Sharif Digital Repository

High temperature shape memory NiTiHf thin films with varying hafnium contents up to 28.7 at.% were fabricated by DC magnetron sputtering using simultaneous sputter deposition from separate elemental targets. The required film composition was achieved by adjusting the power ratio to the targets. The as-deposited films were amorphous; a post deposition annealing was performed at 550 °C to crystallize the films. Two-micron thick films were characterized by energy dispersive spectroscopy in a scanning electron microscope, temperature controlled X-ray diffraction, differential scanning calorimetry, and atomic force microscopy. The results showed that above 10 at.% Hf additions the transformation... 

In recent years, subsidy payment has been made a main challenge for governments due to growth of population and energy price in global markets. Targeted subsidy plan has been implemented in Iran since last year, and this article discusses its effects on costs and revenues of Tehran Electricity Company as one of the major subdivisions of Iran's electricity industry. In the new system, structural changes have been made in electricity tariffs, so it is not possible to predict the future trends in electricity consumption only based on the past consumptions. In order to model the decision making structure in the recent conditions, a system dynamics method is applied. In addition to modeling the... 

Understanding the nature of interaction between metal nanoparticles and biomolecules such as amino acids is important in the development and design of biosensors. In this paper, binding of M3 clusters (M = Au, Ag and Cu) with neutral and anionic forms of histidine amino acid was studied using density functional theory (DFT-B3LYP). It was found that the interaction of histidine with M3 clusters is governed by two major bonding factors: (a) the anchoring N-M and O-M bonds and (b) the nonconventional N-H⋯M and O-H⋯M hydrogen bonds. The nature of these chemical bonds has been investigated based on quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. In the next... 

The relative stabilities and noncovalent interactions of the six low-lying energy tautomers of cytosine nucleobase with some biological anions (such as F-, Cl-, and CN-) have been investigated in gas phase by density functional theory (DFT) method in conjunction with 6-311++G (d,p) atomic basis set. Furthermore, to systematically investigate all possible tautomerisms from cytosine induced by proton transfer, we describe a study of structural tautomer interconversion in the gas phase and in a continuum solvent using DFT calculation. We carried out geometrical optimizations with the integral equation formalism of polarizable continuum (IEF-PCM) model to account for the solvent effect, and the... 

Understanding the nature of the interaction between metal nanoparticles and biomolecules has been important in the development and design of sensors. In this paper, structural, electronic, and bonding properties of the neutral and anionic forms of glutathione tripeptide (GSH) complexes with a Au 3 cluster were studied using the DFT-B3LYP with 6-31+G**-LANL2DZ mixed basis set. Binding of glutathione with the gold cluster is governed by two different kinds of interactions: Auâ€"X (X = N, O, and S) anchoring bond and Au··•·•H-X nonconventional hydrogen bonding. The influence of the intramolecular hydrogen bonding of glutathione on the interaction of this peptide with the gold cluster has been... 

As digital technology has developed, relays have evolved from simple electro-mechanical devices into robust microprocessor-embedded intelligent electronic devices (IEDs). Distance protection, one of the most important and sophisticated forms of substation protection, quickly and selectively detects and clears phase faults in sub-transmission and transmission lines. The installation of a substation automation system (SAS) involves implementing control, monitoring, and protection logic by programming the IEDs and providing an appropriate communication network. IEC61850 has gradually satisfied the need for a standard communication protocol so that IEDs from different manufacturers can... 

The first asymmetric synthesis of α,β-disubstituted γ-phosphono sulfonates is reported. The key step is the Michael addition of a lithiated enantiopure sulfonate bearing an inexpensive chiral sugar auxiliary to α,β-unsaturated phosphonates in good diastereoselectivities. After chromatographic purification, the cleavage of the chiral sugar auxiliary proceeds without any epimerization or racemization to form the corresponding isopropyl sulfonate in very good overall yield (75%) and excellent diastereomeric and enantiomeric excess (de, ee ≥ 95%). © 2009 Elsevier Ltd. All rights reserved  

In this study, UV‐Vis-NIR photodetectors based on decorated ZnO nanofibers (NFs) with optimized coverage of Au nanoparticles (NPs) fabricated via combined simple electrospinning and sputtering techniques are introduced. The effect of different coverages of Au NPs resulted from different Au nominal layer thicknesses on the morphology and optical properties of the ZnO fibers are investigated through various characterization methods. It is discovered that 4 nm Au nominal thickness provides the highest UV on/off ratio (~460), responsivity (~332 A/W), detectivity (~2.93×10 11 Jones) as well as faster rise and decay times as compared to pure ZnO nanofibers. A broad spectral response from UV to NIR... 

