Journal of the Korean Physical Society最新文献

The discovery of the universe’s accelerated expansion has posed significant challenges to the standard cosmological model based solely on General Relativity and a cosmological constant. Modified gravity theories offer an intriguing geometric alternative to dark energy models, in which the acceleration arises from modifications to gravity itself. Among these, the class of teleparallel gravity theories—in which gravity is described by torsion instead of curvature—has emerged as a theoretical framework. In particular, (fleft(Tright)) gravity generalizes the Teleparallel Equivalent of General Relativity by promoting the torsion scalar (T) to an arbitrary function (fleft(Tright)), formulated on the Weitzenböck spacetime. In this work, a novel and viable (fleft(Tright)) gravity model of the form: (fleft(Tright)=T+frac{alpha {(-T)}^frac{1}{n}}{1+beta {(-T)}^frac{1}{n}}) is proposed, where α, β are model parameters and (n) governs the onset and scaling behavior of the torsion-induced corrections. This construction ensures a smooth interpolation between early time General Relativity and late-time accelerated expansion sourced by an effective torsional dark energy density ({rho }_{DE}sim {a}^{-frac{2}{n}}), where (a(t)) is the scale factor. The novelty of the formulation lies in its sigmoid-type rational structure that smoothly activates the torsional dark energy sector, preserves early time consistency with standard cosmology, and predicts a late-time accelerating universe driven by a dynamically induced energy density. We have also proposed a novel extension involving the inclusion of parity-violating Chern–Simons-like terms and the Nieh–Yan topological invariant.

This study develops exact soliton solutions for the (2+1)-dimensional Kundu–Mukherjee– Naskar equation, a versatile model describing signal transmission in telecommunications and long-distance optical fiber pulse propagation. The equation is reduced to a nonlinear ordinary differential form using a traveling wave transformation derived from Lie symmetry infinitesimals. Two analytical approaches, the modified Sardar sub-equation method and the modified auxiliary equation method, are applied to obtain diverse classes of solutions, including hyperbolic, Jacobi, trigonometric, and rational forms. Numerical simulations, performed in MATLAB, visualize bright, dark, singular, kink, periodic, and anti-kink soliton structures through 3D, 2D, and density plots. The sensitivity of the dynamical system to changes in initial conditions is analyzed, with Lyapunov exponents computed to quantify its stability and dynamic complexity. Both qualitative and quantitative perspectives are considered. The results are significant for optical fiber communications, where such stable soliton solutions can minimize signal distortion, enhance transmission quality, and support high-capacity, long-distance data transfer.

Owing to the continuous temperature variations in nuclear reactor operations, on-the-fly Doppler broadening methods are widely adopted in neutron transport simulations to generate nuclear cross-sections for various temperatures. In current approaches, the widely used SIGMA1 method is inefficient because it involves complementary error and Taylor series expansions. In this paper, we present a new on-the-fly Doppler broadening method based on non-zero-temperature cross-sections. In this method, the improved Gauss–Hermite quadrature and free gas model are adopted to broaden the cross-sections at low-energy range. Meanwhile, the Gauss–Hermite quadrature of different orders is adopted to broaden the cross-sections at the resolved resonance energy range. The paper presents a detailed introduction to the typical nuclide cross-sections and designed tests with the NPTS program. Results demonstrate that this method efficiently generates temperature-dependent neutron cross-sections while maintaining target accuracy.

This paper presents a novel method for achieving parametric excitation in an optical polarization-modulated magneto-optical trap for a two-level atom. The proposed method has a unique mechanism that is different from that of the existing methods, which modulate the laser intensity, magnetic field gradient, or laser detuning, because the excitation realized through the polarization modulation originates from the competition between the repulsive and attractive forces on a two-level atom. The theoretical calculation is based on the simple Doppler cooling theory, and we derive atomic motion in a rotating frame and coupled equation for motional amplitude and phase, in detail.

Organometal trihalide perovskites have gained interest in recent years as a potential component in low-cost, bendable, and highly efficient solar cells. Despite their potential utility in processing, organic–inorganic hybrid perovskite materials are unstable when subjected to the elements. Removing the A-cation and X-anion from perovskite materials has dramatically improved their chemical stability. This review will discuss the current state of the art and recent advances. To use this to rationally design perovskite materials, which will ultimately lead to perovskite solar cells with unprecedented stability. Perovskite solar cells (PSCs) have recently attracted the attention of scientists in both the academic and commercial sectors due to their meteoric rise in efficiency from 3.8% to 22.1%. Although there has been progress toward PSC, many obstacles still exist. Although there are still many unanswered questions in the PSC study, it is essential to work toward creating stable, high-efficiency devices and environmentally friendly perovskites. Recent developments in related fields were the primary focus of this review article. High-efficiency PSC fabrication methods were presented, and subsequent discussions addressed instability and lead-free perovskite concerns. The result has been shown, along with some quick suggestions for improving PSCs for future use in reliable and efficient solar-to-electricity technologies. Perovskite solar cells have made solar panels using aqueous solutions possible. Since these devices use lead, they are less appealing than others, but research is being done on using perovskites as a substitute for metals. Since chemical decomposition in humid environments is the main pathway for the degradation of perovskite materials, PSCs are still unsuitable for use in industrial settings. Although encapsulation techniques are commonly used in organic photovoltaics to slow the degradation of organic materials, it is crucial to find stable perovskite materials or device architectures capable of achieving long-term stability to resolve the degradation issues related to PSCs. Most current efforts to enhance PSC stability focus on adjusting the charge transport layers or perovskite material, which this overview discusses. PSCs can be improved through compositional engineering by adding halides and cations, respectively.

