• 한국건설순환자원학회논문집
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• 제9권1호
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• pp.41-49
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• 2021

3D 프린팅 시공기술은 주로 거푸집 없이 시멘트계 재료를 적층하여 생산하는 방식을 활용한다. 3D 프린팅 시멘트계 재료는 굳지 않은 상태에서 이송성, 토출성, 적층성 관련 성능이 요구되기 때문에 기존 시공방식에서 사용되던 재료 물성에 대한 추가적인 고려가 필요하다. 이 연구의 목적은 국내외의 3D 프린팅 시멘트계 재료의 유변학적 특성에 대한 기존 연구 사례들을 비교 분석하여 3D 프린팅 시멘트계 재료의 요구 성능과 유변학적 물성과의 연관성을 조사하는 것이다. 3D 프린팅 시멘트계 재료의 점성, 항복응력, 틱소트로피에 대한 실험을 진행했던 이전 연구 사례들의 장비, 실험 및 평가 방식, 사용한 혼화제 특징을 기준으로 분류하여 조사하였다. 본 연구에서는 3D 프린팅 재료의 요구 성능을 정성적으로 유변학적 물성과의 연관성을 나타내었다. 이 연구의 결과로부터 점성은 주로 이송성과 관련이 있고 시간에 따른 항복응력의 변화, 틱소트로피는 3D 프린팅 시멘트계 재료의 적층 성능과 밀접한 관련이 있음을 확인하였다.

• 한국재료학회지
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• 제31권11호
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• pp.619-625
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• 2021

Cu₂ZnSn(S,Se)₄ (CZTSSe) based thin-film solar cells have attracted growing attention because of their earth-abundant and non-toxic elements. However, because of their large open-circuit voltage (V_oc)-deficit, CZTSSe solar cells exhibit poor device performance compared to well-established Cu(In,Ga)(S,Se)₂ (CIGS) and CdTe based solar cells. One of the main causes of this large V_oc-deficit is poor absorber properties for example, high band tailing properties, defects, secondary phases, carrier recombination, etc. In particular, the fabrication of absorbers using physical methods results in poor surface morphology, such as pin-holes and voids. To overcome this problem and form large and homogeneous CZTSSe grains, CZTSSe based absorber layers are prepared by a sputtering technique with different RTA conditions. The temperature is varied from 510 ℃ to 540 ℃ during the rapid thermal annealing (RTA) process. Further, CZTSSe thin films are examined with X-ray diffraction, X-ray fluorescence, Raman spectroscopy, IPCE, Energy dispersive spectroscopy and Scanning electron microscopy techniques. The present work shows that Cu-based secondary phase formation can be suppressed in the CZTSSe absorber layer at an optimum RTA condition.

• The Journal of Advanced Prosthodontics
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• 제13권6호
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• pp.373-384
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• 2021

PURPOSE. This study aimed to compare the marginal and internal fit of 3-unit monolithic zirconia restorations that were designed by using the data obtained with the aid of intraoral and laboratory scanners. MATERIALS AND METHODS. For the fabrication of 3-unit monolithic zirconia restorations using impressions taken from the maxillary master cast, plaster cast was created and scanned in laboratory scanners (InEos X5 and D900L). The main cast was also scanned with different intraoral scanners (Omnicam [OMNI], Primescan [PS], Trios 3 [T3], Trios 4 [T4]) (n = 12 per group). Zirconia fixed partial dentures were virtually designed, produced from presintered block, and subsequently sintered. Marginal and internal discrepancy values (in ㎛) were measured by using silicone replica method under stereomicroscope. Data were statistically analyzed by using 1-way ANOVA and Kruskal Wallis tests (P<.05). RESULTS. In terms of marginal adaptation, the measurements on the canine tooth indicated better performance with intraoral scanners than those in laboratory scanners, but there was no difference among intraoral scanners (P<.05). In the premolar tooth, PS had the lowest marginal (86.9 ± 19.2 ㎛) and axial (92.4 ± 14.8 ㎛), and T4 had the lowest axio-occlusal (89.4 ± 15.6 ㎛) and occlusal (89.1 ± 13.9 ㎛) discrepancy value. In both canine and premolar teeth, the D900L was found to be the most marginally and internally inconsistent scanner. CONCLUSION. Within the limits of the study, marginal and internal discrepancy values were generally lower in intraoral scanners than in laboratory scanners. Marginal discrepancy values of scanners were clinically acceptable (< 120 ㎛), except D900L.

