Direct Experimental Validation of Computational Current Flow Models with Intra-Cranial Recordings in Human and Non-Human Primates

A model is derived for a multi-stage crystallization with cross-current flows of the solution and the crystals being purified. The purity of the product is compared with that achieved in the countercurrent arrangement. A suitable function has been set up which allows the cross-current and countercurrent flow models to be compared and reduces substantially the labour of computation for the countercurrent arrangement. Using the recrystallization of KAl(SO4)2.12 H2O as an example, it is shown that, when the cross-current and countercurrent processes are operated at the same output, the countercurrent arrangement is more advantageous because its solvent consumption is lower.

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tDCS changes in motor excitability are specific to orientation of current flow

10.1101/149633 ◽

2017 ◽

Author(s):

Vishal Rawji ◽

Matteo Ciocca ◽

Andre Zacharia ◽

David Soares ◽

Dennis Truong ◽

...

Keyword(s):

Animal Studies ◽

Current Flow ◽

Motor Evoked Potentials ◽

Flow Direction ◽

Brain Regions ◽

Afferent Pathways ◽

Flow Models ◽

Cortical Columns ◽

Local Fluctuations ◽

Hand Region

Measurements and models of current flow in the brain during transcranial Direct Current Stimulation (tDCS) indicate stimulation of regions in-between electrodes. Moreover, the cephalic cortex result in local fluctuations in current flow intensity and direction, and animal studies suggest current flow direction relative to cortical columns determines response to tDCS. Here we test this idea by measuring changes in cortico-spinal excitability by Transcranial Magnetic Stimulation Motor Evoked Potentials (TMS-MEP), following tDCS applied with electrodes aligned orthogonal (across) or parallel to M1 in the central sulcus. Current flow models predicted that the orthogonal electrode montage produces consistently oriented current across the hand region of M1 that flows along cortical columns, while the parallel electrode montage produces none-uniform current directions across the M1 cortical surface. We find that orthogonal, but not parallel, orientated tDCS modulates TMS-MEPs. We also show modulation is sensitive to the orientation of the TMS coil (PA or AP), which is through to select different afferent pathways to M1. Our results are consistent with tDCS producing directionally specific neuromodulation in brain regions in-between electrodes, but shows nuanced changes in excitability that are presumably current direction relative to column and axon pathway specific. We suggest that the direction of current flow through cortical target regions should be considered for targeting and dose-control of tDCS.

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Verification Benchmarks to Assess the Implementation of Computational Fluid Dynamics Based Hemolysis Prediction Models

Journal of Biomechanical Engineering ◽

10.1115/1.4030823 ◽

2015 ◽

Vol 137 (9) ◽

Cited By ~ 12

Author(s):

