The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Chinchang Yang - One of the best experts on this subject based on the ideXlab platform.
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enhancing differential evolution utilizing eigenvector based crossover operator
IEEE Transactions on Evolutionary Computation, 2015Co-Authors: Chinchang YangAbstract:Differential evolution has been shown to be an effective methodology for solving optimization problems over continuous space. In this paper, we propose an eigenvector-based crossover operator. The proposed operator utilizes Eigenvectors of covariance matrix of individual solutions, which makes the crossover rotationally invariant. More specifically, the donor vectors during crossover are modified, by projecting each donor vector onto the eigenvector basis that provides an alternative coordinate system. The proposed operator can be applied to any crossover strategy with minimal changes. The experimental results show that the proposed operator significantly improves DE performance on a set of 54 test functions in CEC 2011, BBOB 2012, and CEC 2013 benchmark sets.
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enhancing differential evolution utilizing eigenvector based crossover operator
IEEE Transactions on Evolutionary Computation, 2015Co-Authors: Shumei Guo, Chinchang YangAbstract:Differential evolution has been shown to be an effective methodology for solving optimization problems over continuous space. In this paper, we propose an eigenvector-based crossover operator. The proposed operator utilizes Eigenvectors of covariance matrix of individual solutions, which makes the crossover rotationally invariant. More specifically, the donor vectors during crossover are modified, by projecting each donor vector onto the eigenvector basis that provides an alternative coordinate system. The proposed operator can be applied to any crossover strategy with minimal changes. The experimental results show that the proposed operator significantly improves DE performance on a set of 54 test functions in CEC 2011, BBOB 2012, and CEC 2013 benchmark sets.
Werner J A Dahm - One of the best experts on this subject based on the ideXlab platform.
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direct assessment of vorticity alignment with local and nonlocal strain rates in turbulent flows
Physics of Fluids, 2008Co-Authors: Peter E Hamlington, Jorg Schumacher, Werner J A DahmAbstract:A direct Biot-Savart integration is used to decompose the strain rate into its local and nonlocal constituents, allowing the vorticity alignment with the local and nonlocal strain rate Eigenvectors to be investigated. These strain rate tensor constituents are evaluated in a turbulent flow using data from highly resolved direct numerical simulations. While the vorticity aligns preferentially with the intermediate eigenvector of the combined strain rate, as has been observed previously, the present results, for the first time, clearly show that the vorticity aligns with the most extensional eigenvector of the nonlocal strain rate. This, in turn, reveals a significant linear contribution to the vortex stretching dynamics in turbulent flows.
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direct assessment of vorticity alignment with local and nonlocal strain rates in turbulent flows
arXiv: Fluid Dynamics, 2008Co-Authors: Peter E Hamlington, Jorg Schumacher, Werner J A DahmAbstract:A direct Biot-Savart integration is used to decompose the strain rate into its local and nonlocal constituents, allowing the vorticity alignment with the local and nonlocal strain rate Eigenvectors to be investigated. These strain rate tensor constituents are evaluated in a turbulent flow using data from highly-resolved direct numerical simulations. While the vorticity aligns preferentially with the intermediate eigenvector of the \textit{combined} strain rate, as has been observed previously, the present results for the first time clearly show that the vorticity aligns with the most extensional eigenvector of the \textit{nonlocal} strain rate. This in turn reveals a significant linear contribution to the vortex stretching dynamics in turbulent flows.
Andrew L Alexander - One of the best experts on this subject based on the ideXlab platform.
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axial asymmetry of water diffusion in brain white matter
Magnetic Resonance in Medicine, 2005Co-Authors: Mariana Lazar, Andrew L Alexander, Jong Hoon LeeAbstract:The diffusion tensor (DT) is a three-dimensional (3D) model of diffusivity in biological tissues. In white matter (WM), the major eigenvector, which is the direction of greatest diffusivity, is generally assumed to align with the direction of the fiber bundles. The distribution of major Eigenvectors in WM has been investigated using color-based maps and WM tractography (WMT). However, anatomical patterns in the medium and minor eigenvector directions have largely been ignored in DTI studies of the human brain. In this study, the patterns of medium and minor Eigenvectors in the brain were investigated using both color-based maps and WMT. Specific WM structures, such as the corona radiata, internal and external capsules, sagittal stratum, cingulum, and superior longitudinal fasciculus, demonstrated coherent patterns in the medium and minor eigenvector directions. These patterns were consistent across subjects. The orthogonal or axial diffusion asymmetry may be explained by merging, diverging, or crossing fiber geometries. The effects of orthogonal diffusion asymmetry on WMT were also investigated. This study shows that WM axial asymmetry causes anisotropic dispersion patterns in the estimated tract trajectories. The medium and minor eigenvector patterns may be useful for elucidating the local dispersion distributions of WM tracts.
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quantitative analysis of diffusion tensor orientation theoretical framework
Magnetic Resonance in Medicine, 2004Co-Authors: Aaron S Field, Moo K Chung, Benham Badie, Andrew L AlexanderAbstract:Diffusion-tensor MRI (DT-MRI) yields information about the magnitude, anisotropy, and orientation of water diffusion of brain tissues. Although white matter tractography and eigenvector color maps provide visually appealing displays of white matter tract organization, they do not easily lend themselves to quantitative and statistical analysis. In this study, a set of visual and quantitative tools for the investigation of tensor orientations in the human brain was developed. Visual tools included rose diagrams, which are spherical coordinate histograms of the major eigenvector directions, and 3D scatterplots of the major eigenvector angles. A scatter matrix of major eigenvector directions was used to describe the distribution of major Eigenvectors in a defined anatomic region. A measure of eigenvector dispersion was developed to describe the degree of eigenvector coherence in the selected region. These tools were used to evaluate directional organization and the interhemispheric symmetry of DT-MRI data in five healthy human brains and two patients with infiltrative diseases of the white matter tracts. In normal anatomical white matter tracts, a high degree
D Sturm - One of the best experts on this subject based on the ideXlab platform.
