Brazilian Journal of Physics最新文献

The concepts and dynamic processes related to complex financial networks (CFNs) are explored in this review article. After providing a definition of CFNs, we discuss the most important dynamic process associated with them, i.e., contagion. We then examine the relationship between interconnectedness and systemic risk in CFNs. Next, we discuss approaches to the measurement of systemic risk and the challenges associated with this task. Finally, we highlight three research avenues that, in our opinion, are crucial for a better understanding of the dynamics of the contagion process in CFNs: loss distribution regime, endogenous complex networks, and multilayer complex networks.

In this work, we investigated the electrical and dielectric properties of a new biocomposite-based vinyl resin emulsion reinforced with microparticles of green microcrystalline cellulose. We measured the electrical response of each sample by assessing AC electrical conductivity in the temperature range of 260–340 K and in the frequency range of 100 Hz–1 MHz. The electrical conductivity dispersion is well described by Jonscher’s power law. Accordingly, the associated mechanism conductivity is due to the correlated barrier-hopping conduction mechanism. Dielectric properties were performed using the electric modulus formalism and analyzed according to the Havriliak-Negami model. For the neat vinyl resin emulsion, the observed relaxation process is attributed to the α-relaxation. When the fillers are added to the vinyl resin emulsion, a water dipolar polarization is identified for temperatures below the glass transition temperature and a superposition of α-relaxation and an interfacial polarization, known as Maxwell–Wagner-Sillars, for temperatures above the glass transition point. The activation energies of these are determined according to the Arrhenius law. Dielectric analysis allowed for probing the reinforcement/matrix adhesion, which can control the electrical conductivity performance of the composite materials.

Our research explored an environmentally friendly approach for the synthesis of bimetallic zinc oxide-cerium oxide nanoparticles (ZC NP) through the utilization of Salvadora persica extract. We characterized the physicochemical properties of the synthesized nanoparticles using PXRD, Raman spectroscopy, FESEM, and EDX analyses. As a result, both main peaks of zinc oxide and cerium oxide NP appeared in the PXRD graph, which indicated the formation of bimetallic NP. Spherical morphology showed in the FESEM image which particles have a size of about 30–40 nm. The analysis of hemocompatibility indicated that the NP does not appreciably affect the integrity of erythrocytes at concentrations nearing 2000 µg mL⁻¹. The toxicity function of synthesized sample on human colon cancer (HT-29) and fibroblast (NIH/3T3) cells was considered through the results of MTT trial. The outcomes of synthesized NP displayed significant cytotoxic effects against HT-29 cells at 20.73 μg mL⁻¹ concentration as its IC50, while it was non-toxic on NIH-3T3 cells. Therefore, we suggest the applicability of our product in therapeutic applications such as drug delivery as well as industrial implementations.

The characterization of covalent interactions between atoms is controlled and modified by the analysis of the dispersion relation of surface plasmon polariton (SPP) waves. The analysis was conducted at the interface of gold and dielectric cesium medium for the generation of SPPs and to extract information on covalent bonding among the atoms. Crucial information regarding atom localization and electron sharing among atoms is reported by damping and dispersion spectrums of SPPs. The real and imaginary components of the dispersion relation of SPP waves serve as indicators for the arrangement of atoms in elongated chains of covalent interactions. It is investigated that each atom contributes two electrons to the formation of double covalent bonds with neighboring atoms. The localization of atoms and the precise sharing of electrons is governed by the higher-order Kerr nonlinearity and the superposition of standing waves of control fields. Furthermore, the investigation extends to the identification of crystal defects within the optical lattice structure, which is achieved through an examination of the dispersion relation of surface SPP waves. Quantitatively eight atoms and twenty-four double covalent bonds are reported in the position ranges of (2lambda ) in xy-plane. Our results provide useful information about material structure and nanotechnology.

We investigate the properties of a double-path Josephson junction connected to Bose-Einstein condensate reservoirs. By comparing the current in the proposed setup with that in a similar system connected to superconductors, we elucidate the key differences between the two systems. The systems are influenced by the Aharonov-Bohm effect, Rashba spin-orbit interaction, and phase difference of order parameters between left and right leads. Utilizing the Keldysh formalism, it turns out that, in the system connected to Bose-Einstein condensate reservoirs, the Josephson current includes higher frequency components of the phase difference between left and right reservoirs. Additionally, the dependence of critical current on energy level does not show the complete symmetric resonance but the Fano-type resonance with single or double peaks. These differences result from the bosonic statistics of reservoirs.

A series of blue light-emitting Li₂SiO₃:xGd³⁺ phosphors were prepared via a solid-state reaction method at 950℃ for 3 h in an air atmosphere. According to the powder X-ray diffractometer (PXRD) and Rietveld refinment analysis, the crystalline structure of the Li₂SiO₃:xGd³⁺ phosphors matrix did not significantly change. The optical band gaps E_g of the sintered Li₂SiO₃:0.03Gd³⁺ material has been calculated by 5.62 eV by the Tauc plot. Photoluminescence (PL) investigation of Li₂SiO₃:xGd³⁺ phosphors displayed an intense blue emission peak of Gd³⁺ ions ⁸S_7/2 → ⁶I_7/2 transition, under near utra-violet (NUV) excitation of 276 nm. After the concentration of Gd³⁺ ions in the Li₂SiO₃ host reached 0.03 mol, the concentration quenching occurred, indicating that it had reached an optimal concentration. Under the UV excitation (276 nm); theLi₂SiO₃: 0.03Gd³⁺ materials exhibit good temperature stability. The emission intensity, Commission Internationale de lEclairage (CIE) chromaticity coordinates, correlated color temperature (CCT), color purity, and quantum efficiency of Li₂SiO₃:0.03Gd³⁺ phosphor were comprehensively enhanced by Gd³⁺ doping. The blue region's CIE coordinate value confirms that Li₂SiO₃:Gd³⁺ can be utilized as a component in solid-state display applications and artificial blue light-emitting diode (LED) generation.

