Iranian Journal of Physics Research
Year:2009 | Volume:8 | Issue:4|Papers Count:13

In this work, using a tight-binding Hamiltonian model, a generalized Green's function method and Lowdin's partitioning techniques, some of the significant properties of the conductance of, poly (dG) -poly (dC) DNA molecule in SWNT/DNA/SWNT structure are numerically investigated. In Fishb ne model, we consider DNA as a planar molecule which contains M cells and 3 further sites (one base pair site and two backbone sites) in each cell sandwiched between two semi-infinite single-walled carbon nanotubes (SWNT) as the nano-electrodes. Relying on Landauer formalism as the basis for investigating the conductance properties of this system, we focus on the studying of the electron transmission and the current-voltage characteristics of DNA in the foregoing structure. In addition, in the presence of the electric potential between DNA molecule ends, our results suggest that the increasing of the value of applied bias give rise to the large enhancement in the conductance of the system. We also find that, as the tube radius increases, the conductance of the system considerably increases.

Secondary electrons at ground level of simulated extensive air showers have been analyzed using a wavelet transform based technique, in order to investigate the variation of fractal dimensions of the lateral distribution of the electrons with shower energy and primary particle mass number. The fractal dimension is shown to increase with shower energy and seems to saturate to constant values near the core of the shower at higher energies. Using the fractal dimension properties at different core distances, a multi-parameter separation technique is then applied to the data. It has been shown that the technique has good accuracy at high energy, provided the energy of the shower is obtained independently.

In this paper, two La0.8Sr0.2MnO3 samples, isotropic (press without magnetic field) and anisotropic (press with magnetic field) have been prepared. Then we have investigated structural, magnetic and magnetotransport properties of these samples using XRD, SEM, Ac susceptibility and m, magnetoresistance measurements. These studies show that a magnetic property of anisotropic sample is improved and magnetoresistance is decreased.

Polycrystalline samples of Nd1-xCaxBa2-xLaxCU3O7-d (with 0.0£x£0.15) were prepared by the standard solid state method. The transport and superconducting properties have been studied by the resistivity and thermoelectric power measurements as a function of temperature and doping concentration. With increasing doping concentration, the resistivity was increased and thermoelectric power was constant at high temperature while it was increased slightly at low temperature. The critical temperature Tc was linearly decreased with increasing doping. The density of statets at Fermi energy g (eF) were obtained from the thermoelectric power. They were decreased as x increased. The thermoelectric power as a function of temperature was analyzed in terms of the phenomenological narrow band model. The model well described thermoelectric power data up to near the critical temperature. Severl property results such as the resistivity r (x, T), thermoelectric power S (x, T), critical temperature Tc (x), and g (eF) variation suggested that the hole localization is the main reason of superconducting suppression in the charge neutral doped cuprates.

The behavior of ions in a Paul trap has been investigated using numerical solution of the set of Mathieu's differential equations. Afterwards, the trajectories of two typical ions such as H+ and 208Pb+ in the trap have been obtained using the fourth-order Runge-Kutta method. For specific dimensions of a Paul trap and a given frequency, the stability regions for separation of H+ and 2H+ ions have been determined in terms of the DC and AC voltages applied to the trap. Furthermore, five stability regions in which ion trapping occurs have been obtained accurately. Computation of the fifth stability region has not been reported in the literature previously.

Diquarks may play an important role in hadronic physics particularly near the phase transitions (chiral, deconfinement points). By using vector diquark ideas in the chiral limit diquark correlations in the relativistic region and imposing HF interactions between quarks in a vector diquark, we calculate the mass of Theta pentaquark state. Also by using the tunneling method we simultaneously calculate its decay width. Our results are in good agreement with experimental results.

In this paper by using DC arc discharge method and acetylene gas, as the carbon source, and nitrogen, as the carrier gas, canrbon nanotubes, CNTs, doped with trivalent element boron, B, have been produced. The deposited CNTs on the cathod electrod, which have structural doped properties to boron element, have been collected and after purification have been investigated by back-scattering Raman spectroscopy. The results reveal that the high frequency G mode component in CNTs doped with electron acceptor element, B, shift to higher wavenumbers. The low frequency G mode component which can appear at approximately 1540-1570 cm-1 wavenumber region, called BWF mode, is a sign of metallic CNT. In the synthesized doped CNTs due to the presence of boron dopant, D mode has sharp peaks and has relatively high intensity in the Raman spectra.

Moving single bubble sonoluminescence has been discovered after searches to find the fluids other than water for observing SBSL. The main property of these fluids is their more viscosity rather than water. In this paper, after introducing the forces which act on sonoluminescing bubble, the moving of the bubble have been simulated. For this purpose, the bubble's equation of motion is coupled with the Rayleigh-Plesset and temperature equations. For solving these equations we have used the Runge-Kutta method. We have shown that the path of the bubble is the same as an ellipsoidal movement near the center of the flask. One of the main results of this simulation is that the maximum temperature (at collapse moment) of the bubble is increased by reducing the distance of the bubble from the center of flask. Due to direct relation between light emission and the temperature of the bubble, the same result can be get for intensity of the light. In other words, we have shown that the intensity of the emitted light from bubble oscillates. Accordingly we propose that the measurement of the light oscillation from the moving bubble is as a criterion for experiment on moving single bubble sonolurninescence.

In this work structural, electronic and magnetic properties of alpha and gamma phases of cerium crystal have been calculated by means of the LDA and LDA+U methods. The equilibrium volume and magnetic moment obtained from the GGA approximation in agreement with the experiment are equal to 27.64 Å3 and 0.00018 mB, respectively. This agreement shows that the 4f electrons in alpha phase are itinerant due to the use of the GGA, where no strong correlations have been yet thaken into account. We gave observed that even after applying the GGA+U method with U=6.1 eV, the density of states of f orbital remains still at Fermi surface. Therefore, in complete accord with the experiment, our results show that the 4f electrons in the alpha phase are not localized. This is the case where the LDA and the GGA approximations could not describe the gamma phase properly. Indeed, physical properties of the gamma phase is consistent with the experiment and could only be reproduced after applying LDA+U method with U=4.4 eV. In this way, the value of equilibrium volume and magnetic moment calculated for the gamma phase were found to be 34.33 Å3 and 1.15 mB, respectively. After including correlations among 4f electrons the ¡-Ce DOS is positiol1edat its more reasonable place lower than Fermi level compared with the DOS obtained from GGA calculations. Our results, then, show that the 4f electrons in the gamma phase, as opposed to the alpha phase, are localized which is indicative of the fact that gamma cerium is a strongly correlated system. The volume of 11 kbar has been obtained for the pressure of the alpha-gamma phase transition.

The aim of this article is apply modification to limited diffusion aggregation model. The method can simulate the doping type and current density on obtained structures forms within porous silicon growth. For doping type effect, the sticking coefficient parameter and for the current density effect, mean field parameter applied to limited diffusion aggregation. Simulation results showed that the sticking coefficient parameter influences pores thickness controlling. Meanwhile, the mean field parameter could control tree or rod characteristics of pores. Results on porous silicon growth simulation showed that the applied modifications accompany with these two parameters on structure simulation formation are consistence with experimental data of the samples.