Search for: supersaturation
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    Neural Synchrony of Spiking Local Neurons and Local Field Potential Activities in Primary Visual Cortex of Awake Monkeys

    , M.Sc. Thesis Sharif University of Technology Masoudian, Saeed (Author) ; Jafari, Mehdi (Supervisor) ; Rabiee, Hamid Reza (Supervisor) ; Lashgari, Reza (Co-Supervisor)
    Primary visual cortex plays a paramount role in processing visual information. Visual information after the primitive processing by LGN and Thalamus, will be sent to the primary visual cortex which is called V1 area. According to the fact that V1 neurons have the definitive sensitivity to the edge and contrast of visual stimuli so their behavior are very selective to the certain features, specially contrast, of visual stimuli. These neurons have different response behavior to contrast. In fact most of them have some nonlinear behavior to this feature. Normally we expect that response of them or spiking rate of them grow linearly by the contrast increases but in most many cases they have some... 

    Control of Size of Graphene Domain Synthesized by Chemical Vapor Deposition

    , M.Sc. Thesis Sharif University of Technology Amini, Negar (Author) ; Ghotbi, Sirus (Supervisor) ; Karimi Sabet, Javad (Supervisor)
    The chemical vapor deposition (CVD) of graphene from methane on a copper substrate is the most promising method for production of large-area graphene films. There have been long-standing challenges in this field such as controlling the graphene coverage, film quality, the number of layers, and the nucleation density of graphene domain. These challenges can be overcome by developing a fundamental understanding of the graphene growth process. The main aim of this study is to control nucleation density of graphene domains. Chemical vapor deposition (CVD) graphene is polycrystalline, and grain boundaries in graphene film have been identified to degrade the properties of graphene as a membrane... 

    Coupled effects of suction and degree of saturation on large strain shear modulus of unsaturated sands

    , Article Unsaturated Soils: Research and Applications - Proceedings of the 6th International Conference on Unsaturated Soils, UNSAT 2014 ; Vol. 2, issue , July , 2014 , p. 1559-1564 ; 978-1-138-00150-3 Jafarzadeh, F ; Ahmadinezhad, A ; Sadeghi, H ; Sharif University of Technology
    Predictions of soil behavior in response to dynamic loads require an understanding of dynamic properties of soil. Studies on dynamic properties of unsaturated soils at large-strains are quite limited, while some dynamic loadings, like earthquakes, are in the medium to large-strain ranges. A cyclic simple shear apparatus was developed to measure large-strain shear modulus and damping ratio under different matric suction or degree of saturation. Six cyclic tests, with referring to the soil-water retention curve, were conducted on clean medium sand. Results indicated that shear modulus slightly increases when suction varies from zero up to the air entry value. Approaching the residual value, a... 

    Constitutive modeling of hot deformation behavior of the AA6063 alloy with different precipitates

    , Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 44, Issue 13 , December , 2013 , Pages 5853-5860 ; 10735623 (ISSN) Anjabin, N ; Taheri, A. K ; Kim, H. S ; Sharif University of Technology
    The current study proposes a simple constitutive model that integrates the kinetics of precipitation during static aging and the kinetics of precipitate dissolution during preheating to deformation temperature to predict the hot flow behavior of AA6063 alloy. The model relates the flow behavior of the age-hardenable alloy to the alloy chemistry, thermal history as well as deformation temperature, strain, and strain rate by means of a physically based model. Different aging conditions, including supersaturated solid solution and overaging conditions with different deformation parameters, were assessed. Each part of the model was in good agreement with those of experimental and other model... 

    Application of Rosin-Rammler model for analysis of CSD in sugar crystallization

    , Article Crystal Research and Technology ; Volume 50, Issue 11 , 2015 , Pages 873-878 ; 02321300 (ISSN) Mohebbi Zinab, J ; Alamolhoda, A. A ; Matloubi Moghaddam, F ; Nayeri, S ; Sharif University of Technology
    Wiley-VCH Verlag  2015
    Crystal-size distribution (CSD) is one of the most important parameters in sugar production. The objective is to grow crystals of uniform sizes or narrow CSD. CSD appears to be determined by the growth-rate history of the crystals and the relative supersaturation (SS) of the solution from which crystals growth takes place. Three methods for preparation of nucleation seeds were described and used for industrial crystallization of raw and white sugars; these are wet milling filtered sugar (ML), agitating saturated solution (AS) and powdered sugars (PD). Rosin-Rammler (RR) and mathematical models were adopted to investigate CSD and the uniformity of the produced crystals. Higher uniformity... 

