Brazilian Journal of Physics最新文献

We reveal that inclusion of fission barrier, nuclear level densities, neutron and fission decay widths in a better way in the advanced statistical method and dinuclear system model can lead to reproduce well the measured production cross sections of the cold and hot fusion reactions in the range (Z=102-118). In addition, we show that the optimal beam energies, where the production cross section reaches its maximum, can also be effectively determined using quasielastic barrier distribution curves. This theoretical approach helps us to verify the cause of low production cross section measured for the super-heavy element (SHE) (^{278})Nh with the reaction (^{70})Zn + (^{209})Bi and null results from the reaction (^{86})Kr+(^{208})Pb used for synthesizing the SHE Z=118. Furthermore, the same has been employed to explore the reason for the failure of many trials in synthesizing the SHEs for (Z=119) and 120. ER cross sections at the optimal energies for a few heavy-ion reactions in synthesizing the SHE (Z=119) and 120 are seen to be measurable. Thus, the synthesis of the SHEs for (Z=)119 and 120 is on the cards.

The proposed model employs curvelet-based techniques to generate anisotropic Fractional Brownian Fields, simulating systems with orientation-dependent self-similar properties. Curvelets are a mathematical tool that allows for an efficient representation of data with edges and other anisotropic singularities, being essential for capturing the directional complexity in the self-similar properties of the modeled systems. The synthesis procedure involves generating coefficients in curvelet space with a zero-mean Gaussian distribution. This approach is tailored to depict the stochastic behavior of natural systems, particularly in scenarios where angular distributions of correlations are critical. The main contribution of this paper is presenting a novel method for generating 2-D anisotropic Fractional Brownian Fields (AFBFs) using the Curvelet Transform, demonstrating the Curvelet Transform’s efficiency in modeling anisotropic properties. Potential applications include modeling heterogeneous geological structures, anisotropic materials, and complex disordered media.

A single crystal of L-lysine iodide (LLI) was created by utilizing a room-temperature slow evaporation approach. The monoclinic of the crystal lattice system was confirmed by estimating the lattice parameters of the synthesized single crystals using single crystal X-ray diffraction analysis. The crystalline structure and planar indexing were confirmed by powder XRD. In order to confirm that the produced LLI crystals included functional groups, the FT-IR spectra were analyzed. Spectra of visible, near-infrared, and ultraviolet light (ranging from 200 to 1100 nm) were analyzed and the cutoff wavelength of 268 nm. Vickers microhardness tester was used to find out how strong the formed crystal was mechanically stable. From 50 Hz to 3 MHz, the dielectric response of the manufactured crystal was studied at different temperatures. Thermogravimetric analysis used to look at the thermal characteristics. Human pathogens were the primary focus of antimicrobial research. Using scanning electron microscopy (SEM), the surface characteristics of the generated crystal were examined. The produced LLI crystal was recommended for use in opto-electronic and biological applications.

Titanium oxide (TiO₂) nanoparticles (NPs) codoped with (La/Mn) ions were synthesized by a hydrothermal decomposition technique. The prepared codoped NPs were hydrogenated at 400 °C and systematically studied by X‐ray diffraction (XRD), optical diffuse reflection spectroscopy (DRS), and electrical insulating measurements. The codoped solid solution (SS) NPs were prepared to be built of core/shell-like electronic nanostructures that having giant permittivity (GP) of order 10⁴, which is extremely higher than that of undoped TiO₂. The electronic nature of the built structures was described according to the foundation of the doping mechanisms. Thus, the codoping was employed in the present work to fabricate coalesce dielectric crystalline medium of GP. Two Mn-dopant concentrations were used in the present investigation for comparison. Thus, the objective of creation of GP properties was successfully achieved. Moreover, the results of the electrical measurements were analyzed according to the available models: the correlated barrier hopping (CBH) model, the polarons-hopping conduction model, and Jonsher’s AC power law.

In an effort to further expand the simplification of the bulk production of carbon nanotube (CNT) foams, herein, a new approach based on one-step synthesis procedure is developed, where the production of the catalyst is followed by CNT foam growth in a chemical vapor deposition (CVD) furnace during acetylene decomposition over three various mole ratios of Fe: Mo: MgO: PEG (polyethylene glycol) sol-gel viscous precursor catalyst (viz., 1: 0.5: 13: 4.8, 1: 1: 13: 5, and 1: 1: 50: 17.3) under Ar/H₂ atmosphere at various reaction conditions. The growth of multi-walled CNT foams was directly carried out, i.e., without preceding any reduction and oxidation phases over viscous gels. The various parameters such as molar ratio, reaction temperature, and acetylene flow rate were optimized individually for the production of ultra-lightweight foamed CNTs. The CNT foams grown from the optimized reaction conditions were discussed by using various physicochemical characterization studies, such as XRD, FT-Raman, SEM, TEM, FE-SEM with EDX, N₂ sorption isotherms, and thermal analysis. The issues regarding the growth mechanism of high specific surface area CNT foams are taken in the present approach. Such a mechanism has been proposed for the carbo-thermal reduction of acetylene over the optimized viscous catalyst precursors gel at 800 °C in a CVD furnace.

