Sharif Digital Repository

Several methods have been developed in the past for analyzing the porosity and other types of well logs for large-scale porous media, such as oil reservoirs, as well as their permeability distributions. We developed a method for analyzing the porosity logs φ(h) (where h is the depth) and similar data that are often nonstationary stochastic series. In this method one first generates a new stationary series based on the original data, and then analyzes the resulting series. It is shown that the series based on the successive increments of the log y(h)=φ(h+δh)-φ(h) is a stationary and Markov process, characterized by a Markov length scale hM. The coefficients of the Kramers-Moyal expansion for... 

Solute-solvent and solvent-solvent interactions were investigated for binary mixtures of an ionic liquid (IL) 2-hydroxy ethylammonium formate as with methanol, ethylene glycol and glycerol. The physicochemical properties of the solvent mixtures at 25 °C, over the whole range of mole fractions, were determined using solvatochromic probes. High normal polarity (ETN) in the alcohol-rich region confirms solute-solvent interactions in this medium. Dipolarity/polarizability (π *) show a different trend to ETN with a positive deviation from ideal behavior in IL-glycerol mixtures. However, these deviations for other solvent mixtures are insignificant. Contrary to what is observed for E TN and π*,... 

Biomass residues due to their low bulk density typically require frequent transportation from biomass plantations in rural areas to conversion bio-energy power plants. This issue contrasts with environmental protection strategies, especially when power plants are facing different carbon reduction policies that enforce them to emit less than a given specific carbon amount. Although several researchers have investigated bio-energy supply chains concerning environmental policies, the majority of studies have been devoted to strategic decisions over a single planning period. This paper presents a multi-period bio-energy supply chain under carbon pricing (carbon tax) and carbon trading... 

In this paper, the soave-Redlich-Kwong (SRK) Eos is modified based on perturbation theory. The parameter of the new cubic equation of state considered reduced temperature and a centric factor dependent. The average of absolute deviations of predicted vapor pressure, vapor volume and saturated liquid density of 30 pure compounds are 0.814.2.G14 and 5.814%, respectively. Also comparison with the new equation of vaporization of pure compounds are given. The florry-Hugines (FH) model is similarly modified by an adjustable parameter. This parameter is defined based on molecular weight of asphaltene to molecular weight of heavy oil ratio in form of polynomial function. The phase behavior of... 

Calendula alata plants were tested for their potential to remove stable cesium and lead from solutions in a 15-day period. The plants were grown hydroponically and placed in solutions containing CsCl and Pb(C 2H 3O 2)2 at different concentrations (0.6, 2 and 5 mg l-1). When plants were incubated in CsCl solutions 46.84 ± 2.12%, 41.35 ± 1.59%, and 52.06 ± 1.02% cesium was found to be remediated after 15 days. Moreover, more than 99% lead was removed from the Pb(C 2H 3O 2)2solution in all three concentrations after 15 days during the same period. When both CsCl and Pb(C 2H 3O 2)2were supplemented together in the solution, 9.92 ± 1.22%, 45.56 ± 3.52%, and 46.16 ± 1.48% cesium and 95.30 ± 0.72%,... 

Surfaces and interfaces behave differently from their bulk counterparts especially when the dimensions approach small scales. The recent studies have shown that the surface/interface free energy (surface stress) plays an important role in the effective mechanical properties of solids with nanosized inhomogeneities. In this work, within a micromechanical framework, the effect of surface stress is taken into account to obtain a macroscopic yield function for nanoporous materials containing cylindrical nanovoids. Gurtin-Murdoch model of surface elasticity is incorporated in the generalized self-consistent method to obtain a closed-form expression for the transverse shear modulus of transversely... 

Today, many limitations are faced in sludge treatment and disposal. Therefore evaluation of different approaches to reduce sludge production in the activated sludge process has attracted great attention. Application of ultrasonic waves in sludge treatment caused to reduce sludge volume and accelerate sludge digestion. This research intended to study the efficiency of ultrasound in dewatering biological sludge in wastewater treatment plants under different conditions. In this study, response surface method was used to investigate results and optimum conditions were determined. Sludge was treated in different conditions as follows: 330–920 W ultrasound power, 1.5–3.9 L sample volume and... 

The impact behavior of aluminum/epoxy laminates was studied by changing the number of layers and the interface strength. It should be noted that although the overall thickness did not changed, the individual layers decreased in thickness when the number of layers increased. The results indicate that the impact resistance of the laminate increases with the number of layers, while the interface strength has a less pronounced influence (50%) on the impact resistance of the laminate. It is also deducted that if the ratio of layer thickness to plastic zone size is smaller than or equal to 1, the impact behavior of the laminates is sensitive to the interface strength. © 2008 Elsevier Ltd. All... 

It is well known that strain localization and indeed displacement discontinuity can arise in materials exhibiting plastic behaviour. Indeed such localization is almost certain to occur if strain softening or non-associated behaviour exists, though it can be triggered even when ideal plasticity is assumed. This study is concerned mainly with the manner in which the numerical discretization process has to be devised so as to capture the localization phenomenon. In this paper, a method is presented for applying the mixed formulation to study the prediction of localization phenomenon in powder-forming processes. This study is focused on the performance of mixed u - π triangular elements to study... 

The effects of Sr additions, heat treatment (T4 and T6), and multi-directional forging on the microstructural evolution, mechanical properties and biodegradability of Mg-4Zn-xSr alloys were investigated. Corrosion behavior of the alloys was evaluated by the polarization and hydrogen evolution tests. Shear punch and hardness tests were employed to determine the mechanical properties. It was found that mechanical properties and corrosion resistance of the as-cast Mg-4Zn alloy increased by 0.3 wt% Sr addition. However, further increasing the Sr content not only did not improve the mechanical strength, but also had detrimental effects on the corrosion resistance, due to the increased size and... 

