Pramana最新文献

In this study, the Hamiltonian formalism was extended to include continuous dynamical systems involving fractional derivatives, with application to a two-dimensional asymmetric oscillator system. The results were compared with those obtained using the Dirac method to validate the accuracy of the findings related to the behaviour of this class of oscillators. The Riemann–Liouville fractional derivative was employed alongside fractional variational principles to derive the fractional Euler–Lagrange equations and fractional Hamiltonian equations of motion. The results demonstrated consistency between the Hamiltonian equations of motion and the Euler–Lagrange equations. The scope of the research was further expanded to analyse the dynamics of the two-dimensional asymmetric oscillator within the framework of fractional calculus, focussing on the stability properties and distinctive behaviours of the system. This extension allowed for a deeper understanding of the complex interactions and nonlinear characteristics inherent to such systems. Subsequently, the Taylor series expansion was used to linearise the nonlinear equations, enabling their analytical solution through eigenvalue and eigenfunction techniques. This approach helped enhance the theoretical understanding of the system's dynamics and supported the validation of the results.

This work presents the development of a compact and efficient antenna designed for high-frequency applications, specifically targeting D-band (110–170 GHz) communication. A comprehensive link budget analysis was initially conducted for 100-m range and a target data rate of 25 Gbps at an operating frequency of 150 GHz. Key parameters, including transmission power, antenna gain, received power and signal-to-noise ratio, were evaluated. Based on these values, a novel rectangular microstrip patch antenna with dimensions of (1.48 times 1.48 times 0.3, text {mm}^{3}) was designed by incorporating a metamaterial-inspired complementary split ring resonator (CSRR) structure. The S-parameters of the unit cell were extracted using MATLAB, and the antenna performance was validated through simulations in the high-frequency structure simulator (HFSS). The proposed antenna achieves dual-band operation with enhanced bandwidths of 17 GHz and a peak gain of 17.49 dBi, making it highly suitable for D-band applications in terahertz (THz) communication systems.

This article focusses on the dynamics of the well-known pressureless Cargo–LeRoux model. The pressureless Cargo–LeRoux model provides a simplified framework for understanding fluid dynamics by focussing on the motion of fluid particles without considering pressure effects. It represents the one-dimensional hyperbolic flow of fluid particles and is significant in cases where pressure effects are negligible. An extensive study of the symmetries within the governing system is presented. It includes the computation of several types of symmetries, such as classical, non-classical and non-classical potential symmetries. The symmetries obtained using non-classical and non-classical potential approaches are more generalised, and the non-classical symmetries include the classical symmetries in particular. Symmetry reduction is performed corresponding to the obtained symmetries, and a few of the physically relevant reduced differential equations are shown here. Consequently, several novel analytic solutions to the considered model were found in terms of the Lambert, trigonometric, inverse trigonometric, exponential, hyperbolic, inverse hyperbolic and hypergeometric functions. Lastly, conservation laws are constructed through Ibragimov’s approach.

The dynamics of the Burridge–Knopoff (BK) model have been modified by taking into account simultaneously the fractional order and the long-range interactions (LRI) of each block. It is shown that the dynamics of the model becomes a nonlinear fractional Schrödinger equation, where the dispersion and non-linearity parameters depend strongly on the order of fractional derivative and long-range coefficients. We found that, for low values of the LRI parameter, the system exhibits an unusual behaviour, indicating a probable earthquake warning. A high value of LRI leads to crucial phenomena. An earthquake can occur at a high value of LRI. At a high value of LRI, the wave’s amplitude increases with time, showing that our system has high energy, which justifies the catastrophic processes observed in earthquakes. The results show that when the fractional order (gamma ) increases, the velocity and amplitude of the waves decrease, and when the exponent s increases, the velocity decreases and amplitude of the seismic waves increases. Consequently, for low values of s, the system exhibits highly localised waves with high amplitude and slow velocity. The numerical results are in perfect agreement with the theory and show that the nonlinear dynamics of seismic soliton wave can be well understood when we introduce LRI and fractional derivative order.

In this paper, the ontological aspects of the many-worlds interpretation (MWI) of quantum mechanics are studied by employing measure-theoretical methods of the ergodic theory. Before everything it is shown that the frequency interpretation of the Born rule is independent of the measurement postulate and hence, must be extended to the statistical ontology of the MWI. Then, based on the Birkhoff’s ergodic theorem we will prove that except for a Lebesgue null set of extremely rare parallel worlds, the Born rule will be refuted in all the parallel worlds created in a long-term process of consecutive experiments in the MWI of quantum mechanics. This reduces the unlimited ontology of the MWI to an extremely confined but still uncountable set of possible parallel worlds in long-term processes and allow us to acknowledge a pseudo-deterministic mechanism of quantum mechanics in the statistical picture of the theory. Hence, we conclude that the common understanding of the unconstrained MWI ontology, even if considered valid, cannot survive in long-term consecutive observations and must soon collapse into a more constrained interpretation of quantum mechanics.

