Brazilian Journal of Physics最新文献

Low-frequency electrostatic oscillations in three electron–positron, electron–positron-ion, and electron–ion quantum non-uniform magnetoplasmas in the presence of the ponderomotive force of the short pulse laser have been investigated in a comparative mode. According to the investigations, the oscillations in the direction parallel to the external magnetic field, where the plasmas are uniform in this direction, behave in the same way to a great extent in the three plasmas. In this direction, the oscillations are mostly influenced by the ponderomotive force of the laser, and in the absence of this force, they propagate stably with a constant phase and group velocities. In the presence of this force, the oscillations become unstable, and by the increase of this force, the instability rate and also the group and phase velocities of the oscillations increase. In the perpendicular direction, the oscillations indicate different behaviors in each of the three plasmas, and they are strongly affected by the number density, external magnetic field, and their transverse gradients. In this direction, the transverse gradient of the external magnetic field is the necessary condition for propagation of plasma waves in the electron–positron plasma, and also in the electron–ion plasma when the amount of ion charge is equal to the electron charge. However, in the electron–positron-ion plasma, due to the lack of charge symmetry, this condition is not necessary for perpendicular propagation.

In this paper, we discuss an extension of the geometric description of graphene wormholes in a non-inertial situation. We present an effective metric that describes the wormhole connection between two graphene sheets with matter content in rotation. Additionally, a stretching term as a function of the classical redshift of space has been found and discussed. We also explore the influence of a rotation term on quantum holonomy, recovering previous results found for the static case.

Ce_(2-x–y)Gd_xDy_yO_2-δ nanoparticles with x = 0.02 and y = 0.02, 0.04, 0.06, and 0.08 with a size range of 15.81 to 40.42 nm have been obtained by annealing the solid-state reaction-derived nanocrystalline powders. Correlations between Gd and Dy doping and lattice expansion were found; lattice parameters increased from 5.423 to 5.468 Å. When Gd and Dy content increased, optical investigations showed unexpected bandgap behaviour that did not follow the predicted reduction. Red, green, blue, and violet emissions have been identified via photoluminescence analysis. SEM and EDS verified the homogenous elemental distribution of spherical nanoparticles. With a growing magnetic moment and coercive field, magnetic measurements showed paramagnetic activity.

This study investigates nonlinear wave structures in electron-ion plasma. We use reductive perturbation theory to derive the Gardner equation, exploring the impact of plasma parameters. The study extends beyond standard homogeneous plasma assumptions, uncovering breather soliton structures. These breathers serve as energy carriers and have applications in diverse fields. We explore breather solitons and analyze a range of structures, including compressive and rarefactive two-soliton solutions, which could revolutionize our understanding of energy transport. These findings hold significance for atmospheric studies, ocean dynamics, optic fibers, signal processing, and more. This study deepens our comprehension of complex wave phenomena, providing insights into various applications, including Saturn. Furthermore, potential applications extend to quantum computing, advanced telecommunications, and medical imaging technologies. This study deepens our comprehension of complex wave phenomena and their practical implications.

Even if Lorentz symmetry is not a fundamental property of condensed matter physics, there are many instances where the relevant physics of some material is well described by a relativistic field theory. Actually, in some cases, this effective description is not of an exact Lorentz invariant model, but of a model including some small Lorentz-violating correction. In this case, a connection can be made between condensed matter physics and the Standard Model Extension (SME) that have been developed to look for Lorentz violation in fundamental physics. We are interested in particular in the connection between the SME and planar physics. We study the connection between part of the non-minimal SME and a planar model, and we calculate the interaction energies and torques appearing between point-like charges in the planar model. We show how the dimensional reduction leads to new sectors appearing in the planar theory and that the interplay between those sectors can lead to very distinctive phenomena.

In this paper, the modulational instability (MI) of dust acoustic waves (DAWs) is examined in a strongly coupled dusty plasma system containing negatively charged dust grains, nonthermal ions, and superthermal electrons. To describe the MI criteria of DAWs, the nonlinear Schrödinger equation (NLSE) is derived using the Krylov–Bogoliubov-Mitropolsky (KBM) perturbation method. Our results show that both modulationally stable and unstable domains exist in such a strongly coupled dusty plasma system. It is found that modulational stable and unstable domains are significantly modified by the related dusty plasma parameters such as ion nonthermality, electron superthermality, and the temperatures of both electron and ion. Moreover, the MI growth rate was found to be strongly modified by those parameters. The results of this investigation may be important in understanding nonlinear phenomena in laboratory and space plasmas, particularly in the upper layer of the Earth’s atmosphere (viz., Earth’s mesosphere).