Synthetic quantum Hall bilayer (SQHB), realized by optically driven monolayer graphene in the quantum Hall regime, provides a flexible platform for engineering quantum Hall phases as discussed in Ghazaryan et al. [Phys. Rev. Lett. 119, 247403 (2017)PRLTAO0031-900710.1103/PhysRevLett.119.247403]. The coherent driving which couples two Landau levels mimics an effective tunneling between synthetic layers. The tunneling strength, the effective Zeeman coupling, and two-body interaction matrix elements are tunable by varying the driving frequency and the driving strength. Using infinite density matrix renormalization group techniques combined with exact diagonalization, we show that the system... 

In this research, the effect of Ni, Pd and Ni-Pd catalysts have studied on morphology and structure of synthesized multi-wall carbon nanotubes (MWCNTs). Initially, thin films of Ni (with two thicknesses of 10 and 20 nm), Pd/Ni (5/10 nm) and Pd (10 nm) were deposited as catalysts on SiO 2 (60 nm)/Si(1 0 0) substrates, using dc magnetron sputtering technique. The deposited films were annealed at 900 °C in ammonia environment for 45 min, in order to obtain nano-structured catalyst on the surface. Using scanning electron microscopy (SEM), the average size of Ni nano-islands (synthesized by the 10 and 20 nm Ni films), Pd and Ni-Pd nano-islands were measured about 55, 110, 45 and 50 nm,... 

Mass transfer efficiency and catalytic reactivity are the two major hurdles for heterogeneous catalytic wet peroxide oxidation (CWPO) technologies. To address these issues, nanocomposite CuFeO2/Al2O3 was synthesized and assessed as a novel catalyst for enhanced adsorption and oxidation of anionic pollutants (catechol and reactive red 195 (RR195)) in waters. With a positive charge on the nanocomposite by introducing Al2O3, the adsorption of anionic pollutants was promoted. The surface complexation reaction on CuFeO2/Al2O3, which fits well to the Langmuir isotherm, has engined the mass transfer of pollutants to the nanocatalyst that demonstrated 96.46% and 99.75% removal of catechol and RR195... 

Correlations between electrical and thermal conduction in polymer composites are blurred due to the complex contribution of charge and heat carriers at the nanoscale junctions of filler particles. Conflicting reports on the lack or existence of thermal percolation in polymer composites have made it the subject of great controversy for decades. Here, we develop a generalized percolation framework that describes both electrical and thermal conductivity within a remarkably wide range of filler-to-matrix conductivity ratios (Y f / Y m), covering 20 orders of magnitude. Our unified theory provides a genuine classification of electrical conductivity with typical Y f / Y m ≥ 10 10 as... 

Kinetics of oxidation of MgO-C refractories was investigated by shrinking core modeling of the gas-solid reactions taking place during heating the porous materials to the high temperatures. Samples containing 4.5-17 wt pct graphite were isothermally oxidized at 1000-1350°C. Weight loss data was compared with predictions of the model. A mixed 2-stage mechanism comprised of pore diffusion plus boundary layer gas transfer was shown to generally control the oxidation rate. Pore diffusion was however more effective, especially at graphite contents lower than 10 wt pct under forced convection blowing of the air. Model calculations showed that effective gas diffusion coefficients were in the range... 

