Sharif Digital Repository

We present in this paper a simple method of obtaining various equations of state for hard sphere fluid in a simple unifying way. Using the first several virial coefficients of hard sphere fluid, we will guess equations of state by using the asymptotic expansion method. Among the equations of state obtained in this way are Percus-Yevick, Scaled Particle Theory, and Carnahan-Starling equations of state. Also by combining the Monte Carlo results on hard sphere fluid with the asymptotic expansion method many other equations of state for hard sphere fluid can be found where all of them give essentially similar results in the region of isotropic hard sphere liquid, i.e., up to η < 0.5, in which η... 

The Ghotbi-Vera hard sphere equation of state as the reference system, coupled with the mean spherical approximation, (GV-MSA), has been used to accurately correlate the mean ionic activity coefficients of aqueous solutions of single 1:1 electrolytes. The new equation of state considers the ions to be hard spheres in Kelvin tetrakaidekahedron cells. The mean ionic activity coefficients of the electrolytes can be correlated with constant diameter of anions, equal to the crystallographic Pauling diameter and with a concentration dependent relation for the cations. In comparison to their crystallographic Pauling diameters, the new model for the mean ionic activity coefficient produces realistic... 

The predictions of the pair radial distribution function (RDF) at contact value, compressibility factor, and chemical potentials for binary and ternary hard-sphere mixtures obtained with the Barrio-Solana, the Santos et al., and the generalized Lebowitz mixing rules are compared using the Carnahan-Starling, Kolafa, and Khoshkbarchi-Vera one-component hard-sphere EOS. An expression for the pair RDF at contact value for Barrio-Solana mixing rule and the expressions for the chemical potentials in multicomponent hard-sphere fluids are derived. As a general rule, the equations of state obtained based on the generalized Lebowitz mixing rule predict better the pair RDF at contact value simulated... 

Macroscopic properties of granular materials are important in modeling a variety of flow and transport phenomena in many fields of science. Determination of these parameters has always been an issue among both researchers and engineers, mainly in view of tortuosity and permeability. This paper presents analytical functions for the tortuosity and permeability of monosized sphere arrays based on a volume averaging approach and eliminates some ambiguities by modification of the original representative elementary volume model. Veracity of the proposed formulations has been illustrated through comparisons with the latest available results on the subject. Good agreement is found  

Due to unique advantages, the development of high-performance supercapacitors has stimulated a great deal of scientific research over the past decade. The electrochemical performance of a supercapacitor is strongly affected by the surface and structural properties of its electrode materials. Herein, we report a facile synthesis of high-performance supercapacitor electrode material based on CuS nano-hollow spheres with nanoporous structures, large specific surface area (97 m2 g−1) and nanoscale shell thickness (<20 nm). This interesting electrode structure plays a key role in providing more active sites for electrochemical reactions, short ion and electron diffusion pathways and facilitated... 

A new method for structural optimization is presented for successive approximation of the objective function and constraints in conjunction with Lagrange multipliers approach. The focus is on presenting the methodology with simple examples. The basis of the iterative algorithm is that after each iteration, it brings the approximate location of the estimated minimum closer to the exact location, gradually. In other words, instead of the linear or parabolic term used in Taylor expansion, which works based on a short step length, an arch is used that has a constant curvature but a longer step length. Using this approximation, the equations of optimization involve the Lagrange multipliers as the... 

To investigate boiling heat transfer characteristics of nanofluids, transient quenching experiments of a high temperature silver sphere in water-based nanofluids with Ag and TiO2 nanoparticles were performed. A silver sphere with a diameter of 10 mm and an initial temperature of 700 °C was quenched in these nanofluids at a temperature of 90 °C. The results showed a considerable reduction in the quenching ability of nanofluids compared to that of pure water. The presence of nanoparticles in water caused the film boiling mode to vanish at lower temperatures depending on the mixture concentration. Calculated heat transfer rates in nanofluids were lower than those in pure water. In the quenching... 

Hollow carbon spheres (HCS) are spherical forms of carbon materials that can be used as nanocontainers due to their empty cores. In this work, zinc cations were doped in HCS (Zn@HCS) from an aquatic solution of zinc nitrate salt. Corrosion inhibition of released zinc cations in saline solution on bare mild steel samples was assessed by EIS, polarization, and electrochemical noise measurements. The sample surfaces were characterized through FTIR spectroscopy and grazing incidence XRD analyses after exposure to the test solutions. The results showed improvement in the corrosion resistance in the presence of Zn@HCS in a long immersion period. Zn@HCS were also incorporated in organosilane... 

