• 비파괴검사학회지
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• 제21권6호
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• pp.598-606
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• 2001

최근 전자장치의 고기능화에 따라서 반도체 장치의 고집적화는 물론 반도체 패키지의 박형화 추세에 있다. 이러한 반도체가 장치에 실장된 후에도 안정된 성능을 발휘할 수 있는지 여부에 대한 신뢰성을 보장하기 위해 조립 완료된 반도체 패키지에 대한 preconditioning 시험을 수행하게 된다. 또한 preconditioning 시험 전후에 초음파 주사 현미경을 이용한 검사를 실시함으로써 반도체 패키지에 대한 들뜸이나 패키지 크랙과 같은 내부 결함의 존재 여부를 알아보게 된다. 본 논문에서는 반도체 내부의 결함 유무를 효과적으로 검사할 수 있는 초음파를 이용한 신뢰성 평가 방법과 절차를 제시하고, preconditioning 시험 과정에서 수행되는 시험법을 통해 패키지 내부 결함을 야기하는 가장 중요한 요인이라 할 수 있는 수분에 의한 고장 메커니즘을 분명히 함으로써 반도체 패키지에 대한 일련의 고장 분석 및 신뢰성 평가 방법을 정립하고자 하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 추계 학술대회논문집
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• pp.7-14
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• 2004

It is well known that preconditioning methods are efficient for convergence acceleration at compressible low Mach number flows. In this study, the original Euler equations and three preconditioners nondimensionalized differently are implemented in two dimensional inviscid bump flows using the 3rd order MUSCL and DADI schemes as flux discretization and time integration respectively. The multigrid and local time stepping methods are also used to accelerate the convergence. The test case indicates that a properly modified local preconditioning technique involving concepts of a global preconditioning one produces Mach number independent convergence. Besides, an asymptotic analysis for properties of preconditioning methods is added.

• 한국항공우주학회지
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• 제33권8호
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• pp.8-17
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• 2005

저속 압축성 유동에서 사용하는 예조건화 기법은 수렴성 증진에 효과적이다. 본 연구에서는 일반적인 오일러 지배 방정식과 각각 다르게 무차원화한 세 가지 종류의 예조건화 기법을 3차 공간 정확도의 MUSCL, DADI, 다중 격자, 국소 시간 전진 기법을 이용하여 2차원 비점성 bump 유동에 적용하였다. 결과적으로 국소 예조건화 기법에 전역 예조건화 기법의 압력 항 무차원화 방법을 적용하면, 마하수에 무관한 수렴 특성을 얻을 수 있다. 또한, 점근해석을 이용하여 각 예조건화 기법의 특성에 대해 언급하였다.

• The Korean Journal of Physiology
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• 제29권1호
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• pp.51-59
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• 1995

This study was designed to test whether or not 1) ischemia-reperfusion attenuates endothelium-dependent relaxation of coronary arteries and 2) preconditioning protects the arterial endothelium from ischemia-reperfusion injury. In anesthetized open chest rabbits, branches of the left circumflex artery were exposed to different combinations of the experimental conditions; ischemia (15 minutes), ischemia (15 minutes)-reperfusion (10 minutes), preconditioning ischemia, and pre-conditioning fellowed by ischemia-reperfusion. Preconditioning consisted of 3 occlusions of 2-min duration, each followed by n 5-min reperfusion. Rings of the artery exposed to the experimental condition and of normal left anterior descending coronary artery were prepared and suspended for isometric force measurement in organ chambers containing Krebs Ringer bicarbonate solution. The rings were contracted with 29.6 mM KCI. Ischemia alone did not attenuate endothelium-dependent relaxation by acetylcholine. However, ischemia-reperfusion significantly impaired endothelium-dependent relaxation. Endothelium-independent relaxation by sodium nitroprusside was not impaired by ischemia-reperfusion and the constrictive response to acetylcholine was not altered in reperfused rings without endothelium, compared with control rings. Arterial rings exposed to preconditioning followed by ischemia-reperfusion exhibited impaired endothelium-dependent relaxation by acetyl-choline. However, although preconditioning not fellowed by ischemia-reperfusion, attenuated endothelium-dependent relaxation at low concentrations of acetylcholine, the magnitude of the impairment by preconditioning followed by ischemia-reperfusion was significantly less than that of the impairment by ischemia-reperfusion alone. These data demonstrate that ischemia-reperfusion significantly attenuates endothelium-dependent relaxation by producing endothelial dysfunction and preconditioning Protects the endothelium of coronary arteries from ischemia-reperfusion injury.

• Nuclear Engineering and Technology
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• 제41권9호
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• pp.1215-1222
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• 2009

The present work pertains to a research program to study Molten Fuel-Coolant Interactions (MFCI), which may occur in a nuclear power plant during a hypothetical severe accident. Dynamics of the hot liquid (melt) droplet and the volatile liquid (coolant) were investigated in the MISTEE (Micro-Interactions in Steam Explosion Experiments) facility by performing well-controlled, externally triggered, single-droplet experiments, using a high-speed visualization system with synchronized digital cinematography and continuous X-ray radiography. The current study is concerned with the MISTEE-NCG test campaign, in which a considerable amount of non-condensable gases (NCG) are present in the film that enfolds the molten droplet. The SHARP images for the MISTEE-NCG tests were analyzed and special attention was given to the morphology (aspect ratio) and dynamics of the air/ vapor bubble, as well as the melt drop preconditioning. Energetics of the vapor explosion (conversion ratio) were also evaluated. The MISTEE-NCG tests showed two main aspects when compared to the MISTEE test series (without entrapped air). First, analysis showed that the melt preconditioning still strongly depends on the coolant subcooling. Second, in respect to the energetics, the tests consistently showed a reduced conversion ratio compared to that of the MISTEE test series.

