Chinese Journal of Physics最新文献

Based on a one-to-one mapping and Darboux method, 3D partially nonlocal dark-bright vector ring-like Peregrine structure solutions are derived. From these solutions, colorful excitations of dark-bright vector ring-like Peregrine structures in two kinds of diffraction control systems are studied. In the periodical system, periodically recurred fully excitations and inhibited excitations of ring-like dark-bright Peregrine structures are discussed. In the exponential system, inhibited excitations, peak-maintenance excitations and full excitations of ring-like dark-bright Peregrine structures are analyzed. The influence of diffraction parameter, radius parameter and thickness parameter of ring, and Hermite parameter on the formation of these excitations for dark-bright Peregrine structures are investigated. These results will deepen the comprehension of the partially nonlocal nonlinear wave in the fields of optical communication, cold atom and other domains.

The paper investigates the collapse of the generalized emergent Vaidya spacetime in the setting of $f(\bar{R},\bar{T})$ gravity, specifically in K-essence theory. In this study, the Dirac–Born–Infeld type non-standard Lagrangian is used to calculate the emergent metric ${\bar{G}}_{\mu \nu }$, which is not conformally equivalent to the conventional gravitational metric. We use the function $f(\bar{R},\bar{T})$ to reflect the additive nature of the emergent Ricci scalar ($\bar{R}$) and the trace of the emergent energy–momentum tensor ($\bar{T}$). Our study demonstrates that certain choices of $f(\bar{R},\bar{T})$ may result in the existence of a naked singularity caused by gravitational collapse. The alternative $f(\bar{R},\bar{T})$ values resulted in an accelerating universe dominated by dark energy. Moreover, the investigation showed the presence of both positive and negative masses, which might suggest the coexistence of dark matter and dark energy. In addition, when a certain amount of kinetic energy is present in the K-essence scalar field, mass is entirely converted into energy, indicating that spacetime is Minkowskian. The K-essence theory may also be employed as a dark energy framework and a basic gravitational theory, making it possible for researchers to investigate a wide ranges of cosmic phenomena.

The synchronization of neural networks is crucial for neural information processing and represents a key feature of various functional brain diseases. Memristors are ideal electronic components for mimicking biological synapses, among which discrete memristors have the advantage of fast computing speed and are often used in memristor-based neural networks. For these reasons, this paper proposes a novel discrete memristor-coupled Scale-Free neural network (DMSNN). Phase diagrams and time series of membrane potential are employed to analyze the firing pattern coexistence of individual neurons in the network. Furthermore, Spatiotemporal patterns, heat maps of the Spearman correlation coefficient matrix and the values of neuron membrane potential at a particular time point are adopted to declare the spatio-temporal dynamics of the complex neural network, encompassing asynchronization, chimeric state, synchronization and synchronization transition. The study also identifies the phenomenon of topology-induced coexistence and elucidates the underlying reasons for the emergence of chimeric states in the DMSNN as the coupling strength increases. Finally, a hardware implementation platform is constructed using a highly integrated SSD202 processor to validate the accuracy of the DMSNN. The results are consistent with the numerical simulations.

In this numerical study, we investigate the effect of aspect ratio (AR) on the natural convection (NC) flow and entropy generation (S_gen) in a stratified fluid confined inside a trapezoidal enclosure with thermally stratified side walls. The bottom of the enclosure is heated, and top of the enclosure is cooled. We use the Finite Volume Method (FVM) for simulating unsteady flows. We consider a Prandtl number (Pr = 0.71 for air) and explore AR of 0.2, 0.5, and 1.0, covering a wide range of Grashof numbers (Gr) from 10 to 10⁸. The outcomes are presented for Grashof numbers and the effect of the AR on fluid flow, rates of heat transfer (HT), and S_gen inside the enclosure. Critical Grashof numbers are identified, marking the shift in flow behavior from being influenced by baroclinic to Rayleigh–Bénard instability, and from a steady to an unsteady state for various AR. In the context of this transition to chaotic flow, several supercritical bifurcations are observed, including a Pitchfork bifurcation from symmetric to asymmetric states and a Hopf bifurcation from a steady state to an unsteady state. Additionally, we analyze the discrepancies in average entropy generation (S_avg) and average Bejan number (Be_avg) across the entire enclosure, considering various AR and Gr values. It is observed that for enclosures with Gr ≥ 10⁵, S_avg increases as AR decreases, indicating an enhancement in HT rate with decreasing AR. Furthermore, a quantitative relationship between S_avg, HT, AR, and Gr is presented. The study concludes that, as AR increases, the ecological coefficient of performance (ECOP) decreases, signifying a reduction in thermodynamics efficiency.

