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Search Results: 1 - 10 of 6873 matches for " prior boundary conditions "
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Coronary vessel intimal sequence extraction based on prior boundary constraints in optical coherence tomography image

- , 2018, DOI: 10.7507/1001-5515.201712058
Abstract: 光学相干断层影像(OCT)是一种应用于血管的影像新技术,其高分辨率和可量化分析等特点,使其能够检测血管内膜和斑块表面的特殊结构并发现微小病变。特别是随着其在识别冠状动脉粥样硬化斑块、优化经皮冠状动脉介入(PCI)治疗、辅助医生制定相关诊断和治疗策略以及支架术后评估等方面的应用相继展开,OCT 已经成为心血管疾病诊断的有效工具。本文提出了一种基于先验边界条件的冠脉 OCT 内膜轮廓序列提取算法,在 Chan-Vese 模型基础上通过改进演化权函数把轮廓曲线的局部信息引入模型,控制曲线边界演化速度,并在模型中加入梯度能量项和基于先验边界条件的内膜轮廓形状限制项,进一步约束曲线演化轮廓的形状,最终实现冠脉血管内膜轮廓的序列提取。与作为金标准的专业医生手动分割结果进行实验对比,结果表明本算法在冠脉 OCT 内膜轮廓模糊、失真、有导丝阴影及有斑块干扰等情况下均能准确提取冠脉血管内膜轮廓,提示本研究成果或可应用于临床辅助诊断和精确诊疗之中。
Optical coherence tomography (OCT) is a new technique applied in cardiovascular system. It can detect vessel intimal, small structure of plaque surface and discover small lesions with its high axial resolution and quantification character. Especially with the application of OCT in characterization of coronary atherosclerotic plaque, diagnosis and treatment strategy making, optimizing percutaneous coronary intervention therapy and assessment after stent planting make the OCT become an efficient tool for cardiovascular disease diagnosis and treatment. This paper presents a novel coronary vessel intimal sequence extraction method based on prior boundary constraints in OCT image. On the basis of conventional Chan-Vese model, we modified the evolutionary weight function to control the evolutionary rate of boundary by adding local information of boundary curve. At the same time, we added the gradient energy term and intimal boundary constraint term based on priori boundary condition to further control the evolutionary of boundary curve. At last, coronary vessel intimal is extracted in a sequence way. The comparison with vessel intimal, manual segmented by clinical scientists (golden standard), indicates that our coronary vessel intimal extraction method is robust to intimal boundary blur, distortion, guide wire shadow and plaque disturbs. The results of this study can be applied to clinical aid diagnosis and precise diagnosis and treatment.
Surface Wave Propagation in a Generalized Thermoelastic Material with Voids  [PDF]
Baljeet Singh, Raj Pal
Applied Mathematics (AM) , 2011, DOI: 10.4236/am.2011.25068
Abstract: In the present paper, the propagation of surface wave in a generalized thermoelastic solid with voids is considered. The governing equations are solved to obtain the general solution in x-z plane. The appropriate boundary conditions at an interface between two dissimilar half-spaces are satisfied by appropriate particular solutions to obtain the frequency equation of the surface wave in the medium. Some special cases are also discussed.
A Method for Setting the Artificial Boundary Conditions of Groundwater Model  [PDF]
Yipeng Zhou, Zhaoli Shen, Weijun Shi, Jinhui Liu, Yajie Liu
Open Journal of Geology (OJG) , 2013, DOI: 10.4236/ojg.2013.32B012

Numerical simulation technology is nowadays an important means for groundwater issues because of its efficiency and economical advantages. But in case of natural hydrogeological boundaries are not within the interest area, it may be a big trouble to set boundary conditions of the model artificially without enough field investigation information. This paper introduced a method for solving such problem applying field pumping test and recovery test. The method was applied to build an in-situ leaching of uranium model. Results showed that the model boundary conditions can be set satisfactorily, and also the calculated heads matched the observed data well in both two models.

