Sharif Digital Repository

In this paper, the coupled thermo–mechanical simulation of hot isostatic pressing (HIPing) is presented for metal powders during densification process. The densification of powder is assumed to occur due to plastic hardening of metal particles. The constitutive model developed is used to describe the nonlinear behavior of metal powder. The numerical modeling of hot powder compaction simulation is performed based on the large deformation formulation, powder plasticity behavior, and frictional contact algorithm. A Lagrangian finite element formulation is employed for the large powder deformations. A modified cap plasticity model considering temperature effects is used in numerical simulation... 

In this paper, the large deformation frictional contact of powder forming process is modeled based on a new computational algorithm by imposing the contact constraints and modifying the contact properties of frictional slip. A simple and efficient numerical algorithm is presented for imposing the contact constraints and frictional contact properties based on the node-to-surface contact technique to simulate the large deformation contact problem in the compaction process of powder. The Coulomb friction law is used to simulate the friction between the rigid punch and the workpiece by the use of penalty approach. A double-surface cap plasticity model is employed together with the nonlinear... 

Single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) were synthesized in aqueous solutions containing FeCl2, FeCl3, FeSO4 and Fe2(SO4)3. The effects of iron charge and the counter ions on the formation of carbon nanotubes (CNTs) were investigated. Thermogravimetric (TG) analysis indicated that carbon multilayer structures including CNTs and multishell graphite particles were formed in deionized (DI) water without the iron precursor. SWCNTs were also synthesized in the presence of the iron ions. It was also found that the mole ratio of [Fe2+]/[Fe3+] in the solution has a significant influence on the purity of CNTs and the process yield. The highest yield was... 

This paper presents a new mechanism with unique and prominent features for a helical swimmer robot. "Double Helices Propulsion Mechanism" consists of two parallel helices with a single axis rotating in the same direction. The outer helix acts as the main propulsion component, and the inner helix, which is made of a Shape Memory Alloy (SMA), controls the forward velocity during swimming. This mechanism, by varying the geometrical parameters of its helical tail, can change the forward velocity of the helical swimmer robot that is required by its predefined missions. In order to study the effects of geometric parameters on the forward velocity in the single helical swimmer, a hydrodynamic model... 

Nowadays there are more than thirty maturity models in different knowledge areas. Maturity model is an area of interest that contributes organizations to find out where they are in a specific knowledge area and how to improve it. As Information Resource Management (IRM) is the concept that information is a major corporate resource and must be managed using the same basic principles used to manage other assets, assessment of the current IRM status and reveal the improvement points can play a critical role in developing an appropriate information structure in organizations. In this paper we proposed a framework for information resource management maturity model (IRM3) that includes ten best... 

Data Envelopment Analysis (DEA) is a method to measure the efficiency of a DMU (Decision Making Unit, e.g. school, public agencies and banks). One of the ways for determining rank of DMUs is efficient score of each DMU. An interesting research issues is to discriminate between efficient DMUs. In literatures, supper efficiency is an applicable method for ranking efficient DMUs. The main drawback of this method is an inability of this method to rank non-extreme efficient DMUs. Therefore, this issue reduces the usefulness of this method. In this paper we propose a new ranking system for non-extreme efficient DMUs (Decision Making Units) based upon the omission of DMUs from reference set of the... 

The purpose of this paper is to present a polynomial time algorithm which determines the lot sizes for purchase component in Material Requirement Planning (MRP) environments with deterministic time-phased demand with zero lead time. In this model, backlog is not permitted, the unit purchasing price is based on the all-units discount system and resale of the excess units is possible at the ordering time. The properties of an optimal order policy are argued and on the basis of them, a branch and bound algorithm is presented to construct an optimal sequence of order policies. In the proposed B&B algorithm, some useful fathoming rules have been proven to make the algorithm very efficient. By... 

In the framework of a household’s collective decision processes, this study presents a structural empirical model to test the hypothesis that child labour is compelled by household’s poverty and parent’s bargaining power against one another. To this end, a measure for mother’s intra-household bargaining power is developed. I use Iranian Household’s Income and Expenditures Surveys (2005 and 2010). Estimation method used in this study is multinomial logit. Findings indicate that household’s poverty is not the sole cause of child’s work incidence. Instead, given the other factors such as poverty, being the first born, local labour market prospect and gender fixed, mother’s bargaining power is... 

Novel types of highly swelling hydrogels were prepared by grafting crosslinked polyacrylamide-co-poly-2-acrylamido-2-methylpropane sulfonic acid (PAAm-co-PAMPS) chains onto sodium alginate (Na-Alg) through a free radical polymerization method. The superabsorbent formation was confirmed by Fourier transform infrared spectroscopic (FTIR). The controlled release behavior of diclofenac sodium (DS) from superabsorbent polymer was factinvestigated, and shown that the release profiles of DS from superabsorbent polymer were slow in simulated gastric fluid (SGF, pH 1.2) over 3 h, but nearly all of the initial drug content was released in simulated intestinal fluid (SIF, pH 7.4) within 21 h after... 

