Sharif Digital Repository

The propagation of acoustic waves in strongly heterogeneous media is studied using direct numerical simulations. Two types of heterogeneous media are considered. In one type, the spatial distribution of the local elastic constants contain long-range correlations with a power law, nondecaying correlation function. The correlation length is, therefore, as large as the linear size of the system. In the second type of heterogeneous media the correlation length is decreased, up to the linear size of the blocks in the computational grid and, therefore, the distribution of the elastic constants is uncorrelated or white noise, but with the same mean and variance as that of the correlated media. We... 

A highly efficient and simple procedure for the synthesis of quinazolin-4(3H)-ones from the condensation of 2-aminobenzamide with triethylorthoesters in presence of a catalytic amounts of heteropolyacids in various solvents is reported  

Epoxides are important materials in the production of fine chemicals. Selective oxidation of alkenes to epoxides remains a challenge in synthetic chemistry. There has been considerable progress in tungsten-catalyzed epoxidation of alkenes in recent years. This review highlights the use of monomeric and dimeric oxido-peroxido tungsten(VI) complexes as catalysts or oxidants in homogeneous or heterogeneous catalytic systems for epoxidation of olefins  

The purpose of this study is to predict the activation barriers and enthalpy for elementary steps in the process of Fischer-Tropsch (F-T) on the surfaces of Fe(110), Cu(111) and Fe/Cu alloys catalyst using "Unity Bond Index-Quadratic Exponential Potential" method aimed at predicting the activity and selectivity on the basis of energy criteria. The elementary steps, such as dissociation of CO, hydrogenation of carbidic carbon, C-C chain growth by insertion of CH2 versus CO into the metal-alkyl bonds, and chain termination, which lead to hydrocarbons (alkanes versus α-olefins) or oxygenates are discussed in detail. The results show that metallic Fe(110) is necessary to produce the carbidic... 

This study reports synthesis and characterization of polymeric [MoO2(Salen)] complexes that combine MoO2(acac)2 and polymeric ligands bearing N2O2 coordination sites, abbreviated herein as [piperazinCH2{MoO2(Salen)}]n (6), [piperazinCH2{MoO2(Salophen)}]n (7), and [piperazinCH2{MoO2(Salpn)}]n (8). The epoxidation of alkenes using tert-butyl hydroperoxide and oxidation of sulfides to sulfoxides by urea hydrogen peroxide were enhanced with excellent selectivity under the catalytic influence of these coordination polymers. No relevant difference in activity was found due to change in the diamine in the Schiffs base ligands. The stability of polymeric catalysts was assessed by recycling a sample... 

Aromatic and cyclic organic compounds such as nitrobenzene (NB) are widely used in various industries and are present in their wastewater. In addition, the photocatalytic process has received considerable attention due to its lower chemical consumption and more efficient degradation of refractory pollutants. In this study, a CoFe2O4-ZnO (CFZ) composite was prepared and evaluated its efficiency in the degradation of NB from aqueous solution under UV light. The optical, structural, and physicochemical properties of catalysts were characterized using PL, UV–vis DRS, XRD, TEM, FESEM-EDS, and VSM techniques and then discussed in detail. It was found that not only does the use of CF facilitate the... 

The evaluation of multigroup constants in reactor calculations depends on several parameters. One of these parameters is the Dancoff factor which is used for calculating the resonance integral and flux depression in the resonance region in heterogeneous systems. In the current paper, a computer program (MCDAN-3D) is developed for calculating three dimensional black and gray Dancoff coefficients, based on Monte Carlo, escape probability and neutron free flight methods. The developed program is capable to calculate the Dancoff factor for an arbitrary arrangement of fuel and moderator pebbles. Moreover this program can simulate fuels with homogeneous and heterogeneous compositions. It might... 

Synchronous heterogeneous catalytic hydrogenation of cyclohexene and acetone, catalyzed by Pt/Al2O3, was carried out in solutions of 2-hydroxy ethylammonium formate (a room temperature ionic liquid, RTIL) with ethanol and propan-1-ol at 25 °C. Rate constants and selectivity of the reaction (relative to cyclohexene hydrogenation) increase with mole fraction of the ionic liquid (IL). The reactants tendency to the catalyst surface increases by addition of the ionic liquid and thus the reaction rate increases, especially for cyclohexene hydrogenation. Consequently the selectivity to cyclohexene hydrogenation was increased. Single-parameter correlations of log kvs.π* (dipolarity/polarizibility)... 

