Brazilian Journal of Physics最新文献

{"title":"Double Split Ring Resonator-Based Four and Six Port Multiple Input Multiple Output Antenna Structure for Terahertz Application","authors":"Sunil Lavadiya,&nbsp;Vipul M. Dabhi,&nbsp;Raj Tala,&nbsp;Vishal Sorathiya,&nbsp;Fahd M. Aldosari,&nbsp;Abdullah Alwabli,&nbsp;Amar Jaffar","doi":"10.1007/s13538-025-01871-1","DOIUrl":"10.1007/s13538-025-01871-1","url":null,"abstract":"<div><p>The multiple input multiple output (MIMO) technology is gaining greater attention as the demand for elevated data transmission rates escalates. MIMO enhances capacity and throughput, which are needed in high-capacity communication systems. MIMO improves the speed and signal reliability, and addresses fast and robust communication. For the applications of 5G, high-speed wireless broadband and terahertz communication, MIMO has become the foundation technology in the present era. This paper presents an eight-port MIMO antenna for terahertz (THz) applications to fulfil the requirement of high-capacity communication. The proposed antenna is designed on the polyamide substrate with a loss tangent of 0.02 and a relative permittivity of 4.0. At resonant, the eight-port MIMO antenna achieves a gain of 22.17 dB for 17 THz; the value of the envelope correlation coefficient (ECC) remains 0.01, directive gain (DG) of around 10 dB, and total active reflection coefficient (TARC) below − 5 dB. Diversity gain and envelope correlation coefficient show the effective reduction in the signal fading and improved link quality for the proposed MIMO antenna.\u0000</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"55 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2025-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144869084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Role of Ion Temperature Gradient, Shear Flow, and Nonthermal Electron Population in the Formation of Global Vortices in Magnetoplasma","authors":"Javaria Razzaq,&nbsp;Arshad M. Mirza,&nbsp;Nazia Batool,&nbsp;Adnan Mehmood Bhatti","doi":"10.1007/s13538-025-01883-x","DOIUrl":"10.1007/s13538-025-01883-x","url":null,"abstract":"<div><p>In this study, we investigate the formation of global vortices in magnetized non-Maxwellian plasma subjected to density and temperature gradients, in the presence of ion-temperature-gradient (ITG) instability and shear flow. Utilizing the Braginskii model of transport equations, we analytically and numerically derive solutions for global vortices, highlighting their distinct characteristics compared to conventional dipolar vortices. We derive a modified linear dispersion relation and explore its various limiting cases, revealing that the growth rate of low-frequency ITG instability is influenced by the kappa factor and Cairn’s non-Maxwellian parameter. Numerical illustrations are provided using laboratory plasma parameters. Our findings are pertinent to understanding space plasmas and tokamak plasma environments, particularly in contexts involving resonant frequency heating and electron cyclotron heating experiments.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"55 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2025-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144858570","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Analysis of Leptospirosis Disease with Contaminated Environment in Human and Animal Population via Stochastic Mathematical Model","authors":"Gul Khan,&nbsp;Abdelaziz Hendy,&nbsp;Rasha Kadri Ibrahim,&nbsp;Sally Mohammed Farghaly Abdelaliem,&nbsp;Ahmed Hendy","doi":"10.1007/s13538-025-01851-5","DOIUrl":"10.1007/s13538-025-01851-5","url":null,"abstract":"<div><p>This study investigates the impact of contaminated environment on leptospirosis disease using stochastic mathematical models through neural networks. Initially, we demonstrate that the solution exists globally and remains positive. Secondly, we determine the key stochastic reproduction number that will determine whether the disease persists or extinct from the population. If <span>({R}_{0}^{s}&lt;1)</span>, then the disease will die out from the population. And if <span>({R}_{0}^{s}&gt;1)</span>, the disease continues to persist in the population. Using numerical simulations, the dynamics of leptospirosis within both human populations and animals was examined. Simulations showed that a contaminated environment plays a critical role in the spread of leptospirosis, thereby increases the disease’s transmission. Meanwhile, treating the disease plays a critical role in controlling it. This highlights the critical importance of a contaminated environment in disease management. Furthermore, neural networks (NNs) were utilized to improve the simulation and validation of disease dynamics. Public health strategists can use the findings of this study to reduce or eliminate leptospirosis infection.