Brazilian Journal of Physics最新文献

Bubble nuclei are an exotic class of nuclear systems showing a central region of reduced nucleon density. The occurrence of such depletion (a bubble)is an interesting nuclear phenomenon, whose underlying microscopic origin provides a rapidly developing field of research in nuclear structure. In the present work, the properties of (medium) bubble nuclei are analyzed using shell model calculations. We addressed the question of deriving a criterion that allows identifying experimentally bubble nuclei using the form factor. As an extension of the seminal work of Wong in the 70 s, different mean fields have been proposed and their properties discussed. In addition, the effect of a bubble structure on the charge density distribution, the form factor and the single-particle levels, is discussed through their dependence on the inner-to-outer radius ratio p. In this way, level crossing and inversion have been obtained. Such results lead to the magic numbers 18 and 32, low angular momentum state occupancy reduction, and hence to candidates for bubble structure in exotic nuclei.

Perovskite based compounds have demonstrated unique performance in range of applications. Particularly, KMnF₃ has gained much importance in recent years. However, loading various contents of H ion to be situated at F site would improve the desired physical properties of the pristine KMnF₃. This account carries out density functional theory (DFT) calculations via using CASTEP code. GGA approximation and PW91 functional were adopted to investigate the structural, optoelectronic, and mechanical properties of KMnH_xF_3-x at (x = 0.25 and 0.50). The optimized lattice constants of the pure configuration were in good agreements with the published literature. Moreover, KMnF₃ exhibits a semiconducting nature with a direct electronic band gap of 2.177 eV. The modelled configurations demonstrate negative values of formation energies indicating the possibility of experimental synthesis. The analysed band structure reveals reducing tendency after H insertion. Furthermore, Optical results show an enhancement in the absorption spectra after the insertion of Hydrogen toward visible region of the electromagnetic radiation. Finally, elastic properties have been recorded and suggested that these compounds are mechanically stable. The current findings would significantly contribute in the field of solar cell applications and optoelectronic devices.

The effects of electron-acoustic (EA) waves’ head-on collisions and rogue wave (RW) production are studied in a collisionless, unmagnetized plasma composed of stationary ions, deformed Kaniadakis-distributed hot electrons, and cold fluid electrons. The nonlinear Schrödinger equation is generated using the standard reductive perturbation (SRP) approach, and the Korteweg-de Vries (KdV) equations (KdVEs) and modified KdVEs (mKdVEs) are determined via the general case using the extended Poincaré-Lighthill-Kuo (ePLK) perturbation method (ePLKM). In particular, the influence of the density ratio and the deformed Kaniadakis parameter on the RW structure, the creation of EA soliton structures, and phase shifts resulting from head-on collisions are examined. The construction of EA solitons, the generation of RW, and the variations of phase shifts are found to be significantly influenced by the parameters in question. In this work, the collisions of KdV solitons show positive and negative phase shifts. Though both the positive and negative phase shifts result from the interaction of mKdV solitons and the influence of the relevant parameters, only the positive phase shifts are studied here.

This study explores the origins of cosmic rays and their secondary messengers, focusing on the potential role of four BL Lacs—W Comae, 1ES 1959+650, PKS 2005-489, and PKS 2155-304—as potential sources of astrophysical neutrinos and gamma rays. We analyzed a single-zone model to understand the interactions between high-energy protons and ambient photons within blazar jets, leading to neutrino production observables and gamma-ray emission. This modeling contextualizes the emissions within multiwavelength observations and evaluates the capabilities of the next-generation Cherenkov Telescope Array Observatory (CTAO) in detecting these emissions. Our estimations suggest that these sources could be effective emitters of CRs, highlighting the need for future multimessenger observations to further investigate and constrain this class of sources.

An annealed version of the quenched mean-field model for epidemic spread is introduced and investigated analytically and assisted by numerical calculations. The interaction between individuals follows a prescription that is used to generate a scale-free network, and we have adjusted the number of connections to produce a sparse network. Specifically, the model’s behavior near the infection threshold is examined, as well as the behavior of the stationary prevalence and the probability that a connection between individuals encounters an infected one. We found that these functions display a monotonically increasing dependence on the infection rate. Subsequently, a modification that mimics the mitigation in the probability of encountering an infected individual is introduced, following an old idea rooted in the Malthus-Verhulst model. We found that this modification drastically changes the probability that a connection meets an infected individual. However, despite this change, it does not alter the monotonically increasing behavior of the stationary prevalence.

