مجله پژوهش فیزیک ایران
سال هجدهم شماره 2 (تابستان 1397)

In the ADM the dark matters interact with the ordinary matters exclusively through the electromagnetic anapoles. Meanwhile, the only allowed electromagnetic form factor for the spin 1/2 Majorana fermions is the anapole one. We study the electromagnetic interaction of the Majorana neutrinos in non-commutative standard model (NCSM) and the Lorentz violated extension of the standard model (SME). Consequently, we obtain the anapole form factors in the both models. Comparing the obtained results in the SME with the experimental data only put a bound on dý00ý-parameter among the SME- parameters which is of the order of 0.04. We estimate a bound of the order of 0.5 TeV on the parameter of non-commutativity

In this work, the effects of inner radius and width variation on energy spectrum and persistent current in hexagonal graphene quantum rings with zigzag edges have been studied by using the tight-binding model. Our investigation show that the energy spectra of these rings are grouped into subbands which each one consists of six coupled energy levels that separated by energy gaps. The pattern of these subbands and gaps are strongly affected by inner radius and width. In other words, width and inner radius of the HGRs plays a very important role in gap engineering. Narrow HGRs have more regular energy subband patterns and also larger gaps, which is due to increasing the quantum confinement and the edge effects, especially in the corners of the structure. Increasing the inner radius leads to the compression of six coupled energy levels in each subbands therewith decreasing the subband gap near the Fermi level. Furthermore, increasing the inner radius or width have similar effects on the energy spectrum, so the effect of increasing one of them can be neutralized by decreasing the other one. Specially, it is dominant for the energy gap near the Fermi level. Additionally, increasing the inner radius or width leads to increasing in the amplitude and oscillations of persistent current versus magnetic flux. Meanwhile, width variation is more effective than variation of inner radius on persistent current.

In this research we have studied the Brownian motion of a heavy particle in thermalized plasma. This plasma is made of quarks and gluons and it is different with normal plasma. Since, coupling constant is strong in this plasma, usual perturbation method does not work for the study of this plasma. For this purpose AdS/CFT duality is used. Based on the AdS/CFT duality to consider temperature we have to consider a black hole in the bulk. Also, the particle is described by end of the classical string that starts from the boundary of AdS5 space and continues to the black hole . Brownian motion of the particle leads to perturbation in the string and coefficients of the Langevin equation can be obtained precisely from the study of behavior string under this perturbation. With this method longitudinal and transverse Langevin coefficients calculated precisely and we investigate the Einstein relation

The intensity of Compton scattered γ-ray photons provide useful information about the electron density distribution of a test sample. Because of photon attenuation, the application of this method is limited to a certain depth of the sample (saturation depth). The saturation depth value depends on the energy and intensity of primary photons and on the material of the sample. In this study, we measured the energy spectrum of the scattered photons of 662 keV at 90° with a NaI(Tl) scintillator; and determined the saturation depth of the sample by the Artificial Neural Network (ANN) algorithm. Two sets of samples with known and unknown density were used to train and test the network, respectively. The highest precision (with 0.15% relative error) was achieved by using the Levenbert-Marquardt algorithm with five hidden layers

. An annular cell with elliptical cross section and small physical size is introduced and simulated for increasing the absorption length in the spectroscopy. In this investigation by changing of the geometrical radius of the ellipse an absorption length of 15.50 m is obtained. By the optimization of the cell and including the sagittal and tangential radius of the ellipse that reflect the beam, it is shown that at the obtained absorption length, it is possible to reduce the divergence of the beam down to 54 µm. Then, signal-to-noise ratio (SNR) is calculated for R(16) CO2 absorption line by assuming that the cell is filled by the gas. The results of this calculation indicated that under optimum condition the SNR can be increased up to 310. Finally, the cell is optimized using Genetic algorithm by including all the effective parameters which affect the efficiency of the cell. We found that in the best case an absorption length of 8.24 m with a SNR of 107 can be achieved when the geometrical radius of the cell being fixed at 5.95 and 4.59 cm.

In this paper, we investigate optical properties of silver pyramid nanostructures (SPNs) by means of discrete dipole approximation (DDA), when these nanoparticles are embedded into the water. Absorption, scattering and extinction cross-sections of the SPNs were calculated by change of incident wavelength in visible and near infra-red region. Moreover, height, wavelength and full width at half maximum (FWHM) of extinction cross-section peaks (due to plasmon resonances) were studied by change of nanostructure's size and dielectric constant of medium. Our results show that, there are only two peaks of dipole and quadruple modes in this spectrum.

