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경계확장과 복합 유전알고리즘을 이용한 비선형 입체트러스의 최적설계
현승협,이광순,한상을 대한건축학회 2001 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.21 No.2
A genetic algorith(GA) is adaptible to discrete and constrainted problem. But in structure optimization problem, optimum solutions exist at the comer(boundary between feasible and infeasible regions) of the search space and the boundary are much complecated. In this case some crossover operators do not work well because the outcomes of the operator are apt to be infeasible. and especially much time is repuired to estimate the constraints in large scale or nonlinear structures. In this paper, to cope with these problem we propose to reduce the intensity of penalty in order to extend the boundary of search space and to use the hybrid genetic algorithm by gradient-like-selection. Micro GA effective in small population size is used and design variables are selected from practically used standard steel sections. An incremental load approach with a modified Newton-Raphson iteration is used.
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경계확장과 복합 유전알고리즘을 이용한 비선형 입체트러스의 최적설계
현승협(Hyun Seung-Hyup),김종범(Kim Jong-Bum),한상을(Han Sang-Eul) 대한건축학회 2003 大韓建築學會論文集 : 構造系 Vol.19 No.5
Genetic algorithms(GAs) are adaptable to discrete and constrained problems and do not require continuity, unimodality, and derivatives of function. But GAs have a demerit of late convergence, which means to be examined many individuals until find the best individual. And especially much time is required to compute the constraints of an individual in large scale or nonlinear structural problem. So it needs to be developed the genetic algorithm to converges fast in small population. Although the selected algorithm is superior, it's performance could be very fluctuate depending on search space. And it is possible to vary and adapt the algorithm to a placed circumstance. Therefore it is very important for user to create more efficient algorithm. In this paper, micro genetic algorithm effective in small population size is used to save computing time in size optimization of geometrically nonlinear space truss. But in practical structural size optimization problem, many design variables are needed and search space is very complicated. Also optimum solutions exist at the corner (boundaries between feasible and infeasible regions) of the search space. In this case, micro GAs exist so far are liable to fall into dead corner and some genetic operators of those do not work well because the outcomes of the operator are apt to be infeasible. To cope with these problem it is proposed to reduce the intensity of penalty in order to extend the boundaries of search space and to use the hybrid genetic algolithm by gradient-like-selector to converge fast and avoid the genetic drift as a result of copies.
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현승협(Seung-Hyop Hyun),서한복(Han-Bok Seo),박은애(Eun-Ae Park),이승엽(Seung-Yop Lee) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
This paper suggests a novel self-assembled technique to fabricate photonic crystal structures with large scales. Nano-sized colloidal suspension is injected into cylindrical substrates rotating by a spindle motor, and then the solvent of suspension evaporates. Simultaneously, colloidal particles are stacked on the wall of the curved substrates, forming face centered crystal structures. We have cylindrical basket device rotating on the center axis to implement large-scale self-assembled method. The substrates are laid on water poured in the basket. Rotation of the substrates cause floating on the water and rotating without eccentricity. Inner surface of the substrates is coated, and then silica colloidal suspension is injected into the substrates. As the solvent of suspension evaporates, we can obtain curved silica photonic structures. We have fabricated red iridescent colored photonic structures with the area of a centimeter scale. The proposed self-assembled technique easily fabricates large scale photonic crystal structures for the application to various optical devices.
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Prognostic Significance of Volume-Based PET Parameters in Cancer Patients
문승환,현승협,최준영 대한영상의학회 2013 Korean Journal of Radiology Vol.14 No.1
Accurate prediction of cancer prognosis before the start of treatment is important since these predictions often affect the choice of treatment. Prognosis is usually based on anatomical staging and other clinical factors. However, the conventional system is not sufficient to accurately and reliably determine prognosis. Metabolic parameters measured by 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) have the potential to provide valuable information regarding prognosis and treatment response evaluation in cancer patients. Among these parameters, volume-based PET parameters such as metabolic tumor volume and total lesion glycolysis are especially promising. However, the measurement of these parameters is significantly affected by the imaging methodology and specific image characteristics, and a standard method for these parameters has not been established. This review introduces volume-based PET parameters as potential prognostic indicators, and highlights methodological considerations for measurement, potential implications, and prospects for further studies.
