• Journal of the Korean Chemical Society
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• v.34 no.5
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• pp.413-417
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• 1990

The structural variation process of amorphous SiO$_2$ gel upon heat-treatment conditions of 80, 250, 450 and 1000$^{\circ}C$ has been studied by using the radial distribution functions (RDF$_{obs}$) estimated from the X-ray diffraction intensities. The expected gel structure was determined by comparing the RDF$_{obs}$ with those for the other six standard samples selected appropriately. The structure of specimens prepared by sol-gel method is well consistent with that of fused SiO$_2$ (${\beta}$-cristobalite with cubic symmetry) except a slight difference in O-O band distance.

• Journal of the Mineralogical Society of Korea
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• v.9 no.1
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• pp.43-53
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• 1996

The detailed crystal chemistry of ilmenite from the Hadong massif was studied by the EPMA, M ssbauer spectroscopy, and Rietveld structural refinement using X-ray powder diffraction data. The ilmenite-bearing anorthosite shows complicated mineral assemblage which consists of plagioclase, clinopyroxene, hornblende, biotite, chlorite, apatite, allanite, and zircon. Anorthite is andesine in composition (Ab 28-57), and clinopyroxene drops in ferro-hypersthene (Fs 62-70). Ilmenite is trigonal symmetry with R space group, whose structure shows the alternation of Fe2+ (M1 site) octahedral layer and Ti (M2 site) layer along c axis. M ssbauer spectroscopy indicates that there are three doubles which assigned to couple of Fe2+($\delta$=0.812, 0.890mm/sec) and one Fe3+($\delta$=0.303mm/sec) in octahedral sites. Their Fe3+/$\Sigma$Fe is 0.065 and chemical formula is established as Fe2+0.94Fe3+0.07Ti0.97O3 using both EPMA and M ssbauer analysis. Rietveld structural refinement reveals that site occupancies of Fe in M1 and Ti in M2 are 91.2% and 89.4%, respectively. This implies that Ti and Fe2+ are alternatively occupy M1 and M2 sites. In addition, smaller M2 site is more preferable to Fe3+ occupancy over M1.

• Bulletin of the Korean Chemical Society
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• v.13 no.4
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• pp.375-381
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• 1992

In this study we have synthesized two spiro orthocarbonates, which can be polymerized with volume expansion, and determined their crystal structures. The crystal data are as follows; 3,4,10,11-Di(9,10-dihydro-9,10-ethanoanthracenyl)- 1,6,8,13-tetraoxa-6.6-tridecane 5: a = 16.898 (1), b = 9.299 (1), c = 24.359 (2) ${\AA}$, $\beta$ = 123.73 $(7)^{\circ}$, space group P21/c and R = 0.073 for 2954 reflections; compound 8: a = 15.244 (4), b = 15.293 (3), c = 10.772 (3) $\AA$, ${\beta}$ = 99.45 $(2)^{\circ}$, space group P21/c and R = 0.082 for 2346 reflections. The seven-membered rings of compound 5 are chair forms and all the six-membered rings are boat shaped. For a six-membered spiro orthocarbonate, 3,9-Di(9-fluorenylidenyl)-1,4,6,9-tetraoxa-5,5-und ecane 8, fluorene groups [C(1) atom through C(13) atom] are planar within ${\pm}0.09{\AA}$ and the six-membered rings have chair conformations. The whole molecule has pseudo-C2 symmetry. The water molecules in the crystal are linked with each other through the hydrogen bond with distance of 2.790 (20) ${\AA}$.

• Journal of the Korean earth science society
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• v.23 no.1
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• pp.52-58
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• 2002