A hybrid differential evolution algorithm is used in this work to study the rotating transport of Falkner-Skan flow. The problem is modeled as an equivalent optimization problem by using Padé rational approximation functions. The primary model of the governing partial differential equations is imposed to subjugate the error between profiles. A hybrid evolutionary algorithm based on differential evolution and a convergent version of Nelder-Mead direct search algorithm is employed to perform global exploratory search along with an enhanced exploitation to improve the accuracy of the proposed solution scheme. The resulting scheme is named as evolutionary Padé approximation (EPA) scheme. The performance of the proposed EPA scheme on the Falkner-Skan boundary value problem is investigated by considering various values of the rotation parameters. The developed optimizer in EPA scheme was able to minimize the residuals up to${10}^{-10}$. Results are displayed graphically in order to study the effect of various types of parameters. EPA scheme determined that angular velocity increases or decreases accordingly as fluid parameter $\left(\beta \right)$ and the rotation parameter $\left(\lambda \right)$ but shows inverse behavior with respect to power law index$\left(n\right)$. Similarly, the response of velocity profile along $y-axis$ was decreasing function of $\beta$ as well as $n$ but increasing function of λ. The performance of the proposed EPA scheme has been demonstrated by comparing results with a hybrid neural network scheme and found in excellent agreement.

The study of bioconvection within porous medium saturated with a suspension of phototactic microorganisms is a research area of substantial importance, with wide-ranging implications in scientific and engineering disciplines. Understanding bioconvection in such systems is crucial for optimizing light distribution and reduces reliance on mechanical mixing. Hence, we examine the light-induced bioconvection in a suspension of phototactic microorganisms in an isotropic porous medium illuminated by collimated irradiation from above. The main objective of this study is to investigate the effects of key parameters such as the Darcy number, critical light intensity, and cell swimming speed on the initiation of bioconvection. The findings via linear stability analysis reveal that an increase in these parameters stimulates bioconvection, which leads to enhanced nutrient distribution within the medium. Additionally, the study reveals that the bioconvective solution transits from stationary and oscillatory types and vice-versa as the Darcy number increases. These results may help to optimize biofuel production and enhance industrial filtration processes.

We model the massive pulsar J0740+6620 and the light HESS J1731-347 compact object assuming (i) quark matter and (ii) dark energy stars. Within Einstein’s General Relativity, and assuming objects made of isotropic matter, we adopt analytic equations-of-state for both matter contents. Although the inner composition of the objects is very different in each case, both equations-of-state imply qualitatively very similar mass-to-radius relationships. We compute the spectra of radial equations for all four cases and the corresponding wave functions as well as the large frequency separations. A comparison between the different matter contents is made as well.

Perfect vortex beam (PVB) is a propagating light field with radial intensity distribution independent of topological charge and carrying orbital angular momentum (OAM). PVBs can be generated through the Fourier transformation of a Bessel-Gaussian (BG) beam, which traditionally requires a precisely aligned optical setup consisting of a spiral phase plate, a conical lens, and a Fourier lens. However, such traditional schemes are usually bulky and unstable. Here, we have utilized a method that differs from conventional approaches, employing metasurfaces designed as planar Pancharatnam-Berry (PB) phase elements to substitute for all the required components. Unlike traditional methods based on reflective or refractive elements, metasurface elements can significantly reduce the system's footprint. Because the use of metallic metasurfaces allows for a more flattened design plane, in this paper, we have demonstrated the generation of PVB within the 8 GHz microwave frequency band based on a single-layer metallic metasurface. The metasurface is composed of a square ring metal structure, which can serve as a half wave plate to provide the required geometric phase distribution for incident circularly polarized light to generate PVB. By rigorously optimizing the parameters of the square-ring structures, we have generated vortex beams carrying OAM with different topological charges. These vortex beams exhibit a constant radial intensity distribution, which validates their "perfect" characteristics. In addition, we also extracted the mode purity of different vortex beams, so that the mode states of different vortex beams can be distinguished. These results provide broader value for the application of perfect vortex beams in communication.

The present paper examines the effect of a uniform horizontal throughflow on the linear stability of buoyancy-driven convection in an infinite vertical fluid layer saturating a Brinkman porous medium. Two different constant temperature distributions are assigned on the rigid-permeable boundaries, so that there exists a horizontal temperature gradient. The resulting eigenvalue problem is solved numerically using the Chebyshev collocation method. The neutral stability curves are presented, and the critical values of the Rayleigh number are calculated for various prescribed values of the governing parameters. The onset of convection relies on several dimensionless parameter values of Darcy number Da, Péclet number Pe (it determines the strength of the horizontal throughflow), and Darcy-Prandtl number Pr_D. It is shown that there exists a critical value of the throughflow parameter Pe, which will increase with Da. Below the critical value of Pe, critical Rayleigh number Ra_c becomes smaller with the increase of Pe, which means the horizontal throughflow has a destabilizing effect. However, when Pe is larger than the critical value, an opposite conclusion can be drawn and the horizontal throughflow has a stabilizing effect. Moreover, the influence of the Pr_D on convection instability exhibits a dual behavior depending on Pe. The Pr_D stabilizes the system when Pe is small, and it destabilizes the system when Pe is large.