Adaptive current-flow models of ECT: Explaining individual static impedance, dynamic impedance, and brain current density

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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A Numerical Investigation Into the Interaction Between Current Flow and Fuel Consumption in a Segmented-in-Series Tubular SOFC

Journal of Fuel Cell Science and Technology ◽

10.1115/1.3005386 ◽

2009 ◽

Vol 6 (3) ◽

Cited By ~ 1

Author(s):

B. A. Haberman ◽

A. J. Marquis

Keyword(s):

Density Distribution ◽

Fuel Consumption ◽

Current Density ◽

Current Flow ◽

Flow Direction ◽

Ionic Current ◽

Leading Edge ◽

Current Density Distribution ◽

Fuel Flow ◽

In Series

A typical segmented-in-series tubular solid oxide fuel cell (SOFC) consists of flattened ceramic support tubes with rows of electrochemical cells fabricated on their outer surfaces connected in series. It is desirable to design this type of SOFC to operate with a uniform electrolyte current density distribution to make the most efficient use of the available space and possibly to help minimize the onset of cell component degradation. Predicting the electrolyte current density distribution requires an understanding of the many physical and electrochemical processes occurring, and these are simulated using the newly developed SOHAB multiphysics computer code. Of particular interest is the interaction between the current flow within the cells and the consumption of fuel from an adjacent internal gas supply channel. Initial simulations showed that in the absence of fuel consumption, ionic current tends to concentrate near the leading edge of each electrolyte. Further simulations that included fuel consumption showed that the choice of fuel flow direction can have a strong effect on the current flow distribution. The electrolyte current density distribution is biased toward the upstream fuel flow direction because ionic current preferentially flows in regions rich in fuel. Thus the correct choice of fuel flow direction can lead to more uniform electrolyte current density distributions, and hence it is an important design consideration for tubular segmented-in-series SOFCs. Overall, it was found that the choice of fuel flow direction has a negligible effect on the output voltage of the fuel cells.

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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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Magnetisation and Critical Currents in High Tc Powders

MRS Proceedings ◽

10.1557/proc-99-883 ◽

1987 ◽

Vol 99 ◽

Cited By ~ 3

Author(s):

A. M. Campbell ◽

A. D. Hibbs ◽

J. Eberharde ◽

S. Male ◽

M. F. Ashby ◽

...

Keyword(s):

Penetration Depth ◽

Current Density ◽

Current Flow ◽

Theoretical Calculations ◽

Hot Isostatic Pressing ◽

Critical Currents ◽

High Tc ◽

Isostatic Pressing

ABSTRACTMagnetisation curves have been measured on powders of various sizes. The hysteresis decreases with size for articles smaller than 20μ showing that barriers to current flow are at least this far apart. The current density is 6×106 amps/cm2 at 1.5T and this is consistent with theoretical calculations of Jc. Inductive transitions are consistent with a penetration depth of about 0.5μ at 78K. The results of Hot Isostatic Pressing are also discussed.

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Interaction Between Solid Copper Jets and Powerful Electrical Current Pulses

Journal of Applied Mechanics ◽

10.1115/1.4002568 ◽

2010 ◽

Vol 78 (2) ◽

Cited By ~ 2

Author(s):

Patrik Appelgren ◽

Torgny E. Carlsson ◽

Andreas Helte ◽

Tomas Hurtig ◽

Anders Larsson ◽

...

Keyword(s):

Current Pulse ◽

Current Density ◽

Energy Deposition ◽

Current Flow ◽

Contact Region ◽

Electrical Energy ◽

Electrical Current ◽

Separation Distance ◽

Flow Through ◽

Solid Copper

The interaction between a solid copper jet and an electric current pulse is studied. Copper jets that were created by a shaped-charge device were passed through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. The electrodes were connected to a pulsed-power supply delivering a current pulse with amplitudes up to 250 kA. The current and voltages were measured, providing data on energy deposition in the jet and electrode contact region, and flash X-ray diagnostics were used to depict the jet during and after electrification. The shape of, and the velocity distributions along, the jet has been used to estimate the correlation between the jet mass flow through the electrodes and the electrical energy deposition. On average, 2.8 kJ/g was deposited in the jet and electrode region, which is sufficient to bring the jet up to the boiling point. A model based on the assumption of a homogenous current flow through the jet between the electrodes underestimates the energy deposition and the jet resistance by a factor 5 compared with the experiments, indicating a more complex current flow through the jet. The experimental results indicate the following mechanism for the enhancement of jet breakup. When electrified, the natural-formed necks in the jet are subjected to a higher current density compared with other parts of the jet. The higher current density results in a stronger heating and a stronger magnetic pinch force. Eventually, the jet material in the neck is evaporated and explodes electrically, resulting in a radial ejection of vaporized jet material.

