Search for: thermodynamic-stability
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    Vole Population Dynamics Under the Influence of Specialist and Generalist Predation

    , M.Sc. Thesis Sharif University of Technology Heidary, Samira (Author) ; Hesaraki, Mahmud (Supervisor)
    To understand the impact of predation by different types of predators on the vole population dynamics,we formulate a three differential equation model describing the population dynamics of voles, the “specialist predator”and the “generalist predator.” First we perform a local stability study of the different steady states of the basic model and deduce that the predation rates of the “specialist” as well as the “generalist” predator are the main parameters controlling the existence/extinction criteria of the concerned populations. Next we analyze the model from a thermodynamic perspective and study the thermodynamic stability of the different equilibria. The analysis revealsthat when the... 

    The effect of Si addition and Ta diffusion barrier on growth and thermal stability of NiSi nanolayer

    , Article Microelectronic Engineering ; Volume 85, Issue 3 , 2008 , Pages 548-552 ; 01679317 (ISSN) Kargarian, M ; Akhavan, O ; Moshfegh, A. Z ; Sharif University of Technology
    Formation and thermal stability of nanothickness NiSi layer in Ni(Pt 4 at.%)/Si(1 0 0) and Ni0.6Si0.4(Pt 4 at.%)/Si(1 0 0) structures have been investigated using magnetron co-sputtering deposition method. Moreover, to study the effect of Si substrate in formation of NiSi and its thermal stability, we have used Ta diffusion barrier between the Ni0.6Si0.4 layer and the Si substrate. Post annealing treatment of the samples was performed in an N2 environment in a temperature range from 200 to 900 °C for 2 min. The samples were analyzed by four point probe sheet resistance (Rs) measurement, X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. It was found that the annealing... 

    Mechanism of catalytic decomposition of CH3I on the Cu(111) surface: A UBI-QEP approach

    , Article Langmuir, Washington, DC, United States ; Volume 16, Issue 21 , 2000 , Pages 8095-8099 ; 07437463 (ISSN) Azizian, S ; Gobal, F ; Sharif University of Technology
    ACS  2000
    The method of unity bond index-quadratic exponential potential (UBI-QEP) and the computer simulation of the temperature programmed desorption (TPD) patterns are employed to derive the kinetic and thermodynamic parameters associated with the steps of the pathway we propose for the catalytic decomposition of methyl iodide on the Cu(111) surface. Assuming a highly reactive `hot methyl' surface intermediate and on the basis of our calculations it is concluded that the desorption of a part of this species is responsible for the reported methyl radical TPD peak at 140 K, while a part of this surface species is trapped in the three-fold sites of the Cu(111) surface and desorbs to form the reported... 

    Synthesis and study of a new class of red pigments based on perovskite YAlO3 structure

    , Article Ceramics International ; Volume 33, Issue 8 , December , 2007 , Pages 1427-1433 ; 02728842 (ISSN) Shirpour, M ; Faghihi Sani, M. A ; Mirhabibi, A ; Sharif University of Technology
    A red pigment has been prepared by substituting chromium ions in aluminum ion sites in YAlO3 perovskite structure. In a first step, effect of various mineralizers on YAlO3 formation has been investigated, which resulted in decrease of formation temperature down to 1400 °C. In the next step, a red pigment corresponding to YAl1-yCryO3 (y = 0.05), has been prepared by heating a mixture containing Y2O3, Al2O3 and Cr2O3 at 1500 °C for 6 h. Later, effect of the doped chromium amount on the pigment redness (a*) has been studied. The highest redness has been obtained when y was 0.04(YAl1-yCryO3). Application of the prepared red pigment in low and high temperature glazes, demonstrated its high... 

    Thickness dependence on thermal stability of sputtered Ag nanolayer on Ti/Si(1 0 0)

    , Article Applied Surface Science ; Volume 254, Issue 2 , 2007 , Pages 548-551 ; 01694332 (ISSN) Akhavan, O ; Moshfegh, A.Z ; Sharif University of Technology
    Elsevier  2007
    Thermal stability of Ag layer on Ti coated Si substrate for different thicknesses of the Ag layer have been studied. To do this, after sputter-deposition of a 10 nm Ti buffer layer on the Si(1 0 0) substrate, an Ag layer with different thicknesses (150-5 nm) was sputtered on the buffer layer. Post annealing process of the samples was performed in an N 2 ambient at a flow rate of 200 ml/min in a temperature range from 500 to 700 °C for 30 min. The electrical property of the heat-treated multilayer with the different thicknesses of Ag layer was examined by four-point-probe sheet resistance measurement at the room temperature. Phase formation and crystallographic orientation of the silver... 

