Iranian Journal of Physics Research
Year:2016 | Volume:16 | Issue:3 |Papers Count:11

Lyapunov exponent method is one of the best tools for investigating the range of stability and the transient behavior of the dynamical systems. In beryllium-moderated and heavy water-moderated reactors, photo-neutron plays an important role in dynamic behavior of the reactor. Therefore, stability analysis for changes in the control parameters of the reactor in order to guarantee safety and control nuclear reactor is important. In this work, the range of stability has been investigated using Lyapunov exponent method in response to step, ramp and sinusoidal external reactivities regarding six groups of delayed neutrons plus nine groups of photo-neutrons. The qualitative results are in good agreement with quantitative results of other works.

Magneto hydrodynamic waves, propagating along spicules, may become unstable and the expected instability is of Kelvin-Helmholtz type. Such instability can trigger the onset of wave turbulence leading to an effective plasma heating and particle acceleration. In present study, two-dimensional magneto hydrodynamic simulations performed on a Cartesian grid is presented in spicules with different densities, moving at various speeds depending on their environment. Simulations being applied in this study show the onset of Kelvin-Helmholtz type instability and transition to turbulent flow in spicules. Development of Kelvin-Helmholtz instability leads to momentum and energy transport, dissipation, and mixing of fluids. When magnetic fields are involved, field amplification is also possible to take place.

Tungsten trioxide (WO3) thin films were coated onto fluorine tin oxide coated glass substrates, using electrodeposition technique via aqueous solution of peroxotungstic acid. WO3 films were evaluated as a function of annealing temperature (60° C, 100° C, 250° C and 400° C). The films were analyzed by field emission Scanning Electron Microscopy (SEM), UV-visible spectrometer and cyclic voltammogram. The films had high transmission in optical visible region. Using optical transmittance and cyclic voltammogram measurements, the electrochromic properties of WO3 films were investigated in a non-aqueous lithium perchlorate in propylene carbonate electrolyte. Increasing the annealing temperature will decrease electrochromic and optical properties of WO3 films, since it leads to increasing the size of grains. Therefore, having been annealed at 60° C, WO3 film exhibited a noticeable electrochromic performance with a high transmission modulation and Coloration Efficiency Efficiency (CE) of 64. 1 cm2 C− 1 at wavelength equal to 638 nm.

Interest in the P3HT: ZnS nanocomposites are increased due to their applicability as an active layer for bulk heterojunction solar cells of high open circuit voltage and charge transport in this type of solar cells determines their performance. So the study of the conduction mechanism of the P3HT: ZnS nanocomposites is significant to improve the efficiency of such solar cells, and this paper discusses both the Arrhenius Model and the Variable Range Hopping (VRH) conduction mechanism in the P3HT: ZnS nanocomposite films. It is found that the addition of the semiconductor nanoparticles does not make any remarkable change in the room temperature DC conduction of P3HT polymer. Further, the films have been studied by their absorption spectra, x-ray diffractogram, scanning electron microscope and noncontact profilometer.

In this paper, by placing the electro optical modulator (EOM) into the external cavity of the semiconductor laser (SL) and amplitude modulation of the optical feedback, the dynamical variation of the output intensity ( E 2 ) of the laser has been studied. This is analyzed numerically via bifurcation and time series diagrams with respect to the applied amplitude modulation index, and modulation voltage frequency of the EOM. It has been shown that, by modulating the amplitude of the optical feedback beam, various changes in the types of the dynamics of E 2 can be observed, and various periodic states can be generated. This makes it possible to receive the desired dynamics without any variations in the main parameters of the SL. Also, in present study, a method of chaos control in the SL has been presented based on EOM in the external cavity. The obtained results confirm that based on this method the chaotic dynamics can be controlled single-periodic dynamics.

