Brazilian Journal of Physics最新文献

Cardiovascular disorders, particularly stenotic arteries, require comprehensive investigation due to their potential to cause life-threatening complications such as stroke and heart attack. This study aims to investigate the significance of Casson nanofluid, which finds applications in targeted drug delivery. The primary objective is to mathematically predict and analyze the impacts of gold and iron oxide nanofluids on blood flow through an artery. The combination of gold and iron oxide nanoparticles in hybrid nanofluids can be utilized in various biological treatments. The study records changes in blood flow patterns to achieve desired temperature, velocity, and pressure changes. The artery is modeled as a cylindrical structure, and governing equations are derived using boundary layer flow fundamentals. These equations are solved using similarity variables and MATLAB software’s bvp4c solver. Artificial neural networks (ANNs) are employed to validate the results by training, testing, and evaluating data. The findings reveal that adjusting the concentration of nanoparticles enhances blood velocity, while reducing the Prandtl number results in subtle trends in temperature curves. Furthermore, increasing nanoparticle concentrations reduces the skin friction coefficient. This work highlights the novelty of integrating deep learning techniques to predict blood flow patterns, paving the way for advancements in the healthcare system.

Graphical Abstract

This study explores the complex behavior of ion-acoustic (IA) solitary waves (SWs) in unmagnetized collisionless plasmas composed of electrons, thermal positrons, and positive ions, with particular attention to the influence of electron drift velocity. By employing a fluid model and the reductive perturbation method (RPM), we retrieve the Korteweg-de Vries (KdV) equation, which describes the weakly nonlinear progression of such waves. The findings show the presence of two distinct IA modes, i.e., fast and slow. In the fast mode, KdV solitons occur within two different ranges of drift velocities ((0<{{v}_{e}^{prime}}le 172) and ({{v}_{e}^{prime}}ge 199)), whereas for the slow mode, solitons appear when ({{v}_{e}^{prime}}ge 223). Numerical simulations indicate that the fast mode supports both compressive and rarefactive solitons, while the slow mode only supports compressive solitons. The study underscores the importance of distinct factors such as positron density (left(mu right)), electron drift velocity (left({v}_{e}^{prime}right)), and temperature ratios of electron to positron (left(delta right)) in determining the properties of solitons. The results offer valuable insights into space plasmas where similar plasma compositions and drift velocities can affect the transmission of IA waves in planetary ionospheres and interstellar spaces.

We have studied the effect of nuclear dissipation on the fusion-fission dynamics by performing statistical model analysis of the available neutron multiplicity ((nu _{pre})) data of the even-even isotopes of Pb (Z= 82) in the mass range (192le A le 204), where strong shell effects are expected. Here, a comparative study with the neutron shell closure of neutron number N = 126 has been also carried out. Our statistical model calculation includes finer corrections such as shell effects, collective enhancement in the level density parameter (CELD), and modification in fission decay widths due to the orientation of the compound nuclear spin. The reduced dissipation strength (beta ) is used as a tunable parameter in order to reproduce the experimental data, viz-a-viz to understand the behavior of nuclear dissipation. Particularly, the influence of various properties of the target-projectile combination such as the fissility parameter and N/Z of the compound system are investigated to extract a systematic trend of the nuclear dissipation strength. The nuclear dissipation increases with the increasing value of the N/Z, and decreases with the increasing value of fissility for the nuclei of proton magic number Z= 82 and the neutron magic number N = 126. Nuclear dissipation also shows a strong dependence on the excitation energy. The higher values of (beta ) in the energy range 50–60 MeV indicate a strong dissipation effect due to the dominating nature of the shell effect and a clear systematics of the nuclear dissipation has not been observed in this energy range. Here, we have also studied the role of different forms of the level density parameter on the nuclear dissipation and a higher value of dissipation strength (beta ) is obtained when all the effects like CELD and shell correction in the level density are included.

Polarized far-infrared spectroscopy analysis is presented on highly [210] textured α-Fe₂O₃ microcrystals grown on pure Fe substrate, using a facile and one step process. Main objective is to understand relationship between intensity of A_2u and E_u modes with incident polarization. In literature, the shape of E_u band at 460 cm⁻¹ was shown to be sensitive on crystallinity, particle shape and size. In this report it is shown that shape of this E_u band also varies the most with polarization compared to the other bands. The observed variation is attributed to different response of LO and TO components of the E_u band to incident polarization. The intensity of A_2u modes remains almost unchanged whereas that of the E_u modes shows a systematic variation. The observed intensity variation has been elucidated on the basis of direction of the texture and experimental geometry of measurement. A simulation of intensity of the E_u modes is presented, which shows cos²θ variation with different phase shifts and matches well with the experimental data.

This study investigates the ground state phase diagrams of a borophene-like nanostructure containing atoms with spin values S-1 and σ-3/2. In addition, the magnetic features of the nanosystem, comprising bilayers separated by non-magnetic planes L = 1, 2, and 3, were examined under varying physical parameters employing the Blum-Capel model under the Metropolis algorithm with the RKKY interactions. The Monte Carlo analysis indicates that the rising number of non-magnetic layers impacts the magnetization M and magnetic susceptibility χ marking the system’s transition from the ferromagnetic to superparamagnetic state and also affects the blocking temperature t_B for L ≤ 3. Also, the hysteresis cycles exhibit magnetization plateaus as the parameter L rises, offering valuable insights in use of the borophene nanostructure for advancing spintronics and data storage nanotechnologies.

