• 한국결정성장학회지
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• 제31권4호
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• pp.182-189
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• 2021

무기질 단열재 개발을 위해 포말법을 이용하여 다공성 세라믹스를 제조하였다. 실리카 흄과 SiO₂를 주 원료로 사용하였으며, 다공성 세라믹의 균일한 기공 형성을 위한 첨가제로 벤토나이트를 사용하였다. 다공성 세라믹은 1200℃에서 소결하였으며, 기공율, 밀도, 압축강도, 미세구조 그리고 열전도도 분석을 수행하였다. 다공성 세라믹은 SiO₂에 대한 실리카흄의 함량이 70~90 % 증가할수록 비중이 0.63에서 0.69로 증가하였으며, 압축강도는 9.41 Mpa에서 12.86 Mpa로 증가하였다. 그러나, 기공율은 비중과 반대로 72.07 %에서 70.82 %로 감소하는 경향을 나타내었다. 열전도도 측정 결과, 실리카 흄의 함량이 70 %인 F7S3 다공성 세라믹의 경우 25~800℃ 온도조건에서 0.75~0.72 W/m·K의 열전도도를 나타내었으며, 실리카 흄의 함량이 90 %인 F9S1 다공성 세라믹의 경우 0.66~0.86 W/m·K를 나타내어 실리카 흄 함량이 적을수록 낮은 열전도도를 나타내었다. 이는 기공율 결과와 일치한 것을 확인하였다. SEM(Scanning Electron Microscope)을 이용한 미세구조 분석 결과, 다공성 세라믹 내/외부에 전체적으로 수십~수백 ㎛ 범위 기공이 관찰되었으며 기공 분포가 비교적 균일한 것을 확인할 수 있었다.

• Imaging Science in Dentistry
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• 제53권3호
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• pp.193-198
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• 2023

Purpose: Artificial intelligence (AI) is poised to play a major role in medical diagnostics. Periodontal disease is one of the most common oral diseases. The early diagnosis of periodontal disease is essential for effective treatment and a favorable prognosis. This study aimed to assess the effectiveness of AI in diagnosing periodontal bone loss through radiographic analysis. Materials and Methods: A literature search involving 5 databases (PubMed, ScienceDirect, Scopus, Health and Medical Collection, Dentistry and Oral Sciences) was carried out. A specific combination of keywords was used to obtain the articles. The PRISMA guidelines were used to filter eligible articles. The study design, sample size, type of AI software, and the results of each eligible study were analyzed. The CASP diagnostic study checklist was used to evaluate the evidence strength score. Results: Seven articles were eligible for review according to the PRISMA guidelines. Out of the 7 eligible studies, 4 had strong CASP evidence strength scores (7-8/9). The remaining studies had intermediate CASP evidence strength scores (3.5-6.5/9). The highest area under the curve among the reported studies was 94%, the highest F1 score was 91%, and the highest specificity and sensitivity were 98.1% and 94%, respectively. Conclusion: AI-based detection of periodontal bone loss using radiographs is an efficient method. However, more clinical studies need to be conducted before this method is introduced into routine dental practice.

• 한국지반환경공학회 논문집
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• 제4권4호
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• pp.45-51
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• 2003

암반 내에서 주입재는 토사지반에서와는 달리 절리면을 따라 맥상으로 주입되며 그 결과 암반 내의 불연속면의 특성을 변화시키게 된다. 그러므로 그라우팅 후 암반의 변형특성은 주입재가 주입되는 절리의 방향, 절리의 특성, 그리고 현지암반의 응력상태에 따라 달라지게 된다. 즉 그라우팅에 의한 보강효과를 정확히 평가하기 위해서는 암반 내의 불연속면의 특성과 주입재의 특성이 암반의 변형거동에 미치는 영향을 규명하여야 한다. 그러나 현재까지 현장에서 적용되고 있는 그라우팅공법은 시공자의 경험에 의존하고 있으며, 그 효과에 대한 검증도 현장에서의 탄성파속도 측정, 투수시험 등을 통하여 평가하고 있다. 따라서, 본 연구에서는 그라우팅에 의한 댐 기초 암반절리면의 전단변형특성을 파악하기 위해서 자연암석 절리면에 OPC(Ordinary Portland Cement)와 Micro Cement를 각각 주입하여, 주입재의 종류, 절리면 거칠기의 평균진폭(a)에 대한 주입두께(t)를 변화시켜가면서 암석절리면 직접전단시험을 실시한 실험결과들을 비교 분석하여 최대전단강도, 잔류전단강도 등의 전단특성에 미치는 영향에 대하여 검토하였다.

