مجله پژوهش فیزیک ایران
سال بیستم شماره 3 (پاییز 1399)

In present research,  the electrical, structural, quantum and 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, we consider seven models for adsorption of N2O gas on the exterior surfaces of BPNTs 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 reveal that the adsorption energy of all studied models of BPNTs is negative values and 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 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 decrease 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 the 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 adsorbing and making N2O gas sensor.

In this work, nickel oxide nanoparticles (NiO NPs) have been synthesized via photo irradiation as ‎a novel method. It is a simple and cost effective method. The average particle size and morphology ‎were examined by AFM, TEM, SEM and the crystallinity was estimated by XRD analysis and the ‎strength of magnetic field of samples were measured by using gaussmeter device. XRD studies ‎confirm the nickel oxide nanoparticles have a high degree of crystallinity nature. Their particle size ‎of nickel oxide was found about 12nm. The values inhibition zone indicates that nanoparticles effect on different bacteria. The outcome considered a new synthesis of NiO ‎nanoparticles to promise antimicrobial agents against bacteria.

At the present time, Magnetic Confinement Fusion (MCF) is considered as a way to produce energy. In this work, one of the Magnetohydrodynamic (MHD) limitations has been discussed. As closed magnetic surfaces, the Magnetic Islands (MIs) which are generated due to pressure effects, need to be surrounded by a separatrix which separate them from the other parts. External Magnetic Fields (EMFs), the safety factor (q) and the pressure profiles would be used to take the MIs under control. This could be achieved through an exterior medium, exclusively the Electron Cyclotron Heating (ECH) as well as the Current Drive (ECCD). Study of the magnetic flux surfaces and the effect of magnetic perturbation on tokamak plasmas, inform us about the formation of the MIs and their locations. In this work, together with the comprehensive review of the MIs and their importance, the conventional methods for improving the magnetic confinement has been introduced and discussed. In this regards, the Hot Limiter Biasing (HLB) method and the Resonant Helical Field (RHF) which is produced by external Helical Coils (HCs) were introduced and used. Then, the plasma current (), the Loop voltage, and the MO were obtained for different  states. Finally, the Magnetic Islands Width (W) and their Growth Rate (GR) were calculated and compared with the experimental results.

In this work, we have studied the tunneling of a single atom in a double-well. The atom is interacting with a single ion in a simple harmonic trap placed in the center of the double-well. The tunneling of the atom is controlled by the spin and/or motional state of the ion. Considering a model potential, we have shown that it is possible to generate an entangled state between the spatial state of the ion and the atomic wavefunction.  By employing the optimal control method,  the quantum speed limit of generating this entangled process has been explored. This system can be used as qubit in quantum computers.

Cobalt – palladium thin films with different Co:Pd ratio, CoxPd100-x (x=23, 36, 42), have been deposited on fused silica (amorphous SiO2) by pulsed laser deposition (PLD). For the structural characterization of the thin films, X-ray reflectivity (XRR) and X-ray diffraction (XRD) are used and for investigation the magnetic characteristics of the films, physical properties measurement system (PPMS) is used. The results show that the thickness of the thin films is in the range of 16-20 nm and the crystal structure of the films is FCC. Also, the films have a [111] preferred growth direction. The study of the magnetic properties shows that the magnetic anisotropy tends to align in the perpendicular direction by the increase of Pd:Co ratio, which is attributed to the enhancement of the spin-orbit interaction. Also, in this work, the effect of thickness on the magnetic anisotropy is investigated.

We develop a model to study how invasion front depends on the relevant properties of a cellular environment. To do so, we use a nonlinear reaction-diffusion equation, the Fisher equation, to model the population dynamics. Our study is intended to understand how heterogeneity in the cellular environment's stiffness, as well as spatial correlations in its morphology,  given that the existence of both has been demonstrated by experiments, affects the properties of  the invasion front. It is demonstrated that three important factors affect the properties of the front; these are  the spatial distribution of the local diffusion coefficients, the correlations between them, and R/D, the ratio of  the cells' duplication rate R to  the cells' average diffusion coefficient D. Analyzing the scaling properties of  the Fisher equation invasion front, we show that , contrary to several previous claims, invasion fronts, including those of tumors and cancerous cells colonies, cannot be described by the well-known model of kinetic growth, such as the Kardar-Parisi-Zhang equation.

