物理最新文献

We consider a semi-classical approximation to the dynamics of a point particle in a noncommutative space. In this approximation, the noncommutativity of space coordinates is described by a Poisson bracket. For linear Poisson brackets, the corresponding phase space is given by the cotangent bundle of a Lie group, with the Lie group playing the role of a curved momentum space. We show that the curvature of the momentum space may lead to rather unexpected physical phenomena such as an upper bound on the velocity of a free nonrelativistic particle, bounded motion for repulsive central force, and no-fall-into-the-centre for attractive Coulomb potential. We also consider a superintegrable Hamiltonian for the Kepler problem in 3-space with (mathfrak {su}(2)) noncommutativity. The leading correction to the equations of motion due to noncommutativity is shown to be described by an effective monopole potential.

The sol-gel approach prepared Sr-doped BiFeO₃ samples using citric acid as fuel. The structure, lattice dynamics, magnetization, and dielectric properties have all been studied using various techniques, including the LCR meter for dielectric analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and vibrating sample magnetometer (VSM). X-ray diffraction (XRD) analysis of powdered Sr-doped BiFeO₃ shows the formation of a pure BiFeO₃ rhombohedral structure of the perovskite-type. The FESEM micrograph shows the morphology of the pallets of the samples unaffected by Sr doping at low concentrations. Vibrational modes surrounding the Fe–O–Fe stretching bonds are briefly described by FTIR spectra in transmittance mode. Moreover, it has been found that at room temperature, the dielectric constant and dielectric loss tangent of the samples, evaluated in the frequency range of 100–10⁷ Hz, decrease significantly. The magnetic investigation results indicate that the saturation magnetization is slightly enhanced with an increased concentration of Sr²⁺. The pristine BiFeO₃ had the lowest remanent magnetization value. The ions’ saturation magnetization and remanence magnetization values reached 1.85 emu/g and 0.88 emu/g, respectively, at x = 0.25.

The bonding between Bi₂Te₃ and Si wafers is prepared under low temperature through forming Si-O-Te and Si-O-Bi. Under the irradiation of vacuum ultraviolet, oxygen radicals and ozone are formed from oxygen molecules, which produces the thin oxide layers on the wafers’ surfaces. By absorbing water molecules and by dehydration-condensation reaction, the bonds of Si-O-Te and Si-O-Bi are formed. During the annealing process, Te atoms more easily diffuse into Si wafers than Bi atoms because the surface of Bi₂Te₃ is terminated with Te atoms. The layered crystal structure of Bi₂Te₃ weakens the bonding strength because only the surface layer of Bi₂Te₃ can bond with Si. The fabricated Bi₂Te₃/Si heterojunctions have the typical I-V curve of PN junctions.

The paper is devoted to the study of magnetic properties of magnetic colloids placed in porous media. The importance of this study is due to the development of new applications of such media. The paper presents the results of an experimental study of the temperature and frequency dependences of the magnetic susceptibility of magnetic colloids on different bases placed in a porous medium. For this purpose, a kerosene-based magnetic colloid and a water-based magnetic colloid were used. White electrocorundum was used as a porous medium. Magnetic susceptibility was studied by the bridge method in a wide range of frequencies and temperatures. It was found that the frequency and temperature dependences of magnetic susceptibility of bulk and magnetic colloids placed in porous media significantly differ depending on the pore size. The explanation of the obtained results is based on the assumption of the influence of surface forces on the relaxation processes of the magnetic moment of colloidal particles.

We study pseudoscalar (pi ), K and (eta ) meson properties, such as masses and couplings, in dense matter at zero temperature. We use a recently proposed phenomenological quark model, known as the PNJL0, which takes into account the confinement/deconfinement phase transition by means of the traced Polyakov loop ((varPhi )) which serves as an order parameter at zero temperature. We consider two different scenarios, namely, symmetric quark matter with equal chemical potentials for all the flavors, and the beta equilibrated matter. In the latter case the hadron-quark phase transition is implemented by a two model approach. For the hadron side we use a relativistic mean-field model with density dependent couplings. We show that (varPhi ) induces abrupt changes in the mesons properties with gap sizes regulated by the phenomenological gluonic sector of the model.

This article examines the cosmic evolution in the framework of symmetric teleparallel theory, characterized by the function of non-metricity scalar ((mathcal {Q})). We use the e-folding number and reconstruction method with a suitable parametrization of the scale factor to obtain the functional form of symmetric teleparallel theory. Using this reconstructed model, we examine the behavior of different cosmographic parameters to demonstrate the bouncing scenarios of the cosmos by considering the contraction and expansion phases of cosmos before and after the bouncing point, respectively. It is found that the null energy condition is violated which shows that the singularity issue can be resolved in this extended theoretical framework. Moreover, we observe that the acceleration occurs near the bouncing point and the reconstructed model aligns with the current cosmic expansion. Finally, we check the validity of second law of thermodynamics in the bouncing framework of our model.