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Clinical Significance of Incidental Focal 18F-FDG Uptake in the Spinal Cord of Patients with Cancer
임채홍,현승협,문승환,조영석,최연성,이경한,김병태,최준영 대한핵의학회 2017 핵의학 분자영상 Vol.51 No.3
Purpose We investigated the incidence, location, and clinical significance of focal 18F-FDG uptake of the spinal cord in patients with cancer. Methods We reviewed the medical records of 22,937 consecutive adult patients with known or suspicious malignancy who underwent 18F-FDG PET/CT. PET/CT scans with incidental focal spinal cord uptake were selected and retrospectively reviewed to determine the presence, location, number, and maximum standardized uptake value (SUVmax) of any focal hypermetabolic lesions of the spinal cord. In subjects with focal spinal uptake, clinical characteristics and clinical follow-up results, including follow-up PET/CT, were reviewed. Results Incidental focal spinal cord uptake was observed in 69 of 22,937 adult patients (incidence = 0.3%; M:F = 31:38; age, 55.8 ± 14.7 years). Seventy-eight focal hypermetabolic lesions on spinal cord in the PET/CT scans of the 69 study subjects were analyzed. The most common sites of focal spinal cord uptake were the T12 vertebra (47/78; 60.3%) and L1 vertebra (20/78; 25.6%). Multifocal cord uptake was found in 8 of 69 patients (11.6%). The average SUVmax for cord uptake was 2.5 ± 0.5 (range, 1.4∼3.9). There was no clinical or imaging evidence of abnormalities in the spinal cord, both at the time of PET/CT and during clinical follow-up. Conclusions Although incidental focal 18F-FDG uptake of the spinal cord is rare in patients with cancer, it may be physiological or benign, but it should not be considered as malignant involvement. Common sites for the uptake were in the T12 and L1 spine levels.
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무패턴 마이크로 채널을 이용한 마이크로 막대 광결정 제작
서한복(Han-Bok Seo),현승협(Seung-Hyeop Hyun),이승엽(Seung-Yop Lee) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
The photonic crystals have been developed in various fields for the applications to optical devices, bioelectronics and biosensors. In this paper, we fabricate rod-shaped photonic crystals with micro-scale thickness, width, and macro-scale length by using a simple self-assembly process. The micro-channel of hydrophilic substrates without pre-patterns was used to crystalize nanoparticles from the colloidal suspensions injecting in the channels. A lot of long micro-rods were simply fabricated with relatively low defects by a rotational drying process. The fabricated micro-rods with structural color have the width about 1~2 times larger than the thickness, which is identical to the thickness of the micro-channel. The rod-shaped photonic crystals can be applied to biomimetic structural colors with specific patterns, micro-cantilevers and optical devices.
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이지영,최준영,최윤호,현승협,문승환,장수진,최연성,이경한,김병태 대한영상의학회 2013 Korean Journal of Radiology Vol.14 No.3
Objective: We investigated the clinical significance of incidental diffuse thyroid uptake (DTU) on 18F-FDG PET in subjects without a history of cancer. Materials and Methods: This study included 2062 studies from adults who underwent 18F-FDG PET as a cancer screening program. Subjects were divided into the following two groups: with (group I) or without (group II) DTU. The presence of DTU and the thyroid visual grading score were compared with thyroid function tests, serum anti-microsomal antibody (AMA) levels, and the presence of diffuse parenchymal change (DPC) on ultrasonography (USG). Results: DTU was found in 6.6% of the scans (137/2062). Serum thyroid stimulating hormone (TSH) and AMA levels were significantly higher in group I than in group II. Increased AMA level (55.1%) and DPC (48.7%) were more frequently found in group I (p < 0.001). The proportion of subjects with any abnormal results in serum free thyroxine, triiodothyronine, TSH, or AMA levels or DPC on USG was significantly higher in group I than in group II (71.5% vs. 10.6%, p < 0.001), and was significantly and gradually increased according to the visual grading score group (0 vs. 1-2 vs. 3-4 = 10.6% vs. 58.5% vs. 90.9%, p < 0.001). TSH and is AMA levels were significantly increased according to the visual grading score. Conclusion: The presence or degree of incidental DTU on 18F-FDG PET is closely correlated with increased serum AMA and TSH levels, and the presence of DPC on USG. Therefore, the most plausible pathological cause of DTU may be cell damage by an autoimmune mechanism.
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