Gravitational and Electromagnetic Perturbations of a Charged Black Hole in a General Gauge Condition

We derive a set of coupled equations for the gravitational and electromagnetic perturbation in the Reissner–Nordström geometry using the Newman–Penrose formalism. We show that the information of the physical gravitational signal is contained in the Weyl scalar function Ψ4, as is well known, but for the electromagnetic signal, the information is encoded in the function χ, which relates the perturbations of the radiative Maxwell scalars φ2 and the Weyl scalar Ψ3. In deriving the perturbation equations, we do not impose any gauge condition and as a limiting case, our analysis contains previously obtained results, for instance, those from Chandrashekhar’s book. In our analysis, we also include the sources for the perturbations and focus on a dust-like charged fluid distribution falling radially into the black hole. Finally, by writing the functions on the basis of spin-weighted spherical harmonics and the Reissner–Nordström spacetime in Kerr–Schild type coordinates, a hyperbolic system of coupled partial differential equations is presented and numerically solved. In this way, we completely solve a system that generates a gravitational signal as well as an electromagnetic/gravitational one, which sets the basis to find correlations between them and thus facilitates gravitational wave detection via electromagnetic signals.

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Simulation on the Physical Process of Neural Electromagnetic Signal Generation Based on a Simple but Functional Bionic Na+ Channel

Chinese Physics B ◽

10.1088/1674-1056/ac3cac ◽

2021 ◽

Author(s):

Fan Wang ◽

Jingjing Xu ◽

Yanbin Ge ◽

Shengyong Xu ◽

Yanjun Fu ◽

...

Keyword(s):

Dynamic Equilibrium ◽

Electromagnetic Signal ◽

Na Channel ◽

Physical Processes ◽

Flux Transport ◽

Ionic Flux ◽

Concentration Difference ◽

Voltage Gated ◽

Electromagnetic Signals ◽

The Impact

Abstract The physical processes occurring at open Na+ channels in neural fibers are essential for understanding the nature of neural signals and the mechanism by which the signals are generated and transmitted along nerves. However, there is less generally accepted description of these physical processes. We studied changes in the transmembrane ionic flux and the resulting two types of electromagnetic signals by simulating the Na+ transport across a bionic nanochannel model simplified from voltage-gated Na+ channels. Results show that the Na+ flux can reach a steady state in approximately 10 ns owing to the dynamic equilibrium of Na+ ions concentration difference between the both sides of membrane. After characterizing the spectrum and transmission of these two electromagnetic signals, the low-frequency transmembrane electric field is regarded as the physical quantity transmitting in waveguide-like lipid dielectric layer and triggering the neighboring voltage-gated channels. Factors influencing the Na+ flux transport are also studied. The impact of the Na+ concentration gradient is found higher than that of the initial transmembrane potential on the Na+ transport rate, and introducing the surface-negative charge in the upper third channel could increase the transmembrane Na+ current. This work can be further studied by improving the simulation model; however, the current work helps to better understand the electrical functions of voltage-gated ion channels in neural systems.

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Parametrized black hole quasinormal ringdown. II. Coupled equations and quadratic corrections for nonrotating black holes

Physical Review D ◽

10.1103/physrevd.100.044061 ◽

2019 ◽

Vol 100 (4) ◽

Cited By ~ 16

Author(s):

Ryan McManus ◽

Emanuele Berti ◽

Caio F. B. Macedo ◽

Masashi Kimura ◽

Andrea Maselli ◽

...

Keyword(s):

Black Holes ◽

Black Hole ◽

Coupled Equations

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Constraining LQG Graph with Light Surfaces: Properties of BH Thermodynamics for Mini-Super-Space, Semi-Classical Polymeric BH

Entropy ◽

10.3390/e22040402 ◽

2020 ◽

Vol 22 (4) ◽

pp. 402

Author(s):

Daniela Pugliese ◽

Giovanni Montani

Keyword(s):

