• 대한치과보철학회지
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• 제37권4호
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• pp.454-464
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• 1999

The metal ceramic crown is currently the most popular complete veneer restoration in dentistry, but in many cases, the metal cervical collar at the facial margin is unesthetic and unacceptable. Facial porcelain margin has been used in place of it. But this dose not solve the problems, such as dark gingival discoloration and cervical opaque reflection of porcelain veneer. Recently, metal copings which were designed to terminate its labio-cervical end on the axial walls coronal to the shoulder have been clinically used to solve the esthetic problem of metal ceramic crown. But in this design, porcelain veneer of labio-cervical area which is not supported by metal may not be able to resist the stress during cementation and mastication. The purpose of this study was to evaluate fracture strength and fractured appearance of crowns according to different coping designs. A resin maxillary left central incisor analogue was prepared for a metal ceramic crown, and metal dies were made with duplication mold. Metal copings were made and assigned to one of four groups based on facial framework designs: group 1, coping with 0.5mm metal collar; group 2, metal extended to the shoulder; group 3, metal extended to 1mm coronal tn the shoulder: group 4, metal extended to 2mm coronal to the shoulder. Copings and crowns were adjusted to be same size and thickness, and cemented to metal dies with zinc phosphate cement by finger pressure. Fracture strength was measured with Instron Universal Testing Machine. Metal dies were anchored in Three-way-vice at 3mm below finish line and at $130^{\circ}$ inclined to the long axis of the crown. Load was directed lingually at 2mm below midincisal edge. Load value at initial crack and at catastrophic fracture was recorded. The results obtained were as follows : 1. Fracture strength values at initial crack were higher in groups 1, 2 than in groups 3, 4 but this difference was not statistically significant(P<0.05). 2. Conventional metal collared crown had greater catastrophic fracture strength than any other collarless crowns. 3. The greater the labial metal coping reduction, the lower the catastrophic fracture strength of crowns but when more than 1mm of labial metal reduction was done, the difference in strengths was not statistically significant(p<0.05). 4. The strongest collarless coping design was group 2.

• 한국세라믹학회지
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• 제39권7호
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• pp.649-656
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• 2002

Zn(NO$_3$)$_2$ 수용액과 urea[CO(NH$_2$)$_2$]를 이용한 침전법과 Self-Assembled Monolayers(SAMs)를 이용한 microcontact printing 방법으로 미세 패턴화된 ZnO 박막을 Al/si0$_2$/si 기판 위에 제조하였다. Zn(NO$_3$)$_2$와 urea를 혼합하여 제조한 Zn(OH)$_2$ 박막은 침전온도와 urea 량이 증가할수록 Zn(OH)$_2$의 침전량이 증가하였고 Zn(NO$_3$)$_2$와 urea의 반응 시간이 증가함에 따라, Zn(OH)$_2$ 박막의 두께와 입자 크기가 증가하였다. Zn(NO$_3$)$_2$와 urea의 혼합비를 1 : 8, 용액의 침전 온도를 오일 bath내에서 8$0^{\circ}C$, 반응시간을 1시간으로 하여 Al/SiO$_2$/Si 기판 위에 침전된 Zn(OH)$_2$ 박막을 $600^{\circ}C$에서 1시간 동안 열처리하여, 미세 패턴을 형성하기 위한 균질한 크기의 ZnO 박막을 제조할 수 있었다. Microcontact printing방법으로 소수성과 친수성 SAMs인 Octadecylphosphonic Acid(OPA)와 2-Carboxyethylphosphonic Acid(CPA)를 각각 Al/SiO$_2$/Si 기판 위에 선택적으로 흡착한 후에 친수성 SAM인 CPA위에 Zn(OH)$_2$를 침전시켜 미세 패턴화된 ZnO 박막을 제조할 수 있었다

• 대한영양사협회학술지
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• 제10권4호
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• pp.407-416
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• 2004

