Iranian Journal of Physics Research
Year:2017 | Volume:17 | Issue:4 |Papers Count:20

Modular invarinat, constraints the spectrum of the theory. Using the medum temprature expansion, for first and third order of derivative, a universal upper bound on the lowest primary field has been obtained in recent researches. In this paper, we will improve the upper bound, on the scaling dimension of the lowest primary field. We use by the medium temprature expansion for an arbitrary order of derivatives. We show that the upper bound depends on the order of derivative. In this research, we obtain the optimal values of the order of derivatives which leads to the best upper bound.

In the present work, KTiOPO4 (KTP) crystals have been grown by spontaneous nucleation technique in flux medium using K6P4O13 flux. Cooling rates of 0. 4-1 ° C/h were applied in the spontaneous nucleation process. The presence and amount of impurities has been determined by using X-Ray Fluorescence (XRF). The optical transmission spectra of impure KTP crystals in the UV– Visible region are discussed. The transmission cut-off is clearly shown at the optical absorption edge, as well as the rapidly reduced absorption with increasing wavelength. It is shown that the presence of impurity shifts the absorption edge of KTP towards lower energy region. The wavelength dependence of absorption coefficient is determined in the UV– visible range, and the characteristics of the optical absorption edge are discussed. Results reveal that the absorption edge and the type of optical charge carrier transition can be attributed to indirect transition for these crystals. It is shown that presence of impurity decreases the indirect band gap (Eg) of KTP crystals, causing the indirect transition absorption edge to move towards lower energy. Also, structural characterization was carried out employing XRD and IR analysis, confirming the growth of KTP crystal.

A novel method is presented to describe the physics of space-charge region in a planar diode. The method deals with the issue in the time domain and as a consequence transient time behavior before stabilization can be achieved. Potential distributions and currents obtained using this technique, supposing zero initial velocity for electrons, reveal absolute agreement with other studies results. Moreover, applying the method for non-zero uniform initial velocity for electrons gives the results which are in good agreement with previous works.

The impact parameter formalism of the single-center close-coupling, first-, and second-order Born approximations have been applied to investigate direct excitations of He+(2s) and Li++(2s) ions by colliding with protons or antiprotons. The total 3s, 3p, and 3d scaled excitation cross sections are calculated in the scaled impact energy region (2 to 1000 keV). The present work aims to explore the sensitivity of the cross sections to different electronic transition mechanisms of the considered approaches as well as the charge of each projectile and target nucleus. Also, the calculated cross sections are compared with those obtained by previous theoretical calculations.

In this work, we determined the analytical expressions of the form factor of a cubical particle in the WKB approximation. We adapted some variables (size parameter, refractive index, the scattering angle) and found the form factor in the approximation of Rayleigh-Gans-Debye (RGD), Anomalous Diffraction (AD), and determined the efficiency factor of the extinction. Finally, to illustrate our formalism, we analyzed some numerical examples.

One of the most important requirements for gas and fluid industrial pipelines is the on-line leakage detection and investigation. In this paper, detection of leak and determination of its amount using radioactive tracer injection method has been simulated by Monte Carlo MCNP code. The detector array included two NaI (Tl) detectors which were located before and after the considered position, measures emitted gamma from radioactive tracer. After calibration of radiation detectors, the amount of leakage can be calculated based on the count difference of areas under the radiation detectors. Also, the factors affecting the detectable amount of leakage such as the material, thickness, diameter of pipe, types of fluid, radiation detector crystal dimension, the activity of tracer and its type (24Na, 82Br, 131I, 99mTc, 113mIn) have been investigated. According to the results, for example, leakage more than 0. 007% in volume of the inlet fluid for iron pipe with outer diameter 4 inch and thickness of 0. 5 cm, petrol as fluid inside pipe, 3 3 inch detector and 24Na with activity of 100 mCi as detector can be detected by the presented method.

This paper has been prepared by using experimental and simulated data obtained from a large and a small Filippov type plasma focus devices. In the first part of the paper, the plasma-focusing phenomenon is introduced and the parameters of the devices are presented. Then, the results of empirical studies of the pinch-time dependence to the gas pressure are provided. In the next part, the theoretical basis of the ML-model is reviewed and the results of applying this model to simulate the two devices are presented. Both simulated and experimental results showed that in the larger device, the pinch time is clearly more sensitive to the pressure variations. The study also showed that probably the model predictions for larger device are more accurate than the predictions for the smaller device.

