Dipole Method Research Articles

Coarse-grained polarizable soft solvent models, with applications in dissipative particle dynamics.

We critically examine a broad class of explicitly polarizable soft solvent models aimed at applications in dissipative particle dynamics. We obtain the dielectric permittivity using the fluctuating box dipole method in linear response theory and verify the models in relation to several test cases, including demonstrating ion desorption from an oil-water interface due to image charge effects. We additionally compute the Kirkwood factor and find that it uniformly lies in the range gK≃0.7-0.8, indicating that dipole-dipole correlations are not negligible in these models. This is supported by the measurements of dipole-dipole correlation functions. As a consequence, Onsager theory over-predicts the dielectric permittivity by 20%-30%. The mean square molecular dipole moment can be accurately estimated with a first-order Wertheim perturbation theory.

An Independent Measure of the Kinematic Dipole from SDSS

We utilize the Sloan Digital Sky Survey (SDSS) extended Baryon Oscillation Spectroscopic Survey and Baryon Oscillation Spectroscopic Survey catalogs with precise spectroscopic redshifts to estimate the kinematic redshift dipole caused by the proper motion of the solar system. We find that the velocity extracted from the kinematic dipole is consistent with cosmic microwave background (CMB) inferred values. Although the small sky coverage and limited number density of the SDSS sources constrain us from obtaining precise and robust measurements, we leverage the redshift dipole method to estimate the kinematic dipole. The velocity measurements in this study are insensitive to intrinsic clustering, associated with the source count dipole. The kinematic dipole measured in this work and its consistency with CMB values do not guarantee isotropy at large scales. The anisotropy (excess dipole) measured with the NRAO VLA Sky Survey and the Wide-field Infrared Survey Explorer Catalog could be due to the intrinsic distribution of galaxies. The results in this work focus solely on the kinematic dipole term.

Implementation of a Highly Mobile UAVs Direction Finding Complex Using Virtual Magnetic Dipoles

Relevance. In the context of the development of modern broadband communication systems, the task of performing direction finding of signals using highly mobile direction finding systems (UAVs) is becoming especially urgent. They impose restrictions on the size of antenna elements and the distance between them, which leads to an increase in the mathematical error of the bearing. Problem statement. The paper sets the task of considering the possibility of increasing the direction finding accuracy of a highly mobile complex by using virtual magnetic dipole technology. A feature of this method is the minimization of distortions introduced by the carrier body into the characteristics of the measured field. To measure the field characteristics, as well as their partial components, vector antenna elements were used. Goal of the work is to study the characteristics of a radio direction finding complex using virtual magnetic dipole methods in conditions of distortions introduced by the carrier body. As an example, cases of direction finding of differently polarized waves, taking into account the influence of radomes of antenna elements, assessment of the maximum resolution accuracy, as well as noise stability are considered. The finite element method implemented in DS CST Studio Suite 2024 was used in the modeling. Result. During the research, a plane wave with different bearings fell on a UAV with a direction finding complex, which made it possible to carry out the most accurate research. The results of the work also include the creation of a model of a radio direction finding complex, which can be installed on a small UAV, providing high accuracy of wave direction finding in passive mode.The novelty of the method used lies in the application of methods for the formation of virtual magnetic dipoles based on the measured characteristics of the distorted electric field. New to this work are modeling cases that are associated with noise suppression, the influence of antenna element housings, as well as assessment of the maximum resolution accuracy.Practical significance of the work lies in the creation of a model of a radio location system based on vector antenna elements, which are used to measure the characteristics of the electromagnetic field with subsequent direction finding based on the magnetic field.

Modified FDM with cartesian expansions for electromagnetic scattering from PEC targets

AbstractIn this article, a modified scheme of the fast dipole method (FDM) is proposed based on the Cartesian tensor. To achieve separation between the field and the source, the Taylor series used in the FDM is an incomplete second‐order expansion, which limits computational accuracy and flexibility. To address this issue, a Cartesian tensor is employed to expand the interactions between the far‐group pairs. This approach allows for a complete expansion of any order and offers flexibility in precision control, enabling a balance between computational efficiency and accuracy requirements across different application scenarios. Moreover, the computational accuracy of the proposed method can be improved without a substantial increase in time and memory requirements compared to the FDM. The validity and accuracy of the proposed method are demonstrated with numerical examples.

