JOURNAL OF THEORETICAL AND APPLIED PHYSICS (IRANIAN PHYSICAL JOURNAL)
Year:2011 | Volume:5 | Issue:3|Papers Count:8

In the present paper, the phonon dispersion curves (PDC) of some equiatomic liquid alkali binary alloys are reported in second order approach through the equation given by Hubbard and Beeby (HB). The pair correlation function g (r) is directly computed from the interatomic pair potential, which is used in the present computation. Two different forms of local field correction functions proposed by Hartree (H) and Ichimaru-Utsumi (IU) are used in the present study the screening dependence of the phonon frequencies in the equiatomic liquid alkali binary alloys. The pseudo-alloy-atom (PAA) model is applied for the first time for the alloying elements.

The modified Kretschmann configuration theroretically was used to excite surface plasmon-polariton wave at the planar interface of a silver and chiral sculptured magnesium fluoride thin film. Plasmonic modes were calculated in absorbance spectra as a function of incident angle. The results showed that there exist multiple plasmonic modes for P-polarization, while did not appear surface plasmon-polariton mode for S-polarized incidence.

Using the transfer-matrix method, Spin transport in ferromagnetic bilayer graphene superlattice, which can be realized by putting a series of ferromagnetic insulator layers on top of a bilayer grapheme is studied. The ferromagnetic layers with exchange energy Eex are in contact with gate of potential energy V0. It is considered that the magnetization in the two ferromagnetic layers are aligned parallel (P) and antiparallel (AP) to each other. The spin transmissions probability (T­ and T¯) and the spin conductance (G­ and G¯) are studied. The spin polarization is calculated through the spin conductance. The total conductance (Gpq and GAPq) is also considered. It is found that perfect reflection can occur at normal incident, i.e., T­=T= 0. The spin conductance and the swpin polarization are found to exhibit oscillatory depending on the barrier height. The highest value of oscillating amplitude for SP% can rich 100% or (-100%) under special condition.

An intense, short-pulse laser interacting with underdense plasma can generate huge amplitude plasma wave wake field. This wakefield can be described in tree-dimensional. A differential equation for wake potential corresponding to this wakefield is derived analytically and is solved numerically for various laser-plasma conditions. It is shown by numerical studies that the amplitude of the wakefield is increased for the large frequency and higher laser intensity, but is decreased with the spot size of laser. The study conducted for various pulse durations and background plasma density reveals that there is an optimum value on excited plasma wake.

A gas sensor is designed on the basis of field ionization and the performance of 90 nm thick obliquely grown manganese nano-wires thin film on copper substrate using the designed sensor is investigated. It is shown that this design in conjunction with this type of thin films (i.e., sculptured thin films) that consist of relatively sharp tips and high degree of void fraction can be used under appropriate pressure and potential difference, to ionize any gas (e.g., nitrogen and argon used in this work) at a certain break voltage. This work shows that use of nano-structures, in particular nano-sculptured thin films, as anode and cathode instead of conductive metals such as copper reduces the break voltage considerably. In addition, minute amount of gas can be detected in this sensor and it works fine at room temperature and there is no need for heating accessories.

For the study of heavy ion induced fission fragment angular distribution reaction in nuclei, which have a>aBG, TSM statistical model is suitable and if a<aBG, SSM model is suitable. In SSM model, parameters a and ED are unknown. We use a new way to find these unknown parameters and apply it for reaction. In this way, we select a heavy ion reaction, which has a compound nucleus, and fission fragments of the same reaction. In addition, TSM model must be usable for this selected reaction. We calculate unknown parameters by using TSM model for the selected reaction then use known parameters and SSM model for reactions. Then we use desired variances and calculate Isph/Ieff and x for both reactions. Our results are in agreement with Rossner et.al’s results that are calculated for the same nuclei.

The electromagnetic form factors of the K* meson are investigated in the framework of light cone QCD sum rules. The values of magnetic and quadrupole moments are calculated with the help of a suitable fit function. Comparing the results with the predictions of other approaches especially DSE based models reveals the difference between the values. Deciding which technique gives the better result in absence of experimental data is hard, so precise data on K* meson form factor is needed.

The influence of fluid flow and heat transfer study within a Pressurized Water Reactor is of significant importance for the demonstration of the reactor performance and its safety in both steady and transient states. In the present paper, the three dimensional flow distributions in the downcomer and the lower plenum of the reactor were calculated with the computational fluid dynamics (CFD) codes. Calculations were performed for the VVER-1000, V446 reactor at the Bushehr nuclear power plant, Iran. Although CFD codes provide an effective tool for the calculation of flow distribution in the reactor pressure vessel (RPV), computer capacity puts restrictions on the capacity of CFD calculations. Consequently, simplified models had to be used in simulating the RPV. Nevertheless, our investigation shows a reasonable agreement between the numerical results and the measured data.