Symmetric Source Research Articles

General framework for calculating irradiance distributions of symmetric surface sources.

Symmetries in system modeling can be exploited to obtain analytical results on the system behavior and to speed up computations using the symmetric model. This work explores the use of symmetries in radiant surfaces for calculating the induced irradiance distributions by developing a general mathematical expression. The obtained model is applied to flat, cylindrical, and spherical sources to obtain explicit expressions. An experimental evaluation of the flat source is carried out and compared with a traditional point source, and the obtained procedure for the flat scenario is compared with the direct integration approach, which shows an improvement in the computation time of at least two orders of magnitude with a relative root mean square error of less than 10%. The results show that the proposed approach enhances short-range predictions for extended sources. To demonstrate the impact of this in optical wireless communications we have outlined a few applications.

The Spherical Harmonic Family of Beampatterns

The free space solution to the wave equation in spherical coordinates is well known as a separable product of functions. Re-examination of these functions, particularly the sums of spherical Bessel and harmonic functions, reveals behaviors which can produce a range of useful beampatterns from radially symmetric sources. These functions can be modified by several key parameters which can be adjusted to produce a wide-ranging family of beampatterns, from the axicon Bessel beam to a variety of unique axial and lateral forms. We demonstrate that several special properties of the simple sum over integer orders of spherical Bessel functions, and then the sum of their product with spherical harmonic functions specifying the free space solution, lead to a family of useful beampatterns and a unique framework for designing them. Examples from a simulation of a pure tone 5 MHz ultrasound configuration demonstrate strong central axis concentration, and the ability to modulate or localize the axial intensity with simple adjustment of the integer orders and other key parameters related to the weights and arguments of the spherical Bessel functions.

Performance Analysis of an Optimized Asymmetric Multilevel Inverter on Grid Connected SPV System

The purpose of this research is to develop an efficient single-phase grid-connected PV system using a better performing asymmetrical multilevel inverter (AMI). Circuit component reduction, harmonic reduction, and grid integration are critical criteria for better inverter efficiency. The proposed inverter’s optimized topology requires seven unidirectional switches, three symmetric dc sources, and three diodes to produce an asymmetric fifteen level output; whereas, the same configuration will generate 7, 11, and 15-level output with an appropriate choice of dc source magnitudes. It is possible to reduce inverter losses and boost efficiency by decreasing the number of switches used. The integration of an asymmetric 15-level inverter with a grid-connected solar photovoltaic system is discussed in this article. A grid-connected solar photovoltaic (GCSPV) system is modelled and simulated using an asymmetric 15-level inverter. The dc sources of the 15-level inverter are replaced with PV sources. The results were analyzed with different operating temperatures and solar irradiance conditions. The GCSPV system is controlled by a closed-loop control system using Particle Swarm Optimization (PSO), Harris Hawk Optimization (HHO), and Hybrid Particle Swarm Optimization-Genetic Algorithm (PSOGA) based Proportional plus Integral (PI) controllers. Grid voltage, grid current, grid power, and total harmonic distortion (THD) of grid currents were analyzed. The performance of the 15-level asymmetric inverter was evaluated by comparing the THD of the grid current and the efficiency of the grid-connected photovoltaic system.

The Double-Sided Information Bottleneck Function.

A double-sided variant of the information bottleneck method is considered. Let be a bivariate source characterized by a joint pmf . The problem is to find two independent channels and (setting the Markovian structure ), that maximize subject to constraints on the relevant mutual information expressions: and . For jointly Gaussian and , we show that Gaussian channels are optimal in the low-SNR regime but not for general SNR. Similarly, it is shown that for a doubly symmetric binary source, binary symmetric channels are optimal when the correlation is low and are suboptimal for high correlations. We conjecture that Z and S channels are optimal when the correlation is 1 (i.e., ) and provide supporting numerical evidence. Furthermore, we present a Blahut–Arimoto type alternating maximization algorithm and demonstrate its performance for a representative setting. This problem is closely related to the domain of biclustering.

Axially Symmetric Source Field Penetration Through a Circular Aperture in a Thin Impedance Plate

The field penetration through a circular aperture in an infinite plane with a nonzero surface impedance excited by an axially symmetric source is analytically investigated. The problem is formulated in terms of an original dual-integral-equation approach and solved through the method of moments in the Hankel spectral domain. The proposed formulation is applied to the calculation of the axial magnetic field when the source is a current loop of finite radius coaxial with the aperture and it is shown that it is possible to separate the contributions of the aperture and of the nonzero impedance plate to the transmitted field. In the case of low frequencies and small apertures, closed-form expressions are also derived. Moreover, the approach is also applied to the case of a perfectly conducting plane giving rise to results that coincide with those recently presented in the literature. Finally, the accuracy of the proposed approach is validated through full-wave calculations.

