物理最新文献

By considering the possibility of higher dimensions for nonrelativistic quantum particles, we rederive the Schrödinger equation (SE) for such particles in a (d-1)-dimensional curved space embedded within a d-dimensional flat space. This approach generalizes de Costa’s formalism, which describes a nonrelativistic quantum particle confined to a two-dimensional curved surface embedded in three-dimensional Euclidean space. The original d-dimensional SE is separated into two parts: a one-dimensional global SE, which includes a confining potential to ensure the particle’s wavefunction does not propagate into the extra dimension, and a (d-1)-dimensional local SE. The local equation reveals an induced geometric potential, a distinctive feature arising from the presence of higher dimensions. This provides a hypothetical framework for probing the existence of higher-dimensional spaces. We apply this formalism to curved spaces generated by massive central objects, such as black holes or stars, and specifically revisit the behavior of a quantum particle near the Ellis wormhole.

The objective of this article is to study mathematically the magnetohydrodynamic (MHD) unsteady non-Newtonian oscillatory blood flow and heat transfer in microchannels containing a Darcy–Brinkman porous medium. The Casson fluid model is deployed. Additionally, the effects of heat source, nonlinear thermal radiation and Hall current are included. Convective heating and slip at the internal boundaries of the microchannel are also examined. Utilising a set of non-dimensional variables, the governing partial differential equations and associated boundary conditions are transformed into a non-dimensional form. By solving the transformed model, exact solutions are obtained. Graphical representations depict the influence of different physical characteristics on the velocity and temperature patterns. In addition, this study incorporated a parametric analysis to demonstrate the impacts of key parameters on Nusselt number and wall shear stress. Increased values of thermal radiation and Casson rheological parameters produce intensified velocity fields. Blood flow is also controlled by modulating the intensity of the external magnetic field and the regulation of the blood temperature is achieved by modifying its thermal conductivity. With an increment in thermal Biot number (Bh) (stronger convective heating at the microchannel walls) there is a uniform increase in temperatures. With the elevation in the Hall parameter, more complex streamline patterns are generated and there is an increase in the magnitude of trapped boluses. An increment in Grashof number (Gr), i.e. stronger thermal buoyancy force, accelerates the flow. Elevation in the Nusselt number is produced with a stronger heat source (S). With greater frequency (ω), the blood flow is more strongly modified by periodic fluctuations in the driving pressure and this produces an elevated amplitude of velocity oscillations, thereby increasing the average velocity of the blood. Increasing slip ((gamma )) generates significant flow deceleration in the microchannel. This work, which focusses on the thermal radiation in the blood flow, will significantly influence therapeutic strategies for hyperthermia. Specifically, the analysis provides a good foundation for more sophisticated computational fluid dynamics (CFD) studies and will enhance our understanding and management of blood flow and heat transfer in, for example, arterial hemodynamics.

An image encryption algorithm enhances the security of an image by transforming its content into a scrambled format. This process employs mathematical techniques, including chaos theory, permutation, and diffusion, to prevent unauthorized access or tampering. To improve the security of images during transmission, we introduce an efficient and innovative image encryption algorithm based on a time-delay predator–prey model, integrating principles from ecological dynamics into cryptography. By appropriately selecting parameters of the proposed predator–prey model, chaotic phenomena are generated. We use these chaotic sequences for image encryption and combine them with the Arnold scrambling algorithm to rearrange pixel positions within the image. Additionally, a diffusion algorithm is employed to alter pixel values, achieving the encryption effect. Various experimental analyses, such as initial value sensitivity, histogram analysis, adjacent pixel correlation, and overall robustness evaluations, are conducted. The computational experiments indicate that the chaotic sequence generated by the proposed predator–prey model can effectively implement image encryption with a favorable encryption effect. We present the results of the model on the best Number of Pixel Change Rate (NPCR) and Unified Average Change Intensity (UACI) scores for various selected test images. In the end, the average NPCR and average UACI are 99.6067% and 33.4687% respectively. We also calculated the value of the information entropy indicator, which reaches 7.9986. Through these empirical validations, the numerical results highlight the robustness and viability of using chaotic sequences in the context of image encryption, offering promising prospects for enhancing data security in digital transmission systems.

The temperature dependence of the laser output properties of the Fe:ZnSe single crystal was compared under its excitation by 2.94 ({upmu })m Q-switched Er:YAG laser radiation and by (sim)4.04 ({upmu })m gain-switched second Fe:ZnSe laser radiation within the same semi-longitudinal configuration. A non-selective laser cavity consisted of a flat highly reflective mirror at (sim)4–5 ({upmu })m and a concave (r = 200 mm) output coupler with a reflectivity of 88% at (sim)3.9(-)5.3 ({upmu })m. To keep the energy at both excitation wavelengths the same of (sim)9.4 mJ, a special filters were used for attenuation of 2.94 ({upmu })m radiation. The output energy almost doubled since the angle between pumping and generated laser radiation was reduced from (sim)20(^{circ }) to (sim)12(^{circ }). The generated laser oscillation wavelength was shifted by (sim)100 nm in the case of (sim)4.04 ({upmu })m compared to excitation by 2.94 ({upmu })m radiation. The maximum laser output energy of (sim)1.7 mJ under 2.94 ({upmu })m excitation was obtained at 78 K. However, at (sim)4.04 ({upmu })m pumping, the maximum of (sim)0.5 mJ was obtained at 260 K. The efficiency at 2.94 ({upmu })m excitation decreased from (sim)33% at 78 K to (sim)12% at 340 K. At (sim)4.04 ({upmu })m radiation excitation, the efficiency increased from the laser threshold at 120 K to its maximum of (sim)9% at 260 K.

