Iranian Journal of Physics Research
Year:2018 | Volume:18 | Issue:3 |Papers Count:23

By means of ab-initio calculations on the basis of the FPLAPW method, we compared the energy loss near edge structure (ELNES) of carbon K edges in crystalline phenanthrene and its isomer, anthracene. In these two organic compounds, different non-equivalent carbon atoms can result in distinct K edge spectra due to the different carbon-carbon bond lengths, as a characteristic behavior of the molecular crystals. The smaller bond lengths push the ELNES features to the higher energies. In anthracene, the energy position of the edge-onset appears at lower energies due to its smaller electronic band gap. At the onset of the C K edge of anthracene, the strong splitting of the π * peak into two peaks is observable. Compared to the C K edge in anthracene, due to the slightly larger C– C bond length in phenanthrene, the peak position of the main σ structure has a red shift. The ELNES spectrum of crystalline phenanthrene includes electron transition of 1s carbon orbital to π * and σ * states. In anthracene, the first two intense features have contributions of π * orbitals. Consideration of the core-hole approximation by means of super-cells and the collection of semi-angles at magic value are essential to obtain reasonable ELNES spectra.

It is important to examine the factors that determine the properties of graphene. Various factors can affect the properties of graphene nano sheets. Understanding such factors can revolutionize the use of graphene. One such factor is ultrasonic waves, which have significant effects on graphene physical and chemical properties such as (electronic and optical). In this research, we studied the effect of ultrasonic waves with different power levels (35, 50, 360, and 420 W) on four graphene samples for 10 minute. So all the samples were fabricated by electrochemical exfoliation. In this method, ammonium sulfate nonorganic salt was used for producing solution and electrodes PT and graphite were used, where +10 volt was applied to the electrodes. Ultrasonic waves were used to homogenize the electrolyte for the samples. The samples were analyzed using scanning electron microscope (SEM) imaging and Fourier transform infrared spectroscopy (FTIR) spectroscopy. The I-V curves of the samples were measured after spraying on the glass substrate. Then, FTIR spectra and I-V characteristics were studied. Our results showed t he increase of ultrasonic power could cause some changes in the intensity of spectral FTIR and the conductivity of graphene sheets.

Accurate detection of weak periodic signals within noise and the possibility of secure messaging have made Duffing oscillator (DO) highly important in the field of communication. Investigation on the properties of DO is, thus, very important. An elegant approach to accomplish this is to fabricate electronic circuit simulating DO non-linear equation and to study the effect of input signal amplitude (Vin) and frequency (f), disentangling these two from each other. Recently, Vin-driven chaotic dynamics has been studied by constructing a simple Duffing-Holmes (DH) oscillator circuit. However, the f-driven characteristics of the oscillator remain unknown at constant Vin. The present work is based on the MATLAB simulation of the f-driven chaotic dynamics of the DH equation. Similar output, mixed with chaos and non-chaos, is obtained by constructing the circuit, both in lab and by PSPICE simulation. The circuit moves into complete chaos at f=270 Hz, while period-2 bifurcation appears at f=680 Hz for the constant Vin 0. 9V. The chaos control is also achieved by two simple methods. In the first method, the variation of the circuit parameter (capacitance) induces chaos control. In the second one, synchronization is achieved by coupling two similar oscillators. These two methods, though apparently simple, could be highly beneficial for using DH in secure communication.

In this paper, the reported experimental data related to electrical transport properties in bulk ZnO, ZnMgO/ZnO and ZnMgO/ZnO/ZnMgO single and double heterostructures were analyzed quantitavely and the most important scattering parameters on controlling electron concentration and electron mobility were obtained. Treatment of intrinsic mechanisms included polar-optical phonon scattering, piezoelectric scattering and acoustic deformation potential scattering. For extrinsic mechanisms, ionized impurity, dislocation scattering and strain induced fields were considered. For the bulk ZnO, the reported experimental data were corrected for removing the effects of a degenerate layer at the ZnO/sapphire interface via a two – layer Hall – effect model. Also, donor density, acceptor density and donor activation energy were determined via the charge balance equation. This sample exhibited hopping conduction below 50K and dislocation scattering controled electron mobility closely. Obtained results indicated that the enhancement of electron mobility in the double sample, as compared with single one, could be attributed to the reduction of dislocation density, two-dimensional impurity density in the potential well due to background impurities, and/or interface charge and strain induced fields which can be related to the better electron confinement in the channel and enhancement in the sheet carrier concentration of 2DEG in this sample.

