Sharif Digital Repository

The microstructures of stainless steels consist of an austenitic matrix with almost continuous network of primery carbides.This class of steel had replaced the traditional super alloys with a reduction in costs and has similar properties under conditions of creep, which is one of the principal degradation mechanisms leading to failure in service at elevated temperaturs , therefore, their mechanical properties such as tensile strength and creep resistance are particularly important in hot deformation. Recently the effects of temperature and aging time on static strain aging in worked stainless steel have been investigated. In this study the deformation behavior of HP-series austenitic... 

Can economics be a value-free science? The issue of values in science is a topic of discussion in the philosophy of science, and obviously in the social sciences, especially in economics, this issue becomes more controversial. Throughout the history of economics, these controversies have been the source of challenging debates among economists, philosophers, and sociologists. This question is still posed to philosophers and social scientists. Certainly, the answer to this question will have methodological implications. The issue of values has been an issue for economists from the very beginning of the Austrian school of economics. This dissertation deals with a view presented by a group of... 

Moving towards a sustainable energy system in the evolving society requires the utilization of new applications like Electrical Vehicles (EVs) and integration of Renewable Energy Sources (RESs) which will make new challenges for today’s power grids. To address these challenges, it is essential for emerging demand control paradigm to not only adapt the required demand with available supply but also consider the comfort and the level of lifestyle each customer may have in practice. In this research, due to the ever-growing interconnectivity of the grids, a distributed Commodity Market (CM) framework is proposed in which intelligent agents embedded in Demand Control Entity (DCE) units in... 

The research examines the influence of Kant’s practical philosophy on John Rawls’ theory of justice, under the concept of “autonomy”. In the initial chapter, foundational concepts of the study such as “autonomy” and “duty” are discussed in detail within the context of prevailing views in moral philosophy, particularly deontological ethics. The overarching idea of this chapter is to establish a general conceptual framework for posing the main research question. The second chapter of this research specifically and independently elucidates Kant’s practical philosophy and clarifies his interpretation of the concept of “autonomy”. The aim of structuring this chapter is to demonstrate that... 

With the growth of spreading information across social networks, users face with many options. More specifically, try to find out information is so troublesome in this context.In response to this problem, recommender systems aim at providing suggestions of interest for end-users. Also, we see many social networks in real-life which have the potential to be used in a variety of recommender systems. In the bipartite networks of users and items weighted edges is formed between each user and each item in the training set. On the other hand, developing a recommender system that takes into account the social network of the user improves the accuracy of traditional recommender systems.The purpose... 

Photochromism is defined as a reversible transformation of a chemical species between two forms having different absorption spectra induced in one or both directions by photoirradiation. Among various organic photochromic compounds, including spiropyrans, azobenzenes, spirooxazines, dyarylethenes and fulgides, spiropyranes have been attracted more attention due to their more sensitivity towards photo, pH, heat, pressure and solvent polarity. UV irradiation of spiropyrans, breaks the C-O bond of pyran ring and makes cis-trans isomers. Therefore, closed structure of the molecule, named as spiro (SP), is converting into the flattered and conjugated merocyanine (MC). Mc is photochromism, polar... 

It is undeniable that there is a great disagreement in the every field of religion. Reductionists argue that awareness of disagreements reduces the justification and rationality of beliefs, including religious beliefs. In contrast, non-reductionists believe that while reductionism may be true in other domains, it is not necessarily true in religion, because religious beliefs have characteristics that can deny a reductionist argument. They are in the realm of religion. In this thesis, I will discuss issues related to those characteristics that can deny reductionist argument in the realm of religion. In this thesis, I try to show that the arguments and responses presented in defense of the... 

The complexity of today's world has led us to the point where we will have problems in the intellectual and practical fields without relying on the testimony of experts. Maybe if we could measure the validity of the information by our own knowledge, we would definitely choose this option. But social life has made us rely on others to get the beliefs we need. We consider most of the beliefs we acquire in school, universities, in science books, news, debates and television documentaries to be examples of knowledge. We also claim to know a set of beliefs presented to us by experts. We consider experts as reliable people and we rely on them. In the meantime, we know that we have no other reason... 

The precipitation hardenable 7075 Aluminum Alloy is one of the most important heat-treated aluminum alloys. The high strength of this alloy has led to its widespread use in the manufacture of various components in the automotive, aerospace, marine, defense and military industries. Although the production costs of this alloy sheet are high, but since the 7075 aluminum alloy has the capacity to be as strong as steels, by reducing the production process and thus reducing production costs, this alloy can be used more widely in various industries. Therefore, in this study, the mechanical properties of the 7075 aluminum sheet are improved by a new quenching method in the die (HFDQ), which is a... 

Black holes are theoretically significant because they are (ideal) entities fully described by just three properties: mass, charge, and spin. Their importance also stems from their unique status as spacetime entities with universal properties, including the event horizon and—when including the singularity—representing the boundary of space and time. Beyond their spacetime properties, black holes are also thermodynamic systems. Their behavior requires a theory that integrates both spacetime and thermodynamics. A black hole is something that requires both a theory of spacetime and a theory of thermodynamics to describe and explain its behavior. A consistent description of time, spacetime, and... 

