate determination of folic acid in infant milk formula. Sample was spiked with 13C5-folic acid and then extracted with phosphate buffer (pH 6) solution. The extract was further cleaned up by deproteinization followed by a C18 solid-phase extraction cartridge. The extract was analyzed by using LC/ ESI/MS/MS with selectively monitoring the collisionally induced dissociation channels of m/z 442 → m/z 295 and m/z 447 → m/z 295, which are the neutral glutamyl loss from the [M+H]+ ions of folic acid and 13C5-folic acid, respectively. LC/MS/MS chromatograms showed substantially reduced background from chemical noises compared to LC/MS chromatograms. Repeatability and reproducibility studies showed that the LC/MS/ MS method is a reliable and reproducible method which can provide less than 1.5 relative percentage of method precision.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.7
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• pp.1211-1217
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• 2000

The three-dimensional finite-difference time-domain (FDTD) method and the two-dimensional quasi-static formulation have been used to calculate the characteristic impedance and the microwave effective index of coplanar waveguide structures on Lithium Niobate ($LiNBO_3$) single crystal substrates with a yttria-stabilized zirconia (YSZ) or $SiO_2$ buffer layer. The results shown can be a good source to predict the modulator characteristics. The effects of the thin buffer layer and anisotropy of the $LiNBO_3$ crystal (x-cut and z-cut) are discussed. The comparison between the FDTD and quasi-static results shows good agreement. In this paper, the efficient modeling technique of the FDTD method for the coplanar waveguide (CPW) structures based on an anisotropic substrate with a thin buffer layer is developed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.12
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• pp.1051-1057
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• 2000

A traveling-wave CPW(coplanar waveguide) electrode with abruptly broken input/output-taper for LiNbO$_3$optical modulator was designed and fabricated. The electrical characteristics of traveling-wave electrode on z-cut LiNbO$_3$crystal with SiO$_2$buffer layers were measured by network analyzer. To confirm the possibility of the electro-optic modulator electrode, detailed calculations of the impedance, microwave effective index and attenuation constants are presented as a function of the microwave electrode thickness, but the buffer layer thickness is fixed as 1${\mu}{\textrm}{m}$. These characteristics are discussed from the viewpoint of the device optimization and are expected to be design guides for the LiNbO$_3$modulator’s electrodes.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.319-322
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• 1999

In this paper, we report characteristics of a internal chip of LiNbO$_3$ modulator with low-driving-voltage at 150nm wavelength. A Ti diffusion method for LiNbO$_3$ optical waveguide and a buffer layer for improving phase velocity mismatch between optical and microwave waves were employed. The traveling-wave coplanar waveguide electrode of 35mm is used for reducing the driving voltage. From this work, wideband modulation of 10㎓ and low-driving voltage of 3.9volts are realized.

• JSTS:Journal of Semiconductor Technology and Science
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• v.3 no.4
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• pp.175-180
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• 2003

In this paper, we present a new method for early depth test for a 3D rendering engine. We add a filter stage to the rasterizer in the 3D rendering engine, in an attempt to identify and avoid the occluded pixels. This filtering block determines if a pixel is hidden by a certain plane. If a pixel is hidden by the plane, it can be removed. The simulation results show that the filter reduces the number of pixels to the next stage up to 71.7%. As a result, 67% of memory bandwidth is saved with simple extra hardware.

• Journal of Ocean Engineering and Technology
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• v.9 no.2
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• pp.83-88
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• 1995

In this paper, the solid modeller suitable for PC was developed for Top-down 3-D representation and analysis of fixed offshore structures. Also solid modelling and hidden line removal were conducted in order to visualize the offshore structures based on the scan line z-buffer algorithm.

• Korean Journal of Microbiology
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• v.24 no.3
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• pp.228-235
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• 1986

The aims of the present studies were to develop conditions for the spheroplast formation of Zymomonas mobilis and regeneration of the spheroplasts to normal cells in synthetic media. Z. mobilis cells harvested from exponential growth phase were treated with lysozyme, mutanolysin, and glycine in various conditions. It was found that spheroplasts were formed only with the treatment of glycine but not with the enzymes treatments. It was therefore considered that the tetrapeptide strand of peptide strand of peptidoglycan might play more important roles than the glycan strand in maintaining the vital mechanical function of Z. mobilis. It was found also that removal of outher membrane was the major problem in protoplast formation of Z.mobilis. As results, It was observed that over 85% of cells were readly converted to spheroplasts with sole glycine treatment for 4 hr and 7-10% of the spheroplasts were regenerated to normal cells in synthetic media.

• Journal of KIISE:Computer Systems and Theory
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• v.30 no.10
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• pp.579-585
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• 2003

Recently most of 3D graphics rendering Processors have the pixel cache storing depth data and color data to reduce the memory latency and the bandwidth requirement. In this paper, we propose the effective pixel cache for improving the performance of a rendering processor. The proposed cache system stores the depth data selectively based on the result of Z-test and the color data are stored into the auxiliary buffer. Simulation results show that the 16Kbyte proposed cache system provides better performance than the 32Kbyte conventional cache.

• The Korean Journal of Pesticide Science
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• v.3 no.2
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• pp.37-46
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• 1999

In order to ascertain the safety of the systemic insecticide carbofuran-treated crops, samples of garlic, peanut and potato were collected randomly from markets located in the main producing areas and analyzed for the residue of carbofuran and its main metabolite, 3-hydroxycarbofuran. The in vitro metabolism of carbofuran in phosphate buffer extracts of the crops was investigated. Two (M-12 and M-16) out of 20 mature garlic samples contained 0.13 and 0.07 mg/kg of carbohran, respectively, showing a detection incidence of 10%. The residue levels were less than the maximum residue limit (0.5 ppm) set by Korean Food and Drug Administration. Only one sample of mature garlic (M-12) out of 20 contained 0.13 mg/kg of 3-hydroxycarbofuran. The residues of carbofuran and 3-hydroxycarbofuran in the immature garlic, peanut and potato samples were less than the detection limits, 0.02 mg/kg for carbofuran and 0.06 mg/kg for 3-hydroxycarbofuran. The application of carbofuran to the fields of garlic, peanut and potato would be safe, considering that the estimated maximum acceptable daily intake of carbofuran from garlic was 0.0013 mg which is 0.24% of the maximum acceptable daily intake (0.55 mg). Carbofuran was hydrolyzed in vitro mainly to carbofuran phenol (m/z 164) in the respective phosphate buffer extracts of the three crops in contrast to the major oxidative metabolism in situ. The amount of the metabolite increased with the incubation time.