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    Synthesis and properties of biodegradable hydrogels of κ-carrageenan grafted acrylic acid-co-2-acrylamido-2-methylpropanesulfonic acid as candidates for drug delivery systems

    , Article Reactive and Functional Polymers ; Volume 67, Issue 7 , 2007 , Pages 644-654 ; 13815148 (ISSN) Pourjavadi, A ; Barzegar, Sh ; Zeidabadi, F ; Sharif University of Technology
    2007
    Abstract
    Novel types of highly swelling hydrogels were prepared by grafting crosslinked polyacrylic acid-co-poly-2-acrylamido-2-methylpropanesulfonic acid (PAA-co-PAMPS) chains onto κ-carrageenan through a free radical polymerization method. Here, we propose a mechanism for κ-carrageenan-g-PAA-co-PAMPS formation and confirm the hydrogel structure using FTIR spectroscopy. The effect of grafting variables (i.e. concentration of methylenebisacrylamide (MBA), acrylic acid/-2-acrylamido-2-methylpropanesulfonic acid (AA/AMPS) weight ratio, ammonium persulfate (APS), κ-carrageenan, neutralization percent and reaction temperature) were systematically optimized to achieve a hydrogel with a maximum swelling... 

    Optimal control of an aerial tail sitter in transition flight phases

    , Article Journal of Aircraft ; Volume 53, Issue 4 , Volume 53, Issue 4 , 2016 , Pages 914-921 ; 00218669 (ISSN) Banazadeh, A ; Taymourtash, N ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc 
    Abstract
    The main purpose of this study is to generate optimal transition trajectories for an aerial tail sitter that uses cross-coupled thrust-vectoring control. A transition maneuver is most challenging for such configurations due to coupling of the forces and moments with instability in the most critical low-speed flight phases. Based on the classical Cauchy method, an improved gradient-based algorithm is developed in a collaborative process in order to find transition trajectories and increase the convergence rate. The cost function is defined in terms of minimum time in transition from hover to cruise and minimum altitude variations from cruise to hover. In addition, physical constraints are... 

    Dye-sensitized solar cells based on a single layer deposition of TiO 2 from a new formulation paste and their photovoltaic performance

    , Article Solar Energy ; Volume 86, Issue 9 , 2012 , Pages 2654-2664 ; 0038092X (ISSN) Mohammadi, M. R ; Louca, R. R. M ; Fray, D. J ; Welland, M. E ; Sharif University of Technology
    Abstract
    A new strategy for enhancing the efficiency and reducing the production cost of TiO 2 solar cells by design of a new formulated TiO 2 paste with tailored crystal structure and morphology is reported. The conventional three- or four-fold layer deposition process was eliminated and replaced by a single layer deposition of TiO 2 compound. Different TiO 2 pastes with various crystal structures, morphologies and crystallite sizes were prepared by an aqueous particulate sol-gel process. Based on simultaneous differential thermal (SDT) analysis the minimum annealing temperature to obtain organic-free TiO 2 paste was determined at 400°C, being one of the lowest crystallization temperatures of TiO 2... 

    Optimal Design of Brushless Doubly-Fed Induction Generator Considering Harmonic Effects for Maximizing Volumetric Power Density

    , Ph.D. Dissertation Sharif University of Technology Gorgin-Poor, Hamed (Author) ; Oraee Mirzamani, Hashem (Supervisor)
    Abstract
    In recent decades, electricity generation using renewable energy sources especially wind has gained considerable attention worldwide. Various generating systems have been proposed for wind turbines to convert wind mechanical power into electrical power. Up to 70% of the installed wind turbines incorporate Doubly-Fed Induction Generator (DFIG) and a fractionally rated power converter. Other schemes still have technological and economic penalties such as high cost of active materials, complexity of machine manufacturing and control systems and large and expensive converter, which limit their spread in wind power plants. Among these, Brushless Doubly-Fed Induction Generator (BDFIG) has... 