Theoretical Search for Gravitational Bound States of Tachyons

The mission here is to see if we can find bound states for tachyons in some gravitational environment. That could provide an explanation for the phenomena called Dark Matter. Starting with the standard Schwarzschild metric in General Relativity, which is for a static and spherically symmetric source, it appears unlikely that such localized orbits exist. In this work, the usual assumption of isotropic pressure is replaced by a model that has different pressures in the radial and angular directions. This should be relevant to the study of neutrinos, especially if they are tachyons, in cosmological models. We do find an arrangement that allows bound orbits for tachyons in a galaxy. This is a qualitative breakthrough. Then we go on to estimate the numbers involved and find that we do have a fair quantitative fit to the experimental data on the Galaxy Rotation Curve. Additionally we are led to look in the neighborhood of a Black Hole and there we find novel orbits for tachyons.

A New Fault-Tolerant Multilevel Inverter Structure With Reduced Device Count and Low Total Standing Voltage

A new fault-tolerant (FT) multilevel inverter (MLI) structure that can tolerate the faults on the switches and sources is introduced in this article. The presence of redundant states in the proposed structure ensures the FT capability, which is an important requirement for emergency loads. Initially, the operation of the proposed FTMLI for fault-free and different fault conditions under symmetric and asymmetric source configurations is discussed. Furthermore, this article explores the ability of the proposed topology operating at different voltage levels in positive and negative half cycles of the output voltage to improve the reliability of the system. For this case, the modified pulsewidth modulation control strategy ensuring minimized lower order harmonics and zero dc offset is presented. The feasibility of the proposed topology is verified through simulation and experimental studies. Lower total standing voltage, reduced switch count, higher efficiency, and improved reliability are the key features of the proposed topology. A comprehensive evaluation and comparative study are performed to evaluate the performance of the proposed MLI over other structures.

Consequences of electric charge on anisotropic hyperbolically symmetric static spacetime

The investigation of hyperbolically symmetric sources under the impact of electromagnetic field is conducted in this paper, with a focus on the fluid distributed in static spacetime. To do this, we choose the metric f(R) gravity. It is observed that the fluid does not have the capacity to occupy the space surrounding the center, meaning that it exhibits cavity around the core. Furthermore, calculating the energy density indicates that it is invariably negative in the presence of correction terms, which might be crucial in comprehending certain quantum field occurrences, due to the fact that negative energies are directly tied with the quantum field theory. In this modified gravity, we implement the orthogonal splitting of the curvature tensor and derive the structure scalars. Following that, some cosmological models exhibiting the hyperbolical symmetry as well as their substantial determinants are investigated using two generating functions. The model of less-complex relativistic system of Einstein gravity is offered to explore precisely the role of f(R) terms under the influence of electromagnetic field.

Electromagnetic influence on hyperbolically symmetric sources in f(T) gravity

The present study aims to see how gravitational modification, specifically, the f(T) gravitational field, where T is torsion scalar, impacts static fluid content with hyperbolic symmetry and electromagnetic field. We enlarge Herrera’s strategy (Herrera et al. in Phys Rev D 103:024037, 2021) to analyze the impact of electromagnetic field on f(T) gravity. We distinguish the stress–energy tensor by considering the ingredients of the tetrad field in the Minkowski co-ordinate frame, commencing with modified field equations. With the advent of negative density, this sort of fluid is supposed to surpass extreme physical conditions, enabling quantum impacts to be detected. We calculate a viable formulation of mass utilizing the Tolman mass from the viewpoint of f(T) gravity along with the electromagnetic field. The gravitational interference is repulsive, as made evident by the negative value of the Tolman mass. Also, we explored the structure scalars in f(T) gravity and found significant solutions in presence of electric charge.

Axion homeopathy: screening dilaton interactions

Cosmologically active Brans-Dicke (or dilaton) scalar fields are generically ruled out by solar system tests of gravity unless their couplings to ordinary matter are much suppressed relative to gravitational strength, and this is a major hindrance when building realistic models of light dilatons coupled to matter. We propose a new mechanism for evading such bounds if matter also couples to a light axion, that exploits nonlinear target-space curvature interactions to qualitatively change how the fields respond to a gravitating source. We find that dilaton-matter couplings that would be excluded in the absence of an axion can become acceptable given an additional small axion-matter coupling, and this is possible because the axion-dilaton interactions end up converting the would-be dilaton profile into an axion profile. The trajectories of matter test bodies are then controlled by the much weaker axion-matter couplings and can easily be small enough to escape detection. We call this mechanism Axion Homeopathy because the evasion of the dilaton-coupling bounds persists for extremely small axion couplings provided only that they are nonzero. We explore the mechanism using axio-dilaton equations that are SL(2,ℝ) invariant (as often appear in string compactifications), since for these the general solutions exterior to a spherically symmetric source can be found analytically. We use this solution to compute the relevant PPN parameters, γ PPN and β PPN, and verify that their deviation from unity can be much smaller than it would have been in the absence of axion-matter couplings and can therefore evade the experimental bounds.

