Tehran, Iran

Sharif University of Technology is a public research university in Tehran, Iran known traditionally to be first choice of top ranked Iranian high school and university students in engineering and physical science. The university is located in the Tarasht neighborhood of Tehran within close proximity of Azadi Square, and also has an international campus in Kish, a resort island in the Persian Gulf.Established in 1966, it was formerly named the Aryamehr University of Technology and for a short period after the 1979 revolution, the university was called Tehran University of Technology. Following the revolution the university was named after Majid Sharif Vaghefi, a former student who was killed in 1975.Today, the university provides both undergraduate and graduate programs in 15 main departments. The student body consists of about 6,000 undergraduate students and 4,700 graduate students from all the 30 provinces of Iran. Funding for Sharif University is provided by the government and through private funding. Undergraduate admission to Sharif is limited to the top 1 percent of students who pass the national entrance examination administered annually by the Iranian Ministry of Science, Research and Technology.In the 2013 Academic Ranking of World Universities Engineering/Technology and Computer science rankings, SUT is ranked 5th in the Middle East. It is in the top 251-275 universities in the world and 37th in Asia in the 2014 Times Higher Education World University Rankings. SUT also ranked 1st in the Middle East, 6th in Asia, and 27th in the world in Times Higher Education's top 100 universities under 50. Wikipedia.


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Bacteriorhodopsin (bR) molecules were utilized as light-driven proton pumps for green as well as effective reduction of single-layer graphene oxide (GO) sheets. The bR molecules and graphene sheets were separated from each other in an aqueous environment by using a polytetrafluoroethylene membrane filter, in order to prevent their direct interactions (including attachment of the bR molecules onto the GO). Although reduction of GO using hydrazine or bR showed similar deoxygenation levels (based on X-ray photoelectron spectroscopy), the former resulted in formation of CAN bonds which can substantially decrease the electrical conductivity of the reduced sheets. The electrical characteristics of the singlelayer graphene sheets were studied by recording current-voltage curves of the sheets located between two Au electrodes on a SiO2 (300 nm)/Si (100) substrate. The electrical conductivity of the bR-reduced graphene oxide (rGO) sheets was found about one order of magnitude better than that of hydrazine-rGO sheets. The excellent electrical conductivity of the bR-rGO sheets (with sheet resistance of ∼7.1 × 104 X/sq) was assigned to the effective deoxygenation (without formation of any CAN bonds) and better restoration of the graphitic structure of the GO sheets, using the protons pumped by the bR molecules. © 2014 Elsevier Ltd. All rights reserved.


Akhavan O.,Sharif University of Technology
Carbon | Year: 2011

Graphene oxide platelets synthesized by using a chemical exfoliation method were dispersed in a suspension of ZnO nanoparticles to fabricate ZnO/graphene oxide composite. Formation of graphene oxide platelets (with average thickness of ∼0.8 nm) hybridized by ZnO nanoparticles (with average diameter of ∼20 nm) was investigated. The 2D band in Raman spectrum confirmed formation of single-layer graphene oxides. The gradual photocatalytic reduction of the graphene oxide sheets in the ZnO/graphene oxide suspension of ethanol was studied by using X-ray photoelectron spectroscopy for different ultra violet (UV)-visible irradiation times. After 2 h irradiation, the relative concentration of the C-OH, CO and OC-OH bonds showed nearly 80% reduction relative to the corresponding concentrations before irradiation. The chemical reduction was accompanied by variations in the optical absorption of the ZnO/graphene (oxide) suspension, as its color changed from light brown to black. The current-voltage measurement showed that electrical sheets resistance of the ZnO/graphene oxide sheets decreased by increasing the irradiation time. Therefore, the ZnO nanoparticles in the ZnO/graphene oxide composite could be applied in gradual chemical reduction and consequently tuning the electrical conductivity of the graphene oxide platelets by variation of UV irradiation time in a photocatalytic process. © 2010 Elsevier Ltd. All rights reserved.


Tavazoei M.S.,Sharif University of Technology
Automatica | Year: 2010

In this paper, it is shown that the fractional-order derivatives of a periodic function with a specific period cannot be a periodic function with the same period. The fractional-order derivative considered here can be obtained based on each of the well-known definitions Grunwald-Letnikov definition, Riemann-Liouville definition and Caputo definition. This concluded point confirms the result of a recently published work proving the non-existence of periodic solutions in a class of fractional-order models. Also, based on this point it can be easily proved the absence of periodic responses in a wider class of fractional-order models. Finally, some examples are presented to show the applicability of the paper achievements in the solution analysis of fractional-order systems. © 2010 Elsevier Ltd. All rights reserved.