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"55 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2025-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144843312","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Machine Learning Approach to Analyze the Role of Antiretroviral Therapy in an HIV/AIDS Model with Both Vertical and Sexual Transmission by Using Physics-Informed Neural Networks","authors":"Purnendu Sardar,&nbsp;Biswadip Pal,&nbsp;Rafiqur Rahaman,&nbsp;Tshering Dorjee Bhutia,&nbsp;Md Firoj Ali,&nbsp;Santosh Biswas,&nbsp;Sandip Banerjee,&nbsp;Manab Biswas,&nbsp;Krishna Pada Das","doi":"10.1007/s13538-025-01873-z","DOIUrl":"10.1007/s13538-025-01873-z","url":null,"abstract":"<div><p>In this study, we develop and analyze a compartmental SEIA (Susceptible–Exposed–Infected–AIDS) model that incorporates both horizontal (sexual) and vertical (mother-to-child) HIV transmission mechanisms. The model further includes the impact of Antiretroviral Therapy (ART) efficacy in slowing the progression from HIV infection to AIDS. While traditional numerical techniques are often used to study such epidemiological systems, we adopt a cutting-edge Physics-Informed Neural Network (PINN) framework to solve the system of nonlinear ordinary differential equations. The PINN method combines data-driven learning with the underlying biological laws to estimate system dynamics and unknown parameters more efficiently and accurately. Analytical investigation of the model ensures positivity, boundedness, and local stability of equilibria based on the basic reproduction number (<span>(mathcal {R}_0)</span>). Our results demonstrate that the HIV-free steady state is locally stable when the basic reproduction number <span>(mathcal {R}_0 &lt; 1)</span>, but becomes unstable as <span>(mathcal {R}_0 &gt; 1)</span>, giving rise to a stable HIV infected steady state. Sensitivity analyses show that the rate of sexual transmission and the effectiveness of ART significantly affect the long-term disease dynamics. Notably, increasing ART efficacy reduces the AIDS population substantially but does not eliminate the infected class entirely, indicating the persistence of the virus. Additionally, scenarios with strong vertical transmission exhibit delayed but sustained resurgence of infections even under high ART coverage, highlighting the challenge of latent reservoirs and therapy fatigue. The PINN-based simulations corroborate theoretical findings and reveal critical thresholds for ART efficacy and transmission rates. This hybrid mathematical-ML approach provides a powerful framework for studying infectious disease dynamics and optimizing public health interventions.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"55 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2025-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144832264","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stochastic Thermodynamics of Ecosystems","authors":"Tânia Tomé,&nbsp;Mário J. de Oliveira","doi":"10.1007/s13538-025-01878-8","DOIUrl":"10.1007/s13538-025-01878-8","url":null,"abstract":"<div><p>We investigate the thermodynamics as well as the population dynamics of ecosystems based on a stochastic approach in which the biomasses of the several species of the ecosystem are treated as stochastic variables. The several species are connected by feeding relationships that are understood as unidirectional processes in which a certain amount of biomass is exchanged between species. We show that the equations for the averages in the biomass of species are those given by the deterministic approach. We determine the fluxes of mass, energy, and entropy as well as the rate of the entropy production. In the stationary state, the entropy production and the input of energy into the ecosystem are both found to be proportional to the organic mass generated by the autotrophs per unit time per unit mass of the autotrophs.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"55 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2025-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144810872","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Controlled Synthesis Approaches for Tuning the Structural, Optical, and Morphological Features of Chemo-catalytically Active Covellite (CuS) Nanostructures","authors":"Deepthi S. Nair,&nbsp;V. M. Anandakumar","doi":"10.1007/s13538-025-01860-4","DOIUrl":"10.1007/s13538-025-01860-4","url":null,"abstract":"<div><p>Covellite (CuS) nanostructures were meticulously engineered using chemical precipitation, mechanochemical, and hydrothermal methods, with copper chloride and thiourea as key precursors. The influence of each synthesis route on the structural, optical, and morphological properties was systematically explored through comprehensive characterization techniques, including XRD, EDS, FESEM, HR-TEM with