Sharif Digital Repository

Asphaltene precipitation is known to be responsible for serious challenges in oil industry such as wellbore damage, oil flow reduction, and plugging of transportation lines. The traditional methods to remove asphaltene deposition are mostly based on chemical solvent. One of the recent proposed green and cost–effect remedial methods is the application of microorganisms capable of consuming the heavy hydrocarbon chains. The cell surface hydrophobicity among others effectively manipulates the efficiency of the microorganism for asphaltene degradation. Besides, surface active agents would affect the microorganism adhesion and cell surface properties, and alters its hydrophobicity. Investigating... 

Asphaltene precipitation is known to be responsible for serious challenges in oil industry such as wellbore damage, oil flow reduction, and plugging of transportation lines. The traditional methods to remove asphaltene deposition are mostly based on chemical solvent. One of the recent proposed green and cost–effect remedial methods is the application of microorganisms capable of consuming the heavy hydrocarbon chains. The cell surface hydrophobicity among others effectively manipulates the efficiency of the microorganism for asphaltene degradation. Besides, surface active agents would affect the microorganism adhesion and cell surface properties, and alters its hydrophobicity. Investigating... 

The recent status of female students and faculties in physics departments in Iran is presented. Growth in female contributions has occurred mainly at the PhD level. A positive trend toward reducing the gender gap in the field of teaching and university research careers has been observed during recent years. However, the percentage of women in decision-making and management positions in universities is weak, at about 2%. © 2019 Author(s)  

Low-cost ethanol vapor sensors are fabricated by electrospinning of TiS2/PVP fibers on pre-patterned metal electrodes. TiS2 ribbons have been synthesized through sulfuration of titanium (Ti) foil using chemical vapor transport (CVT). We found selective and stable responses at a low concentration of ethanol vapor (2 ppm) at room temperature with the transient response and recovery times experimentally around 60 s and 2 s respectively. The relatively high responses of sensors (6800% at 18 ppm) are attributable to the synergy effect of TiS2/PVP composite structure. The mechanism of sensing is discussed based on proton hopping while the sensors exposed to ethanol vapor. © 2019 Wiley-VCH Verlag... 

This paper describes the photoluminescence study of titanium dioxide (TiO2) nanorods grown by a hydrothermal synthesis method on the surface of fluorine doped tin oxide (FTO) coated glass. The effects of growth conditions including: reaction time, precursor concentration and adding NaCl to hydrothermal solution on the structural and optical properties of productions are examined by using SEM, XRD, TEM and room temperature photoluminescence measurements. Also, the performance of the TiO2 nanorods as a photoanode of dye sensitized solar cells is investigated. The different excitation energies and intensities are chosen to verify the discrete electronic state of radiative recombination centers... 

A hierarchical core-shell structure composed of ZnO nanotubes/MnO2 nanosheets was fabricated via a two-step electrochemical deposition procedure on the surface of a 3D graphene network (3DGN) as a free-standing monolithic electrode. In the first step, ZnO nanorod arrays were grown on the surface of a 3DGN followed by electrochemical deposition of MnO2 nanosheets in the next step, which caused the inner parts of initial ZnO nanorods to etch away and resulted in the formation of ZnO nanotubes (ZnO NTs). The highly porous interconnected graphene backbone offers very high conductivity and a large accessible surface area. On the other hand, the formation of ZnO nanotubes can enhance the... 

Polyaniline/graphene oxide (PANI/GO) co-doped with Zn2+ and Fe3+ was synthesized via a simple and low cost one-step chronoamperometry method on stainless steel (SS) as the substrate. The Fe3+-Zn2+-PANI/GO nanocomposite is characterized using X-ray diffraction as well as Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and field emission scanning electron microscopy. Also, cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy are used to study the electrochemical performance of the as-prepared electrode materials. Significantly, the Fe3+-Zn2+-PANI/GO nanocomposite exhibits a specific... 

Iron‑vanadium oxysulfide (Fe-VO-S) nanostructures with different Fe:VO atomic ratios are synthesized by a facile and low cost electrochemical deposition method. The synthesis of the various samples is confirmed by the physicochemical characterizations such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). For different Fe-VO-S nanostructures, the correlation between the physicochemical and the electrochemical properties is investigated. It is found that the Fe:VO atomic ratio has an important effect on the structure and size of the resulted particles.... 

Herein, a novel sensing platform based on NiCo layered double hydroxide (LDH) nanosheets/graphene nanoribbons (GNRs) modified glassy carbon electrode is presented for sensitive non-enzymetic determination of glucose. In the first step, nanoflower-like NiCo LDH nanosheets were grown on the surface of ZIF-67 dodecahedron nanocrystals which used as sacrificial template and were further characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD) and FTIR. In the next step, in order to fabricate a mechanically stable modified electrode, the as-prepared nanosheets were mixed with... 

Design and fabrication of highly efficient and low-cost oxygen reduction reaction (ORR) electrocatalysts is of paramount importance for practical applications. Herein, we proposed a cost-effective, metal-free catalyst based on ZIF-8 metal-organic framework nanoparticles/electro-polymerized poly(3,4-ethylenedioxythiophene) (PEDOT) film on the surface of flexible carbon cloth (CC) electrode (ZIF-8/PEDOT/CC) via a two-step procedure. For this purpose, worm-like PEDOT nanostructures were deposited on the surface of carbon fibers using a pulse electro-polymerization technique followed by facile growth of ZIF-8 polyhedra nanoparticles via a chemical bath deposition method. The ORR measurements in... 