    A semi-empirical shear strength model for infilled rock fractures with infills in an unsaturated state

    , Article Geotechnical Frontiers 2017, 12 March 2017 through 15 March 2017 ; Issue GSP 280 , 2017 , Pages 529-538 ; 08950563 (ISSN) Khosravi, A ; Mousavi, S ; Khosravi, M ; Brandon T. L ; Valentine R. J ; Geo-Institute (G-I) of the American Society of Civil Engineers; Industrial Fabrics Association International (IFAI) ; Sharif University of Technology
    American Society of Civil Engineers (ASCE)  2017
    Based on the results of recent studies, comprehensive characterization of the behavior of infilled rock fractures under saturated and unsaturated conditions requires knowledge of morphological details of fracture surface, as well as state of stress of infill materials and their initial innate conditions (e.g., void ratio, water content, degree of saturation and dry density). This paper describes a semi-empirical equation to interpret the effects of wall-roughed nature of the fractures and presence of partially saturated fine materials within the fractures on the behavior of infilled rock fractures during shear. The proposed equation incorporates the soil-water retention curve parameters as... 

    Phase segregation susceptibility of ZA27 alloy at different shear rates

    , Article 9th International Conference on Semi-Solid Processing of Alloys and Composites, S2P 2006, Busan, 11 September 2006 through 13 September 2006 ; Volume 116-117 , 2006 , Pages 225-230 ; 10120394 (ISSN); 3908451264 (ISBN); 9783908451266 (ISBN) Mola, J ; Aashuri, H ; Shalchi, B ; Sharif University of Technology
    Trans Tech Publications Ltd  2006
    Back extrusion technique was employed to characterize phase segregation tendency of mechanically stirred ZA27 alloy at different deformation rates. Variation of segregation intensity with ram diameter was found to follow opposite trends at low and high ram speeds. At sufficiently high ram speeds, small rams are of better performance in minimizing segregation whereas at low ram speeds, large rams result in less pronounced segregation. In addition, increasing ram speed invariably decreases segregation degree. Back extrusion at very high shear rates provided via a Drop Extruder Apparatus capable of displacing ram at speeds in excess of 1m/s results in production of very homogeneous products in... 

    Determination of the Metastable Zone and Induction Time in Nucleation of Aluminum Sulfate Nanoparticles in Presence of Anti-solvent and Surface Active Agents

    , M.Sc. Thesis Sharif University of Technology Bagheri, Mohammad (Author) ; Ghorbani, Mohammad (Supervisor) ; Manteghian, Mehrdad ($item.subfieldsMap.e)
    Aluminum sulfate is widely used in water treatment as a polyelectrolyte. Its dissolution and recrystallization into nanoparticles directly affects the working conditions. This study concerns determination of the metastable zone and induction time in nucleation of aluminum sulfate nanoparticles in aqueous media and in presence of acetone as anti-solvent. Later the effect of SDS on the metastable zone and induction time are also studied.. The study also shows if the presence of anti-solvents and surface active agents can vary this phenomenon. The study also adds to our understanding of the media in creation and stabilization of nanoparticles. This project has a special focus on the changes... 

    Synthesis of barium sulfate nanoparticles using a spinning disk reactor: Effects of supersaturation, disk rotation speed, free ion ratio, and disk diameter

    , Article Industrial and Engineering Chemistry Research ; Volume 48, Issue 16 , 2009 , Pages 7574-7580 ; 08885885 (ISSN) Dehkordi, A. M ; Vafaeimanesh, A ; Sharif University of Technology
    The aim of this research was to synthesize barium sulfate nanoparticles using a spinning disk reactor. Barium sulfate was produced by continuously pumping two aqueous solutions of BaCl2 and Na2SO 4, respectively, into the chamber of spinning disk reactor, where a liquid-liquid reaction took place to form BaSO4. The influences of various operating and design parameters such as the initial supersaturation, disk rotation speed, free ion ratio, and the disk diameter on the size of barium sulfate nanoparticles were carefully investigated. By varying the supersaturation and disk rotation speed, a broad range of particle size ranging from micrometer sizes down to nanoparticles smaller than 100 nm... 

    Investigation the structural and magnetic properties of FINEMET type alloy produced by mechanical alloying

    , Article Advanced Materials Research ; Vol. 970, issue , 2014 , p. 252-255 Gheiratmand, T ; Siyani, S. M ; Hosseini, H. R. M ; Davami, P ; Sharif University of Technology
    In this research, FINEMET alloy with composition of Fe73.5Si13.5B9Nb3Cu1 was produced by mechanical alloying from elemental powders. The effect of milling time on the magnetic and structural properties of alloy has been investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometery. The results showed that milling for 53 hr leads to the formation of Fe supersaturated solid solution which includes Si, B and Nb atoms with mean crystallite size of ~30 nm. The shift of the main peak of Fe to the higher angles indicated that Si and B atoms dissolve in the Fe solid solution, at primary stage of mechanical alloying, up to the... 

