Sharif Digital Repository

This study deals with the heuristic solution of flexible flow shop scheduling problems with unrelated parallel machines. No preemption of jobs is allowed. As an objective function, this paper considers the minimization of total tardiness. As a first step to propose solution, two different mixed integer mathematical models are developed which tackle the problem at hand. The problem is NP-hard and thus the developed mathematical program can only solve problem instances for small sizes in a reasonable amount of time. The next step is to build heuristics which can provide feasible solutions in polynomial time for larger problem instances. Then in the study develops a constructive heuristic for... 

The aim of this thesis is to study invariants of Diophantine forms and equations. These invariants are the transformations that do not change the original equations and forms. This thesis has a different view to the concept of invariants from Hlibertian view. Based on this new definition, by having one of the solutions of the equation, new solutions can be found with invariant method. The number of these solutions can be finite or infinite. In case of infinite solutions this method is more important. The focus of this thesis is on forms and linear invariants. The most important result in this text is about two main theorems that can classify the invariants of all completely decomposable... 

The main topic of this dissertation is to find methods for obtaining parametric solutions and linear/nonlinear invariants of Diophantine equations and consists of 4 chapters. The first chapter consists of some introductory discussions. The second chapter begins with a review of linear invariant, U-invariants, covariants and the concept of semi-invariants. The generators of maximum degree 3 for producing all linear invariants are introduced in Chapter 2 as well. Moreover, the relations between 3rd and 4th degree Hilbert invariants in terms of Procesi bases are included in this chapter.In chapter 3, a general conjecture is given to check whether there are finitely many solutions to a... 

Lightweight aluminum and magnesium alloy sheets do not generally possess as much strength as steel sheets and their strength need to be increased by a suitable process such as Accumulative Roll Bonding (ARB). One of the most important limitations of ARB is the low ductility and formability of the sheets produced by this process. In the present research conducted on the 5083 aluminum and AZ31 magnesium alloy sheets efforts have beem made to overcome this limitation by heating up the sheets whether during metal forming process as hot deformation or as distinct controlled annealing process subsequent to the deformation, in order to develop the application domain of the sheets. Results... 

To produce polyurea, a secondary or higher amine must be combined with a diisocyanate. For this purpose, we first combined diethylenetriamine, and hexamethylene diisocyanate, which did not have good mechanical properties due to the aliphatic nature of the molecules. Then, instead of hexamethylene diisocyanate, we used MDI, which was mixed using a mechanical mixer but became a paste that was not suitable for coating applications. To reduce the viscosity of MDI, propylene carbonate was added to improve mixing, but the gel time also increased. Because the solvent was non-polar and the amine was polar, it was decided to add the solvent, amine, and polyvinyl alcohol as surfactants to allow faster... 

The importance of optimizing the extraction process of available resources increases each day due to the increasing energy consumption and the lack of energy resources. Oil and gas are one of the most important sources of energy. Although existing oil and gas resources are thought to be sufficient to meet the growing energy demand for the next few decades, given the non-renewable nature of these resources and the growing demand for oil and gas, it will become much harder to meet the future energy demand. Many existing oil fields are now in the process of maturing, and the discovery of large new oil fields is rare. As a result, new technologies must be used in the future to meet this demand,... 

Phospholipid membranes and vesicles play important roles in the cellular functioning, otein signaling and material transport inside cells. Protein-embedded vesiclesare also used for targeted drug delivery. In this thesis, we use molecular dynamicsmethods and study (i) the formation of vesicles from flat lipid bilayers (ii) the mechanicalproperties of vesicles under compressive forces (iii) the shape variations ofvesicles with and without transmembrane proteins (iv) protein clustering.We grow our vesicles from lipid bilayers, which may contain proteins with differentconcentrations. We start with a random initial distribution of proteins that allowsus to monitor the clustering and... 

Energy and environment crisis in past decades raised concerns about fossil fuels use and has accelerated renewable energy application in terms of solar electric, solar thermal and wind turbines. Due to the fluctuating nature in renewable resources, renewable electric power generation has a stochastic nature that makes it difficult to use by the electricity consumers. Energy storage plays a key role to put more control on renewable power generation.Lead-acid battery is a storage technology that is widely used in photovoltaic systems. Battery investment and maintenance costs account for a big part of photovoltaic system costs. Charging and discharging profiles of the battery has a great impact... 

The design and development process of menu systems has always been a focus of researchers and engineers in the fields of software engineering and human-computer interaction. Considering the large and complex nature of the design space, it is nec- essary to provide automatic methods that aid designers during the design process. In this study, natural language processing is used to investigate the semantic relationship between menu system commands. Users expect related commands to be conveniently located next to each other, and a properly designed interface satisfies this need. As a result of this research, a fast-text-based model is developed that uses the data of past menu systems. In a... 