SAED, BET, UV–VIS, FT-IR, and Raman spectroscopy. The results unveiled striking morphological variations, where flake- and sheet-like CuS nanoparticles self-assembled into distinct architectures—cuboids, microflowers, or staircase-like formations—demonstrating the pivotal role of synthesis conditions in shaping their structure. Growth mechanisms were analyzed for each method, and their chemocatalytic efficiency in methylene blue (MB) dye degradation was critically evaluated. The reaction mechanism for chemocatalytic dye degradation was investigated, and kinetic analysis demonstrated that it adheres to pseudo-first-order kinetics as described by the Langmuir–Hinshelwood model. Notably, the mechanochemical approach emerged as a promising strategy for enhancing catalytic activity, underscoring the significance of synthesis optimization in advancing CuS-based materials for sustainable environmental remediation.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"55 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2025-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145142797","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Collective Circular Swimmer-Like Behavior of Chiral Active Nematics Confined to a Circular Cavity","authors":"Marcelo L. Lyra,&nbsp;Maria S. S. Pereira,&nbsp;Leonid V. Mirantsev,&nbsp;Italo N. de Oliveira","doi":"10.1007/s13538-025-01876-w","DOIUrl":"10.1007/s13538-025-01876-w","url":null,"abstract":"<div><p>Understanding the development of collective motion of chiral active nematics is a relevant issue in physics and biology. Here, we perform molecular dynamics simulations of dilute ensembles of active chiral elongated particles confined to a two-dimensional circular cavity under both radial and tangential boundary conditions. In addition to interparticle isotropic Lennard-Jones and anisotropic Maier-Saupe-like interactions, the active nematic particles exert self-propelling forces and torques. We show that active nematic particles form compact clusters which acquire a circular swimmer-like behavior with the clockwise or counterclockwise directions of their rotations being defined by the chiralities of individual particles. The vectors associated with the average orientation of clusters and the velocity of their center of mass rotate synchronously. Further, in a mixture of particles having opposite chiralities, they self-organize and separate into clusters with well-defined chiralities. Our results shed light on the physical mechanisms underlying the development of self-organization in chiral active nematic matter.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"55 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2025-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145142971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Analyzing Negativity Criterion in Qubit-Qutrit System Located in External Magnetic Fields with the Dzyaloshinskii-Moriya Interaction","authors":"Seyed Mohsen Moosavi Khansari,&nbsp;Fazlollah Kazemi Hasanvand","doi":"10.1007/s13538-025-01846-2","DOIUrl":"10.1007/s13538-025-01846-2","url":null,"abstract":"<div><p>This investigation delves into the intricate entanglement dynamics exhibited by qubit-qutrit systems when subjected to the intricate dynamics of both the XXX isotropic Heisenberg model and the anisotropic XYZ model. These models are enriched by the presence of Dzyaloshinskii-Moriya (DM) interactions and external magnetic fields, creating a complex interplay of quantum phenomena. The exploration commences by initializing the system in a superposition of spin-coherent states, setting the stage for a nuanced analysis of entanglement evolution over time. By employing the negativity metric as the pivotal criterion for assessing entanglement, we gain insights into the subtle relationships between DM interactions, external magnetic fields, and the entanglement dynamics within this composite system. Through this comprehensive investigation, we aim to unravel the intricate dynamics and behaviors that emerge from the interplay of these fundamental elements, shedding light on the underlying principles governing quantum entanglement in this context.