In present research, the electrical, structural, quantum and Nuclear Magnetic Resonance (NMR) parameters of interaction of N2O gas on the B and P sites of pristine, Ga-, Si-and SiGa-doped (4, 4) armchair models of boron phosphide nanotubes (BPNTs) are investigated by using density functional theory (DFT). For this purpose, seven models for adsorption of N2O gas on the exterior surfaces of BPNTs have been considered and then all structures are optimized by B3LYP level of theory and 6– 31G (d) base set. The optimized structures are used to calculate the electrical, structural, quantum and NMR parameters. The computational results revealed that the adsorption energy of all studied models of BPNTs is negative; all processes are exothermic and favorable in thermodynamic approach. When N2O gas is adsorbed from its O atom head on the B site of nanotube, N2O gas is dissociated to O atom and N2 molecule. The adsorption energy of this process is more than those of other models and more stable than other models. In A, B and C models, the global hardness decreases significantly from original values and so the activity of nanotube increases from original state. On the other hand, the electrophilicity index (ω ), electronic chemical potential (μ ), electronegativity (χ ) and global softness (S) of the A, B and C models increase significantly from original value and CSI values of the C model are larger than those of other models. The results demonstrate that the Ga-, Si-and SiGa-doped BPNTs are good candidates to adsorb N2O and make N2O gas sensor.

In present study, the effect of different defect layer refractive indices and thicknesses on group velocity has been studied in onedimensional photonic crystal. It is found that the increase of refractive index, number of defects and defect layer thickness will induce the decrease of group velocity. Taking advantage of these results, a novel technique has been introduced to tune and control the slowing light in photonic crystal.

The propagation of nonlinear quantum dust ion-acoustic (QDIA) solitary waves in a unmagnetized quantum plasma whose constituents are inertialess quantum electrons and positrons, classical cold ions and stationary negative dust grains are studied by deriving the Korteweg– de Vries (KdV) equation under the reductive perturbation method. Quantum Hydrodynamic (QHD) equations are used to take into account the quantum diffraction in quantum statistics corrections. It is shown that depending on some critical values of the dust density (d) which is function of quantum diffraction parameter (H), both rarefactive and compressive type of solitons can exist in the model plasma. Further, the amplitude and width of both solitons increase as d increases. Moreover, it is pointed out that an increase in quantum diffraction parameter, decreases the width of compressive soliton but increases the width of rarefactive soliton, and the amplitude of both solitons is independent of H. The present investigation could be useful for researches on astrophysical plasmas as well as for ultra small micro-and nano-electronic devices.

In this study, some characteristics of a Mather type Plasma Focus (PF) device such as a discharge current, pinch time, ion flux and hard x-ray intensity has been investigated simultaneously in argon and nitrogen gases separately for various operating gas pressures and charging voltages of capacitor bank. It was observed that pinch phenomena was energy and pressure dependent in current sheath as well as ion and hard x-ray emission intensity. Optimum pressure with maximum ion flux and the most intense hard x-ray showed a nearly linear dependence on the charging voltage of the device. Maximum ion flux was estimated in the order of 1018 ions per steradian in both gases. Hard x-ray emission was registered a little after discharge current and Faraday cup (FC) signals. Also, optimum pressure for maximum ion flux was not the same as the pressure for intense hard x-rays. Hard x-ray intensity reached its peak at higher pressures.

This article, introduces a new pixel which can emit infrared wavelengths from its surface and can be used for the purpose of cloaking objects from thermal cameras. This pixel can simulate the temperatures between 0 and 100º C emited from an infrared radiation in LWIR (8-12 micrometres) region. Nanocomposite material is used in the pixel structure and this has increased its capacities like ZT factor %40-50 better than the commercial material like Bi2Te3. Technical aspects of the pixel such as the emission wavelengths, rate of temperature changing, thermal contrast, ZT factor and so on are discussed in this paper and were determined by using thermography, non-contact thermometry, radiometry, four probe ac method and temperature differential.

We study the Casimir effect for a Bosonic string extended between D-branes, and living in a flat space with an antisymmetric background B-field. We find the Casimir energy as a function of the B-field, and the mass-parameter of the string, and accordingly we obtain a B-dependence correction term to the ground-state mass of the string. We show that for sufficiently large B-field, the ground state of the string contains real (i. e. non-Tachyonic) particles.