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Using finite element analysis, we studied the steady current field distribution under the configuration of four point probe method for resistivity measurement in a diamond anvil cell (DAC). Based on the theoretical analysis, we made a correction to the formula by Valdes [L. B. Valdes, Proc IRE, 42, 420 (1958)]. The results show that our formula provides more accurate determination of sample resistivity, especially when the sample thickness is less than the probe spacing. We found that finite size of the electrode could lead to significant errors in resistivity measurement for semiconducting samples. We also found that the probe spacing is a key factor in the resistivity measurement accuracy for samples in DAC. When the sample thickness t is close to the probe spacing s, the error becomes larger and reaches a maximum. [ABSTRACT FROM AUTHOR]

This paper systematically describes a real-time dissection approach for digital organs by strong coupling of geometric metaballs and physically correct mesh-free method. For organ geometry, we employ a novel hybrid model comprising both inner metaballs and high-resolution surface mesh with texture information. Through the use of metaballs, the organ interior is geometrically simplified via a set of overlapping spheres with different radii. As for digital organ's physical representation, we systematically articulate a hybrid framework to interlink metaballs with physics-driven mesh-free method based on moving least squares (MLS) shape functions. MLS approach enables the direct and rapid transition from metaball geometry to local nodal formulations, which afford potential-energy-correct physical modeling and simulation over continuum domain with physical accuracy. For soft tissue dissection, the nature of our MLS-driven mesh-free method also facilitates adaptive topology modification and cutting surface reconstruction. To expedite simulation towards real-time performance, at the numerical level, we resort to position-based dynamics to simplify physical deformation to drive metaballs participating in the mesh-free formulation. Since nodal points participating in the physical process exist temporarily only in localized regions adjacent to the cutting path, our method could warrant accurate cutting surface without sacrificing real-time computational efficiency. This hybrid dissection technique has already been integrated into a VR-based laparoscopic surgery simulator with a haptic interface. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper advocates a method for real-time physical deformation and arbitrary cutting simulation of heterogeneous objects with multi-material distribution, whose originality centers on the tight coupling of domain-specific finite element method (FEM) and material distance-aware meshless approach in a CUDA-centric parallel simulation framework. We employ hierarchical hexahedron serving as basic building blocks for accurate material-aware FEM simulation. Meanwhile, local meshless systems are designed to support cross-FEM-domain coupling and material-sensitive propagation while respecting the regularity of finite elements. Directly benefiting from the structural regularity and uniformity of finite elements, our hybrid solution enables the local stiffness matrix pre-computation and dynamic assembling, adaptive topological updating and precise cutting reconstruction. Moreover, our mathematically-rigorous solver guarantees unconditional stableness. Experiments demonstrate the superiorities of our system. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper systematically advocates an interactive volumetric image manipulation framework, which can enable the rapid deployment and instant utility of patient-specific medical images in virtual surgery simulation while requiring little user involvement. We seamlessly integrate multiple technical elements to synchronously accommodate physics-plausible simulation and high-fidelity anatomical structures visualization. Given a volumetric image, in a user-transparent way, we build a proxy to represent the geometrical structure and encode its physical state without the need of explicit 3-D reconstruction. On the basis of the dynamic update of the proxy, we simulate large-scale deformation, arbitrary cutting, and accompanying collision response driven by a non-linear finite element method. By resorting to the upsampling of the sparse displacement field resulted from non-linear finite element simulation, the cut/deformed volumetric image can evolve naturally and serves as a time-varying 3-D texture to expedite direct volume rendering. Moreover, our entire framework is built upon CUDA (Beihang University, Beijing, China) and thus can achieve interactive performance even on a commodity laptop. The implementation details, timing statistics, and physical behavior measurements have shown its practicality, efficiency, and robustness. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel method to couple Smoothed Particle Hydrodynamics (SPH) and nonlinear FEM to animate the interaction of fluids and deformable solids in real time. To accurately model the coupling, we generate proxy particles over the boundary of deformable solids to facilitate the interaction with fluid particles, and develop an efficient method to distribute the coupling forces of proxy particles to FEM nodal points. Specifically, we employ the Total Lagrangian Explicit Dynamics (TLED) finite element algorithm for nonlinear FEM because of many of its attractive properties such as supporting massive parallelism, avoiding dynamic update of stiffness matrix computation, and efficient solver. Based on a predictor-corrector scheme for both velocity and position, different normal and tangential conditions can be realized even for shell-like thin solids. Our coupling method is entirely implemented on modern GPUs using CUDA. We demonstrate the advantage of our two-way coupling method in computer animation via various virtual scenarios. [ABSTRACT FROM AUTHOR]

Using finite element analysis, the authors studied the steady current field distribution under the configuration of van der Pauw method [L. J. van der Pauw, Philips Tech. Rev. 20, 220 (1958)] for resistivity measurement in a diamond anvil cell. Based on the theoretical analysis, the authors obtained the theoretical accuracy curve of the van der Pauw method. This method provides accurate determination of sample resistivity when the ratio of sample thickness to its diameter is less than 0.45. They found that the contact area between electrode and sample is a key factor in the resistivity measurement accuracy and its size is dependent on the sample diameter for a given measurement accuracy. [ABSTRACT FROM AUTHOR]

The effect of electrode resistivity on the in situ resistivity measurement in a diamond anvil cell was studied using finite element analysis. The theoretical analysis reveals that the origin of significant error for a thin sample is mainly caused by the resistivity difference between the electrodes and the sample. The authors found that reducing such resistivity differences can improve the accuracy. The result shows that the van der Pauw method [L. J. van der Pauw, Philips Tech. Rev. 20, 220 (1958)] can provide more accurate results for thin samples compared with the four-point probe method. This approach provides means to simulate actual experiments and to eliminate the measurement error. [ABSTRACT FROM AUTHOR]

Powerful global modal reduction techniques have received growing recognition towards significant performance gain in physical simulation, yet such numerical methods generally will fail when handling deformation of heterogeneous materials across multiple sub-domains involving cutting simulation. This is because the corresponding topological changes (due to cutting across multiple sub-domains) and/or drastic local deformations tend to invalidate the global subspace techniques. To ameliorate, this paper systematically advocates a novel deformation and arbitrary cutting simulation approach by adaptively integrating FEM-based fully-physical simulation and local deformation's modal reuse into a CUDA-enabled parallel computation framework. This paper's originality hinges upon the maximal reuse of the space–time-varying local modes from prior fully-physical simulations and the adaptively coupling of sub-domain behaviors, which give rise to great improvement of computational complexity while guaranteeing high-fidelity simulation effects. Other key advantages include, being independent of underlying physical models (e.g., either FEM or meshless methods), being flexibly accommodating sub-domains' heterogeneous material distributions, and being accurately responding to local user interactions. During the initialization stage, we partition the object into multiple sub-domains according to its material distributions and/or geometric structures, and respectively employ FEM for physics-based representation/simulation. During the dynamic stage, for each sub-domain, we leverage its local modal reduction in order to project complex deformations onto a low-dimensional subspace. We dynamically determine the sub-domain-specific switch between deformation reconstruction based on modal reuse and FEM-based physical simulation according to the physically-consistent error estimates, and couple all the sub-domains' physical behaviors together by imposing adjacent sub-domains' geometric-continuity constraints. To validate our method, we conduct extensive and quantitative evaluations over comprehensive and well-designed experiments, and all the experimental results have confirmed the advantages of our method in terms of efficiency, accuracy, and unconditional stableness in practical graphics applications. [ABSTRACT FROM AUTHOR]