Indian Journal of Physics最新文献

The valley polarization is a fundamental concept in valleytronic applications. However, the combined effects of the electrostatic potential barrier and the magnetic field as well as strains on the valley polarization in a graphene have been rarely reported. Therefore, in this paper, we use the transfer-matrix method to illustrate effects of the height and width of the electrostatic barrier and the strength of the applied magnetic field on the valley polarization of electrons in a graphene, and we find that the valley polarization strongly depends on the strength and width of the electrostatic barrier. We also find that the 100% valley polarization can be achieved continuously and smoothly over a wide range of Fermi energy region by controlling the strength of the applied magnetic field. This point makes it easier to design novel valleytronic devices based on graphene with the presence of the magnetic field and the electrostatic potential barrier as well as strains.

The propagation of cylindrical shock wave influenced by monochromatic radiation and magnetic field in a self-gravitating non-ideal gas for a rotating medium has been investigated by using the Lie symmetry method. Ahead of the shock front, the ambient density of the medium is taken as constant, while the magnetic field, azimuthal and axial velocities vary over time. By using the Lie symmetry approach, the optimal system for the governing equations, the similarity variable and transformations are obtained. By the use of derived similarity transformations, the governing equations change into a system of ODEs (ordinary differential equations). The software package “Mathematica” has been utilized to solve the system of ODEs numerically and to generate the graphs for the flow variables distribution. In this article, the strength of the shock wave and variations in the flow variables of the flow field region behind the shock front, which are influenced by the strength of the ambient magnetic field, gravitational parameter, non-idealness parameter, adiabatic exponent, and rotational parameter, are examined in detail. It has been demonstrated that the magnetic field, non-idealness parameter, adiabatic exponent, and rotational parameter have decaying effect on the shock wave. In contrast, the gravitational parameter has reversed impact on the shock strength.

SiO₂:x% Cr³⁺ (0 ≤ x ≤ 8) nanopowder samples were synthesized using the sol-gel method. The effect of Cr³⁺ doping concentration on the SiO₂ nanoparticles was studied for possible application in light-emitting diodes (LEDs). Structure and optical properties of undoped and Cr³⁺ doped SiO₂ nanoparticles were investigated in detail. X-ray diffraction (XRD) results confirmed the amorphous phase for undoped SiO₂ (A-SiO₂) nanopowder. However, above 0.8% Cr³⁺ there were secondary peaks due rhombohedral structure of chromium (III) oxide (R-Cr₂O₃). Ultraviolet-visible spectroscopy (UV-Vis) spectra showed a reflectance peak at around 320 nm for the undoped sample. The results showed that when the concentration of Cr³⁺ is increased there was an emergence of reflectance peaks at around 309, 419, and 553 nm which were attributed to the presence of the Cr₂O₃ lattices. The photoluminescence (PL) results revealed that with an increase in the amount of Cr³⁺, the maximum peaks in blue and near red emerge at around 2.82 and 1.89 eV, respectively. Those peaks may be due to defects within both SiO₂ and R-Cr₂O₃. The emission peaks of undoped and Cr³⁺ doped SiO₂ match well with the Uv-vis results. The international illumination colour chromaticity showed that above 0.8% Cr³⁺ the colour shifts from yellow to blue with an increase in Cr³⁺ concentration. The investigation indicated that Cr³⁺ doped SiO₂ have a potential application in blue and yellow LED chips for lighting.

The orbital angular momentum (OAM) has attracted widespread attention due to its ability to carry information in multiple dimensions. However, a high-dimensional entanglement carrying OAM can be affected by environment and undergoes decoherence. How to control the entangled states and ensure the stability and high fidelity of entangled states is a crucial part of quantum communication. In this paper, we produce the polarization entangled photon pairs by spontaneous parametric down-conversion, we achieve the polarization-OAM hybrid entangled states by manipulating the multi-degrees of freedom of the quantum state. The polarization entangled photon pairs have the characteristics of OAM. We use polarization degree of freedom to modulate OAM degree of freedom, our polarization-OAM hybrid entangled states can slow down the reduction of the fidelity in the transmission process. This method can provide a theoretical guidance for improving the transmission fidelity of OAM states in fiber.

We have demonstrated a domain-wall dark pulse by using a polyacrylonitrile film as a saturable absorber (SA) in Erbium-doped fiber laser (EDFL) cavity. The preparation of the polyacrylonitrile thin film SA and the performance analysis of the film were described. The dual wavelengths are stably lased at 1560.43 nm and 1561.17 nm to induce topological defect in temporal domain. Within the pumping range of 97.76–165.26 mW, we observed the dark pulse oscillation in the fiber laser cavity with repetition rate of 0.99 MHz and pulse width of 306 µs. The highest average pulse energy of 6.54 nJ was achieved at pump power of 165.26 mW, with a signal-to-noise ratio of 67 dB. The stable formation of dark pulses in the fiber laser system demonstrates that the polyacrylonitrile thin film SA has significant potential for commercial applications. This advancement not only highlights its promise for future industry use but also establishes a foundation for growth in sustainable technologies.

