Dipole Source Research Articles

Auditory Cortical Temporal Processing and Hemispheric Asymmetry Revealed by N1 Dipole Source Activity in Adult Cochlear Implant Users

Auditory Cortical Temporal Processing and Hemispheric Asymmetry Revealed by N1 Dipole Source Activity in Adult Cochlear Implant Users

Simulations and Experimental Investigations on the Acoustic Characterization of Centrifugal Pumps of Different Specific Speed

Subject of discussion are simulations and experimental investigations on the acoustic characterization of three single stage centrifugal pumps of different specific speed. In operation, these pump-types generate pressure pulsation at blade passing frequency, primarily due to rotor-volute-interaction. In order to determine the acoustic excitation it is necessary to know about the pumps’ acoustic transmission parameters. In this paper, a one-dimensional numerical model for transient time-domain simulation is presented, which takes into account the pump geometry as well as the volutes’ structural behaviour by means of the local effective speed of sound. Numerical results for the transmission characteristics of the three different pumps are shown in terms of scattering matrices and evaluated against parameters calculated from measurement results. The experimental analyses are carried out using dynamic pressure sensors in both the suction and the discharge pipe. Assuming solely plane wave propagation, the complex acoustic field on each side is evaluated independently. The so called “two source” method is then used to determine the transmission parameters of the pumps in standstill for a range of frequencies experimentally. Subsequently, the acoustic excitation at varying rotational speed is evaluated by means of measurements at the pumps in operation and presented as monopole and dipole source types for cavitation-free conditions.

Wavefield separation for borehole acoustic reflection survey using parametric decomposition and waveform inversion

We have developed a wavefield separation filter for borehole acoustic reflection surveys (BARS) that uses parametric decomposition and waveform inversion, which we call the PWI filter. A BARS survey uses a sonic logging tool in a fluid-filled borehole to image near-borehole structure. Signals from a monopole or dipole source are reflected from geologic interfaces and recorded by arrays of receivers of the same tool. Because amplitudes of direct head waves and borehole modes are significantly larger than those of the event signals, wavefield separation to extract the event signals is crucial for BARS processing. The PWI filter estimates the direct head waves and borehole modes using the parametric decomposition, which is based on a 1D wave propagation model in the frequency domain. The wave-propagation model is calibrated using waveform inversion, which solves for the slowness and attenuation of the waves. The inversion is regularized using the assumption that the slowness and attenuation smoothly vary with frequency; the nonlinear system of equations is iteratively solved using the Newton method. An example of wavefield separation is shown for field data for a very fast formation for a monopole source. After using the PWI filter to separate the S-waves and direct and reflected Stoneley waves, we obtain the final filtered waveforms by further applying a median filter to separate the residual waveforms, which are not separated by the PWI filter.

The dual-frequency zero-backward scattering realized in a hybrid metallo-dielectric nanoantenna

In this paper, we propose a hybrid metallo-dielectric core-shell nanorod for the Kerker-type effect at two different frequencies. The effect arises from the interference of the scattering waves of the nanorod, which are generated by the magnetic dipole moment (MD) of the high-index hollow particle and the electric dipole moment (ED) induced in both metallic and dielectric particles. Interestingly, we find that such kind of unidirectional radiation properties, (i.e., zero back scattering occurring at dual frequencies) can be sustained with a single nanorod, which usually being equivalent to a local electric dipole source. The effect of substrate is also considered to investigate the typical experimental realization for the dual-frequency unidirectionalities of the nanoantenna. Furthermore, the unidirectionality can be further improved by the design of one-dimensional array of the hybrid nanoantenna. Our results could provide an additional degree of freedom for light scattering manipulation, and widen the versatile applications in nanoantennas, optical sensor, light emitters, as well as photovoltaic devices.

Constrained maximum intensity optimized multi-electrode tDCS targeting of human somatosensory network.