CoupledElectricMagneticDipoles.jl - Julia modules for coupled electric and magnetic dipoles method for light scattering, and optical forces in three dimensions

CoupledElectricMagneticDipoles.jl is a set of modules implemented in the Julia language. Several modules are provided to solve typical problems encountered in nano-optics and nano-photonics including light emission by point sources in complex environments, electromagnetic wave scattering by single objects with complex geometry or collections of them. Optical forces can also be computed with this software package.Two closely related computational methods are implemented in this library, the discrete dipole approach (DDA) and the coupled electric and magnetic dipoles (CEMD) method.PROGRAM SUMMARYProgram Title: CoupledElectricMagneticDipoles.jlCPC Library link to program files:https://doi.org/10.17632/nrny5z4cmt.1Developer's repository link:https://github.com/augustinmuster/CoupledElectricMagneticDipoles.jlLicensing provisions: MITProgramming language: JuliaSupplementary material: AvailableNature of problem: Full classical solution of the problem of scattering and emission of electromagnetic waves by arbitrary objects. The problem includes near- and far-field distributions, total cross sections, differential cross sections, local density of states and optical forces. The formulation of the problem is in the frequency domain and for linear response.Solution method: Either discrete dipole approximation (DDA) with electric-only dipoles or the coupled electric and magnetic dipoles (CEMD) approximation is used to solve for extended objects (DDA only) or collections of small objects whose individual optical response can be described by a single electric and magnetic dipole excitation (CEMD). Facilities to discretize simple objects and calculate electric and magnetic polarizabilities are provided together with post-processing functions to calculate cross-sections, local density of states, differential scattering cross sections and optical forces. Any external electromagnetic field can be considered, but functions for several specific input fields are provided, such as plane waves, point dipole source, as well as Gaussian, Gaussian-Hermite and Laguerre-Gaussian beams.Additional comments including restrictions and unusual features: Although functions to calculate electric and magnetic polarizabilities are provided, these work only for spherical objects (through Mie coefficients) and cubes with scalar or tensor permittivity and relative magnetic permeability μ=1 everywhere. The host medium must be non-absorbing. The user can provide with generic 6×6 polarizability tensors. The implementation calculates the full interaction matrix and inverts it, hence the computation is valid for any incoming field at the cost of an increase of memory usage and computation time. The code has been tested with standard workstations up to ∼10000 electric and magnetic dipoles. We expect the limits to be set by available memory and computing time.

Revealing the Invisible: Imaging Through Non-Radiating Subspace

This paper presents a novel modification to the subspace optimization method (SOM) for solving inverse scattering problems in diverse background media. By incorporating sequential quadratic programming (SQP), a fast and accurate optimization technique, our approach aims to improve the reconstruction of dielectric objects buried in complex environments. We investigate the influence of non-radiating (NR) subspace reconstruction on imaging quality by analyzing the induced current-exterior field mapping operator's singular values. The scattering formulation of direct problems is performed through numerical methods such as coupled dipole method, finite elements-boundary integral, and electric field integral equations. Radiating and non-radiating objective functions are defined and minimized using SQP to evaluate the effectiveness of the proposed method. Numerical experiments demonstrate significant enhancements in imaging quality, robustness, and computational efficiency compared to existing techniques. This modified SOM offers a promising avenue for precise and reliable reconstruction of electromagnetic scattering objects, with potential applications in various fields including medical imaging, remote sensing, and non-destructive evaluation.

An Equivalent Modeling Method for Wideband Magnetic Radiation Interference of Power-Electronic Equipment

As more and more new power electronics with high switching frequencies are used in power-electronic equipment on ships and other platforms, the wideband radiation that power-electronic equipment gives off could affect sensitive equipment on the platform. Therefore, it is crucial to accurately model and characterize its wideband radiation properties to predict the wideband field distribution near such equipment. The traditional equivalent dipole method is commonly used to model power-electronic equipment at a single frequency. It is difficult to apply this method to wideband applications, and the precision of equivalent dipole array modeling at each frequency is insufficient. Additionally, acquiring the near-field phase data necessary for comparable modeling through practical measurement is frequently difficult. To solve the above problems, this paper proposes an equivalent dipole hybrid modeling method for power-electronic equipment’s broadband radiation characteristics. Starting with the near-field data at finite frequency points in a wideband, the method employs a global optimization algorithm to find the best equivalent dipole array, which characterizes the power-electronic equipment’s radiation characteristics. Furthermore, the interpolation technique is used to predict the wideband radiation properties of power-electronic equipment. Finally, test and numerical examples demonstrate the method’s accuracy and effectiveness.

