مجله فیزیک کاربردی
سال پنجم شماره 1 (پیاپی 8، بهار و تابستان 1394)

In this work، the order parameter and dichroic ratios of two synthesized dyes in a C7 mixture are obtained. In our measurements، the different concentrations of dye dopants in the uniform planar cells are used and the orientation ordering is studied based on the guest-host phenomenon. The polarized absorption spectroscopy method is used to determine the linear dichroism and the order parameter of doped liquid crystal. The parallel and perpendicular components of absorption are obtained. Then، the results for some compositional percentage of the dyes are compared and the ordering behavior of the system is studied. Our obtained results confirm that the molecular structure of the dyes is a significant factor in orientation ordering of liquid crystal host. Moreover، it is found that even in low concentrations of the dyes، the order parameters are effectively changed. Dye doped liquid crystals are broadly used in various electro optical devices to enhance their physical and photo-physical properties. Hence، study of these materials that have initially attracted interest as a technological improvement of the optical devices، are crucial in applications like displays with faster switching rates and larger viewing angle.

In this paper، structural properties such as lattice constant، bulk module، compressibility and volume optimization of ReO3compound have been investigated. Calculations have been performed by Full-Potential Linear Approximation Plane Wave in Density Functional Theory framework with WIEN2k package. The results show that the energy band have been connected with Fermi level in several points، which is an evidence for metallic properties، and also the results shown the contribution of different orbitals related to its atoms gives an strong overlap between 5d orbitals of Re and 2p orbitals of O، in the vicinity of the Fermi level، which emphasizes that the metallic properties are in a good agreement with experimental and theoretical results of the others.

Zinc selenide (ZnSe) thin films were prepared by spray pyrolysis technique on glass substrate at substrate temperatures of 380، 400 ºC and then annealed in 400 ºC. Structure of the samples were studied by XRD and UV-Vis spectroscopy was used to investigate the optical properties. The results of the XRD data indicated that the samples are amorphous before annealing with small ZnO phase، but after annealing the optical studies showed that the band gap of the sample decreases and approached to the ZnSe band gap value. The one which was grown at 400 ºC substrate temperature is polycrystalline ZnSe with prefer orientation of (111).

In this paper، we investigate the electronic conductance and occupation number of a benzene molecule which is connected to two simple metallic leads via ortho، meta، and para connections. We study the effect of some factors such as the position of lead connections، the dimerization strength and applied voltage on behavior of electronic occupation number for different electron paths. The calculation reveals the high sensitivity of the occupation number on these factors. The average value of occupation number for two electron paths in benzene molecule shows that the path with more number of double bond contributes more in determination of the conductance behavior.

Arrays of dielectric barrier discharge are used for control of various aerodynamic phenomena such as control flow separation. In order to control this phenomenon by the generated momentum، it is needed to determine the maximum discharge voltage required to the momentum generation. By image processing، maximum momentum produced and consequently maximum discharge voltage can be determined with using plasma flame length and light intensity. The advantage of this method compared to other methods is simplicity and availability of a camera as the only required equipment. In this study، an array of 8DBD actuators arranged perpendicular to flow on NACA0012 is installed in a wind tunnel. Performance and maximum discharge voltage can be determined by processing the images captured from the arrays in different discharge voltages and dynamic pressures. Using image processing method for evaluating the efficiency of DBD actuators and accessing the maximum discharge voltage for flow separation control is unprecedented.

In this study we investigate The Casimir force on the rough dielectric surfaces. In order to accomplish this goal we simulated a 2D rough dielectric surface in das-sarma model as one of the discrete models of MBE and then we calculated the Casimir force by using the Lifshitz relation when it is approximated for small separations. At the final stage we calculated the repulsive force of two surfaces as a function of separation. The results show that both forces relate directly to the roughness and change over separation inversely، but the attraction force changes over separation more rapid than the repulsive force.