Transcranial direct current stimulation (tDCS) is a noninvasive method that delivers current through the scalp to enhance or suppress brain activity. The standard way of applying tDCS is by the use of two large rectangular sponge electrodes on the scalp. The resulting currents often stimulate a broad region of the brain distributed over brain networks. In order to address this issue, recently, multi-electrode transcranial direct current stimulation with optimized montages has been used to stimulate brain regions of interest (ROI) with improved trade-off between focality and intensity of the electrical current at the target brain region. However, in many cases only the location of target region is considered and not the orientation. Here we emphasize the importance of calculating the individualized target location and orientation by combined electroencephalography and magnetoencephalography (EMEG) source analysis in individualized skull-conductivity calibrated finite element method (FEM) head models and stimulate the target region by four different tDCS montages. We have chosen the generator of the P20/N20 component, located at Brodmann area 3b and oriented mainly from posterior to anterior directions as our target for stimulation because it can be modeled as a single dipole source with a fixed position and orientation. The simulations will deliver optimized excitatory and inhibitory electrode montages that are in future investigations compared to standard and sham tDCS in a somatosensory experiment. We also present a new constrained maximum intensity (CMI) optimization approach that better distributes the currents over multiple electrodes, therefore should lead to less tingling and burning sensations at the skin, and thus allows an easier realization of the sham condition significantly reducing the current intensity parallel to the target.

Streamline Computation Study on Rotation Aerodynamic Noise Prediction of Cross-flow Fan

The approach of resolving analysis the cross-flow relative motion streamline on the cross-flow straight blade is presented to predict the rotation aerodynamic noise performance of cross-flow fan by solving the dipole source term of Ffowcs Williams and Hawkings equation, while the cross-flow fan is applied in the indoor unit of split-type air-conditioner and operated in the rated condition. The calculating results of the method are respectively drawn by programming in Matlab computational language, and compared with the results of CAA numerical simulation and noise experiment. There are some differences in the distribution condition of aerodynamic force fluctuation amplitude on the blade surface, and sound pressure in the related frequency on the indoor unit casing, or on the sphere far field, between the streamline computation approach and numerical simulation. The orders of magnitudes of these calculating results solved by the analysing streamline method are similar with that attained by the numerical simulation. The resolving analysis approach has the characteristics of decreasing the computing cost and not constructing the acoustics grid model of fan, compared with the numerical simulation. The error between the result of numerical simulation and noise test is larger than that between the result of theoretical calculation and noise test, so the approach could be used for the rotation aerodynamic noise analysis of the cross-flow fan.

Effectiveness of exponential heat source, nanoparticle shape factor and Hall current on mixed convective flow of nanoliquids subject to rotating frame

PurposeThe study of novel exponential heat source (EHS) phenomena across a flowing fluid with the suspension of nanoparticles over a rotating plate in the presence of Hall current and chemical reaction has been an open question. Therefore, the purpose of this paper is to investigate the impact of EHS in the transport of nanofluid under the influence of strong magnetic dipole (Hall effect), chemical reaction and temperature-dependent heat source (THS) effects. The Khanafer-Vafai-Lightstone model is used for nanofluid and the thermophysical properties of nanofluid are calculated from mixture theory and phenomenological laws. The simulation of the flow is also carried out using the appropriate values of the empirical shape factor for five different particle shapes (i.e. sphere, hexahedron, tetrahedron, column and lamina).Design/methodology/approachUsing Laplace transform technique, exact solutions are presented for the governing nonlinear equations. Graphical illustrations are pointed out to represent the impact of involved parameters in a comprehensive way. The numeric data of the density, thermal conductivity, dynamic viscosity, specific heat, Prandtl number and Nusselt number for 20 different nanofluids are presented.FindingsIt is established that the nanofluid enhances the heat transfer rate of the working fluids; the nanoparticles also cause an increase of viscous. The impact of EHS advances the heat transfer characteristics significantly than usual thermal-based heat source (THS).Originality/valueThe effectiveness of EHS phenomena in the dynamics of nanofluid over a rotating plate with Hall current, chemical reaction and THS effects is first time investigated.

Image theory for a sphere with negative permittivity

An image system for a point charge outside a dielectric sphere is presented for all complex values of relative permittivity ϵ = ϵ′ + iϵ″. The standard image integral solution of a point charge outside a dielectric sphere involving an image point charge plus a line source is shown to diverge for ϵ′ < −1, and a correction is proposed for this case, involving image multipoles of infinite magnitude which regularize the divergent line integral. The number of these multipoles depends on the position of ϵ relative to the resonant values ϵ = −1 − 1/n for positive integer n. The internal potential and dipole sources are also considered.

