Sharif Digital Repository

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  

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... 

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 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... 

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... 

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... 

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.... 

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... 

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... 

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