The non-primitive mean spherical approximation (NP-MSA) based models were used to correlate the individual and the mean ionic activity coefficients of the symmetric and asymmetric aqueous electrolyte solutions. The results of the models for the mean ionic activity coefficients were directly used to calculate the osmotic coefficient for the electrolyte solutions studied in this work. In the NP-MSA models, the Ghotbi-Vera and the Boublik-Mansoori-Carnahan-Starling- Leland hard sphere equation of state as the reference system coupled with the non-primitive mean spherical approximation model (NP-GV-MSA and NP-BMCSL-MSA models, respectively). In correlating the mean ionic activity coefficients of... 

A new potential function, which can in a simple and reasonable manner represent the molecular interaction of many kinds of hard-core fluids by varying the value of its parameter, is proposed. For prediction of thermodynamic properties of hard-core fluids such as the square-well (SW) and hard core Lennard-Jones (HCLJ), a simple perturbed equation of state (EOS) is derived by using the new potential function along with the Barker-Henderson perturbation theory. This method yields a simple and general analytical expression for each thermodynamic property of such fluids. The most important feature of these expressions is that they have no adjustable parameter and in some regions in which there is... 

Two new hard-sphere EOS are proposed and tested using the same attractive potential terms used by the SAFT EOS. Generalized expressions for the pair RDF at contact value, the compressibility factor, and the excess chemical potentials have been derived. Extension to mixtures is tested using three mixing rules for multicomponent hard-sphere fluids. The proposed EOS combined with the Santos et al. and the Barrio-Solana mixing rules reproduced the compressibility factors and the excess chemical potentials more accurately than the Boublik-Mansoori-Carnahan-Starling-Leland (BMCSL) EOS. However the pair RDF at contact value had larger deviations than those obtained with the BMCSL EOS. The... 

Finite Element Method (FEM) has proved to be a powerful tool for the analysis of mechanical problems such as finding natural frequency and deformation of structures. Design and implementation of super elements with a purpose in reduction of computational time along with accuracy is one of the challenges facing engineers in the past decade. In this study a newly spherical super element is designed and implemented to some problems. This element is generated in such a way that the user can select as many numbers of nodes as desired. Proper formulation is presented to generate the shape function for each node in this element. Some examples of static and vibration analysis using this element are... 

The Chirikov diffusion in the sphere–ellipsoid binary asteroids through the spin–orbit resonance model is analytically and numerically studied. The primary and the secondary of the binary system are considered sphere and ellipsoid, respectively. The gravitational potential function is expanded up to the fourth-order. The geography of the first- and second-order resonances is derived and studied for different values of asphericity and dynamical flattening of the secondary asteroid and the semimajor axis and eccentricity of the mutual orbit. The Chirikov diffusion due to overlapping of the first- and second-order resonances is examined. For this end, the previously derived criterion for... 

In this article, we propose a three-dimensional model of a low-Reynolds-number swimmer that consists of three small spheres connected to a larger sphere via three perpendicular adjustable rods which enable the micro robot to swim along arbitrary trajectories. Then we focus on dynamic modelling of the swimmer and propose a control method to control the position of the micro swimmer in a low Reynolds number flow. The control aim intended in this article is that the middle sphere to follow a desired trajectory and respective simulation results from control indicates successful accomplishment in application. © 2018 IEEE  

Developing high-performance supercapacitors is of great significance in the area of renewable energies by virtue of having both high energy and power densities. In this work, an innovative strategy is employed for the fabrication of binder-free binary nickel–cobalt-sulfide (NCS) nanosheets (NSs) directly decorated onto the hydrothermal nickel-sulfide (Ni3S2) nanowires (NWs) as the positive electrodes. The NCS/Ni3S2-nickel foam (NF) positive electrodes rendered superior specific capacity of 499.1 mAh.g−1 at 6 A.g−1. Encapsulated iron into the carbon sphere hosts (Fe-HTCSs) are used as the negative counterparts, exhibiting remarkable specific capacitance of 336.6 F.g−1 (at 0.1 A.g−1). The... 

Graphene-based carbon hollow spheres (CHSs) fabrication, doped with 2-mercaptobenzimidazole (MBI) was successfully done in previous work. The active/barrier corrosion protection performance (CPP) of epoxy coatings was evaluated using salt spray test, electrochemical impedance spectroscopy (EIS), and scanning vibrating electrode technique (SVET). Results proved the active/barrier CPP enhancement of epoxy coatings in the presence of 3 wt. % MBI@CHSs. While the presence of MBI and empty CHSs in epoxy coatings did not further improve the active performance. An improvement in the adhesion loss of the epoxy coating, ca. 58 %, was observed in the presence of 3 wt. % MBI@CHSs. © 2021  

Using the newly introduced asymptotic expansion method to obtain equations of state for hard sphere fluid, new simple equations of state for hard disks based on known virial coefficients are derived. Comparison of the obtained equations of state with computer simulation data shows that they are accurate in the whole fluid region. © 2007 Elsevier B.V. All rights reserved