The purpose of this study was to examine the comparison of growth development, bone mineral density and nutrient intakes between double income families' preschool children(DIFPC) and full-time housewives' preschool children(FHPC). Subjects were 111 preschool children. Anthropometric characteristics and bone mineral density in right forearm were measured. The questionnaire was composed of health status, life style, dietary behaviors, and dietary intakes and was completed by the children's mothers. The average age of the DIFPC(n=60) was 53.02 months and that of the FHPC(n=51) was 54.80 months. The birth height and weight of the subjects were 50.47㎝ and 3.27㎏ for DIFPC and 50.85㎝ and 3.36㎏ for FHPC, respectively. The average height, weight, % body fat, and obesity index were 108.50㎝, 18.35㎏, 15.35%, 96.71% in DIFPC and 111.46㎝, 19.64㎏, 16.80%, 97.31% in FHPC, respectively. The bone mineral density in forearm of two groups were 0.24g/㎠ in all. The infant feeding method was significantly different between DIFPC and FHPC; 58.9% of DIFPC was fed formula, while 44.4% of FHPC was fed breast milk(p<0.05). Proportions of children for their regular meal were 59.4%, 89.6%, and 61.0% for breakfast, lunch, and dinner, respectively. The major reasons for irregular meal were lack of time and poor appetite for breakfast and snacks for lunch and dinner. Most of the children answered they have snack over once a day, and 60.0% have unbalanced diet. The intakes of energy, calcium, iron, zinc, vitamin A, vitamin B1, niacin, and vitamin C did not meet the Korean RDAs. The intakes of K and vitamin A for DIFPC were significantly higher than those of FHPC(p<0.05, p<0.05). In conclusion, double income families' preschool children more have a low frequency of breast feeding and low intakes of micro nutrients, such as K and vitamin A than full-time housewives' ones.

• 청정기술
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• 제8권3호
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• pp.151-165
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• 2002

중금속($Cu^{2+}$, $Zn^{2+}$, $Ni^{2+}$, $Cr^{3+}$)을 함유한 폐수가 최적운전압력과 운전시간에서 침전-응집-정밀여과의 공정으로 처리되었을 때, pH 및 응집제의 영향 그리고 막 종류 및 세공크기에 따른 투과유속과 제거효율이 조사되었다. 구리폐수의 경우는 pH10.0~10.5에서 $0.45{\mu}m$-polysulfone막과 PAC을, 아연폐수의 경우는 pH10.0~10.5에서 $0.1{\mu}m$-PVDF막과 PAC을, 니켈의 경우는 pH11.0~11.5에서 $0.1{\mu}m$-PVDF막과 응집제를, 크롬의 경우는 pH8.0~8.5에서 $0.2{\mu}m$막과 응집제를, 그리고 혼합폐수의 경우는 pH11.0~11.5에서 $0.2{\sim}0.45{\mu}m$막과 응집제를 사용하여 처리하였을 때, 처리효율이 가장 높았다. 투과유속은 구리폐수를 제외하고는 대부분 응집제 사용으로 더 높게 향상시킬 수 있었다.

• Corrosion Science and Technology
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• 제9권4호
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• pp.147-152
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• 2010

