• Bulletin of the Korean Chemical Society
• /
• 제30권9호
• /
• pp.2132-2134
• /
• 2009

• 한국분말재료학회지
• /
• 제6권4호
• /
• pp.307-313
• /
• 1999

The effect of carbon content on the shape of WC grains dispersed in the Co-rich matrix during liquid phase sintering of WC-35%Co hard metals has been determined. The shape of WC grains was observed using SEM stereography after removing cobalt matrix with boiling hydrochloric acid solution. The WC grains changed from hexagonal to trigonal prism as the carbon content increased in the two-phase region of(WC + $\beta$ - Co), while the morphology of WC grains changed from trigonal to hexagonal shape as the carbon content decreased. The morphology of WC grains changes reversibly along with carbon loss or carbon pick-up. Morphology change of WC grains is attributed to crystal structure of WC, which has an asymmetric array of carbon atoms. There are two types of prismatic planes having different numbers of broken W-C bonds in WC grains. It is scrutinized that as the carbon content increases, the high energy prism planes grow fast and the crystals change from hexagonal to trigonal shape. On the other hand, when the carbon content decreases, the high energy prism planes are dissolved accompanying split of (100) plane into (101) and (101) planes.

• 한국결정학회지
• /
• 제7권2호
• /
• pp.183-190
• /
• 1996

수열법을 이용하여 은(Ag)이 내장된 고온고압용 autoclave에서 KOH를 광화제로 하여 ZnO 단결정을 성장하고, LiOH 및 NH4OH의 첨가에 따른 결정외형의 변화에 대해 고찰하였다. 성장된 단결정은 연한 녹색을 띠고 있었으며 최대크기는 30×30×20mm3였다. KOH 광화제에 1.0-2.0M의 LiOH를 첨가하면 (0001)면의 flaw의 수가 감소하였다. 또한 NH4OH를 첨가한 결과 Vc/Va(c 축의 방향의 성장속도/a축 방향의 성장속도)가 증가함을 확인하였고, 이 방법을 응용하여 판상형의 종자결정 대신 침상형의 종자결정으로도 등방주상(Equant hexagonal prism)형의 ZnO 단결정을 성장할 수 있었다.

• 한국세라믹학회지
• /
• 제29권6호
• /
• pp.463-470
• /
• 1992

Corundum single crystals were grown in cryolite flux with the composition of Na3AlF6:Al2O3=80:20 wt%. This mixture was melted at 115$0^{\circ}C$, followed by slow cooling at a rate of 2$^{\circ}C$/hr to 96$0^{\circ}C$. And by adding of La2O3 to the flux, the change of crystal forms were observed. Crystal forms of corundum grown in cryolite flux had the habits of hexagonal plate which consist of well developed {0001} face and small {101} face. As La2O3 was added and its content was increased, {223} and {110} faces were developed, and crystal habits of equidimensional forms changed into hexagonal prism form. In a charge of 8 mole% B2O3, Al2O3:La2O3=15:1, transparent corundum single crystals of equent form were grown. As the content of B2O3 was increased, twineed crystals which have twin law of 2-fold parallel to [0001], and composition plane of (110) were grown.

• 한국결정학회지
• /
• 제14권2호
• /
• pp.93-104
• /
• 2003

The crystals of group-Ⅲ nitride semiconductors with wurtzite structure exhibit a strong polarity. Especially, GaN has characteristics of different growth rate, anisotropic electrical and optical properties due to the polarity. In this work, GaN epilayer was grown and the polarities of the crystals were observed by the chemical wet etching and SP-EFM. GaN thin films were deposited on c-plane A1₂O₃ substrate under the variations of growth conditions by HVPE such as the deposition temperature of the buffer layer, the deposition time, the ratio of Group-V and Ⅲ and the deposition temperature of the film. The adquate results were obtained under the conditions of 500℃, 90 seconds, 1333 and 1080℃, respectively. It is observed that the GaN layer grown without the buffer layer has N-polarity and the GaN layer grown on the buffer layer has Ga-polarity. Fine crystal single particles were grown on c-plane A1₂O₃ and SiO₂, layer. The external shape of the crystal shows ｛10-11｝｛10-10｝(000-1) planes as expected in the PBC theory and anisotropic behavior along c-axis is obvious. As a result of etching on each plane, (000-1) and ｛10-11｝planes were etched strongly due to the N-polarity and ｛10-10｝ plane was not affected due to the non-polarity. In the case of the crystal grown on c-plane A1₂O₃, two types of crystals were grown. They were hexagonal pyramidal-shape with ｛10-11｝plane and hexagonal prism with basal plane. The latter might be grown by twin plane reentrant edge (TPRE) growth.

