Sharif Digital Repository

Future of the network stability is endangered by increasing the number of Distributed Generation (DG) and Renewable Energy Source (RES) units. The idea of the Virtual Synchronous Machine (VSM) has been raised to control the power electronic-based DG/RES converters in order to have better integration with the grid. This paper introduces a new stabilizer design for VSM-based converters to guarantee the stability of the micro-grid (MG). In this regard, the Sliding Mode Control (SMC) theory, which is robust against the disturbances and uncertainties, is employed to cope with the intermittent and nonlinear nature of DGs. The mutual operation of the proposed inverter and MG stabilizer has the... 

A homemade immersed solvent microextraction (SME) device was successfully developed for the trace enrichment of phenols from aqueous samples. A microdrop of butyl acetate was suspended from the tip of a microsyringe needle, immersed in an aqueous spiked solution for a preset time. The microdrop was then retracted into the microsyringe and injected directly into a gas chromatography-mass spectrometry (GC-MS) injection port. Effects of different parameters such as the type of solvent, extraction time, stirring rate, and temperature were investigated and optimized. To reduce the polarity of phenols and prevent tailing effects, all the phenols were derivatized prior to extraction using acetic... 

We design and simulate the motion of a swimmer, the Quadroar, with three-dimensional translation and reorientation capabilities in low-Reynolds-number conditions. The Quadroar is composed of an I-shaped frame whose body link is a simple linear actuator and four disks that can rotate about the axes of flange links. The time symmetry is broken by a combination of disk rotations and the one-dimensional expansion or contraction of the body link. The Quadroar propels on forward and transverse straight lines and performs full three-dimensional reorientation maneuvers, which enable it to swim along arbitrary trajectories. We find continuous operation modes that propel the swimmer on planar and... 

This paper presents a method for ECG characteristic points detection based on Wavelet Transform (WT). Wavelet Transform leads to more accurate results in analyzing nonstationary signals such as ECG. The selected wavelet is quadratic spline wavelet. Using quadratic spline mother wavelet, a method for detection of QRS complex and T and P waves is presented and evaluated with the help of MIT-BIH Arrhythmia database. Experimental results show excellent performance of the proposed method. © 2009 IEEE  

The magnetic response of a polyamide nanocomposite membrane under applying a magnetic field has been modeled to evaluate elastic deformation order of magnitude. A PA-Fe3O4 nanocomposite membrane is considered to be modeled under influence of volume plane stress caused by a magnetic field. The modeling of the mechanical behavior of Fe3O4-PA nanocomposite membrane suggests that nanoparticle displacements within the nanocomposite, in the order of 200 nm under applying an external magnetic field, are greater than free volumes or porosities of the polyamide membrane. The membrane can be excited to mechanically vibrate by applying an alternating magnetic field lower than 0.1 T. As the results... 

The authors regret Acknowledgement: The authors would like to express his gratitude to Iran National Science Foundation (INSF) for supporting this research under grant number 92037628. The authors would like to apologise for any inconvenience caused. © 2019 Elsevier B.V  

Mobile Ad Hoc Networks (MANETs) are networks with selforganizing capabilities and without a fixed infrastructure. Wireless nodes communicate among themselves using multi-hop radio relaying, without requiring the packets to pass through a central access point or a base station. In a highly mobile and infrastructure-less scenario, pre-configuration of addresses is not possible. Therefore node addresses need to be configured dynamically with minimum delay and packet loss. Existing solutions for IP address auto-configuration do not address security issues. In this paper we propose a secure address autoconfiguration for Mobile Ad hoc Networks (MANET) based on Virtual Address Space Mapping [1].... 

In this study, the ability of Aspergillus niger and Penicillium simplicissimum to extract heavy metals from a spent refinery catalyst was investigated. For the first step, a spent processing catalyst from one of the oil refineries in Iran was physically and chemically characterized. Aspergillus niger and Penicillium simplicissimum were used to mobilize Al/Co/Mo/Ni from hazardous spent catalysts. The fungi were adapted to the mixture of metals at 100-800 mg L -1 with increments in concentration of 100 mg L -1. Bioleaching experiments were carried out in batch cultures. To investigate the production of organic acids in sucrose medium, analyses of the culture medium by HPLC were performed at... 

A spent processing catalyst from an Iranian oil refinery was initially characterized physically and chemically. Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans were used to mobilize Al, Co, Mo and Ni from the spent catalysts under optimized conditions in batch cultures. The characteristics of the bioleach solution (pH, Eh, cell concentration and Fe(II)/Fe(III) concentration) were determined along with the concentration of metal values extracted from the catalyst. The results showed that after bioleaching using A. ferrooxidans in the presence of ferrous sulfate, maximum extractions of 63% Al, 96% Co, 84% Mo and 99% Ni were achieved after 30 days at pH 1.8-2.0. However, the... 

In this paper, we present a method to dynamically observe two important variables of a Gas Metal Arc Welding (GMAW) process, i.e. arc voltage and arc length. To do this, we use Kalman filter to estimate these two variables in a high level noisy environment of GMAW process both in open and closed loop modes  

The control of thin film nanocomposite (TFN) membranes cross-linking degree is an important factor to design new membranes and optimizing permeation characteristics. The Fe3O4 nanoparticle's based TFN membranes due to potentially added magnetic responsive properties to the membrane has a great importance in developing membrane architectures. Fe3O4/polyamide (PA) TFN membranes filled with nanoparticles in different sizes and concentrations have been synthesized. Cross-linking degree of PA layer characterized with Fourier transform spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) methods to evaluate size dependency of the cross-linking degree of PA layer network. Obvious... 

