• 대한치과교정학회지
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• 제51권3호
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• pp.157-165
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• 2021

Objective: This study aimed to identify the clinical effectiveness of two different penetration depths of micro-osteoperforations (MOPs) on the rate of orthodontic tooth movement. Methods: Twenty-four patients requiring the removal of the upper first premolar teeth were selected and randomly divided into two groups. The control group participants did not undergo MOPs. Participants in the experimental group underwent three MOPs each at 4-mm (MOP-4) and 7-mm (MOP-7) depths, which were randomly and equally performed to either the left or right side distal to the canine. The retraction amount was measured on three-dimensional digital models on the 28th day of retraction. MOP-related pain was measured using a visual analog scale (VAS). Between-group statistical differences in the VAS scores were determined using an independent t-test and those in canine retraction were determined using analysis of variance and post-hoc Tukey test. Results: No significant difference was found between the MOP-4 (1.22 ± 0.29 mm/month) and MOP-7 (1.29 ± 0.31 mm/month) groups in terms of the canine retraction rate. Moreover, both the groups demonstrated a significantly higher canine movement than the control group (0.88 ± 0.19 mm/month). MOPs did not significantly affect the mesialization of the posterior teeth (p > 0.05). Moreover, the pain scores in the MOP-4 and MOP-7 groups were similar and showed no statistically significant difference. Conclusions: Three MOPs with a depth of 4 mm can be performed as an effective method to increase the rate of tooth movement. However, three MOPs with depths of 4-7 mm does not additionally enhance tooth movement.

• 한국기계가공학회지
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• 제17권6호
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• pp.68-74
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• 2018

Study on the Ti-6Al-4V have been carried out using cutting simulation, and researches for cutting force and chip shape prediction have been actively conducted under various conditions. However, a 3D printer application method using Ti-6Al-4V metal powder material as a high-power method has been studied for the purpose of prototyping, mold modification and product modification while lowering material removal rate. However, in the case of products / parts made of 3D printers using powder materials, problems may occur in the contact surface during tolerance management and assembly due to the degradation of the surface quality. As a result, even if a 3D printer is applied, post-processing through cutting is essential for surface quality improvement and tolerance management. In the cutting simulation, the cutting force and the chip shape were predicted based on the Johnson-Cook composition equation, but the shape of the shear type chip was not predictable. To solve this problem, we added a damaging term or strain softening term to the Johnson-Cook constitutive equation to predict chip shape. In this thesis, we applied the constant value of the S-K equations to the cutting simulation to predict the cutting force and compare with the experimental data to verify the validity of the cutting simulation and analyzed the machining characterization by considering conditions.

• 청정기술
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• 제24권4호
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• pp.301-306
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• 2018

최근 미세먼지의 증가로 인해 디젤 자동차로부터 발생되는 PM에 대한 규제가 강화되고 있다. 디젤 자동차의 배기가스를 제거하는 후처리 장치인 매연여과장치(diesel particulate filter, DPF)에 대한 관심이 급증하고 있다. 따라서 DPF 효율 향상의 하나로 DPF 내의 압력강하를 줄여서 필터 및 재생(Regeneration)의 효율을 증가시키고 있다. 본 연구에서는 ANSYS FLUENT를 이용하여 5.66" SiC와 Cordierite DPF의 셀 밀도, 채널 형상, 벽두께, 입 출구 채널 비에 따른 압력강하 영향을 시뮬레이션했다. 실험결과로서 200 CPSI보다 300 CPSI에서 압력강하가 작게 나타났으며, Anisotropy과 O/S 셀이 Isotropy보다 약 1,301 Pa 작은 압력강하를 나타냈다. 공극률은 10% 증가할 때 마다 압력강하가 약 300 Pa씩 작아졌고, 벽 두께에 따른 영향은 0.05 mm 두꺼워질수록 약 500 Pa 씩 커지는 경향을 나타냈다.

