• 한국수학사학회지
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• 제25권4호
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• pp.1-10
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• 2012

중국의 명수법은 기록은 구어체를 사용하고, 계산은 산대를 사용하는 이중 구조를 가지고 있었다. 또 산서는 실생활의 문제만 다루는 과정에서 수학적 구조를 나타내는 방법을 택하여 계산 과정을 제외하면 이들에서 취급한 수는 모두 명수(名數)들이어서 순수한 수론의 발전을 이룰 수 없었다. 송대에 0의 도입과 함께, 천원술의 표현에서 나타나는 계수를 산대로 표시하는 방법을 통하여, 산대가 계산 도구와 함께 추상수의 기수법(記數法)이 되는 과정을 밝힌다. 수량의 단위를 사용한 소수의 표현도 이 과정에서 산대 표현으로 대치되었다. 그러나 명대에 산대 계산이 주산으로 대치되고 천원술이 잊히게 되어 추상수의 개념도 함께 잊히게 되었다. 청대의 산학자 심사계(沈士桂)가 저서 간첩이명산법(簡捷易明算法)에서 분수의 소수표시와 계산을 하는 과정에서 순환소수를 인지하고 이들의 계산법을 확립한 것도 보인다.

• 대한치과교정학회지
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• 제51권5호
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• pp.329-336
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• 2021

Objective: To compare the magnitude of external apical root resorption (EARR) 6 months after starting orthodontic treatment using orthodontic aligners (OAs) and fixed appliances (FAs). Methods: This parallel randomized clinical trial included 40 patients randomized into two groups: OA group (n = 20, 160 incisors) and FA group (n = 20, 160 incisors). For evaluation of the tooth length, periapical radiographs and standardized linear measurements of the maxillary and mandibular incisors were acquired before (T0) and 6 months after treatment initiation (T1). EARR was calculated through the difference in length between the two time points (T1-T0). Statistical comparisons were performed by means of using t-tests, chi-squared test and covariance analysis (a = 5%). Results: Rounding of the root apex was observed in both groups; the resorption involved 2.88% of the root length, so 97.12% of the tooth length remained intact. Intragroup comparisons between the two time points revealed a significant difference, with (T1-T0) ranging from -0.52 to -0.88 mm in the FA group and from -0.52 to -0.85 mm in the OA group. In the intergroup comparisons, only tooth #21 presented a statistically significant difference (OA: -0.52 ± 0.57 mm, FA: -0.86 ± 0.60 mm); however, the overall differences between groups were not clinically relevant, ranging from 0.03 to 0.35 mm. Conclusions: OA and FA treatment resulted in a similar degree of EARR in the maxillary and mandibular incisors at 6 months after treatment initiation. However, the amount of resorption was small and does not impair tooth longevity.

• 한국수학교육학회지시리즈C:초등수학교육
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• 제24권2호
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• pp.103-114
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• 2021

본 연구는 소수 나눗셈에서의 '몫'과 '나머지' 용어 사용의 문제점을 인식하고 이를 개선하기 위한 방안을 탐색하였다. 지금까지의 선행 연구와 현행 교과서를 분석한 결과, '몫', '나머지' 용어 사용에 대해 연구자마다 상이한 견해를 주장한 근원에 나눗셈 알고리즘에서의 q, r값과 계산 결과의 해석에 따른 결과 값과 남는 양을 동일하게 보는 데에 원인이 있음을 밝히고, 소수 나눗셈의 '몫'과 '나머지' 취급에 대한 일관된 관점과 교과서 개선 방안을 제안하였다. 즉, 나눗셈 알고리즘 b=a×q+r에 의한 소수 나눗셈의 결과인 q, r을 '몫', '나머지'로 보고, 문제 맥락에 따라 q와 같거나 작은 양을 최종적인 '결과 값'으로, 결과 값을 취하고 난 잔여량을 '남는 양'으로 지칭할 것을 제안하였다. 또한, 몫을 반올림하여 나타낸 근삿값을 '몫'으로 지칭하지 않을 것을 제안하였다.

• Wind and Structures
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• 제34권1호
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• pp.43-58
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• 2022

The BARC flow is studied via Direct Numerical Simulation at a relatively low turbulent Reynolds number, with focus on the geometrical representation of the leading-edge (LE) corners. The study contributes to further our understanding of the discrepancies between existing numerical and experimental BARC data. In a first part, rounded LE corners with small curvature radii are considered. Results show that a small amount of rounding does not lead to abrupt changes of the mean fields, but that the effects increase with the curvature radius. The shear layer separates from the rounded LE at a lower angle, which reduces the size of the main recirculating region over the cylinder side. In contrast, the longitudinal size of the recirculating region behind the trailing edge (TE) increases, as the TE shear layer is accelerated. The effect of the curvature radii on the turbulent kinetic energy and on its production, dissipation and transport are addressed. The present results should be contrasted with the recent work of Rocchio et al. (2020), who found via implicit Large-Eddy Simulations at larger Reynolds numbers that even a small curvature radius leads to significant changes of the mean flow. In a second part, the LE corners are fully sharp and the exact analytical solution of the Stokes problem in the neighbourhood of the corners is used to locally restore the solution accuracy degraded by the singularity. Changes in the mean flow reveal that the analytical correction leads to streamlines that better follow the corners. The flow separates from the LE with a lower angle, resulting in a slightly smaller recirculating region. The corner-correction approach is valuable in general, and is expected to help developing high-quality numerical simulations at the high Reynolds numbers typical of the experiments with reasonable meshing requirements.

