• 대한토목학회논문집
• /
• 제26권1A호
• /
• pp.1-9
• /
• 2006

선박충돌의 위험이 있는 교량의 교각에 대해 연파괴빈도 계산을 수행하였다. 이러한 해석을 통해 각각의 교각에 대한 선박충돌 수평내하력을 결정할 수 있다. 교각의 수평내하력은 선박충돌 위험도 평가로부터 예측된 연파괴빈도와 허용기준을 비교하는 확률기반 해석과정을 통해 결정된다. 해석과정은 교량 각 부재요소에 대한 초기 충돌저항력을 가정하여 계산된 연파괴빈도가 허용기준을 만족하도록 해석변수를 반복 수정하면서 해를 찾는 과정이다. 일반적으로 선박충돌 위험이 있는 교각들에 대한 연파괴빈도 허용기준의 분배는 설계자의 공학적 판단에 근거한다. 본 연구에서는 선박충돌 위험도 평가로부터 사전 계산되는 연파괴빈도 할당 가중치에 의해 각각의 교각에 허용기준을 분배하였다. 주탑과 교각 등 교량 부재요소의 설계 수평내하력을 결정하기 위해 주탑과 교각의 충격저항력 비를 변수로 수치해석을 수행하였다. 설계 수평내하력은 수로의 기하형상, 수심, 교각의 배치, 선박 통행량의 특성에 의해 동일한 교량에서도 많은 변화가 있다. 따라서 연파괴빈도의 분배 모델과 수평내하력 결정에 대한 많은 연구가 요구된다.

• 대한토목학회논문집
• /
• 제30권2A호
• /
• pp.81-92
• /
• 2010

강프레임 부재의 설계에서 탄성 시스템좌굴해석은 프레임의 실제 거동을 예측하기 어려운 반면, 비탄성 시스템좌굴해석은 압축부재의 세장비에 따른 비탄성 거동이 고려됨으로써 보다 현실적인 부재의 좌굴거동을 예측할 수 있다. 그러나 시스템좌굴해석 수행후 오일러좌굴식을 이용한 방법은 압축력이 비교적 작게 발생하는 부재에서 과도한 유효좌굴길이를 산정한다는 문제점을 내포하고 있다. 본 연구에서는 강프레임 구조의 모든 부재의 탄성 및 비탄성 유효좌굴길이계수를 산정할 수 있는 새로운 해석방법을 제안하였다. 제안된 방법은 가상축력계수 개념을 기반으로 비탄성 강도감소계수를 도입하고 반복고유치해석을 수행하여 각 부재의 유효좌굴길이계수를 산정한다. 제안된 방법의 타당성을 검증하기 위하여 예제 강프레임 구조물을 제안된 방법에 의거한 유효좌굴길이와 기존 방법에 의거한 결과를 비교하였다. 검증 결과, 제안된 방법은 강프레임의 모든 부재의 탄성 및 비탄성 유효좌굴길이계수를 합리적으로 산정할 수 있었다. 부가적으로 재료의 비탄성 거동이 부재의 유효좌굴길이에 미치는 영향도 논의되었다.

• 디지털정책학회지
• /
• 제2권4호
• /
• pp.1-10
• /
• 2023

본 연구는 경찰교통에서의 효과적 ChatGPT 활용 방안 도출을 위한 사전 연구로서 운전면허 학과시험과 도로교통사고감정사 시험에 대한 ChatGPT의 응답을 분석하였다. ChatGPT가 뛰어난 성능과 접근성으로 여러 분야에서 기대를 받고 있으나 경찰 교통법규와 같이 고도의 정확성이 요구되는 분야에서는 사전에 그 성능과 한계를 탐색할 필요가 있다. 이에 본 연구에서는 운전면허 학과시험 문제은행과 도로교통사고감정사 1차 시험을 대상으로 파이썬 코드로 OpenAI API를 이용해 30회의 반복 실험으로 ChatGPT의 응답을 수집하고 응답 결과를 바탕으로 시험별·연도별·내용 영역별 정답률, 일관성 능력을 분석하였다. 분석 결과 첫째, 운전면허 학과시험 및 도로교통사고감정사 1차 시험의 평균 정답률은 각 44.60%, 35.45%로 합격기준보다 낮았다. 연도별로는 2022년 이후 정답률이 평균 정답률을 하회했다. 둘째, 영역별 정답률은 29.69%~56.80%로 나타나 큰 편차를 보였다. 셋째, 정답을 맞힌 경우 95% 이상 일관되게 같은 응답을 출력하였다. ChatGPT의 효과적 활용을 위해서는 사용자의 전문 지식, 평가 데이터 및 방법 마련, 양질의 교통법규 말뭉치 설계와 주기적 학습이 필요하다고 판단된다.

