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김국현,성우제,Kim, Kook-Hyun,Seong, Woo-Jae 한국음향학회 1996 韓國音響學會誌 Vol.15 No.2
본 논문에서는 2차원 양방향 포물선 방정식 법과 푸리에 변환을 이용하여 3차원 굴절현상 및 3차원 후방 산란파를 포함하는 $2\frac12$차원 문제를 푸는 방법에 대해 다루었다. 여기서 $2\frac12$ 차원 문제란 2차원적 해양환경 하에 3차원적 음원이 존재할 경우를 의미한다. 2차원 양방향 포물선 방정식법은 수치기법으로 깊이 방향과 수평거리 방향에 대해 각각 Galerkin법과 Crank-Nicolson법을 사용하며 수직 불연속 경계면에 의한 후방 산란파를 포함한 수평거리 의존 문제에 대해 유용한 해를 제공한다. 2차원 해양환경에서는 파수 k가 종 또는 횡 수평거리 방향과 깊이 방향에 대한 함수이므로 3차원 Helmholtz방정식 법을 이용해 스펙트럴 해를 구하여 다시 푸리에 역변환하면 최종 해를 구할 수 있다. 본 연구방법의 정확성을 시험하기 위해서 계단형 해저면을 갖는 간단한 해양환경에서 계산을 수행해 보았으며 대한해협의 특정지역에서의 3차원적 음파전달 특성을 살펴보았다. This thesis deals with a method to solve a two-and-one-half-dimensional ($2\frac12$ D) problem, which means that the ocean environment is two-dimensional whereas the source is fully three-dimensionally propagating, including three-dimensional refraction phenomena and three-dimensional back-scattering, using two-dimensional two-way parabolic equation method combined with Fourier synthesis. Two dimensional two-way parabolic equation method uses Galerkin's method for depth and Crank-Nicolson method and alternating direction for range and provides a solution available to range-dependent problem with wave-field back-scattered from discontinuous interface. Since wavenumber, k, is the function of depth and vertical or horizontal range, we can reduce a dimension of three-dimensional Helmholtz equation by Fourier transforming in the range direction. Thus transformed two-dimensional Helmholtz equation is solved through two-way parabolic equation method. Finally, we can have the $2\frac12$ D solution by inverse Fourier transformation of the spectral solution gained from in the last step. Numerical simulation has been carried out for a canonical ocean environment with stair-step bottom in order to test its accuracy using the present analysis. With this spectral parabolic equation method, we have examined three-dimensional acoustic propagation properties in a specified site in the Korean Straits.
김국현,조대승,김진형,Kim, Kook-Hyun,Cho, Dae-Seung,Kim, Jin-Hyeong 한국군사과학기술학회 2007 한국군사과학기술학회지 Vol.10 No.3
The high-frequency analysis method of back-scattering cross section spectrum of rotating targets is established. The time history of the back-scattering cross section is calculated using a quasi-stationary approach, based on a physical optics and a physical theory of diffraction, combining an adaptive triangular beam method to consider the shadow effect. And the spectra of back-scattering cross section by the Doppler effect are analyzed applying a simple fast Fourier transform method to its time history. The numerical calculation for rotating targets, such as rotating metal plates and underwater propeller, are carried out. The time history appears to be periodic with respect to the number of wings. The backscattering cross section spectrum level and its frequency shift are dependent on the rotating speed, direction, and the shape of the targets.
김국현,조대승,성우제,Kim, Kook-Hyun,Cho, Dae-Seung,Seong, Woo-Jae 한국음향학회 2008 韓國音響學會誌 Vol.27 No.3
본 연구에서는 물리광학법 (physical optics)과 푸리에 변환 (Fourier transform)을 바탕으로 잠수함과 같이 크고 형상이 복잡한 수중표적의 시간영역 음파 후방산란 신호를 모의하기 위한 수치해석방법을 구현하였다. 키르코프-헬름홀쯔 적분식 (Kirchhoff-Helmholtz integral equation)에 키르코프 근사이론 (Kirchhoff approximation)을 적용하여 유도한 물리광학법을 바탕으로 수중표적의 후방산란 음파에 대한 주파수 응답을 계산하였으며, 시간영역 신호모의를 위해 구해진 주파수응답에 고속 역푸리에 변환 (inverse fast Fourier transform)을 취하였다. 입사 음파의 직접조사 면적을 산정하기 위한 적응 삼각형 빔 방법과 다중반사 효과를 고려하기 위한 가상면 개념을 도입하였다. 평면 음파가 정사각형 평판에 수직으로 입사하는 경우에 대한 수치해석 결과를 시간영역 물리광학법에 근거한 해석해와 비교하여 본 연구에서 구현한 수치해석방법의 정확성을 검증하였으며, 반구형 원통모델에 대한 수치모의 결과를 측정결과와 비교하여 본 연구방법이 거울반사 (specular reflection) 효과가 우세한 경우에 유효한 해를 제공할 수 있으나 작은 표적에 대해서는 오차를 줄 수 있음을 확인하였다. 또한, 이상화된 잠수함 모델에 대한 수치해석을 통해 실제 수중표적에 대한 시간영역 후방산란 해석으로의 적용 가능성을 확인하였다. In this study, a numerical method for a time-domain acoustic wave backscattering analysis is established based on a physical optics and a Fourier transform. The frequency responses of underwater targets are calculated based on physical optics derived from the Kirchhoff-Helmholtz integral equation by applying Kirchhoff approximation and the time-domain signals are simulated taking inverse fast Fourier transform to the obtained frequency responses. Particularly, the adaptive triangular beam method is introduced to calculate the areas impinged directly by acoustic incident wave and the virtual surface concept is adopted to consider the multiple reflection effect. The numerical analysis result for an acoustic plane wave field incident normally upon a square flat plate is coincident with the result by the analytic time-domain physical optics derived theoretically from a conventional physical optics. The numerical simulation result for a hemi-spherical end-capped cylinder model is compared with the measurement result, so that it is recognized that the presented method is valid when the specular reflection effect is predominant, but, for small targets, gives errors due to higher order scattering components. The numerical analysis of an idealized submarine shows that the established method is effectively applicable to large and complex-shaped underwater targets.
