Sharif Digital Repository

Three-dimensional gold nanoelectrode ensembles (3D GNE) have proven to be promising nanoelectrodes by representing much higher sensitivity compared to both their 2D nanostructures and bulk counterparts. The sensitivity of 3D gold nanotubes (GNTs) fabricated through electrodeposition inside the pores of polycarbonate templates, was examined toward metronidazole (MTZ) as one of their pharmaceutical applications. The electrochemical behavior of MTZ at the 3D GNT-modified electrode was discussed in detail through cyclic voltammetry (CV) which suggested an irreversible reduction of nitro group to the corresponding hydroxylamine and a subsequently reversible redox peak for the corresponding... 

Fabrication of well-defined gold nanowires (GNWs) is of significant importance in many fields such as sensing applications. In this study, the electrodeposition of well-defined GNWs inside polycarbonate (PC) template has been discussed in detail. GNWs were potentiostatically electrodeposited at different filling rates. The growth of GNWs at different stages of pore filling was monitored by electrochemical measurements and field-emission scanning electron microscopy (FE-SEM). It was confirmed that under growth rates between 2.5 and 4 nm/s, GNWs with smooth ends grew uniformly inside the template without any imperfections or corrugations. The length of GNWs was electrochemically controlled to... 

As a novel and highly sensitive sensor, three-dimensional gold nanoelectrode ensembles (3D GNE) prepared by gold deposition inside the parallel pores of a porous template have been successfully applied in electrochemical determination experiments. In this study, we report on the fabrication of 3D gold nanotubes (GNT) and their application in determination of Hg (II) in water. The morphology and crystal structure of the 3D GNT were characterized by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD), respectively. The sensitivity of the fabricated electrode towards Hg (II) was examined using anodic stripping voltammetry (ASV) as a powerful technique in... 

Deployment of low-power low-cost small access points such as femtocell access points (FAPs) constitute an attractive solution for improving the existing macrocell access points' (MAPs) capacity, reliability, and coverage. However, FAP deployment faces challenging problems such as interference management and the lack of flexible frameworks for deploying the FAPs by the service providers (SPs). In this paper, we propose a novel solution that jointly associates the user equipment (UE) to the APs, and allocates the FAPs to the SPs such that the the total satisfaction of the UEs in an uplink OFDMA network is maximized. We model the competitive behaviors among the UEs, FAPs, and SPs as a dynamic... 

The effect of an intermediate standing baffle on the flow structure in a rectangular open channel has been investigated by a three-dimensional acoustic Doppler velocimeter. Investigation of time-averaged velocity profiles at different streamwise positions reveals that the approach flow is fully developed upstream of the baffle. By analysing the space-averaged power spectra of streamwise velocity, a peak structure was observed in the upstream baffle region. Downstream of the baffle this peak structure has been alleviated by the baffle. The same analysis for the vertical component indicates the existence of a peak structure both up- and downstream of the baffle. Consequently, a baffle affects... 

The present study investigates the possibility of using a small hydropower/PV hybrid power system for low-cost electricity production which can satisfy the energy load requirements of a typical rural-urban area. In this context, the optimal dimensions to improve the technical and economical performances of the hybrid system are determined according to the load energy requirements and the solar and hydro resources data using linear programming. The application of the model is demonstrated using a case study of a rural-urban area in Mazandaran province, Iran. Two scenarios were considered for optimizing the system components. In the first scenario, a stand-alone hybrid small hydropower/PV... 

A comparison of various hydrogen production processes indicates that the thermal decomposition of methane (TDM) provides an attractive option from both economical and technical points of view. The main problem for this process is the deposition of the nano-carbon particles on the reactor wall (or catalyst surface). This research concentrates on the numerical simulation of the TDM process without use of a catalyst to find a technique that decreases the carbon accumulation in a tubular reactor. In this model, the produced carbon particles are tracked with the Lagrangian method under thermophoretic, Brownian, van der Waals, Basset, drag, lift, gravity, pressure and virtual mass forces. In... 

In this paper the process of knowledge accumulation for a particular technology is studied. Two countries, say the technology follower and the technology frontier, are considered. The frontier's knowledge growth is determined by its R&D efforts on the technology. The level of knowledge stock for the follower country is augmented by its R&D activities for the technology and absorbing some of the external knowledge through spillover from the frontier. The extent to which the follower is able to exploit the external knowledge depends on technological gap, absorptive capacity, absorption time and degree of spillover. New concepts such as natural and enhanced degree of spillover, background and... 

The paper presents further experiments with an extended version of a comprehensive model for assessment of energy technologies and research and development (R&D) planning to evaluate the impact of innovation programs on development of Iranian electricity-supply system. This analytical instrument is a model of energy R&D resource allocation with an explicit perspective of developing countries which has been linked to a bottom-up energy-systems model. Three emerging electricity generation technologies of solar PV, wind turbine and gas fuel cell are considered in the model and the impact of innovation programs on cost-reducing innovation for them is examined. The main results provided by the... 