• Korean Journal of Radiology
• /
• 제25권4호
• /
• pp.384-394
• /
• 2024

Objective: To evaluate the image quality of novel dark-blood computed tomography angiography (CTA) imaging combined with deep learning reconstruction (DLR) compared to delayed-phase CTA images with hybrid iterative reconstruction (HIR), to visualize the cervical artery wall in patients with Takayasu arteritis (TAK). Materials and Methods: This prospective study continuously recruited 53 patients with TAK (mean age: 33.8 ± 10.2 years; 49 females) between January and July 2022 who underwent head-neck CTA scans. The arterial- and delayed-phase images were reconstructed using HIR and DLR. Subtracted images of the arterial-phase from the delayed-phase were then added to the original delayed-phase using a denoising filter to generate the final-dark-blood images. Qualitative image quality scores and quantitative parameters were obtained and compared among the three groups of images: Delayed-HIR, Dark-blood-HIR, and Dark-blood-DLR. Results: Compared to Delayed-HIR, Dark-blood-HIR images demonstrated higher qualitative scores in terms of vascular wall visualization and diagnostic confidence index (all P < 0.001). These qualitative scores further improved after applying DLR (Dark-blood-DLR compared to Dark-blood-HIR, all P < 0.001). Dark-blood DLR also showed higher scores for overall image noise than Dark-blood-HIR (P < 0.001). In the quantitative analysis, the contrast-to-noise ratio (CNR) values between the vessel wall and lumen for the bilateral common carotid arteries and brachiocephalic trunk were significantly higher on Dark-blood-HIR images than on Delayed-HIR images (all P < 0.05). The CNR values were significantly higher for Dark-blood-DLR than for Dark-blood-HIR in all cervical arteries (all P < 0.001). Conclusion: Compared with Delayed-HIR CTA, the dark-blood method combined with DLR improved CTA image quality and enhanced visualization of the cervical artery wall in patients with TAK.

• Korean Journal of Radiology
• /
• 제24권4호
• /
• pp.294-304
• /
• 2023

Objective: We aimed to investigate whether image standardization using deep learning-based computed tomography (CT) image conversion would improve the performance of deep learning-based automated hepatic segmentation across various reconstruction methods. Materials and Methods: We collected contrast-enhanced dual-energy CT of the abdomen that was obtained using various reconstruction methods, including filtered back projection, iterative reconstruction, optimum contrast, and monoenergetic images with 40, 60, and 80 keV. A deep learning based image conversion algorithm was developed to standardize the CT images using 142 CT examinations (128 for training and 14 for tuning). A separate set of 43 CT examinations from 42 patients (mean age, 10.1 years) was used as the test data. A commercial software program (MEDIP PRO v2.0.0.0, MEDICALIP Co. Ltd.) based on 2D U-NET was used to create liver segmentation masks with liver volume. The original 80 keV images were used as the ground truth. We used the paired t-test to compare the segmentation performance in the Dice similarity coefficient (DSC) and difference ratio of the liver volume relative to the ground truth volume before and after image standardization. The concordance correlation coefficient (CCC) was used to assess the agreement between the segmented liver volume and ground-truth volume. Results: The original CT images showed variable and poor segmentation performances. The standardized images achieved significantly higher DSCs for liver segmentation than the original images (DSC [original, 5.40%-91.27%] vs. [standardized, 93.16%-96.74%], all P < 0.001). The difference ratio of liver volume also decreased significantly after image conversion (original, 9.84%-91.37% vs. standardized, 1.99%-4.41%). In all protocols, CCCs improved after image conversion (original, -0.006-0.964 vs. standardized, 0.990-0.998). Conclusion: Deep learning-based CT image standardization can improve the performance of automated hepatic segmentation using CT images reconstructed using various methods. Deep learning-based CT image conversion may have the potential to improve the generalizability of the segmentation network.