This study presents anisotropic cosmological models in f(T) theory of gravity with mixture of fluids. The (fleft( T right)) theory of gravity is the generalization of the Teleparallel theory of gravity, where T is the torsion scalar. In order to obtain a deterministic solution of the field equations, I have assumed that the two sources of the perfect fluid and dark energy interact minimally with separate conservation of their energy–momentum tensors as well EoS parameter of the perfect fluid is assumed to be constant. In this paper, I have investigated dark energy models such as quintessence, chaplygin gas, cosmological constant with assist of f(T) gravity. Role of the cosmological constant (Lambda) term in the evolution of the anisotropic universe has been studied. The diagnostics parameters (r(z)), (s(z)) and (om(z)) are investigated. I have discussed observational fitting concerning.

The forecasting method emerged in the middle of the twentieth century; its usage has grown exponentially in all aspects of life. More importantly, estimating modern meteorological parameters helps make good decisions regarding weather, health, and agricultural safety measures. Similarly, this study aims to find a better-fitting technique to translate Quetta’s (Pakistan) temperature distribution using its three neighboring stations, Chaman, Kalat, and Sibi. In this regard, a well-known machine learning technique named Artificial Neural Network was utilized. Additionally, four training algorithms are also considered to optimize the model performance. Apart from that, another traditional statistical model is incorporated, which is a Multiple Linear Regression (MLR). Since the temperature distribution has a nonlinear trend, MLR techniques are also useful for making predictions. Machine learning and linear statistical models are provided with seven years of data from 2011 to 2017 for training purposes. Three sets of data for 2018, 2019, and 2020 are fed to determine how these trained models show close agreements with the actual temperature distribution. Different errors are evaluated to assess model performance, such as mean squared error (MSE), mean absolute percentage error (MAPE), mean absolute bias error (MABE), and chi-squared error. ({chi }^{2}), and coefficient of determination (R²). For ANN, the models with the lowest MABE and MAPE values are ANN-RB and ANN-BR, whereas the model with the lowest MSE value, 1.3604, is the ANN-BFG model. The model with the highest correlation is the ANN-BFG model. On the other hand, MLR has an MSE of 1.4253 and a coefficient of determination of 0.9860.

This paper presents a computational methodology aimed at precisely estimating the physical law governing equivalent flow resistivity in multilayer rigid porous materials, with a specific focus on applications in acoustic insulation systems. While existing models are capable of predicting sound transmission through individual layers, they lack a direct theoretical analytical link between the flow resistivity of multilayer materials and the properties of their constituent layers. To address this gap, the study harnesses equivalent fluid theory, which integrates visco-inertial interactions between the material structure and the interstitial fluid. By establishing simplified expressions for the transmission coefficient of a bilayer medium under low-frequency Darcy conditions, the paper introduces a novel approach to estimation. Furthermore, it formulates a concise relationship between the resistivity of the bilayer medium and the resistivity and thickness of each layer, which extends to multilayer configurations. Experimental validation with bilayer samples demonstrates significant agreement between the directly obtained equivalent flux resistivity and the theoretically predicted values, with relative errors ranging from 3 to 18%. The significance of this paper lies in its practical implications for acoustic insulation systems, where accurate predictions of acoustic performance are crucial. The research introduces a reliable physical relationship for estimating the equivalent flow resistivity of a multilayer as a function of the flow resistivity of each constituent layer and its thickness, offering theoretical correlation with empirical data and providing an alternative to labor-intensive experimental methods and software. This contribution to acoustics facilitates accurate prediction and characterization of the acoustic properties of multilayer materials, thereby aiding in the design of effective noise control systems.

The structural and electronic properties, as well as the stability of Ag₂O_1−xS_x (x = 0, 0.25, 0.5, 0.75 and 1) compounds have been investigated through first-principles calculation.The FP-LAPW method within theGGA-PBE, TB-mBJ and HSE06 functional approximations was chosen in the computational approach. The computed lattice constant for Ag₂O and Ag₂S was found to be consistent with the theoretical and experimental results. For electronic properties,the reproduction of the experimental band gap energy is seen with the hybrid-DFT functionalHSE06, compared to GGA-PBE and for TB-mBJ.In order to better understand the behavior of electronic states of Silver-based compounds, details of the electronic properties would be valuable. It is believed that changes of the Fermi level of a semiconductor will definitely affect its photocatalytic properties due to the contribution of strong hybridization between the O and S p states and Ag d states.From the optical results we demonstrate that the studied materials are important for optoelectronic devices because it exhibited a wide range of absorption spectra.

This paper presents an analysis on the basis of factorial correlators and oscillatory multiplicity moments among the pions extracted from Monte Carlo (MC) generated PYTHIA(v8.3), AMPT(v2.26) and UrQMD(v3.4) models in pp collisions at different center-of-mass (c.m) energies (sqrt{s}=) 2.76 – 13 TeV. During this investigation, we have found the presence of short-range correlation and our overall findings are accordant with the predictions of the (alpha)-model and (log)-normal approximation which indicates the existence of intermittent nature of self-similar dynamical fluctuations. Short-range Correlation strength gradually decreases with the increase in collision energies from (sqrt{s}) = (2.76-13) TeV is observed. From the analysis of oscillatory multiplicity moments, the ratios (H_q) (cumulant over factorial moments (K_q/F_q)) have been derived for each MC generated Model with LHC energies. It is extremely interesting to observe that the oscillations from PYTHIA and UrQMD are quite different from the AMPT model at (sqrt{s}) = 13 TeV.