Sharif Digital Repository

In this research, Friction stir welding (FSW) of 7075-O and 7075-T6 aluminum alloys was performed to investigate the effects of the base material conditions, effects of process parameters on the FSW characteristics and optimum parameters which lead to best mechanical properties of joints. The experimental results indicated that the base material condition has a significant effect on weld morphologies, weld defects, and mechanical properties of joints. The optimum parameters were 1230 rpm and 60 mm/min for 7075-O and 1230 rpm and 100mm/min for 7075-T6. Also, Double welded friction stir welding of 7075 aluminum alloy was performed to investigate the effects of the second pass of weld on the... 

In this research, first of all, the main question of Heidegger and his epoch is investigated. If we read Heidegger along the tradition of German philosophy, then it is perceived that the problem of science is the most central subject matter standing against Heidegger. My question is this: how Heidegger reaches to this existential phenomenological view about science. Regarding that, by giving a coherent narration about a crucial problem called 'the crisis of science', in the first chapter I gave a short view to philosophies preceding Heidegger, some important of which is Dilthey's philosophy of life, phenomenology of Husserl, and south-west school of neo-Kantianism. The second chapter... 

In this thesis we review different approaches to the theory of value laden technology and realize that there are at least two major ideas about this. Some philosophers believe that technology is not a mere instrument and has a value laden nature. In contrast some others count technology as something neutral which contains no social or moral value. After explaining this ideas, in the second chapter we examine different models which explain the relation between technology and moral and social values and show how this values can contribute in design and use of technologies. In chapter three we talk about different methods used to steer technology in a desirable way which is in accordance with... 

Let M be a connected, compact, Riemannian manifold. Geodesic flow is a flow on the unit tangent bundle of M . This flow can be studied in dynamics prespective. for example entropy or complexity of the geodesic flow. in this thesis we will follow methods of entropy estimation or computing for geodesic flow. we will follow the method of anthony manning and Ricardo Mañe for proving such result. Maning present two results linking the topological entropy of the geodesic flow on M. we expalin how he find exponential growth rate volume of balls in universal cover as a lower bound for topologycal entropy. another theorem , Mañe represent the equlity between exponential growth rate of avrage of... 

In this dissertation, we will study partially hyperbolic diffeomorphisms. First, we are going to introduce partially hyperbolic diffeomorphisms and construct some examples. One of the important questions in the study of partially hyperbolic diffeomorphisms is their classification problem, which provides a deeper understanding of manifolds and also of partially hyperbolic diffeomorphisms themselves. We will go through this problem by examining Hammerlindl, Potrie’s [1]’s work. They have proved that a partially hyperbolic diffeomorphism on a 3-manifold with a virtually solvable fundamental group, that has no periodic torus tangent to contraction-center or expansion-center, is dynamically... 

This dissertation deals with nonwandering (e.g. area-preserving) homeomorphisms of the torus which are homotopic to the identity and strictly toral, in the sense that they exhibit dynamical properties that are not present in homeomorphisms of the annulus or the plane. This includes all homeomorphisms which have a rotation set with nonempty interior. There are two types of points: inessential and essential. It is known that the set of inessential points Ine(f ) is a disjoint union of periodic topological disks ("elliptic islands"), while the set of essential points Ess(f ) is an essential continuum, with typically rich dynamics ("the chaotic region"). One of the key results in this context is... 

Let be a sub-semigroup of SL(d;Z) which acts strongly irreducible on Rd, i.e. there is not any invariant finite union of nontrivial proper subspaces of Rd. acts on Td by homeomorphisms. We will show that under these assumptions every infinite invariant subset of Td under the action of is dense in Td. For instance, if x is a point in Td which is not rational, then x = Td. In this thesis, we will follow the method of Y. Benoist and J.F. Quint for proving such results. Their method is to prove some kind of rigidity for the stationary measures for the action of on Td. Actually, every atomless stationary measure is the lebesgue measure on Td which is invariant under all the elements of... 

The object of this study is to determine the buckling load of reinforced composite conical shells under axial compression. . Shells are reinforced by stringers and rings and the boundary conditions are assumed to be simply supported. At first the equilibrium equations are obtained using the first order shear deformation theory (FSDT), smeared stiffener technique and principle of minimum potential energy. In the following, the resulting equations which are the system of five variable coefficient partial differential equations in terms of displacement components are investigated by generalized differential quadrature method (GDQM). Finally the standard eigenvalue equation is formed and the... 

Non-statistical dynamics are those dynamical systems for which a large subset of points in the phase space (positive measure subset) have non-statistical behavior, meaning that the orbit of these points does not have asymptotic distribution in the phase space. We introduce two new classes of these kinds of dynamics: non-statistical rational maps on the Reimann sphere and non-statistical Anosov-Katok maps of the annulus. We then give a general formalization of the notion of "statistical (in)stability" and show how it is connected to the existence of non-statistical dynamics in a general family of maps  

Today, the pollution of heavy metals in wastewater and surface waters, which is a global environmental problem, has increased with the expansion of various industrial activities. Heavy metals cause serious health problems due to their accumulation in human and animal tissues. Thorium, is a radioactive element with an atomic number of 90 that is widely used in the optics, aerospace, metallurgy and chemical industries, in the manufacture of high-strength alloys, in UV photocells, and especially in the nuclear industry. The primary sources of radioactive wastewater include nuclear power plants, nuclear energy industry research centers, medical institutions, industrial production, universities,... 

Molybdenum is one of the important elements of the intermediary metal with atomic number 42, which is used in various industries, but among the important uses of this metal in the nuclear industry, we can mention the presence of this element in the production of yellow cake as an impurity and also as a precursor for the production of radiopharmaceuticals. It is one of the impurities that remain in all stages of yellow cake production along with uranium, and the high presence of this element causes the centrifuges to become unbalanced during the injection of "U" "F" _"6" gas, and on the other hand, technetium, the main ingredient in the production of radiopharmaceuticals, It comes from the...