مجله فیزیک کاربردی
پیاپی 1 (پاییز و زمستان 1390)

The band structure and structure parameters such as lattice constant، bulke module and… of SrHfO3 in tetragonal phase were studied by first principle using the density functional theory (DFT). The band structure and structure parametrs are calculated using the Pseudo-potential. The results show a direct band gap of 4. 5eV at the Γ point in the Brillouin zone. The calculated band structure and structure parametrs of SrHfO3 are in good agreement with theoretical and experimental results.

In this paper we investigate grayity IR effects on quantum machanics considering minimum momentum. First، we investigate afew cases in quantum mechanics by minimum momentum، also we show hydrogen atom spectrum is corrected and produce limit on minimum momentum by prices measurements done on hydro-gen atom. also we investigate aharonove-bohm eff-ect and show its topological phase is corrected. Con-sidering appropriate experiments، this corrections will be observed

In this paper the threshold characteristics of an Er-doped λ/4 phase-shifted DFB fiber laser have been studied theoretically. The main purpose of this analysis is to investigate the dependence of threshold pump power and threshold gain on the coupling coefficient. The numerical results show that threshold pump power and threshold gain of Er-doped DFB fiber laser decreas with increasing the normalized coupling coefficient، κL. In this paper the gain margin of laser، the threshold gain difference between the main and side modes، has been evaluated. The obtained results show that the gain margin decreases with increasing of κL. The gain margin is a single mode operation norm of laser. As a result، grating and coupling coefficient have important role in designing the DFB fiber lasers. Numerical ca-lculations have been done by solving the rate equation and coupled wave equations simultaneously using tra-nsfer matrix method

In this experimental study the collisional relaxation time of SO2 and SF6 was determined using laser pho-toacoustic spectroscopy method. A homemade LPAS cell was fabricated in order to investigate the variation of signal and resonant frequency in terms of buffer gas pressure for several species such as: He، N2، and Ar. By this method collisional relaxation (which is the origin of photoacoustic effect) time was measured. It was shown that the buffer gas pressure notably affects the collisional relaxation times of gases such as SO2 and SF6. The measured relaxation times of SO2 and SF6 were at order of milliseconds and 100 microseconds respectively.

In this paper، the output power behavior of the wave-guide CW-CO2 laser versus efficient parameters of laser performance was investigated. The output power variation versus the discharge current، the pressure and the gas mixture ratio was studied and optimized. The maximum output powers of 6 and 14. 5 W were respectively obtained at operating pressures 78 and 50 mbar in two tubes of 3 mm same diameter and 35 and 70 cm lengths

ZnO and ZnO: Mn nanoparticles synthesized via reve-rse micelle method. The size، structural and optical properties of nanoparticles was investigated by XRD، TEM and UV-Vis spectroscopy. The XRD results indica-ted that the synthesized nanoparticles had a pure wur-tzite (hexagonal phase) structure. The various optical properties of these nanocrystals such as extinction coefficient، optical band gap energy، Urbach energy، threshold wavelength، penetration depth، refractive in-dex، dielectric constants and optical conductivity have been analyzed by using UV-Vis data

Tumor growth has a number of features in common with a physical process known as molecular beam epitaxy (MBE). So using the same equations for tumor growth is sensible. However، tumor substrate unlike MBE is not planar that makes necessary a geometrical treatment of the growth equations. A variety of mathematical models have been proposed to describe tumor growth. The justification for these models mainly depends on how well they fit the clinical datas. We can then include the effects of different therapies as mathematical terms. The valid models are used to predict optimal sequencing of different therapies. Tumors diffuse as well as they proliferate. So considering spatial changes as well as temporal changes is necessary. These considerations are involved in reaction-diffusion equation. Here، we consider the growth equation analytically by using of small noise expansion to study the scaling behavior of tumor growth