Search for: solutions
0.011 seconds
Total 1682 records

    Exact solution for the massless cylindrically symmetric scalar field in general relativity, with cosmological constant

    , Article International Journal of Modern Physics A ; Volume 24, Issue 31 , 2009 , Pages 5991-6000 ; 0217751X (ISSN) Momeni, D ; Miraghaei, H ; Sharif University of Technology
    In this paper we present a new exact solution for scalar field with cosmological constant in cylindrical symmetry Associated cosmological models including a model that describes a cyclic universe are discussed  

    Intersection with the vertical isocline in the generalized Liénard equations

    , Article Journal of Mathematical Analysis and Applications ; Volume 334, Issue 2 , 2007 , Pages 787-798 ; 0022247X (ISSN) Hesaaraki, M ; Moradifam, A ; Sharif University of Technology
    We consider the generalized Liénard systemfrac(d x, d t) = frac(1, a (x)) [h (y) - F (x)],frac(d y, d t) = - a (x) g (x), where a, F, g, and h are continuous functions on R and a (x) > 0, for x ∈ R. Under the assumptions that the origin is a unique equilibrium, we study the problem whether all trajectories of this system intersect the vertical isocline h (y) = F (x), which is very important in the global asymptotic stability of the origin, oscillation theory, and existence of periodic solutions. Under quite general assumptions we obtain sufficient and necessary conditions which are very sharp. Our results extend the results of Villari and Zanolin, and Hara and Sugie for this system with h... 

    Evaluation of electrical breakdown of anodic films on titanium in phosphate-base solutions

    , Article Surface and Coatings Technology ; Volume 186, Issue 3 , 2004 , Pages 398-404 ; 02578972 (ISSN) Afshar, A ; Vaezi, M. R ; Sharif University of Technology
    Titanium is a highly reactive metal, so that whenever it is exposed to air or other environments containing available oxygen, a thin layer of oxide is formed on the surface. This layer increases the corrosion resistance of titanium. The formation of the oxide film can be electrochemically performed by anodizing. In this research, anodizing of titanium was performed in phosphate-base solutions such as H3PO4, NaH2PO 4·2H2O and Na2HPO4 at 9.75 mA/cm2 and 35 °C under galvanostatic conditions. The potential-time curves in the above mentioned solutions show that the anodic films formed on Ti are compact and their thickness depends on the solution type and concentration. The SEM and XRD studies... 

    A new model for predicting activity coefficients in aqueous solutions of amino acids and peptides

    , Article Journal of Chemical Thermodynamics ; Volume 35, Issue 1 , 2003 , Pages 101-112 ; 00219614 (ISSN) Mortazavi Manesh, S ; Ghotbi, C ; Taghikhani, V ; Sharif University of Technology
    A new two-parameter model based on the perturbation of a hard-sphere reference has been developed to correlate the activity coefficients of several amino acids and simple peptides in aqueous solutions. The hard-sphere equation of state used as the reference in the model was proposed recently by Ghotbi and Vera. The perturbation terms coupled with the reference hard-sphere equation of state are attributed to the dispersion forces and the dipole-dipole interactions. The Lennard-Jones and Keesom potential functions are used to represent the dispersion and dipole-dipole interactions, respectively. The results of the new model are compared with those obtained by other models. It is shown that the... 

    Mechanism and estimation of Al(OH)3 crystal growth

    , Article Journal of Crystal Growth ; Volume 234, Issue 4 , 2002 , Pages 721-730 ; 00220248 (ISSN) Farhadi, F ; Bahrami Babaheidary, M ; Sharif University of Technology
    Precipitation is an important stage of the Bayer process. For simulation of this section, growth-rate estimation of Al(OH)3 crystals, is vital for the solution of population balance. Various published equations for linear growth rate of Al(OH)3 are reviewed. In all of these equations, a square exponent was considered for supersaturation terms. In some of the previous works, it was believed that BCF model is the governing mechanism for surface growth of crystals. It is shown that polynuclear model is the most probable mechanism. Also, a modification of the best previous correlation is performed, which results in a considerable improvement of the growth-rate estimation over the available... 

