Sharif Digital Repository

In the present study, the TiO2 nanotubes were grown on the surface of porous titanium foam by the anodization method. The surface of titanium foam before and after the coating of TiO2 nanotubes was structurally and morphologically characterized by X-ray diffraction (XRD), field emission electron microscope (FESEM) equipped with energy-dispersive X-ray (EDX). Additionally, the cytocompatibility of TiO2-coated porous titanium foam was evaluated by methyl thiazol tetrazolium (MTT) assay. The results have shown that the anatase crystalline phase was formed on the surface with a uniform thickness of 2.5 μm. Finally, TiO2-coated porous titanium foam was biocompatible and significantly enhanced the... 

Integrating implants with the surrounding bone tissue is a significant challenge in medical engineering. A promising option with appropriate biological and mechanical characteristics is porous titanium, which can be employed in mineralizing bones and ingrowth applications. In the present study, titanium foams were fabricated using titanium hydride powder and the following space holders: (1) needle-shaped urea, (2) spherical urea, and (3) cubic sodium chloride. All samples were characterized by means of scanning electron microscopy with an energy-dispersive X-ray spectrometer, X-ray diffraction, and mechanical compression testing. Our results revealed that powder metallurgy is suitable for... 

Conductive self -electrical stimuli bioactive scaffolds could be used the potential for peripheral nerve regeneration with the maximum efficiency. To produce such conductive self-electrical stimuli bioactive scaffolds, chopped spun piezoelectric nanofibers of polyvinylidene fluoride/mesoporous silica nanoparticle (PVDF/MCM41) are prepared and incorporated in gellan/polyaniline/graphene (gellan/PAG) nanocomposites which have been previously prepared by incorporation of polyaniline/graphene (PAG) nanoparticles in gellan gel at 80 °C. Highly conductive binary doped polyaniline/graphene nanoparticles are prepared by chemical oxidative polymerization of aniline monomer using in-suite... 

Mechanical alloying and sintering were used to fabricate nanostructured Ti6Al4V scaffolds of highly controllable pore geometry and fully interconnected porous network. Elemental powders were milled for different periods of time (10, 20, 30, 40 and 60 h), mixed with 40-60 vol.-% of 200-400 μm cuboidal NaCl, compacted at 500-600 MPa and sintered according to single or double stage heat treatment regimes at 790 and 950°C under vacuum. After sintering, the samples were soaked in distilled water to washout the NaCl. Foamy microstructures were obtained showing well shaped biopores and fragmentary embedded micropores. The shape of initial NaCl was copied into the biopores which had highly... 

Gel-fiber structure with the potential of extracellular matrix (ECM) mimics can be introduced as a suitable candidate for bioengineering applications. In this study, piezoelectric gellan gel-fiber was prepared with incorporating poly(vinylidenefluoride) (PVDF)/glass-flake in the gellan matrix. Glass-flake nanoparticles were modified with silane group, PVDF/glass-flake nanofibers were synthesized and short-strand nanofibers were fabricated using the mechanical homogenizer method. Brunauer–Emmett–Teller (BET), Fourier-transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA) analyses were used for surface modification study, and scanning electron microscopy (SEM),... 

Gel-fiber structure with the potential of extracellular matrix (ECM) mimics can be introduced as a suitable candidate for bioengineering applications. In this study, piezoelectric gellan gel-fiber was prepared with incorporating poly(vinylidenefluoride) (PVDF)/glass-flake in the gellan matrix. Glass-flake nanoparticles were modified with silane group, PVDF/glass-flake nanofibers were synthesized and short-strand nanofibers were fabricated using the mechanical homogenizer method. Brunauer–Emmett–Teller (BET), Fourier-transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA) analyses were used for surface modification study, and scanning electron microscopy (SEM),... 

Marvelous bending/straightening effects of two-way shape memory alloy (TWSMA) help their employment in design and manufacturing of new medical appliances. Constrained ageing with bending load scheme can induce two-way shape memory effect (TWSME). Scanning electron microscopic (SEM) analysis, electrical resistivity measurement (ERM) and differential scanning calorimetry (DSC) are employed to determine the property change due to flat strip constrained aging. Results show that flat-annealing prior to the aging shifts NiTi transformations temperatures to higher values. Superelastic behavior of the as-received/flat- annealed/aged samples with more adequate transition temperatures due to... 

Creating laser texture on dental implants is a novel method for accelerating osseointegration and prolongation of lifespan. The purpose of this research was twofold: (1) Creating intersecting lines pattern with different angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°) on the surface of Ti6Al4V, using pulse Nd:YAG laser with a wavelength of 1064 nm and a pulse length of 170 ns and (2) comparing optical and SEM images, EDS analyses, contact angles (CAs), and surface free energies (FEs) for different intersecting lines angles. CA and FE depended on the intersecting lines angle according to Y = Y 0 + A sin (x B + C), where Y is the CA or FE; x is the intersecting lines angle; and Y0, A, B, and C... 

