Sharif Digital Repository

Integration of forward osmosis (FO) and osmotically assisted reverse osmosis (OARO) provides low energy consumption and controlled fouling for brine treatment. This study explains the membrane properties required for cost–optimal OARO-based systems. A detailed model accounting for the relationship between burst pressure, permeate spacer gap, and structural parameters of OARO membranes was implemented with woven and non-woven spacers. Results indicate that the tradeoff between internal concentration polarization (ICP) and permeate–side pressure drop in OARO stages is a crucial consideration for optimal membrane element design. Due to the lower ICP of no-woven spacers, a system using non-woven... 

In this paper, we study a supply chain problem where a whole seller/producer distributes goods among different retailers. Such problems are always faces with uncertainty with input data and we have to use various techniques to handle the uncertainty. The proposed model of this paper considers different input parameters such as demand, capacity and cost in trapezoid fuzzy forms and using two ranking methods, we handle the uncertainty. The results of the proposed model of this paper have been compared with the crisp and other existing fuzzy techniques using some randomly generated data. The preliminary results indicate that the proposed models of this paper provides better values for the... 

This study aims at analyzing the performance of three units known as low salt rejection reverse osmosis (LSRRO), split-feed counterflow reverse osmosis (SF-CFRO), and split-brine counterflow reverse osmosis (SB-CFRO) and implementing them in a modified multi-stage multi-feed counter-current membrane with cascade recycle for dewatering hypersaline streams to the salinity appropriate for crystallizers' feed. Exergy and primitive pinch analysis showed that dewatering is limited in SF-CFRO as the permeate inlet dictates the maximum salinity difference at the pinch point as well as high frictional pressure loss in the permeate channel. SB-CFRO and LSRRO units can reach high salinities by... 

Purpose: Lack of a consistent standardized housing pricing system in Iran has led housing valuation to become solely dependent on appraisers' opinions. The purpose of this paper is to investigate some behavioral aspects of real estate decision makers, i.e. buyers and appraisers. Design/methodology/approach: First, and based on a content analysis of the valuation literature, a preliminary housing valuation model is proposed. This model is then contextualized and tested on two separate samples of 23 appraisers and 145 buyers, using interviewing technique and self-administered questionnaires. Findings: This study shows that buyers and appraisers may have different views about property valuation... 

Abstract New bi-anchoring donor-π-acceptor metal-free organic dyes based on diphenylamine as donor, and barbituric acid and thiobarbituric acid as the acceptor/anchor were synthesized, characterized and used in dye-sensitized solar cells applications. Among the fabricated dye sensitized solar cells, device based on the diphenylamine as donor, and barbituric acid as the acceptor exhibits a high power conversion efficiency of 1.53% with a short circuit current density of 3.71 mA cm-2, an open-circuit photo voltage of 0.55 V and a fill factor of 0.75% under AM 1.5 illumination (85 mW cm-2) compared to the other fabricated devices. The structure of synthesized dyes was optimized and their... 

In this study, cobalt-ruthenium nanocatalysts supported on nitrogen-doped graphene aerogel (NGA) and carbon nanotubes (CNT) were synthesized using the wet impregnation method for Fischer-Tropsch process with a cobalt to ruthenium ratio of 1:50. The synthesized catalysts underwent various characterizations such as FTIR, ICP, BET, XRD, EDX, TPR and TEM. The performance of the synthesized catalysts was compared to that of a cobalt-ruthenium nanostructured catalyst supported on NGA and CNTs. The catalysts were evaluated in a fixed-bed reactor at 25 bar, with a gas ratio H2/CO: 2 and Gas Hourly Space Velocity (GHSV) 10,000 mlg-1h-1, at temperatures of 260 °C and 280 °C. The use of NGA as a cobalt... 

In this paper, modified Adomian decomposition (MAD) is introduced to investigate the effect of the Casimir attraction on pull-in instability of beam-type NEMS theoretically. Two engineering cases including cantilever and double cantilever nano-beam are considered. The proposed MAD method is employed to solve the nonlinear constitutive equation of nano-beams. The basic engineering parameters such as critical deflection and pull-in voltage of nano-beams are computed. It is found that the Casimir forces decrease the pull-in deflection and voltage of nano-beams. On the other hand, the fringing field increases the pull-in deflection while decreases the pull-in voltage of the actuators. As a... 

Fatigue behavior of quasi-isotropic carbon/epoxy laminates were studied, using six stacking sequences. Experimental results show that there is a significant stacking sequence effect on monotonic and cyclic performance of laminates. Though by changing the stacking sequence the difference between failure strength of the strongest and weakest lay-ups reaches only to ∼ 12 %, the difference between fatigue lives (cycles to failure) increased ∼ 1000% in some loading regions. In addition, both linear and sigmoidal functions were examined to model the fatigue life behavior  

In the current investigation, four novel donoracceptor type organic dyes including (DPA-Ba, DPA-Hy, DPA-Rh, DPA-Cy), are proposed and their photophysical and electrochemical properties as well as dye-sensitized solar cell performance are systematically investigated. Among these dyes diphenylamine is utilized as an-electron donor while barbituric acid, hydantoin, rhodanine-n-acetic acid and cyano acetic acid, are proposed as anchoring groups as dye-sensitized solar cells (DSSCs). The synthesized dyes are characterized using FT-IR, NMR, mass spectrometry, absorbance and electrochemical measurements. The photophysical, electrochemical and photovoltaic properties of the solar cells based on... 

