Brazilian Journal of Physics最新文献

This work presents the preliminary thermal analysis of the SPORT microsatellite, based on its initial configuration. A simplified analysis, using control volumes, is conducted, considering the power dissipated by the equipment and solar radiation as heat sources. Internal conduction and radiation processes between components, as well as radiation into space, are also taken into account. A system of ordinary differential equations is constructed and solved using a simple time-marching method. The results are presented as the average temperatures of the components over a 24-h period and are compared with the numerical simulation of the definitive configuration performed by CFD. The main objective is to apply a quick and simplified version of the thermal lumped method to identify which elements may exceed temperature limits during operation, using the results to adjust the design where those limits are not met. The results are compared with CFD data for the final configuration, showing that the overall temperature behavior is consistent, and that all elements remained below the temperature limits. This validates the use of the methodology in the early phases of nanosatellite design, though some improvements may still be required.

We investigate theoretically the design and application of nine triazine (Tr)-core star-shaped molecules built with thiophene (Th), phenyl (Ph), and carbazole (Cz) moieties in dye-sensitized solar cells (DSSCs) and bulk heterojunction (BHJ) organic solar cells. Density functional theory and time-dependent density functional theory are employed to rationalize the electronic structure, charge transfer properties, and photovoltaic performance of these systems. Tr-Th-Cz and Tr-Ph-p-Th-Cz display power conversion efficiency ((text{PCE})) values close to 30% due to a favorable alignment of the energy levels. Computed open-circuit voltage values show that lack of π-bridges, as in the Tr-Th and Tr-Cz, favor higher voltage generation. Systems containing thiophene (Th) and carbazole (Cz) present the most favorable values for efficient electron injection and dye regeneration. Furthermore, the incorporation of these Th and Cz donor substituents into the triazine core combined with π-bridges significantly impacts other optoelectronic properties of the organic solar cells. The computed high singlet–triplet gap values indicate limited potential of these molecules as thermally activated delayed fluorescence (TADF) emitters for applications in organic light-emitting diodes (OLEDs).

We evaluate thermodynamic equation of state (EOS) under one loop correction at finite chemical potential. Due to the presence of the chemical potential in the one loop correction, there is change in formation of bubble/droplet of quark-gluon plasma (QGP) and this chemical potential has the effect on the evaluation of EOS. The effect is particularly studied at the values of quark and gluon parametrization ({gamma }_{q} = 1/8) and (12{gamma }_{q} le {gamma }_{g} le 16{gamma }_{q}) at which the equilibrating bubbles/droplets sizes are obtained. The study indicates that the dynamics of the quark, anti-quark, and gluon fluids with the presence of chemical potential improves the results of the EOS from the earlier result of thermodynamic EOS without the chemical potential. It means that the effect of chemical potential in one loop correction cannot be neglected in the bubble/droplet formation of quark-gluon plasma and this chemical potential can signify the presence of a large number of charge particles in the earlier universe formation.

Diffuse reflectance spectroscopy (DRS) and photoacoustic absorption spectroscopy (PAS) are investigated in model systems that mimic topological structures found in vegetal fibers, e.g., made of oriented hollow channels. Among this wide family, the shiny optical aspect of Golden grass stems has motivated detailed investigations of their chemical composition, microstructure, and electronic properties. In this work, diffuse reflectance and absorption of a photon flux within a collection of parallel hollow fibers are addressed using 2D optical models, neglecting interface scattering. Analytical results obtained for hollow square tube (HST) and plane parallel membrane (PPM) arrays are validated by full ray-tracing calculations. Optical paths with multiple reflection/refraction events at air-fiber interfaces selectively enhance DRS and PAS intensities and thus explain the shiny golden-like aspect of Golden grass, in contrast with specular reflectance calculated from the complex refractive index. A simple method is proposed to retrieve the complex dielectric function of fiber walls from the measured PAS and DRS intensities, using analytical equations obtained with hollow fiber topologies, in a low-energy region not easily accessible by photoelectron energy loss spectroscopy.

We show evidence of particle acceleration at GeV energies associated directly with protons from the prompt emission of a long-duration M6-class solar flare on July 17, 2023, rather than from protons acceleration by shocks from its associated coronal mass ejection (CME), which erupted with a speed of 1342 km/s. Solar energetic particles (SEP) accelerated by the blast have reached Earth, up to an almost S3 (strong) category of a radiation storm on the NOAA scale. Also, we show a temporal correlation between the fast increase in the GOES-16 proton flux and the ground-level count rate excess of the New-Tupi muon detector, located in the central region of the South Atlantic Anomaly (SAA) an area where the Earth’s magnetic field is anomalously weak. A Monte Carlo spectral analysis based on muon excess at New-Tupi is consistent with the acceleration of electrons and protons (ions) up to relativistic energies (GeV energy range) in the impulsive phase of the flare. In addition, we present another two marginal particle excesses (with low confidence) at ground-level detectors in correlation with the solar flare prompt emission.

