Charged Holes Research Articles

Unraveling carrier distribution in far-UVC LEDs by temperature-dependent electroluminescence measurements

The hole transport and the carrier distribution in AlGaN-based far-ultraviolett (UVC) light emitting diodes (LEDs) emitting around 233 nm was investigated. Temperature-dependent electroluminescence measurements on dual wavelength AlGaN multiple quantum well (MQW) LEDs show a strong shift in the spectral power distribution from 250 to 233 nm with decreasing temperature. Comparing experimental data with simulation shows that the hole mobility and the electron to hole mobility ratios have a significant influence on the carrier injection efficiency (CIE) and that the change in the spectral power distribution is originating from a change in the hole distribution in the MQWs. Poor hole injection and charge carrier confinement in the AlGaN MQW active region was identified as one of the main reasons for the low CIE in far-UVC LEDs.

Zn-doped tubular graphene nitride for visible light and sacrificial-agent-free H2O2 photosynthesis in water

Graphitic carbon nitride (g-C3N4) has become a favored universal photocatalyst. Despite its numerous advantages, the photocatalytic efficiency of g-C3N4 is hindered by the substantial recombination of photoexcited charge carriers and holes. In this work, we demonstrate that Zn-doped tubular carbon nitride photocatalyst (Zn-tCN) can serve as highly efficient catalysts for H2O2 photosynthesis. Mechanism studies confirm that the presence of Zn in g-C3N4 prolongs the lifetimes of photogenerated carriers and inhibits their recombination, which triggers the reduction of O2 to reaction intermediates (O2−), as supported by in situ electron paramagnetic resonance (EPR) spectroscopy. More importantly, sacrificial agent experiments coupled with in situ EPR results confirmed that the reaction mechanism involves a concerted two-electron transfer process. The optimal catalyst displays a H2O2 productivity of 162.4μmol g–1h−1 under visible-light irradiation without a sacrificial agent, which is 11.7 times higher than that of pristine g-C3N4 (13.8μmol g–1h−1). This work proposes a synthetic strategy for the preparation of high-performance Zn-doped g-C3N4, which offers insights and perspectives for developing highly active photocatalysts and deepening the understanding of photocatalytic mechanisms.

Shadow and quasinormal modes of novel charged rotating black hole in Born–Infeld theory: Constraints from EHT results

This work investigates the shadow and quasinormal modes of a novel rotating Born–Infeld-type black hole. First, we study the effect of interaction between nonlinear electrodynamic fields and photons on shadow radius and show that it is less than the error of shadow measurements in Event Horizon Telescope (EHT) observations. Then, we obtain a rotating metric using the Newman–Janis algorithm, starting with the initial metric of the nonrotating novel Born–Infeld black hole solution. Next, we analyze the null geodesics to determine the celestial coordinates. The black hole’s shadow radius is determined by using celestial coordinates. The mass, spin, charge, and nonlinearity parameters all influence the shape and size of the black hole shadow. An increase in the spin parameter results in a gradual reduction in the size of black hole shadows and further distortion of the shadows. Furthermore, constraints on the spin and electric charge of black holes, as well as the nonlinearity parameter, are derived through the utilization of the shadow sizes of supermassive black holes Sagittarius (Sgr) A* and M87* obtained from observations of the EHT. Also, we investigate the correlation between the standard shadow radius and the equatorial and polar quasinormal modes for revolving black holes. Finally, we analyze the emission energy rate from the black hole based on different spacetime parameters. Our observation indicates that the emission energy rate decreases as the values of spin and nonlinearity parameters increase, keeping the charge-to-mass ratios of the Born–Infeld black hole constant.

A thermodynamic study of (2+1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ extbf {(2+1)}}$$\\end{document}-dimensional analytic charged hairy black holes with Born–Infeld electrodynamics

This work presents analytical black hole solutions for a coupled Einstein–Born–Infeld–Scalar gravity system in AdS spacetime with two different non-minimal coupling functions f(z). For both solutions, we establish the regularity of the scalar field and curvature scalars outside the horizon. For one of the considered coupling cases, thermodynamic analysis in the canonical ensemble reveals stability across all temperatures, while the other case exhibits the Hawking/Page phase transition between the stable large phase of the black hole and thermal-AdS. We investigate the effect of the scalar hair parameter and black hole charge on the phase transition temperature and observe that the critical values of the scalar hair and the charge parameters constrain the feasibility of Hawking/Page phase transition.

