Brazilian Journal of Physics最新文献

{"title":"Thermoforesis from Generalized Caldeira-Leggett Models","authors":"Daniel Valente,&nbsp;Maurício Matos,&nbsp;Thiago Werlang","doi":"10.1007/s13538-026-02131-6","DOIUrl":"10.1007/s13538-026-02131-6","url":null,"abstract":"<div><p>The standard Caldeira-Leggett model addresses the problem of Brownian motion in a thermal equilibrium environment. Here, we look for generalizations of the Caldeira-Leggett model to account for thermal gradients in the environment. We devise two types of models, and discuss the advantages and limitations of each one. From both models, we find signatures of thermophoresis, i.e., particle transport due to a thermal gradient. In principle, our models can be employed to describe thermophoresis in quantum Brownian particles, an open problem so far.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 5","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13538-026-02131-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148751093","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"THz Generation by a Self-Focused Gaussian Laser Beam in a QMCNTs-Based Plasma","authors":"Atal Bharati,&nbsp;Sandeep Kumar,&nbsp;Vishal Thakur","doi":"10.1007/s13538-026-02138-z","DOIUrl":"10.1007/s13538-026-02138-z","url":null,"abstract":"<div><p>The generation of terahertz (THz) radiation through the self-focusing of a Gaussian laser beam in an array of vertically aligned quasi-metallic carbon nanotubes (VA-QMCNTs) embedded on a non-conductive glass substrate is investigated. Since ω / ω_p &gt; 1, the Gaussian laser beam propagates through the plasma. During propagation, the laser field modifies the plasma refractive index, and the resulting intensity-dependent change in refractive index leads to self-focusing of the beam. As the Gaussian beam traverses the plasma, its transverse intensity gradient exerts a nonlinear ponderomotive force on the electrons within the VA-QMCNTs. This interaction modifies the electron density and induces nonlinear currents, which serve as the source of THz radiation. The output THz power is substantially enhanced in regions where self-focusing is more pronounced. Furthermore, resonant enhancement of THz generation is observed at specific laser parameters, such as normalised pulse duration, beam width parameter, and spot size. The role of electron collision frequency in shaping the THz output is also examined. Numerical analysis reveals that the proposed scheme offers a promising pathway for THz generation. Given the strong sensitivity of THz radiations to tissue water content, the proposed scheme is relevant to non-invasive imaging of superficial tissues, including burn-depth and hydration assessment.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 5","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148751423","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":"Design of a Target System for an e-Linac-Based 6 MeV SS-ADS Neutron Source","authors":"Syarip Syarip,&nbsp;Isdandy Rezki Febrianto,&nbsp;Taxwim Taxwim,&nbsp;Taufik Taufik,&nbsp;Saefurrochman Saefurrochman,&nbsp;Wijono Wijono,&nbsp;Aniti Payudan","doi":"10.1007/s13538-026-02137-0","DOIUrl":"10.1007/s13538-026-02137-0","url":null,"abstract":"<div><p>This research aims to identify the optimal target design for generating neutrons using a 6 MeV electron linear accelerator (e-Linac) within the Small Scale - Accelerator Driven System (SS-ADS) experimental facility of ⁹⁹Mo isotope production. The methodology employs particle transport simulations using the Particle and Heavy Ion code Transport System (PHITS), combined with Response Surface Methodology (RSM) for statistical optimization. With a beam radius of 0.1 cm, the optimal target system for the 6 MeV e-Linac incorporates an iridium pitcher and a beryllium catcher (Ir-Be) configuration. The optimal radius and thickness dimensions of the pitcher are 0.1 cm and 0.21 cm respectively, while the catcher should have a radius and thickness of 1 cm each. This Ir-Be target system configuration design can produce a total neutron flux of 3.85 10⁶ n/cm².s.µA. Since the external neutron source requirement for experimental SS-ADS is on the order of 10⁸ n/cm2.s, the design plan of 6 MeV e-Linac should have an electron current of 0.1 mA.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 5","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148750992","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":"EEG Time–Frequency Image Encoding with Convolutional Networks for Alzheimer’s and FTD Classification","authors":"Salleh Sonko,&nbsp;Gahangir Hossain,&nbsp;Wael Korani","doi":"10.1007/s13538-026-02135-2","DOIUrl":"10.1007/s13538-026-02135-2","url":null,"abstract":"<div><p>Dementia is a neurological disorder that causes memory loss and other symptoms. Alzheimer’s disease (AD) and frontotemporal dementia (FTD) are clinically important forms of dementia, yet differentiating them from each other and from cognitively normal (CN) individuals remains a major clinical challenge due to overlapping electrophysiological signatures. Monitoring brain function using electroencephalography (EEG) signals enables real-time assessment of neurophysiological changes associated with dementia. This study presents a deep learning framework that leverages EEG-derived time–frequency (TF) images and convolutional neural networks (CNNs) for robust, non-invasive classification of dementia subtypes. The proposed custom lightweight CNN was trained and evaluated using the public OpenNeuro database, which includes 88 participants. The EEG