In this paper, a double-surface plasticity model, based on a combination of a convex yield surface consisting of a failure envelope, such as a Mohr-Coulomb yield surface and, a hardening cap model, is developed for the nonlinear behaviour of powder materials in the concept of a generalized plasticity formulation for the description of cyclic loading. This model reflects the yielding, frictional and densification characteristics of powder along with strain and geometrical hardening which occur during the compaction process. The solution yields details on the powder displacement from which it is possible to establish the stress state in the powder and the densification is derived from... 

Co/SBA-15 nanoparticle catalysts (CoNP) were prepared using a commonly adapted synthetic route and then utilised for esterification and amidation reactions using aromatic and linear chain compounds for the production of long chain esters and amides. The study shows that the use of CoNP catalysts favours the use of aromatic reactants with electron donating substituents specifically in the para position. For the amidation reaction, good to excellent yields were obtained demonstrating tolerance towards differently substituted aromatic compounds. Overall, the synthesized catalysts proved to be efficient and highly versatile, and recyclable under the investigated conditions  

Controlled graphitization has become known as a practical method for improvement of wear resistance and machining properties in steels. In this paper, the effect of heat treatment on microstructure of CK45 steel has been investigated. Austenitising was carried out at 920 °C for 5 h. Besides, isothermal transformation was conducted at 750 °C in the time range of 1-20 h. In this work, full potential carbon resource was tried to be used around samples as a factor to prevent the burning of the limited carbon in steel and also to increase the percentage of sample surface carbon in order to improve wear capability and machining. The microstructure of the steel considerably changes by this heat... 

Carbon nanotubes (CNTs) have been recently taken into consideration as mechanical resonators of distinguished capabilities. This study aims at investigating the free vibration characteristics of a single-walled CNT in the vicinity of a fully constrained graphene sheet. Using a molecular structural mechanics model and considering nonlinear van-der-Waals interactions, the static deformation of the nanotube is obtained using an iterative procedure. Then, the governing equations of motion are linearized about the static equilibrium state and the natural frequencies are obtained. The molecular structural mechanics model is verified using established results in literature and then a survey is... 

The flowshop sequence dependent group scheduling problem with minimization of makespan as the objective (F m |fmls, S plk, prmu|C max ) is considered in this paper. It is assumed that several groups with different number of jobs are assigned to a flow shop cell that has m machines. The goal is to find the best sequence of processing the jobs in each group and the groups themselves with minimization of makespan as the objective. A mathematical model for the research problem is developed in this paper. As the research problem is shown to be NP-hard, a hybrid ant colony optimization (HACO) algorithm is developed to solve the problem. A lower bounding technique based on relaxing a few... 

In this paper, for the first time, we present a small signal circuit model of quantum dot laser considering two photon modes, i.e., ground and first excited states lasing. By using the presented model, effect of temperature variations on modulation response of quantum dot laser is investigated. Simulation results of modulation response are in agreement with the numerical and experimental results reported by other researchers  

In this study, the instability of spinning cylindrical shells partially filled with viscous liquid is investigated. Based on the Navier-Stokes equations for the incompressible flow, a 2D model is developed for liquid motion at each section of the cylinder. The governing equations of the cylinder vibrations are obtained based on the first-order shear deformable shell theory. The nonpenetration and no-slip boundary conditions of the flow on the wetted surface of the cylinder relate the liquid motion to the shell vibrations. Also the liquid pressure exerted on the cylinder wall combines the vibrations of the rotary cylinder to the liquid motion. By using the obtained coupled liquid-structure... 

Enzymatic decolorization of reactive blue 221 (RB221) using laccase was investigated in a dual-chamber microbial fuel cell (MFC). Suspended laccase was used in the cathode chamber in the absence of any mediators in order to decolorize RB221 and also improve oxygen reduction reaction in the cathode. Molasses was utilized as low cost and high strength energy source in the anode chamber. The capability of MFC for simultaneous molasses and dye removal was investigated. A decolorization efficiency of 87% was achieved in the cathode chamber and 84% COD removal for molasses was observed in the anode chamber. Laccase could catalyze the removal of RB221 and had positive effect on MFC performance as... 

In this paper, a new zero-voltage-switching high power-factor (PF) rectifier with Line-Modulated Fixed-Off-Time current control is introduced, that off time is a function of the instantaneous line voltage. The auxiliary circuit provides soft switching for all semiconductor devices, without any extra current and voltage stress on the main switches. The proposed converter is bridgeless, and all semiconductor devices are soft switched. In addition, there is no extra stress on the switches. Thus, the conduction and switching losses are reduced and maximum efficiency is achieved. A 250W, with an input ac voltage of 90265 Vrms and an output voltage 400 Vdc, 100 kHz is designed and simulated to... 

In this paper, a new zero-voltage-switching, high power-factor, bridgeless rectifier is introduced. In this topology, an auxiliary circuit provides soft switching for all of the power semiconductor devices. Thus the switching losses are reduced and the highest efficiency can be achieved. The proposed converter has been analyzed and a design procedure has been introduced. The control circuit for the converter has also been developed. Based on the given approach, a 250 W, 400 Vdc prototype converters has been designed at 100 kHz for universal input voltage (90-264 Vrms) applications. A maximum efficiency of 94.6% and a power factor correction over 0.99 has been achieved. The simulation and...