In this research, the dispersion properties of magneto-acoustic waves in a plasma in the presence of quantum effects are studied. For this purpose, we employ a system of quantum fluid equations and Maxwell equations to derive a generalized dispersion relation. Our analytical results show that the wave frequency is modified by quantum corrections. Also, numerical estimations reveal that the effects of thermal aspects dominate compared to the magnetic and quantum effects. Further, except for very short wavelengths, our findings show that quantum effects can be ignored compared to the thermal and magnetic effects. Finally, the results of some special limiting cases are discussed.

Nanostructured TiO2-SnO2 thin-film ethanol sensors have been fabricated on glass substrates using electron beam and sol-gel methods. The surface structure, morphology and optical transmission characteristics of the films were analyzed by X ray diffraction, scanning electron microscopy and UV/VIS/NIR spectrometry. The TiO2-SnO2 films were less than 300 nm thick and consisted of nanocrystallines about 20 nm and 33nm for electron beam and sol-gel methods respectively. The sensing characteristics of TiO2-SnO2 nano structure thin film in electron beam and sol-gel methods, in the flow rate of ethanol at 1800, 2000 and 2400 cc/min at the operating temperature of 200˚C were measured

At the beginning of thermonuclear ignition in fusion plasma, the bremsstrahlung radiation is dominant phenomenon, the photons distribution function is Planckian and plasma is considered as optically thick one. But at a certain energy, the bremsstrahlung radiation and Compton scattering losses rates become equal and plasma makes a transition from optically thick to optically thin and photons distribution switches from Planckian to a Bose-Einstein one. Dominating the Compton scattering and conservation of photon number density in this event, cause to increase the photons temperature and to decrease the negative role of Compton scattering in electrons balance equation. In this paper the photons distribution change effect in calculating of critical burn-up parameter by using of a Fortran programming code is investigated and the results are compared with a typical case where the photons have Planckian distribution throughout the ignition

One of the most important results of neutron irradiation on targets is that atoms are displaced from their lattice sites after that a nuclear reaction. The neutron irradiation damage is often simulated by using light/heavy ion irradiations, which prepare flexible irradiation conditions. The knowledge of primary knock-on atoms (PKA) and point defect energy distribution is the first step to simulate radiation damage induced by neutrons and also calculation of the amount of damage in “displacements per atom” (DPA) and damage profile in target is another purpose. In this study the MCNP code and SRIM code have been used to simulate the interaction of neutrons and energetic ions with materials then a new program was written by MATLAB software, AMTRACK, which analyzed PKA and point defect specifications. Finally the comparison of fraction of recoils spectra as well as weighted recoil spectra induced by ions/neutrons leads to determine best ions and its energy to simulate damage in reactors and our final goal is to be able to predict the amount and profile of radiation damage by best ion and neutron spectrum

In this paper, we consider a system including two maghnetodielectric slabs with different temperature that are placed in vacuum at zero temperature and very short separation distances from each other. Based on the canonical quantization of the electromagnetic field in the presence of dissipative media, we investigate the radiative heat transfer arising from thermal and quantum fluctuations in out of thermal equilibrium but stationary situation. For this purpose, we calculate the ensemble average of Poynting vector by driving quantum correlation relations between noise polarization and magnetization operators and extracting the electromagnetic Green tensor of the system. Finally, we analyze the transferred radiation of aforementioned system by employing the numerical result of the Poynting vector

In this paper, the influence of initial momentum and the injection angle of electron in to the magnetized plasma in a laser wake-field accelerator have been studied.It has been seen that the use of external magnetic field in the opposite direction of laser pulse propagation leads to an increase in the wake-field amplitude and a decrease in laser pulse group velocity in comparison to the use of external magnetic field in same direction of laser pulse propagation or unmagnetized plasma case. The results show, the effect of initial momentum variation on the final energy gained by electron is lower in comparison with the effect of injection angle variation. It is observed when the injection angle is increased, the electron can stay more in acceleration phase and reach to more final energy. The maximum final energy of accelerated electron is about 2.5 GeV when the magnetic field is applied along the reverse direction. Also, the electron energy is increased with the increase of injection angle and lowest energy is related to the case of magnetic field applied along the reverse direction.