• 기본간호학회지
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• 제13권3호
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• pp.390-400
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• 2006

Purpose: To develop & to examine the effect of a Tailored Exercise Program (TEP) on physical fitness in patients with Parkinson's disease (PD). Method: In a two-group pre-and post-test design, from a total 41 participants. 21 were assigned th the experimental group find the remainder to the control group. The experimental group participated in a 4-day a week, 8 week program in which one session a week was by direct instruction with the self-help group and two sessions a week were by videotaped instruction at home by themselves. The control group did not receive any intervention. Results: The eight week TEP in patients with PD was found to be significantly effective in enhancing muscle strength, ankle flexibility, and balance. However instrumental activities of daily living was not changed by the intervention. Conclusion: These results suggest that TEP can have an effect on physical fitness in patients with PD. Further research with a larger sample and for a longer follow up period is needed to expand our understanding of the effects of TEP for patients with PD.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume II
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• pp.969-972
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• 2006

The long-range High-Frequency (HF) ocean radar system has observed surface velocity field in the upstream of the Kuroshio north of Ishigaki Island and east of Taiwan since 2001. Applying a new method to extract geostrophic velocity component from the HF surface velocity data with the aid of satellite-born wind data, time series of daily surface geostrophic velocity field has been determined. Despite limited width of the study area of the HF radar, analysis of the sea surface height anomaly determined from the satellite altimetry data in a wider area can provide estimated dates of arrival of mesoscale eddies in the study area of the HF radar. Variations of the Kuroshio position and strength are studied in detail for these cases of interaction with mesoscale eddy, although number of occurrence of direct interaction with the Kuroshio in the study area is not statistically enough. For example, when an anticyclonic eddy approaches to the Kuroshio, the Kuroshio axis is found tend to move northward, keeping away from the approaching eddy from the east.

• Carbon letters
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• 제20권
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• pp.39-46
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• 2016

In this work, the effects of maleic anhydride (MA) content on mechanical properties of chopped carbon fibers (CFs)-reinforced MA-grafted-polypropylene (MAPP) matrix composites. A direct oxyfluorination on CF surfaces was applied to increase the interfacial strength between the CFs and MAPP matrix. The mechanical properties of the CFs/MAPP composites are likely to be different in terms of MA content. Surface characteristics were observed by scanning electron microscope, Fourier transform infrared spectroscopy, and single fiber contact angle method. The mechanical properties of the composites were also measured by a critical stress intensity factor (K_IC). From the K_IC test results, the K_IC values were increased to a maximum value of 3.4 MPa with the 0.1 % of MA in the PP, and then decreased with higher MA content.

• Geomechanics and Engineering
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• 제16권2호
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• pp.205-215
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• 2018

Strain-based criteria are known as a direct method in determining the stability of the geomechanical structures. In spite of the widely use of Sakurai critical strain criterion, it is so conservative to make use of them in rocks with initial plastic deformation on account of the considerable difference between the failure and critical strains. In this study, a new criterion has been developed on the basis of the failure strain to attain more reasonable results in determining the stability status of the tunnels excavated in the rocks mostly characterized by plastic-elastic/plastic behavior. Firstly, the stress-strain curve was obtained having conducted uniaxial compression strength tests on 91 samples of eight rock types. Then, the initial plastic deformation was omitted making use of axis translation technique and the criterion was presented allowing for the modified secant modulus and by use of the failure strain. The results depicted that the use of failure strain criterion in such rocks not only decreases the conservativeness of the critical strain criterion up to 42%, but also it determines the stability status of the tunnel more accurately.

• 한국안전학회지
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• 제20권1호
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• pp.1-6
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• 2005

Stick type ignition coil is new development that connect directly with ECU(Electronic control unit), without needing a spark plug cable and distributor. Glass-fiber reinforced ploymeric composites provide the desirable properties of high stiffness and strength as well as low specific weight. Stick type ignition coil jacket is using PBT CF30 resin. PBT CF30 resin is a kind of electric insulation which is a superior engineering plastic that is used to prevent the leakage of the electrical current. If PET receive a mistake of design or excessive force when HV terminal oppress on jacket, it can happen to crack. Local stress concentrations occurring on the contact surface, the contact phenomenon becomes a direct cause to the wear and failure of mechanical structures. When it is cracked, it can allow a leakage of the electrical current. So, in this study, we analyze the contact stress to PBT jacket using ANSYS program, when HV terminal oppress on jacket. We suppose PBT to be Jacket and we analyzed contact stress that happens in PET like PBT analysis method. We compared the use of PBT and PET.

• 한국주조공학회지
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• 제28권2호
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• pp.79-84
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• 2008

Metal foam is one of the most interesting materials with various multi-functional properties such as light weight, energy absorption, high stiffness and damping capability. Among them, energy absorption property has keen interests in the field of automotives for passenger protection. Nowadays, researches about pore size and porosity control of the foam are increased to correspond them. However, though energy absorption properties are improved, these results are not cost-effective process. In present research, however, as a part of improving the energy absorption property of metallic foams, 606X aluminum alloy was used for cell wall material which has higher strength than pure aluminum. And its morphological features are characterized. As a results, porosity and pore size are uniformity distribution with increasing foaming temperature in the case of 6061 alloy foams. 6063 alloy foam specimens have opposite tendency because of the influence of alloying element and viscosity of the molten melt.

• 대한조선학회논문집
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• 제44권6호
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• pp.612-618
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• 2007

There are a lot of openings, holes and slots in ship structural members. It is not easy to solve the troubles around the openings adequately at the detail design stage, because there are a lot of concerning locations. There are not also clear design rules of classification societies and it is not possible to apply direct calculation for all the concerning members. Therefore, it is necessary to set up simplified approach such as a standard or guidance in order to decide the opening design quickly. For this study, guidance and regulations of each classification and several companies were surveyed. Grillage analysis and the refined mesh method were used to evaluate the strength around hole considering boundary condition and more detailed member arrangement. As a result, the standard for opening design was established and verified.