Sharif Digital Repository

We extend the work of Chari et al. (2007) to Iran’s economy institutions and introduce two additional wedges—the trade wedge and the oil wedge. The measured trade wedge value is regressed on nominal exchange rate, and thus we decompose the measured trade wedge into two components. One component represents the effect of nominal exchange rate on trade barriers and the other is representative of the effect of international sanctions in trade barriers. Then we evaluate the contribution of these two components of the trade wedge to the macroeconomic fluctuations in Iran from 2012 to 2014. Our results suggest that the trade wedge is crucial to account for the behavior of imported intermediate... 

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... 

The PTC effect which is one of the most important properties of electroceramics is being used in lots of electrical devices. This effect is observed in ceramics based on Barium Titanate. In the present study, the effects of grain size and two-step sintering method on PTC effect of Barium Titanate were investigated and La2O3 was used as an additive to improve the PTC effect and sintering behaviors of BaTiO3. Characterization analysis showed that the BaTiO3 powders had Cubic structure up to 700°C and Tetragonal structure at 1150°C. The FE-SEM analysis and density analysis showed that the samples which were two-step sintered at T1 less than 1200°C only reached 90% of relative density. Under... 

In this project, a “Ku” band (16.3GHz-17.3GHz) 6-bit phase shifter for realizing a phase array T/R module is designed, implemented and measured in CMOS 0.18μm technology. Design specifications for this block were: RMS phase error should be less than 2.5 degree in bandwidth, better than 12dB loss and better than 16dBm input 1dB compression point. High-pass/low-pass filter structure is used to implement this phase shifter. In order to decrease phase shift error in process and temperature corners, a new structure for one of bits was introduced. This structure is less sensitive to process and temperature corners and furthermore it conSumes less area in layout, but it has more loss variation... 

The significant increase in data volume makes it difficult to choose from a variety of options. Recommender systems help people choose their priorities in a limited time and facilitate the selection process for users. These systems predict users 'interest in the future by examining users' information and their preferences. Recently, with the significant increase in the number of users, studies in this field have changed so that groups of people with similar priorities are correctly identified and a list of recommendations is provided for each group. Identifying groups and presenting a suggestion list each require high computational cost and are often inefficient. The centrality of nodes will... 

In all electronic systems, the power management unit, as one of the main parts of the system, has the task of providing the necessary voltage for each sub-block of the system. Also, different blocks of electronic systems require different levels of supply voltage. In addition, the supply voltage level of the systems has increased due to the increase in the possibility of power transmission, and at the same time, there is a possibility of a drop in the supply voltage in battery-powered systems. Therefore, a DC-DC voltage converter that has a wide range of input and output voltage can increase the flexibility of the system. The design of DC-DC voltage converters whose output noise is at the... 

Through history, increased energy consumption has been encouraged researchers to improve the performance of energy-using devices. Some researchers believe that hydrophobic surfaces can play an important role in this regard.The encounter and the presence of water on different surfaces can have different effects on them. The surface sedimentation of these surfaces, the eating of metal surfaces, the drag force (water friction) due to water collision with the moving object in water and the attachment of algae And other marine organisms to the surfaces, including the limitations and problems faced by professionals and staff associated with this sector.In the present study, the drag reduction of... 

Possessing second place among gas reserve owner countries worldwide, Iran enjoys a very particular position in energy supply field. The crude oil is about to be replaced by natural gas in fuel sector because of growing demand for natural gas along with depletion of crude oil reserves. Some other drivers to this change are the increase in the known reserves of natural gas, the need to monetize stranded gas reserves and the environmental pressure to minimize the flaring of associated gas and carbon dioxide emissions. In such conditions the optimum consumption of these national abundant resources results in obtaining considerable revenues and strong presence of Iran in world consumption... 

A novel optoelectronic property of two-dimensional (2D) materials suggests they can be used for high-performance photodetector design. There has been a lot of attention paid to MoS2 and Despite its higher optical absorbance, MoSe2 has received little attention. A chemical vapor deposition system was used to prepare atomically thin MoSe2 films. Our research developed a method of preparing hexagon-shaped MoSe2 photodetector on Si/SiO2 substrates in atmospheric pressure with sawtooth edges, leading to large-scale MoSe2 layers with the size of ∼ 70µm . The Raman characterization of the grown flakes indicated that they possessed high quality few layers of MoSe2 and the distance between the two... 

The level of current and voltage harmonics in power networks has been increased due to the widespread use of power electronic equipment. This increase may, in turn, result in damage to power system equipment in addition to extra power losses in the network. In order to assess the level of harmonics, it is required to monitor power networks using power quality analyzers. However, due to the high costs, only limited number of measurements can be used in practice. The task of harmonic state estimation is to identify the location and magnitude of harmonic sources and to estimate the harmonic voltage and current by partial measurements. Due to the high price of measurement instruments and... 

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... 

Nanocrystalline steel was developed by severe cold-rolling and subsequent annealing of HSLA steel with an original microstructure of lath martensite. Specimens are austenitized at 1000 ºC for 30 min followed by quenching in brine. The quenched specimens are cold rolled with 80% to 90 % reduction and then annealed at temperatures from 400 to 700ºC for 10 to 120 min.The specimens annealed at temperature 500oC for 60 min showed the multiphased ultrafine structure composed of equiaxed ultrafine ferrite grains with the mean grain size of 180 nm, nano-carbides distributed uniformly and blocks of tempered martensite. The produced nanostructured steel exhibited a yield stress and UTS, of 1280 MPa... 

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...