scholarly journals Using reciprocity for relating the simulation of transcranial current stimulation to the EEG forward problem

2016 ◽  
Author(s):  
Sven Wagner ◽  
Felix Lucka ◽  
Johannes Vorwerk ◽  
Christoph Herrmann ◽  
Guido Nolte ◽  
...  
Keyword(s):  
Forward Problem ◽  
The Finite Element Method ◽  
Hexahedral Elements ◽  
Integration Approach ◽  
Shell Models ◽  
Surface Segmentation ◽  
Volume Conductor Model ◽  
Adjoint Approach ◽  
The Relationship ◽  
Primary Current

To explore the relationship between transcranial current stimulation (tCS) and the electroencephalography (EEG) forward problem, we investigate and compare accuracy and efficiency of a reciprocal and a direct EEG forward approach for dipolar primary current sources both based on the finite element method (FEM), namely the adjoint approach (AA) and the partial integration approach in conjunction with a transfer matrix concept (PI). By analyzing numerical results, comparing to analytically derived EEG forward potentials and estimating computational complexity in spherical shell models, AA turns out to be essentially identical to PI. It is then proven that AA and PI are also algebraically identical even for general head models. This relation offers a direct link between the EEG forward problem and tCS. We then demonstrate how the quasi-analytical EEG forward solutions in sphere models can be used to validate the numerical accuracies of FEM-based tCS simulation approaches. These approaches differ with respect to the ease with which they can be employed for realistic head modeling based on MRI-derived segmentations. We show that while the accuracy of the most easy to realize approach based on regular hexahedral elements is already quite high, it can be significantly improved if a geometry-adaptation of the elements is employed in conjunction with an isoparametric FEM approach. While the latter approach does not involve any additional difficulties for the user, it reaches the high accuracies of surface-segmentation based tetrahedral FEM, which is considerably more difficult to implement and topologically less flexible in practice. Finally, in a highly realistic head volume conductor model and when compared to the regular alternative, the geometry-adapted hexahedral FEM is shown to result in significant changes in tCS current flow orientation and magnitude up to 45 degrees and a factor of 1.66, respectively.

scholarly journals Investigations on Torsion of the Two-Chords Single Laced Members

2017 ◽  
Vol 25 (2) ◽  
pp. 147-160
Author(s):  
Paweł Lorkowski ◽  
Bronisław Gosowski
Keyword(s):  
Cross Sections ◽  
Experimental Studies ◽  
The Finite Element Method ◽  
Second Moment ◽  
Steel Columns ◽  
Numerical Studies ◽  
Traction Network ◽  
Railway Traction ◽  
Parametric Analyses ◽  
The Relationship

Abstract The paper presents experimental and numerical studies to determine the equivalent second moment of area of the uniform torsion of the two-chord steel single laced members. The members are used as poles of railway traction network gates, and steel columns of framed buildings as well. The stiffness of uniform torsion of this kind of columns allows to the determine the critical loads of the spatial stability. The experimental studies have been realized on a single - span members with rotation arrested at their ends, loaded by a torque applied at the mid-span. The relationship between angle of rotation of the considered cross-section and the torque has been determined. Appropriate numerical model was created in the ABAQUS program, based on the finite element method. A very good compatibility has been observed between experimental and numerical studies. The equivalent second moment of area of the uniform torsion for analysed members has been determined by comparing the experimental and analytical results to those obtained from differential equation of non-uniform torsion, based on Vlasov’s theory. Additionally, the parametric analyses of similar members subjected to the uniform torsion, for the richer range of cross-sections have been carried out by the means of SOFiSTiK program. The purpose of the latter was determining parametrical formulas for calculation of the second moment of area of uniform torsion.