Thermodynamic topology of D = 4,5 Horava Lifshitz black hole in two ensembles

In this paper, we investigate the thermodynamic topology of four and five-dimensional Hořava-Lifshitz (HL) black holes within Hořava gravity. To analyze their thermodynamic topology, we treat these HL black holes as topological defects in their thermodynamic spaces and compute the winding numbers at these defects. Our study is conducted in two different ensembles: the fixed ϵ ensemble and the fixed ζ ensemble, where ϵ is a parameter of the HL black holes, and ζ is its conjugate parameter. In the fixed ϵ ensemble, we consider three different horizon types: spherical (k=+1), flat (k=0), and hyperbolic (k=−1), while in the fixed ζ ensemble, we examine two horizon types: spherical (k=+1) and hyperbolic (k=−1). For all the aforementioned cases, we study the local and global topology of these black holes and classify them into topological classes based on their topological charges. We calculate the topological number for each case. This process uncovers some novel phase diagrams that reveal a number of multiple defect curve phenomenon. Additionally, we explore how the topological charge of these black holes depends on the values of the thermodynamic parameters. Our findings indicate that the thermodynamic topology of Hořava-Lifshitz black holes in D=4,5 is significantly influenced by the type of horizon, the choice of ensemble, the values of pressure, and the parameters ϵ or ζ.

Charged Particles Capture Cross-section by a Weakly Charged Schwarzschild Black Hole

We study the capture cross-section of charged particles by a weakly charged Schwarzschild black hole. The dependence of the maximum impact parameter for capture on the particle’s energy is investigated numerically for different values of the electromagnetic coupling strength between the particle and the black hole. The capture cross-section is then calculated. We show that the capture cross-section is independent of the electromagnetic coupling for ultra-relativistic particles. The astrophysical implications of our results are discussed.

Triple points of gravitational AdS solitons and black holes

We present a triple point of a new kind for general relativity, at which two gravitational solitons can coexist with a planar black hole in anti–de Sitter space. Working in the context of nonlinear electrodynamics, we obtain simple, sensible spacetimes for which the thermodynamics can be studied in an analytic manner. The spacetimes are charged under the nonlinear electrodynamics leading to an electric charge for black holes and a magnetic flux for solitons. In the grand-canonical ensemble, we show that the phase space of the theory is very rich, containing reentrant phase transitions, as well as triple points, for small values of the coupling controlling the nonlinearity of the electrodynamics Lagrangian. Published by the American Physical Society 2024

Photoelectrochemical Water Splitting: A Visible-Light-Driven CoTiO3@g-C3N4-Based Photoanode Interface Follows the Type II Heterojunction Scheme.

Harnessing solar energy can be efficiently used to generate hydrogen by photochemical water splitting, which is a sustainable and environmentally benign energy source. Here, a unique visible-light-driven CoTiO3@g-C3N4 (CTOCN)-based photoanode interface has been optimized and developed with modification to follow the type II heterojunction for the enhancement of photoelectrochemical water splitting. Initially, a graphitic carbon nitride-loaded CoTiO3 (with 10 wt % g-C3N4) composite was obtained using a one-pot solvothermal method. Accordingly, the type II heterojunction interface between g-C3N4 and CoTiO3 has been successfully created and confirmed by the acquired phase, morphological, and optical examinations. Thereby, heterostructure generations with interfacial interaction were enabled to decrease photogenerated electron-hole pair recombination, leading to enhanced charge transfer for water oxidation kinetics. The minimal charge transfer resistance and hole relaxation lifetime (p) shown in Nyquist and Bode plots have further confirmed the rapid electron transport across the electrode/electrolyte interfaces, which is attributed to an enhanced absorption of holes for the water splitting process. Additionally, UV-vis spectroscopy, Mott-Schottky analysis, and UPS studies were used to determine the band edge locations of g-C3N4 and CoTiO3. In comparison to previously developed nanohybrids and their equivalents, the CTOCN-d photoanode follows the type II charge transfer mechanism, resulting in a higher photocurrent density of 55.51 mA cm-2.