Among 2D nanomaterials, WS2 monolayers with a direct bandgap and sharp absorption at 619 nm have  opened a new horizon for the use of these materials in photonics and electropopics. In this paper, in order to increase the absorption, the role of Ag thin film as a plasmonic layer on the substrate and also,  the effect  of spacer and cover layers are theoretically investigated. The optical properties of the designed structures are investigated by the transfer matrix method in the visible wavelength region. In the structure consisting of a WS2 monolayer with Ag and spacer layers, the absorption at 619 nm was increased to 57%. Sharp optical absorption as high as 40% for a large range of incidence angles in both polarizations was retained, giving  a good perspective on the realization of WS2 applications

In this paper we study the anomalous triple gauge boson couplings (aTGCs) via proton-proton collisions at the high luminosity phase of LHC through the process of central exclusive production pp→pWWγp at the center of mass energy 14 TeV and integrated luminosity 3 ab^(-1). In this study to reduce the background processes, the leptonic decay of bosons is considered. In order to distinguish this process from inclusive processes in proton-proton collision, final intact protons must be detected. For this purpose, we use the feature of the forward detectors embedded at a distance of about two hundred meters on both sides of the proton interaction point and a few millimeters transverse distance from the proton beam. Using the kinematics of the particles produced in the central detector and their dependence on the kinematics of the intact protons in the very forward region, we set the appropriate cuts and obtained the expected limits on aTGCs. Comparing the obtained results with the existing experimental limits indicates that this process can be considered as a complementary process to the study of these couplings and improve the existing limits on the aTGCs.

In this study, calcium nitrate tetrahydrate (Ca (NO3)2.4H2O) and phosphorus pentoxide (p < sub>2O5) were used to synthetize hydroxyapatite nanoparticles through the sol-gel method at the ambient temperature. In order to examine the structure and identify the chemical bonds and to compare them with the  intact tooth, X-ray diffraction analysis (XRD) and Fourier transform infrared spectrum (FT-IR) were used, respectively. Also, through scanning electron microscope (SEM) images, the microstructure and morphology of both synthesized hydroxyapatite nanoparticles and intact tooth were investigated. The results of X-ray diffraction analysis and Fourier transform infrared spectrum indicated  that the produced powder was  pure hydroxyapatite, i.e. without any discernible amount of impurity in the sample. Crystal structure of the synthesized hydroxyapatite was  nearly identical to the crystal structure of intact tooth; moreover,  the chemical bonds of the  intact tooth were also seen in hydroxyapatite. Furthermore, the synthesized sample featured a high degree of crystallinity. On the other hand, analysis of SEM images showed  that the morphology of the synthesized hydroxyapatite and intact tooth (with nanoscale dimensions and average particle size distribution of 25.69 nm and 23.15 nm, respectively), was almost spherical, thereby confirming the similarity of  the synthesized nanoparticle structure to thr intact tooth. In these images, the agglomeration of the synthesized nanoparticles was also seen. Compressive strength of the synthesized sample was equal to  5.5 MPa, which was approximately the same as that  of the  cancellous bone.

In the present work, the triple and double differential cross sections of atomic hydrogen ionization in the collision with protons at intermediate and high energy ranges are calculated. Interaction potentials were considered as Coulomb form and the calculations of the triple differential cross section have been performed entirely analytically by using the first-order Born-Faddeev approximation. The triple differential cross sections at different energies and momentum transfers are compared with the first Born approximation results. Finally, the results of the double differential cross section have been obtained by this approximation are compared with experiment and available theoretical results.

In this paper,  we investigate the instability of the quasi-confining gauge theory D3+D(-1) induced by the simultaneous application of constant electric and magnetic fields. According to the gauge-gravity duality, the decay rate due to the presence of external fields can be calculated using the imaginary part of the DBI action. Since the quarks are confined in the theory under study, the decay rate of the quarks, even the massless ones, is nonzero only if the electric field is greater than a threshold value,  which is the critical electric field of the theory. We also observe that the application of a constant magnetic field parallel to (perpendicular to) the electric field direction increases (decreases) the decay rate. On the other hand, the dependence of the critical electric field on the magnetic field shows the magnetic catalysis, i.e., the application of the magnetic field enhances  the critical electric field above which the Schwinger effect occurs.