Black Hole ◽

Loop Quantum Gravity ◽

Causal Structure ◽

Thermodynamic Characteristics ◽

Kerr Geometry ◽

Regular Black Hole ◽

Loop Area ◽

Symmetric Spacetimes ◽

Wide Range ◽

Limiting Case

This work participates in the research for potential areas of observational evidence of quantum effects on geometry in a black hole astrophysical context. We consider properties of a family of loop quantum corrected regular black hole (BHs) solutions and their horizons, focusing on the geometry symmetries. We study here a recently developed model, where the geometry is determined by a metric quantum modification outside the horizon. This is a regular static spherical solution of mini-super-space BH metric with Loop Quantum Gravity (LQG) corrections. The solutions are characterized delineating certain polymeric functions on the basis of the properties of the horizons and the emergence of a singularity in the limiting case of the Schwarzschild geometry. We discuss particular metric solutions on the base of the parameters of the polymeric model related to similar properties of structures, the metric Killing bundles (or metric bundles MBs), related to the BH horizons’ properties. A comparison with the Reissner–Norström geometry and the Kerr geometry with which analogies exist from the point of their respective MBs properties is done. The analysis provides a way to recognize these geometries and detect their main distinctive phenomenological evidence of LQG origin on the basis of the detection of stationary/static observers and the properties of light-like orbits within the analysis of the (conformal invariant) MBs related to the (local) causal structure. This approach could be applied in other quantum corrected BH solutions, constraining the characteristics of the underlining LQG-graph, as the minimal loop area, through the analysis of the null-like orbits and photons detection. The study of light surfaces associated with a diversified and wide range of BH phenomenology and grounding MBs definition provides a channel to search for possible astrophysical evidence. The main BHs thermodynamic characteristics are studied as luminosity, surface gravity, and temperature. Ultimately, the application of this method to this spherically symmetric approximate solution provides us with a way to clarify some formal aspects of MBs, in the presence of static, spherical symmetric spacetimes.

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REGULAR BLACK HOLES IN AN ASYMPTOTICALLY DE SITTER UNIVERSE

Modern Physics Letters A ◽

10.1142/s0217732308028715 ◽

2008 ◽

Vol 23 (40) ◽

pp. 3377-3392 ◽

Cited By ~ 20

Author(s):

JERZY MATYJASEK ◽

DARIUSZ TRYNIECKI ◽

MARIUSZ KLIMEK

Keyword(s):

Black Holes ◽

Black Hole ◽

Nonlinear Electrodynamics ◽

Spherically Symmetric ◽

De Sitter ◽

Coupled Equations ◽

Sitter Universe ◽

De Sitter Universe ◽

Horizon Geometry ◽

Interesting Solution

A regular solution of the system of coupled equations of the nonlinear electrodynamics and gravity describing static and spherically-symmetric black holes in an asymptotically de Sitter universe is constructed and analyzed. Special emphasis is put on the degenerate configurations (when at least two horizons coincide) and their near horizon geometry. It is explicitly demonstrated that approximating the metric potentials in the region between the horizons by simple functions and making use of a limiting procedure one obtains the solutions constructed from maximally symmetric subspaces with different absolute values of radii. Topologically they are AdS2×S2 for the cold black hole, dS2×S2 when the event and cosmological horizon coincide, and the Plebański–Hacyan solution for the ultraextremal black hole. A physically interesting solution describing the lukewarm black holes is briefly analyzed.

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Promise of Persistent Multi-Messenger Astronomy with the Blazar OJ 287

Galaxies ◽

10.3390/galaxies10010001 ◽

2021 ◽

Vol 10 (1) ◽

pp. 1

Author(s):

Mauri J. Valtonen ◽

Lankeswar Dey ◽

Achamveedu Gopakumar ◽

Staszek Zola ◽

S. Komossa ◽

...

