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    Anderson Localization in Random Potential with Long Range Correlation

    , M.Sc. Thesis Sharif University of Technology Lotfallahzadeh, Shiva (Author) ; Rahimi Tabar, Mohammad Reza (Supervisor)
    Abstract
    In a one-dimensional disordered system, Anderson localization is known to occur at any energy in the thermodynamic limit when the disorder is uncorrelated and white noise structure.
    A great interest for 1D disordered models with correlated disorder has been growing since 2002, as it has become progressively clear that the correlation of the random potentials can deeply affect the electronic localization properties. Spatial correlation of disorder can unexpectedly create extended states at some particular energies.
    In this thesis, we study the metal-insulator transition in one dimensional Anderson binary alloy with long range disordered hopping integral and on-site energy, using the... 

    Study on the Exfoliation of Graphite into Graphene by Electrochemical Method and Its Application in Thermoplastic Polyurethane Nanocomposite

    , M.Sc. Thesis Sharif University of Technology Razeghi, Mohammad Ali (Author) ; Pircheraghi, Gholamreza (Supervisor)
    Abstract
    Graphene is two dimensional nanomaterial, single layer of carbon atoms that exhibited excellent properties like high electrical conductivity and stiffness, but producing graphene and obtaining a good dispersion of graphene in a polymer matrix is still a major challenge. In this study by using the electrochemical route several graphene with different degree of oxidation produced in different electrolyte medium. According to XRD data, product of electrochemical exfoliation in dilute HNO3 medium includes 50% few-layer graphene (5 layers) and 25% GO and the rest are multi-layer graphene. Nonsolvent induced phase separation method were used to prepare TPU/Graphene nanocomposite. Different methods... 

    Synthesis and Characterization of 3D Reduced Graphene Oxide with Phosphorus and Nitrogen Dopants as an Efficient Supercapacitor Electrode Material

    , M.Sc. Thesis Sharif University of Technology Nazari, Neda (Author) ; Malek Khachatourian, Adrineh (Supervisor)
    Abstract
    Supercapacitors are safe and environmentally friendly energy storage devices that have been considered for their diverse applications. One of the most important factors that control supercapacitors' capacity is the electrode material's structure and properties. Adding heteroatoms or composite materials synthesis is one way to improve electrode performance. In this study, a facile, fast, and economical hydrothermal method was used to synthesize N doped, P doped or N/P co-doped 3D reduced graphene oxide (rGO) for high-performance supercapacitor application. Nitrogen and phosphorus elements were replaced by carbon atoms simultaneously during the graphene oxide hydrothermal reduction procedure.... 

    Accelerated differentiation of neural stem cells into neurons on ginseng-reduced graphene oxide sheets

    , Article Carbon ; Volume 66 , January , 2014 , Pages 395-406 Akhavan, O ; Ghaderi, E ; Abouei, E ; Hatamie, S ; Ghasemi, E ; Sharif University of Technology
    Abstract
    Asian red ginseng was used for green reduction of chemically exfoliated graphene oxide (GO) into reduced graphene oxide (rGO). The reduction level and electrical conductivity of the ginseng-rGO sheets were comparable to those of hydrazine-rGO ones. Reduction by ginseng resulted in repairing the sp 2 graphitic structure of the rGO, while hydrazine-rGO showed more defects and/or smaller aromatic domains. The ginseng-rGO sheets presented a better stability against aggregation than the hydrazine-rGO ones in an aqueous suspension. Whilst the hydrophobic hydrazine-rGO films exhibited no toxicity against human neural stem cells (hNSCs), the hydrophilic GO and ginseng-rGO films (as more... 

    The effects of a hydrochloric acid pre-treatment on the physicochemical properties and pozzolanic performance of rice husk ash

    , Article Cement and Concrete Composites ; Volume 39 , 2013 , Pages 131-140 ; 09589465 (ISSN) Gholizadeh Vayghan, A ; Khaloo, A. R ; Rajabipour, F ; Sharif University of Technology
    2013
    Abstract
    This paper investigates the effects of acid normality (0.01-6 N HCl) and combustion retention time (0.25- 16 hours) on the pozzolanic properties of pre-combustion acid-treated rice husk ash. The pozzolanic reactivity was quantified by adding ground ash to saturated Ca(OH)2 solutions and monitoring the time-dependent electrical conductivity and pH of the solutions. Also, the strength activity of ashes from different processes was measured by testing the compressive strength of mortars. It was observed that acid treatment results in ashes with higher SiO2 content, lower alkali and unburned carbon content, better grindability, and smaller particle size, in comparison with ash from non-acid... 

