Brazilian Journal of Physics最新文献

This study investigates the synthesis and photocatalytic performance of α-Fe₂O₃–graphene oxide (GO) nanocomposites with varying GO contents (15, 30, and 45 mg) for the degradation of p-nitrophenol (PNP) under ultraviolet (UV) and Xenon light irradiation. The structural, morphological, optical, and magnetic properties of the nanocomposites are comprehensively characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Raman spectroscopy, UV–Vis spectroscopy, and vibrating sample magnetometry (VSM). Initially, α-Fe₂O₃–30GO demonstrates the highest photocatalytic efficiency under Xenon light (36.26%), attributed to enhanced surface area and improved charge separation. Meanwhile, α-Fe₂O₃–45GO exhibits degradation under UV light with 30.50% PNP removal. Surprisingly, long-term analysis after 21 days of dark rest reveal a significant increase in PNP degradation across all samples, for α-Fe₂O₃–15GO (90.93 and 97.40), α-Fe₂O₃–30GO (93.24 and 95.67), and α-Fe₂O₃–45GO (58.21 and 26.92) after UV and Xenon pre-treatment, respectively. This delayed degradation suggests persistent reactive species or slow adsorption–desorption dynamics that continue pollutant breakdown even in the absence of light. Magnetic characterization shows that the nanocomposites exhibit weak ferromagnetic behavior. Coercivity values are notably high for hematite-based systems and decreases with increasing GO content. The combination of photocatalytic activity and GO-modulated magnetic properties suggests that α-Fe₂O₃–GO nanocomposites are promising multifunctional materials for further investigation in environmental technologies. This work demonstrates, for the first time, that α-Fe₂O₃–GO nanocomposites not only act as environmentally friendly photocatalysts for p-nitrophenol removal but also sustain significant long-term degradation under dark conditions, highlighting their potential for practical and sustainable water treatment applications.

Finding the minimum value in a large unstructured database is a common and fundamental task in computer science with broad applications across science and industry. However, the optimal classical deterministic algorithm can find the minimum value with a time complexity that grows linearly with the number of elements in the database. In this paper, we present the proposal of a quantum algorithm for finding the minimum value of a database, which is quadratically faster than its best classical analogs. We assume a quantum random access memory (QRAM) that stores values from a database and performs an iterative search based on an oracle whose role is to limit the searched values by controlling the states of the most significant qubits. We provide a detailed description of the quantum circuit implementation, analyze its complexity, and demonstrate a significant computational advantage, particularly for large-scale datasets. In addition, a complexity analysis was performed in order to demonstrate the advantage of this quantum algorithm over its classical counterparts. Thus, the presented quantum minimum search (QMS) algorithm represents a promising tool for practical computing scenarios, offering a robust foundation for further research into fault-tolerant quantum algorithms.

We employ extensive NPT molecular dynamics simulations to explore the thermal transitions of two-dimensional colloidal crystals interacting via a core-softened potential with competing length scales. The system stabilizes three distinct solid phases, namely low-density triangular (LDT), stripe, and kagome, which exhibit markedly different responses to heating and cooling. Our simulations reveal that the LDT and kagome phases melt via first-order transitions, but only the former recrystallizes smoothly. The kagome phase displays strong hysteresis and metastability, while the stripe phase undergoes a continuous and nearly reversible transformation. These results highlight the role of lattice geometry and frustration in shaping non-universal melting and freezing pathways in 2D soft matter.

A topological insulator (TI) is characterized by its band inversion (in its bulk) which is caused by the strong spin-orbit interaction and an exotic metallic state in its surface. In this work, using a DFT study, we prove that (Bi_2Te_3) has a band inversion in its bulk form and becomes conducting in its surface. The existence of single band inversion is analyzed with PBE and TB-mBJ potential taking spin-orbit interaction into consideration. The metallic surface state is confirmed with the PBE and LmBJ potential. The LmBJ potential enables the study of heterogeneous, finite, and low-dimensional systems and has not been studied yet for (Bi_2Te_3). We also prove that (Bi_2Te_3) is a ( mathbb {Z}_2 ) topological insulator from the ( mathbb {Z}_2 ) invariant calculation by computing an evolution of hybrid Wannier charge centers.

Our experimental study has focused on exploring visible random lasing phenomena in disordered active XFJ151-magnetic mesoporous silica nanoparticle thin films under optical pump excitation. The results reveal that the random lasing characteristics, which stem from multiple light scattering within these systems, generate lasing spectra associated with plasma excitation and localized photon fields. This mechanism facilitates lasing behavior at visible wavelengths. Furthermore, variations in emission intensity and shifts in the lasing threshold observed in these films are attributed to differences in photon localization intensity across random microcavities at distinct wavelengths. These lasing features originate from the confinement of laser microcavity modes due to photon localization within the active XFJ151-magnetic mesoporous silica nanoparticle thin film.

This paper presents a four-port multiple-input-multiple-output (MIMO) antenna, which has dimensions of 108 μm × 104 μm × 2.84 μm, with improved isolation and operating across multiple terahertz (THz) frequency bands. The antenna design supports triple-band operation at resonant frequencies of 6.7 THz, 7.8 THz, and 9.1 THz, and to improve isolation, vias are loaded around the resonating patch. The MIMO antenna experiences mutual coupling issues at THz frequencies, which is due to shorter wavelengths. The substrate integrated waveguide (SIW) ensures excellent signal transmission while reducing unwanted coupling between antenna elements. Also, multi-layering is used by placing a rectangular truncated patch between two substrates to enhance the gain, resulting in a peak gain of 10.8 dBi. The proposed design is a viable option for use in THz MIMO antenna systems that require improved isolation and gain. It may be suitable for multiband THz communications, including wireless body area networks, sensing and imaging, and the Internet of things applications.

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.