Sharif Digital Repository

A novel optimized chelating hydrogel was synthesized via graft copolymerization of acrylamide and 2-hydroxyethyl methacrylate (as two-dentate chelating co-monomer) onto salep (a multicomponent polysaccharide obtained from dried tubers of certain natural terrestrial orchids) using N,N′-methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator. Reaction parameters (N,N′-methylenebisacrylamide and ammonium persulfate amounts as well as acrylamide/2-hydroxyethyl methacrylate weight ratio) affecting the water absorption of the chelating hydrogel were optimized using a systematic method to achieve a hydrogel with high swelling capacity as possible. Heavy metal ion adsorption... 

Rather vertically aligned ZnO rods with flower-like structures were grown on quartz substrates through vapor phase transport method. X-ray diffraction (XRD) analysis and photoluminescence (PL) measurement were performed to determine crystalline structure and defects, respectively. H2S gas sensing properties of the grown structure were investigated at both room temperature and 250 °C for comparison. A remarkable increase in response and selectivity at room temperature compared to 250 °C was observed. High response and selectivity to low concentrations of H2S at room temperature as well as good stability make the sensor a promising candidate for practical applications  

A fluorometric method was developed for simultaneous determination of Cr(VI) and Cr(III) ions using graphitic carbon nitride nanosheets (g-C3N4 NS) as a nanosized fluorescent indicator probe. The g-C3N4 NS were prepared using high-temperature carbonization of melamine followed by ultrasonication-assisted liquid exfoliation. The g-C3N4 NS display fluorescence with excitation/emission peaks located at 320 and 450 nm. The chromium speciation is based on the quenching of g-C3N4 NS fluorescence. The total concentration of chromium is determined after oxidation of Cr(III) to Cr(VI). The Cr(III) content was then calculated by subtracting the concentration of Cr(VI) from that of total chromium. The... 

To the best knowledge of us, survivability for WSN has never been studied considering failure affects on network. We perceive the network survivability as a composite measure consisting of both network failure duration and failure impact on the network. In this paper we will study network survivability in unstably state: in this state, network is affected by the failures that occur temporarily and instantly also may occur several times. In other words, the main characteristics of these failures are their frequency and being temporary. In this paper we will propose a survivability model for network in unstable state that is based on network availability. This availability model, presents... 

Traffic assignment problem (TAP) is traditionally defined without side constraints. Although introducing the side constraints into the TAP is used as a way of refining the applied assignment models, it brings some computational difficulties preventing the refined model to be applicable in the real-case problems. In this paper an iterative solution algorithm is developed for TAP with linear side constraints. This method is based on implicitly considering the side constraints by means of adding a dynamic penalty function (DPF) to the link travel times. Each of the iterations of the algorithm is reduced to an unconstrained assignment followed by updating the penalty functions. The unconstraint... 

Novel ZnO-carbon and ZnO nanofibers were fabricated by electrospinning of polymer precursor followed by subsequent annealing in nitrogen and air, respectively. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) indicated the smooth and beadless nanofibers with wurtzite crystal structure. X-ray photoelectron spectroscopy (XPS) showed the presence of oxygen vacancies (VO) and chemisorbed O2 on the surface of the samples. Band gap narrowing of the ZnO-carbon nanofibers in comparison to ZnO were measured by diffuse reflectance spectroscopy (DRS). Photo-degradation of azo dye under the UV and visible light was evaluated and ZnO-carbon showed an enhancement in... 

Network survivability is one of the main design challenges in wireless sensor networks (WSN). Survivability is the ability of the network to provide essential services in the presence of attacks and/or failures, and recover full service in a timely manner. To the best knowledge of us, survivability for WSN has never been studied considering failure effects on network. We consider the network survivability as a composite measure consisting of both network failure duration and failure impact on the network. In this paper we model network survivability in steady state. In this state, network is affected by predicted failures. This modeling is based on network connectivity and coverage, when an... 

In this work, we have studied thermal stability of nanoscale Ag metallization and its contact with CoSi 2 in heat-treated Ag(50 nm)/W(10 nm)/Co(10 nm)/Si(1 0 0) multilayer fabricated by sputtering method. To evaluate thermal stability of the systems, heat-treatment was performed from 300 to 900 °C in an N 2 ambient for 30 min. All the samples were analyzed by four-point-probe sheet resistance measurement (R s ), Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD), and atomic force microscopy (AFM). Based on our data analysis, no interdiffiusion, phase formation, and R s variation was observed up to 500 °C in which the Ag layer showed a (1 1 1) preferred crystallographic... 

In this research, we have focused on the formation of Ag nanoparticles dispersed in SiO2 matrix using sol-gel method. The influences of the metal concentration on the size variation of Ag nanoparticles and the size effect on the surface plasmon absorption have been studied. Sol-gel silica thin films containing Ag particles were synthesized by dip-coating on soda-lime glasses. The molar ratio of Ag / Si was chosen from 0.2% to 8%. All films were dried in air at 100 °C for 1 h. Using X-ray photoelectron spectroscopy, the Ag / Si ratios in the prepared films have been measured. In addition, it was shown that the prepared matrix was a stoichiometric composition as SiO2, and the synthesized... 

A heat-transfer model was formulated to determine the distribution of temperature within a bioheap of chalcopyrite of Sarcheshmeh copper mine. Bioleaching employs mixed mesophilic and thermophilic microbes for Cu extraction. Thermophiles are better than mesophiles to dissolve CuFeS2. The solution irrigation and aeration rates were taken into account as the main operational factors. The model was validated by comparing the temperature profiles of test columns with those of bioheap. The model was used to find the optimal ratio of irrigation to aeration. It was found that when the solution was fed at a flow rate of 5 kg/m2 h and air was blown at a flow rate of 7.5 kg/m2 h, the transition from a... 

