철근 콘크리트 빔의 노화도 평가를 위한 음향방출 기술의 응용

윤동진,박휘립,이승석 한국비파괴검사학회 2000 한국비파괴검사학회지 Vol.20 No.4

콘크리트 구조물의 노화도 평가를 위한 기초 연구로써 철근 및 무근 콘크리트 빔의 4점 굽힘 시험시 발생하는 음향방출 신호의 발생 거동을 관찰하였다. 본 연구는 미세 균열의 전개, 국부 균열의 진전, 부식, 철근의 박리 등 균열 발생 및 손상기구에 대한 AE 특성 고찰에 주안점을 두었다. 이들 각각의 손상 메카니즘을 모사하기 위해 무근 콘크리트, 노치를 가공한 무근 콘크리트, 정상적인 철근 콘크리트 그리고 부식된 철근 콘크리트 빔을 제작하였다. 손상 정도 및 펠리시티 효과(Felicity effect)를 관찰하기 위해 4점 굽힘 시험시 단계별 하중 증가 방식을 택하였다. AE 파형은 물론 AE event에 대한 발생 특성을 분석하였으며, 노화도 평가에 주요한 영향을 미치는 주요 변수들에 대해 조사하였다. AE event 발생의 누계치 및 Felicity ratio값 등은 손상의 정도에 따라 민감하게 변하는 것을 관찰하였으며, 노화도와도 상관관계가 있음을 확인하였다. 결과적으로 본 연구에서 얻은 AE 분석 기술은 철근 콘크리트 구조물의 균열이나 부식 손상과 같은 노화도 평가를 위해 적용할 수 있는 가능성을 제시하였다.

주성분 회귀분석 및 인공신경망을 이용한 AE 변수와 응력확대계수와의 상관관계 해석

윤동진,김기복,정중채,박휘립,이승석 한국비파괴검사학회 2001 한국비파괴검사학회지 Vol.21 No.1

AE 신호와 재료의 기계적 물성과의 관계를 정량적으로 제시할 수 있는 방법을 개발하였다. 재료의 여러 가지 기계적 성질들 중 피로균열 거동에 관련된 응력확대계수를 중심으로 AE 신호와 같은 다변량 데이터의 처리에 많이 사용되고 있는 주성분 회귀분석과 비선형적 문제 해결에 적합한 신경회로망 기법을 이용하였다. 이를 위하여 강교량 부재인 SWS490B 강에 대한 피로균열전파 실험을 수행하였으며 표준 CT 시편에 대한 피로균열진전 시 발생하는 AE 신호의 각 변수와 응력확대계수와의 관계를 고찰하였다. 통계분석 방법인 변수선택법을 적용한 결과 AE 카운트(RC), 에너지(EN), 신호지속시간(ED)의 각각에 대한 유의성이 높은 것으로 나타났으나 전반적으로 전체 AE 변수를 모두 이용할 경우 통계적 유의성이 높은 것으로 나타났다. 부재의 반복하중 시 발생하는 피로균열진전을 정량적으로 도출할 수 있는 응력확대계수 추정모델을 개발하고 평가하였다. 미지 시료에 대하여 개발된 모델의 응력확대계수 예측 성능을 분석한 결과 주성분 회귀모델과 인공신경망 모델 모두 우수한 예측성능을 나타내었으나 전반적으로 인공신경망 모델이 주성분 회귀모델보다 다소 양호한 것으로 분석되었 다. The aim of this study is to develop the methodology which enables to identify the mechanical properties of element such as stress intensity factor by using the AE parameters. Considering the multivariate and nonlinear properties of AE parameters such as ringdown count, rise time, energy, event duration and peak amplitude from fatigue cracks of machine element, the principal component regression(PCR) and artificial neural network(ANN) models for the estimation of stress intensity factor were developed and validated. The AE parameters were found to be very significant to estimate the stress intensity factor. Since the statistical values including correlation coefficients, standard error of calibration, standard error of prediction and bias were stable, the PCR and ANN models for stress intensity factor were very robust. The performance of ANN model for unknown data of stress intensity factor was getter than that of PCR model.

