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Spatial Accuracy (spatial + accuracy)
Selected Abstracts1-Hz repetitive TMS over ipsilateral motor cortex influences the performance of sequential finger movements of different complexityEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2008Laura Avanzino Abstract To elucidate the role of ipsilateral motor cortex (M1) in the control of unilateral finger movements (UFMs) in humans we used a conditioning protocol of 1-Hz repetitive transcranial magnetic stimulation (1-Hz rTMS) over M1 in 11 right-handed healthy subjects. We analysed the effects of conditioning rTMS on UFMs of different complexity (simple vs sequential finger movements), and performed with a different modality (internally vs externally paced movements). UFMs were monitored with a sensor-engineered glove, and a quantitative evaluation of the following parameters was performed: touch duration (TD); inter-tapping interval (ITI); timing error (TE); and number of errors (NE). 1-Hz rTMS over ipsilateral M1 was able to affect the performance of a sequence of finger opposition movements in a metronome-paced condition, significantly increasing TD and reducing ITI without TE changes. The effects on motor behaviour had a different magnitude as a function of the sequence complexity. Further, we found a different effect of the ipsilateral 1-Hz rTMS on externally paced movements with respect to an internally paced condition. All these findings indicate that ipsilateral M1 plays an important role in the execution of sequential UFMs. Interestingly, NE did not change in any experimental condition, suggesting that ipsilateral M1 influences only the temporal and not the spatial accuracy of UFMs. Finally, the duration (up to 30 min) of 1-Hz rTMS effects on ipsilateral M1 can indicate its direct action on the mechanisms of cortical plasticity, suggesting that rTMS can be used to modulate the communication between the two hemispheres in rehabilitative protocols. [source] The moment-of-fluid method in actionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2009Hyung Taek Ahn Abstract The moment-of-fluid (MOF) method is a new volume-tracking method that accurately treats evolving material interfaces. The MOF method uses moment data, namely the material volume fraction, as well as the centroid, for a more accurate representation of the material configuration, interfaces and concomitant volume advection. In contrast, the volume-of-fluid method uses only volume fraction data for interface reconstruction and advection. Based on the moment data for each material, the material interfaces are reconstructed with second-order spatial accuracy in a strictly conservative manner. The MOF method is coupled with a stabilized finite element incompressible Navier,Stokes solver for two materials. The effectiveness of the MOF method is demonstrated with a free-surface dam-break and a two-material Rayleigh,Taylor problem. Copyright © 2008 John Wiley & Sons, Ltd. [source] Practical evaluation of five partly discontinuous finite element pairs for the non-conservative shallow water equationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2010Richard Comblen Abstract This paper provides a comparison of five finite element pairs for the shallow water equations. We consider continuous, discontinuous and partially discontinuous finite element formulations that are supposed to provide second-order spatial accuracy. All of them rely on the same weak formulation, using Riemann solver to evaluate interface integrals. We define several asymptotic limit cases of the shallow water equations within their space of parameters. The idea is to develop a comparison of these numerical schemes in several relevant regimes of the subcritical shallow water flow. Finally, a new pair, using non-conforming linear elements for both velocities and elevation (P,P), is presented, giving optimal rates of convergence in all test cases. P,P1 and P,P1 mixed formulations lack convergence for inviscid flows. P,P2 pair is more expensive but provides accurate results for all benchmarks. P,P provides an efficient option, except for inviscid Coriolis-dominated flows, where a small lack of convergence is observed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Assessment of algorithms for the no-slip boundary condition in the lattice Boltzmann equation of BGK modelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2008Yong Kweon Suh Abstract Three kinds of algorithms for the lattice Boltzmann equation of the BGK model in the implementation of the no-slip boundary condition on the wall are assessed by using the analytical formula for the slip velocity of the fully developed pressure-driven channel flow. It is shown that the bounce-back algorithm results in the spatial accuracy of 1st order, except for the case when the wall is located at half way between the two grid lines. The interpolation scheme proposed by Yu et al. (Prog. Aerospace Sci. 2003; 39:329,367) and the similar one by Bouzidi et al. (Phys. Fluids 2001; 13(11):3452,3459) are of 2nd order, but the error increases quadratically with the relaxation time. The extrapolation scheme of Guo et al. (Phys. Fluids 2002; 14(6):2007,2010) is also shown to be of 2nd order, and the error level increases linearly with the relaxation time, but it turns out that this scheme is unstable for a certain range of parameter values. Numerical experiments with various parameter sets have been performed to obtain the stability diagram. Three algorithms are then applied to a circular-Couette flow and their performance is also studied in terms of the numerical accuracy and stability. Copyright © 2008 John Wiley & Sons, Ltd. [source] A collocated, iterative fractional-step method for incompressible large eddy simulationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2008Giridhar Jothiprasad Abstract Fractional-step methods are commonly used for the time-accurate solution of incompressible Navier,Stokes (NS) equations. In this paper, a popular fractional-step method that uses