• 한국CDE학회논문집
• /
• 제10권1호
• /
• pp.70-75
• /
• 2005

A 3D solid element mesh generation algorithm was newly developed. 3D surface points of global rectangular coordinates were supplied by a 3D laser scanner. The algorithm is strait forward and simple but it generates mixed solid elements such as hexagonal, pyramid and prism types. Then, the surface triangular or rectangular elements were generated from the solid elements. The key of the algorithm is elimination of elements and 3D adaptive surface smoothing using given 3D surface point data.

• 대한방사선기술학회지:방사선기술과학
• /
• 제40권1호
• /
• pp.13-18
• /
• 2017

본 논문은 GATE (geant4 application for tomographic emission) 시뮬레이션을 이용하여 다양한 모양과 재질의 팬텀에서 CTDI (computed tomography dose index)를 평가하였다. GATE 시뮬레이션은 실린더 기둥, 타원 기둥과 육각 기둥 형태와 물, PMMA (polymethyl methacrylate), polyethylene 그리고 polyoxymethylene 재질의 다양한 지름(1 ~ 50 cm)의 팬텀을 모사하여 $CTD_{I100center}$ 값을 비교하였다. 120 kV, 200 mAs에서 실린더 기둥, 타원 기둥과 육각 기둥의 $CTDI_{100center}$ 값은 각각 11.1, 13.4 그리고 12.2 mGy이었다. 이 결과는 동일 볼륨이지만 팬텀의 형태에 따라 $CTDI_{100center}$ 값의 차이가 있음을 알 수 있다. 그리고 물, PMMA 그리고 polyoxymethylene 팬텀의 $CTDI_{100center}$ 값을 비교했을 때 물질의 밀도가 높을수록 상대적으로 $CTDI_{100center}$ 값이 낮게 측정되었다. 하지만 polyethylene의 경우 지름이 15 cm ($CTDI_{100center}$ : 35.0 mGy) 이 상에서는 PMMA 보다 $CTDI_{100center}$ 값이 증가하였다. 그리고 30 cm ($CTDI_{100center}$ : 17.7 mGy) 이 상의 지름에서는 물 보다 더 높은 $CTDI_{100center}$ 값을 보였다. 본 실험을 통해 팬텀의 재질 및 모양에 따른 $CTDI_{100center}$ 값을 GATE 시뮬레이션을 이용하여 평가하였다. CT 선량 평가시 다양한 재질 및 인체에 가까운 모양의 팬텀을 사용함으로써 좀 더 정확한 환자선량을 평가할 수 있을 것이다.

• Bulletin of the Korean Chemical Society
• /
• 제22권2호
• /
• pp.164-170
• /
• 2001

The crystal structures of fully dehydrated Ni2+- and Tl+ -exchanged zeolite X (Ni17Tl58-X, and Ni12Tl68-X; X=Si100Al92O384) have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3 at $21(1)^{\circ}C$ (a=24.380(4) $\AA$, 24.660(4) $\AA$, respectively). Their structures have been refined to the final error indices R1=0.037 and R2=0.043 with 485 reflections, and R1=0.039 and R2=0.040 with 306 reflections, respectively, for which I >36(I). In Ni17Tl58-X, 17 Ni2+ ions per unit cell were found at only two sites: 15 at site I at the center of the hexagonal prism (Ni-O=2.203(9) $\AA)$ and the remaining 2 at site II near single six-oxygen rings in the supercage (Ni-O=2.16(3) $\AA).$ Fifty-eight Tl+ ions were found at five crystallographic sites: 28 at site II (Tl-O=2.626(8) $\AA)$, 2 at site I' in the sodalite cavity near the hexagonal prism (Tl-O=2.85(1) $\AA)$, another 2 at site II' in the sodalite cavity (Tl-O=2.77(1) $\AA).$ The remaining 26 were found at two nonequivalent Ⅲ' sites with occupancies of 23 and 3. In Ni12Tl68-X, 12 Ni2+ ions per unit cell were found at two sites: 10 at site I (Ni-O=2.37(2) $\AA)$ and the remaining 2 at site II (Ni-O=2.13(2) $\AA).$ Sixty-eight Tl+ ions were found at five crystallographic sites: 28 at site II (Tl-O=2.63(1) $\AA)$, 12 at site I' (Tl-O=2.62(1) $\AA)$, 2 at site II' (Tl-O=3.01(2) $\AA)$, and the remaining 26 at two III' sites with occupancies of 23 and 3. It appears that Ni 2+ ions prefer to occupy site I and II, in that order. The large Tl+ ions occupy the remaining sites, I', II, II' and two different III' sites. In both crystals, only the Ni2+ ions at site II were reduced and migrated to the external surface of zeolite X when these crystals were treated with hydrogen gas.

