سال:1392 | دوره: | شماره: |تعداد مقالات:5

The programs ROYPROF, VEPFIT, and POSTRAP4 are widely used in the field of positron physics. They are mainly employed in analyzing experimental Doppler-broadened data from studying condensed matter samples with variable energy positron beams. A comparative study of analysis results on the same set of data has shown to be consistent. Performance differences are reported. The small differences found may not lead to wrong interpretation of physical results.

The exact bound state solutions of the Feinberg-Horodecki equation with the rotating time-dependent Deng-Fan oscillator potential are presented within the framework of the generalized parametric Nikiforov-Uvarov method. It is shown that the solutions can be expressed in terms of Jacobi polynomials or the generalized hypergeometric functions. The energy eigenvalues and the corresponding wave functions are obtained in closed forms.

The effect of negative ions on the density, temperature, and potential of plasma in a direct current discharge regime has been studied experimentally. Nitrogen as an electronegative gas was used to produce negative ions in the plasma. Langmuir probe was employed to measure plasma parameters. Discharge was performed in an evacuated glass tube, with circular disk electrodes at different pressures. To obtain the spatial variation of plasma characters, measurements were done at different points on the axis of discharge tube. Argon and nitrogen gases were used as the working gas, and plasma current was kept constant at 5 mA during the experiments. Discharge voltage decreased sharply with increasing pressure for both argon and nitrogen plasmas, however, to sustain the discharge at constant current in nitrogen plasma, higher voltage was required in comparison with argon plasma. The plasma electron density was decreased from cathode to anode during the discharge process, while electron temperature was increased. Results confirm that nitrogen plasma contains negative ions, and discharge process is influenced by them noticeably.

Polypyrrole (PPy) fine powder was synthesized via a chemical route in the presence of various concentrations of the cationic surfactant cetyltrimethylammonium bromide. The effect of the concentration of the surfactant used on electronic, structural, thermal, and surface properties of the final product was investigated. The sample prepared with the highest concentration of surfactant yielded mostly the best electronic, thermal, and physical characteristic properties, a lot closer to the materials used in conductive inks. The electrical conductivity of the sample underwent an increase of 320%. Fourier transform infrared spectroscopy indicated that all surfactant has been excluded at the final stage of the synthesis, and the results indicated higher doping levels for higher concentrations of surfactant used. Surface energy showed a dramatic increase, and spherical nanoparticles were seen in scanning electron microscopy images. The PPy powder became soluble in polar solvents, becoming highly hydrophilic and indicating good mass retention upon thermal degradation.

In this paper, we investigate two of the analytical approximate techniques, energy balance method and amplitude-frequency formulation, and these approximate techniques are applied to solve the strongly nonlinear differential equation of a mass attached to the center of a stretched elastic wire. We present a comparative study between the energy balance method and amplitude-frequency formulation with exact solution. The approximate results reveal that these methods are very effective and convenient for determining the frequencies of nonlinear dynamical systems.