New Research in Physics

Abstract In the present paper, electron acceleration by a laser pulse propagating through plasma has been studied in the simultaneous presence of a helical wiggler and an obliquely external magnetic field. To obtain the electron energy and electron trajectory, a relativistic single particle code has been used based on the fourth-order Runge-Kutta method. Numerical results indicate that electron energy increases with decreasing θ-angle of obliquely external magnetic field. Besides, it enhances with increasing the laser intensity in the absence of the wiggler field, whereas it increases with decreasing the laser intensity in the presence of wiggler field. It is also found that the electron attains a higher energy at shorter distances for higher amplitude of wiggler field, Employing a wiggler magnetic field in the laser based electron accelerators can be worth in the design of table top accelerators.

Abstract Solution of the inverse problem of calculation of variations results in several Lagrangians for a classical system which give the same equation of motion. On the other hand, quantizing these Lagrangians gives quantum relations which do not conform to the experimental results. So there have to be found a criteria for selecting the correct Lagrangian. Here on the basis of quantum commutation relations and by direct quantization of equations of motion we show that the function obtained in this way conforming experiments, is the standard Lagrangian. We do this by two different methods: first, by the algebraic approach to the inverse problem and second, by discrete-time method in quantum systems.

Abstract In this work, we review the field perturbations in inflationary models with multi-sound speeds. To be able to do explicit calculation, we consider only two fields. We obtain the evolution equations of perturbations, then we project the field perturbations along (adiabatic) and perpendicular (entropy) to the background fields’ trajectory. Direct computation, we obtain the equation of the projections evolution, these equations cannot be written in the form of an evolution equation of a perturbed field with specified field equations, (in the evolution equation of a perturbed field, the coefficient of second order spatial derivative is proportion to square of propagation or sound speed), therefore the common formalism in which the adiabatic and entropy perturbations are defined and with their evolution equations, the influence on the observational parameters is investigated, cannot be applied to this model.

Abstract In this work firstly Nickel Ferrite (NiFe₂O₄) nano particles (pure and 10% Cobalt doped-) were synthesized by microwave assisted combustion method. Some disks with radius of 2.5 cm were made by NiFe₂O₄ and Ni_0.9Co_0.1Fe₂O₄ nanoparticles. The prepared disks were annealed at 600 °C, 650 °C and 700 °C for 4 hours. The structural and surface morphology of the samples were studied using X-ray diffraction (XRD) and field emission scanning microscope (FESEM). XRD Spectra indicated the formation of spinel phase. The gas sensing properties of the samples were investigated in presence of 2500ppm acetone gas. The results of this work were shown that as grown samples (pure and doped without annealing) have a higher sensitivity at operating temperature of 250°C. Although, the sensitivity of as grown NiFe₂O₄ was also higher than as grown Ni_0.9Co_0.1Fe₂O₄ sample. Moreover, the sensitivity of the samples was significantly affected by the operating temperature of the gas sensor. Comparison of the results showed that as grown pure Nickel Ferrite is more suitable sample for acetone gas sensing.

Abstract In this work, Ag nanoparticles in polyvinylpyrrolidone (PVP) solution at different concentrations have been prepared using gamma-radiation method. A single beam Z-scan method with an excited laser beam 532 nm wavelength and an output power of 50mW, applied for measuring the nonlinear refraction and absorption coefficient of samples. The sign of the nonlinear refractive index shows a self-defocusing phenomena happened in this measurements and also the magnitude of nonlinear refraction and absorption are in order of 10^-8cm²/W and 10^-3cm/W, respectively. The measurements show that the optical susceptibilities of the samples tend to be increased with increasing of the concentration of Ag nanoparticles. Ag nanoparticles can be promising in different aspects of applied optics and optical devices.

Abstract The entanglement is one of the key features of the quantum mechanics, that can be exploited for teleportation of quantum states. In this respect many solid state systems (e.g quantum dot) can be used quantum information processors. However, solid state modeling many-body systems is often calculation very difficult, so the approximation is used. In this work, the calculation of entanglement of ground state of many-body systems by density functional theory has been performed . For this purpose , first the charge electronic density, has been calculated than the entanglement has been investigated by the linear entropy calculation. The investigated systems is the Hooke’s atom is the system and after calculating the electric charge density of the system for different frequencies, we obtained of change entanglement system with frequency .The results indicated that with decreasing the frequency in the Hooke's atom model ,the potential was reduced and entanglement was according by also reduced.

Abstract In this paper, the effect of Sb and Pb doping on the critical current density and microstructure of Bi_1.6Pb_xSb_ySr₂Ca₂Cu₃O_z (BPSSCCO) were studied. The BPSSCCO superconductor was made by a solid state reaction method. The superconductivity properties of Pb- and Sb-doped Bi-based superconductor, such as critical current density, flux pinning energy and microstructure, have been investigated. In order to study the effect of Sb and Pb on the critical current density of the samples, the V-J curves were measured at 77 K temperature. The critical current density of the Sb-doped samples at 77 K temperature increases when the amount of Sb is increased. In addition, for all the samples, the relationship between the current and voltage in the mixed state region is found to follow the model relationship of V = aI^b.