In this study, the effects of pulse current parameters on corrosion resistance and mechanical properties of anodized coatings were evaluated. Hardness measurements, polarization and electrochemical impedance spectroscopy tests were employed to investigate the mechanical properties and corrosion behavior of these coatings. Also, field emission scanning electron microscopy (FE-SEM) was used to analyze the surface morphology and microstructure of the coatings. It was found that the properties of anodized coatings were dependent on various parameters, among which, time, temperature and pulse current parameters (current density limit, frequency and duty cycle) were optimized. Analysis of Variance... 

Calculation of camera projection matrix, also called camera calibration, is an essential task in many computer vision and 3D data processing applications. Calculation of projection matrix using vanishing points and vanishing lines is well suited in the literature; where the intersection of parallel lines (in 3D Euclidean space) when projected on the camera image plane (by a perspective transformation) is called vanishing point and the intersection of two vanishing points (in the image plane) is called vanishing line. The aim of this paper is to propose a new formulation for easily computing the projection matrix based on three orthogonal vanishing points. It can also be used to calculate the... 

Novel types of highly swelling hydrogels were prepared by grafting crosslinked polyacrylic acid-co-poly-2-acrylamido-2-methylpropanesulfonic acid (PAA-co-PAMPS) chains onto κ-carrageenan through a free radical polymerization method. Here, we propose a mechanism for κ-carrageenan-g-PAA-co-PAMPS formation and confirm the hydrogel structure using FTIR spectroscopy. The effect of grafting variables (i.e. concentration of methylenebisacrylamide (MBA), acrylic acid/-2-acrylamido-2-methylpropanesulfonic acid (AA/AMPS) weight ratio, ammonium persulfate (APS), κ-carrageenan, neutralization percent and reaction temperature) were systematically optimized to achieve a hydrogel with a maximum swelling... 

In dealing with human nervous system, the sensation of pain is as sophisticated as other physiological phenomena. To obtain an acceptable model of the pain, physiology of the pain has been analysed in the present paper. Pain mechanisms are explained in block diagram representation form. Because of the nonlinear interactions existing among different sections in the diagram, artificial neural networks (ANNs) have been exploited. The basic patterns associated with chronic and acute pain have been collected and then used to obtain proper features for training the neural networks. Both static and dynamic representations of the ANNs were used in this regard. The trained networks then were employed... 

The subject of the present paper is the investigation of the sharp edged gust effects on the aeroelastic behavior of a flexible wing. It is important to determine the response of the wing to the atmospheric turbulences during normal flight. So, linear modal analysis technique and linear quasi-steady aerodynamic are used for structural modeling and aerodynamic loading, respectively. Also, Lagrange method is used to obtain the system of equations of motion. Using the normal modes of free vibration, structural and aerodynamic matrices can be constructed. Then the aeroelastic instability of the system is determined using p method. Kussner function is used to model the sharp gust effects on the... 

This paper provides an empirical investigation on the individual labor supply of Iranian spouses in an intra-household collective decision framework in which gender ratio and divorce rate play a central role for resource allocation of household. The dataset is taken from the Households’ Expenditures Survey (2008) and the Annual Statistical Yearbook (2008) of Iran. I have conducted the parameters estimation and hypothesis testing using switching regression technique to catch the presence of the widespread non-participation of spouses across Iranian households. Reduced forms of labor supply are estimated considering the endogeneity of wage rates. The findings show that the unitary model of... 

In this research, the flexible flowshop sequence-dependent group scheduling problem with minimisation of makespan as the criterion (FFm|fmls, shgi|Cmax) is investigated. A mixed integer linear mathematical model for the research problem is developed. Since the research problem is shown to be NP-hard, a meta-heuristic algorithm based on memetic algorithm (MA) is developed to efficiently solve the problem. Also, a lower bounding technique based on the developed mathematical model is proposed to evaluate the quality of the proposed MA. The performance of the proposed MA is compared with the existing algorithm in the literature, i.e. tabu search (TS), by solving the available test problems in... 

In this research, a permutation flowshop sequence-dependent group scheduling problem with minimisation of total completion time is considered. Since the problem is shown to be strongly NP-hard, a hybrid genetic (HG) algorithm is proposed. The only available lower bounding (LB) method for the proposed research problem in the literature based on branch and price (B&P) algorithm is also enhanced by proposing efficient method to solve sub-problems and proposing a better branching rule. A statistical comparison shows that both the proposed HG algorithm and the proposed LB have better performance than the other methods from the literature with an average 5.96% percentage gap. [Received 13 December...