Brazilian Journal of Physics最新文献

The Neutrinos Angra Experiment, a water-based Cherenkov detector, is located at the Angra dos Reis nuclear power plant in Brazil. Designed to detect electron antineutrinos produced in the nuclear reactor, the primary objective of the experiment is to demonstrate the feasibility of monitoring reactor activity using an antineutrino detector. This effort aligns with the International Atomic Energy Agency (IAEA) program to identify potential and novel technologies applicable to nonproliferation safeguards. Operating on the surface presents challenges such as high noise rates, necessitating the development of very sensitive, yet small-scale detectors. These conditions make the Angra experiment an excellent platform for both developing the application and gaining expertise in new technologies and analysis methods. The detector employs a water-based target doped with gadolinium to enhance its sensitivity to antineutrinos. In this work, we describe the main features of the detector and the electronics chain, including front-end and data acquisition components. We detail the data acquisition strategies and the methodologies applied for signal processing and event selection. Preliminary physics results suggest that the detector can reliably monitor reactor operations by detecting the inverse beta decay induced by electron antineutrinos from the reactor.

Silver-carbon (Ag/C) composite films were successfully fabricated on PET/ITO substrates using a novel two-step electrochemical deposition method. The impact of silver concentration on the structural, optical, and electrical properties of the films was systematically investigated. Scanning electron microscopy (SEM) revealed a heterogeneous film structure, with carbon conforming to the underlying silver morphology, which varied with silver concentration. Higher silver concentrations resulted in larger and denser silver structures. Optical characterization demonstrated that the addition of carbon significantly enhanced transmittance, particularly at lower silver concentrations, making these films promising candidates for transparent conductive electrodes. Both Ag and Ag/C films exhibited ohmic behavior, as evidenced by linear current–voltage (I-V) characteristics. Ag/C films showed superior conductivity compared to pure Ag films, attributed to the contribution of the carbon layer to electron transport. Hall measurements further confirmed the enhanced electrical properties of Ag/C films, revealing lower sheet resistance and resistivity compared to Ag films. The improved homogeneity of Ag/C films, due to the incorporation of carbon, is beneficial for achieving uniform electrical properties. These findings highlight the potential of electrochemically deposited Ag/C composites for various technological applications, including flexible electronics, optoelectronics, sensors, and energy storage devices.

A new toroidal capacitive discharge plasma (TCDP) system is designed and constructed for the first time to our knowledge. This device has been created for the exploration of plasma-material interactions including metal and semiconductor samples for different pressure rates. By using two materials, namely copper (Cu) and tungsten (W), initially, electrode couples have been tested for high-voltage DC excitations. The reactions of electron material to the low-pressure helium (He) have been observed. Then, Paschen’s curve exploration has been performed to find out the gas discharge threshold electrical potentials for various pressure (P) rates. The simulations of TCDP device have been performed in a particle in cell (PIC) analyzed 3D structure in the CST Studio medium for various excitation frequencies and toroidal/poloidal field values. It is observed that the breakdown voltage for He is U_B = 500 V. The DC excitation via the electrodes reveals that the torus-structured plasma gas media produces a stable torus-shaped media for plasma formation. Besides, toroidal and poloidal fields affect the plasma stabilization in the TCDP. Especially toroidal field coils in TCDP assist in keeping the plasma in the middle of the torus channel. According to the experiments, the poloidal fields increase the electric field strength in the angular direction and improve the electrical stability of the plasma between the electrodes.

Massive stars in the pre-supernova stage are characterized by a compound core of chemical elements of the iron group, subject to nuclear reactions provided by the weak interaction. The rates at which these reactions occur, particularly the (varvec{beta })-decay and the electron capture, influence the electron fraction in the core, and these particles are responsible for generating a degeneracy pressure that counteracts the gravitational collapse. We calculate electron capture and (varvec{beta }^-)-decay rates for a set of (textbf{63}) nuclei (previously adopted in Dimarco et al., J. Phys. G Nucl. Part. Phys. 28 121 2002) of relevance in the pre-supernova stage for transitions not only from the ground state but also considering first excited states in the parent nucleus, using the gross theory of beta decay (GTBD) associated to Brink’s hypothesis. The evolution of the electron fraction has been calculated using these weak interaction rates, and the results have been compared with other models, showing that transitions between low-lying first excited states and Gamow-Teller resonances can contribute at this stage of stellar evolution as the temperature and density increase.

In this study, an electric field (E^*) has been used to tune the disorder structures of complex plasmas (CPs) using molecular dynamics (MD) simulations. The ψ(τ) (lattice correlation) and RDF (radial distribution function) are computed for CPs under the presence and absence of different E^* intensities to analyze structures. The influence of E^* strengths, coupling (Γ), and screening length (κ) on structure transitions is investigated. Without E^*, MD simulation results for ψ(τ) and RDF indicated self-organization of dust particles with increasing Γ and decreasing κ. Additionally, CPs subjected to higher E^* intensities exhibited signs of condensation and solidification. Achieving solidification required a significantly higher E^* intensity for disordered structures (nonideal gases), whereas liquid-like or nearly solid-like structures required intermediate to low E^* intensities. Moreover, to induce crystalline long-range order in the presence of E^*, by keeping the Γ constant, higher values of κ required a larger E^*. It was observed that CPs exhibited behavior akin to conventional electrorheological fluids in the presence of E^*. This characteristic renders CPs valuable for investigating electrorheological properties in soft and condensed matter physics.