A significant feature of alloys is their surfaces hardness which its measurement by common mechanical techniques is always accompanied by challenges. In this investigation, we used Laser Induced Breakdown Spectroscopy (LIBS) as a replacement method for common mechanical techniques employed for the surfaces hardness measurement of different alloys. After recording the spectrum of alloy samples, K-Nearest Neighbors (KNN) method was used in order to identify the surface hardness of analyzed sample. The obtained results showed that the LIBS-KNN method can distinguish and identify the surfaces hardness of samples with 93. 3% accuracy. In addition, in order to identify the percentage of constituent elements of alloys and their hardness, calibration approach was applied showing that there is an appropriate linear relation between recorded emission lines from the LIB spectra of sample alloys and the percentage of their constituent elements as well as their Vickers hardness numbers. Therefore, considering the exclusive advantages of LIBS technique, its high speed analysis, its non-destructive analysis and being portable, some of the current difficulties in conventional mechanical techniques can be removed.

In this study, designing and manufacturing of solar imaging and tracking system for research and spectroscopy applications are investigated for the first time in Iran, under the supervision of Adib astronomy center of Isfahan. The device has the ability to be used as a telescope, spectroscope, spectrophotometer and spectrohelioscope and shows acceptable efficiency in evaluations. The results obtained from this device used in various field of research such as investigating absorption spectra of the sun surface, studying the transit of planets in front of the sun, perusing Doppler effects, evaluation of the Fraunhofer lines, plotting of intensity versus wavelength and studying of solar flares have close conformity with theoretical expectations. In this research, the design and manufacture of the device, along with some of the results, are reported.

In the present study, the structural and microwave absorption properties of the iron nanoparticles and iron-carbon coreshell nanoparticles were studied. The investigated nanoparticles were synthesized by hydrothermal route and by hematite nanoparticles reduction in argon-hydrogen atmosphere. Hematite-iron phase transformation during the reduction process was studied by X-Ray Diffraction (XRD). XRD patterns showed that in iron nanoparticles, hematiteiron phase transformation was completed after 30 min annealing, whereas for iron-carbon nanoparticles, the phase transformation completion occurred after 65 min, and wustite (FeO) phase was still present in XRD patterns before 65 min annealing. Moreover, M-H loops, relative complex permittivity (ε ) and permeability (μ ) of the iron nanoparticles and iron-carbon nanocapsules were investigated. According to the ε and μ spectra in 1-18 GHz, the carbon shell can affect microwave properties of the iron nanoparticles. It can reduce microwave permeability and permittivity of the iron nanoparticles-paraffin composites.

The present paper introduces the Bayesian spectral analysis as a powerful and efficient method for spectral analysis of photometric time series. For this purpose, Bayesian spectral analysis is programmed in Matlab software for XZ Dra photometric time series which are non-uniform containing large gaps. Then, the power spectrum of this analysis is compared with the power spectrum obtained from the Period04 software, designed for statistical analysis of astronomical time series, which uses artificial data for unifying the time series. Although in the power spectrum of this software, the main spectral peak which represents the main frequency of XZ Dra variable star oscillations in the f = 2. 09864 (day-1) is well detected, but false spectral peaks are also seen. Also, in this software, it is not clear how to generate the synthetic data. These false peaks have been removed in the power spectrum obtained from the Bayesian analysis; also this spectral peak around the desired frequency has a shorter width and is more accurate. It should be noted that in Bayesian spectral analysis, it is not necessary to unify the time series for obtaining a desired power spectrum. Moreover, the researcher also becomes aware of the exact calculation process.

In this paper, we investigate the Casimir nanosystem composed of two dielectric disks separated by a thin gap. The two disks have quadrisected surface dielectric distributions, the same surface of one is exactly against that of the other. Using scatting approach in the weak coupling limit we show that if the top disk rotates about its axes by an angle θ , the lower disk experiences a torque τ  θ   sinθ . In the following, we investigate the dynamics of the system and calculate the mean non-zero angular velocity.

In this study, encapsulated ZnO nanorods with different amount of chromium (Cr) dopant (0-4. 5 at. %) were prepared with hydrothermal method, and their sensitivities as gas sensors against ethanol vapor were investigated. Morphologies of samples were explored by field emission scanning electron microscope (FESEM) which showed that encapsulation process increased the diameter of ZnO nanorods. Existence of Cr in ZnO nanorods structures was confirmed by Energydispersive X-ray spectroscopy (EDX). Based on X-ray diffraction (XRD) analysis, the ZnO: Cr nanorods had wurtzite crystal structure, and adding Cr did not alter the crystal structure of ZnO. Electrical measurements revealed that current levels of samples were decreased by adding Cr, while the current level of the sample with 4. 5 at. % was increased. This reduction could be attributed to the presence of Cr3+ ions, which led to decrease of charge carriers. Besides, due to the catalytic properties of Cr and its lower ionization energy than Zn, it was observed that Cr dopant improved the detection sensitivity of samples, and decreased the optimum operating temperature of samples. Among all samples, the most sensitivity (14) was obtained based on the sample with 1. 5 at. % of Cr for 500 ppm ethanol vapor at the optimum temperature (250  C). In fact, by encapsulating the samples, they became rougher, so the appropriate places to absorb and decompose of gas molecules are increased.