We present the results of quantum Ising and longer range quantum Ising model for strongly correlated emergent Hamiltonian. We show explicitly that the ordered ferromagnetic (FM) phase to the disorder quantum paramagnet (dqpI) quantum phase transition occurs only in the strongly correlated regime for the quantum Ising model otherwise only dqpI phase appears for a non-interacting and attractive regime. We show that short-range FM coupling and longer range coupling are competing with each other and also the effect of strong correlation in this competition. We also show the most interesting feature that the transverse field opposes the FM coupling of quantum Ising model but it favours the longer range coupling. We find the evidence of another disorder quantum paramagnetic (dqpII) phase due to the relevance of longer-range coupling. We also present the existence of another quantum phase the transition from dqpII phase to the FM phase. We also observe three different kinds of coexistence phases depending on the correlated regime. The fixed point analysis of the three sets of RG equations is carried out.

For possible uses in the THz frequency range, we investigated the one-dimensional gyroidal superconductor photonic crystals in the current work. In this regard, each unit cell is designed from gyroidal Bi₂Sr₂CaCu₂O₈ (BSCCO) and SrTiO₃ layers. Here, BSCCO is embedded in a hosting dielectric medium of SrTiO₃ to design the gyroidal layer. The transfer matrix approach and the two-fluid model are both used in the computational analysis of the suggested structure. Studying the optical properties and investigating how several factors, including filling fraction, operating temperature, and layer thicknesses, affect the PC's performance. The results showed the emergence of the cutoff frequency at 5.35 THz. In this regard, the value of the cutoff frequency can be tuned based on the filling fraction, operating temperature, and refractive index of the hosting medium, making the structure promising for optical communication applications.

Two-dimensional graphene systems present considerable advantages for quantum information processing. Electrons within graphene possess not just spin but also additional attributes associated with their specific positions within the lattice and valley index. This study investigates how decoherence channels impact thermal quantum correlations within individual electrons in a two-dimensional graphene system, considering the electron pseudospin and valley index degrees of freedom. Using quantum metrics such as uncertainty-induced non-locality (UIN) and local quantum Fisher information (LQFI), this research evaluates skew-information and non-classical correlations among these extra degrees of freedom of electrons within the graphene system. The dynamics of the intra-particle quantum correlations in graphene’s thermal state is analyzed with respect to factors such as scattering strength, the band structure of graphene, and wavenumber operators. The findings suggest that adjusting the parameters of the graphene system holds promise for enhancing LQFI and UIN, thereby mitigating the adverse effects of increasing equilibrium temperature. Moreover, the study examines how intra-particle thermal quantum correlations evolve under various decoherence channels, including phase damping (PD), phase flip (PF), and amplitude damping (AD). It is observed that under AD and PD channels, both metrics display similar evolution, diminishing as the decoherence parameter increases, with LQFI demonstrating greater resilience compared to UIN. However, distinct behavior is observed when graphene’s thermal state undergoes the PF channel, where both metrics display symmetrical behaviors around the decoherence parameter of (p=0.5).

In this paper, the effects of hot pressing and cold pressing on the superconducting properties of pyrene (C₁₆H₁₀) added bulk MgB₂ were compared. For this aim, the polycrystalline disk-shaped MgB₂ samples with addition of 4 wt % C₁₆H₁₀ powder were fabricated by a pellet/closed tube method at 850 °C, after hot pressing at 200 °C and cold pressing. The XRD and SEM results showed that although a-lattice parameters reduce for both C₁₆H₁₀ added samples, the average crystallite size increases after cold pressing because of the accumulation and inhomogeneous distribution of C in the MgB₂ structure while it reduces for the C₁₆H₁₀ added hot pressed sample. The resistivity measurements showed that the increment of electron scattering is higher for the C₁₆H₁₀ added cold pressed sample than that of the C₁₆H₁₀ added hot pressed one which shows relatively better grain connectivity, and the T_c values of the samples are not appreciably affected by the pressing conditions. From the magnetisation measurements the in-field J_c values at 10 K and 5.5 T were obtained as 8.41 × 10³ A/cm², 1.62 × 10⁴ A/cm², 6.90 × 10³ A/cm² and the H_irr values while J_c = 100 A/cm² at 20 K were obtained as 5.99 T, 6.55 T and 6.19 T for the pure sample and the C₁₆H₁₀ added hot and cold pressed samples, respectively. The higher J_c and H_irr values obtained for the C₁₆H₁₀ added hot pressed sample is because of the homogenous C substitution into MgB₂ grains, as compatible with its lower Δρ value, and thus increased flux pinning ability.

This study investigates the thermoluminescence (TL) emission spectra of various doped CaF₂ materials after exposure to ionizing radiation. The understanding of the TL spectra of these single-doped materials, systematically produced under the same sintering conditions, contributes to the interpretation of complex TL spectra observed in naturally occurring fluorite crystals. The production of Ce³⁺, Tm³⁺, Tb³⁺, Dy³⁺, Er³⁺, Pr³⁺, Nd³⁺, and Yb³⁺ doped calcium fluoride was carried out using the combustion synthesis method. The emission spectrum lines could be ascribed to the RE transitions that occur when a trapped hole center recombines with a RE²⁺. Emissions range from the ultra-violet to the near-infrared. This study aids in tailoring new materials for specific applications and the matching of emitted light to specific filters and instrumentation used for detection.