Electroencephalography-Based Source Localization for Depression Using Standardized Low Resolution Brain Electromagnetic Tomography – Variational Mode Decomposition Technique

Background: Electroencephalography (EEG) may be used as an objective diagnosis tool for diagnosing various disorders. Recently, source localization from EEG is being used in the analysis of real-time brain monitoring applications. However, inverse problem reduces the accuracy in EEG signal processing systems. Objectives: This paper presents a new method of EEG source localization using variational mode decomposition (VMD) and standardized the low resolution brain electromagnetic tomography (sLORETA) inverse model. The focus is to compare the effectiveness of the proposed approach for EEG signals of depression patients. Method: As the first stage, real EEG recordings corresponding to depression patients are decomposed into various mode functions by applying VMD. Then, closely related functions are analyzed using the inverse modelling-based source localization procedures such as sLORETA. Simulations have been carried out on real EEG databases for depression to demonstrate the effectiveness of the proposed techniques. Results: The performance of the algorithm has been assessed using localization error (LE), mean square error and signal to noise ratio output corresponding to simulated EEG dipole sources and real EEG signals for depression. In order to study the spatial resolution for cortical potential distribution, the main focus has been on studying the effects of noise sources and estimating LE of inverse solutions. More accurate and robust localization results show that this methodology is very promising for EEG source localization of depression signals. Conclusion: It can be said that proposed algorithm efficiently suppresses the influence of noise in the EEG inverse problem using simulated EEG activity and EEG database for depression. Such a system may offer an effective solution for clinicians as a crucial stage of EEG pre-processing in automated depression detection systems and may prevent delay in diagnosis.

Routing emission with a multi-channel nonreciprocal waveguide

In this work, we present a multi-channel nonreciprocal waveguide, which is composed of a gyrotropic-bounded dielectric on the bottom and a plasmonic material on the top. The Lorentz reciprocity in the time-invariant system is broken when applying an external static magnetic field on the gyrotropic material. The nonreciprocal emission from the dipole source located in the center of the waveguide is observed in extended waveband channels. The proposed heterostructure serves as a photonic dichroism once the dielectric is replaced by a nonlinear material. The associated second harmonic generated in the nonlinear process can be separated from the fundamental signal under proper magnetic field intensity. Our findings may provide significant guidance for designing nonreciprocal photonic devices with superiorities of a tunable waveband, multiple channels, and small footprint.

Azimuth ambiguity elimination for borehole imaging using 3D borehole RTM scheme

A key technical challenge facing borehole acoustic reflection imaging is the uncertainty concerning the azimuth (i.e. the direction about the axis of the borehole) from which a reflected event arrives. In generating images of formation boundaries near the borehole this is referred to as azimuthal ambiguity. The phenomenon is comparable to the 3D out-of-plane effects encountered in imaging of 2D surface data. Systems with multiple receivers (e.g., the sonic scanner tool developed by Schlumberger) acquire sufficient information to uniquely image reflected wave energy at its correct azimuth. However, a full use of this information requires the wave data to be analyzed in the context of 3D, two-way elastic wave propagation and a suitable anisotropic medium. Here we summarize the development of a 3D anisotropic reverse time migration imaging scheme to sonic data, and demonstrate that within this imaging formulation azimuthal ambiguity is resolved for data from both monopole and dipole sources.

Acoustic radiation and reflection of a logging-while-drilling dipole source

SUMMARY With the comparison to the resistivity ultra-deep measurement, the single-well reflection survey in acoustic logging-while-drilling (ALWD) measurement lags far behind, especially ALWD dipole measurement has long been thought to be little added value. In this paper, we extended the dipole shear-wave (S-wave) reflection survey technology in wireline logging into ALWD and demonstrated the theoretical feasibility of adopting a dipole source–receiver system to perform ALWD reflection survey. For this purpose, we investigated the radiation patterns of radiantSH, SV and P waves, the energy fluxes of guided and radiant waves and their acoustical radiation efficiencies from an LWD dipole acoustic source by comparisons with the wireline results. The analysis results reveal that a dominant excitation-frequency band does exist in ALWD dipole S-wave reflection. Consequently, the expected excitation frequency should be located in the band of the signal with high radiation efficiency, guaranteeing the best radiation performance. In fast formations, SH wave is the best candidate for ALWD reflection survey due to its highest radiation efficiency. In contrast, the dominant excitation-frequency band of SH wave gets wider in a slow formation. Besides, the SV- and P-wave radiation efficiencies are also remarkable, implying that both waves can also be used for ALWD reflection survey in slow formations. We expounded the SH-, SV- and P-reflection behaviours at three typical excitation frequencies by our 3-D finite difference. Simulations to single-well reflection validate the key role of dominant excitation-frequency band and demonstrate the theoretical feasibility of applying the technology to ALWD. Our results can guide the design and measurement methods of ALWD dipole S-wave reflection survey tool, which could have extensive application prospect for geo-steering.