In this research, we have studied the band structure, optical properties and thermal emission spectrum of 2D silicon photonic crystal with hexagonal structure. The band structure, band gap map and theb and gap size have been calculated by plane wave expansion method in terms of radius. The maximum band gap size of TE and TM polarization, and the complete gap size are 51%, 20% and 17% at air hole radii of r=0. 43a, 0. 50a and r=0. 48a, respectively. The thermal emission spectrum has been calculated by Finite Difference Time Domain (FDTD) methd and Kirchhoff's Law in the range of 1 to 10. The obtained results show that by adjusting the geometric parameters, one can engineer the band structure, and the thermal emission spectrum of 2D silicon photonic crystal can be controlled in a manner that can be used in thermophotovoltaic systems.

Motivated by recent experiments that detects Dzyaloshinskii-Moriya (DM) interaction in Bi3Mn4O12 (NO3), we study the effects of DM interaction on magnetic orders of J1-J2 antiferromagnetic Heisenberg model. First, we find the classical phase diagram of the model using Luttinger-Tisza approximation. In this approximation, the classical phase diagram has two phases. For 2 J2  (1 D ) / 6, the model has canted Neel and DM interaction cants the spins of one on the subluttices. The ground state of model is classically degenerate for 2 J2  (1 D ) / 6, including infinit numbers of vorticity vectors that are able to minimize the model. This phase is important because of the probability of the existence of quantum spin liquid in this region. To investigate the effect of quantum fluctuation on the stability of the classical phase diagram, linear spin wave theory of Holstein-Primakoff is used. The results show that in the classical degeneracy regime, the quantum fluctuations for 2 J2  (1 D ) / 2 cause spiral order in this region. The ground state of model remains disorder for 2 2 (1 D ) / 6  J2  (1 D ) / 2, and this region is a good place for finding quantum spin liquid.

In a gravitational microlensing event, at caustic crossing, the flux of a spot can be magnified several times with respect to the source star. This magnification contrast provides a unique opportunity to measure the magnetic field over a source star. In this work, we investigate the possibility of magnetic field detection through the Zeeman effect when a source crosses a caustic line. Using Fourier analysis, one can separate other broadening agents from actual Zeeman broadening. At next stage, we use gravitational microlensing formalism to measure the magnification contrast of spot and source, and finally, using two reliable strategies of observation and Monte Carlo method, we find the detectability of magnetic field. The resolution and the signal to noise rate in each strategy determine which magnetic fields are detectable.

In this study, the exclusive measurement of charged pions are reported in the proton-proton collisions, in them, protons are not broken. This measurement is performed in Large Hadron Collider (LHC) using Compact Muon Solenoid (CMS) detector collected at a center-of-mass energy of =7 TeV and with an integrated luminosity of 450  b-1. The dipion cross section is measured for single-pion transverse momentum pT > 0. 2 GeV/c and rapidity |y| < 2, is 20. 5  0. 3 (stat)  3. 1 (syst)  0. 8 (lumi)  b. Besides, the differential cross sections as a function of  +-invariant mass are compared to phenomenological predictions.

Using a computing code, Nilsson Hamiltonian energies have been calculated based on the perturbative treatment at different deformation parameters. Special attention is given to the projection of a proton state on the asymptotic basis functions. The calculations show that the spin-orbit and  2 terms couple different asymptotic eigenstates and thus the Nilsson Hamiltonian would not be diagonal in these basis functions. With increasing the deformation, the non-diagonal terms become smaller. Therefore, at enough large deformations   0. 4, the asymptotic quantum numbers will be good quantum numbers.

In this work, we calculate DGLAP evolution equation at LO and NLO by Laplace method for fragmentation function of gluon to meson or baryon. To prove the validity of this method, we evolve the fragmentation functions of g   c and g  j / by using this method. In this method, it is not necessary to calculate these functions in Laplace space. This method is just used for simplifing the equations.

In this paper, SiO2 thin film is produced by two methods: at the first method, SiO2 is directly evaporated by the electron gun and the oxygen gas is injected to compensate for oxygen loss due to dissociation. At the second method, silicon monoxide is evaporated by thermal evaporation and during the evaporation time, the substrate is bombarded by the oxygen ion that is produced by an ion source. The refraction index, the extinction coefficient and the layer thickness are calculated by numerical method of the transmittance and reflectance equations. By the shift in the spectral transmittance, the amount of non-uniformity is calculated. The results show that if the quantity of the current and the ion energy are selected properly, SiO2 film will not have absorption in the second method. Moreover, SiO2 film produced by the second method is more uniform than that produced by the first method.