    Synthesis of FeNiCoTi powder alloy by mechanical alloying and investigation of magnetic and shape memory properties

    , Article Journal of Superconductivity and Novel Magnetism ; Volume 25, Issue 6 , March , 2012 , Pages 1893-1899 ; 15571939 (ISSN) Gheiratmand, T ; Madaah Hosseini, H. R ; Sharif University of Technology
    Springer  2012
    FeNiCo base powder alloy with nominal composition Fe-27Ni-17Co-4Ti (wt%) was prepared from elemental powders by mechanical alloying. The structure of milled powders was characterized by XRD and SEM. The effect of nanosize structure on magnetic properties and shape memory behavior was studied using VSM and DSC. After milling for 240 minutes by high energy vibrational ball mill under argon atmosphere, supersaturated solid solution formed with mean crystallite size of ∼20 nm. Results of VSM examinations showed that by milling for 240 minutes saturation magnetization and intrinsic coercivity reached 304 emu/gr and 21 Oe, respectively. XRD analyses made it clear that transformation from BCC to... 

    Experimental study on dynamic properties of sand with emphasis on the degree of saturation

    , Article Soil Dynamics and Earthquake Engineering ; Volume 32, Issue 1 , 2012 , Pages 26-41 ; 02677261 (ISSN) Jafarzadeh, F ; Sadeghi, H ; Sharif University of Technology
    Cyclic drained and undrained tests were performed in a modified simple shear device in order to specifically investigate the effect of saturation ratio on shear modulus and damping parameters of sand. In addition to the degree of saturation, the effects of number of cycles, vertical consolidation stress, shear strain amplitude and relative density on dynamic properties of sand were investigated. Dynamic stiffness and damping characteristic were found to be substantially independent of saturation ratio in the range of 25-75%. However, by approaching the full saturation state, the values of modulus fall sharply and damping of loose samples increases dramatically from corresponding values of... 

    Dynamic parameters of saturated and unsaturated sand at different ranges of shear strain levels in cyclic simple shear tests

    , Article 14th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering ; 2011 Jafarzadeh, F ; Golshan, Z ; Sharif University of Technology
    In order to evaluate dynamic properties of Babolsar and Toyoura sands at saturation levels of 25, 50, 75 & 100%, a series of cyclic simple shear tests were carried out. The SGI type cyclic simple shear device was used to study the shear modulus, G, and damping ratio, D, of the above mentioned sands at cyclic shear strain of 0.5, 5 & 10%. The effect of degree of saturation (S), vertical consolidation stress (σ vc) and number of loading cycles (N) were investigated. On the basis of the tests results, the shear modulus approximately remains constant by change of degree of saturation from 25 to 50% and decreases when reaches the degree of saturation 75%. Damping ratio approximately is constant... 

    Effects of different operating parameters on the particle size of silver chloride nanoparticles prepared in a spinning disk reactor

    , Article Applied Physics A: Materials Science and Processing ; Volume 120, Issue 1 , July , 2015 , Pages 105-113 ; 09478396 (ISSN) Dabir, H ; Davarpanah, M ; Ahmadpour, A ; Sharif University of Technology
    Springer Verlag  2015
    The aim of this research was to present an experimental method for large-scale production of silver chloride nanoparticles using spinning disk reactor. Silver nitrate and sodium chloride were used as the reactants, and the protecting agent was gelatin. The experiments were carried out in a continuous mode by injecting the reactants onto the surface of the spinning disk, where a chemical precipitation reaction took place to form AgCl particles. The effects of various operating variables, including supersaturation, disk rotational speed, reactants flow rate, disk diameter, and excess ions, on the particle size of products were investigated. In addition, the AgCl nanoparticles were... 

    Hydraulic Behavior of Infilled Fractured Rocks under Unsaturated Conditions

    , Article Joint Geotechnical and Structural Engineering Congress 2016, 14 February 2016 through 17 February 2016 ; 2016 , Pages 1708-1718 ; 9780784479742 (ISBN) Khosravi, A ; Mousavi, S ; Dadashi Serej, A ; Sharif University of Technology
    American Society of Civil Engineers (ASCE) 
    Slip along fractures or hydrothermal alternation may lead to formation of weak layers of soils intercalated between the existing rock layers. In this situation, characterization of the behavior of rock fractures requires consideration of a complicated interaction of mechanical properties and geometrical characteristics of the fracture, coupled together with the properties of infill materials. Of the most important parameters which may considerably affect the behavior of an infilled fractured rock are the hydraulic properties of the infill material. These properties reflect the water retention ability of the infill material and determine the meniscus arrangements between the particles. This... 