From the wrapping of the (anti)membranes of 11-dimensional supergravity over , on the internal directions along with an ansatz for its 4-form flux, by  solving the original equations and identities, we arrive at scalar differential equations in the  Euclidean  space; note that the associated bulk solutions and setups break all supersymmeties, parity and scale invariance; the resulting (pseudo) scalar potential, which is Higgs-like with two nearly homogeneous vacua, provides the first-order phase transition and tunneling from the false- to true- vacuum.  Here, concentrating on the three (pseudo) scalar modes m2=-2, 4, 10 , which are, in turn, realizable in Wick-rotated and skew-whiffed M2-branes backgrounds, we employ approximate methods and, particularly, Adomian decomposition method to solve the nonlinear second-order partial differential equations, valid in the  probe approximation, with the  Dirichlet boundary condition or the initial data from a basic exact solution, to get solutions in series expansions near the boundary in different orders of perturbation. Next, making use of the AdS4/CFT3 correspondence rules, after swapping the three fundamental representations of  for gravitino, we build the dual singlet  operators from the (scalar, fermion and gauge) fields in a 3-dimensional Chern-Simons-matter  gauge field theory living on the resultant anti-M2-brnaes; after that, by deforming the corresponding boundary actions with the operators, we get   invariant solutions with nonzero finite actions, which ,in turn, are small instantons sitting at the origin of a 3-sphere at infinity, causing  instability and mediating false vacuum decay. In other words, the boundary potentials unbounded from below are duals for the collapse of the bulk (thin-wall) vacuum bubbles and big crunch singularities.

Theoretical studies and numerical simulations of the protoplanetary discs (PPDs) indicate that magnetorotational instability (MRI) is a dominant mechanism in the accretion process. Recent observational evidence, however, implies that magnetic winds present in these systems. Launching the magnetic winds leads to further angular momentum removal and a higher mass accretion rate. Non-ideal MHD disc simulations have shown than there is a correlation with MRI and the magnetic winds. Thus exploring the structure of the PPDs with the magnetic winds plays a vital role. We present fully analytical solutions for the evolution of a PPD with the magnetic wind. Relations for the stress tensor components associated with the disc turbulence and the magnetic wind are motivated by recent MHD disc simulations. These relations are written in terms of the ratio of the gas and the magnetic pressures. In the case with a strong magnetic field, the role of the magnetic wind in the angular momentum removal is dominant. We show that a PPD undergoes a non-significant mass loss during the early stage of the evolution. But the mass loss rate is significantly amplified beyond a certain time. It seems that role of the magnetic wind in the older PPDs is more noticeable. We also indicate that the two-stage evolution of a PPD with the magnetic wind is more or less independent of the disc radial temperature distribution.

Spherical property of stars means that the flux received from different parts of their surface is not uniform and less than its center at the edges. Thus, the edges appear darker than the center of the star; this is called the limb-darkening effect. The amount of the limb-darkening effect depends on the stellar atmosphere, stellar temperature, gravity and metallicity. In this paper, we offer a method to  better characterize  the source stars in high-magnification microlensing events. In high-magnification microlensing events in  which the lens is transiting the source surface, the  non-uniformity of the stellar flux and the magnification factor as a function of the lens location can both cause the stellar color changes with time. Measuring the stellar color while lens is crossing the source surface will offer additional  information regarding  the dependence of the limb-darkening parameters on  the wave length and hence, the stellar atmosphere parameters and the source star parameters.

In the  recent years, with advances in material growth, there has been a considerable interest in the compound semiconductors of group III-V, in particular GaAs. Silicon (Si) is the most suitable substance for the n-gallium arsenide type [1]. In this study, the structural and electron properties of Ga6As4H10 and Ga6As3SiH10 nanocrystals are investigated using the quasi-potential and density functional formulation (DFT) method and with the approximation of LDA in the quantum espresso package. The results of the calculations show that the larger the size of the nanocrystal, the more the decrease of  band gap. By replacing the Si atomic impurity by  the As atom in the Ga6As4H10 nanocrystal, the energy gap becomes smaller than the non-degenerate state, and the fermi level approaches the edge of the conduction band, in which the Ga6As3SiH10 nanocrystal is a n-type semiconductor. The charge density of the charge around the atoms shows an ion-covalent bond between  Si and Ga atoms. In this study, the optical properties of gallium arsenide nanocrystals have been investigated; calculations are performed with single-particle approximation. Gusin software is also used to obtain the optical spectrum of the nanocrystal. The optical spectrometry for gallium arsenide nanocrystals shows the transition to blue.