The most challenging requirement for depositing NiTi-based shape memory thin films is the control of film composition because a small deviation can strongly shift the transformation temperatures. This article presents a technique to control film composition via adjustment of the power supplied to the targets during simultaneous sputter deposition from separate Ni, Ti, and X (e.g., Hf) targets. After optimization of sputter parameters such as working gas pressure, target-substrate distance, and target power ratio, binary Ni100-x Tix thin films were fabricated and characterized by energy dispersive x-ray spectroscopy in a scanning electron microscope (to measure the film composition and... 

Visibility graph of a simple polygon in a plain is a graph in which the number of its vertices corresponds with the number of vertices in the polygon and each of its edges corresponds with a pair of visible vertices in the polygon. Visibility graph reconstruction of a polygon is one of the old and important problems in computational geometry for which no algorithm has been offered yet. Considering that the problem of visibility graph reconstruction of a pseudo-triangle has been solved, we present an O(n2)-time algorithm for pseudo-triangulation of a simple polygon, using the visibility graph corresponding with the polygon (n is number of vertices of the polygon). To do so, first we present a... 

Multi-walled carbon nanotubes (MWCNTs) with diameter of about 50 nm were synthesized using thermal chemical vapor deposition. We have investigated the influence of Mg doping to the MWCNTs on its hydrogen storage property. TEM micrographs showed that Mg was attached to the MWCNTs and discontinuous arrangement of the carbon walls was recognized in the MWCNTs. According to XPS and BET analyses, the surface functional groups and pore size of the Mg-MWCNTs are increased by interactions between the Mg and the MWCNT's outer walls. The electrochemical discharging curves of the MWCNTs and Mg-doped MWCNTs revealed that the hydrogen storage capacity was 363 and 450 mAhg -1, respectively. Volumetric... 

Using multi-walled carbon nanotubes (MWCNTs), the present study focuses on their electrochemical hydrogen storage capacities. The results showed that the hydrogen desorption process is composed of two steps with voltages around -0.75 and -0.15 V. Hydrogen adsorption at -0.15 V took place at temperatures above 30 °C, and the amount of energy required for adsorbing hydrogen was 1.68 eV. The hydrogen storage capacity increased with increasing electrolyte temperature from 30 to 60 °C in both steps. The hydrogen storage capacity of the MWCNTs treated at different atmospheres showed that the decrease in the graphitization of MWCNTs led to the increase in hydrogen adsorption. The results also... 

The effects of HCl, HNO3, H2SO4 and HF acids on the purification and the electrochemical hydrogen storage of multi-walled carbon nanotubes (MWCNTs) were studied. The MWCNTs were synthesized on Fe-Ni catalyst by thermal chemical vapor deposition method. The X-ray diffraction and thermal gravimetric analysis results indicated that the MWCNTs purified by HF acid had the highest impurities as compared with the other acids. The N2 adsorption results at 77 K indicated that all the samples were mainly mesoporous and the purified MWCNTs by HF acid had the highest surface area as compared with the other acids. The hydrogen storage capacities of the purified MWCNTs by the following acids were in... 

Fabrication of organohalide perovskite materials on the top of ZnO nanoparticles (NPs) has some beneficial advantages such as room temperature processing; however, the perovskite is not stable on ZnO NPs layer during the annealing process. In fact, there are only a few reports about the fabrication of perovskite solar cells on ZnO NPs layer. Herein, the decomposition mechanism of CH3NH3PbI3 perovskite materials on ZnO is reported, and it is found that the perovskite film on the top of the ZnO layer is converted into PbI2 during the annealing process due to the existence of hydroxide groups on the surface of the ZnO NPs. Depending on the annealing temperature, the reaction rate and the... 

A technique that expands dynamic range (DR) of frequency down-converters in the C band frequency is presented. Primary characteristics of down-converter are evaluated to confirm that it can be used in microwave receivers. The C band down-converter is carried out by the combination of RF mixers, band pass interdigital filter, and X band combline filter which are designed entirely for this project. Attainment of the perfect receiver is the final purpose of this paper, and a method that causes 72 dB dynamic range, high tangential signal sensitivity and fine gain flatness is used for achieving the mentioned purpose. These efforts improve the dynamic range about 19 dB and gain flatness about 3.07...