Sharif Digital Repository

The goal of this thesis is to understand the physical properties of lanthanum based manganites and barium based ruthenates. In order to obtain negative colossal magnetoresistance in manganites and fabrication of barium ruthenate in ordinary condition, the effects of variables such as ionic radii, chemical composition, temperature, magnetic field and processing in manganites and ruthenates systems are investigated. In the first part, the effects of potassium doping on structure, metalinsulator transition and magnetoresistance in )La1-yKy)0.7 Ca0.3 MnO3 and)La1-yKy)0.7 Ba0.3 MnO3 manganites systems are studied. Polycrystalline samples of manganites are synthesized by the sol‐gel method. In the... 

Several potential models such as Sutherland (ST) and square-well (SW) potential models are used for studying the equilibrium and transport properties. Near and above the inversion temperature these potential models fail to predict the second virial coefficient, so they are not applicable at high temperatures. ST and SW potential models have two different branches; one branch is related to the attraction forces and the other to the repulsive forces. Each branch has its own unique parameters, for example parameters of attraction branch are ε/k (the depth of the potential model) and λ (the width of the potential model). Repulsive branch has only one parameter, σ (the molecular diameter).... 

In this research, a method based on the modified Enskog theory (MET) and some equations of state has been used to calculate the transport properties of some dense fluids. The main limitation to using the MET is the lack of experimental data for the co-volume, b0, that are substituted from the hard sphere (HS) theory, and the zero density transport properties that are substituted from the kinetic theory of gases for the HS in the MET expression, because of the fact that dense fluids behave more and less like a HS fluid. So a quadratic expression for both ηY/(√T ρ) and λY/(ρ√T) (C_(V,m)+ (9/4)R) in terms of Y at high densities (ρ > ρc) for each isotherm is expected, where Y = (T (∂p/∂T))/ρRT... 

The coexistence of long-range magnetic order and superconductivity in the ruthenocuprate families, Ru1212 and Ru1222 has been studied both theoretically and experimentally. Historically these two different phases are incompatible with each other and in the most previous research reported on the coexistence of these phases, there have been observed separated magnetic and superconducting phases. However in the ruthenocuprate families, there is a single phase with both magnetic and superconducting phase which coexist with each other. It has been determined that superconductivity arises in CuO2 planes, and magnetic orders occur in RuO2. From experimental point of view, we have investigated the... 

Porous burner technology has many advantages in comparison with conventional burners such as higher burner thermal performance, lower pollutants emission, high power ranges, fuel flexibility, compact geometry and higher turn down ratios. These kinds of burners are made of preheated porous combustion zone and combustion porous zone that have different thermophysical and geometrical properties. In this work, the transient one-dimensional multi-step premixed laminar reacting flows in a two-stage porous media burner have been investigated. The combustible mixture is considered H2-Air (9 species and 19 reactions) and CH4-Air (22 species and 49 reactions). In porous media, without lateral wall... 

Presently, a wide range of devices operate at supercritical condition. In fact, supercritical condition refers to a condition in which both temperature and pressure of injected fluid exceed the critical point. In the case of modern internal combustion engine, the temperature and pressure of combustion chamber is high enough that can be considered as supercritical condition, whilst the fuel injected may be subcritical or transcritical.It has been widely accepted that in supercritical state, vaporization enthalpy is vanished and there is no distinction between gas and liquid. Hence, only a single state will remain which is neither liquid nor gas and referred to as fluid. Moreover, many... 

This thesis analyzes the scattering of a propagating electron from a single bound electron .The study demonstrates how the scattering of the propagating electron from the bound electron causes entanglement between two electrons. The study then considers the impact of spin-dependent scattering in the presence of Hartree and exchange potentials. In the first step, only an exchange potential is studied. Transmission coefficients are calculated for spin-flip and non-spin-flip states by solving the Hamiltonian equation in different regions, applying the continuity boundary conditions for the wave function and its derivative in each region, and using the transfer matrix method. Transmission... 

Alkali-activated fly ash-slag (AAFS) is a new type of sustainable construction material widely studied in recent years for its desirable mechanical properties and low environmental impacts. In this study, the effects of the slag incorporation from 10 to 30% of fly ash are investigated on the strength, pore structure, and transport properties of the AAFS with various levels of fly ash replacements with slag. The unconfined compression and ultrasonic pulse velocity tests were performed to evaluate the mechanical properties of the AAFS concrete. Microstructural and mineralogical changes were studied by porosity, N2-adsorption/desorption, and SEM/EDX tests. Additionally, transport properties...