Brazilian Journal of Physics最新文献

Narrowband bandpass filters (BPFs) are in great need in future terahertz (THz) technologies to suppress EM signals beyond the operating band. THz filters and antennas play a crucial role in controlling and transmitting THz signals for the application of high data rate (6G) communication, non-destructive sensing, imaging, switching, and filtering. The proposed filtenna is designed using a dual-band THz BPF with a complementary split ring resonator (CSRR) metamaterial (MM). This paper suggests the circle in the pentagon (CP) filtenna and the simulation results show the filtering characteristics of two pass bands with resonant frequency (f_r) between 6.3 and 7 THz and between 8 and 9.8 THz with a squared ratio of 0.54. Also, the maximum 3-dB bandwidth (BW) of 1.3 THz, low return loss (RL) of −28.46 dB, and low insertion loss (IL) of almost 0 were attained. The proposed antenna radiates at the frequency of 6.8 THz with an RL of −27.72 dB. The proposed CP filtenna applies to various wireless communication, especially in drone-to-drone communication with excellent data rates.

The investigation of plasma waves and instabilities in the context of relativistic, anisotropic drifting astrophysical plasma is the focus of this study. Utilizing fluid equations in the linear regime, the research reveals the emergence of novel instabilities as a result of drift velocity. Furthermore, the study uncovers a modification in the condition for the mirror instability due to the drift velocity. These findings potentially hold significant implications for comprehending plasma behavior in space environments, particularly in regions like the solar wind or the interstellar medium. The study proposes the further development of the theory to directly apply to space plasma, which could enhance our understanding of the intricate astrophysical systems that are driven by plasma dynamics.

In this note, we calculate susceptibilities, as derivatives of a thermodynamical potential, for the general perturbative holographic setup for transport with magnetic field, charge density and topological term, and compare with the quantities obtained in the standard (AdS_4) dyonic black hole analysis of Hartnoll and Kovtun. We find that the results do not match, despite previous expectations.

The present study focuses on investigating the shape evolution of neutron-rich even-even osmium (Os) transitional nuclei within the range of neutron number N = 82 to N = 190. The investigation is conducted using density-dependent meson-nucleon and point-coupling models within the framework of the covariant density functional theory (CDFT). Additionally, the results obtained from the CDFT calculations are compared with those obtained using the relativistic mean-field model with a nonlinear meson-nucleon interaction. The potential energy curve for Os isotopes (ranging from (^{158})Os to (^{260})Os) is analyzed in order to identify phase shape transitions, such as oblate-spherical-prolate. Furthermore, ground state bulk properties are calculated to gain insights into the structure of Os isotopes. The self-consistent calculations reveal a clear shape transition in the even-even Os isotopes, and overall, good agreement is observed among the different models employed as well as with the available experimental data.

The present study aimed to investigate pure lithium tetraborate (LTB) and silver (0.2%) doped LTB obtained via the solid-state route. XRD results revealed that the pure sample consisted of LTB crystals, while doped samples comprised lithium tetraborate (Li₂B₄O₇), lithium triborate (LiB₃O₅), and Li₂B₄O₄, with an average crystallite size of about (40 ± 2) nm. TL (UV-VIS) analysis of LTB exhibited a peak at 125 °C, while doped samples supplied additional peaks at 205 °C, 315 °C, and 380 °C. LTB showed TL (UV) peaks at 120 °C and 210 °C, whereas doped samples exhibited peaks at 120 °C, 180 °C, and 295 °C. The TL response demonstrated a linear increase within the 0.081 to 5 Gy dose interval. Experimental TL glow curves could be fitted using a general order kinetics (GOK) model. TL emission spectra of LTB revealed bands at 330 nm and 580 nm, while LTB:Ag exhibited bands at 280 nm, 300 nm, and 584 nm. The presence of Ag substantially increased the TL intensity and introduced new peaks at high temperatures.

Intrinsic and chromium (Cr) doped zinc sulfide (ZnS) nanoparticles (NPs) have been synthesized by the co-precipitation method. The X-ray diffraction (XRD) studies reveals that the nanoparticles are crystalline in nature with cubic phase that have the (111) as preferential orientation. Even though the Cr ions have ionic radii greater than Zn, no significant modification in the crystal structure occurs as revealed by the XRD pattern. The doping induces a reduction in the peak intensities. The optical energy band gap values decrease and the Urbach exponential tail width increases with an increase in Cr level. When the dopant concentration is increased, the microstrain decreases and crystallite size increases. The surface morphology analysis has been carried out using scanning electron microscopy (SEM). The presence of the elements Zn, S, and Cr has been conformed using energy-dispersive X-ray spectroscopy (EDAX). The intensity that corresponds to Cr lines increases as the dopant increases with respect to Zn which is an evidence of the increased Cr level.