pressure corrections in the projection step and its iterative variants are investigated using block-matrix analysis and an improved algorithm with reduced computational cost is developed. Since the governing equations for large eddy simulation (LES) using linear eddy-viscosity-based sub-grid models are similar in form to the incompressible NS equations, the improved algorithm is implemented in a parallel LES solver. A collocated grid layout is preferred for ease of extension to curvilinear grids. The analyzed fractional-step methods are viewed as an iterative approximation to a temporally second-order discretization. At each iteration, a linear system that has an easier block-LU decomposition compared with the original system is inverted. In order to improve the numerical efficiency and parallel performance, modified ADI sub-iterations are used in the velocity step of each iteration. Block-matrix analysis is first used to determine the number of iterations required to reduce the iterative error to the discretization error of. Next, the computational cost is reduced through the use of a reduced stencil for the pressure Poisson equation (PPE). Energy-conserving, spatially fourth-order discretizations result in a 7-point stencil in each direction for the PPE. A smaller 5-point stencil is achieved by using a second-order spatial discretization for the pressure gradient operator correcting the volume fluxes. This is shown not to reduce the spatial accuracy of the scheme, and a fourth-order continuity equation is still satisfied to machine precision. The above results are verified in three flow problems including LES of a temporal mixing layer. Copyright © 2008 John Wiley & Sons, Ltd. [source] Theoretical analysis for achieving high-order spatial accuracy in Lagrangian/Eulerian source termsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2006David P. Schmidt Abstract In a fully coupled Lagrangian/Eulerian two-phase calculation, the source terms from computational particles must be agglomerated to nearby gas-phase nodes. Existing methods are capable of accomplishing this particle-to-gas coupling with second-order accuracy. However, higher-order methods would be useful for applications such as two-phase direct numerical simulation and large eddy simulation. A theoretical basis is provided for producing high spatial accuracy in particle-to-gas source terms with low computational cost. The present work derives fourth- and sixth-order accurate methods, and the procedure for even higher accuracy is discussed. The theory is also expanded to include two- and three-dimensional calculations. One- and two-dimensional tests are used to demonstrate the convergence of this method and to highlight problems with statistical noise. Finally, the potential for application in computational fluid dynamics codes is discussed. It is concluded that high-order kernels have practical benefits only under limited ranges of statistical and spatial resolution. Additionally, convergence demonstrations with full CFD codes will be extremely difficult due to the worsening of statistical errors with increasing mesh resolution. Copyright © 2006 John Wiley & Sons, Ltd. [source] Fourth-order compact formulation of Navier,Stokes equations and driven cavity flow at high Reynolds numbersINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2006E. Erturk Abstract A new fourth-order compact formulation for the steady 2-D incompressible Navier,Stokes equations is presented. The formulation is in the same form of the Navier,Stokes equations such that any numerical method that solve the Navier,Stokes equations can easily be applied to this fourth-order compact formulation. In particular, in this work the formulation is solved with an efficient numerical method that requires the solution of tridiagonal systems using a fine grid mesh of 601 × 601. Using this formulation, the steady 2-D incompressible flow in a driven cavity is solved up to Reynolds number with Re = 20 000 fourth-order spatial accuracy. Detailed solutions are presented. Copyright © 2005 John Wiley & Sons, Ltd. [source] Use of slopelimiter techniques in traditional numerical methods for multi-phase flow in pipelines and wellsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2005R. J. Lorentzen Abstract The aim of this paper is to show how simple and traditional methods for simulating multi-phase flow can be improved by introducing higher order accuracy. Numerical diffusion is reduced to a minimum by using slopelimiter techniques, and better predictions of flow rates and pressure are obtained. Slopelimiter techniques, originally developed to achieve higher order of accuracy in Godunov's method, is applied to a method following a finite element approach and a predictor,corrector shooting technique. These methods are tested and compared to a Godunov-type scheme recently developed for multi-phase flow. Implementation of Godunov-type schemes for multi-phase flow tends to be a complicated and challenging task. Introducing the slopelimiter techniques in the finite element approach and the predictor,corrector shooting technique is however simple, and provides an overall reduction of the numerical diffusion. The focus is on using these techniques to improve the mass transport description, since this is the main concern in the applications needed. The presented schemes represent different semi-implicit approaches for simulating multi-phase flow. An evaluation of higher order extensions, as well as a comparison by itself, is of large interest. We present a model for two-phase flow in pipelines and wells, and an outline of the numerical methods and the extensions to second order spatial accuracy. Several examples motivated by applications in underbalanced drilling are presented, and the advantages of using higher order schemes are illustrated. Copyright © 2005 John Wiley & Sons, Ltd. [source] An algebraic algorithm for generation of three-dimensional grain maps based on diffraction with a wide beam of hard X-raysJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2004T. Markussen