Akhavan O.,Sharif University of Technology
Carbon | Year: 2010

Graphene thin films with very low concentration of oxygen-containing functional groups were produced by reduction of graphene oxide nanosheets (prepared by using a chemical exfoliation) in a reducing environment and using two different heat treatment procedures (called one and two-step heat treatment procedures). The effects of heat treatment procedure and temperature on thickness variation of graphene platelets and also on reduction of the oxygen-containing functional groups of the graphene oxide nanosheets were studied by atomic force microscopy and X-ray photoelectron spectroscopy. While formation of the thin films composed of single-layer graphene nanosheets with minimum thickness of 0.37 nm and nearly without any functional group bonds was observed at the high temperature of 1000 °C in the one-step reducing procedure, similar high quality graphene thin films were obtained at the lower temperature of 500 °C in our two-step reducing temperature. The results also indicated possibility of efficient reduction of the graphene oxide thin films at even lower heat treatment temperatures (≤500 °C). © 2009 Elsevier Ltd. All rights reserved.


Khavasi A.,Sharif University of Technology
Optics Letters | Year: 2013

Li's Fourier factorization rules [J. Opt. Soc. Am. A 13, 1870 (1996)] should be applied to achieve a fast convergence rate in the analysis of diffraction gratings with the Fourier modal method. I show, however, that Li's inverse rule cannot be applied for periodic patterns of graphene when the conventional boundary condition is used. I derive an approximate boundary condition in which a nonzero but sufficiently small height is assumed for the boundary. The proposed boundary condition enables us to apply the inverse rule, leading to a significantly improved convergence rate. A periodic array of graphene ribbons is in fact a special type of finite-conductivity strip grating, and thus the proposed approach is also applicable to these kinds of structures. © 2013 Optical Society of America.


Akhavan O.,Sharif University of Technology
ACS Nano | Year: 2010

Local photodegradation of graphene oxide sheets at the tip of ZnO nanorods was used to achieve semiconducting graphene nanomeshes. The chemically exfoliated graphene oxide sheets, with a thickness of ∼0.9 nm, were deposited on quartz substrates. Vertically aligned ZnO nanorod arrays with diameters of 140 nm and lengths of <1 μm were grown on a glass substrate by using a hydrothermal method. The graphene oxide sheets were physically attached to the tip of the ZnO nanorods by assembling the sheets on the nanorods. UV-assisted photodegradation of the graphene oxide sheets (with dimension of ∼5 × 5 μm) at a contact place with the ZnO nanorods resulted in graphene nanomeshes with a pore size of ∼200 nm. The graphene nanomeshes prepared by using the photocatalytic property of the ZnO nanorods contained smaller oxygen-containing carbonaceous bonds and higher defects as compared to the as-prepared graphene oxide sheets. When chemical reduction of the graphene nanomeshes by hydrazine was used, the oxygen bonds of the nanomeshes more decreased while their graphitization increased. Based on X-ray photoelectron spectroscopy at low binding energies, the graphene nanomeshes reduced by hydrazine exhibited as a broad sheet a p-type semiconductor with an ∼1.2 eV energy gap between the valence band and the Fermi level. © 2010 American Chemical Society.


Akhavan O.,Sharif University of Technology | Ghaderi E.,Sharif University of Technology
ACS Nano | Year: 2010

Bacterial toxicity of graphene nanosheets in the form of graphene nanowalls deposited on stainless steel substrates was investigated for both Gram-positive and Gram-negative models of bacteria. The graphene oxide nanowalls were obtained by electrophoretic deposition of Mg2+-graphene oxide nanosheets synthesized by a chemical exfoliation method. On the basis of measuring the efflux of cytoplasmic materials of the bacteria, it was found that the cell membrane damage of the bacteria caused by direct contact of the bacteria with the extremely sharp edges of the nanowalls was the effective mechanism in the bacterial inactivation. In this regard, the Gram-negative Escherichia coli bacteria with an outer membrane were more resistant to the cell membrane damage caused by the nanowalls than the Gram-positive Staphylococcus aureus lacking the outer membrane. Moreover, the graphene oxide nanowalls reduced by hydrazine were more toxic to the bacteria than the unreduced graphene oxide nanowalls. The better antibacterial activity of the reduced nanowalls was assigned to the better charge transfer between the bacteria and the more sharpened edges of the reduced nanowalls, during the contact interaction. © 2010 American Chemical Society.