Plasmonic nanoparticles exhibit remarkable photothermal properties, making them valuable in various fields such as renewable energy and medicine. These photothermal properties depend on several factors, including the type of noble metal, particle size, and the stabilizing layer. This study investigates the photothermal properties of colloidal silver nanoparticles synthesized photochemically using UV LEDs. Silver nanoparticles capped with citrate and a combination of citrate and polyvinylpyrrolidone (PVP) were prepared. While the nanoparticle size remained unaffected by the amount of citrate, the nonlinear refractive index did show dependence. As the citrate concentration increased, the nonlinear refractive index decreased. Additionally, increasing the amount of PVP not only reduces the nanoparticle size—suggesting a reverse Ostwald ripening process induced by UV light—but also leads to a diminished photothermal response.

Breast cancer ranks as the second most common cause of mortality among women globally, with the potential to increase survival rates by 97% through early detection. This study focuses on developing an innovative triple-band microstrip patch antenna designed to operate within the 2–6 GHz frequency spectrum. Simulation tests were conducted to evaluate its efficacy in early breast cancer detection. The antenna, constructed from copper tape and five different substrates (Felt, FR4, PET, PLA, TPU), was chosen considering its advantages for various applications. This design prioritizes wearer comfort while ensuring functionality and allows for producing antenna structures in desired geometries using 3D printing, even in complex configurations. With a general size of 30 × 30 mm², the antenna underwent analyses on tumor-free models with tumors of different shapes and sizes, and additionally, to evaluate the performance of multiple antennas in detecting cancers, tumor models with 2 and 3 antenna numbers were analyzed in a total of six different breast scenarios. Critical performance parameters such as specific absorption rate (SAR), return loss (S11), and voltage standing wave ratio (VSWR) were obtained for each generated model. Simulation outcomes indicated SAR values within the permissible threshold for medical applications. Moreover, VSWR values maintained acceptability, while variations in return losses were contingent upon tumor dimensions, location, and the number of antennas used. Furthermore, the antenna’s adaptability to bending was scrutinized through bending analyses, affirming its robustness, and sustained operational capability. One of the significant contributions of the study is the utilization of recyclable filaments such as PLA, TPU, and Protopasta in experimental investigations, providing a pathway for producing environmentally friendly and flexible antennas and breast phantoms. This study offers a way to develop more sensitive and reliable breast cancer screening and early diagnosis tools.

This study investigates the effects of lanthanum oxide (La₂O₃) and strontium oxide (SrO) on polyvinyl alcohol (PVA) polymer membranes. The PVA membranes, fabricated using an ultrasound-assisted casting method, include variations with (PVA-SrO), (PVA-La₂O₃), and a combination of both metal oxides (PVA-SrO-La₂O₃). X-ray diffraction (XRD) analysis reveals that these membranes exhibit a combination of semi-crystalline and amorphous properties, with the introduction of crystalline peaks due to the addition of SrO and La₂O₃. Electrical performance assessments, conducted using an I-V source meter and impedance spectroscopy, demonstrate that the metal oxide composite membranes showed improved performance. Mechanical properties were evaluated using Load–Displacement curves, where PVA-SrO-La₂O₃ exhibited the highest elongation with a value (ɛ) of 134, as measured by Young's modulus, and a resistance value of 12.230 kΩ.

Copper selenide (Cu₂Se) is a promising semiconductor with notable potential for optoelectronic and thermoelectric applications. This study investigates the impact of film thickness on the physical properties of Cu₂Se thin films. Cu₂Se thin films of varying thicknesses were synthesized using the thermal evaporation technique. These films were then analyzed for optical properties, structural characteristics, and surface morphology. Optical analysis was conducted using absorption spectra over a wavelength range of 200 to 900 nm. From these spectra, we determined key optical parameters such as the energy band gap (E_g), extinction coefficient (k), and refractive index for films of different thicknesses. Dielectric properties were evaluated, allowing us to calculate the dielectric constant and dielectric loss for various film thicknesses. Additionally, current–voltage (I-V) characteristics and Raman spectroscopy were performed, and the results are presented and discussed in detail.

In this paper, the fusion cross sections of ⁶He + ¹⁹⁷Au and ⁸He + ¹⁹⁷Au systems have been investigated at center-of-mass energies from below to above the Coulomb barrier, 14.5 to 60.0 and 15.0 to 29.0 MeV, respectively. The required nucleus-nucleus potential has been calculated by using the Monte Carlo method, applying four different phenomenological density distributions. The results obtained from both systems reveal that considering the suitable halo structure for distribution of the nuclear matter increases the height of fusion barrier, giving a better agreement with the experimental data. In addition, by using the generalized function of the two-parameter Fermi distribution for the nuclear density of the halo nucleons of ⁶He and ⁸He nuclei, a better agreement with experimental data was achieved. Using the same potential with the above-mentioned density distributions, we also studied the elastic scattering cross sections for the ⁶He + ¹⁹⁷Au system measured at E_lab. = 29 MeV and E_lab. = 40 MeV, with similar good results as for the fusion reaction.