Exploring the Light-Emitting Agents in Renilla Luciferases by an Effective QM/MM Approach.

Bioluminescence is a fascinating natural phenomenon, wherein organisms produce light through specific biochemical reactions. Among these organisms, Renilla luciferase (RLuc) derived from the sea pansy Renilla reniformis is notable for its blue light emission and has potential applications in bioluminescent tagging. Our study focuses on RLuc8, a variant of RLuc with eight amino acid substitutions. Recent studies have shown that the luminescent emitter coelenteramide can adopt multiple protonation states, which may be influenced by nearby residues at the enzyme's active site, demonstrating a complex interplay between protein structure and bioluminescence. Herein, using the quantum mechanical consistent force field method and the semimacroscopic protein dipole-Langevin dipole method with linear response approximation, we show that the phenolate state of coelenteramide in RLuc8 is the primary light-emitting species in agreement with experimental results. Our calculations also suggest that the proton transfer (PT) from neutral coelenteramide to Asp162 plays a crucial role in the bioluminescence process. Additionally, we reproduced the observed emission maximum for the amide anion in RLuc8-D120A and the pyrazine anion in the presence of a Na+ counterion in RLuc8-D162A, suggesting that these are the primary emitters. Furthermore, our calculations on the neutral emitter in the engineered AncFT-D160A enzyme, structurally akin to RLuc8-D162A but with a considerably blue-shifted emission peak, aligned with the observed data, possibly explaining the variance in emission peaks. Overall, this study demonstrates an effective approach to investigate chromophores' bimolecular states while incorporating the PT process in emission spectra calculations, contributing valuable insights for future studies of PT in photoproteins.

Second‐Order Topological Corner States in Square Lattice Plasmonic Metasurfaces with C4 and Glide Symmetries

Recently, plasmonic metasurfaces have emerged as a platform for topological photonics, exhibiting both advantages of plasmon‐induced tight confinement of local field and topological robustness. Most previous works regarding plasmonic systems are limited to the first‐order topologies and only a few studies dealt with higher‐order topological states in honeycomb lattices. Moreover, second‐order topologies of square lattice plasmonic systems have not yet been studied. This work presents second‐order topological corner states in the square lattices of metallic nanoparticles (NPs) with various symmetries, taking two different C4 and glide symmetries as examples. Their unit cells are obtained from nonprimitive cells, consisting of four equal spheroidal NPs, by expanding (or shrinking), rotating, and resizing. Bulk bands and spectral functions of the unit cells calculated by using the coupled dipole method well agree with COMSOL simulation results, revealing the accuracy of the numerical calculations as well as the experimental realizability of the systems. Second‐order topological corner states and their robustness against structural disorder are numerically shown for three different square lattices. This work will trigger extensive investigations to open a new realm of topological metasurfaces with promising applications.

Continuum strain of point defects

We propose a new Regularized Green's Function Method (RGFM) derived from electron densities and captures the disturbance due to point defects, successfully extending the elastic strain determination to the lattice scales. The RGFM circumvents the use of concentrated point forces, which results in unrealistic singular fields. The objective is to determine the force variations at the atomic scales from Ab-initio calculations as Quantum Mechanical Force Density (QMFD). QMFD encodes the information regarding the electronic structure of the defect since it is related to the gradients of electron wavefunctions generated from the Density Functional Theory (DFT) calculations. Once the QMFD is calculated, RGFM solves the force equilibrium equation via Fourier transforms to compute elastic fields. Therefore, the present treatment reflects the electronic structure of the atomic positions, hence the complex elastic deformations and interactions at short range, which represents a significant advancement compared to previous studies. The RGFM can also capture the long-range fields since it calculates the decay of the force fields away from the nuclei. Previous theories, such as the elastic dipole method, face two main shortcomings: they can only handle the long-range elastic fields, and contain an unphysical singularity at the center of the point defect. Our novel derivation of distributed forces addresses both challenges, i.e., it renders non-singular displacement and strain fields at the nuclei, and can also describe the elastic response accurately far from the nuclei center. The application of the method to the NV (nitrogen-vacancy) center in SiC is demonstrated in comparison with the elastic dipole theory, showing the advantages of the present methodology.

