Brazilian Journal of Physics最新文献

Synthesis of the Urea l-malic acid (ULM) crystal was accomplished through a gradual evaporation growth technique. The characterization encompassed a thorough examination of its structural, spectral, optical, thermal, and dielectric aspects. The single-crystal X-ray diffraction (SCXRD) study elucidated a monoclinic pattern characterized by a non-centrosymmetric P2₁ space group. Fourier transform infrared (FTIR) study validated the existence of functional groups essential for hydrogen bonding and crystal sustainability. Optical investigations demonstrated significant UV absorbance at 261 nm, accompanied by a broad optical bandgap (4.185 eV). The Urbach energy was approximated at 0.228 eV, suggesting a high degree of crystallinity. A notable photoluminescence (PL) emission was detected at 460 nm, exhibiting a high degree of color purity at 77.15%, thereby endorsing its potential utility in blue-light display systems. Measurements of second-harmonic generation (SHG) showed that it was 2.2 times more effective than regular KDP, thereby underscoring its potential for nonlinear optical applications. The thermal stability was verified at temperatures reaching 120 °C, accompanied by a calculated activation energy (9.50 kJ/mol). Dielectric investigations revealed behavior that is dependent on both frequency and temperature, with AC conductivity exhibiting an increase in response to rising temperature. Impedance analysis demonstrated a non-Debye relaxation mechanism and a single semicircular Nyquist graph. The findings validate the multifunctional capabilities of ULM crystals for prospective applications in optoelectronic, photonic, and electrochemical systems.

The coupling of thermal, concentration, and electromagnetic fields arises in various industrial and environmental processes. The presence of a magnetic field alters flow dynamics and energy transport through the Lorentz force, while chemical reactions affect the concentration boundary layer and influence mass transfer. This study focuses on the numerical investigation of fluid flow, heat transfer, and forced magnetohydrodynamic (MHD) convection through a semi-infinite horizontal porous plate, taking into account the effects of chemical parameters. By analyzing the boundary layer, a reduced model was developed to represent the time-independent governing equations for momentum, energy, and concentration. These equations were expressed in a dimensionless, nonlinear form and subsequently transformed into a system of nonlinear ordinary differential equations (ODEs). The resulting ODE system was solved using the BVP4C method implemented in the MATLAB R2024b environment. Numerical simulations were conducted to examine the influence of various parameters—including the magnetic parameter, porous medium permeability, Eckert number, Schmidt number, Prandtl number, Dufour number, blowing/suction velocity, and Soret number—on the velocity, temperature, and concentration profiles, as well as on the skin friction coefficient, Nusselt number, and Sherwood number. The study reveals that an increase in the magnetic parameter leads to higher velocity, temperature, and concentration profiles. Blowing (positive velocity) enhances both temperature and concentration distributions and increases the Sherwood number; however, it reduces the velocity profile, skin friction coefficient, and Nusselt number. In contrast, suction (negative velocity) exhibits the opposite effects on these parameters.

This study provides a thorough analysis of the multiplicities of charged particles ((pi ^{pm }, varvec{K}^{pm })) produced in (p-varvec{P}b) collisions at (sqrt{s_textrm{NN}}) = 5.02 and 8.16 TeV. We utilize the scaled factorial moment (SFM) method to analyze events generated by the AMPT model, specifically examining cases with (pi ^0) and (varvec{K}_s^0) decays both turned off as AMPT (Decay = Off) and both these decays turned on as AMPT (Decay = On). We derive the anomalous fractal dimension ((d_q)) from the intermittency exponent ((alpha _q)) and analyze its variations with changing order (q). Several measures, including the anomalous fractal dimension, degree of multifractality (r), critical exponent ((nu )), Lévy index ((mu )), and multifractal specific heat (c), show the observed intermittent variations. Additionally, we investigate the quark-hadron phase transition through a second-order phase transition, adopting a scaled factorial moment approach with Ginzburg-Landau theory. This study includes a comparison of critical exponent ((nu )) values derived from AMPT-simulated datasets and data from Au+Au collisions at energies ranging from (sqrt{s_textrm{NN}} = mathbf {7.7}) to 200 GeV. Also, we have presented a comparison of the generalized fractal dimension ((varvec{D}_q)) and specific heat (c) across various emulsion interactions with the AMPT-simulated datasets.