In this paper, plasma main characteristics such as electron mean temperature, electron number density, and oscillation frequency have been measured experimentally using the double Langmuir probe diagnostic system. In our experiment, the plasma was generated by applying the low pressure dc glow discharge in several common gases. The experimental results indicated the highest plasma density and oscillation frequency for the plasma originating from argon and the highest mean value of temperature for hydrogen plasma. The experimental results were then confirmed by COMSOL simulator, showing reasonable consistency with the simulations. The data were then used to compare the degree of ionization with the measured plasma parameters.

In this article, by using the method of finite difference time domain (FDTD) and PML boundary conditions, we have studied the photonic band gaps for both TE and TM modes in square and triangular lattices consisting of air holes in the dielectric medium; the results have been compared too. In addition, the effect of the nonlinearity of the photonic crystal background on the photonic band gaps and comparison with the results of the linear case (holes in a background medium with the linear dielectric constant) have been presented. Comparison of the transmission spectra in the linear and nonlinear cases shows a red shift in the minimum transmission for both triangular and square lattices.

Magnetic abrasive finishing can be classified as a non-traditional super finishing method for finishing surfaces with different shapes and working materials like flat plates, shafts, bearings parts, screws, tubes and many other mechanical parts that need good surface finishing properties. MAF is effective in polishing, cleaning, deburring and burnishing metal parts. The most important parameter affecting the performance of this method, such as surface roughness, is the magnetic force. The magnetic force is obtained from a permanent Magnet or a DC magnet. In this article, the magnetic field strength, magnetic flux density and magnetic force in different states are studied using simulation with some finite element method software (Maxwell). The shapes of magnets, various sizes and the material of fixture are studied. The magnetic properties of the material of the work piece are simulated too. To verify the simulation results, the situation is also measured by a Gauss meter. The intensity of the magnetic field required for the micro chipping is obtained for different geometric shapes and various materials of work piece in the magnetic abrasive finishing process. The results show that increasing the distance from the magnet surface results in a decrease in the magnetic flux density and significance of the edge phenomenon effect. The effect of work piece material, work piece fixture material, and the interaction of them were is shown to be significant on magnetic flux density. To concentrate the magnetic abrasive powder in the polishing process of non-ferromagnetic parts, the ferromagnetic fixture for these parts can be provided.

Spatially homogeneous Bianchi type-II, VIII and IX anisotropic, as well as isotropic cosmological models can be obtained in a scalar tensor theory of gravitation proposed by Saez and Ballester (1986) when the source for energy momentum tensor is a bulk viscous fluid containing one-dimensional cosmic strings. All the models obtained and presented here are expanding, non-rotating and accelerating. Also, some important features of the models thus obtained have been discussed.

In the present study, the most useful stainless steels of in nuclear industry, i. e. 304, 304L and 316L were provided and laser cut into 0. 5*0. 5 cm dimension. The effect of radiation on physical properties of samples were investigated. Gamma irradiation on samples was done with a 60Co radioisotope to the doses of 100 and 200 kGy. The resistance of the samples was measured through the Four-Probe technique, and also the special resistance and the electrical conductivity of the samples were measured from resistance. The conductivity of the samples was obtained through Widman-Frantz. The magnetic properties of the samples were also measured by the Vibrating Sample Magnetometer.

