Sharif Digital Repository

In the current research, colloidal stability of two different types of coating on the surface of Superparamagnetic Iron Oxide nanoparticles (SPIONs) was studied. In the first triumph, a dual-layer coating was achieved by utilizing optimum amount of Dextran and different PEG (Poly(ethylene glycol)) concentrations which the weight ratios of iron oxide/PEG were 1/1, 2/1, 4/1, 8/1, and 16/1. Then, the presence of the coating was characterized by XRD, FT-IR, DLS and FE-SEM methods. These results together with the TGA ones revealed that as the concentration of PEG surfactant increases, the thickness of coating increases. Moreover, VSM test was performed to specify the effect of coating on the... 

Selective laser sintering is a technique which uses a laser as the power source to sintering some selected points at a bed of powder in order to create a solid structure. In this research the SLS mechanisms of powder deposition is simulated and surface smoothness and layer density created by each mechanism is computed. For this purpose roller, blade and hopper mechanisms are simulated. For this simulation, polyamide 12 (PA2200) which is a common material is used. In this simulation at first powder specifications are extracted according to the references and for particle shape instead of using the spherical particle shape we use a certain shape that is more close to reality which created by... 

This study was conducted to investigate a theoretical and experimental two-dimensional model of a floating fish cage in regular waves and uniform current. Due to the inefficiency of computational fluid dynamics (CFD) in solving such problems, developing a simple model to predict the results is highly advantageous. In this study, a simple mass-spring model was developed to simulate the problem. After validating the results of this simple model through a series of model tests in a wave tank, it was further utilized to extract additional results. Experiments were conducted at six different wave heights and four current velocities. In all experiments, wave steepness was maintained at a ratio of... 

Global energy consumption is on a trajectory to surge by 50% by 2050, primarily driven by prevailing energy consumption patterns. Consequently, the imperative to innovate and develop novel energy sources, such as the utilization of recycled waste heat, has become paramount for the foreseeable future. In light of this, this paper delves into the transformative potential of employing Phase Change Materials (PCMs) for cooling Thermoelectric Generators (TEGs) and harnessing waste heat for productive purposes. The research investigates three distinct configurations to evaluate the efficacy of PCMs in enhancing thermal management. Configuration 1 exclusively relies on an active cooling fan, while... 

Mechanical behavior of tissue engineering scaffolds plays a key role in their biological performance; however the effect of microstructural features on mechanical behavior of such scaffolds is still under investigation. The objective of this study was to investigate the influence of pore architecture and relative density on mechanical behavior of rapid prototyped scaffolds. In this regard, scaffolds with different cubic, hexagonal and trigonal unit cells were designed. These unit cells were repeated in different arrangements in 3D space to produce different nodal connectivities. The internal dimension of pores varied from 500 to 600 μm. Plastic models of scaffolds then fabricated by 3D... 

Today, the importance of scientific collaborations is due to the fact that researchers who jointly publish an article, research connections are formed between them, and as a result, professional learning is obtained. Each of these researchers brings a feature and advantage to the research team, such as mastering a particular topic and its subdivisions, team thinking, and division of labor between them. The importance of these collaborations is doubled when researchers collaborate with each other at the international level, because the networking of researchers through collaboration with colleagues from different countries, especially central and developed countries in science, in addition to... 

Considering the widespread applications of amides, synthesis of these compounds is of great importance. The one pot oxidative addition of amines to aldehydes is one of the most simple and appealing approaches to synthesis amides. With the aim of developing a mild and convenient approach towards preparation of amides, numerous methods have been reported for this important process over the past few decades. These improvements have been mostly related to the optimization of reaction conditions and the use of more challenging substrates including diverse derivatives of aldehydes, and also design a novel and effective catalytic systems. Due to the various advantages of supported heterogeneous... 

In recent years, the widespread investigation on multi-transition metal oxides that with two or more transition metal oxides, have been increased rapidly for electrochemical application due to low cost, high conductivity and good electrochemical performance other than single metal oxides. In this project, CuCo2O4 nanoparticles were firstly fabricated by decomposing of CuCo-MOF as the template. The as prepared samples were used to synthesis a new nanocomposite of MoS2 and CuCo2O4. The best ratio of the two component were optimized to prepare the best electrocatalyst for Hydrogen evolution reaction (HER). The structure of prepared nanocomposite were investigated by various techniques such as... 

Perovskite solar cells are the new generation of solar cells, and are mainly introduced in two types of structures.1) planer and 2) mesoscopic structure. The difference between these two structures derives from the absence of mesoporous layer in the planer structures. The mesoporous layer acts as an electron transporting layer, and is mainly a titanium dioxide semiconductor. To apply the mesoporous layer, the preparation of the TiO2 paste is needed.The synthesis of titanium dioxide nanopowder for the preparation of TiO2 paste requires high temperature heat treatment and is not desirable in terms of energy consumption.Another weakness of this layer is the presence of surface defects, which... 

In this thesis, a coarse-grained multi-scale method for 2D crystallyn solids based-on finite element consepts has presented. In this method, both scales are atomic scale and similar to what we see in non-local QC method, the entire atomic structure will be intact. Accordingly, calculations of potential functions and forces in the domain will have the atomic accuracy. In the presented method to reduce the domain’s degrees of freedom, the classical finite-element meshing concept to mesh the elastic linear areas in the domain is used and the MD calculations will done on the mesh nodes. Therefore, degrees of freedom in the system will reduce and consequently, the computational cost will reduce.... 

