http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
후두와 혈관아세포종의 방사선학적 소견: MR 소견을 중심으로
김선교 대한영상의학회 1995 대한영상의학회지 Vol.32 No.3
Purpose: To review MR findings of the posterior fossa hemangioblastomas and to evaluate diagnostic value of MRI correlated with CT and angiographic findings. Materials and Methods: The MR findings in twelve patients with surgically proven posterior fossa hemangioblastomas including one case of von Hippel- Lindau disease were retrospectively analyzed and correlated with CT (7 patients) and angiographic findings (9 patients). Results: On MRI, five hemangioblastomas were located in the cerebellar hemisphere and seven in the vermis. The masses appeared to be solid in 3 cases(25%), solid tumors with central cyst in 2 cases(17%), and cyst with mural nodules in 7cases(58%). Abnormal tumor vessels represented by characteristic signal voids on MRI were observed in 9 cases(75%) and were not seen in 3 cases(25%) with mural nodule below 1.5 cm in diameter. On pre-contrast CT, hemangioblastomas appeared poorly marginated slightly hyperdense masses in solid tumors, and hypodense cystic masses in cysts. After contrast enhancement, solid tumors were markedly enhanced, but it was difficult to differentiate hemangioblastomas from other tumors. In nine patients, angiograms demonstrated hypervascular blush corresponding to the solid component of the tumors. Conclusion: MRI was superior to CT in evaluating the characteristic of abnormal tumor vessels and mural nodules, delineation of tumor margin and tumor extent. Angiography was useful in the diagnosis of cystic hemangioblastomas which contain small mural nodule (less than1.5 cm in diameter) without definite vascular signal voids on MRI. MRI demonstrated solid or cystic tumor with small mural nodule and abnormal vascular signal voids in the posterior fossa should suggest hemangioblastoma.
A Simulation Study on the Variability Function of the Arrival Process in Queueing Networks
김선교,Kim, Sun-Kyo The Korea Society for Simulation 2011 한국시뮬레이션학회 논문지 Vol.20 No.2
본 연구에서는 대기행렬네트워크 성과측정 방법 중의 한 가지로서 널리 이용되는 분해법의 구성요소로 제안된 변동성 함수 의 이론적 근거를 살펴보고 성과척도 측정의 정확도 제고를 위하여 회귀분석을 통한 변동성 함수의 모수추정 개선방안을 제안하고자 한다. 이를 위하여 변동성이 높은 도착과정과 서비스 과정이 포함된 직렬 대기행렬 네트워크에서의 이탈과정의 자동상관계수 함수를 추정하여 분해법에 사용할 수 있는 방안을 알아본다. In queueing network analysis, arrival processes are usually modeled as renewal processes by matching mean and variance. The renewal approximation simplifies the analysis and provides reasonably good estimate for the performance measures of the queueing systems under moderate conditions. However, high variability in arrival process or in service process requires more sophisticated approximation procedures for the variability parameter of departure/arrival processes. In this paper, we propose an heuristic approach to refine Whitt's variability function with the k-interval squared coefficient of variation also known as the index of dispersion for intervals(IDI). Regression analysis is used to establish an empirical relationships between the IDI of arrival process and the IDI of departure process of a queueing system.
Counting Process of MAP(3)s and Moment Fittings
김선교,Kim, Sunkyo The Korean Operations Research and Management Scie 2017 한국경영과학회지 Vol.3 No.1
Moments of stationary intervals and those of the counting process can be used for moment fittings of the point processes. As for the Markovian arrival processes, the moments of stationary intervals are given as a polynomial function of parameters whereas the moments of the counting process involve exponential terms. Therefore, moment fittings are more complicated with the counting process than with stationary intervals. However, in queueing network analysis, cross-correlation between point processes can be modeled more conveniently with counting processes than with stationary intervals. A Laplace-Stieltjies transform of the stationary intervals of MAP (3)s is recently proposed in minimal number of parameters. We extend the results and present the Laplace transform of the counting process of MAP (3)s. We also show how moments of the counting process such as index of dispersions for counts, IDC, and limiting IDC can be used for moment fittings. Examples of exact MAP (3) moment fittings are also presented on the basis of moments of stationary intervals and those of the counting process.
Jordan Representation of the Markovian Arrival Process of Order 2 and Moments Fitting
김선교 한국경영과학회 2020 한국경영과학회지 Vol.45 No.1
The Markovian arrival process can be represented in different ways. The most intuitive way is the Markovian representation with two transition rate matrices (D0, D1). Markovian arrival processes can be represented by the Laplace transform or the moments of the stationary intervals. In this study, we consider the Jordan representation specifically for the Markovian arrival process of order 2. The Jordan representation is also given in two matrices (E, R). However, the Jordan representation is minimal, whereas the Markovian representation is not. We present closed-form Jordan representations for the Markovian arrival process of order 2 in terms of moments and parameters of other representations. The transformation between the Jordan and other representations including the Markovian representation, the Laplace transform, and characteristic polynomial coefficients is also presented.