JOURNAL OF THEORETICAL AND APPLIED PHYSICS (IRANIAN PHYSICAL JOURNAL)
Year:2012 | Volume:6 | Issue:6|Papers Count:11

A systematic study of the dependence of the local magnetic moment, M, on the Fe-Pn layer separation has been carried out. Within the Ehrenfest classification of orders of phase transition, we propose a continuous (>2) phase transition for studying the dependence of M on the Fe-Pn layer separation. Our model is tested with available experimental data.

Thermoelectric power (S) of Rb3C60 fullerides in the metallic phase is theoretically estimated. We first develop a Hamiltonian model that incorporates the scattering rates within the relaxation time approximation to estimate the phonon-drag thermoelectric power (Sph drag) incorporating the scattering of phonons with defects, electrons as carriers, grain boundaries, and phonon-phonon interactions. As a next step, Mott expression within parabolic band approximation is used to analyze the electron diffusive thermoelectric power (Sc diff) using Fermi energy as electron parameter, and Sc diff shows a linear temperature dependence. The Sph drag is nonzero in both normal and superconducting states. Its behavior is determined by competition among the several operating scattering rates for heat carriers and a balance between diffusive carrier and phonon-drag contributions. Acoustic phonons are effectively scattered by various scatterers for the thermoelectric power. S infers a change in slope above transition temperature and becomes almost linear above 70 K.

A plasma cathode electron (PCE) gun has capabilities for generating high-current, broad, and focused beams for plasma-assisted microwave sources. A pseudospark-based hollow cathode PCE gun has been designed and developed for microwave generation which is operated in argon atmosphere. An analysis of the electron beam profile inside the drift space at different operating conditions has been carried out. This has been performed at several axial and radial locations inside the drift space which shows coherent phases of beam profiles in radial direction. The focusing and defocusing points in axial direction are also obtained. The beam current at different axial location for different applied voltages has been estimated. The obtained beam current is in close agreement with the beam current estimated by the particle-in-cell simulation code for the same geometry.

Radio-frequency (RF) Ar plasma treatment is carried out on natural muga silk fibers in a capacitively coupled plasma reactor. The physical and thermal properties of the muga fibers are investigated at an RF power of 20 W and in the treatment time range of 5 to 20 min. The virgin and plasma-treated muga fibers are characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The effect of Ar plasma treatment can be observed only on the outermost layer of the muga fibers without any significant variation in their bulk and thermal properties, as supported by differential scanning calorimetry and thermogravimetric analysis. Improvement in tensile strength and hydrophobicity of the plasma-treated muga fibers is observed at lower treatment time and RF power.Attempts are made to correlate the properties of the plasma-treated muga fibers with their surface chemistry and surface morphologies.

A new application of variational Monte Carlo method is presented to study the helium atom under the compression effect of a spherical box with radius (rc). The ground-state energies of the helium atom were calculated for different values of rc. Our calculations were extended to include Li+ and Be2+ions. The calculations were based on the use of a compact accurate trial wave function with five variational parameters. To optimize variational parameters, we used the steepest descent method. The obtained results are in good agreement with previous results.

This paper reports the plasma discharge analysis of a dielectric barrier discharge (DBD) source. Helium is used as a working gas. The analysis is performed at fixed working pressure and operating frequency. The investigations are carried out using sinusoidal supply for the generation of discharges where two current pulses have been observed with different polarities in one period. A homogeneous type of discharge has been observed for different operating conditions in this DBD source. Sincein situ diagnostics are not possible due to the small geometries in the used DBD source, the electrical measurements and spectroscopic analysis of the discharge have been performed to analyse the plasma discharge. The electrical analysis has been carried out using equivalent electrical circuit model.The plasma density and temperature within the discharge have been estimated using line ratio technique of the observed visible neutral helium lines. The estimated electron plasma density is found to be in close proximity with the plasma simulation code ‘OOPIC Pro’.

Effects of ball diameter on the crystalline size, induced strain, and atomic diffusion in Cu-50%Fe immiscible alloy system have been investigated. Milling parameters affect atomic diffusion in binary or ternary systems separately.The aim of this research work is to prove the fact that ball diameter is an important parameter. It is shown that different diameters can change milling power, and consequently, the final crystalline size and atomic diffusion can alter. X-ray diffraction and scanning electron microscopy were used to analyze the effect of ball diameter. It is shown that the strain increases from 0.0025 to 0.0052, while the crystalline size decreases to 18 nm.

In this paper, uniform argon glow discharge at atmospheric pressure in a diffuse mode driven by a 300-W radiofrequency (13.56 MHz) power supply based on dielectric barrier discharge was investigated. In this work, the effect of the parasitic capacitor on the electrical characteristics of the capacitively coupled atmospheric pressure plasma was investigated. It was revealed that more than half of the RF current is parasitic in our system as a characteristic of the capacitively coupled plasma. It was also proved that the discharge resistance and sheath capacitance increase at higher input powers while the impedance decreases. In order to recognize plasma, optical emission spectroscopy apparatus was used. Argon, oxygen, copper, and nitrogen spectrum lines were diagnosed. The plasma gas temperature and electronic excitation temperature were investigated showing a non-equilibrium discharge.

In this work, a xenon-filled quartz coaxial dielectric barrier discharge (DBD) tube (ID 6 mm, OD 12 mm) at 400-mbar pressure has been studied at different operating conditions. High-frequency sinusoidal and unipolar pulse-like voltages are applied at the discharge electrodes for the generation of micro-discharge plasma. Visual images of the discharge and the electrical waveform confirm the diffused-type discharge. The mechanism that is involved in the ignition, development and extinction of DBDs is quantitatively explained by dynamic processes in the discharge. An equivalent electrical model representing the DBD phenomenon has also been used to validate the characteristic discharge parameters. The relative intensity analysis of the Xe continuum peak at wavelength 172 nm in the optical emission spectra of the vacuum ultraviolet region has been carried out for different operating conditions.Approximately three times increment in the radiation is observed in pulse excitation over sinusoidal excitation. It infers that the pulsed excitation of DBD sources is advantageous for excimer light sources.

Different forms of the well-known Grad-Shafranov (G-S) equations that define the equilibrium behavior of tokomak plasma have been already obtained. None of these equations contain explicitly the triangularity  d and the elongation ratio ks. The aim of this work is to obtain a new form of G-S equation which includes both the triangularity and the elongation ratio. For verifying the correctness of the obtained equation, the triangularity is set to 0, which leads to a G-S equation for circular cross section. Also, the magnetic field and current density obtained from this new G-S equation is reduced to the quantities already derived for circular cross section.

A 2.2-kJ Mather type plasma focus device charged at 18 kV was used to deposit titanium nitride on 304 type stainless steel substrates. The plasma focus device is fitted with solid titanium anode and operated with nitrogen as the filling gas. The process of deposition was done at room temperature, and samples were deposited at a constant distance and at different angles with respect to the anode axis. X-ray diffractometry (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX) were employed to characterize crystalline structure, morphology, nanostructure, distribution, and elemental composition of deposited films, respectively. As the ion flux and energy of the ions change with angular position from the head of the anode (titanium), it is observed that these changes directly affect both surface morphology and the nanostructure of the films. XRD patterns show the growth of polycrystalline titanium nitride thin films of different phases. AFM and SEM images show that the grain size is affected by the energy of ions that reached the surface. Grain size, average roughness, and root mean square decreased by increasing the angle with respect to the anode axis. EDX mapping verifies the elemental distributions of titanium nitride on the surface. In this work we have shown the possibility of production of titanium nitride thin films of different phases, using a Mather type plasma focus system.