The integrative supply chain management is one of the main business processes between final consumer and supplier and it is formed by responsibilities such as production, services and information those have added value for customers and beneficiaries. Therefore and as the goal of a chain is maximization of gained value for the factors involved in chain, so, this goal can be more accessible by decreasing transportation (transportation method, tracking, …) and stock costs (conservation, ordering, …). As its purpose, this thesis intends to introduce and increase the options of goods transportation possibilities between retailers’ warehouses and evaluation of its effect on transportation and... 

Artificial immune systems (AIS) constitute a novel area of bio-inspired computing. Biological models of the natural immune system, in particular the theories of clonal selection, immune networks and negative selection, have provided the inspiration for AIS algorithms. Moreover, such algorithms have been successfully employed in a wide variety of different areas, but have not been applied for chemical processes yet. One important part of the immune systems is lymphatic system. Clonal selection is one of the few algorithms that belong to the family of AIS techniques. Clonal selection algorithm is the computational implementation of the clonal selection principle. In this project, we have... 

The unsteady phenomena occur in rotors of helicopters, wind turbines and compressors. Investigation of the unsteady flow is a very important test, since it can affect and restrict the performance of rotors of helicopters and wind turbine's blades when operating at high angles of attack. Dynamic tests, such as pitching and plunging oscillations are one of the best methods for studying these phenomena due to the complexity of the unsteady flows. In analyzing the results of dynamic tests one must consider the interference effects of wind tunnel walls. Different investigations show that in dynamic tests, the interference effects of flow field around the model, wind tunnel walls and support of... 

Peak Floor Acceleration (PFA) is a necessary requirement in Industrial Buildings for the design of equipment, piping, cable tray and ventilation duct supports. The seismic analysis of equipments needs the determination of PFA at the points where the equipments are fixed on the supporting structure. The classical spectral methods (SRSS, CQC) do not allow this determination which can be done in using the time integration method. This last approach needs to perform numerous calculations with various realizations of the seismic excitation. This thesis aims to present a method allowing calculating the response properties of a linear elastic shear building structure loaded by a transient... 

Chatter in machining systems is a limiting factor of workpiece surface, tool and machine life and material removal rate. Because of this, studying and modeling of vibrations is very important in the machining. This study is much importer in the boring operation because boring bar's length to diameter ratio is very high and so it is very sensitive to vibrations. As we know, vibration characteristics of a machine change between its operating condition and its resting mode. Because of this it's better to study machine's vibrations when it's working. This study requires some methods that can find operating parameters of machine. The aim of this work is to find these parameters. For finding these... 

Investigation about Hydraulic Fracturing phenomenon in fractured porous medium which was occurred by in-situ fracture pressure upon the crack wings, owes the fact that creating enormous damages. However, it might include advantages such as increasing the rate of crude oil production from deep and high pressure/ high temperature reservoirs. On account of the fact that, existence of cracks and natural discontinuities and heat sources such as boundary of geo thermal reservoirs in porous mediums it is undeniable fact. Also, cross sectioning hydraulic fracturing cracks with natural cracks it is an obvious impact. Actually, investigation and analyzing the break throw of HF crack with natural... 

In the present work, one dimensional ZnO nanostructures were grown by seed-assisted hydrothermal method. Hydrothermal processing parameters were controlled to obtain ZnO nanorods with diameter lower than 120 nm. The products were characterized by FE-SEM, EDAX, XRD, PL, and ATR-FTIR analyses. ZnO nanoparticles were also synthesized via a simple solvothermal method and their photo peropeties were compared with onedimensional nanostructures. Thereafter dye-sensitized solar cells based on TiO2-ZnO double layer nanostructured film were fabricated. It was observed that DSSC efficiency increased with decreasing the thickness of the film. The highest efficiency of 2.41% was obtained  

Dye-sensitized solar cells (DSSCs) are Photoelectrochemical cells using wide band gap nanoporous oxide semiconductors sensitized by dye molecules. For achieving high efficiency DSSCs preparation of photoanode electrode with high surface aea which leads to adequate dye absorption is necessary. In order to achieve proper morphology, thickness, particles size and porosity, producing a TiO2 nano-structured paste is required. TiO2 powder was prepared using sol-gel method. following a calcination process at 300 degrees, XRD patterns showed presence of anatase and brookite structures with average crystallite size of 9 nm. Additives such as diethylene glycol, acetylacetone and Triton X-100 were used... 

In present work, hydroxyapatite nano-rods are synthesized using a simple sol-gel method with calcium nitrate and potassium dihydrogenphosphate as calcium and phosphorus precursors respectively and ammonia was used for adjusting the pH=9. To obtain rod shape hydroxyapaite powder, multi wall carbon nanotubes were added to the solution, nHA powder was calcinated at 60 and 450 ℃. In second step, chitosan-gelatin/nanoHA solution were prepared by blending chitosan and gelatin in different concentrations with nanoHA powder, then the solution was freeze dried to maintain a composite scaffold. The prepared HA powder and bio-composite scaffold were characterized by X-ray diffraction (XRD), field... 

The Mesoporous Titanium Dioxide film using Sol-Gel method and Evaporation-Induced Self-Assembly technique (EISA) was prepared. In this study, in order to employ the best coatings in anode electrode of dye-sensitized solar cell, different conditions of making this film, the effective parameters in final structure, and various methods of coating were analyzed. After optimizing the conditions of film creating, images of field emission scanning electron microscope (FESEM) proved the formation of a layer of mesoporous structure which thickness after three times of coating is about 1.5 micrometers. In order to increase the energy conversion efficiency of solar cells, a new formulation for...