The European Physical Journal D最新文献

Building on our previous explorations of fractional KdV-solitary waves [Part (I)] ( El-Tantawy in Braz J Phys 55:123, 2025) and fractional modified KdV (mKdV)-solitary waves [Part (II)] (El-Tantawy in Braz J Phys 55:176, 2025), this research now explores the complex realm of fractional Gardner-solitary waves (FGSWs) in unmagnetized electronegative plasmas (ENPs) with nonthermal electrons. First, the reductive perturbation technique is applied to reduce the fluid model equations to the integer cubic-quadratic nonlinear Gardner/Extended KdV (EKdV) equation. This equation can describe the propagation of various nonlinear structures (e.g., solitary waves (SWs) and shock waves) in different plasma models and fluids, especially when the quadratic nonlinearity coefficient is close to zero. The second goal of the current study is to investigate the characteristics of fractional nonlinear structures that can arise and propagate in the current model. For this purpose, a novel technique, namely the Tantawy technique (TT), is applied to analyze the planar fractional EKdV (FEKdV) equation and model FEKdV-SWs. This approach produces accurate and stable analytical approximations. Additionally, the FEKdV equation is analyzed using the new iterative method (NIM) within the Laplace transform framework to compare its results with those of TT. To assess the accuracy of all generated approximations, the absolute error against the exact solution for the integer case is numerically estimated. Moreover, we numerically investigate the impact of different plasma parameters—negative ion concentration, ion mass ratio, and the fractional parameter—on the characteristic behavior of the FEKdV-SWs. This research provides important details about fractional nonlinear structures that can exist and propagate in laboratory, space, and astrophysical plasma systems.

The purpose of this work is to investigate the interaction of time-dependent external electric sources with the electronic modes induced in a cylindrical cavity of nanoscopic dimensions. We use the hydrodynamic model to describe the dielectric properties of the material, and solve the Poisson equation to obtain the induced fields inside the cavity. We consider different configurations of the external electric sources (point charge, extended charge distribution and electric dipole), with two types of time dependency: exponential pulse and harmonic oscillations. We analyze the enhancement of the field intensity in terms of the different relevant physical parameters, such as the cavity radius and the oscillation frequency.

Induced electric field amplitudes in Fourier space for the considered time-dependent charge configurations, obtained with a hydrodynamic dielectric function (upepsilon (textrm{k},upomega )). Left: point charge; center: dipole oriented along the cavity’s axis; right: dipole oriented perpendicular to the cavity’s axis. The material is silver, with plasmon frequency (upomega _{textrm{p}}=3.78) eV, damping constant (upgamma =0^{textrm{p}}).075eV, and cavity radius R=10 a.u. Dotted line: Drude model’s result for constant value of (A_{i}).

Non-relativistic energies, squared magnitude of the dipole matrix elements, oscillator strengths of one-electron GaAs–( text {Ga}_{1-x}text {Al}_{x} ) cylindrical quantum dot are studied within the framework of the effective mass approximation and by using a variational Galerkin-type approach based on B-spline functions. A three-dimensional (cylindrical symmetry) model potential representing the effects of the confinement in the two directions is employed along with the consideration of the off-center displacement. The results show that when the impurity is located at the center of the wire, both the transversal and the longitudinal transition energies exhibit a maximum as a function of the wire radius, while the dipole matrix elements as well as the oscillator strengths present a more complex variation with respect to the wire radius. Increasing the potential well depth raises the transition energies and shifts the position of their maximum toward smaller wire radii. Introducing an off-center displacement decreases the transition energies and reverses their dependence on the wire radius, demonstrating a significant impact on the electronic structure. Moreover, the dipole oscillator strengths exhibit a minimum, slightly depending on the well depth, whose appearance could mean a weaker transition probability, which would reveal a strong localization of the electronic density around this point and then a possible stability of the impurity out from the center of the cylindrical quantum dot. Furthermore, the dipole oscillator strengths display a minimum whose position depends on the well depth. The occurrence of a certain singular value of the off-center displacement is observed depending on the wire radius where the variations of the transversal oscillator strengths with respect to the potential depth invert. Finally, the dipole matrix elements and oscillator strengths exhibit minima at peculiar wire radius, beyond which the excited state merges into the unbound states.

The multi-configuration Dirac–Hartree–Fock method implemented in the Grasp2018 package was employed to calculate the magnetic dipole hyperfine interaction constants and electric field gradients of levels in the ground configuration of the neutral bismuth atom. Combining the calculated electric field gradient of the ground state with the measured electric quadrupole hyperfine interaction constant, we extracted the nuclear quadrupole moment for the (^{209})Bi isotope, (textrm{Q}(^{209} {textbf {Bi}}) = -422(22)) mb. A “world average” value of the nuclear quadrupole moment of this isotope, (textrm{Q}(^{209} {textbf {Bi}}) = -420(17)) mb, was deduced from the present result combined with a large sample of other theoretical values obtained with elaborate atomic- and molecular-structure calculations.

The single-center convergent close-coupling (CCC) method is applied to calculate positron scattering from beryllium. A model potential approach is utilized to extract positronium formation, direct ionization, and values between the positronium formation and direct ionization threshold. For this scattering system, we present results for total, electron loss, elastic, momentum transfer, excitation, positronium formation, direct ionization, stopping power, and mean excitation energy from threshold to 5000 eV. A modified independent atom approach is used to calculate total, electron loss, and elastic cross sections for beryllium oxide for energies above 1 eV. For beryllium, good agreement is viewed with past theory for intermediate and high energies. At lower energies, different theoretical models exhibit substantial differences.