Zn_(1-x)Cu_xO (x = 0.00, 0.01, 0.03, and 0.05) nanostructures have been synthesized by a simple chemical co-precipitation method, and the prepared samples have been analyzed by Powder X-ray diffraction (PXRD), UV–visible spectrophotometry (UV–Vis), Photoluminescence (PL), Fourier Transform Infrared spectroscopy (FTIR), and antibacterial activity. The Bragg peaks of XRD data matched well with the standard JCPDS data (PDF #89-1397). X-ray investigation reveals that all the synthesized samples are crystallized in a hexagonal wurzite structure with space group P63mc and space group number 186. The average crystallite size is calculated using Scherrer’s formula and falls in the range of 28 nm to 37 nm. Lattice parameters are calculated using relevant formulae and are in good agreement with the standard values. From UV–Vis absorption spectra, optical band gap values are increased from 3.574 eV to 3.569 eV which confirms the wide band gap of ZnO useful for sensor applications. PL emission spectra show the emission peaks around 380 nm which confirms that undoped and copper-doped ZnO samples are optically active in the ultraviolet region. The presence of key functional groups throughout the steps of this synthesis is explained based on the results obtained from FTIR analysis. Antibacterial activity for ZnO and Cu-ZnO nanoparticles was also analyzed using the well diffusion method.

Lanthanum manganite (LaMnO₃) and its doped derivatives have become an important class of perovskite materials due to their adaptable structural, electronic, and magnetic properties. A-site substitution with rare-earth elements and alkaline-earth elements has been shown to manipulate the Mn³⁺/Mn⁴⁺ ratio, alter oxygen vacancy concentrations, and perturb lattice distortions; all of this can impact conductivity, catalytic activity, and magnetism. These properties render a wide variety of applications appealing for doped LaMnO₃ materials, including solid oxide fuel cells, catalysis, spintronics, and energy storage. Even so, several challenges have limited their broader use, such as secondary-phase formation, electrolyte reactivity, dopant segregation, and processing at high temperatures. This article discusses advancements toward addressing these challenges with synthesis, defect engineering, and computational methods. Additionally, it reflects on the potential of new tools (machine learning and nanoscale design) to speed up the discovery of optimized compositions and processing conditions. Despite present problems, doped LaMnO₃ perovskites remain a promising material for energy and electrical applications.

Impedance spectroscopy has been used to investigate the relaxation processes over the static permittivity (ε_s) frequency regime in the plastic crystalline phase (PC) of neopentylglycol (NPG) at the temperature range (313.3–353.6 K) and frequency from 20 Hz to 1 MHz. The data have been critically analyzed in the form of complex dielectric function (ε*), ac conductance (σ*), electric modulus (M*), and impedance (Z*) of NPG spectra. The presence of the phenomena of electrode polarization and ionic conduction was explored based on a comparative analysis of the spectra of all the complex quantities. The T-dependence of various physical quantities such as static permittivity (ε_s), Kirkwood correlation factor (g_k), dc conductivity (σ_dc), time constant due to ionic conductivity relaxation (τ_σ), electrode polarization (τ_ep), and the activation energies have been determined using well-known Arrhenius law. It was found that on a log–log scale, the dependence of dc conductivity (σ_dc) on the structural relaxation time (τ_α) of pure NPG shows a linear behavior with a negative slope of unity; hence, it fulfills the Stokes–Einstein–Debye relation quite well. This suggests that temperature has no effect on the size of the molecular environment in which ions’ movement takes place.