    Nonhomogeneous Boundary Value Problems for some Nonlinear Equations with Singular Ø-Laplacian

    , M.Sc. Thesis Sharif University of Technology Jannat, Farzaneh (Author) ; Hesaaraki, Mahmoud (Supervisor)

    Biodegradation of phenol from a synthetic aqueous system using acclimatized activated sludge

    , Article Arabian Journal of Geosciences ; Volume 6, Issue 10 , 2013 , Pages 3847-3852 ; 18667511 (ISSN) Jalayeri, H ; Doulati Ardejani, F ; Marandi, R ; Rafiee pur, S ; Sharif University of Technology
    Phenol is one of the aromatic hydrocarbons. Phenol and its derivatives are highly toxic. These pollutants can be observed in the effluents of many industries. This research investigates the removal of phenol by the use of activated sludge in a batch system. The effects of influencing factors on biodegradation efficiency have been evaluated. The main factors considered in this study were the volume of acclimatized activated sludge inoculation, pH, temperature, and initial concentration of phenol. The inoculation volumes of 1, 3, and 5 mL of acclimatized activated sludge were taken into account. Different pH values of 3, 5, 7, 9, and 11 were examined. The experiments were conducted for... 

    The cooperative game theory foundations of network bargaining games

    , Article Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 6 July 2010 through 10 July 2010, Bordeaux ; Volume 6198 LNCS, Issue PART 1 , 2010 , Pages 67-78 ; 03029743 (ISSN) ; 3642141641 (ISBN) Bateni, M ; Hajiaghayi, M ; Immorlica, N ; Mahini, H ; Sharif University of Technology
    We study bargaining games between suppliers and manufacturers in a network context. Agents wish to enter into contracts in order to generate surplus which then must be divided among the participants. Potential contracts and their surplus are represented by weighted edges in our bipartite network. Each agent in the market is additionally limited by a capacity representing the number of contracts which he or she may undertake. When all agents are limited to just one contract each, prior research applied natural generalizations of the Nash bargaining solution to the networked setting, defined the new solution concepts of stable and balanced, and characterized the resulting bargaining outcomes.... 

    Predictive construction of phase diagram of ternary solutions containing polymer/solvent/nonsolvent using modified Flory-Huggins model

    , Article Journal of Molecular Liquids ; Volume 263 , 2018 , Pages 282-287 ; 01677322 (ISSN) Sadeghi, A ; Nazem, H ; Rezakazemi, M ; Shirazian, S ; Sharif University of Technology
    Elsevier B.V  2018
    The Flory-Huggins (FH) model has been one of the most used models in theoretical calculations which has been proved to be sensitive to values assigned as interaction parameters. In this work, a predictive equation is implemented to implicitly couple the concept of compressible regular solution theory of Ruzette and Mayes into the original FH model to obtain a new concertation-dependent interaction parameter equation. Then, the modified model (m-FH) is applied for construction of phase diagram of ternary solutions containing polymer/solvent/nonsolvent where experimental data for ternary systems were collected from the literature. In order to compare and analyze the model performance, the... 

    A new hydration model in correlating the mean ionic activity coefficient and density of aqueous electrolyte solutions

    , Article Journal of Dispersion Science and Technology ; Volume 31, Issue 5 , 2010 , Pages 641-649 ; 01932691 (ISSN) Pazuki, G. R ; Taghikhani, V ; Vossoughi, M ; Sharif University of Technology
    In this article, a new hydration model has been proposed to study the phase behavior of aqueous electrolyte solutions. The proposed model distinguishes between an anion and cation in the electrolyte solution. The model has three adjustable parameters which can be obtained using the experimental data of the mean ionic activity coefficients for 113 electrolyte solutions. The results of the proposed model were compared with those of obtained from the Pitzer, the E-NRTL and the E-Wilson models. The results showed that the proposed model can accurately correlate the mean ionic activity coefficients of the aqueous electrolyte solutions than the other models. Also, the proposed model was used in... 