IDENTIFICATION OF THE POWER OF THE IMBALANCE OF THE THREE-PHASE FOUR-WIRE POWER SUPPLY SYSTEM FOR THE NEEDS OF ITS DISTRIBUTED COMPENSATION

The idea of distributed active filtration is to compensate for the currents of higher harmonics and undesirable components of the power of the main network with inverters of renewable energy converters of the connected microgrid, which have reserves of apparent power. For the convenience of distributed compensation, it is proposed to identify the sinusoidal mode of the three-phase four-wire power system, provided that the symmetric source is six mutually orthogonal components of the three-coordinate vector of line currents. The power of imbalance is shown to be due to four mutually orthogonal components of the three-coordinate vector of line currents with defined reference voltage vectors, each of which is proportional to a separate orthogonal component of the power of imbalance. Integral formulas for determining the scalar values of the four specified orthogonal components of imbalance powers have been obtained, which open the possibility of accounting for their contribution to the deterioration of the quality of electrical energy and the synthesis of control signals for active distributed filtration. The connection between the four specified orthogonal components of the power of imbalance and the parameters of the linear unbalanced load was established, which made it possible to verify these integral formulas using a computer experiment. It is analytically established and experimentally confirmed that the squares of the two orthogonal components of the imbalance powers associated with the current of the neutral wire are included in the decomposition of the square of apparent power and power losses with the multiplier, depending on the ratio of the resistances of the transmission line of the three-phase four-wire power system. References 17, figures 3.

Towards optimal thermal distribution in magnetic hyperthermia

A linear combination of spherically symmetric heat sources is shown to provide optimal stationary thermal distribution in magnetic hyperthermia. Furthermore, such spatial location of heat sources produces suitable temperature distribution in biological medium even for assemblies of magnetic nanoparticles with a moderate value of specific absorption rate (SAR), of the order of 100–150 W/g. We also demonstrate the advantage of using assemblies of spherical magnetic nanocapsules consisting of metallic iron nanoparticles covered with non magnetic shells of sufficient thickness in magnetic hyperthermia. Based on numerical simulation we optimize the size and geometric structure of biocompatible spherical capsules in order to minimize the influence of strong magneto-dipole interaction between closely spaced nanoparticles. It is shown that assembly of capsules can provide sufficiently high SAR values of the order of 250–400 W/g at moderate amplitudes H0 = 50–100 Oe and frequencies f = 100–200 kHz of alternating magnetic field, being appropriate for application in clinics.

A compact symmetric radio source born at one-tenth the current age of the Universe

ABSTRACT Studies of high-redshift radio galaxies can shed light on the activity of active galactic nuclei (AGNs) in massive elliptical galaxies, and on the assembly and evolution of galaxy clusters in the Universe. J1606+3124 has been tentatively identified as a radio galaxy at a redshift of 4.56, at an era of one-tenth of the current age of the Universe. Very long baseline interferometry (VLBI) images show a compact triple structure with a size of 68 pc. The radio properties of J1606+3124, including the edge-brightening morphology, peaked GHz radio spectrum, slow variability, and low jet speed, consistently indicate that it is a compact symmetric object (CSO). The radio source size and expansion rate of the hotspots suggest that J1606+3124 is a young (kinematic age of ∼3600 yr) radio source. Infrared observations reveal a gas- and dust-rich host galaxy environment, which may hinder the growth of the jet; however, the ultra-high jet power of J1606+3124 gives it an excellent chance to grow into a large-scale double-lobe radio galaxy. If its redshift and galaxy classification can be confirmed by further optical spectroscopic observations, J1606+3124 will be the highest redshift CSO galaxy known to date.

Hyperbolically symmetric sources in [formula omitted] gravity

This paper studies the static fluid distributions admitting the hyperbolically symmetric structure by extending the work of Herrera et al. (2021) in f(R,T) gravity. The unavailability of the fluid distribution in the region which is close to the center of symmetry has been observed. A vacuum cavity can be used to depict this region around the center. The effective matter density emerges inevitably to be negative and this implies that the conceivable use of such fluids needs transcendental physical conditions when the significant quantum effects are observed. Furthermore, the Tolman mass, as well as an appropriate formulation of the mass function, are particularly computed. Along with this, we evaluated the structure scalars through the orthogonal splitting of the Riemann tensor in this modified gravity. Imposing the conditions of conformal flatness and stiff equation of state, we constructed several models for the less-complex systems. We also evaluated the generating functions to study the fluid distribution in this theory. A general hypothesis to attain precise solutions are also conferred through matter-curvature coupling.