Humidity sensors play a critical role in diverse applications. Therefore, high-performance humidity sensors based on titanium trisulfide (TiS₃) nanoribbons (NRs) were developed. TiS₃ NRs were synthesized and characterized thoroughly using morphological, structural, and chemical compositional techniques. Then, the humidity sensing performance of the fabricated TiS₃-based sensor was systematically evaluated. Key findings include a sensitivity of 0.50 kΩ/%RH, a relatively short response and recovery time of approximately 21 s and 12 s, respectively, along with excellent long-term stability, low hysteresis (1.96% RH), high repeatability, and reproducibility. The performance of TiS₃ NRs-based sensors in practice was tested using exhaled breath, and the results were satisfactory. The sensing mechanism is attributed to the adsorption and condensation of water molecules on the layered TiS₃ surface, followed by the formation of a conductive path by water molecules at high RH. The results underscore the significant potential of TiS₃ as a robust material for highly sensitive and stable humidity sensors.

This study investigates the size-dependent dispersion and slow-light phenomena in CdS@Ag core-shell quantum dot nanostructures embedded within various dielectric host materials. A comprehensive theoretical framework is developed by integrating the Maxwell-Garnett effective medium theory with the electrostatic approximation, alongside a size-corrected Drude model to characterize the metallic shell. This approach enables the accurate modeling of the effective dielectric function, polarizability, refractive index, and group velocity. Numerical simulations are conducted across a range of core radii, shell thicknesses, and host permittivities to systematically examine the influence of geometrical and environmental parameters on plasmonic resonances and pulse propagation dynamics. The results reveal two distinct, tunable surface plasmon resonances at the CdS/Ag and Ag/host interfaces, whose hybridization significantly alters the refractive index dispersion. Pronounced slow-light effects are observed in proximity to these resonances, including a reduction in group velocity by more than an order of magnitude and the emergence of negative group velocity regimes. These findings offer valuable insights into the geometry- and environment-dependent plasmon-exciton coupling mechanisms in core-shell quantum dots and provide guiding principles for the design of advanced nanophotonic devices such as optical delay lines, modulators, and plasmon-enhanced sensors.

In this study, we successfully resynthesized the compound 2-(3-methoxyphenylamino)-2-oxoethyl methacrylate (3MPAEMA) and characterized it using experimental spectroscopic methods and advanced computational analyses. Theoretical investigations encompassed Natural Bond Orbital (NBO) analysis, Band Gap (BG) calculations, Molecular Electrostatic Potential (MEP) mapping, and Density of States (DOS) evaluations, offering a comprehensive understanding of the molecule's electronic structure. We also employed thermochemical parameters, electronic descriptors, and Non-Covalent Interaction (NCI) analyses to assess the compound’s stability, reactivity, and intramolecular interactions. We performed toxicological profiling through in silico oral toxicity prediction models, validating model performance metrics. We conducted molecular docking and 50-ns molecular dynamics (MD) simulations to elucidate the binding behavior of 3MPAEMA with the oncogenic transcription factor STAT3, specifically targeting its SH2 domain. Docking studies revealed a strong binding affinity, while MD simulations confirmed the structural stability of the 3MPAEMA–STAT3 complex. Collectively, these results underscore the promising potential of 3MPAEMA as a STAT3-targeting agent in anticancer therapy. However, further in vitro and in vivo investigations must confirm its therapeutic potential. This comprehensive study offers valuable insights into the physicochemical, toxicological, and biological attributes of 3MPAEMA, supporting its candidacy for future biomedical applications.

The propagation of magnetosonic, nonlinear monotonic, and oscillatory shock structures in a homogeneous plasma with arbitrary degeneracy of electrons is investigated using a quantum magneto-hydrodynamic model (QMHD). The ions are classical, and dissipation in the system is taken through their kinematic viscosity. The electrons are degenerate, and their quantum effects through Bohm potential term are included. The reductive perturbation method is used to study the energy transfer mechanism, and the nonlinear Korteweg–de Vries–Burgers (KdVB) equation is derived for arbitrary degenerate plasmas. The different solutions of the KdVB equation are presented for monotonic and oscillatory shock structures in the presence of degeneracy of electrons. The effects of chosen values of equilibrium fugacity, electron temperature, magnetic field, and the corresponding electron density of a physical quantum plasma system on the height (intensity) of the monotonic and oscillatory shock structures are pointed out. These findings may be helpful to understand the excitation of magnetosonic shock wave phenomena in astrophysical, space, and fusion plasmas.