Due to the high aspect-ratio of 2D graphene oxide nanosheets in water,  the lyotropic nematic liquid crystal phases of graphene oxide dispersions can be  spontaneously formed. The unique visco-elastic characteristics of such liquid crystals can make them a  novel category of soft materials. The fundamental insights ensued in this work can be used as a basis for the development of new guidelines for the processing of soft 2D materials by means of vastly available traditional fabrication methods. The concentration range of isotropic, biphasic and nematic phases was determined by employing polarized optical microscopy. Using 2D sheets with  a high aspect ratio (over 35000) resulted in the formation of the biphasic region at a concentration as low as 0.05 g/l and the fully nematic region at concentrations higher than 0.25 g/l. Shear rotational rheology and interfacial dilational rheology were employed, as the tools of choice, to correlate the nematic phase formation with the processability and the change in modulus. Our results underpin the argument that the combination of the  low concentration of 2D sheets in the supporting media and high elastic modulus can  facilitate the use of graphene oxide based formulations for an array of processing and fabrication techniques including but not limited to wet-spinning, electro-spraying, inkjet printing, and 3D printing.

In this study, the detection of cosmic ray from the earth’s atmosphere is addressed. The speed and the lifetime of the muons are measured with plastic scintillator coupled to photomultiplier detector. In this research, the digital system is used over the analog system due to its reliability, high speed performance, small volume, and accurate response. We find that the mean speed of muons to be around ( 2.831 ± 0.0394) *108 m/s ,(β = 0.944 ± 0.0131), with the mean lifetime of 2.033 ± 0.177 microsecond which are consistent with the theoretical results. In this experiment, we use the facilities at the School of Particles and Accelerator in IPM.

In this study, the relationship between daimagnetic shielding (σd), paramagnetic shielding (sp+s´p) and 13C isotropic shielding tensors 13C(σiso) with Mulliken, NBO and QTAIM atomic charges and also the relationship between chemical shielding and magnetizability in (5,0) zigzag single Walled Carbon Nanotube (SWCNT) as potassium doped and without potassium are investigated using Density Functional Theory (DFT) based on Periodic Boundary Condition (PBC) approach at the PBEPBE/6-31G(d) level of calculation.The doped (5,0) zigzag SWCNT with potassium is converted to n-type more stable Carbon Nanotube.There are linear relationship between the Mulliken, NBO and QTAIM atomic charges with 13C isotropic chemical shielding (σiso) and with dia-magnetic shielding (σd) in the SWCNT with and without potassium doping.The relationships are nonlinear between the total para-magnetic shielding (σp+σ´p) and all charges in the potassium doped SWCNT. In the both of structures of potassium doped and without potassium SWCNT, there are strong linear correlation between the Total-atomic magnetizability (Χ(Ω)) and 13C isotropic chemical shielding (σiso).

The study of cosmic large-scale structures provides valuable information regarding the initial condition and the evolution of random filed approaches. In this paper, relying on  the scaling properties of stochastic field, we examine the geometric properties of the dark matter density field in the N-body simulations. To this end, we examine the scaling properties of iso-density lines in the (1+2)-dimensional fields that are cut-out from the (1+3)-dimensional fields of the N-body simulations that are quantifiable using the modified multifractal dimension, D_q. The scaling properties holds for the afore-mentioned fields in all existing redshifts in the simulation. All iso-density threshold contours display a regular geometric shape in the highest accessible redshift, but they exhibit a multifractal property when reducing the redshift. Due to the non-Gaussianity of the low redshift transitioning fields, the multifractal property can mostly be caused by the distribution function's deviation from Gaussianity. The evolution of the D_q scaling exponent with respect to redshift demonstrates that for  the positive q's, the monofractal property mostly holds, while the  mentioned exponent is highly redshift dependent for the negative q's. This can be employed as a sensitive criterion for distinguishing different models for large-scale cosmic structure formations.

In this research, the protection properties of tellurites metal oxide glasses such as TPZ, TNS, TBN, TSW, TBB glass and concrete (SSC) against 10 radiation gamma radioisotopic sources were investigated. For this purpose, the MCNPX code was used to simulate the photon transport in the samples and the XCOM cross section database was applied to calculate the mass attenuation coefficient. The effective atomic number, linear attenuation coefficient, and flux buildup factor against radiation of gamma radioisotopic sources were determined for the mentioned shields. The results show that considering the average energy in the radiation protection calculations for a multienergy gamma source cannot be a suitable criterion; therefor it should be considered the whole energy spectrum of the source. The TBB glass was the best photon attenuator compared to other tellurites metal oxide glasses, because it had the highest effective atomic number, linear attenuation coefficient, and minimum flux buildup factor for all gamma-radioisotopic sources.