    A semilinear PDE with free boundary

    , Article Nonlinear Analysis, Theory, Methods and Applications ; Volume 151 , 2017 , Pages 145-163 ; 0362546X (ISSN) Fotouhi, M ; Shahgholian, H ; Sharif University of Technology
    Elsevier Ltd  2017
    We study the semilinear problem Δu=λ+(x)(u+)q−1−λ−(x)(u−)q−1inB1, from a regularity point of view for solutions and the free boundary ∂{±u>0}. Here B1 is the unit ball, 1

    The UNIQUAC-NRF segmental interaction model for vapor-liquid equilibrium calculations for polymer solutions

    , Article Polimeri (Zagreb) ; Volume 26, Issue 3 , 2005 , Pages 115-120 ; 03511871 (ISSN) Radfarnia, H. R ; Bogdanić, G ; Taghikhnai, V ; Ghotbi, C ; Sharif University of Technology
    This paper presents a new segment-based thermodynamic model containing the combinatorial and energetic contributions to the excess Gibbs energy for correlating/predicting of the vapor-liquid equilibrium (VLE) of polymer solutions. The model is derived from the UNIQUAC-NRF model, recently proposed by Haghtalab and Asadollahi, following the idea to associate the nonideality of polymer-solvent mixture with polymer segment-solvent interaction parameters, Segment activity coefficients are calculated by means of the UNIQUAC-NRF model. At the present state of development, 16 binary segmental interaction parameters have been estimated, The capability of the model is demonstrated with successful... 

    Analytical solution for creeping motion of a viscoelastic drop falling through a Newtonian fluid

    , Article Korea Australia Rheology Journal ; Vol. 26, issue. 1 , 2014 , pp. 91-104 ; ISSN: 1226119X Vamerzani, B. Z ; Norouzi, M ; Firoozabadi, B ; Sharif University of Technology
    In this paper, an analytical solution for steady creeping motion of viscoelastic drop falling through a viscous Newtonian fluid is presented. The Oldroyd-B model is used as the constitutive equation. The analytical solutions for both interior and exterior flows are obtained using the perturbation method. Deborah number and capillary numbers are considered as the perturbation parameters. The effect of viscoelastic properties on drop shape and motion are studied in detail. The previous empirical studies indicated that unlike the Newtonian creeping drop in which the drop shape is exactly spherical, a dimpled shape appears in viscoelastic drops. It is shown that the results of the present... 

    Activity coefficient prediction for binary and ternary aqueous electrolyte solutions at different temperatures and concentrations

    , Article Journal of Solution Chemistry ; Volume 41, Issue 1 , 2012 , Pages 75-88 ; 00959782 (ISSN) Sadeghi, M ; Ghotbi, C ; Abdekhodaie, M. J ; Sharif University of Technology
    The mean spherical approximation (MSA) model, coupled with two hard sphere models, was used to predict the activity coefficients of mixtures of electrolyte solutions at different temperatures and concentrations. The models, namely the Ghotbi-Vera-MSA (GV-MSA) and Mansoori et al.-MSA (BMCSL-MSA), were directly used without introducing any new adjustable parameters for mixing of electrolyte solutions. In the correlation step, the anion diameters were considered to be constant, whereas the cation diameters were considered to be concentration dependent. The adjustable parameters were determined by fitting the models to the experimental mean ionic activity coefficients for single aqueous... 

    Photocatalytic decolorization of methylene blue using immo bilized ZnO nanoparticles prepared by solution combustion method

    , Article Desalination and Water Treatment ; Volume 44, Issue 1-3 , May , 2012 , Pages 174-179 ; 19443994 (ISSN) Rezaee, A ; Masoumbeigi, H ; Soltani, R. D. C ; Khataee, A. R ; Hashemiyan, S ; Sharif University of Technology
    Taylor and Francis Inc  2012
    Photocatalytic decolorization of methylene blue (MB) in aqueous solution was investigated using ZnO nanoparticles immobilized on glass plate. The ZnO nanoparticles were prepared by solution combustion method (SCM) using zinc nitrate as oxidant and glycine as fuel. In the slurry ZnO system the separation and recycling of the photocatalyst is practically difficult. Thus, the ZnO nanoparticles were immobilized on glass supports to solve this problem. The effects of process parameters like, catalyst loading, initial dye concentration, and UV-radiation intensity have been investigated. The best results of MB removal were reported in the 1800 μW cm-2 UVC using two layers immobilized ZnO... 