There is a major interest to manufacturers of automobile and aerospace parts towards the tailor-welded blanks (TWBs) to reduce the weight and cost of the parts and improve their performance. In this work, formability of four groups of TWBs (two groups with similar thicknesses and different steels and two groups with similar steels and different thicknesses) are investigated. To produce the TWBs, DX54, E275 and E335 steel sheets were used. The results indicate that the inclined laser beam causes the sample failure from the weld zone in the tensile test. Setting the focal point on the top surface of the sheets results in enhancement of yield strength in comparison to the other positions. ... 

The purpose of this project is to correct the surface defects of the reverse osmosis membrane. The membrane tested in this project was a thin film made of three layers of polyester, polysulfone and polyamide. These three layers provide mechanical resistance to operating pressure, suitable substrate for polyamide layer synthesis and membrane selectivity, respectively.In order to improve the surface properties and modify the reverse osmosis membrane, it was first attempted to coat it with a protective layer of polyvinyl alcohol, then by modifying this layer and improving the properties of polyvinyl alcohol and synthesizing the sulfite agent on it by the esterification reaction, to the best... 

These days the usage of welded tailor blanks with sufficient stability and flexibility is accelerating rapidly in order to production of slighter parts and reduction of fuel consumption in transportation means. Therefore, the conjuncture of blanks by welding methods is highly considerable before forming and ultimate production. Friction Stir Welding is greatly appealing to industry as one of the newest methods of solid state welding in production of TWB blanks. In this research, the feasibility study of Friction Stir Welding of thin Al 1100 – H18 alloy blanks with 1.5, 2 and 2.5mm thickness has been evaluated first. After creation of sound welds with same thicknesses, Friction Stir Welding... 

Liver metastasis is the leading cause of death in patients with colorectal cancer (CRC). An increasing number of studies have shown that mRNAs, miRNAs, can play an important role in various biological processes that are related to cancer. Identifying and determining the relationship between them can help to diagnose and treat cancer.The aim of this study is to identify miRNA and molecular mRNA markers in the stage of polyp formation in order to diagnose colorectal cancer early and also to introduce therapeutic targets in the stage of metastasis.In this study, two microarray data sets GPL15207 and GPL16384 were analyzed to identify different miRNAs and mRNAs from the GEO database in three... 

Al 5083 is a non-heat treatable alloy that widely used in the aerospace and automotive industry due to its low density and high strength. However, poor wearing behavior and low elastic modulus restrict its engineering applications. Metal matrix composites (MMCs) have advantages of high strength and modulus by reinforcement of second phase. Also, MMCs have excellent dimensional stability, damping capacity and wear, creep and fatigue resistances as compared with the corresponding monolithic alloys. Vast loss in ductility and toughness occurs by non- deformable ceramic reinforcements. For the surface engineering purposes, ceramic particles are added in the surface layers of components, whereas... 

Emission of the greenhouse gases is a great concern and use of lightweight materials in transport vehicles has found a major importance in this respect. Metal/polymer laminated composites are of great interest due to their special mechanical properties and thoughness. Application of metal/polymer sheets is limited because of low bonding strength of metals and polymers in these sheets, which is not sufficient, to endure the stresses and strains during deformation processes such as deep drawing and bending. In this research, roll bonding of AA5052/Polypropylene sheets is investigated and the effects of bonding parameters on strength are evaluated and finally the bonding mechanisms during... 

The adsorption equilibria of carbon dioxide, methane, and nitrogen on pelletized cation-exchanged faujasite zeolite (with alkali, alkaline earth, and transition metal ions) have been investigated by a volumetric apparatus. The standard instrumental analytical techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) coupled with energy dispersive X-ray spectroscopy (EDX), and atomic absorption spectroscopy (AAS) were utilized to characterize binder-free modified zeolites. The EDX spectra and AAS results revealed that the ion-exchange was successfully achieved with expected tendencies. The results indicate that the type of cation present in the zeolite... 

Acidic gases separation from hydrocarbon mixtures is very important in natural gas industry. In this study, the separation of CO2 and H2S from CH4 investigates by experimental and molecular dynamics simulation approaches. For achievement to this goal, it is used two polymeric families, as be divided to polyurethanes and PEBAX copolymers. It is used 4 polyurethane membranes as are named PU-1, PU-2, PU-Ether, and PU-Ester from polyurethanes group. Also, it is applied 5 PEBAX commercial membranes have be known PEBAX-2533, PEBAX-4033, PEBAX-5533, PEBAX-4011, and PEBAX-1074. It is compared between simulation and experimental works and found that there is good agreement between... 

In this study, membrane distillation process was used for treatment of high salinity waters. The focus of this study is to simulate and build a setup of membrane distillation process. Since the membrane distillation process is based on the driving force of the temperature difference, the required temperature is provided by both the use of heaters and the use of solar energy. To increase the feed temperature by solar energy, a black polymer coating on the main membrane is used. The main membrane used in this process is PVDF polymer and the polymer coated on the surface is the PAN polymer. After simulating and constructing the laboratory setup, the influence of a variety of parameters on the...