Base on the non-relativistic Faddeev AGS method, three-body calculations of the coupled and quasi-bound KKN-πKΣ system are performed in the momentum space. Different phenomenological models of KN-πΣ potentials with one and two-pole structures of KN-πΣ resonance are used to study the dependence of double-kaonic system binding energy on the coupled KN-πΣ interaction. Also, the effect of the KK repulsive interaction is investigated in this system. The results of this work show that the binding energy of KKN-πKΣ quasi-bound state is 61-110MeV and the width is about

In this study, waves instability in free electron laser with background plasma, under the influence of self-electric and self-magnetic fields, are analyzed. A dispersion relation in the Raman regime for free electron laser with a helical wiggler magnetic field and an axial magnetic field derived in which all possible wave modes can have unstable couplings with each other. This dispersion relation is solved numerically to investigate the influence of self-fields on unstable couplings. It was found that self-fields reduce the growth rate of the group I orbits and increase it in the group II orbits

In this paper size effects, growth orientation and also doping by Ammonia molecule (NH3) on the carbon nanowire properties with saturated diamond structure by (DNw:H) have been investigated. This study was carried out using DFT theory and Kohn-Sham equation by self-consistent field (SCF) that performed by local density approximation (LDA). The nanowires morphology is cylindrical with [111] growth orientation and their lateral surface was saturated by hydrogen atoms. The results show that band gap of these nanowires is smaller to bulk diamond due to high surface to volume ratio and formation surface level. The results of ammonia molecule doping with carbon surface atoms at saturated diamond nanowire in [100] orientation lead to decrease in band gap until nanowire converted into a n-type semiconductor.

This paper shows a theoretical study of the thermal properties of armchair grapehen nanoribbons in the presence of extended vacancies. Each graphene nanoribbons formed by superlattices with a periodic geometric structure, different size and symmetry of vacancies. The phonon dispersion, specific heat and thermal conductivity properties are described by a force-constant model and also by Landauer theory calculations. Our results show that the geometric structure of the vacancies and their positions have a significant roles in controlling the thermal properties, especially at low temperatures. Moreover, the out-of-plane and in-plane phonon modes exhibit a different role in the heat capacity and thermal phonon transport properties. Moreover, the out-of-plane phonon modes have more contribution in low temperature regime rather than in-plane phonon modes even in the presence of extended vacancies. The result may be useful for the design and improvement of thermal or thermoelectric nanodevices

After a short review of nematic liquid crystals and their interactions with the external fields, we investigate the effect of a disordered field which destabilizes the orientational molecular order of a nematic film. We analyze the effect of the disorder in the applied field on the pseudo-Casimir force which is induced due to thermal fluctuationsbetween the confining walls of the nematic film. It is shown that an annealed disorder gives rise to a characteristic way, leading to the enhancement of the strength of the interaction. This, in turn, has some impacts on the fluctuation-induced force studied here

In this paper, the effect of the material and distance of the substrate on the characteristics of gamma alumina nanopowder coated by plasma spray method are investigated. For this purpose alumina nanopowder were coated on the two types of stainless steel and Pyrex glass substrates using a plasma torch. Morphological characteristics of the prepared nanolayer are studied by investigating the scanning electron microscope patterns. Also, the structure and phase changes of deposited alumina are investigated by X-ray diffraction spectrum. The results of this study show that the amount of particles deposition on the steel substrate is more than the glass case. Also, it is shown that by increasing the substrate distance, the amount of particle deposition is decreased for substrates. There is one optimum distance for substrate position with respect to the nozzle exit of the torch for produce and suitable coating and its control. One important result of this experimental study is the phase transfer of alumina from gamma to alpha due to the high temperature of the plasma torch

The electronic transport in an infinite arrays of driven quantum wells coupled to a quantum ring is studied via a single-band tunneling tight-biding Hamiltonian by perturbing and numerical simulations approaches. In the perturbing approach, an analytical relationship in terms of the coupling constants between nearest-neighbors in quantum wire coupled to a ring based on the quantum dynamical algebra is obtained. With a choice of three wells on the quantum ring, the transmission probabilities of electron of the number zero well of an  wire under the effect of a constant field to the first, second and third well of quantum ring has been obtained for different values of the nearest-neighbors coupling constants in  wire and quantum ring of the system. The effect of changes these parameters on the location and height of the first peaks related to the diagrams of transmission probability have been studied.

In this paper 5 different samples of Ni-Cu-Zn nanoparticles (Ni0.8-xCuxZn0.2Fe2O4) with different compositions of  x=0.2,0.4,0.6,0.8  synthesized through auto-combustion method using glycine as fuel and then structural, magnetic and optical properties of this samples investigated. Characterization of these samples done using XRD, FTIR, UV-Visible, SEM and SEM. XRD data proves existence of spinel structure for all samples. FTIR spectrum shows the existence of oxygen-metal M-O bond at tetrahedral and octahedral bonds. SEM images showed the semispherical shape of particles. Using UV-Visible spectrum we measured by increasing the amount of Cu dopant the gap energy of Ni-Cu-Zn nano particles decreases and also results of VSM showed that saturation magnetization decreases by increasing amount of Cu dopant.