Brazilian Journal of Physics最新文献

The channel coupling effects of internal degrees of freedom like deformations of the interacting nuclei and vibrations have been accounted very well in fusion reactions. The neutron transfer channels with positive Q-values have resulted in the enhancement in the sub-barrier fusion cross-sections in various systems. However, there are few cases in which such effects are not observed, thus, remaining an open question for discussion and further studies. In this respect, the fusion cross-sections of the various combination of projectile - targets have been calculated and compared with experimental data using the coupled channel approach by employing CCFULL and ECC codes. Fusion excitation functions were calculated for (^{varvec{30}})Si + (^{varvec{58,62,64}})Ni and (^{varvec{32,34,36}})S + (^{varvec{58,64}})Ni systems using two different approaches to unravel the effect of different collective excitations and neutron transfer channels on the sub-barrier fusion cross-sections. Inclusion of coupling to the inelastic excitations in the calculations for (^{varvec{30}})Si + (^{varvec{62,64}})Ni, (^{varvec{32}})S + (^{varvec{58}})Ni and (^{varvec{36}})S + (^{varvec{64}})Ni systems explained the experimental data. The coupling to the transfer channels with positive Q-values along with the inelastic channels was incorporated in calculations and showed a significant influence on fusion cross-sections in (^{varvec{32,34}})S + (^{varvec{64}})Ni and (^{varvec{34,36}})S + (^{varvec{58}})Ni systems. Upon investigating the role of the two-neutron transfer channels (pick-up and stripping), it was concluded that in the case of (^{varvec{30}})Si, (^{varvec{34}})S, (^{varvec{36}})S + (^{varvec{58}})Ni systems, the coupling to the two-neutron stripping channel with positive Q-value showed a weak channel coupling effect in the sub-barrier region. For (^{varvec{32,34}})S + (^{varvec{64}})Ni systems, a two-neutron pick-up channel with positive Q-value showed a strong influence on the fusion cross-sections.

The Rayleigh-Taylor instability is a fundamental fluid instability of significant importance in various fields of physics, such as supernova explosions and nuclear fusion. It has been shown recently that an interface in a dusty plasma can be realized experimentally under microgravity conditions. This indicates that the Rayleigh-Taylor instability may occur at the interface of a dusty plasma. This study employs fluid dynamics models to theoretically analyze the Rayleigh-Taylor instability in dusty plasmas. The results show that the Rayleigh-Taylor instability in dusty plasmas not only depends on the number density of dust particles but also on the mass of individual dust particles. This result is different from previous studies, which show that the Rayleigh-Taylor instability depends on the mass density difference of the two fluids at the interface. By adjusting either the mass or the number density of dust particles in a dusty plasma, we can control the Rayleigh-Taylor instability in a dusty plasma.

We consider the radiation reaction experienced by a charge undergoing harmonic oscillations, and from a canonical transformation for the canonical moments, we present a new diagonalized Hamiltonian structure in the commutative and noncommutative spacetime. By using the path integral formulation, we obtained the partition function, which leads to the quantization of the system.

The present paper studies the formation and characteristics of dust-ion-acoustic solitary waves of small amplitude in a multi-component warm magnetized plasma having inertial positive and negative ions together with negatively charged static dusts under the influences of inertial elections, considering a three-dimensional fluid dynamical model with the Poisson equation. We consider a uniform external magnetic field along the z-direction, and the wave propagation occurs obliquely to the direction of the magnetic field. Precisely, the reductive perturbation method is applied to derive the Korteweg-de Vries equations and obtained the solitary wave solution to investigate the variations in wave nature caused by different physical parameters. This theoretical study shows the coexistence of compressive and rarefactive dust-ion-acoustic solitons in the plasma. Depending on Q (=negative-to-positive ion mass ratio) and various ion temperatures, compressive solitons for (Q<1) and rarefactive solitons for (Q>1) are shown to exist. Additionally, the domination of different physical parameters of our plasma on the propagation of oblique dust-ion-acoustic solitary waves is numerically analyzed within the paper. The present study might be helpful for better understanding the propagation of nonlinear electrostatic waves in laboratory and space plasma environments.

This study aims to synthesize of new type of nanocomposites based on polyvinyl alcohol(PVA)-polyvinyl pyrrolidone(PVP) bend doped with cerium oxide(CeO₂) nanoparticles to apply in various photonics and energy storage fields. The structural, optical, and electrical features of PVA/PVP/CeO₂ nanocomposites were examined. The results indicated that the optical absorption of PVA/PVP blend enhanced of 94.9% when the CeO₂ NPs concentration reached of 3 wt.% at wavelength of 260 nm. The energy gap of PVA/PVP blend decreased of 54.2% with rising CeO₂ NPs concentration to 3 wt.%. The other factors of optical properties enhanced with increasing CeO₂ NPs concentration. The electrical properties were investigated in frequency ranging from100 Hz to 5 MHz. The results showed that the dielectric constant and electrical conductivity are improved of 12.3% and 66%, respectively, at frequency of 1 kHz with rising CeO₂ NPs concentration to 3 wt.%. The elaborated optical and electrical improvements of the PVA/PVP blend would definitely introduce the PVA/PVP/CeO₂ nanocomposites as precious UV-shielding materials for a wide set of optoelectronics industry. The PVA/PVP/CeO₂ nanocomposites included excellent UV-absorption, low energy gap, and good physical and chemical properties compared with other nanocomposites.

