Tabriz, Iran

University of Tabriz
Tabriz, Iran

The University of Tabriz is a national university in Tabriz, East Azarbaijan. It is one of the five high-ranked universities in Iran and one of the ten most selective universities in country. University of Tabriz is the second-oldest university in Iran after the University of Tehran, and has the second largest campus area in country which is the biggest academic institution in northwest of country. Wikipedia.

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Koohestani K.,University of Tabriz
Communications in Nonlinear Science and Numerical Simulation | Year: 2014

We develop an alternative approach for the form-finding of the minimal surface membranes (including cable membranes) using discrete models and nonlinear force density method. Two directed weighted graphs with 3 and 4-sided regional cycles, corresponding to triangular and quadrilateral finite element meshes are introduced as computational models for the form-finding problem. The triangular graph model is closely related to the triangular computational models available in the literature whilst the quadrilateral graph uses a novel averaging approach for the form-finding of membrane structures within the context of nonlinear force density method. The viability of the mentioned discrete models for form-finding are studied through two solution methods including a fixed-point iteration method and the Newton-Raphson method with backtracking. We suggest a hybrid version of these methods as an effective solution strategy. Examples of the formation of certain well-known minimal surfaces are presented whilst the results obtained are compared and contrasted with analytical solutions in order to verify the accuracy and viability of the suggested methods. © 2013 Elsevier B.V.

This paper re-examines the causal relationship between energy use and Gross Domestic Product (GDP) in the United States for the period 1960-2005. To that end, we use Markov-switching vector autoregressive (MS-VAR) models, rather than vector autoregressive (VAR) models, which allows for regime shifts. These models are capable of detecting changes in the relationship between variables; in addition, the coefficients of the model are time dependent and they depend on the states of the variables. Therefore, in contrast to VAR and vector error correction models (VECM), which assume a stable relationship, the relationship between the variables could be different in the separate regimes.Results from the estimation of MS models show changes in the pattern of causality relationship between GDP and energy use. That is, we found evidence of bidirectional Granger causality (GC) between the variables in the first regime, while there is no GC between the variables in the second regime. The first regime consists of 1971-1975, 1977-1982, 1989-1995, and from 2001 to the end of the sample. This regime includes the energy crises in 1970s, the recessions in the early 1980s, 1990s, and the recession in 2001. © 2011 Elsevier Ltd.

Kangarlu M.F.,University of Tabriz | Babaei E.,University of Tabriz
IEEE Transactions on Power Electronics | Year: 2013

Application of multilevel inverters for higher power purposes in industries has become more popular. This is partly because of high-quality output waveform of multilevel inverters in comparison with two-level inverters. In this paper, initially a new topology for submultilevel inverter is proposed and then series connection of the submultilevel inverters is proposed as a generalized multilevel inverter. The proposed multilevel inverter uses reduced number of switching devices. Special attention has been paid to obtain optimal structures regarding different criteria such as number of switches, standing voltage on the switches, number of dc voltage sources, etc. The proposed multilevel inverter has been analyzed in both symmetric and asymmetric conditions. The validity of the proposed multilevel inverter is verified with both computer simulations using PSCAD/EMTDC software and laboratory prototype implementation. © 1986-2012 IEEE.

A recently reported microextraction technique namely air-assisted liquid-liquid microextraction (AALLME) has been described for the extraction/preconcentration of some triazole pesticides from different samples prior to gas chromatography-flame ionisation detection (GC-FID). This technique is similar to dispersive liquid-liquid microextraction (DLLME) but in this method there is no need to use a disperser solvent and also volume of the used extraction solvent is less than DLLME. In this study, toluene with a density lower than that of water was used as an extraction solvent. Under the optimum extraction conditions, the method showed wide linear ranges with R2 < 0.996 and low limits of detection and quantification between 0.53-1.13 and 1.76-3.77 ng mL-1, respectively. Enrichment factors (EFs) and extraction recoveries (ERs) were in the ranges of 713-808 and 100-113%, respectively. Relative standard deviations (RSDs) for the extraction of 25 and 250 ng mL-1 of each selected triazole pesticide were less than 7% for intra-day (n = 6) and inter-days (n = 5) precision. The method was successfully used for analytes determination in different surface water, grape juice, cucumber, and tomato samples. © 2013 Elsevier Ltd. All rights reserved.

Barvestani J.,University of Tabriz
Optics Communications | Year: 2011

We have studied the dielectric-superconducting pair defect embedded into one-dimensional photonic crystals by an analytical method based on the Kronig-Penny model. The superconducting defect has been considered by using of two-fluid model whose permittivity depends on the frequency and superconductor parameters. We have showed that in contrast to the usual defect modes, superconducting defect modes are nearly invariant upon the change of defect size and with increasing defect sizes, the enhancement behavior is observed in the peak of electric field profiles. In addition, the physical parameters have less effect on the defect modes, which is placed under cutoff frequency of superconductor. © 2010 Elsevier B.V. All rights reserved.