    Electromagnetic-thermal design optimization of the brushless doubly fed induction generator

    , Article IEEE Transactions on Industrial Electronics ; Vol. 61, issue. 4 , October , 2014 , PP. 1710-1721 ; ISSN: 02780046 Gorginpour, H ; Oraee, H ; McMahon, R. A ; Sharif University of Technology
    Abstract
    In view of its special features, the brushless doubly fed induction generator (BDFIG) shows high potentials to be employed as a variable-speed drive or wind generator. However, the machine suffers from low efficiency and power factor and also high level of noise and vibration due to spatial harmonics. These harmonics arise mainly from rotor winding configuration, slotting effects, and saturation. In this paper, analytical equations are derived for spatial harmonics and their effects on leakage flux, additional loss, noise, and vibration. Using the derived equations and an electromagnetic-thermal model, a simple design procedure is presented, while the design variables are selected based on... 

    A novel rotor configuration for brushless doubly-fed induction generators

    , Article IET Electric Power Applications ; Volume 7, Issue 2 , 2013 , Pages 106-115 ; 17518660 (ISSN) Gorginpour, H ; Jandaghi, B ; Oraee, H ; Sharif University of Technology
    2013
    Abstract
    Brushless Doubly-Fed Induction Generator has attractive features to be the first choice in next generation of wind generators. However, its efficiency and power-to-weight ratio are slightly lower in comparison to induction machine with the same rating. Considerable part of these imperfections arises from the rotor design, which produces magnetic field with considerable undesirable spatial harmonics. This paper proposes a novel rotor configuration to reduce spatial harmonic distortion of air-gap magnetic field as well as improving some drawbacks of the conventional structure, including unequal magnitudes of rotor bar currents, teeth saturation at low average air gap magnetic fields, high core... 

    Study the influence of ultrasonic vibration on grinding of Ti6Al4V

    , Article Proceedings of the 6th International Conference on Leading Edge Manufacturing in 21st Century, LEM 2011, 8 November 2011 through 10 November 2011 ; Novembe , 2011 Ghahramani Nick, M ; Movahhedy, M. R ; Akbari, J ; Sharif University of Technology
    2011
    Abstract
    Titanium alloys, in particular Ti6Al4V, are increasingly used recently due to high strength-to-weight ratio, biocompatibility and robust mechanical-properties at high temperatures. However, Ti6Al4V have poor machinability because of their poor thermal conductivity and high reactivity. Usually in conventional grinding (CG) of these alloys, surface burning is unavoidable. Ultrasonic assisted grinding (UAG) is an efficient method for overcoming the poor machinability of such materials. In this research, effect of imposed vibration on grinding of Ti6Al4V is studied. Obtained results show forces and surface roughness are reduced 18% and 12% by UAG comparing to CG respectively. It also results in... 

    Study the effect of ultrasonic irradiation and surfactant/fe ions weight ratio on morphology and particle size of magnetite nanoparticles synthesised by co-precipitation for medical application

    , Article World Academy of Science, Engineering and Technology ; Volume 64 , 2010 , Pages 457-460 ; 2010376X (ISSN) Azimipour Meibod, S. S ; Pourafshary, P ; Madaah Hosseini, H. R ; Sharif University of Technology
    2010
    Abstract
    A biocompatible ferrofluid have been prepared by coprecipitation of FeCl 2.4H 2O and FeCl 3.6H 2O under ultrasonic irradiation and with NaOH as alkaline agent. Cystein was also used as capping agent in the solution. Magnetic properties of the produced ferrofluid were then determined by VSM test and magnetite nanoparticles were characterized by XRD and TEM techniques. The effect of surfactant to Fe ion weight ratio was also studied during this project by using two different amount of Dextran. Results showed the presence of a biocompatible superparamagnetic ferrofluid including magnetite nanoparticles with particle size ranging under 20 nm. The increase in the surfactant content results in the... 