Keyword(s):

Black Hole ◽

Spectral Lines ◽

Host Galaxy ◽

Central Engine ◽

Multi Wavelength ◽

Hole Model ◽

Electromagnetic Signals ◽

The Times ◽

Spectral Survey ◽

Blazar Oj 287

Successful observations of the seven predicted bremsstrahlung flares from the unique bright blazar OJ 287 firmly point to the presence of a nanohertz gravitational wave (GW) emitting supermassive black hole (SMBH) binary central engine. We present arguments for the continued monitoring of the source in several electromagnetic windows to firmly establish various details of the SMBH binary central engine description for OJ 287. In this article, we explore what more can be known about this system, particularly with regard to accretion and outflows from its two accretion disks. We mainly concentrate on the expected impact of the secondary black hole on the disk of the primary on 3 December 2021 and the resulting electromagnetic signals in the following years. We also predict the times of exceptional fades, and outline their usefulness in the study of the host galaxy. A spectral survey has been carried out, and spectral lines from the secondary were searched for but were not found. The jet of the secondary has been studied and proposals to discover it in future VLBI observations are mentioned. In conclusion, the binary black hole model explains a large number of observations of different kinds in OJ 287. Carefully timed future observations will be able to provide further details of its central engine. Such multi-wavelength and multidisciplinary efforts will be required to pursue multi-messenger nanohertz GW astronomy with OJ 287 in the coming decades.

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Ad Hoc Communications for Wireless Robots in Indoor Environments

Mobile Ad Hoc Robots and Wireless Robotic Systems - Advances in Computational Intelligence and Robotics ◽

10.4018/978-1-4666-2658-4.ch016 ◽

2013 ◽

pp. 279-290 ◽

Cited By ~ 1

Author(s):

Laura Victoria Escamilla Del Río ◽

Juan Michel García Díaz

Keyword(s):

Ad Hoc ◽

Experimental Comparison ◽

Electromagnetic Signal ◽

Indoor Environments ◽

Electromagnetic Propagation ◽

Propagation Models ◽

Electromagnetic Signals ◽

The University ◽

The Mathematical Model ◽

Robot Communication

This chapter presents a theoretical and experimental comparison of electromagnetic propagation models for indoor robot communication using mobile ad-hoc IEEE802.11 and IEEE802.15.4. The analysis includes the behavior of the electromagnetic signal using the abovementioned standards in two scenarios, both located inside the building of the College of Telematics of the University of Colima. The results of the propagation of the electromagnetic signals in the two scenarios were then compared with the mathematical model.

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Convolutional Neural Networks for Automated Rolling Bearing Diagnostics in Induction Motors Based on Electromagnetic Signals

Applied Sciences ◽

10.3390/app11177878 ◽

2021 ◽

Vol 11 (17) ◽

pp. 7878 ◽

Cited By ~ 1

Author(s):

Marcello Minervini ◽

Maria Evelina Mognaschi ◽

Paolo Di Barba ◽

Lucia Frosini

Keyword(s):

Neural Network ◽

Convolutional Neural Network ◽

Induction Motor ◽

Experimental Tests ◽

Rolling Bearing ◽

Electromagnetic Signal ◽

Bearing Faults ◽

Bearing Diagnostics ◽

Bearing Defects ◽

Electromagnetic Signals

Bearing faults account for over 40% of induction motor faults, and for this reason, for several decades, much attention has been paid to their condition monitoring, through vibration measurements and, more recently, through electromagnetic signal analysis. Furthermore, in the last few years, research has been focused on evaluating deep learning algorithms for the automatic diagnosis of these faults. Therefore, the purpose of this study is to propose a novel procedure to automatically diagnose different types of bearing faults and load anomalies by means of the stator current and the external stray flux measured on the induction motor in which the bearings are installed. All the data were collected by performing experimental tests in the laboratory. Then, these data were processed to obtain images (scalograms and spectrograms), which were elaborated by a pre-trained Deep Convolutional Neural Network, modified through the transfer learning technique. The results demonstrated the ability of the electromagnetic signals, and in particular of the stray flux, to detect bearing faults and mechanical anomalies, in agreement with the recent literature. Moreover, the Convolutional Neural Network has been proven to be able to automatically discriminate bearing defects and with respect to the healthy condition.

