Sharif Digital Repository

This paper presents a multi-model robust control (MMRC) design for an offshore variable speed wind turbine with tension leg platform. The proposed control scheme covers the model uncertainty in the above rated wind speed, and it provides a reliable control for power regulation while minimizing the mechanical loads on the wind turbine structure. For this purpose, the above rated wind speed region is divided into several wind speed groups, and a set of linearized models are obtained from the Fatigue, Aerodynamics, Structures, and Turbulence (FAST) simulator for various mean wind speeds of each group. Using Weibull wind speed distribution, a nominal model with additive uncertainty is generated... 

Diffusion flame from electrospray of liquid ethanol and butanol was investigated experimentally. Stable flames were observed at two distinct modes recognized at different flow rates, applied voltages, and distances between the nozzle and counter electrode. The first mode occurred at minimum voltages in which individual larger droplets are dominantly generated. The second mode at higher voltages corresponds to multijets, which produce finer distribution of droplets. Using flame-imaging anal- ysis, flammability margins are introduced and flame lengths are measured versus nondimensional parameters for both fuels and modes of spraying. The fluctuation of the flames is characterized and the... 

Graph embedding is an important approach for graph analysis tasks such as node classification and link prediction. The goal of graph embedding is to find a low dimensional representation of graph nodes that preserves the graph information. Recent methods like Graph Convolutional Network (GCN) try to consider node attributes (if available) besides node relations and learn node embeddings for unsupervised and semi-supervised tasks on graphs. On the other hand, multi-layer graph analysis has been received attention recently. However, the existing methods for multi-layer graph embedding cannot incorporate all available information (like node attributes). Moreover, most of them consider either... 

A novel ion selective electrode is fabricated for naltrexone HCl and used in pharmaceutical analysis and drug determination in biological fluids without complicated pretreatments and extractions, using direct potentiometry. The naltrexone complex with sodium tetraphenyl borate (NaTPB) is obtained by in situ soaking PVC membrane electrode in an 1 × 10 -3 M naltrexone solution. The sensor exhibited fast, reproducible and linear sub-Nernstian response over concentration range of 1 × 10 -5 - 1 × 10 -3 M with a detection limit of 5 × 10 -6 M. The membrane sensor was successfully applied to the determination of naltrexone in capsules as well as for its determination in urine and plasma samples  

A sensitive and selective electrochemical sensor was fabricated via the drop-casting of carbon nanoparticles (CNPs) suspension onto a glassy carbon electrode (GCE). The application of this sensor was investigated in simultaneous determination of acetaminophen (ACE) and tramadol (TRA) drugs in pharmaceutical dosage form and ACE determination in human plasma. In order to study the electrochemical behaviors of the drugs, cyclic and differential pulse voltammetric studies of ACE and TRA were carried out at the surfaces of the modified GCE (MGCE) and the bare GCE. The dependence of peak currents and potentials on pH, concentration and the potential scan rate were investigated for these compounds... 

A new sensitive and selective electrochemical sensor was developed for determination of naltrexone (NAL) in pharmaceutical dosage form and human plasma. Naltrexone is an opioid antagonist which is commonly used for the treatment of narcotic addiction and alcohol dependence. A voltammetric study of naltrexone has been carried out at the surface of glassy carbon electrode (GCE) modified with Nafion-doped carbon nanoparticles (CNPs). The electrochemical oxidation of naltrexone was investigated by cyclic and differential pulse voltammetric techniques. The dependence of peak currents and potentials on pH, concentration and the potential scan rate was investigated. The electrode characterization... 

Chatter vibration is a major obstacle in achieveing increased machining performance. In this research, a finite element model of chip formation in a 2D milling process is used to predict the occurrence of chatter vibrations, and to investigate the effects of various machining parameters on this phenomenon. The dynamic properties of the machine tool at the tool tip are obtained based on experimental modal analysis, and are used in the model as the cutter dynamics. The model allows for the natural development of vibration as the result of the chip-tool engagement, and accounts for various phenomena that occur at the chip-tool interface ultimately leading to stable or unstable cutting. The... 

Due to inherent potential of General Regression Neural Network(GRNN) to approximate nonlinear functions, it can be implemented as a nonlinear state-feedback controller. In this paper the methodology of direct collocation and nonlinear programming is utilized in combination with GRNN to determine the optimal control of dynamical systems. Application of this method to the design of an optimal controller for a chaotic flexible beam as a non-autonomous, nonlinear system is investigated. © 2002 The American Institute Aeronautics and Astronautics Inc. All rights reserved  

A new heterogeneous copper catalyst was synthesized by immobilization of copper ions onto magnetic nanoparticles with a new ligand based on triazole. The catalyst was characterized using scanning and transmission electron microscopies, atomic absorption and Fourier transform infrared spectroscopies, and thermogravimetric, elemental and energy-dispersive X-ray analyses. The results confirmed that a good level of organic groups was immobilized on the magnetic nanoparticles. Huisgen cycloaddition reaction was chosen as a model reaction for the investigation of catalyst activity under green conditions. Phenylacetylene and benzyl bromide derivatives were used for the synthesis of triazoles. The... 