The utilization of optical directional couplers has emerged as a viable alternative to conventional systems for the execution of error detection using optical signals. The proposed circuit efficiently converts 4-bit binary input signals to gray code representation in the optical domain, reducing errors during transmission and computation. An even/odd parity checker module is also included in the circuit, which improves data integrity and detects single-bit errors in transmitted data. The theoretical basis for the electro-optic effect and its use in directional couplers (EODC) for optical signal transmission inside the proposed circuit. The framework for sophisticated efficient photonic circuit designs with improved error detection and correction capabilities is laid by using EODC, which simplify design and enable seamless integration with existing optical communication technologies. The proposed device layout is made of (GaAlAs) material produced from a (3mu mtimes 3um) modulator. The coupling length ({(L}_{C})) of the device is set to ({L}_{C}=1text{ cm}). The EODC performs perfect switching with a light wavelength of (900text{ nm}) by creating a refractive index change ((Delta n)) of approximately (Delta ncong 1times {10}^{-4}). An electric field magnitude of approximately (3times {10}^{4}text{ V}/text{cm}) is required to achieve this switching, which corresponds to a voltage of 10 V applied across the electrodes of an EODC over a (3 mu text{m}) channel.

We performed a thorough investigation of the structural, mechanical, electrical, and optical characteristics of the lead-free perovskite Cs₂LiInBr₆ by employing the Density Functional Theory (DFT) methods. Our analysis included the use of GGA-PBE and HSE06 functionals. Our results validate that Cs₂LiInBr₆ forms a cubic Fm̅3m space group with a lattice constant of 11.09 Å, which is consistent with earlier theoretical and experimental investigations. The material possesses a direct bandgap at 1.50 eV and 2.34 eV, calculated by GGA-PBE and HSE06 methods respectively. This shows that the material is suitable for solar cell and optoelectronic applications. Finally, the substantial UV and visible region absorption (90,455 cm⁻¹ with GGA-PBE) observed for Cs₂LiInBr₆ makes it an attractive material for solar applications. The moderate level of compressibility and ductile nature of the mechanical properties further validate the structural integrity of Cs₂LiInBr₆. The details of the physical properties including mechanical, electrical, optical, and structural features suggest that Cs₂LiInBr₆ is a promising material for photovoltaic as well as optoelectronic applications.

It is imperative for many problems of physical interest to incorporate the geometrical curvature. Examples include plasma physics, oceanography, nonlinear optics, and laser-driven systems. Therefore, we consider planar wave propagation in a cylindrical geometry in light of the aforementioned applications, and the propagation is considered solely in the radial direction. Using the small amplitude perturbation approximation, the cylindrical Korteweg-de Vries (CKdV) equation is obtained using multiple-scale analysis to study nonlinear ion-acoustic waves in a dense plasma with electron trapping by incorporating the effects of the quantizing magnetic field and the smearing effects of the Fermi distribution function. The Bäcklund transformation is employed to obtain single and multiple soliton solutions of the CKdV equation, which are found to be very different from the planar KdV equation. A general mathematical framework is also presented to find the N-soliton solutions. The effects of the quantizing magnetic field and finite electron temperature on the structure of the cylindrical ion-acoustic solitons are also explored using the parameters representative of white dwarf stars. This research endeavor is expected to trigger interest in the plasma community to pursue this fascinating and abstruse research direction.

We conducted a review of the fundamental aspects of describing and detecting the baryon acoustic oscillation (BAO) feature in galaxy surveys, emphasizing the optimal tools for constraining this probe based on the type of observation. Additionally, we included new results with two spectroscopic datasets to determine the best-fit model for the power spectrum, P(k). Using the framework described in a previous analysis, we applied this to a different sub-sample of the BOSS survey, specifically galaxies with redshifts (0.3<z<0.65). We also examined the eBOSS dataset with redshifts (0.6<z<1.0), adjusting the number of parameters in the traditional polynomial fit to account for the higher redshift range. Our results showed that the dilation scale parameter (alpha ) derived from the BOSS dataset had smaller error bars compared to the eBOSS dataset, attributable to the larger number of luminous red galaxies (LRGs) in the BOSS sample. We also compared our findings with other surveys such as WiggleZ, DES Y6, and DESI III, noting that photometric surveys typically yield larger error bars due to their lower precision. The DESI III results were in good agreement with ours within (1sigma ), with most bins close to unity. The variation of (alpha ) with respect to the redshift is an unresolved issue in the field, appearing in both three-dimensional and angular tomographic analyses.

In this paper, we investigate how the geometrical parameter of spheroidicity, which quantifies the deviation from spherical symmetry, influences the complexity of self-gravitating, static systems. We employ the concept of complexity in self-gravitating systems as formulated by Herrera et al. (Phys. Rev. D 97, 044010, 2018) and apply it to various models of compact stellar structures, all set within the framework of the Vaidya-Tikekar (VT) background geometry. Specifically, we analyze three models: (i) the anisotropic compact stellar model by Das et al. (Gen. Relativ. Gravit. 52, 101, 2020), constrained by the Karmakar condition, (ii) the stellar model by Das et al. (Eur. Phys. J. C 84, 13, 2024) employing the VT metric ansatz under the vanishing complexity condition, and (iii) the compact stellar model using a polytropic equation of state with the VT metric ansatz (Baskey et al., New Astron. 108, 102164, 2024). These models were selected based on whether their solutions are complexity-free or not. We establish a connection between the complexity factor and the spheroidal parameter to analyze how pressure anisotropy and density inhomogeneity, as constituent components, are influenced by this geometric parameter. Our findings indicate that deviations from spherical symmetry lead to a marked increase in the complexity of the stellar structure for all the models based on VT metric ansatz. Moreover, our results indicate an inconsistent pattern in the dependence of the complexity factor ((varvec{Y}_{varvec{TF}})) and its components on spheroidicity ((varvec{K})), demonstrating that this relationship is both model-dependent and is not generic.