The problem of time delay estimation (TDE) in the presence of zero mean white Gaussian noise is addressed. A novel and efficient algorithm for obtaining Conditional Maximum Likelihood (CML) estimates of delays, attenuation factors and the number of paths from a transmitter to a receiver is introduced. This approach is quite suitable for the cases in which time delay difference is less than the duration of signal autocorrelation  

Voltammetric behavior of two mercaptopyrimidine derivatives (2-thiouracil and 2-thiobarbituric acid) has been studied by cyclic voltammetry at a cobalt phthalocyanine (CoPc)-modified carbon-paste electrode. The results of voltammetric determinations showed that the CoPc in the matrix of modified electrode acts as catalyst for electrooxidation of these thiols (RSH), lowering the overpotential of the reaction and significantly increasing the sensitivity for detection of thiols in neutral conditions. The results of voltammetric and polarization measurements in solutions with various pHs were used for prediction of the mechanism of electrocatalytic oxidation at the surface of modified electrode.... 

The potentiometric response characteristics with respect to salicylate anion of several membrane electrodes based on iron(II) tetraphenylporphyrin chloride (FeTPPCl) and derivatives with electrophilic and nucleophilic substituents, incorporated into plasticized polyvinylchloride (PVC) membranes were investigated. Complexes tetraphenyl porphyrin iron(III) chloride (FeTPPCl; A), tetrakis (4-methoxyphenyl) porphyrin iron(III) chloride (Fe(TOCH 3PP)Cl; B), tetrakis (2,6-dichlorophenyl) porphyrin iron(III) chloride (Fe(TDClPP)Cl; C), tetrakis (4-nitrophenyl) porphyrin iron(III) chloride (Fe(TNO2PP)Cl; D), and tetrakis (pentafluorophenyl) porphyrin iron(III) chloride (Fe(TPFPP)Cl; E) were used as... 

A metallophthalocyanine complex with zirconium(IV) ion in the center (as an oxo-zirconium, Zr=O, group) was used in poly vinyl chloride (PVC) membranes for the selective detection of 5-sulfosalicylic acid (SSA). The resulting electrodes demonstrate Nernstian responses over a wide range of sulfosalicylic acid concentration (10-6 to 10-1 mol dm-3) with a slope of about -29 mV per decade. The influence of lipophilic ion-exchanger sites on the response properties of the electrodes was investigated. The optimal potentiometric response was observed for the electrode in the presence of about 150 mol% of cationic additive (relative to ionophore) in the phase membrane. The electrodes have a fast... 

In this paper, the three-dimensional large deformation frictional contact of powder forming process is modeled using a simple computational algorithm based on the augmented-Lagrange approach. The technique is applied by imposing the contact constraints and modifying the contact properties of frictional slip through the node-to-surface (NTS) contact algorithm. The Coulomb friction law is employed to simulate the friction between the rigid punch and the work-piece by the use of penalty and augmented-Lagrange approaches. It is shown that the augmented-Lagrange technique significantly improves imposing of the constraints on contact surfaces. The nonlinear contact friction algorithm is employed... 

In present work, a novel supported bucky paper (BP) membrane was fabricated and evaluated for humic acid (HA) removal from water. For better understanding the effect of operating variables, response surface methodology (RSM) was also applied. Three independent parameters namely TOC concentration (5, 10 and 15 mg l-1), operating time (10, 20 and 30 min) and transmembrane pressure (TMP) (1, 2 and 3 bar) were selected for TOC removal (%) and permeate flux analysis. The results revealed that the membrane could effectively remove HA primarily through electrostatic repulsion and then adsorption mechanisms. The study also showed that about 65% and 35% of the removed HA were through repulsion and... 

Based on series of crude oil rheological properties and asphaltene flocculation confocal microscopy analysis, Najafi et al., (2011) reported the existence of an optimum radiation time at which asphaltenic crude oils reach the minimum kinematic viscosity. Accordingly, they proposed the idea of asphaltene flocculation inhibition due to wave radiation.The present investigation is a continuous effort to provide more information about the process of flocculation inhibition. Confocal microscopy and rheological analyses are performed on different crude oils to prove the repeatability of the observed phenomena. The asphaltene content analysis was done based on IP143 procedure, which provides more... 

Human Brain is one of the most wonderful and complex systems which is designed for ever; A huge complex network composed of neurons as tiny biological and chemical processors which are distributed and work together as a super parallel system to do control and vital activities of human body. Brain learning simulation and hardware implementation is one of the most interesting research areas in order to make artificial brain. One of the researches in this area is Active Learning Method in brief ALM. ALM is an adaptive recursive fuzzy learning algorithm based on brain functionality and specification which models a complex Multi Input Multi Output System as a fuzzy combination of Single Input... 

In the present study, the effect of electromagnetic field on the salt and water transport and reduction of carbonate deposit during reverse osmosis desalination was investigated. The electromagnetic field was generated by AC current through a solenoid wound around the membrane separation module. The current intensity and frequency was 25 A and 50 Hz, respectively. Experiments were conducted using CaCO3 solution at the concentration of 5.5 mmol/L. For comparison purposes, desalination by the membrane, in the presence and absence of an electromagnetic field was conducted. While the desalination process temperature was kept constant, the product temperature increased by less than 2 °C when the...