Pharyngeal flow simulations during sibilant sound in a patient-specific model with velopharyngeal insufficiency.

Dysfunction of the velopharyngeal valve in the human airway causes speech disorders because there is no separation between the oral and nasal cavities during normal oral speech. The speech literature hypothesizes that undesired sound is formed by turbulent flow in the nasal cavity in cases of small velopharyngeal openings. The aim is to determine the flow behavior and the sound-generating mechanism in the vocal tract using computational fluid dynamics in two patient-specific models with small and large velopharyngeal openings and contrast it with cases of complete velopharyngeal closure. The geometry for the models was reconstructed from computed tomography scans that were taken while the patients were sustaining a sibilant sound. The results for the turbulence are correlated with the broadband acoustic models of Proudman and Curle. The models show that turbulence in the vocal tract increases downstream of a constriction and that sound may be generated from it. Furthermore, most of the sound due to turbulence in the nasal cavity is governed by a dipole source where turbulence interacts with the nasal cavity walls. The generated sound power by turbulence itself in the nasal cavity (the quadrupole source) is two orders of magnitude less than the dipole source.

EM telemetry assessment for horizontal drilling in part of the Tarim basin through numerical simulation

AbstractElectromagnetic telemetry is bi‐directional transmission of borehole data for effective drilling, especially in unconventional wells. In this study, numerical simulations was used to investigate the possibility of applying EM telemetry for measurement while drilling (MWD) in an ultra‐deep borehole in the Tahe region of the Tarim basin, using the drill string as an antenna excited as a gaped dipole source to quantify spatial variations of the electromagnetic field from subsurface to the surface. Results confirm that the distribution of the electric field along the drill string is sensitive to vertical variations of electric conductivity in the host rock. The simulated results show a high attenuation within the conductive formations, thereby limiting the effectiveness of EM telemetry in data transfer to the surface. In addition, the changes in thickness and resistivity of the target region affects the amplitude of the desired response.

Pseudo-projection approach to reconstruct locations of point-like scatterers characterized by Lamé parameters and mass densities in an elastic half-space

A method for reconstructing the locations of point-like scatterers in an elastic half-space is developed in this article. Point-like scatterers are characterized by fluctuations of the Lamé parameters and the mass densities from the background structure of the wavefield. A representation of the wavefield is realized with the monopole and dipole Green’s functions. The main contribution of the present work is to clarify the far-field properties of the Green’s functions for both the monopole and dipole sources, which yields the pseudo-projection approach to the wave problem. Indicator functions that reconstruct the locations of point-like scatterers are defined by the far-field operator derived from the pseudo-projections and the near-field observation. Numerical computations were carried out to verify the accuracy of the pseudo-projection method. The sensitivities of the accuracy of the reconstruction results for the proposed method to random noise, the grid resolution at the free surface, and the analyzed frequency were also examined.

Hybrid Time-Domain PTD and Physical Optics Contour Integral Representations for the Near-Field Backscattering Problem

Time-domain physical optics (TDPO) contour integral representations are developed for backscattered near fields from a perfectly conducting surface illuminated by a dipole source. The proposed representations are derived from the TDPO surface integral representations by introducing two theorems: surface gradient and surface divergence theorems. The proposed representations are free from singularities for all the source/observer positions in which the dipole antenna is located. In addition, the time-domain physical theory of diffraction is introduced to modify the physical optical field considering the effect of the edge diffraction. Numerical examples are presented to demonstrate the efficiency and accuracy of the proposed method.

Equivalent current dipole source localization of deceptive response during crime-relevant sentence processing

Equivalent current dipole source localization of deceptive response during crime-relevant sentence processing

Benchmark analytical solutions for steady state high frequency broadband sound fields in three rectangular enclosures.