The channel coupling effects of internal degrees of freedom like deformations of the interacting nuclei and vibrations have been accounted very well in fusion reactions. The neutron transfer channels with positive Q-values have resulted in the enhancement in the sub-barrier fusion cross-sections in various systems. However, there are few cases in which such effects are not observed, thus, remaining an open question for discussion and further studies. In this respect, the fusion cross-sections of the various combination of projectile - targets have been calculated and compared with experimental data using the coupled channel approach by employing CCFULL and ECC codes. Fusion excitation functions were calculated for (^{varvec{30}})Si + (^{varvec{58,62,64}})Ni and (^{varvec{32,34,36}})S + (^{varvec{58,64}})Ni systems using two different approaches to unravel the effect of different collective excitations and neutron transfer channels on the sub-barrier fusion cross-sections. Inclusion of coupling to the inelastic excitations in the calculations for (^{varvec{30}})Si + (^{varvec{62,64}})Ni, (^{varvec{32}})S + (^{varvec{58}})Ni and (^{varvec{36}})S + (^{varvec{64}})Ni systems explained the experimental data. The coupling to the transfer channels with positive Q-values along with the inelastic channels was incorporated in calculations and showed a significant influence on fusion cross-sections in (^{varvec{32,34}})S + (^{varvec{64}})Ni and (^{varvec{34,36}})S + (^{varvec{58}})Ni systems. Upon investigating the role of the two-neutron transfer channels (pick-up and stripping), it was concluded that in the case of (^{varvec{30}})Si, (^{varvec{34}})S, (^{varvec{36}})S + (^{varvec{58}})Ni systems, the coupling to the two-neutron stripping channel with positive Q-value showed a weak channel coupling effect in the sub-barrier region. For (^{varvec{32,34}})S + (^{varvec{64}})Ni systems, a two-neutron pick-up channel with positive Q-value showed a strong influence on the fusion cross-sections.

The Rayleigh-Taylor instability is a fundamental fluid instability of significant importance in various fields of physics, such as supernova explosions and nuclear fusion. It has been shown recently that an interface in a dusty plasma can be realized experimentally under microgravity conditions. This indicates that the Rayleigh-Taylor instability may occur at the interface of a dusty plasma. This study employs fluid dynamics models to theoretically analyze the Rayleigh-Taylor instability in dusty plasmas. The results show that the Rayleigh-Taylor instability in dusty plasmas not only depends on the number density of dust particles but also on the mass of individual dust particles. This result is different from previous studies, which show that the Rayleigh-Taylor instability depends on the mass density difference of the two fluids at the interface. By adjusting either the mass or the number density of dust particles in a dusty plasma, we can control the Rayleigh-Taylor instability in a dusty plasma.

We consider the radiation reaction experienced by a charge undergoing harmonic oscillations, and from a canonical transformation for the canonical moments, we present a new diagonalized Hamiltonian structure in the commutative and noncommutative spacetime. By using the path integral formulation, we obtained the partition function, which leads to the quantization of the system.

The present paper studies the formation and characteristics of dust-ion-acoustic solitary waves of small amplitude in a multi-component warm magnetized plasma having inertial positive and negative ions together with negatively charged static dusts under the influences of inertial elections, considering a three-dimensional fluid dynamical model with the Poisson equation. We consider a uniform external magnetic field along the z-direction, and the wave propagation occurs obliquely to the direction of the magnetic field. Precisely, the reductive perturbation method is applied to derive the Korteweg-de Vries equations and obtained the solitary wave solution to investigate the variations in wave nature caused by different physical parameters. This theoretical study shows the coexistence of compressive and rarefactive dust-ion-acoustic solitons in the plasma. Depending on Q (=negative-to-positive ion mass ratio) and various ion temperatures, compressive solitons for (Q<1) and rarefactive solitons for (Q>1) are shown to exist. Additionally, the domination of different physical parameters of our plasma on the propagation of oblique dust-ion-acoustic solitary waves is numerically analyzed within the paper. The present study might be helpful for better understanding the propagation of nonlinear electrostatic waves in laboratory and space plasma environments.

This study aims to synthesize of new type of nanocomposites based on polyvinyl alcohol(PVA)-polyvinyl pyrrolidone(PVP) bend doped with cerium oxide(CeO₂) nanoparticles to apply in various photonics and energy storage fields. The structural, optical, and electrical features of PVA/PVP/CeO₂ nanocomposites were examined. The results indicated that the optical absorption of PVA/PVP blend enhanced of 94.9% when the CeO₂ NPs concentration reached of 3 wt.% at wavelength of 260 nm. The energy gap of PVA/PVP blend decreased of 54.2% with rising CeO₂ NPs concentration to 3 wt.%. The other factors of optical properties enhanced with increasing CeO₂ NPs concentration. The electrical properties were investigated in frequency ranging from100 Hz to 5 MHz. The results showed that the dielectric constant and electrical conductivity are improved of 12.3% and 66%, respectively, at frequency of 1 kHz with rising CeO₂ NPs concentration to 3 wt.%. The elaborated optical and electrical improvements of the PVA/PVP blend would definitely introduce the PVA/PVP/CeO₂ nanocomposites as precious UV-shielding materials for a wide set of optoelectronics industry. The PVA/PVP/CeO₂ nanocomposites included excellent UV-absorption, low energy gap, and good physical and chemical properties compared with other nanocomposites.