• 한국멀티미디어학회논문지
• /
• 제14권11호
• /
• pp.1438-1449
• /
• 2011

수중센서네트워크 응용은 적용 대상 및 지역적 범위에 따라 효과적인 모델링이 필요하고 이러한 특정화된 응용 모델 기반에서 에너지 효율적인 데이터통합 방법이 필요하다. 본 논문에서는 수중에 고정된 닻으로 좌우 움직임이 가능한 센서노드들로 구성된 3차원 육각기둥 벌집모델에 기초하여 오염 및 침투 감시용 응용 모델링 및 이를 기초로 한다. 이 모델에서는 층별 구성 셀들의 이벤트 감지 데이터와 해당 층 위치 데이터를 수면기지국까지 효율적으로 전송하면 그 목적이 달성된다. 여기서 기존의 데이터통합 방법을 적용하면 최소 경로나 멀티캐스트 트리에 기반된 관계로 과정이 복잡하여 에너지 비효율적이다. 본 논문에서는 층별 셀들에서 발생되는 이벤트 데이터를 해당 층 헤드노드로 효과적으로 전달하기위한 클러스터 내부에서 클러스터 기반의 에너지 효율적인 세 가지 가능한 데이터통합 방법을 제시한다. 그리고 층별 클러스터 헤드노드에서 수집된 데이터를 기지국까지 효율적으로 전달하기위한 클러스터 간 세 가지 데이터통합 방법도 제시한다. 제시된 데이터통합 방법들은 주어진 영역 침투 감시등과 같은 특정화된 응용 대상으로 동작의 단순성과 에너지 효율화 측면이 주된 고려 요소이다. 마지막으로 시뮬레이션과 성능 비교분석을 통해 제시된 클러스터 층별 및 층간 데이터통합 방법의 조합 중 가장 우수한 에너지 효율적인 데이터통합 방법을 도출한다.

• Bulletin of the Korean Chemical Society
• /
• 제23권12호
• /
• pp.1759-1764
• /
• 2002

Two crystal structures of dehydrated $Ag^+-andTl^+$-exchanged zeolite X$Ag_{27}Tl_{65-}X\;and\;Ag_{23}Tl_{69-}X$have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3 at 21(1) $^{\circ}C(a=24.758(4)\AAa=24.947(4)$, ${\AA}respectively).$, Their structures were refined to the final error indices $R_1$=0.055 and $wR_2$=0.057 with 375 reflections, and $R_1$=0.057 and $wR_2$=0.057 with 235 reflections, respectively, for which I > $3\sigma(I).$ In the structure of $Ag_{27}Tl_{65-}X,\;27\;Ag^+$ ions were found at two crystallographic sites: 15$Ag^+$ ions at site I at the center of the hexagonal prism and the remaining 12$Ag^+$ ions at site II' in the sodalite cavity. Sixty-five $Tl^+$ ions were located at three crystallographic sites: 20$Tl^+$ ions at site II opposite single six-rings in the supercage, 18$Tl^+$ ions at site I' in the sodalite cavity opposite the D6Rs, and the remaining 27$Tl^+$ ions at site III' in the supercage. In the structure of $Ag_{23}Tl_{69-}X$, 23$Ag^+$ ions were found at two crystallographic sites: 15 at site I and 8 at site II'. Sixty-nine $Tl^+$ ions are found at four crystallographic sites: 24 at site II, 17 at stie I', and the remaining 28 at two III' sites with occupancies of 22 and 6.