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.

Corrigendum to "Clinical Features and Treatment of Pediatric Cerebral Cavernous Malformations" by Phi et al. (J Korean Neurosurg Soc 67 : 299-307, 2024)

Ji Hoon Phi The Korean Neurosurgical Society 2024 Journal of Korean neurosurgical society Vol.67 No.4

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

Vessel Wall Imaging in Angiogram-Negative Diffuse Subarachnoid Hemorrhage Reveals a Ruptured Lenticulostriate Aneurysm

Phi Huy Quang,Alkhatib Suehyb Ghazi,Raymond Scott Bruce,Choudhri Omar Aftab,Song Jae Won 대한신경중재치료의학회 2024 Neurointervention Vol.19 No.2

A patient presented with acute onset headache and subsequent unconsciousness. The neurologic exam showed left-sided myoclonic jerking and right flaccid hemiparalysis. Noncontrast computed tomography revealed diffuse subarachnoid hemorrhage (SAH) with acute hydrocephalus. Initial digital subtraction angiography (DSA) showed no culprit source for SAH. Repeat DSA on day 7 after initial presentation raised suspicion for left internal carotid artery ophthalmic segment and left lateral lenticulostriate artery (LSA) aneurysms. A magnetic resonance vessel wall imaging (VWI) exam was performed given the presence of multiple potential culprit aneurysms. Vessel wall enhancement around the dome of the left LSA aneurysm suggested rupture, which then facilitated treatment with surgical clipping. LSA aneurysms are exceedingly rare and challenging to treat. Given the associated high degree of morbidity, expedient diagnosis is critical to direct management. VWI could be a valuable tool for detecting ruptured aneurysms in the setting of angiogram-negative SAH.

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>

Epilepsy Surgery in 2019 : A Time to Change

Phi, Ji Hoon,Cho, Byung-Kyu The Korean Neurosurgical Society 2019 Journal of Korean neurosurgical society Vol.62 No.3

Epilepsy has been known to humankind since antiquity. The surgical treatment of epilepsy began in the early days of neurosurgery and has developed greatly. Many surgical procedures have stood the test of time. However, clinicians treating epilepsy patients are now witnessing a huge tide of change. In 2017, the classification system for seizure and epilepsy types was revised nearly 36 years after the previous scheme was released. The actual difference between these systems may not be large, but there have been many conceptual changes, and clinicians must bid farewell to old terminology. Paradigms in drug discovery are changing, and novel anti-seizure drugs have been introduced for clinical use. In particular, drugs that target genetic changes harbor greater therapeutic potential than previous screening-based compounds. The concept of focal epilepsy has been challenged, and now epilepsy is regarded as a network disorder. With this novel concept, stereotactic electroencephalography (SEEG) is becoming increasingly popular for the evaluation of dysfunctioning neuronal networks. Minimally invasive ablative therapies using SEEG electrodes and neuromodulatory therapies such as deep brain stimulation and vagus nerve stimulation are widely applied to remedy dysfunctional epilepsy networks. The use of responsive neurostimulation is currently off-label in children with intractable epilepsy.

Direct Adaptive Fuzzy Control with Less Restrictions on the Control Gain

Phi Anh Phan,Timothy J. Gale 제어로봇시스템학회 2007 International Journal of Control, Automation, and Vol.5 No.6

A Design of Free Velocity Bias for GPS Receiver

Phi-Long Nguyen,Hyunsoo Kim(김현수),Hansil Kim 대한전기학회 2007 Journal of Electrical Engineering & Technology Vol.2 No.4

This paper proposes a 2-step Kalman filter model for land vehicle navigation using civilian-band GPS measurements. The velocity bias caused by the Earth's rotation would be removed completely when applying this model. Because the linearization of velocity equations in this model is not necessary, the error is significantly reduced. The experiment reveals that estimated position error with stationary data is about 5m during a 15-20 minute interval. The other benefit of this model is that it can be feasibly applied as a GPS receiver module thanks to the small sizes of the necessary manipulating matrices.