Most commercially available phosphors are made from appropriately doped polycrystalline materials while the activation methods have often been examined, the impact of fuels on the host preparation and its effect on the final performance of the products has received less focus. This paper explores the use of various fuels in the synthesis of Dy-doped CaAl₂O₄ phosphors. Dysprosium-doped monoclinic CaAl₂O₄ phosphors were obtained at low temperatures (500 °C) by the process of combustion of the corresponding metal nitrate–fuel mixtures, over a period of 5 min. In this paper, attention has been paid to the influence of fuels on the luminescence properties of the phosphor sample which is prepared by solution combustion method. Dy-activated CaAl₂O₄ phosphor was synthesized by combustion technique using hydrazine, carbohydrazide, and urea as fuels. XRD analysis reveals that introducing a small quantity of rare earth ions into the raw materials did not alter the crystal structure of CaAl₂O₄. XRD result confirms the formation of the sample. Photoluminescence (PL) emission spectrum showed characteristic emission of Dy doped in the CaAl₂O₄ samples. The highest photoluminescence intensity was observed at a 0.02 mol% concentration of Dy. The PL spectrum exhibits wide peaks near 488 and 573 nm when excited at 347 nm. Mechanoluminescence (ML) and Thermoluminescence (TL) properties of the material have been emphasized. Various ML and TL curves have been recorded to assess which of the fuels yields the most efficient CaAl₂O₄: Dy compound. The prepared sample may be useful in TL dosimetry. In the present investigation it is found that urea is a better fuel for preparing CaAl₂O₄: Dy phosphors and enhances the ML and TL intensity of the sample.

Graphical abstract

PL emission spectra of CaAl2O4: Dy phosphors synthesized by urea, carbohydrazide and hydrazine, where urea provides the highest PL intensity, making it an optimal choice for enhancing optical performance.

Mineral oils are commonly used as cutting fluids; however, their use comes with the potential for soil contamination. Hence, vegetable oils could be a possible solution. Vegetable oils are currently investigated as potential environmentally friendly sources for cutting oils. However, significant improvements are needed to enhance the heat transfer rate of these conventional cutting oils for cooling purposes. Keeping in mind, the significance of the nanoparticles in heat transfer applications, the present research investigates the need for efficient and sustainable cutting fluids, analyzes the potential of vegetable oils as a base fluid, and considered palm oil as a base fluid with promising results for their prospective role as cutting, lubricating, and heat transfer fluids. (mathrm {Al_2 O_3})-NPs are suspended in the base fluid for heat transfer rate enhancement. More precisely, the present study examines the magnetohydrodynamic flow of a second-grade dusty nanofluid between two vertical plates. To formulate the flow phenomena, partial differential equations are employed. In contrast with the preceding published research, the governing equations of the fluid flow are transformed into a time-fractional model from their constitutive equations before dimensionalization by employing Fick’s and Fourier’s laws. The nondimensional fractionalized equations are solved by the joint application of the Laplace and Fourier sine transforms. However, Zakian’s numerical approach is employed to find the final solution of the velocity profile. Furthermore, the impact of different embedded physical parameters on temperature, concentration, and velocity profiles is calculated using Python software and visualized through graphs. Quantities of engineering interests, including skin friction, the Nusselt number, and the Sherwood number, are tabulated. It is worth mentioning that the fluid’s velocity diminishes with increasing (phi), (M), and (Re). An addition of (4%) (mathrm {Al_2O_3})-NPs significantly increases the heat transfer rate at the left plates to (7.89 %), respectively.

We report the smectic layer reorientation process in a surface-stabilized ferroelectric liquid crystal subject to the surface mode dominance at certain temperature and application of the controlled measuring field strength. The process is investigated by dielectric spectroscopy and optical textures analysis simultaneously in heating and cooling cycle. First the smectic layers are reoriented just 1–2 ^oC below T_c by applying a bias of 0.5 V as the material is soft here and cooled the sample to room temperature in absence of bias field which we call this a treated cell. In second type, the cell was taken to just above the T_c and taken the measurement in cooling cycle which we call an untreated cell. We have observed that there is a distinct molecular dynamic in the heating and cooling cycles of the material due to reoriented smectic layering and surface effect which assists the reorientation. It has also been observed that in heating cycles, the surface effect phenomenon is dominant, and in cooling cycles, it is weaker. Sometimes, the heating and cooling of the sample under electric field has been found affecting the optical performance of sample due to the readjustment of smectic layers. This study may clarify the control over the layer reorientation by surface effect and may open the possible application in displays and optical communication devices.

The new type of Fe_83 − xSi_2.5B₁₂P_2.5C_x (x = 0, 0.5, 1.0, 1.5, 2.0 at%) amorphous soft magnetic system with low cost, high saturation magnetization and low coercivity were designed and prepared by means of rapid quenching. The effect of C on the amorphous formability, thermal stability, and soft magnetic properties in the alloy system were studied. Results suggest that the addition of small atom C can promote the formation of densely atomic structure of alloy, thereby promoted the enhancement of amorphous formability. With the increase of C content, the temperature interval between two crystallization peaks increases first and then decreases. When C content is 1.0 at%, ΔT (T_x2-T_x1) reaches the maximum value, of about 109.9 ℃, which is beneficial to enhance the thermal stability and soft magnetic properties. As the concentration of C is raised, the B_s exhibit a pattern of increases followed by a subsequent decrease, while coercivity changes in the opposite way. When the C content is 1.0 at%, the B_s of the alloy reaches the highest value of 1.78 T and the coercivity exhibits the best which is 14.055 A/m. The results offer important contributions to the design and advancement of high B_s amorphous soft magnetic materials for industrial applications involving amorphous electric motors.