Brazilian Journal of Physics最新文献

Electron tunneling in ZnO/ZnCdO double-barrier trilayer semiconductor heterostructure is theoretically examined using the transfer matrix method. The effect of well width influences the energy of resonance transmission and the full width at half maximum of the resonance peak. The Dresselhaus spin–orbit interaction causes the separation between the spin components, and the increasing in-plane wave vector enhances the spin separation. The dwell time of electrons in the heterostructure is high at a high well width. The full width at half maximum of the barrier transparency peak is examined, and hence, the tunneling lifetime for various in-plane wave vectors is reported. The difference between the tunneling lifetime of spin-up and spin-down electrons is high at higher values of the in-plane wave vector.

Using a self-consistent theoretical method, the coherent dynamics of particles in a coupled liquid of sodium atoms at 423 K have been predicted. The modified microscopic theory for collective dynamics of simple liquids has been applied to compute various dynamical properties of liquid Na: detailed dynamical structure factors, current–current correlation functions, dispersion relation, velocity of sound, and the diffusion coefficient, at a temperature that is fairly above the melting point (323 K) and hence, comprises a classical system of interacting particles whose motions are strongly correlated. The detailed coherent dynamical structure factors, (S(k,omega )), and the current–current correlation functions have been evaluated for a huge wave vector, (kappa), range: 2.5 nm⁻¹ ≤ (kappa) ≤ 88.0 nm⁻¹ and have further been analysed to deduce the dispersion curve and the velocity of sound in the correlated fluid for the entire range of (kappa). The computed dynamical structure factors and the dispersion curve exhibit typical patterns of variation. The velocity of sound is found to align with the experimental result as (kappa) approaches zero. The modified microscopic theory, therefore, is an ample approach that makes use of inter-particle interactions to determine the dynamical behaviour of a given fluid. The computed dynamical structure factors are applied with quantum corrections due to the detailed balance condition, which are found to be perceptible for higher (omega) values.

This work presents a novel THz antenna for 6G wireless and sensing applications, featuring multi-port frequency tunability with MIMO and self-multiplexing capabilities. The antenna consists of four fractal-shaped graphene patches arranged orthogonally on the top layer of a SiO₂ substrate, coupled with a CPW feed. Electrostatic potential applied to the graphene-loaded radiators enables diverse functionalities. A metamaterial structure, functioning as a band-reject filter, is integrated into the lower layer of the SiO₂ substrate to inhibit surface wave propagation. The proposed metamaterial structure uses Hilbert-shaped curves separated by high-impedance open-circuited stubs to improve isolation within the desired frequency band. The compact antenna (140 μm × 135 μm) offers a combined impedance bandwidth of 115% (3.98 to 14.5 THz) while utilizing frequency tunability and achieving over 25 dB isolation between radiators, with a peak gain of 7.7 dBi. The design operates in tunable four-port MIMO, self-duplexing two-port MIMO, and self-quadruplexing modes. MIMO parameters such as Envelope Correlation Coefficient (ECC), Total Active Reflection Coefficient (TARC), Diversity Gain (DG), and Channel Capacity Loss (CCL) are evaluated to confirm the antenna’s diversity performance. An equivalent circuit model (ECM) is also analyzed to explain the working principle and validate the results.

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.