Polyvinylidene fluoride (PVDF) is a flexible polymer that can be widely used in water treatment processes. However, its hydrophobic nature limits its potential applications in this field. This study aimed to enhance the durability and stability of an electrospun PVDF membrane by incorporating TiO₂ nanoparticles and polydopamine (PDA) to improve membrane performance. The self-polymerisation and strong adhesion properties of PDA enhance surface modification of the electrospun PVDF(/)TiO₂ nanocomposite membrane using a dip coating process. SEM and FTIR analyses confirmed that adding 0.5% nanocomposite and PDA did not alter the structure of the PVDF matrix, ensuring uniform distribution of TiO₂ nanoparticles on the surface of the fabricated membrane. TGA analysis showed that the PVDF(/)TiO₂(/)PDA membrane exhibited mass loss at 650 °C, indicating thermal stability, along with high tensile strength (2.7%) and porosity (86.3%), which promote surface modification and improve the membrane's strength and stability. This research successfully expanded the application of the fabricated PVDF(/)TiO₂(/)PDA membrane, making it suitable for various water purification and separation techniques.

This study examines the combined effects of heat transfer and entropy generation in non-Newtonian nanofluid flow subjected to mechanical vibration within a cylindrical pipe. Using the volume of fluid method, the impacts of vibrational parameters—amplitude, frequency and Reynolds number—are analysed under two thermal boundary conditions: constant heat flux (HF) and constant wall temperature (WT). While Vibration boosts convective heat transfer through increased radial mixing and flow instability, it also influences entropy Generation by changing the balance between thermal and viscous irreversibility. At a frequency of 20 Hz and an amplitude of 5 mm, the entropy generation rate decreased from 0.58 to 0.28 under WT conditions, indicating enhanced thermodynamic performance. A sensitivity analysis shows amplitude as the most influential parameter affecting both heat and entropy transport. The results demonstrate that selecting optimal vibrational parameters can simultaneously improve heat transfer and reduce irreversibility, providing a second-law-based approach for designing energy-efficient thermal systems with nanofluids.

The study of micropolar and hybrid nanofluids has garnered considerable interest due to their enhanced thermal and mass transfer capabilities, as well as their wide-ranging applications in industrial and engineering fields. This work considers hybrid micropolar nanofluids between rotating parallel plates, studies the influence of thermal radiation, which significantly enhances thermal efficiency and evaluates hybrid nanoparticles–copper (Cu) and aluminium oxide ((hbox {Al}_{2} hbox {O}_{3})). It also examines the influence of nanoparticle volume fraction, magnetic field intensity, and fuzzy-defined parameters on the hydromagnetic flow, emphasising the velocity, microrotation, thermal and concentration profiles. A novel double-parametric homotopy approach is introduced, combining fuzzy with the homotopy analysis method (HAM) to account for uncertainties and improve computational precision. The study emphasises the hybrid nanofluid’s improved heat and mass transfer capabilities over single-nanoparticle fluids and computes the skin friction, Nusselt and Sherwood numbers. Validation of the results against precise, crisp solutions demonstrates the reliability and accuracy of the proposed methodology, showcasing its potential application in complex engineering systems that involve porous media and advanced heat transfer techniques. The results show that hybrid nanofluids have much better thermal performance and concentration retention in the flow than nanofluids and also a reduction in micro-rotation is observed. By removing nanoparticles from heated areas, thermophoresis improves thermal diffusion and reduces local concentration. Additionally, it is found that increased particle collisions, caused by Brownian motion, improve heat transfer at the expense of concentration uniformity.

This study presents computational results for the proton radiative capture by triton ((^3mathrm H)) using the Argonne V18 (AV18) potential model enhanced with three-body forces. We develop a comprehensive computational framework combining the AV18 nucleon–nucleon potential with Urbana IX three-nucleon forces to calculate the astrophysical S-factor, scattering length and effective range for the (^3mathrm H(p, gamma )^4He) reaction. Our methodology involves solving the Schrödinger equation numerically using variational Monte Carlo (VMC) techniques with explicit treatment of three-body correlations. The results show improved agreement with the experimental data compared to the two-body potential models, particularly in the low-energy region relevant for astrophysical applications. We provide detailed comparisons with previous theoretical studies and experimental measurements, demonstrating the importance of three-body forces in accurately describing this radiative capture process.

We present a comprehensive spectral study of the supersoft X-ray source RX J0925.7-4758 using six observations from ASCA, Chandra, XMM-Newton and NICER, spanning 25 years. Our primary objective is to identify a robust non-local thermodynamic equilibrium (NLTE) spectral model that consistently fits the continuum emission across all data sets. A systematic fitting procedure revealed that only a pure-hydrogen NLTE model with effective gravity (log g = 7) could achieve acceptable fits for all observations. The composite model incorporates photoelectric absorption, interstellar medium (ISM) absorption with non-solar abundances and discrete absorption edges at known threshold energies. The effective temperatures are found to be of the order of (sim !!! 10^{5}) K and the luminosities are estimated to be (sim !! 10^{41} mathrm {erg, s}^{-1}), suggesting that the emission arises from a hot accretion disk around a white dwarf undergoing steady hydrogen burning. Additionally, we examine the relative strengths of the bound-free absorption edges in all six observations. While consistent trends are seen in earlier missions, the NICER data show variability in edge dominance, likely due to the instrumental or calibration differences. Although the continuum spectra can be modelled satisfactorily, high-resolution grating spectra from XMM-Newton reveal complex line features, including P Cygni profiles, which are not reproduced by static atmosphere models. This highlights the need for future NLTE+wind models to interpret these data more completely. Our study lays a foundation for such future analyses of high-resolution grating spectra of supersoft X-ray sources.