• 한국추진공학회지
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• 제8권1호
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• pp.16-26
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• 2004

본 연구의 목적은 예조건화 방법론을 난류모델을 포함한 Navier-Stokes 방정식에 적용하는 것이다. 가상 음속 개념을 적용하였다 공간차분을 위해 Roe의 FDS를 사용하였고, 시간 적분을 위해 LU-SGS 기법을 사용하였다. 알고리즘을 검증하기 위하여 NACA 날개 주위의 저속유동, 초음속 노즐 유동을 계산하였다. 본 연구에서 개발된 알고리즘은 저속유동 및 초음속 유동의 계산에서 충분한 계산 성능을 보이는 것으로 판단된다.

• 대한기계학회논문집B
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• 제25권11호
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• pp.1581-1593
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• 2001

An efficient variable-reordering method for finite element meshes is used and the effect of variable-reordering is investigated. For the element renumbering of unstructured meshes, Cuthill-McKee ordering is adopted. The newsy reordered global matrix has a much narrower bandwidth than the original one, making the ILU preconditioner perform bolter. The effect of variable reordering on the convergence behaviour of saddle point type matrix it studied, which results from P2/P1 element discretization of the Navier-Stokes equations. We also propose and test 'level(0) preconditioner'and 'level(2) ILU preconditioner', which are another versions of the existing 'level(1) ILU preconditioner', for the global matrix generated by P2/P1 finite element method of incompressible Navier-Stokes equations. We show that 'level(2) ILU preconditioner'performs much better than the others only with a little extra computations.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권7호
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• pp.362-368
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• 2006

This paper presents the results of a small capacitive current interruption test for the three types of interrupter which are called 'serial type', 'parallel/separated type' and 'puffer type' according to the arrangement of the thermal expansion chamber and the puffer cylinder. After the preconditioning test the small current interruption capability of the 'puffer type' decreased, on the contrary, that of the hybrid interrupters increased. A number of reignition have been occurred in the 'serial type' hybrid interrupter and the change of small current interruption capability after preconditioning test is mainly influenced by the structure of interrupter. Finally it has been proved that the 'parallel/separated type' hybrid interrupter has the best interruption performance through the verification tests.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제5권2호
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• pp.63-69
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• 2001

In this study, we shall be concerned with computing in parallel a few of the smallest eigenvalues and their corresponding eigenvectors of the eigenvalue problem, $Ax={\lambda}Bx$, where A is symmetric, and B is symmetric positive definite. Both A and B are large and sparse. Recently iterative algorithms based on the optimization of the Rayleigh quotient have been developed, and CG scheme for the optimization of the Rayleigh quotient has been proven a very attractive and promising technique for large sparse eigenproblems for small extreme eigenvalues. As in the case of a system of linear equations, successful application of the CG scheme to eigenproblems depends also upon the preconditioning techniques. A proper choice of the preconditioner significantly improves the convergence of the CG scheme. The idea underlying the present work is a parallel computation of the Multi-Color Block SSOR preconditioning for the CG optimization of the Rayleigh quotient together with deflation techniques. Multi-Coloring is a simple technique to obatin the parallelism of order n, where n is the dimension of the matrix. Block SSOR is a symmetric preconditioner which is expected to minimize the interprocessor communication due to the blocking. We implemented the results on the CRAY-T3E with 128 nodes. The MPI(Message Passing Interface) library was adopted for the interprocessor communications. The test problems were drawn from the discretizations of partial differential equations by finite difference methods.

• The Korean Journal of Physiology and Pharmacology
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• 제2권6호
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• pp.753-761
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• 1998

Preconditioning of a heart with small doses of catecholamines induces a tolerance against the subsequent lethal ischemia. The present study was performed to find a specific receptor pathway involved with the catecholamine preconditioning and to test if adenosine plays a role in this cardioprotective effect. Isolated rat hearts, pretreated with small doses of ${\alpha}-\;or\;{\beta}-adrenergic$ agonists/antagonists, were subjected to 20 minutes ischemia and 20 minutes reperfusion by Langendorff perfusion method. Cardiac mechanical functions, lactate dehydrogenase and adenosine release from the hearts were measured before and after the drug treatments and ischemia. In another series of experiments, adenosine $A_1\;or\;A_2$ receptor blockers were treated prior to administration of adrenergic agonists. Pretreatments of a ${\beta}-agonist,\;isoproterenol(10^{-9}{\sim}10^{-7}\;M)$ markedly improved the post-ischemic mechanical function and reduced the lactate dehydrogenase release. Similar cardioprotective effect was observed with an ?-agonist, phenylephrine pretreatment, but much higher $concentration(10^{-4}\;M)$ was needed to achieve the same degree of cardioprotection. The cardioprotective effects of isoproterenol and phenylephrine pretreatments were blocked by a ${\beta}_1-adrenergic$ receptor antagonist, atenolol, but not by an ${\alpha}_1-antagonist,$ prazosin. Adenosine release from the heart was increased by isoproterenol, and the increase was also blocked by atenolol, but not by prazosin. A selective $A_1-adenosine$ receptor antagonist, 1,3-dipropyl-8-cyclopentyl xanthine (DPCPX) blocked the cardioprotection by isoproterenol pretreatment. These results suggest that catecholamine pretreatment protects rat myocardium against ischemia and reperfusion injury by mediation of ${\beta}_1-adrenergic$ receptor pathway, and that adenosine is involved in this cardioprotective effect.