    Transition flight feasibility of a fluidic thrust vectored aerial tail-sitter: Numerical approach

    , Article 2007 ASME Turbo Expo, Montreal, Que., 14 May 2007 through 17 May 2007 ; Volume 1 , 2007 , Pages 229-235 ; 079184790X (ISBN); 9780791847909 (ISBN) Saghafi, F ; Banazadeh, A ; Sharif University of Technology
    2007
    Abstract
    This paper describes a feasibility study of using numerical analysis technique, coupled with a non-linear simulation model of a conceptual fluidic-thrust-vectored unmanned aerial tailsitter to obtain required thrust deflection angles for a transition manoeuvre in take-off. It also studies the aircraft behaviour in transition subjected to the changes in specified parameters like the thrust value and the engine distance from the centre of gravity. The focus of the research presented was to get the vehicle from zero speed on the ground, in vertical position, to a specified velocity at a specified attitude, in cruise position. It was also specified that, when the vehicle was considered to be... 

    High performance Dyneema® fiber laminate for impact resistance/macro structural composites

    , Article Journal of Thermoplastic Composite Materials ; Volume 25, Issue 4 , 2012 , Pages 403-414 ; 08927057 (ISSN) Karbalaie, M ; Yazdanirad, M ; Mirhabibi, A ; Sharif University of Technology
    2012
    Abstract
    UHMWPE composite materials are increasingly used in armors design due to their high strength-to-weight ratios and energy absorption capacities. In this study the effect of production parameters upon the terminal ballistic properties of UHMWPE composite were examined under different conditionings. The composite armor plate laminates were produced by hot pressing with three different pressing times from 10-30 minutes and the laminates conditioned at +115, +125, and +135°C. The molding temperature of SK66 fiber composite has the main direct effect on the ballistic absorption energy, so the relation of molding temperature with the adhesive bonding force between layers, the thickness of the... 

    Salep-g-poly(sodium acrylate)/alumina as an environmental-sensitive biopolymer superabsorbent composite: Synthesis and investigation of its swelling behavior

    , Article Advances in Polymer Technology ; Volume 31, Issue 1 , 2012 , Pages 41-51 ; 07306679 (ISSN) Bardajee, G. R ; Pourjavadi, A ; Soleyman, R ; Ghavami, S ; Sharif University of Technology
    Abstract
    A novel kind of a biopolymer-based superabsorbent composite, salep-g-poly(sodium acrylate)/alumina, was prepared from salep, sodium acrylate, and alumina by aqueous polymerization, using N,N'-methylenebisacrylamide (MBA) as a cross-linker and ammonium persulfate (APS) as an initiator. The reaction parameters [i.e., acrylic acid (AA), MBA, APS amounts, and neutralization percentage of AA as well as alumina/salep weight ratio] affecting the water absorbency of the hydrogel composite were optimized using systematic method to achieve a composite with high swelling capacity as possible. The swelling behavior of optimum superabsorbent composite was measured in various pH solutions. In addition,... 

    Photoresponse and H2 production of topographically controlled PEG assisted Sol-gel WO3 nanocrystalline thin films

    , Article International Journal of Hydrogen Energy ; Volume 36, Issue 21 , October , 2011 , Pages 13461-13472 ; 03603199 (ISSN) Naseri, N ; Yousefzadeh, S ; Daryaei, E ; Moshfegh, A. Z ; Sharif University of Technology
    2011
    Abstract
    WO3 thin films were fabricated by sol-gel method using polyethylene glycol (PEG) as dispersing agent. Physical and photoelectrochemical properties of the synthesized nanocrystalline films were studied by varying weight ratio of PEG to tungsten precursor (x). Based on AFM observations and statistical modeling of the WO3 surface, the thickness of the films increased by increasing the amount of x with a nearly linear fashion while the surface roughness reached to a saturated value. However, the film synthesized with x = 4 showed a chaotic surface behavior. Optical analysis revealed that by increasing the x, transmittance of the films decreased while their band gap energies remained unchanged.... 