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Electromagnetic and gravitational signatures of accretion into black holes

International Journal of Modern Physics D ◽

10.1142/s0218271815420043 ◽

2015 ◽

Vol 24 (09) ◽

pp. 1542004

Author(s):

Juan Carlos Degollado

Keyword(s):

Black Hole ◽

Maxwell Equations ◽

Einstein Equations ◽

System Of Differential Equations ◽

Charged Fluids ◽

Schwarzschild Black Hole ◽

Initial Value ◽

Stationary Black Hole ◽

Electromagnetic Signals ◽

Set Up

In this paper, the gravitational and electromagnetic signals due to accretion of charged fluids into a Schwarzschild black hole is revisited. We set up the perturbed Einstein equations and Maxwell equations coupled to the fluid equations on a stationary black hole as a system of differential equations that can be integrated as an initial value problem. We numerically investigate cases in which we varied the properties of the fluid. Our scenario may provide an electromagnetic counterpart to gravitational waves in many situations of interest, enabling easier extraction and verification of gravitational waveforms from gravitational wave detection. We find that the features of the resulting electromagnetic signals depend on the properties and dynamics of the flow.

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Static charged fluid in (2 + 1)-dimensions admitting conformal Killing vectors

International Journal of Modern Physics D ◽

10.1142/s0218271814500424 ◽

2014 ◽

Vol 23 (05) ◽

pp. 1450042 ◽

Cited By ~ 11

Author(s):

Farook Rahaman ◽

Saibal Ray ◽

Indrani Karar ◽

Hafiza Ismat Fatima ◽

Saikat Bhowmick ◽

...

Keyword(s):

Black Hole ◽

Charge Density ◽

Hawking Radiation ◽

Central Charge ◽

Radiation Temperature ◽

Conformal Killing ◽

Btz Black Hole ◽

Charged Fluid ◽

Exterior Region ◽

Conformal Killing Vectors

New solutions for (2 + 1)-dimensional Einstein–Maxwell spacetime are found for a static spherically symmetric charged fluid distribution with the additional condition of allowing conformal Killing vectors (CKV). We discuss physical properties of the fluid parameters. Moreover, it is shown that the model actually represents two structures, namely (i) Gravastar as an alternative of black hole and (ii) Electromagnetic Mass model depending on the nature of the equation of state of the fluid. Here the gravitational mass originates from electromagnetic field alone. The solutions are matched with the exterior region of the Bañados–Teitelboim–Zanelli (BTZ) type isotropic static charged black hole as a consequence of junction conditions. We have shown that the central charge density is dependent on the value of M0, the conserved mass of the BTZ black hole. This, in turn, depends on the black hole event horizon which again is related to the Hawking radiation temperature of a BTZ black hole. Thus, one may have a clue that the central charge density is related with Hawking radiation temperature of the BTZ black hole on the exterior region of the static charged fluid sphere.

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A Lockable Abnormal Electromagnetic Signal Joint Detection Algorithm

International Journal of Pattern Recognition and Artificial Intelligence ◽

10.1142/s0218001419580096 ◽

2019 ◽

Vol 33 (13) ◽

pp. 1958009

Author(s):

Jiazhong Lu ◽

Weina Niu ◽

Xiaolei Liu ◽

Teng Hu ◽

Xiaosong Zhang

Keyword(s):

Network Security ◽

Detection Algorithm ◽

Electromagnetic Signal ◽

Detection Accuracy ◽

Power Sources ◽

Machine Learning Classification ◽

Streaming Technology ◽

Electromagnetic Signals ◽

Network Technologies ◽

Signal Sources

With the development of computers and network technologies, network security has gradually become a global problem. Network security defenses need to be carried out not only on the Internet, but also on other communication media, such as electromagnetic signals. Existing electromagnetic signal communication is easily intercepted or infiltrated. In order to effectively detect the abnormal electromagnetic signal to find out the specific location, then classify it, it is necessary to study the way of communication. The existing electromagnetic signal detection accuracy is low and cannot be located. Considering the characteristics of different power sources in different locations, combined with spark streaming technology and machine learning classification technology, a joint platform for electromagnetic signal anomaly detection based on big data analysis is proposed. The electromagnetic signal is abnormally detected by feature comparison and small signal analysis, and the position and number between the signal sources are determined by three-point positioning and signal attenuation. The experimental results show that the method can detect abnormal electromagnetic signals and classify abnormal electromagnetic signals well, the accuracy rate can reach 95%, and the positioning accuracy can reach 89%.

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