Deep Symmetric Adaptation Network for Cross-Modality Medical Image Segmentation.

Unsupervised domain adaptation (UDA) methods have shown their promising performance in the cross-modality medical image segmentation tasks. These typical methods usually utilize a translation network to transform images from the source domain to target domain or train the pixel-level classifier merely using translated source images and original target images. However, when there exists a large domain shift between source and target domains, we argue that this asymmetric structure, to some extent, could not fully eliminate the domain gap. In this paper, we present a novel deep symmetric architecture of UDA for medical image segmentation, which consists of a segmentation sub-network, and two symmetric source and target domain translation sub-networks. To be specific, based on two translation sub-networks, we introduce a bidirectional alignment scheme via a shared encoder and two private decoders to simultaneously align features 1) from source to target domain and 2) from target to source domain, which is able to effectively mitigate the discrepancy between domains. Furthermore, for the segmentation sub-network, we train a pixel-level classifier using not only original target images and translated source images, but also original source images and translated target images, which could sufficiently leverage the semantic information from the images with different styles. Extensive experiments demonstrate that our method has remarkable advantages compared to the state-of-the-art methods in three segmentation tasks, such as cross-modality cardiac, BraTS, and abdominal multi-organ segmentation.

Dynamics of perturbative Karmarkar collapse of radiating star in [formula omitted] gravity

The significance of the shear free condition on perturbative collapse of radiating anisotropic fluid with Karmarkar condition in the formalism of f(R,T) gravity is analyzed in this manuscript. The gravitational collapse of spherically symmetric radiating object proceeds from initially static regime satisfying the time dependent Karmarkar condition and further established by huge amount of energy dissipation in the form of heat flux. A perturbation approach is applied to get the collapse equation and the gravitational nature of our model is entirely governed by the Karmarkar condition and its boundary condition in scheme of f(R,T) gravity, where R is Ricci scalar and T is trace of energy momentum tensor. Vaidya’s time-like hypersurface is smoothly matched with the interior solution, which further entitles to examine physical viability of spherically symmetric source. Furthermore, a viable linear f(R,T) model is chosen to achieve the exact solution for anisotropic radiating fluid model. Stability tests are demonstrated, indicating that our model is well-behaved. Furthermore, General Relativity results have obtained by simply taking coupling parameter χ to zero.

Bandwidth and Common Mode Optimization for Current and Voltage Sources in Bioimpedance Spectroscopy.

Bioimpedance measurements use current or voltage sources to inject an excitation signal into the body. These sources require a high bandwidth, typically from 1 kHz to 1 MHz. Besides a low common mode, current limitation is necessary for patient safety. In this paper, we compare a symmetric enhanced Howland current source (EHCS) and a symmetric voltage source (VS) based on a non-inverting amplifier between 1 kHz and 1 MHz. A common mode reduction circuit has been implemented in both sources. The bandwidth of each source was optimized in simulations and achieved a stable output impedance over the whole frequency range. In laboratory measurements, the output impedance of the EHCS had its -3 dB point at 400 kHz. In contrast, the VS reached the +3 dB point at 600 kHz. On average over the observed frequency range, the active common mode compensation achieved a common mode rejection of -57.7 dB and -71.8 dB for the EHCS and VS, respectively. Our modifications to classical EHCS and VS circuits achieved a low common mode signal between 1 kHz and 1 MHz without the addition of complex circuitry, like general impedance converters. As a conclusion we found VSs to be superior to EHCSs for bioimpedance spectroscopy due to the higher bandwidth performance. However, this only applies if the injected current of the VS can be measured.

Hyperbolically symmetric sources, a comprehensive study in f(T) gravity

Hyperbolically symmetric sources, a comprehensive study in f(T) gravity

Evolution of axially and reflection symmetric source in energy–momentum squared gravity

Evolution of axially and reflection symmetric source in energy–momentum squared gravity

A Simple Procedure to Design Virtual Experiments for Microwave Inverse Scattering

In a virtual experiment (VE), the data available to solve an inverse scattering problem are linearly combined in order to make the inversion task simpler. This goal is achieved by conditioning contrast sources radiating the scattered fields and exploiting their properties in the inversion procedure, for instance, by devising data-driven approximations or regularization schemes. In this framework, the design of a VE amounts to determine the coefficients ruling the recombination of the available data. In this article, we present a general and simple procedure to design VEs capable of enforcing contrast sources with desired properties. The proposed procedure is computationally straightforward and stable, as it does not require an explicit inversion and regularization process, and just consists in the evaluation of the adjoint solution of an auxiliary problem. The design approach is tested in the case of VE enforcing circularly symmetric contrast sources, and the corresponding inversion procedure is assessed using both simulated and experimental data.