Indian Journal of Physics最新文献

This study employs Total Electron Content (TEC) values, derived from signal delays in Global Positioning System (GPS), to monitor ionospheric activity over Türkiye. TEC values were calculated using data from 92 GNSS stations, employing various Global Ionosphere Models (GIMs) alongside the continuously operating reference stations-Türkiye (CORS-TR). The study period was chosen during a phase of low solar activity to minimize the influence of solar-induced ionospheric disturbances. The analysis covers the years 2019, 2020, and 2021, with TEC calculations performed using the GPS-TEC software developed by Gopi Seemala at the Institute for Scientific Research, Boston College. A comparative analysis of TEC estimates from the CODE, ESA, JPL, and IGS models yielded yearly average of Root Mean Square Error (RMSE) values of 3.957, 3.958, 5.180, and 4.344 for 2019; 3.758, 4.102, 5.391, and 4.875 for 2020; and 4.360, 4.433, 5.711, and 5.104 for 2021 respectively. The highest RMSE values were observed for the JPL model, whereas the CODE model produced the lowest RMSE values. Furthermore, the monthly averaged absolute TEC differences between the GIMs and GPS-TEC indicate a notable increase in TEC values toward 2021. This increase is likely attributed to variations in solar activity during the analysed period.

In this report, we have performed frequency dependent dielectric study of Sr₂RuMn_1−xFe_xO₆ (0 ≤ x ≤ 0.4) double perovskite materials synthesized by conventional solid-state route. The initial two samples of the series (x = 0 and 0.1) crystallized in tetragonal structure with space group P4/mmm and last two samples (x = 0.2 and 0.3) crystallized in cubic structure with Pm-3 space group. The frequency dependent dielectric studies of the compounds reveal colossal dielectric constant (~ 10⁷) at different temperatures. The dielectric constant of all the samples maintains a constant value up to 500 kHz. The dielectric behavior of all the compounds is best interpreted using Maxwell–Wagner interfacial polarization model. The Cole–Cole model was used to study the dielectric relaxation of the samples which indicated a polydispersive nature of the dielectric relaxation. The temperature variation of mean relaxation time ((tau)) follows Arrhenius law with activation energy in the range of 0.013–0.152 eV.

The present study investigates the cause of oscillation in the critical frequency (foF2) and peak height (hmF2) of the F2 layer during evening hours in the low solar activity year 2020 using 5-min resolution ionogram data from the midlatitude stations Nicosia (35.025°N, 33.157°E) and Athens (38.0°N, 23.5°E). Analysis of geomagnetically quiet days reveals that the normalized fluctuations in foF2 and hmF2 exhibit oscillations with periodicities ranging from 120 to 240 min, which are associated with large-scale atmospheric gravity waves (AGWs)/traveling ionospheric disturbances. Observations reveal two distinct types of wave-induced oscillations in foF2 and hmF2: one that begins in the afternoon, intensifies after sunset, and fades before midnight; and another that initiates shortly after sunset and similarly weakens before midnight. Analysis of the events indicates westward-propagating acoustic-gravity waves (AGWs), with estimated propagation velocities ranging from 439 to 615 m/s for afternoon AGWs and 256 to 341 m/s for solar terminator AGWs.

In this study, we explore the characteristics of the Laguerre-Gaussian laser beam as they propagate through a thermal quantum plasma (TQP), considering relativistic non-linearity effects. The field distribution within the medium is characterized by parameters such as the width of the beam a and the Laguerre-Gaussian mode. We employ a variational approach to analytically solve the appropriate nonlinear Schrödinger wave equation. We analyze how the beam width parameter a evolves with the propagation distance z across various values of the (L-G) modes. Furthermore, we examine phenomena such as self-phase modulation and self-trapping under a range of parameters. Additionally, we explore the impact of different plasma regimes, including classical relativistic, relativistic cold quantum, and thermal quantum, on the self-focusing behavior of the laser beam. Our investigation reveals that self-focusing occurs earlier and is more pronounced in the case of thermal quantum plasma (TQP) compared to other plasma regimes.

In this study, a one-dimensional photonic crystal sensor based on an alternating arrangement of silica and zinc selenide is theoretically proposed. The defect-mode resonance is excited by introducing the analyte as a defect layer within the photonic crystal structure. Simulations were performed using the transfer matrix method and MATLAB software, demonstrating the sensor’s capability for efficient and effective measurement of DMF solution concentration. The effects of defect layer thickness and position, number of photonic crystal periods, and angle of incidence on sensor performance were systematically investigated. Simulation results indicate that the maximum sensitivity of the sensor reaches 530 nm/RIU, with a quality factor of up to 19,100.

