Sharif Digital Repository

In this paper the setup assembly line balancing and scheduling problem (SUALBSP) is considered. Since this problem is NP-hard, a hybrid genetic algorithm (GA) is proposed to solve the problem. This problem involves assigning the tasks to the stations and scheduling them inside each station. A simple permutation is used to determine the sequence of tasks. To determine the assignment of tasks to stations, the algorithm is hybridized using a dynamic programming procedure. Using dynamic programming, at any time a chromosome can be converted to an optimal solution (subject to the chromosome sequence). Since population diversity is very important to prevent from being trapped in local optimum... 

Tolerances naturally generate an uncertain environment for design and manufacturing. In this paper, a novel fuzzy based tolerance representation approach for modeling the variations of geometric features due to dimensional tolerances is presented. The two concepts of fuzzy theory and small degrees of freedom are combined to introduce the fuzzy-small degrees of freedom model (F-SDOF). This model is suitable for tolerance analysis of mechanical assemblies with linear and angular tolerances. Based on the fuzzy concept, a new index (called the assemblability index) is introduced which signifies the fitting quality of parts in the assembly. Graphical and numerical representations of tolerance... 

Morphology tailored TiO2 nano assemblies consisting of nanorods with and without nanoparticle attachments were hydrothermally synthesized and their characteristics and light scattering properties were determined by x-ray diffraction (XRD), nitrogen sorption analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS) and ultraviolet-visible spectroscopy (UV-Vis). The nanorod-nanoparticles (NR-NP) assemblies and smooth nanorod (NR) double layers were screen printed onto fluorine doped tin oxide coated glass underlayers to fabricate dye-sensitized solar cell (DSSC) photoanodes. The double layer heterogeneous... 

A new facile strategy for preparation of mesoporous anatase-TiO2 films by a combination of sol–gel and evaporation-induced self-assembly (EISA) processes aided by tri-block Pluronic F127 is reported. Two major parameters, sol preparation and EISA processing parameters, are identified for preparation of mesoporous crack-free films with desired thickness. The mesoporous crack-free films with thickness of 650 nm can be obtained with low water: precursor molar ratio (e.g., 2.5:1) under aging in 10 % relative humidity for 72 h at the low temperature of 5 °C. Although template: precursor molar ratio and annealing temperature show little influence on preparation of crack-free films the optimum... 

The light scattering and harvesting effects in dye-sensitized solar cells (DSSCs) is studied by controlling morphology, phase composition, and thickness of monolayer and double-layer TiO2 photoanode electrodes. The starting materials for preparation of TiO2 cells, including 25 nm mesoporous anatase nanoparticles, 200 nm anatase microspheres, 10 µm dandelion-like rutile particles and 40 nm nanoparticles containing 80% anatase-20% rutile, are synthesized by evaporation-induced self-assembly, sol-gel, and hydrothermal processes. It was found that the mesoporous anatase nanoparticles may improve light harvesting and dye-sensitization due to their high surface area and small particle size,... 

An accurate and fast method for guided modes extraction in monolayer colloidal crystals and their inverse replicas is presented. These three-dimensional structures are composed of a monolayer of spherical particles that can easily and simply be prepared by self-assembly method in close packed hexagonal lattices. In this work, we describe how the guided modes, even or odd modes and light cone boundary can be easily determined using phase variations of reflection and transmission coefficients. These coefficients are quickly calculated by Fourier modal method. The band structures are obtained for a monolayer of polystyrene particles and two-dimensional TiO2 inverse opal by this proposed method  

In this paper, a simultaneous lead time quotation and lot sizing problem in an assembly system is investigated. We address a production system with a product that has deterministic demand over a T-period planning horizon and is produced in lots because of the economy of scale. If a lot is completed before the demand period, inventory carrying cost is incurred. On shortages, a lead time is quoted to customers and a lead time quotation cost is incurred. Finally, if the order is delivered later than its due date period, a tardiness cost is charged. The components supply lead time is stochastic, which follows a discrete distribution. The problem is to decide on the lot size of products and... 

Specific and sensitive electroanalysis of blood-circulating protein cancer biomarkers is often complicated by interference from serum proteins nonspecifically adsorbing at the biosensing interface and masking specific reactions of interest. Here, we have developed an electrocatalytically amplified assay for specific and sensitive analysis of human epidermal growth factor receptor-2 (HER-2/neu, a protein cancer biomarker over-expressed in breast cancers) that allows us to avoid both the interference from bovine serum albumin (BSA) and electrocatalytic amplification of the signal stemming from the specific aptamer−HER-2/neu binding. A HER-2/neu-specific thiolated aptamer sequence was... 

Optimal tolerance design is a time-consuming and multi-disciplinary procedure and involves several aspects of design, manufacturing, quality and cost problems. In addition, the quality of assemblies can be significantly affected by the flexibility of components which has not been considered in most of the previous research. In this paper, a new method is proposed for multi-objective optimal tolerance design of compliant assemblies based on an integrated Kriging meta-modelling–NSGA-II–Shannon’s Entropy TOPSIS algorithm. The tolerance propagation of flexible components in the assembly process is modelled through the enhanced Method of Influence Coefficients (MIC). Geometrical variations of key... 