A colorless and transparent zirconium oxide ($Zr_{0.73}Y_{0.27}O_{1.87}$) crystal has been synthesized by the Bridgman-Stockbager method. The gem-quality material is produced by adding 20${\sim}$25 wt.% $Y_2O_3$ (stabilizer) and 0.04 wt.% $Nd_2O_3$ (decolorising agent) to the $ZrO_2$ powder. It shows a vitreous luster with a slight oily appearance. Under a polarizing microscope, it shows isotropic nature with no appreciable anisotropism. Mohs hardness value and specific gravity is measured to be 8${\sim}$$8{\frac{1}{2}}$ and 5.85, respectively. Under ultraviolet light it shows a faint white glow. The crystal structure of yttria-stabilized zirconia with 0.27 at.% Y has been re-investigated, using single crystal X-ray diffraction, and confirmed to be a cubic symmetry, space group $Fm{\overline{3}}m$ ($O^5_h$) with a=5.1552(5) ${{\AA}}$, V=136.99(5) ${{\AA}}^3$, Z=4. The stabilizer atoms randomly occupy the zirconium sites and there are displacements of oxygen atoms with amplitudes of ${\Delta}/a{\sim}$0.033 and 0.11 along <110> and <111> from the ideal positions of the fluorite structure, respectively.

• Progress in Superconductivity and Cryogenics
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• v.20 no.3
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• pp.1-4
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• 2018

The effect of sulfate substitution on the formation of (Pb,S)-1201 type phase was investigated. Polycrystalline samples with nominal compositions of $(Pb_{0.5}B_{0.5-x}S_x)(Sr_{2-y}La_y)CuO_z$, (x = 0 - 0.5, y = 0.7 - 1.0) and $(Pb_{0.5}S_{0.5})(Sr_{2-y}La_y)CuO_z$ (y = 0.5 - 1.0) were prepared by using a solid-state reaction method. The samples were characterized by powder X-ray diffraction (XRD) and resistivity measurements. XRD data revealed that almost-single (Pb,S)-1201 phase samples could be obtained for x = 0.5 and y = 0.9-1.0, judging from the similar results of the XRD patterns between the (Pb,S)-1201 and (Pb,B)-1201 phases. Each of the samples has a crystal structure with tetragonal symmetry. The sample with x = 0.5 and y = 0.9 is found to show an onset of resistivity dropping at over 23 K and zero resistivity at 12 K.

• Journal of Biomedical Engineering Research
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• v.16 no.2
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• pp.129-138
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• 1995

High-energy and high-dose X-ray and electron beam have been used in radiation therapy after developing particle accelerators. It is recommended to irradiate patients exect real dose for improving therapy effectiveness by International Committee on Radiation Units and Measurement. The radiation detector for daily beam checks of medical accelerators is described. Using thirteen silicon diodes, we have designed the diode detector providing information about calibration, beam symmetry, flatness, stability variation according to radiation damage, time and general quality assurance for both photon and eletron beams. we also compared these measurement values with those of using ionization chamber, film and semiconductor dosimeter.

• Korean Journal of Optics and Photonics
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• v.6 no.3
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• pp.188-200
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• 1995

A design of unit magnification 2-mirror system with high resolution is presented. It is for soft X-ray(wavelength of 13 nm) projection imaging and suitable for preparation of high density semiconductor chip. In general, a holosymmetric system with unit magnification has the advantage that both coma and distortion are completely eliminated. In our holosymmetric 2-mirror system, spherical aberration is addtionally removed by using two identical paraboloidal mirror surfaces and field curvature aberration is also corrected by balancing Petzval sum and astigmatism which depends on the distance between two mirrors, so that the system is a aplanatic flat-field paraboloidal 2-mirror holosymmetric system. This 2-mirror system is small in size, and has a simple configuration with rotational symmetry about optical axis, and has also small central obscuration. Residual finite aberrations, spot diagrams, and diffraction-based MTF's are analyzed for the check of performances as soft X-ray lithography projection system. As a result, the image sizes for the resolutions of$0.25\mum$and $0.18\mum$are 4.0 mm, 2.5 mm respectively, and depths of focus for those are $2.5\mum$, $2.4\mum$respectively. This system should be useful in the fabrication of 256 Mega DRAM or 1 Giga DRAM. DRAM.