• The Journal of Advanced Prosthodontics
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• 제14권5호
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• pp.273-284
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• 2022

PURPOSE. Computer-aided design and manufacturing (CAD-CAM) of implant abutments has been shown to result in surface contamination from site-specific milling and fabrication processes. If not removed, these contaminants can have a potentially adverse effect and may trigger inflammatory responses of the peri-implant tissues. The aim of the present study was to evaluate the bacterial disinfection and cleaning efficacy of ultrasonic reprocessing in approved disinfectants to reduce the microbial load of CAD-CAM abutments. MATERIALS AND METHODS. Four different types of custom implant abutments (total N = 32) with eight specimens in each test group (type I to IV) were CAD-CAM manufactured. In two separate contamination experiments, specimens were contaminated with heparinized sheep blood alone and with heparinized sheep blood and the test bacterium Enterococcus faecium. Abutments in the test group were processed according to a three-stage ultrasonic protocol and assessed qualitatively and quantitatively by determination of residual protein. Ultrasonicated specimens contaminated with sheep blood and E. faecium were additionally eluted and the dilutions were incubated on agar plates for seven days. The determined bacterial counts were expressed as colony-forming units (CFU). RESULTS. Ultrasonic reprocessing resulted in a substantial decrease in residual bacterial protein to less than 80 ㎍ and a reduction in microbiota of more than 7 log levels of CFU for all abutment types, exceeding the effect required for disinfection. CONCLUSION. A three-stage ultrasonic cleaning and disinfection protocol results in effective bacterial decontamination. The procedure is reproducible and complies with the standardized reprocessing and disinfection specifications for one- or two-piece CAD-CAM implant abutments.

• 한국재료학회지
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• 제32권5호
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• pp.258-263
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• 2022

Porous ceramics have the advantages of low density, low thermal conductivity, and excellent mechanical properties. Among porous ceramic manufacturing methods, the replica template method allows the easy manufacturing of porous filters with the highest porosity and pores of the desired size, but it also has the disadvantage that the resulting filters have low mechanical strength. To overcome this shortcoming, mullite (3Al₂O₃·2SiO₂) whiskers, which have excellent thermal stability and high mechanical strength, were introduced in porous ceramic structure. The mullite whiskers were synthesized using a composition of Al₂O₃, flyash and MoO₃. The morphologies and crystal structures of the mullite whiskers with MoO₃ contents were investigated in detail. When the porous ceramic with mullite whiskers was fabricated using 20 wt% MoO₃ catalyst the most uniform microstructure was obtained, and the mullite whiskers showed the highest aspect ratio of 47.03. The porosity and compressive strength of the fabricated porous ceramic were 82.12 % and 0.83 MPa, respectively.

• Advances in nano research
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• 제12권2호
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• pp.213-221
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• 2022

Silicon carbide (SiC) is a binary carbon-silicon compound. In its two-dimensional form, monolayer SiC is composed of a monolayer carbon and silicon atoms constructed as a honeycomb lattice. SiC has recently been receiving increasing attention from researchers owing to its intriguing electronic properties. In this present work, SiC nanoribbons (SiCNRs) are modelled and simulated to obtain accurate electronic properties, which can further guide fabrication processes, through bandgap engineering. The primary objective of this work is to obtain the electronic properties of monolayer SiCNRs by applying numerical computation methods using nearest-neighbour tight-binding models. Hamiltonian operator discretization and approximation of plane wave are assumed for the models and simulation by applying the basis function. The computed electronic properties include the band structures and density of states of monolayer SiCNRs of varying width. Furthermore, the properties are compared with those of graphene nanoribbons. The bandgap of ASiCNR as a function of width are also benchmarked with published DFT-GW and DFT-GGA data. Our nearest neighbour tight-binding (NNTB) model predicted data closer to the calculations based on the standard DFT-GGA and underestimated the bandgap values projected from DFT-GW, which takes in account the exchange-correlation energy of many-body effects.