음향방사문제에서 직접경계요소법의 비유일성 회피방법에 관한 고찰
김국현(Kim, Kook-Hyun) 한국산학기술학회 2010 한국산학기술학회논문지 Vol.11 No.7
직접경계요소법은 음향방사문제 해석에 널리 적용되는 수치해석기법중 하나이지만, 외부 음향방사 문제에 있 어서는 방사면 내부공간의 고유주파수 근방에서 비유일성이 나타나게 된다. 이를 해결하기 위한 방법으로 CHIEF 방 법이 일반적으로 적용되어 왔으며, 최근 들어서는 ICA-Ring 방법과 같은 새로운 기법이 제안되어 해의 정확도 향상 에 기여하고 있다. 본 논문에서는 앞서 언급한 두 가지 비유일성 회피기법들의 특성을 살피고, 각각의 기법 구현을 포함한 직접경계요소법 기반의 수치해석 코드를 작성한다. 또한, 법선방향 균일속도로 진동하는 구의 음향방사문제에 대한 수치해석을 수행하고 그 결과를 해석 해와 비교하여 각각의 기법들에 대한 비유일성 회피 성능을 고찰한다. A direct boundary element method(DBEM) is widely applied for various acoustic wave problems. But this method has numerically non-unique solutions around the eigenfrequencies of the interior Dirichlet problem for the region enveloped with the acoustic boundary. A CHIEF method had been generally adopted to resolve the non-uniqueness problem and a new technique called ICA-Ring method has been suggested recently. In this paper, the characteristics of two techniques for avoiding the non-uniqueness of DBEM are examined and numerical codes embodying both techniques are developed. Numerical calculations are also carried out for an uniformly pulsating sphere, of which the results are investigated by including the comparisons with theoretical solutions.
증례 : 대장에서 발생한 혈관주위 상피모양세포 종양 1예
김국현 ( Kook Hyun Kim ),장병익 ( Byung Ik Jang ),김태년 ( Tae Nyeun Kim ),장재천 ( Jae Chun Jang ),심민철 ( Min Chul Shim ),심영란 ( Young Ran Shim ),최준혁 ( Joon Hyuk Choi ) 대한내과학회 2007 대한내과학회지 Vol.72 No.5
혈관주위 상피모양세포 종양(PEComa)은 여러 장기의 중간엽에서 발생하며 조직학적으로 상피모양세포를 가지는 종양을 총칭하는 드문 질환이다. 저자들은 1개월 간의 좌상복부 불편감과 발열을 주소로 내원한 환자를 대장에서 유래하는 악성 GIST로 의심하고 수술을 시행한 후, 절제된 조직의 면역조직화학염색검사에서 멜라닌세포 표지자인 HMB-45에 강한 양성 염색을 보여 GIST가 아닌 PEComa로 확진한 1예를 경험하였기에 문헌고찰과 함께 보고한다. Perivascular epithelioid cell tumor (PEComa) is a rare family of related mesenchymal neoplasms that include angiomyolipoma, lymphangiomyomatosis and clear cell `sugar` tumor of the lung. Although this type of tumor has been described in the literature in organs such as kidney, lung, uterus and urinary bladder, there are few reports of gastrointestinal tract-related tumor. We report here on a case of PEComa arising in the transverse colon. This occurred in a 41-year-old male who had no history of tuberous sclerosis complex. Histopathologically, the tumor consisted of nests or sheets of epithelioid cells with eosinophilic cytoplasm. The tumor cells were positive for HMB-45, vimentin and caldesmon, but they were negative for S-100 protein, cytokeratin and CD117, according to immunohistochemical staining. Careful follow up is warranted because the biological behavior of PEComa has not yet been documented. We present here a case of colonic PEComa that was confirmed by immunohistochemical staining and the histopathologic findings, and we include a review of the literature. (Korean J Med 72:540-545, 2007)
김국현 ( Kook Hyun Kim ),김왕복 ( Wang Bok Kim ),김근세 ( Keunsei Kim ) 성균관대학교 국정관리대학원 2010 국정관리연구 Vol.5 No.2
이 연구는 지금까지 한국의 국가발전 과정에서 행정이 어떠한 기능을 수행하였는지 검토하였다. 그리고 미래 행정환경의 변화에 대응하여 어떠한 국가행정의 패러다임이 요구되는지 제안하였다. 구체적으로, 첫째, 시민사회의 참여와 협조를 기본정신으로 하는 거버넌스 체제를 발전시켜야 하고, 둘째, 시민사회가 거버넌스 체제 하에서 충분한 전문적 지식을 가지고 정부를 지원하고 협력할 수 있도록 지원해 나가야 하며, 마지막으로 국민들 간에 ‘사회적 신뢰’라는 사회적 자본이 축적될 수 있도록 행정 관료들의 과감한 의식개혁이 선행되어야 한다. This paper reviews the role of public administration in the process of the state development in Korea, and suggests several recommendations for a new paradigm of Public Administration in the future. First, it emphasizes new governance framework to foster participation and cooperation of the civil society. Second, it posits that the civil society that has sufficient professional capabilities cooperates with government. Third, it needs substantial attitude change of bureaucrats to understand the importance of social capital aspects of the civil society.
