Indian Journal of Physics最新文献

Power-law distribution is one of the most important laws known in nature. Such a special universal behaviour is known to occur in very few physical systems. In this study, we analyse the mortality distribution of the Covid-19 pandemic tails for different countries and continents to discuss the possible universal behaviour of the pandemic. Surprisingly, we found that the mortality distribution of Covid-19 final, i.e., the latest tails in 2023 or 2024 follows inverse power-law decays. These universal behaviours for the pandemic are reported in the present work for the first time. Furthermore, we showed that these mortality tails also decay with time obeying the inverse power law.

In this paper, the combination of the conformal Killing vector and equations of state for double layered stars provides new solutions to the Einstein field equations in the core-envelope setting. The matter composition in the core layer obeys a linear equation of state, while in the envelope is described by a quadratic equation of state. The behavior of the matter variables in the stellar sphere is found to be well behaved, and the model satisfies stability conditions. The generated compact star model satisfies the energy and equilibrium conditions for the behavior of the natural forces. The mass, compactness, and surface redshift also fall within the required range for observed stars. Radii and masses of the stars PSRJ1903+0327, SAXJ1808.4-3658, VelaX-1, 4U1608-52, HerX-1, SMCX-1 and EXO1785-248 have been regained. This signifies the astrophysical importance of our generated class of exact solutions.

Recently, the LHCb collaboration has analyzed first observation of the (B_s^0rightarrow (chi _{c1}(3872)rightarrow J/psi pi ^+pi ^-)pi ^+pi ^-) decay. The ratio of branching fractions relative to the (B_s^0rightarrow (psi (2,S)rightarrow J/psi pi ^+pi ^-)pi ^+pi ^-) decay is measured to be (begin{aligned} mathcal {R}= & frac{mathcal {B}r(B_s^0rightarrow chi _{c1}(3872)pi ^+pi ^-)times mathcal {B}r(chi _{c1}(3872)rightarrow J/psi pi ^+pi ^-)}{ mathcal {B}r(B_s^0rightarrow psi (2S)pi ^+pi ^-)times mathcal {B}r(psi (2S)rightarrow J/psi pi ^+pi ^-)}= & (6.8pm 1.1pm 0.2)times 10^{-2}. end{aligned})They also measured the product of the branching fraction for the (B_s^0rightarrow (chi _{c1}(3872)rightarrow J/psi pi ^+pi ^-)pi ^+pi ^-) decay as(begin{aligned} mathcal {B_X}= & mathcal {B}r(B_s^0rightarrow chi _{c1}(3872)pi ^+pi ^-)times mathcal {B}r(chi _{c1}(3872)rightarrow J/psi pi ^+pi ^-)= & (1.6pm 0.3pm 0.1pm 0.3)times 10^{-6}. end{aligned}) For the first time, we have estimated the theoretical calculation of the ratio of branching fractions and products related to branching fractions using factorization with values of (mathcal {R}=(6.80pm 2.40)times 10^{-2}) and (mathcal {B_X}=(1.43pm 0.25)times 10^{-6}) at (mu =m_b). The results are consistent with the reported experiment.

Fission dynamics is a complex and intriguing field where factors such as mass distribution (MD), neutron multiplicity ((v_{M})), and multi-chance fission (MCF) play crucial roles. At low excitation energies (up to 40 MeV approx.), shell effects are prominent, but these effects diminish at higher energies. However, asymmetric mass distribution (AMD) may still occur, a phenomenon explained by the MCF concept. Recent studies have provided insights into MCF and its impact on fission dynamics. This study investigates the mass distribution of heavy ions such as ²²⁸U, ²³⁷U, and ²³⁸U, with particular emphasis on the first chance fission (FCF) of the daughter nuclei of ²³⁸U at (text {E}^*_{text {CN}} = 46) MeV. The role of FCF events in the daughter nuclei is highlighted, showing how neutron emissions reduce the effective excitation energy ((E^*_{text {eff}})). This study presents a two-dimensional spectrum of fission Mass-TKE, illustrating both projectile-like and target-like particles, along with fission events. For the first two isotopes, an asymmetric pattern is observed, reflecting distinct fission characteristics. However, for the CN ²²⁸U, no asymmetric pattern is seen, indicating a symmetric fission distribution at higher energies. We analyze the progression from symmetric to asymmetric first-chance fission fragment mass distributions (FFMD) and observe that asymmetry is driven by dominant FCF events in ²³⁵U and ²³⁴U at lower (E^*_{text {eff}}) for the system ²³⁸U. Additionally, multi-chance fission (MCF) for these systems is explored with a focus on pre-neutron multiplicity ((v_{text {pre}})) as a function of excitation energy and neutron mass across various energy levels. The results suggest that incorporating MCF provides a new perspective on fission dynamics, deepening our understanding of the intricate processes governing nuclear fission. Our findings show that asymmetric FFMD arises primarily from MCF, which is governed by the FCF of the daughter nuclei. However, for higher mass systems, even at lower (text {E}^*_{text {CN}}), both symmetric and asymmetric distributions are also observed. The dynamics of this, in our view, are closely linked to excitation energy and neutron emission, as the latter reduces the (E^*_{text {eff}}). This study builds on the understanding of nuclear fission by emphasizing the importance of MCF and (v_{M}), offering insights into the transition from symmetric to asymmetric fission dynamics in heavy ion systems. These systematics highlight the role of excitation energy and MCF in shaping the fission observables and advancing our comprehension of nuclear reaction dynamics.