• 한국산업정보학회논문지
• /
• 제29권2호
• /
• pp.169-190
• /
• 2024

본 연구는 한국중부발전(주)의 사례를 기반으로 소통중심의 공공서비스디자인 혁신 모델을 개발하고자 한국중부발전(주)의 고객 및 직원참여 활동 사례를 분석하였다. 소통을 위한 활동 사례를 중심으로 (1) 현상인식 및 변화관리 추진을 위한 준비 단계; (2) 공공서비스 개선을 위한 문제해결 단계; (3) 업무 프로세스 개선을 위한 문제해결 단계; (4) 협업 강화를 위한 문제해결 단계; (5) 혁신 모델 디자인 단계로 도출하였다. 도출된 결과를 기반으로 더블다이아몬드 디자인 프로세스를 적용하여 공공서비스디자인 혁신모델을 개발하였다. 제안된 모델은 1차 발산(발견)과 수렴(정의), 2차 발산(개발)과 수렴(전달)의 반복 과정을 통해 최종산출물이 도출되는 프로세스 구조이다. 한국중부발전(주)의 우수사례 중 아이디어발전소 활동을 본 연구에서 제안한 모델에 적용하여 활용가능성도 제안하였다. 비록 본 연구는 특정 공기업 사례를 기반으로 소통중심의 공공서비스디자인 혁신 모델을 제안하였지만, 본 모델은 고객 및 직원참여 기반의 효율적인 소통을 위한 운영방안에 활용될 수 있다.

• 한국환경복원기술학회지
• /
• 제26권6호
• /
• pp.155-164
• /
• 2023

Sedirea japonica is one of the critically endangered species in South Korea mostly due to artificial harms such as illegal collection and habitat destruction. Therefore, artificial propagation through improving germination rate, increasing growth, and controlling flowering is meaningful for the conservation and reintroduction of S. japonica. It is suggested that cytokinins are one of the multi-factors that contribute to plant growth and floral responses. Especially, exogenous cytokinins have been known to induce or promote shoot growth or earlier flowering in orchids. Therefore, it was investigated how the application of 6-benzylaminopurine (BA) influenced the growth and inflorescence of S. japonica. A foliar spray containing BA at 100, 200, 300, and 400 ppm was applied from 1st July to 30th December 2021. Leaf length, leaf length growth rate, leaf width, and width and length ratio were measured as growth-related factors. Visible inflorescence rate, inflorescence length, the number of flowers per inflorescence, and the distance between the stalks were measured as flowering-related factors. Growth-related factors except for leaf growth rate were not affected by BA treatments, while leaf growth rate was significantly increased by 200 ppm of BA treatment. The visible inflorescence rate increased by 200 ppm of BA treatment, and there seems an optimal concentration and threshold of BA treatment. An iterative experiment with more seedlings and measurement factors would be helpful to figure out the effects of exogenous BA treatment on S. japonica, and it can be applied for mass propagation.

• Korean Journal of Radiology
• /
• 제22권4호
• /
• pp.624-633
• /
• 2021

Objective: To evaluate the reliability of CT measurements of muscle quantity and quality using variable CT parameters. Materials and Methods: A phantom, simulating the L2-4 vertebral levels, was used for this study. CT images were repeatedly acquired with modulation of tube voltage, tube current, slice thickness, and the image reconstruction algorithm. Reference standard muscle compartments were obtained from the reference maps of the phantom. Cross-sectional area based on the Hounsfield unit (HU) thresholds of muscle and its components, and the mean density of the reference standard muscle compartment, were used to measure the muscle quantity and quality using different CT protocols. Signal-to-noise ratios (SNRs) were calculated in the images acquired with different settings. Results: The skeletal muscle area (threshold, -29 to 150 HU) was constant, regardless of the protocol, occupying at least 91.7% of the reference standard muscle compartment. Conversely, normal attenuation muscle area (30-150 HU) was not constant in the different protocols, varying between 59.7% and 81.7% of the reference standard muscle compartment. The mean density was lower than the target density stated by the manufacturer (45 HU) in all cases (range, 39.0-44.9 HU). The SNR decreased with low tube voltage, low tube current, and in sections with thin slices, whereas it increased when the iterative reconstruction algorithm was used. Conclusion: Measurement of muscle quantity using HU threshold was reliable, regardless of the CT protocol used. Conversely, the measurement of muscle quality using the mean density and narrow HU thresholds were inconsistent and inaccurate across different CT protocols. Therefore, further studies are warranted in future to determine the optimal CT protocols for reliable measurements of muscle quality.