• 대한치과보철학회지
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• 제60권4호
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• pp.354-361
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• 2022

디지털 기술의 발달은 치의학의 큰 변화를 일으키고 있고, 이러한 디지털 워크플로는 보철 치료 영역에서도 다양한 3D 데이터들을 하나로 중첩시켜, 진단과 보철물 제작에 활용되고 있다. 디지털 데이터를 종합하여 형성된 가상 환자에게서 계획된 진단과 보철물의 형성은 기존 통상적인 방법에 비해 보다 더 직관적으로 보철 치료의 결과를 시뮬레이션 할 수 있고, 이로 인해 심미적인 보철 치료의 예측성을 높일 수 있다. 본 증례에서는 디지털 워크플로를 통해 상악 전치부 선천성 결손 부위를 고정성 보철물로 제작하여 기능적, 심미적으로 만족할 만한 임상적 결과를 얻었으므로 이를 보고하는 바이다.

• The Journal of Advanced Prosthodontics
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• 제15권1호
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• pp.33-43
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• 2023

PURPOSE. This study investigated the physical and mechanical changes in the titanium base of three different hybrid abutment materials after cyclic loading by estimating the post-load reverse torque value (RTV), compressive side fulcrum wear pattern of titanium base, and surface roughness. MATERIALS AND METHODS. A total of 24 dental implants were divided into three groups (n = 8 each): Group Z, LD, and P used zirconia, lithium disilicate, and polyetheretherketone, respectively, for hybrid abutment fabrication. RTV was evaluated after cyclic loading with 50 N for 1.2 × 10⁶ chewing cycles. The compressive sides of the titanium bases were analyzed using a scanning electron microscope, and the roughness of the affected areas was measured using an optical profilometer after loading. Datasets were analyzed using Kruskal-Wallis test followed by Mann-Whitney tests with the Bonferroni correction (α = .05). RESULTS. Twenty-three samples passed the test; one LD sample fractured after 770,474 cycles. Post-load RTV varied significantly depending on the hybridabutment material (P = .020). Group P had a significantly higher median of post-load RTVs than group Z (16.5 and 14.3 Ncm, respectively). Groups LD and P showed minor signs of wear, and group Z showed a more pronounced wear pattern. While evaluating compressive side affected area roughness of titanium bases, lower medians were shown in group LD (Ra 0.16 and Rq 0.22 ㎛) and group P (Ra 0.16 and Rq 0.23 ㎛) than in group Z (Ra 0.26 and Rq 0.34 ㎛); significant differences were found only among the unaffected surface and group Z. CONCLUSION. The hybrid abutment material influences the post-load RTV. Group Z had a more pronounced wear pattern on the compressive side of titanium base; however, the surface roughness was not statistically different among the hybridabutment groups.

• 대한융합한의학회지
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• 제2권1호
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• pp.5-12
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• 2021

Objectives: The purpose of this study is to fabricate an ultra-fine ginsenoside particle atomizer that can provide a new treatment method by delivering ginsenoside components that have a therapeutic effect on respiratory diseases directly to the lungs. Methods: We fabricated the AAO vibrating mesh by using the micromachining process. The starting substrate of an AAO wafer has a 350nm pore diameter with 50㎛ thickness. A photomask having several 5㎛ opening holes with a 100㎛ pitch was used to separate each nanopore nozzle. The photoresist structure was optimized to pattern the nozzle area during the lift-off process precisely. The commercial vibrating mesh was removed from OMRON's NE-U100 product, and the fabricated AAO vibrating mesh was installed. A diluted sample of 20mL with 30% red ginseng concentrate was prepared to atomize from the device. Results: As a result of liquid chromatography analysis before spraying the ginsenoside solution, ginsenoside components such as 20S-Rg3, 20R-Rg3, and Rg5 were detected. After spraying through the AAO vibrating mesh, ginsenosides of the same component could be detected. Conclusion: A nutrient solution containing ginsenosides was successfully sprayed through the AAO vibrating mesh with 350 nm selective pores. In particular, during the atomizing experiment of ginsenoside drug solution having excellent efficacy in respiratory diseases, it was confirmed that atomizing through the AAO vibrating mesh while maintaining most of the active ingredients was carried out.