The study of highly dispersive optical solitons in birefringent fibers is crucial for advancing high-speed optical communication and nonlinear fiber optics. In this research, we analyze the properties of such solitons by employing the eighth-order nonlinear perturbed Kundu–Eckhaus equation, incorporating multiplicative white noise in the Itô sense. To this end, we apply three robust analytical methods: the addendum to Kudryashov’s method, the unified Riccati equation expansion method, and the addendum to the modified sub-ODE method. These techniques enable the derivation of explicit solutions relevant to various physical and engineering problems. Our analysis reveals multiple soliton solutions, including Jacobi elliptic solutions, bright solitons, straddled solitary solutions, singular solitons, and Weierstrass elliptic functions. The findings significantly contribute to the understanding of nonlinear optical pulse propagation in birefringent fibers, potentially enhancing the design and optimization of advanced optical communication systems. These results offer deeper insight into soliton dynamics and provide new perspectives on practical applications in fiber optics and nonlinear wave theory.

We study the isotropic and anisotropic Hamiltonian of two coupled harmonic oscillators from an algebraic approach of the SU(1,1) and SU(2) groups. In order to obtain the energy spectrum and eigenfunctions of this problem, we write its Hamiltonian in terms of the boson generators of the SU(1,1) and SU(2) groups. We use the one boson and two boson realizations of the su(1,1) Lie algebra, and the one boson realization of the su(2) Lie algebra to apply three tilting transformations to diagonalize the original Hamiltonian. These transformations allow us to obtain the energy spectrum and eigenfunctions of the isotropic and the anisotropic cases, from which the particular expected results are obtained for the cases where the coupling is neglected.

This paper addresses the issues of vibrational resonance and dynamics of the nonlinear electromagnetic model. After the mathematical modeling, the analytical study of the resonance is done by considering the slow and fast movements. The study of the effect of the parameters is done in order to identify those which are unfavorable to the appearance of the vibrational resonance. Subsequently, the influence of the amplitude modulated disturbances on the dynamics of the system is numerically studied by solving the dynamic equation obtained using a Runge–Kutta algorithm of order 4 executed on fortran. The different movements are sought when the modulation frequency is rational and irrational.

This study begins by examining the susceptibility of ferromagnetic particles and introducing magnetic dipole theory. A two-dimensional multichain microstructure model that incorporates ferromagnetic particles within a superconducting matrix has been developed. By integrating this superconducting composite model with the AC susceptibility method, the relationship between the volume fraction of ferromagnetic particles and their relative permeability is investigated. Furthermore, the influence of relative permeability on flux dynamics and key superconducting electrical parameters is analyzed. The results demonstrate a linear correlation between relative permeability and the volume fraction of ferromagnetic particles. Additionally, relative permeability significantly affects superconducting electrical coefficients, magnetic relaxation, hysteresis loops, and the real and imaginary components of AC susceptibility, as well as superconductor surface barriers.

The Bismuth Ferrite samples with the nominal composition BiFe_0.95Cr_0.05-xPr_xO₃ (x = 0.00, 0.01, 0.02, 0.03) were synthesized using a nitrate-based sol–gel method. The X-ray diffraction results confirm the formation of rhombohedral phase (R3c space group) without presence of impurity phases till x = 0.02. Scanning electron microscopy showed feature of grain growth, which is consistent with the decrease in microstrain computed using Williamson-Hall analysis. The dielectric measurements reveal the reduction of grain boundary resistance and increased magnetodielectric coupling for the x = 0.02 sample. The most striking magnetic enhancement is seen in the remanent magnetization, which rises from just 0.1769 emu g⁻¹ in the Cr-only sample (x = 0.00) to 3.9015 emu g⁻¹ at x = 0.02. On the ferroelectric side, the remanent polarization jumps from 0.7187 µC cm⁻² for x = 0.00 to 6.4007 µC cm⁻² at x = 0.02. The ME Coupling and Photoluminance results reveal that the Cr–Pr co-doping up to x = 0.02 has pronounced effect on the multiferroic properties of BiFeO₃ to suggest its use in nano-devices where strong magnetoelectric coupling is desired.