Using low molecular weight polyethylenimine (PEI), transparent thin films of TiO2 nanoparticles were prepared by layer-by-layer self assembly method. UV-visible spectrophotometry was employed in a quantitative manner to monitor the adsorbed mass of TiO2 and PEI after each dip cycle. The adsorption of both TiO2 and PEI showed a saturation dip time of 10 min. The effect of dip time on the growth mode and surface morphology was investigated by scanning electron microscopy (SEM) and non-contact atomic force microscopy (AFM). It was found that growth proceeds in the form of laterally broad islands in case of short dip times, and taller but laterally smaller islands in case of longer dip times. A... 

Optimal tolerance design is a time-consuming and multi-disciplinary procedure and involves several aspects of design, manufacturing, quality and cost problems. In addition, the quality of assemblies can be significantly affected by the flexibility of components which has not been considered in most of the previous research. In this paper, a new method is proposed for multi-objective optimal tolerance design of compliant assemblies based on an integrated Kriging meta-modelling–NSGA-II–Shannon’s Entropy TOPSIS algorithm. The tolerance propagation of flexible components in the assembly process is modelled through the enhanced Method of Influence Coefficients (MIC). Geometrical variations of key... 

Nanoparticle halo mechanism is a stabilization method for microparticle suspensions. This study investigates suspension pH and nanoparticles–microparticles collision effects on the stabilization of an aqueous binary suspension. The long-term turbidity measurements show that for the nanosilica suspension stability is directly correlated with pH values; however, in the cases of zirconia and binary suspensions, it is not a monotonic function of pH. It is shown that for binary suspension, the halo mechanism is the primary method affecting the stability of the suspension. The suspension is best-stabilized at pH = 5 that is associated with high halo mechanism efficiency, while increased repulsive... 

Supported Pt–TiO₂ photocatalysts on carbonaceous supports were synthesized by the electrostatic self-assembly method to study CO₂ photoreduction to produce CH₄. Catalytic activities of the prepared photocatalysts were correlated with the particle size and dispersion of the active metal, which in turn depended on the type of carbonaceous support used, varying in the order of multi-walled carbon nanotubes (MWCNT) > Single-walled carbon nanotubes (SWCNT) > reduced graphene oxide > activated carbon. Generally, all catalysts were highly photoresistant with less than 5% loss of activity in terms of CH₄ yield. Pt–TiO₂/multi-walled carbon nanotubes exhibited better catalytic activity compared with... 

Self-assembled dandelion-like hydroxyapatite (HAp) nanostructures were successfully synthesized via a mild template-free hydrothermal process, using ethylenediaminetetraacetic acid (EDTA) as the surfactant. The obtained dandelion-like HAp nanostructures were between 5 and 8 μm in diameter and were composed of radially oriented nanorods with an average diameter of about 200 nm. The X-ray diffraction analysis and Fourier transform infrared spectroscopy were used to characterize the crystalline phase and purity of the synthesized nanostructures. The Brunauer-Emmett-Teller surface area of the dandelion-like nanostructures was measured to be about 39 m2/g. The results of thermal analysis revealed... 

Human society is becoming more intransigent on removing organic dyes from polluted water before discharging to the environment. To fulfill this goal, a magnetic metal-organic framework adsorbent based on functionalized magnetic Fe3O4 nanoparticles and highly water stable UiO-66 with high porosity and sensitivity to the external magnetic field was designed and synthesized via an easy step-by-step self-assembly technique. The synthesized adsorbent magnetic nanoparticles (Fe3O4@UiO-66) were applied to remove organic dyes, i.e., methyl orange (MO) and methylene blue (MB), from a contaminated aqueous solution. The experiments displayed that magnetic Fe3O4@UiO-66 has good adsorption uptake for MO... 

Human society is becoming more intransigent on removing organic dyes from polluted water before discharging to the environment. To fulfill this goal, a magnetic metal-organic framework adsorbent based on functionalized magnetic Fe3O4 nanoparticles and highly water stable UiO-66 with high porosity and sensitivity to the external magnetic field was designed and synthesized via an easy step-by-step self-assembly technique. The synthesized adsorbent magnetic nanoparticles (Fe3O4@UiO-66) were applied to remove organic dyes, i.e., methyl orange (MO) and methylene blue (MB), from a contaminated aqueous solution. The experiments displayed that magnetic Fe3O4@UiO-66 has good adsorption uptake for MO... 

Controlling evaporation plays an essential role in arid and semi-arid water resources systems where it accounts for a considerable amount of reservoirs outflow. In this study, we have evaluated evaporation reduction efficiency of different kinds of self-assembled nano-thickness films. The films consist of six different combinations of stearyl and cetyl alcohols with additives such as jojoba oil, stearic acid, and calcium hydroxide. The study lasted from July to August and utilized two pairs of class A evaporation pans: one pair was semi-floating on Chitgar lake water surface while the other one was located on the shore. The experimental results showed that a monolayer containing 3:1 stearyl... 

Nanoparticle halo mechanism is a stabilization method for microparticle suspensions. This study investigates suspension pH and nanoparticles–microparticles collision effects on the stabilization of an aqueous binary suspension. The long-term turbidity measurements show that for the nanosilica suspension stability is directly correlated with pH values; however, in the cases of zirconia and binary suspensions, it is not a monotonic function of pH. It is shown that for binary suspension, the halo mechanism is the primary method affecting the stability of the suspension. The suspension is best-stabilized at pH = 5 that is associated with high halo mechanism efficiency, while increased repulsive...