• 한국입자에어로졸학회지
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• 제15권1호
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• pp.1-13
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• 2019

Current desulfurization and denitrification technologies have reached a considerable level in terms of reduction efficiency. However, when compared with the simultaneous reduction technology, the individual reduction technologies have issues such as economic disadvantages due to the difficulty to scale-up apparatus, secondary pollution from wastewater/waste during the treatment process, requirement of large facilities for post-treatment, and increased installation costs. Therefore, it is necessary to enable practical application of simultaneous SOx and NOx treatment technologies to remove two or more contaminants in one process. The present study analyzes a technology capable of maintaining simultaneous treatment of SOx and NOx even at low temperatures due to the electrochemically generated strong oxidation of the wet-pulse complex system. This system also reduces unreacted residual gas and secondary products through the wet scrubbing process. It addresses common problems of the existing fuel gas treatment methods such as SDR, SCR, and activated carbon adsorption (i.e., low treatment efficiency, expensive maintenance cost, large installation area, and energy loss). Experiments were performed with varying variables such as pulse voltage, reaction temperature, chemicals and additives ratios, liquid/gas ratio, structure of the aeration cleaning nozzle, and gas inlet concentration. The performance of individual and complex processes using the wet-pulse discharge reaction were analyzed and compared.

• 한국입자에어로졸학회지
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• 제14권4호
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• pp.145-151
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• 2018

Rod shaped Potassium hexatitanate ($K_2Ti_6O_{13}$) was synthesized from colloidal mixture of $TiO_2$, KOH and graphene oxide (GO) by aerosol spray drying and post heat treatment. Firstly, $TiO_2-KOH-GO$ composites were fabricated by aerosol spray drying in argon atmosphere. The composites were then calcined to form a rod shaped morphology of potassium titanate (KTO) in the presence of graphene at $900^{\circ}C$ for 3 h in argon atmosphere. Finally, the rod shaped KTO was obtained after removal of graphene (GR) at $800^{\circ}C$ and 3 h in air atmosphere. Characterization of the synthesized $K_2Ti_6O_{13}$ was carried out using the XRD, BET and FE-SEM. The length and diameter of the synthesized $K_2Ti_6O_{13}$ could be controlled by weight fraction of GO in the aerosol precursor. The length of $K_2Ti_6O_{13}$ rod increased with decreasing its diameter as GO concentration increased. The aspect ratio of the synthesized $K_2Ti_6O_{13}$ rod was controlled from 5 to 13.

• Advances in environmental research
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• 제10권1호
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• pp.59-86
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• 2021

Landfilling is the most commonly adopted method for a large quantity of waste disposal. But, the main concern related to landfills is the generation of leachate. The leachate is high strength wastewater that is usually characterized by the presence of high molecular recalcitrant organics. Several conventional methods are adopted for leachate treatment. However, these methods are only suitable for young leachate, having high biodegradability and low toxicity levels. The mature and stabilized leachate needs advanced technologies for its effective treatment. Advanced oxidation processes (AOPs) are very suitable for such complex wastewater treatment as reported in the literature. After going through the literature survey, it can be concluded that Fenton-based approaches are effective for the treatment of various high/low strength wastewaters treatment. The applications of the Fenton-based approaches are widely adopted and well recognized due to their simplicity, cost-effectiveness, and reliability for the reduction of high chemical oxygen demand (COD) as reported in several studies. Besides, the process is relatively economical due to fewer chemical, non-sophisticated instruments, and low energy requirements. In this review, the conventional and advanced Fenton's approaches are explained with their detailed reaction mechanisms and applications for landfill leachate treatment. The effect of influencing factors like pH, the dosage of chemicals, nature of reaction matrix, and reagent ratio on the treatment efficiencies are also emphasized. Furthermore, the discussion regarding the reduction of chemical oxygen demand (COD) and color, increase in biodegradability, removal of humic acids from leachate, combined processes, and the pre/post-treatment options are highlighted. The scope of future studies is summarized to attain sustainable solutions for restrictions associated with these methods for effective leachate treatment.

• 국제초고층학회논문집
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• 제10권4호
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• pp.311-321
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• 2021

Perception of the public to structural fires is very important because there are only a number of tall timber buildings constructed in the world. People are hesitating to accept tall timber buildings, so it is essential to ensure the first generation of tall timber buildings to a very high standard, especially fire safety. Right now, there are no specific design standards or regulations for fire design of tall timber buildings in Europe. Even though heavy timber members have better fire resistance than steel components, many conditions still need to be verified before considering the use of timber materials, e.g. fire spread, post-fire collapse, etc. This research numerically explores the structural behaviours of a tall Glulam building when one of its internal Glulam (Glued laminated timber) columns fails after sustaining a full 120-min standard fire and is removed from the established finite element building model created in SAP2000. The numerical results demonstrate that the failure and removal of the selected internal Glulam column may lead to the local failure of the adjacent CLT (Cross laminated timber) floor slabs, but will not lead to large disproportionate damage and collapse of the whole building. Here, the building is assumed to be located in Glasgow, Scotland, UK.

