Brazilian Journal of Physics最新文献

There is an experimental attempt to synthesize superheavy elements Z=120 at various labs. Superheavy nuclei are highly unstable and decay through channels such as alpha decay, spontaneous fission, cluster decay, and heavy particle decay. In this context, we have studied all possible decay modes for superheavy nuclei (^{302})120 using a Modified Generalized Liquid Drop Model (MGLDM). The half-lives produced by the present model are validated with experiments. By studying the competition between different decay modes, it is observed that the superheavy nuclei (^{302})120 shows alpha decay. The decay chain of (^{302})120 is presented. It undergoes three alpha decay chains and terminates with spontaneous fission. The present study is certainly useful in the synthesis of superheavy elements.

In the Amazonian region, where quartzose sand sediments are abundant, OSL dating provides a direct method for establishing the depositional timing of sediments, thereby aiding in understanding the Quaternary River dynamics of the area. This is particularly valuable in reconstructing past environmental changes, such as shifts in river courses, sedimentation patterns, and climate variations. The present study was conducted in the Mariuá Archipelago in the middle course of the Negro River (Western Amazon), a vital area for biodiversity preservation, focused on analyzing sediment samples collected on the river terraces and bars of the archipelago. These samples underwent analysis using optically stimulated luminescence (OSL) techniques specifically applied to quartz crystals found within the sediments. This allowed researchers to determine the ages of the sediments. The SAR OSL dating protocol, combined with a Central Age Model, was employed in the analysis, resulting in promising outcomes. The estimated average equivalent dose obtained from the analysis led to the determination of ages for various terraces and bars within the range of 0.41 to 135.1 ka. These age determinations provide valuable insights into the geological history and environmental changes that have occurred in the Mariuá Archipelago over millennia, contributing to the understanding of sedimentation, ecological evolution, and biodiversity dynamics.

In this paper, we consider the effect of a topological Maxwell term (W(Phi )F_{mu nu }tilde{F}^{mu nu }) on holographic transport and thermodynamics in 2 + 1 dimensions, in the case with a dyonic black hole in the gravity dual. We find that for a constant W the modifications to the thermodynamics are easily quantified, and transport is affected only for (sigma _{xy}). If one considers also the attractor mechanism, and writing the horizon transport in terms of charges, the transport coefficients are affected explicitly. We also introduce the case of radially dependent W(z), in which case, however, analytical calculations become very involved. We also consider the implications of the two models for the S-duality of holographic transport coefficients.

A series of novel lead free tungsten bronze (T-B) structured Ba₄(La_2-xBi_x)Fe₂Nb₈O₃₀(x = 0, 0.05, 0.1, 0.15, 0.2, and 0.25) were formulated by traditional high temperature solid-state method and calcined at 1200 °C. The structural property was investigated by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Tetragonal structure was confirmed from Rietveld analysis. The scanning electron micrograph (SEM) shows uniform distribution of rod-shaped grains with less porosity. The UV–vis analysis shows that the materials have band gaps in the range 2.17–2.29 eV which makes them useful for photocatalytic applications. The dielectric measurement of the samples was carried out in a broad range of frequency as well as temperature. The impedance of the materials falling off with the rise in temperature showing their negative temperature coefficient (NTCR) behavior. The variation of polarization with electric field confirms the ferroelectric nature of the samples.

The growing rate of bump-on-tail instability has been investigated in unmagnetized plasma with Cairns distribution. The growing rate depends significantly on the number density ratio n₁/n₂, temperature ratio T₁/T₂, and the nonthermal parameter α. The influence of these parameters on the maximum growing rate is analyzed numerically by using solar data. The higher α can enhance the growing rate of bump-on-tail instability. The maximum growth rate also will increase with the decrease of number density ratio n₁/n₂ and the increase of temperature ratio T₁/T₂. These interesting results will be helpful for understanding some phenomena in space plasma.

Random packing of binary mixtures of spherical particles in viscous fluid is numerically investigated via CFD-DEM, where moderate size ratios (d/D) are specially considered. Results indicate that binary packing in fluid is much looser than that in the absence of fluid, and two distinct phenomena can be identified as the global packing density varies with the volume fraction of coarse particle (X_D). For small size ratios, the global packing density first increases with increasing X_D due to the occupation mechanism, and then it reaches the maximum value when X_D ≈ 0.6, beyond which the global packing density decreases as X_D increases further. However, for large size ratios, the global packing density always decreases with increasing X_D. These phenomena are further discussed by using the local packing density determined by Voronoi tessellation, the mean and local coordination number, and radial distribution function, with which the particle arrangements within binary mixtures are well identified.

In this communication, the design of broad band optical reflector and selective polarization filter using a one-dimensional photonic crystal (1D-PC) containing superconductor and semiconductor layer has been proposed and investigated theoretically. The proposed design consists of alternate layers of yttrium barium copper oxide YBa₂Cu₃O₇ (YBCO) and silicon (Si), respectively. The refractive indices of YBCO and Si layers are modulated as the function of temperature and wavelength both. This characteristic brings this study closer to actual physical implementation. To obtain the reflectance and transmittance properties of the proposed structure and to analyze the propagation characteristics of electromagnetic waves, the transfer matrix method (TMM) has been employed. The analysis of the reflectance spectra shows that near the critical temperature of YBCO layers no broad band reflection (from 0 to 85°) is observed. On the other hand, when the temperature is lowered below the critical temperature, ODR arises. The proposed YBCO/Si structure gives a broad band reflection band (from 1394 to 1621 nm (bandwidth 227 nm)) for both TE and TM modes of polarizations at 85 K. Also, at higher incident angles, the proposed structure acts as a selective polarization-based filter without introducing any defect in the geometry.