Analysis of high-frequency limit in absorption cross-section for Kerr–Newman–de Sitter black hole

In this paper, we study the critical impact parameter and Lyapunov exponent for a massive charged particle and a photon in the Kerr–Newman–de Sitter (KNdS) spacetime. From the geodesic equations obtained for the particle traveling parallel to the rotation axis (on-axis) of the KNdS spacetime and using the complex angular momentum (CAM) technique, it is found that the total absorption cross-section at a high-frequency limit oscillates with decreasing amplitude. We show that the black hole charge and spin affect the total absorption cross-section in the case of both the massive charged particle and photon.

High-performance oxygen terminated synthetic single crystal diamond detector for high gamma dose rate measurement

A high-performance oxygen terminated synthetic single crystal diamond (SCD) detector (4.5 × 4.5 × 0.5 mm3) is presented. The SCD detector exhibits an extremely low leakage current value of 0.29 pA/mm2 with an electric field of 0.3 V/μm. The charge collection spectrum measured with a238Pu source (5.48 MeV α-particles) irradiation shows that the electron and hole charge collection efficiency (CCE) reach as high as 99.1% and 98.9%, with an energy resolution as low as 2.87% and 2.53%, respectively, compared to Si detector. The SCD detector shows excellent radiation hardness and stability under 60Co γ-ray irradiation with a dose rate of 12.737 kGy/h at 150 V bias and is able to withstand a cumulative dose of up to at least 9.3 kGy. The detector output in current mode is linearly related to the dynamic dose rate (0.409 Gy/h-12.737 kGy/h). Similarly, the counting rate of the detector in counting mode exhibits a strong linear variation within the range of 2.6 mGy/h-1269.36 Gy/h. Our results fully indicate that our fabricated SCD detector can be potentially applied to harsh γ irradiation scenarios, which is of guiding significance on real-time dose monitoring.

Shadow and quasinormal modes of rotating charged black holes in Kalb–Ramond gravity and implications from EHT data

The recent observations of the Event Horizon Telescope for the supermassive black holes M87* and Sgr A* can potentially test gravity theories and acquire further knowledge on black holes and gravity parameters. An essential field of research focuses on the shadow and quasinormal modes of black holes. Therefore, we used the Newman–Janis algorithm to get a rotating charged black hole solution in Kalb–Ramond gravity. Then, we looked at the event horizon radius, the static limit, and the ergoregion of spacetime. We derive the null geodesic equations and the effective potential for photon radial motion. We also investigate how the black hole’s Kalb–Ramond, spin, and charge parameters affect the shadow size and distortion. It is obtained that an increase in the Kalb–Ramond parameter causes a decrease in the radius and increases the distortion of the shadow size. We obtain constraints on black hole charge and spin using the data obtained from Event Horizon Telescope observations of M87* and Sgr A* by testing the effects of the Kalb–Ramond gravity parameter. We examine the energy emission rate using Hawking radiation and demonstrate that a rise in the Kalb–Ramond parameter diminishes this rate. Finally, we calculated and analyzed the typical shadow radius, equatorial, and polar quasinormal modes using the geometric–optic connection between quasinormal mode parameters and conserved quantities along geodesics.

Orbital motion and epicyclic oscillations around Bardeen black hole surrounded by perfect fluid dark matter

We study the orbital and oscillatory motion of test particles moving around a rotating Bardeen black hole immersed in perfect fluid dark matter. We obtain the analytical solutions for the radial profiles of specific energy as well as the specific angular momentum of the equatorial stable circular orbits. Using the effective potential approach, we also discuss the stability of circular orbits. We compute the frequencies of radial and latitudinal harmonic oscillations as a function of mass, charge, and angular momentum of the black hole as well as the parameter describing the perfect fluid dark matter. The main characteristics of test particle quasi-periodic oscillations near stable circular orbits are examined in the equatorial plane. Furthermore, we study precessions of Periastron and Lense-Thirring. It is observed that the particle's motion around the black hole is strongly influenced by the model parameters.