Analytical solutions are presented for broadband sound fields in three rectangular enclosures with absorption applied on the floor and ceiling, rigid sidewalls, and a vertically oriented dipole source. The solutions are intended to serve as benchmarks that can be used to assess the performance of broadband techniques, particularly energy-based methods, in a relatively straightforward configuration with precisely specified boundary conditions. A broadband Helmholtz solution is developed using a frequency-by-frequency modal approach to determine the exact band averaged mean-square pressures along spatial trajectories within each enclosure. Due to the specific choice of enclosure configuration and absorption distribution, an approximate specular solution can be obtained through a summation of uncorrelated image sources. Comparisons between the band averaged Helmholtz solution and the uncorrelated image solution reveal excellent agreement for a wide range of absorption levels and improve the understanding of correlation effects in broadband sound fields. A boundary element solution with diffuse boundaries is also presented, which produces consistently higher mean-square pressures in comparison with the specular solution, emphasizing the careful attention that must be placed on correctly modeling reflecting boundary conditions and demonstrating the errors that can result from assuming a Lambertian surface.

Research on the characteristic of noise and pressure fluctuation in the oil-gas mixing transportation of screw-axial pump

In order to study the spiral gas-liquid mixing loss and noise characteristics of the oil-gas mixing transportation of screw-axial pump, with the oil-gas mixing transportation of screw-axial pump as the research object, based on the RNG k–ε psilon internal unsteady flow model to simulate the pump parameter change of gas and liquid delivery information, extract the unsteady gas-liquid transfer information parameters and pressure fluctuation signals, using acoustic software LMS Virtual Lab IBEM indirect boundary element method is used to solve the helical axial multiphase mixture pumps in dipole source caused by noise. The distribution law of pressure field, pressure pulsation and sound pressure level in the pump and outlet of the helical axial flow multiphase flow pump is analyzed. The results show that the gas-liquid mixing in the helical-axial-flow oil-gas mixing pump, from impeller inlet to impeller outlet, is aggravated, the pressure increases and the flow is turbulent. From the inlet of the guide vane to the exit of the guide vane, the bubbles gradually move from the hub to the middle of the runner, then the pressure gradually decreases, and the low voltage area leads to the vortex phenomenon; for the internal pressure fluctuation of helical axial flow type oil-gas mixing pump, the pressure gradient in the static and static interference area between the impeller and the guide blade is large, which is an important area affecting hydraulic performance. The pressure pulsation in the cascade is affected by the blade passing frequency and the mutual interference between the rotor and stator blades. The pressure pulsation maximum value is mainly corresponding to the blade frequency and its doubling frequency, and under the interaction of rotor - stator cascade, the pressure pulsation of the monitoring point near the static and static interface is superimposed, and the main frequency is the blade’s triple leaf frequency. For screw axial flow noise in the oil-gas mixture pumps, screw axial multiphase flow pump hydrodynamic noise exports more than imports, sound pressure level frequency in low frequency band is evident, for impeller pressure impulses and its frequency doubling, after three times the pressure impulses, sound pressure level decline slows, the distribution of sound pressure level along with the increase of flow rate, shows the tendency of increase after decreases first. The research results are of great theoretical value and practical significance for the unsteady turbulent gas-liquid mixed transport, pressure fluctuation and noise characteristics in the oil-gas mixed transport pump.

CustEM: Customizable finite-element simulation of complex controlled-source electromagnetic data

We have developed the open-source toolbox custEM (customizable electromagnetic modeling) for the simulation of complex 3D controlled-source electromagnetic (CSEM) problems. It is based on the open-source finite-element library FEniCS, which supports tetrahedral meshes, multiprocessing, higher order polynomials, and anisotropy. We use multiple finite-element approaches to solve the time-harmonic Maxwell equations, which are based on total or secondary electric field and gauged potential formulations. In addition, we develop a secondary magnetic field formulation, showing superior performance if only magnetic fields are required. Using Nédélec basis functions, we robustly incorporate the current density on the edges of the mesh for the total field formulations. The latter enable modeling of CSEM problems taking topography into account. We evaluate semianalytical 1D layered-earth solutions with the pyhed library, supporting arbitrary configurations of dipole or loop sources for secondary field calculations. All system matrices have been modified to be symmetric and solved in parallel with the direct solver MUMPS. Aside from the finite-element kernel, mesh generation, interpolation, and visualization modules have been implemented to simplify and automate the modeling workflow. We prove the capability of custEM, including validation against analytic-solutions, crossvalidation of all implemented approaches, and results for a model with 3D topography with four examples. The object-oriented implementation allows for customizable modifications and additions or to use only submodules designed for special tasks, such as mesh generation or matrix assembly. Therefore, the toolbox is suitable for crossvalidation with other codes and as the basis for developing 3D inversion routines.