• Wind and Structures
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• 제35권1호
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• pp.55-66
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• 2022

Tall buildings are often subjected to steady and unsteady forces due to external wind flows. Measurement and mitigation of these forces becomes critical to structural design in engineering applications. Over the last few decades, many approaches such as modification of the external geometry of structures have been investigated to mitigate wind-induced load. One such proven geometric modification involved the rounding of sharp corners. In this work, we systematically analyze the impact of rounded corner radii on the reducing the flow-induced loading on a square cylinder. We perform 3-Dimensional (3D) simulations for high Reynolds number flows (Re=1 × 105) which are more likely to be encountered in practical applications. An Improved Delayed Detached Eddy Simulation (IDDES) method capable of capturing flow accurately at large Reynolds numbers is employed in this study. The IDDES formulation uses a k-ω Shear Stress Transport (SST) model for near-wall modelling that prevents mesh-induced separation of the boundary layer. The effects of these corner modifications are analyzed in terms of the resulting variations in the mean and fluctuating components of the aerodynamic forces compared to a square cylinder with no geometric changes. Plots of the angular distribution of the mean and fluctuating coefficient of pressure along the square cylinder's surface illustrate the effects of corner modifications on the different parts of the cylinder. The windward corner's separation angle was observed to decrease with an increase in radius, resulting in a narrower and longer recirculation region. Furthermore, with an increase in radius, a reduction in the fluctuating lift, mean drag, and fluctuating drag coefficients has been observed.

• Journal of Trauma and Injury
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• 제19권2호
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• pp.121-125
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• 2006

Purpose: There is ongoing demand to deliver better procedural training to medical students in the emergency department. Thus, we studied the efficacy of a cadaver-based training model for teaching simple suture techniques to medical students. Methods: We investigated ten fourth-year medical students, who were rounding and being trained in the Emergency Department of Chungnam National University Hospital. They were educated with slides about a simple suture technique for 30 minutes to evaluate the efficacy of the cadaver-based training model. We prospectively measured their skill by administering a test on the cadaver-based simple suture technique in 3cm sized linar wound separately to each of them. Results: A total of ten fourth-year medical students completed the investigation. The tension, the direction of suture, the degree of cleanness, the number of sutures, the adequacy of the cutting thread length, and the suturing time in the first attempt were compared with those in the second one. The second results were compared with those in the third one, and the third results were compared with those in the fourth one. All the results had statistical significance. Conclusion: These findings support the value of the cadaver-based simple suture technique training model as a medical student teaching model. The cadaver-based simple suture technique teaching model is a good way of teaching several medical skills to medical students.

• 간호행정학회지
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• 제5권2호
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• pp.389-400
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• 1999

The purpose of this study is to examine a possibility of applying the ABC system to analyze the cost of nursing service on one obstetrics and gynecology (OB/GYN) unit in a major medical center. The activities of nurses on an OB/GYN unit were analyzed for 4 days for 96 hours. 2 week days and 2 days on weekend. Total cases included in the study were activities of 12 charge nurses and 12 staff nurses. Activities were categorized into direct and indirect activities in order to calculate the cost of activities. Nursing activities were defined multidimesionally in order to utilize the ABC system. The 60 nursing activities were classified into the direct nursing activities and the indirect nursing activities based on a literature review, interview, and survey results. The direct activities were further categorized into the single nursing activities and the multiple nursing activities. The indirect activities were classified into the indirect nursing service activities and the general management activities. The major findings of this study were as follows : 1. There were differences in activities according to the positions and duties of the nurses. The charge nurses mostly performed the indirect nursing service activities and the general management activities. Almost all of their indirect nursing activities spent on each patient were similar. The staff nurses performed the single nursing activities and the multiple nursing activities. 2. The activities of staff nurses included medication, patient assessment, rounding and organizing the unit. patient education, nursing treatment, admission and discharging of patients. There was no differences in types and amount of time spent between the nurses on day-time duty and evening-time duty, but the patient assessment activity increased during the night-time. 3. The cost of post partum nursing services for women who had a normal vaginal delivery using the ABC system included the cost incurred by direct nursing activities provided by the staff nurses (85.9%), indirect nursing activities incurred by the staff nurses(19.0%) and the nursing activities by the charge nurses and the head nurse(14.1%). The ABC system is a relatively new method of cost analysis. The results of this study can provide the nursing and hospital managers with useful information on cost control. It is suggested that more studies should be done using the ABC system and extend the scope of studies to include value analysis to aid the Activity-Based Management(ABM) and/or the reengineering of hospital process.