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Exploring design tradeoffs in analog IC placement with current-flow & current-density considerations

2015 International Conference on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design (SMACD) ◽

10.1109/smacd.2015.7301697 ◽

2015 ◽

Cited By ~ 2

Author(s):

Ricardo Martins ◽

Ricardo Povoa ◽

Nuno Lourenco ◽

Nuno Horta

Keyword(s):

Current Density ◽

Current Flow ◽

Analog Ic ◽

Design Tradeoffs

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Sensitivity and resolution improvement for in-vivo magnetic resonance current density imaging (MRCDI) of the human brain

10.1101/2021.03.23.436558 ◽

2021 ◽

Author(s):

Cihan Goksu ◽

Klaus Scheffler ◽

Frodi Gregersen ◽

Hasan H Eroglu ◽

Rahel Heule ◽

...

Keyword(s):

Magnetic Resonance ◽

Human Brain ◽

Current Density ◽

Current Flow ◽

Transcranial Electrical Stimulation ◽

Physiological Noise ◽

Flow Simulations ◽

Current Density Imaging ◽

Resonance Current

Purpose: Magnetic resonance current density imaging (MRCDI) combines MR brain imaging with the injection of time-varying weak currents (1-2 mA) to assess the current flow pattern in the brain. However, the utility of MRCDI is still hampered by low measurement sensitivity and poor image quality. Methods: We recently introduced a multi-gradient-echo-based MRCDI approach that has the hitherto best documented efficiency. We now advanced our MRCDI approach in three directions and performed phantom and in-vivo human brain experiments for validation: First, we verified the importance of enhanced spoiling and optimize it for imaging of the human brain. Second, we improved the sensitivity and spatial resolution by using acquisition weighting. Third, we added navigators as a quality control measure for tracking physiological noise. Combining these advancements, we tested our optimized MRCDI method by using 1 mA transcranial electrical stimulation (TES) currents injected via two different electrode montages in five subjects. Results: For a session duration of 4:20 min, the new MRCDI method was able to detect magnetic field changes caused by the TES current flow at a sensitivity level of 84 pT, representing in a twofold increase relative to our original method. Comparing both methods to current flow simulations based on personalized head models demonstrated a consistent increase in the coefficient of determination of ∆R2=0.12 for the current-induced magnetic fields and ∆R2=0.22 for the current flow reconstructions. Interestingly, some of the simulations still clearly deviated from the measurements despite of the strongly improved measurement quality. This suggests that MRCDI can reveal useful information for the improvement of head models used for current flow simulations. Conclusion: The advanced method strongly improves the sensitivity and robustness of MRCDI and is an important step from proof-of-concept studies towards a broader application of MRCDI in clinical and basic neuroscience research.

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When Current Does Not Follow Bonds: Current Density in Saturated Molecules

10.26434/chemrxiv.7851587.v1 ◽

2019 ◽

Author(s):

Anders Jensen ◽

Marc Hamilton Garner ◽

Gemma C. Solomon

Keyword(s):

Spatial Distribution ◽

Current Density ◽

Current Flow ◽

Structure Property ◽

Conjugated Molecules ◽

Structure Property Relationships ◽

Electron Transport Properties ◽

Current Flows ◽

Molecular Conductance ◽

Insight Into

<div> <div> <div> <p>The tools commonly used to understand structure-property relationships in molecular conductance, inter-atomic currents and conductance eigenchannels, generally give us a sense of familiarity, with the chemical bonding framework and molecular orbitals reflected in the current. Here we show that while this picture is true for conjugated molecules, it breaks down in saturated systems. We investigate the current density in saturated chains of alkanes, silanes and germanes and show that the current density does not follow the bonds, but rather the nuclei define the diameter of a pipe through which the current flows. We discuss how this picture of current density can be used to understand details about the electron transport properties of these molecules. Understanding the spatial distribution of current through molecules, rather than simply the magnitude, provides a powerful tool for chemical insight into physical properties of molecules that are related to current flow. </p> </div> </div> </div>

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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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