Physics Open最新文献

We consider dusty plasma in a cometary environment comprising of positively and negatively charged dust ions, kappa distributed - solar electrons, cometary electrons and hydrogen ions. The existence of non linear waves such as solitons in these systems were explored in detail by various researchers analytically. In this article we solve the system numerically by deriving KdV equation and solving it using Fourier transform. Hence we study the generation and existence of solitons. We also explore the characteristics of the solitons formed by simulation of the system for various initial conditions. The system is found to have single soliton wave as exact solution and set of soliton wave train solutions for varied initial conditions. The soliton wave trains can be compressive, rarefactive or mixed in nature according to the initial condition. The simulation is helpful in understanding and modelling various dusty plasma systems.

Dispersion associated with the complex band structure of a periodic potential can be used to explain single-electron wave packet tunneling through a finite-sized tunnel barrier. The imaginary $k$-space dispersion in a tunnel barrier may be viewed as a filter that controls the arrival time, shape, and group velocity of a transmitted wave packet. This $k$-space filter can be designed to increase or decrease the group velocity of the transmitted pulse and a transmitted peak-pulse probability arrival time can be engineered to occur before or after that of an electron wave packet propagating in the absence of the tunnel barrier.

The role of Sn doping on the structural, magnetic and power loss properties of Li_0.5+0.5xSn_xFe_2.5-1.5xO₄ ferrites (x = 0.0 to 0.20 in step of 0.05) + 0.5 wt % Bi₂O₃, prepared by solid state technique, has been investigated. X-ray diffraction reveals that Sn ions doped in lithium ferrite up to small concentration. Surface morphology recorded by SEM micrographs illustrates uniform, well connected grain growth in all samples. A small concentration of Sn doping in lithium ferrite improves the grain growth and densification. Magnetic parameters have been evaluated by M − H curves measured at room temperature by VSM. Saturation magnetization was found to be decreasing with Sn concentration in Li_0.5+0.5xSn_xFe_2.5-1.5xO₄ ferrites. In view of applicability of prepared samples for power devices, the magnetic permeability (μ* = μ′-jμ'′) has been recorded in the frequency range of 1 MHz–10³ MHz at room temperature. Further, Power loss response has also been recorded in presence of magnetic induction (B = 10 mT) in frequency range of 50 kHz to 3 MHz. It was depicted a significant reduction in power loss in Sn = 0.05 doped lithium ferrite sample. Reduction in power loss with Sn doping makes it suitable for power applications.

An analysis of the bioconvective slump point flow of nanofluid is addressed. The studied nanofluid, which contains gyrotactic microorganisms, was investigated in a porous medium on a nonlinear tensile plate in which it was placed. The scaling group transformation approach converted the analyzed PDEs to ODEs. ODEs obtained are solved using the numerical method (rkf-45) and AGM, and the results are compared with DTM and RKF methods. The accuracy of the obtained answers is remarkable compared to the mentioned methods. An increase in the density of motile microorganism distribution caused by the increment in values of bioconvection Peclet number is desired. In addition, a rapid increase in heat transfer rate and mass transfer rate happens when there is an increase in the thermophoresis parameter, heat source parameter, chemical reaction parameter, and Brownian motion parameter in a sequence. In this study, we investigated the SPF of bioconvective nanofluids containing GM. It is observed that the flow velocity increases as Da⁻¹ decreases. As Rb increases, bioconvection increases. These studies may be used for biotechnological applications, such as the design of bioconjugates or the increase of mass transfer in microfluidics.

This paper presents a detailed study on the performance of the new modified Morse potential in representing the vibrational motion of several diatomic molecules. The matrix Numerov method has been used to solve the time-independent Schrödinger equation for the new modified Morse potential, Morse potential, and Varshni potential. The vibrational energy eigenvalues of the 20 diatomic molecules in various electronic states were calculated. The vibrational energy eigenvalues and anharmonicity constants calculated using the new modified Morse potential were closer to the experimental values for all 20 molecules than the eigenvalues calculated from the Morse and Varshni potential functions.

Large scale calculations for the energy levels, transition rates, oscillator strengths, lifetimes, hyperfine interaction constants, Landé $g_J$ factors, and isotope shift factors have been performed for $1s^2$ and $1snl$ $(n=2-8\mathrm{and}l\le n-1)$ levels of He-like Sc XX ion. The general-purpose relativistic atomic structure package (GRASP2018) based on the fully relativistic multiconfiguration Dirac–Fock (MCDF) method is used to carry out the calculations. The leading quantum electrodynamic corrections, Breit interaction and nuclear recoil effects are also included in the succeeding relativistic configuration interaction (RCI) calculations. The relativistic isotope shift (RIS4) programme is used to determine the mass and field shifts factors. Furthermore, the percentage uncertainty in the transition parameters and lifetimes is estimated. A detailed comparison of the present results with the corresponding values from the NIST database and other theoretical and experimental works, wherever available, has been done, and an excellent agreement is achieved. A large section of the results is reported for the first time in the present work.

Quantum Key Distribution (QKD) offers unconditional security in principle. Many QKD protocols have been proposed and demonstrated to ensure secure communication between two authenticated users. Continuous variable (CV) QKD offers many advantages over discrete variable (DV) QKD since it is cost-effective, compatible with current classical communication technologies, efficient even in daylight, and gives a higher secure key rate. Keeping this in view, we demonstrate a discrete modulated CVQKD protocol in the free space which is robust against polarization drift. We also present the simulation results with a noise model to account for the channel noise and the effects of various parameter changes on the secure key rate. These simulation results help us to verify the experimental values obtained for the implemented CVQKD.

We have derived a novel equation to accurately predict the third harmonic generation (THG) conversion efficiency in hybrid periodically poled nonlinear medium. Our equation considers the general case that takes both depleted pump regime and phase mismatching cases, resulting in more precise predictions of efficiency. This level of accuracy is crucial for certain applications like high-power THG lasers. Moreover, accurate calculation of THG power density is essential to prevent exceeding the crystal damage threshold. We applied our equation on hybrid MgO:PPLN crystal to determine the optimal SHG region length corresponding to two different power densities, namely, $0.25$ and $0.5MW/c{m}^2$. The effect of crystal temperature on efficiency was also studies. Furthermore, a comparison between the derived equation and the commonly used nondepleted pump regime equation was performed. We found that the latter equation is significantly less accurate, particularly at high power densities, with the efficiency of the depleted pump regime being 50.6% less than nondepleted one. To demonstrate the effectiveness of the equation, our results were compared with experimental data, and we observed a good agreement between them.

The mass of an astrophysical object can be estimated by the amount of gravitational lensing of another object that it causes. To arrive at the estimation however, one assumes the validity of the inverse square law of gravity, or equivalently an attractive $1/r$ potential. We show that the above, augmented by a logarithmic potential at galactic length scales, proposed earlier to explain the flat galaxy rotation curves, predicts a larger deflection angle for a given mass. In other words, the true mass of the object is less than its estimated value. This may diminish the importance and role of dark matter in explaining various observations.