• 한국구조물진단유지관리공학회 논문집
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• 제21권2호
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• pp.13-23
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• 2017

본 연구는 사각형 콘크리트 압축부재를 CFRP 쉬트로 감쌌을 때의 보강효과와 거동 특성에 대한 연구로, CFRP 쉬트로 보강한 경우 쉬트의 구속효과에 의하여 압축내력이 향상되었으나 사각형 단면이므로 원형단면보다 구속효과는 작게 나타났다. 보강효과와 거동특성을 확인하기 위하여 CFRP 쉬트의 보강겹수, 시험체의 크기, 형상비, 모따기, 및 단면 개량을 변수로 선정하여 실험을 계획하였다. 11개의 실험변수별로 각각 5개씩, 총 55개의 실험체를 제작하여 실험하였다. 압축시험결과 CFRP 쉬트의 구속에 의해 보강효과가 나타났으나 실험체의 크기가 증가함에 따라 구속효과는 떨어졌다. 반면에 CFRP 쉬트의 구속효과에 의하여 사각형 콘크리트 기둥의 연성은 매우 크게 증가되었다. 단면형상을 사각형에서 원형으로 변형한 경우 압축강도와 연성 모두 증가되었다. 또한 실험결과와 기존연구결과를 사용하여 CFRP로 구속된 사각형 콘크리트 부재에 대한 기존 강도추정식의 정확성과 신뢰성을 검증하였다.

• Restorative Dentistry and Endodontics
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• 제33권1호
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• pp.28-38
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• 2008

본 연구는 3차원 유한요소 분석법적 연구를 통해 쐐기형 비우식성 치경부병소의 복합레진 수복물에서 다른 탄성계수를 가진 복합레진의 수복과 와동의 형태와 응력의 방향에 따른 응력분포의 영향에 대해 알아보고자 하였다. 발거된 상악 제2소구치를 Micro-CT로 스캔한 후 3D-DOCTOR로 3차원유한요소 모형을 제작하였다. 제작된 소구치 모형에 쐐기형 와동과 변형시킨 와동을 형성하고 각 와동을 탄성계수가 서로 다른 혼합형 복합레진 또는 흐름성 복합레진으로 수복하였다. 수복 전, 후 협측교두와 설측교두에 500N의 하중을 가한 후 응력분포를 ANSYS 프로그램을 이용하여 주 응력 분석법으로 평가한 바 다음과 같은 결과를 얻었다. 1. 수복 전 응력은 근심측 백악법랑경계와 와동저 선각부에 집중되었으며 최대응력은 근심협측우각부에서 나타났다. 2. 와동수복 후 와동저 선각의 응력은 현저히 감소했으나 치경부측 변연의 응력은 수복전보다 증가하였다. 3. 쐐기형태의 병소의 수복 시 와동저 선각부는 탄성계수가 높은 재료가 유리하고 치경부측 변연은 탄성계수가 낮은 재료가 유리하였다. 4. 와동저 선각부를 둥글게 변화시키는 것은 압축응력은 감소시키지 않으나 인장응력은 감소시켰다.

• 대한의용생체공학회:의공학회지
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• 제22권5호
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• pp.403-412
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• 2001

수두증 환자의 뇌압을 조절하기 위해 사용되는 션트밸브의 압력-유량제어 특성과 설계변수 변화에 따른 특성곡선의 변화를 수치적으로 해석 하였다. 해석에 사용된 션트밸브는 국내에서 설계 제작된 일정 압력형 다이아프램 타입이며 실험을 통하여 해석의 타당성을 검증하였다. 션트밸브 내부에 장착된 압력-유량 제어용 소형 다이아프램이 실리콘 일래스토머 계통의 유연한 재질이므로 유동구조 상호해석을 수행하였다 구조해석시의 재료 비선형성을 고려하여 고탄성 재료에 대한 므니 리블린(Mooney-Rivlin) 근사를 적용하였다. 수치해석결과 얻어진 압력-유량제어 특성곡선은 실험결과와 유사하였고 션트밸브를 통한 압력강하의 대부분은 소형 다이아프램에서 이루어짐을 확인할 수 있었다 본 연구에서 해석된 션트밸브의 압력-유량 특성곡선의 기울기는 7.37mm$H_2O$.hr/cc로서 상용 션트밸브의 기울기 평균값 0.40mm$H_2O$.hr/cc과 비슷하여 일정압력형 션트밸브의 특성을 잘 나타내었다. 오프닝압력의 크기는 밸브 다이아프램의 초기쳐짐량 크기에 의존하였고. 25mm$H_2O$와 80mm$H_2O$의 오프닝압력을 얻기 위해서는 10.2$\mu$m와 35.3$\mu$m의 초기쳐짐량이 필요하였다. 밸브가 열리면서 유동이 발생할 경우, 유동 오리피스 간극이 107m 이내이므로 션트밸브의 성공적인 동작을 위해서는 정밀설계와 제작기술이 요구된다. 본 연구를 통해 다이아프램의 초기쳐짐량과 유동 오리피스를 형성하는 다이아프램 끝단의 라운딩 크기가 압력-유량 특성곡선의 기울기에 영향을 미치는 주요 설계변수임을 확인하였다.