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.

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.

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.

A Grey MCDM Based on DEMATEL Model for Real Estate Evaluation and Selection Problems: A Numerical Example

Phi-Hung NGUYEN,Jung-Fa TSAI,Thanh-Tam NGUYEN,Thi-Giang NGUYEN,Dang-Duong VU 한국유통과학회 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.11

Real estate markets play an essential role in the economic development of both developed and developing countries. Investment decisions in private real estate demand the consideration of several qualitative and quantitative criteria. Especially in Vietnam, demand for housing, apartments are rising which has resulted because of the migration from rural to urban areas. This study aims to determine the influencing factors of the real estate purchasing behavior and then recommend a grey Multi-Criteria Decision Making (MCDM) support model to evaluate real estate alternatives based on a numerical example in Vietnam. A set of essential criteria are identified based on experts’ opinion, and the proposed determinants are initial investment, maintenance cost, prestige location, distance to interesting places, parking lot, public transportation, property condition, total area size, number of rooms, and neighbors. The subjective weights were obtained by using the Decision-Making Trial and Evaluation Laboratory (DEMATEL) model, and the Grey Relational Analysis (GRA) technique is employed to prioritize and rank real estate alternatives. The results reveal that this approach can be useful to make purchasing decisions for many kinds of real estate property under uncertain business environments. These findings indicate that the presented hybrid model has advantages in granting flexibility to the preferences of decision makers.

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>

Germinomas in the basal ganglia: magnetic resonance imaging classification and the prognosis

Phi, Ji Hoon,Cho, Byung-Kyu,Kim, Seung-Ki,Paeng, Jin Chul,Kim, In-One,Kim, Il Han,Kim, Dong Gyu,Jung, Hee-Won,Kim, Jeong Eun,Wang, Kyu-Chang Springer-Verlag 2010 Journal of neuro-oncology Vol.99 No.2

Atypical cell clusters expressing both neuronal and oligodendrocytic markers: Novel histological pattern of glioneuronal tumors?

Phi, Ji Hoon,Park, Sung-Hye,Chung, Chun Kee,Wang, Kyu-Chang,Cho, Byung-Kyu,Kim, Seung-Ki Blackwell Publishing Asia 2009 Pathology international Vol.59 No.10

<P>Glioneuronal tumors are a group of brain tumors that consist of both neuronal and glial cells. The spectrum of glioneuronal tumors is currently expanding, and many atypical glioneuronal tumors require further characterization. Two patients are described who had an atypical glioneuronal tumor with peculiar pathological features. One patient was a 7-year-old girl with a tumor in the right cerebellar hemisphere. This patient had no recurrence after total resection. The other was a 37-year-old man with a tumor in the spinal cord. He suffered incessant recurrence and received operative treatment four times. Although the clinical features (age at diagnosis, tumor location, and recurrence) were very different in these patients, the tumors had a characteristic common feature of atypical cell clusters. Intriguingly, the tumor cells in the clusters expressed both neuronal and oligodendroglial markers, indicating aberrant differentiation. Furthermore, the cluster-forming cells had modest proliferative indices and CD133 expression, indicating their role in the growth of the tumor. It is believed that these atypical cell clusters are a novel pattern of differentiation of glioneuronal tumors and that they need further investigation.</P>

Long-term social outcome in children with moyamoya disease who have reached adulthood

Phi, Ji Hoon,Wang, Kyu-Chang,Cho, Byung-Kyu,Lee, Myung Sook,Lee, Jong-Hwa,Yu, Kyung-Sang,Hahm, Bong-Jin,Kim, Seung-Ki Journal of Neurosurgery Publishing Group 2011 Journal of Neurosurgery: Pediatrics Vol.8 No.3

<B>Object</B><P>Although the reported surgical outcome is favorable, there is little information regarding the long-term quality of life in pediatric patients with moyamoya disease (MMD) when they grow to adulthood. The authors conducted a survey to provide details of social adaptation and satisfaction in adults who underwent revascularization surgery for MMD during childhood.</P><B>Methods</B><P>One hundred twenty-three patients with MMD who had undergone surgery during childhood and were older than 18 years of age were recruited for this study. The authors mailed self-administered questionnaires regarding each patient's education, employment, marriage, driver's license, physical condition, and satisfaction. Sixty-five patients (53%) responded.</P><B>Results</B><P>Compared with the general population, the patients showed a similar rate of attaining a higher education. Forty-nine (80%) of 61 patients who were not currently high school students had entered college or university. However, the presence of neurological deficits on preoperative examination was a negative predictor of entrance into a college or university, as well as employment. Some patients had difficulty in planning marriage because of physical handicaps, and the rate of acquiring a driver's license and actual driving were relatively low. Approximately 80% of the responders were satisfied with their treatment outcomes, but more than one-half reported subjectively assessed neurological problems.</P><B>Conclusions</B><P>In this study, pediatric patients with MMD showed favorable social adaptation in adulthood. The findings also indicated that early diagnosis and intervention before the establishment of neurological deficits are essential to children with MMD in becoming better socially adapted. Further, more thorough clinical examinations are required during follow-up in patients with MMD.</P>