We investigate the non-perturbative effects of a deformation of the Mathieu differential equation consistent with ({varvec{mathcal{P}mathcal{T}}}) symmetry. First, we develop a connection between the non-Hermitian and Hermitian scenarios by a reparameterization in the complex plane, followed by a restriction of the ({varvec{mathcal{P}mathcal{T}}}) deformation parameter. The latter is responsible for preserving the information about ({varvec{mathcal{P}mathcal{T}}}) symmetry when we choose to work in the Hermitian scenario. We note that this factor is present in all non-perturbative results and in the transseries representation of the deformed Mathieu partition function that we have obtained. In quantum mechanics, we found that the deformation parameter of ({varvec{mathcal{P}mathcal{T}}}) symmetry has an effect on the real instanton solution for the deformed Mathieu potential in the Hermitian scenario. As its value increases, the non-Hermiticity factor makes it smoother for the instanton to pass from one minimum to another, that is, it modifies the instanton width. The explanation for this lies in the fact that the height of the potential barrier decreases as we increase the value of the deformation parameter. We present how this effect extends to the multi-instanton level and to the bounce limit of an instanton-anti-instanton pair. As an application of the obtained results, we show that the equation of motion under a tilted version of the potential in the Hermitian scenario compares to the resistively shunted junction (RSJ) model for the Josephson junction.

This study investigates the influence of fear, refuge, and migration in a predator–prey model, where the interactions between the species follow an asymmetric function response. In contrast to some other findings, we propose that prey develop an anti-predator response in response to a concentration of predators, which in turn increases the fear factor of the predators. The conditions under which all ecologically meaningful equilibrium points exist are discussed in detail. The local and global dynamics of the model are determined at all equilibrium points. The model admits several interesting results by changing the rate of fear of predators and predator aggregate sensitivity. Numerical simulations have been performed to verify our theoretical findings. We found that under certain conditions, the system appears to be losing the stability to acquire the periodic attractor when the trait-mediated direct effect of one of each (prey growth, competition, fear, and prey death).

Terahertz (THz) technology is helpful in innovative applications and enormously affects wireless technology. To address THz transmission loss, recent modernizations in digital devices for the ultimate data rate of THz communication systems offer a highly efficient metamaterials (MTM) antenna concept with high directionality. This paper suggests that the dual triangular split-ring resonator (TSRR) structure incorporates the patch antenna function, which works at 1.2 THz. The analysis is carried over by optimizing the triangular ring angle of the TSRR structure’s inner and outer ring width. The optimized TSRR patch antenna with breast phantom produces the excellent result of − 61.54 dB RL, 7.929 dBi gain, 1. 0016 VSWR, and 8.715 dB directivity owing to the influence of MTM structure. The suggested TSRR antenna structure is suitable for various THz applications, which include breast cancer detection, imaging, scanning, and spectrometer with the support of high data rates in wireless transmission.

We study the Schwinger mechanism in QCD, which refers to the production of quark-antiquark pairs in the presence of a pure electric field strength eE, for a higher number of colors (N_c) and flavors (N_f). Our unified formalism is based on the Schwinger-Dyson equations, a flavor-dependent symmetry-preserving vector-vector contact interaction model of quarks, and an optimal time regularization scheme. For fixed (N_c=3) and (N_f=2), the dressed quark mass decreases as we increase eE, and near or above the pseudo-critical electric field (eE_c), the chiral symmetry is restored, and quarks become deconfined. The pair production rate (Gamma) becomes stable and grows quickly above (eE_c). For fixed (N_c=3) and upon increasing (N_f), the dynamically generated mass suppresses, and as a result, the (eE_c) reduces to smaller values, and the pair production rate (Gamma) tends to initiate and grow quickly for smaller values of (eE_c). In contrast, for fixed (N_f=2) and upon increasing (N_c), the chiral symmetry is restored for larger and larger values of (eE_c); and for (N_cge 4), the transition changes from smooth cross-over to the first order at some critical endpoint ((N_{c,p}, eE_{c,p})). Consequently, the quark-antiquark production rate (Gamma) requires higher values of (eE_c) for stable and quick growth as we increase (N_c). Our findings are satisfactory and in agreement with the already predicted results for the pair production rate (for fixed (N_c=3) and (N_f=2)) by other reliable effective models of QCD.