Sharif Digital Repository

In this study, a review of the overlay/index methods served for delineation of vulnerable zones in coastal aquifers affected by SWI is provided. Then, a more realistic presentation of the vulnerability mapping of coastal aquifers to SWI through modified GALDIT index method by incorporating the influential factors on SWI is established. The modifications on GALDIT method including incorporating the seaward hydraulic gradient (i) instead of the height of groundwater level above sea level (L) (so-called GAiDIT), and considering hydraulic gradient (i) as an additional parameter to the GALDIT (so-called GALDIT-i). Three GALDIT, GAiDIT, and GALDIT-i methods were evaluated with data from three... 

Increasing use of networks and their complexity make the task of security analysis more and more complicated. Accordingly, automatic verification approaches have received more attention recently. In this paper, we investigate applying of an actor-based language based on reactive objects for analyzing a network environment communicating via Transport Protocol Layer (TCP). The formal foundation of the language and available tools for model checking provide us with formal verification support. Having the model of a typical network including client and server, we show how an attacker may combine simple attacks to construct a complex multiphase attack. We use Rebeca language to model the network... 

Multi-walled carbon nanotube decorated with silver nanoparticles (AgNPs-MWCNT) is used as an effective strategy for modification of the surface of pyrolytic graphite electrode (PGE). This modification procedure improved colloidal dispersion of the decorated MWCNTs in water, affording uniform and stable thin films for altering the surface properties of the working electrode. Robust electrode for sensing applications is obtained in a simple solvent evaporation process. The electrochemical behavior of sumatriptan (Sum) at the bare PGE and AgNPs-MWCNT modified PGE is investigated. The results indicate that the AgNPs-MWCNT modified PGE significantly enhanced the oxidation peak current of Sum. A... 

By using graphene nanosheets decorated with Ag nanoparticles (AgNPs-G) as an effective approach for the surface modification of pyrolytic graphite electrode (PGE), a sensing platform was fabricated for the sensitive voltammetric determination of Azathioprine (Aza). The prepared AgNPs-G nanosheets were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis and Raman spectroscopy techniques. The electrochemical behavior of Aza was investigated by means of cyclic voltammetry. Comparing to the bare PGE, a remarkable enhancement was observed in the response characteristics of Aza on the surface of the modified electrode (AgNPs-G/PGE) as well as a noticeable... 

With the increasing penetration of renewable energies as distributed generation (DG) in power systems, technical problems arise in both distribution and transmission system level. Voltage rise is the main barrier for connection of DGs in rural areas, while excessive reactive power demand from transmission system is the major concern for Transmission System Operators (TSO). Here, a centralized control scheme based on the Smart Grid is proposed to reduce the impact on the transmission system voltages and improve its stability, while mitigating the voltage rise issue in the distribution network. Reactive power output of DGs, substation capacitors and tap setting of transmission transformer are... 

The introduction of demand response concept, in addition to increment of penetration of distributed generation (DG) based on renewable energies, make opportunities for the novel control schemes to be integrated in power system on a smart grid framework. Voltage control methods in power systems needs proper coordination among reactive power resources and conventional volt/var control equipments. In this work, potential reactive power resources are investigated and then, reactive power output of renewable DG units and controllable loads along with operation of conventional voltage controllers are optimized using a centralized control scheme. Considering the variability of demand and... 

This article proposes a scheme for balancing the voltage of series-connected insulated gate bipolar transistors (IGBTs), which is also very effective under short-circuit conditions. An optimized clamp-mode snubber is proposed, including an active-driver to balance the currents of the IGBTs during short-circuit, which in turn allows for a considerable reduction of the snubber capacitance. The approach is proven to be effective under short-circuit conditions by a maximum of 55 V voltage increment and a negligible difference in the current values. The effectiveness of the proposed approach is demonstrated through simulations in PSPICE software and experimental tests performed at 2 kV. ©... 

In this article, a novel cooperative secondary voltage/frequency control considering time-varying delays and noises in fading channels is presented for an autonomous alternating current (AC) voltage sourced-based converter (VSC)-based microgrid (MG), including inverter-interfaced distributed generations (DGs). Fading phenomenon makes complex random fluctuations on the voltage and frequency of every DG received from its neighbor DGs. In multi-agent cooperative systems, in addition to the total additive noise and time-variant delay, a multiplicative complex random variable is considered to model the main received signal and its replicas due to multipath propagation. The proposed... 

In the last decades, much attention has been paid to the design of multi-speaker voice conversion. In this work, a new method for voice conversion (VC) using nonlinear principal component analysis (NLPCA) is presented. The principal components are extracted and transformed by a feed-forward neural network which is trained by combination of Genetic Algorithm (GA) and Back-Propagation (BP). Common pre- and post-processing approaches are applied to increase the quality of the synthesized speech. The results indicate that the proposed method can be considered as a step towards multi-speaker Voice conversion. © 2007 IEEE  

Simplicity of manufacturing and high reliability of airlift pumps have promoted these pumps to be used in different industries, such as petrochemical and oil industries, especially in oil recovery from dead wells. One of the main parameters affecting the performance of these pumps is two-phase flow regime in the main pipe of the pump. In this research, experimental data are utilized to investigate the influence of the flow regimes on the performance of an airlift pump. The data are obtained for air-water two-phase flow in a vertical pipe with a diameter of d = 50. mm and an aspect ratio of L/d = 120. In this study, the gas liquid upward two-phase flow regime in the upriser pipe is... 