Tumors in the cerebellopontine angle in children: warning of a high probability of malignancy.

Phi, Ji Hoon,Wang, Kyu-Chang,Kim, In-One,Cheon, Jung-Eun,Choi, Jung Won,Cho, Byung-Kyu,Kim, Seung-Ki M. Nijhoff ; Kluwer Academic Publishers 2013 Journal of neuro-oncology Vol.112 No.3

<P>Cerebellopontine angle (CPA) tumors are uncommon in children, and the pathological spectrum is different from that of adults. In this study, we reviewed the pathological diagnosis of pediatric patients with a CPA tumor to determine the pattern in this age group. In a cohort of 267 patients with posterior fossa tumor, tumor locations were determined with preoperative magnetic resonance imaging (MRI). The pathological diagnosis, imaging characteristic, and treatment outcomes of patients with CPA tumors was reviewed and analyzed. Twenty-six patients (9.7 %) had a tumor in the CPA. The pathological spectrum was wide, from malignant intrinsic brain tumors to benign extra-axial tumors and sarcomatous lesions. Eighteen patients (69 %) had malignant tumors. The pathological nature was strongly linked to patient age. The mean age of malignant tumor group was significantly younger than that of benign tumor group. MRI findings that favored malignant histology included a plastic feature of the tumor, multiple signal voids, encasement of major arteries, widening of lateral recess, focal cerebellar edema, and hydrocephalus. The presence of seeding in the neuraxis also indicated malignant pathology. Especially, increased density on precontrast computed tomography was a strong predictor of malignant pathology. Malignant CPA tumors showed high surgical morbidity rate and grim long-term prognosis. Patient age and tumor location are the two most important clues for the diagnosis of any brain tumor. Unlike in adult patients, clinicians should expect a high probability of malignant histology for pediatric CPA tumors, especially in infants and young children.</P>

Pediatric infratentorial ependymoma: prognostic significance of anaplastic histology.

Phi, Ji Hoon,Wang, Kyu-Chang,Park, Sung-Hye,Kim, Il Han,Kim, In-One,Park, Kyung Duk,Ahn, Hyo Seop,Lee, Ji Yeoun,Son, Young-Je,Kim, Seung-Ki M. Nijhoff ; Kluwer Academic Publishers 2012 Journal of neuro-oncology Vol.106 No.3

<P>Pediatric infratentorial ependymomas are difficult to cure. Despite the availability of advanced therapeutic modalities for brain tumors, total surgical resection remains the most important prognostic factor. Recently, histological grade emerged as an independent prognostic factor for intracranial ependymoma. We retrospectively reviewed the treatment outcome of 33 pediatric patients with infratentorial ependymoma. Progression-free survival (PFS) and overall survival (OS) rates were calculated and relevant prognostic factors were analyzed. Fourteen patients (42%) were under the age of 3 at diagnosis. Gross total resection was achieved in 16 patients (49%). Anaplastic histology was found in 13 patients (39%). Adjuvant therapies were delayed until progression in 12 patients (36%). Actuarial PFS rates were 64% in the first year and 29% in the fifth year. Actuarial OS rates were 91% in the first year and 71% in the fifth year. On univariate analysis, brainstem invasion (P = 0.047), anaplastic histology (P = 0.004), higher mitotic count (P = 0.001), and higher Ki-67 index (P = 0.004) were significantly related to a shorter PFS. Gross total resection (P = 0.029) and a greater age at diagnosis (P = 0.033) were significantly related to a longer PFS. On multivariate analysis, anaplastic histology alone was significantly related to a shorter PFS (P = 0.023). Gross total resection (P = 0.039) was significantly related to a longer overall survival (OS) on multivariate analysis. Anaplastic histology and gross total resection were the most important clinical factors affecting PFS and OS, respectively. Anaplastic histology, mitotic count, and Ki-67 index can be used as universal and easily available prognostic parameters in infratentorial ependymomas.</P>