• 한국기계가공학회지
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• 제21권2호
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• pp.109-115
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• 2022

The demand for metal 3D printing technology is increasing in various industries. The materials commonly used for metal 3D printing include aluminum alloys, titanium alloys, and stainless steel. In particular, for applications in the aviation and defense industry, aluminum alloy 3D printing parts are being produced. To improve the corrosion resistance in the 3D printed aluminum alloy outputs, a post-treatment process, such as chromate coating, should be applied. However, powdered materials, such as AlSi7Mg and AlSi10Mg, used for 3D printing, have a high silicon content; therefore, a suitable pretreatment is required for chromate coating. In the desmut step of the pretreatment process, the chromate coating can be formed only when a smut composed of silicon compounds or oxides is effectively removed. In this study, suitable desmut solutions for 3D printed AlSi7Mg and AlSi10Mg materials with high silicon contents were presented, and the chromate coating properties were studied accordingly. The smut removal effect was confirmed using an aqueous desmut solution composed of sulfuric, nitric, and hydrofluoric acids. Thus, a chromate coating was successfully formed. The surfaces of the aluminum alloys after desmut and chromate coating were analyzed using SEM and EDS.

• 한국정보통신학회논문지
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• 제26권11호
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• pp.1660-1665
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• 2022

최근 많은 산업체에서 3차원 스캐닝 기술을 활용하고 있다. 3D 스캐너의 성능이 향상됨에 따라 점데이터를 획득하면 후처리를 통해서 일정 비율만큼 줄이는 샘플링 단계를 수행하거나, 잡음이라고 판단되는 부분을 제거한다. 하지만, 이와 같은 추가과정 수행에도 불구하고 오랜 시간 동안 스캐닝하면 점데이터들을 한꺼번에 처리할 수 없다. 일반적으로 멀티스레드 환경을 이용하여 기획득된 점데이터를 먼저 처리하는 방식을 이용하지만, 스캐닝 프로세스 작업 시간이 증가함에 따라 다양한 환경 조건과 누적된 연산으로 인하여 점차 처리 성능이 낮아진다. 본 연구에서는 3D 스캐너로부터 실시간으로 들어오는 점데이터를 누적된 고속 특징점 히스토그램 계산을 이용하여 불필요하다고 판단되는 점데이터를 초기에 제거하는 방식을 제안한다. 이 방법을 이용하면 전체 3D 스캐닝 프로세스의 속도 향상을 가져온다.

• Restorative Dentistry and Endodontics
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• 제46권1호
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• pp.9.1-9.9
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• 2021

Objectives: This randomized clinical trial aimed to assess the effectiveness of buccal infiltration with piroxicam on the anesthetic efficacy of inferior alveolar nerve block (IANB) with buccal infiltration in irreversible pulpitis, with pain assessed using the Heft-Parker visual analogue scale (HP-VAS). Materials and Methods: This study included 56 patients with irreversible pulpitis in mandibular molars, randomly distributed between 2 groups (n = 28). After evaluating the initial pain score with the HP-VAS, each patient received IANB followed by buccal infiltration of 2% lignocaine with adrenaline (1:80,000). Five minutes later, the patients in groups 1 and 2 were given buccal infiltration with 40 mg/2 mL of piroxicam or normal saline, respectively. An access opening procedure (AOP) was performed 15 minutes post-IANB once the individual showed signs of lip numbness as well as 2 negative responses to electric pulp testing. The HP-VAS was used to grade the patient's pain during caries removal (CR), AOP, and working length measurement (WLM). Successful anesthesia was identified either by the absence of pain or slight pain through CR, AOP, and WLM, with no requirement of a further anesthetic dose. A statistical analysis was done using the Shapiro-Wilk and Mann-Whitney U tests. Results: The piroxicam group presented a significantly lower (p < 0.05) mean pain score than the saline group during AOP. Conclusions: Buccal infiltration with piroxicam enhanced the efficacy of anesthesia with IANB and buccal infiltration with lignocaine in patients with irreversible pulpitis.