In this work, the morphology and fractal properties of Zn–Mg and Zn–Mg–Cu nanocomposites were investigated. Zn–Mg–Cu nanocomposites with 2, 3 and 4% by weight of Cu were prepared by electrochemical method on FTO glass substrate and compared with Zn–Mg nanocomposite. The surface properties of the nanocomposites were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM images confirm that the morphology and grain size depend on the amount of Cu doping. The grain size decreases with increasing Cu concentration. Statistical analysis based on 3D AFM images showed that surface roughness (S_q) and fractal dimension (D_f) decreased with increasing Cu concentration. D_f obtained using the log(count) vs. log(box size) curve showed that D_f is independent of scan size and pixel resolution. The D_f values of ZM3, ZM3C2, ZM3C3 and ZM3C4 were calculated to be 2.48, 2.44, 2.36 and 2.30, respectively. It can be concluded that the lacunarity coefficient β of all the nanocomposites has a high degree of surface microstructure homogeneity with β < 0.07. Multifractal behaviour was observed for all nanocomposites, with the multifractal degree of Zn–Mg–Cu nanocomposites being reduced compared to that of Zn–Mg nanocomposites.

We present the scattering properties of parity–time (PT)-symmetric and anti-parity–time (APT)-symmetric systems embedded in a new electronic waveguide. The set-up is built around imaginary resistors and positive or negative other components. These combinations give rise to a real spectrum in breakable and unbreakable PT symmetries. When it exists, the transition marks the passage from real to complex eigenvalues whereas in the APT symmetry, the eigenvalues pass from pure imaginary to complex eigenvalues. The frequencies of cells in PT-symmetric configurations must have the same sign whereas in APT-symmetric configurations, the frequencies must have opposite signs. The electrical line presented can drive negative frequencies and gives the possibility to demonstrate the existence of a mirror behaviour in scattering properties of the PT symmetry. We derive the condition of appearance of the coherent perfect absorber and laser, unidirectional invisibility from one or both sides of the system. In APT symmetry, only the coherent perfect absorber exists in the two configurations of waveguides used. The respect of the law of conservation depends on the nature of the eigenspectrum peculiar to each type of the dimer.

This work is focused on the identification of cracking points in charged spherically symmetric stellar configurations in the vicinity of f(R) gravitational theory. To identify cracking points, the hydrostatic equilibrium equation is for the application of local density perturbation scheme. We apply local density perturbation technique to test the viability of 4U 1820-30, Vela X-1, and SAX J1808.4-3658 according to different physical parameters involved in model presented by Nazar and Abbas (Adv Astron 2021:6698208, 2021). It is concluded through graphical illustrations that cracking points help in the refinement of the stability regions by exhibiting cracking in different interior regions.

Primordial black holes (PBHs) are a promising candidate for dark matter, as they can form in the very early universe without invoking new particle physics. This work explores PBH formation within a curvaton scenario featuring an ultraslow-roll (USR) phase. An inflaton–curvaton mixed field model is presented, where the inflaton drives early inflation and then transits into the USR phase, amplifying the small-scale curvature perturbation. During inflation, the curvaton generates entropy perturbation, which later converts into curvature perturbation after the curvaton decays in the radiation-dominated era. Using the (delta N) formalism, we compute the power spectrum of the total primordial curvature perturbation and analyze the relevant non-Gaussianity. Our results show that adding a curvaton field not only has a significant impact on primordial non-Gaussianity, but also introduces more complex inflationary dynamics, even saving the inflaton potentials that generate too low scalar spectral indices. Our model can produce PBHs with mass around (10^{-14},M_odot ) that account for all dark matter, while remaining consistent with current observational constraints.

This work intents to obtain symmetry reductions and exact solutions of Kadomtsev–Petviashvili (KP) equation, which describes propagation of long waves on the surface of shallow water. The Lie symmetry method under one-parameter transformation is used to ensure invariance and derive infinitesimal generators. These generators provide similarity variables, which is directed to symmetry reductions of the test equation. This process of reductions recasts test equation into ordinary differential equations (ODEs). These ODEs have finally been solved under various constraints and as a result, exact solutions consisting of arbitrary functions and several arbitrary constants are produced. The solutions are novel and have not yet been published. Due to the existence of arbitrary functions (f_1(t)), (f_2(t)), (f_3(t)) and constants, these solutions present a more generalised form than the existing results and give a wide range of possibilities for the interpretation of various physical phenomena. The physical importance of these solutions is demonstrated by numerical simulation revealing a rich variety of soliton structures including line soliton, doubly soliton, multisoliton, solitons on parabolic surface, soliton fission and annihilation behaviour.