Modern Physics Letters B

In this paper, an impulsive Kolmogorov-type system using the Caputo fractional-order derivative is developed. The fractional-order system displays many interesting dynamic behaviors and fractional integrals can be used to describe the fractal media. The existence and stability of integral manifolds for the impulsive fractional model are considered. The main results are proved by means of piecewise continuous Lyapunov functions and the new fractional comparison principle. The impulses are realized at variable impulsive moments of time and can be considered as a control. Finally, an example is given to illustrate our results.

In this paper, doped bismuth ferrite nanoparticles with barium (Bi${}_{1-x}$Ba${}_x$FeO${}_3$, $x$ = 0.1, 0.15, 0.2) were synthesized by co-precipitation method in the presence of various surface activators. Structural properties, magnetic properties and the size of synthesized nanoparticles were investigated by different techniques such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), dynamic light scattering (DLS) and vibration sample magnetometry (VSM). The data obtained from XRD analysis showed a phase shift from rhombohedral to tetragonal structure by the enhancement of Barium amount in Bismuth ferrite structure. The results of TEM exhibit that the size of particles are 10 nm in average for the synthesized Bi${}_{0.85}$Ba${}_{0.15}$FeO${}_3$ and SEM analysis clarifies the uniform shape of particles which confirms the benign purity of the obtained material. VSM analysis shows that the best magnetic function will be observed when stoichiometric amount of Barium (Bi${}_{0.85}$Ba${}_{0.15}$FeO${}_3)$ is $x$ = 0.15. The effect of diverse surface activators including Triton X-100, polyvinyl alcohol (PVA), sodium dodecyl sulfate (SDS), and cetyl trimethylammonium bromide (CTAB) was studied in the synthesis of Bi${}_{0.85}$Ba${}_{0.15}$FeO${}_3$ nanoparticles and CTAB presented the best effect on the magnetic properties of these nanoparticles.

Equilibrium geometries, relative stabilities, electronic stabilities and magnetic properties of Co${}_n$Sn ($n$ = 1–12) clusters have been systematically investigated by using relativistic all-electron density functional theory with generalized gradient approximation. The results indicated that the lowest-energy structures of Co${}_n$Sn ($n$ = 1–5, 7, 9 and 10) clusters are similar to those of corresponding Co${}_{n+1}$ clusters. As for Co₆Sn, Co₈Sn, Co${}_{11}$Sn and Co${}_{12}$Sn clusters, the most stable structures give rise to a geometry reconstruction. In the low-lying structures of Co${}_n$Sn ($n$ = 1–12) clusters, tin impurity prefers to occupy the external site. The second-order difference energy of the ground-state Co${}_n$Sn ($n$ = 1–12) clusters shows a pronounced odd–even oscillation with the number of Co atoms, and the clusters exhibit higher stability at $n$ = 5. Compared with corresponding pure Co${}_{n+1}$ clusters, the total magnetic moment of the Co${}_n$Sn clusters reduces with 1, 3 and 5 ${\mu }_B$, respectively. The different magnetic changes of the tin doped Co clusters are analyzed in detail based on the magnetism coupling, density of state and hybridization between cobalt and tin atoms.

The charge densities, band structure, density of states, dielectric functions of Si-doped $\beta$-Ga₂O₃ have been investigated based on the density functional theory (DFT) within the hybrid functional HSE06. The heavy doping makes conduction band split out more bands and further influences the band structure. It decreases the band gap and changes from a direct gap to an indirect gap. After doping, the top of the valence bands is mainly composed by the O-2p states, Si-3p states and Ga-4p states and the bottom of the conduction bands is almost formed by the Si-3s, Si-3p and Ga-4s orbits. The anisotropic optical properties have been investigated by means of the complex dielectric function. After the heavy Si doping, the position of absorption band edges did not change much. The slope of the absorption curve descends and indicates that the absorption became more slow for Si-doped $\beta$-Ga₂O₃ than undoped one due to the indirect gap of Si-doped $\beta$-Ga₂O₃.

In this paper, potassium sodium niobate (KNN) nanopowders were successfully obtained by sol–gel combustion method. According to thermogravimetric analysis (TGA) results, the produced xerogel was calcined at 500${}^{\circ }$C, 600${}^{\circ }$C, and 700${}^{\circ }$C to obtain KNN powders. The structural and optical properties of the prepared powders were studied using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), and UV–vis spectroscopy. The XRD patterns indicated formation of orthorhombic KNN samples. The Scherrer formula and size–strain plot (SSP) method were employed to calculate crystallite size and lattice strain of the KNN powders. The TEM image revealed that the average particle size of the prepared samples is about 30 nm and they have cubic shape. The optical band gap energy of the samples was calculated using UV–vis absorbance spectra of the samples along with Tauc relation.

Perfect metamaterial absorber (MA)-based sensor applications are presented and investigated in the microwave frequency range. It is also experimentally analyzed and tested to verify the behavior of the MA. Suggested perfect MA-based sensor has a simple configuration which introduces flexibility to sense the dielectric properties of a material and the pressure of the medium. The investigated applications include pressure and density sensing. Besides, numerical simulations verify that the suggested sensor achieves good sensing capabilities for both applications. The proposed perfect MA-based sensor variations enable many potential applications in medical or food technologies.

Three-component pillared phononic crystal plates (PPCPs) usually contain viscoelastic materials. The influence of viscoelasticity on the band structures cannot be ignored. Based on the finite element method (FEM) and the standard linear solid model, this paper proposes a method to obtain the band structures of three-component PPCP containing viscoelastic rubber. The influence of the rubber storage modulus shifting along with frequency on the vibration band gaps is investigated, and the band structures of loss factor under different relaxation time are obtained.

An adaptive Harris corner detection algorithm based on the iterative threshold is proposed for the problem that the corner detection algorithm must be given a proper threshold when the corner detection algorithm is extracted. In order to avoid the phenomenon of clustering and restrain the pseudo corner, this algorithm realizes the adaptive threshold selection by iteration instead of the threshold value of the Harris corner detection algorithm. Simulation results show that the proposed method achieves good results in terms of threshold setting and feature extraction.

In this paper, PE100 pipes with the diameter of 200 mm and the thickness of 11.9 mm were used as material. The welded joints were obtained in different welding pressures with the optimal welding temperature of 220${}^{\circ }$C. Reheating process on the welded joints with the temperature of 130${}^{\circ }$C was carried out. The joints exhibited X-type, and the cause of X-type joints was discussed. The temperature field in the forming process of welded joints was measured, and tensile and bending tests on welded joints were carried out. The fracture surface of welded joints was observed by scanning electron microscopy (SEM), and crystallinity calculation was taken by X-ray diffraction (XRD). The mechanism of X-type weld profile effects on welded joints properties was analyzed. It was concluded that the mechanical properties of welded joints decrease with the reduced X distance between lines.

The paper studies the dynamics of optical solitons in $(n+1)$-dimensional nonlinear Schrödinger equation with Kerr and power law nonlinearities that describe the propagation of light pulses in optical fibers. First time the dark and singular optical solitons are extracted in $(n+1)$ dimensions. The $(G^{\prime }/G)$-expansion scheme is used to analyze these solutions. Additionally, the constraint conditions for the existence of the solutions are also listed. However, the scheme fails to retrieve the bright soliton.