    Immobilization of cellulase on non-porous ultrafine silica particles

    , Article Scientia Iranica ; Volume 14, Issue 4 , 2007 , Pages 379-383 ; 10263098 (ISSN) Afsahi, B ; Kazemi, A ; Kheirolomoom, A ; Nejati, S ; Sharif University of Technology
    Sharif University of Technology  2007
    The immobilization of cellulase onto non-porous ultrafine silica particles was studied. Cellulase was extracted from a Trichoderma reesei culture after partial purification with ammonium sulfate (pH = 5.0), which was then immobilized onto non-porous ultrafine silica particles, with or without the use of glutaraldehyde as a crosslinking agent. Cellulase was immobilized by adsorption onto ultrafine silica particles efficiently, as well as by covalent cross-linking with glutaraldehysde. Increasing the concentration of the free form of enzyme increased the amount of immobilized cellulase. The maximum enzyme immobilization happened at the free enzyme concentration of 0.48 mg/ml. In general, the... 

    Thermal stability of nanoscale silver metallization in Ag/W/Co/Si(1 0 0) multilayer

    , Article Applied Surface Science ; Volume 252, Issue 15 , 2006 , Pages 5335-5338 ; 01694332 (ISSN) Akhavan, O ; Azarm, A ; Moshfegh, A. Z ; Bahrevar, M. A ; Sharif University of Technology
    Elsevier  2006
    In this work, we have studied thermal stability of nanoscale Ag metallization and its contact with CoSi 2 in heat-treated Ag(50 nm)/W(10 nm)/Co(10 nm)/Si(1 0 0) multilayer fabricated by sputtering method. To evaluate thermal stability of the systems, heat-treatment was performed from 300 to 900 °C in an N 2 ambient for 30 min. All the samples were analyzed by four-point-probe sheet resistance measurement (R s ), Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD), and atomic force microscopy (AFM). Based on our data analysis, no interdiffiusion, phase formation, and R s variation was observed up to 500 °C in which the Ag layer showed a (1 1 1) preferred crystallographic... 

    Partially aromatic polyamides based on tetraphenylthiophene diamine: synthesis and characterization

    , Article Journal of Applied Polymer Science, New York, NY, United States ; Volume 77, Issue 5 , 2000 , Pages 1144-1153 ; 00218995 (ISSN) Pourjavadi, A ; Zamanlu, M. R ; Zohuriaan Mehr, M. J ; Sharif University of Technology
    John Wiley & Sons Inc  2000
    Tetraphenylthiophene diamine (TPTDA) was prepared through a modified three-step route to achieve an improved overall yield. TPTDA reacted with succinic, adipic, suberic, sebasic, and fumaric acids via the Yamazaki phosphorylation method to yield novel partially aromatic polyamides (TPT series). A counterpart polyamide series based on p-phenylene diamine (Ph series) was also synthesized under the same conditions. All of the polymers were characterized by means of spectrochemical (Fourier transform infrared spectroscopy. 1H-nuclear magnetic resonance (NMR), and 13C-NMR) and thermal (differential scanning calorimetry and thermogravimetric) methods of analysis. Solubility of TPT polyamides was... 

    Effect of Doping la/nd in pr Site and fe/cu in ni Site on Thermal Stability of the Pr2NiO4+δ as the Cathode of Intermediate Temperature Solid Oxide Fuel Cell

    , M.Sc. Thesis Sharif University of Technology Behsam, Shadi (Author) ; Fagihi Sani, Mohammad Ali (Supervisor)
    Solid oxide fuel cells (SOFCs) are a route to highly efficient and clean power, which have been attracting interest due to the issues associated with the ever-increasing energy demand and pollution. However, their commercialization is hindered by the high operating temperatures (700-1000℃). One of the challenges faced by intermediate temperature solid oxide fuel cells (IT-SOFCs) with operating temperature in the range of 500-700℃ is the increased overpotentials of the components, especially cathode. Lanthanide nickelates (Ln2NiO4+δ, Ln = La,Pr,Nd) with mixed ionic and electronic conduction (MIEC) have already been introduced as promising IT-SOFC cathode materials. Among them, Pr2NiO4+δ... 