Emergent mobility edges and intermediate phases in one-dimensional quasiperiodic plasmonic chains

Anderson localization has been widely studied in low-dimensional aperiodic electronic, photonic, and acoustic systems. However, the disorder effect in the plasmonic system, where retardation and long-range couplings interact in complex ways, remains an open question. In this work, we investigate the localization properties of one-dimensional quasiperiodic plasmonic chains using the coupled dipole method and linearized Green's function. Our models, which incorporate nearest-neighbor or long-range dipole interactions, reveal localization transitions, mobility edges, and intermediate phases. It is found that long-range dipole interactions and non-Hermiticity due to retardation both play crucial roles in Anderson localization, yielding the emergence of intermediate phases with varying widths. A link between non-Hermiticity and Anderson transition is established by the mean phase rigidity, revealing strong non-Hermiticity along the phase boundary. The plasmonic model involving long-range interplay and retarded effect presents richer localization phenomena than the electronic counterpart that usually includes only nearest-neighbor coupling, laying a foundation for experimental observations of Anderson localization on plasmonic platforms. Published by the American Physical Society 2024

Constructing a zero leak landfill cell

Engineered landfill barriers are the last line of defence in protecting precious groundwater resources from contamination. A landfill cell without any leaks at the conclusion of construction is the exception rather than the rule. From design to materials testing to installation practices and contractor care, all of these elements contribute to both the short and long-term integrity of the lining system. Electrical leak location (ELL) methods can be used to detect leaks in installed landfill cells after construction so that leaks can be repaired before a landfill cell begins filling operations. However, the thorough testing of landfill cells using ELL can be complicated by their complex configuration. The dipole method, employed after cover material placement, requires electrical isolation of the cover material, which is difficult to achieve with a landfill expansion cell configuration. Additionally, employing only this type of testing can leave the tie-in area untested, which is a critical area prone to damage. This paper provides solutions for complete landfill expansion cell testing, including a relatively new testing methodology (ASTM D8265, [1]), which provides protocol for verifying that a geomembrane has been successfully installed with no leaks. A case study is included to show how ASTM D8265 can be used to provide documentation of a zero-leak condition of a landfill cell after construction. Common elements of design, geomembrane installation, and quality assurance are discussed in order to provide a road map of how to reach a zero-leak condition at the end of a landfill expansion cell construction project. This paper can be used as a guide to constructing a zero-leak landfill cell using state-of-the art construction practices and ELL testing methodologies.

Experience in locating leaks in geomembrane-lined ponds

This study presents the results of five years of applying the dipole method in geomembrane-lined ponds to locate leaks arising from either the construction or operational stage. Inspections were conducted on 136 projects designed with single (n=57) or double (n=79) liner and located in the United States (n=108), Mexico (n=5), or Canada (n=23). The ponds were tested either full or at a depth between 0.3m and 0.8m, both sets of results were compared to the available literature. Approximately 210 ha of primary geomembrane-lined ponds were surveyed, uncovering 825 leaks during the study period. An average number of leaks/ha was 13.2 ranging from 0 to 272. The highest results were 272, 242, and 131 leaks/ha in double-lined, and 80 and 77 leaks/ha in single-lined ponds. The inspected data revealed that 43% of projects had 0-2 leaks/ha, 20% had >2-5 leaks/ha, 14% had >5-10 leaks/ha, and 16% of the ponds had >20 leaks/ha. The results of this study are crucial for designers, Landfill Operators, and Environmental Agencies in establishing inspection practiced for lined ponds, particularly after a period of operation.

