Sharif Digital Repository

In this thesis, based on the taking-off and landing of aircraft with GE 21-J85 turbine, the low cycle fatigue (LCF) test for superalloy used in first stage blades is considered. The LCF tests were performed on both coated and uncoated Rene 80 which are used in GE 21-J85 turbine at R = (min/max) = 0, strain rate of 2 10-3 s-1 and 760oC, 871oC and 982oC. To produce specimens, an investment casting method was used so that adequate amount of polycrystalline round bars could be obtained. The specimens were all homogenized and solution treated. After the inspection, some specimens were coated with pack cementation method in CODEP-B powder in H2 atmosphere. The coated and uncoated specimens all... 

For an undirected graph G, a zero-sum flow is an assignment of non-zero real numbers on the edges of G such that the total sum of all edges incident with any vertex of G is zero. A zero-sum k-flow for a graph G is a zero-sum flow with labels from the set {±1, . . . , ±(k ? 1)}. In this thesis for a graph G, a necessary and sufficient condition forthe existence of zero-sum flow is given. It has been conjectured that if a graph G has azero-sumflow, then it has a zero-sum 6-flow. Also, it has been proved that this conjectureand Bouchet’s Conjecture for bidirected graphs are equivalent. It is shown that the con-jecture is true for 2-edge connected bipartite graphs, and every r-regular graph... 

The goal of the present study is to investigate the effect of rejuvenation treatment on microstructure and creep properties of damaged IN738LC superalloy. Virgin alloy was damaged by interrupted creep tests at 926°C and 170 MPa for 100, 200 and 250 hours. The results obtained showed that damaging the virgin alloy by interrupted creep tests resulted in microstructural deterioration (consisting of coarsening of ' precipitates, formation of continuous films of ' on grain boundary regions and formation of transition zone around MC carbides) and, consequently, degradation of creep properties. Rejuvenation treatment was carried out with the purpose of healing the damaged alloy and restoration of... 

The concurrent flow of oil and water is a common occurrence in the field of multiphase flow in different fields including petroleum industry. In oil and gas, production engineers often face a situation in which more than one phase is flowing through the producers. In such conditions an accurate assessment of pressure loss inside the well plays a vital role in efficient and effective production planning. Changes in well orientation, wellbore diameter, reservoir and fluid properties as well as fluid flow rates are among parameters in which will affect the flow patterns that can occur inside a well during its life time. These flow patterns are created as a result of a competition between... 

Casing design is one of the most expensive parts in the drilling of oil wells, and any cost reduction with the basic design of these casing strings will significantly reduce the total cost of the operation. In recent years, occurring scenarios-based casing design has become popular; Because in many cases, it eliminates non-occurring scenarios such as gas kick and saves on drilling costs. In this study, we have tried to investigate all scenarios that may occur during the lifetime of the well, whether drilling or production, and for each well, based on its own field information, possible scenarios for each casing part are selected separately and the applying loads are calculated. For this... 

The electrochemical oxidation behavior of the anti-inflammatory drug piroxicam was investigated. A carbon nanoparticle (CNP)-chitosan (CS) film-coated graphite electrode (PGE) was fabricated and the electrochemical behaviors of piroxicam on its surface was investigated by the means of cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). In comparison to the bare PGE, at the surface of the CNP-CS film modified electrode, the oxidation peak current of piroxicam increased significantly and the peak potential shifted negatively. Consequently, a simple and sensitive electroanalytical method was developed for the determination of piroxicam. The... 

There are high attractions in the development of conducting polymer (CP) coatings to improve the electrochemical properties and biocompatibility of electrodes in the area of biosensors. In the first part of this thesis, a new type of modified electrodes, constructing multi-walled carbon nanotubes (MWCNTs) and polypyrrole is prepared in a layer-by-layer process. In this procedure, the glassy carbon electrode is casted first by a drop suspension of MWCNTs, leading to formation a thin film on its surface. In the second step, electrochemical polymerization of pyrrole in the presence of tiron (used as doping anion) is performed on the surface of the MWCNTs pre-coated electrode. The modification... 

At the first part of this thesis, a pyrolitic graphite electrode (PGE) modified with graphite/nanodiamond film (GND) was applied as a sensitive electrochemical sensor for determination and study of electrochemical behavior of tryptophan (Trp) and 5-hydroxytryptophan (5-HTP) in aqueous solutions. The results showed that GND caused a remarkable increase in the peak currents so the GND/PGE electrode surface was more sensitive to the concentration of Trp and 5-HTP than the PGE surface. The determination of Trp and 5-HTP were investigated by stripping voltammetry. Experimental parameters such as scan rate, pH, accumulation conditions and amount of the modifier used on the PGE surface were... 

Part 1: A novel modified pyrolytic graphite electrode with nanodiamond/graphite was fabricated. The electrochemical response characteristics of the modified electrode toward the epinephrine (EN) and uric acid (UA) are studied by means of cyclic and linear sweep voltammetry. The structural morphology and thickness of the film was characterized by SEM technique.The prepared electrode shows an excellent catalytic activity in the electrochemical oxidation of EN and UA, leading to remarkable enhancements in the corresponding peak currents and lowering the peak potentials. The prepared modified electrode acts as a highly sensitive sensor for simultaneous determination of EN and UA in the presence...