Sharif Digital Repository

How is it possible for mind to be directed to the world? Or for it to be opened to the world? This question – formulated as the problem of knowledge - has been the central question of the modern philosophy. Rediscovering of the concept of "intentionality" as the mark of the mental by Franz Brentano, Contemporary philosophy succeeded in addressing this central question in a more direct and explicit a way. Intentional character of mind is more obvious in sensory experiences. Perception seems to be the minds openness to the world. But the possibility of having illusory or hallucinatory experiences challenges that very conception of perceptual experiences as openness. In analytic philosophy... 

This research aimed to investigate the relationship between household poverty and the gender of the head in the Iranian households. The self-reported gender of the head of household (FHH), underestimates the rate of poverty in female- head households (FHH). The self-reported gender of the head of household considers, conventionally, a family as male-head, even if the man of the family is incapable of making money. In much of these families the wife is the sole income holder even though she is not recognized as the head. In this study, a definition for household headship is introduced, which considers head of household the one who provides more than 50% of household income. Using household’s... 

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 most important researchers’ purposes in superconductivity are achievement of the room temperature superconductivity and to understand the high temperature superconductivity mechanism. Researchers’ goal in to increase the transition temperature by applying pressure, changing oxygen content, different doping, and changing stoichiometry in the families of the high temperature superconductors. In this research, which has been carried out in the Magnet Research Laboratary of Sharif University of Technology, samples of Y3Ba5Cu8O18, Gd3Ba5Cu8O18, and Pr3Ba5Cu8O18 have been synthesized by the standard solid-state reaction technique, the structure, electrical and magnetic properties of the... 

In communications systems, coding is used to combat channel errors. The redundancy introduced by coding enables the detection and/or correction of errors occurring in the channel. In addition to communications systems, coding is also beneficial in various other systems such as distributed storage systems and blockchain systems to cope with node failures, data erasures, and adversarial behaviors attempting to modify information. In existing applications of coding, it is generally assumed that the encoding operation is performed correctly and without errors, and errors are applied to the encoded data. In recent years, applications have emerged where the assumption of error-free encoding is not... 

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... 

In sliding wear, the process of making debris takes place with different mechanisms. Previous works estimating the wear rate have been carried out based on contact mechanics and material failure mechanisms. In present work, the possibility of existence of low-cycle fatigue as the dominant mechanism in the wear of an as-cast eutectoid steel is investigated. Moreover, wear coefficient and the the volume loss per distance of that steel was predicted. At first, wear tests were done in order to obtain the wear trend of the steel in different loads. Then, regarding the roughness of the disk surface, a finite element model was built to simulate the sliding of the pin surface over the asperities... 

This study was conducted in order to investigate on production and propeties of lead free solder alloy. For this purpose, Sn-Ag alloy with 3.5 weight percent of silver and sn-3.5Ag-0.7Cu at eutectic composition were produced with casting procedure.Single-lap Specimens were used to simulate real solder joints with the solder reflowed between two pure Cu substrate.Microstructural characterization, electrical resistance measurements and shear-tension test were performed.A deacrease of electrical resistance was observed in produced alloys in comparison with Sn-Pb . Experimental results showed that mechanical properties of produced alloys was better than common pb content alloy.The effect of... 

A Coiled Carbon Nanotube (CCNT) can be geometrically viewed as a graphene sheet whose rolled and twisted to form a helically coiled nanotube. It is the strongest material ever measured with strengthexceeding more than hundred times of steel.The strength of a CCNT iscritically influenced by temperature, tube diameter, strain rate and pitch angle. In this study,a Molecular Dynamics (MD) simulationis performed to understand the effect of temperature, strain rate, tube diameter and pitch angle on the mechanical properties of CCNTs. Results indicate thatexisting the stone-wales defects is necessaryfor thermodynamic stability of CCNTs.According to the stress-strain curves it was observed thatyield... 

The specific properties of some of magnesium alloys have caused these alloys to be used in medical and industrial applications. Adding new elements and applying severe plastic deformation to these alloys have been considered as a clue for improving their mechanical properties. The aim of this project is to improve the mechanical properties of a magnesium alloy by using new alloying elements and applying the ECAP process.
In this project, a new magnesium alloy by composition of Mg-1.78Zn-0.72Si-0.41Ca was cast. After casting, solution treating and annealing of the alloy were studied. Then, the effect of ECAP process on microstructure and mechanical properties of the annealed and solution... 

The austenitic heat resistant stainless steels have been widely used in petrochemical industry as furnace tubes which are exposed to extremely high temperatures. In this study, the quench aging process of a HP modified heat resistant stainless steel is assessed and the kinetics of aging is evaluated by the JMAK model. The microstructure of steel in as cast and aged conditions was characterized by optical microscope and scanning electron microscope equipped with EDS. The effects of aging time and temperature on the microstructure, tensile propertices, shear strength, hardness, and ductility of the aged steel were determinded. The results of tensile and shear punch tests show a linear... 

In this project the effect of rolling temperature on mechanical properties and microstructure evolution of a low carbon steel was studied. The steel was rolled up to a nominal strain of 67% at three different temperatures consisted of room, blue brittleness, and subzero temperature. Micreohardnessand tensile tests were used to characterize the recrystallization kinetics. Optical and scanning electron microscopic examinations were carried out to evaluate the mechanical, grain size, and the kinetics of static recrystallization by the Avrami equation. The results indicated that the volume fraction of static recrystallization increases with the increase in annealing period. The Avrami exponent...