A reconstruction method is presented for generation of three-dimensional maps of the grain boundaries within powders or polycrystals. The grains are assumed to have a mosaic spread below 1°. They are mapped by diffraction with a wide beam of hard X-rays, using a setup similar to that of parallel-beam absorption contrast tomography. First the diffraction spots are sorted with respect to grain of origin. Next, for each grain the reconstruction is performed by an algebraic algorithm known as three-dimensional ART. From simulations it is found that reconstructions with a spatial accuracy better than the pixel size of the detector can be obtained from as few as five diffraction spots. The results are superior to three-dimensional reconstructions based on the same data using a variant of the filtered back-projection algorithm. In comparison with layer-by-layer type reconstructions based on the two-dimensional ART algorithm, as introduced by Poulsen & Fu [J. Appl. Cryst. (2003), 36, 1062,1068], the quality of the maps is found to be similar, provided that five to ten spots are available for analysis, while data acquisition with the three-dimensional method is much faster. The three-dimensional ART methodology is validated on experimental data. With state-of-the-art detectors, the spatial accuracy is estimated to be 5,µm. [source] Assessing the spatial and temporal variation in the skill of precipitation forecasts from an NWP modelMETEOROLOGICAL APPLICATIONS, Issue 1 2008Nigel Roberts Abstract It is becoming increasingly important to be able to verify the spatial accuracy of precipitation forecasts, especially with the advent of high-resolution numerical weather prediction (NWP) models. In this article, the fractions skill score (FSS) approach has been used to perform a scale-selective evaluation of precipitation forecasts during 2003 from the Met Office mesoscale model (12 km grid length). The investigation shows how skill varies with spatial scale, the scales over which the data assimilation (DA) adds most skill, and how the loss of that skill is dependent on both the spatial scale and the rainfall coverage being examined. Although these results come from a specific model, they demonstrate how this verification approach can provide a quantitative assessment of the spatial behaviour of new finer-resolution models and DA techniques. Copyright © 2008 Royal Meteorological Society [source] Planar Droplet Sizing for the Characterization of Droplet Clusters in an Industrial Gun-Type BurnerPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3 2003Laurent Zimmer Abstract An important problem in spray combustion deals with the existence of dense regions of droplets, called clusters. To understand their formation mechanism, the droplet dynamics and fuel concentration profile are investigated by means of planar laser techniques in an industrial gun-type burner. The simultaneous measurement of elastic Mie scattering and Laser Induced Fluorescence (LIF) allows the instantaneous measurement of the Sauter Mean Diameter (SMD), after proper calibration. Using two different CCDs to get the two signals requires a detailed calibration of the CCD response before getting absolute diameters. Pixels are binned 6 by 6 to obtain the final SMD map, this is a compromise between spatial accuracy and noise. Velocity field is measured on both sets of images using standard Particle Image Velocimetry (PIV) algorithms. The comparison of cross-correlation technique with PDA results shows that the velocity measured on the LIF images are close to the velocity based on D30, whereas the Mie scattering results are similar to D20. On Mie scattering images, regions of high interfacial area forming clusters can be detected. A special tracking scheme is used to characterize their dynamics in terms of velocity and diameters by ensuring that the same volume of fluid is tracked. It is shown that the clusters have a velocity similar to the velocity of droplets with the same diameter as the mean SMD of the cluster. It is also shown that an increase of pressure tends to trigger the appearance of such a group of droplets, due to a smaller diameter of the droplets caused by the increase of pressure discharge. Uncertainties for the different techniques used are discussed. [source] Saccadic eye movement task identifies cognitive deficits in children with schizophrenia, but not in unaffected child relativesTHE JOURNAL OF CHILD PSYCHOLOGY AND PSYCHIATRY AND ALLIED DISCIPLINES, Issue 12 2005Randal G. Ross Background:, The delayed oculomotor response (DOR) task requires response inhibition followed by movement of gaze towards a known spatial location without a current stimulus. Abnormalities in response inhibition and in the spatial accuracy of the eye movement are found in individuals with schizophrenia and in many of their relatives, supporting the use of these saccadic abnormalities as endophenotypes in genetic studies. It is unknown whether school-age children, either with psychosis or as relatives of a schizophrenic proband, can be included. Method:, One hundred eighty-seven children, ages 5.8,16.0 years , 45 children with childhood-onset schizophrenia, 64 children with a first-degree relative with schizophrenia, and 84 typically developing children , completed DOR tasks with 1 and 3 second delays. Results:, Children with childhood-onset schizophrenia demonstrated impaired response inhibition and impaired spatial accuracy compared to both relatives and typicals; however, relatives and typicals did not differ from each other. Conclusions:, Children with childhood-onset schizophrenia have saccadic abnormalities similar to those found in adults with schizophrenia, supporting the continuity of executive function deficits in childhood-onset with adolescent and adult-onset schizophrenia. However, saccadic tasks are not sensitive to genetic risk in non-psychotic children and 6,15-year-old children should not be included in genetic studies utilizing this endophenotype. [source] | ||||||||||