    Voltammetric behavior and determination of trace amounts of omeprazole using an edge-plane pyrolytic graphite electrode

    , Article Iranian Journal of Pharmaceutical Research ; Volume 14, Issue 2 , Spring , 2015 , Pages 465-471 ; 17350328 (ISSN) Shahrokhian, S ; Ghalkhani, M ; Bayat, M ; Ghorbani Bidkorbeh, F ; Sharif University of Technology
    Iranian Journal of Pharmaceutical Research  2015
    Abstract
    The voltammetric performance of edge-plane pyrolytic graphite (EPG) electrode via adsorptive stripping voltammetry was investigated for study of the electrochemical behavior of omeprazole (OMZ) in aqueous solution. The results revealed that the oxidation of OMZ is an irreversible pH-dependent process that proceeds with the transfer of one electron and one proton in an adsorption-controlled mechanism. The determination conditions, such as the pH values of the supporting electrolyte, accumulation time and scan rate were optimized. Simplicity, high reproducibility and low detection limit (3 nM) of the electrode response as well as wide linear range (0.01 to 4.0 µM) can be stated as significant... 

    Fourier transform infrared spectroscopy and scanning tunneling spectroscopy of porous silicon in the presence of methanol

    , Article Sensors and Actuators, B: Chemical ; Volume 132, Issue 1 , 2008 , Pages 40-44 ; 09254005 (ISSN) Razi, F ; Rahimi, F ; Iraji zad, A ; Sharif University of Technology
    2008
    Abstract
    Porous silicon samples were obtained from p+- and n-type silicon wafers. Gas sensing measurements showed that the electrical conductivity of porous Si on p+- and n-type wafers increases strongly and decreases weakly in the presence of methanol gas, respectively. Scanning tunneling spectroscopy (STS) indicates that the adsorption of methanol on the surface of n-porous silicon decreases the average density of states especially in the band gap. Fourier transform infrared (FTIR) spectroscopy reveals that after methanol exposure partial surface oxidation occurs which produces electron traps as well as methanol adsorption on the porous surfaces. These observations imply that the number of... 

    Synthesis parameters and their effects on the resistivity anomaly in GdPr1113 ceramic

    , Article Journal of Superconductivity and Novel Magnetism ; Volume 20, Issue 4 , 2007 , Pages 279-283 ; 15571939 (ISSN) Kariminezhad, M ; Akhavan, M ; Sharif University of Technology
    2007
    Abstract
    Tetragonal Gd 1-x Pr x BaSrCu 3O 7-δ (GdPr1113) polycrystalline high-temperature superconducting ceramic samples have been synthesized by the standard solid-state reaction process with different calcination and sintering temperatures and characterized by XRD and SEM. The optimum synthesis temperatures for obtaining single phase varied with Pr doping. Higher temperatures were necessary to obtain single phase for x ≥ 0.3. It was found that higher synthesis temperatures improved the electrical characteristics of these materials. The effects of different calcination and sintering temperatures on the anomalous hump in the ρ(T) curves observed at about 80 K is investigated. The percentage of the... 

    The effect of sintering temperature on the weak link behavior of Bi-2223 superconductors

    , Article 4th International Conference on Magnetic and Superconducting Materials, MSM'05, Agadir, 5 September 2006 through 8 September 2006 ; Volume 3, Issue 9 , 2006 , Pages 3011-3014 ; 18626351 (ISSN) Kameli, P ; Salamati, H ; Eslami, M ; Akhavan, M ; Sharif University of Technology
    2006
    Abstract
    We have studied the effect of sintering temperature on the weak link behavior of polycrystalline Bi2223 superconductors with different intergranular coupling using the XRD, electrical resistivity and AC susceptibility techniques. The XRD results show that by increasing sintering temperature up to 865°C the Bi2212 phase fraction decrease. It was found that the Bi2212 phase on the grain boundaries is likely to play the role of weak links and consequently reduces the intergranular critical current densities. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA  

    Effect of Pr doping on transport properties of Nd(Ba2-xPr x)Cu3O7+8

    , Article Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers ; Volume 44, Issue 11 , 2005 , Pages 7934-7942 ; 00214922 (ISSN) Maleki, P ; Akhavan, M ; Sharif University of Technology
    2005
    Abstract
    Solid-state-reacted polycrystalline Nd(Ba2-xPr x)Cu3O7+8 materials have been prepared and investigated using X-ray diffraction and resistivity measurements. Our results show that Nd(Ba2-xPrx)Cu3O7+8 is a superconductor when x < 0.3. The Tc depression in superconductivity of Pr at Ba sites is due to both hole filling/localization and depairing effects. The normal state conductivity undergoes a dimensional crossover from two-dimensional to three-dimensional in the frame of the variable range hopping regime. The localization length of carriers shows that Pr doping localizes carriers in the normal state and causes the Tc depression. The magnetoresistance of the samples has been investigated... 