김국현 ( Kook Hyun Kim ),최재원 ( Jae Won Choi ),이지은 ( Ji Yun Lee ),김태동 ( Tae Dong Kim ),백종해 ( Jong Hae Paek ),이은주 ( Eun Ju Lee ),오현아 ( Hyun A Oh ),김준환 ( Jun Hwan Kim ),장병익 ( Byeong Ik Jang ),김태년 ( Tae Nyeu 대한소화기학회 2005 대한소화기학회지 Vol.45 No.3
Metronidazole is a 5-nitroimidazole compound known as an antimicrobial agent widely used for the treatment of protozoal infection, anaerobic infection, Helicobacter pylori infection and hepatic encephalopathy. It may produce a number of neurologic side ef
혈액담즙증의 병인, 임상적 특징 및 내시경적 치료: 37예의 후향적 분석
김국현 ( Kook Hyun Kim ),김태년 ( Tae Nyeun Kim ) 대한소화기학회 2012 대한소화기학회지 Vol.59 No.4
Background/Aims: Hemobilia is a rare cause of upper gastrointestinal bleeding. Endoscopic retrograde cholangiopancreaticography (ERCP) is considered to be an excellent diagnostic and treatment modality. Thirty-seven cases of hemobilia with different underlying pathologies were analyzed to illustrate clinical features and to evaluate the role of endoscopic management. Methods: A total of 37 patients (26 men and 11 women; mean age, 66.2±15.3 years) who were confirmed to have hemobilia by ERCP in a single center from 2000 to 2010 were reviewed retrospectively. Patients with iatrogenic causes of hemobilia were excluded in this study. Results: The causes of hemobilia were hepatocellular carcinoma in 14, bile duct and gallbladder malignancies in 12, common bile duct stones with cholangitis in 4, acute cholecystitis in 4, and pancreatic cancer in 2 patients. The clinical features of hemobilia were jaundice (89.2%), abdominal pain (78.4%), and melena (13.5%). The cholangiographic findings of hemobilia were amorphous filling defects in 15, tubular filling defects in 6, and cast-like filling defects in 6 patients. Endoscopic management included endoscopic nasobiliary drainage in 26 patients and endoscopic retrograde biliary drainage in 7 patients. Biliary obstruction caused by hemobilia was successfully treated with endoscopic biliary drainages in most cases. Conclusions: The most common non-iatrogenic causes of hemobilia were hepatobiliary malignancies, and the majority of patients presented with jaundice and abdominal pain. Endoscopic biliary drainage is recommended as the initial management to control biliary obstruction. (Korean J Gastroenterol 2012;59:296-302)
김국현 ( Kook Hyun Kim ) 영남대학교 의과대학 2016 Yeungnam University Journal of Medicine Vol.33 No.2
Pancreatic cancer, the 4th leading cause of cancer-related death in the United States, has a very poor prognosis. Cholangiocarcinoma originates from either intrahepatic or extrahepatic bile duct, and its incidence is gradually increasing worldwide. Endoscopic retrograde cholangiopancreatography with brush cytology has a high false-negative rate for the diagnosis of biliary malignancy. Recently, endoscopic ultrasonography (EUS) has emerged as the potential modality to detect pancreatic cancer. EUS-guided fine needle aspiration for cytologic analysis made it possible to overcome the obstacle in differentiating between benign and malignant lesions in the pancreatobiliary lesion, and it has been well established as a safe and effective procedure. Herein, the clinical application of EUS in the diagnosis of pancreatobiliary cancer was reviewed.