응력확대계수와 음향방출 변수를 이용한 피로균열 거동 연구

윤동진,정중채,박휘립,김기복,이승석 한국비파괴검사학회 2000 한국비파괴검사학회지 Vol.20 No.5

응력확대계수와 음향방출 발생 관계를 이용해 균열 길이 및 균열 검출 능력을 평가할 수 있는 새로운 접근 방법을 파괴역학적인 관점에서 제시하였다. 이를 위해 강 교량 부재인 SWS 490B 강의 피로 균열 활동도를 음향방출시험을 통해 관찰하였다. 표준 CT 시편에 대한 피로균열 진전 시 AE 특성을 관찰하는 실험을 진행하였으며, 기존의 AE 파라미터 분석은 물론 응력확대계수와 AE 발생거동 사이의 관계를 논의하였다. CT 시편 실험 결과에서 균열 성장 길이, AE 최대진폭, AE 에너지, AE hit 발생율 등과 같은 특정 변수들은 응력확대계수 값이 증가함에 따라 이들값도 증가하는 경향을 나타내었다. 또한 피로사이클 수에 따른 AE 에너지의 변화는 균열진전에 대한 활동성을 평가하는데 사용되는 효과적인 변수중의 하나임을 보여 주었으며, AE 에너지 분석은 균열 활동도와 AE 변수 사이의 관계를 평가하는데 사용될 수 있을 것으로 판단된다. By using the relation between stress intensity factor and AE parameter, new approach method for assessing the crack length and detectability of crack was proposed. Laboratory experiment was carried out to identify AE characteristics of fatigue cracks for compact tension specimen. The relationship between a stress intensity factor and AE signals activity as well as conventional AE parameter analysis was discussed. As a result, the features of specific parameters such as the length of crack growth, the AE energy, the AE peak amplitude, and the cumulative AE hits, showed the almost same trend in their increase as the number of fatigue cycle increased. From the comparisons of peak amplitude and AE energy with stress intensity factor, it was verified that the higher stress intensity factors generated AE signals with higher peak amplitude and a larger number of AE counts. If we can get more reliable database for the relation between AE parameters and stress intensity factor, this approach will provide a good information for evaluating both the existence of crack and the minimum detectable size of crack.

Performance Evaluation of Volt-Var Control with Distributed Renewable Energy Resources in Power Distribution System

Phi-Hai Trinh(트린피하이),Yung-Su Cho(조용수),A-Eon Han(한아언),Il-Yop Chung(정일엽),Jaesung Sim(심재성),MinHo Ban(반민호),Seong-soo Cho(조성수) 대한전기학회 2022 대한전기학회 학술대회 논문집 Vol.2022 No.7

Antithrombotic Phenolics from the Stems of Parthenocissus tricuspidata Possess Anti-inflammatory Effect

Phi-Hung Nguyen,Bing Tian Zhao,이정형,김영호,민병선,우미희 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.6

In the course of our program to search for antithrombotic and anti-inflammatory agents from plants, twelve phenolics (1–12) were isolated from the stems of Parthenocissus tricuspidata. Their structures were elucidated on the basis of spectroscopic (1D and 2D NMR, and MS) data analyses, and comparison with published data. At the concentration of 100 μg/mL, compounds 2, 4, 6 and 10 possessed potential effects on anti-blood coagulation, with inhibitory percentage of 216, 174, 148 and 225%, respectively; while aspirin used as positive control showed 181% inhibition at the same concentration. Furthermore, the anti-inflammatory activity of isolated compounds (1–12) was investigated on lipopolysaccharide (LPS)-induced murine macrophage cells (RAW264.7). Compounds 2, 4 and 6 also potential inhibited the production of nitric oxide, with IC50 values of 11.9 ± 0.3, 2.9 ± 0.2 and 29.0 ± 0.6 μM, respectively. Celastrol, the positive control used, gave an IC50 value of 1.0 ± 0.1 μM.

Simulation Method for the Performance of an Adjustable-Preload Spindle with Cutting Force

Phi Tran Van,Jongyoup Shim,Jooho Hwang,Jeong-Seok Oh 한국생산제조학회 2016 한국생산제조시스템학회 학술발표대회 논문집 Vol.2016 No.10

Modeling and Controlling the Descent Operation of a Fish Robot using Neural Networks

Phi Luan Nguyen,Byung Ryong Lee,Kyung Kwan Ahn 제어로봇시스템학회 2015 제어로봇시스템학회 국제학술대회 논문집 Vol.2015 No.10

This paper presents a neural networks model (NNM) and for modeling and identifying the nonlinear behavior of a fish robot. Firstly, a set of driving moment signals were applied to the fish robot in order to investigate the fish robot operation. Consequently, a neural networks model was constructed and an identification scheme based on Genetic Algorithm was developed. Validation results proved the ability of proposed scheme to tracking the descent operation of the fish robot. The combination of PID controller and NNM was implemented and successfully control fish robot follow given trajectories.