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"55 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2025-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145142398","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Magnetism, Half-Metallicity, Structural Stability, and Thermoelectric Properties of Ba2MTaO6 (M = V, Ni): A Computational Perspective","authors":"Atika Guendouz,&nbsp;Mokhtar Hjiri,&nbsp;Abdelkader Nabatti Ech-Chergui,&nbsp;Walid Mohamed Mohamedi,&nbsp;Kouider Driss-Khodja,&nbsp;Adjdir Mehdi,&nbsp;Bouhalouane Amrani","doi":"10.1007/s13538-025-01858-y","DOIUrl":"10.1007/s13538-025-01858-y","url":null,"abstract":"<div><p>The double perovskite oxides Ba₂MTaO₆ (M = V, Ni) are investigated for the first time due to their promising properties in materials science and spintronics. Using the FP-LAPW method within the framework of density functional theory (DFT), we examine the effects of magnetic transition metal cations (M) on the structural and electronic behavior of these compounds. The calculations are carried out using the generalized gradient approximation (GGA), GGA with Hubbard U correction (GGA + U), and the exact exchange for correlated electrons (EECE) approach for the exchange correlation functional. Both compounds crystallize in a cubic structure (space group: Fm-3m, No. 225) under ambient conditions, with optimized lattice parameters of 8.13 Å for Ba₂VTaO₆ and 8.08 Å for Ba₂Ni TaO₆. Moreover, the bulk modulus and its pressure derivative have been calculated. The elastic constants satisfy Born’s mechanical stability criteria, indicating that both compounds exhibit ductile behavior and elastic anisotropy. Notably, these oxides demonstrate half-metallic behavior, with a narrow band gap in the spin-down channel, as confirmed by band structure and density of states analyses. The calculated total magnetic moments are nearly integer values, around 2.00 and 1.00 µ_B per formula unit for Ba₂VTaO₆ and Ba₂Ni TaO₆, respectively. For Ba₂VTaO₆, the band gap values obtained using GGA, GGA + U, and EECE are 2.58 eV, 3.18 eV, and 3.29 eV, respectively. In the case of Ba₂Ni TaO₆, the corresponding values are 0.88 eV (GGA), 2.74 eV (GGA + U), and 2.95 eV (EECE). These results highlight the significant influence of the magnetic M³⁺ cation on both the magnetic moment and electronic transport, in contrast to the non-magnetic Ta⁵⁺ cation. Thermodynamic properties were also investigated over the temperature range of 0–1000 K using the quasi-harmonic Debye model, which remains valid across this range. Furthermore, thermoelectric properties such as the Seebeck coefficient, electrical conductivity, and thermal conductivity were evaluated using the BoltzTraP code between 200 and 800 K.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"55 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2025-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145142406","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Inclusion of Resonances from the Second and Third Region in (pi )-Photoproduction on Nucleons Within the Effective Lagrangian Approach","authors":"J. J. Quirós,&nbsp;C. Barbero,&nbsp;D. E. Jaramillo,&nbsp;A. Mariano","doi":"10.1007/s13538-025-01869-9","DOIUrl":"10.1007/s13538-025-01869-9","url":null,"abstract":"<div><p>We develop a formalism based on the effective Lagrangian approach (ELA) to evaluate the Chew-Goldberger-Low-Nambu (CGLN) amplitudes for the <span>(pi )</span>-photoproduction process on nucleons, <span>(gamma Nrightarrow pi N')</span>. This formalism allows us systematically include any spin <span>(frac{1}{2})</span>-isospin <span>(frac{1}{2})</span>, spin <span>(frac{1}{2})</span>-isospin <span>(frac{3}{2})</span>, spin <span>(frac{3}{2})</span>-isospin <span>(frac{1}{2})</span>, and spin <span>(frac{3}{2})</span>-isospin<span>(frac{3}{2})</span> resonance, with both positive and negative parities. In particular, we analyze the effect of the <span>( P_{33}(1232))</span> resonance, the second region four-star <span>(N^*)</span> resonances <span>( P_{11}(1440))</span>, <span>( D_{13}(1520))</span>, <span>( S_{11}(1535))</span>, <span>( P_{33}(1600))</span>, and also the third region <span>(S_{11}(1650) )</span> and <span>(P_{11}(1710) )</span> resonances on total cross-sections and simultaneously on the <span>(E_{1+}^{3/2})</span> and <span>(M_{1+}^{3/2})</span> electromagnetic multipoles. To reproduce the experimental data of the total cross-sections for both proton-induced <span>(gamma p rightarrow npi ^+)</span> and <span>(gamma p rightarrow ppi ^0)</span> processes, we describe the strategy for performing the fitting, highlighting the region where each model parameter will be varied, consistently with existing literature information on the same. We have established a reliable set of parameters for the model in accordance with experimental data, which include the coupling constants, the magnetic moments, masses, and widths of the nucleon resonances. With the fitted parameters, we have evaluated the electric and magnetic multipoles, which have shown an excellent agreement with the experimental data, after incorporating the effects of unitarity. Additionally, we have predicted a value for the electric to magnetic ratio of the <span>(P_{33}(1600))</span> resonance, <span>(R_{EM}=-0.115)</span>, not yet reported in the literature.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"55 5","pages":""},"PeriodicalIF":1.7,"publicationDate":"2025-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145142050","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}