Nanoparticles optimal shape designing in the cylindrical coordinate to use for optical devices

Nanoparticles have unique optical properties that can enhance the performance of optical devices. In this regard size and shape of nanoparticles are very important factors that influence these properties. Although there are many different sample shapes of nanoparticles but researchers have not yet identified the best shape to use, especially in general. This article presents a mathematical model to determine the optimal shape of nanoparticles for use in various optical devices. We use the shape-measure method in cylindrical coordinates to solve this problem. This method has many advantages like it is independent of the initial shape and transforming the optimal shape design problem into a simple optimization one, even in strongly nonlinear cases. The use of cylindrical coordinates also makes calculations faster and more straightforward. First the optical properties of nanoparticles is described by using the discrete dipole method; then, simultaneously the optimal surface and image for the optimal shape and size of the nanoparticles are determined. Numerical simulations are also provided to demonstrate the effectiveness and benefits of the new approach.

Numerical prediction of noise generated from a box fan

The noise generated from a box fan is numerically predicted with two approaches. The first one is the FW-H method that can simulate flow and acoustic together by the flow solver scFLOW but assumes sound propagation in free-space. The second one is the ring of dipoles method that is a hybrid approach between the flow solver scFLOW and the acoustic solver Actran. These approaches are validated for small box fans of two different blade configurations with experimental data available for comparison. An incompressible unsteady LES solver with WALE model is used with a fine mesh to solve unsteady flow fields. The numerical results show quantitatively agreement of the pressure rise performance with the experimental results and that the ring of dipoles method gave closer result to the experiment than the FW-H method especially on the low frequency range. Also, we show that the flow rate dependence of the radiated sound pressure of the experiment can be qualitatively well captured with the ring of dipoles method. Finally, we discuss the causes of the different sound characteristics with different blade configurations.

Visualization of the Spatiotemporal Propagation of Interictal Spikes in Temporal Lobe Epilepsy: A MEG Pilot Study.

Magnetoencephalography (MEG) is clinically used to localize interictal spikes in discrete brain areas of epilepsy patients through the equivalent current dipole (ECD) method, but does not account for the temporal dynamics of spike activity. Recent studies found that interictal spike propagation beyond the temporal lobe may be associated with worse postsurgical outcomes, but studies using whole-brain data such as in MEG remain limited. In this pilot study, we developed a tool that visualizes the spatiotemporal dynamics of interictal MEG spikes normalized to spike-free sleep activity to assess their onset and propagation patterns in patients with temporal lobe epilepsy (TLE). We extracted interictal source data containing focal epileptiform activity in awake and asleep states from seven patients whose MEG ECD clusters localized to the temporal lobe and normalized the data against spike-free sleep recordings. We calculated the normalized activity over time per cortical label, confirmed maximal activity at onset, and mapped the activity over a 10 ms interval onto each patient's brain using a custom-built Multi-Modal Visualization Tool. The onset of activity in all patients appeared near the clinically determined epileptogenic zone. By 10 ms, four of the patients had propagated source activity restricted to within the temporal lobe, and three had propagated source activity spread to extratemporal regions. Using this tool, we show that noninvasively identifying the onset and propagation of interictal spike activity in MEG can be achieved, which may help provide further insight into epileptic networks and guide surgical planning and interventions in patients with TLE.

Analytical solutions for resonant radiation performance of bending-mode magnetoelectric antennas

This paper proposes analytical solutions for the resonant radiation performance of bending-mode magnetoelectric (ME) antennas. The strain-mediated Converse ME (CME) coupling model of bending-mode ME antennas is first established by solving nonlinear constitutive equations and bending governing equations using the elastic mechanics method. Then, the calculated magnetic flux and electric displacement are employed to propose a resonant radiation field model based on the dipole method. The numerical results for the CME coefficient show a good agreement with the experimental data. It can be observed that the volume fraction ratio of the piezoelectric layer can control the CME coefficient and radiation efficiency with the same variation trend since it can determine the bending strain via changing the location of the neutral layer of the ME antennas, which also demonstrates the strain-mediated essence of the ME antennas. In addition, the volume fraction ratio can tune the resonant frequency within a wide range. The gain of the ME antenna is stable and higher than −168 dB with the volume fraction ratio ranging from 0.2 to 0.7. The tensile stress and compressive stress have the opposite effect on the resonant frequency at low and high bias magnetic fields. Meanwhile, the tensile (compressive) stress is beneficial for both the radiation and gain in the low (high) bias field region. This model may facilitate the understanding of the bending-mode radiation mechanism of ME antennas and provide a basis for designing asymmetric ME antennas.