    Analytical results on coherent conductance in a general periodic quantum dot: Transfer matrix method

    , Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 28, Issue 2 , 2005 , Pages 150-161 ; 13869477 (ISSN) Mardaani, M ; Shokri, A. A ; Esfarjani, K ; Sharif University of Technology
    2005
    Abstract
    In this work, we study the conductance of a general periodic quantum dot (QD) attached to ideal semi-infinite uniform metallic leads (nanocrystals), fully analytically. We propose a new general formula which relates conductance to transfer matrix (TM) for an isolated cell in the periodic dot. The equation describes exactly the dependence of the transmission coefficient (TC) on Fermi energy, dot-size, dot-lead coupling, and gate voltage for an arbitrary periodic dot. Then, we derive a nonlinear equation which gives the resonance, bound, and surface state energies. Finally, the TC has been calculated for gapless, single, and double gap models exactly. Moreover, we have also calculated the... 

    Flux dynamics, superconducting, and normal state properties of Gd(Ba 2-xPrx)Cu3O7+δ

    , Article European Physical Journal B ; Volume 42, Issue 3 , 2004 , Pages 321-336 ; 14346028 (ISSN) Mohammadizadeh, M. R ; Akhavan, M ; Sharif University of Technology
    2004
    Abstract
    Gd(Ba2-xPrx)Cu3O7+δ single phase polycrystalline samples with 0.0 ≤ x ≤ 1.0 were investigated for structural, electronic and flux dynamics properties. Two-dimensional variable range hopping (VRH) is the dominant conduction mechanism in the normal state of the system. Pr doping strongly localizes the carriers in normal state, and finally causes the suppression of superconductivity. The effect of Pr substitution in 123 structure of HTSC at R or Ba sites is to increase the pseudogap temperature Ts, although, Pr at Ba sites has a stronger effect on the increase of Ts and suppression of superconductivity. The magnetoresistance of the samples have been studied within thermally activated flux creep... 

    Microstructure Modification and Electrical Conductivity Development in PA6/PS Blend using PANI Coated CNT

    , M.Sc. Thesis Sharif University of Technology Soleimani, Elahe (Author) ; Bagheri, Reza (Supervisor)
    Abstract
    In this research, a nanocomposite blend of polyamide 6/polystyrene containing polyaniline-coated carbon nanotubes was fabricated via melt blending method, aiming to achieve electrical conductivity in the range of static dissipation. The effect of weight percentage of nanofillers and surface modification of carbon nanotubes with polyaniline on the electrical properties and microstructure of the nanocomposite was investigated. To promote compatibility between the immiscible polyamide 6 and polystyrene polymers, PS-g-MA compatibilizer was utilized, and its effect on the morphology of the nanocomposite blend was examined. Additionally, the influence of weight percentage of nanofillers and the... 

    Application of sol-gel technique to synthesis of copper-cobalt spinel on the ferritic stainless steel used for solid oxide fuel cell interconnects

    , Article Journal of Power Sources ; Vol. 266, issue , 2014 , pp. 79-87 ; ISSN: 03787753 Paknahad, P ; Askari, M ; Ghorbanzadeh, M ; Sharif University of Technology
    Abstract
    The conductive CuCo2O4 spinel coating is applied on the surface of the AISI 430 ferritic stainless steel by the dip-coating sol-gel process and it is evaluated in terms of the microstructure, oxidation resistance and electrical conductivity. The results show that the CuCO2O 4 coating forms a double-layer scale consisting of a Cr, Fe-rich subscale and Cu-Co spinel top layer after 500 h in air at 800 °C. This scale is protective, acts as an effective barrier against Cr migration into the outer oxide layer and alleviates the cathode Cr-poisoning. The oxidation resistance is significantly enhanced by the protective coating with a parabolic rate constant of 5.8 × 10-13 gr2 cm-4 s -1, meanwhile... 

    Effect of Sr and Ca dopants on oxidation and electrical properties of lanthanum chromite-coated AISI 430 stainless steel for solid oxide fuel cell interconnect application

    , Article Ceramics International ; Volume 39, Issue 7 , September , 2013 , Pages 8123-8131 ; 02728842 (ISSN) Rashtchi, H ; Sani, M. A. F ; Dayaghi, A. M ; Sharif University of Technology
    2013
    Abstract
    Lanthanum chromite coating occupies a noticeable position as a ceramic coating on metallic interconnects in solid oxide fuel cells because of its excellent electrical conductivity, high oxidation resistance and desirable chemical stability in both oxidizing and reducing atmospheres. In the present work, a sol-gel process based on the dip-coating technique was used to prepare dense and uniform coatings on metallic alloy for interconnect application (AISI 430 type). The effect of strontium and calcium doping into lanthanum chromite structure on electrical conductivity and oxidation behavior of the coated sample has been investigated. The oxidation behavior was evaluated by cyclic oxidation... 