Conventional paints for conversion coating applications in steel production derived mainly from water-based polymer dispersions containing several additives actually show good general performance, but suffer from poor scratch and abrasion resistance during use. The reason for this is because the relatively soft organic binder matrix dominates the mechanical surface properties. In order to maintain the high quality and decorative function of coated steel sheets, the mechanical performance of the surface needs to be improved significantly. In fact the wear resistance should be enhanced without affecting the optical appearance of the coatings by using appropriate nanoparticulate additives. In this direction, nanocomposite coating compositions (Nanomer$^{(R)}$) have been derived from water-based polymer dispersions with an increasing amount of surface-modified nanoparticles in aqueous dispersion in order to monitor the effect of degree of filling with rigid nanoparticles. The surface of nanoparticles has been modified for optimum compatibility with the polymer matrix in order to achieve homogeneous nanoparticle dispersion over the matrix. This approach has been extended in such a way that a more expanded hybrid network has been condensed on the nanoparticle surface by a hydrolytic condensation reaction in addition to the quasi-monolayer type small molecular surface modification. It was expected that this additional modification will lead to more intensive cross-linking in coating systems resulting in further improved scratch-resistance compared to simple addition of nanoparticles with quasi-monolayer surface modification. The resulting compositions have been coated on zinc-galvanized steel and cured. The wear resistance and the corrosion protection of the modified coating systems have been tested in dependence on the compositional change, the type of surface modification as well as the mixing conditions with different shear forces. It has been found out that for loading levels up to 50 wt.-% nanoparticles, the mechanical wear resistance remains almost unaffected compared to the unmodified resin. In addition, the corrosion resistance remained unaffected even after $180^{\circ}$ bending test showing that the flexibility of coating was not decreased by nanoparticle addition. Electron microscopy showed that the inorganic nanoparticles do not penetrate into the organic resin droplets during the mixing process but rather formed agglomerates outside the polymer droplet phase resulting in quite moderate cross linking while curing, because of viscosity. The proposed mechanisms of composite formation and cross linking could explain the poor effect regarding improvement of mechanical wear resistance and help to set up new synthesis strategies for improved nanocomposite morphologies, which should provide increased wear resistance.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.65-65
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• 2012

Copper zinc tin sulfide ($Cu_2ZnSnS_4$, CZTS) is a very promising material as a low cost absorber alternative to other chalcopyrite-type semiconductors based on Ga or In because of the abundant and economical elements. In addition, CZTS has a band-gap energy of 1.4~1.5eV and large absorption coefficient over ${\sim}10^4cm^{-1}$, which is similar to those of $Cu(In,Ga)Se_2$(CIGS) regarded as one of the most successful absorber materials for high efficient solar cell. Most previous works on the fabrication of CZTS thin films were based on the vacuum deposition such as thermal evaporation and RF magnetron sputtering. Although the vacuum deposition has been widely adopted, it is quite expensive and complicated. In this regard, the solution processes such as sol-gel method, nanocrystal dispersion and hybrid slurry method have been developed for easy and cost-effective fabrication of CZTS film. Among these methods, the hybrid slurry method is favorable to make high crystalline and dense absorber layer. However, this method has the demerit using the toxic and explosive hydrazine solvent, which has severe limitation for common use. With these considerations, it is highly desirable to develop a robust, easily scalable and relatively safe solution-based process for the fabrication of a high quality CZTS absorber layer. Here, we demonstrate the fabrication of a high quality CZTS absorber layer with a thickness of 1.5~2.0 ${\mu}m$ and micrometer-scaled grains using two different non-vacuum approaches. The first solution-processing approach includes air-stable non-toxic solvent-based inks in which the commercially available precursor nanoparticles are dispersed in ethanol. Our readily achievable air-stable precursor ink, without the involvement of complex particle synthesis, high toxic solvents, or organic additives, facilitates a convenient method to fabricate a high quality CZTS absorber layer with uniform surface composition and across the film depth when annealed at $530^{\circ}C$. The conversion efficiency and fill factor for the non-toxic ink based solar cells are 5.14% and 52.8%, respectively. The other method is based on the nanocrystal dispersions that are a key ingredient in the deposition of thermally annealed absorber layers. We report a facile synthetic method to produce phase-pure CZTS nanocrystals capped with less toxic and more easily removable ligands. The resulting CZTS nanoparticle dispersion enables us to fabricate uniform, crack-free absorber layer onto Mo-coated soda-lime glass at $500^{\circ}C$, which exhibits a robust and reproducible photovoltaic response. Our simple and less-toxic approach for the fabrication of CZTS layer, reported here, will be the first step in realizing the low-cost solution-processed CZTS solar cell with high efficiency.