Two newly synthesised Schiff bases [H2A3, N,N′-ortho-phenylene(salicylaldimine-acetylacetone imine) and H2A4, N,N′-ortho-phenylene(salicylaldimine-2-hydroxy-1-naphthaldimine)] were studied as inhibitors for the corrosion of mild steel in 0.5 mol dm-3 sulphuric acid. Results of weight loss, electrochemical impedance and Tafel polarisation measurements consistently identify both compounds as good inhibitors, with efficiencies of around 95% at a concentration of 400 ppm. The inhibition is in both cases of a mixed anodic-cathodic nature. Differences in inhibition efficiency between H2A3 and H2A4 are correlated with their chemical structures. Several adsorption isotherms are assessed, and the... 

To achieve higher accuracy in the prediction of cutting forces in finish milling process of sculptured parts, the curvatures of in-process workpiece surface are necessary to be taken into consideration in the calculation of cutter-workpiece engagement boundaries. These curvatures, however, are not readily available in tool path data, as the main existing source of geometrical information of the process. In this paper, first, a new straightforward algorithm is proposed to extract the principal curvatures and principal directions of the in-process workpiece surface from ball-end finish milling tool path data. These quantities, then, are employed to calculate the boundaries of engagement... 

This paper presents a new analytical model for calculating the cutter-workpiece engagement (CWE) boundaries in the ball-end finish milling process of curved surfaces. To this end, first, a quadratic mathematical representation considering the principal curvatures of the surface is employed to locally describe the workpiece surface around the instantaneous cutting region. This description, then, is utilized to find the intersection curves of the tool rotary and workpiece surfaces in three ball-end milling modes including slotting, first cutting, and following cutting. Through comparison studies, the model predictions are verified by the corresponding results obtained via solid modeling in... 

The minimum number of complete bipartite subgraphs needed to partition the edges of a graph G is denoted by b (G). A known lower bound on b (G) states that b (G) ≥max {p (G), q (G)}, where p (G) and q (G) are the numbers of positive and negative eigenvalues of the adjacency matrix of G, respectively. When equality is attained, G is said to be eigensharp and when b (G) = max {p (G), q (G)} + 1, G is called an almost eigensharp graph. In this paper, we investigate the eigensharpness of graphs with at most one cycle and products of some families of graphs. Among the other results, we show that Pm ∨ Pn, Cm ∨ Pn for m ≡ 2, 3 (mod 4) and Qn when n is odd are eigensharp. We obtain some results on... 

In this paper we describe some mechanical, hardware and software aspects of our robots specially used in teamwork. The pneumatic design of the gripers and kicker enables the robot to make a good control of ball when dribbling and also passing the ball in short and long distances. The teamwork software enables our robots to perform a cooperative behavior by dividing the field to three major regions and assigning each robot a role such as defender, forward and middle in these three regions. The server can order the robots to change their role when needed and make them return to their original state after a short time. © 2002 Springer-Verlag Berlin Heidelberg  

This article studies a multi-product and multi-period location-routing-inventory problem in which location-allocation, inventory and routing decisions are to be taken in a three-level supply chain including suppliers, depots and customers. Products are distributed from depots to customers by a homogeneous fleet of vehicles. Backlogging is allowable on condition that the backlog quantity of each customer does not exceed a predefined fraction of his demand. A mixed-integer programming formulation is presented to describe the problem then a new hybrid heuristic algorithm based on the simulated annealing and imperialist competitive algorithm is designed to solve the model. Comprehensive... 

In this study, the performance of a proposed friction damper with two slip loads in controlling the seismic response of steel moment resisting buildings structures under moderate and intense earthquake excitations is investigated. The proposed friction damper initially operates with a smaller slip load and could shift to the higher slip load after a certain amount of slippage when subjected to intense ground motions. In this regard, the hysteresis behavior of the proposed double slip loads (DSL) friction damper is modeled and after necessary verifications is imported to the material library of OpenSees software to be used for parametric study. To evaluate the performance of the proposed DSL... 

The effect of plasma electrolytic oxidation (PEO) pre-treatments on corrosion behavior of titanium in simulated body fluid (SBF) is investigated. Three pre-treatments are compared, using silicate, calcium phosphate and mixed silicate and calcium phosphate (1:1) electrolytes, respectively. The resultant coatings in different compositions and morphologies were examined by high-resolution field emission scanning electron microscopy equipped with energy-dispersive spectrometer and x-ray diffraction. The PEO-treated specimens revealed distribution of coating species, mainly the titanium-rich inner coating region. However, findings show highly localized variations in composition within their... 

We synthesize TiO2@SnO2 core-shell nanoparticles (NPs) by a facile two-step aqueous sol-gel method and their photocatalytic activity is compared with the pure TiO2 and SnO2 NPs for degradation of methylene blue under UV irradiation. The chemical property, crystal structure and morphology of the synthesized samples are studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM) techniques. The mechanisms of electron–hole recombination and separation of charge carriers are studied by photoluminescence (PL) and diffuse reflectance spectroscopy (DRS). Furthermore, the kinetics... 

Resonating valence bond (RVB) states are suitable candidates for ground state of the Heisenberg model on various two dimensional lattices. When a singlet valence bond is broken to produce a triplet state, the resulting excitation is called a triplon. In this paper, we obtain formulas for the overlap and also matrix elements of si sjoperator between states with arbitrary number of triplons. Our results are valid for any 2D lattice