Small amplitude propagation and quasielastic head-on collision of ion-acoustic solitary waves (IASWs) are investigated in a degenerate Thomas-Fermi electron-positron-ion magnetized plasma using extended Poincaŕ-Lighthill-Kuo reductive perturbation method for both ultrarelativistic and nonrelativistic electron/positron degeneracy cases. It is observed that both bright- and dark-type solitary shapes can exist in such plasma, depending on two critical values. The shape of ion-acoustic solitary structures as well as sign of their collision phase shifts are both determined by the same critical values. It is further revealed that relativistic degeneracy of electrons/positrons has significant effect on the propagation as well as interaction of IASWs. © 2010 American Institute of Physics.

Kiani G.,University of Tabriz
Applied Clay Science | Year: 2014

The adsorption of silver ions onto Halloysite nanotubes (HNTs) was investigated in aqueous solution in a batch system. The natural HNTs used as adsorbent in this work were initially characterized by TEM. The amounts of the silver ions adsorbed onto HNTs were influenced by initial silver ion concentration, temperature, pH, contact time and adsorbent dose.Adsorption increased with increasing initial silver ion concentration, initial pH, and temperature. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were considered to evaluate the rate parameters. The adsorption followed pseudo-second-order kinetic model with correlation coefficients greater than 0.999. The experimental isotherm data were analyzed using the Langmuir, Freundlich and Temkin equations. The Langmuir isotherm model showed significant fit to the equilibrium adsorption data and the maximum adsorption capacity of 109.79mgg-1 (99.8% removal) of silver ions was achieved. The thermodynamic parameters of activation such as Gibbs free energy, enthalpy and entropy were also evaluated. The results indicate that HNTs could be employed as effective nanoadsorbent for the removal of heavy metal ions. © 2014 Elsevier B.V.

Koohestani K.,University of Tabriz
International Journal of Solids and Structures | Year: 2012

We propose an efficient method for the form-finding of tensegrity structures. The force densities of each tensegrity are obtained by the minimisation of a particular objective function, leading to a semi-positive definite force density matrix (a super-stable tensegrity) with a required rank deficiency. A genetic algorithm is used as a global search technique for the minimisation. The geometry of a tensegrity is subsequently formed based on those eigenvectors of the force density matrix corresponding to zero eigenvalues. Furthermore, two other methods are introduced to convert the asymmetrical geometry obtained from the main algorithm into its symmetrical counterparts. This transformation in geometry is performed by finding a suitable linear combination of the mentioned eigenvectors. Examples from well-known tensegrities including prismatic, truncated tetrahedron, expandable octahedron and truncated icosahedron tensegrities are studied using the present method, and the results obtained are compared with those documented in the literature to verify the efficiency of the present method. © 2011 Elsevier Ltd. All rights reserved.

Akbari-Moghanjoughi M.,University of Tabriz
Physics of Plasmas | Year: 2010

Quantum-hydrodynamics model is applied to investigate the nonlinear propagation of electrostatic solitary excitations in a quantum dusty pair plasma. A Korteweg de Vries evolution equation is obtained using reductive perturbation technique and the higher-nonlinearity effects are derived by solving the linear inhomogeneous differential equation analytically using Kodama-Taniuti renormalizing method. The possibility of propagation of bright- and dark-type solitary excitations is examined. It is shown that a critical value of quantum diffraction parameter H exists, on either side of which, only one type of solitary propagation is possible. It is also found that unlike for the first-order amplitude component, the variation of H parameter dominantly affects the soliton amplitude in higher-order approximation. The effect of fractional quantum number density on compressive and rarefactive soliton dynamics is also discussed. © 2010 American Institute of Physics.

Akbari-Moghanjoughi M.,University of Tabriz
Physics of Plasmas | Year: 2012

In this paper, we use the conventional quantum hydrodynamics (QHD) model in combination with the Sagdeev pseudopotential method to explore the effects of Thomas-Fermi nonuniform electron distribution, Coulomb interactions, electron exchange, and ion correlation on the large-amplitude nonlinear soliton dynamics in Fermi-Dirac plasmas. It is found that in the presence of strong interactions, significant differences in nonlinear wave dynamics of Fermi-Dirac plasmas in the two distinct regimes of nonrelativistic and relativistic degeneracies exist. Furthermore, it is remarked that first-order corrections due to such interactions (which are proportional to the fine-structure constant) are more significant on soliton characteristics (particularly the amplitude) in the nonrelativistic plasma degeneracy regime rather than the relativistic one. In the relativistic degeneracy regime, however, these effects become less important and the electron quantum-tunneling and Pauli-exclusion dominate the nonlinear wave dynamics. Hence, application of non-interacting Fermi-Dirac QHD model to study the nonlinear wave dynamics in quantum plasmas, such as in compact stars is most appropriate for the relativistic degeneracy regime rather than nonrelativistic one. © 2012 American Institute of Physics.

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