• 열처리공학회지
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• 제17권4호
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• pp.236-240
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• 2004

Effect of plasma power on PECVD process were investigated in this study. TiN and TiCN films were deposited on nitrided STD11 steel with 600W, 1,200W and 1,600W plasma power. As the plasma power was increased, the preferred orientation was reinforced from (200) to (111) and the hardness of films was improved. The low plasma power was, however, effective for improving of adhesion force of films. Regarding above properties, TiN and TiCN films were deposited by gradient plasma power. It was possible to get high hardness as well as adhesion force through gradient plasma power.

• Journal of Mechanical Science and Technology
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• 제20권5호
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• pp.621-633
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• 2006

To reflect the size effect of material $(1\sim15{\mu}m)$ during plastic deformation of polycrystalline copper, a constitutive equation which includes the strain gradient plasticity theory and intrinsic material length model is coupled with the finite element analysis and applied to plane strain deformation problem. The method of least square has been used to calculate the strain gradient at each element during deformation and the effect of distributed force on the strain gradient is investigated as well. It shows when material size is less than the intrinsic material length $(1.54{\mu}m)$, its deformation behavior is quite different compared with that computed from the conventional plasticity. The generation of strain gradient is greatly suppressed, but it appears again as the material size increases. Results also reveal that the strain gradient leads to deformation hardening. The distributed force plays a role to amplify the strain gradient distribution.

• 소성∙가공
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• 제15권8호
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• pp.544-549
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• 2006

In this work, we have employed the strain gradient plasticity theory to investigate the effect of material size on the deformation behavior in metal forming process. Flow stress is expressed in terms of strain, strain gradient (spatial derivative of strain) and intrinsic material length. The least square method coupled with strain gradient plasticity was used to calculate the components of strain gradient at each element of material. For demonstrating the size effect, the proposed approach has been applied to plane compression process and micro rolling process. Results show when the characteristic length of the material comes to the intrinsic material length, the effect of strain gradient is noteworthy. For the microcompression, the additional work hardening at higher strain gradient regions results in uniform distribution of strain. In the case of micro-rolling, the strain gradient is remarkable at the exit section where the actual reduction of the rolling finishes and subsequently strong work hardening take places at the section. This results in a considerable increase in rolling force. Rolling force with the strain gradient plasticity considered in analysis increases by 20% compared to that with conventional plasticity theory.

• 한국가시화정보학회지
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• 제12권2호
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• pp.13-17
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• 2014

In the present study, the optofluidic droplet manipulation in a microfluidic platform was demonstrated via theoretical and experimental approaches. Optical scattering force and gradient force were used to separate and trap droplets. Two types of droplets were generated by a T-junction method in the microfluidic channel. While they approach a test region where the optical beam illuminates the droplets, they were pushed by the optical scattering beam. The displacement by the laser beam is dependent on the refractive index of the droplets. By using the optical gradient force, the droplets can be trapped and coalesced. In order to bring the droplets in a direct contact, the optical gradient force was used to trap the droplets. A theoretical modeling of the coalescence was derived by combining the optical force and drag force on the droplet.

• 한국광학회:학술대회논문집
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• 한국광학회 2003년도 제14회 정기총회 및 03년 동계학술발표회
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• pp.16-17
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• 2003

수 십 ∼ 수 마이크로 크기의 미세 입자에 강하게 집속된 빔을 산란시키게 되면 입자들은 운동량의 변화에 따라 광의 초점부근에서 포획되는 힘을 받게 된다. 이런 힘은 scattering force와 gradient force로 구분할 수 있고, Optical tweezers는 광의 gradient force를 이용하여 미세입자를 포획하고 조작하는 기술이다. 광에 의해 물리적인 접촉 없이 입자를 포획할 수 있다는 사실로부터 optical tweezers는 생물학을 비롯한 많은 분야에서 유용한 도구로 사용되어지고 있다. (중략)

• 한국정보과학회논문지:소프트웨어및응용
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• 제37권1호
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• pp.9-18
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• 2010

본 논문에서는 호기와 흡기에 촬영된 흉부 CT 영상간 폐 영상정합을 위해 데몬 알고리즘을 이용한 비강체 정합 방법을 제안한다. 먼저 두 영상에 어파인 변환을 적용하여 폐를 전역적으로 정렬한 후, 데몬 알고리즘에 기반한 비강체 정합 방법을 적용하여 지역적으로 변형시킨다. 데몬 힘의 계산을 위해 기준영상의 기울기 정보 뿐 아니라 부유영상의 기울기 정보를 함께 사용하여 기준영상의 기울기가 약한 부분에서 빠른 수렴을 돕는다. 활성-셀 기반 데몬 알고리즘은 두 영상 간 정합도가 높은 셀에서의 불필요한 변위 계산을 방지함으로써 정합 과정을 가속화시키고 변형 접힘 현상의 확률을 줄여주는 역할을 한다. 제안방법의 성능을 평가하기 위해 기준 기울기 힘을 사용한 방법과 부유 기울기 힘을 함께 사용한 방법을 비교하고, 활성-셀을 사용한 방법과 사용하지 않은 방법을 비교하였다. 실험 결과는 제안 방법이 변형이 큰 폐를 정확하게 정합하며 수행시간을 감소시킴을 보여준다.