    Thermal stability investigation of expanded martensite

    , Article Surface and Coatings Technology ; Volume 300 , 2016 , Pages 87-94 ; 02578972 (ISSN) Baniasadi, F ; Bahmannezhad, B ; Nikpoor, N ; Asgari, S ; Sharif University of Technology
    Elsevier  2016
    The aim of this work is to investigate thermal stability of expanded martensite. For this purpose, two martensitic stainless steels, PH 17-4 and 13-8Mo, were low temperature gas carburized. After heat treatment, it was found out that thermal stability of expanded layer of PH 17-4 is higher than that of PH 13-8Mo. Auger Electron Spectroscopy and microhardness machines were used to investigate carbon concentration and hardness of samples, respectively. X-ray diffraction was done to study crystal structures of samples before and after heat treatment  

    Thermal stability of the two-dimensional topological color code

    , Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 94, Issue 2 , 2016 ; 10502947 (ISSN) Mohseninia, R ; Sharif University of Technology
    American Physical Society 
    Thermal stability of the topological color code in the presence of a thermal bath is studied. We study the Lindblad evolution of the observables in the weak-coupling limit of the Born-Markov approximation. The autocorrelation functions of the observables are used as a figure of merit for the thermal stability. We show that all of the observables autocorrelation functions decay exponentially in time. By finding a lower bound of the decay rate, which is a constant independent of the system size, we show that the topological color code is unstable against thermal fluctuations from the bath at finite temperature, even though it is stable at T=0 against local quantum perturbations  

    The Role of Carbon Nanotubes in Improving Thermal Stability of Polymeric Fluids: Experimental and Modeling

    , Article Industrial and Engineering Chemistry Research ; Volume 55, Issue 27 , 2016 , Pages 7514-7534 ; 08885885 (ISSN) Halali, M. A ; Ghotbi, C ; Tahmasbi, K ; Ghazanfari, M. H ; Sharif University of Technology
    American Chemical Society  2016
    At harsh conditions of high pressure high temperature (HPHT), polymers undergo thermal degradation leading to serious loss in fluid rheological and filtration properties. Nanoparticles are the most promising additives proposed to address this challenge. The stability of nanofluids is perused from various facets including rheological and filtration properties, shale stability, and zeta potential. The presence of nanoparticles could amazingly reduce the filtration at high temperatures even by 95%, and it also had a conspicuous effect on shale stability, thermal conductivity, and zeta potential. Experimental data were fit to rheological models to determine the best models describing the... 

    Influence of monoethanolamine on thermal stability of starch in water based drilling fluid system

    , Article Shiyou Kantan Yu Kaifa/Petroleum Exploration and Development ; Volume 45, Issue 1 , 2018 , Pages 157-160 ; 10000747 (ISSN) Nasiri, A ; Sharif Nik, M. A ; Heidari, H ; Valizadeh, M ; Sharif University of Technology
    Science Press  2018
    To improve the thermal stability of starch in water-based drilling fluid, monoethanolamine (MEA) was added, and the effect was investigated by laboratory experiment. The experimental results show that the addition of monoethanolamine (MEA) increases the apparent viscosity, plastic viscosity, dynamic shear force, and static shear force of the drilling fluid, and reduces the filtration rate of drilling fluid and thickness of mud cake apparently. By creating hydrogen bonds with starch polymer, the monoethanolamine can prevent hydrolysis of starch at high temperature. Starch, as a natural polymer, is able to improve the rheological properties and reduce filtration of drilling fluid, but it works... 

    Mechanical properties of Al-Al2O3 nanocomposite produced by mechanical milling and powder hot extrusion

    , Article European Powder Metallurgy Congress and Exhibition, Euro PM 2007, Toulouse, 15 October 2007 through 17 October 2007 ; Volume 2 , 2007 , Pages 259-264 ; 9781899072293 (ISBN) Hesabi, Z. R ; Simchi, A ; Seyed Reihani, S. M ; Simancik, F ; Balog, M ; Csuba, A ; Sharif University of Technology
    European Powder Metallurgy Association (EPMA)  2007
    In the present work, ultrafine-grained Al-5vol.% Al2O3 nanocomposite was synthesized through mechanical milling followed by direct powder extrusion method. The characteristics of the processed nanocomposite were examined by electron microscopy (SEM and TEM), Xray diffraction (XRD), tensile test and Vickers hardness measurement. It was shown that the addition of the reinforcement nanoparticles accelerates the milling process of the aluminum matrix and enhances the grain refinement of the aluminum matrix. An improved mechanical strength as compared with Al-Al2O3 microcompoiste was obtained. A dimple-type fracture mode was observed, which is a clear evidence of micro-deformation. In addition,... 

    An experimental study on kerosene spray combustion under conventional and hot-diluted conditions

    , Article Combustion Science and Technology ; 2021 ; 00102202 (ISSN) Mardani, A ; Azimi, A ; Karimi Motaalegh Mahalegi, H ; Sharif University of Technology
    Bellwether Publishing, Ltd  2021
    The combustion of kerosene spray under hot-diluted conditions and conventional conditions was experimentally investigated. By examining flame photographs, chemiluminescence images, and in-field temperature measurements, the separate effect of different variables including oxygen concentration, temperature and velocity of the co-flowing air, fuel flow rate and injection pressure, and eventually the type of spray nozzle on multiple parameters such as flame stability, structure, luminosity, temperature field, and qualitative CH radical distribution, as well as HCO and NO2 with lower precision, in the reaction region, have been studied. It was observed that an increment in injection pressure and... 