• Journal of the Korean Society of Radiology
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• v.16 no.6
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• pp.687-695
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• 2022

To find a 3D printer material that can replace lead used as a shield for high-energy electron beam treatment, the shielding composites were simulated by using MCNP6 programs. The Percent Depth Dose (PDD), Flatness, and Symmetry of linear accelerators emitting high-energy electron beams were measured, and the linear accelerator was compared with MCNP6 after simulation, confirming that the source term between the actual measurement and simulation was consistent. By simulating the lead shield, the appropriate thickness of the lead shield capable of shielding 95% or more of the absorbed dose was selected. Based on the absorption dose data for lead shield with a thickness of 3 mm, the shielding performance was analyzed by simulating 1, 5, 10, and 15 mm thicknesses of ABS+W (10%), ABS+Bi (10%), and PLA+Fe (10%). Each prototype was manufactured with a 3D printer, measured and analyzed under the same conditions as in the simulation, and found that when ABS+W (10%) material was formed to have a thickness of at least 10mm, it had a shielding performance that could replace lead with a thickness of 3mm. The surface morphology and atomic composition of the ABS+W (10%) material were evaluated using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS). From these results, it was confirmed that replacing the commercialized lead shield with ABS+W (10%) material not only produces a shielding effect such as lead, but also can be customized to patients using a 3D printer, which can be very useful for high-energy electron beam treatment.

• Progress in Medical Physics
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• v.29 no.3
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• pp.92-100
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• 2018

The manufacturer of a linear accelerator (LINAC) has reported that the target melting phenomenon could be caused by a non-recommended output setting and the excessive use of monitor unit (MU) with intensity-modulated radiation therapy (IMRT). Due to these reasons, we observed an unexpected beam interruption during the treatment of a patient in our institution. The target status was inspected and a replacement of the target was determined. After the target replacement, the beam profile was adjusted to the machine commissioning beam data, and the absolute doses-to-water for 6 MV and 10 MV photon beams were calibrated according to American Association of Physicists in Medicine (AAPM) Task Group (TG)-51 protocol. To verify the beam data after target replacement, the beam flatness, symmetry, output factor, and percent depth dose (PDD) were measured and compared with the commissioning data. The difference between the referenced and measured data for flatness and symmetry exhibited a coincidence within 0.3% for both 6 MV and 10 MV, and the difference of the PDD at 10 cm depth ($PDD_{10}$) was also within 0.3% for both photon energies. Also, patient-specific quality assurances (QAs) were performed with gamma analysis using a 2-D diode and ion chamber array detector for eight patients. The average gamma passing rates for all patients for the relative dose distribution was $99.1%{\pm}1.0%$, and those for absolute dose distribution was $97.2%{\pm}2.7%$, which means the gamma analysis results were all clinically acceptable. In this study, we recommend that the beam characteristics, such as beam profile, depth dose, and output factors, should be examined. Further, patient-specific QAs should be performed to verify the changes in the overall beam delivery system when a target replacement is inevitable; although it is more important to check the beam output in a daily routine.

• Journal of the Mineralogical Society of Korea
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• v.6 no.2
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• pp.116-121
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• 1993

A single crystla of zeolite $Na_{78}Rb_{28}-X$ (approximate composition) was prepared by exposing $Na_{92}-X$ at $350^{\circ}C$ to 0.1 Torr of rubidium vapor, and its structure was determined by single-crystal x-ray diffraction methods in the cubic space group, Fd3, ${\alpha}=25.045(4){\AA}$. The structure was refined to the final error indices $R_1=0.082$ and $R_2=0.084$ with 353 for which I>$3{\sigma}(I)$. Only about 28 of the 92 $Na^+$ ions per unit cell were reduced and only about 14 of the 28 $Na^0$ atoms produced were retained within the zeolite. A $Na_5{^{4+}}$ cluster is present within each sodalite cavity. It is a centered tetrahedron (like $CH_4$) with bond $length=2.80(2){\AA}$ and angle tetrahedral by symmetry, and shows the full symmetry of its site. $T_d$, at the center of the sodalite cavity. Each of the four terminal atoms of the $Na_5{^{4+}}$ cluster bond to three framework oxygens at $2.36(2){\AA}$. At the centers of some double 6-rings are sodium atoms which bridge linearly between $Na_5{^{4+}}$ clusters to form agglomerations such as short zig-zag chains $Na_5{^{4+}}$ clusters. Delocalized electrons, located primarily on the sodiums at centers of the sodalite and (likely) double-six-ring cavities, contribute to the stability of the clusters.