Abstract Miscible carbon dioxide (CO2) flooding has become the most commonly and favorable approach in Enhanced Oil Recovery (EOR) because of its high oil reservoir sweep efficiency and contribution to the reduction of greenhouse gas emissions. Despite this, it can significantly favor the asphaltene deposition, which leads to the wettability reversal and formation damage. A novel experimental setup was utilized to study asphaltene deposition on the model rock at reservoir condition. The evolution of asphaltene deposition was monitored by a microscope; then analyzed by image processing software to check the amount of deposited asphaltene and its size distribution at different... 

Tight unmanned aerial vehicle (UAV) autonomous missions such as formation flight and aerial refueling (AR) requires an active controller that works in conjunction with a precise vision-based sensor that is able to extract In-front aircraft relative position and orientation from captured images. A key point in implementing such a sensor is its robustness in the presence of noises and other uncertainties. In this paper, a new vision-based algorithm that uses neural networks to estimate the In-front aircraft relative orientation and position is developed. The accuracy and robustness of the proposed algorithm has been validated via a detailed modeling and a complete virtual environment based on... 

Tight unmanned aerial vehicle (UAV) autonomous missions such as formation flight (FF) and aerial refueling (AR) require an active controller that works in conjunction with a precise sensor that is able to identify an in-front aircraft and to estimate its relative position and orientation. Among possible choices vision sensors are of interest because they are passive in nature and do not require the cooperation of the in-front aircraft in any way. In this paper new vision-based estimation and navigation algorithms based on neural networks is developed. The accuracy and robustness of the proposed algorithm have been validated via a detailed modeling and a complete virtual environment based on... 

A new plasmonic Ag hybridized CuWO4/WO3 heterostructure was successfully synthesized via a ligand-assisted sol gel method. The as-prepared plasmonic nanohybrid was thoroughly characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy, photoluminescence (PL) spectrometry, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis and electrochemical impedance spectroscopy (EIS). Moreover, the photocatalytic activity was evaluated by photo-degradation of methylene blue (MB) under visible light irradiation. The results indicate that the as-prepared plasmonic Ag-CuWO4/WO3 nanohybrid (compared to pure... 

Today, regarding the limitation and environmental side effects of fossil fuel resources, solar hydrogen production is one of the main interests in the energy research area. The development of visible light sensitized semiconductors based on non-toxic components, low cost and available bio-species is an ongoing approach for H2 generation based on water splitting reactions. Here, two different morphologies of TiO2 photoanodes, nanoparticulated and nanotubular, have been modified with simply extracted bacteriorhodopsin (bR) without any linker. Achieving a significant enhancement in photoconversion efficiency of TiO2 photoanodes, η% was increased from 2.9 to 16.5 by bR addition to the TiO2... 

Carbon nanotube (CNT)-doped TiO2 thin films with various CNT contents were synthesized by sol-gel method for visible light photoinactivation of Escherichia coli bacteria. Post annealing of the CNT-doped TiO2 thin films at 450 °C resulted in anatase TiO2 and formation of Ti-C and Ti-O-C carbonaceous bonds in the film. By increasing the CNT content, the thin films could further inactivate the bacteria in the dark. Meanwhile, as the CNT content increased from zero to 40 wt% the effective optical band gap energy of the CNT-doped TiO2 thin films annealed at 450 °C decreased from 3.2-3.3 to less than ∼2.8 eV providing light absorption in the visible region. Concerning this, visible light... 

In this paper, we design a dimming compatible visible light communication (VLC) system with asynchronous and optimum indoor positioning method in a standard office room in combination with asynchronous and optimum indoor positioning method according to illumination standards under channel constraints. We use overlapping pulse position modulation (OPPM) to support dimming control by changing the code weights. The system parameters such as a valid interval for dimming together with an upper bound for bit rate according to the channel delay spread are investigated. Moreover, considering the dispersive VLC channel and using Monte Carlo (MC) simulations, a method is proposed to determine the... 

We study two well-known planar visibility problems, namely visibility testing and visibility counting, in a model where there is uncertainty about the input data. The standard versions of these problems are defined as follows: we are given a set S of n segments in R 2 , and we would like to preprocess S so that we can quickly answer queries of the form: is the given query segment s∈S visible from the given query point q∈R 2 (for visibility testing) and how many segments in S are visible from the given query point q∈R 2 (for visibility counting). In our model of uncertainty, each segment may or may not exist, and if it does, it is located in one of finitely many possible locations, given by a... 

To achieve economic stability, distribution Company as an economic institution should be managed by various processes. In this way, knowledge of different processes is the first step. Furthermore, expectations, outputs, requirement data, and sub-processes should be extracted and determined. Accordingly, to assign the performance responsibility of each process, the decision making points must be introduced and, the deviation or change in set-points should be investigated into processes. Also, the performance of processes could be monitored by introducing of the sub-indictors. In this study, a practical method is presented for monitoring of reliability and power loss indices from viewpoint... 

Viscous fingering is one of the main challenges that could reduce areal sweep efficiency during waterflooding in oil reservoirs. A series of waterflooding experiments were carried out in a Hele-Shaw cell at ambient temperature during which areal sweep efficiency was estimated and techniques to ease the fingering problem were examined. The onset and propagation of viscous fingers were monitored as a function of both injection rate and injection/production positions. Image processing techniques were utilized to quantitatively investigate the propagation of fingers. The experimental results show that, under specific conditions, increasing the number of finger branches could improve the areal...