Study on the Range of Freeze-Thaw of Surrounding Rock from a Cold-Region Tunnel and the Effects of Insulation Material

2011 ◽  
Vol 399-401 ◽  
pp. 2222-2225 ◽  
Author(s):  
Peng Qi ◽  
Jing Zhang ◽  
Zhi Rong Mei ◽  
Yue Xiu Wu
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Surrounding Rock ◽  
Insulation Material ◽  
The Finite Element Method ◽  
Cold Region ◽  
Coupled Problem ◽  
Fluid Transfer ◽  
Tunnel Depth ◽  
The Relationship

A mathematical models for the coupled problem is established by considering heat and mass transfer and phase change for rock mass at low temperature, according to the theory of heat and mass transfer for porous media. It is considered of the influences of fluid transfer on the heat conduction and the temperature gradient on the seepage. By adopting the finite element method, the numerical simulation is done to study the range of frost-thaw of surrounding rock and the effects of insulation material in cold regions, which analysis the influence of tunnel depth and surrounding rock class on the range of frost-thaw, the change law of the frost-thaw area of different insulation material and the relationship between the frost-thaw area and the thickness of insulation material.

scholarly journals Influence of the flexibility of beams and slabs in static response and dynamic properties

2016 ◽  
Vol 9 (6) ◽  
pp. 842-855 ◽  
Author(s):  
J. R. BUENO ◽  
◽  
D. D. LORIGGIO ◽  
Keyword(s):  
Finite Element Method ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Vibration Modes ◽  
Linear Regime ◽  
Static Response ◽  
The Finite Element Method ◽  
Standard Code ◽  
The Relationship ◽  
Brazilian Standard

Abstract This article examines numerically the flexibility influence of support beams in static response and dynamic properties of a symmetric plate formed by massive slabs of reinforced concrete in elastic linear regime, using the Finite Element Method. In the static response the variation of bending mo-ments and displacements are evaluated, which depend on the relationship between the flexibility of the slab and the beam. The evaluation of dynamic properties is held in undamped free vibration, through which the vibration modes and the values of the natural frequencies is obtained, which are compared with the limits of the Brazilian standard code for design of concrete structures. Results show that the response may show great variation due to the change in the relationship between bending stiffness of the slabs and the beams.

scholarly journals Underwater Spiral Wave Sound Source Based on Phased Array with Three Transducers

Sensors ◽  
2019 ◽  
Vol 19 (14) ◽  
pp. 3192
Author(s):  
Lu ◽  
Guo ◽  
Lan ◽  
Sun ◽  
Li ◽  
...  
Keyword(s):  
Finite Element Method ◽  
Sound Source ◽  
Piezoelectric Ceramic ◽  
Phased Array ◽  
Fem Simulation ◽  
Spiral Wave ◽  
Sound Field ◽  
The Finite Element Method ◽  
The Relationship ◽  
Made In

This paper realizes an underwater spiral wave sound source by using three omni-directional spherical transducers with three different phases. The pressure distribution of the sound field for a phased array is derived using the superposition theory of sound field. The generation of spiral wave field is presented, the relationship between the performance of phased array sound field and the array parameters is analyzed, and also verified by the finite element method (FEM). A spiral wave sound source with three spherical piezoelectric ceramic transducers is then designed and fabricated based on FEM simulation, and the performance of the sound source is analyzed. Measurements are made in a reverberation pool, and the result shows that the fabricated spiral wave sound source is capable of producing a spiral sound wave. Under a frequency of 3.5 kHz, the phase directivity has a fluctuation of ±21°, and the amplitude directivity range is 4.3 dB, which verifies the realization of the spiral wave sound source.

scholarly journals Generation of field potentials and modulation of their dynamics through volume integration of cortical activity

2015 ◽  
Vol 113 (1) ◽  
pp. 339-351 ◽  
Author(s):  
Yoshinao Kajikawa ◽  
Charles E. Schroeder
Keyword(s):  
Current Source ◽  
Quantitative Description ◽  
Critical Issue ◽  
Synaptic Activity ◽  
Field Potentials ◽  
Cortical Layers ◽  
Physiological Processes ◽  
Volume Conductor Model ◽  
The Relationship ◽  
The Brain

Field potentials (FPs) recorded within the brain, often called “local field potentials” (LFPs), are useful measures of net synaptic activity in a neuronal ensemble. However, due to volume conduction, FPs spread beyond regions of underlying synaptic activity, and thus an “LFP” signal may not accurately reflect the temporal patterns of synaptic activity in the immediately surrounding neuron population. To better understand the physiological processes reflected in FPs, we explored the relationship between the FP and its membrane current generators using current source density (CSD) analysis in conjunction with a volume conductor model. The model provides a quantitative description of the spatiotemporal summation of immediate local and more distant membrane currents to produce the FP. By applying the model to FPs in the macaque auditory cortex, we have investigated a critical issue that has broad implications for FP research. We have shown that FP responses in particular cortical layers are differentially susceptible to activity in other layers. Activity in the supragranular layers has the strongest contribution to FPs in other cortical layers, and infragranular FPs are most susceptible to contributions from other layers. To define the physiological processes generating FPs recorded in loci of relatively weak synaptic activity, strong effects produced by synaptic events in the vicinity have to be taken into account. While outlining limitations and caveats inherent to FP measurements, our results also suggest specific peak and frequency band components of FPs can be related to activity in specific cortical layers. These results may help improving the interpretability of FPs.