Prasanna Hariharan ◽

Gavin D’Souza ◽

Marc Horner ◽

Richard A. Malinauskas ◽

Matthew R. Myers

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Power Law ◽

Analytical Solutions ◽

Experimental Validation ◽

Cfd Simulations ◽

Flow Models ◽

Flow Acceleration ◽

Blood Damage ◽

Eulerian Models

As part of an ongoing effort to develop verification and validation (V&V) standards for using computational fluid dynamics (CFD) in the evaluation of medical devices, we have developed idealized flow-based verification benchmarks to assess the implementation of commonly cited power-law based hemolysis models in CFD. The verification process ensures that all governing equations are solved correctly and the model is free of user and numerical errors. To perform verification for power-law based hemolysis modeling, analytical solutions for the Eulerian power-law blood damage model (which estimates hemolysis index (HI) as a function of shear stress and exposure time) were obtained for Couette and inclined Couette flow models, and for Newtonian and non-Newtonian pipe flow models. Subsequently, CFD simulations of fluid flow and HI were performed using Eulerian and three different Lagrangian-based hemolysis models and compared with the analytical solutions. For all the geometries, the blood damage results from the Eulerian-based CFD simulations matched the Eulerian analytical solutions within ∼1%, which indicates successful implementation of the Eulerian hemolysis model. Agreement between the Lagrangian and Eulerian models depended upon the choice of the hemolysis power-law constants. For the commonly used values of power-law constants (α = 1.9–2.42 and β = 0.65–0.80), in the absence of flow acceleration, most of the Lagrangian models matched the Eulerian results within 5%. In the presence of flow acceleration (inclined Couette flow), moderate differences (∼10%) were observed between the Lagrangian and Eulerian models. This difference increased to greater than 100% as the beta exponent decreased. These simplified flow problems can be used as standard benchmarks for verifying the implementation of blood damage predictive models in commercial and open-source CFD codes. The current study used only a power-law model as an illustrative example to emphasize the need for model verification. Similar verification problems could be developed for other types of hemolysis models (such as strain-based and energy dissipation-based methods). And since the current study did not include experimental validation, the results from the verified models do not guarantee accurate hemolysis predictions. This verification step must be followed by experimental validation before the hemolysis models can be used for actual device safety evaluations.

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Theoretical simulation and experimental validation of inverse quasi-one-dimensional steady and unsteady glottal flow models

The Journal of the Acoustical Society of America ◽

10.1121/1.2931959 ◽

2008 ◽

Vol 124 (1) ◽

pp. 535-545 ◽

Cited By ~ 18

Author(s):

Julien Cisonni ◽

Annemie Van Hirtum ◽

Xavier Pelorson ◽

Jan Willems

Keyword(s):

Experimental Validation ◽

Theoretical Simulation ◽

One Dimensional ◽

Flow Models ◽

Glottal Flow

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Experimental validation of multiphase flow models and testing of multiphase flow meters: a critical review of flow loops worldwide

Computational Methods in Multiphase Flow IV ◽

10.2495/mpf070101 ◽

2007 ◽

Cited By ~ 2

Author(s):

O. O. Bello ◽

G. Falcone ◽

C. Teodoriu

Keyword(s):

Multiphase Flow ◽

Critical Review ◽

Experimental Validation ◽

Flow Meters ◽

Flow Models

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The impact of brain lesions on tDCS-induced electric field magnitude

10.1101/2021.03.19.436124 ◽

2021 ◽

Author(s):

Ainslie Johnstone ◽

Catharina Zich ◽

Carys Evans ◽

Jenny Lee ◽

Nick S Ward ◽

...

Keyword(s):

Electric Fields ◽

Primary Motor Cortex ◽

Current Flow ◽

Region Of Interest ◽

Lesion Size ◽

Brain Lesions ◽

Flow Models ◽

Dose Control ◽

Flow Through ◽

The Impact

Background: Transcranial direct current stimulation (tDCS) has been used to enhance motor and language rehabilitation following a stroke. However, improving the effectiveness of clinical tDCS protocols depends on understanding how a lesion may influence tDCS-induced current flow through the brain. Objective: We systematically investigated the effect of brain lesions on the magnitude of electric fields (e-mag) induced by tDCS. Methods: We simulated the effect of 630 different lesions - by varying lesion location, distance from the region of interest (ROI), size and conductivity - on tDCS-induced e-mag. We used current flow models in the brains of two participants, for two commonly used tDCS montages, targeting either primary motor cortex (M1) or Brocas area (BA44) as ROIs. Results: The effect on absolute e-mag change was highly dependent on lesion size, conductance and distance from ROI. Larger lesions, with high conductivity, close to the ROI caused e-mag changes of more than 30%. The sign of this change was determined by the location of the lesion. Specifically, lesions located in-line with the predominant direction of current flow increased e-mag in the ROI, whereas lesions located in the opposite direction caused a decrease. Conclusions: These results demonstrate that tDCS-induced electric fields are profoundly influenced by lesion characteristics. This highlights the need for individualised targeting and dose control in stroke. Additionally, the variation in electrical fields caused by assigned conductance of the lesion underlines the need for improved estimates of lesion conductivity for current flow models.

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