• Korean Journal of Radiology
• /
• 제22권8호
• /
• pp.1341-1351
• /
• 2021

Objective: To compare the quality of various polychromatic and monochromatic images with or without using an iterative metal artifact reduction algorithm (iMAR) obtained from a dual-energy computed tomography (CT) to evaluate total knee arthroplasty. Materials and Methods: We included 58 patients (28 male and 30 female; mean age [range], 71.4 [61-83] years) who underwent 74 knee examinations after total knee arthroplasty using dual-energy CT. CT image sets consisted of polychromatic image sets that linearly blended 80 kVp and tin-filtered 140 kVp using weighting factors of 0.4, 0, and -0.3, and monochromatic images at 130, 150, 170, and 190 keV. These image sets were obtained with and without applying iMAR, creating a total of 14 image sets. Two readers qualitatively ranked the image quality (1 [lowest quality] through 14 [highest quality]). Volumes of high- and low-density artifacts and contrast-to-noise ratios (CNRs) between the bone and fat tissue were quantitatively measured in a subset of 25 knees unaffected by metal artifacts. Results: iMAR-applied, polychromatic images using weighting factors of -0.3 and 0.0 (P_-0.3i and P_0.0i, respectively) showed the highest image-quality rank scores (median of 14 for both by one reader and 13 and 14, respectively, by the other reader; p < 0.001). All iMAR-applied image series showed higher rank scores than the iMAR-unapplied ones. The smallest volumes of low-density artifacts were found in P_-0.3i, P_0.0i, and iMAR-applied monochromatic images at 130 keV. The smallest volumes of high-density artifacts were noted in P_-0.3i. The CNRs were best in polychromatic images using a weighting factor of 0.4 with or without iMAR application, followed by polychromatic images using a weighting factor of 0.0 with or without iMAR application. Conclusion: Polychromatic images combined with iMAR application, P_-0.3i and P_0.0i, provided better image qualities and substantial metal artifact reduction compared with other image sets.

• Structural Engineering and Mechanics
• /
• 제90권6호
• /
• pp.551-568
• /
• 2024

The present study deals with static and dynamic behaviors including forced vibrations of an elastic rectangular nano plate on the two-parameter foundation. Firstly, the rectangular plate is assumed to be subjected to uniformly distributed and eccentrically applied concentrated loads. The governing equations of the problem are derived by considering the dynamic response of the plate, employing a series of the Chebyshev polynomials for the displacement function and applying the Galerkin method. Then, effects of the non-essential boundary conditions of the plate, i.e., the boundary conditions related to the shearing forces, the bending moments and the corner forces, are included in the governing equation of motion to compensate for the non-satisfied boundary conditions and increase the accuracy of the Galerkin method. The approximate numerical solution is accomplished using an iterative process due to the non-linearity of the unilateral property of the two-parameter foundation. The plate under static concentrated load is investigated in detail numerically by considering a wide range of parameters of the plate and the foundation stiffnesses. Numerical treatment of the problem in the time domain is carried out by assuming a stepwise variation of the concentrated load and the linear acceleration procedure is employed in the solution of the system of governing differential equations derived from the equation of motion. Time variations of the contact region and those of the displacements of the plate are presented in the figures for various numbers of the two-parameter of the foundation, as well as the classical and nano parameters of the plate particularly focusing on the non-linearity of the problem due to the plate lift-off from the unilateral foundation. The effects of classical and nonlocal parameters and loading are investigated in detail. Definition of the separation between the plate and the two-parameter foundation is presented and applied to the given problem. The effect of the lift-off on the static and dynamic behavior of the rectangular plate is studied in detail by considering various loading conditions. The numerical study shows that the effect of nonlocal parameters on the behavior of the plate becomes significant, when nonlinearity becomes more profound, due to the lift-off of the plate. It is seen that the size effects are significant in static and dynamic analysis of nano-scaled rectangular plates and need to be included in the mechanical analyses. Furthermore, the corner displacement of the plate is affected more significantly from the lift-off, whereas it is less marked in the time variation of the middle displacement of the plate. Several numerical examples are presented to examine the sensibility of various parameters associated with nonlocal parameters of the plate and foundation. Both stiffening and softening nonlocal parameters behavior of the plate are identified in the numerical solutions which show that increasing the foundation stiffness decreases the extent of the contact region, whereas the stiffness of the shear layer increases the contact region and reduces the foundation settlement considerably.