Recently, photoelectrochemical conversion (PEC) of water into fuel is attracting great attention of researchers due to its outstanding benefits. Herein, a systematic study on PEC of water using CuFe2O4/ α-Fe2O3 composite thin films is presented. CuFe2O4/ α-Fe2O3 composite thin films were deposited on two different substrates; (1) planner FTO glass and (2) 3-dimensional nanospike (NSP). The films on both substrates were characterized and tested as anode material for photoelectrochemical water splitting reaction. During PEC studies, it was observed that the ratio between two components of composite is crucial and highest PEC activity results were achieved by 1:1 component ratio (CF-1) of... 

In this research, nickel thin films have been deposited on Si (1 0 0) substrate using the dc sputtering method. Then, the deposited layers were annealed in different temperatures to oxidize and crystallize the as prepared layers. Scanning electron microscopy (SEM) analysis indicated that the nanorod shape of the nickel oxides has grown on the substrate and x-ray photoelectron spectroscopy determined the formation of stoichiometric NiO on the surface. Field emission (FE) measurements of the NiO nanorods exhibited the lowest turn-on electric field at about 3.8 V μm-1 in the 300 μm vacuum gap. Moreover, the field enhancement factor (β) was measured of about 4109 for this sample. The FE... 

Modern societies are strongly dependent on the continuous and efficient operation of electric power systems as a critical infrastructure. Besides, information and communication systems play a crucial role in the resiliency enhancement of the power system. As power communication systems are vulnerable against physical and cyber attack, these systems themselves can be an internal source of threat for power grids. Therefore, there is a need to identify and study the threats and weaknesses of power communication systems using a comprehensive framework. This framework helps power communication network planners evaluate all challenges and their numerous effects on the system, as a very important... 

A method for two dimensional position finding of stationary targets whose bearing measurements suffers from indeterminable bias and random noise has been proposed. The algorithm uses convex optimization to minimize an error function which has been calculated based on circular as well as linear loci of error. Taking into account a number of observations, certain modifications have been applied to the initial crude method so as to arrive at a faster, more accurate method. Simulation results of the method illustrate up to 30% increase in accuracy compared with the well-known least square filter  

A new type of composite material based on carbon nanotubes (CNTs) and sol-gel chemistry was prepared and used as sorbent for needle trap device (NTD). The synthesized composite was prepared in a way to disperse CNTs molecules in a sol-gel polymeric network. CNT/silica composites with different CNT doping levels were successfully prepared, and the extraction capability of each composite was evaluated. Effects of surfactant and the oxidation duration of CNTs on the extraction efficiency of synthesized composites were also investigated. The applicability of the synthesized sorbent was examined by developing a method based on needle trap extraction (NTE) and gas chromatography mass spectrometry... 

The electrooxidation of clozapine (CLZ) was studied on the surface of a glassy carbon electrode (GCE) modified with a thin film of multiwalled carbon nanotubes (MWCNTs)/new coccine (NC) doped polypyrrole (PPY) by using linear sweep voltammetry (LSV). The pH of the supporting electrolyte (D), drop size of the cast MWCNTs suspension (E) and accumulation time of CLZ on the surface of modified electrode (F) was considered as effective experimental factors and the oxidation peak current of CLZ was selected as the response. By using factorial-based response-surface methodology, the optimum values of factors were obtained as 5.44, 10 μL and 300 s for D, E and F respectively. Under the optimized... 

An electric power supply is the backbone of development in advanced as well as in developing economies. An integral part of ensuring a secure power supply system is a power communication system. Due to the high and sustained performance requirements of power communication systems, electric companies prefer to construct their own communication networks privately rather than relying solely on a public communication system. The focus of this paper is on the optimal topological design of a power communication network. Based on advanced optimization models in public communication networks, and taking into account the specific Quality of Service, as demanded by various applications, such as... 

In this study, the crystallisation of nano hydroxyapatite (HA) films on stainless steel 316L was studied. The film was prepared by sol-gel technique. The process was started with preparation of an HA sol. After aging of the sol at room temperature, a stainless steel 316L substrate was dip coated and then was heat treated from 350 to 450°C at different periods of time in air. The crystallisation behaviour and the transformation-temperature-time diagram of HA films were achieved and analysed using the avrami equation. The results showed that the crystallisation of HA began at 250°C and was increased up to 450°C. The obtained HA film showed a nanostructure character with a suitable crystalinity... 

Micro flora of the effluents from a dairy factory in Tehran(Pegah Dairy Processing Plant) were isolated and screened for their ability to reduce the organic matter content and COD of the effluents. 10 bacteria were selected due to reduction in COD content from the 4th to 6th day of incubation at 30 °C and pH =11. Highest COD reduction were obtained by two isolates, BP3 and BP4, 70.7 % and 69.5 %, respectively (The initial COD concentration was 3000 mg/l and reduced to 880 and 920 mg/l).After optimization of the condition for test organisms, big reductions in COD, carbohydrate, fat and protein content of the effluents were observed by BP3 up to 84.70 %, 98 %, 45.30 % and 53 %, respectively... 

The Multi-walled carbon nanotube (MWCNT)/WO3 nanocomposite thin films with different MWCNT's weight percentages were prepared by sol-gel method as visible light induced photoanode in water splitting reaction. Weight percentage of MWCNT in the all nanocomposite thin films was confirmed by TGA/DSC analysis. According to XPS analysis, oxygenated groups at the surface of the MWCNT and stoichiometric formation of WO3 thin films were determined, while the crystalline structure of the nanocomposite samples was studied by XRD indicating (0 0 2) peak of MWCNT in the monoclinic phase of WO3. The influence of different weight percentage (wt%) of MWCNT on WO3 photoactivity showed that the electron...