recordings were preprocessed to remove artifacts and noise, and three TF methods—Continuous Wavelet Transform (CWT), Wavelet Synchrosqueezing Transform (WSST), and Discrete Wavelet Transform (DWT)—were applied to generate spectro-temporal images capturing multiscale neural dynamics. The results show that the proposed lightweight architecture achieves 95.00% accuracy with CWT, 94.00% with WSST, and 81.00% with DWT under an image-level 10-fold cross-validation strategy. Comprehensive comparisons were then conducted against both EEG-specific architectures (EEGNet, EEGNet-SSVEP, DeepConvNet, ShallowConvNet) and vision-based pretrained models (DenseNet121, EfficientNetV2-S, Xception). The proposed framework consistently outperforms all baseline methods across accuracy, precision, recall, and F1-score. Notably, these continuous and reassigned TF representations improved differentiation among the three classes, addressing a long-standing limitation of EEG-based dementia classification. Overall, this framework offers a promising EEG-based approach for dementia classification by combining high accuracy with relatively low computational complexity, supporting its potential application in early dementia diagnosis.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 5","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148750951","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":"Over Forty Years of Research Towards the Understanding of Quantum Brownian Motion – The Contributions of A. O. Caldeira","authors":"Marcus V. S. Bonança,&nbsp;Sebastian Deffner,&nbsp;Gert-Ludwig Ingold","doi":"10.1007/s13538-026-02127-2","DOIUrl":"10.1007/s13538-026-02127-2","url":null,"abstract":"<div><p>This article presents a brief account of Amir O. Caldeira’s contributions to the theory of quantum Brownian motion. Motivated by its importance, we outline the description of Brownian motion in the quantum regime following Caldeira’s first works. In this context, we particularly highlight the effect of dissipation on the tunneling rate out of a metastable state. We then journey along the alternative ways to approach quantum Brownian motion developed by Caldeira during his career, which go beyond the so-called Caldeira-Leggett model. We conclude by summarizing some of Caldeira’s contributions to contemporary fields such as the theory of quantum decoherence and quantum thermodynamics, that were strongly inspired by his eponymous approach to quantum Brownian motion.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 5","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13538-026-02127-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148750832","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Early Dark Energy: A Review of Theoretical Models and Updated Observational Constraints","authors":"Thárcio Cerqueira,&nbsp;Cássio Pigozzo","doi":"10.1007/s13538-026-02123-6","DOIUrl":"10.1007/s13538-026-02123-6","url":null,"abstract":"<div><p>The discrepancy between early- and late-time determinations of the Hubble constant, known as the Hubble tension, has motivated a variety of extensions to the standard cosmological model. Among the proposed solutions, Early Dark Energy (EDE) scenarios have received significant attention due to their ability to modify the sound horizon at recombination and potentially alleviate this tension. In this review, we present an overview of EDE models, focusing on their theoretical foundations and phenomenological features. We also provide a dataset-oriented synthesis of EDE constraints, discussing how the inferred viability of EDE depends on the interplay between CMB datasets, local <span>(H_0)</span> priors, large-scale structure probes, and parameter-volume effects. Our goal is to provide a unified and pedagogical account of how the theoretical realization of the EDE component and the choice of observational dataset jointly determine the inferred values of <span>(H_0)</span>, <span>(f_{EDE})</span>, <span>(z_c)</span> and <span>(S_8)</span>. We further discuss the main challenges faced by these models, including their impact on large-scale structure observables, theoretical consistency issues, and remaining tensions with late-time data. Finally, we highlight prospects for future observational tests aimed at clarifying their role in the Hubble tension.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 5","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13538-026-02123-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148750739","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shortcut to Adiabatic Transfer in a Four-Level N-type System using Counterdiabatic Driving","authors":"Marius Romuald Kamsap,&nbsp;Simon Evehe Ndong,&nbsp;Maïk Delon Mboumba,&nbsp;Mathurin Esouague Ateuafack,&nbsp;Christian Kenfack-Sadem,&nbsp;Thierry Blanchard Ekogo,&nbsp;Alain-Brice Moubissi,&nbsp;Caroline Champenois","doi":"10.1007/s13538-026-02133-4","DOIUrl":"10.1007/s13538-026-02133-4","url":null,"abstract":"<div><p>The stimulated Raman shortcut-to-adiabatic passage (STIRSAP) technique has been demonstrated to accelerate adiabatic population transfer processes. Traditionally applied to three-level atomic systems, this method enables rapid and efficient population transfer in a short interaction time. In this work, we extend this approach to a four-level <span>(varvec{N})</span>-type system driven by three laser fields. Under the three-photon phase matching condition, the first-order Doppler effect can be completely eliminated, making this configuration more suitable for applications in frequency metrology and quantum information processing. By adiabatically eliminating the intermediate state, the four-level system is effectively reduced to a two-level model, enabling the application of counterdiabatic driving without requiring additional couplings. This approach allows for fast and efficient population transfer between metastable states. We analyze the influence of laser intensity peaks and detuning, and we show that the transfer time is significantly shorter than that achieved with the STIRAP technique. Moreover, we also show that an optimal coupling strength between the ground and metastable states further minimizes the operation time.