1,721,729 research outputs found
무전해 Ni(P) 및 Ni(P)/Sn 박막의 잔류응력과 Cu/Cr/Polyimide 계의 필강도 해석에 대한 연구
No full text학위논문(박사) - 한국과학기술원 : 재료공학과, 2003.8, [ xi, 139 p. ]Electronic packages include various materials such as metals, polymers and ceramics, to perform their electrical and mechanical functions. Resultantly, many interfaces of dissimilar materials exist in the package. Therefore, the reliability related to the interfaces of dissimilar materials is important. This study covered the adhesion strength of bonded dissimilar films and residual stress in multilayered thin films used in electronic packaging.
First, the analysis of peel test to estimate the adhesion strength of Cu/Cr/Polyimide system has been conducted. The T peel strengths were measured using a Cu/Cr/polyimide system under varying metal layer thickness and rf plasma pretreatment conditions. Measured peel strength showed reversed camel back shape against the metal layer thickness, which is quite different from the results of the 90° peel test. Elementary analysis suggests that the T peel strength variation is a combined outcome of the plastic bending work of the metal and polymer strips, and when the latter were subtracted from the measured peel strength, interfacial fracture energies, quite independent of the metal layer thickness but increasing with the rf plasma power density were procured. Another interesting outcome is that the peel angle, the angle between the unpeeled ligament and the load axis normal, can be actually predicted and is a useful measure of the root curvature and the interfacial fracture energy.
Secondly, the residual stresses in electroless plated Ni(P) films were investigated. Electroless plated Ni(P) films have been widely used as under-bump-metallurgy in microelectronic packaging, however high tensile stresses in the films often cause reliability concerns. Here, Ni(P) films with varying P content were made by changing the pH of the plating solution, and the residual stresses in electroless Ni(P) films in as-prepared samples were all tensile regardless of the P content, but tended to decrease in magnitude with increasing P content. T...한국과학기술원 : 재료공학과
Numerical method for the determination of contact areas of a rock joint under normal and shear loads
No full textA numerical method to determine the contact areas of a rock joint under normal and shear loads is proposed. The method requires only three-dimensional surface coordinates at the initial stage before shearing, while some disparate materials are inserted between the joint surfaces or particular equipments are adopted for measurement of the contact areas during the test in other conventional methods. The joint surface is modeled as a group of triangular planes, and the contact condition of each plane is examined by calculating the relative displacements of both surfaces from their initial locations. To verify the method, a direct shear test on a rock joint was simulated using a bonded particle model in a discrete element code. The locations of the contact areas observed in the simulation showed good agreement with those determined using the proposed method. To characterize the roughness of the joint surface including the contact area, the concept of 'active and inactive micro-slope angle' was defined based on the apparent inclination of the triangular element to the shear direction. To apply these techniques, the experimental results of shear tests on replicas of rock joints were analyzed for the location, size and micro-slope angle of contact areas according to the following shearing stages: pre-peak, peak, post-peak and residual. The locations of the contact areas were closely correlated with the distribution of the micro-slope angle, which indicates that the joint roughness should be qualified with respect to the shear direction and the corresponding contact area. Additionally, the proposed method was applied to estimation of the distribution of aperture size within a rock joint. (C) 2012 Elsevier Ltd. All rights reserved.N
내열성 포스포리파아제 A1 돌연변이체와 동일한 것을 제조하기 위한 공정
No full textThe present invention provides thermostable phospholipase TA3 and TA13 which are mutants of phospholipase A1 involving the hydrolysis/synthesis of phospholipids, the mutated genes encoding the same, microorganisms transformed with recombinant expression vectors comprising the mutated genes and a process for preparing phospholipase A1 mutants therefrom. The process for preparing phospholipase A1 mutant of the invention comprises the steps of: culturing E. coli strain transformed with a recombinant expression vector comprising a gene coding for phospholipase A1 mutant derived from Serratia sp.; and, isolating and purifying phospholipase A1 mutant from the culture. Since phospholipase A1 mutants of the invention have been improved in terms of thermal stability and enzyme activity as well, they can be practically applied to various biological process, pharmaceutics, cosmetics and food industries
Empirical Model for Shear Strength of Artificial Rock Containing a Single Nonpersistent Joint
No full textThis paper proposes an empirical equation to evaluate the shear strength of rock mass with nonpersistent joints. A novel specimen preparation method is proposed and is used to created plaster specimens containing nonpersistent joints. Utilizing the proposed method, it is possible to create specimens with nonpersistent closed joints with different roughness levels along different directions. The normal stress applied to embedded nonpersistent joints is the key factor for estimating the joint friction contribution to the shear strength of rock mass with the joints. An analytical equation and an experimental approach are proposed to calculate the normal stress applied to the nonpersistent joints. Seemingly good agreement was found between the normal stress values obtained using the analytical equation and those measured by the experimental approach. To study the effects of four influential parameters, namely rock bridge ratio, material strength, joint roughness, and normal stress, on the shear strength of specimens with a single nonpersistent joint, an experimental layout was designed based on the Taguchi method. The results of the extensive experimental work were then expressed in terms of an empirical equation to calculate the shear strength of specimens embedding a single nonpersistent joint.N
The Effect of Joint Roughness on Shear Behavior of 3D-Printed Samples Containing a Non-Persistent Joint