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modeling the spatiotemporal organization of velocity storage in the vestibuloocular reflex by optokinetic studies
Journal of Neurophysiology, 1991Co-Authors: Theodore Raphan, D SturmAbstract:1. A generalized three-dimensional state space model of visual vestibular interaction was developed. Matrix and dynamical system operators associated with inputs from the semicircular canals, otolith velocity estimator, and the visual system have been incorporated into the model, which focus on their relationship to the velocity storage integrator. 2. A relationship was postulated between the eigenvalues and the direction of the Eigenvectors of the system matrix and the orientation of the spatial vertical. It was assumed that the system matrix for a tilted position was a composition of two linear transformations of the system matrix for the upright position. One transformation modifies the eigenvalues of the system matrix, whereas another rotates the Eigenvectors of the system matrix. The pitch and roll Eigenvectors rotate with the head, whereas the yaw axis eigenvector remains approximately spatially invariant. 3. Based on the three-dimensional model, a computational procedure was formulated to identify the eigenvalues and Eigenvectors of the system matrix with the use of a modification of the marquardt algorithm. With the use of data obtained from a monkey, it was shown that the three-dimensional behavior of velocity storage cannot be predicted solely in terms of its time constants, i.e., the inverse of its eigenvalues. With the use of the same eigenvalues the data could either be fit or not fit, depending on the eigenvector directions. Therefore, it is necessary to specify eigenvector directions when characterizing velocity storage in three dimensions. 4. Parameters found with the use of the Marquardt algorithm were incorporated into the model. Diagonal matrices in a head coordinate frame were introduced for coupling the visual system to the integrator and to the direct optokinetic pathway. Simulations of optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN) were run. The model predicted the behavior of yaw and pitch OKN and OKAN when the animal is upright. It also predicted the cross-coupling in the side down position. The trajectories in velocity space were also accurately simulated. 5. One of the predictions of the model is that when the stimulus direction is along an eigenvector, the trajectory in velocity space is a straight line. Using the "spectral width" of the residuals from a straight line sequence during OKAN, we developed a methodology to estimate how close the OKAN decay was to an eigenvector trajectory. 6. Thus we have developed a model-based approach for studying and interpreting the response characteristics of velocity storage in three dimensions.(ABSTRACT TRUNCATED AT 400 WORDS)
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modeling the spatiotemporal organization of velocity storage in the vestibuloocular reflex by optokinetic studies
Journal of Neurophysiology, 1991Co-Authors: Theodore Raphan, D SturmAbstract:1. A generalized three-dimensional state space model of visual vestibular interaction was developed. Matrix and dynamical system operators associated with inputs from the semicircular canals, otolith velocity estimator, and the visual system have been incorporated into the model, which focus on their relationship to the velocity storage integrator. 2. A relationship was postulated between the eigenvalues and the direction of the Eigenvectors of the system matrix and the orientation of the spatial vertical. It was assumed that the system matrix for a tilted position was a composition of two linear transformations of the system matrix for the upright position. One transformation modifies the eigenvalues of the system matrix, whereas another rotates the Eigenvectors of the system matrix. The pitch and roll Eigenvectors rotate with the head, whereas the yaw axis eigenvector remains approximately spatially invariant. 3. Based on the three-dimensional model, a computational procedure was formulated to identify ...
Peter E Hamlington - One of the best experts on this subject based on the ideXlab platform.
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direct assessment of vorticity alignment with local and nonlocal strain rates in turbulent flows
Physics of Fluids, 2008Co-Authors: Peter E Hamlington, Jorg Schumacher, Werner J A DahmAbstract:A direct Biot-Savart integration is used to decompose the strain rate into its local and nonlocal constituents, allowing the vorticity alignment with the local and nonlocal strain rate Eigenvectors to be investigated. These strain rate tensor constituents are evaluated in a turbulent flow using data from highly resolved direct numerical simulations. While the vorticity aligns preferentially with the intermediate eigenvector of the combined strain rate, as has been observed previously, the present results, for the first time, clearly show that the vorticity aligns with the most extensional eigenvector of the nonlocal strain rate. This, in turn, reveals a significant linear contribution to the vortex stretching dynamics in turbulent flows.
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direct assessment of vorticity alignment with local and nonlocal strain rates in turbulent flows
arXiv: Fluid Dynamics, 2008Co-Authors: Peter E Hamlington, Jorg Schumacher, Werner J A DahmAbstract:A direct Biot-Savart integration is used to decompose the strain rate into its local and nonlocal constituents, allowing the vorticity alignment with the local and nonlocal strain rate Eigenvectors to be investigated. These strain rate tensor constituents are evaluated in a turbulent flow using data from highly-resolved direct numerical simulations. While the vorticity aligns preferentially with the intermediate eigenvector of the \textit{combined} strain rate, as has been observed previously, the present results for the first time clearly show that the vorticity aligns with the most extensional eigenvector of the \textit{nonlocal} strain rate. This in turn reveals a significant linear contribution to the vortex stretching dynamics in turbulent flows.