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 5","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148628648","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":"Compositional Design of Bi₂O₃-Substituted Strontium–Barium Borate Glasses with Tunable Thermal Stability and Efficient Gamma-Ray Attenuation","authors":"Yurii Hordieiev","doi":"10.1007/s13538-026-02136-1","DOIUrl":"10.1007/s13538-026-02136-1","url":null,"abstract":"<div><p>Lead-free glasses that combine processability with efficient photon attenuation are needed for radiation-shielding applications. This study investigates melt-quenched 10SrO–10BaO–(80 − m)B₂O₃–mBi₂O₃ glasses with m = 0–40 mol% to isolate the effect of Bi₂O₃ substitution on glass structure, thermal response, and gamma-ray attenuation. Melt-quenched samples remained predominantly amorphous by XRD, while FTIR showed progressive restructuring of the borate network, including an increased relative contribution from BO₄-associated environments at higher Bi₂O₃ contents. Bi₂O₃ strongly lowered the glass-transition temperature, from 545 to 376 °C by DTA, and increased thermal expansion, with CTE_20–300 rising from 6.24 to 11.03 ppm/°C. Moderate Bi₂O₃ additions maintained good resistance to crystallization, whereas Bi₂O₃-rich glasses exhibited narrower stability windows and multistage devitrification. Density increased from 2.71 to 6.57 g/cm³, accompanied by a rise in molar volume, indicating a heavier but more open network. Photon-shielding calculations showed major attenuation gains: at 0.662 MeV, the tenth-value layer decreased from 11.26 cm for the Bi₂O₃-free glass to 3.45 cm for the glass containing 40 mol% Bi₂O₃. Thus, Bi₂O₃ substantially improves gamma-ray shielding efficiency, although high Bi₂O₃ loading introduces thermal-stability and processing trade-offs.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 5","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148614908","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":"Optimization of Subwavelength Ultrasonic Focusing Beams in Core-shell Lenses through Numerical Simulations","authors":"Gutemberg S. Cardoso,&nbsp;José P. Leao-Neto,&nbsp;José H. Lopes","doi":"10.1007/s13538-026-02128-1","DOIUrl":"10.1007/s13538-026-02128-1","url":null,"abstract":"<div><p>In this study, we numerically examined the correlation between the mechanical parameters of core-shell lenses and the main characteristics of subwavelength ultrasonic focusing beams generated by these lenses. These beams possess unique properties that can be utilized in high-resolution imaging systems. We conducted numerical simulations for various core materials and different core and shell sizes of the core-shell lenses. Our simulations revealed that the full width at half maximum (FWHM) and depth of focus (<span>(z_{0})</span>) of the beams can reach 0.437 and 6.44 wavelengths, respectively. Additionally, we discovered that the intensity of the generated beams can be optimized by selecting a ratio of 0.43 between the inner and outer core, regardless of the core material of the lens. This work provides a deeper understanding of the design of lenses that produce beams below the diffraction limit, which can be applied in the development of high-resolution single element transducers.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 5","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13538-026-02128-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148613625","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Synthesis and Characterization of Magnetic Cellulose Nanocomposites","authors":"Karolina Natasha Jarochewski,&nbsp;Angélica Daiane Schneider,&nbsp;Alana Torres Viero,&nbsp;Cristiano Rodrigo Bohn Rhoden,&nbsp;Lucio Strazzabosco Dorneles,&nbsp;João Zorzi Konradt,&nbsp;Artur Harres de Oliveira","doi":"10.1007/s13538-026-02132-5","DOIUrl":"10.1007/s13538-026-02132-5","url":null,"abstract":"<div><p>Magnetic and structural properties of cellulose decorated with magnetite nanoparticles prepared via a co-precipitation method were analyzed. All samples presented magnetisation loops coherent with a superposition of superparamagnetic and ferromagnetic contributions. This feature is attributed to the size distribution of the magnetic nanoparticles and it was observed that weak and demagnetising inter-particle interactions are present. Magnetic parameters like coercivity and remanent magnetisation, however, are mainly governed by the average particle size, and not by such interactions. X-ray diffraction, transmission and scanning electron microscopy were employed for structural investigation, and revealed the presence of magnetite and goethite in some samples.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 5","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13538-026-02132-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148613624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}