• Geomechanics and Engineering
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• 제13권6호
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• pp.947-961
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• 2017

An innovative spiral variable-section capillary model is established for piping critical hydraulic gradient of cohesion-less soils causing water/mud inrush in tunnels. The relationship between the actual winding seepage channel and grain-size distribution, porosity, and permeability is established in the model. Soils are classified into coarse particles and fine particles according to the grain-size distribution. The piping critical hydraulic gradient is obtained by analyzing starting modes of fine particles and solving corresponding moment equilibrium equations. Gravities, drag forces, uplift forces and frictions are analyzed in moment equilibrium equations. The influence of drag force and uplift force on incipient motion is generally expounded based on the mechanical analysis. Two cases are studied with the innovative capillary model. The critical hydraulic gradient of each kind of sandy gravels with a bimodal grain-size-distribution is obtained in case one, and results have a good agreement with previous experimental observations. The relationships between the content of fine particles and the critical hydraulic gradient of seepage failure are analyzed in case two, and the changing tendency of the critical hydraulic gradient is accordant with results of experiments.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.591-610
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• 2017

This paper is concerned with the static analysis of variable thickness of two directional functionally graded porous materials (FGPM) circular plate resting on a gradient hybrid foundation (Horvath-Colasanti type) with friction force and subjected to compound mechanical loads (e.g., transverse, in-plane shear traction and concentrated force at the center of the plate).The governing state equations are derived in terms of displacements based on the 3D theory of elasticity, assuming the elastic coefficients of the plate material except the Poisson's ratio varying continuously throughout the thickness and radial directions according to an exponential function. These equations are solved semi-analytically by employing the state space method (SSM) and one-dimensional differential quadrature (DQ) rule to obtain the displacements and stress components of the FGPM plate. The effect of concentrated force at the center of the plate is approximated with the shear force, uniformly distributed over the inner boundary of a FGPM annular plate. In addition to verification study and convergence analysis, numerical results are displayed to show the effect of material heterogeneity indices, foundation stiffness coefficients, foundation gradient indices, loads ratio, thickness to radius ratio, compressibility, porosity and friction coefficient of the foundation on the static behavior of the plate. Finally, the responses of FG and FG porous material circular plates to compound mechanical loads are compared.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제50권2호
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• pp.59-64
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• 2001

The distribution of current in the conductors influenced by the armature geometry and velocity is an important parameter for determining performance of an electromagnetic launcher(EML). the electric current in the early launching stage tends to flow on the outer surfaces of the conductors, resulting in very high local electric current density. However, the tendency for current to concentrate on the surface is driven by the velocity skin effect later in launching stage. The high current density produces high local heating and, consequently, increases armature wear which causes several defects on EML system. This paper investigates the effects of rail/armature geometry on current density distribution, launcher inductance gradient (L'), and contact force. Three geometrical parameters are used here to characterize the railgun system. These are the ratio of contact length to root length, relative position of contact leading edge to root trailing edge, and the ratio of rail overhang to the rail height. The distribution of current density, L', contact force between various configurations of the armature and the rail are analyzed and compared by using the EMAP3D program.

• 한국정보과학회논문지:소프트웨어및응용
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• 제33권1호
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• pp.95-104
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• 2006

Gradient vector flow(GVF) snake 또는 active contour 모델은 영상 분할에서 훌륭한 성능을 보여준다. 그러나 기존의 snake 모델에는 제한된 캡쳐 영역과 요면으로의 느린 진행과 같은 문제점들이 존재한다. 본 논문은 주변의 필드로부터 외부장(external force field)을 확장시키고 변형된 평탄화기법을 이용하여 확장된 필드를 정규화 함으로서 GVF snake 모델의 성능을 개선시키는 새로운 방법을 제시한다. 시뮬레이션을 위해 사용된 U자 모양 이미지에서의 결과는 제안된 방법이 좀 더 큰 캡쳐 영역을 갖고 기존의 GVF snake 모델에 비하여 요면으로 빠르게 진행하는 것이 가능함을 보여준다.