Moyamoya Syndrome : A Window of Moyamoya Disease

Phi, Ji Hoon,Wang, Kyu-Chang,Lee, Ji Yeoun,Kim, Seung-Ki The Korean Neurosurgical Society 2015 Journal of Korean neurosurgical society Vol.57 No.6

Moyamoya-like vasculopathy develops in association with various systemic diseases and conditions, which is termed moyamoya syndrome. Relatively common diseases and conditions are related to moyamoya syndrome, including neurofibromatosis type 1, Down syndrome, thyroid disease, and cranial irradiation. Moyamoya syndrome shares phenotypical characteristics with idiopathic moyamoya disease. However, they differ in other details, including clinical presentations, natural history, and treatment considerations. The study of moyamoya syndrome can provide clinicians and researchers with valuable knowledge and insight. Although it is infrequently encountered in clinical practice, moyamoya-like vasculopathy can severely complicate outcomes for patients with various underlying diseases when the clinician fails to expect or diagnose moyamoya syndrome development. Furthermore, moyamoya syndrome could be used as a doorway to more enigmatic moyamoya disease in research. More comprehensive survey and investigation are required to uncover the secrets of all the moyamoya-like phenomena.

Sacrococcygeal Teratoma : A Tumor at the Center of Embryogenesis

Phi, Ji Hoon The Korean Neurosurgical Society 2021 Journal of Korean neurosurgical society Vol.64 No.3

Sacrococcygeal teratoma (SCT) is an extragonadal germ cell tumor (GCT) that develops in the fetal and neonatal periods. SCT is a type I GCT in which only teratoma and yolk sac tumors arise from extragonadal sites. SCT is the most common type I GCT and is believed to originate through epigenetic reprogramming of early primordial germ cells migrating from the yolk sac to the gonadal ridges. Fetal SCT diagnosed in utero presents many obstetrical problems. For high-risk fetuses, fetal interventions (devascularization and debulking) are under development. Most patients with SCT are operated on after birth. Complete surgical resection is the key for tumor control, and the anatomical location of the tumor determines the surgical approaches. Incomplete resection and malignant histology are risk factors for recurrence. Approximately 10-15% of patients have a tumor recurrence, which is frequently of malignant histology. Long-term surveillance with monitoring of serum alpha fetoprotein and magnetic resonance imaging is required. Survivors of SCT may suffer anorectal, urological, and sexual sequelae later in their life, and comprehensive evaluation and care are required.

Clinical and Anatomic Features of Supraglandular Pituitary Adenomas

Phi, Ji Hoon,Kim, Yong Hwy,Kim, Jung Hee,Kim, Dong Gyu Elsevier 2016 World neurosurgery Vol.92 No.-

<P><B>Objective</B></P> <P>Supraglandular pituitary adenoma (SGPA) is one of the extraordinary pituitary adenomas and shows different clinical and radiologic features. We retrospectively reviewed our cases of SGPAs to elucidate the radiologic, anatomic, and clinical features.</P> <P><B>Methods</B></P> <P>We identified 9 patients with pathologically proven SGPA and classified them into 2 groups radiologically: either glandular or stalk types. Magnetic resonance images were correlated with intraoperative anatomic differences between the groups. Clinical and endocrinologic characteristics and surgical outcomes were reviewed.</P> <P><B>Results</B></P> <P>The proportion of SGPAs was 1.2% of all pituitary adenomas surgically treated in our patient cohort. The glandular-type tumors (<I>n</I> = 7) had a thinned or defective diaphragma sellae. There was a clear plane between the tumor and pituitary stalk. For the stalk-type tumors (<I>n</I> = 2), the diaphragma sellae was intact and no clear border between the mass and stalk was found. Endocrinologic and immunohistochemical evaluation showed that 5 of 7 glandular-type tumors (71%) were functioning pituitary adenomas, whereas 2 stalk-type tumors were nonfunctioning. Eight of 9 patients underwent an endoscopic endonasal approach and tumor was totally removed in 7 (78%).</P> <P><B>Conclusions</B></P> <P>SGPAs are rare and preoperative diagnosis is possible based on their distinct radiologic, clinical, and anatomic features. SGPAs can be divided into 2 groups according to the anatomic features. The origin of tumor, whether the superior surface of the gland or the pituitary stalk, determined the location, extent, and relationship with the diaphragma sellae. The surgical outcome via an endoscopic endonasal approach was favorable.</P>