Akhavan O.,Sharif University of Technology | Ghaderi E.,Sharif University of Technology
Small | Year: 2013

Reduced graphene oxide nanomesh (rGONM), as one of the recent structures of graphene with a surprisingly strong near-infrared (NIR) absorption, is used for achieving ultraefficient photothermal therapy. First, by using TiO2 nanoparticles, graphene oxide nanoplatelets (GONPs) are transformed into GONMs through photocatalytic degradation. Then rGONMs functionalized by polyethylene glycol (PEG), arginine-glycine-aspartic acid (RGD)-based peptide, and cyanine 7 (Cy7) are utilized for in vivo tumor targeting and fluorescence imaging of human glioblastoma U87MG tumors having ανβ3 integrin receptors, in mouse models. The rGONM-PEG suspension (1 μg mL -1) exhibits about 4.2- and 22.4-fold higher NIR absorption at 808 nm than rGONP-PEG and graphene oxide (GO) with lateral dimensions of ≈60 nm and ≈2 μm. In vivo fluorescence imaging demonstrates high selective tumor uptake of rGONM-PEG-Cy7-RGD in mice bearing U87MG cells. The excellent NIR absorbance and tumor targeting of rGONM-PEG-Cy7-RGD results in an ultraefficient photothermal therapy (100% tumor elimination 48 h after intravenous injection of an ultralow concentration (10 μg mL-1) of rGONM-PEG-Cy7-RGD followed by irradiation with an ultralow laser power (0.1 W cm-2) for 7 min), whereas the corresponding rGO- and rGONP-based composites do not present remarkable treatments under the same conditions. All the mice treated by rGONM-PEG-Cy7-RGD survived over 100 days, whereas the mice treated by other usual rGO-based composites were dead before 38 days. The results introduce rGONM as one of the most promising nanomaterials in developing highly desired ultraefficient photothermal therapy. Reduced graphene oxide nanomesh (rGONM) functionalized by polyethylene glycol (PEG), arginine-glycine-aspartic acid (RGD)-based peptide, and cyanine 7 (Cy7) is utilized for in vivo tumor targeting and fluorescence imaging of human glioblastoma tumors in mice. Simultaneous application of an ultralow concentration of injected rGO-based composite and an ultralow near-infrared (NIR) laser power provide tumor ablation with 100% efficiency. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Asghari M.,Sharif University of Technology
International Journal of Engineering Science | Year: 2012

The couple stress theory is a non-classical continuum theory which is capable to capture size effects in small-scale structures. This property makes it appropriate for modeling the structures in micron and sub-micron scales. The purpose of this paper is the derivation of the governing motion equations and boundary conditions for the geometrically nonlinear micro-plates with arbitrary shapes based on the modified version of the couple stress theory. The consistent boundary conditions are provided at smooth parts of the plate periphery and also at the sharp corners of the periphery using variational approach. © 2011 Elsevier Ltd. All rights reserved.


Tavazoei M.S.,Sharif University of Technology
IEEE Industrial Electronics Magazine | Year: 2012

Proportional-integral (PI) controllers are the most common form of feedback used in industrial applications today [1][3]. The use of proportional and integral feedback also has a long history of practical applications [4]. For example, in the middle of the 18th century, centrifugal governors as the proportional feedback were applied to regulate the speed of windmills [5]. By the 19th century, it was known that using integral feedback could remove the offsets appearing in working with governors [6]. At present, PI control, still a very basic form of feedback, is also one of the first solutions often considered in the control of industrial systems [7]. On the other hand, in some applications, using the PI controller in its traditional form may not be satisfactory, and a more advanced controller is needed to achieve control objectives. In such cases, modified versions of the PI controller have been proposed to enhance the controller's performance. The fractional-order PI controller is one of these modified versions, and it is attracting increased interest in control system design uses [8], [9]. The idea of using such a controller originated with fractional calculus, known as a generalization for classical calculus [10]. The following section presents a brief review of recent fractional calculus applications in control system design. © 2011 IEEE.

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