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.
Fallahi F.,University of Tabriz
Energy | Year: 2011
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.
Air-assisted liquid-liquid microextraction-gas chromatography-flame ionisation detection: A fast and simple method for the assessment of triazole pesticides residues in surface water, cucumber, tomato and grape juices samples
Farajzadeh M.A.,University of Tabriz
Food Chemistry | Year: 2013
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.
Akbari-Moghanjoughi M.,University of Tabriz
Physics of Plasmas | Year: 2010
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.
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.
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.