Spherical Casimir Effect for a Massive Scalar Field on the Three Dimensional Ball  [PDF]
Andrea Erdas
Journal of Modern Physics (JMP) , 2015, DOI: 10.4236/jmp.2015.68115
Abstract: The zeta function regularization technique is used to study the Casimir effect for a scalar field of mass m satisfying Dirichlet boundary conditions on a spherical surface of radius a. In the case of large scalar mass, \"\", simple analytic expressions are obtained for the zeta function and Casimir energy of the scalar field when it is confined inside the spherical surface, and when it is confined outside the spherical surface. In both cases the Casimir energy is exact up to order \"\"and contains the expected divergencies, which can be eliminated using the well established renormalization procedure for the spherical Casimir effect. The case of a scalar field present in both the interior and exterior region is also examined and, for \"\", the zeta function, the Casimir energy, and the Casimir force are obtained. The obtained Casimir energy and force are exact up to order \"\"and \"\"respectively. In this scenario both energy and force are finite and do not need to be renormalized, and the force is found to produce an outward pressure on the spherical surface.
A Review of the Effectiveness and Boundary Conditions of Leader Humility  [PDF]
Shuang Xu
Journal of Service Science and Management (JSSM) , 2019, DOI: 10.4236/jssm.2019.122016
Abstract: In recent years, top-down leadership style such as humility has received widespread attention in academic and practical areas. Although theoretical and empirical studies have shown that the humble leadership has a positive impact, it lacks systematic review of its mechanism and the research about boundary conditions of its positive impact. The article begins with a brief overview of the research status of humble leaders, and then combs the study of the boundary conditions of the humble leadership when it comes to individual and group levels. Finally, the future research is proposed.
A Computational Study with Finite Element Method and Finite Difference Method for 2D Elliptic Partial Differential Equations  [PDF]
George Papanikos, Maria Ch. Gousidou-Koutita
Applied Mathematics (AM) , 2015, DOI: 10.4236/am.2015.612185
Abstract: In this paper, we consider two methods, the Second order Central Difference Method (SCDM) and the Finite Element Method (FEM) with P1 triangular elements, for solving two dimensional general linear Elliptic Partial Differential Equations (PDE) with mixed derivatives along with Dirichlet and Neumann boundary conditions. These two methods have almost the same accuracy from theoretical aspect with regular boundaries, but generally Finite Element Method produces better approximations when the boundaries are irregular. In order to investigate which method produces better results from numerical aspect, we apply these methods into specific examples with regular boundaries with constant step-size for both of them. The results which obtained confirm, in most of the cases, the theoretical results.
Generalized viscosity solutions of elliptic PDEs and boundary conditions
Gustaf Gripenberg
Electronic Journal of Differential Equations , 2006,
Abstract: Sufficient conditions are given for a generalized viscosity solution of an elliptic boundary value problem to satisfy the boundary values in the strong sense.
Multiple solutions for semilinear elliptic equations with nonlinear boundary conditions
Junichi Harada,Mitsuharu Otani
Electronic Journal of Differential Equations , 2012,
Abstract: We consider the elliptic problem with nonlinear boundary conditions: $$displaylines{ -Delta u +bu=f(x,u)quadhbox{in }Omega,cr -partial_{ u}u=|u|^{q-1}u-g(u)quadhbox{on }partialOmega, }$$ where $Omega$ is a bounded domain in $mathbb{R}^n$. Proving the existence of solutions of this problem relies essentially on a variational argument. However, since $L^{q+1}(partialOmega)subset H^1(Omega)$ does not hold for large q, the standard variational method can not be applied directly. To overcome this difficulty, we use approximation methods and uniform a priori estimates for solutions of approximate equations.
Experimental Investigation of Boundary Layer Characteristics on Blade Surface under Different Inlet Flow Conditions  [PDF]
Xiangfeng Bo, Bo Liu, Pengcheng Zhao, Zhiyuan Cao
Energy and Power Engineering (EPE) , 2010, DOI: 10.4236/epe.2010.24044
Abstract: In this paper, an experimental study is conducted on cascade boundary layer under different inlet conditions. New method is used to measure the total pressure in blade surface boundary layer directly using total pressure probe. Total pressure in both suction and pressure surfaces are acquired at different inlet conditions by changing incidence angle and inlet Mach number. In addition, a series of parameters related to boundary layer characteristics are calculated. The objective of the experiment is to investigate the influence of inlet flow conditions on them. The results indicate that influence of incidence angle is significant when other conditions are the same. Displacement thickness, momentum thickness as well as other parameters display some disciplines for variation. In contrast, inlet Mach number has only a small influence in that boundary layer becomes a litter thinner with increasing Mach number. Comparisons of experimental results with theoretical expectations demonstrate that the method in this experiment is effective and reliable.
Turbulent Flow Simulations through Tarbela Dam  [PDF]
Muhammad Abid, Adnan Aslam Noon
Engineering (ENG) , 2010, DOI: 10.4236/eng.2010.27067
Abstract: Tarbela dam is one of the largest earth filled dam in the world. The sediments inflow in the Tarbela reservoir has resulted in reduction in water storage capacity. In addition damage to the tunnels, power generating units and ultimately to the plant equipment by the sediments particles carried by water is observed. To the authors knowledge, to-date no comprehensive simulation studies are performed for this dam reservoir and tunnels, especially at present when sediment delta and presence of sediment particles in the tunnels is observed to a reasonable extent. The aim of this study is to investigate the damage to the Tunnel 2 of the Tarbela Dam with and without considering the affect of sediment particles for one way and two way/full coupling during summer, winter and average seasons, using turbulent flows of water. Numerically calculated erosion results are compared with the experimental erosion results. Pressure, velocity and erosion rate density results are discussed in detail.
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