This paper addresses the modulation instability of ion-acoustic waves in a rotating plasma subjected to a magnetic field, focusing on how inhomogeneities in equilibrium density, electron temperature, and magnetic field influence wave behavior. We employ a combined hydrodynamic approach and perturbation method to derive the nonlinear Schrödinger equation (NLSE), effectively balancing nonlinearity with dispersive effects. Our analysis reveals various localized ion-acoustic excitations, including bright and dark envelope solitons, which emerge from modulational instability. We also demonstrate that specific solutions of the NLSE, such as the Peregrine soliton, Akhmediev breather, and Kuznetsov-Ma breather, represent rogue wave phenomena within this context. Numerical simulations indicate that plasma structural parameters, including rotational frequency and scale lengths, significantly impact modulation instability conditions. Notably, while these parameters enhance instability, further increases can lead to a reduction in rogue wave amplitude. Our findings provide insights into the formation mechanisms of nonlinear electrostatic excitations in both ultra-dense astrophysical and experimental plasma environments.

In this paper, we report on synthesis and magnetic properties of dispersed Fe(_x)Ni(_{1-x}) (x = 10, 20, 30, 40, and 50) nanoalloys grown by thermal decomposition. X-ray diffraction patterns show that the majority crystalline phase is consistent with a fcc crystal structure (space group Fm3m) for all samples. Magnetization as a function of magnetic field and temperature shows that Fe(_x)Ni(_{1-x}) are superparamagnetic with blocking temperatures around 10 K. However, for all samples, it is possible to observe a second very broad maximum, which can be ascribed to a bimodal nanoparticle size distribution and/or Ni nanoparticles for the case of samples grown with x = 10, 20, and 30. Finally, we argue that the nanoalloy size distribution and/or interaction effects should play a crucial role in determining the magnetic behavior of samples once we are not able to fit our (H_C)(T) data using the Néel relaxation and the Bean-Livingston approaches in a wide temperature range.

An equation for estimating the effective diffusivity (chi _varphi ^textrm{eff}) based on the thermal and frictional forces arising from the interactions with neutral particles is provided. These interactions are primarily attributed to charge-exchange processes between ions and neutral particles. Our analysis indicates that the proposed forces are strong candidates to act as sources or sinks of momentum at the plasma edge. Furthermore, although we only have an estimated profile of neutral particles, the results demonstrate a strong dependence of the effective diffusivity on the ion-neutral collision frequency and a comparatively weaker dependence on ion temperature. We showed that the toroidal rotation profile in the TCABR tokamak is well described by the Helander model for toroidal rotation velocity in the Pfirsch-Schlüter regime, which depends on the ion temperature gradient in the presence of the neutral particles. The toroidal rotation profile has been reconstructed by a sum of Bessel functions, derived from the solution of a second-order differential equation for the toroidal velocity. In this initial study on momentum transport in TCABR, our findings indicate that (chi _varphi ^textrm{eff})—which accounts for both the diffusivity and pinch terms in the momentum equation—increases significantly in the outer plasma region. Additionally, it achieves a reasonable maximum value of approximately (chi _varphi ^textrm{eff} approx 20) m(^2/)s near the plasma edge at (r/a simeq 0.87), in the same radial position of the maximum ion-neutral collision frequency, demonstrating that the applied method successfully captures the general behaviour of this component as reported in other works, and guiding future experimental validation.

This study focuses on examining the molecular geometry, biological activities, as well as the electronic and vibrational properties of 2-(4-tert-butyl-2,6-dimethyl-3-hydroxybenzyl)-2-imidazoline (oxymetazoline). The investigation integrates quantum chemical calculations, molecular docking, and experimental methods. The ground state geometry and electronic structure of oxymetazoline are optimized using the DFT/B3LYP/6–311 + + G(d,p) basis set. To predict the chemical reactivity of the title molecule, MEPS, frontier orbital analysis, and electronic reactivity descriptors were used. Charge transfer within the molecule was presented using HOMO and LUMO energies. The energies of intra and intermolecular hydrogen bonds in molecules, as well as their electronic properties, were examined using natural bond orbitals (NBOs). To determine the efficiency of the title chemical, molecular docking tests were undertaken against α1A and α2A adrenergic receptors (α1A; PDB ID: 7YM8, 4MQT, and α2A; PDB ID: 3QAK, 7EJ8). According to the results, we found that the situation with the lowest binding score and therefore the best binding affinity is the OMZ-7YM8 interaction. The analysis of drug-likeness, physicochemical properties, and ADMET results indicates that the title molecule possesses a favorable pharmacokinetic profile and adheres to Lipinski’s Rule of Five, demonstrating efficient absorption and distribution. Consequently, the study supports the use of oxymetazoline as an inhibitor of α1A and α2A adrenergic receptors.