    Annealing behavior of aluminum after low-temperature severe plastic deformation

    , Article Materials Science and Engineering A ; Volume 824 , 2021 ; 09215093 (ISSN) Alyani, A ; Kazeminezhad, M ; Sharif University of Technology
    Elsevier Ltd  2021
    Severe plastic deformation (SPD) processes have received less attention at low temperatures (sub-zero and cryogenics). Hence, in this study, SPD of a commercially pure aluminum (AA1050) through Multi-Directional Forging (MDF) at Low-Temperature (LTMDF) and Room-Temperature (RTMDF) is investigated for different strains. Multi-directionally forged (MDFed) samples were annealed at 150, 250, 350, and 450 °C for 1 h, and some samples were stored at room temperature for periods up to 1 year. Results show that the hardness values and flow stress of LTMDFed aluminum are higher than those of RTMDFed ones. The ratio of yield strength to hardness for LTMDF is similar to that for RTMDF. Surprisingly,... 

    Effect of nanostructuring on thermal stability and decomposition of aluminium titanate (Al2TiO5): a phase transformation study

    , Article Materials Characterization ; Volume 173 , 2021 ; 10445803 (ISSN) Azarniya, A ; Madaah Hosseini, H. R ; Amutha, C ; Ramakrishna, S ; Sharif University of Technology
    Elsevier Inc  2021
    As a refractory ceramic, the thermal instability of aluminium titanate (AT or Al2TiO5) has been in the crosshairs of research works in recent years. The studies have indicated that different parameters such as atmosphere, grain size, additives, oxygen pressure, and synthesis method can bilaterally affect the thermal decomposition of AT ceramic and resultant physicomechanical properties. In the present study, the AT nanostructure was synthesized by a citrate sol-gel method and influence of nanostructuring nature on its thermal instability and reaction pathway was explored in some details. It was shown that the reduction of grain size down to 30 nm can destabilize AT, so that the reaction... 

    Efficient aerobic oxidation of alcohols using a novel combination N-hydroxy phthalimide (NHPI) and a recyclable heterogeneous cobalt complex

    , Article Journal of Molecular Catalysis A: Chemical ; Volume 232, Issue 1-2 , 2005 , Pages 95-99 ; 13811169 (ISSN) Rajabi, F ; Karimi, B ; Sharif University of Technology
    A novel combination between N-hydroxy phthalimide (NHPI) and a silica based cobalt (II) interphase catalyst (1) efficiently catalyzes the aerobic oxidation of various types of alcohols to the corresponding carbonyl compounds. The catalyst 1 shows high thermal stability and also could be recovered and reused in combination with NHPI for at least five reaction cycles without considerable loss of reactivity. © 2005 Elsevier B.V. All rights reserved  

    Softening behaviour of alumina reinforced copper processed by equal channel angular pressing

    , Article Materials Science and Technology (United Kingdom) ; Volume 30, Issue 2 , February , 2014 , Pages 220-226 ; ISSN: 02670836 Ranjbar Motlagh, S ; Maghsoudi, M. H ; Serajzadeh, S ; Sharif University of Technology
    In this present work, the softening behaviour of Cu-1·1 wt-%Al2O3 alloy containing nanometric alumina particles was investigated. Single pass equal channel angular pressing was first applied on cylindrical specimens, and then, the deformed samples were subjected to annealing treatments in the temperature range of 700-1000°C. Afterwards, finite element analysis, microstructural observations, Vickers hardness and shear punch testing were employed to study strain distribution as well as the recrystallisation behaviour of the examined alloy. It was found that the alloy is softened at 800°C or above, which shows its high thermal stability. Furthermore, a very fine completely recrystallised... 

    Thermal stability during annealing of friction stir welded aluminum sheet produced by constrained groove pressing

    , Article Materials and Design ; Volume 45 , 2013 , Pages 222-227 ; 02613069 (ISSN) Sarkari Khorrami, M ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
    The severely deformed aluminum sheets with strain of 2.32 were successfully joined by friction stir welding (FSW) process. Welding was carried out at various rotation speeds of 600, 800, and 1000. rpm at traveling speed of 200. mm/min corresponding to various revolution pitches of 0.33, 0.25, and 0.20. mm/r, respectively. In order to investigate the thermal stability of the joints, annealing was carried out at temperature of 200 °C for 1. h. Microstructure examinations revealed that severely deformed samples were quite unstable upon FSW process. However, during annealing it was found that in contrast to regions of heat affected zone (HAZ) and thermo mechanical affected zone (TMAZ) where...