    Developing a mathematical model for the oxidative dehydrogenation of propane in a fluidized bed reactor

    , Article Asia-Pacific Journal of Chemical Engineering ; Volume 11, Issue 3 , 2016 , Pages 448-459 ; 19322135 (ISSN) Torabi, A ; Kazemeini, M ; Fattahi, M ; Sharif University of Technology
    John Wiley and Sons Ltd 
    In this research, a mathematical model to simulate a two-phase fluidized bed reactor for oxidative dehydrogenation of propane to propylene was developed. The developed model was solved numerically using the matlab software. Moreover, effects of the reaction temperature, operating pressure, feed composition, particle's size and gas superficial velocity on the reactant conversion, product selectivity and desired product's yield were understudied. The model was validated using previously published experimental data for simulation of the case at the exit of the circulating fluidized bed reactor. The results revealed that, as the temperature raised from 783 to 823 K, the propane conversion... 

    Effects of initial static bed height on fractional conversion and bed pressure drop in tapered-in and tapered-out fluidized bed reactors

    , Article International Journal of Multiphase Flow ; Volume 79 , 2016 , Pages 50-61 ; 03019322 (ISSN) Askaripour, H ; Molaei Dehkordi, A ; Sharif University of Technology
    Elsevier Ltd  2016
    In this article, a standard 2D Two-Fluid Model (TFM) closed by the kinetic theory of granular flow (KTGF) has been applied to simulate the behavior of tapered-in and tapered-out fluidized bed reactors. In this regard, two types of chemical reactions with gas volume reduction and increase were considered to investigate the effects of initial static bed height on the fractional conversion and bed pressure drop. To validate the CFD model predictions, the results of hydrodynamic simulations concerning bed pressure drop and bed expansion ratio were compared against experimental data reported in the literature and excellent agreement was observed. The obtained simulation results clearly indicate... 

    Failure analysis of bolt connections in fired heater of a petrochemical unit

    , Article Engineering Failure Analysis ; Volume 92 , 2018 , Pages 327-342 ; 13506307 (ISSN) Farrahi, G. H ; Chamani, M ; Reza Kashyzadeh, K ; Mostafazade, A ; Mahmoudi, A. H ; Afshin, H ; Sharif University of Technology
    Elsevier Ltd  2018
    The main function of a fired heater in a petrochemical site is to produce supersaturated steam. Due to extremely difficult working conditions and high temperatures, there is a very high probability of failures in different parts of a fired heater. In the fired heater under study, tube guides are frequently damaged due to malfunctions and fractures in bolt connections. To investigate the nature of such fractures, Computational Fluid Dynamics (CFD), Finite Element (FE) method, Charpy impact test and fractography were used. To obtain the temperature of various components of the fired heater, a CFD analysis was carried out by considering the combustion process and modeling the central and side... 

    Two-dimensional CFD simulation of chemical reactions in tapered-in and tapered-out fluidized bed reactors

    , Article Advanced Powder Technology ; 2018 ; 09218831 (ISSN) Askaripour, H ; Dehkordi, A. M ; Sharif University of Technology
    Elsevier B.V  2018
    This article presents a simulation study of tapered-in and tapered-out fluidized bed reactors to investigate the influences of apex angle on the fractional conversion and the pressure drop of the fluidized beds in the presence of two types of chemical reaction with gas volume increase and reduction. The 2D behavior of tapered-in and -out fluidized beds was also compared with a columnar one from fractional conversion and bed pressure drop point of views. To validate the simulation results, the numerical predictions for the expansion ratio and the pressure drop of a tapered fluidized bed were compared with experimental data and good agreement was observed. The obtained simulation results... 

    Compartment model for steam reforming of methane in a membrane-assisted bubbling fluidized-bed reactor

    , Article International Journal of Hydrogen Energy ; Volume 34, Issue 3 , 2009 , Pages 1275-1291 ; 03603199 (ISSN) Dehkordi, A.M ; Memari, M ; Sharif University of Technology
    A compartment model was developed to describe the flow pattern of gas within the dense zone of a membrane-assisted fluidized-bed reactor (MAFBR), in the bubbling mode of operation for steam reforming of methane both with (adiabatic) and without (isothermal) entering oxygen. Considering such a flow pattern and using the experimental data reported elsewhere [Roy S, Pruden BB, Adris AM, Grace JR, Lim CJ. Fluidized-bed steam methane reforming with oxygen input. Chem Eng Sci 1999; 54:2095-2102.], the parameters of the developed model (i.e., number of compartments for the bubble and emulsion phases) were determined and fair agreements were obtained between model predictions and experimental data....