The organic single crystal of aniline-4-sulphonic acid (A4SA) was synthesized and grown by slow evaporation solution technique (SEST) using distilled water as a solvent. The lattice parameters of the grown crystal were confirmed by single-crystal X-ray diffraction analysis. The X-ray diffraction exposes that the A4SA crystal belongs to an orthorhombic system with space group Pca2₁. Functional groups of A4SA crystal were confirmed by Fourier transform infrared (FTIR) and FT-Raman spectrum analyses. The optical quality of the grown crystal was identified by the UV-Visible NIR spectrum analysis. The grown crystal has good optical transmittance in the range of 300–900 nm. The photoconductivity analysis was carried out to calculate the photo and dark current values. Photoconductivity study indicates that A4SA crystal shows a negative photoconductivity nature. Intermolecular interactions of A4SA are executed by the Hirshfeld surface analysis. The chemical etching was investigated to calculate the etch pit density. Photoluminescence analysis for grown crystals is obtained. Thermogravimetric, differential thermogravimetric analysis and differential scanning calorimetry (TG, DTA, DSC) measurements investigate the thermal stability of a grown crystal. Vickers microhardness analysis was performed to study the mechanical properties of the material. The Nd:YAG laser, with a wavelength of 1064 nm, was used to examine the LDT analysis. It shows a good LDT value of 5.02 GW/cm². The third-order non-linear susceptibility was measured and analysed by Z-scan technique using (He–Ne) laser of wavelength 632.8 nm.

It is generally known that the production of SHE is hampered by the quasifission (QF) and fusion-fission (FF) lifetimes. So, utilizing nucleus-nucleus potential, we looked into the quasifission durations and fusion-fission lifetimes of seven fusion reactions. For the fusion process of (^{58})Fe+(^{244})Pu, the quasifission and fusion-fission lifetimes of 8.4 zs and 92.4 as, respectively, are found to be longer. The optimal energies at which maximum cross-sections of fusion, quasifission, fusion-fission, and evaporation residue exist have been reported. The fusion reactions of (^{51})V+(^{249})Bk show a greater evaporation residue cross-section, whereas (^{55})Mn+(^{243})Am show a smaller cross-section. Therefore, thorough research as well as optimal energies, quasifission lifetimes, and fusion-fission lifetimes provide insight into the formation of SHE Z=120.

The present work deals with the study of the effect of temperature on the Raman spectroscopy and electrical properties of the silicon nanowires. The nanowires are fabricated through silver assisted electrochemical etching process. Prior to these studies, the fabricated nanowires are characterized through field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM), and X-ray diffraction (XRD) measurements. FESEM reveals the vertical alignment of the nanowires. FETEM indicates the materials to be highly crystalline, which is also complemented by the XRD result. Raman peak is blue-shifted with a decrease of temperature suggesting lattice disturbance at low temperature. Temperature-dependent current-voltage (I-V) measurements are fitted with Cheung’s model and the characteristic parameters viz. ideality factor (n), barrier height (ϕ_b), and series resistance (R_s) are estimated from the fitted plots. At lower temperatures, the value of n highly deviates from the ideal value of unity and is 23.42 at 110 K. The materials are observed to obey space charge limited conduction (SCLC) to trap charge limit current (TCLC) with increasing bias at lower temperatures.

In this study, TiO₂-ZnO:Yb³⁺/Ho³⁺ upconversion phosphors are synthesized by a solid-phase reaction method and their Yb³⁺ concentration dependence is analyzed. The crystal structure of the phosphors is analyzed by X-ray diffractometry, where each sample is composed of Zn₂TiO₄ and Yb₂Ti₂O₇. Photoluminescence characteristics are analyzed and peaks are observed at wavelengths of 539 nm (⁵F₄, ⁵S₂ → ⁵I₈) and 669 nm (⁵F₅ → ⁵I₈). High intensity luminescence is obtained for samples with Yb = 7–8 mol%. Analysis of temperature characteristics shows absolute and relative sensitivities of 0.0052 K⁻¹ and 0.40% K⁻¹, respectively. The samples are found to be chemically stable, indicating that TiO₂-ZnO:Yb³⁺/Ho³⁺ could be used as a temperature sensor.