Acoustic levitation is a method through which an object is suspended at a stable position against gravity by means of an acoustic radiation force produced by intense sound waves. This technique encompasses two different approaches: standing wave acoustic levitation and near-field acoustic levitation. Over the last few decades, the application of near-field acoustic levitation in the development of squeeze film bearings has been investigated by a number of researchers. In most works, the bearings were experimentally tested on a vertical test rig that could be tilted to control the radial load applied to the bearings. Besides, the dynamic modeling of the rotor-bearing systems was performed by considering the rotor as a rigid body. In this context, the present work proposes to develop a finite element model to investigate the dynamic behavior of a horizontal flexible rotor supported by two bearings, one of them being a squeeze film air bearing based on near-field acoustic levitation. The numerical results demonstrate that due to its limited load capacity, low damping, and small radial clearance, this type of bearing is recommended for use in light rotating machines with low unbalance level.

A theoretical investigation of dust acoustic shock waves (DAShWs) in a magnetized dusty plasma containing Cairns distributed electrons, inertial negatively and positively charged dust grains, and Maxwellian ions has been carried out. The Burgers equation is derived by employing the reductive perturbation method to examine the propagation of small but finite amplitude DAShWs. The effect of intrinsic parameters (viz. nonthermal parameter, the kinematic viscosity of the dust grains, number density of positive-to-negative dust, ion-to-negative dust number density, electron-to-ion temperature ratio, oblique angle) on the basic characteristics of DAShWs has been examined. The coexistence of shock structures with positive and negative potential is found. It has been found that the polarity of DAShWs depends on the ratio of electron-to-ion temperature as well as the number density of ion-to-negative dust. The results of this study could aid in understanding wave propagation in both laboratory and space plasmas.

In the presented research, a 2-D optical structure made of photonic crystals is presented. It is based on 30*28 arrays of silicon in medium made of air. Designed system is made of linear media (no nonlinear rods) for overcoming nonlinearity and gain problems. Applicability of designed system can be studied through extracting photonic band gap and field distribution spectra. Latter diagrams would be obtained by utilizing PWE and FDTD techniques. After applying incident light wave, signal can be propagated along the waveguide reaching outputs 1 or 2 according to the resonant wavelengths. Output1 can be considered for diagnosis of glucose levels in blood with Quality factor (Q): (122.72 – 132.5), Sensitivity (S): 1730 nm/RIU, detection limit (DL): (7.01e-4 – 7.15e-4) RIU and Figure of merit (FOM): (134.4 –142.5) RIU⁻¹. In another case, output2 can be considered for diagnosis of hemoglobin levels in blood with (Q): (106.56 – 112.8), (S): 1154.6 nm/RIU, (DL): (1.1e-3 – 1.2e-3) RIU, (FOM): (84.8–87.5) RIU⁻¹. As a result, designed structure would effectively aid researchers in prognosis of diabetes (Output1) and anemia (Output2). Diagnosis of anemia and diabetes (fast and with high precision) in a simple and applicable configuration (made of only linear rods) with considerable characteristics (sensitivity, DL, FOM and Q-factor) are the most important features of the proposed device.

In this article, the influence of the surface roughness (effective conductivity) on the open cavity of a gyrotron is analyzed and discussed theoretically. Based on electromagnetic field and wave theory, rough surface effects and metallic conductivity are analyzed considering terahertz cylindrical waveguides. The electromagnetic field distribution of a 360° cylindrical waveguide in TE₄₈ mode is divided into eight parts, and every part is TE₁₁ mode with 360/8° = 45° angle. The TE₁₁ mode was designed by analyzing the TE₄₈ mode. The electromagnetic field distribution of TE₁₁ mode on the radial surface of the sector waveguide is as one-eighth (45° angle) of the surface of the cylindrical waveguide in TE₄₈ mode. This cylindrical waveguide’s radius of TE₄₈ mode is 1.375 mm, for which the operating frequency is 1 THz. MATLAB tool is used to analyze the cylindrical waveguide’s field distribution profile and electrical field characteristics. The characteristics of the effective conductivity of different cavity-cutting materials on smooth surfaces and rough surfaces are studied through numerical simulations. The results indicate that the attenuation coefficient (α) decreases with a rise in frequency considering enhancement in the surface roughness and metal conductivity. TE₄₈ mode of the cylindrical waveguide and TE₁₁ mode of the sector waveguide are discussed through MATLAB analysis. By optimizing through CST simulation, better numerical simulation results are obtained. Overall, this article contributes to attaining the design of the 1 THz gyrotron and a clear understanding of surface roughness improvement for the cylindrical waveguides.

In this research, we designed and constructed a multi-channel logarithmic analyzer capable of simultaneously measuring nuclear events in mixed fields with both high and low energies. This analyzer is essential for microdosimetry, where continuous spectra in the range of (varvec{10^{-2}}) keV to (varvec{10^3}) keV must be observed. As the energy measurement range increases, the pulse height analysis range also expands, necessitating improvements in the analyzer’s performance for pulse height analysis. The use of high-voltage amplifiers and block sampling in this multi-channel logarithmic analyzer enables pulse height analysis up to (varvec{10^5}) mV. We validated the analyzer using a signal generator, observing spectra corresponding to pulse heights of (varvec{3times 10^0}), (varvec{3times 10^1}), (varvec{3times 10^2}), (varvec{3times 10^3}), and (varvec{3times 10^4}) mV in channels 394, 1208, 2030, 2849, and 3666, respectively. In simultaneous gamma-ray spectroscopy using Am-241 and Co-60 sources and pulses from a pulse generator with an amplitude of 32,000 mV, the designed logarithmic analyzer detected all energy peaks, whereas the linear MCA detected only some peaks. The logarithmic analyzer, with a 16-bit conversion gain in the (varvec{10^5}) keV energy range, provides optimal energy resolution compared to lower conversion gains and linear MCA.