The present study describes the formation of complex structures with the evolution of sheath-plasma instability in a novel glow discharge system regulated by specific combinations of plasma boundaries during different Negative Differential Resistance (NDR) regimes. The boundary conditions alter dramatically when biased grids are introduced in the presence of a low magnetic field, leading to both significant trapping of charged particles and constrained axial flow of charged particles inside the system. This results in the formation of intricate structures near the electrodes and the existence of sheath-plasma interactions within the system. The instability is thoroughly investigated using a variety of nonlinear techniques in order to comprehend the transition states and signal resilience in this discharge plasma throughout different NDR regimes. The non-stationarity in the time series domain is further enhanced by the transition energy modes identified using the empirical mode decomposition technique, which causes both low-frequency and high-frequency oscillations to interact with harmonic production during various discharge regimes. These low-frequency mode decomposition techniques suggest that sheath modulation resulting from insufficient electron supply across the biased grid is responsible for complex structure formation and associated sheath-plasma instability during the NDR regimes.

Holmium-doped calcium–strontium hexaferrite (Ca_0.5Sr_0.5Fe_12−xHo_xO₁₉) is synthesized via the sol–gel auto-combustion method with varying Ho concentrations (x = 0.00, 0.03, 0.06, and 0.09) to investigate its structural and magnetic properties. Comprehensive characterization are performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). XRD analysis confirms the formation of a single-phase hexagonal structure (P₆₃/mmc space group) with crystallite sizes ranging from 51 to 58 nm. SEM micrographs reveals that Ho incorporation promots grain growth, influencing the material’s microstructure. Magnetic studies demonstrate a progressive enhancement in both saturation magnetization (26.995–34.663 emu/g) and remanence magnetization (15.648–19.921 emu/g) with increasing Ho content, indicating an improvement in the material’s intrinsic magnetic performance. Furthermore, the synthesized nanoparticles exhibit excellent stability and reusability in recycling assessments. These findings underscore the potential of Ca–SrFO hexaferrite for advanced applications in data storage, magnetic filtration, and next-generation magnetic technologies.

In this work, we performed an energy-dependent study of low-frequency oscillations observed in GX 13+1 using AstroSat (Large Area X-ray Proportional Counter and Soft X-ray Telescope). The hardness-intensity diagram (HID) of the observation resembles a ‘(nu)’-shaped track, while the color-color diagram exhibits a ‘<’-shaped track, similar to the horizontal and normal branches of the Z source. We conducted flux-resolved temporal studies focusing on low-frequency variability and divided the HID into five regions: A, B, C, D, and E. Low-frequency quasi-periodic oscillations (QPOs) were detected in Regions A, B, and C. The QPO in Region A has a frequency of (5.06^{+0.54}_{-0.48}) Hz with a quality factor (Q-factor) of 2.80. In Region B, the QPO was detected at (4.52^{+0.14}_{-0.13}) Hz with a Q-factor of 5.79, while in Region C, it was observed at (4.70^{+0.62}_{-0.42}) Hz with a Q-factor of 4.35. The QPO frequencies, Q-factors, and low root-mean-square (rms) values (1.32%, 1.34%, and 0.7%) suggest that these oscillations are Normal Branch Oscillations, similar to those reported in GX 340+0. We modeled the rms and lag of the QPOs using a propagative model, considering variations in blackbody temperature, coronal heating rate, and optical depth. Our findings indicate that the observed QPOs are likely driven by interactions between the corona and variations in the blackbody temperature.

This work investigates the effect of applied voltage on the plasma characteristics of an Al–Ni alloy using optical emission spectroscopy (OES). The alloy, composed of 80% aluminum and 20% nickel by weight, was locally fabricated using a gas furnace to ensure compositional uniformity. Argon gas was used to sustain the plasma discharge, and a DC voltage ranging from 5 to 13 kV was applied. Emission spectra were recorded using an S3000-UV-NIR spectrometer. The results revealed a linear increase in both electron temperature and electron density with rising voltage, indicating that voltage plays a critical role in tuning plasma properties. Prominent spectral lines were observed at 811.53 nm (argon), 296.12 nm (aluminum), and 52.263 nm (nickel). The electron temperature increased from 0.108 eV to 0.662 eV, while electron density rose from 4.80 × 10¹⁷ cm⁻³ to 9.88 × 10¹⁷ cm⁻³. Additionally, the combined influence of gas flow rate and voltage on plasma flame length was examined, revealing a direct and interactive relationship that contributes to producing a more stable and homogeneous plasma. These findings emphasize the importance of optimizing operating conditions to generate controlled plasma suitable for industrial, technological, and medical applications.

In this article, we propose three gravastar models within the framework of f(T) gravity, inspired by the Mazur-Mottola conjecture as a viable alternative to black holes. Each gravastar consists of three distinct regions: (i) the interior core region, (ii) the intermediate thin shell, and (iii) the exterior spherical region. The exterior region can be characterized by the Schwarzschild-de Sitter solution and other novel solutions. With these specifications, we have derived a set of exact, singularity-free solutions for the gravastar, showcasing several physically interesting and valid features within the context of alternative gravity. The field equations for the shell case were solved using a novel technique based on Killing vectors, avoiding the approximations commonly employed in previous studies. Additionally, we analyzed several physical properties of the thin shell, including its proper length, entropy, energy content, and the relevant energy conditions.

The defect states of thin films of the GeS compound were investigated. Thin films with thicknesses of d = 250, 500, and 750 nm were obtained using the thermal evaporation method. The Doppler Broadening Spectroscopy (DBS) method was employed to study the defects. It was determined that the nature of the defects remains consistent regardless of the thickness of the thin films and that they are vacancy-type defects. Furthermore, it was identified that for thin films with a thickness of d = 500 nm, the S parameter reaches its maximum value, indicating the highest concentration of defects. This process corresponds to the completion of phase formation in GeS thin films with a thickness of d = 750 nm.