    Fabrication and high-temperature corrosion of sol-gel Mn/Co oxide spinel coating on AISI 430

    , Article Surface and Coatings Technology ; Volume 223 , 2013 , Pages 110-114 ; 02578972 (ISSN) Dayaghi, A. M ; Askari, M ; Rashtchi, H ; Gannon, P ; Sharif University of Technology
    2013
    Abstract
    MnCo oxide spinels have received recent interest as surface coatings on ferritic stainless steel (FSS) interconnects in solid oxide fuel cell (SOFC) stacks, where they provide relatively stable electrical conductivity and reduced Cr volatility compared to uncoated FSS interconnects. In this study, sol-gel deposited MnCo surface coatings on FSS, with post-deposition treatments, were investigated in laboratory air at up to 750°C for up to 750h. The protective coating formed and evolved isomorphic crystallites, (Mn,Co,Fe,Cr)3O4, following fifteen (15) fifty hour (50h) cycles in air up to 750°C. Relative to the surface oxide on the uncoated FSS, the coating was dense, crack-free and exhibited... 

    Effect of chemical substitution on the morphology and optical properties of Bi1-xCaxFeO3 films grown by pulsed-laser deposition

    , Article Journal of Materials Science: Materials in Electronics ; Volume 24, Issue 1 , 2013 , Pages 248-252 ; 09574522 (ISSN) Ahadi, K ; Mahdavi, S. M ; Nemati, A ; Sharif University of Technology
    2013
    Abstract
    The morphological characteristics as well the optical properties of Ca-doped BiFeO3 films grown by pulsed-laser deposition technique have been investigated. AFM images revealed that calcium has a radical effect on the surface features of BiFeO3 films. By utilizing spectrophotometer, transmission behaviour of the films was investigated. Local IV characteristics of the films disclosed about three orders of magnitude enhancement concerning electrical conductivity through Ca doping. X-ray photoelectron spectroscopy results revealed that Ca can reduce the valence state of iron in the compound  

    Conductor-insulator transition and electronic structure of Ca-doped BiFeO 3 films

    , Article Materials Letters ; Volume 83 , 2012 , Pages 124-126 ; 0167577X (ISSN) Ahadi, K ; Nemati, A ; Mahdavi, S. M ; Sharif University of Technology
    Elsevier  2012
    Abstract
    The electronic conductor-insulator transition in Ca-doped BiFeO 3 films grown by pulsed-laser deposition technique has been investigated. Nature of the transition is resolved to be Mott type through the control of band-filling. Calcium resolved to have colossal effect on enhancing the electrical conductivity of BiFeO 3, but it did not affect band gap of the mother phase perceptibly. UV-visible study yielded band gap of 2.72-2.81 eV (at 300 K) for different concentrations of calcium. Both UV-visible and photoluminescence spectra revealed sub-band gap transitions at 2.17 and 2.38 eV, of which the latter might be ascribed to the oxygen vacancies  

    Practical design of low-cost instrumentation for industrial electrical impedance tomography (EIT)

    , Article ; 2012 IEEE I2MTC - International Instrumentation and Measurement Technology Conference, Proceedings, 13 May 2012 through 16 May 2012, Graz , 2012 , Pages 1259-1263 ; 9781457717710 (ISBN) Khalighi, M ; Vosoughi Vahdat, B ; Mortazavi, M ; Hy, W ; Soleimani, M ; Sharif University of Technology
    IEEE  2012
    Abstract
    Electrical Impedance Tomography (EIT), is one of the medical imaging technologies. It can also be used in industrial process monitoring. In this method, the image of the electrical conductivity distribution of the inner part of a conductive subject can be reconstructed. The image reconstruction process is done by injecting an accurate current into the boundary of a conductive subject (e.g. body), measuring the voltages around the boundary and transmitting them to a computer, and processing on acquired data with a software (e.g., MATLAB). The images are obtained from the peripheral data by using an algorithm. Precise EIT instrumentation plays an important role in the final images quality. In... 

    Stability of titania nano-particles in different alcohols

    , Article Ceramics International ; Volume 38, Issue 5 , 2012 , Pages 3893-3900 ; 02728842 (ISSN) Farrokhi Rad, M ; Ghorbani, M ; Sharif University of Technology
    2012
    Abstract
    The alcoholic suspensions of titania nano-particles were prepared using the methanol, ethanol, isopropanol and butanol as the solvents as well as triethanolamine (TEA) as an dispersant. The colloidal stability of suspensions, both in the absence as well as presence of TEA, was studied by measuring the zeta potential, sedimentation, pH and electrical conductivity of suspensions, dispersant adsorption and particles size distribution. Results showed that in the absence of TEA, the stability of the suspensions increases with the molecular size of alcohol (from methanol to butanol), while the zeta potential decreases. It was also observed that with the addition of TEA up to the optimum dosage (4...