    New protein-based hydrogel with superabsorbing properties: Effect of monomer ratio on swelling behavior and kinetics

    , Article Industrial and Engineering Chemistry Research ; Volume 47, Issue 23 , 2008 , Pages 9206-9213 ; 08885885 (ISSN) Pourjavadi, A ; Salimi, H ; Sharif University of Technology
    2008
    Abstract
    In this paper we report an efficient synthesis of hydrolyzed collagen-g-poly(sodium acrylate-co-2-hydroxyethyl aery late) hydrogel through chemical cross-linking by graft copolymerization of these two monomers onto the protein backbone in the presence of a cross-linker. Infrared spectroscopy and thermogravimetric analysis (TGA) were carried out to confirm the chemical structure of the hydrogel. Moreover, morphology of the samples was examined by scanning electron microscopy (SEM). To investigate the effect of monomer ratio on swelling behavior in various media three hydrogels with different acrylic acid/2-hydroxyethyl acrylate (AA/HEA) weight ratios were synthesized and swelling capacity was... 

    Temperature sensitive superabsorbent hydrogels from poly(N-t-butyl acrylamide-co-acrylamide) grafted on sodium alginate

    , Article Macromolecular Symposia ; Volume 274, Issue 1 , December , 2008 , Pages 177-183 ; 10221360 (ISSN) Pourjavadi, A ; Samadi, M ; Ghasemzadeh, H ; Sharif University of Technology
    2008
    Abstract
    Temperature-sensitive hydrogels based on N-t-butylacrylamide (TBA), acrylamide (AAm), and sodium alginate were prepared by free radical polymerization method. Methylenebisacrylamide (MBA) and amonium persulfate (APS) were applied as water soluble crosslinker and initiator, respectively. The chemical structure of the hydrogels was confirmed by FT-IR spectroscopy and thermogravimetric analysis (TCA) methods. Morphology of the samples was examined by scanning electron microscopy (SEM). By changing the initial TBA/AAm mole ratios, hydrogels with different swelling properties were obtained. The rate parameters were found to be 2.0, 2.4, and 3.5 min for the superabsorbents with AAm/TBA weight... 

    Study of cemented carbonitrides with nickel as binder: Experimental investigations and computer calculations

    , Article International Journal of Refractory Metals and Hard Materials ; Volume 31 , 2012 , Pages 164-170 ; 02634368 (ISSN) Mohammadpour, M ; Abachi, P ; Parvin, N ; Pourazrang, K ; Sharif University of Technology
    2012
    Abstract
    Cobalt is the most common binder in cemented carbides industry. However, there are some interests in use of alternatives. The similarity in properties has made nickel the first choice. In the present work, the effect of initial composition on modern hardmetals containing transition metal carbides/carbonitrides that are called "cemented carbonitrides" with nickel as binder was investigated. Change in quantity of additive carbides and tungsten to carbon (C/W) weight ratio through applying metallic tungsten powder in primary powder mixture had some effects on final hardness, transverse rupture strength, and microstructure of studied alloys. Addition of vanadium carbide not more than 0.2 wt.%,... 

    New smart carrageenan-based superabsorbent hydrogel hybrid: Investigation of swelling rate and environmental responsiveness

    , Article Journal of Applied Polymer Science ; Volume 117, Issue 6 , September , 2010 , Pages 3228-3238 ; 00218995 (ISSN) Salimi, H ; Pourjavadi, A ; Seidi, F ; Eftekhar Jahromi, P ; Soleyman, R ; Sharif University of Technology
    2010
    Abstract
    Synthesis of novel natural-based superabsorbents with improved properties is of prime importance in many applications. In this article we report an efficient synthesis of new polysaccharide-based superabsorbent hybrid composing carrageenan, acrylic acid, sodium acrylate, and 2-hydroxyethyl acrylate through homogenous solution polymerization process. Infrared spectroscopy and thermogravimetric analysis (TGA) were carried out to confirm the chemical structure of the hydrogel. Moreover, morphology of the samples was examined by scanning electron microscopy (SEM). To deeper studies on the structure-property relation in SAP hydrogels, three hydrogels with different acrylic acid/2-hydroxyethyl... 