No full textThe goal of this paper is to study the applicability of 3D printing technology to assess the effect of joint roughness on the shear strength of weakness planes with non-persistent discontinuities. Three disc-shaped profiles were generated to make joints with low, intermediate, and high levels of roughness. Powder-based 3D printing technology was applied to provide two types of samples: Type-A samples (joint samples) and Type-B samples (samples with a non-persistent joint). Type-A samples were printed to assess the shear behavior of 3D-printed joints, and Type-B samples were printed to investigate the joint roughness and rock bridge cohesion contributions to the shear strength of partially discontinuous planes. For comparison purposes, several plaster samples containing a non-persistent joint were cast as well. Three series of direct shear experiments were performed on Type-A, Type-B, and plaster samples under constant normal load conditions. The effects of two parameters, namely normal stress and joint roughness, on the shear behavior of the 3D-printed specimens were separately investigated, and the interaction between them was analyzed. The evaluation of the experimental results indicates the existence of two-way interaction between the joint roughness and the applied normal stress of Type-B samples. The experimental results obtained from plaster samples were compared with those obtained from Type-B samples. The comparison reveals that 3D-printed samples properly reflect the effects of joint roughness and normal stress on the shear strength of partially discontinuous planes, although their prepeak and post-peak behaviors are different from those of plaster specimens.N
Design, performance prediction and test of axial-flow pump
No full text학위논문(석사) - 한국과학기술원 : 기계공학과, 1999.2, [ vi, 51 p. ]한국과학기술원 : 기계공학과
원자로 핵연료다발 계산의 중성자 수송 병렬처리
No full text학위논문(석사) - 한국과학기술원 : 원자력공학과, 1992.2, [ [iv], 45 p. ]Group constants, which are used for reactor analyses by nodal method, are generated by fuel assembly calculations based on the neutron transport theory, since one or a quarter of the fuel assembly corresponds to a unit mesh in the current nodal calculation. The group constant calculation for a fuel assembly is performed through spectrum calculations, a two-dimensional fuel assembly calculation, and depletion calculations. The purpose of this study is to develop a parallel algorithm to be used in a parallel processor for the fuel assembly calculation and the depletion calculations of the group constant generation. A serial program, which solves the neutron integral transport equation using the transmission probability method and the linear depletion equation, was prepared and verified by a benchmark calculation. Small changes from the serial program was enough to parallelize the depletion calculation which has inherent parallel characteristics. In the fuel assembly calculation, however, efficient parallelization is not simple and easy because of the many coupling parameters in the calculation and data communications among CPU``s. In this study, the group distribution method is introduced for the parallel processing of the fuel assembly calculation to minimize the data communications. The parallel processing was performed on Quadputer with 4 CPU``s operating in NURAD Lab. at KAIST. Efficiencies of 54.3 \% and 78.0 \% were obtained in the fuel assembly calculation and depletion calculation, respectively, which lead to the overall speedup of about 2.5. As a result, it is concluded that the computing time consumed for the group constant generation can be easily reduced by parallel processing on the parallel computer with small size CPU``s.한국과학기술원 : 원자력공학과
몬테칼로 방법에 기반한 산개된 연료를 갖는 페블에서의 온도분포 계산
No full text학위논문(석사) - 한국과학기술원 : 원자력및양자공학과, 2008. 8., [ v, 29 p. ]A Monte Carlo method is described to solve heat conduction problems with extremely heterogeneous and complicated geometry. The method is based on observation that the heat conduction equation is a special form of the neutron diffusion equation, which in turn is an approximation to the transport equation. The heat conduction equation is solved by the transport Monte Carlo method with appropriate boundary layer correction and scaling factor rendering the problem diffusive. As applications, the Monte Carlo results are obtained for randomly distributed fuel particles of a pebble, providing realistic temperature distributions (showing the kernel and graphite-matrix temperatures distinctly). The volumetric analytic solution commonly used in the literature underestimates the Monte Carlo results.한국과학기술원 : 원자력및양자공학과
동력로 시뮬레이션에서의 지논진동을 위한 해석적 초기화 방법
No full text학위논문(박사) - 한국과학기술원 : 원자력공학과, 1998.8, [ vii, 73 p. ]The purpose of simulating nuclear power reactor core transients is to predict variations in core behavior due to changes in operating conditions. In the simulation, the initial condition of the core transient should be consistent with the real core state. Especially, the initial conditions of iodine and xenon distributions, which cannot be measured in the core, have dominant effects on the accuracy of the simulation for the transients related with xenon dynamics. If the transient starts from non-equilibrium xenon condition, the accurate initialization of the non-equilibrium iodine and xenon distributions is essential for the prediction of the core transient behavior.
In this study, a simple initialization method of non-equilibrium iodine and xenon distributions for the core transient simulation was developed using axial power difference, which is the only measurable parameter related with the non-equilibrium state of the core. For this purpose, the spatial distribution of two-group one-dimensional neutron diffusion equation combined with xenon dynamics equation was expanded with Fourier sine series. It was found that the nonlinearly combined terms of flux and xenon distributions in the equations were canceled by the orthogonal characteristics of the Fourier series using adequate approximation. Therefore, the dynamics equations for axial difference parameters of power, iodine and xenon can be completely linearized and can be converted into an equation system which can be solved analytically. Because the equation system provides with an analytic relationship between the axial differences of power, iodine and xenon, the non-equilibrium iodine and xenon can be represented as functions of the axial power difference. It implies that the initial condition of the transient starting from a non-equilibrium state can be determined from the initial condition of the axial power difference which is a measurable parameter of the core.
Using the analytic solution obtained in...한국과학기술원 : 원자력공학과
Wedge plate phase-shifting lateral-shearing interferometer
No full text학위논문(박사) - 한국과학기술원 : 물리학과, 2004.2, [ viii, 100 p. ]한국과학기술원 : 물리학과
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