• 한국재료학회지
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• 제21권10호
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• pp.563-567
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• 2011

We report the structural characterization of $Bi_xZn_{1-x}O$ thin films grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. By increasing the Bi flux during the growth process, $Bi_xZn_{1-x}O$ thin films with various Bi contents (x = 0~13.17 atomic %) were prepared. X-ray diffraction (XRD) measurements revealed the formation of Bi-oxide phase in (Bi)ZnO after increasing the Bi content. However, it was impossible to determine whether the formed Bi-oxide phase was the monoclinic structure ${\alpha}-Bi_2O_3$ or the tetragonal structure ${\beta}-Bi_2O_3$ by means of XRD ${\theta}-2{\theta}$ measurements, as the observed diffraction peaks of the $2{\theta}$ value at ~28 were very close to reflection of the (012) plane for the monoclinic structure ${\alpha}-Bi_2O_3$ at 28.064 and the reflection of the (201) plane for the tetragonal structure ${\beta}-Bi_2O_3$ at 27.946. By means of transmission electron microscopy (TEM) using a diffraction pattern analysis and a high-resolution lattice image, it was finally determined as the monoclinic structure ${\alpha}-Bi_2O_3$ phase. To investigate the distribution of the Bi and Bi-oxide phases in BiZnO films, elemental mapping using energy dispersive spectroscopy equipped with TEM was performed. Considering both the XRD and the elemental mapping results, it was concluded that hexagonal-structure wurtzite $Bi_xZn_{1-x}O$ thin films were grown at a low Bi content (x = ~2.37 atomic %) without the formation of ${\alpha}-Bi_2O_3$. However, the increased Bi content (x = 4.63~13.17 atomic %) resulted in the formation of the ${\alpha}-Bi_2O_3$ phase in the wurtzite (Bi)ZnO matrix.

• 대한화학회지
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• 제46권4호
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• pp.363-377
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• 2002

이 연구의 목적은 중${\cdot}$고등학교 교과서에 제시된 볼타전지에 대한 문제점을 분석하여 개선 방안을 제시하는데 있다. 이를 위하여 과학 교과서 중 관련 단원 내용을 분석하였으며 추출한 문제점을 실험을 통해 해결하였고 이를 바턍으로 교과서의 개선 방향을 제안하였다. 교과서 분석 결과, 화학전지의 작용 여부를 확인하는 방법, 아연판에서 수소 기체가 발생하는 이유에 대한 설명, 기전력에 대한 실험연구 결과, 전극용어 사용의 통일, 전류에 대한 설명 등 에 문제점이 있었다. 이러한 문제점을 해결하기 위한 방안을 제시하였다. 기전력에 대한 실험연구 결과, 기전력 측정 값에 대한 과학적인 설명은 각 전극에서의 산화환원 반응에 대한 기전력과 표준 환원 전위, 전기음성도, 일함수, 이온화 에너지 등과 같은 전극의성질을 함께 고려하여 설명해야 함을 알 수 있었다. 이는 볼타전지의 기전력이 여러 가지 요인에 영향을 받기 때문이다. 이와 같이 볼타전지의 기전력에 대한 정확한 설명은 용이 하지 않으므로 볼타전지는 화학전지의 도입 부분에서 역사적으로만 간단하게 기술하고 개념 설명은 다니엘 전지를 이용하여 기술하는 방향으로 교과서를 개선 할 것을 제한하였다.

• Restorative Dentistry and Endodontics
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• 제26권2호
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• pp.141-152
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• 2001