This research is aimed at investigating the potential of using fluorescent dyes, specifically fluorescein sodium salt dye (FSSD), embedded within epoxy resin (EP) as a material for luminescent solar concentrators (LSCs). LSCs are devices that capture and concentrate sunlight onto a smaller area, increasing the efficiency of solar cells. The study revealed a relationship between FSSD at different concentrations and EP molecules. The FSSD might be well-dispersed on a molecular level within the EP matrix. This homogeneous distribution is supported by the lack of distinct peaks in the XRD pattern, indicating the absence of any ordered crystal structure of FSSD within the composite. FSSD significantly influences the optical properties of the EP. It reduces light transmittance while increasing absorbance at specific wavelengths, which is crucial for efficient light capture in LSCs. The high polarizability of FSSD molecules and their random orientation can give rise to nonlinear optical phenomena. The enhanced light sensitivity of the FSSD@EP composite materials affects its nonlinear optical properties. These nonlinearities describe how the material’s response to light changes with increasing light intensity. The peak observed suggests a frequency range (10⁵–10⁷ rad/s) where this energy dissipation is most prominent. This points towards a relaxation process occurring within the material at those frequencies. As the frequency of the electric field increases, both the real part (M′) and the imaginary part (M″) of the complex modulus (M*) are expected to change in the FSSD@EP composite materials.

Cobalt-doped bismuth ferrite (Bi_1-xCo_xFeO₃) nanoparticles (NPs) at x = 0.00, 0.03, 0.07 were synthesized using the sol–gel auto-combustion method and studied the influence of cobalt (Co) on structural, surface, chemical, optical, magnetic, and photocatalytic properties on Bi_1-xCo_xFeO₃ nanoparticles. X-ray diffraction (XRD) studies revealed the rhombohedral structure of the synthesized nanoparticles with a mean crystallite size of 51 nm. Using Tauc’s relation, the optical band gap was calculated, and it decreased from 2.13 to 1.6 eV with increased Co concentration. The iron-oxygen (Fe–O) stretching vibrations were confirmed from Fourier transform infrared (FT-IR) spectra. Magnetic properties of the nanoparticles were studied using a vibrating sample magnetometer and found that Bi_1-xCo_xFeO₃ nanoparticles are ferromagnetic at room temperature. The strength of magnetization increased with an increase of Co doping concentration. Photocatalytic properties of the Bi_1-xCo_xFeO₃ nanoparticles were studied using a UV–Vis-NIR spectrophotometer, and it was found that Bi_1-xCo_xFeO₃ nanoparticles can be used as a photocatalyst in the visible region of the spectrum. Methyl blue (MB) dye was used to study the dye degradation property of pure and Co-doped BiFeO₃ nanoparticles, and the results were explained in detail. The Bi_1-xCo_xFeO₃ nanoparticles at x = 0.07 exhibited the highest photocatalytic activity (97.9%).

We present a numerical study of the erosion of channel walls applied to the PHALL Hall thruster being developed at the Plasma Physics Laboratory at the University of Brasilia. The simplified two-dimensional model retains the axial and radial directions to evaluate the erosion rate due to energetic ions. Plasma particles and fields are solved using the particle-in-cell and Monte Carlo collision techniques. The electrostatic potential and ion density profiles are obtained after the simulation reaches the steady state. We compute the channel wall erosion rate from the time series of the number of sputtered particles. We also perform and analyze a simulation of an SPT-100 Hall thruster. Our results show that the erosion acts mainly near the middle of the channel walls of the PHALL thruster, in agreement with patterns of wall material degradation observed in the laboratory device after experimental tests. The implications of the erosion pattern predicted for the PHALL thruster are discussed.

This study aimed to investigate the atherogenicity (quality) of LDL particles in patients with acute and recovered from COVID-19 infection. The participants were adults, aged 18 years or older of both sexes. Those with positive RT-PCR results at baseline were included in the Acute COVID-19 group (n = 33), and those with negative RT-PCR six months after acute infection, were included in the Recovered COVID-19 group (n = 30). The LDL quality was evaluated using three validated methods: Z-scan, UV–visible spectroscopy, and Lipoprint system. The Recovered COVID-19 group showed significantly higher numbers of large LDL particles (less atherogenic) than the Acute COVID-19 group (P < 0.05). We also found that COVID-19 infection was associated with the oxidative modification of LDL particles. D-dimer and CRP levels were correlated with Z-scan results and antioxidant-amount estimate. Moreover, we noticed that the infection left a sequel in LDL quality, even after six months of recovery. These findings highlight the importance of monitoring lipids during and after recovery from COVID-19 infection, and their potential deleterious effect on the LDL profile might correlate with the progression of atherosclerosis and poor clinical outcomes.