Scattering of 15N ions with the energy of Elab = 23 MeV on the CH2(Au) target is investigated. Elastic scattering of these ions in the angular range of 7°-19° was measured by employing the silicon strip detector, “ LEDA” . Using the measured scattering data, deviation of ion beam, number of incident ions on the target and differential cross sections of the 12C(15N, 15N)12C elastic scattering in the angular range of 7°-19° were determined. Moreover, by applying the optical model and using the Fresco software, the scattering cross sections in the angular range of 0°-60° in the laboratory framework were obtained by entering the extrapolated optical parameters. The obtained cross section data were then compared with the experimental ones. The theoretical cross section data resulting from the optical potential exhibit meaningful difference with the experimental data obtained in this research work in the covered angular range.

In this research, design and fabrication of an integrated heterodyne electrooptic modulator in lithium niobate have been presented. In this modulator, the waveguide is made by using proton exchange process; to exert two high frequency signals, deposited electrodes with Mach-Zender arms between them are used. In this method, every electrical signal is applied on one of the Mach-Zender arms, so that it can be stimulated by one specific frequency; these two signals are united optically to create frequencies equal to sum and subtraction of the input signal frequencies in the output. Also, by using finite element method, the influence of proton diffusion scale in the output light mode, electrode dimension, and configuration in the overlap integral of the light mode and electrical field, as well as electrode impedance, is estimated.

In this work, magnetic Ni nanowire arrays were ac-pulse electrodeposited into the anodic aluminum oxide (AAO) template fabricated by the common two-step anodization technique. The barrier layers at the bottom of the pores were exponentially thinned in a non-equilibrium anodization process to 8, 12, 16 and 20 V. These were fabricated using the constant of 15 mA deposition current, 48 mS off-time between pulses, 10, 20 substrate temperatures, and 30° C electrolyte temperature. The effects of thinning voltage and substrate temperature on the electrodeposition efficiency and the magnetic quality of the Ni nanowires were investigated by a Vibrating sample magnetometer (VSM) and a scanning electron microscope (SEM). In this paper, we realized that the bed temperature of 10° C, by increasing the thickness of the barrier layer, reduced deposition efficiency and the temperature was 20 degrees backfired.

Computer modeling for the design of inductors for different applications in the induction heating process often seems to be necessary to save costs caused by the trial and error. In this paper, the effects of the number of loops in the induction heating process with the numerical solution of the Maxwell equations have been investigated using finite element method (FEM) and the COMSOL MULTIPHYSICS software package in three dimensions. Therefore, considering the effect of the number of coil turns on the amount and pattern of heat produced in the workpiece for special applications in the industry and technology is critical. This is because the number of coil turns is one of the important parameters in the design of induction heating systems. At first, a single turn coil is simulated in a three-dimensional model; then multi-turn coils with the turns number 2, 3, and 4 have been considered. The voltage of 200 V with the frequency of 1 KHz has been used, as applied to the coil, to serve as the source of electromagnetic fields. The results of numerical calculations show that the number of coil turns can have a significant effect on quantities such as distribution and intensity of magnetic flux density, eddy currents density in the workpiece, and the volume of heat produced in the coil and workpiece.

The high-Tc Y1-xNixBa2Cu3O7-δ samples doped by Ni for Y atom, with x=0, 0. 002, 0. 004, 0. 006 and 0. 01 were synthesized by the standard solid-state reaction method. The XRD diffraction of samples showed no impurity phase in all samples. Magnetic susceptibility of the samples under two different magnetic fields of 0. 8 and 400 A/m was measured. The results showed that by increasing nickel element to an optimum value, the intragranular connection and flux pinning were improved.

In this study, molybdenum oxide thin films are deposited by using high power impulse magnetic sputtering (HiPIMS) at different pulses length of 60, 90, 120, 150 and 180 μ s on glass substrates in a combination of reactive and non-reactive gases with a ratio of O2/Ar = 0. 66. The structural and optical properties of these coatings are studied. The chemical composition of these metal oxides is determined by analyzing X-ray photoelectron spectroscopy (XPS), and are determined by MoOx stoichiometry with different x-values. By studying the optical properties, it is found that the oxygen deficiency with increasing pulse width cause to reduce the average of optical transmittance and also decrease the optical band gap of coatings.