    CMC/celite superabsorbent composites: Effect of reaction variables on saline-absorbency under load

    , Article Iranian Polymer Journal (English Edition) ; Volume 19, Issue 8 , May , 2010 , Pages 571-579 ; 10261265 (ISSN) Pourjavadi, A ; Soleyman, R. A ; Ghasemzadeh, H ; Salimi, H ; Sharif University of Technology
    Abstract
    A series of superabsorbent composites were synthesized through graft copolymerization of acrylic acid (AA) onto carboxymethyl cellulose (CMC) in the presence of celite powder using N,N'-methylenebisacrylamide (MBA) as a cross-linking agent and ammonium persulphate (APS) as an initiator. The chemical structure and thermal properties of the composite hydrogels were characterized by FTIR spectroscopy and TGA methods, respectively. Morphology of the samples was examined by scanning electron microscopy (SEM). In free-state, the swelling conditions and hence the related data are not real, because in all their applications the swelling particles of superabsorbent must absorb aqueous solutions while... 

    Swelling properties of CMC-g-Poly (AAm-co-AMPS) superabsorbent hydrogel

    , Article Journal of Applied Polymer Science ; Volume 113, Issue 6 , 2009 , Pages 3442-3449 ; 00218995 (ISSN) Pourjavadi, A ; Ghasemzadeh, H ; Mojahedi, F ; Sharif University of Technology
    2009
    Abstract
    A series of biopolymer-based superabsorbent hydrogels based on carboxymethyl cellulose has been prepared by free-radical graft copolymerization of acrylamide and 2-acrylamido-2-methylpropan sulfonic acid (AMPS) in aqueous solution using methylenebisacrylamide as a crosslinking agent and ammonium persulfate as an initiator. The effect of variables on the swelling capacity such as: acrylamide/AMPS weight ratio, reaction temperature, and concentration of the initiator and crosslinker were systematically optimized. The results indicated that with increasing the amount of AMPS, the swelling capacity is increased. FT-IR spectroscopy and scanning electron microscope analysis were used to confirm... 

    Effect of hydrogen reduction on microstructure and magnetic properties of mechanochemically synthesized Fe-16.5Ni-16.5Co nano-powder

    , Article Journal of Magnetism and Magnetic Materials ; Volume 321, Issue 18 , 2009 , Pages 2729-2732 ; 03048853 (ISSN) Azizi, A ; Yoozbashizadeh, H ; Sadrnezhaad, S. K ; Sharif University of Technology
    2009
    Abstract
    Most recent findings on structural and magnetic properties of Fe-Ni-Co nano-powders produced by mechanical alloying and subsequent low-temperature hydrogen reduction are presented in this paper. At 300 rpm, with ball to powder weight ratio of 20, single phase nickel-cobalt ferrite is mechanically synthesized for 50 h. The as-milled powder is then subjected to 1 h hydrogen reduction at 700 °C. Hydrogen reduction results in the formation of Fe-16.5%Ni-16.5%Co nano-powders. The phases of the powders are identified by X-ray diffraction (XRD) utilizing Cu Kα radiation. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to study the morphology and the average... 

    Synthesis and properties of partially hydrolyzed acrylonitrile-co- acrylamide superabsorbent hydrogel

    , Article Bulletin of the Korean Chemical Society ; Volume 31, Issue 11 , 2010 , Pages 3163-3172 ; 02532964 (ISSN) Pourjavadi, A ; Hosseinzadeh, H ; Sharif University of Technology
    2010
    Abstract
    In this work, a novel method to synthesis of an acrylic superabsorbent hydrogel was reported. In the two stage hydrogel synthesis, first copolymerization reaction of acrylonitrile (AN) and acrylamide (AM) monomers using ammonium persulfate (APS) as a free radical initiator was performed. In the second stage, the resulted copolymer was hydrolyzed to produce carboxamide and carboxylate groups followed by in situ crosslinking of the polyacrylonitrile chains. The results from FTIR spectroscopy and the dark red-yellow color change show that the copolymerization, alkaline hydrolysis and crosslinking reactions have been do take place. Scanning electron microscopy (SEM) verifies that the synthesized...