Our findings examine how the instability parameter ((Delta ')) impacts the evolution of tearing instability in various viscous settings through two-dimensional MHD (magnetohydrodynamics) simulations. Increasing (Delta ') triggers distinct stages of instability dynamics, influencing critical island width, current sheet aspect ratio, and plasmoid characteristics. Conversely, reducing (Delta ') suppresses plasmoid instability beyond a critical Lundquist number, suggesting retardation in plasmoid formation in thin current sheets. Critical island width experiences rapid initial growth with (Delta '), stabilizing after (Delta ' = 24). Viscosity ((P_r), Prandtl number) affects critical island width differently in the (P_r < 1) and (P_r > 1) regimes, with a transitional shift observed at (P_r = 1). Aspect ratios demonstrate transitional behaviors at (P_r = 1), increasing exponentially with viscosity in (P_r < 1) and decreasing in (P_r > 1). Saturated island width declines with (Delta '), while smaller (Delta ') values maintain lower saturated plasmoid widths. The dependence of island width on (Delta ') diminishes at higher (Delta ') values, contrasting with trends in saturated plasmoid width. These results highlight the intricate interplay of (Delta '), viscosity, and equilibrium conditions in the dynamics of magnetic reconnection.

This study presents a comprehensive analysis of the structural, electronic, mechanical, and thermal properties of wurtzite-phase cadmium sulfide (CdS) colloidal nanocrystals (NCs), combining experimental data with theoretical modeling. X-ray diffraction confirmed the wurtzite crystal structure, while UV–Vis absorption and Tauc plot analysis determined the optical bandgap. First-principles density functional theory (DFT) calculations were employed to investigate the electronic and mechanical properties, revealing a direct bandgap of 1.59 eV and lattice parameters that closely match experimental measurements. The calculated elastic constants (C₁₁, C₁₂, and C₄₄) confirmed the mechanical stability of CdS NCs, while thermodynamic analysis provided crucial insights into their thermal behavior. These findings demonstrate strong agreement with experimental data and offer a deeper understanding of CdS NCs’ stability and performance. This work bridges gaps in the mechanical property analysis of CdS NCs and contributes to optimizing CdS-based optoelectronic devices.

We consider the possibility that the weak cosmic censorship conjecture can be violated using the Oppenheimer–Snyder collapse model with a perfect fluid star interior. In the first strategy, we assumed a metric model with a naked singularity; in this case, the Oppenheimer–Snyder collapse was possible, and the null energy condition is also satisfied. However, this is just a toy model because there is no known solution to the Einstein equation. To avoid this problem, in the second strategy, we can consider a naked singularity solution as a proper solution of the Einstein equations; however, in this case, we need to introduce a thin shell on top of the perfect fluid star. In this case, gravitational collapse is allowed, but the null energy condition should be violated at the thin shell. In conclusion, we could not find a physically viable model that violates weak cosmic censorship; however, it opens a window for studying the properties of cosmic censorship constructively. The violation of weak cosmic censorship may be possible if a modified gravity model provides a solution that allows the Oppenheimer–Snyder collapse to occur without a shell. Additionally, regarding the thin-shell case, the shell approaches the naked singularity closely without violating the null energy condition, although it must eventually violate the null energy condition at the singularity; this might be regarded as an effective violation of cosmic censorship.

The low-temperature states of Sr(_{1-x})Ca(_{x})TiO(_3) exhibit intriguing dielectric properties with increasing Ca substitution. Pure SrTiO(_3) is a quantum paraelectric. However, a slight Ca doping induces a quantum ferroelectric state. Additionally, a relaxor-like state emerges when the Ca concentration exceeds (x = 0.016), characterized by rounded and diffused peaks in the dielectric constant. This phenomenon is attributed to local polarizations resulting from structural disorder. We performed neutron total scattering measurements on Sr(_{1-x})Ca(_{x})TiO(_3) ((x=0, 0.06, 0.1)) at 15 K to investigate the structural origin of these relaxor-like behaviors. Using Rietveld refinements, we discussed that Ca substitution intensifies the antiferrodistortive octahedral rotations. Local structural distortions were further studied through reverse Monte Carlo modeling, revealing that Sr/Ca-O bond length distributions become broader and more asymmetric with increasing Ca concentration. We propose that octahedral rotational disorders, dependent on local Sr/Ca configurations, are responsible for the asymmetry in Sr/Ca-O bond length distributions and the induction of local polarizations.

This study presents a systematic investigation into the effects of gamma (γ) irradiation (1–4 kGy) on the structural, optical, and electrical properties of aluminum-doped zinc oxide (AZO) thin films deposited by radio frequency (RF) magnetron sputtering. The films were analyzed using fiber-coupled optical spectroscopy, spectroscopic ellipsometry (SE), X-ray diffraction (XRD), and current–voltage (I-V) measurements to assess irradiation-induced alterations. Optical transmittance exhibited a dose-dependent reduction. The optical bandgap decreased from 3.43 eV to 3.25 eV, which we attribute to defect-induced tail states in the band structure. SE results indicated a gradual decrease in the refractive index and extinction coefficient with increasing radiation dose, reflecting changes in the material’s dielectric response. XRD analysis revealed significant structural degradation, as evidenced by reduced peak intensities and increased full width at half maximum (FWHM), particularly for the (100) crystallographic orientation, suggesting decreased crystallinity and enhanced lattice disorder. Electrical characterization showed an increase in sheet resistance from 146 Ω/□ to 298 Ω/□ and a corresponding decrease in electrical conductivity, attributed to carrier trapping at radiation-induced defect sites and reduced mobility. The combined structural, optical, and electrical findings clearly understand the mechanisms underlying radiation-induced degradation in AZO thin films, which is crucial for evaluating its reliability in radiation-prone environments.