A repeated inflation-unemployment game within the linear-quadratic frame-work of Barro and Gordon is studied assuming that the government would like to cheat optimally and the finite heterogeneous population of private agents attempts to learn the government's targets using a reinforcement learning algorithm. Private agents are heterogeneous in their initial expectations of inflation rate but are assumed to utilize an identical anticipatory reinforcement learning process, namely Q-learning. In our heterogeneous setting, the only way for the private agents to achieve a zero value for their loss function, is for all of them to correctly anticipate the Nash equilibrium. It is of particular... 

The thermal decomposition of manganese and cobalt-terephthalate Metal-Organic Framework precursors was utilized as a synthetic route for fabrication of Co3O4, Mn3O4 and Mn2O3 nanoparticles. The prepared metal oxide nanoparticles of Co3O4, Mn3O4 and Mn2O3 possess average size diameter of 40, 60 and 80 nm respectively. The findings demonstrate that spinel structure nanoparticles of Co3O4 and Mn3O4 exhibit efficient catalytic activity toward heterogeneous olefin epoxidation in the presence of tert-butyl hydroperoxide. In... 

Water channeling due to reservoir heterogeneity is an important factor that could decrease the displacement efficiency of a water flooding process. In this study, the ability of polyacrylamide/ chromium acetate system on altering water path in heterogeneous layered media was investigated using glass bead micromodels. After the relevant parameters were optimized, a series of water and gel injection experiments were conducted in glass bead micromodel. The experimental results show that sweep efficiency is basically controlled by gel strength. The gel strength has a minor impact on the oil recovery from the higher permeable zone, whereas the oil recovery from the lower permeable zone is a... 

A heterogeneous nanocatalyst was prepared via covalent anchoring of dioxomolybdenum(VI) Schiff base complex on core-shell structured Fe3O4@SiO2. The properties and the nature of the surface-fixed complex have been identified by a series of characterization techniques such as SEM, EDX, XRD, TGA, FT-IR, and VSM. The synthesized hybrid material was an efficient nanocatalyst for selective oxidation of olefins to corresponding epoxides with t-BuOOH in high yields and selectivity. The catalyst could be conveniently recovered by applying an external magnetic field and reused several times without significant loss of efficiency. © 2016 Taylor and Francis  

Magnetic nanoparticles of CuFe2O4 were applied as catalyst system for one-pot thiophosphate synthesis via the reaction of aryl sulfonyl chlorides with H-phosphonates under conventional heating conditions. This is an extremely efficient and green method for thiophosphate synthesis under base- and solvent-free conditions. Various thiophosphates were obtained in good to excellent yields under the optimized reaction conditions in a short time. The catalyst can be easily recycled from the reaction by an external magnetic field and reused for the next run. In this study, TD-DFT B3LYP/6-31 + G(d) calculations are in good accord with the experimental results. A comparison between experimental and... 

Influence maximization deals with identification of the most influential nodes in a social network given an influence model. In this paper, a game theoretic framework is developed that models a competitive influence maximization problem. A novel competitive influence model is additionally proposed that incorporates user heterogeneity, message content, and network structure. The proposed game-theoretic model is solved using Nash Equilibrium in a real-world dataset. It is shown that none of the well-known strategies are stable and at least one player has the incentive to deviate from the proposed strategy. Moreover, violation of Nash equilibrium strategy by each player leads to their reduced... 

Tackling the dark silicon problem in a heterogeneous multi-core system, the temperature constraints across the system should be addressed carefully by assigning a proper set of tasks to a pool of the heterogeneous cores during the run-time. When such a system is utilized in a reliable/realtime application, the reliability/timing constraints of the application should also be augmented to the temperature constraints and make the tasks mapping problem more and more complex. To solve the mapping problem in such a situation, we propose READY; an online reliability-and deadline-aware mapping and scheduling algorithm for heterogeneous multi-core systems. READY utilizes an adaptive power constraint... 

It has long been understood that flow behavior in heterogeneous porous media is largely controlled by the continuity of permeability contrasts. With this in mind, we are looking in new methods for a fast estimation of the effective permeability which concentrates on the properties of the percolating cluster. From percolation concepts we use a threshold permeability value (Kth) by which the gridblocks with the highest permeability values connect two opposite side of the system in the direction of the flow. Those methods can be applied to heterogeneous media of a range of permeabilities distribution and various underlying structures. We use power law relations and weighted power averages that... 

In this paper we consider the problem of joint location and pricing optimization for a firm in a heterogeneous market producing a single product. We assume that customers have a different willingness to pay for the product. We consider two classes of customers who are not uniformly distributed in the market and develop an analytical framework to determine the relationship between the optimal price and location of the firm. We demonstrate that the optimal price and location are closely related to each other, and thus there is a need for simultaneous optimization of the price and location. We provide both analytical and numerical results to illustrate the impact of transportation cost and the...