Sharif Digital Repository

Written by Husserl, “Cartesian meditations”, a short book with subtitle of an introduction to phenomenology offers easy and accessible presentation to phenomenology for every beginner. But, despite of this, the book involves technical concepts of phenomenology which he has developed up to that time and unfortunately he did not bother to explain in this book. On the other hand, understanding of the book is made much harder by being a short book. Husserl’s philosophy is complicated and covers wide variety which its component interrelated mutually. Consequently, although in this work he just elaborate just limited issues, reading of the book for a novice reader with his philosophy is more... 

In this thesis, the molecular dynamics simulation is used to investigate the melting transition of B-DNA molecule, via of configurational entropy, the fraction of broken hydrogen bonds (f-curve) and hydrogen bonding energy.We have performed molecular dynamics simulation on Drew-Dickerson oligomer with sequence of (CGCGAATTGCGC) at different temperatures, within the range of 280-400 K with the 20 K intervals. The simulation was done in two different mediums (pure water and 1 M NaCl), to see influences of water and salt in stabilizing the DNA molecule. At each temperature, configurational entropy is calculated by the Schlitter’s formula, using the Cartesian coordinate of all atoms. So, in each... 

The physical characteristics of Pt nanoclusters with different sizes (256-8788 atoms) have been investigated via molecular dynamics simulations. The Pt-Pt radial distribution function, internal energy, heat capacity, enthalpy, entropy of the nanoclusters are calculated at some temperatures. The melting point predicted by the various properties is consistent with each other and shows that the melting temperature increases with the particle size. We have calculated the Gibbs free energy for the Pt bulk and also for its nanoparticle. We have used the thermodynamic integration method to obtain the Gibbs free energy. The total Gibbs free energy is taken as the sum of its central bulk and its... 

A general regularity has been found based on an effective pair potential of Lennard-Jones LJ (12, 6) for both dense nonmetallic and nonionic fluids and solids; namely, (Z-1)V2 linearly varies with respect to ρ2, this equation of state (EoS I) is known as LIR. The other equation of state (EoS II), according to wich the isotherm of (Z-1)V2 is linear in term of 1/ρ, wich gives a good description for the metallic and ionic fluids and solids. This equation of state was suggested based on an effective pair potential of LJ (6, 3). Unexpectedly, solid and liquid Ne indicates a significant deviations from EoS I. Recently, a general equation of state (EoS III) based on an effective near-neighbor pair... 

Ising model in nano systems are studied, in the presence of a magnetic field. For a one-dimensional(1-D) array of spins interacting via nearest-neighbor and next-nearest-neighbor interactions we calculated the heat capacity , the surface energy, the finite-size free energy, and bulk free energy per site. The heat capacity versus temperature exhibited a common wide peak for systems of any size. A small peak also appears at lower temperatures for small arrays when the ratio of magnetic field- spin interaction energy over the nearest-neighbour spin-spin interaction energy f is within and size. The peak becomes smaller for longer array and eventually vanishes for long arrays, disappearing when... 

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... 

In this thesis, we use two simple simulation models for ionic liquids, and the efficiency of the Lennard Jones equations and the state equation obtained from this potential were investigated. Then, using these models, the temperature-dependent coefficients were calculated in two equations at different temperatures, and then analytical expressions were reported to them. Given that ion fluid data is reported only in a small range of densities, these data were used to evaluate the equations used, using a model in a wider range of densities. For this purpose, simulation of molecular dynamics simulation data was simulated. In these two models, the relative size of cations and anions is different.... 

Prediction and calculation of shielding tensors of H, C, F and P nuclei of different molecules has been the subject of much research, because these nuclei have the greatest importance in NMR experiments. The optimum wave functions and calculation method were obtained using empirical models and factorial design. Based on preliminary experiences, the following four factors at two levels were selected: electron correlation, triple-ξ valence shell, diffuse function and polarization function. The wave functions for calculating gas phase 1H and 13C chemical shifts of various types of alcohols, amines and simple hydrocarbons were optimized using empirical model. The B3LYP/6-311+G wave function is... 

Microrobots are the robots which manufactured or operated in micro dimentions. High accuracy, compatibility with harsh situations and caring or assembling in micro dimensions are the most important advantages of these robots. Manufacturing new microrobots with higher speed or increasing the velocity of existed microrobots is the discussion of these days.An A-shape microrobot designed and manufacturared before. The goal of this thesis is to model, identify the friction and observe the velocity of the A-shape microrobot. In low speeds both legs of microrobots are on the ground; it walks with the stick-slip motion principle. Increasing the velocity of the microrobot causes separation of one or... 

Aluminum alloy (A356.0) is used in the production of cylinder head. Automobile engines are often subjected to thermo-mechanical loadings. In order to investigate the material performance, it is crucial to obtain fatigue properties of the material under thermo-mechanical and isothermal fatigue tests. The specimen is subjected to tensile and compressive stresses in a constant temperature. But in thermo-mechanical tests, the temperature and the strain vary in a specific span (between maximum and minimum values). By using the strain- stress hysteresis loop (obtained by fatigue tests), we can determine fatigue properties. Then, these properties are used in the simulation. In this thesis,... 

Most engineering components must be manufactured so they are safe to use and are ‘‘fit for purpose’’. However despite all the efforts, cracking of the engineering components is inevitable. Residual stresses play an important role in either increasing or decreasing the possibility of failure. For instance, enhancement in apparent toughness following pre-loading arises principally because of the creation of local crack tip compressive residual stresses. Introducing compressive residual stresses can also slow the fatigue crack growth. Yet, the dilemma is choosing an efficient method growth to introduce such stresses for retardation of fatigue crack growth. There are many methods available in...