Sharif Digital Repository

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... 

Obtaining polymers with desired properties is very important from industrial point of view. Weight average molecular weight and polydispersity are two important polymer properties. It is also important to obtain a high monomer conversion. In this thesis production of polyvinyl acetate is considered. Under special conditions, the vinyl acetate reactor dynamics become oscillatory which makes the reactor control difficult. For obtaining polymer with desired properties, an objective function which includes weight average molecular weight, polydispersity and monomer conversion has been defined. Then by minimizing this objective function the optimal temperature trajectory is obtained. In this... 

In the current situation, kidney transplantation is the most appropriate and least costly treatment for patients with end-stage renal disease (ESRD). Related or altruistic living donors, as well as deceased donors, are considered as a supply source for donated kidneys. Researches have shown deceased donor kidney may not work as well as a living donor kidney because the deceased donor kidney is outside the donor's body for a longer time. If the donor has an incompatibility with the patient (in terms of the blood group, HLA, etc.), a kidney exchange between the pairs can be used to resolve the issue and make the transplantation possible. Pairs with blood group compatibility have also... 

The purpose of this study is extracting a dynamic model of longitudinal motions of high speed catamaran in regular and irregular waves, and then motion control of vessels by using of foil control elements and interceptor. For simulating longitudinal motions in regular waves, at first the longitudinal hydrodynamic coefficients of vessels should be extracted, then by substituting extracted coefficients in cumminz equation and using system identification methods, some equations are presented to estimate longitudinal two degree of freedom motions of high speed catamaran in waves. In this thesis the extraction of hydrodynamic coefficients is based on both numerical and experimental methods. ANSYS... 

In this thesis, free vibration of composite conical sandwich panel with a flexible is presented. Simply supported boundary condition are applied on the face’s edge only. Hamilton principle and energy method are used to derive equilibrium equations. In the mathematical formulation higher-order sandwich panel theory (HSAPT) was used. First shear deformation theory (FSDT) is used for faces.
Core displacement in various directions is modeled by polynomial function with indeterminate coefficient. It is assumed that the core is able to sustain shear and in-plane stresses. Temprature and humidity effects are neglected. Equations solved using generalized differential quadrature (GDQ) method.... 

This study provides a comprehensive understanding of the digital transformation process in a constrained environment, offering practical insights for practitioners and a robust basis for future academic research. Conducted within the manufacturing industry in Iran, this research explores how companies navigate and succeed in digital transformation under the constraints of global sanctions. Employing an extreme case study methodology, the research focused on a leading organization renowned for its innovation and patented technologies. This organization offered a unique perspective on digital transformation under restrictive conditions, meeting all requirements for an "extreme case" in... 

In this research a mathematical formulation is presented for project scheduling problem subject to non-renewable perishable resources where the objective is minimize the cost of ordering and maintenance of resources. We use the framework of a resource constrained project scheduling problem (RCPSP) with finish-start precedence relations between activities and resources will be perished after a determined duration and must be procured. Resource procurement have ordering and purchasing costs and excess resources must be stored and have maintenance cost. There is a unique way to perform the activities and preemption is not allowed.
This work employs Genetics Algorithms to solve the problem... 

The silicon vacancy in silicon carbide is a strong emergent candidate for applications in quantum information processing. 4H, 6H and 3C polytypes of SiC all host coherent and optically addressable defect spin states. Electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) investigations suggest that silicon vacancy point defects in SiC possess properties similar to those of the NV center in diamond. We provide a new theoretical frame to explain a wider range of experimental results. Employing a proposed generalized Hubbard model, with the help of electronic structure programs, DFT, second quantization, and various computational approaches, we obtain new... 

Identifying driving behaviors and building an efficient and accurate driving behavior recognition model is of paramount importance for improving driving safety. Nowadays, with the ubiquity of smartphone sensors, many researchers are using smartphone sensory data to create models which forecast driving behaviors. This research introduces a logit model that predicts nine types of driving events using accelerometer and gyroscope sensors with an accuracy of 76 percent  

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... 