Eliminating the infecting bacteria of the root canal system and preventing reinfection must be the main objectives of all endodontic works. None of commercially available root canal sealers have the properties of desirable tissue compatibility and strong antibacterial activity. The purpose of this study is to develope an ideal root canal sealer using commercially available polyphosphate (polyP), Calgon, which is known to be antibacterial and safe. For the study. resin type AH26, zinc oxide eugenol type Tubli Seal. Ca(OH)$_2$ type Apexit as base sealers for polyP (0~3%) and para formaldehyde containing N2 as a control base were selected. Specimens (3$\times$4mm) of the sealers were prepared in a 37$^{\circ}C$ incubator for 3 and 10 days and their antibacterial activity against streptococci and black pigmented anaerobic rods was observed using an agar diffusion method. The result were as follows: 1. Among 3 day old root canal sealers. N2 as a positive control showed the strongest antibacterial effect. followed by AH26. Tubli Seal and. Apexit which barely showed antibacterial activity against the test bacteria. In contrast. 10 day old AH26 showed a greater antibacterial activity than 10 day old N2. 2. All sealer specimens showed a greater antibacterial activity against black pigmented anaerobic rods than streptococci. Three day old ones appeared to be more antibacterial than 10 day old ones except for Apexit. 3. As compared to N2, 3 day old AH26 demonstrated a similar antibacterial activity against black pig mented anaerobic rods but to a lesser extent to streptococci. Ten day old AH26 showed a greater antibacterial activity against black pigmented anaerobic rods than 10 day old N2. 4. As compared to AH26. Tubli Seal generally revealed a lower antibacterial activity but it showed a greater antibacterial activity aginst S. gordonii Challis. 5. Enhancement of antibacterial activity by polyP was more clearly observed when it was added to Ca(OH)$^{\circ}C$ based root canal sealers. Tubli Seal and N2. 6. The addition of polyP enhanced the antibacterial activity of 3 day old AH26 against S. gordonii G9B (16%) and Challis (29%), and P. gingivalis 2561 (24%) only. Moreover, polyP failed to increase antibacterial activity of 10 day old AH26 against the test strains but P. gingivalis A7A1 28(13%). 7. The addition of polyP increased the antibacterial effect of 3 day old Tubli Seal on several test bacteria including s. mutans GS 5 (50%). s. gordonii G9B (47%) and Challis (122%). and all the test strains of P. gingivalis (13~35%) except for 9 14K 1. The addition of polyP to 10 day old Tubli Seal increased antibacterial activity of the root canal sealer against most test strains. 8. 3 day old Apexit failed to show antibacterial activity. if any very little against S. mutans GS 5 and Pr. intermedia ATCC 49046. However. polyP increased its antibacterial activity by 50 and 69%, respectively. Increase of antibacterial activity of 10 day old Apexit by polyP was more clearly observed than that of 3 day old one.

• 한국광학회지
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• 제28권4호
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• pp.153-157
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• 2017

지향성적외선방해장비의 정렬 정밀도를 높히고 중량을 감소시키기 위해 적용된 적외선 카메라-레이저 공통광학계 구조에서 영상 성능 저하를 야기시키는 레이저빔 열 영향성을 분석하였다. 높은 에너지 밀도를 가지는 레이저빔이 광부품에 흡수되면 열이 발생하고 온도가 상승한다. 공통광학계 광부품 표면에서 발생한 열은 시스템 투과율을 감소시켜 적외선 카메라의 영상 품질을 저하시킬 수 있다. 지향성적외선방해장비의 운용개념을 고려하여 파장 $4{\mu}m$, 출력 3 W의 레이저빔이 10초간 미러(알루미늄, 실리카 글래스, 실리콘) 및 렌즈(사파이어, 셀레늄화아연, 실리콘, 게르마늄) 재료에 조사되는 상황을 가정하여 온도 분포를 계산하였다. 계산 결과, 미러 재료로는 실리카 글래스, 렌즈 재료로는 사파이어의 온도 상승이 상대적으로 컸고, 재료 온도 분포에 가장 큰 영향을 미치는 요소는 재료의 레이저빔 흡수율과 열전도도임을 확인하였다. 결론적으로 적외선 카메라-레이저 공통광학계에 사용하는 광부품은 흡수율이 낮고 열전도도가 높은 특성을 갖도록 선정되어야 광부품 온도 상승에 의한 적외선 카메라의 영상 품질 저하를 방지할 수 있다.