Optimal allocation of resources for R&D on new energy technologies is an important issue in the process of development of energy system models. In this study, a model of R&D planning in energy sector has been developed and it is then linked to the energy system model. Energy system model is used as a tool for the technology assessment and prioritization of new energy technologies is evaluated with the help of this model. Based on the economic and environmental impact of new technologies, the optimal allocation of resources for R&D of new technology is estimated with the help of the R&D planning model. The conceptual formulation of the model and its integration with the energy technology... 

A heat transfer model was developed for a new non-electric infant's transport incubator. The source of heat comprises a super saturated solution of Sodium Acetate and a metal disk (activator) in a plastic container. Estimating the number of the chemical bags required for different ambient temperature was the goal. First the quantity of heat generated by the chemical was appointed through experiments and use of a parameter estimation method. The number of the chemical bags were also estimated through a numerical-experimental method  

As an important precursor of crystalline phases, amorphous calcium carbonate (ACC), especially ultrasmall ACC clusters, have been attracting great interest in fundamental research, materials chemistry, as well as industrial applications. However, it is still challenging to synthesize stable ACC clusters in water that can be isolated and concentrated without severe aggregation. Herein, we report a facile dialysis method for producing colloidally stable ACC clusters that are well dispersed in water with the protection of specific polycarboxylic acids, which could be also easily deprotected by small-molecule acids like sodium citrate. Inherent proto-calcite short-range order is found to be... 

The proper modeling of radiation is of great importance in numerical simulation of combustion processes. A simple gray weighted-sum-of-gray-gases (WSGG) model has been intensively used in CFD simulations of industrial combustion applications, mainly because of its low computational costs. However, the gray assumption is far from the real behavior of non-gray combustion gases. This could consequently affect the accuracy of temperature field and heat flux distribution predictions. On the other hand, modern non-gray global radiation models such as the standard spectral line-based weighted-sum-od-gray-gases (SLW) model are still computationally expensive for many engineering purposes. To... 

In many developing countries, restructuring is usually started by dividing vertically integrated power systems into regional companies. Analysis of the procedure of restructuring requires appropriate analytical tools for modeling interactive behavior of the regional companies in a competitive energy market. The problem of generation expansion planning in the competitive environment becomes more complex where the new generation units are constructed on the basis of decentralized decisions. Recent studies of long term expansion planning show that market equilibrium modeling is an effective technique to analyze the long-term optimum development of the generation systems. In the present paper, a... 

In this paper, a dynamic-hybrid automatic repeat request (D-HARQ) scheme with guaranteed delay performance is proposed. As opposed to the conventional HARQ that the maximum number of re-transmissions, L, is fixed, in the proposed scheme packets can be re-transmitted more times given that the previous packet was received with less than L re-transmissions. The dynamic of the proposed scheme is analyzed using the Markov model. For delay sensitive applications, the proposed scheme shows a superior performance in terms of packet error rate compared with the conventional HARQ and Fixed retransmission schemes when the channel state information is not available at the transmitter. We further show... 

Double oxide films (hereafter: oxides), inclusions and Fe-rich phases are known to be the most detrimental defects in cast Al-Si-Mg alloys. The effects of these defects on reproducibility of tensile properties in Al-7Si-0.35Mg alloy have been investigated in this study. Four different casting conditions (low oxide-low Fe, high oxide-low Fe, low oxide-high Fe and high oxide-high Fe) were studied. In each case, 30 tensile test samples were prepared by casting in a metallic mold and machining (total of 120 tensile test samples). Results of tensile test were analyzed by Weibull three-parameter and mixture analyses. The microstructure and fracture surface of samples were studied by optical and... 

Electrochemical co-deposition approach was expanded to prepare composite bio-ceramic coating of hydroxyapatite (HA)/polyvinyl acetate on the surface of titanium. The role is to improve the bioactive and crystallization properties. The results of XRD, XPS, SEM and TEM characterization showed that by increasing amount of vinyl acetate in the composite bio-ceramic coating before and after immersing in the simulated body fluid (SBF), an oriented growth of HA planes on the (0 0 2) direction had been observed on titanium substrate. Also significant surface morphology changes were obtained  

The aim of this paper is to provide a solution to decrease water consumption in the slab-cooling unit of Mobarakeh Steel Complex in Iran. The plan should give an hourly decline in water consumption during a one-year operation period to calculate the annual reduction in water consumption of the proposed process. Recommended solutions for the conversion scheme of an existing wet cooling tower to a dry or hybrid cooling system require modeling of the slab cooling process. The curves of temperature drop in slabs are extracted in this paper by modeling the transient heat transfer of the slabs in the cooling process. This will reduce the computational volume. Then, the design and optimization of... 

In this paper, the effect of different parameters on the thermal operation of a Closed Loop Pulsating Heat Pipe (CLPHP) has been investigated. These parameters include the working fluid, the inclination angle, the filling ratio, and the input heat flux. The effect of nanoparticle mass concentrations has been analyzed as well. It was observed that the CLPHP can decrease thermal resistance up to 11.5 times compared to the same empty copper tube with thermal resistance of 9.4 K/W. Optimum thermal operation for a system with the water-silver nanofluid was achieved at conditions of the 50% filling ratio with thermal resistance of 0.9 K/W, and for the water-titanium oxide system, the optimal...