In this study, zirconia antistatic coatings were synthesized by a simple dip coating sol-gel route on glass substrates, then applied to polymer-based composites to potentially improve their dust or water repellent capabilities. The coating solution contained a precursor (ZrCl4), solvent (isopropanol) and coupling agent. FTIR spectra confirmed ZrO2 and ZrO compounds in both solution and antistatic coating. FE-SEM images indicated ZrO2 fibers’ thickness was controlled by changing ZrCl4 concentration (150 g–15 g ZrCl4/l) or relative humidity (20%–60%) during coating drying. Fibers grew thicker when decreasing the former or increasing the latter. The surface electrical resistivity for all... 

Recent observations of gravitational waves motivate investigations for the existence of primordial black holes (PBHs). We propose the observation of gravitational microlensing of distant quasars for the range of infrared to the submillimeter wavelengths by sublunar PBHs as lenses. The advantage of observations in the longer wavelengths, comparable to the Schwarzschild radius of the lens (i.e., Rsch≃λ) is the detection of the wave optics features of the gravitational microlensing. The observation of diffraction pattern in the microlensing light curve of a quasar can break the degeneracy between the lens parameters and determine directly the lens mass as well as the distance of the lens from... 

This paper presents the kinematic and dynamic modeling of a two degrees of freedom manipulator attached to a vehicle with a two degrees of freedom suspension system. The vehicle is considered to move with a constant linear speed over an irregular ground-surface while the end-effector tracks a desired trajectory in a fixed reference frame. In addition, the effects of highly coupled dynamic interaction between the manipulator and vehicle (including the suspension system's effects) have been studied. Finally, simulation results for the end-effector's straight-line trajectory are presented to illustrate these effects  

Partial discharges are well known as a source for insulation degradation in power transformers. A hybrid transformer model is introduced to simulate the transformer winding transient response. Transformer structural data is used to determine the hybrid model parameters. Calculations of the hybrid transient model parameters are based on the parameters of the lumped parameter equivalent transformer model and electromagnetic rules. Modern computation techniques and optimizations are employed beside this model for PD location using the multi conductor transmission line model and also to analyze its propagation aimed at achieving (i) more reliable simulation results (ii) less computational time... 

This study outlines the necessary and sufficient criteria for swarm stability asymptotically, meaning consensus in a class of fractional-order multi-agent systems (FOMAS) with interval uncertainties for both fractional orders 0 < α < 1 and 1 < α < 2. The constraints are determined by the graph topology, agent dynamics, and neighbor interactions. It is demonstrated that the fractional-order interval multi-agent system achieves consensus if and only if there are some Hermitian matrices that satisfy a particular kind of complex Lyapunov inequality for all of the system vertex matrices. This is done by using the existence condition of the Hermitian matrices in a Lyapunov inequality. To do this,... 

Asymmetric contact problem of an elastic wedge and an elastic half-plane has been considered. Contact pressure distributions as well as the lengths of the contact zones are extracted analytically. The results have been compared with the results of the symmetric problem and also the FE modelling of the problem which show excellent agreement. The method of approach is a completely analytical method based on the singular integral equations. In this method, the boundary conditions of the problem are stated as some singular integrals and distribution of the contact pressure is determined. Then, with the aid of the equilibrium equations and the consistency conditions of the singular integral... 

In order to be a powerful tool, finite-element and finite-volume methods must be capable of handling complex flow in complex geometries. In this work, a structured finite volume element method is suitably developed for solving incompressible flow on a collocated grid topology. The method is generally-applicable to arbitrarily shaped elements and orientations and, thus, challenges the potential to unify many of the different grid topologies into a single formulation. The correct estimation of the convec-tive and diffusive flux terms at cell faces remarkably enhances the solution accuracy of the extended formulation. It is shown that the current formulation is enough robust to treat any... 

Arbitrary Lagrangian Eulerian (ALE) method is widely used for simulation of large deformation problems, such as metal forming. However, in many such applications, modeling of the heat generation and transfer in conjunction with the stress analysis is necessary. In this work, a fully coupled dynamic ALE formulation is developed. The ALE form of energy balance equation is derived, and is coupled with the dynamic, rate dependent ALE stress analysis. The proposed formulation is used for simulation of a few thermo-mechanical problems. The effectiveness and efficiency of the ALE method is verified by comparing the results of this simulation with available experimental and numerical results