A new ternary nanocomposite based on graphene oxide (GO), polypyrrole (PPy) and vanadium pentoxide (V2O5) is obtained via one-step electrochemical deposition process. Electrochemical deposition of V2O5, PPy and GO on a stainless steel (SS) substrate is conducted from an aqueous solution containing vanadyl acetate, pyrrole and GO to get V2O5/PPy/GO nanocomposite. Characterization of the electrode material is carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). The electrochemical performance of the as-prepared nanocomposite is evaluated by... 

In this work, nanostructured composites of Cr2O3-graphene oxide (Cr2O3/GO) with conducting polymers; polyaniline (PANI) and polypyrrole (PPy) with the shape of cauliflower were synthesized via s simple and low cost one-step chronoamperometry method. The structures and morphologies of the resulting ternary nanocomposites were characterized by using Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The electrochemical capacitive properties of the prepared nanocomposites were evaluated by using cycle voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The... 

Design and fabrication of highly efficient and low-cost oxygen reduction reaction (ORR) electrocatalysts is of paramount importance for practical applications. Herein, we proposed a cost-effective, metal-free catalyst based on ZIF-8 metal-organic framework nanoparticles/electro-polymerized poly(3,4-ethylenedioxythiophene) (PEDOT) film on the surface of flexible carbon cloth (CC) electrode (ZIF-8/PEDOT/CC) via a two-step procedure. For this purpose, worm-like PEDOT nanostructures were deposited on the surface of carbon fibers using a pulse electro-polymerization technique followed by facile growth of ZIF-8 polyhedra nanoparticles via a chemical bath deposition method. The ORR measurements in... 

The ODYSSEY design methodology is an object-oriented design methodology which models a system in terms of its constituting objects and their corresponding method calls. Some of these method calls are implemented in hardware functional units, while others are simply executed by a general-purpose processor. There is a communication overhead because functional units must communicate with each other and with the processor core. In this paper we utilize the custom instructions capability of Nios II processor to enhance the performance of our ASIP. Since these instructions are in the processor itself, there will be no communication overhead for using them. We analyze the performance of the... 

We have investigated an oxidation of substrate effect on structural morphology of zinc oxide (ZnO) rods. ZnO rods are grown on porous silicon (PS) and on thermally oxidized porous silicon substrates by carbothermal reduction of ZnO powder through chemical vapour transport and condensation. Porous silicon is fabricated by electrochemical etching of silicon in hydrofluoric acid solution. The effects of substrates on morphology and structure of ZnO nanostructures have been studied. The morphology of substrates is studied by atomic force microscopy in contact mode. The texture coefficient of each sample is calculated from X-ray diffraction data that demonstrate random orientation of ZnO rods on... 

Here, the UV photodetection of ZnO rods grown on porous silicon substrates are reported. Laterally interconnected ZnO rods have been synthesized by chemical vapor transport and condensation method on porous silicon substrates. As characterized by current-voltage measurements the I-V characteristics have linear behavior, indicating space charge effect. The device exhibits photocurrent response of 0.027 A/W for 325 nm UV light under -5 V bias. The rise and decay time constants under these conditions are 19 and 62 s, respectively  

A uniformly distributed ZnO nanowire array has been grown on silicon (100) substrates by catalyst-free chemical vapor transport and condensation. The effect of growth conditions including source heating temperature, substrate temperature, and gas flow rate on growth properties of ZnO nanowire arrays are studied. Scanning electron microscopy, X-ray diffraction, and room temperature photoluminescence are employed to study the structural features and optical properties of the samples. The results show a correlation among experimental growth parameters. There is a zone for substrate temperature, by controlling gas flow rate, that uniformly distributed and well aligned ZnO nanowire arrays can be... 

During the past few years, a considerable attention has been devoted to the development of textile- based energy storage devices and wearable electronics applications. In this paper, for the first time, we report a flexible high performance graphene-based supercapacitor using silver fiber fabric as the current collector. The silver fiber fabric offers remarkable advantages such as light weight, mechanical flexibility and ease of integration with electronic textiles, which well-suited for wearable energy storage devices. A new hybrid material of graphene-silver fiber fabric (rGO/SFF) was prepared through a facile electrophoretic deposition of graphene and being used as a binder-free flexible... 

The effects of Pd addition to Fe (Pd/Fe = 0, 2.5/7.5, 5/5, 7.5/2.5 and 1) and growth temperatures (920 and 970 °C) on density, diameter and growth mode of carbon nanotubes (CNTs) have been studied. SEM observations and TG analyses confirmed that the CNT yields depend on Pd/Fe ratios as (7.5/2.5) > (5/5) > Pd > (2.5/7.5) > Fe at both growth temperatures. TEM data showed that addition of Pd results in tip growth mode. From Raman spectroscopy data, the order of samples' structural quality (I G /I D ratio) are Fe > Pd/Fe (2.5/7.5) > (5/5) > (7.5/2.5) > Pd and the I G /I D ratios increase by decreasing the growth temperature. Films with higher concentration of Fe (Pd/Fe = 0, 2.5/7.5) contain some... 

Modified tungsten oxide films by vanadium oxide provide neutrally coloring electrochromic electrodes for smart windows technology. In this study W-V-O mixed oxide films were fabricated by Nd:YAG pulsed laser deposition (PLD), λ=1064 nm, from mixed pressed powders of (WO3)1-x(V2O5)x, x=0, 0.09, 0.17, 0.23, 0.29 and 0.33, at 13.3 Pa oxygen partial pressure and 200 °C temperature on glass substrates. X-ray photoelectron spectroscopy (XPS) revealed V5+, V4+, W6+ and W5+ surface oxide states, where the ratio of W5+/W6+ enhances by the amount of vanadium in the films. Surface morphology was studied by scanning electron microscope (SEM) and optical properties by transmission-reflection spectra....