Constraints on quasinormal modes from black hole shadows in regular non-minimal Einstein Yang–Mills gravity

This work deals with scalar quasinormal modes using the higher-order WKB method and black hole shadow in non-minimal Einstein–Yang–Mills theory. To validate the results of quasinormal modes, time domain profiles are also investigated. We find that with an increase in the magnetic charge of the black hole, the ringdown gravitational wave increases non-linearly and the damping rate decreases non-linearly. The presence of a magnetic charge also results in a non-linear decrease in the black hole shadow. For large values of the coupling parameter, the black hole becomes a soliton solution and the corresponding ringdown gravitational wave frequency increases slowly with a decrease in the damping rate. For the soliton solutions, the shadow is also smaller. The constraints on the model parameters calculated using shadow observations of M87* and Sgr A* and an approximate analytical relation between quasinormal modes and shadows at the eikonal limit are discussed.

Computer Simulation of Charge Transfer In a DNA Molecule within a Simple Model of an Open Quantum System

The quantum-statistical model proposed earlier by Skourtis and Nitzan to describe a charge (hole) propagation in a fragment of artificial DNA molecule has been generalized and further investigated. A numerical simulation of a charge transport was carried out taking into account two different dissipative processes, including the capture of the charged carrier by the environment and the decoherence of its quantum wave properties due to the influence of stochastic fields of the environment. The interaction of the carrier with the environment is regulated by a small set of phenomenological parameters whose values vary in the process of simulation. Within this model, the propagation of a hole carrier in DNA is described by solving the quantum Franke-Kossakovski–Lindblad–Glauber–Sudarshan equation (hereinafter referred to as the Lindblad equation) for the carrier density matrix using the Lindblad MPO Solver program. Results of numerical analysis of the model are in a good agreement with experimental observations and demonstrate two different types of the charged carrier motion, presumably tunneling and incoherent hopping. The model is put in more general context and non-unitary dynamics of the hole carrier is treated within the framework of a theory of continuous quantum measurements by the environment in an open quantum system. The main concepts of the theory of decoherence and superselection for open quantum systems and the prospects for their application for further study of various mechanisms of motion of a charged carrier in DNA are briefly discussed.

Quasinormal modes of charged BTZ black holes

We investigate the scalar field equation in a (2+1) -dimensional charged BTZ black hole. The quasinormal spectra of the solution are obtained applying two different methods and good convergence between both is achieved. Using the characteristic integration technique we tested the geometry evidencing its stability against linear scalar perturbations. As a consequence a two pattern set of frequencies (families) emerges, one oscillatory and another purely imaginary. In that spectra, the fundamental modes without angular momentum are hugely affected by the presence of the black hole charge surprisedly even for small values of this. Their evolution are controlled by purely imaginary frequencies as in the non-rotating chargeless BTZ case. Similar to others AdS black holes, the fundamental oscillations scale the black hole event horizon and the temperature of the hole (far from maximal charges).

Thermal chaos of charged-flat black hole via Rényi formalism

Charged-flat black holes in the Rényi extended phase space demonstrate phase structures akin to those of a van der Waals fluid in four-dimensional spacetime and mirror the behaviors of Reissner-Nordstrom-Anti-de-Sitter black holes within the standard Gibbs-Boltzmann extended phase space. This study delves into the dynamics of states initially positioned within the unstable spinodal region of the phase space associated with the charged-flat black hole when subjected to time-periodic thermal perturbations. Our analysis based on the Mel'nikov method reveals that chaos emerges when the δ parameter surpasses a critical threshold, δc. This critical quantity is dependent on the black hole charge; notably, a larger value of Q impedes the onset of chaos.Furthermore, we examine the effects of space-periodic thermal perturbations on its equilibrium state and find that chaos invariably occurs, irrespective of the perturbation amplitude. Hence, the chaotic dynamics observed in the analysis of charged-flat black holes under Rényi statistics exhibit resemblances to those of asymptotically AdS-charged black holes investigated via the Gibbs-Boltzmann formalism. This serves as yet another example of a potential and significant connection between the cosmological constant and the nonextensivity Rényi parameter.