Sponge Iron production is conducted in various methods that one of them is using coal as a reduction agent. Hoganas process is a different coal-based method that has not been investigated in details. Therefore, the heat transfer method in the system is one of the basic steps to a better recognition of this process (with special Hoganas charging). The present paper investigates the temperature distribution method in the Hoganas cylinder through a numerical model using finite elements. The effects of different parameters, namely preheating and porosity were studied on ceramic crucible made from silicon carbide and it was observed that the consumption energy decreases with the increase of... 

Different causes in the exploration, production and transport of oil in the marine environment result in oil spill events. Since elimination of the probability of occurrence of spills is not possible, it is important to have a plan to control the risk of oil spills by optimal response. In this research, a general stucture is presented for the DSS required for oil spill response planning. This system can be used for evaluation of the effectiveness of response drills, and risk-based ranking of receptor areas and spill sources. Ranking based on risk is realized through probabilistic or stochastic risk assessment. The applicability of the proposed system is examined in differnet case studies in... 

Parallel kinematics machine tools (PKMs) are being received in recent years and their capability for machining has been widely studied. One of the disadvantages of these kinds of machine tools is dependency of their structural properties on their configuration. In this thesis, the effect of this dependency on machine stability for the case of a hexapod and a hexaglide machine tool is studied. The process of modeling and analysis are implemented for the hexaglide and hexapod machine tools. In the modeling, the legs are modeled using rod and beam elements whereas platform is assumed to be rigid. Both experimental and analytical analysis show that dominant frequencies of PKMs at tool tip are in... 

mazandaran cement co.( the second biggest cement company in Iran) is located in Mazandaran province north of Iran. Thesis is about the weakness and strength points of available maintenance strategy (which is mostly CBM) in this company and offers some remedies to enhance the current maintenance situation. Maintenance information is assessed over a period of two years in a row and turn into some informative charts and diagrams for easier exploration. Eventually, some solutions are suggested for omitting shortages in current maintenance strategy  

Regarding the increasing application of fast boats in the world, studying the dynamic performances of these boats is consequently effective and vital. So one can evaluate the hull performance in different sea forces. Vast activities take place in all over the world yearly. General performances hull tests occur in marine laboratories such as Wave maker and carriage. Model hull test is one of effective branches of the naval architecture engineering. This method is also based on dimensional analysis. In this thesis, after understanding the waves and the methodology some experimental tests are done in the conditions of frontal static waves, and heave, pitch and roll activities of the craft are... 

With the depletion of fossil resources, price of these energy careers increases. Therefore, researchers investigate for other alternative choices. One of the most interesting choice is the renewable energies. These sources of energies are attractive due to either they are permanent resources or they are environmentally friendly. The most important renewable energy resource is solar energy that in fact is the source of other renewable energies. The most important and economic method of solar energy absorption is the thermal method. Common technology in thermal method is the Parabolic-Trough. But, recently a new technology have been developed called Compact Linear Fresnel Reflector (CLFR) that... 

In this thesis, the application of solar energy in the steam injection as a thermal enhanced oil recovery (TEOR) is evaluated. The motivations of this project are using a renewable energy, suitable solar potential of Iran, successful experience in the world, undeveloped heavy oilfield reservoirs in Iran. This application is investigated by three aspects which are:Reservoir Engineering aspect: the heavy oilfield are determined and then screening for selection good candidate of steam injection are done. One of the reservoirs is analyzed by simulation and optimization the steam injection to determine how much it’s production will be improved by using steam injection (contionous and cyclic)... 

Policies affect supply chain management in oil, gas and petrochemical industries. In this study, structural equation modeling was used to evaluate the relationship between variables in AMOS software. The findings also indicated that international policies affect different aspects of supply chain management in the following order: product realization management (coordination), customer delivery management (partnership), planning management (planning) and resource management (implementation). Finally, suggestions were made on how to find financing such as bank loans, prioritizing payments in the light of their criticality, as well as on the creation. This study aimed to investigate the impact...