    Preparation of a cuins2 nanoparticle ink and application in a selenization-free, solution-processed superstrate solar cell

    , Article European Journal of Inorganic Chemistry ; Volume 2015, Issue 35 , November , 2015 , Pages 5793–5800 ; 14341948 (ISSN) Cheshme Khavar, A. H ; Mahjoub, A. R ; Tajabadi, F ; Dehghani, M ; Taghavinia, N ; Sharif University of Technology
    Wiley-VCH Verlag  2015
    We report a study on chalcopyrite solar cells fabricated by low-cost, nonvacuum, and selenization-free methods. Superstrate-type CuInS2 (CIS) thin-film solar cells were prepared by sequential ink deposition. The CIS film was formed from a stable low-carbon ink, which was synthesized at low temperature (<120 °C). The CIS nanoparticle ink was prepared with n-butylamine and acetic acid as the solvent and stabilizer, respectively. The viscous and stable ink that formed through the dispersion of the final nanoparticles in N,N-dimethylformamide (DMF) could be deposited readily onto the substrate. The major features of the obtained ink are the small amount of impurity phases and negligible carbon... 

    New solutions of LR fuzzy linear systems using ranking functions and ABS algorithms

    , Article Applied Mathematical Modelling ; Volume 34, Issue 11 , November , 2010 , Pages 3363-3375 ; 0307904X (ISSN) Ghanbari, R ; Mahdavi Amiri, N ; Sharif University of Technology
    We propose an approach for computing the general compromised solution of an LR fuzzy linear system by use of a ranking function when the coefficient matrix is a crisp m×n matrix. The solution is so that mean values of a compromised solution satisfies the corresponding crisp linear system. We show that if the corresponding crisp system is incompatible, then the fuzzy linear system lacks any solution. Otherwise, we solve a constrained least squares problem to compute a compromised solution. If the optimal value of the constrained least squares problem is zero, then we obtain the LR solution, namely the exact solution, of the system with respect to a ranking function. On the other hand, if the... 

    Groundwater travel time computation for two-layer islands

    , Article Hydrogeology Journal ; Volume 24, Issue 4 , 2016 , Pages 1045-1055 ; 14312174 (ISSN) Ketabchi, H ; Mahmoodzadeh, D ; Ataie Ashtiani, B ; Sharif University of Technology
    Springer Verlag  2016
    A closed-form analytical computation of groundwater travel time (GWTT) for two-layer oceanic small island aquifers is developed assuming steady-state and sharp-interface conditions. The two-layer geology impacts on the GWTT are investigated using the developed analytical solution to achieve a greater transparency of such conceptualizations. The results demonstrate that the inclusion of geologic layering leads to large changes in the GWTT. Sensitivity analyses, using specified dimensionless parameters, are employed to assess the influences of hydraulic conductivity, recharge rate, upper layer thickness, and seawater/freshwater density difference parameters, which influence the GWTT. These... 

    Effective removal of mercury from aqueous solution using thiol-functionalized magnetic nanoparticles

    , Article Environmental Nanotechnology, Monitoring and Management ; Volume 7 , 2017 , Pages 130-138 ; 22151532 (ISSN) Oveisi, F ; Nikazar, M ; Razzaghi, M. H ; Mirrahimi, M. A. S ; Jafarzadeh, M. T ; Sharif University of Technology
    Elsevier B.V  2017
    The present investigation demonstrates the effective removal of Hg(II) ions from aqueous solution by means of thiol-functionalized magnetic nanoparticles (TF-MNPs). After preparation, TF-MNPs have been characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform-infrared spectroscopy (FT-IR), Thermogravimetric (TG) and vibrating sample magnetometer (VSM). The XRD and FESEM analyses revealed the presence of magnetic nanoparticles with an average particle size of 15–30 nm. The result of FT-IR analysis confirmed that the magnetite nanoparticles have been successfully functionalized by thiol groups. The particles illustrated enough response... 

    Efficient solutions of interval programming problems with inexact parameters and second order cone constraints

    , Article Mathematics ; Volume 6, Issue 11 , 2018 ; 22277390 (ISSN) Sadeghi, A ; Saraj, M ; Mahdavi Amiri, N ; Sharif University of Technology
    MDPI AG  2018
    In this article, a methodology is developed to solve an interval and a fractional interval programming problem by converting into a non-interval form for second order cone constraints, with the objective function and constraints being interval valued functions. We investigate the parametric and non-parametric forms of the interval valued functions along with their convexity properties. Two approaches are developed to obtain efficient and properly efficient solutions. Furthermore, the efficient solutions or Pareto optimal solutions of fractional and non-fractional programming problems over R + n S (0) are also discussed. The main idea of the present article is to introduce a new concept for...