Nowadays, Thermomechanical processes are used to change the microstructure and create desirable mechanical properties in metals. In this research, with the aim of improving the mechanical properties and formability of 7000 series aluminum alloys, the Cyclic Quench-Rolling (CQR) process was designed and investigated as a new thermomechanical process with solid solution strengthening mechanism. First, for solution heat treatment, the 7075-T6 aluminum sheet was placed in the oven at 460 °C for 5 hours and quenched in water. After making the solid solution, in each cycle of CQR, a rolling step was performed, then intermediate solutioning heat treatment and then quenching was performed. To study... 

The process of aging is accompanied by problems that can affect the daily activities of an elderly. Recent studies have shown that the use of virtual reality technology provides a variety of diagnostic methods and clinical systems to prevent and delay cognitive aging to ensure the normal life of the elderly. In this project, efforts have been made to design some virtual reality-based games focusing on memory and recall in the form of three scenarios of finding address, finding car, and virtual-reality based maze game for the elderly to prevent cognitive decline and developing the dementia so that the difficulty of the game level ahead of each elderly can be adjusted according to his or her... 

In a distributed system, each solution for the problem of Byzantine Agreement requires that some of correct processes reach a common decision value from a set of proposed values while Byzantine processes may behave arbitrary. This problem is one of the most fundamental problems in the theory of distributed systems. While the problem has been widely studied in fully-connected fixed networks, few studies have been carried out in the context of self-organizing mobile networks such as Mobile Ad-Hoc Networks.
This research presents a randomized consensus protocol with three additional modules for the case of dynamic networks: Participant Detectors, Failure Detectors and Maintainer. We assume... 

Use of renewable energy has already increased significantly. One of the renewable and suitable sources for replacement with fossil fuels is wind energy, especially wind turbines. But the design, construction, installation maintenance and operation of wind turbines are relatively expensive. One of the most expensive parts of a wind turbine is its gearbox. Wind turbines gearbox due to fluctuating loads unexpected is likely to suffer a premature fatigue. The purpose of this project is to calculate some of the oscillating loads applied to the gearbox and then to investigate the effect of these loads on the service life of the gearbox components. Tower shadow effect and wind shear effect are the... 

The Austenitization, influence of ageing condition and the prediction kinetics of AISI 420 martensitic stainless steel were studied in this paper. The Austenitizing temperature of 9200C, 9500C and 10200C were achieved. The specimens were heated for 15, 30 and 60 minutes then quenched in 250C Oil. The cooled samples were tempered at 2000C for 1 hour. The maximum tensile strength obtained at 10200C and 60 minutes were about 1800 MPa. The effect and ageing temperature and time on the strengthening behavior of this steel was modeled and analyzed by shear punch test and means of artificial neural networks (ANNs). Johnson-Mehl-Avrami-Kolmogorov (JMAK) analyses were applied to characterize the... 

This study was conducted in order to investigate the effect of difference in electrical resistivity between low carbon steel and austenitic stainless steel on the physical and mechanical properties and fracture mode of dissimilar resistance spot welds of these alloys. For this purpose, plastic deformation using constrained groove pressing combined with rolling applied to low carbon steel in three levels of 40%, 156% and 272%. Microstructural characterization, micro-hardness measurements and shear-tension test were performed. It was shown that by increasing the pre-strain in low carbon steel its electrical resistivity increases from 13.08 μΩ.cm to 19.5 μΩ.cm and because of reduction of... 

The manufacture of ultra high strength materials has always been a target for aerospace and transportation industries. Currently, the limitation of energy resources even makes this goal more serious. Nowadays, more than 50% of total extrusion products are made from Al alloys and around 90% of them are the 6000 series alloys. Therefore, regarding to high strength, low weight, and hardening aluminum AA6000 alloys capabilities can play a major role in fulfilling this task. Over the last decade, a number of techniques collectively referred to as severe plastic deformation (SPD), have emerged as a promising approach for the production of bulk ultrafine-grained (UFG) nano-structured materials.... 

Sever plastic deformation can be used for decreasing the grain size and increasing the mechanical properties. In this method a square or circular cross section specimen is passed from two intersecting channel with equal cross section. Thereby, a large plastic strain without change of cross section is produced in the specimen. This large strain is the main reason for the interest of researchers in many fields. In the experimental research fields, researchers can study the response of material in the large plastic strain range, investigation of stage III of hardening and after it, change of microstructure to submicron and Nano, and increase of strength simultaneously with preserving of... 

Springs parts are widely used in many industries including the automative industries where the disability of the springs can cause damage. Spring forming processes induce residual stresses on the surface of spring. Residual stress is affected by various processes, such as heat treatment or shot peening. When a coiled spring is heat treated, depending on the temperature and time of heat treatment residual stresses are partially relieved, but they generally do not disappear.An important characteristic of spring steel is its resistance against stress relaxation at different temperatures and times. Stress relaxation in valve springs working at high temperatures causes some problems for... 

A new method for production of bimetallic rods, utilizing the equal channel angular extrusion (ECAE) process has been introduced before by previous researchers, but no attempt has been made to assess the effect of different temperatures and holding times in order to achieve a diffusional bond between the mating surfaces. In present research copper sheathed aluminum rods have been ECAEed at room temperature and subsequently held at a constant ECAE pressure, at different temperatures and holding times to produce a diffusional bond between the copper sheath and the aluminum core. The bonding quality of the joints was examined by shear strength test. The microstructure examinations were carried...