A theoretical study on magneto-mechano-electric coupling of nonlinear tristable magnetic energy harvesters

Linear magnetic energy harvester has been previously proposed to achieve low-frequency ambient magnetic field. However, its harvesting efficiency is relatively low in the off-resonant frequency region. The paper proposes a nonlinear tristable magnetic energy harvester (TMEH) and analyzes the sensitivity of the dynamic characteristics of the TMEH to the system parameters. The nonlinear magnetic force between magnets is quantitatively analyzed using magnetic dipole method. Meanwhile, the magnetic moment form the external ac magnetic field is derived. Sequentially, a magneto-mechano-electric (MME) coupled model for TMEHs is developed using Euler Bernoulli-beam theory and the extended Hamilton principle. The developed theory is highlighted with a direct comparison with experiments that shows their close agreement. It is revealed that a high-performance tristable system can be obtained by adjusting gap distance or separate distance between magnets. In addition, the quantitative relation between the system parameters and the voltage output is determined. More importantly, the parameter region for the stiffness coefficients corresponding to different stable systems is discussed based on harmonic balance mothed, which offers convenience for performance improvement of the nonlinear harvesters. Given the significance of this study, it may be utilized in the development of high-performance magnetic energy harvesters.

Near-field formation of the UCA-based OAM EM fields and short-range EM power flux profiles

Orbital angular momentum (OAM) multiplexing is a recently considered solution for enhancing wireless and free-space optical communications channel capacity, whether implemented separately or in combination with existing multiplexing techniques. The theoretically infinite number of paraxially propagating and mutually orthogonal OAM modes is expected to increase the channel capacity. However, the orthogonality for different OAM modes has been shown to decrease for far link range distances, and the paraxiality of the OAM beams is not very good for small radiating sources. Based on the current knowledge, OAM beams are most likely to be used for short-range communications. Many models of the electromagnetic (EM) fields carrying the OAM neglect the fact that the OAM beam sources could be electrically large or introduce other approximations that are appropriate for far-field analysis only. An in-depth analysis of the short-range properties of OAM EM fields is still lacking. To address this problem, we propose the use of the infinitesimal (Hertz) dipole method customized for the analysis of the OAM EM fields. This technique can model the positioning and basic radiation properties of separate antennas or antenna sub-arrays that are the building blocks of OAM arrays exactly and efficiently. Similar modeling can represent the OAM sources for free-space optical communications. We focus here on the uniform circular antenna arrays and provide an in-depth analysis of what can and cannot be expected, in the best case, in their utilization. We assume low losses, which is a common assumption for many methods, except for computationally much more demanding full-wave simulations. The obtained results indicate the need to simultaneously optimize the transmission of all planned OAM modes and allow estimates of the link distances that could provide adequate OAM wave reception in various cases.

Dipole formalism for massive initial-state particles and its application to dark matter calculations

The dark matter abundance plays a crucial role in the determination of the valid parameter space of models both in the case of a discovery of dark matter and in the context of exclusion limits. Reliable theoretical predictions of the dark matter relic density require technically demanding precision calculations, which were so far limited in their automation due to challenges in the treatment of infrared divergences appearing in higher order calculations. In particular, massive initial states need to be considered in early Universe computations, so that the known dipole subtraction methods could not be directly exploited. We therefore provide a full generalization of the dipole subtraction method by Catani and Seymour to supersymmetric (SUSY) QCD with massive initial states. All dipole splitting functions and their integrated counterparts are given explicitly for four different dimensional schemes. To showcase their application, we apply our results to dark matter (co)annihilation processes in the context of the minimal supersymmetric Standard Model. We also demonstrate the accuracy of the dipole method by comparing our numerical results with those obtained with the phase space slicing method. Our analytical results will facilitate future automation of dark matter abundance calculations at next-to-leading order for both SUSY and non-SUSY models.