Pharmaceutical drug Research and Development (R&D) outsourcing to contract research organizations (CROs) has experienced a significant growth in recent decades and the trend is expected to continue. A key question for CROs and firms in similar environments is which projects should be included in the firm's portfolio of projects. As a distinctive contribution to the literature this paper develops and evaluates a business support tool to help a CRO decide on clinical R&D project opportunities and revise its portfolio of R&D projects given the existing constraints, and financial and resource capabilities. A new mathematical programming model in the form of a capital budgeting problem is... 

An important manufacturing technology spectrum is to consider rapid and sensitive assemblies through convergent product (CP) in digital environment. We integrate functions and sub-functions using a comprehensive mathematical optimization process. To form the CP, a web-based fuzzy network is considered in which a collection of base functions and sub-functions configure the nodes and each arc in the network is to be a link between two nodes. The aim is to find an optimal tree of functionalities in the network adding value to the product in the web environment. First, a purification process is performed in the product network to assign the links among bases and sub-functions. Then, fuzzy... 

We propose a methodology to determine value by adding functionalities for convergent products. A collection of base functions and sub-functions configure the nodes of a web-based (digital) network representing functionalities. Each arc in the network is to be assigned as the link between two nodes. The aim is to find an optimal tree of functionalities in the network adding value to the product in the web environment. First, a purification process is performed in the product network to assign the links among bases and sub-functions. Then, numerical values as benefits and costs are determined for arcs and nodes respectively, using a mathematical approach. Finally, the Steiner tree methodology... 

In the proposed work, by applying the Steiner tree, a bi-objective mathematical model is developed to consider promotion of convergent products to satisfy two objectives of cost and benefit. The results are some new products with more utility for both the buyer and the producer. The methodology proposed to determine value adding functionalities for convergent products. A collection of base functions and sub-functions configure the nodes of a web-based (digital) network representing functionalities. Each arc in the network is to be assigned as the link between two nodes. The aim is to find an optimal tree of functionalities in the network adding value to the product in the web environment.... 

The effects of both Li modification and cooling rate on the microstructure and tensile properties of an in situ prepared Al-15%Mg2Si composite were investigated. It was found that the addition of 0.3%Li reduces the average size of Mg2Si primary particles from ∼30 to ∼6 μm. The effect of cooling rate was investigated by the use of a mold with different section test bars. The results showed an increase in both UTS and elongation values with reduction in section thicknesses corresponding to increasing cooling rates. Adding Li also raised the tensile strength and elongation values and reduced the number of decohered particles observed in fracture surfaces thereby increasing the alloy's... 

We consider nonlinear optimization problems constrained by a system of fuzzy relation equations. The solution set of the fuzzy relation equations being nonconvex, in general, conventional nonlinear programming methods are not practical. Here, we propose a genetic algorithm with max-product composition to obtain a near optimal solution for convex or nonconvex solution set. Test problems are constructed to evaluate the performance of the proposed algorithm showing alternative solutions obtained by our proposed model  

We are concerned with the design of a model and an algorithm for computing the shortest path in a network having various types of fuzzy arc lengths. First, a new technique is devised for the addition of various fuzzy numbers in a path using α-cuts by proposing a least squares model to obtain membership functions for the considered additions. Due to the complexity of the addition of various fuzzy numbers for larger problems, a genetic algorithm is presented for finding the shortest path in the network. For this, we apply a recently proposed distance function for comparison of fuzzy numbers. Examples are worked out to illustrate the applicability of the proposed approach  

We address the two-stage assembly scheduling problem where there are m machines at the first stage and n assembly machines at the second stage under lot sizing environment. Lot streaming (lot sizing) means breaking a lot into some sublots, where each sublot is transferred to the next machine for continuing operations. This problem can be considered as a production system model consisting of production stage and assembly stage. If different production operations are done in parallel machines independently, then the manufactured parts transferred to the next stage are assembled with purchased parts at n machines according to the operation process chart to produce the final products. Here,... 

We propose an approach for computing the product of various fuzzy numbers using a-cuts. A regression model is used to obtain the membership function of the product. Then, we make use of the approach to compute solutions of fully fuzzy linear systems. We also show how to compute solutions of fully fuzzy linear systems with various fuzzy variables. Examples are worked out to illustrate the approach. Copyright © 2018 Inderscience Enterprises Ltd  

In cloud investment markets, consumers are looking for the lowest cost and a desirable fairness while providers are looking for strategies to achieve the highest possible profit and return. Most existing models for auction-based resource allocation in cloud environments only consider the overall profit increase and ignore the profit of each participant individually or the difference between the rich and the poor participants. This paper proposes a multi-dimensional fairness combinatorial double auction (MDFCDA) model which strikes a balance between the revenue and the fairness among participants. We solve a winner determination problem (WDP) through integer programming which incorporates the... 

Recent uses of intelligent composites in biomedical appliances aggrandize the necessity of bonding-strength improvement in NiTi/silicone matrix interface. SEM micrographs and pull-out tests are employed to determine the strength of the NiTi/silicone bonds in a flexible composite piece. Greater adhesion strengths are obtained due to the presence of thin oxide layer, surface roughness and frictional forces between the embedded-wires and the contacting phase. Effect of curing treatment on phase transformation temperatures of the wires is determined by electrical resistivity (ER) measurements. Results show that the curing treatment shifts the transition points of the wires towards higher...