Error Bounds in an Optimization Problem Using the Finite-Element Method

1973 ◽  
Vol 40 (1) ◽  
pp. 204-208
Author(s):  
R. W. McLay ◽  
E. M. Buturla
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Error Bounds ◽  
Optimization Problem ◽  
Finite Element Solution ◽  
Element Solution ◽  
The Finite Element Method ◽  
The Relationship ◽  
Circular Disks ◽  
Element Method

An optimization problem involving the thermal deflections of two parallel circular disks is examined. Error bounds are developed for both the finite-element solution and the optimization problem. The relationship between the errors is illustrated in a single bound.

Structure Analysis with 2D Quadrilateral Meshes Generated by a Label-Driven Subdivision

2016 ◽  
Vol 10 (2) ◽  
pp. 187-194 ◽  
Author(s):  
Bo Liu ◽  
◽  
Kenjiro T. Miura ◽  
Shin Usuki ◽  
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Structural Analysis ◽  
Structure Analysis ◽  
Two Dimensional ◽  
The Finite Element Method ◽  
Tetrahedral Element ◽  
Hexahedral Elements ◽  
Hexahedral Element ◽  
Preliminary Research

For a structural analysis using the finite element method, a hexahedral element is preferable to a tetrahedral element from the viewpoint of accuracy. However, it is very difficult to subdivide a mesh consisting of hexahedral elements if the shape of the mesh is complicated. Hence, in this paper, as a preliminary research, we use a label-driven subdivision method for a two-dimensional mesh, and show that meshes subdivided nonuniformly can guarantee as much accuracy as meshes with uniform subdivision.

no

2016 ◽  
Vol 4 (1) ◽  
pp. 0-0
Author(s):  
Олег Ещенко ◽  
Oleg Eshchenko ◽  
Игорь Болгов ◽  
Igor Bolgov
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
The Finite Element Method ◽  
Retaining Structures ◽  
The Relationship ◽  
Element Method

In this article an example of Tuapse refinery examines the relationship deformations tank foundation and pile retaining structures at various embodiments, the construction of both objects. The finite element method determined the effect of tech-energy building by the amount of heel tank. Advice on selecting the best option erection paired structures

Design and modeling of an electromagnetic launcher for weft insertion system

2018 ◽  
Vol 89 (5) ◽  
pp. 834-844 ◽  
Author(s):  
Emad Owlia ◽  
Seyed Abbas Mirjalili ◽  
Mostafa Shahnazari
Keyword(s):  
Numerical Procedure ◽  
Processing Technique ◽  
Experimental Methodology ◽  
Image Processing Technique ◽  
Weft Yarn ◽  
The Finite Element Method ◽  
Projectile Velocity ◽  
Electromagnetic Launcher ◽  
The Relationship ◽  
Specific Amount

An electromagnetic launcher can be used as an accelerator for yarn attached to a ferromagnetic projectile. As a result, yarn endures a specific amount of tension. In addition to the yarn variables and the type of weft insertion system, the parameters of the weft yarn accelerator strongly affect the weft yarn velocity, its tension, and consequently the fabric quality. An applicable model that can represent the relationship between input and output parameters of this weft insertion system is very useful for predicting the strike of the projectile. Therefore, in this research a 3D imitating launching model was developed by the finite element method. A coil electromagnetic launcher was employed. An experimental methodology using an image-processing technique was also utilized to measure the projectile velocity. Numerical results were compared with experimental results to verify the numerical procedure. A validated model can be a reliable tool to investigate the effects of many process parameters on the strike of the projectile and to optimize them. Therefore, the system parameters can be scientifically defined by this model to insert a weft yarn.

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