Evolution Characteristics of Strain and Displacement Fields in Double-Hole Short-Delay Blasting Based on DIC

In the process of porous blasting excavation in engineering projects such as mining, hydropower stations, and tunnels, the delay time between adjacent blast holes significantly influences the characteristics of rock fracture and fragmentation. In order to visually explore the changing characteristics of strain and displacement between adjacent blast holes under different delay times, polymethyl methacrylate (PMMA) plates were used to simulate rock materials, and 2D digital image correlation (2D-DIC) testing methods were employed to measure the explosive strain field with different delay times (0 µs, 5 µs, 15 µs, 40 µs, 70 µs) for dual holes. Full-field principal strain cloud maps and displacement fields of PMMA boards in two-dimensional spatial coordinates were obtained, and the representative monitoring points were analyzed. The experimental results show that the maximum values of the first compressive principal strain peak and the first tensile principal strain peak at the connecting center of the two holes exist at a delay time of 0~40 µs under blasting conditions with the same hole distance and single hole charge. At the center point of the connection between the two holes, the interval time between the two principal strain peaks decreases with the increase in delay time. The maximum principal strain on the central vertical line of the connection line decreases exponentially with the increase in hole distance, and the attenuation trend increases first and then decreases with the delay time between 0 and 40 µs. At the peak of strain, the maximum average displacement of the connecting center of the two holes exists in the delay time between 0 and 40 µs. With the increase in delay time, the displacement trend between the two explosion holes gradually changes from shear to tension, and the vulnerable damage area increases, which makes the communication between the two explosion holes easier. This study can provide a basis for the precise selection of delay times between blasting holes in engineering.

Shadows and weak gravitational lensing for black holes within Einstein-Maxwell-scalar theory* *Supported by the National Natural Science Foundation of China (11675143), and the National Key Research and Development Program of China (2020YFC2201503). M.A and B.A wish to acknowledge the support from Research Grant F-FA-2021-432 of the Ministry of Higher Education, Science and Innovations of the Republic of Uzbekistan.

In this study, we investigated the optical properties of charged black holes within the Einstein-Maxwell-scalar (EMS) theory. We evaluated the shadow cast by these black holes and obtained analytical solutions for both the radius of the photon sphere and that of the shadow. We observed that black hole parameters γ and β both influence the shadow of black holes. We also found that the photon sphere and shadow radius increase as a consequence of the presence of the parameter γ. Interestingly, the shadow radius decreases first and then remains unchanged owing to the impact of the parameter β. Finally, we analyzed the weak gravitational lensing and total magnification of lensed images around black holes. We found that the charge of the black holes and the parameter β both have a significant impact, reducing the deflection angle. Similarly, the same behavior for the total magnification was observed, also as a result of the effect of the charge of the black holes and the parameter β.

Probing black hole charge from the binary black hole inspiral

Probing black hole charge from the binary black hole inspiral

On the mechanisms of charge weld evolution in aluminum extrusion

This study aims to provide new insights into the governing mechanisms of material property evolution within the charge weld zone in the hot extrusion process of aluminum profiles. A set of 6xxx series aluminum alloy tubular profiles was produced through carefully designed industrial experiments of billet-to-billet extrusion. The evolution of material integrity within the charge weld zones was experimentally characterized by microhardness tests, optical microscopy, scanning electron microscopy (SEM), and drift-expansion tests. The experimental analyses reveal that the material integrity of charge welds gradually increases from the onset to the end, primarily driven by the ‘local’ pressure history experienced. Towards the end of the charge weld zone, grooves and holes, and oxide particles gradually vanish, leading to enhanced material integrity. A through-process finite element (FE) model was developed using QForm-Extrusion software to analyze the thermo-mechanical history of charge weld formation, providing a deeper understanding of how material properties evolve and the underlying mechanisms governing this evolution. The model was experimentally validated in terms of the extrusion load and distribution of the charge welds in extruded profiles. Overall, the new insights gained in this study offer valuable knowledge for enhancing the process and quality control in billet-to-billet extrusion, as well as reducing in-process scrap towards more sustainable production of aluminum profiles.