In this paper, the cluster emission half-lives have been calculated by using the WKB approximation and the proximity potential Prox77 as the nuclear potential part and considering the deformations and different relative orientations of the cluster and daughter nuclei. The calculated results are in good agreement with the experimental data and the results of the Liquid Drop Model, LDM. It is seen that with increasing the angle of the relative orientation, the systems under consideration, will be more stable against this phenomenon.

Using Langevin dynamics and the dissipative nature of the fission process, we have studied dynamical variations of nucleus from the formation of the compound nucleus to separation stage of two fission fragments. During this dissipative process, particles such as neutron, proton, alpha particle and gamma ray emit from the compound system. In the present work, the number of emitted particles using Langevin equation are calculated, dynamically. Obtained results for emitted alpha particles, protons and neutrons are compared with the experimental data. Also, we have studied the influence of the dissipative coefficient on these quantities. These results show that the dissipative coefficient affects the results, as well as the good agreement between the experimental data and theoretical results can be reproduced by using the dynamical approach.

We use gauge-gravity duality to study the effect of corrections to the coupling constant on equilibration time in field theory for scalar operators with Delta=2, 3. We will show that for larger correction in coupling constant the equilibration time enhances and this behavior is independent of the method we use to make the system out of equilibrium. Interestingly we observe that for fast energy injection the rescaled equilibration time is independent of temperature of field theory.

The generation of coherent Terahertz (THz) radiation is studied which is produced from moving the relativistic electron beam through a helical wiggler with axial magnetic field. The relativistic electron beam is modulated via interacts with the beat wave of two laser beams that have frequency difference in THz range. When the modulated relativistic beam of electrons go through the helical wiggler with axial magnetic field, it radiates coherent THz electromagnetic wave as an antenna. In addition, the numerical study has shown the maximum THz power increases with the increasing axial magnetic field power.

Inside living cells, many essential processes involve deformations of charged helical molecules and the interactions between them. Actin filaments and DNA molecules are important examples of charged helical molecules. In this paper, we consider an impermeable double stranded charged molecule in the solvent. According to the nature, the dielectric constant of the molecule is considerably different from that of the bulk. In order to calculate the electrostatic potential in the problem in the Debye-Huckel regime, we find the proper Debye-Huckel Green function for the problem. Using this Green function, we calculate the electrostatic potential in the system. Furthermore, we study the dependence of the electrostatic potential on the dielectric inhomogeneity, structural parameters and the salt concentration. This study could shed some light on the role of electrostatic interactions in many essential processes involving charged helical molecules such as actin filaments and DNA molecules.

The experimental study of passively Q-switched, LED-pumped Ce: Nd: YAG laser is reported. The active medium is a 3 mm diameter laser rod with 60 mm length; it is optically pumped with four segments of blue LEDs at 460 nm, with each segment consisting of 32 single LEDs. The 14 cm length optical resonator with 2 dielectric mirrors and the reflectivity of 99 and 93 percent at 1064 nm produced more than 200 micro-joules laser spikes at the free-running mode of operation. By using a passive optical switch with 96% initial transmission and 0. 6 J electrical pumping energy, the single Q-switch (QS) laser pulse with 240 ns pulse-width and 17 micro-joules optical energy was produced. By increasing the pumping energy to 1. 2 J, two nearly similar QS laser pulses were generated. Moreover, we have proposed a method for decreasing the pulse-width and increasing the energy of single QS laser pulse that is based on controlling the pumping rate by shaping the current of LEDs.

The purpose of this paper is to present a new generalized form of the Appleton-Hartree formulation. To that end, we use a system of linearized quantum plasma equations to include quantum corrections due to the quantum force produced by the density fluctuations of electrons. Dispersion relations and their modifications resulting form quantum effects are derived for both quasi-parallel and quasi-perpendicular wave modes. In comparison to the previous studies, the results show that quantum effects modify the dispersion of the whistler, helicon, left-handed, ordinary and extraordinary waves. Furthermore, the analysis of results, in particular cases, confirms those of previous studies and, in limiting cases, leads to known relationships in classical plasma physics.